Method for recycling graphite material in decommissioned power battery

Abstract

The present invention discloses a method for recycling a graphite material in a decommissioned power battery. The method of the present invention comprises: sequentially adding acid and hydrogen peroxide into the black powder of a lithium battery to perform soaking, filtering and graphite residue collection; dispersing the graphite residue with water, then vibrating and sieving the graphite residue; adding acid to perform soaking, and after adding a metal complexing agent to perform a reaction, washing and drying to obtain pre-treated graphite residue; performing gas-phase decomposition on the pre-treated graphite residue, then performing resin fusion coating, and after carbonizing the resin into hard carbon, using soft carbon to perform boundary coating on the hard carbon repaired graphite material; and finally demagnetizing and filtering, to obtain recycled graphite. The recycled graphite material of the present invention has high purity, displays extremely high rate performance and cycle performance, has a capacity retention rate of about 90% at a rate of 3C, and after 1000 cycles at normal-temperature, the attenuation thereof is less than 1%. The product quality reaches the level of a negative electrode material of a high-end lithium battery.

Description

A method for recycling graphite materials in retired power batteries Technical Field

[0001] The present invention relates to the technical field of battery material recycling, and in particular to a method for recycling graphite materials in retired power batteries. Background Art

[0002] Lithium-ion battery anode materials, acting as carriers of lithium ions and electrons during the charging process, are a key raw material for lithium-ion batteries, accounting for 15%-22% of the battery cell's mass. Currently, the industry typically processes anode materials through incineration, stockpiling, or using them as steelmaking additives, resulting in significant environmental pollution and resource waste. Based on current processing volumes of retired batteries, approximately 300,000 tons of batteries will be retired in 2022 alone, corresponding to approximately 50,000 tons of scrapped graphite, representing a market value of tens of billions of yuan. Current methods of incineration and landfilling result in significant resource waste and economic losses.

[0003] The recycling of graphite materials from retired batteries is still in its infancy. During recycling, graphite anode materials experience an increase in defects and a decrease in graphitization due to the continuous intercalation and deintercalation of lithium ions and the co-intercalation of solvents. This leads to a decrease in capacity and initial efficiency. Research has shown that even re-graphitization of graphite materials that have failed after cycling cannot restore their defective structures. Technical issues

[0004] Currently, regeneration research is mainly carried out through technical methods such as pickling and impurity removal, high-temperature calcination, and secondary coating. However, targeted, systematic, and in-depth research has not been carried out based on the failure mechanism of graphite, resulting in poor practical applicability of recycled materials and low overall performance. Technical Solutions

[0005] To address the shortcomings of the existing technology, the present invention provides a method for recycling graphite materials from retired power batteries. The present invention provides a method for recycling graphite materials from retired power batteries. Through deep purification, directional digestion, hard carbon repair, and interface coating, the resulting recycled graphite material has a purity of up to 99.9% and excellent material performance. The capacity of the negative electrode material, which has decayed to 345mAh / g, is increased to 360mAh / g. It also exhibits extremely high rate performance and cycle performance. The capacity retention rate at 3C rate is approximately 90%, a 15% increase compared to (recycled graphite materials). The decay is less than 1% after 1,000 cycles at room temperature, and the product quality reaches the level of high-end lithium battery negative electrode materials.

[0006] The technical solutions of the present invention are as follows:

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

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

[0009] (2) adding water to the graphite slag to obtain a dispersion, vibrating and sieving; adding acid for impregnation, adding a metal complexing agent for reaction, washing, and drying to obtain pretreated graphite slag;

[0010] (3) performing gas phase digestion on the pretreated graphite slag to obtain gas phase digested graphite slag;

[0011] (4) The graphite slag obtained by gas phase digestion is fused and coated with resin, and the resin is carbonized into hard carbon to obtain a hard carbon repaired graphite material;

[0012] (5) Using soft carbon to coat the interface of hard carbon-repaired graphite materials;

[0013] (6) Demagnetize and screen the interface-coated graphite material to obtain regenerated graphite, thereby achieving graphite regeneration.

[0014] Furthermore, 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 the impregnation, the solid content of the impregnation solution is 10-30%, and the acid concentration in the impregnation solution is 0.5-2 mol / L; the impregnation temperature is 40-80°C, and the time is 30 min-2 h.

[0015] Furthermore, in step (1), the acid includes one or more of sulfuric acid, hydrochloric acid, and nitric acid; and 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 and carbon powder obtained by disassembling, crushing, screening, pyrolysis, and sorting waste lithium-ion batteries.

[0017] Furthermore, 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 during the acid impregnation, the concentration of the acid in the impregnation solution is 0.5-2 mol / L; the time of the acid impregnation is 1-3 hours, and the temperature is 40-80°C.

[0018] Furthermore, in step (2), the metal complexing agent includes one of disodium ethylenediaminetetraacetic acid 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 minutes; the washing is performed with water until the pH is ≥5; and the drying temperature is 100-110°C.

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

[0020] Furthermore, in step (4), the resin is a liquid resin; the filling amount of hard carbon in the hard carbon-repaired graphite material is 1.5-2.5wt%; the carbonization temperature is 900°C-1500°C, the time is 2-4h, and the protective atmosphere is one of nitrogen and argon.

[0021] Furthermore, the hard carbon repair is achieved by adding liquid resin to the graphite powder, filling and coating the resin in the graphite gaps through mechanical fusion, and then carbonizing to obtain the hard carbon repaired graphite material.

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

[0023] Furthermore, in step (5), the soft carbon is carbonized asphalt, and the coating amount of the soft carbon is 0.5-1.5 wt%; the interface coating temperature is 1100°C-1400°C, the time is 2-4 hours, and the protective atmosphere is one of nitrogen and argon.

[0024] Furthermore, in step (6), the purity of the regenerated graphite is greater than 99.9%.

[0025] The present invention also protects regenerated graphite prepared by the method.

[0026] Furthermore, the purity of the recycled graphite material is above 99.9%. The recycled graphite increases the capacity of the negative electrode material that has decayed to 345 mAh / g to 360 mAh / g, and the capacity retention rate at a 3C rate is about 90%. Beneficial effects

[0027] The beneficial technical effects of the present invention are:

[0028] The present invention not only achieves efficient removal of metal ions from graphite waste through deep purification and directional digestion, but more importantly, it can eliminate the failed parts in the material structure and simultaneously create a micro-mesoporous structure (<50nm), which can provide a fast channel for the insertion and extraction of lithium ions.

[0029] While the mesoporous structure provides a fast channel for the insertion and extraction of lithium ions, a large number of micro-mesoporous structures will also cause negative effects such as a decrease in material density and an increase in specific surface area. Therefore, a regeneration treatment method of hard carbon filling the gaps and soft carbon interface coating is further adopted. The microcrystalline structure of hard carbon is below 50nm, similar to isotropic material, which will not affect the fast charging performance of the material and can better fill the gaps generated by digestion. The soft carbon shows higher order and can reduce the specific surface area of ​​the material. The combination of hard carbon filling and soft carbon coating improves the comprehensive performance of the regenerated graphite.

[0030] The present invention not only solves the problem of the difficulty of deep purification of waste graphite through technical means such as deep purification, directional digestion, hard carbon repair, and interface coating, but also upgrades and reuses waste graphite to bring out higher performance value. The micro-mesoporous structure and hard carbon repair and soft carbon coating structure in the recycled material can improve higher capacity and rate performance. The purity of the obtained recycled graphite can reach 99.9%, which can increase the negative electrode material with a capacity decay of 345mAh / g to 360mAh / g. It also has extremely high rate performance and cycle performance. The capacity retention rate at 3C rate is about 90%, which is a 15% increase compared to the raw material. The decay rate is less than 1% after 1000 cycles at room temperature, and the product quality reaches the level of high-end lithium battery negative electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic diagram of the process of the present invention.

[0032] FIG2 is a diagram showing the capacity utilization and initial effect of Example 1 of the present invention.

[0033] FIG3 is a diagram showing the capacity and initial effect of the comparative example. Modes for Carrying Out the Invention

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

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

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

[0037] (2) adding water to the graphite slag to obtain a dispersion, vibrating and sieving; adding acid for impregnation, adding a metal complexing agent for reaction, washing, and drying to obtain pretreated graphite slag;

[0038] (3) performing gas phase digestion on the pretreated graphite slag to obtain gas phase digested graphite slag;

[0039] (4) The graphite slag obtained by gas phase digestion is fused and coated with resin, and the resin is carbonized into hard carbon to obtain a hard carbon repaired graphite material;

[0040] (5) Using soft carbon to coat the interface of hard carbon-repaired graphite materials;

[0041] (6) Demagnetize and screen the interface-coated graphite material to obtain regenerated graphite, thereby achieving graphite regeneration.

[0042] In one embodiment of the present invention, 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%, 15%, 20% or 30%, and the concentration of the 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; and the mass ratio of hydrogen peroxide to lithium battery black powder is 5:100, 10:100, 15:100, 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 regenerated graphite can be improved by combining the 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 and carbon powder obtained by disassembling, crushing, screening, pyrolysis and sorting of waste lithium-ion batteries.

[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 comprises one or more of sulfuric acid, hydrochloric acid or nitric acid, and during the acid impregnation, the concentration of the acid in the impregnation solution is 0.5 mol / L, 1 mol / L or 2 mol / L; the time of the 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, in order to prevent the dissolved metal ions from being adsorbed on the graphite surface, a metal complexing agent is used in step (2), and the metal complexing agent includes one of disodium ethylenediaminetetraacetic acid 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 performed with water until the pH is ≥5; and the drying temperature is 100°C, 105°C or 110°C.

[0048] Directed digestion utilizes the principle that the crystallinity of the failed structure decreases, and the heat resistance and oxidation resistance decrease. Through heat treatment and oxidation treatment, the failed parts in the graphite material are eliminated in a directed manner. At the same time, the eliminated parts can provide a pore structure, which can provide a faster path for lithium ion insertion and extraction. In one embodiment of the present invention, in step (3), gas phase digestion is used for further treatment. The gas phase digestion temperature is 500℃, 600℃ or 800℃, the time is 1h, 2h, 3h or 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%, 3% or 5%; preferably, the atmosphere is carbon dioxide containing oxygen. In one embodiment of the present invention, in step (4), the resin is a liquid resin; the filling amount of hard carbon in the hard carbon-repaired graphite material is 1.5wt%, 2.0wt%, 2.2wt% or 2.5wt%; the carbonization temperature is 900°C, 1100°C or 1500°C, the time is 2h, 3h or 4h, and the protective atmosphere is one of nitrogen and argon.

[0049] In one embodiment of the present invention, in order to fill the pore structure generated by elimination while ensuring the fast charging performance of the material, repair is performed using hard carbon. The microcrystalline structure of hard carbon is about 50nm and isotropic, which can just fill the above-mentioned pore structure.

[0050] The hard carbon repair is achieved by adding liquid resin into graphite powder, filling and coating the resin in the graphite gaps through mechanical fusion, and then carbonizing to obtain the hard carbon repaired 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, and the coating amount of the soft carbon is 0.5-1.5 wt%; the temperature of the interface coating is 1100°C, 1200°C, 1300°C or 1400°C, 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 regenerated graphite is greater than 99.9%.

[0054] Example 1:

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

[0056] (1) The recovered graphite black powder was impregnated and dispersed in a sulfuric acid and hydrogen peroxide solution, wherein the acid concentration 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, and the mixture was stirred at 80°C for 2 h, then filtered and filtered to obtain graphite slag;

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

[0058] (3) The dried graphite is 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;

[0059] (4) The graphite after directional digestion is repaired with hard carbon, specifically: using liquid resin as a hard carbon precursor, after mechanical fusion for 20 minutes, the resin is adsorbed in the empty structure by a mechanical fusion device, and the hard carbon filling amount in the hard carbon repaired graphite material is controlled to be 1.5wt%. Subsequently, nitrogen is used as a protective gas and heat treated at 900℃ for 4h to form a hard carbon repaired graphite material. The hard carbon filling amount in the hard carbon repaired 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 hard carbon-repaired graphite material 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 1g of soft carbon). The asphalt coating is carried out in a heated VC mixer, wherein nitrogen is used as a protective gas and heat treatment is carried out at 1100°C for 4h to form soft carbon after asphalt cracking, thereby obtaining a soft carbon-coated graphite material;

[0061] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0062] Example 2:

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

[0064] (1) The recovered graphite black powder was impregnated and dispersed in a sulfuric acid and hydrogen peroxide solution, wherein the acid concentration 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, and the mixture was stirred at 40°C for 2 h, then filtered and filtered to obtain graphite slag;

[0065] (2) The graphite slag obtained by leaching was dispersed in pure water to obtain a graphite dispersion, wherein the mass fraction of the graphite slag in the dispersion was 10%, and the dispersion was sieved twice with a 600-mesh sieve, and then filtered to remove excess water; the sieved graphite slag was soaked in 2.0 M sulfuric acid at 40°C for 3 h; 0.2 wt% disodium ethylenediaminetetraacetic acid was then added, and the reaction was continued for 30 min, and then the metal impurities were removed. The graphite material after impurity removal was washed with pure water until the pH was ≥5, and then dried at 100°C;

[0066] (3) The dried graphite is subjected to gas phase digestion, using nitrogen containing oxygen (2%) as the gas atmosphere, digested at 500 ° C for 1 hour to eliminate the defective parts of the material;

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

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

[0069] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0070] Example 3:

[0071] A method for recycling graphite materials in retired power batteries comprises 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 acid concentration 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, and the mixture was stirred at 40°C for 1 hour, then filtered and filtered to obtain graphite slag;

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

[0074] (3) The dried graphite is 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) The graphite after directional digestion was repaired with hard carbon. Liquid resin was used as a hard carbon precursor. After mechanical fusion for 30 minutes, the resin was adsorbed in the pore structure. The filling amount of hard carbon in the hard carbon repaired graphite material was controlled to be 2wt%. Subsequently, nitrogen was used as a protective gas and heat treated at 1100℃ for 3 hours to form a hard carbon repaired graphite material.

[0076] (5) The hard carbon-repaired graphite material was asphalt-coated, the carbonized asphalt coating amount was controlled to 0.5 wt%, nitrogen was used as the protective gas, and the asphalt was heat-treated at 1200 °C for 3 h to form soft carbon after asphalt cracking;

[0077] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0078] Example 4:

[0079] A method for recycling graphite materials in retired power batteries comprises 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 acid concentration 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 to be 5:100, and the mixture was stirred at 60°C for 0.5 h, then filtered and filtered to obtain graphite slag;

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

[0082] (3) The dried graphite is subjected to gas phase digestion, using oxygen-containing nitrogen as the gas atmosphere, digesting at 600°C for 3 hours to eliminate the defective parts of the material; (the atmosphere is oxygen-containing nitrogen, and the volume fraction of oxygen is 3%);

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

[0084] (5) The hard carbon-repaired graphite material was asphalt-coated, the carbonized asphalt coating amount was controlled to 1.0 wt%, nitrogen was used as the protective gas, and the asphalt was heat-treated at 1400 °C for 2 h to form soft carbon after asphalt cracking;

[0085] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0086] Comparative Example 1:

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

[0088] (1) Lithium battery black powder is leached by adding sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite slag;

[0089] (2) Soak the leached graphite slag in 0.5 M sulfuric acid at 80°C for 1 hour; then add 0.2 wt% disodium ethylenediaminetetraacetic acid for 30 minutes to remove metal impurities. Wash the graphite material with pure water until the pH is ≥5 and dry it at 100°C.

[0090] (3) Carbonize the dried graphite directly at a temperature of 900 degrees Celsius in a nitrogen atmosphere;

[0091] (4) The carbonized graphite was repaired with hard carbon using liquid resin as a hard carbon precursor, mechanically fused for 20 min, and the resin carbonization rate was controlled at 1.5%. Subsequently, nitrogen was used as a protective gas and heat treated at 900 °C for 4 h.

[0092] (5) The hard carbon-repaired graphite material is coated with asphalt, the asphalt carbonization rate is controlled at 1%, nitrogen is used as the protective gas, and the asphalt is heat treated at 1100 °C for 4 h to form soft carbon after the asphalt is cracked;

[0093] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0094] Comparative Example 2:

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

[0096] (1) Lithium battery black powder is leached by adding sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite slag;

[0097] (2) Soak the leached graphite slag in 2 M sulfuric acid at 40°C for 2 h; add 0.2 wt% disodium ethylenediaminetetraacetic acid and soak for 10 min to remove metal impurities. Wash the graphite material with pure water until the pH is ≥5 and dry at 100°C.

[0098] (3) The dried graphite is 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;

[0099] (4) The graphite after directional digestion is coated with asphalt, the asphalt carbonization rate is controlled at 1.5%, nitrogen is used as the protective gas, and the graphite is heat treated at 1100°C for 4 hours to form soft carbon after asphalt cracking;

[0100] (5) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0101] Comparative Example 3

[0102] (1) Lithium battery black powder is leached by adding sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite slag;

[0103] (2) Soak the leached graphite slag in 0.5 M sulfuric acid at 80°C for 1 hour to remove metal impurities. Wash the impurity-removed graphite material with pure water until the pH is ≥5, and dry it at 100°C.

[0104] (3) Carbonize the dried graphite directly at a temperature of 900 degrees Celsius in a nitrogen atmosphere;

[0105] (4) The carbonized graphite was repaired with hard carbon using liquid resin as a hard carbon precursor, mechanically fused for 20 min, and the resin carbonization rate was controlled at 1.5%. Subsequently, nitrogen was used as a protective gas and heat treated at 900 °C for 4 h.

[0106] (5) The hard carbon-repaired graphite material is coated with asphalt, the asphalt carbonization rate is controlled at 1%, nitrogen is used as the protective gas, and the asphalt is heat treated at 1100 °C for 4 h to form soft carbon after the asphalt is cracked;

[0107] (6) The coated graphite powder is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0108] Comparative Example 4

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

[0110] (1) Lithium battery black powder is leached by adding sulfuric acid, hydrogen peroxide, etc., and then filtered to obtain graphite slag;

[0111] (2) Soak the leached graphite slag in 0.5 M sulfuric acid at 80°C for 1 hour; then add 0.2 wt% disodium ethylenediaminetetraacetic acid and react for 30 minutes to remove metal impurities. Wash the graphite material with pure water until the pH is ≥5 and dry it at 100°C.

[0112] (3) Carbonize the dried graphite directly at a temperature of 900 degrees Celsius in a nitrogen atmosphere;

[0113] (4) The carbonized graphite was repaired with hard carbon using liquid resin as a hard carbon precursor, mechanically fused for 20 min, and the resin carbonization rate was controlled at 1.5%. Subsequently, nitrogen was used as a protective gas and heat treated at 900 °C for 4 h.

[0114] (5) The graphite powder filled with hard carbon is demagnetized and screened to further remove trace magnetic and metallic foreign matter in the powder to form the final product.

[0115] Test example:

[0116] The reversible capacity, first efficiency, and high-rate capacity retention rates of the examples, comparative examples, and recycled graphite were measured. The specific measurement method was as follows: recycled graphite was slurried, coated, roll-pressed, and slit in a ratio of 96% (main material: sp: CMC: SBR): 0.6%: 1.3%: 2.1% to produce a negative electrode sheet with a single-sided surface density of 96 and a compaction density of 1.6. The cut electrode sheet was then combined with a lithium sheet to form a half-cell, and with a ternary positive electrode sheet to form a full cell.

[0117] Using an electrochemical test cabinet, the reversible capacity and initial efficiency were tested at a 0.1C rate, and the high-rate performance of the material was tested at 2C and 3C rates. The test results are shown in Table 1.

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

[0119] Reversible capacity (mAh / g) First efficiency (%) High rate (3C) Capacity retention rate Recycled graphite 345.290.080.0% Example 1360.093.289.6% Example 2359.293.589.1% Comparative example 1350.591.282.6% Comparative example 2353.592.884.8% Comparative example 3352.290.581.2% Comparative example 4355.690.783.5%

[0120] As can be seen from Table 1, the regeneration technology of the present invention can achieve high-performance repair of waste graphite with reduced capacity, and the capacity of the material is increased from 345mAh / g to 360mAh / g; in addition, the recycled material also has a high rate performance, and the capacity retention rate at 3C rate is about 90%, reaching the standard of high-end graphite materials.

[0121] Figure 2 shows the capacity utilization and initial efficiency of Example 1 of the present invention; Figure 3 shows the capacity utilization and initial efficiency of the comparative example. As shown in Figures 2 and 3, the recycled material exhibits a typical graphite charge-discharge curve, with the lithium insertion and extraction platform in Figure 2 significantly longer than that in Figure 3, indicating that the material's reversible capacity has been restored, with higher lithium insertion ability and higher capacity.

[0122] The purity test results of the regenerated graphite of the embodiment are shown in Table 2.

[0123] Table 2 Purity of recycled graphite

[0124] CuFeNiAl carbon content waste graphite 68453857786810352 / Example 18.58.85.72.599.95% Example 27.89.56.82.199.96% standard <10ppm <10ppm <10ppm <10ppm >99.9%

[0125] As can be seen from the table, the types and contents of impurities in recycled waste graphite are numerous and easily adsorbed within the material, making effective removal difficult and making reuse difficult. After treatment using the present invention, the metal impurities in the graphite plummeted, with all impurity contents below 10 ppm, meeting current national standards and reaching the standards for use as graphite negative electrode materials for lithium batteries.

[0126] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A method for recycling graphite materials in retired batteries, characterized in that: The method comprises the following steps: (1) Add acid and hydrogen peroxide to the lithium battery black powder in sequence for impregnation, filter, and collect graphite slag; (2) adding water to the graphite slag to obtain a dispersion, vibrating and sieving; adding acid for impregnation, adding a metal complexing agent for reaction, washing, and drying to obtain pretreated graphite slag; (3) performing gas phase digestion on the pretreated graphite slag to obtain gas phase digested graphite slag; (4) The graphite slag obtained by gas phase digestion is fused and coated with resin, and the resin is carbonized into hard carbon to obtain a hard carbon-repaired graphite material; (5) Using soft carbon to coat the interface of hard carbon-repaired graphite material; (6) Demagnetizing and screening the interface-coated graphite material to obtain regenerated graphite, thereby achieving graphite regeneration.

2. The method according to claim 1, characterized in that 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 the impregnation, the solid content of the impregnation solution is 10-30%, and the acid concentration in the impregnation solution is 0.5-2 mol / L; the impregnation temperature is 40-80°C, and the time is 30min-2h.

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

100.

4. The method according to claim 1, characterized in that: In step (2), the mass fraction of graphite slag in the dispersion is 10%-30%; sieving refers to sieving through a 200-600 mesh sieve; the acid includes one or more of sulfuric acid, hydrochloric acid or nitric acid, and during acid impregnation, the acid concentration in the impregnation solution is 0.5-2 mol / L; the acid impregnation time is 1-3 hours, and the temperature is 40-80°C.

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

6. The method according to claim 1, characterized in that In step (3), the temperature of the gas phase digestion is 500°C-800°C, the time is 1-4 hours, and the atmosphere is carbon dioxide or nitrogen containing oxygen; the volume fraction of oxygen in the nitrogen containing oxygen is 2%-5%.

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

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

9. The method according to claim 1, characterized in that: In step (6), the purity of the regenerated graphite is >99.9%.

10. Regenerated graphite prepared by the method according to any one of claims 1 to 9.

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