Successive Redox Mediation Supported by Pnictogen Chalcohalide Enables High-Performance Zinc-Sulfur Batteries.

Sulfur is a promising high-capacity cathode but suffers from sluggish redox kinetics and severe side reactions in aqueous electrolytes. We introduce pnictogen chalcohalide Bi12.67S18Br2 nanorods (abbreviated as Bi-S-Br) as a multifunctional cathode material that functions as a sulfur/bismuth reservoir and a catalytic redox mediator (RM). By integrating a trace amount of iodide electrolyte additive, we demonstrate a potential pathway, featuring several redox couples with gradient potentials: I0/I- (0.530 V, RM1) > Bi3+/Bi0 (0.308 V, RM2) > S0/S2- (0.144 V vs. standard hydrogen electrode), whose stepwise dual mediation accelerates sulfur redox kinetics. The sulfurphilic Bi-S-Br nanorods also strengthen surface Bi-S interfacial interactions, thus localizing active species and suppressing sulfur disproportionation. As a result, Zn||Bi-S-Br cells exhibit synergistic discharge plateaus at 0.66 and 0.59 V and deliver a high specific capacity of 792 mAh gBi-S-Br -1 at 0.4 A g-1, with an energy density of 488.2 Wh kg-1 and a power density of 244.1 W kg-1, normalized to the Bi-S-Br mass. The practical Zn||Bi-S-Br pouch cell configuration sustains 250 cycles at 0.8 mA cm-2 with capacity retention of 70.1%. This study elucidated the successive redox mediation strategy for enhanced sulfur redox kinetics, offering a new design principle for high-performance aqueous energy storage systems.