Characterization of the Electrochemical Reactions in the Li 1+x V 3 O 8 /Li Cell by Soft X-ray Absorption Spectroscopy and Two-Dimensional Correlation Analysis

Abstract

We applied soft X-ray absorption spectroscopy (XAS) and two-dimensional (2D) correlation analysis to the first lithium insertion–extraction cycle in a Li_1+xV₃O₈/Li cell in order to investigate the electrochemical reactions of lithium with the Li_1+xV₃O₈ electrode. The V L_II,III-edge and O K-edge spectra of the Li_1+xV₃O₈ electrode were obtained for varying electrode lithium content. The insertion of lithium leads to the reduction of the V⁵⁺ species present in the pristine Li_1+xV₃O₈ electrode, and to the red shift and the broadening of the spectral features of the V L_II,III edge compared to those of the pristine electrode. In the extraction process, the main spectral features at the highest value of the extraction of lithium show some differences compared to the features of the pristine electrode spectrum due to the residual lithium ions in the Li_1+xV₃O₈ structure. The O K-edge spectra revealed that the insertion of lithium mainly affects the V 4sp–O 2p bonds and consequently induces a change in bonding geometry. The 2D correlation analysis of these spectra clearly shows that V–O bonds are significantly perturbed by the insertion–extraction of lithium into the Li_1+xV₃O₈ electrode.