Preparation And Application Of Graphene/metal Oxide Composites

As one of the key factors affecting the performance of supercapacitors,electrode materials have become the focus of research for improving the power density and the energy density of supercapacitors.This thesis,a simple and easy method to prepare graphene/transition metal oxide composites is introduced.The preparation process of composite electrodes and the electrochemical performances of assembled button capacitors are studied to improve the specific capacitance and energy density of composite supercapacitors.Firstly,a simple nano-scale GN/Fe₃O₄ composite was prepared by a simple two-step reflow-high-temperature reaction.The structural test of the composite materials shows that the Fe₃O₄ particles have a well distributed and uniform diameter on the surface of the graphene.The composite materials electrodes prepared with different loadings were used to study their electrochemical performance.The cyclic voltammograms of different composite electrodes show similar redox peaks around-0.1V,meaning the composite electrodes possessing composite electrodes characteristics.When the current density value is 0.5 A/g,the galvanostatic charge-discharge composite electrode GN/Fe₃O₄-0.05 has the best specific capacitance of 265.6 F/g,which is higher than the graphene?138.9 F/g?and reported graphene/iron oxide?220.1F/g?.The power density increases up to 20.27 kW/kg and the energy density reaches to11.26 Wh/kg for our GN/Fe₃O₄-0.05 composites.Then GN/Fe₃O₄-0.05 composite electrodes were assembled to a button-type supercapacitor.The galvanostatic charge/discharge was performed for 100 times.The capacitance efficiency value is very good for 100 times charge/discharge and the discharge specific capacity gradually became stable.After 500 times of charge and discharge,the capacitance efficiency still reached over 80%.Secondly,graphene/lanthanum oxide composites?GN/La₂O₃?were prepared by the similar method,but the different reacting temperature and pressure were used to evaluate the best electrochemical performance condition.The results show that the graphene/lanthanum oxide composite electrode prepared at a reaction temperature of100?display the high rate performance and low inernal resistance.The composite electrode prepared at 8 MPa pressure has the best electrochemical characteristics.The electrode prepared at 8 MPa in the low middle frequency region is close to perpendicular to the X-axis for the impedance curve,and it also has very small diffusion resistance and interface resistance.Third,composite electrode GN/La₂O₃ were prepared under optimal conditions.In the three-electrode test,the cyclic voltammogram shows the characteristics of double-layer capacitor.The galvanostatic charge-discharge current density of 0.1 A/g,the specific capacitance of composite electrode GN/La2O3-0.1 is 156.25 F/g,which is higher than the RGO?138.90 F/g?.When the energy density is 13.02 Wh/kg,the power density value increases to 15.62 kW/kg.The composite GN/La2O3-0.1 button-type supercapacitor has high capacitance efficiency and stable discharge specific capacity before 100 times of galvanostatic charge and discharge.After 500 times of charge and discharge,the capacitance efficiency reaches over 70%.