Modeling Singlet Oxygen-Induced Degradation Pathways Including Environmental Effects of 1,2-Dimethoxyethane in Li-O₂ Batteries through Density Functional Theory

We employ density functional theory (DFT) to examine reaction mechanisms involving singlet oxygen ¹Δ_g (¹O₂) and 1,2-dimethoxyethane (DME) to probe potential parasitic reactions occurring in Li-O₂ batteries. First, we investigate the attack of ¹O₂ on the ethylene group (-CH₂-CH₂-) to form H₂O₂ and a C-C double bond in a single step. Second, we look at hydroperoxide formation that occurs via a two-step mechanism. We employ an implicit solvent model, Li⁺ coordination, and external electric fields to model the complex electrolyte environment near the cathode of a Li-O₂ battery. The initial barriers for these reactions are decreasing functions of the dielectric constant of the implicit solvent model as well as the strength of the electric field. These initial barriers range between 17 and 26 kcal mol^-1 for large dielectric constants and in the presence of electric fields. We discuss the implications of these results on ether-based electrolytes for Li-O₂ batteries.