Method for recovering graphite from battery negative electrode by molten salt assisted regeneration and application thereof

Abstract

This invention provides a method and application for the molten salt-assisted regeneration of graphite anodes in battery recycling. The method includes the following steps: grinding and thoroughly mixing graphite powder and inorganic salts recovered from waste battery anodes to obtain a mixed powder; calcining the mixed powder in air at 800–1100°C; washing the calcined product multiple times, filtering and drying it to obtain regenerated graphite. With the aid of simple molten salt and water washing, significant reductions in impurities in waste graphite anode materials and a marked improvement in electrochemical performance can be achieved. The graphite regeneration method of this invention is simple and easy to implement, and the molten salt can be reused, which is beneficial for promoting the resource recycling of retired lithium-ion anode materials.

Description

Technical Field

[0001] This invention relates to the field of waste graphite recycling technology and resource utilization, and in particular to a method and application for the recycling of graphite molten salt-assisted regeneration of battery negative electrodes. Background Technology

[0002] Graphite is widely used as an anode material in lithium-ion batteries due to its excellent conductivity, high reversible capacity, and good cycle stability. As the most commonly used anode material, graphite accounts for 12% to 21% of the total battery weight and has wide applications in commercial lithium batteries, especially in the power battery field. However, the booming lithium battery industry has generated a massive number of end-of-life batteries, with an estimated 11 million tons to be generated by 2030. Currently, recycling technology for retired power batteries focuses on the recovery of cathode materials, while the dismantled waste graphite is difficult to utilize efficiently due to a lack of effective technologies. Most companies are still at the stage of inefficient incineration for fuel or landfill disposal, resulting in significant resource waste and environmental pollution.

[0003] Current conventional waste graphite remediation and regeneration technologies typically involve first removing surface adhesives through high-temperature calcination in an inert atmosphere, then soaking in an acid solution to remove internal metallic impurities, followed by a series of operations such as drying, ball milling, and sieving to obtain preliminarily purified graphite. This material processing method is quite cumbersome and requires high-temperature calcination in an inert atmosphere, significantly increasing processing costs for enterprises. Furthermore, the acid treatment process removes metal ions and other impurities from the graphite, which to some extent significantly increases the cost of graphite recycling and regeneration and causes environmental pollution. Therefore, there is an urgent need for a simple, economical, and environmentally friendly graphite recycling and regeneration technology to obtain purified and regenerated graphite, which is of great significance for the reuse of waste graphite resources in lithium-ion battery anode materials. Summary of the Invention

[0004] This invention provides a method and application for recovering graphite molten salt-assisted regeneration of battery negative electrodes, the purpose of which is to solve the above-mentioned problems existing in the background art.

[0005] To achieve the above objectives, embodiments of the present invention provide a method and application for the molten salt-assisted regeneration of graphite anode materials in battery recycling. By employing simple molten salt assistance and water washing, a significant reduction in impurities in waste graphite anode materials and a marked improvement in electrochemical performance can be achieved. The graphite regeneration method of the present invention is simple and easy to implement, and the molten salt can be reused, which is beneficial for promoting the resource-based reuse of retired lithium-ion anode materials.

[0006] A method for recovering graphite molten salt-assisted regeneration of battery negative electrodes includes the following steps:

[0007] S1: Grind and thoroughly mix the graphite powder and inorganic salt recovered from the negative electrode of the waste battery to obtain a mixed powder;

[0008] S2: The mixed powder is calcined in air at 800-1100°C;

[0009] S3: After washing the calcined product multiple times, filtering and drying it, regenerated graphite is obtained.

[0010] According to one aspect of an embodiment of the present invention, in step S1, the inorganic salt is sodium chloride.

[0011] According to one aspect of an embodiment of the present invention, in step S1, the mass ratio of graphite powder to inorganic salt is 1:9 to 9:1.

[0012] According to one aspect of an embodiment of the present invention, in step S1, the mass ratio of graphite powder to inorganic salt is 1:1 to 4. Preferably, the mass ratio of graphite powder to inorganic salt includes 1:1, 1:2, 1:3, and 1:4.

[0013] According to one aspect of an embodiment of the present invention, in step S2, the calcination time is 0.2 to 4 hours and the heating rate is 2 to 10 °C / min.

[0014] According to one aspect of an embodiment of the present invention, in step S2, the calcination time is 1 hour.

[0015] According to one aspect of an embodiment of the present invention, in step S3, the washing process involves soaking and stirring in deionized water at a temperature of 25–90°C, and the washing is performed 1–3 times.

[0016] Based on a general inventive concept, embodiments of the present invention provide recycled graphite prepared by the above-described method for the regeneration of graphite molten salt-assisted graphite in the recovery of battery negative electrodes.

[0017] Embodiments of the present invention also provide the application of the regenerated graphite prepared by the above-described method for the recovery of graphite molten salt-assisted regeneration of battery negative electrode in lithium-ion batteries.

[0018] According to one aspect of an embodiment of the present invention, the mixture obtained by mixing the recycled graphite with PVDF and conductive carbon black is dispersed in an N-methylpyrrolidone solution to form a uniform slurry, and then the slurry is coated on a conductive copper foil and dried to obtain a lithium-ion battery negative electrode.

[0019] Molten salt calcination uses one or more low-melting-point salts as the calcination medium. Because of the low-melting-point salts as the reaction medium, a liquid phase appears during the synthesis process, increasing the solubility of the reactants in the molten salt medium and greatly accelerating the ion diffusion rate. This allows the calcined reactants to achieve atomic-scale mixing in the liquid phase, enabling the calcination reaction to occur at the atomic level, resulting in high efficiency. After the reaction, the salts are dissolved in a suitable solvent, and the calcined product is obtained after filtration and washing. Compared to conventional high-temperature calcination methods, this method has advantages such as simple process, low synthesis temperature, short holding time, and high processing efficiency. Therefore, molten salt calcination, with its advantages of low calcination temperature, high solubility, atomic-level mixing process, and easy salt separation and recycling, holds promise for lowering the calcination temperature in the molten salt auxiliary process of graphite recovery. It utilizes the high solubility and atomic-level mixing process of molten salt to remove impurities from graphite, thereby developing a novel technology for the purification and reuse of recovered graphite.

[0020] The molten salt-assisted regeneration technology of the present invention has the following effects:

[0021] A. In the traditional field of waste graphite recycling, graphite contains impurities such as binders and electrolytes, requiring high-temperature calcination to remove organic impurities. However, traditional inert atmosphere calcination processes leave small amounts of organic residue, forming amorphous carbon and affecting the electrochemical performance of the graphite. This application ingeniously utilizes a molten salt-assisted low-temperature air atmosphere calcination process to completely oxidize and remove organic carbon before the molten salt melts. After the molten salt melts, it forms a liquid phase that protects the graphite from further oxidation and loss due to burn-off.

[0022] B. During calcination in an air atmosphere in a muffle furnace, before the low-melting-point molten salt melts, graphite undergoes a surface oxidation process. Oxygen in the air reacts with the graphite at the gas-solid interface, reducing the number of active sites on the graphite surface and minimizing the initial irreversible capacity loss. Simultaneously, it generates more micropores and nanopores, increasing the lithium-ion storage space and thus improving reversible capacity and anode performance. Furthermore, the oxide layer formed during oxidation bonds tightly to the graphite, forming a dense passivation film that prevents the electrolyte from solvating the graphite, further enhancing its reversible capacity.

[0023] C. Inorganic salts, in their molten state, possess exceptional solubility for reactants. Their low viscosity and rapid diffusion allow them to drive impurity ions in graphite to migrate from the deeper layers to the surface via concentration gradient. Cooling followed by water washing removes these impurity ions, significantly reducing the negative impact of inorganic impurities such as Ni, Co, and Mn in waste graphite on the lithium storage capacity and cycle life of the graphite anode. Compared to other cleaning methods such as acid washing, this approach offers advantages such as being environmentally friendly, simple to operate, low-cost, and easily scalable for mass production.

[0024] The above-described solution of the present invention has the following beneficial effects:

[0025] (1) The present invention provides a method for the recycling of graphite anodes with molten salt-assisted regeneration. By using simple molten salt assistance and water washing, the impurities in waste graphite anode materials can be significantly reduced, and the electrochemical performance can be significantly improved. The graphite regeneration method is simple and easy to implement, and the molten salt can be reused, which is conducive to promoting the resource reuse of retired lithium-ion anode materials.

[0026] (2) This invention provides a method for regenerating waste graphite molten salt. The regenerated graphite anode material prepared therefrom has better electrochemical performance than the regenerated graphite material prepared by conventional high-temperature heat treatment and acid washing and impurity removal process when it is used as a lithium-ion battery anode material. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic flowchart of a method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to Embodiment 1 of the present invention;

[0029] Figure 2 These are SEM images of the samples from the recycled graphite waste (a), Comparative Example 1 (b), Comparative Example 2 (c), and Example 1 (d) of the present invention;

[0030] Figure 3 This is a schematic diagram of the cycle stability of a regenerated graphite-assembled negative electrode prepared by a method for the assisted regeneration of a battery negative electrode using molten graphite auxiliaries according to Embodiment 1 of the present invention at a rate of 0.1C. Detailed Implementation

[0031] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0032] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0033] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0034] This invention addresses existing problems by providing a method for recovering graphite molten salt-assisted regeneration of battery negative electrodes, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0035] S1: Grind and thoroughly mix the graphite powder and inorganic salt recovered from the negative electrode of the waste battery to obtain a mixed powder;

[0036] S2: The mixed powder is calcined in air at 800-1100°C;

[0037] S3: After washing the calcined product multiple times, filtering and drying it, regenerated graphite is obtained.

[0038] According to one aspect of an embodiment of the present invention, in step S1, the inorganic salt is sodium chloride.

[0039] According to one aspect of an embodiment of the present invention, in step S1, the mass ratio of graphite powder to inorganic salt is 1:9 to 9:1.

[0040] According to one aspect of an embodiment of the present invention, in step S1, the mass ratio of graphite powder to inorganic salt is 1:1 to 4. Preferably, the mass ratio of graphite powder to inorganic salt includes 1:1, 1:2, 1:3, and 1:4.

[0041] According to one aspect of an embodiment of the present invention, in step S2, the calcination time is 0.2 to 4 hours and the heating rate is 2 to 10 °C / min.

[0042] According to one aspect of an embodiment of the present invention, in step S2, the calcination time is 1 hour.

[0043] According to one aspect of an embodiment of the present invention, in step S3, the washing process involves soaking and stirring in deionized water at a temperature of 25–90°C, and the washing is performed 1–3 times.

[0044] Based on a general inventive concept, embodiments of the present invention provide recycled graphite prepared by the above-described method for the regeneration of graphite molten salt-assisted graphite in the recovery of battery negative electrodes.

[0045] Embodiments of the present invention also provide the application of the regenerated graphite prepared by the above-described method for the recovery of graphite molten salt-assisted regeneration of battery negative electrode in lithium-ion batteries.

[0046] According to one aspect of an embodiment of the present invention, the mixture obtained by mixing the recycled graphite with PVDF and conductive carbon black is dispersed in an N-methylpyrrolidone (NMP) solution to form a uniform slurry, and then the slurry is coated on a conductive copper foil and dried to obtain a lithium-ion battery negative electrode.

[0047] The following is a detailed description through specific embodiments.

[0048] Example 1

[0049] A method for recovering graphite molten salt-assisted regeneration of battery negative electrodes includes the following steps:

[0050] S1. Grind 2g of recycled graphite waste and 2g of sodium chloride for 10 minutes to mix them thoroughly and obtain a mixed powder.

[0051] S2. Place the mixed powder directly in a muffle furnace in an air atmosphere and calcine at 850°C for 1 hour, with a heating rate of 10°C / min.

[0052] S3. The calcined product is washed three times with deionized water at 80℃, with each washing time lasting 2 hours. After filtration and drying, regenerated graphite is obtained.

[0053] Using the above-mentioned recycled graphite as a negative electrode material to assemble lithium-ion batteries includes the following steps:

[0054] A1: The above-mentioned recycled graphite, PVDF and conductive carbon black are mixed evenly in a mass ratio of 8:1:1, dispersed in NMP solution to form a uniform slurry, and then the slurry is coated on copper foil and vacuum dried at 120°C to obtain graphite electrode sheets.

[0055] A2: Graphite electrode sheets were paired with lithium metal anodes, and CR2016 coin cells were assembled in an inert atmosphere within a glove box. The electrochemical performance of the hard carbon electrode was then tested. The coin cell structure includes a positive electrode shell (stainless steel), a negative electrode shell (stainless steel), a gasket (stainless steel), a hard carbon electrode, a lithium sheet, an electrolyte, and a separator (PP).

[0056] Example 2

[0057] A method for the regeneration of graphite molten salt-assisted regeneration of battery negative electrodes (calcination time differs from Example 1) includes the following steps:

[0058] S1. Grind 2g of recycled graphite waste and 2g of sodium chloride for 10 minutes to mix them thoroughly and obtain a mixed powder.

[0059] S2. Place the mixed powder directly into a muffle furnace in an air atmosphere and calcine at 850°C for 0.5 h, with a heating rate of 10°C / min.

[0060] S3. The calcined product is washed three times with deionized water at 80℃, with each washing time lasting 2 hours. After filtration and drying, regenerated graphite is obtained.

[0061] Example 3

[0062] The difference lies in the mass ratio of recycled graphite waste to sodium chloride being 1:2, while the other steps are the same as in Example 1.

[0063] Example 4

[0064] The difference lies in the mass ratio of recycled graphite waste to sodium chloride being 1:3, while the other steps are the same as in Example 1.

[0065] Comparative Example 1

[0066] Compared with the treatment method of Example 1, Comparative Example 1 did not add inorganic salts during the calcination process, and included the following steps:

[0067] S1. Grind 2g of recycled graphite waste for 10 minutes;

[0068] S2. Place the ground graphite waste in an air-filled muffle furnace and calcine it at 850°C for 1 hour, with a heating rate of 10°C / min, to obtain the desired result.

[0069] Comparative Example 2

[0070] Compared to the treatment method in Example 1, this comparative example involves a conventional high-temperature calcination and pickling process, including the following steps:

[0071] S1. Place 2g of recycled graphite waste in a tube furnace and calcine it at 850℃ for 1h in an argon atmosphere, with a heating rate of 10℃ / min.

[0072] S2. The calcined product was washed with 1 mol / L sulfuric acid and deionized water, respectively, and then filtered and dried to obtain regenerated graphite.

[0073] Comparative Example 3

[0074] A method for recovering graphite molten salt-assisted regeneration of battery negative electrodes (the type of inorganic salt is different from that in Example 1) includes the following steps:

[0075] S1. Grind 2g of recycled graphite waste and 2g of potassium chloride for 10 minutes to mix them thoroughly and obtain a mixed powder.

[0076] S2. Place the mixed powder directly in a muffle furnace in an air atmosphere and calcine at 850°C for 1 hour, with a heating rate of 10°C / min.

[0077] S3. The calcined product is washed three times with deionized water at 80℃, with each washing time lasting 2 hours. After filtration and drying, regenerated graphite is obtained.

[0078] Comparative Example 4

[0079] The difference is that the inorganic salt is sodium nitrate, and the other steps are the same as in Example 1.

[0080] Comparative Example 5

[0081] The difference is that the inorganic salt is sodium carbonate, and the other steps are the same as in Example 1.

[0082] Comparative Example 6

[0083] The difference is that the inorganic salt is sodium sulfate, and the other steps are the same as in Example 1.

[0084] Comparative Example 7

[0085] A method for recovering graphite molten salt-assisted regeneration of battery negative electrodes (the type of inorganic salt is different from that in Example 1) includes the following steps:

[0086] S1. Grind 2g of recycled graphite waste and 2g of a mixed molten salt of sodium chloride and sodium sulfate (mixed molten salt mass ratio 1:1) for 10 minutes to fully mix and obtain a mixed powder;

[0087] S2. Place the mixed powder directly in a muffle furnace in an air atmosphere and calcine at 850°C for 1 hour, with a heating rate of 10°C / min.

[0088] S3. Water washing and purification: The calcined product is washed three times with deionized water at 80℃, with each washing time lasting 2 hours. After filtration and drying, regenerated graphite is obtained.

[0089] Comparative Example 8:

[0090] A method for the regeneration of graphite molten salt-assisted regeneration of battery negative electrodes (calcination temperature differs from Example 1), comprising the following steps:

[0091] S1. Grind 2g of recycled graphite waste and 2g of sodium chloride for 10 minutes to mix them thoroughly and obtain a mixed powder.

[0092] S2. Place the mixed powder directly in a muffle furnace in an air atmosphere and calcine at 750°C for 1 hour, with a heating rate of 10°C / min.

[0093] S3. The calcined product is washed three times with deionized water at 80℃, with each washing time lasting 2 hours. After filtration and drying, regenerated graphite is obtained.

[0094] Characterization and performance testing

[0095] like Figure 2 SEM images of samples from the recycled graphite waste of this invention (a), Comparative Example 1 (b), Comparative Example 2 (c), and Example 1 (d). Figure 2 It is known that recycled graphite waste has a large number of adhering substances on its surface. Dry firing in a muffle furnace can remove these adhering substances through oxidation, resulting in graphite particles with a relatively smooth surface. However, calcination in an inert atmosphere is insufficient to remove impurities from the graphite sheet surface. Dry firing in a muffle furnace with molten salt assistance can also yield graphite particles with a relatively smooth surface.

[0096] Taking the coin cells assembled with recycled graphite prepared in Examples 1-4 and Comparative Examples 1-8 as examples, the performance of the cells assembled with recycled graphite electrodes prepared in Examples 1-4 and Comparative Examples 1-8 was evaluated using a charge-discharge device (Blue Electric 3001), and the results are shown in Table 1.

[0097] Table 1. Charge-discharge capacity and first-efficiency performance of batteries assembled with regenerated graphite electrodes in Examples 1 to 4 and Comparative Examples 1 to 8 at a 0.1C rate.

[0098]

[0099]

[0100] The results in Table 1 show that, under a first charge-discharge of 0.1C, the initial discharge specific capacities of the negative electrodes prepared with sodium chloride molten salt (Example 1), sodium sulfate + sodium chloride molten salt (Comparative Example 7), and potassium chloride molten salt (Comparative Example 3) were 385.70 mAh / g, 340.68 mAh / g, and 323.92 mAh / g, respectively; the initial charge specific capacities were 295.30 mAh / g, 256.42 mAh / g, and 246.43 mAh / g, respectively; and the initial coulombic efficiencies were 76.56%, 75.27%, and 76.08%, respectively. The technical effect of using sodium chloride molten salt in Example 1 of this invention is clearly superior to other molten salts and their combinations. The regenerated graphite anode prepared by direct air calcination without molten salt treatment in Comparative Example 1 had initial discharge / charge specific capacities of 329.62 mAh / g and 249.5 mAh / g, respectively, and an initial coulombic efficiency of 75.69%. In contrast, the regenerated graphite obtained by conventional calcination and acid treatment methods had discharge / charge specific capacities of 322.54 mAh / g and 232.10 mAh / g, respectively. Therefore, the molten salt-assisted method of this invention can significantly improve the specific capacity of regenerated graphite.

[0101] Furthermore, the initial discharge specific capacities of the regenerated graphite electrodes prepared with sodium chloride molten salt (calcination temperature of 750℃ in Comparative Example 8) and sodium chloride molten salt (calcination time of 0.5h in Example 2) were 310.54 mAh / g and 354.3 mAh / g, respectively, and the charge specific capacities were 229.41 mAh / g and 278.65 mAh / g, respectively, with initial coulombic efficiencies of 73.88% and 78.65%. Their initial charge-discharge specific capacities were both lower than those of Example 1 (calcination temperature of 850℃ and time of 1h). This demonstrates that calcination temperature and time also have a significant impact on the electrochemical performance of the regenerated graphite anode.

[0102] Figure 3Cyclic stability tests of the anode material in Example 1 of this invention at a 0.1C rate showed good stability and capacity retention. These results demonstrate that the method for recovering graphite molten salt-assisted regeneration of battery anodes according to this invention significantly improves the electrochemical performance of the regenerated graphite anode material.

[0103] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering graphite molten salt-assisted regeneration of battery negative electrodes, characterized in that, Includes the following steps: S1: The graphite powder and inorganic salt recovered from the negative electrode of the waste battery are ground and thoroughly mixed to obtain a mixed powder; wherein, the inorganic salt is sodium chloride; the mass ratio of the graphite powder to the inorganic salt is 1:1~4; S2: The mixed powder is calcined in air at 800~1100℃; wherein the calcination time is 0.2~4 h and the heating rate is 2~10℃ / min; S3: The calcined product is washed multiple times, filtered and dried to obtain regenerated graphite; the washing process involves soaking and stirring in deionized water at a temperature of 25~90 ℃, and the washing is performed 1~3 times.

2. The method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to claim 1, characterized in that, In step S1, the mass ratio of graphite powder to inorganic salt is 1:1, 1:2, 1:3 or 1:

4.

3. The method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to claim 1, characterized in that, In step S2, the calcination time is 1 hour.

4. The method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to claim 1, characterized in that, In step S2, the calcination temperature is 850°C.

5. The method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to claim 1, characterized in that, In step S3, the washing water temperature is 80°C.

6. The method for recovering graphite molten salt-assisted regeneration of a battery negative electrode according to claim 1, characterized in that, In step S3, the washing is performed 3 times.

7. Regenerated graphite prepared by the method of graphite molten salt-assisted regeneration of battery negative electrode as described in any one of claims 1 to 6.

8. The application of the regenerated graphite prepared by the method of graphite molten salt-assisted regeneration of battery negative electrode as described in any one of claims 1 to 6 in lithium-ion batteries.

9. The application according to claim 8, characterized in that, The mixture obtained by mixing the recycled graphite with PVDF and conductive carbon black is dispersed in an N-methylpyrrolidone solution to form a uniform slurry. The slurry is then coated onto a conductive copper foil and dried to obtain a lithium-ion battery negative electrode.

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