An Energetic S ⁰ /S ⁺ Redox Chemistry for Aqueous and Nonaqueous Sulfur Batteries

Abstract

Abstract State‐of‐the‐art sulfur‐based batteries are primarily driven by the S 0 /S 2− redox chemistry, yet their performance is limited by sluggish kinetics and low practical energy densities. In aqueous systems, slow solid‐solid conversion leads to high overpotentials (∼1 V) that restricts energy efficiency, while in nonaqueous systems, the sophisticated dissolution‐precipitation mechanism involving soluble polysulfide intermediates induces shuttle effects and capacity loss, necessitating catholyte configurations that compromise energy density. Here, we report an energetic and reversible S 0 /S + redox couple enabled by the formation of liquid‐phase S 2 Br 2 in both aqueous and nonaqueous electrolytes. Compared to traditional S 0 /S 2− reactions (0.45 V vs. Zn 2+ /Zn; 2.2 V vs. Li + /Li), the S 0 /S + redox chemistry offers significantly higher equilibrium redox potentials (1.68 V vs. Zn 2+ /Zn; 3.4 V vs. Li + /Li), a direct one‐step conversion pathway that avoids polysulfide intermediates formation, and intrinsically faster kinetics attributed to its solid‐liquid transition nature, enabling full sulfur utilization with a capacity of 837 mAh g −1 . When paired with Zn or Li anodes in tailored aqueous and organic electrolytes, respectively, this chemistry delivers high energy densities of 1406 and 2689 Wh kg −1 based on sulfur mass (402 and 768 Wh kg −1 based on S 2 Br 2 mass) and demonstrating strong potential for high‐performance batteries.