Solid oxide fuel cell (SOFC) and Solid oxide electrolysis cell (SOEC) stacks are assembly of metal interconnector, ceramic cells, and have multiple layers of various ceramics such as an electrolyte and electrodes. It is necessary to clarify the deterioration mode of each material and between materials to suppress the deterioration rate. Cr poisoning of the cathode was one of the most significant deteriorations in SOFC. As a candidate for suppressing Cr poisoning deterioration of cathodes, we have developed a ceramic coating for metal-interconnectors using an electrodeposition coating method and confirmed that it can suppress Cr poisoning under SOFC operating environments. SOFC cells, which consist of the electrolyte and electrodes, undergo large amount of deterioration, and many reports have been published on the reaction mechanism at the solid-solid interface and the deterioration due to impurity poisoning. However, in SOFC cell stacking, it is necessary to discuss the effects of ceramic interfaces on durability other than electrode reactions. For example, thermal cycles associated with startup and shutdown may cause peeling of multilayers interfaces and effects on other layers of ceramic bonding material such as bonding materials that electrically connect metal-interconnectors and SOFC cathodes. In this study, we have evaluated the effect on the long-term durability of the metal-interconnector / ceramic coating / bonding material multilayer interface to clarify the effect on the durability of SOFC and SOEC cell stacks. For the electrode contact materials, we selected the similar composition of Co-Mn spinel oxides as the electrode contact material so that it can be sintered even at lower temperatures than the general stacking temperatures. In designing the SOFC/SOEC interface, we focused on two methods: diffusion bonding and metal addition. The compositions of Co and Mn were graded at the ceramic coating / the electrode contact material interface. As a result, during stacking and during SOFC/SOEC operation, mutual diffusion occurred by virtue of the difference in activity between Co and Mn, and the ASR was reduced by improved adhesion between the ceramic coating and the electrode contact material. Mutual diffusion between the ceramic coating and the electrode contact material occurred over time during the long-term durability test, and the ASR continued to decrease. As a second method, by adding metallic Co to the electrode contact material (Co-Mn oxide) and sintered it, the adhesion at the ceramic coating/the electrode contact material interface was significantly improved. By utilizing the heat of oxidation when the metallic Co oxidized for sintering, we have achieved sintering at low temperatures by locally increasing the temperatures at the interface, even at low stacking temperatures. In the presentation, we will explain the design of the electrode contact material for SOFC cathodes and SOEC anodes and metal interconnectors based on the results of long-term high temperature accelerated tests more than 10,000 hours and the thermal cycle tests.