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

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 1595 cm−1, which was assigned to an E band, was observed at potentials below about 0.9 V in trimethyl phosphate (TMP)-containing electrolyte solution. After potential cycling between 3.0 and 0.01 V, 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.

► The influence of TMP on intercalation reaction of lithium ion at graphite is studied by electrochemical Raman spectroscopy.
► Exfoliated graphite sheets are seen after potential cycling in TMP-containing electrolyte.
► Co-intercalation of TMP with lithium ion occurs at graphite.
► The mechanism of lithium-ion intercalation at graphite is different between TMP- and TEP-containing electrolytes.