Characterization of the electrochemical reactions in the Li(1+x)V3O8/Li cell by soft X-ray absorption spectroscopy and two-dimensional correlation analysis.

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+x)V3O8/Li cell in order to investigate the electrochemical reactions of lithium with the Li(1+x)V3O8 electrode. The V L(II,III)-edge and O K-edge spectra of the Li(1+x)V3O8 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+x)V3O8 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+x)V3O8 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+x)V3O8 electrode.