A method for recovering graphite from waste lithium battery black powder acid leaching residue

Abstract

The present application relates to a method for recovering graphite from waste lithium battery black powder acid leaching residue: the acid leaching residue is dried and crushed into powder; the powder is calcined to remove organic binder; the powder is mixed with organic solvent and surfactant, and the slurry is subjected to high shear homogenization emulsification to refine the particles; organic acid is added to the slurry, and the solvothermal reaction is carried out in a reaction kettle under closed and stirring conditions; the slurry is filtered and washed with water in multiple stages, and then dried and crushed; the powder is mixed with additives and pure water and stirred to form a muddy material with certain viscosity; the muddy material is pressed into a hollow graphite part; the hollow graphite part is subjected to high-temperature graphitization; the graphitized hollow graphite part is crushed to obtain graphite powder; the graphite powder is mixed with one or more of pitch, petroleum coke, needle coke, green coke and forged coke; the material is sintered under inert atmosphere to form carbon-coated graphite. The beneficial effect is that the structure defects of the graphite are repaired, and the electrochemical performance is improved.

Description

Technical Field

[0001] This invention relates to the field of graphite recycling, and specifically to a method for recovering graphite from the acid leaching residue of waste lithium battery black powder. Background Technology

[0002] With the widespread use of 3C devices and the rise of new energy vehicles, the production of lithium-ion batteries, as a power source, is constantly increasing. Consequently, the disposal of large quantities of waste batteries has become a very important and urgent task. The gradual depletion of natural resources and environmental pollution are driving the continuous development of lithium battery recycling. Currently, most people focus on the recycling of precious metals in positive electrode materials, while graphite, as a conventional negative electrode material, is often overlooked.

[0003] Currently, battery recycling methods mainly include three aspects: direct processing, hydrometallurgy, and pyrometallurgy. Typically, after being discharged, used batteries undergo crushing, calcination, and sorting to obtain a powder containing a mixture of positive and negative electrodes, also known as black powder. Most companies now extract metals from this black powder using acid leaching. However, the residue after acid leaching and filtration mainly consists of negative electrode graphite, but it also contains many residual metals and organic impurities. Because of the presence of these substances, the residue is often treated as solid waste or even hazardous waste, leading to a significant waste of graphite.

[0004] The continuous depletion of natural graphite resources, coupled with the rapid increase in the price of synthetic graphite in recent years, makes the effective recycling of waste graphite crucial. This not only addresses resource scarcity and environmental pollution but also broadens recycling channels for businesses, increasing their profits. Furthermore, the recycling of negative electrode graphite primarily involves recovering scraps from unassembled negative electrode sheets and manually disassembling battery cells to separate the positive and negative electrodes. While this method yields relatively high-purity negative electrode raw materials, it is not suitable for large-scale production. The purification and recycling of graphite from black powder acid leaching residue has been largely unexplored due to its high impurity content and significant structural damage, making recycling technically challenging. Effectively recycling and utilizing the graphite from these residues would pave a new path for negative electrode graphite recycling. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for recovering graphite from the acid leaching residue of waste lithium battery black powder, so as to overcome the shortcomings of the prior art.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for recovering graphite from acid leaching residue of waste lithium battery black powder, comprising the following steps:

[0007] S1. Dry the acid leaching residue and crush it into powder;

[0008] S2. Calcine the powder to remove the organic binder.

[0009] S3. Mix the powder obtained in S2 with organic solvent and surfactant, and perform high-shear homogenization emulsification on the resulting slurry to refine the particles.

[0010] S4. Add organic acid to the slurry and carry out a solvothermal reaction in a reactor under closed and stirred conditions;

[0011] S5. The slurry obtained in S4 is filtered and washed in multiple stages, then dried and crushed.

[0012] S6. Mix the powder obtained in S5 with additives and pure water to form a mud-like material with a certain viscosity.

[0013] S7. Press the mud-like material into hollow graphite parts;

[0014] S8. High-temperature graphitization of hollow graphite parts;

[0015] S9. The graphitized hollow graphite parts are crushed to obtain graphite powder;

[0016] S10. Mix graphite powder with one or more of the following: pitch, petroleum coke, needle coke, raw coke, and calcined coke.

[0017] S11. The material obtained in S10 is sintered under an inert atmosphere to form carbon-coated graphite.

[0018] Based on the above technical solution, the present invention can be further improved as follows.

[0019] Furthermore, the drying temperature in S1 is 80℃~200℃, the drying time is 4h~20h, and the mesh size of the crushed powder is below 120 mesh.

[0020] Furthermore, the calcination temperature in S2 is 350℃~550℃, the time is 1h~4h, and the calcination is carried out in an air atmosphere.

[0021] Furthermore, the organic solvent in S3 is one or more of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, chloroform, toluene, and tetrahydrofuran, and the solid-liquid ratio of the powder to the organic solvent is 1:2 to 1:5 g / mL;

[0022] The surfactant is one or more of the following: sulfated castor oil, sodium lauryl sulfate, sodium dioctyl succinate sulfonate, sodium dodecylbenzene sulfonate, sodium glycocholate, cocoyl glucoside, lauryl glucoside, cetearyl glucoside, fatty acid sorbitan, and sodium carboxymethyl cellulose. The mass of the surfactant is 0.1% to 3% of the powder mass.

[0023] Furthermore, in S3, an ultra-high-speed shear homogenizer is used for shearing the slurry, with a rotation speed of 5000 rpm to 20000 rpm and a time of 5 min to 30 min.

[0024] Furthermore, the organic acid in S4 is one or more of benzenehexacarboxylic acid, nitrothiolic acid, trichloroacetic acid, trinitrobenzenesulfonic acid, and trifluoromethanesulfonic acid. The organic acid is added to the slurry to form an acid solution of 3 mol / L to 8 mol / L. The solvothermal reaction temperature is 80℃ to 180℃ and the time is 3h to 10h.

[0025] Furthermore, the reactor used is a reactor equipped with mechanical stirring.

[0026] Furthermore, in S5, drying is carried out at 80℃~150℃ for 5h~24h, and the crushed powder has a mesh size of less than 120 mesh.

[0027] Furthermore, the additives in S6 are one or more of cellulose, polyvinyl alcohol, polyvinyl acetate, styrene-butadiene rubber, isoprene rubber, polysulfide rubber, and polyacrylate. The mass of the additives accounts for 3% to 12% of the powder mass, and the mass of pure water accounts for 30% to 60% of the powder mass.

[0028] Furthermore, S6 specifically refers to:

[0029] Add 3% to 12% of the additive by weight of the powder to the powder, and place it in a high-speed mixer and stir at 300 rpm to 800 rpm for 5 to 20 minutes. Then add 30% to 60% of the pure water by weight of the powder and continue stirring for 10 to 30 minutes to form a mud-like material with a certain viscosity.

[0030] Furthermore, S7 specifically refers to:

[0031] The mud-like material is placed in a mold and pressed into a hollow part. The part is then dried at 80℃~120℃ for 10h~24h to finally obtain a graphite part.

[0032] Furthermore, hollow components are objects shaped like honeycomb briquettes or hollow tubes.

[0033] Furthermore, objects resembling honeycomb briquettes or hollow tubes have a diameter of 10cm to 20cm and a length of 20cm to 40cm.

[0034] Furthermore, the sintering temperature in S8 is 2600℃~3100℃, and the sintering time is 2h~4h.

[0035] Furthermore, the graphite components in S9 are mechanically pulverized into graphite powder of less than 200 mesh.

[0036] Furthermore, S10 specifically refers to:

[0037] Graphite powder is mixed with one or more of the following: asphalt, petroleum coke, needle coke, raw coke, and calcined coke in a high-speed mixer at a speed of 400 rpm to 800 rpm for 5 min to 20 min, with a mass ratio of 1:0.02 to 0.06.

[0038] Furthermore, the sintering temperature in S11 is 900℃~1300℃, and the time is 1h~4h.

[0039] Furthermore, the inert atmosphere is one or more of nitrogen, argon, and helium.

[0040] The beneficial effects of this invention are as follows:

[0041] 1. Calcination of the powder removes the organic binder and increases the powder's fluidity. At the same time, in an air atmosphere, the high temperature causes the metal impurities to transform into metal oxides, which helps with subsequent acid washing and purification.

[0042] 2. By shearing to refine the particles, the metal impurities encased within are exposed, and with the help of surfactants in organic solvents, the refined graphite particles are evenly dispersed in the solution without agglomeration, which helps with acid leaching purification.

[0043] 3. Using organic acids in a closed reaction vessel to remove metal impurities. On the one hand, organic acids have higher solubility in organic solvents, and heating increases the reactivity. The volatilized organic solvent increases the pressure in the closed container, further improving the reaction efficiency between the acid and the metal impurities. At the same time, solvothermal reduction can effectively remove oxygen-containing functional groups on the graphite surface.

[0044] 4. The graphitization process uses hollow graphite parts instead of powder in a graphitization furnace. On the one hand, the large pores and surface area of ​​the graphite parts help metal impurities to vaporize and escape at high temperatures, while powder poses a safety hazard of furnace spraying. On the other hand, hollow graphite parts help increase the packing resistance of the material, thereby improving the self-heating efficiency of the material and reducing the energy consumption required for heating the graphitization furnace.

[0045] 5. Add one or more of the following additives to graphite powder: asphalt, petroleum coke, needle coke, raw coke, and calcined coke. During the subsequent graphitization process, a phase change occurs, which tightly binds the graphite particles together. In addition, the added materials form graphite carbon to fill the defects and pores of the original waste graphite particles and reduce their specific surface area.

[0046] 6. Graphitization further purifies the material, causing carbon atoms to re-pick up, thus repairing defects in the graphite structure.

[0047] 7. The graphitized material is then coated with amorphous carbon, which increases the channels for lithium ion migration, thereby improving the electrochemical performance of the material. Attached Figure Description

[0048] Figure 1 This is a SEM image of the graphite recovered in Example 2 of this embodiment;

[0049] Figure 2 The image shows the XRD pattern of the graphite recovered in Example 2.

[0050] Figure 3 The nitrogen isothermal adsorption-desorption curve of the graphite recovered in Example 2 of this embodiment;

[0051] Figure 4 This is the pore size distribution curve of the graphite recovered in Example 2. Detailed Implementation

[0052] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0053] Example 1

[0054] A method for recovering graphite from acid leaching residue of waste lithium battery black powder includes the following specific steps:

[0055] S1. Dry the acid leaching residue at 110℃ for 15 hours, and crush the resulting blocky solid into powder below 120 mesh in a crusher.

[0056] S2. Place the powder in a sagger and then place it in a calcining furnace and calcine it in an air atmosphere at 500°C for 2 hours to remove the organic binder and increase the powder's fluidity. At the same time, the high temperature in the air atmosphere causes the metal impurities to transform into metal oxides, which helps with subsequent acid washing and purification.

[0057] S3. Pour the calcined powder into N-methylpyrrolidone at a solid-liquid ratio of 1:3 g / mL, and then add 1% sodium dodecylbenzenesulfonate by weight of the powder. The mixed slurry is then processed by an ultra-high-speed shear homogenizer at 16,000 rpm for 15 minutes. Under the action of high-speed shearing, the graphite particles are refined, and the metal impurities coated in the graphite particles are fully exposed. Furthermore, under the action of sodium dodecylbenzenesulfonate (surfactant), the refined graphite particles are uniformly dispersed in the solution without agglomeration.

[0058] S4. Add trichloroacetic acid, an organic acid, to the solution to prepare a 5 mol / L acid solution. Pour the acid solution into a sealed reaction vessel equipped with a mechanical stirrer and stir at 150°C for 4 hours. During this period, in addition to the high-temperature stirring which helps the collision reaction between acid molecules and metal impurities, the solvent volatilized due to heating increases the pressure inside the sealed reaction vessel, allowing the acid to penetrate further into the material for reaction, thereby improving the efficiency of impurity removal. In addition, the solvothermal reaction helps remove oxygen-containing functional groups from waste graphite.

[0059] S5. Filter and wash the reacted slurry through multiple stages, then dry it at 100℃ for 20 hours. The dried material is then mechanically pulverized into powder of 120 mesh.

[0060] S6. Add 8% by weight of cellulose to the powder, place it in a high-speed mixer and stir at 700 rpm for 10 minutes. Then, add 60% by weight of pure water and continue stirring for 20 minutes to form a mud-like material with a certain viscosity.

[0061] S7. Place the mud-like material in a mold and press it into a hollow part, such as an object with a diameter of 10cm and a length of 30cm, similar to a honeycomb briquette or a hollow tube. Place the hollow part at 90℃ for 24 hours to dry, and finally obtain a hollow graphite part.

[0062] S8. The hollow graphite part is placed in a graphitization furnace and sintered at 2600℃ for 2 hours to form carbon-coated graphite. During this process, the metal impurities that have not been removed turn into vapor and evaporate from the pores of the graphite part. At the same time, carbon atoms begin to rearrange at high temperature, structural defects are repaired, and the organic additives added to the powder are also transformed into carbon and intercalated with the original graphite benzene rings, maintaining the original shape of the graphite part.

[0063] S9. The graphitized graphite parts are mechanically crushed into graphite powder of less than 200 mesh.

[0064] S10. Place graphite powder and asphalt in a high-speed mixer and mix at 600 rpm for 5 minutes, with a mass ratio of 1:0.05.

[0065] S11. The mixed material is placed at 1100℃ and sintered under nitrogen for 2 hours to form carbon-coated graphite. The amorphous carbon coating on the graphite surface helps to increase the migration channels of lithium ions and improve the electrochemical performance of the material.

[0066] S12. The sintered carbon-coated graphite is crushed and sieved, and the median particle size of the powder is controlled at 14um to 16um.

[0067] Example 2

[0068] A method for recovering graphite from acid leaching residue of waste lithium battery black powder includes the following specific steps:

[0069] S1. Dry the acid leaching residue at 110℃ for 15 hours, and crush the resulting blocky solid into powder below 120 mesh in a crusher.

[0070] S2. Place the powder in a sagger and then place it in a calcining furnace and calcine it in an air atmosphere at 500°C for 2 hours to remove the organic binder and increase the powder's fluidity. At the same time, the high temperature in the air atmosphere causes the metal impurities to transform into metal oxides, which helps with subsequent acid washing and purification.

[0071] S3. Pour the calcined powder into N-methylpyrrolidone at a solid-liquid ratio of 1:3 g / mL, and then add 1% sodium dodecylbenzenesulfonate by weight of the powder. The mixed slurry is then processed by an ultra-high-speed shear homogenizer at 16,000 rpm for 15 minutes. Under the action of high-speed shearing, the graphite particles are refined, and the metal impurities coated in the graphite particles are fully exposed. Furthermore, under the action of sodium dodecylbenzenesulfonate (surfactant), the refined graphite particles are uniformly dispersed in the solution without agglomeration.

[0072] S4. Add trichloroacetic acid, an organic acid, to the solution to prepare a 5 mol / L acid solution. Pour the acid solution into a sealed reaction vessel equipped with a mechanical stirrer and stir at 150°C for 4 hours. During this period, in addition to the high-temperature stirring which helps the collision reaction between acid molecules and metal impurities, the solvent volatilized due to heating increases the pressure inside the sealed reaction vessel, allowing the acid to penetrate further into the material for reaction, thereby improving the efficiency of impurity removal. In addition, the solvothermal reaction helps remove oxygen-containing functional groups from waste graphite.

[0073] S5. Filter and wash the reacted slurry through multiple stages, then dry it at 100℃ for 20 hours. The dried material is then mechanically pulverized into powder of 120 mesh.

[0074] S6. Add 8% by weight of cellulose to the powder, place it in a high-speed mixer and stir at 700 rpm for 10 minutes. Then, add 60% by weight of pure water and continue stirring for 20 minutes to form a mud-like material with a certain viscosity.

[0075] S7. Place the mud-like material in a mold and press it into a hollow part, such as an object with a diameter of 10cm and a length of 30cm, similar to a honeycomb briquette or a hollow tube. Place the hollow part at 90℃ for 24 hours to dry, and finally obtain a hollow graphite part.

[0076] S8. The hollow graphite part is placed in a graphitization furnace and sintered at 2700℃ for 2 hours to form carbon-coated graphite. During this process, the metal impurities that have not been removed turn into vapor and evaporate from the pores of the graphite part. At the same time, carbon atoms begin to rearrange at high temperature, structural defects are repaired, and the organic additives added to the powder are also transformed into carbon and intercalated with the original graphite benzene rings, maintaining the original shape of the graphite part.

[0077] S9. The graphitized graphite parts are mechanically crushed into graphite powder of less than 200 mesh.

[0078] S10. Place graphite powder and asphalt in a high-speed mixer and mix at 600 rpm for 5 minutes, with a mass ratio of 1:0.05.

[0079] S11. The mixed material is placed at 1100℃ and sintered under nitrogen for 2 hours to form carbon-coated graphite. The amorphous carbon coating on the graphite surface helps to increase the migration channels of lithium ions and improve the electrochemical performance of the material.

[0080] S12. The sintered carbon-coated graphite is crushed and sieved, and the median particle size of the powder is controlled at 14um to 16um.

[0081] Figure 1 The image shows an SEM image of the graphite recovered in this embodiment. The graphite particles are irregularly shaped blocks stacked in layers, with a relatively clean surface and no impurities attached.

[0082] Figure 2 The image shows the XRD pattern of the graphite recovered in this embodiment. It can be seen from the image that the graphite is located at the (002) characteristic peak at 2θ = 26.54°, the interlayer spacing is 0.3355 nm, and there are no other impurity characteristic peaks, indicating that the graphite has high purity and crystallinity.

[0083] Figure 3 The figure shows the nitrogen isothermal adsorption-desorption curve of the graphite recovered in this embodiment. It can be seen from the figure that the curve type belongs to type III, and the hysteresis loop belongs to H3, indicating that the graphite structure is basically repaired, with no obvious defects and pores. The adsorption mainly originates from the slits generated by the stacking of graphite layered structures.

[0084] Figure 4 The figure shows the pore size distribution curve of the graphite recovered in this embodiment. It can be seen from the figure that the width of the pores in the graphite is mainly concentrated below 10 nm, and it is mainly mesoporous. However, because the strength is low, it indicates that the number of pores is small.

[0085] Furthermore, since the data differences between different embodiments are mainly reflected in the impurity content and electrochemical performance, and the characterization methods selected in the accompanying drawings are not significantly different between different embodiments, only one is selected as representative.

[0086] Example 3

[0087] A method for recovering graphite from acid leaching residue of waste lithium battery black powder includes the following specific steps:

[0088] S1. Dry the acid leaching residue at 110℃ for 15 hours, and crush the resulting blocky solid into powder below 120 mesh in a crusher.

[0089] S2. Place the powder in a sagger and then place it in a calcining furnace and calcine it in an air atmosphere at 500°C for 2 hours to remove the organic binder and increase the powder's fluidity. At the same time, the high temperature in the air atmosphere causes the metal impurities to transform into metal oxides, which helps with subsequent acid washing and purification.

[0090] S3. Pour the calcined powder into N-methylpyrrolidone at a solid-liquid ratio of 1:3 g / mL, and then add 1% sodium dodecylbenzenesulfonate by weight of the powder. The mixed slurry is then processed by an ultra-high-speed shear homogenizer at 16,000 rpm for 15 minutes. Under the action of high-speed shearing, the graphite particles are refined, and the metal impurities coated in the graphite particles are fully exposed. Furthermore, under the action of sodium dodecylbenzenesulfonate (surfactant), the refined graphite particles are uniformly dispersed in the solution without agglomeration.

[0091] S4. Add trichloroacetic acid, an organic acid, to the solution to prepare a 5 mol / L acid solution. Pour the acid solution into a sealed reaction vessel equipped with a mechanical stirrer and stir at 150°C for 4 hours. During this period, in addition to the high-temperature stirring which helps the collision reaction between acid molecules and metal impurities, the solvent volatilized due to heating increases the pressure inside the sealed reaction vessel, allowing the acid to penetrate further into the material for reaction, thereby improving the efficiency of impurity removal. In addition, the solvothermal reaction helps remove oxygen-containing functional groups from waste graphite.

[0092] S5. Filter and wash the reacted slurry through multiple stages, then dry it at 100℃ for 20 hours. The dried material is then mechanically pulverized into powder of 120 mesh.

[0093] S6. Add 8% by weight of cellulose to the powder, place it in a high-speed mixer and stir at 700 rpm for 10 minutes. Then, add 60% by weight of pure water and continue stirring for 20 minutes to form a mud-like material with a certain viscosity.

[0094] S7. Place the mud-like material in a mold and press it into a hollow part, such as an object with a diameter of 10cm and a length of 30cm, similar to a honeycomb briquette or a hollow tube. Place the hollow part at 90℃ for 24 hours to dry, and finally obtain a hollow graphite part.

[0095] S8. The hollow graphite part is placed in a graphitization furnace and sintered at 2800℃ for 2 hours to form carbon-coated graphite. During this process, the metal impurities that have not been removed turn into vapor and evaporate from the pores of the graphite part. At the same time, carbon atoms begin to rearrange at high temperature, structural defects are repaired, and the organic additives added to the powder are also transformed into carbon and intercalated with the original graphite benzene rings, maintaining the original shape of the graphite part.

[0096] S9. The graphitized graphite parts are mechanically crushed into graphite powder of less than 200 mesh.

[0097] S10. Place graphite powder and asphalt in a high-speed mixer and mix at 600 rpm for 5 minutes, with a mass ratio of 1:0.05.

[0098] S11. The mixed material is placed at 1100℃ and sintered under nitrogen for 2 hours to form carbon-coated graphite. The amorphous carbon coating on the graphite surface helps to increase the migration channels of lithium ions and improve the electrochemical performance of the material.

[0099] S12. The sintered carbon-coated graphite is crushed and sieved, and the median particle size of the powder is controlled at 14um to 16um.

[0100] Example 4

[0101] A method for recovering graphite from acid leaching residue of waste lithium battery black powder includes the following specific steps:

[0102] S1. Dry the acid leaching residue at 110℃ for 15 hours, and crush the resulting blocky solid into powder below 120 mesh in a crusher.

[0103] S2. Place the powder in a sagger and then place it in a calcining furnace and calcine it in an air atmosphere at 500°C for 2 hours to remove the organic binder and increase the powder's fluidity. At the same time, the high temperature in the air atmosphere causes the metal impurities to transform into metal oxides, which helps with subsequent acid washing and purification.

[0104] S3. Pour the calcined powder into N-methylpyrrolidone at a solid-liquid ratio of 1:3 g / mL, and then add 1% sodium dodecylbenzenesulfonate by weight of the powder. The mixed slurry is then processed by an ultra-high-speed shear homogenizer at 16,000 rpm for 15 minutes. Under the action of high-speed shearing, the graphite particles are refined, and the metal impurities coated in the graphite particles are fully exposed. Furthermore, under the action of sodium dodecylbenzenesulfonate (surfactant), the refined graphite particles are uniformly dispersed in the solution without agglomeration.

[0105] S4. Add trichloroacetic acid, an organic acid, to the solution to prepare a 5 mol / L acid solution. Pour the acid solution into a sealed reaction vessel equipped with a mechanical stirrer and stir at 150°C for 4 hours. During this period, in addition to the high-temperature stirring which helps the collision reaction between acid molecules and metal impurities, the solvent volatilized due to heating increases the pressure inside the sealed reaction vessel, allowing the acid to penetrate further into the material for reaction, thereby improving the efficiency of impurity removal. In addition, the solvothermal reaction helps remove oxygen-containing functional groups from waste graphite.

[0106] S5. Filter and wash the reacted slurry through multiple stages, then dry it at 100℃ for 20 hours. The dried material is then mechanically pulverized into powder of 120 mesh.

[0107] S6. Add 8% by weight of cellulose to the powder, place it in a high-speed mixer and stir at 700 rpm for 10 minutes. Then, add 60% by weight of pure water and continue stirring for 20 minutes to form a mud-like material with a certain viscosity.

[0108] S7. Place the mud-like material in a mold and press it into a hollow part, such as an object with a diameter of 10cm and a length of 30cm, similar to a honeycomb briquette or a hollow tube. Place the hollow part at 90℃ for 24 hours to dry, and finally obtain a hollow graphite part.

[0109] S8. The hollow graphite part is placed in a graphitization furnace and sintered at 2900℃ for 2 hours to form carbon-coated graphite. During this period, the metal impurities that have not been removed turn into vapor and evaporate from the pores of the graphite part. At the same time, carbon atoms begin to rearrange at high temperature, structural defects are repaired, and the organic additives added to the powder are also transformed into carbon and intercalated with the original graphite benzene rings, maintaining the original shape of the graphite part.

[0110] S9. The graphitized graphite parts are mechanically crushed into graphite powder of less than 200 mesh.

[0111] S10. Place graphite powder and asphalt in a high-speed mixer and mix at 600 rpm for 5 minutes, with a mass ratio of 1:0.05.

[0112] S11. The mixed material is placed at 1100℃ and sintered under nitrogen for 2 hours to form carbon-coated graphite. The amorphous carbon coating on the graphite surface helps to increase the migration channels of lithium ions and improve the electrochemical performance of the material.

[0113] S12. The sintered carbon-coated graphite is crushed and sieved, and the median particle size of the powder is controlled at 14um to 16um.

[0114] Comparative Example 1

[0115] The acid leaching residue was dried at 110℃ for 15 hours, and the resulting blocky solid was crushed into fine powder of less than 200 mesh in a crusher.

[0116] Comparative Example 2

[0117] 1) Dry the acid leaching residue at 110℃ for 15 hours, and then crush the resulting blocky solid into fine powder of less than 120 mesh in a crusher;

[0118] 2) Place the powder in a sagger and then place it in a calcining furnace at 5000℃ in air atmosphere for 2 hours;

[0119] 3) Pour the calcined powder into N-methylpyrrolidone at a solid-liquid ratio of 1:3 g / mL, and then add 1% sodium dodecylbenzenesulfonate by weight of the powder. The mixed slurry is then processed by an ultra-high speed shear homogenizer at 16,000 rpm for 15 min.

[0120] 4) Add trichloroacetic acid, an organic acid, to the solution to prepare a 5 mol / L acid solution. Pour the acid solution into a sealed reaction vessel equipped with a mechanical stirrer and stir at 150°C for 4 hours.

[0121] (5) The reacted slurry is filtered and washed in multiple stages, and then dried at 100°C for 20 hours. The dried material is then mechanically pulverized into powder with a mesh size of 200.

[0122] Physicochemical properties:

[0123] Table 1 shows the analysis and comparison of metal impurities in the samples prepared in Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2 using inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that high-pressure organic acid leaching can effectively remove metal impurities from the residue, but the content is still much higher than the requirements for commercial graphite. High-temperature graphitization can deeply purify the graphite residue to meet commercial requirements, and the purification effect is more obvious as the graphitization temperature increases.

[0124] Table 1. Metal impurity content (ppm) of the examples and comparative samples.

[0125] Metal elements Al Co Cr Cu Fe Li Mn Ni Zn Example 1 97 146 7 101 53 36 71 297 26 Example 2 55 28 5 33 14 7 3 53 20 Example 3 18 4 1 2 5 2 1 12 15 Example 4 2 0 0 0 2 0 0 1 2 Comparative Example 1 3249 22463 47 16461 2485 7532 10449 198606 1333 Comparative Example 2 435 3599 14 5108 207 369 1225 105588 469

[0126] Electrochemical performance:

[0127] Regenerated negative electrode material, styrene-butadiene rubber, sodium carboxymethyl cellulose, and carbon black conductive agent were mixed in deionized water at a ratio of 94:3:1.5:1.5, then coated onto copper foil to fabricate a 2025 type coin cell for electrochemical performance testing. The electrolyte consisted of 1M LiPF6 dissolved in ethylene carbonate and diethyl carbonate at a volume ratio of 1:1, and the counter electrode was lithium metal. Charge-discharge tests were conducted using a Blue Electric testing system, with a test voltage of 0.01–2.5V vs. Li. + Table 2 compares the electrochemical performance of samples prepared in Examples 1, 2, 3, and 4 with those in Comparative Examples 1 and 2. It was found that as the graphitization temperature increased, the initial coulombic efficiency and specific capacity of the prepared regenerated graphite anodes improved, and their performance was much higher than that of Comparative Examples 1 and 2.

[0128] Table 2 Electrochemical performance test data of sugar-polystyrene composite material and comparative sample

[0129]

[0130] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for recovering graphite from acid leaching residue of waste lithium battery black powder, characterized in that, Includes the following steps: S1. Dry the acid leaching residue and crush it into powder; S2. Calcine the powder to remove the organic binder. S3. Mix the powder obtained in S2 with organic solvent and surfactant, and perform high-shear homogenization emulsification on the resulting slurry to refine the particles. S4. Add organic acid to the slurry and carry out a solvothermal reaction in a reactor under closed and stirred conditions; S5. The slurry obtained in S4 is filtered and washed in multiple stages, then dried and crushed. S6. Mix the powder obtained in S5 with additives and pure water to form a mud-like material with a certain viscosity. S7. Press the mud-like material into hollow graphite parts; S8. High-temperature graphitization of hollow graphite parts; S9. The graphitized hollow graphite parts are crushed to obtain graphite powder; S10. Mix graphite powder with one or more of the following: pitch, petroleum coke, needle coke, raw coke, and calcined coke. S11. The material obtained in S10 is sintered under an inert atmosphere to form carbon-coated graphite.

2. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: The drying temperature in S1 is 80℃~200℃, the drying time is 4h~20h, and the particle size of the crushed powder is below 120 mesh.

3. A method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1 or 2, characterized in that: The calcination temperature of S2 is 350℃~550℃, and the time is 1h~4h.

4. A method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, 2, or 3, characterized in that: The organic solvent in S3 is one or more of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, chloroform, toluene, and tetrahydrofuran, and the solid-liquid ratio of powder to organic solvent is 1:2 to 1:5 g / mL. The surfactant is one or more of the following: sulfated castor oil, sodium lauryl sulfate, sodium dioctyl succinate sulfonate, sodium dodecylbenzene sulfonate, sodium glycocholate, cocoyl glucoside, lauryl glucoside, cetearyl glucoside, fatty acid sorbitan, and sodium carboxymethyl cellulose. The mass of the surfactant is 0.1% to 3% of the powder mass.

5. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: In S3, the slurry is sheared using an ultra-high-speed shear homogenizer with a rotation speed of 5000 rpm to 20000 rpm and a time of 5 min to 30 min.

6. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: The organic acid in S4 is one or more of the following: benzenehexacarboxylic acid, nitrothiolic acid, trichloroacetic acid, trinitrobenzenesulfonic acid, and trifluoromethanesulfonic acid. The organic acid is added to the slurry to form an acid solution of 3 mol / L to 8 mol / L. The solvothermal reaction temperature is 80℃ to 180℃ and the time is 3h to 10h.

7. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: Dry in S5 at 80℃~150℃ for 5h~24h, and the crushed powder should have a mesh size of less than 120 mesh.

8. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: The additives in S6 are one or more of cellulose, polyvinyl alcohol, polyvinyl acetate, styrene-butadiene rubber, isoprene rubber, polysulfide rubber, and polyacrylate. The additives account for 3% to 12% of the powder mass, and the pure water accounts for 30% to 60% of the powder mass.

9. The method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: The sintering temperature in S8 is 2600℃~3100℃, and the sintering time is 2h~4h.

10. A method for recovering graphite from acid leaching residue of waste lithium battery black powder according to claim 1, characterized in that: The sintering temperature in S11 is 900℃~1300℃, and the time is 1h~4h.

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