CN117003235A - A method for regenerating graphite in waste batteries - Google Patents

Abstract

The invention discloses a method for regenerating negative electrode graphite in waste batteries, and relates to the field of recycling negative electrode materials of lithium ion batteries. It includes: acid treatment of disassembled graphite from used batteries under mechanical stirring to obtain preliminary purified graphite; placing the initially purified graphite in a tube furnace, calcining it under inert atmosphere and high temperature conditions, and in-situ modification on the graphite surface; The graphite is then placed in a ball milling tank containing the coating liquid, and the surface is coated by wet ball milling, and then dried to remove the solvent. The dried product is then placed in a tube furnace and carbonized to obtain a regenerated graphite anode material. This method is used to realize the recycling of waste graphite negative electrodes, which alleviates the problem of large particle size and uneven coating of graphite negative electrode materials obtained by existing methods, as well as low capacity and low first efficiency when used as negative electrode materials in lithium-ion batteries. , technical problems such as rapid capacity fading, and it can also avoid the "black pollution" problem caused to the environment due to the ineffective use of waste graphite anodes.

Description

A method for regenerating graphite in waste batteries

Technical field

The invention discloses a method for regenerating graphite in waste batteries and relates to the field of recycling negative electrode materials of lithium ion batteries.

Background technique

In recent years, the new energy market has developed rapidly, and the number of lithium-ion batteries has increased rapidly. Among them, since the industrialization of Sony Corporation, power lithium batteries have become the preferred power battery for new energy vehicles due to their advantages such as high energy density, long cycle life, low self-discharge, and green environmental protection. At the same time, energy storage technologies led by lithium batteries have promoted the electrification wave in the transportation field, while also increasing the demand for lithium-ion battery material resources and exacerbating the scarcity of such resources. How to recycle used lithium-ion batteries using simple and green methods is an urgent problem in the sustainable development of the industrial chain in the new energy field.

In recent years, waste lithium-ion battery cathode materials have been industrialized through mature technologies such as hydrometallurgy and pyrometallurgy. In contrast, lithium-ion battery anodes are usually landfilled or incinerated at high temperatures. This unreasonable treatment method exacerbates environmental problems such as dust pollution and the greenhouse effect. In addition, as a key strategic resource, there are only 250 million tons of graphite that can be mined in the world. If waste lithium battery anode materials cannot be properly processed, it will cause huge waste of resources and economic losses. More importantly, if not handled carefully, as the number of used lithium-ion batteries continues to increase, the remaining lithium, heavy metal ions (nickel, cobalt, manganese) and organic electrolytes (lithium hexafluorophosphate, carbonate) in the used graphite will cause fires, Disastrous consequences such as explosions and leakage of harmful and harmful substances. Considering resource shortage, serious environmental pollution and safety hazards, we should continue to pay attention to the recycling of used lithium-ion battery anode materials and the resource utilization of products.

At present, silicon-based, lithium titanate and other materials only account for about 9% of the commercial anode material market, while graphite accounts for up to 90%, and is showing an upward trend. The market will be huge in the future, and the regeneration and repair of waste graphite anode materials will become a field of battery recycling. hot spots. Although long-term charge and discharge cycles will cause changes in surface structure and composition, the bulk structure of graphite materials shows relatively high structural stability, and can meet the secondary use of lithium-ion batteries after deep purification and structural repair. For the deep purification and structural repair of negative electrode materials, finding a suitable recycling process will create additional economic value. The recycling process of used lithium-ion battery negative electrode materials in the existing technology has the following problems:

1. The graphite recovered from the leaching slag contains many metal impurities, which makes the recovery difficult and the recovery rate low, and the recovered graphite cannot meet the raw material grade required for battery manufacturing;

2. The enlarged interlayer spacing, changes in the lattice structure and the incorporation of impurities are the salient characteristics of the negative electrode graphite after the failure of used lithium-ion batteries, resulting in significant changes in the surface structure and composition of graphite particles, limiting the performance of regenerated graphite. At the same time, in The structural repair of waste graphite during the recycling process of waste lithium-ion batteries has not been explored.

In view of the above, there is an urgent need for an efficient regeneration method to repair the structural defects of waste graphite so that the regenerated graphite can achieve higher electrochemical activity and excellent cycle stability.

Contents of the invention

A method for regenerating graphite in waste batteries of the present invention solves the problem of recycling graphite in negative electrode materials of lithium batteries.

In order to achieve the above purpose, the technical solutions adopted are as follows:

A method for regenerating graphite in used batteries, including the following steps:

S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the negative electrode material on its surface. Then soak the recycled negative electrode material in an organic solvent and remove the electrolytic residue on its surface through constant stirring. The liquid is then filtered, dried, crushed and sieved to obtain the graphite negative electrode material;

S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as raw material, fully dissolve the metal impurities in the graphite anode material into the solution phase through acid leaching and mechanical stirring, and then transform the metal ions entering the solution phase. It is a soluble metal salt sulfate. It is repeatedly washed with deionized water until the pH value is 6 to 8, and vacuum dried at 80°C to obtain initially purified graphite;

S3. High-temperature calcination: Place the graphite initially purified in step S2 in a tube furnace and calcine in an inert atmosphere, so that the remaining binder-like organic matter on the graphite surface is completely cracked and transformed into amorphous carbon, which is modified in situ on the graphite. On the surface, secondary purified graphite is obtained;

S4. Coating and secondary calcination: Wet the secondary purified graphite in step S3 into the coating solution containing the carbon source, perform surface coating by wet ball milling, and then evaporate and dry to remove the solvent, and then coat the surface with The carbon coating material is placed in a tube furnace and calcined twice in an inert atmosphere. After cooling, it is screened to obtain battery-grade regenerated graphite anode material.

Preferably, the organic solvent in step S1 is one of dimethyl carbonate, ethylene carbonate, and propylene carbonate.

Preferably, the mesh number of the screening process in step S1 is 100 mesh.

Preferably, in step S2, the graphite negative electrode material is acid washed with sulfuric acid, and the concentration of the acid solution is 0.5-4 mol/L.

Preferably, the mass ratio of graphite to acid solution in step S2 is 1:(1-10)g/ml, the reaction time of the acid leaching process is 0.5-6h, and the treatment temperature is 25-80°C.

Preferably, the inert atmosphere in step S3 is one of argon and nitrogen, the temperature rise rate during the calcination is 2-5°C/min, the calcination temperature is 800-1000°C, and the calcination time is 3-6h.

Preferably, in step S4, the ball-to-material ratio of the materials in the ball mill tank is 1:5, the rotation speed is 350-500 r/min, and the ball milling time is 6-10 hours.

Preferably, in step S4, the coating carbon source is pitch, the coating solvent is one of tetrahydrofuran, pyridine, and toluene, and the amount of pitch added is 3 wt% to 15 wt% of the graphite mass.

Preferably, the product in step S4 is placed in a tube furnace, using one of argon and nitrogen, the heating rate during high temperature treatment is 2-5°C/min, the calcination temperature is 800-1000°C, and the calcination time is 3-6h.

Preferably, the mesh size of the screening process in step S4 is 100 meshes.

Compared with the existing technology, the beneficial effects of the present invention are:

1. This plan designs a graphite recycling method. The graphite anode material recovered from used lithium-ion batteries is soaked in an organic solvent to remove the electrolyte on the surface of the anode material; the pretreated graphite is used as the raw material for pickling and purification. The acid solution and metal impurities are fully reacted to form soluble metal salts, which effectively removes the remaining metal impurities in the graphite, improves the purity of the graphite, and solves the problem of large residual metal impurities, which is not conducive to graphite recycling. Then, the powder is calcined using high-temperature roasting to further carbonize the organic residues such as polyvinylidene fluoride and acetylene black into amorphous carbon, and remove most of the volatile impurities such as F, P, and S, improving the quality of the material. of purity. In addition, the high-temperature calcination process also causes the rearrangement of carbon atoms, and the structural defects of graphite can be repaired; finally, through the ball milling process and rapid heating technology, the surface of the waste graphite is coated with a layer of carbon material to perform surface reconstruction, and the added asphalt forms Amorphous carbon fills the defects and pores originally formed due to long-term charge and discharge cycles, reducing its specific surface area, thereby improving the electrochemical activity and cycle stability of the material.

2. Compared with the existing technology, the method of the present invention not only has a simple process and low recovery energy consumption and cost, but also has high purity of recycled materials, and the process is environmentally friendly and pollution-free. After organic solvent cleaning, acid leaching purification and high-temperature calcination, impurities such as electrolyte, metal ions, and binders attached to the graphite surface are efficiently removed, significantly improving the purity of the material. In this solution, the ball mill coating process can not only reduce the particle size of graphite, but also enable the carbon materials dispersed in the graphite to evenly adhere to the surface of the material to achieve uniform coating of graphite; the traditional graphite repair process involves a ball mill screen The separation and liquid phase coating processes are combined into one, simplifying the recycling process and making the process simple and efficient; more importantly, this method can alleviate the excessive particle size and uneven coating of graphite materials obtained by existing graphite recycling methods. And when used as a negative electrode material, the battery graphite structure cannot be maintained and the capacity rapidly decays and other technical problems. It solves the two problems of graphite recycling and repair in one fell swoop, and has important guiding significance for the resource utilization of used lithium batteries. The half-cell assembled by it is superior to traditional liquid-phase repaired graphite materials in terms of specific capacity, rate performance and long cycle performance.

3. The method provided by this solution has a simple process and is easy for large-scale industrial production. It has low material recovery cost and high recovery rate. The prepared graphene-coated carbon negative electrode material recycled from waste has excellent high-current charge and discharge performance and excellent Cycling stability, high first Coulombic efficiency and charge-discharge specific capacity.

Description of the drawings

Figure 1 is a scanning electron microscope image of acid-treated graphite and regenerated graphite prepared by the present invention;

Figure 2 is a flow chart of the traditional regeneration method of Comparative Examples 1 and 2;

Figure 3 is a flow chart of the regeneration method of Examples 1-4.

Implementation

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments:

Example 1

A method for regenerating graphite in used batteries, including the following steps:

S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the graphite negative electrode material on its surface. Then soak the recycled graphite negative electrode material in dimethyl carbonate and stir continuously for 2 hours, and then filter it out. dimethyl carbonate, dried and passed through a 100-mesh sieve to obtain a 100-mesh graphite negative electrode material.

S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as raw material, place the graphite in a sulfuric acid solution with a concentration of 0.5mol/L, control the mass ratio of graphite to acid solution to 1:1g/ml, and oil Heat the bath to 25°C and stir evenly for 0.5h. After the slurry was suction-filtered, it was transferred to a vacuum drying oven and dried at 80°C for 5 hours. The impurities in the material are fully dissolved through mechanical stirring (stirring speed is 200 rpm/min), and the metal ions in the graphite are converted into soluble metal salts. Then, deionized water is used to repeatedly wash until the pH value is 6 to 8, and the water is dried at 80 Carry out vacuum drying at ℃ temperature to obtain preliminary purified graphite.

S3. High-temperature calcination: Place the graphite initially purified in step S2 into a tube furnace and calcine it in an argon atmosphere from room temperature to 800°C at a rate of 2°C/min for 3 hours. Then the tube furnace is cooled to below room temperature and taken out. The binder organic substances in the product are converted into amorphous carbon, which is modified in situ on the graphite surface to obtain secondary purified graphite.

S4. Coating and secondary calcination: First weigh 3wt% of medium-temperature asphalt in a beaker, add 25ml of toluene, stir evenly for 30 minutes, then place it in a centrifuge tube for centrifugation, remove the asphalt that is insoluble in the toluene solution, and the supernatant Pour into 500ml ball mill jar. Wet the graphite in step S3 into a ball mill jar containing 25 ml of toluene, and then use wet ball milling at 350 rpm/min for 6 hours. After the solvent has completely evaporated, transfer it to a vacuum drying oven and dry it at 100°C for 10 hours. Finally, the dried product Place it in a tube furnace and calcine it in an argon atmosphere at a rate of 2°C/min from room temperature to 800°C for 3 hours. As the furnace cools to below room temperature, take it out and pass it through a 100-mesh sieve to obtain battery-grade regenerated graphite anode material.

Example 2

A method for regenerating graphite in used batteries, including the following steps:

S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the natural graphite negative electrode material on its surface. Then soak the recycled graphite negative electrode material in ethylene carbonate and stir continuously for 3 hours, and then filter out the carbonic acid. Vinyl ester, dried and passed through a 100-mesh sieve to obtain a 100-mesh graphite anode material;

S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as the raw material. Place the graphite in a sulfuric acid solution with a concentration of 2 mol/L. Control the mass ratio of graphite to acid solution to 1:5g/ml. Oil bath Heat to 40°C and stir evenly for 3 hours. After the slurry was suction-filtered, it was transferred to a vacuum drying oven and dried at 80°C for 5 hours. Fully dissolve the impurities in the material through mechanical stirring (stirring speed is 300 rpm/min), convert the metal ions in the graphite into soluble metal salts, use deionized water to repeatedly wash until the pH value is 6 to 8, and heat it at 80°C Perform vacuum drying at high temperature to obtain initially purified graphite.

S3. High-temperature calcination: Place the graphite initially purified in step S2 into a tube furnace and calcine it in a nitrogen atmosphere from room temperature to 900°C at 3°C/min for 4 hours. Then the tube furnace is cooled to below room temperature and taken out. The binder organic substances in the product are converted into amorphous carbon and modified in situ on the graphite surface to obtain secondary purified graphite.

S4. Coating and secondary calcination: First weigh 5wt% medium-temperature asphalt into a beaker, add 25ml of pyridine, stir evenly for 30 minutes, then place it in a centrifuge tube for centrifugation, remove the asphalt that is insoluble in the pyridine solution, and the supernatant Pour into 500ml ball mill jar. Soak the graphite in step S2 into the ball milling tank, and then use wet ball milling at 400 rpm/min for 8 hours. After the solvent has completely evaporated, transfer it to a vacuum drying oven and dry it at 100°C for 10 hours. Place the material with asphalt on the surface in the In a tube furnace, in a nitrogen atmosphere, the temperature was raised to 900°C for carbonization at a rate of 3°C/min for 4 hours to obtain regenerated graphite anode material.

Example 3

A method for regenerating graphite in used batteries, including the following steps:

S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the graphite negative electrode material on its surface. Then soak the recycled graphite negative electrode material in propylene carbonate and stir continuously for 3 hours, and then filter out the carbonic acid. Propylene ester is dried and passed through a 100-mesh sieve to obtain a 100-mesh graphite anode material;

S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as the raw material. Place the graphite in a sulfuric acid solution with a concentration of 4 mol/L. Control the mass ratio of graphite to acid solution to 1:10g/ml. Oil bath Heat to 60°C and stir evenly for 6 hours. After the slurry was suction-filtered, it was transferred to a vacuum drying oven and dried at 80°C for 5 hours. Fully dissolve the impurities in the material through mechanical stirring (stirring speed is 300 rpm/min), convert the metal ions in the graphite into soluble metal salts, use deionized water to repeatedly wash until the pH value is 6 to 8, and heat it at 80°C Perform vacuum drying at high temperature to obtain initially purified graphite.

S3. High-temperature calcination: Place the graphite initially purified in step S2 in a tube furnace and calcine it in a nitrogen atmosphere at 5°C/min from room temperature to 1000°C for 6 hours. Then the tube furnace is cooled to below room temperature and taken out to make the product The binder organic substances in the graphite are converted into amorphous carbon, and the graphite surface is modified in situ to obtain secondary purified graphite.

S4. Coating and secondary calcination: First weigh 7wt% medium-temperature asphalt into a beaker, add 25ml tetrahydrofuran, stir evenly for 30 minutes, then place it in a centrifuge tube for centrifugation, remove the asphalt that is insoluble in the tetrahydrofuran solution, and the supernatant Pour into 500ml ball mill jar. Soak the graphite in step S2 into the ball milling tank, and then use wet ball milling to mill at 500 rpm/min for 10 hours. After the solvent has completely evaporated, transfer it to a vacuum drying oven and dry it at 100°C for 10 hours. Place the material with asphalt attached to the surface in a In a tube furnace, under a nitrogen atmosphere, the temperature was raised to 1000°C for carbonization at a rate of 5°C/min for 6 hours to obtain regenerated graphite anode material.

Example 4

A method for regenerating graphite in used batteries, including the following steps:

S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the natural graphite negative electrode material on its surface. Then soak the recovered natural graphite negative electrode material in dimethyl carbonate and stir continuously for 3 hours. Filter out the propylene carbonate, dry it, and pass it through a 100-mesh sieve to obtain a 100-mesh graphite negative electrode material;

S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as the raw material. Place the graphite in a sulfuric acid solution with a concentration of 4 mol/L. Control the mass ratio of graphite to acid solution to 1:5g/ml. Oil bath Heat to 80°C and stir evenly for 6 hours. After the slurry was suction-filtered, it was transferred to a vacuum drying oven and dried at 80°C for 5 hours. Fully dissolve the impurities in the material through mechanical stirring (stirring speed is 300 rpm/min), convert the metal ions in the graphite into soluble metal salts, use deionized water to repeatedly wash until the pH value is 6 to 8, and heat it at 80°C Perform vacuum drying at high temperature to obtain initially purified graphite.

S3. High-temperature calcination: Place the graphite initially purified in step S2 in a tube furnace and calcine it in a nitrogen atmosphere at 5°C/min from room temperature to 1000°C for 6 hours. Then the tube furnace is cooled to below room temperature and taken out to make the product The binder organic substances in the graphite are converted into amorphous carbon, and the graphite surface is modified in situ to obtain secondary purified graphite.

S4. Coating and secondary calcination: First weigh 15wt% medium-temperature asphalt and place it in a beaker. Add 25ml of tetrahydrofuran. Stir evenly for 30 minutes and then place it in a centrifuge tube for centrifugation. Remove the asphalt that is insoluble in the tetrahydrofuran solution and the supernatant. Pour into 500ml ball mill jar. Soak the graphite in step S2 into the ball milling tank, and then use wet ball milling to mill at 500 rpm/min for 10 hours. After the solvent has completely evaporated, transfer it to a vacuum drying oven and dry it at 100°C for 10 hours. Place the material with asphalt attached to the surface in a In a tube furnace, under a nitrogen atmosphere, the temperature was raised to 1000°C for carbonization at a rate of 5°C/min for 6 hours to obtain regenerated graphite anode material.

Technical principles of this plan:

The recycling method of graphite from used batteries provided in this program example first uses pickling to remove metal impurities in graphite slag, and then controls the temperature, stirring rate and holding time to carry out the reaction, which promotes the dissolution of refractory metal impurities. At the same time, this solution also controls the acid solution and the treatment time and temperature of the acid solution to promote the collision reaction between acid molecules and metal impurities, thereby improving the efficiency of impurity removal. After the above treatment, preliminary purified graphite is obtained.

Then, the preliminary purified graphite is calcined at high temperature, so that the remaining binder organic substances in the graphite are fully contacted with the inert, completely cracked and transformed into amorphous carbon, which is modified in situ on the graphite surface; at the same time, by accurately controlling the calcination temperature and The calcination time allows the carbon atoms to be re-emitted while purifying the material, and the structural defects of the graphite can be repaired. By controlling the calcination temperature, heating rate and time, the organic matter in the waste graphite anode material is decomposed and carbonized, the shape of the graphite is fixed, and the structural defects of the graphite are restored.

Finally, a specific weight of asphalt is added to the graphite, and wet ball milling is used to mix and high-temperature calcination to form an asphalt coating layer on the surface of the graphite to repair the cracks on the surface of the directly recycled anode material caused by long-term charge and discharge cycles. This makes the anode material have excellent electrochemical activity and cycle stability.

This solution has no special limitations on the preparation method of the asphalt coating liquid, and technical solutions known in the art can be used. This solution uses the above types of organic solvents to dissolve the asphalt, mix the components evenly, and improve the coating effect of the asphalt on the recycled graphite. At the same time, this solution controls the mixing parameters of graphite and asphalt coating liquid within the above range, which can form a uniform asphalt coating layer on the graphite surface, making the coating layer smoother, providing better coating effect, and improving the utilization of recycled graphite. The first efficiency of the battery as the negative electrode; and this solution also controls the temperature, time and heating rate of the carbonization process to facilitate the carbonization process, which can completely carbonize the pitch and form an integrated structure with the graphite to improve the surface defects of the graphite , Improving the surface properties of graphite materials can further improve the first efficiency of batteries using recycled graphite as the negative electrode, and obtain better cycle performance and rate performance.

Comparative example 1

This comparative example adopts the traditional regeneration method. A certain amount of waste graphite is weighed and placed in a sulfuric acid solution with a concentration of 4mol/L. The mass ratio of graphite and acid solution is controlled to 1:5g/ml. The oil bath is heated to 60°C to make it uniform. Stir for 6 hours; after filtering the obtained slurry, transfer it to a vacuum drying oven and dry it at 80°C for 5 hours. The dried graphite is placed in a tube furnace and calcined in a nitrogen atmosphere at 5°C/min from room temperature to 1000°C for 6 hours. The tube furnace is then cooled to below room temperature and taken out to eliminate the binder organic substances in the product. Transformed into amorphous carbon, the graphite surface is modified in situ and becomes a graphite anode material.

Comparative example 2

This comparative example adopts the traditional regeneration method. A certain amount of waste graphite is weighed and placed in a sulfuric acid solution with a concentration of 2 mol/L. The mass ratio of graphite and acid solution is controlled to 1:5g/ml. The oil bath is heated to 60°C to make it uniform. Stir for 6 hours; after filtering the obtained slurry, transfer it to a vacuum drying oven and dry it at 80°C for 5 hours. Place the dried graphite in a tube furnace, raise the temperature to 800°C with the furnace, keep it warm for 4 hours, and then cool it with the furnace to below room temperature and take it out.

Weigh 5wt% medium-temperature asphalt into a beaker, add 25ml of pyridine, stir evenly for 30 minutes, then place it in a centrifuge tube for centrifugation, remove the asphalt that is insoluble in the pyridine solution, and pour the supernatant into the beaker; pretreat graphite in batches Add it to the coating liquid, and adjust the speed appropriately during this period; after stirring at room temperature for 4 hours, raise the temperature of the oil bath to 70°C, and continue stirring until the solvent is completely evaporated; place the material with asphalt attached to the surface in a tube furnace, and stir for 5 hours under a nitrogen atmosphere. The temperature was raised to 900°C for 4 hours at a rate of ℃/min to obtain battery-grade regenerated graphite anode material.

The products obtained in Examples 1-4 and Comparative Examples 1-2 were used for characterization, and the obtained characterization results are as follows.

As shown in Figure 1, the scanning electron microscope images of acid-treated graphite (a in Figure 1) and regenerated graphite (b in Figure 1) have particle sizes of approximately 15-20 μm. There are varying degrees of cracks and impurity adhesion on the surface of the initially purified graphite; after repair with asphalt, the surface defects of the regenerated graphite gradually decrease, and a layer of dense and round amorphous carbon gradually forms on the surface of the graphite, which is conducive to the insertion of lithium ions. /Extraction, has good electrochemical properties.

As shown in Table 1 below,

Table 1: Electrical properties of recycled graphite

The graphite prepared in the example was used as the negative electrode material, and the lithium sheet was used as the counter electrode, and a button battery was assembled. Conduct charge and discharge cycle tests at 20-25°C, in the voltage range of 0.01-2V, and at a current density of 0.5C (1C=372mA g-1). The following conclusions can be drawn from Table 1: (1) Reducing the graphite particle size will help shorten the lithium ion transmission path, thereby improving the cycle stability of the electrode material. (2) Compared with traditional liquid phase coating, the ball milling coating process can achieve uniform coating of the carbon coating, which not only stabilizes the electrode structure, but also improves the rate performance of the electrode material. (3) Reasonably adjust the thickness of the asphalt coating to better optimize the overall performance of graphite. The thickness of the cladding layer is critical to the structure of the electrode material. If the asphalt coating content is too much, the amorphous carbon content formed will increase, which will reduce the overall Coulombic efficiency of the coated material; if the coating amount is too small, the coating formed by the asphalt will be too weak to support the structure of the graphite. During the cycling process, the graphite layers peel off and the capacity decays rapidly.

As shown in Figures 2 and 3, the ball mill coating process of Examples 1 to 4 can combine the ball mill screening and liquid phase coating in the traditional process of Examples 1 and 2 into one process. The production process is simple and efficient. It is scalable, and the resulting product has excellent electrochemical properties. This work provides an effective strategy for graphite recycling in industry, provides a new way to prepare high-performance lithium-ion battery graphite anode, and has good commercial application prospects. .

The above are only embodiments of the present invention, and common knowledge such as well-known specific structures and/or characteristics in the solutions are not described in detail here. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention. These should also be regarded as the protection scope of the present invention and will not affect the implementation of the present invention. effectiveness and patented practicality. The scope of protection claimed in this application shall be based on the content of the claims, and the specific implementation modes and other records in the description may be used to interpret the content of the claims.

Claims (10)

1. A method for regenerating graphite in used batteries, which is characterized in that it includes the following steps: S1. Raw materials: First remove the negative electrode sheet from the used lithium-ion battery and directly scrape off the negative electrode material on its surface. Then soak the recycled negative electrode material in an organic solvent and remove the electrolytic residue on its surface through constant stirring. The liquid is then filtered, dried, crushed and sieved to obtain the graphite negative electrode material; S2. Acid leaching pretreatment: Use the graphite anode material pretreated in step S1 as raw material, fully dissolve the metal impurities in the graphite anode material into the solution phase through acid leaching and mechanical stirring, and then transform the metal ions entering the solution phase. It is a soluble metal salt sulfate. It is repeatedly washed with deionized water until the pH value is 6 to 8, and vacuum dried at 80°C to obtain initially purified graphite; S3. High-temperature calcination: Place the graphite initially purified in step S2 in a tube furnace and calcine in an inert atmosphere, so that the remaining binder-like organic matter on the graphite surface is completely cracked and transformed into amorphous carbon, which is modified in situ on the graphite. On the surface, secondary purified graphite is obtained; S4. Coating and secondary calcination: Wet the secondary purified graphite in step S3 into the coating solution containing the carbon source, perform surface coating by wet ball milling, and then evaporate and dry to remove the solvent, and then coat the surface with The carbon coating material is placed in a tube furnace and calcined twice in an inert atmosphere. After cooling, it is screened to obtain battery-grade regenerated graphite anode material. 2. A method for regenerating graphite in waste batteries as claimed in claim 1, characterized in that: the organic solvent in step S1 is one of dimethyl carbonate, ethylene carbonate and propylene carbonate. 3. A method for regenerating graphite in waste batteries as claimed in claim 2, characterized in that: the mesh number of the screening process in step S1 is 100 meshes. 4. A method for regenerating graphite in waste batteries according to claim 1, characterized in that: in step S2, the graphite anode material is pickled with sulfuric acid, and the concentration of the acid solution is 0.5-4 mol/L. 5. A method for regenerating graphite in waste batteries as claimed in claim 4, characterized in that: the mass ratio of graphite and acid solution in step S2 is 1: (1-10) g/ml, and the reaction time of the acid leaching process is 0.5-6h, treatment temperature is 25-80℃. 6. A method for regenerating graphite in waste batteries as claimed in claim 1, characterized in that: in step S3, the inert atmosphere is one of argon and nitrogen, and the heating rate during the calcining process is 2-5°C/min. The temperature is 800-1000℃, and the calcination time is 3-6h. 7. A method for regenerating graphite in waste batteries as claimed in claim 1, characterized in that: in step S4, the ball-to-material ratio of the material in the ball mill tank is 1:5, the rotation speed is 350-500r/min, and the ball milling time is 6-10h . 8. A method for regenerating graphite in waste batteries as claimed in claim 7, characterized in that: in step S4, the coating carbon source is asphalt, the coating solvent is one of tetrahydrofuran, pyridine, and toluene, and the addition amount of the asphalt It is 3wt%-15wt% of the graphite mass. 9. A method for regenerating graphite in waste batteries as claimed in claim 8, characterized in that: in step S4, the product is placed in a tube furnace, using one of argon and nitrogen, and the heating rate during the high temperature treatment is 2-5 ℃/min, the calcination temperature is 800-1000℃, and the calcination time is 3-6h. 10. A method for regenerating graphite in used batteries as claimed in claim 1, characterized in that: the mesh number of the screening process in step S4 is 100 meshes.