High-nickel positive electrode material and preparation method thereof

Abstract

The invention belongs to the technical field of positive electrode materials, and particularly relates to a high-nickel positive electrode material and a preparation method thereof. The invention aims to solve the problem that the cycle life and the energy density of the existing high-nickel positive electrode material are difficult to obtain at the same time. The preparation method comprises the following steps: dissolving nickel sulfate, cobalt sulfate and manganese sulfate in water to prepare a metal salt solution, and adding an inner dopant; introducing a base solution into a reaction kettle under the protection of nitrogen, adjusting the pH value and the ammonia concentration, adding a metal salt solution, a precipitator and a complexing agent in a parallel flow manner, and controlling the pH value and the free ammonia concentration of the system for reaction; linearly reducing the pH value and the free ammonia concentration; after stopping feeding, carrying out aging treatment, and carrying out centrifugal washing and vacuum drying on a solid product to obtain a spherical precursor; and mixing the spherical precursor with lithium hydroxide, adding tungsten trioxide powder, sintering in an oxygen atmosphere, annealing at a constant temperature in a nitrogen atmosphere to obtain an electrode material, cleaning, and carrying out flash annealing to obtain the high-nickel positive electrode material.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a high-nickel cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, have become the core power source for electric vehicles and large-scale energy storage systems worldwide. As a decisive component in the electrochemical performance of batteries, cathode materials not only account for more than 40% of the cell cost, but their crystal structure stability is also directly related to the upper limit of the battery's energy density and the risk of thermal runaway.

[0003] With the increasing market demand for extended driving range, high-nickel layered oxides, due to the multi-electron redox capability provided by nickel, have become a technological route for achieving high specific capacity. However, existing high-nickel material systems are facing severe physicochemical challenges in the development of extreme performance. Nickel ions are highly reactive ions, and during charging and discharging, changes in their electron orbital configuration lead to axial distortion of oxygen octahedra. With increasing delithiation depth, this microscopic lattice distortion accumulates into macroscopic anisotropic volume changes, resulting in microcracks within the particles. These cracks not only cut off electron transport paths but also provide channels for electrolyte penetration, exacerbating side reactions. Because the ionic radii of divalent nickel ions and lithium ions are extremely close, divalent nickel ions readily migrate to lithium layer sites during high-temperature synthesis or cycling. This mixing effect blocks the two-dimensional diffusion channels of lithium ions, significantly reducing the rate performance of the material. Simultaneously, the surface of high-nickel materials tends to react with water and carbon dioxide in the air, generating lithium hydroxide and lithium carbonate residues. This not only increases the risk of gelation during battery slurry preparation but also easily induces gas expansion under high temperature and pressure. In existing technologies, chromium doping and other methods are commonly used to stabilize the crystal structure of high-nickel cathode materials. However, in conventional high-temperature solid-state sintering processes, it is difficult to control the process conditions, and the distribution of chromium elements will significantly affect the overall performance of the electrode, resulting in an irreconcilable contradiction between the cycle life, safety and energy density of high-nickel electrodes.

[0004] To address the challenge of achieving both high cycle life and high energy density in existing high-nickel cathode materials, a high-nickel cathode material and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-nickel cathode material and its preparation method. This invention involves dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in water to prepare a metal salt solution, then adding an internal dopant; under nitrogen protection, a base liquid is introduced into a reactor while adjusting the pH and ammonia concentration, and the metal salt solution, precipitant, and complexing agent are added sequentially, controlling the pH and free ammonia concentration of the system for reaction; subsequently, the pH and free ammonia concentration are linearly reduced; after stopping the feed, the material is aged, and the solid product is centrifuged, washed, and vacuum dried to obtain a spherical precursor; the spherical precursor is mixed with lithium hydroxide, and tungsten trioxide powder is added; the mixture is sintered under an oxygen atmosphere, followed by isothermal annealing under a nitrogen atmosphere to obtain the electrode material; after cleaning, it is flash annealed to obtain the high-nickel cathode material.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A high-nickel cathode material and its preparation method, comprising the following steps: A metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 83:11:5, wherein the total metal ion concentration was 2.0-2.2 mol / L.

[0007] An internal dopant is added to the metal salt solution. Specifically, the internal dopant is chromium nitrate nonahydrate, wherein the molar amount of chromium accounts for 1.5% of the total molar amount of nickel, cobalt and manganese.

[0008] Under nitrogen protection, a base liquid was introduced into the reactor. The pH of the base liquid was adjusted to 11.8 and the ammonia concentration was adjusted to 0.7 mol / L using ammonia water. Stirring was started at a speed of 800 rpm to begin the precursor synthesis stage.

[0009] The specific process of precursor synthesis is as follows: a metal salt solution, a precipitant, and a complexing agent are added concurrently to a reactor, controlling the pH value of the system between 11.2 and 11.6, and the free ammonia concentration in the reactor between 0.58 and 0.63 mol / L. After the reaction continues for 5 hours, the reaction parameters are adjusted. Within 15 hours, the pH value is linearly reduced to 10.5, and the free ammonia concentration is linearly reduced to 0.35 mol / L. Then, the feed is stopped, and after aging for 5 hours, the solid product is centrifuged, washed, and vacuum dried to obtain a spherical precursor. The precipitant is a 2 mol / L sodium hydroxide solution, and the complexing agent is a 2 mol / L ammonia solution.

[0010] Lithium-containing sintering process: Spherical precursors are mixed with lithium hydroxide in a ratio of 55:68-77, where the total molar amount of other metal elements to the molar amount of lithium is 55:68-77. Simultaneously, 0.5 wt% tungsten trioxide powder is added to the precursor mixture, and the mixture is stirred at 2000 rpm for 15 min. The mixture is then heated to 780 °C in a 98% oxygen atmosphere at a heating rate of 2-4 °C / min and sintered at this temperature for 12 hours. After cooling to 450 °C in the furnace, the temperature is maintained at this constant temperature, and the atmosphere is replaced with pure nitrogen. After annealing at this constant temperature for 2 hours, the electrode material is obtained.

[0011] The electrode material was cleaned using a buffer cleaning solution, ultrasonically washed and treated for 5 minutes, then centrifuged to dry, controlling the moisture content of the filter cake to be <5%. Subsequently, flash annealing was performed, and the filter cake was heat-treated at 400-430℃ for 30 minutes in air, followed by pulverization to obtain the high-nickel cathode material. The solute in the buffer cleaning solution was ammonium dihydrogen phosphate, and the buffer pH range was 6.0-6.5.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: During precursor synthesis, the pH and ammonia concentration within the reactor are dynamically adjusted. High pH and high ammonia concentration are used in the initial stages of synthesis to promote nucleation, while the ammonia concentration is reduced as the reaction progresses, encouraging faster radial grain growth. This specific process design results in a precursor with a more regular radial arrangement, effectively dissipating lattice expansion stress during charge and discharge, suppressing microcrack formation, and thus improving the cycle life of the cathode material.

[0013] Introducing a chromium source during precursor synthesis stabilizes the crystal lattice framework while suppressing nickel and lithium mixing. Tungsten is introduced during the lithium-mixing sintering stage, allowing chromium to support the layered structure of the precursor within the crystal lattice, while tungsten accumulates on the outer layer of the particles, achieving a hard-on-the-outer-toughness effect. The internally doped chromium effectively improves the cycle stability of the electrode material without accumulating on the outer layer, and the tungsten accumulation on the outer layer effectively blocks electrolyte erosion and penetration. This results in different electrochemical properties between the bulk and near-surface phases of the electrode material, thereby increasing both cycle life and electrode energy density.

[0014] A specific coupling curve between sintering temperature and atmosphere was designed during the lithium mixing sintering stage. High-purity oxygen was introduced during the heating and isothermal stages to ensure sufficient oxidation of divalent nickel to trivalent nickel, resulting in a high-capacity layered phase. During the annealing stage after cooling, a nitrogen atmosphere was switched to reduce the outermost layer of trivalent nickel to divalent nickel, generating a more chemically stable shell layer in situ. This shell layer has a good chemical bond with the internal lattice, improving the material's resistance to overcharging and thermal stability while avoiding the risk of peeling off of the coating formed in situ.

[0015] A weakly acidic buffer cleaning solution is used to clean the electrode material. This removes residual alkali from the particle surface and binds some lithium ions and phosphate ions from the cleaning solution to the structural collapse sites on the particle surface, preventing lithium loss and resolving the gelation problem in the slurry preparation. The cleaned wet material is not subjected to conventional drying but instead undergoes a short-term flash annealing process. This allows for a certain degree of interfacial fusion between the surface lithium phosphate layer and the shell layer, forming a composite interface layer. This reduces the surface impedance of the high-nickel electrode material and ensures its good chemical stability. Attached Figure Description

[0016] Figure 1 This is a scanning electron microscope image of the high-nickel cathode material prepared in Example 5 of this invention. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a high-nickel cathode material and its preparation method, the technical solution of which is as follows:

[0019] Example 1 A metal salt solution was prepared by mixing nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 83:11:5, with a total metal ion concentration of 2.0 mol / L.

[0020] An internal dopant is added to the metal salt solution. Specifically, the internal dopant is chromium nitrate nonahydrate, wherein the molar amount of chromium accounts for 1.5% of the total molar amount of nickel, cobalt and manganese.

[0021] Under nitrogen protection, a base liquid was introduced into the reactor. The pH of the base liquid was adjusted to 11.8 and the ammonia concentration was adjusted to 0.7 mol / L using ammonia water. Stirring was started at a speed of 800 rpm to begin the precursor synthesis stage.

[0022] The specific process of precursor synthesis is as follows: a metal salt solution, a precipitant, and a complexing agent are added concurrently to a reactor, controlling the pH value of the system between 11.2 and 11.6, and the free ammonia concentration in the reactor between 0.58 and 0.63 mol / L. After the reaction continues for 5 hours, the reaction parameters are adjusted. Within 15 hours, the pH value is linearly reduced to 10.5, and the free ammonia concentration is linearly reduced to 0.35 mol / L. Subsequently, the feed is stopped, and after aging for 5 hours, the solid product is centrifuged, washed, and vacuum dried to obtain a spherical precursor.

[0023] Lithium-mixed sintering process: Spherical precursors are mixed with lithium hydroxide, wherein the total molar ratio of other metal elements to lithium is 55:68. Simultaneously, tungsten trioxide powder at 0.5 wt% of the precursor is added, and the mixture is stirred at 2000 rpm for 15 min. The mixture is then heated to 780 °C in a 98% oxygen atmosphere at a heating rate of 2 °C / min and sintered at this temperature for 12 hours. After cooling to 450 °C in the furnace, the temperature is maintained at this constant temperature, and the atmosphere is replaced with pure nitrogen. After annealing at this constant temperature for 2 hours, the electrode material is obtained.

[0024] The electrode material was cleaned with a buffer cleaning solution, ultrasonically washed and treated for 5 minutes, then centrifuged to dry, controlling the moisture content of the filter cake to be <5%. Subsequently, flash annealing was performed, and the filter cake was heat-treated at 400℃ for 30 minutes in air atmosphere, and then pulverized to obtain high-nickel cathode material.

[0025] Examples 2-16 differ from Example 1 in operating parameters, but the other process steps and the range of raw material selection are the same.

[0026] The specific changes in operating parameters are summarized in Table 1.

[0027] Table 1. Changes in operating parameters in Examples 1-16 Total concentration of metal ions in a metal salt solution (mol / L) Lithium hydroxide added by mass ratio Heating rate for mixed lithium sintering (°C / min) Filter cake heat treatment temperature (°C) Example 1 2.0 68 2.0 400 Example 2 2.2 77 4.0 430 Example 3 2.1 72 3.1 415 Example 4 2.0 75 2.8 422 Example 5 2.1 70 3.5 408 Example 6 2.0 74 2.4 419 Example 7 2.2 69 3.9 403 Example 8 2.0 76 2.1 427 Example 9 2.1 71 3.3 411 Example 10 2.0 73 2.6 425 Example 11 2.2 77 3.7 406 Example 12 2.0 68 2.2 429 Example 13 2.1 74 3.0 418 Example 14 2.0 70 3.8 421 Example 15 2.2 76 2.5 405 Example 16 2.0 72 3.2 412 Comparative Example 1 Unlike Example 1, the pH value was kept constant at 11.6 and the free ammonia concentration was kept constant at 0.63 mol / L throughout the precursor synthesis process. The adjustment process was eliminated, and all other process parameters were the same.

[0028] Comparative Example 2 Unlike Example 1, the pH value was kept constant at 10.5 and the free ammonia concentration was kept constant at 0.35 mol / L throughout the precursor synthesis process. The adjustment process was eliminated, and all other process parameters remained the same.

[0029] Comparative Example 3 Unlike Example 1, in the entire process of precursor synthesis, the pH value increased linearly from 10.5 to 11.6, the ammonia concentration increased linearly from 0.35 mol / L to 0.63 mol / L, and other process parameters remained the same.

[0030] Comparative Example 4 Unlike Example 5, chromium nitrate was not added during the synthesis of the precursor, but all other process parameters remained the same.

[0031] Comparative Example 5 Unlike Example 5, tungsten trioxide was not added during the lithium mixing sintering process, while all other process parameters remained the same.

[0032] Comparative Example 6 Unlike Example 9, during the lithium mixing sintering process, after cooling to 450°C, the atmosphere was not switched to nitrogen, but continued to be maintained in an oxygen atmosphere, while other process parameters remained the same.

[0033] Comparative Example 7 Unlike Example 9, nitrogen atmosphere was used in both the heating and isothermal sintering stages of the lithium mixing process, while other process parameters remained the same.

[0034] Comparative Example 8 Unlike Example 9, in the lithium mixing sintering process, the atmosphere was switched to nitrogen after the constant temperature of 780°C was reached, and then the temperature was lowered. All other process parameters were the same.

[0035] Comparative Example 9 Unlike Example 13, deionized water was used for cleaning instead of a buffer cleaning solution, while all other process parameters remained the same.

[0036] Comparative Example 10 Unlike Example 13, the flash annealing stage was omitted, and the product was dried in a vacuum oven at an operating temperature of 120°C, while all other process parameters remained the same.

[0037] Experimental Example 1 The cycle life of the high-nickel cathode materials prepared in Examples 1-4 and Comparative Examples 1-3 was tested, and the relevant results are summarized in Table 2.

[0038] The cycle life test method is as follows: the positive electrode material to be tested is coated on an aluminum foil current collector, and the areal density on one side is controlled at 16±0.2 mg / cm³. 2 After drying, the compaction density of the electrode sheets is controlled to be 3.3-3.4 g / cm³. 3 The electrode was prepared as the positive electrode of the battery. The electrolyte was 1 mol / L LiPF6 with a solvent ratio of EC:DEC:EMC = 1:1:1 (volume ratio), and 2% vinylene carbonate was added as a film-forming additive. The negative electrode was a graphite electrode. After activation by 0.1C low-rate charge-discharge at 25℃, the initial capacity was recorded. Then, constant current charge-discharge was performed at 1.0C for 500 cycles, and the capacity after degradation was recorded. The capacity retention rate (%) after 500 cycles was calculated.

[0039] Table 2 Cycle life of the high-nickel cathode materials prepared in Examples 1-4 and Comparative Examples 1-3 Capacity retention rate (%) Example 1 92.7 Example 2 94.1 Example 3 93.6 Example 4 93.5 Comparative Example 1 82.6 Comparative Example 2 77.4 Comparative Example 3 76.9 As shown in Table 2, the capacity retention rates of Examples 1 to 4 after 500 cycles were significantly higher than those of Comparative Examples 1, 2 and 3, indicating that the dynamic gradient complexation co-precipitation process used in the examples has a significant advantage in improving the cycle stability of high-nickel cathode materials.

[0040] Comparative Example 1 maintained a constant high pH and high free ammonia concentration throughout the synthesis process, eliminating the parameter adjustment process. This resulted in an excessively rapid nucleation rate and disordered crystal growth within the reaction system, failing to form an ordered radial arrangement structure. Consequently, the material exhibited insufficient structural stability in the later stages of cycling, leading to a significant decrease in capacity retention. Comparative Example 2 maintained a constant low pH and low free ammonia concentration throughout the synthesis process, resulting in insufficient nucleation and excessively rapid crystal growth. The resulting particles had a loose internal structure and poor mechanical strength, making them prone to structural collapse during rolling and cycling, further deteriorating their cycling performance. Comparative Example 3 employed a reverse gradient adjustment strategy from low to high, i.e., low parameters initially and high parameters later. This resulted in the precursor forming a structure that was loose inside and dense outside. This structure not only failed to effectively buffer volume expansion but also, due to its overly rigid outer shell and loose interior, was highly susceptible to breakage under stress. Therefore, its capacity retention was the worst among all experimental groups, demonstrating the necessity and rationality of the high and low gradient adjustment process in the original technical scheme.

[0041] In summary, this invention creatively introduces a dynamic parameter adjustment mechanism in the precursor synthesis stage. The initial high pH and high ammonia concentration environment promotes rapid nucleation to form a dense core, which, combined with the linear reduction of parameters in subsequent stages, induces rapid radial grain growth. These two mechanisms produce a significant synergistic effect: the dense core ensures the material's volumetric density, while the radially growing grains construct a regular radial structure. This specific microstructure acts as a stress dissipation channel, effectively alleviating the anisotropic expansion stress caused by the lattice breathing effect during the charging and discharging process of high-nickel materials. From a physical perspective, it significantly inhibits the initiation and propagation of intergranular microcracks, thereby greatly improving the long cycle life of high-nickel cathode materials.

[0042] Experiment Example 2 The cycle life and energy density of the high-nickel cathode materials prepared in Examples 5-8 and Comparative Examples 4-5 were tested, and the relevant results are summarized in Table 3.

[0043] The test method for cycle life is shown in Experiment Example 1.

[0044] The energy density is tested by calculating the discharge specific capacity (mAh / g) of the corresponding cathode material under a 0.1C discharge condition. A higher discharge specific capacity indicates a higher energy density under this condition.

[0045] Table 3. Cycle life and energy density of the high-nickel cathode materials prepared in Examples 5-8 and Comparative Examples 3-5 Capacity retention rate (%) Discharge specific capacity (mAh / g) Example 5 93.3 217.8 Example 6 94.1 220.6 Example 7 94.0 219.2 Example 8 94.6 218.3 Comparative Example 4 86.4 204.2 Comparative Example 5 87.1 211.7 As shown in Table 3, and with reference to... Figure 1The SEM images shown indicate that the capacity retention and discharge specific capacity of Examples 5 to 8 after 500 cycles are significantly higher than those of Comparative Examples 4 and 5. Furthermore, the microstructure of the material prepared in Example 5 is regular, indicating that the chromium-tungsten synergistic dual-doping strategy adopted in these examples has significant advantages in balancing the cycle life and energy density of high-nickel cathode materials.

[0046] Comparative Example 4 did not introduce a chromium source during the precursor synthesis stage, resulting in the lack of chromium's support for the bulk lattice framework. This led to increased cation mixing during charging and discharging, decreased stability of the layered structure, and consequently, a significant reduction in discharge specific capacity and accelerated cycle decay. Comparative Example 5 did not introduce a tungsten source during the lithium mixing sintering stage, resulting in the lack of a tungsten-rich protective layer on the particle surface. This caused the active material to be directly exposed to the electrolyte, which could not effectively prevent the electrolyte from corroding and penetrating, leading to an increase in surface side reactions. Although the bulk phase had a certain degree of stability, the overall cycle life and capacity performance were still significantly lower than those of the examples.

[0047] In summary, this invention introduces a chromium source during the precursor synthesis stage and a tungsten source during the sintering stage, resulting in a significant synergistic effect: the internally doped chromium stabilizes the crystal framework and suppresses nickel-lithium mixing, ensuring high stability and high capacity of the layered structure; the externally enriched tungsten constructs a tough surface protective layer, effectively preventing electrolyte corrosion of the material surface. This spatiotemporally separated doping design, characterized by internal hardness and external toughness, synergistically optimizes the electrochemical properties of the material from the bulk phase to the surface, achieving a dual improvement in structural stability and interfacial safety, and significantly enhancing the cycle life and discharge specific capacity of the high-nickel cathode material.

[0048] Experimental Example 3 The initial coulombic efficiency and thermal stability of the high-nickel cathode materials prepared in Examples 9-12 and Comparative Examples 6-8 were tested. The relevant results are summarized in Table 4.

[0049] The initial coulombic efficiency test method is as follows: the battery is charged at a constant current of 0.1C until the battery voltage reaches 4.3V, and then discharged at a constant current of 0.1C. After completion, the ratio of the 0.1C discharge capacity to the 0.1C charge capacity is calculated and recorded as the initial coulombic efficiency (%).

[0050] The thermal stability test method is as follows: After the assembled battery is charged to 4.3V at a constant current rate of 0.1C, the positive electrode is removed, and the battery is kept at 200℃ for 12 hours under a nitrogen atmosphere before being reassembled. The specific capacity retention rate (%) is then calculated. The higher the specific capacity retention rate, the better the thermal stability of the electrode.

[0051] Table 4. Initial coulombic efficiency and thermal stability of the high-nickel cathode materials prepared in Examples 9-12 and Comparative Examples 6-8 First-time Coulomb efficiency (%) Specific capacity retention (%) Example 9 89.4 84.7 Example 10 89.2 82.3 Example 11 90.1 83.6 Example 12 90.7 83.0 Comparative Example 6 87.2 73.1 Comparative Example 7 Electrochemically inactive Electrochemically inactive Comparative Example 8 78.4 89.3 As shown in Table 4, Examples 9 to 12 are significantly better than Comparative Examples 6, 7 and 8 in terms of initial coulombic efficiency and peak temperature of thermal stability, indicating that the variable atmosphere sintering process used in the examples has obvious advantages in improving the thermal safety and electrochemical activity of high-nickel cathode materials.

[0052] Comparative Example 6 did not switch to a nitrogen atmosphere during the cooling stage, resulting in the particle surface remaining in a highly active trivalent nickel state. The lack of a chemically inert protective layer significantly reduced its thermal decomposition temperature and deteriorated its safety. Comparative Example 7 used a nitrogen atmosphere throughout the process, which prevented the divalent nickel in the precursor from being oxidized to trivalent nickel, making it difficult to form a layered structure with high electrochemical activity, resulting in the material essentially losing its charge and discharge capabilities. Comparative Example 8 switched to a nitrogen atmosphere too early during the high-temperature isothermal stage, causing the reduction reaction to extend into the bulk phase, destroying the main layered structure and resulting in a significant decrease in capacity and efficiency.

[0053] In summary, this invention introduces high-purity oxygen during the heating and isothermal stages and switches to a nitrogen atmosphere during the cooling stage. These two processes produce a significant synergistic effect: the high-temperature, high-oxygen environment ensures the full oxidation of bulk nickel ions and the complete construction of the layered structure, guaranteeing the material's high specific capacity; the cooling, low-oxygen environment induces in-situ reconstruction of the particle surface to form a shell, significantly improving the thermal stability of the interface. This stepwise atmosphere control strategy synergistically optimizes the crystal structure of both the bulk and surface phases of the material, constructing a robust safety barrier without sacrificing electrochemical activity, and achieving a balance between high capacity and high safety in high-nickel cathode materials.

[0054] Experiment Example 4 The surface impedance and chemical stability of the high-nickel cathode materials prepared in Examples 13-16 and Comparative Examples 9-10 were tested, and the relevant results are summarized in Table 5.

[0055] The surface impedance test method is as follows: After cycling the assembled battery three times at 0.1C, it is charged to 4.3V for testing. The charge transfer impedance R is measured within a frequency range of 100kHz-10MHz with a perturbation amplitude of 5mV. ct (Ω·cm) 2 This reflects the resistance of lithium ions across the cathode / electrolyte interface.

[0056] The chemical stability test method is as follows: After 3 cycles at 0.1C, the assembled battery is charged to 4.3V. The positive electrode is then removed and immersed in a weakly acidic buffer solution (acetic acid / sodium acetate) at pH 5.0 for 12 hours. After drying, the battery is reassembled. The specific capacity retention rate (%) before and after acid immersion is tested.

[0057] Table 5. Surface impedance and chemical stability of the high-nickel cathode materials prepared in Examples 13-16 and Comparative Examples 9-10 <![CDATA[Charge transfer resistance R ct (Ω·cm 2 )]]> Specific capacity retention (%) Example 13 22.4 87.2 Example 14 21.8 84.6 Example 15 22.1 86.9 Example 16 22.3 85.7 Comparative Example 9 64.2 80.3 Comparative Example 10 41.7 84.8 As shown in Table 5, Examples 13 to 16 are significantly better than Comparative Examples 9 and 10 in terms of chemical stability and electrochemical interface impedance, indicating that the reactive buffer cleaning combined with flash annealing process used in the examples has obvious advantages in improving the surface chemical stability and electrochemical kinetic performance of high-nickel cathode materials.

[0058] Comparative Example 9 used pure water washing combined with conventional vacuum drying, but lacked the chemical neutralization effect of acid buffer and high-temperature heat treatment step, resulting in incomplete removal of residual lithium salt on the surface and easy regeneration during the drying process, causing severe gelation of the slurry. At the same time, the surface structure damage caused by water washing significantly increased the interfacial impedance. Although Comparative Example 10 used a buffer washing process, it only carried out conventional drying without high-temperature flash evaporation. As a result, the phosphate precursor generated on the surface existed only in the form of physical adhesion and failed to fuse with the substrate to form a dense fast ion conductor layer. Although it effectively controlled the residual alkali and slurry viscosity, its interfacial impedance was significantly higher than that of the example, and charge transport was hindered.

[0059] In summary, this invention introduces ammonium dihydrogen phosphate as a reactive cleaning agent and combines it with a high-temperature flash annealing process. These two processes produce a significant synergistic effect: the acidic buffer cleaning agent converts harmful residual alkali on the surface into lithium phosphate precursors in situ, solving the problem of pulp gelation; the high-temperature flash annealing induces atomic-level diffusion and fusion between the precursor and the substrate surface, constructing a low-impedance fast-ion conductor interface layer. This combination of chemical conversion and thermal activation synergistically optimizes the processing and electrochemical properties of the material surface, turning surface waste alkali into a valuable resource, significantly reducing processing difficulty while greatly improving the interfacial conductivity of the high-nickel cathode material.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-nickel cathode material, characterized in that: The preparation method is as follows: After dissolving nickel sulfate, cobalt sulfate, and manganese sulfate in water to prepare a metal salt solution, an internal dopant is added. Under nitrogen protection, the bottom liquid is introduced into the reactor and the pH value and ammonia concentration are adjusted to enter the precursor synthesis stage; The precursor synthesis stage specifically involves: adding the metal salt solution concurrently to the base liquid, along with a precipitant and a complexing agent, and controlling the pH and free ammonia concentration of the system to carry out the reaction; subsequently, linearly reducing the pH and free ammonia concentration; aging after stopping the feed, and centrifuging, washing, and vacuum drying the solid product to obtain a spherical precursor; Lithium-mixed sintering process: The spherical precursor is mixed with lithium hydroxide and then tungsten trioxide powder is added. After sintering in an oxygen atmosphere, it is annealed at a constant temperature in a nitrogen atmosphere to obtain the electrode material. The electrode material is cleaned with a buffer cleaning solution and then flash annealed to obtain the high-nickel cathode material.

2. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: In the metal salt solution, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate is 83:11:5; the internal dopant is chromium nitrate nonahydrate.

3. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: In the precursor synthesis stage, the precipitant is sodium hydroxide solution and the complexing agent is ammonia solution; the pH value of the system is controlled between 11.2 and 11.6 during the reaction stage, the free ammonia concentration in the reactor is between 0.58 and 0.63 mol / L, and the reaction lasts for 5 hours.

4. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: During the precursor synthesis stage, the pH value is linearly reduced to 10.5 and the free ammonia concentration is linearly reduced to 0.35 mol / L within 15 hours, after which the feed is stopped.

5. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: During the mixing process of the spherical precursor and lithium hydroxide, the ratio of the total molar amount of other metal elements to the molar amount of lithium element is 55:68-77; the sintering temperature under the oxygen atmosphere is 780℃; and the isothermal annealing temperature under the nitrogen atmosphere is 450℃.

6. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: The buffer cleaning solution is specifically an aqueous solution of ammonium dihydrogen phosphate, with a buffer pH range of 6.0-6.

5.

7. The method for preparing a high-nickel cathode material according to claim 1, characterized in that: The flash annealing operation temperature is 400-430℃, and the processing atmosphere is air.

8. A high-nickel cathode material, characterized in that: The high-nickel cathode material is prepared by the preparation method described in any one of claims 1-7.

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