Reusable and Robust Hydrogel With Dynamic Sacrificial S─S Bonds: In Situ Construction of an Integrated SEI/Hydrogel Interface for Highly Stable Zn–I 2 Batteries

ABSTRACT The trade‐off among mechanical strength, ionic conductivity, and interfacial stability remains a core challenge for high‐performance hydrogel interfacial layers. Herein, an integrated SEI/polyurea–polyurethane hydrogel (PUMA) interface was constructed on the Zn anode via in situ gelation coupled with interfacial electrochemical reduction. Polyurea–polyurethane hard segments containing octuple H‐bonds, Zn 2+ coordination bonds, and dynamic S─S bonds reinforce PUMA through multi‐level energy dissipation and suppress side reactions by regulating interfacial water. Polyanionic soft segments rich in carboxyl and sulfonic acid groups construct low‐barrier, ion‐selective pathways, optimizing Zn 2+ transport and deposition by solvation regulation and mitigation of concentration polarization. Crucially, interfacial sacrificial S─S bonds undergo cleavage during electrochemical reduction, generating an integrated SEI/PUMA interface with enhanced interfacial stability. The dynamic polyanionic network also blocks polyiodide shuttling and enables thermal reprocessing. Consequently, PUMA@Zn achieves a Zn 2+ transference number of 0.79 and symmetric cell cycling for 5080 h (1 mA cm −2 and 0.5 mAh cm −2 ). PUMA@Zn//I 2 cells retain 88% capacity after 43 000 cycles at 4 A g −1 and operate for over 11 000 cycles even at high iodine loading (16.58 mg cm −2 ). This strategy provides a novel pathway to achieve robust, ion‐conductivity, and chemically bonded hydrogel–metal interfaces for high‐performance aqueous batteries.