Research On Hierarchical Structured Metallic Mesh Based Flexible Transparent Supercapacitor

Fully transparent flexible energy storage devices are critical components in flexible transparent electronics.Significantly,the supercapacitor electrode must simultaneously exhibits high capacity,high optical transmittance and excellent mechanical properties for practical applications in flexible transparent devices.It is difficult to meet the extreme requirements of flexible transparent supercapacitor electrodes because the existing flexible transparent conductive electrodes still suffer from single function and complicated fabrication processes.In this project,a high-aspect-ratio freestanding flexible transparent metallic mesh structured current collector is proposed.The freestanding electrochemically active material/metallic mesh hybrid electrode with unique hierarchical microstructure can be realized by precisely regulating the hierarchical structured surface of the metallic mesh electrode to induce electrochemically active nanomaterial deposition,breaking through the contradiction and limitation of traditional flexible transparent electrode in high capacity,high transparency and mechanical flexibility.The design and fabrication of the high-aspectratio freestanding metallic mesh electrode,the regulation mechanism of hierarchical structures to the morphology of active material,and the mechanism of electrochemical behavior promotion are also well studied.With enormous efforts,high-performance supercapacitor electrode and solid-state device with high transparency,superior electrochemical performance and excellent mechanical flexibility will be developed in this project.This project provides a novel route for developing high-performance energy storage device for future flexible transparent electronics.The main contents of this thesis are as follows:(1)Simulation analysis of the hierarchical micro/nano-structure metallic mesh electrode structure and electrochemical characteristics.Auto-CAD is used to design Ni metallic mesh structure with different structures and line widths.The size of the bottom area,surface area,volume,and porosity of these structures at specific sizes is analyzed.Furthermore,the optimal electrode structure parameters are determined by combining air pressure and airflow conditions.In addition,the electrical simulation analysis of the current distribution characteristics of the Ni metallic mesh electrode is adopted to provide a theoretical basis for the construction of the hierarchical micro/nano-structure metallic mesh electrode in the subsequent work.(2)The self-supporting Ni metallic mesh is prepared by patterned lithography and selective electrodeposition technology.The optical transmittance of the electrode in the visible light range reaches 90%.Subsequently,conductive polymer poly(3,4ethylenedioxythiophene)(PEDOT)is electrochemically deposited on the surface of the selfsupporting Ni metallic mesh.The electrochemical characteristics of the PEDOT@Ni composite electrode are systematically studied,and the surface capacitance of the composite electrode reaches 4.8 mF/cm2,with a capacitance retention rate of 98%after 10,000 cycles.(3)Hierarchical micro/nano-structured metallic mesh-based supercapacitors were constructed to obtain high-performance flexible and transparent supercapacitors.By modulating the micro/nano-structure,a hierarchical "coral-like" conductive electrode with a larger specific surface area was obtained,which could induce the in-situ controllable growth of PEDOT electroactive materials and precisely control the microstructure of PEDOT to construct a high-performance flexible transparent PEDOT@Ni composite electrode.The growth control of the "coral-like" Ni layer on the Ni metallic mesh and the surface control during the subsequent PEDOT deposition,under the synergistic effect of micro/nanostructure modulation of both,can increase the surface capacitance of the composite electrode by more than 196%(surface capacitance of 9.4 mF/cm2).Based on this hierarchical micro/nano-structure,a fully solid-state flexible transparent supercapacitor was constructed with a surface capacitance of 1.95 mF/cm2,and the capacitance retention rate remained above 95%after 10,000 cycles.The PEDOT used in this thesis has stable chemical properties and a high conductivity that endows PEDOT with fast ion transport performance.Developing hierarchical micro/nano-structures on self-supporting metallic mesh can increase the effective surface area and shorten the diffusion pathway of ions and electrons.The hierarchical micro/nanostructured composite PEDOT@Ni electrode prepared in this thesis has unique advantages in the field of flexible storage and can provide a new design concept for the future development of flexible supercapacitors.