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POSITIVE ELECTRODE MATERIAL, PREPARATION METHOD THEREOF AND LITHIUM-ION BATTERY

20250125351 · 2025-04-17

    Inventors

    Cpc classification

    International classification

    Abstract

    Provided are a positive electrode material, a preparation method thereof and a lithium-ion battery. The positive electrode material has a composition as represented by formula (I): Ni.sub.xCo.sub.yMn.sub.1-x-yD.sub.kLi.sub.zO.sub.2 (I); where value ranges of x, y, z and k in the positive electrode material are respectively as follows: 0.6<x<1,0<y<0.2, and x+y<1; 1z1.05, 0k0.05; D is a modifying element including at least one of S, P, F, B, Al, Ti, Mg, Cr, Zr, V, Nb, Y, W, Ta, Co, Ce and Zn. A three-electrode battery cell is prepared with the positive electrode material of the present disclosure, and a change rate of an electrochemical active surface area of the positive electrode material is less than 5% during charge and discharge cycles of the three-electrode battery cell.

    Claims

    1. A positive electrode material, wherein the positive electrode material has a composition as shown by formula (I):
    Ni.sub.xCo.sub.yMn.sub.1-x-yD.sub.kLi.sub.zO.sub.2(I); wherein value ranges of x, y, z and k in the positive electrode material are respectively as follows: 0.6<x<1, 0<y<0.2, and x+y<1; 1z1.05, 0k0.05; wherein D is a modifying element, and the modifying element comprises at least one of S, P, F, B, Al, Ti, Mg, Cr, Zr, V, Nb, Y, W, Ta, Co, Ce and Zn; a value range of a compaction density, PD, of a positive electrode piece prepared by the positive electrode material is as follows: 3.0 g/cm.sup.3<PD<3.8 g/cm.sup.3; a particle size distribution of the positive electrode material is as follows: D10<8 m, 5 m<D50<15 m, and 10 m<D90<30 m; a value range of a lithium-nickel mixing degree, Li/Ni mixing, of the positive electrode material is as follows: 0%<Li/Ni mixing<2.5%; a three-electrode battery cell is prepared with the positive electrode material, and a change rate of electrochemical active surface area a of the positive electrode material is less than 5% during a charge and discharge cycle of the three-electrode battery cell.

    2. The positive electrode material according to claim 1, wherein a calculation mode of the change rate of electrochemical active surface area a is represented by formula (II): a = ( S n - S 0 ) / n 100 % ; ( II ) wherein n is a number of the charge and discharge cycle of the three-electrode battery cell, S.sub.0 is an electrochemical active surface area of the positive electrode material at a first cycle of the three-electrode battery cell; S.sub.n is an electrochemical active surface area of the positive electrode material after n charge and discharge cycle of the three-electrode battery cell.

    3. The positive electrode material according to claim 1, wherein the electrochemical active surface area is obtained by following method: testing a positive electrode overpotential response n of the three-electrode battery cell caused by an exciting current I; performing least-square fitting on exciting currents I with different current sizes and corresponding positive electrode overpotential responses through a Bulter-Volmer equation to obtain the electrochemical active surface area of the positive electrode material.

    4. The positive electrode material according to claim 2, wherein the electrochemical active surface area is obtained by following method: testing a positive electrode overpotential response n of the three-electrode battery cell caused by an exciting current I; performing least-square fitting on exciting currents I with different current sizes and corresponding positive electrode overpotential responses through a Bulter-Volmer equation to obtain the electrochemical active surface area of the positive electrode material.

    5. The positive electrode material according to claim 3, wherein the Bulter-Volmer equation expresses a relationship between the exciting current I and an exchange current i.sub.0; wherein the exchange current i.sub.0 is proportional to the electrochemical active surface area; the exchange current i.sub.0 is a product of the electrochemical active surface area and a proportional coefficient.

    6. The positive electrode material according to claim 4, wherein the Bulter-Volmer equation expresses a relationship between the exciting current I and an exchange current i.sub.0; wherein the exchange current i.sub.0 is proportional to the electrochemical active surface area; the exchange current i.sub.0 is a product of the electrochemical active surface area and a proportional coefficient.

    7. The positive electrode material according to claim 5, wherein the Bulter-Volmer equation is represented by Formula (III): I = N .Math. 1 R CT .Math. A .Math. [ e 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT - e - 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT ] ( III ) wherein I is the exciting current, N is the proportional coefficient obtained by fitting, R.sub.S is ohmic impedance, R.sub.SEI is interfacial impedance, R.sub.CT is charge transfer impedance, F is Faraday constant, R is gas constant, T is temperature of the three-electrode battery cell during a test, A is the electrochemical active surface area obtained by fitting, and is the positive electrode overpotential response.

    8. The positive electrode material according to claim 6, wherein the Bulter-Volmer equation is represented by Formula (III): I = N .Math. 1 R CT .Math. A .Math. [ e 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT - e - 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT ] ( III ) wherein I is the exciting current, N is the proportional coefficient obtained by fitting, R.sub.S is ohmic impedance, R.sub.SEI is interfacial impedance, R.sub.CT is charge transfer impedance, F is Faraday constant, R is gas constant, T is temperature of the three-electrode battery cell during a test, A is the electrochemical active surface area obtained by fitting, and is the positive electrode overpotential response.

    9. A preparation method of a positive electrode material, wherein the preparation method is used for preparing the positive electrode material according to claim 1, and the preparation method comprises the following steps: primary calcination: calcining a nickel-cobalt-manganese ternary precursor to obtain an oxide precursor P.sub.1; secondary calcination: mixing the oxide precursor P.sub.1 with a first lithium source, and calcining to obtain an oxide precursor P.sub.2; tertiary calcination: mixing the oxide precursor P.sub.2 with a second lithium source, and calcining to obtain the positive electrode material.

    10. The preparation method according to claim 9, wherein an amount of substance M.sub.1 of lithium element in the first lithium source and a sum of amounts of substances M.sub.0 of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary precursor satisfy: 0<M.sub.1/M.sub.00.8; an amount of substance M.sub.2 of lithium element in the second lithium source, the amount of substance M.sub.1 of lithium element in the first lithium source and the sum of amounts of substances M.sub.0 of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary precursor satisfy: 1-M.sub.1/M.sub.0M.sub.2/M.sub.01.05M.sub.1/M.sub.0.

    11. The preparation method according to claim 9, wherein process conditions of the primary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 300-500 C., and a calcination time of 1-5h.

    12. The preparation method according to claim 9, wherein process conditions of the secondary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 2-8h, and a cooling rate controlled to 2-5 C./min.

    13. The preparation method according to claim 11, wherein process conditions of the secondary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 2-8h, and a cooling rate controlled to 2-5 C./min.

    14. The preparation method according to claim 9, wherein process conditions of the tertiary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 6-20h, and a cooling rate controlled to 2-5 C./min.

    15. The preparation method according to claim 11, wherein process conditions of the tertiary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 6-20h, and a cooling rate controlled to 2-5 C./min.

    16. The preparation method according to claim 12, wherein process conditions of the tertiary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 6-20h, and a cooling rate controlled to 2-5 C./min.

    17. The preparation method according to claim 13, wherein process conditions of the tertiary calcination comprise: a heating rate of 2-5 C./min, a calcination temperature of 600-1000 C., a calcination time of 6-20h, and a cooling rate controlled to 2-5 C./min.

    18. The preparation method according to claim 9, wherein in steps of the tertiary calcination, a dopant, the oxide precursor P.sub.2 and the second lithium source are mixed and calcined; wherein the dopant comprises at least one element of S, P, F, B, Al, Ti, Mg, Cr, Zr, V, Nb, Y, W and Ta.

    19. The preparation method according to claim 9, wherein the preparation method further comprises performing a sintering for modification on the positive electrode material for one or more times; wherein the sintering for modification includes mixing and sintering the positive electrode material and a coating agent, and a sintering temperature of the sintering for modification is not more than 600 C.; wherein the coating agent comprises at least one element of Co, P, F, B, Al, Ti, Mg, Cr, Zr, Ce, W and Zn.

    20. A battery, comprising the positive electrode material according to claim 1.

    Description

    BRIEF DESCRIPTION OF DRAWINGS

    [0041] The foregoing and/or additional aspects and advantages of the present disclosure will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

    [0042] FIG. 1 is a fitting diagram of a charging current and an overpotential of a positive electrode material H1 according to an embodiment of the present disclosure;

    [0043] FIG. 2 shows an ECSA change rate of a positive electrode material H1 according to an embodiment of the present disclosure;

    [0044] FIG. 3 is a fitting diagram of a charging current and an overpotential of a positive electrode material Q1 according to an embodiment of the present disclosure;

    [0045] FIG. 4 shows an ECSA change rate of a positive electrode material Q1 according to an embodiment of the present disclosure;

    [0046] FIG. 5 shows a comparison of cycle capacity retention rates of a positive electrode material H1 and a positive electrode material Q1 according to an embodiment of the present disclosure;

    [0047] FIG. 6 is a SEM image of a positive electrode material Q1 according to an embodiment of the present disclosure; and

    [0048] FIG. 7 is a SEM image of a positive electrode material H1 according to an embodiment of the present disclosure.

    DESCRIPTION OF EMBODIMENTS

    [0049] In order to make the above objects, features and advantages of the present disclosure more obvious and understandable, the technical solutions in embodiments of the present disclosure will be clearly and comprehensively described below. Apparently, the described embodiments are merely a part of rather than all embodiments of the present disclosure. All other embodiments obtained by persons of ordinary skill in the art based on embodiments of the present disclosure without creative labor belong to the protection scope of the present disclosure.

    [0050] Embodiments of the present disclosure provide a preparation method of a positive electrode material, the prepared positive electrode material and a battery prepared by the positive electrode material.

    [0051] On the one hand, since particles of the positive electrode material are broken in the cycling process, which results in a larger change rate of the electrochemical active surface area; and the preparation method provided by the embodiments adopts a refined lithium distribution and a multi-stage sintering process. Primary particles of the positive electrode material obtained by sintering with two additions of lithium sources are larger, so that when the secondary particles are broken in the cycling process, the change rate of the electrochemical active surface area is smaller.

    [0052] On the other hand, there are a variety of methods for determining the electrochemical active surface area in the related art. For example, ECSA is directly estimated by a gas adsorption BET specific surface area test method. This method utilizes the adsorption characteristics of particle surface to gas to estimate the surface area, and has the advantages of high test speed and good test stability. However, the surface area measured by the BET method is not exactly identical to the ECSA, and the BET surface area measures the surface size associated with gas adsorption; while the ECSA measures the surface size in contact with electrolyte solution. The two may be quite different for porous electrode materials. In addition, the BET test method is only applicable to the test of an initial electrode powder sample and is not applicable to the test of the electrode material in a battery cell, because in most cases, the electrode material in the battery cell has been mixed with conductive carbon, binder, etc., which is not easy to be separated out, and the BET test method cannot distinguish the surface area of the electrode material alone.

    [0053] For example, the electrochemical impedance spectroscopy (Electrochemical Impedance Spectroscopy, EIS) testing and the equivalent circuit fitting method are also common methods for determining the ECSA. The resistance response and capacitance response of a charge transfer reaction may be obtained by the EIS testing and fitting of the battery cell. The capacitance response is closely related to the ECSA of the electrode material, and may represent the relative magnitude of the ECSA. However, the surface of the electrode material is rough and porous in fact, and its capacitance response does not appear in the form of a pure capacitance component, but is manifested by some kind of constant-phase element, which makes it difficult to obtain the capacitance value. Therefore, the EIS fitting method for determining the ECSA has large limitations and also leads to large errors and mistakes in the results due to uncertainties in the model construction.

    [0054] In addition, cyclic voltammetry (CV) may also be used as an ECSA determination method. ECSA may be fitted by CV tests with different sweep speeds, but CV testing of ECSA needs to select a reasonable sweep voltage or search a suitable supporting electrolyte to avoid the Faraday reaction interval of the substance to be tested, which makes it difficult to measure ECSA by CV method in electrode materials.

    [0055] In this embodiment, for the determination of ECSA, the electrochemical active surface area of the material is calculated by fitting the Bulter-Volmer equation for different exciting currents I and corresponding positive electrode overpotential responses n.

    Embodiment 1

    [0056] This embodiment provides a preparation method of a positive electrode material, including the following steps.

    [0057] S10, primary calcination: obtaining a nickel-cobalt-manganese ternary precursor Ni.sub.0.85Co.sub.0.1Mn.sub.0.05(OH).sub.2, and calcining Ni.sub.0.85Co.sub.0.1Mn.sub.0.05(OH).sub.2 in air to obtain an oxide precursor P.sub.1.

    [0058] The process parameters of the primary calcination are as follows: the heating rate of 5 C./min, the calcination temperature of 500 C., and the calcination time of 2 h.

    [0059] S20, secondary calcination: calcining the oxide precursor P1 and a first lithium source in oxygen to obtain an oxide precursor P2. The first lithium source is lithium hydroxide monohydrate.

    [0060] The amount of substance M.sub.1 of lithium element in the first lithium source and the sum of amounts of substance M.sub.0 of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary precursor satisfy: M.sub.1/M.sub.0=0.4.

    [0061] The process conditions of the secondary calcination include: the heating rate of 2 C./min, the calcination temperature of 600 C., the calcination time of 2h, and the cooling rate controlled to 2 C./min.

    [0062] S30, tertiary calcination: calcining the oxide precursor P2 and a second lithium source in oxygen to obtain a positive electrode material H1. The second lithium source is a mixture of lithium hydroxide monohydrate and lithium nitrate (molar ratio 8:2).

    [0063] The amount of substance M.sub.2 of lithium element in the second lithium source and the sum of amounts of substance M.sub.0 of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary precursor satisfy: M.sub.2/M.sub.0=0.6025.

    [0064] The process conditions of the tertiary calcination include: the heating rate of 2 C./min, the calcination temperature of 750 C., the calcination time of 12h, and the cooling rate controlled to 2 C./min.

    [0065] The change rate of ECSA (i.e. the change rate of electrochemical active surface area a) of the above positive electrode material is determined as follows. [0066] 1. 9.5 g of the positive electrode material H1 is taken; a slurry is prepared according to the positive electrode material: HVDF:SH=95:2.5:2.5, and coated on an aluminum foil to form an electrode piece, and the surface density of the electrode piece is controlled to be 15 mg/cm.sup.2; the electrode piece is punched into small discs with a diameter of 1.5 cm; small discs are assembled into two button-type three-electrode batteries, noted as batteries H1-1 and H1-10; and the three-electrode lithium plating is completed. [0067] 2. The battery H1-1 is fully charged and left to stand for 1 hour, the equilibrium voltage is recorded, the EIS is tested, and the ohmic impedance R.sub.S, the interfacial impedance R.sub.SEI, and the charge transfer impedance R.sub.CT are fitted. [0068] 3. The battery H1-1 is charged with direct current for 10s for several times, and is left to stand for 60s after each charge to recover to the equilibrium state. The charging exciting current I is 0 mA, 0.1 mA, 0.2 mA, 0.4 mA, 0.6 mA, 0.8 mA, 1.2 mA, 1.5 mA, and 2 mA in sequence. The positive-reference voltage at the end of each charging step is recorded, and the difference between this voltage and the equilibrium voltage is the positive overpotential response n. [0069] 4. Different exciting currents I and the corresponding positive electrode overpotential responses of the battery H1-1, and the ohmic impedance R.sub.S, the interfacial impedance R.sub.SEI and the charge transfer impedance R.sub.CT that are obtained by fitting are substituted into the Bulter-Volmer equation for data fitting. The ECSA of the positive electrode material of the battery H1-1 is set to 1 (i.e., A=1), and the fitting is performing to obtain the proportional coefficient N to be 0.059.

    [0070] The Bulter-Volmer equation has the following form:

    [00004] I = N .Math. 1 R CT .Math. A .Math. [ e 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT - e - 0.5 .Math. F .Math. ( - I .Math. R s - I .Math. R SEI ) RT ] [0071] where I is the exciting current, N is the proportional coefficient obtained by fitting, R.sub.S is ohmic impedance, R.sub.SEI is interfacial impedance, R.sub.CT is charge transfer impedance, F is Faraday constant, R is gas constant, T is temperature of the three-electrode battery cell during a test, A is the electrochemical active surface area obtained by fitting, and is the positive electrode overpotential response. [0072] 5. The battery H1-10 is subjected to 10 cycles at a high temperature 45 C. and then fully charged, and operations of the above steps 2 and 3 are performed. Similarly, different exciting currents I and the corresponding positive electrode overpotential responses n, and the ohmic impedance R.sub.S, the interfacial impedance R.sub.SEI and the charge transfer impedance R.sub.CT that are obtained from fitting are substituted into the above Bulter-Volmer equation for data fitting. The proportional coefficient is set to be equal to that of the battery H1-1, i.e., N=0.059. The ESCA of the positive electrode material of the battery H1-10 relative to the positive electrode material of the battery H1-1 obtained by fitting according to the above method is 1.27. Therefore, the change rate of the ESCA a is (1.271)/10100%=2.7%.

    [0073] FIG. 1 is a fitting diagram of the exciting current I and the positive overpotential response n in this embodiment. FIG. 2 shows the relative values and the change rate of the ECSA a obtained by fitting in this embodiment.

    Comparative Embodiment 1

    [0074] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 1, the nickel-cobalt-manganese ternary precursor Ni.sub.0.85Co.sub.0.1Mn.sub.0.05(OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 750 C. at 2 C./min and then kept for 12h for sintering, obtaining Li.sub.1.025Ni.sub.0.85Co.sub.0.1Mn.sub.0.05O.sub.2 (noted as positive electrode material Q1).

    [0075] The change rate of the ECSA of the positive electrode material Q1 is measured, and the specific steps are the same as those in Embodiment 1. 9.5 g of the positive electrode material Q1 is taken to prepare a slurry, and the slurry is prepared into an electrode piece. The electrode piece is punched and assembled into two button-type three-electrode batteries, noted as batteries Q1-1 and Q1-10. The three-electrode lithium plating is completed. The battery Q1-1 is fully charged and left to stand for 1 hour for testing. The battery Q1-10 is subjected to 10 cycles at a high temperature of 45 C. and then fully charged for testing. According to the above method, the ESCA of the positive electrode material of the battery Q1-10 relative to the positive electrode material of the battery Q1-1 obtained by fitting according to the above method is 1.82. Therefore, the change rate of the ESCA is that (1.821)/10100%=8.2%.

    [0076] FIG. 3 is a fitting diagram of the exciting current I and the positive overpotential response n in this comparative embodiment. FIG. 4 shows the relative values and the change rate of the ECSA obtained by fitting in this comparative embodiment. Since the change rate of the ECSA of the positive electrode material Q1 is greater than 5%, indicating that the cycle stability of positive electrode material Q1 is poor. The cycle comparison between the positive electrode material H1 and the positive electrode material Q1 is shown in FIG. 5.

    TABLE-US-00001 TABLE 1 Positive electrode BET D50 D10 D90 D99 Dmax Dmin material (m.sup.2/g) (m) (m) (m) (m) (m) (m) H1 0.3406 10.216 5.429 18.444 25.109 28.767 2.581 Q1 0.4616 9.814 5.33 17.558 23.688 27.789 2.994

    [0077] Test parameters of the positive electrode material H1 and the positive electrode material Q1 are shown in Table 1. FIG. 7 is an electron micrograph of the positive electrode material H1 in Embodiment 1. FIG. 6 is an electron micrograph of the positive electrode material Q1 in Comparative Embodiment 1. It can be seen that the primary particles of the positive electrode material H1 provided in Example 1 have a larger particle size, and thus have a smaller change rate of ECSA.

    Embodiment 2

    [0078] This embodiment provides a preparation method of a positive electrode material. The preparation steps are referred to those in Embodiment 1, with the difference that: the nickel-cobalt-manganese ternary precursor is Ni.sub.0.85Co.sub.0.06Mn.sub.0.11(OH).sub.2; the time of the secondary calcination is 4h; and the calcination temperature of the tertiary calcination is 770 C. The obtained positive electrode material is noted as H2.

    Comparative Embodiment 2

    [0079] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 2, the nickel-cobalt-manganese ternary precursor Ni.sub.0.85Co.sub.0.06Mn.sub.0.11(OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 770 C. at 2 C./min and then kept for 12h for sintering.

    [0080] The obtained positive electrode material is noted as Q2.

    Embodiment 3

    [0081] This embodiment provides a preparation method of a positive electrode material. The preparation steps are referred to those in Embodiment 1, with the difference the that: nickel-cobalt-manganese ternary precursor is Ni.sub.0.9Co.sub.0.05Mn.sub.0.05(OH).sub.2; the time of the secondary calcination is 4h; and the calcination temperature of the tertiary calcination is 740 C. The obtained positive electrode material is noted as H3.

    Comparative Embodiment 3

    [0082] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 3, the nickel-cobalt-manganese ternary precursor Ni.sub.0.9Co.sub.0.05Mn.sub.0.05(OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 740 C. at 2 C./min and then kept for 12h for sintering. The obtained positive electrode material is noted as Q3.

    Embodiment 4

    [0083] This embodiment provides a preparation method of a positive electrode material. The preparation steps are referred to those in Embodiment 1, with the difference that: the nickel-cobalt-manganese ternary precursor is Ni.sub.0.92Co.sub.0.03Mn.sub.0.05 (OH).sub.2; the time of the secondary calcination is 4h; and the calcination temperature of the tertiary calcination is 740 C. The obtained positive electrode material is noted as H4.

    Comparative Embodiment 4

    [0084] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 4, the nickel-cobalt-manganese ternary precursor Ni.sub.0.92Co.sub.0.03Mn.sub.0.05(OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 740 C. at 2 C./min and then kept for 12h for sintering. The obtained positive electrode material is noted as Q4.

    Embodiment 5

    [0085] This embodiment provides a preparation method of a positive electrode material. The preparation steps are referred to those in Embodiment 1, with the difference that: the nickel-cobalt-manganese ternary precursor is Ni.sub.0.96Co.sub.0.01Mn.sub.0.03 (OH).sub.2; the time of the secondary calcination is 4h; and the calcination temperature of the tertiary calcination is 730 C. The obtained positive electrode material is noted as H5.

    Comparative Embodiment 5

    [0086] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 5, the nickel-cobalt-manganese ternary precursor Ni.sub.0.96Co.sub.0.01Mn.sub.0.03 (OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 730 C. at 2 C./min and then kept for 12h for sintering. The obtained positive electrode material is noted as Q5.

    Embodiment 6

    [0087] This embodiment provides a preparation method of a positive electrode material. The preparation steps are referred to those in Embodiment 1, with the difference that: the precursor is Ni.sub.0.92Mn.sub.0.08 (OH).sub.2. The obtained positive electrode material is noted as H6.

    Comparative Embodiment 6

    [0088] Samples in this embodiment are synthesized by a conventional primary sintering process. Referring to the ratio of each element in Embodiment 6, the precursor

    [0089] Ni.sub.0.92Mn.sub.0.08 (OH).sub.2 and lithium hydroxide monohydrate are mixed, heated under an oxygen atmosphere to 500 C. at 2 C./min and then kept for 2h, and then heated to 750 C. at 2 C./min and then kept for 12h for sintering. The obtained positive electrode material is noted as Q6.

    [0090] Performance tests are conducted on the positive electrode materials provided in Embodiments 2-6 and Comparative Embodiments 2-6, and the test results are shown in Tables 2 and 3. The testing method for the change rate of the ECSA is shown in Embodiment 1. Through the comparison of each performance parameter, the positive electrode material with better performance is prepared by the preparation method of the positive electrode material provided by the embodiments of the present disclosure, and the capacity retention rate of the positive electrode material in the cycling process is larger, and the growth rate of the DCR (Direct Current Resistance) is smaller.

    TABLE-US-00002 TABLE 2 Positive electrode material BET(m.sup.2/g) D10(m) D50(m) D90(m) H2 0.627 5.462 9.859 17.205 Q2 0.682 5.262 9.559 17.118 H3 0.5636 2.754 10.463 18.342 Q3 0.6045 2.455 10.278 18.023 H4 0.5922 2.544 10.703 17.722 Q4 0.625 2.653 10.572 18.021 H5 0.5873 2.965 10.084 18.005 Q5 0.6161 2.856 10.852 17.837 H6 0.5735 2.241 10.406 18.342 Q6 0.5983 2.457 10.372 18.842

    TABLE-US-00003 TABLE 3 Capacity Growth rate Capacity Growth rate Change retention rate of DCR retention rate of DCR Positive rate of after 200 after 200 after 200 after 200 electrode ECSA cycles at cycles at cycles at cycles at material (%) 25 C. (%) 25 C. (%) 45 C. (%) 45 C. (%) H2 3.2 97.24 1.73 94.88 7.52 Q2 8.7 95.18 1.65 91.26 20.68 H3 4.1 97.05 4.51 93.57 12.36 Q3 10.6 94.96 4.18 90.35 27.25 H4 3.9 96.84 4.67 93.54 14.53 Q4 11.5 94.17 4.9 89.27 30.32 H5 4.6 93.92 8.48 90.06 24.38 Q5 11.8 90.85 11.52 87.69 72.53 H6 4.7 94.77 7.85 88.63 25.36 Q6 14.3 90.2 10.26 81.94 64.89

    Embodiment 7

    [0091] This embodiment provides a series of positive electrode materials and preparation methods thereof, where the preparation method of each positive electrode material is referred to that in Embodiment 1, the difference between them lies in the selection of each process parameter, and the specific process parameters are shown in

    Table 4.

    TABLE-US-00004 TABLE 4 Embodiment 7-1 7-2 7-3 7-4 7-5 Primary Heating 3 C./min 2 C./min 5 C./min 4 C./min 5 C./min calcination rate Calcination 500 C. 500 C. 300 C. 300 C. 400 C. temperature Calcination 1 h 3 h 4 h 5 h 2 h time Secondary Heating 3 C./min 5 C./min 4 C./min 3 C./min 2 C./min calcination rate Calcination 600 C. 800 C. 700 C. 1000 C. 900 C. temperature Calcination 3 h 4 h 5 h 2 h 8 h time Cooling 3 C./min 5 C./min 4 C./min 3 C./min 2 C./min rate Tertiary Heating 2 C./min 4 C./min 3 C./min 5 C./min 5 C./min calcination rate Calcination 800 C. 700 C. 1000 C. 900 C. 600 C. temperature Calcination 6 h 10 h 15 h 20 h 18 h time Cooling 2 C./min 5 C./min 4 C./min 3 C./min 5 C./min rate

    [0092] In this embodiment, each performance parameter of the positive electrode materials was shown in Table 5.

    TABLE-US-00005 TABLE 5 Embodiment 7-1 7-2 7-3 7-4 7-5 Compaction density PD 3 3.2 3.3 3.15 3.1 (g/cm.sup.3) XRD refined lithium-nickel 1 1 2 0.5 0.5 mixing degree Li/Ni mixing(%) Change rate of ECSA (%) 2 1.2 3 4.2 2.3

    Embodiment 8

    [0093] This embodiment provides a positive electrode material and a preparation method thereof. The preparation method is referred to that in Embodiment 1, with the difference that: the dopant, the oxide precursor P2 and the second lithium source are mixed and calcined at the tertiary calcination in this embodiment, and the dopant is alumina.

    Embodiment 9

    [0094] This embodiment provides a positive electrode material and a preparation method thereof. The preparation method is referred to that in Embodiment 1, with the difference that: the dopant, the oxide precursor P2 and the second lithium source are mixed and calcined at the tertiary calcination in this embodiment, and the dopant is sulfur.

    Embodiment 10

    [0095] This embodiment provides a positive electrode material and a preparation method thereof. The preparation method is referred to that in Embodiment 1, with the difference that: the obtained positive electrode material is mixed with a coating agent for the sintering for modification in this embodiment.

    [0096] The coating agent is red phosphorus, the sintering temperature of the sintering for modification is 500 C., and the sintering time of the sintering for modification is 4h.

    Embodiment 11

    [0097] This embodiment provides a positive electrode material and a preparation method thereof. The preparation method is referred to that in Embodiment 1, with the difference that: the obtained positive electrode material is mixed with a coating agent for sintering for modification in this embodiment.

    [0098] The coating agent is magnesium hydroxide, the sintering temperature of the sintering for modification is 500 C., and the sintering time of the sintering for modification is 5h.

    [0099] Each performance parameter of the positive electrode materials provided in Embodiments 8-11 are shown in Table 6.

    TABLE-US-00006 TABLE 6 Embodiment 8 9 10 11 Compaction density PD 3.3 3.25 3.35 3.2 (g/cm.sup.3) XRD refined lithium- 1.5 1.8 1 0.5 nickel mixing degree Li/Ni mixing(%) Change rate of ECSA (%) 2.3 3 1.6 3.6

    [0100] Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present disclosure other than limiting the present disclosure. Although the present disclosure is described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent substitutions to some of technical features thereof. However, these modifications and substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of various embodiments of the present disclosure.