Lithium-Ion-Conducting Argyrodite-Type Li 6 PS 5 X (X = Cl, Br, I) Solid Electrolytes Prepared by a Liquid-Phase Technique Using Ethanol as a Solvent

Argyrodite-type crystals, Li 6 PS 5 X (X = Cl, Br, I), are promising solid electrolytes (SEs) for bulk-type all-solid-state lithium-ion batteries with excellent safety and high energy densities because of their high ionic conductivities and electrochemical stabilities. However, these advantageous features alone are not sufficient to achieve good cell performance. It is also critically important to have a simple and effective synthetic route to SEs and techniques for forming favorable solid–solid interfaces with large contact areas between the electrode and electrolyte particles. Here, we report an effective route for the preparation of argyrodite-type crystals using a liquid-phase technique via a homogeneous ethanol solution to improve cell performance using an SE-coating on the active material. The preparation conditions, such as appropriate halogen species and alcohol solvents, dissolution time, and drying temperature, are examined, finally resulting in Li 6 PS 5 Br with a lithium-ion conductivity of 1.9 × 10 –4 S cm –1 . Importantly, the obtained solution forms a favorable solid–solid electrode–electrolyte interface with a large contact area in the all-solid-state cells, resulting in a higher capacity than conventional techniques such as hand mixing using a mortar.