Preparation And Electrochemical Properties Of Biomass Based Carbon Materials And Their Composites

In recent years, the synthesis of carbonaceous materials with unique structure and excellent electrochemical properties using biomass materials has attracted much attention due to their renewable inherence, low cost, environmental friendliness, and unique structure. In this dissertation, we used biomass and their polyaniline (PANI) composite materials as precursors to prepare porous carbon materials under carbonization and activation. The effects of carbonization and activation on the microstructure and electrochemical properties of the materials were investigated in detail. Moreover, porous carbon materials/MnO2 composites were prepared by a hydrothermal process. The effects of preparation process on microstructure and the electrochemical properties of the composite materials were investigated in detail. Finally, we assembled asymmetric supercapacitor using C/MnO2 composites materials and porous carbon material as positive and negative electrode materials,respectively. The morphology and microstructure of the materials were characterized by scanning electron microscope, transition electron microscope, X-ray diffraction,X-ray photoelectron spectroscopy and N2 adsorption. The electrochemical properties of the materials were characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The main research content and results are summarized as follows:In this dissertation, we used cattail biomass (CP) as the precursor to prepare the different morphologies of the carbon materials under different carbonization temperature and activation,and the effects of the different process of carbonization, activation, activation agent dosage on the electrochemical performances of carbon materials were investigated. The results indicated that the as-obtained porous carbon material (CP-AC-1:1, the mass ratio of KOH and CP carbon precursor is 1:1) retains tubular fiber-like morphology with excellent electrochemical performance for the two step activation, and the specific capacitance of 250 F·g-1 for CP-AC-1:1 can be obtained at a scan rate of 2mV·s-1. For the one step activation, the as-obtained carbon material (CP-CK-1:1, the mass ratio of KOH and carbonized carbon is 1:1)had a high specific surface area (1951 m2·g-1) and cross-linked porous carbon foam structure.As a result, CP-CK-1:1 showed a specific capacitance of 336 F·g-1 at 2 mV·s-1 as well as an excellent cycling performance with 92% specific capacitance retention after 5000 cycles.In addition, bacterial cellulose (BC) was used as substrate, BC-PANI composite materials were obtained by in situ polymerization. After carbonization and KOH activation,the effects of activation temperature, activation time, activating agent dosage on the electrochemical performances of porous carbon materials were systematically studied. The results indicated that the as-prepared porous carbon material (BC-PANI-C-1:1, the mass ratio of KOH and BC-PANI carbon precursor is 1:1) showed excellent electrochemical properties due to the interaction network between conductive carbon nano wires and N-doped porous carbon nanosheet. BC-PANI-C-1:1 showed a specific capacitance of 296 F-g"1 at 2 mV·s-1 as well as an excellent cycling stability with 99% specific capacitance retention after 10000 cycles.Moreover, we tried to synthesize MnO2 composite electrode materials by hydrothermal reaction using BC-PANI based carbon materials as the substrate, and the effects of ultrasonic treatment on microstructure and the electrochemical performances of composite materials were investigated. The results showed that C/MnO2 composite materials with flower-shaped MnO2 nanorods had excellant electrochemical performances because of the increased interfacial contact between MnO2 and conductive carbon network, C/MnO2 had high specific capacitance of 273 F·g-1 at 2 mV·s-1.Finally, we assembled asymmetric supercapacitors using BC-based porous carbon materials and C/MnO2 composite as negative and positive electrode materials, respectively.After optimization, the supercapacitor device can be reversibly charge/discharge at a voltage of 2.0 V in 1.0 M Na2SO4 aqueous solution, obtaining a considerably high energy density of 63 Wh kg-1. Additionally, this asymmetric supercapacitor also exhibits an excellent cycling performance with 92% specific capacitance retained after 5000 cycles.