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

Zinc-iodine batteries (ZIBs), operating via either the two-electron I^-/I⁰ (2eZIB) or four-electron I^-/I⁰/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·I₂ charge-transfer complexation and strong polyiodides-PAN interactions, integrating a robust, elastic structure further reinforced by the kosmotropic effect in ZnSO₄ electrolyte. This architecture accelerates both I^-/I⁰ and I⁰/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.