Li⁺-Ion Dynamics in β-Li₃PS₄ Observed by NMR: Local Hopping and Long-Range Transport

Abstract

A detailed structural characterization is performed on β-Li3PS4 using 6Li and 31P magic-angle spinning NMR spectroscopy in combination with X-ray and neutron diffraction. High-temperature synchrotron X-ray diffraction was used to determine the phase stability and observe phase transitions. In addition, we investigated the Li+-ion dynamics by temperature-dependent 7Li NMR lineshape analysis, 7Li NMR relaxometry, and 7Li pulsed field-gradient (PFG) NMR measurements. A good agreement is obtained between the local hopping observed by T1 relaxation time measurements and the long-range transport investigated by PFG NMR with a Li+ diffusion coefficient of 9 × 10–14 m2/s at 298 K and an activation energy of 0.24 eV. From this, a Li+ conductivity of 1.0 × 10–4 S/cm is estimated, which corresponds well with impedance measurements on β-Li3PS4 pellets.