Li_5.5PS_4.5Cl_1.5 is a chloride-rich argyrodite sulfide electrolyte that crystallizes in a cubic crystal structure (space group F-43m). It manifests as a light grey powder with a remarkable crystal structure that facilitates high ionic conductivity, typically ranging from 4 to 10 mS/cm at 298 K. This conductivity is nearly four times greater than that of Li₆PS₅Cl under identical processing conditions. The substantial enhancement in ionic conductivity is attributed to the weakened interactions between the mobile Li-ions and the surrounding framework anions, resulting from the substitution of divalent S2- by monovalent Cl-. Additionally, increased site disorder and a higher lithium vacancy population contribute to the improved ionic conductivity.

Li_5.5PS_4.5Cl_1.5 is primarily employed as a catholyte in solid-state batteries, often in conjunction with LiNbO3-coated NMC (LiNixMnyCozO₂) or LFP (LiFePO₄) cathodes. It exhibits compatibility with silicon and graphite anodes but is not directly compatible with lithium metal anodes. The material′s high ionic conductivity and low activation barrier (0.29 eV) render it an ideal candidate for room-temperature solid-state batteries, offering a safer and more stable alternative to traditional organic electrolytes. By virtue of its crystal structure and conductivity up to 9 mS/cm at 298 K, Li_5.5PS_4.5Cl_1.5 can significantly enhance the performance of solid-state batteries, providing excellent energy storage capabilities and improved safety features. The material′s ability to exhibit high ionic conductivity under various processing conditions makes it a valuable component in the development of advanced solid-state battery technologies.