Preparation And Capacitance Performance Of Biomass-based Carbon Composites

Supercapacitors play an increasingly important role in modern power source application due to their high capacitance, high power density, long cycle life and good operational safety. An electrode material is one of the key factors that affect the electrochemical properties of the supercapacitor. The researches in the electrode materials are mainly the following three types: carbon materials; transition metal oxides and conducting polymers. In this dissertation, the preparation, characterization and electrochemical properties of biomass/Mn O2, biomass/PANI and WO₃ nanowires were reported. The morphologies, structures, and electrochemical properties of these materials were characterized using X-ray diffraction（XRD）, raman spectra, emission scanning electron microscopy（FE-SEM）, transmission electron microscopy（TEM）, N2 adsorption-desorption and thermogravimetric analyses（TGA）. Their electrochemical properties were also investigated by cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy techniques. The main contents are as follows:1. Orange peel based biomass carbon（OAC） is prepared by carbonization orange peel at various temperatures. The biomass carbon-Mn O2（OAC-Mn O2） composites with different Mn O2 content are prepared through redox reaction and adjusting the ratio of KMn O₄ to OAC. The OM1 synthesized from weight ratio of OAC-8 to KMn O₄ at 4:1 shows excellent electrochemical properties such as specific capacitance as high as 656 F g^-1, and good long-term cycling stability（above 80% capacitance retention over 5000 cycles） at a current density of 1.0 A g^-1 in 6 M aqueous KOH electrolyte, moreover it can still remains 62 Wh kg^-1 at a power density of 5000 W kg^-1. Such intriguing electrochemical properties indicate that the OM1 is very promising candidates to be further exploited in supercapacitor devides.2. A novel activated carbon material with multi-level structure is prepared under different carbonization temperature using chestnut shell as raw materials. The specific surface area and pore volume of the activated carbon obtained at 800 ℃（CAC8） are as high as 1568.0 m2 g^-1 and 0.94 cm3 g^-1. The electrochemical properties of the CAC8 are very promising, the specific capacitance is 207 F g^-1 at current density of 1 A g^-1 in 1 M H2SO₄ electrolyte. A CAC8/PANI composite, which was synthesized through an interfacial polymerization method, presents a good electrochemical performance, including an excellent specific capacitance of 597 F g^-1 and 80 % retention of capacitance after 1000 cycles at a current density of 1 A g^-1 in 1 M H2SO₄ electrolyte.3. Asymmetric supercapacitor（ASC） with high energy density has been developed successfully using CAC/PANI composite as positive electrode and WO₃ nanowires as negative electrode in a neutral aqueous H2SO₄ electrolyte. Because of its unique structure, high capacitive performance, and complementary potential window, the ASC device can be cycled reversibly at a cell voltage of 1.5 V, delivering a high energy density of 21.4 Wh kg^-1 at a power density of 374.5 k W kg^-1. Moreover, the ASC device also exhibits a superior long cycle life with 83% retention of the initial specific capacitance after 1500 cycles.