A cascade reaction pathway enabled by sub-micron bismuth-decorated cathode for aqueous Zn-I2 batteries

Sub-micron Bi chemically anchors polyiodides via Bi-I bonds to suppress shuttling. • S-Bi acts as both an iodine host and an electroactive capacity contributor. • A cascade reaction involving I 0 /I − and Bi 3+ /Bi redox couples is realized. • The Zn–I₂ battery delivers 245 mAh g −1 and cycles 20,000 times with 77.7% retention. • A pouch cell achieves 5.26 mAh cm −2 under 22 mg cm −2 mass loading. Polyiodide shuttling is the primary obstacle to impede the practical application of aqueous zinc–iodine batteries (AZIBs). Although various host materials have been developed to suppress the shuttle effect, most of them are electrochemically inactive and inevitably reduce the overall energy density of the cathode. Herein, sub-micron bismuth (S-Bi) powder as a multifunctional redox-active iodophilic additive was introduced into the iodine electrode to simultaneously regulate iodine conversion chemistry and contribute additional electrochemical capacity. Experiment results showed that S-Bi powder with high electronic conductivity and mesopore structure can chemically anchor polyiodide by forming Bi-I bonds, which benefits suppressing polyiodide shuttling and enhancing reaction kinetics. More importantly, a cascade reaction process containing I 0 /I − and Bi 3+ /Bi redox couples is realized, significantly boosting battery capacity. In-situ XRD characterization revealed the conversion route of bismuth species (BiOI ↔ Bi 2 O 3 ↔ Bi) during the reaction, providing the direct evidence for the bismuth-involved cascade reaction mechanism. As a result, the assembled AZIBs based on S-Bi powder deliver a high discharge specific capacity of 245.19 mAh g −1 at 0.5 A g −1 and operate stably for 20,000 cycles at 3 A g −1 with a capacity retention of 77.7%. Encouragingly, the pouch battery achieves an areal capacity of 5.26 mAh cm −2 under a high active material mass loading of 22 mg cm −2 , demonstrating practical application potential. This work paves the way for designing materials with iodine affinity and redox activity to simultaneously suppress polyiodide shuttling and contribute extra capacity for AZIBs. Submicron mesoporous bismuth as a functional additive in I₂/KB cathode establishes a cascade reaction mechanism and inhibits polyiodide shuttling by forming Bi-I bonding, enabling 20,000-cycle stability. Download: Download high-res image (105KB) Download: Download full-size image