Preparation And Electrochemical Properties Of Nanostructured Electrode Materials For Supercapacitors

Supercapacitors have the merits of very high power density, extremely stable cycle life, long shelf life, high efficiency, wide range of operating temperatures, safety, environmental friendliness and therefore can be used as an energy storage devices for the supplementary power sources for EVs and HEVs. In recent years, the huge progress in nanoscience and nanotechnology has provided an impetus for the development of new supercapacitor electrode structures. The small size can significantly enhance the utilization of active materials and shorten the transport path of ion and electron. However, single-phased nanomaterials are still insufficient in performance because of their intrinsic weaker material properties in conductivity, cycling stability and mechanical stability in despite making them in the form of nanomaterials. As a result, an advanced approach is to hybridize the electrode materials by adding electrochemically active structured metal oxide materials to conductive carbon or metal matrix. In this configuration, each component is tailored to meet different demands, e.g. high energy density, and high conductivity. The resulting materials exhibit synergistic properties by integrating the individual components, not only increase the utilization of the active materials, but also improve the electrical conductivity and mechanical strength of the composite materials, greatly enhance the supercapacitive performance.The thesis can be mainly divided into the following three parts:(1) We have utilized a commercial resin after the adsorbtion of hexavalent chromium as a precursor to prepare carbon possessing very high graphite degree and very large specific surface area, and successfully converted the high toxic Cr6+into Cr3+with very low toxicity. Being tested as electrode for symmetric capacitors, the Cr-treated sample displays high specific capacitance, very stable lifespan, and particularly excellent rate capability.(2) MnO2/carbon composites have been synthesized using a self-limiting growth method. The generated nanowire structure MnO2 uniform growth in the Cr-treated carbon matrix. MnO2content of the product is controlled by controlling the reaction time. The specific capacitance of the composites increased with the MnO2loading; the conductivity measured by electrochemical impedance spectroscopy, on the other hand, decreased with increasing MnO2loading. Optimization of the MnO2loading resulted in composites with high specific capacitance and excellent rate capability.(3) A facile ammonia solvent thermal method is developed for large-scale growth of spinel nickel cobaltite (NiCo2O4) nanoneedles on conductive nickel foam, the as-prepared sample are directly served as binder-and conductive-agent-free electrodes for supercapacitors. Benefi-ting from the rational structural features, the NiCo2O4nanoneedles on Ni foam electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance and excellent rate capability.