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. Aqueous batteries suffer from poor performance in extreme cold. Here, authors design an electrolyte enabling a high-energy zinc-sulfur battery that operates at –50 °C, offering a promising solution for low-temperature energy storage.