All-solid-state lithium batteries employing sulfide-based solid electrolytes have emerged as promising next-generation batteries for large-scale energy storage applications because of their safety and high energy density. Among them, Li 6 PS 5 X (X = Cl, Br, I) with an argyrodite structure synthesized by planetary milling exhibits a rather high lithium ion conductivity of 10 −2 -10 −3 S cm −1 at room temperature. Unfortunately, the planetary milling process has the disadvantage of producing the solid electrolytes with large, round-shaped particles. Recently, the solid electrolytes have been synthesized by not the mechanical milling but the liquid-phase process, which facilitates synthesis of sub-micrometer-to nanometer-sized solid electrolyte particles. It is important to reduce the particle size of the solid electrolyte to promote intimate contact with the active material in the composite cathode. Here, rod-like Li 6 PS 5 Cl solid electrolyte with a high ionic conductivity of 1.1 × 10 −3 S cm −1 at room temperature was, for the first time, directly prepared by a liquid phase process using only a stirring method. SEM images showed the electrolyte had a rod-like morphology with a length of 20-30 μm and a width of 2-3 μm. The composite cathode was prepared from a slurry and the cell performances were investigated.

To enhance the packing density of composite cathode for all-solid-state lithium-ion batteries, the effect of a bimodal sized solid electrolyte was studied. The composite cathode, which is fabricated using the powder compression method, consisted of the cathode active material, a conductive agent, and the solid electrolyte. However, the composite cathode construction had voids. The voids in the composite cathode were restricted to ionic conduction between the cathode active materials and the solid electrolytes. Suppression of the voids in the composite cathode improved the electrochemical performance of the all-solid-state battery. A composite cathode using bimodal sized electrolyte powders demonstrated better cell performance than that using only fine or coarse sized electrolyte powders. These results demonstrated that the composite cathode using the bimodal sized electrolyte enhanced the electrochemical performance of the all-solid-state battery because it improved the packing density of the cathode.

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