Understanding the Structural Disorder Related to Ionic Conductivity Enhancement in Anti-Perovskite Ion Conductors

Abstract

Amongst known families of solid electrolytes of potential interest for solid-state batteries, the anti-perovskites (APs) have recently attracted great attention for the high ionic conductivities observed in certain compositions, and, like perovskites, the compositional flexibility provided by the possibility for ion substitution onto multiple lattice sites. [1] For example, variations in the extent of disorder, that are accompanied by changes in the distribution of lithium migration energies.[2] In surveying transport in this family of ion conductors, we observed a trend wherein numerous compositions show upwards curvature on an Arrhenius plot, indicating a non-constant activation energy. This is unusual as most solids exhibiting non-Arrhenius behavior exhibit a negative deviation. The structure origins of such deviations are not well understood.Among the AP-structure SSEs, Li2OHCl and its variants are particularly interesting because of their relatively high conductivities at room temperature. Unlike Li3OCl, where six Li atoms occupy the vertices of the Li6O octahedral, in Li2OHX the vertices are occupied by four lithium atoms with two other sites vacant. H in Li2OHX sits at the oxygen atom in the center of the octahedron. The Li defects and the movement of H around the oxygen atom give rise to a change in the ionic conduction pathway as temperature varies (Figure 1). Figure 1. The ionic conduction pathway of Li and H in Li2OHCl at different temperatureHerein, we explain the non-Arrhenius conduction behavior in relation to defect and H movement, and our attempts to understand the structural origin(s) of this behavior through temperature-dependent X-ray and neutron scattering, calorimetry, and other methods. Implications for the design of solid electrolytes for solid state batteries will be discussed.This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Reference s : [1] Zhao, Y.; Daemen, L. L. Superionic conductivity in Lithium-rich anti-perovskites. J. Am. Chem. Soc. 2012, 134, 15042−15047.[2] Kwangnam Kim and Donald J. Siegel. "Correlating lattice distortions, ion migration barriers, and stability in solid electrolytes." Journal of Materials Chemistry A 7, no. 7 (2019): 3216-3227. Figure 1