An argyrodite sulfide coated NCM cathode for improved interfacial contact in normal-pressure operational all-solid-state batteries

The need for safe secondary power sources has generated significant interest in the development of all-solid-state batteries. Despite the development of solid electrolytes with excellent Li-ion conductivity, the challenges inherent to forming an intimate and stable interface between the cathode active material and the solid electrolyte limit the potential performance of all-solid-state batteries. Herein, we propose an efficient process by which a thin and uniform coating of layered oxide cathodes with sulfide solid electrolytes (argyrodite Li₆PS₅Cl) may be obtained. The morphology of the coating agent with a thickness of approximately 30 nm and high uniformity is controlled by preparing Li₆PS₅Cl by one-pot synthesis. As a result, the material exhibits an excellent Li-ion conductivity of 4.6 mS cm⁻¹ at a particle size of less than 1 μm. The controlled argyrodite Li₆PS₅Cl was directly coated onto the LiNi_0.5Co_0.2Mn_0.3O₂ cathode in an aprotic solvent environment. The coin-type all-solid-state cell developed using these argyrodite-coated cathode materials delivered a high discharge capacity of 149.6 mA h g⁻¹ at 0.1C without additional external operating pressure during the charge-discharge process and retained 93.7% of its initial capacity after 100 cycles at 0.1C. It is revealed that the concrete contact between the LiNi_0.5Co_0.2Mn_0.3O₂ cathode and Li₆PS₅Cl suppresses the cathode degradation reactions. The proposed method for coated cathode materials, which features the synthesis of controlled sulfide solid electrolyte materials and their simple coating process in the liquid-phase, can accelerate the development of all-solid-state batteries.