Nonaggregated Anions Enable the Undercooled Aqueous Electrolyte for Low-Temperature Applications.

Aqueous batteries, with the advantages of high safety and low cost, are highly promising for large-scale energy storage. However, freezing of the aqueous electrolyte limits the low-temperature operation. Here, we propose and achieve a highly dispersed solvation structure in the electrolyte by coupling nonaggregated Cl - anions, which reduces the water cluster size and prevents the solidification of the aqueous electrolyte until -136.3 °C. The low-temperature LiCl electrolyte exhibits a high ionic conductivity (1.0 mS cm -1 ) at -80 °C and enables a stable low-temperature Ag/AgCl reference electrode at -50 °C. Moreover, the polyaniline-based battery can work at an extremely low temperature of -100 °C and shows superior cycling performance of 4000 cycles at -40 °C with 95.7% capacity retention. This work elucidates the correlation between the anion effect and the thermodynamic transition of the electrolyte, offering a novel approach for designing low-temperature electrolytes.