CN115709989B - 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 by large-scale self-adaptive electrochemical stripping, graphene and a thermal management film, and relates to the technical field of nano carbon materials. The invention makes indentation or increases surface roughness on the surface of graphite, and cuts the graphite, and increases ion intercalation sites through the preprocessing; according to the invention, the pre-intercalation step is arranged in the electrolytic stripping link, so that the ion concentration near the graphite electrode is increased, and the ion intercalation channel is gradually opened, thus the intercalation efficiency can be effectively improved; the invention introduces a voltage/current feedback regulation mechanism in the electrolytic stripping process, carries out detection feedback on current density, dynamically and adaptively regulates voltage, effectively controls electrolytic voltage and current density, enables intercalation sequence to be carried out from bottom to top, and avoids the defects of integral intercalation and easy electrode falling in the traditional electrolytic process. The method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of the electrochemical stripping 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 by large-scale self-adaptive electrochemical stripping, graphene and a thermal management film.
Background
Graphene (Graphene) is formed from sp 2 Two-dimensional planar crystals with a honeycomb hexagonal structure composed of hybridized carbon atoms. The unique structural characteristics of the graphene enable the graphene to have excellent physical, chemical, mechanical and other properties, and can be used in lithium ion batteries, supercapacitors, thermal management materials, electric heating films, functional protective coatings and heterogeneous catalysisThe preparation has good application prospect in the fields of agent carriers and the like. The preparation method of the graphene has great influence on the quality and performance of the graphene, and a low-cost, high-quality and large-batch preparation technology is a key of the graphene entering the market and widely applied. There are many methods for preparing graphene, including a mechanical graphite stripping method, a liquid phase stripping method, a chemical vapor deposition method, an epitaxial growth method, an electrochemical method and the like. Among them, electrochemical methods are attracting attention due to their advantages of low cost, simple operation, environmental friendliness, mild conditions, and recyclable electrolyte.
Although the electrochemical method is also utilized in chinese patent CN111217361A, CN107954420a, the electrolyte component is mainly water system, which results in too much working voltage exceeding the hydrolysis potential (1.23V), otherwise the generated hydrogen gas causes explosion hazard and the electrolysis intercalation efficiency is reduced. Although the organic solvent is introduced into Chinese patent CN102530930A, CN103693638A and the like to improve the electrolytic voltage, the stripping efficiency in the electrolytic stripping process is low, and the electrolytic voltage and the current density are not effectively controlled in the electrolytic process, so that the electrolytic stripping effect is difficult to accurately control; in addition, the intercalation position in the graphite intercalation cannot be accurately regulated, that is, the intercalation process is performed on the whole electrode, and thus incomplete stripping may be caused.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for preparing graphene by large-scale self-adaptive electrochemical stripping, graphene and a thermal management film. The method provided by the invention has the advantages of high stripping efficiency and good stripping effect, and the obtained graphene has high quality.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for preparing graphene by large-scale self-adaptive electrochemical stripping, which comprises the following steps:
manufacturing indentation on the surface of the flaky or film-shaped graphite or adding surface roughness, fixing the flaky or film-shaped graphite on a metal clamp, cutting the treated graphite along one end of the non-fixed metal clamp to form a graphite pre-processing structure with an integral upper end and a dispersed lower end;
respectively taking the graphite pre-processing structure as an anode and a cathode to form a graphite electrode system; a plurality of graphite electrode systems are connected in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte, electrifying to perform pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and inorganic salt;
carrying out electrolytic stripping on the pre-intercalated electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and a voltage/current signal feedback is arranged in the electrolytic line of the electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, and the voltage value is dynamically and adaptively adjusted according to the monitored current density, so that the current density is kept stable at a preset value.
Preferably, the graphite comprises one or more of artificial graphite, high-orientation pyrolytic graphite, natural crystalline flake graphite and microcrystalline graphite; the thickness of the graphite is 0.001-3 mm.
Preferably, the dispersion is a regular shape or an irregular shape; the length of the cutting is 1/10-4/5 of the whole length of the graphite, and the width of the cutting is 3-20 mm.
Preferably, the number of graphite electrode systems in the graphite array electrode is 1 or more.
Preferably, in the pre-intercalation, the depth of the graphite array electrode inserted into the electrolyte is not 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 The method comprises the steps of carrying out a first treatment on the surface of the The time of the pre-intercalation is 12-36 h.
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, in the electrolytic stripping process, the positive electrode and the negative electrode are exchanged every 12-72 hours.
Preferably, (a) when the voltage/current signal feedback detects a decrease in current density to 80% of a preset current density during electrolytic stripping, adaptively increasing the voltage to restore the current density to the preset current density;
(b) When the current density cannot be recovered to the preset current density after the voltage in the step (a) is increased to 15V, feeding back the electrolyte by the voltage/current signal to automatically supplement the electrolyte until the current density is recovered to the preset current density, and then continuing to perform electrolytic stripping; in the electrolytic stripping process, the process is carried out according to the operation of (a);
and (c) circularly performing the operations (a) - (b), and ending the electrolytic stripping when the current density cannot be recovered to the preset current density after the electrolyte is supplemented to the depth of immersing the graphite array electrode to be 4/5 of the total height of graphite in the graphite array electrode.
The invention provides the graphene prepared by the preparation method; the transverse dimension of the graphene is 1-50 mu m, and the thickness of the graphene is 0.5-10 nm.
The invention also provides a thermal management film, and the preparation raw materials comprise the graphene according to the technical scheme.
The invention provides a method for preparing graphene by large-scale self-adaptive electrochemical stripping, which comprises the steps of manufacturing indentation on the surface of graphite or increasing surface roughness, and cutting the graphite, wherein the graphite preprocessing mode can increase intercalation sites of ions on a graphite electrode; according to the invention, the pre-intercalation step is arranged in the electrolytic stripping link, so that 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 dynamic process of inserting solvated ions between graphite sheets in the electrolytic intercalation and stripping process causes the resistance value of the graphite electrode to be in dynamic change, and the invention also introduces a voltage/current feedback adjustment mechanism in the electrolytic stripping process to detect and feed back current density, dynamically and adaptively adjust voltage, thus being capable of effectively controlling electrolytic voltage and current density, leading the intercalation sequence to be carried out from bottom to top and avoiding the defects of integral intercalation and easy electrode falling in the traditional electrolytic process. The preparation method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of the electrochemical stripping parameters, good stripping effect, high quality of the obtained graphene, and realization of modularized design and large-scale production.
The invention provides the graphene prepared by the preparation method. 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 materials comprise the graphene according to the technical scheme. The thermal management film provided by the invention has excellent heat conduction performance. Example results show that the graphene has a lateral dimension of 1-50 μm and a thickness of 0.5-10 nm, and the thermal management film has a density of 0.8-2.0 g cm -3 Coefficient of thermal diffusion>300mm 2 /s。
Drawings
FIG. 1 is a schematic diagram of a graphite pre-processing structure according to an embodiment of the present invention, wherein in FIG. 1, L is the overall length of graphite, L is the cutting length, and d is the cutting width;
FIG. 2 is a logic diagram of a voltage/current signal adaptive feedback system in electrochemically exfoliated graphene according to the present invention;
FIG. 3 is an optical photograph of the graphene film prepared in example 1;
fig. 4 is an optical photograph and a scanning electron microscope photograph of the graphene slurry obtained in example 2, wherein the left side of fig. 4 is an optical photograph, and the right side is a scanning electron microscope photograph.
Detailed Description
The invention provides a method for preparing graphene by large-scale self-adaptive electrochemical stripping, which comprises the following steps:
manufacturing indentation on the surface of the flaky or film-shaped graphite or adding surface roughness, fixing the flaky or film-shaped graphite on a metal clamp, cutting the treated graphite along one end of the non-fixed metal clamp to form a graphite pre-processing structure with an integral upper end and a dispersed lower end;
respectively taking the graphite pre-processing structure as an anode and a cathode to form a graphite electrode system; a plurality of graphite electrode systems are connected in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte, electrifying to perform pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and inorganic salt;
carrying out electrolytic stripping on the pre-intercalated electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; and a voltage/current signal feedback is arranged in the electrolytic line of the electrolytic stripping, the current density is monitored in real time according to the voltage/current feedback in the electrolytic stripping process, and the voltage value is dynamically and adaptively adjusted according to the monitored current density, so that the current density is kept stable at a preset value.
In the present invention, unless otherwise specified, all the raw materials involved are commercially available products well known to those skilled in the art or are prepared by methods well known to those skilled in the art.
The invention makes the surface of the flaky or film-shaped graphite to be provided with the indentation or increases the surface roughness and then is fixed on the metal clamp, and the treated graphite is cut along one end of the unfixed metal clamp to form a graphite pre-processing structure with an integral upper end and a dispersed lower end. In the present invention, the graphite preferably includes one or more of artificial graphite, highly oriented pyrolytic graphite, natural crystalline flake graphite and microcrystalline graphite; the thickness of the graphite is preferably 0.001 to 3mm, more preferably 0.2 to 1.5mm. The method for manufacturing the indentation has no special requirement, and can be used for forming the indentation; the invention has no special requirement 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 concave-convex pressing plate is used for pressing the graphite surface, concave fold line-shaped pattern indentations are formed on the graphite surface, and the depth of each indentation on the surface of one side of the graphite is 7-10% of the thickness of the graphite. The method for increasing the surface roughness is not particularly required, and any method capable of increasing the surface roughness can be used. The metal clamp is not particularly limited, and metal clamps known to those skilled in the art, such as stainless steel or titanium alloy metal clamps, can be used. In the present invention, the dispersion 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 cut (in the present embodiment, the cut is also referred to as a cut) 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 cut is preferably 3 to 20mm, more preferably 3 to 10mm.
The edge of the original flaky or film-shaped graphite raw material is generally subjected to pressing treatment, and intercalation ions are difficult to enter between graphite layers in the electrolytic stripping process. Fig. 1 is a schematic diagram of a graphite pre-processing structure according to 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 pre-processing structure is obtained, the graphite pre-processing 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 a 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 graphite electrode systems in the graphite array electrode is greater than 1, the interval between adjacent graphite electrode systems is preferably 5 to 25mm, more preferably 15mm. The graphite array electrode is assembled by the graphite pre-processing structure, so that the electrode is beneficial to large-scale efficient intercalation and the expansion of the preparation scale.
After the graphite array electrode is obtained, the graphite array electrode is inserted into electrolyte and electrified to perform pre-intercalation, so that 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 dimethyl sulfoxide, propylene carbonate, dimethyl carbonate,One or more of ethylene carbonate, ethylene glycol dimethyl ether, acetonitrile, diethyl carbonate, butyrolactone and methyl ethyl carbonate, more preferably 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 the water is preferably 2.5-10:1, more preferably 10:1; the mass of the inorganic salt is preferably 0.5-a% of the mass of water, wherein a% is the percentage of the mass of the inorganic salt in the mass of water when the inorganic salt is saturated in water. The preparation method of the electrolyte has no special requirement, and the components are uniformly mixed. In the present invention, in the pre-intercalation, the depth of insertion of the graphite array electrode into the electrolyte is preferably not more than 4/5, more preferably 1/3 to 4/5, of the total height of graphite in the graphite array electrode; 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 The method comprises the steps of carrying out a first treatment on the surface of the The time for the pre-intercalation is preferably 12 to 36 hours, more preferably 24 to 36 hours. During the pre-intercalation process, the graphite array electrode is fully immersed in the electrolyte, intercalation ions (cationic complexes formed with organic solvents after dissolution of the inorganic salts in the electrolyte) begin to "attack" these defects of the graphite electrode that have undergone indentation or increased surface roughness, and intercalation of graphite is further initiated through these open channels, which open relatively slowly, and the intercalation process is controlled not to be too severe in order to better build up this channel, thus controlling the voltage and current density 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 preset voltage and preset current density to obtain graphene; the electrolytic stripping electrolytic circuit is provided with voltage/electricityAnd feeding back a flow signal, monitoring the current density in real time according to the voltage/current feedback in the electrolytic stripping process, and dynamically and adaptively adjusting the voltage value according to the monitored current density to keep the current density stable at a preset value. In the electrolytic stripping, 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 total height of graphite in the graphite array electrode. If the electrodes of the graphite array are fully inserted into the electrolyte or the electrolyte liquid level is too high at first, the intercalation cannot be ensured to be started from the lower part of the electrodes and is carried out from bottom to top, and the initial electrolyte liquid level is limited to be not higher than 1/4 of the overall height of the graphite in the electrodes of the graphite array, so that the stripping process can be ensured to be carried out from bottom to top, and the electrode stripping is ensured to be thorough. In the present invention, the preset voltage for 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 positive electrode and the negative electrode are exchanged at intervals of 12-72 h, so that the electrodes on both sides can be intercalated, 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 self-adaptive voltage rising is preferably carried out 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 be within a deviation range of +/-5% of the preset current density; (b) When the current density cannot be recovered to the preset current density after the voltage in the step (a) is increased to 15V, the voltage/current signal feedback automatically supplements the electrolyte until the current density is recovered to the preset current density, and then electrolytic stripping is continued; the electrolytic stripping is performed according to the operation (a). And (c) circularly performing the operations (a) - (b), and ending the electrolytic stripping when the current density cannot be recovered to the preset current density after the electrolyte is supplemented to the depth of immersing the graphite array electrode to be 4/5 of the total height of graphite in the graphite array electrode. Fig. 2 is a logic diagram of a voltage/current signal adaptive feedback system in electrochemical stripping graphene according to the present invention.
After the electrolytic stripping is completed, the invention also preferably carries out post-treatment on the stripping product system, and the post-treatment method is preferably as follows: filtering the stripped crude product to remove the non-stripped complete product, 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 limited by the present invention, and filtration methods well known to those skilled in the art, such as filter bag or plate pressure filtration, may be employed. In the invention, the alkaline reagent used for alkaline washing is preferably sodium hydroxide solution or potassium hydroxide solution, and 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 the acid washing is preferably sulfuric acid or hydrochloric acid, and the concentration of the sulfuric acid or the hydrochloric acid is preferably 0.5-3 mol/L. In the present invention, the water is washed until the slurry supernatant is a neutral solution. After the washing, the invention also preferably disperses the obtained washing product in the dispersion liquid, and carries out 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 the ultrasonic treatment is preferably 80-1000W, and the temperature of the 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 invention, the graphene can exist in the form of graphene slurry or graphene powder, and the invention is not particularly required.
The preparation method provided by the invention has the advantages of high stripping efficiency, self-adaptive adjustment of the electrochemical stripping parameters, good stripping effect, realization of modular design (each electrolytic tank is used as a preparation module, and the yield can be enlarged by adding the electrolytic tank), and large-scale production.
The invention provides the graphene prepared by the preparation method. In the invention, the graphene has low defect content, excellent intrinsic property and high quality; the transverse dimension of the graphene is 1-50 mu m, and the thickness of the graphene is 0.5-10 nm.
The invention also provides a thermal management film, and the preparation raw materials comprise the graphene according to the technical scheme. In the present invention, the preparation method of the thermal management film preferably comprises: and sequentially carrying out emulsification homogenization, film formation and heat treatment on the graphene slurry to obtain the thermal management film. In the preparation of the heat management film, the solid content of the graphene slurry is more preferably 1 to 20wt%, and when the solid content of the graphene slurry is less than the range, the graphene slurry may be concentrated to the range and then emulsified and homogenized. In the invention, the emulsification and homogenization are specifically shear emulsification, the shear rate of the shear emulsification is preferably 300-3000 r/min, and the shear direction is kept consistent and the direction cannot be changed. In the invention, the film forming mode can be specifically doctor blade film forming, spray film forming, self-leveling film forming, 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 temperature of the carbonization is preferably 1200-1500 ℃, the time is preferably 60-180 min, the temperature of the graphitization 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, through the heat treatment, non-carbon components (decomposed into gas at high temperature and discharged) such as electrolyte, acid-base washing liquid and the like remained in the electrolytic stripping process are removed; and repairing structural defects caused to graphene in the intercalation process, and providing transmission performance (migration of carbon atoms at high temperature to repair defects in lattice planes); in addition, the density of the film can be improved, and the heat dissipation capacity and mechanical property of the macroscopic film are enhanced. After the heat treatment, the resulting film is preferably subjected to a rolling treatment, and the rolling treatment method is not particularly limited and may be any rolling method known to those skilled in the art. In the present invention, the thickness of the thermal 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 thermal management film provided by the invention has excellent heat conduction performance.
The method for preparing graphene, graphene and thermal management film by large-scale self-adaptive electrochemical stripping provided by the invention are described in detail below with reference to examples, but they are not to be construed as limiting the scope of the invention.
Example 1
The method comprises the steps of (1) using 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 concave patterns to appear on the surface of the natural graphite paper; the graphite electrode is fixed on a stainless steel strip electrode by using a screw, the lower part of the graphite electrode is cut, the cutting shape is rectangular strip, the length is 4/5 of the length of the graphite paper electrode, and the width is 3mm.
The electrolyte comprises the following components in percentage by mass: 0.5:1, a step of; the prepared graphite electrode is inserted into electrolyte, the insertion depth is 1/3 of the whole height of the electrode, and the voltage is 5V and the current density is 0.1mAcm -1 Pre-intercalation for 12h under parameters; adjusting the liquid level of the electrolyte to make the depth of the graphite electrode inserted into the electrolyte be 1/5 of the total height of the electrode, and increasing the voltage and current density to 10V and 0.5mAcm respectively -1 After the parameter is maintained for 12h of intercalation, the electrode direction is changed, the intercalation is continued, the steps are repeated, and the self-adaptive adjustment of voltage and current density is implemented. When the current value in the electrolytic circuit is reduced to 80% of the preset current density value, the voltage is raised to maintain the current density value within the range of +/-5% of the preset value, and under the condition that the current density cannot be maintained after the voltage value is continuously raised to 15V, the electrolyte is automatically injected, and the injection is stopped after the current density is restored to the preset value. Repeating the step of lifting voltage and injecting the electrolyte until the depth of the electrolyte is 4/5 of the original height of the graphite electrode after the graphite electrode is immersed, and the current density value cannot be lifted to a set value, and ending the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter bag, and respectively carrying out alkaline washing, acid washing and water washing on the obtained slurry product by using a 6mol/L concentration potassium hydroxide solution, a 1mol/L concentration hydrochloric acid solution and deionized water until the supernatant of the slurry is neutral. Mixing the washed slurry with deionized water to obtain a dilute slurry with 1wt% of solid content, and carrying out effective ultrasonic treatment at 500W for 6 hours to obtain graphene slurry, wherein the transverse dimension interval of the graphene is 1-50 mu m, and the thickness of the graphene is 0.5-5 nm.
Concentrating graphene slurry to obtain 3wt% solid content slurry, shearing and emulsifying to obtain homogeneous slurry, and carrying out blade coating to form a film with a film thickness of 20 mu m; then the graphene heat dissipation film is obtained through calendaring treatment after carbonization for 1h at 1500 ℃ and graphitization treatment for 30min at 2000 ℃, and the thermal diffusivity of the graphene heat dissipation film is obtained>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 film prepared in example 1, and it can be seen that the film has uniform material quality.
Example 2
Repeatedly sticking the surface of a high-orientation pyrolytic graphite film with the thickness of 0.5mm serving as a raw material by using an adhesive tape to enable a rough trace to appear on the surface; 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 saw-tooth, the length is 3/5 of the length of the graphite paper electrode, and the width is 10mm.
The electrolyte comprises the following components in percentage by weight: 1:2; the prepared graphite electrode is inserted into electrolyte, the insertion depth is 1/2 of the whole height of the electrode, and the voltage is 3V and the current density is 0.5mAcm -1 Pre-intercalation for 24h under parameters; adjusting the liquid level of the electrolyte to increase the voltage and current density to 12V and 1mAcm after the graphite electrode is inserted into the electrolyte to a depth of 1/4 of the total height of the electrode -1 After the parameter 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 raised to maintain the current density value within the range of +/-5% of the preset value; under the condition that the current density cannot be maintained after the voltage value continues to rise to 15V, the electrolyte is automatically injected, and the injection is stopped after the current density is recovered to the set value. Repeating the step-up voltage-injection of the electrolyte until the electrolyte is supplemented to a depth of immersing the graphite electrode of 4 +_ of the original height of the graphite electrodeAnd 5, when the current density value cannot be raised to the set value, ending the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter bag, and respectively carrying out alkaline washing, acid washing and water washing on the obtained slurry product by using a 3mol/L concentration sodium hydroxide solution, a 1mol/L concentration sulfuric acid solution and deionized water until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a dilute slurry, and performing effective ultrasonic treatment for 10 hours at 500W to obtain the graphene slurry. The transverse dimension interval of the graphene is 1-50 mu m, the thickness is 0.5-5 nm, and the concentration of the graphene thin slurry is 3wt.%.
Fig. 4 is an optical photograph and a scanning electron microscope photograph of the graphene slurry obtained in example 2, wherein the left side of fig. 4 is an optical photograph, and the right side is a scanning electron microscope photograph. As can be seen from fig. 4, the prepared black graphene (left-side optical photograph) microscopically shows typical two-dimensional lamellar structure characteristics (right-side electron microscope photograph).
Concentrating graphene slurry to obtain slurry with 5wt% of solid content, shearing and emulsifying to obtain homogeneous slurry, and carrying out blade coating to form a film with the thickness of 10 mu m; then the graphene heat dissipation film is obtained by calendaring after being respectively processed for 60min and 20min by carbonization at 1500 ℃ and graphitization at 2200 ℃ and the thermal diffusivity thereof>1000mm 2 The density of the graphene film is 0.8+/-0.2 g/cm 3 。
Example 3
Repeatedly adhering the surface of a flake graphite sheet with the thickness of 2mm serving as a raw material by using an adhesive tape to enable rough marks to appear on the surface of the flake graphite sheet; and fixing the graphite sheet between two titanium sheets by using rivets to serve as working electrodes, cutting the lower part of the graphite electrode, wherein the cutting shape is rectangular strip, the length is 1/2 of the length of the graphite paper electrode, and the width is 5mm.
The electrolyte comprises the following components of propylene carbonate, acetonitrile, lithium borate and deionized water in a weight ratio of 8:2:1:4, a step of; the prepared graphite electrode is inserted into electrolyte, the insertion depth is 2/3 of the whole height of the electrode, and the voltage is 5V and the current density is 0.2mAcm -1 Pre-intercalation for 36h under parameters; adjusting the electrolyte level to make the depth of the graphite electrode inserted into the electrolyte be the electrodeThe voltage and current density are raised to 9V and 1mAcm after 1/5 of the whole height -1 After the parameter is maintained for 36h, 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 raised to maintain the current density value within the range of +/-5% of the preset value. Under the condition that the current density cannot be maintained after the voltage value continues to rise to 15V, the electrolyte is automatically injected, and the injection is stopped after the current density is recovered to the set value. Repeating the step of lifting voltage and injecting the electrolyte until the depth of the electrolyte is 4/5 of the original height of the graphite electrode after the graphite electrode is immersed, and the current density value cannot be lifted to a set value, and ending the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter press, and respectively carrying out alkaline 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 until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a dilute slurry, and performing effective ultrasonic treatment at 1000W for 8 hours to obtain the graphene slurry. The transverse dimension interval of the graphene is 1-50 mu m, and the thickness is 1-5 nm.
Concentrating graphene slurry to obtain 1wt% solid content slurry, shearing and emulsifying to obtain homogeneous slurry, and performing suction filtration to form a film with a film thickness of 50 μm; then the graphene heat dissipation film is obtained through calendaring treatment after being respectively treated by carbonization at 1200 ℃ and graphitization at 2100 ℃ for 1.5h and 10min>500mm 2 The density of the graphene film is 1.3+/-0.1 g/cm 3 。
Example 4
Using 0.2mm thick natural graphite paper as a raw material, and pressing the surface of the natural graphite paper by using a concave-convex pressing plate to enable concave patterns to appear on the surface of the natural graphite paper; the electrode is fixed on a stainless steel electrode, the lower part of the graphite electrode is cut, the cutting shape is saw-tooth, 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, and the weight ratio of the four components is about 9:1:2:2, the prepared graphite is used for electric heatingThe electrode is inserted into the electrolyte, the insertion depth is 4/5 of the total height of the electrode, and the voltage is 3V and the current density is 0.05mAcm -1 Pre-intercalation for 36h under parameters, adjusting the electrolyte level to make the depth of the graphite electrode inserted into the electrolyte be 1/4 of the total height of the electrode, and then raising the voltage and current density to 7V and 0.5mAcm -1 After the parameter is maintained for 72h of intercalation, 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 raised to maintain the current density value within the range of +/-5% of the preset value. Under the condition that the current density cannot be maintained after the voltage value continues to rise to 15V, the electrolyte is automatically injected, and the injection is stopped after the current density is recovered to the set value. And repeating the step of lifting voltage, namely injecting electrolyte to supplement until the depth of immersing the graphite electrode is 4/5 of the original height of the graphite electrode, and then, stopping the electrolytic stripping process when the current density value cannot be lifted to a set value.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter bag, and respectively carrying out alkaline 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 until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a dilute slurry, performing effective ultrasonic treatment for 12 hours at 750W, and performing freeze drying to obtain graphene powder. The transverse dimension interval of the graphene is 1-50 mu m, and the thickness is 1-10 nm.
Example 5
The method comprises the steps of taking a flake graphite plate with the thickness of 1.5mm as a raw material, pressing the surface of the flake graphite plate by using a concave-convex pressing plate to enable concave patterns to appear on the surface of the flake graphite plate, fixing the flake graphite plate on a stainless steel electrode, cutting the lower part of the graphite electrode, wherein the cutting shape is in an irregular strip shape, the cutting length is 4/5 of the length of a graphite paper electrode, and the width is 3mm.
The electrolyte comprises the following components in percentage by weight: 4:2:2; inserting the prepared graphite electrode into electrolyte, wherein the insertion depth is 3/5 of the total height of the electrode, and the voltage is 5V and the current density is 0.3mAcm -1 Pre-inserting parameters for 24h; adjusting electrolysisThe liquid makes the depth of the graphite electrode inserted into the electrolyte be 1/4 of the total height of the electrode, and then the voltage and current density are raised to 10V and 2mAcm -1 After the parameter 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 raised to maintain the current density value within the range of +/-5% of the preset value. Under the condition that the current density cannot be maintained after the voltage value continues to rise to 15V, the electrolyte is automatically injected, and the injection is stopped after the current density is recovered to the set value. Repeating the step of lifting voltage and injecting the electrolyte until the depth of the electrolyte is 4/5 of the original height of the graphite electrode after the graphite electrode is immersed, and the current density value cannot be lifted to a set value, and ending the electrolytic stripping process.
And (3) carrying out solid-liquid separation on the stripping product and the electrolyte by using a filter press, and respectively carrying out alkaline 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 until the supernatant of the slurry is neutral. And mixing the washed slurry with deionized water to obtain a dilute slurry, and performing effective ultrasonic treatment for 12 hours at 500W to obtain the graphene slurry. The transverse dimension interval of the graphene is 1-50 mu m, and the thickness is 0.5-10 nm.
Concentrating graphene slurry to obtain slurry with solid content of 5wt%, shearing and emulsifying to obtain homogeneous slurry, and performing suction filtration to form a film with a film thickness of 60 μm; then the graphene heat dissipation film is obtained through calendaring treatment after being carbonized at 1500 ℃ and graphitized at 2200 ℃ for 2 hours and 20 minutes respectively>300mm 2 And/s, the density of the graphene film is 1.6+/-0.1 g/cm 3 。
From the above embodiments, it can be seen that the method provided by the invention has high stripping efficiency, self-adaptive adjustment of electrochemical stripping parameters, good stripping effect, high quality of the obtained graphene, and excellent heat conductivity of the thermal management film prepared from the graphene.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. A method for preparing graphene by large-scale self-adaptive electrochemical stripping comprises the following steps:
manufacturing indentation on the surface of the flaky or film-shaped graphite or adding surface roughness, fixing the flaky or film-shaped graphite on a metal clamp, cutting the treated graphite along one end of the non-fixed metal clamp to form a graphite pre-processing structure with an integral upper end and a dispersed lower end;
respectively taking the graphite pre-processing structure as an anode and a cathode to form a graphite electrode system; a plurality of graphite electrode systems are connected in parallel to form a graphite array electrode;
inserting the graphite array electrode into electrolyte, electrifying to perform pre-intercalation to obtain a pre-intercalation electrode; the electrolyte comprises an organic solvent, water and inorganic salt;
carrying out electrolytic stripping on the pre-intercalated electrode in the electrolyte according to a preset voltage and a preset current density to obtain graphene; a voltage/current signal feedback is arranged in an electrolysis line of electrolysis stripping, the current density is monitored in real time according to the voltage/current feedback in the process of electrolysis stripping, and the voltage value is dynamically and adaptively adjusted according to the monitored current density, so that the current density is kept stable at a preset value;
in the electrolytic stripping, the depth of the graphite array electrode inserted into the electrolyte is not more than 1/4 of the whole 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 ；
(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 self-adaptive voltage rise is carried out to restore the current density to the preset current density;
(b) When the current density cannot be recovered to the preset current density after the voltage in the step (a) is increased to 15V, feeding back the electrolyte by the voltage/current signal to automatically supplement the electrolyte until the current density is recovered to the preset current density, and then continuing to perform electrolytic stripping; in the electrolytic stripping process, the process is carried out according to the operation of (a);
and (3) circularly performing the operations (a) - (b), and ending the electrolytic stripping after the electrolyte is supplemented until the depth of the immersed graphite array electrode is 4/5 of the total height of graphite in the graphite array electrode and the current density cannot be recovered to the preset current density.
2. The method of claim 1, wherein the graphite comprises one or more of highly oriented pyrolytic graphite, natural crystalline flake graphite, and microcrystalline graphite; the thickness of the graphite is 0.001-3 mm.
3. The method of claim 2, wherein the graphite comprises synthetic graphite.
4. The method of claim 1, wherein the length of the cut is 1/10-4/5 of the overall length of the graphite, and the width of the cut is 3-20 mm.
5. The method of claim 1, wherein the number of graphite electrode systems in the graphite array electrode is 1 or more.
6. 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 The method comprises the steps of carrying out a first treatment on the surface of the The pre-intercalation time is 12-36 h.
7. The method according to claim 1, wherein the positive electrode and the negative electrode are exchanged at intervals of 12-72 h in the electrolytic stripping process.
8. The method according to any one of claims 1 to 7, wherein the graphene has a lateral dimension of 1 to 50 μm and a thickness of 0.5 to 10nm.
9. The thermal management film is characterized in that the preparation raw material comprises graphene prepared by the preparation method according to any one of claims 1-8.
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