Optimizing Electrolyte Physiochemical Properties toward 2.8 V Aqueous Supercapacitor

Achieving a wide potential window of aqueous supercapacitor has been one of the key research interests to address its poor energy density. However, in this process, water decomposition becomes an increasingly significant issue that has to be tackled in order to attain a reliable aqueous supercapacitor. In order to avoid possible water decomposition at a wide potential, benign interaction between electrolyte and electrode during the cell operation has to be considered. In this work, a water-in-bisalt electrolyte consisting of 21 M lithium bis(trifluoromethane)sulfonamide and 1 M lithium sulfate was proposed. To complement the electrolyte, Li+ inserted MnO2 and carbon were selected as electrode materials due to their low oxygen evolution reaction/hydrogen evolution reaction activities. The resultant aqueous supercapacitor was able to operate at 2.8 V which, to the best of our knowledge, is one of the widest potential windows reported for an aqueous supercapacitor system. The cell was able to deliver an energy density of 55.7 Wh kg–1 at power density of 1 kW kg–1, while attaining a good cyclic stability of 84.6% retention after 10000 cycles at a current density of 30 A g–1. Such a strategy may be effective in the design of wide potential aqueous supercapacitors, which is crucial toward future supercapacitor development.