Method for repairing graphite negative electrode of waste lithium ion battery based on sucrose high-temperature carbonization and application

Abstract

The invention relates to a method for repairing a graphite negative electrode of a waste lithium ion battery based on sucrose high-temperature carbonization and application, and belongs to the technical field of battery recovery and resource reutilization. In order to solve the problems of complex process, high cost and insufficient performance recovery of the traditional invalid graphite recovery process, the invention provides the method which takes invalid graphite as a matrix and cane sugar as a carbon source, and amorphous carbon generated by pyrolysis of cane sugar effectively fills the structural defects (such as microcracks and interlayer stripping) of the invalid graphite and reconstructs a three-dimensional conductive network; efficient regeneration of electrochemical performance of the negative electrode material is realized. According to the method, the process is simple, the raw materials are cheap and environment-friendly, the specific capacity of the regenerated graphite negative electrode can be recovered to 95% or above of that of the original material, the cycling stability is remarkably improved, and meanwhile, good electrochemical reaction kinetics is achieved. The invention provides a feasible scheme for low-cost and high-efficiency regeneration of the lithium battery negative electrode material, and has both environmental benefits and economic values.

Description

Technical Field

[0001] The present invention relates to the technical field of waste lithium-ion battery recycling, and in particular to a method and application of repairing a waste lithium-ion battery graphite negative electrode based on sucrose high-temperature carbonization. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and portable electronic devices, the demand for lithium-ion batteries has surged, and the number of waste lithium-ion batteries generated has also increased exponentially. Graphite, as the core material for lithium-ion battery negative electrodes, is prone to failure during long-term charge and discharge cycles due to problems such as lithium dendrite growth, excessive thickening of the solid electrolyte interface (SEI) film, structural collapse, and loss of active lithium, leading to battery capacity decay or even scrapping. However, the direct landfill or incineration of discarded graphite negative electrodes not only wastes strategic metal resources such as cobalt, nickel, and lithium, but may also cause environmental problems such as heavy metal pollution. Therefore, the development of efficient and low-cost failed graphite regeneration technology is of great significance to promoting the sustainable development of the lithium battery industry.

[0003] At present, the regeneration methods for waste graphite negative electrodes mainly include pyrometallurgy, wet leaching and direct repair strategies. Although pyrometallurgy and wet leaching processes can achieve the recovery of metal elements, they have problems such as high energy consumption, high risk of secondary pollution, and serious damage to the graphite structure. Direct repair technologies (such as high-temperature heat treatment, chemical lithium replenishment, etc.) are often difficult to restore the electrochemical performance of the regenerated negative electrode to commercial levels due to the residual SEI film on the graphite surface or incomplete repair of carbon defects. In recent years, repair strategies based on carbon coating modification have attracted much attention because they can simultaneously repair graphite structural defects and improve conductivity. However, the use of traditional carbon sources (such as asphalt and polymers) is often accompanied by the release of toxic gases from high-temperature pyrolysis or increased process complexity. In this context, the development of green, low-cost and efficient carbon source materials to achieve the synergistic regeneration of the structure and electrochemical properties of failed graphite has become a research difficulty and breakthrough point in this field. Summary of the Invention

[0004] The present invention innovatively proposes to use biomass-derived carbon (sucrose) as a repair medium to regenerate failed graphite through a high-temperature carbonization strategy. The inventors tried different sucrose processes to repair failed graphite and selected a process method that has both process and performance advantages, and at the same time has a higher initial coulombic efficiency than the traditional acid leaching method. Sucrose, as a natural and renewable carbon precursor, has the advantages of wide sources, low cost, and environmentally friendly carbonization process. The amorphous carbon layer generated by its high-temperature decomposition can effectively fill graphite surface defects, inhibit electrolyte side reactions, and enhance interfacial ion transfer kinetics. This strategy provides a new idea for the high-value regeneration of waste lithium-ion battery graphite negative electrodes, which is in line with the development needs of resource recycling and green chemistry.

[0005] The primary objective of this invention is to provide a method for repairing spent lithium-ion battery graphite anodes using high-temperature carbonization of sucrose. This method uses controlled carbon layer reconstruction to simultaneously repair bulk defects and optimize surface chemical stability. An amorphous carbon precursor is hydrothermally synthesized and then composited with pretreated graphite to achieve crystal structure regeneration and conductive network reconstruction. This regeneration process is both highly efficient and sustainable, and the regenerated graphite anode exhibits electrochemical performance comparable to virgin material.

[0006] Another object of the present invention is to provide regenerated graphite prepared by the above method.

[0007] Another object of the present invention is to provide application of the above-mentioned regenerated graphite in lithium-ion batteries.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for repairing a waste lithium-ion battery graphite negative electrode based on high-temperature carbonization of sucrose, characterized by comprising the following steps:

[0010] (1) heating a sucrose solution in a reactor for hydrothermal reaction, filtering, and vacuum drying to obtain a sucrose hydrothermal carbonization product; the hydrothermal reaction temperature is 150-250° C., and the time is 10-15 hours;

[0011] (2) mixing and grinding a sucrose hydrothermal carbonization product with spent graphite, and subjecting the mixture to a high-temperature carbonization treatment to obtain regenerated graphite; wherein the weight of the sucrose hydrothermal carbonization product is 5 wt% to 30 wt% of the spent graphite.

[0012] Preferably, in step (2), the conditions for the high-temperature carbonization treatment are: a heating rate of (2-5)°C / min, a temperature of 1000-1500°C, a holding time of 1-5h; and the gas atmosphere is argon or nitrogen.

[0013] Preferably, in step (1), the vacuum drying temperature is 70-90° C. and the time is 15-25 h.

[0014] Preferably, in step (1), the concentration of the sucrose solution is 5wt% to 30wt%; and the sucrose hydrothermal carbonization product is an amorphous carbon powder with a particle size of 50-200nm.

[0015] Preferably, in step (1), the hydrothermal reaction temperature is 200±20° C. and the time is 12±1 h; in step (2), the weight of the sucrose hydrothermal carbonization product is 5wt% to 20wt% of the spent graphite.

[0016] Preferably, in step (2), the weight of the sucrose hydrothermal carbonization product is 10±3wt% of the spent graphite; and the spent graphite is derived from the disassembly of a lithium battery pack.

[0017] The regenerated graphite is prepared by the method of the present invention.

[0018] Preferably, the surface of the regenerated graphite is coated with sucrose carbonization products.

[0019] The application of the regenerated graphite of the present invention is characterized in that it is applied to lithium-ion batteries.

[0020] Preferably, the negative electrode material of the lithium-ion battery is the regenerated graphite, and the adhesive is sodium carboxymethyl cellulose and / or polyvinylidene fluoride.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The recycling and regeneration method proposed in the present invention regenerates the spent graphite negative electrode of a lithium-ion battery by coating and modifying it with amorphous carbon carbonized from sucrose. Sucrose, as a natural and renewable carbon precursor, has a moderate carbon chain length and can effectively fill the lattice defects of graphite materials. It is also inexpensive and easily available, resulting in low cost. In addition, its high-temperature carbonization process only produces carbon dioxide and water, without any hazardous waste, reducing the risk of secondary pollution and complying with the principles of green chemistry.

[0023] (2) The recycling and regeneration method proposed in the present invention does not require complex chemical leaching and purification steps, and avoids the damage to the graphite body caused by the traditional pickling / stripping process. Repair and regeneration can be achieved through a one-step high-temperature carbonization, which is easy to promote on a large scale.

[0024] (3) The recycling and regeneration method proposed in the present invention is to coat the graphite surface with amorphous carbon generated by carbonization of sucrose, thereby reducing the continuous growth of the SEI film and the decomposition of the electrolyte during the charge and discharge process, improving the cycle stability, and providing additional lithium ion transmission channels. At the same time, it improves the conductive network between graphite particles, reduces the interface impedance, and improves the rate performance.

[0025] (4) The recycling and regeneration method proposed in the present invention does not require the stripping of active metal impurities (such as lithium and transition metals) remaining on the SEI film on the graphite surface. The sucrose carbonization layer can in situ coat them and convert them into active components, thereby improving the specific capacity of the regenerated negative electrode. The initial coulombic efficiency (ICE), specific capacity and cycle stability of the regenerated graphite negative electrode are significantly improved, approaching the level of commercial graphite, giving waste graphite a "second life". BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The XRD patterns of the failed graphite (DG), RG1 (DG-0.1Suc(HP)-1200) in the example, RG3 (DG-Ar-600-3h), RG4 (DG-Ar-600-1M HCl), and RG6 ((DG-0.1Suc)-HP-1200) in the comparative example are compared. The scanning speed is 5°C / min and the scanning range is 10-90°.

[0027] Figure 2 (a) is the SEM image of commercial graphite; Figure 2 (b) is the SEM image of the failed graphite material; Figure 2 (c) is a SEM image of amorphous carbon spheres, a product of sucrose hydrothermal carbonization, prepared in Example 1; Figure 2 (d) is the SEM image of the regenerated graphite RG1 prepared in Example 1.

[0028] FIG3( a) is a comparison of the charge-discharge curves of spent graphite (DG), RG4 (DG-Ar-600-1M HCl) of Comparative Example 1, RG6 ((DG-0.1Suc)-HP-1200) of Comparative Example 2, and RG1 (DG-0.1Suc(HP)-1200) of Example 1;

[0029] FIG3( b ) is a comparison of the charge and discharge curves of failed graphite (DG), RG1 (DG-0.1Suc(HP)-1200) of Example 1, and RG2 (DG-0.2Suc(HP)-1200) of Example 2.

[0030] Figure 4 (b) and (c) are comparison charts of the cycle performance and rate performance of failed graphite (DG), RG1 (DG-0.1Suc(HP)-1200) of Example 1, and RG2 (DG-0.2Suc(HP)-1200) of Example 2.

[0031] Figure 5 (a) and (b) are charge-discharge curves and cycle performance comparison diagrams of failed graphite (DG) and RG6 ((DG-0.1Suc)-HP-1200) of comparative example 2.

[0032] Figure 6 Comparison of the charge and discharge curves, rate performance, and cycle performance of commercial graphite (CC), failed graphite (DG), comparative examples RG3 (DG-Ar-600-3h), RG4 (DG-Ar-600-1M HCl), and RG5 (DG-1M HCl). DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below with reference to the embodiments and the accompanying drawings, but the implementation manner and protection scope of the present invention are not limited thereto.

[0034] The failed graphite in this experiment came from the dismantling of the lithium iron phosphate battery pack of Yiwei Lithium Energy. Its retired state was that the battery capacity was less than 80% of the initial value, and the average failure degree was 75%.

[0035] Example 1

[0036] The present invention provides a method for recycling and regenerating graphite negative electrode materials of waste lithium batteries, comprising the following steps:

[0037] 1. Preparation of sucrose hydrothermal carbonization product - amorphous carbon spheres

[0038] Sucrose was dissolved in deionized water to prepare a 10 wt% solution, which was transferred to a hydrothermal reactor and reacted at 200°C for 12 hours. The solution was filtered with deionized water and then dried under vacuum drying conditions at 80°C for 20 hours. After centrifugal drying, amorphous carbon powder with a particle size of 50-200 nm was obtained.

[0039] 2. Preparation of 10wt% sucrose carbonization product-coated regenerated graphite

[0040] Weigh 0.1 g of the sucrose hydrothermal carbonization product obtained in step 1, weigh 1 g of spent graphite (DG), mix and grind them evenly using a mortar, place them in a corundum crucible, and place them in a tubular furnace with an argon atmosphere. Keep warm at 1200°C for 3 h at a heating rate of 2°C / min for coating to obtain regenerated graphite RG1 (DG-0.1Suc(HP)-1200) coated with 10 wt% sucrose carbonization product.

[0041] Example 2

[0042] The present invention provides a method for recycling and regenerating graphite negative electrode materials of waste lithium batteries, comprising the following steps:

[0043] 1. Preparation of sucrose hydrothermal carbonization product - amorphous carbon spheres

[0044] Sucrose was dissolved in deionized water to prepare a 10 wt% solution, which was transferred to a hydrothermal reactor and reacted at 200 ° C for 12 hours. The product was filtered with deionized water and then dried under vacuum drying conditions at a temperature of 80 ° C for 20 hours. After centrifugal drying, amorphous carbon powder with a particle size of 50-200 nm was obtained.

[0045] 2. Preparation of 20wt% sucrose carbonization product-coated regenerated graphite

[0046] Weigh 0.2 g of the sucrose hydrothermal carbonization product obtained in step 1, weigh 1 g of spent graphite (DG), mix and grind them evenly using a mortar, place them in a corundum crucible, and place them in a tubular furnace with an argon atmosphere. Keep warm at 1200°C for 3 h at a heating rate of 2°C / min for coating to obtain regenerated graphite RG2 (DG-0.2Suc(HP)-1200) coated with 10 wt% sucrose carbonization product.

[0047] Comparative Example 1

[0048] The spent graphite was first calcined at low temperature in a tube furnace with argon as the gas at 600°C to obtain sample RG3 (DG-Ar-600-3h). After removing organic matter, it was acid-leached and immersed in 1M HCl for 8h to remove metal impurities to obtain comparative sample RG4 (DG-Ar-600-1M HCl).

[0049] The spent graphite was directly immersed in 1M HCl for 8 h to obtain the comparative sample RG5 (DG-1M HCl).

[0050] Comparative Example 2

[0051] The spent graphite and 10 wt% sucrose were dissolved in deionized water, transferred to a hydrothermal reactor and reacted at 200°C for 12 h. The solution was filtered with 1 M HCl to obtain a mixed product (DG-Suc)-HP. The product was then vacuum-dried and placed in a corundum crucible. The product was placed in a tube furnace and kept at 1200°C for 3 h at a heating rate of 2°C / min to obtain the comparative sample RG6 ((DG-0.1Suc)-HP-1200).

[0052] The amorphous carbon spheres, the sucrose hydrothermal carbonization product prepared in Example 1, were characterized by SEM and XRD.

[0053] The regenerated graphite prepared in Example 1 and the comparative example was characterized by SEM and XRD.

[0054] The spent graphite (DG) disassembled from discarded lithium-ion batteries was characterized by SEM and XRD.

[0055] Figure 1The figure shows the XRD comparison spectra of the regenerated graphite material prepared in Example 1, failed graphite and commercial graphite. It can be seen that the (002) diffraction peak of the regenerated graphite RG1 (DG-0.1Suc (HP) -1200) is shifted to the left compared with the (002) and (004) diffraction peaks of the failed graphite (DG) and commercial graphite (CC). This may be because their carbon atoms are not arranged on ordered graphite rings due to the control of the sucrose carbohydrate chain. The diffraction peaks (002) and (004) of the acid-leached regenerated graphite are also shifted to the left. This is because acid leaching causes structural defects in the graphite layer and increases the interlayer spacing.

[0056] Figure 2 The following is a SEM comparison of amorphous carbon spheres, spent graphite, commercial graphite, and the regenerated graphite RG1 (DG-0.1Suc(HP)-1200) prepared in Example 1. As can be seen from the figure, the spent graphite has a damaged structural layer compared to the commercial graphite. The SEM image of the regenerated graphite RG1 shows that the amorphous carbon spheres hydrothermally carbonized with sucrose are successfully coated on the spent graphite.

[0057] The two regenerated graphites prepared in Examples 1-2, the regenerated graphites and the spent graphites in Comparative Examples 1 and 2 were applied to the negative electrode materials of lithium-ion batteries. The specific steps were as follows:

[0058] Active materials (DG, RG1, RG2, RG4, RG6) and carboxymethyl cellulose (CMC) were weighed according to a mass ratio of 90:5:5, and an appropriate amount of deionized water was taken, mixed and ground to obtain a slurry. The slurry was coated on a copper foil current collector, vacuum dried, and then cut into 12 mm circular pieces. The pieces were then transferred to an argon atmosphere glove box, and a CR2025 button half-cell was assembled using the active material as the positive electrode, the metal lithium sheet as the negative electrode (the button half-cell was reversed), Celgard2325 (PP / PE / PP) as the separator, and LB200 (1MLiPF6 in DEC:EC (2:1, Vol%) + 10% FEC) solution as the electrolyte. The cycle and rate performance of the button half-cell were measured on the LAND system.

[0059] Active materials (DG, RG3, RG4, RG5) and PVDF were weighed according to the mass ratio of 8:1:1, and an appropriate amount of NMP solution was taken, mixed and ground to obtain a slurry. The slurry was coated on a copper foil current collector, vacuum dried, and then cut into 12 mm circular electrode pieces. Then, they were transferred to a glove box with an argon atmosphere. The active materials were used as the positive electrode, the metal lithium sheet was used as the negative electrode (the button half-cell was reversed), Celgard2325 (PP / PE / PP) was used as the separator, and LB200 (1M LiPF6 in DEC:EC (2:1, Vol%) + 10% FEC) solution was used as the electrolyte to assemble a CR2025 button half-cell, and the cycle and rate performance of the button half-cell were measured on the LAND system.

[0060] The performance tests of different systems of Examples 1-2 and Comparative Examples 1-2 are shown in Tables 1 and 2.

[0061] Table 1: Comparison of initial coulombic efficiency (ICE) and first cycle charge and discharge specific capacity of button cells prepared in Examples 1-2 and Comparative Examples 1-2 (CMC system)

[0062]

[0063] Table 2: Comparison of initial coulombic efficiency (ICE) and first cycle charge and discharge specific capacity of button cells prepared from spent graphite, commercial graphite, and comparative example 1 (PVDF system)

[0064]

[0065] As can be seen from Table 2, the specific capacity and cycle stability of the recycled graphite RG4 (DG-Ar-600-3h-1M HCl) are significantly improved compared with the failed graphite. It has the best performance compared with other recycled graphites and is comparable to that of commercial graphite.

[0066] As can be seen from Table 1 and Figure 3, RG1 has good cycle stability and high initial Coulombic efficiency, and its reversible specific capacity and initial Coulombic efficiency are significantly improved compared with the failed graphite DG. The performance of the regenerated graphite RG1 coated with 0.1g carbonization product is better than that of the regenerated graphite RG2 coated with 0.2g carbonization product. In addition, compared with other repaired regenerated graphites, it has a higher initial Coulombic efficiency, charge and discharge specific capacity and cycle stability, which is comparable to the acid-impregnated graphite RG4 (DG-Ar-600-1M HCl). However, acid-impregnated graphite requires long-term immersion in 1M HCl, which involves the input of secondary wastewater and is not as environmentally friendly as sucrose-repaired regenerated graphite.

[0067] like Figure 4As shown in the figure, the cycle performance and rate performance of failed graphite and repaired and regenerated graphite materials at different current densities are shown. It can be seen from the figure that the repaired and regenerated graphite RG1 and RG2 have good cycle stability, and as the current density changes, the repaired and regenerated graphite can stably embed and extract lithium ions. Figure 5 As shown, in RG6 ((DG-0.1Suc)-HP-1200), due to hydrothermal treatment, sucrose failed to uniformly coat the failed graphite, resulting in low first coulombic efficiency.

[0068] Referring to the above specific embodiments and experimental characterization results, it can be seen that the present invention coats and modifies the failed graphite negative electrode of the lithium-ion battery by using amorphous carbon hydrothermally carbonized with sucrose, and repairs and regenerates it to obtain a regenerated graphite material.

[0069] The repaired and regenerated graphite material provided by the present invention is applied to lithium-ion battery anode materials. Through controlled carbon layer reconstruction technology, graphite bulk defects are repaired and surface chemical stability is optimized. An amorphous carbon precursor is hydrothermally synthesized and then composited with pretreated graphite to achieve crystal structure regeneration and conductive network reconstruction. This regeneration process is both efficient and sustainable, and the regenerated graphite anode exhibits electrochemical performance comparable to virgin material.

[0070] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for repairing waste lithium-ion battery graphite negative electrodes based on high-temperature carbonization of sucrose, characterized in that: The following steps are involved: (1) heating a sucrose solution in a reactor for hydrothermal reaction, filtering, and vacuum drying to obtain a sucrose hydrothermal carbonization product; the hydrothermal reaction temperature is 150-250° C., and the time is 10-15 hours; (2) mixing and grinding a sucrose hydrothermal carbonization product with spent graphite, and subjecting the mixture to a high-temperature carbonization treatment to obtain regenerated graphite; wherein the weight of the sucrose hydrothermal carbonization product is 5 wt% to 30 wt% of the spent graphite.

2. The method for repairing the graphite negative electrode of waste lithium-ion batteries based on high-temperature carbonization of sucrose according to claim 1, characterized in that: In step (2), the conditions for the high-temperature carbonization treatment are: a heating rate of (2-5)°C / min, a temperature of 1000-1500°C, a holding time of 1-5h; and an argon or nitrogen gas atmosphere.

3. A method for repairing a waste lithium-ion battery graphite negative electrode based on high-temperature carbonization of sucrose according to claim 2, characterized in that: In step (1), the vacuum drying temperature is 70-90° C. and the time is 15-25 hours.

4. A method for repairing a waste lithium-ion battery graphite negative electrode based on high-temperature carbonization of sucrose according to claim 3, characterized in that: In step (1), the concentration of the sucrose solution is 5wt% to 50wt%; the sucrose hydrothermal carbonization product is an amorphous carbon powder with a particle size of 50-200nm.

5. A method for repairing a waste lithium-ion battery graphite negative electrode based on high-temperature carbonization of sucrose according to claim 4, characterized in that: In step (1), the hydrothermal reaction temperature is 200±20° C. and the time is 12±1 h; in step (2), the weight of the sucrose hydrothermal carbonization product is 5wt% to 20wt% of the spent graphite.

6. A method for repairing waste lithium-ion battery graphite negative electrodes based on high-temperature carbonization of sucrose according to claim 5, characterized in that: In step (2), the weight of the sucrose hydrothermal carbonization product is 10±3wt% of the spent graphite; the spent graphite comes from the disassembly of a lithium battery pack.

7. Regenerated graphite prepared by the method according to any one of claims 1 to 6.

8. The regenerated graphite according to claim 7, characterized in that The surface of the regenerated graphite is coated with sucrose carbonization products.

9. The use of the regenerated graphite according to claim 7 or 8, characterized in that: Used in lithium-ion batteries.

10. The use according to claim 9, characterized in that The negative electrode material of the lithium-ion battery is the regenerated graphite, and the adhesive is sodium carboxymethyl cellulose and / or polyvinylidene fluoride.

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