Tetrahedral Tilting and Lithium-Ion Transport in Halide Argyrodites Prepared by Rapid, Microwave-Assisted Synthesis

Abstract

This study demonstrates a rapid, dry, microwave-assisted (MW) synthesis method that enables preparation of halide argyrodites ${\mathrm{Li}}_6{\mathrm{PS}}_{5}X$ ($X=$ ${\mathrm{Cl}}^{-}$, ${\mathrm{Br}}^{-}$, ${\mathrm{I}}^{-}$) in less than 20 min. The structures and ion transport properties of the resulting materials are compared with those synthesized by conventional solid-state synthesis methods. The microwave-assisted method leads to increased $4a/4d$ site disorder and elevated Arrhenius prefactors (${\sigma }_0$), which lead to an order of magnitude improvement in the 30 ${}^{\circ }\mathrm{C}$ ionic conductivity of MW-${\mathrm{Li}}_6{\mathrm{PS}}_5\mathrm{I}$. X-ray pair distribution function analysis (XPDF) reveals significant rotational disorder of the ${{\mathrm{PS}}_4}^{3-}$ units, which is impacted by the synthesis method, choice of halide, and presence of ${\mathrm{S}}^{2-}$/$X^{-}$ site disorder. These rotational displacements are strongly correlated with ion transport, specifically ${\sigma }_0$ and entropy of migration ($\mathrm{\Delta }{S}_m$). Overall, this study demonstrates a rapid synthesis route for preparing high-quality halide argyrodite solid-state electrolytes in less than 20 min, and further unravels atomistic insights into the interplay of structural disorder, rotational dynamics, and ion transport mechanisms.