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A New Phase of the Na+ Ion Conductor Na3PS4

preprint
submitted on 17.04.2019 and posted on 18.04.2019 by Theodosios Famprikis, James Dawson, François Fauth, Emmanuelle Suard, Benoit Fleutot, Matthieu Courty, Jean-Nöel Chotard, Saiful Islam, Christian Masquelier

Solid electrolytes are crucial for next‑generation solid‑state batteries and Na3PS4 is one of the most promising Na+ conductors for such applications. At present, two phases of Na3PS4 have been identified and it had been thought to melt above 500 °C. In contrast, we show that it remains solid above this temperature and transforms into a third polymorph, γ, exhibiting superionic behavior. We propose an orthorhombic crystal structure for γ‑Na3PS4 based on scattering density analysis of diffraction data and density functional theory calculations. We show that the Na+ superionic behavior is associated with rotational motion of the thiophosphate polyanions pointing to a rotor phase, based on ab initio molecular dynamics simulations and supported by high‑temperature synchrotron and neutron diffraction, thermal analysis and impedance spectroscopy. These findings are of importance for the development of new polyanion‑based solid electrolytes.

History

Email Address of Submitting Author

famprikis@gmail.com

Institution

Laboratoire de Réactivité et Chimie des Solides - CNRS

Country

France

ORCID For Submitting Author

0000-0002-7946-1445

Declaration of Conflict of Interest

no conflict of interest

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