Review of various sulfide electrolyte types for solid-state lithium-ion batteries

The high sulfide ion polarization is known to cause increased ionic conductivity in the solid sulfide-type electrolytes. Three groups of sulfide-based solid-state electrolytes, namely, Li-P-S, Li₆PS₅X (X: Cl, Br, and I), and Li _x MP _x S _x (M: Sn, Si, and Al) were reviewed systematically from several aspects, such as conductivity, stability, and crystal structure. The advantages and disadvantages of each electrolyte were briefly considered and compared. The method of the preparation was presented with experimental and theoretical studies. The analysis that has been carried out showed that the solid electrolyte Li₁₀GeP₂S₁₂ is superior to others with an ionic conductivity of 12 × 10⁻²S cm⁻¹. This conductivity is comparable to that of conventional liquid electrolytes. However, the availability and high price of Ge are the problems encountered. Furthermore, because sulfide-based solid electrolytes have low chemical stability in ambient humidity, their handling is restricted to inert gas environments. When solid sulfide electrolytes are hydrolyzed, structural changes occur and H₂S gas is produced. The review’s objective includes presenting a complete knowledge of sulfide-solid electrolyte synthesis method, characteristics, such as conductivity, structure, and stability, as well as generating more efficient and targeted research in enhancing the performance of the chemical substance.