Influence of Graphite Characteristics on the Electrochemical Performance in Alkylcarbonate LiTFSI Electrolyte for Li-Ion Capacitors and Li-Ion Batteries

This work presents the influence of some graphite physico-chemical characteristics such as morphology, structure, textural properties, surface functionality and active surface area (ASA) on the electrochemical performance. The reversible and irreversible capacities, SET formation at different charging rates, cycling ability have been determined using alkylcarbonate based electrolytes containing LiTFSI as main salt. Three families of graphites have been investigated by SEM, XRD, N-2 adsorption, Temperature Programmed Desorption (TPD-MS), and their physico-chemical properties have been correlated to some extent to their electrochemical performances. The irreversible capacity at first cycle increases with the active surface area (ASA) and the specific surface area. The applied current density plays an important role in the SET formation as shown by the reversible and irreversible capacities and the SEM observations. The passivation layer is mainly formed by polymeric species along with inorganic salts such as Li2CO3 or Li alkylcarbonates (ROLi) as revealed by XPS measurements. Nevertheless, very small quantities of LiTFSI degradation compounds have been detected (LiF, SOx) along with a reversible capacity fade. (C) 2013 The Electrochemical Society. All rights reserved.