On the Lithium Distribution in Halide Superionic Argyrodites by Halide Incorporation in Li7–xPS6–xClx

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–/S2– positions, with higher disorder realizing better Li+ transport. Further replacement of the sulfide by chloride anions (for the series Li7–xPS6–xClx) 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 S2– 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.