Preparation And Supercapacitance Properties Of Fluorine And Nitrogen Co-Doped Carbon Matrix Composites

Supercapacitor is a new type of electrochemical energy storage device with rapid charge and discharge,high power density,long cycle life and it’s also green environmental.With the rapid developmentofelectronicequipmentandtheincreaseofenergydemand,the gravimetric capacitance and energy density of carbon-based electrode materials for commercial supercapacitors are low,which can not meet the development requirements of miniaturization,flexible wearability and high energy density of portable energy storage devices.Therefore,it is urgent that we need to prepare high volumetric capacity capacitors and flexible bendable capacitors through reasonable structural design.Herein,we improve the hydrophilicity,stability,specific surface area,pore structure and electron transfer rate of carbon-based materials by surface modification of fluorine and nitrogen functional groups,which can greatly increase the gravimetric specific capacitance of carbon-based electrode materials.（1）Fluorine and nitrogen co-doped carbon nanosheet（F/N-CNS）with high stacking density were prepared by eutectic salt constrained pyrolysis using glucosamine as carbon source and nitrogen source,polyvinylidene fluoride as carbon source and fluorine source respectively.Eutectic salt plays the role of good solvent and pore-forming agent of carbon precursor in the process of high temperature pyrolysis,which makes the carbon precursor form multi-stage pore structure in the process of high temperature pyrolysis.By regulating the ratio of fluorine source to carbon source,the evolution of F/N-CNS morphology and C-F chemical bond species were studied systematically.The electrochemical performance test results show that the gravimetric specific capacitance of F/N-CNS electrode material in 1 M H₂SO₄ electrolyte is as high as 266 F g^-1,and the volumetric specific capacity is as high as 255 F cm^-3.F/N-CNS has a capacitance retention of 100%after 20000 cycles of constant current charge-discharge test in H₂SO₄ solution at a current density of 10 A g^-1.（2）The bacterial cellulose（BC）flexible film obtained by vacuum filtration was pyrolysis with ammonium fluoride powder at high temperature to prepare fluorine and nitrogen co-doped bacterial cellulose derived carbon nanofiber（F/N-CNF）.Ammonium fluoride can slowly release hydrogen fluoride gas and ammonia gas during high temperature pyrolysis,and the mixed atmosphere of hydrogen fluoride and ammonia gas can be formed in the covered graphite crucible,and the chemical pore formation and fluorine and nitrogen co-doping of bacterial cellulose flexible film are realized.By regulating the feed ratio of bacterial cellulose to ammonium fluoride,the morphology of bacterial cellulose flexible membrane and the evolution of C-F chemical bonds were investigated.F/N-CNF retained the mechanical properties of bacterial cellulose flexible film to a certain extent,and a series of electrochemical energy storage properties were tested.The gravimetric specific capacitance of F/N-CNF electrode material is as high as 350 F g^-11 at 1 A g^-1current density in 1 M H₂SO₄ electrolyte,and its rate performance remains 85%at 10 A g^-11 high current density.After 20000 cycles of charge and discharge,the capacity retention rate is 100%.The F/N-CNF electrode material retains the good flexibility of the bacterial cellulose film and can still maintain its initial specific capacitance when bending at 135°.This paper shows that fluorine and nitrogen co-doping plays a very important role in improving the specific capacitance and cyclic stability of carbon electrode materials.The high temperature pyrolysis carbonation and fluorine and nitrogen co-doping of environmentally friendly carbon materials were realized by selecting two different fluorine sources,and a new type of fluorine and nitrogen co-doped carbon materials with high specific capacitance and long cycle life were obtained.