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.