We report a synthesis of lithium sulfide, the cost-determining material for making sulphide solid electrolytes (SSEs), via spontaneous metathesis reactions between lithium salts (halides and nitrate) and sodium sulfide. This...

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Li 6 PS 5 Cl is an extensively studied sulfide-solidelectrolyte for developing all-solid-state lithium batteries. However, its practical application is hindered by the high cost of its raw material lithium sulfide (Li 2 S), 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 highperformance Li 6 PS 5 Cl without using commercial Li 2 S but instead in situ making Li 2 S from cheap materials of lithium chloride (LiCl) and sodium sulfide. LiCl, a raw material needed for making both Li 2 S and Li 6 PS 5 Cl, can be added at a full-scale in the beginning and unrequired to separate when making the intermediate Li 3 PS 4 . Such a consecutive feature makes this method time-efficient; and the excess amount of LiCl in the step of making Li 2 S also facilitates removing the byproduct of sodium chloride via the common ion effect. The materials cost of this method for Li 6 PS 5 Cl is ∼ $55/kg, comparable with the practical need of $50/kg. Moreover, the obtained Li 6 PS 5 Cl 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.

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