Revisiting the Sodiation Mechanism of TiO2 via Operando X-ray Absorption Spectroscopy

The sodiation mechanism of TiO2 anatase was thoroughly investigated via X-ray absorption spectroscopy under operando conditions. The data set was analysed via an innovative and smart approach based on chemometric tools that allows the unbiased and reliable extraction of the maximum amount of meaningful information. The resulting data analysis reveals that the electrochemical sodiation mechanism is mainly based on the reduction of Ti4+ to Ti3+, going along with the irreversible amorphisation of the pristine anatase structure. At least one semi-amorphous intermediate is formed during the first discharge, whose local structure resembles those obtained at the end of the charge.