Chloride‐Bridged Compact Interfacial Shielding for Practical Seawater Zinc Batteries

Abstract Substituting natural seawater (NS) for deionized water significantly reduces the electrolyte manufacturing cost of aqueous zinc (Zn) ion batteries, but it also poses severe corrosion challenges to the Zn metal anode, given the presence of the Cl − /H 2 O‐rich Zn‐electrolyte interface. Here, a NS electrolyte featuring NS solvent and the host–guest complex additive is designed. The 2‐mercaptobenzothiazole (MBT) guest shows sustained‐release behavior from the cyclodextrin host dominated by its aqueous solubility in the NS electrolyte. Crucially, Cl − ions facilitate a compact MBT shield at the interface via bridging effects, creating a Cl − /H 2 O‐poor microenvironment that suppresses corrosion and extends Zn anode cycle life. Thus, the Zn anode achieves an extended cycling life of 400 h in the Zn||Zn symmetric cell even under a practical depth of discharge of 42.7%. The Zn||NaV 3 O 8 ·1.5H 2 O full cell with a low negative/positive capacity ratio of 1.92 exhibits 99% capacity retention at 0.5 A g −1 after 600 cycles, and the Ah‐level pouch cell with an initial discharge capacity of 1.21 Ah maintains stable cycling for 50 cycles.