Preparation And Electrochemical Properties Of Nitrogen - Doped Activated Carbon Nanofiber / Carbon Microspheres

Electrochemical supercapacitors are a new type of energy storage device. Compared to traditional capacitors and lithium-ion batteries, electrochemical supercapacitors have a good potential application in energy storage due to its fast charge and discharge time, long service life, high power density, low temperature performance, can be widely used in the fields such as Smart Grid, military force, electric vehicles and other related fields. Electrode material is an important part of supercapacitors as the key to govern the performance of supercapacitors. At present, studies on supercapacitors are mainly focused on the preparation of high performance electrode material. Electrospinning/electrospraying can be used to prepare activated carbon nanofiber or activated carbon nanosphere, which has high surface area, porosity, temperature resistance and conductivity properties. There are two pathways to increase the specific capacitance of the Carbon electrode material:(1) enlarging specific surface area and control porosity; (2) nitrogen doping.In this paper, CA/PAN-based activated carbon nanofibers (ACF)/activated carbon nanospheres (ACS) were prepared by electrospinning/electrospraying and subsequent oxidation, carbonization and activation. Then, SEM, TGA, XRD, Raman, XPS and N2 adsorption and desorption were used to characterize thermal stability, surface morphology, crystal structure, specific surface area and pore structure of the fibers. The performance of electrochemical capacitor can be characterized by galvanostatic charge discharge and cyclic voltammetry methods. The detailed contents are as follows:Cellulose acetate (CA) and Polyacrylonitrile (PAN) used as precursors, CA/PAN-based activated carbon nanofibers were prepared by electrospinning. Investigating the effect of mass ratio of CA and PAN, carbonization temperature, impregnation ratio and activation time on the physical properties and electrochemical properties of the activated carbon nanofibers. The results show that:the higher surface of 1306 m2/g area and appropriate pore size distribution are obtained when the mass ratio of CA and PAN is 60:40 and the maximal specific capacitance of 199 F/g at 1 A/g; When carbonization temperature increases, the specific surface area of the activated carbon nanofibers increases from 792 m2/g to 1306 m2/g and the specific capacitance increases from 163 F/g to 199 F/g; With increasing the impregnation ratio, the specific surface area of the activated carbon nanofibers decreased from 1306 m2/g to 823 m2/g and the capacitance retention decreased from 71% to 43%; With increasing activation time, the specific surface area of the activated carbon nanofibers decreased from 1306 m2/g to 861 m2/g and the capacitance retention decreased from 71% to 49%.N-doped activated carbon nanofibers were prepared by hydrothermal and using urea、 ammonia and ammonium chloride as N source. The electrochemical performance of the N-doped activated carbon nanofibers using different N sources are studied as well. The atomic content of the N-doped activated carbon nanofibers is 5.66%, which was used ammonia as N source. And the specific capacitance is 241 F/g at 1 A/g, the capacitance retention reached to 66%.CA/PAN-based activated carbon nanospheres (CA/PAN=60:40) were prepared by electrospraying. The physical properties and electrochemical properties of the ACS was investigated, the result show that the specific surface area of the ACS is 1162 m2/g and the specific capacitance is 195 F/g at 1A/g. Then, N-doped activated carbon nanospheres(N-ACS) were prepared by hydrothermal and using urea、ammonia and ammonium chloride as N source. The electrochemical performance of the N-ACS using different N sources is studied as well. The atomic content of the N-doped activated carbon nanofibers is 4.21%, which was used ammonia as N source. And the specific capacitance is 226 F/g at 1 A/g, the capacitance retention reached to 69%.