Electrostatic‐Sieving Zn 2+ Transport in a Biodegradable HSiO 2 ‐Crosslinked Cationic Hydrogel Enables Ultralong‐Life Zinc‐Ion Batteries

ABSTRACT Quasi‐solid‐state aqueous zinc‐ion batteries (ZIBs) represent a promising platform for next‐generation energy storage, yet their practical implementation is hindered by an inherent trade‐off among ionic conductivity, Zn 2+ transference number, and mechanical robustness in gel electrolytes. Herein, we report a rationally designed cationic composite hydrogel electrolyte PAM‐N + /HSiO 2, that breaks this long‐standing performance bottleneck. The hydrophilic cationic ‐N + R 3 side chains anchor SO 4 2− anions via electrostatic interactions to drive directional Zn 2+ migration, while concurrently weakening the Zn 2+ solvation effect to promote uniform Zn deposition. Consequently, the PAM‐N + /HSiO 2 electrolyte simultaneously achieves a high Zn 2+ transference number of 0.75 and an exceptional ionic conductivity of 27.06 mS cm −1 . Moreover, the rigid siloxane cage of HSiO 2 serves as a multifunctional covalent crosslinker, forming a robust 3D network (elongation at break > 1000%) that effectively resists dendrite penetration. The assembled Zn||Zn symmetric cell delivers stable cycling for 5182 h at 1 mA cm −2 and 1332 h at 5 mA cm −2 , and the Zn||V 2 O 5 cell maintains excellent cycling stability over 2275 cycles at 5 A g −1 . Notably, this hydrogel electrolyte also exhibits remarkable flame retardancy and biodegradability, opening new avenues for high‐performance, eco‐friendly quasi‐solid‐state energy storage.