Functionalized carbon onions, detonation nanodiamond and mesoporous carbon as cathodes in Li-ion electrochemical energy storage devices

Functionalization of carbon surface leads to the enhancement of ion storage capacity of carbon cathodes due to the additional pseudocapacitive reactions. In order to gain additional insights on the effects of the carbon specific surface area, porosity and oxygeni-containing functional groups on their electrochemical performance, we have investigated thick (>150 μm) electrodes based on carbon onion nanopowder with and without functional groups present on carbon surface as well as nanodiamond soot and mesoporous activated carbon. Oxidation of carbon onion surface was found to result in a 2.4–2.8-fold increase in their specific capacitance. The larger average pore size and the absence of micropores in carbon nanoparticles based electrodes resulted in a better rate performance compared to that of mesoporous activated carbon. However, significant self-discharge was observed in all the oxidized samples. The low electrode density combined with limited overall charge storage capacity of carbon samples resulted in a volumetric capacity of less than 23 mAh cm−3, compared to 450–700 mAh cm−3 offered by state of the art high-density cathodes used in commercial Li-ion batteries. Even with further improvements, our estimations suggest that porous carbon cathodes will unlikely be able to offer more than 15% of the energy density of traditional cathodes.