A surface micro-nano structured graphene supercapacitor based on femtosecond laser processing and a preparation method thereof

Abstract

The application discloses a kind of based on femtosecond laser processing surface micro-nano structured graphene supercapacitor and preparation method thereof, adopt femtosecond laser processing a surface micro-nano structured graphene interdigital electrode, its surface has with the periodic grating micro-nano structure parallel to interdigital electrode direction long axis direction;Periodic micro-nano grating structure parallel to the supercapacitor of interdigital electrode direction, it is favorable to increase specific surface area, provide more active site, while adjustable control electric field improves the migration rate of electrolyte ion.The application prepares periodic micro-nano grating structure parallel to the supercapacitor of interdigital electrode direction, compared with micro-nano grating structure perpendicular to the supercapacitor of interdigital electrode direction and no micro-nano structure supercapacitor, electrochemical performance has somewhat improved.Based on this, large-area supercapacitor array can also be prepared, in the wide application potential of portable electronic equipment, smart wearable device, energy storage system and the like.

Description

Technical Field

[0001] This invention relates to the field of micro energy storage device technology, and in particular to a supercapacitor based on femtosecond laser-processed surface micro / nano-structured graphene and its preparation method. Background Technology

[0002] With the increasing demand for miniaturized, multifunctional portable electronic devices, the fabrication of high-performance, portable micro-energy storage devices has become particularly important. Micro-supercapacitors (MSCs) are the core components of micro-energy storage devices, possessing advantages such as high power density, high cycle stability, and safety and reliability, and have the potential to meet future energy demands. Graphene, due to its unique conductivity and large specific surface area, has become a research hotspot for supercapacitor electrode materials. However, how to construct controllable micro / nano structures on the graphene surface to further improve electrochemical performance remains a current research challenge. Although significant progress has been made in the fabrication of graphene-based supercapacitors, current methods (such as electrophoretic deposition, photolithography, printing processes, chemical vapor deposition, and other chemical methods) often require complex steps such as high-temperature processing, masking, 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 fabrication, but its efficiency is limited in the mass production of micro-array devices, thus restricting its widespread application. Therefore, this paper proposes a method for fabricating surface micro / nano-structured graphene supercapacitors based on femtosecond lasers to better balance the requirements of processing precision 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 / nano-structured supercapacitor, which can efficiently construct specific high-quality micro / nano structures on the surface of graphene materials, thereby significantly improving its capacitance performance.

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

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

[0006] The graphene oxide was prepared using the Hummers method, with an average radial dimension of 20 μm to 30 μm for the graphene oxide sheets and a spin-coated graphene oxide film thickness of 50 to 300 nm.

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

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

[0009] The interdigitated electrodes have 6 interdigitations, an aspect ratio of 6:1, and a gap of 2.5–200 μm.

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

[0011] Another objective of this invention is to provide a surface micro / nano structured graphene interdigitated electrode array, which uses the aforementioned interdigitated electrodes and a 5×5 array structure to connect 5 columns of supercapacitors 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 fabricating surface micro / nano-structured interdigitated electrodes, comprising:

[0013] 1) The graphene oxide solution was ultrasonically dispersed, the silicon wafer was treated with oxygen plasma, and the silicon wafer was spin-coated and dried.

[0014] 2) A femtosecond laser processing device is used to process the pattern using a slicing program, and the pattern is then input into the SLM control program;

[0015] 3) The laser source has a pulse width of 40 fs, a center wavelength of 800 nm, and the laser processing power can be adjusted to 100–150 mW. The scanning speed of the three-dimensional moving platform is 0.001–0.2 mm / s. The focal line formed by the beamline focusing component has a focal length of 10.5 mm, a width of 50 μm, and an adjustable polarization direction.

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

[0017] This invention provides a graphene-based surface micro / nanostructured supercapacitor and its preparation method. The advantages are: It prepares an ultrathin graphene supercapacitor with a surface micro / nanostructure, with a thickness only on the nanometer scale. Compared to supercapacitors without surface micro / nanostructures, the surface micro / nanostructure has a nanometer-scale periodic grating structure, and the porous surface facilitates increased specific surface area, providing more active sites. Simultaneously, the horizontal micro / nanostructure can enhance the electric field, thereby facilitating the regulation of electrolyte ion distribution and migration, and improving capacitance performance. The supercapacitor with a periodic micro / nano grating structure parallel to the interdigitated electrode direction achieves a volumetric specific capacitance of 118.56 F / cm² at a scan rate of 10 mV / s. 3Compared to supercapacitors with micro / nano grating structures perpendicular to the interdigitated electrode direction and supercapacitors without micro / nano structures, this method improves capacitance by 30.89% and 116.86%, respectively, while maintaining a 93.3% capacitance retention after 5000 cycles. Furthermore, the proposed method can be used to fabricate large-area supercapacitor arrays with controllable micro / nano structures on the electrode surface. This method enables the fabrication of 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, demonstrating broad application potential in portable electronic devices, smart wearable devices, and energy storage systems. Attached Figure Description

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

[0019] Figure 2 This is a sample image of a supercapacitor manufactured in Case Study 1;

[0020] Figure 3 This is a scanning electron microscope (SEM) image of the processed electrode surface in Implementation Case 1;

[0021] Figure 4 This is a scanning electron microscope (SEM) image of the processed electrode surface in Implementation Case 3;

[0022] Figure 5 This is an atomic force microscopy (AFM) image of the electrode surface of the micro / nano structure in Implementation Case 1;

[0023] Figure 6 This is an atomic force microscopy (AFM) image of the electrode surface of the micro / nano structure in Implementation Case 3;

[0024] Figure 7 This is the cyclic voltammetry (CV) curve for Implementation Case 1;

[0025] Figure 8 This is the constant current charge-discharge (GCD) curve for Implementation Case 1;

[0026] Figure 9 This is the cycle life curve for Implementation Case 1;

[0027] Figure 10 These are the cyclic voltammetry (CV) curves for implementation cases 1, 2, and 3 at a scan rate of 10 mV / s;

[0028] Figure 11 These are comparison graphs of volumetric capacitance at different scan rates in implementation cases 1, 2, and 3;

[0029] Figure 12 This is a sample image of the array electrode fabricated in Case Study 4. Detailed Implementation

[0030] Example 1: A graphene-based supercapacitor with a periodic grating micro / nano structure on the electrode surface parallel to the long axis of the interdigital fingers.

[0031] The processing steps are as follows:

[0032] 1. Sample preparation: A silicon wafer with a 300nm oxide layer was cut to prepare a 2×2 cm sample. 2 A square substrate was treated with oxygen plasma at 90 W for 1 min to make the silicon wafer hydrophilic. A graphene oxide solution with a concentration of 2 mg / ml was then dispersed by ultrasonication at 1200 W for 10 min, resulting in graphene oxide sheets with an average radial dimension of 20 μm–30 μm. The solution was then spin-coated 25 times onto the hydrophilic silicon wafer at an initial spin speed of 500 rad / 5 s, followed by 2400 rad / 30 s, to obtain a graphene oxide film with a thickness of approximately 100 nm on the silicon substrate.

[0033] 2. Design interdigitated electrode patterns

[0034] The interdigitated electrode pattern was drawn using drawing software. A total of six interdigitated electrodes were designed, each 3600 μm long, 600 μm wide, and with a 60 μm gap between them. The designed pattern was processed using a slicing program, distinguishing the processed and unprocessed areas based on grayscale values. Each sliced ​​pattern included the size of the light spot corresponding to the processed area and the position information of the moving platform in that area. The pattern was then input into the linkage program between the spatial light modulator and the 3D moving platform, enabling simultaneous control of the light spot size and processing position during the electrode pattern processing.

[0035] 3. Machining interdigitated electrodes

[0036] The selected laser source unit is a Ti:sapphire chirped pulse amplified laser, whose output laser source is a linearly polarized femtosecond laser pulse. The pulse width of the laser source is 40 fs, the center wavelength is 800 nm, and the Gaussian spot diameter is 6 mm. According to the designed optical path... Figure 1As shown, the system includes a laser source, an energy modulation component, a beam expander, a spatial light modulator, a polarization end adjustment component, a beamline focusing component, and a three-dimensional moving platform. By adjusting the spatial light modulator, the spatial distribution of laser intensity can be controlled. The polarization end adjustment component can change the polarization direction of the processed light, enabling micro / nano-structuring of the sample surface while simultaneously photoreducing and drawing electrode patterns. The processing power is adjusted to 120 mW, the scanning speed of the three-dimensional moving platform is 0.1 mm / s, and the focal line length formed by the beamline focusing component is adjusted to 10.5 mm with a width of 50 μm. The laser polarization direction is adjusted to be parallel to the long axis of the interdigitated electrode, and the sample is positioned at the focal line. The linkage program between the spatial light modulator and the three-dimensional moving platform is activated. The beamline length and the moving platform change simultaneously according to the input sliced ​​image information. The beamline sweeps across the graphene oxide film surface to pattern it, simultaneously achieving microstructuring and reduction of the processed area, obtaining reduced graphene oxide interdigitated electrodes with a periodic grating micro / nano structure parallel to the long axis of the interdigitates.

[0037] 4. Supercapacitor Assembly and Testing: The electrolyte was prepared as a PVA / H3PO4 electrolyte. 5g of PVA and 5g of H3PO4 were weighed and added to 50ml of deionized water, respectively. The mixture was heated in a water bath at 85℃ and stirred for 4 hours. The solution became transparent and was allowed to cool naturally in a ventilated area before use. The electrolyte was added dropwise to cover the middle area of ​​the interdigitated electrodes. Silver wires were attached to both ends of the supercapacitor using silver paste, and the capacitor was connected to an electrochemical workstation for testing. Cyclic voltammetry (CV) tests were performed at 0V–0.8V with a scan rate of 10 mV / s–100 mV / s, and the specific capacitance was calculated.

[0038] Example 2: A graphene-based supercapacitor with a periodic grating micro / nano structure on the electrode surface perpendicular to the long axis of the interdigital fingers.

[0039] The preparation steps are as follows:

[0040] A graphene supercapacitor with a periodic grating micro / nano structure on the electrode surface perpendicular to the long axis of the interdigital fingers was prepared according to the scheme of Example 1. The difference from Example 1 is that in step 3 of Example 1, the polarizer direction was adjusted so that the laser polarization direction of the processed sample was perpendicular to the designed long axis of the interdigital fingers.

[0041] Example 3: Graphene-based supercapacitor with no micro / nano structure on the electrode surface

[0042] The graphene supercapacitor with no micro / nano structure on the electrode surface was prepared according to the scheme of Example 1. The difference from Example 1 is that in step 3 of Example 1, a quarter polarizer was placed in front of the cylindrical lens 1 so that the processing laser is circularly polarized light and the processing electrode surface has no microstructure.

[0043] Example 4: Graphene-based supercapacitor array with micro / nano structures on the electrode surface

[0044] A graphene supercapacitor array with a micro / nano structure was prepared according to the scheme of Example 1. The difference from Example 1 is that the spin film substrate used in step 1 is a circular silicon wafer with a diameter of 3 cm. The pattern designed in step 3 is an interdigitated array structure, which is a 5×5 array of micro supercapacitors, with 5 supercapacitors connected in series in each row and 5 micro supercapacitors connected in parallel in each column.

[0045] Example 5 Device Performance Characterization

[0046] The samples obtained in Examples 1 to 4 were characterized and their electrochemical data were analyzed.

[0047] Figure 1 The optical path diagram for processing samples includes a laser source, energy modulation components, beam expander components, spatial light modulator, polarization end adjustment components, beamline focusing components, and a three-dimensional moving platform. By adjusting the spatial light modulator, the spatial distribution of laser intensity can be controlled. The polarization end adjustment components can change the polarization direction of the processed light, enabling the simultaneous optical reconstruction of electrode patterns on the sample surface through micro / nano-structuring. A quarter-polarizer is added between the cylindrical lens 1 and the three-dimensional moving platform to adjust the processing laser to circularly polarized light, allowing for the processing of electrodes without surface stripes.

[0048] Figure 2 The image shows a supercapacitor sample fabricated for Case 1. 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.

[0049] Figure 3 To illustrate the scanning electron microscopy (SEM) image of the electrode with micro-nano structures on the surface in Case 1, the width and spacing of the grating micro-nano structures are basically similar. The micro-nano structures are continuous, complete, and have a uniform period of 680nm±20nm. The surface of each stripe is relatively rough, which significantly increases the specific surface area.

[0050] Figure 4 This is a scanning electron microscope (SEM) image of an electrode surface without micro / nano structures. Many irregular strip-like structural veins can be seen on the surface, distributed rather dispersedly and randomly. This contrasts with surfaces containing micro / nano structures, which appear smoother.

[0051] Figure 5To obtain atomic force microscopy (AFM) images of the electrode surface with micro / nano structures in Case 1, the microstructure undulations of the graphene oxide film are ~40 nm, and it has a thickness of ~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 its electrode surface is ~60 nm.

[0052] Figure 6 To implement Case 3, atomic force microscopy (AFM) images of the electrode surface without micro / nano structures are obtained, with a thickness of ~60 nm.

[0053] Figure 7 For example, the cyclic voltammetry (CV) curves at voltage scan rates of 10 mV / s to 100 mV / s in Case 1 are symmetrical rectangles, which conforms to ideal capacitance characteristics.

[0054] Figure 8 To implement 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 exhibit a quasi-triangular shape, indicating that the asymmetric supercapacitor of Example 1 has good rate performance and stability.

[0055] Figure 9 Implementation Case 1: Cyclic life curve, still maintaining a 93.3% capacitance retention rate after 5000 cycles.

[0056] Figure 10 The comparison graphs of cyclic voltammetry (CV) curves for samples 1, 2, and 3 at a voltage scan rate of 10 mV / s show that the graphene-based supercapacitor with periodic grating micro / nano structures on the electrode surface parallel to the long axis of the interdigital fingers has the best electrochemical performance, followed by the graphene-based supercapacitor with periodic grating micro / nano structures on the electrode surface perpendicular to the long axis of the interdigital fingers, and the graphene-based supercapacitor with no micro / nano structures on the electrode surface has the worst performance.

[0057] Figure 11 To compare the areal capacitance at different scan rates in implementation schemes 1, 2, and 3, and with... Figure 7The conclusions are consistent because the introduction of horizontal and vertical micro / nano structures on the electrode surface can effectively modulate 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. Simultaneously, the micro / nano structures can increase the specific surface area of ​​the electrode, providing more reaction sites and thus improving the rate and efficiency of electrochemical reactions. Furthermore, the grating micro / nano structures on the electrode surface help improve the diffusion path of electrolyte ions, further promoting ion transport and enhancing the overall performance of the capacitor. The efficient supercapacitor fabrication method proposed in this paper holds great potential for the preparation of high-performance supercapacitors.

[0058] Figure 12 The sample image shown in Case Study 4 depicts a 5×5 array of miniature supercapacitors fabricated using this method. The array exhibits a regular arrangement and excellent macroscopic structural color effect, indicating the regularity of the micro / nano structure on the electrode surface. This method can fabricate large-area supercapacitor arrays with controllable surface micro / nano structures, demonstrating broad application potential.

Claims

1. A surface micro / nano-structured graphene interdigitated electrode, characterized in that: The electrode surface has a periodic grating micro / nano structure parallel to the long axis of the interdigital fingers; The electrode is an interdigitated electrode, and the electrode and the periodic grating micro / nano structure on the electrode surface are fabricated using a femtosecond laser processing device, with the laser polarization direction parallel to the long axis of the interdigitated fingers; The femtosecond laser processing apparatus includes: a polarization end adjustment component; the polarization end adjustment component is used to adjust and change the polarization direction of the processing laser.

2. The surface micro / nano structured graphene interdigitated electrode according to claim 1, characterized in that: The electrode is prepared by the following method: 1) The graphene oxide solution was ultrasonically dispersed, the silicon wafer was treated with oxygen plasma, and the silicon wafer was spin-coated and dried. 2) A femtosecond laser processing device is used to process the pattern using a slicing program, and the pattern is then input into the SLM control program; 3) The laser source has a pulse width of 40 fs, a center wavelength of 800 nm, and the laser processing power is adjusted to 100–150 mW. The scanning speed of the three-dimensional moving platform is 0.001–0.2 mm / s, and the focal line formed by the beamline focusing assembly has a focal length of 10.5 mm and a width of 50 μm.

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

4. The surface micro / nano structured graphene interdigitated electrode according to claim 3, characterized in that: The graphene oxide was prepared by the Hummers method, with an average radial dimension of 20 μm to 30 μm for the graphene oxide sheets and a spin-coated graphene oxide film thickness of 50 to 300 nm.

5. The surface micro / nano structured graphene interdigitated electrode according to claim 4, characterized in that: The thickness of the oxide layer on the silicon wafer is 300 nm.

6. A surface micro / nano-structured graphene interdigitated electrode according to any one of claims 1-5, characterized in that: The periodicity of the periodic grating micro / nano structure is 680nm ± 20nm.

7. The surface micro / nano structured graphene interdigitated electrode according to claim 6, characterized in that: The interdigitated electrodes have 6 interdigitations, an aspect ratio of 6:1, and a gap of 2.5–200 μm.

8. The surface micro / nano structured graphene interdigitated electrode according to claim 7, characterized in that: The substrate is a circular silicon wafer with a diameter of 3cm.

9. A surface micro / nano-structured graphene interdigitated electrode array, characterized in that: Using the interdigitated electrode as described in claim 6, a 5×5 array structure is adopted, in which 5 columns of supercapacitors are connected in parallel, wherein each column consists of 5 supercapacitors connected in series.

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