Aqueous Supercapacitors with Wide Operative Voltage Window and Long Cycling Life Enabled by Electrolyte Hybridization Effect

Developing supercapacitors (SCs) with long cycling life and wide operative voltage window is a significant topic in the field of aqueous electrolytes. Although the design of water in salt (WIS) electrolytes has pushed the development of aqueous electrolytes to a new height, the WIS electrolytes with an operative voltage window of up to 2.5 V is still very scarce. Herein, in order to enrich the type of aqueous electrolyte with high operative voltage, tetramethylammonium trifluoromethanesulfonate (TMAOTf) based WIS electrolyte was used as a model to construct WIS based hybrid electrolyte with acetonitrile (ACN) co-solvent and LiTFSI co-solute. In view of the coordination effect of ACN and Li+ on free water in TMAOTf based WIS electrolyte, the TMA+-Li+-AWIS electrolyte has the electrochemical stabilization window of up to 3.35 V. Further coupled with the commercial YP-50F electrodes, TMA+-Li+-AWIS based SCs exhibited wide operative voltage window (2.5 V), long cycling life (45,000 cycles) and good low-temperature performance (99.99 % capacitance retention after 2000 cycles at –20 oC). The design of this hybrid electrolyte will enrich the types of aqueous hybrid electrolytes with long cycling life and wide operative voltage window.