Structure and Ionic Conductivity of the Li-disordered Bismuth ortho-Thiophosphate Li60– 3xBi16+x(PS4)36 with x = 4.2 to 6.7

The structure of the first lithium containing bismuth ortho-thiophosphate was solved using a combination of powder X-ray, neutron, and electron diffraction. Li60–3xBi16+x(PS4)36 with x in the range of 4.2 to 6.7 possesses a complex monoclinic structure (space group C2/c, no. 15) and a large unit cell with lattice parameters a = 15.487Å, b = 10.323Å, c = 33.767Å, and = 85.394° for Li44.4Bi21.2(PS4)36. The disordered distribution of lithium ions within the interstices of the dense host-structure as well as the Li ion dynamics and diffusion pathways have been investigated by X-ray and neutron PDF analysis, solid-state NMR spectroscopy, PFG-NMR diffusion measurements, and BVS calculations. The total lithium ion conductivities range from 2.6 × 10−7 to 2.8 × 10−6 S cm−1 at 20 °C with activation energies between 0.29 and 0.32 eV, depending on the bismuth content. Despite the highly disordered nature of lithium ions in Li60–3xBi16+x(PS4)36, the underlying dense host-framework appears to limit the dimensionality of the lithium diffusion pathways and emphasizes once more the necessity of a close inspection of structure-property relationships in solid electrolytes.