A sulfonamide-based electrolyte for high-temperature and high-voltage lithium metal batteries

Increasing the charge cut-off voltage represents one of the effective ways to increase the energy density of Li-metal batteries (LMBs). However, this approach is hindered by the poor oxidation stability of conventional electrolytes, which tends to be more severe under high temperatures. To address this challenge, we synthesized a solvent, N-pyrrolidine-trifluoromethanesulfonamide (TFSPY), and formulated an electrolyte using 2 M lithium bis(fluorosulfonyl)imide (LiFSI) salt. This electrolyte enables stable long-term cycling of Li||LiCoO₂ cells (≈10.8 mg cm⁻²) at a high voltage of 4.5 V, demonstrating a capacity retention of 90 % after 200 cycles—significantly outperforming conventional carbonate-based electrolytes. Mechanistic analysis reveals that TFSPY promotes the formation of an FSI⁻-enriched solvation structure, thereby facilitating the decomposition of FSI⁻, which leads to the formation of a robust SEI on the lithium metal anode, thereby effectively suppressing dendrite growth. Furthermore, TFSPY is partially oxidative and decomposed, generating a Li₃N-enriched CEI that significantly enhances high-voltage cycling stability even at high temperature up to 60 °C. The synergistic stabilization of both electrode interfaces—through the formation of protective SEI and CEI layers—enables reliable battery operation under high voltage and temperature conditions. Furthermore, the broad endothermic platform of the TFSPY molecule is key to its application in high-temperature fields. These findings provide valuable insights for the design of advanced electrolytes for high-energy-density LMBs.