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

State-of-the-art sulfur-based batteries are primarily driven by the S⁰/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 S⁰/S⁺ redox couple enabled by the formation of liquid-phase S₂Br₂ in both aqueous and nonaqueous electrolytes. Compared to traditional S⁰/S^2- reactions (0.45 V vs. Zn²⁺/Zn; 2.2 V vs. Li⁺/Li), the S⁰/S⁺ redox chemistry offers significantly higher equilibrium redox potentials (1.68 V vs. Zn²⁺/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 S₂Br₂ mass) and demonstrating strong potential for high-performance batteries.