High‐Reversibility Sulfur Anode for Advanced Aqueous Battery

Abstract Despite being extensively explored as cathodes in batteries, sulfur (S) can function as a low‐potential anode by changing charge carriers in electrolytes. Here, a highly reversible S anode that fully converts from S₈⁰ to S²⁻ in static aqueous S–I₂ batteries by using Na⁺ as the charge carrier is reported. This S anode exhibits a low potential of −0.5 V (vs standard hydrogen electrode) and a near‐to‐theoretical capacity of 1404 mA h g⁻¹. Importantly, it shows significant advantages over the widely used Zn anode in aqueous media by obviating dendrite formation and H₂ evolution. To suppress “shuttle effects” faced by both S and I₂ electrodes, a scalable sulfonated polysulfone (SPSF) membrane is proposed, which is superior to commercial Nafion in cost (US$1.82 m⁻² vs $3500 m⁻²) and environmental benignity. Because of its ultra‐high selectivity in blocking polysulfides/iodides, the battery with SPSF displays excellent cycling stability. Even under 100% depth of discharge, the battery demonstrates high capacity retention of 87.6% over 500 cycles, outperforming Zn–I₂ batteries with 3.1% capacity under the same conditions. These findings broaden anode options beyond metals for high‐energy, low‐cost, and fast‐chargeable batteries.