A method for recycling and modifying graphite negative electrode materials of failed batteries

Abstract

The present invention proposes a method for recycling and modifying graphite negative electrode materials from spent batteries, comprising: dispersing the spent battery's negative electrode sheets in water, collecting the graphite negative electrode material separated from the current collector, washing it multiple times with deionized water, and filtering it to obtain a recovered graphite negative electrode material; dispersing the recovered graphite negative electrode material, graphene oxide, and silicon dioxide in a solvent, mixing the resulting dispersions, and then adding a reducing agent for a reduction reaction to obtain a precursor composite material; and carbonizing the precursor composite material at high temperature to obtain a regenerated graphite negative electrode material. The present method combines a recycling process with performance modification of the recycled graphite, resulting in simple operation and low energy consumption. By compounding the recovered graphite negative electrode material with graphene oxide and silicon dioxide, it not only repairs the surface of the recovered graphite but also significantly improves its capacity, rate capability, and cycle performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery negative electrode materials, and in particular to a method for recovering and modifying graphite negative electrode materials of failed batteries. Background Art

[0002] Currently, the recycling of spent lithium-ion batteries typically focuses on the recovery of cathode materials, while research on the recycling of anode materials is relatively limited. However, graphite is used in large quantities in lithium-ion batteries, requiring approximately 1 kg of graphite per kilowatt-hour of production. A small or medium-sized electric vehicle requires approximately 50 kg of graphite anode material. Therefore, the recycling and reuse of anode graphite from spent lithium-ion batteries is of great practical significance for reducing the production cost of battery-grade graphite, preventing environmental pollution, and promoting the sustainable development of the lithium-ion battery industry.

[0003] Existing recycling technologies for graphite anode materials are primarily categorized into pyrometallurgy and hydrometallurgy. Pyrometallurgy involves heating the recycled graphite anode material to temperatures exceeding 3000°C to remove impurities and achieve a graphite purity exceeding 99.9%. This process also repairs lattice defects generated during charging and discharging. However, this method is energy-intensive and requires specialized equipment to purify toxic combustion gases, making it relatively costly. Hydrometallurgy involves dissolving the metals in spent lithium batteries using acids, alkalis, or other solutions, followed by separation of the graphite anode material from the metals through sedimentation, extraction, and other methods. Hydrometallurgy offers significant energy savings, reduces air pollution, and is relatively easy to operate. However, the acid and alkali solutions used in the recycling process can pollute water bodies, and the hydrometallurgical process also produces toxic wastes such as organic solvents. Furthermore, achieving high-purity metals through the hydrometallurgical process requires a long production cycle. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a method for recycling and modifying graphite negative electrode materials of failed batteries. The method combines the recycling process with the performance modification of the recycled graphite, is simple to operate and has low energy consumption. By compounding the recycled graphite negative electrode material with graphene oxide and silicon dioxide, it can not only repair the surface of the recycled graphite, but also greatly improve its capacity, rate performance and cycle performance.

[0005] The present invention proposes a method for recycling and modifying graphite negative electrode materials of spent batteries, comprising the following steps:

[0006] S1. Dispersing the negative electrode sheets of the failed battery in water, collecting the graphite negative electrode material separated from the current collector, washing it with deionized water multiple times, and filtering it to obtain the recovered graphite negative electrode material;

[0007] S2, dispersing the recycled graphite negative electrode material, graphene oxide and silicon oxide in a solvent respectively, mixing the obtained dispersions, and adding a reducing agent to carry out a reduction reaction to obtain a precursor composite material;

[0008] S3. Carbonizing the precursor composite material at high temperature to obtain a regenerated graphite negative electrode material.

[0009] In the present invention, recycled graphite anode material is used as a substrate, silicon dioxide (SiO) is doped, a layer of graphene oxide is coated on the surface by a graphene oxide reaction, and then the graphene oxide is reduced by heating with a reducing agent to convert the graphene oxide into reduced graphene oxide, thereby forming a regenerated graphite anode material of silicon dioxide-graphite@graphene (G-SiO-rGO). On the one hand, the presence of SiO greatly increases the specific capacity of the anode material. On the other hand, the graphene coated on the outside has excellent mechanical properties and can inhibit the expansion of SiO. The graphene also repairs the surface of the recycled graphite anode material. At the same time, the graphene has good electrical conductivity, which can improve the electrical conductivity of the anode material and the charge and discharge rate of the battery. The two-dimensional structure of the graphene gives the anode material a high specific surface area, providing more active sites for the insertion and deinsertion of lithium ions, which can significantly improve the capacity and cycle stability of the battery.

[0010] Preferably, in step S1, the failed battery is a lithium-ion battery whose capacity has dropped to less than 80% of the initial capacity.

[0011] Preferably, in step S2, the graphene oxide is prepared by using a modified Hummers method; and the silicon oxide is nano-silicon oxide.

[0012] Preferably, in step S2, the mass ratio of the recovered graphite negative electrode material, silicon oxide and graphene oxide is 10:0.5-1:0.2-0.5.

[0013] Preferably, in step S2, the solvent is at least one of water, ethanol, propanol, ethylene glycol or nitrogen methyl pyrrolidone;

[0014] Preferably, the solid content of the recycled graphite negative electrode material dispersed in the solvent is 5-15wt%, the solid content of the graphene oxide dispersed in the solvent is 0.1-1wt%, and the solid content of the silicon oxide dispersed in the solvent is 0.5-2wt%.

[0015] Preferably, in step S2, the silicon iodide is silicon iodide pretreated with quaternary ammonium;

[0016] Preferably, the quaternization pretreatment specifically comprises: performing a ring-opening coupling reaction on silicon oxide and epoxypropyltrimethylammonium chloride to obtain the product.

[0017] In the present invention, silicon oxide that has undergone quaternary ammonium pretreatment carries a positive charge due to quaternary ammonium salt ions grafted onto its surface, and graphene oxide sheets carry a large amount of negative charge due to the presence of abundant oxygen-containing functional groups. Therefore, after the silicon oxide that has undergone quaternary ammonium pretreatment and graphene oxide are compounded, the two can form electrostatic adsorption due to the different charges they carry, thereby ensuring the effective adsorption and wrapping of silicon oxide by graphene oxide, and ultimately forming a tightly bonded graphene layer with a rich pore structure on the surface of silicon oxide, thereby further inhibiting the expansion of silicon oxide and more effectively improving the rate performance and cycle performance of the regenerated graphite negative electrode material.

[0018] Preferably, the reducing agent is at least one of hydrazine hydrate or sodium borohydride.

[0019] Preferably, in step S3, the temperature of the high-temperature carbonization reaction is 1000-1200° C., and the time is 3-5 hours;

[0020] Preferably, the heating rate of the high-temperature carbonization reaction is 5-10°C / min.

[0021] The present invention also provides a regenerated graphite negative electrode material obtained by the above-mentioned recovery and modification method.

[0022] The present invention also proposes an application of the above-mentioned regenerated graphite negative electrode material in a lithium ion battery.

[0023] The present invention provides a method for recovering and modifying graphite anode material from spent batteries. This method effectively recovers graphite anode material, is simple to process, and is low-cost, possessing practical application value in promoting the recycling and reuse of spent batteries. The method simultaneously utilizes graphene oxide and silicon oxide in combination with the recycled graphite anode material to repair and expand the capacity, improving the specific capacity while also addressing the poor cycling stability of the resulting silicon oxide due to volume expansion during charge and discharge. DETAILED DESCRIPTION

[0024] Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration only and are not to be construed as limiting the scope of the present invention.

[0025] The raw materials used in the following examples are all commercially available products, as follows:

[0026] Graphite powder: analytical grade, purchased from Shanghai Aladdin Reagent Co., Ltd.

[0027] Sodium nitrate: analytical grade, purchased from Tianjin Damao Chemical Reagent Factory;

[0028] Concentrated sulfuric acid: analytical grade, Guangzhou Chemical Reagent Factory;

[0029] Potassium permanganate: analytical grade, purchased from Hengyang Kaixin Chemical Reagent Co., Ltd.

[0030] Hydrogen peroxide: analytical grade, purchased from Tianjin Fuyu Fine Chemical Co., Ltd.

[0031] Hydrochloric acid (HCl): analytical grade, purchased from Guangzhou Chemical Reagent Factory;

[0032] Nano-silicon dioxide (SiO) powder: analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0033] Hydrazine hydrate (N2H4·H2O) was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0034] Example 1

[0035] This embodiment proposes a method for recycling and modifying graphite negative electrode materials of spent batteries, which specifically includes:

[0036] (1) Add the negative electrode of the lithium-ion battery after cycle failure to deionized water for ultrasonic dispersion. After the graphite negative electrode material is completely separated from the current collector, the current collector is removed and the obtained graphite negative electrode material is collected. Then, the obtained graphite negative electrode material is ultrasonically washed with deionized water for 5 times, filtered, vacuum dried, and passed through a 325 mesh sieve to obtain a recovered graphite negative electrode material, which is recorded as G;

[0037] (2) Graphite powder and sodium nitrate in a mass ratio of 2:1 were added to concentrated sulfuric acid 25 times the mass of the graphite powder, stirred in an ice bath for 1 hour, and then potassium permanganate 1 times the mass of the graphite powder was slowly added and the temperature was controlled below 20 ° C. After the addition of potassium permanganate was completed, the mixture was stirred in a 35 ° C water bath for 4 hours, and then deionized water 50 times the mass of the graphite powder was added. After heating to 80 ° C, the mixture was stirred and reacted for 30 minutes. Deionized water 50 times the mass of the graphite powder was continued to be added, stirred to room temperature, and an appropriate amount of hydrogen peroxide (30wt%) was added until there were no bubbles. After washing with hydrochloric acid 3 times, it was washed with deionized water until neutral, freeze-dried, and ground into powder to obtain graphene oxide, which was recorded as GO.

[0038] (3) adding the recycled graphite negative electrode material to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it uniformly to obtain a G dispersion with a solid content of 10 wt%; adding nano-silicon dioxide (SiO) powder to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it uniformly to obtain a SiO dispersion with a solid content of 1 wt%; adding graphene oxide to deionized water, and ultrasonically dispersing it uniformly to obtain a GO dispersion with a solid content of 0.2 wt%; mixing the above-mentioned G dispersion, SiO dispersion and GO dispersion in a mass ratio of G, SiO and GO of 10:0.75:0.35, and then adding N2H4·H2O solution (85 wt%) containing 2 wt% of G to the mixed solution, and performing reduction reaction in a water bath at 85°C for 12 h. After cooling to room temperature, filtering with an organic filter membrane, and vacuum drying, a precursor composite material is obtained;

[0039] (4) The precursor composite material is placed in a muffle furnace for high-temperature carbonization reaction, with argon protective gas, the high-temperature carbonization temperature is 1100°C, the heating rate is 10°C / min, and the time is 4 hours to obtain a regenerated graphite negative electrode material, which is recorded as G-SiO-rGO.

[0040] Example 2

[0041] This embodiment proposes a method for recycling and modifying graphite negative electrode materials of spent batteries, which specifically includes:

[0042] (1) Add the negative electrode of the lithium-ion battery after cycle failure to deionized water for ultrasonic dispersion. After the graphite negative electrode material is completely separated from the current collector, the current collector is removed and the obtained graphite negative electrode material is collected. Then, the obtained graphite negative electrode material is ultrasonically washed with deionized water for 5 times, filtered, vacuum dried, and passed through a 325 mesh sieve to obtain a recovered graphite negative electrode material, which is recorded as G;

[0043] (2) Graphite powder and sodium nitrate in a mass ratio of 2:1 were added to concentrated sulfuric acid 25 times the mass of the graphite powder, stirred in an ice bath for 1 hour, and then potassium permanganate 1 times the mass of the graphite powder was slowly added and the temperature was controlled below 20 ° C. After the addition of potassium permanganate was completed, the mixture was stirred in a 35 ° C water bath for 4 hours, and then deionized water 50 times the mass of the graphite powder was added. After heating to 80 ° C, the mixture was stirred and reacted for 30 minutes. Deionized water 50 times the mass of the graphite powder was continued to be added, stirred to room temperature, and an appropriate amount of hydrogen peroxide (30wt%) was added until there were no bubbles. After washing with hydrochloric acid 3 times, it was washed with deionized water until neutral, freeze-dried, and ground into powder to obtain graphene oxide, which was recorded as GO.

[0044] (3) adding the recycled graphite negative electrode material to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it uniformly to obtain a G dispersion with a solid content of 10 wt%; adding nano-silicon dioxide (SiO) powder to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it uniformly to obtain a SiO dispersion with a solid content of 1 wt%; adding graphene oxide to deionized water, and ultrasonically dispersing it uniformly to obtain a GO dispersion with a solid content of 0.2 wt%; mixing the above-mentioned G dispersion, SiO dispersion and GO dispersion in a mass ratio of G, SiO and GO of 10:0.5:0.2, and then adding a N2H4·H2O solution (85 wt%) containing 2 wt% of G to the mixed solution, and performing a reduction reaction in a water bath at 85°C for 12 h. After cooling to room temperature, filtering with an organic filter membrane, and vacuum drying, a precursor composite material is obtained;

[0045] (4) The precursor composite material is placed in a muffle furnace for high-temperature carbonization reaction, with argon protective gas, the high-temperature carbonization temperature is 1100°C, the heating rate is 5°C / min, and the time is 5 hours to obtain a regenerated graphite negative electrode material, which is recorded as G-SiO-rGO.

[0046] Example 3

[0047] This embodiment proposes a method for recycling and modifying graphite negative electrode materials of spent batteries, which specifically includes:

[0048] (1) Add the negative electrode of the lithium-ion battery after cycle failure to deionized water for ultrasonic dispersion. After the graphite negative electrode material is completely separated from the current collector, the current collector is removed and the obtained graphite negative electrode material is collected. Then, the obtained graphite negative electrode material is ultrasonically washed with deionized water for 5 times, filtered, vacuum dried, and passed through a 325 mesh sieve to obtain a recovered graphite negative electrode material, which is recorded as G;

[0049] (2) Graphite powder and sodium nitrate in a mass ratio of 2:1 were added to concentrated sulfuric acid 25 times the mass of the graphite powder, stirred in an ice bath for 1 hour, and then potassium permanganate 1 times the mass of the graphite powder was slowly added and the temperature was controlled below 20 ° C. After the addition of potassium permanganate was completed, the mixture was stirred in a 35 ° C water bath for 4 hours, and then deionized water 50 times the mass of the graphite powder was added. After heating to 80 ° C, the mixture was stirred and reacted for 30 minutes. Deionized water 50 times the mass of the graphite powder was continued to be added, stirred to room temperature, and an appropriate amount of hydrogen peroxide (30wt%) was added until there were no bubbles. After washing with hydrochloric acid 3 times, it was washed with deionized water until neutral, freeze-dried, and ground into powder to obtain graphene oxide, which was recorded as GO.

[0050] (3) adding the recycled graphite negative electrode material to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing the mixture to obtain a G dispersion with a solid content of 10 wt%; adding nano-silicon dioxide (SiO) powder to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing the mixture to obtain a SiO dispersion with a solid content of 1 wt%; adding graphene oxide to deionized water, and ultrasonically dispersing the mixture to obtain a GO dispersion with a solid content of 0.2 wt%; mixing the G dispersion, SiO dispersion, and GO dispersion in a mass ratio of G, SiO, and GO of 10:1:0.5, and then adding sodium borohydride (2 wt% of the mass of G) to the mixture, and performing reduction reaction in a water bath at 85°C for 12 h. After cooling to room temperature, filtering with an organic filter membrane, and vacuum drying, a precursor composite material is obtained;

[0051] (4) The precursor composite material is placed in a muffle furnace for high-temperature carbonization reaction, with argon protective gas, the high-temperature carbonization temperature is 1200°C, the heating rate is 10°C / min, and the time is 3 hours to obtain a regenerated graphite negative electrode material, which is recorded as G-SiO-rGO.

[0052] Example 4

[0053] This embodiment proposes a method for recycling and modifying graphite negative electrode materials of spent batteries, which specifically includes:

[0054] (1) Add the negative electrode of the lithium-ion battery after cycle failure to deionized water for ultrasonic dispersion. After the graphite negative electrode material is completely separated from the current collector, the current collector is removed and the obtained graphite negative electrode material is collected. Then, the obtained graphite negative electrode material is ultrasonically washed with deionized water for 5 times, filtered, vacuum dried, and passed through a 325 mesh sieve to obtain a recovered graphite negative electrode material, which is recorded as G;

[0055] (2) Graphite powder and sodium nitrate in a mass ratio of 2:1 were added to concentrated sulfuric acid 25 times the mass of the graphite powder, stirred in an ice bath for 1 hour, and then potassium permanganate 1 times the mass of the graphite powder was slowly added and the temperature was controlled below 20 ° C. After the addition of potassium permanganate was completed, the mixture was stirred in a 35 ° C water bath for 4 hours, and then deionized water 50 times the mass of the graphite powder was added. After heating to 80 ° C, the mixture was stirred and reacted for 30 minutes. Deionized water 50 times the mass of the graphite powder was continued to be added, stirred to room temperature, and an appropriate amount of hydrogen peroxide (30wt%) was added until there were no bubbles. After washing with hydrochloric acid 3 times, it was washed with deionized water until neutral, freeze-dried, and ground into powder to obtain graphene oxide, which was recorded as GO.

[0056] (3) Add nano-silicon dioxide (SiO) powder and 2,3-epoxypropyltrimethylammonium chloride (GTA) in a mass ratio of 20:1 to a mixed solution of ethanol / propylene glycol (v / v = 9:1) containing 10 wt% sodium hydroxide, stir and react in a water bath at 80°C for 6 h, centrifuge, wash 3 times with ethanol, and dry to obtain quaternary ammonium pretreated silicon dioxide, which is recorded as GTA-SiO;

[0057] (4) adding the recycled graphite negative electrode material to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it to obtain a G dispersion with a solid content of 10 wt%; adding the silicon oxide pretreated by quaternization to a mixed solvent consisting of deionized water and ethanol in a volume ratio of 5:3, and ultrasonically dispersing it to obtain a GTA-SiO dispersion with a solid content of 1 wt%; adding graphene oxide to deionized water, and ultrasonically dispersing it to obtain a GO dispersion with a solid content of 0.2 wt%; mixing the above-mentioned G dispersion, GTA-SiO dispersion and GO dispersion in a mass ratio of G, GTA-SiO and GO of 10:0.75:0.35, and then adding 2 wt% of G by mass N2H4·H2O solution (85 wt%) to the mixed solution, and performing reduction reaction in a water bath at 85°C for 12 h, cooling to room temperature, filtering with an organic filter membrane, and vacuum drying to obtain a precursor composite material;

[0058] (5) The precursor composite material is placed in a muffle furnace for high-temperature carbonization reaction, with argon protective gas, the high-temperature carbonization temperature is 1100°C, the heating rate is 10°C / min, and the time is 4 hours to obtain a regenerated graphite negative electrode material, which is recorded as G-SiO-rGO.

[0059] The regenerated graphite negative electrode material and the recycled graphite negative electrode material obtained in the embodiment were stirred and mixed with conductive carbon black (SP) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10, respectively. PVDF was dissolved with N-methylpyrrolidone (NMP). The resulting mixed slurry was evenly coated on a copper foil and dried in a vacuum drying oven at 110°C for 12 h. The obtained electrode sheet was used as the positive electrode of the simulated battery, the metal lithium sheet was used as the negative electrode, the separator was a Celgard 2400 microporous polypropylene membrane, and the electrolyte was a 1 mol / L LiPF6 solution (solvent was EC / DMC, v / v=1:1). The battery was assembled into a button cell CR2016 in a glove box filled with argon and deoxygenated and dehydrated.

[0060] The above button cell was placed on a LAND battery tester for electrochemical performance testing. The charge and discharge voltage range was 0.001-2.0 V, and the charge and discharge current was 0.1 C. The test results are listed in Table 1.

[0061] Table 1 Electrochemical test results of silicon-carbon negative electrode materials obtained in Examples and Comparative Examples

[0062]

[0063]

[0064] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for recycling and modifying graphite negative electrode materials of spent batteries, characterized in that: The steps include: S1. Dispersing the negative electrode sheets of the failed battery in water, collecting the graphite negative electrode material separated from the current collector, washing it with deionized water multiple times, and filtering it to obtain the recovered graphite negative electrode material; S2, dispersing the recycled graphite negative electrode material, silicon oxide and graphene oxide in a solvent respectively, mixing the obtained dispersions and adding a reducing agent to carry out a reduction reaction to obtain a precursor composite material; S3. Carbonizing the precursor composite material at high temperature to obtain a regenerated graphite negative electrode material.

2. The method for recycling and modifying graphite negative electrode materials of failed batteries according to claim 1, characterized in that: In step S1, the failed battery is a lithium-ion battery whose capacity has dropped to less than 80% of the initial capacity.

3. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: In step S2, the graphene oxide is prepared by using a modified Hummers method; and the silicon oxide is nano-silicon oxide.

4. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: In step S2, the mass ratio of the recovered graphite negative electrode material, silicon oxide and graphene oxide is 10:0.5-1:0.2-0.

5.

5. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: In step S2, the solvent is at least one of water, ethanol, propanol, ethylene glycol or nitrogen methyl pyrrolidone.

6. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 5, characterized in that: The solid content of the recycled graphite negative electrode material dispersed in the solvent is 5-15wt%, the solid content of the graphene oxide dispersed in the solvent is 0.1-1wt%, and the solid content of the silicon oxide dispersed in the solvent is 0.5-2wt%.

7. The method for recovering and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: In step S2, the silicon iodide is silicon iodide pretreated with quaternary ammonium.

8. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 7, characterized in that: The quaternization pretreatment specifically includes: performing a ring-opening coupling reaction on silicon oxide and epoxypropyltrimethylammonium chloride to obtain the product.

9. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: The reducing agent is at least one of hydrazine hydrate and sodium borohydride.

10. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 1 or 2, characterized in that: In step S3, the temperature of the high-temperature carbonization reaction is 1000-1200° C., and the time is 3-5 hours.

11. The method for recycling and modifying graphite negative electrode materials of spent batteries according to claim 10, characterized in that: The heating rate of the high-temperature carbonization reaction is 5-10°C / min.

12. A regenerated graphite negative electrode material obtained by the recovery and modification method according to any one of claims 1 to 11.

13. Use of the regenerated graphite negative electrode material according to claim 12 in a lithium-ion battery.

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