Observation of Li+ jumps in solid inorganic electrolytes over a broad dynamical range: A case study of the lithium phosphidosilicates Li8SiP4 and Li14SiP6

Abstract

⁷Li NMR spectroscopy is known to be very sensitive to translational motion in solids and therefore highly suited for investigating temperature-dependent Li⁺ dynamics. A number of different NMR methods are available for choosing the dynamical range of the observed Li⁺ jump frequencies present in inorganic solid-state electrolytes. This includes ⁷Li spin-alignment echo NMR spectroscopy, static ⁷Li lineshape analysis, and ⁷Li spin-lattice relaxometry that can be used to detect Li⁺ jumps in the Hz, kHz, and MHz range, respectively. We introduce and discuss these NMR techniques with respect to their theoretical description and practical application to investigate the Li⁺ dynamics at different time scales for the two solid-state electrolytes Li₈SiP₄ and Li₁₄SiP₆. The data evaluation for all methods is discussed in detail, focusing on the determination of Li⁺ jump frequencies and activation energies for the investigated self-diffusion processes in a given structure.