Among many types of all-solid-state lithium batteries (ASSLBs), the one based on argyrodite crystalline electrolyte is considered as one of the most promising batteries because of their safety and high energy density. Significant efforts have been devoted toward developing argyrodite-type ASSLBs, but the commercialization of these batteries still needs to resolve some scientific and technical problems. Two problems that need to be addressed are reducing the interfacial resistance between the electrolyte and electrode active materials and minimizing the reaction between the electrolyte and electrode active materials. One method to solve these two problems is to coat the electrode active material with a material which is compatible with argyrodite electrolyte. The aims of this paper are (1) to compare two methods of synthesizing and coating of cathode active material and (2) to evaluate the capacity and cycling performance of the coated active material. In this study the emphasis is on lithium niobate (LiNbO3) as the coating material and LiNi0.85Mn0.1Co0.05O2 (NMC) as the nickel-rich cathode active material.