| Supercapacitors are of great interest due to their fast charging and discharging speed,high power density,good stability and long cycle life,and their wide application in electronic equipment and electrical appliances.Biomass-based carbon materials have many advantages and offer unique advantages and prospects for use as electrode materials in double layer capacitors.In this thesis,tobacco wastes and rice husk with unique 3D nanostructure rich in Enshi region were used as precursors to prepare biomass-based carbon materials by molten salt carbonization process in which carbonization,activation and impurity removal simultaneously occur.The universality of molten salt carbonization of different biomasses was investigated.Furthermore,the influence law between the structure and properties of carbon materials were also studied which can provide,theoretical as well as scientific and technological support for the development of high-performance biomass-based carbon materials.The main research contents of the thesis are as follows.（1）Tobacco-based carbon materials were prepared by carbonization of tobacco stems and stalks in molten eutectic Na2CO3-K2CO3 at 850°C and the effect of carbonization time on structure-and performance was investigated.By comparison,tobacco stem-based carbon（2 hours）and stalk-based carbon（3 hours）possessed better performance.The specific capacitance in the three-electrode system（1 M H2SO4）was 219.8-225.3 F g-1(0.2 A g-1)and 168.2-168.4 F g-1(2 A g-1)with a capacitance retention of 75.0%～76.6%and energy and power densities of 30.5-31.2 Wh kg-1(0.2 A g-1)and 989.5～989.6 W kg-1(2 A g-1).The specific capacitance of symmetrical supercapacitors（6 M KOH）is 143.3～143.5 F g-1(0.2 A g-1)and 133.9～134.3 F g-1(2 A g-1),with capacitance retention of 93.3%～93.7%,energy density and power density of 4.9～5.0 Wh kg-1(0.2A g-1)and 488.6～491.3 W kg-1(2 A g-1)and had good cycle stability.Although the stem and stalk are located in different parts in tobacco plant with different natural structures,the structure and properties of their derived carbon materials are almost the same.（2）Rice husk-based carbon materials were prepared by carbonization of rice husk in molten eutectic Na2CO3-K2CO3 and the effect of carbonization time and temperature on structure and performance was investigated.The results showed that the Si O2template could be removed simultaneously during carbonization process in the alkaline molten salt,and 850°C was the preferred temperature.By comparison,the rice husk-based carbon material prepared by carbonization for 10 hours possessed better performance.The specific capacitance of the three-electrode system（1 M H2SO4）was195.2 F g-1(0.2 A g-1)and 136.9 F g-1(20 A g-1),with a capacitance retention of 70.1%and energy and power densities of 27.1 Wh kg-1(0.2 A g-1)and 9.2 k W kg-1(20 A g-1),respectively;the specific capacitance of a symmetrical supercapacitor（6 M KOH）was156.2 F g-1(0.2 A g-1)and 112.2 F g-1(20 A g-1),with a capacitance retention of 71.8%and energy and power densities of 5.4 Wh kg-1(0.2 A g-1)and 4.6 k W kg-1(20 A g-1),respectively.The specific capacitance of Zn-ion hybrid supercapacitors（ZHSCs）in 3M Zn（CF3SO3）2 was 149.8 F g-1(0.2 A g-1)and 69.8 F g-1(20 A g-1),with a capacitance retention of 47%and energy and power densities of 58.6 Wh kg-1(0.2 A g-1)and 10.0k W kg-1(20 A g-1),respectively.The capacitance retention of ZHSCs at 2 A g-1 for3005 cycles was 95.8%and the Coulomb efficiency was close to 99%.The detailed analysis results by ex situ characterization means of SEM,XRD,FT-IR,Raman and XPS show that all the different biomass-based carbon materials have a hierachically porous structure,high specific surface area(>1000 m2 g-1),good electrical conductivity and self-doping of oxygen atoms,indicating that good universality is present in the molten salt carbonization of different biomasses to prepare carbon materials and these factors together determine the capacitive properties of carbon materials exhibiting obvious synergistic effects. |
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