Aqueous Alkaline Zinc–Iodine Battery with Two-Electron Transfer

While many cathode materials have been developed for mild electrolyte-based Zn batteries, the lack of cathode materials hinders the progress of alkaline zinc batteries. Halide iodine, with its copious valence nature and redox possibilities, is considered a promising candidate. However, energetic alkaline iodine redox chemistry is impeded by an alkali-unadapted I₂ element cathode and thermodynamically unstable reaction products. Here, we formulated and evaluated an aqueous alkaline Zn-iodine battery with a two-electron transfer employing an organic iodized salt cathode and a Cl^--manipulated electrolyte. The single-step redox reaction of the I^-/I⁺ couple resulted in a high discharge plateau of 1.68 V and a capacity of 385 mA h g^-1. Our battery reached an energy density of 577 W h kg^-1, superior to that of reported counterparts. Theoretical and experimental characterizations determined the redox chemistry between alkaline and iodine. We believe the developed iodine chemistry in alkaline environments can enrich cathode materials for alkaline batteries.