Toward Flexible Zinc‐Ion Hybrid Capacitors with Superhigh Energy Density and Ultralong Cycling Life: The Pivotal Role of ZnCl2 Salt‐Based Electrolytes

Zinc ion hybrid capacitors (ZIHCs) are promising energy storage devices for emerging flexible electronics, but they still suffer from trade-off in energy density and cycling life. Herein, we show that such a dilemma can be well-addressed by deploying ZnCl₂ based electrolytes. Combining experimental studies and density functional theory (DFT) calculations, for the first time, we demonstrate an intriguing chloride ion (Cl^- ) facilitated desolvation mechanism in hydrated [ZnCl]⁺ (H₂ O)_n-1 (with n=1-6) clusters. Based on this mechanism, a water-in-salt type hydrogel electrolyte filled with ZnCl₂ was developed to concurrently improve the energy storage capacity of porous carbon materials and the reversibility of Zn metal electrode. The resulting ZIHCs deliver a battery-level energy density up to 217 Wh kg^-1 at a power density of 450 W kg^-1 , an unprecedented cycling life of 100 000 cycles, together with excellent low-temperature adaptability and mechanical flexibility.