Sulfur–Fluoride Exchangeable Moiety‐Integrated Mediator of Benzenesulfonyl Fluoride Additives in Low‐Electrolyte Lithium–Sulfur Batteries

Lithium–sulfur batteries have attracted significant attention because of their high theoretical capacity and energy density. Reducing the amount of inert electrolyte in the cell is essential for further improving the practical energy density. However, high viscosity and poor sulfur utilization issues occur from the saturation of soluble long‐chain lithium polysulfides (LiPSs, Li 2 S x , 4 ≤ x ≤ 8) in low‐electrolyte systems, leading to sluggish redox kinetics. In this study, we propose benzenesulfonyl fluoride (BF) as a sulfur–fluoride exchangeable moiety‐integrated mediator (SFEMM) that alleviates the solubility limitation by promoting the chemical conversion of LiPSs. The SO 2 F group of BF acts as an electrophile, inducing a reaction with nucleophilic LiPSs. Ultraviolet‐visible spectroscopy and X‐ray photoelectron spectroscopy (XPS) analyses confirmed that BF promotes LiPSs conversion while producing LiF as reaction evidence, confirming the SFEMM behavior of BF. Moreover, density functional theory (DFT) calculations revealed that BF undergoes a thermodynamically favorable sulfur–fluoride exchange reaction with LiPSs, further supporting its role in promoting polysulfide conversion. Electrochemical evaluations demonstrate that improved sulfur utilization is enabled by BF, even at a low electrolyte‐to‐sulfur (E/S) ratio of 7 μL mg −1 , with a high initial discharge capacity of 1317 mAh g −1 and an initial coulombic efficiency of 97.9%.