Abstract
Imidazolium-Based Ionic Liquids in Graphene-Capped Liquid Cells Probed by Synchrotron Infrared Nanospectroscopy: Insights into Electric Double Layers for Advanced Energy Storage
Electrical double layer capacitors (EDLCs) are prominent energy storage devices owing to their advantages such as rapid charge/discharge processes, extremely long cycle life, and environmental and safety benefits. However, the generally low energy density of EDLCs hinders their broad application. A major strategy to improve the energy density of EDLCs involves employing electrolytes capable of withstanding high operation voltages. Ionic liquids (ILs) are a novel class of electrolytes typically composed of asymmetric organic cations and weakly coordinated anions. They appear to be ideal candidates to replace the diluted aqueous and organic electrolytes in traditional EDLCs for their wide electrochemical windows, which enable operation voltages much higher than conventional EDLCs and thus significantly improve the energy density. Moreover, the unique properties of ILs, including high thermal stability, non-flammability, high charge density, as well as their distinct EDL structure with oscillating ion concentration, not only make them safe and environmentally friendly electrolytes for EDLCs, but also present great potential for superior performance to traditional electrolytes. The implementation of ILs as electrolytes in EDLCs for enhanced performance is contingent upon understanding the behaviors of IL EDLs, a knowledge gap that exists thus far. Here, we incorporate ILs in custom-made graphene liquid cells and perform synchrotron infrared nanospectroscopy (SINS) to investigate IL EDLs interfaced with graphene electrodes, complemented by density functional theory (DFT) analysis and electrochemical evaluation. This approach correlates the chemical characterization and vibrational response of IL EDLs with their nanoscale ion ordering and displacement under electrochemical conditions, enabling in-depth observations of IL EDLs that were previously unattainable. Insights into IL EDL behaviors highlight the dependence of capacitive performance on the molecular-level ion dynamics decided by IL chemical structures, thereby guiding the design of next-generation EDLCs employing novel IL-based electrolytes.
Biography
Dr. Zixuan Li is an assistant professor in the Department of Physics and Astronomy at Hunter College of the City University of New York. He earned his B.S. in Optical Information Science and Technology from Sun Yat-sen University and his M.S.E. in Materials Science and Engineering from the University of Pennsylvania. He received his Ph.D. degree in Materials Science and Engineering from the University of Texas at Austin. Prior to joining Hunter, Dr. Li was a postdoctoral scholar in the Advanced Light Source (ALS) Division at Lawrence Berkeley National Laboratory (LBL). Dr. Li’s research focuses on using spectromicroscopy techniques to elucidate fundamental phenomena at liquid/solid interfaces, with the aim of enhancing the functional properties of interface-based devices across energy storage, microelectronics, and quantum information technologies.