Journal of Power Sources, Vol.276, 299-308, 2015
How does lithium oxalyldifluoroborate enable the compatibility of ionic liquids and carbon-based capacitors?
Lithium oxalyldifluoroborate (LiODFB) has several unique characteristics, such as high ionic conductivity over a wide temperature range and the ability to form and stabilize solid electrolyte interface films on graphite surfaces. A series of binary, room-temperature, molten electrolytes composed of LiODFB and organic compounds with acylamino groups (acetamide, oxazolidinone or OZO) have been synthesized. Fourier-transform infrared (FT-IR) spectroscopy indicates that C=O and N-H functional groups undergo blue or red shifts upon addition of LiODFB. The electrolytes have excellent thermal stabilities and electrochemical characteristics that allow them to be promising electrolytes for electrochemical double layer capacitors (EDLCs). Here, we examine 1:5 molar ratio LiODFB and acetamide/OZO ionic liquid (IL) electrolytes in EDLCs. IL compatibility with two types of carbon-based electrodes is investigated theoretically and experimentally. We simulate possible structures and ion diameters for the ILs, which must be compatible with pore sizes of the carbon electrodes. Mesoporous activated carbon AC2, with a pore size similar to the ionic diameter of LiODFB acetamide, has a specific capacitance of 154.2 Fg(-1) at 20 m Ag-1. Additionally, typical capacitive and reversibility behaviors can be seen in the charge discharge curves over 0-2 V. Finally, the EDLCs exhibit good charging/discharging performances. (C) 2014 Elsevier B.V. All rights reserved.