Synthesis of the lithium titanate spinel using an alkoxide-free sol-gel method was described. This yielded very pure crystalline samples at 850C, and 6Li magic angle spinning nuclear magnetic measurements were carried out in a high magnetic field (21.1T) over a temperature range of 295 to 680K. The temperature dependence of the chemical shifts and integral intensities of the three 6Li resonances demonstrated the migration of lithium ions from the tetrahedral 8a to the octahedral 16c sites and progressive phase transition from a spinel to a defective NaCl-type structure. This defective structure had an increased number of vacancies at the 8a site, which facilitated lithium diffusion through 16c → 8a → 16c pathways. Molecular dynamics simulations of spinel Li4+xTi5O12, with 0 ≤ x ≤ 3, were also performed using a potential shell model at 300 to 700K. The simulations supported the conclusions drawn from the nuclear magnetic measurements and showed a significant timescale separation between lithium diffusion through 8a and 16c sites and that out of the 16d sites.

Lithium Diffusion in Li4Ti5O12 at High Temperatures. Vijayakumar, M., Kerisit, S., Rosso, K.M., Burton, S.D., Sears, J.A., Yang, Z., Graff, G., Liu, J., Hu, J.: Journal of Power Sources, 2011, 196[4], 2211-20