Scalable Synthesis of Li₂S Nanocrystals for Solid-State Electrolyte Applications

Abstract

Lithium sulfide (Li 2 S) 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 Li 2 S 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∼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. Li 2 S-P 2 S 5 based glassy electrolytes formed by a combination of ball milling and cold pressing were used to illustrate the benefits of these Li 2 S NCs. It was shown that Li 2 S NCs reduced the mechanical ball mixing time required to make Li 2 S-P 2 S 5 based glasses by at least 70% relative to commercial Li 2 S 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 (∼10 −5 s cm −1 ), low electronic conductivity (∼10 −10 s cm −1 ), and reasonable activation barrier (∼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.