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

Owing to the large availability of sodium, Na-ion batteries could be a viable and cheap alternative to Li-ion batteries, and the development of new electrode materials for this promising technology, such as TiO2, is necessary to accelerate their adoption in large-scale applications. The sodiation mechanism of TiO2 anatase was thoroughly investigated via X-ray absorption spectroscopy underoperandoconditions. 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.