Lithium diffusion in Li4Ti5O12 at high temperatures

Synthesis of the spinel lithium titanate Li4Ti5O12 by an alkoxide-free sol-gel method is described This method yields highly pure and crystalline LiO4Ti5O12 samples at relatively low temperature (850 Ci and via short thermal treatment (2 h) Li-6 magic angle spinning nuclear magnetic resonance (MAS NMR) measurements on these samples were carried out at high magnetic field (21 1T) and over a wide temperature range (295-680 K) The temperature dependence of the chemical shifts and integral inten ities of the three Li-6 resonances demonstrates the migration of lithium ions from the tetrahedral 8a to the octahedral 16c sites and the progressive phase transition from a spinel to a defective NaCl-type structure This defective structure has an increased number of vac moles at the 8a site which facilitate lithium diffusion through 16c -> 8a -> 16c pathways hence providing an explanation for the reported increase in conductivity at high temperatures Molecular dynamics simulations of the spine, oxides Li4+xTi5O12 with 0 <= x <= 3 were also performed with a potential shell model in the temperature range 300-700K The simulations support the conclusions drawn from the NMR measurements and show a significant timescale separation between lithium diffusion through 8a and 16c sites and that out of the 16d sites (C) 2010 Elsevier B V All rights reserved