This paper focuses on the thermodynamic performance and techno-economic assessment of a novel electrical energy storage technology using carbon dioxide as a working fluid. This technology, named CO2 battery and recently patented by Energy Dome SpA., addresses an energy market which has a great need for energy storage solutions able to handle the increasing share of nondispatchable renewable energy sources like photovoltaic and wind energy. After a brief introduction, the present study presents the concept of CO2 batteries and their operation. Then the detailed numerical model developed for the accurate calculation of system round trip efficiency is presented with the adopted assumptions and the optimization routine description. Results on the reference case and following sensitivity analysis confirm a round trip efficiency of around 77% (±2%) which makes CO2 batteries a very promising technology with respect to other energy storage systems based on thermodynamic cycles like compressed air and liquid air energy storage thanks to the high performance and the easiness of installation. Finally, calculation of system footprint, capital investment cost and levelized cost of storage are discussed.