A high-nickel positive electrode material and a preparation method and application thereof

Abstract

The application provides a high-nickel positive electrode material and a preparation method and application thereof, and the preparation method of the high-nickel positive electrode material comprises the following steps: S1, mixing and sintering a lithium source and a nickel-cobalt hydroxide precursor to obtain an intermediate; wherein the ratio of the molar amount of lithium in the lithium source to the total molar amount of nickel and cobalt in the nickel-cobalt hydroxide is (0.94-0.98):1; S2, mixing and sintering the intermediate, the lithium source and an aluminum source to obtain the high-nickel positive electrode material; and the ratio of the molar amount of lithium in the obtained high-nickel positive electrode material to the total molar amount of nickel, cobalt and aluminum in the high-nickel positive electrode material is 1.00-1.05:1. The preparation method of the high-nickel positive electrode material provided by the application can simultaneously achieve the following advantages: low total residual alkali content on the surface of the high-nickel positive electrode material, good cycle stability, excellent rate performance, no need to add complex equipment, high controllability of process parameters and easy realization of industrialized scale production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a high-nickel cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high specific capacity, long cycle life, and environmental friendliness, are widely used in consumer electronics, new energy vehicles, and energy storage systems. High-nickel layered oxide (NCA) cathode materials, due to their high nickel content, high specific capacity, and excellent voltage platform, have become a core research direction for high-energy-density lithium-ion batteries. Traditional polycrystalline high-nickel cathode materials suffer from significant structural defects. During charging and discharging, repeated lithium-ion insertion and extraction induces volumetric deformation at grain boundaries, generating and expanding microcracks, ultimately leading to particle pulverization. Simultaneously, electrolyte intrusion along the cracks triggers side reactions, significantly reducing the material's cycle stability and safety performance. Compared to polycrystalline materials, monocrystalline high-nickel NCA cathode materials can effectively suppress microcrack formation, reduce electrolyte side reactions, mitigate irreversible phase transitions, and significantly improve battery cycle life and structural stability, representing the mainstream upgrade direction for high-nickel cathode materials. Currently, single-crystal high-nickel NCA materials are generally prepared by a one-time high-temperature solid-state sintering method, which involves mixing lithium source, aluminum source and hydroxide precursor in one step and then sintering at high temperature. However, this process has significant shortcomings when adapted to high-nickel systems and cannot fully utilize the excellent performance of single-crystal materials.

[0003] The existing high-temperature solid-state sintering process for preparing high-nickel NCA materials has three main drawbacks. First, impurity phases are difficult to suppress: When lithium, aluminum, and precursors are mixed and sintered at high temperatures in a single process, the high concentration of lithium in contact with aluminum for extended periods under high-temperature conditions easily generates a large amount of inactive Li5AlO4 impurity phase, distributed in the bulk and surface of the material. This hinders lithium-ion insertion / extraction and diffusion, ultimately resulting in low discharge specific capacity and deteriorated rate performance. Second, excessive residual alkali on the surface: The simultaneous addition of all lithium sources prevents lithium ions from fully embedding into the crystal lattice, leaving a large amount of free lithium on the material surface. This forms high-content Li2CO3 and LiOH residual alkali, which continuously reacts with the electrolyte during battery cycling, accelerating capacity decay and shortening cycle life. Third, poor controllability of crystal structure: The single-crystal growth temperature window for high-nickel systems is narrow. The simultaneous completion of lithiation and crystal growth in a single sintering process easily exacerbates cation mixing and insufficient material crystallinity, leading to decreased material structural stability and intensified irreversible phase transitions during cycling. This severely restricts the improvement of overall material performance and its industrial application. Summary of the Invention

[0004] This invention provides a high-nickel cathode material, its preparation method, and its application, to solve the problem in the prior art of reducing residual alkali on the material surface and synergistically improving electrochemical performance.

[0005] In a first aspect, the present invention provides a method for preparing a high-nickel cathode material, comprising the following steps: S1, the lithium source and nickel cobalt hydroxide precursor are mixed and sintered to obtain an intermediate; The ratio of the molar amount of lithium in the lithium source to the total molar amount of nickel and cobalt in the nickel-cobalt hydroxide is (0.94-0.98):1. S2, the intermediate, lithium source and aluminum source are mixed and sintered to obtain the high-nickel cathode material; The ratio of the molar amount of lithium in the obtained high-nickel cathode material to the total molar amount of nickel, cobalt and aluminum in the high-nickel cathode material is 1.00-1.05:1.

[0006] In one optional implementation, in step S2, the molar percentage of aluminum is 1.5-2% based on the total molar amount of aluminum in the aluminum source and cobalt and nickel in the intermediate; In one optional embodiment, the sintering temperature of step S1 is 700-760°C, preferably 700-740°C; In one optional embodiment, the sintering temperature of step S2 is 760-800°C.

[0007] In one optional implementation, in steps S1 and S2, the heating rate of the sintering is 3-8°C / min.

[0008] It is understood that the two-step sintering process used in this invention first forms a stable layered precursor structure, and then promotes the uniform growth of single crystal particles through secondary high-temperature sintering, effectively reducing cation mixing degree, resulting in good material crystallinity, uniform single crystal particle size distribution (3-5μm), and strong structural stability during charge and discharge.

[0009] In an optional embodiment, step S1 further includes a pre-sintering step of mixing a lithium source and a nickel-cobalt hydroxide precursor to form a mixture at 520-580°C for 4-6 hours before sintering.

[0010] In one optional embodiment, the pre-sintering heating rate is 3-8°C / min; In one optional implementation, the sintering time in step S1 and / or step S2 is 8-12 hours.

[0011] In one optional embodiment, the sintering atmosphere in step S1 and / or step S2 is a pure oxygen atmosphere. Optionally, the oxygen concentration of the pure oxygen atmosphere is ≥99%.

[0012] In an optional embodiment, in step S1, the general chemical formula of the nickel-cobalt hydroxide precursor is Nix Co y (OH)2, where x+y=1, x=0.85-0.92, y=0.08-0.15.

[0013] Optionally, the preparation method of the nickel-cobalt hydroxide precursor includes the following steps: Nickel and cobalt salts were dissolved in deionized water according to the stoichiometric ratio of the nickel-cobalt hydroxide precursor to prepare a mixed salt solution with a total metal ion concentration of 1.8-2.2 mol / L. A strong alkali solution with a concentration of 3.5-4.5 mol / L was prepared as a precipitant, and a complexing agent of ammonia water with a concentration of 9.5 mol / L-10.5 mol / L was added to it, controlling the molar ratio of ammonia to strong alkali to be 0.24-0.28. The solution was prepared under an inert gas (N2) protective atmosphere. The ammonia-alkali solution and the mixed salt solution were added to a continuously stirred reactor at a flow rate of 5-15 L / h (based on a 100L reactor) at a flow ratio of 1.0-1.2:1. The reaction temperature was controlled at 45-55℃, and the pH of the reaction system was stabilized at 11.3-11.7. The feed was stopped when the particle size Dv50 of the precipitate reached 3.0-4.0 μm. The precipitate was filtered, washed with deionized water, and vacuum dried to obtain the nickel-cobalt hydroxide precursor.

[0014] Further optionally, the nickel salt forming the nickel-cobalt hydroxide precursor is at least one of nickel sulfate and nickel nitrate; Further optionally, the cobalt salt forming the nickel-cobalt hydroxide precursor is at least one of cobalt sulfate and cobalt nitrate; Further optionally, the strong base for forming the nickel-cobalt hydroxide precursor is at least one of sodium hydroxide and potassium hydroxide.

[0015] In one optional embodiment, the lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium nitrate; In one optional embodiment, the aluminum source is at least one selected from aluminum hydroxide, aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0016] Secondly, the present invention also provides a high-nickel cathode material prepared by the above-described preparation method.

[0017] Thirdly, the present invention also provides a positive electrode sheet comprising the above-mentioned high-nickel positive electrode material.

[0018] Fourthly, the present invention also provides a lithium-ion battery comprising the aforementioned high-nickel cathode material.

[0019] Those skilled in the art will understand that the lithium-ion battery provided by the present invention may include structural components such as an electrolyte, a positive electrode, a negative electrode, a separator, and a casing. During the charging and discharging process, lithium ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor between the positive and negative electrode. The separator is disposed between the positive and negative electrode, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing lithium ions to pass through.

[0020] As an example, the positive electrode sheet includes a positive current collector and a positive active layer. The positive current collector has two opposing surfaces in its own thickness direction, and the positive active layer is disposed on either or both of the opposing surfaces of the positive current collector. The material of the positive electrode sheet used in the lithium-ion battery of the present invention is a high-nickel positive electrode material prepared by the preparation method provided by the present invention.

[0021] As an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer. The negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode active layer is disposed on either or both of the opposing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the lithium-ion battery of the present invention may include any techniques disclosed in the prior art.

[0022] The material and shape of the separator used in the lithium-ion battery of the present invention are not particularly limited, and may include any technology disclosed in the prior art.

[0023] The electrolyte used in the lithium-ion battery of the present invention may also include any technology disclosed in the prior art.

[0024] This invention does not specifically limit the preparation method of lithium-ion batteries; lithium-ion batteries can be prepared using conventional preparation methods in the art. For example, positive electrode sheets, separators, and negative electrode sheets are stacked sequentially, with the separator located between the positive and negative electrode sheets. A cell is obtained through stacking or winding processes, and then the lithium-ion battery of this invention is obtained through baking, electrolyte injection, formation, and packaging.

[0025] Fifthly, the present invention also provides an electrical device including the aforementioned lithium-ion battery.

[0026] It is understood that in the electrical equipment provided by this invention, the lithium-ion battery can be used as a power source for the electrical equipment, or as an energy storage unit for the electrical equipment. The electrical equipment may be, but is not limited to, stationary energy storage systems (including grid peak shaving, renewable energy support, and industrial and commercial energy storage), light electric vehicles (including electric bicycles, electric scooters, and site work vehicles), short-to-medium range electric vehicles (pure electric vehicles / plug-in hybrid electric vehicles), backup power supply devices (including communication base station UPS and emergency power supplies), and energy density-insensitive equipment (stationary power tools, outdoor power supplies), etc.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method of high-nickel cathode material provided by the present invention adopts a two-stage sintering process of "segmented lithium replenishment and secondary synchronous aluminum doping". The lithium source is added in two steps. In the first sintering stage, lithium ions are fully embedded in the nickel-cobalt matrix lattice. After the second lithium replenishment, the free lithium on the surface of the high-nickel cathode material is greatly reduced, and the total residual alkali content is reduced by more than 40% compared with the first lithiation method. This effectively reduces electrolyte side reactions during cycling and improves cycle stability. The aluminum source is introduced in the second sintering stage, which can avoid the high concentration of lithium components and aluminum source coexisting for a long time and causing side reactions in the high temperature environment of the first sintering, reduce lithium ion diffusion obstacles, and significantly improve the discharge specific capacity and rate performance of the high-nickel cathode material.

[0028] In addition, during the sintering process in step S1, the ratio of the molar amount of lithium in the lithium source to the total molar amount of nickel and cobalt in the nickel-cobalt hydroxide is (0.94-0.98):1. Within this parameter range, a low-lithium matrix with moderate crystallinity and stable structure can be formed, providing a structural basis for the single crystal growth and uniform aluminum doping in step S2. The amount of lithium source added during the sintering stage in step S2 is controlled to be the target total lithium amount minus the remaining lithium amount added during the first sintering. This achieves a ratio of the molar amount of lithium in the high-nickel cathode material to the total molar amount of nickel, cobalt, and aluminum in the high-nickel cathode material of 1.00-1.05:1. This can promote the uniform development of single crystal particles while ensuring that lithium ions are fully embedded in the lattice and reducing the residual free lithium on the surface of the high-nickel cathode material.

[0029] Based on this, the preparation method of high-nickel cathode material provided by the present invention can simultaneously achieve low total residual alkali content on the surface of high-nickel cathode material, good cycle stability, and excellent rate performance. Moreover, based on the improvement of traditional solid-state sintering process, no new complex equipment is required, the process parameters are highly controllable, and it is compatible with existing cathode material production lines, making it easy to achieve industrial-scale production.

[0030] 2. The present invention provides a method for preparing a high-nickel cathode material. In step S2, based on the total molar amount of aluminum in the aluminum source and cobalt and nickel in the intermediate, the molar amount of aluminum is 1.5%-2.5%, which allows it to be stably doped into the transition metal layer. The strong bond energy of Al-O bonds enhances the stability of the layered structure and suppresses irreversible phase transitions during charge and discharge, thereby improving the cycle stability and thermal stability of the high-nickel cathode material. At the same time, it avoids the problem of reduced active material and reduced discharge specific capacity caused by excessive aluminum doping.

[0031] 3. The present invention provides a method for preparing a high-nickel cathode material. In step S1, the pre-sintering is carried out at 520-580℃ for 4-6 hours before sintering. This can promote the initial decomposition and diffusion of the lithium source, so that lithium ions are partially embedded in the precursor lattice to form a preliminary layered structure, providing a structural basis for the full lithiation and single crystal growth of the subsequent main sintering. At the same time, the pre-sintering can reduce the volume shrinkage and thermal stress during the main sintering process, reduce the generation of microcracks in the particles, and help improve the crystal uniformity of the high-nickel cathode material.

[0032] 4. The present invention provides a method for preparing a high-nickel cathode material. The sintering temperature of step S1 is preferably 700-740℃. A sintering temperature lower than that of step S2 can form a low-lithium matrix with moderate crystallinity in a single sintering stage, avoiding excessive lithium volatilization and premature growth of single crystals at high temperatures. Step S2 is carried out at a higher temperature, which is beneficial for the full insertion of lithium source and uniform doping of aluminum element, promoting the full development and growth of single crystal particles, thereby obtaining a high-nickel cathode material with good crystallinity and stable structure. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having” and any variations thereof in the text of this invention are intended to cover non-exclusive inclusion.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment 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 separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] The "range" disclosed in this invention is defined by 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 range can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of the embodiments of the present invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0038] In the description of the embodiments of the present invention, the term "at least one" refers to one or more (including two).

[0039] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may 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.

[0040] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0041] The preparation method of the nickel-cobalt hydroxide precursor used in the following examples includes the following steps: Nickel salt (nickel sulfate) and cobalt salt (cobalt sulfate) were dissolved in deionized water according to the required stoichiometric ratio of the nickel-cobalt hydroxide precursor to prepare a mixed salt solution with a total metal ion concentration of 2 mol / L. A strong alkali solution (sodium hydroxide) with a concentration of 4 mol / L was prepared as a precipitant, and a complexing agent of ammonia water with a concentration of 10 mol / L was added to it, controlling the molar ratio of ammonia to strong alkali to be 0.26. Under an inert gas (N2) protective atmosphere, the ammonia-alkali solution and the mixed salt solution were added to a continuously stirred reactor at a flow rate of 10 L / h (based on a 100 L reactor) at a flow ratio of 1.1:1, while controlling the reaction temperature at 50℃ and the pH value of the reaction system at 11.5. The feed was stopped when the particle size Dv50 of the precipitate reached 3.0-4.0 μm. The precipitate was filtered, washed with deionized water, and vacuum dried to obtain the nickel-cobalt hydroxide precursor.

[0042] Example 1 This embodiment provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, weigh the nickel-cobalt hydroxide precursor and lithium source according to the molar ratio of Li:(Ni+Co)=0.96:1, and weigh the nickel-cobalt hydroxide precursor (Ni... 0.88 Co 0.12 (OH)2 and lithium source (LiOH·H2O) are placed in a high-speed mixer (1000 rpm, 30 min) and mixed evenly to obtain a mixture. The mixture is placed in an alumina crucible and placed in an atmosphere sintering furnace. High-purity oxygen (99% concentration) is introduced. The temperature is first raised to 550℃ at 5℃ / min and held for 5 h, then raised to 720℃ at 5℃ / min and held for 10 h. After sintering, the furnace is cooled and the mixture is pulverized by airflow to obtain an intermediate. S2, lithium source (LiOH·H2O) and aluminum source (aluminum hydroxide) are added to the intermediate and mixed evenly in a high-speed mixing device (1000 rpm, 30 min). The mixture is then placed in an oxygen atmosphere furnace (oxygen volume fraction 99.9%) and heated to 780℃ at 5℃ / min and held for 10 h. After cooling in the furnace, the mixture is pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1.02:1. The molar ratio of aluminum is 2% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0043] Example 2 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S1, the sintering process is as follows: first, the temperature is increased to 550°C at 5°C / min and held for 5 hours, and then the temperature is increased to 700°C at 5°C / min and held for 10 hours.

[0044] Example 3 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S1, the sintering process is as follows: first, the temperature is increased to 550°C at 5°C / min and held for 5 hours, and then the temperature is increased to 740°C at 5°C / min and held for 10 hours.

[0045] Example 4 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S1, the molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 0.94:1.

[0046] Example 5 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S1, the molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 0.98:1.

[0047] Example 6 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S2, the molar ratio of lithium in the high-nickel cathode material to the total molar ratio of nickel, cobalt and aluminum in the high-nickel cathode material is 1:1.

[0048] Example 7 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S2, the molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1.05:1.

[0049] Example 8 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that the sintering temperature in step S2 is 760°C.

[0050] Example 9 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that the sintering temperature in step S2 is 800°C.

[0051] Example 10 This embodiment provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, the nickel-cobalt hydroxide precursor (Ni 0.85 Co 0.15(OH)2 and lithium source (lithium hydroxide) are mixed evenly in a high-speed mixer to obtain a mixture. The mixture is placed in an alumina crucible and then placed in an atmosphere sintering furnace. High-purity oxygen (concentration of 99%) is introduced, and the temperature is first raised to 520℃ at 8℃ / min and held for 6 hours. Then, the temperature is raised to 740℃ at 3℃ / min and held for 8 hours. After sintering, the mixture is cooled in the furnace and pulverized by airflow to obtain an intermediate. The molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 0.98:1. S2, lithium source (lithium nitrate) and aluminum source (aluminum sulfate) are added to the intermediate and mixed evenly in a high-speed mixer. The mixture is then placed in an oxygen atmosphere furnace (oxygen volume fraction of 99%) and heated to 760℃ at 8℃ / min and held for 12 hours. After cooling in the furnace, the mixture is pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1:1. The molar ratio of aluminum is 2% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0052] Example 11 This embodiment provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, the nickel-cobalt hydroxide precursor (Ni 0.92 Co 0.08 (OH)2 and lithium source (LiOH•H2O) are mixed evenly in a high-speed mixer to obtain a mixture. The mixture is placed in an alumina crucible and then placed in an atmosphere sintering furnace. High-purity oxygen (concentration of 99.9%) is introduced, and the temperature is first raised to 580℃ at 3℃ / min and held for 4h. Then, the temperature is raised to 700℃ at 8℃ / min and held for 12h. After sintering, the mixture is cooled in the furnace and pulverized by airflow to obtain an intermediate. The molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 0.94:1. S2, lithium source (lithium carbonate) and aluminum source (aluminum nitrate) are added to the intermediate and mixed evenly in a high-speed mixer. The mixture is then placed in an oxygen atmosphere furnace (oxygen volume fraction of 99.9%) and heated to 800℃ at 3℃ / min and held for 8 hours. After cooling in the furnace, the mixture is pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1.05:1. The molar ratio of aluminum is 1.5% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0053] Example 12 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: in step S1, the sintering process is as follows: first, the temperature is increased to 550°C at 5°C / min and held for 5 hours, and then the temperature is increased to 760°C at 5°C / min and held for 10 hours.

[0054] Example 13 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that the molar percentage of aluminum is 1.5% based on the total molar amount of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0055] Example 14 This embodiment provides a high-nickel cathode material, which differs from Embodiment 1 only in that: the molar proportion of aluminum is 2% based on the total molar amount of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0056] Example 15 This embodiment provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, 1 mol of nickel-cobalt hydroxide precursor (Ni 0.88 Co 0.12 (OH)2) and 0.96 mol of lithium source (LiOH·H2O) were placed in a high-speed mixer (1000 rpm, 30 min) and mixed evenly to obtain a mixture. The mixture was placed in an alumina crucible and placed in an atmosphere sintering furnace. High-purity oxygen (99% concentration) was introduced. The temperature was first increased to 550℃ at 5℃ / min and held for 5 h, and then increased to 720℃ at 5℃ / min and held for 10 h. After sintering, the furnace was cooled and the mixture was pulverized by airflow to obtain an intermediate. S2, 0.08 mol of lithium source (LiOH·H2O) and 0.02 mol of aluminum source (aluminum hydroxide) are added to the intermediate and mixed evenly in a high-speed mixing device (speed of 1000 rpm, time of 30 min). The mixture is then placed in an oxygen atmosphere furnace (oxygen volume fraction of 99.9%) and heated to 780℃ at 5℃ / min and held for 10 h. After cooling in the furnace, the mixture is pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material.

[0057] Comparative Example 1 This comparative example provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, the nickel-cobalt hydroxide precursor (Ni 0.88 Co 0.12(OH)2), lithium source (LiOH·H2O), and aluminum source (aluminum hydroxide) are mixed evenly in a high-speed mixer to obtain a mixture. The mixture is placed in an alumina crucible and then placed in an atmosphere sintering furnace. High-purity oxygen (concentration of 99%) is introduced, and the temperature is first raised to 550℃ at 5℃ / min and held for 5h. Then, the temperature is raised to 780℃ at 5℃ / min and held for 12h. After sintering, the mixture is cooled in the furnace and then pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1.02:1. The molar ratio of aluminum is 2% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0058] Comparative Example 2 This comparative example provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, the nickel-cobalt hydroxide precursor (Ni 0.88 Co 0.12 (OH)2), lithium source (LiOH·H2O), and aluminum source (aluminum hydroxide) are mixed evenly in a high-speed mixer to obtain a mixture. The mixture is placed in an alumina crucible and then placed in an atmosphere sintering furnace. High-purity oxygen (concentration of 99%) is introduced, and the temperature is first raised to 550℃ at 5℃ / min and held for 5h. Then, the temperature is raised to 720℃ at 5℃ / min and held for 10h. After sintering, the furnace is cooled and the intermediate is obtained by air jet pulverization. The molar ratio of lithium in the lithium source to the total molar ratio of nickel, cobalt, and aluminum in the nickel-cobalt hydroxide and aluminum source is 0.96:1. The molar ratio of aluminum is 2% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0059] S2, Lithium source (LiOH·H2O) is added to the intermediate and mixed evenly in a high-speed mixing device. The mixture is then placed in an oxygen atmosphere furnace (oxygen volume fraction of 99.9%) and heated to 780℃ at 5℃ / min and held for 10h. After cooling in the furnace, the mixture is pulverized and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium element in the high-nickel cathode material to the total molar ratio of nickel, cobalt and aluminum elements in the high-nickel cathode material is 1.02:1.

[0060] Comparative Example 3 This comparative example provides a high-nickel cathode material, and the specific steps and operating parameters are as follows: S1, the nickel-cobalt hydroxide precursor (Ni 0.88 Co 0.12(OH)2), lithium source (LiOH·H2O), and aluminum source (aluminum hydroxide) are mixed evenly in a high-speed mixer to obtain a mixture. The mixture is placed in an alumina crucible and then placed in an atmosphere sintering furnace. High-purity oxygen (concentration of 99%) is introduced, and the temperature is first raised to 550℃ at 5℃ / min and held for 5h. Then, the temperature is raised to 720℃ at 5℃ / min and held for 10h. After sintering, the mixture is cooled in the furnace, pulverized, and sieved through a 300-mesh sieve to obtain the high-nickel cathode material. The molar ratio of lithium to the total molar ratio of nickel, cobalt, and aluminum in the high-nickel cathode material is 1.02:1. The molar ratio of aluminum is 2% based on the total molar ratio of aluminum in the aluminum source and cobalt and nickel in the intermediate.

[0061] Comparative Example 4 This comparative example provides a high-nickel cathode material, which differs from Example 1 only in that: in step S1, the molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 1:1.

[0062] Comparative Example 5 This comparative example provides a high-nickel cathode material, which differs from Example 1 only in that: in step S1, the molar ratio of lithium in the lithium source to the total molar ratio of nickel and cobalt in the nickel-cobalt hydroxide is 0.92:1.

[0063] Experimental Example 1 The performance of the high-nickel cathode materials provided in Examples 1-15 and Comparative Examples 1-5 was tested, and the specific test methods are as follows: The total amount of LiOH and Li2CO3 (residual alkali content) was determined using an automatic potentiometric titrator in accordance with GB / T 9725-2007 standard, with hydrochloric acid as the titrant. The results were expressed as the mass fraction of LiOH.

[0064] The elemental contents of LiOH and Li2CO3 in the prepared high-nickel cathode material were determined using an inductively coupled plasma atomic emission spectrometer (Agilent 5110, Agilent Technologies, USA).

[0065] The specific test results are shown in the table below: Table 1 Material property test data

[0066] As can be seen from the data in Table 1, Examples 1-3 all adopted the standard process of two-stage sintering and delayed aluminum source introduction of the present invention. The residual alkali was at a low level and the difference between the residual alkali values ​​was not significant, verifying the stability of the basic technical solution of the present invention. Examples 4 and 5 adjusted the molar ratio of lithium to nickel-cobalt in the first lithiation step to the lower and higher ends of the range, respectively, based on Example 1. The results showed that increasing this ratio helped to reduce residual alkali. Even with the lower end of the lithium-nickel-cobalt molar ratio in the first lithiation step, the residual alkali was still much better than the comparative example of a single lithiation treatment, proving that the lower and higher ends of the range of the lithium-nickel-cobalt molar ratio in the first lithiation step were generally effective. Examples 6 and 7 further adjusted the total molar ratio of lithium to nickel-cobalt-aluminum in the second lithiation step to the lower and upper limits of the range. The residual alkali increased slightly with the increase of the total ratio, attributed to the enrichment of excess lithium on the surface, but it was significantly better than the single lithiation process, indicating that the range of the total ratio was reasonable. Examples 8 and 9 set the second-step sintering temperature to a lower and higher level, respectively. Compared with the moderate temperature in Example 1, the moderate temperature resulted in optimal residual alkali. Temperatures that were too low or too high caused a rebound in residual alkali, attributed to insufficient lithium solid solution and increased lithium volatilization / segregation, respectively, thus clarifying the optimal temperature window. Examples 10 and 11 changed the precursors with different nickel-cobalt ratios and adjusted the aluminum content and total lithium ratio accordingly; the residual alkali remained at a similarly low level, demonstrating the process's universality. Example 12 raised the first-step sintering temperature above the preferred range; the residual alkali significantly deteriorated, indicating that this temperature should not be too high. Examples 13 and 14 changed the aluminum content; the difference in residual alkali was minimal, highlighting that the timing of aluminum source introduction (second step) rather than the amount is the key factor. Example 15 repeated the conditions of Example 1, with consistent results, verifying the data's reproducibility. The influence of the above parameters is consistent, collectively supporting the synergistic effect of two-stage sintering and delayed aluminum source introduction.

[0067] Furthermore, Comparative Examples 1 and 3 employed a traditional single-step lithiation process, with all lithium sources added at once. The residual alkali was significantly higher than in all other examples, exposing the shortcomings of single-step lithiation. Although Comparative Example 2 involved step-by-step lithium replenishment, the aluminum source was added in the first step, yet the residual alkali was still higher than in the preferred embodiment, indicating that the timing of aluminum source introduction is crucial. Comparative Examples 4 and 5 adjusted the first-step lithium-to-nickel-cobalt molar ratio to the upper and lower limits, respectively, which were outside the range. The former resulted in severe surface residue due to excessive lithium addition, while the latter weakened the secondary lithium replenishment effect due to insufficient lithiation. Both examples showed significantly higher residual alkali than all other examples, demonstrating the irreplaceable nature of this molar ratio range from both positive and negative perspectives. All comparative examples demonstrate that any deviation from the present invention in any single step significantly weakens the alkali control effect.

[0068] Experiment Example 2 The high-nickel cathode materials provided in Examples 1-15 and Comparative Examples 1-5 were applied to lithium-ion batteries, and then their electrical performance was tested.

[0069] The method for preparing the lithium-ion battery includes the following steps: The high-nickel cathode material prepared in Examples 1-15 or Comparative Examples 1-5 was used as the cathode active material and homogenized with polyvinylidene fluoride (PVDF) and acetylene black in a ratio of 80:10:10, with the areal density controlled at 4 mg / cm³. 2 The electrode compaction density is 2 g / cm³. 3 The electrode was fabricated using a lithium metal sheet as the counter electrode and a glass fiber separator. A 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) was used as the electrolyte. The cells were assembled into CR2032 coin cells in an argon-filled glove box. Finally, the cells were placed in the Blue Electric CT3001 battery testing system for electrical performance testing.

[0070] The specific method for the electrical performance test is as follows: (1) First charge and discharge performance test After the open-circuit voltage stabilizes at 25℃, the battery's first charge and discharge performance is tested in one 0.1C / 5C cycle: the initial charge capacity is obtained by constant current charging at 0.1C until the voltage reaches 4.5V, and the initial discharge capacity is obtained by constant current discharging at 5C until the cutoff voltage reaches 3.0V. The first-cycle coulombic efficiency (first-cycle efficiency) is then calculated.

[0071] The coulomb efficiency for the first lap is calculated as follows: ; Where: ICE is the initial coulomb efficiency; D1 is the initial discharge capacity (mAh) at the specified rate. C1 represents the initial charge capacity (mAh) at the same charging rate.

[0072] The discharge specific capacity (mAh / g) is calculated as follows: ; Where m is the mass (g) of the active material in the positive electrode.

[0073] (2) Cyclic stability test The assembled coin cell was charged at a constant current of 1C to 4.5V and then discharged at a constant current of 1C until the cutoff voltage of 3.0V was reached. This process was repeated 60 times, and the cycle capacity retention rate of the battery after 60 cycles was calculated.

[0074] The cycle capacity retention rate (%) is calculated as follows: .

[0075] The specific test results are shown in Table 2 below: Table 2 Electrical performance test data

[0076] As can be seen from the data in Table 2, Examples 4 and 5, based on Example 1, adjusted the lithium to nickel-cobalt molar ratio during the first lithiation step to a lower and higher end, respectively. A lower ratio resulted in insufficient lithiation of the matrix, affecting lattice integrity; a higher ratio resulted in premature single-crystal growth during the first sintering stage, which was detrimental to uniform crystal formation during the second sintering. Examples 6 and 7, based on Example 1, adjusted the lithium to nickel-cobalt-aluminum total molar ratio during the second lithiation step to a lower and higher end, respectively. An increased total molar ratio was beneficial for lithium insertion into the lattice, improving the capacity and rate capability of the high-nickel cathode material; however, an excessively high ratio increased surface residual alkali, leading to a decrease in cycle retention. Examples 8 and 9, based on Example 1, adjusted the second sintering temperature to the lowest and highest values, respectively. At lower temperatures, insufficient lithiation and aluminum doping resulted in incomplete crystal development; at higher temperatures, cation mixing and particle agglomeration intensified. Example 10, using a low-nickel precursor combined with high aluminum content and a low total lithium ratio, achieved the highest cycle retention rate. Example 11, using a high-nickel precursor combined with low aluminum content and a relatively high total lithium ratio, achieved the highest capacity and rate capability, demonstrating the trade-off between nickel and aluminum content. In Example 12, raising the first-step sintering temperature above the preferred range resulted in a decrease in all performance characteristics. Examples 13 and 14 used lower and higher aluminum contents, respectively; the low-aluminum solution achieved higher capacity and rate capability, while the high-aluminum solution demonstrated better cycle retention. Example 15, repeating the conditions of Example 1, showed a high degree of agreement, verifying the reliability.

[0077] Comparative Examples 1 and 3 employed a conventional one-step lithiation process, with all lithium sources added at once. The resulting high-nickel cathode materials exhibited significantly lower initial discharge specific capacity, 5C rate performance, and cycle retention compared to all other examples, with the 5C rate performance being particularly poor. This revealed the defect of the Li5AlO4 impurity phase hindering lithium-ion diffusion due to one-step lithiation. Comparative Example 2, although involving step-by-step lithiation, introduced the aluminum source in the first step. All electrochemical performance indicators were lower than those of the preferred embodiment of this invention, demonstrating the necessity of delaying the introduction of the aluminum source to the second step. Comparative Examples 4 and 5 adjusted the lithium-to-nickel-cobalt molar ratio in the first step to the upper and lower limits, respectively, which were outside the defined range. Both examples showed significantly lower performance than the other examples. The former resulted in a decrease in matrix crystal quality due to excessive initial lithium addition, while the latter affected the lithiation efficiency during secondary sintering and single-crystal growth due to insufficient lithiation. These examples, from both positive and negative perspectives, confirmed the crucial role of this molar ratio range in obtaining excellent electrochemical performance. Based on the combined residual alkali and electrochemical data, a clear correlation was found between various performance characteristics and residual alkali levels, further verifying the synergistic effect of the two-stage sintering process in simultaneously improving the discharge specific capacity, rate performance, and cycle stability of high-nickel cathode materials.

[0078] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a high-nickel cathode material, characterized in that, Includes the following steps: S1, the lithium source and nickel cobalt hydroxide precursor are mixed and sintered to obtain an intermediate; The ratio of the molar amount of lithium in the lithium source to the total molar amount of nickel and cobalt in the nickel-cobalt hydroxide is (0.94-0.98):

1. S2, the intermediate, lithium source and aluminum source are mixed and sintered to obtain the high-nickel cathode material; The ratio of the molar amount of lithium in the obtained high-nickel cathode material to the total molar amount of nickel, cobalt and aluminum in the high-nickel cathode material is 1.00-1.05:

1.

2. The preparation method according to claim 1, characterized in that, In step S2, the molar percentage of aluminum is 1.5-2% based on the total molar amount of aluminum in the aluminum source and cobalt and nickel in the intermediate. And / or, the sintering temperature of step S1 is 700-760℃, preferably 700-740℃; And / or, the sintering temperature of step S2 is 760-800℃.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, before sintering, the mixture formed by mixing the lithium source and the nickel cobalt hydroxide precursor is pre-sintered at 520-580°C for 4-6 hours.

4. The preparation method according to any one of claims 1-3, characterized in that, In step S1 and / or step S2, the sintering time is 8-12 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The sintering atmosphere in step S1 and / or step S2 is a pure oxygen atmosphere. Optionally, the oxygen concentration of the pure oxygen atmosphere is ≥99%.

6. The preparation method according to claim 1, characterized in that, In step S1, the general chemical formula of the nickel-cobalt hydroxide precursor is Ni x Co y (OH)2, where x+y=1, x=0.85-0.92, y=0.08-0.

15.

7. The preparation method according to claim 1, characterized in that, The lithium source is at least one of lithium hydroxide, lithium carbonate, and lithium nitrate. And / or, the aluminum source is at least one of aluminum hydroxide, aluminum nitrate, aluminum sulfate, and aluminum chloride.

8. A high-nickel cathode material prepared by the preparation method according to any one of claims 1-7.

9. A positive electrode sheet, characterized in that, Including the high-nickel cathode material as described in claim 8.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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