The Graphene/manganese(?,?)Oxide Composites Applied On Energy Storage Device

As two dimensional conductive material,graphene may result to revolutionary change in the energy industry in the near future.But because of low density,pure graphene hardly obtain impressive volumetric energy density.At the same time,manganese oxide is abundant and Eco-friendly,costs cheaply and has various morphologies,what's more,manganese oxide possesses excellent theoretical energy storage potentiality,so manganese oxide is applied in the energy storage device extensively by researchers while its low conductivity and poor cyclic stability need to be improved imperatively.However,if we can combine graphene and manganese oxide reasonably,we maybe synthesize a composite material,which inherits the good characteristics of graphene and manganese oxide and shows well conductivity,long cycle life and high volumetric energy density.Herein,we report the synthesis and characterization of two different composites,graphene/8-manganese dioxide and graphene/manganous oxide,which are applied in supercapacitor and lithium-ion battery respectively.The main contents are displayed as following:1.N-doped reduced graphene oxide/?-manganous dioxide composite(N-rGO/?-MnO2)was synthesized through in-suit reaction,then was charactered by x-ray powder diffraction(XRD),x-ray photoelectron spectroscopy(XPS),Raman spectroscopy(RS),scanning electron microscope(SEM)and transmission electron microscope(TEM).The results of characterization proved that the ?-manganous dioxide formed in suit taking the reduced graphene oxide as a template on the reduced graphene oxide.The cyclic votammetry(CV)test showed that N-rGO/?-MnO2 possessed a specific capacitance of 305 F/g at a scan of 5 mV/s in a 5mol/L LiCl solution.Significantly,a asymmetric flexible supercapacitor device was manufactured taking N-rGO/MnO2 and commercial activated carbon as cathode and anode material,solid PVA-LiCl gel electrolyte as separator and flexible graphite layer as current collector,respectively.The device can reach a high voltage widow of 1.8 V,showed a energy density of 3.5 mWh/cm2 and power density 0.019 W/cm2,performed almost unchanged during bending test.moreover,the capacitance of the device still kept as 90%as the initial capacitance through 1500 cycles galvanostatic charge/discharge.2.Reduced graphene oxide/manganous oxide composites(rGO/MnO)and pureoctahedral manganous oxide(MnO)particles was synthesized by a facile freeze-drying method followed by N2 annealing.As anode materials for lithium ion batteries,their properties were tested respectively and compared mutually.The test results suggest that rGO/MnO composites exhibited more enhanced performance in Li-ion reversible capacities and cyclability than the pure MnO particles.The rGO/MnO hybrid anode exhibits a reversible capacity as high as 886 mAh/g at 200 mA/g after 150 discharge/charge cycles,and an excellent rate capability of 412 mAh/g at 2000 mA/g,while the pure octahedral MnO particles anode has only 685 mAh/g and 132 mAh/g at the same condition.The enhanced property of rGO/MnO composites may also concern with three dimensional conductive graphene network and extra fresh red-ox reaction,not like that the pure MnO particles only depend on the lithiation and delithiation of the MnO.The presence of conductive graphene in rGO/MnO not only reduces the particle aggregation but also remedies the deficiency of the MnO as anode materials.