Scalable Synthesis of Alkali Sulfide Nanocrystals Using a Bubble Column Reactor

Alkali sulfide nanocrystals (Li2S and Na2S) are critical materials used to make solid-state electrolytes and cathodes for advanced battery technologies. We have recently developed a green chemistry for the synthesis of these materials through reactive precipitation by contacting organic solutions with hydrogen sulfide at ambient temperature. In this work, the use of bubble columns was developed as a platform for scalable manufacturing of these nanomaterials. Initial attempts to reproduce the batch reactor synthesis were complicated by nanoparticles clogging the sparger. This was resolved through the introduction of an inert column of fluid between the sparger and the solution. Using this 4-phase bubble column, anhydrous, phase-pure Li2S and Na2S nanocrystals were synthesized across the full range of conditions explored. X-ray characterization showed that the primary crystallite size was 20-40 nm, assembling into aggregates of hundreds of nanometers in size. This work validates the potential of bubble columns for large-scale manufacturing of nanocrystals by reactive precipitation in gas-liquid systems.