Li-ion diffusion in Li_4Ti_5O_(12) and LiTi_2O_4 battery materials detected by muon spin spectroscopy

摘要

Lithium diffusion in spinel Li_4Ti_5O_(12) and LiTi_2O_4 compounds for future battery applications has been studied with muon spin relaxation (μ~+SR). Measurements were performed on both thin-film and powder samples in the temperature range between 25 and 500 K. For Li_4Ti_5O_(12) and above about ～200 K, the field distribution width (Δ) is found to decrease gradually, while the field fluctuation rate (v) increases exponentially with temperature. For LiTi_2O_4, on the contrary, the Δ(T) curve shows a steplike decrease at ～350 K, around which the v(T) curve exhibits a local maximum. These behaviors suggest that Li~+ starts to diffuse above around 200 K for both spinels. Assuming a jump diffusion of Li~+ at the tetrahedral 8a site to the vacant octahedral 16c site, diffusion coefficients of Li~+ at 300 K in the film samples are estimated as (3.2 ± 0.8) × 10~(-11) cm~2/s for Li_4Ti_5O_(12) and (3.6 ± 1.1) × 10~(-11) cm~2/s for LiTi_2O_4. Further, some small differences are found in both thermal activation energies and Li-ion diffusion coefficients between the powder and thin-film samples.