Cathode Material, Preparation Method and Lithium-Ion Battery

Abstract

The present invention relates to the technical field of lithium-ion battery materials, and specifically discloses a cathode material, as well as a preparation method thereof and a lithium-ion battery including the cathode material. The chemical formula of the cathode material provided by the present invention is: Li a Ni b Co C N1 d M (1‑b‑c‑d‑e) N2 e O2. The cathode material provided by the present invention can exhibit a higher capacity during charge and discharge, and the cycle stability of the cathode material is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery materials, and particularly relates to a cathode material, a preparation method thereof, and a lithium-ion battery including the cathode material. Background Art

[0002] In the prior art, lithium ions in some cathode materials have a long diffusion path during charge and discharge, resulting in poor rate performance and cycle stability. In order to improve the rate performance and cycle stability of the cathode material, the prior art generally improves it by means of bulk doping of the cathode material.

[0003] However, when some elements are doped into the lattice, lattice expansion will occur. In addition, during the long-term cycling process of the cathode material, lattice expansion will also occur. The superposition of the two effects will make it easier to generate microcracks inside the cathode material particles, which will cause the particles to crack and deteriorate the performance of the lithium battery.

[0004] Therefore, how to improve the rate performance, cycle stability, etc. of the cathode material is still an urgent technical problem to be solved at present. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a cathode material, and the present invention also aims to provide a preparation method of the cathode material of the present invention. In addition, the present invention also aims to provide a lithium-ion battery including the cathode material.

[0006] To achieve the above purposes, the technical solutions adopted by the present invention are as follows.

[0007] In the first aspect, the present invention provides a cathode material, and the chemical formula of the cathode material is: Li a Ni b Co c N1 d M (1-b-c-d-e) N2 e O2, where: 0.95 ≤ a ≤ 1.2, 0 < b ≤ 1, 0 < c ≤ 1, 0 < d ≤ 1, 0 ≤ e < 1, and b + c + d + e < 1; the element M is selected from at least one element in Group IA and Group IIA of the periodic table; the element N1 is selected from at least one of Mn or Al, and the element N2 is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y;

[0008] The cathode material includes a plurality of crystal grains, and the cross-section of the crystal grains includes a central region and a surface layer region. By EDS testing the cross-section of the crystal grains, the average concentration of the element M in the central region is measured as X1, and the average concentration of the element M in the surface layer region is measured as X2, and X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 20.

[0009] In a second aspect, the present invention provides a method for preparing a cathode material, comprising the steps of:

[0010] S1: Mix a salt solution containing Ni element, Co element, and N1 element with a salt solution containing element M to obtain a precursor solution; wherein, the element N1 is selected from at least one of Mn or Al;

[0011] S2: The precursor solution is prepared into an oxide precursor by spray pyrolysis treatment. The spray pyrolysis treatment includes spray treatment and annealing treatment. The atomizing air flow rate of the spray treatment is 100 m 3 / h to 300 m 3 / h, the atomizing pressure is 400 Kpa to 700 Kpa, the pyrolysis temperature is 400 °C to 1000 °C, and the temperature of the annealing treatment is 500 °C to 1200 °C;

[0012] S3: Mix the oxide precursor with a lithium source and a metal oxide containing element N2 and sinter to obtain a cathode material; the element N2 is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y.

[0013] In a third aspect, the present invention further provides a lithium-ion battery, which includes the cathode material of the present invention or the cathode material obtained by the preparation method of the present invention.

[0014] For the cathode material provided by the present invention, by selecting element M from the elements in Group IA and Group IIA of the periodic table, controlling the concentration of element M in the crystal grains to satisfy 1.2 ≤ X2 / X1 ≤ 20, the content of element M in the region near the crystal grain surface is relatively large. Element M increases the unit cell volume in the surface layer region of the crystal grain, while the content of element M in the region near the crystal grain center is relatively small, making the unit cell volume in the crystal grain center region relatively small, thereby forming a compressive stress from the surface towards the center of the crystal grain. The compressive stress can inhibit the lattice expansion during charge and discharge, and further improve the gas generation performance and long-term cycling performance.

[0015] For the preparation method of the cathode material provided by the present invention, doping of target elements is carried out at the precursor end, that is, first forming a precursor solution of element M and a ternary nitrate solution containing Ni, Co, and N1, then preparing it into an oxide precursor by spray pyrolysis, and then controlling conditions such as atomizing air flow rate, atomizing pressure, and annealing temperature during the spray pyrolysis process to regulate the enrichment of element M in the surface layer region of the oxide precursor, so that the concentration of element M in the central region of the precursor is less than that in the surface layer region, thereby making the concentration of element M in the surface layer region of the cathode material crystal grains greater than that in the central region. Description of the Drawings

[0016] Figure 1 It is a schematic diagram for testing the concentration distribution of element M in the crystal grains of the positive electrode material of the present invention;

[0017] Figure 2 It is a comparison diagram of the concentration distribution of K element on the cross-sections of multiple particles obtained by line scanning of the positive electrode materials respectively provided in Example 1, Example 6, Example 7, and Comparative Example 2 of the present invention;

[0018] Figure 3 It is a comparison diagram of the concentration distribution of Mg element on the cross-sections of multiple particles obtained by line scanning of the positive electrode materials respectively provided in Example 2, Example 6, Example 10, and Comparative Example 2 of the present invention;

[0019] Figure 4 It is a comparison diagram of internal cracks of the positive electrode materials provided in Example 6 and Comparative Example 2 of the present invention;

[0020] Figure 5 It is a schematic diagram of a lithium-ion battery provided by the present invention in a discharging state;

[0021] Figure 6 It is an explanatory diagram of the point scanning areas for testing the average concentration X1 of element M in the central region and the average concentration X2 in the surface layer region in the crystal grains of the positive electrode material of the present invention. Detailed implementation manners

[0022] The technical solutions of the present invention will be clearly and completely described below through examples. Obviously, the described examples are some but not all of the examples of the present invention. All other examples obtained by those skilled in the art based on the examples of the present invention without creative efforts belong to the scope of protection of the present invention.

[0023] It should be understood that the terms "first", "second", "third", "fourth", etc. in the claims, description, and drawings of the present invention are used to distinguish different objects, rather than to describe a specific order. The terms "including" and "comprising" used in the description and claims of the present invention indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0024] It should also be understood that the terms used in the specification of the present invention are merely for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification and claims of the present invention, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms. It should be further understood that the term "and / or" used in the specification and claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0025] Unless otherwise specified, the materials, reagents, and equipment used in the examples and comparative examples of this application are all obtained through conventional commercial channels.

[0026] In a first aspect, the present invention provides a positive electrode material, the chemical formula of which is: Li a Ni b Co c N1 d M (1-b-c-d-e) N2 e O2, where: 0.95 ≤ a ≤ 1.2, 0 < b ≤ 1, 0 < c ≤ 1, 0 < d ≤ 1, 0 ≤ e < 1, and b + c + d + e < 1; the element M is selected from at least one element in Group IA and Group IIA of the periodic table; the element N1 is selected from at least one of Mn or Al, and the element N2 is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y;

[0027] The positive electrode material includes a plurality of crystal grains. By performing EDS testing on the cross-section of the crystal grains, the cross-section of the crystal grains includes a central region and a surface region. The average concentration of the element M in the central region is measured as X1, and the average concentration of the element M in the surface region is measured as X2. X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 20.

[0028] Thus, by selecting the element M from the elements in Group IA and Group IIA of the periodic table and controlling the concentration of the element M in the crystal grains to satisfy 1.2 ≤ X2 / X1 ≤ 20, the content of the element M in the surface region near the crystal grains is relatively large. The element M increases the unit cell volume of the surface region of the crystal grains, while the content of the element M in the central region near the crystal grains is relatively small, making the unit cell volume in the central region of the crystal grains relatively small. Thus, a compressive stress is formed from the surface towards the center of the crystal grains. The compressive stress can inhibit lattice expansion during charge and discharge, and further improve the gas generation performance and long-term cycling performance.

[0029] It should be noted that after the M element enters the transition metal layer and occupies the sites of Ni / Co / N1 elements, the M element will expand the interlayer spacing of the transition metal layer, thereby increasing the unit cell volume. When the M element shows enrichment near the grain surface, the unit cell volume in the surface layer region of the grain will be larger than that in the central region of the grain. The stress in the surface layer region of the grain is relatively large, resulting in a compressive stress towards the grain center, and further causing the grain to have a tendency to shrink from the surface layer to the grain center (i.e., the shrinkage state).

[0030] It should be noted that as Figure 1 shown, in the sectional view of the grain, the radius of the grain is L. The region from the center of the grain to a distance of L / 2 from the grain center is the central region, and the region from the position of L / 2 of the grain to the grain surface is the surface layer region.

[0031] In some preferred embodiments, the element M is selected from at least one element in Group IA and Group IIA of the periodic table, such as at least one selected from Na, K, Mg, Ca, Sr, Ba, Sr, Rb, Cs. These elements are monovalent and have a fixed valence state after oxidation, which plays a role in stabilizing the crystal structure of the cathode material. Moreover, the ionic radii of the above elements are relatively large. After entering the transition metal layer and occupying the sites of Ni / Co / N1 elements, the M element with a large ionic radius will expand the interlayer spacing of the transition metal layer, thereby increasing the unit cell volume.

[0032] In some preferred embodiments, the element N1 is selected from at least one of Mn or Al. Selecting Mn or Al for the element N1 can play a role in stabilizing the crystal structure of the cathode material.

[0033] In some preferred embodiments, the element N2 is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, Y. Selecting the above elements for the element N2 can play a role in stabilizing the crystal structure of the cathode material and improving the ionic conductivity. Moreover, by coating on the particle surface, the element N2 can also serve the purpose of delaying the reaction between the cathode material and the electrolyte.

[0034] As an embodiment of the present invention, the value of X2 / X1 can be 1.2, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or any value between 1.2 and 20.

[0035] As an embodiment of the present invention, X1 is 10 ppm to 400 ppm. Specifically, X1 can be 10 ppm, 20 ppm, 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 180 ppm, 200 ppm, 250 ppm, 280 ppm, 300 ppm, 320 ppm, 350 ppm or 400 ppm, etc. Of course, it can also be other values within the above range, which are not limited herein. When the value range of X1 is within the above range, while stabilizing the crystal structure, it will not affect the capacity of the cathode material; if the content is relatively high, it will occupy more transition metal or lithium ion sites, thereby affecting the normal charge and discharge performance.

[0036] As an embodiment of the present invention, X2 is 10 ppm to 400 ppm. Specifically, X2 can be 10 ppm, 20 ppm, 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 180 ppm, 200 ppm, 250 ppm, 280 ppm, 300 ppm, 320 ppm, 350 ppm or 400 ppm, etc. Of course, it can also be other values within the above range, which are not limited herein. When the value range of X2 is within the above range, while stabilizing the crystal structure, it will not affect the capacity of the cathode material; if the content is relatively high, it will occupy more transition metal or lithium ion sites, thereby affecting the normal charge and discharge performance.

[0037] As an embodiment of the present invention, the content of element M in the cathode material is 10 ppm to 400 ppm. Specifically, the content of element M in the cathode material can be 10 ppm, 20 ppm, 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 180 ppm, 200 ppm, 250 ppm, 280 ppm, 300 ppm, 320 ppm, 350 ppm or 400 ppm, etc. Of course, it can also be other values within the above range, which are not limited herein. When the content of element M is too low, the doping effect cannot be achieved. When the content of element M is too high, due to the excessive content of M element in the crystal grains, the unit cell volume will change greatly, resulting in a decrease in its structural stability, which is not conducive to the long-term electrochemical performance of the battery. When the content of element M is controlled within the range of 10 ppm to 400 ppm, fewer cracks will occur during the long-term cycling process, and the cycling stability is better.

[0038] As an embodiment of the present invention, the content of element N2 in the positive electrode material is 0ppm~5000ppm. Specifically, the content of element N2 in the positive electrode material can be 0ppm, 5ppm, 100ppm, 500ppm, 1000ppm, 1500ppm, 1800ppm, 2000ppm, 2400ppm, 2800ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 4800ppm or 5000ppm, etc., and of course, it can also be other values ​​within the above range, which is not limited here. When the concentration of element N2 is within the above range, the crystal structure can be stabilized, the ionic conductivity can be improved, and the reaction between the positive electrode material and the electrolyte can be delayed.

[0039] As an embodiment of the present invention, the lattice strain ε of the positive electrode material is less than 0.1%. Specifically, the lattice strain ε of the positive electrode material can be 0.095%, 0.09%, 0.05%, 0.01%, 0.005%, 0%, -0.01%, -0.05%, -0.08%, -0.10% or -0.15%, etc., and of course, it can also be other values ​​within the above range, which are not limited here. By controlling the lattice strain ε within 0.1%, the microcracks inside the particles can be reduced, so that the particles of the positive electrode material are not easy to crack and fail during the cycle.

[0040] As an embodiment of the present invention, the specific surface area S of the positive electrode material is 0.4 m 2 / g~0.9m 2 / g. Specifically, the specific surface area S of the positive electrode material can be 0.4 m 2 / g, 0.45 m 2 / g, 0.50 m 2 / g, 0.55 m 2 / g, 0.58 m 2 / g, 0.60 m 2 / g, 0.70 m 2 / g, 0.75 m 2 / g, 0.80 m 2 / g, 0.85 m 2 / g or 0.9 m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited here. Studies have found that the specific surface area S of the positive electrode material is greater than 0.9 m 2 / g, there are more particle powders, which are easy to react with the electrolyte during the charge and discharge process, resulting in gas production; and when the specific surface area S of the positive electrode material is less than 0.4 m 2When it is [specific value] g, the particle size is relatively large. The relatively large particle size results in an overly long lithium-ion transmission channel, a relatively large internal resistance, which affects the kinetic process and thus the rate performance of the cathode material will be affected.

[0041] As an embodiment of the present invention, the tapped density ρ1 of the cathode material is > 2.0 g / cm 3 ; the tap density ρ2 of the cathode material is ≥ 2.8 g / cm 3 . Specifically, the tapped density ρ1 of the cathode material can be 2.10 g / cm 3 , 2.12 g / cm 3 , 2.18 g / cm 3 , 2.20 g / cm 3 , 2.22 g / cm 3 , 2.24 g / cm 3 , 2.30 g / cm 3 , 2.32 g / cm 3 , 2.35 g / cm 3 or 2.40 g / cm 3 etc. Of course, it can also be other values within the above range, which are not limited here. The tap density ρ2 of the cathode material can be 2.80 g / cm 3 , 2.90 g / cm 3 , 3.00 g / cm 3 , 3.10 g / cm 3 , 3.15 g / cm 3 , 3.18 g / cm 3 , 3.20 g / cm 3 , 3.22 g / cm 3 , 3.25 g / cm 3 or 3.30 g / cm 3 etc. Of course, it can also be other values within the above range, which are not limited here. The cathode material with a relatively high tapped density and tap density has a relatively high tap density of the electrode sheet during the process of making the electrode sheet, and can exhibit a higher capacity.

[0042] As an embodiment of the present invention, the volume particle size distribution width Span value of the cathode material satisfies: 1.5 ≥ Span value ≥ 1.0. Specifically, the Span value can be 1.0, 1.15, 1.18, 1.19, 1.20, 1.22, 1.24, 1.30, 1.35, 1.40, 1.45 or 1.50 etc. Of course, it can also be other values within the above range, which are not limited here. When the volume particle size distribution of the cathode material satisfies the above range, the overall volume distribution of the cathode material particles can be relatively wide, which is conducive to obtaining a relatively high tap density of the electrode sheet, thereby improving the battery capacity.

[0043] As an embodiment of the present invention, the positive electrode material is a single-crystal material, the positive electrode material includes at least one grain with the same orientation, and the average grain size of the grains is 1 µm to 5 µm. The positive electrode material contains a single grain with the same orientation, wherein the average grain size of the single grain is 1 µm to 5 µm. Specifically, the average grain size of the single grain is 1 µm, 2 µm, 3 µm, 4 µm, 5 µm or any value within the range formed by any two of the above values, which is not limited herein. The primary particles of the positive electrode material have the same orientation, and the average particle size of the primary particles is 1 µm - 5 µm. Specifically, the average particle size of the primary particles is 1 µm, 2 µm, 3 µm, 4 µm, 5 µm or any value within the range formed by any two of the above values, which is not limited herein. The positive electrode material particles of the present application have a single grain with the same orientation. Since single crystals have a more stable structure, a more uniform bulk phase composition distribution, and better particle strength than polycrystals, the material can significantly reduce the cracking of particles during the pressing process of the electrode sheet, and improve the compaction density and volume energy density of the electrode sheet.

[0044] It should be noted that the difference between the single-crystal positive electrode material and the polycrystalline positive electrode material (i.e., polycrystalline secondary particles) is that the smallest particles of the polycrystalline secondary particles are secondary particles formed by the aggregation of nanoscale primary particles. For the single-crystal positive electrode material, the smallest particles are usually micron-scale monomer primary particles. Generally speaking, in addition to the EBSD test method, it is also possible to determine whether the obtained positive electrode product is a single-crystal material through characterization means such as scanning electron microscopy (SEM). For example, for the single-crystal positive electrode material, the morphology of the single-crystal particles can be characterized by SEM, and it can be seen that the shape of the single-crystal particles generally shows regular or irregular spherical shapes, and there is no significant particle aggregation. It is also possible to characterize the orientation of the single-crystal positive electrode material by EBSD. Through EBSD, it can be observed that the colors within at least one grain are the same to judge that the orientations within at least one grain are the same, and the grains with the same orientation are single crystals. It should be specifically noted that the "single-crystal positive electrode material" well-known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. Crystallographically, an ideal single crystal refers to a crystal with exactly the same arrangement and direction. However, limited by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal positive electrode material well-known in the art is actually more a "single-crystal-like morphology" positive electrode material, which only shows a large particle size similar to that of a single crystal in terms of size, different from the polycrystal composed of many small primary particles.

[0045] As an embodiment of the present invention, the crystal grains include a matrix and a coating, and at least part of the coating covers the surface of the matrix. The coating is selected from at least one of ZrO2, TiO2, Al2O3, CoO, MgO, WO3, CeO2, and Y2O3. Coating can improve and enhance the chemical stability of the surface of the matrix material and improve the electrochemical performance of the cathode material.

[0046] It should be noted that for the cathode material provided by the present invention, there are two situations for its crystal grains: in one situation, the crystal grains are the matrix and there is no coating on the matrix; in another situation, the crystal grains include the matrix and a coating on the matrix.

[0047] In the second aspect, the present invention provides a preparation method for preparing the cathode material of the present invention, including the steps:

[0048] S1: Mix a salt solution containing Ni element, Co element, and N1 element with a salt solution containing element M to obtain a precursor solution; wherein, the element N1 is selected from at least one of Mn or Al;

[0049] S2: The precursor solution is prepared into an oxide precursor by spray pyrolysis treatment. The spray pyrolysis treatment includes spray treatment and annealing treatment. The atomizing air flow rate of the spray treatment is 100 m 3 / h to 300 m 3 / h, the atomizing pressure is 400 Kpa to 700 Kpa, the pyrolysis temperature is 400 °C to 1000 °C, and the temperature of the annealing treatment is 500 °C to 1200 °C;

[0050] S3: Mix the oxide precursor with a lithium source and a metal oxide containing element N2 and sinter them to obtain a cathode material; the element N2 is selected from at least one of Zr, Ti, Al, Co, Mg, W, Ce, and Y.

[0051] The preparation method of the cathode material provided by the present invention can use recycled cathode material or use pure metal salts of Ni, Co, and N1 as raw materials for preparation.

[0052] If recycled ternary cathode material is used, it is necessary to first perform component detection on the recycled ternary cathode material. This process is to confirm the content ratio of the main elements and the types and content ratios of the impurity elements in the recycled material. Then, the cathode material with confirmed components is mixed with pure metal salts of Ni / Co / N1 according to the final target molar ratio of Ni:Co:N1 to prepare a nitrate solution.

[0053] As an embodiment of the present invention, in step S1, the molar ratio of Ni, Co, and N1 in the salt solution containing Ni, Co, and N1 is (55-70):(10-12):(20-33). Specifically, the molar ratio of Ni, Co, and N1 in the nitrate solution containing Ni, Co, and N1 can be 55:12:33, 70:12:33, 55:10:20, 70:10:20, 60:10:30, 65:12:33, 55:11:30, 70:11:30, 60:12:33, or 68:11:28, etc. Of course, it can also be other values within the above range, which are not limited herein.

[0054] As an embodiment of the present invention, in step S1, the N1 element can be Mn and / or Al.

[0055] Add the salt solution of element M to the nitrate solution according to the target ratio to prepare a precursor solution; if the recovered ternary cathode material contains the target element M, the concentration of element M to be added can be adjusted to ensure that the final concentration is the target concentration.

[0056] As an embodiment of the present invention, in step S1, the mass percentage concentration of element M in the precursor solution is 0.01% - 0.06%. Specifically, the mass percentage concentration of element M in the precursor solution can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or 0.06%, etc. Of course, it can also be other values within the above range, which are not limited herein. By controlling the mass percentage concentration of element M in the precursor solution within the above range, the content of element M in the prepared cathode material can meet the range of 10 ppm - 400 ppm.

[0057] As an embodiment of the present invention, in step S1, the salt of element M includes at least one of the chloride, sulfate, sulfite, nitrate, carbonate, and phosphate of element M. Element M is selected from at least one element in Group IA and Group IIA of the periodic table. For example, element M can be at least one of Na, K, Mg, Ca, Sr, Ba, Sr, Rb, and Cs.

[0058] As an embodiment of the present invention, the total concentration of Ni, Co, N1, and M in the precursor solution is 2 mol / L to 8 mol / L. Specifically, the total concentration of Ni, Co, N1, and M in the precursor solution can be 2.0 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L, 5.5 mol / L, 6.0 mol / L, 6.4 mol / L, 6.8 mol / L, 7.0 mol / L, or 8.0 mol / L. Of course, it can also be other values within the above range, which are not limited herein. When the total concentration of Ni, Co, N1, and M in the precursor solution is within the above range, the solid content of the spray droplets formed is moderate, and the solid phase, as the nucleation site, is conducive to the rapid solidification and nucleation of the droplets.

[0059] As an embodiment of the present invention, the spray pyrolysis includes spray treatment and annealing treatment. The atomizing air flow rate of the spray treatment is 100 m 3 / h to 300 m 3 / h, the atomizing pressure is 400 Kpa to 700 Kpa, and the pyrolysis temperature is 400 °C to 1000 °C. Specifically, the atomizing air flow rate of the spray treatment can be 100 m 3 / h, 120 m 3 / h, 150 m 3 / h, 180 m 3 / h, 200 m 3 / h, 240 m 3 / h, 280 m 3 / h, or 300 m 3 / h. Of course, it can also be other values within the above range, which are not limited herein. The atomizing pressure can be 400 Kpa, 420 Kpa, 450 Kpa, 500 Kpa, 540 Kpa, 580 Kpa, 600 Kpa, 650 Kpa, or 700 Kpa. Of course, it can also be other values within the above range, which are not limited herein. The pyrolysis temperature can be 400 °C, 450 °C, 500 °C, 600 °C, 650 °C, 700 °C, 800 °C, 900 °C, or 1000 °C. Of course, it can also be other values within the above range, which are not limited herein. By controlling the atomizing air flow rate, atomizing pressure, and pyrolysis temperature of the spray treatment within the above range, and by adjusting the appropriate atomizing air flow rate, atomizing pressure, and pyrolysis temperature, the time for the precursor solution to form dehydrated particles can be controlled, and the M element can be enriched in the surface layer region of the dehydrated particles.

[0060] As an embodiment of the present invention, the temperature of the annealing treatment is 500°C to 1200°C. Specifically, the temperature of the annealing treatment can be 500°C, 600°C, 650°C, 700°C, 800°C, 850°C, 900°C, 960°C, 1000°C, 1050°C, 1100°C, 1140°C or 1200°C. Of course, it can also be other values within the above range, which are not limited herein. A higher annealing temperature can cause the dehydrated particles to form an oxide precursor.

[0061] The method for preparing the cathode material of the present invention provided by the present invention can effectively regulate the internal and external distribution difference of element M by controlling the spray treatment and annealing treatment during the spray pyrolysis process, so that the concentration X1 of element M in the central region and the concentration X2 in the surface layer region of the grains of the prepared cathode material satisfy: 1.2 ≤ X2 / X1 ≤ 20.

[0062] As an embodiment of the present invention, in step S3, the oxide precursor is first pulverized to D50 of 2.0 μm to 4.0 μm, and then used for mixing. Specifically, the oxide precursor can be pulverized to D50 of 2.0 μm, 2.2 μm, 2.5 μm, 3.0 μm, 3.5 μm, 3.8 μm or 4.0 μm. Of course, it can also be other values within the above range, which are not limited herein. After the oxide precursor is pulverized to D50 of 2.0 μm to 4.0 μm and then used for mixing, the cathode material prepared from the precursor at this particle size has fewer fine powders and more rounded grains.

[0063] As an embodiment of the present invention, in step S3, the lithium source can be selected from any one or several of lithium carbonate, lithium nitrate, and lithium hydroxide.

[0064] As an embodiment of the present invention, in step S3, the metal oxide containing element N2 is selected from any one or more of ZrO2, TiO2, Al2O3, CoO, MgO, WO3, CeO2, and Y2O3; preferably, the metal oxide containing element N2 is CeO2 and / or WO3, and further preferably the metal oxide containing element N2 is CeO2.

[0065] As an embodiment of the present invention, in step S3, the oxide precursor, the lithium source, and the metal oxide containing element N2 are mixed in a mass ratio of 1:(0.4 - 0.8):(0.003 - 0.006). Specifically, the oxide precursor, the lithium source, and the metal oxide containing element N2 are mixed in a mass ratio of 1:0.4:0.003, 1:0.5:0.004, 1:0.6:0.006, 1:0.5:0.003, 1:0.5:0.005, 1:0.8:0.003, 1:0.8:0.006, 1:0.4:0.006, or 1:0.5:0.004. Of course, it can also be other values within the above range, which are not limited herein. By limiting the mass ratio of the several reaction materials of the oxide precursor, the lithium source, and the metal oxide containing element N2, the cathode material with the chemical formula described in the present invention can be obtained.

[0066] As an embodiment of the present invention, in step S3, the heating rate of the heating section during sintering is controlled to be 0.5°C / min to 3°C / min, and the heat preservation time during sintering is 8h to 16h. Specifically, the heating rate of the heating section during sintering can be controlled to be 0.5°C / min, 1.0°C / min, 1.2°C / min, 1.5°C / min, 1.8°C / min, 2.0°C / min, 2.5°C / min, or 3.0°C / min. Of course, it can also be other values within the above range, which are not limited herein. By controlling the heating rate of the heating section within the above range, more sufficient lithium intercalation and more sufficient grain nucleation can be achieved through slow heating. Specifically, the heat preservation time during sintering can be 8h, 8.5h, 9.0h, 10h, 10.5h, 11h, 12h, 13h, 14h, 15h, or 16h. Of course, it can also be other values within the above range, which are not limited herein. When the heat preservation time during sintering is within the above range, the grain growth is more sufficient, and there is less grain agglomeration in the obtained cathode material. As an embodiment of the present invention, the sintered product is subjected to air flow pulverization and then coating treatment, and the median volume distribution particle size D50 of the pulverized sintered product is controlled to be 3.0μm to 5.0μm. Specifically, the matrix can be pulverized to D50 of 3.0μm, 3.5μm, 3.8μm, 4.0μm, 4.5μm, or 5.0μm. Of course, it can also be other values within the above range, which are not limited herein. The particle size D50 of the air flow pulverization of the matrix is controlled within the above range, and this particle size range corresponds to the particle size range of the pulverized oxide precursor, ensuring a good pulverization effect.

[0067] As an embodiment of the present invention, the coating agent used for the coating treatment is selected from at least one of ZrO2, TiO2, Al2O3, CoO, MgO, WO3, CeO2, and Y2O3.

[0068] In a third aspect, the present invention also provides a lithium-ion battery, which includes the positive electrode material of the present invention or the positive electrode material obtained by the preparation method of the present invention.

[0069] As an implementation mode of the present application, the present application provides a secondary battery, which includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing. The housing can be a packaging bag obtained by encapsulating with a packaging film (such as an aluminum-plastic film). For example, when the secondary battery is a soft-pack battery. In some other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0070] Figure 5 The schematic diagram of the battery in the discharging state, that is, during the working operation, is shown. As shown in the figure, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120, and a separator 130. The separator is disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly can be a stacked structure, which is formed by alternately laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence. In some other embodiments, the electrode assembly can also be a wound structure, which is formed by laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence and then winding them.

[0071] 〈Positive Electrode Sheet〉

[0072] The positive electrode sheet 110 includes a positive electrode current collector 111 and a positive electrode active layer 112 disposed on at least one surface of the positive electrode current collector. The positive electrode current collector can use aluminum foil, nickel foil, etc., or can also be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes the positive electrode material provided by the present invention or the positive electrode material obtained by the preparation method of the present invention.

[0073] 〈Negative Electrode Sheet〉

[0074] The negative electrode sheet 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can use at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, etc., or can also be a composite current collector disclosed in any 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.

[0075] During battery operation, i.e., when the battery is in a discharging state, metal ions 140 (such as lithium ions) in the negative electrode escape from the lattice of the negative electrode material, pass through the electrolyte / electrolyte across the separator 130, and are embedded into the lattice of the positive electrode material. Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to escape from the lattice of the positive electrode material, pass through the electrolyte / electrolyte across the separator, and move to the negative electrode; at the same time, a reduction reaction occurs in the negative electrode material, causing metal ions to be embedded into the lattice of the negative electrode material. As the metal ions reciprocate between the positive electrode and the negative electrode, the battery can achieve the discharging and charging processes in thousands of cycles.

[0076] In some embodiments, the silicon-based material in the negative electrode material may include at least one of amorphous silicon, crystalline silicon, silicon oxide, and silicate.

[0077] In some embodiments, the silicon-based material includes silicon oxide, the silicon oxide includes silicon element and oxygen element, and the atomic ratio of silicon element to oxygen element is 0 to 2, and 0 is not included.

[0078] In some embodiments, the silicon-based material includes silicon oxide, and the chemical general formula of the silicon oxide is SiOx, where 0 < x ≤ 2. Specifically, SiOx may specifically be SiO 0.5 、SiO 0.7 、SiO 0.9 、SiO、SiO 1.2 、SiO 1.5 、SiO 1.8 、SiO 1.9 etc., which are not limited herein. The silicon oxide can be represented by the general formula SiOx (0 < x ≤ 2). It can be a material formed by silicon dispersed in SiO2; or it can be a material with a tetrahedral structural unit, where the silicon atom is located at the center of the tetrahedral structural unit, and oxygen atoms and / or silicon atoms are located at the four vertices of the tetrahedral structural unit.

[0079] In some embodiments, the graphite-based material in the negative electrode material may include at least one of natural graphite, artificial graphite, expanded graphite, and oxidized graphite.

[0080] In some embodiments, the negative electrode material includes a carbon material, and the carbon material includes at least one of amorphous carbon and graphitized carbon.

[0081] Specific examples and comparative examples

[0082] Example 1

[0083] This example provides a positive electrode material, and the preparation process is as follows:

[0084] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a K chloride solution to the nitrate solution to prepare a precursor solution. The mass ratio content of K element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and K in the precursor solution is 5 mol / L;

[0085] (2) Spray the precursor solution and then perform annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 550 Kpa, the pyrolysis temperature is 500 °C, and the annealing treatment temperature is 1000 °C;

[0086] (3) Crush the oxide precursor. The median diameter D50 of the volume distribution particle size of the crushed oxide precursor is 3.24 μm; Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0087] (4) Crush the sintered product to obtain a crushed material. The median diameter D50 of the volume distribution particle size of the crushed material is 4.2 μm; Mix 300 g of the crushed material with 0.5 g of WO3 and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain a cathode material.

[0088] Example 2

[0089] This example provides a cathode material, and the preparation process is as follows:

[0090] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 60:10:30. Add a Mg sulfate solution to the nitrate solution to prepare a precursor solution. The mass ratio content of Mg element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and Mg in the precursor solution is 5 mol / L;

[0091] (2) Spray pyrolysis includes spraying the precursor solution and then performing annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 220 m 3 / h, the atomizing pressure is 500 Kpa, the pyrolysis temperature is 600 °C, and the annealing treatment temperature is 900 °C;

[0092] (3)Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.16 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter in an oxygen atmosphere at 950 °C. The heating rate in the heating section of the sintering is controlled at 3 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product.

[0093] (4)Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 4.5 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter in an oxygen atmosphere at 550 °C for 8 h to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0094] Example 3

[0095] This example provides a cathode material, and the preparation process is as follows:

[0096] (1)Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a Ca chloride solution to the nitrate solution to make a precursor solution. The mass ratio content of Ca element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and Ca in the precursor solution is 5 mol / L.

[0097] (2)Spray pyrolysis includes spraying the precursor solution and then performing an annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spraying treatment is 180 m 3 / h, the atomizing pressure is 600 Kpa, the pyrolysis temperature is 800 °C, and the annealing treatment temperature is 1100 °C.

[0098] (3)Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.36 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter in a compressed air atmosphere at 960 °C. The heating rate in the heating section of the sintering is controlled at 1 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product.

[0099] (4)Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the sintered material is 4.8 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter in an oxygen atmosphere at 550 °C for 8 h to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0100] Example 4

[0101] This example provides a cathode material, and the preparation process is as follows:

[0102] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a barium chloride solution to the nitrate solution to make a precursor solution. The mass ratio content of barium element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and Ba in the precursor solution is 5 mol / L;

[0103] (2) Spray the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 500 Kpa, the pyrolysis temperature is 800 °C, and the annealing treatment temperature is 1000 °C;

[0104] (3) Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.05 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 1 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0105] (4) Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 3.5 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain a cathode material.

[0106] Example 5

[0107] This example provides a cathode material, and the preparation process is as follows:

[0108] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a strontium nitrate solution to the nitrate solution to make a precursor solution. The mass ratio content of strontium element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and Sr in the precursor solution is 5 mol / L;

[0109] (2) Spray the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 150 m 3 / h, the atomizing pressure is 650 Kpa, the pyrolysis temperature is 700 °C, and the annealing treatment temperature is 800 °C;

[0110] (3) Crush the oxide precursor, and the median volume distribution particle size D50 of the crushed oxide precursor is 3.50 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0111] (4) Crush the sintered product to obtain a crushed material, and the median volume distribution particle size D50 of the crushed material is 4.2 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0112] Example 6

[0113] This example provides a cathode material, and the preparation process is as follows:

[0114] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a chloride solution of K and a chloride solution of Mg to the nitrate solution respectively to prepare a precursor solution. The mass ratio content of K element and Mg element in the precursor solution is 0.02% each, and the total concentration of Ni, Co, Mn, K, and Mg in the precursor solution is 5 mol / L;

[0115] (2) Spray the precursor solution, and then perform annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 550 Kpa, the pyrolysis temperature is 900 °C, and the annealing treatment temperature is 1000 °C;

[0116] (3) Crush the oxide precursor, and the median volume distribution particle size D50 of the crushed oxide precursor is 3.28 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 3 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0117] (4) Crush the sintered product to obtain a crushed material, and the median volume distribution particle size D50 of the crushed material is 4.0 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0118] Example 7

[0119] This embodiment provides a cathode material, and the preparation process is as follows:

[0120] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a sulfate solution of K and a nitrate solution of Ca to the nitrate solution respectively to make a precursor solution. The mass ratio content of K element and Ca element in the precursor solution is 0.02% each, and the total concentration of Ni, Co, Mn, K, and Ca in the precursor solution is 5 mol / L;

[0121] (2) Spray-treat the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 240 m 3 / h, the atomizing pressure is 450 Kpa, the pyrolysis temperature is 600 °C, and the annealing treatment temperature is 950 °C;

[0122] (3) Crush the oxide precursor, and the median volume distribution particle size D50 of the crushed oxide precursor is 2.96 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0123] (4) Crush the sintered product to obtain a crushed material, and the median volume distribution particle size D50 of the crushed material is 4.7 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0124] Example 8

[0125] This embodiment provides a cathode material, and the preparation process is as follows:

[0126] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a chloride solution of K and a chloride solution of Ba to the nitrate solution respectively to make a precursor solution. The mass ratio content of K element and Ba element in the precursor solution is 0.02% each, and the total concentration of Ni, Co, Mn, K, and Ba in the precursor solution is 5 mol / L;

[0127] (2) Spray-treat the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 600 Kpa, the pyrolysis temperature is 700 °C, and the annealing treatment temperature is 1000 °C;

[0128] (3) Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.10 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 1.5 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product.

[0129] (4) Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 3.7 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the positive electrode material.

[0130] Example 9

[0131] This example provides a positive electrode material, and the preparation process is as follows:

[0132] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a chloride solution of K and a chloride solution of Sr to the nitrate solution respectively to prepare a precursor solution. The mass ratio content of K element and Sr element in the precursor solution is 0.02% each, and the total concentration of Ni, Co, Mn, K, and Sr in the precursor solution is 5 mol / L.

[0133] (2) Spray the precursor solution, and then perform annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 180 m 3 / h, the atomizing pressure is 500 Kpa, the pyrolysis temperature is 650 °C, and the annealing treatment temperature is 1000 °C.

[0134] (3) Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.25 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 0.5 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product.

[0135] (4) Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 4.3 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the positive electrode material.

[0136] Example 10

[0137] This embodiment provides a cathode material, and the preparation process is as follows:

[0138] (1) Take metal salts of Ni, Co, and Mn, and prepare a chloride solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a magnesium chloride solution and a calcium chloride solution to the chloride solution respectively to make a precursor solution. The mass ratio content of Mg element and Ca element in the precursor solution is 0.03% each, and the total concentration of Ni, Co, Mn, Mg, and Ca in the precursor solution is 5 mol / L;

[0139] (2) Spray the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 580 Kpa, the pyrolysis temperature is 700 °C, and the annealing treatment temperature is 1000 °C;

[0140] (3) Crush the oxide precursor, and the median value D50 of the volume distribution particle size of the crushed oxide precursor is 3.75 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 1.5 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0141] (4) Crush the sintered product to obtain a crushed material, and the median value D50 of the volume distribution particle size of the crushed material is 4.8 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0142] Example 11

[0143] This embodiment provides a cathode material, and the preparation process is as follows:

[0144] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a magnesium nitrate solution and a barium nitrate solution to the nitrate solution respectively to make a precursor solution. The mass ratio content of Mg element and Ba element in the precursor solution is 0.03% each, and the total concentration of Ni, Co, Mn, Mg, and Ba in the precursor solution is 5 mol / L;

[0145] (2) Spray the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 150 m 3 / h, the atomization pressure is 550 Kpa, the pyrolysis temperature is 800 °C, and the annealing temperature is 1000 °C;

[0146] (3) Crush the oxide precursor, and the median volume distribution particle size D50 of the crushed oxide precursor is 3.21 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 1 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0147] (4) Crush the sintered product to obtain a crushed material, and the median volume distribution particle size D50 of the crushed material is 4.1 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0148] Example 12

[0149] This example provides a cathode material, and the preparation process is as follows:

[0150] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a chloride solution of Mg and a chloride solution of Sr to the nitrate solution respectively to prepare a precursor solution. The mass ratio content of Mg element and Sr element in the precursor solution is 0.03% each, and the total concentration of Ni, Co, Mn, Mg, and Sr in the precursor solution is 5 mol / L;

[0151] (2) Spray the precursor solution, and then perform annealing treatment to prepare an oxide precursor. Among them, the atomization air flow rate of the spray treatment is 120 m 3 / h, the atomization pressure is 700 Kpa, the pyrolysis temperature is 900 °C, and the annealing temperature is 1000 °C;

[0152] (3) Crush the oxide precursor, and the median volume distribution particle size D50 of the crushed oxide precursor is 3.19 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 3 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0153] (4) The sintered product was pulverized to obtain a pulverized material, and the median value D50 of the volume distribution particle size of the pulverized material was 4.2 μm; 300 g of the pulverized material was mixed with 0.5 g of WO3 and sintered at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material, and the sintered material was sieved to remove magnetism to obtain the cathode material.

[0154] Example 13

[0155] This example provides a cathode material, and the preparation process is as follows:

[0156] (1) Metal salts of Ni, Co, and Mn were taken and formulated into a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. A chloride solution of Ca and a chloride solution of Ba were respectively added to the nitrate solution to prepare a precursor solution. The mass ratio content of Ca element and Ba element in the precursor solution was both 0.03%, and the total concentration of Ni, Co, Mn, Ca, and Ba in the precursor solution was 5 mol / L;

[0157] (2) The precursor solution was subjected to spray treatment and then annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment was 200 m 3 / h, the atomizing pressure was 600 Kpa, the pyrolysis temperature was 600 °C, and the annealing treatment temperature was 1000 °C;

[0158] (3) The oxide precursor was pulverized, and the median value D50 of the volume distribution particle size of the pulverized oxide precursor was 3.38 μm; 400 g of the pulverized oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2 were uniformly mixed and sintered at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering was controlled at 3 °C / min, and the holding time of the sintering was 8 h to obtain a sintered product;

[0159] (4) The sintered product was pulverized to obtain a pulverized material, and the median value D50 of the volume distribution particle size of the pulverized material was 4.2 μm; 300 g of the pulverized material was mixed with 0.5 g of WO3 and sintered at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material, and the sintered material was sieved to remove magnetism to obtain the cathode material.

[0160] Example 14

[0161] This example provides a cathode material, and the preparation process is as follows:

[0162] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add nitrate solutions of Ca and Sr to the nitrate solution respectively to make a precursor solution. The mass ratio content of Ca element and Sr element in the precursor solution is 0.03% each, and the total concentration of Ni, Co, Mn, Ca, and Sr in the precursor solution is 5 mol / L;

[0163] (2) Spray-treat the precursor solution and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 600 Kpa, the pyrolysis temperature is 1000 °C, and the annealing treatment temperature is 1000 °C;

[0164] (3) Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.48 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0165] (4) Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 4.4 μm; mix 300 g of the crushed material with 0.5 g of WO3 and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is screened and demagnetized to obtain a cathode material.

[0166] Example 15

[0167] This example provides a cathode material, and the preparation process is as follows:

[0168] (1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add chloride solutions of Ba and Sr to the nitrate solution respectively to make a precursor solution. The mass ratio content of Ba element and Sr element in the precursor solution is 0.03% each, and the total concentration of Ni, Co, Mn, Ba, and Sr in the precursor solution is 5 mol / L;

[0169] (2) Spray-treat the precursor solution and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 550 Kpa, the pyrolysis temperature is 600 °C, and the annealing treatment temperature is 1200 °C;

[0170] (3)Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.52 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0171] (4)Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 4.7 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0172] Example 16

[0173] This example provides a cathode material, and the preparation process is as follows:

[0174] (1)Take metal salts of Ni, Co, and Al, and prepare a nitrate solution according to the molar ratio of Ni:Co:Al = 55:12:33. Add a K chloride solution to the nitrate solution to make a precursor solution. The mass ratio content of K element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Al, and K in the precursor solution is 5 mol / L;

[0175] (2)Perform spray treatment on the precursor solution, and then perform annealing treatment to make an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 550 Kpa, the pyrolysis temperature is 500 °C, and the annealing treatment temperature is 1000 °C;

[0176] (3)Crush the oxide precursor. The median volume distribution particle size D50 of the crushed oxide precursor is 3.19 μm. Uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0177] (4)Crush the sintered product to obtain a crushed material. The median volume distribution particle size D50 of the crushed material is 4.4 μm. Mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0178] Example 17

[0179] This example provides a cathode material, and the preparation process is as follows:

[0180] (1)Take metal salts of Ni, Co, and Mn and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a K chloride solution to the nitrate solution to prepare a precursor solution. The mass ratio content of K element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and K in the precursor solution is 5 mol / L;

[0181] (2)Spray the precursor solution, and then perform annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 200 m 3 / h, the atomizing pressure is 550 Kpa, the pyrolysis temperature is 500 °C, and the annealing treatment temperature is 1000 °C;

[0182] (3)Crush the oxide precursor. The median diameter D50 of the volume distribution particle size of the crushed oxide precursor is 3.20 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in a compressed air atmosphere. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the heat preservation time of the sintering is 8 h to obtain a sintered product.

[0183] Example 18

[0184] The difference between this example and Example 1 is that the metal salts of Ni, Co, and Mn are prepared into a nitrate solution according to the molar ratio of Ni:Co:Mn = 70:10:20, and the mass ratio content of K element in the precursor solution is 0.04%; the atomizing air flow rate of the spray treatment is 100 m 3 / h, the atomizing pressure is 700 Kpa, the pyrolysis temperature is 400 °C, and the annealing treatment temperature is 1200 °C. Other steps are the same as those in Example 1.

[0185] Example 19

[0186] The difference between this example and Example 1 is that the metal salts of Ni, Co, and Mn are prepared into a nitrate solution according to the molar ratio of Ni:Co:Mn = 80:10:10; the atomizing air flow rate of the spray treatment is 300 m 3 / h, the atomizing pressure is 400 Kpa, the pyrolysis temperature is 1000 °C, and the annealing treatment temperature is 500 °C. Other steps are the same as those in Example 1.

[0187] Example 20

[0188] The difference between this example and Example 1 is that the metal salts of Ni, Co, and Mn are prepared into a nitrate solution according to the molar ratio of Ni:Co:Mn = 90:5:5; other steps are the same as those in Example 1.

[0189] Comparative Example 1

[0190] This comparative example provides a cathode material, which is obtained by the following preparation method:

[0191] (1) Synthesize a hydroxide precursor with a molar ratio of Ni:Co:Mn = 55:12:33 by the co-precipitation method;

[0192] (2) Crush the oxide precursor and control the D50 of the crushing to be 3.24 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C for 8 h in a compressed air atmosphere to obtain a sintered product.

[0193] The obtained sintered product is crushed, and the crushing particle size D50 is 4.2 μm to obtain a crushed material; 300 g of the crushed material is mixed with 0.5 g of WO3, and sintered at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material, and the sintered material is sieved and demagnetized to obtain the cathode material.

[0194] Comparative Example 2

[0195] This comparative example provides a cathode material, which is obtained by the following preparation method:

[0196] (1) Synthesize a hydroxide precursor with a molar ratio of Ni:Co:Mn = 55:12:33 by the co-precipitation method;

[0197] (2) Crush the oxide precursor and control the D50 of the crushing to be 3.16 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, 1.8 g of CeO2, 0.1 g of MgO, and 0.1 g of KOH, and sinter at 960 °C for 8 h in a compressed air atmosphere to obtain a sintered product.

[0198] The obtained sintered product is crushed, and the crushing particle size D50 is 4.5 μm to obtain a crushed material; 300 g of the crushed material is mixed with 0.5 g of WO3, and sintered at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material, and the sintered material is sieved and demagnetized to obtain the cathode material.

[0199] Comparative Example 3

[0200] This comparative example provides a cathode material, which is obtained by the following preparation method:

[0201] (1) Take pure metal salts of Ni, Co, and Mn, and prepare a ternary nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33, and make an oxide precursor by spray pyrolysis;

[0202] (2) Crush the oxide precursor and control the D50 of the crushing to be 3.48 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C for 8 h in an atmosphere of compressed air to obtain a sintered product.

[0203] Crush the obtained sintered product, with the crushing particle size D50 being 4.1 μm, to obtain a crushed material; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0204] Comparative Example 4

[0205] 1) Take metal salts of Ni, Co, and Mn, and prepare a nitrate solution according to the molar ratio of Ni:Co:Mn = 55:12:33. Add a K chloride solution to the nitrate solution to prepare a precursor solution. The mass ratio content of K element in the precursor solution is 0.01%, and the total concentration of Ni, Co, Mn, and K in the precursor solution is 5 mol / L;

[0206] (2) Spray the precursor solution, and then perform annealing treatment to prepare an oxide precursor. Among them, the atomizing air flow rate of the spray treatment is 80 m 3 / h, the atomizing pressure is 900 Kpa, the pyrolysis temperature is 1000 °C, and the annealing treatment temperature is 700 °C;

[0207] (3) Crush the oxide precursor, and the median value D50 of the volume distribution particle size of the crushed oxide precursor is 3.24 μm; uniformly mix 400 g of the crushed oxide precursor, 186.72 g of lithium carbonate, and 1.8 g of CeO2, and sinter at 960 °C in an atmosphere of compressed air. The heating rate in the heating section of the sintering is controlled at 2 °C / min, and the holding time of the sintering is 8 h to obtain a sintered product;

[0208] (4) Crush the sintered product to obtain a crushed material, and the median value D50 of the volume distribution particle size of the crushed material is 4.2 μm; mix 300 g of the crushed material with 0.5 g of WO3, and sinter at 550 °C for 8 h in an oxygen atmosphere to obtain a sintered material. The sintered material is sieved and demagnetized to obtain the cathode material.

[0209] Test method:

[0210] The test method for the average concentration X1 of element M in the central region and the average concentration X2 in the surface region of the grains of the positive electrode material is as follows: Use a Hitachi ion cutting instrument to prepare a cross-section sample, select a suitable cross-section field of view with a Hitachi S4800 scanning electron microscope, and then use EDS to perform line scanning or point scanning on the grain cross-section within a 5k field of view. For example, the point scanning method can be adopted to measure the content of element M at 10 positions (generally at least 5 points) in the central region of the grain cross-section, and after summing and averaging the content of element M, X1 is obtained; measure the content of element M at 10 positions in the surface region of the grain cross-section, and after summing and averaging the content of element M, X2 is obtained. As Figure 1 shown, in the grain cross-section view, the radius of the grain is L, the region from the center of the grain to a distance of L / 2 from the center of the grain is the central region, and the region from the position of L / 2 of the grain to the grain surface is the surface region. When the positive electrode material contains two or more elements M, the X1 and X2 of each element M are measured separately, and the X2 / X1 value of the corresponding element is calculated accordingly.

[0211] For point scanning and line scanning, the combination is Figure 6 explained as follows:

[0212] Point scanning: Select 5 - 10 points within the central region (inside the red circle shown in Figure 6 ) for EDS measurement, and after measurement, take the average value to obtain the X1 value; select 5 - 10 points within the surface region (outside the red circle shown in Figure 6 ) for EDS measurement, and after measurement, take the average value to obtain the X2 value.

[0213] Line scanning: Randomly select at least three line positions within the central region (that is, inside the red circle shown in Figure 6 ) for line scanning, and after measurement, take the average value to obtain the X1 value; randomly select at least three line positions within the surface region (that is, outside the red circle shown in Figure 6 ) for line scanning, and after measurement, take the average value to obtain the X2 value. In actual testing, point scanning and line scanning can also be used in combination.

[0214] The test method for the content of each element contained in the positive electrode material: Take 0.3 g of the positive electrode material sample to be tested, dissolve it with aqua regia, cool and make the volume constant to 100 ml to prepare a determination mother liquor; take 1 mL of the determination mother liquor, dilute it 100 times and then test the content of the main elements Li, Ni, Co, Mn, Al and the content of other elements such as element M. The determination is all carried out with an Agilent 5110 ICP - OES detection device.

[0215] Test method for the magnitude of microstrain ε: The test was carried out using a Rigaku XRD diffractometer in Japan within the range of 10° - 70° at a rate of 1° / min with a step size of 0.005°; then the obtained XRD images were subjected to Rietveld refinement through GASA to obtain information such as the unit cell parameters and peak shape parameters of the sample, and the magnitude of the strain was calculated based on the obtained peak shape parameters according to the Scherrer formula; among them, the unit cell volume after doping with element M was compared with the unit cell volume without doping with element M. If the unit cell volume becomes smaller after doping with element M, it indicates that compressive strain is introduced into the lattice (represented by a negative number), otherwise it is tensile strain; the test results of the magnitude of the strain are shown in Table 3.

[0216] Test method for specific surface area S: The specific surface area was tested using a Micromeritics instrument in the United States after degassing at 300 °C in vacuum for 1 h.

[0217] Test method for tapped density ρ1: The tapped density was tested using a BETTER BT - 303 in Dandong with a vibration frequency of 3000 times / min, a vibration time of 1 min, and a vibration amplitude of 3 mm ± 0.1 mm.

[0218] Test method for powder compacted density ρ2: The powder compacted density was tested using a compacted density tester with a pressure of 6 t for 30 s.

[0219] The volume particle size of the cathode material was tested using a Malvern laser particle size analyzer MS 3000.

[0220] The calculation formula for the volume particle size distribution width Span value is: Span value = (D90 - D10) / D50.

[0221] The surface morphology, particle size, etc. of the sample were observed using a Hitachi S4800 scanning electron microscope.

[0222] The following methods were used to test the electrochemical performance of the cathode materials provided in the above examples and comparative examples respectively.

[0223] First, the cathode materials provided in each example and comparative example were mixed with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 80:10:10, then NMP (N - methylpyrrolidone) was added to make a uniform slurry, which was coated on a copper foil, dried in an oven, and then cut into circular electrodes with a diameter of 14 mm after rolling under a pressure of 10 Mpa.

[0224] Lithium - ion batteries were assembled according to the industrial CR2025 type button battery. The separator was a Cellgard separator, and the electrolyte was a 1 mol / L LiPF6 solution with a solvent of EC / PC / DEC, and the counter electrode was a lithium sheet.

[0225] The entire assembly process of the lithium-ion battery is carried out in a glove box filled with argon, and the oxygen content and moisture content in the glove box are both controlled below 0.5 ppm.

[0226] The test conditions for the lithium-ion battery are: the temperature is 25°C ± 1°C.

[0227] The lithium-ion battery was tested for its electrochemical cycling performance, capacity, and initial efficiency (first efficiency). Among them, the voltage range for charge and discharge cycling is 2.8V - 4.35V, the current magnitude is 0.1C (20mAh / g), and the cycling test is carried out at 0.5C charge and 1C discharge for 50 cycles. The capacity unit is mAh / g, and the initial efficiency unit is %.

[0228] The test results of the average concentration X1 and average concentration X2 of element M in the cathode materials provided by the above examples and comparative examples are shown in Table 1.

[0229]

[0230] The X2 / X1 values of element M in the cathode materials provided by the above examples and comparative examples are shown in Table 2 below. The contents of element M and element N2 in the cathode materials provided by the above examples and comparative examples were also tested, and the specific test result data are shown in Table 2.

[0231]

[0232] The physical and chemical property test results of the cathode materials provided by the above examples and comparative examples are shown in Table 3 below.

[0233]

[0234] The electrochemical property test results of the cathode materials provided by the above examples and comparative examples are shown in Table 4.

[0235]

[0236] In Examples 1 - 20 of the present invention, a variety of different elements M were respectively used to control different X1 and X2 values of element M and different X2 / X1 values within the range of 1.2 ≤ X2 / X1 ≤ 20. It can be seen from the above examples that for the cathode material provided by the present invention, by doping element M in the cathode material and making the concentration of element M in the surface layer region of the cathode material grains greater than that in the internal region, the lattice expansion during charge and discharge is inhibited, and the purpose of improving the long-term cycling performance is achieved. In Comparative Example 1, the precursor was prepared by co-precipitation, and no M element was used for doping, and its capacity and initial efficiency were significantly weaker. In Comparative Example 2, the precursor prepared by the co-precipitation method was used, and K element was simultaneously used for doping, and the value of X2 / X1 was significantly less than 1.2, and at the same time combined with Figure 3It can be seen that the distribution of K element is relatively uniform, the concentration difference between the surface region and the internal region is small, and its capacity and initial efficiency are significantly poor. In Comparative Example 3, the precursor was prepared by spray pyrolysis, but M element was not used for doping, and its capacity and initial efficiency were significantly weak. In Comparative Example 4, the precursor was prepared by spray pyrolysis, and M element was used for doping. The X2 / X1 of the prepared cathode material was greater than 20, indicating that M element was enriched in the surface region of the crystal grains. At the same time, its cycle stability was weak. The inventor speculated that due to the excessive element concentration difference between the surface region and the inner region, the compressive stress was too large. During the cycling process, cracks were more likely to form in the crystal grains, thus reducing the cycle stability.

[0237] From Table 2 and in combination with Figure 2 , it can be seen that there is an obvious concentration difference between the surface region and the internal region of the K element in Examples 1, 6, and 7. The X1 / X2 satisfies the value range of 1.2 ≤ X2 / X1 ≤ 20. In Comparative Example 2, the distribution of the K element is relatively uniform, and the concentration difference between the surface region and the internal region is small. Combining with Table 4, it can be seen that compared with Comparative Example 2, the capacity and initial efficiency of the lithium batteries made of the cathode materials in Examples 1, 6, and 7 have been significantly improved, and the electrochemical cycling performance has also been significantly improved. The internal cracks of the cathode materials provided in Example 6 and Comparative Example 2 were also compared. The specific comparison figure is shown in Figure 4 . Figure 4 As can be seen in

[0238] , in Comparative Example 2, the grain section shows that there are multiple cracks inside the grains, specifically at the positions marked by the white circles in the figure, indicating that Example 6 generates fewer microcracks, which is beneficial to improving the gas generation performance and is beneficial to long-term cycling.

[0238] As can be seen from Table 3, the lattice strain ε of the cathode material of the present invention is less than 0.1%. The cathode material with this strain has fewer internal microcracks and a high long-term cycle capacity retention rate. The specific surface area S of the cathode material is in the range of 0.4 m 2 / g to 0.9 m 2 / g, indicating that the surface coating of the cathode material is uniform and the discharge capacity is high. The tapped density ρ1 of the cathode material is > 2.0 g / cm 3 , the tapped density is high, the compaction of the electrode sheet is higher, and the energy density is higher. The compression density ρ2 of the cathode material is ≥ 2.8 g / cm 3 , the powder compression density is high, the compaction of the electrode sheet is higher, and the energy density is also higher. The volume particle size distribution width Span value of the cathode material: 1.5 ≥ Span value ≥ 1.0; the cathode material satisfying this particle size distribution has higher electrode sheet compaction, and thus higher energy density.

[0239] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent transformation made using the content of the specification of the present invention, directly or indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A cathode material, characterized in that, The chemical formula of the positive electrode material is: Li a Ni b Co c N1 d M (1-b-c-d-e) N2 e O2, where: 0.95 ≤ a ≤ 1.2, 0 < b ≤ 1, 0 < c ≤ 1, 0 < d ≤ 1, 0 ≤ e < 1, and b + c + d + e < 1; the element M is selected from at least one element in Group IA or Group IIA of the periodic table; the element N1 is selected from at least one of Mn or Al, and the element N2 is selected from at least one of Zr, Ti, Al, Co, W, Ce, Y; The positive electrode material includes a plurality of crystal grains. The cross-section of the crystal grain includes a central region and a surface layer region. The radius of the crystal grain is L. The region from the center of the crystal grain to a distance of L / 2 from the center of the crystal grain is the central region, and the region from the position of L / 2 of the crystal grain to the surface of the crystal grain is the surface layer region. By performing an EDS test on the cross-section of the crystal grain, the average concentration of element M in the central region is measured as X1, and the average concentration of element M in the surface layer region is measured as X2. X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 4. In the positive electrode material, X2 is 10 - 400 ppm. The crystal grain includes a matrix and a coating, and the coating at least partially coats the surface of the matrix. The coating is selected from at least one of ZrO2, TiO2, Al2O3, CoO, WO3, CeO2, and Y2O3.

2. The cathode material according to claim 1, wherein The content of element M in the positive electrode material is 10 ppm - 400 ppm; and / or, the content of element N2 in the positive electrode material is 0 ppm - 5000 ppm.

3. The cathode material according to claim 1 or 2, characterized in that, The positive electrode material includes at least one of the following characteristics (a) - (g): (a) The positive electrode material includes at least one crystal grain with the same orientation, and the average particle size of the crystal grain is 1 µm - 5 µm; (b) The lattice strain ε of the positive electrode material is less than 0.1%; (c) The specific surface area S of the positive electrode material is 0.4 m 2 / g to 0.9 m 2 / g; (d) The tap density ρ1 of the positive electrode material > 2.0 g / cm 3 ; (e) The tap density ρ2 of the positive electrode material ≥ 2.8 g / cm 3 ; (f) The Span value of the volume particle size distribution width of the positive electrode material satisfies: 1.5 ≥ Span value ≥ 1.0; (g) The positive electrode material is a single crystal material.

4. The cathode material according to claim 1, characterized in that, Element M is selected from at least one of Na, K, Mg, Ca, Sr, Ba, Sr, Rb, and Cs.

5. The cathode material according to claim 1, wherein X1 is 10 ppm - 400 ppm.

6. The cathode material according to claim 1, characterized in that The value of X2 / X1 is 1.2, 2, 3, 4, or any value between 1.2 - 4.

7. A method for preparing a cathode material as described in any one of claims 1-6, characterized in that, It includes the steps: S1: Mix a mixed salt solution containing Ni element, Co element, and N1 element with a salt solution containing element M to obtain a precursor solution; wherein, element N1 is selected from at least one of Mn or Al; S2: The precursor solution is prepared into an oxide precursor by spray pyrolysis treatment. The spray pyrolysis treatment includes spray treatment and annealing treatment. The atomizing air flow rate of the spray treatment is 100 m 3 / h to 300 m 3 / h, the atomizing pressure is 400 Kpa to 700 Kpa, the pyrolysis temperature is 400 °C to 1000 °C, and the temperature of the annealing treatment is 500 °C to 1200 °C; S3: Mix and sinter the oxide precursor with a lithium source and a metal oxide containing element N2 to obtain a positive electrode material; element N2 is selected from at least one of Zr, Ti, Al, Co, W, Ce, and Y.

8. The preparation method according to claim 7, wherein, The preparation method satisfies at least one of the following conditions: (1) The total concentration of Ni, Co, N1, and M in the precursor solution is 2 mol / L - 8 mol / L; (2) The heating rate in the heating section of the sintering is controlled at 0.5 °C / min - 3 °C / min, and the heat preservation time of the sintering is 8 h - 16 h; (3) The oxide precursor, the lithium source, and the metal oxide containing element N2 are mixed in a mass ratio of 1: (0.4 - 0.8): (0.003 - 0.006).

9. A lithium-ion battery, characterized in that, The lithium ion battery includes the positive electrode material according to any one of claims 1 - 6 or the positive electrode material obtained by the preparation method according to any one of claims 7 - 8.

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