Study On Prepartion And Electrochmical Properties Of High Specific Capacitance Electrode Materials For Supercapacitors

Supercapacitors,also known as electrochemical capacitoris,are a new type of efficient green energy storage device with great power density and long cycle life compared with batteries and higher energy density compared with traditional dielectric capacitors.In recent years,supercapacitors have attracted much attention and have good applications and development prospects in the field of hybrid-electric vehicles.However,as for supercapacitor,the energy density of it is much lower than that of lithium-ion batteries.According to the equation of supercapacitor E=1/2CU²,there are two effective ways which can be used to improve the energy density of supercapacitors.One is to improve the working voltage and the other is to increase the specific capacitance of the electrode material.Based on above analysis,the present work focuses on the research and development of high specific capacitance carbon materials and carbon/metallic oxide composites.The following three aspects have been studied in the present thesis.Owing to the advantages of high specific surface area,low-cost,high conductivity and good corrosion resistance,activated carbons from biomass materials have gained much more attention for being used as the materials for EDLCs.Soybean hulls,an agricultural waste from soybeans cultivated abundantly in the south of China,are applied to prepare activated carbons by carbonization and activation with ZnCl₂ and tested as electrode material in supercapacitor.The pore structure,morphology and chemistry structural of carbons are characterized by using scanning electron microscope?SEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,Raman spectroscopy and the results of N₂ adsorption-desorption isotherms indicate that pore size of nanoporous carbons ranging from 2.81 nm to 3.93 nm and pore volume ranging from 0.314 cm³·g^-1 to 0.501 cm³·g^-1.The soybean hulls carbon prepared with a ZnCl₂ ratio of 3 exhibits the most stable electrochemical performance at fast charge-discharge rates and displays a good cycle performance behavior evaluate using both three-electrode systems and supercapacitor.In a three-electrode,a high specific capacitance of 455F·g^-1 was observed at the current density of 1 A·g^-1,indicating an ideal electrochemical property.The energy density of supercapacitor electrodes prepared from soybean hulls carbon is up to 15.8 Wh·kg^-1 in 1 mol·L^-1H₂SO₄ and has a good stability after 5000 charge/discharge cycles.The excellent electrochemical performance of the soybean hulls carbon is attributed to the appropriate pore diameter with the width of 2-5 nm and the electrochemically active quinone oxygen groups.Activated carbon was modified by nitric acid to create oxygen-containing functional groups in order to provide anchor sites between the activated carbon and manganese dioxide?MnO₂?nanorods.MnO₂ nanorods were synthesized in the surface of activated carbon using a fluid phase method.The morphology and structure of MnO₂/oxidized activated carbon?MnO₂/OAC?were characterized using SEM,XPS,XRD and N₂ adsorption-desorption.The results showed that the MnO₂ nanorods in the composite were dispersed homogeneously on the nitric acid treated activated carbon surface with the width of 20-50 nm.The specific capacitance of the MnO₂/OC6 composite formed with a MnO₂/OC6 mass ratio of 2:1?MnO₂?2?/OC6?showed the best electrochemical performance among the MnO₂/OC6 composite electrodes fabricated,the specific capacitance of the MnO₂?2?/OAC6 composite was 200.3 F·g^-1 in 1mol·L^-1 Na₂SO₄ solution with a scan rate of 10mV·s^-1,the composite electrode exhibited a loss of less than 14%in the specific capacitance after 1000 cycles,indicating good electrochemical stability.The excellent electrochemical performance of the composite electrode was attributed to the synergistic effect of both the activated carbon porous structure and the pseudo-Faradaic reactions of the MnO₂nanorods.Porous carbons were synthesized using zeolite 13X as a template and furfuryl alcohol as carbon precursor,via a four-step process of liquid impregnation,pyrolysis,template elimination and activation with KOH.The pore structure,morphology and chemistry structural of porous carbons are characterized by using SEM and XRD.The electrochemical performances of porous carbons are tested by curves of CV and GCD.The results showed that the optimized parameters for synthesis of porous carbons are at a carbonization temperature of 1000?,an activated temperature of 750?,a concentration of activator of 50%.In a three-electrode,a high specific capacitance of 179.3 F·g^-1 was observed at the current density of 1 A·g^-1,indicating an ideal electrochemical property.