Polymer‐Salt Effects with Enhanced Eutectic Behavior in Hydrogel Electrolytes for Aqueous Zinc Batteries at −70 °C

Abstract Aqueous Zn batteries have attracted substantial attention due to their low cost and inherent safety. However, achieving stable operation under ultra‐low temperature conditions remains a challenge. An antifreeze polyelectrolyte hydrogel is described with ten times break elongation even at −70 °C based on a double cross‐linked network and a polymer‐salt synergistic effect. By incorporating the optimized ratio of lithium chloride (LiCl) and Zn chloride (ZnCl 2 ), this study discovers that ionic interactions between dual‐salt metal ions and hydrophilic groups (─CONH 2 and ─SO 3 − ) in the polymer network can induce polymer‐enhanced eutectic behavior. This synergistic effect plays an essential role in simultaneously improving the ionic conductivity, mechanical properties, and antifreeze capability of the electrolytes. The polyelectrolyte hydrogel demonstrates outstanding performance in a polyaniline Zn || (PANI) battery with an exceptional capacity of 118 mAh g −1 /0.2 A g −1 even at −70 °C. At a higher current density of 0.5 A g −1 , it retains nearly 100% capacity after 12 000 cycles, offering a robust energy storage solution for extreme conditions.