Study On Supercapacitors Based On Three-Dimensional Drilled Graphene Sheets Hydrogel

In addition to the advantages of high conductivity,high specific surface area and high mechanical strength of graphene,the three-dimensional drilled graphene sheets hydrogel also obtain a rich aperture structure after to the drilling process,and because of the unique three-dimensional hydrogel structure,the agglomeration between graphene layers is effectively prevented.A supercapacitor with the three-dimensional drilling graphene sheets hydrogel as electrode materials exhibits a high ratio of capacitance and excellent rate performance and cycle life.Although supercapacitors with nickel oxide as electrode materials exhibit ultrahigh ratio of capacitance and energy density,the low conductivity of nickel oxide leads to poor rate performance and cycle life.Combining nickel oxide with high conductivity graphene sheets or carbon nanotubes,the graphene sheets@nickel oxide and carbon nanotubes@nickel oxide core-shell composite materials were prepared,and the high conductivity was obtained.In this article,we will make some effort on the development of high-performance electrode materials(three-dimensional drilled graphene sheets hydrogel,graphene sheets@nickel oxide and carbon nanotubes@nickel oxide)and assembling asymmetric supercapacitors,through increasing the ratio of capacitors and expanding potential window to improving the energy density of supercapacitors.The main research contents are as follows:(1)Three-dimensional drilled graphene sheets hydrogel were synthesized by using chemically reduced graphene oxide,and then through cobalt catalytic gasification and pickling process.After research and analysis of the relationship between cobalt particle mass fraction and the degree of graphene surface drilling,a set of process parameters for the preparation of the three-dimensional drilled graphene sheets hydrogel with optimum pore diameter and distribution state were obtained.When the mass fraction of cobalt particles is 10 wt%,the three-dimensional drilling graphene sheets hydrogel has the best drilling degree.A symmetrical supercapacitor was assembled with the three-dimensional drilling graphene sheets hydrogel with optimum drilling degree as electrodes and the performance was tested.(2)Graphene sheets@nickel oxide core-shell composites were prepared by chemical deposition and annealing.Electrochemical properties of graphene sheets@nickel oxide and nickel oxide were tested and compared,the electrochemical performance of graphene sheets@nickel oxide was significantly increased.A asymmetric supercapacitor with graphene sheets@nickel oxide and three-dimensional drilled graphene sheets hydrogel used as positive and negative electrodes,respectively,was assembled.The asymmetric supercapacitor was tested and compared to the two symmetrical supercapacitors(graphene sheets@nickel oxide//graphene sheets@nickel oxide and three-dimensional drilled graphene sheets hydrogel//three-dimensional drilled graphene sheets hydrogel).(3)By using chemical deposition and annealing,we synthesized carbon nanotubes@nickel oxide core-shell composites.Electrochemical performance of carbon nanotubes@nickel oxide and nickel oxide were tested and compared,the electrochemical performance of carbon nanotubes@nickel oxide was better.A asymmetric supercapacitor was prepared based on carbon nanotubes@oxidized nickel as positive electrode and drilled graphene sheets as negative electrode,respectively.The carbon nanotubes@nickel oxide//drilled graphene sheets asymmetric supercapacitor was tested and compared with the two symmetrical supercapacitors carbon nanotubes@oxidized nickel//carbon nanotubes@oxidized nickel and drilled graphene sheets//drilled graphene sheets.