Redirecting iodine reduction pathways by decoupling adsorption energies for long-life Zn-I2 batteries

Abstract

Zinc-iodine (Zn-I2) batteries are promising for grid-scale energy storage, yet rapid capacity fade from polyiodide shuttling remains a fundamental challenge. This shuttling arises from the coupled, stepwise iodine reduction pathway (*I2 *I5 *I3 *I), wherein conventional single-site catalysts that accelerate the rate-limiting *I3 reduction inevitably stabilize long-chain *I5, exacerbating capacity fading. Herein, we introduce atom-cluster catalysts (ACCs) with tailored atomic geometries that decouple the adsorption energetics of key intermediates. The ACCs destabilize *I5 chain formation while optimizing *I3 reduction kinetics, thereby redirecting the reaction toward a low-barrier *I2 *I3 *I pathway and suppressing soluble I5- at its source. As a result, Zn1Co ACCs/I2 cathode delivers a high specific capacity of 230.5 mAh g-1 at 6.5 mg cm-2 over 15 000 cycles (2 A g-1). This atomic-scale pathway-engineering strategy resolves the intrinsic trade-off imposed by linear scaling in stepwise conversion reactions and provides a general approach to enabling long-life operation in Zn-I2 batteries and other multi-intermediate electrochemical systems.