Enhanced safety of sulfone-based electrolytes for lithium-ion batteries: broadening electrochemical window and enhancing thermal stability

To meet the demands of high-voltage lithium-ion batteries (LIBs), we develop a novel electrolyte through theoretical calculations and electrochemical characterization. Triphenylphosphine oxide (TPPO) is introduced as a film-forming additive into a sulfone-based electrolyte containing 1 mol L⁻¹ lithium difluoro(oxalate)borate (LiDFOB). Density functional theory (DFT) calculations show that TPPO has a lower reduction potential compared to the sulfone-based solvent. Hence, it is expected that TPPO will be oxidized before the sulfone-based solvent and form a cathode electrolyte interphase (CEI) layer on the Li-rich cathode. Our research findings demonstrate that the addition of 2 wt.% TPPO to the sulfone-based electrolyte significantly enhances the ionic conductivity within the temperature range of 20–60 °C. Additionally, it increases the discharge capacity of LIBs in the range of 2–4.8 V while maintaining excellent rate performance and cycling stability. Flammability tests and thermal gravimetric analysis (TGA) results indicate the excellent non-flammability and thermal stability of the electrolyte.