Positive electrode material, positive plate and battery

Abstract

The invention provides a positive electrode material and a preparation method thereof, a positive plate and a battery. The positive electrode material is a lithium nickel cobalt oxide composite oxide; xPS etching is used for characterizing the positive electrode material, when the etching depth is 90 nm, the Ni2p3 / 2 peak binding energy of the positive electrode material is a, when the etching depth is 60 nm, the Ni2p3 / 2 peak binding energy of the positive electrode material is b, when the etching depth is 30 nm, the Ni2p3 / 2 peak binding energy of the positive electrode material is c, and a, b and c meet the conditions that c > b > a, the difference value of c and b is larger than 0.3 ev, and the difference value of b and a is larger than 0.3 ev. The positive electrode material has more Ni < 2 + > with larger particle radius in the transition layer region, so that the stability of the layered structure in the region is favorably maintained, harmful phase change during deep lithium removal is reduced, and meanwhile, the charge of Ni < 2 + > is lower, and the electrostatic repulsion effect with Li < + > is weaker, so that the smoothness of a lithium ion diffusion channel is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials for batteries, and in particular, to a cathode material, a cathode sheet, and a battery. Background Art

[0002] With the rapid rise of the new energy industry, in the field of rechargeable batteries, lithium-ion batteries have become a core part of the industry due to their excellent high energy density and outstanding cycle stability. The cathode material plays a core role in the process of lithium-ion insertion and extraction during battery charging and discharging. It is one of the core components of lithium-ion batteries, and its types and characteristics directly affect the overall performance of lithium-ion batteries.

[0003] Due to the continuous change of market demand, consumers' requirements for key indicators such as the energy density, cycle life, and safety and reliability of lithium-ion batteries are increasing day by day. Currently, layered nickel-based ternary cathode materials (such as LiNi 1-x-y Co x M y O2, where M represents Mn or Al, abbreviated as NCM or NCA) have won wide attention in the market due to their advantages such as high energy density, long cycle life, and high safety. In order to further improve the energy density of the battery, the improvement approach within the industry focuses on increasing the proportion of nickel element in the cathode material. However, the increase in nickel content will make the chemical properties of nickel-based layered oxides more active, and a large number of active oxygen sites will appear on their surfaces, resulting in the cathode material becoming sensitive to moisture and carbon dioxide in the air during storage, and the surface active lithium is converted into residual alkalis such as LiOH and Li2CO3. At the same time, it is prone to redox side reactions with the electrolyte during the charge and discharge process, both of which lead to a decrease in the utilization rate of active lithium in the cathode material. In addition, the increase in nickel content makes the reaction activity of oxygen atoms in the layered structure increase, and oxygen evolution is likely to occur during the charge and discharge process, which will continuously damage the surface layered structure of the primary particle material, and then cause potential safety hazards in the battery. A series of problems caused by increasing the energy density by increasing the nickel content have an adverse impact on the performance and long-term stability of the battery. Summary of the Invention

[0004] The main purpose of the present invention is to provide a cathode material, a cathode sheet, and a battery to solve the technical problems in the prior art that the utilization rate of active lithium decreases with the increase in nickel content in the cathode material and it is prone to cause a decrease in the long-term stability of the battery.

[0005] To achieve the above object, according to one aspect of the present invention, a positive electrode material is provided. The positive electrode material is a lithium nickel cobalt oxide-based composite oxide. When the positive electrode material is characterized by XPS etching, at an etching depth of 90 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is a; at an etching depth of 60 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is b; at an etching depth of 30 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is c. Wherein, a, b, and c satisfy: c > b > a, and the difference between c and b is greater than 0.3 eV, and the difference between b and a is greater than 0.3 eV.

[0006] Further, the positive electrode material satisfies at least one of the following technical characteristics:

[0007] (1) The value range of a is 853.5 eV to 855.5 eV;

[0008] (2) The value range of b is 853.5 eV to 855.5 eV;

[0009] (3) The value range of c is 853.5 eV to 855.5 eV.

[0010] Further, for the positive electrode material according to claim 2, the value range of c is 854.5 eV to 855.5 eV; the value range of b is 854.0 eV to 855.0 eV; the value range of a is 853.5 eV to 854.5 eV.

[0011] Further, the positive electrode material includes zirconium element. At an etching depth of 30 nm, the atomic number content of zirconium is y1, and the value range of y1 is 1.9% to 2.3%; at an etching depth of 90 nm, the atomic number content of zirconium is y3, and the value range of y3 is 2.7% to 3.2%; at an etching depth of 60 nm, the atomic number content of zirconium is y2, and the value of y2 satisfies y1 < y2 < y3, and the difference between y1 and y2 is greater than 0.15, and the difference between y2 and y3 is greater than 0.15.

[0012] Further, the positive electrode material includes zirconium element and aluminum element. At an etching depth of 0 nm, the ratio of the atomic number of zirconium to the atomic number of aluminum in the positive electrode material is 0.3 to 0.5.

[0013] Further, the positive electrode material includes zirconium element and aluminum element. By characterizing the cross-section of the positive electrode material with EDS, the distribution width of zirconium element in the cross-section EDS of the secondary particles of the positive electrode material is greater than 7 μm, and the distribution width of aluminum element is less than 7 μm.

[0014] Further, the positive electrode material satisfies at least one of the following technical characteristics:

[0015] (1) The mass content of zirconium element in the positive electrode material is 2500 ppm to 3500 ppm;

[0016] (2) The positive electrode material further includes aluminum element, and the mass content of aluminum element is 2000 ppm to 3500 ppm;

[0017] (3) The Dmin particle size of the positive electrode material is 4.6 μm to 5.4 μm, the D50 particle size is 9.3 μm to 9.5 μm, the Dmax particle size is 16.0 μm to 19.0 μm, and the span value is 0.4 to 0.6;

[0018] (4) The chemical formula of the positive electrode material is Li(Ni o Co p Mn q Al d Zr e P f )O2, where the value of o is 0.5 to 1.0, the value of p is 0 to 0.2, the value of q is 0 to 0.3, and q is not 0, the value of d is 0.0015 to 0.002, the value of e is 0.0015 to 0.002, P is a doping element, P is selected from any one or more of B, Ti, and Sr, and the value of f is 0.001 to 0.005;

[0019] (5) The specific surface area of the positive electrode material is 0.35 m 2 / g to 0.45 m 2 / g;

[0020] (6) The tap density of the positive electrode material is 2.85 g / m 3 to 3.05 g / m 3 .

[0021] According to another aspect of the present application, a method for preparing a positive electrode material is provided. The preparation method includes: performing a first mixing of a positive electrode material precursor, a lithium source, and a zirconium source under stirring conditions to obtain a first mixture; performing a second mixing of the first mixture and an aluminum source under stirring conditions to obtain a second mixture, and the stirring speed of the second mixing is lower than that of the first mixing; subjecting the second mixture to a first calcination and a second calcination in sequence, and performing pulverization, screening, and demagnetization to obtain the positive electrode material; the temperature of the first calcination is 300 to 500 °C, and the temperature of the second calcination is 700 to 1000 °C.

[0022] According to still another aspect of the present application, a positive electrode sheet is provided, and the positive electrode sheet includes the positive electrode material of any one of the above.

[0023] According to yet another aspect of the present application, a battery is provided, and the battery includes the above positive electrode sheet.

[0024] Applying the technical solution of the present invention, in the XPS spectrum of the cathode material, the peak position of Ni2p2 / 3 decreases with the increase of the etching depth, indicating that the proportion of Ni in the surface layer of the cathode material particles 2+ gradually increases. Since the ionic radius of Ni²⁺ (0.69 Å) is slightly larger than that of Ni³⁺ (0.60 Å), and in the region of the transition layer (60 - 90 nm), during the process of deep de-lithiation, the cathode material is more likely to undergo harmful phase transitions (such as layered → spinel phase). Therefore, having more Ni with a larger particle radius in the transition layer region 2+ helps to maintain the stability of the layered structure in this region, reduce harmful phase transitions during deep de-lithiation. At the same time, the charge of Ni 2+ is relatively low, and the electrostatic repulsion with Li + is weak, thereby improving the smoothness of the lithium-ion diffusion channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0026] Figure 1 shows a schematic structural diagram of a battery provided according to an embodiment of the present invention;

[0027] Figure 2 shows the distribution diagram of the atomic number ratio of zirconium atoms at different etching depths according to Embodiment 1 of the present invention;

[0028] Figure 3 shows the Ni2p2 / 3 curve graph at different etching depths according to Embodiment 1 of the present invention.

[0029] Among them, the above-mentioned accompanying drawings include the following reference numerals: 001, positive electrode sheet; 002, separator; 003, negative electrode sheet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0031] As analyzed in the background art of this application, in the prior art, there are technical problems that the utilization rate of active lithium decreases with the increase of the nickel content in the cathode material, and it is easy to cause the reduction of the battery life. To solve this technical problem, this application provides a cathode material, its preparation method, a positive electrode sheet, and a battery.

[0032] According to a typical embodiment of the present application, a cathode material is provided. The cathode material is a lithium nickel cobaltate-based composite oxide. When the etching depth is 90 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is a. When the etching depth is 60 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is b. When the etching depth is 30 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is c. Among them, a, b, and c satisfy: c > b > a, and the difference between c and b is greater than 0.3 eV, and the difference between b and a is greater than 0.3 eV.

[0033] In the XPS spectrum of the cathode material of the present application, the peak position of Ni2p2 / 3 decreases with the increase of the etching depth, indicating that the proportion of Ni in the surface layer of the cathode material particles 2+ gradually increases. Since the ionic radius of Ni²⁺ (0.69 Å) is slightly larger than that of Ni³⁺ (0.60 Å), in the transition layer (60 - 90 nm) region, during the process of deep de-lithiation, the cathode material is more likely to undergo harmful phase transitions (such as layered → spinel phase). Therefore, by having more Ni with a larger particle radius in the transition layer region 2+ , it helps to maintain the stability of the layered structure in this region, reduce harmful phase transitions during deep de-lithiation, and at the same time, the charge of Ni 2+ is lower, and the electrostatic repulsion with Li + is weaker, thereby improving the smoothness of the lithium-ion diffusion channel.

[0034] Among them, the lithium nickel cobaltate-based composite oxide can be a lithium nickel cobalt aluminum ternary cathode material or a lithium nickel cobalt manganese ternary cathode material.

[0035] Specifically, the cathode material includes a matrix and a coating layer, and the coating layer is located on at least part of the surface of the matrix. It should be noted that the transition layer region refers to the region between the etching depths of 30 - 90 nm, that is, the region between the matrix and the coating layer. The region with a depth of 0 nm - 30 nm is defined as the coating layer region, the region with a depth of 30 nm - 90 nm is defined as the transition layer region, and the region with a depth greater than 90 nm is defined as the matrix. Among them, the matrix includes Ni, Co, and Mn elements, and the coating layer includes Zr and Al elements.

[0036] In some embodiments of the present application, the value range of a is 853.5 eV - 855.5 eV. When the etching depth is 90 nm, the binding energy a of the Ni2p3 / 2 peak of the cathode material is within the above range, which helps to maintain the stability of the layered structure in this region, reduce harmful phase transitions during deep de-lithiation, and further improve the smoothness of the lithium-ion diffusion channel.

[0037] Specifically, when the etching depth is 90 nm, the binding energy a of the Ni2p3 / 2 peak of the positive electrode material takes values such as 853.5 eV, 853.7 eV, 853.9 eV, 854 eV, 854.2 eV, 854.4 eV, 854.5 eV, 854.7 eV, 854.9 eV, 855 eV, 855.2 eV, 855.4 eV, etc., and can also be other values within the above range, which are not limited herein. Preferably, the value range of a is 853.5 eV to 854.5 eV.

[0038] In some embodiments of the present application, the value range of b is 853.5 eV to 855.5 eV. By way of example, the binding energy b of the Ni2p3 / 2 peak of the positive electrode material takes values such as 853.5 eV, 853.7 eV, 853.9 eV, 854 eV, 854.2 eV, 854.4 eV, 854.5 eV, 854.7 eV, 854.9 eV, 855 eV, 855.2 eV, 855.4 eV, etc., and can also be other values within the above range, which are not limited herein. Preferably, the value range of b is 854.0 eV to 855.0 eV. The value of b within the above range helps to maintain the stability of the layered structure in this region, reduce harmful phase changes during deep de-lithiation, and further improve the smoothness of the lithium-ion diffusion channel.

[0039] In some embodiments of the present application, the value range of c is 853.5 eV to 855.5 eV. Specifically, the value of c takes values such as 853.5 eV, 853.7 eV, 853.9 eV, 854 eV, 854.2 eV, 854.4 eV, 854.5 eV, 854.7 eV, 854.9 eV, 855 eV, 855.2 eV, 855.4 eV, etc., and can also be other values within the above range, which are not limited herein. Preferably, the value range of c is 854.5 eV to 855.5 eV.

[0040] In some embodiments of the present application, the value range of c is 854.5 eV to 855.5 eV, the value range of b is 854.0 eV to 855.0 eV, and the value range of a is 853.5 eV to 854.5 eV. The Ni2p2 / 3 peak position increases with the increase of the etching depth, and within the above range, the promoting effect on the conduction of lithium ions is particularly obvious, which is beneficial to further improving the electrochemical performance of the positive electrode material.

[0041] In some embodiments, in the transition layer region of the positive electrode material, the positive electrode material further includes zirconium. When the positive electrode material is characterized by XPS etching, when the etching depth is 30 nm, the content of zirconium atoms is y1; when the etching depth is 90 nm, the content of zirconium atoms is y3; when the etching depth is 60 nm, the content of zirconium atoms is y2, and the value of y2 satisfies y1 < y2 < y3, and the difference between y1 and y2 is greater than 0.15, and the difference between y2 and y3 is greater than 0.15.

[0042] As the etching depth of the positive electrode material of the present application increases, the content of zirconium element gradually increases. Since the zirconium element can form a zirconium-oxygen metal bond with a greater bond energy with oxygen atoms in the layered structure, the layer oxygen is effectively fixed in the layered structure, reducing the tendency of lattice distortion. Thus, it is possible to further inhibit Ni 2+ due to the similar ionic radii of + Ni and Li 2+ causing Ni

[0043] to migrate to the lithium layer, thereby further increasing the stability of the layered structure in the transition layer region, reducing the occurrence of harmful phase transitions (such as layered → spinel phase) more easily in the positive electrode material during deep de-lithiation, ensuring the structural stability of the material during the cycling process, increasing the lifespan of the battery during the cycling process, and improving the battery cycling capacity retention rate.

[0044] In some embodiments, when the etching depth is 30 nm, the value range of the content y1 of zirconium atoms is 1.9% - 2.3%. Specifically, the value of the content y1 of zirconium atoms can be 1.9%, 1.95%, 2%, 2.05%, 2.1%, 2.15%, 2.2%, 2.25%, 2.3% or any value within the range formed by any two of the above values, which is not limited herein.

[0045] In some embodiments, when the etching depth is 60 nm, the value range of the content y2 of zirconium atoms is 2.3% - 2.7%, and specifically can be 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, etc., or other values within the above range.

[0046] In some embodiments of the present application, the positive electrode material includes zirconium and aluminum elements. When the etching depth is 0 nm, the ratio of the number of zirconium atoms to the number of aluminum atoms in the positive electrode material is 0.3 to 0.5. Since there is more Ni in the region of the positive electrode material close to the surface 3+ more, Ni 3+ When in direct contact with the electrolyte, it is likely to exacerbate the oxidative decomposition of the electrolyte, generate a thick and uneven CEI layer, and increase the impedance. Thus, by controlling the ratio of the number of zirconium atoms to the number of aluminum atoms in the positive electrode material at an etching depth of 0 nm to be 0.3 to 0.5, the content of Al element on the surface of the positive electrode material is greater than that of Zr element, so that there can be a coating layer formed by more Al element on the surface of the positive electrode material. This protective layer has stable chemical properties and can form a barrier between Ni 3+ and the electrolyte, inhibiting the reaction between Ni 3+ and the electrolyte, and improving the surface stability of the positive electrode material.

[0047] Specifically, when the etching depth is 0 nm, the ratio of the number of zirconium atoms to the number of aluminum atoms in the positive electrode material can be 0.3, 0.33, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, or 0.5, etc., or other values within the above range, which are not limited herein.

[0048] In some embodiments of the present application, the mass content of aluminum element in the positive electrode material is 2000 ppm to 3500 ppm. Specifically, it can be 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3100 ppm, 3200 ppm, 3300 ppm, 3400 ppm, 3500 ppm, etc., or other values within the above range, which are not limited herein. When the mass content of aluminum element in the positive electrode material is within the above range, it can effectively improve the stability of the positive electrode material, inhibit surface side reactions, optimize lithium ion migration, improve the compaction density, better balance the cost and performance of the positive electrode material, and thus further improve the cycle performance, safety and energy density of the lithium ion battery.

[0049] In some embodiments of the present application, the cathode material includes zirconium element and aluminum element. By characterizing the cross-section of the cathode material through EDS, the distribution width of zirconium element in the cross-section EDS of the secondary particles of the cathode material is greater than 7 μm, such as 7.1 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 10 μm, etc., and the distribution width of aluminum element in the cross-section EDS of the secondary particles of the cathode material is less than 7 μm, specifically it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 6.5 μm, etc., or other values within the above range. The large distribution width of Zr element indicates that Zr element is effectively doped into the matrix material, promoting the rapid conduction of lithium ions in the layered structure, further improving the smoothness of the lithium ion diffusion channel, and can fully improve the performance of the material; the lower distribution width of Al element and its concentration on the surface layer indicate that a coating layer with inert metal aluminum oxide is constructed. During the charge-discharge cycle of the material, direct contact between the surface of the secondary particles and the electrolyte is avoided, the decomposition of the electrolyte during the cycle is inhibited, and the cyclic gas generation of the battery is reduced, thereby improving the cyclic safety of the battery. The distribution widths of zirconium element and aluminum element in the cross-section of the secondary particles within the above range are beneficial to promoting the doping and modification effect of zirconium metal element on the layered structure, thereby greatly improving the structural stability of the cathode material and further enhancing the cycle life of the material.

[0050] The mass content of zirconium element in the cathode material is 2500 ppm to 3500 ppm. Specifically, it can be 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3100 ppm, 3200 ppm, 3300 ppm, 3400 ppm, 3500 ppm, etc., or other values within the above range. When the mass content of zirconium element in the cathode material is within the above range, it can form an appropriate concentration gradient on the surface layer of the cathode material while ensuring the energy density of the cathode material, better realizing the differential function of the coating layer on the surface of the cathode material, fully exerting its gain effect, and enabling the battery to have a higher cycle capacity retention rate and cycle life after the cathode material is applied to the battery.

[0051] In some embodiments of the present application, in the volume particle size distribution of the positive electrode material, the Dmin particle size of the positive electrode material is 4.6 μm to 5.4 μm (such as 4.6 μm, 4.8 μm, 5 μm, 5.2 μm, 5.4 μm, etc.), the volume median particle size D50 is 9.3 μm to 9.5 μm (such as 9.3 μm, 9.35 μm, 9.4 μm, 9.45 μm, 9.5 μm, etc.). Among them, the D50 particle size is the particle size value corresponding to when the particle size of the positive electrode material particles is sorted from small to large and the volume distribution percentage reaches 50%. The Dmax particle size is 16.0 μm to 19.0 μm (such as 16.0 μm, 17.0 μm, 17.5 μm, 18.0 μm, 19.0 μm, etc.), and the volume particle size distribution span value is 0.4 to 0.6 (such as 0.4, 0.45, 0.5, 0.55, 0.6, etc.). The positive electrode material with the above particle size distribution can further enhance the cycle performance and structural stability of the material. The control of these parameters plays an important role in ensuring the consistency of the material and the reliability of the battery performance. Among them, Dmin represents the diameter of the smallest particle in the positive electrode material, meaning that there are no particles smaller than this size in the material; Dmax represents the largest particle diameter in the positive electrode material, and this index indicates the upper limit of the particle size in the material, that is, the size of all particles will not exceed Dmax. The span value is an index to measure the width of the particle size distribution and is used to describe the uniformity of the particle size distribution.

[0052] In some embodiments of the present application, the chemical formula of the positive electrode material is Li(Ni o Co p Mn q Al d Zr e P f )O2, where the value of o is 0.5 to 1.0 (such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, etc.), the value of p is 0 to 0.2 (such as 0, 0.05, 0.1, 0.15, 0.2, etc.), the value of q is 0 to 0.3, and q is not 0 (such as q can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, etc.), the value of d is 0.0015 - 0.0020 (such as 0.0015, 0.0018, 0.0020, etc.), the value of e is 0.0015 to 0.002 (such as 0.0015, 0.0018, 0.0020, etc.). P is a doping element, and the type of the positive electrode material can be selected according to actual needs and is not limited here. As an example, P is selected from any one or more of B, Ti, and Sr. The value of f is 0.001 to 0.005 (such as 0.001, 0.003, 0.005, etc.), or other values within the above range.

[0053] The specific surface area affects the reaction activity of the cathode material and the diffusion path of lithium ions. In some embodiments of the present application, the specific surface area of the cathode material is 0.35 m 2 / g to 0.45 m 2 / g, specifically it can be 0.35 m 2 / g, 0.37 m 2 / g, 0.39 m 2 / g, 0.41 m 2 / g, 0.43 m 2 / g, 0.45 m 2 / g, etc., or other values within the above range. For the cathode material of the present application, controlling the specific surface area within the above range is beneficial to provide sufficient active sites, promote the rapid adsorption and desorption of lithium ions, and at the same time avoid an increase in surface side reactions caused by an overly large specific surface area, such as reactions with the electrolyte, thereby ensuring the high capacity and long cycle life of the battery and improving the overall performance of the battery.

[0054] The tap density of the cathode material is closely related to the energy density of the battery. In some embodiments of the present application, the tap density of the cathode material is 2.85 g / m 3 to 3.05 g / m 3 , which is beneficial to better balance the energy density, power density and structural stability of the battery. Specifically, the tap density of the cathode material can be 2.85 g / m 3 , 2.9 g / m 3 , 2.95 g / m 3 , 3 g / m 3 , 3.05 g / m 3 , etc., or other values within the above range.

[0055] According to another typical embodiment of the present application, a method for preparing a cathode material is provided. The preparation method includes: performing a first mixing of a cathode material precursor, a lithium source and a zirconium source under stirring conditions to obtain a first mixture; performing a second mixing of the first mixture and an aluminum source under stirring conditions to obtain a second mixture; the stirring speed of the second mixing is lower than that of the first mixing; subjecting the second mixture to a first calcination and a second calcination in sequence, followed by pulverization, screening and demagnetization to obtain the cathode material; the temperature of the first calcination is 300 - 500 °C, and the temperature of the second calcination is 700 - 1000 °C.

[0056] The preparation method of the cathode material of the present application ensures the uniform mixing of the lithium source and the transition metal precursor in the first mixture, reduces the Ni oxidation caused by the rich lithium in the layout, and simultaneously reduces the lattice stress and the migration tendency of Ni²⁺ by precisely controlling the temperature gradient through staged roasting of the second mixture. At the same time, the prepared cathode material forms a matrix-transition layer region-cladding layer structure from the center to the outside. By XPS etching characterization of the prepared cathode material, when the etching depth is 90 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is a; when the etching depth is 60 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is b; when the etching depth is 30 nm, the binding energy of the Ni2p3 / 2 peak of the cathode material is c, where a, b, and c satisfy: c > b > a, and the difference between c and b is greater than 0.3 eV, and the difference between b and a is greater than 0.3 eV. This is achieved by adding a multi-stage mixing process to the preparation method of the cathode material of the present application, with the zirconium source in the additive being added before the aluminum source, and the stirring speed of the first mixture being lower than that of the second mixture.

[0057] On the other hand, the preparation method of the present application adds a first roasting with a relatively low sintering temperature. This low-temperature sintering process provides a platform for the full melting reaction of the cathode material precursor with the aluminum source and the zirconium source during roasting, promotes the mutual fusion of the additive and the high-nickel layered material, and makes the width of the distribution range of zirconium elements on the surface of the formed secondary particles greater than the width of the distribution range of aluminum elements. Specifically, the temperature of the first roasting can be 300°C, 330°C, 350°C, 380°C, 400°C, 420°C, 450°C, 480°C, 500°C, etc., or other values within the above range, which are not limited herein. Preferably, the temperature of the first roasting is 350 - 400°C.

[0058] As an example, the temperature of the second roasting can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, etc., or other values within the above range, which are not limited herein.

[0059] The above-mentioned cathode material precursor and lithium source can be selected in the prior art, and there is no special limitation in the present application, so no detailed introduction will be made here.

[0060] In some embodiments of the present application, the molar ratio of the cathode material precursor to the lithium source is 1:1.00 - 1:1.02.

[0061] In some embodiments of the present application, the zirconium source is nano-zirconia. Preferably, the addition amount of the zirconium source is 0.001 wt% - 2 wt% of the mass of the first mixture, specifically it can be 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, etc., or other values within the above range.

[0062] In some embodiments of the present application, the stirring speed of the first mixing is 300 rpm - 350 rpm, and the stirring time of the first mixing is 15 min - 30 min.

[0063] The first mixture and the aluminum source are subjected to a second mixing under stirring conditions. In some embodiments of the present application, the addition amount of the aluminum source is 0.001 wt% - 2 wt% of the mass of the second mixture, specifically it can be 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, etc., or other values within the above range.

[0064] By way of example, the aluminum source includes, but is not limited to, one or more of nano-aluminum oxide and nano-hydroxyaluminum oxide.

[0065] In some embodiments of the present application, the stirring speed of the second mixing is 150 rpm - 250 rpm, and the time is 15 min - 30 min. If the speed of the second mixing is too fast or the mixing time is too short, it is not conducive to the formation of a characteristic of different-depth component differential distribution of the coating layer on the surface of the secondary particles, which has an adverse effect on the cycling performance of the material. Preferably, the stirring speed of the second mixing is 200 - 250 rpm.

[0066] In some embodiments of the present application, the time of the first calcination is 0.5 - 2 h, specifically it can be 0.5 h, 0.8 h, 1.0 h, 1.2 h, 1.5 h, 1.8 h, 2 h, etc., or other values within the above range, which is not limited herein. Calcination within this time range at a relatively low temperature can enable the zirconium source in the additive to fully fuse with the cathode material precursor, promoting the differential distribution of zirconium elements at different radial depths of the material particles.

[0067] In some embodiments of the present application, when the stirring speed of the second mixing is 200 - 250 rpm and the time is 20 to 30 min, and the temperature of the first calcination is 350 - 400 °C and the time is 0.5 - 1.5 h, under such process conditions, the zirconium element in the prepared cathode material conforms to the differential distribution at the etching depths of 30 nm, 60 nm, and 90 nm, and the ratio of zirconium / aluminum atomic numbers on the surface of the coating layer is relatively appropriate. The change trend of the binding energy corresponding to the Ni2p3 / 2 peak conforms to c > b > a. The battery using this cathode material has better cycle stability and safety.

[0068] In some embodiments of the present application, the time of the second calcination is 4 - 9 h, specifically it can be 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, etc., or other values within the above range, which are not limited herein.

[0069] In some embodiments of the present application, the gas atmosphere for the first calcination and the second calcination is air or an oxidizing atmosphere. For example, it can be air, oxygen, or a mixture of the two.

[0070] The above-mentioned cathode material can be obtained by pulverizing, screening, and demagnetizing the calcined product. The specific methods of pulverizing, screening, and demagnetizing can refer to the prior art, and the present application has no special requirements for this.

[0071] Among them, pulverizing means breaking the larger material particles after sintering into smaller particles to achieve the required particle size distribution. Pulverizing can be achieved by mechanical force, such as using equipment like ball mills, stirred mills, air classifiers, etc. Screening is to remove oversize or undersize particles in the powder after pulverizing to make the particle size distribution reasonable. In some embodiments of the present application, the D50 particle size of the cathode material obtained after pulverizing and screening is 9.3 μm - 9.5 μm. Screening can be achieved by using sieves with different mesh numbers, such as using vibrating screens, rotary screens, etc.

[0072] Since the presence of magnetic impurities will affect the performance of the battery, demagnetizing means removing the magnetic impurities in the cathode material. As an example, equipment such as magnetic separators and high-intensity magnetic separators can be used for demagnetization treatment.

[0073] According to another typical embodiment of the present application, a cathode sheet is provided, and this cathode sheet includes the above-mentioned cathode material. The preparation of the cathode sheet makes full use of the excellent performance of the cathode material, can further improve the overall performance of the battery, is suitable for battery assembly lines and battery module manufacturing, provides high-quality cathode sheet materials for the battery industry, and helps to promote the innovation and upgrade of battery technology.

[0074] According to still another exemplary embodiment of the present application, a battery is provided, which includes the above-mentioned positive electrode sheet. Due to the use of the positive electrode sheet with the above-mentioned positive electrode material, the battery of the present application not only has a high energy density, but also has significantly improved cycling performance and service life.

[0075] An embodiment of the present invention also provides a battery, which includes a housing and an electrode assembly. As Figure 1 shown, the electrode assembly includes a positive electrode sheet 001, a negative electrode sheet 003, and a separator 002. The separator is disposed between the positive electrode sheet and the negative electrode sheet. Among them, the positive electrode sheet 001 contains the above-mentioned positive electrode material. The electrode assembly may be a stacked structure, which is formed by alternately laminating the positive electrode sheet 001, the separator 002, and the negative electrode sheet 003 in sequence. In some other embodiments, the electrode assembly may also be a wound structure, which is formed by laminating the positive electrode sheet 001, the separator 002, and the negative electrode sheet 003 in sequence and then winding them.

[0076] In some embodiments, the positive electrode sheet 001 includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector.

[0077] In some embodiments, the positive electrode current collector may be made of aluminum foil, nickel foil, etc., or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil (aluminum foil, nickel foil, etc.) and a polymer substrate. The positive electrode active layer contains the above-mentioned positive electrode active material.

[0078] In some embodiments, the negative electrode sheet 003 includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0079] In some embodiments, the negative electrode current collector may be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, etc., or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material, and 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, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more. The battery provided by the embodiment of the present application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low swelling. The battery may be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., which is not limited herein.

[0080] The beneficial effects that can be achieved by the present application will be further described below in combination with examples and comparative examples.

[0081] Example 1

[0082] 1) The ternary precursor, lithium salt, and additive zirconia are mixed at a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr) of 1.05:1:0.002, i.e., the first-stage mixing, with a mixing speed of 300 rpm / min and a mixing time of 30 min to obtain mixture B;

[0083] 2) Nano-hydroxyaluminum oxide with a molar ratio of n(Li):n(Al) = 1.05:0.005 is added to mixture B described in step 1) for the second-stage mixing, with a mixing speed of 150 rpm / min and a mixing time of 20 min to obtain mixture C;

[0084] 3) Mixture C is calcined successively on a low-temperature heat preservation platform and a high-temperature heat preservation platform. Among them, the temperature of the low-temperature heat preservation platform is 400 °C, the heat preservation time is 1 h, the high-temperature heat preservation platform is 740 °C, the heat preservation time is 8 h, and the calcination atmosphere is oxygen;

[0085] 4) The sintered product obtained in step 3) is pulverized by a coating machine at a rotation speed of 70 rpm, and the pulverized material is screened by a screening machine with a 400-mesh sieve. The screened product is demagnetized, and the demagnetization current of the demagnetizer is 30 A, and the included angle of the magnetic medium network is 45 degrees to obtain the cathode material.

[0086] After testing, the chemical formula composition of the prepared cathode material is Li 1.002 Ni 0.8292 Co 0.0502 Mn 0.1205 Zr 0.0002 Al 0.0005 O2. The cathode material is characterized by XPS etching. When the etching depth x = 0 nm, the zirconium / aluminum atomic number ratio is 0.39. As Figure 2 shown, when the etching depth x = 30 nm, the zirconium atomic ratio is 2.14%, when the etching depth x = 60 nm, the ratio is 2.42%, and when the etching depth x = 90 nm, the ratio is 2.95%. The binding energy of the Ni2p2 / 3 peak at different etching depths in this example is as Figure 3 shown.

[0087] The electrochemical performance of this cathode material is tested. The initial discharge specific capacity is 210 mAh / g, the first-cycle Coulombic efficiency is 90.47%, and the 50-cycle capacity retention rate is 94.47%.

[0088] Example 2-13 uses the same technological process as Example 1, with the difference being the mixing parameters in the second stage and the low-temperature platform parameters during kiln roasting. The relevant parameters are shown in Table 1 or 2;

[0089] Table 1

[0090]

[0091] Table 2

[0092]

[0093] Example 14

[0094] The difference from Example 1 is only that in step 1), the ternary precursor, lithium salt, and additive zirconia are mixed at a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr) of 1.05:1:0.0015.

[0095] Example 15

[0096] The difference from Example 1 is only that in step 3), the high-temperature platform temperature is set to 745 °C.

[0097] Example 16

[0098] The difference from Example 1 is only that in step 3), the high-temperature platform holding time is set to 9 h.

[0099] Comparative Example 1

[0100] 1) Mix the ternary precursor, lithium salt, additive zirconia, and nano-hydroxyaluminum at a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr):n(Al) of 1.05:1:0.003:0.005 at a mixing speed of 300 rpm / min for 30 min to obtain mixture B;

[0101] 2) Roast mixture B successively on a low-temperature holding platform and a high-temperature holding platform. Among them, the temperature of the low-temperature holding platform is 400 °C, the holding time is 1 h, the high-temperature holding platform is 740 °C, the holding time is 8 h, and the calcination atmosphere is oxygen;

[0102] 3) Use a coating machine to crush the sintered product obtained in step 2) at a rotation speed of 70 rpm. The crushed material is screened by a screening machine with a 400-mesh sieve, and the screened product is demagnetized. The demagnetization current of the demagnetizer is 30 A, and the included angle of the magnetic medium network is 45 degrees to obtain the polycrystalline cathode material.

[0103] Comparative Example 2

[0104] 1) Mix the ternary precursor, lithium salt, and additive zirconia dioxide at a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr) of 1.05:1:0.003, with a mixing speed of 300 rpm / min and a mixing time of 30 min to obtain mixture B;

[0105] 2) Add nano-hydroxyaluminum oxide with a molar ratio of n(Li):n(Al) of 1.05:0.005 to the mixture B described in step 1) for a second-stage mixing, with a mixing speed of 150 rpm / min and a mixing time of 20 min to obtain mixture C;

[0106] 3) Calcinate mixture C at a temperature of 740 °C for a holding time of 8 h, with an oxygen calcination atmosphere;

[0107] 4) Grind the sintered product obtained in step 3) using a coating machine at a rotation speed of 70 rpm, screen the ground material using a screening machine with a 400-mesh screen, and demagnetize the screened product. The demagnetization current of the demagnetizer is 30 A, and the included angle of the magnetic medium network is 45 degrees to obtain a polycrystalline cathode material.

[0108] Comparative Example 3

[0109] 1) Mix the ternary precursor, lithium salt, additive zirconia dioxide, and nano-hydroxyaluminum oxide at a molar ratio of n(Li):[n(Ni)+n(Co)+n(Mn)]:n(Zr):n(Al) of 1.05:1:0.003:0.005, with a mixing speed of 300 rpm / min and a mixing time of 30 min to obtain mixture B;

[0110] 2) Calcinate mixture B at a temperature of 740 °C for a holding time of 8 h, with an oxygen calcination atmosphere;

[0111] 3) Grind the sintered product obtained in step 2) using a coating machine at a rotation speed of 70 rpm, screen the ground material using a screening machine with a 400-mesh screen, and demagnetize the screened product. The demagnetization current of the demagnetizer is 30 A, and the included angle of the magnetic medium network is 45 degrees to obtain a polycrystalline cathode material.

[0112] Test the cathode materials prepared in the above examples and comparative examples according to the following method, and the test results are listed in Table 3.

[0113] XPS etching test:

[0114] Take a number of finished product example materials and comparative example materials. Fix the samples on a conductive sample stage (such as a copper or aluminum substrate) to ensure good contact with the instrument to reduce the charging effect. First, perform an XPS test on the unetched original surface and record the initial surface composition and valence state. Use an Ar⁺ ion beam (energy range 0.5–5 keV), calculate the etching time according to the calibration rate, start the ion gun, set the energy (1 keV) and beam current density (0.5 μA / cm²), etch the samples by 30 nm, 60 nm and 90 nm respectively. The etching rate is 0.2 nm / s, and the etching times corresponding to 30 nm / 60 nm / 90 nm are 150 s, 300 s and 450 s respectively. Turn on the rotation of the sample stage, turn off the ion beam after etching is completed, and enter the vacuum stabilization stage. After the test, obtain the XPS full spectrum and the Ni element fine spectrum, and record the atomic content percentages of Zr and Al elements at different etching depths. At the same time, analyze the Ni element fine spectrum at different etching depths, read the corresponding peak positions, that is, the corresponding binding energies. The analysis methods for the XPS full spectrum and the Ni element fine spectrum are as follows:

[0115] 1. Data import and preliminary processing: Use Advantage software to import XPS data, view basic information such as the energy range, number of channels, and signal-to-noise ratio of the spectrum, and ensure the integrity and correctness of the data. Remove the background signal and use the Shirley correction method to improve the signal-to-noise ratio.

[0116] 2. Peak fitting and peak deconvolution analysis: Select the Gaussian fitting model, manually or automatically set the initial peak position, full width at half maximum and peak area, and correct it with reference to the standard peak position (C 1s is calibrated to 284.8 eV). Adjust the parameters through the built-in optimization algorithm of the software to make the fitting curve highly coincide with the experimental data, and check the residuals to evaluate the fitting quality.

[0117] 3. Chemical state analysis and element quantification: Compare with the standard binding energy database to determine the different chemical states of the Ni element. Based on the peak area and relative sensitivity factor, calculate the atomic percentage of the Ni element, and draw a proportion diagram of each chemical state through the peak deconvolution results.

[0118] 4. Data visualization and report generation: Overlay the original data and the fitting curve, adjust the coordinate axes, colors and annotations to highlight the key peak positions and chemical state information.

[0119] SEM / EDS testing:

[0120] Take a number of finished product example materials and comparative example materials, adhere them to conductive glue, use ion beam etching to obtain ternary polycrystalline materials with a cut surface, send them into the vacuum chamber of an SEM scanning electron microscope, and characterize the cut surface morphology through SEM. After completion, switch to the EDS scanning mode, perform an EDS scan on the cut surface to obtain the corresponding EDS distribution maps of the Zr and Al element cut surfaces. With the intersection of the major and minor axes of the particle cut surface as the center, on the major axis, in the direction from the outer intersection point to the center, the width with an EDS distribution density of the corresponding element greater than 40 is the distribution width d of the corresponding element, thereby obtaining the zirconium element distribution width d1 μm and the aluminum element distribution width d2 μm.

[0121] Particle size test method for the positive electrode material:

[0122] Test the particle size distribution range of the material through a Malvern laser particle size analyzer, and obtain the volume median particle size D50, Dmin particle size, and Dmax particle size.

[0123] Specific surface area test method for the positive electrode material:

[0124] Use the gas adsorption method to test the specific surface area. Utilize the adsorption characteristics of gas on the solid surface - the surface of the adsorbent (particles) has reversible physical adsorption for the adsorbate (gas molecules), and the corresponding equilibrium adsorption amount under a certain pressure. Calculate the specific surface area from the adsorption amount through a theoretical model.

[0125] Compacted density test method for the positive electrode material: Use a 4350 model compacted density tester from Micronor in the United States to test the compaction performance of the positive electrode material. Take 1 g of the positive electrode material, after treatment, compact it under a pressure of 3 t for 30 s to obtain the compaction data of the material.

[0126] Test method for the mass content of Zr element and Al element

[0127] Test the content of various metal elements in the positive electrode material through ICP. Use an Agilent 5800 type ICP spectrometer to analyze the element content in the material. The specific operation steps are as follows: Take 0.4 g of the ternary positive electrode material and add it to a conical flask, then add 60 mL of pure water and 8 mL of aqua regia, place it on a graphite heating platform, and digest it at 375 °C until it is clear. Dilute the obtained solution to 100 mL with a volumetric flask and take a sample for dilution, and then analyze the components of the diluted solution.

[0128] Table 3

[0129]

[0130] Table 4

[0131]

[0132] The cathode materials prepared in the above examples and comparative examples were tested for their electrochemical performance according to the following method, and the results are listed in Table 5.

[0133] Take 0.8 g of the cathode material, 0.1 g of conductive carbon black, and 0.1 g of polyvinylidene fluoride and put them into a ball mill jar. Add 15 mL of N-methylpyrrolidone and ball mill to form a uniform slurry. Then, uniformly coat it on an aluminum foil and vacuum dry it at 110 °C for 12 h to obtain a cathode electrode sheet. Cut the dried electrode sheet into circular pieces with a diameter of 15 mm. Assemble and seal it in a glove box in the order of the cathode shell, electrode sheet, electrolyte (EC / DMC / EMC volume ratio 1:1:1, LiPF6 concentration is 1 mol / L), separator (Celgard PP / PE / PP three-layer composite membrane), lithium sheet, electrolyte, nickel foam, and anode shell to obtain a button cell, and let it stand for 24 h. Then, put the obtained cell into a constant temperature oven for testing.

[0134] Use the LAND battery test system to conduct a coin cell charge-discharge test at 25 °C and 3.0 V - 4.3 V:

[0135] Charge at 0.1C and discharge at 0.1C for 2 weeks, with a constant voltage cut-off current of 0.005C, and measure the first-cycle discharge specific capacity and the first-cycle Coulombic efficiency.

[0136] Charge at 0.5C and discharge at 1C for 50 cycles, with a constant voltage cut-off current of 0.05C. The ratio of the measured capacity to the first-cycle capacity measured at 0.1C is the 50-cycle capacity retention rate.

[0137] Table 5

[0138]

[0139] It can be seen from the data in Tables 1 - 5 that for the cathode materials obtained in Examples 1 - 15, when these cathode materials were characterized by XPS etching, their secondary particle surfaces had the characteristics of a coating surface and a differential distribution of zirconium components at different depths, indicating that having more Ni with a larger particle radius in the transition layer region 2+ helps to maintain the stability of the layered structure in this region, reduce harmful phase transitions during deep de-lithiation, and at the same time, Ni 2+ has a lower charge, and the electrostatic repulsion with Li + is weaker, thus improving the smoothness of the lithium-ion diffusion channels. Compared with the comparative examples, the electrochemical performance such as the cycle life and capacity retention rate of the corresponding batteries has been significantly improved.

[0140] The binding energy differences of the Ni2p3 / 2 peaks of the cathode materials prepared in Comparative Examples 1-3 at different etching depths of 90 nm, 60 nm, and 30 nm are too small to meet the requirements that the difference between c and b is greater than 0.3 eV and the difference between b and a is greater than 0.3 eV. The content of Ni with a relatively large radius in the transition layer region of the cathode material particles is insufficient, making it difficult to maintain the stability of the layered structure in this region. During the deep de-lithiation process, the cathode material is more likely to undergo harmful phase changes, resulting in insufficient energy density when used in batteries and a low cycle retention rate. Moreover, the ratio of zirconium / aluminum atomic numbers on the material surface is small, the content of surface alumina is low, the proportion of zirconium atoms inside the coating layer increases slowly, and the penetration and doping effect of zirconium elements on the layered structure are weak. This leads to poor cycle performance of the cathode material prepared in the comparative example when applied to the battery, and the corresponding electrochemical performance indicators are inferior to those of the examples. 2+ The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0141] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cathode material, characterized in that, The positive electrode material is a nickel cobalt lithium oxide-based composite oxide; The positive electrode material is characterized by XPS etching. When the etching depth is 90 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is a. When the etching depth is 60 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is b. When the etching depth is 30 nm, the binding energy of the Ni2p3 / 2 peak of the positive electrode material is c. Among them, a, b, and c satisfy: c > b > a, and the difference between c and b is greater than 0.3 eV, and the difference between b and a is greater than 0.3 eV.

2. The cathode material according to claim 1, characterized in that, The positive electrode material satisfies at least one of the following technical characteristics: (1) The value range of a is 853.5 eV to 855.5 eV; (2) The value range of b is 853.5 eV to 855.5 eV; (3) The value range of c is 853.5 eV to 855.5 eV.

3. The cathode material according to claim 2, characterized in that, The value range of c is 854.5 eV to 855.5 eV; the value range of b is 854.0 eV to 855.0 eV; the value range of a is 853.5 eV to 854.5 eV.

4. The cathode material according to claim 1, characterized in that, The positive electrode material includes zirconium element, When the etching depth is 30 nm, the zirconium atomic number content is y1; when the etching depth is 90 nm, the zirconium atomic number content is y3; When the etching depth is 60 nm, the zirconium atomic number content is y2. The value of y2 satisfies y1 < y2 < y3, and the difference between y1 and y2 is greater than 0.15, and the difference between y2 and y3 is greater than 0.

15.

5. The cathode material according to claim 1, wherein The positive electrode material includes zirconium element and aluminum element. When the etching depth is 0 nm, the ratio of the zirconium atomic number to the aluminum atomic number of the positive electrode material is 0.3 to 0.

5.

6. The cathode material according to claim 1, characterized in that, The positive electrode material includes zirconium element and aluminum element. The cross-section of the positive electrode material is characterized by EDS. The distribution width of zirconium element in the cross-section EDS of the secondary particles of the positive electrode material is greater than 7 μm, and the distribution width of aluminum element is less than 7 μm.

7. The cathode material according to claim 1, wherein The positive electrode material satisfies at least one of the following technical characteristics: (1) The mass content of zirconium element in the positive electrode material is 2500 ppm to 3500 ppm; (2) The positive electrode material further includes aluminum element, and the mass content of the aluminum element is 2000 ppm to 3500 ppm; (3) In the volume particle size distribution of the positive electrode material, the Dmin particle size is 4.6 μm to 5.4 μm, the D50 particle size is 9.3 μm to 9.5 μm, the Dmax particle size is 16.0 μm to 19.0 μm, and the span value is 0.4 to 0.

6.

8. The cathode material according to claim 1, characterized in that, The positive electrode material satisfies at least one of the following technical characteristics: (1) The chemical formula of the positive electrode material is Li(Ni o Co p Mn q Al d Zr e P f )O2, where the value of o is 0.5 - 1.0, the value of p is 0 - 0.2, the value of q is 0 - 0.3, and q is not 0, the value of d is 0.0015 - 0.002, the value of e is 0.0015 - 0.002, P is selected from any one or more of B, Ti, and Sr, and the value of f is 0.001 - 0.005; (2) The specific surface area of the positive electrode material is 0.35 m 2 / g to 0.45 m 2 / g; (3)The tap density of the positive electrode material is 2.85 g / m 3 ~3.05 g / m 3 .

9. A positive electrode sheet, characterized in that, Includes the positive electrode material according to any one of claims 1 to 8.

10. A battery, characterized in that, Includes the positive electrode sheet according to claim 9.

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