Method for recycling and regenerating graphene from waste lithium battery negative electrode

Abstract

This invention provides a method for recovering and regenerating graphene from the negative electrode of spent lithium batteries, comprising the following steps: S1. Charging the spent lithium batteries to a state of charge (SOC) of 20-40%; S2. Disassembling and crushing the spent lithium batteries in an inert atmosphere to obtain a negative electrode sheet; S3. Separating the negative electrode current collector and the negative electrode active material layer from the negative electrode sheet. The negative electrode active material layer contains graphite. The negative electrode active material layer is collected and subjected to ultrasonic, centrifugation, and drying treatments in sequence to obtain a solid mixture; S4. Calcining the solid mixture at a temperature not exceeding 400℃ to obtain spent graphite; S5. Dispersing the spent graphite evenly in an organic solvent, followed by ultrasonic-assisted exfoliation. After ultrasonication, the graphite is centrifuged, filtered, and freeze-dried to obtain graphene. The organic solvent includes at least two of DMSO, NMP, GBL, CYC, and IPA. This invention achieves a gentle and efficient recovery of spent graphite and obtains high-quality graphene through a dual-solvent method.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling technology, specifically relating to a method for recovering and regenerating graphene from the negative electrode of waste lithium batteries. Background Technology

[0002] The raw materials for industrial-grade graphene production are highly concentrated in two types of graphite resources: natural graphite relies on mining, with energy consumption reaching 11,000 megajoules per ton of product and accompanied by 5.3 tons of CO2 emissions; artificial graphite uses fossil derivatives such as petroleum coke or coal tar as raw materials, resulting in a high carbon footprint. In contrast, recovering graphite resources from the negative electrodes of spent lithium iron phosphate batteries can avoid primary mining and fossil raw material processing, while simultaneously alleviating the pressure of solid waste disposal, achieving the dual benefits of resource recycling and emission reduction.

[0003] There are various technical solutions for preparing graphene from waste graphite, but each has its own advantages and disadvantages: For example, the thermal oxidation-liquid phase exfoliation method has a high monolayer rate (>70%), but the high-temperature pretreatment (>500℃) causes damage to the carbon skeleton; the electrochemical exfoliation method is fast (<30 minutes), but the strong acid electrolyte causes equipment corrosion and sulfur doping (S>2 at.%), requiring complex purification; the microwave expansion method has low energy consumption, but the residual metal (>500 ppm) leads to uneven sheet size and deterioration of electrochemical performance; the ball milling method is low cost, but the mechanical and violent exfoliation causes high defects, low monolayer rate (<30%) and media contamination. Summary of the Invention

[0004] To address the problems and shortcomings of existing technologies, this invention provides a method for recovering and regenerating graphene from the negative electrode of spent lithium-ion batteries. This method, without introducing strong acids / bases or damaging the sp² framework of carbon materials, gently and efficiently recovers spent graphite while simultaneously achieving efficient, low-defect graphene exfoliation. This has significant scientific and engineering value for promoting the recycling of power batteries and the greening of the graphene industry.

[0005] According to a first aspect of the present invention, a method for recovering and regenerating graphene from the negative electrode of a spent lithium battery is provided, comprising the following steps: S1. Charging the spent lithium battery to a state of charge (SOC) of 20-40%; S2. Disassembling and crushing the spent lithium battery to obtain a negative electrode sheet; S3. Separating the negative electrode current collector and the negative electrode active material layer of the negative electrode sheet, wherein the negative electrode active material layer contains graphite, collecting the negative electrode active material layer and subjecting it to ultrasonic, centrifugation, and drying treatments in sequence to obtain a solid mixture; S4. Calcining the solid mixture at a temperature not exceeding 400°C to obtain spent graphite; S5. Dispersing the spent graphite evenly in an organic solvent, performing ultrasonic-assisted exfoliation, and after ultrasonic treatment, centrifuging, filtering, and freeze-drying to obtain graphene; wherein the organic solvent includes at least two of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), cyclohexanone (CYC), and isopropanol (IPA).

[0006] In the method for recycling and regenerating graphene from the negative electrode of spent lithium batteries provided by this invention, firstly, the spent lithium batteries are pre-charged to a SOC of 20-40%, and LiC is generated in situ inside the graphite. x (such as LiC) 12 ~LiC 20 Intercalation compounds are used to increase the interlayer spacing and loosen the structure of graphite. Combined with optimized separation processes, the primary separation rate between the negative electrode current collector (e.g., copper foil) and graphite is significantly improved (primary separation rate = (final obtained graphite mass / theoretical mass of graphite on the initial electrode) * 100%), directly reducing material loss and subsequent processing costs. In particular, during the treatment of waste graphite, the traditional high-temperature oxidation removal method (>500℃) is abandoned, and a low-temperature calcination heat treatment (no higher than 400℃) is adopted. This effectively removes organic residues (such as binder PVDF and electrolyte) while minimizing the damage to graphite sp. 2 Thermal damage to the carbon skeleton ensures the structural integrity of graphene from the source.

[0007] After obtaining relatively pure graphite through calcination, a dual-solvent system is used. The two solvents are specifically selected and have good polarity complementarity. Therefore, by utilizing the synergistic "polar gradient + hydrogen bond network" effect of the two solvents, efficient intercalation kinetics and excellent stabilization ability can be provided. This allows for more effective insertion between graphite layers, significantly reducing the interlayer interaction energy barrier. Compared with a single solvent, this can effectively assist in the physical exfoliation of graphite and improve the exfoliation efficiency and amount of graphene.

[0008] It is worth noting that, due to the previous charging process of the spent lithium batteries, the LiC generated in situ inside the graphite is... xIntercalation compounds can act as "natural intercalating agents," enabling graphite layers to pre-enter a metastable state. Therefore, not only can organic residues be effectively removed using low-temperature calcination heat treatment at no higher than 400℃, but they can also produce a synergistic intercalation effect with the aforementioned dual-solvent system. This allows for efficient and low-defect graphene exfoliation under mild conditions, significantly improving exfoliation efficiency and yield, while balancing green processes with high product performance. Regarding exfoliation efficiency and yield, thanks to the activation of the graphite structure by pre-lithiation and the synergistic exfoliation effect of the dual solvents, the required ultrasonic-assisted exfoliation time can be reduced from the traditional minimum of 20 hours to 4-10 hours. Furthermore, even with the reduced exfoliation time, high-concentration graphite can still be fully exfoliated. It should be noted that excessively long ultrasonic times can lead to a high sheet breakage rate (>30%). Therefore, this invention reduces the ultrasonic exfoliation time and significantly improves the structural integrity of the graphene sheets, thereby enhancing the quality of the recycled graphene product.

[0009] In summary, the synergistic process of pre-charging, low-temperature pyrolysis, and dual solvents ensures that the recycled graphene has few defects and high sheet quality. This structural advantage directly translates into excellent electrical properties, enabling it to exhibit superior conductivity when used as a conductive agent or electrode material, which is beneficial for lithium-ion transport. Therefore, the graphene recovered and prepared from the negative electrode of spent lithium batteries in this invention still retains its complete structure, ensuring good electrochemical performance when reused in lithium batteries.

[0010] Preferably, in S1, the waste lithium battery represents a battery with a state of health (SOH) of less than 80%.

[0011] Preferably, in S1, the charging parameters for the waste lithium battery are as follows: constant current charging at 0.09~0.11C to SOC 20~40%.

[0012] Preferably, in step S2, the waste lithium batteries are dismantled and crushed in a glove box with a water and oxygen content of <1 ppm. Dismantling in an argon-filled glove box with a water and oxygen content of <1 ppm completely avoids the risk of combustion and explosion that may be caused by the contact of residual lithium with air, providing crucial safety assurance for the entire recycling process.

[0013] Preferably, in step S3, the ultrasonic treatment of the negative electrode active material layer uses a power of 50–100 W, a frequency of 30–80 kHz, and a duration of 10–30 min. The ultrasonic treatment at specific power and frequency generates a strong cavitation effect, which can penetrate the gaps and surface pores of graphite particles, effectively "washing away" and "stripping away" these stubborn conductive agent particles and organic residues, achieving effective cleaning. In particular, it can effectively disrupt the bonding network of binders such as PVDF, causing them to desorb from the graphite particle surface and disperse into the solvent. This reduces the burden on subsequent calcination for impurity removal and makes the solid mixture more loose.

[0014] Preferably, in S3, the water temperature during the ultrasonic process is 25–35°C.

[0015] Preferably, in S3, the centrifugation speed is 600-1800 rpm and the time is 10-30 min.

[0016] Preferably, in step S3, the drying temperature is 60~80℃ and the time is 12~24h.

[0017] Preferably, in step S4, the solid mixture needs to be ground before calcination. After grinding, the solid mixture is uniform and free of lumps.

[0018] Preferably, in S4, the calcination temperature is 300–400℃, and the time is 2–6 hours. Too low a temperature is not conducive to fully removing residual binders and electrolytes, while too high a temperature is not conducive to ensuring the integrity and layered ordered structure of the graphite microcrystals, such as sp... 2 Hybridized carbon bonds break, introducing a large number of vacancies and sp246 sites. 3 Hybrid defects cause thermal damage, which is detrimental to efficient cleavage along the crystal plane during the subsequent solvent stripping stage. Moreover, the aforementioned lower temperature heat treatment significantly reduces heat energy consumption and avoids the safety risks that may be caused by violent reactions of residual lithium at high temperatures, making the operation process more controllable and safer.

[0019] Preferably, in step S4, the temperature is increased to 300–400°C at a heating rate of 3.5–6.5°C / min. If the heating rate is too fast, a large instantaneous temperature difference will occur between the particle surface and interior, causing uneven thermal expansion. This thermal stress will promote the generation and propagation of microcracks, damaging the integrity of the graphite structure and weakening the mechanical strength of the graphite particles. Simultaneously, an excessively fast heating rate will cause polymers such as binders (PVDF) to crosslink and carbonize in the molten state, rather than completely decompose. This will generate disordered, amorphous carbonaceous residues. These residues, covering the graphite surface, will severely hinder subsequent solvent intercalation and exfoliation, and reduce the conductivity of the final graphene. Conversely, if the heating rate is too slow, it will prolong the overall process time, reduce overall efficiency, and, more importantly, for some organic materials, excessively slow heating may cause adverse chemical changes (such as slow crosslinking), hindering complete removal.

[0020] Preferably, in step S4, an inert gas is introduced during the calcination process. Preferably, the inert gas includes at least one of N2 and Ar.

[0021] Preferably, in S5, the organic solvent includes N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO). The combination of these two solvents, through the formation of a dynamic hydrogen bond network, not only generates a polar complementary effect to significantly reduce the interfacial energy and barrier required for graphite exfoliation, but also synergistically promotes the penetration and intercalation of solvent molecules into the graphite layers. This kinetically accelerates the insertion and expansion process of the "molecular wedge," ultimately making it more conducive to achieving efficient and high-yield graphite exfoliation.

[0022] Preferably, when the organic solvent includes N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO), the volume ratio of NMP to DMSO is 6-7.5:2.5-4. This specific NMP / DMSO volume ratio is more conducive to the intercalation effect of these two solvents, further improving the exfoliation efficiency and amount of graphene, while ensuring the structural integrity of the graphene.

[0023] Preferably, when the organic solvent includes N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO), the volume ratio of N-methylpyrrolidone (NMP) to dimethyl sulfoxide (DMSO) is 6.5:3.5.

[0024] Preferably, in step S5, graphite is dispersed evenly in an organic solvent by stirring for 2-4 hours.

[0025] Preferably, in step S5, the ultrasonic treatment power is 80–150 W, the frequency is 30–50 kHz, and the duration is 4–10 h. At these ultrasonic power and frequency levels, the ultrasonic treatment works synergistically with the dual-solvent system, greatly promoting the diffusion, penetration, and exchange of dual-solvent molecules between graphite layers. Furthermore, the intercalation of solvent molecules softens the graphite structure, making the transfer and exfoliation of ultrasonic energy more effective. Therefore, at these specific ultrasonic power and frequency levels, the results of chemical intercalation can be efficiently converted into complete physical separation, thereby maximizing exfoliation efficiency and minimizing energy consumption time while protecting the structural integrity of the graphene.

[0026] Preferably, in step S5, ultrasonic treatment is accompanied by a stirring operation at a speed of 200-400 rpm.

[0027] Preferably, in step S5, the centrifugation speed is 800–1600 rpm and the time is 10–30 min.

[0028] Preferably, in step S5, the specific operation of the freeze-drying process is as follows: pre-freezing for 6-8 hours, followed by drying at a temperature of -40 to -25°C for 12-24 hours. This specific freeze-drying process can utilize the ice crystal template effect to inhibit the re-agglomeration of the sheets, ensuring the integrity of the graphene structure's stacking and conductive network.

[0029] Preferably, in step S5, the graphene obtained includes few-layer graphene, with 2 to 10 layers. The graphene obtained by the method for recycling and regenerating graphene provided by this invention is few-layer graphene. Compared to monolayer graphene, although the number of layers increases, few-layer graphene is still very thin (<5 nanometers), thus possessing a high specific surface area, making it suitable for applications such as composite materials and high-performance electrodes.

[0030] According to a second aspect of the present invention, a graphene is provided, which is prepared by any of the methods described above for recovering and regenerating graphene from waste lithium battery negative electrodes.

[0031] According to a third aspect of the present invention, a lithium battery is provided, comprising the above-described graphene. The graphene prepared by the present invention can be applied to improve the performance of positive / negative electrode materials and improve the separator in lithium batteries.

[0032] In summary, the method for recycling and regenerating graphene from waste lithium battery anodes provided by this invention achieves closed-loop recycling and regeneration of high-quality graphene from waste lithium battery anode graphite through a triple innovation of "residual lithium endogenous intercalation + low-temperature pyrolysis + dual solvent synergy". The process is environmentally friendly and low-cost, providing an industrially feasible path for the high-value regeneration of waste lithium battery graphite. Attached Figure Description

[0033] Figure 1 The images are SEM images of waste graphite (a) and few-layer graphene (b) from Example 1.

[0034] Figure 2 The XRD patterns of waste graphite and few-layer graphene in Example 1 are shown.

[0035] Figure 3 The image shows the Raman spectrum of the few-layer graphene in Example 1.

[0036] Figure 4 This is an AFM image of the few-layer graphene in Example 1.

[0037] Figure 5 The image shows the XPS spectrum of the few-layer graphene in Example 1. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] Example 1 The following steps are used to recover and regenerate graphene from the negative electrode of spent lithium batteries (in this example, spent LFP batteries are selected, whose negative electrode active material layer contains graphite): S1. Charge used lithium batteries with SOH < 80% to 30% SOC at 25℃ and 0.1C constant current. S2. Disassemble the charged waste lithium battery in a glove box (water and oxygen content <1 ppm) to obtain the negative electrode sheet; S3. Separate the negative electrode current collector and the negative electrode active material layer of the negative electrode sheet, collect the negative electrode active material layer and subject it to ultrasonication, centrifugation and drying in sequence to obtain a solid mixture; wherein, the ultrasonication power is 80W, the frequency is 50kHz, the time is 20min, and the water temperature during the ultrasonication process is 25~35℃; the centrifugation speed is 600~1800rpm, the time is 10~30min; the drying temperature is 60~80℃, and the time is 12~24h; S4. Grind the solid mixture to obtain a uniform, lumpy powder, place it in a tube furnace, heat it to 350°C in Ar gas at a rate of 5°C / min, and hold it for 4 hours to obtain waste graphite. S5. Take 5g of the waste graphite obtained above and place it in a round-bottom flask. Slowly add a dual solvent system (NMP:DMSO=6.5:3.5, volume ratio) to prepare a mixed solution with a graphite concentration of 0.5mg / mL. Add a stir bar and stir magnetically for 2-4 hours to ensure uniform mixing. Then place the round-bottom flask in an ultrasonic device and use ultrasonic-assisted exfoliation at a power of 120W, a frequency of 40kHz, and a duration of 8 hours. Stirring is also performed during ultrasonication at a speed of 300rpm. After ultrasonication, centrifuge the mixed solution (800-1600 rpm), filter, and freeze-dry (pre-freeze for 6-8 hours, then dry at -30℃ for 12-24 hours). Finally, collect the few-layer graphene.

[0040] Test Example 1 Electron microscopy and XRD were performed on the waste graphite obtained in S4 and the few-layer graphene prepared in S5. Raman spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy were also performed on the few-layer graphene prepared in S5. The test results are as follows: (1) such as Figure 1 As shown, the images are SEM images of waste graphite and few-layer graphene. In image (a), the material is mainly composed of large, blocky particles ranging in size from several micrometers to tens of micrometers. The edges of the particles are relatively thick and sharp, indicating a large number of layers and a dense structure. This is a typical morphology of thick or multilayer graphite that has not been effectively peeled off. In image (b), the material exhibits a large, independent, thin-film structure with numerous wrinkles on the surface of the sheets, a typical characteristic of graphene. Fine curls can be seen at the edges of the sheets, further demonstrating its extremely thin nature. The electron microscopy results demonstrate that the recycling method of this invention successfully transforms blocky waste graphite into few-layer graphene with an ideal microstructure.

[0041] (2) For example Figure 2 As shown, the XRD patterns of waste graphite and few-layer graphene are presented. In the XRD pattern of waste graphite, there is a very sharp, narrow, and extremely high-intensity diffraction peak at approximately 26.5°, which corresponds to the (002) crystal plane diffraction of graphite. This indicates that the material has a highly perfect crystal structure and long-range ordered layered stacking, and most of the graphite sheets are stacked together in a very regular and compact manner with constant interlayer spacing. This indicates that the waste graphite raw material is a thick-layered graphite with good crystallinity and numerous layers. Compared with waste graphite, the (002) diffraction peak of the few-layer graphene obtained after exfoliation is significantly wider and more diffuse, and the absolute intensity of the peak is also significantly reduced. This indicates that the number of graphite layers is significantly reduced, forming few-layer or even oligolayer graphene.

[0042] Furthermore, the relevant XRD parameters for waste graphite and few-layer graphene are shown in Table 1, where the diffraction angle (2 Å) is... θ The changes in peak position directly reflect the changes in interplanar spacing; the decrease in diffraction intensity also indicates that the number of regularly stacked layers has been greatly reduced, forming graphene dominated by few layers (usually <10 layers); the significant increase in half-width at half-maximum (WHM) indicates that the size in the direction perpendicular to the (002) crystal plane, which represents the stacking thickness of graphite, has become very small; at the same time, the increase in interplanar spacing indicates that the interlayers have been successfully separated. The above results show that waste graphite has been successfully exfoliated into few-layer graphene.

[0043] Table 1 Key parameters corresponding to XRD samples

[0044] (3) such as Figure 3 As shown, this is the Raman spectrum of few-layer graphene. The presence of the G peak and the 2D peak, and the fact that the intensity of the 2D peak is much lower than that of the G peak, indicates that this sample is few-layer graphene. Calculations show that the peak integral area ratio (IG) of the D peak to the G peak is... D / I G The value is approximately 1.2, and I 2D / I G The value is approximately 0.42, indicating that the prepared graphene has low structural defects.

[0045] (4) such as Figure 4 As shown, this is an AFM image of few-layer graphene. The image clearly shows the sheet-like structure of graphene, and it can also be observed that these sheets have irregular boundaries and lateral dimensions (usually in the micrometer range). This is consistent with the wrinkled film morphology seen in the SEM image, indicating the two-dimensional sheet characteristics of graphene.

[0046] (5) such as Figure 5 As shown, this is the XPS spectrum of few-layer graphene. The results indicate that the material prepared in this embodiment is composed of carbon (C) and oxygen (O). The C 1s peak, located at a binding energy of approximately 284.8 eV, is the signal generated by the excitation of the innermost (1s) electron of the carbon atom, providing direct evidence that the material is predominantly carbon. Simultaneously, the O 1s peak, located at a binding energy of approximately 532 eV, is the signal generated by the excitation of the innermost (1s) electron of the oxygen atom, proving the presence of oxygen in the material. These results indicate that this material is a graphene material rich in oxygen-containing functional groups.

[0047] Example 2 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the NMP:DMSO ratio in the dual solvent is 7.0:3.0 (volume ratio), and the rest is the same as in Example 1.

[0048] Example 3 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the NMP:DMSO ratio in the two solvents is 8:2 (volume ratio), and the rest is the same as in Example 1.

[0049] Example 4 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the NMP:DMSO ratio in the two solvents is 5:5 (volume ratio), and the rest is the same as in Example 1.

[0050] Example 5 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the dual solvents are NMP and GBL, and the ratio of NMP: GBL is 6.5:3.5 (volume ratio). The rest is the same as in Example 1.

[0051] Example 6 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the dual solvents are NMP and GBL, and the ratio of NMP:GBL is 6.5:3.5 (volume ratio). The rest is the same as in Example 1.

[0052] Example 7 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the dual solvents are CYC and IPA, and the ratio of CYC:IPA is 6.5:3.5 (volume ratio). The rest is the same as in Example 1.

[0053] Example 8 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the ultrasonic power is 170W, while the rest is the same as Example 1.

[0054] Comparative Example 1 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that a single solvent, NMP, is used, while the rest is the same as in Example 1.

[0055] Comparative Example 2 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that a single solvent, DMSO, is used, while the rest is the same as in Example 1.

[0056] Comparative Example 3 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the two solvents used are DMSO and DMF, and the ratio of DMSO:DMF is 3.5:6.5 (volume ratio). The rest is the same as in Example 1.

[0057] Comparative Example 4 The graphite prepared in S4 of Example 1 was directly used for the subsequent operation S5. The difference between S5 and Example 1 is that the dual solvents are NMP and DMF, and NMP:DMF=6.5:3.5 (volume ratio). The rest is the same as in Example 1.

[0058] Comparative Example 5 The difference between this comparative example and Example 1 is that in S4, the temperature is increased to 500°C at a rate of 5°C / min, while the rest is the same as in Example 1.

[0059] Test Example 2 Raman spectroscopy tests were performed on the graphene products obtained in Examples 2-8 and Comparative Examples 1-5, and Ig was calculated. D / I G I 2D / I G The values ​​and related results are shown in Table 2, where the relevant values ​​of the graphene products obtained in Example 1 are also recorded in Table 1.

[0060] Table 2. XRD parameters of graphene products in Examples 1-8 and Comparative Examples 1-5

[0061] As shown in Table 2, the graphene obtained by the method for recycling and regenerating graphene from waste lithium battery negative electrodes provided by this invention has good graphene structural integrity, specifically manifested in I. D / I G Lower, I 2D / I G The value is relatively high; please refer to Examples 1-8 in Table 2 for details. Furthermore, it can be seen that Example 1's I... D / I G Lowest, I 2D / I G The highest value indicates that graphene has the fewest defects and the best sheet quality.

[0062] Comparative Example 1 used a single solvent, NMP; Comparative Example 2 used a single solvent, DMSO; Comparative Example 3 used DMSO and DMF as dual solvents, with DMSO:DMF = 3.5:6.5 (volume ratio); Comparative Example 4 used NMP and DMF as dual solvents, with NMP:DMF = 6.5:3.5 (volume ratio). All of these variables affected the Ig of the final regenerated graphene.D / I G I 2D / I G The values ​​were all unsatisfactory because the single solvents in Comparative Examples 1 and 2 resulted in insufficient intercalation and low exfoliation efficiency; and the presence of DMF in Comparative Examples 3 and 4 prevented the formation of an effective polar gradient and hydrogen bond network, thus significantly increasing the defect level of graphene.

[0063] In Comparative Example 5, in S4, the temperature was increased to 500℃ at a rate of 5℃ / min. This excessively high calcination temperature would damage the graphite sp² framework, introducing numerous structural defects and causing I... D / I G When the maximum value is reached, the quality of graphene is at its worst.

[0064] Further observation of Examples 1 and 2-4 reveals that, under NMP and DMSO dual solvent conditions, the optimal ratio is NMP:DMSO = 6.5:3.5 (Example 1). Deviations from this ratio (Examples 2-4) will cause I... D / I G Rise, I 2D / I G The decrease indicates an increase in defects in graphene.

[0065] Furthermore, from Examples 1-4 and Examples 5-7, we can further discover that the NMP+DMSO system (Examples 1-4) is superior to NMP+GBL (Examples 5-6) and CYC+IPA (Example 7). This is because the combination of NMP and DMSO has better polarity complementarity and intercalation effect, which is more conducive to obtaining better quality and fewer defects in the regenerated graphene.

[0066] Observing Examples 1 and 8, the ultrasonic power in Example 8 was too high, causing damage to the graphene sheets and a significant increase in defects, i.e., I. D / I G I 2D / I G The numerical values ​​are not ideal compared to Example 1.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for recovering and regenerating graphene from the negative electrode of spent lithium batteries, characterized in that, Includes the following steps: S1. Charge the used lithium batteries to a state of charge (SOC) of 20-40%; S2. Disassemble and crush the waste lithium battery to obtain a negative electrode sheet; S3. Separate the negative electrode current collector and the negative electrode active material layer of the negative electrode sheet. The negative electrode active material layer contains graphite. Collect the negative electrode active material layer and subject it to ultrasonic, centrifugal and drying treatments in sequence to obtain a solid mixture. S4. The solid mixture is calcined at a temperature not exceeding 400°C to obtain waste graphite; S5. After dispersing the waste graphite evenly in an organic solvent, perform ultrasonic-assisted exfoliation. After ultrasonication, centrifuge, filter, and freeze-dry to obtain graphene. The organic solvent includes at least two of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), cyclohexanone (CYC), and isopropanol (IPA).

2. The method for recovering and regenerating graphene from waste lithium battery negative electrodes as described in claim 1, characterized in that: In step S3, the ultrasonic power of the negative electrode active material layer is 50-100W, the frequency is 30-80kHz, and the time is 10-30min.

3. The method for recovering and regenerating graphene from the negative electrode of a spent lithium battery as described in claim 1, characterized in that: In step S4, the calcination temperature is 300–400°C, and the calcination time is 2–6 hours.

4. The method for recovering and regenerating graphene from waste lithium battery negative electrodes as described in claim 1, characterized in that: In step S5, the organic solvent includes N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

5. The method for recovering and regenerating graphene from the negative electrode of a spent lithium battery as described in claim 4, characterized in that: The volume ratio of the N-methylpyrrolidone (NMP) to the dimethyl sulfoxide (DMSO) is 6~7.5:2.5~4.

6. The method for recovering and regenerating graphene from the negative electrode of a spent lithium battery as described in claim 5, characterized in that: The volume ratio of the N-methylpyrrolidone (NMP) to the dimethyl sulfoxide (DMSO) is 6.5:3.

5.

7. The method for recovering and regenerating graphene from waste lithium battery negative electrodes as described in claim 1, characterized in that: In step S5, the ultrasonic treatment power is 80-150W, the frequency is 30-50kHz, and the time is 4-10h.

8. The method for recovering and regenerating graphene from waste lithium battery negative electrodes as described in claim 1, characterized in that: In step S5, the graphene obtained includes few-layer graphene, and the number of layers of the few-layer graphene is 2 to 10.

9. A graphene, characterized in that, The graphene is prepared by the method described in any one of claims 1 to 8 for recovering and regenerating graphene from the negative electrode of a spent lithium battery.

10. A lithium battery, characterized in that: Includes the graphene as described in claim 9.

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