A simple and practical hybrid ionic liquid/aqueous dual electrolyte configuration for safe and ion-exchange membrane-free high cell potential supercapacitor

A simple and practical hybrid dual ionic liquid (IL)/1.0 M LiTFSI(aq.) is proposed using ILs in the nanopores of activated carbon for high cell potential supercapacitor. Unlike previously reported system, the proposed supercapacitors use no ion-exchange membrane, a low quantity of ILs (similar to 20 mu L/cell) and a simple coin cell (single compartment). Hydrophilic and hydrophobic ILs were tested in the hybrid dual electrolyte configuration. The dual electrolyte with hydrophobic ILs enables the maximum operational cell potential of 2.2 V with the excellent capacitance retention of 94% after continuous charge-discharge cycles up to 30,000 at 0.5 A g(-1). The identified maximum cell potential is higher than the previously reported value of 1.9 V for the supercapacitors with the dual electrolyte comprising an ion-exchange membrane and, also comparable with the supercapacitors using water-in-salt electrolytes (2.2 V). The supercapacitor cell using proposed hybrid dual IL/aqueous electrolyte delivers the specific capacitance of 34.0 F g(-1) and the specific energy of 22.0 Wh kg(-1). The proposed hybrid dual IL/aqueous electrolyte may be useful for many energy storage devices requiring high cell potentials. (C) 2019 Elsevier Ltd. All rights reserved.