Computational comparison of oxidation stability: Sulfones vs. fluorinated sulfones

Abstract

The oxidation stability and initial decomposition reaction of sulfones and fluorinated sulfones are compared through quantum chemical calculations. The fluorination of isolated sulfones does not always increase the oxidation potential, which is related to the fluorination position and molecular configuration. The effects of incorporating another solvent molecule/lithium salt anion (PF6−, FSI−) on oxidation stability are investigated. The addition of the solvent molecule slightly reduces the oxidation potential of sulfones or fluorinated sulfones. PF6− has a weak influence on the oxidation potential of sulfones, except for the branched methyl isopropyl sulfone. When the α-CH3 group of the sulfones is fluorinated to -CF3, PF6− is found to significantly reduce the oxidation potential of the solvent-PF6− complexes, while the effect is small on the fluorinated non-α-CH3 group. The greater impact on oxidation potential is due to the chemical reaction of sulfones or fluorinated sulfones with PF6− following the loss of electrons. Furthermore, although the oxidation potential of FSI− is lower than that of sulfones and fluorinated sulfones, the oxidation potential of most solvent-FSI− complexes is higher than that of isolated FSI−. This study provides important information for the design of electrolytes suitable for high-voltage applications.