Synthesis, Structural Characterization, and Lithium Ion Conductivity of the Lithium Thiophosphate Li2P2S6

Inspired by the ongoing search for new superionic lithium thiophosphates for use in solid-state batteries, we present the synthesis and structural characterization of Li2P2S6, a novel crystalline lithium thiophosphate. Whereas M2P2S6 with the different alkaline elements (M = Na, K, Rb, Cs) is known, the lithium counterpart has not been reported yet. Herein, we present a combination of synchrotron pair distribution function analysis and neutron powder diffraction to elucidate the crystal structure and possible Li+ diffusion pathways of Li2P2S6. Additionally, impedance spectroscopy is used to evaluate its ionic conductivity. We show that Li2P2S6 possesses P2S62- polyhedral units with edge-sharing PS4 tetrahedra and only one-dimensional diffusion pathways with localized Li-Li pairs, leading to a low ionic conductivity for lithium.