Local Structural Investigations, Defect Formation, and Ionic Conductivity of the Lithium Ionic Conductor Li4P2S6

Glassy, glass ceramic, and crystalline lithium thiophosphates have attracted interest in their use as solid electrolytes in all-solid-state batteries. Despite similar structural motifs, including PS43-, P2S64-, and P2S74- polyhedra, these materials exhibit a wide range of possible compositions, crystal structures, and ionic conductivities. Here, we present a combined approach of Bragg diffraction, pair distribution function analysis, Raman spectroscopy, and P-31 magic angle spinning nuclear magnetic resonance spectroscopy to study the underlying crystal structure of Li4P2S6. In this work, we show that the material crystallizes in a planar structural arrangement as a glass ceramic composite, explaining the observed relatively low ionic conductivity, depending on the fraction of glass content. Calculations based on density functional theory provide an understanding of occurring diffusion pathways and ionic conductivity of this Li+ ionic conductor.