An account on the deep eutectic solvents-based electrolytes for rechargeable batteries and supercapacitors

The state-of-the-art rechargeable batteries mostly utilize organic electrolytes; nevertheless, the flammable organic electrolyte imposes serious safety concerns. Recently deep eutectic solvent (DES) has emerged as a promising alternative electrolyte, which possesses ionic liquid (IL) like physical properties, such as, extremely low vapor pressure, non-flammability, high ionic conductivity, etc. However, unlike conventional IL electrolytes, DESs are inexpensive, non-corrosive, compatible with the electrode components, and eco-friendly, which makes them attractive towards developing sustainable and cost-efficient energy storage devices. Over the last ten years, considerable research efforts have been carried out towards designing novel DES systems and employing them as electrolytes in electrochemical energy storage devices. Herein we have reviewed the recent advances made in the designing and development of different eutectic electrolytes, their physicochemical characteristics, and electrochemical performances in various rechargeable batteries and supercapacitors. The challenges and future prospect of the DES electrolyte have been discussed and insights to further improve the electrolyte performance has been proposed.