Electronic and local structural changes with lithium-ion insertion in TiO2-B: X-ray absorption spectroscopy study

Abstract

X-Ray absorption fine structure (XAFS) spectroscopy was carried out on submicron sized TiO₂-B, which is one of the promising candidates for negative electrode materials, in order to clarify the electronic and local structural changes during its lithium-ion insertion process. From the extended X-ray absorption fine structure (EXAFS) results of lithiated Li_xTiO₂-B, we propose the changes in lithium-ion insertion sites during electrochemical discharging. The lithium ions are inserted into the five-fold coordinated sites and/or distorted octahedral sites distributed at the vicinity of O layers parallel to the ab plane for x ≤ 0.5, while the lithium ions are accommodated into the five-fold coordinated site distributed at the vicinity of TiO₂ layers parallel to the ab plane for x > 0.5. The interaction between the inserted lithium ion and TiO₆ octahedra affects the lattice distortion of Li_xTiO₂-B for x > 0.5, as well as the titanium reduction during discharging. It is suggested through the X-ray absorption near edge structure (XANES) spectroscopy of Ti K-, Ti L- and O K-edges that the distortion of TiO₆ octahedra makes the hybridized state of O 2p and Ti 3d broad, and has a significant effect on the lithium-ion insertion properties of TiO₂-B.