A Multifunctional Additive for Long‐Cycling Lithium‐Sulfur Batteries Under Lean‐Ether‐Electrolyte Conditions

Abstract The failure of lithium‐sulfur (Li‐S) batteries operating under lean‐ether‐electrolyte conditions can be ascribed to the deterioration of electrolytes, the passivation of cathodes, and the degeneration of lithium anodes. Efforts to address these challenges by exploring alternative electrolytes beyond commonly used ether‐based systems often introduce new complications. In this study, the utilization of a multifunctional additive, 2‐Bromoacetamide (BA), for ether electrolytes is proposed to achieve stable Li‐S batteries under lean‐electrolyte conditions. These investigations reveal that the amide bond in BA forms hydrogen bonds with sulfur atoms, promoting the dissolution of lithium sulfides (Li 2 S) in ether electrolytes and mediating the conversion of lithium polysulfides. This enhanced solubility of Li 2 S facilitates 3D deposition (vertical to the substrate) rather than the typical 2D deposition (parallel to the substrate) of Li 2 S, and thus alleviates the passivation of cathodes. Furthermore, the incorporation of BA promotes uniform and dense lithium deposition. The use of the BA‐containing electrolyte enables stable cycling of a Li‐S pouch cell for 40 cycles, even under a low electrolyte‐to‐sulfur ratio of 4 µL mg −1 . This multifunctional strategy offers an effective solution to extend the lifetime of Li‐S batteries under lean‐electrolyte conditions, thereby paving the way for practical applications of Li‐S battery technology.