Electrochemical Behavior of Nanoporous Supercapacitors with Oligomeric Ionic Liquids

According to a recent study [Matsumoto, M. et al.; J. Am. Chem. Soc. 2017, 139, 16072-16075], an oligomeric ionic liquid (OIL) may exhibit a wide electrochemical window and an exceptionally high capacitance in electric double layer (EDL) transistors. However, little is known on applicability of OILs in EDL capacitors with porous electrodes. To understand the capacitive performance of OILs, here we investigate the charging behavior, EDL structure, and capacitance for different types of OILs using the classical density functional theory. In contrast to their application to field-effect transistors, the capacitive performance of OILs in nanoporous electrodes is sensitive to the charging potential. Although adoption of oligomeric cations shows little advantage for the electrical charging of a positive electrode, they enhance the energy storage density for negative electrodes.