| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 105 === We prepare a lithium hybrid ion capacitor, consisting of a negative electrode of CNT/Sb2O3 composite, activated carbon positive electrode, LiPF6/DEC:EC:DMC electrolyte, and try to measure its capability of energy storage.
The research efforts are focused on modification of the negative electrode, in which one-dimensional CNT has been oxidized and electroless plating antimony trioxide. The CNT surface is essentially hydrophobic, coating of antimony trioxide cannot be done homogeneously over the entire CNT assembly without oxidizing the CNT surface. On the other hand, if the CNT surface is oxidized excessively, the electrical conductivity of CNT shall be degraded.
XRD shows that peaks of CNT and antimony trioxide are both appeared, which means the electroless plating antimony trioxide on CNT surface is successful. SEM images indicate the antimony trioxide wrap the nanotube up and also suspend among the nanotube crosses.
The so-prepared two different mass ratio of CNT and antimony trioxide negative electrodes exhibit huge capacity, 1012/995 mAh g-1 in the first discharge cycle, 500/450 mAh g-1 in the second cycle, and 450/430 mAh g-1 in the third cycle. The high irreversible capacity indicates that not all lithium antimony alloy involves in the charge process. The sample with high ratio of antimony trioxide seems to have better reversibility than less ratio sample.
The energy and power densities of the lithium hybrid ion capacitor are measured with a mass ratio of 2:1 for positive and negative electrodes. The capacitor which contains high ratio of antimony trioxide negative electrode shows higher energy density 88.5 Wh kg-1 at 0.1 A g-1. However, the capacitor with less ratio of antimony trioxide negative electrode has higher power density 5.7 kW kg-1 at 3.0 A g-1. At current density 0.1 A g-1, the two kinds of capacitors demonstrate 53.2 F g-1 and 51.7 F g-1.
Lithiation and delithiation is an intrinsically slow process, determining the charge/discharge rate of capacitor. Hence the capacitor equipped with CNT/Sb2O3 negative is righteously operated at low current densities.
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