| Summary: | 碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 101 === Asymmetric supercapacitor has the dual functions of the persuade-capacitor and the electrochemical double-layer capacitor, which has the advantages of energy density and high power density. Thus, the research of asymmetric supercapacitor is a hot topic developed in both academic and industrial fields.
In this thesis, MnO2 were synthesized by hydrothermal method, respectively. The effects of the microstructures on the MnO2 electrochemical performances were also investigated. The results indicate that the electrochemical performances of the δ-MnO2 are better than those of the α-MnO2, the maximum specific capacitance of the former is 265 F/g, but those of the latter is 120 F/g. Additionally, the specific capacitance is decreased about 18% of initial capacitance after 5000 cycles.
Nano-scale of polyacrylonitrile (PAN) fiber was prepared using electrospinning method, and then stabilization and carbonization were preformed. The effect of different carbonization temperatures and the additional CNTs on the electrochemical performances were investigated. According to characterization results of CV and GV test, the optimal conditions were added by 3% CNT with 750oC carbonization for 2 hr. The specific capacitance of the 3%CNTs-CNFs is 272 F/g in acidic solution and129 F/g in neutral solution. The specific capacitance after 5000 cycles keeps constant.
The asymmetric supercapacitor, whose positive electrode is δ-MnO2 and negative electrodes is 3%CNTs-CNFs, show working voltage of 2 V, and the specific energy of 56.7 Wh/kg at a current density of 0.1 A/g. It also keeps good cycling performance of 92% after 5000 cycles.
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