| 摘要: | 本研究主要是利用Staudenmaier法製備石墨烯，用來做為超高電容器的電極，電解液則是選用擁有廣大電位窗的離子液體，藉以得到高的能量密度以及功率密度。
首先選用每分鐘1℃升溫到300℃並無持溫的石墨烯 (GNS-300)在不同離子液體內進行比較，使用的離子液體分別為1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMI-NTf2)、N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfony)imide (BMP-NTf2)、1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4)、1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) 以及N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA)，結果顯示在低速充放電下的比電容值與離子液體中的陰離子有關，且在DCA系列的離子液體中具有較佳的比電容值，其中以BMP-DCA的比電容值為最高，約234 F/g左右， 若陰離子相同，在高速充放電下，EMI系列的比電容值皆高於BMP系列的比電容值，但因BMP-DCA的電位窗可達3.3 V，而EMI-DCA只有2.5 V，所以其能量密度 (88.5 Wh/kg)以及功率密度 (17.1 kW/kg)皆高於EMI-DCA，所以便選用BMP-DCA做為電解液。
目前碳材皆以多孔碳材方向發展，但製程皆過於繁複，本研究期望利用簡便的熱還原法，利用不同升溫速率製造孔洞，以及升溫至不同溫度比較含氧官能基對於石墨烯之影響。本研究選用五種碳材在離子液體BMP-DCA中進行比較，石墨烯方面，選用三種情況下製程之石墨烯進行比較，分別是GO放入300 ℃的高溫爐並無持溫 (多孔含氧官能基多石墨烯，HGNS-300)、每分鐘升溫1℃直到300℃並無持溫 (無孔洞含氧官能基多石墨烯，GNS-300)以及每分鐘升溫60℃直到1100℃並無持溫(多孔含氧官能機少石墨烯，HGNS-1100)，另外兩種則分別為活性碳 (Activated carbon)以及多壁奈米碳管 (Multiwalled Carbon Nanotubes)，根據結果顯示，多孔含氧官能基多石墨烯的比電容值高於其他碳材，並且擁有高的比電容值 (327 F/g)、能量密度 (123.7 Wh/kg)以及高的功率密度 (17.3 kW/kg)。兩千圈後維持率仍有79 %。目前超高電容普遍是以活性碳在有機中為主軸，本研究比較多孔含氧官能基多石墨烯以及活性碳在有機溶液TEABF4/PC以及離子液體BMP-DCA的超高電容行為，由結果得知多孔含氧官能基多石墨烯在離子液體BMP-DCA中有最好的超高電容性能。在高溫60 ℃下比較BMP-DCA以及TEABF4/PC，由結果得知高溫下有機溶液性能提升不多，而離子液體的性能大幅提升，其比能量密度由123.7 Wh/kg提升為138.8 Wh/kg，比功率密度則由17.3 kW/kg提升為51.6 kW/kg。
;The graphene sheets were prepared by Staudenmaier method in this study, and were used for the electrode in supercapacitor. We chose ionic liquids as electrolyte for their wide potential window to get better energy density and power density.
First we chose graphene (GNS-300) which is made by raising temperature 1℃ per 1 min to 300°C. We used this GNS-300 to test in different ionic liquids, and compare their properties. The ionic liquids included EMI-NTf2, BMP-NTf2, EMI-BF4, EMI-DCA, and BMP-DCA. The results showed that the specific capacitance at low scan rate was related to the anion of ionic liquids. And the graphene sheets in the DCA-based ionic liquids had the best capacitance performance. In particular, in BMP-DCA, the specific capacitance of graphene sheets was 234 F/g. At high scan rate, EMI-NTf2 and EMI-DCA have higher specific capacitance than BMP-NTf2 and BMP-DCA. But the potential window of graphene sheets in BMP-DCA was 3.3 V, it’s bigger than EMI-DCA, so BMP-DCA can get better enrgy density for 88.5 Wh/kg and power density for 17.1 kW/kg.
In my research, we want to use thermal reduction to change different raising temperature rate and different temperature. We hope that we can get holes and oxygen containing groups to improve graphene’s superapacitor performance. So we choosing five carbon materials to compare in BMP-DCA. We chose three kinds of graphene sheets like HGNS-300 which is made by raising temperature to 300°C directly, GNS-300 which is made by raising temperature to 300°C per 1°C per 1min, and HGNS-1100 which is made by raising temperature to 1100°C per 60°C per 1min. The other carbon materials were activated carbon (AC) and multiwalled carbon nanotubes (MWCNT). The studies showed HGNS-300 had the highest specific capacitance than others because HGNS-300 had holes and many oxygen containing functional group. HGNS-300 had highest specific capacitance of 327 F/g, energy density of 123.7 Wh/kg and power density of 17.3 kW/kg. After 2000 cycles, the retention still have 79 %. Compare HGNS-300 and activated carbon in BMP-DCA and TEABF4/PC, we can get that HGNS-300 in BMP-DCA have best supercapacitor performance. Compare HGNS-300 in BMP-DCA and TEABF4/PC at 60 ℃, the results show that test in BMP-DCA, getting better energy density for 138.8 Wh/kg and power density for 51.6 kW/kg. |
