High-capacity graphite negative electrode material and preparation method thereof

Abstract

This invention relates to the field of battery materials technology and discloses a high-capacity graphite anode material and its preparation method. The preparation method includes the following steps: raw material selection and pretreatment, exfoliation and activation treatment, elemental doping modification, in-situ polymerization coating, carbonization treatment, crushing and sieving. By crushing, classifying and pretreating the waste graphite raw material with two-step acid washing (hydrochloric acid to remove metals and hydrofluoric acid to remove silicon), impurities in the raw material are removed, providing a high-purity graphite base for subsequent modification. Combined with liquid-phase exfoliation and high-pressure homogenization treatment, the number of graphite layers is reduced and the specific surface area is increased. At the same time, low-temperature plasma activation introduces active sites on its surface, enhancing the chemical reactivity of graphite. This lays a solid structural foundation for subsequent elemental doping and polymerization coating, thereby ensuring the stability and excellent performance of the final material.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a high-capacity graphite anode material and its preparation method. Background Technology

[0002] With the rapid popularization of electric vehicles in the global market, the demand for fast charging capabilities is increasing. The lithium-ion batteries used in electric vehicles are mainly composed of four parts: positive electrode, negative electrode, electrolyte, and separator. The negative electrode material plays a crucial role in the capacity and rate capability of lithium-ion batteries. Graphite negative electrode is the most widely used negative electrode material in lithium-ion batteries. Graphite has rapidly gained widespread attention due to its abundant resources, low price, high reversible capacity, low charge and discharge voltage plateau, no voltage hysteresis, and excellent conductivity.

[0003] Currently, traditional graphite materials are limited by their theoretical specific capacity, making it difficult to meet the growing market demand for high-energy-density batteries. To address this, the industry typically modifies graphite to improve its capacity. Common modification methods include surface coating, element doping, or structural design. However, these methods often suffer from limited modification effects, complex processes, or high costs.

[0004] Therefore, a high-capacity graphite anode material and its preparation method are proposed to solve the above problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-capacity graphite anode material and its preparation method, which solves the problems of limited modification effect, complex process or high cost of common modification methods mentioned in the background.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a high-capacity graphite anode material and its preparation method, wherein the preparation method includes the following steps: Step 1: Raw material selection and pretreatment: Select waste graphite raw materials, crush, remove impurities and purify them to obtain pretreated graphite powder; Step 2, stripping and activation treatment: The pretreated graphite powder is dispersed in the stripping liquid and subjected to liquid phase stripping treatment to obtain stripped graphite slurry. Then, the stripped graphite slurry is subjected to low-temperature plasma activation treatment to obtain activated graphite slurry. Step 3, element doping modification: The dopant solution is mixed with activated graphite slurry and a hydrothermal reaction is carried out under a protective atmosphere to allow the dopant element to enter the graphite interlayer or replace some carbon atoms. After the reaction is completed, the dopant is separated into solid and liquid, washed and dried to obtain the doped modified graphite precursor. Step 4, In-situ Polymerization Coating: The doped modified graphite precursor is uniformly dispersed in a mixed solution composed of polymeric monomers and initiators, and an in-situ polymerization reaction is carried out to form a polymer coating layer on the graphite surface and interlayer edges. After the reaction is completed, the graphite is washed and dried to obtain a polymer-coated graphite composite material. Step 5, Carbonization treatment: The polymer-coated graphite composite material is placed in a tube furnace and subjected to programmed temperature rise carbonization treatment under inert atmosphere protection, so that the polymer coating layer is transformed into an amorphous carbon layer, and primary carbon-coated graphite material is obtained. Step 6: Crushing and Sieving: The primary carbon-coated graphite material is crushed and sieved to obtain high-capacity graphite anode material products with a specific particle size range.

[0007] Preferably, in step one, the raw material selection and pretreatment includes: the waste graphite raw material is selected from at least one of lithium-ion battery recycled graphite, graphite electrode processing waste, or natural graphite flotation tailings; firstly, the waste graphite raw material is placed in a jaw crusher for coarse crushing, and then transferred to an air jet mill for crushing under an air pressure of 0.4-0.8 MPa for 5-15 minutes to obtain coarse graphite powder with a particle size D50 of 10-50 micrometers; then, the coarse graphite powder is placed in an acid washing tank, and a hydrochloric acid solution with a concentration of 3-6 mol / L is added, and the solution is washed at 6... The filter cake is stirred and acid-washed at 0-80℃ for 2-4 hours to dissolve metallic impurities. After acid washing, it is filtered and washed with deionized water until the filtrate is neutral. The filter cake is then transferred to a 10-20wt% hydrofluoric acid solution and soaked at 40-60℃ for 1-3 hours to remove silica impurities. Finally, it is filtered again and washed with deionized water until the filtrate is neutral. The filter cake is then placed in a vacuum drying oven and dried at 80-120℃ and -0.08 to -0.1MPa for 8-12 hours to obtain the pretreated graphite powder.

[0008] Preferably, in step two, the stripping solution is composed of the following raw materials in parts by weight: 40-60 parts of a high-boiling-point polar solvent, 5-15 parts of a surfactant, 2-8 parts of an intercalating agent, and 20-40 parts of deionized water; wherein the high-boiling-point polar solvent is at least one of N-methylpyrrolidone, dimethyl sulfoxide, and γ-butyrolactone; the surfactant is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyethylene glycol octylphenyl ether; and the intercalating agent is at least one of ammonium persulfate, potassium permanganate, and potassium chlorate.

[0009] Preferably, the stripping solution is prepared and used by the following method: First, a high-boiling-point polar solvent, surfactant, intercalating agent, and deionized water are added sequentially to a dispersion vessel equipped with constant temperature circulation and high-speed shearing functions. Then, the temperature of the dispersion vessel is controlled at 25-35℃, and the mixture is premixed at a speed of 300-500 r / min for 5-10 minutes. Then, the speed is increased to 2000-5000 r / min, and high-speed shearing dispersion is performed for 30-60 minutes until the mixture is transparent or semi-transparent, thus obtaining the stripping solution. Next, pretreated graphite powder is slowly added to the stripping solution at a solid-liquid ratio of 1:20-1:50 g / mL. With the assistance of an ultrasonic cell disruptor, the mixture is ultrasonically treated for 1-3 hours at a power of 300-500W under ice-water bath conditions to obtain a preliminary stripped graphite dispersion. Then, the preliminary stripped graphite dispersion is transferred to a high-pressure homogenizer and homogenized 5-10 times under a pressure of 80-150 MPa to obtain a stripped graphite slurry with a reduced number of layers and an increased specific surface area.

[0010] Preferably, in step two, the low-temperature plasma activation treatment includes: first, spray drying the exfoliated graphite slurry to obtain dried exfoliated graphite powder; then, uniformly spreading the dried exfoliated graphite powder on the sample tray of the plasma treatment equipment and sending it into the reaction chamber; starting the vacuum system to pump the pressure of the reaction chamber to 10-100 Pa; then, introducing activation gas at a flow rate of 20-100 sccm to maintain the pressure inside the chamber at 50-500 Pa; then, starting the plasma generator, setting the radio frequency power to 100-500 W, and the treatment time to 5-30 minutes; after the treatment, turning off the plasma and gas sources, filling the chamber with inert gas to atmospheric pressure, removing the sample to obtain activated graphite powder; and finally, redispersing the activated graphite powder in deionized water or low alcohol to prepare an activated graphite slurry with a solid content of 5-15 wt%; wherein the activation gas is oxygen, nitrogen, ammonia, argon, or a mixture thereof.

[0011] Preferably, in step three, the elemental doping modification includes: first, preparing a dopant solution by dissolving the dopant source in a solvent to prepare a dopant solution with a concentration of 0.1-2.0 mol / L. The dopant source is at least one of urea, melamine, ammonium dihydrogen phosphate, phosphoric acid, boric acid, sodium borohydride, sodium sulfide, and thiourea. The solvent is at least one of deionized water, ethanol, and isopropanol. Then, the activated graphite slurry and the dopant solution are mixed at a volume ratio of 1:1-1:3 and placed in a high-shear emulsifier for high-speed emulsification and dispersion at a speed of 5000-15000 r / min for 10-30 minutes to form a mixed slurry. The mixture is then transferred to the polytetrafluoroethylene liner of a hydrothermal reactor, with a filling degree of 60-80%. The hydrothermal reactor is then sealed and placed in a forced-air drying oven, where it is reacted at 120-200℃ for 6-24 hours. After the reaction, it is allowed to cool naturally to room temperature. The reaction product is then centrifuged, and the precipitate is washed 3-5 times alternately with deionized water and ethanol until the supernatant is neutral and no impurity ions are detected. Finally, the washed precipitate is placed in a vacuum freeze dryer and dried at -50 to -30℃ and a pressure below 10Pa for 24-48 hours to obtain the doped modified graphite precursor.

[0012] Preferably, in step four, the in-situ polymerization coating includes: first, preparing a polymerization solution by dissolving the monomer in 0.5-2.0 mol / L acidic aqueous solution or deionized water to prepare a monomer solution with a concentration of 0.1-0.5 mol / L. The acidic aqueous solution is an aqueous solution of hydrochloric acid, sulfuric acid, or p-toluenesulfonic acid. Then, the doped modified graphite precursor is added to the monomer solution and dispersed for 30-60 minutes under the combined action of ultrasound and mechanical stirring to form a graphite monomer suspension. Next, the suspension is transferred to a reactor equipped with reflux condensation and temperature control, stirred under ice-water bath conditions, and an oxidant initiator solution is added dropwise while controlling the temperature. The dropping rate is maintained at the reaction system temperature of 0-10℃. The oxidant initiator is at least one of ammonium persulfate, ferric chloride, and hydrogen peroxide, with a molar ratio of 0.5:1 to 1.5:1 to the polymer monomer. After the dropping is complete, the ice-water bath is removed, and the reaction system temperature is slowly raised to 20-25℃. The reaction is continued to be stirred for 4-12 hours. The reaction product is then filtered, and the filter cake is washed several times with deionized water and ethanol until the filtrate is colorless and transparent. Finally, the washed filter cake is placed in a vacuum drying oven and dried at 60-80℃ and -0.08 to -0.1 MPa for 10-16 hours to obtain the polymer-coated graphite composite material.

[0013] Preferably, in step five, the carbonization treatment is microwave-assisted carbonization treatment, including: first, placing the polymer-coated graphite composite material in a microwave-specific quartz crucible with a thickness not exceeding 2 cm; then, placing the crucible in the constant temperature zone of a microwave tube furnace, sealing the furnace body, and then introducing high-purity argon or nitrogen gas into the furnace cavity at a flow rate of 200-500 mL / min as a protective gas, purging for more than 30 minutes to remove all air; after that, starting the microwave generator and the programmed temperature control system, and setting the carbonization program: the first stage, at 5... The temperature is increased from room temperature to 300-400℃ at a rate of -10℃ / min and held for 30-60 minutes to allow the polymer to undergo initial cross-linking and decomposition. In the second stage, the temperature is increased from 300-400℃ to the final carbonization temperature of 800-1200℃ at a rate of 3-8℃ / min and held for 1-3 hours. After carbonization, the furnace body is allowed to cool naturally to below 100℃ while continuously purging with protective gas. The furnace door is then opened and the furnace is allowed to continue cooling to room temperature. The sample is then removed to obtain the primary carbon-coated graphite material.

[0014] Preferably, in step six, the crushing and sieving includes: first, coarsely crushing the primary carbon-coated graphite material using a roller crusher, controlling the roller gap to be 0.5-2.0 mm; then, feeding the coarsely crushed material into a high-efficiency mechanical fusion machine or an air jet mill for fine crushing. When using a high-efficiency mechanical fusion machine, the rotation speed is controlled at 1000-3000 r / min, and the processing time is 10-30 minutes. When using an air jet mill, the working pressure is controlled at 0.6-1.2 MPa, and the classifying wheel rotation speed is 2000-6000 r / min, controlling the crushing energy and time. Next, the finely crushed powder is classified using a 200-600 mesh vibrating screen, collecting powder with a particle size D50 in the range of 8-25 micrometers as qualified products. Finally, a wind classifier is used to perform secondary classification on the qualified products, controlling the classification wind speed at 5-15 m / s to remove extremely fine powder and coarse particles, obtaining the high-capacity graphite anode material product.

[0015] Preferably, the material is prepared by processing raw materials comprising the following parts by weight: based on 100 parts by weight of pretreated graphite powder, it comprises 10-30 parts by weight of polymeric monomer and 1-10 parts by weight of dopant source. The material has a multi-level composite structure, including: Core layer: is a graphite material that has been stripped and plasma activated, and has been modified by elemental doping to introduce doping elements, which exist in the form of heteroatoms between graphite layers or in the lattice; Intermediate buffer layer: an amorphous carbon layer formed by carbonization of the polymerized monomers, covering the core layer; Surface functional layer: a composite conductive layer containing the conversion products of the dopant source, attached to the intermediate buffer layer.

[0016] Compared with the prior art, the present invention provides a high-capacity graphite anode material and its preparation method, which has the following beneficial effects: 1. In this invention, impurities in waste graphite raw materials are removed through crushing, grading, and two-step acid washing pretreatment (hydrochloric acid to remove metals and hydrofluoric acid to remove silicon), providing a high-purity graphite base for subsequent modification. Combined with liquid phase exfoliation and high-pressure homogenization, the number of graphite layers is reduced and the specific surface area is increased. At the same time, active sites are introduced on its surface through low-temperature plasma activation, which enhances the chemical reactivity of graphite and lays the structural foundation for subsequent element doping and polymerization coating, thereby ensuring the stability and excellent performance of the final material.

[0017] 2. In this invention, a hydrothermal reaction is used to achieve the doping modification of graphite with heterogeneous elements, including nitrogen, phosphorus, and sulfur. These doping elements enter the interlayer of graphite or partially replace carbon atoms, which can regulate its electronic structure, enhance conductivity, and alleviate the volume change during lithium ion insertion and extraction. On this basis, a polymer coating layer is formed on the surface and edge of the doped graphite through an in-situ polymerization reaction, and then carbonized to transform it into an amorphous carbon layer. This carbon layer can not only serve as a stable solid electrolyte interface film precursor to reduce side reactions, but also serve as a buffer layer to suppress particle pulverization during cycling, thereby synergistically improving the material's initial coulombic efficiency, cycle stability, and rate performance.

[0018] 3. In this invention, a multi-step synergistic modification strategy of elemental doping, in-situ polymerization coating, and carbonization is adopted, along with a microwave-assisted carbonization process. This results in a composite structure in the prepared anode material with enhanced core conductivity and a well-protected outer buffer layer. This structural design overcomes the shortcomings of traditional graphite materials, such as limited specific capacity and poor rate performance, and compensates for the inadequacy of single modification methods. Without using expensive raw materials, it comprehensively improves the material's reversible specific capacity, long cycle life, and fast charge / discharge capability. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: A high-capacity graphite anode material and its preparation method, wherein the preparation method includes the following steps: Step 1: Raw material selection and pretreatment: Select waste graphite raw materials, crush, remove impurities and purify them to obtain pretreated graphite powder; Step 2, stripping and activation treatment: The pretreated graphite powder is dispersed in the stripping liquid and subjected to liquid phase stripping treatment to obtain stripped graphite slurry. Then, the stripped graphite slurry is subjected to low-temperature plasma activation treatment to obtain activated graphite slurry. Step 3, elemental doping modification: The dopant solution is mixed with activated graphite slurry and subjected to a hydrothermal reaction under a protective atmosphere, so that the dopant element replaces part of the carbon atoms. After the reaction is completed, the dopant is separated into solid and liquid, washed and dried to obtain the doped and modified graphite precursor. Step 4, In-situ Polymerization Coating: The doped modified graphite precursor is uniformly dispersed in a mixed solution composed of polymeric monomers and initiators, and an in-situ polymerization reaction is carried out to form a polymer coating layer on the graphite surface and interlayer edges. After the reaction is completed, the graphite is washed and dried to obtain a polymer-coated graphite composite material. Step 5, Carbonization treatment: The polymer-coated graphite composite material is placed in a tube furnace and subjected to programmed temperature rise carbonization treatment under inert atmosphere protection, so that the polymer coating layer is transformed into an amorphous carbon layer, and primary carbon-coated graphite material is obtained. Step 6: Crushing and Sieving: The primary carbon-coated graphite material is crushed and sieved to obtain high-capacity graphite anode material products with a specific particle size range.

[0021] In step one, the raw material selection and pretreatment include: the waste graphite raw material is recycled graphite from lithium-ion batteries; firstly, the waste graphite raw material is placed in a jaw crusher for coarse crushing, and then transferred to an air jet mill for crushing for 5 minutes under an air pressure of 0.4 MPa to obtain coarse graphite powder with a particle size D50 of 12 micrometers. Next, the coarse graphite powder is placed in an acid washing tank, and a 3 mol / L hydrochloric acid solution is added. The mixture is stirred and acid washed at 60°C for 2 hours to dissolve metal impurities. After acid washing, the mixture is filtered and washed with deionized water until the filtrate is neutral. The filter cake is then transferred to a 10 wt% hydrofluoric acid solution and soaked at 40°C for 1 hour to remove silica impurities. Finally, the mixture is filtered again and washed with deionized water until the filtrate is neutral. The filter cake is then placed in a vacuum drying oven and dried at 80°C and -0.08 MPa for 8 hours to obtain pretreated graphite powder.

[0022] In step two, the stripping solution is composed of the following raw materials in parts by weight: 40 parts of high-boiling-point polar solvent, 5 parts of surfactant, 2 parts of intercalating agent and 20 parts of deionized water; wherein the high-boiling-point polar solvent is N-methylpyrrolidone, the surfactant is sodium dodecylbenzenesulfonate and the intercalating agent is ammonium persulfate.

[0023] The stripping solution was prepared and used as follows: First, a high-boiling-point polar solvent, surfactant, intercalating agent, and deionized water were added sequentially to a dispersion vessel equipped with constant temperature circulation and high-speed shearing functions. Then, the temperature of the dispersion vessel was controlled at 25℃, and the mixture was premixed at 300 r / min for 5 minutes. The speed was then increased to 2000 r / min, and the mixture was dispersed under high-speed shearing for 30 minutes until the mixture became transparent, thus obtaining the stripping solution. Next, pretreated graphite powder was slowly added to the stripping solution at a solid-liquid ratio of 1:20 g / mL. With the assistance of an ultrasonic cell disruptor, the mixture was ultrasonically treated for 1 hour at 300W power under ice-water bath conditions to obtain a preliminary stripped graphite dispersion. The preliminary stripped graphite dispersion was then transferred to a high-pressure homogenizer and homogenized 5 times under 80 MPa pressure to obtain a stripped graphite slurry with a reduced number of layers and an increased specific surface area.

[0024] Step two, the low-temperature plasma activation treatment includes: first, spray drying the exfoliated graphite slurry to obtain dried exfoliated graphite powder; then, evenly spreading the dried exfoliated graphite powder on the sample tray of the plasma treatment equipment and sending it into the reaction chamber; starting the vacuum system to evacuate the reaction chamber pressure to 10 Pa; then, introducing activation gas at a flow rate of 20 sccm to maintain the chamber pressure at 50 Pa; next, starting the plasma generator, setting the radio frequency power to 100 W, and the treatment time to 5 minutes; after the treatment, turning off the plasma and gas sources, filling the chamber with inert gas to atmospheric pressure, removing the sample to obtain activated graphite powder; finally, redispersing the activated graphite powder in deionized water to prepare an activated graphite slurry with a solid content of 5 wt%; wherein the activation gas is oxygen.

[0025] Step three, elemental doping modification, includes: first, preparing a dopant solution by dissolving the dopant source in a solvent to prepare a 0.1 mol / L dopant solution, with melamine as the dopant source and deionized water as the solvent; then, mixing the activated graphite slurry with the dopant solution at a volume ratio of 1:1 and placing it in a high-shear emulsifier, emulsifying and dispersing it at a high speed of 5000 r / min for 10 minutes to form a mixed slurry; then transferring the mixed slurry to the polytetrafluoroethylene liner of a hydrothermal reactor with a filling degree of 60%; then sealing the hydrothermal reactor and placing it in a forced-air drying oven, reacting at 120℃ for 6 hours; after the reaction, naturally cooling to room temperature; centrifuging the reaction product; washing the precipitate three times alternately with deionized water and ethanol until the supernatant is neutral and no impurity ions are detected; finally, placing the washed precipitate in a vacuum freeze dryer and drying it for 24 hours at -50℃ and a pressure below 10 Pa to obtain the doped modified graphite precursor.

[0026] Step four, the in-situ polymerization coating, includes: first, preparing a polymerization solution by dissolving the monomer in a 0.5 mol / L acidic aqueous solution to prepare a 0.1 mol / L monomer solution; the acidic aqueous solution being an aqueous solution of hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid; then, adding the doped modified graphite precursor to the monomer solution and dispersing it for 30 minutes under the combined action of ultrasound and mechanical stirring to form a graphite monomer suspension; next, transferring the suspension to a reactor equipped with reflux condensation and temperature control, stirring under ice-water bath conditions, and adding oxide dropwise. An initiator solution was added, and the dropping rate was controlled to maintain the reaction system temperature at 0℃. The oxidant initiator was ammonium persulfate, with a molar ratio of 0.5:1 to the monomer. After the addition was complete, the ice-water bath was removed, and the reaction system temperature was slowly raised to 20℃. The reaction was continued to be stirred for 4 hours. The reaction product was then filtered, and the filter cake was washed several times with deionized water and ethanol until the filtrate was colorless and transparent. Finally, the washed filter cake was placed in a vacuum drying oven and dried at 60℃ and -0.08MPa for 10 hours to obtain the polymer-coated graphite composite material.

[0027] In step five, the carbonization process is microwave-assisted carbonization, which includes: First, the polymer-coated graphite composite material is placed in a microwave-specific quartz crucible with a thickness not exceeding 2 cm. Then, the crucible is placed in the constant temperature zone of a microwave tube furnace, and the furnace body is sealed. Next, high-purity argon gas is introduced into the furnace cavity at a flow rate of 200 mL / min as a protective gas, and the furnace is purged for more than 30 minutes to remove all air. After that, the microwave generator and the programmed temperature control system are started, and the carbonization program is set: In the first stage, the temperature is increased from room temperature to 300°C at a rate of 5°C / min and held for 30 minutes to allow the polymer to undergo initial cross-linking and decomposition. In the second stage, the temperature is increased from 300°C to the final carbonization temperature of 800°C at a rate of 3°C / min and held for 1 hour. After carbonization, the furnace body is allowed to cool naturally to below 100°C while the protective gas is continuously introduced. Then, the furnace door is opened, and the furnace is allowed to continue cooling to room temperature. The sample is then removed to obtain the primary carbon-coated graphite material.

[0028] In step six, the crushing and screening process includes: first, the primary carbon-coated graphite material is coarsely crushed using a roller crusher with a roller gap of 0.5 mm; then, the coarsely crushed material is fed into a high-efficiency mechanical fusion machine for fine crushing at a speed of 1000 r / min for 10 minutes, controlling the crushing energy and time; next, the finely crushed powder is graded using a 200-mesh vibrating screen, collecting powder with a particle size D50 of 8 micrometers as qualified product; finally, a wind classifier is used to perform secondary grading on the qualified product, controlling the grading wind speed at 5 m / s to remove extremely fine powder and coarse particles, resulting in a high-capacity graphite anode material product.

[0029] The material is prepared by processing raw materials containing the following parts by weight: based on 100 parts by weight of pretreated graphite powder, it contains 10 parts by weight of polymeric monomer and 3 parts by weight of dopant source. The material has a multi-level composite structure, including: Core layer: is a graphite material that has been stripped and plasma activated, and has been modified by elemental doping to introduce dopant elements. The dopant elements exist in the graphite interlayer in the form of heteroatoms. Intermediate buffer layer: an amorphous carbon layer formed by the carbonization transformation of polymerized monomers, covering the core layer; Surface functional layer: a composite conductive layer containing dopant source conversion products attached to the intermediate buffer layer.

[0030] Example 2: A high-capacity graphite anode material and its preparation method, wherein the preparation method includes the following steps: Step 1: Raw material selection and pretreatment: Select waste graphite raw materials, crush, remove impurities and purify them to obtain pretreated graphite powder; Step 2, stripping and activation treatment: The pretreated graphite powder is dispersed in the stripping liquid and subjected to liquid phase stripping treatment to obtain stripped graphite slurry. Then, the stripped graphite slurry is subjected to low-temperature plasma activation treatment to obtain activated graphite slurry. Step 3, elemental doping modification: The dopant solution is mixed with activated graphite slurry and subjected to a hydrothermal reaction under a protective atmosphere, so that the dopant element replaces part of the carbon atoms. After the reaction is completed, the dopant is separated into solid and liquid, washed and dried to obtain the doped and modified graphite precursor. Step 4, In-situ Polymerization Coating: The doped modified graphite precursor is uniformly dispersed in a mixed solution composed of polymeric monomers and initiators, and an in-situ polymerization reaction is carried out to form a polymer coating layer on the graphite surface and interlayer edges. After the reaction is completed, the graphite is washed and dried to obtain a polymer-coated graphite composite material. Step 5, Carbonization treatment: The polymer-coated graphite composite material is placed in a tube furnace and subjected to programmed temperature rise carbonization treatment under inert atmosphere protection, so that the polymer coating layer is transformed into an amorphous carbon layer, and primary carbon-coated graphite material is obtained. Step 6: Crushing and Sieving: The primary carbon-coated graphite material is crushed and sieved to obtain high-capacity graphite anode material products with a specific particle size range.

[0031] In step one, the raw material selection and pretreatment include: the waste graphite raw material is recycled graphite from lithium-ion batteries; firstly, the waste graphite raw material is placed in a jaw crusher for coarse crushing, and then transferred to an air jet mill for crushing for 10 minutes under an air pressure of 0.6 MPa to obtain coarse graphite powder with a particle size D50 of 30 micrometers. Next, the coarse graphite powder is placed in an acid washing tank, and a hydrochloric acid solution with a concentration of 4 mol / L is added. The mixture is stirred and acid washed at 70°C for 3 hours to dissolve metal impurities. After acid washing, the mixture is filtered and washed with deionized water until the filtrate is neutral. The filter cake is then transferred to a hydrofluoric acid solution with a concentration of 15 wt% and soaked at 50°C for 2 hours to remove silica impurities. Finally, the mixture is filtered again and washed with deionized water until the filtrate is neutral. The filter cake is then placed in a vacuum drying oven and dried at 100°C and -0.09 MPa for 10 hours to obtain pretreated graphite powder.

[0032] In step two, the stripping solution is composed of the following raw materials in parts by weight: 50 parts of high-boiling-point polar solvent, 10 parts of surfactant, 5 parts of intercalating agent and 30 parts of deionized water; wherein the high-boiling-point polar solvent is N-methylpyrrolidone, the surfactant is sodium dodecylbenzenesulfonate and the intercalating agent is ammonium persulfate.

[0033] The stripping solution was prepared and used as follows: First, a high-boiling-point polar solvent, surfactant, intercalating agent, and deionized water were added sequentially to a dispersion vessel equipped with constant temperature circulation and high-speed shearing functions. Then, the temperature of the dispersion vessel was controlled at 30℃, and the mixture was premixed at 400 r / min for 7 minutes. The speed was then increased to 3500 r / min, and the mixture was dispersed under high-speed shearing for 45 minutes until the mixture became transparent, thus obtaining the stripping solution. Next, pretreated graphite powder was slowly added to the stripping solution at a solid-liquid ratio of 1:30 g / mL. With the assistance of an ultrasonic cell disruptor, the mixture was ultrasonically treated for 2 hours at 400W power under ice-water bath conditions to obtain a preliminary stripped graphite dispersion. The preliminary stripped graphite dispersion was then transferred to a high-pressure homogenizer and homogenized 7 times under 120 MPa pressure to obtain a stripped graphite slurry with a reduced number of layers and an increased specific surface area.

[0034] Step two, the low-temperature plasma activation treatment includes: first, spray drying the exfoliated graphite slurry to obtain dried exfoliated graphite powder; then, evenly spreading the dried exfoliated graphite powder on the sample tray of the plasma treatment equipment and sending it into the reaction chamber; starting the vacuum system to evacuate the reaction chamber pressure to 50 Pa; then, introducing activation gas at a flow rate of 60 sccm to maintain the chamber pressure at 300 Pa; next, starting the plasma generator, setting the radio frequency power to 350 W, and the treatment time to 15 minutes; after the treatment, turning off the plasma and gas sources, filling the chamber with inert gas to atmospheric pressure, removing the sample to obtain activated graphite powder; finally, redispersing the activated graphite powder in deionized water to prepare an activated graphite slurry with a solid content of 10 wt%; wherein the activation gas is oxygen.

[0035] Step three, elemental doping modification, includes: first, preparing a dopant solution by dissolving the dopant source in a solvent to prepare a 1 mol / L dopant solution. The dopant source is melamine, and the solvent is deionized water. Then, the activated graphite slurry and the dopant solution are mixed at a volume ratio of 1:2 and placed in a high-shear emulsifier. The mixture is emulsified and dispersed at a high speed of 10,000 r / min for 20 minutes to form a mixed slurry. The mixed slurry is then transferred to the polytetrafluoroethylene liner of a hydrothermal reactor with a filling degree of 70%. The hydrothermal reactor is then sealed and placed in a forced-air drying oven. The reaction is carried out at 160℃ for 12 hours. After the reaction, the mixture is naturally cooled to room temperature. The reaction product is centrifuged and the precipitate is washed four times alternately with deionized water and ethanol until the supernatant is neutral and no impurity ions are detected. Finally, the washed precipitate is placed in a vacuum freeze dryer and dried at -40℃ and a pressure below 10 Pa for 36 hours to obtain the doped modified graphite precursor.

[0036] In step four, the in-situ polymerization coating includes: first, preparing a polymerization solution by dissolving the monomer in a 1.2 mol / L acidic aqueous solution to prepare a 0.3 mol / L monomer solution. The acidic aqueous solution is an aqueous solution of hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid. Then, the doped modified graphite precursor is added to the above monomer solution and dispersed for 45 minutes under the combined action of ultrasound and mechanical stirring to form a graphite monomer suspension. Next, the suspension is transferred to a reactor equipped with reflux condensation and temperature control, stirred under ice-water bath conditions, and oxygen is added dropwise. An oxidizing agent initiator solution was added, and the dropping rate was controlled to maintain the reaction system temperature at 5°C. The oxidizing agent initiator was ammonium persulfate, with a molar ratio of 1:1 to the monomer. After the addition was complete, the ice-water bath was removed, and the reaction system temperature was slowly raised to 22°C. The reaction was continued to be stirred for 8 hours. The reaction product was then filtered, and the filter cake was washed several times with deionized water and ethanol until the filtrate was colorless and transparent. Finally, the washed filter cake was placed in a vacuum drying oven and dried at 70°C and -0.09 MPa for 13 hours to obtain the polymer-coated graphite composite material.

[0037] In step five, the carbonization process is microwave-assisted carbonization, which includes: First, the polymer-coated graphite composite material is placed in a microwave-specific quartz crucible with a thickness not exceeding 2 cm. Then, the crucible is placed in the constant temperature zone of a microwave tube furnace, and the furnace body is sealed. Next, high-purity argon gas is introduced into the furnace cavity at a flow rate of 350 mL / min as a protective gas, and the furnace is purged for more than 30 minutes to remove all air. After that, the microwave generator and the programmed temperature control system are started, and the carbonization program is set: In the first stage, the temperature is increased from room temperature to 350°C at a rate of 7°C / min and held for 45 minutes to allow the polymer to undergo initial cross-linking and decomposition. In the second stage, the temperature is increased from 350°C to the final carbonization temperature of 1000°C at a rate of 5°C / min and held for 2 hours. After carbonization, the furnace body is allowed to cool naturally to below 100°C while the protective gas is continuously introduced. Then, the furnace door is opened, and the furnace is allowed to continue cooling to room temperature. The sample is then removed to obtain the primary carbon-coated graphite material.

[0038] In step six, the crushing and screening process includes: first, the primary carbon-coated graphite material is coarsely crushed using a roller crusher with a roller gap of 1.5 mm; then, the coarsely crushed material is fed into an air classifier for fine crushing with a working pressure of 1 MPa and a classifying wheel speed of 4000 r / min; next, the finely crushed powder is classified through a 400-mesh vibrating screen, and powder with a particle size D50 of 15 micrometers is collected as qualified product; finally, an air classifier is used to perform secondary classification on the qualified product, with the classifying air velocity controlled at 10 m / s, to remove extremely fine powder and coarse particles, thus obtaining the high-capacity graphite anode material product.

[0039] The material is prepared by processing raw materials containing the following parts by weight: based on 100 parts by weight of pretreated graphite powder, it contains 20 parts by weight of polymeric monomer and 5 parts by weight of dopant source. The material has a multi-level composite structure, including: Core layer: is a graphite material that has been stripped and plasma activated, and has been modified by elemental doping to introduce dopant elements. The dopant elements exist in the graphite interlayer in the form of heteroatoms. Intermediate buffer layer: an amorphous carbon layer formed by the carbonization transformation of polymerized monomers, covering the core layer; Surface functional layer: a composite conductive layer containing dopant source conversion products attached to the intermediate buffer layer.

[0040] Example 3: A high-capacity graphite anode material and its preparation method, wherein the preparation method includes the following steps: Step 1: Raw material selection and pretreatment: Select waste graphite raw materials, crush, remove impurities and purify them to obtain pretreated graphite powder; Step 2, stripping and activation treatment: The pretreated graphite powder is dispersed in the stripping liquid and subjected to liquid phase stripping treatment to obtain stripped graphite slurry. Then, the stripped graphite slurry is subjected to low-temperature plasma activation treatment to obtain activated graphite slurry. Step 3, elemental doping modification: The dopant solution is mixed with activated graphite slurry and subjected to a hydrothermal reaction under a protective atmosphere, so that the dopant element replaces part of the carbon atoms. After the reaction is completed, the dopant is separated into solid and liquid, washed and dried to obtain the doped and modified graphite precursor. Step 4, In-situ Polymerization Coating: The doped modified graphite precursor is uniformly dispersed in a mixed solution composed of polymeric monomers and initiators, and an in-situ polymerization reaction is carried out to form a polymer coating layer on the graphite surface and interlayer edges. After the reaction is completed, the graphite is washed and dried to obtain a polymer-coated graphite composite material. Step 5, Carbonization treatment: The polymer-coated graphite composite material is placed in a tube furnace and subjected to programmed temperature rise carbonization treatment under inert atmosphere protection, so that the polymer coating layer is transformed into an amorphous carbon layer, and primary carbon-coated graphite material is obtained. Step 6: Crushing and Sieving: The primary carbon-coated graphite material is crushed and sieved to obtain high-capacity graphite anode material products with a specific particle size range.

[0041] In step one, the raw material selection and pretreatment include: the waste graphite raw material is recycled graphite from lithium-ion batteries; firstly, the waste graphite raw material is placed in a jaw crusher for coarse crushing, and then transferred to an air jet mill for crushing for 15 minutes under an air pressure of 0.8 MPa to obtain coarse graphite powder with a particle size D50 of 50 micrometers. Next, the coarse graphite powder is placed in an acid washing tank, and a 6 mol / L hydrochloric acid solution is added. The mixture is stirred and acid washed at 80°C for 4 hours to dissolve metal impurities. After acid washing, the mixture is filtered and washed with deionized water until the filtrate is neutral. The filter cake is then transferred to a 20 wt% hydrofluoric acid solution and soaked at 60°C for 3 hours to remove silica impurities. Finally, the mixture is filtered again and washed with deionized water until the filtrate is neutral. The filter cake is then placed in a vacuum drying oven and dried at 120°C and -0.1 MPa for 12 hours to obtain pretreated graphite powder.

[0042] In step two, the stripping solution is composed of the following raw materials in parts by weight: 60 parts of high-boiling-point polar solvent, 15 parts of surfactant, 8 parts of intercalating agent and 40 parts of deionized water; wherein the high-boiling-point polar solvent is N-methylpyrrolidone, the surfactant is sodium dodecylbenzenesulfonate and the intercalating agent is ammonium persulfate.

[0043] The stripping solution was prepared and used as follows: First, a high-boiling-point polar solvent, surfactant, intercalating agent, and deionized water were added sequentially to a dispersion vessel equipped with constant temperature circulation and high-speed shearing functions. Then, the temperature of the dispersion vessel was controlled at 35℃, and the mixture was premixed at 500 r / min for 10 minutes. The speed was then increased to 5000 r / min, and the mixture was dispersed under high-speed shearing for 60 minutes until the mixture became transparent, thus obtaining the stripping solution. Next, pretreated graphite powder was slowly added to the stripping solution at a solid-liquid ratio of 1:50 g / mL. With the assistance of an ultrasonic cell disruptor, the mixture was ultrasonically treated for 3 hours at 500W power under ice-water bath conditions to obtain a preliminary stripped graphite dispersion. The preliminary stripped graphite dispersion was then transferred to a high-pressure homogenizer and homogenized 10 times under a pressure of 150 MPa to obtain a stripped graphite slurry with a reduced number of layers and an increased specific surface area.

[0044] Step two, the low-temperature plasma activation treatment includes: first, spray drying the exfoliated graphite slurry to obtain dried exfoliated graphite powder; then, evenly spreading the dried exfoliated graphite powder on the sample tray of the plasma treatment equipment and sending it into the reaction chamber; starting the vacuum system and pumping the pressure in the reaction chamber to 100 Pa; then, introducing activation gas at a flow rate of 100 sccm to maintain the pressure inside the chamber at 500 Pa; next, starting the plasma generator, setting the radio frequency power to 500 W, and the treatment time to 30 minutes; after the treatment is completed, turning off the plasma and gas sources, filling the chamber with inert gas to atmospheric pressure, removing the sample to obtain activated graphite powder; finally, redispersing the activated graphite powder in deionized water to prepare an activated graphite slurry with a solid content of 15 wt%; wherein the activation gas is oxygen.

[0045] Step three, elemental doping modification, includes: first, preparing a dopant solution by dissolving the dopant source in a solvent to prepare a 2.0 mol / L dopant solution, with melamine as the dopant source and deionized water as the solvent; then, mixing the activated graphite slurry with the dopant solution at a volume ratio of 1:3 and placing it in a high-shear emulsifier, emulsifying and dispersing it at a high speed of 15000 r / min for 30 minutes to form a mixed slurry; then transferring the mixed slurry to the polytetrafluoroethylene liner of a hydrothermal reactor with a filling degree of 80%; then sealing the hydrothermal reactor and placing it in a forced-air drying oven, reacting at 200℃ for 24 hours; after the reaction, naturally cooling to room temperature; centrifuging the reaction product; washing the precipitate five times alternately with deionized water and ethanol until the supernatant is neutral and no impurity ions are detected; finally, placing the washed precipitate in a vacuum freeze dryer and drying it at -30℃ and a pressure below 10 Pa for 48 hours to obtain the doped modified graphite precursor.

[0046] Step four, the in-situ polymerization coating, includes: first, preparing a polymerization solution by dissolving the monomer in a 2.0 mol / L acidic aqueous solution to prepare a 0.5 mol / L monomer solution; the acidic aqueous solution being an aqueous solution of hydrochloric acid, sulfuric acid, and p-toluenesulfonic acid; then, adding the doped modified graphite precursor to the monomer solution and dispersing it for 60 minutes under the combined action of ultrasound and mechanical stirring to form a graphite monomer suspension; next, transferring the suspension to a reactor equipped with reflux condensation and temperature control, stirring under ice-water bath conditions, and adding an oxidant dropwise. The initiator solution was added at a controlled rate to maintain the reaction system temperature at 10°C. The oxidant initiator was ammonium persulfate, with a molar ratio of 1.5:1 to the monomer. After the addition was complete, the ice-water bath was removed, and the reaction system temperature was slowly raised to 25°C. The reaction was continued to be stirred for 12 hours. The reaction product was then filtered, and the filter cake was washed several times with deionized water and ethanol until the filtrate was colorless and transparent. Finally, the washed filter cake was placed in a vacuum drying oven and dried at 80°C and -0.1 MPa for 16 hours to obtain the polymer-coated graphite composite material.

[0047] In step five, the carbonization process is microwave-assisted carbonization, which includes: First, the polymer-coated graphite composite material is placed in a microwave-specific quartz crucible with a thickness not exceeding 2 cm. Then, the crucible is placed in the constant temperature zone of a microwave tube furnace, and the furnace body is sealed. Next, high-purity argon gas is introduced into the furnace cavity at a flow rate of 500 mL / min as a protective gas, and the furnace is purged for more than 30 minutes to remove all air. After that, the microwave generator and the programmed temperature control system are started, and the carbonization program is set: In the first stage, the temperature is increased from room temperature to 400°C at a rate of 10°C / min and held for 60 minutes to allow the polymer to initially crosslink and decompose. In the second stage, the temperature is increased from 400°C to the final carbonization temperature of 1200°C at a rate of 8°C / min and held for 3 hours. After carbonization, the furnace body is allowed to cool naturally to below 100°C while the protective gas is continuously introduced. Then, the furnace door is opened, and the furnace is allowed to continue cooling to room temperature. The sample is then removed to obtain the primary carbon-coated graphite material.

[0048] In step six, the crushing and screening process includes: first, the primary carbon-coated graphite material is coarsely crushed using a roller crusher with a roller gap of 2.0 mm; then, the coarsely crushed material is fed into a high-efficiency mechanical fusion machine for fine crushing at a speed of 3000 r / min for 30 minutes, with controlled crushing energy and time; next, the finely crushed powder is graded using a 600-mesh vibrating screen, and powder with a particle size D50 of 25 micrometers is collected as qualified product; finally, a wind classifier is used to perform secondary grading on the qualified product, with the grading wind speed controlled at 15 m / s, to remove extremely fine powder and coarse particles, resulting in a high-capacity graphite anode material product.

[0049] The material is prepared by processing raw materials containing the following parts by weight: based on 100 parts by weight of pretreated graphite powder, it contains 30 parts by weight of polymeric monomer and 10 parts by weight of dopant source. The material has a multi-level composite structure, including: Core layer: is a graphite material that has been stripped and plasma activated, and has been modified by elemental doping to introduce dopant elements. The dopant elements exist in the graphite interlayer in the form of heteroatoms. Intermediate buffer layer: an amorphous carbon layer formed by the carbonization transformation of polymerized monomers, covering the core layer; Surface functional layer: a composite conductive layer containing dopant source conversion products attached to the intermediate buffer layer.

[0050] Comparative Example 1: The difference between this comparative example and Example 1 is that no elemental doping modification was performed during the preparation process of this comparative example.

[0051] Comparative Example 2 differs from Example 1 in that: no in-situ polymerization coating was performed during the preparation process of this comparative example.

[0052] Comparative Example 3 differs from Example 1 in that the graphite raw material was not subjected to plasma activation treatment during the preparation process.

[0053] Comparative Example 4 differs from Example 1 in that it does not use waste graphite in the selection of raw materials, but uses commercially available high-purity artificial graphite.

[0054] The high-capacity graphite anode materials prepared in Examples 1-3 and Comparative Examples 1-4 were used to fabricate battery electrodes, and their electrochemical performance was tested. The test items and methods are as follows: For specific capacity testing, the material was charged at a constant current of 0.1C to 0.01V, then charged at a constant voltage until the current dropped to 0.05C, and then discharged at a constant current of 0.1C to 1.5V. The first discharge capacity was recorded, and the mass specific capacity of the material was calculated. Cyclic stability test: Under the conditions of 1C rate and voltage range of 0.01V-1.5V, the battery is subjected to constant current charge and discharge cycle test, the discharge capacity of the 100th cycle is recorded, and its capacity retention rate relative to the first discharge capacity is calculated. Rate performance testing involved constant current discharge of the battery at different rates of 0.2C, 0.5C, 1C, and 2C, recording the discharge capacity at each rate, and calculating the capacity retention rate at each high rate using the discharge capacity at 0.1C as a benchmark. The initial charge and discharge efficiency test records the specific values ​​of the initial charge capacity and initial discharge capacity at a 0.1C rate. The ratio of the initial discharge capacity to the initial charge capacity is calculated to obtain the initial coulombic efficiency.

[0055] The test data of the high-capacity graphite anode materials prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: By comparing and analyzing the data in the table, it can be seen that the high-capacity graphite anode materials prepared using the processes in Examples 1-3 exhibit superior performance compared to those prepared using the processes in Comparative Examples 1-4. This indicates that the two-step acid washing pretreatment—crushing, classifying, and removing metals with hydrochloric acid and silicon with hydrofluoric acid—removes impurities from the waste graphite raw materials, providing a high-purity graphite base for subsequent modification. Furthermore, the combination of liquid-phase exfoliation and high-pressure homogenization reduces the number of graphite layers and increases the specific surface area. Simultaneously, low-temperature plasma activation introduces active sites on the surface, enhancing the chemical reactivity of the graphite and laying a solid structural foundation for subsequent elemental doping and polymerization coating, thus ensuring the stability and superior performance of the final material. Hydrothermal reactions were used to modify graphite by doping with heterogeneous elements, including nitrogen, phosphorus, and sulfur. These dopants entered the interlayer of graphite or partially replaced carbon atoms, which could regulate its electronic structure, enhance conductivity, and mitigate volume changes during lithium-ion insertion and extraction. Based on this, a polymer coating layer was formed on the surface and edges of the doped graphite through in-situ polymerization, and then carbonized to transform it into an amorphous carbon layer. This carbon layer not only serves as a stable precursor for the solid electrolyte interface film, reducing side reactions, but also acts as a buffer layer to suppress particle pulverization during cycling, thereby synergistically improving the material's initial coulombic efficiency, cycle stability, and rate performance. A multi-step synergistic modification strategy of elemental doping-in-situ polymerization coating-carbonization, coupled with microwave-assisted carbonization, resulted in a composite structure in the prepared anode material with enhanced core conductivity and a well-protected outer buffer layer. This structural design overcomes the shortcomings of traditional graphite materials, such as limited specific capacity and poor rate performance, and makes up for the shortcomings of the poor effect of single modification methods. Without using expensive raw materials, it comprehensively improves the material's reversible specific capacity, long cycle life and fast charge and discharge capability.

[0056] By comparing and analyzing the relevant data in the table, it can be seen that the high-capacity graphite anode material prepared by the process of this invention exhibits superior performance in terms of specific capacity, initial efficiency, cycle life and rate performance, and has excellent comprehensive performance.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0058] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-capacity graphite anode material, characterized in that: Includes the following steps: Step 1: Raw material selection and pretreatment: Select waste graphite raw materials, crush, remove impurities and purify them to obtain pretreated graphite powder; Step 2, stripping and activation treatment: The pretreated graphite powder is dispersed in the stripping liquid and subjected to liquid phase stripping treatment to obtain stripped graphite slurry. Then, the stripped graphite slurry is subjected to low-temperature plasma activation treatment to obtain activated graphite slurry. Step 3, element doping modification: The dopant solution is mixed with activated graphite slurry and a hydrothermal reaction is carried out under a protective atmosphere to allow the dopant element to enter the graphite interlayer or replace some carbon atoms. After the reaction is completed, the dopant is separated into solid and liquid, washed and dried to obtain the doped modified graphite precursor. Step 4, In-situ Polymerization Coating: The doped modified graphite precursor is uniformly dispersed in a mixed solution composed of polymeric monomers and initiators, and an in-situ polymerization reaction is carried out to form a polymer coating layer on the graphite surface and interlayer edges. After the reaction is completed, the graphite is washed and dried to obtain a polymer-coated graphite composite material. Step 5, Carbonization treatment: The polymer-coated graphite composite material is placed in a tube furnace and subjected to programmed temperature rise carbonization treatment under inert atmosphere protection, so that the polymer coating layer is transformed into an amorphous carbon layer, and primary carbon-coated graphite material is obtained. Step 6: Crushing and Sieving: The primary carbon-coated graphite material is crushed and sieved to obtain high-capacity graphite anode material products with a specific particle size range.

2. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step one, the raw material selection and pretreatment include: the waste graphite raw material is selected from at least one of lithium-ion battery recycled graphite, graphite electrode processing waste, or natural graphite flotation tailings; firstly, the waste graphite raw material is placed in a jaw crusher for coarse crushing, and then transferred to an air jet mill for crushing at an air pressure of 0.4-0.8 MPa for 5-15 minutes to obtain coarse graphite powder with a particle size D50 of 10-50 micrometers; then, the coarse graphite powder is placed in an acid washing tank, and a hydrochloric acid solution with a concentration of 3-6 mol / L is added, and the solution is washed at 60- The metal impurities are dissolved by stirring and acid washing at 80℃ for 2-4 hours. After acid washing, the filter cake is filtered and washed with deionized water until the filtrate is neutral. The filter cake is then transferred to a 10-20wt% hydrofluoric acid solution and soaked at 40-60℃ for 1-3 hours to remove silica impurities. Finally, the filter cake is filtered again and washed with deionized water until the filtrate is neutral. The filter cake is then placed in a vacuum drying oven and dried at 80-120℃ and -0.08 to -0.1MPa for 8-12 hours to obtain the pretreated graphite powder.

3. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step two, the stripping solution is composed of the following raw materials in parts by weight: 40-60 parts of high-boiling-point polar solvent, 5-15 parts of surfactant, 2-8 parts of intercalating agent, and 20-40 parts of deionized water; wherein the high-boiling-point polar solvent is at least one of N-methylpyrrolidone, dimethyl sulfoxide, and γ-butyrolactone, the surfactant is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and polyethylene glycol octylphenyl ether, and the intercalating agent is at least one of ammonium persulfate, potassium permanganate, and potassium chlorate.

4. The method for preparing a high-capacity graphite anode material according to claim 3, characterized in that: The stripping solution is prepared and used by the following method: First, a high-boiling-point polar solvent, surfactant, intercalating agent, and deionized water are added sequentially to a dispersion vessel equipped with constant temperature circulation and high-speed shearing functions. Then, the temperature of the dispersion vessel is controlled at 25-35℃, and the mixture is premixed at a speed of 300-500 r / min for 5-10 minutes. Then, the speed is increased to 2000-5000 r / min, and high-speed shearing dispersion is performed for 30-60 minutes until the mixture is transparent or semi-transparent, thus obtaining the stripping solution. Next, pretreated graphite powder is slowly added to the stripping solution at a solid-liquid ratio of 1:20-1:50 g / mL. With the assistance of an ultrasonic cell disruptor, the mixture is ultrasonically treated for 1-3 hours at a power of 300-500W under ice-water bath conditions to obtain a preliminary stripped graphite dispersion. Then, the preliminary stripped graphite dispersion is transferred to a high-pressure homogenizer and homogenized 5-10 times under a pressure of 80-150 MPa to obtain a stripped graphite slurry with a reduced number of layers and an increased specific surface area.

5. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step two, the low-temperature plasma activation treatment includes: first, spray drying the exfoliated graphite slurry to obtain dried exfoliated graphite powder; then, uniformly spreading the dried exfoliated graphite powder on the sample tray of the plasma treatment equipment and sending it into the reaction chamber; starting the vacuum system and pumping the pressure in the reaction chamber to 10-100 Pa; then, introducing activation gas at a flow rate of 20-100 sccm to maintain the pressure inside the chamber at 50-500 Pa; next, starting the plasma generator, setting the radio frequency power to 100-500 W, and the treatment time to 5-30 minutes; after the treatment, turning off the plasma and gas sources, filling the chamber with inert gas to atmospheric pressure, removing the sample to obtain activated graphite powder; finally, redispersing the activated graphite powder in deionized water or low alcohol to prepare an activated graphite slurry with a solid content of 5-15 wt%; wherein the activation gas is oxygen, nitrogen, ammonia, argon, or a mixture thereof.

6. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step three, the elemental doping modification includes: first, preparing a dopant solution by dissolving the dopant source in a solvent to prepare a dopant solution with a concentration of 0.1-2.0 mol / L. The dopant source is at least one of urea, melamine, ammonium dihydrogen phosphate, phosphoric acid, boric acid, sodium borohydride, sodium sulfide, and thiourea. The solvent is at least one of deionized water, ethanol, and isopropanol. Then, the activated graphite slurry and the dopant solution are mixed at a volume ratio of 1:1-1:3 and placed in a high-shear emulsifier for high-speed emulsification and dispersion at a speed of 5000-15000 r / min for 10-30 minutes to form a mixed slurry. The mixed slurry was then transferred to the polytetrafluoroethylene liner of a hydrothermal reactor, with a filling degree of 60-80%. The hydrothermal reactor was then sealed and placed in a forced-air drying oven, where it was reacted at 120-200℃ for 6-24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The reaction product was then centrifuged, and the precipitate was washed 3-5 times alternately with deionized water and ethanol until the supernatant was neutral and no impurity ions were detected. Finally, the washed precipitate was placed in a vacuum freeze dryer and dried at -50 to -30℃ and a pressure below 10Pa for 24-48 hours to obtain the doped modified graphite precursor.

7. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step four, the in-situ polymerization coating includes: first, preparing a polymerization solution by dissolving the monomer in 0.5-2.0 mol / L acidic aqueous solution or deionized water to prepare a monomer solution with a concentration of 0.1-0.5 mol / L. The acidic aqueous solution is an aqueous solution of hydrochloric acid, sulfuric acid, or p-toluenesulfonic acid. Then, the doped modified graphite precursor is added to the above monomer solution and dispersed for 30-60 minutes under the combined action of ultrasound and mechanical stirring to form a graphite monomer suspension. Next, the suspension is transferred to a reactor equipped with reflux condensation and temperature control, stirred under ice-water bath conditions, and an oxidant initiator solution is added dropwise, with controlled addition. The reaction system temperature is maintained at 0-10℃. The oxidant initiator is at least one of ammonium persulfate, ferric chloride, and hydrogen peroxide, with a molar ratio of 0.5:1 to 1.5:1 to the polymer monomer. After the addition is complete, the ice-water bath is removed, and the reaction system temperature is slowly raised to 20-25℃. The reaction is continued to be stirred for 4-12 hours. The reaction product is then filtered, and the filter cake is washed several times with deionized water and ethanol until the filtrate is colorless and transparent. Finally, the washed filter cake is placed in a vacuum drying oven and dried at 60-80℃ and -0.08 to -0.1 MPa for 10-16 hours to obtain the polymer-coated graphite composite material.

8. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step five, the carbonization process is microwave-assisted carbonization, which includes: first, placing the polymer-coated graphite composite material in a microwave-specific quartz crucible with a thickness not exceeding 2 cm; then, placing the crucible in the constant temperature zone of a microwave tube furnace and sealing the furnace body; next, introducing high-purity argon or nitrogen gas as a protective gas into the furnace cavity at a flow rate of 200-500 mL / min for at least 30 minutes to purge the air; then, starting the microwave generator and the programmed temperature control system and setting the carbonization program: the first stage, at 5-1 The temperature is increased from room temperature to 300-400℃ at a rate of 0℃ / min and held for 30-60 minutes to allow the polymer to undergo initial cross-linking and decomposition. In the second stage, the temperature is increased from 300-400℃ to the final carbonization temperature of 800-1200℃ at a rate of 3-8℃ / min and held for 1-3 hours. After carbonization, the furnace body is allowed to cool naturally to below 100℃ while continuously purging with protective gas. The furnace door is then opened and the furnace is allowed to continue cooling to room temperature. The sample is then removed to obtain the primary carbon-coated graphite material.

9. The method for preparing a high-capacity graphite anode material according to claim 1, characterized in that: In step six, the crushing and sieving process includes: first, coarsely crushing the primary carbon-coated graphite material using a roller crusher, controlling the roller gap to be 0.5-2.0 mm; then, finely crushing the coarsely crushed material into a high-efficiency mechanical fusion machine or an air jet mill. When using a high-efficiency mechanical fusion machine, the rotation speed is controlled at 1000-3000 r / min, and the processing time is 10-30 minutes. When using an air jet mill, the working pressure is controlled at 0.6-1.2 MPa, and the classifying wheel rotation speed is 2000-6000 r / min, controlling the crushing energy and time. Next, the finely crushed powder is classified using a 200-600 mesh vibrating screen, collecting powder with a particle size D50 in the range of 8-25 micrometers as qualified products. Finally, a wind classifier is used to perform secondary classification on the qualified products, controlling the classification wind speed at 5-15 m / s to remove extremely fine powder and coarse particles, obtaining the high-capacity graphite anode material product.

10. A high-capacity graphite anode material, prepared by the preparation method of a high-capacity graphite anode material according to any one of claims 1-9, characterized in that: The material is prepared by processing raw materials containing the following parts by weight: based on 100 parts by weight of pretreated graphite powder, it contains 10-30 parts by weight of polymeric monomer and 1-10 parts by weight of dopant source. The material has a multi-level composite structure, including: Core layer: is a graphite material that has been stripped and plasma activated, and has been modified by elemental doping to introduce doping elements, which exist in the form of heteroatoms between graphite layers or in the lattice; Intermediate buffer layer: an amorphous carbon layer formed by carbonization of the polymer monomers, covering the core layer; Surface functional layer: a composite conductive layer containing the conversion products of the dopant source, attached to the intermediate buffer layer.

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