We propose to carry out muon-spin relaxation to examine Li+ diffusion in AC-treated Li4Ti5O12 which contains a small amount of rutile TiO2. Measurements will be carried out over a temperature range from 20 K to 500 K, in zero field (ZF) and with a longitudinal field (LF) of 0.5 mT and 1 mT. This temperature range is chosen to observe the thermally activated region for Li+ diffusion (above 200 K) and to compare the increase of the exponential relaxation rate of the KT signal (lambda) below 100 K which is due to the localized moments. We plan to complement these measurements with neutron powder diffraction and pair distribution function studies to get a fuller understanding of the relationship between crystal structure, defect chemistry, and diffusion behaviour. All measurements will be done on three samples, Li4Ti5O12 treated with 0, 6, and 10 wt% of AC.