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](+)(H2O)(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.

Automated summary

By developing ZnCl2-based electrolytes, researchers have successfully improved the energy density and cycling life of zinc ion hybrid capacitors. Through the mechanism of desolvation facilitated by chloride ions and the use of a water-in-salt hydrogel electrolyte, they were able to achieve this goal.