Lithium ion diffusion in Li4+xTi5O12: From ab initio studies

Lithium ion dynamics in Li4+xTi5O12 spinel are investigated from first principles calculations. The diffusion pathways are optimized and the energy barriers of lithium migration under four types of dilute defect extremes: Li4+δTi5O12, Li4−δTi5O12, Li7+δTi5O12 and Li7−δTi5O12 (δ ≪ 1) are calculated with the nudged elastic band method. Results show that lithium diffusion in the charged state (energy barriers are 1.0 and 0.7 eV for interstitial Li and Li vacancy diffusion, respectively) is much slower than in the discharged state (energy barriers are 0.13 and 0.35 eV for interstitial Li and Li vacancy diffusion, respectively). The diffusion coefficients are evaluated based on lattice gas model and hopping mechanism. The obtained results are compared with available experimental data within a two-phase co-existence framework.

► Li diffusion pathways in Li4Ti5O12 and Li7Ti5O12 are obtained from ab initio calculations.
► Cooperative Li migration in Li7+δTi5O12 with very low energy barrier is proposed.
► Li diffusion is faster in lithiated state than in delithiated state is confirmed theoretically.