Janus Covalent Organic Framework Hydrogel Electrolyte via Multi‐Phase Regulation for Aqueous Zinc‐Ion Batteries

ABSTRACT Covalent organic framework (COF) gel‐based electrolytes, characterized by their rich microporous structures, hold substantial promise for applications in aqueous batteries. However, the inherent water‐insolubility and non‐melting properties of COFs pose significant challenges for their processing and shaping, and research on COF hydrogel‐based electrolytes remains limited. In this study, a multi‐phase regulation strategy is proposed to fabricate COF‐based hydrogel electrolytes featuring a dense COF film on one surface. The cathode‐facing dense side could suppress the hydrated H + transfer, favoring the preservation of both the structural stability and crystallinity of the NH 4 V 4 O 10 (NVO) cathode for aqueous zinc‑ion batteries. The bulk hydrogel is engineered with a microporous structure with uniformly distributed ion migration channels, facilitating the rapid transport of Zn 2+ ions within a confined environment (─OH, ─H, ─CH 3 ). Moreover, the incorporation of hydrophilic groups into the side chains effectively suppresses hydrogen evolution reactions and zinc dendrite growth at the anode. The Zn/NVO (NH 4 V 4 O 10 ) full cell with the Janus COF‐OH hydrogel electrolyte achieves 79.3% capacity retention after 1000 cycles, outperforming those with a symmetric COF‐OH hydrogel electrolyte. This strategy highlights the potential of unsymmetric surface engineering of hydrogels for aqueous batteries and beyond.