| dc.description.abstract | 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. | en_US |