Repair and regeneration method of retired graphite, regenerated graphite negative electrode material and lithium battery

Abstract

The invention relates to the technical field of lithium battery recovery, and provides a method for repairing and regenerating retired graphite, which comprises the following steps: pretreating and purifying a retired graphite negative electrode, performing hydrophilic reaction treatment on the retired graphite negative electrode to obtain hydrophilic graphite rich in oxygen functional groups, and mixing the hydrophilic graphite with a water-soluble nitrogen-containing biomass carbon source and a metal-based catalyst to form a precursor mixture; performing centrifugation and vacuum freeze drying to obtain black precursor powder, performing heat treatment, performing pyrolysis and catalytic graphitization on the black precursor powder, forming a nitrogen-doped carbon coating layer on the surface of the decommissioned graphite, and performing ultrasonic acid pickling on the obtained primarily regenerated graphite material to obtain the high-performance regenerated graphite material. According to the present invention, the hydrophilic treatment is combined with the two-component synergistic coating, and the low-temperature catalytic graphitization process is adopted to construct the high-graphitization-degree nitrogen-doped carbon layer modified regenerated graphite negative electrode, such that the efficient repair and the performance improvement of the retired graphite are achieved. The invention also provides the regenerated graphite negative electrode material prepared by the method and a lithium battery containing the negative electrode material.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery recycling technology, specifically involving a method for regenerating and repairing decommissioned graphite, as well as regenerated graphite anode materials and lithium batteries. Background Technology

[0002] Lithium-ion batteries, as a novel energy storage power source, are widely used in consumer electronics fields such as mobile phones, automobiles, and computers due to their advantages such as high energy density, no memory effect, long cycle life, and environmental friendliness. Graphite, on the other hand, dominates the market as a negative electrode material for commercial lithium batteries due to its low cost and excellent chemical properties. However, during prolonged charge-discharge cycles, the repeated insertion and extraction of lithium ions damages the microstructure of graphite, leading to problems such as increased internal resistance, reduced battery capacity, and shortened cycle life. With the surge in lithium-ion battery applications, a large amount of retired graphite will be generated in the future.

[0003] Currently, common technologies for regenerating decommissioned graphite mainly include leaching followed by high-temperature calcination, surface coating, elemental doping, and the preparation of composite materials. Among these technologies, surface coating has the advantages of high efficiency, low cost, and low pollution, and has attracted widespread attention from researchers. Currently, surface coating mainly uses carbon-based, metal-based, polymer-based, and inorganic non-metallic materials as precursors to repair and regenerate decommissioned graphite.

[0004] Patent CN 119018888A discloses a method for preparing and applying a recycled negative electrode active material based on waste graphite. This method uses resins such as polypropylene and polyvinyl chloride as carbon sources and achieves coating modification of decommissioned graphite through high-temperature carbonization. While this method can repair surface defects in graphite, it requires carbonization at temperatures between 900 and 1350°C to form a conductive carbon layer, resulting in significant energy consumption and potentially damaging the original spline properties of the graphite. 2 The conjugated layer structure damages the lithium-ion insertion / extraction channels. Patent CN 117185289A discloses a method for regenerating waste graphite, which uses magnesium powder to catalyze graphitization at 800–1000℃, combined with two-stage conventional stirring and acid washing and resin-based carbon source coating, to achieve performance restoration of waste graphite. However, this method is prone to "local agglomeration" or "exposed areas," resulting in uneven distribution of lithium-ion active sites. Furthermore, the carbon layer formed relies solely on physical contact with the graphite, lacking chemical anchoring. During recycling, the carbon layer is prone to peeling due to the slight expansion of graphite volume, affecting the stability of the SEI film.

[0005] Therefore, in the current field of regenerating graphite anodes from retired lithium-ion batteries, there are shortcomings such as weak interfacial bonding between the carbon layer and the retired graphite, high energy consumption in regeneration processing, and easy shedding of the carbon layer during subsequent cycles. As a result, the capacity, rate performance, and cycle stability of the regenerated graphite anode cannot simultaneously meet the usage requirements. Summary of the Invention

[0006] The purpose of this application is to overcome the shortcomings of the prior art and to provide a method for the repair and regeneration of decommissioned graphite.

[0007] The method for repairing and regenerating decommissioned graphite provided in this application includes the following steps: S1. Pre-treat the decommissioned graphite negative electrode to obtain purified decommissioned graphite; S2. The purified decommissioned graphite obtained in step S1 is subjected to a hydrophilic reaction treatment to obtain a hydrophilic graphite material rich in oxygen functional groups. S3. The hydrophilic graphite material obtained in S2 is mixed with a water-soluble nitrogen-containing biomass carbon source and a metal-based catalyst, and ultrasonically stirred to form a uniform precursor mixture solution. S4. Centrifuge and freeze-dry the precursor mixture solution obtained in step S3 to obtain black precursor powder. S5. The black precursor powder obtained in step S4 is heat-treated under an inert atmosphere to pyrolyze and catalyze graphitization of the black precursor powder, so as to repair the decommissioned graphite and form a nitrogen-doped carbon coating layer on the surface, thereby obtaining a preliminary regenerated graphite material. S6. The preliminary recycled graphite material obtained in step S5 is subjected to ultrasonic acid washing to finally obtain high-performance recycled graphite material.

[0008] The decommissioned graphite repair and regeneration method provided in this application has the following advantages: (1) The method for repairing and regenerating decommissioned graphite in this application introduces a metal-based catalytic graphitization mechanism. Through traditional heat treatment, catalysts such as nitrates, acetates, chlorides, citrates or oxalates containing at least one element from cobalt, iron, nickel, manganese or copper are used to significantly reduce the temperature of amorphous carbon to graphitic carbon, thereby achieving efficient graphitization at low temperature. While reducing energy consumption, it can also induce the generation of highly conductive graphitic carbon layers, providing a "highway" for rapid electron transport.

[0009] (2) The method for repairing and regenerating decommissioned graphite in this application constructs a regenerated graphite with a nitrogen-doped carbon layer modified with a high degree of graphitization by combining hydrophilic treatment with two-component synergistic coating and low-temperature catalytic graphitization. The water-soluble nitrogen-containing carbon source is used to strengthen the interfacial bonding force and provide active sites. The synergistic effect of nitrogen doping and catalytic graphitization with metal-based catalysts enables the directional control of the carbon layer crystal structure at low temperature. In this way, in-situ doping of nitrogen atoms is achieved during pyrolysis, effectively controlling the electronic structure of the carbon layer and providing more lithium-ion active sites. At the same time, combined with the highly conductive carbon layer generated by transition metal catalysis, an interfacial layer with excellent conductivity and high reactivity is constructed, forming a nitrogen-doped mesoporous structure that is conducive to the rapid transport of lithium ions. This significantly enhances the adsorption capacity of lithium ions and promotes their rapid migration at the interface, achieving efficient repair of decommissioned graphite and greatly improving the rate performance of graphite anode materials.

[0010] (3) The decommissioned graphite repair and regeneration method of this application fundamentally solves the technical defect of uneven coating on the surface of waste graphite during the repair of decommissioned graphite through a multi-stage treatment of "hydrophilic treatment-ultrasonic dispersion-freeze drying". It can make the final nitrogen-doped graphitized carbon coating layer continuous, dense and complete, effectively repairing the cracks and defects on the graphite surface and avoiding the shortcomings of electrochemical performance caused by uneven coating.

[0011] (4) The method for repairing and regenerating decommissioned graphite in this application is low in cost, simple to operate, and meets environmental protection requirements. The entire process can be completed in a traditional tube furnace, avoiding the use of expensive equipment such as microwaves, significantly reducing energy consumption, and is suitable for large-scale industrial production.

[0012] This application also provides a regenerated graphite anode material, prepared using the above-described method for repairing and regenerating decommissioned graphite.

[0013] This application also provides a lithium battery comprising the above-described recycled graphite anode material.

[0014] The recycled graphite anode material prepared in this application exhibits excellent electrochemical performance. Its unique coating structure enables it to demonstrate high reversible capacity, excellent rate performance and ultra-long cycle stability when used as a lithium-ion battery anode again, providing a reliable technical path for the high-value recycling of waste graphite.

[0015] The recycled graphite anode material prepared using the method described in this application has broad application prospects in the field of low-cost, green and environmentally friendly lithium battery manufacturing and recycling. It can be further extended to other electrochemical energy storage systems such as sodium-ion batteries, with significant economic and social benefits. Attached Figure Description

[0016] Figure 1This is a TEM image of the regenerated graphite anode material repaired using the method in Example 3; Figure 2 SEM image of the regenerated graphite anode material repaired by the method in Example 3; Figure 3 The image shows the XPS (N 1s) plot of the regenerated graphite anode material repaired by the method in Example 3. Figure 4 SEM image of the recycled graphite anode material prepared in Comparative Example 1; Figure 5 SEM image of the recycled graphite anode material prepared in Comparative Example 2; Figure 6 The graph shows a comparison of the cycling performance of various embodiments and comparative examples at different scaling factors. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] This application provides a method for the repair and regeneration of decommissioned graphite, including the following steps: S1 pre-treats the decommissioned graphite anode to obtain purified decommissioned graphite. The pretreatment process in this step includes: low-temperature heat treatment under an inert atmosphere to decompose the organic binder and SEI decomposition products on the decommissioned graphite negative electrode; followed by ultrasonic acid washing to remove residual metallic impurities from the decommissioned graphite, making them soluble for easy removal. The inert atmosphere is one or a mixture of argon, nitrogen, or hydrogen; the ultrasonic power is 0.12 kW to 0.24 kW; the ultrasonic frequency is 40 kHz; and the acid is at least one of hydrochloric acid, sulfuric acid, or nitric acid with a concentration of 1 mol / L to 5 mol / L, preferably hydrochloric acid, to avoid introducing excess impurities and improve the purity of the regenerated graphite material. The ratio of decommissioned graphite to acid solution is 1 g: 15–25 ml, and the acid washing time is 15–40 min, preferably 20–30 min.

[0019] S2. The purified decommissioned graphite obtained in step S1 is subjected to a hydrophilic reaction treatment to obtain a hydrophilic graphite material rich in oxygen functional groups.

[0020] The hydrophilic reaction treatment in this step can be as follows: The purified decommissioned graphite and hydrogen peroxide solution were placed in a reaction vessel and subjected to hydrothermal treatment under sealed conditions. The hydrothermal treatment temperature was 80℃~160℃, preferably 110~120℃; the reaction time was 12~48h, preferably 12~24h; the mass concentration of hydrogen peroxide was 25~35%, preferably 28~32%; and the ratio of decommissioned graphite to hydrogen peroxide was 1g:5~10ml.

[0021] This step combines purified decommissioned graphite with hydrogen peroxide to introduce oxygen-containing functional groups (-OH, -COOH), changing the graphite from hydrophobic to hydrophilic. This modification can significantly improve the wettability, spreadability, and interfacial adhesion of the subsequent aqueous coating solution on the graphite surface. It is a key prerequisite for forming a nitrogen-doped carbon coating layer and can avoid defects such as "local agglomeration" or "exposed areas" and uneven distribution of lithium-ion active sites when mixed with nitrogen-containing carbon sources in the future.

[0022] In this step, when the purified decommissioned graphite is mixed with hydrogen peroxide, a hydrothermal treatment at 80℃~160℃ is performed for 12~48h to address defects such as numerous cyclically generated cracks and pores on the surface of the decommissioned graphite. This accelerates the hydrogen peroxide oxidation reaction process, extends the activation time, and ensures that oxygen-containing functional groups can uniformly cover the entire decommissioned graphite, laying the foundation for a firm bond in the subsequent coating layer.

[0023] This step uses hydrogen peroxide of the above-mentioned mass concentration and ratio to perform hydrophilic treatment on purified decommissioned graphite under closed conditions. This avoids the influence of strong oxidizing / corrosive reagents on the properties and conjugated structure of decommissioned graphite, thus eliminating the need for subsequent separation of other reagent residues, reducing wastewater treatment costs, and simplifying the process.

[0024] This hydrophilic reaction treatment is achieved by directly activating the graphite surface with hydrogen peroxide, eliminating the need for additional solvents. This avoids the problems of other introduced solvents being difficult to remove completely, harmful volatiles generated during carbonization contaminating the carbon layer, solvent molecules occupying functional group sites on the graphite surface, and hindering subsequent nitrogen-containing carbon sources – NH3. + The process of electrostatically binding with COOH in graphite and requiring an additional solvent recovery process that increases costs are drawbacks that make it suitable for the simple process and electrochemical performance requirements of regenerated decommissioned graphite.

[0025] The hydrophilic reaction treatment in this step can also be: The purified decommissioned graphite is directly placed into a vacuum plasma cleaner for ultraviolet hydrophilic treatment. The hydrophilic treatment time is 15-60 minutes, the lamp power is 100-300W, and the wavelengths of the treated light are 185nm and 254nm. The 185nm wavelength can decompose oxygen into ozone, and the 254nm wavelength can decompose ozone into oxygen and reactive oxygen. The power of the cleaner is 10-200W.

[0026] The purified decommissioned graphite is hydrophilically treated by vacuum plasma cleaning combined with ultraviolet light. This physical method does not require the introduction of any oxidation reaction solvents and can directly treat the powder, improving the quality of the decommissioned graphite. The treatment time is relatively short, only 15-20 minutes, and the process is simple.

[0027] The two hydrophilic reaction treatment methods in this step can be used in combination. First, the purified decommissioned graphite and hydrogen peroxide solution can be placed in a reaction vessel for sealed hydrothermal treatment, and then vacuum plasma cleaning combined with ultraviolet light treatment can be used. Alternatively, vacuum plasma cleaning combined with ultraviolet light treatment can be used first, followed by hydrophilic treatment with hydrogen peroxide. Using the two methods in combination can reduce the concentration of hydrogen peroxide, greatly shorten the treatment time, reduce production costs, and improve the hydrophilic effect of decommissioned graphite.

[0028] S3. The hydrophilic graphite material obtained in S2 is mixed with a water-soluble nitrogen-containing carbon source and a metal-based catalyst, and ultrasonically stirred to form a uniform precursor mixture solution.

[0029] In this step, the water-soluble nitrogen-containing carbon source includes at least one of the following: natural high molecular weight polysaccharides containing amino and / or amide groups, synthetic polymers, small molecule organic compounds, and ionic liquids. The natural high molecular weight polysaccharides containing amino and / or amide groups are chitosan, sodium alginate, and gelatin; the synthetic polymers are polyethyleneimine and polyacrylamide; and the small molecule organic compounds are such as urea and melamine.

[0030] The metal-based catalyst includes: a nitrate, acetate, chloride, citrate or oxalate containing at least one element selected from cobalt (Co), iron (Fe), nickel (Ni), manganese (Mn) and copper (Cu), preferably at least one of cobalt nitrate and iron nitrate.

[0031] The water-soluble nitrogen-containing carbon source accounts for 3% to 10 wt% of the hydrophilic graphite material; the metal-based catalyst accounts for 3% to 10 wt% of the total mass of the nitrogen-containing biomass carbon source and the hydrophilic graphite material.

[0032] This step utilizes the synergistic enhancement effect of nitrogen doping and catalytic graphitization. A water-soluble nitrogen-containing carbon source is mixed with graphite products rich in oxygen functional groups, facilitating the formation of coordination bonds with catalysts such as cobalt and iron, resulting in exceptionally uniform dispersion. Ultrasonic stirring further ensures uniform dispersion and mixing, effectively regulating the electronic structure of the carbon layer, providing more lithium-ion active sites, and enhancing ion migration rates. This provides a more effective guarantee for in-situ nitrogen doping during subsequent pyrolysis. Simultaneously, the addition of 3%–10% transition metal catalysts not only catalyzes graphitization but also forms Co-N bonds, allowing the carbon layer to adhere more firmly to the graphite. This leaves more pores and increases the number of active sites during subsequent acid washing. Thus, the combination of the water-soluble nitrogen-containing carbon source, the graphite products rich in oxygen functional groups, and the highly conductive carbon layer generated by transition metal catalysis constructs an interface layer with both excellent conductivity and high reactivity. This facilitates the induction of highly conductive graphite-like carbon layers, accelerating electron transport and improving conductivity.

[0033] This step involves mixing the hydrophilic graphite product with a water-soluble nitrogen-containing carbon source and a metal-based catalyst, followed by ultrasonic treatment and agitation. This effectively disperses graphite aggregates and strongly drives the coating solution to penetrate the microscopic defects of the graphite particles, ensuring that the carbon source and catalyst form a uniformly dispersed nanoscale precursor mixture on the graphite surface. The ultrasonic treatment power is 0.12–0.24 kW, the ultrasonic frequency is 40 kHz, and the agitation time is 40–70 min, preferably 50–60 min.

[0034] S4. Centrifuge and freeze-dry the precursor mixture solution obtained in step S3 to obtain black precursor powder.

[0035] The freezing temperature for this step is -50℃ to -60℃, the vacuum degree is <10Pa, and the freeze-drying time is 36 to 48 hours.

[0036] This step involves freeze-drying followed by heat treatment, which makes the black precursor powder more fluffy and better dispersible. This allows the heat to penetrate evenly to the surface of each graphite particle during subsequent carbonization, avoiding localized overheating that could lead to graphite layer collapse or underheating that could result in insufficient pyrolysis of the nitrogen-containing carbon source and uneven nitrogen doping. This improves the uniformity of the subsequent carbon coating layer.

[0037] S5. The black precursor powder obtained by ultrasonic vibration and stirring in step S4 is subjected to heat treatment under an inert atmosphere, so that the nitrogen-containing carbon source in the black precursor powder is rapidly carbonized in situ into a nitrogen-containing amorphous carbon layer and catalyzed to graphitize, so as to repair the surface defects and damage of the decommissioned graphite and form a nitrogen-doped carbon coating layer on the surface, thus obtaining the preliminary regenerated graphite material.

[0038] The inert atmosphere in this step is one or a mixture of argon, nitrogen, or hydrogen. The heat treatment temperature is 500–900℃, preferably 500–700℃, the heating rate is 3–10℃ / min, and the holding time is 1–6 h. This achieves in-situ carbonization of the nitrogen-containing organic sugar coating layer to form a nitrogen-containing carbon layer. The presence of nitrogen atoms on the surface of the regenerated graphite can reduce the negative electrode's influence on Li. + The adsorption energy of Li promotes + The migration of the anode material enhances the conductivity of the negative electrode surface.

[0039] S6. The preliminary recycled graphite material obtained in step S5 is then subjected to ultrasonic acid washing to remove impurities generated during the process, which helps to improve the purity of the recycled graphite material and ultimately obtain a high-performance recycled graphite anode material.

[0040] In this step, the ultrasonic power is 0.12kw to 0.24kw, the ultrasonic frequency is 40KHz, the acid is selected from at least one of hydrochloric acid, sulfuric acid or nitric acid with a concentration of 1mol / L to 5mol / L, preferably hydrochloric acid, the treatment time is 10-30min, preferably 15-20min, and the ratio of the initial regenerated graphite material to the acid solution is 1g:15-25ml.

[0041] The above-mentioned method for regenerating and repairing decommissioned graphite in this application first employs a hydrophilic treatment to gently oxidize the surface of the decommissioned graphite, introducing oxygen-containing functional groups (such as -OH, -COOH), thus changing the graphite from hydrophobic to hydrophilic. This significantly improves the wettability and spreadability of the subsequent aqueous coating solution on the graphite surface, providing an effective guarantee for the uniform coating of nitrogen-containing carbon sources. Secondly, the added water-soluble nitrogen-containing carbon source has a dual function: firstly, as a carbon source, it forms an amorphous carbon layer after pyrolysis, repairing cracks and defects on the graphite surface; secondly, as a nitrogen source, its inherent amino (-NH2) functional groups can achieve in-situ doping of nitrogen atoms during pyrolysis, forming a nitrogen-containing carbon source. The nitrogen-doped layer effectively modulates the electronic structure of the carbon layer, providing more active sites, significantly enhancing the adsorption capacity for lithium ions and promoting their rapid migration at the interface. Finally, the added metal-based catalyst plays a catalytic role in graphitization during the heat treatment process, which can significantly reduce the activation energy of the transformation of amorphous carbon into an ordered graphite structure. In this way, at a relatively low heat treatment temperature, the amorphous carbon layer generated by the pyrolysis of nitrogen-containing biomass carbon source can be transformed into a highly conductive graphite-like carbon layer. This highly graphitized coating layer can provide a high-speed channel for electron transport, realizing efficient repair and performance improvement of decommissioned graphite, and greatly improving the rate performance of graphite anode materials.

[0042] The recycled graphite anode material provided in this application is prepared using the above-mentioned method for repairing and regenerating decommissioned graphite.

[0043] This application uses the above-mentioned method for repairing and regenerating decommissioned graphite to prepare recycled graphite anode materials, which can be applied to lithium batteries to reduce the manufacturing cost of lithium batteries.

[0044] The above-mentioned method for repairing and regenerating decommissioned graphite will be further described in detail below with reference to specific embodiments.

[0045] Example 1: The method for repairing and regenerating decommissioned graphite in Example 1 includes the following specific steps: S1 Retired Graphite Pretreatment: Decommissioned graphite was placed in a tube furnace, and nitrogen gas with a concentration ≥99% was introduced. The temperature was increased to 600℃ at a rate of 3℃ / min and held for 1 hour to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. The graphite was then cooled to room temperature, followed by ultrasonic acid washing at room temperature. The ultrasonic power was 0.24 kW, the ultrasonic frequency was 40 kHz, and a 3 mol / L hydrochloric acid solution was used. The graphite to hydrochloric acid solution ratio was 1 g: 25 ml, and the washing time was 30 min. The resulting purified decommissioned graphite was then obtained by filtration and drying.

[0046] S2 hydrophilic treatment: Hydrogen peroxide with a mass concentration of 35% was prepared. The purified decommissioned graphite was mixed with hydrogen peroxide at a ratio of 10g:100ml and transferred to the inner liner of the reactor. The inner liner of the reactor was then placed in the reactor for sealed hydrothermal treatment at a temperature of 120℃ for 12 hours. After the reaction was completed, the mixture was cooled to room temperature and then filtered and dried to obtain hydrophilic graphite rich in oxygen functional groups.

[0047] S3 two-component synergistic encapsulation: Prepare an 8% (w / w) chitosan aqueous solution and a 10% (w / w) cobalt nitrate aqueous solution. Add the above-mentioned hydrophilic graphite to the chitosan aqueous solution, with a mass ratio of 10 ml: 100 g. Then add 10 wt% (w / w) cobalt nitrate aqueous solution equal to the total mass of the chitosan solution and hydrophilic graphite. Ultrasonically vibrate for 60 min at an ultrasonic power of 0.24 kW and an ultrasonic frequency of 40 kHz to form a homogeneous precursor mixture.

[0048] S4 freeze-drying: The precursor mixture was transferred to a freeze dryer and freeze-dried at -50°C and a vacuum of <10Pa for 24 hours to remove moisture and obtain a black, fluffy precursor powder.

[0049] S5 Low-Temperature Catalytic Heat Treatment: The precursor powder was placed in a tube furnace, and nitrogen gas with a concentration of ≥99% was introduced. The temperature was increased to 700℃ at a heating rate of 10℃ / min, held for 2 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0050] S6 Post-Processing: Preliminary regenerated graphite and 3 mol / L hydrochloric acid were ultrasonically vibrated at room temperature for 20 min at a solid-liquid ratio of 1 g: 25 ml, followed by filtration and drying to obtain a high-performance regenerated graphite anode material (denoted as RG).

[0051] The prepared recycled graphite anode material was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form a lithium-ion battery anode. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0052] The structure and performance characterization of this embodiment 1 are as follows: Depend on Figure 6 Electrochemical data show that the discharge capacity at 2C rate in Example 1 reaches 191.91 mAh / g. This indicates that the regeneration and repair method described in this application can effectively repair decommissioned graphite and transform it into a high-performance lithium-ion battery anode material.

[0053] Example 2: The method for repairing and regenerating decommissioned graphite in Example 2 includes the following specific steps: S1 Retired Graphite Pretreatment: Decommissioned graphite was placed in a tube furnace, and nitrogen gas with a concentration ≥99% was introduced. The temperature was increased to 550℃ at a rate of 5℃ / min and held for 2 hours to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. The graphite was then cooled to room temperature, followed by ultrasonic acid washing at room temperature. The ultrasonic power was 0.12 kW, the ultrasonic frequency was 40 kHz, and a 2.5 mol / L hydrochloric acid solution was used. The ratio of graphite to sulfuric acid solution was 1 g: 15 ml, and the washing time was 20 min. The graphite was then filtered and dried to obtain purified decommissioned graphite.

[0054] S2 hydrophilic treatment: The purified decommissioned graphite obtained in S1 was placed in a vacuum plasma cleaner for ultraviolet hydrophilic treatment. The ultraviolet lamp power was 100W, the wavelength of the light was 185nm and 254nm, and the treatment time was 45min, resulting in hydrophilic graphite rich in oxygen-containing functional groups.

[0055] S3 two-component synergistic encapsulation: Prepare an 8% (w / w) chitosan aqueous solution and a 10% (w / w) cobalt nitrate aqueous solution. Add the above-mentioned hydrophilic graphite to the chitosan aqueous solution, with a mass ratio of 10 ml: 100 g. Then add 6 wt% (w / w) of cobalt nitrate aqueous solution, which is the total mass of the chitosan solution and hydrophilic graphite. Ultrasonically vibrate for 60 min at an ultrasonic power of 0.24 kW and an ultrasonic frequency of 40 kHz to form a homogeneous precursor mixture.

[0056] S4 freeze-drying: The precursor mixture was transferred to a freeze dryer and freeze-dried at -50°C and a vacuum of <10Pa for 48 hours to remove moisture and obtain a black, fluffy precursor powder.

[0057] S5 Low-Temperature Catalytic Heat Treatment: The precursor powder was placed in a tube furnace, and nitrogen gas with a concentration of ≥99% was introduced. The temperature was increased to 500℃ at a heating rate of 5℃ / min, held for 6 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0058] S6 Post-Processing: Preliminary regenerated graphite and 2.5 mol / L hydrochloric acid solution were ultrasonically vibrated at room temperature for 30 min at a solid-liquid ratio of 1 g: 15 ml, followed by vacuum filtration and drying to obtain high-performance regenerated graphite anode material.

[0059] The prepared recycled graphite anode material was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form a lithium-ion battery anode. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0060] The structure and performance characterization of this embodiment 2 are as follows: Depend on Figure 6 Electrochemical data show that the discharge capacity at 2C rate in Example 2 reaches 207.05 mAh / g. This indicates that the regeneration and repair method described in this application can effectively repair decommissioned graphite and transform it into a high-performance lithium-ion battery anode material.

[0061] Example 3: The method for repairing and regenerating decommissioned graphite in Example 3 includes the following specific steps: S1 Retired Graphite Pretreatment: Decommissioned graphite was placed in a tube furnace and purged with argon gas of ≥99% concentration. The temperature was increased to 500℃ at a rate of 4℃ / min and held for 1.5h to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. The graphite was then cooled to room temperature and subsequently subjected to ultrasonic acid washing at room temperature. The ultrasonic power was 0.20 kW, the ultrasonic frequency was 40 kHz, and 2 mol / L hydrochloric acid was used. The graphite to hydrochloric acid solution ratio was 1 g: 20 ml, and the washing time was 25 min. The resulting purified decommissioned graphite was then obtained by filtration and drying.

[0062] S2 hydrophilic treatment: Hydrogen peroxide with a mass concentration of 30% was prepared. The purified decommissioned graphite was mixed with hydrogen peroxide at a ratio of 10g:50ml and transferred to the inner liner of the reactor. The inner liner of the reactor was then placed in the reactor for sealed hydrothermal treatment at a temperature of 80℃ for 12 hours. After the reaction, the graphite was placed in a plasma cleaner for ultraviolet hydrophilic treatment for 15 minutes. The ultraviolet lamp power was 100W, and the wavelengths of the treated light were 185nm and 254nm. The power of the cleaning machine was 50W. The graphite was then filtered and dried to obtain hydrophilic graphite rich in oxygen-containing functional groups.

[0063] S3 two-component synergistic encapsulation: Prepare a 10wt% ferric nitrate aqueous solution. Add 50g of urea to 1000ml of hydrophilic graphite solution, mix, and then add 50ml of ferric nitrate aqueous solution. Ultrasonically vibrate for 70min at an ultrasonic power of 0.20kw and an ultrasonic frequency of 40KHz to form a homogeneous precursor mixture.

[0064] S4 freeze-drying: The precursor mixture was transferred to a freeze dryer and freeze-dried at -60°C and a vacuum of <10Pa for 24 hours to remove moisture and obtain a black, fluffy precursor powder.

[0065] S5 Low-Temperature Catalytic Heat Treatment: The precursor powder was placed in a tube furnace, and argon gas with a concentration of ≥99% was introduced. The temperature was increased to 600℃ at a heating rate of 7℃ / min, held for 4 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0066] S6 Post-Processing: Preliminary regenerated graphite and 2 mol / L hydrochloric acid were ultrasonically vibrated at room temperature for 15 min at a solid-liquid ratio of 1 g: 20 ml, followed by filtration and drying to obtain a high-performance regenerated graphite anode material.

[0067] The prepared recycled graphite anode material was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form a lithium-ion battery anode. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0068] The structure and performance characterization of this embodiment 3 are as follows: Depend on Figure 1-3 Material structure characterization images show that the TEM image reveals a carbon coating thickness of approximately 1.57 nm. SEM images show a smooth surface of the repaired regenerated graphite, free of obvious cracks and impurities. XPS images also show peaks at approximately 398.3, 400.1, and 401.8 eV, corresponding to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen, respectively. Further analysis... Figure 6 The rate performance comparison shows that the discharge performance of Example 3 at different rates is superior to other examples, with a discharge capacity of 210.96 mAh / g at 2C rate. This demonstrates that the regeneration and repair method of this application can effectively repair decommissioned graphite and make it a high-performance lithium-ion battery anode material.

[0069] Comparative Example 1: S1 retired graphite pretreatment: Decommissioned graphite was placed in a tube furnace under an inert atmosphere and heated to 600°C at a rate of 10°C / min, then held at that temperature for 2 hours to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. It was then cooled to room temperature, and subsequently acid-washed with hydrochloric acid at a solid-liquid ratio of 1g:25ml at room temperature for 30 minutes. The resulting purified decommissioned graphite was then obtained by filtration and drying.

[0070] S2 single-component coating: Prepare an 8% chitosan aqueous solution by adding 10 ml of chitosan aqueous solution to 100 g of purified decommissioned graphite and stirring for 60 min to form a homogeneous precursor mixture.

[0071] S3 drying: The precursor mixture was dried under a vacuum of <10 Pa for 48 h to remove moisture and obtain a black, fluffy precursor powder.

[0072] S4. Heat treatment: The precursor powder was placed in a tube furnace, and nitrogen gas with a concentration of ≥99% was introduced. The temperature was increased to 900℃ at a heating rate of 10℃ / min, held for 2 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0073] S5. Post-processing: The regenerated graphite was initially filtered and dried to obtain the regenerated graphite anode.

[0074] The prepared recycled graphite was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form the negative electrode of a lithium-ion battery. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0075] Test results: The decommissioned graphite in Comparative Example 1 was restored without any hydrophilic treatment, catalytic treatment, or freezing treatment. Figure 4 and Figure 2 As can be seen, the carbon layer on its surface is not uniformly coated, and it is composed of... Figure 6 Electrochemical data show that the discharge capacity of Comparative Example 1 at different rates is lower than that of the above examples. The discharge capacity at 2C rate reaches 159.98 mAh / g, indicating that the temperature required for graphitization is higher without a catalyst, and 900℃ cannot completely graphitize it. In addition, the lack of hydrophilic treatment makes it impossible to uniformly coat the water-soluble nitrogen-containing carbon source, which affects the subsequent electrochemical performance.

[0076] Comparative Example 2: S1 retired graphite pretreatment: Decommissioned graphite was placed in a tube furnace under an inert atmosphere and heated to 500°C at a rate of 3-5°C / min, and held at that temperature for 2 hours to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. It was then cooled to room temperature, and subsequently acid-washed with hydrochloric acid at a solid-liquid ratio of 1g:25ml at room temperature for 30 minutes. The resulting purified decommissioned graphite was then obtained by filtration and drying.

[0077] S2 single-component coating: Prepare a 10 wt% cobalt nitrate solution by adding 10 ml of the cobalt nitrate solution to 100 g of purified decommissioned graphite and mixing for 60 min to form a homogeneous precursor mixture.

[0078] S3 drying: The precursor mixture was dried under a vacuum of <10 Pa for 36 h to remove moisture and obtain a black, fluffy precursor powder.

[0079] S4 Low-Temperature Catalytic Heat Treatment: The precursor powder was placed in a tube furnace, and nitrogen gas with a concentration of ≥99% was introduced. The temperature was increased to 900℃ at a heating rate of 10℃ / min, held for 5 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0080] S5. Post-processing: Preliminary regenerated graphite and hydrochloric acid were mixed and stirred at room temperature with a solid-liquid ratio of 1g:25ml, and then filtered and dried to obtain the regenerated graphite anode.

[0081] The prepared recycled graphite was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form the negative electrode of a lithium-ion battery. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0082] Test results: The decommissioned graphite restored in Comparative Example 2 underwent no hydrophilic treatment, no nitrogen source, and no freezing process. Figure 5 and Figure 2 As can be seen, some tiny cracks still exist on the surface of the regenerated graphite, while... Figure 6 Electrochemical data show that the discharge capacity of Comparative Example 2 at different rates is much lower than that of the above examples. The discharge capacity at 2C rate is only 117.24 mAh / g, indicating that catalyst alone cannot effectively repair decommissioned graphite.

[0083] Comparative Example 3: S1 retired graphite pretreatment: Decommissioned graphite was placed in a tube furnace under an inert atmosphere and heated to 550°C at a rate of 10°C / min, then held at that temperature for 2 hours to remove binders, thickeners, and SEI film decomposition products from the surface of the decommissioned graphite. It was then cooled to room temperature, and subsequently acid-washed with hydrochloric acid at a solid-liquid ratio of 1g:25ml at room temperature for 30 minutes. The treated graphite was then filtered and dried to obtain purified decommissioned graphite.

[0084] S2 hydrophilic treatment: Hydrogen peroxide with a mass concentration of 35% was prepared. The purified graphite was mixed with hydrogen peroxide at a ratio of 1g:10ml and transferred to the inner liner of the reactor. The inner liner of the reactor was then placed in the reactor for sealed hydrothermal treatment at a temperature of 120℃ for 12 hours. After the reaction was completed, the mixture was cooled to room temperature and then filtered and dried to obtain hydrophilic graphite rich in oxygen-containing functional groups.

[0085] S3 single-component coating: Prepare an 8% chitosan aqueous solution by adding 10 ml of chitosan aqueous solution to 100 g of hydrophilic graphite and stirring for 60 min to form a homogeneous precursor mixture.

[0086] S4 drying: The precursor mixture was dried under a vacuum of <10 Pa for 48 h to remove moisture and obtain a black, fluffy precursor powder.

[0087] S5. Heat treatment: The precursor powder was placed in a tube furnace, and nitrogen gas with a concentration of ≥99% was introduced. The temperature was increased to 1100℃ at a heating rate of 10℃ / min, held for 2 hours, and then naturally cooled to room temperature to obtain preliminary regenerated graphite.

[0088] S6. Post-processing: The regenerated graphite was initially filtered and dried to obtain the regenerated graphite anode.

[0089] The prepared recycled graphite was mixed with conductive carbon black and sodium alginate in a ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to form the negative electrode of a lithium-ion battery. A coin cell was assembled with lithium metal as the counter electrode and its electrochemical performance was tested.

[0090] Test results: Depend on Figure 6 As can be seen, the discharge capacity of Comparative Example 3 at different rates is still lower than that of the above examples. The discharge capacity at 2C rate is 159.52 mAh / g, indicating that even with hydrophilic treatment and carbon source coating, the carbon source on the surface is uniformly coated, but due to the lack of a catalyst to reduce the activation energy required for graphitization, the carbon source on the surface cannot be completely graphitized, resulting in a decrease in the electrochemical performance of the regenerated graphite.

[0091] The above embodiments of the present invention are only part of the preferred embodiments of the present invention and should not be construed as limiting the present invention. Any modifications, equivalent substitutions and improvements made by those skilled in the art without departing from the spirit of the present invention shall be within the protection scope of the present invention.

Claims

1. A method for regenerating and repairing decommissioned graphite, characterized in that, Includes the following steps: S1. Pre-treat the decommissioned graphite negative electrode to obtain purified decommissioned graphite; S2. The purified decommissioned graphite obtained in step S1 is subjected to a hydrophilic reaction treatment to obtain a hydrophilic graphite material rich in oxygen functional groups. S3. The hydrophilic graphite material obtained in S2 is mixed with a water-soluble nitrogen-containing biomass carbon source and a metal-based catalyst, and ultrasonically stirred to form a uniform precursor mixture solution. S4. Centrifuge and freeze-dry the precursor mixture solution obtained in step S3 to obtain black precursor powder. S5. The black precursor powder obtained in step S4 is heat-treated under an inert atmosphere to pyrolyze and catalytically graphitize the black precursor powder, so as to repair the decommissioned graphite and form a nitrogen-doped carbon coating layer on the surface to obtain a preliminary regenerated graphite material. S6. The preliminary recycled graphite material obtained in step S5 is subjected to ultrasonic acid washing to finally obtain high-performance recycled graphite material.

2. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, The pretreatment in step S1 includes: performing low-temperature heat treatment under an inert atmosphere to decompose the organic binder and SEI decomposition products on the decommissioned graphite negative electrode, and then using ultrasonic acid washing to remove residual metal impurities from the decommissioned graphite, wherein the mass ratio of decommissioned graphite to acid solution is 1g:15-25ml, the ultrasonic treatment power is 0.12-0.24kw, the ultrasonic frequency is 40KHz, and the acid washing time is 15-40min.

3. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, The hydrophilic reaction treatment in step S2 is as follows: The purified decommissioned graphite and hydrogen peroxide solution were placed in a reaction vessel and subjected to hydrothermal treatment under sealed conditions. The hydrothermal treatment temperature was 80℃~160℃, the time was 12~48h, the mass concentration of hydrogen peroxide was 25~35%, and the mass ratio of purified decommissioned graphite to hydrogen peroxide was 1g:5~10ml; or / and, The purified decommissioned graphite is placed in a vacuum plasma cleaner for ultraviolet hydrophilic treatment. The hydrophilic treatment time is 15-60 minutes, the power of the ultraviolet lamp is 100-300W, the wavelengths of the treated light are 185nm and 254nm, and the power of the cleaner is 10-200W.

4. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, In step S3, the water-soluble nitrogen-containing carbon source includes at least one of natural high-molecular-weight polysaccharides, synthetic polymers, small-molecule organic compounds, and ionic liquids containing amino and / or amide groups; the metal-based catalyst includes nitrates, acetates, chlorides, citrates, or oxalates containing at least one element from cobalt, iron, nickel, manganese, and copper; wherein the mass of the water-soluble nitrogen-containing carbon source is 3%-10 wt% of the mass of the hydrophilic graphite material; and the amount of the metal-based catalyst added is 3%-10 wt% of the total mass of the nitrogen-containing biomass carbon source and the hydrophilic graphite material.

5. The method for regenerating and repairing decommissioned graphite as described in claim 1 or 4, characterized in that, The ultrasonic processing power in step S3 is 0.12–0.24 kW, the ultrasonic frequency is 40 kHz, and the oscillation and stirring time is 40–70 min.

6. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, The S4 step involves freezing at a temperature of -50℃ to -60℃, a vacuum degree of <10Pa, and a freeze-drying time of 36 to 48 hours.

7. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, The heat treatment temperature in step S5 is 500–900℃, the heating rate is 3–10℃ / min, and the holding time is 1–6h.

8. The method for regenerating and repairing decommissioned graphite as described in claim 1, characterized in that, The ultrasonic acid washing process in step S6 has a power of 0.12kw to 0.24kw, an ultrasonic frequency of 40KHz, a time of 10-30min, and a ratio of 1g to 15-25ml for the initial regenerated graphite material.

9. A recycled graphite anode material, characterized in that, Obtained by the method described in any one of claims 1-8.

10. A lithium battery, characterized in that, It includes the recycled graphite anode material as described in claim 9.

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