A positive electrode material, a preparation method thereof, a positive electrode sheet, and a lithium ion battery

Abstract

This invention relates to a cathode material and its preparation method, a cathode sheet, and a lithium-ion battery. The cathode material includes Li... 1+ b Ni x Co y Mn z Al w A j O2, where 0≤b≤0.1, 0.5≤x≤1, 0≤y≤0.2, 0≤j≤0.01, x+y+z+w=1; the cell parameter c / a value u of the cathode material satisfies: 4.9555-0.05(x-0.5)-u>0; A includes doping elements Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P or F. This invention achieves thermodynamic metastable structure by directionally controlling the crystal structure of layered cathode materials. Compared to conventional thermodynamically stable cathode materials, it has a smaller c / a, which is beneficial for improving its capacity and rate performance, while also enhancing structural stability and resulting in good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to cathode materials, and more particularly to a cathode material and its preparation method, a cathode sheet, and a lithium-ion battery. Background Technology

[0002] Layered lithium nickel cobalt manganese oxide ternary cathode materials or lithium nickel cobalt manganese aluminum oxide quaternary cathode materials have the advantages of high energy density and good cycle performance, and are widely used in lithium-ion batteries. However, with the increase of nickel content, the inherent defects of layered cathode materials become more and more prominent.

[0003] Firstly, there's the issue of structural stability. High-nickel-content layered cathode materials are prone to transformation from layered structure to spinel or rock salt phases during cycling, leading to capacity decay. Secondly, due to the Ni... 2+ The ionic radius is 0.69 Å and that of Li + The ionic radii are close to 0.76 Å, leading to Ni 2+ Easy to migrate to Li + The layer undergoes cation mixing, hindering lithium-ion diffusion, reducing reversible capacity, and the highly active Ni... 4+ Under high voltage, side reactions such as electrolyte oxidation and decomposition can easily occur, accelerating performance degradation. Furthermore, residual alkaline lithium salts (such as Li₂CO₃ and LiOH) on the material surface can react with the electrolyte, increasing interfacial impedance and potentially generating gas, affecting battery safety and cycle life. The key to improving these issues lies in enhancing the stability of the material's bulk crystal structure and interfacial stability.

[0004] CN120184230A discloses a ternary cathode material, its preparation method, a cathode, and a battery. The ternary cathode material includes a self-supporting microcage structure made of a high-nickel ternary material. The microcage structure has internal cavities, some of which are filled with a conductive agent. These cavities allow for the entry and exit of lithium ions. This structural design effectively suppresses volume expansion or contraction of the high-nickel ternary material during charge and discharge, reducing structural changes and improving the stability of the material, thereby enhancing the battery's cycle performance.

[0005] CN109950534A discloses a Sc-doped modified high-nickel ternary cathode material, belonging to the field of chemical energy storage batteries. The material is obtained by grinding and uniformly mixing a mixture of nickel-cobalt-manganese hydroxide precursor, scandium source, and LiOH·H2O to obtain a solid powder, followed by calcination of the solid powder in an oxygen atmosphere and cooling. After Sc doping modification, the high-nickel ternary cathode material exhibits a stable layered structure, improved lithium-ion and electron migration rates, and increased battery capacity, along with excellent electrochemical activity, rate performance, and cycle stability. The method is simple to operate, and the process and technology are easily industrialized.

[0006] CN107394154A discloses a method for improving the performance of ternary cathode materials, including coating the surface of the ternary cathode material with a molybdenum-sulfur modifier. The molybdenum-sulfur modifier has good cycle stability and a stable structure in the electrolyte, which can prevent the electrolyte from corroding the electrode, prevent the occurrence of side reactions in the electrode, suppress the phenomenon of nickel-lithium mixing in the electrode, reduce the residual lithium content on the electrode surface, stabilize the layered structure of the ternary cathode material, and allow lithium ions to be stably inserted and extracted, thereby improving the cycle stability of the ternary cathode material and ensuring the full utilization of its electrochemical performance.

[0007] Therefore, it is of great significance to provide a cathode material with a stable crystal structure and excellent electrochemical performance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a cathode material, its preparation method, a cathode sheet, and a lithium-ion battery. The present invention achieves thermodynamic metastable structure by directionally controlling the crystal structure of the layered cathode material. Compared to conventional thermodynamically stable cathode materials, it has a smaller c / a ratio, which is beneficial for improving its capacity and rate performance. Simultaneously, structural stability is enhanced, resulting in good cycle performance.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a cathode material, the cathode material comprising Li 1+b Ni x Co y Mn z Al w A jO2, where 0≤b≤0.1, 0.5≤x≤1, 0≤y≤0.2, 0≤j≤0.01, x+y+z+w=1; the value u of the cell parameter c / a of the cathode material satisfies: 4.9555-0.05(x-0.5)-u>0; A includes any one or at least two combinations of doping elements Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P or F.

[0011] In layered cathode materials, the c / a value of the crystal structure tends to decrease gradually with increasing Ni content. This invention uses the standard c / a value of 4.9555 for a transition metal with a Ni content of 50 mol% as a benchmark. By identifying and directionally controlling the crystal structure of the layered cathode material, it achieves a thermodynamically metastable structure. This not only makes the crystal structure of the cathode material closer to that of thermodynamically stable cathode materials with relatively higher nickel content, but also results in a smaller cell parameter c / a. Furthermore, it exhibits capacity and rate performance close to that of cathode materials with relatively high nickel content. Simultaneously, due to the lower actual nickel content, it mitigates the negative impacts of electrolyte oxidation and ion mixing caused by increased nickel content, resulting in superior cycle performance.

[0012] The metastable crystal structure of the cathode material provided by this invention exhibits stronger resistance to the transformation of layered structures into disordered spinel or rock salt phases under high voltage and long-cycle conditions, and can more effectively suppress nickel ions (Ni). 2+ The cation mixing caused by migration to the lithium layer. The cathode material provided by this invention breaks through the limitation of traditional doping or coating which can only fine-tune local performance, and systematically solves the core contradiction between energy density and structural stability of ternary materials without sacrificing energy density.

[0013] Preferably, the value u of the cell parameter c / a of the positive electrode material satisfies: 4.9555-0.05(x-0.5)-u≥0.0011.

[0014] Preferably, the positive electrode material further includes a coating layer, the material of which comprises a compound of any one element selected from Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P or F, or a combination of compounds of at least two elements.

[0015] In a second aspect, the present invention provides a method for preparing the cathode material as described in the first aspect, the method comprising:

[0016] A cathode precursor and a lithium source are mixed and sintered for the first time to obtain a cathode matrix; the cathode matrix and an additive are mixed and sintered for the second time to obtain the cathode material; the temperature of the second sintering is not higher than the temperature of the first sintering; the additive contains Li and a transition metal element, wherein the molar ratio of Li to the total amount of the transition metal element is e:1; the transition metal element includes any one or at least two elements selected from Ni, Co, Mn, or Al, and the molar percentages of Ni, Co, Mn, and Al are f, g, h, and i, respectively, where f+g+h+i=1; in the cathode precursor, based on the total amount of Ni, Co, Mn, and Al, the molar percentages of Ni, Co, Mn, and Al are m, n, p, and q, respectively, where m+n+p+q=1, and m>0.5; the cathode precursor and the additive satisfy f<m.

[0017] This invention uses a cathode precursor with a relatively high nickel content as raw material, mixes it with a lithium source, and performs a first sintering to obtain a cathode matrix with a crystal framework of this high nickel content. In the subsequent second sintering process, it is mixed with an additive with a relatively low nickel content. Since the cathode matrix has already formed a highly ordered crystal structure, the diffusion and migration of Li, Ni, Co, Mn, and Al in the additives face a greater kinetic barrier than in the first sintering. By controlling the temperature of the second sintering to be no higher than that of the first sintering, the diffusion kinetics of the elements in the additives are restricted, and they can only migrate within the crystal framework of the cathode matrix, without changing the crystal structure to reach a thermodynamic equilibrium state. This makes the crystal structure of the final cathode material closer to that of the cathode matrix with a high nickel content, exhibiting thermodynamic metastable state. Furthermore, since the elements in the additives tend to migrate along grain boundaries, surfaces, or crystal defects, the crystal structure of the cathode material is more complete, further improving the structural stability of the cathode material.

[0018] Therefore, this invention, through stepwise sintering and utilizing the kinetic barrier of two-step sintering, creates a non-equilibrium, structurally inherited metastable state. Furthermore, while inheriting the crystal structure characteristics of the substrate with relatively high nickel content, the crystal structure is controlled and optimized to achieve precise orientation design of the macroscopic cell parameters (especially the c / a value) of the cathode material, thus preparing a thermodynamically metastable cathode material. The metastable crystal structure of this cathode material exhibits stronger resistance to the transformation of layered structures into disordered spinel or rock salt phases under high voltage and long-cycle conditions, and can more effectively suppress nickel ion (Ni) ion (Ni...) phase transitions. 2+ The cation mixing caused by migration to the lithium layer. The preparation method provided by this invention breaks through the limitation of traditional doping or coating, which can only fine-tune local performance, and systematically solves the core contradiction between energy density and structural stability of ternary materials without sacrificing energy density.

[0019] This invention achieves directional control of the crystal structure, making the crystal structure of the cathode material closer to that of a thermodynamically stable cathode material with a relatively higher nickel content than its actual nickel content. The cell parameter c / a is smaller, resulting in higher capacity and rate performance. Furthermore, due to the lower actual nickel content, the negative impacts of electrolyte oxidation and decomposition and ion mixing caused by the increase in nickel content are reduced, resulting in better cycle performance.

[0020] Preferably, the ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor to the total molar amount of Li in the lithium source is 1:y, where y = 1~1.1.

[0021] Preferably, the ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor used to prepare the positive electrode substrate to the total molar amount of Ni, Co, Mn and Al in the additive is 1:x, where x = 0.01~0.1.

[0022] Preferably, the content of Mn and Al in the additive satisfies: (h+i)x / (x+1)≤0.05.

[0023] Preferably, the Li content in the additive satisfies: 1≤(y+ex) / (1+x)≤1.1.

[0024] Preferably, the temperature of the first sintering is 700℃~1000℃.

[0025] Preferably, the first sintering time is 6h to 15h.

[0026] Preferably, the second sintering temperature is 650℃~950℃.

[0027] Preferably, the second sintering time is 6h to 15h.

[0028] Preferably, both the first sintering and the second sintering are carried out in an oxygen-containing atmosphere.

[0029] Preferably, the concentration of O2 in the oxygen-containing atmosphere is 20 vol% to 100 vol%.

[0030] Preferably, the preparation method further includes: mixing the positive electrode material with the coating material, and then sintering it to obtain a coating layer on the surface of the positive electrode material; the coating material includes a compound of any one of the elements Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P or F, or a combination of compounds of at least two elements.

[0031] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material as described in the first aspect, or comprising the positive electrode material prepared by the preparation method described in the second aspect.

[0032] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode material as described in the first aspect, or a positive electrode material prepared by the preparation method described in the second aspect, or a positive electrode sheet as described in the third aspect.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) This invention achieves a thermodynamically metastable structure by directionally controlling the crystal structure of the layered cathode material. The crystal structure of the cathode material is closer to that of a thermodynamically stable cathode material with a relatively higher nickel content than its actual nickel content. The cell parameter c / a is smaller, which is beneficial to improving its capacity and rate performance. At the same time, the structural stability is improved, resulting in good cycle performance.

[0035] (2) This invention utilizes the kinetic barrier of two-step sintering to create a non-equilibrium, structurally inherited metastable state, thereby achieving directional control of the crystal structure and preparing a thermodynamically metastable cathode material. The prepared cathode material not only has a crystal structure that is closer to that of a thermodynamically stable cathode material with a relatively higher nickel content than its actual nickel content, but also has the high specific capacity and good rate performance of a cathode material with a relatively higher nickel content, and excellent cycle performance. Attached Figure Description

[0036] Figure 1 These are the XRD patterns of the cathode materials provided in Example 1 and Comparative Example 1.

[0037] Figure 2 This is an enlarged view of the XRD pattern (003) crystal plane of the cathode material provided in Example 1 and Comparative Example 1.

[0038] Figure 3 This is an enlarged view of the XRD pattern (104) crystal plane of the cathode material provided in Example 1 and Comparative Example 1.

[0039] Figure 4 These are the first charge-discharge curves of the cathode materials provided in Example 1 and Comparative Example 1.

[0040] Figure 5 These are the cycle curves of the cathode materials provided in Example 1 and Comparative Example 1. Detailed Implementation

[0041] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0042] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0045] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0046] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0048] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0049] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0050] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0051] In this invention, unless otherwise specified, it is assumed that the experiments are conducted at room temperature or a temperature conventionally set in the art. "Room temperature" generally refers to 4°C to 35°C, and may refer to 20°C ± 5°C. In some embodiments of this invention, room temperature refers to 20°C to 30°C.

[0052] In one specific embodiment, the present invention provides a positive electrode material, the positive electrode material comprising Li 1+ b Ni x Co y Mn z Al w A j O2, where 0 ≤ b ≤ 0.1, for example, it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1; 0.5 ≤ x ≤ 1, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or 1; 0 ≤ y ≤ 0.2, for example, it can be 0, 0.05, 0.1, 0.15, or 0.2; 0 ≤ j ≤ 0.01, for example, it can be 0, 0.002, 0.004, 0.006, 0.008, or 0.01; x + y + z + w =1; the value u of the cell parameter c / a of the cathode material satisfies: 4.9555-0.05(x-0.5)-u>0, for example, u can be 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045, 0.005, 0.0055, 0.006, 0.0065 or 0.007; A includes any one or at least two combinations of doping elements Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P or F.

[0053] In layered cathode materials, the c / a value of the crystal structure tends to decrease gradually with increasing Ni content. This invention uses the standard c / a value of 4.9555 for a transition metal with a Ni content of 50 mol% as a benchmark. By identifying and directionally controlling the crystal structure of the layered cathode material, it achieves a thermodynamically metastable structure. This not only makes the crystal structure of the cathode material closer to that of thermodynamically stable cathode materials with relatively higher nickel content, but also results in a smaller cell parameter c / a. Furthermore, it exhibits capacity and rate performance close to that of cathode materials with relatively high nickel content. Simultaneously, due to the lower actual nickel content, it mitigates the negative impacts of electrolyte oxidation and ion mixing caused by increased nickel content, resulting in superior cycle performance.

[0054] The metastable crystal structure of the cathode material provided by this invention exhibits stronger resistance to the transformation of layered structures into disordered spinel or rock salt phases under high voltage and long-cycle conditions, and can more effectively suppress nickel ions (Ni). 2+ The cation mixing caused by migration to the lithium layer. The cathode material provided by this invention breaks through the limitation of traditional doping or coating which can only fine-tune local performance, and systematically solves the core contradiction between energy density and structural stability of ternary materials without sacrificing energy density.

[0055] In some embodiments, the value u of the cell parameter c / a of the cathode material satisfies: 4.9555-0.05(x-0.5)-u≥0.0011.

[0056] In some embodiments, the cathode material further includes a coating layer, the coating layer being a compound of any one of the elements selected from Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P, or F, or a combination of compounds of at least two elements. The mass of the coating layer is 0.05wt% to 1wt% of the mass of the cathode material, for example, it can be 0.05wt%, 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%.

[0057] In another specific embodiment, the present invention provides a method for preparing the cathode material as described in the foregoing specific embodiment, the method comprising:

[0058] A cathode precursor and a lithium source are mixed and sintered for the first time to obtain a cathode matrix; the cathode matrix is ​​then mixed with an additive and sintered for the second time to obtain the cathode material; the temperature of the second sintering is not higher than the temperature of the first sintering; the additive contains Li and a transition metal element, wherein the molar ratio of Li to the total amount of the transition metal element is e:1; the transition metal element includes any one or at least two elements selected from Ni, Co, Mn, or Al, and the molar percentages of Ni, Co, Mn, and Al are... The molar percentages of Ni, Co, Mn, and Al are f, g, h, and i, respectively, where f + g + h + i = 1; in the positive electrode precursor, the molar percentages of Ni, Co, Mn, and Al, based on the total amount of Ni, Co, Mn, and Al, are m, n, p, and q, respectively, where m + n + p + q = 1, and m > 0.5, for example, 0.505, 0.51, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95; the positive electrode precursor and additives satisfy f < m.

[0059] This invention uses a cathode precursor with a relatively high nickel content as raw material, mixes it with a lithium source, and performs a first sintering to obtain a cathode matrix with a crystal framework of this high nickel content. In the subsequent second sintering process, it is mixed with an additive with a relatively low nickel content. Since the cathode matrix has already formed a highly ordered crystal structure, the diffusion and migration of Li, Ni, Co, Mn, and Al in the additives face a greater kinetic barrier than in the first sintering. By controlling the temperature of the second sintering to be no higher than that of the first sintering, the diffusion kinetics of the elements in the additives are restricted, and they can only migrate within the crystal framework of the cathode matrix, without changing the crystal structure to reach a thermodynamic equilibrium state. This makes the crystal structure of the final cathode material closer to that of the cathode matrix with a high nickel content, exhibiting thermodynamic metastable state. Furthermore, since the elements in the additives tend to migrate along grain boundaries, surfaces, or crystal defects, the crystal structure of the cathode material is more complete, further improving the structural stability of the cathode material.

[0060] Therefore, this invention, through stepwise sintering and utilizing the kinetic barrier of two-step sintering, creates a non-equilibrium, structurally inherited metastable state. Furthermore, while inheriting the crystal structure characteristics of the substrate with relatively high nickel content, the crystal structure is controlled and optimized to achieve precise orientation design of the macroscopic cell parameters (especially the c / a value) of the cathode material, thus preparing a thermodynamically metastable cathode material. The metastable crystal structure of this cathode material exhibits stronger resistance to the transformation of layered structures into disordered spinel or rock salt phases under high voltage and long-cycle conditions, and can more effectively suppress nickel ion (Ni) ion (Ni...) phase transitions. 2+The cation mixing caused by migration to the lithium layer. The preparation method provided by this invention breaks through the limitation of traditional doping or coating, which can only fine-tune local performance, and systematically solves the core contradiction between energy density and structural stability of ternary materials without sacrificing energy density.

[0061] This invention achieves directional control of the crystal structure, making the crystal structure of the cathode material closer to that of a thermodynamically stable cathode material with a relatively higher nickel content than its actual nickel content. The cell parameter c / a is smaller, resulting in higher capacity and rate performance. Furthermore, due to the lower actual nickel content, the negative effects of electrolyte oxidation and decomposition and ion mixing caused by the increase in nickel content are reduced, resulting in better cycle performance.

[0062] In this invention, the positive electrode precursor includes oxides or hydroxides of transition metals, the additives include oxides or acid salts of Li, Ni, Co, Mn and Al, and the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate.

[0063] In some embodiments, the ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor to the total molar amount of Li in the lithium source is 1:y, where y = 1 to 1.1. For example, y can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09 or 1.1.

[0064] In some embodiments, the ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor used to prepare the positive electrode substrate to the total molar amount of Ni, Co, Mn and Al in the additive is 1:x, where x = 0.01 to 0.1. For example, x can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0065] In layered cathode materials, Mn and Al, as capacity-inert elements, are beneficial for maintaining the structural stability of the cathode material, but not for improving capacity. Therefore, if the content of Mn and Al in the additive is too high, it will be detrimental to the improvement of the capacity and rate performance of the cathode material.

[0066] In some embodiments, the content of Mn and Al in the additive satisfies: (h+i)x / (x+1)≤0.05, for example, (h+i)x / (x+1) can be 0.001, 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045 or 0.05.

[0067] In some embodiments, the Li content in the additive satisfies: 1≤(y+ex) / (1+x)≤1.1, for example, (y+ex) / (1+x) can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09 or 1.1.

[0068] In some embodiments, the temperature of the first sintering is 700°C to 1000°C, for example, it can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C or 1000°C.

[0069] In some embodiments, the first sintering time is 6h to 15h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.

[0070] In some embodiments, the second sintering temperature is 650°C to 950°C, for example, it can be 650°C, 700°C, 750°C, 800°C, 850°C, 900°C or 950°C.

[0071] In some embodiments, the second sintering time is 6h to 15h, for example, it can be 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.

[0072] In some embodiments, both the first sintering and the second sintering are carried out in an oxygen-containing atmosphere.

[0073] In some embodiments, the concentration of O2 in the oxygen-containing atmosphere is 20 vol% to 100 vol%, for example, it can be 20 vol%, 30 vol%, 40 vol%, 50 vol%, 60 vol%, 70 vol%, 80 vol%, 90 vol% or 100 vol%.

[0074] In some embodiments, the preparation method further includes: mixing the positive electrode material with a coating material, followed by a third sintering to obtain a coating layer on the surface of the positive electrode material; the coating material includes a compound of any one of the elements Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P, or F, or a combination of compounds of at least two elements.

[0075] In this invention, the coating material may be any one or a combination of at least two of Al2O3, ZrO2, WO3, TiO2, MgO, Nb2O5, ZnO, Fe2O3, La2O3, AlF3, AlPO4, or BPO4. Typical but non-limiting combinations include combinations of Al2O3 and ZrO2, combinations of WO3 and TiO2, combinations of MgO and Nb2O5, combinations of ZnO and Fe2O3, combinations of La2O3 and AlF3, and combinations of AlPO4 and BPO4.

[0076] In some embodiments, the temperature of the third sintering is 250°C to 600°C, for example, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, and the time is 6h to 15h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h.

[0077] In yet another embodiment, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described in one of the preceding embodiments, or comprising the positive electrode material prepared by the preparation method described in another of the preceding embodiments.

[0078] In another specific embodiment, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode material as described in one of the preceding specific embodiments, or comprising a positive electrode material prepared by the preparation method described in another of the preceding specific embodiments, or comprising a positive electrode sheet as described in yet another of the preceding specific embodiments.

[0079] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0080] To better understand the present invention, the following embodiments and comparative examples are provided, and the cell parameters c / a and electrical properties of the cathode materials provided in all embodiments and comparative examples are tested. The test methods are as follows:

[0081] Cell parameter c / a calculation: XRD tests were performed on the cathode materials prepared in all examples and comparative examples. The scanning range was selected as 2θ=0°~90° and the step size was 0.02° to obtain the raw XRD data. Then, the raw XRD data obtained by the test were refined by Rietveld using Fullprof software to obtain the refined cell parameter a value and c value, and c / a was calculated.

[0082] Electrical performance testing:

[0083] (1) Preparation of button half-cell: The positive electrode materials provided in all examples and comparative examples were mixed with acetylene black and polyvinylidene fluoride at a mass ratio of 95:3:2 to prepare a positive electrode sheet, which was then rolled to a compaction density of 3.5 g / cm³. 3 Using lithium foil as the negative electrode, they are assembled into coin cell half-cells.

[0084] (2) Set the charging and discharging voltage range to 3.0V~4.4V, the test temperature to 25℃, and the charging and discharging rate to 0.1C / 0.1C. Test the 0.1C discharge specific capacity of the coin cell.

[0085] (3) Set the charging and discharging voltage to 3.0V~4.4V, the test temperature to 25℃, the charging and discharging rate to 0.1C / 1C, test the 1C discharge specific capacity, and the 1C discharge capacity retention rate = 1C discharge specific capacity / 0.1C discharge specific capacity.

[0086] (4) Set the charge and discharge voltage to 3.0V~4.5V, the test temperature to 45℃, the charge and discharge rate to 1C / 1C, cycle charge and discharge 50 times, and the cycle capacity retention rate = specific capacity of the 50th discharge / specific capacity of the first discharge.

[0087] Example 1

[0088] This embodiment provides a Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode material, wherein the cell parameter c / a of the cathode material has a value of u=4.9436, 4.9555-0.05×(0.651-0.5)-u=0.00435.

[0089] The Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 The surface of the O2 cathode material also includes a coating layer, the coating layer being composed of Al2O3 and TiO2, wherein the mass of Al2O3 is Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 The O2 cathode material is 0.2 wt%, and the mass of TiO2 is equal to that of Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 0.8 wt% of O2 cathode material.

[0090] The Li 1.03 Ni 0.651 Co 0.122 Mn 0.227The preparation methods of O2 cathode materials include:

[0091] (1) According to Ni 0.69 Co 0.08 Mn 0.23 The total molar ratio of Ni, Co, and Mn in the (OH)₂ precursor to the molar ratio of Li in lithium carbonate is 1:1.05. The mixed Ni... 0.69 Co 0.08 Mn 0.23 (OH)2 precursor and lithium carbonate were sintered at 915℃ for 12 hours in an oxygen atmosphere to obtain the positive electrode substrate.

[0092] (2) Using LiNi 0.3 Co 0.5 Mn 0.2 O2 is used as an additive, and the content of Mn in the additive satisfies: (h+i)x / (x+1)=0.0182≤0.05, and the content of Li satisfies: 1≤(y+ex) / (1+x)=1.0455≤1.1. According to Ni... 0.69 Co 0.08 Mn 0.23 The total molar amounts of Ni, Co, and Mn in the (OH)2 precursor, and LiNi 0.3 Co 0.5 Mn 0.2 The total molar ratio of Ni, Co and Mn in the O2 additive is 1:0.1. The positive electrode precursor prepared in step (1) is mixed with LiNi 0.3 Co 0.5 Mn 0.2 O2 additives were mixed and subjected to a second sintering at 880℃ for 10 hours under an oxygen atmosphere to obtain Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode material;

[0093] (3) The Li prepared in step (2) 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode material, with a mass of Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 The O2 cathode material contains 1 wt% Al2O3 and Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 The O2 cathode material was mixed with 0.8 wt% TiO2 and sintered at 500℃ for 8 hours in air atmosphere. The mixture was then subjected to a third sintering process in Li... 1.03Ni 0.651 Co 0.122 Mn 0.227 A coating layer was prepared on the surface of the O2 cathode material.

[0094] Example 2

[0095] This embodiment provides a Li 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 O2 cathode material, wherein the cell parameter c / a of the cathode material has a value of u=4.9468, 4.9555-0.05×(0.651-0.5)-u=0.00113.

[0096] The Li 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 The surface of the O2 cathode material also includes a coating layer, the coating layer being composed of WO3 and ZrO2, wherein the mass of WO3 is Li. 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 The O2 cathode material is 0.1 wt%, and the mass of ZrO2 is equal to that of Li. 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 0.2 wt% of O2 cathode material.

[0097] The Li 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 The preparation methods of O2 cathode materials include:

[0098] (1) According to Ni 0.655 Co 0.12 Mn 0.195 Al 0.03 The total molar ratio of Ni, Co, and Mn in the (OH)₂ precursor to the molar ratio of Li in lithium carbonate is 1:1.05. The mixed Ni... 0.655 Co 0.12 Mn 0.195 Al 0.03 (OH)2 and lithium carbonate were subjected to a first sintering at 700°C for 15 hours under an oxygen atmosphere to obtain the positive electrode substrate.

[0099] (2) Using LiNi 0.3 Co0.5 Mn 0.2 O2 is used as an additive, and the content of Mn in the additive satisfies: (h+i)x / (x+1)=0.0020≤0.05, and the content of Li satisfies: 1≤(y+ex) / (1+x)=1.0495≤1.1. According to Ni... 0.655 Co 0.12 Mn 0.195 Al 0.03 The total molar amounts of Ni, Co, Mn, and Al in the (OH)2 precursor, and LiNi 0.3 Co 0.5 Mn 0.2 The molar ratio of Ni, Co and Mn in the O2 additive is 1:0.01. The positive electrode substrate prepared in step (1) is mixed with LiNi 0.3 Co 0.5 Mn 0.2 O2 additives were mixed and subjected to a second sintering at 700℃ for 6 hours under an oxygen atmosphere to obtain Li. 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 O2 cathode material;

[0100] (3) The Li prepared in step (2) 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 O2 cathode material, with a mass of Li 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 The O2 cathode material contains 0.5 wt% WO3 and Li. 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 The O2 cathode material was mixed with 0.5 wt% ZrO2 and sintered at 450 °C for 15 h in air atmosphere. The mixture was then subjected to a third sintering process in Li. 1.03 Ni 0.651 Co 0.124 Mn 0.195 Al 0.030 A coating layer was prepared on the surface of the O2 cathode material.

[0101] Example 3

[0102] This embodiment provides a Li 1.03 Ni 0.652 Co 0.120 Mn0.228 O2 cathode material, wherein the cell parameter c / a of the cathode material has a value of u=4.9454, 4.9555-0.05×(0.652-0.5)-u=0.00252.

[0103] The Li 1.03 Ni 0.652 Co 0.120 Mn 0.228 The surface of the O2 cathode material also includes a coating layer, the coating layer being made of Al2O3 and La2O3, wherein the mass of Al2O3 is equal to that of Li. 1.03 Ni 0.652 Co 0.120 Mn 0.228 The O2 cathode material is 0.2 wt%, and the mass of La2O3 is equal to that of Li. 1.03 Ni 0.652 Co 0.120 Mn 0.228 0.1 wt% of O2 cathode material.

[0104] The Li 1.03 Ni 0.652 Co 0.120 Mn 0.228 The preparation methods of O2 cathode materials include:

[0105] (1) According to Ni 0.67 Co 0.1 Mn 0.23 The total molar ratio of Ni, Co, and Mn in the (OH)₂ precursor to the molar ratio of Li in lithium carbonate is 1:1.05. The mixed Ni... 0.67 Co 0.1 Mn 0.23 (OH)2 precursor and lithium nitrate were sintered at 1000℃ for 6 hours in an oxygen atmosphere to obtain the positive electrode substrate;

[0106] (2) Using LiNi 0.3 Co 0.5 Mn 0.2 O2 is used as an additive, and the content of Mn in the additive satisfies: (h+i)x / (x+1)=0.0095≤0.05, and the content of Li satisfies: 1≤(y+ex) / (1+x)=1.0476≤1.1. According to Ni... 0.67 Co 0.1 Mn 0.23 The total molar amounts of Ni, Co, and Mn in the (OH)2 precursor, and LiNi 0.3 Co 0.5 Mn 0.2The molar ratio of Ni, Co and Mn in the O2 additive is 1:0.05. The positive electrode substrate prepared in step (1) is mixed with LiNi 0.3 Co 0.5 Mn 0.2 O2 additives were mixed and subjected to a second sintering at 950°C for 7 hours under an oxygen atmosphere to obtain Li. 1.03 Ni 0.652 Co 0.120 Mn 0.228 O2 cathode material;

[0107] (3) The Li prepared in step (2) 1.03 Ni 0.652 Co 0.120 Mn 0.228 O2 cathode material, with a mass of Li 1.03 Ni 0.652 Co 0.120 Mn 0.228 The O2 cathode material contains 2wt% Al2O3 and Li. 1.03 Ni 0.652 Co 0.120 Mn 0.228 The O2 cathode material was mixed with 0.3 wt% La2O3 and subjected to a third sintering at 550°C for 6 hours in air atmosphere. 1.03 Ni 0.652 Co 0.120 Mn 0.228 A coating layer was prepared on the surface of the O2 cathode material.

[0108] Examples 4 to 6

[0109] Examples 4 to 6 each provide a cathode material. Except for the types of cathode precursors and additives added during the second sintering, and the molar ratios of the total amount of transition metals in the cathode precursors and additives, as shown in Table 1, all other aspects are the same as in Example 1. The ratios of Mn and Al content in the additives to the total amount of transition metals in the cathode material, the relationship between the lithium content in the additives, the value of the cell parameter c / a u of the prepared cathode material, and the difference between u and the cell parameter c / a of the thermodynamically stable cathode material with the same ratio, 4.9555-0.05(x-0.5)-u, are shown in Table 2.

[0110] Table 1

[0111]

[0112] Table 2

[0113]

[0114] In Examples 1 to 6, by controlling the content relationship of transition metal elements and lithium elements in the cathode precursor and additives, as well as the addition ratio of precursor to additives, a cathode precursor with a relatively high nickel content was used as raw material. It was mixed with a lithium source for a first sintering to obtain a cathode matrix with a high nickel content crystal framework. Then, it was mixed with an additive with a relatively low nickel content for a second sintering. Utilizing the kinetic barrier of the two-step sintering, Li, Ni, Co, Mn, and Al in the additives tended to migrate based on the crystal framework of the cathode matrix, thereby inheriting the crystal framework of the cathode matrix. This resulted in a cathode material with a crystal structure close to that of a cathode matrix with a relatively high nickel content. The cell parameter c / a value u of the cathode materials provided in Examples 1 to 6 is all smaller than the cell parameter c / a of the thermodynamically stable cathode material with the same ratio, and the difference is all above 0.0011.

[0115] The electrical performance test results of the coin half-cells prepared with the cathode materials provided in Examples 1 to 6 are shown in Table 3. The specific capacity of 0.1C discharge is above 200mAh / g, the capacity retention rate of 1C discharge is above 91.5%, and the capacity retention rate after 50 cycles at 45℃ is above 95.1%.

[0116] Table 3

[0117]

[0118] Examples 7 to 8

[0119] Examples 7 and 8 each provide a cathode material. Except for the type of cathode precursor used to prepare the corresponding cathode material, and the molar ratio of the cathode precursor to the total amount of transition metals in the additive, as shown in Table 4, all other aspects are the same as in Example 1. The ratio of the content of Mn and Al in the additive to the total content of transition metals in the cathode material, the relationship between the content of lithium in the additive, the value of the cell parameter c / a u of the prepared cathode material, and the difference between u and the cell parameter c / a of the thermodynamically stable cathode material with the same ratio, 4.9555-0.05(x-0.5)-u, are shown in Table 5.

[0120] Table 4

[0121]

[0122] Table 5

[0123]

[0124] In Examples 7 and 8, if the type of additive remains unchanged, the molar ratio of transition metal elements in the precursor to transition metal elements in the additive is increased to 1:0.005 or decreased to 1:0.11. Even if the final cathode material has a similar ratio to that in Example 1, the difference between the cell parameter c / a of the cathode material and that of the thermodynamically stable cathode material with the same ratio decreases to below 0.0011, indicating a greater tendency towards thermodynamic stability. This is attributed to the fact that when the amount of additive is too large, it will destroy the relatively stable layered lattice already formed in the cathode matrix during the second sintering process, resulting in local lattice distortion and stress concentration. When the amount of additive is too small, ion migration only occurs in the shallower surface layer, which cannot have a sufficient positive impact on the bulk crystal structure of the material, nor can it eliminate defects in the cathode matrix lattice, thus failing to achieve the expected structural control target.

[0125] As shown in Table 6, the capacity, rate performance, and cycle performance of the cathode materials provided in Examples 7 and 8 all decreased.

[0126] Table 6

[0127]

[0128] Examples 9 to 11

[0129] Examples 9 and 11 each provide a cathode material. Except for the type of cathode precursor used to prepare the corresponding cathode material and the type of additives, as shown in Table 7, they are the same as in Example 1. The ratio of the content of Mn and Al in the additives to the total content of transition metals in the cathode material, the relationship between the content of lithium in the additives, the value of the cell parameter c / a u of the prepared cathode material, and the difference between u and the cell parameter c / a of the thermodynamically stable cathode material with the same ratio, 4.9555-0.05(x-0.5)-u, are shown in Table 8.

[0130] Table 7

[0131]

[0132] Table 8

[0133]

[0134] In Example 9, the content of Mn and Al in the additives accounted for 0.0727% of the total transition metal content in the cathode material, which is higher than 0.05%. Although the diffusion of Mn and Al into the cathode matrix is ​​beneficial to improving the structural stability of the cathode material, the excessive proportion of Mn and Al is not conducive to improving the capacity of the cathode material. According to Table 9, although the cathode material provided in Example 9 has a capacity retention rate of 95.6% after 50 cycles at 45°C, which is comparable to that of Examples 1 to 6, its 0.1C specific capacity can only reach 198.4 mAh / g, and its 1C capacity retention rate is only 91.2%. That is, due to the excessive diffusion of Mn and Al, the rate performance and cycle performance of the cathode material decrease.

[0135] In Example 10, the additives used in the preparation of the cathode material did not contain lithium, resulting in insufficient lithium content in the prepared cathode material. This prevented capacity improvement and caused discontinuous lithium-ion transport, which was detrimental to rate performance and cycle life. In Example 11, the additives used had a high molar ratio of lithium to transition metal elements of 2:1, leading to an excess of Li in the cathode material. This could induce increased cation mixing, decreased kinetic performance, and increased surface alkali residue, causing electrolyte decomposition and gas generation. This, in turn, was detrimental to improving the capacity, rate performance, and cycle life of the cathode material. According to the test results shown in Table 9, the rate performance of the cathode material provided in Example 10 decreased to 91.2%, and the capacity retention rate after 50 cycles at 45°C decreased to 94.5%. The specific capacity of the cathode material in Example 11 was only 196.3 mAh / g, the rate performance decreased to 91.1%, and the capacity retention rate after 50 cycles at 45°C decreased to 94.7%.

[0136] Table 9

[0137]

[0138] Comparative Example 1

[0139] This comparative example provides a Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode material, wherein the preparation method of the cathode material is as follows:

[0140] Ni 0.651 Co 0.122 Mn 0.227 The (OH)₂ precursor and lithium carbonate were mixed uniformly at a molar ratio of 1:1.05 (total amount of all transition metal elements in the precursor to Li in the lithium source). The mixture was then sintered at 915°C for 12 hours under an oxygen atmosphere to obtain Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227O2 cathode material; then Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode material, with a mass of Li 1.03 Ni 0.651 Co 0.122 Mn 0.227 The O2 cathode material contains 1 wt% Al2O3 and Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 The O2 cathode material was mixed with 0.8 wt% TiO2, heated to 500℃ and sintered for 8 hours in air atmosphere, and then sintered in Li. 1.03 Ni 0.651 Co 0.122 Mn 0.227 A coating layer was prepared on the surface of the O2 cathode material.

[0141] The Li prepared in this comparative example 1.03 Ni 0.651 Co 0.122 Mn 0.227 The cell parameter c / a of the O2 cathode material is u = 4.9555 - 0.05 × (0.651 - 0.5) = 4.94795. This is attributed to the fact that in this comparative example, a precursor with the cathode material ratio was directly used as raw material, mixed with a lithium source, and a thermodynamically stable Li with the target ratio was prepared by one-step sintering. 1.03 Ni 0.651 Co 0.122 Mn 0.227 O2 cathode materials do not have the inheritance process of the cathode matrix crystal structure achieved by two-step sintering.

[0142] like Figure 1 The XRD patterns shown correspond to the main diffraction peaks of the cathode materials provided in Example 1 and Comparative Example 1, but according to... Figure 2 and Figure 3 The magnified views of crystal planes (003) and (104) show that the diffraction angle of the cathode material provided in Example 1 is shifted, and both are shifted to larger angles, confirming that the crystal structure of the thermodynamically metastable cathode material provided in Example 1 is different from the crystal structure of the thermodynamically stable cathode material provided in Comparative Example 1.

[0143] As shown in Table 12, the specific capacity of the cathode material provided in Comparative Example 1 is only 198.5 mAh / g. Figure 4It is easy to see from the first charge-discharge curves of Example 1 and Comparative Example 1 that the positive electrode material provided in Comparative Example 1 exhibits voltage polarization earlier, reaching the termination voltage. The capacity retention rate of Comparative Example 1 at 1C is only 91.0%, and the capacity retention rate after 50 cycles at 45°C is only 94.5%. Figure 5 The cycle curves of Example 1 and Comparative Example 1 are shown. The decay trend of Comparative Example 1 is much greater than that of Example 1.

[0144] Comparative Example 2

[0145] This comparative example provides a cathode material. Except for the types of cathode precursors and additives used to prepare the corresponding cathode material, as shown in Table 10, which are different from Example 1, everything else is the same as Example 1. The ratio of the content of Mn and Al in the additives to the total content of transition metals in the cathode material, the relationship between the content of lithium in the additives, the value of the cell parameter c / a u of the prepared cathode material, and the difference between u and the cell parameter c / a of the thermodynamically stable cathode material with the same ratio, 4.9555-0.05(x-0.5)-u, are shown in Table 11.

[0146] Table 10

[0147]

[0148] Table 11

[0149]

[0150] In Comparative Example 2, a cathode matrix with a relatively low nickel content was prepared using a precursor with a relatively low nickel content as raw material. Then, an additive with a relatively high nickel content was sintered with the cathode matrix for the second time. The Li, Ni, Co and Mn in the additive diffused and moved along the framework of the cathode matrix and inherited the crystal structure of the cathode matrix. Although a thermodynamically metastable cathode material was also prepared, the cathode material had a higher c / a ratio than the actual nickel content, that is, it had the crystal structure of a cathode material with a relatively low nickel content, which was not conducive to improving the specific capacity, rate performance and cycle performance of the cathode material.

[0151] As shown in Table 12, the cathode material provided in Comparative Example 2 has a specific capacity of only 198.9 mAh / g, a 1C rate capacity retention rate of only 91.1%, and a capacity retention rate of only 94.6% after 50 cycles at 45°C, which is far inferior to the electrical performance of the cathode materials provided in Examples 1 to 6 of this invention.

[0152] Comparative Example 3

[0153] This comparative example provides a Li 1.03 Ni 0.651 Co 0.122Mn 0.227 The O2 cathode material, in step (2) of the preparation method of the cathode material, the second sintering temperature is 980℃, that is, the second sintering temperature is higher than the first sintering temperature, and the rest is the same as in Example 1.

[0154] Because the second sintering temperature is higher than the first sintering temperature, sufficient energy is provided for the lattice transformation. This causes the additive to diffuse into the cathode precursor lattice while the lattice structure tends to transform towards a thermodynamically stable structure. Therefore, it is impossible to obtain a crystal structure with a relatively high nickel content, i.e., it is impossible to obtain a cathode material with a thermodynamically metastable structure. The Li prepared in this comparative example... 1.03 Ni 0.651 Co 0.122 Mn 0.227 The value of the cell parameter c / a of the O2 cathode material is u = 4.9555 - 0.05 × (0.651 - 0.5) = 4.94795.

[0155] According to the test results shown in Table 12, the capacity of the cathode material provided by Comparative Example 3 is only 198.1 mAh / g, the capacity retention rate at 1C rate is only 91.0%, and the capacity retention rate after 50 cycles at 45℃ is only 94.7%.

[0156] Table 12

[0157]

[0158] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that, The positive electrode material comprises Li 1+b Ni ε Co η Mn z Al w A j O2, wherein 0≤b≤0.1, 0.5≤ε≤0.7, 0≤η≤0.2, 0≤j≤0.01, ε+η+z+w=1; The value of the cell parameter c / a u of the cathode material satisfies: 4.9555-0.05(ε-0.5)-u>0; A includes any one or a combination of at least two of the following doping elements: Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P, or F; The preparation method includes: A cathode precursor and a lithium source are mixed and sintered for the first time to obtain a cathode matrix; the cathode matrix and an additive are mixed and sintered for the second time to obtain the cathode material; the temperature of the second sintering is not higher than the temperature of the first sintering. In the positive electrode precursor, the molar percentages of Ni, Co, Mn and Al, based on the total amount of Ni, Co, Mn and Al, are m, n, p and q, respectively, m+n+p+q=1, m>0.5; The additive contains Li and transition metal elements, wherein the molar ratio of Li to the total amount of transition metal elements is e:1; the transition metal elements include any one or at least two of Ni, Co, Mn or Al, and the molar percentages of Ni, Co, Mn and Al are f, g, h and i, respectively, where f+g+h+i=1. The positive electrode precursor and the additive satisfy f < m; The ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor used to prepare the positive electrode substrate to the total molar amount of Ni, Co, Mn and Al in the additive is 1:x, where x = 0.01~0.1; The ratio of the total molar amount of Ni, Co, Mn and Al in the positive electrode precursor to the total molar amount of Li in the lithium source is 1:y, where y = 1~1.1; The Li content in the additive satisfies: 1≤(y+ex) / (1+x)≤1.1; The content of Mn and Al in the additive satisfies: (h+i)x / (x+1)≤0.

05.

2. The preparation method according to claim 1, characterized in that, The value of the cell parameter c / a u of the cathode material satisfies: 4.9555-0.05(ε-0.5)-u≥0.0011.

3. The preparation method according to claim 1, characterized in that, The cathode material further includes a coating layer, the material of which comprises a compound of any one of the elements selected from Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P, or F, or a combination of compounds of at least two elements.

4. The preparation method according to claim 1, characterized in that, The first sintering temperature is 700℃~1000℃, and the time is 6h~15h; And / or, the second sintering temperature is 650℃~950℃, and the time is 6h~15h; And / or, both the first sintering and the second sintering are carried out in an oxygen-containing atmosphere.

5. The preparation method according to claim 1, characterized in that, The preparation method further includes: The positive electrode material is mixed with the coating material and then sintered in a third step to obtain a coating layer on the surface of the positive electrode material. The coating material includes a compound of any one of the elements Al, Zr, W, Ti, Mg, Nb, Zn, Fe, La, Ce, Nd, Ca, B, P, or F, or a combination of compounds of at least two elements.

6. A positive electrode plate, characterized in that, The positive electrode sheet comprises a positive electrode material prepared by the preparation method according to any one of claims 1 to 5.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode material prepared by any one of the preparation methods described in claims 1 to 5, or includes a positive electrode sheet as described in claim 6.

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