Electronic structure of the spinel Li₄Ti₅O ₁₂ studied by ab initio calculations and X-ray absorption spectroscopy

The electronic structure of the spinel compound Li₄Ti ₅O₁₂, used as anode material in Li-ion batteries, is studied both theoretically and experimentally. The partial densities of occupied and vacant s, p and d electronic states were calculated for Li, Ti and O, using the linear augmented plane wave formalism (LAPW) in order to obtain information on the chemical bond. X-ray absorption spectra were recorded at the Ti L₂₃, Ti K and O K absorption edges and calculated within the dipolar approximation by considering both the electronic ground state and the effect of core holes. The atomic origin of the observed main peaks is analysed from the comparison between the experimental and calculated spectra. We show that the two types of lithium in Li₄Ti₅O₁₂ which are found in tetrahedral and octahedral sites could be distinguished by X-ray absorption spectroscopy. We suggest to use such a technique for the investigation of Li-insertion mechanisms in lithium titanate spinels.