Positive electrode material and preparation method therefor, and battery

Abstract

A positive electrode material and a preparation method therefor, and a battery. The positive electrode material comprises a core, a first coating layer, and a second coating layer; the core comprises a lithium cobalt oxide, and the space group of the lithium cobalt oxide is P63mc; the first coating layer covers a portion of the surface of the core, the first coating layer comprises one or more metal oxides, and metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, etc.; and the second coating layer is arranged on the surface of the first coating layer and the surface of the core that is not covered by the first coating layer, and the second coating layer comprises one or more of a metal fluoride, a phosphate, a sulfate, and a borate. By sequentially arranging, outside the lithium cobalt oxide core, a first coating layer and a second coating layer having specific coating modes and materials, the cycling stability of the positive electrode material can be improved, and a positive electrode material having both high reversible capacity and good cycling stability at a high voltage is finally obtained.

Description

Cathode material, preparation method thereof and battery

[0001] The present application claims priority to the Chinese patent application No. 202411396055.9, filed on September 30, 2024, and entitled "Cathode material, preparation method thereof and battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] Embodiments of the present application relate to the technical field of batteries, in particular to a cathode material, a preparation method thereof and a battery. BACKGROUND

[0003] Currently, the most commonly used lithium cobalt oxide cathode material for commercialization of lithium ion batteries in the 3C field is O3 phase structure, which belongs to R-3m space group. Compared with lithium cobalt oxide of R-3m space group, lithium cobalt oxide of P63mc space group exhibits higher reversible capacity and is expected to achieve higher battery energy density. However, during the charge and discharge cycle process, lithium cobalt oxide of P63mc space group is prone to side reactions with electrolyte, leading to continuous dissolution of transition metal elements such as cobalt, and further causing reversible capacity attenuation; and as the charging voltage increases, the capacity attenuation will be more serious. Therefore, in order to better meet the application requirements in the 3C field, it is necessary to provide a cathode material with high reversible capacity and good cycle stability at high voltage. SUMMARY

[0004] In view of this, embodiments of the present application provide a cathode material, a preparation method thereof and a battery. The cathode material is provided by sequentially arranging a first coating layer and a second coating layer with specific coating modes and materials outside the lithium cobalt oxide core, which can improve the cycle stability of the cathode material, and ultimately obtain a cathode material with high reversible capacity and good cycle stability at high voltage.

[0005] In a first aspect, embodiments of the present application provide a cathode material, which includes a core, a first coating layer and a second coating layer.

[0006] The core includes lithium cobalt oxide, and the space group of the lithium cobalt oxide is P63mc.

[0007] The first coating layer coats part of the surface of the core, and the first coating layer includes one or more metal oxides, and the metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb and Ti.

[0008] The second coating layer is arranged on the surface of the first coating layer and the surface of the core not covered by the first coating layer, and the second coating layer comprises one or more of metal fluoride, phosphate, sulfate and borate.

[0009] The positive electrode material of the embodiment of the present application comprises a core and a first coating layer and a second coating layer coated on the surface of the core. The positive electrode material can have high reversible capacity, high structural stability and good cycle performance at high voltage. The core adopts lithium cobalt oxide with a space group of P63mc. Compared with O3 phase, the lithium cobalt oxide has higher structural stability and reversible capacity, and a more stable output voltage, which is conducive to improving the reversible capacity of the positive electrode material and enhancing the energy density of the battery. The first coating layer and the second coating layer are arranged on the surface of the core in sequence to form a composite coating layer. The composite coating layer can effectively inhibit the capacity attenuation caused by the side reaction between the core and the electrolyte during the charge and discharge cycle, thereby improving the cycle structural stability of the positive electrode material. The composite coating layer can also inhibit the increase in polarization caused by the growth of CEI (Chemical-Electrochemical Interface) during the charge and discharge cycle, thereby improving the electrochemical performance and service life of the battery. The presence of the composite coating layer can also effectively inhibit the dissolution of cobalt in the core and inhibit gas production, thereby improving the safety performance of the battery. In addition, the first coating layer comprising a metal oxide is arranged on the inner layer and covers part of the surface of the core. This is conducive to the partial doping of the metal elements in the metal oxide into the lattice of the core to stabilize the interface of the material and provide a lithium-sodium exchange channel, thereby making it feasible to obtain the first coating layer through high-temperature sintering, obtaining a first coating layer stably combined on the surface of the core and improving the cycle stability of the positive electrode material. The second coating layer comprising metal fluoride, phosphate, sulfate and / or borate is coated on the outer layer, which can cover the first coating layer and the exposed area of the core, regulate the dominant ion species of the IHL (Helmholtz Layer) of the positive electrode interface, and further regulate the formation of the CEI, which is conducive to the formation of a more uniform and dense CEI, thereby protecting the interface and further improving the cycle stability of the positive electrode material. The second coating layer can be effectively combined with the first coating layer and the core through coprecipitation and low-temperature sintering, which can avoid damaging the phase structure of the core.

[0010] In the embodiment of the present application, the inner core contains the metal elements of the first coating layer in the surface layer on the side close to the first coating layer. The doping of the metal elements of the first coating layer in the surface layer of the core can effectively inhibit the surface phase transition of the core material, improve the cycle stability and structural reversibility of the positive electrode material, and further improve the cycle life and reversible capacity.

[0011] In the embodiments of the present application, the depth of the surface layer is greater than 0 and less than or equal to 5 μm. Doping the first cladding layer metal element in the surface layer at a certain depth of the core is conducive to better inhibiting the surface phase transition of the core and improving the material performance. The depth of the surface layer, that is, the doping depth of the first cladding layer metal element on the surface of the core, can be obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) or energy dispersive X-ray spectroscopy (SEM-EDS) on the cross section after three-dimensional focused ion beam (3D-FIB) processing or X-ray photoelectron spectroscopy at different etching depths.

[0012] In the embodiments of the present application, the first cladding layer includes one or more metal oxides of Y2O3, Al2O3, MgO, Gd2O3, ZrO2, La2O3, CeO2, Pr2O3, SiO2, SnO2, CuO, W2O3, Eu2O3, In2O3, ZnO, Fe2O3, Sb2O3, and TiO2. Since the core is generally obtained by lithium-sodium ion exchange of a sodium precursor, the use of the above metal oxides can form a partially cladded first cladding layer on the surface of the sodium precursor by solid-phase cladding, so that part of the surface of the sodium precursor is exposed, thereby providing an exchange channel for subsequent lithium-sodium ion exchange of the sodium precursor, better achieving lithium-sodium ion exchange, reducing the sodium residual amount of the core, improving the capacity of the positive electrode material, and also making it feasible to obtain the first cladding layer by high-temperature sintering at greater than 300 ℃, and high-temperature sintering can improve the bonding of the first cladding layer on the surface of the core. Moreover, the above oxides have good lattice matching with the core, can be well attached to the surface of the core, and are conducive to the penetration of the metal elements contained in the above metal oxides in the surface layer of the core, inhibiting the occurrence of surface phase transition of the core and improving the stability of the positive electrode material. The first cladding layer is a crystalline material layer, and the material of the first cladding layer can be obtained by XRD (X-ray diffraction) characterization.

[0013] In the embodiments of the present application, the first cladding layer is discontinuously and dispersedly distributed on the surface of the core. That is, the first cladding layer is a non-continuous film layer structure, the first cladding layer is in direct contact with the core, the metal oxides of the first cladding layer are non-continuously and dispersedly attached to the surface of the entire core by solid-phase cladding, forming a structure in which the first cladding layer clads part of the surface of the core, and the surface of the core not covered by the first cladding layer constitutes a dispersedly distributed channel for lithium-sodium ion exchange.

[0014] In some embodiments of the present application, the first coating layer is discontinuously distributed on the surface of the core in the form of dots and / or islands. The metal oxides of the first coating layer are dispersed on the entire surface of the core, so that the first coating layer only covers part of the surface of the core, and the surface of the core not covered by the first coating layer constitutes a channel for lithium-sodium ion exchange. Therefore, the discontinuous distribution of the first coating layer on the surface of the core in the form of dots and / or islands can not only protect the core and improve the material performance by using metal oxides, but also provide a channel for lithium-sodium exchange, so that high-temperature sintering to obtain the first coating layer becomes feasible, and a first coating layer stably combined with the surface of the core is obtained. The morphology and distribution of the first coating layer can be observed by SEM (Scanning Electron Microscope).

[0015] In some embodiments of the present application, the first coating layer covers 10%-50% of the surface area of the core. That is, the coverage of the first coating layer on the surface of the core is 10%-50%, that is, the coverage area of the first coating layer accounts for 10%-50% of the total surface area of the core, which can be obtained by SEM (Scanning Electron Microscope) combined with software statistics. A suitable coverage of the first coating layer can not only better protect the core, but also provide sufficient lithium-sodium ion exchange channels for the preparation of the positive electrode material.

[0016] In some embodiments of the present application, the mass of the metal elements in the first coating layer accounts for 0.1%-10% of the total mass of the metal elements in the core and the first coating layer. Controlling the coating amount of the first coating layer in a suitable range can improve the cycle performance while making the positive electrode material have a higher capacity. The value can be characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0017] In some embodiments of the present application, the mass ratio of the first coating layer to the core is (0.2-4):100. The coating amount of the first coating layer can be characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0018] In the embodiments of the present application, the second coating layer is a continuous film layer, and the second coating layer is an amorphous material layer. The second coating layer is a continuous film layer, which can completely coat the surface of the first coating layer and the surface of the core not covered by the first coating layer, and better protect the core. The morphology and distribution of the second coating layer can be observed by SEM. The internal structure of the second coating layer can be detected by TEM (Transmission Electron Microscope). The second coating layer is an amorphous material layer, i.e. an amorphous material layer. In some embodiments of the present application, the second coating layer is an amorphous metal fluoride layer; in some embodiments, the second coating layer is an amorphous phosphate layer; in some embodiments, the second coating layer is an amorphous sulfate layer; and in some embodiments, the second coating layer is an amorphous borate layer. The second coating layer is insoluble in non-aqueous electrolyte but soluble in water, so the second coating layer can not only adapt to the non-aqueous electrolyte system, but also be dissolved by water to realize the characterization of the material of the second coating layer, and facilitate the characterization of the core and the coating layer.

[0019] In the embodiments of the present application, the second coating layer completely covers the surface of the first coating layer and the surface of the core not covered by the first coating layer. The second coating layer completely coats the surface of the first coating layer and the surface of the core not covered by the first coating layer, which can better protect the core and improve the cycle stability of the positive electrode material.

[0020] In the embodiments of the present application, the metal fluoride includes Li x M 2 y F z , or one or more of LiPF6; the phosphate includes Li x M 2 y (PO4) z ; the sulfate includes Li x M 2 y (SO4) z ; and the borate includes Li x M 2 y (BO3) z ; wherein in each compound, M 2 is independently selected from one or more of Al, La, Ti, Zr, Mg, Zn, Y, Ca, Fe, Ce, x and y are independently integers of 0-6 and x+y≥1, z is independently an integer of 1-6, and x, y and z satisfy valence balance. The above-mentioned materials can form a continuous amorphous structure film layer by wet coating and sintering, and better improve the cycle performance of the positive electrode material.

[0021] It should be noted that x in each of the above chemical formulas has no correlation, y in each of the chemical formulas has no correlation, and z in each of the chemical formulas has no correlation. The subscript variable used in the following chemical formulas to represent the molecular number ratio is also the same as that of x, y and z, and the same letters such as x, y and the like in different chemical formulas have no correlation, but are not distinguished for the convenience of description.

[0022] In the embodiments of the present application, the mass ratio of the second coating layer to the core is (0.2-4):100. Controlling the mass of the second coating layer in a suitable range can maintain a high capacity of the positive electrode material while improving the cycle performance of the positive electrode material by using the second coating layer.

[0023] In the embodiments of the present application, the thickness of the second coating layer is 5 nm-100 nm. A suitable thickness of the second coating layer can maintain a high capacity of the positive electrode material while improving the cycle performance of the positive electrode material by using the second coating layer.

[0024] In the embodiments of the present application, the core is a single crystal particle, and the particle size can be 2 μm-18 μm. A suitable particle size of the core can make the finally obtained positive electrode material have a suitable particle size, obtain a suitable tap density and specific surface area, and thus improve the volume capacity and safety performance of the positive electrode material.

[0025] In the embodiments of the present application, the main peak in the XRD pattern of the lithium cobalt oxide is located at 18.5°±0.5°; or the main peak in the XRD pattern of the positive electrode material is located at 18.5°±0.5°. 18.5°±0.5° is the peak position of the 002 crystal face.

[0026] In the embodiments of the present application, the lithium cobalt oxide can be various P63mc structure lithium cobalt oxides. In some embodiments, the lithium cobalt oxide includes a lithium cobalt nickel manganese oxide, and the chemical formula of the lithium cobalt nickel manganese oxide is Li x1 Na x2 Ni a Mn b M 1 c Co 1-a-b-c O 2+y , wherein 0.8≤x1<1.0, 0.005≤x2≤0.02, 0 1 is selected from one or more of Al, Mg, Y, Zr, Ti, La, Zn, La, Ce, Eu, Er, Zn, Ca, W, -0.1≤y≤0.1.

[0027] In the embodiment of the present application, the first peak temperature of the DSC (Differential Scanning Calorimetry) curve of the positive electrode sheet prepared by using the positive electrode material is greater than 195℃ at a half-cell voltage of 4.62V. The first peak is a decomposition peak of the positive electrode material caused by the decomposition of the electrolyte. The higher the first peak temperature, the better the high-temperature resistance of the positive electrode material of the present application, which can improve the high-temperature cycle stability, and also indicates that it can have good cycle stability at a high voltage of 4.62V.

[0028] The second aspect of the embodiment of the present application provides a preparation method of the positive electrode material of the first aspect, comprising:

[0029] The sodium precursor and the first coating layer raw material are mixed in solid phase and subjected to first sintering to obtain a sodium precursor with a first coating layer on the surface; the first coating layer coats part of the surface of the sodium precursor, and the first coating layer comprises one or more metal oxides, and the metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb, Ti;

[0030] The sodium precursor with the first coating layer on the surface is mixed with a lithium salt to perform lithium-sodium ion exchange to obtain an inner core with the first coating layer on the surface; the inner core comprises lithium cobalt oxide, and the space group of the lithium cobalt oxide is P63mc; and the first coating layer coats part of the surface of the inner core;

[0031] The inner core with the first coating layer on the surface is mixed with an aqueous solution of a second coating layer raw material, and subjected to reaction and second sintering to form a second coating layer on the surface of the first coating layer and the surface of the inner core not covered by the first coating layer, thereby obtaining the positive electrode material; and the second coating layer comprises one or more of metal fluoride, phosphate, sulfate and borate.

[0032] In the embodiment of the present application, the particle size of the first coating layer raw material is 1nm-100nm; the solid phase mixing adopts ball milling mixing, the ball milling rotation speed is 200-400r / min, and the time is 4-8h; and the temperature of the first sintering is 700℃-1000℃, and the time is 8-12h.

[0033] In the embodiment of the present application, the lithium salt comprises a first lithium salt and a second lithium salt, the first lithium salt comprises lithium nitrate, and the second lithium salt comprises at least one of lithium chloride, lithium bromide, lithium oxalate and lithium iodide; the temperature of the ion exchange is 250℃-280℃, and the time is 6-10h.

[0034] In the embodiments of the present application, the temperature of the reaction is 60-80 DEG C, and the time is 6-10 hours; the temperature of the second sintering is 200-500 DEG C, and the time is 2-8 hours.

[0035] In the embodiments of the present application, the atmosphere of the first sintering is air; and the atmosphere of the second sintering is air or nitrogen.

[0036] In the embodiments of the present application, the second coating layer raw material comprises a metal source and a non-metal source, the metal source comprises a soluble metal salt, and the non-metal source comprises one or more of ammonium fluoride, ammonium phosphate, ammonium sulfate and ammonium borate.

[0037] The third aspect of the embodiments of the present application provides a positive electrode sheet, which comprises the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the second aspect. The positive electrode sheet is used in a battery, and can improve the high-pressure cycle stability of the battery.

[0038] The fourth aspect of the embodiments of the present application provides a battery, which comprises the positive electrode sheet of the third aspect or the positive electrode material of the first aspect. The battery is used in an electric device, and can improve the performance of the device.

[0039] The embodiments of the present application also provide an electric device, which comprises the battery of the fourth aspect, and the battery provides electric energy for the electric device. The battery provided by the embodiments of the present application can improve the performance of the electric device and the competitiveness of the product.

[0040] The embodiments of the present application also provide an energy storage device, which comprises the battery of the fourth aspect, and the battery stores electric energy for the energy storage device. The battery provided by the embodiments of the present application can improve the performance of the energy storage device and the competitiveness of the product. BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 is a schematic diagram of the cross-sectional structure of the positive electrode material 100 provided by the embodiments of the present application;

[0042] FIG. 2 is a schematic diagram of the preparation method of the positive electrode material 100 provided by the embodiments of the present application;

[0043] FIG. 3 is a schematic diagram of the cross-sectional structure of the positive electrode sheet 200 provided by the embodiments of the present application;

[0044] FIG. 4 is a schematic diagram of the structure of the battery 300 provided by the embodiments of the present application;

[0045] FIG. 5 is a schematic diagram of an electric device 400 provided by the embodiments of the present application;

[0046] Figure 6 is an SEM picture and EDS (Energy Dispersive Spectrometer) elemental analysis result chart of the sodium precursor with a first coating layer prepared in step (2) of Example 1 of the present application;

[0047] Figure 7 is an SEM picture and EDS elemental analysis result chart of the positive electrode material prepared in Example 1;

[0048] Figure 8 is an SEM picture and EDS elemental analysis result chart of the sodium precursor with a first coating layer prepared in step (2) of Example 6;

[0049] Figure 9 is an XRD chart of the positive electrode material of Example 1;

[0050] Figure 10 is an XRD chart of the positive electrode material of Comparative Example 1;

[0051] Figure 11 is a discharge curve of the button cell of Examples 12-15 and Comparative Examples 4-5 of the present application. DETAILED DESCRIPTION

[0052] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0053] The most commonly used lithium cobalt oxide positive electrode material for commercial lithium ion batteries in the field of 3C is of O3 phase structure, belonging to R-3m space group. The theoretical gravimetric capacity of the commonly used commercial lithium cobalt oxide positive electrode material is 274 mAh / g, and when charged to 4.45 V (vs. Li / Li + ), the actual gravimetric capacity is only 175 mAh / g, far lower than the theoretical value; when charged to 4.6 V (vs. Li / Li +), which can increase the specific capacity to 220 mAh / g, but inevitably brings structural and surface instability problems, and cycle performance deterioration. Compared with lithium cobalt oxide with R-3m space group (O3 phase), lithium cobalt oxide with P63mc space group shows higher reversible capacity, and is expected to realize higher battery energy density. However, lithium cobalt oxide with P63mc space group is prone to side reactions with electrolyte during charge and discharge cycles, leading to continuous dissolution of transition metal elements such as cobalt, and further causing reversible capacity attenuation; and with the increase of charging voltage, the capacity attenuation will be more serious. Therefore, in order to better meet the application requirements in the field of 3C, it is necessary to provide a positive electrode material with high reversible capacity and good cycle stability at high voltage. However, lithium cobalt oxide with P63mc space group cannot be directly synthesized, and needs to be synthesized from sodium precursor NCO (sodium cobalt oxide), potassium precursor KCO (potassium cobalt oxide) and the like through ion exchange; and lithium cobalt oxide with P63mc space group is thermodynamically unstable, and if high-temperature heat treatment above 300 DEG C is performed, the material is prone to R-3m phase transition; thus, it is very difficult for the industry to modify lithium cobalt oxide with P63mc space group to improve the cycle stability at high voltage. In view of this, the positive electrode material and the preparation method thereof provided in the embodiments of the present application can improve the cycle stability of the positive electrode material by sequentially arranging the first coating layer and the second coating layer with specific coating modes and materials outside the core of lithium cobalt oxide with P63mc space group, and obtain a positive electrode material with high reversible capacity and good cycle stability at high voltage.

[0054] Referring to FIG. 1, FIG. 1 is a schematic diagram of the cross-sectional structure of the positive electrode material 100 provided in the embodiments of the present application, the positive electrode material 100 includes a core 11, a first coating layer 12 and a second coating layer 13; the first coating layer 12 coats part of the surface of the core 11; and the second coating layer 13 is arranged on the surface of the first coating layer 12 and the surface of the core 11 which is not covered by the first coating layer 12.

[0055] Among them, the core 11 includes lithium cobalt oxide, and the space group of the lithium cobalt oxide is P63mc; the first coating layer 12 includes one or more metal oxides, and the metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb, Ti; and the second coating layer 13 includes one or more of metal fluoride, phosphate, sulfate and borate.

[0056] It should be noted that FIG. 1 only illustrates the coating relationship between the first coating layer 12 and the second coating layer 13 and the core 11, and does not limit the structure of the positive electrode material of the embodiments of the present application.

[0057] The positive electrode material 100 of the embodiment of the present application comprises an inner core 11 and a first coating layer 12 and a second coating layer 13 coated on the surface of the inner core 11, and can have high reversible capacity, high structural stability and good cycle performance at high voltage. The inner core 11 adopts lithium cobalt oxide with a space group of P63mc, which has higher structural stability and reversible capacity than O3 phase, and a more stable output voltage, which is conducive to improving the reversible capacity of the positive electrode material and improving the energy density of the battery; the composite coating layer is formed by sequentially arranging the first coating layer 12 and the second coating layer 13 on the surface of the inner core 11, which can effectively inhibit the capacity attenuation caused by the side reaction between the inner core 11 and the electrolyte during the charge and discharge cycle, thereby improving the cycle structural stability of the positive electrode material; the composite coating layer can also inhibit the increase of polarization caused by the growth of CEI (Chemical-Electrochemical Interface) during the charge and discharge cycle, thereby improving the electrochemical performance and service life of the battery; at the same time, the existence of the composite coating layer can also effectively inhibit the cobalt dissolution of the inner core 11, inhibit the gas production, and improve the safety performance of the battery; in addition, the first coating layer 12 comprising metal oxide is arranged in the inner layer and arranged to coat part of the surface of the inner core 11, which is conducive to the partial doping of the metal elements in the metal oxide into the lattice of the inner core 11 to stabilize the interface of the material, and can provide a lithium-sodium exchange channel, thereby making it feasible to obtain the first coating layer 12 through high-temperature sintering, obtaining the first coating layer 12 stably combined on the surface of the inner core 11, and improving the cycle stability of the positive electrode material 100; and the second coating layer 13 comprising metal fluoride, phosphate, sulfate and / or borate can cover the first coating layer 12 and the exposed area of the inner core 11 at the same time, control the advantage ion species of the IHL (Helmholtz Layer) of the positive electrode interface, and then control the formation of the CEI, which is conducive to the formation of a more uniform and dense CEI, thereby protecting the interface and further improving the cycle stability of the positive electrode material 100; and the second coating layer 13 can be effectively combined with the first coating layer 12 and the inner core 11 through coprecipitation and low-temperature sintering, which can avoid damaging the phase structure of the inner core 11.

[0058] In the embodiment of the present application, the inner core 11 is a single crystal particle, and the particle size can be 2-18 μm. In some embodiments, the particle size of the inner core 11 can be, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm. Suitable inner core particle size can enable the final obtained positive electrode material to have a suitable particle size, obtain a suitable tap density and specific surface area, and thereby improve the volume capacity and safety performance of the positive electrode material. The inner core 11 can be regular or irregular particles, for example, spherical or spherical-like particles.

[0059] In the embodiments of the present application, the main peak in the XRD pattern of the lithium cobalt oxide is located at 18.5°±0.5°. Based on the structure of the positive electrode material 100 of the present application, the presence of the first coating layer 12 and the second coating layer 13 does not affect the position of the main peak of the lithium cobalt oxide, so the main peak in the XRD pattern of the positive electrode material 100 is also located at 18.5°±0.5°. 18.5°±0.5° is the peak position of the 002 crystal plane.

[0060] In the embodiments of the present application, the lithium cobalt oxide can be various P63mc structure lithium cobalt oxides. The lithium cobalt oxide can include only lithium and cobalt two metal elements, or only lithium, sodium, and cobalt three metal elements. In some embodiments, the lithium cobalt oxide includes lithium cobalt nickel manganese oxide, and the chemical formula of the lithium cobalt nickel manganese oxide is Li x1 Na x2 Ni a Mn b M 1 c Co 1-a-b-c O 2+y , wherein 0.8≤x1<1.0, 0.005≤x2≤0.02, 0 1 selected from one or more of Al, Mg, Y, Zr, Ti, La, Zn, La, Ce, Eu, Er, Zn, Ca, W, -0.1≤y≤0.1, each value satisfying the valence balance. In some embodiments, x1may be 0.8, 0.85, 0.9, 0.95, 1.0. In some embodiments, x2may be 0.005, 0.006, 0.007, 0.008, 0.01, 0.012, 0.014, 0.015, 0.018, 0.02. In some embodiments, a can be 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments, b can be 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1. In some embodiments, c can be 0, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05.

[0061] In the embodiments of the present application, the core 11 contains the metal elements of the first coating layer 12 in the surface layer 111 close to the first coating layer 12. The doping amount of the metal elements of the first coating layer 12 in the surface layer 111 can be in the range of 1000-10000 ppm. Referring to FIG. 1, the surface layer 111 is schematically shown by a dashed line (which does not exist in the actual product) in FIG. 1, and the surface layer 111 is a shallow layer region of the core 11 containing the metal elements of the first coating layer 12 close to the surface. For example, the first coating layer 12 contains Y elements, and the surface layer 111 of the core 11 contains Y elements; the first coating layer 12 contains Mg elements, and the surface layer 111 of the core 11 contains Mg elements; the first coating layer 12 contains Al elements, and the surface layer 111 of the core 11 contains Al elements; the first coating layer 12 contains Gd elements, and the surface layer 111 of the core 11 contains Gd elements. The doping of the metal elements of the first coating layer 12 in the surface layer of the core 11 can effectively inhibit the surface phase transition of the lithium cobalt oxide of the core 11, improve the cycle stability and structural reversibility of the positive electrode material, and further improve the cycle life and reversible capacity.

[0062] In the embodiments of the present application, the doping depth of the metal elements of the first coating layer 12 on the surface of the core 11 is greater than 0 and less than or equal to 5 μm, that is, the thickness of the surface layer 111. In some embodiments, the doping depth can be, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, and the doping of the metal elements of the first coating layer 12 in the surface layer 111 of the core 11 at a certain depth is beneficial to better inhibit the surface phase transition of the core and improve the material performance. In some embodiments, the doping depth can also be 0 μm, that is, there is no doping of the metal elements of the first coating layer into the surface of the core 11. The doping depth of the metal elements of the first coating layer on the surface of the core can be obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) or energy dispersive X-ray spectroscopy (SEM-EDS) on the cross section after three-dimensional focused ion beam (3D-FIB) treatment or X-ray photoelectron spectroscopy at different etching depths.

[0063] In some embodiments, the first coating layer 12 comprises one or more metal oxides, wherein the metal element in the metal oxide is selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb, Ti. The metal oxide can be an oxide containing one metal, or an oxide containing two or more metals, or an oxide containing two or more oxidation states of the same metal (i.e., a metal composite oxide). In some embodiments, the first coating layer 12 can comprise one or more metal oxides selected from Y2O3, Al2O3, MgO, Gd2O3, ZrO2, La2O3, CeO2, Pr2O3, SiO2, SnO2, CuO, W2O3, Eu2O3, In2O3, ZnO, Fe2O3, Sb2O3, TiO2. In some embodiments, the first coating layer 12 comprises one or more of Y2O3, Al2O3, MgO, Gd2O3. In some embodiments, the first coating layer 12 comprises one metal oxide, for example, Y2O3, or Al2O3, or MgO, or Gd2O3; in some embodiments, the first coating layer 12 comprises multiple (two or more) metal oxides, for example, Y2O3 and Al2O3, or Y2O3 and MgO, or Y2O3, Al2O3 and MgO, or Y2O3 and Gd2O3. In some embodiments, when the first coating layer 12 comprises multiple metal oxides, the mass ratio of the metal oxide with the largest content to the metal oxide with the smallest content is less than 10:1, for example, the mass ratio of the metal oxide with the largest content to the metal oxide with the smallest content is 1:1, 2:1, 3:1, 4:1, 5:1, which is conducive to improving the performance of the positive electrode material. Since the inner core 11 is generally obtained by lithium-sodium ion exchange of a sodium precursor, the use of the above metal oxides can form a partially coated first coating layer on the surface of the sodium precursor by a solid-phase coating method, so that part of the surface of the sodium precursor is exposed, thereby providing an exchange channel for the subsequent lithium-sodium ion exchange of the sodium precursor, better realizing lithium-sodium ion exchange, reducing the sodium residual amount of the inner core, reducing the risk of gas generation, improving the capacity of the positive electrode material, and also making it feasible to obtain the first coating layer by high-temperature sintering of greater than 300°C, and high-temperature sintering can improve the bonding of the first coating layer on the surface of the inner core. Moreover, the above metal oxides have good lattice matching with the inner core, can be well attached to the surface of the inner core, and are conducive to the penetration of the metal elements contained in the above metal oxides into the surface layer of the inner core, inhibiting the occurrence of phase transformation on the surface of the inner core, and improving the stability of the positive electrode material. The first coating layer 12 is a crystalline material layer, and the material of the first coating layer 12 can be characterized by XRD (X-ray diffraction).

[0064] In some embodiments of the present application, the first coating layer 12 is discontinuously distributed on the surface of the core 11 in the form of dots and / or islands. The metal oxide of the first coating layer 12 is discontinuously distributed on the surface of the core 11, so that the first coating layer 12 only covers part of the surface of the core 11, and the surface of the core 11 not covered by the first coating layer 12 constitutes a channel for lithium-sodium ion exchange. Therefore, the discontinuous distribution of the first coating layer 12 on the surface of the core 11 in the form of dots and / or islands can not only protect the core 11 and improve the material performance by using metal oxides, but also provide a channel for lithium-sodium exchange, so that high-temperature sintering to obtain the first coating layer 12 becomes feasible, and the first coating layer 12 stably combined on the surface of the core 11 is obtained. The morphology and distribution of the first coating layer 12 can be observed by SEM (Scanning Electron Microscope).

[0065] In some embodiments of the present application, the first coating layer 12 is discontinuously distributed on the surface of the core 11 in the form of dots and / or islands. The metal oxide of the first coating layer 12 is discontinuously distributed on the surface of the core 11, so that the first coating layer 12 only covers part of the surface of the core 11, and the surface of the core 11 not covered by the first coating layer 12 constitutes a channel for lithium-sodium ion exchange. Therefore, the discontinuous distribution of the first coating layer 12 on the surface of the core 11 in the form of dots and / or islands can not only protect the core 11 and improve the material performance by using metal oxides, but also provide a channel for lithium-sodium exchange, so that high-temperature sintering to obtain the first coating layer 12 becomes feasible, and the first coating layer 12 stably combined on the surface of the core 11 is obtained. The morphology and distribution of the first coating layer 12 can be observed by SEM (Scanning Electron Microscope).

[0066] In some embodiments of the present application, the first coating layer 12 covers 10%-50% of the surface area of the core 11. That is, the coverage of the first coating layer 12 on the surface of the core 11 is 10%-50%, that is, the coverage area of the first coating layer 12 accounts for 10%-50% of the total surface area of the core 11, which can be obtained by SEM (Scanning Electron Microscope) combined with software statistics. In some embodiments, the coverage of the first coating layer 12 on the surface of the core 11 is 10%, 20%, 30%, 40%, or 50%. A suitable coverage of the first coating layer can not only better protect the core 11, but also provide sufficient lithium-sodium ion exchange channels for the preparation of the positive electrode material 100.

[0067] In some embodiments of the present application, the mass of the metal elements in the first coating layer 12 accounts for 0.1%-10% of the total mass of the metal elements in the core 11 and the first coating layer 12. For example, the mass of the metal elements in the first coating layer 12 accounts for 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the total mass of the metal elements in the core 11 and the first coating layer 12. Controlling the coating amount of the first coating layer 12 in a suitable range can improve the cycle performance while making the positive electrode material 100 have a higher capacity. The value can be characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0068] In this embodiment, the mass ratio of the first coating layer 12 to the core 11 is (0.2-4):100. In some embodiments, the mass ratio of the first coating layer 12 to the core 11 is 0.2:100, 0.5:100, 1:100, 2:100, 3:100, or 4:100. The coating amount of the first coating layer can be characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0069] In this embodiment, the second coating layer 13 is a continuous film layer that can completely cover the surface of the first coating layer 12 and the surface of the core 11 not covered by the first coating layer 12, thereby better protecting the core 11. The morphology and distribution of the second coating layer 13 can be observed by SEM.

[0070] In this application, the second coating layer 13 is an amorphous material layer, i.e., an amorphous material layer. In some embodiments of this application, the second coating layer 13 is an amorphous metal fluoride layer; in some embodiments, the second coating layer 13 is an amorphous phosphate layer; in some embodiments, the second coating layer 13 is an amorphous sulfate layer; and in some embodiments, the second coating layer 13 is an amorphous borate layer. The internal structure of the second coating layer 13 can be detected by TEM (Transmission Electron Microscope). The second coating layer 13 is insoluble in non-aqueous electrolytes but soluble in water. Therefore, the second coating layer 13 can not only adapt to non-aqueous electrolyte systems and protect the core 11, but also can be dissolved in water. This allows the second coating layer 13 to be dissolved and removed with water to characterize its material, and also facilitates the characterization of the core 11 and the first coating layer 12.

[0071] In this embodiment, the second coating layer 13 completely covers the surface of the first coating layer 12 and the surface of the core 11 not covered by the first coating layer 12. The second coating layer 13 completely covers the surface of the first coating layer 12 and the surface of the core 11 not covered by the first coating layer 12, which can better protect the core 11, improve the interface between the positive electrode and the electrolyte, and enhance the cycle stability of the positive electrode material 100.

[0072] In this embodiment, the second coating layer 13 comprises one or more of metal fluorides, phosphates, sulfates, and borates. The metal fluoride may include Li... x M 2 y F z One or more of LiPF6; the phosphate may include Li x M 2 y (PO4)z ; the sulfate can be Li x M 2 y (SO4) z ; the borate can be Li x M 2 y (BO3) z ; each of the above M 2 in the compounds involving x, y, z, M 2 is independently selected from one or more of Al, La, Ti, Zr, Mg, Zn, Y, Ca, Fe, Ce, x, y are independently an integer from 0 to 6 and x+y > 1, z is independently an integer from 1 to 6, and x, y, z satisfy the valence balance. The integer from 0 to 6 can be specifically 0, 1, 2, 3, 4, 5, 6. The integer from 1 to 6 can be specifically 1, 2, 3, 4, 5, 6. It should be noted that x in each of the above chemical formulas has no correlation, y in each of the above chemical formulas has no correlation, and z in each of the above chemical formulas has no correlation, but is only for the convenience of description. When the second coating layer 13 includes Li x M 2 y F z , Li x M 2 y (PO4) z , Li x M 2 y (SO4) z , and Li x M 2 y (BO3) z , M 2 in different chemical formulas can be the same metal element or different metal elements. The above materials can form a continuous amorphous structure film layer through wet coating and sintering, preferably improve the cycle performance of the positive electrode material, and can be uniformly deposited on the inner core and the surface of the first coating layer through co-precipitation and the like, and low-temperature re-sintering can achieve good interface fusion effect. In addition, for the metal fluoride, phosphate, sulfate and borate containing lithium, active lithium can also be provided, which can additionally supplement lithium for the positive electrode material 100.

[0073] In some embodiments, Li x M 2 y F z may be represented as M 2 y F z or LiF. In some embodiments, Li x M2 y (PO4) z may be represented as M 2 y (PO4) z or Li3PO4. In some embodiments, Li x M 2 y (SO4) z may be represented as M 2 y (SO4) z or Li2SO4. In some embodiments, Li x M 2 y (BO3) z may be represented as M 2 y (BO3) z or Li3BO3. In some embodiments, the second coating layer 13 comprises one or more of Li3Al(PO4)2, LiAl(SO4)2, LiAlF4, Li3Al(BO3)2.

[0074] In embodiments of the present application, the mass ratio of the second coating layer 13 to the core 11 is (0.2-4): 100. In some embodiments, the mass ratio of the second coating layer 13 to the core 11 is 0.2: 100, 0.5: 100, 1: 100, 2: 100, 3: 100, 4: 100. Controlling the mass of the second coating layer 13 in a suitable range can improve the cycle performance of the positive electrode material 100 while ensuring that the interface polarization does not increase much, so that the positive electrode material 100 maintains a high capacity.

[0075] In embodiments of the present application, the thickness of the second coating layer 13 is 5 nm-100 nm. In some embodiments, the thickness of the second coating layer 13 may, for example, be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm. A suitable thickness of the second coating layer can improve the cycle performance of the positive electrode material while maintaining a high capacity of the positive electrode material.

[0076] In embodiments of the present application, the total thickness of the first coating layer 12 and the second coating layer 13 is 5 nm-100 nm. Exemplarily, the total thickness is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm.

[0077] In the embodiments of the present application, the particle size Dv50 of the positive electrode material 100 is 2-18 μm. Dv50 is the volume median particle size, which is the particle size when the cumulative volume distribution is 50%. For example, the particle size Dv50 of the positive electrode material 100 is 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, or 18 μm.

[0078] In the embodiments of the present application, the first peak temperature of the DSC (Differential Scanning Calorimetry) curve of the positive electrode sheet prepared by using the positive electrode material 100 at a half-cell voltage of 4.62 V is greater than 195℃. The first peak is a decomposition peak of the positive electrode material 100 caused by electrolyte decomposition. A higher first peak temperature indicates that the positive electrode material 100 of the present application has good high-temperature resistance, which can improve the high-temperature cycle stability, and also indicates that it has good cycle stability at a high voltage of 4.62 V.

[0079] The positive electrode material 100 provided in the embodiments of the present application can effectively block the side reaction of P63mc lithium cobalt oxide and electrolyte, inhibit the growth of CEI on the positive electrode surface, inhibit the dissolution of cobalt in P63mc lithium cobalt oxide, and inhibit gas production, thereby improving the electrochemical performance, service life, and safety performance of the material. Moreover, the positive electrode material 100 can be prepared by using a method of high-temperature coating before ion exchange of a sodium precursor and low-temperature coating after ion exchange, without affecting the crystal phase structure of the P63mc lithium cobalt oxide core.

[0080] The embodiments of the present application also provide a preparation method of the positive electrode material 100 described above. Referring to FIG. 2, FIG. 2 is a flowchart of the preparation method of the positive electrode material 100 provided in the embodiments of the present application. The preparation method comprises the following steps:

[0081] S10, solid-phase coating of a first coating layer: solid-phase mixing the sodium precursor 101 and the first coating layer raw material 102 and first sintering to obtain a sodium precursor 103 with a first coating layer on the surface; the first coating layer raw material 102 comprises one or more metal oxides;

[0082] The sodium precursor 101 is the precursor of the core 11, and the lithium cobalt oxide of the core 11 can be obtained after lithium-sodium ion exchange of the sodium precursor 101. The sodium precursor 101 also has a P63mc space group structure. For example, the sodium precursor 101 can be Na 0.86 Co 0.93 Ni 0.02 Mn 0.05 O2、Na 0.86 Co 0.93 Ni0.02 Mn 0.05 O2, etc. The sodium precursor 101 can be selected according to the desired size of the core particle. The first coating layer material can be in the form of particles, and the particle size Dv50 of the particles can be 1 nm-100 nm. For example, the particle size Dv50 of the first coating layer material can be 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm. The use of nanoscale metal oxide particles for solid-phase mixing with the sodium precursor facilitates the dispersion of the metal oxide on the surface of the sodium precursor, forming a relatively uniform first coating layer that is stably combined with the surface of the core. The feed ratio of the sodium precursor 101 to the first coating layer material 102 can be controlled according to the stoichiometric ratio.

[0083] The sodium precursor 101 can be purchased from the market or prepared by the user. In some embodiments, the sodium precursor 101 is prepared as follows:

[0084] After the sodium precursor material is mixed according to the stoichiometric ratio, the mixture is first pre-sintered at 400-600°C, then cooled to room temperature and ground, and then heated to 700-900°C and sintered for 20-30 hours.

[0085] It can be understood that the sodium precursor material is selected according to the composition of the pre-prepared sodium precursor. For example, the sodium precursor includes sodium elements, cobalt elements, nickel elements, manganese elements, M 1 elements, and accordingly the sodium precursor material includes sodium salts, cobalt salts, nickel salts, manganese salts, M 1 salts. The sodium salt can include sodium carbonate. The cobalt salt includes but is not limited to one or more of cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt chloride, and cobalt acetate. The manganese salt includes but is not limited to one or more of manganese nitrate, manganese sulfate, manganese carbonate, manganese chloride, and manganese acetate. The nickel salt includes but is not limited to one or more of nickel nitrate, nickel carbonate, nickel sulfate, nickel chloride, and nickel acetate. The stoichiometric ratio of sodium ions in the sodium salt to the total metal ions in the cobalt salt, nickel salt, manganese salt, and M 1 salt is 0.5-1.05, and for example, the stoichiometric ratio is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or 1.05.

[0086] Solid-phase mixing can be performed using ball milling, and the ball milling speed can be 200-400 rpm, for example, 200 rpm, 300 rpm, or 400 rpm, for a time period of 4-8 hours, for example, 4 hours, 6 hours, or 8 hours. The use of solid-phase mixing can effectively avoid the adverse effects of the sodium precursor 101 due to its water absorption. Suitable speeds facilitate sufficient mixing and avoid breaking the sodium precursor particles.

[0087] In the embodiments of the present application, the temperature of the first sintering can be 700-1000℃, and the time can be 8-12 hours. Exemplarily, the temperature of the first sintering is 700℃, 800℃, 900℃, 1000℃, and the time is 8 hours, 10 hours, 12 hours. High-temperature sintering is conducive to forming the first coating layer with strong binding force, high density and high strength from the metal oxide.

[0088] The first coating layer is prepared by the solid-phase coating method, which not only protects the sodium precursor from contacting with water, but also forms a structure covering part of the surface of the sodium precursor, thereby providing an exchange channel for the lithium-sodium ion exchange in the subsequent step S20, and enabling the metal oxide to form the first coating layer with strong binding force, high density and high strength on the surface of the sodium precursor through high-temperature sintering.

[0089] S20, lithium-sodium ion exchange: mixing the sodium precursor 103 with the first coating layer on the surface with a lithium salt to perform lithium-sodium ion exchange, to obtain the inner core 104 with the first coating layer on the surface;

[0090] The lithium salt can include a first lithium salt and a second lithium salt, the first lithium salt includes lithium nitrate, and the second lithium salt includes at least one of lithium chloride, lithium bromide, lithium oxalate and lithium iodide. The molar ratio of the first lithium salt to the second lithium salt can be 1-10:1, which is conducive to better ion exchange. Exemplarily, the molar ratio of the first lithium salt to the second lithium salt can be 1:1, 2:1, 3:1, 5:1, 7:1, 8:1, 10:1. The sodium precursor 103 with the first coating layer on the surface can be mixed with the lithium salt in a stoichiometric ratio of 1.2-10.

[0091] The temperature of the lithium-sodium ion exchange can be 250-280℃, and the time can be 6-10 hours. Exemplarily, the temperature of the lithium-sodium ion exchange can be 250℃, 260℃, 270℃, 280℃, and the time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours. After the ion exchange is completed, the inner core 104 with the first coating layer on the surface is washed with water and then dried.

[0092] S30, wet coating of the second coating layer: mixing the inner core 104 with the first coating layer on the surface with an aqueous solution of the second coating layer raw material, and forming the second coating layer on the surface of the inner core 104 with the first coating layer on the surface through reaction and second sintering, to obtain the positive electrode material 100.

[0093] In the embodiments of the present application, the second coating layer raw material includes a metal source and a non-metal source. The metal source includes a soluble metal salt, for example, the metal source includes a soluble lithium source and / or a soluble M 2 source, the metal source specifically can include a soluble lithium salt and / or a soluble M 2Salt. The soluble metal salt can be an inorganic salt or an organic salt. The soluble lithium salt is, for example, lithium hydroxide, and the soluble aluminum salt is, for example, aluminum nitrate nine hydrate. In some embodiments, the soluble metal salt includes an inorganic salt or an organic salt of Li, Al, La, Ti, Zr, Mg, Zn, Y, Ca, Fe, and / or Ce. The non-metal source can include one or more of ammonium fluoride, ammonium phosphate, ammonium sulfate, and ammonium borate. The second coating layer raw material can be specifically selected according to the pre-prepared second coating layer. For example, if the pre-prepared second coating layer contains lithium fluoride, the second coating layer raw material includes a soluble lithium salt and ammonium fluoride; if the pre-prepared second coating layer contains aluminum fluoride, the second coating layer raw material includes a soluble aluminum salt and ammonium fluoride; and if the pre-prepared second coating layer contains aluminum sulfate, the second coating layer raw material includes a soluble aluminum salt and ammonium sulfate. The second coating layer raw material is added according to the stoichiometric ratio.

[0094] In the embodiments of the present application, the reaction temperature can be 60-80°C, and the reaction time is 6-10 hours. For example, the reaction temperature is 60°C, 70°C, 80°C, and the reaction time is 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. The second sintering temperature is 200-300°C, and the second sintering time is 2-8 hours. For example, the second sintering temperature can be 200°C, 220°C, 250°C, 280°C, or 300°C, and the second sintering time can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours. Sintering at a lower temperature is conducive to forming the second coating layer with an amorphous continuous film layer structure.

[0095] In the embodiments of the present application, the second sintering atmosphere can be air or nitrogen. The second sintering in a nitrogen atmosphere is conducive to improving the coating effect and the performance of the positive electrode material compared with sintering in an air atmosphere.

[0096] In an embodiment, the process of wet coating the second coating layer is specifically as follows: the core 104 with the surface having the first coating layer obtained in step S20 is put into a reaction kettle at 60-80°C, a certain amount of water is added and stirred, then a soluble metal salt is added, and after complete dissolution, a non-metal source is added, the temperature is maintained, and after stirring for 6-10 hours, filtration, washing, and drying are performed, and then second sintering is performed to obtain the positive electrode material 100.

[0097] In some embodiments, after the second sintering is completed, a crushing treatment is further performed, and soluble salts are removed by washing until the supernatant conductivity is less than 200 μS / cm, and then the washed powder is subjected to suction filtration, drying, and sieving, and the like, to finally obtain the positive electrode material 100.

[0098] The preparation method of the positive electrode material in the embodiment of the present application can obtain a composite coating layer with an inner part coating and a continuous outer coating by performing solid-phase high-temperature coating before ion exchange of the sodium precursor and performing low-temperature wet coating after ion exchange. The composite coating layer can effectively block the side reaction between the P63mc lithium cobalt oxide core and the electrolyte, inhibit the growth of the CEI on the positive electrode surface, inhibit the cobalt dissolution in the P63mc lithium cobalt oxide, and inhibit gas production, thereby improving the electrochemical performance, service life, and safety performance of the material. The preparation method is simple and can realize industrial production.

[0099] Referring to FIG. 3, FIG. 3 is a schematic diagram of a cross-sectional structure of a positive electrode sheet 200 provided by an embodiment of the present application. The positive electrode sheet 200 includes a current collector 201 and a positive electrode active layer 202 disposed on the current collector 201. The current collector 201 can be a metal foil, such as an aluminum foil, etc. The positive electrode active layer 202 includes the positive electrode material 100 described above in the embodiments of the present application. The positive electrode active layer 202 can include only the positive electrode material 100, or can include the positive electrode material 100 and other positive electrode materials. The other positive electrode materials can be various positive electrode materials that can be used in combination with the positive electrode material 100 in the embodiments of the present application. The positive electrode sheet 200 includes the positive electrode material 100 in the embodiments of the present application, which is beneficial to improving the cycle stability of the positive electrode sheet 200, especially at high voltage. The positive electrode active layer 202 further includes a conductive agent and a binder. The binder can be, for example, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), etc. The conductive agent can be, for example, Super P carbon black, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc.

[0100] Referring to FIG. 4, FIG. 4 is a schematic diagram of a structure of a battery 300 provided by an embodiment of the present application. The battery 300 includes a positive electrode 301, a negative electrode 302, an electrolyte 304 between the positive electrode 301 and the negative electrode 302, and corresponding circuits. The positive electrode 301 includes the positive electrode sheet 200 described above in the embodiments of the present application.

[0101] In the embodiments of the present application, the battery 300 is a lithium ion secondary battery. The battery 300 can be a liquid battery, a solid-state battery, or a semi-solid battery. In some embodiments of the present application, the battery 300 is a liquid battery, the electrolyte 304 is a liquid electrolyte, and the battery 300 further includes a separator 303 between the positive electrode 301 and the negative electrode 302. In some embodiments of the present application, the battery 300 is a solid-state battery, and the electrolyte 304 is a solid-state electrolyte.

[0102] The negative electrode 302 can be various commercially available or self-prepared battery negative electrodes, and the present application does not make special limitations. The separator 303 includes, but is not limited to, a single-layer polypropylene (PP) separator, a single-layer polyethylene (PE) separator, a double-layer PP / PE separator, a double-layer PP / PP separator, a three-layer PP / PE / PP separator, and a ceramic-coated PE separator.

[0103] As shown in FIG. 4, the reaction principle of the battery 300 is as follows: during charging, metal ions (such as lithium ions) are separated from the positive electrode 301 and migrate to the negative electrode 302 through the electrolyte 304, while electrons (e-) flow from the positive electrode 301 to the negative electrode 302 through the external circuit, the open-circuit voltage of the battery 300 increases, and the electrical energy is stored; during discharging, metal ions (such as lithium ions) are separated from the negative electrode 302 and return to the positive electrode 301 through the electrolyte 304, and the corresponding electrons (e-) migrate from the negative electrode 302 to the positive electrode 301 through the external circuit, the voltage decreases, and the electrical energy is released. In FIG. 4, the solid arrows represent the charging process, and the dashed arrows represent the discharging process. Relatively speaking, the more the number of metal ion migration and the faster the migration speed, the higher the capacity and rate performance of the battery.

[0104] The battery provided by the embodiments of the present application adopts the positive electrode material provided by the embodiments of the present application, and the positive electrode material can have good structural stability at a high charging and discharging voltage, which is beneficial to improving the cycle stability of the battery at a high charging voltage. The battery provided by the embodiments of the present application can be used in terminal devices, for example, consumer electronic products such as mobile phones, earphones, tablet computers, mobile power sources, portable computers, notebook computers, and other wearable or movable electronic devices, and can also be used in vehicle products (such as electric vehicles, electric bicycles, etc.), unmanned aerial vehicles, energy storage devices, power stations, base stations, and other equipment products, so as to improve the performance of the products.

[0105] Referring to FIG. 5, FIG. 5 is a structural schematic diagram of an electric device 400 provided by the embodiments of the present application. The electric device 400 includes a housing 411, and electronic components 412 and the battery 300 provided by the embodiments of the present application received in the housing 411, and the battery 300 supplies power to the electronic components 412. In the present application, the electric device 400 can be any device that uses electricity, and can be a consumer electronic product such as a mobile phone, a tablet computer, a desktop computer, a notebook computer, a mobile power source, a portable computer, a smart screen, a display, a sound system, a vehicle-mounted product, and other wearable or movable electronic devices (such as glasses, watches, bracelets, earphones, etc.), and can also be a vehicle product (such as an electric vehicle, an electric bicycle, etc.), a ship, an aerospace device, an unmanned aerial vehicle, a power station, a base station, and other equipment products. The use of the battery provided by the embodiments of the present application can improve the performance of the electric device and improve the competitiveness of the product.

[0106] The embodiment of the present application further provides a storage energy device, comprising a containing cavity and a battery accommodated in the containing cavity, wherein the battery stores electric energy for the storage energy device.

[0107] The embodiment of the present application further provides a storage energy system, comprising a storage energy device and a power converter connected electrically, wherein the power converter is used for power conversion processing of voltage and / or current, and the changed voltage and / or current are input to the storage energy device.

[0108] The technical solutions of the present application will be further described in the following embodiments.

[0109] Embodiment 1

[0110] Step (1): Sodium precursor preparation: according to the molar ratio, sodium carbonate, cobalt oxalate, nickel oxalate and manganese oxalate powders with a stoichiometric ratio of 0.43:0.86:0.07:0.07 are mechanically mixed, and then the mixed materials are placed in a crucible, pre-sintered at 450 DEG C, cooled to room temperature, ground into powder, heated to 800 DEG C and sintered for 24 hours to obtain a sodium precursor with a chemical formula of Na 0.86 Co 0.86 Ni 0.07 Mn 0.07 O2.

[0111] Step (2): solid phase coating of the first coating layer: the sintered Na 0.86 Co 0.86 Ni 0.07 Mn 0.07 O2 is mixed with nano Y2O3 and nano Al2O3 with a mass ratio of 1:1 by solid phase mixing at a speed of 200 revolutions per hour for 5 hours; then the mixed materials are taken out and transferred to a crucible, sintered at 800 DEG C in an air atmosphere for 10 hours to obtain a sodium precursor with a first coating layer on the surface, wherein the first coating layer contains Y2O3 and Al2O3, and the first coating layer coats part of the surface of the sodium precursor.

[0112] Figure 6 is an SEM picture and EDS element analysis result picture of the sodium precursor with the first coating layer prepared in step (2) of embodiment 1. As shown in Figure 6, the first coating layer is distributed in the form of dots and / or islands, and the sodium precursor with the first coating layer on the surface can be seen from the EDS picture.

[0113] Step (3): lithium-sodium ion exchange: the sodium precursor with the first coating layer on the surface and lithium salt (including lithium nitrate and lithium oxalate with a molar ratio of 1:1) are mixed according to a stoichiometric ratio of 1:2 for ion exchange, and the ion exchange is carried out at 250 DEG C in air for 10 hours, and then the ion exchange product is washed with water and dried to obtain a core with the first coating layer on the surface. The chemical formula of the core is Li 0.85 Na 0.01 Co0.86 Ni 0.07 Mn 0.07 O2, the core is denoted as L8677.

[0114] Step (4): wet coating of the second coating layer: the core with the first coating layer on the surface is put into a reaction kettle with water at 70°C, and then a certain amount of lithium hydroxide and aluminum nitrate nonahydrate is added and stirred until completely dissolved. Then, according to the amount of lithium hydroxide and aluminum nitrate nonahydrate added, a stoichiometric amount of ammonium fluoride is added, the temperature is maintained, and stirring is carried out for 8 h, followed by filtration, washing, and drying.

[0115] The dried product is sintered in a muffle furnace at 280°C for 6 h in an air atmosphere, followed by crushing treatment, and then washed with deionized water multiple times to remove soluble sodium and lithium salts, until the conductivity of the supernatant is less than 200 μS / cm. Then, the residual powder is subjected to suction filtration, drying, and sieving, and finally the target lithium cobalt oxide positive electrode material, denoted as L8677-YA-LAF, is obtained. The median particle size Dv50 of the positive electrode material is about 10 μm, the mass of the first coating layer is 0.1% of the mass of the core, and the mass of the second coating layer is 0.5% of the mass of the core, and the second coating layer comprises LiAlF4. Figure 7 is an SEM image and EDS element analysis result graph of the positive electrode material prepared in Example 1.

[0116] Example 2

[0117] The difference from Example 1 is only that the mass of the first coating layer is 0.2% of the mass of the core.

[0118] Example 3

[0119] The difference from Example 1 is only that the mass of the first coating layer is 0.3% of the mass of the core.

[0120] Example 4

[0121] The difference from Example 1 is only that the mass of the first coating layer is 0.5% of the mass of the core.

[0122] Example 5

[0123] The difference from Example 1 is only that in step (2), nano Y2O3, nano Al2O3 are replaced by nano Y2O3, nano MgO and nano Al2O3 with a mass ratio of 1:1:1, and the first coating layer contains Y2O3, MgO and Al2O3.

[0124] Example 6

[0125] The difference from Example 1 is that in step (2), nano Y2O3 and nano Al2O3 are replaced by nano Y2O3 and nano MgO with a mass ratio of 1:1, and the first coating layer contains Y2O3 and MgO. Figure 8 is an SEM picture of the sodium precursor prepared in step (2) of Example 6 and an EDS element analysis (Y, Mg) result chart.

[0126] Comparative Example 1

[0127] Step (1): Sodium precursor preparation: according to the molar ratio, mechanically mix sodium carbonate, cobalt oxalate, nickel oxalate, and manganese oxalate powders with a stoichiometric ratio of 0.43:0.86:0.07:0.07, then place the mixed materials in a crucible, pre-sinter at 450°C, cool to room temperature, grind, and then heat to 800°C and sinter for 24h to obtain a sodium precursor with the chemical formula Na 0.86 Co 0.86 Ni 0.07 Mn 0.07 O2.

[0128] Step (2): Lithium-sodium ion exchange: mix the sodium precursor and lithium salt (including 1:1 ratio of lithium nitrate and lithium oxalate) according to the stoichiometric ratio of 1:2, perform ion exchange, exchange at 250°C in air for 10h, wash with water and dry to obtain an uncoated lithium cobalt oxide material Li 0.85 Na 0.01 Co 0.86 Ni 0.07 Mn 0.07 O2, as a positive electrode material, denoted as L8677-0.

[0129] Comparative Example 2

[0130] The inner core with the first coating layer obtained in step (3) of Example 1 is used as a positive electrode material, denoted as L8677-YA.

[0131] Comparative Example 3

[0132] The difference from Example 1 is that no first coating layer is coated, only a second coating layer is set, and the second coating layer is the same as in Example 1, denoted as L8677-LAF.

[0133] The inner core with the first coating layer obtained in step (3) of Example 6 and the positive electrode material of Comparative Example 1 are tested by an inductively coupled plasma spectrometer (ICP) to measure the content of each metal element as shown in Table 1:

[0134] Table 1

[0135] From the results of Table 1, it can be seen that the surface obtained from Example 6 via step (3) has a lower Na content in the core material of the first coating layer.

[0136] The positive electrode material was tested by X-ray powder diffractometer (XRD) with Cu Ka target; the voltage and current were 40 KV / 35 mA, the scanning angle range was 10° to 90°, and the scanning rate was 5° / min. FIG. 9 is the XRD pattern of the positive electrode material of Example 1, and FIG. 10 is the XRD pattern of the positive electrode material of Comparative Example 1. As can be seen from FIGS. 9 and 10, the main peak of the XRD pattern of the positive electrode material of Example 1 and Comparative Example 1 is located near 18.5°, which is the peak position of the 002 crystal plane, also indicating that the main peak position does not change before and after coating.

[0137] The positive electrode materials prepared in Examples 1-6 and Comparative Examples 1-3 were respectively prepared into half-cells in the following manner:

[0138] The positive electrode material, conductive agent and binder were added into N-methyl pyrrolidone (NMP) in a mass ratio of 96:2:2, and were fully stirred and mixed uniformly. The slurry was coated on an aluminum foil current collector, and was dried, cold-pressed and cut to obtain a positive electrode sheet. A metal lithium sheet was used as a counter electrode, a commercial PE separator and a solvent were used, and the 1 mol / L LiPF6 electrolyte was a volume ratio of 1:1 of EC (ethylene carbonate) and DEC (diethyl carbonate). A 2032 type button cell was assembled in an argon glove box.

[0139] Button cell performance test:

[0140] After the button cell was aged at a constant temperature (25°C) for 24 h, 100 charge-discharge cycles were carried out at room temperature in a voltage range of 3.0 V to 4.62 V (Vs. Li + / Li) at a current density of 0.3 mA / cm 2 The discharge capacity of the 1st cycle and the n th cycle was recorded, and the initial coulombic efficiency was calculated according to the following formula:

[0141] The initial coulombic efficiency = the initial discharge specific capacity / the initial charge specific capacity x 100%.

[0142] The capacity retention rate (%) = the discharge specific capacity of the n th cycle / the discharge specific capacity of the 1st cycle x 100%.

[0143] The initial coulombic efficiency and the 100-week cycle capacity retention rate of the half-cells prepared in Examples 1-6 and Comparative Examples 1-3 are shown in Table 2.

[0144] Table 2

[0145] From the results of Table 2, it can be seen that the positive electrode materials with the composite coating layer of Examples 1-6 can have both high capacity and good cycle performance, compared with the uncoated lithium cobalt oxide positive electrode material of Comparative Example 1, the lithium cobalt oxide positive electrode material coated only with the first coating layer of Comparative Example 2, and the lithium cobalt oxide positive electrode material coated only with the second coating layer of Comparative Example 3.

[0146] Example 7

[0147] The difference from Example 1 is only that the mass of the first coating layer is 0.25% of the mass of the core, and the mass of the second coating layer is 0.3% of the mass of the core.

[0148] Example 8

[0149] The difference from Example 7 is only that the mass of the second coating layer is 0.5% of the mass of the core.

[0150] Example 9

[0151] The difference from Example 7 is only that the mass of the second coating layer is 1.0% of the mass of the core.

[0152] Example 10

[0153] The difference from Example 7 is only that the mass of the second coating layer is 2.0% of the mass of the core.

[0154] Example 11

[0155] The difference from Example 8 is only that in step (4), the dried product is sintered in a muffle furnace under a nitrogen atmosphere at 280°C for 6h.

[0156] The positive electrode materials prepared in Examples 7-11 are respectively prepared into half-cells in the above manner, and performance tests are carried out. The first coulombic efficiency and the 40-week cycle capacity retention rate are shown in Table 3.

[0157] Table 3

[0158] From the results of Examples 7-10 in Table 3, it can be seen that controlling the amount of the second coating layer to 0.5% can better have both high capacity and good cycle performance. It can also be known from Comparative Example 8 and Example 11 that sintering in N2gas can obtain a higher capacity retention rate than sintering in air.

[0159] Example 12

[0160] Step (1): Sodium precursor preparation: according to the molar ratio, sodium carbonate, cobalt oxalate, nickel oxalate, and manganese oxalate powders in a stoichiometric ratio of 0.43:0.93:0.02:0.05 are mechanically mixed, and then the mixed materials are placed in a crucible, pre-sintered at 450°C, cooled to room temperature, ground, and then heated to 800°C and sintered for 24h to obtain a sodium precursor with the chemical formula Na 0.86 Co 0.93 Ni 0.02 Mn 0.05 O2.

[0161] Step (2): Solid-phase coating of the first coating layer: the sintered Na 0.86 Co 0.93 Ni 0.02 Mn 0.05 O2 is mixed with nano-Y2O3 and nano-Al2O3 in a mass ratio of 1:1 at a rotation speed of 200 rpm for 5h; then the mixed materials are transferred to a crucible and sintered at 800°C for 10h in an air atmosphere to obtain a sodium precursor with a first coating layer on the surface, the first coating layer containing Y2O3 and Al2O3, and the first coating layer coating part of the surface of the sodium precursor.

[0162] Step (3): Lithium-sodium ion exchange: the sodium precursor with the first coating layer on the surface is mixed with lithium salt (including lithium nitrate and lithium oxalate in a molar ratio of 1:1) in a stoichiometric ratio of 1:2 for ion exchange, and the ion exchange is carried out at 250°C for 10h in air, followed by water washing and drying to obtain an inner core with the first coating layer on the surface. The chemical formula of the inner core is Li 0.85 Na 0.01 Co 0.93 Ni 0.02 Mn 0.05 O2, and the inner core is denoted as L9325.

[0163] Step (4): Wet coating of the second coating layer: the inner core with the first coating layer on the surface is placed in a reaction kettle at 70°C, a certain amount of water is added and stirred, then a stoichiometric amount (i.e. 0.5% of the mass of the inner core) of lithium hydroxide and aluminum nitrate nonahydrate is added, and after complete dissolution, a stoichiometric amount of diammonium hydrogen phosphate is added according to the amount of lithium hydroxide and aluminum nitrate nonahydrate added, the temperature is maintained, and stirring is carried out for 8h, followed by filtration, washing, and drying;

[0164] The dried product was sintered in a muffle furnace under air atmosphere at 280°C for 6h, followed by crushing and washing with deionized water for several times to remove soluble sodium and lithium salts, until the conductivity of the supernatant was less than 200μS / cm, then the residual powder was treated by filtration, drying and sieving, and finally the target lithium cobalt oxide positive electrode material was obtained, denoted as L9325-YA-LAP, the median particle size Dv50 of the obtained positive electrode material was about 10μm, the mass of the first coating layer was 0.25% of the mass of the core, the mass of the second coating layer was 0.5% of the mass of the core, and the second coating layer included Li3Al(PO4)2.

[0165] Example 13

[0166] The difference from Example 12 was only that the diammonium hydrogen phosphate in step (4) was replaced by ammonium fluoride, and the obtained positive electrode material was denoted as L9325-YA-LAF, and the second coating layer included LiAlF4.

[0167] Example 14

[0168] The difference from Example 12 was only that the diammonium hydrogen phosphate in step (4) was replaced by ammonium sulfate, and the obtained positive electrode material was denoted as L9325-YA-LAS, and the second coating layer included LiAl(SO4)2.

[0169] Example 15

[0170] The difference from Example 12 was only that the diammonium hydrogen phosphate in step (4) was replaced by ammonium borate, and the obtained positive electrode material was denoted as L9325-YA-LAB, and the second coating layer included Li3Al(BO3)2.

[0171] Comparative Example 4

[0172] The core with the first coating layer on the surface obtained in step (3) of Example 12 was taken as the positive electrode material, denoted as L9325-YA.

[0173] Comparative Example 5

[0174] Step (1): Sodium precursor preparation: according to the molar ratio, sodium carbonate, cobalt oxalate, nickel oxalate and manganese oxalate powders with a stoichiometric ratio of 0.43:0.93:0.02:0.05 were mechanically mixed, and then the mixed materials were placed in a crucible, pre-sintered at 450°C, cooled to room temperature and ground, and then heated to 800°C and sintered for 24h to obtain a sodium precursor with a chemical formula of Na 0.86 Co 0.93 Ni 0.02 Mn 0.05 O2.

[0175] Step (2): Lithium-sodium ion exchange: the sodium precursor and lithium salt (including 1:1 ratio of lithium nitrate and lithium oxalate) were mixed in a stoichiometric ratio of 1:2, ion exchange was carried out at 250°C in air for 10h, and after water washing and drying, an uncoated lithium cobalt oxide material was obtained as a positive electrode material Li 0.85 Na 0.01 Co 0.93 Ni 0.02 Mn 0.05 O2, denoted as L9325-0.

[0176] The positive electrode materials prepared in Examples 12-15 and Comparative Examples 4-5 were respectively prepared into half-cells in the above manner and subjected to performance testing.

[0177] The first coulombic efficiency and the capacity retention rate after 100 cycles are shown in Table 4 and Figure 11, which is the discharge curve of the button cell of Examples 12-15 and Comparative Examples 4-5.

[0178] Table 4

[0179] As can be seen from the results in Table 4, the cycle performance of the composite-coated positive electrode material of Examples 12-15 is significantly better than that of the uncoated lithium cobalt oxide material of Comparative Example 5, and is also significantly better than that of the positive electrode material of Comparative Example 4 which is only coated with a single island-shaped first coating layer. It can also be learned from Comparative Examples 12-15 that the second coating layer including phosphate and fluoride is beneficial to better improving the cycle performance of the battery.

[0180] The positive electrode sheets of Examples 12-15 and Comparative Example 5 were subjected to DSC testing under full charge state (charged to 4.62V), and the testing conditions were: the high-pressure crucible was heated from room temperature to 400K at a heating rate of 5K / min, the nitrogen flow rate was maintained at 50.0mL / min, and the DSC curve of the material was recorded. The results of the first peak starting position, the first peak peak position, and the first peak integral area in the DSC curve are shown in Table 5.

[0181] Table 5

[0182] Among them, the first peak is a decomposition peak of the positive electrode material caused by the decomposition of the electrolyte. As can be seen from the results in Table 5, the temperature of the DSC first peak peak position of the positive electrode sheet of Examples 12-15 under full charge state (4.62V) is higher than that of Comparative Example 5, which indicates that the positive electrode material of the present application will decompose at a higher temperature, and has higher stability; the DSC first peak integral area of the positive electrode sheet of Examples 12-15 under full charge state (4.62V) is significantly reduced compared with Comparative Example 5, which indicates that the side reaction of the positive electrode material of the present application with the electrolyte at high temperature is reduced, and the safety performance and cycle performance are improved.

[0183] The positive electrode material provided by the embodiment of the present application is composed of a composite coating layer of a first coating layer and a second coating layer, which can reduce the side reaction of the interface and electrolyte in the charging and discharging process, stabilize the interface, and improve the cycle performance of the positive electrode material; the composite coating layer enables the positive electrode material to be used at a higher charging cutoff voltage, thereby improving the energy density of the lithium ion battery, and enabling the positive electrode material after coating to have high discharge capacity and excellent cycle life at high voltage; the composite coating layer can increase the temperature at which the first peak of the DSC of the full charged electrode appears, and significantly reduce the first peak integral area; the composite coating layer can also inhibit the growth of CEI and reduce polarization. The positive electrode material of the present application can be coated by combining solid phase method and liquid phase method, and can be produced on a large scale by using existing equipment.

[0184] It should be understood that the first, second, and various numerical numbers referred to herein are only for the convenience of differentiation, and do not limit the scope of the present application.

[0185] In the present application, "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can mean that A exists alone, A and B exist together, and B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after it.

[0186] In the present application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or the like means any combination of these items, including any combination of single item or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0187] In the present application, "-" represents a range value, including the end point values at both ends, for example, the value of a can be 0.5-15, which means that the value of a can be between 0.5 and 15, and includes the end point values 0.5 and 15.

[0188] It should be understood that in various embodiments of the present application, the size of the sequence number of the above-mentioned processes does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises an inner core, a first coating layer and a second coating layer; The inner core comprises lithium cobalt oxide, and the space group of the lithium cobalt oxide is P63mc; The first coating layer coats part of the surface of the inner core, and the first coating layer comprises one or more metal oxides, and the metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb and Ti; The second coating layer is arranged on the surface of the first coating layer and the surface of the inner core not covered by the first coating layer, and the second coating layer comprises one or more of metal fluorides, phosphates, sulfates and borates.

2. The positive electrode material of claim 1, wherein, The inner core contains the metal elements of the first coating layer in the surface layer of the side close to the first coating layer.

3. The positive electrode material of claim 2, wherein, The depth of the surface layer is greater than 0 and less than or equal to 5 μm.

4. The positive electrode material according to any one of claims 1 to 3, wherein The first coating layer comprises one or more metal oxides selected from Y2O3, Al2O3, MgO, Gd2O3, ZrO2, La2O3, CeO2, Pr2O3, SiO2, SnO2, CuO, W2O3, Eu2O3, In2O3, ZnO, Fe2O3, Sb2O3 and TiO2.

5. The positive electrode material according to any one of claims 1 to 4, wherein The first coating layer is discontinuously and dispersedly distributed on the surface of the inner core.

6. The positive electrode material of claim 5, wherein, The first coating layer is discontinuously distributed in the form of dots and / or islands on the surface of the inner core.

7. The positive electrode material according to any one of claims 1 to 6, wherein The mass of the metal elements in the first coating layer accounts for 0.1% to 10% of the total mass of the metal elements in the inner core and the first coating layer; and / or, the first coating layer covers 10% to 50% of the surface area of the inner core.

8. The positive electrode material according to any one of claims 1 to 7, wherein The mass ratio of the first coating layer to the inner core is (0.2-4):

100.

9. The positive electrode material according to any one of claims 1 to 8, wherein The second coating layer is a continuous film layer, and the second coating layer is an amorphous material layer.

10. The positive electrode material according to any one of claims 1 to 9, wherein The second coating layer completely covers the surface of the first coating layer and the surface of the inner core not covered by the first coating layer.

11. The positive electrode material according to any one of claims 1 to 10, wherein The metal fluoride includes Li x M 2 y F z , one or more of LiPF6; the phosphate includes Li x M 2 y (PO4) z ; the sulfate includes Li x M 2 y (SO4) z ; the borate includes Li x M 2 y (BO3) z ; in each compound, M 2 is independently selected from one or more of Al, La, Ti, Zr, Mg, Zn, Y, Ca, Fe, Ce, x, y are independently integers from 0 to 6 and x+y≥1, z is independently an integer from 1 to 6, and x, y, z satisfy valence balance.

12. The positive electrode material according to any one of claims 1 to 11, wherein The mass ratio of the second coating layer to the inner core is (0.2-4):

100.

13. The cathode material of any one of claims 1-12, wherein, The thickness of the second coating layer is 5 nm to 100 nm.

14. The cathode material of any one of claims 1-13, wherein, The inner core is a single crystal particle with a particle size of 2 μm to 18 μm.

15. The cathode material of any one of claims 1-14, wherein, The main peak in the XRD pattern of the lithium cobalt oxide is located at 18.5°±0.5°; or the main peak in the XRD pattern of the positive electrode material is located at 18.5°±0.5°.

16. The cathode material of any one of claims 1-15, wherein, The lithium cobalt oxide includes lithium cobalt nickel manganese oxide, and a chemical formula of the lithium cobalt nickel manganese oxide is Li x1 Na x2 Ni a Mn b M 1 c Co 1-a-b-c O 2+y , wherein, 0.8≤x1<1.0, 0.005≤x2≤0.02, 0 1 is selected from one or more of Al, Mg, Y, Zr, Ti, La, Zn, La, Ce, Eu, Er, Zn, Ca, W, -0.1≤y≤0.

1.

17. The cathode material of any one of claims 1-16, wherein, The first peak temperature of the DSC curve of the positive electrode sheet prepared by using the positive electrode material is greater than 195°C at a half-cell voltage of 4.62 V.

18. A method of producing a positive electrode material, characterized by, Comprise: mixing a sodium precursor with first coating layer raw materials by solid phase and performing first sintering to obtain a sodium precursor with a first coating layer on the surface; The first coating layer coats part of the surface of the inner core, and the first coating layer comprises one or more metal oxides, and the metal elements in the metal oxides are selected from one or more of Y, Al, Mg, Gd, Zr, La, Ce, Pr, Si, Sn, Cu, W, Eu, Sm, In, Zn, Fe, Sb and Ti; mixing the sodium precursor with a first coating layer on the surface with a lithium salt to perform lithium-sodium ion exchange to obtain a core with a first coating layer on the surface; the core comprises lithium cobalt oxide, and a space group of the lithium cobalt oxide is P63mc; the first coating layer coats part of the surface of the core; mixing the core with a first coating layer on the surface with an aqueous solution of a second coating layer raw material, and performing reaction and second sintering to form a second coating layer on the surface of the first coating layer and the surface of the core not covered by the first coating layer to obtain the positive electrode material; the second coating layer comprises one or more of metal fluoride, phosphate, sulfate and borate.

19. The production method according to claim 18, wherein The particle size of the first coating layer raw material is 1 nm-100 nm; the solid phase mixing adopts ball milling mixing, a ball milling rotation speed is 200-400 revolutions per hour, and a time is 4-8 hours; the temperature of the first sintering is 700°C-1000°C, and a time is 8-12 hours.

20. The production method according to claim 18 or 19, wherein The lithium salt comprises a first lithium salt and a second lithium salt, the first lithium salt comprises lithium nitrate, and the second lithium salt comprises at least one of lithium chloride, lithium bromide, lithium oxalate and lithium iodide; the temperature of the ion exchange is 250°C-280°C, and a time is 6-10 hours.

21. The method of any one of claims 18-20, wherein the method is performed in a single step. The temperature of the reaction is 60°C-80°C, and a time is 6-10 hours; the temperature of the second sintering is 200°C-300°C, and a time is 2-8 hours.

22. The method of any one of claims 18-21, wherein the method is performed in a single step. An atmosphere of the first sintering is air; and an atmosphere of the second sintering is air or nitrogen.

23. The method of any one of claims 18-22, wherein the method is performed in a single step. 23 The second coating layer raw material comprises a metal source and a non-metal source, the metal source comprises a soluble metal salt, and the non-metal source comprises one or more of ammonium fluoride, ammonium phosphate, ammonium sulfate and ammonium borate.

24. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the positive electrode material according to any one of claims 1-17; or comprises the positive electrode material prepared by the preparation method according to any one of claims 18-23.

25. A battery, characterized by The battery comprises the positive electrode sheet according to claim 24; or comprises the positive electrode material according to any one of claims 1-17.

26. An electrical device, comprising: The electric device comprises the battery according to claim 25.

27. An energy storage device, comprising: The energy storage device comprises the battery according to claim 25.

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