Recycling method of waste graphite material, graphene, conductive material and secondary battery

Abstract

The invention discloses a waste graphite material recovery method, which comprises: 1, mixing concentrated sulfuric acid and sodium nitrate under a first reaction condition, uniformly stirring, sequentially adding a waste graphite material and potassium permanganate, and uniformly stirring to obtain a solution A; 2, stirring and diluting the solution A under a second reaction condition, a first reaction condition and a third reaction condition in sequence, and adding peroxide to obtain a solution B; 3, stirring the solution B under a first reaction condition, performing suction filtration, and sequentially performing acid pickling and drying on filter residues to obtain a graphene oxide material; and 4, heating the graphene oxide material in inert gas, and cooling to room temperature to obtain the recycled reproduced graphene. Compared with the prior art, according to the recycling method, the improved Hummers method is adopted for recycling the waste graphite material, impurities are removed, the prepared graphene oxide has larger interlayer spacing and richer oxygen-containing functional groups, meanwhile, efficient recycling of resources is achieved, the regenerated graphene can be used as a battery conductive agent, and the resource utilization efficiency is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a recycling method of waste graphite material, graphene, conductive material and secondary battery. BACKGROUND

[0002] With the rapid development of new energy industry, lithium ion batteries (LIBs) have been widely used in electric vehicles, portable electronic devices and energy storage systems. The continuous growth of this trend has led to a sharp increase in the number of waste lithium ion batteries, which has raised urgent demand for recycling and utilization of materials in waste batteries. Lithium ion batteries are composed of a variety of complex materials, including positive electrodes, negative electrodes, electrolytes and separators, among which the recycling technology of positive electrode materials is relatively mature and has realized industrialized operation. However, the recycling of negative electrode materials, especially graphite negative electrode materials, is still in the exploratory stage and still faces many technical bottlenecks.

[0003] Graphite, as the main material of lithium ion battery negative electrode, is a non-renewable non-metallic mineral resource with excellent electrical conductivity, high temperature resistance and chemical stability, and plays an irreplaceable role in battery manufacturing. However, a large amount of waste graphite material is usually simply discarded or only used as a reducing agent, which not only causes great waste of resources, but also further aggravates environmental pollution problems. In addition, traditional graphite recycling technology is complex and usually needs to go through multi-step acid-base treatment and high-temperature roasting, which significantly increases the recycling cost and hinders the commercial application of graphite negative electrode regeneration.

[0004] At present, with the development of technology, the high-value recycling of graphite material has become a research hotspot. The recycling and utilization of graphite material not only can be used as industrial raw materials, but also can be processed into graphene material through innovative process. Graphene is widely used in conductive materials, energy storage devices and functional coatings due to its excellent electrical conductivity, mechanical properties and specific surface area. Preparing waste graphite material into graphene not only can realize efficient utilization of resources, but also provides new materials with better performance for lithium batteries and related fields.

[0005] In view of this, the present application aims to develop an efficient and simple recycling method of waste graphite material, which can convert waste graphite material into high-value graphene material through a relatively low-cost process. The recycling method can significantly reduce the recycling cost, reduce the use of a large amount of reagents in traditional process and the energy consumption caused by high-temperature operation, avoid the negative impact of waste on the environment, and realize resource recycling. Through the present application, not only can the problem of graphite resource shortage be alleviated, but also the sustainable development of new energy industry can be promoted, new economic value can be created for enterprises, and the development direction of clean production and circular economy can be promoted. SUMMARY

[0006] The application aims to provide a waste graphite material recycling method, which can solve the problems of damaged structure of waste graphite material and high recycling cost.

[0007] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0008] A waste graphite material recycling method comprises the following steps:

[0009] Step one: mixing concentrated sulfuric acid and sodium nitrate under a first reaction condition, stirring uniformly, adding waste graphite material and potassium permanganate in sequence, stirring uniformly, and obtaining solution A;

[0010] Step two: stirring, diluting and adding peroxide to solution A under a second reaction condition, the first reaction condition and a third reaction condition in sequence, and obtaining solution B;

[0011] Step three: stirring solution B under the first reaction condition, filtering, and performing acid pickling and drying on the filter residue in sequence, and obtaining graphene oxide material;

[0012] Step four: heating and treating graphene oxide material under an inert gas, cooling to room temperature, and obtaining recycled graphene.

[0013] Preferably, in the step one, the waste graphite material recycling method according to claim 1 is characterized in that, in the step one, the volume of concentrated sulfuric acid and the mass of sodium nitrate are in a ratio of 50-100 ml:0.3-0.8 g; and the mass ratio of sodium nitrate, potassium permanganate and waste graphite material is 0.3-0.8:2.5-3.5:0.8-1.2.

[0014] Preferably, in the step two, the peroxide is hydrogen peroxide.

[0015] Preferably, in the step one, the stirring time is 100-180 min, and the temperature is not higher than 10℃.

[0016] Preferably, in the step one, the solution color of solution A is dark green.

[0017] Preferably, in the step two, the temperature of the second reaction condition is 30-50℃, and the time is 120-240 min; and the temperature of the third reaction condition is 80-100℃, and the time is 20-40 min.

[0018] Preferably, the temperature of the first reaction condition is -15--5℃.

[0019] Preferably, in the step two, the color of solution B is yellow.

[0020] Preferably, in the step four, the heating treatment comprises a first stage and a second stage, the first stage has a temperature of 10-30℃ and a time of 60-180min; the second stage has a temperature increasing rate of 4-6℃ / min, a temperature of 700-900℃ and a holding time of 100-140min.

[0021] The application also provides a graphene prepared by the above-mentioned waste graphite material recycling method, and the content of the graphene is not less than 80%.

[0022] The application also provides a conductive material, which is a mixture of the above-mentioned graphene and a conductive agent, and the conductive agent comprises at least one of super-P, acetylene black, ketjen black and carbon nanotube.

[0023] The application also provides a secondary battery comprising the above-mentioned conductive material.

[0024] Compared with the prior art, the application has at least the following beneficial effects: the waste graphite material recycling method of the application uses an improved Hummers method to recycle waste graphite material, successfully realizes recycling of the graphite material, effectively removes impurities in the graphite material, and realizes comprehensive recycling of the graphite material; the prepared graphene has a larger interlayer spacing and more abundant oxygen-containing functional groups; the prepared graphene material is directly recycled as a battery conductive agent, thereby greatly improving the resource utilization efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The XRD curves of the graphene oxide and the reduced graphene oxide prepared in Example 1 of the application.

[0026] Figure 2 The SEM images of the graphene oxide and the reduced graphene oxide prepared in Example 1 of the application.

[0027] Figure 3 The SEM images of the waste graphite material (a) and the prepared graphene oxide (b) in Comparative Example 1 of the application.

[0028] Figure 4 The SEM images of the graphite material after oxidation roasting at 500℃ (a) and 400℃ (b) in Comparative Example 2 of the application. DETAILED DESCRIPTION

[0029] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0030] In the first aspect according to the present application, the present application provides a recycling method of waste graphite material, comprising the following steps:

[0031] Step one: mix concentrated sulfuric acid and sodium nitrate under the first reaction condition, stir uniformly, add waste graphite material and potassium permanganate in turn, stir uniformly, and obtain solution A;

[0032] Step two: stir solution A under the second reaction condition, the first reaction condition and the third reaction condition in turn, dilute, and add peroxide to obtain solution B;

[0033] Step three: stir solution B under the first reaction condition, suction filter, and perform acid pickling and drying on the filter residue in turn to obtain graphene oxide material;

[0034] Step four: heat treat the graphene oxide material under inert gas, cool to room temperature, and obtain recycled regenerated graphene.

[0035] The present application adopts an improved Hummers method to convert waste graphite material into graphene oxide (GO) material for recycling. The traditional Hummers method produces a large amount of harmful gases, such as nitrogen oxides, during the oxidation process. The recycling method of the present application reduces the use of nitric acid, thereby reducing environmental pollution. At the same time, the recycling method of the present application simplifies the process flow, and also improves the yield and quality of graphene oxide, and the prepared graphene oxide has a larger interlayer spacing and more abundant oxygen-containing functional groups, which is more suitable for the preparation of high-performance composite materials.

[0036] In step one, the method controls the reaction environment through low-temperature ice bath of the first reaction temperature condition, avoiding the problem of local overheating caused by exothermic reaction in the traditional Hummers method, thereby effectively reducing the explosion risk and ensuring the uniformity of the oxidation reaction; the oxidation effect of potassium permanganate can effectively peel off the interlayer structure of graphite and remove impurities and pollutants in the graphite material. Therefore, through the synergistic effect of low-temperature ice bath and potassium permanganate, impurities (including adhered organic matter, metal oxides, etc.) in the waste graphite material are successfully removed, and the graphite material is converted into graphene oxide containing oxygen-containing functional groups, laying a foundation for subsequent reduction and regeneration. Compared with the traditional Hummers method, the process of the present application is more environmentally friendly and safe, and the oxidation efficiency and purity are higher, greatly improving the quality of the recycled material.

[0037] In step two, the multi-stage temperature control reaction effectively avoids the problems of uneven local reaction or excessive oxidation in traditional methods, ensuring the consistency and quality stability of the graphene oxide. The addition of hydrogen peroxide further removes the residual oxidizing agents such as potassium permanganate in the reaction system, preventing performance loss caused by impurity residues, and providing a purer intermediate product for subsequent reduction and calcination steps.

[0038] In steps three and four, the freeze-drying process avoids structural damage caused by thermal stress in traditional drying processes, ensuring the integrity of the interlayer structure of the graphene material. The introduction of inert gas during calcination avoids the secondary occurrence of oxidation reactions at high temperatures, while achieving efficient reduction of graphene oxide. The obtained graphene material has a large interlayer spacing and abundant oxygen-containing functional groups, significantly improving the specific surface area and electrochemical performance, making it suitable for use as a conductive agent in batteries or other high-value-added applications.

[0039] The recycling method of the present application effectively reduces the cost of recycling waste graphite materials, improves the recycling efficiency, and at the same time converts waste into high-performance graphene materials, creating new economic value. Through large-scale application, the present application can significantly reduce environmental pollution, promote the sustainable recycling of lithium-ion battery materials, and provide protection for the green development of the new energy industry.

[0040] In an embodiment of the present application, in step one, the volume of concentrated sulfuric acid and the mass of sodium nitrate are in the ratio of 50-100 ml: 0.3-0.8 g; the mass ratio of sodium nitrate, potassium permanganate, and waste graphite material is 0.3-0.8: 2.5-3.5: 0.8-1.2.

[0041] In some embodiments of the present application, the temperature of the first reaction conditions in step one is -15℃ to -5℃, and the ice bath time is 120-240 min.

[0042] In an embodiment of the present application, in step one, the stirring time is 100-180 min, and the temperature is not higher than 10℃. The present application is carried out at low temperature, which can reduce the excessive local heat release during the preparation process of strong oxidizing agents, prevent thermal runaway or explosion, and improve the safety of the experiment and the protection of the experiment personnel. In the process of recycling waste graphite, the diffusion of oxidizing agents in the interlayer of graphite is slow, leading to uneven oxidation, affecting the product quality and performance. Therefore, the present application needs to fully stir the materials when adding raw materials at each step, so that the oxidation-reduction reaction occurs more completely, and in particular, when adding potassium permanganate, the potassium permanganate needs to be added slowly and the rotation speed needs to be increased, and stirring needs to be uniform.

[0043] In one embodiment of the present application, in step one, the solution color of solution A is dark green. The solution color of solution A turns dark green, indicating that the oxidation reaction has started.

[0044] In one embodiment of the present application, in step two, the peroxide is hydrogen peroxide.

[0045] In one embodiment of the present application, in step two, the temperature of the second reaction condition is 30-50℃, and the time is 2-4h; the temperature of the ice bath condition is -15--5℃; the temperature of the second water bath condition is 80-100℃, and the time is 20-40min.

[0046] In one embodiment of the present application, in step two, the dilution step specifically comprises adding deionized water under ice bath condition and adjusting the pH of the reaction system. The deionized water serves to neutralize part of the acidic substances and adjust the pH of the reaction system.

[0047] In one embodiment of the present application, in step two, the hydrogen peroxide needs to be added slowly in several times until the solution turns yellow to obtain solution B.

[0048] In one embodiment of the present application, in step two, the color of solution B is yellow. When the solution color of solution B turns yellow, it indicates that graphene oxide has been successfully generated.

[0049] In one embodiment of the present application, in step three, the acid washing step specifically comprises repeatedly washing the filter residue with acid solution, and the acid solution is preferably dilute hydrochloric acid. The purpose of using dilute hydrochloric acid for washing is to remove impurities in the filter residue.

[0050] In one embodiment of the present application, in step three, the filter residue is further washed after acid washing. The washing step specifically comprises centrifugal washing of the filter residue with deionized water. The deionized water is repeatedly used to wash the filter residue, and the washing is continued until the solution is neutral. This step is particularly important, which can remove residual acidic substances and KMnO4, and is related to the purity and quality of the final GO material.

[0051] In one embodiment of the present application, in step four, the heating treatment comprises a first stage and a second stage. The temperature of the first stage is 10-30℃, and the time is 60-180min. The temperature of the second stage is 700-900℃ at a heating rate of 4-6℃ / min, and the holding time is 100-140min.

[0052] In one embodiment of the present application, in step four, the inert gas is preferably argon.

[0053] The second aspect of the present application aims to provide a graphene prepared from the above-mentioned recycling method of waste graphite material, which has a content of not less than 80%.

[0054] The graphene material of the present application is recovered by the recovery method, and then mixed with an N-methyl pyrrolidone (NMP) solution. Subsequently, the solution is subjected to a breaking shearing treatment using a high-speed shearing machine, aiming to break the van der Waals force between the graphene layers, so as to make the reduced graphene oxide (rGO) better dispersed in the NMP solution. To further enhance the dispersibility of the rGO, the solution is subjected to an ultrasonic treatment for 1 minute using a high-power ultrasonic machine. The breaking shearing and ultrasonic treatment steps are repeated for 10 times to ensure that the rGO material achieves the best dispersion effect in the NMP solution. Finally, the treated solution is placed in a vacuum oven at 120°C for drying operation to remove the NMP in the solution, thereby obtaining the uniformly dispersed rGO material.

[0055] The present application also provides a conductive material, which is a mixture of the graphene and a conductive agent, wherein the conductive agent includes at least one of super-P, acetylene black, ketjen black, and carbon nanotube.

[0056] The present application also provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet and / or the negative electrode sheet includes the conductive material described above.

[0057] The positive electrode sheet in the present application includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes one or more of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiMnPO4, LiFePO4, LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.85 Co 0.15 Al 0.05 O2. The positive electrode current collector can be any material suitable for use as a positive electrode current collector of a lithium ion battery in the art, for example, the positive electrode current collector can be, but is not limited to, a metal foil, and more specifically, the positive electrode current collector can be, but is not limited to, an aluminum foil.

[0058] The negative electrode sheet in the present application comprises a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can be one or more of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based material, tin-based material, lithium titanate, or other metals capable of forming alloys with lithium. The graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, and silicon alloy; and the tin-based material can be selected from one or more of elemental tin, tin oxide compound, and tin alloy. The negative electrode current collector is generally a structure or part that collects current, and can be any material suitable for use as a negative electrode current collector in a lithium ion battery, for example, the negative electrode current collector can be, but not limited to, a metal foil, and more specifically can be, but not limited to, a copper foil.

[0059] The separator in the present application can be any material suitable for use as a separator in a lithium ion battery, for example, can be a combination of one or more of, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

[0060] The secondary battery in the present application further comprises an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and an additive. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolyte, at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolyte, at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-preventing electrolyte, or at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; a chain carbonate, including DFC, DMC, or EMC; or a carboxylic acid ester, including MF, MA, EA, and MP. The additive includes, but not limited to, at least one of a film-forming additive, a conductive additive, a flame-retardant additive, an overcharge-preventing additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

[0061] In order to make the technical solutions and advantages of the present application clearer, the following will further describe the present application and its beneficial effects in detail with reference to the specific embodiments, but the embodiments of the present application are not limited thereto.

[0062] Example 1

[0063] Recycling of waste graphite material:

[0064] Step 1: Pre-cool the ice bath machine to -10°C and keep this state for 2 hours; in a 250 mL three-necked flask, slowly and sequentially add 70 mL of concentrated sulfuric acid and 0.5 g of NaNO3, transfer the three-necked flask to the ice bath machine and start the mechanical stirring device in the ice bath machine, mix and stir for 30 minutes, slowly add 1 g of pretreated waste graphite to the three-necked flask, continue to stir for 30 minutes, continue to slowly add 3 g of KMnO4, and increase the stirring speed, continue to stir for 1 hour. During this process, the temperature needs to be strictly monitored to ensure that it does not exceed 10°C. As the reaction proceeds, the solution gradually turns dark green.

[0065] Step 2: Transfer the three-necked flask to a preheated 35°C water bath and continue to stir at a constant temperature for 3 hours, then transfer the three-necked flask back to the -10°C ice bath machine and slowly add 100 mL of deionized water, then transfer the flask to a preheated 85°C water bath and continue to stir at a constant temperature for 30 minutes, pour the mixture into a 1000 mL beaker and dilute with deionized water to 500 mL, then dilute 17 mL of H2O2 to 100 mL and slowly add it to the beaker in several portions until the solution turns yellow.

[0066] Step 3: Place the beaker in step S2 in the ice bath machine and continue to stir for 20 minutes. Then, the reaction in the beaker is filtered and washed repeatedly with dilute hydrochloric acid to remove impurities, the filter residue is transferred to a 500 mL beaker, an appropriate amount of deionized water is added for centrifugal washing until the solution is neutral, and the washed product is freeze-dried to remove water to obtain graphene oxide material.

[0067] Step 4: Place the prepared graphene oxide material in a crucible and place the entire crucible in a tube furnace. The initial temperature of the tube furnace is set to 20°C, and high-purity argon gas is first introduced for 2 hours to ensure the purity of the atmosphere in the furnace. Under this argon atmosphere, the tube furnace is gradually heated to 800°C at a rate of 5°C / min, and isothermal calcination is carried out at this temperature for 2 hours. After calcination, the tube furnace is naturally cooled to room temperature to obtain reduced graphene oxide material.

[0068] Preparation of graphene:

[0069] The obtained reduced graphene oxide material is placed in a small beaker and an appropriate amount of N-methyl pyrrolidone (NMP) solution is added. Then, the solution is subjected to a high-speed shearing treatment using a high-power ultrasonic machine for 1 minute. This shearing and ultrasonic treatment step is repeated 10 times, and finally, the treated solution is placed in a 120°C vacuum oven for drying operation to remove NMP from the solution, thereby obtaining uniformly dispersed reduced graphene oxide material.

[0070] Conductive material: the prepared reduced graphene oxide material is mixed with SuperP and used as a conductive agent in the battery.

[0071] Separator: the PE surface is coated with a ceramic mixture as a separator.

[0072] Electrolyte: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a proportion of 1 mol / L to prepare an electrolyte.

[0073] Lithium ion battery preparation: the above positive electrode sheet, separator, and negative electrode sheet are wound or laminated to make a bare cell, and then packaged and injected with electrolyte to make a finished lithium ion battery.

[0074] Comparative Example 1

[0075] Preparation of graphene oxide:

[0076] Step one: measure 180 mL of concentrated sulfuric acid into a 500 mL beaker, then measure 20 mL of concentrated phosphoric acid and mix with the concentrated sulfuric acid, move the beaker to the water bath and continuously stir to promote cooling, add 5 g of pretreated waste graphite after cooling to room temperature, and continuously stir until the waste graphite is completely dispersed.

[0077] Step two: slowly add 9 g of potassium permanganate, control the reaction system temperature not higher than 30℃, then turn on the heating, heat to 50℃, and then heat for 9 hours to make the liquid color change from black to dark green.

[0078] Step three: add 15 mL of hydrogen peroxide to 200 mL of deionized water, mix well and freeze in the refrigerator until completely frozen, slowly pour the dark green reaction liquid into ice under ice water bath condition and stir vigorously, stand for 1 day after cooling to room temperature.

[0079] Step four: pour off the upper liquid, add a large amount of deionized water to the precipitate, centrifuge several times at 6000 rpm, and wash with 10% hydrochloric acid solution and deionized water until weakly acidic.

[0080] Step five: add 200 mL of deionized water and ultrasonic clean for 2 hours in an ultrasonic cleaner, manually shake every 30 minutes during the period to prevent solid settlement, freeze in the refrigerator for 12 hours after sufficient peeling, freeze dry at -60℃ for two days, and obtain graphene oxide.

[0081] Comparative Example 2

[0082] Step one: first, use the balance to take 1g of waste graphite into the crucible, and carry out high temperature treatment experiment on the waste graphite. Use the balance to take a certain mass of waste graphite into the crucible, use the tube furnace to carry out heating treatment under the condition of 500℃, and the temperature rising rate of the furnace is set to 10℃ / min -1 , N2 is used as the protection atmosphere to roast for 1h to remove the organic binder.

[0083] Step two: continue to use the tube furnace to carry out heating treatment on the graphite material, and the temperature rising rate is 10℃ / min -1 , N2 is used as the protection atmosphere, the temperature is set to 900℃, and the airflow flow rate is set to 5L / min -1 .

[0084] Step three: pour the high temperature treated graphite material into a beaker, add deionized water for water washing, stir the suspension liquid with a glass cup, and then stand still for 2h, clean the residual floating scum, repeat the operation for 2-3 times, filter, take out the lower layer precipitate, and place it in a 80℃ air drying oven for drying for 4h. Next, use a cutting knife to cut the copper foil into a size of 20*20mm.

[0085] Step four: use the balance to take the mass of the single copper foil to be about 0.0360g, and use the tube furnace at 400℃ to carry out roasting treatment. Then, carry out acid immersion treatment on the material after the roasting treatment at 400℃, the acid immersion solution adopts a mixed solution of concentrated sulfuric acid (concentration is 98%), hydrogen peroxide (concentration is 30%) and deionized water in a volume ratio of 5:5:90, the solid-liquid ratio of the roasting graphite and the acid immersion solution is 1g:20mL, and the stirring reaction is carried out for 4h. After sufficient reaction until the supernatant is blue, filter the acid immersion treated solution, pour the upper layer solution into the waste liquid tank after neutralizing to neutral with an alkaline solution.

[0086] Step five: add deionized water to the lower layer precipitate for 3-5 times of washing, finally wash with ethanol solution until the upper layer solution after washing is neutral, take out the lower layer graphite after filtering, place it in a 80℃ air drying oven for drying for 4h, grind the agglomerated graphite block after drying to obtain the pyrometallurgical recovery graphite material.

[0087] From the data ( Figure 1 ) and SEM diagram ( Figure 2 ) of example 1, it can be shown that the present application provides a recovery method of waste graphite material, which recovers the waste graphite material by using the improved Hummers method, successfully realizes the recycling of the graphite material, effectively removes the impurities therein, the prepared graphene oxide has larger interlayer spacing and more abundant oxygen-containing functional groups, the graphite material is comprehensively recovered, and the prepared graphene material is reused as a battery conductive agent, thereby greatly improving the resource utilization efficiency.

[0088] As can be seen from the SEM images of Example 1 and Comparative Example 1, the graphene oxide prepared from the recycled graphite in Comparative Example 1 also has a layered structure, but the degree of oxidation is lower, and after preparation, it is not used again, only the recycling step, while in the example, not only is a high degree of oxidation of the graphene oxide material prepared, but it is also reduced and then reused in the battery.

[0089] As can be seen from the test results of Example 1 and Comparative Example 2, Comparative Example 2 uses pyrometallurgical recycling of graphite and regeneration, and the experimental process of the recycled material requires high-temperature roasting, which consumes a lot of energy, and the experimental process is complex and consumes energy compared to Example 1, and the material cannot be completely recycled and reused.

[0090] Based on the disclosure and teachings of the above specification, a person of ordinary skill in the art can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. A method for recycling waste graphite materials, characterized in that: The following steps are involved: Step 1: Mix concentrated sulfuric acid and sodium nitrate under the first reaction condition, stir evenly, add waste graphite material and potassium permanganate in sequence, stir evenly, and obtain solution A; Step 2: stirring the solution A under the second reaction condition, the first reaction condition, and the third reaction condition in sequence, diluting the solution, and adding peroxide to obtain a solution B; Step 3: stirring solution B under the first reaction conditions, filtering, and sequentially acid-washing and drying the filter residue to obtain graphene oxide material; Step 4: Heat the graphene oxide material under an inert gas and cool it to room temperature to obtain recycled graphene.

2. The method for recycling waste graphite materials according to claim 1, wherein: In the step 1, the volume ratio of the concentrated sulfuric acid to the mass ratio of the sodium nitrate is 50-100 ml: 0.3-0.8 g; the mass ratio of the sodium nitrate, the potassium permanganate and the waste graphite material is 0.3-0.8: 2.5-3.5: 0.8-1.

2.

3. The method for recycling waste graphite materials according to claim 1, wherein: In the step 1, the stirring time is 100 to 180 minutes, and the temperature is no more than 10°C.

4. The method for recycling waste graphite materials according to claim 1, wherein: In the step 2, the peroxide is hydrogen peroxide.

5. The method for recycling waste graphite materials according to claim 1, characterized in that: In the step 2, the temperature of the second reaction condition is 30-50° C., and the time is 120-240 min; the temperature of the third reaction condition is 80-100° C., and the time is 20-40 min.

6. The method for recycling waste graphite materials according to claim 1, characterized in that: The temperature of the first reaction condition is -15 to -5°C.

7. The method for recycling waste graphite materials according to claim 1, characterized in that: In step four, the heating treatment includes a first stage and a second stage. The temperature of the first stage is 10-30°C and the time is 60-180 minutes. The heating rate of the second stage is 4-6°C / min, the temperature is 700-900°C, and the holding time is 100-140 minutes.

8. A graphene, characterized in that: The graphene is obtained by the method for recycling waste graphite materials according to any one of claims 1 to 7, and its content is not less than 80%.

9. A conductive material, characterized in that A mixture comprising the graphene according to claim 8 and a conductive agent, wherein the conductive agent comprises at least one of super-P, acetylene black, Ketjen black, and carbon nanotubes.

10. A secondary battery, characterized in that: Comprising the conductive material as claimed in claim 9.

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