Method for recycling graphite material in decommissioned power battery

Abstract

The application discloses a method for recycling graphite material in decommissioned power batteries. The method comprises the following steps: sequentially adding acid and hydrogen peroxide into lithium battery black powder for impregnation, filtering, and collecting graphite residue; dispersing the graphite residue in water, oscillating, and screening; adding acid for impregnation again, adding a metal complexing agent for reaction, washing, and drying to obtain pretreated graphite residue; performing gas phase digestion on the pretreated graphite residue, and then performing resin fusion coating; after resin carbonization into hard carbon, using soft carbon to coat the interface of the graphite material repaired by the hard carbon; finally, removing magnetic screening to obtain regenerated graphite. The regenerated graphite material has high purity, and exhibits extremely high rate performance and cycle performance, the capacity retention rate at 3C rate is about 90%, the attenuation is less than 1% after 1000 cycles at normal temperature, and the product quality reaches the level of high-end lithium battery negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of battery material recycling technology, and in particular to a method for recycling graphite materials in retired power batteries. Background Technology

[0002] Lithium-ion battery anode materials, serving as carriers of lithium ions and electrons during charging, are a crucial raw material for lithium batteries, accounting for 15%-22% of the total cell weight. Currently, the industry typically disposes of anode materials through combustion, stockpiling, or as steelmaking additives, causing significant environmental pollution and resource waste. Based on current retired battery disposal volumes, it is estimated that approximately 300,000 tons of batteries were retired in 2022 alone, corresponding to about 50,000 tons of scrap graphite, representing a market size of several billion yuan. Current incineration and landfill methods result in enormous resource waste and economic losses.

[0003] The recycling of graphite materials in retired batteries is still in its early stages. During cycling, graphite anode materials experience an increase in defects and a decrease in graphitization due to the continuous insertion and extraction of lithium ions and the co-intercalation of solvents, leading to a decline in capacity and reduced first-time efficiency. Studies have shown that for graphite materials that have failed after cycling, re-graphitization cannot restore their defective structure.

[0004] Currently, the main methods for regeneration research are acid washing to remove impurities, high-temperature calcination, and secondary coating. However, targeted, systematic, and in-depth research based on the failure mechanism of graphite has not been carried out, resulting in poor practical application of recycled materials and low overall performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for recycling graphite materials from retired power batteries. This method utilizes deep purification, directional digestion, hard carbon repair, and interface coating techniques to obtain recycled graphite materials with a purity of up to 99.9%. The materials exhibit excellent performance, increasing the capacity of the anode material from 345 mAh / g to 360 mAh / g, and demonstrating extremely high rate performance and cycle performance. The capacity retention rate at 3C is approximately 90%, a 15% improvement compared to (recycled graphite materials). After 1000 cycles at room temperature, the capacity decay is less than 1%, achieving product quality levels comparable to high-end lithium-ion battery anode materials.

[0006] The technical solution of the present invention is as follows:

[0007] This invention first protects a method for recycling graphite materials in retired batteries, comprising the following steps:

[0008] (1) Add acid and hydrogen peroxide to lithium battery black powder in sequence, filter, and collect graphite residue;

[0009] (2) The graphite slag is dispersed in water to obtain a dispersion, shaken and sieved; acid is added for impregnation, and then a metal complexing agent is added for reaction, followed by washing and drying to obtain pretreated graphite slag.

[0010] (3) The pretreated graphite slag is subjected to gas phase digestion to obtain gas phase digested graphite slag;

[0011] (4) The graphite slag from gas phase digestion is coated with resin and the resin is carbonized into hard carbon to obtain graphite material for hard carbon repair.

[0012] (5) Use soft carbon to coat the interface of graphite material repaired by hard carbon;

[0013] (6) Demagnetize and screen the graphite material coated on the interface to obtain recycled graphite and realize graphite regeneration.

[0014] Further, in step (1), the lithium battery is a retired lithium battery, and the lithium battery includes one or more of ternary lithium, lithium iron phosphate, and lithium manganese oxide; during impregnation, the solid content of the impregnation solution is 10-30%, and the concentration of acid in the impregnation solution is 0.5-2 mol / L; the impregnation temperature is 40-80℃, and the time is 30 min-2 h.

[0015] Further, in step (1), the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid; the mass ratio of hydrogen peroxide to lithium battery black powder is 5-20:100.

[0016] Furthermore, the waste battery black powder is a black powder containing metals such as nickel, cobalt, manganese, copper, aluminum and lithium, as well as carbon powder, obtained from waste lithium-ion batteries through processes such as dismantling, crushing, screening, pyrolysis and sorting.

[0017] Further, in step (2), the mass fraction of graphite slag in the dispersion is 10%-30%; sieving refers to passing through a 200-600 mesh sieve; the acid includes one or more of sulfuric acid, hydrochloric acid or nitric acid, and the concentration of acid in the impregnation solution is 0.5-2 mol / L during acid impregnation; the time for acid impregnation is 1-3 hours, and the temperature is 40-80℃.

[0018] Further, in step (2), the metal complexing agent includes one of disodium ethylenediaminetetraacetate and hexadecyltriethylammonium bromide; the mass ratio of the metal complexing agent to graphite is 0.1-0.2:100; the reaction time is 10-30 min; the washing is with water until pH≥5; and the drying temperature is 100-110℃.

[0019] Further, in step (3), the temperature of the gas phase digestion is 500℃-800℃, the time is 1-4h, and the atmosphere is nitrogen or carbon dioxide containing oxygen; the volume fraction of oxygen in the nitrogen or carbon dioxide containing oxygen is 2%-5%; preferably, the atmosphere is carbon dioxide containing oxygen.

[0020] Further, in step (4), the resin is a liquid resin; the hard carbon filling amount in the hard carbon repair graphite material is 1.5-2.5 wt%; the carbonization temperature is 900℃-1500℃, the time is 2-4h, and the protective atmosphere is either nitrogen or argon.

[0021] Furthermore, the hard carbon repair involves adding liquid resin to phase graphite powder, mechanically fusing the resin to fill and coat the graphite gaps, and then carbonizing to obtain a graphite material for hard carbon repair.

[0022] Furthermore, the mechanical fusion time is 5-30 minutes.

[0023] Further, in step (5), the soft carbon is carbonized asphalt, the coating amount of soft carbon is 0.5-1.5wt%, the interface coating temperature is 1100℃-1400℃, the time is 2-4h, and the protective atmosphere is either nitrogen or argon.

[0024] Furthermore, in step (6), the purity of the recycled graphite is >99.9%.

[0025] The present invention also protects a recycled graphite prepared by the method described above.

[0026] Furthermore, the purity of the recycled graphite material is above 99.9%, and the recycled graphite increases the capacity of the negative electrode material from 345 mAh / g to 360 mAh / g, with a capacity retention rate of approximately 90% at 3C rate.

[0027] The beneficial technical effects of this invention are as follows:

[0028] This invention achieves efficient removal of metal ions from graphite waste through deep purification and targeted digestion. More importantly, it eliminates the failed parts in the material structure and creates a microporous structure (<50nm), which provides a fast channel for lithium ion insertion and extraction.

[0029] While mesoporous structures provide a fast channel for lithium-ion insertion and extraction, a large number of micro-mesoporous structures can also cause negative effects such as decreased material density and increased specific surface area. Therefore, a regeneration process using hard carbon to fill the voids and soft carbon to coat the interface is further adopted. The microcrystalline structure of hard carbon is below 50nm, similar to an isotropic material, which does not affect the fast-charging performance of the material and can better fill the voids generated by digestion. Soft carbon, on the other hand, exhibits higher orderliness and can reduce the specific surface area of ​​the material. The combination of hard carbon filling and soft carbon coating improves the overall performance of regenerated graphite.

[0030] This invention, through deep purification, directional digestion, hard carbon repair, and interface coating, not only solves the problem of difficult deep purification of waste graphite, but also upgrades and reuses it, giving it higher performance value. The microporous structure and the hard carbon repair and soft carbon coating structure in the recycled material can improve capacity and rate performance. The purity of the obtained recycled graphite can reach 99.9%, increasing the capacity of the anode material from 345mAh / g to 360mAh / g, while exhibiting extremely high rate performance and cycle performance. The capacity retention rate at 3C rate is about 90%, which is 15% higher than that of the raw material; the capacity decay is less than 1% after 1000 cycles at room temperature, and the product quality reaches the level of high-end lithium battery anode materials. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the process of the present invention.

[0032] Figure 2 This is a diagram showing the capacity utilization and initial effect of Embodiment 1 of the present invention.

[0033] Figure 3 To demonstrate the capacity utilization and initial effect of the proportional diagram. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] The method for recycling graphite materials in retired batteries according to the present invention includes the following steps:

[0036] (1) Add acid and hydrogen peroxide to lithium battery black powder in sequence, filter, and collect graphite residue;

[0037] (2) The graphite slag is dispersed in water to obtain a dispersion, shaken and sieved; acid is added for impregnation, and then a metal complexing agent is added for reaction, followed by washing and drying to obtain pretreated graphite slag.

[0038] (3) The pretreated graphite slag is subjected to gas phase digestion to obtain gas phase digested graphite slag;

[0039] (4) The graphite slag from gas phase digestion is coated with resin and the resin is carbonized into hard carbon to obtain graphite material for hard carbon repair.

[0040] (5) Use soft carbon to coat the interface of graphite material repaired by hard carbon;

[0041] (6) Demagnetize and screen the graphite material coated on the interface to obtain recycled graphite and realize graphite regeneration.

[0042] In one embodiment of the present invention, in step (1), the lithium battery is a retired lithium battery, which includes one or more of ternary lithium, lithium iron phosphate, and lithium manganese oxide; during impregnation, the solid content of the impregnation solution is 10%, 15%, 20% or 30%, and the concentration of acid in the impregnation solution is 0.5 mol / L, 1.0 mol / L, 1.5 mol / L or 2 mol / L; the impregnation temperature is 40°C, 50°C, 60°C, 70°C or 80°C, and the time is 30 min, 45 min, 1 h or 2 h.

[0043] In one embodiment of the present invention, in step (1), the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid; the mass ratio of hydrogen peroxide to lithium battery black powder is 5:100, 10:100, 15:100h, or 20:100.

[0044] In one embodiment of the present invention, most metal ions can be removed by acid leaching, and the purity of the prepared recycled graphite can be improved by combining the re-acid leaching and metal complexation in step (2).

[0045] In one embodiment of the present invention, the waste battery black powder is a black powder containing metals such as nickel, cobalt, manganese, copper, aluminum and lithium, as well as carbon powder, obtained from waste lithium-ion batteries through processes such as dismantling, crushing, screening, pyrolysis and sorting.

[0046] In one embodiment of the present invention, in step (2), the mass fraction of graphite slag in the dispersion is 10%, 20%, or 30%; sieving refers to passing through a 200-600 mesh sieve; the acid includes one or more of sulfuric acid, hydrochloric acid, or nitric acid; during acid impregnation, the concentration of acid in the impregnation solution is 0.5 mol / L, 1 mol / L, or 2 mol / L; the time for acid impregnation is 1 h, 2 h, or 3 h, and the temperature is 40°C, 60°C, 70°C, or 80°C.

[0047] In one embodiment of the present invention, to prevent the dissolved metal ions from adsorbing onto the graphite surface, a metal complexing agent is used in step (2), the metal complexing agent including disodium ethylenediaminetetraacetate and hexadecyltriethylammonium bromide; the mass ratio of the metal complexing agent to graphite is 0.1:100, 0.15:100 or 0.2:100; the reaction time is 10 min, 20 min or 30 min; the washing is with water until pH ≥ 5; the drying temperature is 100℃, 105℃ or 110℃.

[0048] Targeted digestion utilizes the principle that the crystallinity of the failed structure decreases, as does its heat resistance and oxidation resistance. Through heat treatment and oxidation, the failed portions of the graphite material are selectively eliminated. Simultaneously, the eliminated portions provide a porous structure, enabling faster pathways for lithium-ion insertion and extraction. In one embodiment of the invention, step (3) involves further processing using gas-phase digestion. The temperature of the gas-phase digestion is 500°C, 600°C, or 800°C, and the time is 1 hour, 2 hours, 3 hours, or 4 hours. The atmosphere is oxygen-containing nitrogen or carbon dioxide; the volume fraction of oxygen in the oxygen-containing nitrogen or carbon dioxide is 2%, 3%, or 5%; preferably, the atmosphere is oxidized carbon dioxide. In one embodiment of the present invention, in step (4), the resin is a liquid resin; the hard carbon filling amount in the hard carbon repair graphite material is 1.5wt%, 2.0wt%, 2.2wt%, or 2.5wt%; the carbonization temperature is 900℃, 1100℃, or 1500℃, the time is 2h, 3h, or 4h, and the protective atmosphere is one of nitrogen or argon.

[0049] In one embodiment of the present invention, in order to fill the pore structure caused by elimination while ensuring the fast charging performance of the material, hard carbon is used for repair. The microcrystalline structure of hard carbon is about 50nm and is isotropic, which can fill the aforementioned pore structure.

[0050] The hard carbon repair process involves adding liquid resin to phase graphite powder, mechanically fusing the resin to fill and coat the graphite gaps, and then carbonizing to obtain a hard carbon repair graphite material.

[0051] In one embodiment of the present invention, the mechanical fusion time is 5 min, 10 min, 15 min, 20 min or 30 min.

[0052] In one embodiment of the present invention, in step (5), the soft carbon is carbonized asphalt, the coating amount of soft carbon is 0.5-1.5wt%, the interface coating temperature is 1100℃, 1200℃, 1300℃ or 1400℃, the time is 2h, 3h or 4h, and the protective atmosphere is nitrogen or argon.

[0053] In one embodiment of the present invention, in step (6), the purity of the recycled graphite is >99.9%.

[0054] Example 1:

[0055] The method for recycling graphite materials in retired power batteries includes the following steps:

[0056] (1) The recovered graphite black powder was impregnated and dispersed in a solution of sulfuric acid and hydrogen peroxide, wherein the concentration of acid was 2.0 mol / L; the solid content of the impregnation solution was 30%; the mass ratio of hydrogen peroxide to graphite black powder was controlled to be 10:100; the reaction was stirred at 80℃ for 2 hours and then filtered; the graphite residue was obtained by pressure filtration.

[0057] (2) The graphite slag obtained by leaching is dispersed in pure water to obtain a graphite dispersion with a mass fraction of 30% graphite slag in the dispersion. The dispersion is sieved twice through a 600-mesh sieve and then filtered to remove excess water. The sieved graphite is soaked in 1.0 mol / L sulfuric acid at 80°C for 2 hours. Then, 0.2 wt% disodium ethylenediaminetetraacetate is added and reacted for 10 minutes to remove metal impurities. The graphite material after impurity removal is washed with pure water until pH≥5 and dried at 100°C.

[0058] (3) The dried graphite was digested in the gas phase using carbon dioxide as the gas atmosphere at 800℃ for 1 hour to eliminate the defective parts of the material.

[0059] (4) Hard carbon repair is performed on the graphite after directional digestion. Specifically, liquid resin is used as a hard carbon precursor. After mechanical fusion for 20 minutes, the resin is adsorbed into the empty structure through a mechanical fusion device. The hard carbon filling amount in the graphite material is controlled to be 1.5 wt%. Then, nitrogen is used as a protective gas and heat-treated at 900℃ for 4 hours to form a hard carbon repair graphite material. The hard carbon filling amount in the hard carbon repair graphite material is 1.5% (mass fraction). The amount of resin added can be calculated based on the final hard carbon filling amount.

[0060] (5) The graphite material repaired with hard carbon is coated with asphalt, and the coating amount of asphalt is controlled to be 1% (the carbonization rate of asphalt is 50%, that is, 2g of asphalt is added to make 1g of soft carbon). The asphalt coating is carried out by a heated VC mixer, in which nitrogen is used as a protective gas and heat treatment is performed at 1100℃ for 4h. After the asphalt is cracked, soft carbon is formed, and the graphite material coated with soft carbon is obtained.

[0061] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0062] Example 2:

[0063] The method for recycling graphite materials in retired power batteries includes the following steps:

[0064] (1) The recovered graphite black powder was impregnated and dispersed in a solution of sulfuric acid and hydrogen peroxide, wherein the concentration of acid was 2.0 mol / L; the solid content of the impregnation solution was 30%; the mass ratio of hydrogen peroxide to graphite black powder was controlled to be 10:100; the reaction was stirred at 40℃ for 2 hours and then filtered; the graphite residue was obtained by pressure filtration.

[0065] (2) The graphite slag obtained by leaching is dispersed in pure water to obtain a graphite dispersion with a mass fraction of 10% of graphite slag in the dispersion. The dispersion is sieved twice through a 600-mesh sieve and then filtered to remove excess water. The sieved graphite slag is soaked in 2.0M sulfuric acid at 40°C for 3 hours. Then 0.2wt% of disodium ethylenediaminetetraacetate is added and reacted for 30 minutes to remove metal impurities. The graphite material after impurity removal is washed with pure water until pH≥5 and dried at 100°C.

[0066] (3) The dried graphite was digested in the gas phase using oxygen-containing (2%) nitrogen gas as the gas atmosphere, and digested at 500℃ for 1 hour to eliminate the defective parts of the material.

[0067] (4) Hard carbon repair was performed on the graphite after directional digestion. Liquid resin was used as a hard carbon precursor. After mechanical fusion for 20 min, the resin was adsorbed into the empty structure. The hard carbon filling amount in the graphite material was controlled to be 2.5 wt%. Then, nitrogen was used as a protective gas and heat-treated at 1500℃ for 2 h to form the graphite material with hard carbon repair.

[0068] (5) The graphite material repaired with hard carbon is coated with asphalt, and the coating amount of soft carbon is controlled to be 0.5wt%. Nitrogen is used as a protective gas and heat-treated at 1400℃ for 2h to form soft carbon after asphalt cracking.

[0069] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0070] Example 3:

[0071] The method for recycling graphite materials in retired power batteries includes the following steps:

[0072] (1) The recovered graphite black powder was impregnated and dispersed in a solution of sulfuric acid and hydrogen peroxide, wherein the concentration of acid was 0.5 mol / L; the solid content of the impregnation solution was 10%; the mass ratio of hydrogen peroxide to graphite black powder was controlled to be 20:100; the reaction was stirred at 40℃ for 1 h and then filtered, and graphite residue was obtained by pressure filtration.

[0073] (2) The graphite slag obtained by leaching is dispersed in pure water to obtain a graphite dispersion with a mass fraction of 20% graphite slag in the dispersion. The dispersion is sieved twice through a 200-mesh sieve and then filtered to remove excess water. The sieved graphite slag is soaked in 0.5M hydrochloric acid at 60℃ for 1 hour. Then 0.1wt% disodium ethylenediaminetetraacetate is added and reacted for 30 minutes to remove metal impurities. The graphite material after impurity removal is washed with pure water until pH≥5 and dried at 110℃.

[0074] (3) The dried graphite was subjected to gas phase digestion using carbon dioxide as the gas atmosphere at 800°C for 1 hour to eliminate the defective parts of the material.

[0075] (4) Hard carbon repair is performed on the graphite after directional digestion. Liquid resin is used as a hard carbon precursor. After mechanical fusion for 30 min, the resin is adsorbed in the pore structure. The hard carbon filling amount in the graphite material is controlled to be 2wt%. Then, nitrogen is used as a protective gas and heat-treated at 1100℃ for 3 h to form a graphite material with hard carbon repair.

[0076] (5) The graphite material repaired with hard carbon is coated with asphalt, the amount of carbonized asphalt coating is controlled at 0.5wt%, nitrogen is used as protective gas, and heat treatment is carried out at 1200℃ for 3h to form soft carbon after asphalt cracking.

[0077] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0078] Example 4:

[0079] The method for recycling graphite materials in retired power batteries includes the following steps:

[0080] (1) The recovered graphite black powder was impregnated and dispersed in a solution of sulfuric acid and hydrogen peroxide, wherein the concentration of acid was 1.0 mol / L; the solid content of the impregnation solution was 20%; the mass ratio of hydrogen peroxide to graphite black powder was controlled at 5:100; the reaction was stirred at 60℃ for 0.5 h and then filtered, and graphite residue was obtained by pressure filtration.

[0081] (2) The graphite slag obtained by leaching is dispersed in pure water to obtain a graphite dispersion with a mass fraction of 30% graphite slag in the dispersion. The dispersion is sieved twice through a 400-mesh sieve and then filtered to remove excess water. The sieved graphite slag is soaked in 1.0M nitric acid at 40°C for 3 hours. Then 0.15wt% hexadecyltriethylammonium bromide is added and reacted for 20 minutes to remove metal impurities. The graphite material after impurity removal is washed with pure water until pH≥5 and dried at 105°C.

[0082] (3) The dried graphite is digested in the gas phase using nitrogen containing oxygen as the gas atmosphere at 600°C for 3 hours to eliminate the defective parts of the material; (the atmosphere is nitrogen containing oxygen with a volume fraction of 3%).

[0083] (4) Hard carbon repair was performed on the graphite after directional digestion. Liquid resin was used as a hard carbon precursor. After mechanical fusion for 5 minutes, the resin was adsorbed into the empty structure. The hard carbon filling amount in the graphite material was controlled to be 2.5 wt%. Then, nitrogen was used as a protective gas and heat-treated at 1500℃ for 2 hours to form the graphite material with hard carbon repair.

[0084] (5) The graphite material repaired by hard carbon is coated with asphalt, the amount of carbonized asphalt coating is controlled at 1.0wt%, nitrogen is used as protective gas, and heat treatment is carried out at 1400℃ for 2h to form soft carbon after asphalt cracking.

[0085] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0086] Comparative Example 1:

[0087] The method for recycling graphite materials in retired power batteries includes the following steps:

[0088] (1) Lithium-ion battery black powder is leached with sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite residue;

[0089] (2) The graphite residue obtained by leaching was soaked in 0.5M sulfuric acid at 80°C for 1 hour; then 0.2wt% disodium ethylenediaminetetraacetate was added, and after 30 minutes, the metal impurities were removed. The graphite material after impurity removal was washed with pure water until pH≥5 and dried at 100°C.

[0090] (3) The dried graphite is directly carbonized at a temperature of 900 degrees Celsius under a nitrogen atmosphere.

[0091] (4) Hard carbon repair is performed on the carbonized graphite. Liquid resin is used as a hard carbon precursor and mechanically fused for 20 minutes. The carbonization rate of the resin is controlled at 1.5%. Then, nitrogen is used as a protective gas and heat-treated at 900℃ for 4 hours.

[0092] (5) The graphite material repaired by hard carbon is coated with asphalt, the carbonization rate of asphalt is controlled at 1%, nitrogen is used as protective gas, and heat treatment is carried out at 1100℃ for 4 hours to form soft carbon after asphalt cracking.

[0093] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0094] Comparative Example 2:

[0095] The method for recycling graphite materials in retired power batteries includes the following steps:

[0096] (1) Lithium-ion battery black powder is leached with sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite residue;

[0097] (2) The graphite residue obtained by leaching was soaked in 2M sulfuric acid at 40°C for 2 hours; 0.2wt% disodium ethylenediaminetetraacetate was added and soaked for 10 minutes to remove metal impurities. The graphite material after impurity removal was washed with pure water until pH≥5 and dried at 100°C.

[0098] (3) The dried graphite was digested in the gas phase using carbon dioxide as the gas atmosphere at 800℃ for 1 hour to eliminate the defective parts of the material.

[0099] (4) The graphite after directional digestion is coated with asphalt, the carbonization rate of asphalt is controlled at 1.5%, nitrogen is used as protective gas, and heat treatment is carried out at 1100℃ for 4 hours to form soft carbon after asphalt cracking.

[0100] (5) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0101] Comparative Example 3

[0102] (1) Lithium-ion battery black powder is leached with sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite residue;

[0103] (2) The graphite residue obtained by leaching was soaked in 0.5M sulfuric acid at 80°C for 1 hour to remove metal impurities. The graphite material after impurity removal was washed with pure water until pH≥5 and dried at 100°C.

[0104] (3) The dried graphite is directly carbonized at a temperature of 900 degrees Celsius under a nitrogen atmosphere.

[0105] (4) Hard carbon repair is performed on the carbonized graphite. Liquid resin is used as a hard carbon precursor and mechanically fused for 20 minutes. The carbonization rate of the resin is controlled at 1.5%. Then, nitrogen is used as a protective gas and heat-treated at 900℃ for 4 hours.

[0106] (5) The graphite material repaired by hard carbon is coated with asphalt, the carbonization rate of asphalt is controlled at 1%, nitrogen is used as protective gas, and heat treatment is carried out at 1100℃ for 4 hours to form soft carbon after asphalt cracking.

[0107] (6) The coated graphite powder is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder, forming the final product.

[0108] Comparative Example 4

[0109] The method for recycling graphite materials in retired power batteries includes the following steps:

[0110] (1) Lithium-ion battery black powder is leached with sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite residue;

[0111] (2) The graphite residue obtained by leaching was soaked in 0.5M sulfuric acid at 80°C for 1 hour; then 0.2wt% disodium ethylenediaminetetraacetate was added and reacted for 30 minutes to remove metal impurities. The graphite material after impurity removal was washed with pure water until pH≥5 and dried at 100°C.

[0112] (3) The dried graphite is directly carbonized at a temperature of 900 degrees Celsius under a nitrogen atmosphere.

[0113] (4) Hard carbon repair is performed on the carbonized graphite. Liquid resin is used as a hard carbon precursor and mechanically fused for 20 minutes. The carbonization rate of the resin is controlled at 1.5%. Then, nitrogen is used as a protective gas and heat-treated at 900℃ for 4 hours.

[0114] (5) The graphite powder filled with hard carbon is demagnetized and sieved to further remove trace amounts of magnetism and metallic foreign matter from the powder to form the final product.

[0115] Test example:

[0116] The reversible capacity, first-efficiency performance, and high-rate capacity retention of the examples, comparative examples, and recycled graphite were determined. The specific determination method was as follows: recycled graphite was mixed into a slurry, coated, rolled, and slit according to the ratio of main material:sp:CMC:SBR = 96%:0.6%:1.3%:2.1% to form a negative electrode sheet with a single-sided areal density of 96 and a compaction density of 1.6. After cutting, the electrode sheet was used to make a half-cell with lithium-ion sheets and a full-cell with ternary positive electrode sheets.

[0117] The reversible capacity and first-efficiency were tested at 0.1C using an electrochemical testing cabinet; the high-rate performance of the material was tested at 2C and 3C. The test results are shown in Table 1.

[0118] Table 1 Performance tests of embodiments and comparative examples of the present invention

[0119]

[0120]

[0121] As shown in Table 1, the recycling technology of the present invention can achieve high-performance repair of waste graphite with reduced capacity, increasing the material capacity from 345mAh / g to 360mAh / g. In addition, the recycled material also has high rate performance, with a capacity retention rate of about 90% at 3C rate, reaching the standard of high-end graphite materials.

[0122] Figure 2 This is a diagram showing the capacity utilization and initial effect of Embodiment 1 of the present invention; Figure 3 This is a diagram showing the capacity utilization and initial effect of the scale. (From...) Figure 2-3 It can be seen that recycled materials can exhibit typical graphite charge-discharge curves. Figure 2 The lithium insertion / extraction platform is significantly longer than Figure 3 This indicates that the material's reversible capacity has been restored, resulting in higher lithium intercalation capability and exhibiting higher capacity.

[0123] The purity test results of the recycled graphite in the examples are shown in Table 2.

[0124] Table 2 Purity of Regenerated Graphite

[0125] Cu Fe Ni Al Carbon content Waste graphite 6845 3857 7868 10352 / Example 1 8.5 8.8 5.7 2.5 99.95％ Example 2 7.8 9.5 6.8 2.1 99.96％ standard <10ppm <10ppm <10ppm <10ppm >99.9％

[0126] As shown in the table, the recycled waste graphite contains a large variety and quantity of impurities, which are easily adsorbed into the material and difficult to remove effectively, making reuse challenging. After treatment by the method of this invention, the metallic impurities in the graphite decrease dramatically, with all impurity contents <10ppm, meeting current national standards and reaching the standards for use as graphite anode materials in lithium batteries.

[0127] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for recycling graphite material in decommissioned batteries, characterized by, The method comprises the following steps: (1) sequentially adding acid and hydrogen peroxide into the lithium battery black powder for impregnation, filtering, and collecting graphite residue; (2) dispersing the graphite residue in water to obtain a dispersion liquid, oscillating and sieving; adding acid for impregnation, then adding a metal complexing agent for reaction, washing, and drying to obtain pretreated graphite residue; (3) performing gas phase digestion on the pretreated graphite residue to obtain gas phase digested graphite residue; (4) performing resin fusion coating on the gas phase digested graphite residue, carbonizing the resin into hard carbon to obtain hard carbon repaired graphite material; (5) using soft carbon to perform interface coating on the hard carbon repaired graphite material; (6) performing demagnetization and sieving on the interface coated graphite material to obtain regenerated graphite, and realizing graphite regeneration. In step (3), the temperature of the gas phase digestion is 500-800 DEG C, the time is 1-4 h, and the atmosphere is carbon dioxide or nitrogen containing oxygen; In step (6), the purity of the regenerated graphite is > 99.9%.

2. The method of claim 1, wherein, In step (1), the lithium battery is a retired lithium battery, and the lithium battery comprises one or more of ternary lithium, lithium iron phosphate, and lithium manganate; during impregnation, the solid content of the impregnation liquid is 10-30%, and the concentration of the acid in the impregnation liquid is 0.5-2 mol / L; the temperature of the impregnation is 40-80 DEG C, and the time is 30 min-2 h.

3. The method of claim 1, wherein, In step (1), the acid comprises one or more of sulfuric acid, hydrochloric acid, and nitric acid; and the mass ratio of the hydrogen peroxide to the lithium battery black powder is 5-20:

100.

4. The method of claim 1, wherein, In step (2), the mass fraction of the graphite residue in the dispersion liquid is 10%-30%; the sieving refers to passing through a 200-600 mesh sieve; the acid comprises one or more of sulfuric acid, hydrochloric acid, or nitric acid; during acid impregnation, the concentration of the acid in the impregnation liquid is 0.5-2 mol / L; the time of the acid impregnation is 1-3 h, and the temperature is 40-80 DEG C.

5. The method of claim 1, wherein, In step (2), the metal complexing agent comprises one or more of disodium ethylenediaminetetraacetate and cetyltriethylammonium bromide; the mass ratio of the metal complexing agent to the graphite is 0.1-0.2:100; and the reaction time is 10-30 min.

6. The method of claim 1, wherein, In step (3), in the nitrogen containing oxygen, the volume fraction of oxygen is 2%-5%.

7. The method of claim 1, wherein, In step (4), the resin is a liquid resin; the filling amount of the hard carbon in the hard carbon repaired graphite material is 1.5-2.5 wt%; the carbonization temperature is 900 DEG C-1500 DEG C, the time is 2-4 h, and the protective atmosphere is nitrogen or argon.

8. The method of claim 1, wherein, In step (5), the soft carbon is carbonized pitch, and the coating amount of the soft carbon is 0.5-1.5 wt%; the temperature of the interface coating is 1100 DEG C-1400 DEG C, the time is 2-4 h, and the protective atmosphere is nitrogen or argon.

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