High performance supercapacitor under extremely low environmental temperature

Supercapacitors with a broad operational temperature range, especially with the capability of operating at low temperature (below -50 degrees C), are required for applications in extreme environments. This paper presents a high performance supercapacitor, consisting of highly aligned nano-porous graphene (A-NPG) with an eutectic mixture of ionic liquids (ILs), 1-butyl-4-methylpyridinium tetrafluoroborate (BMPBF4) in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), which exhibits a high capacitance performance over a temperature range from -50 degrees C to 80 degrees C. The experimental results reveal a reducing of melting temperature T-m of the eutectic mixture to -74 degrees C, compared with -39 degrees C of BMIBF4. The increased ionic conductivity and reduced T-m of the eutectic mixture, combined with ultrahigh density A-NPG electrodes, enable the supercapacitor to show a high capacitance of 125 F cm(-3) at room temperature and 106 F cm(-3) at -50 degrees C. In contrast, the supercapacitor with pure BMIBF4 shows a capacitance of 119 F cm(-3) and 16.5 F cm(-3) at room temperature and -50 degrees C, respectively.