(361c) Nanostructured Surfactant Ionic Liquids with Unusually High Capacitances for High-Temperature Flexible Supercapacitors

We report a new class of electrolytes, surfactant ionic liquids (SILs), that give rise to unprecedentedly high intrinsic areal capacitances (~100 to 200 µF/cm²), much larger than the values (~5 to 20 µF/cm²) of other known ionic liquids (ILs) based on smaller anions as well as commonly used aqueous/organic electrolytes. Such high capacitances can probably be attributed to an increased molecular structuring at the nanometer scale due to the presence of large non-polar alkyl chains and charged heads in these fluids. We demonstrate that extremely high gravimetric/volumetric capacitances can be achieved by combining SILs with proper porous electrodes with high surface areas. Due to the extremely wide potential working windows of ILs (~ 4 to 5 V), we show that the SIL-based devices exhibit ultrahigh energy densities. In addition, the SIL-based devices show an increasing capacitance with higher temperatures, which highlights another unique advantage of SILs, which is the suitability for operation at extremely high temperature (~200 ^oC), with myriad niche applications such as powering sensors and actuators for oil industry downhole operations (above 120 ^oC), electronics in hybrid electric vehicles (HEV, >60 ^oC), or military weapons and space equipment. Furthermore, we demonstrate that SILs can be easily polymerized to generate a quasi-solid yet flexible gel-like structure, as well as form seamless binding with current collectors/porous electrodes, for the development of next-generation solid-state highly flexible energy devices.