Direct Evidence of Reversible Changes in Electrolyte and its Interplay with LiO 2 Intermediate in Li-O 2 Batteries.

Lithium-oxygen batteries show promising energy storage potential with high theoretical energy density; however, further investigation of chemical reactions is required. In this study, experimental Raman and theoretical analyzes are performed for a Li-O 2 battery with LiClO 4 /dimethyl sulfoxide (DMSO) electrolyte and carbon cathode to understand the role of intermediate species in the reactional mechanism of the cell using a high donor number solvent. Operando Raman results reveal reversible changes in the DMSO bands, in addition to the formation and decomposition of Li 2 O 2 . On discharge, a decrease in DMSO polarizability is observed and bands of DMSO-Li + -anion interactions are evidenced and supported by ab initio density functional theory (DFT) calculations. Molecular dynamics (MD) force field simulations and operando Raman show that DMSO interacts with LiO 2 (sol), highlighting the stability of the electrolyte compared to the interaction with reactive O 2 - ${\rm O}_2^{-}$ . On charging, the presence of Li + indicates the formation of a lithium-deficient phase, followed by the release of Li + and oxygen. Therefore, this study contributes to understanding the discharge/charge chemistry of a Li-O 2 cell, employing a common carbon cathode and DMSO electrolyte. The combination of a simple characterization technique in operando mode and theoretical studies provides essential information on the mechanism of Li-O 2  system.