Method for preparing graphene material based on suspension electrolysis of lithium battery waste graphite

Abstract

The invention discloses a method for preparing a graphene material based on suspension electrolysis of lithium battery waste graphite. The method comprises the following steps: by taking waste graphite powder obtained by tempering and separating lithium battery waste graphite slurry or scrapped lithium battery negative electrode waste graphite powder as a raw material, directly dispersing the waste graphite powder into electrolyte, applying an electric field with proper strength to an electrolysis system by taking platinum sheets as positive and negative electrodes and sampling a direct current or pulse electrolysis method, and graphite particles dispersed in the electrolyte are fully intercalated, so that the vast majority of graphite particles in the electrolyte are deeply and non-destructively stripped into a high-quality graphene material under the action of electric field force. According to the suspension electrolysis method for preparing the graphene, the defects that graphite is directly used for stripping an electrode, the graphite electrode needs to be frequently replaced, stripping is not thorough, and the graphene yield is low are overcome. According to the method, cyclic utilization of the lithium battery waste graphite is achieved, pollution reduction and carbon reduction in the lithium battery industry are promoted, and meanwhile the preparation approach of graphene is enriched.

Description

Technical Field

[0001] The present invention belongs to the field of recycling of lithium battery material resources, and in particular relates to a method for preparing graphene materials based on suspended electrolysis of lithium battery waste graphite. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, long life, light weight, and low self-discharge rate, and are crucial to modern energy storage. As the global society's urgent demand for sustainability and environmental protection continues to grow, lithium-ion batteries have become a key driver for achieving clean energy transformation and reducing greenhouse gas emissions. Electrode sheets are an important component of lithium batteries. Their manufacturing process includes slurrying, coating, drying, rolling, etc. of active powders (positive electrode: lithium cobalt oxide, lithium iron phosphate, etc., negative electrode: graphite), dispersing thickeners and binders. In 2023, global lithium-ion battery production exceeded 900GWh and is expected to reach 7290GWh by 2030. However, as a chemical substance, the battery itself will cause serious environmental pollution during its production process and after scrapping, posing a major challenge to resources and the environment.

[0003] Graphene is the monomer form of graphite, a 2 A novel two-dimensional carbon nanomaterial composed of hybridized carbon atoms. With its exceptional optical, mechanical, electronic, and thermal properties, it has attracted significant attention in science and engineering. Current graphene production methods, including chemical vapor deposition (CVD), silicon carbide (SiC) epitaxial growth, and chemical oxidation, are compromised solutions but not ideal for large-scale graphene production. In recent years, electrochemical exfoliation of graphite to produce graphene has been widely studied due to its mild conditions, simple process, and strong scalability.

[0004] Currently, electrochemical exfoliation for graphene production typically utilizes graphite blocks (foil or rods) as electrodes. The graphite electrode and counter electrode are placed in a prepared electrolyte, and then a voltage or current is applied between the two electrodes to perform the exfoliation. During the exfoliation process, the electric field forces drive the anions / cations in the electrolyte to migrate to the graphite electrode. Under the action of the electric field, the ions surrounding the electrode further intercalate into the graphite interlayers, expanding the distance between the graphite interlayers and weakening the van der Waals attraction between the layers. Subsequently, bubbles generated by the electrolysis reaction further promote the separation of the graphite interlayers, and the graphene sheets eventually fall off the electrode into the solution. Electrode-localized exfoliation relies on electrical contact between the graphite electrode and the power supply. During the exfoliation process, due to the disintegration of the graphite electrode, many graphite particles will detach from the electrode uncontrollably, losing electrical contact before a high degree of exfoliation is achieved. This limits the efficiency and yield of graphite exfoliation. Summary of the Invention

[0005] To overcome the shortcomings of existing electrochemical exfoliation methods for graphene production, the present invention provides a method using graphite powder suspension electrolysis. By suspending graphite particles in an electrolytic cell, the method increases mass transfer between the particles and the electrolyte and electrodes, thereby improving the efficiency of electrochemical graphene production. Furthermore, the present invention utilizes waste graphite from lithium batteries as a precursor to produce graphene through suspension electrolysis, achieving high-value recycling of waste graphite.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing graphene material based on suspension electrolysis of lithium battery waste graphite, comprising the following steps:

[0007] (1) Add waste graphite powder to the electrolyte at a certain solid-liquid ratio and stir to mix;

[0008] (2) applying an electric field to the electrolysis system of (1) and performing an electrolysis reaction under stirring;

[0009] (3) After the electrolysis reaction has proceeded for a predetermined time, the resulting slurry is subjected to solid-liquid separation, and the separated solid is transferred to an N-methylpyrrolidone solution and subjected to water bath ultrasonic dispersion treatment for a predetermined time to obtain a graphene material dispersion of a certain concentration.

[0010] Preferably, the waste graphite powder is obtained by adding sulfuric acid to the graphite slurry of waste lithium batteries, adjusting the pH value to 1-4, stirring the reaction for 0.5-1h, and then separating the solid and liquid. The obtained solid graphite is dried, crushed and sieved.

[0011] Preferably, the waste graphite powder is obtained by disassembling waste lithium batteries, separating the negative electrodes, removing impurities, drying and screening.

[0012] Preferably, in the electrolysis reaction, the electrolyte is a solution composed of one or more of sulfuric acid, sodium sulfate, methanesulfonic acid, potassium persulfate and water, and the preferred concentration of the electrolyte is 10 to 18 mol / L.

[0013] The electrolyte may further contain an electrolytic additive, which may be an oxidant or / surfactant, wherein the oxidant is ammonium persulfate or hydrogen peroxide, and the surfactant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and sodium lauryl sulfate, wherein the content of ammonium persulfate in the electrolyte is 0.02 to 0.2 mol / L, the content of hydrogen peroxide in the electrolyte is 0.1 to 3 mol / L; and the content of the surfactant in the electrolyte is 1 to 10 mg / L.

[0014] Preferably, in the electrolysis reaction, platinum is used as the positive and negative electrodes, and the distance between the positive and negative electrodes is 1 to 4 cm.

[0015] Preferably, the solid-liquid ratio of waste graphite powder to electrolyte is 1:500-2000 g / mL.

[0016] Preferably, the electric field type is direct current or pulse current.

[0017] Specifically, when the electric field type is direct current, the current density is 0.1 to 0.5 A / cm 2 .

[0018] Specifically, when the electric field type is pulse current, the pulse frequency is 100 to 1000 Hz, and the duty cycle is 10 to 90%.

[0019] Preferably, the electrolysis time is 2 to 6 hours, and the stirring speed is 200 to 500 rpm.

[0020] Compared with the existing electrochemical method for preparing graphene, the present invention has the following significant advantages:

[0021] (1) The existing electrochemical method for preparing graphene locates the exfoliation of graphite at the electrode, relying on the electric potential to trigger the expansion and shedding of graphite on the electrode. The intercalation reaction of graphite can only be carried out on the electrode surface. During the exfoliation process, due to the expansion and disintegration of the graphite electrode, some graphite particles will uncontrollably detach from the electrode surface and lose electrical contact before high exfoliation, resulting in reduced graphene yield and quality, and the graphite electrode needs to be replaced frequently. The present invention uses a suspension electrolysis method to prepare graphene, directly dispersing graphite particles in the electrolyte. The conductive network established by the electrode-graphite particle-electrolyte allows the graphite particles and the electrode plate to conduct electric potential in a dynamic manner. The ions in the electrolyte are fully in contact with the graphite particles, so that the intercalation and exfoliation of graphite occur in the entire electrode-electrolyte area, so that most particles can be deeply and non-destructively exfoliated into high-quality graphene under the action of the electric field force. The preparation of graphene by suspension electrolysis exfoliation can avoid the subsequent graphene screening process and has obvious advantages in reaction conditions and process flow.

[0022] (2) The suspension electrolysis method for preparing graphene provided by the present invention has strong adaptability to graphite raw materials and can not only realize the electrochemical exfoliation of lithium battery waste graphite to prepare graphene materials. It can also be applied to the electrochemical exfoliation of commercial graphite to prepare high-quality graphene materials. In addition, by regulating the electrolyte concentration and electric field conditions, controllable exfoliation of graphite can be achieved, or different types of graphene-like materials can be produced. The preparation of graphene by suspension electrolysis has advantages in operability and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of graphene obtained by suspension electrolysis of waste graphite in Example 1.

[0024] Figure 2 Comparison of Raman spectra of waste graphite and graphene obtained by suspension electrolysis of waste graphite in Example 1.

[0025] Figure 3 This is the SEM image of graphene obtained by suspension electrolysis of waste graphite in Example 2.

[0026] Figure 4 Comparison of Raman spectra of waste graphite and graphene obtained by suspension electrolysis of waste graphite in Example 2.

[0027] Figure 5 This is the SEM image of graphene obtained by suspension electrolysis of waste graphite in Example 3.

[0028] Figure 6 Comparison of Raman spectra of waste graphite and graphene obtained by suspension electrolysis of waste graphite in Example 3.

[0029] Figure 7 This is the SEM image of expanded graphite obtained by suspension electrolysis of waste graphite in Example 7.

[0030] Figure 8 This is the SEM image of expanded graphite obtained by suspension electrolysis of waste graphite in Example 8.

[0031] Figure 9 AFM images of the graphene sheets obtained by electrolysis in (a) Example 1 and (b) Example 3.

[0032] Figure 10 Statistical AFM analysis of graphene obtained by suspension electrolysis of waste graphite in Example 1, where a: 0.25 A / cm 2 AFM image of graphene obtained under electrolytic conditions; b: layer number distribution of a typical graphene sheet; c: lateral size of a typical graphene sheet.

[0033] Figure 11 This is the SEM image of waste graphite powder from lithium batteries.

[0034] Figure 12 This is a schematic diagram of the process of suspended electrolysis of waste graphite from lithium batteries. DETAILED DESCRIPTION

[0035] To better illustrate the present invention, specific embodiments and drawings are given below to describe the present invention in more detail. The protection scope of the present invention is not limited to the examples given.

[0036] For the high value recycling of lithium battery waste graphite, combined with Figure 12The present invention provides a method for preparing graphene by suspended electrolysis of waste graphite, which comprises constructing a waste graphite suspended electrolysis system, including the selection of electrodes, electrolyte, and electric field types. Lithium battery waste graphite is directly placed in the suspended electrolysis system, and an electric field of appropriate strength is applied to enable controllable exfoliation of graphite particles in the electrolyte to obtain a few-layer graphene material. This method not only solves the problem that lithium battery waste graphite lacks a specific electrode shape due to its particle characteristics, and the traditional electrochemical exfoliation method positioned at the electrode is not applicable. At the same time, it overcomes the drawbacks of using graphite directly as an electrode for exfoliation, requiring frequent replacement of graphite electrodes, and resulting in low graphene yield. This method realizes the recycling of lithium battery waste graphite, promotes pollution reduction and carbon reduction in the lithium battery industry, and also enriches the preparation methods of graphene.

[0037] The waste graphite slurry and waste graphite powder involved in the embodiment are from a lithium battery production enterprise, wherein the waste graphite slurry has a moisture content of 90%, and is conditioned, filtered, dried, crushed and passed through a 200 mesh sieve for later use. The waste graphite powder is dried and passed through a 200 mesh sieve for later use. The SEM image of the waste graphite powder is as follows: Figure 11 As shown, Figure 11 It shows that the waste graphite has high crystallinity and the layers are tightly stacked.

[0038] Example 1

[0039] Weigh 0.1 g of waste graphite powder, add it to 100 mL of 18 mol / L sulfuric acid, use platinum as positive and negative electrodes, stir at 300 rpm, and apply a current density of 0.25 A / cm 2 A direct current of 1000 rpm was applied during the electrolysis, and the stirring rate was maintained at 300 rpm for 5 hours. After the electrolysis, the slurry was filtered, and the resulting graphene material was transferred to 100 mL of N-methylpyrrolidone solution. Subsequently, ultrasonic dispersion was performed in a water bath for 30 minutes to obtain a 1 g / L graphene material dispersion. Figure 1 This is the SEM image of the few-layer graphene prepared under these conditions. After suspension electrolytic exfoliation, the graphene sheets show a typical morphology of random stacking and sheet wrinkles, indicating that the ordered interlayer structure of graphite is destroyed, forming the distribution characteristics of few-layer graphene sheets. Figure 2 The results show that the waste graphite has a weak D peak (~1350cm -1 ), strong G peak (~1580cm -1 ), the ratio of peak D to peak G (I D / I G ) is 0.03, indicating that the in-plane region of the waste graphite has relatively few defects, and the 2D peak (~2700 cm -1) splits into two peaks (2D1 and 2D2), indicating strong interaction between graphite layers. Compared with waste graphite, after suspension electrolysis, the 2D peak split disappears and the intensity increases, indicating that the graphite sheets have been peeled off into few-layer graphene. Under this electrolysis condition, I D / I G The value is 0.04, which is slightly higher than that of the waste graphite raw material, indicating that the formed graphene sheet structure is relatively complete and has fewer defects. The average crystal domain size L of the graphene was further calculated by Raman spectroscopy. a =418.79nm, the defect distance L of the graphene sheet D It is about 49.52nm, and the defect density n D About 1.30×10 10 cm -2 .

[0040] Figure 9 Figure a is an AFM image of the graphene sheet obtained by electrolysis in Example 1. The graphene sheet obtained in this example has a complete structure and few defects, indicating that the waste graphite is effectively exfoliated while maintaining good graphene crystal quality under suitable electrolysis conditions.

[0041] Figure 10 For the statistical AFM analysis of graphene obtained by suspension electrolysis of waste graphite in Example 1, 100 graphene sheets ( Figure 10 The number of layers and lateral dimensions of the graphene sheets were statistically analyzed. The results showed that the number of layers of graphene sheets obtained by suspension electrolysis of waste graphite under these conditions was concentrated in the range of 2-4 layers ( Figure 10 b), the lateral size is about 2.43 μm ( Figure 10 c) in the above example.

[0042] Example 2

[0043] Take 1L of waste graphite slurry, slowly add sulfuric acid to the slurry, adjust the pH value to 1.0, place the slurry with adjusted pH value in a stirred reactor and stir at room temperature for 30 minutes. After the reaction is completed, filter to obtain waste graphite slag, dry and crush the waste graphite slag and pass it through a 200-mesh sieve to obtain waste graphite particles. Weigh 0.3g of waste graphite particles, the electrolyte is 12mol / L sulfuric acid solution, containing 0.05mol / L ammonium persulfate as an electrolytic additive. Add 0.3g of waste graphite particles to the electrolyte and apply 0.2A / cm 2 The electrolysis was carried out with direct current for 3 h, and the stirring rate was maintained at 400 rpm during the electrolysis process. After the electrolysis was completed, the liquid was filtered, and the obtained graphene material was uniformly dispersed in 300 mL of N-methylpyrrolidone solution by water bath ultrasound. Figure 3 This is the SEM image of the few-layer graphene prepared under these conditions. The interlayer structure of the graphite is destroyed, the layers are separated, and it is converted into few-layer graphene sheets. Figure 4The results show that compared with the waste graphite, after suspension electrolysis, the 2D peak splitting disappears and the intensity increases, indicating that the graphite sheet has been peeled off into few-layer graphene. D / I G The value is 0.232. Further calculation shows that the average crystal domain size L of the prepared graphene is a =72.21nm, the defect distance L of the graphene sheet D It is about 19.55nm, and the defect density n D About 8.33×10 10 cm -2 .

[0044] Example 3

[0045] Weigh 0.1 g of waste graphite powder, add it to 100 mL of 18 mol / L sulfuric acid, use platinum as positive and negative electrodes, stir at 300 rpm, and apply a current density of 0.35 A / cm 2 A direct current of 1000 rpm was applied during the electrolysis, and the stirring rate was maintained at 300 rpm for 5 hours. After the electrolysis, the slurry was filtered, and the resulting graphene material was transferred to 100 mL of N-methylpyrrolidone solution. Subsequently, ultrasonic dispersion was performed in a water bath for 30 minutes to obtain a 1 g / L graphene material dispersion. Figure 5 This is the SEM image of the few-layer graphene prepared under these conditions. The graphene sheets show a wrinkled morphology, indicating that the ordered interlayer structure of graphite is destroyed, forming the distribution characteristics of the few-layer graphene sheets. Figure 6 The results show that under the electrolysis conditions, I D / I G The value is 0.15, which is significantly increased compared with the waste graphite raw material, and the graphene (I D / I G The average crystal domain size L of the graphene obtained by further calculation is 0.04). a =111.68nm, the defect distance L of the graphene sheet D It is about 27.73nm, and the defect density n D About 4.14×10 10 cm -2 .

[0046] Figure 9 Figure b is an AFM image of the graphene sheet obtained by electrolysis in Example 3. The graphene prepared in this example shows large structural defects, with local structural damage occurring at its edges and interior, and the sheet structure of the graphene is destroyed. This indicates that although excessive current can achieve the exfoliation of waste graphite into graphene, it will also cause structural damage.

[0047] Example 4

[0048] Weigh 0.1g of waste graphite powder, add it to 100mL of 12mol / L sulfuric acid, add 5mg / L of sodium dodecylbenzenesulfonate as electrolytic additive, use platinum as positive and negative electrodes, stir evenly and apply a current density of 0.25A / cm 2 The electrolysis was carried out for 4 hours with a stirring rate of 400 rpm. After the electrolysis was completed, the liquid was filtered and the obtained graphene material was transferred to 100 mL of N-methylpyrrolidone solution. The obtained graphene material was then dispersed in a water bath with ultrasonic treatment for 30 minutes to obtain a 1 g / L graphene material dispersion. The average crystal domain size of the prepared graphene was L a =72.21nm, the defect distance L of the graphene sheet D It is about 19.83nm, and the defect density nD is about 8.10×10 10 cm -2 .

[0049] Example 5

[0050] Weigh 0.3g of waste graphite powder, add it to 50mL of 18mol / L sulfuric acid, add 0.1mol / L of ammonium persulfate and 0.65mol / L of hydrogen peroxide as electrolytic additives, use platinum as positive and negative electrodes, stir evenly and apply a current density of 0.2A / cm 2 The electrolysis was carried out for 4 hours with a stirring rate of 300 rpm. After the electrolysis was completed, the liquid was filtered and the obtained graphene material was transferred to N-methylpyrrolidone solution, followed by ultrasonic dispersion treatment in a water bath for 30 minutes to obtain a graphene material dispersion. The average crystal domain size of the prepared graphene was L a =97.39nm, the defect distance L of the graphene sheet D It is about 23.30nm, and the defect density n D About 5.87×10 10 cm -2 .

[0051] Example 6

[0052] Weigh 0.15g of waste graphite powder, add it to 100mL of 16mol / L sulfuric acid, use platinum as positive and negative electrodes, stir evenly and apply pulse current with a current density of 0.2A / cm 2 The frequency was 200 Hz, the duty cycle was 90%, and the stirring rate was maintained at 300 rpm during the electrolysis process. The electrolysis was continued for 3.5 hours. After the electrolysis was completed, the liquid was filtered and the obtained graphene material was transferred to N-methylpyrrolidone solution. Then, ultrasonic dispersion treatment was carried out in a water bath for 30 minutes to obtain a graphene material dispersion. The average crystal domain size of the prepared graphene was L a=57.76nm, the defect distance L of the graphene sheet D It is about 17.95nm, and the defect density n D About 9.88×10 10 cm -2 .

[0053] Example 7

[0054] Take 0.15g of waste graphite powder and add it to 100mL of a mixed solution of 2mol / L sodium sulfate and 1mol / L sulfuric acid. Use platinum as the positive and negative electrodes and the current density is 0.3A / cm 2 , electrolysis for 4.5 hours, stirring speed is 200 rpm, after the electrolysis is completed, the feed liquid is filtered to obtain expanded graphite. Figure 7 The SEM image of the electrolysis product under these conditions shows that the product obtained under these conditions is expanded graphite. The graphite only expands at the edges, the interlayer spacing increases, and the layers fail to separate.

[0055] Example 8

[0056] Take 0.1g of waste graphite powder and add it to 100mL of 14mol / L sulfuric acid. Use platinum as positive and negative electrodes and the current density is 0.3A / cm 2 , electrolysis for 4.5 hours, stirring speed is 300 rpm, after the electrolysis is completed, the feed liquid is filtered to obtain expanded graphite. Figure 8 The SEM image of the electrolysis product under these conditions shows that the product obtained under these conditions is expanded graphite. The graphite only expands at the edges, the interlayer spacing increases, and the layers fail to separate.

[0057] The above implementation demonstrates that electrolytic additives such as ammonium persulfate and hydrogen peroxide during the suspension electrolysis of waste graphite provide oxidative conditions in the early stages of the electrolysis process, promoting oxidative intercalation of the waste graphite under electric field conditions, enabling exfoliation even at relatively low current densities. Surfactants such as sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfate increase the hydrophilicity of the waste graphite, ensuring its uniform dispersion in the relatively low-concentration electrolyte and preventing its aggregation, which can affect the exfoliation process.

[0058] The above description is a preferred embodiment of the present invention, but does not limit the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements to the present invention based on the above invention content, which still fall within the scope of protection of the present invention.

Claims

1. A method for preparing graphene materials based on suspension electrolysis of lithium battery waste graphite, characterized in that: The following steps are involved: (1) Add waste graphite powder into the electrolyte at a certain solid-liquid ratio and stir to mix; (2) applying an electric field to the electrolysis system of (1) and performing an electrolysis reaction under stirring; (3) After the electrolysis reaction reaches a preset time, the resulting slurry is subjected to solid-liquid separation, and the separated solid is transferred to an N-methylpyrrolidone solution and subjected to water bath ultrasonic dispersion treatment for a certain period of time to obtain a graphene material dispersion of a certain concentration.

2. The method according to claim 1, wherein Waste graphite powder is obtained by adding sulfuric acid to the graphite slurry of waste lithium batteries, adjusting the pH value to 1-4, stirring the reaction for 0.5-1 hour, and then separating the solid and liquid. The resulting solid graphite is dried, crushed and sieved.

3. The method according to claim 1, wherein Waste graphite powder is obtained by disassembling waste lithium batteries, separating the negative electrodes, removing impurities, drying and screening.

4. The method according to claim 1, wherein In the electrolysis reaction, the electrolyte is a solution composed of one or more of sulfuric acid, sodium sulfate, methanesulfonic acid, potassium persulfate and water, and the preferred concentration of the electrolyte is 10-18 mol / L.

5. The method according to claim 1, wherein The electrolyte further contains an electrolytic additive, which is an oxidant or / surfactant, the oxidant is ammonium persulfate or hydrogen peroxide, and the surfactant is one or more of sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, and sodium lauryl sulfate, wherein the content of ammonium persulfate in the electrolyte is 0.02-0.2 mol / L, the content of hydrogen peroxide in the electrolyte is 0.1-3 mol / L; and the content of the surfactant in the electrolyte is 1-10 mg / L.

6. The method according to claim 1, wherein In the electrolysis reaction, platinum is used as the positive and negative electrodes, and the distance between the positive and negative electrodes is 1~4 cm.

7. The method according to claim 1, wherein The solid-liquid ratio of waste graphite powder to electrolyte is 1:500~2000g / mL.

8. The method according to claim 1, wherein When the electric field type is direct current, the current density is 0.1~0.5 A / cm 2 .

9. The method according to claim 1, wherein When the electric field type is pulse current, the pulse frequency is 100~1000 Hz and the duty cycle is 10~90%.

10. The method according to claim 1, wherein The electrolysis time is 2~6 h, and the stirring speed is 200~500 rpm.

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