Surficial Sulfur Loss of Jet-Milled Li₆PS₅Cl Powder under Mild-Temperature Heat Treatment

All-solid-state batteries employing inorganic solid electrolytes are considered a promising next-generation energy storage system. Especially, argyrodite-type Li6PS5Cl (LPSCl) was highlighted for its good ionic conductivity and malleability. In the electrode level, achieving an efficient Li+ pathway even with the maximized active material proportion and electrode mass loading is vital for a high energy density. Therefore, a smaller solid electrolyte particle is highly sought for. Herein, we demonstrated a spiral jet mill process for refining LPSCl particle size. The mean particle size (D50) of LPSCl was reduced from 39.9 to 1.9 μm where the ionic conductivity was decreased from 2.0 to 0.23 mS cm–1. The post-annealing in a mild-temperature range (T < 250 °C) led to the even more decreased ionic conductivity. Although the ionic conductivity was restored when T > 300 °C, this high-temperature annealing resulted in severe particle agglomeration. Spectroscopic observations revealed that particle surfaces were damaged during pulverization and irreversible sulfur losses occurred during the mild-temperature annealing.