Wide‐Potential‐Window Bimetallic Hydrated Eutectic Electrolytes with High‐Temperature Resistance for Zinc‐Ion Hybrid Capacitors

Abstract Aqueous zinc‐ion hybrid capacitors (ZHCs) are considered ideal energy‐storage devices. However, the common aqueous Zn²⁺‐containing electrolytes used in ZHCs often cause parasitic reactions during charging–discharging owing to free water molecules. Hydrated eutectic electrolytes (HEEs) that bind water molecules through solvation shells and hydrogen bonds can be applied at high temperatures and within a wide potential window. This study reports a novel bimetallic HEE (ZnK–HEE), consisting of zinc chloride, potassium chloride, ethylene glycol, and water, which enhances the capacity and electrochemical reaction kinetics of ZHCs. The bimetallic solvation shell in ZnK‐HEE is studied by molecular dynamics and density functional theory, confirming its low step‐by‐step desolvation energy. A Zn//activated carbon ZHC in ZnK–HEE shows a high operating voltage of 2.1 V, along with an ultrahigh capacity of 326.9 mAh g⁻¹, power density of 2099.7 W kg^–1, and energy density of 343.2 Wh kg^–1 at 100 °C. The reaction mechanisms of charging–discharging process are investigated by ex situ X‐ray diffraction. This study reports a promising electrolyte for high‐performance ZHCs, which exhibits high‐temperature resistance and is operable within a wide potential window.