POSITIVE ELECTRODE ACTIVE MATERIAL AND PREPARATION METHOD THEREOF, POSITIVE ELECTRODE PLATE, BATTERY, AND ELECTRIC DEVICE

Abstract

The present application discloses a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery, and an electric device. The positive electrode active material includes:

##STR00001##

where M1 includes a rare earth element; M2 includes at least one of a group IA element, a group IIA element, a group IIIA element, a group IVA element, a group VA element, a group VIA element, and a transition element; and 0.6x1.2, 0<a0.5, 0<b0.4, 0.3c0.75, 0.001d0.05, 0e0.3, 0.10.1, 0f0.1, 0.005d/c0.05, and a+b+c+d+e=1.

Claims

1. A positive electrode active material, wherein the positive electrode active material comprises: ##STR00004## wherein M1 comprises a rare earth element; M2 comprises at least one of a group IA element, a group IIA element, a group IIIA element, a group IVA element, a group VA element, a group VIA element, and a transition element; and 0.6x1.2, 0<a0.5, 0<b0.4, 0.3c0.75, 0.001d0.05, 0e0.3, 0.10.1, 0f0.1, 0.005d/c0.05, and a+b+c+d+e=1.

2. The positive electrode active material according to claim 1, wherein the rare earth element comprises at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

3. The positive electrode active material according to claim 1, wherein M2 comprises at least one of B, Mg, Al, Si, K, Ca, Ga, Ge, Se, Rb, Sr, In, Sn, Sb, Te, Sc, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au.

4. The positive electrode active material according to claim 1, wherein 0.01d/c0.03.

5. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies at least one of the following conditions: ##STR00005##

6. The positive electrode active material according to claim 1, wherein 1.75(a+b+c)/b9.5.

7. The positive electrode active material according to claim 1, wherein 0.8<x1.0, a phase of the positive electrode active material comprises an O3 phase, a space group comprises R3m, and an interlayer spacing ranges from 0.53 nm to 0.55 nm.

8. The positive electrode active material according to claim 1, wherein 0.6x0.8, a phase of the positive electrode active material comprises a P2 phase, a space group comprises P63/mmc, and an interlayer spacing ranges from 0.54 nm to 0.57 nm.

9. The positive electrode active material according to claim 1, wherein a pH value of a soaking solution of the positive electrode active material is less than or equal to 13, optionally, the pH value of the soaking solution of the positive electrode active material is less than or equal to 12.7, more optionally, the pH value of the soaking solution of the positive electrode active material is 11.0<pH12.7.

10. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies at least one of the following conditions: D.sub.v50 of the positive electrode active material ranges from 3 m to 30 m; a specific surface area of the positive electrode active material ranges from 0.1 m.sup.2/g to 5 m.sup.2/g; a tap density of the positive electrode active material ranges from 1 g/cm.sup.3 to 3 g/cm.sup.3; and a compacted density of the positive electrode active material under a pressure of 300 MPa ranges from 3.0 g/cm.sup.3 to 4.0 g/cm.sup.3.

11. A method for preparing the positive electrode active material according to claim 1, comprising: mixing an Na source, an Ni source, an Fe source, an Mn source, an M1 source, and an M2 source to obtain a precursor; and calcining the precursor to obtain the positive electrode active material.

12. A method for preparing the positive electrode active material according to claim 1, comprising: mixing an Ni source, an Fe source, an Mn source, an M1 source, and an M2 source with water to obtain a mixed solution; reacting the solution with a precipitant to obtain a precursor; and mixing the precursor with an Na source and calcining to obtain the positive electrode active material.

13. A positive electrode plate, wherein the positive electrode plate comprises the positive electrode active material according to claim 1.

14. A battery, wherein the battery comprises the positive electrode plate according to claim 13.

15. An electric device, comprising the battery according to claim 14.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0035] Persons of ordinary skill in the art can clearly understand various other advantages and benefits by reading the detailed description of the preferred embodiments below. The accompanying drawings are merely intended to illustrate the preferred embodiments and are not intended to limit the present application. In addition, in all the accompanying drawings, the same reference signs represent the same components. In the drawings:

[0036] FIG. 1 is a schematic structural diagram of a battery according to an embodiment of the present application;

[0037] FIG. 2 is a schematic structural diagram of a battery module according to an embodiment of the present application;

[0038] FIG. 3 is a schematic structural diagram of a battery pack according to an embodiment of the present application;

[0039] FIG. 4 is an exploded view of FIG. 3;

[0040] FIG. 5 is a schematic diagram of an electric device using a battery as a power source according to an embodiment;

[0041] FIG. 6 is an XRD pattern of positive electrode active materials of Example 1 and Comparative Example 1 of the present application;

[0042] FIG. 7 is an XRD pattern of positive electrode active materials of Example 1 and Comparative Example 2 of the present application;

[0043] FIG. 8 is a charge and discharge diagram of a positive electrode plate at 1.5-4.2/4.2-1.5 V of Example 1 of the present application; and

[0044] FIG. 9 is a comparison diagram of capacity retention rates of batteries of Example 1 and Comparative Example 4 of the present application.

REFERENCE SIGNS:

[0045] 1: secondary battery; 2: battery module; 3: battery pack; 4: upper box body; and 5: lower box body.

DESCRIPTION OF EMBODIMENTS

[0046] The following describes in detail embodiments of the technical solutions of the present application. The following embodiments are merely intended for a clearer description of the technical solutions of the present application and therefore are merely used as examples which do not constitute any limitation on the protection scope of the present application.

[0047] In this specification, reference to embodiment means that specific features, structures, or characteristics described with reference to the embodiment may be included in at least one embodiment of the present application. The term embodiment appearing in various places in the specification does not necessarily refer to the same embodiment or an independent or alternative embodiment that is exclusive of other embodiments. It is explicitly or implicitly understood by persons skilled in the art the embodiments described herein may be combined with other embodiments.

[0048] For brevity, this specification specifically discloses only some numerical ranges. However, any lower limit may be combined with any upper limit to form a range not explicitly recorded; any lower limit may be combined with another lower limit to form a range not explicitly recorded; and likewise, any upper limit may be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or individual single numerical value may itself be a lower limit or an upper limit which can be combined with any other point or individual numerical value or combined with another lower limit or upper limit to form a range not expressly recorded.

[0049] In the description of the embodiments of the present application, the term and/or is only an associative relationship for describing associated objects, indicating that three relationships may be present. For example, A and/or B may indicate the following three cases: presence of only A, presence of both A and B, and presence of only B. In addition, the character / in this specification generally indicates an or relationship between the contextually associated objects.

[0050] Unless otherwise defined, all technical and scientific terms used herein shall have the same meanings as commonly understood by persons skilled in the art to which the present application relates. The terms used herein are intended to merely describe the specific embodiments rather than to limit the present application. The terms include, comprise, and have and any other variations thereof in the specification, claims and brief description of drawings of the present application are intended to cover non-exclusive inclusions.

[0051] With the technological development and increasing demand for electric vehicles and rechargeable mobile devices, secondary batteries, as representatives of the new energy field, have seen rapid development in related research. Compared to traditional lithium-ion batteries, sodium-ion batteries have a strong cost advantage and broad application prospects in large-scale energy storage systems.

[0052] Layered transition metal oxides, due to their high electrical conductivity, high energy density, large capacity, and long cycle life, have become one of the popular positive electrode active materials for sodium-ion batteries.

[0053] However, existing layered transition metal oxides have the following issues: on one hand, moisture in the air can penetrate from a surface of the layered transition metal oxide to a bulk phase, leading to structural damage if the layered transition metal oxide is exposed to air for too long; on the other hand, during high-voltage charging, oxygen coordinated with metals in the layered transition metal oxide may undergo oxidation reactions, that is, lattice oxygen release, leading to structural damage to the material; additionally, during high-voltage charging, phase transitions accompanying the deintercalation of sodium ions in the layered transition metal oxide can cause cracks, allowing electrolyte to infiltrate into the material and react, further deteriorating the structure of the material. The structural damage of the layered transition metal oxide material leads to reduced stability of the material, thereby directly resulting in a low capacity retention rate of a battery.

[0054] In the present application, the positive electrode active material uses NiFeMn as the main material, doped with a rare earth element M1 and a doping element M2, with the ratio of the rare earth element M1 to Mn controlled. On one hand, the large radius of the rare earth element M1 remains on a surface of the positive electrode active material, forming a dense and uniform doping layer on the surface of the positive electrode active material, and the doping layer can effectively block moisture from penetrating from the surface to the bulk phase of the positive electrode active material, improving the structural stability of the material. Furthermore, during high-voltage charging, the doping layer can suppress the release of lattice oxygen and the infiltration of electrolyte into the material, improving the structural stability of the material and thus enhancing the capacity retention rate of a battery containing the material. On the other hand, the doping element M2, distributed in the bulk phase of the positive electrode active material, can form strong chemical bonds with O in the positive electrode active material, suppressing the deintercalation of Na ions in the positive electrode active material from the bulk phase and reducing changes in the interlayer spacing of the positive electrode active material, delaying phase transitions, and improving the cycling stability of the positive electrode active material. Additionally, in the present application, the ratio d/c of the rare earth element M1 to Mn in the positive electrode active material is controlled within 0.005 to 0.05, which is conducive to improving the air stability and cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material.

[0055] The positive electrode active material disclosed in the embodiments of the present application is suitable for secondary batteries, and the batteries disclosed in the embodiments of the present application can be used in electric devices using batteries as power sources or in various energy storage systems using batteries as energy storage elements. The electric device may include, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric bicycle, an electric vehicle, a ship, or a spacecraft. The electric toy may include a fixed or mobile electric toy, for example, a game console, an electric toy car, an electric toy ship, and an electric toy airplane. The spacecraft may include an airplane, a rocket, a space shuttle, a spaceship, and the like.

[0056] A first aspect of the present application provides a positive electrode active material. The positive electrode active material includes:

##STR00003##

where M1 includes a rare earth element; M2 includes at least one of a group IA element, a group IIA element, a group IIIA element, a group IVA element, a group VA element, a group VIA element, and a transition element; and 0.6x1.2, 0<a0.5, 0<b0.4, 0.3c0.75, 0.001d0.05, 0e0.3, 0.10.1, 0f0.1, 0.005d/c0.05, and a+b+c+d+e=1.

[0057] The present application includes at least the following beneficial effects: The positive electrode active material of the present application includes a main material including NiFeMn, doped with a rare earth element M1 and a doping element M2, and the aforementioned content of Fe can enhance the specific capacity of the positive electrode active material. The large radius of the rare earth element M1 forms a dense and uniform doping layer on the surface of the positive electrode active material, and the doping layer can effectively block moisture from penetrating from the surface to the bulk phase of the positive electrode active material, improving the structural stability of the material. During high-voltage charging, the doping layer also suppresses the release of lattice oxygen and the infiltration of electrolyte into the material, improving the structural stability of the material and thus enhancing the capacity retention rate of the battery containing the material. The doping element M2, distributed in the bulk phase of the positive electrode active material, can form strong chemical bonds with O in the positive electrode active material, suppressing the deintercalation of Na ions in the positive electrode active material from the bulk phase and reducing changes in the interlayer spacing of the positive electrode active material, delaying phase transitions, and improving the cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery.

[0058] Furthermore, the ratio d/c of the rare earth element M1 to Mn in the positive electrode active material within the aforementioned range can reduce the probability of insufficient solid solubility between the rare earth element and Mn, which could lead to aggregation of the rare earth element on the surface of the positive electrode active material and the formation of impurity phases, while also reducing the probability of not being able to form a rare earth doping layer due to insufficient rare earth elements. This is conducive to the rare earth element forming a dense and uniform rare earth doping layer on the surface of the positive electrode active material, effectively blocking moisture from penetrating from the surface to the bulk phase of the positive electrode active material, and suppressing the release of lattice oxygen and the infiltration of electrolyte into the bulk phase, improving the air stability and cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material.

[0059] In summary, the positive electrode active material includes a main material including NiFeMn, doped with a rare earth element M1 and a doping element M2, with controlled doping amounts of each element and d/c. These features collectively contribute to enhancing the specific capacity of the positive electrode active material.

[0060] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, x may satisfy 0.6x1.2, for example, 0.7x1.1, 0.8x1, 0.9x1.1, 1x1.1, or the like. Thus, including this content of sodium element in the positive electrode active material enables the battery to have a high capacity.

[0061] It should be noted that in the positive electrode plate, the battery, or an electric apparatus, due to processes such as formation and cycling of the battery, sodium ions may be consumed, resulting in a measured content x of element sodium in the positive electrode active material being less than 1. Additionally, if a sodium supplement is used in a positive electrode plate and a negative electrode plate, the measured content x of element sodium in the positive electrode active material may be greater than 1 after the battery is subjected to processes such as formation and cycling.

[0062] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, a may satisfy 0<a0.5, for example, 0.001a0.5, 0.005a0.5, 0.1a0.5, 0.15a0.45, 0.2a0.4, 0.25a0.35, 0.25a0.3, or the like. Thus, including this content of nickel in the positive electrode active material can improve the energy density of the battery. In other embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, a may satisfy 0.1a0.4, for example, 0.15a0.3.

[0063] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, b may satisfy 0<b0.4, for example, 0.001b0.4, 0.005b0.4, 0.1b0.4, 0.15b0.35, 0.2b0.35, 0.25b0.35, 0.3b0.35, or the like. Thus, during the deintercalation of Na ions from the material, Fe, as a charge compensation metal element, oxidizes from a trivalent state to a tetravalent state. When Na ions are re-intercalated into the material, Fe is reduced from the tetravalent state back to the trivalent state. Including this content of Fe in the positive electrode active material can enhance the specific capacity of the material. In other embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, b may satisfy 0.1b0.35, for example, 0.15b0.35.

[0064] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, c may satisfy 0.3c0.75, for example, 0.35c0.75, 0.4c0.7, 0.45c0.65, 0.5c0.6, 0.55c0.6, or the like. Thus, this content of Mn may undergo a solid solution with the rare earth element M1 to form a uniform and dense doping layer on the surface of the positive electrode active material, improving the structural stability of the positive electrode active material, and thereby enhancing the capacity retention rate of the battery containing the material. In other embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, c may satisfy 0.35c0.6, for example, 0.35c0.5.

[0065] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, M1 includes at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Thus, M1 with this composition can form a dense and uniform doping layer on the surface of the positive electrode active material and can effectively block moisture from penetrating from the surface to the bulk phase of the positive electrode active material, improving the structural stability of the material. Additionally, during high-voltage charging, the doping layer with this composition can suppress the release of lattice oxygen and the infiltration of electrolyte into the material, improving the structural stability of the material and thus enhancing the capacity retention rate of the battery containing the material.

[0066] Furthermore, using at least one of the aforementioned elements as M1 is environmentally friendly and causes minimal pollution.

[0067] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, d may satisfy 0.001d0.05, for example, 0.005d0.05, 0.01d0.05, 0.015d0.045, 0.02d0.04, 0.025d0.035, 0.03d0.035, or the like. Thus, including this content of the M1 element in the positive electrode active material can form a dense and uniform doping layer on the surface of the positive electrode active material, effectively blocking moisture from penetrating from the surface to the bulk phase of the positive electrode active material, improving the structural stability of the material. Additionally, during high-voltage charging, the doping layer with this composition can suppress the release of lattice oxygen and the infiltration of electrolyte into the material, improving the structural stability of the material and thus enhancing the capacity retention rate of the battery containing the material.

[0068] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, the contents of the rare earth element M1 and Mn satisfy the following relationship: 0.005d/c0.05, for example, 0.01d/c0.05, 0.015d/c0.045, 0.02d/c0.04, 0.025d/c0.035, 0.03d/c0.035, or the like. The ratio d/c of the rare earth element M1 to Mn in the positive electrode active material within the aforementioned range can reduce the probability of insufficient solid solubility between the rare earth element and Mn, which could lead to aggregation of the rare earth element on the surface of the positive electrode active material and the formation of impurity phases, while also reducing the probability of not being able to form a rare earth doping layer due to insufficient rare earth elements. This is conducive to the rare earth element forming a dense and uniform rare earth doping layer on the surface of the positive electrode active material, effectively blocking moisture from penetrating from the surface to the bulk phase of the positive electrode active material, and suppressing the release of lattice oxygen and the infiltration of electrolyte into the bulk phase, improving the air stability and cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material. In other embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, the contents of the rare earth element M1 and Mn satisfy the following relationship: 0.01d/c0.03. Thus, this is conducive to improving the air stability and cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material.

[0069] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, M2 includes at least one of B, Mg, Al, Si, K, Ca, Ga, Ge, Se, Rb, Sr, In, Sn, Sb, Te, Sc, Ti, V, Cr, Co, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, and Au. Specifically, in the positive electrode active material, the element M2 is uniformly distributed in the bulk phase thereof, and M2 can form strong chemical bonds with O in the positive electrode active material. These chemical bonds, on one hand, suppress the deintercalation of Na elements in the positive electrode active material from the bulk phase, and on the other hand, stabilize the structure of a metal layer of the positive electrode active material, reducing changes in the interlayer spacing of the positive electrode active material, lowering the occurrence of phase transitions, and improving the cycling performance of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material.

[0070] In some embodiments, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, and f satisfy: 0.10.1, 0f0.1, for example, 0.090.09, 0.080.08, 0.070.07, 0.060.06, 0.050.05, 0.040.04, 0.030.03, 0.020.02, 0.010.01, 0.010, 00.01, 0.01f0.09, 0.02f0.08, 0.03f0.07, 0.04f0.06, 0.05f0.06, or the like. Specifically, doping the oxygen sites with this content of F in the positive electrode active material of the present application can effectively stabilize the oxygen in the positive electrode active material, thereby reducing structural damage due to lattice oxygen release in the positive electrode active material, improving the stability of the material, thereby enhancing the capacity retention rate of the battery.

[0071] It should be noted that in the positive electrode plate, the battery, or the electric apparatus, due to the battery being subjected to processes such as cycling, there may be a loss of oxygen elements in the positive electrode active material, resulting in a measured content 2+f of element oxygen in the positive electrode active material being less than 2.

[0072] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, 1.75(a+b+c)/b9.5, for example, 1.8(a+b+c)/b9.5, 1.9(a+b+c)/b9.4, 2(a+b+c)/b9.3, 2.1(a+b+c)/b9.2, 2.2(a+b+c)/b9.1, 2.3(a+b+c)/b9, 2.5(a+b+c)/b8.5, 3(a+b+c)/b8, 3.5(a+b+c)/b7.5, 4(a+b+c)/b7, 4.5(a+b+c)/b6.5, 5(a+b+c)/b6, 5(a+b+c)/b5.5, or the like. Specifically, controlling the ratio of the sum of the contents of Ni, Fe, and Mn to the content of Fe in the positive electrode active material within the aforementioned range, on one hand, reduces the reduction in deintercalatable Na ions in the positive electrode active material due to insufficient variable valence metal component Fe, enabling the positive electrode active material to have excellent specific capacity; on the other hand, this reduces the effect of the deintercalation of Na ions due to excessive Fe content in the positive electrode active material causing significant Fe migration to an Na ion layer, improving the cycling performance of the positive electrode active material, thereby enhancing the capacity retention rate of the battery containing the material.

[0073] In some embodiments of the present application, in the positive electrode active material Na.sub.xNi.sub.aFe.sub.bMn.sub.cM1.sub.dM2.sub.eO.sub.2+fF.sub.f, 0.8<x1.0, a phase of the positive electrode active material includes an O3 phase, a space group includes R3m, and an interlayer spacing ranges from 0.53 nm to 0.55 nm. For example, x may satisfy 0.82 to 1.0, 0.85 to 0.95, 0.88 to 0.90, or the like; and the interlayer spacing may satisfy 0.53 nm to 0.545 nm, 0.535 nm to 0.54 nm, or 0.536 nm to 0.539 nm. Specifically, with x in the aforementioned range, the formed positive electrode active material with the O3 phase has a high Na content, enabling more Na ions to deintercalate and the battery to exhibit high capacity.

[0074] In some embodiments of the present application, 0.6x0.8, the phase of the positive electrode active material includes a P2 phase, the space group includes P63/mmc, and the interlayer spacing ranges from 0.54 nm to 0.57 nm. For example, x may satisfy 0.6 to 0.78, 0.65 to 0.75, 0.68 to 0.7, or the like; and the interlayer spacing may satisfy 0.54 nm to 0.565 nm, 0.545 nm to 0.56 nm, 0.55 nm to 0.555 nm, or the like. Specifically, with x in the aforementioned range, the positive electrode active material with the P2 phase has a large interlayer spacing, which can enhance the transport rate of Na ions and maintain the integrity of the layered structure, enabling the battery to have excellent rate performance and cycling performance.

[0075] It should be noted that the characterization methods for the phase, the space group, and the interlayer spacing of the positive electrode active material in the present application may include X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and the like. Specifically, in an X-ray diffraction pattern, a characteristic peak in the range of 40.5 to 42.5 indicates that the positive electrode active material is in the O3 phase, with the space group including R3m; and a characteristic peak in the range of 48 to 50 indicates that the positive electrode active material is in the P2 phase, with the space group including P63/mmc. The interlayer spacing of the positive electrode active material in the O3 phase can be calculated from the position of the (003) peak in X-ray diffraction; and the interlayer spacing of the positive electrode active material in the P2 phase can be calculated from the position of the (002) peak in X-ray diffraction.

[0076] In some embodiments of the present application, a pH value of a soaking solution of the positive electrode active material is less than or equal to 13, for example, the pH value of the soaking solution of the positive electrode active material may satisfy 7 to 13, 7.2 to 13, 7.5 to 13, 8 to 13, 8.5 to 13, 9 to 13, 10 to 12.9, 10.5 to 12.7, 11.0 to 12.7, 11.2 to 12.5, 11.5 to 12.3, 11.7 to 12.0, or the like. Controlling the pH value of the soaking solution of the positive electrode active material within the aforementioned range can reduce the formation of gel during a slurry preparation process, facilitating subsequent slurry applying of the positive electrode active material. In other embodiments of the present application, the pH value of the soaking solution of the positive electrode active material is less than or equal to 12.7, for example, the pH value of the soaking solution of the positive electrode active material is 11.0pH12.7.

[0077] Specifically, the pH value of the soaking solution of the positive electrode active material can be measured using the following method:

[0078] The positive electrode active material is dispersed in pure water for soaking, filtered to obtain the soaking solution, and titrated the measured soaking solution with a standard hydrochloric acid solution.

[0079] In some embodiments of the present application, D.sub.v50 of the positive electrode active material ranges from 3 m to 30 m, for example, the D.sub.v50 of the positive electrode active material may satisfy 3 m to 29 m, 4 m to 28 m, 5 m to 15 m, 6 m to 14 m, 8 m to 13 m, 9 m to 12 m, 10 m to 11 m, or the like. In other embodiments of the present application, the D.sub.v50 of the positive electrode active material ranges from 5 m to 15 m.

[0080] In the present application, D.sub.v50 refers to a particle size when a cumulative volume distribution percentage reaches 50%. For example, it can be measured using a laser particle size analyzer (for example, Malvern Master Size 3000) in accordance with GB/T 19077-2016.

[0081] In some embodiments of the present application, a specific surface area of the positive electrode active material ranges from 0.1 m.sup.2/g to 5 m.sup.2/g, for example, the specific surface area of the positive electrode active material may satisfy 0.1 m.sup.2/g to 4.5 m.sup.2/g, 0.2 m.sup.2/g to 4 m.sup.2/g, 0.3 m.sup.2/g to 3 m.sup.2/g, 0.5 m.sup.2/g to 2.5 m.sup.2/g, 1 m.sup.2/g to 2 m.sup.2/g, 1.2 m.sup.2/g to 1.8 m.sup.2/g, or the like. In other embodiments of the present application, the specific surface area of the positive electrode active material ranges from 0.3 m.sup.2/g to 3 m.sup.2/g.

[0082] In the present application, the specific surface area of the positive electrode active material can be tested using the following method: Approximately 7 g of the sample is placed in a 9 cc long tube with a bulb using a Micromeritics Gemini VII 2390 multi-station automatic specific surface area and pore analyzer, degassed at 200 C. for 2 h, and then tested in the main unit to obtain the BET (specific surface area) data of the positive electrode active material.

[0083] In some embodiments of the present application, a tap density of the positive electrode active material ranges from 1 g/cm.sup.3 to 3 g/cm.sup.3, for example, the tap density of the positive electrode active material may satisfy 1 g/cm.sup.3 to 2.8 g/cm.sup.3, 1.5 g/cm.sup.3 to 2.5 g/cm.sup.3, 1.7 g/cm.sup.3 to 2.4 g/cm.sup.3, 1.8 g/cm.sup.3 to 3 g/cm.sup.3, or the like. In other embodiments of the present application, the tap density of the positive electrode active material ranges from 1.5 g/cm.sup.3 to 2.5 g/cm.sup.3.

[0084] In the present application, tap density refers to the mass per unit volume measured after the powder in the container was tapped under specified conditions. The method for measuring the tap density of the positive electrode active material is as follows:

[0085] Load the weighed positive electrode active material into a measuring cylinder of a tapping device, and fix the measuring cylinder on a support. Rotate a cam, causing a guide rod to drive the support to slide up and down, impacting an anvil. Vibrate at 25015 times per minute for 12 minutes. Measure the volume of the positive electrode active material in the measuring cylinder, and the ratio of the mass to the volume of the positive electrode active material is the tap density.

[0086] The formula for calculating tap density is: bt=m.sub.0/V [0087] where bt refers to tap density, in g/cm.sup.3; [0088] m.sub.0 refers to mass of the positive electrode active material, in g; and [0089] V refers to volume of the positive electrode active material after tapping (volume of a measuring cup), in cm.sup.3.

[0090] In some embodiments of the present application, a compacted density of the positive electrode active material under a pressure of 300 MPa ranges from 3.0 g/cm.sup.3 to 4.0 g/cm.sup.3, for example, the compacted density of the positive electrode active material under a pressure of 300 MPa may satisfy 3.0 g/cm.sup.3 to 3.9 g/cm.sup.3, 3.1 g/cm.sup.3 to 3.8 g/cm.sup.3, 3.2 g/cm.sup.3 to 3.7 g/cm.sup.3, 3.3 g/cm.sup.3 to 3.6 g/cm.sup.3, 3.4 g/cm.sup.3 to 3.5 g/cm.sup.3, or the like.

[0091] In some embodiments of the present application, compacted density refers to the compacted density of the electrode plate after the material is made into an electrode plate. Compacted density=surface density/(thickness of the electrode plate after rolling-thickness of the current collector). Specifically, the method for measuring the compacted density of the positive electrode active material under a pressure of 300 MPa is as follows:

[0092] A rolled electrode plate is taken, and a circular or square region with an area of s is cut using a cutting die, with the thickness measured as a and weighed as m.sub.1. The positive electrode material is washed off with a mixture of acetone and alcohol and dried, and the remaining aluminum foil is weighed as m.sub.2, with the thickness of the aluminum foil measured as b. The difference in weight of the region and the aluminum foil is divided by the area s of the circular or square shape to calculate the surface density, that is, surface density=(m.sub.1m.sub.2)/s. The surface density is divided by the thickness difference to obtain the compacted density, that is, compacted density=(m.sub.1m.sub.2)/[s(ab)].

[0093] Specifically, when at least one of the D.sub.v50, the specific surface area, the tap density, and the compacted density under a pressure of 300 MPa of the positive electrode active material of the present application falls within the aforementioned ranges, a conduction distance of Na ions within the positive electrode active material is short, the surface side reaction is less, promoting the positive electrode active material to achieve the specific capacity thereof, and improving the capacity retention rate of the battery containing the material.

[0094] A second aspect of the present application provides a method for preparing the positive electrode active material described in the first aspect, including:

[0095] S100: An Na source, an Ni source, an Fe source, an Mn source, an M1 source, and an M2 source are mixed to obtain a precursor.

[0096] In some embodiments of the present application, the Na source, the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source are mixed according to the composition of the positive electrode active material described above.

[0097] It should be noted that the Na source, the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source in the present application are conventional materials in the field, and those skilled in the art can select them based on actual needs. For example, the Na source may include at least one of Na.sub.2CO.sub.3, NaHCO.sub.3, NaOH, and Na.sub.2O.sub.2; the Ni source may include NiO; the Fe source may include at least one of FeO, Fe.sub.2O.sub.3, and Fe.sub.3O.sub.4; the Mn source may include at least one of Mn.sub.2O.sub.3, Mn.sub.3O.sub.4, MnO, and MnO.sub.2; the M1 source may include at least one of an oxide of M1, a salt containing M1, and other compounds; and the M2 source may include at least one of an oxide of M2, a salt containing M2, and other compounds.

[0098] It should be noted that if doping with the F element is required in the positive electrode active material, at least one of the Na source, the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source uses at least one of the corresponding fluoride-containing salt thereof and other compounds, for example, sodium fluoride, nickel fluoride, iron fluoride, manganese fluoride, M1 fluoride (fluoride salt of M1), and M2 fluoride (fluoride salt of M2).

[0099] S200: The precursor is calcined.

[0100] In some embodiments of the present application, the obtained precursor is calcined in a muffle furnace under an air atmosphere, then cooled to room temperature and mechanically crushed to obtain the positive electrode active material, where the calcination temperature may satisfy 600 C. to 1200 C., for example, 600 C. to 1100 C., 700 C. to 1000 C., 800 C. to 900 C., or the like; and the holding time may satisfy 10 h to 20 h, for example, 10 h to 19 h, 11 h to 18 h, 12 h to 17 h, 13 h to 16 h, 14 h to 15 h, or the like.

[0101] Additionally, before calcining the precursor, the precursor can be pre-calcined and held according to needs, with a pre-calcination temperature of 600 C. to 900 C., for example, 600 C. to 850 C., 650 C. to 800 C., 600 C. to 750 C., 550 C. to 700 C., 500 C. to 650 C., 550 C. to 600 C., or the like; and a holding time of 10 h to 20 h, for example, 10 h to 19 h, 11 h to 18 h, 12 h to 17 h, 13 h to 16 h, 14 h to 15 h, or the like.

[0102] Thus, using the solid-phase method can prepare the positive electrode active material with excellent air stability and cycling stability, improving the capacity retention rate of the battery.

[0103] A third aspect of the present application provides another method for preparing the positive electrode active material described in the first aspect, including:

[0104] Sa: An Ni source, an Fe source, an Mn source, an M1 source, and an M2 source are mixed with water to obtain a mixed solution.

[0105] In some embodiments of the present application, the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source are mixed with water according to the composition of the positive electrode active material described above to obtain a mixed solution.

[0106] It should be noted that the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source in the present application are conventional materials in the field, and those skilled in the art can select them based on actual needs. For example, the Ni source may include at least one of nickel chloride, nickel sulfate, nickel nitrate, and nickel oxalate; the Fe source may include at least one of iron chloride, iron sulfate, iron nitrate, and iron oxalate; the Mn source may include at least one of manganese chloride, manganese sulfate, manganese nitrate, and manganese oxalate; the M1 source may include at least one of chlorides, sulfates, nitrates, and oxalates of M1; and the M2 source may include at least one of chlorides, sulfates, nitrates, oxalates of M2, and other compounds.

[0107] Sb: The solution is reacted with a precipitant to obtain a precursor.

[0108] In some embodiments of the present application, the solution obtained in step Sa is reacted with a solution containing a precipitant to obtain a precursor, where the solution containing the precipitant includes at least one of ammonia water, carbonate, and oxalate.

[0109] Sc: The precursor is mixed with an Na source and then calcined.

[0110] In some embodiments of the present application, the obtained precursor is mixed with an Na source according to the composition of the positive electrode active material described above, uniformly mixed through ball milling or mechanical stirring, calcined in a muffle furnace, then cooled to room temperature and mechanically crushed to obtain the positive electrode active material, where the calcination temperature may satisfy 600 C. to 1200 C., for example, 700 C. to 1100 C., 800 C. to 1000 C., 900 C. to 950 C., or the like; the calcination atmosphere can be air or oxygen; and the holding time may satisfy 10 h to 20 h, for example, 10 h to 19 h, 11 h to 18 h, 12 h to 17 h, 13 h to 16 h, 14 h to 15 h, or the like.

[0111] It should be noted that, as needed, before mixing and calcining the precursor with the Na source, the precursor mixed with the Na source can be pre-calcined and held, with a pre-calcination temperature of 600 C. to 900 C., for example, 600 C. to 850 C., 650 C. to 800 C., 600 C. to 750 C., 550 C. to 700 C., 500 C. to 650 C., 550 C. to 600 C., or the like; and a holding time of 10 h to 20 h, for example, 10 h to 19 h, 11 h to 18 h, 12 h to 17 h, 13 h to 16 h, 14 h to 15 h, or the like. The Na source may include at least one of Na.sub.2CO.sub.3, NaHCO.sub.3, NaOH, and Na.sub.2O.sub.2.

[0112] It should be noted that if doping with the F element is required in the positive electrode active material, at least one of the Na source, the Ni source, the Fe source, the Mn source, the M1 source, and the M2 source uses at least one of the corresponding fluoride-containing salt thereof and other compounds, for example, sodium fluoride, nickel fluoride, iron fluoride, manganese fluoride, M1 fluoride (fluoride salt of M1), and M2 fluoride (fluoride salt of M2).

[0113] Thus, using the co-precipitation method can prepare the positive electrode active material with excellent air stability and cycling stability, improving the capacity retention rate of the battery.

[0114] A fourth aspect of the present application provides a positive electrode plate, including the positive electrode active material described in the first aspect, the positive electrode active material prepared by the method described in the second aspect, or the positive electrode active material prepared by the method described in the third aspect of the present application.

[0115] The positive electrode plate typically includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, where the positive electrode active material layer includes the positive electrode active material.

[0116] The positive electrode current collector may be a common metal foil or a composite current collector (the composite current collector may be formed by providing a metal material on a polymer matrix). In an example, the positive electrode current collector may include at least one of copper foil, aluminum foil, nickel foil, stainless steel foil, a stainless steel mesh, and carbon-coated aluminum foil.

[0117] The positive electrode active material includes the positive electrode active material described in the first aspect, the positive electrode active material prepared by the method described in the second aspect, or the positive electrode active material prepared by the method described in the third aspect of the present application.

[0118] The positive electrode active material layer may optionally include a conductive agent and a binder, where the conductive agent is used to improve the electrical conductivity of the positive electrode active material layer, and the binder is used to firmly adhere the positive electrode active material and the binder to the positive electrode current collector. The types of conductive agent and binder are not specifically limited in the present application and can be selected based on actual needs.

[0119] In 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; and the binder may include at least one of styrene-butadiene rubber (SBR), water-based acrylic resin (water-based acrylic resin), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).

[0120] These materials are all commercially available.

[0121] A fifth aspect of the present application provides a battery, including the positive electrode plate described in the fourth aspect of the present application. Thus, the battery has an excellent capacity retention rate.

[0122] The battery is a battery that can be charged after being discharged to activate the active materials for continuous use.

[0123] It can be understood that the battery proposed in the present application is a sodium-ion battery.

[0124] Typically, a battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. In a charge and discharge process of the battery, active ions are intercalated and deintercalated between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate for separation. The electrolyte conducts ions between the positive electrode plate and the negative electrode plate.

Negative Electrode Plate

[0125] In the battery, the negative electrode plate typically includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, where the negative electrode active material layer includes a negative electrode active material.

[0126] The negative electrode current collector may be a common metal foil or a composite current collector (for example, the composite current collector may be formed by providing a metal material on a polymer matrix). In an example, the negative electrode current collector may be a copper foil.

[0127] A specific type of the negative electrode active material is not limited. An active material known in the art that can be used as a negative electrode of a sodium-ion battery can be used, and persons skilled in the art can make selection based on actual needs. In an example, the negative electrode active material may include, but is not limited to, at least one of sodium metal, carbon materials, alloy materials, transition metal oxides and/or sulfides, phosphorus-based materials, and titanate materials. Specifically, the carbon material may include at least one of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon materials. The alloy material may include an alloy material formed from at least one of Si, Ge, Sn, Pb, and Sb. The transition metal oxides and sulfides have the general formula M.sub.xN.sub.y, where M includes at least one of Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; and N includes O or S. The phosphorus-based material may include at least one of red phosphorus, white phosphorus, and black phosphorus. The titanate material may include at least one of Na.sub.2Ti.sub.3O.sub.7, Na.sub.2Ti.sub.6O.sub.13, Na.sub.4Ti.sub.5O.sub.12, Li.sub.4Ti.sub.5O.sub.12, and NaTi.sub.2(PO.sub.4).sub.3. These materials are all commercially available.

[0128] The negative electrode active material layer typically may also optionally include a binder and a conductive agent, where the conductive agent is used to improve the electrical conductivity of the negative electrode active material layer, and the binder is used to firmly adhere the negative electrode active material and the binder to the negative electrode current collector. The types of conductive agent and binder are not specifically limited in the present application and can be selected based on actual needs.

[0129] In 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.

[0130] In an example, the binder may include at least one of styrene-butadiene rubber (SBR), styrene-butadiene copolymers (SBCs), water-based acrylic resin (water-based acrylic resin), and carboxymethyl cellulose (CMC).

[0131] The negative electrode active material layer may also optionally include a thickener, for example, carboxymethyl cellulose (CMC). However, the present application is not limited thereto, and may alternatively use other materials that can be used as thickeners for negative electrode plates of sodium-ion batteries.

Electrolyte

[0132] The electrolyte may include an electrolytic salt and a solvent.

[0133] In an example, the electrolytic salt may include at least one of sodium hexafluorophosphate, sodium difluoro(oxalato)borate, sodium tetrafluoroborate, sodium bis(oxalate)borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethanesulfonyl)imide.

[0134] In an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), gamma-butyrolactone (GBL), sulfolane (SF), methyl sulfonyl methane (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0135] In some embodiments, the electrolyte may also include an additive. For example, the additive may include a negative electrode film-forming additive, or may include a positive electrode film-forming additive, or may include an additive capable of improving some performance of the battery, for example, an additive for improving overcharge performance of the battery, an additive for improving high-temperature performance of the battery, or an additive for improving low-temperature performance of the battery.

Separator

[0136] The separator is not particularly limited in the present application, and any common porous structure separator with electrochemical and mechanical stability can be selected based on actual needs, for example, it may include a single-layer or multi-layer film containing at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0137] The battery is not particularly limited in shape in the embodiments of the present application, and may be cylindrical, rectangular, or of any other shape. FIG. 1 shows a battery 1 of a rectangular structure as an example.

[0138] In some embodiments, the battery may include an outer package. The outer package is used for packaging the positive electrode plate, the negative electrode plate, and the electrolyte.

[0139] In some embodiments, the outer package may include a housing and a cover plate. The housing may include a base plate and a side plate connected onto the base plate, and the base plate and the side plate enclose an accommodating cavity. The housing has an opening communicating with the accommodating cavity, and the cover plate can cover the opening to close the accommodating cavity.

[0140] The positive electrode plate, the negative electrode plate, and the separator may be made into an electrode assembly through winding or lamination. The electrode assembly is packaged in the accommodating cavity. There may be one or more electrode assemblies in the battery, and the quantity may be adjusted as required.

[0141] In some embodiments, the outer package of the battery may include a hard shell, for example, a hard plastic shell, an aluminum shell, or a steel shell.

[0142] The outer package of the battery may alternatively include a soft pack, for example, a soft pouch. A material of the soft package may be plastic, for example, may include at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0143] In some embodiments, batteries may be assembled into a battery module, and the battery module may include a plurality of batteries. The specific quantity may be adjusted based on application and capacity of the battery module.

[0144] FIG. 2 shows a battery module 2 as an example. Referring to FIG. 2, in the battery module 2, a plurality of batteries 1 may be sequentially arranged in a length direction of the battery module 2. Certainly, the batteries may alternatively be arranged in any other manners. Further, the plurality of batteries 1 may be fixed by fasteners.

[0145] The battery module 2 may further include a shell with an accommodating space, and the plurality of batteries 1 are accommodated in the accommodating space. In some embodiments, the battery module may be further assembled into a battery pack, and a quantity of battery modules included in the battery pack may be adjusted based on application and capacity of the battery pack.

[0146] FIGS. 3 and 4 show a battery pack 3 as an example. Referring to FIG. 3 and FIG. 4, the battery pack 3 may include a battery box and a plurality of battery modules 2 arranged in the battery box. The battery box includes an upper box body 4 and a lower box body 5. The upper box body 4 can fit the lower box body 5 to form an enclosed space for accommodating the battery modules 2. The plurality of battery modules 2 may be arranged in the battery box in any manner.

[0147] A sixth aspect of the present application provides an electric device, including the battery described in the fifth aspect. Specifically, the battery may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The electric device may include, but is not limited to, a mobile device (for example, a mobile phone or a notebook computer), an electric vehicle (for example, a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicle, or an electric truck), an electric train, a ship, a satellite system, and an energy storage system.

[0148] FIG. 5 shows an electric device as an example. The electric device includes a battery electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0149] In another example, the electric device may include a mobile phone, a tablet computer, or a notebook computer. Such electric device is generally required to be light and thin and may use a battery as its power source.

[0150] To describe the technical problems solved by the embodiments of the present application, technical solutions, and beneficial effects more clearly, the following further describes the present application in detail with reference to the embodiments and accompanying drawings. Apparently, the described embodiments are only some but not all of these embodiments of the present application. The following description of at least one exemplary example is merely illustrative and definitely is not construed as any limitation on the present application or on use of the present application. All other embodiments obtained by persons of ordinary skill in the art on the basis of the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

EXAMPLE 1

Preparation of NaNi.SUB.0.2.Fe.SUB.0.2.Mn.SUB.0.5.La.SUB.0.02.Cu.SUB.0.08.O.SUB.2

[0151] Raw materials were mixed according to the stoichiometric ratio of the molecular formula, with 23.666 g of Na.sub.2CO.sub.3, 6.672 g of NiO, 7.131 g of Fe.sub.2O.sub.3, 17.627 g of Mn.sub.2O.sub.3, 1.455 g of La.sub.2O.sub.3, and 2.841 g of CuO (with a molar ratio of Na, Ni, Fe, Mn, La, and Cu being 1:0.2:0.2:0.5:0.02:0.08) mixed in an agate milling jar of a planetary ball mill. The raw materials were ground at a speed of 600 r/min, then heated in a muffle furnace to 950 C. at a temperature rise rate of 5 C./min, calcined at this temperature for 15 h, and then naturally cooled to room temperature to obtain a black positive electrode active material NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2.

Preparation of Positive Electrode Plate

[0152] The prepared NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2, a conductive agent carbon black, a binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) were stirred and mixed at a weight ratio of 60:5:5:30 to uniformity to obtain a positive electrode slurry; the positive electrode slurry was uniformly applied onto a positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode plate.

Preparation of Negative Electrode Plate

[0153] The negative electrode plate used a metal sodium sheet.

Preparation of Electrolyte

[0154] In an argon atmosphere glove box (with H.sub.2O<0.1 ppm, O.sub.2<0.1 ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3:7 to obtain a mixed solvent, then NaPF.sub.6 was dissolved in the mixed solvent, stirred uniformly to obtain an electrolyte with a sodium salt concentration of 1 mol/L.

Separator

[0155] Glass fiber was used as the separator.

[0156] The positive electrode plate, the separator, and the negative electrode plate were sequentially stacked such that the separator was sandwiched between the positive and negative electrode plates for separation, and then the resulting stack was wound to form an electrode assembly, the electrode assembly was placed in an outer package and the prepared electrolyte was injected into the outer package that was dried, followed by processes of vacuum packaging, standing, formation, and shaping, to obtain a secondary battery.

[0157] The secondary batteries containing positive electrode active materials in Examples 2 to 24 and Comparative Examples 1 to 4 were the same as in Example 1, except for differences in parameters (see Table 1).

[0158] The compositions of the positive electrode active materials in the batteries of Examples 1 to 24 and Comparative Examples 1 to 4 of the present application are shown in Table 1 .

TABLE-US-00001 TABLE 1 M1 M2 Value Value Value Value Chemical formula composition composition of x of a of b of c Example 1 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.2 0.2 0.5 Example 2 NaNi.sub.0.405Fe.sub.0.2Mn.sub.0.3La.sub.0.015Cu.sub.0.08O.sub.2 La Cu 1 0.405 0.2 0.3 Example 3 NaNi.sub.0.4185Fe.sub.0.2Mn.sub.0.3La.sub.0.0015Cu.sub.0.08O.sub.2 La Cu 1 0.4185 0.2 0.3 Example 4 NaNi.sub.0.0225Fe.sub.0.11Mn.sub.0.75La.sub.0.0375Cu.sub.0.08O.sub.2 La Cu 1 0.0225 0.11 0.75 Example 5 NaNi.sub.0.05625Fe.sub.0.11Mn.sub.0.75La.sub.0.00375Cu.sub.0.08O.sub.2 La Cu 1 0.05625 0.11 0.75 Example 6 NaNi.sub.0.3Fe.sub.0.1Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.3 0.1 0.5 Example 7 NaNi.sub.0.087Fe.sub.0.313Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.087 0.313 0.5 Example 8 Na.sub.0.6Ni.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 0.6 0.2 0.2 0.5 Example 9 NaNi.sub.0.07Fe.sub.0.11Mn.sub.0.5La.sub.0.02Cu.sub.0.3O.sub.2 La Cu 1 0.07 0.11 0.5 Example 10 NaNi.sub.0.28Fe.sub.0.2Mn.sub.0.5La.sub.0.02O.sub.2 La 0 1 0.28 0.2 0.5 Example 11 NaNi.sub.0.35Fe.sub.0.05Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.35 0.05 0.5 Example 12 NaNi.sub.0.07Fe.sub.0.33Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.07 0.33 0.5 Example 13 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5Pr.sub.0.02Cu.sub.0.08O.sub.2 Pr Cu 1 0.2 0.2 0.5 Example 14 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5Nd0.sub..02Cu.sub.0.08O.sub.2 Nd Cu 1 0.2 0.2 0.5 Example 15 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Mg.sub.0.08O.sub.2 La Mg 1 0.2 0.2 0.5 Example 16 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Si.sub.0.08O.sub.2 La Si 1 0.2 0.2 0.5 Example 17 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Ti.sub.0.08O.sub.2 La Ti 1 0.2 0.2 0.5 Example 18 NaNi.sub.0.1Fe.sub.0.2Mn.sub.0.6La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.1 0.2 0.6 Example 19 NaNi.sub.0.15Fe.sub.0.2Mn.sub.0.55La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.15 0.2 0.55 Example 20 NaNi.sub.0.25Fe.sub.0.15Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.25 0.15 0.5 Example 21 NaNi.sub.0.11Fe.sub.0.29Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.11 0.29 0.5 Example 22 NaNi.sub.0.23Fe.sub.0.17Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 La Cu 1 0.23 0.17 0.5 Example 23 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.1.9F.sub.0.1 La Cu 1 0.2 0.2 0.5 Example 24 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.1.95F.sub.0.05 La Cu 1 0.2 0.2 0.5 Comparative NaNi.sub.0.3184Fe.sub.0.2Mn.sub.0.4La.sub.0.0016Cu.sub.0.08O.sub.2 La Cu 1 0.3184 0.2 0.4 Example 1 Comparative NaNi.sub.0.19Fe.sub.0.2Mn.sub.0.5La.sub.0.03Cu.sub.0.08O.sub.2 La Cu 1 0.19 0.2 0.5 Example 2 Comparative NaNi.sub.0.46Fe.sub.0.2Mn.sub.0.25La.sub.0.01Cu.sub.0.08O.sub.2 La Cu 1 0.46 0.2 0.25 Example 3 Comparative NaNi.sub.0.048Fe.sub.0.11Mn.sub.0.8La.sub.0.032Cu.sub.0.01O.sub.2 La Cu 1 0.048 0.11 0.8 Example 4 Value Value Value (a + b + Value Value Chemical formula of d of d/c of e c)/b of of f Example 1 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 2 NaNi.sub.0.405Fe.sub.0.2Mn.sub.0.3La.sub.0.015Cu.sub.0.08O.sub.2 0.015 0.05 0.08 4.975 0 0 Example 3 NaNi.sub.0.4185Fe.sub.0.2Mn.sub.0.3La.sub.0.0015Cu.sub.0.08O.sub.2 0.0015 0.005 0.08 4.5925 0 0 Example 4 NaNi.sub.0.0225Fe.sub.0.11Mn.sub.0.75La.sub.0.0375Cu.sub.0.08O.sub.2 0.0375 0.05 0.08 8 0 0 Example 5 NaNi.sub.0.05625Fe.sub.0.11Mn.sub.0.75La.sub.0.00375Cu.sub.0.08O.sub.2 0.00375 0.005 0.08 8.33 0 0 Example 6 NaNi.sub.0.3Fe.sub.0.1Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 9 0 0 Example 7 NaNi.sub.0.087Fe.sub.0.313Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 2.88 0 0 Example 8 Na.sub.0.6Ni.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 9 NaNi.sub.0.07Fe.sub.0.11Mn.sub.0.5La.sub.0.02Cu.sub.0.3O.sub.2 0.02 0.04 0.3 6.18 0 0 Example 10 NaNi.sub.0.28Fe.sub.0.2Mn.sub.0.5La.sub.0.02O.sub.2 0.02 0.04 0 4.9 0 0 Example 11 NaNi.sub.0.35Fe.sub.0.05Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 18 0 0 Example 12 NaNi.sub.0.07Fe.sub.0.33Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 2.73 0 0 Example 13 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5Pr.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 14 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5Nd0.sub..02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 15 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Mg.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 16 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Si.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 17 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Ti.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 18 NaNi.sub.0.1Fe.sub.0.2Mn.sub.0.6La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.03 0.08 4.5 0 0 Example 19 NaNi.sub.0.15Fe.sub.0.2Mn.sub.0.55La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 4.5 0 0 Example 20 NaNi.sub.0.25Fe.sub.0.15Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 6 0 0 Example 21 NaNi.sub.0.11Fe.sub.0.29Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 3.1 0 0 Example 22 NaNi.sub.0.23Fe.sub.0.17Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.2 0.02 0.04 0.08 5.29 0 0 Example 23 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.1.9F.sub.0.1 0.02 0.04 0.08 4.5 0 0.1 Example 24 NaNi.sub.0.2Fe.sub.0.2Mn.sub.0.5La.sub.0.02Cu.sub.0.08O.sub.1.95F.sub.0.05 0.02 0.04 0.08 4.5 0 0.05 Comparative NaNi.sub.0.3184Fe.sub.0.2Mn.sub.0.4La.sub.0.0016Cu.sub.0.08O.sub.2 0.0016 0.004 0.08 4.592 0 0 Example 1 Comparative NaNi.sub.0.19Fe.sub.0.2Mn.sub.0.5La.sub.0.03Cu.sub.0.08O.sub.2 0.03 0.06 0.08 4.45 0 0 Example 2 Comparative NaNi.sub.0.46Fe.sub.0.2Mn.sub.0.25La.sub.0.01Cu.sub.0.08O.sub.2 0.01 0.04 0.08 4.55 0 0 Example 3 Comparative NaNi.sub.0.048Fe.sub.0.11Mn.sub.0.8La.sub.0.032Cu.sub.0.01O.sub.2 0.032 0.04 0.01 8.71 0 0 Example 4

[0159] The D.sub.v50, the specific surface area, the tap density, the compacted density under a pressure of 300 MPa, the pH value of the soaking solution, the phase, the space group, and the interlayer spacing of the positive electrode active materials, as well as the capacity and capacity retention rate of the resulting sodium-ion batteries in Examples 1 to 24 and Comparative Examples 1 to 4, were characterized, with the results shown in Table 2.

Performance Testing:

[0160] 1. Testing of phase, space group, and interlayer spacing of positive electrode active material: XRD patterns were obtained for the positive electrode active material. The phase and the space group of the positive electrode active material were determined based on the positions of characteristic peaks in an XRD pattern. The interlayer spacing d of the positive electrode active material was calculated based on the position of the (003) peak or (002) peak in X-ray diffraction, the corresponding peak, and the formula d=/(2sin), where in the formula d=/(2sin), the radiation wavelength =1.5406 . A characteristic peak in the 2 angle range of 40.5 to 42.5 indicated that the positive electrode active material was in the O3 phase, with a space group including R3m A characteristic peak in the 2 angle range of 48 to 50 indicated that the positive electrode active material was in the P2 phase, with a space group including P63/mmc. [0161] 2. Measurement of D.sub.v50 of positive electrode active material: Measurement was performed using a Malvern Master Size 3000 laser particle size analyzer in accordance with standard GB/T 19077-2016. [0162] 3. Measurement of tap density: The weighed positive electrode active material was loaded into a measuring cylinder of a tapping device, and the measuring cylinder was fixed on a support. The cam was rotated, causing a guide rod to drive the support to slide up and down, impacting an anvil. Vibration was performed 25015 times per minute for 12 minutes. The volume of the positive electrode active material in the measuring cylinder was measured, and the ratio of the mass to the volume of the positive electrode active material was the tap density of the positive electrode active material.

[0163] The formula for calculating tap density was: bt=m.sub.0/V, [0164] where bt referred to tap density, in g/cm.sup.3; [0165] m.sub.0 referred to mass of the positive electrode active material, in g; and [0166] V referred to volume of the positive electrode active material after tapping (volume of a measuring cup), in cm.sup.3. [0167] 4. Compacted density of positive electrode active material under pressure of 300 MPa: A rolled electrode plate was taken, and a circular or square region with an area of s was cut using a cutting die, with the thickness measured as a and weighed as m.sub.1. The positive electrode material was washed off with a mixture of acetone and alcohol and dried, and the remaining aluminum foil was weighed as m.sub.2, with the thickness of the aluminum foil measured as b. The difference in weight of the region and the aluminum foil was divided by the area s of the circular or square shape to calculate the surface density, that is, surface density=(m.sub.1m.sub.2)/s. The surface density was divided by the thickness difference to obtain the compacted density, that is, compacted density=(m.sub.1m.sub.2)/[s(ab)]. [0168] 5. Measurement of pH value of soaking solution of positive electrode active material: The positive electrode active material was dispersed in pure water for soaking, filtered to obtain the soaking solution, and the soaking solution was titrated with a standard hydrochloric acid solution. [0169] 6. Capacity testing of positive electrode plate: The positive electrode plate was prepared, and the negative electrode plate was prepared, punched, and weighed. The masses of the positive and negative electrode plates were correspondingly fit according to the types of the positive and negative electrode materials. The positive electrode plate and the negative electrode plate were placed in a glove box for 2 h. A button battery was assembled in the glove box, and the prepared button battery was clamped on an electrochemical testing cabinet. The charge-discharge current was calculated based on a test rate (0.2C, 1C, 3C, or 5C), current=ratetheoretical specific capacity(M.sub.2M.sub.1)%, where theoretical specific capacity was determined based on the theoretical specific capacity of the positive electrode material; [0170] M2 referred to actual weight of the electrode plate; [0171] M1 referred to average weight of the current collector; and [0172] % referred to actual mass fraction of the active material. [0173] 7. Battery capacity retention rate testing:

[0174] Taking Example 1 as an example, at 25 C., the secondary battery was charged to a charge cut-off voltage of 4.2 V at a constant current rate of 0.1C, then discharged to 1.5 V at 0.1C, left standing for 5 min, and then discharged to a discharge cut-off voltage of 2.8 V at a constant current rate of 0.5C, and left standing for 5 min; and a discharge capacity of the battery at this time was recorded as C.sub.0. The battery was subjected to 500 charge-discharge cycles according to this method, and the discharge capacity of the battery after 500 cycles was recorded as C.sub.1.

[0175] The cycling capacity retention rate of the secondary battery=C.sub.1/C.sub.0100%.

[0176] The testing processes for the capacity retention rates of the secondary batteries in Examples 2 to 24 and Comparative Examples 1 to 4 were the same as above.

[0177] The XRD patterns of the positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 2 are shown in FIG. 6 and FIG. 7. Compared to Example 1, in Comparative Example 1, the ratio d/c of the rare earth element M1 to Mn in the positive electrode active material is 0.004, which is less than 0.005, and the peaks between 10 to 20 of the positive electrode active material are not significant, while the impurity peaks between 30 to 40 are more evident, indicating that too little rare earth element is not conducive to improving the air stability and cycling stability of the positive electrode active material. Compared to Example 1, in Comparative Example 2, the ratio d/c of the rare earth element M1 to Mn in the positive electrode active material is 0.06, which is greater than 0.05, and the positive electrode active material shows obvious impurity peaks, indicating that excessive rare earth element leads to insufficient solid solubility between the rare earth element and Mn, causing aggregation of the rare earth element on the surface of the positive electrode active material and the formation of impurity phases.

[0178] FIG. 8 is a charge-discharge curve of the sodium-ion battery prepared in Example 1 at 0.1C for the first cycle, indicating that the operating voltage range of the battery is 1.5 V to 4.2 V.

[0179] The comparison diagram of the capacity retention rates of Example 1 and Comparative Example 4 is shown in FIG. 9, indicating that the capacity retention rate of Example 1 of the present application is significantly better than that of Comparative Example 4.

TABLE-US-00002 TABLE 2 Capacity Compacted Value of Capacity retention Interlayer density at pH of at rate after Space spacing D.sub.v50 300 MPa soaking 0.1 C 200 cycles group (nm) (m) (g/cm.sup.3) solution (mAh/g) (%) Example 1 R3m 0.537 8.6 3.5 12.7 155 96 Example 2 R3m 0.541 7.2 3.5 12.6 134 92 Example 3 R3m 0.544 8.1 3.6 12.7 132 93 Example 4 R3m 0.542 8.2 3.6 12.7 129 91 Example 5 R3m 0.539 8.5 3.5 12.7 133 92 Example 6 R3m 0.533 8.3 3.4 12.6 124 91 Example 7 R3m 0.543 8.1 3.5 12.7 147 81 Example 8 P63/mmc 0.551 7.1 3.5 12.6 125 94 Example 9 R3m 0.534 9 3.5 12.6 146 95 Example 10 R3m 0.54 8.1 3.4 12.8 143 90 Example 11 R3m 0.532 8.4 3.5 12.6 131 90 Example 12 R3m 0.548 8.1 3.5 12.6 151 81 Example 13 R3m 0.535 8.1 3.6 12.6 129 84 Example 14 R3m 0.538 8.3 3.6 12.5 137 90 Example 15 R3m 0.546 8.5 3.5 12.6 134 88 Example 16 R3m 0.538 8.8 3.4 12.7 140 85 Example 17 R3m 0.533 8.7 3.5 12.5 136 89 Example 18 R3m 0.537 8.4 3.5 12.6 143 93 Example 19 R3m 0.54 8.3 3.5 12.7 141 91 Example 20 R3m 0.543 8.4 3.4 12.5 148 87 Example 21 R3m 0.539 8.6 3.5 12.6 144 86 Example 22 R3m 0.542 8.7 3.4 12.6 139 93 Example 23 R3m 0.547 8.3 3.5 12.5 140 94 Example 24 R3m 0.539 8.9 3.5 12.6 137 96 Comparative R3m 0.548 9.3 3.3 12.8 116 74 Example 1 Comparative R3m 0.544 8.7 3.2 12.6 111 72 Example 2 Comparative R3m 0.539 8.6 3.1 12.6 112 79 Example 3 Comparative R3m 0.541 8.5 3.3 12.7 113 70 Example 4

[0180] It can be seen from Table 2, in the embodiments of the present application, using NiFeMn as the main material, doping with a rare earth element M1 and a doping element M2, and controlling the ratio of the rare earth element M1 to Mn can improve the air stability and cycling stability of the positive electrode active material, thereby enhancing the capacity retention rate of a battery containing the material. Compared to the Examples, in Comparative Examples 1 and 2, the d/c values do not fall within the range of the embodiments of the present application, and in Comparative Examples 3 and 4, the Mn content c values do not fall within the range of the embodiments of the present application, resulting in significantly lower capacity retention rates and capacities of the batteries containing the material.

[0181] In conclusion, it should be noted that the foregoing embodiments are merely for describing the technical solutions of the present application rather than for limiting the present application. Although the present application has been described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should appreciate that they can still make modifications to the technical solutions described in the embodiments or make equivalent replacements to some or all technical features thereof without departing from the scope of the technical solutions of the embodiments of the present application. All such modifications and equivalent replacements shall fall within the scope of claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any manner. The present application is not limited to the specific embodiments disclosed in this specification, but includes all technical solutions falling within the scope of the claims.