Enabling low-temperature aqueous zinc/copper-sulfur hybrid batteries through electrolyte design

Rechargeable aqueous batteries show promise for large-scale energy storage, yet suffer from low specific energy and poor low-temperature performance. Existing low-temperature aqueous batteries typically use ion-insertion positive electrodes with limited capacity. While aqueous sulfur-based batteries offer high theoretical capacity, their low-temperature operation remains challenging. Current improvement strategies often compromise room-temperature performance due to the inclusion of non-active additives. Here, we present a low-temperature sulfur-based battery using a Cu(BF₄)₂-based electrolyte, which boasts a low glass transition temperature of -115.1 °C, and an ionic conductivity of 5.16 mS cm^-1 at -60 °C. This electrolyte enables faster reaction kinetics and higher overall specific energy than traditional CuSO₄-based systems. The resulting zinc-sulfur battery delivers a discharge capacity of 348 mA h g_(S+Zn)^-1and an specific energy of 339 W h kg_(S+Zn)^-1 at -50 °C, based on the total mass of both the positive and negative electrodes, competitive with existing aqueous batteries.