Thermal Phase Transition Electrolyte for High‐Temperature Aqueous Zinc‐Metal Batteries

Abstract The operational stability of aqueous zinc‐metal batteries (AZMBs) under extreme temperatures is crucial for long‐term energy storage, yet remains hindered by intensified water activity and thermodynamic instability that exacerbate zinc dendrite growth and parasitic reactions. While incorporation of high‐boiling‐point organic solvents has shown effectiveness for high‐temperature operation by reducing water content and disrupting hydrogen‐bonding networks, it compromises the intrinsic safety of aqueous electrolyte especially in high‐temperature scenario. Here, a thermoresponsive electrolyte approach is reported leveraging phase transition of a synthesized polymer with upper critical solution temperature (UCST), which achieves temperature‐adaptive electrochemical performance in AZMBs. By modulating polymer‐water interactions and entropy‐enthalpy balance, the engineered aqueous electrolyte undergoes reversible phase transformation above 40 °C, forming a dynamically polymer‐water network that essentially suppresses water reactivity. Consequently, the optimized Zn–Zn symmetric cells exhibit stable Zn plating/stripping for 450 h at 60 °C and 210 h even under extreme 80 °C conditions. High‐loading Zn–I 2 full batteries with enhanced cycling stability further validate practical viability of the thermal phase transition electrolyte at elevated temperature. This work establishes a polymer phase transition paradigm for developing temperature‐resilient electrolytes, providing mechanistic insights into interfacial stabilization and advancing metal anode technologies for extreme‐condition energy storage systems.