Tetragonal Li10GeP2S12 and Li7GePS8 – exploring the Li ion dynamics in LGPS Li electrolytes

Abstract

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 E_A ≈ 0.22 eV.