Abstract Heat storage technologies are subject of great research efforts aimed at improving the energy efficiency of power plants and heat recovery processes. In this context, the development of highly efficient and low-cost materials for thermal energy storage is imperative for a large use of this technology. The storage of thermal energy using reversible thermo-chemical reactions can provide large storage capacities especially at high temperatures. Within this class of materials, the red-ox reactions have particular interest due to the low cost of the materials involved (metal oxides) and the use of air both as reacting gas and heat transfer fluid. Therefore, many efforts are doing to improve the efficiency and reversibility of this type of reactions. In this work the synthesis and thermal performances of a novel mixed metal oxide based on cobalt/nickel metals with spinel structure Co3-xNixO4 is reported. A deep study was carried out in order to find the best synthesis conditions and optimum relative metal content in the structure with the objective of decreasing as much as possible the red-ox temperature. The study allowed to determine the optimum Ni content in the oxide structure in order to minimize the reaction temperature. In particular, a linear relationship of the red-ox temperature as a function of the Ni content was observed, enabling reaching red-ox temperature below 700 °C. These results are very promising and open the perspective of using of these types of materials to a wider field of application.