High-performance micro supercapacitor assembled by laser-induced graphene electrode and hydrogel electrolyte with excellent interfacial wettability for high capacitance

In this work, we demonstrate a facile, rational and novel strategy to assemble micro-supercapacitors (MSCs) via employing laser-induced graphene (LIG) microelectrodes and sodium alginate/polyacrylamide hydrogel electrolytes soaked in sulfuric acid solution (SA/PAAM-H2SO4). The microelectrodes are conductive graphene materials with porous structure that use laser direct writing technology to carbonize insulating polyimide (PI) sheets. The importance of good wetting of the electrode material by the electrolyte on the performance of the device is explained. There is good compatibility and interfacial contact between electrode and electrolyte. Impressively, the SA/PAAM-H2SO4 hydrogel electrolyte with high ionic conductivity (574.7 mS cm−1) also exhibit good water retention capability and performs normally even after 60 h of exposure to air. The capacitance of LIG-MSCs based on SA/PAAM-H2SO4 hydrogel is comparable to that of PVA/H2SO4 hydrogel. The LIG-MSCs exhibit high areal capacitance of 7.12 mF cm−2 and outstanding cycling stability. Moreover, our LIG-MSCs displays excellent mechanical flexibility and stable performance, the capacitance is almost unaffected even in highly bent states and during continuously hammering. Furthermore, the LIG-MSCs can be arbitrarily connected in series and in parallel without the requirement of metal-based interconnects for high-voltage and high-capacitance output. Our design strategy aims to provide new insights for the development of flexible MSCs.