An Innovative Poly(Ionic Liquid) Hydrogel-Based Anti-Freezing Electrolyte with High Conductivity for Supercapacitor

The rapid development of intelligent and wearable electronic products poses new challenges to flexible energy storage devices with wide operating temperature range, stable performance and safety. Hydrogel electrolytes own high room-temperature, but suffer from the inevitable freezing of water below zero centigrade. To address this problem, an innovative poly(ionic liquid) hydrogel-based anti-freezing electrolyte is fabricated by copolymerization of 1-vinyl-3-butyl imidazole bromide (VBIMBr) monomer and acrylamide (AM) monomer, and assembled with activated carbon electrode to form a symmetrical supercapacitor. Poly(acrylamide) (PAM) is as the scaffold and poly(1-vinyl-3-butylimidazolium bromide) (P(VBIMBr)) not only provides structural units with stable size, but also dissolves lithium salts and acts as functional units for conducting lithium ions. The anti-freezing electrolyte exhibits outstanding conductivity at 26 mS/cm and the specific capacitance of the supercapacitor assembled with AC is 204 mF/cm2 at 1 mA/cm2. At the same time, the capacitance loss of the supercapacitor at -20 °C is only 20.1%. In addition, the electrolyte also exhibits the functional characteristics of acid and alkali resistance and no fear of bending. The overall merits of the electrolyte will open up new ideas for the development of hydrogel electrolyte.