The electrochemical performance of nano- and micron-sized Co3O4 is investigated, highlighting the substantial influence of the specific surface area on the obtainable specific capacities as well as the cycling stability. In fact, Co3O4 materials with a high surface area (i.e. a small particle size) show superior specific features, which are, however, accompanied by a rapid capacity fading, owing to the increased formation of an insulating polymeric surface film that results from transition-metal-catalyzed electrolyte decomposition. The simultaneous coating with carbon of Co3O4 nanoparticles and in situ reduction of the Co3O4 by a carbothermal route yields a CoOCoC nanocomposite. The formation of this material substantially enhances the long-term cycling stability and coulombic efficiency of the lithium-ion active material used. Although the metallic cobalt enhances the electronic conductivity within the electrode and remains electrochemically inactive (as revealed by in situ powder X-ray diffraction analysis), it might have a detrimental effect on the long-term cycling stability by catalytically inducing continuous electrolyte decomposition.