Coated ternary positive electrode precursor, preparation method and application thereof

Abstract

The application provides a coated ternary positive electrode precursor and a preparation method and application thereof. The preparation method comprises the following steps: mixing a zirconium sulfate solution, a hydroxyl carboxylic acid complexing agent and a pH regulator to prepare a zirconium complex solution with a pH of 0.8-1.2; adding the zirconium complex solution into a ternary positive electrode precursor slurry with a pH of 9-11, blending under the condition that the pH of the system is 2-4, then increasing the pH of the system to 5-7 to perform a coating reaction, and obtaining the coated ternary positive electrode precursor. The process provided by the application inhibits the hydrolysis of zirconium ions in the zirconium sulfate solution storage and the initial mixing, so that the zirconium ions exist in the form of stable complexes; and the blending is completed in a specific pH window, so that the zirconium species is fully and uniformly adsorbed on the surface of the precursor; then the pH of the system is increased to guide the directional heterogeneous precipitation of the zirconium species on the surface of the core, so that a uniform, dense and firmly combined zirconium-containing coating layer is constructed.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a coated ternary cathode precursor, its preparation method, and its application. Background Technology

[0002] Ternary lithium-ion batteries, due to their high energy density, have become an important development direction in the field of power batteries. Nickel-cobalt-manganese ternary cathode materials are a core component, and their capacity is positively correlated with nickel content. However, with increasing nickel content, problems such as decreased cycle stability under high voltage, intensified interfacial side reactions, and insufficient thermal stability become increasingly prominent, hindering their further application. Existing improvement strategies mainly include bulk element doping, single crystallization, concentration gradient structure design, and surface coating modification.

[0003] Among surface coating modification strategies, zirconium-based coatings have become a research hotspot due to their ability to effectively stabilize crystal structures and inhibit electrolyte corrosion. Currently, zirconium sulfate is commonly used as the zirconium source in industry. However, it is highly susceptible to hydrolysis in aqueous solutions, generating zirconium hydroxide or basic zirconium sulfate precipitates, resulting in poor stability of the coating agent solution and difficulties in storage and transportation. More critically, under the trend of hydrolysis, when zirconium sulfate solution is directly mixed with alkaline ternary precursor slurry, zirconium species are instantly precipitated due to drastic local pH changes, causing uneven bulk precipitation rather than forming a uniform and dense coating layer on the surface of the core particles. This severely limits the controllability and repeatability of the coating process, ultimately affecting the stable improvement of the material's electrochemical performance.

[0004] Therefore, how to effectively suppress premature hydrolysis of zirconium sources and achieve directional, uniform, and dense coating of zirconium species on the surface of core particles is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a coated ternary cathode precursor, its preparation method, and its applications. This invention employs a hydroxycarboxylic acid complexing agent combined with a stepwise pH control strategy to effectively suppress the hydrolysis of zirconium ions during storage and initial mixing in zirconium sulfate solution, ensuring their existence in a stable complex form. Furthermore, by completing the blending within a specific pH window, sufficient and uniform adsorption of zirconium species on the precursor surface is achieved. Subsequently, by increasing the system pH, the zirconium species are guided to undergo directional heterogeneous precipitation on the core surface, thereby constructing a uniform, dense, and firmly bonded zirconium-containing coating layer. This process improves the controllability and reproducibility of the coating process.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a coated ternary cathode precursor, the method comprising the following steps: A zirconium sulfate solution, a hydroxycarboxylic acid complexing agent, and a pH adjuster were mixed to prepare a zirconium complexing solution with a pH of 0.8-1.2. The zirconium complex solution was added to a ternary cathode precursor slurry with a pH of 9-11, and the system was blended while maintaining a pH of 2-4. Then, the pH of the system was raised to 5-7 to carry out a coating reaction, thereby obtaining the coated ternary cathode precursor.

[0007] This invention employs a hydroxycarboxylic acid complexing agent combined with a stepwise pH control strategy to effectively suppress the hydrolysis of zirconium ions during storage and initial mixing in zirconium sulfate solution, ensuring their existence in a stable complex form. Furthermore, by completing the blending within a specific pH window, sufficient and uniform adsorption of zirconium species on the precursor surface is achieved. Subsequently, by increasing the system pH, the zirconium species are guided to undergo directional heterogeneous precipitation on the core surface, thereby constructing a uniform, dense, and firmly bonded zirconium-containing coating layer. This process improves the controllability and reproducibility of the coating process and reduces costs. The ternary cathode material prepared based on this coated ternary cathode precursor exhibits significantly improved cycle stability and safety performance under high voltage.

[0008] In this invention, a zirconium complex solution with a pH of 0.8-1.2 is used, wherein the pH can be, for example, 0.8, 0.9, 1, 1.1, or 1.2. This strongly acidic condition effectively inhibits the hydrolysis of zirconium ions, ensuring that the complex solution remains clear and stable over a long period during storage and transportation.

[0009] In this invention, the ternary cathode precursor slurry has a pH of 9-11, where the pH can be, for example, 9, 10, or 11. The slurry environment with a pH of 9-11 creates conditions for establishing a controllable buffer zone when mixed with a strongly acidic zirconium complex solution.

[0010] In this invention, the system is blended under conditions of pH 2-4, where the pH can be, for example, 2, 3, or 4. Blending the system under pH conditions of 2-4 prevents the zirconium complex from instantly precipitating due to a sudden increase in pH, while also maintaining appropriate reactivity, thus allowing sufficient time for uniform adsorption and enrichment on the surface of the precursor.

[0011] In this invention, the pH of the system is raised to 5-7, for example, it can be 5, 6 or 7. This pH range is the critical range for the precipitation of zirconium species. Raising it to this range can induce the zirconium ions adsorbed on the surface of the precursor to undergo directional and slow hydrolysis and precipitation, forming a uniform and dense coating layer, while maximally inhibiting its homogeneous nucleation in the bulk solution phase.

[0012] Preferably, the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:(0.5-3), for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc.

[0013] In this invention, limiting the molar ratio of zirconium ions to hydroxycarboxylic acid complexing agents in the zirconium sulfate solution to a suitable range is crucial for achieving effective complexation and controlled release. If the ratio is too high, the complexation is insufficient, failing to adequately suppress hydrolysis under acidic conditions; if the ratio is too low, the complex becomes overly stable, making dissociation difficult in subsequent reactions, resulting in incomplete coating. Therefore, a suitable molar ratio ensures the stable presence of zirconium ions during acidic storage and weakly acidic blending, while allowing for timely and quantitative release and precipitation on the precursor particle surface upon pH increase, thereby achieving the preparation of a uniform, dense, and controllable coating layer.

[0014] Preferably, the hydroxycarboxylic acid complexing agent includes any one or a combination of at least two of citric acid, tartaric acid, or gluconic acid.

[0015] Preferably, the preparation method of the ternary cathode precursor slurry with a pH of 9-11 includes: A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution were added concurrently to the base solution to carry out a co-precipitation reaction. After the reaction was completed, post-processing was performed to obtain the ternary cathode precursor slurry with a pH of 9-11.

[0016] Preferably, the post-processing includes: first filtering, then washing the filtered solid precipitate, and finally redispersing the washed solid precipitate in water to obtain a ternary cathode precursor slurry with a solid content of 10-30 wt%.

[0017] Preferably, the blending process is accompanied by stirring.

[0018] Preferably, the blending time is 10-60 minutes, for example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0019] Preferably, the blending temperature is 25-40°C, for example, it can be 25°C, 30°C, 35°C or 40°C.

[0020] Preferably, during the process of raising the pH of the system to 5-7, the pH adjuster used includes an alkaline solution with a concentration of 0.5-2 mol / L. For example, the concentration can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2 mol / L, and the alkaline solution can be, for example, sodium hydroxide solution, potassium hydroxide solution, or ammonia solution.

[0021] Preferably, during the process of raising the pH of the system to 5-7, the rate of pH increase is 0.1-1 pH units / minute. For example, the rate of increase could be 0.1 pH units / minute, 0.2 pH units / minute, 0.3 pH units / minute, 0.5 pH units / minute, 0.7 pH units / minute, 0.8 pH units / minute, 0.9 pH units / minute, or 1 pH unit / minute, etc.

[0022] In this invention, during the process of controlling the pH of the system to increase to 5-7, the pH increase rate is 0.1-1 pH units / minute, which allows the supersaturation of the system to increase gradually, ensuring that the zirconium ions adsorbed on the core surface preferentially and orderly precipitate and grow, thereby forming a uniform and firmly bonded coating layer.

[0023] Preferably, the temperature of the coating reaction is 55-65°C, for example, 55°C, 60°C or 65°C.

[0024] Preferably, the coating reaction time is 2-6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0025] Preferably, the preparation method includes the following steps: (1) A zirconium sulfate solution and a hydroxycarboxylic acid complexing agent are mixed, and then a pH adjuster is added to adjust the pH of the system to 0.8-1.2 to obtain a zirconium complexing solution; wherein the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:(0.5-3); the hydroxycarboxylic acid complexing agent includes any one or a combination of at least two of citric acid, tartaric acid or gluconic acid.

[0026] A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution are added concurrently to the base solution to carry out a co-precipitation reaction. The temperature of the reaction system is controlled at 55-65℃ (e.g., 55℃, 60℃, or 65℃), the pH of the reaction system is controlled at 11-12 (e.g., 11, 11.2, 11.4, 11.6, 11.8, or 12), and the reaction time is controlled at 20-40h (e.g., 20h, 30h, or 40h), thus obtaining a ternary cathode precursor. The slurry; wherein, in the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel ions, cobalt ions, and manganese ions is 1:(0.01-0.2):(0.01-0.2) (for example, the selection range of cobalt ions "0.01-0.2" can be, for example, 0.01, 0.05, 0.1, 0.15, or 0.2, etc., and the selection range of manganese ions "0.01-0.2" can be, for example, 0.01, 0.05, 0.1, 0.15, or 0.2, etc.).

[0027] The ternary cathode precursor slurry is post-processed to obtain a ternary cathode precursor slurry with a solid content of 10-30 wt% (e.g., 10 wt%, 20 wt%, or 30 wt%) and a pH of 9-11.

[0028] (2) Under stirring conditions, the zirconium complex solution is added to the ternary cathode precursor slurry. The addition rate is controlled so that the pH of the mixed system is stable in the range of 2-4. The mixing temperature is controlled at 25-40℃ and the time is 10-60min. Then, an alkaline solution with a concentration of 0.5-2mol / L is added so that the pH of the mixed system is increased to 5-7 at a rate of 0.1-1 pH units / min. Then, a coating reaction is carried out at 55-65℃ for 2-6h. After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain the coated ternary cathode precursor.

[0029] In a second aspect, the present invention provides a coated ternary cathode precursor, which is prepared by the preparation method described in the first aspect.

[0030] Thirdly, the present invention provides a ternary cathode material, wherein the ternary cathode material is obtained by mixing and sintering a coated ternary cathode precursor as described in the second aspect with a lithium source.

[0031] For example, the lithium source can be lithium carbonate or lithium hydroxide.

[0032] Fourthly, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery comprises a ternary positive electrode material as described in the third aspect.

[0033] 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.

[0034] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a hydroxycarboxylic acid complexing agent combined with a stepwise pH control strategy to effectively suppress the hydrolysis of zirconium ions during storage and initial mixing in zirconium sulfate solution, ensuring their existence in a stable complex form. Furthermore, by completing the blending within a specific pH window, sufficient and uniform adsorption of zirconium species on the precursor surface is achieved. Subsequently, by increasing the system pH, the zirconium species are guided to undergo directional heterogeneous precipitation on the core surface, thereby constructing a uniform, dense, and firmly bonded zirconium-containing coating layer. This process improves the controllability and reproducibility of the coating process and reduces costs. The ternary cathode material prepared based on this coated ternary cathode precursor exhibits significantly improved cycle stability and safety performance under high voltage. Detailed Implementation

[0035] 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.

[0036] Example 1 This embodiment provides a method for preparing a coated ternary cathode precursor, the method comprising the following steps: (1) A zirconium sulfate solution and a hydroxycarboxylic acid complexing agent are mixed, and then a pH adjuster is added to adjust the pH of the system to 1 to obtain a zirconium complexing solution; wherein, the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:1.5; the hydroxycarboxylic acid complexing agent is citric acid, and the pH adjuster is concentrated sulfuric acid.

[0037] A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution were co-circulated into deionized water to carry out a co-precipitation reaction. The temperature of the reaction system was controlled at 60°C, the pH of the reaction system was 11.5, and the reaction time was 30 h to obtain a ternary cathode precursor slurry. In the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel ions, cobalt ions, and manganese ions was 1:0.1:0.1.

[0038] The ternary cathode precursor slurry was filtered, and then the filtered solid precipitate was washed. Finally, the washed solid precipitate was redispersed in water to obtain a ternary cathode precursor slurry with a solid content of 20 wt% and a pH of 10.

[0039] (2) Under stirring conditions, the zirconium complex solution is added to the ternary cathode precursor slurry. The addition rate is controlled so that the pH of the mixed system is stable in the range of 2-4. The mixing temperature is controlled at 30°C and the time is controlled at 35 min. Then, a sodium hydroxide solution with a concentration of 1 mol / L is added so that the pH of the mixed system is increased to 6 at a rate of 0.5 pH units / min. Then, the coating reaction is carried out at 60°C for 4 h. After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain the coated ternary cathode precursor.

[0040] Example 2 This embodiment provides a method for preparing a coated ternary cathode precursor, the method comprising the following steps: (1) A zirconium sulfate solution and a hydroxycarboxylic acid complexing agent are mixed, and then a pH adjuster is added to adjust the pH of the system to 0.8 to obtain a zirconium complexing solution; wherein, the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:0.5; the hydroxycarboxylic acid complexing agent is tartaric acid, and the pH adjuster is concentrated sulfuric acid.

[0041] A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution were co-circulated into deionized water to carry out a co-precipitation reaction. The temperature of the reaction system was controlled at 55°C, the pH of the reaction system was 11, and the reaction time was 40 h to obtain a ternary cathode precursor slurry. In the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel ions, cobalt ions, and manganese ions was 1:0.1:0.1.

[0042] The ternary cathode precursor slurry was filtered, and then the filtered solid precipitate was washed. Finally, the washed solid precipitate was redispersed in water to obtain a ternary cathode precursor slurry with a solid content of 10 wt% and a pH of 9.

[0043] (2) Under stirring conditions, the zirconium complex solution is added to the ternary cathode precursor slurry, and the addition rate is controlled so that the pH of the mixed system is stable in the range of 2-4. The mixing temperature is controlled at 25°C and the time is controlled at 60 min. Then, a sodium hydroxide solution with a concentration of 1 mol / L is added so that the pH of the mixed system is increased to 5 at a rate of 0.2 pH units / min. Then, the coating reaction is carried out at 55°C for 6 h. After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain the coated ternary cathode precursor. The pH adjuster is sodium hydroxide solution.

[0044] Example 3 This embodiment provides a method for preparing a coated ternary cathode precursor, the method comprising the following steps: (1) A zirconium sulfate solution and a hydroxycarboxylic acid complexing agent are mixed, and then a pH adjuster is added to adjust the pH of the system to 1.2 to obtain a zirconium complexing solution; wherein, the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:3; the hydroxycarboxylic acid complexing agent is gluconic acid, and the pH adjuster is concentrated sulfuric acid.

[0045] A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution were co-circulated into deionized water to carry out a co-precipitation reaction. The temperature of the reaction system was controlled at 65°C, the pH of the reaction system was 12, and the reaction time was 20 h to obtain a ternary cathode precursor slurry. In the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel ions, cobalt ions, and manganese ions was 1:0.1:0.1.

[0046] The ternary cathode precursor slurry was filtered, and then the filtered solid precipitate was washed. Finally, the washed solid precipitate was redispersed in water to obtain a ternary cathode precursor slurry with a solid content of 30 wt% and a pH of 11.

[0047] (2) Under stirring conditions, the zirconium complex solution is added to the ternary cathode precursor slurry, and the addition rate is controlled so that the pH of the mixed system is stable in the range of 2-4. The mixing temperature is controlled at 40°C and the time is 15 min. Then, a sodium hydroxide solution with a concentration of 1 mol / L is added so that the pH of the mixed system is increased to 7 at a rate of 0.8 pH units / min. Then, a coating reaction is carried out at 65°C for 2 h. After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain the coated ternary cathode precursor. The pH adjuster is sodium hydroxide solution.

[0048] Example 4 The difference between this embodiment and Embodiment 1 is that the molar ratio of zirconium ions to the hydroxycarboxylic acid complexing agent in the zirconium sulfate solution is 1:3.5.

[0049] The remaining preparation methods and parameters are consistent with those in Example 1.

[0050] Example 5 The difference between this embodiment and Embodiment 1 is that the molar ratio of zirconium ions to the hydroxycarboxylic acid complexing agent in the zirconium sulfate solution is 1:0.2.

[0051] The remaining preparation methods and parameters are consistent with those in Example 1.

[0052] Example 6 The difference between this embodiment and Embodiment 1 is that the pH of the mixture is increased to 6 at a rate of 0.05 pH units / minute.

[0053] The remaining preparation methods and parameters are consistent with those in Example 1.

[0054] Example 7 The difference between this embodiment and Embodiment 1 is that the pH of the mixed system is increased to 6 at a rate of 1.5 pH units / minute.

[0055] The remaining preparation methods and parameters are consistent with those in Example 1.

[0056] Comparative Example 1 The difference between this comparative example and Example 1 is that the pH of the zirconium complex solution is 1.5.

[0057] The remaining preparation methods and parameters are consistent with those in Example 1.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that the pH of the ternary cathode precursor slurry is 11.5.

[0059] The remaining preparation methods and parameters are consistent with those in Example 1.

[0060] Comparative Example 3 The difference between this comparative example and Example 1 is that the pH of the mixed system is 5 during the blending process.

[0061] The remaining preparation methods and parameters are consistent with those in Example 1.

[0062] Comparative Example 4 The difference between this comparative example and Example 1 is that the pH of the mixed system is 8 during the coating reaction.

[0063] The remaining preparation methods and parameters are consistent with those in Example 1.

[0064] Performance testing The coated ternary cathode precursors provided in the above embodiments and comparative examples were mixed and sintered with lithium carbonate (pre-fired at 500°C for 3 hours, and then sintered at 800°C for 15 hours) to obtain nickel-cobalt-manganese ternary cathode materials.

[0065] Preparation of coin cells: The above-mentioned nickel-cobalt-manganese ternary cathode material, acetylene black and polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone at a mass ratio of 90:5:5, and then coated on aluminum foil. The mixture was then dried in a vacuum drying oven. After drying, the cathode was pressed into a positive electrode sheet using a tablet press in an argon glove box. In the glove box, the positive electrode sheet, polypropylene porous separator, negative lithium sheet and electrolyte were assembled into a coin cell. The solute in the electrolyte was LiPF6 with a concentration of 1 mol / L, and the solvent was EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1.

[0066] The coin cell was subjected to constant current charge-discharge test to test the initial discharge specific capacity of the ternary cathode material. The test voltage was 2.8V-4.3V and the test rate was 0.5C.

[0067] The coin cell battery was subjected to a high-voltage cycle performance test. The test conditions included: 25°C, voltage range of 3-4.5V, 0.5C charge-discharge rate, and 200 cycles.

[0068] The results are shown in Table 1.

[0069] Table 1 analyze: As shown in Table 1, this invention effectively suppresses the hydrolysis of zirconium ions during storage and initial mixing in zirconium sulfate solution by employing hydroxycarboxylic acid complexing agents and a stepwise pH control strategy, ensuring that zirconium ions exist in a stable complex form. Furthermore, by completing the blending within a specific pH window, sufficient and uniform adsorption of zirconium species on the precursor surface is achieved. Subsequently, by increasing the system pH, the zirconium species are guided to undergo directional heterogeneous precipitation on the core surface, thereby constructing a uniform, dense, and firmly bonded zirconium-containing coating layer. This process improves the controllability and reproducibility of the coating process and reduces costs. The ternary cathode material prepared based on this coated ternary cathode precursor exhibits significantly improved cycle stability under high voltage, with a capacity retention rate of up to 94.8%.

[0070] As can be seen from the comparison between Example 1 and Examples 4-5, if the molar ratio of zirconium ions to hydroxycarboxylic acid complexing agents in the zirconium sulfate solution is too small, the resulting complex is too stable and dissociates slowly under the subsequent precipitation pH conditions, resulting in insufficient release of zirconium species and an incomplete and thin coating layer. If the molar ratio of zirconium ions to hydroxycarboxylic acid complexing agents in the zirconium sulfate solution is too large, the complexation is insufficient and cannot effectively suppress the hydrolysis tendency of zirconium ions in acidic storage and the initial stage of mixing, resulting in a small amount of disordered components in the coating layer due to premature hydrolysis.

[0071] As can be seen from the comparison between Example 1 and Examples 6-7, if the pH of the mixed system is increased to 6 at a rate of 0.05 pH units / minute, the slow increase rate will prolong the process time and may cause adverse changes on the surface of the adsorbed zirconium species or precursors under long-term working conditions; if the pH of the mixed system is increased to 6 at a rate of 1.5 pH units / minute, the fast increase rate will cause violent homogeneous nucleation of zirconium ions in the bulk solution phase, generating a large amount of free zirconium oxide impurity phase, which will seriously damage the uniformity and density of the coating.

[0072] As can be seen from the comparison between Example 1 and Comparative Example 1, if the pH of the zirconium complex solution is too high, the acidity of the solution will be weakened, the ability to inhibit the hydrolysis of zirconium ions will decrease, and hydrolysis may occur during preparation or storage, resulting in uneven coating in the later stage.

[0073] As can be seen from the comparison between Example 1 and Comparative Example 2, if the pH of the ternary cathode precursor slurry is too high, its alkalinity is too strong. When mixed with the zirconium complex solution, the local pH buffering capacity is weak, and the pH jump at the interface between the two is violent, which can easily cause instantaneous and disordered precipitation of zirconium species.

[0074] As can be seen from the comparison between Example 1 and Comparative Example 3, if the pH of the mixed system is too high during the blending process, it will enter the rapid precipitation zone of zirconium species. The zirconium complex will begin to precipitate in large quantities before it has fully diffused and adsorbed onto the surface of the precursor, resulting in a loose coating layer and weak binding force with the precursor.

[0075] As can be seen from the comparison between Example 1 and Comparative Example 4, if the pH of the mixed system is too high during the coating reaction, the excessive alkalinity will not only promote the unfavorable crystal transformation and excessive growth of the zirconium precipitate, forming a thick and porous coating layer, but may also erode the ternary precursor and damage its bulk structure.

[0076] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a coated ternary cathode precursor, characterized in that, The preparation method includes the following steps: A zirconium sulfate solution, a hydroxycarboxylic acid complexing agent, and a pH adjuster were mixed to prepare a zirconium complexing solution with a pH of 0.8-1.

2. The zirconium complex solution was added to a ternary cathode precursor slurry with a pH of 9-11, and the system was blended while maintaining a pH of 2-4. Then, the pH of the system was raised to 5-7 to carry out a coating reaction, thereby obtaining the coated ternary cathode precursor.

2. The preparation method according to claim 1, characterized in that, The molar ratio of zirconium ions to the hydroxycarboxylic acid complexing agent in the zirconium sulfate solution is 1:(0.5-3); And / or, the hydroxycarboxylic acid complexing agent includes any one or a combination of at least two of citric acid, tartaric acid, or gluconic acid.

3. The preparation method according to claim 1 or 2, characterized in that, The preparation method of the ternary cathode precursor slurry with a pH of 9-11 includes: A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution were added concurrently to the base solution to carry out a co-precipitation reaction. After the reaction was completed, post-processing was performed to obtain the ternary cathode precursor slurry with a pH of 9-11.

4. The preparation method according to any one of claims 1-3, characterized in that, The blending process is accompanied by stirring; And / or, the blending time is 10-60 min; And / or, the blending temperature is 25-40°C.

5. The preparation method according to any one of claims 1-4, characterized in that, During the process of raising the pH of the system to 5-7, the pH adjusting agent used includes an alkaline solution with a concentration of 0.5-2 mol / L; And / or, during the process of raising the pH of the system to 5-7, the pH of the system is raised at a rate of 0.1-1 pH units / minute.

6. The preparation method according to any one of claims 1-5, characterized in that, The coating reaction is carried out at a temperature of 55-65℃. And / or, the coating reaction takes 2-6 hours.

7. The preparation method according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) A zirconium sulfate solution and a hydroxycarboxylic acid complexing agent are mixed, and then a pH adjuster is added to adjust the pH of the system to 0.8-1.2 to obtain a zirconium complexing solution; wherein, the molar ratio of zirconium ions in the zirconium sulfate solution to the hydroxycarboxylic acid complexing agent is 1:(0.5-3); the hydroxycarboxylic acid complexing agent includes any one or a combination of at least two of citric acid, tartaric acid or gluconic acid; A nickel-cobalt-manganese mixed salt solution, a precipitant solution, and a complexing agent solution are added concurrently to the base solution to carry out a co-precipitation reaction. The temperature of the reaction system is controlled at 55-65℃, the pH of the reaction system is 11-12, and the reaction time is 20-40h to obtain a ternary cathode precursor slurry. In the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel ions, cobalt ions, and manganese ions is 1:(0.01-0.2):(0.01-0.2). The ternary cathode precursor slurry was post-processed to obtain a ternary cathode precursor slurry with a solid content of 10-30 wt% and a pH of 9-11. (2) Under stirring conditions, the zirconium complex solution is added to the ternary cathode precursor slurry. The addition rate is controlled so that the pH of the mixed system is stable in the range of 2-4. The mixing temperature is controlled at 25-40℃ and the time is 10-60min. Then, an alkaline solution with a concentration of 0.5-2mol / L is added so that the pH of the mixed system is increased to 5-7 at a rate of 0.1-1 pH units / min. Then, a coating reaction is carried out at 55-65℃ for 2-6h. After the reaction is completed, solid-liquid separation, washing and drying are performed to obtain the coated ternary cathode precursor.

8. A coated ternary cathode precursor, characterized in that, The coated ternary cathode precursor is prepared by the preparation method described in any one of claims 1-7.

9. A ternary cathode material, characterized in that, The ternary cathode material is obtained by sintering the coated ternary cathode precursor as described in claim 8 with a lithium source.

10. A lithium-ion battery, characterized in that, The positive electrode of the lithium-ion battery includes the ternary positive electrode material as described in claim 9.

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