Microwave-plasma synergistic stripping waste lithium battery graphite regeneration and graphene preparation method

Abstract

The invention discloses a microwave-plasma synergistic stripping waste lithium battery graphite regeneration and graphene preparation method, and belongs to the field of lithium battery recovery. The preparation method comprises the following steps: discharging the waste lithium battery, crushing, magnetically separating, crushing and screening to obtain a solid mixture containing graphite, drying the solid mixture, and calcining to obtain graphite slag containing metal impurities; the method comprises the following steps: treating graphite slag and mixed acid under microwaves, dispersing the treated graphite slag and mixed acid in an ionic liquid, and carrying out ultrasonic treatment in a plasma environment to obtain a graphene dispersion liquid; and separating the graphene dispersion liquid to obtain graphene powder. According to the method, graphite is recycled through microwave-assisted acid leaching pretreatment, metal impurities and residual binders are efficiently removed, meanwhile, the integrity of an interlayer structure of the graphite is reserved, and the acid consumption and secondary pollution are reduced. In the ultrasonic stripping process, low-temperature plasma is introduced, high-energy particles are used for bombarding graphite interlayers, the Van der Waals force is further weakened, and the stripping efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of waste batteries, and particularly relates to a method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic exfoliation. Background Art

[0002] With the rapid development of the lithium battery industry, the recycling of graphite anode materials in waste batteries faces huge challenges. Traditional recycling processes mostly use high-temperature calcination or strong acid leaching methods, which have problems such as incomplete removal of metal impurities (residual rate > 5%) and serious damage to the graphite structure (defect density I D / I G > 1.5), etc., and it is difficult to achieve efficient exfoliation of graphene. Existing graphene preparation technologies (such as the Hummers method, electrochemical exfoliation) usually rely on high-purity graphite raw materials and need to use a large amount of strong oxidants such as concentrated sulfuric acid and potassium permanganate, resulting in environmental pollution and high costs. In recent years, although there have been research attempts on microwave-assisted exfoliation (such as CN115285983 B) or ionic liquid dispersion (such as CN119391468A), single technologies are difficult to balance impurity removal and interlayer exfoliation efficiency, and often require multiple steps of treatment (such as pre-intercalation, reduction modification), with complex processes. In addition, traditional ultrasonic exfoliation has a low energy transfer efficiency, requires long-term treatment (> 5h) and the number of layers of the product is uneven (3 - 10 layers), while plasma technology can enhance the exfoliation effect, but it is prone to agglomeration of graphite sheets due to the lack of medium regulation. Therefore, developing an efficient, low-consumption, and environmentally friendly integrated method for recycling graphite of waste lithium batteries and preparing graphene is of great significance for resource recycling and green manufacturing. Summary of the Invention

[0003] To overcome the problems of low interlayer exfoliation efficiency and complex process of graphene in waste batteries in the prior art, the object of the present invention is to provide a method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic exfoliation. This method innovatively integrates the microwave-plasma synergistic exfoliation technology, realizes the efficient removal of metal impurities and residual binders through microwave-assisted mixed acid leaching; combines plasma directional bombardment between layers to weaken the van der Waals force in one step, improves the exfoliation efficiency, and uses organic solvents to replace traditional NMP to construct a green process, constructing a recycled graphene manufacturing system with both high efficiency and environmental friendliness.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic exfoliation, comprising the following steps:

[0006] Discharge, crush, magnetically separate and pulverize and screen the waste lithium batteries to obtain a solid mixture containing graphite. After drying the solid mixture, calcine it to obtain graphite slag containing metal impurities;

[0007] Treat the graphite slag with a mixed acid under microwave and disperse it in an ionic liquid, and ultrasonicate it under a plasma environment to obtain a graphene dispersion;

[0008] Separate the graphene dispersion to obtain graphene powder.

[0009] Further, the specific process of discharging, crushing, magnetically separating and pulverizing and screening the waste lithium batteries is as follows: Immerse the batteries in a 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V, and then dry them and perform subsequent crushing, magnetic separation and pulverizing and screening.

[0010] Further, the calcination is carried out under argon, the calcination temperature is 400 - 800 °C, and the time is 1 - 2 h.

[0011] Further, the dosage ratio of the graphite slag to the mixed acid is 1 g:10 - 100 mL.

[0012] Further, the mixed acid is a mixture of one of sulfuric acid, hydrochloric acid and nitric acid and one of citric acid, oxalic acid, ascorbic acid and acetic acid.

[0013] Further, the volume ratio of one of sulfuric acid, hydrochloric acid and nitric acid to one of citric acid, oxalic acid, ascorbic acid and acetic acid is 1:1 - 3:1;

[0014] And / or the pH value of the mixed acid is 1.5 - 2.5.

[0015] Further, the power of the microwave is 300 - 500 W, the temperature is 60 - 80 °C, and the treatment time is 20 - 40 min.

[0016] Further, the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0017] Further, the plasma environment is nitrogen or argon, and the plasma flow rate is 10 - 20 L / min.

[0018] Further, the frequency of the ultrasonication is 40 - 60 Hz, the power is 500 - 800 W, and the ultrasonication time is 1 - 3 h.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention innovatively realizes the efficient regeneration of graphite from waste lithium batteries and the green preparation of high-quality graphene by integrating microwave activation, plasma energy injection, and ionic liquid intercalation exfoliation technologies. Through the synergistic effect of high-energy particle bombardment of plasma and intercalation lubrication of ionic liquid, efficient exfoliation of graphene is achieved with the assistance of ultrasonic cavitation. The obtained graphene has a proportion of 1 - 3 layers > 70%, a specific surface area of 600 - 800 m 2 / g, a conductivity > 2000 S / m, and no oxidation defects. Compared with the traditional method, the preparation method of the present invention shortens the reaction time by 60%, reduces the strong acid dosage by 50%, the ionic liquid can be recycled 5 - 8 times, synchronously realizes a metal recovery purity > 99% and high value-added of graphene products, and has the characteristics of high efficiency, low consumption, and environmental friendliness.

[0021] Furthermore, argon protection gradient calcination is adopted to accurately remove the binder and metal impurities on the graphite surface while retaining the integrity of the graphite crystal.

[0022] Furthermore, a compound system of strong acid and organic acid is used to rapidly leach metal impurities in the microwave field, avoiding the corrosion of the graphite structure. Description of the Drawings

[0023] Figure 1 SEM image of graphene regenerated from graphite of waste lithium batteries in Example 1;

[0024] Figure 2 Raman image of graphene regenerated from graphite of waste lithium batteries in Example 1. Detailed Embodiments

[0025] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0026] A method for regenerating graphite from waste lithium batteries and preparing graphene by microwave-plasma synergistic exfoliation according to the present invention includes the following steps:

[0027] (1) Discharge, crush, magnetically separate, and pulverize and screen the waste lithium batteries to obtain a solid mixture containing graphite. After drying the solid mixture, it is calcined to obtain graphite slag containing metal impurities;

[0028] (2) Place the graphite slag and the mixed acid in a microwave reactor, and control the microwave power, temperature, and treatment time to remove metal impurities and residual binders;

[0029] (3)Disperse the acid-leached graphite in an ionic liquid, and under a plasma environment, simultaneously perform ultrasonic treatment for a period of time to obtain a graphene dispersion;

[0030] (4)Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0031] (1) The discharge crushing, magnetic separation and screening of waste lithium batteries refers to first soaking the batteries in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V, and after natural drying, putting them into a battery disassembly machine for subsequent crushing, magnetic separation and pulverization screening.

[0032] (1) The calcination conditions are calcination at 400 - 800 °C for 1 - 2 h under argon;

[0033] (2) The solid-liquid mass-volume ratio of the graphite slag to the mixed acid is 1 g:10 - 100 mL;

[0034] (2) The mixed acid is a mixed acid of strong acid (sulfuric acid / hydrochloric acid / nitric acid) and weak acid (citric acid / oxalic acid / ascorbic acid / acetic acid); the volume ratio of strong acid to weak acid in the mixed acid is 1:1 - 3:1;

[0035] (2) The pH value of the mixed acid is controlled at 1.5 - 2.5;

[0036] (2) The power of the microwave is 300 - 500 W, the temperature is 60 - 80 °C, and the treatment time is 20 - 40 min;

[0037] (3) The ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI);

[0038] (3) The plasma environment is nitrogen or argon;

[0039] (3) The plasma flow rate is 10 - 20 L / min;

[0040] (3) The frequency of the ultrasonic wave is 40 - 60 Hz, the power is 500 - 800 W, and the ultrasonic time is 1 - 3 h.

[0041] The following are specific examples.

[0042] Example 1

[0043] (1) Immerse the waste lithium batteries in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put them into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverization and screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 400 °C for 1 h under argon conditions to obtain graphite slag containing metal impurities;

[0044] (2) Place the graphite slag and the mixed acid (the volume ratio of sulfuric acid to acetic acid is 1:1, pH = 1.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:50 mL, control the microwave power at 300 W, the temperature at 60 °C, and the treatment time at 30 min to remove metal impurities and residual binders;

[0045] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), and under a N2 flow rate of 10 L / min, synchronously perform ultrasonic treatment at a frequency of 40 Hz and a power of 500 W for 2 h to obtain a graphene dispersion;

[0046] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0047] See Figure 1 , it can be seen that the graphene regenerated from the waste graphite anode presents a flaky and multi-layer intertwined structure, with certain voids between the layers, forming a network-like structure. This structure endows it with a large specific surface area, which is beneficial to the adsorption and reaction of substances and has potential application value in the fields of energy storage, catalysis, etc.

[0048] See Figure 2 , it can be seen that the G peak is sharp and has a high intensity, indicating a high degree of sp 2 hybridization of carbon atoms in graphene and good crystallinity. The ratio of I D / I G is 0.144, and the value is relatively low, indicating that fewer structural defects are introduced during the regeneration process and the quality of the material is high. The ratio of I 2D / I G is 0.511, indicating that this graphene may be a few-layer structure, and graphene with fewer layers usually has more advantages in electrical and optical properties.

[0049] Example 2

[0050] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverization and screening to obtain a solid mixture containing graphite. After drying the solid mixture, calcine it at 500 °C for 1 h under argon conditions to obtain graphite slag containing metal impurities;

[0051] (2) Place the graphite slag and the mixed acid (the volume ratio of hydrochloric acid to citric acid is 1:1, pH = 2.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:50 mL. Control the microwave power at 300 W, the temperature at 70 °C, and the treatment time at 30 min to remove metal impurities and residual binders;

[0052] (3) Disperse the acid-leached graphite in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). Under a N2 flow rate of 10 L / min, synchronously perform ultrasonic treatment at a frequency of 50 Hz and a power of 500 W for 1 h to obtain a graphene dispersion;

[0053] (4) Perform solid-liquid separation on the above graphene dispersion. Perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0054] Example 3

[0055] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverization and screening to obtain a solid mixture containing graphite. After drying the solid mixture, calcine it at 500 °C for 1 h under argon conditions to obtain graphite slag containing metal impurities;

[0056] (2) Place the graphite slag and the mixed acid (the volume ratio of hydrochloric acid to oxalic acid is 1:1, pH = 2.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:75 mL. Control the microwave power at 300 W, the temperature at 60 °C, and the treatment time at 40 min to remove metal impurities and residual binders;

[0057] (3) Disperse the acid-leached graphite in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). Under a N2 flow rate of 20 L / min, synchronously perform ultrasonic treatment at a frequency of 40 Hz and a power of 500 W for 2 h to obtain a graphene dispersion;

[0058] (4) Perform solid-liquid separation on the above graphene dispersion. Perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0059] Example 4

[0060] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverizing and screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 650 °C for 1.5 h under argon conditions to obtain graphite slag containing metal impurities;

[0061] (2) Place the graphite slag and the mixed acid (the volume ratio of hydrochloric acid to citric acid is 2:1, pH = 1.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:100 mL. Control the microwave power at 500 W, the temperature at 80 °C, and the treatment time at 20 min to remove metal impurities and residual binders;

[0062] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4). Under a N2 flow rate of 10 L / min, synchronously perform ultrasonic treatment at a frequency of 60 Hz and a power of 500 W for 1 h to obtain a graphene dispersion;

[0063] (4) Perform solid-liquid separation on the above graphene dispersion. Perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0064] Example 5

[0065] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverizing and screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 650 °C for 1.5 h under argon conditions to obtain graphite slag containing metal impurities;

[0066] (2) Place the graphite slag and the mixed acid (the volume ratio of nitric acid to citric acid is 3:1, pH = 1.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:25 mL. Control the microwave power at 500 W, the temperature at 60 °C, and the treatment time at 40 min to remove metal impurities and residual binders;

[0067] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4). Under a N2 flow rate of 20 L / min, synchronously perform ultrasonic treatment at a frequency of 60 Hz and a power of 600 W for 2 h to obtain a graphene dispersion;

[0068] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the precipitate after separation, wash and dry the precipitate to obtain graphene powder.

[0069] Example 6

[0070] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation and pulverization screening to obtain a graphite-containing solid mixture. Dry the solid mixture and calcine it at 650 °C for 1.5 h under argon conditions to obtain graphite slag containing metal impurities;

[0071] (2) Place the graphite slag and mixed acid (the volume ratio of nitric acid to acetic acid is 1:1, pH = 2) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:60 mL, control the microwave power at 500 W, the temperature at 60 °C and the treatment time at 40 min to remove metal impurities and residual binders;

[0072] (3) Disperse the acid-leached graphite in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI), and under a N2 flow rate of 10 L / min, at a frequency of 60 Hz and a power of 600 W, perform synchronous ultrasonic treatment for 2 h to obtain a graphene dispersion;

[0073] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the precipitate after separation, wash and dry the precipitate to obtain graphene powder.

[0074] Example 7

[0075] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation and pulverization screening to obtain a graphite-containing solid mixture. Dry the solid mixture and calcine it at 800 °C for 1 h under argon conditions to obtain graphite slag containing metal impurities;

[0076] (2) Place the graphite slag and mixed acid (the volume ratio of sulfuric acid to acetic acid is 1.5:1, pH = 1.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:10 mL, control the microwave power at 400 W, the temperature at 65 °C and the treatment time at 25 min to remove metal impurities and residual binders;

[0077] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), and under a N2 flow rate of 15 L / min, at a frequency of 40 Hz and a power of 800 W, perform synchronous ultrasonic treatment for 2 h to obtain a graphene dispersion;

[0078] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0079] Example 8

[0080] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverization and screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 700 °C for 2 h under argon conditions to obtain graphite slag containing metal impurities;

[0081] (2) Place the graphite slag and the mixed acid (the volume ratio of sulfuric acid to acetic acid is 2:1, pH = 2.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:100 mL, control the microwave power at 350 W, the temperature at 75 °C, and the treatment time at 35 min to remove metal impurities and residual binders;

[0082] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), and under a N2 flow rate of 20 L / min, at a frequency of 45 Hz and a power of 700 W, perform synchronous ultrasonic treatment for 3 h to obtain a graphene dispersion;

[0083] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0084] Comparative Example 1

[0085] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation, and pulverization and screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 700 °C for 2 h under argon conditions to obtain graphite slag containing metal impurities;

[0086] (2) Place the graphite slag and the mixed acid (the volume ratio of sulfuric acid to acetic acid is 2:1, pH = 2.5) in an oil bath at a solid-liquid mass-volume ratio of 1 g:100 mL and heat it in an oil bath at 90 °C for 60 min;

[0087] (3) Disperse the acid-leached graphite in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4), and perform synchronous ultrasonic treatment at a frequency of 45 Hz and a power of 700 W for 3 h to obtain a graphene dispersion;

[0088] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0089] Comparative Example 2

[0090] (1) Immerse the waste lithium battery in 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V. After natural drying, put it into a battery disassembly machine for subsequent crushing, magnetic separation and pulverization screening to obtain a solid mixture containing graphite. Dry the solid mixture and calcine it at 700 °C for 2 h in an air atmosphere to obtain graphite slag containing metal impurities;

[0091] (2) Place the graphite slag and the mixed acid (the volume ratio of sulfuric acid to acetic acid is 2:1, pH = 2.5) in a microwave reactor at a solid-liquid mass-volume ratio of 1 g:100 mL, control the microwave power at 350 W, the temperature at 75 °C and the treatment time at 35 min to remove metal impurities and residual binders;

[0092] (3) Disperse the acid-leached graphite in N-methylpyrrolidone (NMP), and perform synchronous ultrasonic treatment at a frequency of 45 Hz and a power of 700 W for 3 h to obtain a graphene dispersion;

[0093] (4) Perform solid-liquid separation on the above graphene dispersion, perform solid-liquid separation on the collected upper liquid again, collect the separated precipitate, wash and dry the precipitate to obtain graphene powder.

[0094] Table 1 Key performance parameters of the regenerated graphene prepared in each example and comparative example

[0095]

[0096] As can be seen from Table 1, due to the lack of plasma energy injection, the exfoliation efficiency of Comparative Example 1 is greatly reduced, the number of layers increases to 6 - 8 layers, and the specific surface area is only 60% of that of the example, which is difficult to meet the requirements of high-precision electronic devices; in Comparative Example 2, graphite oxidation (C / O ratio < 12) occurs due to air calcination. Even when using organic solvent exfoliation, the product is mainly composed of 6 - 8-layer thick flakes, and the conductivity drops sharply to below 1000 S / m. In contrast, the examples of the present invention obtain graphene with 1 - 2 layers and extremely few defects through microwave-activated acid leaching and plasma-ionic liquid synergistic exfoliation, and its specific surface area breaks through 720 m 2 / g, with a conductivity of over 2500 S / m, showing significant performance advantages in applications such as flexible electrodes and sensors.

[0097] The method of the present invention recovers graphite through microwave-assisted acid leaching pretreatment, efficiently removing metal impurities and residual binders while maintaining the integrity of the graphite interlayer structure, reducing acid consumption and secondary pollution, and shortening the treatment time. During the ultrasonic exfoliation process, low-temperature plasma is used. Through the plasma-ultrasonic synergistic exfoliation technology, high-energy particles bombard the graphite interlayer to further weaken the van der Waals force and improve the exfoliation efficiency. In addition, a strong acid / weak acid compound system (pH 1.5 - 2.5) and low-toxicity ionic liquids are used to replace traditional NMP (N-methylpyrrolidone), avoiding its toxicity problems, reducing the wastewater discharge by more than 70%, and enhancing the dispersion stability of graphene. The obtained graphene has high conductivity and can be applied in fields such as the negative electrode of lithium batteries and conductive composite materials, combining environmental protection and economy.

[0098] The above is only an illustration of the best embodiments of the present invention and should not be construed as a limitation of the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to vary. Any changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0099] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

Claims

1. A method for recycling graphite from waste lithium batteries and preparing graphene by microwave-plasma synergistic exfoliation, characterized in that, It includes the following steps: Discharge, crush, magnetically separate and pulverize and screen the waste lithium battery to obtain a solid mixture containing graphite. After drying the solid mixture, calcine it to obtain graphite slag containing metal impurities; Treat the graphite slag with a mixed acid under microwave and disperse it in an ionic liquid, and ultrasonicate it in a plasma environment to obtain a graphene dispersion; Separate the graphene dispersion to obtain graphene powder.

2. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that, The specific process of discharging, crushing, magnetically separating and pulverizing and screening the waste lithium battery is as follows: Immerse the battery in a 1 mol / L NaCl solution for 24 h until the voltage is lower than 1.5 V, and then air-dry it for subsequent crushing, magnetic separation and pulverizing and screening.

3. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, wherein The calcination is carried out under argon, the calcination temperature is 400 - 800 °C, and the time is 1 - 2 h.

4. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, wherein The dosage ratio of the graphite slag to the mixed acid is 1 g:10 - 100 mL.

5. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that The mixed acid is a mixture of one of sulfuric acid, hydrochloric acid and nitric acid and one of citric acid, oxalic acid, ascorbic acid and acetic acid.

6. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that, The volume ratio of one of sulfuric acid, hydrochloric acid and nitric acid to one of citric acid, oxalic acid, ascorbic acid and acetic acid is 1:1 - 3:1; and / or the pH value of the mixed acid is 1.5 - 2.

5.

7. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that, The power of the microwave is 300 - 500 W, the temperature is 60 - 80 °C, and the treatment time is 20 - 40 min.

8. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that, The ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

9. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, characterized in that, The plasma environment is nitrogen or argon, and the plasma flow rate is 10 - 20 L / min.

10. The method for recycling graphite of waste lithium batteries and preparing graphene by microwave-plasma synergistic stripping according to claim 1, wherein, The frequency of the ultrasonication is 40 - 60 Hz, the power is 500 - 800 W, and the ultrasonication time is 1 - 3 h.

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