A comprehensive first-principles investigation was made of Li diffusion in spinel Li1+xTi2O4. Concentration-dependent diffusion coefficients were calculated by applying kinetic Monte Carlo simulation to a first-principles parameterized cluster expansion of the configurational energy and migration barriers. Diffusion mechanisms in spinel transition metal oxide intercalation compounds were sensitive to the Li concentration. Below x = 0 in Li1+xTi2O4, Li ions occupy tetrahedral sites and individual Li hops between neighboring tetrahedral sites pass through intermediate octahedral sites, which were found to be activated states as opposed to local minima. The migration barriers were sensitive to the overall Li concentration, decreasing as the Li concentration over the tetrahedral sites was increased. A miscibility gap exists between LiTi2O4 and Li2Ti2O4. The Li-diffusion mechanisms in Li2Ti2O4 were qualitatively different to those in Li1+xTi2O4 when x < 0; with Li hops between neighboring octahedral sites passing through intermediate tetrahedral sites that were locally stable. The present study provided insight to the origin of the high Li mobility in spinel crystal structures compared to the layered crystal structures of common intercalation compounds.

Phase Stability and Nondilute Li Diffusion in Spinel Li1+xTi2O4. J.Bhattacharya, A.Van Der Ven: Physical Review B, 2010, 81[10], 104304