Li/K mixed superconcentrated aqueous electrolyte enables high-performance hybrid aqueous supercapacitors

Aqueous electrochemical energy storage devices are always limited in the inherited weaknesses of water, such as narrow operation temperature range and electrochemical stability window (ESW). Herein, we develop a lowcost aqueous hybrid electrochemical supercapacitor, assembled with LiMn2O4 (LMO) as the cathode and activated carbon (AC) as the anode in a novel economical Li+/K+ mixed superconcentrated (SC) aqueous electrolyte with a widened electrochemical stability window of 2.85 V, in which the hydrogen bonding between water molecules is inhibited via the confinement of water molecule by intense solvation. As a result, considering the advantages of this SC electrolyte in promoting the formation of intensive solid-electrolyte-interphase (SEI) analogue on AC anode and suppressing the structural destruction of LMO cathode, this supercapacitor demonstrates outstanding performances including improved working voltage (2.0-2.5 V), wide operation temperature range, high capacity (47.5 mA h g(-1) at 60 degrees C), superb capacity retention (similar to 100% at 10 A g(-1) even after 20,000 cycles at 2.0 V), and ultrahigh energy density (77.9Wh kg(-1) at 60 degrees C).