Observation of lithiation-induced structural variations in TiO2 nanotube arrays by X-ray absorption fine structure

We report here a study of self-organized TiO2 nanotube arrays both in the amorphous and anatase phases with superior electrochemical performance upon lithiation and delithiation. X-ray absorption fine structure (XAFS) study at the Ti K and L, O K and Li K edges has been conducted to track the behavior. Characteristic features for amorphous and anatase TiO2 are identified. After lithiation, it is found that although no obvious variation of chemical states is apparent at the Ti K and L edges, charge transfer from Ti 3d to O 2p and also partial amorphization of anatase TiO2 are evident from spectral intensities. The Li and O K edge XAFS show the successful intercalation of lithium and reveal the existence of a nearly linear O-Li-O arrangement in the lithiated TiO2 nanotube. This study helps in understanding of the lithiation process in nanostructured TiO2 anodes from a spectroscopic viewpoint.