Zinc Anode Interface Engineering Breaks the Chloride Corrosion and Four‑Electron Redox Compatibility Dilemma for Sustainable Seawater‐Based Zn‐I 2 Batteries

ABSTRACT Aqueous zinc–iodine (Zn–I 2 ) batteries using seawater electrolytes offer a promising route toward sustainable and low‐cost energy storage for four‐electron zinc–iodine (Zn–I 2 ) batteries, owing to their inherent safety and natural chloride content that stabilizes high‐valent iodine species. However, severe Cl − ‐induced corrosion and hydrogen evolution at the zinc anode fundamentally conflict with the iodine redox chemistry at the cathode, aggravating dendrite growth and leading to rapid battery failure. Herein, we propose a synergistic interfacial engineering strategy by constructing a dense Ti protective layer on zinc metal via magnetron sputtering (Ti@Zn). The Ti layer with desirable Zn‐affinity and Cl − ‐repelling properties, synchronously suppresses chloride corrosion, accelerates Zn 2+ migration/desolvation kinetics, and inhibits undesirable side reactions. Thus, uniform Zn 2+ flux and deposition morphology are realized by homogenizing the interfacial electric field. Consequently, the optimized Ti@Zn anode enables high reversibility in both symmetric cells (500 h at 10 mA cm −2 ) and Ti@Zn//Cu cells (Coulombic efficiency of 99.89% for 4000 cycles). Moreover, the Ti@Zn//AC@I 2 pouch cells display high‐capacity retention ratio of 97.1% at 1 A g −1 after 850 cycles, and excellent rate capability of 144.5 mAh g −1 at 5 A g −1 , demonstrating sustainable four‐electron iodine conversion chemistry.