A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li6PS5Cl Solid-Electrolyte

Li₆PS₅Cl is an extensively studied sulfide-solid-electrolyte for developing all-solid-state lithium batteries. However, its practical application is hindered by the high cost of its raw material lithium sulfide (Li₂S), the difficulty in its massive production, and its substandard performance. Herein we report an economically viable and scalable method, denoted as "de novo liquid phase method", which enables in synthesizing high-performance Li₆PS₅Cl without using commercial Li₂S but instead in situ making Li₂S from cheap materials of lithium chloride (LiCl) and sodium sulfide. LiCl, a raw material needed for making both Li₂S and Li₆PS₅Cl, can be added at a full-scale in the beginning and unrequired to separate when making the intermediate Li₃PS₄. Such a consecutive feature makes this method time-efficient; and the excess amount of LiCl in the step of making Li₂S also facilitates removing the byproduct of sodium chloride via the common ion effect. The materials cost of this method for Li₆PS₅Cl is ∼ $55/kg, comparable with the practical need of $50/kg. Moreover, the obtained Li₆PS₅Cl shows high ionic conductivity and outstanding cyclability in full battery tests, that is, ∼2 mS/cm and >99.8% retention for 400+ cycles at 1 C, respectively. Thus, this innovative method is expected to pave the way to develop practical sulfide-solid-electrolytes for all-solid-state lithium batteries.