Research On Preparation And Electrochemical Application Of Nitrogen And Fluorine Co-doped Carbon Materials

Carbon materials have good electrical and thermal conductivity and high chemical stability,and are often used as electrode materials for supercapacitors.However,the specific capacitance of carbon itself is low.The method of incorporating heteroatoms into the carbon skeleton can improve the hydrophilicity between the electrode and the electrolyte,provide more active sites,and generate reversible pseudocapacitance,thereby enhancing the ratio of carbon capacitance value.In this paper,benzoxazines of different structures are used as the precursors of carbon materials,and SBA-15 is used as a hard template to synthesize mesoporous carbon materials co-doped with nitrogen and fluorine which have ordered pores,and study it’s electrochemical performance.The main work content and conclusions are summarized as follows:(1)Nitrogen and fluorine co-doped carbon materials(NFCA)were prepared using 2-fluorophenol-type benzoxazine as carbon precursor and SBA-15 as template under different process conditions.The influence of the ratio of the amount of the precursor and the template,the carbonization temperature,the heating rate and the introduction of the fluorine element on the material properties are studied.The results show that the carbon material(NFCA-700)prepared under the conditions of 1:1.2 mass ratio of template agent to precursor,700°C carbonization temperature,and 0.5°C/min heating rate has better electrochemical performance.The specific surface area is 1227m~2/g,the total pore volume is 2.03 cm~3/g,the nitrogen doping amount is 1.79 at.%,and the fluorine doping amount is 0.2 at.%;its morphology and internal structure are successfully replicated with the template,It has a rod-like ordered mesoporous structure;according to the electrochemical performance test results,its specific capacitance is as high as 461 F/g at a low current density of 0.5 A/g,and its specific capacitance is as high as 291 F/g at a high current density of 10 A/g.the capacitance retention rate is 63.1%.After 5000 charge and discharge cycles,the capacitance retention rate is 96.94%.The introduction of fluorine element forms a C-F semi-ionic bond,which improves the specific capacity and cycle performance of the material,and its performance is better than that of pure nitrogen-doped carbon materials.(2)A nitrogen-fluorine co-doped carbon material(NFCF)was prepared using p-trifluoromethylphenol-type benzoxazine as the carbon precursor and SBA-15 as the template.The influence of the ratio of the amount of the precursor to the template,the carbonization temperature,the heating rate,and the amount of fluorine introduced on the performance of the prepared electrode material was also investigated.The results show that when the mass ratio of precursor to template is 1:0.6,the carbonization temperature is 750°C,and the heating rate is 4°C/min,the prepared carbon material(NFCF-750)has better electrochemical performance;The pore structure is ordered,the specific surface area is 1094 m~2/g,the total pore volume is 1.25 cm~3/g,and the doping amounts of nitrogen and fluorine are 1.39 at.%and 0.5 at.%,respectively.The electrochemical test results show that:at a current density of 0.5 A/g,the specific capacitance of NFCF-750 is 660 F/g,which is higher than the 461 F/g of NCFA-700,and it remains 450 at a current density of 10 A/g,capacitance retention rate is 68.1%.After 5000 cycles of charging and discharging,it still maintains 100%of the initial specific capacity.Due to the introduction of more fluorine elements,NFCF has further improved its electrochemical performance,which is better than NFCA and similar materials.(3)The best performance carbon materials(NFCA-700,NFCF-750)prepared with 2-fluorophenol-type benzoxazine and p-trifluoromethylphenol-type benzoxazine as precursors were used to assemble two-electrode symmetric supercapacitors.electrochemical performance test.The results show that the energy density of the symmetrical device assembled with NFCA-700 as the electrode material is 13.1 Wh/kg and the power density is 2500 W/kg;at a current density of 10 A/g,after 4000 cycles of constant current charge and discharge,it still maintain 90.5%of the initial specific capacity.The symmetrical device assembled with NFCF-750 as the electrode material also has a higher energy density(14.8 Wh/kg)and power density(2500 W/kg).Under the current density of 10 A/g,after 4000 cycles of charging and discharge,91.3%ofthe initial specific capacity is still maintained,and the cycle performance is excellent.