Li 7 PS 6 and Li 6 PS 5 X ( X : Cl, Br, I): Possible Three‐dimensional Diffusion Pathways for Lithium Ions and Temperature Dependence of the Ionic Conductivity by Impedance Measurements

Possible three‐dimensional diffusion pathways of lithium ions in crystalline lithium argyrodites are discussed based on earlier studies of local dynamics and site preferences. The specific Li‐ionic conductivities of the lithium argyrodites Li 7 PS 6 and Li 6 PS 5 X ( X : Cl, Br, I) and their temperature dependences are measured by impedance spectroscopy using different electron‐blocking and ion‐blocking electrode systems. Measurements were carried out between 160 K and 550 K depending on the respective sample. Bulk and grain boundary contributions and the influence of sample preparation are discussed. Typical values for the ionic conductivities at room temperature are in the range 10 –7 to 10 –5 S ·  cm –1 and at 500 K between 10 –6 and 10 –3 S ·  cm –1 . Thermal activation energies are in the range 0.16 to 0.56 eV. The electronic conductivity at room temperature was measured by polarization measurements for the samples Li 6 PS 5 X ( X : Cl, Br) and was shown to be in the order of magnitude of 10 –8 S ·  cm –1 . Chemical diffusion coefficients of lithium were calculated based on the polarization measurements. For Li 6 PS 5 Br a high value of 3.5 × 10 –6  cm 2 · s –1 was found.