Effect of the Anion Disorder on Lithium Conductivity of Argyrodite Li_6−xPS_5−xClBr_x Solid Electrolytes

Li-argyrodite Li₆PS₅Cl is considered a promising solid electrolyte for all-solid-state batteries due to the low cost of raw materials, mechanical flexibility, and high ionic conductivity. Halide-rich argyrodites obtained by replacing S in Li₆PS₅Cl with Br have been reported to exhibit significantly improved conductivity compared to Li₆PS₅Cl. In this study, using density functional theory calculations and <i>ab</i> initio molecular dynamics simulations, we systematically investigated more than 300 Li₆PS₅Cl structures and 500 Br-substituted Li_5.75PS_4.75ClBr_0.25 structures and found that anion disorder greatly enhances the stability and conductivity of Li₆_−<i>x</i>PS₅_−<i>x</i>ClBr<i>_x</i>. The most stable Li₆PS₅Cl and Li_5.75PS_4.75ClBr_0.25 structures have the highest level of anion disorder, with S, Cl, and Br anions evenly occupying the Wyckoff 4a and 4d sites. The anion disorder significantly increases Li conductivity in both Li₆PS₅Cl and Li_5.75PS_4.75ClBr_0.25 by activating all three types of Li jumps, i.e., doublet, intracage, and intercage, in Li-cage structures of argyrodite. The overlap of Li-cages in Li_5.75PS_4.75ClBr_0.25 creates a continuous diffusion path for Li ions, leading to about two times higher conductivity of Li_5.75PS_4.75ClBr_0.25 than Li₆PS₅Cl.<br/> <br/>[1] <i>J. Mater. Chem. A</i>, 2024, 12, 993