Effect of Temperature during Open Vessel Sintering on Li₆PS₅Cl Solid-State Electrolyte Powders for Use in Cathode Composite Electrodes

The sulfide solid electrolyte Li6PS5Cl has been shown to be an ideal candidate for use in composite electrodes for all solid-state lithium-ion batteries due to its high ionic conductivity, low activation energy, and rapid processability in solvents (solution-based processing). Many reports for solution-based processing of Li6PS5Cl required the electrolyte to be densified or sealed inside of a closed-quartz vessel prior to a final high-temperature sintering step. This pre-sintering step is useful for understanding the full electrochemical properties of the electrolyte but provides little information about usable electrolyte powders for commercialization. Modern applications of solid electrolyte powders require a feedstock of powdered electrolyte, which can be processed by tape-casting, screen-printing, aerosol deposition, electrophoretic deposition, and hot powder rolling. The lack of information regarding the sintering of Li6PS5Cl powders for bulk processing warrants an investigation into open vessel sintering of solely the Li6PS5Cl electrolyte powders, which can later be used in composite electrodes. This research uses a solution-based processing technique to synthesize Li6PS5Cl prior to sintering in open-top borosilicate glass containers. Here we show the effects that sintering temperatures have on Li6PS5Cl electrolyte powders during open-vessel sintering using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy for morphological analysis. Electrochemical characterization was performed using AC electrical impedance spectroscopy, cyclic voltammetry, and chronoamperometry. Lastly, a full solid-state electrochemical cell was constructed with a cathode composite electrode made from the Li6PS5Cl to illustrate the functionality of the electrolyte.