Preparation Of Graphene-based Ematerils And Their Electrochamical Performance For Symmetric/Asymmetric Supercapacitor

Supercapacitor has been paid great attention for features such as longer cycle life, wider operating temperature range and faster charging and discharging rate as new type of energy storage device. Electrode materials become hot research issue since it is a key factor for supercapacitor. Graphene shows great potential in electronics, mechanics, magnetic and optics et al as a tow-dimensional material which could provide a theoretical specific capacitance as high as 550 F/g.In our work, we prepare graphite oxide in modified Hummers method then Zn（NO3）2 and NH4HCO3 are added into the GO solution. After thermal reduction and corresponding follow-up treatments, reduced graphite oxide material with high density（RGO-HD） is prepared and tested by XRD, SEM, FT-IR, TEM, TG, BET methods to analyze the structure and physicochemical properties of the materials. The reduced graphite oxide material is used as electrode material to assemble symmetric and asymmetric supercapacitors. The electrochemical performance is characterized by cyclic voltammetry（CV）, constant current charge and discharge（CD）, AC impedance（EIS） methods. Research shows that the electrode material shows a high density of 1.42 g/cm3. in 6 M KOH electrolyte the electrode material for the symmetrical supercapacitor exhibits a specific capacitance of 128 F/g even at a current density of 10 A/g. In asymmetric supercapacitor using RGO–HD and Ni（OH）₂ as electrode materials, the specific capacitance can reach 50 F/g based the total mass of electrodes at a current density of 10 A/g.The power density and energy density of supercapacitor can be 10.1 Kw/kg and 12.7 Wh/kg.Graphene oxide and commercial activated carbon are mixed in different mass ratio of 1:1, 1:3, and 1:5 in ethanol and water solution that is mixed in the ratio of VH2O:Vethanol =1:1. Graphene/activated carbon composite materials（named GAC1, GAC2, GAC3） are prepared using hydrothermal method. Similar to the above testing methods for characterizing the physicochemical properties and the electrochemical properties of materials, the results shows that when the graphene and activated carbon are mixed in the ratio of 1:5, the composites（GAC3） show the best properties and a porous structure. The material shows the best electrochemical performance for symmetric supercapacitor. At the current density of 1, 2, 5 and 10 A/g, the specific capacitance can reach 190, 180, 150 and 120 F/g respectively, The stable performance is more than 95%, the energy density and power density can be 4.2 Wh/kg and 1.3 kW/kg respevtively. The energy density of asymmetric supercapacitor that using GAC3 and LTO as electrode materials can be 22.5 Wh/kg. The specific capacitance can be 85 F/g at the current density of 0.5A/g and remain 89% after 1000 cycles.