Scalable Synthesis of Li2S Nanocrystals for Solid-State Electrolyte Applications

Lithium sulfide (Li2S) is a key component and major cost driver for sulfide-based solid-state electrolytes. However, this material is not commercially available in nanocrystal form. We previously demonstrated solution-based synthesis of Li2S nanocrystals (NCs) with tunable size in a small Parr reactor and validated their potential as cathode active materials. Herein, we report on the scale-up of both the synthesis and purification steps, generating meaningful quantities for solid-state electrolyte formation. Use of a bubble column reactor significantly increased production capacity by two orders of magnitude, from similar to 100 mg/batch to >10 g/batch. An evaporator/condenser and fluidized bed with corresponding capacity were introduced for solvent evaporation and annealing, respectively. Intrinsic purity, thermal stability, and morphology of those NCs are characterized by XRD, TGA, and SEM respectively. It is shown that the NC size and purity could be tuned by varying the annealing temperature. Li2S-P2S5 based glassy electrolytes formed by a combination of ball milling and cold pressing were used to illustrate the benefits of these Li2S NCs. It was shown that Li2S NCs reduced the mechanical ball mixing time required to make Li2S-P2S5 based glasses by at least 70% relative to commercial Li2S micro-powders. 70Li(2)S-30P(2)S(5) glassy electrolytes were fabricated by cold pressing at various pressures and characterized by impedance spectroscopy and chronoamperometry. SSEs formed at the optimum condition exhibited high ionic conductivity (similar to 10(-5) s cm(-1)), low electronic conductivity (similar to 10(-10) s cm(-1)), and reasonable activation barrier (similar to 35 kJ mol(-1)). These properties were comparable to leading reports in the literature, validating the use of our material for solid-state electrolyte fabrication. (c) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.