Lewis Acid‐Base Electrolyte Additive Mediates Zn Anode Interface Chemistry and Iodine Conversion for Advanced Four‐Electron Zn||I 2 Batteries

ABSTRACT Aqueous zinc‐iodine (Zn||I 2 ) batteries, combining inherent safety and environmental friendliness, hold great promise for large‐scale energy storage. However, the system faces an unstable Zn interface and insufficient iodine utilization. Herein, we propose 1‐ethyl‐3‐methylimidazolium bromide (EMBr) functions as a Lewis acid‐base additive to promote anode and cathode stability in aqueous Zn||I 2 batteries. Specifically, the EM + cation of EMBr stabilizes the Zn metal anode (ZMA) by forming water‐poor Helmholtz double layer, inhibiting water‐induced side reactions. This enables the ZMA with excellent cyclic stability of 2100 h and a high average Coulombic efficiency of 98.73%, superior to its counterpart (100 h and 95.7%). EM + cation also effectively captures polyiodide species, inhibiting polyiodide shuttle. Meanwhile, the Br − anion facilitates I − /I 0 /I + conversion reactions by forming interhalogen compounds. The synthetic Fe 3 C loaded on the ZIF8 derived carbon (ZFeC) is selected as the host material because of its catalytic activity. The Zn|EMBr|ZFeC‐I 2 batteries with multi‐electron conversion reactions achieve 52 000 cycles with 324.3 mAh g −1 , equivalent to ∼2.5 times that of Zn|EMBr|ZC‐I 2 batteries at 5 A g −1 . Besides, ZFeC shows a pseudocapacitance proportion of 94.8% higher than ZC (85.6%), achieving quick conversion reaction kinetics. This work offers a versatile Lewis acid‐base paradigm for practical high‐valence aqueous zinc‐based batteries.