Atomic and electronic bulk versus surface structure:: Lithium intercalation in anatase TiO2

Lithium intercalation in anatase TiO2 results in structural and electronic changes. X-ray absorption at the Ti K edge as a function of lithium content is interpreted as a sum of two coexisting crystallographic phases (anatase and Li-titanate), both in the case of chemically lithiated microcrystalline samples and electrochemically intercalated thin film samples. The changes in the near edge region of the Ti K edge (XANES region) indicate that the charge-compensating electron of the Li-ion mainly occupies the crystal field split Ti 3d t(2g) orbitals located at the bottom of the conduction band. Surface sensitive reflection mode XAFS indicates that intercalation leads to a 3-4 nm surface region characterized by an effective Ti oxidation state close to 3+. The composition is determined to be close to Li1TiO2, and appears to be the reason for a poor cycle-lifetime of the anatase TiO2 electrode material.