Electronic structure evolution upon lithiation: A Li K-edge study of silicon oxide anode through X-ray Raman spectroscopy

The comprehensive understanding of the local structural changes surrounding lithium in lithium silicate (Li_xSiO_y) and silicide (Li_xSi) within Li/SiO_x batteries during the reversible structural transformations has been hindered by the limitations of current methodologies. In this work, the evolution of electronic structure at various lithiation stages has been addressed well by examining the Li K-edge spectra through X-ray Raman spectroscopy (XRS). The features observed in the Li K-edge XRS spectra provide insights into the development and alteration of Li_xSiO_y, which emerges in the initial phases and may be accompanied by a reduction in the ionicity of Li–O bonding during lithiation. These features also agree well with the accompanying FDMNES code simulation. The correlation between electrochemical mechanisms and spectral characteristics is further explored by applying pseudo-Voigt peaks and cumulative pseudo-Voigt functions for fitting purposes. The absence of a significant edge shift indicates a similarity in the electronic structure of Li_xSi throughout lithiation, and no evidence of Li₂O formation has also been observed. The Li K-edge XRS spectra exhibit strong agreement with the electrochemical behavior, establishing it as a valuable tool for investigating the evolution of electronic structure in Li/SiO_x batteries.