A first-principles study was made of non-dilute Li diffusion in spinel LixTiS2 with the aim of clarifying the effect of crystal structure and chemistry upon Li mobility in intercalation compounds. In contrast to transition-metal oxide spinels, where the Li ions occupied tetrahedral interstitial sites, Li ions in spinel LixTiS2 preferentially occupied octahedral sites. Elementary Li hops between neighboring octahedral sites passed through intermediate tetrahedral sites. High coordination of these intermediate tetrahedral sites with octahedral sites caused the migration barrier to be sensitive to the local Li concentration and configuration. Kinetic Monte Carlo simulations predicted that diffusion mechanisms were mediated by triple vacancies and divacancies; leading to a strong concentration dependence of the chemical diffusion coefficient. It was concluded that crystal structures with activated states that were highly coordinated by Li sites would be associated with diffusion mechanisms that were mediated by vacancy clusters, resulting in a chemical diffusion coefficient that decreased with increasing Li composition.

First-Principles Study of Competing Mechanisms of Nondilute Li Diffusion in Spinel LixTiS2. J.Bhattacharya, A.Van Der Ven: Physical Review B, 2011, 83[14], 144302