Stabilizing Iodine Redox Mediator Enables High‐Performance Aqueous Zinc–Sulfur Batteries

ABSTRACT Aqueous zinc–sulfur batteries (AZSBs) are regarded as promising candidates for high‐energy‐density and low‐cost energy storage devices. However, sluggish conversion reaction of sulfur‐loading cathode and notorious polyiodide shuttle of iodine redox mediator in aqueous electrolytes severely hinder the development of AZSBs. Herein, ammonia‐oxidized lignin (AOL) is introduced as electrolyte additive to stabilize the redox mediator function of ZnI 2 , which effectively facilitates the reversible sulfur conversion reaction (S 8 ↔ZnS). As demonstrated, AOL monomer is rich in active hydroxyl/amide moieties, and exhibits strong chemisorption capability for polyiodides as well as remarkable thermodynamic condition for iodine conversion reaction (I 3 − ↔I − ), which significantly blocks the ZnI 2 mediator loss and I 3 − /I 5 − shuttle behavior during cycling, thereby maximizing the catalytic effect of ZnI 2 for S 8 ↔ZnS reaction and high‐performance AZSBs. Consequently, the optimized AZSBs deliver high specific capacity of 1532 mAh g −1 at 0.5 A g −1 , and high reversible capacity of 326.2 mAh g −1 after 320 cycles at 2 A g −1 . Even if assembled into pouch batteries with high sulfur loading of 10 mg cm −2 , high capacity of 514.5 mAh g −1 is still maintained after 134 cycles at 0.5 A g −1 . This work provides novel insights to accelerate sulfur conversion reaction kinetics through stabilizing the redox mediators of AZSBs.