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 conductivity at room temperature, but will freeze below zero inevitably, limiting ion transport and thus affecting electrochemical performance. 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 (AC) electrode to form a symmetrical supercapacitor. Poly(acrylamide) (PAM hydrogel) as the scaffold and poly(1-vinyl-3-butyl imidazolium bromide) (P(VBIMBr)) not only provides structural units with stable size, but also acts as functional units for conducting lithium ions. The anti-freezing electrolyte exhibits remarkable conductivity (26 mS/cm) and the symmetrical supercapacitor possesses excellent electrochemical properties (the specific capacitance is 204 mF/cm2 at 1 mA/cm2). It is worth noting that the capacitance loss of the supercapacitor is only 20.1% at −20 ℃. In addition, the electrolyte also shows the functional characteristics of acid and alkali resistance and bending resistance. The overall merits of the electrolyte will reveal new ideas for the development of hydrogel electrolyte.