The advantage of the co-precipitation method is that the precursors react uniformly at the molecular level. Both Ni-rich cathode materials and garnet-type lithium-ion conductor materials have typically been synthesized by the co-precipitation method. In this paper, we report on a composite of lithium-ion conductive and Ni-rich cathode materials with improved electrochemical properties, synthesized by simultaneous co-precipitation. This process is a very simple and useful method for preparing the composite due to uniform precipitation from the precursor phase. The physical, chemical, and electrochemical characteristics of the ionic conductor Ni-rich cathode composite material were investigated. (C) 2018 The Electrochemical Society.