(217di) Controlling Morphology and Enhancing Electrochemical Performance of Cobalt Oxide By Addition of Graphite

Co₃O₄ has been intensively studied as battery anode materials due to its high theoretical capacity of 890 mAh/g. However, Co₃O₄ suffers from poor conductivity and large volume change during the insertion and extraction of Li ions. It has been well proven that introduction of carbon material to metal oxide is very helpful on improving conductivity and remaining structure stability. Among those widely studied carbon additives (e.g. graphene, carbon nanotubes/ fibers), the currently applied commercial anode material—graphite, not only possesses merits of other carbon materials like  high electronic conductivity, superior mechanical properties, excellent chemical tolerance, but also are naturally abundant.  Therefore, it is promising and economic to make Co₃O₄/graphite composite as anode material. This strategy combines the properties of two individual materials and avoids steps necessary for modification or preparation of other carbon-based materials. For example, the Hummer method, one of the most popular methods for the preparation of graphene, involves strong oxidant and acid, while catalysts and chemical vapor deposition are often required for making CNTs or CNFs.

Here, we synthesized Co₃O₄ nanowire, Co₃O₄ nanoparticle network, and Co₃O₄/graphite nanocomposite via a simple hydrothermal route and compared their electrochemical performance. We found the addition of graphite not only influenced the morphology of Co₃O₄, but also enhanced its electrochemical performance. In detail, the Co₃O₄ nanowire was formed without adding graphite; after introducing graphite, the morphology of the Co₃O₄ nanocomposite changed to a network through the partial overlapping of nanoparticles. When studied as anode material in lithium-ion batteries, the Co₃O₄/graphite nanocomposite outperforms two different pure Co₃O₄ samples by showing superior Li-ion battery performance with dramatically enhanced cyclic stability and excellent rate performance. Its reversible capacity remains as high as 551 mAh/g after 50th cycle at a current density of 500 mA/g while that of  the other two pure Co₃O₄ samples drops below 400 mAh/g.