Chain–Chain Synergistic Hydrogel Electrolytes Regulate Zinc Ions Desolvation for Stabilized Anodes and High Operating Voltage in Flexible Zinc Ions Hybrid Capacitors

To maximize the energy density output, the complementary charge storage mechanism of aqueous zinc ion hybrid capacitors (ZIHCs) is superior and advanced, but continuous water-induced side reactions and uncontrolled dendrite growth of zinc anodes remain challenging. Additionally, the optimization of the hydrogel electrolyte/electrode interface is necessary for the stability and kinetic reversibility of the flexible zinc-based energy storage device. Herein, the P(AM-SBMA) (copolymer of acrylamide AM and zwitterionic compound SBMA)/gelatin hydrogel electrolyte (PSG) with a special semi-interpenetrating network is designed based on the chain-chain synergistic regulation mechanism to regulate the desolvation of zinc ions and optimize the operating voltage of flexible ZIHCs and stabilize surface chemistry of zinc anode. The obtained PSG-5 hydrogel electrolyte widens the electrochemical stability windows (ESW) of the flexible ZIHC to 2.45 V and achieves high Zn²⁺ transference number of 0.87 and highly reversible plating/stripping of the zinc anode. Furthermore, the corresponding flexible ZIHC exhibits a high operating voltage of 2.2 V and provides a favorable energy density of 117 Wh kg^-1 at a power density of 293 W kg^-1. This work provides useful insights for the development of efficient, flexible ZIHCs by preparing hydrogel electrolytes capable of stabilizing zinc anodes and widening ESW.