Positive electrode material and preparation method therefor, and lithium-ion battery

Abstract

The present invention provides a positive electrode material and a preparation method therefor, and a lithium-ion battery. The chemical general formula of the positive electrode material provided in the present application is LixNiaCobMncNdO2, where 0.98 ≤ x ≤ 1.1, 0.50 ≤ a ≤ 0.98, 0 < b ≤ 0.20, 0 < c ≤ 0.30, 0 ≤ d ≤ 0.10, and a + b + c + d = 1. The content of free SO4 2- of the positive electrode material is less than or equal to 800 ppm, and the surface enrichment degree of SO4 2- is less than or equal to 70%. The positive electrode material provided in the present application has a free SO4 2- content of ≤ 800 ppm and a SO4 2- surface enrichment degree of ≤ 70%. A portion of the SO4 2- is doped into the internal crystal lattice, and SO4 2- in the bulk phase inhibits c-axis contraction, reduces the activation energy for Li migration, thereby improving the cycling performance and rate performance of the positive electrode material.

Description

Cathode materials and preparation methods and lithium-ion batteries

[0001] This application claims priority to Chinese Patent Application No. 202411935345.6, filed on December 26, 2024, entitled "Cathode Material and Preparation Method and Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of cathode material technology, and more specifically, to a cathode material cathode, a preparation method thereof, and a lithium-ion battery. Background Technology

[0003] Cathode materials possess high energy density and are among the mainstream cathode materials for power lithium batteries, widely used in mid-to-high-end new energy vehicles. Cathode materials are typically prepared by high-temperature sintering of precursor compounds containing Ni, Co, and Mn with lithium salts. However, existing cathode materials exhibit poor rate performance and cycle stability.

[0004] In view of the above, this application is hereby submitted.

[0005] Application content

[0006] The main objective of this application is to provide a cathode material precursor, cathode material, preparation method, and lithium-ion battery to solve the problems of poor rate performance and cycle stability of cathode materials in the prior art.

[0007] To achieve the above objectives, according to the first aspect of this application, a cathode material is provided, the general chemical formula of which is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y, and free SO4 in the cathode material. 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

[0008] According to a second aspect of this application, a method for preparing a cathode material is provided, the cathode material having the general chemical formula Li. x Ni a Co b M c Nd O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; free SO4 in the cathode material 2- The content of [unspecified substance] is ≤800ppm, and the volume percentage of particles smaller than 1μm in the cathode material is ≤4% under 6T pressure.

[0009] According to a third aspect of this application, a positive electrode sheet is also provided, which includes the positive electrode material provided in the first or second aspect described above.

[0010] According to a fourth aspect of this application, a lithium-ion battery is also provided, which includes the positive electrode material provided in the first or second aspect described above.

[0011] Applying the technical solution of this application, the cathode material provided by this application contains free SO4 2- The content is ≤800ppm, and SO4 2- Surface enrichment ≤70%; some SO4 2- SO42- doped into the internal crystal lattice, in the bulk phase 2- It can suppress c-axis contraction, reduce the activation energy of Li migration, thereby increasing the migration rate of Li, suppress heterogeneous reactions, reduce lattice rotation, and thus improve the cycle performance and rate performance of cathode materials.

[0012] Applying the technical solution of this application, the free SO4 in the cathode material provided by this application 2- The content of SO42- is ≤800ppm. Under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is ≤4%. Since micro-particles smaller than 1μm in the cathode material easily adhere to the surface of larger particles, they strongly adsorb free sulfate ions in the electrolyte environment, causing a large accumulation of sulfate ions on the micro-particle surface, which in turn drastically increases the side reactions caused by free sulfate ions. The fact that the volume percentage of particles smaller than 1μm in the cathode material is ≤4% under 6T pressure indicates that the proportion of micro-particles smaller than 1μm in the cathode material is low, which can suppress free SO42-. 2- The synergistic deterioration reaction with the micronized particles further enhances the cycle stability of the cathode material. Attached Figure Description

[0013] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0014] Figure 1 shows the Williamson-Hall analysis fitting curve of the cathode material according to Embodiment 1 of this application;

[0015] Figure 2 shows a SEM image of the cathode material according to Embodiment 1 of this application. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0017] As described in the background section of this application, existing cathode materials exhibit poor rate performance and cycle stability. To address this issue, this application provides a cathode material, a preparation method thereof, and a lithium-ion battery.

[0018] In a first typical embodiment of this application, a positive electrode material is provided, the chemical formula of which is Li x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

[0019] In this application, SO4 2- Surface enrichment refers to free SO4 2- Content and SO4 in cathode materials 2- The ratio of total content.

[0020] Free SO4 in cathode materials 2- It has a significant impact on the electrochemical performance of materials, when free SO4 2- High SO4 content can lead to a deterioration in material capacity and rate capability. The cathode material provided in this application contains free SO4. 2- The content is ≤800ppm, and SO4 2- A surface enrichment of ≤70% indicates that some SO4 is present. 2- SO42- doped into the internal crystal lattice, in the bulk phase 2-It can suppress c-axis contraction, reduce the activation energy of Li migration, thereby increasing the migration rate of Li, suppress heterogeneous reactions, reduce lattice rotation, and thus improve the cycle performance and rate performance of cathode materials.

[0021] Typically, but not limitingly, in the cathode material provided in this application, the value of x can be 0.98, 0.99, 1.0, 1.01, 1.03, 1.05, 1.08, 1.09, 1.1, or any range of two values; the value of a can specifically be 0.50, 0.55, 0.60, 0.63, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.95, 0.98, or any range of two values; the value of b can be 0.01, 0.05, ... The values ​​of c can be 0.08, 0.10, 0.11, 0.13, 0.15, 0.18, 0.20, or any two of these values; the values ​​of c can be 0.01, 0.05, 0.10, 0.15, 0.18, 0.20, 0.23, 0.27, 0.30, or any two of these values; the values ​​of d can be 0, 0.01, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any two of these values; the free SO4 in the positive electrode material. 2- The content is such as 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm, or any range of two values; SO4 2- The surface enrichment can be 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or any range of two values.

[0022] In some embodiments, under a pressure of 6T, the volume percentage of particles smaller than 1μm in the cathode material is ≤4%, and the cathode material contains an appropriate amount of microparticles that can fill the gaps between the particles, thereby improving cycle stability. If the volume percentage of particles smaller than 1μm in the cathode material is too high, the microparticle content in the cathode material is excessive, the specific surface area of ​​the microparticles is too large, and the solution and electrolyte will react, thus affecting cycle stability. Specifically, under a pressure of 6T, the volume percentage of particles smaller than 1μm in the cathode material is, for example, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any combination of two values. On the other hand, since microparticles smaller than 1 μm in the cathode material easily adhere to the surface of large particles, when the volume percentage of particles smaller than 1 μm is greater than 4%, in the electrolyte environment, excessive microparticles easily adsorb free sulfate ions, causing a large accumulation of sulfate ions on the surface of microparticles, which in turn drastically increases the side reactions caused by free sulfate ions. By controlling the volume percentage of particles smaller than 1 μm in the cathode material to be ≤4% under 6T pressure, it is shown that a low proportion of microparticles smaller than 1 μm in the cathode material can suppress free SO42-. 2- The synergistic deterioration reaction with microparticles further enhances the cycle stability of the cathode material.

[0023] In some embodiments, the lattice strain of the cathode material is ≤0.2% to improve the structural stability of the cathode material, reduce the probability of particle cracking during cycling, and thus improve its cycling stability. Specifically, the lattice strain of the cathode material can be 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.18%, 0.19%, 0.2%, or any range of two values.

[0024] In some embodiments, the cathode material further includes a coating layer comprising at least one element selected from Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn. The coating layer helps reduce direct contact between the cathode material and the electrolyte, reduces side reactions between them, and improves cycle performance, rate performance, and DCR (DC internal resistance). Specifically, the cathode material includes a substrate material and a coating layer, with the coating layer covering at least a portion of the surface of the substrate material. Characterization of the cathode material using transmission scanning electron microscopy (TEM) reveals a clear boundary between the coating layer and the substrate material. The region closer to the particle center is the substrate material, while the region closer to the particle surface is the coating layer. Under TEM view, energy-dispersive X-ray spectroscopy (EDS) characterizes the coating layer, allowing for the identification of the elements present within it.

[0025] In some embodiments, the particle size D50 of the cathode material is 2.5 μm-5 μm to improve the compaction density for forming the cathode, thereby enhancing its electrochemical performance. Specifically, the volume distribution D50 of the cathode material precursor can be 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any range of two values.

[0026] In some embodiments, the particle size Dmin of the cathode material is greater than 0.3 μm. Smaller particle size is more conducive to improving the particle strength of the cathode material; however, excessively small particle size is detrimental to improving its electrochemical performance. Specifically, the volume distribution Dmin of the cathode material can be 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.6 μm, or any range of two such values. Microparticles smaller than 1 μm contain both large-volume particles (particle size greater than 0.3 μm) and small-volume particles (particle size less than 0.3 μm), i.e., ultrafine microparticles. The cathode material has a particle size Dmin > 0.3 μm, indicating the presence of a certain amount of microparticles smaller than 1 μm, with the smallest particle size greater than 0.3 μm. Thus, in this application, large-volume microparticles constitute a higher proportion of particles smaller than 1 μm, filling the gaps between larger particles and improving the energy density of the cathode material. However, because ultrafine microparticles in the cathode material more readily adsorb free sulfate ions in the electrolyte environment, leading to a large accumulation of sulfate ions on the surface of the ultrafine powder, and further exacerbating side reactions caused by free sulfate ions, controlling the particle size Dmin of the cathode material to be greater than 0.3 μm indicates a low proportion of ultrafine microparticles among particles smaller than 1 μm in the cathode material, thereby further suppressing free SO42-. 2- The synergistic deterioration reaction with ultrafine powder particles further enhances the cycle stability performance of the cathode material.

[0027] In some embodiments, the particle size Dmax of the cathode material is <14 μm. Excessively large particle size of the cathode material is detrimental to increasing its compaction density, and consequently, to improving its electrochemical performance. Specifically, the volume distribution Dmax of the cathode material precursor can be 13.9 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm, or any range of two such values.

[0028] In some embodiments, the specific surface area of ​​the cathode material is 0.5-1.2 m². 2 / g. If the specific surface area of ​​the cathode material is too large, its electrochemical performance will be poor; if the specific surface area is too small, it will be detrimental to improving its compaction density. Therefore, selecting a cathode material with an appropriate specific surface area is more conducive to improving the electrochemical performance of the cathode material. Specifically, the specific surface area of ​​the cathode material can be 0.5m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g or a range of values ​​consisting of any two numbers.

[0029] In some embodiments, the pH of the positive electrode material satisfies 11.0 ≤ pH ≤ 12.0. If the pH of the positive electrode material is too low, it is not conducive to stable dispersion in the slurry; if the pH of the positive electrode material is too high, the alkalinity is too great, which is not conducive to improving the stability of the positive electrode sheet. Specifically, the pH of the positive electrode material can be 11.0, 11.2, 11.5, 11.8, 12.0, or any range of two values.

[0030] In some embodiments, the cathode material is a single-crystal material comprising grains with the same orientation and a grain size of 1 μm-5 μm. This is beneficial for improving the stability of the cathode material during cycling, reducing the probability of cracking, and thus improving its cycling stability. Specifically, the grain size can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, or any range of two values.

[0031] It is important to clarify that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that polycrystalline secondary particles are secondary particles formed by the agglomeration of nanoscale primary particles. Single-crystal cathode materials, on the other hand, are typically micrometer-sized single primary particles. Generally, the determination of whether the obtained cathode product is a single-crystal material can be made using testing methods such as SEM and EBSD. For example, for single-crystal cathode materials, the morphology of single-crystal particles can be characterized by SEM; under SEM, single-crystal particles generally appear as regular or irregular spheres without significant particle agglomeration. The orientation of single-crystal cathode materials can also be characterized by EBSD; EBSD shows that most grains of single-crystal cathode materials have the same color, indicating that most grains are single primary particles with the same orientation. It is important to note that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations imposed by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in a laboratory. Therefore, the single-crystal cathode materials known in the art are actually more "single-crystal-like" cathode materials, which only differ from polycrystalline materials composed of many small primary particles in size, exhibiting a large particle size similar to single crystals.

[0032] In a second typical embodiment of this application, a positive electrode material is provided, the general chemical formula of which is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; free SO4 in the cathode material 2- The content of [unspecified substance] is ≤800ppm, and the volume percentage of particles smaller than 1μm in the cathode material is ≤4% under 6T pressure.

[0033] Because microparticles smaller than 1 μm in the cathode material easily adhere to the surface of larger particles, they readily adsorb free sulfate ions in the electrolyte environment, leading to a large accumulation of sulfate ions on the surface of the microparticles. This, in turn, drastically increases the side reactions caused by free sulfate ions. By controlling the volume percentage of particles smaller than 1 μm in the cathode material to ≤4% under a 6T pressure, it is shown that the proportion of microparticles smaller than 1 μm in the cathode material is low, thus suppressing free SO42-. 2- The synergistic deterioration reaction with microparticles further enhances the cycle stability of the cathode material.

[0034] Typically, but not limitingly, in the cathode material provided in this application, the value of x can be 0.98, 0.99, 1.0, 1.01, 1.03, 1.05, 1.08, 1.09, 1.1, or any range of two values; the value of a can specifically be 0.50, 0.55, 0.60, 0.63, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.95, 0.98, or any range of two values; the value of b can be 0.01, 0.05, 0... The values ​​of 0.08, 0.10, 0.11, 0.13, 0.15, 0.18, 0.20, or any two of these values; the value of c can be 0.01, 0.05, 0.10, 0.15, 0.18, 0.20, 0.23, 0.27, 0.30, or any two of these values; the value of d can be 0, 0.01, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any two of these values; free SO4 in the cathode material. 2-The content is within a range of 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm, or any two of these values. Preferably, the free SO4 in the cathode material... 2- The content is 100ppm to 300ppm. Preferably, the free SO4 in the cathode material... 2- The content is 500ppm to 800ppm. Under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is 0%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any combination of two values. Preferably, under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is 0.1% to 3%; more preferably, under 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is 0.5% to 3.5%.

[0035] In some embodiments, the particle size Dmin of the cathode material is greater than 0.3 μm. Microparticles smaller than 1 μm contain both large-volume microparticles (particle size greater than 0.3 μm) and small-volume microparticles (particle size less than 0.3 μm), i.e., ultrafine microparticles. Smaller particle size of the cathode material is more conducive to improving its particle strength; however, excessively small particle size is detrimental to improving its electrochemical performance. Specifically, the volume distribution Dmin of the cathode material precursor can be 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.6 μm, or any combination of two values ​​within a range. The cathode material contains a certain amount of microparticles smaller than 1 μm, with the smallest particle size greater than 0.3 μm. Thus, in this application, the proportion of larger microparticles smaller than 1 μm is relatively high, which can fill the gaps between larger particles, improving the energy density of the cathode material. However, because smaller microparticles (particles smaller than 0.3 μm), i.e., ultrafine powder particles, are more likely to strongly adsorb free sulfate ions in the electrolyte environment, causing a large accumulation of sulfate ions on the surface of the ultrafine powder, further exacerbating the side reactions caused by free sulfate ions, by further controlling the particle size Dmin of the cathode material to be greater than 0.3 μm, it indicates that the proportion of ultrafine powder particles among the particles smaller than 1 μm in the cathode material is low, thereby further suppressing free SO42-. 2- The synergistic deterioration reaction with ultrafine powder particles further enhances the cycle stability performance of the cathode material.

[0036] In some embodiments, the SO4 in the positive electrode material 2- The surface enrichment of SO4 is ≤70%. In this application, SO4 2- Surface enrichment refers to free SO42- Content and SO4 in cathode materials 2- The ratio of total content. Free SO4 in the cathode material. 2- It has a significant impact on the electrochemical performance of materials, when free SO4 2- High SO4 content can lead to a deterioration in material capacity and rate capability. The cathode material provided in this application contains free SO4. 2- The content is ≤800ppm, and SO4 2- A surface enrichment of ≤70% indicates that some SO4 is present. 2- SO42- doped into the internal crystal lattice, in the bulk phase 2- It can suppress c-axis contraction, lower the activation energy of Li migration, thereby increasing the Li migration rate, and suppress heterogeneous reactions, reducing lattice rotation, thus improving the cycle performance and rate performance of the cathode material. SO4 2- The surface enrichment is within a range of 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or any two of these values. Preferably, SO4 2- The surface enrichment of SO4 is 20%–70%. Preferably, SO4... 2- The surface enrichment is 30%–60%.

[0037] In some embodiments, the lattice strain of the cathode material is ≤0.2%, indicating that the lattice strain of the cathode material is small, which is beneficial to improving the structural stability of the cathode material, reducing the probability of particle cracking during cycling, and thus improving its cycling stability. Specifically, the lattice strain of the cathode material can be 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.18%, 0.19%, 0.2%, or any range of two values.

[0038] In some embodiments, the specific surface area of ​​the cathode material is 0.5-1.2 m². 2 / g. If the specific surface area of ​​the cathode material is too large, its electrochemical performance will be poor; if the specific surface area is too small, it will be detrimental to improving its compaction density. Therefore, selecting a cathode material with an appropriate specific surface area is more conducive to improving the electrochemical performance of the cathode material. Specifically, the specific surface area of ​​the cathode material can be 0.5m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g or a range of values ​​consisting of any two numbers.

[0039] In some embodiments, the median volumetric particle size D50 of the cathode material is 2.5 μm-5 μm. This is beneficial for increasing the compaction density of the cathode and thus improving its electrochemical performance. Specifically, the volumetric distribution D50 of the cathode material precursor can be 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any range of two values.

[0040] In some embodiments, the particle size Dmax of the cathode material is <14 μm. Excessively large particle size of the cathode material is detrimental to increasing its compaction density, and consequently, to improving its electrochemical performance. Specifically, the volume distribution Dmax of the cathode material precursor can be 13.9 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm, or any combination of two values ​​within a range.

[0041] In some embodiments, the pH of the positive electrode material satisfies 11.0 ≤ pH ≤ 12.0. If the pH of the positive electrode material is too low, it is not conducive to stable dispersion in the slurry; if the pH of the positive electrode material is too high, the alkalinity is too great, which is not conducive to improving the stability of the positive electrode sheet. Specifically, the pH of the positive electrode material can be 11.0, 11.2, 11.5, 11.8, 12.0, or any range of two values.

[0042] In some embodiments, the cathode material is a single-crystal material comprising grains with the same orientation and a grain size of 1 μm-5 μm. This is beneficial for improving the stability of the cathode material during cycling, reducing the probability of cracking, and thus improving its cycling stability. Specifically, the grain size can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, or any range of two values.

[0043] It is important to clarify that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that polycrystalline secondary particles are secondary particles formed by the agglomeration of nanoscale primary particles. Single-crystal cathode materials, on the other hand, are typically micrometer-sized single primary particles. Generally, the determination of whether the obtained cathode product is a single-crystal material can be made using testing methods such as SEM and EBSD. For example, for single-crystal cathode materials, the morphology of single-crystal particles can be characterized by SEM; under SEM, single-crystal particles generally appear as regular or irregular spheres without significant particle agglomeration. The orientation of single-crystal cathode materials can also be characterized by EBSD; EBSD shows that most grains of single-crystal cathode materials have the same color, indicating that most grains are single primary particles with the same orientation. It is important to note that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations imposed by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in a laboratory. Therefore, the single-crystal cathode materials known in the art are actually more "single-crystal-like" cathode materials, which only differ from polycrystalline materials composed of many small primary particles in size, exhibiting a large particle size similar to single crystals.

[0044] In a third typical embodiment of this application, a method for preparing a cathode material is also provided. This method includes: step S1, adding an appropriate amount of H2SO4 to a mixed solution containing Ni salt, Co salt, Mn salt, and N salt to obtain a mixed solution; step S2, atomizing and pyrolyzing the mixed solution to obtain a pyrolytic cathode material precursor; and step S3, mixing the cathode material precursor with a lithium source and sintering to obtain the cathode material. The general formula of the cathode material precursor is Ni... a Co b Mn c N d O e Wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, N is a doping element, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the general chemical formula of the cathode material is Li x Ni a Co b M c N dO2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is ≤800ppm, and SO4 2- The surface richness is ≤70% and / or the volume percentage of particles smaller than 1μm in the cathode material is ≤4% under 6T pressure.

[0045] Therefore, this application adds a certain amount of H2SO4 during the preparation of the cathode material precursor to mix the solution, so that some of the SO4 is released during the atomization and pyrolysis process. 2- It can be doped into the bulk phase, thereby enabling the preparation of free SO4. 2- The content is ≤800ppm, and SO4 2- A cathode material with a surface enrichment of ≤70% can improve the cycle performance and rate performance of the cathode material.

[0046] In some embodiments, the molar ratio of Ni, Co, M, and N in the metal salt mixed solution is (50-98):(0-20):(0-35):(0-0.10), and neither Co nor M is 0. Specifically, the molar ratio of Ni, Co, and M in the metal salt mixed solution can be 50:0.1:0.1, 60:10:30, 65:15:20, 65:5:30, 70:5:25, 70:10:20, 80:5:15, 85:10:5, 98:1:1, or any range of two values. The molar ratios of Ni, Co, M, and N can be 50:0.1:0.1:0.01, 60:10:30:0.02, 65:15:20:0.05, 65:5:30:0.08, 70:5:25:0.1, 70:10:20:0.1, 80:5:15:0.01, 85:10:5:0.1, 98:1:1:0.05, or any range of two values.

[0047] In some embodiments, the concentration of total metals in the metal salt mixed solution is 100 g / L to 500 g / L, wherein the total metals include Ni, Co, M, and N. Specifically, the concentration of total metals in the metal salt mixed solution can be 200 g / L, 220 g / L, 260 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L, 480 g / L, 500 g / L, or any range of two such values.

[0048] In some embodiments, in a metal salt mixed solution, based on the total mass of Ni, Co, Mn, and N elements, SO4 2- The content is ≤2400ppm. Specifically, in a mixed solution of metal salts, SO42- 2- The content can be 2400ppm, 2300ppm, 2200ppm, 2100ppm, 2000ppm, 1800ppm, 1500ppm, 1300ppm, 1100ppm, 800ppm or any range of two values.

[0049] In step S2, the mixed solution is atomized through a plasma rotating electrode to form microparticles of 2–200 μm in size, which are then pyrolyzed in a calcination furnace to obtain the precursor. By controlling the size of the atomized droplets, precursor particles of suitable size are formed after atomization, which is beneficial for SO42-. 2- Doping is introduced into the crystal lattice; at the same time, controlling the size of the atomized droplets is beneficial for controlling the content of microparticles smaller than 1 μm in the precursor particles.

[0050] In some embodiments, the pressure of the atomization process is 0.4 MPa to 0.8 MPa. Specifically, the pressure of the atomization process can be 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.75 MPa, 0.8 MPa, or any range of two values.

[0051] In step S2, the atomized droplets pass sequentially through two temperature zones of the calcining furnace. The first temperature zone has a temperature of 1000-1200℃, and the material stays in this zone for 2-10 seconds to prevent the precursor particles from growing too large and affecting the reactivity of the precursor. The brief high temperature also promotes the doping of sulfur. The second temperature zone has a pyrolysis temperature of 500-800℃, which promotes the further decomposition of the metal salt to form an oxide precursor.

[0052] The size of the precursor particles is related to the pyrolysis temperature of the first temperature zone; the higher the temperature, the larger the precursor particles. In some embodiments, in step S2, the temperature of the first temperature zone is controlled at 1000-1200℃, and the residence time is 2-10s to facilitate the pyrolysis of precursor particles with suitable particle size, and also to promote the decomposition of SO4. 2- Doping is incorporated into the crystal lattice. Specifically, the pyrolysis temperature of the first temperature zone can be controlled to be 1000℃, 1020℃, 1050℃, 1080℃, 1200℃, or any range of two values.

[0053] When the temperature in the first temperature zone is too high, the precursor particles formed are too large, resulting in low particle strength and large lattice strain in the prepared cathode material. When the temperature is too low, SO4... 2-It is difficult to dop into the interior of the crystal lattice, and the particle growth is insufficient, resulting in a large number of particles smaller than 1 μm.

[0054] SO4 2- Due to their large ionic radii, it is very difficult to dope them into the crystal lattice of the precursor or cathode material during actual synthesis. In this application, the applicant discovered through extensive experiments that by controlling the O2 content in the calcination furnace to ≤12%, the SO4 content of the precursor can be reduced. 2- The surface enrichment was significantly reduced; the likely reason is that when the O2 volume content is ≤12%, a reducing atmosphere is easily formed in the roasting furnace. In a reducing atmosphere, some SO4... 2- The medium energy can be reduced to S 2- Low-valence ions are more likely to enter the crystal lattice inside the cathode material precursor. Specifically, in the pyrolysis atmosphere, the volume content of O2 can be 0%, 1%, 2%, 5%, 8%, 9%, 10%, 11%, 12%, or any combination of two values.

[0055] In some embodiments, step S2 further includes pulverizing the solid obtained from pyrolysis using airflow to obtain a cathode material precursor. The airflow pulverization pressure is 0.3–0.5 MPa, the grading frequency is 20–160 Hz, and the particle size D50 of the precursor is controlled to be 2.0–5.0 μm.

[0056] In some embodiments, the specific type of lithium source is not limited, and any commonly used lithium-containing compound in the art can be used, including but not limited to at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0057] In some embodiments, the molar ratio of lithium in the lithium source to the total metal in the cathode material precursor is 0.98-1.10; wherein the molar ratio of the total metal in the cathode material precursor is the sum of the molar ratios of Ni, Co, Mn, and N in the cathode material precursor. Specifically, the molar ratio of lithium in the lithium source to the total metal in the cathode material precursor is a range of 0.98, 0.99, 1.01, 1.03, 1.05, 1.06, 1.08, 1.09, 1.10, or any two of these values.

[0058] In some embodiments, in step S3, the sintering atmosphere is an oxygen-containing atmosphere with an O2 volume content ≥95%, which facilitates the provision of an oxidizing atmosphere for oxidative sintering of the cathode material precursor and the lithium source, thereby preparing a cathode material with a more stable layered structure. Specifically, in the sintering atmosphere, the O2 volume content can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 99%, 100%, or any range of two values.

[0059] In some embodiments, in step S3, the sintering temperature is 750-980℃, and the sintering time is 10h-30h, which helps to reduce crystal structure defects in the cathode material, reduce lattice strain, control particle size distribution, and thus improve the electrochemical performance of the cathode material. Specifically, the sintering temperature can be 750℃, 760℃, 780℃, 800℃, 850℃, 900℃, 920℃, 950℃, 980℃, or any range of two values; the sintering time can be 10h, 12h, 15h, 16h, 18h, 20h, 24h, 28h, 30h, or any range of two values.

[0060] In a third typical embodiment of this application, a lithium-ion battery is also provided, which includes the positive electrode material provided in the first typical embodiment or the positive electrode material obtained by the preparation method provided in the second typical embodiment.

[0061] The lithium-ion battery provided in this application uses free SO4. 2- The content is ≤800ppm, and SO4 2- Cathode materials with a surface enrichment of ≤70% or a particle volume ratio of ≤4% below 1μm under 6T pressure exhibit excellent cycle performance and rate performance.

[0062] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0063] Example 1

[0064] This embodiment provides a cathode material, which is prepared according to the following steps:

[0065] (1) Mass ratio (n) Ni :n Co :n Mn =0.60:0.1:0.3) Weigh out nickel nitrate, cobalt nitrate, and manganese nitrate and add them to water to prepare a mixed metal salt solution. Control the total metal concentration in the mixed metal salt solution to be 300 g / L. Add H2SO4 to adjust the SO4 concentration in the mixed solution. 2- The mass ratio relative to the total metal is 1200 ppm, where the total metal mass refers to the sum of the masses of Ni, Co, and Mn elements in the metal salt mixture solution.

[0066] (2) After the metal salt mixed solution is atomized into droplets through a plasma rotating electrode, it is placed in a calcining furnace under a pyrolysis atmosphere and subjected to pyrolysis in the first and second temperature zones. The solid obtained from pyrolysis is then pulverized by airflow to obtain a cathode material precursor. The chemical formula of the cathode material precursor is Ni. 0.60 Co 0.1 Mn0.3 O; wherein, the volume concentration of O2 in the pyrolysis atmosphere is controlled at 8%, and during the atomization process, the flow rate is controlled at 200L / h, the atomization pressure is 0.6MPa, the heating temperature of the first temperature zone is 1100℃, the material residence time is 5s, the heating temperature of the second temperature zone is 750℃, and the residence time is 60s.

[0067] (3) After uniformly mixing the cathode material precursor with lithium hydroxide, the mixture was heated to 930°C under an oxygen atmosphere and sintered for 20 hours to obtain the cathode material LiNi. 0.60 Co 0.1 Mn 0.3 O2. The molar ratio of lithium hydroxide to the total metal in the cathode material precursor is 1:1. The total molar amount of metal in the cathode material precursor refers to the sum of the molar amounts of Ni, Co, and Mn elements.

[0068] Example 2

[0069] The difference between this embodiment and Embodiment 1 is that, in step (1), the SO4 in the metal salt mixed solution... 2- The mass ratio relative to the total metals is 500 ppm.

[0070] Example 3

[0071] The difference between this embodiment and Embodiment 1 is that, in step (1), the SO4 in the metal salt mixed solution... 2- The mass ratio relative to the total metals is 1500 ppm.

[0072] Example 4

[0073] The difference between this embodiment and Embodiment 1 is that, in step (1), the SO4 in the metal salt mixed solution... 2- The mass ratio of the total metal is 900 ppm, and in step (2), the heating temperature of the first temperature zone is 1000℃, the material residence time is 5s, the temperature of the second temperature zone is pyrolysis 750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 11%.

[0074] Example 5

[0075] The difference between this embodiment and embodiment 1 is that in step (2), the heating temperature of the first temperature zone is 1200℃, the material residence time is 9s, the temperature of the second temperature zone is pyrolysis 750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 5%.

[0076] Example 6

[0077] The difference between this embodiment and Embodiment 1 is that, in step (1), the SO4 in the metal salt mixed solution... 2-The mass ratio relative to the total metal is 2400 ppm. In step (2), the heating temperature of the first temperature zone is 1100℃, the material residence time is 5s, the temperature of the second temperature zone is pyrolysis 8750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 6%.

[0078] Example 7

[0079] The difference between this embodiment and embodiment 1 is that in step (2), the heating temperature of the first temperature zone is 1000℃, the material residence time is 2s, the temperature of the second temperature zone is 500℃, and the volume concentration of O2 in the pyrolysis atmosphere is 12%.

[0080] Example 8

[0081] The difference between this embodiment and Embodiment 1 is that, in step (1), the molar ratio of nickel, cobalt, and manganese is n. Ni :n Co :n Mn = 0.90:0.05:0.05, in step (3), the sintering temperature is 750℃ and the sintering time is 30h. The sintering atmosphere is an oxygen-containing atmosphere with an O2 volume concentration of 99%.

[0082] Example 9

[0083] The difference between this embodiment and Embodiment 1 is that, in step (1), the molar ratio of nickel, cobalt, and manganese is n. Ni :n Co :n Mn =0.55:0.10:0.25, in step (3), the sintering temperature is 980℃ and the sintering time is 10h. The sintering atmosphere is an oxygen-containing atmosphere with an O2 volume concentration of 95%.

[0084] Example 10

[0085] The difference between this embodiment and embodiment 1 is that, in step (1), the total metal concentration in the metal salt mixed solution is 100 g / L, and in step (2), the pressure of the atomization treatment is 0.4 MPa.

[0086] Example 11

[0087] The difference between this embodiment and embodiment 1 is that, in step (1), the total metal concentration in the metal salt mixed solution is 500 g / L, and in step (2), the pressure of the atomization treatment is 0.8 MPa.

[0088] Example 12

[0089] The difference between this embodiment and embodiment 8 is that, in step (1), the molar ratio (n) Ni :n Co :n Al=0.90:0.05:0.05) Weigh out nickel nitrate, cobalt nitrate, and aluminum nitrate and add them to water to prepare a mixed solution of metal salts.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is that in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 25%, and only the second temperature zone is set, with the heating temperature of the second temperature zone being 750°C.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that, in step (1), the metal salt mixed solution contains SO4. 2- With a total metal mass ratio of 650 ppm, in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 25%, and only the second temperature zone is set, with a heating temperature of 750 °C.

[0094] Comparative Example 3

[0095] The difference between this comparative example and Example 1 is that, in step (1), the metal salt mixed solution contains SO4. 2- The mass ratio relative to the total metals is 2900 ppm.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that, in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 15%.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 1 is that in step (2), the temperature of the first temperature zone is 1400°C and the volume concentration of O2 in the pyrolysis atmosphere is 15%.

[0100] Experimental Example 1

[0101] The cathode material precursors and cathode materials prepared in the examples and comparative examples were analyzed for particle size Dmin, D50, grain size, pH value, and free SO4. 2- Content, SO4 2- The total amount and surface enrichment were tested, and the results are shown in Table 1 below. In addition, the lattice strain of the cathode materials prepared in the examples and comparative examples was measured, and the results are shown in Table 1 below.

[0102] Among them, (1) the particle size determination method is as follows: the average particle size D50 and Dmin of the volumetric fabric of the cathode material precursor or cathode material are obtained by using a Malvern 3000 laser particle size analyzer. Specifically, take an appropriate amount of sample, pour it into pure water for ultrasonic dispersion, the ultrasonic time is 30s, the ultrasonic power is 240w, then add an appropriate amount of sodium hexametaphosphate to the dispersed sample, stir evenly and pour it into the sample pool of the detection device, wait for 10s and then click to start the sample test.

[0103] (2) The method for testing grain size is as follows: A cross-section sample was prepared using an ion cutter (IM5000), and the cross-section morphology of the cathode material was tested using a Hitachi S4800 scanning electron microscope. Ten photos were taken at 5K magnification. All images were imported into the Nano Measure software, the scale was set, and the grain size of all particles in the image was marked. Finally, the average grain size was calculated as the size of the single crystal particle.

[0104] (3) The pH test method is as follows: The pH of the positive electrode material is tested using a METTLER TOLEDO FE28. The specific procedure is as follows: Take about 5g of positive electrode material sample, add 45mL of water, sonicate for 5min, and then let it stand for 10min. After calibrating the pH meter, insert the composite electrode into the supernatant solution to be tested. Calculate the pH value of the solution based on the potential difference between the measuring electrode and the reference electrode.

[0105] (4) The method for determining lattice strain is as follows: the lattice strain of the cathode material is calculated from XRD data using Williamson-Hall analysis. Specifically, it is measured using a Rigaku Uitimaiv X-ray diffractometer (Japan), under the following conditions: 0.75 degrees / minute, step size 0.02, continuous scanning within the 2θ range from 10 to 90 degrees. The lattice strain is plotted using 4sinθ... hkl Let β be the x-axis. hkl cosθ hkl Using the vertical axis as the ordinate, a curve is plotted and linearly fitted. The strain ε can be calculated from the slope. It should be noted that the half-width at half maximum (WHM) βhkl used for fitting needs to eliminate the influence of the instrument, i.e., βhkl = βtotal - βinstrument, where βtotal is the actual measured WHM value, and βinstrument is the WHM broadening caused by the instrument. This value can be calculated by XRD of the test standard silicon wafer. The βinstrument of the test equipment used in this application is 0.000103. In addition, the data of seven strong diffraction peaks (003), (101), (102), (104), (015), (107), and (113) are selected for fitting to improve the linear fitting degree and reduce the experimental error.

[0106] Where β is the full width at half maximum (FWHM), θ is the diffraction angle (both in radians), k is a constant of 0.89, λ is the X-ray wavelength of 0.154 nm, D is the grain size (in nm), and ε is the lattice strain, which is dimensionless.

[0107] (5) Volume ratio test of 1μm cathode material particles under 6T pressure: Weigh 1g of sample and put it into the mold of the compaction density meter (Carver 4350, USA) and press it with 6T pressure for 30s. Then take out the sample and use the above method (1) to test the volume ratio of particles under 1 micrometer.

[0108] (6) Free anions (SO4) 2- The method for determining the SO4 content is as follows: Dissolve 0.5 g of the positive electrode material in 50 ml of pure water, sonicate for 5 min, filter, and measure the SO4 content of the filtrate using ion chromatography (Thermo Fisher ICS6000 HPIC). 2- Free ion content.

[0109] (7)SO4 2- The method for determining the total content is as follows: Dissolve 0.3g of sample in aqua regia, cool and bring to a final volume of 100ml to prepare the stock solution; take 1mL of the stock solution, dilute 100 times, and measure the S content using an Agilent 5110 ICP-OES analyzer, recording it as ms; SO4 2- Total content = ms × SO4 2- The molecular weight of S / the molecular weight of S.

[0110] Table 1

[0111] Figure 1 shows the Williamson-Hall analysis fitting curve of the cathode material provided in Example 1. As can be seen from Figure 1, there is a good linear relationship between βcosθ and 4sinθ. The lattice strain of the cathode material prepared in Example 1 is the slope of the fitted straight line, which is 0.1%, indicating that the lattice strain of the cathode material prepared in the example is less than 0.2%.

[0112] Figure 2 shows the SEM image of the cathode material provided in Example 1. As can be seen from Figure 2, the cathode material prepared in Example 1 mainly exhibits a single crystal morphology.

[0113] Experimental Example 2

[0114] The electrochemical performance of the cathode materials prepared in the above examples and comparative examples was evaluated using coin cell half-cells. The specific procedure was as follows: Cathode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) was added at a solid content of 50%, and the mixture was stirred into a viscous slurry using a high-speed disperser. This slurry was then uniformly coated onto aluminum foil using a scraper, dried in an oven at 80°C, and then rolled at a pressure of 3T. After rolling, the slurry was cut into cathode sheets with a diameter of 14 mm. A lithium-ion battery was assembled according to the industrial LIR2016 coin cell standard, using a 16 mm lithium sheet as the negative electrode, a Celgard polypropylene membrane as the separator, and a 1 mol / L LiPF6 carbonate solution as the electrolyte. Assembly was performed in an argon-filled glove box to obtain the LIR2016 coin cell half-cell.

[0115] The LAND battery testing system was used to test the 0.1C capacity, 2C capacity, 2C / 0.1C, 50-cycle capacity retention and DC internal resistance (DCR).

[0116] The 0.1C capacity test is as follows: 0.1C / 0.1C rate, charge and discharge test is carried out in the discharge range of 3.0V-4.4V (except for Example 8, whose voltage range is 3.0-4.3V) at 25℃. The reference capacity is set to 200mA / g. The 0.1C capacity is obtained as: discharge capacity / mass of cathode material.

[0117] The 2C capacity test was conducted as follows: at 1C / 2C rate, charge and discharge tests were performed in the discharge range of 3.0V-4.4V (except for Example 8, whose voltage range is 3.0-4.3V) at 25°C. The reference capacity was set to 200mA / g, and the 2C capacity was obtained as: discharge capacity / mass of cathode material.

[0118] 2C / 0.1C is the ratio of the 2C capacity to the 0.1C capacity.

[0119] The 2C cycle 50-cycle capacity retention rate test is as follows: 50 cycles were performed at 45°C in the discharge range of 3.0V-4.4V (except for Example 8, whose voltage range is 3.0-4.3V) at a rate of 0.5C / 2C. The cycle capacity retention rate was measured. 2C cycle 50-cycle capacity retention rate = discharge specific capacity in the 50th cycle / discharge specific capacity in the 1st cycle.

[0120] The DC internal resistance (DCR) test is as follows: In the above 2C cycle 50-cycle capacity retention test, the voltage U at the initial moment of discharge each cycle is recorded. A And the voltage data U at 60s B Discharge current I Dis The formula for calculating DC internal resistance is DCR = (U A -U B) / I Dis .

[0121] The test results are shown in Table 2 below.

[0122] Table 2

[0123] Referring to Tables 1 and 2, the free SO4 in Examples 1-12 of this application 2- The content is ≤800ppm, and SO4 2- The surface enrichment degree is ≤70%, and its cycle performance and capacity are significantly better than those of comparative examples 1-4. Tests yielded free SO4 in the cathode material provided in this application. 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%, indicating that some SO4 is present. 2- Doping into the internal lattice suppresses c-axis contraction, lowers the activation energy for Li migration, and thus improves the cycle performance and rate performance of the cathode material, while also counteracting free SO4. 2- The negative impacts it brings.

[0124] Compared with Example 1, Example 2 reduced the SO4 content of the metal salt solution in step (1). 2- The content of free SO4 in the prepared cathode material 2- The content decreased, while SO4 2- The enrichment degree remained basically unchanged, and the cycle performance and rate performance of the cathode material were good, indicating that under a certain amount of SO4, 2- Based on doping, reduce free SO4 2- The increased SO4 content is beneficial for improving the electrochemical performance of the cathode material. In Example 3, the SO4 content of the metal salt solution in step (1) was increased. 2- The content of free SO4 2- Content and SO4 2- The enrichment of free SO4 increased, but the cycle performance and rate performance of the cathode material decreased. 2- Excessive content can affect the cycle performance and rate performance of the cathode material.

[0125] Compared to Example 1, Example 4 reduces the SO4 content of the metal salt solution in step (1). 2- The content of SO42-3 decreased the heating temperature and material residence time in the first temperature zone, resulting in a higher concentration of free SO42-3 in the cathode material. 2- Content and SO4 2- The enrichment degree of free SO42- increased, but the cycle performance and rate performance of the cathode material were poor. This indicates that increasing the enrichment degree of free SO42-... 2- The content of SO4 decreased at the same time 2-The doping amount is detrimental to improving the electrochemical performance of the cathode material. In Example 5, the heating temperature of the first temperature zone was increased, and the material residence time in the first temperature zone was extended, resulting in a cathode material with free SO4. 2- The content decreased, and SO4 2- The enrichment level of SO42- has increased, and the cycle performance and rate performance of the cathode material are good, indicating that the enrichment of free SO42- has been reduced. 2- The content of SO4 increases simultaneously 2- The doping amount can further suppress c-axis contraction, reduce the activation energy of Li migration, and thus improve the cycle performance and rate performance of the cathode material, and counteract free SO4. 2- The negative impacts it brings.

[0126] Compared to Example 1, Examples 4-6 changed the heating temperature and material residence time in the first temperature zone, resulting in a change in the volume percentage of particles smaller than 1 μm in the obtained cathode material at 6t. In Example 5, the heating temperature in the first temperature zone was 1200℃, which was higher than the heating temperatures in Examples 4 and 6, and the material residence time was 9s, which was also longer than the residence times in Examples 4 and 6. The resulting cathode material had a particle volume percentage of 4% smaller than 1 μm at 6t, and the obtained cathode material exhibited good cycle performance and rate performance, indicating that the presence of a certain amount of micro-powder can increase the cycle stability and rate performance of the cathode material.

[0127] In Comparative Examples 1 and 2, the volume concentration of O2 in the pyrolysis atmosphere was 25%, and only the second temperature zone was set. The resulting positive electrode material contained SO4. 2- The surface enrichment rate was as high as 90%, indicating that SO4 in the precursor solution was high. 2- It is difficult to reduce S to S. 2- The presence of low-valence ions and a relatively low pyrolysis temperature leads to SO42- 2- It is difficult to incorporate SO4 into the bulk phase, resulting in SO4 content within the cathode material. 2- The inability to suppress c-axis contraction results in poor cycle performance and rate performance of the cathode material.

[0128] In Comparative Example 3, the SO4 in the solution in step (1) 2- If the concentration is too high, the resulting cathode material will contain free SO4. 2- The concentration was 832 ppm. During the circulation process, free SO42... 2- It easily reacts with the electrolyte, leading to poor cycle stability of the cathode material. In Comparative Example 4, the volume concentration of O2 in the pyrolysis atmosphere was 15%. During spray pyrolysis, SO4... 2- Difficult to be reduced to S 2- Low-valence ions lead to SO4 2-SO4 in cathode materials is difficult to incorporate into the bulk phase. 2- The high enrichment of these elements leads to poor cycle stability of the cathode material.

[0129] In Comparative Example 5, the temperature of the first temperature zone in step (2) is 1400℃, and the volume concentration of O2 in the pyrolysis atmosphere is 15%. The volume percentage of particles with a diameter of 1μm at 6t of the obtained cathode material is 5%, and SO4 content is also low. 2- The high surface enrichment indicates a high content of micronized powder in the cathode material and a high concentration of free SO4. 2- The high content of [agent] leads to poor cycle stability of the cathode material.

[0130] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The general chemical formula of the cathode material is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

2. The cathode material according to claim 1, characterized in that, The cathode material includes at least one of the following characteristics: (1) Free SO4 in the cathode material 2- The content is 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm or within any two of the above values. (2) Free SO4 in the positive electrode material 2- The content is 100ppm to 300ppm; (3) Free SO4 in the positive electrode material 2- The content is 500ppm to 800ppm; (4) The SO4 2- The surface enrichment is 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or within any two of the above values; (5) The SO4 2- The surface enrichment is 40%–70%; (6) The SO4 2- The surface enrichment is 10%–35%.

3. The cathode material according to claim 1, characterized in that, The positive electrode material has a particle volume ratio of less than 1μm of ≤4% under a pressure of 6T; And / or, the lattice strain of the cathode material is ≤0.2%.

4. The cathode material according to claim 1, characterized in that, The cathode material further includes a coating layer, which includes at least one element selected from Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn.

5. The positive electrode material according to claim 1, characterized in that, The median volumetric particle size D50 of the cathode material is 2.5 μm-5 μm; And / or, the particle size Dmin of the positive electrode material is greater than 0.3 μm; And / or, the particle size Dmax of the cathode material is <14μm.

6. The cathode material according to claim 1, characterized in that, The specific surface area of ​​the positive electrode material is 0.5-1.2 m². 2 / g; And / or, the pH of the positive electrode material satisfies 11.0 ≤ pH ≤ 12.

0.

7. The cathode material according to claim 1, characterized in that, The cathode material is a single-crystal material, and the cathode material includes grains with the same orientation, the grain size being 1μm to 5μm.

8. A positive electrode material, characterized in that, The general chemical formula of the cathode material is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content of [missing information] is ≤800ppm, and the volume percentage of particles smaller than 1μm in the cathode material is ≤4% under 6T pressure.

9. The cathode material according to claim 8, characterized in that, The particle size Dmin of the cathode material is greater than 0.3 μm.

10. The cathode material according to claim 8, characterized in that, The cathode material is a single-crystal material, and the cathode material includes grains with the same orientation, the grain size being 1μm to 5μm.

11. The cathode material according to claim 8, characterized in that, The cathode material satisfies at least one of the following conditions: 1) SO4 of the positive electrode material 2- Surface enrichment ≤70%; 2) The lattice strain of the cathode material is ≤0.2%; 3) The specific surface area of ​​the positive electrode material is 0.5-1.2 m². 2 / g.

12. The cathode material according to claim 8, characterized in that, The cathode material satisfies at least one of the following conditions: 1) The median volumetric particle size D50 of the cathode material is 2.5 μm-5 μm; 2) The particle size Dmax of the positive electrode material is less than 14 μm.

13. The cathode material according to claim 8, characterized in that, The cathode material satisfies at least one of the following conditions: (1) Free SO4 in the cathode material 2- The content is 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm or within any two of the above values. (2) Free SO4 in the positive electrode material 2- The content is 100ppm to 300ppm; (3) Free SO4 in the positive electrode material 2- The content is 500ppm to 800ppm; (4) The positive electrode material, under a pressure of 6T, has a volume ratio of particles smaller than 1μm of 0, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or any two of these values. (5) Under a pressure of 6T, the volume percentage of particles smaller than 1μm in the positive electrode material is 1% to 4%; (6) Under a pressure of 6T, the volume percentage of particles smaller than 1μm in the cathode material is 2% to 4%.

14. A positive electrode plate, characterized in that, The positive electrode sheet includes the positive electrode material as described in any one of claims 1 to 13.

15. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in any one of claims 1 to 13.

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