From Ultraslow to Fast Lithium Diffusion in the 2D Ion Conductor Li_(0.7)TiS_2 Probed Directly by Stimulated-Echo NMR and Nuclear Magnetic Relaxation

摘要

~7Li stimulated-echo NMR and classical relaxation NMR techniques are jointly used for the first time for a comprehensive investigation of Li diffusion in layer-structured Li_(0.7)TiS_2. One single 2D Li diffusion process was probed over a dynamic range of almost 10 orders of magnitude. So far, this is the largest dynamic range being measured by ~7Li NMR spectroscopy directly, i.e., without the help of a specific theoretical model. The jump rates obey a strict Arrhenius law, determined by an activation energy of 0.41(1) eV and a preexponential factor of 6.3(1) X 10~(12) s~(-1), and range between 1 X 10~(-1) s~(-1) and 7.8 X 10~8 s~(-1) (148-510 K). Ultraslow Li jumps in the kHz to sub-Hz range were measured directly by recording ~7Li spin-alignment correlation functions. The temperature and, in particular, the frequency dependence of the relaxation rates fully agree with results expected for 2D diffusion.