Bridging the Gap to Practical Aqueous Zinc-Iodine Batteries: Advanced Hydrogel Electrolytes via Interfacial Chemistry...

Aqueous zinc-iodine (Zn-I₂) batteries are promising for grid-scale storage and flexible electronics because of their nonflammable chemistry, low cost, and high theoretical capacity. Their deployment, however, is limited by uneven Zn deposition, water-driven hydrogen evolution and corrosion, and polyiodide shuttling. Functional hydrogel electrolytes can regulate these coupled processes through solvent confinement, ion-selective transport, and mechanically persistent electrode contact. This review critically examines recent advances in hydrogel electrolytes for Zn-I₂ batteries from interfacial chemistry to architectural engineering. Distinct from broader hydrogel reviews for aqueous Zn batteries, it focuses on the chemically asymmetric coupling between a water-reactive Zn anode and a soluble polyiodide cathode and organizes the field through a structure-mechanism-performance framework that links molecular affinity, fixed charge, and water-state regulation to measurable interfacial parameters, spatially decoupled architectures, and scale-relevant device metrics. We analyze dual-interface regulation across solvation and nucleation, polyiodide confinement, tortuosity control, and asymmetric/Janus structures. Broad-temperature and voltage-tolerant operation, together with self-healing, self-sensing, and biosensing functions, is also evaluated. Finally, we distinguish materials-level evidence from pouch- and Ah-level validation and propose an application-specific roadmap centered on high iodine loading, lean electrolyte, limited Zn inventory, water retention, and scalable manufacturing.