Describing Ionic Conducting Sodium Halides Using the Perovskite Toolbox

Na-ion solid electrolytes are currently being investigated as promising candidates for solid state batteries. Due to the scarcity of the Li metal in the current Li-ion technology and the safety issues of liquid batteries, the scientific interest has been shifted to alternative ways with the desire to meet the demands for high energy density capabilities in solid state batteries.^1,2 Chalcogenides and oxides materials have been thoroughly studied. Although both families show a reasonable transport performance, they lack electrochemical stability, mechanical stability and/or easy processing.

In this context, halides stand out as promising candidates since they combine large stability windows with good mechanical deformability. Recently, Na-containing ternary chlorides with nominal composition Na_xMCl₆ (M³⁺ = In³⁺, Y³⁺, Zr⁴⁺, Nb⁵⁺ or Ta⁵⁺) have been experimentally found as promising ionic conducting electrolytes.³ The fact that some of them crystallize in a perovskite structure make those particular systems an unparalleled framework to search for novel ionic conductors and to get deeper insights in the structure-transport properties relationships.

Here we have performed different cationic and anionic substitutions on the NaTaCl₆ perovskite-related material. The relationship between the crystal structure and ionic transport properties in those materials was investigated by means of X-ray diffraction, pair distribution function analyses, nuclear magnetic resonance, quasi-elastic neutron scattering and impedance spectroscopy. By fully analysing those materials using the perovskite toolbox, we hope to offer a reliable guidance to improve the structure-property relationships in the current halide electrolyte materials.

References:

1, J. Janek, W.G. Zeier Nat. Energy 2016, 1, 16141.
2, B. L. Ellis, L.F. Nazar Current Opinion in Solid State and Materials Science 2012, 16, 168-177.
3. T. Zhao, A. N. Sobolev, R. Schlem, B. Helm, M. A. Kraft, W. G. Zeier, Applied Energy Materials 2023, 6, 4334-4341.