J. Liu, W. Liu
Zhengzhou University, Zhengzhou , Henan , China,
Keywords: all-solid-state, supercapacitor, laser-scribed graphene
Summary:With the rapid growth of energy needs and depletion fossil fuels, more concerns have been given to energy storage for renewable wind, wave and solar power, etc.. The development of reliable and cost-effective energy storage devices has greatly satisfied upspring energy demands for diverse applications, ranging from electrical vehicles to micro-chips, of which supercapacitors (SCs) have emerged as potential high-performance energy storage devices for long operation lifetimes, high power densities and environment-friendly operations[2-3]. Recently, all-solid-state supercapacitors, in which solid or gel electrolytes have been used, are attracting more attentions due to their excellent performances in electrochemistry and mechanics, and this suitable for wearable and miniaturized electronic devices. Flexible solid-state supercapacitors generally consist of flexible electrons, solid or gel-like electrolytes. Graphene is a ultra-thin graph-based material, serving as one of promising candidates of making flexible electrons of supercapacitors, due to its outstanding properties, including large theoretic specific surface area (2630m2/g), extraordinary conductivity (106s/cm), great flexibility and transparency[5-7]. An attractive approach for fabricating flexible electrons is coating or growing graphene on flexible, porous and light-weight substrates, another promising approach is to directly prepare free-standing graphene films and transfer on substrates.  However, there is a big challenge for both preparation methods in term of economy, efficiency and scalability, especially in planar and on-chip application. We developed the method of using laser engraver to directly write graphene electrons onto solid-state electrolyte membranes coated with a film of graphene oxide (GO), which can be reduced to graphene during the process. In this scenario, the graphene reduced from graphene oxide (GO) via laser writing is called laser-scribed graphene (LSG), acting as the electron and collector in the supercapacitor. Hydrated graphene oxide (GO) is reported to be a good ionic conductor and as well as an electronic insulator, playing the roles of both separator and electrolyte in planar on-chip device. For sandwich-like devices, PVA/LiCl-H2O system is used for solid-state electrolyte, due to properties of low-cost, non-toxic, high ionic conductivity at ambient temperature, and excellent cycling stability. The large problem of graphene electrons in supercapacitors (SCs) is restacking of graphene sheet, leading to serious degradation of their electrochemical performance. In our work, laser-scribed graphene(LSG) can effectively solve the problems, with large specific surface area (1524m2/g), high conductivity (1738s/cm).[10-11] The electrochemical performance of as-fabricated supercapacitors were measured in a two electrons system by CV and galvanostatic CD at an electrochemical workstation. Electrochemical impedance measurements was performed in same configuration. The cycling stability of the graphene supercapacitor was performed at room temperature with a sweep charge and discharge rate. In conclusion, laser-scribed graphene (LSG) have great performances in mechanics and electrochemistry, we anticipate it will be the suitable material to fabricate next-generation all-solid-state flexible supercapacitors.