A route towards understanding the kinetic processes of bis(trifluoromethanesulfonyl) imide anion intercalation into graphite for dual-ion batteries

Even though lithium ion batteries are the state-of-the-art battery technology for numerous applications, there is extensive research on alternative battery technologies. Dual-ion batteries (DIBs) and in particular their all carbon/graphite versions, the dual-carbon (DCBs) and dual-graphite batteries (DGBs), have emerged as an upcoming and alternative approach for stationary energy storage systems. However, there are still fundamental electrochemical processes during charge and discharge operation of DIBs not fully understood so far. In this work, the kinetic processes during bis(trifluoromethanesulfonyl) imide (TFSI) anion intercalation into graphitic carbon, that proceeds by stage formation, are discussed in detail. The computational calculation of structural parameters of TFSI-graphite intercalation compounds (TFSI-GICs) indicates a possible maximum specific capacity of 140 mAh g(-1) and a walking-like diffusion of the TFSI anion within the graphite lattice. Moreover, a particular focus is set on understanding the overpotential generation during the charge process and its correlation to different specific capacities for varying graphite particle sizes and operating temperatures. In this context, a mechanism, supported by electrochemical and computational experiments, is proposed explaining the overpotential evolution on the basis of (apparent) anion diffusion coefficients in graphite. Temporarily higher (apparent) diffusion activation energies close to filled stages seem to be responsible for temporarily lower (apparent) diffusion coefficients and, thus, for the evolution of additional overpotentials during intercalation. (c) 2018 Elsevier Ltd. All rights reserved.