Lithium-salt monohydrate melt: A stable electrolyte for aqueous lithium-ion batteries

Concentrated aqueous electrolytes are promising for high-voltage and safe aqueous lithium-ion batteries because of their wide potential window. For Li system, a room-temperature dihydrate melt (27.8 mol kg(-1)) has been demonstrated to function as a stable aqueous electrolyte, but more concentrated electrolytes have yet to be discovered due to the limited solubility of Li salts. Here we report a room-temperature monohydrate melt of Li salts (55.5 mol kg(-1)) as an ultimate system of concentrated aqueous electrolytes. It has been discovered by adopting a Li salt with an asymmetric imide anion that shows ultra-high solubility in water. The monohydrate-melt electrolyte provides a wide potential window of similar to 5 V based on its dramatically improved passivation ability, which, for the first time, enables the Li-alloying reaction of Al in aqueous electrolytes.