Li Conductivity of Nanocrystalline Li4Ti5O12Prepared by a Sol-Gel Method and High-Energy Ball Milling

摘要

Spinel-type structured Li_(4+x)Ti_5O_(12)(0 ≤ x 3 ) is actually one of the most promisinganode materials for Li ion batteries. In its nanostructured form it is already used in some commerci-ally available Li ion batteries. As was recently shown by our group (Wilkening et al., Phys. Chem.Chem. Phys. 9 (2007) 1239), Li diffusivity in microcrystalline Li_(4+x)Ti_5O_(12)with x = 0 is rather slow.In the present contribution the Li conductivity in nanocrystalline samples of the electronic insula-tor Li_4Ti_5O_(12)prepared by different routes is investigated using impedance spectroscopy. The meancrystallite size of the samples is about 20 nm. The ionic conductivity of nanocrystalline Li_4Ti_5O_(12)obtained by mechanical treatment is higher by about two orders of magnitude compared to that foundfor a material which was prepared following a sol-gel method. The latter resembles the behaviour ofthe microcrystalline sample with an average particle size in the range rather than that of a nano-crystalline ball milled one with a mean crystallite size of about than 20 nm. The larger conductivityof the ball milled sample is ascribed to a much higher defect density generated when the particle sizeis reduced mechanically.