| Supercapacitors have become the focus of new energy storage devices because of their high power density,excellent stability,good cycle performance and wide application range.The characters of electrode materials is one of the key factors determining the performance of supercapacitors.Graphene aerogel?GA?is an ideal carbon-based electrode material due to its excellent electrical conductivity,large specific surface area and good cycle stability.However,it mainly provides the double layer capacitance that limit its practical application.Based on GA,this paper achieves the purpose of improving the specific capacitance by doping modification and composite modification of GA,so as to obtain GA composites with better performance.In this study,first,the graphite oxide?GO?is prepared by Hummers method with natural flake graphite as raw material.And then GA is prepared by hydrothermal reduction combing with freeze drying.A series of composite modification was carried out on the basis of GA to prepare composite materials.The morphology and electrochemical tests were carried out on the materials.The specific research work and results are as follows:?1?N-GA,B-GA and NB-GA composites were prepared by doping the GA with N and B elements in a double-pot hot steam method.The results showed that the composites exhibit three-dimensional network structure and element doping effectively increases the specific capacitance of GA.At the same time,the effect of N?B co-doped composites has higher specific capacitance than single-doped composites.The specific capacitance order of the composites was NB-GA(310.2 F g-1)>B-GA(248.5 F g-1)>N-GA(232.6 F g-1)at the current density of 1 A g-1.There was a significant improvement of all the composites compared with GA(201.0 F g-1).They were assembled into a symmetrical supercapacitor.The specific resistance of all the composites were small after 1000 cycles of stability testing.It suggests that the composites have good cycle stability.?2?Co3O4/GA composites were prepared by hydrothermal method combined with high temperature calcination.The effects of different GO and cobalt source mass ratios on the properties of composites were discussed.The results showed that the composite has the best performance when the mass ratio of CoCl2·6H2O to GO was1:4.In the composite material,spherical Co3O4 was homogenously distributed in the three-dimensional network structure of GA.It can effectively reduces the agglomeration of GA as well as to improve its electrochemical performance.The specific capacitance of Co3O4/GA was 380.0 F g-1 at a current density of 1 A g-1,which was 89.1%higher than that of GA.And its specific capacitance retention after the 1000 cycles was 85.0%.?3?In order to further improve the cycle stability of Co3O4/GA,a SiO2@Co3O4/GA composite with core-shell structure was prepared.It used CoCl2·6H2O and Si?OC2H5?4 as the cobalt and silicon sources,respectively.It was found that both double-layer capacitance and faradaic pseudo-capacitance existed in SiO2@Co3O4/GA.The specific capacitance of SiO2@Co3O4/GA is up to 620.0 F g-1 at a current density of 1 A g-1,which was 208.5%higher than that of GA.The specific capacitance retention was 94.0%after 1000 cycles,which was 9.0%higher than that of Co3O4/GA.Simultaneous introduction of SiO2 and Co3O4 significantly improved the capacitance performance of the composite.The formation of core-shell structure by SiO2 coated Co3O4 effectively inhibited the volume expansion of Co3O4,improved the stability,corrosion resistance and aging resistance of the material.Thus made the material show more excellent electrochemical performance. |
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