One Step Preparation Of Transition Metal Sulfide Electrode Materials And Study On Performance Of Supercapacitor

Supercapacitors have higher energy density than traditional capacitors and more outstanding power density than secondary batteries.Supercapacitors have attracted significant interest as energystorage edvices because of their low cost,short charging time,high power density and long cycle life.The performance of supercapacitors mainly depends on the electrode materials and the development of efficient and cheap electrode materials is crucial to supercapacitors.When used as electrode material,the transition metal sulfide has good conductivity and high theoretical capacitance,so,in this paper,a series of transition metal sulfide electrode materials are prepared by a simple one-step hydrothermal method and microwave method and their electrochemical performances are tested.The contents are summarized as follows:(1)A facile one step hydrothermal process is developed for the synthesis of Ni Co2S4@reduced graphene oxide(Ni Co2S4@RGO)composite materials.The morphology and structure properties of the composite materials are investigated by FT-IR,Raman spectroscopy,scanning electron microscopy(SEM)and X-ray diffraction(XRD).The electrochemical properties of Ni Co2S4@RGO electrode are studied with cyclic voltammetry(CV),galvanostatic charge-discharge analysis(GCD)and electrochemical impedance spectroscopy(EIS).The results show that the as-prepared Ni Co2S4@RGO shows a high specific capacitance of 2003 F g-1 at a current density of 1 A g-1,and outstanding cycling stability of 86% capacitance retention after 3500 cycles.In addition,a asymmetric supercapacitor(ASC)is composed of Ni Co2S4@RGO as positive electrode and activated carbon as negative electrode,which exhibits a high energy density of 21.9 Wh kg-1 at a power density of 417 W kg-1,even at a high power density of 2700 W kg-1,it still remains an energy density of 13.5 Wh kg-1.(2)A facile and cost-effective microwave method is developed to prepare ternary nickel cobalt sulfide(Ni Co2S4)interconnected nanosheet arrays on nickel foam(NF).The morphology and structure properties of the Ni Co2S4/NF are investigated by SEM,TEM,XPS and XRD.When acting as an electrochemical supercapacitor electrode material,the Ni Co2S4/NF shows a high specific capacitance of 1502 F g-1 at a current density of 1 A g-1,and outstanding cycling stability of 91% capacitance retention after 8000 cycles.In addition,a asymmetric supercapacitor(ASC)is composed of Ni Co2S4/NF as positive electrode and activated carbon as negative electrode,which exhibits a high energy density of 34.7 Wh kg-1 at a power density of 750 W kg-1 and long-term cyclic stability(83.7% capacity retention after 8000 cycles).Even at a high power density of 15 k W kg-1,it still remains an energy density of 17.9 Wh kg-1,which is able to light up a light-emitting diode.(3)Three-dimensional flower-like molybdenum disulfide(Mo S2)microspheres composed of nanosheets are prepared by hydrothermal method using ammonium molybdate as molybdenum source and thiourea as sulfur source.The structure and morphology of the composites are characterized by SEM,TEM,XPS and XRD.The electrochemical properties of these materials as electrode materials for supercapacitors are investigated by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy.The results show that the specific capacitance of Mo S2 flower-like microsphere electrode material is 518.7 F g-1 at a current density of 1 A g-1.The symmetrical supercapacitor Mo S2//Mo S2(SSC)is designed with Mo S2 as electrode material,which exhibits the energy density of 12.46 Wh kg-1 at a power density of 70 W kg-1,even at a high power density of 7000 W kg-1,it still remains an energy density of 6.42 Wh kg-1.