Soft X-Ray Irradiation Effects of Li2O2, Li2CO3 and Li2O Revealed by Absorption Spectroscopy

Li2O2, Li2CO3, and Li2O are three critical compounds in lithium-air and lithium-ion energy storage systems. Extensive measurements have been carried out to study the chemical species and their evolutions at difference stages of the device operation. While x-ray spectroscopy has been demonstrated to be one of the most powerful tools for such purpose, no systematic study on the irradiation effects have been reported. Here we carry out extensive time, position, and irradiation dependent Li K-edge soft x-ray absorption spectroscopy on these compounds with so far the best energy resolution. The ultra-high resolution in the current study allows the features in the absorption spectra to be well-resolved. The spectral lineshape thus serves as the fingerprints of these compounds, enabling the tracking of their evolution under x- ray irradiation. We found that both Li2O2 and Li2CO3 evidently evolve towards Li2O under the soft x- ray irradiation with Li2CO3 exhibiting a surprisingly higher sensitivity to x-rays than Li2O2. On the other hand, Li2O remains the most stable compound despite experiencing substantial irradiation dose. We thus conclude that high resolution soft x- ray spectroscopy could unambiguously fingerprint different chemical species, but special cautions on irradiation effects would be needed in performing the experiments and interpreting the data properly.