Concomitant Zinc Dendrite Mitigation and Iodide Shuttle Confinement: A Bifunctional Zwitterionic Hydrogel Electrolyte Unlocking Ultralong‐Cycling Aqueous Zinc‐Iodine Batteries

Abstract Aqueous zinc‐iodine (Zn//I 2 ) batteries face critical challenges of zinc dendrite growth and polyiodide shuttling, hindering practical deployment. To address this dual bottleneck, a bifunctional zwitterionic hydrogel electrolyte (BZHE) featuring strategically segregated anionic (‐BF 3− ) and cationic (‐C‐N + ) groups is engineered. The cationic groups facilitate regulated Zn 2+ transport and uniform zinc deposition. Concurrently, the strongly polar ‐BF 3− groups restructure the Zn 2+ solvation sheath via water coordination to suppress side reactions and exert robust electrostatic repulsion against polyiodides (I 3− /I 5− ) to mitigate shuttling. Critically, the cationic moieties actively intercept escaped polyiodides, establishing a synergistic dual‐action shielding mechanism. This dual confinement strategy, corroborated by theoretical simulations and a multitude of experimental evidence, significantly suppresses the shuttle effect and extends battery lifespans. As a result, the BZHE enables Zn//Zn symmetric cells achieve ultralong cycling over 6300 h (1 mA cm −2 /0.25 mAh cm −2 ) and 1500 h (5 mA cm −2 /1.25 mAh cm −2 ). When applied in Zn//I 2 full cells, it delivers exceptional cycling performance (89.7% capacity retention after 28 000 cycles at 5.0 A g −1 ). Furthermore, the corresponding pouch battery with high‐iodine loading achieves a high reversible capacity of 136.8 mAh g −1 after 500 cycles at 0.5 A g −1 , highlighting the scalability of this approach.