CN115223801A - A method for improving the specific capacitance of laser direct writing carbon-based supercapacitors - Google Patents

Abstract

The invention discloses a method for improving the specific capacitance of a laser direct writing carbon-based supercapacitor, belonging to the technical field of capacitors. The method provided by the present invention includes the following steps: (1) preparing a fiber film by electrospinning; (2) heat-treating the fiber film by vacuum high temperature; (3) using laser direct writing to induce carbon-based fibers, which have high conductivity; Direct-writing carbon-based fiber materials are used as electrodes to assemble a laser-direct-writing carbon-based capacitor with improved specific capacitance. The present invention can obtain high-conductivity carbon-based materials by spinning, preheating and laser direct writing on the precursor material, and at the same time, the voids in the fibers can effectively improve the ion mobility, thereby effectively improving the laser direct writing carbon-based materials. The specific capacitance of the capacitor; at the same time, the method provided by the present invention overcomes the problems of complicated operation, high cost and environmental pollution of the traditional method. The electrodes prepared by the invention not only have good plasticity and flexibility, but also have wide application prospects in wearable devices.

Description

A method for improving the specific capacitance of laser direct writing carbon-based supercapacitors

technical field

The invention belongs to the technical field of capacitors, and in particular relates to a method for improving the specific capacitance of laser direct writing carbon-based supercapacitors.

Background technique

With the rapid development of industry and the rapid increase of population, people's attention has gradually turned to sustainable, renewable and clean energy to meet the development needs of modern society and alleviate the increasingly prominent environmental problems. At the same time, more and more electronic devices are developing towards thinness, flexibility and wearability, and there is an indispensable energy storage device in these devices. As an emerging energy storage device, supercapacitors can be used either as a supplement to flexible batteries or as an independent micro power source due to their high power density, fast charge and discharge speed, and long cycle life. It has attracted great attention from researchers and the market.

The planar interdigitated structure of supercapacitors can provide a better electrode material/electrolyte interface, increase the active specific surface area accessible to ions, and provide higher energy and power for electronic devices in a limited space. An option for addressing micro-energy storage devices. At present, the preparation and processing technology of supercapacitors is constantly developing in the direction of high efficiency, high precision, low cost, environmental friendliness, scalability and controllable design. The commonly used processing technologies mainly include inkjet printing, screen printing, spraying, electrophoresis, etc. Deposition, 3D printing, nanolithography and laser direct writing technology, etc. Recent studies have found that using laser direct writing technology, precursor materials can be directly induced into multilayer graphene or porous carbon structures, which can be directly used as electrode materials for supercapacitors for energy storage. This simple and scalable method of laser direct writing to induce carbon-based materials brings new opportunities for the fabrication of supercapacitors. However, the specific capacitance of laser-induced graphene-based capacitors is only about 4.0 mF/cm ² (Nature Communication, 2014, 5, 5714), which is comparable to other carbon-based capacitors, which hinders its wide application in high-power capacitors to a certain extent. .

At present, a lot of research has been done to improve the specific capacitance of laser-induced carbon-based capacitors, and several common methods include (1) changing the hydrophilic and hydrophobic properties of the electrode surface, (2) doping or surface deposition of heteroatoms and pseudocapacitive materials. In the former, the surface is converted into a hydrophilic surface by plasma treatment after the laser-induced electrode, thereby increasing the effective contact of the electrolyte. For example, Akira Watanabe et al. (Journal of Materials Chemistry A, 2016, 4, 1671-167,) found that the wettability of the carbonized electrode also has a great influence on the capacitance, and the surface of the laser direct writing induced material exhibits surface hydrophobicity, After plasma treatment, it will become hydrophilic due to the introduction of oxygen-containing functional groups, and its specific capacitance reaches 31.9 mF/cm ² . The latter is to change the lattice structure of graphene by element replacement, or to increase the surface redox reaction by loading pseudocapacitive materials to improve the specific capacitance. For example, James M Tour et al. (Advanced Materials, 2016, 28(5): 838-845.) loaded pseudocapacitive electrode materials such as manganese oxide, polyaniline and basic iron oxide on the laser-induced graphene film by electrophoretic deposition, and then Increase capacity by 1-2 orders of magnitude.

The above methods have improved the specific capacitance of laser direct writing carbon-based supercapacitors to a certain extent, but there is a limited improvement in operating specific capacitance. The electrodeposition method is used to deposit pseudocapacitive electrode materials on the surface of laser direct writing porous carbon or graphene electrode materials. , which also affects its flexibility to a certain extent, making it difficult for micro-supercapacitors to meet the current needs of wearable devices, limiting practical industrial applications.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for improving the specific capacitance of laser direct writing carbon-based supercapacitors. The present invention can efficiently improve the conductivity of carbon-based fiber materials by combining electrospinning, preheating and laser direct writing technology. As well as the specific surface area, the specific capacitance of the laser direct writing carbon-based supercapacitor can be effectively improved.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a method for improving the specific capacitance of a laser direct writing carbon-based supercapacitor, comprising the following steps:

(1) using electrospinning technology to prepare a precursor fiber film; (2) preheating the precursor fiber film to obtain a preheated fiber film; (3) using laser direct writing technology to induce carbonization to obtain carbon-based fibers electrode material, the laser direct writing induced carbon-based fiber material has high conductivity; (4) using the laser direct writing induced carbon-based fiber material as an electrode, assembling a laser direct writing carbon-based supercapacitor with improved specific capacitance.

Preferably, the precursor fiber membrane is prepared from lignin and a co-spun material by electrospinning technology, and the lignin material is a doped lignin material or an undoped lignin material.

Preferably, the doped lignin material comprises transition metal sulfide doped lignin material or transition metal oxide doped lignin material.

Preferably, the temperature of the preheating treatment is 200-550°C; the time of the preheating treatment is 200-1000 min.

Preferably, the laser direct writing induced carbon-based fiber material has a pore size of 1-50 nm, a specific surface area of 10-150 m ² /g, and a sheet resistance of 4-500 Ω/sq.

Preferably, the specific capacitance of the laser direct writing carbon-based supercapacitor is 55-600 F/g.

Preferably, the laser direct writing carbon-based supercapacitor comprises a planar interdigitated electrode structure, a series-parallel structure or a stacked structure.

Compared with the related art, the present invention provides a method for improving the specific capacitance of laser direct writing carbon-based supercapacitors, which has the following beneficial effects:

By performing electrostatic spinning, preheating and laser direct writing processing on the raw material, the invention can efficiently realize the improvement of the specific capacitance of the laser direct writing carbon-based supercapacitor, and can be used for energy storage and conversion of wearable portable electronic products.

Description of drawings

In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with the accompanying drawings, wherein:

Fig. 1 is the flow chart of laser direct writing carbon-based supercapacitor;

Fig. 2 is the electron microscope photograph of electrospinning fiber membrane;

Figure 3 is an electron microscope photograph of fiber membranes preheated at different temperatures;

Figure 4 is an electron microscope photograph of fiber membranes preheated at different temperatures after laser direct writing;

Fig. 5 is the CV curve, the CC curve of the fiber membrane electrode preheated at different temperatures, and the specific capacitance diagram calculated from the CV curve;

Fig. 6 is the CV curve, CC curve and the specific capacitance calculated from the CC curve of doped and undoped MoS ₂ laser direct writing carbon-based supercapacitor comparison chart;

Figure 7 shows the CV and CC curves of two fiber membrane electrodes preheated at 450°C in series and parallel conditions, as well as the photos of red light-emitting diodes lit by a series-connected laser direct-writing carbon-based supercapacitor.

Detailed ways

In the present invention, the precursor fiber membrane is prepared from lignin and co-spun material by electrospinning technology, and the lignin material is doped lignin material or undoped lignin material. In the present invention, the doped lignin material includes transition metal sulfide doped lignin material or transition metal oxide doped lignin material. The present invention does not specifically limit the specific types of heteroatoms in the heteroatom-doped precursor fiber membrane material. In the present invention, taking lignin/polyacrylonitrile as an example, an electrospinning method is used to prepare a precursor fiber membrane.

After the precursor fiber membrane is obtained, the present invention preheats the precursor fiber membrane. In the present invention, the precursor fiber membrane prepared by electrospinning is put into a tube furnace for preheating, and the temperature of the preheating treatment is 200-550°C, specifically 200°C, 250°C, 300°C, 350°C , 400°C, 450°C, 500°C or 550°C. In the present invention, the time of the vacuum preheating treatment is preferably 1430min, which specifically includes a heating time of 800min, a holding time of 450min, and a cooling time of 180min; Hold time after steady state temperature.

In the present invention, the operating conditions induced by the laser direct writing preferably include: the scanning mode is progressive scanning, the scanning rate is 100 mm/s, and the laser power is 0.8-1.5 W. In the present invention, the laser direct writing induction is preferably performed at room temperature and in an atmospheric environment; in an embodiment of the present invention, the room temperature is specifically 25°C. In the present invention, the laser processing system used for the laser induction is preferably a semiconductor laser processing system with a wavelength of 450 nm.

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings; it should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

(1) Preparation of precursor fiber membrane

Lignin (6g) and polyacrylonitrile (4g) were selected as raw materials, and N,N-dimethylformamide (32g) was used as solvent. The lignin and polyacrylonitrile were added to the N,N-dimethylformamide solution, and the solution was stirred in an oil bath at 50° C. for 5 hours to obtain an electrospinning solution. To prepare the doped fiber membranes, ₅ mg of MoS was added to the above solution. Then put the prepared electrospinning solution in a 10mL syringe, configure a 21G needle, set the electrospinning voltage to 20kV, the speed of the receiving roller to be 80r/min, the injection speed of the syringe to be 0.17mL/min, and the collection distance to be 15cm. . At room temperature, a precursor fiber membrane with a thickness of about 200 μm was obtained after 7 hours of electrospinning. Among them, the lignin fiber membrane is yellow, and the MoS ₂ -doped fiber membrane is light brown.

(2) Preheating treatment of precursor fiber membrane

A vacuum tube heating furnace is used to preheat the precursor fiber membrane in step (1). First, put the precursor fiber membrane prepared by electrospinning into a quartz boat or a quartz sheet, and place it in a vacuum tube furnace, evacuate to 2×10 ^-4 Pa, set the heating temperature to 450°C, the heating time to 800min, and the holding time It is 450 ℃, and the cooling time is 180min. After cooling to room temperature, it was taken out to obtain a preheated fiber film.

(3) Laser direct writing preheating fiber film

Use a semiconductor laser processing system with a wavelength of 450 nm to irradiate the preheated fiber film in step (2), focus the light spot on the upper surface of the preheated fiber film, and then set the scanning mode to progressive scanning, and scan the scribe line spacing line by line. is 100 μm, the scanning rate is 100 mm/s, and the laser power is 1.1 W; the laser direct writing process of the interdigital electrode is carried out at room temperature (25° C.) and in an atmospheric environment. The interdigital electrode pattern of laser direct writing is designed through the computer, and then imported into the laser direct writing system software, and the laser direct writing is carried out through software control.

(4) Laser direct writing carbon-based supercapacitor assembly

The laser direct writing interdigital electrode is pasted on one side of a flexible substrate (specifically a polyimide film) with double-sided tape, and the copper foil is pasted on one side of the flexible substrate with double-sided tape to connect For the interdigitated electrodes, conductive silver glue is coated on the joints between the interdigitated electrodes and the copper foil, and then an electrolyte solution is coated on the surface of the interdigitated electrodes, and the solvent in the electrolyte solution is deionized water, The electrolyte is a sulfuric acid-polyvinyl alcohol gel electrolyte (the mass ratio of sulfuric acid and polyvinyl alcohol is 1:1), and the mass fraction of the electrolyte in the electrolyte solution is 10%; after the coating of the electrolyte solution is completed, under vacuum and room temperature conditions After drying for 12 h, the electrolyte solution was solidified, and the laser direct writing carbon-based supercapacitor was obtained.

(5) Electrochemical performance test of laser direct writing carbon-based supercapacitors with different preheating temperatures

The electrochemical properties of the prepared laser direct-writing carbon-based supercapacitors were tested. Figure 5 shows the electrochemical performance of laser direct writing carbon-based supercapacitors at different preheating temperatures. Figure 5(a) is the CV curve when the scan rate is 10mV/s. All the curves are approximately "rectangular", indicating that the laser direct-writing carbon-based supercapacitors have good charge-discharge characteristics at low scan rates. As the preheating temperature increases, the area of the curve becomes larger, indicating that the increase in temperature will increase the specific capacitance of the device. When the preheating temperature is 450°C, the area of the CV curve reaches the maximum value. After the temperature exceeds 450°C, the area of the CV curve decreases. Figure 5(b) shows the GCD curves of laser direct writing carbon-based supercapacitors at different preheating temperatures with a current density of 1 A/g. The GCD curve is almost triangular, indicating double layer capacitance behavior. As the preheating temperature increases, the charge and discharge time increases, and the charge and discharge time of the supercapacitor reaches the maximum value at 450 °C. When the temperature is higher than 450°C, the charge-discharge time begins to decrease. Both Figures 5(a) and (b) show that when the preheating temperature is 450 °C, the CV curve area of the device is the largest and the charging and discharging time is the longest, indicating that the ratio of the laser direct writing carbon-based supercapacitors prepared at this temperature is higher. Capacitors are the best. Figure 5(c) is the specific capacitance curve calculated from the CV curve. When the temperature is 200 °C, the specific capacitance of the laser direct writing carbon-based supercapacitor is about 55.4 F/g. As the preheat temperature increases, the specific capacitance increases. At 450 °C, the specific capacitance of the laser direct writing carbon-based supercapacitor reaches a maximum value of about 326.5 F/g. When the temperature is higher than 450℃, the specific capacitance begins to decrease, and the specific capacitance is about 176F/g at 550℃. When the preheating temperature is higher than 450 °C, the carbonization resistance of the lignin fibers decreases due to the high temperature, and the short circuit of the device leads to the decrease of the specific capacitance. Figure 5(c) further verifies that the laser direct writing carbon-based supercapacitor prepared at a preheating temperature of 450 °C has the largest specific capacitance.

(6) Electrochemical performance test of doped and undoped laser direct writing carbon-based supercapacitors

Electrochemical performance testing of laser direct writing carbon-based supercapacitors _doped and undoped with MoS2. Figure 6 is an electrochemical comparison diagram of two laser direct writing carbon-based supercapacitors. Figure 6(a) is a comparison of the CV curves when the scan rate is 10mV/s, and the two curves as a whole show a similar "rectangular" shape. After doping with MoS ₂ , the area of the CV curve increases significantly. Figure 6(b) is a comparison of the GCD curves of _doped and undoped MoS2, where the current density is 1 A/g. The total charge-discharge time increased from 948s to _1365s after doping with MoS2. Figure 6(c) is a comparison of the specific capacitances of the two supercapacitors calculated from the GCD curves. When the current density was increased from 1A/g to 6A/g, the specific capacitance of the undoped laser direct writing carbon-based supercapacitor ranged from 391F/g to 326F/g, and the laser direct writing capacity of MoS ₂ The specific capacitance of carbon-based supercapacitors ranges from 528F/g to 473F/g. The specific capacitance of the laser direct writing carbon-based supercapacitor _doped with MoS2 is 1.4 times that of the undoped one. It shows that the addition of pseudocapacitive materials has a positive effect on the improvement of device capacitance.

(6) Series and parallel assembly of laser direct writing carbon-based supercapacitors

The prepared laser direct-writing carbon-based supercapacitors were connected in series and parallel, respectively, and then the electrochemical performance was tested respectively. Figure 7 shows the CV and CC curves of two laser direct writing carbon-based supercapacitors preheated at 450°C in series and parallel conditions, and the red light-emitting diode (LED lamp) lighted by the series-connected laser direct writing carbon-based supercapacitor. , where (a) is the CV curve of two series/parallel laser direct writing carbon-based supercapacitors, and the CV curve of a single laser direct writing carbon-based supercapacitor for comparison; (b) is two series/parallel laser direct writing Write the CC curve of the carbon-based supercapacitor, and the CC curve of a single laser direct-writing carbon-based supercapacitor as a comparison; (c) is a photo of a 4×3 series-parallel array laser direct-writing carbon-based supercapacitor lighting a red LED light. The results show that, compared with a single laser direct writing carbon-based supercapacitor, when two laser direct writing carbon-based supercapacitors are connected in series, the window voltage of the laser direct writing carbon-based supercapacitor changes from 1V to 2V, and the current remains unchanged. When two laser direct writing carbon-based supercapacitors are connected in parallel, the current of the capacitor is doubled, and the output time is almost doubled. The 4×3 series-parallel array laser direct writing carbon-based supercapacitor can also successfully light up the red LED light, indicating that the supercapacitor has a high energy density.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (8)

1. A method for improving the specific capacitance of a laser direct writing carbon-based supercapacitor is mainly based on a mode of combining electrostatic spinning, preheating treatment and a laser direct writing technology, and provides a flexible carbon-based fiber electrode material which is low in cost and easy to produce, and is characterized by comprising the following steps:

(1) Preparing a precursor fiber membrane by using an electrostatic spinning technology;

(2) Preheating the precursor fiber film to obtain a preheated fiber film;

(3) Then, a carbon-based fiber electrode material is obtained by inducing carbonization by using a laser direct writing technology, wherein the laser direct writing induced carbon-based fiber material has high conductivity;

(4) And assembling the laser direct-writing induced carbon-based fiber material serving as an electrode to obtain the laser direct-writing carbon-based supercapacitor with the improved specific capacitance.

2. The method of claim 1, wherein the precursor fiber membrane is prepared from lignin and a co-spun material by an electrospinning technique, and the lignin material is a doped lignin material or an undoped lignin material.

3. The method according to claim 2, wherein the doped lignin material comprises a transition metal sulfide doped lignin material or a transition metal oxide doped lignin material.

4. The method of claim 1, wherein the temperature of the pre-heating treatment is 200 to 550; the preheating treatment time is 300-2000 min.

5. The method according to any one of claims 1 to 4, wherein the laser direct write induced carbon-based fiber material has a pore size of 1 to 50nm and a specific surface area of 10 to 150cm ² The square resistance is 4-500 omega/sq.

6. The method of claim 5, wherein the specific capacitance of the laser-direct-write carbon-based capacitor is 50-600F/g.

7. The method of claim 1, wherein the laser-direct-write carbon-based capacitor comprises a planar interdigitated electrode structure, a series-parallel structure, or a stacked structure.

8. The method of claim 1, wherein the laser direct write induced carbon based material comprises amorphous carbon, three-dimensional graphitic structure and graphene material.

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