Tetragonal Li10GeP2S12 (LGPS) is the best solid Li electrolyte reported in the literature. In this study we present the first in-depth study on the structure and Li ion dynamics of this structure type. We prepared two different tetragonal LGPS samples, Li10GeP2S12 and the new compound Li7GePS8. The Li ion dynamics and the structure of these materials were characterized using a multitude of complementary techniques, including impedance spectroscopy, 7Li PFG NMR, 7Li NMR relaxometry, X-ray diffraction, electron diffraction, and 31P MAS NMR. The exceptionally high ionic conductivity of tetragonal LGPS of ∼10−2 S cm−1 is traced back to nearly isotropic Li hopping processes in the bulk lattice of LGPS with EA ≈ 0.22 eV.
