A positive electrode material, a preparation method and application thereof

Abstract

The application provides a positive electrode material and a preparation method and application thereof, and relates to the technical field of lithium ion batteries.A preparation method of a positive electrode material comprises the following steps: S1, raw materials are weighed according to a stoichiometric ratio of a positive electrode active material precursor, mixed with water, and uniformly mixed with a precipitating agent and a complexing agent, and then a pH is adjusted to obtain a mixture; the mixture is subjected to freeze-drying to obtain the positive electrode active material precursor; S2, the positive electrode active material precursor is uniformly mixed with a lithium source, and then subjected to sintering treatment to obtain the positive electrode active material; and S3, the positive electrode active material is subjected to ball milling with a modified layered double hydroxide and a grinding aid, and then dried to obtain the positive electrode material.The positive electrode material provided by the application has good single crystal property and stable performance, and is helpful to improve the electrochemical performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are widely used in various fields due to their advantages such as light weight, high energy density, no memory effect, long cycle life, and environmental friendliness. The cathode material largely determines these key performance characteristics. Among various cathode materials, ternary cathode materials have become the mainstream cathode material for lithium-ion power batteries due to their advantages such as controllable composition, high energy density, and large specific capacity. However, their actual energy density is relatively low and their cycle performance is poor. Therefore, there is an urgent need to improve the actual energy density and cycle performance of ternary cathode materials to solve the range problem of electric vehicles.

[0003] Increasing the charging voltage of ternary lithium batteries can improve their energy density. However, increasing the charging voltage of ternary lithium batteries has two main consequences: First, it causes excessive delithiation of the cathode material, leading to the collapse of the layered structure of the material and reducing the battery's cycle performance. Second, the polycrystalline cathode material will be corroded by HF generated from the decomposition of the electrolyte, causing structural damage to the cathode material and the formation of new interfaces. These new interfaces increase the occurrence of side reactions between the cathode material and the electrolyte, resulting in a decrease in the battery's capacity, cycle performance, and safety performance.

[0004] Therefore, there is an urgent need to prepare a stable, high-voltage, and high-energy-density single-crystal ternary cathode material. Summary of the Invention

[0005] Based on the technical problems existing in the background technology, the present invention proposes a positive electrode material, its preparation method and application.

[0006] The present invention proposes a positive electrode material comprising a core layer and a shell layer, wherein the core layer is a positive electrode active material and the shell layer is a modified layered double hydroxide.

[0007] Preferably, the positive electrode active material is LiNi. x Co y Mn z O2, where 0≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and x+y+z=1.

[0008] The cathode material provided by this invention is a modified layered double hydroxide coated cathode active material structure. When modified LDHs are used as a coating material to modify ternary single-crystal cathode materials, their interlayer anions can effectively replace harmful anions generated during battery cycling, such as fluoride anions (F...). - HF2 - ), boron-based anions (such as BOB) -Modified LDHs, etc., prevent frequent decomposition and reconstruction of the SEI membrane and oxidative decomposition of the electrolyte at high temperatures, thus improving cycle stability. Modified LDHs can provide Li... + Provides dedicated inter-layer transmission channels, increasing Li + The improved transport path and efficiency enhance the electrochemical performance of the material.

[0009] Preferably, the method for preparing the modified layered double hydroxide includes the following steps: mixing divalent metal salt, trivalent metal salt, and water evenly, adding precipitant and complexing agent, performing water bath treatment, and freeze-drying to obtain layered double hydroxide; mixing layered double hydroxide, amino acid, and solvent evenly, and heating treatment to obtain modified layered double hydroxide.

[0010] LDHs particles prepared by freeze-drying also exhibit good dispersibility and uniform crystal structure. Then, modified LDHs are prepared by dehydration condensation reaction of carboxyl groups rich in hydroxyl groups and amino acids between the LDHs layers at high temperature; the LDHs layers are bridged with a large number of branches with amino groups.

[0011] More preferably, the divalent metal salt is selected from Zn. 2+ Mg 2+ Mn 2+ Fe 2+ Ni 2+ Co 2+ It contains one or more of the following: nitrates, acetates, sulfates, and chlorides; the trivalent metal salt is selected from Al. 3+ Cr 3+ Fe 3+ Mn 3+ ,Sc 3+ Co 3+ It contains one or more of the following: nitrates, acetates, sulfates, and chlorides; the molar ratio of divalent metal salts to trivalent metal salts is (2~4):1.

[0012] The LDHs used in this invention have different stable interlayer anions depending on the metal salt used in their synthesis (chloride ions, sulfate ions, nitrate ions, acetate ions, etc.), and these interlayer anions can be replaced, allowing other ions to enter their interlayer. When LDHs are used as coating materials to modify ternary single-crystal cathode materials, their interlayer anions can effectively replace harmful anions generated during battery cycling, such as fluoride anions (F...). - HF2 - ), boron-based anions (such as BOB) - Modified LDHs, etc., prevent frequent decomposition and reconstruction of the SEI membrane and oxidative decomposition of the electrolyte at high temperatures, thus improving cycle stability. Modified LDHs can provide Li... +Provides dedicated inter-layer transmission channels, increasing Li + The improved transport path and efficiency enhance the electrochemical performance of the material.

[0013] More preferably, the precipitant is selected from one or more of sodium carbonate, ammonium carbonate, sodium hydroxide, lithium hydroxide, and sodium oxalate; the concentration of the precipitant is 3-8 mol / L; the complexing agent is selected from one or more of ammonia, tartaric acid, and citric acid; the concentration of the complexing agent is 2-4 mol / L.

[0014] Precipitating agents react with metal cations in the solution to form insoluble hydroxides or carbonate precipitates by raising the pH of the solution or providing anions; complexing agents form soluble complexes with metal ions, reducing the concentration of free ions, thereby slowing down the precipitation rate and inhibiting stepwise precipitation caused by differences in the solubility products of different metal hydroxides.

[0015] More preferably, the temperature of the water bath treatment is 60~80℃.

[0016] The water bath treatment time is until the reaction is complete and no more precipitates are produced.

[0017] More preferably, the freeze-drying process includes first cooling the reaction system to 2~8℃, then placing it in a freeze-drying chamber at -30℃~-50℃ with the vacuum degree controlled at 10~20Pa, until it is completely frozen; turning on the vacuum diffusion pump, reducing the vacuum degree to below 5Pa, and the ice begins to sublimate, with a sublimation drying time of 12~24h; maintaining the vacuum degree, raising the temperature to 25~45℃, and the desorption drying time of 5~10h.

[0018] This invention utilizes freeze-drying to prepare well-dispersible LDHs and ternary precursors with good single-crystal properties. Because the solvent in the reaction system is rapidly condensed into ice during freeze-drying and then sublimated for dehydration, the absence of liquid water during the drying process avoids hydrogen bonding between water and product particles. During solvent removal, the particles transform from a solid-solid interface to a gas-solid interface. Although the gas-solid interface is thermodynamically unstable, the energy barrier present during the process makes this type of interface more conducive to maintaining the primary particle state of the nanoparticles, fundamentally preventing the formation of hard agglomerates between particles during drying. In subsequent processing, the use of water-based solvents is abandoned in favor of organic solvents, increasing solvent volatility and the driving force of the process. This effectively maintains the single-crystal morphology of the particles.

[0019] More preferably, the amino acid is selected from one or more of glycine and lysine.

[0020] More preferably, the molar ratio of the layered double hydroxide to the amino acid is 1:(0.005~0.025).

[0021] In this invention, LDHs are modified by blending with amino acids, resulting in a high-temperature dehydration condensation reaction between the numerous hydroxyl groups between the LDH layers and the carboxyl groups on the amino acids, thus producing modified LDHs with a large number of amine groups. Since the surface of the ternary single-crystal cathode material prepared by the co-precipitation method is rich in hydroxyl groups, high-energy ball milling can break the surface hydroxyl hydrogen bonds, exposing highly active sites. During the co-milling process with the modified LDHs, amine groups can be directly bonded, thereby achieving the effect of LDHs coating the modified ternary single-crystal cathode material.

[0022] More preferably, the solvent is selected from one or more of dipropylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether, ethylene glycol butyl ether, and diethylene glycol butyl ether.

[0023] Solvents with boiling points above 150°C are helpful for material preparation.

[0024] More preferably, the temperature of the heat treatment is 160~200℃, and the heat treatment time is 2~5h.

[0025] This invention also proposes a method for preparing a cathode material, comprising the following steps:

[0026] S1. Weigh the raw materials according to the stoichiometric ratio of the positive electrode active material precursor, mix them evenly with water, add precipitant and complexing agent, adjust the pH to obtain a mixture, freeze-dry the mixture to obtain the positive electrode active material precursor.

[0027] S2. After uniformly mixing the positive electrode active material precursor with the lithium source, sintering is performed to obtain the positive electrode active material.

[0028] S3. The positive electrode active material and the modified layered double hydroxide are ball-milled with a grinding aid and dried to obtain the positive electrode material.

[0029] This method utilizes freeze-drying technology to prepare precursors for cathode active materials, and then modifies ternary single-crystal cathode materials through bonding reactions. The ternary cathode materials prepared by this method exhibit good single-crystal properties, few side reactions, and stable performance.

[0030] Preferably, in S1, the raw materials for the positive electrode active material precursor include one or more of nickel source, cobalt source, and manganese source; the nickel source is selected from one or more of nickel nitrate, nickel sulfate, nickel acetate, and nickel chloride; the cobalt source is selected from one or more of cobalt nitrate, cobalt sulfate, cobalt acetate, and cobalt chloride; and the manganese source is selected from one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride.

[0031] Preferably, in S1, the positive electrode active material precursor is Ni. x Co y Mn z (OH)2 or Nix Co y Mn z CO3, where 0≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and x+y+z=1.

[0032] Preferably, in S1, the precipitant is selected from one or more of sodium carbonate, ammonium carbonate, sodium hydroxide, lithium hydroxide, and sodium oxalate; the concentration of the precipitant is 3~10 mol / L; the complexing agent is selected from one or more of ammonia, tartaric acid, and citric acid; the concentration of the complexing agent is 1.5~6 mol / L.

[0033] Preferably, in step S1, the pH is adjusted to 10.5~11.5.

[0034] Preferably, in S1, the freeze-drying process includes first cooling the reaction system to 2~8℃, then placing it in a freeze-drying chamber at -30℃~-50℃ with the vacuum degree controlled at 10~20Pa, until it is completely frozen; turning on the vacuum diffusion pump, the vacuum degree drops to below 5Pa, the ice begins to sublimate, and the sublimation drying time is 12~24h; maintaining the vacuum degree, the temperature is raised to 25~45℃, and the desorption drying time is 5~10h.

[0035] Preferably, in S2, the lithium source is selected from one or more of lithium hydroxide and lithium carbonate.

[0036] Preferably, in S2, the molar ratio of the positive electrode active material precursor to the lithium source is 1:(1.03~1.10).

[0037] Preferably, in S2, the sintering treatment includes heating to 450-550°C at a rate of 1-3°C / min and holding for 6-8 hours; then heating to 700-850°C at a rate of 2-5°C / min and holding for 24-48 hours; and then cooling to room temperature in the furnace.

[0038] Sintering temperatures within a certain range help to form particles with uniform size.

[0039] Preferably, in S3, the molar ratio of the positive electrode active material to the modified layered double hydroxide is 1:(0.005~0.05).

[0040] The molar ratio of the positive electrode active material to the modified layered double hydroxide directly affects the thickness and uniformity of the coating layer within a certain range. Too low a molar ratio may result in incomplete coating and ineffective protection of the core; too high a molar ratio may increase the internal resistance of the material and reduce energy density. Therefore, selecting an appropriate molar ratio range is crucial for optimizing the performance of ternary materials.

[0041] Preferably, in S3, the grinding aid is selected from one or more of benzene, cyclohexane, methanol, ethanol, and isopropanol.

[0042] Choosing the right type of grinding aid can help increase the contact between the material and the grinding balls, thereby improving the grinding effect and efficiency.

[0043] Preferably, in step S3, the ball milling speed is 350~1000 rpm, and the ball milling time is 1~5 hours.

[0044] Preferably, in step S3, the drying is vacuum drying, the drying temperature is 100~150℃, and the drying time is 2~6h.

[0045] Application of the above-described cathode material or the cathode material prepared by the above-described method in lithium-ion batteries.

[0046] The cathode material provided by this invention, when applied to lithium-ion batteries, helps to improve the electrochemical performance of lithium-ion batteries.

[0047] The beneficial effects of this invention are as follows:

[0048] This invention prepares a precursor for the positive electrode active material using a freeze-drying method, optimizing the preparation process of single-crystal materials. During precursor preparation, the primary particles are dispersed independently, avoiding lithium burn-off and energy loss caused by excessively high-temperature sintering, resulting in a higher degree of single-crystal formation in the prepared positive electrode material. Similarly, the LDH particles prepared by the freeze-drying method also exhibit good dispersibility and uniform crystal structure. Then, modified LDHs are obtained by utilizing the dehydration condensation reaction of carboxyl groups rich in hydroxyl and amino acid groups between the LDH layers at high temperature. These modified LDHs have numerous amine-based branched chains bridging the interlayers. Finally, this invention utilizes high-energy ball milling to coat the prepared positive electrode active material with the modified LDHs. During this process, because the surface of the positive electrode active material prepared by the co-precipitation method is rich in hydroxyl groups, high-energy ball milling can break the surface hydroxyl hydrogen bonds, exposing highly active sites. During co-milling with the modified LDHs, amine groups can be directly bonded, thereby achieving the effect of LDHs coating the modified positive electrode active material. The positive electrode active material prepared by this invention has a high degree of single crystallization and a more stable structure; the LDHs particles have good dispersion, ensuring uniform coating. Both LDHs and the positive electrode active material are modified through active group bonding, exhibiting high bonding strength, ensuring coating effect and quality, and improving material stability. When LDHs are used as a coating material to modify the positive electrode active material, they can, on the one hand, purify the electrolyte to prevent frequent decomposition and reconstruction of the SEI film and oxidative decomposition of the electrolyte at high temperatures, thus improving cycle stability; on the other hand, they increase Li... + The improved transport path and efficiency enhance the electrochemical performance of the material. Attached Figure Description

[0049] Figure 1This is a schematic diagram of the freeze-drying process in Example 1.

[0050] Figure 2 This is a schematic diagram of the LDHs modification principle in Example 1.

[0051] Figure 3 This is a schematic diagram of the principle of the ternary single crystal material coated with modified LDHs in Example 1. Detailed Implementation

[0052] The technical solution of the present invention will be described in detail through specific embodiments.

[0053] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.

[0054] Example 1

[0055] A method for preparing a positive electrode material includes the following steps:

[0056] S1. Weigh nickel nitrate, cobalt nitrate and manganese nitrate according to a stoichiometric ratio of 7:1:2, and fully dissolve them in deionized water. Add 8 mol / L sodium carbonate and 4 mol / L ammonia water, and control the pH of the system at 11.2. After the reaction is completed, freeze-dry the reaction system to obtain the precursor of the positive electrode active material.

[0057] S2. After uniformly mixing the positive electrode active material precursor with lithium hydroxide at a molar ratio of 1:1.05, the mixture is heated to 500℃ at a rate of 1.5℃ / min under an oxygen atmosphere and held for 6 hours; then heated to 800℃ at a rate of 3℃ / min and held for 30 hours; the positive electrode active material is obtained by cooling the mixture to room temperature in the furnace.

[0058] S3. After mixing the positive electrode active material with the modified layered double hydroxide at a molar ratio of 1:0.03, add isopropanol and perform high-energy ball milling at a speed of 550 rpm for 3 hours. Finally, vacuum dry at 120°C for 4 hours to obtain the modified LDHs-coated ternary single crystal positive electrode material.

[0059] The preparation of modified layered double hydroxides includes: weighing zinc nitrate and aluminum nitrate at a molar ratio of 3:1 and completely dissolving them in deionized water, adding 4.5 mol / L sodium hydroxide and 2.5 mol / L tartaric acid, heating in a water bath at 75°C, and freeze-drying the reaction system after the reaction is complete to obtain LDHs; weighing and mixing the obtained LDHs with glycine at a molar ratio of 1:0.008 and dispersing them in propylene glycol butyl ether, heating, maintaining the temperature at 180°C, stirring and reacting for 4 hours to obtain modified LDHs;

[0060] The freeze-drying process includes first cooling the reaction system to 2°C, then placing it in a freeze-drying chamber that is cooled to -40°C at a rate of 1°C / min, with the vacuum degree controlled at 10Pa, until it is completely frozen; turning on the vacuum diffusion pump, the vacuum degree is reduced to 2Pa, and the ice begins to sublimate, with a sublimation drying time of 16h; maintaining the vacuum degree, the temperature is raised to 30°C, and the desorption drying time is 6h.

[0061] Example 2

[0062] A method for preparing a positive electrode material includes the following steps:

[0063] S1. Weigh nickel nitrate, cobalt nitrate and manganese nitrate according to a stoichiometric ratio of 7:1:2, and fully dissolve them in deionized water. Add 5 mol / L sodium carbonate and 2 mol / L ammonia water, and control the pH of the system at 10.8. After the reaction is completed, freeze-dry the reaction system to obtain the precursor of the positive electrode active material.

[0064] S2. After uniformly mixing the positive electrode active material precursor with lithium hydroxide at a molar ratio of 1:1.08, the mixture is heated to 450°C at a rate of 2°C / min under an oxygen atmosphere and held for 8 hours; then heated to 750°C at a rate of 2°C / min and held for 36 hours; the positive electrode active material is obtained by cooling the mixture to room temperature in the furnace.

[0065] S3. After mixing the positive electrode active material with the modified layered double hydroxide at a molar ratio of 1:0.01, add isopropanol and perform high-energy ball milling at a speed of 700 rpm for 2 hours. Finally, vacuum dry at 130°C for 3 hours to obtain the modified LDHs-coated ternary single crystal positive electrode material.

[0066] The preparation of modified layered double hydroxides includes: weighing zinc nitrate and aluminum nitrate at a molar ratio of 2.5:1 and completely dissolving them in deionized water, adding 6 mol / L sodium hydroxide and 3 mol / L tartaric acid, heating in a water bath at 70°C, and freeze-drying the reaction system after the reaction is complete to obtain LDHs; weighing and mixing the obtained LDHs with glycine at a molar ratio of 1:0.015 and dispersing them in propylene glycol butyl ether, heating, maintaining the temperature at 160°C, and stirring the reaction for 3 hours to obtain modified LDHs.

[0067] Example 3

[0068] A method for preparing a positive electrode material includes the following steps:

[0069] S1. Weigh nickel nitrate, cobalt nitrate and manganese nitrate according to the stoichiometric ratio of 7:1:2, and fully dissolve them in deionized water. Add 10 mol / L sodium carbonate and 5 mol / L ammonia water, and control the pH of the system at 11.5. After the reaction is completed, freeze-dry the reaction system to obtain the precursor of the positive electrode active material.

[0070] S2. After uniformly mixing the positive electrode active material precursor with lithium hydroxide at a molar ratio of 1:1.03, the mixture is heated to 550°C at a rate of 2.5°C / min under an oxygen atmosphere and held for 7 hours; then heated to 850°C at a rate of 4°C / min and held for 20 hours; the positive electrode active material is obtained by cooling the mixture to room temperature in the furnace.

[0071] S3. After mixing the positive electrode active material with the modified layered double hydroxide at a molar ratio of 1:0.025, add isopropanol and perform high-energy ball milling at a speed of 900 rpm for 1 hour. Finally, vacuum dry at 140°C for 5 hours to obtain the modified LDHs-coated ternary single crystal positive electrode material.

[0072] The preparation of modified layered double hydroxides includes: weighing zinc nitrate and aluminum nitrate at a molar ratio of 4:1 and completely dissolving them in deionized water, adding 8 mol / L sodium hydroxide and 4 mol / L tartaric acid, heating in a water bath at 80°C, and freeze-drying the reaction system after the reaction is complete to obtain LDHs; weighing and mixing the obtained LDHs with glycine at a molar ratio of 1:0.02 and dispersing them in propylene glycol butyl ether, heating, maintaining the temperature at 200°C, and stirring the reaction for 5 hours to obtain modified LDHs.

[0073] Comparative Example 1

[0074] The only difference between Comparative Example 1 and Example 1 is that "modified layered double hydroxide" in Example 1 is changed to "layered double hydroxide", and the other steps are the same as in Example 1.

[0075] The preparation of layered double hydroxides includes: weighing zinc nitrate and aluminum nitrate at a molar ratio of 3:1 and completely dissolving them in deionized water; adding 4.5 mol / L sodium hydroxide and 2.5 mol / L tartaric acid; heating in a water bath at 75°C; and freeze-drying the reaction system after the reaction is complete to obtain LDHs.

[0076] Comparative Example 2

[0077] Compared with Example 1, Comparative Example 2 differs only in that the "freeze-drying" in step S1 of Example 1 and the preparation process of the modified layered double hydroxide is changed to "drying at 120°C". The remaining steps are the same as in Example 1.

[0078] Comparative Example 3

[0079] The only difference between Comparative Example 3 and Example 1 is that step S3 is different, while the other steps are the same as in Example 1.

[0080] Specifically: S3, the positive electrode active material and alumina are mixed at a molar ratio of 1:0.03 and sintered at a temperature of 550℃ for 8 hours, and then cooled in the furnace to obtain the alumina-coated ternary single crystal positive electrode material.

[0081] Test case

[0082] The positive electrode materials from Examples 1-3 and Comparative Examples 1-3 were used to fabricate 3Ah wound pouch batteries. The specific methods are as follows: Positive electrode material, PVDF, and carbon nanotube slurry were mixed in a mass ratio of 97.2:1.2:1.6 to form a slurry. This slurry was then coated, rolled, baked, cut, and had tabs welded to form a positive electrode sheet. Graphite, SP, CMC, and SBR were mixed in a mass ratio of 96.9:0.8:0.8:1.5 to form a slurry. This slurry was then coated, rolled, baked, cut, and had tabs welded to form a negative electrode sheet. The positive and negative electrodes were then wound, casing, top-side sealed, injected with electrolyte, sealed, formed, aged, sealed again, and capacity tested to obtain the 3Ah wound pouch battery. The battery was tested at 0.2C for initial discharge and initial efficiency, and at 25℃ and 45℃ for cycling, with the test results shown in Table 1.

[0083] Table 1

[0084]

[0085] As can be seen from the test results in Table 1, compared with the ternary cathode material in the example and the comparative example, the first discharge, first efficiency and cycle performance of the example are significantly better than those of the comparative example.

[0086] Comparative Example 1 did not modify the LDHs compared to the Examples. Since LDHs decompose above 400°C, they cannot be coated using a mixing-sintering method, and mechanical mixing makes it difficult to uniformly and stably coat them onto the matrix. However, the modified LDHs bridged a large number of amine groups. The mechanical force of high-energy ball milling disrupted the surface hydroxyl hydrogen bonds, exposing highly active sites for direct carboxyl group bonding, ensuring coating effectiveness and quality, and improving material stability.

[0087] Compared to the examples, Comparative Example 2 did not involve freeze-drying. Firstly, the resulting LDH particles exhibited poor dispersibility, leading to a correspondingly poor coating effect. Secondly, sintering at the same temperature failed to yield ternary materials with a single-crystal morphology. Freeze-drying rapidly condenses the solvent in the reaction system into ice, which then sublimates and dehydrates. The absence of liquid water during this process prevents the formation of hydrogen bonds between water and product particles. This type of interface is more conducive to maintaining the primary particle state of the nanoparticles, fundamentally preventing the formation of hard agglomerates between particles during drying. Ternary materials with a single-crystal morphology have advantages in structural stability, thus exhibiting superior electrochemical performance.

[0088] Comparative Example 3, compared to the Examples, uses conventional alumina coated by high-temperature sintering. High-temperature sintered alumina coating is significantly brittle, prone to uneven coating thickness or particle agglomeration due to localized agglomeration, resulting in inconsistent coating uniformity. Furthermore, high temperatures may exacerbate lithium volatilization, forming a lithium-deficient phase and reducing material conductivity. LDHs, with their layered structure, can purify the electrolyte and improve cycle stability through interlayer anion displacement; additionally, after modification, they can become Li... + Provides a dedicated transmission channel, improving Li + Improve the transport path and efficiency, and enhance the electrochemical performance of the material.

[0089] Figure 1 The diagram illustrates the freeze-drying process in Example 1. It shows that during freeze-drying, the solvent in the reaction system is rapidly condensed into ice, which is then sublimated and dehydrated. The absence of liquid water during the drying process prevents hydrogen bonding between water and the product particles. During solvent removal, the particles transform from a solid-solid interface to a gas-solid interface. Although the gas-solid interface is thermodynamically unstable, the energy barrier present during the process makes it more conducive to maintaining the primary particle state of the nanoparticles, fundamentally preventing hard agglomeration between particles during drying. In subsequent processing, the use of water-based solvents is abandoned in favor of organic solvents, increasing solvent volatility and the driving force of the process. This effectively maintains the single-crystal morphology of the particles.

[0090] Figure 2 The diagram below illustrates the modification principle of LDHs in Example 1. It can be seen that through the blending modification of LDHs with amino acids, a large number of hydroxyl groups between the LDHs layers undergo a high-temperature dehydration condensation reaction with the carboxyl groups on the amino acids, resulting in modified LDHs with a large number of amine groups.

[0091] Figure 3 The diagram below illustrates the principle of the ternary single-crystal material coated with modified LDHs in Example 1. It can be seen that the surface of the ternary single-crystal cathode material prepared by the co-precipitation method is rich in hydroxyl groups. High-energy ball milling can destroy the surface hydroxyl hydrogen bonds and expose highly active sites. During the co-milling process with modified LDHs, amine groups can be directly bonded, thereby achieving the effect of LDHs coating the modified ternary single-crystal cathode material.

[0092] In summary, the cathode material provided by this invention has good single-crystal properties and stable performance, which helps to improve the electrochemical performance of lithium-ion batteries.

[0093] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, It consists of a core layer and a shell layer. The core layer is the positive electrode active material, and the shell layer is a modified layered double hydroxide. The positive electrode active material is LiNi. x Co y Mn z O2, wherein 0≤x≤1, 0≤y≤0.4, 0≤z≤0.4, and x+y+z=1; the preparation method of the modified layered double hydroxide includes the following steps: mixing divalent metal salt, trivalent metal salt, and water evenly, adding precipitant and complexing agent for water bath treatment, and freeze-drying to obtain layered double hydroxide; mixing layered double hydroxide, amino acid, and solvent evenly, and heating treatment to obtain modified layered double hydroxide.

2. The cathode material according to claim 1, characterized in that, The divalent metal salt is selected from Zn. 2+ Mg 2+ Mn 2 + Fe 2+ Ni 2+ Co 2+ It contains one or more of the following: nitrates, acetates, sulfates, and chlorides; the trivalent metal salt is selected from Al. 3+ Cr 3+ Fe 3+ Mn 3+ ,Sc 3+ Co 3+ The precipitant is selected from one or more of nitrates, acetates, sulfates, and chlorides; the molar ratio of divalent metal salt to trivalent metal salt is (2~4):1; the precipitant is selected from one or more of sodium carbonate, ammonium carbonate, sodium hydroxide, lithium hydroxide, and sodium oxalate; the concentration of the precipitant is 3~8 mol / L; the complexing agent is selected from one or more of ammonia, tartaric acid, and citric acid; the concentration of the complexing agent is 2~4 mol / L; the temperature of the water bath treatment is 60~80℃.

3. The cathode material according to claim 1, characterized in that, The freeze-drying process includes first cooling the reaction system to 2-8°C, then placing it in a freeze-drying chamber at -30°C to -50°C with a vacuum degree controlled at 10-20 Pa until it is completely frozen; turning on the vacuum diffusion pump and lowering the vacuum degree to below 5 Pa, at which point the ice begins to sublimate, with a sublimation drying time of 12-24 hours; maintaining the vacuum degree and raising the temperature to 25-45°C, with a desorption drying time of 5-10 hours; the amino acid is selected from one or more of glycine and lysine; the molar ratio of layered double hydroxide to amino acid is 1:(0.005-0.025); the solvent is selected from one or more of dipropylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether, ethylene glycol butyl ether, and diethylene glycol butyl ether; the heat treatment temperature is 160-200°C, and the heat treatment time is 2-5 hours.

4. A method for preparing the positive electrode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Weigh the raw materials according to the stoichiometric ratio of the positive electrode active material precursor, mix them evenly with water, add precipitant and complexing agent, adjust the pH to obtain a mixture, freeze-dry the mixture to obtain the positive electrode active material precursor. S2. After uniformly mixing the positive electrode active material precursor with the lithium source, sintering is performed to obtain the positive electrode active material. S3. The positive electrode active material and the modified layered double hydroxide are ball-milled with a grinding aid and dried to obtain the positive electrode material.

5. The preparation method according to claim 4, characterized in that, In S1, the raw materials for the positive electrode active material precursor include one or more of nickel source, cobalt source, and manganese source; the nickel source is selected from one or more of nickel nitrate, nickel sulfate, nickel acetate, and nickel chloride; the cobalt source is selected from one or more of cobalt nitrate, cobalt sulfate, cobalt acetate, and cobalt chloride; and the manganese source is selected from one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride.

6. The preparation method according to claim 4, characterized in that, In S1, the precipitant is selected from one or more of sodium carbonate, ammonium carbonate, sodium hydroxide, lithium hydroxide, and sodium oxalate; the concentration of the precipitant is 3~10 mol / L; the complexing agent is selected from one or more of ammonia, tartaric acid, and citric acid; the concentration of the complexing agent is 1.5~6 mol / L; and the pH is adjusted to 10.5~11.

5.

7. The preparation method according to claim 4, characterized in that, In S1, the freeze-drying process includes first cooling the reaction system to 2~8℃, then placing it in a freeze-drying chamber at -30℃~-50℃ with the vacuum degree controlled at 10~20Pa until it is completely frozen; turning on the vacuum diffusion pump, the vacuum degree drops to below 5Pa, and the ice begins to sublimate, with a sublimation drying time of 12~24h; maintaining the vacuum degree, the temperature is raised to 25~45℃, and the desorption drying time is 5~10h.

8. The preparation method according to claim 4, characterized in that, In S2, the lithium source is selected from one or more of lithium hydroxide and lithium carbonate; the molar ratio of the positive electrode active material precursor to the lithium source is 1:(1.03~1.10); the sintering treatment includes heating to 450~550℃ at a rate of 1~3℃ / min and holding for 6~8h; then heating to 700~850℃ at a rate of 2~5℃ / min and holding for 24~48h; and then cooling to room temperature in the furnace.

9. The preparation method according to claim 4, characterized in that, In S3, the molar ratio of the positive electrode active material to the modified layered double hydroxide is 1:(0.005~0.05); the grinding aid is selected from one or more of benzene, cyclohexane, methanol, ethanol, and isopropanol; the ball milling speed is 350~1000 rpm, and the ball milling time is 1~5 h.

10. The application of a cathode material according to any one of claims 1 to 3 or a cathode material prepared by any one of claims 4 to 9 in a lithium-ion battery.

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