Charge-Discharge Behavior of Graphite in Propylene Carbonate-Containing Electrolytes

The electrochemical intercalation of lithium-ion into natural graphite cannot take place in propylene carbonate (PC)-based electrolytes. Continuous decomposition of PC, accompanied by the exfoliation of graphite, is observed instead of the intercalation of lithium-ion. One of the plausible hypotheses to explain this behavior is that PC-solvated lithium-ion intercalates into graphite during the first charge, resulting in the exfoliation of graphite. Therefore, we consider that the solvation structure of lithium-ion in PC-based electrolytes should strongly influence the charge-discharge behavior of natural graphite.

We studied the charge-discharge properties of natural graphite in binary electrolytes consisting of PC and dimethyl carbonate (DMC) with various mixing ratios. The average solvation numbers of PC molecules per lithium-ion (N_PC,ave) in PC:DMC binary electrolytes were evaluated with Raman spectroscopy. We examined the correlation between the solvation number of PC molecules and the charge-discharge behavior of natural graphite and discuss the mechanism of the exfoliation of graphite.