| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 100 === We have investigated preparation and properties of three miniaturized ultracapacitors with different working potential windows, which are governed by the commercial available electrolytes of 1M LiPF6,EC:DMC=1:1(v/v) organic electrolyte, PVdF-HFP-based gel electrolyte, and 1M TEABF4/PC ionic liquid. The three ultracapacitors are featured with interdigital electrodes of vertically aligned carbon nanotubes (CNTs), patterned and grown using the standard technologies of photolithography and chemical vapor deposition. The comb-like electrodes of 20 μm spacing, denoted as CNT_CNTx, are later sputtered with gold, inverted, and transferred to a plastic tape, which allows the capacitor be integrated with flexible electronics. We further measured the electrochemical properties using using cyclic voltammetry, impedance spectroscopy, galvanostatic charge/ discharge test, and stability test.
With the organic electrolyte of 1M LiPF6,EC:DMC=1:1(v/v), the symmetric capacitor CNT_CNTo can be operated in a wide potential window 4.0 V. And the sufficient ion conductivity of this electrolyte gives a minimum equivalent series resistance (ESR) 1.53 ? cm2. Combination of wide potential window and conductive electrolyte makes possible the best performance of CNT_CNTo. At a current density of 30 Ag-1 and a window 4.0 V, the CNT_CNTo cell discharges at a power level 57.5 kWkg-1 with energy density 19.7 Wh kg-1. The interdigital CNT electrodes in the PVdF-HFP-based gel electrolyte can also be operated in the potential widow 4.0 V, but the ESR value of this capacitor CNT_CNTg is slightly higher, 1.97 ? cm2. Although the resistance of gel electrolyte is slightly larger, but the gel has the advantage of preventing the probable short circuiting between two opposing CNT electrodes. The cell CNT_CNTg, at current density of 30 Ag-1 and a window 4.0V, discharges at a power level 55.5 kWkg-1 with energy density 16.5 Wh kg-1. The potential window of 1M TEABF4/PC ionic liquid of CNT_CNTi is 2.8 V, which is relatively narrow compared with the other two capacitors. And the ESR value of CNT_CNTi is also higher, 2.45 ? cm2. Hence its capacitor power and energy densities are inferior to those of the previous two cells. The CNT_CNTi cell, at current density 10 A g-1 and a window 2.8 V, discharges at a power level 15.2 kWkg-1 with energy density 2.0 Wh kg-1.
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