Self-Organized Growth of the Mo₂C/Graphene Core-Shell Nanostructured Anode Material for Lithium-Ion Batteries via a Catalytic CVD Process

Metal catalysts in the chemical vapor deposition (CVD) growth of graphene have played a vital role in the development of various growth concepts. Here, we report a self-organized growth of a Mo₂C/few-layer graphene core-shell type nanostructure on the oxide (SiO₂) substrate under the bifunctional catalytic effect of the group VI transition metal molybdenum (Mo). Due to its stable metal carbide-forming ability, the Mo catalyst promoted the formation of a few-layer graphene by bulk segregation of carbon atoms. Cross-sectional transmission electron microscopy provided evidence for the few-layer graphene formation not only on the catalyst surface but also at the SiO₂/catalyst interface, embedding the Mo₂C nanoisland formed due to thermal dewetting. Control experiments performed on the sapphire substrate helped us unveil the synergistic role of the catalyst-substrate interaction and catalyst morphology in the formation of graphene on the oxide substrate. The underlying growth mechanism resembled that of the famous tip growth model of carbon nanotube growth, leading to the formation of Mo₂C/graphene core-shell type structures. Electrochemical studies performed on transferred Mo₂C/graphene composite anode film in a coin-cell configuration revealed an areal capacity of 14 μAh/cm² with an excellent capacity retention of 86% over 100 cycles at a current density of 0.5 μA/cm². Our results demonstrate that the Mo₂C-few-layer graphene composite film grown via the CVD route can be a potential anode material for Li-ion microbatteries.