| As an electrochemical energy storage device,supercapacitors have the advantages of fast charge and discharge speed,high power density,long service life,economical and environmental protection,and its electrochemical performance is limited by the electrode material used.As a natural available resource,biomass carbon prepared by carbonization faces the problems of small specific surface area and low specific capacitance.In order to improve the high energy density of supercapacitors without sacrificing high power density and long cycle life,the introduction of non-metallic doping pseudo-capacitors is a widely accepted strategy.The research focus of this paper is to use biomass as a carbon source.Carbonization and non-metallic modulation methods are used to prepare different biomass carbons.By adjusting the pore structure,increasing the specific surface area,and doping with nitrogen and oxygen heteroatoms to increase the electric double layer capacitance,Pseudocapacitance characteristics are introduced to increase the energy density of the capacitor.The main research contents are as follows:Firstly,cotton,loofah,grapefruit rind,popcorn,and Hawaiian husk are selectedfor high-temperature carbonization to obtain five types of biomass carbon(CC,VS,PP,POP,and MS).The specific surface area(4.9 m2/g)of cotton-derived biomass carbon(CC)is 2.79 times that of VS,40.45 times that of PP,14.48 times that of POP,and 6.30 times that of MS.It has a large pore volume,many ion transmission channels,and high electrical conductivity.Among the four aqueous electrolytes,the test results of the three-electrode system show that the biomass carbon exhibits double-layer capacitance,and CC has the best electrochemical performance.In the KOH electrolyte,the current density is 0.5 A/g.The specific capacitance is 2.31 times of VS,2.29 times of PP,7.79 times of POP,and 1.66times of MS.Secondly,nitrogen and oxygen doped biomass carbon(CCN)was prepared by introducing nitrogen and oxygen elements by one-step pyrolysis.The specific surface area of CCN(849.2 m2/g)is 173.5 times that of CC,the pore volume is 47 times that of CC,and there are more ion transmission channels.N doping will use different types of nitrogen(pyridine nitrogen,quaternary nitrogen/graphite nitrogen and pyridine nitrogen)Oxide)into the carbon lattice.Under the three-electrode system,the test results of the eight aqueous electrolytes show that CCN exhibits electric double layer capacitance.When the current density is 0.5 A/g,its specific capacitance is more than twice that of CC.In the Li2SO4 electrolyte,CCN shows a pseudocapacitance characteristic,and the electrochemical window is widened to 2V.Under the double-electrode system,the test results of the eight aqueous electrolytes show that the materials all exhibit excellent capacitance characteristics;and the pseudocapacitance characteristics in the Li2SO4 electrolyte,achieving a high specific capacitance at a current density of 0.5 A/g(149.9 F/g),when the power density is 500 W/kg,the energy density is as high as 77.50 Wh/kg.After 5000 cycles,the capacitance retention rate is 87.5%.Finally,NH3-CCN was obtained by further modulating thenitrogen-oxygen-doped biomass carbon through ammoniation activation technology.The specific surface area(1368.8 m2/g)is 1.6 times that of CCN,the pore volume is 1.5 times that of CCN,and the conductivity(68.92 S/cm)is 1.28 times that of CCN.N-doping introduces different types of nitrogen into the carbon lattice.Regulate nitrogen and oxygen content.Among the four aqueous electrolytes,the test results of the three-electrode system show that NH3-CCN exhibits double-layer capacitance.In KOH electrolyte,the current density is 0.5 A/g,and the specific capacitance(728 F/g)is 2.5 of CCN.Times.In a two-electrode system,the current density in KOH electrolyte is 0.5 A/g,and the specific capacitance value(135.2 F/g)is 2.1 times that of CCN.When the power density is 250 W/kg,the energy density is 18.10 Wh/kg,after 20000 cycles,the capacitance retention rate is 95.67%. |
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