Preparation process of lithium ion composite battery negative electrode material with low impedance and high rate performance

Abstract

The invention relates to a preparation process of a lithium ion composite battery negative electrode material with low impedance and high rate performance. The preparation method comprises the following steps: pretreatment of artificial graphite, preparation of hollow ferroferric oxide nanospheres (H-Fe3O4), preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4 (at) NC), preparation of carbon-coated artificial graphite (Ag (at) C), preparation of a porous graphite composite material (PG (at) C (at) SEI for rapid charging, preparation of an artificial SEI high-conductivity porous graphite negative electrode material (PG (at) C (at) SEI), and construction of the composite negative electrode material (rGO (at) PG (at) C (at) SEI (at) H-Fe3O4 (at) NC). According to the preparation method, a high-temperature treatment method, a doping combination method, a carbonization combination method and an etching method are creatively combined, the prepared battery negative electrode material shows good impedance high-rate performance, and the charging and discharging efficiency and the cycling stability of a lithium ion battery can be effectively improved.

Description

Technical Field

[0001] The present invention relates to a battery negative electrode material, in particular to a preparation process of a lithium ion composite battery negative electrode material with low impedance and high rate performance. Background Art

[0002] With the rapid development of electric vehicles, portable electronic devices, and renewable energy storage systems, the performance requirements for lithium-ion batteries are increasing, especially the demand for high energy density, fast charge and discharge capabilities, and long cycle life. As a key component of lithium-ion batteries, the performance of negative electrode materials directly affects the overall performance of the battery. Commercial lithium-ion batteries mainly use graphite-based carbon materials as negative electrodes, but their theoretical specific capacity is low (approximately 372mAh / g), which makes it difficult to meet high energy density requirements. Graphite materials are prone to problems such as lithium dendrite growth and capacity decay during fast charging, limiting their performance in high-power applications.

[0003] To overcome the limitations of graphite, a variety of new anode materials have been explored, including silicon-based materials, metal oxides Fe3O4, SnO2, and composite carbon materials. Silicon (Si) has attracted considerable attention due to its extremely high theoretical specific capacity, but it suffers from severe volume expansion during charge and discharge, leading to structural damage and poor cycling stability. Metal oxides Fe3O4 also have high theoretical capacity, but suffer from poor conductivity and similar volume expansion issues.

[0004] In recent years, improving the electrochemical performance of negative electrode materials by constructing composite structures: carbon coating, hollow or porous structures has become a research hotspot. For example: carbon-coated silicon (Si@C): the carbon layer can buffer the volume expansion of silicon and improve conductivity, but the agglomeration problem of silicon still needs to be optimized. Hollow structure materials (such as H-Fe3O4): the hollow structure can provide additional space to alleviate volume changes, but the cycle stability still needs to be improved. Nitrogen-doped carbon materials (NC): nitrogen doping can enhance the conductivity and lithium ion transport capacity of carbon materials, but its combination with active substances needs to be optimized. Artificial SEI film: constructing a stable solid electrolyte interface (SEI) through pre-film technology can reduce side reactions and improve cycle life. Although the above methods have improved the performance of negative electrode materials to a certain extent, the following challenges still exist: Balance between conductivity and structural stability: High-capacity materials Si and Fe3O4 have poor conductivity, and although carbon coating can improve conductivity, it may sacrifice some active sites.

[0005] Limitations of fast charging performance: Traditional graphite negative electrodes are prone to lithium deposition during fast charging, while the rate performance of new materials such as porous carbon and metal oxides still needs to be optimized.

[0006] Cycle life issues: Silicon-based and metal oxide materials still face electrode pulverization and capacity attenuation caused by volume expansion during long-term cycles.

[0007] After solving the above problems, developing a composite negative electrode material with high capacity, high rate performance and long cycle stability is of great significance to promoting the development of the next generation of lithium-ion batteries. Summary of the Invention

[0008] In response to the above problems, the present invention provides a process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance, comprising the following steps: step (1) pretreatment of artificial graphite, step (2) preparation of hollow ferroferric oxide nanospheres (H-Fe3O4), step (3) preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC), step (4) preparation of carbon-coated artificial graphite (AG@C), step (5) preparation of a porous graphite composite material (PG@C) for fast charging, step (6) preparation of an artificial SEI high-conductivity graphite negative electrode material (PG@C@SEI), and step (7) construction of a composite negative electrode material (rGO@PG@C@SEI@H-Fe3O4@NC).

[0009] Among them, step (7) construction of composite negative electrode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), are added, and ultrasonic dispersion is performed to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0010] As a preference, step (1) artificial graphite pretreatment High-quality artificial graphite powder is selected and placed in a high-temperature furnace under argon (Ar) protection for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. After ultrasonic dispersion, the precursors are uniformly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tubular furnace to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in an organic solvent, ethylene glycol, stirred evenly, and then transferred to a reactor. After the reaction, H-Fe3O4 nanospheres were obtained by cooling, centrifugation, washing, and drying. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) are used as templates, and dopamine, a nitrogen-containing carbon source, is added. The pH value is adjusted with ammonia water under alkaline conditions, and dopamine undergoes self-polymerization to form a polymer coating layer on the surface of the nanospheres. Subsequently, the nanospheres are centrifuged, washed, and dried, and placed in a tube furnace for high-temperature carbonization under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with sucrose as a carbon source, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at high temperature under argon protection to form a uniform and tight carbon coating layer to obtain G@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, stirred to react, and the graphite structure is etched to form a porous structure; after the reaction is completed, a porous graphite composite material PG@C with fast charging performance is obtained through filtering, washing, drying and other steps; the porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance; Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), are added, and ultrasonic dispersion is performed to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0011] As a preference, step (1) artificial graphite pretreatment High-quality artificial graphite powder is selected and placed in a high-temperature furnace. Under the protection of argon (Ar), the temperature is increased to 2800-3000℃ at a heating rate of 1-5℃ / min for high-temperature graphitization treatment to improve the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion is carried out for 30-60 minutes to allow the precursors to be evenly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tubular furnace at 800-1000℃ for 2-4 hours to achieve uniform distribution of doping atoms in the graphite structure.

[0012] The advantages of adopting the present invention are that high-temperature graphitization treatment can reduce defects in graphite, enhance conductivity, and reduce internal resistance; doping with elements such as nitrogen and phosphorus can optimize the electronic structure, introduce more active sites, and improve lithium ion storage capacity; ultrasonic-assisted dispersion and sintering processes ensure uniform distribution of doping elements to avoid local aggregation that affects performance.

[0013] As a preference, step (2) preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in an organic solvent, ethylene glycol. After stirring evenly, the mixture was transferred to a reactor and reacted at 150-200°C for 10-15 hours. After the reaction, the mixture was cooled, centrifuged, washed, and dried to obtain H-Fe3O4 nanospheres.

[0014] The advantages of adopting the present invention are that Fe3O4 undergoes volume changes during the charge and discharge process, and the hollow structure can provide a buffer space to reduce the breakage of the electrode material; the solvothermal method can accurately control the size and shell thickness of the nanospheres, optimizing the lithium ion transmission path; compared with graphite, Fe3O4 can significantly improve the energy density of the battery.

[0015] Preferably, step (3) preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) are used as a template, and dopamine, a nitrogen-containing carbon source, is added. The pH value is adjusted with ammonia water under alkaline conditions, and dopamine undergoes self-polymerization to form a polymer coating layer on the surface of the nanospheres. Subsequently, the nanospheres are centrifuged, washed, and dried, and placed in a tubular furnace for high-temperature carbonization at 750-800°C under nitrogen to obtain H-Fe3O4@NC.

[0016] The advantages of the present invention are that amorphous carbon coating can enhance the electronic conductivity of Fe3O4 and improve the rate performance; the introduction of nitrogen atoms into the carbon skeleton can increase defect sites and accelerate the diffusion of Li⁺; dopamine self-polymerizes to form a uniform coating layer, thereby preventing Fe3O4 from directly contacting the electrolyte and reducing side reactions.

[0017] As a preference, step (4) preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with sucrose as a carbon source, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 180-200°C for 8-12 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tubular furnace and treated at a high temperature of 1000-1200°C for 2-3 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C.

[0018] The advantages of adopting the present invention are that the outer carbon layer can reduce the decomposition of the electrolyte, inhibit the excessive growth of the SEI film, and improve the cycle stability; the coating layer formed by carbonization of sucrose is tightly bonded to the graphite to prevent it from falling off; and the carbon coating can reduce the interfacial impedance, making it easier for lithium ions to be embedded / eliminated.

[0019] Preferably, step (5) prepares a porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 80-100°C for 3-6 hours to etch the graphite structure to form a porous structure. After the reaction is completed, the porous graphite composite material PG@C with fast charging performance is obtained through filtering, washing, drying and other steps. The porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance.

[0020] The advantage of adopting the present invention is that the pores formed by etching can accelerate ion transmission and improve fast charging performance. By adjusting the concentration and temperature, the pore structure can be optimized to avoid excessive etching affecting the mechanical strength.

[0021] As a preference, step (6) preparation of artificial SEI high conductive graphite negative electrode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 12-24 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained.

[0022] The advantages of adopting the present invention are that the artificial SEI can reduce the irreversible capacity loss in the first cycle and improve the coulombic efficiency; by adding FEC additives to optimize the preparation process, FEC can form a stable interface film with lithium salt, effectively inhibiting the production of SEI film during the charge and discharge process and improving the cycle stability of the material; a uniform SEI layer can prevent local lithium deposition and improve safety.

[0023] As a preference, step (7) construction of composite negative electrode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methyl pyrrolidone (NMP), are added, and ultrasonic dispersion is performed for 60-90 minutes to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated at 600-800°C for 2-4 hours in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0024] The advantages of adopting the present invention are that reduced graphene oxide rGO enhances the overall conductivity and improves the cyclic stability of the material, PG@C effectively alleviates volume expansion and provides fast charging capability, H-Fe3O4@NC contributes to high capacity, artificial SEI improves interface stability, freeze-drying ensures uniformity, avoids the agglomeration problem caused by traditional mechanical mixing, and ensures consistent material performance.

[0025] In summary, the present invention has the following beneficial effects: 1. The advantages of the present invention are that high-temperature graphitization treatment can reduce defects in graphite, enhance conductivity, and reduce internal resistance. By doping with elements such as nitrogen and phosphorus, the electronic structure is optimized, more active sites are introduced, and the lithium ion storage capacity is improved. The ultrasonic-assisted dispersion and sintering process ensures uniform distribution of doping elements to avoid local aggregation that affects performance.

[0026] 2. The advantages of adopting the present invention are that Fe3O4 undergoes volume changes during the charge and discharge process, and the hollow structure can provide a buffer space to reduce the breakage of the electrode material; the solvothermal method can accurately control the size and shell thickness of the nanospheres, optimizing the lithium ion transmission path; compared with graphite, Fe3O4 can significantly improve the energy density of the battery.

[0027] 3. The advantages of the present invention are that amorphous carbon coating can enhance the electronic conductivity of Fe3O4 and improve rate performance; the introduction of nitrogen atoms into the carbon skeleton can increase defect sites and accelerate Li⁺ diffusion; dopamine self-polymerizes to form a uniform coating layer, thereby preventing Fe3O4 from directly contacting the electrolyte and reducing side reactions.

[0028] 4. The advantages of the present invention are that the outer carbon layer can reduce electrolyte decomposition, inhibit excessive growth of the SEI film, and improve cycle stability; the coating layer formed by carbonization of sucrose is tightly bonded to the graphite to prevent it from falling off; and the carbon coating can reduce the interfacial impedance, making it easier for lithium ions to be inserted / extracted.

[0029] 5. The advantage of adopting the present invention is that the pores formed by etching can accelerate ion transmission and improve fast charging performance. The pores formed by etching can accelerate ion transmission and improve fast charging performance. By adjusting the concentration and temperature, the pore structure can be optimized to avoid excessive etching affecting the mechanical strength.

[0030] 6. The advantages of the present invention are that the artificial SEI can reduce the irreversible capacity loss in the first cycle and improve the coulombic efficiency. By adding FEC additives to optimize the preparation process, FEC can form a stable interface film with lithium salts, effectively inhibiting the production of SEI film during the charge and discharge process and improving the cyclic stability of the material; a uniform SEI layer can prevent local lithium deposition and improve safety.

[0031] 7. The advantages of the present invention are that reduced graphene oxide (rGO) enhances overall conductivity and improves the cyclic stability of the material, PG@C effectively alleviates volume expansion and provides fast charging capability, H-Fe3O4@NC contributes to high capacity, artificial SEI improves interface stability, freeze-drying ensures uniformity, avoids agglomeration problems caused by traditional mechanical mixing, and ensures consistent material performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a process flow for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance. DETAILED DESCRIPTION

[0033] The following examples are provided to illustrate the present invention but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0034] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. In addition, all the components and raw materials used in the examples are known commercial products.

[0035] Example 1

[0036] Step (1) Artificial graphite pretreatment High-quality artificial graphite powder is selected and placed in a high-temperature furnace. Under argon (Ar) protection, the temperature is increased at a rate of 1°C / min to 2800°C for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion is performed for 30 minutes to ensure that the precursors are evenly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tube furnace at 800°C for 2 hours to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 150°C for 10 hours. After the reaction, the mixture was cooled, centrifuged, washed, and dried to obtain H-Fe3O4 nanospheres. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 750°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with carbon source sucrose, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 180°C for 8 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1000°C for 2 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The G@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 80°C for 3 hours to etch the graphite structure to form a porous structure; after the reaction, the porous graphite composite material PG@C with fast charging performance is obtained by filtering, washing, drying, etc.; the porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance; Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 12 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 60 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 600°C for 2 hours in a mixed atmosphere of hydrogen and argon in a tubular furnace to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0037] Example 2

[0038] Step (1) Artificial graphite pretreatment High-quality artificial graphite powder was selected and placed in a high-temperature furnace. Under argon (Ar) protection, the temperature was increased at a rate of 2°C / min to 2900°C for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder was dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion was performed for 35 minutes to ensure that the precursors were evenly adsorbed on the surface of the artificial graphite. The powder was then filtered and dried, and the dried powder was sintered in a tube furnace at 900°C for 3 hours to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 160°C for 13 hours. After the reaction, the H-Fe3O4 nanospheres were obtained by cooling, centrifugation, washing, and drying. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 755°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with carbon source sucrose, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 190°C for 9 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1100°C for 2 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 85°C for 4 hours to etch the graphite structure to form a porous structure. After the reaction, the porous graphite composite material PG@C with fast charging performance is obtained by filtering, washing, drying, etc. The porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance. Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 15 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 70 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 650°C for 2 hours in a mixed atmosphere of hydrogen and argon in a tubular furnace to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0039] Example 3

[0040] Step (1) Artificial graphite pretreatment High-quality artificial graphite powder was selected and placed in a high-temperature furnace. Under argon (Ar) protection, the temperature was increased at a rate of 5°C / min to 2900°C for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder was dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion was performed for 50 minutes to ensure that the precursors were evenly adsorbed on the surface of the artificial graphite. The powder was then filtered and dried, and the dried powder was sintered in a tube furnace at 900°C for 3 hours to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 190°C for 15 hours. After the reaction, the H-Fe3O4 nanospheres were obtained by cooling, centrifugation, washing, and drying. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 780°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with carbon source sucrose, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 190°C for 11 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1100°C for 3 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 95°C for 6 hours to etch the graphite structure to form a porous structure. After the reaction, the porous graphite composite material PG@C with fast charging performance is obtained by filtering, washing, drying, etc. The porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance. Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 24 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 85 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 700°C for 4 hours in a mixed atmosphere of hydrogen and argon in a tubular furnace to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0041] Example 4

[0042] Step (1) Artificial graphite pretreatment High-quality artificial graphite powder is selected and placed in a high-temperature furnace. Under argon (Ar) protection, the temperature is increased at a rate of 5°C / min to 3000°C for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion is performed for 60 minutes to ensure that the precursors are evenly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tube furnace at 1000°C for 4 hours to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 200°C for 12 hours. After the reaction, the mixture was cooled, centrifuged, washed, and dried to obtain H-Fe3O4 nanospheres. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 800°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with carbon source sucrose, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 200°C for 12 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1200°C for 3 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 100°C for 6 hours to etch the graphite structure to form a porous structure. After the reaction, the porous graphite composite material PG@C with fast charging performance is obtained by filtering, washing, drying, etc. The porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance. Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 24 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 90 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 600°C for 4 hours in a mixed atmosphere of hydrogen and argon in a tubular furnace to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0043] Comparative Example 1

[0044] Step (1) Artificial graphite pretreatment Select high-quality artificial graphite powder, place it in a high-temperature furnace, and heat it to 3000℃ under argon (Ar) protection at a heating rate of 10℃ / min for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, it is then filtered and dried. The dried powder is sintered in a tube furnace at 1000℃ for 5 hours. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 220°C for 20 hours. After the reaction, the H-Fe3O4 nanospheres were obtained by cooling, centrifugation, washing, and drying. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 900°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite pretreated in step (1) is mixed with carbon source sucrose, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 220°C for 15 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1300°C for 5 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 100°C for 10 hours to etch the graphite structure to form a porous structure; after the reaction, the porous graphite composite material PG@C with fast charging performance is obtained through filtering, washing, drying and other steps; the porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance; Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 24 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 90 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 800°C for 4 hours in a mixed atmosphere of hydrogen and argon in a tube furnace to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0045] Comparative Example 2

[0046] Step (1) Artificial graphite pretreatment High-quality artificial graphite powder is selected and placed in a high-temperature furnace. Under argon (Ar) protection, the temperature is increased at a rate of 1°C / min to 2500°C for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity. After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion is performed for 20 minutes to ensure that the precursors are evenly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tube furnace at 700°C for 2 hours to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in ethylene glycol, stirred evenly, and then transferred to a reactor for reaction at 100°C for 5 hours. After the reaction, the mixture was cooled, centrifuged, washed, and dried to obtain H-Fe3O4 nanospheres. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) were used as templates, and dopamine, a nitrogen-containing carbon source, was added. The pH value was adjusted with ammonia water under alkaline conditions, and dopamine self-polymerized to form a polymer coating layer on the surface of the nanospheres. The nanospheres were then placed in a tubular furnace and carbonized at 700°C under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with sucrose as a carbon source, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 100° C. for 8 h to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at 1000° C. for 2 h under argon protection to form a uniform and compact carbon coating layer to obtain AG@C; Step (5) Preparation of artificial SEI highly conductive graphite anode material (AG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive fluoroethylene carbonate is prepared in a glove box; the AG@C prepared in step (4) is immersed in the electrolyte and allowed to stand at room temperature for 12 hours to form an artificial SEI film on the surface of the AG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material AG@C@SEI is obtained; Step (6) Construction of composite anode material (rGO@AG@C@SEI@H-Fe3O4@NC) The AG@C@SEI prepared in step (5) was mixed with rGO (reduced graphene oxide) and H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), were added, and ultrasonic dispersion was performed for 50 minutes to uniformly disperse the components. The solvent was then removed from the mixture by freeze drying to obtain a composite powder. The composite powder was heat-treated at 500°C for 2 hours in a mixed atmosphere of hydrogen and argon in a tube furnace to form an rGO@G@C@SEI@H-Fe3O4@NC composite negative electrode material.

[0047] Comparison of detection experiments:

[0048] The composite negative electrode materials obtained in Examples 1 to 4 and the comparative examples 1 and 2 were tested. The specific testing methods are as follows: Electrochemical impedance spectroscopy

[0049] Electrochemical impedance spectroscopy (EIS) was performed using an electrochemical workstation with a measurement frequency range of 0.01-10 5 Hz, and the AC amplitude was set to 5mV; by analyzing the impedance spectrum obtained from the test, key information such as the charge transfer resistance and ion diffusion resistance of the electrode material was obtained to evaluate the kinetic performance of different materials in the electrochemical process.

[0050] Charge and discharge test

[0051] The materials prepared in the above examples and comparative examples were used to form negative electrode sheets. Using metallic lithium as the counter electrode, CR2032 button cells were assembled in a glove box and subjected to constant current charge-discharge tests using a battery testing system. The tests were performed using a Wuhan LAND-CT2001A instrument, with a voltage range of 0.01-3.0V and a test rate of 0.1C. The charge-discharge curves of the materials were analyzed to investigate their performance, including platform specific capacity and initial coulombic efficiency.

[0052] Cycle life test

[0053] The battery was subjected to 50 long-cycle charge and discharge tests at a selected appropriate current rate of 0.5C, and the changes in battery capacity with the number of cycles were recorded. When the battery capacity decayed to 80% of the initial capacity, the corresponding number of cycles was the cycle life of the battery; this was used to evaluate the effects of different composite negative electrode materials on the battery cycle stability.

[0054] Table 1 Electrochemical impedance spectroscopy Example Charge transfer resistance Ω 1 90 2 80 3 70 4 50 Comparative Example 1 120 Comparative Example 2 140 As can be seen from Table 1, Example 4 is the best, while Comparative Examples 1 and 2 are relatively poor. The lower the charge transfer resistance, the easier the electron transfer in the electrode reaction, and the better the electrochemical kinetic performance of the material. The charge transfer resistance of Example 4 is significantly lower than that of Comparative Examples 1 and 2. This is because the artificial graphite pretreatment process, the appropriate heating rate, the high temperature graphitization temperature, and the doping treatment precisely controlled in the embodiment optimize the crystallinity and electron conduction path of the material. At the same time, the subsequent precise regulation of the steps of hollow ferroferric oxide nanospheres, nitrogen-doped carbon coating, and the construction of the artificial SEI film forms a structure that is conducive to electron transport. However, the heating rate of Comparative Example 1 is too fast, some reaction conditions are too severe, and the reaction temperature and time of Comparative Example 2 are insufficient, resulting in more structural defects in the material, which hinders electron transfer and thus has a higher charge transfer resistance.

[0055] Table 2 Charge and discharge test Example First discharge specific capacity (mAh / g) First charge specific capacity (mAh / g) First coulombic efficiency (%) 1 1433 1247 87 2 1491 1312 88 3 1622 1444 89 4 1717 1545 90 Comparative Example 1 1214 1032 85 Comparative Example 2 1168 958 82 As can be seen from Table 2, Example 4 is the best, while Comparative Examples 1 and 2 are relatively poor. The first discharge specific capacity and the first charge specific capacity reflect the ability of the material to store and release lithium ions, and the first coulombic efficiency reflects the utilization efficiency of lithium ions in the first charge and discharge process. All indicators of the embodiment are better than those of the comparative example; in the embodiment, high-temperature graphitization improves the conductivity and lithium ion storage sites of artificial graphite, the construction of the artificial SEI film reduces the irreversible capacity loss in the first cycle, improves the coulombic efficiency, and the design of the carbon coating and composite structure provides a stable transmission channel and storage space for lithium ions. In comparison, in the preparation process of Comparative Example 1, some links over-reacted, destroying the material structure, and the reaction degree of Comparative Example 2 was insufficient, resulting in poor material performance and low lithium ion storage and utilization efficiency.

[0056] Table 3 Cycle life test Example Capacity retention after 50 cycles (%) 1 78 2 82 3 85 4 88 Comparative Example 1 68 Comparative Example 2 62 As can be seen from Table 3, Example 4 is the best, while Comparative Examples 1 and 2 are relatively poor. The cycle life test measures the stability of a material after multiple charge and discharge cycles. The capacity retention rate of the embodiment after 50 cycles is significantly higher than that of the comparative example. The stable artificial SEI film in the embodiment can effectively prevent further reaction between the electrode material and the electrolyte. The various components in the composite structure cooperate with each other to buffer the volume changes during the charge and discharge process, reduce structural damage, and thus maintain a higher capacity. The SEI film quality of Comparative Examples 1 and 2 is unstable, the buffering effect of the composite structure is poor, and the electrode structure is gradually destroyed during the cycle, resulting in rapid capacity decay and a low capacity retention rate.

[0057] This specific embodiment is merely an explanation of the present invention and does not limit the present invention. After reading this specification, those skilled in the art can make non-creative modifications to this embodiment as needed, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance, characterized in that: include: Step (1) pretreatment of artificial graphite, step (2) preparation of hollow ferroferric oxide nanospheres (H-Fe3O4), step (3) preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC), step (4) preparation of carbon-coated artificial graphite (AG@C), step (5) preparation of porous graphite composite material (PG@C) for fast charging, step (6) preparation of artificial SEI high conductive graphite negative electrode material (PG@C@SEI), step (7) construction of composite negative electrode material (rGO@PG@C@SEI@H-Fe3O4@NC); Among them, step (7) the construction of the composite negative electrode material (rGO@PG@C@SEI@H-Fe3O4@NC) includes: The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), are added, and ultrasonic dispersion is performed to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

2. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 1, characterized in that: Step (1) Artificial graphite pretreatment Select high-quality artificial graphite powder, place it in a high-temperature furnace, and perform high-temperature graphitization treatment under argon (Ar) protection to improve the degree of graphitization and enhance conductivity; After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. After ultrasonic dispersion, the precursors are uniformly adsorbed on the surface of the artificial graphite. The powder is then filtered and dried, and the dried powder is sintered in a tube furnace to achieve uniform distribution of the doping atoms in the graphite structure. Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in an organic solvent, ethylene glycol, stirred evenly, and then transferred to a reactor. After the reaction, H-Fe3O4 nanospheres were obtained by cooling, centrifugation, washing, and drying. Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) are used as templates, and dopamine, a nitrogen-containing carbon source, is added. The pH value is adjusted with ammonia water under alkaline conditions, and dopamine undergoes self-polymerization to form a polymer coating layer on the surface of the nanospheres. Subsequently, the nanospheres are centrifuged, washed, and dried, and placed in a tube furnace for high-temperature carbonization under nitrogen to obtain H-Fe3O4@NC. Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with sucrose as a carbon source, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tube furnace and treated at high temperature under argon protection to form a uniform and tight carbon coating layer to obtain AG@C; Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, stirred to react, and the graphite is etched to form a porous structure; after the reaction is completed, a porous graphite composite material PG@C with fast charging performance is obtained through filtering, washing, drying and other steps; the porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance; Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive of fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained; Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methylpyrrolidone (NMP), are added, and ultrasonic dispersion is performed to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

3. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 2, characterized in that: Step (1) Artificial graphite pretreatment Select high-quality artificial graphite powder, place it in a high-temperature furnace, and heat it to 2800-3000℃ at a heating rate of 1-5℃ / min under argon (Ar) protection for high-temperature graphitization treatment to increase the degree of graphitization and enhance conductivity; After cooling, the artificial graphite powder is dispersed in a specific solution containing doping element precursors: nitrogen source, cyanamide, phosphorus source, and ammonium dihydrogen phosphate. Ultrasonic dispersion is carried out for 30-60 minutes to allow the precursors to be evenly adsorbed on the surface of the artificial graphite. It is then filtered and dried, and the dried powder is sintered in a tube furnace at 800-1000°C for 2-4 hours to achieve uniform distribution of the doping atoms in the graphite structure.

4. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 3, characterized in that: Step (2) Preparation of hollow ferroferric oxide nanospheres (H-Fe3O4) Using a solvothermal method, ferric chloride hexahydrate (FeCl3·6H2O) and an organic ligand, sodium citrate, were dissolved in an organic solvent, ethylene glycol. After stirring evenly, the mixture was transferred to a reactor and reacted at 150-200°C for 10-15 hours. After the reaction, the mixture was cooled, centrifuged, washed, and dried to obtain H-Fe3O4 nanospheres.

5. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 4, characterized in that: Step (3) Preparation of disordered nitrogen-doped carbon-coated hollow ferroferric oxide nanospheres (H-Fe3O4@NC) The H-Fe3O4 (hollow ferroferric oxide nanospheres) prepared in step (2) are used as a template, and dopamine, a nitrogen-containing carbon source, is added. The pH value is adjusted with ammonia water under alkaline conditions, and dopamine undergoes self-polymerization to form a polymer coating layer on the surface of the nanospheres. Subsequently, the nanospheres are centrifuged, washed, and dried, and placed in a tubular furnace for high-temperature carbonization at 750-800°C under nitrogen to obtain H-Fe3O4@NC.

6. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 5, characterized in that: Step (4) Preparation of carbon-coated artificial graphite (AG@C) The artificial graphite doped in step (1) is mixed with sucrose as a carbon source, and deionized water is added and stirred to form a uniform slurry; the slurry is transferred to a reactor and subjected to a hydrothermal reaction at 180-200°C for 8-12 hours to polymerize the carbon source on the surface of the artificial graphite; after the reaction is completed, the slurry is cooled, centrifuged, and washed, and then placed in a tubular furnace and treated at a high temperature of 1000-1200°C for 2-3 hours under argon protection to form a uniform and compact carbon coating layer to obtain AG@C.

7. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 6, characterized in that: Step (5) Preparation of porous graphite composite material (PG@C) for fast charging The AG@C prepared in step (4) is dispersed in a specific etchant solution, KOH (potassium hydroxide) solution, and stirred at 80-100°C for 3-6 hours to etch the graphite structure to form a porous structure. After the reaction is completed, the porous graphite composite material PG@C with fast charging performance is obtained through filtering, washing, drying and other steps. The porous structure can effectively shorten the lithium ion diffusion path and improve the fast charging performance.

8. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 7, characterized in that: Step (6) Preparation of artificial SEI highly conductive graphite anode material (PG@C@SEI) An electrolyte containing LiPF6 (lithium hexafluorophosphate), an organic solvent (a mixed solvent of ethylene carbonate and diethyl carbonate) and an additive fluoroethylene carbonate is prepared in a glove box; the PG@C prepared in step (5) is immersed in the electrolyte and allowed to stand at room temperature for 12-24 hours to form an artificial SEI film on the surface of the PG@C; after drying, an artificial SEI (solid electrolyte interface film) highly conductive graphite negative electrode material PG@C@SEI is obtained.

9. The process for preparing a negative electrode material for a lithium-ion composite battery with low impedance and high rate performance according to claim 8, characterized in that: Step (7) Construction of composite anode material (rGO@PG@C@SEI@H-Fe3O4@NC) The PG@C@SEI prepared in step (6) is mixed with rGO (reduced graphene oxide) and the H-Fe3O4@NC prepared in step (3), and a dispersant, polyvinyl pyrrolidone (PVP), and a solvent, N-methyl pyrrolidone (NMP), are added, and ultrasonic dispersion is performed for 60-90 minutes to uniformly disperse the components. The solvent is then removed from the mixture by freeze drying to obtain a composite powder. The composite powder is heat-treated at 600-800°C for 2-4 hours in a tube furnace in a mixed atmosphere of hydrogen and argon to form an rGO@PG@C@SEI@H-Fe3O4@NC composite negative electrode material.

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