Study Of Carbon Material Based On Biomass For High Performance Supercapacitors

Supercapacitors are one of the crucial energy storage devices and have been attracted tremendous attention,due to the advantages of high power density,long cycle life,wide range of operating temperatures,safety and environmentally friendly.However,the energy density of commercial supercapacitors is lower than those of lithium-ion batteries and fuel cells which restrict the supercapacitors to be further widely applied in various fields.According to the equation of E = 1/2 CV2,to improve the energy density(E)of symmetric/asymmetric supercapacitors,we can improve both the capacitance of electrode materials and the operating voltage(V).In order to improve the energy density of symmetric/asymmetric supercapacitors,after the analysis,the low cost biomass materials are used as raw materials to design and prepare carbon material or the carbon based composite material as electrodes,and simultaneous the appropriate electrolytes or metal oxide as the negative electrode materials to construct the novel symmetric/asymmetric supercapacitors.The main research contents and results are as follows:1.Sorghum stalk-based porous activated carbons(SSCs)have been prepared through a simple chemical activation method using sorghum stalk as carbon source and Zn Cl2 as activating agent.By optimizing the carbonization temperature and the amount of Zn Cl2 activating agent,the specific surface area is 1354.7 m2 g-1 for SSC1.0 sample is obtained when the sorghum stalk/Zn Cl2 mass ratio is 1:1 at the carbonization temperature of 800 o C.As an electrode material for supercapacitor,the SSC1.0 has high capacitive performance with a specific capacitance of 216.5 F g-1 in 2 M KOH aqueous electrolyte in three-electrode systems at a current density of 0.5 A g-1,75% capacitance retention even at 8 A g-1 and excellent cyclic stability with 92% capacitance retention after 5000 cycles at 5 A g-1.Moreover,the assembled SSC1.0//SSC1.0 symmetric cell has wide voltage range of 1.8 V in 0.5 mol L-1Na2SO4 aqueous electrolyte.2.The carrot is used as a precursor to prepare porous carbon materials(CCs).The anthraquinone(AQ),amino-anthraquinone(1-AAQ),and 2-aminoanthraquinone(2-AAQ)are used to modify the carbon skeletons.The composite electrode material(1-AAQ-CC2)has maximum capacitance(328 F g-1at 0.5 A g-1),excellent cyclic stability(95%capacitance retention after 5000 cycles at 3 A g-1)in 2 mol L-1 KOH aqueous electrolyte.Moreover,the assembled 1-AAQ-CC2//1-AAQ-CC2 symmetric supercapacitor exhibits a high energy density of 14.8 Wh kg-1at a power density of 240 W kg-1operated at the voltage range of 0 to 1.8 V in 0.5 mol L-1 Na2SO4 aqueous electrolyte.The improved energy storage is attributed to Faradaic pseudocapacitance related to the redox-active species of organization-composite electrode material in the KOH electrolyte.3.A novel asymmetric supercapacitor device for energy storage is fabricated using WO3-2.0 materials as negative electrode and porous carbon(APAC-2)based on agricultural wastes alfalfa as positive electrode.The WO3 nanostructures prepared at p H of 1.6,1.8,2.0,2.5 and 3.0 displays hexagonal disc-like,nanorod bundles,inerratic hexagonal-like,sphere-like and needle-shaped nanorods suface morphology.The WO3-2which are prepared at 2.0 p H,exhibit high specific capacitance of 415.3 F g-1at 0.5 A g-1.The APAC prepared by simultaneous activation-graphitization method has porous structure and large surface area.Thus,the asymmetric supercapacitor exhibits high energy density about 27.3 Wh kg-1at power density of 403.1 W kg-1in the wide voltage region of 0-1.6 V,as well as a good electrochemical stability(82.6% capacitance retention after 5000 cycles).Such outstanding electrochemical behaviors imply the APAC-2//WO3-2.0 asymmetric supercapacitor is a promising practical energy-storage device.