Detecting Correlated Lithium Ion Hopping in Li3YCl6 (LYC) via Cross-Correlation Analysis

Li3YCl6 (LYC) is a fast ion-conducting halide that shows promise for use in all-solid-state batteries (ASSBs), which offer significant advantages over traditional lithium-ion batteries, including enhanced safety, energy density, and environmental sustainability. These halide materials exhibit a close-packed stacking that differs from the body-centered cubic anion framework typically found in many fast lithium-conducting materials. Therefore, identifying the mechanisms of ion conduction in these compounds is important to establish design rules for fast ion conductors. In this study, we use classical molecular dynamics (MD) simulations, using machine-learned interatomic potentials, to simulate lithium-ion diffusion behavior, establish conduction pathways, and investigate the potential for correlated ion movement. We find significant, anisotropic diffusion, where lithium ions move more efficiently with lower activation energy along the c-axis perpendicular to the close packed planes. To explore the possibility of concerted ion migration beyond the typical Haven ratio, we implement a numerical framework to detect ionic jumps from long time MD trajectories and carry out a time-correlation analysis between jumps. While the correlated hopping behavior may be more complicated as a result of cation disordering, the overall behavior for prototype structures suggests largely independent ion movement with minimal correlated hopping occurring in more practical temperature regimes.