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

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-I2 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.