Atomically Dispersed Cu Sites Promote Facile Iodine Conversion for High-Performance Zinc-Iodine Batteries

Aqueous zinc-iodine (Zn-I₂) batteries are attracting attention as next-generation energy storage systems based on their excellent safety and economic feasibility. However, due to the slow reaction rate of the iodine conversion reaction and the polyiodide shuttle effect, there is a limitation in that the electrochemical reaction efficiency and cyclability are deteriorated. This study attempted to address this problem by applying the Cu-N₃@AC electrode, which contains a single-atom copper (Cu) catalyst in activated carbon (AC). The Cu-N3 coordination structure serves as dual-functional active sites that strongly immobilize iodine species and simultaneously promote reversible oxidation and reduction reactions. As a result, the Cu-N₃@AC electrode showed a high capacity of 416.17 mAh g_cat ^-1 at 5 A g^-1. It maintained a capacity of 203.4 mAh g_cat ^-1 and a Coulombic efficiency of 99.36% even after 30,000 cycles of a high current density of 10 A g^-1. This excellent performance is attributed to the Cu-N3 coordination structure, which promotes charge transfer and effectively mitigates polyiodide diffusion. This study demonstrates that electronic structure control of Cu-based single-atom catalysts plays a key role in improving the speed and stability of iodine conversion reactions and provides practical design guidelines for the development of a high capacity and stable Zn-I₂ battery.