CN115709989A - Method for preparing graphene through large-scale self-adaptive electrochemical stripping, graphene and thermal management film - Google Patents
Method for preparing graphene through large-scale self-adaptive electrochemical stripping, graphene and thermal management film Download PDFInfo
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Abstract
The invention provides a method for preparing graphene through large-scale self-adaptive electrochemical stripping, the graphene and a thermal management film, and relates to the technical field of nano carbon materials. The method comprises the steps of making indentations on the surface of graphite or increasing the surface roughness, cutting the graphite, and increasing ion intercalation sites through preprocessing; the method has the advantages that the step of pre-intercalation is arranged in the electrolytic stripping link, the ion concentration near the graphite electrode is increased, and the ion intercalation channel is gradually opened, so that the intercalation efficiency can be effectively improved; the invention introduces a voltage/current feedback regulation mechanism in the electrolytic stripping process, detects and feeds back current density, dynamically and adaptively regulates voltage, effectively controls electrolytic voltage and current density, and ensures that intercalation is sequentially carried out from bottom to top, thereby avoiding the defects of integral intercalation and easy electrode stripping of the traditional electrolytic process. The method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of stripping electrochemical parameters, good stripping effect and high quality of the obtained graphene.
Description
Technical Field
The invention relates to the technical field of nano carbon materials, in particular to a method for preparing graphene through large-scale self-adaptive electrochemical stripping, the graphene and a thermal management film.
Background
Graphene (Graphene) is prepared from sp 2 Two-dimensional planar crystals with honeycomb hexagonal structures, which are formed by hybridized carbon atoms. Due to the unique structural characteristics of the graphene, the graphene has excellent physical, chemical and mechanical properties and the like, and has good application prospects in the fields of lithium ion batteries, supercapacitors, heat management materials, electric heating films, functional protective coatings, heterogeneous catalyst carriers and the like. The preparation method of graphene has great influence on the quality and performance of graphene, and a low-cost, high-quality and large-batch preparation technology is the key for the graphene to enter the market and be widely applied. There are many existing methods for preparing graphene, including mechanical graphite stripping, liquid phase stripping, chemical vapor deposition, epitaxial growth, and electrochemical methods. Among them, the electrochemical method is receiving more and more attention due to its advantages of low cost, simple operation, environmental friendliness, mild conditions, and recyclable electrolyte.
Although the chinese patents CN111217361A and CN107954420A use electrochemical method, the electrolyte component mainly uses water system, which results in that the working voltage should not exceed the hydrolysis potential (1.23V) too much, otherwise the generated hydrogen would cause explosion hazard and the efficiency of electrolytic intercalation would be reduced. Although the chinese patents CN102530930A, CN103693638A, etc. introduce organic solvents to improve electrolytic voltage, stripping efficiency in the electrolytic stripping process is low, and electrolytic voltage and current density are not effectively controlled in the electrolytic process, so that the electrolytic stripping effect is difficult to be accurately controlled; in addition, the intercalation position in the graphite intercalation cannot be accurately regulated, i.e. the intercalation process is performed on the whole electrode, and thus incomplete exfoliation may be caused.
Disclosure of Invention
In view of this, the present invention aims to provide a method for preparing graphene by scale adaptive electrochemical stripping, graphene and a thermal management film. The method provided by the invention has the advantages of high stripping efficiency, good stripping effect and high quality of the obtained graphene.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for preparing graphene through large-scale self-adaptive electrochemical stripping, which comprises the following steps:
making indentation on the surface of the sheet or film graphite or increasing the surface roughness, fixing the sheet or film graphite on a metal fixture, and cutting the treated graphite along one end of the unfixed metal fixture to form a graphite preprocessing structure with an integral upper end and a dispersed lower end;
the graphite preprocessing structure is respectively used as a positive electrode and a negative electrode to form a graphite electrode system; connecting a plurality of graphite electrode systems in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte and electrifying to carry out pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and an inorganic salt;
carrying out electrolytic stripping on the pre-intercalation electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and voltage/current signal feedback is arranged in the electrolytic circuit for electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, the voltage value is dynamically and adaptively adjusted according to the monitored current density, and the current density is kept stable at a preset value.
Preferably, the graphite comprises one or more of artificial graphite, highly oriented pyrolytic graphite, natural flake graphite and microcrystalline graphite; the thickness of the graphite is 0.001-3 mm.
Preferably, the dispersion shape is a regular shape or an irregular shape; the cutting length is 1/10-4/5 of the whole length of the graphite, and the cutting width is 3-20 mm.
Preferably, the number of graphite electrode systems in the graphite array electrode is greater than or equal to 1.
Preferably, in the pre-intercalation, the depth of the graphite array electrode inserted into the electrolyte is not greater than the overall height of graphite in the graphite array electrode4/5 of (1); the voltage of the pre-intercalation is 0.5-5V, and the current density is 0.05-0.5 mAcm -1 (ii) a The time of the pre-intercalation is 12 to 36 hours.
Preferably, in the electrolytic stripping, the depth of the graphite array electrode inserted into the electrolyte is not more than 1/4 of the overall height of graphite in the graphite array electrode; the preset voltage of the electrolytic stripping is 3.5-15V, and the preset current density is 0.5-3.0 mAcm -1 。
Preferably, the positive electrode and the negative electrode are exchanged at intervals of 12-72 h in the electrolytic stripping process.
Preferably, (a) when the voltage/current signal feedback detects that the current density is reduced to 80% of the preset current density in the electrolytic stripping process, the voltage is increased adaptively to restore the current density to the preset current density;
(b) When the current density can not be recovered to the preset current density after the voltage in the step (a) is increased to 15V, feeding back the voltage/current signal to automatically supplement the electrolyte until the current density is recovered to the preset current density, and then continuously carrying out electrolytic stripping; the electrolytic stripping process is carried out according to the operation (a);
and (c) circularly performing the operations (a) to (b), and ending the electrolytic stripping when the current density cannot be recovered to the preset current density after the electrolyte is replenished to the depth of immersing the graphite array electrode to 4/5 of the overall height of the graphite in the graphite array electrode.
The invention provides the graphene prepared by the preparation method in the technical scheme; the graphene has a transverse dimension of 1-50 μm and a thickness of 0.5-10 nm.
The invention also provides a heat management film, and the preparation raw material comprises the graphene in the technical scheme.
The invention provides a method for preparing graphene by large-scale self-adaptive electrochemical stripping, which is characterized in that indentation is made on the surface of graphite or the surface roughness is increased, and the graphite is cut, wherein the graphite preprocessing mode can increase intercalation sites of ions on a graphite electrode; the method has the advantages that the step of pre-intercalation is arranged in the electrolytic stripping link, the ion concentration near the graphite electrode is increased, and the ion intercalation channel is gradually opened, so that the intercalation efficiency can be effectively improved; because the dynamic process of inserting the solvated ions into the graphite flake layers exists in the electrolytic intercalation and stripping processes, the resistance value of the graphite electrode is in dynamic change, a voltage/current feedback regulation mechanism is also introduced in the electrolytic stripping process, the current density is detected and fed back, the voltage is dynamically and adaptively regulated, the electrolytic voltage and the current density can be effectively controlled, the intercalation sequence is carried out from bottom to top, and the defects of integral intercalation and easy falling of the electrode in the traditional electrolytic process are avoided. The preparation method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of stripping electrochemical parameters, good stripping effect, high quality of the obtained graphene, and realization of modular design and large-scale production.
The invention provides graphene prepared by the preparation method in the technical scheme. In the invention, the graphene has low defect content, excellent intrinsic properties (electric conduction and heat conduction) and high quality.
The invention also provides a thermal management film, and the preparation raw material comprises the graphene in the technical scheme. The heat management film provided by the invention has excellent heat conduction performance. The example result shows that the transverse dimension of the graphene is 1-50 mu m, the thickness of the graphene is 0.5-10 nm, and the density of the thermal management film is 0.8-2.0 g-cm -3 Coefficient of thermal diffusion>300mm 2 /s。
Drawings
Fig. 1 is a schematic diagram of a graphite preprocessing structure in an embodiment of the present invention, in fig. 1, L is an overall length of graphite, L is a cutting length, and d is a cutting width;
FIG. 2 is a logic diagram of an adaptive feedback system for voltage/current signals in electrochemically exfoliated graphene according to the present invention;
fig. 3 is an optical photograph of the graphene thin film prepared in example 1;
fig. 4 is an optical photograph and a scanning electron micrograph of the graphene paste obtained in example 2, the left side of fig. 4 is an optical photograph, and the right side is a scanning electron micrograph.
Detailed Description
The invention provides a method for preparing graphene through large-scale self-adaptive electrochemical stripping, which comprises the following steps:
making an indentation on the surface of the flake or film graphite or increasing the surface roughness and then fixing the flake or film graphite on a metal clamp, and cutting the treated graphite along one end of the unfixed metal clamp to form a graphite preprocessing structure with an integral upper end and a dispersed lower end;
the graphite preprocessing structure is respectively used as a positive electrode and a negative electrode to form a graphite electrode system; connecting a plurality of graphite electrode systems in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte and electrifying to carry out pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and an inorganic salt;
carrying out electrolytic stripping on the pre-intercalation electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and voltage/current signal feedback is arranged in the electrolytic circuit for electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, the voltage value is dynamically and adaptively adjusted according to the monitored current density, and the current density is kept stable at a preset value.
In the present invention, unless otherwise specified, all the starting materials are commercially available or prepared by methods known to those skilled in the art.
The invention makes indentation on the surface of flake or film graphite or increases the surface roughness, then fixes it on the metal fixture, cuts the processed graphite along one end of the unfixed metal fixture, forms the graphite preprocessing structure with integral upper end and dispersed lower end. In the invention, the graphite preferably comprises one or more of artificial graphite, highly oriented pyrolytic graphite, natural flake graphite and microcrystalline graphite; the thickness of the graphite is preferably 0.001 to 3mm, more preferably 0.2 to 1.5mm. The invention has no special requirements on the manufacturing method of the indentation, and can form the indentation; the invention has no special requirements on the shape of the indentation, and can be straight lines, broken lines, wavy lines and the like; the invention has no special requirement on the depth of the indentation and ensures that the graphite electrode is not easy to fall off in the electrolytic stripping process. In the embodiment of the invention, the surface of the graphite is pressed by using a concave-convex pressing plate, so that sunken zigzag pattern indentations are formed on the surface of the graphite, and the depth of the indentations on one side surface of the graphite is 7-10% of the thickness of the graphite. The method for increasing the surface roughness has no special requirement, any method capable of increasing the surface roughness can be adopted, and in the embodiment of the invention, the graphite surface is repeatedly pasted by using the adhesive tape, so that the roughness mark appears on the graphite surface. The metal clamp of the present invention has no special requirement, and may be made of metal clamps known to those skilled in the art, such as stainless steel or titanium alloy metal clamps. In the present invention, the dispersion shape may be a regular shape, such as a rectangle, or an irregular shape, such as a zigzag shape. In the present invention, the length of the cutting (in the embodiment of the present invention, the cutting is also referred to as cutting) is preferably 1/10 to 4/5, more preferably 1/2 to 4/5 of the entire length of the graphite, and the width of the cutting is preferably 3 to 20mm, more preferably 3 to 10mm.
The invention makes indentation or increase surface roughness on the surface of the flake or film graphite, provides a defect channel for the intercalation ions to enter initially, and cuts the lower end of the graphite, and the combined action of the indentation and the surface roughness can effectively increase the ion intercalation sites. Fig. 1 is a schematic diagram of a graphite preprocessing structure in an embodiment of the present invention, in fig. 1, L is an overall length of graphite, L is a cutting length, and d is a cutting width.
After the graphite preprocessing structure is obtained, the graphite preprocessing structure is respectively used as an anode and a cathode to form a graphite electrode system; and connecting a plurality of graphite electrode systems in parallel to form the graphite array electrode. In the invention, the number of graphite electrode systems in the graphite array electrode is preferably more than or equal to 1, and the graphite electrode systems are adaptively set according to the specification of an electrolytic cell and the size of a power supply; when the number of the graphite electrode systems in the graphite array electrode is more than 1, the interval between the adjacent graphite electrode systems is preferably 5-25 mm, and more preferably 15mm. The graphite preprocessing structure is assembled into the graphite array electrode, so that large-scale efficient intercalation of the electrode is facilitated, and expansion of preparation scale is facilitated.
After obtaining the graphite array electrode, the graphite array electrode is inserted into electrolyte and electrified for pre-intercalation, and the pre-intercalation electrode is obtained. In the present invention, the electrolyte preferably includes an organic solvent, water, and an inorganic salt; the organic solvent preferably comprises one or more of dimethyl sulfoxide, propylene carbonate, dimethyl carbonate, ethylene glycol dimethyl ether, acetonitrile, diethyl carbonate, butyrolactone and methyl ethyl carbonate, and more preferably comprises one or more of dimethyl sulfoxide, propylene carbonate, ethylene carbonate, acetonitrile and dimethyl carbonate; the inorganic salt preferably comprises one or more of perchlorate, sulfate, chlorate, chloride, borate and quaternary ammonium salt, more preferably one or more of perchlorate, borate and chloride, and the metal element in the inorganic salt is preferably potassium or lithium; the mass ratio of the organic solvent to water is preferably 2.5 to 10, more preferably 10; the mass of the inorganic salt is preferably 0.5-a% of the mass of water, wherein the a% is the mass percentage of the inorganic salt in the water when the inorganic salt is saturated in the water. The preparation method of the electrolyte has no special requirements, and all the components are uniformly mixed. In the invention, in the pre-intercalation, the depth of the graphite array electrode inserted into the electrolyte is preferably not more than 4/5 of the overall height of graphite in the graphite array electrode, and more preferably 1/3-4/5; the voltage of the pre-intercalation is preferably 0.5-5V, more preferably 3-5V, and the current density is preferably 0.05-0.5 mAcm -1 More preferably 0.1 to 0.5mAcm -1 More preferably 0.2mAcm -1 (ii) a The time of the pre-intercalation is preferably 12 to 36 hours, and more preferably 24 to 36 hours. In the pre-intercalation process, the graphite array electrode is fully soaked into electrolyte, and intercalation ions (cation complexes formed by inorganic salt dissolved in the electrolyte and organic solvent) start to attack the graphite electrode which is pressed and indented or has increased surface roughnessThe process of opening the intercalation channels is relatively slow and the invention, in order to better build up the channels, cannot control the insertion process too vigorously and therefore the voltage and current density are controlled at a lower level. The invention can effectively improve the intercalation efficiency by adding the pre-intercalation link.
After obtaining a pre-intercalation electrode, carrying out electrolytic stripping on the pre-intercalation electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and voltage/current signal feedback is arranged in the electrolytic circuit for electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, the voltage value is dynamically and adaptively adjusted according to the monitored current density, and the current density is kept stable at a preset value. In the electrolytic exfoliation, the depth of insertion of the graphite array electrode into the electrolyte is preferably not more than 1/4, more preferably 1/5 to 1/4, of the overall height of graphite in the graphite array electrode. If the graphite array electrode is completely inserted into the electrolyte, or the liquid level of the electrolyte is too high at first, so that the intercalation can not be ensured to be carried out from the lower part of the electrode and from bottom to top. In the present invention, the preset voltage for the electrolytic stripping is preferably 3.5 to 15V, more preferably 7 to 12V, and the preset current density is preferably 0.5 to 3.0mAcm -1 More preferably 0.5 to 2mAcm -1 . In the electrolytic stripping process, the anode and the cathode are exchanged at intervals of 12-72 h, so that the intercalation of the electrodes on both sides is ensured, and the yield is improved. In the invention, (a) when the voltage/current signal feedback detects that the current density is reduced to 80% of the preset current density in the electrolytic stripping process, the voltage is preferably adaptively increased to restore the current density to the preset current density, and in the actual operation process, the current density is ensured to be restored to the deviation range of +/-5% of the preset current density; (b) When the current density can not be recovered to the preset current density after the voltage in (a) is increased to 15V, the voltage/current signal feedback automatically supplementsThe electrolyte is charged until the current density is recovered to the preset current density, and then electrolytic stripping is continuously carried out; the electrolytic stripping process is carried out according to the operation (a). And (c) circularly performing the operations (a) to (b), and ending the electrolytic stripping when the current density cannot be recovered to the preset current density after the electrolyte is replenished to the depth of immersing the graphite array electrode to be 4/5 of the overall height of graphite in the graphite array electrode. Fig. 2 is a logic diagram of a voltage/current signal adaptive feedback system in electrochemically exfoliated graphene according to the present invention.
After the electrolytic stripping is finished, the invention also preferably carries out post-treatment on the obtained stripping product system, and the post-treatment method is preferably as follows: and filtering the obtained stripped crude product to remove the product which is not completely stripped, and sequentially performing alkali washing, acid washing and water washing on the obtained filtered product to obtain a purified product. The method of filtration is not particularly critical to the present invention and filtration methods known to those skilled in the art, such as, in particular, bag or plate filtration, may be used. In the invention, the alkaline reagent used for alkaline cleaning is preferably a sodium hydroxide solution or a potassium hydroxide solution, the concentration of the sodium hydroxide solution or the potassium hydroxide solution is preferably 3 mol/L-bmol/L, wherein bmol/L is the saturated concentration of the sodium hydroxide solution or the potassium hydroxide solution; the acid reagent used for acid washing is preferably sulfuric acid or hydrochloric acid, and the concentration of the sulfuric acid or hydrochloric acid is preferably 0.5-3 mol/L. In the present invention, the water washing is performed until the slurry supernatant is a neutral solution. After the washing, the obtained washing product is preferably dispersed in a dispersion liquid and subjected to ultrasonic treatment to obtain graphene slurry. In the present invention, the dispersion preferably includes one or more of water, ethanol, and isopropanol; the power of ultrasonic treatment is preferably 80-1000W, and the temperature of ultrasonic treatment is preferably not higher than 60 ℃; the ultrasonic treatment preferably adopts an intermittent working mode, the working time is 15-60 min, the interval time is 15-60 min, and the effective ultrasonic time is not less than 300min. In the present invention, the solid content of the graphene slurry is preferably 0.1 to 20wt%. After the graphene slurry is obtained, the graphene slurry can be dried to obtain graphene powder; the drying method is preferably oven drying, freeze drying, spray drying or evaporation drying. In the present invention, the graphene may be present in the form of a graphene slurry or in the form of a graphene powder, which is not particularly required in the present invention.
The preparation method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of stripping electrochemical parameters and good stripping effect, and can realize modular design (each electrolytic tank is used as a preparation module, and the yield can be enlarged by increasing the electrolytic tanks) and large-scale production.
The invention provides graphene prepared by the preparation method in the technical scheme. In the invention, the graphene has low defect content, excellent intrinsic property and high quality; the graphene has a transverse dimension of 1-50 μm and a thickness of 0.5-10 nm.
The invention also provides a thermal management film, and the preparation raw material comprises the graphene in the technical scheme. In the present invention, the preparation method of the thermal management film is preferably: and sequentially emulsifying, homogenizing, forming a film and carrying out heat treatment on the graphene slurry to obtain the thermal management film. When the thermal management film is prepared, the solid content of the graphene slurry is further preferably 1-20 wt%, and when the solid content of the graphene slurry is smaller than the range, the graphene slurry can be concentrated to the range and then emulsified and homogenized. In the invention, the emulsification homogenization is specifically shear emulsification, the shear rate of the shear emulsification is preferably 300-3000 r/min, the shear direction is consistent, and the direction cannot be changed. In the invention, the film forming mode can be blade coating film forming, spray film forming, self-leveling film forming, flow casting film forming or suction filtration film forming. In the present invention, the temperature of the heat treatment is preferably 1000 to 3000 ℃; in the embodiment of the invention, the heat treatment comprises carbonization and graphitization which are sequentially carried out, wherein the carbonization temperature is preferably 1200-1500 ℃, the time is preferably 60-180 min, the graphitization temperature is preferably 2000-2500 ℃, and the time is preferably 10-90 min; the heat treatment is preferably performed in an inert atmosphere. According to the invention, non-carbon components (at high temperature) such as electrolyte, acid-base washing liquid and the like remained in the electrolytic stripping process are removed through the heat treatmentDecomposed into gas exhaust); and repair the structural defect that causes graphene in the intercalation process, provide its transport properties (carbon atom migration repair lattice in-plane defect at high temperature); in addition, the film density can be improved, and the heat dissipation capacity and the mechanical property of the macro film can be enhanced. After the heat treatment, the film obtained is preferably subjected to a rolling treatment in the present invention, and the rolling treatment method is not particularly required in the present invention, and a rolling method well known to those skilled in the art may be used. In the present invention, the thickness of the heat management film is preferably 1 to 100. Mu.m, and the density is preferably 0.8 to 2.0 g/cm -3 The thermal conductivity is preferably 200 to 1500W/mK. The heat management film provided by the invention has excellent heat conduction performance.
The method for preparing graphene by scale-up adaptive electrochemical exfoliation, graphene and thermal management thin film provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Taking natural graphite paper with the thickness of 1mm as a raw material, and pressing the surface of the natural graphite paper by using a concave-convex pressing plate to enable the surface of the natural graphite paper to have concave patterns; the graphite electrode is fixed on a stainless steel strip electrode by using screws, the lower part of the graphite electrode is cut, the cut shape is a rectangular strip, the length of the cut strip is 4/5 of the length of the graphite paper electrode, and the width of the cut strip is 3mm.
The electrolyte comprises the components of a mixture of propylene carbonate, lithium perchlorate and deionized water, and the mass ratio of the propylene carbonate to the lithium perchlorate to the deionized water is 10:0.5:1; inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 1/3 of the overall height of the electrode, the voltage is 5V, and the current density is 0.1mAcm -1 Pre-intercalation for 12h under parameters; adjusting the electrolyte level to make the depth of the graphite electrode inserted into the electrolyte be 1/5 of the overall height of the electrode, and increasing the voltage and current density to 10V and 0.5mAcm respectively -1 After the parameter intercalation is kept for 12h, the electrode direction is changed, the intercalation is continued, the steps are repeated, and the voltage and the current density are adaptively adjusted. When the current value in the electrolytic circuit is reduced to 80% of the preset current density value, the voltage is increased to maintain the current density value within the range of +/-5% of the preset value, and the voltage value is continuously increasedAnd under the condition that the current density can not be maintained after 15V, automatically injecting the electrolyte, and stopping injecting after the current density is recovered to a set value. And repeating the voltage boosting and electrolyte injection until the current density value cannot be raised to a set value after the electrolyte is supplemented to the depth of the immersed graphite electrode which is 4/5 of the original height of the graphite electrode, and finishing the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripped product and electrolyte by using a filter bag, carrying out alkali washing, acid washing and water washing on the obtained slurry product by using a potassium hydroxide solution with the concentration of 6mol/L, a hydrochloric acid solution with the concentration of 1mol/L and deionized water respectively, and washing until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a dilute slurry with the solid content of 1wt%, and performing effective ultrasonic treatment for 6 hours at 500W to obtain graphene slurry, wherein the transverse size interval of graphene is 1-50 mu m, and the thickness of the graphene is 0.5-5 nm.
Concentrating the graphene slurry to obtain slurry with solid content of 3wt%, shearing and emulsifying to obtain homogeneous slurry, and blade-coating to form a film with the film thickness of 20 μm; then carbonizing at 1500 ℃ for 1h and graphitizing at 2000 ℃ for 30min, and calendering to obtain the graphene heat dissipation film with thermal diffusion coefficient>700mm 2 The density of the graphene film is 1.0 +/-0.2 g/cm 3 . Fig. 3 is an optical photograph of the graphene thin film prepared in example 1, and it can be seen that the material of the film is uniform.
Example 2
Taking a highly oriented pyrolytic graphite film with the thickness of 0.5mm as a raw material, and repeatedly sticking the surface of the highly oriented pyrolytic graphite film by using an adhesive tape to enable the surface of the highly oriented pyrolytic graphite film to have rough marks; the graphite film is clamped between two titanium plates to be used as a working electrode, the lower part of the graphite electrode is cut, the cutting shape is zigzag, the length of the cutting shape is 3/5 of the length of the graphite paper electrode, and the width of the cutting shape is 10mm.
The electrolyte comprises the mixture of dimethyl carbonate, potassium perchlorate and deionized water, and the weight ratio of the dimethyl carbonate to the potassium perchlorate to the deionized water is 10:1:2; inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 1/2 of the overall height of the electrode, the voltage is 3V, and the current density is 0.5mAcm -1 Pre-intercalation for 24 hours under the parameters; adjusting the liquid level of the electrolyte to ensure that the depth of the graphite electrode inserted into the electrolyte is 1/4 of the overall height of the electrodeIncreasing the voltage and the current density to 12V and 1mAcm -1 After the parameter intercalation is maintained for 24 hours, the electrode direction is changed, the intercalation is continued, the steps are repeated, and the voltage and the current density are adaptively adjusted. When the current value in the electrolytic circuit is reduced to 80% of the preset current density value, the voltage is increased to maintain the current density value within the range of +/-5% of the preset value; and under the condition that the current density can not be maintained after the voltage value is continuously increased to 15V, automatically injecting the electrolyte, and stopping injecting after the current density is recovered to a set value. And repeating the voltage boosting and electrolyte injection until the current density value cannot be raised to a set value after the electrolyte is supplemented to the depth of the immersed graphite electrode which is 4/5 of the original height of the graphite electrode, and finishing the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripped product and electrolyte by using a filter bag, respectively carrying out alkali washing, acid washing and water washing on the obtained slurry product by using a sodium hydroxide solution with the concentration of 3mol/L, a sulfuric acid solution with the concentration of 1mol/L and deionized water, and washing until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a thin slurry, and performing effective ultrasonic treatment for 10 hours at 500W to obtain the graphene slurry. The graphene has the transverse size interval of 1-50 mu m, the thickness of 0.5-5 nm and the graphene thin slurry concentration of 3wt.%.
Fig. 4 is an optical photograph and a scanning electron micrograph of the graphene paste obtained in example 2, the left image in fig. 4 is an optical photograph, and the right image is a scanning electron micrograph. As can be seen from fig. 4, the prepared black graphene (left optical photograph) microscopically shows a typical two-dimensional lamellar structure (right electron micrograph).
Concentrating the graphene slurry to obtain slurry with solid content of 5wt%, shearing and emulsifying to obtain homogeneous slurry, and blade-coating to form a film with the film thickness of 10 μm; then carbonizing at 1500 ℃ and graphitizing at 2200 ℃ for 60min and 20min respectively, and calendaring to obtain the graphene heat dissipation film with thermal diffusion coefficient>1000mm 2 The density of the graphene film is 0.8 +/-0.2 g/cm 3 。
Example 3
Repeatedly sticking a flake graphite sheet with the thickness of 2mm as a raw material to the surface of the flake graphite sheet by using an adhesive tape to enable the surface of the flake graphite sheet to have rough marks; fixing the graphite thin plate between two titanium plates by using a rivet to be used as a working electrode, cutting the lower part of the graphite electrode, wherein the cut shape is a rectangular strip shape, the length is 1/2 of the length of the graphite paper electrode, and the width is 5mm.
The electrolyte comprises the components of a mixture of propylene carbonate, acetonitrile, lithium borate and deionized water, wherein the weight ratio of the four components is 8:2:1:4; inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 2/3 of the overall height of the electrode, the voltage is 5V, and the current density is 0.2mAcm -1 Pre-intercalation for 36h under the parameters; the liquid level of the electrolyte is adjusted to ensure that the depth of the graphite electrode inserted into the electrolyte is 1/5 of the whole height of the electrode, and then the voltage and the current density are increased to 9V and 1mAcm -1 After the parameter intercalation is kept for 36h, the electrode direction is changed, the intercalation is continued, the steps are repeated, and the voltage and the current density are adjusted in a self-adaptive manner. When the current value in the electrolytic circuit is reduced to 80% of the predetermined current density value, the voltage is increased to maintain the current density value within the range of +/-5% of the predetermined value. And under the condition that the current density can not be maintained after the voltage value is continuously increased to 15V, automatically injecting the electrolyte, and stopping injecting after the current density is recovered to a set value. And repeating the voltage boosting and electrolyte injection until the current density value cannot be raised to a set value after the electrolyte is supplemented to the depth of the immersed graphite electrode which is 4/5 of the original height of the graphite electrode, and ending the electrolytic stripping process.
And (3) performing solid-liquid separation on the stripping product and the electrolyte by using a filter press, performing alkali washing, acid washing and water washing on the obtained slurry product by using a saturated sodium hydroxide solution, a hydrochloric acid solution with the concentration of 0.5mol/L and deionized water respectively, and washing until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a thin slurry, and performing effective ultrasonic treatment for 8 hours at 1000W to obtain the graphene slurry. The graphene has a transverse size interval of 1-50 μm and a thickness of 1-5 nm.
Concentrating the graphene slurry to obtain slurry with solid content of 1wt%, shearing and emulsifying to obtain homogeneous slurry, and performing suction filtration to form a film with the film thickness of 50 μm; then respectively treated by carbonization at 1200 ℃ and graphitization at 2100 ℃ for 1.5h and 10min, and then rolled to obtain the graphene heat dissipation film with thermal diffusion coefficient>500mm 2 (s) graphene film densityThe degree is 1.3 +/-0.1 g/cm 3 。
Example 4
Taking natural graphite paper with the thickness of 0.2mm as a raw material, and pressing the surface of the natural graphite paper by using a concave-convex pressing plate to enable the surface of the natural graphite paper to have concave patterns; the graphite electrode is fixed on a stainless steel electrode, the lower part of the graphite electrode is cut, the cut shape is zigzag, the length is 3/5 of the length of the graphite paper electrode, and the width is 7mm.
The electrolyte comprises the components of a mixture of dimethyl carbonate, dimethyl sulfoxide, lithium chloride and deionized water, wherein the weight ratio of the four components is about 9:1:2:2, inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 4/5 of the overall height of the electrode, the voltage is 3V, and the current density is 0.05mAcm -1 Pre-intercalation for 36h under the parameters, adjusting the liquid level of the electrolyte to ensure that the depth of the graphite electrode inserted into the electrolyte is 1/4 of the overall height of the electrode, and then increasing the voltage and current density to 7V and 0.5mAcm -1 And after the parameter intercalation is maintained for 72 hours, the electrode direction is changed, the intercalation is continued, and the steps are repeated, and the voltage and the current density are adaptively adjusted. When the current value in the electrolytic circuit is reduced to 80% of the predetermined current density value, the voltage is increased to maintain the current density value within the range of +/-5% of the predetermined value. And under the condition that the current density can not be maintained after the voltage value is continuously increased to 15V, automatically injecting the electrolyte, and stopping injecting after the current density is recovered to a set value. And repeating the voltage boosting and electrolyte injection until the depth of the immersed graphite electrode is 4/5 of the original height of the graphite electrode, and then finishing the electrolytic stripping process when the current density value cannot be raised to a set value.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter bag, respectively carrying out alkali washing, acid washing and water washing on the obtained slurry product by using a 3mol/L potassium hydroxide solution, a 1mol/L sulfuric acid solution and deionized water, and washing until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a thin slurry, carrying out effective ultrasonic treatment for 12 hours under 750W, and carrying out freeze drying to obtain the graphene powder. The graphene has a transverse size interval of 1-50 μm and a thickness of 1-10 nm.
Example 5
The method comprises the steps of taking a 1.5 mm-thick flake graphite plate as a raw material, pressing the surface of the flake graphite plate by using a concave-convex pressing plate to enable the surface of the flake graphite plate to have sunken patterns, fixing the flake graphite plate on a stainless steel electrode, cutting the lower part of the graphite electrode to be irregular strips, wherein the cutting length is 4/5 of the length of the graphite paper electrode, and the width is 3mm.
The electrolyte comprises the mixture of dimethyl carbonate, ethylene carbonate, lithium chloride and deionized water, and the weight ratio of the dimethyl carbonate to the ethylene carbonate to the lithium chloride to the deionized water is 6:4:2:2; inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 3/5 of the overall height of the electrode, the voltage is 5V, and the current density is 0.3mAcm -1 Pre-intercalation for 24h; adjusting the electrolyte to ensure that the depth of the graphite electrode inserted into the electrolyte is 1/4 of the overall height of the electrode, and then increasing the voltage and current density to 10V and 2mAcm -1 After the parameter intercalation is maintained for 24 hours, the electrode direction is changed, the intercalation is continued, the steps are repeated, and the voltage and the current density are adaptively adjusted. When the current value in the electrolytic circuit is reduced to 80% of the predetermined current density value, the voltage is increased to maintain the current density value within the range of +/-5% of the predetermined value. And under the condition that the current density can not be maintained after the voltage value is continuously increased to 15V, automatically injecting the electrolyte, and stopping injecting after the current density is recovered to a set value. And repeating the voltage boosting and electrolyte injection until the current density value cannot be raised to a set value after the electrolyte is supplemented to the depth of the immersed graphite electrode which is 4/5 of the original height of the graphite electrode, and finishing the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter press, and carrying out alkali washing, acid washing and water washing on the obtained slurry product by using a saturated sodium hydroxide solution, a sulfuric acid solution with the concentration of 1mol/L and deionized water respectively until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a thin slurry, and performing effective ultrasonic treatment for 12 hours at 500W to obtain the graphene slurry. The graphene has a transverse size interval of 1-50 μm and a thickness of 0.5-10 nm.
Concentrating the graphene slurry to obtain 5wt% of solid content slurry, shearing and emulsifying to obtain homogeneous slurry, and performing suction filtration to form a film with the thickness of 60 micrometers; then carbonizing at 1500 ℃ and graphitizing at 2200 ℃ for 2h and 20min respectively, calendering to obtain the graphene heat dissipation film, and performing thermal diffusionCoefficient of performance>300mm 2 (s) the density of the graphene film is 1.6 +/-0.1 g/cm 3 。
The embodiment shows that the method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of stripping electrochemical parameters, good stripping effect and high quality of the obtained graphene, and the thermal management film prepared from the graphene has excellent heat conduction performance.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A method for preparing graphene through large-scale self-adaptive electrochemical stripping comprises the following steps:
making an indentation on the surface of the flake or film graphite or increasing the surface roughness and then fixing the flake or film graphite on a metal clamp, and cutting the treated graphite along one end of the unfixed metal clamp to form a graphite preprocessing structure with an integral upper end and a dispersed lower end;
the graphite preprocessing structure is respectively used as a positive electrode and a negative electrode to form a graphite electrode system; connecting a plurality of graphite electrode systems in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte, and electrifying to perform pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and an inorganic salt;
carrying out electrolytic stripping on the pre-intercalation electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and voltage/current signal feedback is arranged in the electrolytic circuit for electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, the voltage value is dynamically and adaptively adjusted according to the monitored current density, and the current density is kept stable at a preset value.
2. The method of claim 1, wherein the graphite comprises one or more of artificial graphite, highly oriented pyrolytic graphite, natural flake graphite, and microcrystalline graphite; the thickness of the graphite is 0.001-3 mm.
3. The method according to claim 1, wherein the dispersion shape is a regular shape or an irregular shape; the cutting length is 1/10-4/5 of the whole length of the graphite, and the cutting width is 3-20 mm.
4. The method of claim 1, wherein the number of graphite electrode systems in the graphite array electrode is 1 or more.
5. The method of claim 1, wherein in the pre-intercalation, the graphite array electrode is inserted into the electrolyte to a depth of no more than 4/5 of the overall height of graphite in the graphite array electrode; the voltage of the pre-intercalation is 0.5-5V, and the current density is 0.05-0.5 mAcm -1 (ii) a The time of the pre-intercalation is 12 to 36 hours.
6. The method of claim 1, wherein in the electrolytic stripping, the graphite array electrode is inserted into the electrolyte to a depth of not more than 1/4 of the overall height of graphite in the graphite array electrode; the preset voltage of the electrolytic stripping is 3.5-15V, and the preset current density is 0.5-3.0 mAcm -1 。
7. The method as claimed in claim 1 or 6, wherein the positive electrode and the negative electrode are exchanged at intervals of 12-72 h during the electrolytic stripping.
8. The method according to claim 6, wherein (a) when the voltage/current signal feedback detects that the current density during the electrolytic stripping process is reduced to 80% of the preset current density, the voltage is adaptively increased to restore the current density to the preset current density;
(b) When the current density can not be recovered to the preset current density after the voltage in the step (a) is increased to 15V, the voltage/current signal is fed back to automatically supplement the electrolyte until the current density is recovered to the preset current density, and then electrolytic stripping is continuously carried out; the electrolytic stripping process is carried out according to the operation (a);
and (c) circularly performing the operations (a) to (b), and finishing the electrolytic stripping when the current density cannot be recovered to the preset current density after the electrolyte is replenished to the position where the depth of the immersed graphite array electrode is 4/5 of the overall height of the graphite in the graphite array electrode.
9. Graphene obtained by the production method according to any one of claims 1 to 8; the graphene has a transverse dimension of 1-50 μm and a thickness of 0.5-10 nm.
10. A thermal management film, wherein a raw material for production comprises the graphene according to claim 9.
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