Electrostatic–Immobilized Polyiodides via Bifunctional Quaternary Ammonium Binder for Shuttle–Free and Ultra–Stable Zn–I₂ Batteries

Aqueous zinc–iodine batteries (AZIBs) show great promise for sustainable energy storage due to inherent safety, cost‐effectiveness, and environmental compatibility. However, their practical implementation is critically hindered by polyiodide shuttling, particularly under low current densities, leading to rapid capacity decay. Herein, poly(diallyldimethylammonium chloride) (PDDA) is employed as a functional binder to construct carbon nanotubes (CNTs)/PDDA composite cathodes. Unlike conventional carboxymethyl cellulose (CMC) based CNTs/CMC cathodes with compromised Coulombic efficiency (49.6% at 0.1 A g −1 ), the CNTs/PDDA architecture effectively anchors polyiodides to suppress the shuttle effect and self‐discharge through robust electrostatic interaction between quaternary ammonium groups and polyiodide ions. The optimized AZIBs exhibit high Coulombic efficiency (>98.2% at 0.1 A g −1 ), large specific capacity (231.1 mAh g −1 at 0.1 A g −1 ), high durable cycling stability (45 000 cycles at 3.0 A g −1 ), and sustained open‐circuit voltage (1.326 V after 12‐h rest). Mechanism studies reveal the dual functionalities of the PDDA binder in mitigating polyiodide shuttling and zinc anode corrosion. The PDDA system exhibits reduced Gibbs free energy (ΔG) and narrowed redox potential gaps, which effectively immobilize polyiodide species and promote the complete conversion of I − → I 3 − → I 2 . This work highlights the great potential of PDDA as a functional binder for high‐performance AZIBs.