NMR relaxometry as a versatile tool to study Li ion dynamics in potential battery materials

Abstract

NMR spin relaxometry is known to be a powerful tool for the investigation of Li+ dynamics in (non-paramagnetic) crystalline and amorphous solids. As long as significant structural changes are absent in a relatively wide temperature range, with NMR spin–lattice (as well as spin–spin) relaxation measurements information on Li self-diffusion parameters such as jump rates and activation energies are accessible. Diffusion-induced NMR relaxation rates are governed by a motional correlation function describing the ion dynamics present. Besides the mean correlation rate of the dynamic process, the motional correlation function (i) reflects deviations from random motion (so-called correlation effects) and (ii) gives insights into the dimensionality of the hopping process. In favorable cases, i.e., when temperature- and frequency-dependent NMR relaxation rates are available over a large dynamic range, NMR spin relaxometry is able to provide a comprehensive picture of the relevant Li dynamic processes. In the present contribution, we exemplarily present two recent variable-temperature 7Li NMR spin–lattice relaxation studies focussing on Li+ dynamics in crystalline ion conductors which are of relevance for battery applications, viz. Li7 La3Zr2O12 and Li12Si7.