Cobalt carbonate/ and cobalt oxide/graphene aerogel composite anodes for high performance li-ion batteries

Nanocomposites consisting of ultrafine, cobalt carbonate nanoneedles and 3D porous graphene aerogel (CoCO₃/GA) are in situ synthesized based on a one-step hydrothermal route followed by freeze-drying. A further heat treatment produces cobalt oxide nanoparticles embedded in the conductive GA matrix (Co₃O₄/GA). Both the composite anodes deliver excellent specific capacities depending on current density employed: the CoCO₃/GA anode outperforms the Co₃O₄/GA anode at low current densities, and vice versa at current densities higher than 500 mA g^-1. Their electrochemical performances are considered among the best of similar composite anodes consisting of CoCO₃ or Co₃O₄ active particles embedded in a graphene substrate. The stable multistep electrochemical reactions of the carbonate compound with a unique nanoneedle structure contribute to the excellent cyclic stability of the CoCO₃/GA electrode, whereas the highly conductive networks along with low charge transfer resistance are responsible for the high rate performance of the Co₃O₄/GA electrode.