Stable Four-Electron Zinc-Iodine Battery Realized by Polyacrylamide as Catalytic Binder

Realizing stable four-electron reactions ( $I^{-}{/I}_2^0/I^{+}$ ) is the key to boosting the energy density of aqueous zinc-iodine batteries (ZIBs). In most of the traditional studies, the four-electron reactions are realized by catalytic halogen ions as electrolyte additives. Herein, we utilize commercial polyacrylamide (PAM) powder as a cost-friendly electrode binder to catalyze the stable interconversion between I⁰ and I⁺, enabling a four-electron reaction in the absence of halogen ions. We show that PAM obtained from various suppliers can serve as a catalytic binder and induce the 4e reactions due to the presence of a large amount of nucleophilic -CONH₂ group, which strongly binds with I⁺. Furthermore, PAM also exhibits a strong affinity to polyiodide species, which suppresses the polyiodide shuttling and thus mitigates the anode side reactions between polyiodide and Zn. As a result of the above two beneficial effects, the Zn-I₂ battery demonstrates a high capacity of 416 mAh g^-1 (calculated from available iodine mass in electrolyte) and an extended cycle life of over 10 000 cycles at 5 A g^-1. This low-cost and fluorine-free commercial binder for four-electron iodine reaction will boost the progress of high-energy-density aqueous Zn batteries.