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POSITIVE ELECTRODE ACTIVE MATERIAL, POSITIVE ELECTRODE PLATE, SECONDARY BATTERY, BATTERY MODULE, BATTERY PACK AND POWER CONSUMING DEVICE

20240282969 ยท 2024-08-22

    Inventors

    Cpc classification

    International classification

    Abstract

    A positive electrode active material has an inner core and a shell coating the inner core, wherein the inner core comprises at least one of a ternary material, dLi.sub.2MnO.sub.3.Math.(1?d)LiMO.sub.2 and LiMPO.sub.4, where 0<d<1, and M includes one or more selected from Fe, Ni, Co, and Mn; and the shell contains a crystalline inorganic substance having a full width at half maximum of the main peak of 0-3? as measured by means of X-ray diffraction, and the crystalline inorganic substance includes one or more selected from a metal oxide and an inorganic salt.

    Claims

    1. A positive electrode active material comprising: an inner core comprising at least one of a ternary material, dLi.sub.2MnO.sub.3.Math.(1?d)LiMO.sub.2 and LiMPO.sub.4, where 0<d<1, and M includes one or more selected from Fe, Ni, Co, and Mn; and a shell comprising a crystalline inorganic substance, the crystalline inorganic substance having a full width at half maximum of the main peak of 0-3? as measured by means of X-ray diffraction, and the crystalline inorganic substance including one or more selected from a metal oxide and an inorganic salt.

    2. The positive electrode active material according to claim 1, wherein the shell comprises at least one of the metal oxide and the inorganic salt, and carbon.

    3. The positive electrode active material according to claim 1, wherein the inner core comprises LiMPO.sub.4, and M includes Mn and a non-Mn element, wherein the non-Mn element satisfies at least one of the following conditions: the ionic radius a of the non-Mn element and the ionic radius b of manganese element satisfy that |a?b|/b is not greater than 10%; the valence alternation voltage U of the non-Mn element satisfies 2 V<U<5.5 V; the chemical activity of a chemical bond formed by the non-Mn element and O is not less than that of a PO bond; and the highest valence of the non-Mn element is not greater than 6.

    4. The positive electrode active material according to claim 3, wherein the non-Mn element includes one or two of a first doping element and a second doping element, the first doping element is doped at the manganese site, and the second doping element is doped at the phosphorus site.

    5. The positive electrode active material according to claim 4, wherein the first doping element satisfies at least one of the following conditions: the ionic radius a of the first doping element being denoted and the ionic radius b of manganese element satisfy that |a?b|/b is not greater than 10%; and the valence alternation voltage U of the first doping element satisfies 2 V<U<5.5 V.

    6. The positive electrode active material according to claim 4, wherein the second doping element satisfies at least one of the following conditions: the chemical activity of a chemical bond formed by the second doping element and oxygen is not less than that of a PO bond; and the highest valence of the second doping element is not greater than 6.

    7. The positive electrode active material according to claim 4, wherein the positive electrode active material contains at least two of the first doping elements.

    8. The positive electrode active material according to claim 4, wherein the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge.

    9. The positive electrode active material according to claim 8, wherein the first doping element includes at least two selected from Fe, Ti, V, Ni, Co, and Mg.

    10. The positive electrode active material according to claim 4, wherein the second doping element includes one or more elements selected from B (boron), S, Si and N.

    11. The positive electrode active material according to claim 1, wherein the inner core has a compound with a chemical formula of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4, where x is any numerical value in a range of 0.100-0.100, y is any numerical value in a range of 0.001-0.500, z is any numerical value in a range of 0.001-0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements selected from B (boron), S, Si and N.

    12. The positive electrode active material according to claim 11, wherein the ratio of y to 1?y is 1:10 to 1:1.

    13. The positive electrode active material according to claim 11, wherein the ratio of z to 1?z is 1:9 to 1:999.

    14. The positive electrode active material according to claim 11, wherein x is selected from a range of 0.001 to 0.005; and/or, y is selected from a range of 0.01 to 0.5; and/or, z is selected from a range of 0.001 to 0.005; and/or, n is selected from a range of 0.001 to 0.005.

    15. The positive electrode active material according to claim 1, wherein the inner core has a compound with a chemical formula of Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n, where C includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, R includes one or more elements selected from B (boron), S, Si and N, D includes one or more elements selected from S, F, Cl and Br, and x is any numerical value in a range of 0.100-0.100, y is any numerical value in a range of 0.001-0.500, z is any numerical value in a range of 0.001-0.100, n is any numerical value in a range of 0.001 to 0.1, and m is any numerical value in a range of 0.9 to 1.1.

    16. The positive electrode active material according to claim 15, wherein C, R and D are each independently any element within the respective ranges above, and A is at least two elements within the range thereof.

    17. The positive electrode active material according to claim 1, wherein the lattice change rate of the positive electrode active material is 8% or less.

    18. The positive electrode active material according to claim 1, wherein the Li/Mn antisite defect concentration of the positive electrode active material is 4% or less.

    19. The positive electrode active material according to claim 1, wherein the surface oxygen valency of the positive electrode active material is ?1.89 to ?1.98.

    20. The positive electrode active material according to claim 1, wherein the positive electrode active material has a compacted density under 3 T of 2.0 g/cm.sup.3 or more.

    21. The positive electrode active material according to claim 1, wherein the crystalline inorganic substance includes a pyrophosphate of QP.sub.2O.sub.7 and a phosphate of XPO.sub.4, and the metal oxide includes Q.sub.eO.sub.f, where: Q and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; Q is selected from one or more elements of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al; M is selected from one or more elements of an alkali metal, an alkaline earth metal, a transition metal, a group IIIA element, a group IVA element, a lanthanide and Sb; e is greater than 0 and less than or equal to 2; and f is greater than 0 and less than or equal to 5.

    22. The positive electrode active material according to claim 21, wherein the pyrophosphate includes Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, where 0?a?2, 1?b?4, 1?c?6, the values of a, b, and c satisfy the condition of keeping the Li.sub.aQP.sub.2O.sub.7 or Q.sub.b(P.sub.2O.sub.7).sub.c electrically neutral, and Q in the Li.sub.aQP.sub.2O.sub.7 and Q.sub.b(P.sub.2O.sub.7).sub.c is each independently selected from one or more elements of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

    23. The positive electrode material according to claim 21, wherein: the phosphate has an interplanar spacing of 0.244-0.425 nm, and an included angle of crystal orientation (111) of 20.00?-37.00?; and the pyrophosphate has an interplanar spacing of 0.293-0.470 nm.

    24. The positive electrode active material according to claim 21, wherein the pyrophosphate and the phosphate each independently have a crystallinity of 10% to 100%.

    25. The positive electrode active material according to claim 21, wherein the shell comprises a carbon coating layer, the crystalline inorganic substance is between the inner core and the carbon coating layer, and the carbon for the carbon coating layer is a mixture of SP2-form carbon and SP3-form carbon.

    26. The positive electrode active material according to claim 21, wherein: the shell comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer; and the first coating layer comprises a pyrophosphate of QP.sub.2O.sub.7 and a phosphate of XPO.sub.4, and the second coating layer is a carbon coating layer.

    27. The positive electrode active material according to claim 26, wherein the coating amount of the first coating layer is greater than 0 wt % and less than or equal to 7 wt %, based on the weight of the inner core.

    28. The positive electrode active material according to claim 26, wherein the weight ratio of the pyrophosphate to the phosphate in the first coating layer is 1:3 to 3:1.

    29. The positive electrode active material according to claim 26, wherein the coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, based on the weight of the inner core.

    30. The positive electrode active material according to claim 21, wherein: the shell comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer; and the first coating layer comprises a crystalline pyrophosphate of QP.sub.2O.sub.7 and a metal oxide of Q.sub.eO.sub.f, and the second coating layer is a carbon coating layer.

    31. The positive electrode active material according to claim 30, wherein the coating amount of the first coating layer is greater than 0 wt % and less than or equal to 7 wt %, based on the weight of the inner core.

    32. The positive electrode active material according to claim 30, wherein the weight ratio of the pyrophosphate to the oxide in the first coating layer is 1:3 to 3:1.

    33. The positive electrode active material according to claim 30, wherein the coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, based on the weight of the inner core.

    34. The positive electrode material according to claim 21, wherein: the shell comprises a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer; the first coating layer comprises a crystalline pyrophosphate; the second coating layer comprises a metal oxide of Q.sub.eO.sub.f; the crystalline pyrophosphate includes Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, where a is greater than 0 and less than or equal to 2, b is any numerical value in a range of 1-4, and c is any numerical value in a range of 1-3; and the third coating layer comprises carbon.

    35. The positive electrode active material according to claim 34, wherein: the coating amount of the first coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core; and/or the coating amount of the second coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core; and/or the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core.

    36. The positive electrode active material according to claim 34, wherein: the first coating layer has a thickness of 2-10 nm; and/or the second coating layer has a thickness of 3-15 nm; and/or the third coating layer has a thickness of 5-25 nm.

    37. The positive electrode active material according to claim 34, wherein based on the weight of the positive electrode active material: the content of manganese element is in a range of 10 wt %-35 wt %; and the content of phosphorus element is in a range of 12 wt %-25 wt %.

    38. The positive electrode active material according to claim 21, wherein: the positive electrode active material comprises a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer; the first coating layer comprises a crystalline pyrophosphate of Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c; the second coating layer comprises a crystalline phosphate of XPO.sub.4; and the third coating layer is carbon.

    39. The positive electrode active material according to claim 38, wherein: the coating amount of the first coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core; and/or the coating amount of the second coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core; and/or the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt %, based on the weight of the inner core.

    40. The positive electrode active material according to claim 38, wherein: the first coating layer has a thickness of 1-10 nm; and/or the second coating layer has a thickness of 2-15 nm; and/or the third coating layer has a thickness of 2-25 nm.

    41. The positive electrode active material according to claim 38, wherein based on the weight of the positive electrode active material, the content of manganese element is in a range of 10 wt %-35 wt %, the content of phosphorus element is in a range of 12 wt %-25 wt %, and the weight ratio of manganese element to phosphorus element is in a range of 0.90-1.25.

    42. A positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material according to claim 1.

    43. The positive electrode plate according to claim 42, wherein the content of the positive electrode active material in the positive electrode film layer is 10 wt % or more, based on the total weight of the positive electrode film layer.

    44. A secondary battery, comprising the positive electrode active material according to any one of claim 1.

    45. A battery module, comprising the secondary battery according to claim 44.

    46. A battery pack, comprising the secondary battery according to claim 44.

    47. A power consuming device, comprising the secondary battery according to claim 44.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0097] FIG. 1 shows X-ray diffraction (XRD) spectrum of undoped LiMnPO4 and a positive electrode active material prepared in example 2.

    [0098] FIG. 2 shows energy-dispersive X-ray spectroscopy (EDS) images of the positive electrode active material prepared in example 2.

    [0099] FIG. 3 shows a schematic diagram of a positive electrode active material with a core-shell structure described in the present application.

    [0100] FIG. 4 shows a schematic diagram of a positive electrode active material with a core-shell structure in an embodiment of the present application.

    [0101] FIG. 5 shows a schematic diagram of a secondary battery in an embodiment of the present application.

    [0102] FIG. 6 shows an exploded view of the secondary battery in an embodiment of the present application as shown in FIG. 5.

    [0103] FIG. 7 shows a schematic diagram of a battery module in an embodiment of the present application.

    [0104] FIG. 8 shows a schematic diagram of a battery pack in an embodiment of the present application.

    [0105] FIG. 9 is an exploded view of the battery pack in an embodiment of the present application as shown in FIG. 8.

    [0106] FIG. 10 shows a schematic diagram of a power consuming device using a secondary battery in an embodiment of the present application as a power source.

    DESCRIPTION OF REFERENCE SIGNS

    [0107] 11 inner core; 12 first coating layer; 13 second coating layer; 14 third coating layer; 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly

    DETAILED DESCRIPTION OF EMBODIMENTS

    [0108] The embodiments of the present application are described in detail herebelow, with examples thereof being shown in the accompanying drawings, where identical or similar reference numerals throughout represent identical or similar elements or elements with identical or similar functions. The embodiments with reference to accompanying drawings described below are exemplary and are merely for explaining the present application, and should not be construed as limiting the present application.

    [0109] It should be noted that the features and effects described in various aspects of the present application can be mutually applicable and will not be repeated here.

    [0110] Hereinafter, embodiments of the positive electrode active material and the preparation method therefor, the negative electrode plate, the secondary battery, the battery module, the battery pack, and the power consuming device of the present application are described in detail and specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed illustrations may be omitted in some instances. For example, there are situations where detailed description of well-known items and repeated description of actually identical structures are omitted. This is to prevent the following description from being unnecessarily verbose, and facilitates understanding by those skilled in the art. Moreover, the accompanying drawings and the descriptions below are provided for enabling those skilled in the art to fully understand the present application, rather than limiting the subject matter disclosed in the claims.

    [0111] The ranges disclosed in the present application are defined in the form of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it should be understood that the ranges 60-110 and 80-120 are also contemplated. Additionally, if minimum range values 1 and 2 are listed and maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless stated otherwise, the numerical range a-b denotes an abbreviated representation of any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range 0-5 means that all the real numbers between 0-5 have been listed herein, and 0-5 is just an abbreviated representation of combinations of these numerical values. In addition, when a parameter is expressed as an integer ?2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. In the present application, about a numerical value means a range, i.e., a range of ?10% of the numerical value.

    [0112] All the embodiments and optional embodiments of the present application can be combined with one another to form new technical solutions, unless otherwise stated. All the technical features and optional technical features of the present application can be combined with one another to form a new technical solution, unless otherwise stated. Unless otherwise stated, all the steps of the present application may be performed sequentially or randomly, in some embodiments sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may also comprise steps (b) and (a) performed sequentially. For example, reference to the method may further comprise step (c) indicates that step (c) may be added to the method in any order, e.g., the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), or also steps (c), (a), and (b), etc.

    [0113] The terms comprise and include mentioned in the present application are open-ended, unless otherwise stated. For example, comprise and include may mean that other components not listed may or may not further be comprised or included. In the present application, the term or is inclusive unless otherwise specified. For example, the phrase A or B means A, B, or both A and B. More specifically, the condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present). In this disclosure, the phrases at least one of A, B, and C and at least one of A, B, or C both mean only A, only B, only C, or any combination of A, B, and C.

    [0114] It should be noted that, herein, the terms coating layer and coating refer to a material layer coated on an inner core material such as lithium manganese phosphate, and the material layer can completely or partially coat the inner core, and the use of coating layer is just for convenience of description and is not intended to limit the present disclosure. In addition, each coating layer may be completely coated or may also be partially coated. Likewise, the term thickness of the coating layer refers to the thickness of the substance layer coated on the inner core in the radial direction of the inner core.

    [0115] In an aspect of the present application, the present application provides a positive electrode active material comprising an inner core and a shell coating the inner core, wherein the inner core comprises at least one of a ternary material, dLi.sub.2MnO.sub.3.Math.(1?d)LiMO.sub.2 and LiMPO.sub.4, where 0<d<1, and M includes one or more selected from Fe, Ni, Co, and Mn; and the shell comprises a crystalline inorganic substance having a full width at half maximum of the main peak of 0-3? as measured by means of X-ray diffraction, and the crystalline inorganic substance comprises one or more selected from a metal oxide and an inorganic salt. The crystalline substance has a stable crystal lattice structure and has a better retention effect on active metal ions such as Mn that are easily dissolved.

    [0116] The inventors of the present application have found that in order to improve the battery performance, such as increasing the capacity, improving the rate performance, the cycling performance, etc., it is common for the positive electrode active materials currently used for lithium ion secondary batteries to be prepared by adding doping elements to materials, such as a ternary positive electrode active material, LiMPO.sub.4 that can be applied in a high-voltage system, such as LiMnPO.sub.4, LiNiPO.sub.4, and LiCoPO.sub.4, or a Li-rich manganese based positive electrode active material. The doping elements above can replace active transition metals and other sites in the above-mentioned materials, thereby having the effect of improving the performance of the battery comprising the materials achieved. On the other hand, the material such as lithium iron phosphate may be added with an Mn element, but the addition or doping of these active transition metals and other elements may easily lead to the dissolution of active metals such as Mn ions caused by the material during deep charging and discharging processes. The dissolved active metal elements, on the one hand, will further migrate to the electrolyte solution and cause a catalyst-like effect after the reduction of the negative electrode, leading to the dissolution of the SEI film (solid electrolyte interphase, solid electrolyte interphase film) on the negative electrode surface. On the other hand, the dissolution of the above metal elements will also cause the capacity loss of the positive electrode active material, and lattice defects of the positive active material will occur after dissolution, leading to problems such as poor cycling performance. Therefore, it is needed to improve the above positive electrode materials containing active metal elements to alleviate or even solve the above-mentioned problems. The inventors have found that the crystalline inorganic substance, with the main peak measured by means of X-ray diffraction of which having the above full width at half maximum, has a good ability to intercept and retain the dissolved active metal ions, and the crystalline inorganic substance can be well combined with the inner core materials above with a stable bonding force and thus is not easy to peel off during use; moreover, a coating layer with appropriate area and good uniformity can be formed by relatively simple methods.

    [0117] Specifically, taking lithium manganese phosphate positive electrode active material as an example, the inventors of the present application have found in practical work that the existing lithium manganese phosphate positive electrode active material suffers from severe dissolution of manganese ions during deep charging and discharging. Although there is an attempt in the related art to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the dissolved manganese ions from continuing to migrate into the electrolyte solution. After migration to a negative electrode, the dissolved manganese ions are reduced to the metal manganese. The metal manganese produced in this way is equivalent to a catalyst, which can catalyze the decomposition of the SEI film (solid electrolyte interphase, solid electrolyte interphase film) on the surface of the negative electrode to produce by-products; a part of the by-products is gas, thus causing the secondary battery to swell and affecting the safety performance of the secondary battery; in addition, another part of the by-products is deposited on the surface of the negative electrode, and hinders the passage of lithium ions into and out of the negative electrode, resulting in an increase in the impedance of the secondary battery, thus affecting the dynamic performance of the secondary battery. In addition, in order to supplement the lost SEI film, the active lithium in the electrolyte solution and the battery are continuously consumed, which will have an irreversible impact on the capacity retention rate of the secondary battery. A novel positive electrode active material with a core-shell structure can be obtained by modifying lithium manganese phosphate and coating lithium manganese phosphate with multiple layers. The positive electrode active material can achieve a significantly reduced dissolution of manganese ions and lowered lattice change rate, and when such a positive electrode active material is applied to a secondary battery, the cycling performance, rate performance, safety performance and capacity of the battery can be improved.

    [0118] In some embodiments of the present application, the inner core comprises LiMPO.sub.4, and M includes Mn and a non-Mn element, wherein the non-Mn element satisfies at least one of the following conditions: the ionic radius of the non-Mn element being denoted as a, and the ionic radius of manganese element being denoted as b, |a?b|/b is not greater than 10%; the valence alternation voltage of the non-Mn element being denoted as U, 2 V<U<5.5 V; the chemical activity of a chemical bond formed by the non-Mn element and O is not less than that of a PO bond; and the highest valence of the non-Mn element is not greater than 6.

    [0119] As positive electrode active materials for lithium ion secondary batteries, compounds such as lithium manganese phosphate, lithium iron phosphate, or lithium nickel phosphate that can be applied in a high-voltage system in the future have lower costs and better application prospects. However, taking lithium manganese phosphate as an example, it has a disadvantage of a poor rate performance when compared with other positive electrode active materials, and this problem is now usually solved by means of coating or doping, etc. However, it is still desirable to further improve the rate performance, cycling performance, high-temperature stability and the like of the lithium manganese phosphate positive electrode active material.

    [0120] The inventors of the present application have repeatedly studied the effects of doping the Li, Mn, P, and O sites of lithium manganese phosphate with various elements and found that the capacity per gram, rate performance, and cycling performance of the positive electrode active material can be improved by controlling the doping sites, and the specific elements and doping amounts.

    [0121] Specifically, selecting a suitable manganese-site doping element can reduce the lattice change rate of the lithium manganese phosphate material during the process of lithium intercalation and de-intercalation, improve the structural stability of the positive electrode material, greatly reduce the dissolution of manganese, and reduce the oxygen activity on the particle surface, such that the capacity per gram of the material can be increased, and the interfacial side reactions with the electrolyte solution during the use of the material can be reduced, thereby improving the cycling performance of the material. More specifically, selecting an element with an ionic radius similar to Mn element as the Mn-site doping element, or selecting an element with a valence that is variable within the valence conversion range of Mn for doping can control the length change of the bond formed by the doping element and O and the MnO bond, which is conducive to stabilizing the lattice structure of the doped positive electrode material. In addition, a vacancy element has a lattice supporting effect can also be introduced at the Mn site, such as elements with a valence greater than or equal to the sum of the valence of Li and Mn. This is equivalent to introducing vacancy points that cannot bind with Li at the active and easily soluble Mn site, thereby providing support for the lattice.

    [0122] For another example, selecting a suitable P-site doping element can help to reduce the difficulty in changing the length of the MnO bond, thereby improving the electronic conductivity and reducing the migration barrier of lithium ions, accelerating the migration of lithium ions, and improving the rate performance of a secondary battery. Specifically, the tetrahedral structure of the PO bonds itself is relatively stable, such that it is difficult to change the length of the MnO bond, resulting in a higher overall lithium ion migration barrier of the material. However, appropriate P-site doping elements can improve the firmness of the PO bond tetrahedron, thereby promoting the improvement of the rate performance of the material. Specifically, elements for which the chemical bond formed with O has a chemical activity not less than that of a PO bond can be selected for doping at the P site, thereby reducing the difficulty in changing the length of MnO bonds. In the present application, unless otherwise stated, the chemical activity of the chemical bond formed with O that is not less than that of a PO bond can be determined by testing methods known to those skilled in the art to determine the chemical bond activity. For example, it can be determined by detecting the bond energy, or by referring to the electrochemical potential of a oxidation or reduction reagent that is used to break the chemical bond. Alternatively, an element with a valency that is not significantly higher than P, for example, 6 or less, can be selected for doping at the P site, which is beneficial for reducing the repulsive effect between Mn and P elements, and can also improve the capacity per gram, rate performance, etc., of the material.

    [0123] Similarly, appropriate element doping at the Li site can also improve the lattice change rate of the material and maintain the capacity of the battery comprising the material.

    [0124] Element doping at the O site can help to reduce the interfacial side reactions between the material and the electrolyte solution and reduce the interface activity, thus facilitating the improvement of the cycling performance of the positive electrode active material. In addition, element doping at the O site can also provide the material with an improved resistance to acid corrosion by HF, etc., which is beneficial for improving the cycling performance and service life of the material.

    [0125] In some embodiments, the non-Mn element for doping at the above sites includes one or two of a first doping element and a second doping element, the first doping element is doped at the manganese site, and the second doping element is doped at the phosphorus site. The first doping element satisfies at least one of the following conditions: the ionic radius of the first doping element being denoted as a, and the ionic radius of manganese element being denoted as b, |a?b|/b is not greater than 10%; and the valence alternation voltage of the first doping element being denoted as U, 2 V<U<5.5 V. The second doping element satisfies at least one of the following conditions: the chemical activity of a chemical bond formed by the second doping element and O is not less than that of a PO bond; and the highest valence of the second doping element of the doping element M is not greater than 6. In some embodiments, the positive electrode active material also can contain two of the first doping elements.

    [0126] In some embodiments, both the Mn site and the P site among the sites described above can be doped. Thus, this doping can not only effectively reduce the dissolution of manganese, which in turn reduces the migration of manganese ions to the negative electrode and the consumption of electrolyte solution due to the SEI film decomposition, thereby improving the cycling performance and safety performance of secondary batteries, but also can facilitate the adjustment of the MnO bond, lower the migration barrier of lithium ions and accelerate the migration of lithium ions, thereby improving the rate performance of secondary batteries.

    [0127] In some other embodiments of the present application, doping at all the four sites with specific amounts of specific elements can achieve a significantly improved rate performance and improved cycling performance and/or high-temperature stability, thereby obtaining an improved lithium manganese phosphate positive electrode active material.

    [0128] The positive electrode active material of the present application can, for example, be used in a lithium ion secondary battery.

    [0129] The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge. The first doping element includes at least two selected from Fe, Ti, V, Ni, Co, and Mg. The second doping element includes one or more elements selected from B (boron), S, Si and N.

    [0130] The doping elements mentioned above should keep the system electrically neutral, which can ensure that the defects and impurity phases in the positive electrode active material are as few as possible. If there is an excess of a transition metal (such as manganese) in the positive electrode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely prone to be precipitated in the form of an elementary substance, or form impurity phases inside the lattice to keep the electrical neutrality, so that such an impurity can be as little as possible. In addition, ensuring the electrical neutrality of the system can also result in lithium vacancies in the material in some cases, so that the dynamic performance of the material is more excellent.

    [0131] Taking lithium manganese phosphate material as an example, the specific parameters of the positive electrode active material proposed in the present application and the principles of achieving the above-mentioned beneficial effects will be detailed below:

    [0132] The inventors of the present application have found in practical work that the existing lithium manganese phosphate positive electrode active material at present has relatively serious manganese dissolution during deep charging and discharging. From extensive research, the inventors have found that a novel positive electrode active material that can be obtained by modifying lithium manganese phosphate can achieve significantly reduced manganese dissolution and reduced lattice change rate, and when such a positive electrode active material is applied to a secondary battery, the cycling performance, rate performance, safety performance and capacity of the battery can be improved. Doping the compound of LiMnPO.sub.4 at all the Li, Mn, P and O sites with specific amounts of specific elements can significantly improve the rate performance while reducing the dissolution of Mn and Mn-site doping element, thereby improving the cycling performance and/or high-temperature stability, and the capacity per gram and compacted density of the positive electrode active material can also be increased. In addition, the entire inner core system keeps electrical neutrality, which can ensure that the defects and impurity phases in the positive electrode active material are as small as possible. If there is an excess of a transition metal (such as manganese) in the positive electrode active material, since the structure of the material system itself is relatively stable, the excess transition metal is likely prone to be precipitated in the form of an elementary substance, or form impurity phases inside the lattice to keep the electrical neutrality, so that such an impurity can be as little as possible. In addition, ensuring the electrical neutrality of the system can also result in lithium vacancies in the positive electrode active material in some cases, so that the dynamic performance of the positive electrode active material is more excellent.

    [0133] In some embodiments, the positive electrode active material above may have a compound with a chemical formula of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4, where x is any numerical value in a range of 0.100-0.100, y is any numerical value in a range of 0.001-0.500, z is any numerical value in a range of 0.001-0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and R includes one or more elements selected from B (boron), S, Si and N. The values of x, y, and z satisfy the condition of keeping the entire compound electrically neutral.

    [0134] In some other embodiments, the positive electrode active material above may have a compound with a chemical formula of Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n, wherein C includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, R includes one or more elements selected from B (boron), S, Si and N, D includes one or more elements selected from S, F, Cl and Br, x is any numerical value in a range of 0.100-0.100, y is any numerical value in a range of 0.001-0.500, z is any numerical value in a range of 0.001-0.100, n is any numerical value in a range of 0.001 to 0.1, and m is any numerical value in a range of 0.9 to 1.1. Similarly, the values of x, y, and z satisfy the condition of keeping the entire compound electrically neutral.

    [0135] Unless otherwise stated, in the chemical formula of the above inner core, when a site is doped with two or more of elements above, the above definition of the numerical range of x, y, z or m not only represents a definition of the stoichiometric number of each element at the site, but also represents a definition of the sum of the stoichiometric numbers of the elements at the site. For example, when a compound having a chemical formula of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4 is comprised, where A is two or more of elements A1, A2 . . . An, the stoichiometric numbers y1, y2 . . . yn of A1, A2 . . . An each fall within the numerical range of y defined in the present application, and the sum of y1, y2 . . . yn shall also fall within this numerical range. Similarly, when R is two or more of elements, the definition of the numerical range of the stoichiometric number of R in the present application also has the above meaning.

    [0136] In an optional embodiment, when A is selected from one, two, three or four elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, Ay is G.sub.n1D.sub.n2E.sub.n3K.sub.n4, wherein n1+n2+n3+n4=y, and n1, n2, n3 and n4 are all positive numbers and not zero, and G, D, E and K are each independently selected from one of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and optionally, at least one of G, D, E and K is Fe. Optionally, one of n1, n2, n3 and n4 is zero, and the remaining ones are not zero; more optionally, two of n1, n2, n3 and n4 are zero, and the remaining ones are not zero; and further optionally, three of n1, n2, n3 and n4 are zero, and the remaining one is not zero. In Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4, it is advantageous to dope one, two, three or four of the above A elements, optionally one, two or three of the above A elements, at the manganese site; and in addition, it is advantageous to dope one or two R elements at the phosphorus site, which is conducive to even distribution of doping elements.

    [0137] Specifically, for example, the Mn site can be doped with both Fe and V.

    [0138] In some embodiments, in Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4, the ratio of y to 1?y is 1:10 to 1:1, optionally 1:4 to 1:1. Here, y denotes the sum of the stoichiometric numbers of the Mn-site doping elements A. When the above conditions are satisfied, the energy density and cycling performance of the secondary battery using the positive electrode active material can be further improved. In some embodiments, the ratio of z to 1?z is 1:9 to 1:999, optionally 1:499 to 1:249. Here, z denotes the sum of the stoichiometric numbers of the P-site doping R element. When the above conditions are satisfied, the energy density and cycling performance of the secondary battery using the positive electrode active material can be further improved.

    [0139] In some other embodiments of the present application, the positive electrode active material may comprise Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n. The value of x is affected by the valency of A and R, and the values of y and z, so as to ensure that the entire system is electrically neutral. If the value of x is too small, the lithium content of the entire inner core system will decrease, which will affect the capacity per gram of the material. The value of y will limit the total amount of all doping elements. If y is too small, that is, the doping amount is too small, and the doping elements will have no effect. If y exceeds 0.5, the content of Mn in the system will be less, which will affect the voltage plateau of the material. The doping with element R is in the position of P, and since the PO tetrahedron is relatively stable and the excessive z value will affect the stability of the material, the value of z is defined as being 0.001-0.100. More specifically, x is any numerical value in a range of 0.100-0.100, y is any numerical value in a range of 0.001-0.500, z is any numerical value in a range of 0.001-0.100, n is any numerical value in a range of 0.001 to 0.1, and m is any numerical value in a range of 0.9 to 1.1. For example, 1+x is selected from a range of 0.9 to 1.1, for example, 0.97, 0.977, 0.984, 0.988, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998 and 1.01, x is selected from a range of 0.001 to 0.1, for example, 0.001 and 0.005, y is selected from a range of 0.001 to 0.5, for example, 0.001, 0.005, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.34, 0.345, 0.349, 0.35 and 0.4, z is selected from a range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08 and 0.1, n is selected from a range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08 and 0.1, and the positive electrode active material is electrically neutral.

    [0140] As mentioned previously, the positive electrode active material of the present application is obtained by element doping in compounds such as LiMnPO.sub.4, and without wishing to be bound by theory, it is now believed that the performance improvement of lithium manganese phosphate is related to the decrease of the lattice change rate and surface activity of lithium manganese phosphate during the process of lithium intercalation and de-intercalation. The decrease in the lattice change rate can reduce the difference of lattice constants between two phases at a grain boundary, lower the interface stress and enhance the Li.sup.+ transport ability at the interface, thereby improving the rate performance of the positive electrode active material. A high surface activity can easily lead to severe interfacial side reactions, and exacerbates gas production, electrolyte solution consumption and interface damage, thereby affecting the cycling performance and the like of the battery. In the present application, the lattice change rate is reduced by doping at the sites of Li and Mn. The Mn-position doping also effectively decreases the surface activity, thereby inhibiting the Mn dissolution and the interfacial side reactions between the positive electrode active material and the electrolyte solution. The P-site doping increases the change rate of the MnO bond length and reduces the small-polaron migration barrier of the material, which is beneficial for electronic conductivity. The O-site doping plays a good role in reducing the interfacial side reactions. The P-position and O-position doping also has an effect on the dissolution of Mn of antisite defects and the dynamic performance. Therefore, the doping reduces the antisite effect concentration in the material, improves the dynamic performance and capacity per gram of the material, and can also change the particle morphology, thereby increasing the compacted density. The applicant has unexpectedly found that: Doping the compound of LiMnPO.sub.4 at all the Li, Mn, P and O sites thereof with specific amounts of specific elements can significantly improve the rate performance while significantly reducing the dissolution of Mn and Mn-site doping element, thereby significantly improving the cycling performance and/or high-temperature stability; moreover, the capacity per gram and compacted density of the material can also be increased.

    [0141] Selecting the Li-site doping element in the above ranges can further reduce the lattice change rate during a lithium de-intercalation process, thereby further improving the rate performance of the battery. Selecting the Mn-site doping element in the above ranges can further increase the electronic conductivity while the lattice change rate is further reduced, thereby improving the rate performance and capacity per gram of the battery. Selecting the P-site doping element in the above ranges can further the rate performance of the battery. Selecting the O-site doping element in the above ranges can further alleviate the interfacial side reactions, thereby improving the high-temperature performance of the battery.

    [0142] In some embodiments, x is selected from a range of 0.001 to 0.005; and/or, y is selected from a range of 0.01 to 0.5, and optionally from a range of 0.25 to 0.5; and/or, z is selected from a range of 0.001 to 0.005; and/or, n is selected from a range of 0.001 to 0.005. By selecting the y value in the above ranges, the capacity per gram and rate performance of the material can be further improved. By selecting the x value in the above ranges, the dynamic performance of the material can be further improved. By selecting the z value in the above ranges, the rate performance of the secondary battery can be further improved. By selecting the n value in the above ranges, the high-temperature performance of the secondary battery can be further improved.

    [0143] In some embodiments, the positive electrode active material with all the 4 sites being doped with non-Mn elements satisfies: (1?y):y is in a range of 1 to 4, optionally in a range of 1.5 to 3, and (1+x):m is in a range of 9 to 1100, optionally in a range of 190-998. Here, y denotes the sum of the stoichiometric numbers of the Mn-site doping elements. When the above conditions are satisfied, the energy density and cycling performance of the positive electrode active material can be further improved.

    [0144] In some embodiments, the positive electrode active material may comprise at least one of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4 and Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n. The ratio of y to 1?y is 1:10 to 1:1, optionally 1:4 to 1:1. The ratio of z to 1?z is 1:9 to 1:999, optionally 1:499 to 1:249. C, R and D are each independently any element within the respective ranges above, and A is at least two elements within the range thereof; Optionally, C is selected from any element of Mg and Nb, and/or A is at least two elements selected from Fe, Ti, V, Co and Mg, and optionally is Fe and one or more elements selected from Ti, V, Co and Mg, and/or R is S, and/or D is F. x is selected from a range of 0.001 to 0.005; and/or, y is selected from a range of 0.01 to 0.5, and optionally from a range of 0.25 to 0.5; and/or, z is selected from a range of 0.001 to 0.005; and/or, n is selected from a range of 0.001 to 0.005. Unless otherwise stated, the above parameters can be freely combined, and the combinations thereof will not be enumerated herein.

    [0145] In some embodiments, the lattice change rate of the positive electrode active material is 8% or less, optionally 4% or less. By lowering the lattice change rate, the Li ion transport can be made easier, that is, the Li ions have a stronger migration ability in the material, which is beneficial in improving the rate performance of the secondary battery. The lattice change rate may be measured with a method known in the art, e.g., X-ray diffraction (XRD). The process of lithium intercalation and de-intercalation in LiMnPO.sub.4 is a two-phase reaction. The interfacial stress of the two phases is determined by the lattice change rate. The smaller the lattice change rate, the smaller the interfacial stress and the easier the Li.sup.+ transport. Therefore, reducing the lattice change rate of the doped LiMnPO.sub.4 is beneficial to enhance the Li+ transport capacity, thereby improving the rate performance of the secondary battery.

    [0146] In some embodiments, optionally, the average discharge voltage of a button battery comprising the positive electrode active material is 3.5 V or more and the discharge capacity per gram is 140 mAh/g or more. Optionally, the average discharge voltage is 3.6 V or more and the discharge capacity per gram is 145 mAh/g or more.

    [0147] Although the average discharge voltage of the undoped LiMnPO.sub.4 is 4.0 V or more, the discharge capacity per gram thereof is low, usually less than 120 mAh/g, and thus the energy density is low. By adjusting the lattice change rate by doping, the discharge capacity per gram can be greatly increased, and the overall energy density can be significantly increased when the average discharge voltage reduces slightly.

    [0148] In some embodiments, the Li/Mn antisite defect concentration of the positive electrode active material is 2% or less, and optionally, the Li/Mn antisite defect concentration is 0.5% or less. The so-called Li/Mn antisite defect means that the sites of Li.sup.+ and Mn.sup.2+ have been exchanged in the LiMnPO.sub.4 lattices. The Li/Mn antisite defect concentration refers to the percentage of Li.sup.+ exchanged with Mn.sup.2+ relative to the total amount of the Li.sup.+ in the positive electrode active material. The Mn.sup.2+ of antisite defects can hinder the transport of Li.sup.+, and a reduction in the Li/Mn antisite defect concentration is beneficial in improving the capacity per gram and rate performance of the positive electrode active material. The Li/Mn antisite defect concentration may be measured with a method known in the art, e.g., XRD.

    [0149] In some embodiments, the surface oxygen valency of the positive electrode active material is ?1.82 or less, optionally ?1.89 to ?1.98. By lowering the surface oxygen valency, the interfacial side reactions between the positive electrode active material and an electrolyte solution can be alleviated, thereby improving the cycling performance and high-temperature stability of the secondary battery. The surface oxygen valency may be measured with a method known in the art, e.g., electron energy loss spectroscopy (EELS).

    [0150] In some embodiments, the positive electrode active material has a compacted density under 3 T (ton) of 2.0 g/cm3 or more, optionally 2.2 g/cm3 or more. A higher compacted density indicates a greater weight of the active material per unit volume, and thus, increasing the compacted density is beneficial for increasing the volumetric energy density of a cell. The compacted density may be measured in accordance with GB/T 24533-2009.

    [0151] The average particle size range of the inner core prepared in the present application is 50-500 nm, and the Dv50 is 200-300 nm. The primary particle size of the core is in a range of 50-500 nm, and the Dv50 is 200-300 nm. If the average particle size of the inner core is too large (greater than 500 nm), the capacity per gram of the battery in which this material is used will be affected; and if the average particle size of the inner core is too small, the inner core's specific surface area will be large, and the inner core will be easy to aggregate, making it difficult to achieve uniform coating.

    [0152] It is possible to ensure that each element is uniformly distributed in the crystal lattice without aggregation by means of process control (for example, sufficient mixing and grinding of various source materials). After preparing the positive electrode active material of the present application, the inventors of the present application cut out an middle area (inner core region) of the prepared positive electrode active material particles by a focusing ion beam (abbreviated as FIB), and tested through transmission electron microscope (abbreviated as TEM) and X-ray energy dispersive spectrum (abbreviated as EDS) analysis and found that the elements are uniformly distributed with no aggregation. Meanwhile, the positions of the main characteristic peaks of the inner core of the positive electrode active material according to the present application are basically consistent with those of LiMnPO.sub.4 before doping, indicating that the doped lithium manganese phosphate inner core of the positive electrode active material has no impurity phase, and the improvement of the performance of the battery mainly results from doping with elements, rather than the impurity phase.

    [0153] In some embodiments, the positive electrode active material has a core-shell structure, wherein the shell comprises at least one of a crystalline inorganic substance and a metal oxide. Specifically, the crystalline inorganic substance includes a pyrophosphate of QP.sub.2O.sub.7 and a phosphate of XPO.sub.4, and the metal oxide includes Q.sub.eO.sub.f. Q and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al, and optionally, Q includes Li and one or more selected from Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb or Al; Q is selected from one or more elements of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally from one or more elements of Li, Fe and Zr; M is selected from one or more elements of an alkali metal, an alkaline earth metal, a transition metal, a group IIIA element, a group IVA element, a lanthanide and Sb, optionally from one or more elements of Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, more optionally from one or more elements of Mg, Al, Si, Zn, Zr and Sn; e is greater than 0 and less than or equal to 2; and f is greater than 0 and less than or equal to 5.

    [0154] In some embodiments, the pyrophosphate includes Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, where 0?a?2, 1?b?4, 1?c?6, the values of a, b, and c satisfy the condition of keeping the Li.sub.aQP.sub.2O.sub.7 or Q.sub.b(P.sub.2O.sub.7).sub.c electrically neutral, and Q in the Li.sub.aQP.sub.2O.sub.7 and Q.sub.b(P.sub.2O.sub.7).sub.c is each independently selected from one or more elements of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al.

    [0155] The inventors have found that since metal ions are difficult to migrate in pyrophosphate, pyrophosphate as the coating layer can effectively isolate doped metal ions from the electrolyte solution. Moreover, the structure of the crystalline pyrophosphate is stable, and therefore, coating with the crystalline pyrophosphate can effectively inhibit the dissolution of transition metals and improve cycling performance. The crystalline phosphate and crystalline pyrophosphate have a relatively high lattice matching degree (with a mismatch degree of only 3%), good stability and excellent lithium-ion conductivity; therefore, coating the inner core with the crystalline phosphate and crystalline pyrophosphate can improve the stability of the positive electrode active material and effectively reduce the interfacial side reactions with the electrolyte solution, thereby improving the high-temperature cycling and storage performance of the battery. Similarly, the oxides can also have an effect of stabilizing the dissolution of active doping metals, and oxides are easy to be synthesized with lower costs. In some embodiments, an appropriate ratio of oxides to the crystalline inorganic substances such as pyrophosphate is conducive for the synergistic effect thereof being completely achieved, which can not only further inhibit the dissolution of manganese but also maintain a lower impedance of the secondary battery.

    [0156] In some embodiments, the pyrophosphate and the phosphate each independently have a crystallinity of 10% to 100%, optionally 50% to 100%. The inventors have found that the above inorganic salts in the crystalline form can better combine with the inner core and have an improved ability to intercept and retain the dissolved active metal ions such as Mn. Specifically, the phosphate has an interplanar spacing of 0.244-0.425 nm, optionally 0.345-0.358 nm, and an included angle of crystal orientation (111) of 20.000-37.00?, optionally 24.250-26.45?; and the pyrophosphate has an interplanar spacing of 0.293-0.470 nm, optionally 0.293-0.326 nm, and an included angle of crystal orientation (111) of 18-32.57?, optionally 19.211?-30.846?, more optionally 26.410-32.57?. The pyrophosphate and phosphate with a certain crystallinity enable not only the full achievement of the ability of the pyrophosphate coating layer to prevent the dissolution of manganese ions and the excellent ability of the phosphate coating layer to conduct lithium ions, as well as the reduction of the interfacial side reactions, but also the better lattice matching between the phosphate coating layer and the phosphate coating layer, such that a close combination of the coating layers can be achieved.

    [0157] In some embodiments, the inorganic salts in the coating layers comprised in the shell are all crystalline substances. Specifically, the crystalline pyrophosphate and the crystalline phosphate in the coating layers can be characterized by conventional technical means in the art, and can also be characterized, for example, by means of a transmission electron microscope (TEM). Under TEM, the inner core and the coating layers can be distinguished by testing the interplanar spacing. The specific test method of the interplanar spacing and the included angle of the crystalline pyrophosphate and the crystalline phosphate in the coating layers can comprise the following steps: A certain amount of coated positive electrode active material sample powder is placed in a test tube, and a solvent such as ethanol is injected into the test tube, then fully stirred and dispersed, and then a clean disposable plastic straw is used to take an appropriate amount of the solution, which is dripped on a 300-mesh copper mesh, at this moment, part of the powder will remain on the copper mesh. The copper mesh and the sample are transferred to TEM sample chamber for testing, and the original images of the TEM test is obtained. The original picture obtained from the above TEM test is opened in a diffractometer software and subjected to Fourier transform to obtain a diffraction pattern, the distance from the diffraction spot to the center position in the diffraction pattern is measured to obtain the interplanar spacing, and the included angle is calculated according to the Bragg equation.

    [0158] The difference between the interplanar spacing range of the crystalline pyrophosphate and that of the crystalline phosphate can be directly determined by the value of interplanar spacing. The crystalline pyrophosphate and crystalline phosphate having an interplanar spacing and included angle within the ranges above can more effectively reduce the lattice change rate and the dissolution amount of manganese ions of the positive electrode active material during the process of lithium intercalation and de-intercalation, thereby improving the high-temperature cycling performance and the high-temperature storage performance of the battery.

    [0159] In some embodiments, the coating layer may further contain carbon. The carbon material has a good electronic conductivity. Since an electrochemical reaction occurs in the application of the secondary battery and the participation of electrons is required, carbon with excellent electrical conductivity can be used to coat the positive electrode active material to increase electron transport between particles and at different positions on the particles. Therefore, carbon coating can effectively improve the electrical conductivity and desolvation ability of the positive electrode active material.

    [0160] For example, in some embodiments of the present application, the carbon in the inner coating layer is a mixture of SP2-form carbon and SP3-form carbon, and optionally, the molar ratio of the SP2-form carbon to the SP3-form carbon is any numerical value in a range of 0.1-10, optionally any numerical value in a range of 2.0-3.0. Specifically, the molar ratio of the SP2-form carbon to SP3-form carbon may be about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10, or within any range of any of the above values.

    [0161] The comprehensive electrical performance of the secondary battery is improved by selecting the form of carbon in the carbon coating layer. Specifically, by using a mixed form of SP2-form carbon and SP3-form carbon and limiting the ratio of SP2-form carbon to SP3-form carbon within a certain range, the following can be avoided: if the carbon in the coating layer is in the form of amorphous SP3 only, the electrical conductivity is poor; and if all the carbon is in a graphitized SP2-form, although the electrical conductivity is good, there are few lithium ion paths, which is not conducive to lithium intercalation and de-intercalation. In addition, limiting the molar ratio of SP2-form carbon to SP3-form carbon within the above ranges can not only achieve good electrical conductivity, but also can ensure the paths of lithium ions, which is beneficial to the realization of the function of the secondary battery and the cycling performance thereof.

    [0162] The mixing ratio of the SP2-form carbon to the SP3-form carbon in the carbon coating layer can be controlled by sintering conditions such as the sintering temperature and sintering time. For example, in the case where sucrose is used as the carbon source to prepare the third coating layer, after being subjected to pyrolysis at a high temperature, the sucrose is deposited on the second coating layer, while both the SP3-form and SP2-form carbon coating layers will be produced at a high temperature. The ratio of the SP2-form carbon to the SP3-form carbon may be adjusted by selecting high-temperature pyrolysis conditions and sintering conditions.

    [0163] The structure and characteristics of the carbon coating layer can be determined by a Raman spectroscopy, and the specific test method is as follows: subjecting the energy spectrum of the Raman test to peaking splitting to obtain Id/Ig (wherein Id is the peak intensity of SP3-form carbon, and Ig is the peak intensity of SP2-form carbon), thus confirming the molar ratio of the two forms.

    [0164] In some embodiments of the present application, the shell comprises an inorganic coating layer and a carbon coating layer, wherein the inorganic coating layer is provided to be close to the inner core, and the inorganic coating layer comprises at least one of the phosphates, pyrophosphates, and metal oxides above. For example, in the present application, a person skilled in the art can make choices according to the actual situation: whether the phosphate and pyrophosphate are present in the same coating layer, and which one is provided to be closer to the inner core are not particularly limited. For example, the phosphate and pyrophosphate can together form an inorganic salt coating layer, and the outer side of the inorganic salt coating layer can further be provide with a carbon layer. Alternatively, the pyrophosphate and phosphate each independently form separate coating layers, with one being provided to be closer to the inner core, and the other coating the crystalline inorganic salt coating layer that is closer to the inner core, and a carbon layer is provided on the outermost side. Alternatively, the core-shell structure may be composed of only one inorganic salt coating layer formed by a phosphate or pyrophosphate, and a carbon layer provided on the outer side.

    [0165] The combination between the inorganic coating layer and the inner core is similar to a heterojunction, and the firmness of the combination is limited by the lattice matching degree. When the lattice mismatch is 5% or less, the lattice matching is better, and the two are easy to combine closely. The close combination can ensure that the coating layer will not fall off in the subsequent cycling process, which is beneficial to ensuring the long-term stability of the material. The measurement of the degree of the combination between the coating layer and the core is mainly carried out by calculating the mismatch degree of each lattice constant between the core and the coating layer. In the present application, after element doping in the inner core, in particular element doping at the Mn site and the P site, the matching degree between the inner core and the coating layer is improved compared with that without doping with elements, and the inner core and the crystalline inorganic salt coating layer can be combined more closely.

    [0166] In some embodiments of the present application, the shell comprises a first coating layer, a second coating layer, and a third coating layer, with the first coating layer coating the inner core and comprising a crystalline pyrophosphate. The second coating layer comprises a crystalline phosphate and coats the first coating layer, and the third coating layer is carbon. The pyrophosphate as the first coating layer can effectively isolate doped metal ions from the electrolyte solution. The structure of the crystalline pyrophosphate is stable, and therefore, the coating of the crystalline pyrophosphate can effectively inhibit the dissolution of transition metals and improve cycling performance. The crystalline phosphate as the second coating layer has a relatively high lattice matching degree (with a mismatch degree of only 3%) with the crystalline pyrophosphate as the first coating material, better stability than the pyrophosphate, and excellent lithium-ion conductivity, which is beneficial to improving the stability of the positive electrode active material and reducing the interfacial side reactions between the positive electrode active material and the electrolyte solution. The third coating layer can improve the electronic conductivity of the positive electrode active material, and carbon coating can also effectively improve the electrical conductivity and desolvation ability of the positive electrode active material.

    [0167] In the embodiments above, the coating amount of the first coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core. In some embodiments, the coating amount of the second coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally 2-4 wt %, based on the weight of the inner core. In some embodiments, the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core. In the present application, the coating amount of each layer is not zero.

    [0168] In the positive electrode active material with a core-shell structure of the present application, the coating amount of the three coating layers in the present application is in some embodiments within the above range, which thus can enable the full coating of the inner core, while further improving the dynamic performance, cycling performance and safety performance of the battery without sacrificing the capacity per gram of the positive electrode active material.

    [0169] For the first coating layer, the following situations can be effectively avoided by controlling the coating amount within the above-mentioned range: too small coating amount means that the coating layer is relatively thin, which may not be able to effectively prevent the migration of transition metals; and too high coating amount means that the coating layer is too thick, and may affect the migration of Li+, thereby affecting the rate performance of the positive electrode active material. For the second coating layer, the following situations can be effectively avoided by controlling the coating amount within the above-mentioned range: too high coating amount may affect the overall plateau voltage of the positive electrode active material; too small coating amount may not be able to achieve a sufficient coating effect. For the third coating layer, the carbon coating mainly functions for enhancing the electron transport between particles. However, since a large amount of amorphous carbon is comprised in the structure, the density of the carbon is low. Therefore, if the coating amount is too large, the compacted density of the electrode plate will be affected.

    [0170] In some embodiments, the first coating layer has a thickness of 1-10 nm. In some embodiments, the second coating layer has a thickness of 2-15 nm. In some embodiments, the third coating layer has a thickness of 2-25 nm. In some embodiments, the thickness of the first coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or within any range of any of the above numerical values. In some embodiments, the thickness of the second coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or within any range of any of the above numerical values. In some embodiments, the thickness of the third coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm or about 25 nm, or within any range of any of the above numerical values.

    [0171] When the thickness of the first coating layer is in a range of 1-10 nm, the adverse effect on the dynamic performance of the positive electrode active material resulting from a too thick first coating layer can be avoided, and the problem that the first coating layer cannot effectively hinder the migration of transition metal ions when the first coating layer is too thin can be avoided. When the thickness of the second coating layer is in a range of 2-15 nm, the surface structure of the second coating layer is stable, and less side reaction with the electrolyte solution occurs, so the interfacial side reaction can be effectively reduced, thereby improving the high-temperature cycling performance and the high-temperature storage performance of the battery. When the thickness of the third coating layer is in a range of 2-25 nm, the electrical conductivity of the positive electrode active material can be improved and the compacted density of the positive electrode plate prepared by using the positive electrode active material can be improved. The thickness determination of the coating layer is mainly carried out by FIB, and the specific method may comprise the following steps: randomly selecting a single particle from the positive electrode active material powder to be tested, cut out a thin slice with a thickness of about 100 nm from the middle position or near the middle position of the selected particle, and then conducting a TEM test on the slice, measuring the thickness of the coating layer, at 3-5 positions and taking the average value.

    [0172] In some embodiments, based on the weight of the positive electrode active material, the manganese element content is in a range of 10 wt % to 35 wt %, optionally in a range of 15 wt % to 30 wt %, more optionally in a range of 17 wt % to 20 wt %. In some embodiments, based on the weight of the positive electrode active material, the content of phosphorus element is in a range of 12 wt % to 25 wt %, more optionally in a range of 15 wt % to 20 wt %. In some embodiments, the weight ratio of manganese element to phosphorus element is in the range of 0.90-1.25, optionally 0.95-1.20. In the present application, in the case where manganese is contained only in the inner core of the positive electrode active material, the content of manganese may correspond to that of the inner core.

    [0173] Limiting the content of the phosphorus element within the ranges above can effectively avoid the following situations: if the content of phosphorus element is too high, the covalency of PO may be too strong and affect the conduction of small polarons, thereby affecting the conductivity of the positive electrode active material; if the content of phosphorus element is too low, the stability of the pyrophosphate lattice structure in the inner core and the first coating layer and/or the phosphate lattice structure in the second coating layer may be reduced, thereby affecting the overall stability of the positive electrode active material. The weight ratio of manganese to phosphorus content has the following effects on the performance of the battery: If the weight ratio is too large, it means that there are too many manganese element, and the dissolution of manganese ions may be increased, thereby affecting the stability and capacity per gram performance of the positive electrode active material, and affecting the cycling performance and storage performance of the battery; and if the weight ratio is too small, it means that there are too much phosphorus element, and impurity phases are easily formed, and the discharge voltage plateau of the positive electrode active material may drop, thereby reducing the energy density of the battery. The determination of manganese and phosphorus elements can be carried out by conventional technical means in the art. In particular, the following methods are used to determine the content of the manganese and phosphorus elements: dissolving the positive electrode active material in dilute hydrochloric acid (with a concentration of 10-30%), measuring the content of each element in the solution using ICP, and then determining and converting the content of manganese element to obtain the weight percentage thereof.

    [0174] In some other embodiments of the present application, the inorganic coating layers include a first coating layer coating the inner core and a second coating layer coating the first coating layer, wherein the first coating layer comprises a pyrophosphate of QP.sub.2O.sub.7 and a phosphate of XPO.sub.4, and the second coating layer is a carbon coating layer. The chemical composition and crystallinity of the pyrophosphate QP.sub.2O.sub.7 and the phosphate XPO.sub.4 are similar to those in the previous embodiments, and will not be repeated here.

    [0175] Specifically, in these embodiments, the coating amount of the first coating layer is greater than 0 wt % and less than or equal to 7 wt %, optionally 4-5.6 wt %, based on the weight of the inner core. Optionally, the weight ratio of the pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1. Optionally, the coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, optionally 3-5 wt %, based on the weight of the inner core. The coating amount of each layer is not zero. When the coating amount of the first coating layer is within the above range, the dissolution of manganese can be further inhibited, and at the same time, the transport of lithium ions can be further promoted. Besides, the following situations may be effectively avoided: if the coating amount of the first coating layer is too small, it may lead to insufficient inhibition of the dissolution of manganese by pyrophosphate, and non-significant improvement of lithium ion transport performance; and if the coating amount of the first coating layer is too large, it may cause the coating layer to be too thick, increase the impedance of the battery, and affect the dynamic performance of the battery. The proper ratio of pyrophosphate to phosphate is conducive to the full achievement of the synergistic effect of the two. Besides, the following situations may be effectively avoided: if the pyrophosphate is too much and the phosphate is too little, the impedance of the battery may increase; and if there is too much phosphate and too little pyrophosphate, the effect of inhibiting the dissolution of manganese will not be significant.

    [0176] In the first coating layer of the lithium manganese phosphate positive electrode active material, the pyrophosphate and phosphate with certain crystallinities are beneficial to keep the structure of the first coating layer stable and reduce lattice defects. For one thing, this is conducive to the exertion of the pyrophosphate in hindering the dissolution of manganese; for another thing, this is also beneficial to reducing the surface lithium content and the surface oxygen valency of phosphate, thereby reducing the interfacial side reactions between the positive electrode material and the electrolyte solution, reducing the consumption of electrolyte solution, and improving the cycling performance and safety performance of the battery.

    [0177] In some embodiments, optionally, the phosphate of the first coating layer has an interplanar spacing of 0.345-0.358 nm, and an included angle of crystal orientation (111) of 24.25?-26.45?; and optionally the pyrophosphate of the first coating layer has an interplanar spacing of 0.293-0.326 nm, and an included angle of crystal orientation (111) of 26.41?-32.57?. When the interplanar spacings and the included angles of the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above ranges, the impurity phase in the coating layer may be effectively avoided and thus the capacity per gram, the cycling performance, and the rate performance of the positive electrode active material are improved. Similarly, the crystallinity of the pyrophosphate and phosphate may be adjusted, for example, by adjusting the process conditions of the sintering process, such as the sintering temperature and the sintering time. The crystallinity of the pyrophosphate and phosphate may be measured by a method known in the art, such as by X-ray diffraction, density, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption methods.

    [0178] The carbon-containing layer as the second coating layer can function as a barrier to avoid the direct contact between the positive electrode active material and the electrolyte solution, thereby reducing the corrosion of the active material by the electrolyte solution and improving the safety performance of the battery at high temperatures. Moreover, it has strong electrical conductivity, which can reduce the internal resistance of the battery, thereby improving the dynamic performance of the battery. However, since the capacity per gram of the carbon material is relatively low, when the amount of the second coating layer is excessively large, the capacity per gram of the positive electrode active material as a whole may be reduced. Thus, when the coating amount of the second coating layer is in the above range, the dynamic performance and safety performance of the battery can be further improved without compromising the capacity per gram of the positive electrode active material.

    [0179] In some other embodiments, the shell of the positive electrode active material may also comprise a first coating layer and a second coating layer, wherein the first coating layer comprises a crystalline pyrophosphate of QP.sub.2O.sub.7 and a metal oxide of Q.sub.eO.sub.f, and the second coating layer is a carbon coating layer. The specific composition of the pyrophosphate QP.sub.2O.sub.7 and the metal oxide Q.sub.eO.sub.f has been described in detail above and will not be repeated here.

    [0180] As shown in FIG. 3, the first coating layer 12 comprises a crystalline phosphate and a crystalline oxide; due to the high migration barrier (>1 eV) of transition metals in pyrophosphate, the dissolution of the transition metals can be effectively inhibited; and the crystalline oxide has a high structural stability and a low surface activity; therefore, coating with the crystalline oxide can effectively reduce the interfacial side reactions, thereby improving the high-temperature cycling and storage performance of the battery. In addition, since the second coating layer 13 is a carbon-containing layer, the electrical conductivity and desolvation ability of the inner core 11 can be effectively improved. In addition, the barrier effect of the second coating layer 13 can further hinder the migration of manganese ions into the electrolyte solution and reduce the corrosion of the active material by the electrolyte solution. Therefore, with the inner core being lithium manganese phosphate as an example, the positive electrode active material of the present application obtained by doping lithium manganese phosphate with specific elements and coating the surface thereof can not only reduce the generation of Li/Mn antisite defects and effectively inhabit the dissolution of Mn in the process of lithium intercalation and de-intercalation, but also can accelerate the migration of lithium ions, thereby improving the rate performance of the cell, and improving the cycling performance, high-temperature performance, and safety performance of the secondary battery.

    [0181] In addition, it should be noted that FIG. 3 shows a schematic structural diagram of an positive electrode active material proposed in the present application, and is not limited to the embodiments mentioned above. Any positive electrode active material having two coating layers of the present application can have a structure as shown in FIG. 3. The coating layers (12 and 13 as shown in the figure) can achieve complete or partial coating of the inner structure, with a coating amount or area of 100%, 90%, 80%, 70%, 60%, 50%, etc., of the inner structure.

    [0182] In the embodiments above, the pyrophosphate in the first coating layer has an interplanar spacing of 0.293-0.326 nm and an included angle of crystal orientation (111) of 26.410?-32.57?; optionally, the pyrophosphate in the first coating layer has an interplanar spacing of 0.300-0.310 nm (e.g., 0.303 nm); and/or optionally, the pyrophosphate in the first coating layer has an included angle of crystal orientation (111) of 29.00?-30.00? (e.g., 29.496?). When the interplanar spacing and included angle of crystal direction (111) of the pyrophosphate in the first coating layer are within the ranges above, the impurity phase in the coating layer can be effectively avoided, thereby improving the capacity per gram of the material, and improving the cycling performance and rate performance of the secondary battery.

    [0183] The coating amount of the first coating layer is greater than 0 wt % and less than or equal to 7 wt %, optionally 4-5.6 wt %, based on the weight of the inner core. When the coating amount of the first coating layer is within the ranges above, the dissolution of manganese can be further inhibited while further accelerating the transport of lithium ions and enabling the secondary battery to maintain a low impedance, thereby improving the dynamic performance of the secondary battery. In some embodiments, the weight ratio of the pyrophosphate to the oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1. An appropriate ratio of an pyrophosphate to an oxide is conducive for the full achievement of the synergistic effect thereof, which can not only further inhibit the dissolution of manganese but also maintain a lower impedance of the secondary battery. The coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, optionally 3-5 wt %, based on the weight of the inner core. The properties and advantages of the carbon coating layer are similar to those described in the embodiments above and will not be repeated here.

    [0184] In the above embodiments, the first coating layer has a thickness of 1-100 nm. Thus, due to the high migration barrier of transition metals in the first coating layer, the dissolution of the transition metals can be effectively reduced. The oxide in the first coating layer has a higher stability, which can effective reduce interfacial side reactions, thereby improving the high-temperature stability of the material. In some embodiments, the second coating layer has a thickness of 1-100 nm. In some embodiments, the pyrophosphate in the first coating layer has a crystallinity of 10% to 100%, optionally 50% to 100%. In the first coating layer of the lithium manganese phosphate positive electrode active material of the present application, the pyrophosphate with a certain crystallinity is beneficial for keeping the structure of the first coating layer stable and reducing lattice defects. For one thing, it is conducive for the full achievement of the effect of pyrophosphate on preventing the dissolution of manganese; and for another, it is also beneficial for reducing the content of lithium impurities on the surface and the surface oxygen valency, thereby reducing the interfacial side reactions between the positive electrode material and the electrolyte solution, reducing the consumption of the electrolyte solution, and improving the cycling performance and safety performance of the secondary battery.

    [0185] In some other embodiments of the present application, the shell can also comprise a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer. Similarly, such a positive electrode active material may have a structure as shown in FIG. 4. The first coating layer 12 comprises a crystalline pyrophosphate; the second coating layer 13 comprises a metal oxide of Q.sub.eO.sub.f; the crystalline pyrophosphate includes Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, where a is greater than 0 and less than or equal to 2, b is any numerical value in a range of 1-4, and c is any numerical value in a range of 1-3; and the third coating layer 14 comprises carbon. The specific composition of the crystalline pyrophosphates including Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c and the metal oxide of Q.sub.eO.sub.f has been described in detail above and will not be repeated here.

    [0186] Similarly, the combination between the first coating layer and the inner core is similar to a heterojunction, and the firmness of the combination is limited by the lattice matching degree. The crystalline oxide as the second coating layer has a relatively high lattice matching degree (with a mismatch degree of only 3%) with the crystalline pyrophosphate as the first coating material and better stability than the pyrophosphate, such that coating the pyrophosphate with same is beneficial for improving the stability of the material. Coating with a crystalline oxide can effectively reduce the interfacial side reaction on the surface of the positive electrode active material, thereby improving the high-temperature cycling and storage performance of the secondary battery. The mode for the lattice matching between the second coating layer and the first coating layer is similar to the above combination between the first coating layer and the core. When the lattice mismatch is 5% or less, the lattice matching is better, and the two are easy to combine closely. The main reason why carbon is used as the third layer of coating is that the carbon layer has a better electronic conductivity.

    [0187] In some embodiments, the coating amount of the first coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core; and/or the coating amount of the second coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally 2 wt %-4 wt %, based on the weight of the inner core; and/or the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core. The coating amount of each layer is not zero. The coating amounts of the three coating layers are in some embodiments within the ranges above, such that the inner core can be fully coated, while the dynamic performance and safety performance of the secondary battery can be further improved without sacrificing the capacity per gram of the positive electrode active material. Specifically, with the coating amount of the first coating layer being within the ranges above, the dissolution of the transition metals can be reduced, which ensures the successful migration of lithium ions, thereby improving the rate performance of the positive electrode active material. With the coating amount of the second coating layer being within the ranges above, the positive electrode active material can maintain a certain plateau voltage while ensuring the coating effect. For the third coating layer, the carbon coating mainly functions for accelerating the electron transport between particles. However, since a large amount of amorphous carbon is comprised in the structure, the density of the carbon is low. Therefore, the coating amount of the carbon being within the range above can ensure the compacted density of the electrode plate.

    [0188] In some embodiments, the first coating layer has a thickness of 2-10 nm; and/or the second coating layer has a thickness of 3-15 nm; and/or the third coating layer has a thickness of 5-25 nm. The thickness of the first coating layer may be about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, or about 10 nm, or within any range of any of the above numerical values. In some embodiments, the thickness of the second coating layer may be about 3 nm, about 4 nm, about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, or within any range of any of the above numerical values. In some embodiments, the thickness of the third coating layer may be about 5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm, about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about 22 nm, about 23 nm, about 24 nm or about 25 nm, or within any range of any of the above numerical values. When the first coating layer has a thickness in a range of 2-10 nm, the dissolution of the transition metals can be effectively reduced, and the dynamic performance of the secondary battery can be ensured. When the second coating layer has a thickness in the range of 3-15 nm, the surface structure of the second coating layer is stable, and there will be less side reaction with the electrolyte solution, such that the interfacial side reactions can be effectively reduced, thereby improving the high-temperature performance of the secondary battery. When the third coating layer has a thickness in the range of 5-25 nm, the electrical conductivity of the material can be improved and the compacted density performance of the battery electrode plate prepared by using the positive electrode active material can be improved. Similarly, the thickness of the coating layer is mainly determined by FIB.

    [0189] In the above embodiments, based on the weight of the positive electrode active material, the content of manganese element is in a range of 10-35 wt %, optionally in a range of 15-30 wt %, more optionally in a range of 17-20 wt %, and the content of phosphorus element is in a range of 12-25 wt %, optionally in a range of 15-20 wt %; and optionally, the weight ratio of manganese element to phosphorus element is in a range of 0.90-1.25, more optionally in a range of 0.95-1.20. In the present application, in the case where manganese is contained only in the inner core of the positive electrode active material, the content of manganese may correspond to that of the inner core. In the present application, limiting the content of manganese element within the above ranges can ensure a higher stability and density of the positive electrode active material, such that the cycling performance, storage performance, compacted density, etc., of the secondary battery can be improved; moreover, the positive electrode active material can maintain a certain voltage plateau height, thereby increasing the energy density of the secondary battery. In the present application, limiting the content of phosphorus element within the above ranges can effectively increase the electrical conductivity of the material, and improve the overall stability of the material. In the present application, limiting the weight ratio of the manganese to phosphorus content within the above ranges can effectively reduce the dissolution of transition metal elements such as manganese and increase the stability and capacity per gram of the positive electrode active material, thereby improving the cycling performance and storage performance of the secondary battery; moreover, facilitating to reduce the impurity phases in the material and maintain the discharge voltage plateau height of the material, thereby increasing the energy density of the secondary battery.

    [0190] In some embodiments of the present application, the positive electrode active material comprises a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, wherein the first coating layer comprises a crystalline pyrophosphate of Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, the second coating layer comprises a crystalline phosphate of XPO.sub.4, and the third coating layer is carbon.

    [0191] Similarly, in this embodiment, the coating amount of the first coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core; and/or the coating amount of the second coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally 2-4 wt %, based on the weight of the inner core; and/or the coating amount of the third coating layer is greater than 0 and less than or equal to 6 wt %, optionally greater than 0 and less than or equal to 5.5 wt %, more optionally greater than 0 and less than or equal to 2 wt %, based on the weight of the inner core. The first coating layer has a thickness of 1-10 nm; and/or the second coating layer has a thickness of 2-15 nm; and/or the third coating layer has a thickness of 2-25 nm.

    [0192] Based on the weight of the positive electrode active material, the content of manganese element is in a range of 10 wt %-35 wt %, optionally in a range of 15 wt %-30 wt %, more optionally in a range of 17 wt %-20 wt %, the content of phosphorus element is in a range of 12 wt %-25 wt %, optionally in a range of 15 wt %-20 wt %, and the weight ratio of manganese element to phosphorus element is in a range of 0.90-1.25, optionally 0.95-1.20.

    [0193] The effects of the parameters, such as the thickness, the content of phosphorus, the content of manganese, and the content of the coating layer, and the principles for achieving these effects, have been described in detail above and will not be repeated here.

    [0194] In some embodiments, the primary particles of the positive electrode active material have an average particle size in a range of 50-500 nm and a volume median particle size Dv50 in a range of 200-300 nm. Due to the agglomeration of the particles, the actually measured size of the agglomerated secondary particles may be 500-40000 nm. The particle size of the positive electrode active material affects the processing of the material and the compacted density performance of the electrode plate. By selecting the average particle size of the primary particles within the above range, the following situations can be avoided: if the average particle size of the primary particles of the positive electrode active material is too small, it may cause particle aggregation, difficult dispersion, and need more binder, resulting in poor brittleness of the electrode plate; if the average particle size of the primary particles of the positive electrode active material is too large, the gaps between the particles may be large and the compacted density may be reduced. Through the above solution, the lattice change rate and dissolution of Mn of the lithium manganese phosphate during the process of lithium intercalation and de-intercalation can be effectively inhibited, thereby improving the high-temperature cycling stability and high-temperature storage performance of the secondary battery.

    [0195] A second aspect of the present application relates to a method for preparing the positive electrode active material of the first aspect of the present application. The method comprises steps of forming an inner core and forming a shell at least on the surface of the inner core, wherein the inner core comprises at least one of a ternary material, dLi.sub.2MnO.sub.3.Math.(1?d)LiMO.sub.2 and LiMPO.sub.4, where 0<d<1, and M includes one or more selected from Fe, Ni, Co, and Mn; and the shell comprises a crystalline inorganic substance having a full width at half maximum of the main peak of 0-3? as measured by means of X-ray diffraction, and the crystalline inorganic substance includes one or more selected from a metal oxide and an inorganic salt.

    [0196] The structure and content of the inner core and the coating layers in the shell have been explained in detail above and will not be repeated here. Hereafter, with the inner core containing LiMPO.sub.4 and M including Mn and a non-Mn element as an example, the steps of the method will be explained in detail below:

    [0197] Specifically, the method comprises the operation of forming a LiMPO.sub.4 compound, wherein the LiMPO.sub.4 compound may have all the characteristics and advantages of the LiMPO.sub.4 compounds mentioned above and will not be repeated here. In brief, M includes Mn and a non-Mn element, and the non-Mn element satisfies at least one of the following conditions: the ionic radius of the non-Mn element being denoted as a, and the ionic radius of manganese element being denoted as b, |a?b|/b is not greater than 10%; the variable range of the valence of the non-Mn element is not greater than that of Mn element; the chemical activity of a chemical bond formed by the non-Mn element and O is not less than that of a PO bond; and the highest valence of the non-Mn element is not greater than 6.

    [0198] In some embodiments, when the non-Mn element includes a first doping element and a second doping element, the method comprises: mixing a manganese source, a dopant of the manganese-site element and an acid to obtain manganese salt particles having the first doping element; and mixing the manganese salt particles having the first doping element with a lithium source, a phosphorus source, and a dopant of the second doping element in a solvent to obtain a slurry, and sintering same under the protection of an inert gas atmosphere to obtain the LiMPO.sub.4 compound. The types of the first doping element and the second doping element have been described in detail above and will not be repeated here. In some embodiments, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and the second doping element includes one or more elements selected from B (boron), S, Si and N.

    [0199] In some embodiments, the LiMPO.sub.4 compound is formed according to the chemical formula of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4, and in some other embodiments, the LiMPO.sub.4 compound is formed according to the chemical formula of Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n. The elements of each substitution site and the selection principles and beneficial effects thereof, as well as the atomic ratio range have been described in detail above and will not be repeated here. Here, a source of the C element is selected from at least one of the elementary substance, oxide, phosphate, oxalate, carbonate and sulfate of the C element; a source of the A element is selected from at least one of the elementary substance, oxide, phosphate, oxalate, carbonate, sulfate, chloride, nitrate, organic acid salt, hydroxide and halide of the A element; a source of an R element is selected from at least one of the sulfate, borate, nitrate and silicate, organic acid, halide, organic acid salt, oxide and hydroxide of the R element; and a source of an D element is selected from at least one of the elementary substance and ammonium salt of the D element.

    [0200] In some embodiments, the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, an organic acid like oxalic acid, etc, and may be, for example, oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of 60 wt % or less. In some embodiments, the manganese source may be a manganese-containing substance useful for preparing lithium manganese phosphate that is known in the art. For example, the manganese source may be selected from one or a combination of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate and manganese carbonate. In some embodiments, the lithium source may be a lithium-containing substance useful for preparing lithium manganese phosphate that is known in the art. For example, the lithium source may be selected from one or a combination of lithium carbonate, lithium hydroxide, lithium phosphate and lithium dihydrogen phosphate. In some embodiments, the phosphorus source may be a phosphorus-containing substance useful for preparing lithium manganese phosphate that is known in the art. For example, the phosphorus source may be selected from one or a combination of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and phosphoric acid. The added amounts of respective sources of the doping elements at each site depend on a target doping amount, and the ratio of the amounts of the lithium source, the manganese source and the phosphorus source conforms to a stoichiometric ratio.

    [0201] In some embodiments, the manganese salt particles having a first doping element is obtained when at least one of the following conditions is satisfied: the manganese source, the manganese-site element and the acid are mixed at a temperature of 20-120? C., optionally 40-120? C., optionally 60-120? C., more optionally 25-80? C.; and/or the mixing is carried out under stirring at 200-800 rpm, optionally 400-700 rpm, more optionally 500-700 rpm for 1-9 h, optionally 3-7 h, more optionally 2-6 h.

    [0202] In some embodiments, the positive electrode active material may have a first doping element and a second doping element. In this method, the manganese salt particles having the first doping element, and a lithium source, a phosphorus source, and a dopant of the second doping element are ground and mixed in a solvent for 8-15 h. For example, the manganese salt particles having the first doping element, and a lithium source, a phosphorus source, and a dopant of the second doping element are mixed in a solvent at a temperature of 20-120? C., optionally 40-120? C., for 1-10 h.

    [0203] Specifically, in this method, the LiMPO.sub.4 compound can be formed according to the chemical formula of Li.sub.1+xC.sub.xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n. More specifically, the manganese salt particles having the first doping element, and a lithium source, a phosphorus source, and a dopant of the second doping element can be ground and mixed in a solvent for 8-15 h. For example, a manganese source, a source of the A element and an acid can be dissolved in a solvent to form a suspension of an A element-doped manganese salt, and the suspension is filtered, followed by drying to obtain the A element-doped manganese salt; a lithium source, a phosphorus source, a source of the C element, a source of R element, a source of D element, a solvent and the A element-doped manganese salt are mixed to obtain a slurry; the slurry is subjected to a spray-drying granulation to obtain particles; and the particles are sintered to obtain the positive electrode active material. The sintering may be carried out at a temperature in a range of 600-900? C. for 6-14 hours.

    [0204] By controlling the reaction temperature, the stirring speed and the mixing time during the doping, the doping elements can be uniformly distributed, and the sintered material has a higher degree of crystallinity, thereby improving the capacity per gram, rate performance and the like of the material.

    [0205] In some specific embodiments, the operation of forming the inner core may comprise the following steps: (1) a manganese source, a source of a B element and an acid are dissolved and stirred in a solvent to generate a suspension of a B element-doped manganese salt, the suspension is filtered, and the resultant filter cake is dried, to obtain the B element-doped manganese salt; (2) a lithium source, a phosphorus source, a source of an A element, a source of a C element and a source of a D element, a solvent and the B element-doped manganese salt obtained in step (1) are added into a reaction container, and ground and mixed to obtain a slurry; (3) the slurry obtained in step (2) is transferred into a spray drying apparatus for spray-drying granulation, to obtain particles; and (4) the particles obtained in step (3) are sintered.

    [0206] In some embodiments, the solvents in step (1) and step (2) may each independently be a commonly used solvent for preparing a manganese salt and lithium manganese phosphate by those skilled in the art. For example, the solvents may each independently be selected from at least one of ethanol and water (e.g., deionized water), etc.

    [0207] In some embodiments, the stirring of step (1) is carried out at a temperature in a range of 60? C. to 120? C. In some embodiments, the stirring of step (1) is carried out at a stirring speed of 200 to 800 rpm, or 300 to 800 rpm, or 400 to 800 rpm. In some embodiments, the stirring of step (1) is carried out for 6 to 12 h. In some embodiments, the grinding and mixing of step (2) are carried out for 8 to 15 h.

    [0208] By controlling the reaction temperature, the stirring speed and the mixing time during the doping, the doping elements can be uniformly distributed, and the sintered material has a higher degree of crystallinity, thereby improving the capacity per gram, rate performance and the like of the material.

    [0209] In some embodiments, in step (1), the filter cake may be washed before drying. In some embodiments, the drying in step (1) may be carried out by means and conditions known to those skilled in the art. For example, the temperature of the drying may be in a range of 120? C. to 300? C. Optionally, the dried filter cake may be ground into particles, for example, until the median particle size Dv50 of the particles is in a range of 50-200 nm. Herein, the median particle size Dv50 refers to a particle size corresponding to a cumulative volume distribution percentage of the positive electrode active material reaching 50%. In the present application, the median particle size Dv50 of the positive electrode active material may be determined by using a laser diffraction particle size analysis method. For example, the determination may be performed with reference to the standard GB/T 19077-2016 by using a laser particle size analyzer (e.g., Malvern Master Size 3000).

    [0210] In some embodiments, in step (2), a carbon source is also added into the reaction vessel for grinding and mixing. Thus, the method can obtain a positive electrode active material having a surface coated with carbon. Optionally, the carbon source includes one or a combination of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol and citric acid. A molar ratio of the amount of the carbon source to the amount of the lithium source is usually in a range of 0.1% to 5%. The grinding may be carried out by suitable grinding means known in the art, e.g., sanding.

    [0211] The temperature and time of the spray drying in step (3) may be conventional temperature and time for spray drying in the art, e.g., at 100? C. to 300? C. for 1 to 6 h.

    [0212] In some embodiments, the sintering is carried out in a temperature range of 600? C. to 900? C. for 6 to 14 h. By controlling the sintering temperature and time, the degree of crystallinity of the material can be controlled, and the dissolution of Mn and Mn-position doping element after cycling of the positive electrode active material is reduced, thereby improving the high-temperature stability and cycling performance of the battery. In some embodiments, the sintering is carried in a protective atmosphere, and the protective atmosphere may be nitrogen, an inert gas, hydrogen or a mixture thereof.

    [0213] In some other embodiments, the inner core of the positive electrode active material may only comprise a Mn-site doping element and a P-site doping element. The steps of providing the positive electrode active material may include: step (1): mixing and stirring a manganese source, a dopant of the A element, and an acid in a container to obtain an element-A doped manganese salt particle; step (2): mixing the A element-doped manganese salt particles with a lithium source, a phosphorus source, and a dopant of R element in a solvent to obtain a slurry, and sintering same under the protection of an inert gas atmosphere to obtain an inner core doped with elements A and R. In some optional embodiments, after the manganese source, the A element dopant and the acid react in a solvent to obtain a suspension of an A element-doped manganese salt, the suspension is filtered, dried and sanded to obtain A element-doped manganese salt particles with a particle size of 50-200 nm. In some optional embodiments, the slurry in step (2) is dried to obtain a powder, and the powder is then sintered to obtain a positive electrode active material doped with elements A and R.

    [0214] In some embodiments, in step (1), the mixing is carried out at a temperature of 20-120? C., optionally 40-120? C.; and/or in step (1), the stirring is carried out at 400-700 rpm for 1-9 h, optionally for 3-7 h. Optionally, the reaction temperature in the step (1) can be at about 30? C., about 50? C., about 60? C., about 70? C., about 80? C., about 90? C., about 100? C., about 110? C. or about 120? C.; the stirring in the step (1) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours or about 9 hours; and optionally, the reaction temperature and stirring time in the step (1) may be within any range of any of the above-mentioned numerical values.

    [0215] In some embodiments, in step (2), the mixing is carried out at a temperature of 20-120? C., optionally 40-120? C., for 1-12 h. Optionally, the reaction temperature in the step (2) may be about 30? C., about 50? C., about 60? C., about 70? C., about 80? C., about 90? C., about 100? C., about 110? C. or about 120? C.; the mixing in the step (2) is carried out for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours or about 12 hours; optionally, the reaction temperature and mixing time in the step (2) may be within any range of any of the above-mentioned numerical values.

    [0216] When the temperature and time during the preparation of the positive electrode active particles are within the above ranges, the prepared positive electrode active material prepared therefrom has fewer lattice defects, which is beneficial to inhibiting the dissolution of manganese and reducing the interfacial side reactions between the positive electrode active material and the electrolyte solution, thereby improving the cycling performance and safety performance of the secondary battery.

    [0217] In some embodiments, optionally, during the preparation of dilute acid manganese particles doped with elements A and R, the pH of the solution is controlled to be 3.5-6; optionally, the pH of the solution is controlled to be 4-6; and even more optionally, the pH of the solution is controlled to be 4-5. It should be noted that the pH of the obtained mixture may be adjusted in the present application by a method commonly used in the art, for example by adding an acid or a base. In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particle, the lithium source, and the phosphorus source is 1:0.5-2.1:0.5-2.1, and more optionally, the molar ratio of the A element-doped manganese salt particle, the lithium source, and the phosphorus source is about 1:1:1.

    [0218] In some embodiments, optionally, the sintering condition during the preparation of lithium manganese phosphate doped with element A and element R is: sintering is carried out at 600-950? C. for 4-10 hours under an atmosphere of inert gas or a mixture of inert gas and hydrogen; optionally, the sintering may be performed at about 650? C., about 700? C., about 750? C., about 800? C., about 850? C. or about 900? C. for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; Optionally, the sintering temperature and the sintering time may be in any range of any of the above-mentioned numerical values. During the preparation of the lithium manganese phosphate doped with element A and element R, if the sintering temperature is too low and the sintering time is too short, the crystallinity of the inner core of the material will be relatively low, which will affect the overall performance, and if the sintering temperature is too high, impurity phases are prone to appear in the inner core of the material, thereby affecting the overall performance; if the sintering time is too long, the inner core particles of the material will be grown to be relatively large, which will affect the capacity per gram, compacted density, rate performance, and the like. In some optional embodiments, optionally, the protective atmosphere is a mixed gas of 70-90 vol % nitrogen and 10-30 vol % hydrogen.

    [0219] In some embodiments, with the particle having the above chemical composition being used as the inner core, the method further includes steps of forming a shell coating the inner core.

    [0220] Specifically, the coating steps may include a step of forming a carbon coating layer. Optionally, the carbon source includes one or a combination of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol and citric acid. A molar ratio of the amount of the carbon source to the amount of the lithium source is usually in a range of 0.1% to 5%. The grinding may be carried out by suitable grinding means known in the art, e.g., sanding.

    [0221] Before forming the carbon layer, the method further includes a step of forming the inorganic coating layer mentioned above.

    [0222] For example, when the coating layers include a first coating layer and a second coating layer coating the first coating layer, wherein the first coating layer comprises a pyrophosphate of QP.sub.2O.sub.7 and a phosphate of XPO.sub.4, and the second coating comprises carbon, the method comprises: providing a QP.sub.2O.sub.7 powder and an XPO.sub.4 suspension containing a carbon source, adding the lithium manganese phosphate oxide and the QP.sub.2O.sub.7 powder into the XPO.sub.4 suspension containing a carbon source, and mixing and sintering same to obtain a positive electrode active material.

    [0223] Herein, the QP.sub.2O.sub.7 powder is a commercially available product, or optionally, the QP.sub.2O.sub.7 powder is provided by: adding a source of a Q element and a phosphorus source into a solvent to obtain a mixture, adjusting the pH of the mixture to be 4-6, and stirring same for complete reaction, followed by drying and sintering; and the QP.sub.2O.sub.7 powder is provided when at least one of the following conditions is satisfied: the drying is carried out at 100-300? C., optionally 150-200? C., for 4-8 h; and the sintering is carried out at 500-800? C., optionally 650-800? C., in an inert gas atmosphere for 4-10 h. Specifically, for example, for forming the coating layer, the sintering temperature is 500-800? C., and the sintering time is 4-10 hours.

    [0224] In some embodiments, optionally, the XPO.sub.4 suspension comprising a carbon source is commercially available, or optionally, prepared by the following method: uniformly mixing a lithium source, an X source, a phosphorus source, and a carbon source in a solvent, then heating the reaction mixture to 60-120? C., and maintaining the temperature for 2-8 hours to obtain an XPO.sub.4 suspension containing a carbon source. Optionally, during the process of preparing the XPO.sub.4 suspension containing a carbon source, the pH of the mixture is adjusted to 4-6.

    [0225] In some embodiments, optionally, the primary particles of the two-layer coated lithium manganese phosphate positive electrode active material in the present application have a median particle size Dv50 of 50-2000 nm.

    [0226] In some other embodiments, the coating layers include a first coating layer coating the LiMPO.sub.4 compound, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, wherein the first coating layer comprises a crystalline pyrophosphate of Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c where 0?a?2, 1?b?4, 1?c?6, the values of a, b, and c satisfy the condition of keeping the crystalline pyrophosphate of Li.sub.aQP.sub.2O.sub.7 or Q.sub.b(P.sub.2O.sub.7).sub.c electrically neutral, and Q in the crystalline pyrophosphates of Li.sub.aQP.sub.2O.sub.7 and Q.sub.b(P.sub.2O.sub.7).sub.c is each independently selected from one or more elements of Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al; the second coating layer comprises crystalline phosphate XPO.sub.4 in which X is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, or Al; and the third coating layer is carbon.

    [0227] Specifically, in the first coating step, the pH of the solution in which the source of element Q, the phosphorus source, the acid, and optionally the lithium source are dissolved is controlled to be 3.5-6.5, the solution is then stirred and reacted for 1-5 h, and the solution is then heated to 50-120? C. and maintained at this temperature for 2-10 h and/or sintered at 650-800? C. for 2-6 hours. Optionally, in the first coating step, the reaction is performed completely. Optionally, in the first coating step, the reaction is performed for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours or about 5 hours. Optionally, in the first coating step, the reaction time of the reaction may be within any range of any of the above-mentioned numerical values. Optionally, in the first coating step, the pH of the solution is controlled to be 4-6. Optionally, in the first coating step, the solution is heated to about 55? C., about 60? C., about 70? C., about 80? C., about 90? C., about 100? C., about 110? C. or about 120? C., and maintained at that temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours; optionally, in the first coating step, the heating temperature and maintaining time may be within any range of any of the above-mentioned numerical values. Optionally, in the first coating step, the sintering may be performed at about 650? C., about 700? C., about 750? C., or about 800? C. for about 2 hours, about 3 hours, about 4 hours, about 5 hours or about 6 hours; Optionally, the sintering temperature and the sintering time may be in any range of any of the above-mentioned numerical values.

    [0228] In the first coating step, by controlling the sintering temperature and time within the above ranges, the following situations can be avoided: when the sintering temperature is too low and the sintering time is too short in the first coating step, the crystallinity of the first coating layer may be low, and there may be many amorphous substances, which may lead to a decline in the effect of inhibiting metal dissolution, thereby affecting the cycling performance and the high temperature storage performance of the secondary battery; if the sintering temperature is too high, impurity phases will appear in the first coating layer, which will also affect its effect of inhibiting the dissolution of metals, thereby affecting the performances, such as cycling and high-temperature storage performance, of the secondary battery; and if the sintering time is too long, the thickness of the first coating layer will increase, which will affect the migration of Li+, thereby affecting the performances, such as capacity per gram and rate performance, of the material.

    [0229] In some embodiments, the second coating step, an X element source, a phosphorus source, and an acid are dissolved in a solvent, the solution is then stirred and reacted for 1-10 h, and the solution is then heated to 60-150? C. and maintained at this temperature for 2-10 hours and/or sintered at 500-700? C. for 6-10 hours. Optionally, in the second coating step, the reaction is performed completely. Optionally, in the second coating step, the reaction is carried out for about 1.5 hours, about 2 hours, about 3 hours, about 4 hours, about 4.5 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours. Optionally, in the second coating step, the reaction time of the reaction may be within any range of any of the above-mentioned numerical values. Optionally, in the second coating step, the solution is heated to about 65? C., about 70? C., about 80? C., about 90? C., about 100? C., about 110? C., about 120? C., about 130? C., about 140? C. or about 150? C. and maintained at that temperature for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, in the second coating step, the heating temperature and maintaining time may be within any range of any of the above-mentioned numerical values.

    [0230] In the step of providing the inner core material, the first coating step, and the second coating step, before sintering, i.e., during the preparation of the inner core material with chemical reactions and during the preparation of the first coating layer suspension and the second coating layer suspension, the following situations can be avoided by selecting the selected appropriate reaction temperature and reaction time as described above: if the reaction temperature is too low, the reaction cannot take place or the reaction rate is relatively low; if the temperature is too high, the product decomposes or forms an impurity phase; if the reaction time is too long, the particle size of the product is relatively large, which may prolong the time and increase the difficulty of the subsequent processes; and if the reaction time is too short, the reaction is incomplete and fewer products are obtained.

    [0231] Optionally, in the second coating step, the sintering may be performed at about 550? C., about 600? C., or about 700? C. for about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; Optionally, the sintering temperature and the sintering time may be in any range of any of the above-mentioned numerical values. In the second coating step, by controlling the sintering temperature and time within the above ranges, the following situations can be avoided: when the sintering temperature in the second coating step is too low and the sintering time is too short, the crystallinity of the second coating layer is low and there are more amorphous substances, leading to compromised performance in terms of reducing the surface reactivity of the material, thereby affecting the cycling and high-temperature storage performance, etc., of the secondary battery; if the sintering temperature is too high, impurity phases will appear in the second coating layer, which will also affect its effect of reducing the surface reactivity of the material, thereby affecting the performances, such as cycling and high-temperature storage performance, of the secondary battery; and if the sintering time is too long, the thickness of the second coating layer will increase, which will affect the voltage plateau of the material, thereby reducing the energy density of the material.

    [0232] In some embodiments, in the third coating step, the sintering is carried out at 700-800? C. for 6-10 h. Optionally, in the third coating step, the sintering may be performed at about 700? C., about 750? C., or about 800? C. for about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; Optionally, the sintering temperature and the sintering time may be in any range of any of the above-mentioned numerical values. In the third coating step, by controlling the sintering temperature and time within the above ranges, the following situations can be avoided: when the sintering temperature in the third coating step is too low, the graphitization degree of the third coating layer decreases, which affects the electrical conductivity thereof, thereby affecting the capacity per gram of the material; if the sintering temperature is too high, the degree of graphitization of the third coating layer will be too high, which will affect the transport of Li+, thereby affecting the performances, such as capacity per gram, of the material; if the sintering time is too short, the coating layer will be too thin, which will affect the electrical conductivity of the coating layer, thereby affecting the capacity per gram of the material; and if the sintering time is too long, the coating layer will be too thick, which will affect the performances, such as compacted density, of the material.

    [0233] In all the above first coating step, the second coating step and the third coating step, the drying is carried out at a drying temperature of 100? C. to 200? C., optionally 110? C. to 190? C., more optionally 120? C. to 180? C., even more optionally 120? C. to 170? C., and most optionally 120? C. to 160? C., and the drying time is 3-9 h, optionally 4-8 h, more optionally 5-7 h, and most optionally about 6 h.

    [0234] When the shell of the positive electrode active material above comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer, wherein the first coating layer comprises a crystalline pyrophosphate of QP.sub.2O.sub.7 and the metal oxide of Q.sub.eO.sub.f, and the second coating layer comprises carbon, the shell is formed by: providing a powder comprising a crystalline pyrophosphate of QP.sub.2O.sub.7 and a suspension comprising a carbon source and an oxide of Q.sub.eO.sub.f, and mixing the inner core, the powder comprising a crystalline pyrophosphate of QP.sub.2O.sub.7, and the suspension comprising a carbon source and an oxide of Q.sub.eO.sub.f, and sintering same to obtain a positive electrode active material. The suspension of the oxide Q.sub.eO.sub.f may be a suspension formed by mixing a commercially available metal oxide and raw materials including but not limited to a carbon source such as sucrose in a solvent.

    [0235] Alternatively, when the shell of the positive electrode active material above comprises a first coating layer coating the inner core, a second coating layer coating the first coating layer, and a third coating layer coating the second coating layer, wherein the first coating layer comprises a crystalline pyrophosphate of QP.sub.2O.sub.7, the second coating layer comprises the metal oxide of Q.sub.eO.sub.f, and the third coating layer comprises carbon, the shell is formed by: providing a first mixture comprising a pyrophosphate of Li.sub.aQP.sub.2O.sub.7 and/or Q.sub.b(P.sub.2O.sub.7).sub.c, and mixing an inner core material and the first mixture, followed by drying and sintering to obtain a first coating layer-coated material; providing a second mixture comprising the metal oxide of Q.sub.eO.sub.f, and mixing the first coating layer-coated material and the second mixture, followed by drying and sintering to obtain a second coating layer-coated material; and providing a third mixture comprising a carbon source, and mixing the second coating layer-coated material and the third mixture, followed by drying and sintering to obtain the positive electrode active material.

    [0236] For example, when the coating layer containing a metal oxide, when the first coating layer is formed, a source of a Q element, a phosphorus source, an acid, an optional lithium source, and an optional solvent are mixed to obtain the first mixture; and/or when the second coating layer is formed, a source of a Q element and a solvent are mixed to obtain the second mixture; and/or when the third coating layer is formed, a carbon source and a solvent are mixed to obtain the third mixture; optionally, when the first coating layer is formed, the source of the Q element, the phosphorus source, the acid, the optional lithium source, and the optional solvent are mixed at room temperature for 1-5 h, and the mixture is then heated to 50? C.-120? C. and held at the temperature for mixing for 2-10 h, and the mixing is each carried out at pH of 3.5-6.5; and optionally, when the second coating layer is formed, the source of the Q element and the solvent are mixed at room temperature for 1-10 h, and the mixture is then heated to 60? C.-150? C. and held at the temperature for mixing for 2-10 h.

    [0237] When the shell has a three-layer structure and contains a metal oxide, in the step of forming the first coating layer, the sintering is carried out at 650-800? C. for 2-8 h; and/or in the second coating step, the sintering is carried out at 400-750? C. for 6-10 h; and/or in the third coating step, the sintering is carried out at 600-850? C. for 6-10 h. For example, in some embodiments, in the first coating step, the sintering is carried out at 650-800? C. (e.g., about 650? C., about 700? C., about 750? C., or about 800? C.) for 2-8 hours (about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours or about 8 hours); and/or, in the second coating step, the sintering is carried out at 400-750? C. (e.g., about 400? C., about 450? C., about 500? C., about 550? C., about 600? C., about 700? C., or about 750? C.) for 6-10 hours (e.g., about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours); and/or, in the third coating step, the sintering is carried out at 600-850? C. (e.g., about 600? C., about 650? C., about 700? C., about 750? C., about 800? C., or about 850? C.,) for 6-10 hours (e.g., about 6 hours, about 7 hours, about 8 hours, about 9 hours, or about 10 hours).

    [0238] In all the first coating step, the second coating step, and the third coating step described above, the drying is carried out at a temperature of 80? C. to 200? C., optionally 80? C. to 190? C., more optionally 120? C. to 180? C., even more optionally 120? C. to 170? C., and most optionally 120? C. to 160? C., for 3-9 h, optionally 4-8 h, more optionally 5-7 h, and most optionally about 6 h.

    [0239] A third aspect of the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of the present application or a positive electrode active material prepared by the method of the second aspect of the present application, and the content of the positive electrode active material in the positive electrode film layer is 10 wt % or more, based on the total weight of the positive electrode film layer.

    [0240] In some embodiments, the content of the positive electrode active material in the positive electrode film layer is 95-99.5 wt %, based on the total weight of the positive electrode film layer.

    [0241] A fourth aspect of the present application provides a secondary battery, comprising the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application or the positive electrode plate of the third aspect of the present application.

    [0242] Typically, a secondary battery comprises a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charge/discharge of the battery, active ions are intercalated and de-intercalated back and forth between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate and mainly functions to prevent the positive and negative electrodes from short-circuiting while enabling ions to pass through.

    [0243] The secondary battery, battery module, battery pack, and power consuming device of the present application will be described below by appropriately referring to the accompanying drawings.

    [Positive Electrode Plate]

    [0244] The positive electrode plate comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of the first aspect of the present application.

    [0245] As an example, the positive electrode current collector has two surfaces opposite in its own thickness direction, and the positive electrode film layer is provided on either or both of opposite surfaces of the positive electrode current collector.

    [0246] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector may comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver and a silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

    [0247] In some embodiments, the positive electrode film layer further optionally comprises a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

    [0248] In some embodiments, the positive electrode film layer also optionally comprises a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

    [0249] In some embodiments, the positive electrode plate can be prepared by dispersing the above-mentioned components for preparing the positive electrode plate, such as a positive electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., N-methyl pyrrolidone) to form a positive electrode slurry; and coating the positive electrode current collector with the positive electrode slurry, followed by the procedures such as drying and cold pressing, so as to obtain the positive electrode plate.

    [Negative Electrode Plate]

    [0250] The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material.

    [0251] As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode film layer is provided on either or both of the two opposite surfaces of the negative electrode current collector.

    [0252] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be used. The composite current collector may comprise a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy, etc.) on a polymer material substrate (e.g., polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

    [0253] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for batteries. as an example, the negative electrode active material may comprise at least one of the following materials: synthetic graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, a silicon oxide compound, a silicon carbon composite, a silicon nitrogen composite, and a silicon alloy. The tin-based material may be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials may be used alone or as a combination of two or more.

    [0254] In some embodiments, the negative electrode film layer may optionally comprise a binder. The binder may be selected from at least one of a butadiene styrene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

    [0255] In some embodiments, the negative electrode film layer may optionally comprise a conductive agent. The conductive agent may be selected from at least one of superconductive carbon, acetylene black, carbon black, Ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

    [0256] In some embodiments, the negative electrode film layer may optionally comprise other auxiliary agents, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

    [0257] In some embodiments, the negative electrode plate can be prepared by dispersing the above-mentioned components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; and coating a negative electrode current collector with the negative electrode slurry, followed by procedures such as drying and cold pressing, so as to obtain the negative electrode plate.

    [Electrolyte]

    [0258] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The type of the electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte may be in a liquid state, a gel state, or an all-solid state.

    [0259] In some embodiments, an electrolyte solution is used as the electrolyte. The electrolyte solution comprises an electrolyte salt and a solvent.

    [0260] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate and lithium tetrafluorooxalate phosphate.

    [0261] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

    [0262] In some embodiments, the electrolyte solution further optionally comprises an additive. For example, the additive may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may further include an additive that can improve certain performances of the battery, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high temperature or low-temperature performance of the battery.

    [Separator]

    [0263] In some embodiments, the secondary battery further comprises a separator. The type of the separator is not particularly limited in the present application, and any well-known porous-structure separator with good chemical stability and mechanical stability may be selected.

    [0264] In some embodiments, the material of the separator may be selected from at least one of glass fibers, non-woven fabrics, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be either a single-layer film or a multi-layer composite film, and is not limited particularly. When the separator is a multi-layer composite film, the materials in the respective layers may be same or different, which is not limited particularly.

    [0265] In some embodiments, an electrode assembly may be formed by a positive electrode plate, a negative electrode plate and a separator by a winding process or a stacking process.

    [0266] In some embodiments, the secondary battery may comprise an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte.

    [0267] In some embodiments, the outer package of the secondary battery can be a hard housing, for example, a hard plastic housing, an aluminum housing, a steel housing, etc. The outer package of the secondary battery may also be a soft bag, such as a pouch-type soft bag. The material of the soft bag may be plastics, and the examples of plastics may comprise polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

    [0268] The shape of the secondary battery is not particularly limited in the present application and may be cylindrical, square or of any other shape. For example, FIG. 5 shows a secondary battery 5 with a square structure as an example.

    [0269] In some embodiments, with reference to FIG. 6, the outer package may include a housing 51 and a cover plate 53. Herein, the housing 51 may comprise a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening in communication with the accommodating cavity, and the cover plate 53 may cover the opening to close the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be subjected to a winding process or a laminating process to form an electrode assembly 52. The electrode assembly 52 is encapsulated in the accommodating cavity. The electrolyte solution infiltrates the electrode assembly 52. The number of the electrode assemblies 52 contained in the secondary battery 5 may be one or more, and can be selected by those skilled in the art according to actual requirements.

    [0270] In some embodiments, the secondary battery can be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

    [0271] FIG. 7 shows a battery module 4 as an example. Referring to FIG. 7, in the battery module 4, a plurality of secondary batteries 5 may be sequentially arranged in the length direction of the battery module 4. Apparently, the secondary batteries may also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

    [0272] Optionally, the battery module 4 may further comprise an outer housing with an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

    [0273] In some embodiments, the above battery module may also be assembled into a battery pack, the number of the battery modules contained in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

    [0274] FIGS. 8 and 9 show a battery pack 1 as an example. With reference to FIG. 8 and FIG. 9, the battery pack 1 may comprise a battery box and a plurality of battery modules 4 provided in the battery box. The battery box comprises an upper box body 2 and a lower box body 3, where the upper box body 2 may cover the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of the battery modules 4 may be arranged in the battery box in any manner.

    [0275] In addition, the present application further provides a power consuming device. The power consuming device comprises at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, battery module or battery pack can be used as a power source of the power consuming device or as an energy storage unit of the power consuming device. The power consuming device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, ship, and satellite, an energy storage system, etc., but is not limited thereto.

    [0276] As for the power consuming device, the secondary battery, battery module or battery pack can be selected according to the usage requirements thereof.

    [0277] FIG. 10 shows a power consuming device as an example. The power consuming device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the power consuming device for a high power and a high energy density of a secondary battery, a battery pack or a battery module may be used.

    [0278] As another example, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is generally required to be thin and light, and may have a secondary battery used as a power source.

    [0279] Hereinafter, the examples of the present application will be explained. The examples described below are exemplary and are merely for explaining the present application, and should not be construed as limiting the present application. The examples in which techniques or conditions are not specified are based on the techniques or conditions described in documents in the art or according to the product instructions. The reagents or instruments used therein on which no manufacturers are specified are all commercially available conventional products.

    I. Methods for Testing Properties of Positive Electrode Active Material and Battery Performance

    1. Method for Measuring Lattice Change Rate

    [0280] In a constant-temperature environment at 25? C., a positive electrode active material sample is placed in an XRD (model: Bruker D8 Discover) and tested at 1?/min, and the test data are organized and analyzed; and with reference to the standard PDF card, lattice constants a0, b0, c0 and v0 at this moment are calculated (a0, b0 and c0 represent the lengths of a unit cell on all sides, and v0 represents the volume of the unit cell, which may be obtained directly from XRD refinement results).

    [0281] The positive electrode active material sample is made into a button battery by the method for preparing a button battery in the examples above, and the button battery is charged at a small rate of 0.05 C until the current is reduced to 0.01 C. The positive electrode plate in the button battery is then taken out and soaked in DMC for 8 h. Then, the positive electrode plate is dried and subjected to powder scraping, and particles with a particle size of less than 500 nm are screened out. Sampling is performed, and the lattice constant v1 of the sample is calculated in the same way as that for a fresh sample as described above, and (v0?v1)/v0?100% is shown in Tables as the lattice change rate of the sample before and after complete lithium intercalation and de-intercalation.

    2. Method for Measuring Li/Mn Antisite Defect Concentration

    [0282] The XRD test results in the Method for measuring lattice change rate are compared with the PDF (Powder Diffraction File) card of a standard crystal, so as to obtain the Li/Mn antisite defect concentration. Specifically, the XRD results determined in the Method for measuring lattice change rate are imported into a general structure analysis system (GSAS) software, and refinement results are obtained automatically, including the occupancies of different atoms; and a Li/Mn antisite defect concentration is obtained by reading the refinement results.

    3. Method for Measuring Surface Oxygen Valency

    [0283] 5 g of a positive electrode active material sample is made into a button battery according to the method for preparing a button battery in the examples above. The button battery is charged at a small rate of 0.05 C until the current is reduced to 0.01 C. The positive electrode plate in the button battery is then taken out and soaked in DMC for 8 h. Then, the positive electrode plate is dried and subjected to powder scraping, and particles with a particle size of less than 500 nm are screened out. The obtained particles are measured with an electron energy loss spectroscopy (EELS, instrument model: Talos F200S) to obtain an energy loss near-edge structure (ELNES), which reflected the density of states and the energy level distribution of an element. According to the density of states and the energy level distribution, the number of occupied electrons is calculated by integrating the data of the density of states in the valence band, and the surface oxygen valency after charging is then extrapolated.

    4. Method for Measuring Compacted Density

    [0284] 5 g of powder is put into a dedicated compaction mold (U.S. CARVER mold, model: 13 mm), and then the mold is placed on a compacted density instrument. A pressure of 3 T is exerted, the thickness (after pressure relief) of the powder under the pressure is read from the instrument, and a compacted density is calculated through ?=m/v. Herein, the area value used is a standard small image area of 1540.25 mm.sup.2.

    5. Method for Measuring Dissolution of Mn (and Fe Doped at the Mn Site) after Cycling

    [0285] After cycling at 45? C. until the capacity is attenuated to 80%, the full battery is discharged to a cut-off voltage of 2.0 V at a rate of 0.1 C. Then, the battery is disassembled, the negative electrode plate is taken out, a round piece with 30 unit area (1540.25 mm.sup.2) is randomly taken from the negative electrode plate, and the inductively coupled plasma (ICP) emission spectroscopy is determined with Agilent ICP-OES730. The amount of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn therein is calculated according to the ICP results, and thus the dissolution of Mn (and Fe doped at the Mn site) after cycling is calculated. The testing standard is in accordance with EPA-6010D-2014.

    6. Method for Measuring Initial Capacity Per Gram of Button Battery

    [0286] At 2.5 to 4.3 V, a button battery is charged at 0.1 C to 4.3 V, then charged at a constant voltage of 4.3 V until the current is less than or equal to 0.05 mA, allowed to stand for 5 min, and then discharged at 0.1 C to 2.0 V; and the discharge capacity at this moment is the initial capacity per gram, marked as D0.

    7. Method for Measuring 3 C Charge Constant Current Rate

    [0287] In a constant-temperature environment at 25? C., a fresh full battery is allowed to stand for 5 min and discharged at ? C to 2.5 V. The full battery is allowed to stand for 5 min, charged at ? C to 4.3 V, and then charged at a constant voltage of 4.3 V until the current is less than or equal to 0.05 mA. The full battery is allowed to stand for 5 min, and the charge capacity at this moment is recorded as C0. The full battery is discharged at ? C to 2.5 V, allowed to stand for 5 min, then charged at 3 C to 4.3 V, and allowed to stand for 5 min, and the charge capacity at this moment is recorded as C1. The 3 C charge constant current rate is C1/C0?100%. A higher 3 C charge constant current rate indicated a better rate performance of the battery.

    8. Test of Cycling Performance of Full Battery at 45? C.

    [0288] In a constant-temperature environment at 45? C., at 2.5-4.3 V, a full battery is charged at 1 C to 4.3 V and then charged at a constant voltage of 4.3 V until the current is less than or equal to 0.05 mA. The full battery is allowed to stand for 5 min and then discharged at 1 C to 2.5V, and the discharge capacity at this moment is recorded as D0. The charge/discharge cycle is repeated until the discharge capacity is reduced to 80% of D0. The number of cycles experienced by the battery at this time is recorded.

    9. Expansion Test of Full Battery at 60? C.

    [0289] At 60? C., a full battery with 100% SOC (State of Charge) is stored. Before, after and during the storage, the open-circuit voltage (OCV) and AC internal impedance (IMP) of a cell are measured for monitoring the SOC, and the volume of the cell is measured. Herein, the full battery is taken out after every 48 h of storage and allowed to stand for 1 h, then the open-circuit voltage (OCV) and the internal impedance (IMP) are measured, and the volume of the cell is measured by means of a displacement method after the full battery is cooled to room temperature. The drainage method specifically included that the gravity F.sub.1 of a cell is measured separately using a balance with automatic unit conversion of on-board data, the cell is then completely placed in deionized water (with a density known to be 1 g/cm.sup.3), the gravity F.sub.2 of the cell at this time is measured, the buoyancy force F.sub.buoyancy on the cell is equal to F.sub.1?F.sub.2, and the volume of the cell is calculated as V=(F.sub.1?F.sub.2)/(??g) according to the Archimedes' principle F.sub.buoyancy=??g?V.sub.displacement.

    [0290] From the test results of OCV and IMP, the battery of the example always maintained a SOC of 99% or more in the experimental process till the end of the storage.

    [0291] After 30 days of storage, the volume of the cell is measured, and the percentage increase in cell volume after the storage relative to the cell volume before the storage is calculated.

    [0292] In addition, residual capacity of the cell is measured. At 2.5-4.3 V, the full battery is charged at 1 C to 4.3 V and then charged at a constant voltage of 4.3 V until the current is less than or equal to 0.05 mA. The full battery is allowed to stand for 5 min, and the charge capacity at this moment is recorded as the residual capacity of the cell.

    10. Measurement of Manganese and Phosphorus Elements in Positive Electrode Active Material

    [0293] 5 g of the positive electrode active material prepared above is dissolved in 100 ml of reverse aqua regia (concentrated hydrochloric acid: concentrated nitric acid=1:3) (with the concentration of the concentrated hydrochloric acid being about 37%, and the concentration of the concentrated nitric acid being about 65%). The content of each element in the solution is tested by ICP, and then the content of the manganese element or phosphorus element is measured and converted (the amount of the manganese element or phosphorus element/the amount of the positive electrode active material*100%) to obtain the weight percentage thereof.

    11. Measurement of Interplanar Spacing and Included Angle

    [0294] 1 g of each positive electrode active material powder prepared above is placed in a 50 mL test tube, and 10 mL of ethanol with a mass fraction of 75% is injected into the test tube, then the mixture is fully stirred and dispersed for 30 min, then an appropriate amount of the solution is taken by using a clean disposable plastic straw and dripped on a 300-mesh copper mesh, and at this moment, some powder would remain on the copper mesh. The copper mesh and the sample are transferred to TEM (Talos F200s G2) sample chamber for a TEM test to obtain the original image thereof, and the original image is saved in a format (xx.dm3). The original image obtained from the above TEM test is opened in the Digital Micrograph software and subjected to Fourier transform (automatically completed by the software after a clicking operation) to obtain a diffraction pattern, and the distance from a diffraction spot to the center position in the diffraction pattern is measured to obtain the interplanar spacing, and the included angle is calculated according to Bragg's equation. The different materials in the coating layer could be identified by comparing the obtained interplanar spacing and corresponding included angle data with their standard values.

    12. Measurement of Coating Layer Thickness

    [0295] The thickness of the coating layer is mainly measured as follows: a thin slice with a thickness of about 100 nm is cut from the middle of a single particle of the positive electrode active material prepared above by FIB, and then subjected to a TEM test to obtain the original image thereof, and the original image is save in a format (xx.dm3).

    [0296] The original image obtained from the above TEM test is opened in the Digital Micrograph software, the coating layer is identified with the lattice spacing and included angle information, and the thickness of the coating layer is measured.

    [0297] The thickness is measured at three locations on the selected particle and the average value is taken.

    13. Determination of Molar Ratio of SP2 Form to SP3 Form of Carbon in Third Coating Layer

    [0298] This test is performed by Raman spectroscopy. The energy spectrum obtained from the Raman test is split to obtain Id/Ig, with Id being the peak intensity of SP3-form carbon, and Ig being the peak intensity of SP2-form carbon, thereby determining the molar ratio thereof.

    14. Determination of the Chemical Formula of Inner Core and Composition of Different Coating layers

    [0299] The internal microstructure and surface structure of the positive electrode active material is characterized in high spatial resolution by using a spherical aberration corrected transmission electron microscope (ACSTEM), and the chemical formula of the inner core and the composition of different coating layers of the positive electrode active material is obtained by means of a three-dimensional reconstruction technology.

    II. Preparation of Positive Electrode Material and Secondary Battery

    Example 1

    (1) Preparation of Positive Electrode Active Material

    S1: Preparation of Doped Manganese Oxalate

    [0300] 1.3 mol of MnSO.sub.4.Math.H.sub.2O and 0.7 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    S2: Preparation of Co-Doped Lithium Manganese Phosphate Inner Core

    [0301] 1 mol of the manganese oxalate particles above, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO.sub.4).sub.3, a 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid, 0.001 mol of H.sub.4SiO.sub.4, and 0.0005 mol of NH.sub.4HF.sub.2 were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), thus obtaining Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001, i.e., the co-doped lithium manganese phosphate inner core.

    S3: Preparation of First Coating Layer Suspension

    [0302] Preparation of a Li.sub.2FeP.sub.2O.sub.7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, with pH being controlled to be 5, the mixture was then stirred for reaction at room temperature for 2 hours to obtain a solution, and the solution was then heated to 80? C. and held at this temperature for 4 hours to obtain a first coating layer suspension.

    S4: Coating of First Coating Layer

    [0303] 10 mol (about 1574 g) of the co-doped lithium manganese phosphate inner core material obtained by the process in step S2 was added into the first coating layer suspension (the content of the first coating layer material was 15.7 g) obtained in step S3, and fully stirred and mixed for 6 hours; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 650? C. for 6 hours to obtain a pyrophosphate coated material.

    S5: Preparation of Second Coating Layer Suspension

    [0304] 3.7 g of lithium carbonate, 11.6 g of ferrous carbonate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred for reaction for 6 hours to obtain a solution, and the solution was then heated to 120? C. and held at this temperature for 6 hours to obtain a second coating layer suspension.

    S6: Coating of Second Coating Layer

    [0305] The pyrophosphate coated material obtained in step S4 was added to the second coating layer suspension (the content of the second coating layer material was 47.1 g) obtained in step S5, fully stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 700? C. for 8 hours to obtain a two-layer coated material.

    S7: Preparation of Aqueous Solution of Third Coating Layer

    [0306] 37.3 g of sucrose was dissolved in 500 g of deionized water, then stirred and fully dissolved to obtain an aqueous solution of sucrose.

    S8: Coating of Third Coating Layer

    [0307] The two-layer coated material obtained in step S6 was added to the sucrose solution obtained in step S7, stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 150? C. and dried for 6 h, and then sintered at 700? C. for 10 hours to obtain a three-layer coated material.

    (2) Preparation of Positive Electrode Plate

    [0308] The three-layer coated positive electrode active material prepared above, a conductive agent of acetylene black, a binder of polyvinylidene fluoride (PVDF) were added at a weight ratio of 97.0:1.2:1.8 into N-methylpyrrolidone (NMP), and stirred and mixed until uniform to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to an aluminum foil at 0.280 g/1540.25 mm.sup.2, followed by drying, cold pressing and slitting to obtain a positive electrode plate.

    (3) Preparation of Negative Electrode Plate

    [0309] The negative electrode active material of synthetic graphite, hard carbon, a conductive agent of acetylene black, a binder of styrene butadiene rubber (SBR), and a thickener of sodium carboxymethyl cellulose (CMC) were dissolved in a solvent of deionized water at a weight ratio of 90:5:2:2:1, and stirred and mixed until uniform to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated onto a negative electrode current collector of a copper foil at 0.117 g/1540.25 mm.sup.2, followed by drying, cold pressing, and slitting to obtain a negative electrode plate.

    (4) Preparation of Electrolyte Solution

    [0310] In an argon atmosphere glove box (H.sub.2O<0.1 ppm, and O.sub.2<0.1 ppm), the organic solvent ethylene carbonate (EC)/ethyl methyl carbonate (EMC) was mixed uniformly by a volume ratio of 3/7, and 12.5% (on the basis of the weight of the ethylene carbonate/ethyl methyl carbonate solvent) by weight of LiPF.sub.6 was dissolved in the above organic solvent and stirred uniformly to obtain the electrolyte solution.

    (5) Preparation of Separator

    [0311] A commercially available PP-PE copolymer microporous film having a thickness of m and an average pore size of 80 nm (Model 20, from Zhuogao Electronic Technology Co. Ltd.) was used.

    (6) Preparation of Full Battery

    [0312] The positive electrode plate, separator, and negative electrode plate obtained above were stacked in sequence, such that the separator was located between the positive electrode and the negative electrode and played a role of isolation, and the stack was wound to obtain an electrode assembly. The electrode assembly was placed in an outer package, the above electrolyte solution was injected, and the electrode assembly was packaged to obtain a full battery.

    (7) Preparation of Button Battery

    [0313] The three layer-coated positive electrode active material prepared above, polyvinylidene fluoride (PVDF), and acetylene black were added into N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and stirred in a drying room to form a slurry. An aluminum foil was coated with the slurry above, followed by drying and cold pressing to obtain a positive electrode plate. The coating amount was 0.2 g/cm.sup.2, and the compacted density was 2.0 g/cm.sup.3.

    [0314] A lithium plate as the negative electrode, a solution of 1 mol/L of LiPF.sub.6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) at a volume ratio of 1:1:1 as the electrolyte solution, and the positive electrode plate prepared above were assembled into a button battery in a button battery box.

    Example 2

    [0315] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4885 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with HNO.sub.3, and 0.02 mol of Ti(SO.sub.4).sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 3

    [0316] Except that in step S1 and step S2, the amount of Li.sub.2CO.sub.3 was changed to 0.496 mol, Mo(SO.sub.4).sub.3 was replaced with W(SO.sub.4).sub.3, and H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the other conditions were the same as example 1.

    Example 4

    [0317] Except that in step S1 and step S2, the amount of Li.sub.2CO.sub.3 was changed to 0.4985 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Al.sub.2(SO.sub.4).sub.3, and NH.sub.4HF.sub.2 was replaced with NH.sub.4HCl.sub.2, the other conditions were the same as example 1.

    Example 5

    [0318] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.69 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4965 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.01 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 6

    [0319] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4965 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.01 mol of VCl.sub.2 and 0.01 mol of MgSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 7

    [0320] Except that in step S1 and step S2, MgSO.sub.4 was replaced with CoSO.sub.4, the other conditions were the same as example 6.

    Example 8

    [0321] Except that in step S1 and step S2, MgSO.sub.4 was replaced with NiSO.sub.4, the other conditions were the same as example 6.

    Example 9

    [0322] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.698 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4955 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, NH.sub.4HF.sub.2 was replaced with NH.sub.4HCl.sub.2, and 0.002 mol of Ti(SO.sub.4).sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 10

    [0323] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4975 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, NH.sub.4HF.sub.2 was replaced with NH.sub.4HBr.sub.2, and 0.01 mol of VCl.sub.2 and 0.01 mol of MgSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 11

    [0324] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.69 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.499 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, NH.sub.4HF.sub.2 was replaced with NH.sub.4HBr.sub.2, and 0.01 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 12

    [0325] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.36 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.6 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4985 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with HNO.sub.3, and 0.04 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 13

    [0326] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.16 mol, and the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.8 mol, the other conditions were the same as example 12.

    Example 14

    [0327] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.3 mol, and the amount of VCl.sub.2 was changed to 0.1 mol, the other conditions were the same as example 12.

    Example 15

    [0328] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.494 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 16

    [0329] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.467 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, 0.001 mol of H.sub.4SiO.sub.4 was replaced with 0.005 mol of H.sub.2SO.sub.4, 1.175 mol of 85% phosphoric acid was replaced with 1.171 mol of 85% phosphoric acid, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 17

    [0330] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.492 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the amount of NH.sub.4HF.sub.2 was changed to 0.0025 mol, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 18

    [0331] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.5 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.492 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the amount of NH.sub.4HF.sub.2 was changed to 0.0025 mol, and 0.1 mol of VCl.sub.2 and 0.1 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 19

    [0332] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.4 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18.

    Example 20

    [0333] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.5 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.1 mol, and the amount of CoSO.sub.4 was changed to 0.3 mol, the other conditions were the same as example 18.

    Example 21

    [0334] Except that in step S1 and step S2, CoSO.sub.4 was replaced with NiSO.sub.4, the other conditions were the same as example 18.

    Example 22

    [0335] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.5 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.2 mol, and 0.1 mol of CoSO.sub.4 was replaced with 0.2 mol of NiSO.sub.4, the other conditions were the same as example 18.

    Example 23

    [0336] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18.

    Example 24

    [0337] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.5 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18.

    Example 25

    [0338] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.0 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.7 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18.

    Example 26

    [0339] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4825 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, the amount of H.sub.4SiO.sub.4 was changed to 0.1 mol, the amount of phosphoric acid was changed to 0.9 mol, the amount of NH.sub.4HF.sub.2 was changed to 0.04 mol, and 0.1 mol of VCl.sub.2 and 0.2 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Example 27

    [0340] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.485 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, the amount of H.sub.4SiO.sub.4 was changed to 0.08 mol, the amount of phosphoric acid was changed to 0.92 mol, the amount of NH.sub.4HF.sub.2 was changed to 0.05 mol, and 0.1 mol of VCl.sub.2 and 0.2 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1.

    Examples 28 to 44

    [0341] Except that in steps S3 to S6, different first coating layer materials or second coating layer materials were selected for coating, the other conditions were the same as example 1. The preparation methods of each coating layer material were shown in Table 1 and Table 2.

    Examples 45 to 59

    [0342] Except that in step S4, step S6 and step S8, the amount of the raw materials for each coating layer material used was correspondingly adjusted based on the coating amount shown in Table 8, the other conditions were the same as example 1.

    Example 60

    [0343] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 550? C. and the sintering time was adjusted to 1 hour to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 30%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 2 hours to control the crystallinity of LiFePO.sub.4 to be 30%, the other conditions were the same as example 1.

    Example 61

    [0344] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 550? C. and the sintering time was adjusted to 2 hours to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 50%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 3 hours to control the crystallinity of LiFePO.sub.4 to be 50%, the other conditions were the same as example 1.

    Example 62

    [0345] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 600? C. and the sintering time was adjusted to 3 hours to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 70%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 4 hours to control the crystallinity of LiFePO.sub.4 to be 70%, the other conditions were the same as example 1.

    Comparative Example 1

    [0346] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0347] Preparation of manganese oxalate: 1 mol of MnSO.sub.4.Math.H.sub.2O was added into a reaction kettle, and 10 L of deionized water and 1 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain manganese oxalate particles with a median particle size DV.sub.50 of 50-200 nm.

    [0348] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.5 mol of lithium carbonate, a 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated LiMnPO.sub.4.

    Comparative Example 2

    [0349] Except that in comparative example 2, 1 mol of MnSO.sub.4.Math.H.sub.2O was replaced with 0.85 mol of MnSO.sub.4.Math.H.sub.2O and 0.15 mol of FeSO.sub.4.Math.H.sub.2O, which were added into a mixer and thoroughly mixed for 6 hours before adding into a reaction kettle, the other conditions were the same as comparative example 1.

    Comparative Example 3

    [0350] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0351] Preparation of doped manganese oxalate: 1.9 mol of MnSO.sub.4.Math.H.sub.2O and 0.1 mol of ZnSO.sub.4 were thoroughly mixed for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size Dv.sub.50 of about 100 nm.

    [0352] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.495 mol of lithium carbonate, 0.005 mol of MgSO.sub.4, a 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4.

    Comparative Example 4

    [0353] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0354] Preparation of doped manganese oxalate: 1.2 mol of MnSO.sub.4.Math.H.sub.2O and 0.8 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size Dv.sub.50 of about 100 nm.

    [0355] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.45 mol of lithium carbonate, 0.005 mol of Nb.sub.2(SO.sub.4).sub.5, a 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid, 0.025 mol of NH.sub.4HF.sub.2 and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05.

    Comparative Example 5

    [0356] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0357] Preparation of doped manganese oxalate: 1.4 mol of MnSO.sub.4.Math.H.sub.2O and 0.6 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    [0358] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.38 mol of lithium carbonate, 0.12 mol of MgSO.sub.4, a 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid, 0.001 mol of H.sub.4SiO.sub.4, 0.0005 mol of NH.sub.4HF.sub.2, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001.

    Comparative Example 6

    [0359] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0360] Preparation of doped manganese oxalate: 0.8 mol of MnSO.sub.4.Math.H.sub.2O and 1.2 mol of ZnSO.sub.4 were thoroughly mixed for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    [0361] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.499 mol of lithium carbonate, 0.001 mol of MgSO.sub.4, a 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid, 0.001 mol of H.sub.4SiO.sub.4, 0.0005 mol of NH.sub.4HF.sub.2, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001.

    Comparative Example 7

    [0362] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0363] Preparation of doped manganese oxalate: 1.4 mol of MnSO.sub.4.Math.H.sub.2O and 0.6 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    [0364] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.534 mol of lithium carbonate, 0.001 mol of MgSO.sub.4, a 85% aqueous phosphoric acid solution containing 0.88 mol of phosphoric acid, 0.12 mol of H.sub.4SiO.sub.4, 0.025 mol of NH.sub.4HF.sub.2, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05.

    Comparative Example 8

    [0365] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0366] Preparation of doped manganese oxalate: 1.2 mol of MnSO.sub.4.Math.H.sub.2O and 0.8 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    [0367] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.474 mol of lithium carbonate, 0.001 mol of MgSO.sub.4, a 85% aqueous phosphoric acid solution containing 0.93 mol of phosphoric acid, 0.07 mol of H.sub.4SiO.sub.4, 0.06 mol of NH.sub.4HF.sub.2, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12.

    Comparative Example 9

    [0368] Except that the preparation steps of the positive electrode active material were changed, the other conditions were the same as example 1.

    [0369] Preparation of doped manganese oxalate: 1.3 mol of MnSO.sub.4.Math.H.sub.2O and 0.7 mol of FeSO.sub.4.Math.H.sub.2O were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (in oxalic acid) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe-doped manganese oxalate particles with a median particle size DV.sub.50 of about 100 nm.

    [0370] Preparation of positive electrode active material: 1 mol of the manganese oxalate particles above, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO.sub.4).sub.3, a 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid, 0.001 mol of H.sub.4SiO.sub.4, 0.0005 mol of NH.sub.4HF.sub.2, and 0.01 mol of sucrose were added into 20 L of deionized water. The mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles. The above powder was sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001.

    Comparative Example 10

    [0371] Except that the step S4 was changed and steps S5 and S6 were omitted, the other conditions were the same as example 1.

    S4: Coating of First Coating Layer

    [0372] 10 mol (about 1574 g) of the co-doped lithium manganese phosphate inner core material obtained by the process in step S2 was added into the first coating layer suspension (the content of the first coating layer material was 62.8 g) obtained in step S3, and fully stirred and mixed for 6 hours; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 500? C. for 4 hours to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%, so as to obtain an amorphous Li.sub.2FeP.sub.2O.sub.7 coated material.

    Comparative Example 11

    [0373] Except that the step S6 was changed and steps S3 and S4 were omitted, the other conditions were the same as example 1.

    S6: Coating of Second Coating Layer

    [0374] 10 mol (about 1574 g) of the co-doped lithium manganese phosphate inner core material obtained by the process in step S2 was added into the second coating layer suspension (the content of the second coating layer material was 62.8 g) obtained in step S5, and fully stirred and mixed for 6 hours; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 600? C. for 4 hours to control the crystallinity of LiFePO.sub.4 to be 8%, so as to obtain an amorphous LiFePO.sub.4 coated material.

    Comparative Example 12

    [0375] Except that steps S4 and S6 were changed, the other conditions were the same as example 1.

    S4: Coating of First Coating Layer

    [0376] 10 mol (about 1574 g) of the co-doped lithium manganese phosphate inner core material obtained by the process in step S2 was added into the first coating layer suspension (the content of the first coating layer material was 15.7 g) obtained in step S3, and fully stirred and mixed for 6 hours; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 hours, and then sintered at 500? C. for 4 hours to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%, so as to obtain an amorphous Li.sub.2FeP.sub.2O.sub.7 coated material.

    S6: Coating of Second Coating Layer

    [0377] The amorphous Li.sub.2FeP.sub.2O.sub.7 coated material obtained in step S4 was added into the second coating layer suspension (the content of the second coating layer material was 47.1 g) obtained in step S5, and fully stirred and mixed for 6 hours; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 600? C. for 4 hours to control the crystallinity of LiFePO.sub.4 to be 8%, so as to obtain an amorphous Li.sub.2FeP.sub.2O.sub.7 and amorphous LiFePO.sub.4 coated material.

    TABLE-US-00001 TABLE 1 First coating layer material Preparation of first coating layer suspension Crystalline Al.sub.4(P.sub.2O.sub.7).sub.3 53.3 g of aluminum chloride, 34.5 g of ammonium dihydrogen phosphate and 18.9 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 4, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Li.sub.2NiP.sub.2O.sub.7 7.4 g of lithium carbonate, 11.9 g of nickel carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Li.sub.2MgP.sub.2O.sub.7 7.4 g of lithium carbonate, 8.4 g of magnesium carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Li.sub.2CoP.sub.2O.sub.7 7.4 g of lithium carbonate, 15.5 g of cobalt sulfate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Li.sub.2CuP.sub.2O.sub.7 7.4 g of lithium carbonate, 16.0 g of copper sulfate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Li.sub.2ZnP.sub.2O.sub.7 7.4 g of lithium carbonate, 12.5 g of zinc carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline TiP.sub.2O.sub.7 24.0 g of titanium sulfate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline Ag.sub.4P.sub.2O.sub.7 67.9 g of silver nitrate, 23.0 g of ammonium dihydrogen phosphate and 25.2 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension Crystalline ZrP.sub.2O.sub.7 56.6 g of zirconium sulfate, 23.0 g of ammonium dihydrogen phosphate and 25.2 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, the pH was controlled to be 5, then the mixture was stirred and fully reacted for 2 hours to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension

    TABLE-US-00002 TABLE 2 Second coating layer material Preparation of second coating layer suspension Crystalline LiCoPO.sub.4 3.7 g of lithium carbonate, 15.5 g of cobalt sulfate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension. Crystalline LiNiPO.sub.4 3.7 g of lithium carbonate, 11.9 g of nickel carbonate, 11.5 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension. Crystalline Cu.sub.3(PO.sub.4).sub.2 48.0 g of copper sulfate, 23.0 g of ammonium dihydrogen phosphate and 37.8 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension Crystalline Zn.sub.3(PO.sub.4).sub.2 37.6 g of zinc carbonate, 23.0 g of ammonium dihydrogen phosphate and 37.8 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension Crystalline Ti.sub.3(PO.sub.4).sub.4 72.0 g of titanium sulfate, 46.0 g of ammonium dihydrogen phosphate and 75.6 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension Crystalline Ag.sub.3PO.sub.4 50.9 g of silver nitrate, 11.5 g of ammonium dihydrogen phosphate and 18.9 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension Crystalline Zr.sub.3(PO.sub.4).sub.4 85.0 g of zirconium sulfate, 46.0 g of ammonium dihydrogen phosphate and 37.8 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension Crystalline AlPO.sub.4 13.3 g of aluminum chloride, 11.5 g of ammonium dihydrogen phosphate and 18.9 g of oxalic acid dihydrate were dissolved in 1500 mL of deionized water, then the mixture was stirred and fully reacted for 6 hours to obtain a solution, and then the solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension

    [0378] Table 3 shows the composition of the positive electrode active materials of comparative examples 1 to 12.

    [0379] Table 4 shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of comparative examples 1 to 12 obtained according to the performance test methods above.

    [0380] Table 5 shows the composition of the positive electrode active materials of examples 1-44.

    [0381] Table 6 shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 1 to 44 obtained according to the performance test methods above.

    TABLE-US-00003 TABLE 3 First Second Third coating coating coating No. Inner core layer layer layer Comparative LiMnPO.sub.4 1% of example 1 carbon Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 1% of example 2 carbon Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 1% of example 3 carbon Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 1% of example 4 carbon Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 5 carbon Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 6 carbon Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 1% of example 7 carbon Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 1% of example 8 carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 9 carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 4% of 1% of example 10 amorphous carbon Li.sub.2FeP.sub.2O.sub.7 Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 4% of 1% of example 11 amorphous carbon LiFePO.sub.4 Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of example 12 amorphous amorphous carbon Li.sub.2FeP.sub.2O.sub.7 LiFePO.sub.4

    TABLE-US-00004 TABLE 4 Number of Expansion 3 C cycles for of battery Li/Mn Dissolution Capacity charge capacity upon 30 Lattice antisite of Mn and of button constant retention days of change defect Surface Compacted Fe after battery at current rate of storage rate concentration oxygen density cycling 0.1 C rate 80% at at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (%) 45? C. (%) Comparative 11.4 5.2 ?1.55 1.7 2060 125.6 50.1 121 48.6 example 1 Comparative 10.6 4.3 ?1.51 1.87 1510 126.4 50.4 129 37.3 example 2 Comparative 10.8 3.6 ?1.64 1.88 1028 134.7 51.7 134 31.9 example 3 Comparative 9.7 2.4 ?1.71 1.93 980 141.3 62.3 148 30.8 example 4 Comparative 5.6 1.8 ?1.81 1.98 873 110.8 50.2 387 21.4 example 5 Comparative 3.7 1.5 ?1.8 2.01 574 74.3 65.8 469 15.8 example 6 Comparative 7.8 1.5 ?1.75 2.05 447 139.4 64.3 396 18.3 example 7 Comparative 8.4 1.4 ?1.79 2.16 263 141.7 63.9 407 22.7 example 8 Comparative 6.3 1.2 ?1.82 2.21 192 156 64.2 552 8.4 example 9 Comparative 6.3 1.1 ?1.90 2.22 156 156.2 63.7 802 6.7 example 10 Comparative 6.2 1.1 ?1.91 2.21 164 156.1 62.5 860 6.4 example 11 Comparative 6.2 1.1 ?1.90 2.2 143 156.2 67.1 1013 4.2 example 12

    TABLE-US-00005 TABLE 5 First Second Third coating coating coating No. Inner core layer layer layer Example 1 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 2 Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 3 Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 4 Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 5 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 6 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 7 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 8 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 9 Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 10 Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 11 Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 12 Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 13 Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 14 Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 15 Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 16 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 17 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 18 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 19 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 20 Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 21 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65 Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 22 Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 23 Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 24 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 25 Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 26 Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 27 Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 28 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Al.sub.4(P.sub.2O.sub.7).sub.3 3% LiFePO.sub.4 1% of carbon Example 29 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2NiP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 30 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiCoPO.sub.4 1% of carbon Example 31 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiNiPO.sub.4 1% of carbon Example 32 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2MgP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 33 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2CoP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 34 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2CuP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 35 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2ZnP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 36 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% TiP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 37 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Ag.sub.4P.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 38 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% ZrP.sub.2O.sub.7 3% LiFePO.sub.4 1% of carbon Example 39 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% Cu.sub.3(PO.sub.4).sub.2 1% of carbon Example 40 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% Zn.sub.3(PO.sub.4).sub.2 1% of carbon Example 41 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% Ti.sub.3(PO.sub.4).sub.4 1% of carbon Example 42 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% Ag.sub.3PO.sub.4 1% of carbon Example 43 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% Zr.sub.3(PO.sub.4).sub.4 1% of carbon Example 44 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% AlPO.sub.4 1% of carbon Note: Both the first coating layer material and the second coating layer material in examples 1 to 44 were crystalline

    TABLE-US-00006 TABLE 6 3 C Number of Expansion Li/Mn Dissolution Capacity charge cycles for of battery Lattice antisite of Mn and of button constant capacity upon 30 days change defect Surface Compacted Fe after battery at current retention of storage rate concentration oxygen density cycling 0.1 C rate rate of 80% at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (%) at 45? C. (%) Example 6.1 0.8 1.97 2.25 20 157.6 68.2 1305 2.1 1 Example 6.6 0.4 ?1.98 2.45 5 159.4 79.1 1573 1.8 2 Example 6.3 0.8 ?1.97 2.26 19 156.3 67.3 1367 2.1 3 Example 5.3 0.6 ?1.97 2.24 22 154.7 66.9 1271 2.2 4 Example 5.3 0.4 ?1.98 2.43 5 158.6 80.2 1589 1.6 5 Example 2.4 0.3 ?1.99 2.50 7 160.4 81.1 1532 1.8 6 Example 2.2 0.3 ?1.99 2.51 5 161.2 78.5 1490 1.7 7 Example 3.3 0.3 ?1.99 2.53 5 160.1 78.6 1555 1.6 8 Example 3.4 0.4 ?1.98 2.48 6 159.6 79.6 1624 1.7 9 Example 3.6 0.3 ?1.99 2.52 4 160.4 81.5 1598 1.9 10 Example 3.4 0.4 ?1.98 2.46 3 159.8 78.9 1612 1.6 11 Example 6.8 0.4 ?1.98 2.46 6 152.1 76.1 1443 1.9 12 Example 7.2 0.3 ?1.99 2.47 8 158.3 74.2 1520 1.7 13 Example 7.1 0.5 ?1.95 2.60 7 154.5 77.2 1513 1.8 14 Example 6.2 0.4 ?1.97 2.50 6 156.3 81.9 1427 1.4 15 Example 5.3 0.6 ?1.96 2.44 6 155.9 81.6 1423 1.6 16 Example 3.8 0.5 ?1.99 2.41 8 157.1 83.1 1418 1.7 17 Example 2.4 0.3 ?1.98 2.47 5 159.6 82.5 1562 1.8 18 Example 2.4 0.3 ?1.98 2.46 9 157.8 80.4 1569 1.8 19 Example 2.5 0.3 ?1.95 2.44 6 155.3 82.8 1502 2.2 20 Example 3.1 0.4 ?1.94 2.46 7 154.6 81.9 1512 2.2 21 Example 3.0 0.4 ?1.96 2.47 5 158.3 82.1 1498 2.3 22 Example 2.8 0.5 ?1.99 2.43 7 152.1 85.6 1385 1.8 23 Example 2.4 0.4 ?1.97 2.44 5 153.1 79.8 1508 1.7 24 Example 2.2 0.3 ?1.99 2.45 8 152.9 81.9 1486 2.1 25 Example 3.1 0.5 ?1.97 2.23 5 152.6 82.3 1478 1.9 26 Example 2.5 0.4 ?1.98 2.29 4 152 81.7 1469 1.4 27 Example 6.1 0.9 ?1.98 2.49 25 159.7 83.2 1302 1.9 28 Example 6.1 0.8 ?1.98 2.26 25 153.9 66.3 1289 2.0 29 Example 6.1 0.7 ?1.97 2.29 26 154.3 66.5 1274 2.1 30 Example 6.2 0.8 ?1.98 2.28 25 154.8 66.6 1264 2.2 31 Example 6.1 0.7 ?1.98 2.32 26 156.2 64.6 1274 2.2 32 Example 6.1 0.7 ?1.98 2.29 24 155.8 63.9 1323 2.1 33 Example 6.0 0.8 ?1.97 2.31 27 155.5 66.3 1297 2.0 34 Example 6.1 0.9 ?1.98 2.28 25 154.3 67.4 1345 2.1 35 Example 6.2 0.9 ?1.98 2.30 25 155.2 64.6 1391 2.2 36 Example 6.2 0.8 ?1.98 2.31 26 156.0 65.2 1384 2.2 37 Example 6.1 0.7 ?1.97 2.29 24 153.4 65.5 1321 2.0 38 Example 6.0 0.9 ?1.98 2.33 26 153.4 64.5 1310 2.0 39 Example 6.1 0.9 ?1.97 2.28 25 154.6 65.1 1280 2.0 40 Example 6.1 0.8 ?1.98 2.31 26 154.7 63.6 1292 2.1 41 Example 6.2 0.7 ?1.98 2.31 23 155.0 67.6 1340 2.1 42 Example 6.1 0.7 ?1.98 2.29 22 156.3 63.1 1293 2.2 43 Example 6.1 0.8 ?1.97 2.30 27 155.4 63.6 1321 2.3 44

    [0382] It can be seen from Tables 4 and 6 that the positive electrode active material of the present application obtained by modifying lithium manganese phosphate via simultaneous doping at Li, Mn, P and O sites with certain amount of specific elements and by multi-layer coating of lithium manganese phosphate achieves a smaller lattice change rate, a smaller Li/Mn antisite defect concentration, a larger compacted density, a surface oxygen valency closer to ?2 valence, and less Mn and Fe dissolution after cycling, such that the battery of the present application has better performance, such as a higher capacity, and a better high-temperature storage performance and high-temperature cycling performance.

    [0383] FIG. 1 shows X-ray diffraction (XRD) spectrum of the inner core of undoped LiMnPO.sub.4 and a positive electrode active material prepared in example 2. It can be seen from the figure that the position of main characteristic peaks in the XRD spectra of the inner core of the positive electrode active material of example 2 is consistent with that of the undoped LiMnPO.sub.4, indicating that no impurity phase is introduced in the doping process, and the performance improvement is mainly due to the doping with elements rather than an impurity phase. FIG. 2 shows energy-dispersive X-ray spectroscopy (EDS) images of the inner core of the positive electrode active material prepared in example 2. Those in spotted distribution in the images are the doping elements. It can be seen from the figure that in the inner core of the positive electrode active material of example 2, the elements are uniformly doped.

    [0384] It also can be seen from examples 12-27 that in the case where the other elements are the same, when (1?y):y is in a range of to 4 and m:x is in a range of 9 to 1100, and optionally (1?y):y is in a rage of 1.5 to 3 and m:x is in a range of 190 to 998, the energy density and the cycling performance of the battery can be further improved.

    [0385] Table 7 shows the interplanar spacing and included angle of the first coating layer material and the second coating layer material in examples 32 to 44.

    TABLE-US-00007 TABLE 7 Interplanar Included angle of Interplanar Included angle of spacing crystal orientation spacing crystal orientation of first (111) of first of second (111) of second coating layer coating layer coating layer coating layer No. material (nm) material (?) material (nm) material (?) Example 1 0.303 29.496 0.348 25.562 Example 32 0.451 19.668 0.348 25.562 Example 33 0.297 30.846 0.348 25.562 Example 34 0.457 19.456 0.348 25.562 Example 35 0.437 20.257 0.348 25.562 Example 36 0.462 19.211 0.348 25.562 Example 37 0.45 19.735 0.348 25.562 Example 38 0.372 23.893 0.348 25.562 Example 39 0.303 29.496 0.374 23.789 Example 40 0.303 29.496 0.36 24.71 Example 41 0.303 29.496 0.35 25.428 Example 42 0.303 29.496 0.425 20.885 Example 43 0.303 29.496 0.356 24.993 Example 44 0.303 29.496 0.244 36.808

    [0386] It can be seen from Table 7 that both the interplanar spacing and included angle of the first coating layer and the second coating layer are within the range described in the present application, and it can be known by combining Table 6 that when such first coating layers and second coating layers are used, positive electrode active materials with good performance are obtained and good battery performance results are achieved as well.

    [0387] Table 8 shows the composition of the positive electrode active materials of examples

    [0388] Table 9 shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 45 to 59 obtained according to the performance test methods above.

    TABLE-US-00008 TABLE 8 First Second Third coating coating coating No. Inner core layer layer layer Example 45 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 2% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 1% of carbon Example 46 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 3% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 1% of carbon Example 47 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 4% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 1% of carbon Example 48 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 5.5% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 1% of carbon Example 49 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 6% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 1% of carbon Example 50 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 1% LiFePO4 1% of carbon Example 51 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 2% LiFePO4 1% of carbon Example 52 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 4% LiFePO4 1% of carbon Example 53 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 5.5% LiFePO4 1% of carbon Example 54 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 6% LiFePO4 1% of carbon Example 55 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 2% of carbon Example 56 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 3% of carbon Example 57 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 4% of carbon Example 58 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 5.5% of carbon Example 59 Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7 3% LiFePO4 6% of carbon

    TABLE-US-00009 TABLE 9 Number of Expansion Li/Mn Dissolution Capacity of 3 C charge cycles for of battery Lattice antisite of Mn and button constant capacity upon 30 days change defect Surface Compacted Fe after battery current retention of storage rate concentration oxygen density cycling at 0.1 C rate rate of 80% at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (%) at 45? C. (%) Example 6.1 0.9 ?1.98 2.28 15 157.1 66.3 1458 2 45 Example 6.1 0.9 ?1.99 2.26 12 156.5 64.2 1568 1.8 46 Example 6.1 0.8 ?1.98 2.28 10 155.9 62.8 1685 1.6 47 Example 6.0 0.9 ?1.97 2.25 5 153.3 61.5 1775 1.4 48 Example 6.0 0.8 ?1.97 2.24 5 153.0 60.2 1952 1.2 49 Example 6.1 1 ?1.98 2.25 24 154.2 64.5 1126 3.1 50 Example 6.1 1 ?1.96 2.26 21 156.2 66.8 1456 2.5 51 Example 6.1 0.9 ?1.99 2.25 19 155.4 70.5 1546 1.8 52 Example 6.1 0.8 ?1.97 2.24 17 153.1 72.5 1675 1.5 53 Example 6.0 0.7 ?1.98 2.27 16 152.3 76.8 1787 1.2 54 Example 6.1 0.8 ?1.98 2.25 18 159.3 70.5 1310 1.9 55 Example 6.1 0.7 ?1.96 2.24 15 161.2 74.6 1317 1.9 56 Example 6.1 0.7 ?1.98 2.24 12 159.8 80.4 1328 1.9 57 Example 6.2 0.9 ?1.97 2.21 10 157.3 84.2 1345 1.8 58 Example 6.2 1 ?1.98 2.22 9 156.6 86.5 1284 1.8 59

    [0389] It can be seen from Table 9 that when the coating amount of the coating layers is in a suitable range, the performance of the positive electrode active material and battery can be further improved.

    [0390] Table 10 shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 60 to 62 obtained according to the performance test methods above.

    TABLE-US-00010 TABLE 10 3 C Number Expansion Dissolution Capacity charge of cycles of battery Lattice Li/Mn of Mn and of button constant for capacity upon 30 days Crystallinity of change antisite defect Surface Compacted Fe after battery at current retention of storage pyrophosphate rate concentration oxygen density cycling 0.1 C rate rate of 80% at 60? C. No. and phosphate (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (%) at 45? C. (%) Example 100% 6.1 0.8 ?1.97 2.25 20 157.6 68.2 1305 2.1 1 Example 30% 7.7 1.1 ?1.98 2.22 81 153.2 65.2 1185 3.1 60 Example 50% 7.2 1.0 ?1.97 2.22 53 155.4 67.4 1252 2.4 61 Example 70% 6.7 0.9 ?1.99 2.24 32 156.2 67.8 1275 2.2 62

    [0391] It can be seen from Table 10 that as the crystallinity of pyrophosphate and phosphate gradually increases, the lattice change rate, Li/Mn antisite defect concentration, and dissolution of Fe and Mn after cycling of the corresponding positive electrode active material gradually decrease, the capacity of the battery is gradually increased, and the high-temperature cycling performance and high-temperature storage performance of the battery are also gradually improved.

    [0392] The specific examples of positive electrode active materials having an inner core of Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n and a shell comprising a first coating layer (pyrophosphate and phosphate) and a carbon-containing second coating layer are detailed below:

    Example 1-A

    (1) Preparation of Positive Electrode Active Material

    S1: Preparation of Doped Manganese Oxalate

    [0393] The parameters of step S1 were the same as those in example 1.

    S2: Preparation of Co-Doped Lithium Manganese Phosphate Inner Core

    [0394] The parameters of step S2 were the same as those in example 1, so as to obtain Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001, i.e., a co-doped lithium manganese phosphate inner core.

    S3: Preparation of Lithium Iron Pyrophosphate Powder

    [0395] 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate, and 1.3 g of oxalic acid dihydrate were dissolved in 50 mL of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 650? C. in a nitrogen atmosphere for 8 hours, naturally cooled to room temperature, and then ground to obtain a Li.sub.2FeP.sub.2O.sub.7 powder.

    S4: Preparation of Lithium Iron Phosphate Suspension

    [0396] 11.1 g of lithium carbonate, 34.8 g of ferrous carbonate, 34.5 g of ammonium dihydrogen phosphate, 1.3 g of oxalic acid dihydrate, and 37.3 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were dissolved in 150 mL of deionized water to obtain a mixture, and the mixture was then stirred for 6 hours for complete reaction. Then, the reacted solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising sucrose and LiFePO.sub.4.

    S5: Coating

    [0397] 10 mol (about 1570 g) of the co-doped lithium manganese phosphate inner core obtained by the process in step S2 and 15.7 g of the Li.sub.2FeP.sub.2O.sub.7 powder obtained in step S3 were added to the LiFePO.sub.4 suspension (comprising 37.3 g of sucrose and 47.2 g of LiFePO.sub.4) obtained in step S4, stirred and mixed until uniform, and then transferred to a vacuum oven and dried at 150? C. for 6 hours. The resulting product was then dispersed by sanding. After dispersion, the obtained product was sintered at 700? C. under a nitrogen atmosphere for 6 hours to obtain the positive electrode active material.

    (2) Preparation of Positive Electrode Plate

    [0398] The positive electrode active material above, a conductive agent of acetylene black, a binder of polyvinylidene fluoride (PVDF) were added at a weight ratio of 92:2.5:5.5 into N-methylpyrrolidone (NMP), and stirred and mixed until uniform to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to an aluminum foil at 0.280 g/1540.25 mm.sup.2, followed by drying, cold pressing and slitting to obtain a positive electrode plate.

    (3) Preparation of Negative Electrode Plate

    [0399] The parameters for preparing the negative electrode plate were the same as those in example 1.

    (4) Preparation of Electrolyte Solution

    [0400] The parameters of the electrolyte solution were the same as those in example 1.

    (5) Separator

    [0401] The parameters of the separator were the same as those in example 1.

    (6) Preparation of Full Battery and Button Battery

    [0402] The parameters for obtaining a full battery and a button battery were the same as those in example 1.

    Example 2-A

    [0403] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4885 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with HNO.sub.3, and 0.02 mol of Ti(SO.sub.4).sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 3-A

    [0404] Except that in step S1 and step S2, the amount of Li.sub.2CO.sub.3 was changed to 0.496 mol, Mo(SO.sub.4).sub.3 was replaced with W(SO.sub.4).sub.3, and H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the other conditions were the same as example 1-A.

    Example 4-A

    [0405] Except that in step S1 and step S2, the amount of Li.sub.2CO.sub.3 was changed to 0.4985 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Al.sub.2(SO.sub.4).sub.3, and NH.sub.4HF.sub.2 was replaced with NH.sub.4HCl.sub.2, the other conditions were the same as example 1-A.

    Example 5-A

    [0406] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.69 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4965 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.01 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 6-A

    [0407] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4965 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.01 mol of VCl.sub.2 and 0.01 mol of MgSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 7-A

    [0408] Except that in step S1 and step S2, MgSO.sub.4 was replaced with CoSO.sub.4, the other conditions were the same as example 6-A.

    Example 8-A

    [0409] Except that in step S1 and step S2, MgSO.sub.4 was replaced with NiSO.sub.4, the other conditions were the same as example 6-A.

    Example 9-A

    [0410] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.698 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4955 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, NH.sub.4HF.sub.2 was replaced with NH.sub.4HCl.sub.2, and 0.002 mol of Ti(SO.sub.4).sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 10-A

    [0411] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.68 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4975 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.0005 mol of Nb.sub.2(SO.sub.4).sub.5, NH.sub.4HF.sub.2 was replaced with NH.sub.4HBr.sub.2, and 0.01 mol of VCl.sub.2 and 0.01 mol of MgSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 11-A

    [0412] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.69 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.499 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, NH.sub.4HF.sub.2 was replaced with NH.sub.4HBr.sub.2, and 0.01 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 12-A

    [0413] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.36 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.6 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4985 mol, Mo(SO.sub.4).sub.3 was replaced with MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with HNO.sub.3, and 0.04 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 13-A

    [0414] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.16 mol, and the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.8 mol, the other conditions were the same as example 12-A.

    Example 14-A

    [0415] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.3 mol, and the amount of VCl.sub.2 was changed to 0.1 mol, the other conditions were the same as example 12-A.

    Example 15-A

    [0416] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.494 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 16-A

    [0417] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.467 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, 0.001 mol of H.sub.4SiO.sub.4 was replaced with 0.005 mol of H.sub.2SO.sub.4, 1.175 mol of 85% phosphoric acid was replaced with 1.171 mol of 85% phosphoric acid, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 17-A

    [0418] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.492 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the amount of NH.sub.4HF.sub.2 was changed to 0.0025 mol, and 0.1 mol of VCl.sub.2 was further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 18-A

    [0419] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.5 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.492 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, H.sub.4SiO.sub.4 was replaced with H.sub.2SO.sub.4, the amount of NH.sub.4HF.sub.2 was changed to 0.0025 mol, and 0.1 mol of VCl.sub.2 and 0.1 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 19-A

    [0420] Except that in step S1 and step S2, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.4 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18-A.

    Example 20-A

    [0421] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.5 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.1 mol, and the amount of CoSO.sub.4 was changed to 0.3 mol, the other conditions were the same as example 18-A.

    Example 21-A

    [0422] Except that in step S1 and step S2, CoSO.sub.4 was replaced with NiSO.sub.4, the other conditions were the same as example 18-A.

    Example 22-A

    [0423] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.5 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.2 mol, and 0.1 mol of CoSO.sub.4 was replaced with 0.2 mol of NiSO.sub.4, the other conditions were the same as example 18-A.

    Example 23-A

    [0424] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18-A.

    Example 24-A

    [0425] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.2 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.5 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18-A.

    Example 25-A

    [0426] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.0 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.7 mol, and the amount of CoSO.sub.4 was changed to 0.2 mol, the other conditions were the same as example 18-A.

    Example 26-A

    [0427] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.4825 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, the amount of H.sub.4SiO.sub.4 was changed to 0.1 mol, the amount of phosphoric acid was changed to 0.9 mol, the amount of NH.sub.4HF.sub.2 was changed to 0.04 mol, and 0.1 mol of VCl.sub.2 and 0.2 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Example 27-A

    [0428] Except that in step S1 and step S2, the amount of MnSO.sub.4.Math.H.sub.2O was changed to 1.4 mol, the amount of FeSO.sub.4.Math.H.sub.2O was changed to 0.3 mol, the amount of Li.sub.2CO.sub.3 was changed to 0.485 mol, 0.001 mol of Mo(SO.sub.4).sub.3 was replaced with 0.005 mol of MgSO.sub.4, the amount of H.sub.4SiO.sub.4 was changed to 0.08 mol, the amount of phosphoric acid was changed to 0.92 mol, the amount of NH.sub.4HF.sub.2 was changed to 0.05 mol, and 0.1 mol of VCl.sub.2 and 0.2 mol of CoSO.sub.4 were further added during the preparation of a doped manganese oxalate in step S1, the other conditions were the same as example 1-A.

    Examples 28-A to 32-A

    [0429] Except that in step S3 and step S4, the amount of the raw materials were correspondingly adjusted according to the coating amount as shown in Table 5, such that the amounts of Li.sub.2FeP.sub.2O.sub.7/LiFePO.sub.4 in examples 28-A to 32-A were 12.6 g/37.7 g, 14.1 g/42.4 g, 18.8 g/56.5 g, 22.0 g/66.0 g and 25.1 g/75.4 g, respectively, the other conditions were the same as example 1-A.

    Examples 33-A to 36-A

    [0430] Except that in step S4, the amounts of sucrose were adjusted to be 74.6 g, 149.1 g, 186.4 g and 223.7 g, respectively, such that the corresponding coating amounts of the carbon layers as the second coating layers were 31.4 g, 62.9 g, 78.6 g and 94.3 g, respectively, the other conditions were the same as example 1-A.

    Examples 37-A to 40-A

    [0431] Except that in step S3 and step S4, the amount of the raw materials were correspondingly adjusted according to the coating amount as shown in Table 5, such that the amounts of Li.sub.2FeP.sub.2O.sub.7/LiFePO.sub.4 in examples 37 to 40 were 23.6 g/39.3 g, 31.4 g/31.4 g, 39.3 g/23.6 g and 47.2 g/15.7 g, respectively, the other conditions were the same as example 1-A.

    Example 41-A

    [0432] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 550? C. and the sintering time was adjusted to 1 hour to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 30%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 2 hours to control the crystallinity of LiFePO.sub.4 to be 30%, the other conditions were the same as example 1-A.

    Example 42-A

    [0433] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 550? C. and the sintering time was adjusted to 2 hours to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 50%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 3 hours to control the crystallinity of LiFePO.sub.4 to be 50%, the other conditions were the same as example 1-A.

    Example 43-A

    [0434] Except that in the powder sintering step in step S4, the sintering temperature was adjusted to 600? C. and the sintering time was adjusted to 3 hour to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 70%, and in step S5, the coating sintering temperature was adjusted to 650? C. and the sintering time was adjusted to 4 hours to control the crystallinity of LiFePO.sub.4 to be 70%, the other conditions were the same as example 1-A.

    Examples 44-A to 57-A

    [0435] Except that the stirring rotation speed and the heating temperature during the preparation of a doped manganese oxalate in step S1, and the time for grinding and stirring in a sander and the sintering temperature and sintering time during the preparation of a co-doped lithium manganese phosphate inner core in step S2 were changed, the other conditions were the same as example 1-A. See Table 8-A below for details.

    Examples 58-A to 61-A

    [0436] Except that in step S3 of preparing a lithium iron pyrophosphate powder, the drying temperature/drying time were adjusted to be 100? C./4 h, 150? C./6 h, 200? C./6 h, and 200? C./6 h respectively, and the sintering temperature and sintering time were adjusted to be 700? C./6 h, 700? C./6 h, 700? C./6 h, and 600? C./6 h, respectively, the other conditions were the same as example 1-A.

    Examples 62-A to 64-A

    [0437] Except that in the coating step S5, the drying temperature/drying time were adjusted to be 150? C./6 h, 150? C./6 h, and 150? C./6 h respectively, and the sintering temperature and sintering time were adjusted to be 680? C./4 h, 750? C./6 h, and 800? C./8 h, respectively, the other conditions were the same as example 38-A.

    [0438] The preparation of comparative examples (1-A) to comparative example (9-A) was the same as that in comparative examples 1-9 described above, and details would not be described again here.

    Comparative Example 10-A

    [0439] Except that steps S3 and S5 were changed and step S4 was omitted, the other conditions were the same as example 1-A.

    S3: Preparation of Lithium Iron Pyrophosphate Powder

    [0440] 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 mL of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 500? C. in a nitrogen atmosphere for 4 hours, naturally cooled to room temperature, and then ground to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%. S5: Coating

    [0441] 10 mol (about 1570 g) of the co-doped lithium manganese phosphate inner core obtained by the process in step S2, 62.8 g of the Li.sub.2FeP.sub.2O.sub.7 powder obtained in step S3, and 37.3 g of sucrose were added into 500 mL of deionized water and stirred and mixed until uniform, and then transferred to a vacuum oven and dried at 150? C. for 6 hours. The resulting product was then dispersed by sanding. After dispersion, the obtained product was sintered at 700? C. in a nitrogen atmosphere for 6 hours to obtain an amorphous lithium iron pyrophosphate and carbon coated positive electrode active material.

    Comparative Example 11-A

    [0442] Except that steps S4 and S5 were changed and step S3 was omitted, the other conditions were the same as example 1-A.

    S4: Preparation of Lithium Iron Phosphate Suspension

    [0443] 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, 50.2 g of oxalic acid dihydrate, and 37.3 g of sucrose were dissolved in 500 mL of deionized water to obtain a mixture, and the mixture was then stirred for 6 hours and completely reacted. Then, the reacted solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising LiFePO.sub.4.

    S5: Coating

    [0444] 10 mol (about 1570 g) of the co-doped lithium manganese phosphate inner core obtained by the process in step S2 was added into the LiFePO.sub.4 suspension (comprising 37.3 g of sucrose and 62.8 g of LiFePO.sub.4) obtained in step S4, stirred and mixed until uniform, and then transferred to a vacuum oven and dried at 150? C. for 6 hours. The resulting product was then dispersed by sanding. After dispersion, the obtained product was sintered at 600? C. in a nitrogen atmosphere for 4 hours to obtain an amorphous lithium iron phosphate and carbon coated positive electrode active material.

    Comparative Example 12-A

    [0445] Except that steps S3 to S5 were changed, the other conditions were the same as example 1-A.

    S3: Preparation of Lithium Iron Pyrophosphate Powder

    [0446] 2.38 g of lithium carbonate, 7.5 g of ferrous carbonate, 7.4 g of ammonium dihydrogen phosphate, and 8.1 g of oxalic acid dihydrate were dissolved in 50 mL of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 500? C. in a nitrogen atmosphere for 4 hours, naturally cooled to room temperature, and then ground to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%.

    S4: Preparation of Lithium Iron Phosphate Suspension

    [0447] 11.1 g of lithium carbonate, 34.8 g of ferrous carbonate, 34.5 g of ammonium dihydrogen phosphate, 37.7 g of oxalic acid dihydrate, and 37.3 g of sucrose were dissolved in 1500 mL of deionized water to obtain a mixture, and the mixture was then stirred for 6 hours and completely reacted. Then, the reacted solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising LiFePO.sub.4.

    S5: Coating

    [0448] 10 mol (about 1570 g) of the co-doped lithium manganese phosphate inner core obtained by the process in step S2 and 15.7 g of the Li.sub.2FeP.sub.2O.sub.7 powder obtained in step S3 were added to the LiFePO.sub.4 suspension (comprising 37.3 g of sucrose and 47.2 g of LiFePO.sub.4) obtained in step S4, stirred and mixed until uniform, and then transferred to a vacuum oven and dried at 150? C. for 6 hours. The resulting product was then dispersed by sanding. After dispersion, the obtained product was sintered at 600? C. in a nitrogen atmosphere for 4 hours to control the crystallinity of LiFePO.sub.4 to be 8%, so as to obtain an amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon coated positive electrode active material.

    [0449] The performance of the products of the examples and comparative examples above was tested, and the remaining test parameters were the same as those in example 1. The test parameters of the average discharge voltage (V) of a button battery were as follows:

    [0450] The button battery prepared above was allowed to stand for 5 minutes in a constant-temperature environment at 25? C., discharged to 2.5 V at 0.1 C, allowed to stand for 5 minutes, charged to 4.3 V at 0.1 C, then charged at a constant voltage of 4.3 V until the current was less than or equal to 0.05 mA, and allowed to stand for 5 minutes, and the battery was then discharged to 2.5 V at 0.1 C, and the discharge capacity at the moment was the initial capacity per gram and denoted as D0, and the discharge energy was the initial energy and denoted as E0, and the average discharge voltage (V) of the button battery was E0/D0.

    [0451] Table 1-A shows the composition of the positive electrode active materials of examples 1-A to 11-A and comparative examples 1-A to 12-A.

    [0452] Table 2-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 1-A to 11-A and comparative examples 1-A to 12-A obtained according to the performance test methods above.

    TABLE-US-00011 TABLE 1-A First Second coating coating No. Inner core layer layer Comparative LiMnPO.sub.4 1% of example 1-A carbon Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 1% of example 2-A carbon Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 1% of example 3-A carbon Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 1% of example 4-A carbon Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 5-A carbon Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 6-A carbon Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 1% of example 7-A carbon Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 1% of example 8-A carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of example 9-A carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 4% of amorphous 1% of example 10-A Li.sub.2FeP.sub.2O.sub.7 carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 4% of amorphous 1% of example 11-A LiFePO4 carbon Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of amorphous 1% of example 12-A Li.sub.2FeP.sub.2O.sub.7/3% of carbon amorphous LiFePO4 Example 1-A Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 2-A Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 3-A Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 4-A Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 5-A Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 6-A Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 7-A Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 8-A Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 9-A Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 10-A Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Example 11-A Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 1% of LiFePO.sub.4 carbon Note: 1) the crystallinities of both Li.sub.2FeP.sub.2O.sub.7 and LiFePO.sub.4 in examples 1-A to 11-A were both 100%; and 2) in comparative examples 10-A to 12-A, the crystallinity of Li.sub.2FeP.sub.2O.sub.7 was 5%, and the crystallinity of LiFePO.sub.4 was 8%.

    TABLE-US-00012 TABLE 2-A Number Expansion Capacity Average of cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Comparative 11.4 5.2 ?1.55 1.7 2060 125.6 4.02 121 48.6 example 1-A Comparative 10.6 4.3 ?1.51 1.87 1510 126.4 3.85 129 37.3 example 2-A Comparative 10.8 3.6 ?1.64 1.88 1028 134.7 4.05 134 31.9 example 3-A Comparative 9.7 2.4 ?1.71 1.93 980 141.3 3.69 148 30.8 example 4-A Comparative 5.6 1.8 ?1.81 1.98 873 110.8 3.75 387 21.4 example 5-A Comparative 3.7 1.5 ?1.8 2.01 574 74.3 3.56 469 15.8 example 6-A Comparative 7.8 1.5 ?1.75 2.05 447 139.4 3.75 396 18.3 example 7-A Comparative 8.4 1.4 ?1.79 2.16 263 141.7 3.7 407 22.7 example 8-A Comparative 6.3 1.2 ?1.82 2.21 192 156.0 3.72 552 8.4 example 9-A Comparative 6.3 1.1 ?1.90 2.25 156 156.2 3.73 802 6.7 example 10-A Comparative 6.2 1.1 ?1.91 2.26 164 156.1 3.74 860 6.4 example 11-A Comparative 6.2 1.1 ?1.90 2.21 148 156.2 3.72 950 4.2 example 12-A Example 6.2 0.7 1.97 2.23 83 157.6 3.75 1285 2.1 1-A Example 6.8 0.5 ?1.98 2.45 50 159.4 3.79 1553 1.8 2-A Example 6.4 0.6 ?1.97 2.26 79 156.3 3.78 1337 2.1 3-A Example 5.4 0.7 ?1.97 2.24 86 154.7 3.75 1251 2.2 4-A Example 5.3 0.4 ?1.98 2.43 46 157.6 3.79 1598 1.8 5-A Example 2.4 0.3 ?1.99 2.50 53 161.8 3.8 1474 1.7 6-A Example 2.2 0.3 ?1.99 2.51 51 161 3.8 1592 1.7 7-A Example 3.4 0.3 ?1.99 2.53 59 161.2 3.8 1449 1.6 8-A Example 3.6 0.4 ?1.98 2.48 43 159.3 3.79 1546 1.9 9-A Example 3.8 0.3 ?1.99 2.52 58 160.3 3.8 1660 1.6 10-A Example 3.5 0.4 ?1.98 2.46 49 159.6 3.79 1532 1.9 11-A

    [0453] It can be seen from Table 2-A that the positive electrode active material of the present application obtained by modifying lithium manganese phosphate via simultaneous doping at Li, Mn, P and O sites with certain amount of specific elements and by multi-layer coating of lithium manganese phosphate achieves a smaller lattice change rate, a smaller Li/Mn antisite defect concentration, a larger compacted density, a surface oxygen valency closer to ?2 valence, and less Fe and Mn dissolution after cycling, such that the battery of the present application has better performance, such as a higher capacity, and a better high-temperature storage performance and high-temperature cycling performance.

    [0454] Table 3-A shows the composition of the positive electrode active materials of examples 12-A to 27-A.

    [0455] Table 4-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 12-A to 27-A obtained according to the performance test method above.

    TABLE-US-00013 TABLE 3-A First Second coating coating No. Inner core (1 ? y):y a:x layer layer Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 2.13 997 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 12-A 3% LiFePO.sub.4 carbon Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.38 997 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 13-A 3% LiFePO.sub.4 carbon Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.86 997 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 14-A 3% LiFePO.sub.4 carbon Example Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.0010.sub.3.999F.sub.0.001 1.50 197.6 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 15-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 1.50 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 16-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.50 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 17-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.86 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 18-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.86 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 19-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 3.00 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 20-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.86 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 21-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 3.00 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 22-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.33 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 23-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.50 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 24-A 3% LiFePO.sub.4 carbon Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.00 196.8 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 25-A 3% LiFePO.sub.4 carbon Example Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 2.33 202 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 26-A 3% LiFePO.sub.4 carbon Example Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 2.33 194 1% Li.sub.2FeP.sub.2O.sub.7/ 1% of 27-A 3% LiFePO.sub.4 carbon Note: 1) the crystallinities of both Li.sub.2FeP.sub.2O.sub.7 and LiFePO.sub.4 in examples 12-A to 27-A were both 100%

    TABLE-US-00014 TABLE 4-A Number Expansion Capacity Average of cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 7.0 0.4 ?1.97 2.45 42 155.6 3.79 1448 1.7 12-A Example 7.5 0.3 ?1.99 2.48 43 159.7 3.73 1453 1.8 13-A Example 7.6 0.5 ?1.96 2.47 47 157.8 3.78 1567 1.9 14-A Example 6.3 0.4 ?1.98 2.49 56 158.6 3.7 1438 1.5 15-A Example 5.4 0.6 ?1.95 2.44 46 158.4 3.71 1427 1.7 16-A Example 4.0 0.5 ?1.99 2.42 48 158.9 3.7 1419 1.6 17-A Example 2.5 0.3 ?1.97 2.46 44 159.5 3.75 1557 1.8 18-A Example 2.4 0.3 ?1.98 2.47 54 159.2 3.78 1564 1.7 19-A Example 2.5 0.3 ?1.96 2.45 46 157.3 3.86 1475 2.3 20-A Example 3.2 0.4 ?1.94 2.46 52 158.2 3.87 1489 2.1 21-A Example 3.0 0.4 ?1.96 2.46 55 159.3 3.85 1464 2 22-A Example 2.8 0.5 ?1.97 2.44 47 154.4 3.8 1364 1.9 23-A Example 2.5 0.4 ?1.98 2.45 45 154.7 3.72 1476 1.6 24-A Example 2.2 0.3 ?1.99 2.46 38 155.6 3.68 1486 2.2 25-A Example 3.3 0.5 ?1.96 2.25 25 152.5 3.82 1478 2 26-A Example 2.6 0.4 ?1.99 2.28 22 152.0 3.81 1437 1.5 27-A

    [0456] It can be seen from Table 4-A that in the case where the other elements are the same, when (1?y):y is in a range of 1 to 4 and a:x is in a range of 9 to 1100, and optionally (1?y):y is in a rage of 1.5 to 3 and a:x is in a range of 190 to 998, the energy density and the cycling performance of the battery can be further improved.

    [0457] Table 5-A shows the composition of the positive electrode active materials of examples 28-A to 40-A.

    [0458] Table 6-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 28-A to 40-A obtained according to the performance test method above.

    TABLE-US-00015 TABLE 5-A First Second Inner coating coating No. core layer layer Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 0.8% Li.sub.2FeP.sub.2O.sub.7/2.4% 1% of 28-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 0.9% Li.sub.2FeP.sub.2O.sub.7/2.7% 1% of 29-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1.2% Li.sub.2FeP.sub.2O.sub.7/3.6% 1% of 30-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1.4% Li.sub.2FeP.sub.2O.sub.7/4.2% 1% of 31-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1.6% Li.sub.2FeP.sub.2O.sub.7/4.8% 1% of 32-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 2% of 33-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 4% of 34-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 5% of 35-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% Li.sub.2FeP.sub.2O.sub.7/3% 6% of 36-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1.5% Li.sub.2FeP.sub.2O.sub.7/2.5% 1% of 37-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 2% Li.sub.2FeP.sub.2O.sub.7/2% 1% of 38-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 2.5% Li.sub.2FeP.sub.2O.sub.7/1.5% 1% of 39-A LiFePO.sub.4 carbon Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 3% Li.sub.2FeP.sub.2O.sub.7/1% 1% of 40-A LiFePO.sub.4 carbon

    TABLE-US-00016 TABLE 6-A Number Expansion Capacity Average of cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 6.3 1.5 ?1.98 2.26 105 159.1 3.76 1085 2.6 28-A Example 6.3 0.8 ?1.97 2.25 89 158.7 3.74 1235 2.2 29-A Example 6.2 0.6 ?1.98 2.25 53 157.0 3.75 1329 1.8 30-A Example 6.2 0.4 ?1.97 2.24 31 156.4 3.75 1501 1.5 31-A Example 6.3 0.3 ?1.99 2.26 18 155.3 3.76 1632 1.1 32-A Example 6.2 0.5 ?1.97 2.18 65 156.8 3.77 1312 1.9 33-A Example 6.2 0.4 ?1.98 2.17 51 155.6 3.78 1341 1.7 34-A Example 6.1 0.3 ?1.99 2.16 39 155 3.79 1518 1.5 35-A Example 6.1 0.3 ?1.98 2.15 21 154.5 3.79 1649 1.4 36-A Example 6.2 0.5 ?1.99 2.18 69 156.8 3.76 1258 2.2 37-A Example 6.3 0.4 ?1.97 2.17 71 156.4 3.75 1201 2.3 38-A Example 6.3 0.5 ?1.96 2.16 65 155.9 3.75 1169 2.4 39-A Example 6.3 0.6 ?1.94 2.19 59 155.6 3.74 1131 2.5 40-A

    [0459] From the combination of example 1-A and examples 28-A to 32-A, it can be seen that as the amount of the first coating layer increases from 3.2% to 6.4%, the Li/M/n antisite defect concentration of the obtained positive electrode active material gradually decreases, the dissolution of Fe and Mn after cycling gradually decreases, and the corresponding battery has an improved safety performance and cycling performance as well but a slightly reduced capacity per gram. Optionally, when the total amount of the first coating layer is 4-5.6 wt %, the overall performance of the corresponding battery is the best.

    [0460] From the combination of example 1-A and examples 33-A to 36-A, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the Li/Mn antisite defect concentration of the obtained positive electrode active material gradually decreases, the dissolution of Fe and Mn after cycling gradually decreases, and the corresponding battery has an improved safety performance and cycling performance as well but a slightly reduced capacity per gram. Optionally, when the total amount of the second coating layer is 3-5 wt %, the overall performance of the corresponding battery is the best.

    [0461] From the combination of example 1-A and examples 37-A to 40-A, it can be seen that when the first coating layer comprises both Li.sub.2FeP.sub.2O.sub.7 and LiFePO.sub.4, and in particular the weight ratio of Li.sub.2FeP.sub.2O.sub.7 to LiFePO.sub.4 is 1:3 to 3:1, especially 1:3 to 1:1, the performance of the battery is obviously improved.

    [0462] Table 7-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 1-A, and 41-A to 43-A obtained according to the performance test method above.

    TABLE-US-00017 TABLE 7-A Number Expansion Capacity Average of cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Crystallinity Lattice antisite of Fe and of button voltage to 80% days of of change defect Surface Compacted Mn after battery of button capacity storage pyrophosphate rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. and phosphate (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 100% 6.2 0.7 ?1.97 2.23 83 157.6 3.75 1285 2.1 1-A Example 30% 7.8 1 ?1.98 2.21 139 152.4 3.73 915 5.9 41-A Example 50% 7.2 0.9 ?1.96 2.22 111 154.8 3.74 1002 4.2 42-A Example 70% 6.8 0.8 ?1.97 2.23 98 155.9 3.75 1149 3 43-A

    [0463] It can be seen from Table 7 that as the crystallinity of pyrophosphate and phosphate in the first coating layer gradually increases, the corresponding positive electrode active material has gradually reduced lattice change rate, Li/Mn antisite defect concentration, and dissolution of Fe and Mn after cycling, such that the capacity of the battery is increased gradually and the safety performance and cycling performance thereof are also improved gradually.

    [0464] In examples 44-A to 57-A, except that the stirring rotation speed and the heating temperature during the preparation of a doped manganese oxalate in step S1, and the time for grinding and stirring in a sander and the sintering temperature and sintering time during the preparation of a co-doped lithium manganese phosphate inner core in step S2 were changed, the other conditions were the same as example 1-A. See Table 8-A below for details. Table 9-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 44-A to 57-A obtained according to the performance test method above.

    TABLE-US-00018 TABLE 8-A Step S1 Step S2 Stirring Stirring Grinding Sintering Sintering rotation speed temperature time temperature time No. (rpm) (? C.) (h) (? C.) (h) Example 44-A 200 50 12 700 10 Example 45-A 300 50 12 700 10 Example 46-A 400 50 12 700 10 Example 47-A 500 50 12 700 10 Example 48-A 600 50 10 700 10 Example 49-A 700 50 11 700 10 Example 50-A 800 50 12 700 10 Example 51-A 600 60 12 700 10 Example 52-A 600 70 12 700 10 Example 53-A 600 80 12 700 10 Example 54-A 600 90 12 600 10 Example 55-A 600 100 12 800 10 Example 56-A 600 110 12 700 8 Example 57-A 600 120 12 700 12

    TABLE-US-00019 TABLE 9-A Number of Expansion Capacity Average cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 7.6 0.8 ?1.97 2.23 88 156.2 3.74 1165 2 44-A Example 7.2 0.7 ?1.98 2.22 87 156.8 3.75 1190 2.1 45-A Example 7.3 0.7 ?1.97 2.21 85 156.9 3.76 1198 2.2 46-A Example 7.0 0.7 ?1.98 2.22 84 157 3.74 1213 2.2 47-A Example 6.6 0.7 ?1.97 2.23 83 157.3 3.75 1270 2 48-A Example 6.7 0.6 ?1.99 2.22 81 158 3.76 1301 2.1 49-A Example 6.4 0.6 ?1.97 2.24 79 158.2 3.75 1268 2.1 50-A Example 6.3 0.7 ?1.98 2.22 87 157.6 3.74 1199 2 51-A Example 6.3 0.7 ?1.96 2.24 86 157.8 3.76 1245 2 52-A Example 6.3 0.6 ?1.97 2.21 82 157.8 3.75 1294 2.1 53-A Example 6.4 0.6 ?1.99 2.21 79 156.4 3.76 1287 2.2 54-A Example 6.7 0.6 ?1.98 2.23 88 157.1 3.74 1269 2 55-A Example 7.0 0.7 ?1.97 2.22 79 157.2 3.74 1248 2 56-A Example 7.7 0.8 ?1.99 2.21 84 157 3.76 1212 2.2 57-A

    [0465] It can be seen from Table 9-A at the performance of the positive electrode active material and battery can be further improved by adjusting the stirring rotation speed and the heating temperature during the preparation of a doped manganese oxalate in step S1, and the time for grinding and stirring in a sander and the sintering temperature and sintering time during the preparation of a co-doped lithium manganese phosphate inner core in step S2.

    [0466] In examples 58-A to 61-A, except that the drying temperature, drying time, sintering temperature and sintering time in step S3 of preparing a lithium iron pyrophosphate powder were changed, the other conditions were the same as example 1-A. See Table 10-A below for details. Table 11-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 58-A to 61-A obtained according to the performance test method above.

    [0467] In examples 62-A to 64-A, except that the drying temperature, drying time, sintering temperature and sintering time in the coating step S5 were changed, the other conditions were the same as example 38. See Table 12-A below for details. Table 13-A shows the performance data of the positive electrode active materials, the positive electrode plates, the button batteries or the full batteries of examples 62-A to 64-A obtained according to the performance test method above.

    TABLE-US-00020 TABLE 10-A Step S3 Lattice Included Lattice Included Drying Drying Sintering Sintering spacing of angle of spacing of angle of Li.sub.2FeP.sub.2O.sub.7:LiFePO.sub.4 temperature time temperature time pyrophosphate pyrophosphate phosphate phosphate No. (weight ratio) (? C.) (h) (? C.) (h) (nm) (?) (nm) (?) Example 1:3 100 4 700 6 0.303 29.496 0.348 25.562 58-A Example 1:3 150 6 700 6 0.303 29.496 0.348 25.562 59-A Example 1:3 200 6 700 6 0.303 29.496 0.348 25.562 60-A Example 1:3 200 6 600 6 0.303 29.496 0.348 25.562 61-A

    TABLE-US-00021 TABLE 11-A Number of Expansion Capacity Average cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 6.4 0.7 ?1.98 2.22 78 156.8 3.74 1205 1.8 58-A Example 6.2 0.7 ?1.97 2.23 79 158.1 3.76 1246 2 59-A Example 6.2 0.7 ?1.98 2.24 76 159.9 3.75 1278 2.1 60-A Example 6.3 1.2 ?1.96 2.23 95 155.1 3.74 1179 2.4 61-A

    TABLE-US-00022 TABLE 12-A Step S5 Lattice Included Lattice Included Drying Drying Sintering Sintering spacing of angle of spacing of angle of Li.sub.2FeP.sub.2O.sub.7:LiFePO.sub.4 temperature time temperature time pyrophosphate pyrophosphate phosphate phosphate No. (weight ratio) (? C.) (h) (? C.) (h) (nm) (?) (nm) (?) Example 1:1 150 6 680 4 0.303 29.496 0.348 25.562 62-A Example 1:1 150 6 750 6 0.303 29.496 0.348 25.562 63-A Example 1:1 150 6 800 8 0.303 29.496 0.348 25.562 64-A

    TABLE-US-00023 TABLE 13-A Number Expansion Capacity Average of cycles of battery Li/Mn Dissolution per gram discharge corresponding upon 30 Lattice antisite of Fe and of button voltage to 80% days of change defect Surface Compacted Mn after battery of button capacity storage rate concentration oxygen density cycling at 0.1 C battery retention at 60? C. No. (%) (%) valency (g/cm.sup.3) (ppm) (mAh/g) (V) rate at 45? C. (%) Example 6.5 0.8 ?1.98 2.22 92 155.3 3.76 1185 2.5 62-A Example 6.3 0.5 ?1.96 2.24 65 160.5 3.76 1305 2.2 63-A Example 6.2 0.5 ?1.97 2.24 57 158.7 3.76 1269 1.9 64-A

    [0468] It can be seen from Tables 10-A and 13-A, that the performance of the positive electrode active material and the battery can be further improved by adjusting parameters such as the drying temperature, drying time, sintering temperature and sintering time in steps S3 to S5.

    [0469] The preparation and performance tests of examples of the positive electrode active material having an inner core of Li.sub.1+xMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4 and a shell comprising a first coating layer containing a crystalline pyrophosphate of QP.sub.2O.sub.7 and a metal oxide of Q.sub.eO.sub.f and a second coating layer of a carbon coating layer will be detailed below:

    [0470] The sources of the raw materials involved in the preparation examples and examples are as follows:

    TABLE-US-00024 Name Chemical formula Manufacturer Specification Manganese MnCO.sub.3 Shandong Xiya Chemical 1 Kg carbonate Industry Co., Ltd. Lithium Li.sub.2CO.sub.3 Shandong Xiya Chemical 1 Kg carbonate Industry Co., Ltd. Magnesium MgCO.sub.3 Shandong Xiya Chemical 1 Kg carbonate Industry Co., Ltd. Zinc ZnCO.sub.3 Wuhan Xinru Chemical 25 Kg carbonate Co., Ltd. Ferrous FeCO.sub.3 Xi'an Lanzhiguang Fine 1 Kg carbonate Materials Co., Ltd. Nickel NiCO.sub.3 Shandong Xiya Chemical 1 Kg sulfate Industry Co., Ltd. Titanium Ti(SO.sub.4).sub.2 Shandong Xiya Chemical 1 Kg sulfate Industry Co., Ltd. Cobalt CoSO.sub.4 Xiamen Zhixin Chemical 500 g sulfate Co., Ltd. Vanadium VCl.sub.2 Shanghai Jinjinle 1 Kg dichloride Industrial Co., Ltd. Oxalic acid C.sub.2H.sub.2O.sub.42H.sub.2O Shanghai Jinjinle 1 Kg dihydrate Industrial Co., Ltd. Ammonium NH.sub.4H.sub.2PO.sub.4 Shanghai Chengshao 500 g dihydrogen Biotechnology Co., Ltd. phosphate Sucrose C.sub.12H.sub.22O.sub.11 Shanghai Yuanye 100 g Biotechnology Co., Ltd. Sulfuric H.sub.2SO.sub.4 Shenzhen Hisian Mass fraction 60% acid Biotechnology Co., Ltd. Nitric HNO.sub.3 Anhui Lingtian Fine Mass fraction 60% acid Chemical Co., Ltd. Nitric HNO.sub.3 Anhui Lingtian Fine Mass fraction 85% acid Chemical Co., Ltd. Metasilicic H.sub.2SiO.sub.3 Shanghai Yuanye 100 g acid Biotechnology Co., Ltd. Boronic H.sub.3BO.sub.3 Changzhou Qidi 1 Kg acid Chemical Co., Ltd. Aluminum Al2O3 Hebei Guanlang 25 Kg oxide Biotechnology Co., Ltd. Magnesium MgO Hebei Guanlang 25 Kg oxide Biotechnology Co., Ltd. Zirconium ZrO2 Qingyuan Shengyi 1 Kg dioxid Biotechnology Co., Ltd. Copper CuO Hebei Guanlang 25 Kg oxide Biotechnology Co., Ltd. Silica SiO2 Hebei Guanlang 25 Kg Biotechnology Co., Ltd. Tungsten WO3 Hebei Guanlang 25 Kg trioxide Biotechnology Co., Ltd. Titanium TiO2 Shanghai Yuanye 500 g dioxide Biotechnology Co., Ltd. Vanadium V2O5 Shanghai Jinjinle 1 Kg pentoxide Industrial Co., Ltd. Nickel NiO Hubei Wande Chemical 25 Kg oxide Co., Ltd.

    Example 1-1

    (1) Preparation of Co-Doped Lithium Manganese Phosphate Inner Core

    [0471] Preparation of Fe, Co and V co-doped manganese oxalate: 689.5 g of manganese carbonate (in MnCO.sub.3, the same below), 455.2 g of ferrous carbonate (in FeCO.sub.3, the same below), 4.6 g of cobalt sulfate (in CoSO.sub.4, the same below), and 4.9 g of vanadium dichloride (in VCl.sub.2, the same below) were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate (in C.sub.2H.sub.2O.sub.4.Math.2H.sub.2O, the same below) were added. The reaction kettle was heated to 80? C., and the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe, Co and V co-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

    [0472] Preparation of Fe, Co, V and S co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles (1793.4 g) obtained in the previous step, 369.0 g of lithium carbonate (in Li.sub.2CO.sub.3, the same below), 1.6 g of 60% dilute sulfuric acid (in 60% H.sub.2SO.sub.4, the same below), and 1148.9 g of ammonium dihydrogen phosphate (in NH.sub.4H.sub.2PO.sub.4, the same below) were added into 20 L of deionized water, and the mixture was stirred for 10 hours until mixed uniformly, so as to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain a powder. The above powder was sintered at 700? C. for 4 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain 1572.1 g of Fe, Co, V and S co-doped lithium manganese phosphate.

    (2) Preparation of Lithium Iron Pyrophosphate and Suspension Comprising Aluminum Oxide and Sucrose

    [0473] Preparation of lithium iron pyrophosphate powder: 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate, and 1.3 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 h to obtain a powder. The powder was sintered at 650? C. in a nitrogen atmosphere for 8 hours, naturally cooled to room temperature, and then ground to obtain a Li.sub.2FeP.sub.2O.sub.7 powder.

    [0474] Preparation of suspension comprising aluminum oxide and sucrose: 47.1 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) and 74.6 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were dissolved in 1500 ml of deionized water, and then the mixture was stirred for 6 hours until mixed uniformly. Then, the resulting solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising aluminum oxide and sucrose.

    (3) Coating

    [0475] 1572.1 g of the Fe, Co, V and S co-doped lithium manganese phosphate above and 15.72 g of the lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder above were added into the suspension comprising aluminum oxide and sucrose prepared in the previous step, stirred and mixed until uniform, then transferred to a vacuum oven and dried at 150? C. for 6 h. The resulting product was then dispersed by sanding. After dispersion, the obtained product was sintered at 700? C. in a nitrogen atmosphere for 6 hours to obtain the target product of two-layer coated lithium manganese phosphate.

    Examples 1-2 to 1-6

    [0476] During the preparation of a co-doped lithium manganese phosphate inner core, the preparation conditions for the lithium manganese phosphate inner cores in examples 1-2 to 1-6 were the same as example 1-1, except that vanadium dichloride and cobalt sulfate were not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate, and 369.0 g of lithium carbonate were used.

    [0477] In addition, in the process of preparing the lithium iron pyrophosphate and suspension comprising aluminum oxide and sucrose and in the process of coating the first coating layer and the second coating layer, except that the raw materials used were adjusted correspondingly according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to example 1-1, such that the amount of Li.sub.2FeP.sub.2O.sub.7/Al.sub.2O.sub.3 in examples 1-2 to 1-6 was 12.6 g/37.68 g, 15.7 g/47.1 g, 18.8 g/56.52 g, 22.0 g/65.94 g and 25.1 g/75.36 g, respectively, and the amount of sucrose in examples 1-2 to 1-6 was 37.3 g, the other conditions were the same as example 1-1.

    Examples 1-7 to 1-10

    [0478] The conditions in examples 1-7 to 1-10 were the same as example 1-3, except that the amounts of sucrose were 74.6 g, 149.1 g, 186.4 g and 223.7 g, respectively, such that the corresponding coating amount of the carbon layer as the second coating layer was 31.4 g, 62.9 g, 78.6 g and 94.3 g, respectively.

    Examples 1-11 to 1-14

    [0479] The conditions in examples 1-11 to 1-14 were the same as example 1-7, except that in the process of preparing the lithium iron pyrophosphate and suspension comprising aluminum oxide and sucrose, the amounts of raw materials were adjusted correspondingly according to the coating amount shown in Table 1, such that the amount of Li.sub.2FeP.sub.2O.sub.7/Al.sub.2O.sub.3 was 23.6 g/39.25 g, 31.4 g/31.4 g, 39.3 g/23.55 g and 47.2 g/15.7 g, respectively.

    Example 1-15

    [0480] The conditions in example 1-15 were the same as example 1-14, except that in the process of preparing the co-doped lithium manganese phosphate inner core, ferrous carbonate was replaced with 492.80 g of ZnCO.sub.3.

    Examples 1-16 to 1-18

    [0481] The conditions in examples 1-16 to 1-18 were the same as example 1-7, except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-16, ferrous carbonate was replaced with 466.4 g of NiCO.sub.3, 5.0 g of zinc carbonate and 7.2 g of titanium sulfate; in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-17, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used; and in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-18, 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride and 2.5 g of magnesium carbonate were used.

    Examples 1-19 to 1-20

    [0482] The conditions in examples 1-19 to 1-20 were the same as example 1-18, except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-19, 369.4 g of lithium carbonate was used, and dilute sulfuric acid was replaced by 1.05 g of 60% dilute nitric acid; and in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-20, 369.7 g of lithium carbonate was used, and dilute sulfuric acid was replaced with 0.78 g of metasilicic acid.

    Examples 1-21 to 1-22

    [0483] Except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-21, 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate and 0.78 g of metasilicic acid were used; and in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-22, 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate and 0.78 g of metasilicic acid were used, the conditions in examples 1-21 to 1-22 were the same as example 1-20.

    Examples 1-23 to 1-24

    [0484] Except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-23, 804.6 g of manganese carbonate, 231.7 g of ferrous carbonate, 1156.2 g of ammonium dihydrogen phosphate, 1.2 g of boric acid (with a mass fraction of 99.5%) and 370.8 g of lithium carbonate were used; and in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-24, 862.1 g of manganese carbonate, 173.8 g of ferrous carbonate, 1155.1 g of ammonium dihydrogen phosphate, 1.86 g of boric acid (with a mass fraction of 99.5%) and 371.6 g of lithium carbonate were used, the conditions in examples 1-23 to 1-24 were the same as example 1-22.

    Example 1-25

    [0485] The conditions in example 1-25 were the same as Example 1-20, except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-25, 370.1 g of lithium carbonate, 1.56 g of metasilicic acid and 1147.7 g of ammonium dihydrogen phosphate were used.

    Example 1-26

    [0486] The conditions in example 1-26 were the same as Example 1-20, except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-26, 368.3 g of lithium carbonate, 4.9 g of dilute sulfuric acid (with a mass fraction of 60%), 919.6 g of manganese carbonate, 224.8 g of ferrous carbonate, 3.7 g of vanadium dichloride, 2.5 g of magnesium carbonate and 1146.8 g of ammonium dihydrogen phosphate were used.

    Example 1-27

    [0487] The conditions in example 1-27 were the same as example 1-20, except that in the preparation process of the co-doped lithium manganese phosphate inner core of example 1-27, 367.9 g of lithium carbonate, 6.5 g of 60% dilute sulfuric acid and 1145.4 g of ammonium dihydrogen phosphate were used.

    Examples 1-28 to 1-33

    [0488] Except that in the preparation process of the co-doped lithium manganese phosphate inner core of examples 1-28 to 1-33, 1034.5 g of manganese carbonate, 108.9 g of ferrous carbonate, 3.7 g of vanadium dichloride and 2.5 g of magnesium carbonate were used; the amounts of lithium carbonate were respectively: 367.6 g, 367.2 g, 366.8 g, 366.4 g, 366.0 g and 332.4 g; the amounts of ammonium dihydrogen phosphate were respectively: 1144.5 g, 1143.4 g, 1142.2 g, 1141.1 g, 1139.9 g and 1138.8 g; and the amounts of 60% dilute sulfuric acid were respectively: 8.2 g, 9.8 g, 11.4 g, 13.1 g, 14.7 g and 16.3 g, the conditions in examples 1-28 to 1-33 were the same as example 1-20.

    Examples 1-34 to 1-38, and Example 1-43

    [0489] Except that in the process of preparing the lithium iron pyrophosphate and suspension comprising an oxide and sucrose and in the process of coating the first coating layer and the second coating layer, the raw materials used were adjusted correspondingly according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to example 1-1, such that the amounts of Li.sub.2FeP.sub.2O.sub.7/MgO in example 1-34 were 15.72 g/47.1 g respectively, the amounts of Li.sub.2FeP.sub.2O.sub.7/ZrO.sub.2 in example 1-35 were 15.72 g/47.1 g respectively, the amounts of Li.sub.2FeP.sub.2O.sub.7/ZnO in example 1-36 were 15.72 g/47.1 g respectively, the amounts of Li.sub.2FeP.sub.2O.sub.7/SnO.sub.2 in example 1-37 were 15.72 g/47.1 g respectively, the amounts of Li.sub.2FeP.sub.2O.sub.7/SiO.sub.2 in example 1-38 were 15.72 g/47.1 g respectively, and the amounts of Li.sub.2FeP.sub.2O.sub.7/V.sub.2O.sub.5 in example 1-43 were 15.72 g/47.1 g respectively, the other conditions were the same as example 1-1.

    Example 1-39 to Example 1-41

    [0490] 1) Preparation of Inner Core of Li.sub.1.1Mn.sub.0.6Fe.sub.0.393Mg.sub.0.007P.sub.0.9Si.sub.0.1O.sub.4 in Example 1-39.

    [0491] Preparation of Fe and Mg co-doped manganese oxalate: 689.5 g of manganese carbonate (in MnCO.sub.3, the same below), 455.2 g of ferrous carbonate (in FeCO.sub.3, the same below) and 5.90 g of magnesium carbonate (in MgCO.sub.3, the same below) were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate (in C.sub.2H.sub.2O.sub.4.Math.2H.sub.2O, the same below) were added. The reaction kettle was heated to 80? C., and the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe and Mg co-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe and Mg co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

    [0492] Preparation of Fe, Mg and Si co-doped lithium manganese phosphate: Manganese oxalate dihydrate particles (1791.3 g) obtained in the previous step, 406.3 g of lithium carbonate (in Li.sub.2CO.sub.3, the same below), 7.8 g of metasilicic acid (in H.sub.2SiO.sub.3, the same below) and 1035.0 g of ammonium dihydrogen phosphate (in NH.sub.4H.sub.2PO.sub.4, the same below) were added into 20 L of deionized water, and the mixture was stirred for 10 hours until mixed uniformly, so as to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain a powder. The above powder was sintered at 700? C. for 4 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain 1574.0 g of Fe, Mg, and Si co-doped lithium manganese phosphate.

    2) Preparation of Inner Core of LiMn.sub.0.999Fe.sub.0.001P.sub.0.995N.sub.0.005O.sub.4 in Example 1-40.

    [0493] Preparation of Fe-doped manganese oxalate: 1148.0 g of manganese carbonate (in MnCO.sub.3, the same below) and 11.58 g of ferrous carbonate (in FeCO.sub.3, the same below) were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate (in C.sub.2H.sub.2O.sub.4.Math.2H.sub.2O, the same below) were added. The reaction kettle was heated to 80? C., and the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

    [0494] Preparation of Fe and N co-doped lithium manganese phosphate: Manganese oxalate dihydrate particles (1789.9 g) obtained in the previous step, 369.4 g of lithium carbonate (in Li.sub.2CO.sub.3, the same below), 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) and 1144.3 g of ammonium dihydrogen phosphate (in NH.sub.4H.sub.2PO.sub.4, the same below) were added into 20 L of deionized water, and the mixture was stirred for 10 hours until mixed uniformly, so as to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain a powder. The above powder was sintered at 700? C. for 4 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain 1567.7 g of Fe and N co-doped lithium manganese phosphate.

    3) Preparation of Inner Core of LiMn.sub.0.50Fe.sub.0.50P.sub.0.995N.sub.0.005O.sub.4 in Example 1-41.

    [0495] Preparation of Fe-doped manganese oxalate: 574.7 g of manganese carbonate (in MnCO.sub.3, the same below) and 579.27 g of ferrous carbonate (in FeCO.sub.3, the same below) were mixed thoroughly for 6 hours in a mixer. The mixture was transferred into a reaction kettle, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate (in C.sub.2H.sub.2O.sub.4.Math.2H.sub.2O, the same below) were added. The reaction kettle was heated to 80? C., and the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a Fe-doped manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground, so as to obtain Fe doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

    [0496] Preparation of Fe and N co-doped lithium manganese phosphate: Manganese oxalate dihydrate particles (1794.4 g) obtained in the previous step, 369.4 g of lithium carbonate (in Li.sub.2CO.sub.3, the same below), 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) and 1144.3 g of ammonium dihydrogen phosphate (in NH.sub.4H.sub.2PO.sub.4, the same below) were added into 20 L of deionized water, and the mixture was stirred for 10 hours until mixed uniformly, so as to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain a powder. The above powder was sintered at 700? C. for 4 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain 1572.2 g of Fe and N co-doped lithium manganese phosphate.

    [0497] With regard to the other conditions of example 1-39 to example 1-41, reference can be made to example 1-1.

    Example 1-42

    [0498] In the preparation process of zirconium pyrophosphate, 123.2 g of zirconium dioxide (in ZrO.sub.2, the same below) and 230.6 g of phosphoric acid (in 85% H.sub.3PO.sub.4, the same below) were mixed thoroughly. The mixture was heated to 350? C. while stirring continuously for 2 hours such that the reaction mixture was fully reacted. Then the reacted solution was held at 350? C. for 4 hours to obtain a viscous paste comprising ZrP.sub.2O.sub.7, which finally became a solid; the solid was washed with deionized water, and the resulting product was ground in a ball mill containing ethanol for 4 h, and the resulting product was dried under an infrared lamp to obtain a ZrP.sub.2O.sub.7 powder.

    Example 1-44

    [0499] In the preparation process of silver pyrophosphate, 463.4 of silver oxide (in Ag.sub.2O, the same below) and 230.6 phosphoric acid (in 85% H.sub.3PO.sub.4, the same below) were mixed thoroughly. The mixture was heated to 450? C. while stirring continuously for 2 hours such that the reaction mixture was fully reacted. Then the reacted solution was held at 450? C. for 4 hours to obtain a viscous paste comprising Ag.sub.4P.sub.2O.sub.7, which finally became a solid; the solid was washed with deionized water, and the resulting product was ground in a ball mill containing ethanol for 4 h, and the resulting product was dried under an infrared lamp to obtain a Ag.sub.4P.sub.2O.sub.7 powder.

    Example 1-45

    [0500] Except that in the preparation process of the inner core, 1044.6 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 369.4 g of lithium carbonate were used, and 105.4 g of ferrous carbonate and 10.5 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the others are the same as example 1-1.

    Example 1-46

    [0501] Except that in the preparation process of the inner core, 104.5 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 371.3 g of lithium carbonate were used, and 1052.8 g of ferrous carbonate and 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the rest were the same as example 1-1.

    Example 1-47

    [0502] Except that in the process of preparing the lithium iron pyrophosphate and suspension comprising aluminum oxide and sucrose, the amounts of raw materials were adjusted correspondingly according to the coating amount shown in Table 1, such that the amounts of Li.sub.2FeP.sub.2O.sub.7/Al.sub.2O.sub.3 were 62.9 g/47.1 g, respectively, the conditions in example 1-47 were the same as example 1-1.

    Example 1-48

    [0503] Except that the amount of sucrose was 111.9 g, such that the corresponding amount of the carbon layer as the second coating layer was 47.1 g, the other operations were the same as example 1-1.

    Example 1-49

    [0504] Except that in the preparation process of the inner core, 1034.3 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 371.3 g of lithium carbonate were used, and 115.8 g of ferrous carbonate and 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the rest were the same as example 1-1.

    Example 1-50

    [0505] Except that in the preparation process of the inner core, 1091.8 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 371.3 g of lithium carbonate were used, and 57.9 g of ferrous carbonate and 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the rest were the same as example 1-1.

    Example 1-51

    [0506] Except that in the preparation process of the inner core, 804.5 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 371.3 g of lithium carbonate were used, and 347.4 g of ferrous carbonate and 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the amount of sucrose was 111.9 g, and the corresponding coating amount of carbon was 47.1 g, the rest were the same as example 1-1.

    Example 1-52

    [0507] Except that 747.0 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate and 371.3 g of lithium carbonate were used, and 405.3 g of ferrous carbonate and 5.25 g of dilute nitric acid (in 60% HNO.sub.3, the same below) were additionally added, the amount of sucrose was 111.9 g, and the corresponding coating amount of carbon was 47.1 g, the rest were the same as example 1-1.

    Example 2-1

    [0508] Except that in the powder sintering step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the sintering temperature was 550? C. and the sintering time was 1 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 30%; and in the coating sintering step during the preparation process of Al.sub.2O.sub.3, the sintering temperature was 650? C. and the sintering time was 2 h to control the crystallinity of Al.sub.2O.sub.3 to be 100%, the other conditions were the same as example 1-1.

    Example 2-2

    [0509] Except that in the powder sintering step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the sintering temperature was 550? C. and the sintering time was 2 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 50%; and in the coating sintering step during the preparation process of Al.sub.2O.sub.3, the sintering temperature was 650? C. and the sintering time was 3 h to control the crystallinity of Al.sub.2O.sub.3 to be 100%, the other conditions were the same as example 1-1.

    Example 2-3

    [0510] Except that in the powder sintering step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the sintering temperature was 600? C. and the sintering time was 3 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 70%; and in the coating sintering step during the preparation process of Al.sub.2O.sub.3, the sintering temperature was 650? C. and the sintering time was 4 h to control the crystallinity of Al.sub.2O.sub.3 to be 100%, the other conditions were the same as example 1-1.

    Example 2-4

    [0511] Except that in the powder sintering step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the sintering temperature was 650? C. and the sintering time was 4 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 10%; and in the coating sintering step during the preparation process of Al.sub.2O.sub.3, the sintering temperature was 500? C. and the sintering time was 6 h to control the crystallinity of Al.sub.2O.sub.3 to be 100%, the other conditions were the same as example 1-1.

    Examples 3-1 to 3-12

    [0512] Except that in the preparation process of Fe, Co and V co-doped manganese oxalate particles, the heating temperature/stirring time in the reaction kettle of example 3-1 was 60? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-2 was 70? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-3 was 80? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-4 was 90? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-5 was 100? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-6 was 110? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-7 was 120? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-8 was 130? C./120 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-9 was 100? C./60 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-10 was 100? C./90 min, respectively; the heating temperature/stirring time in the reaction kettle of example 3-11 was 100? C./150 min, respectively; and the heating temperature/stirring time in the reaction kettle of example 3-12 was 100? C./180 min, respectively, the other conditions in examples 3-1 to 3-12 were the same as example 1-1.

    Examples 4-1 to 4-4

    [0513] Except that in the drying step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the drying temperature/drying time was 100? C./4 h, 150? C./6 h, 200? C./6 h and 200? C./6 h, respectively; and in the sintering step during the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the sintering temperature and sintering time were 700? C./6 h, 700? C./6 h, 700? C./6 h and 600? C./6 h, respectively, the other conditions were the same as example 1-7.

    Examples 4-5 to 4-7

    [0514] Except that in the coating process, the drying temperature/drying time in the drying step was 150? C./6 h, 150? C./6 h and 150? C./6 h, respectively; and in the coating process, the sintering temperature and sintering time in the sintering step were 600? C./4 h, 600? C./6 h and 800? C./8 h, respectively, the other conditions were the same as example 1-12.

    Comparative Example 1-1

    [0515] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to a reaction kettle, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate (in C.sub.2H.sub.2O.sub.4.Math.2H.sub.2O, the same below) were added. The reaction kettle was heated to 80? C., the mixture was stirred for 6 hours at a rotation speed of 600 rpm until the reaction was completed (no bubble was generated), so as to obtain a manganese oxalate suspension. Then, the suspension was filtered, and the resultant filter cake was dried at 120? C. and then ground to obtain manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

    [0516] Preparation of carbon-coated lithium manganese phosphate: 1789.6 g of the manganese oxalate dihydrate particles obtained above, 369.4 g of lithium carbonate (in Li.sub.2CO.sub.3, the same below), 1150.1 g of ammonium dihydrogen phosphate (in NH.sub.4H.sub.2PO.sub.4, the same below), and 31 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were added into 20 L of deionized water, and the mixture was stirred for 10 hours until uniformly mixed, so as to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain a powder. The above powder was sintered at 700? C. for 4 hours in a protective atmosphere of nitrogen (90% by volume)+hydrogen (10% by volume), so as to obtain carbon-coated lithium manganese phosphate.

    Comparative Example 1-2

    [0517] Except that 689.5 g of manganese carbonate was used and 463.3 g of ferrous carbonate was additionally added, the other conditions of comparative example 2 were the same as comparative example 1-1.

    Comparative Example 1-3

    [0518] Except that 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate were used and 1.6 g of 60% dilute sulfuric acid was additionally added, the other conditions of comparative example 3 were the same as comparative example 1-1.

    Comparative Example 1-4

    [0519] Except that 689.5 g of manganese carbonate, 1148.9 g of ammonium dihydrogen phosphate, and 369.0 g of lithium carbonate were used and 463.3 g of ferrous carbonate and 1.6 g of 60% dilute sulfuric acid were additionally added, the other conditions were the same as comparative example 1-1.

    Comparative Example 1-5

    [0520] Except for the following additional steps: during the preparation of the lithium iron pyrophosphate powder, 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water; the pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted; then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 h to obtain a powder; and the powder was sintered at 500? C. under a nitrogen atmosphere for 4 h, and naturally cooled to room temperature and then ground to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%; and during the preparation a carbon-coated material, the amount of Li.sub.2FeP.sub.2O.sub.7 was 62.8 g, the other conditions were the same as comparative example 1-4.

    Comparative Example 1-6

    [0521] Except for the following additional steps: 62.92 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) and 37.4 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were dissolved in 1500 ml of deionized water, and then stirred for 6 hours such that the mixture was fully reacted; and then the reacted solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising aluminum oxide and sucrose, the other conditions were the same as comparative example 1-4.

    Comparative Example 1-7

    [0522] Preparation of amorphous lithium iron pyrophosphate powder: 2.38 g of lithium carbonate, 7.5 g of ferrous carbonate, 7.4 g of ammonium dihydrogen phosphate, and 8.1 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 h to obtain a powder. The powder was sintered at 500? C. in a nitrogen atmosphere for 4 hours, naturally cooled to room temperature, and then ground to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%.

    [0523] Preparation of suspension comprising aluminum oxide and sucrose: Except that 47.19 g of nano-Al.sub.2O.sub.3 (with a particle size of 20 nm) and 37.4 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were dissolved in 1500 ml of deionized water, and then stirred for 6 hours such that the mixture was fully reacted; then the reacted solution was heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising aluminum oxide and sucrose;

    [0524] 1573.0 g of the inner core, and 15.73 g of the lithium iron pyrophosphate powder were added into the suspension above; and in the preparation process, the sintering temperature was 600? C. and the sintering time was 4 h in the coating sintering step to control the crystallinity of LiFePO.sub.4 to be 8%, the other conditions in comparative example 7 were the same as comparative example 4, thereby obtaining amorphous lithium iron pyrophosphate, amorphous aluminium oxide, and a carbon-coated positive electrode active material.

    Comparative Examples 1-8 to 1-11

    [0525] Except that in the preparation process of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7), the drying temperature/drying time in the drying step in comparative examples 1-8 to 1-10 was 80? C./3 h, 80? C./3 h and 80? C./3 h, respectively; in the coating process, the sintering temperature and sintering time in the sintering step in comparative examples 1-8-1-10 were 400? C./3 h, 400? C./3 h and 350? C./2 h, respectively; in the coating process of comparative example 1-11, the drying temperature/drying time was 80? C./3 h; in comparative examples 1-8 and 1-9, the weight ratio of Li.sub.2FeP.sub.2O.sub.7/Al.sub.2O.sub.3 was 1:3 and 1:1, respectively; in comparative example 1-10, only Li.sub.2FeP.sub.2O.sub.7 was used; and in comparative example 1-11, only Al.sub.2O.sub.3 was used, the other conditions were the same as examples 1-1 to 1-7.

    Preparation of Positive Electrode Plate

    [0526] The parameters for preparing a positive electrode plate were the same as example 1-A.

    Preparation of Negative Electrode Plate

    [0527] A negative electrode active material of synthetic graphite, a conductive agent of superconducting carbon black (Super-P), a binder of styrene butadiene rubber (SBR) and a thickener of sodium carboxymethylcellulose (CMC-Na) were dissolved in deionized water in a mass ratio of 95%:1.5%:1.8%:1.7%, followed by fully stirring and mixing until uniform to obtain a negative electrode slurry with a viscosity of 3000 mPa.Math.s and a solid content of 52%; and the negative electrode slurry was coated onto a negative electrode current collector of a copper foil having a thickness of 6 ?m, and then baked at 100? C. for 4 hours for drying, followed by roll pressing to obtain a negative electrode plate with a compacted density of 1.75 g/cm.sup.3.

    Separator

    [0528] A polypropylene film was used.

    Preparation of Electrolyte Solution

    [0529] Ethylene carbonate, dimethyl carbonate and 1,2-propylene glycol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF.sub.6 was evenly dissolved in the above solution to obtain an electrolyte solution. In the electrolyte solution, the concentration of LiPF.sub.6 was 1 mol/L.

    Preparation of Full Battery

    [0530] The positive electrode plate, separator, and negative electrode plate obtained above were stacked in sequence, such that the separator was located between the positive electrode and the negative electrode and played a role of isolation, and the stack was wound to obtain a bare cell. The bare cell was placed in an outer package, the above electrolyte solution was injected, and the bare cell was packaged to obtain a full battery.

    Preparation of Button Battery

    [0531] The parameters for assembling a button battery in a button battery box were the same as example 1-A.

    [0532] The above results were shown in Table 1-4.

    TABLE-US-00025 TABLE 1-1 Performance test results of examples 1-1 to 1-52 and comparative examples 1-1 to 1-7 Average Expan- Number Dissolu- dis- sion of of cycles Com- Li/Mn tion of Capacity charge cell corre- pac- Thick- Thick- Lat- antisite Fe and per gram voltage upon 30 sponding to ted ness of ness of tice defect Mn of button of days of 80% capacity den- first Second second change concen- after battery button storage retention sity Example coating coating coating rate tration/ cycling at 0.1 C battery at 60? C rate at (g/ No. Inner core First coating layer layer layer layer (%) % (ppm) (mAh/g) (V) (%) 45? C. cm.sup.3) Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.4 0.4 6 ?1.96 157.4 3.76 1.5 1247 2.40 1-1 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 0.8% 2.4% 7.2 1% of 5 6.6 1.2 56 ?1.96 147.4 3.73 5.2 726 2.41 1-2 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 1% of 5 6.5 1.1 39 ?1.95 147.3 3.72 4.8 783 2.43 1-3 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1.2% 3.6% 10.8 1% of 5 6.5 0.8 23 ?1.96 145.8 3.71 3.4 812 2.42 1-4 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1.4% 4.2% 12.6 1% of 5 6.5 0.7 13 ?1.96 144.9 3.71 2.8 925 2.43 1-5 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1.6% 4.8% 14.4 1% of 5 6.6 0.6 9 ?1.96 143.8 3.70 2.4 1047 2.43 1-6 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 2% of 10 6.5 1 36 ?1.95 146.9 3.72 2.4 824 2.44 1-7 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 4% of 20 6.5 1 28 ?1.96 144.8 3.71 3.5 873 2.44 1-8 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 5% of 25 6.4 1.1 21 ?1.96 142.8 3.71 3.2 986 2.42 1-9 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 6% of 30 6.4 1.1 13 ?1.96 141.8 3.72 2.4 1079 2.39 1-10 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1.5% 2.5% 7.5 2% of 10 6.5 1.1 28 ?1.95 146.5 3.72 4.8 815 2.42 1-11 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 2% 2% 6 2% of 10 6.6 1 15 ?1.94 145.9 3.73 4.6 737 2.45 1-12 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 2.5% 1.5% 4.5 2% of 10 6.7 1.2 13 ?1.94 145.8 3.72 5.4 698 2.43 1-13 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 3% 1% 3 2% of 10 6.7 1.1 6 ?1.95 145.8 3.74 6.1 649 2.43 1-14 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Zn.sub.040P.sub.0.999S.sub.0.001O.sub.4 3% 1% 3 2% of 10 7.5 2.5 14 ?1.95 136.9 3.85 7.2 697 2.42 1-15 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.993Mn.sub.0.6Ni.sub.0.393Zn.sub.0.004Ti.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 2% of 10 5.4 0.8 11 ?1.95 137.7 3.84 3.8 826 2.42 1-16 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.007P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 2% of 10 4.2 0.6 7 ?1.95 151.8 3.76 2.7 1127 2.43 1-17 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.6 0.5 6 ?1.95 153.8 3.79 2.2 1096 2.42 1-18 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.999N.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.3 0.5 5 ?1.96 155.9 3.78 1.7 1207 2.43 1-19 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.001Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.4 0.7 8 ?1.96 155.8 3.78 2.1 1218 2.42 1-20 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.001Mn.sub.0.55Fe.sub.0.40V.sub.0.025Mg.sub.0.025P.sub.0.999Si.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.2 0.5 5 ?1.96 156.9 3.70 1.7 1328 2.41 1-21 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.001Mn.sub.0.65Fe.sub.0.25V.sub.0.05Mg.sub.0.05P.sub.0.999Si.sub.0.001O.sub.4 1% 3% 9 2% of 10 2.5 0.8 8 ?1.96 155.8 3.81 2.2 1142 2.40 1-22 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.004Mn.sub.0.7Fe.sub.0.2V.sub.0.05Mg.sub.0.05P.sub.0.998B.sub.0.002O.sub.4 1% 3% 9 2% of 10 2.6 0.8 8 ?1.96 155.9 3.81 1.7 1137 2.41 1-23 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.006Mn.sub.0.75Fe.sub.0.15V.sub.0.05Mg.sub.0.05P.sub.0.997B.sub.0.003O.sub.4 1% 3% 9 2% of 10 2.6 0.8 7 ?1.96 156.8 3.81 1.9 1148 2.42 1-24 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.1.002Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.998Si.sub.0.002O.sub.4 1% 3% 9 2% of 10 2.3 0.7 7 ?1.96 156.7 3.75 1.8 1197 2.43 1-25 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.997Mn.sub.0.80Fe.sub.0.194V.sub.0.003Mg.sub.0.003P.sub.0.997S.sub.0.003O.sub.4 1% 3% 9 2% of 10 2.8 0.9 8 ?1.96 154.9 3.83 2.7 986 2.43 1-26 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.996Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.996S.sub.0.004O.sub.4 1% 3% 9 2% of 10 2.2 0.6 8 ?1.96 156.7 3.76 2.2 1246 2.44 1-27 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.995Mn.sub.0.9Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.995S.sub.0.005O.sub.4 1% 3% 9 2% of 10 3.2 1.1 10 ?1.94 155.4 3.87 2.6 968 2.43 1-28 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.994Mn.sub.0.90Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.994S.sub.0.006O.sub.4 1% 3% 9 2% of 10 3 1.2 9 ?1.93 154.7 3.87 2.7 859 2.42 1-29 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.993Mn.sub.0.90Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.993S.sub.0.007O.sub.4 1% 3% 9 2% of 10 2.8 1.4 12 ?1.93 154.3 3.87 2.5 798 2.43 1-30 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.992Mn.sub.0.90Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.992S.sub.0.008O.sub.4 1% 3% 9 2% of 10 2.6 1.4 13 ?1.92 154.7 3.87 2.4 726 2.42 1-31 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.991Mn.sub.0.90Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.991S.sub.0.009O.sub.4 1% 3% 9 2% of 10 2.4 1.2 14 ?1.92 153.7 3.88 2.2 753 2.43 1-32 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Li.sub.0.9Mn.sub.0.90Fe.sub.0.094V.sub.0.003Mg.sub.0.003P.sub.0.9S.sub.0.1O.sub.4 1% 3% 9 2% of 10 2.1 0.9 12 ?1.92 152.8 3.86 2.1 738 2.42 1-33 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 carbon Example Same as Same as 3% 7.5 Same as 10 2.4 0.5 7 ?1.95 155.8 3.74 2.2 1142 2.40 1-34 example 1-1 example 1-1 MgO example 1-1 Example Same as Same as 3% 12 Same as 10 2.2 0.4 5 ?1.97 155.7 3.73 1.7 1247 2.43 1-35 example 1-1 example 1-1 ZrO.sub.2 example 1-1 Example Same as Same as 3% 10 Same as 10 2.5 0.6 8 ?1.96 154.8 3.73 2.3 978 2.40 1-36 example 1-1 example 1-1 ZnO example 1-1 Example Same as Same as 3% 15 Same as 10 2.6 0.5 9 ?1.95 154.2 3.72 2.9 868 2.41 1-37 example 1-1 example 1-1 SnO.sub.2 example 1-1 Example Same as Same as 3% 12 Same as 10 2.5 0.6 5 ?1.97 155.7 3.73 1.2 1386 2.42 1-38 example 1-1 example 1-1 SiO.sub.2 example 1-1 Example Li.sub.1.1Mn.sub.0.6Fe.sub.0.393Mg.sub.0.007P.sub.0.9Si.sub.0.1O.sub.4 Same as Same as 9 Same as 10 2.7 0.8 46 ?1.95 153.2 3.87 4.2 879 2.39 1-39 example 1-1 example 1-1 example 1-1 Example LiMn.sub.0.999Fe.sub.0.001P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 Same as 10 2.6 0.7 38 ?1.95 154.6 3.78 3.6 957 2.41 1-40 example 1-1 example 1-1 example 1-1 Example LiMn.sub.0.50Fe.sub.0.50P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 Same as 10 2.5 0.7 29 ?1.95 155.8 3.65 3.9 1123 2.43 1-41 example 1-1 example 1-1 example 1-1 Example Same as 1% Same as 9 Same as 10 2.6 0.6 19 ?1.95 156.3 3.75 2.7 1268 2.43 1-42 example 1-1 ZrP.sub.2O.sub.7 example 1-1 example 1-1 Example Same as Same as 3% 10 Same as 10 2.4 0.4 9 ?1.95 156.4 3.76 2.4 1097 2.41 1-43 example 1-1 example 1-1 V.sub.2O.sub.5 example 1-1 Example Same as 1% Same as 8.5 Same as 10 2.4 0.4 11 ?1.95 156.7 3.74 2.6 1007 2.42 1-44 example 1-1 Ag.sub.4P.sub.2O.sub.7 example 1-1 example 1-1 Example LiMn.sub.0.909Fe.sub.0.091P.sub.0.99N.sub.0.01O.sub.4 Same as Same as 9 Same as 10 3.6 2.5 46 ?1.95 152.4 3.84 3.5 854 2.31 1-45 example 1-1 example 1-1 example 1-1 Example LiMn.sub.0.091Fe.sub.0.909P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 Same as 10 2.1 0.5 8 ?1.98 158.2 3.35 2.7 1324 2.48 1-46 example 1-1 example 1-1 example 1-1 Example Same as 4% 3% 15 Same as 10 2.4 0.4 5 ?1.95 153.4 3.74 2.5 1358 2.41 1-47 example 1-1 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 example 1-1 Example Same as Same as Same as 9 3% of 15 2.4 0.4 8 ?1.95 155.3 3.73 2.4 1397 2.38 1-48 example 1-1 example 1-1 example 1-1 carbon Example LiMn.sub.0.9Fe.sub.0.1P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 Same as 10 5.8 4 38 ?1.92 151.8 3.85 3.4 816 2.25 1-49 example 1-1 example 1-1 example 1-1 Example LiMn.sub.0.95Fe.sub.0.05P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 Same as 10 6 5.1 43 ?1.91 150.9 3.83 4.1 795 2.27 1-50 example 1-1 example 1-1 example 1-1 Example LiMn.sub.0.7Fe.sub.0.3P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 3% of 15 3.2 0.8 15 ?1.94 153.7 3.75 2.3 1121 2.0 1-51 example 1-1 example 1-1 carbon Example LiMn.sub.0.65Fe.sub.0.35P.sub.0.995N.sub.0.005O.sub.4 Same as Same as 9 3% of 15 2.9 0.7 13 ?1.95 154.3 3.74 2.1 1285 2.2 1-52 example 1-1 example 1-1 carbon Compar- LiMnPO.sub.4 0 1% of 5 11.4 3.2 2060 ?1.55 125.6 4.02 48.6 185 1.81 ative carbon example 1-1 Compar- LiMn.sub.0.60Fe.sub.0.40PO.sub.4 0 1% of 5 8.7 2.8 1597 ?1.76 134.8 3.76 42.5 358 1.92 ative carbon example 1-2 Compar- Li.sub.0.999MnP.sub.0.999S.sub.0.001O.sub.4 0 1% of 5 9.8 2.5 1895 ?1.66 128.6 4.05 45.5 267 1.88 ative carbon example 1-3 Compar- Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 0 1% of 5 6.7 1.8 1279 ?1.83 140.5 3.78 38.5 417 1.82 ative carbon example 1-4 Compar- Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 4% of 10 1% of 5 6.5 1.8 208 ?1.9 140.3 3.73 12.5 519 1.79 ative amorphous carbon example Li.sub.2FeP.sub.2O.sub.7 1-5 Compar- Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 4% 12 1% of 5 6.6 1.8 318 ?1.91 140.2 3.74 11.5 528 1.83 ative Al.sub.2O.sub.3 carbon example 1-6 Compar- Li.sub.0.999Mn.sub.0.60Fe.sub.0.40P.sub.0.999S.sub.0.001O.sub.4 1% of 3% 13 1% of 5 6.6 1.8 174 ?1.9 140.1 3.75 8.6 682 1.84 ative amorphous Al.sub.2O.sub.3 carbon example Li.sub.2FeP.sub.2O.sub.7 1-7 Note: the crystallinity of both pyrophosphates and oxides in examples 1-1 to 1-52 was 100%.

    [0533] From the combination of examples 1-1 to 1-52 and comparative examples 1-1 to 1-4, it can be seen that the existence of the first coating layer is beneficial to reducing the Li/Mn antisite defect concentration and the dissolution of Fe and Mn after cycling of the obtained material, increasing the capacity per gram and compacted density of the button battery, and improving the safety performance and cycling performance of the battery. When the Mn site and the phosphorus site are respectively doped with other elements, the lattice change rate, antisite defect concentration, and dissolution of Fe and Mn of the obtained material can be significantly reduced, the capacity per gram and compacted density of the battery can be increased, and the safety performance and cycling performance of the battery can be improved.

    [0534] From the combination of examples 1-2 to 1-6, it can be seen that as the amount of the first coating layer increases from 3.2% to 6.4%, the Li/Mn antisite defect concentration and the dissolution of Fe and Mn after cycling of the obtained material are gradually reduced, and the safety performance and cycling performance at 45? C. of the corresponding battery are also improved, but the capacity per gram of the button battery is reduced slightly. Optionally, when the total amount of the first coating layer is 4-5.6 wt %, the overall performance of the corresponding battery is the best.

    [0535] It can be seen from a combination of examples 1-3 and 1-7 to 1-10 that as the amount of the second coating layer increases from 1% to 6%, the dissolution of Fe and Mn after cycling of the obtained material is gradually decreased, and the corresponding battery has an improved safety performance and cycling performance at 45? C. as well, but the capacity per gram of the button battery is reduced slightly. Optionally, when the total amount of the second coating layer is 3-5 wt %, the overall performance of the corresponding battery is the best.

    [0536] From the combination of examples 1-11 to 1-15 and comparative examples 1-5 and 1-6, it can be seen that when the first coating layer comprises both Li.sub.2FeP.sub.2O.sub.7 and Al.sub.2O.sub.3, and in particular the weigh ratio of Li.sub.2FeP.sub.2O.sub.7 to Al.sub.2O.sub.3 is 1:3 to 3:1, especially 1:3 to 1:1, the performance of the battery is improved more obviously.

    TABLE-US-00026 TABLE 2-1 Performance test results of examples 1-1 and 2-1 to 2-4 Average Expansion Crystal- Li/Mn Dissolution Capacity discharge of cell Cycling linity Crystal- Lattice antisite of Fe and of button voltage of upon 30 days capacity of pyro- linity change defect Mn after Surface battery button of storage retention Example phosphate of oxide rate concen- cycling oxygen at 0.1 C battery at 60? C. rate No. First coating layer (%) (%) (%) tration/% (ppm) valency (mAh/g) (V) (%) at 45? C. Example 1% 3% 100 100 2.4 0.4 6 ?1.96 157.4 3.76 1.5 1247 1-1 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 1% 3% 30 100 6.3 1.9 113 ?1.86 142.1 3.68 4.3 597 2-1 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 1% 3% 50 100 4.7 1.2 59 ?1.87 146.3 3.71 4.1 798 2-2 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 1% 3% 70 100 3.5 0.8 18 ?1.89 150.7 3.72 3.1 968 2-3 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 1% 3% 10 100 6.7 2.0 141 ?1.83 140.9 3.65 4.8 496 2-4 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3

    [0537] It can be seen from Table 2-1 that as the crystallinity of the pyrophosphate in the first coating layer gradually increases, the lattice change rate, Li/Mn antisite defect concentration, and dissolution of Fe and Mn of the corresponding material are gradually decreased, the capacity of the button battery is gradually increased, and the safety performance and cycling performance of the battery are also gradually improved.

    TABLE-US-00027 TABLE 3-1 Performance test results of examples 3-1 to 3-12 Dissolution Temperature Lattice Li/Mn of Fe and in reaction change antisite Mn after kettle Stirring rate defect cycling Example Type and amount of doping element (? C.) time/min (%) concentration/% (ppm) Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 60 120 5.8 2.5 53 3-1 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 70 120 4.9 2.2 41 3-2 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 80 120 3.9 1.6 33 3-3 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 90 120 3.2 1.4 20 3-4 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 100 120 2.7 0.9 13 3-5 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 110 120 2.9 1.6 24 3-6 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 120 120 3.9 2.5 43 3-7 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 130 120 4.8 3.7 49 3-8 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 100 60 5.2 3.4 41 3-9 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 100 90 4.4 2.9 30 3-10 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 100 150 3.7 1.6 18 3-11 Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 100 180 2.9 0.9 15 3-12 Average Expansion of Number of Capacity discharge cell upon 30 cycles for of button voltage days of capacity Surface battery of button storage retention Compacted oxygen at 0.1 C battery at 60? C. rate of 80% density Example valency (mAh/g) (V) (%) at 45? C. (g/cm.sup.3) Example ?1.98 148.9 3.65 6.1 1023 2.42 3-1 Example ?1.98 155.3 3.66 5.2 1124 2.41 3-2 Example ?1.98 155.9 3.69 4.2 1211 2.43 3-3 Example ?1.98 157.4 3.69 3.6 1254 2.42 3-4 Example ?1.98 158.1 3.75 2.9 1267 2.4 3-5 Example ?1.98 155.8 3.71 4.1 1167 2.42 3-6 Example ?1.98 154.1 3.66 5.2 1089 2.43 3-7 Example ?1.98 153.2 3.6 6.7 902 2.41 3-8 Example ?1.98 154.8 3.72 5.3 943 2.42 3-9 Example ?1.98 156.3 3.71 4.5 958 2.43 3-10 Example ?1.98 157.2 3.74 3.6 1067 2.44 3-11 Example ?1.98 157.5 3.73 3.1 1189 2.42 3-12 The parameters of the temperature and stirring time in the reaction kettle were as those during the preparation of element A doped manganese oxalate (i.e., step (1)).

    [0538] It can be seen from Table 3-1 that the performances of the positive electrode material of the present application can be further improved by adjusting the reaction temperature and reaction time in the reaction kettle during the preparation of manganese oxalate particles. For example, when the reaction temperature is gradually increased from 60? C. to 130? C., the lattice change rate and Li/Mn antisite defect concentration first decrease and then increase, and the corresponding dissolution of metal after cycling and the safety performance also vary in a similar trend, while the capacity and cycling performance of the button battery are first increased and then reduced with the increase of temperature. Similar varying trends also can be achieved by keeping the reaction temperature constant and adjusting the reaction time.

    TABLE-US-00028 TABLE 4-1 Performance test results of examples 4-1 to 4-7 and comparative examples 1-8 to 1-11 Included angle of crystal Interplanar orientation spacing of (111) of pyrophosphate pyrophosphate Drying Drying Sintering Sintering in first in first Example Li.sub.2FeP.sub.2O.sub.7:oxide temperature time temperature time coating layer coating layer No. (weight ratio) (? C.) (h) (? C.) (h) (nm) (?) Example 1:3 100 4 700 6 0.303 29.496 4-1 Example 1:3 150 6 700 6 0.303 29.496 4-2 Example 1:3 200 6 700 6 0.303 29.496 4-3 Example 1:3 200 6 600 6 0.303 29.496 4-4 Example 1:1 150 6 600 4 0.303 29.496 4-5 Example 1:1 150 6 600 6 0.303 29.496 4-6 Example 1:1 150 6 800 8 0.303 29.496 4-7 Comparative 1:3 80 3 400 3 example 1-8 Comparative 1:1 80 3 400 3 example 1-9 Comparative Only 80 3 350 2 example Li.sub.2FeP.sub.2O.sub.7 1-10 Comparative Only 80 3 example Al.sub.2O.sub.3 1-11 Average Expansion of Number of Capacity discharge cell upon 30 cycles for Lattice Li/Mn of button voltage days of capacity change antisite Surface battery of button storage retention Example rate defect oxygen at 0.1 C battery at 60? C. rate of 80% No. (%) concentration/% valency (mAh/g) (V) (%) at 45? C. Example 3.2 0.7 ?1.96 154.9 3.68 3.6 1056 4-1 Example 2.8 0.8 ?1.96 157.1 3.76 2.8 1287 4-2 Example 3 0.8 ?1.97 155.8 3.71 3.5 1189 4-3 Example 3.2 1.4 ?1.96 152.9 3.66 4.5 895 4-4 Example 3.1 1.5 ?1.92 154.7 3.68 4.1 816 4-5 Example 2.9 1.1 ?1.93 155.6 3.69 3.6 824 4-6 Example 2.7 0.7 ?1.94 156.3 3.71 3.1 924 4-7 Comparative 3.9 1.8 ?1.91 148 3.67 9.4 779 example 1-8 Comparative 3.6 1.6 ?1.93 149.4 3.7 6.8 683 example 1-9 Comparative 3.7 1.7 ?1.86 147.5 3.68 11.5 385 example 1-10 Comparative 3.4 1.4 ?1.93 150.3 3.72 4.7 526 example 1-11

    [0539] It can be seen from Table 4-1 that the performance of the obtained material can be improved by adjusting the drying temperature/time and the sintering temperature/time during the preparation of lithium iron pyrophosphate by the method of the present application, thereby improving the performance of the battery; and the performance of the obtained material can be improved by adjusting the drying temperature/time and the sintering temperature/time during the coating process, thereby improving the performance of the battery. From comparative examples 1-8 to 1-11, it can be seen that when the drying temperature in the preparation process of lithium iron pyrophosphate is lower than 100? C. or the temperature in the sintering step is lower than 400? C., Li.sub.2FeP.sub.2O.sub.7, which is expected to be prepared in the present application, will not be obtained, thereby failing to improve the properties of the material as well as the performance of the secondary battery comprising same.

    [0540] The preparation and performance tests of examples of the positive electrode active material having an inner core of Li.sub.1+XMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4 and a shell comprising a first coating layer containing a crystalline pyrophosphate, a second coating layer containing a metal oxide O.sub.f Q.sub.eO.sub.f, and a third coating layer containing carbon will be detailed below. Unless otherwise stated, the sources of the involved reagents are the same as examples 1-1 to 1-52.

    Example 1-B

    Step S1: Preparation of Fe, Co, V and S Co-Doped Manganese Oxalate

    [0541] 689.6 g of manganese carbonate, 455.27 g of ferrous carbonate, 4.65 g of cobalt sulfate and 4.87 g of vanadium dichloride were mixed thoroughly for 6 h in a mixer. The resulting mixture was then transferred into a reaction kettle, 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added, heated to 80? C., then stirred thoroughly for 6 h at a rotation speed of 500 rpm and mixed uniformly until the reaction was completed (no bubble was generated), so as to obtain a Fe, Co, and V co-doped manganese oxalate suspension. Then, the suspension was filtered, dried at 120? C. and then sanded, so as to obtain manganese oxalate particles with a particle size of 100 nm.

    Step S2: Preparation of Inner Core of Li.sub.0.997Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.997S.sub.0.003O.sub.4

    [0542] 1793.1 g of manganese oxalate prepared in (1), 368.3 g of lithium carbonate, 1146.6 g of ammonium dihydrogen phosphate and 4.9 g of dilute sulfuric acid were added into 20 L of deionized water, fully stirred, and mixed uniformly and reacted at 80? C. for 10 h to obtain a slurry. The slurry was transferred into a spray drying apparatus for spray-drying granulation, and dried at a temperature of at 250? C. to obtain a powder. In a protective atmosphere (90% of nitrogen and 10% of hydrogen), the powder was sintered in a roller kiln at 700? C. for 4 h to obtain an inner core material. The element content of the inner core material was detected using inductively coupled plasma (ICP) emission spectrometry, and the chemical formula of the obtained inner core was as shown above.

    Step S3: Preparation of First Coating Layer Suspension

    [0543] Preparation of Li.sub.2FeP.sub.2O.sub.7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, with pH being controlled to be 5, the mixture was then stirred and reacted at room temperature for 2 h to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 h to obtain a first coating layer suspension.

    Step S4: Coating of First Coating Layer

    [0544] 1571.9 g of the doped lithium manganese phosphate inner core material obtained in step S2 was added into the first coating layer suspension (with the content of the coating material being 15.7 g) obtained in step S3, fully stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred in an oven at 120? C. and dried for 6 h, and then sintered at 650? C. for 6 h to obtain a pyrophosphate coated material.

    Step S5: Preparation of Second Coating Layer Suspension

    [0545] 47.1 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a second coating layer suspension.

    Step S6: Coating of Second Coating Layer

    [0546] 1586.8 g of the pyrophosphate coated material obtained in step S4 was added into the second coating layer suspension (with the content of the coating material being 47.1 g) obtained in step S5, fully stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred in an oven at 120? C. and dried for 6 h, and then sintered at 700? C. for 8 h to obtain a two-layer coated material.

    Step S7: Preparation of Aqueous Solution of Third Coating Layer

    [0547] 37.3 g of sucrose was dissolved in 500 g of deionized water, then stirred and fully dissolved to obtain an aqueous solution of sucrose.

    Step S8: Coating of Third Coating Layer

    [0548] 1633.9 g of the two-layer coated material obtained in step S6 was added into the sucrose solution obtained in step S7, stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 150? C. and dried for 6 h, and then sintered at 700? C. for 10 h to obtain a three-layer coated material.

    Examples 2-B to 62-B and Comparative Examples 1-B to 11-B

    [0549] The positive electrode active materials of examples 2-B to 62-B and comparative examples 1-B to 11-B were prepared by a method similar to example 1-B, and the differences in the preparation of the positive electrode active materials were shown in Tables 1-B to 6-B.

    [0550] Here, since there was no first coating layer in comparative examples 1-B to 2-B and 4-B to 10-B and example 58-B, steps S3-S4 were omitted; and there was no second coating layer in comparative examples 1-B to 10-B and example 57-B, and therefore steps S5-S6 were not involved.

    TABLE-US-00029 TABLE 1-B Preparation of Fe, Co, V and S co-doped manganese oxalate and preparation of inner core (steps S1-S2) Chemical Raw materials Raw materials formula of used in used in No. inner core* step S1 step S2 Comparative LiMnPO.sub.4 Manganese carbonate, Manganese oxalate dihydrate examples 1-B 1149.3 g; water, 5 L; and obtained in step S1 (in and 11-B oxalic acid dihydrate, C.sub.2O.sub.4Mn2H.sub.2O), 1789.6 g; lithium 1260.6 g; carbonate, 369.4 g; ammonium dihydrogen phosphate, 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.60Fe.sub.0.40PO.sub.4 Manganese carbonate, Iron manganese oxalate dihydrate example 2-B 689.6 g; ferrous carbonate, obtained in step S1 (in 463.4 g; water, 5 L; and C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.402H.sub.2O), 1793.2 g; oxalic acid dihydrate, lithium carbonate, 369.4 g; 1260.6 g; ammonium dihydrogen phosphate, 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.80Fe.sub.0.20PO.sub.4 Manganese carbonate, Iron manganese oxalate dihydrate example 3-B 919.4 g; ferrous carbonate, obtained in step S1 (in 231.7 g; water, 5 L; and C.sub.2O.sub.4Mn.sub.0.80Fe.sub.0.202H.sub.2O), 1791.4 g; oxalic acid dihydrate, lithium carbonate, 369.4 g; 1260.6 g; ammonium dihydrogen phosphate, 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.70Fe.sub.0.295V.sub.0.005PO.sub.4 Manganese carbonate, Vanadium iron manganese oxalate example 4-B 804.5 g; ferrous carbonate, dihydrate obtained in step S1 (in 341.8 g; vanadium C.sub.2O.sub.4Mn.sub.0.70Fe.sub.0.295V.sub.0.0052H.sub.2O), dichloride, 6.1 g; water, 5 1792.0 g; lithium carbonate, 369.4 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.60Fe.sub.0.395Mg.sub.0.005PO.sub.4 Manganese carbonate, Magnesium iron manganese oxalate example 5-B 689.6 g; ferrous carbonate, dihydrate obtained in step S1 (in and example 457.6 g; magnesium C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.395Mg.sub.0.0052H.sub.2O), 60-B carbonate, 4.2 g; water, 5 1791.6 g; lithium carbonate, 369.4 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.60Fe.sub.0.35Ni.sub.0.05PO.sub.4 Manganese carbonate, Nickel manganese oxalate dihydrate example 6-B 689.6 g; ferrous carbonate, obtained in step S1 (in 405.4 g; nickel carbonate, C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.35Ni.sub.0.052H.sub.2O), 1794.6 59.3 g; water, 5 L; and g; lithium carbonate, 369.4 g; oxalic acid dihydrate, ammonium dihydrogen phosphate, 1260.6 g; 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.60Fe.sub.0.395V.sub.0.002Ni.sub.0.003PO.sub.4 Manganese carbonate, Nickel vanadium iron manganese example 7-B 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 and 457.6 g; vanadium (in comparative dichloride, 2.4 g; nickel C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.395V.sub.0.002Ni.sub.0.0032H.sub.2O), example 9-B carbonate, 3.6 g; water, 5 1793.2 g; lithium carbonate, 369.4 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1150.1 g; and water, 20 L; Comparative LiMn.sub.0.60Fe.sub.0.395V.sub.0.002Mg.sub.0.003PO.sub.4 Manganese carbonate, Magnesium vanadium iron example 8-B 689.6 g; ferrous carbonate, manganese oxalate dihydrate 457.6 g; vanadium obtained in step S1 (in dichloride, 2.4 g; C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.395V.sub.0.002Mg.sub.0.0032H.sub.2O), magnesium carbonate, 2.53 1792.1 g; lithium carbonate, 369.4 g; water, 5 L; and oxalic g; ammonium dihydrogen phosphate, acid dihydrate, 1260.6 g; 1150.1 g; and water, 20 L; Comparative Li.sub.0.997Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.997S.sub.0.003O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese example 10-B, 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 examples 57- 455.27 g; cobalt sulfate, (in B and 58-B, 4.65 g; vanadium C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), examples 61- dichloride, 4.87 g; water, 5 1793.1 g; lithium carbonate, 368.3 B and 62-B, L; and oxalic acid g; ammonium dihydrogen phosphate, examples 1-B dihydrate, 1260.6 g; 1146.6 g; dilute sulfuric acid, 4.9 g; to 10-B and and water, 20 L; examples 30- B to 42-B, and examples 45- B to 46-B and 50-B to 56-B Example 59-B Li.sub.1.2MnP.sub.0.8Si.sub.0.2O.sub.4 Manganese carbonate, Manganese oxalate dihydrate 1149.3 g; water, 5 L; and obtained in step S1 (in oxalic acid dihydrate, C.sub.2O.sub.4Mn2H.sub.2O), 1789.6 g; lithium 1260.6 g; carbonate, 443.3 g; ammonium dihydrogen phosphate, 920.1 g; metasilicic acid, 156.2 g; and water, 20 L; Example 11-B Li.sub.1.001Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1793.1 g; lithium carbonate, 369.8 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 12-B LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.998N.sub.0.002O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1793.1 g; lithium carbonate, 369.4 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1147.8 g; dilute nitric acid, 2.7 g; and water, 20 L; Example 13-B Li.sub.0.995Mn.sub.0.65Fe.sub.0.341V.sub.0.004Co.sub.0.005P.sub.0.995S.sub.0.005O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 747.1 g; ferrous carbonate, oxalate dihydrate obtained in step S1 395.1 g; cobalt sulfate, 7.8 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.65Fe.sub.0.341V.sub.0.004Co.sub.0.0052H.sub.2O), g; water, 5 L; and oxalic 1792.7 g; lithium carbonate, 367.6 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1144.3 g; dilute sulfuric acid, 8.2 g; and water, 20 L; Example 14-B Li.sub.1.002Mn.sub.0.70Fe.sub.0.293V.sub.0.004Co.sub.0.003P.sub.0.998Si.sub.0.002O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 804.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 339.5 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.70Fe.sub.0.293V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1792.2 g; lithium carbonate, 370.2 acid dihydrate, 1260.6 g; g; 1147.8; metasilicic acid, 1.6 g; and water, 20 L; Examples 15- LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999N.sub.0.001O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese B and 17-B 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1793.1 g; lithium carbonate, 369.4 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1148.9 g; dilute nitric acid, 1.4 g; and water, 20 L; Example 16-B Li.sub.0.997Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.997S.sub.0.003O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1793.1 g; lithium carbonate, 368.7 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1146.6 g; dilute sulfuric acid, 4.9 g; and water, 20 L; Example 18-B LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.995N.sub.0.005O.sub.4 Manganese carbonate, Magnesium vanadium iron 689.6 g; ferrous carbonate, manganese oxalate dihydrate 455.3 g; magnesium obtained in step S1 (in carbonate, 2.5 g; vanadium C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.0032H.sub.2O), dichloride, 4.9 g; water, 5 1791.1 g; lithium carbonate, 369.4 L; and oxalic acid g; ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1144.3 g; dilute nitric acid, 7.0 g; and water, 20 L; Example 19-B Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 Manganese carbonate, Magnesium vanadium iron 689.6 g; ferrous carbonate, manganese oxalate dihydrate 455.3 g; magnesium obtained in step S1 (in carbonate, 2.5 g; vanadium C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Mg.sub.0.0032H.sub.2O), dichloride, 4.9 g; water, 5 1791.1 g; lithium carbonate, 369.0 L; and oxalic acid g; ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1148.9 g; dilute sulfuric acid, 1.6 g; and water, 20 L; Example 20-B Li.sub.0.998Mn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.003P.sub.0.998S.sub.0.002O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; nickel carbonate, (in 3.6 g; vanadium dichloride, C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.0032H.sub.2O), 4.9 g; water, 5 L; and 1792.2 g; lithium carbonate, 368.7 g; oxalic acid dihydrate, ammonium dihydrogen phosphate, 1260.6 g; 1147.8 g; dilute sulfuric acid, 3.2 g; and water, 20 L; Examples 21- Li.sub.1.001Mn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Nickel vanadium iron manganese B to 24-B 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; nickel carbonate, (in 3.6 g; vanadium dichloride, C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.0032H.sub.2O), 4.9 g; water, 5 L; and 1793.1 g; lithium carbonate, 369.8 g; oxalic acid dihydrate, ammonium dihydrogen phosphate, 1260.6 g; 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 25-B Li.sub.1.001Mn.sub.0.50Fe.sub.0.493V.sub.0.004Ni.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 574.7 g; ferrous carbonate, oxalate dihydrate obtained in step S1 571.2 g; nickel carbonate, (in 3.6 g; vanadium dichloride, C.sub.2O.sub.4Mn.sub.0.50Fe.sub.0.493V.sub.0.004Ni.sub.0.0032H.sub.2O), 4.9 g; water, 5 L; and 1794.0 g; lithium carbonate, 369.8 g; oxalic acid dihydrate, ammonium dihydrogen phosphate, 1260.6 g; 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 26-B Li.sub.1.001Mn.sub.0.999Fe.sub.0.001P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Iron manganese oxalate dihydrate 1148.2 g; ferrous obtained in step S1 (in carbonate, 1.2 g; water, 5 C.sub.2O.sub.4Mn.sub.0.999Fe.sub.0.0012H.sub.2O), 1789.6 g; L; and oxalic acid lithium carbonate, 369.8 g; dihydrate, 1260.6 g; ammonium dihydrogen phosphate, 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 27-B LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.003P.sub.0.9N.sub.0.100O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; nickel carbonate, (in 3.6 g; vanadium dichloride, C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Ni.sub.0.0032H.sub.2O), 4.9 g; water, 5 L; and 1793.1 g; lithium carbonate, 369.4 g; oxalic acid dihydrate, ammonium dihydrogen phosphate, 1260.6 g; 1035.1 g; dilute nitric acid, 140.0 g; and water, 20 L; Example 28-B Li.sub.1.001Mn.sub.0.40Fe.sub.0.593V.sub.0.004Ni.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 459.7 g; ferrous carbonate, oxalate dihydrate obtained in step S1 686.9 g; vanadium (in dichloride, 4.8 g; nickel C.sub.2O.sub.4Mn.sub.0.40Fe.sub.0.593V.sub.0.004Ni.sub.0.0032H.sub.2O), carbonate, 3.6 g; water, 5 1794.9 g; lithium carbonate, 369.8 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 29-B Li.sub.1.001Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 459.7 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.2 g; vanadium (in dichloride, 248.6 g; nickel C.sub.2O.sub.4Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.0032H.sub.2O), carbonate, 3.6 g; water, 5 1785.1 g; lithium carbonate, 369.8 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 43-B Li.sub.0.900Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.003P.sub.0.900S.sub.0.100O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 459.7 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.2 g; vanadium (in dichloride, 248.6 g; nickel C.sub.2O.sub.4Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.0032H.sub.2O), carbonate, 3.6 g; water, 5 1785.1 g; lithium carbonate, 332.5 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1035.0 g; dilute sulfuric acid, 160 g; and water, 20 L; Example 44-B Li.sub.1.100Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.003P.sub.0.900Si.sub.0.100O.sub.4 Manganese carbonate, Nickel vanadium iron manganese 459.7 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.2 g; vanadium (in dichloride, 248.6 g; nickel C.sub.2O.sub.4Mn.sub.0.40Fe.sub.0.393V.sub.0.204Ni.sub.0.0032H.sub.2O), carbonate, 3.6 g; water, 5 1785.1 g; lithium carbonate, 406.4 g; L; and oxalic acid ammonium dihydrogen phosphate, dihydrate, 1260.6 g; 1035.0 g; metasilicic acid, 80 g; and water, 20 L; Example 47-B Li.sub.1.001Mn.sub.0.909Fe.sub.0.091P.sub.0.999Si.sub.0.001O.sub.4 Manganese carbonate, Iorn manganese oxalate dihydrate 1044.8 g; ferrous obtained in step S1 (in carbonate, 109.2 g; water, C.sub.2O.sub.4Mn.sub.0.909Fe.sub.0.0912H.sub.2O), 1790.7 g; 5 L; and oxalic acid lithium carbonate, 369.8 g; dihydrate, 1260.6 g; ammonium dihydrogen phosphate, 1148.9 g; metasilicic acid, 0.8 g; and water, 20 L; Example 48-B LiMn.sub.0.80Fe.sub.0.193V.sub.0.004Co.sub.0.003P.sub.0.999N.sub.0.001O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 919.5 g; ferrous carbonate, oxalate dihydrate obtained in step S1 223.6 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.80Fe.sub.0.193V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1791.6 g; lithium carbonate, 369.4 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1148.9 g; dilute nitric acid, 1.4 g; and water, 20 L; Example 49-B LiMn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.996N.sub.0.004O.sub.4 Manganese carbonate, Cobalt vanadium iron manganese 689.6 g; ferrous carbonate, oxalate dihydrate obtained in step S1 455.3 g; cobalt sulfate, 4.7 (in g; vanadium dichloride, 4.9 C.sub.2O.sub.4Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.0032H.sub.2O), g; water, 5 L; and oxalic 1793.1 g; lithium carbonate, 369.4 acid dihydrate, 1260.6 g; g; ammonium dihydrogen phosphate, 1145.4 g; dilute nitric acid, 5.6 g; and water, 20 L;

    TABLE-US-00030 TABLE 2-B Preparation of first coating layer suspension (step S3) Coating material of first No. coating layer* Preparation of first coating layer suspension Comparative Amorphous 7.4 g of lithium carbonate; 11.6 g of ferrous carbonate; 23.0 example 3-B and Li.sub.2FeP.sub.2O.sub.7 g of ammonium dihydrogen phosphate; and 12.6 g of oxalic example 61-B acid dihydrate; controlling the pH to be 5; Example 57-B, Crystalline 7.4 g of lithium carbonate; 11.6 g of ferrous carbonate; 23.0 examples 60-B Li.sub.2FeP.sub.2O.sub.7 g of ammonium dihydrogen phosphate; and 12.6 g of oxalic and 62-B, and acid dihydrate; controlling the pH to be 5; examples 1-B to 14-B, 19-B, 21- B to 29-B, 37-B to 44-B, and 47- B to 56-B Examples 15-B Crystalline 53.3 g of aluminum chloride; 34.5 g of ammonium and 16-B Al.sub.4(P.sub.2O.sub.7).sub.3 dihydrogen phosphate; and 18.9 g of oxalic acid dihydrate; controlling the pH to be 4; Examples 17-18 Crystalline 7.4 g of lithium carbonate; 11.9 g of nickel carbonate; 23.0 g and 20 Li.sub.2NiP.sub.2O.sub.7 of ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; controlling the pH to be 5; Example 30-B Crystalline 7.4 g of lithium carbonate; 8.4 g of magnesium carbonate; Li.sub.2MgP.sub.2O.sub.7 23.0 g of ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 31-B Crystalline 7.4 g of lithium carbonate; 15.5 g of cobalt sulfate; 23.0 g of Li.sub.2CoP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 32-B Crystalline 7.4 g of lithium carbonate; 16.0 g of copper sulfate; 23.0 g of Li.sub.2CuP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 33-B Crystalline 7.4 g of lithium carbonate; 12.5 g of zinc carbonate; 23.0 g Li.sub.2ZnP.sub.2O.sub.7 of ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 34-B Crystalline 24.0 g of titanium sulfate; 23.0 g of ammonium dihydrogen TiP.sub.2O.sub.7 phosphate; and 12.6 g of oxalic acid dihydrate; Example 35-B Crystalline 67.9 g of silver nitrate; 23.0 g of ammonium dihydrogen Ag.sub.4P.sub.2O.sub.7 phosphate; and 25.2 g of oxalic acid dihydrate; Example 36-B Crystalline 56.6 g of Zirconium sulfate; 23.0 g of ammonium ZrP.sub.2O.sub.7 dihydrogen phosphate; and 25.2 g of oxalic acid dihydrate; Example 45-B Crystalline 3.7 g of lithium carbonate; 13.3 g of aluminum chloride; 23.0 LiAlP.sub.2O.sub.7 g of ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 46-B Crystalline 25.0 g of zinc carbonate; 25.0 g of zinc carbonate; 23.0 g of Zn.sub.2P.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate;

    TABLE-US-00031 TABLE 3-B Coating of first coating layer (step S4) Coating Step S4: Coating of first coating layer material of Amount of first coating corresponding layer and coating amount thereof* Amount of material in (based on inner core first coating Mixing Drying Sintering Sintering weight of added in layer time temperature temperature time No. inner core) step S4 suspension (h) (? C.) (? C.) (h) Comparative 2% of 1570.4 g 31.4 g 6 120 500 4 example 3-B amorphous Li.sub.2FeP.sub.2O.sub.7 Example 57-B 1% of 1571.1 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Comparative 2% of 1568.5 g 31.4 g 6 120 650 6 example 11-B crystalline Li.sub.2FeP.sub.2O.sub.7 Example 59-B 2% of 1562.8 g 31.2 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 60-B 2% of 1570.6 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 61-B 2% of 1571.1 g 31.4 g 6 120 500 4 amorphous Li.sub.2FeP.sub.2O.sub.7 Example 62-B 2% of 1571.1 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Examples 1-B 1% of 1571.9 g 15.7 g 6 120 650 6 to 4-B, 8-B to crystalline 10-B, 37-B to Li.sub.2FeP.sub.2O.sub.7 42-B, 47-B to 49-B, and 52- B to 56-B Example 5-B 2% of 1571.9 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 6-B 3% of 1571.1 g 47.1 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 7-B 5% of 1571.9 g 78.6 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 11-B 1% of 1572.1 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 12-B 1% of 1571.7 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 13-B 2% of 1571.4 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 14-B 2.5% of 1571.9 g 39.3 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 15-B 2% of 1571.9 g 31.4 g 6 120 680 8 crystalline Al.sub.4(P.sub.2O.sub.7).sub.3 Example 16-B 3% of 1571.9 g 47.2 g 6 120 680 8 crystalline Al.sub.4(P.sub.2O.sub.7).sub.3 Example 17-B 1.5% of 1571.9 g 23.6 g 6 120 630 6 crystalline Li.sub.2NiP.sub.2O.sub.7 Example 18-B 1% of 1570.1 g 15.7 g 6 120 630 6 crystalline Li.sub.2NiP.sub.2O.sub.7 Example 19-B 2% of 1571.0 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 20-B 1% of 1571.9 g 15.7 g 6 120 630 6 crystalline Li.sub.2NiP.sub.2O.sub.7 Examples 2% of 1572.1 g 31.4 g 6 120 650 6 21-B to 24-B crystalline Li.sub.2FeP.sub.2O.sub.7 Example 25-B 1% of 1573.0 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 26-B 1% of 1568.6 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 27-B 1% of 1569.2 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 28-B 2% of 1573.9 g 31.4 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 29-B 2% of 1564.1 g 31.2 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 30-B 1% of 1571.9 g 15.7 g 7 120 660 6 crystalline Li.sub.2MgP.sub.2O.sub.7 Example 31-B 1% of 1571.9 g 15.7 g 6 120 670 6 crystalline Li.sub.2CoP.sub.2O.sub.7 Example 32-B 1% crystalline 1571.9 g 15.7 g 8 120 640 6 Li.sub.2CuP.sub.2O.sub.7 Example 33-B 1% of 1571.9 g 15.7 g 8 120 650 6 crystalline Li.sub.2ZnP.sub.2O.sub.7 Example 34-B 1% of 1571.9 g 15.7 g 7 120 660 6 crystalline TiP.sub.2O.sub.7 Example 35-B 1% of 1571.9 g 15.7 g 9 120 670 6 crystalline Ag.sub.4P.sub.2O.sub.7 Example 36-B 1% crystalline 1571.9 g 15.7 g 8 120 680 6 ZrP.sub.2O.sub.7 Example 43-B 1% of 1558.2 g 15.6 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 44-B 1% of 1568.1 g 15.7 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 45-B 1% of 1571.9 g 15.7 g 7 120 675 6 crystalline LiAlP.sub.2O.sub.7 Example 46-B 1% of 1571.9 g 15.7 g 7 120 670 6 crystalline Zn.sub.2P.sub.2O.sub.7 Example 50-B 6% of 1571.9 g 94.3 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7 Example 51-B 5.5% of 1571.9 g 86.5 g 6 120 650 6 crystalline Li.sub.2FeP.sub.2O.sub.7

    TABLE-US-00032 TABLE 4-B Preparation of second coating layer suspension (step S5) Second coating layer Step S5: Preparation of second coating layer No. material* suspension Example 58-B, and Crystalline Al.sub.2O.sub.3 47.1 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 examples 1-B to 7-B, 18-B, nm) was dissolved in 1500 mL of deionized water, 25-B to 27-B, 30-B to 36- and stirred for 2 h to obtain a suspension; B, 45-B to 51-B, and 53-B to 56-B Comparative example 2-B Crystalline Al.sub.2O.sub.3 62.7 of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 59-B Crystalline Al.sub.2O.sub.3 62.5 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Examples 60-B and 61-B Crystalline Al.sub.2O.sub.3 62.8 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 8-B Crystalline Al.sub.2O.sub.3 15.7 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 9-B Crystalline Al.sub.2O.sub.3 62.8 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 10-B Crystalline Al.sub.2O.sub.3 78.6 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 11-B Crystalline Al.sub.2O.sub.3 39.3 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 12-B Crystalline Al.sub.2O.sub.3 47.2 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 13-B Crystalline Al.sub.2O.sub.3 31.4 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 14-B Crystalline Al.sub.2O.sub.3 55.0 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 19-B Crystalline Al.sub.2O.sub.3 62.8 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Examples 15-B and 17-B Crystalline ZrO.sub.2 39.3 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 20-B Crystalline ZrO.sub.2 47.2 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Examples 21-B and 24-B Crystalline ZrO.sub.2 62.9 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 22-B Crystalline ZrO.sub.2 70.8 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 23-B Crystalline ZrO.sub.2 86.5 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Examples 28-B and 29-B Crystalline ZrO.sub.2 63.0 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 62-B Amorphous 7.4 g of lithium carbonate, 15.5 g of cobalt sulfate, LiCoPO.sub.4 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were added into 1500 mL of deionized water, stirred and fully reacted for 6 h to obtain a solution, and then the solution was dried at 120? C. for 12 h to obtain a suspension; Example 16-B Crystalline MgO 47.2 g of nano-MgO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 37-B Crystalline CuO 47.1 g of nano-CuO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 38-B Crystalline SiO.sub.2 47.1 g of nano-SiO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 39-B Crystalline WO.sub.3 47.1 g of nano-WO.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 40-B Crystalline TiO.sub.2 47.1 g of nano-TiO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 41-B Crystalline V.sub.2O.sub.5 47.1 g of nano-V.sub.2O.sub.5 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 42-B Crystalline NiO 47.1 g of nano-NiO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 43-B Crystalline Al.sub.2O.sub.3 47.1 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 44-B Crystalline Al.sub.2O.sub.3 47.0 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 52-B Crystalline Al.sub.2O.sub.3 94.2 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension;

    TABLE-US-00033 TABLE 5-B Coating of second coating layer (step S6) Second Amount of pyrophosphate- Step S6: Coating of second coating layer coating layer coated material added Amount of material and in step S6 (amount of corresponding amount thereof inner core added coating material (based on for comparative in second coating Mixing Drying Sintering Sintering weight of example 12) layer suspension time temperature temperature time No. inner core)* (g) (g) (h) (? C.) (? C.) (h) Example 3% of 1571.1 47.1 6 120 700 8 58-B crystalline Al.sub.2O.sub.3 Comparative 4% of 1599.9 62.7 6 120 750 8 example crystalline 11-B Al.sub.2O.sub.3 Example 4% of 1594.0 62.5 6 120 750 8 59-B crystalline Al.sub.2O.sub.3 Example 4% of 1602.0 62.8 6 120 750 8 60-B crystalline Al.sub.2O.sub.3 Example 4% of 1602.5 62.8 6 120 750 8 61-B crystalline Al.sub.2O.sub.3 Example 4% of 1602.5 62.8 6 120 650 8 62-B amorphous LiCoPO.sub.4 Examples 3% of 1586.8 47.1 6 120 700 8 1-B to crystalline 4-B, 45- Al.sub.2O.sub.3 B to 51- B, and 53-B to 56-B Example 3% of 1602.5 47.1 6 120 700 8 5-B crystalline Al.sub.2O.sub.3 Example 3% of 1618.2 47.1 6 120 700 8 6-B crystalline Al.sub.2O.sub.3 Example 3% of 1649.6 47.1 6 120 700 8 7-B crystalline Al.sub.2O.sub.3 Example 1% of 1586.8 15.7 6 120 700 8 8-B crystalline Al.sub.2O.sub.3 Example 4% of 1586.8 62.8 6 120 700 8 9-B crystalline Al.sub.2O.sub.3 Example 5% of 1586.8 78.6 6 120 700 8 10-B crystalline Al.sub.2O.sub.3 Example 2.50% of 1587.8 39.3 6 120 700 8 11-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.4 47.2 6 120 700 8 12-B crystalline Al.sub.2O.sub.3 Example 2% of 1602.8 31.4 6 120 700 8 13-B crystalline Al.sub.2O.sub.3 Example 3.50% of 1610.5 55.0 6 120 700 8 14-B crystalline Al.sub.2O.sub.3 Example 2.5% of 1603.3 39.3 6 120 750 8 15-B crystalline ZrO.sub.2 Example 3% of 1619.0 47.2 6 120 680 8 16-B crystalline MgO Example 2.5% of 1595.5 39.3 6 120 750 8 17-B crystalline ZrO.sub.2 Example 3% of 1585.9 47.1 6 120 700 8 18-B crystalline Al.sub.2O.sub.3 Example 4% of 1602.4 62.8 6 120 700 8 19-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.7 47.2 6 120 750 8 20-B crystalline ZrO.sub.2 Example 4% of 1603.5 62.9 6 120 750 8 21-B crystalline ZrO.sub.2 Example 4.5% of 1658.6 70.8 6 120 750 8 22-B crystalline ZrO.sub.2 Example 5.50% of 1603.5 86.5 6 120 750 8 23-B crystalline ZrO.sub.2 Example 4% of 1603.5 62.9 6 120 750 8 24-B crystalline ZrO.sub.2 Example 3% of 1588.7 47.1 6 120 700 8 25-B crystalline Al.sub.2O.sub.3 Example 3% of 1584.3 47.1 6 120 700 8 26-B crystalline Al.sub.2O.sub.3 Example 3% of 1584.9 47.1 6 120 700 8 27-B crystalline Al.sub.2O.sub.3 Example 4% of 1605.4 63.0 6 120 750 8 28-B crystalline ZrO.sub.2 Example 4% of 1605.4 63.0 6 120 750 8 29-B crystalline ZrO.sub.2 Example 3% of 1587.6 47.1 6 120 700 8 30-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 31-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 32-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 33-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 34-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 35-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 700 8 36-B crystalline Al.sub.2O.sub.3 Example 3% of 1587.6 47.1 6 120 710 8 37-B crystalline CuO Example 3% of 1587.6 47.1 6 120 750 8 38-B crystalline SiO.sub.2 Example 3% of 1587.6 47.1 6 120 720 8 39-B crystalline WO.sub.3 Example 3% of 1587.6 47.1 6 120 730 8 40-B crystalline TiO.sub.2 Example 3% of 1587.6 47.1 6 120 730 8 41-B crystalline V.sub.2O.sub.5 Example 3% of 1587.6 47.1 6 120 710 8 42-B crystalline NiO Example 3% of 1573.8 47.1 6 120 700 8 43-B crystalline Al.sub.2O.sub.3 Example 3% of 1583.8 47.1 6 120 700 8 44-B crystalline Al.sub.2O.sub.3 Example 6% of 1586.8 94.2 6 120 700 8 52-B crystalline Al.sub.2O.sub.3

    TABLE-US-00034 TABLE 6-B Coating of third coating layer (step S8) Amount of two-layer coated material added in step S8 (amount of inner core added for comparative examples 1-2 and 4-10, amount of first-layer coated material Step S8: Coating of third coating layer Molar added for comparative examples 3 and 11, Amount Third ratio of and amount of only second-layer coated of Mixing Drying Sintering Sintering coating SP2 to material added for comparative example 12) sucrose time temperature temperature time No. layer* SP3* (g) (g) (h) (? C.) (? C.) (h) Comparative 1% of 2.5 1568.5 37.3 6 150 650 8 example carbon 1-B Comparative 2% of 2.8 1572.2 74.7 6 150 680 8 example carbon 2-B Comparative 2% of 2.7 1601.8 74.6 6 150 680 7 example carbon 3-B Comparative 1% of 2.4 1571.0 37.3 6 150 630 8 example carbon 4-B Comparative 1.5% of 2.6 1570.6 56.0 6 150 650 7 example carbon 5-B Comparative 2.5% of 2.8 1573.6 93.4 6 150 680 8 example carbon 6-B Comparative 1% of 2.7 1572.2 37.3 6 150 680 7 example carbon 7-B Comparative 1.5% of 2.9 1571.1 56.0 6 150 680 10 example carbon 8-B Comparative 1% of 2.2 1572.2 37.3 6 150 600 8 example carbon 9-B Comparative 1% of 2.4 1571.1 37.3 6 150 630 8 example carbon 10-B Example 1% of 2.3 1586.8 37.3 6 150 620 8 57-B carbon Example 1% of 2.1 1618.2 37.3 6 150 600 6 58-B carbon Comparative 1% of 2 1662.6 37.3 6 120 600 6 example carbon 11-B Example 1% of 1.8 1656.5 37.1 6 120 600 6 59-B carbon Example 1% of 1.7 1664.8 37.3 6 100 600 6 60-B carbon Example 1% of 3.1 1665.4 37.3 6 150 700 10 61-B carbon Example 1% of 3.5 1665.4 37.3 6 150 750 10 62-B carbon Examples 1% of 2.2 1633.9 37.3 6 150 700 10 1-B, carbon 30-B to 42-B, and 45-B to 52-B Example 3% of 2.3 1633.9 111.9 6 150 600 9 2-B carbon Example 4% of 2.1 1633.9 149.2 6 150 600 6 3-B carbon Example 5% of 2.4 1633.9 186.5 6 150 630 8 4-B carbon Example 1% of 2.5 1649.6 37.3 6 150 650 8 5-B carbon Example 1% of 2.5 1665.3 37.3 6 150 650 8 6-B carbon Example 1% of 2.4 1696.7 37.3 6 150 630 8 7-B carbon Example 1% of 2.3 1602.5 37.3 6 150 600 9 8-B carbon Example 1% of 2.2 1649.6 37.3 6 150 600 8 9-B carbon Example 1% of 2.2 1665.3 37.3 6 150 600 9 10-B carbon Example 1.5% of 2.3 1629.0 56.1 6 150 600 9 11-B carbon Example 2% of 2.4 1634.6 74.7 6 150 630 8 12-B carbon Example 2% of 2.5 1634.2 74.6 6 150 650 8 13-B carbon Example 2.5% of 2.7 1665.5 93.3 6 150 680 7 14-B carbon Example 2% of 2.8 1642.6 74.7 6 150 680 8 15-B carbon Example 1% of 2.7 1666.2 37.3 6 150 680 7 16-B carbon Example 1.5% of 2.3 1634.8 56.0 6 150 600 9 17-B carbon Example 1% of 2.6 1633.0 37.3 6 150 650 7 18-B carbon Example 1.5% of 2.4 1665.2 56.0 6 150 630 8 19-B carbon Example 1.5% of 2.2 1634.8 56.0 6 150 600 9 20-B carbon Example 1% of 2.2 1666.4 37.3 6 150 600 9 21-B carbon Example 1% of 2.3 1721.4 37.3 6 150 600 9 22-B carbon Example 1% of 2.4 1690.0 37.3 6 150 630 8 23-B carbon Example 5.5% of 2.6 1666.4 205.4 6 150 650 7 24-B carbon Example 1% of 2.4 1635.9 37.4 6 150 630 8 25-B carbon Example 1% of 2.3 1631.3 37.3 6 150 600 9 26-B carbon Example 1.5% of 2.1 1631.9 55.9 6 150 600 6 27-B carbon Example 1% of 0.07 1668.3 37.4 6 80 600 6 28-B carbon Example 1% of 13 1668.3 37.4 6 150 850 10 29-B carbon Example 1% of 2.2 1620.5 37.3 6 150 700 10 43-B carbon Example 1% of 2.2 1630.8 37.3 6 150 700 10 44-B carbon Example 1% of 0.1 1633.9 37.3 6 85 600 6 53-B carbon Example 1% of 10 1633.9 37.3 6 150 800 9 54-B carbon Example 1% of 3 1633.9 37.3 6 150 680 8 55-B carbon Example 6% of 2.5 1633.9 223.8 6 150 640 8 56-B carbon

    Preparation of Positive Electrode Plate

    [0551] The parameters were the same as example 1.

    Preparation of Negative Electrode Plate. Separator and Electrolyte Solution

    [0552] The parameters were the same as example 1-1.

    Preparation of Full Battery

    [0553] The positive electrode plate, separator, and negative electrode plate obtained above were stacked in sequence, such that the separator was located between the positive electrode and the negative electrode and played a role of isolation, and the stack was wound to obtain a bare cell. The bare cell was placed in an outer package, the above electrolyte solution was injected, and the bare cell was packaged to obtain a full battery.

    Preparation of Button Battery

    [0554] The positive electrode plate above, a negative electrode and an electrolyte solution were assembled together into a button battery in a button battery box.

    [0555] The performance test results of the positive electrode active materials of the examples and comparative examples were shown in the Table below.

    TABLE-US-00035 TABLE 7-B Properties of positive electrode active material powder and performance of battery Properties of positive electrode active material powder Performance of battery 3 C Expansion Number of Li/Mn charge Dissolution Capacity of cell cycles for Lattice antisite constant of Mn and of button upon 30 d capacity change defect Compacted Surface current Fe after battery of storage retention rate concentration density oxygen rate cycling at 0.1 C at 60? C. rate of 80% No. (%) (%) (g/cm.sup.3) valency (%) (ppm) (mAh/g) (%) at 45? C. Comparative 11.4 5.2 1.5 ?1.55 50.1 2060 125.6 48.6 185 example 1-B Comparative 10.6 3.3 1.67 ?1.51 54.9 1810 126.4 47.3 243 example 2-B Comparative 10.8 3.4 1.64 ?1.64 52.1 1728 144.7 41.9 378 example 3-B Comparative 4.3 2.8 1.69 ?1.82 56.3 1096 151.2 8.4 551 example 4-B Comparative 2.8 2.5 1.65 ?1.85 58.2 31 148.4 7.5 668 example 5-B Comparative 3.4 2.4 1.61 ?1.86 58.4 64 149.6 8.6 673 example 6-B Comparative 4.5 2.4 1.73 ?1.83 59.2 85 148.6 8.3 669 example 7-B Comparative 2.3 2.4 1.68 ?1.89 59.3 30 152.3 7.3 653 example 8-B Comparative 2.3 2.4 1.75 ?1.89 59.8 30 152.3 7.3 672 example 9-B Comparative 2.3 2.2 1.81 ?1.9 64.1 28 154.2 7.2 685 example 10-B Example 2.3 2.2 1.92 ?1.92 65.4 12 154.3 5.4 985 57-B Example 2.3 2.1 1.94 ?1.94 63.5 28 153.6 5.2 695 58-B Comparative 11.4 5.2 1.58 ?1.93 51.4 64 128.2 6.4 492 example 11-B Example 8.5 4.3 1.74 ?1.94 57.3 36 133.6 5.6 574 59-B Example 2 1.8 2.09 ?1.95 61.1 11 153.7 4.2 1054 60-B Example 2 1.9 1.95 ?1.96 60.2 22 151.7 5.2 983 61-B Example 2 1.9 1.9 ?1.89 60.4 24 152.4 5.1 897 62-B Example 2.5 1.8 2.33 ?1.92 69.3 10 156.2 5.2 1079 1-B Example 2.5 1.8 2.27 ?1.93 69.2 8 155.3 4.7 1157 2-B Example 2.5 1.8 2.24 ?1.93 69.1 6 154.4 4.5 1234 3-B Example 2.5 1.8 2.21 ?1.94 69.2 4 152.7 3.1 1362 4-B Example 2.5 1.8 2.33 ?1.95 69.7 5 156.2 3.4 1467 5-B Example 2.5 1.8 2.3 ?1.95 69.4 4 155.7 3.1 1523 6-B Example 2.5 1.8 2.25 ?1.95 69 3 155.2 2.8 1589 7-B Example 2.5 1.8 2.65 ?1.93 68.4 15 155.8 4.1 943 8-B Example 2.5 1.8 2.35 ?1.95 68.5 10 155.2 3.7 1027 9-B Example 2.5 1.8 2.42 ?1.98 68.6 5 154.4 3.1 1275 10-B Example 2.5 1.9 2.36 ?1.96 71.4 8 156.8 3.5 1026 11-B Example 2.3 1.8 2.39 ?1.96 73.5 6 155.7 2.5 1136 12-B Example 2.6 1.9 2.4 ?1.96 74.5 7 155.1 3.5 1207 13-B Example 2.6 1.9 2.42 ?1.96 75.1 5 153.8 4.2 1308 14-B Example 2.2 1.9 2.46 ?1.96 73.7 3 153.4 3.9 1109 15-B Example 2.1 1.9 2.47 ?1.98 73.1 5 153.1 4 1132 16-B Example 2.5 1.7 2.41 ?1.98 75.3 4 154.7 4.1 1258 17-B Example 2.3 1.6 2.42 ?1.97 76.1 4 154.3 4.7 1378 18-B Example 2.2 1.7 2.43 ?1.97 76.8 4 154.3 4.7 1328 19-B Example 2.6 1.8 2.41 ?1.93 74.8 4 152.8 3.5 1379 20-B Example 2.4 1.7 2.39 ?1.96 75.7 4 153.7 3.7 1287 21-B Example 2.4 1.8 2.36 ?1.94 74.3 2 151.4 2.9 1454 22-B Example 2.3 1.7 2.43 ?1.95 75.6 3 150.7 2.7 1438 23-B Example 2.2 1.8 2.42 ?1.97 75.2 3 151.3 2.8 1467 24-B Example 2.1 1.7 2.47 ?1.96 77.4 4 156.7 3.2 1379 25-B Example 3.6 2.5 2.19 ?1.95 55.7 10 151.2 5 953 26-B Example 2.8 2.1 2.21 ?1.96 73.1 8 153.8 4.1 1027 27-B Example 2.5 1.9 1.95 ?1.93 53.4 11 152.7 7.1 869 28-B Example 2.4 1.8 1.98 ?1.94 66.8 8 153.9 5.3 957 29-B Example 2.4 1.9 2.35 ?1.96 67.7 18 155.7 5.3 957 30-B Example 2.5 1.7 2.35 ?1.95 68.9 16 154.3 4.9 1016 31-B Example 2.5 1.7 2.37 ?1.96 68.5 16 155.1 4.9 968 32-B Example 2.6 1.8 2.38 ?1.97 68.7 26 155.4 5.6 927 33-B Example 2.6 1.9 2.32 ?1.94 70.8 19 155.8 4.9 934 34-B Example 2.4 1.7 2.34 ?1.92 70.4 14 156.8 5.5 945 35-B Example 2.5 1.9 2.31 ?1.91 71.1 16 155.1 5.8 967 36-B Example 2.5 1.7 2.31 ?1.9 67.5 21 155.2 5.6 926 37-B Example 2.4 1.9 2.3 ?1.94 68.9 30 153.4 6.4 897 38-B Example 2.2 1.8 2.33 ?1.92 68.7 27 155.7 6.1 957 39-B Example 2.4 1.9 2.34 ?1.89 70.8 35 154.7 5.6 935 40-B Example 2.6 1.9 2.36 ?1.92 69.7 31 153.9 5.5 912 41-B Example 2.4 1.9 2.34 ?1.9 70.9 18 155.8 4.7 1087 42-B Example 2.3 1.9 2.35 ?1.91 70.2 15 153.6 4.9 997 43-B Example 2.4 1.8 2.34 ?1.94 71.3 16 156.1 5.2 983 44-B Example 2.5 1.8 2.35 ?1.93 68.4 12 155.3 4.8 1025 45-B Example 2.6 1.8 2.36 ?1.93 67.9 11 155.5 5.4 1047 46-B Example 2.5 1.8 2.38 ?1.91 68.4 19 154.2 4.8 948 47-B Example 2.4 1.9 2.41 ?1.93 69.3 22 151.3 5.1 953 48-B Example 2.3 1.7 2.34 ?1.92 65.2 20 153.8 4.9 998 49-B Example 2.5 1.8 2.36 ?1.94 68.7 16 154.1 5.2 1002 50-B Example 2.3 1.9 2.39 ?1.92 68.2 25 154.9 5.3 1001 51-B Example 2.5 1.8 2.32 ?1.95 68.1 18 155 5.8 948 52-B Example 2.4 1.9 2.36 ?1.98 69.2 17 155.1 5.4 956 53-B Example 2.5 1.7 2.37 ?1.97 69.4 19 155.2 5.6 992 54-B Example 2.4 1.8 2.35 ?1.94 64.1 18 154.8 4.9 938 55-B Example 2.5 1.9 2.2 ?1.92 65 25 151.2 5.3 957 56-B

    TABLE-US-00036 TABLE 8-B Interplanar spacing and included angle of crystal orientation (111) of crystalline pyrophosphate in first coating layer Interplanar spacing of crystalline Included angle of crystal orientation (111) of pyrophosphate (nm) crystalline pyrophosphate Example 1-B 0.303 29.496? Example 30-B-B 0.451 19.668? Example 31 0.297 30.846? Example 32-B 0.457 19.456? Example 33-B 0.437 20.257? Example 34-B 0.462 19.211? Example 35-B-B 0.450 19.735? Example 36 0.372 23.893?

    [0556] It can be seen from Tables 7-B and 8-B that compared with comparative examples, the examples of the present application achieve a smaller lattice change rate, a smaller Li/Mn antisite defect concentration, a larger compacted density, a surface oxygen valency more closer to ?2 valence, less Mn and Fe dissolution after cycling, and better battery performance, such as a higher capacity of a button battery, better high-temperature storage performance, higher safety performance and better cycling performance of button batteries.

    TABLE-US-00037 TABLE 9-B Thickness of each layer of positive electrode active material and weight ratio of manganese element to phosphorus element Weight Con- Con- ratio Thick- Thick- Thick- tent tent of Mn ness of ness of ness of of Mn of P ele- first second third ele- ele- ment First Second Third coating coating coating ment ment to P coating coating coating layer layer layer (wt (wt ele- No. Inner core layer layer layer (nm) (nm) (nm) %) %) ment Compar- LiMn.sub.0.80Fe.sub.0.20PO.sub.4 2% of 2% of 4 10 26.1 18.9 1.383 ative amorphous carbon example Li.sub.2FeP.sub.2O.sub.7 3-B Compar- LiMn.sub.0.70Fe.sub.0.295V.sub.0.005PO.sub.4 1% of 5 24.3 19.6 1.241 ative carbon example 4-B Example Li.sub.0.999Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999S.sub.0.001O.sub.4 3% of 1% of 9 5 19.6 19.0 1.034 58-B crystalline carbon Al.sub.2O.sub.3 Example Li.sub.0.997Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.997S.sub.0.003O.sub.4 1% of 3% of 1% of 2 9 5 19 18.0 1.053 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 3% of 2 9 15 18.3 17.4 1.053 2-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 4% of 2 9 20 18 17.1 1.053 3-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 5% of 2 9 25 17.9 17.0 1.052 4-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 2% of 3% of 1% of 4 9 5 18.7 18.5 1.011 5-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 3% of 3% of 1% of 6 9 5 18.3 18.3 0.999 6 example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 5% of 3% of 1% of 10 9 5 17.6 18.1 0.975 7-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 1% of 1% of 2 3 5 19.8 19.0 1.043 8-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 4% of 1% of 2 12 5 18.7 18.4 1.014 9-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 5% of 1% of 2 15 5 18.4 17.5 1.053 10-B example 1-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.1.001Mn.sub.0.60Fe.sub.0.393V.sub.0.004Co.sub.0.003P.sub.0.999Si.sub.0.001O.sub.4 1% of 2.50% of 1.5% of 2 7.5 7.5 19 18.5 1.026 11-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.995Mn.sub.0.65Fe.sub.0.341V.sub.0.004Co.sub.0.005P.sub.0.995S.sub.0.005O.sub.4 2% of 2% of 2% of 4 6 10 18.7 16.9 1.108 13-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.1.002Mn.sub.0.70Fe.sub.0.293V.sub.0.004Co.sub.0.003P.sub.0.998Si.sub.0.002O.sub.4 2.5% of 3.50% of 2.5% of 5 10.5 12.5 17.8 15.3 1.166 14-B crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3

    [0557] It can be seen from Table 9-B that the content of manganese element and the weight content ratio of manganese element to phosphorus element in the positive electrode active material are obviously reduced by means of doping at the manganese and phosphorus sites of lithium manganese iron phosphate (containing 35% of manganese and about 20% of phosphorus) and three-layer coating, and in addition, by comparing examples 1-B to 14-B with comparative example 3-B, comparative example 4-B and example 58-B, in combination with Table 7-B, it can be seen that the decrease of the elements manganese and phosphorus in the positive electrode active material will result in less dissolution of manganese and iron and an improvement in the performance of the secondary battery prepared therefrom.

    II. Investigation of Influence of Coating Layer Sintering Method on Properties of Positive Electrode Active Material

    [0558] The batteries of the examples and comparative examples in the Table below were manufactured similarly to example 1-B, except that the method parameters in the Table below were used. The results were shown in Table 10-B below.

    TABLE-US-00038 TABLE 10-B Influence of steps S4, S6 and S8 on properties of positive electrode active material Expansion Number of 3 C charge Dissolution Capacity of cell cycles for Sintering Sintering Sintering Sintering Sintering Sintering Lattice Li/Mn constant of Mn and of button when stored capacity temperature time temperature time temperature time change antisite current Fe after Surface battery at 60? C. retention in S4 in S4 in S6 in S6 in S8 in S8 rate defect Compacted rate cycling oxygen at 0.1 C for 30 d rate of 80% No. (? C.) (h) (? C.) (h) (? C.) (h) (%) concentration density (%) (ppm) valency (mAh/g) (%) at 45? C. Example 650 6 600 8 700 10 2.5 1.8 2.33 69.5 8 ?1.91 156.7 4.8 1087 1-B Example 750 4 500 6 700 6 3 2.4 2.22 63.8 13 ?1.94 153.6 6.8 815 II-1 Example 800 4 500 6 700 6 3.1 2.4 2.19 66.8 14 ?1.94 152.8 7.3 826 II-2 Example 700 2 500 6 700 6 2.9 2.3 2.18 61.7 16 ?1.95 150.7 6.5 764 II-3 Example 700 3 500 6 700 6 2.7 2.1 2.21 63.8 16 ?1.95 151.7 6.1 835 II-4 Example 700 4 400 6 700 6 2.5 1.8 2.29 61.9 31 ?1.94 152.6 5.2 716 II-5 Example 700 4 600 6 700 6 2.5 1.8 2.32 62.8 15 ?1.95 153.8 5.6 795 II-6 Example 700 4 500 8 700 6 2.5 1.8 2.29 66.8 13 ?1.94 155.9 5.2 896 II-7 Example 700 4 500 10 700 6 2.5 1.8 2.32 68.1 12 ?1.95 155.4 5.1 984 II-8 Example 700 4 500 6 750 6 2.5 1.8 2.33 69.8 10 ?1.92 156.4 4.8 1067 II-9 Example 700 4 500 6 800 6 2.5 1.8 2.33 69.6 10 ?1.92 155.7 5.2 1037 II-10 Example 700 4 500 6 700 8 2.5 1.8 2.33 67.8 11 ?1.9 154.9 5.3 897 II-11 Example 700 4 500 6 700 10 2.5 1.8 2.33 66.2 13 ?1.94 153.8 5.3 816 II-12 Example 600 3 500 8 750 8 4.8 5.3 2.26 53.6 97 ?1.89 138.6 11.2 563 II-13 Example 850 3 500 8 750 8 5.3 4.7 2.36 56.7 90 ?1.9 144.7 9.8 627 II-14 Example 750 1.5 500 8 750 8 4.7 4.5 2.23 52.6 91 ?1.9 140.6 9.3 618 II-15 Example 750 4.5 500 8 750 8 4.1 4 2.29 57.5 83 ?1.91 139.5 8.7 628 II-16 Example 750 3 350 8 750 8 4.8 4.6 2.26 51.6 81 ?1.89 140.5 9.3 534 II-17 Example 750 3 650 8 750 8 3.9 4.8 2.33 48.7 82 ?1.94 141.5 9.4 529 II-18 Example 750 3 500 5.5 750 8 4.4 4.2 2.22 44.8 84 ?1.92 143.2 9.5 547 II-19 Example 750 3 500 10.5 750 8 4.1 3.9 2.32 48.6 81 ?1.91 140.7 8.5 617 II-20 Example 750 3 500 8 650 8 5.2 4.1 2.29 47.9 85 ?1.92 140.7 10.9 507 II-21 Example 750 3 500 8 850 8 5 4 2.22 48.6 82 ?1.94 140.6 9.3 614 II-22 Example 750 3 500 8 750 5.5 4.3 4.2 2.25 47.3 86 ?1.9 141.7 10.2 476 II-23 Example 750 3 500 8 750 10.5 50 4.9 2.33 49.4 83 ?1.93 140.8 10.3 594 II-24

    [0559] It can be seen from the above that when the sintering temperature in step S4 is in a range of 650-800? C. and the sintering time is 2-6 h, the sintering temperature in step S6 is 400-600? C. and the sintering time is 6-10 h, and the sintering temperature in step S8 is 700-800? C. and the sintering time is 6-10 h, smaller lattice change rate, lower Li/Mn antisite defect concentration, less dissolution of manganese and iron elements, better 3 C charge constant current rate, larger battery capacity, better battery cycling performance, and better high-temperature storage stability can be achieved.

    [0560] In addition, compared with example 11-16 (with the sintering temperature in step S4 being 750? C. and the sintering time being 4.5 h), example II-1 (with the sintering temperature in step S4 being 750? C. and the sintering time being 4 h) achieves better properties of the positive electrode active material and battery performance, which indicates that when the sintering temperature of step S4 is 750? C. or higher than 750? C., it is needed to control the sintering time to be less than 4.5 h.

    III. Investigation of Influence of Reaction Temperature and Reaction Time During Preparation of Inner Core on Properties of Positive Electrode Active Material

    [0561] The positive electrode active materials and batteries of examples in the Table below were prepared similarly to example 1-B, and reference could be made to the method parameters shown in the Table below for the differences in the preparation of the positive electrode active materials. The results were also shown in the Table below.

    TABLE-US-00039 TABLE 11-B Influence of reaction temperature and reaction time during preparation of inner core on properties of positive electrode active material Number of Step S1 Step S2 Li/Mn 3 C Dissolu- Expansion cycles for Reac- Reac- antisite charge tion of Capacity of cell capacity tion Reac- tion Reac- Lattice defect Com- constant Mn and of button upon 30 d retention temper- tion temper- tion change concen- pacted current Fe after Surface battery of storage rate of ature time ature time rate tration density rate cycling oxygen at 0.1 C at 60? C. 80% at No. (? C.) (h) (? C.) (h) (%) (%) (g/cm.sup.3) (%) (ppm) valency (mAh/g) (%) 45? C. Example 80 6 80 10 2.5 1.8 2.35 70.3 7 ?1.93 157.2 4.2 1128 1-B Example 70 6 80 10 2.8 3.4 2.3 60.1 34 ?1.93 155.4 5.8 876 III-1 Example 60 6 80 10 3.1 3.1 2.33 64.2 18 ?1.92 156.2 5.1 997 III-2 Example 100 6 80 10 2.3 2.4 2.37 71.3 7 ?1.94 156.8 4.1 1137 III-4 Example 120 6 80 10 2.1 2.2 2.38 72.1 5 ?1.92 155.4 4 1158 III-5 Example 80 2 80 10 2.8 3.2 2.27 68.4 24 ?1.9 154.9 5.1 895 III-6 Example 80 3 80 10 2.6 2.7 2.29 69.7 17 ?1.92 156.1 4.7 967 III-7 Example 80 5 80 10 2.4 1.9 2.34 70.6 8 ?1.94 156.8 4.3 1137 III-8 Example 80 7 80 10 2.5 1.8 2.35 68.3 11 ?1.94 156.4 4.8 987 III-9 Example 80 9 80 10 2.6 1.8 2.36 67.2 15 ?1.93 155.9 5.2 921 III-10 Example 80 6 40 10 3.2 3.4 2.28 67.8 35 ?1.94 156.8 5.4 894 III-11 Example 80 6 60 10 2.8 2.9 2.31 68.7 18 ?1.95 157 4.9 927 III-12 Example 80 6 80 10 2.5 2.7 2.35 70.3 7 ?1.93 157.2 4.2 1128 III-13 Example 80 6 100 10 2.7 2.8 2.33 69.4 15 ?1.93 156.7 4.6 957 III-14 Example 80 6 120 10 2.8 3.1 2.32 68.1 24 ?1.94 156.2 4.8 914 III-15 Example 80 6 90 1 3.7 3.8 2.26 67.9 38 ?1.93 155.8 5.2 885 III-16 Example 80 6 90 3 3.4 3.4 2.31 68.2 32 ?1.94 156.1 4.8 915 III-17 Example 80 6 90 5 3.1 3.1 2.33 69.1 27 ?1.92 156.4 4.6 934 III-18 Example 80 6 90 7 2.8 2.9 2.34 69.4 15 ?1.93 156.8 4.5 971 III-19 Example 80 6 90 9 2.5 2.7 2.35 70.3 7 ?1.93 157.2 4.2 1128 III-20

    [0562] It can be seen from Table 11-B that when the reaction temperature is in a range of 60-120? C. and the reaction time is 2-9 hours in step S11, and the reaction temperature is in a range of 40-120? C. and the reaction time is 1-10 hours in step S2, the properties of the positive electrode active material powder (lattice change rate, Li/Mn antisite defect concentration, surface oxygen valency, and compacted density) and the performance of the prepared battery (electric capacity, high-temperature cycling performance, and high-temperature storage performance) are all excellent.

    [0563] The preparation and performance tests of the positive electrode active materials having an inner core of Li.sup.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n and a shell comprising a first coating layer containing a crystalline pyrophosphate and a metal oxide of Q.sub.eO.sub.f and a second coating layer containing carbon will be detailed below:

    Example 1C-1

    Step S1: Preparation of Doped Manganese Oxalate

    [0564] The parameters for preparing the doped manganese oxalate were the same as those in example 1.

    Step S2: Preparation of Inner Core Comprising Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001

    [0565] 1 mol of Fe-doped manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO.sub.4).sub.3, an 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid, 0.001 mol of H.sub.4SiO.sub.4, 0.0005 mol of NH.sub.4HF.sub.2 and 0.005 mol of sucrose were added into 20 L of deionized water, and the mixture was transferred into a sander and thoroughly ground and stirred for 10 hours to obtain a slurry; the slurry was transferred into a spray drying apparatus for spray-drying granulation, where the drying temperature was set at 250? C. and the drying time was 4 h, so as to obtain particles; the particles were sintered at 700? C. for 10 hours in a protective atmosphere of nitrogen (90% v/v)+hydrogen (10% v/v) to obtain an inner core material. The element content of the inner core material was detected using inductively coupled plasma (ICP) emission spectrometry, and the chemical formula of the obtained inner core was as shown above.

    Step S3: Preparation of Lithium Iron Pyrophosphate Powder

    [0566] 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate, and 1.3 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 650? C. in a nitrogen atmosphere for 8 hours, naturally cooled to room temperature, and then ground to obtain a Li.sub.2FeP.sub.2O.sub.7 powder.

    Step S4: Preparation of Suspension Comprising Aluminum Oxide and Sucrose

    [0567] 4.71 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) and 3.73 g of sucrose (in C.sub.12H.sub.22O.sub.11, the same below) were added into 150 ml of deionized water, and stirred for 6 hours until the mixture was fully mixed. The mixture was then heated to 120? C. and held at the temperature for 6 hours to obtain a suspension comprising aluminum oxide and sucrose.

    Step S5: Preparation of Two-Layer Coatings

    [0568] 157.21 g of the above inner core and 1.57 g of the above lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder were added into the suspension comprising aluminum oxide and sucrose prepared in the previous step, stirred and mixed uniformly, then transferred into a vacuum oven and dried at 150? C. for 6 h, then the resulting product was dispersed by sanding; and after dispersion, the product was sintered at 700? C. for 6 hours in a nitrogen atmosphere to obtain two-layer coated lithium manganese phosphate.

    Examples 1C-2 to 1C-59 and Comparative Examples 1C to 12C

    [0569] The positive electrode active materials of examples 1C-2 to 1C-59 and comparative examples 1C to 12C were prepared by a method similar to that of example 1C-1, and the differences in the preparation of the positive electrode active materials were shown in Tables C to 4C.

    [0570] In examples 1C to 9C, there was no steps S3-S5; step S4 was not involved in comparative example 10C and step S3 was not involved in comparative example 1C.

    TABLE-US-00040 TABLE 1C Preparation of doped manganese oxalate and preparation of inner core (steps S1-S2) Chemical formula of inner Raw materials used in No. core* Step S1 Comparative LiMnPO.sub.4 MnSO.sub.4H.sub.2O, 1.0 mol; example 1C water, 10 L; and oxalic acid dihydrate, 1 mol; Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 MnSO.sub.4H.sub.2O, 0.85 example 2C mol; FeSO.sub.4H.sub.2O, 0.15 mol; water, 10 L; and oxalic acid dihydrate, 1 mol; Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 MnSO.sub.4H.sub.2O, 1.9 mol; example 3C ZnSO.sub.4, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.2 mol; example 4C FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.4 mol; example 5C FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 0.8 mol; example 6C ZnSO.sub.4, 1.2 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.4 mol; example 7C FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 MnSO.sub.4H.sub.2O, 1.2 mol; example 8C FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; examples 9C to FeSO.sub.4H.sub.2O, 0.7 mol; 12C, example water, 10 L; and 1C-1, examples oxalic acid dihydrate, 1C-12 to 1C-16, 2 mol; examples 1C-33 to 1C-44, 1C-49, 1C-51 to 1C-52 and 1C-59 Example 1C-2 Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and Ti(SO.sub.4).sub.2, 0.02 mol; Example 1C-3 Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-4 Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-5 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.69 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 1C-6 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and MgSO.sub.4, 0.01 mol; Example 1C-7 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and CoSO.sub.4, 0.01 mol; Example 1C-8 Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and NiSO.sub.4, 0.01 mol; Example 1C-9 Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.698 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and Ti(SO.sub.4).sub.2, 0.002 mol; Example 1C-10 Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and MgSO.sub.4, 0.01 mol; Example 1C-11 Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.69 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 1C-17 Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.36 mol; FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.04 mol; Example 1C-18 Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.16 mol; FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.04 mol; Example 1C-19 Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 1C-20 Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 1C-21 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 1C-22 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 1C-23 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.1 mol; Example 1C-24 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.4 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-25 Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.5 mol; FeSO.sub.4H.sub.2O, 0.1 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.3 mol; Example 1C-26 Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and NiSO.sub.4, 0.1 mol; Example 1C-27 Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.5 mol; FeSO.sub.4H.sub.2O, 0.2 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and NiSO.sub.4, 0.2 mol; Example 1C-28 Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-29 Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-30 Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.0 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-31 Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-32 Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 1C-45 Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 1C-46 Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 1C-47 Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 1C-48 Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.998 mol; FeSO.sub.4H.sub.2O, 0.002 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-50 Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.98 mol; FeSO.sub.4H.sub.2O, 0.02 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-53 Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.6 mol; FeSO.sub.4H.sub.2O, 0.4 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-54 Li.sub.0.5Mg.sub.0.5Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.5F.sub.0.5 MnSO.sub.4H.sub.2O, 1 mol; FeSO.sub.4H.sub.2O, 1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-55 Li.sub.1.2Mg.sub.0.001Mn.sub.0.5Fe.sub.0.5P.sub.0.8Si.sub.0.2O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1 mol; FeSO.sub.4H.sub.2O, 1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-56 Li.sub.0.95Mg.sub.0.005Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1 mol; FeSO.sub.4H.sub.2O, 1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-57 Li.sub.0.95Mg.sub.0.05Mn.sub.0.7Fe.sub.0.3P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 1C-58 Li.sub.0.95Mg.sub.0.05Mn.sub.0.6Fe.sub.0.4P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; No. Raw materials used in Step S2 Comparative Manganese oxalate particles obtained in step S1, 1 example 1C mol; lithium carbonate, 0.5 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles obtained in step example 2C S1, 1 mol; lithium carbonate, 0.5 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles obtained in step example 3C S1, 1 mol; lithium carbonate, 0.495 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles obtained in example 4C step S1, 1 mol; lithium carbonate, 0.45 mol; Nb.sub.2(SO.sub.4).sub.5, 0.005 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles obtained in example 5C step S1, 1 mol; lithium carbonate, 0.38 mol; MgSO.sub.4, 0.12 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles obtained in step example 6C S1, 1 mol; lithium carbonate, 0.499 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles obtained in example 7C step S1, 1 mol; lithium carbonate, 0.534 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.88 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.12 mol; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles obtained in example 8C step S1, 1 mol; lithium carbonate, 0.474 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.93 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.07 mol; NH.sub.4HF.sub.2, 0.06 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles obtained in examples 9C to step S1, 1 mol; lithium carbonate, 0.497 mol; 12C, example Mo(SO.sub.4).sub.3, 0.001 mol; 85% aqueous phosphoric acid 1C-1, examples solution containing 0.999 mol of phosphoric acid; 1C-12 to 1C-16, H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, examples 1C-33 0.005 mol; and water, 20 L; to 1C-44, 1C-49, 1C-51 to 1C-52 and 1C-59 Example 1C-2 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4885 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-3 Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.496 mol; W(SO.sub.4).sub.3, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-4 Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; Al.sub.2(SO.sub.4).sub.3, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HCl.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-5 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-6 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-7 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-8 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-9 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4955 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HCl.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-10 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4975 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HBr.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-11 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.499 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HBr.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-17 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-18 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-19 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-20 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.494 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-21 containing 0.171 mol of phosphoric acid; H.sub.2SO.sub.4, Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.467 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution 0.005 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-22 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-23 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-24 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-25 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-26 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-27 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-28 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-29 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.497 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-30 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-31 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4825 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.04 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-32 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.485 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.92 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.08 mol; NH.sub.4HF.sub.2, 0.05 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-45 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.45 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.05 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-46 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.55 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-47 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.45 mol; MgSO.sub.4, 0.1 mol; 85% aqueous phosphoric acid solution containing 0.95 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.05 mol; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-48 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-50 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-53 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-54 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.25 mol; MgSO.sub.4, 0.5 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.5 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-55 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.6 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.8 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.2 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-56 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.05 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-57 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 1C-58 Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L;

    TABLE-US-00041 TABLE 2C Preparation of pyrophosphate powder only (step S3) Pyrophosphate No. powder Step S3 Examples Crystalline 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium 1C-1 to 1C- Li.sub.2FeP.sub.2O.sub.7 dihydrogen phosphate, and 1.3 g of oxalic acid dihydrate were dissolved in 50 ml 59 of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li2FeP2O7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 650? C. in a nitrogen atmosphere for 8 hours, naturally cooled to room temperature, and then ground to obtain a Li2FeP2O7 powder. Comparative Amorphous 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium examples Li.sub.2FeP.sub.2O.sub.7 dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml 10C and of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 12C hours such that the reaction mixture was fully reacted. Then, the reacted solution was heated to 80? C. and held at the temperature for 4 hours to obtain a suspension comprising Li.sub.2FeP.sub.2O.sub.7, and the suspension was filtered, washed with deionized water, and dried at 120? C. for 4 hours to obtain a powder. The powder was sintered at 500? C. in a nitrogen atmosphere for 4 hours, naturally cooled to room temperature, and then ground to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 5%.

    TABLE-US-00042 TABLE 3C Preparation of suspension containing oxide and sucrose (step S4) Second coating Raw materials used in Step No. First coating layer layer S4 Comparative example 3% 1% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, 3.73 11C Al.sub.2O.sub.3 g; and water, 150 ml; Comparative example Amorphous 3% 1% of carbon 12C Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Examples 1C-1 to 1C- Crystalline 3% 1% of carbon 11, examples 1C-17 to Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 1C-32, examples 1C-45 to 1C-48, and examples 1C-50 to 1C-51 Example 1C-12 Crystalline 3% ZnO 1% of carbon ZnO, 4.71 g and sucrose, Li.sub.2FeP.sub.2O.sub.7 3.73 g; and water, 150 ml; Example 1C-13 Crystalline 3% ZrO.sub.2 1% of carbon ZrO.sub.2, 4.71 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 g; and water, 150 ml; Example 1C-14 Crystalline 3% MgO 1% of carbon MgO, 4.71 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 g; and water, 150 ml; Example 1C-15 Crystalline 3% WO.sub.3 1% of carbon WO.sub.3, 4.71 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 g; and water, 150 ml; Example 1C-16 Crystalline 3% CuO 1% of carbon CuO, 4.71 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 g; and water, 150 ml; Example 1C-33 Crystalline 2.4% 1% of carbon Al.sub.2O.sub.3, 3.77 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-34 Crystalline 3.6% 1% of carbon Al.sub.2O.sub.3, 5.65 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-35 Crystalline 4.2% 1% of carbon Al.sub.2O.sub.3, 6.59 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-36 Crystalline 4.8% 1% of carbon Al.sub.2O.sub.3, 7.54 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-37 Crystalline 3% 2% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, 7.46 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-38 Crystalline 3% 4% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 14.92 g; and water, 150 ml; Example 1C-39 Crystalline 3% 5% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 18.65 g; and water, 150 ml; Example 1C-40 Crystalline 3% 6% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 22.38 g; and water, 150 ml; Example 1C-41 Crystalline 2.5% 2% of carbon Al.sub.2O.sub.3, 3.93 g; sucrose, 7.46 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-42 Crystalline 2% 2% of carbon Al.sub.2O.sub.3, 3.14 g; sucrose, 7.46 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-43 Crystalline 1.5% 2% of carbon Al.sub.2O.sub.3, 2.36 g; sucrose, 7.46 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-44 Crystalline 1% 2% of carbon Al.sub.2O.sub.3, 1.57 g; sucrose, 7.46 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml; Example 1C-49 Crystalline 3% V.sub.2O.sub.5 1% of carbon V.sub.2O.sub.5, 4.71 g; sucrose, 3.73 Li.sub.2FeP.sub.2O.sub.7 g; and water, 150 ml; Example 1C-52 Crystalline 3% 3% of carbon Al.sub.2O.sub.3, 4.71 g; sucrose, Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 11.19 g; and water, 150 ml; Examples 1C-53 to 1C- Crystalline 1% 1% of carbon Al.sub.2O.sub.3, 1.57 g; sucrose, 3.73 59 Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 g; and water, 150 ml;

    TABLE-US-00043 TABLE 4C Preparation of two-layer coatings (step S5) Amount of added Amount of Second Amount of lithium iron oxide in Drying Drying Sintering Sintering coating added inner pyrophosphate suspension temperature time temperature time No. Chemical formula of inner core First coating layer layer core powder in step S4 (? C.) (h) (? C.) (h) Comparative Same as example 1C-1 4% of 1% of 157.2 g 6.28 g 120 6 700 8 example amorphous carbon 10C Li.sub.2FeP.sub.2O.sub.7 Comparative Same as example 1C-1 3% 1% of 157.2 g 4.71 g 120 6 700 8 example Al.sub.2O.sub.3 carbon 11C Comparative Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 680 8 example amorphous Al.sub.2O.sub.3 carbon 12C Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-1 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-2 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.3 g 1.57 g 4.71 g 120 6 750 8 1C-3 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-4 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-5 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.0 g 1.57 g 4.71 g 120 6 750 8 1C-6 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-7 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-8 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-9 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-10 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-11 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 720 8 1C-12 crystalline ZnO carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 780 8 1C-13 crystalline ZrO.sub.2 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 700 8 1C-14 crystalline MgO carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 790 8 1C-15 crystalline WO.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 740 8 1C-16 crystalline CuO carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.0 g 1.57 g 4.71 g 120 6 750 8 1C-17 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-18 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 156.9 g 1.57 g 4.71 g 120 6 750 8 1C-19 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.0 g 1.57 g 4.71 g 120 6 750 8 1C-20 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 1% of 3% 1% of 157.0 g 1.57 g 4.71 g 120 6 750 8 1C-21 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.0 g 1.57 g 4.71 g 120 6 750 8 1C-22 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-23 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-24 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.3 g 1.57 g 4.71 g 120 6 750 8 1C-25 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-26 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-27 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.1 g 1.57 g 4.71 g 120 6 750 8 1C-28 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.3 g 1.57 g 4.71 g 120 6 750 8 1C-29 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1% of 3% 1% of 157.4 g 1.57 g 4.71 g 120 6 750 8 1C-30 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 1% of 3% 1% of 157.4 g 1.57 g 4.71 g 120 6 750 8 1C-31 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-32 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 0.8% of 2.4% 1% of 157.2 g 1.26 g 3.77 g 120 6 750 8 1C-33 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.2% of 3.6% 1% of 157.2 g 1.89 g 5.66 g 120 6 750 8 1C-34 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.4% of 4.2% 1% of 157.2 g 2.20 g 6.60 g 120 6 750 8 1C-35 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.6% of 4.8% 1% of 157.2 g 2.52 g 7.55 g 120 6 750 8 1C-36 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 2% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-37 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 4% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-38 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 5% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-39 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 6% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-40 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.5% of 2.5% 2% of 157.2 g 1.57 g 3.93 g 120 6 750 8 1C-41 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 2% of 2% 2% of 157.2 g 1.57 g 3.14 g 120 6 750 8 1C-42 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 2.5% of 1.5% 2% of 157.2 g 1.57 g 2.36 g 120 6 750 8 1C-43 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 3% of 1% 2% of 157.2 g 1.57 g 1.57 g 120 6 750 8 1C-44 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 1% of 3% 1% of 155.8 g 1.56 g 4.67 g 120 6 750 8 1C-45 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 1% of 3% 1% of 156.8 g 1.57 g 4.70 g 120 6 750 8 1C-46 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 1% of 3% 1% of 158.9 g 1.59 g 4.78 g 120 6 750 8 1C-47 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 1% of 3% 1% of 157.6 g 1.58 g 4.73 g 120 6 750 8 1C-48 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 1% of 157.2 g 1.57 g 4.71 g 120 6 750 8 1C-49 crystalline V.sub.2O.sub.5 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 1% of 3% 1% of 157.6 g 1.57 g 4.71 g 120 6 750 8 1C-50 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Examples Same as example 1C-1 4% of 3% 1% of 154.6 6.28 g 4.73 g 120 6 750 8 1C-51 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1% of 3% 3% of 155.2 1.57 g 4.71 120 6 750 8 1C-52 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 3% of 1% 1% of 157.3 4.73 1.57 120 6 750 8 1C-53 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.5Mg.sub.0.5Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.5F.sub.0.5 3% of 1% 1% of 166 4.73 1.57 120 6 750 8 1C-54 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.2Mg.sub.0.001Mn.sub.0.5Fe.sub.0.5P.sub.0.8Si.sub.0.2O.sub.3.999F.sub.0.001 3% of 1% 1% of 157.8 4.73 1.57 120 6 750 8 1C-55 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.005Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.95F.sub.0.05 3% of 1% 1% of 155.68 4.73 1.57 120 6 750 8 1C-56 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.7Fe.sub.0.3P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 3% of 1% 1% of 156.7 4.73 1.57 120 6 750 8 1C-57 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.6Fe.sub.0.4P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 3% of 1% 1% of 156.7 4.73 1.57 120 6 750 8 1C-58 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 3% of 1% 1% of 156.7 4.73 1.57 120 6 600 8 1C-59 crystalline Al.sub.2O.sub.3 carbon Li.sub.2FeP.sub.2O.sub.7

    Example 2C-1

    [0571] Except that in the preparation of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder in step S3, in the powder sintering step, the sintering temperature was 550? C. and the sintering time was 1 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 30%, the other conditions were the same as example 1C-1.

    Example 2C-2

    [0572] Except that in the preparation of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder of step S3, in the powder sintering step, the sintering temperature was 550? C. and the sintering time was 2 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 50%, the other conditions were the same as example 1C-1.

    Example 2C-3

    [0573] Except that in the preparation of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder of step S3, in the powder sintering step, the sintering temperature was 600? C. and the sintering time was 3 h to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 70%, the other conditions were the same as example 1C-1.

    Example 2C-4

    [0574] Except that in the preparation of lithium iron pyrophosphate (Li.sub.2FeP.sub.2O.sub.7) powder of step S3, in the powder sintering step, the sintering temperature was 500? C. to control the crystallinity of Li.sub.2FeP.sub.2O.sub.7 to be 10%, the other conditions were the same as example 1C-1.

    Preparation of Positive Electrode Plate

    [0575] The two-layer coated lithium manganese phosphate positive electrode active material prepared above, a conductive agent of acetylene black and a binder of polyvinylidene fluoride (PVDF) were added into N-methylpyrrolidone (NMP) in a weight ratio of 92:2.5:5.5, followed by stirring and uniformly mixing to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to an aluminum foil at 0.280 g/1540.25 mm.sup.2, followed by drying, cold pressing and slitting to obtain a positive electrode plate.

    Preparation of Negative Electrode Plate

    [0576] A negative electrode active material of synthetic graphite, a conductive agent of superconducting carbon black (Super-P), a binder of styrene butadiene rubber (SBR) and a thickener of sodium carboxymethylcellulose (CMC-Na) were dissolved in deionized water in a mass ratio of 95%:1.5%:1.8%:1.7%, followed by fully stirring and mixing until uniform to obtain a negative electrode slurry with a viscosity of 3000 mPa.Math.s and a solid content of 52%; and the negative electrode slurry was coated onto a negative electrode current collector of a copper foil having a thickness of 6 ?m, and then baked at 100? C. for 4 hours for drying, followed by roll pressing to obtain a negative electrode plate with a compacted density of 1.75 g/cm.sup.3.

    Separator

    [0577] a polypropylene film was used.

    Preparation of Electrolyte Solution

    [0578] Ethylene carbonate, dimethyl carbonate and 1,2-propylene glycol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF.sub.6 was evenly dissolved in the above solution to obtain an electrolyte solution. In the electrolyte solution, the concentration of LiPF.sub.6 was 1 mol/L.

    Preparation of Full Battery

    [0579] The positive electrode plate, separator, and negative electrode plate obtained above were stacked in sequence, such that the separator was located between the positive electrode and the negative electrode and played a role of isolation, and the stack was wound to obtain a bare cell. The bare cell was placed in an outer package, the above electrolyte solution was injected, and the bare cell was packaged to obtain a full battery.

    Preparation of Button Battery

    [0580] The positive electrode active material prepared above, PVDF and acetylene black at a weight ratio of 90:5:5 were added into NMP, and stirred in a drying room to prepare a slurry. An aluminum foil was coated with the slurry above, followed by drying and cold pressing to obtain a positive electrode plate. The coating amount was 0.2 g/cm.sup.2, and the compacted density was 2.0 g/cm.sup.3.

    [0581] A lithium plate as a negative electrode, a solution of 1 mol/L LiPF.sub.6 in ethylene carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC) in a volume ratio of 1:1:1 as an electrolyte solution, and the positive electrode plate prepared above were assembled into a button battery in a button battery box.

    TABLE-US-00044 TABLE 5C Performance test results of examples 1C-1 to 1C-59 and comparative examples 1C to 12C Thickness of first coating No. Inner core (1 ? y):y m:x First coating layer layer Comparative LiMnPO.sub.4 0 / 0 example 1C Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 0 / 0 example 2C Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 19 / 0 example 3C Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 1.5 900 0 example 4C Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 2.33 6.33 0 example 5C Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 0.67 998 0 example 6C Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 2.33 1068 0 example 7C Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 1.5 948 0 example 8C Comparative Same as example 1C-1 1.86 994 0 example 9C Comparative Same as example 1C-1 1.86 994 4% of 10.5 example amorphous 10C Li.sub.2FeP.sub.2O.sub.7 Comparative Same as example 1C-1 1.86 994 3% 6 example Al.sub.2O.sub.3 11C Comparative Same as example 1C-1 1.86 994 1% of 3% 9.4 example amorphous Al.sub.2O.sub.3 12C Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1.86 994 1% of 3% 9 1C-1 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.86 977 1% of 3% 9 1C-2 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.86 992 1% of 3% 9 C1-3 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1.86 997 1% of 3% 9 1C-4 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.86 993 1% of 3% 9 1C-5 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.86 993 1% of 3% 9 1C-6 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.86 993 1% of 3% 9 1C-7 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.86 993 1% of 3% 9 1C-8 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1.86 991 1% of 3% 9 1C-9 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1.86 995 1% of 3% 9 1C-10 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1.86 998 1% of 3% 9 1C-11 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 8.2 1C-12 crystalline ZnO Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 8.5 1C-13 crystalline ZrO.sub.2 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9.3 1C-14 crystalline MgO Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 8.6 1C-15 crystalline WO.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 8.8 1C-16 crystalline CuO Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 2.13 997 1% of 3% 9 1C-17 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.38 997 1% of 3% 9 1C-18 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.86 997 1% of 3% 9 1C-19 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.5 197.6 1% of 3% 9 1C-20 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 1.5 196.8 1% of 3% 9 1C-21 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.5 196.8 1% of 3% 9 1C-22 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.86 196.8 1% of 3% 9 1C-23 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.86 196.8 1% of 3% 9 1C-24 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 3 196.8 1% of 3% 9 1C-25 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.33 196.8 1% of 3% 9 1C-26 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 3 196.8 1% of 3% 9 1C-27 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.33 196.8 1% of 3% 9 1C-28 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.5 196.8 1% of 3% 9 1C-29 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1 196.8 1% of 3% 9 1C-30 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 2.33 202 1% of 3% 9 1C-31 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 2.33 194 1% of 3% 9 1C-32 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 0.8% of 2.4% 7.2 1C-33 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1.2% of 3.6% 10.8 1C-34 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1.4% of 4.2% 12.6 1C-35 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1.6% of 4.8% 9 1C-36 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9 1C-37 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9 1C-38 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9 1C-39 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9 1C-40 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1.5% of 2.5% 9 1C-41 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 2% of 2% 9 1C-42 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 2.5% of 1.5% 9 1C-43 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 3% of 1% 9 1C-44 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 1.5 18 1% of 3% 9 1C-45 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 1.5 1100 1% of 3% 9 1C-46 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 1.5 9 1% of 3% 9 1C-47 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 999 19 1% of 3% 9 1C-48 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 Same as Same as 1% of 3% 9 1C-49 example 1C-1 example 1C-1 crystalline V.sub.2O.sub.5 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 99 19 1% of 3% 9 1C-50 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Examples Same as example 1C-1 1.86 994 4% of 3% 16.5 1C-51 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 1.86 994 1% of 3% 9 1C-52 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 4 19 3% of 1% 9 1C-53 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.5Mg.sub.0.5Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.5F.sub.0.5 1 1 3% of 1% 9 1C-54 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.1.2Mg.sub.0.001Mn.sub.0.5Fe.sub.0.5P.sub.0.8Si.sub.0.2O.sub.3.999F.sub.0.001 1 1200 3% of 1% 9 1C-55 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.005Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.95F.sub.0.05 1 190 3% of 1% 9 1C-56 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.7Fe.sub.0.3P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 2.3 19 3% of 1% 9 1C-57 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.6Fe.sub.0.4P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 1.5 19 3% of 1% 9 1C-58 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 Same as Same as 3% of 1% 9 1C-59 example 1C-1 example 1C-1 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Number Expansion of cycles Capacity Average of cell corresponding Li/Mn Dissolution per gram discharge upon 30 to 80% Thickness Lattice antisite of Fe and of button voltage days of capacity Second of second change defect Mn after Surface battery of button storage retention Compacted coating coating rate concen- cycling oxygen at 0.1 C battery at 60? C. rate at density No. layer layer (%) tration/% (ppm) valency (mAh/g) (V) (%) 45? C. (g/cm.sup.3) Comparative 1% of 5 11.4 3.2 2060 ?1.55 125.6 4.02 48.6 185 1.81 example carbon 1C Comparative 1% of 5 10.6 4.3 1510 ?1.51 126.4 3.85 37.3 129 1.87 example carbon 2C Comparative 1% of 5 10.8 3.6 1028 ?1.64 134.7 4.05 31.9 134 1.88 example carbon 3C Comparative 1% of 5 9.7 2.4 980 ?1.71 141.3 3.69 30.8 148 1.93 example carbon 4C Comparative 1% of 5 5.6 1.8 873 ?1.81 110.8 3.75 21.4 387 1.98 example carbon 5C Comparative 1% of 5 3.7 1.5 574 ?1.8 74.3 3.56 15.8 469 2.01 example carbon 6C Comparative 1% of 5 7.8 1.5 447 ?1.75 139.4 3.75 18.3 396 2.05 example carbon 7C Comparative 1% of 5 8.4 1.4 263 ?1.79 141.7 3.7 22.7 407 2.16 example carbon 8C Comparative 1% of 5 6.3 1.6 192 ?1.82 143.2 3.72 18.4 552 2.21 example carbon 9C Comparative 1% of 5 5.8 1.3 150 ?1.97 149.8 3.73 6.7 802 2.25 example carbon 10C Comparative 1% of 5 5.6 1.2 198 ?1.98 150.8 3.74 6.4 860 2.26 example carbon 11C Comparative 1% of 5 5.5 1.2 148 ?1.96 151.5 3.72 4.2 950 2.21 example carbon 12C Example 1% of 5 5.2 0.7 91 ?1.96 157.1 3.72 3.2 1197 2.2 1C-1 carbon Example 1% of 5 1.5 0.5 57 ?1.97 156.7 3.74 2.7 1389 2.38 1C-2 carbon Example 1% of 5 4.9 0.6 82 ?1.96 154.7 3.74 3.5 1215 2.2 C1-3 carbon Example 1% of 5 5.1 0.7 91 ?1.96 152.6 3.72 3.7 1089 2.18 1C-4 carbon Example 1% of 5 1.5 0.4 48 ?1.97 155.8 3.74 3.2 1384 2.37 1C-5 carbon Example 1% of 5 1.4 0.3 57 ?1.98 158.4 3.74 3.2 1305 2.42 1C-6 carbon Example 1% of 5 1.4 0.3 61 ?1.98 158.9 3.74 3.2 1392 2.43 1C-7 carbon Example 1% of 5 1.4 0.3 67 ?1.98 158.8 3.74 3.1 1286 2.46 1C-8 carbon Example 1% of 5 1.5 0.4 48 ?1.97 157.3 3.73 3.4 1387 2.41 1C-9 carbon Example 1% of 5 1.4 0.3 68 ?1.98 156.8 3.74 3.1 1469 2.44 1C-10 carbon Example 1% of 5 1.5 0.4 61 ?1.97 158.2 3.73 3.4 1367 2.38 1C-11 carbon Example 1% of 5 5.2 0.7 96 ?1.94 156.4 3.71 3.6 1146 2.18 1C-12 carbon Example 1% of 5 5.2 0.7 102 ?1.96 155.7 3.72 4.2 987 2.2 1C-13 carbon Example 1% of 5 5.2 0.7 87 ?1.97 154.9 3.73 3.1 1235 2.23 1C-14 carbon Example 1% of 5 5.2 0.7 76 ?1.98 155.8 3.73 2.7 1359 2.21 1C-15 carbon Example 1% of 5 5.2 0.7 115 ?1.95 156.3 3.71 4.1 792 2.25 1C-16 carbon Example 1% of 5 6.4 0.4 45 ?1.97 152.4 3.77 1.9 1387 2.43 1C-17 carbon Example 1% of 5 6.6 0.3 47 ?1.99 156.3 3.71 2.1 1379 2.45 1C-18 carbon Example 1% of 5 6.8 0.5 50 ?1.96 154.7 3.75 2.2 1497 2.43 1C-19 carbon Example 1% of 5 5.4 0.4 59 ?1.98 155.3 3.68 1.8 1389 2.46 1C-20 carbon Example 1% of 5 4.4 0.6 50 ?1.95 155.4 3.69 2.1 1346 2.41 1C-21 carbon Example 1% of 5 3.2 0.5 52 ?1.99 156.4 3.68 1.9 1326 2.39 1C-22 carbon Example 1% of 5 1.5 0.3 48 ?1.97 156.7 3.73 2.2 1486 2.43 1C-23 carbon Example 1% of 5 1.4 0.3 58 ?1.98 155.7 3.76 2.3 1492 2.44 1C-24 carbon Example 1% of 5 1.6 0.3 51 ?1.96 153.7 3.84 2.7 1389 2.42 1C-25 carbon Example 1% of 5 2.3 0.4 57 ?1.94 154.8 3.83 2.5 1416 2.43 1C-26 carbon Example 1% of 5 2.1 0.4 60 ?1.96 156.8 3.81 2.2 1397 2.43 1C-27 carbon Example 1% of 5 1.8 0.5 52 ?1.97 150.9 3.78 2.3 1286 2.42 1C-28 carbon Example 1% of 5 1.5 0.4 51 ?1.98 151.7 3.69 1.9 1389 2.42 1C-29 carbon Example 1% of 5 1.2 0.3 43 ?1.99 152.6 3.65 2.5 1405 2.43 1C-30 carbon Example 1% of 5 2.4 0.5 31 ?1.96 146.5 3.79 2.2 1398 2.21 1C-31 carbon Example 1% of 5 1.7 0.4 27 ?1.99 144.9 3.78 1.8 1367 2.26 1C-32 carbon Example 1% of 5 5.2 0.8 112 ?1.98 158.1 3.76 2.7 987 2.25 1C-33 carbon Example 1% of 5 5.2 0.8 67 ?1.98 151.9 3.75 1.9 1269 2.24 1C-34 carbon Example 1% of 5 5.2 0.8 43 ?1.99 147.4 3.75 1.6 1387 2.24 1C-35 carbon Example 1% of 5 5.2 0.8 25 ?1.99 144.3 3.75 1.2 1523 2.23 1C-36 carbon Example 2% of 10 5.2 0.8 67 ?1.97 152.9 3.77 2.5 1167 2.18 1C-37 carbon Example 4% of 20 5.2 0.8 56 ?1.98 148.7 3.78 1.8 1258 2.15 1C-38 carbon Example 5% of 25 5.2 0.8 45 ?1.99 147.2 3.79 1.7 1368 2.09 1C-39 carbon Example 6% of 30 5.2 0.8 34 ?1.98 143.7 3.79 1.3 1576 2.05 1C-40 carbon Example 2% of 10 5.2 0.8 69 ?1.99 151.8 3.76 2.5 1198 2.18 1C-41 carbon Example 2% of 10 5.2 0.8 59 ?1.97 152.8 3.75 2.3 1235 2.17 1C-42 carbon Example 2% of 10 5.2 0.8 48 ?1.96 153.4 3.75 2.2 1308 2.16 1C-43 carbon Example 2% of 10 5.2 0.8 36 ?1.94 154.3 3.74 1.9 1386 2.16 1C-44 carbon Example 1% of 5 4.8 0.9 38 ?1.95 153.8 3.74 1.9 1269 2.38 1C-45 carbon Example 1% of 5 5.5 0.9 42 ?1.96 154.2 3.73 2.0 1213 3.41 1C-46 carbon Example 1% of 5 4.9 0.8 46 ?1.95 155.3 3.74 2.2 1154 2.45 1C-47 carbon Example 1% of 5 5.3 1.0 53 ?1.96 156.2 3.85 2.4 1039 2.37 1C-48 carbon Example 1% of 5 5.4 0.8 85 ?1.97 156.9 3.73 3.6 1205 2.22 1C-49 carbon Example 1% of 5 9.8 2.9 1854 ?1.55 135.6 4.01 15.3 201 1.89 1C-50 carbon Examples 1% of 5 5.1 0.8 79 ?1.96 153.6 3.74 2.9 1264 2.35 1C-51 carbon Example 3% of 15 5 0.7 81 ?1.96 153.2 3.74 3 1251 2.35 1C-52 carbon Example 1% of 5 3.8 0.9 52 ?1.98 156.5 3.78 3.1 1021 2.38 1C-53 carbon Example 1% of 5 2.2 0.7 49 ?1.97 157.2 3.72 2.7 1076 2.41 1C-54 carbon Example 1% of 5 3.8 2.1 39 ?1.76 158.3 3.7 2.6 1126 2.35 1C-55 carbon Example 1% of 5 5.1 1.2 42 ?1.97 157.1 3.71 2.4 1087 2.38 1C-56 carbon Example 1% of 5 4.2 4 37 ?1.96 157.2 3.75 2.5 1098 2.4 1C-57 carbon Example 1% of 5 4.8 2 35 ?1.96 157.5 3.73 2.9 1134 2.39 1C-58 carbon Example 1% of 5 4.3 0.9 36 ?1.88 157.3 3.74 3.2 1126 2.37 1C-59 carbon

    [0582] From the combination of examples 1C-1 to 1C-59 and comparative examples 1C to 9C, it can be seen that the existence of the first coating layer is beneficial to reducing the Li/Mn antisite defect concentration and the dissolution of Fe and Mn after cycling of the obtained material, increasing the capacity per gram of the button battery, and improving the high-temperature storage performance, safety performance and cycling performance of the battery. When the Li site, Mn site, phosphorus site and oxygen site are respectively doped with other elements, the lattice change rate, antisite defect concentration, and dissolution of Fe and Mn of the obtained material can be significantly reduced, such that the capacity per gram and compacted density of the battery are increased, and the high-temperature storage performance, safety performance and cycling performance of the battery are improved.

    [0583] From the combination of examples 1C-33 to 1C-36, it can be seen that as the amount of the first coating layer increases from 3.2% to 6.4%, the dissolution of Fe and Mn after cycling of the obtained material is gradually reduced, the corresponding battery has an improved high-temperature storage performance, safety performance and cycling performance at 45? C. as well, but the capacity per gram of the button battery was slightly reduced. Optionally, when the total amount of the first coating layer is 4-6.4 wt %, the overall performance of the corresponding battery is the best.

    [0584] It can be seen from a combination of examples 1C-1 and examples 1C-37 to 1C-40 that as the amount of the second coating layer increases from 1% to 6%, the dissolution of Fe and Mn after cycling of the obtained material is gradually reduced, the corresponding battery has an improved high-temperature storage performance, safety performance and cycling performance at 45? C. as well, but the capacity per gram of the button battery is slightly reduced. Optionally, when the total amount of the second coating layer is 3-5 wt %, the overall performance of the corresponding battery is the best.

    [0585] From the combination of examples 1C-1 and examples 1C-41 to 1C-44, it can be seen that when the first coating layer comprises both Li.sub.2FeP.sub.2O.sub.7 and Al.sub.2O.sub.3, and in particular the weigh ratio of Li.sub.2FeP.sub.2O.sub.7 to Al.sub.2O.sub.3 is 1:3 to 3:1, the performance of the battery is improved obviously.

    TABLE-US-00045 TABLE 6C Performance test results of example 1C-1 and examples 2C-1 to 2C-4 Lattice Li/Mn Crystallinity change antisite Example of rate defect No. Inner core First coating layer pyrophosphate (%) concentration/% Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% 100% 5.2 0.7 1C-1 crystalline Al.sub.2O.sub.3 Li.sub.2FeP.sub.2O.sub.7 Example Same as example 1C-1 Same as Same as 30% 5.3 1 2C-1 example 1C-1 example 1C-1 Example Same as example 1C-1 Same as Same as 50% 5.3 0.9 2C-2 example 1C-1 example 1C-1 Example Same as example 1C-1 Same as Same as 70% 5.3 0.8 2C-3 example 1C-1 example 1C-1 Example Same as example 1C-1 Same as Same as 10% 5.3 0.9 2C-4 example 1C-1 example 1C-1 Number Expansion of cycles Capacity Average of cell corresponding Dissolution per gram discharge upon 30 to 80% of Fe and of button voltage days of capacity Mn after Surface battery of button storage retention Compacted Example cycling oxygen at 0.1 C battery at 60? C. rate at density No. (ppm) valency (mAh/g) (V) (%) 45? C. (g/cm.sup.3) Example 91 ?1.96 157.1 3.74 3.2 1197 2.2 1C-1 Example 143 ?1.95 151.8 3.73 6.1 879 2.2 2C-1 Example 121 ?1.96 153.9 3.74 4.5 986 2.23 2C-2 Example 102 ?1.97 154.6 3.75 3.3 1078 2.26 2C-3 Example 184 ?1.96 148.9 3.69 6.7 696 2.18 2C-4

    [0586] It can be seen from Table 6C that as the crystallinity of pyrophosphate in the first coating layer gradually increases, the lattice change rate, Li/Mn antisite defect concentration, and dissolution of Fe and Mn of the corresponding material are gradually reduced, the capacity of the button battery is gradually increased, and the safety performance and cycling performance of the battery are also gradually improved.

    TABLE-US-00046 TABLE 7C Performance test results when different parameters are used in steps S1-S2 Step S1 Dissolution Stirring Step S2 Lattice Li/Mn of Fe and rotation Stirring Grinding Sintering Sintering change antisite Mn after Example speed temperature time temperature time rate defect cycling No. (rpm) (? C.) (h) (? C.) (h) (%) concentration/% (ppm) Example 1C-1 600 80 10 700 10 5.2 0.7 91 Example 3C-1 200 50 12 700 10 4.9 0.8 93 Example 3C-2 300 50 12 700 10 5.1 0.6 84 Example 3C-3 400 50 12 700 10 5 0.7 87 Example 3C-4 500 50 12 700 10 5.2 0.7 85 Example 3C-5 600 50 10 700 10 4.8 0.6 103 Example 3C-6 700 50 11 700 10 5.6 0.8 87 Example 3C-7 800 50 12 700 10 5.3 0.6 85 Example 3C-8 600 60 12 700 10 5.5 0.6 85 Example 3C-9 600 70 12 700 10 6 0.7 87 Example 3C-10 600 80 12 700 10 4.8 0.8 86 Example 3C-11 600 90 12 600 10 4 0.8 85 Example 3C-12 600 100 12 800 10 4.8 0.8 94 Example 3C-13 600 110 12 700 8 5.9 0.7 86 Example 3C-14 600 120 12 700 12 5 0.5 91 Capacity Average Expansion of per gram discharge cell upon Number of cycles of button voltage 30 days of corresponding Surface battery of button storage to 80% capacity Compacted Example oxygen at 0.1 C battery at 60? C. retention rate density No. valency (mAh/g) (V) (%) at 45? C. (g/cm.sup.3) Example 1C-1 ?1.96 157.1 3.74 3.2 1197 2.2 Example 3C-1 ?1.97 156.8 3.74 2.2 1187 2.2 Example 3C-2 ?1.98 156.1 3.75 2.4 1114 2.2 Example 3C-3 ?1.97 156.2 7.76 2.5 1123 2.18 Example 3C-4 ?1.98 155.3 3.74 2.5 1134 2.2 Example 3C-5 ?1.97 157.3 3.75 2.3 1203 2.2 Example 3C-6 ?1.99 157.4 3.76 2.4 1243 2.2 Example 3C-7 ?1.97 156.2 3.75 2.4 1187 2.22 Example 3C-8 ?1.98 156.9 3.74 2.3 1103 2.2 Example 3C-9 ?1.96 157.2 3.76 2.3 1156 2.42 Example 3C-10 ?1.97 156.4 3.75 2.4 1187 2.18 Example 3C-11 ?1.99 155.8 3.76 2.5 1205 2.18 Example 3C-12 ?1.98 156.3 3.74 2.3 1186 2.2 Example 3C-13 ?1.97 156.3 3.74 2.3 1135 2.19 Example 3C-14 ?1.99 157 3.76 2.5 1236 2.18

    [0587] It can be seen from Table 7C that the properties of the positive electrode material of the present application can be further improved by adjusting the stirring rotation speed and reaction temperature in the reaction kettle, the grinding time, and the sintering temperature and time during the preparation of the inner core.

    TABLE-US-00047 TABLE 8C Performance test results when different parameters are used in step S3 Included angle of crystal Step S3 Interplanar orientation Lattice Li/Mn Drying Drying Sintering Sintering spacing of (111) of change antisite Example Li.sub.2FeP.sub.2O.sub.7:Al.sub.2O.sub.3 temperature time temperature time pyrophosphate pyrophosphate rate defect No. (weight ratio) (? C.) (h) (? C.) (h) (nm) (?) (%) concentration/% Example 1C-1 1:3 120 4 650 8 0.303 29.496 5.2 0.7 Example 4C-1 1:3 100 4 700 6 0.303 29.496 5.2 0.7 Example 4C-2 1:3 150 6 700 6 0.303 29.496 5.2 0.7 Example 4C-3 1:3 200 6 700 6 0.303 29.496 5.2 0.7 Example 4C-4 1:3 200 6 600 6 0.303 29.496 5.2 0.7 Capacity Average Expansion of Number of Dissolution per gram discharge cell upon cycles of Fe and of button voltage 30 days of corresponding Mn after Surface battery of button storage to 80% capacity Compacted Example cycling oxygen at 0.1 C battery at 60? C. retention rate density No. (ppm) valency (mAh/g) (V) (%) at 45? C. (g/cm.sup.3) Example 1C-1 91 ?1.96 157.1 3.74 3.2 1197 2.2 Example 4C-1 85 ?1.98 156.2 3.72 3.4 1126 2.21 Example 4C-2 81 ?1.97 157.3 3.74 3.6 1107 2.22 Example 4C-3 83 ?1.98 158.7 3.72 3.5 1185 2.23 Example 4C-4 102 ?1.96 154.2 3.71 3.7 1085 2.22

    TABLE-US-00048 TABLE 9C Performance test results when different parameters are used in step S5 Included angle of crystal Step S5 Interplanar orientation Lattice Li/Mn Drying Drying Sintering Sintering spacing of (111) of change antisite Example Li.sub.2FeP.sub.2O.sub.7:Al.sub.2O.sub.3 temperature time temperature time pyrophosphate pyrophosphate rate defect No. (weight ratio) (? C.) (h) (? C.) (h) (nm) (?) (%) concentration/% Example 1C-1 1:3 150 6 700 6 0.303 29.496 5.2 0.7 Example 5C-1 1:3 150 6 600 4 0.303 29.496 5.2 0.7 Example 5C-2 1:3 150 6 600 6 0.303 29.496 5.2 0.7 Example 5C-3 1:3 150 6 800 8 0.303 29.496 5.2 0.7 Capacity Average Expansion of Number of Dissolution per gram discharge cell upon cycles of Fe and of button voltage 30 days of corresponding Mn after Surface battery of button storage to 80% capacity Compacted Example cycling oxygen at 0.1 C battery at 60? C. retention rate density No. (ppm) valency (mAh/g) (V) (%) at 45? C. (g/cm.sup.3) Example 1C-1 91 ?1.96 157.1 3.74 3.2 1197 2.2 Example 5C-1 95 ?1.98 154.7 3.74 3.3 1105 2.22 Example 5C-2 90 ?1.96 158.8 3.75 3.5 1234 2.24 Example 5C-3 80 ?1.97 157.3 3.74 3.1 1167 2.24

    [0588] It can be seen from Table 8C and 9C that the properties of the obtained material can be improved by adjusting the drying temperature/time and the sintering temperature/time in the process of preparing lithium iron pyrophosphate by the method of the present application, thereby improving the performance of the battery; and the performance of the obtained material can be improved by adjusting the drying temperature/time and the sintering temperature/time during the coating process, thereby improving the performance of the battery.

    [0589] The preparation and performance tests of the positive electrode active materials having an inner core of Li.sub.1+xC.sub.mMn.sub.1-yA.sub.yP.sub.1-zR.sub.zO.sub.4-nD.sub.n and a shell comprising a first coating layer (a crystalline pyrophosphate), a second coating layer (a metal oxide of Q.sub.eO.sub.f), and a third coating layer (carbon) will be detailed below:

    Example 1D

    Step S1: Preparation of Doped Manganese Oxalate

    [0590] The operations were the same as example 1.

    Step S2: Preparation of Inner Core Comprising Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001

    [0591] The operations were the same as those in step S2 of example 1C-1.

    Step S3: Preparation of First Coating Layer Suspension

    [0592] Preparation of Li.sub.2FeP.sub.2O.sub.7 solution: 7.4 g of lithium carbonate, 11.6 g of ferrous carbonate, 23.0 g of ammonium dihydrogen phosphate and 12.6 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, with pH being controlled to be 5, the mixture was then stirred and reacted at room temperature for 2 h to obtain a solution, and then the solution was heated to 80? C. and held at the temperature for 4 h to obtain a first coating layer suspension.

    Step S4: Coating of First Coating Layer

    [0593] 157.2 g of doped lithium manganese phosphate inner core material obtained in step S2 was added into the first coating layer suspension (the content of the coating material was 1.572 g) obtained in step S3, fully stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 650? C. for 6 h to obtain a pyrophosphate coated material.

    Step S5: Preparation of Second Coating Layer Suspension

    [0594] 4.71 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a second coating layer suspension.

    Step S6: Coating of Second Coating Layer

    [0595] 158.772 g of the pyrophosphate coated material obtained in step S4 was added into the second coating layer suspension (the content of the coating material was 4.71 g) obtained in step S5, fully stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 120? C. and dried for 6 h, and then sintered at 700? C. for 8 h to obtain a two-layer coated material.

    Step S7: Preparation of Aqueous Solution of Third Coating Layer

    [0596] 37.3 g of sucrose was dissolved in 500 g of deionized water, then stirred and fully dissolved to obtain an aqueous solution of sucrose.

    Step S8: Coating of Third Coating Layer

    [0597] 1633.9 g of the two-layer coated material obtained in step S6 was added into the sucrose solution obtained in step S7, stirred and mixed for 6 h; and after uniformly mixing, the mixture was transferred into an oven at 150? C. and dried for 6 h, and then sintered at 700? C. for 10 h to obtain a three-layer coated material.

    Examples 2D to 89D and Comparative Examples 1D to 12D

    [0598] The positive electrode active materials of examples 2D to 89D and comparative examples 1D to 12D were prepared by a method similar to example 1D, and the differences in the preparation of the positive electrode active materials were shown in Tables 1D to 6D.

    [0599] There was no first coating layer in comparative examples 1D-9D and comparative example 11D, and therefore steps S3-S4 were not involved; and there was no second coating layer in comparative examples 1D-10D, and therefore steps S5-S6 were not involved.

    TABLE-US-00049 TABLE 1D Preparation of doped manganese oxalate and preparation of inner core (steps S1-S2) Chemical formula of Raw materials used in No. inner core* Step S1 Comparative LiMnPO.sub.4 MnSO.sub.4H.sub.2O, 1.0 mol; example 1D water, 10 L; and oxalic acid dihydrate, 1 mol; Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 MnSO.sub.4H.sub.2O, 0.85 example 2D mol; FeSO.sub.4H.sub.2O, 0.15 mol; water, 10 L; and oxalic acid dihydrate, 1 mol; Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 MnSO.sub.4H.sub.2O, 1.9 mol; example 3D ZnSO.sub.4, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.2 mol; example 4D FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.0.3P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.4 mol; example 5D FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 0.8 mol; example 6D ZnSO.sub.4, 1.2 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.4 mol; example 7D FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 MnSO.sub.4H.sub.2O, 1.2 mol; example 8D FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Comparative Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; examples 9D FeSO.sub.4H.sub.2O, 0.7 mol; and 10D, and water, 10 L; and examples 1D, oxalic acid dihydrate, 90D and 91D 2 mol; Example 12D- Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; 28D FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Examples 45D- Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; 62D, FeSO.sub.4H.sub.2O, 0.7 mol; examples 67D- water, 10 L; and 72D, and oxalic acid dihydrate, examples 84D- 2 mol; 89D Example 2D Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and Ti(SO.sub.4).sub.2, 0.02 mol; Example 3D Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 4D Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 5D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.69 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 6D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and MgSO.sub.4, 0.01 mol; Example 7D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and CoSO.sub.4, 0.01 mol; Example 8D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and NiSO.sub.4, 0.01 mol; Example 9D Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.698 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and Ti(SO.sub.4).sub.2, 0.002 mol; Example 10D Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.68 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.01 mol; and MgSO.sub.4, 0.01 mol; Example 11D Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.69 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 29D Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.36 mol; FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.04 mol; Example 30D Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.16 mol; FeSO.sub.4H.sub.2O, 0.8 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.04 mol; Example 31D Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.6 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 32D Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 33D Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 34D Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.1 mol; Example 35D Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.1 mol; Example 36D Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.4 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 37D Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.5 mol; FeSO.sub.4H.sub.2O, 0.1 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.3 mol; Example 38D Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and NiSO.sub.4, 0.1 mol; Example 39D Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.5 mol; FeSO.sub.4H.sub.2O, 0.2 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and NiSO.sub.4, 0.2 mol; Example 40D Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 41D Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.5 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 42D Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 MnSO.sub.4H.sub.2O, 1.0 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 43D Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 44D Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 MnSO.sub.4H.sub.2O, 1.4 mol; FeSO.sub.4H.sub.2O, 0.3 mol; water, 10 L; oxalic acid dihydrate, 2 mol; VCl.sub.2, 0.1 mol; and CoSO.sub.4, 0.2 mol; Example 63D Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 64D Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 65D Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 66D Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.2 mol; FeSO.sub.4H.sub.2O, 0.79 mol; water, 10 L; oxalic acid dihydrate, 2 mol; and VCl.sub.2, 0.01 mol; Example 73D Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.98 mol; FeSO.sub.4H.sub.2O, 0.02 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 74D Li.sub.0.95Mg.sub.0.05Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1 mol; FeSO.sub.4H.sub.2O, 1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 75D Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.6 mol; FeSO.sub.4H.sub.2O, 0.4 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 76D Li.sub.0.95Mg.sub.0.05Mn.sub.0.75Fe.sub.0.25P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 MnSO.sub.4H.sub.2O, 1.5 mol; FeSO.sub.4H.sub.2O, 0.25 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Examples 77D Li.sub.0.998Mg.sub.0.001Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.2 mol; and 83D FeSO.sub.4H.sub.2O, 0.7 mol; VCl.sub.2, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Examples 78D Li.sub.0.996Mg.sub.0.002Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.1 mol; and 80D FeSO.sub.4H.sub.2O, 0.8 mol; VCl.sub.2, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 79D Li.sub.0.996Mg.sub.0.002Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.3 mol; FeSO.sub.4H.sub.2O, 0.7 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 81D Li.sub.0.994Mg.sub.0.003Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 1.1 mol; FeSO.sub.4H.sub.2O, 0.8 mol; VCl.sub.2, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; Example 82D Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Fe.sub.0.55V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 MnSO.sub.4H.sub.2O, 0.8 mol; FeSO.sub.4H.sub.2O, 1.1 mol; VCl.sub.2, 0.1 mol; water, 10 L; and oxalic acid dihydrate, 2 mol; No. Raw materials used in Step S2 Comparative Manganese oxalate particles obtained in example 1D step S1, 1 mol; lithium carbonate, 0.5 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles example 2D obtained in step S1, 1 mol; lithium carbonate, 0.5 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles example 3D obtained in step S1, 1 mol; lithium carbonate, 0.495 mol; MgSO.sub.43, 0.005 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles example 4D obtained in step S1, 1 mol; lithium carbonate, 0.45 mol; Nb.sub.2(SO.sub.4).sub.5, 0.005 mol; 85% aqueous phosphoric acid solution containing 1 mol of phosphoric acid; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles example 5D obtained in step S1, 1 mol; lithium carbonate, 0.38 mol; MgSO.sub.4, 0.12 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Doped manganese oxalate particles example 6D obtained in step S1, 1 mol; lithium carbonate, 0.499 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles example 7D obtained in step S1, 1 mol; lithium carbonate, 0.534 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.88 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.12 mol; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles example 8D obtained in step S1, 1 mol; lithium carbonate, 0.474 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.93 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.07 mol; NH.sub.4HF.sub.2, 0.06 mol; sucrose, 0.005 mol; and water, 20 L; Comparative Fe doped manganese oxalate particles examples 9D obtained in step S1, 1 mol; lithium and 10D, and carbonate, 0.497 mol; Mo(SO.sub.4).sub.3, 0.001 examples 1D, mol; 85% aqueous phosphoric acid solution 90D and 91D containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 12D- Fe doped manganese oxalate particles 28D obtained in step S1, 1 mol; lithium carbonate, 0.497 mol; Mo(SO.sub.4).sub.3, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Examples 45D- Fe doped manganese oxalate particles 62D, obtained in step S1, 1 mol; lithium examples 67D- carbonate, 0.497 mol; Mo(SO.sub.4).sub.3, 0.001 72D, and mol; 85% aqueous phosphoric acid solution examples 84D- containing 0.999 mol of phosphoric acid; 89D H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 2D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4885 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 3D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.496 mol; W(SO.sub.4).sub.3, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 4D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; Al.sub.2(SO.sub.4).sub.3, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HCl.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 5D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 6D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 7D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 8D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4965 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 9D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4955 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HCl.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 10D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4975 mol; Nb.sub.2(SO.sub.4).sub.5, 0.0005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HBr.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 11D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.499 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HBr.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 29D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 30D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 31D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4985 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; HNO.sub.3, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 32D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.494 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 33D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.467 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.171 mol of phosphoric acid; H.sub.2SO.sub.4, 0.005 mol; NH.sub.4HF.sub.2, 0.0005 mol; sucrose, 0.005 mol; and water, 20 L; Example 34D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 35D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 36D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 37D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 38D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 39D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 40D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 41D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.497 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 42D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.492 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.2SO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.0025 mol; sucrose, 0.005 mol; and water, 20 L; Example 43D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.4825 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.04 mol; sucrose, 0.005 mol; and water, 20 L; Example 44D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.485 mol; MgSO.sub.4, 0.005 mol; 85% aqueous phosphoric acid solution containing 0.92 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.08 mol; NH.sub.4HF.sub.2, 0.05 mol; sucrose, 0.005 mol; and water, 20 L; Example 63D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.45 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.05 mol; sucrose, 0.005 mol; and water, 20 L; Example 64D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.55 mol; MgSO.sub.4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.9 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.1 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 65D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.45 mol; MgSO.sub.4, 0.1 mol; 85% aqueous phosphoric acid solution containing 0.95 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.05 mol; NH.sub.4HF.sub.2, 0.025 mol; sucrose, 0.005 mol; and water, 20 L; Example 66D Doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO.sub.4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.005 mol; sucrose, 0.005 mol; and water, 20 L; Example 73D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 74D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 75D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Example 76D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.475 mol; MgSO4, 0.05 mol; 85% aqueous phosphoric acid solution containing 0.96 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.04 mol; NH.sub.4HF.sub.2, 0.01 mol; sucrose, 0.005 mol; and water, 20 L; Examples 77D Fe doped manganese oxalate particles and 83D obtained in step S1, 1 mol; lithium carbonate, 0.499 mol; MgSO4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Examples 78D Fe doped manganese oxalate particles and 80D obtained in step S1, 1 mol; lithium carbonate, 0.498 mol; MgSO4, 0.002 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 79D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.498 mol; MgSO4, 0.002 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 81D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.497 mol; MgSO4, 0.003 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L; Example 82D Fe doped manganese oxalate particles obtained in step S1, 1 mol; lithium carbonate, 0.499 mol; MgSO4, 0.001 mol; 85% aqueous phosphoric acid solution containing 0.999 mol of phosphoric acid; H.sub.4SiO.sub.4, 0.001 mol; NH.sub.4HF.sub.2, 0.001 mol; sucrose, 0.005 mol; and water, 20 L;

    TABLE-US-00050 TABLE 2D Preparation of first coating layer suspension (step S3) Coating material of No. first coating layer* Preparation of first coating layer suspension** Comparative Amorphous 7.4 g of lithium carbonate; 11.6 g of ferrous carbonate; 23.0 g of example 10D Li.sub.2FeP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid and example dihydrate; controlling the pH to be 5 91D Examples 1D- Crystalline 7.4 g of lithium carbonate; 11.6 g of ferrous carbonate; 23.0 g of 11D, 21D- Li.sub.2FeP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid 66D, and 69D- dihydrate; controlling the pH to be 5 89D Example 12D Crystalline 53.3 g of aluminum chloride; 34.5 g of ammonium dihydrogen Al.sub.4(P.sub.2O.sub.7).sub.3 phosphate; and 18.9 g of oxalic acid dihydrate; controlling the pH to be 4 Example 13D Crystalline 7.4 g of lithium carbonate; 11.9 g of nickel carbonate; 23.0 g of Li.sub.2NiP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; controlling the pH to be 5 Example 14D Crystalline 7.4 g of lithium carbonate; 8.4 g of magnesium carbonate; 23.0 g Li.sub.2MgP.sub.2O.sub.7 of ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate Example 15D Crystalline 7.4 g of lithium carbonate, 15.5 g of cobalt sulfate; 23.0 g of Li.sub.2CoP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate Example 16D Crystalline 7.4 g of lithium carbonate, 16.0 g of copper sulfate; 23.0 g of Li.sub.2CuP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate Example 17D Crystalline 7.4 g of lithium carbonate, 12.5 g of zinc carbonate; 23.0 g of Li.sub.2ZnP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate Example 18D Crystalline 24.0 g of titanium sulfate, 23.0 g of ammonium dihydrogen TiP.sub.2O.sub.7 phosphate; and 12.6 g of oxalic acid dihydrate Example 19D Crystalline 67.9 g of silver nitrate, 23.0 g of ammonium dihydrogen Ag.sub.4P.sub.2O.sub.7 phosphate, and 25.2 g of oxalic acid dihydrate Example 20D Crystalline 56.6 g of zirconium sulfate, 23.0 g of ammonium dihydrogen ZrP.sub.2O.sub.7 phosphate, and 25.2 g of oxalic acid dihydrate Example 67D Crystalline 3.7 g of lithium carbonate; 13.3 g of aluminum chloride; 23.0 g of LiAlP.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; Example 68D Crystalline 25.0 g of zinc carbonate; 25.0 g of zinc carbonate; 23.0 g of Zn.sub.2P.sub.2O.sub.7 ammonium dihydrogen phosphate; and 12.6 g of oxalic acid dihydrate; *When the amount of the coating material of the first coating layer increases or decreases by several times, the amount of the raw materials of the first coating layer suspension correspondingly increases or decreases by the same multiple.

    TABLE-US-00051 TABLE 3D Coating of first coating layer (step S4) Step S4: Coating of first coating layer Coating material of Amount Amount of first coating layer of inner corresponding and amount thereof* core coating material Mixing Drying Sintering Sintering (based on weight of added in in first coating time temperature temperature time No. inner core) step S4 layer suspension (h) (? C.) (? C.) (h) Comparative 4% of amorphous 157.2 g 6.288 g 6 120 500 4 example 10D Li.sub.2FeP.sub.2O.sub.7 Example 91D 1% of amorphous 157.2 g 1.572 g 6 120 500 4 Li.sub.2FeP.sub.2O.sub.7 Examples 1D, 1% of crystalline 157.20 g 1.572 g 6 120 650 6 21D-28D, Li.sub.2FeP.sub.2O.sub.7 50D-62D, 69D-83D, and 86D-89D Example 2D 1% of crystalline 157.05 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 3D 1% of crystalline 157.28 g 1.573 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 4D 1% of crystalline 157.18 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 5D 1% of crystalline 157.17 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 6D 1% of crystalline 157.02 g 1.570 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 7D 1% of crystalline 157.19 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 8D 1% of crystalline 157.19 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 9D 1% of crystalline 157.21 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 10D 1% of crystalline 157.09 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 11D 1% of crystalline 157.20 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 12D 1% of crystalline 157.20 g 1.572 g 6 120 680 8 Al.sub.4(P.sub.2O.sub.7).sub.3 Example 13D 1% of crystalline 157.20 g 1.572 g 6 120 630 6 Li.sub.2NiP.sub.2O.sub.7 Example 14D 1% of crystalline 157.20 g 1.572 g 7 120 660 6 Li.sub.2MgP.sub.2O.sub.7 Example 15D 1% of crystalline 157.20 g 1.572 g 6 120 670 6 Li.sub.2CoP.sub.2O.sub.7 Example 16D 1% crystalline 157.20 g 1.572 g 8 120 640 6 Li.sub.2CuP.sub.2O.sub.7 Example 17D 1% of crystalline 157.20 g 1.572 g 8 120 650 6 Li.sub.2ZnP.sub.2O.sub.7 Example 18D 1% of crystalline 157.20 g 1.572 g 7 120 660 6 TiP.sub.2O.sub.7 Example 19D 1% of crystalline 157.20 g 1.572 g 9 120 670 6 Ag.sub.4P.sub.2O.sub.7 Example 20D 1% crystalline 157.20 g 1.572 g 8 120 680 6 ZrP.sub.2O.sub.7 Example 29D 1% of crystalline 157.01 g 1.570 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 30D 1% of crystalline 157.10 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 31D 1% of crystalline 156.85 g 1.569 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 32D 1% of crystalline 156.97 g 1.570 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 33D 1% of crystalline 156.97 g 1.570 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 34D 1% of crystalline 156.96 g 1.570 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 35D 1% of crystalline 157.09 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 36D 1% of crystalline 157.24 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 37D 1% of crystalline 157.30 g 1.573 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 38D 1% of crystalline 157.07 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 39D 1% of crystalline 157.13 g 1.571 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 40D 1% of crystalline 157.15 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 41D 1% of crystalline 157.29 g 1.573 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 42D 1% of crystalline 157.38 g 1.574 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 43D 1% of crystalline 157.37 g 1.574 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 44D 1% of crystalline 157.15 g 1.572 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 45D 2% of crystalline 157.20 g 3.14 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 46D 3% of crystalline 157.20 g 4.71 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 47D 4% of crystalline 157.20 g 6.28 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 48D 5.5% of crystalline 157.20 g 8.635 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 49D 6% of crystalline 157.20 g 9.42 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 63D 1% of crystalline 157.70 g 1.577 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 64D 1% of crystalline 157.61 g 1.576 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 65D 1% of crystalline 158.91 g 1.589 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 66D 1% of crystalline 157.62 g 1.576 g 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 67D 1% of crystalline 157.20 g 1.572 g 8 120 690 6 LiAlP.sub.2O.sub.7 Example 68D 1% of crystalline 157.20 g 1.572 g 8 120 700 6 Zn.sub.2P.sub.2O.sub.7 Example 84D 0.33% of crystalline 157.20 g 0.524 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7 Example 85D 3.3% of crystalline 157.20 g 5.24 6 120 650 6 Li.sub.2FeP.sub.2O.sub.7

    TABLE-US-00052 TABLE 4D Preparation of second coating layer suspension (step S5) Second coating Step S5: Preparation of second coating layer No. layer material* suspension** Examples 1D-20D, 29D- Crystalline Al.sub.2O.sub.3 4.71 g of nano-Al.sub.2O.sub.3 (with a particle size of about 20 71D and 73D-91D nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 21D Crystalline CoO 4.71 g of nano-CoO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 22D Crystalline NiO 4.71 g of nano-NiO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 23D Crystalline CuO 4.71 g of nano-CuO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 24D Crystalline ZnO 4.71 g of nano-ZnO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 25D Crystalline TiO2 4.71 g of nano-TiO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 26D Crystalline MgO 4.71 g of nano-MgO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 27D Crystalline ZrO2 4.71 g of nano-ZrO.sub.2 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 28D Crystalline CaO 4.71 g of nano-CaO (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; Example 72D Crystalline V.sub.2O.sub.5 4.71 g of nano-V.sub.2O.sub.5 (with a particle size of about 20 nm) was dissolved in 1500 mL of deionized water, and stirred for 2 h to obtain a suspension; *When the amount of the coating material of the second coating layer increases or decreases by several times, the amount of the raw materials of the second coating layer suspension correspondingly increases or decreases by the same multiple (except that the amount of deionized water remains unchanged).

    TABLE-US-00053 TABLE 5D Coating of second coating layer (step S6) Amount of Step S6: Coating of second coating layer pyrophosphate- Amount of coated corresponding Second coating material (or coating material layer material and inner core) in second amount thereof added in coating layer Mixing Drying Sintering Sintering (based on weight step S6 suspension time temperature temperature time No. of inner core)* (g) (g) (h) (? C.) (? C.) (h) Example 4% of crystalline 157.2 6.288 6 120 750 8 90D Al.sub.2O.sub.3 Examples 3% of crystalline 158.772 4.71 6 120 700 8 29D-49D, Al.sub.2O.sub.3 55D-68D and 91D Examples 3% of crystalline 158.772 4.71 6 120 700 8 1D and Al.sub.2O.sub.3 88D-89D Example 3% of crystalline 158.621 4.72 6 120 700 8 2D Al.sub.2O.sub.3 Example 3% of crystalline 158.853 4.72 6 120 700 8 3D Al.sub.2O.sub.3 Example 3% of crystalline 158.752 4.72 6 120 700 8 4D Al.sub.2O.sub.3 Example 3% of crystalline 158.742 4.72 6 120 700 8 5D Al.sub.2O.sub.3 Example 3% of crystalline 158.590 4.71 6 120 700 8 6D Al.sub.2O.sub.3 Example 3% of crystalline 158.762 4.72 6 120 700 8 7D Al.sub.2O.sub.3 Example 3% of crystalline 158.762 4.72 6 120 700 8 8D Al.sub.2O.sub.3 Example 3% of crystalline 158.782 4.72 6 120 700 8 9D Al.sub.2O.sub.3 Example 3% of crystalline 158.661 4.71 6 120 700 8 10D Al.sub.2O.sub.3 Examples 3% of crystalline 158.772 4.71 6 120 700 8 11D-20D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 21D CoO Example 3% of crystalline 158.772 4.71 6 120 710 8 22D NiO Example 3% of crystalline 158.772 4.71 6 120 710 8 23D CuO Example 3% of crystalline 158.772 4.71 6 120 730 8 24D ZnO Example 3% of crystalline 158.772 4.71 6 120 730 8 25D TiO.sub.2 Example 3% of crystalline 158.772 4.71 6 120 680 8 26D MgO Example 3% of crystalline 158.772 4.71 6 120 750 8 27D ZrO.sub.2 Example 3% of crystalline 158.772 4.71 6 120 700 8 28D CaO Example 1% of crystalline 158.772 15.71.57 6 120 700 8 50D Al.sub.2O.sub.3 Example 2% of crystalline 158.772 3.14 6 120 700 8 51D Al.sub.2O.sub.3 Example 4% of crystalline 158.772 6.28 6 120 700 8 52D Al.sub.2O.sub.3 Example 5.5% of crystalline 158.772 8.64 6 120 700 8 53D Al.sub.2O.sub.3 Example 6% of crystalline 158.772 9.42 6 120 700 8 54D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 69D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 70D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 71D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 72D V.sub.2O.sub.5 Example 3% of crystalline 159 4.71 6 120 700 8 73D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 74D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 75D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 76D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 77D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 78D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 79D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 80D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 81D Al.sub.2O.sub.3 Example 3% of crystalline 158.772 4.71 6 120 700 8 82D Al.sub.2O.sub.3 Example 1% of crystalline 158.772 1.57 6 120 700 8 83D Al.sub.2O.sub.3 Example Same as example 157.71 4.71 6 120 700 8 84D 1D Example Same as example 162.38 4.71 6 120 700 8 85D 1D Example 0.33% of crystalline 158.772 0.51 6 120 700 8 86D Al.sub.2O.sub.3 Example 6% of crystalline 158.772 9.42 6 120 720 12 87D Al.sub.2O.sub.3

    TABLE-US-00054 TABLE 6D Coating of third coating layer (step S8) Amount of two-layer coated material added in step S8 Step S8: Coating of third coating layer Molar (or amount of inner core of Amount Third ratio first-layer coated material or of Mixing Drying Sintering Sintering coating of SP2 amount of inner core) sucrose time temperature temperature time No. layer* to SP3* (g) (g) (h) (? C.) (? C.) (h) Comparative 1% of 2.5 1568.5 37.3 6 150 650 8 example 1D carbon Comparative 1% of 2.4 1571.0 37.3 6 150 630 8 example 2D carbon Comparative 1% of 2.7 1572.2 37.3 6 150 680 7 example 3D carbon Comparative 1% of 2.2 1572.2 37.3 6 150 600 8 example 4D carbon Comparative 1% of 2.4 1571.1 37.3 6 150 630 8 example 5D carbon Comparative 1% of 2.3 1586.8 37.3 6 150 620 8 example 6D carbon Comparative 1% of 2.1 1618.2 37.3 6 150 600 6 example 7D carbon Comparative 1% of 2 1662.6 37.3 6 120 600 6 example 8D carbon Comparative 1% of 1.8 1656.5 37.1 6 120 600 6 example 9D carbon Comparative 1% of 1.7 1664.8 37.3 6 100 600 6 example 10D carbon Example 90D 1% of 3.1 1665.4 37.3 6 150 700 10 carbon Example 91D 1% of 3.5 1665.4 37.3 6 150 750 10 carbon Examples 1D, 1% of 2.2 1633.9 37.3 6 150 700 10 12D-44D, carbon 60D-68D, and 84D-87D Example 2D 1% of 2.5 1649.6 37.3 6 150 650 8 carbon Example 3D 1% of 2.5 1665.3 37.3 6 150 650 8 carbon Example 4D 1% of 2.4 1696.7 37.3 6 150 630 8 carbon Example 5D 1% of 2.3 1602.5 37.3 6 150 600 9 carbon Example 6D 1% of 2.2 1649.6 37.3 6 150 600 8 carbon Example 7D 1% of 2.2 1665.3 37.3 6 150 600 9 carbon Example 8D 1% of 2.7 1666.2 37.3 6 150 680 7 carbon Example 9D 1% of 2.6 1633.0 37.3 6 150 650 7 carbon Example 10D 1% of 2.2 1666.4 37.3 6 150 600 9 carbon Example 11D 1% of 2.3 1721.4 37.3 6 150 600 9 carbon Example 45D 1% of 2.4 1690.0 37.3 6 150 630 8 carbon Example 46D 1% of 2.4 1635.9 37.4 6 150 630 8 carbon Example 47D 1% of 2.3 1631.3 37.3 6 150 600 9 carbon Example 48D 1% of 0.07 1668.3 37.4 6 80 600 6 carbon Example 49D 1% of 13 1668.3 37.4 6 150 850 10 carbon Example 50D 1% of 2.3 1721.4 37.3 6 150 600 9 carbon Example 51D 1% of 2.4 1690.0 37.3 6 150 630 8 carbon Example 52D 1% of 2.4 1635.9 37.4 6 150 630 8 carbon Example 53D 1% of 2.4 1634.6 37.4 6 150 630 8 carbon Example 54D 1% of 2.3 1633.9 37.4 6 150 600 9 carbon Example 55D 2% of 2.1 1633.9 74.7 6 150 600 6 carbon Example 56D 3% of 2.6 1666.4 111.9 6 150 650 7 carbon Example 57D 4% of 2.6 1633.9 149.2 6 150 650 7 carbon Example 58D 5.5% of 2.8 1642.6 205.4 6 150 680 8 carbon Example 59D 6% of 2.3 1633.9 224.4 6 150 600 9 carbon Example 69D 1% of 0.1 1633.9 37.3 6 85 400 2 carbon Example 70D 1% of 10 1633.9 37.3 6 150 800 20 carbon Example 71D 1% of 3 1633.9 37.3 6 150 680 8 carbon Example 72D 1% of 2.5 1633.9 37.3 6 150 680 8 carbon Example 73D 1% of 2.3 1633.9 37.3 6 150 700 10 carbon Example 74D 1% of 2.6 1633.9 37.3 6 150 700 10 carbon Example 75D 1% of 2.5 1633.9 37.3 6 150 700 10 carbon Example 76D 1% of 2.4 1633.9 37.3 6 150 700 10 carbon Example 77D 1% of 2.6 1633.9 37.3 6 150 700 10 carbon Example 78D 1% of 2.5 1633.9 37.3 6 150 700 10 carbon Example 79D 1% of 2.3 1633.9 37.3 6 150 700 10 carbon Example 80D 1% of 2.6 1633.9 37.3 6 150 700 10 carbon Example 81D 1% of 2.5 1633.9 37.3 6 150 700 10 carbon Example 82D 1% of 2.4 1633.9 37.3 6 150 700 10 carbon Example 83D 1% of 2.4 1633.9 37.3 6 150 700 10 carbon Example 88D 0.4% of 2.2 1633.9 14.92 6 150 700 10 carbon Example 89D 5% of 2.2 1633.9 186.5 6 150 700 10 carbon

    Preparation of Positive Electrode Plate

    [0600] The three-layer coated positive electrode active material prepared above, a conductive agent of acetylene black and a binder of polyvinylidene fluoride (PVDF) were added into N-methylpyrrolidone (NMP) in a weight ratio of 97.0:1.2:1.8, followed by stirring until uniform to obtain a positive electrode slurry. The positive electrode slurry was then uniformly applied to an aluminum foil at 0.280 g/1540.25 mm.sup.2, followed by drying, cold pressing and slitting to obtain a positive electrode plate.

    Preparation of Negative Electrode Plate

    [0601] A negative electrode active material of synthetic graphite, a conductive agent of superconducting carbon black (Super-P), a binder of styrene butadiene rubber (SBR) and a thickener of sodium carboxymethylcellulose (CMC-Na) were dissolved in deionized water in a mass ratio of 95%:1.5%:1.8%: 1.7%, followed by fully stirring and mixing until uniform to obtain a negative electrode slurry with a viscosity of 3000 mPa.Math.s and a solid content of 52%; and the negative electrode slurry was coated onto a negative electrode current collector of a copper foil having a thickness of 6 ?m, and then baked at 100? C. for 4 hours for drying, followed by roll pressing to obtain a negative electrode plate with a compacted density of 1.75 g/cm3.

    Separator

    [0602] a polypropylene film was used.

    Preparation of Electrolyte Solution

    [0603] Ethylene carbonate, dimethyl carbonate and 1,2-propylene glycol carbonate were mixed in a volume ratio of 1:1:1, and then LiPF.sub.6 was evenly dissolved in the above solution to obtain an electrolyte solution. In the electrolyte solution, the concentration of LiPF.sub.6 was 1 mol/L.

    Preparation of Full Battery

    [0604] The positive electrode plate, separator, and negative electrode plate obtained above were stacked in sequence, such that the separator was located between the positive electrode and the negative electrode and played a role of isolation, and the stack was wound to obtain a bare cell. The bare cell was placed in an outer package, the above electrolyte solution was injected, and the bare cell was packaged to obtain a full battery.

    Preparation of Button Battery

    [0605] The positive electrode plate above, a negative electrode and an electrolyte solution were assembled together into a button battery in a button battery box.

    TABLE-US-00055 TABLE 7D Properties of positive electrode active material powder and performance of battery First Second coating coating No. Inner core layer layer Comparative LiMnPO.sub.4 example 1D Comparative LiMn.sub.0.85Fe.sub.0.15PO.sub.4 example 2D Comparative Li.sub.0.990Mg.sub.0.005Mn.sub.0.95Zn.sub.0.05PO.sub.4 example 3D Comparative Li.sub.0.90Nb.sub.0.01Mn.sub.0.6Fe.sub.0.4PO.sub.3.95F.sub.0.05 example 4D Comparative Li.sub.0.76Mg.sub.0.12Mn.sub.0.7Fe.sub.03P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 example 5D Comparative Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Zn.sub.0.6P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 example 6D Comparative Li.sub.1.068Mg.sub.0.001Mn.sub.0.7Fe.sub.0.3P.sub.0.88Si.sub.0.12O.sub.3.95F.sub.0.05 example 7D Comparative Li.sub.0.948Mg.sub.0.001Mn.sub.0.6Fe.sub.0.4P.sub.0.93Si.sub.0.07O.sub.3.88F.sub.0.12 example 8D Comparative Same as example 9D example 1 Comparative Same as 4% of example 10D example 1 amorphous Li.sub.2FeP.sub.2O.sub.7 Example 90D Same as 4% of example 1 crystalline Al.sub.2O.sub.3 Example 91D Same as 1% of 3% of example 1 amorphous crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 1D Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 2D Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 3D Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 4D Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 5D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 6D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 7D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 8D Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 9D Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 10D Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 11D Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 12D Same as 1% of 3% of example 1D crystalline crystalline Al.sub.4(P.sub.2O.sub.7).sub.3 Al.sub.2O.sub.3 Example 13D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2NiP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 14D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2MgP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 15D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2CoP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 16D Same as 1% 3% of example 1D crystalline crystalline Li.sub.2CuP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 17D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2ZnP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 18D Same as 1% of 3% of example 1D crystalline crystalline TiP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 19D Same as 1% of 3% of example 1D crystalline crystalline Ag.sub.4P.sub.2O.sub.7 Al.sub.2O.sub.3 Example 20D Same as 1% 3% of example 1D crystalline crystalline ZrP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 21D Same as Same as 3% of example 1D example 1 crystalline CoO Example 22D Same as Same as 3% of example 1D example 1 crystalline NiO Example 23D Same as Same as 3% of example 1D example 1 crystalline CuO Example 24D Same as Same as 3% of example 1D example 1 crystalline ZnO Example 25D Same as Same as 3% of example 1D example 1 crystalline TiO.sub.2 Example 26D Same as Same as 3% of example 1D example 1 crystalline MgO Example 27D Same as Same as 3% of example 1D example 1 crystalline ZrO.sub.2 Example 28D Same as Same as 3% of example 1D example 1 crystalline CaO Example 45D Same as 2% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 46D Same as 3% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 47D Same as 4% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 48D Same as 5.5% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 49D Same as 6% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 50D Same as 1% of 1% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 51D Same as 1% of 2% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 52D Same as 1% of 4% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 53D Same as 1% of 5.5% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 54D Same as 1% of 6% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 55D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 56D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 57D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 58D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 59D Same as 1% of 3% of example 1D crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 63D Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 64D Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 65D Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 66D Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 1% of 3% of crystalline crystalline Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 67D Same as 1% of 3% of example 1D crystalline crystalline LiAlP.sub.2O.sub.7 Al.sub.2O.sub.3 Example 68D Same as 1% of 3% of example 1D crystalline crystalline Zn.sub.2P.sub.2O.sub.7 Al.sub.2O.sub.3 Example 69D Same as Same as Same as example 1D example 1D example 1D Example 70D Same as Same as Same as example 1D example 1D example 1D Example 71D Same as Same as Same as example 1D example 1D example 1D Example 72D Same as Same as 3% of example 1D example 1D crystalline V.sub.2O.sub.5 Example 73D Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as example 1D example 1D Example 74D Li.sub.0.95Mg.sub.0.05Mn.sub.0.5Fe.sub.0.5P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as example 1D example 1D Example 75D Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as example 1D example 1D Example 76D Li.sub.0.95Mg.sub.0.05Mn.sub.0.75Fe.sub.0.25P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as example 1D example 1D Example 77D Li.sub.0.998Mg.sub.0.001Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 78D Li.sub.0.996Mg.sub.0.002Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 79D Li.sub.0.996Mg.sub.0.002Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 80D Li.sub.0.996Mg.sub.0.002Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 81D Li.sub.0.994Mg.sub.0.003Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 82D Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Fe.sub.0.55V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as example 1D example 1D Example 83D Li.sub.0.998 Mg.sub.0.001Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 (same as inner core of example 77) Same as 1% of example 1D crystalline Al.sub.2O.sub.3 Properties of positive electrode active material powder Li/Mn Lattice antisite Content of Third change defect Compacted Surface manganese coating rate concentration density oxygen element No. layer (1 ? y):y m:x (%) (%) (g/cm.sup.3) valency (%) Comparative 1% of 11.4 5.2 1.7 ?1.55 34.7 example 1D carbon Comparative 1% of 5.67 10.6 4.3 1.87 ?1.51 29.5 example 2D carbon Comparative 1% of 19 198 10.8 3.6 1.88 ?1.64 31.4 example 3D carbon Comparative 1% of 1.5 90 9.7 2.4 1.93 ?1.71 20.7 example 4D carbon Comparative 1% of 2.33 6.33 5.6 1.8 1.98 ?1.81 24.0 example 5D carbon Comparative 1% of 0.67 998 3.7 1.5 2.01 ?1.80 13.3 example 6D carbon Comparative 1% of 2.33 1068 7.8 1.5 2.05 ?1.75 24.2 example 7D carbon Comparative 1% of 1.5 948 8.4 1.4 2.16 ?1.79 20.3 example 8D carbon Comparative 1% of 1.86 994 6.3 1.6 2.21 ?1.82 20.8 example 9D carbon Comparative 1% of 1.86 994 5.7 1.2 2.22 ?1.98 21.7 example 10D carbon Example 90D 1% of 1.86 994 5.5 1.3 2.21 ?1.97 21.7 carbon Example 91D 1% of 1.86 994 5.8 1.3 2.2 ?1.96 21.7 carbon Example 1D 1% of 1.86 994 5.2 0.9 2.26 ?1.97 22.5 carbon Example 2D 1% of 1.86 977 1.4 0.4 2.41 ?1.98 21.7 carbon Example 3D 1% of 1.86 992 5 0.8 2.22 ?1.97 21.6 carbon Example 4D 1% of 1.86 997 4.9 0.6 2.2 ?1.97 21.6 carbon Example 5D 1% of 1.86 993 1.3 0.4 2.39 ?1.98 21.6 carbon Example 6D 1% of 1.86 993 1.5 0.3 2.45 ?1.99 21.7 carbon Example 7D 1% of 1.86 993 1.4 0.3 2.46 ?1.99 21.6 carbon Example 8D 1% of 1.86 993 1.3 0.3 2.49 ?1.99 21.6 carbon Example 9D 1% of 1.86 991 1.5 0.4 2.44 ?1.98 21.6 carbon Example 10D 1% of 1.86 995 1.4 0.3 2.48 ?1.99 21.7 carbon Example 11D 1% of 1.86 998 1.6 0.4 2.42 ?1.98 21.6 carbon Example 12D Same as 1.86 994 5.5 0.9 2.45 ?1.98 21.7 example 1D Example 13D Same as 1.86 994 5.3 0.8 2.22 ?1.98 21.7 example 1D Example 14D Same as 1.86 994 5.6 0.7 2.28 ?1.98 21.7 example 1D Example 15D Same as 1.86 994 5.4 0.7 2.25 ?1.98 21.7 example 1D Example 16D Same as 1.86 994 5.5 0.8 2.27 ?1.97 21.7 example 1D Example 17D Same as 1.86 994 5.5 0.9 2.24 ?1.98 21.7 example 1D Example 18D Same as 1.86 994 5.4 0.9 2.26 ?1.98 21.7 example 1D Example 19D Same as 1.86 994 5.6 0.8 2.27 ?1.98 21.7 example 1D Example 20D Same as 1.86 994 5.3 0.7 2.25 ?1.97 21.7 example 1D Example 21D Same as 1.86 994 5.5 0.7 2.25 ?1.97 21.7 example 1D Example 22D Same as 1.86 994 5.4 0.8 2.2 ?1.98 21.7 example 1D Example 23D Same as 1.86 994 5.3 0.9 2.24 ?1.98 21.7 example 1D Example 24D Same as 1.86 994 5.4 0.9 2.24 ?1.97 21.7 example 1D Example 25D Same as 1.86 994 5.6 0.8 2.27 ?1.98 21.7 example 1D Example 26D Same as 1.86 994 5.6 0.7 2.27 ?1.98 21.7 example 1D Example 27D Same as 1.86 994 5.5 0.7 2.25 ?1.98 21.7 example 1D Example 28D Same as 1.86 994 5.4 0.8 2.26 ?1.97 21.7 example 1D Example 45D 1% of 1.86 994 5.2 0.9 2.27 ?1.98 21.5 carbon Example 46D 1% of 1.86 994 5.2 0.9 2.25 ?1.99 21.3 carbon Example 47D 1% of 1.86 994 5.2 0.9 2.27 ?1.98 21.1 carbon Example 48D 1% of 1.86 994 5.2 0.9 2.24 ?1.97 20.8 carbon Example 49D 1% of 1.86 994 5.2 0.9 2.23 ?1.97 20.7 carbon Example 50D 1% of 1.86 994 5.2 0.9 2.24 ?1.98 22.1 carbon Example 51D 1% of 1.86 994 5.2 0.9 2.25 ?1.96 21.9 carbon Example 52D 1% of 1.86 994 5.2 0.9 2.24 ?1.99 21.5 carbon Example 53D 1% of 1.86 994 5.2 0.9 2.23 ?1.97 21.2 carbon Example 54D 1% of 1.86 994 5.2 0.9 2.26 ?1.98 21.1 carbon Example 55D 2% of 1.86 994 5.2 0.9 2.18 ?1.98 21.5 carbon Example 56D 3% of 1.86 994 5.2 0.9 2.16 ?1.96 21.3 carbon Example 57D 4% of 1.86 994 5.2 0.9 2.14 ?1.98 21.1 carbon Example 58D 5.5% of 1.86 994 5.2 0.9 2.08 ?1.97 20.8 carbon Example 59D 6% of 1.86 994 5.2 0.9 1.98 ?1.98 20.7 carbon Example 63D 1% of 1.5 18 5.3 1.1 2.21 ?1.97 19.9 carbon Example 64D 1% of 1.5 1100 5.2 0.9 2.25 ?1.98 19.9 carbon Example 65D 1% of 1.5 9 5.1 1.0 2.23 ?1.97 19.8 carbon Example 66D 1% of 999 19 4.9 1.0 2.37 ?1.98 33.2 carbon Example 67D 1% of 1.86 994 4.6 1.1 2.35 ?1.97 21.7 carbon Example 68D 1% of 1.86 994 4.8 1.0 2.37 ?1.97 21.7 carbon Example 69D Same as 1.86 994 5.3 1.1 2.02 ?1.9 22.5 example 1D Example 70D Same as 1.86 994 5.2 0.9 2.28 ?1.98 22.5 example 1D Example 71D Same as 1.86 994 5.1 1.2 2.3 ?1.97 22.5 example 1D Example 72D Same as 1.86 994 5.1 1.2 2.42 ?1.97 21.7 example 1D Example 73D Same as 99 19 8.1 3.9 2.51 ?1.96 33.2 example 1D Example 74D Same as 1 19 5 1.3 2.61 ?1.97 33.2 example 1D Example 75D Same as 4 19 4.7 1.1 2.63 ?1.98 33.2 example 1D Example 76D Same as 3 19 4.4 0.9 2.71 ?1.96 33.2 example 1D Example 77D Same as 1.5 998 4 1 2.68 ?1.98 20 example 1D Example 78D Same as 1.2 498 3.8 0.9 2.57 ?1.97 18.3 example 1D Example 79D Same as 1.5 498 4.3 4 2.65 ?1.97 20 example 1D Example 80D Same as 1.2 498 4.8 2.2 2.66 ?1.98 18.3 example 1D Example 81D Same as 1.2 331.3 4.4 1.5 2.65 ?1.97 18.3 example 1D Example 82D Same as 0.67 998 5.1 2.3 2.8 ?1.98 13.3 example 1D Example 83D Same as 1.5 998 5.2 2.1 2.59 ?1.9 20 example 1D Properties of positive electrode active material powder Performance of battery 3 C Expansion Number of Weight charge Dissolution Capacity of cell cycles for Content of ratio constant of Mn and of button upon 30 d capacity phosphorus of Mn current Fe after battery of storage retention element element to rate cycling at 0.1 C at 60? C. rate of 80% No. (%) P element (%) (ppm) (mAh/g) (%) at 45? C. Comparative 19.6 1.77 50.1 2060 125.6 48.6 121 example 1D Comparative 19.5 1.51 50.4 1510 126.4 37.3 129 example 2D Comparative 19.7 1.60 51.7 1028 134.7 31.9 134 example 3D Comparative 19.5 1.06 62.3 980 141.3 30.8 148 example 4D Comparative 19.3 1.24 50.2 873 110.8 21.4 387 example 5D Comparative 18.8 0.71 65.8 574 74.3 15.8 469 example 6D Comparative 17.1 1.41 64.3 447 139.4 18.3 396 example 7D Comparative 17.7 1.14 63.9 263 141.7 22.7 407 example 8D Comparative 18.2 1.14 64.2 192 143.2 18.4 552 example 9D Comparative 18.8 1.15 63.7 156 150.2 6.7 802 example 10D Example 90D 18.8 1.15 62.5 164 149.9 6.4 860 Example 91D 18.8 1.15 67.1 143 151.2 4.2 1013 Example 1D 19.5 1.15 68.1 21 157.3 2.2 1268 Example 2D 18.8 1.15 77.6 9 157.6 2.2 1462 Example 3D 18.7 1.15 65.8 23 155 2.6 1287 Example 4D 18.7 1.15 65.7 26 153.1 2.5 1184 Example 5D 18.7 1.15 78.6 18 157.2 2.1 1469 Example 6D 18.8 1.15 79.5 22 158.4 2.3 1463 Example 7D 18.7 1.15 77.6 20 159.1 2.2 1416 Example 8D 18.7 1.15 76.8 20 158.6 2.2 1462 Example 9D 18.7 1.15 77.9 22 157.6 2.3 1537 Example 10D 18.8 1.15 80.1 19 158.8 2.3 1508 Example 11D 18.7 1.15 77.6 18 157.3 2.2 1526 Example 12D 18.8 1.15 81.6 40 158.1 2.5 1524 Example 13D 18.8 1.15 64.8 40 152.4 2.6 1179 Example 14D 18.8 1.15 63.1 42 154.9 2.8 1203 Example 15D 18.8 1.15 62.7 39 153.7 2.7 1246 Example 16D 18.8 1.15 65.3 41 153.7 2.6 1207 Example 17D 18.8 1.15 65.7 40 152.6 2.7 1285 Example 18D 18.8 1.15 62.7 40 153.8 2.8 1286 Example 19D 18.8 1.15 63.7 41 154.6 2.8 1308 Example 20D 18.8 1.15 64.2 39 152.1 2.6 1254 Example 21D 18.8 1.15 65.3 40 152.8 2.7 1206 Example 22D 18.8 1.15 65.2 39 153.4 2.8 1189 Example 23D 18.8 1.15 63.1 40 152.1 2.6 1169 Example 24D 18.8 1.15 63.7 40 153.3 2.6 1208 Example 25D 18.8 1.15 62.1 41 152.8 2.7 1218 Example 26D 18.8 1.15 65.8 38 153.4 2.7 1264 Example 27D 18.8 1.15 61.8 37 154.6 2.8 1227 Example 28D 18.8 1.15 62.1 42 153.8 2.9 1254 Example 45D 18.6 1.15 65.8 18 152.7 2.2 1403 Example 46D 18.4 1.15 63.7 15 150.7 2 1497 Example 47D 18.3 1.15 61.9 13 147.2 1.8 1611 Example 48D 18.0 1.15 60.8 8 145.1 1.6 1708 Example 49D 17.9 1.15 59.7 8 143.6 1.5 1864 Example 50D 19.2 1.15 64.1 21 153.1 3.3 1045 Example 51D 19.0 1.15 66.1 27 155.7 2.8 1362 Example 52D 18.6 1.15 69.8 22 153.8 2.1 1462 Example 53D 18.4 1.15 71.8 24 152.1 1.8 1598 Example 54D 18.3 1.15 75.9 19 148.6 1.6 1706 Example 55D 18.6 1.15 69.8 26 157.8 2.2 1224 Example 56D 18.4 1.15 73.8 25 159.4 2.3 1213 Example 57D 18.3 1.15 78.6 23 157.8 2.4 1257 Example 58D 18.0 1.15 82.9 27 153.1 2.3 1268 Example 59D 17.9 1.15 84.6 29 148.6 2.1 1197 Example 63D 16.8 1.15 85.9 31 153.7 2.2 1208 Example 64D 16.8 1.18 84.3 29 154.1 2.1 1197 Example 65D 17.6 1.12 83.6 35 155.2 2.0 1103 Example 66D 18.0 1.85 84.1 38 154.8 2.1 1086 Example 67D 18.8 1.15 83.7 36 155.2 2.2 1124 Example 68D 18.8 1.15 84.1 38 156.3 2.1 1076 Example 69D 19.5 1.15 50.2 40 148.6 4.8 853 Example 70D 19.5 1.15 70.1 25 155.6 2.3 1123 Example 71D 19.5 1.15 72.8 20 156.1 2.1 1305 Example 72D 18.8 1.15 85.3 45 154.8 2.5 1135 Example 73D 18 1.85 53.7 700 131.7 31 546 Example 74D 18 1.85 84.2 46 154.9 3.2 1208 Example 75D 18 1.85 82.9 49 156.1 3 1176 Example 76D 18 1.85 83.1 54 154.3 2.8 1105 Example 77D 18.8 1.07 85.5 55 155.8 3.2 1064 Example 78D 18.8 0.98 84.9 58 156.2 2.9 1018 Example 79D 18.8 1.07 84.5 49 156.7 3.2 1147 Example 80D 18.8 0.98 84.1 47 155.9 3.4 1095 Example 81D 18.8 0.98 83.4 34 156.1 3.1 1034 Example 82D 18.8 0.71 82.9 38 157.2 2.9 1127 Example 83D 18.8 1.07 83.1 29 155.4 2.7 1094

    TABLE-US-00056 TABLE 8D Parameters of interplanar spacing and crystal-orientation included angle of pyrophosphate in first coating layer Included angle of crystal Interplanar orientation spacing (111) First Second Third of pyro- of pyro- coating coating coating phosphate phosphate No. Inner core layer layer layer (nm) (?) Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.10.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.977Mg.sub.0.001Mn.sub.0.65Fe.sub.0.34Ti.sub.0.01P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 2D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.992W.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.00 1% of 3% of 1% of 0.303 29.496 3D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.997Al.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% of 1% of 0.303 29.496 4D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 5D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 6D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Co.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 7D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.993Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Ni.sub.0.005P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 0.303 29.496 8D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.991Nb.sub.0.001Mn.sub.0.65Fe.sub.0.349Ti.sub.0.001P.sub.0.999S.sub.0.001O.sub.3.999Cl.sub.0.001 1% of 3% of 1% of 0.303 29.496 9D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.995Nb.sub.0.001Mn.sub.0.65Fe.sub.0.34V.sub.0.005Mg.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% of 1% of 0.303 29.496 10D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.65Fe.sub.0.345V.sub.0.005P.sub.0.999Si.sub.0.001O.sub.3.999Br.sub.0.001 1% of 3% of 1% of 0.303 29.496 11D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as Same as 3% of Same as 0.303 29.496 21D example 1D example 1D crystalline Example 1 CoO Example Same as Same as 3% of Same as 0.303 29.496 22D example 1D example 1D crystalline example 1D NiO Example Same as Same as 3% of Same as 0.303 29.496 23D example 1D example 1D crystalline example 1D CuO Example Same as Same as 3% of Same as 0.303 29.496 24D example 1D example 1 crystalline example 1D ZnO Example Same as Same as 3% of Same as 0.303 29.496 25D example 1D example 1D crystalline example 1D TiO.sub.2 Example Same as Same as 3% of Same as 0.303 29.496 26D example 1D example 1D crystalline example 1D MgO Example Same as Same as 3% of Same as 0.303 29.496 27D example 1D example 1D crystalline example 1D ZrO.sub.2 Example Same as Same as 3% of Same as 0.303 29.496 28D example 1D example 1 crystalline example 1D CaO Example Same as 2% of 3% of 1% of 0.303 29.496 45D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 3% of 3% of 1% of 0.303 29.496 46D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 4% of 3% of 1% of 0.303 29.496 47D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 5.5% of 3% of 1% of 0.303 29.496 48D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 6% of 3% of 1% of 0.303 29.496 49D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 1% of 1% of 0.303 29.496 50D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 2% of 1% of 0.303 29.496 51D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 4% of 1% of 0.303 29.496 52D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 5.5% of 1% of 0.303 29.496 53D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 6% of 1% of 0.303 29.496 54D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 2% of 0.303 29.496 55D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 3% of 0.303 29.496 56D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 4% of 0.303 29.496 57D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 5.5% of 0.303 29.496 58D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as 1% of 3% of 6% of 0.303 29.496 59D example 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.9Mg.sub.0.05Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.9F.sub.0.1 1% of 3% of 1% of 0.303 29.496 63D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.1.1Mg.sub.0.001Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.9Si.sub.0.1O.sub.3.998F.sub.0.002 1% of 3% of 1% of 0.303 29.496 64D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.9Mg.sub.0.1Mn.sub.0.6Fe.sub.0.395V.sub.0.005P.sub.0.95Si.sub.0.05O.sub.3.95F.sub.0.05 1% of 3% of 1% of 0.303 29.496 65D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.999Fe.sub.0.001P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 1% of 3% of 1% of 0.303 29.496 66D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as Same as Same as Same as 0.303 29.496 69D example 1D example 1D example 1D example 1D Example Same as Same as Same as Same as 0.303 29.496 70D example 1D example 1D example 1D example 1D Example Same as Same as Same as Same as 0.303 29.496 71D example 1D example 1D example 1D example 1D Example Same as Same as 3% of Same as 0.303 29.496 72D example 1D example 1D crystalline example 1D V.sub.2O.sub.5 Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.99Fe.sub.0.01P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as Same as 0.303 29.496 73D example 1D example 1D example 1D Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.5Fe.sub.0.5P.sub.0.96S.sub.10.04O.sub.3.99F.sub.0.01 Same as Same as Same as 0.303 29.496 74D example 1D example 1D example 1D Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.8Fe.sub.0.2P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as Same as 0.303 29.496 75D example 1D example 1D example 1D Example Li.sub.0.95Mg.sub.0.05Mn.sub.0.75Fe.sub.0.25P.sub.0.96Si.sub.0.04O.sub.3.99F.sub.0.01 Same as Same as Same as 0.303 29.496 76D example 1D example 1D example 1D Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 77D example 1D example 1D example 1D Example Li.sub.0.996Mg.sub.0.002Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 78D example 1D example 1D example 1D Example Li.sub.0.996Mg.sub.0.002Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 79D example 1D example 1D example 1D Example Li.sub.0.996Mg.sub.0.002Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 80D example 1D example 1D example 1D Example Li.sub.0.994Mg.sub.0.003Mn.sub.0.55Fe.sub.0.40V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 81D example 1D example 1D example 1D Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.4Fe.sub.0.55V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as Same as Same as 0.303 29.496 82D example 1D example 1D example 1D Example Li.sub.0.998Mg.sub.0.001Mn.sub.0.60Fe.sub.0.35V.sub.0.05P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 Same as 1% of Same as 0.303 29.496 83D example 1D crystalline example 1D Al.sub.2O.sub.3

    [0606] It can be seen from Tables 7D-8D that compared with comparative examples, the positive electrode active materials of the examples achieve a smaller lattice change rate, a smaller Li/Mn antisite defect concentration, a larger compacted density, a surface oxygen valency more closer to ?2 valence, less Mn and Fe dissolution after cycling, and better battery performance, such as a higher capacity of a button battery, better high-temperature storage performance, higher safety performance and better cycling performance.

    TABLE-US-00057 TABLE 9D Performance test results of positive electrode active materials (with the first coating layer, second coating layer and third coating layer in examples 29D-44D being same as those in example 1D) Thickness Thickness Thickness of first of second of third Lattice coating coating coating change layer layer layer rate No. Inner core (1 ? y):y m:x (nm) (nm) (nm) (%) Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.68Fe.sub.0.3V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 2.26 997 3 6 5 6.3 29D Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.58Fe.sub.0.4V.sub.0.02P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 1.45 997 3 6 5 6.5 30D Example Li.sub.0.997Mg.sub.0.001Mn.sub.0.65Fe.sub.0.3V.sub.0.05P.sub.0.999N.sub.0.001O.sub.3.999F.sub.0.001 2.17 997 3 6 5 6.9 31D Example Li.sub.0.988Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.999F.sub.0.001 1.71 197.6 3 6 5 5.5 32D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.995S.sub.0.005O.sub.3.999F.sub.0.001 1.71 196.8 3 6 5 4.3 33D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.35V.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.71 196.8 3 6 5 3.3 34D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Co.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.60 196.8 3 6 5 1.4 35D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.20V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 3.25 196.8 3 6 5 1.3 36D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.05V.sub.0.05Co.sub.0.15P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 15.0 196.8 3 6 5 1.7 37D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.65Fe.sub.0.25V.sub.0.05Ni.sub.0.05P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.60 196.8 3 6 5 2.4 38D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.75Fe.sub.0.10V.sub.0.05Ni.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 7.50 196.8 3 6 5 2 39D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 4.67 196.8 3 6 5 1.9 40D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.6Fe.sub.0.25V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 2.40 196.8 3 6 5 1.6 41D Example Li.sub.0.984Mg.sub.0.005Mn.sub.0.5Fe.sub.0.35V.sub.0.05Co.sub.0.10P.sub.0.999S.sub.0.001O.sub.3.995F.sub.0.005 1.43 196.8 3 6 5 1.2 42D Example Li.sub.1.01Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.9Si.sub.0.1O.sub.3.92F.sub.0.08 4.67 202 3 6 5 2.3 43D Example Li.sub.0.97Mg.sub.0.005Mn.sub.0.7Fe.sub.0.15V.sub.0.05Co.sub.0.10P.sub.0.92Si.sub.0.08O.sub.3.9F.sub.0.1 4.67 194 3 6 5 1.8 44D Example Same as example 1D 1.86 994 1 6 5 5.1 84D Example Same as example 1D 1.86 994 10 6 5 5.2 85D Example Same as example 1D 1.86 994 3 2 5 5.1 86D Example Same as example 1D 1.86 994 3 25 5 5 87D Example Same as example 1D 1.86 994 3 6 2 5.1 88D Example Same as example 1D 1.86 994 3 6 25 5.2 89D Expansion 3 C of cell Number of Li/Mn charge Dissolution Capacity upon cycles for antisite constant of Mn and of button 30 d of capacity defect Compacted Surface current Fe after battery storage retention concentration density oxygen rate cycling at 0.1 C at 60? C. rate of 80% No. (%) (g/cm.sup.3) valency (%) (ppm) (mAh/g) (%) at 45? C. Example 0.4 2.44 ?1.98 75.8 9 151.3 2.3 1356 29D Example 0.3 2.43 ?1.99 73.5 11 156.4 2.1 1389 30D Example 0.5 2.51 ?1.95 75.6 12 153.6 2.2 1462 31D Example 0.4 2.15 ?1.97 80.6 9 155.8 1.7 1381 32D Example 0.6 2.39 ?1.96 80.8 9 157.3 2 1356 33D Example 0.5 2.37 ?1.99 81.6 12 155.3 2.1 1246 34D Example 0.3 2.42 ?1.98 81.3 8 157.8 2.2 1426 35D Example 0.3 2.41 ?1.98 78.6 13 156.2 2.2 1483 36D Example 0.3 2.39 ?1.95 81.4 9 153.9 2.6 1367 37D Example 0.4 2.41 ?1.94 79.8 10 152.8 2.6 1352 38D Example 0.4 2.42 ?1.96 80.5 7 156.7 2.8 1359 39D Example 0.5 2.39 ?1.99 83.4 8 150.8 2.2 1276 40D Example 0.4 2.4 ?1.97 77.9 9 151.9 2.1 1364 41D Example 0.3 2.41 ?1.99 80.3 11 151.8 2.5 1362 42D Example 0.5 2.18 ?1.97 81.4 8 146.9 2.3 1358 43D Example 0.4 2.25 ?1.98 80.5 7 143.2 1.8 1365 44D Example 0.9 2.35 ?1.97 68.4 32 157.3 2.8 1002 84D Example 1 2.15 ?1.97 68.3 18 151.2 2.2 1345 85D Example 0.9 2.34 ?1.98 67.9 31 157.3 2.7 1315 86D Example 1.1 2.16 ?1.97 68.5 17 150.1 2.2 1214 87D Example 0.9 2.38 ?1.98 60.2 21 145.6 2.1 1385 88D Example 1 2.1 ?1.97 72.5 21 152.1 2.5 1102 89D

    [0607] It can be seen from Table 9D that by doping lithium manganese iron phosphate at all the Li site, manganese site, phosphorus site and O site thereof and three-layer coating, the present application achieves a smaller lattice change rate, a smaller Li/Mn antisite defect concentration, a larger compacted density, a surface oxygen valency more closer to ?2 valence, less Mn and Fe dissolution after cycling, and better battery performance, such as a higher capacity of a button battery, better high-temperature storage performance, higher safety performance and better cycling performance.

    TABLE-US-00058 TABLE 10D Performance test results of prepared positive electrode active materials Crystallinity Lattice First Second Third of change Example coating coating coating pyrophosphate rate No. Inner core layer layer layer (%) (%) Example Li.sub.0.994Mo.sub.0.001Mn.sub.0.65Fe.sub.0.35P.sub.0.999Si.sub.0.001O.sub.3.999F.sub.0.001 1% of 3% of 1% of 100 5.2 1D crystalline crystalline carbon Li.sub.2FeP.sub.2O.sub.7 Al.sub.2O.sub.3 Example Same as Same as Same as Same as 30 5.1 60D example 1D example 1D example 1D example 1D Example Same as Same as Same as Same as 50 5.1 61D example 1D example 1D example 1D example 1D Example Same as Same as Same as Same as 70 5.1 62D example 1D example 1D example 1D example 1D Expansion 3 C of cell Number of Li/Mn charge Dissolution Capacity upon 30 cycles for antisite constant of Mn and of button d of capacity defect Compacted Surface current Fe after battery storage retention Example concentration density oxygen rate cycling at 0.1 C at 60? C. rate of 80% No. (%) (g/cm.sup.3) valency (%) (ppm) (mAh/g) (%) at 45? C. Example 0.9 2.26 ?1.97 68.1 21 157.3 2.2 1268 1D Example 0.8 2.18 ?1.97 64.8 84 151.2 3.3 1137 60D Example 0.8 2.22 ?1.97 65.7 61 153.7 2.7 1204 61D Example 0.8 2.23 ?1.98 66.9 37 155.8 2.9 1246 62D

    [0608] It can be seen from Table 10D that as the crystallinity of pyrophosphate in the positive electrode active material increases, the positive electrode active material has a gradually increased compacted density, increased 3 C charge constant current rate, less dissolution of Mn and Fe after cycling, an increased capacity of a button battery, and improved high-temperature storage performance, safety performance and cycling performance.

    [0609] The above provides a detailed description of some embodiments of the present application. However, the present application is not limited to the specific details of the above embodiments and multiple simple variations of the technical solution can be made within the scope of the technical concept of the present application, all of which fall within the scope of protection of the present application.

    [0610] Furthermore, it should be noted that the various specific technical features described in the detailed description of embodiments above can be combined in any suitable way without contradiction.

    [0611] In addition, any combination of various different embodiments of the present application is also accessible and should be regarded as the disclosure of the present application as long as same does not depart from the ideas of the present application.

    [0612] In the description of the present application, it should be understood that the orientation or positional relationships indicated by terms upper, lower, front, rear, top, bottom, inner, and outer, etc., is based on the orientation or positional relationships shown in the accompanying drawings and is merely for ease of description of the present application and simplification of the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation or be constructed and operated in a described orientation, and therefore cannot be construed as limiting the present application.