Abstract
Compact graphene films were prepared and electrochemically tested at various temperatures in a eutectic of ionic liquid mixture (1:1 by weight or mole N-methyl-N-propylpiperidinium bis(fluorosulfonyl)imide and N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide) electrolyte. A large temperature window from -30 °C to 80 °C was achieved together with a large potential window of 3.5 V at room temperature and below. A maximum gravimetric capacitance of 175 F.g−1 (85 mAh.g−1) was obtained at 80 °C. 130 F.g−1 (63 mAh.g−1) and 100 F.g−1 (49 mAh.g−1) were still delivered at -20 °C and -30 °C respectively. Besides, a volumetric capacitance of 50 F.cm−3 was achieved with a thick graphene film (60 μm). The outstanding performance of such compact graphene film in the eutectic ionic liquid mixture electrolyte makes it a promising alternative to activated carbon for supercapacitor applications, especially under extreme temperature conditions.