Tailoring terminal groups in sulfonyl solvents to boost compatibility with lithium metal anodes

Sulfonyl-based compounds are considered promising electrolyte solvents because of their high dielectric constant, excellent anodic stability, and non-flammability. However, their use in Li metal batteries (LMBs) is limited by their incompatibility with Li, causing unstable interfacial chemistry and dendrite growth. Herein, we designed an <i>N</i>,<i>N</i>-dimethylsulfamoyl fluoride (DMSF) electrolyte by functionalizing a fluorosulfonyl (FSO₂ ^-) core with an <i>N</i>,<i>N</i>-dimethyl terminal group, enabling the LMB with enhanced cycling stability and energy density. The increased steric hindrance in DMSF with methylation weakens the interaction with Li ions, resulting in a structure that is weakly solvating and exhibits fast ion transport kinetics. Methylation also facilitates the decomposition of DMSF, leading to the formation of a rich LiF/Li₂S hybrid solid electrolyte interphase that suppresses interfacial side reactions. Consequently, the 4.5 V-charged 50 µm Li‖LiNi_0.8Co_0.1Mn_0.1O₂ (4 mAh cm^-2) cells exhibit stable cycling (80% capacity retention for 850 cycles), 5C fast charging, and a wide operating temperature range (-50-60 °C). Moreover, a 5-Ah pouch cell employing DMSF delivers an energy density of 540 Wh kg^-1 and exhibits high stability over 110 cycles. This study establishes terminal group modification as a crucial advance for developing compatible sulfonyl-based electrolytes in high-performance LMBs.