Study On The Supercapacitor Performance Of Carbon Nanotubes And Their Composite Electrodes

Electrode material is an important component that affects the performance of supercapacitors.Aiming to optimize the performance of supercapacitors,we chose carbon nanotubes(CNT)with high specific surface area,excellent electrical and mechanical properties as the main electrode material in this thesis.CNT composite electrodes with high-rate performance,high capacitance and low temperature tolerance were obtained by in-situ growth and self-assembly methods,respectively.The influences of the electrode orientation structure and the three-dimensional open structure on the rate performance,capacitance and low temperature performance were revealed.The main research contents are as follows:(1)The high-purity aligned CNTs were prepared by the water-assisted chemical vapor deposition method,and the electrochemical performances of the aligned CNT electrodes in organic electrolyte were tested.Their morphology and structure were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman spectroscopy and other characterization methods.By comparing with the electrochemical performances,morphology and structure of disordered CNT films,the influence of the orientation structure of CNT electrodes on the rate performance was analyzed.The aligned CNT based supercapacitors showed excellent performance at low temperatures.A high energy density of 43 Wh kg^-1 and a high power density of 40 k W kg^-1 at-50? were obtained.(2)The MnO₂/aligned CNT composite electrodes were prepared by the electrochemical deposition method,and the electrochemical performances of the electrodes in aqueous and organic electrolyte were tested,respectively.Their morphology and structure were characterized by SEM,Raman spectroscopy,X-ray diffraction(XRD)and other characterization methods.By comparing with the electrochemical performance,morphology and structure of MnO₂/nickel foam electrode,the inherent reasons for the high-rate performance and high capacitance of the MnO₂/aligned CNT composite electrodes were analyzed.The relationship between the mass loading and the capacitance of MnO₂/aligned CNT composite electrodes were studied,and a high area capacitance of 5.05 F cm^-2 was finally obtained with a high mass loading of 25 mg cm^-2.However,the MnO₂/aligned CNT based supercapacitors showed poor low temperature performance.(3)The Ti₃C₂/knotted CNT composite electrodes were prepared by the self-assembly method,and the electrochemical performances of the electrodes in the organic electrolyte were tested.Their morphology and structure were characterized by SEM,XRD,X-ray photoelectron spectroscopy and other characterization methods.The influences of the three-dimensional open structure of the composite electrodes on the capacitance and rate performance were revealed.By adjusting the CNT contents(5%to 34%),the relationship between the CNT contents and the capacitance and rate performance of the Ti₃C₂/knotted CNT composite electrodes was clarified.The asymmetric supercapacitors based on Ti₃C₂/knotted CNT composite electrodes showed excellent performance at low temperatures.A maximum voltage of the supercapacitors based on two-dimensional materials was obtained(4.2 V),and a high energy density of 59 Wh kg^-1 and a high power density of 9.6 kW kg^-1 at-30? were obtained.