In situ X-ray Diffraction Studies of Cation and Anion Intercalation into Graphitic Carbons for Electrochemical Energy Storage Applications

Graphite is a redox-amphoteric intercalation host and thus capable to incorporate various types of cations and anions between its planar graphene sheets to form so-called donor-type or acceptor-type graphite intercalation compounds (GICs) by electrochemical intercalation at specific potentials. While the LiCx/C-x donor-type redox couple is the major active compound for state-of-the-art negative electrodes in lithium-ion batteries, acceptor-type GICs were proposed for positive electrodes in the dual-ion and dual-graphite cell, another type of electrochemical energy storage system. In this contribution, we analyze the electrochemical intercalation of different anions, such as bis(tri-fluoromethanesulfonyl)imide or hexafluorophosphate, into graphitic carbons by means of in situ X-ray diffraction (XRD). In general, the characterization of battery electrode materials by in situ XRD is an important technique to study structural and compositional changes upon insertion and de-insertion processes during charge/discharge cycling. We discuss anion (X-) and cation (M+) intercalation/de-intercalation into graphites on a comparative basis with respect to the Mx+Cn and Cn+Xn- stoichiometry, discharge capacity, the intercalant gallery height/gallery expansion and the M-M or X-X in-plane distances.