On the Discrepancy between Local and Average Structure in the Fast Na+ Ionic Conductor Na2.9Sb0.9W0.1S4

Oliver Maus; Matthias T Agne; Till Fuchs; Paul S Till; Björn Wankmiller; Josef Maximilian Gerdes; Rituraj Sharma; Michael Heere; Niina Jalarvo; Omer Yaffe; Michael Ryan Hansen; Wolfgang G Zeier

doi:10.1021/jacs.2c11803

On the Discrepancy between Local and Average Structure in the Fast Na⁺ Ionic Conductor Na_2.9Sb_0.9W_0.1S₄

J Am Chem Soc. 2023 Apr 5;145(13):7147-7158. doi: 10.1021/jacs.2c11803. Epub 2023 Mar 22.

Authors

Oliver Maus^{1

2}, Matthias T Agne¹, Till Fuchs³, Paul S Till¹, Björn Wankmiller^{2

4}, Josef Maximilian Gerdes⁴, Rituraj Sharma⁵, Michael Heere⁶, Niina Jalarvo⁷, Omer Yaffe⁵, Michael Ryan Hansen^{2

4}, Wolfgang G Zeier^{1

2

8}

Affiliations

¹ Institute of Inorganic and Analytical Chemistry, University of Münster, D-48149 Münster, Germany.
² International Graduate School for Battery Chemistry, Characterization, Analysis, Recycling and Application (BACCARA), University of Münster, D-48149 Münster, Germany.
³ Institute of Physical Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 17, D-35392 Giessen, Germany.
⁴ Institute of Physical Chemistry, University of Münster, D-48149 Münster, Germany.
⁵ Department of Chemical and Biological Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
⁶ Institute of Internal Combustion Engines, Technische Universität Braunschweig, Hermann-Blenk-Straße 42, D-38108 Braunschweig, Germany.
⁷ Neutron Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States.
⁸ Institut für Energie- und Klimaforschung (IEK), IEK-12: Helmholtz-Institut Münster, Forschungszentrum Jülich, D-48149 Münster, Germany.

PMID: 36946557
DOI: 10.1021/jacs.2c11803

Abstract

Aliovalent substitution is a common strategy to improve the ionic conductivity of solid electrolytes for solid-state batteries. The substitution of SbS₄^3- by WS₄^2- in Na_2.9Sb_0.9W_0.1S₄ leads to a very high ionic conductivity of 41 mS cm^-1 at room temperature. While pristine Na₃SbS₄ crystallizes in a tetragonal structure, the substituted Na_2.9Sb_0.9W_0.1S₄ crystallizes in a cubic phase at room temperature based on its X-ray diffractogram. Here, we show by performing pair distribution function analyses and static single-pulse ¹²¹Sb NMR experiments that the short-range order of Na_2.9Sb_0.9W_0.1S₄ remains tetragonal despite the change in the Bragg diffraction pattern. Temperature-dependent Raman spectroscopy revealed that changed lattice dynamics due to the increased disorder in the Na⁺ substructure leads to dynamic sampling causing the discrepancy in local and average structure. While showing no differences in the local structure, compared to pristine Na₃SbS₄, quasi-elastic neutron scattering and solid-state ²³Na nuclear magnetic resonance measurements revealed drastically improved Na⁺ diffusivity and decreased activation energies for Na_2.9Sb_0.9W_0.1S₄. The obtained diffusion coefficients are in very good agreement with theoretical values and long-range transport measured by impedance spectroscopy. This work demonstrates the importance of studying the local structure of ionic conductors to fully understand their transport mechanisms, a prerequisite for the development of faster ionic conductors.