The redox-amphoteric character of graphitic carbon makes it possible to intercalate a broad range of anions and cations. These graphite intercalation compounds (GICs) are divided into two types: donor-type GICs, which host cations and acceptor-type GICs, which are formed by anions. A well-known application for a donor-type GIC is lithium-intercalated graphite (LiC₆) as anode material in lithium-ion batteries. Besides this example, also acceptor-type GICs are known as active material in batteries. In this context, Placke et al.¹ presented the “dual-ion cell”, that also deals with anion intercalation into the graphite structure. During charge anions and cations are inserted into the respective electrode and are released back into the electrolyte during discharge. In the charged state the cathode reaches a potential of 5 V (vs. Li/Li⁺). In order to avoid electrolyte degradation, an ionic liquid mixture is chosen as electrolyte. It is composed of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr₁₄TFSI) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI).

The focus of this work is to investigate the influence of different graphite characteristics on the intercalation of the bis(trifluoromethanesulfonyl) imide anion into the graphite structure. For that purpose, nitrogen adsorption measurements were performed in order to determine the porosity of the graphite samples and X-ray diffraction was carried out to identify the crystallite size. Both structural parameters are correlated to the electrochemical performances.

1.            Placke, T.; Bieker, P.; Lux, S. F.; Fromm, O.; Meyer, H. W.; Passerini, S.; Winter, M., Dual-ion cells based on anion intercalation into graphite from ionic liquid-based electrolytes. Zeitschrift für Physikalische Chemie 2012, 226, 391-407.