Breaking the Halide Concentration Reliance of Four‐Electron Zinc‐Iodine Batteries via Interfacial Halide Enrichment

ABSTRACT High‐valence iodine redox chemistry in aqueous batteries is fundamentally constrained by the requirement of highly concentrated halide environments, which stabilize reactive iodine cations but inevitably induce electrolyte corrosion and sluggish interfacial kinetics. In this study, we demonstrate an interfacial halide enrichment strategy that circumvents this long‐standing concentration dependence in four‐electron zinc‐iodine batteries. By introducing only 0.1 M bromo‐pyrrolidinium salt into the electrolyte, a localized halide‐rich microenvironment is spontaneously reconstructed at the cathode interface, enabling reversible I – /I 2 /I + conversion without relying on bulk hyper‐concentrated halides. Spectroscopic analyses and theoretical calculations reveal that the pyrrolidinium cations preferentially anchor at the charged interface through complementary electrostatic and soft interactions with iodine/polyhalide species, thereby promoting interfacial Br – enrichment and stabilizing metastable IBr 2 – intermediates. Meanwhile, ethylene glycol (EG)‐mediated solvation regulation and interfacial water exclusion further suppress iodine hydrolysis and parasitic reactions. As a result, the dilute‐halide electrolyte system achieves a reversible capacity of 413.3 mAh g −1 at 0.4 A g −1 and maintains 88.2% capacity retention after 5000 cycles at 2 A g −1 , while simultaneously improving zinc anode reversibility. This work establishes an interfacial halide enrichment paradigm for regulating high‐valence halogen chemistry beyond conventional electrolyte concentration limitations.