Assessing Correlations between Phonon Features and Migration Barriers in Multivalent Solid Electrolytes

Solid ion conductors with high ionic conductivity can enable the development of solid-state batteries with improved safety and performance. Most materials exhibit insufficient conductivity for commercial applications, particularly for multivalent ions. High-throughput computational approaches, which involve screening large databases of compounds, can accelerate the discovery of new materials with sufficient conductivity. Directly calculating ionic conductivity from first principles is expensive and difficult to automate, which renders such calculations incompatible with screening approaches. Previously, others have proposed the phonon band center (mean phonon frequency) as a metric that is easier to calculate and measure, and they have demonstrated that it is correlated with the energetic barrier for ion migration in lithium and sodium conductors. I will discuss our efforts to extend this approach to investigate magnesium, calcium, and zinc conductors using first-principles calculations of phonon features. In addition to frequencies, we consider the directions of phonon modes as predictors for migration barriers. We compare our results with previous trends for monovalent conductors.