(696a) Scalable Synthesis of Li2S Nanocrystals for Use in Next Generation Batteries

Lithium sulfide (Li₂S) nanocrystals (NCs) are critical materials used to make solid-state electrolytes and cathodes for emerging battery technologies. Li₂S is typically produced by high temperature carbothermal reduction that creates powders, which then require extensive ball milling to produce the nano-sized materials desirable for battery applications. We have recently developed a solution-based synthesis of Li₂S by contacting metalorganic solutions with hydrogen sulfide at ambient temperature, employing bubble columns and fluidized beds for scalable production. Additional benefits include complete abatement of H₂S and recovery of the valuable H₂ stored within. Control of nanocrystal size and uniformity is demonstrated through choice of solvent and manipulation of processing conditions such as precursor concentration and solvent evaporation rate. X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and scanning electron microscopy (SEM) were used to quantify crystallinity, particle size distribution (PSD), and morphology, respectively. These complementary techniques confirmed the production of anhydrous, phase-pure Li₂S nanocrystals with tunable size (5-40 nm) and narrow PSDs. Mild annealing conditions were identified that provide the purity required for battery applications, while retaining the original PSD. These materials were used to synthesize simple cathodes and solid-state electrolytes to validate their electrochemical properties. Li₂S cathodes fabricated using small NCs (<10 nm) achieved capacities approaching the theoretical limit (1166 mAh/g), exhibiting good rate capability and promising stability. Control of size is also expected to provide many benefits for solid-state electrolyte production including reduced thermal budgets, improved ionic conductivity, and minimized interfacial resistance. For Li₂S-P₂S₅ based electrolytes, the use of NCs dramatically shortens the ball mixing time required to create the glassy phase relative to commercial powders. Electrolyte pellets produced by simple cold pressing exhibit good ionic conductivity and exceptional electron resistivity. We will report on this and ongoing work examining the continued scale-up of these production and purification of these electrolytes and the integration of these materials into solid-state architectures.