Method for recycling waste negative electrode sheet and regenerated graphite material and application thereof

Abstract

The application relates to the field of waste battery material resource recycling, in particular to a waste negative pole piece recycling method and a regenerated graphite material obtained by the method and application. The waste negative pole piece recycling method comprises the following steps: immersing a waste negative pole piece into a catalytic solution for catalytic treatment for 0.5h-2h; filtering and taking filter residues to obtain a pole piece after catalytic treatment; the catalytic solution comprises a transition metal-based catalyst and an oxidant; the pole piece after catalytic treatment is subjected to dispersion treatment to obtain dispersed graphite; the dispersed graphite is placed in an inert atmosphere, oxygen-containing carbon source steam is introduced, and then heat treatment is carried out to obtain a regenerated graphite material. The graphite in the negative pole piece is separated through the mode of first catalytic oxidation and then dispersion treatment, defects in the graphite are repaired and the graphite is coated through an oxygen-containing organic carbon source in an inert atmosphere, so that the regenerated graphite with good electrochemical performance is obtained, the regenerated graphite can be used as a battery material, and the waste negative pole piece can be recycled.

Description

Technical Field

[0001] This application relates to the field of resource recycling of waste battery materials, specifically to a method for recycling waste negative electrode sheets and the resulting recycled graphite material and its applications. Background Technology

[0002] With the widespread application of lithium-ion batteries, the amount of negative electrode scraps (mainly copper foil coated with graphite) generated during their production process has increased dramatically, becoming a pressing resource and environmental problem. Graphite in negative electrode sheets is a high-value key material; its efficient recycling and high-performance regeneration can not only alleviate the pressure on natural graphite resource extraction and reduce battery production costs, but also has significant strategic importance for building a resource-recycling industrial system.

[0003] Efficient recycling of high-value graphite and copper foil is crucial for resource recycling and cost reduction. Current waste graphite anode recycling technologies still face significant bottlenecks, struggling to balance environmental friendliness, economic efficiency, and the performance of recycled materials. High-temperature heat treatment methods result in poor cycle stability of recycled graphite, failing to meet the high-performance requirements of secondary batteries and limiting its use to low-value applications. Strong acid and alkali wet treatment methods are difficult and costly to treat, easily causing secondary pollution; simultaneously, the process introduces stubborn impurities and defects, leading to a decline in the electrochemical performance of recycled graphite and difficulty in achieving the required purity. Physical separation methods are prone to introducing new structural defects due to mechanical grinding, further reducing its electrochemical activity and limiting its practical industrial application. Therefore, existing recycling technologies suffer from high pollution, high energy consumption, and low performance of recycled products with little recycling value. Summary of the Invention

[0004] To efficiently recycle batteries and address one of the aforementioned problems, this application provides a method for reusing waste negative electrode sheets, comprising the following steps: The waste negative electrode sheet is immersed in a catalytic solution for catalytic treatment for 0.5h to 2h; filtered, and the filter residue is taken to obtain the catalytically treated electrode sheet; the catalytic solution contains a transition metal-based catalyst and an oxidant; The catalytically treated electrode was dispersed to obtain dispersed graphite. Dispersed graphite is placed in an inert atmosphere and heat-treated by introducing oxygen-containing carbon source steam to obtain recycled graphite material.

[0005] In some embodiments, the transition metal-based catalyst includes an activated carbon catalyst supported on Fe2O3, Co... 2+ Ionic solutions and Cu 2+ At least one of the ionic solutions.

[0006] In some embodiments, the oxygen-containing carbon source vapor includes at least one of methanol, ethanol, acetone, and acetaldehyde.

[0007] In some embodiments, the volume fraction of the oxygen-containing carbon source vapor in the reaction atmosphere is 1% to 10%.

[0008] In some embodiments, during the catalytic treatment, the liquid content of the waste negative electrode catalytic solution is 1:(4~6) in g:mL; the concentration of the transition metal-based catalyst in the catalytic solution is 0.01g / L~0.1g / L; and the concentration of the oxidant in the catalytic solution is 0.5g / L~2g / L.

[0009] In some embodiments, the oxidant includes at least one of persulfate and hydrogen peroxide.

[0010] In some embodiments, the heat treatment temperature is 500°C to 700°C.

[0011] In some embodiments, the heating rate of the heat treatment is 5°C / min.

[0012] In some embodiments, the heat treatment duration is 1 hour to 2 hours.

[0013] In some embodiments, the dispersion process is ultrasound.

[0014] In some embodiments, the ultrasonic conditions include: ultrasonic treatment at 50W~100W and 50℃~60℃ for 15min~30min.

[0015] In some embodiments, the ultrasound includes: placing the catalytically treated electrode in an aqueous or ethanol solution for ultrasound treatment.

[0016] In some embodiments, the volume fraction of ethanol in the ethanol solution is 0.01% to 10%.

[0017] In some embodiments, dispersing the catalytically treated electrode includes ultrasonically treating the catalytically treated electrode, screening the material obtained after ultrasonic treatment to remove metal substances, collecting the remaining material, and obtaining dispersed graphite.

[0018] The second aspect of this application provides a recycled graphite material obtained by any one of the methods in the first aspect.

[0019] A third aspect of this application provides a secondary battery comprising the recycled graphite material as described in the second aspect.

[0020] A third aspect of this application provides an electronic device comprising a secondary battery as described in the third aspect.

[0021] Beneficial effects: This application separates the graphite in the negative electrode sheet by first catalytic oxidation and then dispersion treatment, and then repairs the defects in the graphite and coats the graphite with an oxygen-containing organic carbon source under an inert atmosphere, thereby obtaining recycled graphite with good electrochemical performance. This recycled graphite can be used as the negative electrode material of the battery, realizing the high-value recycling of waste negative electrode sheets. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0023] Figure 1 This is a scanning electron microscope image of the recycled graphite material from Example 1. Detailed Implementation

[0024] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art based on this application are within the scope of protection of this application.

[0025] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0026] To address the aforementioned technical problems, related technologies obtain black powder through steam heat treatment, followed by air calcination, high-temperature chlorination, and displacement water washing to obtain graphite. However, these methods are complex, energy-intensive, and the high temperatures can damage the layered crystal structure of graphite. This not only makes the process cumbersome but also easily leads to a significant reduction in lithium storage capacity and initial coulombic efficiency, resulting in poor graphite reuse. Some related technologies employ a strong acid-base wet treatment method, using alkaline leaching and two-step acid leaching, followed by high-temperature repair to obtain graphite. This method avoids high temperatures but uses highly corrosive reagents, requires sophisticated equipment, and generates large amounts of acidic wastewater containing heavy metals, placing a heavy environmental burden on the plant. Furthermore, acid molecules readily react with graphite or residual metals, causing strong acid to embed between graphite layers, introducing impurities and surface functional groups, thereby reducing the purity and performance of the recovered graphite and impairing its electrochemical properties.

[0027] Therefore, existing technologies, whether heat treatment or strong acid wet processing, have significant drawbacks, namely high energy consumption, high pollution, and secondary damage to graphite materials, resulting in low performance of recycled products and making it difficult to achieve high-value recycling.

[0028] In this regard, the first aspect of this application provides a method for reusing waste negative electrode sheets, comprising the following steps: The waste negative electrode sheet is immersed in a catalytic solution for catalytic treatment for 0.5h to 2h; filtered, and the filter residue is taken to obtain the catalytically treated electrode sheet; the catalytic solution contains a transition metal-based catalyst and an oxidant; The catalytically treated electrode was dispersed to obtain dispersed graphite. Dispersed graphite is placed in an inert atmosphere and heat-treated by introducing oxygen-containing carbon source steam to obtain recycled graphite material.

[0029] In some specific embodiments, the waste negative electrode sheet is a pre-treated negative electrode sheet, and the pre-treatment includes cutting large pieces of waste negative electrode sheet into small pieces of waste negative electrode sheet of 1cm*1cm.

[0030] The waste negative electrode sheet is immersed in a catalytic solution for catalytic treatment for 0.5h to 2h. During the catalytic process, the catalyst activates the oxidant to generate highly active free radicals (such as hydroxyl radicals: ·OH or sulfate radicals: SO4·). - It selectively attacks and degrades the molecular chains of SBR / CMC binders while causing almost no damage to the graphite matrix.

[0031] The separated graphite powder is heat-treated for a short time (0.5–2 hours) at 500–700°C under an inert atmosphere (such as N2 or Ar), while simultaneously introducing a low concentration of oxygen-containing carbon source vapor (such as ethanol or acetone vapor, volume concentration 1–10%), to obtain regenerated graphite material. During this process, the active carbon species generated by carbon source decomposition not only form an amorphous carbon coating layer, but the reducing atmosphere also "heals" the surface of the graphite. 3 Carbon defects are transformed into sps with better conductivity. 2 The structure enables synergy between repair and encapsulation.

[0032] In this application, the recycled graphite material treated as described above can be used as a battery active material after being washed and dried. After testing, the battery assembled in this application has good initial coulombic efficiency (>94%) and reversible capacity (>365 mAh / g), and can be directly used for the preparation of new battery cells. It has significant economic value and realizes a leap from "recycling" to "high-performance regeneration".

[0033] In the above-mentioned treatment process of this application, there is no need to use strong acids or bases, and the entire process is close to neutral pH conditions, making wastewater treatment simple and cost-effective; the energy consumption is greatly reduced compared to thermal treatment methods; the catalyst used in this application can be recycled, further reducing treatment costs.

[0034] In some specific embodiments, the catalytic treatment temperature is 40℃~70℃; in some specific embodiments, the catalytic treatment temperature can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, or a value within any two of these ranges.

[0035] The catalytic treatment temperature of this application avoids low catalytic reaction efficiency to ensure efficient catalysis, while also avoiding excessively high temperatures that could lead to ineffective decomposition of the oxidant and free radical quenching.

[0036] In some specific embodiments, the waste negative electrode sheet is immersed in a catalytic solution for catalytic treatment for 0.5h, 1.0h, 1.5h or 2.0h, or values ​​within any range of two of these values.

[0037] In some embodiments, the transition metal-based catalyst includes an activated carbon catalyst supported on Fe2O3, Co... 2+ Ionic solutions and Cu 2+ At least one of the ionic solutions.

[0038] In some embodiments, the oxygen-containing carbon source vapor includes at least one of methanol, ethanol, acetone, and acetaldehyde.

[0039] In some embodiments, the volume fraction of the oxygen-containing carbon source vapor in the reaction atmosphere is 1% to 10%.

[0040] In some specific embodiments, the volume fraction of the oxygen-containing carbon source vapor in the reaction atmosphere can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a value within any two of these ranges.

[0041] The volume fraction of oxygen-containing carbon source vapor in the reaction atmosphere of this application avoids insufficient coating and repair effects, and also avoids excessive carbon deposition that would affect lithium-ion diffusion.

[0042] In some embodiments, during the catalytic treatment, the liquid content of the waste negative electrode catalytic solution is 1:(4~6) in g:mL; the concentration of the transition metal-based catalyst in the catalytic solution is 0.01g / L~0.1g / L; and the concentration of the oxidant in the catalytic solution is 0.5g / L~2g / L.

[0043] In some embodiments, during the catalytic treatment, the liquid-to-material ratio of the waste negative electrode sheet to the catalytic solution, expressed in g:mL, is 1:4, 1:5, or 1:6, or a value within the range of any two of these values.

[0044] In some embodiments, the concentration of the transition metal-based catalyst in the catalytic solution may be 0.01 g / L, 0.02 g / L, 0.03 g / L, 0.04 g / L, 0.05 g / L, 0.06 g / L, 0.07 g / L, 0.08 g / L, 0.09 g / L, 0.10 g / L, or a value within any two of these ranges.

[0045] In some embodiments, the concentration of the oxidant in the catalytic solution may be 0.5 g / L, 0.6 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, 2.0 g / L, or a value within any range of two of these values.

[0046] In some embodiments, the oxidant includes at least one of persulfate and hydrogen peroxide.

[0047] In some embodiments, the heat treatment temperature is 500°C to 700°C.

[0048] The heat treatment temperature of this application can achieve good repair results while avoiding damage to the graphite matrix structure.

[0049] In some specific embodiments, the heat treatment temperature can be 500°C, 550°C, 600°C, 650°C, 700°C, or a value within a range of any two of these values.

[0050] In some embodiments, the heating rate of the heat treatment is 3~6℃ / min.

[0051] In some specific embodiments, the heating rate of the heat treatment can be 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, or a value within the range of any two of these values.

[0052] In some embodiments, the heat treatment duration is 1 hour to 2 hours.

[0053] In some specific embodiments, the heat treatment duration can be 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, or a value within any range of two of these values.

[0054] In some embodiments, the dispersion process is ultrasound.

[0055] In some embodiments, the ultrasonic conditions include: ultrasonic treatment at 50W~100W and 50℃~60℃ for 15min~30min.

[0056] In some specific embodiments, the ultrasonic conditions include: ultrasonic power of 50W, 60W, 70W, 80W, 90W or 100W, ultrasonic temperature of 50℃, 52℃, 54℃, 56℃, 58℃ or 60℃, ultrasonic treatment time of 15min, 20min, 25min or 30min, or values ​​within the range of any two of the above parameters.

[0057] In some embodiments, the ultrasound includes: placing the catalytically treated electrode in an aqueous or ethanol solution for ultrasound treatment.

[0058] In some embodiments, the volume fraction of ethanol in the ethanol solution is 0.01% to 10%.

[0059] The catalytically treated material is transferred into pure water or a low-concentration ethanol aqueous solution and treated with slight ultrasonication (50-100W) at 50-70°C for 10-30 minutes. Since the binder has been pre-degraded, the graphite coating can be easily peeled off from the copper foil after ultrasonic treatment, and the copper foil and graphite powder can be recovered by sieving.

[0060] In some specific embodiments, the volume fraction of ethanol may be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a value within any range of two of these values.

[0061] In some embodiments, dispersing the catalytically treated electrode includes ultrasonically treating the catalytically treated electrode, screening the material obtained after ultrasonic treatment to remove metal substances, collecting the remaining material, and obtaining dispersed graphite.

[0062] The second aspect of this application provides a recycled graphite material obtained by any one of the methods in the first aspect.

[0063] A third aspect of this application provides a secondary battery comprising the recycled graphite material as described in the second aspect.

[0064] According to a third aspect of this application, a secondary battery is provided, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer comprises recycled graphite material provided in the second aspect of this application or recycled graphite material prepared according to the method provided in the first aspect of this application.

[0065] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a polymer substrate coated with conductive metal, etc.

[0066] The negative electrode active material layer of this application may further include a conductive agent and a binder. This application does not impose any particular limitations on the aforementioned conductive agent and binder, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, carbon materials, metals, or conductive polymers. The binder may include, but is not limited to, at least one of polyacrylol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0067] The secondary battery of this application also includes a positive electrode sheet. This application does not impose any particular limitation on the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil is aluminum foil. In some embodiments, the secondary battery is a lithium-ion battery, and the positive active material may include lithium transition metal oxide, which may include, but is not limited to, at least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese iron phosphate, or lithium titanate.

[0068] The secondary battery of this application also includes an electrolyte. In one embodiment, the electrolyte includes a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of this application is achieved.

[0069] The secondary battery of this application also includes a separator for separating the positive electrode and the negative electrode, preventing internal short circuits in the secondary battery, allowing electrolyte ions to pass freely, and not affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the separator material can be, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) separators based on polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, or aramid membranes.

[0070] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0071] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0072] According to a fourth aspect of this application, an electronic device is provided, the electronic device comprising the secondary battery described in the third aspect of this application. The secondary battery provided in the third aspect of this application has high energy density and good cycle performance, thereby enabling the electronic device provided in the fourth aspect of this application to have a long service life.

[0073] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0074] Example The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0075] The test methods and equipment used in the embodiments and comparative examples of this application are as follows: 1. Scanning Electron Microscopy (SEM) Testing The prepared negative electrode active material particles were observed and SEM images were taken using a scanning electron microscope (ZEISSSEM). The steps included sample preparation, electron microscopy observation, and result analysis. During preparation, the powder sample was firmly and uniformly fixed on the conductive adhesive. After instrument calibration, the sample was placed in the sample chamber and a vacuum was drawn. An accelerating voltage of 1-5 kV was used, and appropriate working distance and beam size were adjusted. After finding a suitable image, high-resolution images were acquired and saved using slow scan mode.

[0076] 2. Copper foil recovery rate and graphite recovery rate test: A certain mass of waste negative electrode sheet m0 is weighed, cut into small pieces, and immersed in a solution containing a transition metal catalyst and a mild oxidant. The treated electrode sheet is then ultrasonically treated in a solution containing a dispersant. After filtration and drying, it is sieved to obtain block copper foil and powdered graphite. The mass of copper foil m2 and the mass of powder m3 are weighed. The copper foil recovery rate = m 2 / m0*100%, Graphite recovery rate = m 3 / m0*100%.

[0077] 3. First Coulomb Efficiency Test of Regenerated Graphite: Using recycled graphite as the working electrode and lithium metal sheet as the counter electrode, a coin cell half-cell was assembled in a glove box. The assembled cell was then subjected to its first charge-discharge test at 0.1C rate within a voltage range of 0.001V to 1.5V or 0.01V to 1.5V on a battery testing system at 25°C ± 2°C.

[0078] Initial coulombic efficiency (%) = (initial charge capacity / initial discharge capacity) × 100%.

[0079] 4. Reversible specific capacity test of recycled graphite: This metric is typically measured during the same first charge-discharge cycle as the "first coulombic efficiency test." The first charge capacity and the mass of the recycled graphite material are recorded, and the ratio is considered the reversible specific capacity.

[0080] Reversible specific capacity of recycled graphite (mAh / g) = initial charge capacity (mAh) / mass of recycled graphite active material (g).

[0081] 5. Capacity retention test after 200 cycles: The assembled coin cells (or full cells with them as the positive electrode) were subjected to continuous cycle testing under a specified charge-discharge regime (e.g., 0.1C constant current charge-discharge, voltage range 0.001–1.5V). The discharge capacity (C1) of the first cycle and the discharge capacity (C2) of the 200th cycle were recorded. 200 ).

[0082] Capacity retention rate (%) after 200 cycles = (Discharge capacity C of the 200th cycle) 200 / Discharge capacity of the first cycle (C1) × 100%.

[0083] Example 1 1. Preparation of recycled graphite Take 100g of waste negative electrode, cut it into small pieces of 1cm*1cm, immerse it in 500mL of aqueous solution containing 0.1g / L Fe2O3 / activated carbon catalyst and 2g / L potassium persulfate (PMS) (pH 5), stir and react at 60℃ for 1 hour; filter, take the filter residue, and obtain the catalytically treated electrode.

[0084] After catalytic treatment, the electrode was transferred into 500 mL of pure water and ultrasonically treated at 60 °C (80 W) for 20 minutes; the mixture of copper foil and graphite was obtained by sieving.

[0085] Wet graphite was heated to 600°C at a rate of 5°C / min under a N2 atmosphere, and ethanol vapor carried by N2 (ethanol volume concentration in the carrier gas was 5%) was introduced. The heat treatment was carried out at a constant temperature for 1 hour. The graphite obtained by the constant temperature heat treatment was cooled, washed with water, and dried to obtain recycled graphite material.

[0086] The copper foil recovery rate obtained from the above process is 99.2%.

[0087] 2. Recycled graphite is used to assemble button cells. <Preparation of Negative Electrode Sheets> The aforementioned negative electrode active material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 97:1.5:1.5. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 40 wt%, and the mixture was stirred until homogeneous. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 50 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 76.6 mm × 875 mm.

[0088] <Preparation of the positive electrode> Lithium cobalt oxide (CCO) as the positive electrode active material, conductive carbon black (SuperP) as the conductive agent, and PVDF as the binder were mixed at a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred until homogeneous, resulting in a positive electrode slurry with a solid content of 72 wt%. The positive electrode slurry was uniformly coated onto one surface of a 13 μm thick aluminum foil used as a positive electrode current collector, and dried at 85 °C to obtain a single-sided coated positive electrode sheet with a positive electrode active material layer thickness of 80 μm. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85 °C for 4 hours to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0089] <Preparation of Electrolyte> In a dry argon atmosphere glove box, the base solvents ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1. Then, 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were added, dissolved, and stirred thoroughly. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. The concentration of lithium salt was 1 mol / L. Based on the mass of the base solvent, the mass percentages of 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and succinate were all 2%.

[0090] <Preparation of the diaphragm> A polyethylene film with a thickness of 7μm was used as the diaphragm.

[0091] <Preparation of Lithium-ion Batteries> The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. The electrodes are then wound to obtain the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the lithium-ion battery is obtained through vacuum sealing, settling, formation, degassing, and shaping processes.

[0092] The assembled coin cells were tested using the aforementioned testing method. The results showed an initial coulombic efficiency of 94.5%, a reversible specific capacity of 365 mAh / g, and a capacity retention of 98.1% after 200 cycles. Example 2 1. Preparation of recycled graphite Take 100g of waste negative electrode, cut it into 1cm*1cm pieces, and immerse it in 500mL of solution containing 0.05g / L Co. 2+ The electrode was stirred at 50°C for 1.5 hours in an ionic solution and an aqueous solution of 1.0 wt% H2O2 (pH=4); the mixture was then filtered, and the residue was collected to obtain the catalytically treated electrode.

[0093] After catalytic treatment, the electrode was transferred into a 500 mL solution of water:ethanol = 95:5 (V / V) and ultrasonically treated at 60 °C (100 W) for 15 minutes; the mixture of copper foil and graphite was obtained by sieving.

[0094] Wet graphite was heated to 600°C at a rate of 5°C / min under a N2 atmosphere, and ethanol vapor carried by N2 (ethanol volume concentration in the carrier gas was 5%) was introduced. The heat treatment was carried out at a constant temperature for 1 hour. The graphite obtained by the constant temperature heat treatment was cooled, washed with water, and dried to obtain recycled graphite material.

[0095] The copper foil recovery rate obtained from the above process is 99.2%.

[0096] 2. Recycled graphite is used to assemble button cells. Meanwhile, in Example 1.

[0097] The assembled coin cells were tested using the aforementioned test method. The test results were as follows: initial coulombic efficiency of 93.8%, reversible specific capacity of 360 mAh / g, and capacity retention of 97.5% after 200 cycles.

[0098] Example 3 Take 100g of waste negative electrode, cut it into small pieces of 1cm*1cm, immerse it in 500mL of aqueous solution containing 0.01g / LFe2O3 / activated carbon catalyst and 0.5g / L potassium persulfate (PMS) (pH 3), stir and react at 70℃ for 0.5 hours; filter, take the filter residue, and obtain the catalytically treated electrode.

[0099] After catalytic treatment, the electrode was transferred into 500 mL of pure water and ultrasonically treated at 50°C (50 W) for 30 minutes; the mixture of copper foil and graphite was obtained by sieving.

[0100] Wet graphite was heated to 600°C at 5°C / min in a N2 atmosphere, and ethanol vapor carried by N2 (ethanol volume concentration in the carrier gas was 1%) was introduced. The heat treatment was carried out at a constant temperature for 2 hours. The graphite obtained by the constant temperature heat treatment was cooled, washed with water, and dried to obtain recycled graphite material.

[0101] 2. Recycled graphite is used to assemble button cells. Meanwhile, in Example 1.

[0102] The assembled coin cells were tested using the aforementioned test method. The test results were as follows: initial coulombic efficiency was 92.0%, and reversible specific capacity was 350 mAh / g.

[0103] Example 4 The difference between Example 4 and Example 1 is that, in the catalytic activation pretreatment step, the transition metal-based catalyst is a CuSO4 solution with an equimolar concentration of metal ions (i.e., Cu...). 2+ (Ion catalyst), the remaining steps are exactly the same as in Example 1.

[0104] Result: Cu 2+ While the PMS system can also generate free radicals to degrade the binder, its catalytic efficiency and reaction pathway differ from those of the Fe-based catalyst. Experiments showed that the exfoliation efficiency under these conditions was slightly lower than in Example 1, and the copper foil recovery rate was acceptable, but trace amounts of blue (Cu) were visible in the washing water of the graphite powder. 2+ (residual), indicating Cu 2+ It may be partially adsorbed on the graphite surface. Although subsequent water washing was performed, trace metal residues may have a negative impact on the electrochemical performance of graphite, as evidenced by lower initial coulombic efficiency and capacity retention compared to Example 1 using an Fe-based catalyst.

[0105] Comparative Example 1 The difference between this comparative example and Example 1 is that in the catalytic activation pretreatment step, only a 2 g / L potassium persulfate (PMS) aqueous solution (pH≈5) was used, and no transition metal catalyst was added. The conditions for the remaining steps were the same as in Example 1.

[0106] The test results showed that the binder had low degradation efficiency and was difficult to peel off; the copper foil recovery rate was <90%; and the initial coulombic efficiency of the recycled graphite was only 85.4%. This demonstrates that the catalytic activation step is beneficial for achieving efficient and selective degradation.

[0107] Comparative Example 2 The difference from Example 1 is that the dispersed graphite was dried and then directly heated to 600°C at a rate of 5°C / min and kept at that temperature for 1 hour in a pure N2 atmosphere, without introducing any oxygen-containing carbon source vapor during the process.

[0108] Electrochemical tests showed that the initial coulombic efficiency of this recycled graphite was low, mainly because defects irreversibly consumed lithium ions to form a solid electrolyte interface film. Simultaneously, its cycle stability was also poor.

[0109] Comparative Example 3 The specific operation of Comparative Example 4 was as follows: 100g of negative electrode scrap was taken and subjected to heat treatment under an inert atmosphere by introducing oxygen-containing carbon source steam. Specifically, the original scrap was placed directly into a tube furnace, and under a N2 atmosphere, 5% ethanol steam was introduced and treated at 600℃ for 1 hour. After treatment, an attempt was made to physically peel the graphite off the copper foil.

[0110] Results and Analysis: In this process, because the binder was not pre-degraded, it underwent cross-linking and carbonization at high temperatures, bonding the graphite particles and copper foil more firmly together to form a hard block. Ethanol vapor could not penetrate this dense binder carbonization layer to act on the internal graphite. After treatment, the graphite coating could not be effectively peeled off from the copper foil; the coating crumbled and fell off when the copper foil was bent, but intact graphite powder could not be collected. The copper foil recovery rate was extremely low, and the surface was severely contaminated, making graphite recovery virtually impossible.

[0111] Comparative Example 4 Take 100g of negative electrode scrap from the same source, separate the graphite powder using hot steam, calcine it in air at 500℃ for 2 hours to remove the binder, and then obtain graphite by high-temperature chlorination to remove copper and displacement washing.

[0112] This process is extremely energy-intensive, and the high-temperature oxidation damages the graphite structure, resulting in an initial coulombic efficiency of only 75.3% for the recovered graphite powder, with a significant decrease in capacity retention. Button cell performance: High temperature causes damage to the graphite structure, resulting in an initial coulombic efficiency of only 75.3%, a reversible capacity of 298 mAh / g, and a significant decrease in cycle performance.

[0113] Comparative Example 5 Take 100g of negative electrode scrap from the same source and place it in a 50g / L sodium hydroxide solution. The resulting graphite is treated with 98% concentrated sulfuric acid and then with 12mol / L hydrochloric acid to obtain graphite.

[0114] The assembled coin cells were tested using the aforementioned test method. The test results showed that due to sulfate intercalation and sulfur residue, the initial coulombic efficiency was 79.6%, the charge-discharge performance was unstable, and the capacity retention rate was only 80.2% after 100 cycles.

[0115] Table 1. Test results of the examples and comparative examples

[0116] As shown in Table 1, the method for reusing waste negative electrode sheets provided in this application possesses high initial coulombic efficiency, reversible specific capacity, and capacity retention. Meanwhile, Figure 1 The recycled graphite material obtained in Embodiment 1 of this application is granular with a complete crystal structure, thin flakes and good toughness, exhibiting the layered stacking characteristics of graphite, and has a high specific surface area and potential anisotropy.

[0117] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present invention are protected by the present invention.

Claims

1. A method for reusing waste negative electrode sheets, characterized in that, Includes the following steps: The waste negative electrode sheet is immersed in a catalytic solution for catalytic treatment for 0.5h to 2h; filtered, and the filter residue is taken to obtain the catalytically treated electrode sheet; the catalytic solution contains a transition metal-based catalyst and an oxidant; The catalytically treated electrode was dispersed to obtain dispersed graphite. Dispersed graphite is placed in an inert atmosphere and heat-treated by introducing oxygen-containing carbon source steam to obtain recycled graphite material.

2. The method of claim 1, wherein, The transition metal-based catalyst includes an activated carbon catalyst supported on Fe2O3 and Co. 2+ Ionic solutions and Cu 2+ At least one of the ionic solutions.

3. The method of claim 1, wherein, The oxygen-containing carbon source vapor includes at least one of methanol, ethanol, acetone, and acetaldehyde.

4. The method of claim 1, wherein, The volume fraction of the oxygen-containing carbon source vapor in the reaction atmosphere is 1% to 10%.

5. The method of claim 1, wherein, In the catalytic treatment, the liquid content of the waste negative electrode catalytic solution is 1:(4~6) in g:mL; the concentration of the transition metal-based catalyst in the catalytic solution is 0.01g / L~0.1g / L; and the concentration of the oxidant in the catalytic solution is 0.5g / L~2g / L.

6. The method according to claim 1, characterized in that, The oxidant includes at least one of persulfate and hydrogen peroxide.

7. The method according to claim 1, characterized in that, The conditions for the catalytic treatment include: a temperature of 40~70℃, and / or a pH of 3~7.

8. A recycled graphite material obtained by the method according to any one of claims 1 to 7.

9. A secondary battery, characterized in that, The secondary battery includes the recycled graphite material as described in claim 8.

10. An electronic device, comprising: The electronic device includes the secondary battery as described in claim 9.

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