In‐Situ Spontaneous Electropolymerization Enables Robust Hydrogel Electrolyte Interfaces in Aqueous Batteries

Abstract Hydrogels hold great promise as electrolytes for emerging aqueous batteries, for which establishing a robust electrode‐hydrogel interface is crucial for mitigating side reactions. Conventional hydrogel electrolytes fabricated by ex situ polymerization through either thermal stimulation or photo exposure cannot ensure complete interfacial contact with electrodes. Herein, we introduce an in situ electropolymerization approach for constructing hydrogel electrolytes. The hydrogel is spontaneously generated during the initial cycling of the battery, eliminating the need of additional initiators for polymerization. The involvement of electrodes during the hydrogel synthesis yields well‐bonded and deep infiltrated electrode‐electrolyte interfaces. As a case study, we attest that, the in situ‐formed polyanionic hydrogel in Zn‐MnO 2 battery substantially improves the stability and kinetics of both Zn anode and porous MnO 2 cathode owing to the robust interfaces. This research provides insight to the function of hydrogel electrolyte interfaces and constitutes a critical advancement in designing highly durable aqueous batteries.