Raman Spectroscopy in Lithium-Oxygen Battery Systems

Abstract

Electrochemical processes in lithium-oxygen (Li-O-2 or Li-air) batteries are complex, with chemistry depending on cycling conditions, electrode materials and electrolytes. In non-aqueous Li-O-2 cells, reversible lithium peroxide (Li2O2) and irreversible parasitic products (i.e., LiOH, Li2CO3, Li2O) are common. Superoxide intermediates (O-2(-), LiO2) contribute to the formation of these species and are transiently stable in their own right. While characterization techniques like XRD, XPS and FTIR have been used to observe many Li-O-2 species, these methods are poorly suited to superoxide detection. Raman spectroscopy, however, may uniquely identify superoxides from O-O vibrations. The ability to fingerprint Li-O-2 products insitu or exsitu, even at very low concentrations, makes Raman an essential tool for the physicochemical characterization of these systems. This review contextualizes the application of Raman spectroscopy and advocates for its wider adoption in the study of Li-O-2 batteries.