Incorporating oxide thermoelectric (TE) materials in TE power generation modules necessitates the study of the interfaces between the oxide TE elements and the interconnect materials used to deliver current between them. In this study, interfaces between pure nickel and undoped calcium cobaltate (Ca3Co4O9) have been formed directly by spark plasma sintering (SPS). An intermediate NiO phase is formed during the SPS processes, which grows during post heating with Co entering from the cobaltate side to form a graded Ni1-xCoxO interfacial layer. The electrical and thermal transport across these interfaces, as well as the long term chemical stability of the intermediate layers, have been studied and are discussed herein.