Quaternary Ammonium Iodide–Functionalized Cathodes for Direct Polyiodide Confinement in Durable Aqueous Zn–I 2 Batteries

ABSTRACT A rational cathode design strategy integrating iodine (I 2 ) complexing agents directly into the solid‐phase cathode (fundamentally distinct from electrolyte additive approaches), confining redox‐active iodide species through synergistic electrostatic interactions and sterically regulated complexation, is proposed to tackle the long‐term stability issue caused by iodide species crossover for zinc−iodine (Zn−I 2 ) batteries. A systematic evaluation of tetraalkylammonium iodides (TXAIs) establishes that low solubility, strong polyiodide binding, and minimal electrolyte dependence are essential for effective stabilization. Among the candidates, tetrabutylammonium iodide (TBAI) enhanced cathode mechanical robustness, demonstrated optimal performance over a broad temperature range, maintaining 112.8 mAh g −1 over 70 000 cycles in a dissolution‐prone situation at 5 C (623 days, 1.70 years; the longest reported), achieving 207.3 mAh g −1 for 1700 cycles (3370 h) at 1 C, and retained 158.1 mAh g −1 capacity even after 1440 h of resting (the lowest self‐discharge behavior to date, mostly < 60 h, 159 mAh g −1 ). Unlike electrolyte additive approaches, this cathode‐anchored design ensures long‐term confinement fidelity with minimal structural complexity and reduced electrolyte dependence, while relying on exceptionally simple implementations and being inherently highly cost‐effective, providing molecular‐level insight into iodide stabilization and establishing a practical framework for designing durable, high‐performance Zn–halogen batteries.