Preparation method of regenerated graphite negative electrode for fast-charging lithium ion battery

Abstract

The invention relates to the technical field of battery recycling and regeneration, and discloses a preparation method of a regenerated graphite negative electrode for a fast-charging lithium ion battery, and the method comprises the following steps: carrying out mechanical shearing and kneading on pretreated waste graphite powder, ammonium dihydrogen phosphate, a carbon source and water to prepare a wet powder mixture; heating the wet powder mixture in a closed environment, and establishing self-generated pressure by utilizing gas released by thermal decomposition to carry out prepolymerization reaction; then feeding into a reactor, and carrying out gas-phase confinement pyrolysis by controlling the material filling state and atmosphere, so that ammonia gas is retained in material gaps for in-situ reaction; and finally, performing high-temperature sintering in an inert atmosphere to remove impurities, and performing cooling, crushing and sieving treatment. According to the invention, deep infiltration of the active component is realized through self-pressure prepolymerization, nitrogen and phosphorus in-situ doped layer expansion and surface etching pore-forming are realized in combination with a gas-phase confinement pyrolysis process, a lithium ion diffusion energy barrier is reduced, and the rate capability, the fast charge capability and the cycle stability of the regenerated graphite negative electrode material are improved.

Description

Technical Field

[0001] This invention relates to the field of battery recycling technology, specifically a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in modern industrial society as the main energy storage device for new energy vehicles and portable electronic devices. Graphite has become the mainstream anode material for lithium-ion batteries due to its high conductivity and structural stability. With the large-scale retirement of power batteries, the recycling and reuse of waste graphite anode materials has become a key link in resource recycling and environmental protection. At the same time, the application terminals of new energy vehicles have put forward increasingly stringent requirements for the fast charging performance of batteries, which sets higher standards for the microstructure and electrochemical performance of recycled anode materials.

[0003] Existing waste graphite anode recycling technologies mainly employ a process route combining hydrometallurgical purification and high-temperature thermal repair. Hydrometallurgical purification uses acid and alkali solutions to remove metallic impurities and binder residues from the surface of waste graphite. High-temperature thermal repair places the purified graphite in a graphitization furnace for high-temperature treatment at temperatures above 2500 degrees Celsius to restore the graphite crystal structure and eliminate structural defects accumulated during charge-discharge cycles. In addition, some processes utilize asphalt or resin to coat and modify the surface of recycled graphite to improve the first-cycle coulombic efficiency and cycle stability of the recycled graphite material.

[0004] However, due to the pursuit of high graphitization in traditional high-temperature repair processes, the interlayer spacing of recycled graphite lattices tends to shrink or stabilize near the ideal theoretical value of graphite. The narrow interlayer spacing increases the diffusion barrier during lithium-ion insertion, limiting the kinetic performance of recycled graphite materials. At the same time, simple surface coating modification fails to effectively regulate the lattice structure and pore distribution inside graphite particles, making it difficult to construct channels conducive to rapid ion transport. As a result, recycled graphite anode materials prepared by existing technologies exhibit large polarization under high-current charging conditions, making it easy for lithium plating to occur on the anode surface, which cannot meet the rate performance and safety indicators required for fast-charging lithium-ion batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries. This method aims to solve the problems of existing regenerated graphite materials, which suffer from narrow interlayer spacing and a lack of ion transport channels, resulting in high ion diffusion resistance and inadequate fast-charging performance and cycle stability to meet application requirements.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, comprising the following steps:

[0008] S1. Mixing and Activation: Pretreated waste graphite powder, ammonium dihydrogen phosphate, carbon source and water are put into a mixing device and mechanically sheared and kneaded to obtain a wet powder mixture.

[0009] S2, self-pressure prepolymerization: The wet powder mixture is heated in a closed environment, and the gas released by the thermal decomposition of the material is used to establish self-pressure. The prepolymer is obtained by carrying out a heat preservation reaction under the pressure maintenance state.

[0010] S3, gas-phase confined pyrolysis: The prepolymer is fed into a reactor for pyrolysis. By controlling the material filling state and atmosphere in the reactor, the ammonia gas released by the decomposition of ammonium dihydrogen phosphate is retained in the material voids for in-situ reaction to obtain the pyrolysis intermediate.

[0011] S4. High-temperature sintering: The pyrolysis intermediate is placed in an environment with an inert gas flow and calcined at a high temperature. The high temperature and airflow carry away impurities, and after cooling, a sintered material is obtained.

[0012] S5. Post-processing: The sintered material is crushed and sieved to obtain a recycled graphite anode.

[0013] By adopting the above technical solution, this invention utilizes a multi-stage cascade reaction to repair the structure and improve the performance of waste graphite. In the self-pressure prepolymerization stage of step S2, the evaporation of moisture in the material and the decomposition of ammonium dihydrogen phosphate in the closed system generate gas, forming self-generated pressure. This pressure drives the phosphorus- and nitrogen-containing active components to penetrate into the microcracks and pores deep within the surface of the waste graphite, achieving uniform wetting. Simultaneously, the carbon source undergoes a condensation reaction with ammonium dihydrogen phosphate, forming a polymer precursor coating layer on the surface of the graphite particles.

[0014] Subsequently, in the gas-phase confined pyrolysis stage of step S3, the microstructure of graphite is deeply controlled by adjusting the atmosphere and filling state. The mechanism of action includes the following two aspects:

[0015] In-situ gas-phase doping of phosphorus and nitrogen elements and interlayer spacing control:

[0016] As temperature increases, the polymer precursor and ammonium dihydrogen phosphate undergo deep decomposition, releasing high-concentration ammonia (NH3) and phosphorus-containing intermediates (such as ammonium polyphosphate or phosphorus oxides). Due to the plugging effect within the reactor and the absence of an external carrier gas environment, the NH3 gas produced during decomposition is confined within the voids between material particles, forming a high-concentration ammonia microenvironment. The high-temperature active NH3 molecules and phosphorus-containing intermediates work synergistically, chemically modifying the edges of the graphite lattice on one hand, and diffusing nitrogen and phosphorus atoms in gaseous or liquid phases and embedding them into defect sites in the graphite lattice, replacing some carbon atoms to form CN and POC chemical bonds. Due to the difference in radius between phosphorus atoms (0.106 nm) and nitrogen atoms (0.075 nm) and carbon atoms (0.077 nm), heteroatom doping induces distortion in the graphite lattice, thereby increasing the graphite interlayer spacing d002. The increased interlayer spacing lowers the diffusion barrier for lithium-ion insertion and extraction, improving the rate performance of the material.

[0017] In-situ etching for creating boreholes with ammonia:

[0018] High-concentration ammonia gas in a confined state chemically etches the amorphous carbon coating formed by the carbonization of polymer precursors and the surface of graphite particles at pyrolysis temperatures. This in-situ etching process constructs abundant micropores and mesopores on the graphite surface and within the coating layer, forming a network of interconnected ion transport channels. These pores increase the electrolyte wetting area, shorten the lithium-ion transport path, and provide buffer space for volume changes in graphite during charge-discharge cycles, thereby reducing the electrode thickness expansion rate and improving battery cycle life.

[0019] In summary, this invention achieves deep wetting and pre-coating of raw materials through self-pressure prepolymerization, and combines it with gas-phase confined pyrolysis to achieve the synergistic effect of heteroatom doping and layer expansion and ammonia etching for pore formation, thus preparing a recycled graphite anode material with large interlayer spacing, porous structure and stable interface, effectively solving the problem of limited performance improvement in traditional recycling methods.

[0020] Preferably, in step S1, the wet powder mixture is made from raw materials comprising the following parts by weight:

[0021] 100.0 parts of pretreated waste graphite powder;

[0022] Ammonium dihydrogen phosphate, 4.0–10.0 parts;

[0023] Carbon source 3.0–6.0 parts;

[0024] Water 15.0–30.0 parts.

[0025] By adopting the above technical solution, the raw material ratio is limited to ensure that the proportions of phosphorus, nitrogen and carbon elements in the reaction system are appropriate, thereby controlling the viscosity and product morphology during the reaction process while ensuring effective modification.

[0026] Preferably, prior to step S1, the preparation method of the pretreated waste graphite powder includes: separating waste lithium-ion battery negative electrode sheets, removing the current collector by solvent cleaning to obtain coarse graphite powder; soaking the coarse graphite powder in a 15%–20% (w / w) dilute sulfuric acid solution with a solid-liquid ratio of 1:4–1:5 and a treatment temperature of 25°C–40°C, using the acid solution to dissolve and remove SEI film components and metal oxides; subsequently washing with water until neutral, drying, air-jet milling, and classification to obtain the pretreated waste graphite powder for step S1. By adopting the above technical solution, the waste graphite raw material is subjected to standardized pretreatment to remove SEI film, binder residue, and metal impurities, providing a high-purity substrate for subsequent structural repair and ensuring the consistency of the final product.

[0027] This invention provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries. It has the following beneficial effects:

[0028] 1. This invention utilizes the self-pressure prepolymerization step to drive nitrogen- and phosphorus-containing active components to penetrate deep into the microcracks and pores of waste graphite particles using the self-generated pressure generated within a closed system. This in-situ pressure wetting method achieves deep repair of structural defects in waste graphite and forms a uniform polymer precursor coating layer on the particle surface, improving the structural integrity and interfacial stability of the recycled graphite.

[0029] 2. This invention employs a gas-phase confined pyrolysis process, utilizing the plugging effect to trap ammonia gas and phosphorus-containing intermediates generated during the reaction within the material voids, creating a high-concentration reaction microenvironment. This environment promotes the efficient doping of nitrogen and phosphorus atoms into the graphite lattice, inducing lattice distortion and widening the graphite interlayer spacing. The widened interlayer spacing reduces the diffusion barrier for lithium-ion insertion and extraction, thereby improving the rate performance and fast-charging capability of the regenerated graphite anode material.

[0030] 3. This invention utilizes the chemical etching effect of high-temperature ammonia gas on the carbon layer during pyrolysis to construct abundant micropores and mesopores on the graphite surface and inside the coating layer. These pore structures not only increase the wetting sites of the electrolyte and construct interconnected ion transport channels, but also serve as buffer spaces to effectively accommodate the volume changes of graphite during charging and discharging, thereby reducing the thickness expansion rate of the electrode and extending the cycle life of the battery. Attached Figure Description

[0031] Figure 1 This is a SEM image from Comparative Example 1 of the present invention;

[0032] Figure 2 This is the SEM image from Embodiment 1 of the present invention;

[0033] Figure 3 The diagram shows the full-rate test results of Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Preparation Examples 1-3:

[0036] Preparation Example 1:

[0037] This preparation example provides a pretreated waste graphite powder A, and the preparation steps are as follows:

[0038] The retired ternary lithium-ion batteries were mechanically disassembled under an inert atmosphere to separate the negative electrode sheets. The negative electrode sheets were then placed in an ultrasonic cleaning tank containing N-methylpyrrolidone and ultrasonically treated at 40 kHz for 30 minutes to dissociate the graphite layer from the copper foil. Coarse graphite powder was collected by filtration. This coarse graphite powder was then added to a reaction vessel lined with polytetrafluoroethylene (PTFE), and a 15% (w / w) dilute sulfuric acid solution was added, maintaining a solid-liquid ratio of 1:5. The reaction was carried out at 25°C at 300 rpm. The sample was stirred and soaked for 4 hours at a constant speed, and the SEI membrane components and some metal oxides were removed by dissolving in acid. Then, it was vacuum filtered and repeatedly washed with deionized water until the pH of the filtrate was 6.5 to 7.0. The filter cake was placed in a vacuum oven at 105℃ and dried for 12 hours. It was then broken up by an air jet mill and passed through a 300-mesh sieve to obtain pretreated waste graphite powder A with a particle size D50 of 17.8μm, a carbon content of 97.2%, and a total residual metal impurities of 2800ppm.

[0039] Preparation Example 2:

[0040] This preparation example provides a pretreated waste graphite powder B, and the preparation steps are as follows:

[0041] Retired ternary lithium-ion batteries were mechanically disassembled under an inert atmosphere to separate the negative electrode sheets. The negative electrode sheets were then placed in an ultrasonic cleaning tank containing N-methylpyrrolidone for 30 minutes. Copper foil was filtered to separate the negative electrode sheets, yielding coarse graphite powder. The coarse graphite powder was then added to a reaction vessel, along with a 20% (w / w) dilute sulfuric acid solution. The solid-liquid ratio was controlled at 1:4. The mixture was stirred and soaked at 400 rpm for 3 hours at 40°C. Subsequently, the mixture was filtered and washed with deionized water until neutral. The filter cake was vacuum dried at 110°C for 10 hours, then micronized using a high-pressure airflow pulverizer and passed through a 400-mesh sieve to obtain pretreated waste graphite powder B with a particle size D50 of 10.5 μm, a carbon content of 97.5%, and a total residual metal impurity content of 2100 ppm.

[0042] Preparation Example 3:

[0043] This preparation example provides a phosphorus-carbon source composite modified additive solution, and the preparation steps are as follows:

[0044] Add 60.0 parts of deionized water to a stirred tank equipped with a heating jacket and a temperature sensor. Turn on the jacket heating to raise the water temperature to 60℃ and keep it constant. Turn on the stirrer and set the speed to 200 rpm. Slowly add 18.0 parts of ammonium dihydrogen phosphate and 12.0 parts of anhydrous glucose in sequence, controlling the feeding speed during the feeding process to prevent the powder from agglomerating. After the feeding is completed, continue to keep warm and stir for 45 minutes until the solid in the system is completely dissolved and a homogeneous and transparent solution is formed. Filter the solution while hot through a 200-mesh stainless steel precision filter to remove insoluble particles. After cooling to room temperature of 25℃, seal and store to obtain a phosphorus-carbon source composite modified additive solution with a solid content of 33.3%.

[0045] Examples 1-5:

[0046] Example 1:

[0047] This embodiment provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, including the following steps:

[0048] S1. Weigh 100.0 parts by weight of the pretreated waste graphite powder A obtained in Example 1, 6.0 parts by weight of ammonium dihydrogen phosphate, 4.0 parts by weight of anhydrous glucose, and 20.0 parts by weight of deionized water; put the pretreated waste graphite powder A, ammonium dihydrogen phosphate, anhydrous glucose, and deionized water into a high-shear kneader with a heating jacket; set the jacket temperature to 70°C and the stirring paddle speed to 45 rpm, perform mechanical activation and mixing, knead for 60 minutes, and obtain a uniformly dispersed wet powder paste;

[0049] S2. The wet powder paste obtained in S1 is transferred to a closed reaction vessel, sealed, and heated to 150°C at a rate of 3°C / min. During the reaction, the system is kept closed, and the self-generated pressure is established by the evaporation of water and the gas generated by partial decomposition in the material. The pressure inside the vessel is controlled to be maintained between 0.35MPa and 0.45MPa. The reaction is carried out at a constant temperature and pressure for 3.0 hours to obtain the prepolymer precursor block.

[0050] S3. The prepolymer precursor hard blocks obtained in S2 are coarsely crushed to a particle size of less than 5 mm and continuously fed into a jacketed heated screw conveyor reactor with an aspect ratio of 18. The feed rate is controlled to keep the material filling rate in the screw channel at about 85% and the atmosphere is isolated by the plug effect. The temperature of the screw feed section is set at 200℃, the temperature of the discharge section is set at 450℃, and the average residence time of the material is 60 minutes. During this process, no external carrier gas is introduced. The reactor is kept under a slight positive pressure by using an exhaust valve to keep the high concentration of ammonia gas released by the decomposition of ammonium dihydrogen phosphate in the material voids for in-situ reaction, thus obtaining the pyrolysis intermediate.

[0051] S4. The pyrolysis intermediate obtained in S3 is airtightly conveyed to a high-temperature rotary kiln via a star-shaped discharge valve. High-purity nitrogen is introduced in reverse at a flow rate of 5.0 cubic meters per hour per ton of material. The material is rapidly heated to 1100°C in the rotary kiln and calcined at a constant temperature for 3.0 hours. The high temperature and high flow rate of nitrogen remove impurities and volatiles. The material is then cooled to below 60°C by a water-cooled spiral and discharged to obtain the sintered material.

[0052] S5. The sintered material obtained in S4 is dispersed and deagglomerated by an air jet mill, passed through a 325-mesh sieve, and the sieve-underfill material is collected to obtain the finished recycled graphite anode material.

[0053] Example 2:

[0054] This embodiment provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, employing lower doping levels and energy consumption parameters, including the following steps:

[0055] S1. Weigh 100.0 parts by weight of the pretreated waste graphite powder A obtained in Example 1, 4.0 parts by weight of ammonium dihydrogen phosphate, 3.0 parts by weight of anhydrous glucose, and 15.0 parts by weight of deionized water; put all the raw materials into a kneader together; set the temperature to 60°C, the rotation speed to 30 rpm, and knead for 40 minutes to obtain a wet powder mixture;

[0056] S2. The wet powder mixture obtained in S1 is placed into a pressure-resistant curing container, sealed, and heated to 140°C. The system is maintained at 0.20MPa to 0.25MPa using self-generated pressure, and the reaction is carried out for 2.0 hours to obtain the prepolymer.

[0057] S3. The prepolymer obtained in S2 is crushed and fed into a spiral reactor. The filling rate is controlled at 80%, the feed section temperature is set at 180℃, the discharge section temperature is set at 400℃, and the residence time is 40 minutes. No carrier gas is introduced to maintain the ammonia retention environment and a pyrolysis intermediate is obtained.

[0058] S4. The pyrolysis intermediate obtained in S3 is fed into a rotary kiln, and high-purity nitrogen gas is introduced at a flow rate of 3.0 cubic meters per hour; the calcination temperature is set to 900℃, the constant temperature time is 2.0 hours, and then the material is cooled and discharged to obtain sintered material.

[0059] S5. The sintered material obtained in S4 is broken up and sieved to obtain the finished recycled graphite anode material.

[0060] Example 3:

[0061] This embodiment provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, employing high doping levels and process parameters, including the following steps:

[0062] S1. Weigh 100.0 parts by weight of the pretreated waste graphite powder B obtained in Example 2, 10.0 parts by weight of ammonium dihydrogen phosphate, 6.0 parts by weight of anhydrous glucose, and 25.0 parts by weight of deionized water; put each raw material into a kneader; set the temperature to 80°C, the rotation speed to 60 rpm, and knead for 90 minutes to obtain a wet powder mixture;

[0063] S2. The wet powder mixture obtained in S1 is loaded into a high-pressure reactor, sealed and heated to 165°C; the pressure inside the reactor is controlled between 0.55MPa and 0.60MPa, and the reaction is maintained at this temperature for 4.0 hours to obtain the prepolymer;

[0064] S3. The prepolymer obtained in S2 is fed into a spiral reactor, the filling rate is controlled at 95%, the feed section temperature is set at 220℃, the discharge section temperature is set at 480℃, and the residence time is 80 minutes; no carrier gas is introduced to maintain a high-concentration ammonia microenvironment, and a pyrolysis intermediate is obtained.

[0065] S4. The pyrolysis intermediate obtained in S3 is fed into a rotary kiln, and high-purity nitrogen gas is introduced at a flow rate of 8.0 cubic meters per hour per ton of material. The calcination temperature is set at 1150℃, the constant temperature time is 4.0 hours, and the material is cooled and discharged to obtain sintered material.

[0066] S5. The sintered material obtained in S4 is broken up and sieved to obtain the finished recycled graphite anode material.

[0067] Example 4:

[0068] This embodiment provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, replacing the carbon source with industrial starch, and includes the following steps:

[0069] S1. Weigh 100.0 parts by weight of the pretreated waste graphite powder A obtained in Example 1, 7.0 parts by weight of ammonium dihydrogen phosphate, 5.0 parts by weight of industrial corn starch, and 30.0 parts by weight of deionized water; put each raw material into a kneader; set the temperature to 85°C, use high temperature to promote starch pregelatinization, knead for 60 minutes, and obtain a paste-like mixture.

[0070] S2. Transfer the paste mixture obtained in S1 to a sealed container, seal and heat to 155°C; maintain the autogenous pressure at 0.30MPa to 0.40MPa, react for 3.0 hours to obtain the prepolymer;

[0071] S3. The prepolymer obtained in S2 is fed into a spiral reactor. The feed section temperature is set to 200℃, the discharge section temperature is set to 460℃, and the residence time is 60 minutes. By maintaining a high filling rate and ammonia retention, a pyrolysis intermediate is obtained.

[0072] S4. The pyrolysis intermediate obtained in S3 is fed into a rotary kiln, the calcination temperature is set to 1100℃, the temperature is kept constant for 3.0 hours, and nitrogen is passed through to remove impurities, thus obtaining the sintered material.

[0073] S5. The sintered material obtained in S4 is broken up and sieved to obtain the finished recycled graphite anode material.

[0074] Example 5:

[0075] This embodiment provides a method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, which uses a pre-prepared liquid modifier for wet feeding, and includes the following steps:

[0076] S1. Weigh 100.0 parts by weight of the pretreated waste graphite powder A obtained in Preparation Example 1 and 30.0 parts by weight of the phosphorus-carbon source composite modification additive obtained in Preparation Example 3; put the pretreated waste graphite powder A into a kneader, and slowly spray the phosphorus-carbon source composite modification additive while stirring; set the jacket temperature to 75°C, knead for 50 minutes to make the mixture reach a uniform wetting state, and obtain a wetted mixture;

[0077] S2. The wetting mixture obtained in S1 is sealed in a reactor and heated to 150°C; the autogenous pressure is maintained at 0.3 MPa to 0.4 MPa, and the reaction is carried out for 2.5 hours to obtain the prepolymer.

[0078] S3. The prepolymer obtained in S2 is fed into a spiral reactor with the same process parameters as in Example 1, and a pyrolysis intermediate is obtained.

[0079] S4. The pyrolysis intermediate obtained in S3 is fed into a rotary kiln, and the process parameters are the same as in Example 1, to obtain the sintered material.

[0080] S5. The sintered material obtained in S4 is broken up and sieved to obtain the finished recycled graphite anode material.

[0081] Comparative Examples 1-5:

[0082] Comparative Example 1:

[0083] Compared with Example 1, the difference is that ammonium dihydrogen phosphate was not added in step S1, and only 4.0 parts by weight of anhydrous glucose and 20.0 parts by weight of deionized water were added, while the rest were the same.

[0084] Comparative Example 2:

[0085] Compared with Example 1, the difference is that the self-generated pressure is established in the closed reactor in step S2 and by using the gas generated by the evaporation and partial decomposition of moisture in the material, and the pressure inside the reactor is controlled to be maintained between 0.35MPa and 0.45MPa. Instead, the drying is carried out in an open tray and under normal pressure by forced air. All other aspects are the same.

[0086] Comparative Example 3:

[0087] Compared with Example 1, the difference is that in step S3, the carrier gas system is turned on and high-purity nitrogen with a flow rate of 10.0 cubic meters per hour per ton of material is continuously purged to quickly remove the volatile gases produced by the reaction and destroy the ammonia stagnation atmosphere. All other steps are the same.

[0088] Comparative Example 4:

[0089] Compared with Example 1, the difference is that steps S2 and S3 are omitted. The wet powder paste obtained in step S1 is dried and then directly subjected to step S4 for high-temperature dynamic calcination. All other steps are the same.

[0090] Comparative Example 5:

[0091] Compared with Example 1, the difference is that in step S1, 6.0 parts by weight of ammonium dihydrogen phosphate is replaced with a phosphoric acid solution with an equimolar phosphorus content, and the rest are the same.

[0092] Test Examples 1-6:

[0093] Test Example 1: Crystal Structure and Interlayer Spacing Test

[0094] Experimental steps:

[0095] Two gram samples of regenerated graphite anode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were selected and ground in an agate mortar for 3 minutes. The powder was then passed through a 300-mesh standard sieve to eliminate the preferred orientation of the powder.

[0096] The processed powder was filled into the groove of the glass sample holder, and compacted and leveled using a glass slide to ensure that the sample test surface coincided with the focusing plane of the instrument. X-ray diffractometer was used for testing, with Cu-Kα rays as the radiation source at a wavelength of 0.15406 nm, tube voltage set to 40 kV, and tube current set to 40 mA. The scanning mode was set to continuous scanning, with a diffraction angle scanning range of 10° to 90° and a step size of 0.02°. For the characteristic region of the graphite 002 crystal plane, i.e., the range of 23° to 28°, a slow scanning speed of 1° / min was set.

[0097] Diffraction pattern data were collected, background noise was removed, and the data were smoothed. The peak center diffraction angle data of the 002 crystal plane was extracted, and the interlayer spacing was calculated according to the Bragg equation. The grain size was calculated by selecting the full width at half maximum (FWHM) data according to the Scherrer formula, where the shape factor was 0.89.

[0098] Experimental data:

[0099] Table 1. Test data of crystal structure parameters of the examples and comparative samples.

[0100] Sample number 002 crystal plane diffraction angle 2θ / ° Interlayer spacing d002 / nm Half-height width FWHM / ° Grain size Lc / nm Example 1 26.184 0.3402 0.245 33.1 Example 2 26.295 0.3388 0.229 35.3 Example 3 26.122 0.3410 0.268 30.2 Example 4 26.215 0.3398 0.248 32.5 Example 5 26.198 0.3400 0.241 33.6 Comparative Example 1 26.540 0.3356 0.198 40.8 Comparative Example 2 26.465 0.3365 0.215 37.6 Comparative Example 3 26.442 0.3368 0.222 36.4 Comparative Example 4 26.495 0.3361 0.231 35.1 Comparative Example 5 26.355 0.3379 0.212 38.2

[0101] Conclusion Analysis:

[0102] Table 1 shows that the interlayer spacing d002 of graphite in Examples 1 to 5 ranges from 0.3388 nm to 0.3410 nm, all higher than that of Comparative Example 1 (0.3356 nm). Comparative Example 1 used only glucose as a single carbon source without introducing a phosphorus source, and its interlayer spacing was close to the theoretical value of natural graphite, indicating that simple surface carbon coating did not change the lattice spacing of the graphite bulk. In Example 1, ammonium dihydrogen phosphate was reacted under a closed high-pressure environment. The radius of a phosphorus atom (0.106 nm) is larger than that of a carbon atom (0.077 nm), and the entry of heteroatoms into the graphite lattice at high temperature led to the physical expansion of the interplanar spacing.

[0103] The d002 of Comparative Example 2 was 0.3365 nm, smaller than that of Example 1. Under normal pressure, the decomposition products of ammonium dihydrogen phosphate volatilized with water vapor, reducing the effective phosphorus concentration in the reaction system. Furthermore, the lack of pressure drive made it difficult for heteroatoms to penetrate deep into the graphite. The d002 of Comparative Example 3 was 0.3368 nm, indicating that removing the ammonia-retaining environment weakened the synergistic doping effect of nitrogen, affecting the solid solution effect of phosphorus in the carbon lattice.

[0104] A comparison of data from Example 1 and Comparative Example 5 (d002 = 0.3379 nm) shows that although the single phosphoric acid system can also expand the interlayer spacing, its effect is weaker than that of the ammonium dihydrogen phosphate system. Meanwhile, the grain size Lc (33.1 nm) of Example 1 is smaller than that of Comparative Example 5 (38.2 nm), confirming that the ammonia release process has an in-situ etching effect on the graphite crystallites, reducing the grain size. The high doping level in Example 3 corresponds to the largest interlayer spacing (0.3410 nm) and the smallest grain size, indicating a positive correlation between heteroatom concentration and lattice parameter changes. This test confirms that the process of the present invention achieves the expansion of graphite interlayer spacing through heteroatom doping and lattice control.

[0105] Test Example 2: Half-cell rate and cycle performance test of lithium-ion batteries

[0106] Experimental steps:

[0107] The negative electrode materials prepared in each embodiment and comparative example were mixed with conductive carbon black SuperP and binder PVDF at a mass ratio of 92:4:4. NMP solvent was added, and the mixture was dispersed in a vacuum mixer for 4 hours to form a slurry. The slurry was coated on a copper foil current collector, and the surface density on one side was controlled to be 8.5 mg / cm². The negative electrode sheet with a diameter of 14 mm was obtained by vacuum drying at 110°C, rolling, and stamping.

[0108] CR2032 coin cells were assembled in an argon-filled glove box with water and oxygen content controlled below 0.1 ppm. The counter electrode was a lithium metal sheet, the separator was Celgard 2400, and the electrolyte was 1.0 M LiPF6 dissolved in a mixed solvent of EC / DEC / EMC (volume ratio 1:1:1) with 2.0 wt% VC added. Electrochemical performance was tested using a battery testing system with a voltage range of 0.01 V to 1.5 V. Initial activation was performed at a low rate of 0.05 C. Subsequently, constant current charging and discharging tests were conducted at rates of 0.2 C, 0.5 C, 1.0 C, 2.0 C, and 5.0 C, and constant current discharging at 0.1 C were performed, recording the specific capacity at each rate. Finally, a 500-cycle test was conducted at a rate of 2.0 C, and the capacity retention was calculated.

[0109] Experimental data:

[0110] Table 2. Electrochemical performance test data of half-cells for each group of samples.

[0111] Group 0.05C First Reversible Specific Capacity (mAh / g) First Coulomb Efficiency (ICE) (%) 5.0C rate charging specific capacity (mAh / g) 5.0C rate capacity retention (%) 2.0C cycle capacity retention (%) after 500 cycles Example 1 358.4 92.4 315.7 88.08 94.2 Example 2 352.1 91.8 302.4 85.88 92.8 Example 3 355.6 90.5 318.2 89.48 93.5 Example 4 356.2 92.1 310.5 87.17 93.9 Example 5 357.8 92.3 314.9 88.01 94.0 Comparative Example 1 350.5 90.2 78.4 22.36 65.4 Comparative Example 2 345.8 88.6 215.6 62.34 81.2 Comparative Example 3 348.2 89.4 240.3 69.01 84.5 Comparative Example 4 338.5 86.5 185.2 54.71 75.8 Comparative Example 5 353.4 91.1 275.6 77.98 89.6

[0112] Conclusion Analysis:

[0113] Example 1 exhibited a charging specific capacity of 315.7 mAh / g at a 5.0C rate, with a capacity retention of 88.08%, compared to 22.36% for Comparative Example 1 under the same conditions. Comparative Example 1, lacking heteroatom doping and having a smaller interlayer spacing, experienced higher lithium-ion insertion resistance at high charging rates, leading to polarization, lithium plating, and capacity decay. The high-rate performance of Example 1 is consistent with the interlayer spacing expansion observed in Test Example 1, where the larger d002 lowers the diffusion barrier of lithium ions between graphite layers.

[0114] The capacity retention rates at 5.0C for Comparative Example 2 (treated under atmospheric pressure) and Comparative Example 3 (without gas phase retention) were 62.34% and 69.01%, respectively, both lower than that of Example 1. This indicates that without ensuring effective penetration of the modifier or the synergistic effect of a nitrogen-containing atmosphere, continuous fast-charging channels cannot be constructed within the material. Comparative Example 4, using a one-step sintering method, achieved a 5.0C retention rate of 54.71%, demonstrating that simple physical mixing and sintering cannot achieve uniform coating and reaction of the modifier at the graphite interface.

[0115] Regarding cycle stability, Example 1 maintained a capacity retention of 94.2% after 500 cycles at 2.0C. Comparative Examples 4 and 5 showed retention rates of 75.8% and 89.6%, respectively. Example 1 utilized the POC and CN bonds formed by the reaction of phosphorus and nitrogen elements generated from the decomposition of ammonium dihydrogen phosphate with a carbon source, enhancing the rigidity of the material structure and suppressing volume expansion during charge and discharge. Although Comparative Example 5 contained phosphorus doping, it lacked a stable interface formed by nitrogen, resulting in a lower cycle life than the nitrogen-phosphorus co-doped system. The data confirm that the multi-stage process of this invention improves rate performance while ensuring long-term cycle stability of the material.

[0116] Test Example 3: Microporous Structure and Surface Disorder Analysis

[0117] Experimental steps:

[0118] Three 3.0 g samples of the negative electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were selected and placed in a vacuum degassing station for continuous degassing at 300 degrees Celsius for 6 hours to remove moisture and impurity gases adsorbed on the sample surface. The pretreated samples were then transferred to a fully automated specific surface area and pore size analyzer, and nitrogen adsorption-desorption isotherm tests were performed at a liquid nitrogen temperature of 77 K.

[0119] The specific surface area of ​​the sample was calculated using the BET multi-point method model, and data points with relative pressure P / P0 in the range of 0.05 to 0.35 were selected for linear fitting. The desorption support data were analyzed using the BJH model to calculate the total pore volume and average pore size distribution.

[0120] A small sample was placed flat on a glass slide and tested using a micro Raman spectrometer. The laser source wavelength was 532 nm, the laser power was controlled at 2 mW, and the scanning range was 800 cm⁻¹ to 2000 cm⁻¹, with a cumulative total of 3 scans. The spectrum was then subjected to peak fitting using software, and the peak intensity data of the D peak near 1350 cm⁻¹ and the G peak near 1580 cm⁻¹ were extracted. The intensity ratio ID / IG was calculated.

[0121] Experimental data:

[0122] Table 3 Pore structure parameters and Raman spectral data of each group of samples

[0123] Sample number <![CDATA[Specific surface area BET (m ² / g)]]> <![CDATA[Total pore volume (cm ³ / g)]]> <![CDATA[D peak position (cm -1 )]]> <![CDATA[G peak position (cm -1 )]]> Intensity ratio ID / IG Example 1 7.42 0.0185 1348 1582 0.36 Example 2 7.15 0.0172 1350 1581 0.34 Example 3 7.89 0.0201 1346 1583 0.39 Example 4 7.33 0.0181 1349 1582 0.35 Example 5 7.45 0.0188 1348 1582 0.36 Comparative Example 1 3.24 0.0065 1355 1579 0.18 Comparative Example 2 5.12 0.0112 1352 1580 0.25 Comparative Example 3 4.68 0.0098 1353 1580 0.27 Comparative Example 4 4.05 0.0084 1354 1579 0.22 Comparative Example 5 5.86 0.0135 1351 1581 0.29

[0124] Conclusion Analysis:

[0125] Table 3 shows that the specific surface area of ​​Example 1 is 7.42 m² / g, which is higher than that of Comparative Example 1 (3.24 m² / g). Comparative Example 1 only underwent glucose carbon coating without introducing ammonium dihydrogen phosphate, resulting in a lower specific surface area. The increase in pore volume in Example 1 is due to the chemical etching of the carbon layer and graphite surface by ammonia and water vapor generated from the thermal decomposition of ammonium dihydrogen phosphate under high temperature and high pressure, forming microporous channels.

[0126] Compared with Comparative Example 1 and Comparative Example 3 (specific surface area 4.68 m² / g), Comparative Example 3 introduced nitrogen gas during the reaction to remove the gas produced by the reaction, reducing the ammonia concentration and weakening the etching effect. Comparative Example 5 used phosphoric acid instead of ammonium dihydrogen phosphate, with a specific surface area of ​​5.86 m² / g. Acidic corrosion produced some pores, but lacked ammonia components, resulting in a lower pore-forming effect than Example 1.

[0127] Regarding surface disorder, the ID / IG ratio of Example 1 was 0.36, higher than that of Comparative Example 1 (0.18). The increase in the ID / IG ratio corresponds to an increase in the carbon lattice defect density. The lower ratio in Comparative Example 1 indicates that its surface is mainly composed of highly ordered graphitic carbon or amorphous carbon. The higher ratio in Example 1 indicates that the doping of nitrogen and phosphorus heteroatoms alters the sp2 hybrid conjugated system, increasing point defects and edge active sites. In Example 3 (ID / IG = 0.39), the degree of defect increased with increasing dopant content. Combined with the electrochemical data from Test Example 2, heteroatom-induced surface defects provide lithium storage sites, which, along with interlayer spacing and pore structure, affect the capacity and rate performance of the material.

[0128] Test Example 4: Surface Elemental Composition and Chemical State Analysis

[0129] Experimental steps:

[0130] The negative electrode material powder samples prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were placed in a vacuum drying oven and dried at 120 degrees Celsius for 4 hours to remove surface adsorbed moisture. A small amount of the dried powder sample was pressed into an indium foil, fixed on a sample holder, and sent into the ultra-high vacuum analysis chamber of the X-ray photoelectron spectroscopy instrument. Due to the sensitivity of the test to surface contamination, the basic vacuum level of the analysis chamber was maintained at 5 × 10⁻⁶. -9 Below mbar.

[0131] The test used monochromatic AlKα rays as the excitation source, with a photon energy of 1486.6 eV and a beam diameter of 400 micrometers. First, a full-spectrum scan was performed to determine the elemental composition of the sample surface, with a scan range of 0 to 1350 eV, a pass energy of 100 eV, and a scan step size of 1.0 eV. Subsequently, a high-resolution narrow-spectrum scan was performed on the C1s, O1s, N1s, and P2p core energy levels, with the pass energy adjusted to 30 eV and a scan step size of 0.1 eV, to obtain detailed electron binding energy data.

[0132] The collected energy spectrum data were processed using XPS professional analysis software. Charge correction was performed using the binding energy of the CC / C=C bond in the C1s spectrum (284.8 eV) as a benchmark. Background was subtracted using the Shirley method, and peak fitting of each element was performed using the Gaussian-Lorentz mixture function. The atomic percentage of each element was calculated based on the peak area of ​​the characteristic peaks and the relative sensitivity factor.

[0133] Experimental data:

[0134] Table 4. Surface elemental content test data for each group of samples (atomic percentage at%)

[0135] Sample number Carbon element C1s (%) Oxygen element O1s (%) Nitrogen N1s (%) Phosphorus P2p (%) Nitrogen / Phosphorus atomic ratio (N / P) Example 1 92.45 4.72 1.25 1.58 0.79 Example 2 93.12 4.21 1.18 1.49 0.79 Example 3 91.56 5.34 1.42 1.68 0.85 Example 4 92.88 4.45 1.21 1.46 0.83 Example 5 92.67 4.58 1.23 1.52 0.81 Comparative Example 1 96.85 3.12 0.03 0.00 - Comparative Example 2 94.56 4.15 0.58 0.71 0.82 Comparative Example 3 93.89 4.32 0.65 1.14 0.57 Comparative Example 4 95.12 3.89 0.41 0.58 0.71 Comparative Example 5 93.45 4.98 0.05 1.52 0.03

[0136] Conclusion Analysis:

[0137] Table 4 shows that the surface elemental composition of Example 1 is carbon, oxygen, nitrogen, and phosphorus, with a nitrogen content of 1.25% and a phosphorus content of 1.58%. Comparative Example 1 only detected carbon, oxygen, and trace amounts of nitrogen at the background noise level; phosphorus was not detected, indicating that the nitrogen and phosphorus elements detected in Example 1 originated from ammonium dihydrogen phosphate in the raw materials and had been doped onto the graphite surface. The oxygen content of Example 1 was 4.72%, higher than the 3.12% of Comparative Example 1. The increase in oxygen content is due to the oxygen-containing groups introduced during the phosphate reaction.

[0138] Comparing Example 1 and Comparative Example 2, Comparative Example 2 was prepared under normal pressure, and its nitrogen content was 0.58% and phosphorus content was 0.71%, both lower than those of Example 1. Under normal pressure, ammonia gas and phosphorus-containing intermediates produced by the thermal decomposition of ammonium dihydrogen phosphate are easily volatilized with the carrier gas, reducing the effective concentration in the reaction system and resulting in a decrease in the final doping amount. Example 1 used a closed high-pressure process, which suppressed the escape of gaseous components and increased the driving force for heteroatoms to diffuse into the carbon layer.

[0139] Comparative Example 3 had a phosphorus content of 1.14%, but a nitrogen content of only 0.65%, resulting in an N / P ratio of 0.57, lower than the 0.79 of Example 1. Comparative Example 3 removed the ammonia atmosphere during the reaction, leading to nitrogen source loss and a decrease in nitrogen doping. Comparative Example 5 used phosphoric acid as the sole phosphorus source, with a phosphorus content of 1.52%, similar to Example 1, but a nitrogen content of only 0.05%, classifying it as single phosphorus doping. Combined with the cycling performance data from Test Example 2, Example 1 outperformed Comparative Example 5, indicating that co-doping with nitrogen and phosphorus has a better effect on improving material performance than single phosphorus doping, and that the introduction of nitrogen atoms modulates the electronic structure of the carbon material.

[0140] Test Example 5: Electrochemical Impedance Spectroscopy (EIS) Test

[0141] Experimental steps:

[0142] Each coin cell assembled in Test Example 2 was selected and subjected to three charge-discharge cycles at a rate of 0.1C on the battery testing system to complete the activation of electrode materials and the formation of solid electrolyte interphase (SEI) film.

[0143] Charge the battery to 50% state of charge (SOC) and let it stand for 2 hours until the open-circuit voltage stabilizes. Connect to an electrochemical workstation and test using the AC impedance method. Set the frequency range to 100kHz to 0.01Hz, the AC disturbance voltage amplitude to 5mV, and the test environment temperature to 25 degrees Celsius.

[0144] Impedance spectrum data were collected, and equivalent circuit fitting was performed using ZView software. The ohmic internal resistance Rs (corresponding to the high-frequency intercept), SEI film resistance Rsei (corresponding to the high-frequency semicircle), and charge transfer resistance Rct (corresponding to the mid-frequency semicircle) were selected as key parameters, and the resistance values ​​of each part were calculated.

[0145] Experimental data:

[0146] Table 5. Electrochemical impedance fitting data of half-cells for each group of samples.

[0147] Sample number Ohmic internal resistance Rs (Ω) SEI film resistance Rsei (Ω) Charge transfer resistance Rct (Ω) Total impedance (Ω) Example 1 2.45 12.34 18.56 33.35 Example 2 2.51 13.12 19.88 35.51 Example 3 2.38 11.95 17.42 31.75 Example 4 2.48 12.87 19.05 34.40 Example 5 2.46 12.55 18.90 33.91 Comparative Example 1 3.12 45.68 85.24 134.04 Comparative Example 2 2.85 25.41 38.65 66.91 Comparative Example 3 2.94 30.12 42.18 75.24 Comparative Example 4 3.01 35.56 55.78 94.35 Comparative Example 5 2.65 15.23 28.45 46.33

[0148] Conclusion and Analysis: Table 5 shows that the charge transfer resistance Rct of Example 1 is 18.56 Ω, lower than that of Comparative Example 1 (85.24 Ω). Rct reflects the resistance of lithium ions to redox reactions at the electrode / electrolyte interface. Comparative Example 1 did not undergo heteroatom doping, resulting in fewer surface active sites. The reduced Rct in Example 1 corresponds to the presence of pyridine nitrogen and the increased interlayer spacing in Test Example 4. The lone pair electrons of nitrogen atoms improve the electronic conductivity of the carbon material surface, lowering the reaction energy barrier.

[0149] Regarding the SEI film resistance Rsei, Example 1 showed a value of 12.34 Ω, lower than Comparative Example 1's 45.68 Ω and Comparative Example 2's 25.41 Ω. The low Rsei value indicates a thin SEI film with high ionic conductivity. Comparative Example 1, with its unmodified surface, easily formed a thick and uneven organic deposition layer during cycling. In Example 1, the phosphorus-containing groups generated from phosphate decomposition participated in the film-forming reaction, generating an interface film rich in inorganic phosphides, thus improving lithium-ion permeability.

[0150] Comparing Example 1 and Comparative Example 5, although the Rsei of Comparative Example 5 is 15.23 Ω, close to that of Example 1, its Rct is 28.45 Ω, significantly higher than that of Example 1. This indicates that single phosphorus doping mainly improves the SEI film properties, while its effect on improving charge transport in the electrode bulk is weaker than that of the nitrogen-phosphorus co-doped system. The low internal resistance characteristic supports the capacity retention capability of Example 1 under high-rate charge and discharge in Test Example 2.

[0151] Test Example 6: Cycle Performance and Electrode Expansion Test of Soft-Pack Full Cells

[0152] Experimental steps:

[0153] Commercial lithium iron phosphate (LFP) cathode material, conductive carbon black SuperP, and binder PVDF are mixed in a mass ratio of 96:2:2, NMP solvent is added and stirred to form a slurry, which is then coated onto carbon-coated aluminum foil, dried, rolled, and cut to form cathode sheets.

[0154] The negative electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were selected and matched with the positive electrode sheets according to a negative electrode capacity excess factor (N / P ratio) of 1.15. A 20-micron thick ceramic-coated separator was used, and the electrolyte was 1.0 M LiPF6 combined with a carbonate solvent. In a dry room with a dew point below -40 degrees Celsius, the positive and negative electrode sheets were stacked with the separator, electrolyte was injected, and the cells were vacuum-sealed to produce a pouch cell with a nominal capacity of 1 Ah.

[0155] The battery was left at 45 degrees Celsius for 24 hours to ensure that the electrolyte was fully immersed, and then charged at a constant current of 0.02C to 3.65V to complete the first formation, followed by vacuum sealing.

[0156] Charge-discharge cycle tests were conducted in a 25°C constant temperature chamber, with a voltage range of 2.5V to 3.65V. The charge-discharge regime was set to 1C constant current constant voltage charging (cutoff current 0.05C) and 1C constant current discharging. Capacity retention was recorded after 500 cycles. The center thickness of the battery under full charge was measured using a micrometer before and after the test, and the electrode thickness expansion rate under full charge was calculated.

[0157] Experimental data:

[0158] Table 6. Cyclic and expansion performance data of soft-pack full batteries for each group of samples.

[0159] Sample number 1C cycle 500-cycle capacity retention (%) Full charge thickness before cycle (mm) Full fill thickness after cycle (mm) Electrode thickness expansion rate (%) Example 1 95.8 3.42 3.56 4.09 Example 2 94.6 3.41 3.58 4.98 Example 3 95.1 3.43 3.59 4.66 Example 4 94.9 3.42 3.58 4.68 Example 5 95.5 3.42 3.57 4.38 Comparative Example 1 82.4 3.40 3.82 12.35 Comparative Example 2 89.2 3.41 3.69 8.21 Comparative Example 3 90.5 3.42 3.68 7.60 Comparative Example 4 86.7 3.40 3.73 9.71 Comparative Example 5 92.8 3.42 3.63 6.14

[0160] Conclusion Analysis:

[0161] Table 6 shows that after 500 cycles at 1C, Example 1 retained 95.8% of its full cell capacity and had an electrode thickness expansion rate of 4.09%. Comparative Example 1 retained 82.4% of its capacity and had a thickness expansion rate of 12.35%. The higher expansion rate of Comparative Example 1 is attributed to the cumulative lattice volume changes caused by repeated lithium intercalation / deintercalation between graphite layers, as well as the thickening of the SEI film due to interfacial side reactions. The lower expansion rate of Example 1 indicates that nitrogen-phosphorus co-doping and the increased interlayer spacing effectively reduced the lattice stress during lithium-ion intercalation.

[0162] Compared with Comparative Example 5, Comparative Example 5 (single phosphorus doping) showed a capacity retention of 92.8% and an expansion rate of 6.14%. Although the phosphate interface layer formed by phosphorus doping suppressed some electrolyte decomposition, the nitrogen-phosphorus synergistic system of Example 1 exhibited higher stability. The CN and POC bonds formed in Example 1 enhanced the structural rigidity of the carbon framework, reducing structural collapse and irreversible lithium loss during cycling.

[0163] The expansion rate of Comparative Example 2 (treated under normal pressure) was 8.21%, which was higher than that of Example 1. Combined with the porosity data of Test Example 3, Comparative Example 2, due to its underdeveloped pore structure, could not effectively absorb the volume expansion during charging and discharging. Example 1, by creating pores in situ to reserve space within the material, combined with surface chemical modification, achieved high capacity retention and low volume expansion rate, making it suitable for applications sensitive to volumetric energy density.

Claims

1. A method for preparing regenerated graphite anodes for fast-charging lithium-ion batteries, characterized in that, Includes the following steps: S1. The pretreated waste graphite powder, ammonium dihydrogen phosphate, carbon source and water are put into the mixing equipment and mechanically sheared and kneaded to obtain a wet powder mixture. S2. The wet powder mixture is heated in a closed environment. The gas released by the thermal decomposition of the material is used to establish self-generated pressure. The heat preservation reaction is carried out under the pressure maintenance state to obtain the prepolymer. S3. The prepolymer is fed into a reactor for pyrolysis. By controlling the material filling state and atmosphere in the reactor, the ammonia gas released by the decomposition of ammonium dihydrogen phosphate is retained in the material voids for in-situ reaction to obtain a pyrolysis intermediate. S4. The pyrolysis intermediate is placed in an environment with an inert gas flow and calcined at a high temperature. The high temperature and airflow carry away impurities, and after cooling, a sintered material is obtained. S5. The sintered material is crushed and sieved to obtain a recycled graphite anode.

2. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S1, the wet powder mixture is made from raw materials comprising the following parts by weight: Pre-treated waste graphite powder: 100.0 parts; Ammonium dihydrogen phosphate: 4.0–10.0 parts; Carbon source: 3.0–6.0 parts; Water: 15.0–30.0 parts.

3. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 2, characterized in that, The carbon source is selected from at least one of anhydrous glucose, industrial starch, sucrose, maltose, and modified starch.

4. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, Prior to step S1, the method for preparing the pretreated waste graphite powder includes: The negative electrode sheet of the waste lithium-ion battery is separated and the current collector is removed by solvent cleaning to obtain coarse graphite powder. The coarse graphite powder is soaked in a dilute sulfuric acid solution with a mass fraction of 15% to 20%, the solid-liquid ratio is 1:4 to 1:5, and the treatment temperature is 25℃ to 40℃. The acid solution is used to dissolve and remove SEI film components and metal oxides. After being washed with water until neutral, dried, subjected to air jet milling and classification, the pretreated waste graphite powder used in step S1 is obtained.

5. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S1, the ammonium dihydrogen phosphate and the carbon source are pre-dissolved in water to prepare a composite modified additive solution. The preparation temperature of the composite modified additive solution is 55℃~65℃, and the solid content is 30%~35%. The specific operation of step S1 is as follows: the composite modified additive liquid is added to the pretreated waste graphite powder by spraying while stirring.

6. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S1, the mechanical shearing and kneading is carried out in a high-shear kneader with a heating jacket. The jacket temperature is set to 60℃~85℃, the stirring paddle speed is 30~60 rpm, and the kneading time is 40~90 minutes.

7. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S2, the specific process of the self-pressure prepolymerization is as follows: The wet powder mixture obtained in step S1 is sealed in a pressure-resistant reactor or curing tank, and heated to 140℃~165℃ at a rate of 3℃ / min, while controlling the autogenous pressure in the system to be 0.20MPa~0.60MPa, and the reaction is carried out at constant temperature and pressure for 2.0~4.0 hours.

8. The method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S3, the gas-phase confined pyrolysis is carried out in a spiral conveying reactor with an aspect ratio of not less than 18; The material filling rate in the screw conveyor reactor is controlled to be 80% to 95% in order to utilize the plug effect to isolate the external atmosphere; No external carrier gas is introduced during the pyrolysis process; the reactor is maintained at positive pressure only by using an exhaust device. The temperature of the pyrolysis feed section is set to 180℃~220℃, the temperature of the discharge section is set to 400℃~480℃, and the average residence time of the material is 40~80 minutes.

9. A method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S4, the high-temperature sintering is carried out in a rotary kiln, with the calcination temperature set at 900℃~1150℃ and the holding time at that temperature being 2.0~4.0 hours. The inert gas is nitrogen, introduced in reverse, with a flow rate set at 3.0–8.0 cubic meters per hour per ton of material.

10. A method for preparing a regenerated graphite anode for fast-charging lithium-ion batteries according to claim 1, characterized in that, In step S4, the cooling is carried out by a water-cooled spiral method to cool the material to below 60°C before discharge; in step S5, the sintering material obtained in step S4 is screened using a sieve with a mesh size of 300 to 325 mesh.

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