High‐Performance Flexible Supercapacitors Based on Ionogel Electrolyte with an Enhanced Ionic Conductivity

Abstract As an electrolyte, ionic liquids (ILs) have unique properties, including a wide potential window, high thermal stability, and safety. In particular, the wide potential window of ILs enables energy storage devices to possess a high energy density. In this work, ionogels were synthesized using 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF 4 ) and poly(hydroxyethyl methacrylate)‐co‐poly(ethylene glycol) dimethacrylate) copolymer (PHEMA‐co‐PEGDMA). The prepared ionogels were characterized and investigated for application as an electrolyte in all‐solid‐state supercapacitors. The ionogel electrolytes offer free‐standing films without any supporting substrate. An increment of the ionic conductivity was observed when the ionogel was prepared with a filler‐added copolymer network. The all‐solid‐state supercapacitors fabricated with these ionogels exhibited excellent performance under various bending conditions. Moreover, the specific capacitance retention was about 91% after 3,500 cycles, which demonstrates long‐term stability.