Dual-Aspect Expanding Electrochemical Characteristics of Flexible Supercapacitors via an Ionic Liquid and a High-Boiling-Point Solvent

The operating window and specific capacitance are key parameters for supercapacitors. Broadening the operating window and boosting specific capacitance simultaneously remain a challenge for researchers. In this work, the ionic liquid 1-butyl-3-methylimidazolium iodide (BMIMI) and dimethylsulfoxide (DMSO) are innovatively introduced into a polyvinyl alcohol (PVA) gel at the same time with KI as conductive ions for supercapacitors. It is found that the use of DMSO obviously increased the potential window from 1 V (with the PVA-H2O-KI system) to 2 V (PVA-DMSO-KI); the use of BMIMI substantially increased the specific capacitance from 39.6 F g–1 (PVA-DMSO-KI) to 56.5 F g–1 (PVA-DMSO-KI-BMIMI). With activated carbon as electrodes, an energy density of 31.39 W h kg–1 (4.28 times that of PVA-H2O-KI at 0.5 A g–1) and a power density of 5012.58 W kg–1 (two times that of PVA-H2O-KI at 5 A g–1) are obtained. Using bendable copper foil as current collectors, the supercapacitor can work stably at any bending angle. In addition, the stability within 100 °C shows its excellent portability. It provides a pathway for the development of commercialized high-performance supercapacitors.