Preparation And Electrochemical Performance Of Porous Ultrafine Carbon Fibers

Ultrafine fibers prepared via electrostatic spinning have many advantages,such as good continuity,good controllability,simple,high efficiency,large scale,wide prospect and so on.Ultrafine carbon fibers with different structure and properties can be prepared by using different spinning precursor with different components and post processing method.It possesses high application value in preparation of electrode materials in electrochemical capacitors with high performance.In this paper,polyacrylonitrile(PAN)electrospinning fiber was prepared,and then,PAN based mesoporous/macroporous ultrafine carbon fiber electrode materials were obtained by method of solvent induced phase separation or non solvent induced phase separation and heat treatment.Finally,the morphology and physicochemical properties of ultrafine carbon fibers characterized by scanning electron microscopy,thermal weight loss analysis and pore structure analysis.The resistance analysis,cyclic voltammograms tests and constant current charge/discharge were investigated by using electrochemical test.Then the relationship between the electrochemical properties and the structure and properties of ultrafine carbon fibers was studied.This research is mainly carried out in the following three aspects.(1)The preparation of ultrafine macroporous carbon fibers via electrospinning process and solvent induced phase separation.PAN electrospinning precursor was prepared by dissolving PAN in a mixture of nitromethane and water,and PAN electrospun fibers were prepared under high voltage electrostatic filed.As PAN has different solubility in the mixed solvent,so the separation and volatilization of different solvents,so different pore structure formed on the surface of high-pressure electrospun fibers in the high voltage electrospinning process.And then the macroporous ultrafine carbonfibers will be obtained through the carbonization process.The influence factors and mechanism of the ratio of nitromethane and water to the pore diameter and the diameter of the high-pressure electrospinning fibers pore were investigated.The result shows,the ratio of nitromethane and water is in the range of 94?96:6?4,where PAN fibers have good electrospinning property,when the ratio of nitromethane and water is 95:5,the ultrafine carbon fibers obtained have a best BET specific surface area.(471.4 m2·g-l),average pore radius(5.4 nm)and average pore volume(30.1×10-3 cm3·g-1).(2)The preparation of mesoporous PAN based ultrafine carbon fibers by method of non solvent induced phase separation.The different proportions of PAN and PVP were dissolved in N,N-dimethylformamide(DMF)and then PAN/PVP hybrid electrospinning fiber was prepared by high voltage electrospinning technique.According to the difference of the solubility of PAN and PVP,The water soluble PVP was dissolved in water by ultrasonic assisted water treatment,and porous PAN ultrafine fibers were obtained.Then mesoporous ultrafine carbonfiber was obtained through high temperature carbonization process.At the same time,the PAN based carbon fiber and PAN/PVP hybrid electrospinning carbon fibers were prepared.The morphology and the structure of the carbonfibers by the above three methods was analyzed and characterized respectively.The result shows,the PAN based ultrafine carbon fibers have higher BET specific surface area((285.806 m2·g-1),average pore radius(9.9 nm)and average pore volume(143.69×10-3 cm3·g-1).(3)Study on electrochemical properties of mesoporous/macroporous carbon fibers electrode.The electrochemical properties of micro porous,medium and large pass PAN based ultrafine fibers were studied.The result shows that the resistance of ultrafine carbon fiber decreases with the increase of the average pore radius,the specific capacitance increased with the increase of the average free volume,power performance and capacity retention rate increased with the increase of the average pore radius.Compared with various electrochemical performance indexes,the results show that the PAN based ultrafine carbon fibers obtained by PVP dissolution method has a high comprehensive electrochemical properties:Mass specific capacitance is 48.2 F·g-1,energy density is 7.8 Wh·kg-1 and the power density is 13.7 kW·kg-1?...