Non-uniform lithium-ion migration on micrometre scale for garnet- and NASICON-type solid electrolytes studied by Li-7 PGSE-NMR diffusion spectroscopy

摘要

The migration behaviours of Li+ in three garnet- and one NASICON-type solid oxide electrolytes were studied on the micrometre scale by pulsed-gradient spin-echo (PGSE) Li-7 NMR diffusion spectroscopy to clarify common and specific characteristics of each electrolyte. In these solid electrolytes, clear evidences of grain boundary effects in the diffusion of Li+ were not observed. The Li+ diffusion constants were dependent on parameters such as observation time () and pulsed field gradient (PFG) strength (g) for all the studied inorganic solid electrolytes. For low values, Li+ ions underwent collisions and diffractions with diffraction distance R-diffraction [m]. The apparent Li+ diffusion constants (D-apparent [m(2) s(-1)]) exhibited distributions in a wide range. In this paper, we introduced the apparent diffusion radius, r(radius) [m], and compared it with R-diffraction and mean square displacement (MSD) [m]; the lengths of these distances were of the micrometre order (10(-6) m). The relations between the values of r(radius), R-diffraction and MSD suggested that the migration behaviours of Li+ on the micrometre scale were complicated. Using high and high g values, we obtained an equilibrated value of D-Li. The temperature dependences of the number of carrier ions were estimated from the D-Li values and ionic conductivities in the four solid oxide electrolytes. For simple comparison and reference, the data of D-Li and ionic conductivity of LiPF6 in 1 M solution of propylene carbonate were added.