Non-blocking grain boundaries for Li-ion transport in Li3YCl6 halide electrolyte

Abstract

Halide solid electrolytes, exemplified by Li3YCl6 (LYC), offer moderate ionic conductivity (∼1 mS/cm), high oxidative stability (>4 V), and good mechanical deformability, making them promising candidates for solid-state lithium batteries. However, the room-temperature ionic conductivity of single-crystal LYC is nearly one order of magnitude higher than that of experimental polycrystalline samples. Grain boundaries (GBs) are considered the primary cause of this discrepancy. Although GBs critically influence Li-ion transport in most solid electrolytes, the impact in LYC remains poorly understood. Herein, we quantify the contribution of GBs to Li-ion transport in LYC utilizing machine learning driven deep potential molecular dynamics. For all GBs considered, the results reveal a strong inherent tendency toward polycrystallinity in LYC due to low GB formation energies. Although the ionic conductivity of all LYC GBs is lower than that of the bulk, among them, the highest activation energy and the lowest ionic conductivity are 0.246 eV and 8.6 mS/cm, respectively. Moreover, the {303¯2}⟨101¯3¯⟩ GB with the lowest GB energy (0.176 J/m2) exhibits the highest ionic conductivity of 13.9 mS/cm. The simulations demonstrate that GBs hinder overall Li-ion transport compared to the bulk, though GBs do not act as the dominant barrier to Li-ion transport in LYC. This work provides insights for the design of halide solid electrolytes.