CN114684814A - Preparation method of self-supporting flexible graphene film and application of self-supporting flexible graphene film to flexible supercapacitor - Google Patents

Abstract

The invention belongs to the technical field of electrochemical energy storage, and relates to a method for preparing a self-supporting flexible graphene film. The prepared graphene nanosheets are prepared by using deionized water as a solvent to prepare a graphene slurry with a concentration of 10-30 mg/ml and a viscosity of 20-30 mPa·s, which is coated on the substrate surface and self-assembled by evaporation. Self-supporting graphene film; patterning the graphene film into a self-supporting flexible graphene film of any shape with a laser engraving machine. The graphene nanosheets with oxidized surface and crystallized inside prepared by the present invention are easy to process, use water as a solvent to prepare slurry without binder and conductive agent, and the prepared graphene film is also applied to flexible self-supporting Supercapacitor electrodes. The assembly of flexible self-supporting planar micro-supercapacitors eliminates the need for substrates and current collectors, which is beneficial for the practical application of supercapacitors.

Description

Preparation method of self-supporting flexible graphene film and its application in flexible supercapacitor

technical field

The invention belongs to the technical field of electrochemical energy storage, relates to electrode materials, in particular to a preparation method of a self-supporting flexible graphene film and its application to a flexible supercapacitor.

Background technique

Supercapacitor is a new type of energy storage system that works on the principle of electrochemical energy conversion, also known as electrochemical capacitor, which is between batteries and traditional capacitors, has high power density compared with batteries, and has Energy storage devices with high energy density.

Electrode materials are an important part of supercapacitors and can be divided into carbon materials, transition metal oxides, conducting polymers and composite materials. At present, the application of new carbon materials such as carbon nanotubes and graphene has promoted the development of the energy storage field. Taking graphene as an example, graphene is a two-dimensional carbon nanomaterial with a hexagonal honeycomb lattice composed of carbon atoms and SP ² hybrid orbitals. It has the characteristics of high strength, high toughness, high conductivity, and large specific surface area. The capacitor electrode has a theoretical specific capacitance of about 550F/g, and has good stability and long service life. In addition, compared with other electrode materials, graphene materials can work at a higher potential window and have great potential as electrode materials for high-energy, high-power supercapacitors.

At present, many research works have used methods such as vacuum filtration, electrophoretic deposition, casting reduction, modified hydrothermal reduction, high temperature reduction, and chemical reduction to prepare free-standing flexible supercapacitor electrodes. Chen et al. in Adv. Mater., 2012, 24, 4144–4150 reported a “blowing” process to convert compact graphene paper into porous graphene films; using the filter-assembled graphene paper as dough, hydrazine Steam was used as foaming and reducing agent; the specific capacitance of the synthesized reduced graphene oxide foam was 110 F/g. Niu et al. in Small, 2012, 8, 3201–3208 reported an electrophoretic deposition layer-by-layer assembly method for the construction of multilayer rgo-gold nanoparticle films; the specific capacitance of supercapacitors at a scan rate of 5mV/s was 61F/g. Yu et al. in Appl.Phys.Lett., 2010, 96, 253105. reported the preparation of an ultrathin graphene film on a PET substrate; when the current density was 0.75A/g, the ultrathin graphene film The specific capacitance is 135F/g, and the film thickness is only 25-100nm. However, the size of the films prepared by the above-mentioned methods are basically in the order of square centimeters, and the preparation process may involve chemical reduction; the preparation process of the method of the present invention does not require reduction, the film size can reach the level of square meters, the thickness is controllable, self-supporting, and can be Directly used as electrode material in supercapacitors.

In addition, the present invention prepares graphene nanosheets with surface oxidation and internal crystallization through the electrolysis method of regulating the voltage and the distance between the two electrodes, which is beneficial to assembling into a film without reduction, has high conductivity, and is easy to process. In addition, using a home laser engraving machine to process the film does not require substrates, complex masks, ink additives and other materials, the preparation process is simple, the cost is low, and it is environmentally friendly. Compared with supercapacitors fabricated by multiple printing or multiple lithography, it can directly arrange positive and negative film electrodes and assemble into flexible self-supporting supercapacitors. Without any substrate, the gel electrolyte can independently support the entire device. , without the need for current collectors and binders.

SUMMARY OF THE INVENTION

In view of the deficiencies in the above-mentioned prior art, the purpose of the present invention is to disclose a preparation method of a self-supporting flexible graphene film.

A preparation method of a self-supporting flexible graphene film, comprising the following steps:

(1) Preparation of graphene nanosheets with surface oxidation and internal crystallization by regulating the voltage and the distance between the two graphite electrodes, wherein the electrolyte is 1M (NH ₄ ) ₂ SO ₄ , the voltage value is ±10V, and the pretreated The two electrodes are placed opposite to each other in the electrolyte, and the distance between the electrodes is 3 to 30 cm;

(2) Using deionized water as a solvent to prepare graphene nanosheets with a concentration of 10 to 30 mg/ml and a viscosity of 20 to 30 mPa·s of graphene slurry, coating and evaporating on the surface of the substrate with a doctor blade Self-assembly to obtain a self-supporting graphene film;

(3) The graphene film is patterned into a self-supporting flexible graphene film of any shape with a laser engraving machine.

In the preferred disclosure example of the present invention, the pretreatment described in step (1) is to pre-treat the electrodes at both ends at a voltage of 2V for 30 to 60 minutes before starting electrolysis. During the pre-treatment process, the electrodes are immersed in the electrolyte at a rate of 5 mm /min, after the pretreatment, take out and squeeze out the electrolyte inside the electrode.

In the preferred disclosure example of the present invention, in step (1), the pretreated electrodes are re-immersed in the electrolyte, and placed relative to each other, and the voltage and electrode spacing control parameters during the electrolysis process are as follows:

Among them, the voltage is a square wave voltage with a period of 2s, and the above four stages are repeated until the electrode is completely electrolytically peeled off.

In the preferred disclosure example of the present invention, the graphene slurry prepared in step (2) is mixed with a high-speed disperser, the rotating speed is 800-1500 r/min, and the time is 2.5-3.5 h, wherein the rotating speed is divided into two adjustments, The first stage: stirring at 800-1000r/min for 1-1.5h; the second stage: stirring at 1000-1500r/min for 1.5-2h.

In the preferred disclosure example of the present invention, the blade coating in step (2), the coating thickness is 0.5-6.0mm; the temperature of evaporation self-assembly is 25-60°C, and the drying time is 1-4h; the substrate is polypropylene single Silk industrial filter cloth.

In a preferred disclosed example of the present invention, the laser engraving machine described in step (3) is a household laser engraving machine, the laser power is 10-20W, the engraving precision is 0.5 μm, and the engraving speed is 5-15 cm/min.

Another object of the present invention is to apply the prepared self-supporting flexible graphene film to a flexible self-supporting supercapacitor electrode, and the steps include:

A. The laser spot is controllably irradiated on the graphene film, and the positive and negative electrodes are fabricated through the designed interdigital path; on the glass slide, the processed positive and negative films are arranged to assemble into a symmetrical flat micro supercapacitor;

B. The PVDF-HFP/EMIM-BF4 gel electrolyte is evenly drop-coated on the surface of the interdigital electrode device, and after solidification, it is peeled off from the glass slide to obtain a flexible self-supporting flat micro supercapacitor;

C. Using the self-supporting graphene film as the electrode, drop the PVDF-HFP/EMIM-BF4 electrolyte at the gap between the two opposite positive and negative film electrodes to assemble multiple flexible self-supporting supercapacitors in series.

In a preferred disclosure example of the present invention, the flexible self-supporting planar micro-supercapacitor described in step (A) is a symmetrical type, the electrodes are in the shape of interdigitated fingers, the interdigital distance is 0.5-1 μm, and the interdigital index is 5-10. Flexible self-supporting planar micro-supercapacitors do not require substrates and current collectors and can be bent arbitrarily.

In a preferred disclosure example of the present invention, in step (C), a plurality of flexible self-supporting supercapacitors connected in series are assembled according to the graphene film electrode-gel electrolyte-graphene film electrode, without the need for a substrate and a current collector.

The characterization of graphene nanosheets by X-ray diffractometer proved that a sharp diffraction peak appeared at 26°, corresponding to the (002) crystal plane of graphite, and the interlayer spacing was 0.34nm calculated by the Bragg formula, which indicated that in graphene nanosheets, a sharp diffraction peak appeared. No appreciable oxygen groups were added to the interlayer of the sheet. However, a lower diffraction peak also appeared at 12°, corresponding to the interlayer spacing of 0.72 nm, and some oxygen groups were introduced into the surface layer of graphene nanosheets, which increased the interlayer distance.

beneficial effect

The graphene nanosheets with oxidized surface and crystallized inside prepared by the invention are favorable for assembling into a film without reduction, have high electrical conductivity, are easy to process, use water as a solvent, are low-cost, environmentally friendly, and do not need a binder for preparing the slurry , Conductive agent. The thin film preparation method has the advantages of simple process, large size and controllable thickness, and can be directly used as a supercapacitor electrode without subsequent reduction treatment. The process of assembling flexible self-supporting planar micro-supercapacitors and multiple series-connected flexible self-supporting supercapacitors does not require substrates and current collectors, which is beneficial for the practical application of supercapacitors. The flexible self-supporting supercapacitor has the advantages of good flexibility, wide voltage window, high areal capacitance and energy density, and is suitable for the preparation of flexible wearable devices.

Description of drawings

Fig. 1. Schematic diagram of preparing graphene film by blade coating, wherein, 1-scraper, 2-substrate, 3-graphene slurry, 4-backup roller;

Fig. 2. SEM image of the graphene film surface prepared in Example 1;

Fig. 3. Graphene film cross-section SEM image prepared by embodiment 1;

Fig. 4. Graphene film flexibility picture prepared by embodiment 1;

Figure 5. Flexible self-supporting planar micro-supercapacitor prepared in Example 1;

Figure 6. Pictures of 10 series-connected capacitors prepared in Example 1 in flat and bent states;

Figure 7. CV curves of 10 capacitors in series at different scan rates.

Detailed ways

The present invention will be described in detail below in conjunction with the examples, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following examples.

Example 1

The graphite powder was pressed into two graphite electrodes with a thickness of about 2mm. The electrodes were placed in an electrolyte of 1M (NH ₄ ) ₂ SO ₄ opposite each other. Under the voltage of 2V, the pretreatment was performed for 30min. During the pretreatment process, the electrodes were immersed in the electrolyte at a rate of is 5mm/min. After pretreatment, remove the electrode and squeeze out the electrolyte inside. Immerse the pretreated electrodes in the electrolyte again and place them relative to each other. The specific voltage and electrode spacing control parameters during the electrolysis process are as follows:

Voltage Electrode distance time The first stage ±10V 3cm 5s second stage ±10V 3～30cm 5s The third phase ±10V 30cm 5s fourth stage ±10V 3～30cm 5s

The voltage in the table is a square wave voltage with a period of 2s, and the above four stages are repeated until the electrode is completely electrolytically peeled off. The exfoliation product was dissolved in deionized water, ultrasonicated for 2 hours to obtain a mixed solution, then centrifuged, the supernatant was taken, and washed with deionized water suction filtration to obtain a separated solid; finally, the separated solid was freeze-dried to obtain graphene nanometers. piece.

Dissolve 15g graphene nanosheets in 100ml of water, ultrasonicate for 2h, stir evenly, prepare 15mg/ml graphene slurry with a viscosity of 22mPa s, and vacuum the prepared slurry to remove air bubbles; adjust the height of the scraper to 1mm, put The graphene slurry was poured on the polypropylene monofilament industrial filter cloth, and it was scraped with a scraper, and the drying time was 2h at 35°C.

The laser spot is controllably irradiated on the graphene film electrode, and the positive and negative electrodes are fabricated through the designed interdigital path; then, the processed positive and negative films are arranged on a glass slide to assemble a symmetrical flat micro supercapacitor; Then, the gel electrolyte was evenly drop-coated on the surface of the interdigital electrode device, and after the gel electrolyte solidified, it was peeled off from the glass slide to obtain a flexible self-supporting planar micro supercapacitor.

The prepared graphene film was peeled off from the substrate, and cut into strips of the same size, arranged in an orderly manner on the glass slide, and then PVDF-HFP was added dropwise at the gap between the two opposite positive and negative film electrodes. /EMIM-BF4 electrolyte, multiple flexible self-supporting supercapacitors in series are assembled without the need for substrates and current collectors.

Figure 2 is the plane SEM image of the film, the graphene sheets are stacked on each other, and the surface is relatively smooth; Figure 3 is the cross-sectional SME image of the film, from which it can be seen that the film is distributed in layers, leaving some gaps for subsequent electrochemical tests. The entry of electrolyte provides access.

Figure 7 shows that the CV curves at different scan rates are all rectangular-like, showing the typical electrochemical capacitance behavior of the electric double layer. In addition, the CV curve is smooth without glitches, indicating that the device has a good current response.

After testing, the electrical conductivity of the graphene nanosheets prepared in Example 1 is 197 S/cm, which indicates that it has good electrical conductivity.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.56F/cm ² .

Example 2

The experimental process and conditions were the same as in Example 1, and the graphene slurry concentration was 20 mg/ml.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V, a current density of 1mA/cm ² , and an area specific capacitance of 0.42F/cm ² .

Example 3

The experimental process and conditions were the same as in Example 1, and the graphene slurry concentration was 30 mg/ml.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.36F/cm ² .

Example 4

The experimental process and conditions were the same as in Example 1, and the thickness of the blade was 2 mm.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.50F/cm ² .

Example 5

The experimental process and conditions were the same as in Example 1, and the thickness of the blade was 3 mm.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.46F/cm ² .

Example 6

The experimental process and conditions were the same as in Example 1, the concentration of the graphene slurry was changed to 20 mg/ml, and the thickness of the scraper was changed to 1.5 mm.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.37F/cm ² .

Example 7

The experimental process and conditions were the same as in Example 1, the concentration of the graphene slurry was changed to 20 mg/ml, and the thickness of the scraper was changed to 2 mm.

The assembled flexible self-supporting supercapacitor can provide a high voltage of 10V at a current density of 1mA/cm ² and an area specific capacitance of 0.34F/cm ² .

The above descriptions are only the embodiments of the present invention, and are not intended to limit the scope of the patent of the present invention. Any equivalent structure or equivalent process transformation made by the description of the present invention, or directly or indirectly applied in other related technical fields, are the same as The principles are included in the scope of patent protection of the present invention.

Claims (9)

1. A preparation method of a self-supporting flexible graphene film is characterized by comprising the following steps:

(1) preparing graphene nanosheets with oxidized surfaces and crystallized interiors by an electrolytic method for regulating and controlling voltage and distance between two graphite electrodes, wherein the electrolyte is 1M (NH)₄)₂SO₄The voltage value is +/-10V, the two pretreated electrodes are oppositely placed in the electrolyte, and the distance between the electrodes is 3-30 cm;

(2) preparing graphene slurry with the concentration of 10-30 mg/ml and the viscosity of 20-30 mPa & s from the prepared graphene nanosheets by taking deionized water as a solvent, and performing scraper coating and evaporation self-assembly on the surface of a substrate to prepare a self-supporting graphene film;

(3) and patterning the graphene film into a self-supporting flexible graphene film in any shape by using a laser engraving machine.

2. The method for preparing a self-supporting flexible graphene film according to claim 1, wherein: and (2) the pretreatment in the step (1) is to carry out pretreatment for 30-60 min under the voltage of 2V on the electrodes at two ends before the beginning of electrolysis, wherein the rate of the electrodes immersed into the electrolyte in the pretreatment process is 5mm/min, and the electrolyte in the electrodes is taken out and extruded after the pretreatment is finished.

3. The method for preparing a self-supporting flexible graphene film according to claim 1, wherein: in the step (1), the electrodes after pretreatment are immersed into the electrolyte again and are oppositely placed, and the voltage and electrode spacing control parameters in the electrolysis process are as follows:

wherein the voltage is square wave voltage with the period of 2s, and the above four stages are repeatedly circulated until the electrodes are completely stripped.

4. The method for preparing the self-supporting flexible graphene film according to claim 1, wherein the method comprises the following steps: preparing graphene slurry in the step (2), mixing by using a high-speed dispersion machine, wherein the rotating speed is 800-1500 r/min, the time is 2.5-3.5 h, the rotating speed is regulated and controlled twice, and the first stage comprises the following steps: stirring for 1-1.5 h at a speed of 800-1000 r/min; and a second stage: stirring at 1000-1500 r/min for 1.5-2 h.

5. The method for preparing a self-supporting flexible graphene film according to claim 1, wherein: and (3) coating with a scraper in the step (2), wherein the coating thickness is 0.5-6.0 mm.

6. The method for preparing the self-supporting flexible graphene film according to claim 1, wherein the method comprises the following steps: in the step (2), the temperature of evaporation self-assembly is 25-60 ℃, and the drying time is 1-4 h.

7. The method for preparing a self-supporting flexible graphene film according to claim 1, wherein: and (3) in the step (2), the substrate is polypropylene monofilament industrial filter cloth.

8. The method for preparing a self-supporting flexible graphene film according to claim 1, wherein: the laser engraving machine in the step (3) is a household laser engraving machine, the laser power is 10-20W, the engraving precision is 0.5 mu m, and the engraving speed is 5-15 cm/min.

9. Use of a self-supporting flexible graphene film prepared according to any one of claims 1 to 8, wherein: it is applied to flexible self-supporting supercapacitor electrodes.

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