Liquid-Phase Synthesis and Structural Analysis of Sulfide-Type Solid Electrolytes

The commercialization of all-solid-state batteries requires well-established large-scale manufacturing processes. Although solid-state methods are commonly employed for the laboratory-scale synthesis of sulfide-based solid electrolytes (SEs), liquid-phase methods are more cost-effective for industrial production. This chapter describes the liquid-phase synthesis of sulfide-based SEs using suspension- and solution-based techniques. Initially, Li2S–P2S5–LiI SEs were synthesized using a suspension method. Analyses of the local structure using transmission electron microscopy and the particle surface states using X-ray photoelectron spectroscopy revealed that the surface layers contribute to improved Li stability. Subsequently, solution methods were developed to achieve rapid synthesis. In particular, Li10GeP2S12 SEs were prepared via solution synthesis using excess sulfur and a mixed solvent of acetonitrile, tetrahydrofuran, and ethanol in 8 h, which is the fastest synthesis time reported to date. This research enables the effective harnessing of particle surface states to develop enhanced sulfide-type SEs.