Working Paper
Authors
- Tanja Scholz Max Planck Institute for Solid State Research ,
- Christian Schneider
Max Planck Institute for Solid State Research ,
- Maxwell W. Terban Max Planck Institute for Solid State Research ,
- Zeyu Deng National University of Singapore ,
- Roland Eger Max Planck Institute for Solid State Research ,
- Martin Etter Deutsches Elektronen-Synchrotron DESY ,
- Robert E. Dinnebier Max Planck Institute for Solid State Research ,
- Pieremanuele Canepa National University of Singapore ,
- Bettina V. Lotsch Max Planck Institute for Solid State Research & Ludwig-Maximilians-Universität München
Abstract
Sodium thiophophates are promising materials for large-scale energy storage applications benefiting from high ionic conductivities and the-political abundance of the elements. A representative of this class is Na4P2S6, which currently shows two known polymorphs–α and β. This work describes a third polymorph of Na4P2S6, γ, that forms above 580◦C, exhibits fast ion conduction with low activation energy, and is mechanically soft. Based on high-temperature diffraction, pair distribution function analysis, thermal analysis, impedance spectroscopy, and ab initio molecular dynamic calculations, γ-Na4P2S6 is identified to be a plastic crystal, characterized by dynamic orientational disorder of the P2S64– anions on a translationally fixed body centered cubic lattice. The prospect of stabilizing plastic crystals at operating temperatures of solid-state batteries and benefiting from their high ionic conductivities as well as mechanical properties could have a strong impact in the field of solid-state battery chemistry.
Content

Supplementary material

Supporting Information
Additional details on diffraction experiments, Raman spectroscopy, pair distribution function analysis, impedance spectroscopy, photographs of impedance samples, and AIMD simulation results.