7Li magic angle spinning solid-state nuclear magnetic resonance was applied to investigate the lithium local environment and lithium ion mobility in tetragonal anatase TiO2 and orthorhombic lithium titanate Li0.6TiO2. Upon lithium insertion, an increasing fraction of the material changes its crystallographic structure from anatase TiO2 to lithium titanate Li0.6TiO2. Phase separation occurred and, as a result, the Li-rich lithium titanate phase was co-existing with the Li-poor TiO2 phase containing only small Li amounts ≈ 0.01. In both the anatase and the lithium titanate lattice, Li was found to be hopping over the available sites with activation energies of 0.2 and 0.09eV, respectively. This led to rapid microscopic diffusion rates at room temperature (Dmicr = 4.7 x 10-12cm2/s in anatase and Dmicr = 1.3 x 10-11cm2/s in lithium titanate). However, macroscopic intercalation data indicated activation energies of about 0.5eV and smaller diffusion coefficients. It was suggested that the diffusion through the phase boundary was determining the activation energy of the overall diffusion and the overall diffusion rate itself. The chemical shift of lithium in anatase was independent of temperature up to about 250K but decreased at higher temperatures, reflecting a change in the 3d conduction electron densities. The Li mobility became prominent from this same temperature showing that such electronic effects possibly facilitated the mobility.

Two Phase Morphology Limits Lithium Diffusion in TiO2 (Anatase): a 7Li MAS NMR Study. Wagemaker, M., Van de Krol, R., Kentgens, A.P.M., Van Well, A.A., Mulder, F.M.: Journal of the American Chemical Society, 2001, 123[46], 11454-61