Origin of graphite exfoliation - An investigation of the important role of solvent cointercalation

To elucidate the origin of graphite exfoliation, we have investigated the influence of various material parameters relevant to solvent co-intercalation, such as the cation, the electrolytic solvents, and the structure of graphite, on the solvent decomposition behavior. By electrochemically probing changes in the electrode, we demonstrated that a large increase of surface area accompanies the decomposition of propylene carbonate (PC). Furthermore. such a change in surface area is dramatically amplified when Li+ is replaced by tetrabutylammonium ion. A slight structural modification of PC exerts a profound influence on the solvent decomposition behavior, as demonstrated with cis- and trans-2.3-butylene carbonate. These reaction behaviors are also altered significantly by the choice of graphite. Such an influence of graphite structure is particularly surprising for t-BC electrolyte, in which SFG44 graphite undergoes extensive exfoliation, whereas SFG6 graphite and MCMB25 can be cycled reversibly. These results can be best explained by incorporating the co-intercalation of cyclic carbonate as a critical process in the solid electrolyte interphase formation mechanism. (C) 2000 The Electrochemical Society.