Direct Evidence of Reversible Changes in Electrolyte and its Interplay with LiO2 Intermediate in Li-O2 Batteries

Abstract

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-O₂ battery with LiClO₄/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 Li₂O₂. 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 LiO₂(sol), highlighting the stability of the electrolyte compared to the interaction with reactive $O_2^{-}$ . 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-O₂ 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-O₂ system.

Keywords: density functional theory; lithium‐oxygen battery; operando raman.