Influence of Graphite Characteristics on the Electrochemical Intercalation of Bis(trifluoromethanesulfonyl) imide Anions into a Graphite-Based Cathode

Electrochemical energy storage devices utilizing graphitic carbons as positive electrode material have been proposed as dual-ion cells. In this type of electrochemical cell, the electrolyte does not only act as a charge carrier, but additionally as the active material. In the charge process, lithium ions are inserted/intercalated or deposited into/on the negative electrode, e.g. Li4Ti5O12, graphite or metallic lithium, and the electrolyte anions are intercalated into the graphite positive electrode. In the discharge process, both lithium ions and anions are released back into the electrolyte. We report herein on the intercalation of bis(trifluoromethanesulfonyl) imide anions (TFSI-) into a graphite cathode from an ionic liquid-based, namely N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr(14)TFSI), electrolyte. We studied the influence of the graphite characteristics, such as the particle size distribution, specific surface area and ratio of basal plane to non-basal plane surface areas, on the electrochemical behavior of TFSI- anion intercalation. The rate performance, long-term cycling behavior and stability of dual-ion cells at high temperatures (60 degrees C) are also discussed. A specific discharge capacity exceeding 100 mAh g(-1) can be achieved at discharge rates of up to 10C, when operating at 60 degrees C. (C) 2013 The Electrochemical Society. All rights reserved.