Rational Design of Nucleophilic Organic Additives for Stable Four‐Electron Aqueous Zinc–Iodine Batteries: A Triple‐Parameter Screening Criterion

ABSTRACT Aqueous zinc–iodine (Zn–I 2 ) batteries featuring four‐electron (I − /I 0 /I + ) redox chemistry have emerged as promising candidates for large‐scale energy storage applications. However, their practical energy density and longevity are severely bottlenecked by the irreversible hydrolysis of the I + cation. Although halogen‐based additives have been employed to stabilize I + , they inevitably trigger aggressive corrosion and parasitic side reactions at the zinc anode, creating a trade‐off between cathode stability and anode integrity. Herein, we propose a molecular design framework—the Nucleophilicity‐pK a ‐Steric effects triad—to systematically screen and optimize halogen‐free organic electrolyte additives for I − /I 0 /I + redox chemistry. By balancing electronic potency with spatial accessibility, we identify acetamide (AC) as an excellent bifunctional stabilizer. Detailed spectroscopic analyses and theoretical calculations reveal that AC effectively “locks” the electrophilic I + through a nucleophilic anchoring mechanism, while simultaneously reconstructing the Zn 2+ solvation sheath to suppress water activity. Consequently, the optimized electrolyte enables the Zn–I 2 battery to achieve an exceptional specific capacity of 418 mAh g −1 and a long lifespan of 2500 cycles. This work not only provides a high‐performance electrolyte for Zn‐I 2 batteries but also establishes a rational and experimentally validated empirical screening framework for the molecular engineering of next‐generation multivalent aqueous energy storage.