Atomistic insight into enhanced ionic conductivity in mixed halide sodium ion conductor Na3YCl<i>x</i>Br6−<i>x</i>

Abstract

Exploring solid-state electrolytes with high ionic conductivity and low electronic conductivity is of great importance in realizing all-solid-state batteries. Here, we provide an atomistic insight into the enhancement of Na ionic conductivity in mixed halides Na3YClxBr6−x (NYCBx) using ab initio calculations and machine-learning interatomic potential-based molecular dynamics simulations. Our calculations reveal that the electronic conductivity decreases as the Cl content increases, while the Na ionic conductivity reaches the highest value in NYCB3 with a middle content. Through analysis of phonon density of states, halogen mixing is found to cause a large distortion of metal–halogen polyhedra and superposition of cation and anion sublattice vibrations, leading to high Na ionic mobility.