Li Conductivity of Nanocrystalline Li_4Ti_5O_(12) Prepared 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 promising anode materials for Li ion batteries. In its nanostructured form it is already used in some commercially 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 insulator Li_4Ti_5O_(12) prepared by different routes is investigated using impedance spectroscopy. The mean crystallite 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 found for a material which was prepared following a sol-gel method. The latter resembles the behaviour of the microcrystalline sample with an average particle size in the μm range rather than that of a nanocrystalline ball milled one with a mean crystallite size of about than 20 nm. The larger conductivity of the ball milled sample is ascribed to a much higher defect density generated when the particle size is reduced mechanically.