Tailoring Solvation Sheaths and Interfacial Chemistry: A Review of Electrolyte Engineering for Highly Reversible Aqueous Zinc–Iodine Batteries

Aqueous zinc–iodine batteries (AZIBs) are emerging as highly promising candidates for next-generation, grid-scale energy storage due to the intrinsic safety of water-based electrolytes, the high theoretical capacity of the zinc anode, and the rapid conversion kinetics of the iodine cathode. However, the practical commercialization of AZIBs is severely impeded by formidable interfacial instabilities, including the uncontrollable growth of zinc dendrites, parasitic hydrogen evolution reactions (HER), and the notorious polyiodide (I3−, I5−) shuttle effect. These macroscopic degradation modes are fundamentally rooted in the robust [Zn(H2O)6]2+ primary solvation sheath and the immense thermodynamic driving force for polyiodide dissolution in highly polar aqueous media. To address these interconnected challenges, electrolyte engineering has evolved into the most potent, holistic strategy. This comprehensive review systematically evaluates the latest advancements in electrolyte engineering for AZIBs. We first deeply decipher the fundamental thermodynamic mechanisms governing Zn2+ desolvation and iodine multiphase conversion. Subsequently, we critically analyze cutting-edge regulation paradigms, including water-in-salt (WIS) and localized high-concentration electrolytes (LHCE), cosolvent networks, functional molecular additives, deep eutectic solvents (DES), and quasi-solid-state hydrogels. By integrating in situ/operando spectroscopic characterizations with multiscale theoretical computations (such as MD and DFT), we elucidate the structure–activity relationships at the atomic level. Finally, we provide strategic perspectives on the future trajectories of the field, emphasizing the stabilization of multi-electron (I−/I0/I+) halogen chemistry, AI-driven high-throughput screening, and the rigorous standardization of Ah-level pouch cell engineering for extreme-environment applications.