Study On Supercapacitor Electrode Materials Based On Nanometer Carbon Materials And Manganese Dioxide

Electrochemical capacitors, one of the new energy storage devices, have been successfully applied in various fields, owing to their high energy density and power density, long-term cycle stability and environmental friendly features. The electrode material, is the key part of the electrochemical capacitors, which has important effect on the capacitance performance. Developing new electrode materials with high specific capacitances, is the effective way to improve the power characteristics of electrochemical capacitors. In this thesis, to prepare new electrode materials with low cost, high energy density and power density, porous carbon and manganese dioxide electrode materials have been prepared by different methods. Their morphologies, structures and electrochemical capacitance behaviors were investigated by various material characterization techniques and electrochemical analysis methods. The main points of this thesis are summarized as follows:?1?Nano porous carbon ?NPCs? have been synthesized by direct carbonization of zeolite like metal organic frameworks ?ZIF-9? and acid etching procedure. The micro morphology and crystal structure of NPCs were characterized by scanning electron microscopy ?SEM?, X-ray diffraction ?XRD?, surface area and pore size analyzer. The electrochemical capacitive behavior of NPCs was characterized by cyclic voltammetry ?CV?, galvanostatic charge-discharge analysis technique in 1 M H2SO4 electrolyte. The results show that the average particle size of the NPCs is 600 nm, the specific surface area is 693 m2 g^-1 and the pore structures are mainly composed of mesoporous. The NPCs electrodes show high specific capacitance (259.2 F g^-1 at 2 A g^-1) and excellent power performance (71.10% capacitance retention rate with the increase of scan rate from 2 to 100 mV s^-1). In addition, the specific capacitance value of NPCs is not reduced obviously after 4000 cycles even at a current density of 10 Ag^-1.?2?MnO₂ NTs-IL/CNTs composites have been prepared by combining MnO₂ nanotubes with ionic liquid modified carbon nanotubes ?IL/CNTs?. The morphology and crystal structure of MnO₂ NTs were investigated by SEM, TEM, XRD. The electrochemical capacitive behavior of MnO₂ NTs-IL/CNTs was investigated by CV and galvanostatic charge-discharge method in 0.5 M Na2SO4 electrolyte. The results show that the MnO₂ NTs-IL/CNTs composite electrode, compared with MnO₂ NTs, have higher specific capacitance (254.6 F g^-1 at 1 A g^-1) and good power characteristic ?65.38% capacitance retention rate with the increase of scan rate from 2 to 100 mV s"1, higher than MnO₂ NTs electrode's 40.28%?. Furthermore, the MnO₂ NTs-IL/CNTs electrode has more excellent long-term cycling stability than the MnO₂ NTs electrode, the capacity rention rate of 94.4%, after 2000 cycles at the current density of 4 A g^-1.?3?Taking malic acid as the carbon sources, carbon coated MnO₂ nanorods ?MnO₂@C NRs? have been prepared using a solid-state grinding/low-temperature calcining synthesis method. The morphology and structure of MnO₂@C NRs were characterized using SEM, TEM, XRD and surface area and pore size analyzer. The electrochemical capacitive property of MnO₂@C NRs was characterized by CV and galvanostatic charge-discharge method in 0.5 M Na2SO4 aqueous solution. The analysis results show that the thickness of the carbon layer on the surface of MnO₂ NRs is about 3 nm and carbon coating has no effect on the crystal structure of MnO₂ NRs. MnO₂@C NRs electrode not only has good capacitive performance (246.6 F g^-1 at 2 A g^-1), and also have excellent power characteristics (69.13% capacitance retention rate with the increase of scan rate from 2 to 100 mV s^-1, higher than MnO₂ NRs electrode's 50.18%). In addition, MnO₂@C NRs possess excellent long-term cycling ability, the capacity retention rate after 3000 cycles at the current density of 10 A g^-1 is as high as 97.6%, significantly higher than that of MnO₂ NRs electrode 75%.