On the Lithium Distribution in Halide Superionic Argyrodites by Halide Incorporation in Li_7–xPS_6–xCl_x

Superionic lithium argyrodites are attractive as solid electrolytes for all-solid-state batteries. These materials of composition Li₆PS₅X (X = Cl, Br, and I) exhibit structural disorder between the X^–/S^2– positions, with higher disorder realizing better Li⁺ transport. Further replacement of the sulfide by chloride anions (for the series Li_7–xPS_6–xCl_x) has been shown to increase the ionic conductivity. However, the underlying changes to the lithium substructure are still relatively unknown. Here, we explore a larger range of nominal halide compositions in this material from x = 0.25 to x = 1.5 and explore the changes with neutron diffraction and impedance spectroscopy. The replacement of S^2– by Cl^– causes a lowered average charge in the center of the prevalent Li⁺ “cages”, which in turn causes weaker interactions with Li⁺ ions. Analysis of neutron diffraction data reveals that the increased Cl^– content causes these clustered Li⁺ “cages” to become more interconnected, thereby increasing Li⁺ conductivity through the structure. This study explores the understanding of the fundamental structure–transport correlations in the argyrodites, specifically structural changes within the Li⁺ ion substructure upon changing the anionic charge distribution.