Lithium diffusion in the intercalation compound, LixTiS2, was investigated from first principles as a function of x. It was found that Li ions hopped between neighboring octahedral interstitial sites of the TiS2 host by passing through an adjacent tetrahedral site. The migration barriers for these hops were significantly reduced when the end-points belonged to a divacancy. within kinetic Monte Carlo simulations. A cluster expansion was used to describe the configurational dependence of the migration barriers, and a diffusion coefficient was predicted that varied by several orders of magnitude with Li concentration; exhibiting a maximum close to x = 0.5. The kinetic Monte Carlo simulations predicted that diffusion was mediated predominantly by divacancies. It was also found that the migration barriers depended strongly upon the c-lattice parameter; which decreased as Li ions were removed from LixTiS2.

Nondilute Diffusion from First Principles: Li Diffusion in LixTiS2. A.Van Der Ven, J.C.Thomas, Q.Xu, B.Swoboda, D.Morgan: Physical Review B, 2008, 78[10], 104306