Preparation And Electrochemical Performance Of Carbon Nanofibers And Their Composite Electrode Materials

In this paper,carbon nanofiber composites were fabricated by electrospinning technique.Polyacrylonitrile（PAN,Mw≈53000）was used as carbon nanofiber precursor,and nickel acetate（C₄H₆NiO₄·4H₂O）was used as the source of nickel,which were dissolved in N,N-dimethylformamide（DMF）under vigorous stirring.Organic micronanofiber membranes were successfully prepared by electrospinning technique.By regulating the conditions of preoxidation and carbonization,the organic micronanofiber membranes were transformed into a flexible carbon fiber/nickel nanocomposite materials.The morphology,structure and chemical composition of carbon fiber/nickel nanocomposite materials were characterized by FT-IR,XRD,SEM,TEM,Raman and XPS.Finally,the carbon fiber/nickel materials were transformed into carbon fiber/nickel sulfide by hydrothermal method.The electrochemical properties of several kinds of nanofiber materials were studied by using three point test system of autolab-electrochemical workstation.Firstly,we studied the properties of the PAN/DMF spinning solution.Afterwards,the microstructure of the as-prepared nanofibers were observed by optical microscope for the optimum spinning parameters.The optimum parameters included mass fraction of PAN of about（10～14）wt%,spinning voltage of（14～18）kV,flow rate of（0.2～0.8）mL/h,as well as needle-collector distance of（15～20）cm.The fibers were observed to have diameter uniformity,smooth surface,no melting phenomenon by optical microscope and SEM.In the process of heating,the fiber membrane gradually presents physical changes including losing water,melting and sublimation and chemical changes including oxidation,reduction and dehydration.The resulting carbon fibers prepared through preoxidation and carbonization were not flexible but brittle.Secondly,different amounts of C₄H₆NiO₄·4H₂O was added into 12 percentage of PAN solution to prepare micronano composite membrane by electrospinning which need to adjust to spinning parameters.The best reaction condition and experimental formula were decided by orthogonal experiment and control variable method for preparing carbon fiber/nickel nanocomposites with excellent flexibility and electrochemical performance.The preoxidation of parameters is 280 ℃ for 120 min in air.The microstructure,fiber diameter and element distribution of the preoxidation membranes were obtained by FT-IR,XRD and SEM.The preoxidation membranes were carbonized at 800 ℃ for 60 min under nitrogen.We have used a series of characterization methods to analyze carbon fiber/nickel nanocomposites.The Carbon fiber/nickel film with mesoporous structure has good flexibility,and its surface area up to 213.9 m2/g.It maintain original flexibility after 200 times of bending experiment.The electrochemical properties of the composites were investigated by CV,GCD,EIS and cycling stability test.In the electrochemical test,no binder and conductive agent were used.The specific capacitance of the composite is up to 615 F/g at a current density of 1 A/g.After 500 cycles of charge and discharge test,the specific capacitance was 58.5 percentage of anteriority at a current density of 1 A/g.Carbon/nickel sulfide was prepared from carbon/nickel composites by hydrothermal method.Through controlling the hydrothermal conditions,the as-obtained composite materials still have good flexibility and Ni was transformed into Ni₃S₂,resulting in better electrochemical properties.In the electrochemical test without using binder and conductive agent,the specific capacitance of composite is up to 1405.7 F/g at the current density of 1 A/g.