Iodide-mediated intermediate regulation strategy enables high-capacity and ultra-stable zinc–iodine batteries†

Abstract

The practical implementation of aqueous zinc–iodine (Zn–I₂) batteries is hindered by the limited cathode capacity, rampant Zn dendrite formation, and anode corrosion issues. In this work, we propose a novel iodide-mediated intermediate regulation strategy achieved through a rationally designed combination of zinc iodide (ZnI₂) and high-loading cathodes. Mechanistic studies reveal that iodide ions (I⁻) generate abundant iodine active sites on the elemental iodine-embedded porous carbon cathode (I₂@PAC), which facilitates the conversion of under-oxidized triiodide (I₃⁻) to pentaiodide (I₅⁻), thereby significantly enhancing cathode capacity. Concurrently, the I⁻ coordinate with Zn²⁺ to suppress the decomposition of coordinated water molecules, effectively mitigating side reactions and enabling dendrite-free Zn deposition morphology. These mechanisms collectively contribute to exceptional Coulombic efficiency (>99.7%) and outstanding cycling stability. The optimized Zn–I₂ full cell achieves a remarkable specific capacity of 250.2 mAh g⁻¹ at 0.2 A g⁻¹, along with ultralong cycling durability exceeding 10 000 cycles while maintaining 85% capacity retention. This iodide-mediated intermediate regulation strategy provides a viable pathway for developing high-capacity and ultra-stable aqueous Zn–I₂ batteries.