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

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 (Pyr 14 TFSI) 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 Li 4 Ti 5 O 12 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 Pyr 14 TFSI-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.