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

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 (EMIMBF4) 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.