Unusually Huge Charge Storage Capacity of Mn₃O₄-Graphene Nanocomposite Achieved by Incorporation of Inorganic Nanosheets

Remarkable improvement in electrode performance of Mn₃O₄-graphene nanocomposites for lithium ion batteries can be obtained by incorporation of a small amount of exfoliated layered MnO₂ or RuO₂ nanosheets. The metal oxide nanosheet-incorporated Mn₃O₄-reduced graphene oxide (rGO) nanocomposites are synthesized via growth of Mn₃O₄ nanocrystals in the mesoporous networks of rGO and MnO₂/RuO₂ 2D nanosheets. Incorporation of metal oxide nanosheets is highly effective in optimizing porous composite structure and charge transport properties, resulting in a remarkable increase of discharge capacity of Mn₃O₄-rGO nanocomposite with significant improvement of cyclability and rate performance. The observed enormous discharge capacity of synthesized Mn₃O₄-rGO-MnO₂ nanocomposite (∼1600 mA·h·g^-1 for the 100th cycle) is the highest value among reported data for Mn₃O₄-rGO nanocomposite. Despite much lower electrical conductivity of MnO₂ than RuO₂, the MnO₂-incorporated nanocomposite at optimal composition (2.5 wt %) shows even larger discharge capacities with comparable rate characteristics compared with the RuO₂-incorporated homologue. This finding underscores that the electrode performance of the resulting nanosheet-incorporated nanocomposite is strongly dependent on its pore and composite structures rather than on the intrinsic electrical conductivity of the additive nanosheet. The present study clearly demonstrates that, regardless of electrical conductivity, incorporation of metal oxide 2D nanosheet is an effective way to efficiently optimize the electrode functionality of graphene-based nanocomposites.