A high-concentration aqueous electrolyte with a wide electrochemical stability window represents a novel development direction for traditional aqueous batteries. Herein, a novel high-concentration water-in-bisalt electrolyte using LiFSI (lithium bis(fluorosulfonyl)imide) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) as supporting salts was first applied as an electrolyte of a dual-ion battery, and the solvated structure changes were studied in detail. Electronic interactions were detected between the two supporting salts. Furthermore, when 37 mol/kg LiFSI-LiTFSI/H2O was applied to a 3 V dual-ion battery, by using graphitic carbon (KS6) and activated carbon (AC) as cathode and anode materials, the full cell delivered a high specific capacity of 72 mAh/g. In addition, excellent cycling stability for ˃100 cycles was achieved with negligible capacity fading.
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