A water-poor zwitterionic hydrogel electrolyte enables aqueous zinc-iodine batteries from -40 to 90 °C.

Aqueous zinc-iodine batteries are promising for safe and low-cost energy storage, but their practical deployment is constrained by coupled instabilities at both electrodes, especially under extreme temperatures. Here, we report a water-poor zwitterionic hydrogel electrolyte that concurrently stabilizes the Zn anode and iodine cathode by regulating both cation and anion chemistries. The hydrogel is built from 3-[bis(2-methacryloyloxy)ethylamino]propane-1-sulfonate and N-hydroxyethyl acrylamide, while partial substitution of water with glycerol lowers water activity without sacrificing ion transport. At the Zn anode, sulfonate groups reconstruct the Zn2+ solvation structure and promote preferred Zn deposition along the (002) plane, suppressing dendrites and parasitic reactions. At the iodine cathode, the zwitterionic network confines polyiodides through electrostatic exclusion and Coulombic adsorption, mitigating shuttle-induced active-material loss. As a result, the electrolyte enables stable aqueous zinc-iodine batteries from -40 to 90 °C. Zn||Zn symmetric cells cycle for over 3600 h at -40 °C and more than 1000 h at 90 °C, while zinc-iodine full batteries deliver durable cycling across the same temperature range. A 120 mAh pouch cell retains 83.1% of its initial capacity after 2300 cycles at 1 C. This work establishes a hydrogel-electrolyte design principle for simultaneously stabilizing both electrodes in aqueous batteries under wide-temperature operation.