Graphene nanosheet and preparation method thereof

Abstract

The invention discloses a graphene nanosheet and a preparation method thereof, and belongs to the technical field of graphene. The preparation method of the graphene nanosheet comprises the following steps: taking a fluoride salt-containing solution as an electrolyte, and performing electrochemical bipolar stripping on a graphite-containing raw material to obtain the graphene nanosheet. The preparation method disclosed by the invention is simple to operate, safe, controllable, low in cost, high in efficiency, green, environment-friendly and small in corrosion to an electrochemical stripping device.

Description

Technical Field

[0001] The present application relates to a graphene nanosheet and a preparation method thereof, and belongs to the technical field of graphene. Background Art

[0002] Graphene is a sp 2 A material in which hybrid connected carbon atoms are tightly stacked into a single-layer two-dimensional honeycomb lattice structure. Graphene has excellent optical, electrical, and mechanical properties, and has important application prospects in materials science, micro-nano processing, energy, biomedicine, and drug delivery. It is considered to be a revolutionary material in the future. However, it is still a challenge to achieve green, non-toxic, pollution-free, low-cost, large-scale preparation of easy-to-process graphene.

[0003] Electrochemical exfoliation is a new method for preparing graphene developed in recent years. It mainly uses an electric field to drive oppositely charged ions and mixtures to insert into graphite electrodes, expand and exfoliate the graphite interlayers to obtain graphene. The main advantages of this method are: the voltage and current can be precisely adjusted, the graphite exfoliation process is reproducible and operable; the electrolysis is usually carried out at room temperature or near room temperature. Therefore, electrochemical exfoliation of graphene is a promising preparation technology for low-cost large-scale production of high-quality graphene. According to the different exfoliation mechanisms, electrochemical exfoliation of graphene can be divided into electrochemical cathode exfoliation and electrochemical bipolar exfoliation. Since oxygen evolution reaction occurs at the anode during anodic exfoliation, the exfoliated graphene has a certain amount of oxygen-containing functional groups, which enables the graphene to form a well-dispersed graphene dispersion in water or organic solvents such as NMP, DMF, etc. This dispersion is easy to process and can be dried or freeze-dried into powder with good redispersibility, so it can be applied in a wide range of fields.

[0004] At present, most of the electrolytes used for electrochemical exfoliation of graphene are highly soluble sulfates (Carbon 149 (2019) 213e221), halogen salts (ACS Appl. Mater. Interfaces 2017, 9, 24085-24099), organic systems (J. Am. Chem. Soc. 2011, 133, 8888-8891), ionic liquids (Carbon 84 (2015) 449-459) systems, etc. The graphene exfoliated from the sulfate system has a high oxygen content and many defects, which greatly affects the conductivity of the graphene. In addition, the amount of salt used is large and the cost is high. The ionic liquid system also involves high cost issues. The organic system and the halogen system are even more involved. The halogen anions will form a single substance that is separated from the system under a huge cell voltage, resulting in a continuous decrease in the salt content. In addition, most of the reported electrolytes can only achieve single-electrode exfoliation, and cannot fully utilize the anode and cathode.

[0005] Therefore, the development of an inorganic salt aqueous solution system with low cost and no corrosiveness for the preparation of graphene by electrochemical bipolar exfoliation has good application value. Summary of the Invention

[0006] In view of this, the present invention provides a graphene nanosheet and a preparation method thereof. The preparation method includes: using a fluoride salt-containing solution as an electrolyte, and obtaining graphene nanosheets by electrochemically bipolar exfoliating a graphite-containing raw material. The main purpose of this application is to solve the technical problems of corrosiveness, high cost, and many defects of graphene in the electrochemical exfoliation process.

[0007] According to the first aspect of the present application, the present invention provides a method for preparing graphene nanosheets, including: using a fluoride salt-containing solution as an electrolyte, and obtaining graphene nanosheets by electrochemically bipolar exfoliating a graphite-containing raw material.

[0008] The above method of the present invention uses a fluoride salt solution as an electrolyte, which reduces corrosiveness, has low cost, high efficiency, simple operation, and is safe and controllable. The prepared graphene has high quality and high electrochemical performance.

[0009] Optionally, the fluoride salt is selected from at least one of lithium fluoride, potassium fluoride, sodium fluoride, and ammonium fluoride;

[0010] The fluoride salt of the present invention can also be selected from the prior art according to actual needs.

[0011] Optionally, the concentration of the fluoride salt-containing solution is 0.01 - 10 mol / L.

[0012] Optionally, the concentration of the fluoride salt-containing solution is 0.01 - 0.03 mol / L.

[0013] Optionally, the concentration of the fluoride salt-containing solution is 0.03 mol / L - 0.06 mol / L.

[0014] Optionally, the concentration of the fluoride salt-containing solution is 0.06 mol / L - 1 mol / L.

[0015] Optionally, the concentration of the fluoride salt-containing solution is independently selected from any value of 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, 1 mol / L or the range value between any two of the above.

[0016] In the present invention, fluoride salts with different concentrations are used as electrolytes, and the oxygen content, sheet diameter size, and number of layers of the prepared graphene nanosheets are different.

[0017] Optionally, the fluoride salt-containing solution includes water, a fluoride salt, and an organic solvent.

[0018] Optionally, the organic solvent is selected from at least one of ethylene glycol, glycerol and nitriles.

[0019] Optionally, before using the graphite raw material as the electrochemical anode, it is cleaned with deionized water.

[0020] Optionally, the graphite-containing raw material is selected from at least one of microcrystalline graphite, graphite rod, natural flake graphite, graphite paper and graphite foil.

[0021] Optionally, the voltage applied in the electrochemical exfoliation is 2 to 20 V.

[0022] Optionally, the voltage is independently selected from any value of 2 V, 5 V, 8 V, 10 V, 12 V, 15 V, 18 V, 20 V or the range value between any two of the above.

[0023] Optionally, the time of the electrochemical bipolar exfoliation is 5 min to 48 h.

[0024] Optionally, the time of the electrochemical bipolar exfoliation is 0.5 h to 5 h.

[0025] Optionally, the time of the electrochemical bipolar exfoliation is independently selected from any value of 5 min, 20 min, 30 min, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 8 h, 10 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, 48 h or the range value between any two of the above.

[0026] Optionally, the temperature of the electrochemical bipolar exfoliation is 5 to 50 °C.

[0027] Optionally, the temperature of the electrochemical bipolar exfoliation is independently selected from any value of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or the range value between any two of the above.

[0028] In the method of the present invention, the voltage, exfoliation time, temperature, etc. in the electrochemical bipolar exfoliation can all be adjusted according to actual needs.

[0029] Optionally, in the electrochemical exfoliation, both the electrochemical bipolar are graphite-containing raw materials.

[0030] Optionally, the ratio of the area of the electrochemical anode immersed in the electrolyte to the area of the electrochemical cathode immersed in the electrolyte is 0.2 to 12.

[0031] Optionally, the ratio of the area of the electrochemical anode immersed in the electrolyte to the area of the electrochemical cathode immersed in the electrolyte is independently selected from any value among 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12 or the range value between any two of the above.

[0032] Optionally, the horizontal distance between the electrochemical cathode and the electrochemical anode immersed in the electrolyte is 1 - 3 cm.

[0033] Optionally, the distance between the electrochemical cathode and the electrochemical anode is independently selected from any value among 1 cm, 1.1 cm, 1.2 cm, 1.3 cm, 1.4 cm, 1.5 cm, 1.6 cm, 1.7 cm, 1.8 cm, 1.9 cm, 2 cm, 2.1 cm, 2.2 cm, 2.3 cm, 2.4 cm, 2.5 cm, 2.6 cm, 2.7 cm, 2.8 cm, 2.9 cm, 3 cm or the range value between any two of the above.

[0034] Optionally, the method further includes: after electrochemically bipolar stripping the graphite-containing raw material, the stripping product is washed and ultrasonically dispersed to obtain a graphene nanosheet slurry, and the slurry is dried to obtain graphene nanosheets.

[0035] Optionally, the washing method is selected from at least one of dialysis, centrifugation, and suction filtration methods.

[0036] Optionally, the drying method is selected from at least one of natural air drying, atmospheric pressure heating drying, vacuum drying, spray drying, and freeze drying;

[0037] Optionally, the time for ultrasonic dispersion is 1 h - 2 h.

[0038] Optionally, the time for ultrasonic dispersion is independently selected from any value among 1 h, 1.2 h, 1.4 h, 1.5 h, 1.6 h, 1.8 h, 2 h or the range value between any two of the above.

[0039] The present invention provides a specific method for preparing graphene nanosheets by electrochemically bipolar stripping graphite, comprising the following steps:

[0040] Using an aqueous solution containing a fluoride salt as the electrolyte, a raw material containing graphite as the electrochemical anode, and a conductive electrochemically inert material as the electrochemical cathode;

[0041] The electrolyte, the electrochemical anode, and the electrochemical cathode form an electrochemical circuit;

[0042] A voltage is applied between an electrochemical cathode and an electrochemical anode, and graphene nanosheets are prepared by electrochemically bipolar exfoliating graphite.

[0043] The method for preparing graphene nanosheets by electrochemically bipolar exfoliating graphite according to the present invention is realized through the following steps: First, a soluble fluoride salt is used as the exfoliating electrolyte, and graphite is used as the raw material to connect the positive and negative electrodes of a DC power supply. Under normal temperature and pressure conditions, a suitable cell voltage is selected for electrochemical exfoliation. The exfoliated product is washed and ultrasonically dispersed to obtain a graphene nanosheet slurry, and then dried to obtain graphene nanosheet powder.

[0044] In the present invention, "room temperature" refers to 10 - 45 °C.

[0045] In a second aspect, the present invention provides a graphene nanosheet, which is prepared by the above preparation method.

[0046] Optionally, the size of the graphene nanosheet is 0.5 - 200 μm.

[0047] Optionally, the number of layers of the graphene nanosheet is 1 - 7 layers.

[0048] The beneficial effects that can be produced by this application include:

[0049] 1) The present invention provides a new method for preparing graphene nanosheets by electrochemically bipolar exfoliating graphite. Using a fluoride salt as the electrolyte, graphene nanosheets are successfully prepared.

[0050] 2) The method for preparing graphene nanosheets by electrochemically bipolar exfoliating graphite provided by the present invention is simple to operate, safe and controllable, low-cost and high-efficiency.

[0051] 3) The present invention is relatively more environmentally friendly, has little corrosion to the electrochemical exfoliation device, uses a soluble fluoride salt as the electrolyte, and synthesizes graphene nanosheets in one step by the method of electrochemically bipolar exfoliating graphite. Description of the Drawings

[0052] Figure 1 It is a slurry diagram of the graphene nanosheets prepared in Example 1 of the present invention;

[0053] Figure 2 It is a scanning electron microscope diagram of the graphene nanosheets prepared in Example 1 of the present invention;

[0054] Figure 3 It is a transmission electron microscope diagram of the graphene nanosheets prepared in Example 1 of the present invention;

[0055] Figure 4 It is an atomic force microscopy analysis diagram of the chemically modified graphene nanosheets prepared in Example 1 of the present invention;

[0056] Figure 5 It is the atomic force microscopy height distribution diagram of few-layer graphene nanosheets prepared in Example 1 of the present invention. Detailed implementation manners

[0057] The present application will be further elaborated below in combination with specific embodiments. The following descriptions are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as follows, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0058] Unless otherwise specified, the raw materials in the embodiments of the present application are purchased through commercial channels and used directly without any special treatment.

[0059] The analysis methods in the embodiments of the present application are as follows:

[0060] SEM analysis is carried out using a Quanta-200F scanning electron microscope.

[0061] TEM analysis is carried out using an HT-7700 transmission electron microscope.

[0062] AFM analysis is carried out using a NanoWizard atomic force microscope.

[0063] Example 1

[0064] Take 100 mL of sodium fluoride solution with a concentration of 0.8 mol / L and put it into a 250 mL beaker. Use expanded graphite paper as the graphite anode respectively, and connect them to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes parallel to each other with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and exfoliate at room temperature for 1 h. A small amount of bubbles are generated at the bottom end face of the cathode, and a very small amount of bubbles are generated in the anode region. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously exfoliated from the bottom end face of the anode. As the electrolysis process proceeds, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 mL of ethanol for dispersion, and disperse it ultrasonically with a power of 100 W for 1 h to obtain graphene slurry, denoted as sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black, drop it onto a flat mica sheet, observe it with an atomic force microscope after drying with an infrared lamp, and drop the graphene slurry with the same concentration onto a copper grid for scanning electron microscope and transmission electron microscope tests.

[0065] Example 2

[0066] Take 100 mL of sodium fluoride solution with a concentration of 1 mol / L and put it into a 250 mL beaker. Use expanded graphite paper as the graphite anode respectively, and connect them to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes parallel to each other with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and exfoliate at room temperature for 1 h. A small amount of bubbles are generated at the bottom end face of the cathode, and a very small amount of bubbles are generated in the anode region. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously exfoliated from the bottom end face of the anode. As the electrolysis process proceeds, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 mL of ethanol for dispersion, and disperse it ultrasonically with a power of 100 W for 1 h to obtain graphene slurry, denoted as sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black, drop it onto a flat mica sheet, observe it with an atomic force microscope after drying with an infrared lamp, and drop the graphene slurry with the same concentration onto a copper grid for scanning electron microscope and transmission electron microscope tests.

[0067] Example 3

[0068] Take 100 mL of sodium fluoride solution with a concentration of 0.5 mol / L and place it in a 250 ml beaker. Use expanded graphite paper as the graphite anode respectively, and connect it to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the upper liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes in parallel with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and strip for 1 h at room temperature. A small amount of bubbles are generated at the bottom end face of the cathode, and an extremely small amount of bubbles are generated in the anode area. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously peeled off from the bottom end face of the anode. As the electrolysis process proceeds, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 ml of ethanol for dispersion, and disperse it ultrasonically at a power of 100 W for 1 hour to obtain graphene slurry, denoted as sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black and drop it on a flat mica sheet. Observe it with an atomic force microscope after drying with an infrared lamp. Drop the graphene slurry with the same concentration on a copper grid for scanning electron microscope and transmission electron microscope tests.

[0069] Example 4

[0070] Take 100 mL of sodium fluoride solution with a concentration of 0.3 mol / L and place it in a 250 mL beaker. Use expanded graphite paper as the graphite anode respectively, and connect them to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the upper liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes parallel to each other with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and exfoliate at room temperature for 1 h. A small amount of bubbles are generated at the bottom end face of the cathode, and an extremely small amount of bubbles are generated in the anode area. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously exfoliated from the bottom end face of the anode. As the electrolysis process proceeds, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 mL of ethanol for dispersion, and disperse it ultrasonically with a power of 100 W for 1 h to obtain graphene slurry, denoted as sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black, drop it on a flat mica sheet, dry it with an infrared lamp, and then observe it with an atomic force microscope. Drop the graphene slurry with the same concentration on a copper grid for scanning electron microscope and transmission electron microscope tests.

[0071] Example 5

[0072] Take 100 mL of sodium fluoride solution with a concentration of 0.1 mol / L and place it in a 250 mL beaker. Use expanded graphite paper as the graphite anode respectively, and connect them to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the upper liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes parallel to each other with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and exfoliate at room temperature for 1 h. A small amount of bubbles are generated at the bottom end face of the cathode, and an extremely small amount of bubbles are generated in the anode area. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously exfoliated from the bottom end face of the anode. As the electrolysis process proceeds, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 mL of ethanol for dispersion, and disperse it ultrasonically with a power of 100 W for 1 h to obtain graphene slurry, denoted as sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black, drop it on a flat mica sheet, dry it with an infrared lamp, and then observe it with an atomic force microscope. Drop the graphene slurry with the same concentration on a copper grid for scanning electron microscope and transmission electron microscope tests.

[0073] Example 6

[0074] Take 100 mL of a sodium fluoride solution with a concentration of 0.2 mol / L and put it into a 250 ml beaker. Use expanded graphite paper as the graphite anode respectively, and connect it to a DC power supply at the same time. Immerse the bottom end face of the above graphite anode vertically at the upper liquid level of sodium fluoride. Immerse the cathode completely below the interface of the sodium fluoride solution, so that the area ratio of the anode and cathode immersed in the electrolyte solution is 1. Place the two electrodes parallel to each other with a spacing of 1 cm. Turn on the DC power supply, control the constant voltage at 10 V, and strip at room temperature for 1 h. A small amount of bubbles are generated at the bottom end face of the cathode, and an extremely small amount of bubbles are generated in the anode region. The bubbles are discharged vertically upward from the system. Under the combined action of interfacial tension, intercalation, and electrochemical force, a large amount of graphene is continuously peeled off from the bottom end face of the anode. As the electrolysis process progresses, the bottom end face of the graphite anode is continuously consumed and floats on the surface of the electrolyte solution. Finally, a mixed system of graphene and sodium fluoride solution is obtained. Filter the above system with deionized water and wash it thoroughly, then add 100 ml of ethanol for dispersion, and disperse it with ultrasound at a power of 100 W for 1 hour to obtain graphene slurry, denoted as Sample 1. Air-dry the above graphene slurry at normal temperature and pressure to obtain graphene powder. Dilute the above-obtained graphene slurry to light black and drop it onto a flat mica sheet. After drying with an infrared lamp, observe it with an atomic force microscope. Drop the graphene slurry with the same concentration onto a copper grid for scanning electron microscope and transmission electron microscope tests.

[0075] Test Example 1 Morphology Characterization

[0076] Sample 1 is in the form of a slurry, as Figure 1 shown; the slurries of other samples are all Figure 1 similar.

[0077] The SEM image of Sample 1 is as Figure 2 shown; Figure 2 it shows that the size range of graphene nanosheets is 1 - 100 μm. The SEM images of other samples are all Figure 2 similar.

[0078] The TEM image of Sample 1 is as Figure 3 shown; Figure 3 it shows that only slight stacking exists in individual graphene nanosheet layers, and the exfoliation of graphene nanosheets is achieved through the electrochemical cathode. The TEM images of other samples are all Figure 3 similar.

[0079] The atomic force microscopy analysis image of few-layer graphene in Sample 1 is as Figure 4 shown, Figure 4 it shows that there are single-layer or few-layer graphene nanosheets in Sample 1.

[0080] The atomic force microscopy height distribution map of few-layer graphene of Sample 1 is as follows Figure 5 shown Figure 5 indicating that there are single-layer or few-layer graphene nanosheets in the graphene nanosheets of Sample 1.

[0081] Through the above detections, the morphology and electrical properties of the graphene material prepared by electrochemically exfoliating with a fluoride salt solution as the electrolyte in the present invention can meet the usage requirements.

[0082] The above are only several embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed with preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing graphene nanosheets, characterized in that, The preparation method includes: using a fluoride salt-containing solution as an electrolyte, and obtaining graphene nanosheets by electrochemically bipolar stripping a graphite-containing raw material.

2. The preparation method according to claim 1, characterized in that, The fluoride salt is selected from at least one of lithium fluoride, potassium fluoride, sodium fluoride, and ammonium fluoride.

3. The preparation method according to claim 1, characterized in that, The concentration of the fluoride salt-containing solution is 0.01 - 10 mol / L.

4. The preparation method according to claim 1, characterized in that, The fluoride salt-containing solution includes water, a fluoride salt, and an organic solvent; the organic solvent is selected from at least one of ethylene glycol, glycerol, and nitriles.

5. The preparation method according to claim 1, characterized in that, The voltage applied in the electrochemically bipolar stripping is 2 - 20 V.

6. The preparation method according to claim 1, characterized in that, The time of the electrochemically bipolar stripping is 5 min - 48 h; the temperature of the electrochemically bipolar stripping is 5 - 50 °C.

7. The preparation method according to claim 1, characterized in that, In the electrochemically bipolar stripping, both the electrochemically bipolar are the graphite-containing raw material; Preferably, the graphite-containing raw material is selected from at least one of microcrystalline graphite, graphite rod, natural flake graphite, graphite paper, and graphite foil.

8. The preparation method according to claim 1, characterized in that, In the electrochemically bipolar stripping, the ratio of the area of the electrochemically anodic immersed in the electrolyte to the area of the electrochemically cathodic immersed in the electrolyte is 0.2 - 12; Preferably, the horizontal distance between the electrochemically cathodic and the electrochemically anodic immersed in the electrolyte is 1 - 3 cm; Preferably, the preparation method further includes: after electrochemically bipolar stripping the graphite-containing raw material, the stripping product is washed and ultrasonically dispersed to obtain a graphene nanosheet slurry, and the slurry is dried to obtain graphene nanosheets.

9. A graphene nanosheet, characterized in that, The graphene nanosheets are prepared by the preparation method according to any one of claims 1 - 8.

10. The graphene nanosheet according to claim 9, characterized in that, The size of the graphene nanosheets is 0.5 - 200 μm; The number of layers of the graphene nanosheets is 1 - 7 layers.

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