Lithium ion micrometer diffusion in a garnet-type cubic LiLaZrO (LLZO) studied using Li NMR spectroscopy.

Mobile lithium ions in a cubic garnet LiLaZrO (Al-stabilized) were studied using Li NMR spectroscopy for membrane and powder samples, the latter of which was ground from the membrane. Lithium diffusion in a micrometer space was measured using the pulsed-gradient spin-echo Li NMR method between 70 and 130 °C. When the observation time (Δ) was shorter than 20 ms, the echo attenuation showed diffusive diffraction patterns, indicating that the Li diffusing space is not free but restricted. For longer Δ, the values of apparent diffusion constant (D) became gradually smaller to approach an equilibrated value (close to a tracer diffusion constant). In addition, the D depends on the pulse field gradient strength (g) and became smaller as g became larger. These experimental results suggest that the lithium ions diffuse through Li pathways surrounded by stationary anions and lithium ions, and are affected by collisions and diffractions. One-dimensional profiles of the membrane sample of thickness 0.5 mm were observed from 65 to 110 °C and the area intensity, as well as the lithium occurrence near the surface, increased with the increase in temperature. The temperature-dependent area intensity showed a correspondence to the number of Li carrier ions estimated from the ionic conductivity and the equilibrated diffusion constant through the Nernst-Einstein relationship.