Dynamically Regulating Polysulfide Degradation via Organic Sulfur Electrolyte Additives in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries offer promising prospects due to their high energy density and cost-effectiveness. However, the sluggish kinetics of lithium polysulfides (LiPSs) conversion, particularly the crucial stage from LiPSs to lithium sulfide (Li₂S), hampers their development. Herein, a novel strategy for dynamically regulating LiPSs conversion by incorporating 4-mercaptopyridine (4Mpy), as a LiPSs Redox Regulator (RR) in the electrolyte is introduced. This organic sulfur additive actively interacts with LiPSs during discharge, facilitating rapid conversion and promoting the formation of a three-dimensional (3D) Li₂S structure, thereby enhancing reaction kinetics. Both theoretical and experimental results reveal that the redox conversion mechanism with the 4Mpy additive differs from traditional electrolytes. Upon lithiation, 4Mpy forms lithium-pyridinethiolate (Li-pyS), which reversibly engages in the LiPSs conversion during the charging/discharging cycles, significantly improving the redox process. As a result, the Li-S battery with 4Mpy additive demonstrates superior performances, achieving 10.05 mAh cm⁻² under a high sulfur loading of 10.88 mg cm⁻², surpassing industrial benchmarks. This study not only presents an approach to mitigating the shuttle effect in Li-S batteries but also offers valuable insights into electrolyte design for other metal batteries.