Synergistic Anion-Mediated Conversion and Single-Atom Catalysis Enable Fast and Reversible Iodine Redox Kinetics

Aqueous Zinc–iodine (Zn–I2) battery represents a promising candidate for large-scale energy storage due to its inherent safety and high theoretical capacity. Its deployment, however, is hampered by the sluggish multi-step iodine conversion kinetics and polyiodide shuttling. While prevailing electrocatalytic strategies are effective at enhancing the redox kinetics of the isolated iodine conversion step, they fail to overcome the overall sluggish reaction kinetics of Zn–I2 batteries. Herein, a dual-pathway strategy is proposed to holistically enhance Zn–I2 battery performance by synergistically combining anionic chemical mediation via a KI-rich electrolyte with single-atom Zn–N4 electrocatalysis in a carbon host. We demonstrate that the anionic chemical mediation efficiently drives the I5–/I3– conversion (I5– + KI → I3–), while the Zn–N4 sites selectively electrocatalyze the I3– to I– reduction. This synergistic mechanism collectively enhances the overall kinetics of I5–/I3–/I– conversion cascade, suppresses the polyiodide shuttle, and increases the utilization of active iodine. The resulting Zn–I2 battery achieves exceptional performance, including a high specific capacity of 154 mAh g–1, ultra-long cycle ability over 30,000 cycles, and a low self-discharge rate of 5.5% after 24 h. Moreover, flexible pouch batteries can retain 81.2% capacity over 1000 cycles and maintain stable voltage under cutting and bending. This work presents a synergistic paradigm for enhancing multi-step conversion kinetics, providing new insights into the design of efficient metal–iodine batteries.