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

The valence electronic structures of Li 2 CO 3, Li 2 O, Li 2 O 2, 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 Li 2 CO 3, Li 2 O, Li 2 O 2, and LiOH in the upper valence band is mainly related to the s- and p-like states of the carbonate anion CO 3 2–, the p-like states of the oxide anion O 2–, the p-like states of the peroxide anion O 2 2–, and the π-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.