Density-functional theory (generalized gradient approximation) was used to study lithium intercalation at low concentration into anatase TiO2. To describe the defect states produced by Li doping a Hubbard “+U” correction was applied to the Ti d states (GGA+U). Uncorrected generalized gradient approximation calculations predict LixTiO2 to be metallic with the excess charge distributed over all Ti sites, whereas GGA+U predicts a defect state 0.96eV below the conduction band, in agreement with experimental photo-electron spectra. This occupied defect state corresponded to charge strongly localized at a single Ti 3d site neighboring the intercalated lithium with a magnetization of 1μeV, in good agreement with experimental data. These barrier heights were found to depend only weakly on the position of the donated electron. The intercalation energy was 2.14eV with generalized gradient approximation and 1.88eV with GGA+ Å along the [001] direction within each octahedron. Nudged elastic band calculations give barriers to inter-octahedral diffusion of ∼0.6 B. This polaronic state produces a red-shifted optical absorption spectrum, which was compared to those for the native O-vacancy and Ti-interstitial defects. The strong localization of charge at a single Ti center lowers the symmetry of the interstitial geometry relative to that predicted by generalized gradient approximation. The intercalated lithium sits close to the center of the octahedral site, occupying a single potential energy minimum with respect to displacement along the [001] direction. This challenges the previous interpretation of neutron diffraction data that there exist two potential energy minima separated by 1.6meV. Li-electron binding energies were also calculated. The [Li , compared to the experimental value of ∼1.9i•-TiTi′] complex had a binding energy of 56meV, and a second electron was predicted to be bound to give [Lii•-2TiTi′] with a stabilization energy of 30meV, indicating that intercalated lithium will weakly trap excess electrons produced during photo-illumination or introduced by additional n-type doping.

GGA+U Description of Lithium Intercalation into Anatase TiO2. Morgan, B.J., Watson, G.W.: 2010, Physical Review B, 2010, 82[14], 144119