Unlocking stable four-electron redox chemistry in aqueous zinc-iodine batteries via solvation structure...

Aqueous zinc‑iodine batteries (AZIBs) utilizing the four-electron (4e^-) redox reaction (I^-/I⁰/I⁺) offer impressive theoretical capacities; however, their practical application is severely impeded by the rapid hydrolysis of electrophilic I⁺ species and uncontrolled Zn dendrite growth. Herein, a novel hybrid electrolyte is engineered by integrating 1-ethyl-3-methylimidazolium chloride (EMIMCl) and ethylene glycol (EG) into the ZnSO₄ aqueous system (denoted as ZEM 1-40) to fundamentally address these challenges. The combination of EMIMCl and EG in the system creates a new structure which blocks water molecules from entering the Zn²⁺ ion environment thus preventing I⁺ from breaking down into I₃^- byproducts. The EMIM⁺ cations at the Zn interface create an electrostatic shield which protects the interface by controlling Zn²⁺ ion movement to achieve uniform deposition and prevent dendrite formation. The ZEM 1-40-based cell enables a 4e^- transfer reaction which becomes reversible to achieve 455.76 mAh g^-1 at 1 A g^-1. Furthermore, the system demonstrates exceptional long-term durability, sustaining over 14,300 cycles at 10 A g^-1 with an ultralow capacity decay rate of 0.0047% per cycle and a near-unity Coulombic efficiency (99.79%). The research establishes a deep comprehension of solvation chemistry mechanisms which enable the stabilization of high-valence iodine species for developing high-energy-density aqueous batteries.