Method and application for preparing graphene nanosheets by ball milling graphite of waste lithium battery anode

Abstract

The present invention belongs to the technical field of lithium battery recycling, and particularly relates to a method for preparing graphene nanosheets by ball milling the graphite of the negative electrode of waste lithium batteries and its application. The method comprises the following steps: S1. Immerse the graphite negative electrode block in a deep eutectic solvent, perform ultrasonic treatment under constant temperature conditions, then filter, wash with deionized water and dry to obtain the preliminarily treated graphite for standby; S2. Place the preliminarily treated graphite in a ball milling tank, then add ball milling media and a delaminating agent, and perform ball milling treatment under the protection of an inert gas; S3. Filter the product after ball milling to obtain a solid residue, wash it with deionized water until it is neutral, and then dry it. The present invention successfully prepares graphene nanosheets by using the graphite of the negative electrode of waste lithium batteries. On the one hand, it realizes the low-carbon treatment of waste lithium batteries. On the other hand, the successfully synthesized graphene nanosheets can be widely used as high-value-added products in the production of high-end products in multiple fields such as electronics, building materials, and biology, which conforms to the concept of green and low-carbon recycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recycling, and particularly relates to a method for preparing graphene nanosheets by ball-milling the negative electrode graphite of waste lithium batteries and its application. Background Art

[0002] Lithium batteries have the advantages of small volume, high specific energy, low self-discharge, and no memory effect, and have currently become the most promising secondary batteries and the fastest-growing chemical energy storage power sources. Due to the wide application of lithium batteries in energy storage systems such as portable communication devices, electric vehicles and ships, aerospace, and military fields, the market scale of lithium batteries is expanding day by day. However, limited by a certain service life, the high demand in the lithium battery market will inevitably lead to the generation of a large number of waste lithium batteries. Waste lithium batteries contain harmful metals, flammable electrolytes, plastic casings, and a large amount of graphite materials, etc. If not properly treated, it will not only cause serious environmental pollution and resource waste, but even endanger human health. In addition, the metals and graphite materials in waste lithium batteries also have important recycling value.

[0003] At present, people's recycling of waste lithium batteries mainly focuses on the recycling of valuable metals in the positive electrode materials. The current main recycling methods include hydrometallurgy, pyrometallurgy, and bioleaching technology. With the continuous development of technology, the recycling of positive electrode materials has been quite mature and an industrial chain has been formed. However, the recycling of the negative electrode materials of waste lithium batteries cannot be ignored. In recent years, due to advantages such as low cost and high energy density, graphite materials have dominated in commercial lithium battery negative electrode materials, accounting for 91% globally in the field of lithium battery negative electrode materials. On the one hand, the usage amount of graphite in lithium batteries is relatively large. About 1 kilogram of graphite is required per kilowatt-hour of battery, and up to 50 kilograms of graphite is needed for a medium-sized or small electric vehicle. Therefore, with the continuous development of the electric vehicle industry, the market demand for graphite is gradually increasing. On the other hand, the graphite required for the negative electrode of lithium batteries has relatively high requirements, and the purity should reach 99.5%. However, graphite mines usually can only produce flake graphite with a purity of 90%-98%. To meet the requirements of battery-grade graphite, additional purification steps are required. The commonly used graphite purification methods are generally chemical methods and heat treatment methods. These methods not only increase the cost of graphite but also have high environmental hazards. Therefore, considering factors such as expensive purification processes, increasing demand, and the huge output of waste negative electrode graphite, recycling the negative electrode graphite material from waste lithium batteries is an effective way to obtain high-quality graphite. The recycling and utilization of the negative electrode graphite in waste lithium batteries has important practical significance for reducing the production cost of battery-grade graphite, avoiding environmental pollution, and the sustainable development of the lithium battery industry.

[0004] As a two-dimensional material, graphene exhibits great application potential in the fields of energy, electronics, biomedicine, etc. due to its excellent electrical, thermal, mechanical and other properties. At present, the preparation methods of graphene mainly include mechanical exfoliation method, chemical vapor deposition method, oxidation-reduction method, etc. However, these methods generally have problems such as high cost, complex process, environmental pollution, etc., which limit the large-scale application of graphene.

[0005] Therefore, it is of great research significance to develop a method for preparing graphene nanosheets by ball milling the graphite of the negative electrode of waste lithium batteries. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and application for preparing graphene nanosheets by ball milling the graphite of the negative electrode of waste lithium batteries in view of the existing problems.

[0007] The present invention is realized through the following technical solutions:

[0008] A method for preparing graphene nanosheets by ball milling the graphite of the negative electrode of waste lithium batteries, comprising the following steps:

[0009] S1. Cut the graphite negative electrode plate into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 80-90 °C, perform ultrasonic treatment for 4-5 h under constant temperature conditions, then filter, wash with deionized water, and place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby;

[0010] S2. Place the preliminarily treated graphite in a ball milling tank, then add ball milling media and a delaminating agent, and perform ball milling treatment under the protection of an inert gas;

[0011] S3. Filter the product after ball milling to obtain solid residues, wash them with deionized water until neutral, and then dry them in a vacuum drying oven at 60-70 °C.

[0012] Further, the preparation method of the deep eutectic solvent in step S1 is: stir a hydrogen bond acceptor and a hydrogen bond donor in a molar ratio of 1:2-4 at 80-100 °C to form a transparent homogeneous liquid; after heating to 120-140 °C, add a functional auxiliary agent to the transparent homogeneous liquid, and stir at a constant temperature for 1-2 h.

[0013] Further, the hydrogen bond acceptor is one or more of choline chloride, betaine, and L-carnitine;

[0014] The hydrogen bond donor is one or more of citric acid, tartaric acid, and proline.

[0015] Further, the addition amount of the functional auxiliary agent is 1-2 wt%;

[0016] The preparation of the functional auxiliary agent comprises the following steps:

[0017] (1) Ultrasonically disperse nano-silica into absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane which is 10 - 18% of the mass of nano-silica, and keep stirring at 60 - 70°C and 100 - 200 rpm for 3 - 5 h to obtain pre-modified nano-silica for standby;

[0018] (2) Add tocopherol and succinic anhydride into a three-necked flask according to a molar ratio of 2 - 3:1, then add isobutyl acetate, stir to dissolve it and then heat up to 90 - 100°C, add ethylenediamine which is 0.7 - 1% of the molar amount of tocopherol, and keep reacting at a constant temperature for 2 - 3 h to obtain a tocopherol derivative for standby;

[0019] (3) Add 0.1 - 0.2 mmol of the tocopherol derivative into MES buffer solution (4-morpholineethanesulfonic acid), stir and mix evenly, then add 0.1 - 0.13 mmol of carbodiimide and 0.15 - 0.17 mmol of N-hydroxysuccinimide, stir at 200 - 300 rpm at room temperature for 20 - 30 min, then add pre-modified nano-silica which is 0.5 - 1 times the amount of the tocopherol derivative, continue to stir for 10 - 12 h, then centrifuge at 9000 - 10000 rpm for 10 - 15 min, collect the solid, wash it with deionized water for 3 - 5 times, and then place it in a vacuum drying oven and dry it at 60 - 70°C for 8 - 12 h.

[0020] Further, the ball milling medium described in step S2 is modified zirconia balls;

[0021] The preparation method of the modified zirconia balls is as follows:

[0022] 1) Prepare a mineralization solution by mixing 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate and 0.1 mg / mL of mussel adhesive protein, then add zirconia balls and stir at 60 - 70°C and 200 - 300 rpm for 8 - 12 h, then filter by suction, and then dry to obtain mineralized zirconia balls;

[0023] 2) Use the supersonic plasma spraying process to spray nano-Al2O3 - 20% graphene, TiN - 15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3 - 20% graphene is 50 - 60 μm, the spraying thickness of TiN - 15MoS2 is 30 - 40 μm, and the spraying thickness of nano-silica is 30 - 50 μm.

[0024] Further, the components and their corresponding weight percentages in the stripping agent described in step S2 are as follows: 1-butyl-3-methylimidazolium tetrafluoroborate 1-2%, 1-ethyl-3-methylimidazolium tetrafluoroborate 1-2%, urea 2-3%, and the balance is sodium dodecylbenzenesulfonate.

[0025] Further, the ball milling speed in step S2 is 200-800 rpm, and the ball milling time is 8-12 h.

[0026] Further, the inert gas in step S2 is nitrogen or argon.

[0027] A graphene nanosheet prepared by the method described in any one of the above.

[0028] An application of the graphene nanosheet described above in silicone rubber modification.

[0029] The present invention has the following advantages compared with the prior art:

[0030] The present invention successfully prepares graphene nanosheets using the graphite of the negative electrode of waste lithium batteries as raw materials. On the one hand, it realizes the low-carbon treatment of waste lithium batteries. On the other hand, the successfully synthesized graphene nanosheets can be widely used as high-value-added products in the production of high-end products in multiple fields such as electronics, building materials, and biology, meeting the concept of green and low-carbon recycling.

[0031] First, the present invention conducts amination treatment on nano-silica, changes the surface charge of nano-silica, enhances its compatibility with tocopherol. Tocopherol reacts with succinic anhydride to generate a tocopherol derivative with a carboxylic acid group. The formed carboxylic acid group and the amino group condense to form a covalent bond through carbodiimide mediation. Tocopherol is firmly anchored on the surface of nano-silica. Adding it to the deep eutectic solvent can improve the stability and viscosity of the solvent, and can inhibit metal corrosion. Under the combined action of the deep eutectic solvent and ultrasonic waves, the dissolution of the binder, the stripping of metal impurities, and the protection of the graphite structure are simultaneously achieved, avoiding the damage problems of the current strong acid / high-temperature technical means. Moreover, the deep eutectic solvent of the present invention can be recycled, reducing the processing cost.

[0032] Secondly, the mineralizing solution acts on the zirconia balls, and a hydroxyapatite / Mfp-5 composite layer is formed on the surface. Mussel proteins bind to the zirconia surface through catechol groups, inducing the directional growth of hydroxyapatite to form a biomimetic interface layer. Then, through supersonic plasma spraying and multi-layer spraying, interface defects are eliminated, fracture toughness is improved, the ball milling effect is enhanced. The ball milling medium and auxiliary delaminating agent of the modified zirconia balls act synergistically. By optimizing the ball milling parameters, the frictional force is increased, the interlayer force is reduced, and the delamination efficiency and quality are improved, effectively regulating the size, number of layers, and defects of graphene nanosheets. The prepared graphene nanosheets have a thinner lamellar structure, a more uniform size distribution, and fewer defects, with significantly improved performance. Detailed implementation manners

[0033] To further explain the present invention, the following specific embodiments are described below.

[0034] Example 1

[0035] A method for preparing graphene nanosheets by ball milling the graphite of the negative electrode of waste lithium batteries, comprising the following steps:

[0036] S1. Cut the graphite negative electrode sheet into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 80°C, perform ultrasonic treatment for 4 h under constant temperature conditions, filter, rinse with deionized water, and then place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby;

[0037] The preparation method of the deep eutectic solvent is as follows: Mix betaine and citric acid in a molar ratio of 1:2 and stir at 80°C to form a transparent homogeneous liquid; after heating to 120°C, add 1 wt% of a functional auxiliary agent to the transparent homogeneous liquid and stir at a constant temperature for 1 h;

[0038] The preparation of the functional auxiliary agent includes the following steps:

[0039] (1) Ultrasonically disperse nano-silica in absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane accounting for 10% of the mass of nano-silica, and keep stirring at 60°C and 100 rpm for 3 h to obtain pre-modified nano-silica for standby;

[0040] (2) Add tocopherol and succinic anhydride to a three-necked flask in a molar ratio of 2:1, then add isobutyl acetate, stir to dissolve it, heat it to 90°C, add ethylenediamine accounting for 0.7% of the molar amount of tocopherol, and react at a constant temperature for 2 h to obtain a tocopherol derivative for standby;

[0041] (3) Add 0.1 mmol of tocopherol derivative into MES buffer (4-morpholineethanesulfonic acid). After stirring and mixing evenly, add 0.1 mmol of carbodiimide and 0.15 mmol of N-hydroxysuccinimide. After stirring at 200 rpm at room temperature for 20 min, add pre-modified nano-silica which is 0.5 times the amount of tocopherol derivative. Continue to stir for 10 h, then centrifuge at 9000 rpm for 10 min. Collect the solid, wash it 3 times with deionized water, and then place it in a vacuum drying oven and dry it at 60 °C for 8 h;

[0042] S2. Place the preliminarily treated graphite in a ball mill jar, then add modified zirconia balls and a delaminating agent, and carry out ball milling treatment under the protection of argon, with ball milling at 200 rpm for 8 h;

[0043] The preparation method of the modified zirconia balls is as follows:

[0044] 1) Prepare a mineralization solution with 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate, and 0.1 mg / mL of mussel adhesive protein, then add zirconia balls and stir at 60 °C and 200 rpm for 8 h, then carry out suction filtration, and then dry to obtain mineralized zirconia balls;

[0045] 2) Use the supersonic plasma spraying process to spray nano-Al2O3-20% graphene, TiN-15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3-20% graphene is 50 μm, the spraying thickness of TiN-15% MoS2 is 30 μm, and the spraying thickness of nano-silica is 30 μm;

[0046] The components and corresponding weight percentages in the delaminating agent are: 1% of 1-butyl-3-methylimidazolium tetrafluoroborate, 1% of 1-ethyl-3-methylimidazolium tetrafluoroborate, 2% of urea, and the balance is sodium dodecylbenzenesulfonate;

[0047] S3. Filter the product after ball milling to obtain a solid residue. After washing it with deionized water until neutral, place it in a vacuum drying oven and dry it at 60 °C;

[0048] Example 2

[0049] A method for preparing graphene nanosheets by ball milling graphite from waste lithium battery anodes, comprising the following steps:

[0050] S1. Cut the graphite negative electrode sheet into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 85 °C, carry out ultrasonic treatment at a constant temperature for 4.5 h, then filter, wash with deionized water, and place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby;

[0051] The preparation method of the eutectic solvent is as follows: Mix betaine and citric acid in a molar ratio of 1:3 and stir at 90 °C to form a transparent homogeneous liquid; after heating to 130 °C, add 1.5 wt% of the functional additive to the transparent homogeneous liquid and stir at a constant temperature for 1.5 h;

[0052] The preparation of the functional additive includes the following steps:

[0053] (1) Ultrasonically disperse nano-silica in absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane which is 14% of the mass of nano-silica, and keep stirring at 65 °C and 150 rpm for 4 h to obtain pre-modified nano-silica for standby;

[0054] (2) Add tocopherol and succinic anhydride into a three-necked flask in a molar ratio of 2.5:1, then add isobutyl acetate, stir to dissolve it and then heat to 95 °C, add ethylenediamine which is 0.85% of the molar amount of tocopherol, and react at a constant temperature for 2.5 h to obtain a tocopherol derivative for standby;

[0055] (3) Add 0.15 mmol of the tocopherol derivative into MES buffer (4-morpholineethanesulfonic acid), stir and mix evenly, then add 0.12 mmol of carbodiimide and 0.16 mmol of N-hydroxysuccinimide, stir at 250 rpm at room temperature for 25 min, then add pre-modified nano-silica which is 0.75 times that of the tocopherol derivative, continue to stir for 11 h, centrifuge at 9500 rpm for 12.5 min, collect the solid, wash it 4 times with deionized water, and then place it in a vacuum drying oven and dry it at 65 °C for 10 h;

[0056] S2. Place the preliminarily treated graphite in a ball mill tank, then add modified zirconia balls and a delaminating agent, and perform ball milling treatment under the protection of argon, ball milling at 500 rpm for 10 h;

[0057] The preparation method of the modified zirconia balls is as follows:

[0058] 1) Prepare a mineralization solution with 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate and 0.1 mg / mL of mussel adhesive protein, then add zirconia balls and stir at 65 °C and 250 rpm for 10 h, then filter by suction, and then dry to obtain mineralized zirconia balls;

[0059] 2) Use the supersonic plasma spraying process to spray nano-Al2O3-20% graphene, TiN-15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3-20% graphene is 55 μm, the spraying thickness of TiN-15% MoS2 is 35 μm, and the spraying thickness of nano-silica is 40 μm;

[0060] The components and their corresponding weight percentages in the stripping agent are as follows: 1-butyl-3-methylimidazolium tetrafluoroborate 1.5%, 1-ethyl-3-methylimidazolium tetrafluoroborate 1.5%, urea 2.5%, and the balance is sodium dodecylbenzenesulfonate;

[0061] S3. Filter the ball-milled product to obtain a solid residue. Wash it with deionized water until neutral, and then place it in a vacuum drying oven to dry at 65 °C.

[0062] Example 3

[0063] A method for preparing graphene nanosheets by ball-milling the graphite of the negative electrode of waste lithium batteries, comprising the following steps:

[0064] S1. Cut the graphite negative electrode sheet into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 90 °C, perform ultrasonic treatment for 5 h under constant temperature conditions, filter, wash with deionized water, and then place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby;

[0065] The preparation method of the deep eutectic solvent is as follows: Stir betaine and citric acid in a molar ratio of 1:4 at 100 °C to form a transparent homogeneous liquid; after heating to 140 °C, add 2 wt% of a functional auxiliary agent to the transparent homogeneous liquid, and stir constantly at a constant temperature for 2 h;

[0066] The preparation of the functional auxiliary agent includes the following steps:

[0067] (1) Ultrasonically disperse nano-silica in absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane accounting for 18% of the mass of nano-silica, keep it at 70 °C, and stir at 200 rpm for 5 h to obtain pre-modified nano-silica for standby;

[0068] (2) Add tocopherol and succinic anhydride in a molar ratio of 3:1 to a three-necked flask, then add isobutyl acetate, stir to dissolve it, heat to 100 °C, add ethylenediamine accounting for 1% of the molar amount of tocopherol, and react at a constant temperature for 3 h to obtain a tocopherol derivative for standby;

[0069] (3) Add 0.2 mmol of the tocopherol derivative to a MES buffer solution (4-morpholineethanesulfonic acid), stir and mix evenly, then add 0.13 mmol of carbodiimide and 0.17 mmol of N-hydroxysuccinimide, stir at 300 rpm at room temperature for 30 min, add pre-modified nano-silica that is 1 time the amount of the tocopherol derivative, continue to stir for 12 h, centrifuge at 10000 rpm for 15 min, collect the solid, wash it 5 times with deionized water, and then place it in a vacuum drying oven to dry at 70 °C for 12 h;

[0070] S2. Place the preliminarily treated graphite into a ball mill jar, then add modified zirconia balls and a delaminating agent, and perform ball milling under the protection of argon. Ball mill at 800 rpm for 12 h;

[0071] The preparation method of the modified zirconia balls is as follows:

[0072] 1) Prepare a mineralization solution by mixing 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate, and 0.1 mg / mL of mussel adhesive protein, then add zirconia balls and stir at 70 °C and 300 rpm for 12 h, then perform suction filtration, and then dry to obtain mineralized zirconia balls;

[0073] 2) Use the supersonic plasma spraying process to spray nano-Al2O3-20% graphene, TiN-15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3-20% graphene is 60 μm, the spraying thickness of TiN-15MoS2 is 40 μm, and the spraying thickness of nano-silica is 50 μm;

[0074] The components and corresponding weight percentages in the delaminating agent are as follows: 2% of 1-butyl-3-methylimidazolium tetrafluoroborate, 2% of 1-ethyl-3-methylimidazolium tetrafluoroborate, 3% of urea, and the balance is sodium dodecylbenzenesulfonate;

[0075] S3. Filter the product after ball milling to obtain a solid residue. Wash it with deionized water until neutral, and then place it in a vacuum drying oven to dry at 70 °C.

[0076] Comparative Example 1

[0077] A method for preparing graphene nanosheets by ball milling the negative electrode graphite of waste lithium batteries, comprising the following steps:

[0078] S1. Cut the graphite negative electrode plate into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 85 °C, perform ultrasonic treatment for 4.5 h under constant temperature conditions, then filter, wash with deionized water, and place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby;

[0079] The preparation method of the deep eutectic solvent is as follows: Stir betaine and citric acid in a molar ratio of 1:3 at 90 °C to form a transparent homogeneous liquid;

[0080] S2. Place the preliminarily treated graphite into a ball mill jar, then add modified zirconia balls and a delaminating agent, and perform ball milling under the protection of argon. Ball mill at 500 rpm for 10 h;

[0081] The preparation method of the modified zirconia balls is as follows:

[0082] 1) Prepare a mineralization solution by mixing 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate, and 0.1 mg / mL of mussel adhesive protein. Then add zirconia balls and stir at 65 °C and 250 rpm for 10 h, followed by suction filtration. After that, dry it to obtain mineralized zirconia balls.

[0083] 2) Use the supersonic plasma spraying process to spray nano-Al2O3-20% graphene, TiN-15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3-20% graphene is 55 μm, the spraying thickness of TiN-15% MoS2 is 35 μm, and the spraying thickness of nano-silica is 40 μm.

[0084] The components and corresponding weight percentages in the stripping agent are as follows: 1.5% of 1-butyl-3-methylimidazolium tetrafluoroborate, 1.5% of 1-ethyl-3-methylimidazolium tetrafluoroborate, 2.5% of urea, and the balance is sodium dodecylbenzenesulfonate.

[0085] S3: Filter the ball-milled product to obtain a solid residue. Wash it with deionized water until neutral, and then place it in a vacuum drying oven to dry at 65 °C.

[0086] Comparative Example 2

[0087] A method for preparing graphene nanosheets by ball-milling the graphite of the negative electrode of waste lithium batteries, comprising the following steps:

[0088] S1: Cut the graphite negative electrode sheet into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 85 °C, perform ultrasonic treatment for 4.5 h under constant temperature conditions, filter, wash with deionized water, and then place them in a drying oven to dry for 24 h to obtain preliminarily treated graphite for standby.

[0089] The preparation method of the deep eutectic solvent is as follows: Stir betaine and citric acid in a molar ratio of 1:3 at 90 °C to form a transparent homogeneous liquid; after heating to 130 °C, add 1.5 wt% of a functional auxiliary agent to the transparent homogeneous liquid, and stir at a constant temperature for 1.5 h.

[0090] The preparation of the functional auxiliary agent includes the following steps:

[0091] (1) Ultrasonically disperse nano-silica in absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane accounting for 14% of the mass of nano-silica, and keep stirring at 65 °C and 150 rpm for 4 h to obtain pre-modified nano-silica for standby.

[0092] (2) Add tocopherol and succinic anhydride to a three-necked flask in a molar ratio of 2.5:1, then add isobutyl acetate, stir to dissolve it, heat up to 95 °C, add ethylenediamine at 0.85% of the molar amount of tocopherol, react at a constant temperature for 2.5 h to obtain a tocopherol derivative for standby;

[0093] (3) Add 0.15 mmol of the tocopherol derivative to MES buffer (4-morpholineethanesulfonic acid), stir and mix evenly, then add 0.12 mmol of carbodiimide and 0.16 mmol of N-hydroxysuccinimide, stir at 250 rpm at room temperature for 25 min, then add pre-modified nano-silica at 0.75 times the amount of the tocopherol derivative, continue to stir for 11 h, centrifuge at 9500 rpm for 12.5 min, collect the solid, wash it 4 times with deionized water, and then place it in a vacuum drying oven and dry it at 65 °C for 10 h;

[0094] S2. Place the preliminarily treated graphite in a ball milling tank, then add zirconia balls and a stripping agent, and perform ball milling treatment under the protection of argon, ball milling at 500 rpm for 10 h;

[0095] The components and corresponding weight percentages in the stripping agent are: 1-butyl-3-methylimidazolium tetrafluoroborate 1.5%, 1-ethyl-3-methylimidazolium tetrafluoroborate 1.5%, urea 2.5%, and the balance is sodium dodecylbenzenesulfonate;

[0096] S3. Filter the product after ball milling to obtain a solid residue, wash it with deionized water until neutral, and then place it in a vacuum drying oven and dry it at 65 °C;

[0097] Comparative Example 3

[0098] A method for preparing graphene nanosheets by ball milling the negative electrode graphite of waste lithium batteries, comprising the following steps:

[0099] S1. Cut the graphite negative electrode plate into negative electrode blocks of 1×1 cm, then immerse them in a deep eutectic solvent, heat them in a water bath to 85 °C, perform ultrasonic treatment for 4.5 h under constant temperature conditions, then filter, rinse with deionized water, and place them in a drying oven and dry for 24 h to obtain preliminarily treated graphite for standby;

[0100] The preparation method of the deep eutectic solvent is: stir betaine and citric acid in a molar ratio of 1:3 at 90 °C to form a transparent homogeneous liquid; heat up to 130 °C, then add 1.5 wt% of a functional additive to the transparent homogeneous liquid, and stir at a constant temperature for 1.5 h;

[0101] The preparation of the functional additive includes the following steps:

[0102] (1) Ultrasonically disperse nano-silica in absolute ethanol. After ultrasonic dispersion is uniform, add 3-aminopropyltriethoxysilane which is 14% of the mass of nano-silica, keep at 65 °C, stir at 150 rpm for 4 h to obtain pre-modified nano-silica for standby;

[0103] (2) Add tocopherol and succinic anhydride into a three-necked flask according to a molar ratio of 2.5:1, then add isobutyl acetate, stir to dissolve it and then heat up to 95 °C, add ethylenediamine which is 0.85% of the molar amount of tocopherol, and react at a constant temperature for 2.5 h to obtain a tocopherol derivative for standby;

[0104] (3) Add 0.15 mmol of the tocopherol derivative into MES buffer solution (4-morpholineethanesulfonic acid), stir and mix evenly, then add 0.12 mmol of carbodiimide and 0.16 mmol of N-hydroxysuccinimide, stir at 250 rpm at room temperature for 25 min, then add pre-modified nano-silica which is 0.75 times that of the tocopherol derivative, continue to stir for 11 h, centrifuge at 9500 rpm for 12.5 min, collect the solid, wash it 4 times with deionized water, and then place it in a vacuum drying oven and dry it at 65 °C for 10 h;

[0105] S2. Place the preliminarily treated graphite in a ball mill tank, then add modified zirconia balls and carry out ball milling treatment under the protection of argon, ball mill at 500 rpm for 10 h;

[0106] The preparation method of the modified zirconia balls is as follows:

[0107] 1) Prepare a mineralization solution with 0.1 mol / L of CaCl2, 0.05 mol / L of sodium dihydrogen phosphate and 0.1 mg / mL of mussel adhesive protein, then add zirconia balls, stir at 65 °C and 250 rpm for 10 h, then filter by suction, and then dry to obtain mineralized zirconia balls;

[0108] 2) Use the supersonic plasma spraying process to spray nano-Al2O3-20% graphene, TiN-15% MoS2, and nano-silica onto the surface of the mineralized zirconia balls in sequence. The spraying power is 80 kW, the spraying thickness of Al2O3-20% graphene is 55 μm, the spraying thickness of TiN-15MoS2 is 35 μm, and the spraying thickness of nano-silica is 40 μm;

[0109] S3. Filter the ball-milled product to obtain a solid residue, wash it with deionized water until neutral, and then place it in a vacuum drying oven and dry it at 65 °C.

[0110] Performance test

[0111] The graphene nanosheets obtained from each example and comparative example were applied to modify the silicone rubber material. The graphene nanosheets and the silicone rubber raw materials were uniformly mixed using a two-roll mill. The mixing temperature was 40 °C and the mixing time was 90 min. The mixing amounts of the graphene nanosheets were 1.0 wt·% respectively to obtain graphene-modified silica gel.

[0112] Then, a laser thermal conductivity meter was used to measure the thermal diffusivity and thermal conductivity of the ordinary silica gel and the graphene-modified silica gel obtained in the present invention by the laser flash method. The test results are shown in Table 1 below.

[0113] Table 1

[0114] <![CDATA[Thermal diffusivity mm 2 / s]]> Thermal conductivity W / (m·K) Common silicone rubber 0.149 0.141 Example 1 1.353 1.682 Example 2 1.365 1.683 Example 3 1.364 1.679 Comparative example 1 1.186 1.226 Comparative example 2 1.152 1.407 Comparative example 3 1.290 1.482

[0115] As can be seen from Table 1 above, applying the graphene nanosheets prepared by the method of the present invention to the silicone rubber material can significantly improve the thermal diffusivity and thermal conductivity of the silica gel.

[0116] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A method for preparing graphene nanosheets by using graphite ball milling of waste lithium battery negative electrode, characterized in that: The steps include: S1. Cut the graphite negative electrode sheet into 1×1 cm negative electrode blocks, immerse them in a low eutectic solvent, heat them in a water bath to 80-90°C, perform ultrasonic treatment for 4-5 hours at a constant temperature, filter them, rinse them with deionized water, and dry them in a drying oven for 24 hours to obtain the preliminarily treated graphite for use; The preparation method of the low eutectic solvent is as follows: stirring a hydrogen bond acceptor and a hydrogen bond donor at a molar ratio of 1:2-4 at 80-100° C. to form a transparent homogeneous liquid; after heating to 120-140° C., adding a functional additive to the transparent homogeneous liquid, and stirring at a constant temperature for 1-2 hours; The added amount of the functional additive is 1~2wt%; The preparation of the functional additive comprises the following steps: (1) Ultrasonic dispersion of nano-silica in anhydrous ethanol, and after uniform ultrasonic dispersion, 10-18% of 3-aminopropyltriethoxysilane by mass of nano-silica is added, and the mixture is stirred at 60-70°C and 100-200 rpm for 3-5 hours to obtain pre-modified nano-silica for use; (2) Tocopherol and succinic anhydride are added into a three-necked flask at a molar ratio of 2-3:1, and then isobutyl acetate is added. After stirring to dissolve, the temperature is raised to 90-100°C, and 0.7-1% of the molar number of tocopherol is added with ethylenediamine. After constant temperature reaction for 2-3 hours, a tocopherol derivative is obtained for use; (3) Add 0.1-0.2 mmol of tocopherol derivative to MES buffer, stir and mix, then add 0.1-0.13 mmol of carbodiimide and 0.15-0.17 mmol of N-hydroxysuccinimide, stir at 200-300 rpm for 20-30 min at room temperature, then add 0.5-1 times of pre-modified nano-silica of tocopherol derivative, continue stirring for 10-12 h, centrifuge at 9000-10000 rpm for 10-15 min, collect the solid, wash with deionized water 3-5 times, place in a vacuum drying oven, and dry at 60-70 °C for 8-12 h; S2, placing the preliminarily treated graphite in a ball milling tank, then adding ball milling media and a stripping agent, and performing ball milling treatment under the protection of an inert gas; S3. The ball-milled product is filtered to obtain a solid residue, which is washed with deionized water until neutral, and then placed in a vacuum drying oven at 60-70°C for drying.

2. A method for preparing graphene nanosheets by using graphite ball milling of the negative electrode of waste lithium batteries according to claim 1, characterized in that: The hydrogen bond acceptor is one or more of choline chloride, betaine, and L-carnitine; The hydrogen bond donor is one or more of citric acid, tartaric acid and proline.

3. A method for preparing graphene nanosheets by using graphite ball milling of the negative electrode of waste lithium batteries according to claim 1, characterized in that: The ball milling medium described in step S2 is a modified zirconia ball; The preparation method of the modified zirconia ball is: 1) 0.1 mol / L CaCl2, 0.05 mol / L sodium dihydrogen phosphate and 0.1 mg / mL mussel adhesion protein were prepared into a mineralization solution, and then zirconium oxide balls were added, stirred at 60-70°C and 200-300 rpm for 8-12 hours, filtered, and then dried to obtain mineralized zirconium oxide balls; 2) The supersonic plasma spraying process is used to spray nano-Al2O3-20% graphene, TiN-15%MoS2, and nano-silicon dioxide onto the surface of the mineralized zirconia ball in sequence. The spraying power is 80kW, the Al2O3-20% graphene spraying thickness is 50~60μm, the TiN-15MoS2 spraying thickness is 30~40μm, and the nano-silicon dioxide spraying thickness is 30~50μm.

4. The method for preparing graphene nanosheets by using graphite ball milling of the negative electrode of waste lithium batteries according to claim 1, characterized in that: The components and corresponding weight percentages of the stripping agent in step S2 are: 1-butyl-3-methylimidazolium tetrafluoroborate 1-2%, 1-ethyl-3-methylimidazolium tetrafluoroborate 1-2%, urea 2-3%, and the balance is sodium dodecylbenzene sulfonate.

5. The method for preparing graphene nanosheets by using graphite ball milling of the negative electrode of waste lithium batteries according to claim 1, characterized in that: The ball milling speed described in step S2 is 200-800 rpm, and the ball milling time is 8-12 h.

6. The method for preparing graphene nanosheets by using graphite ball milling of the negative electrode of waste lithium batteries according to claim 1, characterized in that: The inert gas described in step S2 is nitrogen or argon.

7. Application of the graphene nanosheets prepared by the method according to any one of claims 1 to 6 in silicone rubber modification.