Electrochemical Raman study of edge plane graphite negative-electrodes in electrolytes containing trialkyl phosphoric ester

Abstract

Structural changes in the surface of edge plane graphite electrodes were studied in ethylene carbonate-based electrolytes containing a flame-retardant solvent of trialkyl phosphoric ester by electrochemical Raman spectroscopy. In the Raman spectra, a band that peaked at around 1595cm−1, which was assigned to an E band, was observed at potentials below about 0.9V in trimethyl phosphate (TMP)-containing electrolyte solution. After potential cycling between 3.0 and 0.01V, several pieces of exfoliated graphite sheets were seen in the electrochemical Raman cell. On the other hand, these were not observed in triethyl phosphate (TEP)-containing electrolyte. These results indicate that TMP, unlike TEP, is co-intercalated with lithium ion into graphite, and this should lead to the observed exfoliation of graphite layers. Variation of the Raman shifts of TMP and TEP with the electrolyte composition was also investigated to discuss their different solvating abilities.