Restructuring of aqueous electrolytes using a soft-acidic/hard-basic zwitterion for low-temperature anode-free Zn batteries

초록

Despite the growing interest in aqueous Zn batteries as a safe and low-cost alternative to commercial Li-ion batteries, the use of aqueous electrolytes has limited their application at sub-zero temperatures. Here, we propose a new electrolyte design using zwitterions based on the hard and soft acids and bases principle to restructure aqueous electrolytes. Incorporation of a soft-acidic/hard-basic zwitterion into an aqueous electrolyte results in the disruption of the hydrogen bonds of water molecules, weakening of Zn2+–OTf− interactions, and destabilization of the Zn2+ solvation sheath. The resulting electrolyte (ZT-electrolyte) enhances the anti-freezing phenomena with a solid–liquid transition temperature of −95 °C and Zn2+ desolvation kinetics. Consequently, the anode-free full cell (Cu‖Znxa-V2O5@graphene) with the ZT-electrolyte exhibits high energy and power densities (142 W h kg−1 at 50 mA g−1 and 230 W kg−1 at 2 A g−1) with stable cyclability at −40 °C, which exceeded those of previously reported Zn batteries and are comparable to those of low-temperature Li–metal batteries.

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