Raman Spectroscopy in Lithium–Oxygen Battery Systems

Abstract

Electrochemical processes in lithium–oxygen (Li–O2 or Li–air) batteries are complex, with chemistry depending on cycling conditions, electrode materials and electrolytes. In non‐aqueous Li–O2 cells, reversible lithium peroxide (Li2O2) and irreversible parasitic products (i.e., LiOH, Li2CO3, Li2O) are common. Superoxide intermediates (O2−, 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–O2 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–O2 products in situ or ex situ, 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–O2 batteries.

Palladium-Filled Carbon Nanotubes Cathode for Improved Electrolyte Stability and Cyclability Performance of Li-O2Batteries

“…However, the Pd-coated CNTs cathode showed a pronounced Raman shift peak at 1080 cm −1 , which corresponds to the electrolyte decomposition product Li 2 CO 3 . 47,48 This peak was absent from pristine CNT cathodes. This behavior confirms the observation from CV, indicating reduced electrolyte stability due to the presence of Pd on Pd-coated CNTs and enhanced electrolyte stability for Pd-filled compared to Pd-coated CNTs.…”

An electrochemical surface‐enhanced Raman spectroscopic study on nanorod‐structured lithium prepared by electrodeposition

“…First, in the work of Zhang et al , of which we adopted the method for Li nanorod preparation, XPS spectra exhibit strong signal of F element from the SEI formed on the Li nanorods, indicating the existence of rich amount of LiF in the SEI layer, which is as expected. Second, Raman spectra of Li 2 CO 3 and LiOH powders show strong bands of A g mode at 1093 cm −1 for Li 2 CO 3 and 331 and ca. 630 cm −1 for LiOH.…”

“…The 1020 cm −1 band may well be dominated by the contributions from both Li 2 CO 3 (1090 cm −1 ) and LiF (966 cm −1 ). On the other hand, the 720 cm −1 band may be contributed by LiF (616, 672 and 680 cm −1 bands) and LiOH (630 cm −1 ) . The presence of LiOH is supported by the band at 350 cm −1 .…”

Applications of Conventional Vibrational Spectroscopic Methods for Batteries Beyond Li‐Ion

“…For example, XRD cannot differentiate disordered carbons with their different defect levels, whereas such local defects can be probed by Raman spectroscopy. Furthermore, the breakthrough of high‐sensitivity low‐noise multichannel detectors enables Raman spectroscopy a powerful tool in investigating battery chemistry, such as the evolving properties of electrodes and electrolytes during and/or after cycling …”

“…Some recent review papers on the applications of Raman spectroscopy in LIBs summarized the fields very well, which covered key issues and trends in Raman research on negative or positive materials, the advance of new in situ Raman techniques, such as confocal Raman microscopy, SERS, TERS, and spatially offset Raman spectroscopy on electrodes, electrolytes, and the electrode/electrolyte interface, as well as the applications of SERS to Li–O 2 batteries . Taking into account the large number of articles in the literature in this field, herein, we will focus more on the very recent advance of in situ and/or ex situ Raman characterization of novel electrode materials, electrolyte, and the formation of SEI films in LIBs, NIBs, KIBs, dual ion batteries (DIBs), Li–S batteries, and Li–O 2 batteries, which we hope can help better understand the novel mechanisms for electrochemical energy storage and provide insights into the design of novel electrode materials with high electrochemical performance.…”