Preparation process of lithium battery positive electrode material and lithium battery positive electrode material

Abstract

The application discloses a preparation process and material of a lithium battery positive electrode material and belongs to the technical field of battery materials. The process obtains the positive electrode material with the metal oxide@carbon composite nanosheet coated on the surface through in-situ growth of the metal organic framework nanosheet on the surface of the manganese-based positive electrode material and gradient carbonization. The key lies in that triethylamine and hexadecyl trimethyl ammonium bromide are used as the synergistic structure directing agent to control the nanosheet morphology, and the conversion from the MOF to the stable composite layer is realized through the three-step gradient carbonization process. The material has the characteristics of uniform coating, strong combination, and excellent ion / electron transmission channel, and significantly improves the specific capacity, rate performance and cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery material technology, specifically relating to a preparation process of lithium battery cathode material and the lithium battery cathode material itself. Background Technology

[0002] Lithium-ion batteries are widely used in power, energy storage, and consumer electronics fields due to their high energy density and long cycle life. In recent years, with the rapid development of industries such as electric vehicles, energy storage systems, low-altitude aircraft, humanoid robots, and portable electronic devices, the market demand for lithium-ion batteries has also increased significantly. At the same time, higher requirements have been placed on the energy density, rate performance, low-temperature performance, cycle life, safety, and cost of lithium-ion batteries.

[0003] Among the main components of lithium-ion batteries, the cathode material plays a decisive role in battery performance. Therefore, improving the performance of the cathode material is the most effective way to enhance the electrochemical performance of lithium-ion batteries.

[0004] Traditional lithium-ion battery cathode materials are mainly lithium cobalt oxide, but due to the scarcity and high toxicity of cobalt resources, these batteries are expensive and have poor safety, limiting their application. With the popularization of new energy vehicles, there is increasing focus on improving the performance of lithium-ion batteries in terms of long range and high power. Ternary layered cathode materials have emerged as a research focus in recent years due to their advantages of good safety, high specific capacity, and low cost. For manganese-based layered cathode materials, especially lithium-rich manganese-based materials, oxygen is easily generated during charging, which reduces battery safety. Simultaneously, during cycling, the material's crystal structure transforms from a layered structure to a spinel structure, reducing the material's cycle stability and energy density. Furthermore, the high manganese content and the ease with which manganese ions dissolve under high voltage hinder the large-scale commercialization of manganese-based cathode materials.

[0005] To address the aforementioned problems of manganese-based cathode materials, existing improvement methods mainly focus on two approaches: elemental doping and surface coating. Surface coating of the cathode material can isolate it from the electrolyte, reducing side reactions, inhibiting metal ion dissolution, and minimizing structural collapse during repeated charge-discharge cycles, thereby optimizing the material's cycle performance, safety performance, and rate performance. Regarding cathode material coating methods, the traditional approach involves dry, high-speed mixing of the electrode material and nanoparticles. However, this method cannot effectively control the thickness of the nanoparticles coating the cathode material particles and can lead to uneven nanoparticle distribution, resulting in corrosion, performance degradation, and particle cracking during cycling.

[0006] For example, Chinese patent application CN201610709098.7 discloses a BN-coated cobalt-free Ni-Mn solid solution manganese-based cathode material with the structural formula: LiNixMn1-xO2·aBN, where 0.5≤x<1, 0<a≤0.06, and BN is a coating layer on the surface of the LiNixMn1-xO2 material. The BN coating on the surface of the material of this invention effectively blocks direct contact between the cathode material and the electrolyte, exhibits strong acid resistance, and thus inhibits the dissolution of manganese ions in the electrolyte, thereby stabilizing the material structure and improving the material's cycle performance.

[0007] In addition, commercially available nanomaterials generally suffer from nanoparticle agglomeration and large particle size. Existing coating processes using dry high-speed mixing methods cannot effectively break up agglomerated nanoparticles. Once these impurities are introduced into the cathode material, it will lead to an increase in the internal resistance of the lithium battery and accelerate battery degradation.

[0008] Therefore, developing an efficient, uniform, and controllable surface coating material and process has become a key research direction for improving the electrochemical performance and safety of manganese-based cathode materials. Summary of the Invention

[0009] This invention addresses the problems of uneven surface coating, uncontrollable coating morphology, weak adhesion between the coating and the substrate, and poor rate performance in existing manganese-based cathode materials. This invention provides a preparation process and a lithium-ion battery cathode material. The core of this invention lies in: guiding the in-situ growth of metal-organic frameworks (MOFs) on the surface of the cathode material under mild conditions through the synergistic effect of specific structure-directing agents (triethylamine and hexadecyltrimethylammonium bromide), forming a regular nanosheet-like coating layer; then, through a carefully designed gradient carbonization process, transforming the MOF nanosheets into metal oxide@carbon composite nanosheets, achieving uniform carbon coating and uniform dispersion of the metal oxide while maintaining the nanosheet morphology.

[0010] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: In a first aspect, a process for preparing a lithium battery cathode material includes the following preparation steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60-72 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) is collected by centrifugation, washed repeatedly with deionized water and absolute ethanol in sequence, and then the washed material is placed in a vacuum drying oven for drying to obtain a precursor of a manganese-based cathode material coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment, and after the carbonization is completed, it is cooled to room temperature with the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating layer on its surface.

[0011] Preferably, the manganese-based cathode material in step (1) is Li 1.2 Mn x Ni y Co 0.8-x-y O 2, where 0.4 < x ≤ 0.6, 0 < y ≤ 0.4, and 0.7 ≤ x + y ≤ 0.8; the preparation method of the manganese-based cathode material is to mix nickel salt, cobalt salt and manganese salt in a set molar ratio and disperse them in a solvent (the solvent is water, and the dosage is sufficient to disperse the metal salts), add a complexing agent and control the pH value, and stir and react at a constant temperature under the protection of an inert atmosphere to generate a ternary hydroxide precursor; after filtration, washing and drying, the precursor is uniformly mixed with a lithium salt and sintered at a high temperature of 600-900 °C for 10-20 hours, and then naturally cooled to room temperature to obtain the manganese-based cathode material.

[0012] Furthermore, the nickel salt, cobalt salt and manganese salt are one or more of sulfates, nitrates or chlorides, and their purity is not less than 99.5%; the complexing agent is ammonia water, the concentration is controlled at 2-6 mol / L, the pH value of the reaction system is maintained between 10.5-12.0, the reaction temperature is 45-65 °C, the stirring rate is 300-800 rpm, and the reaction time is 8-16 hours; the lithium salt is one or more of lithium carbonate, lithium hydroxide or lithium acetate.

[0013] Further, the mass concentration of the manganese-based cathode material in the suspension in step (1) is 10-30%, the solvent is deionized water, the stirring rate is 200-600 rpm, the ultrasonic treatment power is 200-500 W, and the time is 30-90 minutes.

[0014] Further, in step (2), the metal salt is at least one of zinc acetate, zinc nitrate, zinc chloride, and cobalt nitrate; the organic ligand is a mixture of long-chain and short-chain ligands; the short-chain ligand is selected from at least one of 2-methylimidazole, imidazole, and benzimidazole; and the long-chain organic ligand is selected from at least one of terephthalic acid, 4,4'-biphenyldicarboxylic acid, 1,3,5-benzenetricarboxylic acid, and 2,5-dihydroxyterephthalic acid; the structure directing agent is triethylamine and hexadecyltrimethylammonium bromide, with a molar ratio of 1:0.3-0.5, and the molar ratio of metal salt, organic ligand, and structure directing agent is 1:1:2; the solid-liquid ratio of the suspension to the metal salt is 50 mL:1 g.

[0015] Furthermore, the gradient carbonization process in step (4) includes: a first stage: heating to 150-200℃ at 1-3℃ / min and holding for 0.5 hours; a second stage: heating to 350-400℃ at 3-6℃ / min and holding for 3 hours; and a third stage: heating to 500-550℃ at 6-10℃ / min and holding for 0.5 hours.

[0016] Furthermore, the protective atmosphere in step (4) is nitrogen or argon, the furnace pressure is maintained at atmospheric pressure during carbonization, and the gas flow rate is controlled at 100-300 mL / min.

[0017] In a second aspect, the present invention provides a lithium battery cathode material obtained by the above-described preparation process.

[0018] A third aspect of the present invention provides a lithium-ion battery, wherein the positive electrode comprises the above-mentioned lithium battery positive electrode material.

[0019] Surface coating is one of the effective means to improve the performance of high-nickel cathode materials. Traditional surface coating methods mainly include physical mixing and solution impregnation. Physical mixing usually involves mixing the cathode material and coating material in a ball mill. This method is difficult to achieve uniform coating, and the coating layer has weak adhesion to the substrate, making it prone to detachment during cycling. Although solution impregnation can achieve relatively uniform coating, it usually forms a dense coating layer, which hinders lithium-ion transport and reduces rate performance. Therefore, this invention designs a porous heterostructure coating method based on in-situ self-assembly. A nanosheet array coating layer is grown in situ. By controlling the coordination reaction kinetics of metal salt and organic ligands, preferential crystal plane growth is induced to form a porous nanosheet framework perpendicular to the cathode material surface. This porous heterostructure not only effectively inhibits the erosion of high-nickel materials by the electrolyte and improves interface stability, but its open pore structure also promotes rapid lithium-ion migration, significantly improving the rate performance and cycle life of the material.

[0020] The beneficial effects of this invention are: 1. Unique Nanosheet-like Coating Morphology: Through the synergistic effect of triethylamine and hexadecyltrimethylammonium bromide as structure-directing agents, with triethylamine acting as a base and coordination competitor, and hexadecyltrimethylammonium bromide serving as a surface-active template, the nucleation and growth kinetics of MOF crystals are precisely controlled, preferentially promoting growth along the two-dimensional direction. This results in the in-situ formation of uniformly thick and regularly arranged nanosheet structures on the cathode material surface. This structure possesses a huge specific surface area, significantly increasing the contact area with the electrolyte, providing abundant lithium-ion insertion / extraction active sites, and establishing a continuous electron conduction network and open ion transport channels, fundamentally improving the rate performance and interfacial reaction kinetics of the material.

[0021] 2. Optimized Gradient Carbonization Process: This invention employs a three-step gradient carbonization method, avoiding the nanosheet fusion, collapse, or structural damage caused by traditional one-step high-temperature carbonization. The first stage (150-200℃) involves slow heating and holding, allowing the organic ligands in the MOF to decompose slowly, forming a preliminary carbon framework. Simultaneously, the released internal gas helps form a porous structure. The second stage (350-400℃) transforms the metal nodes into uniformly dispersed nano-metal oxides and promotes further graphitization of the carbon layer. The third stage (500-550℃) involves a short-duration high-temperature treatment to further optimize the graphitization degree and conductivity of the carbon layer, while ensuring the stability of the metal oxide particle size. This gradient process successfully transforms the MOF precursor into a structurally stable metal oxide@carbon composite nanosheet coating layer, preserving the morphological advantages of the nanosheets while endowing them with excellent conductivity and structural stability.

[0022] 3. Excellent Electrochemical Performance: Benefiting from the unique nanosheet structure and optimized coating composition, the cathode material prepared in this invention exhibits extremely high specific capacity, excellent rate performance, and ultra-long cycle life. The nanosheet structure shortens the lithium-ion diffusion path, the carbon network provides high-speed electron conduction, and the metal oxide effectively suppresses side reactions in the electrolyte and the dissolution of transition metal ions. Therefore, this material exhibits high capacity retention under high-rate charge-discharge conditions, structural stability during long-term cycling, and slow capacity decay.

[0023] 4. Enhanced interfacial bonding: The in-situ growth process enables chemical bonding between the MOF nanosheets and the cathode material matrix, resulting in a bonding force far stronger than that of traditional physical mixing coatings. After gradient carbonization, this interfacial bonding is preserved and strengthened, ensuring that the coating layer does not detach from the substrate surface during long-term charge and discharge processes, thus providing continuous and stable protection.

[0024] 5. Strong process controllability and good repeatability: By precisely controlling the type and proportion of structure-directing agents and the temperature program of gradient carbonization, the morphology, thickness and composition of the coating layer can be finely controlled, resulting in good process repeatability and suitability for large-scale production.

[0025] In summary, this invention successfully addresses the challenges of interfacial instability and limited ion / electron transport faced by traditional cathode materials in high-rate and long-cycle applications through an in-situ MOF-derived nanosheet coating strategy. This technology not only significantly improves the electrochemical performance of the material but also provides a new approach for the design of high-energy-density lithium-ion batteries. Compared to existing modification methods, this approach offers multiple advantages, including simpler processes, controllable structure, and significant performance improvements, demonstrating broad prospects for industrial application. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the lithium battery cathode material obtained in Example 1 of the present invention; Figure 2 These are scanning electron microscope (SEM) images of the lithium battery cathode materials obtained in Comparative Examples 1-3 of this invention. Figure 3 These are scanning electron microscope (SEM) images of the lithium battery cathode materials obtained in Comparative Examples 4-6 of this invention. Figure 4 The image shows the cycling performance spectrum of the lithium battery cathode material prepared in Example 1 of this invention at a 1C rate. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0028] Example 1 A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment. After carbonization, the material is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0029] The manganese-based cathode material mentioned in step (1) is Li 1.2 Mn x Ni y Co 0.8-x-y O2, In the figure, x=0.48, y=0.24; the preparation method of manganese-based cathode material is as follows: nickel salt, cobalt salt and manganese salt are mixed and dispersed in a solvent (the solvent is water, and the amount is enough to fully disperse the metal salt) by co-precipitation method, a complexing agent is added and the pH value is controlled, and the reaction is carried out under an inert atmosphere with stirring and constant temperature to generate a ternary hydroxide precursor; after filtration, washing and drying, the precursor is uniformly mixed with lithium salt, sintered at 600℃ for 20 hours, and naturally cooled to room temperature to obtain manganese-based cathode material.

[0030] The nickel, cobalt, and manganese salts are nickel nitrate, cobalt nitrate, and manganese nitrate, respectively, with a purity of not less than 99.5%. The complexing agent is ammonia water, with a concentration controlled at 2 mol / L. The pH value of the reaction system is maintained between 10.5 and 12.0. The reaction temperature is 45-65℃, the stirring rate is 800 rpm, and the reaction time is 8 hours. The lithium salt is lithium carbonate.

[0031] Step (1) The mass concentration of manganese-based cathode material in the suspension is 10%, the solvent is deionized water, the stirring rate is 200 rpm, the ultrasonic treatment power is 200 W, and the time is 30 minutes.

[0032] In step (2), the metal salt is zinc acetate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is 2-methylimidazole, and the long-chain organic ligand is terephthalic acid; the structure directing agent is triethylamine and hexadecyltrimethylammonium bromide in a molar ratio of 1:0.3, and the molar ratio of metal salt, organic ligand and structure directing agent is 1:1:2; the solid-liquid ratio of suspension to metal salt is 50 mL:1 g.

[0033] Step (4) includes the following gradient carbonization process: First stage: heating to 150-200℃ at 1-3℃ / min and holding for 0.5 hours; Second stage: heating to 350-400℃ at 3-6℃ / min and holding for 3 hours; Third stage: heating to 500-550℃ at 6-10℃ / min and holding for 0.5 hours.

[0034] The protective atmosphere in step (4) is nitrogen. During the carbonization process, the pressure inside the furnace is maintained at atmospheric pressure and the gas flow rate is controlled at 100 mL / min.

[0035] Example 2 A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment. After carbonization, the material is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0036] The manganese-based cathode material mentioned in step (1) is Li 1.2 Mn x Ni y Co 0.8- x-yO 2, In the formula, x=0.5, y=0.3; the preparation method of manganese-based cathode material is as follows: nickel salt, cobalt salt and manganese salt are mixed and dispersed in a solvent (the solvent is water, and the amount is enough to fully disperse the metal salts) by co-precipitation method, a complexing agent is added and the pH value is controlled, and the reaction is carried out under an inert atmosphere with stirring and constant temperature to generate a ternary hydroxide precursor; after filtration, washing and drying, the precursor is uniformly mixed with lithium salt, sintered at a high temperature of 600-900℃ for 10-20 hours, and naturally cooled to room temperature to obtain manganese-based cathode material.

[0037] The nickel, cobalt, and manganese salts are nickel sulfate, cobalt sulfate, and manganese sulfate, respectively, with a purity of not less than 99.5%. The complexing agent is ammonia water, with a concentration controlled at 4 mol / L. The pH value of the reaction system is maintained between 10.5 and 12.0, the reaction temperature is 45-65℃, the stirring rate is 500 rpm, and the reaction time is 12 hours. The lithium salt is lithium hydroxide.

[0038] Step (1) The mass concentration of manganese-based cathode material in the suspension is 20%, the solvent is deionized water, the stirring rate is 400 rpm, the ultrasonic treatment power is 400 W, and the time is 60 minutes.

[0039] In step (2), the metal salt is zinc nitrate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is imidazole, and the long-chain organic ligand is 4,4'-biphenyldicarboxylic acid; the structure directing agent is triethylamine and hexadecyltrimethylammonium bromide, with a molar ratio of 1:0.4, and the molar ratio of metal salt, organic ligand and structure directing agent is 1:1:2; the solid-liquid ratio of suspension to metal salt is 50 mL:1 g.

[0040] Step (4) includes the following gradient carbonization process: First stage: heating to 150-200℃ at 1-3℃ / min and holding for 0.5 hours; Second stage: heating to 350-400℃ at 3-6℃ / min and holding for 3 hours; Third stage: heating to 500-550℃ at 6-10℃ / min and holding for 0.5 hours.

[0041] The protective atmosphere in step (4) is argon. During the carbonization process, the pressure inside the furnace is maintained at atmospheric pressure, and the gas flow rate is controlled at 200 mL / min.

[0042] Example 3 A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 72 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment. After carbonization, the material is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0043] The manganese-based cathode material mentioned in step (1) is Li 1.2 Mn x Ni y Co 0.8- x-yO 2, In the formula x=0.4, y=0.4; the preparation method of manganese-based cathode material is as follows: nickel salt, cobalt salt and manganese salt are mixed and dispersed in a solvent (the solvent is water, and the amount is enough to fully disperse the metal salt) by co-precipitation method, a complexing agent is added and the pH value is controlled, and the reaction is carried out under an inert atmosphere with stirring and constant temperature to generate a ternary hydroxide precursor; after filtration, washing and drying, the precursor is uniformly mixed with lithium salt, sintered at a high temperature of 600-900℃ for 10-20 hours, and naturally cooled to room temperature to obtain manganese-based cathode material.

[0044] The nickel, cobalt, and manganese salts are nickel chloride, cobalt chloride, and manganese chloride, respectively, with a purity of not less than 99.5%. The complexing agent is ammonia water, with a concentration controlled at 6 mol / L. The pH value of the reaction system is maintained between 10.5 and 12.0. The reaction temperature is 45-65℃, the stirring rate is 300 rpm, and the reaction time is 16 hours. The lithium salt is lithium acetate.

[0045] Step (1) The mass concentration of manganese-based cathode material in the suspension is 30%, the solvent is deionized water, the stirring rate is 600 rpm, the ultrasonic treatment power is 500 W, and the time is 90 minutes.

[0046] In step (2), the metal salt is zinc acetate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is benzimidazole, and the long-chain organic ligand is 1,3,5-benzenetricarboxylic acid; the structure directing agent is triethylamine and hexadecyltrimethylammonium bromide, with a molar ratio of 1:0.5, and the molar ratio of metal salt, organic ligand and structure directing agent is 1:1:2; the solid-liquid ratio of suspension to metal salt is 50 mL:1 g.

[0047] Step (4) includes the following gradient carbonization process: First stage: heating to 150-200℃ at 1-3℃ / min and holding for 0.5 hours; Second stage: heating to 350-400℃ at 3-6℃ / min and holding for 3 hours; Third stage: heating to 500-550℃ at 6-10℃ / min and holding for 0.5 hours.

[0048] The protective atmosphere in step (4) is argon. During the carbonization process, the pressure inside the furnace is maintained at atmospheric pressure, and the gas flow rate is controlled at 300 mL / min.

[0049] Comparative Example 1 Compared with Example 1, this comparative example uses the same raw materials and preparation process as Example 1, except that a structure-directing agent is not used. That is: A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt and organic ligand to the suspension and react at 20-30°C for 60 hours to grow a metal-organic framework nanosheet coating layer on the surface of the manganese-based cathode material in situ, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment. After carbonization, the material is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0050] In step (2), the metal salt is zinc acetate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is 2-methylimidazole, the long-chain organic ligand is terephthalic acid, and the molar ratio of metal salt to organic ligand is 1:1; the solid-liquid ratio of suspension to metal salt is 50mL:1g.

[0051] Comparative Example 2 Compared with Example 1, this comparative example differs from Example 1 in that only triethylamine is used in the structure-directing agent, and no hexadecyltrimethylammonium bromide is added. All other raw material ratios and preparation processes are identical to those in Example 1. That is: In step (2), the metal salt is zinc acetate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is 2-methylimidazole, and the long-chain organic ligand is terephthalic acid; the structure directing agent is triethylamine, and the molar ratio of metal salt, organic ligand and structure directing agent is 1:1:2; the solid-liquid ratio of suspension to metal salt is 50mL:1g.

[0052] Comparative Example 3 Compared with Example 1, this comparative example differs from Example 1 in that only hexadecyltrimethylammonium bromide is used in the structure-directing agent, and triethylamine is not added. All other raw material ratios and preparation processes are the same as in Example 1. That is: In step (2), the metal salt is zinc acetate, the organic ligand is a mixture of long-chain organic ligand and short-chain ligand, the short-chain ligand is 2-methylimidazole, and the long-chain organic ligand is terephthalic acid; the structure directing agent is hexadecyltrimethylammonium bromide, and the molar ratio of metal salt, organic ligand and structure directing agent is 1:1:2; the solid-liquid ratio of suspension to metal salt is 50mL:1g.

[0053] Comparative Example 4 This comparative example is identical to Example 1 except that in the carbonization process, only a single temperature program was used instead of a gradient heating method. That is: A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) The dried material is carbonized under a protective atmosphere. After carbonization, it is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0054] The carbonization process in step (4) is as follows: the temperature is increased to 150-200℃ at a rate of 1-3℃ / min and held for 4 hours.

[0055] Comparative Example 5 This comparative example is identical to Example 1 except that in the carbonization process, only a single temperature program was used instead of a gradient heating method. That is: A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) The dried material is carbonized under a protective atmosphere. After carbonization, it is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0056] The carbonization process in step (4) is as follows: the temperature is increased to 350-400℃ at a rate of 1-3℃ / min and held for 4 hours.

[0057] Comparative Example 6 This comparative example is identical to Example 1 except that in the carbonization process, only a single temperature program was used instead of a gradient heating method. That is: A process for preparing a lithium battery cathode material includes the following steps: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) The coated material in step (2) was collected by centrifugation and washed repeatedly with deionized water and anhydrous ethanol. The washed material was then dried in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) The dried material is carbonized under a protective atmosphere. After carbonization, it is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface.

[0058] The carbonization process in step (4) is as follows: the temperature is increased to 500-550℃ at a rate of 6-10℃ / min and held for 4 hours.

[0059] Performance testing The electrode materials of the embodiments and comparative examples of the present invention were tested. The electrode materials and battery preparation methods are as follows: The electrochemical performance of the positive electrode material was tested using a CR2016 coin cell. First, the material sample, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1 to obtain a homogeneous slurry. The slurry was then uniformly coated onto an aluminum foil current collector and vacuum dried. The dried aluminum foil was then pressed into a circular electrode sheet with an area of ​​0.49 cm². A high-purity lithium metal sheet (16 mm in diameter, 2 mm in thickness) was used as the negative electrode, Celgard 2400 polypropylene porous film as the separator, and a 1 mol / L LiPF6 organic solution (V(EC):V(DEC):V(DMC)=1:1:1) as the electrolyte. A self-made foamed nickel sheet was used as a gasket inside the battery casing. The CR2016 coin cell was assembled in a glove box filled with high-purity argon gas, where both moisture and oxygen concentrations were less than 0.0003% (volume fraction). The specific steps for battery assembly are as follows: First, place the positive electrode case on a clean platform and place a positive electrode plate in the center of the positive electrode case; add 1-2 drops of electrolyte to the positive electrode plate, then place the separator on top, and add electrolyte to the separator to wet it; then place the negative electrode lithium metal sheet on top, and place a self-made foam nickel pad on the lithium sheet for filling; finally, place the negative electrode case on top, making it exactly overlap with the positive electrode case, flatten it, and then seal the battery using a battery packaging machine. The assembled battery is left to stand for 12 hours to allow the electrolyte to fully impregnate it. Finally, performance testing is performed on an electrochemical instrument. Five samples are repeated for each experimental group, and the average of the performance test results is taken.

[0060] The particle size and surface morphology of the prepared cathode material were analyzed by scanning electron microscopy (SEM). Charge-discharge tests of the button cells were conducted using a battery testing system (CT2001A) manufactured by Wuhan Landian Electronics Co., Ltd., under a voltage window of 3.0–4.6 V. 1C was defined as 180 mAh / g. Charge-discharge tests were performed at different rates to obtain the electrochemical properties of the material, including charge-discharge specific capacity, rate performance, and cycle performance.

[0061] Table 1 Initial charge-discharge performance (3.0-4.6V, 25℃, 0.2C) Table 2 Rate Performance and Cyclic Performance As can be seen from the data in Table 1-2, the initial discharge specific capacity and initial coulombic efficiency of Examples 1-3 are significantly higher than those of the comparative examples. Among them, Example 3 has an initial discharge specific capacity of 266.5 mAh / g and an initial coulombic efficiency of 91.3%, which is particularly outstanding. In terms of rate performance, the discharge specific capacity of Examples 1-3 at high rates of 2C and 5C is also much better than that of the comparative examples. The discharge specific capacity of Example 3 at 2C is 206.4 mAh / g, and it can still maintain a high level of 164.4 mAh / g at 5C, showing its excellent fast charge and discharge capability. The cycle performance test results further show that the capacity retention rate of Examples 1-3 after 100 cycles and 500 cycles is significantly higher than that of the comparative examples. The capacity retention rate of Example 3 after 100 cycles at 1C is 94.1%, and it can still reach 88.7% after 500 cycles, indicating that it has excellent structural stability and long cycle life. In contrast, Comparative Example 1 (without a structure-directing agent), Comparative Examples 2 and 3 (using only a single structure-directing agent), and Comparative Examples 4 to 6 (without gradient carbonization treatment) all showed varying degrees of decline in their electrochemical performance indicators. Comparative Examples 1 and 4, in particular, exhibited not only low initial discharge specific capacity but also a capacity retention rate of only around 70% after 500 cycles, significantly lower than the examples. This clearly demonstrates that the present invention, through a specific combination of structure-directing agents and a gradient carbonization process, can effectively control the structure and composition of the metal-organic framework nanosheet coating layer, thereby significantly improving the overall electrochemical performance of manganese-based cathode materials. This can also be seen from the electron micrographs of the cathode materials. Figure 1The image shows the SEM image of the cathode material obtained in Example 1 of this invention. Its surface is uniformly coated with continuous and regular nanosheet structures, exhibiting complete morphology and a tightly and orderly arranged layer, effectively improving the material's conductivity and structural stability. In contrast, Comparative Example 1 (without a directing agent), and Comparative Examples 2 and 3 (using only a single-structure directing agent), struggled to form a continuous nanosheet coating. Comparative Examples 2-3, which altered the directing agent, showed significant unevenness in their nanosheet coatings, with some areas exhibiting broken or loosely packed layers, leading to poor interfacial contact and structural collapse during cycling. Comparative Examples 4 to 6 did not employ a gradient carbonization process. Comparative Example 4 had a lower carbonization temperature, resulting in incomplete ligand decomposition and residual organic impurities clogging the nanosheet channels, increasing lithium-ion diffusion resistance. While Comparative Examples 5-6 achieved metal oxide conversion, insufficient graphitization of the carbon layer or excessively high temperatures damaged the carbon layer structure, disrupting the layered structure and causing discontinuous conductive networks, thus affecting the material's rate performance and cycling stability.

[0062] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A process for preparing a lithium battery cathode material, characterized in that, The preparation steps include the following: (1) Disperse the manganese-based cathode material in a solvent, stir and sonicate to form a suspension; (2) Add metal salt, organic ligand and structure directing agent to the suspension and react at 20-30°C for 60-72 hours to grow metal-organic framework nanosheet coating layer in situ on the surface of the manganese-based cathode material, wherein the thickness of the nanosheet is 5-50 nm and the length is 50-500 nm. (3) Collect the coated material in step (2) by centrifugation, wash it repeatedly with deionized water and anhydrous ethanol, and then dry the washed material in a vacuum drying oven to obtain a manganese-based cathode material precursor coated with a metal-organic framework. (4) Under a protective atmosphere, the dried material is subjected to gradient carbonization treatment. After carbonization, the material is cooled to room temperature in the furnace to obtain a lithium battery cathode material with a metal oxide@carbon composite nanosheet coating on the surface. The structure-directing agent is triethylamine and hexadecyltrimethylammonium bromide in a molar ratio of 1:0.3-0.5, and the molar ratio of metal salt, organic ligand and structure-directing agent is 1:1:

2. Step (4) of the gradient carbonization process includes: First stage: heating to 150-200℃ at 1-3℃ / min and holding for 0.5 hours; Second stage: Increase the temperature to 350-400℃ at 3-6℃ / min and hold for 3 hours; Third stage: Increase the temperature to 500-550℃ at 6-10℃ / min and hold for 0.5 hours.

2. The preparation process of the lithium battery cathode material according to claim 1, characterized in that, The manganese-based cathode material in step (1) is Li 1.2 Mn x Ni y Co 0.8-x-y O 2, where 0.4 < x ≤ 0.6, 0 < y ≤ 0.4, and 0.7 ≤ x + y ≤ 0.8; the preparation method of the manganese-based cathode material is to use the coprecipitation method to mix nickel salt, cobalt salt and manganese salt in a set molar ratio and disperse them in a solvent, add a complexing agent and control the pH value, and stir and react at a constant temperature under the protection of an inert atmosphere to generate a ternary hydroxide precursor; after filtration, washing and drying, uniformly mix the precursor with a lithium salt, sinter at 600-900 °C for 10-20 hours, and naturally cool to room temperature to obtain the manganese-based cathode material.

3. The preparation process of the lithium battery cathode material according to claim 2, characterized in that, The nickel, cobalt, and manganese salts are one or more of sulfates, nitrates, or chlorides, with a purity of not less than 99.5%; the complexing agent is ammonia water with a concentration of 2-6 mol / L; the pH value of the reaction system is maintained between 10.5 and 12.0; the reaction temperature is 45-65℃; the stirring rate is 300-800 rpm; and the reaction time is 8-16 hours; the lithium salt is one or more of lithium carbonate, lithium hydroxide, or lithium acetate.

4. The preparation process of the lithium battery cathode material according to claim 1, characterized in that, Step (1) The mass concentration of manganese-based cathode material in the suspension is 10-30%, the solvent is deionized water, the stirring rate is 200-600 rpm, the ultrasonic treatment power is 200-500 W, and the time is 30-90 minutes.

5. The preparation process of the lithium battery cathode material according to claim 1, characterized in that, In step (2), the metal salt is at least one of zinc acetate, zinc nitrate, zinc chloride, and cobalt nitrate. The organic ligand is a mixture of long-chain organic ligands and short-chain ligands. The short-chain ligand is selected from at least one of 2-methylimidazole, imidazole, and benzimidazole. The long-chain organic ligand is selected from at least one of terephthalic acid, 4,4'-biphenyldicarboxylic acid, 1,3,5-benzenetricarboxylic acid, and 2,5-dihydroxyterephthalic acid. The solid-liquid ratio of the suspension to the metal salt is 50 mL: 1 g.

6. The preparation process of the lithium battery cathode material according to claim 1, characterized in that, The protective atmosphere in step (4) is nitrogen or argon. During the carbonization process, the pressure inside the furnace is maintained at atmospheric pressure, and the gas flow rate is controlled at 100-300 mL / min.

7. A lithium battery cathode material obtained by the preparation process according to any one of claims 1-6.

8. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode comprises the lithium battery positive electrode material as described in claim 7.

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