(591b) Impurities in a Room-Temperature Ionic Liquid for Supercapacitors: Friend or Foe?

Recent years have witnessed growing interests in both the fundamentals and applications of electric double layer capacitors (EDLCs), also known as supercapacitors. A number of strategies have been explored to optimize the device performance in terms of both the energy and power densities. Because the properties of electric double layers (EDLs) are sensitive to the ion distributions in the close vicinity of the electrode surfaces, the supercapacitor performance can be easily altered in the presence of impurity. In this work, we study the impurity effects on EDLC performance using a coarse-grained model of room-temperature ionic liquids (RTILs) and the classical density functional theory (CDFT). The theoretical investigation is focused on the generic features of impurity molecules, such as the molecular size, polarity, self-interaction energy, and binding affinities with the electrode surface and surrounding ions. We identify key parameters controlling both positive and detrimental influences of impurity on ionic distribution as well as the energy storage in porous electrodes. The theoretical predictions provide insights for the impurity behavior at the electrolyte/electrode interface and, more important, useful guidance for formulation of additives to boost supercapacitor performance.