Combined 6,7Li NMR and Molecular Dynamics Study of Li Diffusion in Li2TiO3

Understanding lithium diffusion properties in electrode materials is important for designing rechargeable lithium-ion batteries with improved performance. In this work, the lithium dynamics in layered Li2TiO3 were characterized using a combination of Li-6,Li-7 nuclear magnetic resonance (NMR) over a wide temperature range (150-500 K) and molecular dynamics (MD) simulations. The Li-7 static NMR and stimulated echo experiments show slow and partial lithium diffusion in Li2TiO3. The high-field (21.1 T) Li-6 magic-angle spinning NMR shows a new tetrahedral lithium site along with the three crystallographic octahedral sites in Li2TiO3 sample. MD simulations predict that lithium can occupy a tetrahedral site if two or more vacancies exist in the vicinity, which may result, for example, from the presence of a Ti defect in the LiTi2 layer. Li-6 two-dimensional (2D) exchange NMR experiments show evidence of lithium diffusion between the pure Li and LiTi2 layers along the c axis. Although the 2D exchange NMR data are not sensitive to lithium diffusion in the ab plane, MD simulations show that lithium diffusion in the pure Li layer is equally probable. Combining these results, a detailed picture of the lithium diffusion pathways in Li2TiO3 is presented.