In the context of increasing awareness about the necessity to surpass and complement the present Li-ion battery (LIB) technology with next-generation battery technologies, the main aim of the present project is to provide sufficient knowledge for effective future development of a rechargeable, high energy density Ca-O₂ battery. Today's omnipresent LIB technology is now reaching its limits. One direction in the search for novel batteries is multivalent ion technologies based on Mg²⁺, Zn²⁺, Ca²⁺, and Al³⁺ as charge carriers due to the very high energy densities possible and the high natural element abundance. However, the use of a high-capacity metal anode must always be balanced by a cathode of similarly high capacity. Using an O₂/air concept is considered the Holy Grail of batteries. This concept, when applying the above metals as anodes, avoids all the severe limitations and safety problems associated with lithium anodes. This will be accomplished by combining a calcium anode with a metallic oxide catalysed oxygen cathode. The project will strengthen the expertise of a Croatian, a Serbian, and a Swedish partner and promote their efficient cooperation. The project is supported by Solvionic Ltd. (France) as a leader in the design and manufacture of novel electrolytes for batteries.