Surface micro-nano structured graphene supercapacitor based on femtosecond laser processing and preparation method thereof

Abstract

The invention discloses a surface micro-nano structured graphene supercapacitor based on femtosecond laser processing and a preparation method thereof, a surface micro-nano structured graphene interdigital electrode is processed by femtosecond laser, and the surface of the surface micro-nano structured graphene interdigital electrode is provided with a periodic grating micro-nano structure parallel to the interdigital long axis direction; the supercapacitor with the periodic micro-nano grating structure parallel to the interdigital electrode direction is beneficial to increasing the specific surface area, provides more active sites, and can regulate and control the electric field to improve the migration rate of electrolyte ions. According to the supercapacitor with the periodic micro-nano grating structure parallel to the direction of the interdigital electrode, compared with a supercapacitor with the micro-nano grating structure perpendicular to the direction of the interdigital electrode and a supercapacitor without a micro-nano structure, the electrochemical performance of the supercapacitor is improved. A large-area supercapacitor array can be prepared based on the method, and the method has wide application potential in the fields of portable electronic equipment, intelligent wearable equipment, energy storage systems and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of micro energy storage devices, and in particular to a graphene supercapacitor with surface micro-nano structure processed by femtosecond laser and a preparation method thereof. Background Art

[0002] With the growing demand for miniaturized, multifunctional portable electronic devices, the preparation of high-performance, portable micro energy storage devices is particularly important. Micro supercapacitors (MSCs) are the core components of micro energy storage devices. They have the advantages of high power density, high cycle stability, safety and reliability, and have the potential to meet future energy needs. Graphene materials have become a hot topic in the research of supercapacitor electrode materials due to their unique electrical conductivity, large specific surface area and other excellent properties. However, how to construct controllable micro-nano structures on the graphene surface to further improve the electrochemical performance is still a difficult point in current research. Although great progress has been made in the manufacture of graphene-based supercapacitors, current methods (such as electrophoretic deposition technology, photolithography, printing process, chemical vapor deposition and other chemical methods) often require complex steps such as high temperature treatment steps, masks or multi-step chemical synthesis, making it difficult to achieve efficient and high-quality construction of controllable micro-nano structures on the electrode surface. Laser direct writing technology can achieve fine micro-nano structure processing, but its efficiency is limited in the mass production of micro-array devices, which restricts its widespread application. Therefore, this paper proposes a preparation method for surface micro-nanostructured graphene supercapacitors based on femtosecond laser to better balance the needs of processing accuracy and large-scale manufacturing. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a graphene-based surface micro-nanostructured supercapacitor, which efficiently constructs a specific high-quality micro-nanostructure on the surface of the graphene material, and can significantly improve its capacitance performance.

[0004] A surface micro-nano structured interdigital electrode, wherein the electrode surface has a periodic grating micro-nano structure parallel to the long axis direction of the interdigital fingers;

[0005] The substrate is a silicon wafer substrate having an oxide layer and is coated with a graphene oxide film;

[0006] The graphene oxide is prepared by the Hummers method, the average radial size of the graphene oxide sheet is 20 um to 30 um, and the thickness of the spin-coated graphene oxide film is 50 to 300 nm;

[0007] The oxide layer of the silicon wafer is 300nm;

[0008] The period of the periodic grating micro-nano structure is 680nm±20nm.

[0009] The number of interdigital fingers of the interdigital electrode is 6, the electrode length-width ratio is 6:1, and the electrode gap is 2.5-200 um.

[0010] The silicon wafer substrate is a circular silicon wafer with a diameter of 3 cm.

[0011] Another object of the present invention is to provide a surface micro-nanostructured graphene interdigital electrode array, using the above-mentioned interdigital electrodes, using a 5×5 array structure, 5 columns of supercapacitors are connected in parallel, wherein each column consists of 5 supercapacitors connected in series.

[0012] Another object of the present invention is to provide a method for processing a surface micro-nanostructured interdigital electrode, comprising:

[0013] 1) subjecting the graphene oxide solution to ultrasonic dispersion treatment, treating the silicon wafer with oxygen plasma, spin coating the silicon wafer using a spin coating method, and drying;

[0014] 2) Using a femtosecond laser processing device, the pattern is processed using a slicing program and the pattern is input into the SLM control program;

[0015] 3) The pulse width of the laser light source is 40fs, the central wavelength is 800nm, the laser processing power is adjusted to 100-150mW, the scanning speed of the three-dimensional mobile platform is 0.001-0.2mm / s, the focal line length formed by the beam line focusing assembly is 10.5mm, the width is 50μm, and the polarization direction is adjustable.

[0016] The femtosecond laser processing device comprises: a laser light source, an energy modulation component, a beam expansion component, a spatial light modulator, a polarization end adjustment component, a beam line focusing component and a three-dimensional moving platform; the polarization end adjustment component is used to adjust and change the polarization direction of the processing light.

[0017] The present invention provides a graphene-based surface micro-nano structured supercapacitor and a preparation method thereof, which has the beneficial effects of preparing an ultra-thin graphene supercapacitor with a surface micro-nano structure, the thickness of which is only nanometers. Compared with supercapacitors without micro-nano structures on the electrode surface, the surface micro-nano structure has a nanometer-scale periodic grating structure, and the surface porous holes are beneficial to increase the specific surface area and provide more active sites. At the same time, the horizontal micro-nano structure can enhance the electric field, which is beneficial to regulate the distribution and migration of electrolyte ions and improve the capacitance performance. The supercapacitor with a periodic micro-nano grating structure parallel to the direction of the interdigitated electrodes was prepared, and the volume specific capacitance reached 118.56 F / cm at a scanning rate of 10mV / s. 3Compared with supercapacitors with micro-nano grating structures perpendicular to the direction of the interdigital electrodes and supercapacitors without micro-nano structures, the capacitance retention rate is increased by 30.89% and 116.86% respectively, and the capacitance retention rate is still 93.3% after 5000 cycles. At the same time, the method proposed in this paper can be used to prepare large-area supercapacitor arrays with controllable micro-nano structures on the electrode surface. This method can prepare large-area supercapacitor arrays with highly controllable surface micro-nano structures. By precisely controlling the electrode surface structure, the energy storage performance of the capacitor can be significantly improved, and it has broad application potential in portable electronic devices, smart wearable devices, energy storage systems and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the laser processing optical path;

[0019] Figure 2 This is a sample diagram of supercapacitors processed in implementation case 1;

[0020] Figure 3 This is a scanning electron microscopy (SEM) image of the electrode surface processed in implementation case 1;

[0021] Figure 4 This is a scanning electron microscopy (SEM) image of the electrode surface processed in implementation case 3;

[0022] Figure 5 is an atomic force microscopy (AFM) image of the electrode surface of the micro-nano structure of implementation example 1;

[0023] Figure 6 is an atomic force microscopy (AFM) image of the electrode surface of the micro-nano structure of implementation case 3;

[0024] Figure 7 It is the cyclic voltammetry (CV) curve of implementation case 1;

[0025] Figure 8 It is the constant current charge and discharge (GCD) curve of implementation case 1; Fig. 9 It is the cycle life curve of implementation case 1;

[0026] Fig.10 are the cyclic voltammetry (CV) curves of implementation cases 1, 2, and 3 at a scan rate of 10 mV / s;

[0027] Fig.11 is a comparison chart of volume specific capacitance at different scan rates for implementation cases 1, 2, and 3;

[0028] Fig.12 This is a picture of the array electrode sample processed in implementation case 4. DETAILED DESCRIPTION

[0029] Example 1 Graphene-based supercapacitor with a periodic grating micro-nano structure on the electrode surface parallel to the long axis of the interdigitated fingers

[0030] The processing steps are as follows:

[0031] 1. Sample preparation: Cut the silicon wafer with 300nm oxide layer to prepare 2×2 cm 2 The square substrate was treated with oxygen plasma at 90 W for 1 min to make the silicon wafer hydrophilic. The graphene oxide solution with a concentration of 2 mg / ml was dispersed by ultrasound at 1200 W power for 10 min, where the average radial size of the graphene oxide sheet was 20 um~30 um. Then the hydrophilic silicon wafer was spin-coated with the graphene oxide solution 25 times using a spin coating method with an initial spin coating speed of 500 rad / 5 s and then 2400 rad / 30 s to obtain a graphene oxide film with a thickness of about 100 nm on the silicon substrate.

[0032] 2. Design of interdigitated electrode pattern

[0033] The interdigital electrode pattern was drawn using drawing software. The total number of interdigital electrodes designed was 6, the length of the electrode was 3600 μm, the width of the electrode was 600 μm, and the electrode gap was 60 μm. The designed pattern was processed using a slicing program, and the processing area and the non-processing area were distinguished according to the grayscale value. Each slicing pattern contained the size of the line spot corresponding to the processing area and the position information of the mobile platform corresponding to the processing area. The pattern was input into the linkage program of the spatial light modulator and the three-dimensional mobile platform to achieve simultaneous control of the line spot size and the processing position during the electrode pattern processing.

[0034] 3. Processing interdigital electrodes

[0035] The selected laser source unit adopts a titanium-doped sapphire chirped pulse amplified laser, and the laser source output is a linearly polarized femtosecond laser pulse. The pulse width of the laser source is 40 fs, the central wavelength is 800 nm, and the Gaussian spot diameter is 6 mm. According to the designed optical path, Figure 1As shown, it includes a laser light source, an energy modulation component, a beam expansion component, a spatial light modulator, a polarization end adjustment component, a beam line focusing component and a three-dimensional mobile platform. By adjusting the spatial light modulator, the spatial distribution of the laser intensity can be controlled; the polarization end adjustment component can change the polarization direction of the processing light, and the surface of the processed sample can be micro-nanostructured and the electrode pattern can be drawn by photoreduction. The processing power is adjusted to 120 mW, the scanning speed of the three-dimensional mobile platform is 0.1 mm / s, and the focal line length formed by the beam line focusing component is adjusted to 10.5 mm and the width is 50 μm. The polarization direction of the laser is adjusted to be parallel to the long axis direction of the forked finger electrode, and the sample is at the focal line position. Start the linkage program of the spatial light modulator and the three-dimensional mobile platform, the line spot length and the mobile platform change simultaneously according to the input sliced ​​image information, the line spot scans the surface of the graphene oxide film to pattern it, and the microstructuring and reduction treatment of the processing area are realized at the same time, and the reduced graphene oxide forked finger electrode is obtained, and its surface has a periodic grating micro-nano structure parallel to the long axis direction of the forked finger.

[0036] 4. Assembly and testing of supercapacitors: Prepare the electrolyte as PVA / H3PO4 electrolyte, weigh 5g PVA, 5gH3PO4, add them to 50 ml deionized water, heat in a water bath at 85 °C and stir for 4 h. The solution is transparent and placed in a ventilated place to cool naturally for use. Add the electrolyte dropwise to cover the middle area of ​​the interdigital electrode, use silver glue to paste silver wires at both ends of the supercapacitor, and connect the electrochemical workstation for testing. The cyclic voltammetry (CV) test is carried out at 0 V-0.8 V, with a scan rate of 10 mV / s to 100 mV / s, and calculate its specific capacitance.

[0037] Example 2 Graphene-based supercapacitor with a periodic grating micro-nano structure on the electrode surface perpendicular to the long axis direction of the interdigitated fingers

[0038] The preparation steps are as follows:

[0039] A graphene supercapacitor having an electrode surface with a periodic grating micro-nano structure perpendicular to the long axis direction of the interdigitated fingers is prepared according to the scheme of Example 1. The difference from Example 1 is that in step 3 of Implementation Case 1, the direction of the polarizer is adjusted so that the laser polarization direction of the processed sample is perpendicular to the designed long axis direction of the interdigitated fingers.

[0040] Example 3 Graphene-based supercapacitor without micro-nanostructure on electrode surface

[0041] A graphene supercapacitor with no micro-nano structure on the electrode surface is prepared according to the scheme of Example 1. The difference from Example 1 is that in step 3 of Implementation Case 1, a quarter polarizer is placed in front of the cylindrical lens 1 to make the processing laser circularly polarized light and to process the electrode surface without microstructure.

[0042] Example 4 Graphene-based supercapacitor array with micro-nanostructure on electrode surface

[0043] A graphene supercapacitor array with a micro-nano structure was prepared according to the scheme of Example 1, except that a circular silicon wafer with a diameter of 3 cm was used as the spin-film substrate in step 1. The pattern designed in step 3 was an interdigitated array structure, which was a 5×5 array micro-supercapacitor group, and the number of supercapacitors connected in series in each row was 5, and the number of micro-supercapacitors connected in parallel in each column was 5.

[0044] Example 5 Device Performance Characterization

[0045] The samples obtained in Examples 1 to 4 were characterized and electrochemical data analyzed:

[0046] Figure 1 The optical path diagram for processing samples includes a laser light source, an energy modulation component, a beam expansion component, a spatial light modulator, a polarization end adjustment component, a beam line focusing component, and a three-dimensional mobile platform. By adjusting the spatial light modulator, the spatial distribution of the laser intensity can be controlled; the polarization end adjustment component can change the polarization direction of the processing light, and the surface of the processed sample can be micro-nanostructured and the electrode pattern can be drawn by photoreduction. A quarter polarizer is added between the cylindrical lens 1 and the three-dimensional mobile platform to adjust the processing laser to circularly polarized light, so that electrodes without stripes on the surface can be processed.

[0047] Figure 2 This is a picture of the supercapacitor sample processed in implementation case 1, where the direction of the micro-nano structure on the electrode surface is parallel to the long axis of the interdigitated electrode. The yellow-green area is the graphene oxide base film, and the blue area is the laser-processed reduced graphene oxide electrode area.

[0048] Figure 3 This is a scanning electron microscopy (SEM) image of the electrode with micro-nano structure on the surface in Example 1. The width and spacing of the grating micro-nano structure are basically similar. The micro-nano structure is coherent, complete and uniform in period, with a period of 680nm±20nm. The surface of each stripe is relatively rough, which significantly increases the specific surface area.

[0049] Figure 4 This is a scanning electron microscopy (SEM) image of the electrode surface without micro-nano structures. Many irregular strip-shaped structures can be seen on the surface, which are distributed more dispersedly and randomly. Compared with the surface with micro-nano structures, it is relatively smooth.

[0050] Figure 5Atomic force microscopy (AFM) image of the electrode surface with micro-nano structures in Example 1. The microstructure of the graphene oxide film fluctuates by ~40 nm, and the thickness is ~20 nm relative to the silicon substrate, proving that the microstructure is on the surface of the graphene oxide film and does not damage the silicon substrate. The total thickness of the supercapacitor electrode with micro-nano structures on the electrode surface is ~60nm.

[0051] Figure 6 This is an atomic force microscopy (AFM) image of the electrode surface without micro-nano structures in implementation case 3, with a thickness of ~60nm.

[0052] Figure 7 For implementation case 1, the cyclic voltammetry (CV) curve at a voltage scan rate of 10 mV / s ~100 mV / s is a symmetrical rectangle, which conforms to the ideal capacitance characteristics.

[0053] Figure 8 For implementation case 1, at 0.6 μA / cm 2 , 0.7 μA / cm 2 , 0.8 μA / cm 2 , 0.9 μA / cm 2 , 1.0 μA / cm 2 The constant current charge-discharge (GCD) curves all show a quasi-triangular shape, indicating that the asymmetric supercapacitor of Example 1 has good rate performance and stability.

[0054] Fig. 9 Implementation Case 1 Cycle life curve, after 5000 cycles, the capacitance retention rate is still 93.3%.

[0055] Fig.10 The cyclic voltammetry (CV) curves corresponding to the samples of implementation cases 1, 2, and 3 are compared at a voltage scan rate of 10 mV / s. It can be seen that the best electrochemical performance is the graphene-based supercapacitor with a periodic grating micro-nano structure on the electrode surface parallel to the long axis direction of the interdigitated fingers, followed by the graphene-based supercapacitor with a periodic grating micro-nano structure on the electrode surface perpendicular to the long axis direction of the interdigitated fingers, and the worst is the graphene-based supercapacitor with no micro-nano structure on the electrode surface.

[0056] Fig.11 Comparison of area specific capacitance at different scan rates for implementation schemes 1, 2, and 3. Figure 7The conclusions obtained are consistent, because the introduction of horizontal and vertical micro-nano structures on the electrode surface can effectively regulate the electric field, thereby improving the distribution and migration behavior of electrolyte ions and increasing the adsorption and desorption rates of ions at the electrode interface. At the same time, the micro-nano structure can also increase the specific surface area of ​​the electrode and provide more reaction sites, thereby increasing the rate and efficiency of the electrochemical reaction. In addition, the grating micro-nano structure on the electrode surface helps to improve the diffusion path of electrolyte ions, further promote ion transport, and enhance the overall performance of the capacitor. The efficient processing method of supercapacitors proposed in this article has great potential for the preparation of high-performance supercapacitors.

[0057] Fig.12 The sample picture in implementation case 4 is a 5×5 array of micro supercapacitors processed by this method. The processed array is arranged regularly and has excellent macroscopic structural color effect, indicating that the micro-nano structure of the electrode surface is regular. This method can prepare large-area supercapacitor arrays with controllable surface micro-nano structures, and has broad application potential.

Claims

1. A surface micro-nanostructured graphene interdigitated electrode, characterized in that: The electrode surface has a periodic grating micro-nano structure parallel to the long axis direction of the interdigitated fingers.

2. The surface micro-nanostructured graphene interdigitated electrode according to claim 1, characterized in that: The substrate is a silicon wafer substrate with an oxide layer and is coated with a graphene oxide film.

3. The surface micro-nanostructured graphene interdigitated electrode according to claim 2, characterized in that: The graphene oxide is prepared by the Hummers method, the average radial size of the graphene oxide sheet is 20 um to 30 um, and the thickness of the spin-coated graphene oxide film is 50 to 300 nm.

4. The surface micro-nanostructured graphene interdigitated electrode according to claim 3, characterized in that: The oxide layer of the silicon wafer is 300nm.

5. A surface micro-nanostructured graphene interdigitated electrode according to claim 1, 2, 3 or 4, characterized in that: The period of the periodic grating micro-nano structure is 680nm±20nm.

6. The surface micro-nanostructured graphene interdigitated electrode according to claim 5, characterized in that: The number of interdigital fingers of the interdigital electrode is 6, the electrode length-width ratio is 6:1, and the electrode gap is 2.5-200 um.

7. The surface micro-nanostructured graphene interdigitated electrode according to claim 6, characterized in that: The silicon wafer substrate is a circular silicon wafer with a diameter of 3 cm.

8. A surface micro-nanostructured graphene interdigitated electrode array, characterized in that: The interdigital electrode according to claim 6 or 7 is used, and a 5×5 array structure is adopted to connect 5 columns of supercapacitors in parallel, wherein each column consists of 5 supercapacitors connected in series.

9. The method for processing a surface micro-nanostructured interdigital electrode according to claim 1, characterized in that: 1) subjecting the graphene oxide solution to ultrasonic dispersion treatment, treating the silicon wafer with oxygen plasma, spin coating the silicon wafer using a spin coating method, and drying; 2) Using a femtosecond laser processing device, the pattern is processed using a slicing program and the pattern is input into the SLM control program; 3) The pulse width of the laser light source is 40fs, the central wavelength is 800nm, the laser processing power is adjusted to 100-150mW, the scanning speed of the three-dimensional mobile platform is 0.001-0.2mm / s, and the focal line length formed by the beam line focusing component is 10.5mm and the width is 50μm.

10. The method for processing surface micro-nanostructured interdigital electrodes according to claim 1, characterized in that: The femtosecond laser processing device comprises: a laser light source, an energy modulation component, a beam expansion component, a spatial light modulator, a polarization end adjustment component, a beam line focusing component and a three-dimensional moving platform; the polarization end adjustment component is used to adjust and change the polarization direction of the processing light.

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