Localized Anion-Cation Aggregated Aqueous Electrolytes with Accelerated Kinetics for Low-Temperature Zinc Metal Batteries

Aqueous zinc metal batteries hold great promise for large-scale energy storage because of their high safety, rich material resources and low cost. However, the freeze of aqueous electrolytes hinders low-temperature operation of the batteries. Here, aqueous localized anion-cation aggregated electrolytes composed of Zn(BF₄)₂ as the salt and tetrahydrofuran (THF) as the diluent, are developed to improve the low-temperature performance of the Zn anode. THF promotes the inclusion of BF₄⁻ in the solvation sheath of Zn²⁺, facilitating the formation of ZnF₂-rich solid-electrolyte-interphase. THF also affects the hydrogen bonding between neighboring H₂O molecules, effectively lowering the freezing point. Therefore, the full cells of Zn||polyaniline (PANI) exhibit an ultralong cycle life of 8000 cycles with an average Coulombic efficiency of 99.99 % at −40 °C. Impressively, the pouch cells display a high capacity retention of 86.2 % after 500 cycles at −40 °C, which demonstrates the great prospect of such electrolytes in cold regions. This work provides new insights for the design of low-temperature aqueous electrolytes.