Fluoride ion batteries are attracting attention as a high-capacity battery beyond lithium ion batteries. While Cu exhibits excellent properties as a cathode active material, its fluoride CuF₂ formed through fluorination reactions has low fluoride ion conductivity, which limits the amount of Cu utilization in charge/discharge reactions. Therefore, the development of electrode materials in which the paths of ion and electron are independent and finely mixed is necessary. Microstructure control using thermodynamic properties is one of the possible candidates to archive this purpose, and attempts have been made to control the microstructure of electrode materials by spinodal decomposition. We have constructed thermodynamic database and phase diagram for optimizing electrode microstructures. In this study, microstructural control of Cu–(Pb,La)–F ternary system, which is a mixture of cathode active material Cu and fluoride ion conductors PbF₂ and LaF₃, and new cathode active materials Cu-S have been investigated.