Research On The Preparation Of Graphitic Carbon Fibers And Its Ultra-fast Energy Storage Characteristics

Electrochemical double-layer capacitors（EDLCs）can store and release energy rapidly via physical sorption/desorption of ions,showing the advantage of charging/discharging rate.As we all know,electrode material is one of the key factors which can influence the performance of supercapacitors,therefore,the preparation of electrode materials with large accessible surface area,facile pore engineering and high electrical conductivity is essential for accumulating electrolyte ions,promoting ion diffusion and enabling the fast transfer of electrons.The most widely used electrode materials in EDLCs is carbon materials.In this paper,in-situ catalysis is used to increase the graphitization of carbon fibers.The graphite carbon framework,multi-stage pore structure,and the largy specific surface area of the porous graphite carbon material has been prepared and fully characterized,and its ultra-fast energy storage characteristics have been comprehensively studied.In addition,flexible porous graphite carbon nanofibers are prepared by the combination of electrospinning technology and SiO₂ template technology,and its energy storage characteristics are studied.The specific research content is as follows:（1）The porous graphitic carbon fibers were prepared by by in-situ catalysis using Polyacrylonitrile（PAN）,iron（III）chloride（FeCl₃）and N,N-dimethylformamide（DMF）as raw materials,the PAN/FeCl₃ composite fibers were prepared by electrospinning technology,and the carbonization treatment was carried out in a high-temperature tube furnace.The iron nano-particles in the carbon fibers were removed by hydrochloric acid（HCl）pickling to obtain a mesoporous structure,by further activation with potassium hydroxide（KOH）to increase the specific surface area.Finally,porous graphite carbon fibers were successfully prepared.The three-electrode and two-electrode test systems on the electrochemical workstation were used to test its electrochemical behavior.The results showed that the porous graphitic carbon fibers have high degree of graphitization,large specific surface area,micro-meso-macro pore structure and excellent electrochemical behavior at high current density,which are developed that exhibit a fast-charging electrochemical performance with a capacitance of 165 Fg^-1 at high current densities of300 Ag^-1 in an alkaline electrolyte.In addition,it also had a superior power density of54k Wkg^-1 at an energy density of 9.3Whkg^-1 in 1M Na₂SO₄ electrolyte.（2）Flexible porous carbon nanofibers were prepared by using self-made SiO₂nanospheres as templates,polyvinylpyrrolidone（PVP）,PAN and DMF as materials.And further through zinc chloride（ZnCl₂）activation treatment by making pores to increase the specific surface area.The research results showed that the prepared flexible porous carbon fiber was continuous and uniform in diameter,about 400-700 nm,and the SiO₂ template was evenly distributed in the fiber,which was important to prepare the structure.After activation,its capacitance in neutral electrolyte has been greatly improved.They are developed that exhibit a fast-charging electrochemical performance with a capacitance of72 Fg^-1 at high current densities of 100 Ag^-1 in 1 M Na₂SO₄ electrolyte.In conclusion,we used in-situ catalysis technology and electrospinning technology to prepare porous graphite carbon fibers with high specific surface area,multi-stage pore structure and high conductivity,and systematically studied its ultra-fast energy storage characteristics.The results showed that the in-situ catalysis technology was used to improve the graphitization degree of carbon materials,which greatly reduces the working temperature of high-temperature processing.In addition,Si O₂ template technology further increased the flexibility of the of carbon materials.The exploratory work in this paper can provide some reference for fast-charging supercapacitor applications.