| To achieve the leap from the oil and gas era to renewable energy(solar energy,tidal power and wind energy),we need to solve the bottleneck of renewable energy discontinuity and instability.The key to solve this bottleneck is the development of efficient energy storage devices.Supercapacitor is a new type of power compensation and energy storage device,with the advantages of traditional capacitor and lithium ion battery,which is capable of fast charging and discharging and high energy storage density.To fill the gaps between the two kinds of traditional technology,efficient energy storage device is one of the key development object.This paper aims to design high performance asymmetric supercapacitor electrode materials to ensure the material capacity and improve the cyclic performance and rate performance of materials simultaneously,which makes it have certain application value.The main contents of this paper include the following aspects:First,by using the improved phosphating process,the phosphate ions on the surface of Co3O4 nanosheets were introduced,which effectively promoted the surface reactivity and enhanced the electrochemical capacitance performance.Second,a variety of graphene based electrode materials,such as graded porous graphene and three-dimensional porous graphene electrode,are designed and synthesized.Third,asymmetric supercapacitors were assembled based on the modified cobalt oxide cathode and graphene negative electrode,and their electrochemical properties were studied.In this paper,a method of surface modification of four oxidized three cobalt oxide electrode material by phosphate ion(H2PO4-and PO3-)was studied.The surface of Co3O4 ultra-thin nanosheet electrode was modified by different phosphate ions.The evolution mechanism of the surface morphology of ultrathin nanosheets and the mechanism of accelerating the reaction kinetics by the phosphate ion ion are proposed.After the introduction of H2PO4-and PO3-,specific capacity of Co3O4 electrode has been improved seven times,and the specific capacity of 1716 F/g is obtained at the scan rate of 5 mV/s.Moreover,over 85%of the capacity retention is still available after 10000 cycles of charging and discharging cycles.The changes of the unique morphology caused by surface modification and the positive effects of different phosphate ions on the electrode reactions are the main reasons for the improvement of the performance of the Co3O4 electrode.In general,the electrode surface modification method provides a new idea for obtaining high performance pseudocapacitive supercapacitor based on efficient_pseudocapacitive reaction.The three-dimensional graphene gel made of hydrothermal and freeze-drying is very flexible,which provides a way of thinking for the flexible devices in the future.The PCO/3DPG asymmetric supercapacitor reaches 229 F g-1 at 2 A/g current density,and reaches the maximum 71.58 Wh/kg energy density at the average power density of 1500 W/kg.Although the three-dimensional graphene gel has a high mass specific capacity,its volume ratio will be very low because of its larger thickness.Therefore,graded porous graphene has made up for this defect.A graphene made of template and chemical method was used to make graphene.The electrode consisted of three dimensional macroporous 100 nanometer diameter and 2?3 nanometer diameter.The graded porous graphite oxide film electrode has a very high specific capacitance of 262 F g-1 and a volume capacitance of 327 F cm-3 at the current density of 1 A g-1.Hierarchical porous structure is crucial to the capacitance of high capacity and rate capability,so it has great help for the practical application.The prepared porous graphene oxide films have good electrical conductivity and high ionic diffusion coefficient,and also can be used as a good scaffold material. |
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