Valence Electronic Structure of Li2O2, Li2O, Li2CO3, and LiOH Probed by Soft X-ray Emission Spectroscopy

The valence electronic structures of Li2CO3, Li2O, Li2O2, and LiOH were determined by soft X-ray emission spectroscopy (XES) at the oxygen K-edge. To ensure the collection of representative high-quality spectra, beam damage effects were characterized, and their influence on the spectral characteristics was minimized by limiting the exposure time (i.e., scanning the sample under the X-ray beam). We find that the spectral shapes of the four spectra are very compound-specific and allow an unambiguous speciation of these compounds. The emission lines are discussed and assigned based on published calculated oxygen-derived partial density of states. It is shown that the oxygen emission of Li2CO3, Li2O, Li2O2, and LiOH in the upper valence band is mainly related to the s- and p-like states of the carbonate anion CO32-, the p-like states of the oxide anion O2-, the p-like states of the peroxide anion O-2(2-), and the pi-like character of the OH- group, respectively. This work thus creates the basis for XES studies of the chemical reaction mechanism in energy storage devices involving these key compounds.