| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 95 === Cycle stability of MnO2·nH2O electrochemical capacitors has been studied by using chronopotentiometry tests, electrochemical impedance spectroscopy (EIS), and inductively coupled plasma-atomic emission spectrometer (ICP-AES). The extent of capacity fading, ranging from ~30 % to < 5 % in 1000 cycles, increases with current-rate and is markedly reduced with increasing binder content. Two fading mechanisms have been identified. With low binder content and at high current-rate, capacity fading occurs in conjunction with appreciable increase in transmission resistance, suggesting progressively deteriorating electric contacts among the pseudocapacitve oxide particles and conductive carbon. The mechanical failure of the electrode structure may arise from the cyclic volumetric variation of the pseudocapacitive oxide particles. On the other hand, increasing interfacial charge-transfer resistance upon cycling has been found to play an important role in capacity fading at low current-rate. In addition, there are two effective ways to suppress capacity fading under high specific charge/discharge current density. One is to use plenty of binder to strengthen the overall structure of the electrode. The other is to use Styrene-butadiene rubber (SBR) to replace Polyvinylidene difluoride (PVdF) as binder component. SBR binder bonded between the oxide particles is rapider to deform in response to the volume change of the oxide particles without introducing excessive stress at the binder-particle interface. Hence, the cycling stability of MnO2·nH2O electrochemical capacitors can be enhanced.
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