Insights into Lithium Diffusion in Crystalline and Amorphous Solid Electrolytes with Machine Learning Interatomic Potentials

Amorphization is a widely used approach to tune the ionic conductivity in solid electrolytes, but its effect in different anion chemistries remains poorly understood. In this work, we employ molecular dynamics (MD) simulations with machine learning interatomic potentials (MLIPs) to quantify the effects of amorphization on Li-ion transport in lithium solid electrolytes from three anion chemistries: Li3YCl6 (LYC), Li0.33La0.56TiO3 (LLTO) and Li7P3S11 (LPS). With amorphization, it is observed that the ionic conductivity increases for LYC, decreases for LLTO and remains relatively unchanged for LPS, in agreement with previous experiments. Coordination analysis at 300K reveals that these ionic conductivity changes can be correlated with amorphization-induced changes in Li-anion coordination environments; decreases in coordination increase ionic conductivity and vice versa. These different responses show that the effect of amorphization on Li-ion diffusion behavior is not universal and is governed by specific anion coordination motifs.