Three-dimensional Graphene-Co₃O₄Cathodes For Rechargeable Li-O₂Batteries

Li-O2batteries can deliver substantially higher specific capacity (3828mA h g-1) andhigher energy density (11425W h kg-1) when compared with other chemical batteries.However, Li-O2batteries are still in their developmental infancy and at present the energydensity of such Li-O2batteries fails to reach the theoretical value in practical applications.Other limitations of this complex system, such as poor cyclability and low roundtripefficiency, still need to be studied in detail. Among all the factors that strongly influencethe capacity and the cycle efficiency, the catalyst used is considered by many to be key.In this work, we report the fabrication of a three-dimensional (3D), free-standing, porousand binder-free air electrode for Li-O2batteries. The major research contents are presentedas follows:3D graphene was deposited on a Ni foam by chemical vapour deposition (CVD). TheX-ray diffraction and Raman spectroscopy results reveal that the CVD-synthesizedgraphene foams are seamlessly continuous and high-quality due to the low fraction ofsurface defects compared with chemically reduced graphene oxide (rGO). The3D grapheneelectrode exhibited performance with a specific capacity of1536mA h g-1and28cycleswith500mA h g-1.Co3O4nanosheets were grown on the3D graphene through a hydrothermal reaction. Forthe3D graphene–Co3O4composite, the graphene skeleton is almost fully and uniformlycovered by the network of Co3O4nanosheets. The growing Co3O4sheets are interconnectedwith each other, exhibiting an open pore structure. The battery with the3Dgraphene–Co3O4cathode exhibited a higher discharge capacity i.e.2453mA h g-1and62cycles with the capacity limited to583mA h g-1.Flower-like Co3O4films composed of hollowed flakes on3D graphene were prepared byelectrodeposition. The3D graphene-Co3O4electrode exhibited enhanced performance witha specific capacity of2032mA h g-1and45stable cycles with700mA h g-1.