Wet Mechanochemical Synthesis of BH₄-Substituted Lithium Argyrodites

In all-solid-state batteries, a solid electrolyte with high ionic conductivity is required for fast charging, uniform lithium deposition, and increased cathode capacity. Lithium argyrodite with BH₄ ^- substitution has promising potential due to its higher ionic conductivity compared to argyrodites substituted with halides. In this study, Li_5.25PS_4.25(BH₄)_1.75, characterized by a high ionic conductivity of 13.8 mS cm^-1 at 25 °C, is synthesized via wet ball-milling employing o-xylene. The investigation focused on optimizing wet ball-milling parameters such as ball size, xylene content, drying temperature, as well as the amount of BH₄ ^- substitution in argyrodite. An all-solid-state battery prepared using Li_5.25PS_4.25(BH₄)_1.75 as the electrolyte and LiNbO₃ coated NCM811 as the cathode exhibits an initial coulombic efficiency of 90.2% and maintains 93.9% of its initial capacity after 100 cycles at fast charging rate (5C). It is anticipated that the application of this wet mechanochemical synthesis will contribute further to the commercialization of all-solid-state batteries using BH₄-substituted argyrodites.