Composite positive electrode material, preparation method thereof, positive electrode plate, secondary battery and electric device

Abstract

The invention provides a composite positive electrode material, a preparation method thereof, a positive electrode plate, a secondary battery and an electric device. The composite positive electrode material comprises a positive electrode material matrix and a first coating layer at least partially covering the positive electrode material matrix, the general formula of the positive electrode material matrix is LibNixCoyMnzMaO2-c, M comprises one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K and Ca, 0.55 < = x < = 1.0, 0 < = y < = 0.45, 0 < = z < = 0.45, 0 < = a < = 0.45, 0.5 < = b < = 1.2, a + x + y + z + b = 2,-0.1 < = c < = 0.1, and the first coating layer comprises transition metal elements.

Description

Composite positive electrode material, preparation method thereof, positive electrode sheet, secondary battery and electrical device Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a composite positive electrode material, a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] The performance of cathode active materials has a critical impact on the performance of secondary batteries. Currently, cathode active materials have many defects and cannot meet the application requirements of the new generation of electrochemical systems.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a composite positive electrode material, which can reduce the DC internal resistance of the battery, increase the battery's gram capacity and first coulombic efficiency, improve the battery's high-temperature storage performance and high-temperature cycle performance, reduce the battery's high-temperature gas production phenomenon, and comprehensively improve the battery's electrochemical performance.

[0006] In order to achieve the above-mentioned object, the first aspect of the present application provides a composite positive electrode material, which comprises: a positive electrode material substrate and a first coating layer at least partially covering the positive electrode material substrate. The general formula of the positive electrode material substrate is:

[0007] Li b Ni x Co y Mn z M a O 2-c ,

[0008] Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, and Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1,

[0009] The first cladding layer includes a transition metal element.

[0010] The transition metal elements in the first coating layer will activate the lithiated rock salt structure on the surface of the positive electrode material matrix, making the lithium in the lithiated rock salt structure more active, thereby improving the battery's first coulombic efficiency and gram capacity; the transition metal elements in the first coating layer will react with the residual lithium on the surface of the positive electrode material matrix to generate a transition metal-containing lithium salt substance with high ionic conductivity, thereby increasing the transfer rate of lithium ions on the material surface, reducing the battery's DC internal resistance, and improving the battery's kinetic performance; the transition metal elements in the first coating layer can easily form a dense coating layer on the surface of the positive electrode material matrix, thereby reducing the possibility of the material's active sites being corroded by electrolyte byproducts, thereby achieving the purpose of improving high-temperature cycling and high-temperature storage, and reducing high-temperature gas production.

[0011] In any embodiment, the general formula Li b Ni x Co y Mn z M a O 2-c Among them, 0.9≤x≤1.0, 0≤y≤0.1, 0≤z≤0.1, 0≤a≤0.1, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1.

[0012] The positive electrode material matrix that satisfies the above general formula enables the battery to have a high gram capacity, meeting the needs of new batteries.

[0013] In any embodiment, the transition metal element exists in the first coating layer in the form of oxide or fluoride.

[0014] Transition metal elements exist in the form of oxides or fluorides, which are conducive to reacting with the participating lithium on the surface of the material to generate transition metal-containing lithium salts with high ionic conductivity, thereby improving the transmission rate of lithium ions on the surface of the material and reducing the DC internal resistance of the battery. In addition, the oxides or fluorides of transition metal elements form a denser coating on the surface of the material, thereby improving the high-temperature storage performance and high-temperature cycle performance of the battery.

[0015] In any embodiment, the transition metal element includes one or more of Co, Ce, Zr, La, Sb, and W. Optionally, the transition metal element includes one or both of Co and Ce.

[0016] In any embodiment, the first coating layer further comprises a compound having a melting point lower than 900°C.

[0017] Compounds with a melting point below 900°C can be used as fluxing agents, so that they have a lower eutectic point with transition metal elements, which can enhance the coating and melting effect of transition metal elements, so that transition metal elements are solid-dissolved into the surface lattice of the positive electrode material matrix, further increasing the battery's gram capacity, reducing the battery's DC internal resistance, improving the battery's high-temperature storage performance and high-temperature cycle performance, and reducing the battery's high-temperature gas production.

[0018] In any embodiment, the compound having a melting point lower than 900° C. comprises an alkali metal element and a non-metal element, wherein the non-metal element comprises one or more of N, F, Cl, and S.

[0019] In any embodiment, the composite positive electrode material further includes a second coating layer, which at least partially coats the surface of the first coating layer, and the second coating layer includes one or more of Al, B, and W.

[0020] The Al, B, and W contained in the second coating layer can form a glassy substance such as LiAlO2, Li3BO3 or Li2WO4 with the positive electrode material matrix. The above-mentioned glassy substance can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the high-temperature storage performance and high-temperature cycle performance of the battery, and reduce the high-temperature gas production of the battery. At the same time, the glassy substance has excellent ion conductivity, which can increase the transmission rate of lithium ions on the material surface and reduce the DC internal resistance of the battery.

[0021] In any embodiment, based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 100 ppm-20,000 ppm, and can be optionally 1,000 ppm-15,000 ppm.

[0022] The mass content of the transition metal elements is within an appropriate range, so that the transition metal elements are evenly and tightly wrapped on the positive electrode material matrix, effectively improving the structural properties of the material. At the same time, it can also reduce the possibility of excessive coating to form island accumulation, reduce the impact of island accumulation on material properties, and make the battery have low DC internal resistance. The battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0023] In any embodiment, the molar ratio M of Ce to Co in the transition metal element satisfies: 0<M≤10, and optionally satisfies: 0<M≤1.

[0024] When the molar ratio M of Ce to Co in the transition metal elements is within a suitable range, the battery has low DC internal resistance, excellent gram capacity, first coulombic efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0025] In any embodiment, based on the mass of the positive electrode material matrix, the mass content of the alkali metal element in the first coating layer is 100 ppm-15000 ppm, and can be optionally 1000 ppm-8000 ppm.

[0026] The mass content of the alkali metal elements in the first coating layer is within an appropriate range, so that the alkali metal elements are evenly and tightly wrapped on the positive electrode material matrix, effectively reducing the eutectic point of the first coating layer, improving the coating and melting effect of the transition metal elements, and at the same time reducing the possibility of island accumulation due to excessive coating, reducing the impact of island accumulation on material properties, so that the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0027] In any embodiment, based on the mass of the positive electrode material matrix, the mass content of the non-metallic element in the first coating layer is 200 ppm-50000 ppm, and can be optionally 500 ppm-8000 ppm.

[0028] The mass content of the non-metallic elements in the first coating layer is within an appropriate range, so that the non-metallic elements are evenly and tightly wrapped on the positive electrode material matrix, effectively reducing the eutectic point of the first coating layer, improving the coating and melting effect of the transition metal elements, and at the same time reducing the possibility of island accumulation due to excessive coating, reducing the impact of island accumulation on material properties, so that the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0029] In any embodiment, based on the mass of the positive electrode material matrix, the mass content of Al in the second coating layer is 100 ppm-3500 ppm, and can be optionally 500 ppm-2500 ppm.

[0030] The Al content of the first coating layer is within an appropriate range, allowing the Al to be evenly and tightly coated on the cathode material matrix, forming sufficient LiAlO2, effectively suppressing the generation of oxygen defects and reducing the possibility of side reactions between the electrolyte and the material at high temperatures. It also reduces the possibility of island accumulation caused by excessive coating, reducing the impact of island accumulation on material properties, resulting in a battery with low DC internal resistance, excellent gram capacity, initial coulombic efficiency, high-temperature storage performance, and high-temperature cycling performance, and reduces high-temperature gas production.

[0031] In any embodiment, based on the mass of the positive electrode material matrix, the mass content of B in the second coating layer is 100 ppm-2500 ppm, and can be optionally 500 ppm-2000 ppm.

[0032] The mass content of B in the first coating layer is within a suitable range, so that B is evenly and tightly wrapped on the positive electrode material matrix, forming sufficient Li3BO3, effectively inhibiting the generation of oxygen defects, and at the same time reducing the possibility of island accumulation due to excessive coating, reducing the impact of island accumulation on material properties, so that the battery has low DC internal resistance, excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0033] In any embodiment, the mass ratio of Al to B elements in the second coating layer is 0.5-2.

[0034] The mass ratio of Al to B elements is within an appropriate range, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has a small amount of high-temperature gas production.

[0035] In any embodiment, the total thickness of the first cladding layer and the second cladding layer is 0.01 μm to 1 μm.

[0036] The total thickness of the first coating layer and the second coating layer is within a suitable range, which can form an effective protective layer on the positive electrode material matrix while being beneficial to the rapid transmission of lithium ions on the surface of the material, improving the ion conductivity of the material, and making the battery have a low DC internal resistance, and making the battery have excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and making the battery have less high temperature gas production.

[0037] In any embodiment, the aspect ratio of the primary particles of the composite positive electrode material is 1.5-10, and can be 2-4.

[0038] The aspect ratio of the primary particles of the composite positive electrode material is within an appropriate range, which shortens the migration distance of lithium ions, improves the deintercalation kinetics of lithium ions, and reduces the DC internal resistance of the battery. At the same time, the primary particles have a suitable aspect ratio, have smaller stress and higher particle strength. During the cyclic charge and discharge process, as lithium ions repeatedly escape and embed into the primary particles, the primary particles can still maintain their intact structure, and basically will not cause the transition metal inside the primary particles to detach from the primary particles and dissolve into the electrolyte, thereby improving the cycle stability of the battery and improving the high-temperature storage performance and high-temperature cycle performance of the battery.

[0039] In any embodiment, the span of the composite positive electrode material is greater than or equal to 0.5, and can be optionally greater than or equal to 1.2.

[0040] When the span of the composite positive electrode material is within an appropriate range, the compaction density of the electrode sheet can be increased and the gram capacity of the battery can be increased.

[0041] In any embodiment, the oxygen deficiency index ODI of the composite positive electrode material is greater than or equal to 1.75, and can be optionally greater than or equal to 1.8.

[0042] The oxygen defect index ODI of the composite positive electrode material is within an appropriate range, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulombic efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0043] The second aspect of the present application provides a method for preparing a composite positive electrode material, comprising steps (1) and (2):

[0044] Step (1): uniformly mixing a first raw material comprising a lithium source and a cathode material precursor, and performing a first calcination under a first atmosphere to obtain a first product. Optionally, the first raw material further comprises an M source;

[0045] Step (2): in a second atmosphere, uniformly mixing the first product with a second raw material containing a transition metal element source, and performing a second calcination to prepare a composite positive electrode material;

[0046] The composite positive electrode material comprises: a positive electrode material matrix and a first coating layer provided on at least a portion of the positive electrode material matrix. The general formula of the positive electrode material matrix is:

[0047] Li b Ni x Co y Mn z M a O 2-c ,

[0048] Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, and Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1,

[0049] The first cladding layer includes a transition metal element.

[0050] By the above-mentioned preparation method, a transition metal layer is coated on the positive electrode material substrate. The transition metal element will activate the lithiated rock salt structure on the surface of the positive electrode material substrate, making the lithium in the lithiated rock salt structure more active, thereby improving the first coulombic efficiency and gram capacity of the battery; the transition metal element in the first coating layer will react with the residual lithium on the surface of the positive electrode material substrate to generate a transition metal-containing lithium salt substance with high ionic conductivity, thereby improving the transmission rate of lithium ions on the surface of the material and reducing the DC internal resistance of the battery; the transition metal element in the first coating layer can easily form a dense coating layer on the surface of the positive electrode material substrate, which can reduce the possibility of the active sites of the material being corroded by electrolyte byproducts, thereby achieving the purpose of improving high-temperature cycling and high-temperature storage and reducing high-temperature gas production.

[0051] In any embodiment, the transition metal element includes one or more of Ce, Co, Zr, La, Sb, and W.

[0052] In any embodiment, the second raw material further includes a compound having a melting point below 800°C. Adding a compound having a melting point below 900°C to the second raw material allows the first coating layer to also include a compound having a melting point below 900°C, resulting in a lower eutectic point between the compound and the transition metal element. This can enhance the coating and melting effect of the transition metal element, allowing the transition metal element to be solid-dissolved into the surface lattice of the positive electrode material matrix, further increasing the battery's gram capacity, reducing the battery's DC internal resistance, improving the battery's high-temperature storage performance and high-temperature cycle performance, and reducing the battery's high-temperature gassing phenomenon.

[0053] In any embodiment, step (2) specifically includes:

[0054] In a second atmosphere, the first product and the second raw material are uniformly mixed and subjected to a second calcination to obtain a second product;

[0055] The second product is mixed evenly with a third raw material, and a third calcination is performed under a third atmosphere to prepare a composite positive electrode material; wherein the third raw material includes one or more of an Al source, a B source, and a W source.

[0056] Through the third calcination, a second coating layer is formed on the surface of the first coating layer. The Al, B, and W contained in the second coating layer can form a glass-like substance of LiAlO2, Li3BO3 or Li2WO4 with the positive electrode material matrix. The above-mentioned glass-like substance can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the high-temperature storage performance and high-temperature cycle performance of the battery, and reduce the high-temperature gas production of the battery. At the same time, the glass-like substance has excellent ion conductivity, which can improve the transmission rate of lithium ions on the surface of the material and reduce the DC internal resistance of the battery.

[0057] In any embodiment, the first atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the first calcination is 700° C.-900° C., and the calcination time is 10 h-20 h.

[0058] In any embodiment, the second atmosphere is a pure oxygen atmosphere or an air atmosphere, the calcination temperature of the second calcination is 300° C.-650° C., and the calcination time is 3 h-10 h.

[0059] In any embodiment, the third atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the third calcination is 200° C.-500° C., and the calcination time is 5 h-15 h.

[0060] A third aspect of the present application provides a positive electrode plate, which includes the composite positive electrode material of the first aspect or the composite positive electrode material prepared by the preparation method of the second aspect.

[0061] A fourth aspect of the present application provides a secondary battery comprising the positive electrode sheet of the third aspect.

[0062] A fifth aspect of the present application provides an electrical device comprising the secondary battery of the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0064] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0065] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0066] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0067] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0068] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0069] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0070] Below, with appropriate reference to the accompanying drawings, the embodiments of the composite positive electrode active material, its preparation method, secondary battery and electrical device of the present application are specifically disclosed in detail. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0071] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0073] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0074] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0075] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0076] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0077] Ternary materials have attracted widespread attention due to their high energy density and excellent cycle performance. However, in actual production, researchers have found that existing ternary materials have poor conductivity, resulting in an increase in DC internal resistance during cycling, which deteriorates rate performance. Furthermore, during the charge and discharge process, ternary materials are highly susceptible to electrolyte corrosion, leading to structural collapse and affecting the battery's cycle performance. Therefore, it is necessary to develop a positive electrode material that can reduce the battery's DC internal resistance and improve its cycle performance to meet the application needs of the next generation of electrochemical systems.

[0078] [Composite cathode materials]

[0079] The first aspect of the present application provides a composite positive electrode material, comprising: a positive electrode material substrate and a first coating layer at least partially covering the positive electrode material substrate. The general formula of the positive electrode material substrate is:

[0080] Li b Ni x Co y Mn z M a O 2-c ,

[0081] Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, and Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1,

[0082] The first cladding layer includes a transition metal element.

[0083] As used herein, the term "transition metal elements" refers to elements of Groups IIIB to VIIB, VIII, and IB to IIB of the Periodic Table of the Elements.

[0084] In some embodiments, x is any value selected from the group consisting of 0.55, 0.6, 0.7, 0.8, 0.85, 0.9, 0.93, 0.94, 0.95, 1, or a range consisting of any two of these values.

[0085] In some embodiments, y is any value of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, 0.15, 0.2, 0.3, 0.4, 0.45, or a range consisting of any two values ​​thereof.

[0086] In some embodiments, z is any value selected from the group consisting of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, 0.15, 0.2, 0.3, 0.4, and 0.45, or a range consisting of any two of these values.

[0087] In some embodiments, a is any value of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, 0.15, 0.2, 0.3, 0.4, 0.45, or a range consisting of any two values ​​thereof.

[0088] In some embodiments, b is any value selected from 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, or a range consisting of any two values ​​thereof.

[0089] In some embodiments, c is any value among -0.1, 0, 0.1, or a range consisting of any two values ​​therein.

[0090] In some embodiments, the positive electrode material matrix does not contain M elements.

[0091] In some embodiments, the positive electrode material matrix includes an M element.

[0092] In some embodiments, the M element comprises Sb or Zr.

[0093] The positive electrode material matrix contains M elements, which is beneficial to improving the voltage platform of the material, improving the ionic conductivity and electronic conductivity of the material, reducing the DC internal resistance of the battery, reducing the polarization of the battery, improving the first coulombic efficiency and high-temperature cycle performance, high-temperature storage performance, and reducing the high-temperature gas production of the battery.

[0094] The transition metal elements in the first coating layer will activate the lithiated rock salt structure on the surface of the positive electrode material matrix, making the lithium in the lithiated rock salt structure more active, thereby improving the battery's first coulombic efficiency and gram capacity; the transition metal elements in the first coating layer will react with the residual lithium on the surface of the positive electrode material matrix to generate a transition metal-containing lithium salt substance with high ionic conductivity, thereby increasing the transmission rate of lithium ions on the material surface and reducing the battery's DC internal resistance; the transition metal elements in the first coating layer can easily form a dense coating layer on the surface of the positive electrode material matrix, thereby reducing the possibility of the material's active sites being corroded by electrolyte byproducts, thereby achieving the purpose of improving high-temperature cycling and high-temperature storage and reducing high-temperature gas production.

[0095] In summary, by coating a layer of transition metal elements on the positive electrode material matrix, the DC internal resistance of the battery can be reduced, the battery's gram capacity and first coulombic efficiency can be increased, the battery's high-temperature storage performance and high-temperature cycle performance can be improved, the battery's high-temperature gas production phenomenon can be reduced, and the battery's electrochemical performance can be comprehensively improved.

[0096] In some embodiments, Li b Ni x Co y Mn z M a O 2-c Among them, 0.9≤x≤1.0, 0≤y≤0.1, 0≤z≤0.1, 0≤a≤0.1, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1.

[0097] In some embodiments, x is any value selected from 0.9, 0.92, 0.93, 0.94, 0.95, 1, or a range consisting of any two values ​​thereof.

[0098] In some embodiments, y is any value selected from 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, or a range consisting of any two values ​​thereof.

[0099] In some embodiments, z is any value selected from 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, or a range consisting of any two values ​​thereof.

[0100] In some embodiments, a is any value of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, or a range consisting of any two values ​​thereof.

[0101] In some embodiments, b is any value selected from 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 1, 1.1, 1.2, or a range consisting of any two values ​​thereof.

[0102] In some embodiments, c is any value among -0.1, 0, 0.1, or a range consisting of any two values ​​therein.

[0103] The positive electrode material matrix that satisfies the above general formula enables the battery to have a high gram capacity, meeting the needs of new batteries.

[0104] In some embodiments, the transition metal element exists in the first coating layer in the form of oxide or fluoride.

[0105] The form of the transition metal element can be tested using methods known in the art. For example, an inductively coupled plasma spectrometer (ICP) (such as Spectroblue) and an XRD diffractometer can be used to determine the form of the transition metal element.

[0106] Transition metal elements exist in the form of oxides or fluorides, which are conducive to reacting with the participating lithium on the surface of the material to generate transition metal-containing lithium salts with high ionic conductivity, thereby improving the transmission rate of lithium ions on the surface of the material and reducing the DC internal resistance of the battery. In addition, the oxides or fluorides of transition metal elements form a denser coating on the surface of the material, thereby improving the high-temperature storage performance and high-temperature cycle performance of the battery.

[0107] In some embodiments, the transition metal element includes one or more of Co, Ce, Zr, La, Sb, and W.

[0108] In some embodiments, the transition metal element includes Co or Ce.

[0109] In some embodiments, the transition metal elements include Co and Ce.

[0110] In some embodiments, Co is present in the first coating layer in the form of Co 3 O 4 .

[0111] In some embodiments, Ce is present in the first coating layer in the form of CeO 2 or CeF 3 .

[0112] In some embodiments, oxides or fluorides of Ce and Co react with residual lithium on the surface of the positive electrode material matrix to generate LiCeO2 and LiCoO2 with high ionic conductivity, thereby increasing the transfer rate of lithium ions on the surface of the material, reducing the DC internal resistance of the battery, and improving the kinetic performance of the battery.

[0113] In some embodiments, the first coating layer further comprises a compound having a melting point lower than 900°C.

[0114] As used herein, the term "melting point" refers to the melting point of a substance at one atmosphere of pressure.

[0115] In some embodiments, the melting point of the compound is lower than any one of 500°C, 600°C, 700°C, 800°C, and 900°C.

[0116] In some embodiments, the compound having a melting point below 900°C includes one or more of lithium sulfate, sodium sulfate, potassium sulfate, lithium nitrate, sodium nitrate, potassium nitrate, lithium fluoride, sodium fluoride, potassium fluoride, lithium sulfide, sodium sulfide, potassium sulfide, lithium chloride, sodium chloride, potassium chloride, lithium oxalate, sodium oxalate, potassium oxalate, lithium acetate, sodium acetate, and potassium acetate.

[0117] Compounds with a melting point below 900°C can be used as fluxing agents, so that they have a lower eutectic point with transition metal elements, which can enhance the coating and melting effect of transition metal elements, so that transition metal elements are solid-dissolved into the surface lattice of the positive electrode material matrix, further increasing the battery's gram capacity, reducing the battery's DC internal resistance, improving the battery's high-temperature storage performance and high-temperature cycle performance, and reducing the battery's high-temperature gas production.

[0118] In any embodiment, the compound having a melting point lower than 900° C. comprises an alkali metal element and a non-metal element, wherein the non-metal element comprises one or more of N, F, Cl, and S.

[0119] As used herein, the term "alkali metals" refers to the six metal elements in Group IA of the periodic table, excluding hydrogen (H), namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

[0120] In some embodiments, the compound having a melting point below 900° C. comprises lithium.

[0121] Lithium can be used as a lithium supplement to increase the material's gram capacity and improve the energy density of the battery.

[0122] In some embodiments, the composite positive electrode material further includes a second coating layer, which at least partially coats the surface of the first coating layer, and the second coating layer includes one or more of Al, B, and W.

[0123] In some embodiments, the second cladding layer includes one or both of Al and B.

[0124] The Al, B, and W contained in the second coating layer can form a glassy substance such as LiAlO2, Li3BO3 or Li2WO4 with the positive electrode material matrix. The above-mentioned glassy substance can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the high-temperature storage performance and high-temperature cycle performance of the battery, and reduce the high-temperature gas production of the battery. At the same time, the glassy substance has excellent ion conductivity, which can increase the transmission rate of lithium ions on the material surface and reduce the DC internal resistance of the battery.

[0125] In some embodiments, based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 100 ppm-20000 ppm.

[0126] In some embodiments, based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 100ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 15000ppm, 16000ppm, 17000ppm, 18000ppm, 19000ppm, 20000ppm, any value or a range consisting of any two values ​​therein.

[0127] The mass content of transition metal elements can be measured using methods known in the art. For example, the EPA 6010D-2014 standard can be used for determination. Specifically, ICP-OES (Elemental Analysis - Inductively Coupled Plasma Optical Emission Spectrometry) testing can be used. The sample to be tested is first dissolved in a strong acid to form a liquid. The liquid is then atomized and introduced into an ICP light source. The gaseous atoms to be tested are then ionized and excited in a strong magnetic field, returning from the excited state to the ground state. Energy is released during this process and recorded as distinct characteristic spectral lines for quantitative elemental analysis.

[0128] The mass content of the transition metal elements is within an appropriate range, so that the transition metal elements are evenly and tightly wrapped on the positive electrode material matrix, effectively improving the structural properties of the material. At the same time, it can also reduce the possibility of excessive coating to form island accumulation, reduce the impact of island accumulation on material properties, and make the battery have low DC internal resistance. The battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0129] In some embodiments, the mass content of the transition metal element in the first coating layer is 1000ppm-15000ppm based on the mass of the positive electrode material matrix. In some embodiments, the mass content of the transition metal element in the first coating layer is 1000ppm, 1500ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 15000ppm, or any value thereof, or a range consisting of any two values ​​thereof, based on the mass of the positive electrode material matrix.

[0130] When the mass content of transition metal elements is within an appropriate range, more lithium salt substances containing transition metal elements with high ionic conductivity can be generated, thereby improving the transmission rate of lithium ions on the surface of the material and further reducing the DC internal resistance of the battery. In addition, transition metal elements with an appropriate mass content can also form a dense coating layer on the surface of the positive electrode material matrix, reducing the possibility of the material being corroded by electrolyte byproducts and improving the high-temperature cycle performance of the material.

[0131] In some embodiments, the molar ratio M of Ce to Co in the transition metal elements satisfies: 0<M≤10. In some embodiments, the molar ratio M of Ce to Co in the transition metal elements satisfies: any one of: 0<M≤1, 0<M≤2, 0<M≤3, 0<M≤4, 0<M≤5, 0<M≤6, 0<M≤7, 0<M≤8, 0<M≤9, and 0<M≤10.

[0132] The molar content of Ce and Co within the appropriate range is beneficial to improving the structural properties of the material, and thus improving the electrochemical properties of the battery. At the same time, in order to avoid excessive molar content of Ce and Co, which will form deposits on the surface of the matrix material and hinder the transmission of lithium ions, it is necessary to control the molar content of Ce and Co within the appropriate range.

[0133] The molar ratio of Ce to Co in the transition metal element can be tested using methods known in the art. As an example, the determination can be made with reference to EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis - inductively coupled plasma optical emission spectrometry) testing can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then return to the ground state from the excited state. In the above process, energy is released and recorded as different characteristic spectral lines. Elemental quantitative analysis is performed to obtain the mass content of Ce and Co, and the molar ratio M of the two is obtained by calculation.

[0134] When the molar ratio M of Ce to Co in the transition metal elements is within a suitable range, the battery has low DC internal resistance, excellent gram capacity, first coulombic efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0135] In some embodiments, the molar ratio M of Ce to Co in the transition metal elements satisfies: 0<M≤1. In some embodiments, the molar ratio M of Ce to Co in the transition metal elements satisfies: any one of: 0<M≤0.1, 0<M≤0.2, 0<M≤0.3, 0<M≤0.4, 0<M≤0.5, 0<M≤0.6, 0<M≤0.7, 0<M≤0.8, 0<M≤0.9, and 0<M≤1.

[0136] When the molar ratio M of Ce to Co in the transition metal elements is within an appropriate range, the high-temperature cycle performance and high-temperature storage performance of the battery can be improved, the high-temperature gas production of the battery can be reduced, and the operating temperature of the battery can be widened.

[0137] In some embodiments, the mass content of the alkali metal element in the first coating layer is 100 ppm-15000 ppm based on the mass of the positive electrode material matrix. In some embodiments, the mass content of the alkali metal element in the first coating layer is 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 15000 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material matrix.

[0138] The determination of the mass content of alkali metal elements refers to the determination method of transition metal elements mentioned above.

[0139] The mass content of the alkali metal elements in the first coating layer is within an appropriate range, so that the alkali metal elements are evenly and tightly wrapped on the positive electrode material matrix, effectively reducing the eutectic point of the first coating layer, improving the coating and melting effect of the transition metal elements, and at the same time reducing the possibility of island accumulation due to excessive coating, reducing the impact of island accumulation on material properties, so that the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0140] In some embodiments, the mass content of the alkali metal element in the first coating layer is 1000ppm-8000ppm based on the mass of the positive electrode material matrix. In some embodiments, the mass content of the alkali metal element in the first coating layer is any value of 1000ppm, 1500ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material matrix.

[0141] The mass content of the alkali metal in the first coating layer is within an appropriate range, which can take into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, and comprehensively improve the battery's performance.

[0142] In some embodiments, based on the mass of the positive electrode material matrix, the mass content of the non-metallic elements in the first coating layer is 200ppm-50000ppm. In some embodiments, based on the mass of the positive electrode material matrix, the mass content of the non-metallic elements in the first coating layer is 200ppm, 500ppm, 1000ppm, 1500ppm, 2000ppm, 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm, 8000ppm, 9000ppm, 10000ppm, 11000ppm, 12000ppm, 13000ppm, 15000ppm, 20000ppm, 15000ppm, 30000ppm, 35000ppm, 40000ppm, 45000ppm, 50000ppm, any value thereof, or a range consisting of any two values ​​thereof.

[0143] The determination of the mass content of non-metallic elements can refer to the determination method of transition metal elements mentioned above.

[0144] The mass content of the non-metallic elements in the first coating layer is within an appropriate range, so that the non-metallic elements are evenly coated on the positive electrode material matrix, effectively reducing the eutectic point of the first coating layer, improving the coating and melting effect of the transition metal elements, and at the same time reducing the possibility of island accumulation due to excessive coating, reducing the impact of island accumulation on material properties, so that the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has less high-temperature gas production.

[0145] In some embodiments, the mass content of the non-metallic element in the first coating layer is 500 ppm-8000 ppm based on the mass of the positive electrode material matrix. In some embodiments, the mass content of the non-metallic element in the first coating layer is any value of 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material matrix.

[0146] The mass content of the non-metallic elements in the first coating layer is within an appropriate range, which can improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and widen the operating temperature of the battery.

[0147] In some embodiments, the mass content of Al in the second coating layer is 100 ppm to 3500 ppm based on the mass of the positive electrode material substrate. In some embodiments, the mass content of Al in the second coating layer is any value selected from the group consisting of 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, and 3500 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material substrate.

[0148] The determination of the mass content of Al in the second coating layer refers to the determination method of transition metal elements mentioned above.

[0149] The mass content of Al in the first coating layer is within a suitable range, so that Al is evenly and tightly wrapped on the positive electrode material matrix to form sufficient LiAlO2, effectively inhibiting the generation of oxygen defects and reducing the possibility of side reactions between the electrolyte and the material at high temperatures. In addition, LiAlO2 has good ionic conductivity, reduces the polarization of the battery, and improves the capacity of the material. At the same time, it can also reduce the possibility of island accumulation due to excessive coating, reduce the impact of island accumulation on material performance, and make the battery have low DC internal resistance. The battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, so that the battery has less high-temperature gas production.

[0150] In some embodiments, the mass content of Al in the second coating layer is 500 ppm to 2500 ppm based on the mass of the positive electrode material substrate. In some embodiments, the mass content of Al in the second coating layer is any value selected from the group consisting of 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, and 2500 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material substrate.

[0151] When the mass content of Al in the second coating layer is within a suitable range, LiAlO2 with good ionic conductivity can be formed, reducing the polarization of the battery and increasing the battery's gram capacity. At the same time, it can avoid excessive coating, reduce the possibility of island accumulation, and reduce the impact of island accumulation on material properties. It can take into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, and comprehensively improve the battery's performance.

[0152] In some embodiments, the mass content of B in the second coating layer is 100 ppm to 2500 ppm based on the mass of the positive electrode material substrate. In some embodiments, the mass content of B in the second coating layer is any value selected from 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, and 2500 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material substrate.

[0153] The determination of the mass content of B in the second coating layer refers to the determination method of transition metal elements mentioned above.

[0154] The boron content of the first coating layer is within an appropriate range, allowing it to be evenly and tightly coated on the cathode material matrix, forming sufficient Li₃BO₃. This effectively suppresses the generation of oxygen defects and reduces the possibility of side reactions between the electrolyte and the material at high temperatures. Furthermore, Li₃BO₃ exhibits excellent ionic conductivity, reducing battery polarization and increasing the material's capacity. This also reduces the possibility of island accumulation caused by excessive coating, minimizing the impact of island accumulation on material performance. This results in a battery with low DC internal resistance, excellent gram capacity, initial coulombic efficiency, high-temperature storage performance, and high-temperature cycling performance, resulting in minimal high-temperature gas production.

[0155] In some embodiments, the mass content of B in the second coating layer is 500 ppm-2000 ppm based on the mass of the positive electrode material substrate. In some embodiments, the mass content of B in the second coating layer is any value of 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or a range consisting of any two of these values, based on the mass of the positive electrode material substrate.

[0156] When the mass content of B in the second coating layer is within a suitable range, Li3BO3 with good ionic conductivity can be formed, which reduces the polarization of the battery and increases the battery's gram capacity. At the same time, it can avoid excessive coating, reduce the possibility of island accumulation, and reduce the impact of island accumulation on material properties. It can take into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, and comprehensively improve the battery's performance.

[0157] In some embodiments, the mass ratio of Al to B in the second coating layer is 0.5 to 2. In some embodiments, the mass ratio of Al to B in the second coating layer is any value selected from 0.5, 1, 1.5, and 2, or a range consisting of any two of these values.

[0158] The mass ratio of Al to B in transition metal elements can be tested using methods known in the art. As an example, the determination can be made with reference to EPA 6010D-2014. Specifically, ICP-OES (elemental analysis - inductively coupled plasma optical emission spectrometry) testing can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then return to the ground state from the excited state. During this process, energy is released and recorded as different characteristic spectral lines. Elemental quantitative analysis is performed to obtain the mass content of Al and B, and the mass ratio of the two is calculated.

[0159] The mass ratio of Al to B elements is within an appropriate range, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has a small amount of high-temperature gas production.

[0160] In some embodiments, the total thickness of the first cladding layer and the second cladding layer is 0.01 μm to 1 μm.

[0161] The total thickness of the first and second coating layers can be measured using methods known in the art. As an example, a sample preparation glue is mixed evenly with the composite positive electrode material powder (the powder weight is 5 times that of the sample preparation glue), then coated onto copper foil to produce a sample and dried at 60°C for 30 minutes. The prepared sample is cut into 6mm x 6mm pieces using scissors, secured to a sample stage, and placed in an ion polisher (Model: IB-19500CP). The sample edge is adjusted parallel to the centerline (X-axis) and the Y-axis position is 40-60μm for cutting. After cutting, an X-Max energy dispersive spectrometer (EDS) from the Oxford Instruments Group of the United Kingdom was combined with a Sigma-02-33 scanning electron microscope (SEM) from the ZEISS of Germany to select a suitable particle section on the cut sample. The characteristic element content of the first coating layer and the characteristic element of the second coating layer were linearly scanned along the diameter direction of the particle. The radius of the measured particle was R, the distance from the site where the element content of the first coating layer began to increase compared with the particle core to the center position of the particle was L1, and the distance from the site where the element content of the second coating layer began to increase compared with the particle core to the center position of the particle was L2. The total thickness of the first coating and the second coating layer was (R-L1) μm.

[0162] The total thickness of the first coating layer and the second coating layer is within a suitable range, which can form an effective protective layer on the positive electrode material matrix while being beneficial to the rapid transmission of lithium ions on the surface of the material, improving the ion conductivity of the material, and making the battery have a low DC internal resistance, and making the battery have excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and making the battery have less high temperature gas production.

[0163] In some embodiments, the aspect ratio of the primary particles of the composite cathode material is 1.5 to 10. In some embodiments, the aspect ratio of the primary particles of the composite cathode material is any value of 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range consisting of any two values ​​thereof.

[0164] The combined thickness of the first and second coating layers can be measured using methods known in the art. For example, static image processing techniques can be used to perform the test. Using static scanning electron microscope images of powders, NanoMeasure software intelligently identifies the long diameter (RL) and short diameter (RS) of the primary particles, and calculates the primary particle aspect ratio (RL / RS).

[0165] The aspect ratio of the primary particles of the composite positive electrode material is within an appropriate range, which shortens the migration distance of lithium ions, improves the deintercalation kinetics of lithium ions, and reduces the DC internal resistance of the battery. At the same time, the primary particles have a suitable aspect ratio, have smaller stress and higher particle strength. During the cyclic charge and discharge process, as lithium ions repeatedly escape and embed into the primary particles, the primary particles can still maintain their intact structure, and basically will not cause the transition metal inside the primary particles to detach from the primary particles and dissolve into the electrolyte, thereby improving the cycle stability of the battery and improving the high-temperature storage performance and high-temperature cycle performance of the battery.

[0166] In some embodiments, the aspect ratio of the primary particles of the composite cathode material is 2 to 4. In some embodiments, the aspect ratio of the primary particles of the composite cathode material is any value of 2, 2.5, 3, 3.5, 4, or a range consisting of any two of these values.

[0167] The aspect ratio of the primary particles of the composite positive electrode material is within an appropriate range, which can improve the structural stability of the primary structure and improve its cycle stability. At the same time, the aspect ratio of the primary particles is within an appropriate range, which can also reduce the contact area between the material and the electrolyte, reduce the possibility of side reactions between the material and the electrolyte, improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and broaden the operating temperature of the battery.

[0168] In some embodiments, the span of the composite cathode material is greater than or equal to 0.5. In some embodiments, the span of the composite cathode material is greater than or equal to any one of 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0.

[0169] As used herein, the term "span" refers to the value of (Dv90 - Dv10) / Dv50 of a material.

[0170] As used herein, the term "Dv90" refers to a particle size at which 90% of the volume of the powder particles is accumulated from the smallest particle size side in the volume-based particle size distribution.

[0171] As used herein, the term "Dv10" refers to a particle size that represents 10% of the cumulative volume from the smallest particle size side in a volume-based particle size distribution of powder particles.

[0172] In this article, the term "Dv50" refers to the particle size distribution of powder particles based on volume, which is the particle size at which the cumulative volume reaches 50% from the smallest particle size side.

[0173] The span of the composite cathode material can be measured using methods known in the art. For example, the particle size distribution laser diffraction method according to GB / T 19077-2016 / ISO 13320:2009 can be used to measure the volume distribution particle size Dv10, Dv50, and Dv90 using a Malvern 3000 instrument, and the span of the composite cathode material can be calculated.

[0174] The composite positive electrode material has a large particle size distribution. The large and small particles in the material cooperate with each other to fill the gaps, which can increase the space between the particles and the volume utilization rate, making the particles in the composite positive electrode material more densely packed, improving the compressive resistance of the electrode sheet, increasing the compaction density of the electrode sheet, and improving the energy density of the battery.

[0175] In some embodiments, the span of the composite cathode material is greater than or equal to 1.2. In some embodiments, the span of the composite cathode material is greater than or equal to any one of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0.

[0176] When the diameter distance of the composite positive electrode material is within an appropriate range, the compaction density of the electrode sheet can be further improved, thereby increasing the energy density of the battery.

[0177] In some embodiments, the oxygen deficiency index (ODI) of the composite cathode material is greater than or equal to 1.75. In some embodiments, the oxygen deficiency index (ODI) of the composite cathode material is greater than or equal to any one of 1.75, 1.8, 1.9, and 2.0.

[0178] In this article, the term "oxygen deficiency index ODI" refers to (I101 / I012) 0.5 The numerical value of I101 represents the XRD diffraction peak intensity of the (101) crystal plane of the composite positive electrode material in the XRD spectrum, and I012 represents the diffraction peak intensity of the (012) crystal plane of the composite positive electrode material in the XRD spectrum.

[0179] The test method for the oxygen defect index ODI of the composite cathode material can be tested by methods known in the art. As an example, the 35-50° interval in the XRD spectrum of the tested sample is scanned slowly (<2° / min), and the image is processed according to smoothing and filtering to obtain the diffraction peak areas I101 and I012 of the (101) crystal plane and the (012) crystal plane, and the (I101 / I012) is used to determine the diffraction peak area. 0.5 To calculate the oxygen deficiency index.

[0180] When the oxygen defect index ODI of the composite positive electrode material is within an appropriate range, the crystal structure of the composite positive electrode material can be relatively complete and the structural stability can be better. The crystal is not easy to collapse during the process of lithium ion insertion and extraction, thereby improving the high-temperature storage performance and high-temperature cycle performance of the battery and reducing the high-temperature gas production of the battery.

[0181] In some embodiments, the oxygen deficiency index (ODI) of the composite cathode material is greater than or equal to 1.8. In some embodiments, the oxygen deficiency index (ODI) of the composite cathode material is greater than or equal to any one of 1.8, 1.85, 1.9, 1.95, and 2.0.

[0182] The oxygen defect index ODI of the composite positive electrode material is greater than or equal to 1.8, which can further improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and widen the operating temperature of the battery.

[0183] The second aspect of the present application provides a method for preparing a composite positive electrode material, comprising steps (1) and (2):

[0184] Step (1): uniformly mixing a first raw material comprising a lithium source and a cathode material precursor, and performing a first calcination under a first atmosphere to obtain a first product. Optionally, the first raw material further comprises an M source;

[0185] Step (2): in a second atmosphere, uniformly mixing the first product with a second raw material containing a transition metal element source, and performing a second calcination to prepare a composite positive electrode material;

[0186] The composite positive electrode material comprises: a positive electrode material matrix and a first coating layer provided on at least a portion of the positive electrode material matrix. The general formula of the positive electrode material matrix is:

[0187] Li b Ni x Co y Mn z M a O 2-c ,

[0188] Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, and Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1,

[0189] The first cladding layer includes a transition metal element.

[0190] In some embodiments, the lithium source includes one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium oxalate, and lithium sulfate.

[0191] In some embodiments, the M source includes one or more of zirconium oxide, zirconium fluoride, zirconium chloride, yttrium oxide, yttrium sulfate, yttrium nitrate, yttrium oxalate, yttrium acetate, yttrium chloride, aluminum oxide, aluminum fluoride, aluminum chloride, lithium aluminate, titanium oxide, lithium titanate, tungsten oxide, tungstic acid, ammonium tungstate, sodium tungstate, lithium tungstate, strontium oxide, tantalum oxide, antimony oxide, niobium oxide, lithium niobate, molybdenum oxide, lithium molybdate, antimony oxide, lithium antimonate, sodium hydroxide, sodium carbonate, sodium chloride, sodium fluoride, sodium oxide, potassium hydroxide, potassium carbonate, potassium chloride, potassium oxide, calcium hydroxide, calcium carbonate, calcium oxide, calcium chloride, calcium fluoride, ammonium chloride, cerium fluoride, and cerium oxide.

[0192] In some embodiments, the transition metal element source includes one or more of cobaltous oxide, cobalt hydroxide, cobaltous oxide, cobalt oxyhydroxide, cobalt acetate, cobalt oxalate, cobalt carbonate, cerium oxide, cerium fluoride, cerium chloride, cerium sulfide, cerium nitrate, and cerium hydroxide.

[0193] By the above-mentioned preparation method, a transition metal layer is coated on the positive electrode material substrate. The transition metal element will activate the lithiated rock salt structure on the surface of the positive electrode material substrate, making the lithium in the lithiated rock salt structure more active, thereby improving the first coulombic efficiency and gram capacity of the battery; the transition metal element in the first coating layer will react with the residual lithium on the surface of the positive electrode material substrate to generate a transition metal-containing lithium salt substance with high ionic conductivity, thereby improving the transmission rate of lithium ions on the surface of the material and reducing the DC internal resistance of the battery; the transition metal element in the first coating layer can easily form a dense coating layer on the surface of the positive electrode material substrate, which can reduce the possibility of the active sites of the material being corroded by electrolyte byproducts, thereby achieving the purpose of improving high-temperature cycling and high-temperature storage and reducing high-temperature gas production.

[0194] In some embodiments, the transition metal element includes one or more of Ce, Co, Zr, La, Sb, W, and Li.

[0195] In some embodiments, the transition metal element includes one or both of Ce and Co.

[0196] In some embodiments, the second raw material further includes a compound having a melting point below 900°C.

[0197] In some embodiments, the compound having a melting point below 900°C includes one or more of lithium sulfate, sodium sulfate, potassium sulfate, lithium nitrate, sodium nitrate, potassium nitrate, lithium fluoride, sodium fluoride, potassium fluoride, lithium sulfide, sodium sulfide, potassium sulfide, lithium chloride, sodium chloride, potassium chloride, lithium oxalate, sodium oxalate, potassium oxalate, lithium acetate, sodium acetate, and potassium acetate.

[0198] A compound with a melting point lower than 900°C is added to the second raw material, so that the first coating layer also includes a compound with a melting point lower than 900°C, so that it has a lower eutectic point with the transition metal element, which can enhance the coating and melting effect of the transition metal element, so that the transition metal element is solid-dissolved into the surface lattice of the positive electrode material matrix, further increasing the battery's gram capacity, reducing the battery's DC internal resistance, improving the battery's high-temperature storage performance and high-temperature cycle performance, and reducing the battery's high-temperature gas production.

[0199] In any embodiment, step (2) specifically includes:

[0200] In a second atmosphere, the first product and the second raw material are uniformly mixed and subjected to a second calcination to obtain a second product;

[0201] The second product is mixed evenly with a third raw material, and a third calcination is performed under a third atmosphere to prepare a composite positive electrode material; wherein the third raw material includes one or more of an Al source, a B source, and a W source.

[0202] In some embodiments, the Al source includes one or more of aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum chloride, and aluminum nitrate.

[0203] In some embodiments, the B source includes one or more of boron chloride, boron sulfate, boron nitrate, boron nitride, boron oxide, boron fluoride, boron bromide, boron iodide, and boric acid.

[0204] In some embodiments, the W source includes one or more of ammonium metatungstate, ammonium tungstate, ammonium paratungstate, or tungsten trioxide.

[0205] Through the third calcination, a second coating layer is formed on the surface of the first coating layer. The Al, B, and W contained in the second coating layer can form a glass-like substance of LiAlO2, Li3BO3 or Li2WO4 with the positive electrode material matrix. The above-mentioned glass-like substance can be wrapped at the grain boundaries of the particles, which can inhibit the generation of oxygen defects, improve the high-temperature storage performance and high-temperature cycle performance of the battery, and reduce the high-temperature gas production of the battery. At the same time, the glass-like substance has excellent ion conductivity, which can improve the transmission rate of lithium ions on the surface of the material and reduce the DC internal resistance of the battery.

[0206] In some embodiments, the first atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the first calcination is 700° C.-900° C., and the calcination time is 10 h-20 h.

[0207] In some embodiments, the first atmosphere is an air atmosphere.

[0208] In some embodiments, the first atmosphere is a pure oxygen atmosphere.

[0209] In some embodiments, the calcination temperature of the first calcination is any value of 700° C., 800° C., 900° C., or a range consisting of any two of these values.

[0210] In some embodiments, the first calcination time is any value of 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, or a range consisting of any two values ​​thereof.

[0211] The appropriate first calcination temperature and calcination time can obtain a positive electrode material matrix with excellent structural properties, providing a basis for obtaining a composite positive electrode material with excellent structural properties.

[0212] In some embodiments, the second atmosphere is a pure oxygen atmosphere or an air atmosphere, the calcination temperature of the second calcination is 300° C.-650° C., and the calcination time is 3 h-10 h.

[0213] In some embodiments, the second atmosphere is a pure oxygen atmosphere.

[0214] In some embodiments, the second atmosphere is an air atmosphere.

[0215] In some embodiments, the calcination temperature of the second calcination is any value of 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, or a range consisting of any two of these values.

[0216] In some embodiments, the second calcination time is any value of 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or a range consisting of any two values ​​thereof.

[0217] The appropriate second calcination temperature and calcination time can obtain a uniformly distributed first coating layer, and the transition metal elements in the first coating layer have good bonding strength with the positive electrode material matrix, reducing the possibility of peeling between the first coating layer and the positive electrode material matrix during the battery cycle, improving the structural stability of the composite positive electrode material, and allowing the transition metal elements in the first coating layer to fully play their role, thereby reducing the DC internal resistance of the battery, increasing the battery's gram capacity and first coulomb efficiency, improving the battery's high-temperature storage performance and high-temperature cycle performance, reducing the battery's high-temperature gas production, and comprehensively improving the battery's electrochemical performance.

[0218] In some embodiments, the third atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the third calcination is 200° C.-500° C., and the calcination time is 5 h-15 h.

[0219] In some embodiments, the third atmosphere is a pure oxygen atmosphere.

[0220] In some embodiments, the third atmosphere is an air atmosphere.

[0221] In some embodiments, the calcination temperature of the third calcination is any value of 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, or a range consisting of any two of these values.

[0222] In some embodiments, the third calcination time is any value of 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, or a range consisting of any two values ​​thereof.

[0223] The appropriate third calcination temperature and calcination time can obtain a uniformly distributed second coating layer, and the Al, B or W in the second coating layer has good bonding strength with the first coating layer, thereby reducing the possibility of peeling between the second coating layer and the first coating layer during the battery cycle, improving the structural stability of the composite positive electrode material, and allowing the Al, B or W in the second coating layer to fully exert its role, thereby reducing the DC internal resistance of the battery, improving the high-temperature storage performance and high-temperature cycle performance of the battery, and reducing the high-temperature gas production of the battery.

[0224] [Positive electrode]

[0225] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer formed on at least a portion of the surface of the positive electrode current collector. The positive electrode film layer includes a composite positive electrode material in some embodiments.

[0226] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0227] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0228] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0229] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0230] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0231] [Negative electrode]

[0232] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0233] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0234] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0235] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0236] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0237] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0238] In some embodiments, the negative electrode film layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0239] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0240] [Electrolytes]

[0241] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0242] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0243] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0244] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0245] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0246] [Isolation film]

[0247] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0248] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0249] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0250] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0251] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 is an example of a secondary battery 5 having a square structure, and FIG2 is an exploded view of the secondary battery 5 .

[0252] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The non-Newtonian fluid electrolyte composition is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0253] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0254] Figure 3 shows an example battery module 3. Referring to Figure 3 , within the battery module 3, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 3. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0255] Optionally, the battery module 3 may further include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0256] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0257] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0258] [Electrical devices]

[0259] In one embodiment of the present application, an electric device is provided, comprising at least one of a secondary battery according to any embodiment, a battery module according to any embodiment, or a battery pack according to any embodiment.

[0260] The electrical device includes at least one of the secondary batteries, battery modules, or battery packs provided in this application. The secondary batteries, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0261] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0262] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0263] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0264] Example

[0265] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0266] 1. Preparation method

[0267] Example 1

[0268] 1) Preparation of composite cathode materials

[0269] Step (0): Preparation of a composite positive electrode material precursor: nickel sulfate, cobalt sulfate, and manganese sulfate were prepared into a 2 mol / L metal salt solution in a molar ratio of 0.92:0.07:0.01, and then the metal salt solution, 8 mol / L ammonia water, and 5 mol / L NaOH solution were continuously added to a reactor for reaction. The precursor of the positive electrode material (Ni) was prepared by a hydroxide coprecipitation method by controlling the pH value of the reaction process to 11.30, the ammonia concentration to 4.0 g / L, the reaction time to 20 h, and the stirring rate to 300 r / min. 0.92 Co 0.07 Mn 0.01 (OH)2), where the precursor's span is 1.4.

[0270] Step (1): Preparation of composite cathode material

[0271] Step (1-1): Lithium hydroxide and cathode material precursor Ni 0.92 Co 0.07 Mn 0.01 (OH)2 and Sb2O3 were mixed in a high-speed mixer to obtain a first mixed material, wherein the molar ratio of lithium hydroxide to cathode material precursor was 1.03, and the mass content of Sb element was 3600 ppm, based on the mass of the cathode material precursor. The first mixed material was then placed in a kiln for a first calcination under a pure oxygen atmosphere at a temperature of 760°C for 20 hours to obtain a first product;

[0272] Step (1-2): placing the first product, cobalt oxyhydroxide (CoOOH), cerium dioxide (CeO2), and lithium sulfate Li2SO4 into a high-speed mixer for mixing to obtain a second mixture, wherein the mass content of the Co element is 2284 ppm, the mass content of the Ce element is 2716 ppm, the mass content of the Li element is 2000 ppm, the mass content of the S element is 4600 ppm, the mass content of the Al element is 1000 ppm, and the mass content of the B element is 1000 ppm, based on the mass of the first product; placing the second mixture into a kiln in a high-purity oxygen atmosphere for calcination at a calcination temperature of 650° C. for 5 hours to obtain a second product;

[0273] Step (1-3) The second product, aluminum oxide (Al2O3) and orthoboric acid (H3BO3) are mixed in a high-pressure mixer to obtain a third mixture, wherein the mass content of the Al element is 1000 ppm and the mass content of the B element is 1000 ppm, based on the mass of the first product; in a high-purity oxygen atmosphere, the third mixture is placed in a kiln for calcination at a calcination temperature of 400°C and a calcination time of 5 hours to obtain a composite positive electrode material.

[0274] 2) Preparation of positive electrode sheet

[0275] The composite cathode material was premixed in a 5L stirring tank for 30 minutes. The conductive agent, acetylene black (SP), and the binder, polyvinylidene fluoride (PVDF), were then added and stirred for 30 minutes. The solvent, N-methylpyrrolidone (NMP), was then added and rapidly stirred under vacuum to form a cathode slurry. The mass ratio of composite cathode material: acetylene black: PVDF was 96:2:2, and the solids content of the cathode slurry was 70%. The cathode slurry was evenly coated on both sides of a 12μm thick aluminum foil. The coated electrode was oven-dried at 100°C to 130°C for half an hour. The dried electrode was then roll-pressed and punched to produce the cathode electrode sheets.

[0276] 3) Preparation of negative electrode sheet

[0277] The negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) are fully stirred and mixed in a deionized water solvent system in a weight ratio of 90:5:2:2:1, and then coated on copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0278] 4) Electrolyte

[0279] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), lithium salt lithium hexafluorophosphate LiPF6 was dissolved in the organic solvent ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate (the volume ratio of EC+EMC+DMC was 1:1:1) and stirred evenly to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0280] 5) Isolation film

[0281] A polyethylene porous polymer film is used as the separator.

[0282] 6) Preparation of full battery

[0283] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells are then wound to obtain a bare cell. The tabs are welded to the bare cell and placed in an aluminum shell. The cells are then baked at 80°C to remove moisture. The electrolyte is then injected and sealed to obtain an uncharged battery. The uncharged battery then undergoes a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium battery product of Example 1.

[0284] The preparation method of the battery of Example 2 is similar to that of the battery of Example 1, except that Sb2O3 is not added in step (1-1), the Co source added in step (1-2) is hydroxycobalt oxide (CoOOH), and there is no step (1-3).

[0285] The preparation method of the battery of Example 3 is similar to that of the battery of Example 1, and the mass content of Zr added in step (0) is 3600 ppm, based on the mass of the positive electrode material precursor.

[0286] Examples 4 to 9

[0287] The batteries of Examples 4 to 9 were prepared in a similar manner to that of Example 1, except that the mass contents of the transition metal element, alkali metal element, non-metallic element, Al element, and B element based on the first product were adjusted. The specific parameters are shown in Table 1.

[0288] Examples 10 to 13

[0289] The batteries of Examples 10 to 13 were prepared in a similar manner to that of Example 1, except that the Ce source added was CeF3, and the mass contents of the transition metal elements, alkali metal elements, non-metallic elements, Al elements, and B elements based on the first product were adjusted. The specific parameters are shown in Table 1.

[0290] Examples 14 to 16

[0291] The batteries of Examples 14 to 16 were prepared in a similar manner to that of Example 1, except that the mass contents of the transition metal element, alkali metal element, non-metallic element, Al element, and B element based on the first product were adjusted. The specific parameters are shown in Table 1.

[0292] Examples 17 to 22

[0293] The batteries of Examples 17 to 22 were prepared in a similar manner to that of Example 1, except that the added Co source was Co(OH)2 and the added Ce source was CeF3. The mass content of the transition metal element, alkali metal element, non-metallic element, Al element, and B element based on the first product was adjusted. The specific parameters are shown in Table 1.

[0294] Examples 23 to 28

[0295] The batteries of Examples 23 to 28 were prepared in a similar manner to that of Example 1, except that the mass contents of the transition metal element, alkali metal element, non-metallic element, Al element, and B element based on the first product were adjusted. The specific parameters are shown in Table 1.

[0296] Examples 29 to 31

[0297] The preparation methods of the batteries of Examples 29 to 31 are similar to those of Example 1, except that the span value of the precursor is adjusted to 0.2, 0.5, and 1.2, and the span value of the composite positive electrode material is further adjusted. The specific parameters are shown in Table 1.

[0298] Comparative Example 1

[0299] The preparation method of the battery of Comparative Example 1 is similar to that of the battery of Example 2, but the composite positive electrode material only includes the positive electrode material substrate and does not include the first coating. The specific parameters are shown in Table 1.

[0300] Comparative Example 2

[0301] The preparation method of the battery of Comparative Example 2 is similar to that of the battery of Comparative Example 1, but the composition of the positive electrode active material substrate is adjusted. The specific parameters are shown in Table 1.

[0302] 2. Performance Testing

[0303] 1. Composite cathode material performance test

[0304] 1) Determine whether Co and Ce elements exist in the form of oxides or fluorides

[0305] The determination is carried out with reference to the EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis - inductively coupled plasma optical emission spectrometry) testing can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then return to the ground state from the excited state. In the above process, energy is released and recorded as different characteristic spectral lines, and elemental trace analysis is performed to determine whether the Co and Ce elements exist in the form of oxides or fluorides.

[0306] 2) Mass content test of transition metal elements / alkali metal elements / non-metal elements / aluminum elements / boron elements

[0307] The determination is carried out with reference to the EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis - inductively coupled plasma optical emission spectrometry) testing can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then return to the ground state from the excited state. In the above process, energy is released and recorded as different characteristic spectral lines for elemental quantitative analysis.

[0308] 3) Total thickness test of the first and second coating layers

[0309] Mix the sample preparation glue and composite cathode material powder evenly (the powder weight should be 5 times the sample preparation glue), apply it to copper foil to prepare the sample, and dry it at 60°C for 30 minutes. Cut the prepared sample into 6mm × 6mm pieces with scissors, fix it on the sample stage, and place it in an ion polisher (Model: IB-19500CP). Adjust the sample edge parallel to the centerline X-axis and the Y-axis position 40-60μm for cutting. After cutting, an X-Max energy dispersive spectrometer (EDS) from the Oxford Instruments Group of the United Kingdom was combined with a Sigma-02-33 scanning electron microscope (SEM) from the ZEISS of Germany to select a suitable particle section on the cut sample. The characteristic element content of the first coating layer and the characteristic element of the second coating layer were linearly scanned along the diameter direction of the particle. The radius of the measured particle was R, the distance from the site where the element content of the first coating layer began to increase compared with the particle core to the center position of the particle was L1, and the distance from the site where the element content of the second coating layer began to increase compared with the particle core to the center position of the particle was L2. The total thickness of the first coating and the second coating layer was (R-L1) μm.

[0310] 4) Test of aspect ratio of composite cathode materials

[0311] Static image processing technology: Using static powder scanning electron microscope photos taken through NanoMeasure software, intelligent identification is performed to obtain the long diameter RL and short diameter RS ​​data of the powder primary particles, and then the aspect ratio = RL / RS is calculated.

[0312] 5) ODI test

[0313] The XRD spectrum of the tested sample was scanned at a slow speed (<2° / min) in the range of 35-50°, and the image was processed by smoothing and filtering to obtain the diffraction peak area I of the (101) crystal plane and the (012) crystal plane. 101 , I 012 , through (I 101 / I 012 ) 0.5 To calculate the oxygen deficiency index.

[0314] 6) Span test

[0315] According to the particle size distribution laser diffraction method specified in GB / T 19077-2016, 0.1g to 0.13g of the composite cathode material sample to be tested was weighed into a 50mL beaker. 5g of anhydrous ethanol was added, and a stirring bar (approximately 2.5mm in diameter) was placed in the beaker. The sample was then sealed with plastic wrap. After ultrasonic treatment for 5 minutes, it was transferred to a magnetic stirrer and stirred at 500 rpm for at least 20 minutes. Two samples were collected from each batch for testing. Testing was performed using a Malvern 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. Dv90 is the particle size at which the cumulative volume distribution percentage of the composite cathode material's secondary particles reaches 99%, Dv50 is the particle size at which the cumulative volume distribution percentage of the composite cathode material's secondary particles reaches 50%, and Dv10 is the particle size at which the cumulative volume distribution percentage of the composite cathode material's secondary particles reaches 10%. Where span = (Dv90 - Dv10) / Dv50.

[0316] 2. Pole performance test

[0317] 1) Compaction density test

[0318] The compacted density (PD) of the positive electrode sheet is calculated using the formula (PD = M / (d × A). Here, M is the mass of a 40 mm diameter disc cut from the positive electrode sheet, averaged over 10 weighings; d is the thickness of the positive electrode sheet, averaged over 10 thickness measurements; and A is the area of ​​the 40 mm diameter disc.

[0319] 3. Full battery performance test

[0320] 1) 1 / 3C full-charge capacity test

[0321] Under a constant temperature environment of 25℃, let it stand for 5 minutes, discharge at 1 / 3C to 2.8V, let it stand for 5 minutes, charge at 1 / 3C to 4.25V, then charge at constant voltage at 4.25V to a current ≤0.05C, let it stand for 5 minutes, and then discharge at 1 / 3C to 2.8V. The discharge capacity at this time is the initial gram capacity, recorded as D0.

[0322] 2) First Coulombic efficiency test

[0323] At 2.8-4.25V, charge the button battery at 0.1C to 4.3V, then charge at constant voltage at 4.3V to a current ≤ 0.05mA, let it stand for 2 minutes, and the charge capacity at this time is recorded as C0. Then discharge it at 0.1C to 2.8V, and the discharge capacity at this time is the initial gram capacity recorded as D0.

[0324] The first coulombic efficiency is calculated as D0 / C0*100%.

[0325] 3) DC impedance test

[0326] In a constant temperature environment of 25℃, let it stand for 5 minutes, discharge at 1 / 3C to 2.8V, let it stand for 5 minutes, charge at 1 / 3C to 4.25V, then charge at constant voltage at 4.25V to a current ≤0.05C, let it stand for 5 minutes, and then discharge at 1 / 3C to 2.8V. The discharge capacity at this time is recorded as D0.

[0327] In a constant temperature environment of 25℃, let it stand for 30 minutes, charge to 4.25V at a current of 1 / 3D0, then charge at a constant voltage at 4.25V to a current ≤0.05D0, let it stand for 30 minutes, then discharge to the capacity position of 0.5D0 at a current of 1 / 3D0, and let it stand for 10 minutes.

[0328] Place the battery in a constant temperature environment at -25℃ for 120min, discharge it at a current of 0.36D0 for 10s, and record the voltage change ΔU at this time. Calculate the DC internal resistance R at 50% SOC at -25℃ according to Ohm's formula. 50％ =ΔU / (0.36D0).

[0329] 4) High temperature cycle performance

[0330] At 45°C, charge at a constant current of 1C to 4.25V, then charge at a constant voltage of 4.25V until the current drops to 0.05C, and then discharge at a constant current of 1C to 2.8V. This is the first-cycle discharge capacity (Cd1). Repeat this charge and discharge cycle for the 300th cycle, and the discharge capacity after n cycles is recorded as Cdn. Capacity retention = discharge capacity after n cycles (Cdn) / first-cycle discharge capacity (Cd1).

[0331] 5) High-temperature storage performance

[0332] The secondary batteries prepared in the above-mentioned embodiments and comparative examples are respectively left standing for 5 min in a constant-temperature environment at 25°C, discharged at 1 / 3C to 2.8V, left standing for 5 min, charged at 1 / 3C to 4.25V, and then charged at a constant voltage of 4.25V until the current ≤ 0.05 mA, left standing for 5 min. The charging capacity at this time is recorded as C0. Then, it is discharged at 1 / 3C to 2.8V, and the discharge capacity at this time is the initial gram capacity, recorded as D0. Then, the battery is charged at a constant current of 0.33C to 4.25V and held at a constant voltage until the current ≤ 0.05 mA, left standing for 5 min, and then placed in a high and low temperature chamber at 60°C. After leaving it standing for 1 h until the battery temperature reaches the target temperature, storage is carried out. It is taken out after 15 days, and in a constant-temperature environment at 25°C, the previous process is repeated, and the capacity Dn (n = 0, 1, 2...) is recorded every 15 days. Calculate the capacity retention rate after 60 days of storage: (D4 - D0) / D0 * 100%.

[0333] 6) Gas generation performance during high-temperature storage

[0334] Store the full battery with a 100% charged state (SOC) at 70°C. Measure the open-circuit voltage (OCV) and AC internal resistance (IMP) of the battery cell before, during, and after storage to monitor the SOC, and measure the volume of the battery cell. Among them, after every 48 h of storage, take out the full battery, leave it standing for 1 h, then test the OCV and IMP, and measure the volume of the battery cell by the drainage method after cooling to room temperature. The drainage method is to first measure the gravity F1 of the battery cell alone with a balance that automatically performs unit conversion with the dial data, and then place the battery cell completely in deionized water (with a known density of 1 g / cm3), and measure the gravity F2 of the battery cell at this time. The buoyancy F_float of the battery cell is F1 - F2. Then, according to Archimedes' principle F_float = ρgV_drain, calculate the volume of the battery cell V = (F1 - F2) / ρg.

[0335] After each volume test, charge the battery cell. Charge it at a constant current of 1C to 4.25V, and then charge it at a constant voltage of 4.25V until the current drops to 0.05C. After the charging is completed, put it back into the furnace to continue the test.

[0336] After 60 days of storage, measure the volume of the battery cell, and calculate the increase in the volume of the battery cell after storage relative to the volume of the battery cell before storage, that is, the gas generation amount.

[0337] III. Analysis of test results of each embodiment and comparative example

[0338] Prepare the batteries of each embodiment and comparative example according to the above method, and measure various performance parameters. The results are shown in Table 1 and Table 2 below.

[0339] Table 1

[0340] Table 2

[0341] According to the above results, the composite positive electrode materials in Examples 1 to 31 include a positive electrode material matrix and a first coating layer at least partially covering the positive electrode material matrix, wherein the chemical formula of the positive electrode material matrix is ​​LiNi 0.92 Co 0.06 Mn 0.018 Sb 0.002 O2、LiNi 0.92 Co 0.07 Mn 0.01 O2 or LiNi 0.92 Co 0.06 Mn 0.018 Zr 0.002 O2, the first coating layer includes transition metal elements Ce or Co.

[0342] From the comparison of Examples 1 to 31 with Comparative Examples 1 to 2, it can be seen that covering the positive electrode material substrate with a first coating layer including a transition metal element can reduce the DC internal resistance of the battery, increase the gram capacity and first coulomb efficiency of the battery, improve the high-temperature storage performance and high-temperature cycle performance of the battery, reduce the high-temperature gas production phenomenon of the battery, and comprehensively improve the electrochemical performance of the battery.

[0343] It can be seen from Examples 1 to 31 that the transition metal element exists in the first coating layer in the form of fluoride or oxide, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0344] From the comparison between Example 5 and Example 4, it can be seen that the first coating layer also includes the compound Li2SO4 with a melting point lower than 900°C, which can increase the battery's gram capacity, reduce the battery's DC internal resistance, improve the battery's high-temperature storage performance and high-temperature cycle performance, and reduce the battery's high-temperature gas production.

[0345] From the comparison between Example 6 and Example 5, it can be seen that the composite positive electrode material also includes a second coating layer, which is at least partially coated on the surface of the first coating layer. The second coating layer includes Al or B, which can further reduce the DC internal resistance of the battery, improve the high-temperature storage performance and high-temperature cycle performance of the battery, and improve the electrochemical performance of the battery at high temperatures.

[0346] It can be seen from Examples 1 and 10 to 14 that, based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 100ppm-20000ppm, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0347] From the comparison between Examples 1 and 12 and Examples 10, 11 and 14, it can be seen that based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 1000ppm-15000ppm, which can reduce the DC internal resistance of the battery and improve the high-temperature cycle performance of the battery.

[0348] It can be seen from Examples 1 and 14 to 16 that the molar ratio M of Ce to Co in the transition metal elements satisfies: 0<M≤10, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulombic efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0349] From the comparison of Examples 1, 14, and 15 with Example 16, it can be seen that the molar ratio M of Ce to Co in the transition metal elements satisfies: 0<M≤1, which can improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and broaden the operating temperature of the battery.

[0350] It can be seen from Examples 17 to 20 that, based on the mass of the positive electrode material matrix, the mass content of the Li element in the first coating layer is 100ppm-15000ppm, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0351] From the comparison between Example 18 and Examples 17, 19 and 20, it can be seen that based on the mass of the positive electrode material matrix, the mass content of the Li element in the first coating layer is 1000ppm-8000ppm, which can take into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, and comprehensively improve the battery performance.

[0352] It can be seen from Examples 17 to 20 that, based on the mass of the positive electrode material matrix, the mass content of the S element in the first coating layer is 200ppm-50000ppm, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0353] From the comparison of Examples 18 to 20 with Example 17, it can be seen that based on the mass of the positive electrode material matrix, the mass content of the S element in the first coating layer is 500ppm-8000ppm, which can improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and broaden the operating temperature of the battery.

[0354] It can be seen from Examples 1 and 23 to 28 that, based on the mass of the positive electrode material matrix, the mass content of Al in the second coating layer is 100ppm-3500ppm, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0355] From the comparison of Examples 1, 24, 25, 27, and 28 with Examples 23 and 26, it can be seen that based on the mass of the positive electrode material matrix, the mass content of Al in the second coating layer is 500ppm-2500ppm, which can increase the gram capacity of the battery while taking into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, thereby comprehensively improving the battery's performance.

[0356] It can be seen from Examples 1 and 23 to 26 that, based on the mass of the positive electrode material matrix, the mass content of B in the second coating layer is 100ppm-2500ppm, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0357] From the comparison of Examples 1, 24, 25, 27, and 28 with Examples 23 and 26, it can be seen that based on the mass of the positive electrode material matrix, the mass content of B in the second coating layer is 500ppm-2000ppm, which can increase the gram capacity of the battery while taking into account the battery's first coulombic efficiency, high-temperature storage performance, high-temperature storage performance and high-temperature gas production, thereby comprehensively improving the battery's performance.

[0358] It can be seen from Examples 1 and 23 to 28 that the mass ratio of Al to B elements in the second coating layer is 0.5-2, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0359] It can be seen from Examples 1 to 31 that the total thickness of the first coating layer and the second coating layer is 0.01 μm-1 μm, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulombic efficiency, high-temperature storage performance and high-temperature cycle performance, and the battery has low high-temperature gas production.

[0360] It can be seen from Examples 1 to 31 that the aspect ratio of the primary particles of the composite positive electrode material is 1.5-10, the battery has low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0361] From the comparison of Examples 1, 14, and 15 with Example 16, it can be seen that the aspect ratio of the primary particles of the composite positive electrode material is 2-4, which can improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and broaden the operating temperature of the battery.

[0362] It can be seen from Examples 1, 30, 31 and Example 29 that the span of the composite positive electrode material is greater than or equal to 0.5, which can improve the compaction density of the electrode sheet.

[0363] From the comparison between Examples 1 and 31 and Examples 29 and 30, it can be seen that the span of the composite positive electrode material is greater than or equal to 1.2, which can further improve the compaction density of the electrode sheet.

[0364] It can be seen from Examples 1 to 31 that the oxygen defect index ODI of the composite positive electrode material is greater than or equal to 1.75, the battery has a low DC internal resistance, the battery has excellent gram capacity, first coulomb efficiency, high temperature storage performance and high temperature cycle performance, and the battery has low high temperature gas production.

[0365] From the comparison of Examples 1, 10, and 11 with Examples 12 and 13, it can be seen that the oxygen defect index ODI of the composite positive electrode material is greater than or equal to 1.8, which can improve the high-temperature cycle performance and high-temperature storage performance of the battery, reduce the high-temperature gas production of the battery, and broaden the operating temperature of the battery.

Claims

1. A composite positive electrode material, characterized in that: The composite positive electrode material comprises: a positive electrode material matrix and a first coating layer at least partially covering the positive electrode material matrix. The general formula of the positive electrode material matrix is: Li b Ni x Co y Mn z M a O 2-c , Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1, The first coating layer includes a transition metal element.

2. The composite positive electrode material according to claim 1, characterized in that General formula Li b Ni x Co y Mn z M a O 2-c where 0.9 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.1, 0 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, 0.5 ≤ b ≤ 1.2, a + x + y + z + b = 2, -0.1 ≤ c ≤ 0.

1.

3. The composite positive electrode material according to claim 1 or 2, characterized in that: The transition metal element exists in the first coating layer in the form of oxide or fluoride.

4. The composite positive electrode material according to any one of claims 1 to 3, characterized in that The transition metal element includes one or more of Co, Ce, Zr, La, Sb, and W. Optionally, the transition metal element includes one or two of Co and Ce.

5. The composite positive electrode material according to any one of claims 1 to 4, characterized in that: The first coating layer further comprises a compound having a melting point lower than 900°C.

6. The composite positive electrode material according to claim 5, characterized in that: The compound with a melting point lower than 900° C. comprises alkali metal elements and non-metal elements, wherein the non-metal elements include one or more of N, F, Cl, and S.

7. The composite positive electrode material according to any one of claims 1 to 6, characterized in that: The composite positive electrode material further includes a second coating layer, which is at least partially coated on the surface of the first coating layer, and the second coating layer includes one or more of Al, B, and W.

8. The composite positive electrode material according to any one of claims 1 to 7, characterized in that: Based on the mass of the positive electrode material matrix, the mass content of the transition metal element in the first coating layer is 100 ppm-20000 ppm, and can be optionally 1000 ppm-15000 ppm.

9. The composite positive electrode material according to any one of claims 4 to 8, characterized in that: The molar ratio M of Ce to Co in the transition metal element satisfies: 0<M≤10, and optionally satisfies: 0<M≤1.

10. The composite positive electrode material according to any one of claims 6 to 9, characterized in that: Based on the mass of the positive electrode material matrix, the mass content of the alkali metal element in the first coating layer is 100 ppm-15000 ppm, and can be optionally 1000 ppm-8000 ppm.

11. The composite positive electrode material according to any one of claims 6 to 10, characterized in that: Based on the mass of the positive electrode material matrix, the mass content of the non-metallic element in the first coating layer is 200ppm-50000ppm, and can be optionally 500ppm-8000ppm.

12. The composite positive electrode material according to any one of claims 7 to 11, characterized in that: Based on the mass of the positive electrode material matrix, the mass content of Al in the second coating layer is 100 ppm-3500 ppm, and can be optionally 500 ppm-2500 ppm.

13. The composite positive electrode material according to any one of claims 7 to 12, characterized in that: Based on the mass of the positive electrode material matrix, the mass content of B in the second coating layer is 100 ppm-2500 ppm, and can be optionally 500 ppm-2000 ppm.

14. The composite positive electrode material according to any one of claims 7 to 13, characterized in that: The mass ratio of Al to B elements in the second coating layer is 0.5-2.

15. The composite positive electrode material according to any one of claims 7 to 14, characterized in that: The total thickness of the first cladding layer and the second cladding layer is 0.01 μm-1 μm.

16. The composite positive electrode material according to any one of claims 1 to 15, characterized in that: The aspect ratio of the primary particles of the composite positive electrode material is 1.5-10, and can be 2-4.

17. The composite positive electrode material according to any one of claims 1 to 16, characterized in that: The diameter span of the composite positive electrode material is greater than or equal to 0.5, and can be selected to be greater than or equal to 1.

2.

18. The composite positive electrode material according to any one of claims 1 to 17, characterized in that: The oxygen deficiency index ODI of the composite positive electrode material is greater than or equal to 1.75, and can be optionally greater than or equal to 1.

8.

19. A method for preparing a composite positive electrode material, characterized in that: The method comprises steps (1) and (2): Step (1): uniformly mixing a first raw material including a lithium source and a cathode material precursor, and performing a first calcination under a first atmosphere to obtain a first product. Optionally, the first raw material further includes an M source; Step (2): in a second atmosphere, uniformly mixing the first product with a second raw material containing a transition metal element source, and performing a second calcination to prepare the composite positive electrode material; The composite positive electrode material comprises: a positive electrode material matrix and a first coating layer disposed on at least a portion of the positive electrode material matrix. The general formula of the positive electrode material matrix is: Li b Ni x Co y Mr z M a O 2-c , Wherein, M includes one or more of Zr, Y, Al, Ti, W, Sr, Ta, Mo, Sb, Nb, Na, K, Ca, 0.55≤x≤1.0, 0≤y≤0.45, 0≤z≤0.45, 0≤a≤0.45, 0.5≤b≤1.2, a+x+y+z+b=2, -0.1≤c≤0.1, The first coating layer includes a transition metal element.

20. The preparation method according to claim 19, characterized in that: The transition metal element includes one or more of Ce, Co, Zr, La, Sb, and W.

21. The preparation method according to claim 19 or 20, characterized in that: The second raw material also includes a compound with a melting point lower than 900°C.

22. The preparation method according to any one of claims 19 to 21, characterized in that: The step (2) specifically comprises: In a second atmosphere, the first product and the second raw material are uniformly mixed and subjected to a second calcination to obtain a second product; The second product is mixed evenly with a third raw material, and a third calcination is performed under a third atmosphere to prepare the composite positive electrode material; wherein the third raw material includes one or more of an Al source, a B source, and a W source.

23. The preparation method according to any one of claims 19 to 22, characterized in that: The first atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the first calcination is 700° C.-900° C., and the calcination time is 10 h-20 h.

24. The preparation method according to any one of claims 19 to 23, characterized in that: The second atmosphere is a pure oxygen atmosphere or an air atmosphere, the calcination temperature of the second calcination is 300° C.-650° C., and the calcination time is 3 h-10 h.

25. The preparation method according to any one of claims 22 to 24, characterized in that: The third atmosphere is an air atmosphere or a pure oxygen atmosphere, the calcination temperature of the third calcination is 200° C.-500° C., and the calcination time is 5 h-15 h.

26. A positive electrode plate, characterized in that: The positive electrode plate comprises the composite positive electrode material according to any one of claims 1 to 18 or a composite positive electrode material prepared by the preparation method according to any one of claims 19 to 25.

27. A secondary battery, characterized in that: Including the positive electrode sheet as described in claim 26.

28. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 27.

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