Enhanced Chemical and Electrochemical Stability of Sn-Substituted Li6+ x P1- x Sn x S5Cl0.5Br0.5 Sulfide Solid Electrolyte for All-Solid-State Battery

All-solid-state batteries have been regarded as next-generation battery due to their safety and higher energy density. Among the solid electrolytes, argyrodite sulfide solid electrolytes show superior characteristics of high ionic conductivity, scalable synthesis process, and low cost of precursors. However, argyrodite sulfide solid electrolytes encounter challenges such as an unstable interface with Li-metal and poor air stability due to the high reactivity of S species. One of the methods to improve these problems is the elemental substitution. In this study, Sn was substituted in place of P within the mixed-halide Li6PS5Cl0.5Br0.5 electrolyte. The crystal structure was characterized by X-ray diffraction (XRD) and Raman spectra. The interfacial stability of solid electrolytes against Li-metal anode and electrochemical performances were evaluated by symmetric cell test and galvanostatic charge/discharge test. The improved air stability was also investigated by measuring the ionic conductivity after air exposure. These results demonstrate that the substitution of Sn can improve ionic conductivity, interfacial stability, and air stability of sulfide solid electrolytes. Keywords: solid electrolyte, Li6PS5Cl0.5Br0.5, elemental substitution, optimized synthesis method, chemical, and electrochemical stability