Quasi‐Solid Iodine Electrode for High‐Areal‐Capacity Aqueous Iodine Batteries

Abstract

ABSTRACT Zinc–iodine batteries (ZIBs), operating via either the two‐electron I − /I 0 (2eZIB) or four‐electron I − /I 0 /I + (4eZIB) redox couples, offer high theoretical energy density and sustainability. However, achieving practical high energy density requires high iodine content and mass loading, which slow iodine redox kinetics and exacerbate I + hydrolysis and shuttling. Here, we present a robust quasi‐solid electrode (QE) architecture in which molecularly dispersed iodine that spatially confined within a polyacrylonitrile (PAN)–N‐methyl‐2‐pyrrolidone (NMP) gel network—otherwise volatile—enabling high iodine retention during electrode processing. Iodine not only acts as the active material but also drives gel‐phase formation and stabilization via NMP·I 2 charge‐transfer complexation and strong polyiodides–PAN interactions, integrating a robust, elastic structure further reinforced by the kosmotropic effect in ZnSO 4 electrolyte. This architecture accelerates both I − /I 0 and I 0 /I + redox kinetics, achieves high‐loading (up to 100 mg cm −2 ), high iodine fraction in the electrode (∼53 wt.%), and record areal capacities (17.5 mAh cm −2 in 2eZIBs and 23.44 mAh cm −2 in 4eZIBs), along with suppressed self‐discharge and scalable ampere‐hour pouch‐cell stability. This shuttle‐free design combines efficient mass transfer with mechanical robustness, providing a promising solution for energy‐dense iodine batteries.