Capacitance Performance Of Graphene/nickel (cobalt) Hydroxide Composite Electrode

Because of their excellent energy density,power density,good cycle performance,free maintenance and lower cost,electrochemical capacitors or supercapacitors are developed rapidly in recent years and have great potential as emerging power storage devices.Graphene has unique 2D structure,high specific surface area and very good electrical and thermal conductivity.Thus,graphene based composites are promising electric double layer capacitor materials,offering short transport of ions and electrons in the electrode.On the other hand,Ni-Co hydroxides have excellent Fradic pseudo-capacitance properties and be able to replace rare metals in the preparation of Fradic pseudocapacitors.In this study,graphene and Ni-Co hydroxides were deposited in the 3D framework of nickel foam,and their capacitance performance were investigated,respectively.Moreover,asymmetric supercapacitors were assembled based on graphene/nickel foam cathode and Ni-Co hydroxide/nickel foam anode.Followed are the main contents and important results of the thesis.(1)Graphene oxide was prepared with a modified Hummers method and deposited on the framework of nickel foam by immersing process.After reduction by heat/chemical treatment,the composite electrode of graphene/nickel foam was formed.Electrochemical characterization showed that the chemical reduced composite electrode had the specific capacitance of 316.6 F·g-1 at the current density of 5 A·g-1 with the loss of specific capacitance less than 5%after 2000 cycles of charge-discharge test.(2)The composite electrode of nickel-cobalt hydroxide/nickel foam was prepared by solvent thermal method under optimized reaction conditions.Electrochemical characterization demonstrated that the composite electrode had specific capacitance of 1214.7 F g-1 at the current density of 5 A g-1 with the loss of specific capacitance less than 10%after 500 cycles of charge-discharge test.(3)Asymmetric supercapacitor was assembled based on graphene/nickel foam cathode and Ni-Co hydroxide anode,which displayed a remarkable energy density and power density(30.4 Wh.kg-1 at 1.88 kW.kg-1 and 14.1 Wh.kg-1 at 37.5 kW.kg-1)and excellent cycle performance(no capacitance loss in 3000 charge-discharge cycles).