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

Abstract

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 & mu;m. The controlled argyrodite Li6PS5Cl was directly coated onto the LiNi0.5Co0.2Mn0.3O2 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 LiNi0.5Co0.2Mn0.3O2 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. The introduction of the Li6PS5Cl solid electrolyte coating layer forms a better Li+ ionic pathway within the composite cathode. This enables high discharge capacity and long cycle life with intimate interfacial contact.