Study of the Electrochemical Behavior of Dual-Graphite Cells Using Ionic Liquid-Based Electrolytes

Abstract

Dual-ion cells based on the anion intercalation into a graphite positive electrode have been proposed as electrochemical energy storage devices. In this set-up, the electrolyte, in this case a mixture of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr14TFSI) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) acts not only as charge carrier, but also as active material. Since the compatibility of this ionic liquid-based electrolyte mixture with graphitic anodes is relatively poor and not sufficient, the selection of the anode materials for the dual-ion system was limited to metallic lithium or Li4Ti5O12 so far. In this work, we present promising results concerning the use of graphite as both the anode and cathode material in a so-called “dual-graphite cell”. The Pyr14TFSI-LiTFSI ionic liquid electrolyte is used in combination with the SEI-forming additive ethylene sulfite (ES) and allows a stable and highly reversible lithium ion and TFSI- anion intercalation/de-intercalation into the graphite anode and cathode, respectively.