Anti‐Corrosive Covalent Iodo‐Thiadiazole Catalyst Enables Aqueous Zn─S Batteries with High Coulombic Efficiency

Abstract Aqueous zinc‐sulfur batteries (AZSBs) hold great promise for large‐scale energy storage but suffer from low Coulombic efficiency (CE) due to sluggish Zn─S redox kinetics and severe Zn anode corrosion, limiting their cycling life and practical applicability. Although state‐of‐the‐art iodine‐based redox mediators can accelerate cathode kinetics, they typically result in the formation of free I 3 − species, which exacerbate Zn corrosion. Here, we report a covalent iodo–thiadiazole redox mediator (CIM) as an anti‐corrosive and highly efficient catalyst to achieve high CE in AZSBs. The covalently anchored iodine in CIM effectively suppresses free I 3 − formation and mitigates Zn corrosion. More importantly, dynamic electronic restructuring from C5═N to C5─N bonds (C5: 5th‐position carbon in the thiadiazole ring) promotes Zn–S redox kinetics through a σ‐coordination electron pathway facilitated by the Zn─I─C5 bond. As a result, CIM‐based coin cells achieve an average CE of 99.56% and a capacity of 344 mAh g −1 after 700 cycles at 8 C. The CIM‐based pouch cell demonstrates a high capacity of 1398 mAh g −1 after 120 cycles at 0.8 C. This work presents a practical design strategy for iodine‐based catalysts, enabling next‐generation aqueous metal‐sulfur batteries with enhanced durability and performance.