Confining Polyiodide in Polymer Cathode Boosts Cycling Stability in High Energy-Dense Aqueous Zinc-Sulfur Batteries

Aqueous zinc-sulfur (Zn/S) batteries are emerging as sustainable energy storage systems owing to their high theoretical capacity, environmental safety, and cost-effectiveness. However, their practical application is hindered by sluggish solid-solid sulfur conversion kinetics and the persistent need for soluble iodine redox mediators that exacerbate zinc anode corrosion and dendrite formation. Here, we report an integrated polymer-polyiodide confinement strategy employing a cationic poly(vinyl butyl imidazolium iodide) framework ([PVIM]I) complexed with iodine to form a redox-active polymer-polyiodide framework ([PVIM]I_x). The polymer matrix spatially confines polyiodide species, minimizing their crossover and suppressing zinc anode corrosion while enhancing sulfur redox kinetics. The resulting metal-free and binder-free ([PVIM]I_x) cathode delivers a high specific capacity of 1845 mAh g^-1 (1548 mAh g^-1 excluding iodine contribution) at 0.1 A g^-1 with an energy density of 923 Wh kg^-1, maintaining excellent cycling stability with 93.7% capacity retention over 500 cycles at 5 A g^-1. Improved ion diffusion and reduced polarization were confirmed by GITT and in situ impedance spectroscopy. This polymer-iodide composite provides a scalable and stable platform for advancing aqueous Zn/S batteries, addressing key challenges in cathode wettability and redox mediation to enable sustainable, high-performance energy storage solutions.