Upon intercalating Li into anatase TiO2, spontaneous phase separation in a Li0.01TiO2 Li-poor and a Li0.55TiO2 Li-rich phase occurred at sub-micron domain sizes. When applied as an anode, this 2-phase behaviour led to a constant electrochemical potential during discharge; provided that there was thermodynamic equilibrium between the phases. Using high-field solid-state nuclear magnetic resonance, it was possible to observe how diffusion of Li between the 2 phases, at ms time-scales and 100nm length-scales, permitted the establishment of such equilibrium. At room temperature, some 1020/m2s of Li ions continuously crossed the phase boundaries. At much faster μs time-scales, diffusion took place within each of the separate phases. Using state-of-the-art neutron diffraction, the Li ions were found to be located in the Li-poor and Li-rich phases of anatase. It appeared that, due to the distortion of the O octahedra and the small Li-ion size, there were 2 possible positions in each octahedron. At ps time-scales, the Li hopped between these 2 sites within one octahedron; according to quasi-elastic neutron scattering results and molecular dynamics simulations.

The Life and Times of Lithium in Anatase TiO2. Wagemaker, M., van Well, A.A., Kearley, G.J., Mulder, F.M.: Solid State Ionics, 2004, 175[1-4], 191-3