In Situ Surface-Enhanced Infrared Absorption Spectroscopy to Explore the Stability of Electrolyte in Nonaqueous Lithium Oxygen Batteries

Abstract

Tetraethylene glycol dimethyl ether (TEGDME) decomposition on the Au electrode surface is studied using in situ attenuated total reflectance surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). Due to the weak solvation of TEGDME, the superoxide intermediate (LiO₂/O₂⁻) of the discharge process rapidly gains electrons on the electrode surface to generate Li₂O₂. Furthermore, alkyl radical, formed by LiO₂/O₂⁻ extracting hydrogen from ether, undergoes oxidative decomposition reactions to form by-products. During the charge process, amorphous film-like Li₂O₂ obtained from surface-phase mechanism oxidizes in the low potential range of 3–3.4 V, while the oxidation potential of large-sized crystal Li₂O₂ particles obtained from solution-phase mechanism is above 3.4 V. Besides, TEGDME is intrinsically unstable and can decompose at 3.8 V even the solution is saturated with argon, indicating that the degradation of ether-based electrolyte is inevitable during the cycling process. This work confirms the feasibility of ATR-SEIRAS in probing the reaction mechanism and electrolyte stability of lithium oxygen batteries, and provides direct spectroscopic evidence for subsequent optimization of electrolyte components.