(192i) Novel 3-D MnO2/Holey Graphene Nanostructure for Supercapacitor Applications With Enhanced Electrochemical Performances

As an excellent energy storage device with high-power density and long life cycle, supercapacitor has been intensely investigated in many aspects, such as electrode materials, electrode structure engineering, electrolyte compositions, separator improvements, as well as device design.  Among them, one of the most urgent shortcuts is the around 10 times lower energy density compared to the traditional Li-ion batteries.  This drawback has dramatically confined the applications of supercapacitors in electrical vehicles, intermittent energy storages and other occasions where both the power density and energy density are required.  However, many researchers have been working on improving the energy density without significantly scarifying power density.   These researches include increasing the voltage windows by employing organic electrolyte with larger voltage openings, applications of thinner and yet still mechanically strong separators, integrate materials with higher intrinsic capacitance, and so on.  Despite all the effort on supercapacitor research, the current state-of-art on energy density still needs to be improved to meet the fast-growing application demanding in the emerging and potential applications.  Therefore, we propose a mild method of preparing a novel 3-D MnO2/holey graphene composite for supercapacitor electrodes.  The nano MnO2 nanorods in the composites serves as a capacitance booster due to its high intrinct capacitance and spacer to prevent 2-D graphene sheets from stacking back together. At the same time, graphene also serves both as active material to provide large surface area for charge storage and conductive agent to collect electrons generated by the surface redox reactions of semiconductive MnO2.  Holes on graphene sheets enhance the efficient accessibility of electrolyte to the surface of active materials.  With this novel 3-D composite, an increasement of around 30% to 50% in capacitance is expected.