A method for recycling negative electrode graphite of retired nickel cobalt manganese oxide batteries

Abstract

This application relates to the field of lithium-ion battery resource recycling, and more particularly to a method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese (NiCoMn) lithium-ion batteries. This method effectively removes impurities from the graphite powder, repairs surface defects, and improves its discharge capacity and initial efficiency through steps such as ultrasonic de-powdering, heat treatment, acid leaching, washing, and modified hard carbon resin coating of the graphite anode sheet from retired NiCoMn battery. This achieves efficient recycling and reuse of NiCoMn battery anode graphite. The method of this application not only effectively recycles and reuses retired NiCoMn battery anode graphite but also improves the purity and performance of lithium-ion battery anode graphite powder, increases battery cycle life and energy density, and has good economic and environmental benefits.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery resource recycling, and in particular to a method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium batteries. Background Technology

[0002] With economic development, the production of lithium-ion batteries has surged. According to data released by the China Power Battery Alliance, the installed capacity of nickel-cobalt-manganese lithium-ion batteries exceeded 100 GWh in 2023, with production exceeding 200 GWh. In the near future, a large number of nickel-cobalt-manganese lithium-ion batteries will be retired. Graphite, as the most commonly used negative electrode material in lithium batteries, accounts for over 90% of the negative electrode materials. Due to the limited lifespan of lithium batteries, the amount of graphite material used in the negative electrodes of retired lithium-ion batteries will increase year by year, placing enormous pressure on the environment and resource utilization.

[0003] Currently, the recycling of graphite anodes from lithium nickel cobalt manganese oxide batteries typically employs high-temperature calcination and chemical leaching. However, high-temperature calcination generates a large amount of harmful gases that pollute the environment, and chemical leaching, which involves simple acid leaching, cannot deeply purify the impurities inside the graphite. The binder, metal oxides, and residual lithium between the graphite layers cannot be completely removed.

[0004] Even after prolonged charge-discharge cycles, the graphite anode material in failed lithium-ion batteries retains its complete crystal lattice structure. Due to the extended reaction process, some metal ions dissolve from the lithium nickel cobalt manganese oxide cathode, migrate, and deposit on the graphite anode. Furthermore, during the initial cycle, the electrolyte reacts with the graphite to form a solid electrolyte interphase (SEI) film. Effective removal of impurities and the surface SEI is crucial for graphite recycling. Improving the discharge capacity and initial efficiency of the recycled graphite anode material is also essential for its reuse as a lithium-ion battery anode material. Summary of the Invention

[0005] To address the shortcomings of current technologies, this application provides a method for recycling and reusing waste lithium iron phosphate batteries. This method can effectively remove impurity elements and surface SEI. By using modified hard carbon resin to coat the secondary purified graphite powder, its surface defects are repaired, and its discharge capacity and initial efficiency are improved, thus achieving efficient recycling and reuse of graphite, the negative electrode of nickel cobalt manganese oxide batteries.

[0006] This application provides a method for recycling and reusing waste lithium iron phosphate batteries, employing the following technical solution:

[0007] A method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries includes the following steps:

[0008] S1. Select retired nickel-cobalt-manganese lithium batteries, perform deep discharge, dismantle and sort them to obtain nickel-cobalt-manganese lithium positive electrode sheets, graphite negative electrode sheets, separators and shells;

[0009] S2. Place the graphite negative electrode sheet in an ethanol aqueous solution for ultrasonic de-powdering, filtration, drying, pulverization, and sieving using a 100-325 mesh sieve to obtain graphite powder with a particle size of 5-150μm.

[0010] S3. Calcine the graphite powder at 100-400℃ for 3-8 hours to remove the binder and electrolyte remaining on the surface of the graphite powder and to convert the copper element into oxide. Cool to room temperature to obtain the first calcined graphite powder.

[0011] S4. The first calcined graphite powder is added to acid solution A for leaching reaction at a temperature of 30-60℃ for 0.5-3 hours to remove copper and some other metal oxides. Then, the solid and liquid are separated and dried to obtain the preliminarily purified graphite powder.

[0012] S5. The graphite powder after initial purification is heat-treated under an inert atmosphere to reduce nickel oxide, cobalt oxide, manganese oxide and other metal oxide impurities to elemental or low-valence oxides by utilizing the reducing properties of graphite carbon. After cooling to room temperature, the second calcined graphite powder is obtained.

[0013] S6. Add the second-calcined graphite powder to acid solution B for leaching reaction at a temperature of 30-60℃ for 3-5 hours. Then, separate the solid and liquid phases. Wash the solid repeatedly with deionized water until the pH of the washing water reaches 6-7. Dry the solid at 80-200℃ for 3-8 hours to obtain the second-purified graphite powder.

[0014] S7. The secondary purified graphite powder and modified hard carbon resin are stirred and mixed evenly at 150-300℃ to obtain a mixed powder. The mixed powder is then calcined at high temperature under an inert atmosphere and cooled to obtain regenerated graphite powder.

[0015] S8. The recycled graphite powder is crushed, sieved, and demagnetized to obtain lithium-ion battery negative electrode graphite powder.

[0016] By employing the above technical solution, step S1 involves dismantling retired batteries to obtain graphite negative electrode sheets. This step provides raw materials for subsequent graphite recycling. Step S2 involves de-powdering and sieving the graphite negative electrode sheets to obtain graphite powder of a certain particle size. This step helps improve the efficiency of subsequent heat treatment and leaching reactions. Step S3 involves calcining to remove residues from the surface of the graphite powder and converting copper into oxides. This step helps reduce impurities in the graphite powder. Step S4 involves acid leaching to further remove copper and other metal oxides, obtaining preliminarily purified graphite powder. This step helps further improve the purity of the graphite powder. Step S5 involves heat treatment under an inert atmosphere, utilizing the reducing properties of graphite carbon to reduce other metal oxide impurities to elemental or low-valence oxides. This step helps further reduce the impurity content in the graphite powder. Step S6 involves acid leaching and washing with deionized water to further remove impurities, obtaining secondary purified graphite powder. This step significantly improves the purity of the graphite powder. Step S7 involves mixing the graphite powder with modified hard carbon resin and then calcining it at high temperature to repair surface defects and increase the channels for lithium-ion migration. This step helps improve the electrochemical performance of the recycled graphite powder. Step S8 involves pulverizing, sieving, and demagnetizing the recycled graphite powder to obtain lithium-ion battery anode graphite powder. This step enables the recycled graphite powder to meet the requirements of lithium-ion batteries. In summary, these steps, through heat treatment, acid leaching, washing, mixing, and calcination, effectively remove impurities from the graphite powder, repair its surface defects, and improve its discharge capacity and initial efficiency, achieving efficient recycling and reuse of nickel-cobalt-manganese lithium oxide battery anode graphite.

[0017] Preferably, in step S2, the volume ratio of ethanol to water in the ethanol-water solution is 1:2-5; the process parameters for ultrasonic de-powdering are: ultrasonic power of 5-10KW, ultrasonic temperature of 25-35℃, and ultrasonic time of 30-60min; the drying temperature is 80-100℃, and the drying time is 8-12 hours.

[0018] By employing the above technical solution, an appropriate mixing ratio of ethanol and water helps to effectively remove the binder and electrolyte from the surface of the graphite negative electrode. The process parameters for ultrasonic de-powdering, such as power, temperature, and time, affect the effectiveness of ultrasound on the graphite negative electrode; appropriate parameter settings can improve de-powdering efficiency and ensure the quality of the graphite powder. The drying process helps to remove residual moisture, ensuring the graphite powder reaches an appropriate degree of dryness.

[0019] Preferably, in step S4, the concentration of acid solution A is 0.5-3 mol / L, and acid solution A is either sulfuric acid or hydrochloric acid; the mass-to-volume ratio of the first calcined graphite powder to acid solution A is 15-50 g: 1 L.

[0020] By adopting the above technical solution, the concentration and ratio of acid solution A play a crucial role in step S4. The concentration of acid solution A is selected within the range of 0.5-3 mol / L, which can effectively dissolve copper and other metal oxides, achieving the leaching reaction of graphite powder. Sulfuric acid or hydrochloric acid, as one of the choices for acid solution A, can effectively dissolve metal oxides, helping to separate the desired graphite powder. Furthermore, setting the mass-to-volume ratio of the first calcined graphite powder to acid solution A within the range of 15-50 g:1 L ensures sufficient reaction contact area, improves leaching efficiency, and guarantees preliminary purification of the graphite powder. Therefore, by rationally setting the concentration and ratio of acid solution A, the effective removal and separation of metal oxides in graphite powder can be achieved, providing a good foundation for subsequent graphite powder re-purification and remediation, ultimately realizing the efficient recycling and reuse of graphite from retired nickel-cobalt-manganese lithium-ion battery anodes.

[0021] Preferably, in step S5, the inert atmosphere is either nitrogen or argon; the heat treatment process conditions are: temperature 600-900℃, time 3-6 hours.

[0022] By employing the above-mentioned technical solution and using an inert atmosphere such as nitrogen or argon during the heat treatment process, the oxidation reaction of recycled graphite powder with oxygen at high temperatures can be effectively prevented, thus maintaining the stability of the graphite powder's properties and structure. This helps to avoid the impact of oxidation on the subsequent utilization of recycled graphite powder. The selection of heat treatment temperature and time directly affects the physical and chemical properties of recycled graphite powder. Heat treatment within the temperature range of 600-900℃ can effectively reduce metal oxides such as nickel oxide, cobalt oxide, and manganese oxide to elemental or low-valence oxides, while optimizing their crystal structure. Furthermore, a heat treatment time of 3-6 hours is sufficient to ensure the full progress of the reduction reaction, thereby obtaining high-quality recycled graphite powder. Therefore, by rationally selecting the inert atmosphere and heat treatment process conditions, the quality and reuse efficiency of recycled graphite powder can be effectively improved, further realizing the efficient recycling and reuse of graphite for nickel-cobalt-manganese lithium oxide batteries.

[0023] Preferably, in step S6, the concentration of acid solution B is 2-5 mol / L, and acid solution B is either sulfuric acid or hydrochloric acid; the mass-to-volume ratio of the second calcined graphite powder to acid solution B is 10-30 g: 1 L.

[0024] The main purpose of using acid solution B in the leaching reaction, employing the above technical solution, is to further remove residual impurities from the graphite powder, thereby improving its purity and quality. Specifically, an acid solution B concentration in the range of 2-5 mol / L can effectively dissolve residual organic matter, metal oxides, and other impurities in the graphite powder, thus achieving a secondary purification effect. Sulfuric acid or hydrochloric acid is typically chosen as acid solution B, as it can effectively remove metal oxides and organic matter. Furthermore, by controlling the mass-to-volume ratio of the second-calcined graphite powder to acid solution B to be 10-30 g:1 L during the use of acid solution B, optimal leaching results can be achieved, ensuring improved product purity and quality.

[0025] Preferably, in step S7, the inert atmosphere is either nitrogen or argon; the high-temperature calcination process conditions are: heating to 1500-2500℃ at a heating rate of 2-10℃ / min and holding at that temperature for 3-15 hours.

[0026] By adopting the above technical solution, the purpose of using an inert atmosphere (nitrogen or argon) for high-temperature calcination in step S7 is to ensure that the graphite powder is calcined in an oxygen-free environment, avoiding the influence of oxygen, reducing the occurrence of oxidation reactions, and thus maintaining the purity and structural stability of the graphite powder. The setting of the high-temperature calcination process conditions, namely the control of the heating rate and holding time, has a significant impact on the crystal structure and physical properties of the recycled graphite powder. Controlling the heating rate and high-temperature holding facilitates the volatilization or decomposition of residual excess impurities and elements in the graphite powder, further improving its purity. Controlling the holding time ensures uniform heating of the internal structure of the graphite powder and the formation of thermal stability, further enhancing its structural stability and electrode performance. The resulting recycled graphite powder has a purer chemical composition and superior electrochemical performance, and can be used as a negative electrode material for lithium-ion batteries, thus achieving efficient reuse and resource recycling of graphite powder.

[0027] Preferably, in step S7, the mass ratio of the secondary purified graphite powder to the modified hard carbon resin is 100:3-8.

[0028] By employing the above technical solution and controlling the amount of modified hard carbon resin, the thickness and uniformity of the coating layer can be effectively adjusted. Too much hard carbon resin may result in an excessively thick coating layer, affecting the contact and electron conduction between graphite particles, while too little may fail to completely repair surface defects in the graphite powder. Therefore, an appropriate mass ratio can achieve the best coating effect. Modified hard carbon resin, as a coating material, can fill and repair surface defects in graphite powder, improving its electrochemical performance and cycle stability. An appropriate ratio ensures that the hard carbon resin fully covers the graphite powder surface, repairing its active sites and reducing electrode polarization. Hard carbon resin possesses certain electrical conductivity and excellent chemical stability; its coating layer can increase the migration rate of lithium ions on the graphite powder surface, improving the electrode's discharge capacity, initial efficiency, and cycle life.

[0029] Preferably, in step S7, the modified hard carbon resin is composed of asphalt powder, modified phenolic resin and silicon carbide in a mass ratio of (10-20):100:(3-5), and the particle size of the silicon carbide is 3-5 μm.

[0030] By employing the above technical solutions, asphalt powder, as a carbon source, helps to generate a soft carbon layer, increasing the conductivity of graphite powder and constructing a loose structure, thereby improving capacity and conductivity. The relatively soft carbonaceous structure of asphalt can compensate for the internal stress of hard carbon and solid carbon during lithium-ion insertion and extraction, preventing the detachment of graphite powder particles and structural collapse. Modified phenolic resin, with its excellent adhesion and chemical stability, can form a hard carbon coating layer, improving the structural stability, durability, and interfacial properties of recycled graphite powder. Furthermore, modified phenolic resin facilitates lithium-ion diffusion and transport, promoting electrochemical reactions and thus improving battery performance, cycle life, and initial efficiency. Silicon carbide helps to further enhance the conductivity and mechanical strength of the hard carbon coating layer, optimizing its pore structure and surface properties. Fine silicon carbide particles can fill the microscopic voids in the hard carbon layer, improving its density and stability. Therefore, the combined action of these three components in the modified hard carbon resin not only rationally controls the structure and performance of the coating layer and optimizes the surface properties of the recycled graphite powder and battery performance, but also promotes lithium-ion migration and intercalation, thereby improving the battery's cycle stability, capacity retention, and electrochemical efficiency. This synergistic effect provides crucial technical support and assurance for the efficient recycling and reuse of graphite in nickel-cobalt-manganese lithium-ion batteries.

[0031] Preferably, the modified phenolic resin is prepared by adding 100-110 parts by mass of thermoplastic phenolic resin, 1-2 parts by mass of phosphoric acid and 5-8 parts by mass of boron nitride to 1000 parts by mass of a solution composed of isopropanol and water in a volume ratio of 2:1. After stirring evenly, the solution is transferred to a reactor and reacted at 140°C for 6-8 hours. After filtration, the solution is vacuum dried at 85°C for 24-30 hours to obtain the modified phenolic resin, wherein the boron nitride has a particle size of 1-5 μm.

[0032] The modified phenolic resin preparation method, employing the above technical solution, involves adding thermoplastic phenolic resin, phosphoric acid, and boron nitride to a solution composed of isopropanol and water, followed by a series of reaction steps to obtain the modified phenolic resin. Thermoplastic phenolic resin, as the base material for modified phenolic resin, possesses good thermal and chemical stability, maintaining structural stability during battery operation. Phosphoric acid promotes the crosslinking and curing of the phenolic resin during preparation, enhancing its thermal and chemical stability. The addition of boron nitride improves the lubricity of the phenolic resin, which is beneficial for improving the processing performance of the battery negative electrode material. Utilizing the lubricity of boron nitride, it promotes the penetration of boron nitride into the mutually attracted graphite fine powder particles, thereby improving the sphericity and density of the negative electrode material, resulting in a higher discharge capacity and initial efficiency for the finished negative electrode material. The mixed solution of isopropanol and water effectively dissolves and disperses the phenolic resin and boron nitride, ensuring uniform reaction. The modified phenolic resin obtained by the above preparation method is further prepared into a modified hard carbon resin. When mixed and sintered with secondary purified graphite powder, it can form loose and porous soft carbon and hard carbon with a hard texture. This helps to repair the surface defects of graphite powder, increase the channels for lithium ion migration, and thus improve the discharge capacity and initial efficiency of the battery. At the same time, the presence of modified phenolic resin is also conducive to lithium ion diffusion, further improving the electrochemical performance of the battery.

[0033] Preferably, in step S7, the modified hard carbon resin is prepared by mixing asphalt powder, modified phenolic resin and silicon carbide evenly, and then granulating and crushing it at 200-220°C using a twin-screw extruder to obtain modified hard carbon resin with a D50 particle size of 7μm.

[0034] By adopting the above technical solution, the twin-screw extruder can uniformly mix and granulate the raw materials at a controlled temperature during the preparation process, ensuring the homogeneity and consistency of the modified hard carbon resin, which is crucial for the performance of the final product.

[0035] In summary, the beneficial technical effects of this application are as follows:

[0036] 1. Improved leaching efficiency of impurity elements: By combining heat treatment and acid leaching, the method of this application can effectively remove impurity elements from graphite powder, including metal oxides such as copper, nickel, cobalt, and manganese, as well as other surface contaminants. This process helps to reduce the negative impact of these impurities on the performance of graphite powder for lithium-ion battery anodes.

[0037] 2. Removal of the surface SEI layer: The surface SEI (solid electrolyte interface) layer is formed during battery cycling and affects the electrochemical performance of the battery. The method in this application can effectively remove the SEI layer and restore the activity of the graphite anode.

[0038] 3. Repairing surface defects of graphite powder: By coating the secondary purified graphite powder with modified hard carbon resin, its surface defects can be repaired, increasing the channels for lithium ion migration, thereby improving the discharge capacity and initial efficiency of the graphite powder in the negative electrode of lithium-ion batteries.

[0039] 4. Improved electrochemical performance: The addition of silicon carbide can enhance the conductivity and mechanical strength of the carbon layer after the pyrolysis of modified hard carbon resin, while the presence of modified phenolic resin is conducive to the diffusion of lithium ions, further improving the electrochemical performance of the battery.

[0040] 5. Improve the sphericity and density of the negative electrode material: By utilizing the lubricity of boron nitride, it can be promoted to penetrate between mutually attracted graphite fine powder particles, thereby improving the sphericity and density of the negative electrode material, thus enabling the finished negative electrode material to have higher discharge capacity and first-time efficiency.

[0041] 6. Achieving efficient recycling and reuse: The method of this application not only improves the recycling efficiency of graphite anodes from retired lithium batteries, but also achieves efficient reuse, reducing dependence on original resources, lowering production costs, and also has positive significance for environmental protection.

[0042] 7. Controllable preparation process: Continuous physical and chemical treatment methods are adopted to control the process parameters of each step, such as temperature, time, and solution concentration, to ensure the stability and consistency of product quality. Detailed Implementation

[0043] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0044] Preparation Example 1: Preparation of Modified Phenolic Resin

[0045] The modified phenolic resin was prepared by adding 1050g of thermoplastic phenolic resin, 15g of phosphoric acid and 65g of boron nitride to 10000g of a solution composed of isopropanol and water in a volume ratio of 2:1. After stirring evenly, the solution was transferred to a reactor and reacted at 140℃ for 7h. After filtration, the solution was vacuum dried at 85℃ for 27h to obtain modified phenolic resin with a particle size of 1-5μm.

[0046] Preparation Example 2: Preparation of Modified Hard Carbon Resin

[0047] The modified hard carbon resin is prepared by mixing 100g of asphalt powder, 1000g of modified phenolic resin and 30g of silicon carbide evenly, and then granulating and crushing it at 200℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0048] Preparation Example 3: Preparation of Modified Hard Carbon Resin

[0049] The modified hard carbon resin is prepared by mixing 200g of asphalt powder, 1000g of modified phenolic resin and 50g of silicon carbide evenly, and then granulating and crushing it at 220℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0050] Preparation Example 4: Preparation of Modified Hard Carbon Resin

[0051] The modified hard carbon resin is prepared by mixing 150g of asphalt powder, 1000g of modified phenolic resin and 40g of silicon carbide evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0052] Preparation of Comparative Example 1: Preparation of Modified Hard Carbon Resin

[0053] The modified hard carbon resin is prepared by mixing 1150g of asphalt powder and 40g of silicon carbide evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0054] Preparation of Comparative Example 2: Preparation of Modified Hard Carbon Resin

[0055] The modified hard carbon resin is prepared by mixing 1150g of modified phenolic resin and 40g of silicon carbide evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0056] Preparation of Comparative Example 3: Modified Hard Carbon Resin

[0057] The modified hard carbon resin is prepared by mixing 150g of asphalt powder and 1000g of modified phenolic resin evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0058] Preparation of Comparative Example 4: Modified Hard Carbon Resin

[0059] The modified hard carbon resin is prepared by mixing 150g of asphalt powder, 1000g of thermoplastic phenolic resin and 40g of silicon carbide evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0060] Preparation of Comparative Example 5: Modified Hard Carbon Resin

[0061] The modified hard carbon resin is prepared by mixing 150g of asphalt powder, 1000g of thermoplastic phenolic resin, 65g of boron nitride and 40g of silicon carbide evenly, and then granulating and crushing it at 210℃ using a twin-screw extruder to obtain a modified hard carbon resin with a D50 particle size of 7μm; the silicon carbide has a particle size of 3-5μm.

[0062] Example 1

[0063] A method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries includes the following steps:

[0064] S1. Select retired nickel-cobalt-manganese lithium batteries, perform deep discharge, dismantle and sort them to obtain nickel-cobalt-manganese lithium positive electrode sheets, graphite negative electrode sheets, separators and shells;

[0065] S2. Place 2000g of graphite negative electrode sheet into 20L of ethanol aqueous solution for ultrasonic de-powdering, filter, dry at 80℃ for 12 hours, pulverize, and sieve using a 100-mesh sieve to obtain graphite powder with a particle size of 5-150μm; the volume ratio of ethanol to water in the ethanol aqueous solution is 1:2; the ultrasonic de-powdering process parameters are: ultrasonic power 5KW, ultrasonic temperature 35℃, and ultrasonic time 60min.

[0066] S3. Calcine the graphite powder at 100℃ for 8 hours to remove the binder and electrolyte remaining on the surface of the graphite powder and to convert the copper element into oxide. Cool to room temperature to obtain the first calcined graphite powder.

[0067] S4. Add 150g of first-calcined graphite powder to 10L of 0.5mol / L sulfuric acid for leaching reaction at 60℃ for 3 hours to remove copper and some other metal oxides. Then filter and dry to obtain preliminarily purified graphite powder.

[0068] S5. The graphite powder after the first purification is calcined at 600℃ under a nitrogen atmosphere for 6 hours. The reducing properties of graphite carbon are used to reduce nickel oxide, cobalt oxide, manganese oxide and other metal oxide impurities to elemental or low-valence oxides. The mixture is then cooled to room temperature to obtain the second calcined graphite powder.

[0069] S6. Add 100g of the second-calcined graphite powder to 10L of 2mol / L sulfuric acid for leaching reaction at 30℃ for 5 hours. Then filter, and wash the solid repeatedly with deionized water until the pH of the washing water reaches 6. After drying at 80℃ for 8 hours, the second-purified graphite powder is obtained.

[0070] S7. 100g of secondary purified graphite powder and 3g of modified hard carbon resin are stirred and mixed evenly at 150°C to obtain a mixed powder. Then, the mixed powder is heated to 1500°C at a heating rate of 2°C / min under a nitrogen atmosphere and kept at that temperature for 15 hours. After cooling, regenerated graphite powder is obtained. The modified hard carbon resin is the modified hard carbon resin prepared in Preparation Example 2.

[0071] S8. The recycled graphite powder is crushed, sieved, and demagnetized to obtain lithium-ion battery negative electrode graphite powder.

[0072] Example 2

[0073] A method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries includes the following steps:

[0074] S1. Select retired nickel-cobalt-manganese lithium batteries, perform deep discharge, dismantle and sort them to obtain nickel-cobalt-manganese lithium positive electrode sheets, graphite negative electrode sheets, separators and shells;

[0075] S2. Place 2000g of graphite negative electrode sheet into 20L of ethanol aqueous solution for ultrasonic de-powdering, filter, dry at 100℃ for 8 hours, pulverize, and sieve using a 325-mesh sieve to obtain graphite powder with a particle size of 5-45μm; the volume ratio of ethanol to water in the ethanol aqueous solution is 1:5; the ultrasonic de-powdering process parameters are: ultrasonic power 10KW, ultrasonic temperature 35℃, and ultrasonic time 30min.

[0076] S3. Calcine the graphite powder at 400℃ for 3 hours to remove the binder and electrolyte remaining on the surface of the graphite powder and to convert the copper element into oxide. Cool to room temperature to obtain the first calcined graphite powder.

[0077] S4. Add 500g of first-calcined graphite powder to 10L of 3mol / L hydrochloric acid for leaching reaction at 60℃ for 0.5 hours to remove copper and some other metal oxides. Then filter and dry to obtain preliminarily purified graphite powder.

[0078] S5. The graphite powder after the first purification is calcined at 900℃ in an argon atmosphere for 3 hours. The reducing properties of graphite carbon are used to reduce nickel oxide, cobalt oxide, manganese oxide and other metal oxide impurities to elemental or low-valence oxides. The mixture is then cooled to room temperature to obtain the second calcined graphite powder.

[0079] S6. Add 300g of the second-calcined graphite powder to 10L of 5mol / L hydrochloric acid for leaching reaction at 60℃ for 3 hours. Then filter, and wash the solid repeatedly with deionized water until the pH of the washing water reaches 7. After drying at 200℃ for 3 hours, the second-purified graphite powder is obtained.

[0080] S7. 100g of secondary purified graphite powder and 8g of modified hard carbon resin are stirred and mixed evenly at 300°C to obtain a mixed powder. Then, the mixed powder is heated to 2500°C at a heating rate of 10°C / min under an argon atmosphere and kept at that temperature for 3 hours. After cooling, regenerated graphite powder is obtained. The modified hard carbon resin is the modified hard carbon resin prepared in Preparation Example 3.

[0081] S8. The recycled graphite powder is crushed, sieved, and demagnetized to obtain lithium-ion battery negative electrode graphite powder.

[0082] Example 3

[0083] A method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries includes the following steps:

[0084] S1. Select retired nickel-cobalt-manganese lithium batteries, perform deep discharge, dismantle and sort them to obtain nickel-cobalt-manganese lithium positive electrode sheets, graphite negative electrode sheets, separators and shells;

[0085] S2. Place 2000g of graphite negative electrode sheet into 20L of ethanol aqueous solution for ultrasonic de-powdering, filter, dry at 90℃ for 10 hours, pulverize, and sieve using a 200-mesh sieve to obtain graphite powder with a particle size of 5-75μm; the volume ratio of ethanol to water in the ethanol aqueous solution is 1:3; the ultrasonic de-powdering process parameters are: ultrasonic power 8KW, ultrasonic temperature 30℃, and ultrasonic time 45min.

[0086] S3. Calcine the graphite powder at 300℃ for 4 hours to remove the binder and electrolyte remaining on the surface of the graphite powder and to convert the copper element into oxide. Cool to room temperature to obtain the first calcined graphite powder.

[0087] S4. Add 400g of first-calcined graphite powder to 10L of 2mol / L sulfuric acid or hydrochloric acid for leaching reaction. The reaction temperature is 40℃ and the reaction time is 1 hour to remove copper and some other metal oxides. Then, centrifuge to separate the solid and liquid, and dry to obtain the preliminarily purified graphite powder.

[0088] S5. The graphite powder after the first purification is calcined at 750°C under a nitrogen atmosphere for 4.5 hours. The reducing properties of graphite carbon are used to reduce nickel oxide, cobalt oxide, manganese oxide and other metal oxide impurities to elemental or low-valence oxides. The mixture is then cooled to room temperature to obtain the second calcined graphite powder.

[0089] S6. Add 200g of second-calcined graphite powder to 10L of 3.5mol / L sulfuric acid for leaching reaction at 50℃ for 4 hours. Then, centrifuge to separate the solid and liquid. The solid is washed multiple times with deionized water until the pH of the washing water reaches 6.7. After drying at 150℃ for 5 hours, secondary purified graphite powder is obtained.

[0090] S7. 100g of secondary purified graphite powder and 6g of modified hard carbon resin are stirred and mixed evenly at 230°C to obtain a mixed powder. Then, the mixed powder is heated to 2100°C at a heating rate of 6°C / min under a nitrogen atmosphere and kept at that temperature for 7 hours. After cooling, regenerated graphite powder is obtained. The modified hard carbon resin is the modified hard carbon resin prepared in Preparation Example 4.

[0091] S8. The recycled graphite powder is crushed, sieved, and demagnetized to obtain lithium-ion battery negative electrode graphite powder.

[0092] Comparative Example 1

[0093] Similar to Example 3, except that step S5 is not performed; that is, step S6 is performed directly after step S4 is completed.

[0094] Comparative Example 2

[0095] Similar to Example 3, except that the modified hard carbon resin is the same as the modified hard carbon resin prepared in Comparative Example 1.

[0096] Comparative Example 3

[0097] Similar to Example 3, except that the modified hard carbon resin is the same as the modified hard carbon resin prepared in Comparative Example 2.

[0098] Comparative Example 4

[0099] Similar to Example 3, except that the modified hard carbon resin is the same as the modified hard carbon resin prepared in Comparative Example 3.

[0100] Comparative Example 5

[0101] Similar to Example 3, except that the modified hard carbon resin is the same as the modified hard carbon resin prepared in Comparative Example 4.

[0102] Comparative Example 6

[0103] Similar to Example 3, except that the modified hard carbon resin is the same as the modified hard carbon resin prepared in Comparative Example 5.

[0104] Performance testing

[0105] 1. Metal impurity testing: Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to analyze the metal impurities in the graphite powder (i.e. waste graphite powder), the secondary purified graphite powder, and the lithium-ion battery negative electrode graphite powder obtained in Example 3 and Comparative Example 1. The results are shown in Table 1 and Table 2.

[0106] 2. Physicochemical property tests

[0107] The lithium-ion battery negative electrode graphite powders obtained in Examples 1 and 3, and Comparative Examples 1-6, as well as untreated waste graphite powder, were used as reference examples for the following performance tests, and the results are shown in Table 3.

[0108] The particle size D50 was measured by laser method using a Malvern Mastersizer 3000 instrument.

[0109] The tap density was measured using a BT-303 tap density tester.

[0110] The specific surface area is the BET specific surface area, which was measured by nitrogen adsorption method using a JW-DX instrument.

[0111] Moisture content was tested according to GB / T 3521-2008;

[0112] The magnetic material was measured using a ThermoFisher iCAP PRO X instrument;

[0113] Electrochemical performance testing: The negative electrode mixture of lithium-ion batteries, graphite powder, Super P, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC), was mixed uniformly at a weight percentage of 95.4:1:1.8:1.8. Water was then added, and the mixture was coated onto copper foil. The coated electrode was then vacuum-dried in a 120℃ vacuum drying oven for 4 hours. The electrolyte was 1 mol / L LiPF6+EC:DEC:DMC = 1:1:1 (volume ratio). A lithium metal sheet was used as the counter electrode, and a polypropylene microporous membrane was used as the separator. CR2032 coin cells were assembled in an argon-filled dry glove box. Testing was conducted on the Xinwei Battery Testing System, with a charge / discharge voltage range of 0.001-2V and a charge / discharge rate of 0.1C.

[0114] Table 1 Metal impurity content in Example 3

[0115]

[0116] Table 2 Comparative Example 1 Metal Impurity Content

[0117]

[0118] Table 3 Performance indicators of graphite powder for lithium-ion battery anode

[0119]

[0120]

[0121] Analyzing the data in Tables 1 and 2, we can see that:

[0122] 1) The main impurity elements in graphite powder (i.e. waste graphite) are nickel, cobalt, manganese, copper, aluminum, etc., and their sources are as follows: aluminum and copper come from the positive and negative current collectors, respectively, while nickel, cobalt and manganese come from the positive electrode; and the SEI film on the graphite surface is composed of organic and inorganic lithium salts.

[0123] 2) The recycling method for retired nickel-cobalt-manganese lithium oxide battery negative electrode graphite of this application, through a combination of heat treatment and acid leaching, can effectively remove impurity elements from the graphite powder, including metal oxides such as copper, nickel, cobalt, and manganese, as well as other surface contaminants. This process helps to reduce the negative impact of these impurities on the performance of lithium-ion battery negative electrode graphite powder.

[0124] Analyzing the data in Table 3, we can see that:

[0125] 1) The lithium-ion battery negative electrode graphite powder obtained in Examples 1-3 of this application has a discharge capacity that recovers from 290.4 mAh / g to 343.5-346.3 mAh / g and an initial efficiency that recovers from 66.6% to over 93%, reaching the level of commercial application.

[0126] 2) The performance comparison analysis of the lithium-ion battery negative electrode graphite powder obtained by Example 3 and Comparative Example 1 shows that the combination of heat treatment and acid leaching can effectively remove impurity elements in graphite powder, thereby improving the discharge capacity and first-time efficiency of lithium-ion battery negative electrode graphite powder.

[0127] 3) The performance comparison analysis of the lithium-ion battery negative electrode graphite powders obtained in Example 3 and Comparative Examples 2-4 shows that the modified hard carbon resin prepared in Example 4, by utilizing the synergistic effect between pitch powder, modified phenolic resin and silicon carbide, can not only reasonably control the structure and performance of the coating layer and optimize the surface properties and battery performance of the recycled graphite powder, but also promote the migration and intercalation of lithium ions, thereby improving the discharge capacity and first-time efficiency of the lithium-ion battery negative electrode graphite powder.

[0128] 4) The performance comparison analysis of the lithium-ion battery negative electrode graphite powder obtained in Example 3 and Comparative Example 5 shows that the modified phenolic resin prepared in this application, after being further prepared into modified hard carbon resin, can form loose and porous soft carbon and hard carbon when mixed and sintered with secondary purified graphite powder. This helps to repair the surface defects of graphite powder, increase the channels for lithium-ion migration, and thus improve the discharge capacity and first efficiency of lithium-ion battery negative electrode graphite powder.

[0129] 5) A comparative analysis of the performance of lithium-ion battery negative electrode graphite powders obtained in Example 3 and Comparative Example 6 shows that the modified hard carbon resin prepared by directly mixing 150g of asphalt powder, 1000g of thermoplastic phenolic resin, 65g of boron nitride and 40g of silicon carbide is less effective than the modified phenolic resin obtained by first modifying it with thermoplastic phenolic resin and boron nitride, and then preparing the modified hard carbon resin from this modified phenolic resin to modify the recycled graphite powder.

[0130] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries, characterized in that, Includes the following steps: S1. Select retired nickel-cobalt-manganese lithium batteries, perform deep discharge, dismantle and sort them to obtain nickel-cobalt-manganese lithium positive electrode sheets, graphite negative electrode sheets, separators and shells; S2. Place the graphite negative electrode sheet in an ethanol aqueous solution for ultrasonic de-powdering, filtration, drying, pulverization, and sieving using a 100-325 mesh sieve to obtain graphite powder with a particle size of 5-150μm. S3. Calcine the graphite powder at 100-400℃ for 3-8 hours, and cool it to room temperature to obtain the first calcined graphite powder; S4. The first-calcined graphite powder is added to acid solution A for leaching reaction at a temperature of 30-60℃ for 0.5-3 hours. Then, the solid and liquid are separated and dried to obtain preliminarily purified graphite powder. The concentration of acid solution A is 0.5-3 mol / L, and acid solution A is either sulfuric acid or hydrochloric acid. The mass-to-volume ratio of the first-calcined graphite powder to acid solution A is 15-50 g: 1 L. S5. The graphite powder after the first purification is heat-treated under an inert atmosphere and cooled to room temperature to obtain the second calcined graphite powder. S6. The second-calcined graphite powder is added to acid solution B for leaching reaction at a reaction temperature of 30-60℃ for 3-5 hours. Then, the solid and liquid are separated, and the solid is washed multiple times with deionized water until the pH of the washing water is 6-7. After drying at a temperature of 80-200℃ for 3-8 hours, the second-purified graphite powder is obtained. The concentration of acid solution B is 2-5 mol / L, and acid solution B is either sulfuric acid or hydrochloric acid. The mass-to-volume ratio of the second-calcined graphite powder to acid solution B is 10-30 g: 1 L. S7. The secondary purified graphite powder and modified hard carbon resin are stirred and mixed evenly at 150-300℃ to obtain a mixed powder. The mixed powder is then calcined at high temperature under an inert atmosphere and cooled to obtain regenerated graphite powder. The inert atmosphere is either nitrogen or argon. The high-temperature calcination process conditions are: heating to 1500-2500℃ at a heating rate of 2-10℃ / min and holding at that temperature for 3-15 hours. The mass ratio of the secondary purified graphite powder to the modified hard carbon resin is 100:3-8. The modified hard carbon resin is composed of pitch powder, modified phenolic resin, and silicon carbide in a mass ratio of (10-20):100:(3-5), and the particle size of the silicon carbide is 3-5μm. S8. The recycled graphite powder is crushed, sieved, and demagnetized to obtain lithium-ion battery negative electrode graphite powder. The modified phenolic resin is prepared as follows: 100-110 parts by mass of thermoplastic phenolic resin, 1-2 parts by mass of phosphoric acid and 5-8 parts by mass of boron nitride are added to 1000 parts by mass of a solution composed of isopropanol and water in a volume ratio of 2:

1. After stirring evenly, the solution is transferred to a reactor and reacted at 140°C for 6-8 hours. After filtration, the solution is vacuum dried at 85°C for 24-30 hours to obtain the modified phenolic resin. The boron nitride has a particle size of 1-5 μm. The modified hard carbon resin is prepared by mixing asphalt powder, modified phenolic resin and silicon carbide evenly, and then granulating and crushing it at 200-220℃ using a twin-screw extruder to obtain modified hard carbon resin with a D50 particle size of 7μm.

2. The method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries according to claim 1, characterized in that, In step S2, the volume ratio of ethanol to water in the ethanol-water solution is 1:2-5; the process parameters for ultrasonic de-powdering are: ultrasonic power of 5-10KW, ultrasonic temperature of 25-35℃, and ultrasonic time of 30-60min; the drying temperature is 80-100℃, and the drying time is 8-12 hours.

3. The method for recycling and reusing graphite anode material from retired nickel-cobalt-manganese lithium oxide batteries according to claim 1, characterized in that, In step S5, the inert atmosphere is either nitrogen or argon; the heat treatment process conditions are: temperature 600-900℃, time 3-6 hours.

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