In situ Raman microscopy of a single graphite microflake electrode in a W-containing electrolyte

Highly detailed Raman spectra from a single KS-44 graphite microflake electrode as a function of the applied potential have been collected in situ using a Raman microscope and a sealed spectroelectrochemical cell isolated from the laboratory environment. Correlations were found between the Raman spectral features and the various Li+ intercalation stages while recording in real time Raman spectra during a linear potential scan from 0.7 V down ca. 0.0 V vs Li/Li+ at a rate of 0.1 mV/s in a 1 M LiClO4 solution in a 1:1 (by volume) ethylene carbonate (EC):diethyl carbonate (DEC) mixture. In particular, clearly defined isosbestic points were observed for data collected in the potential range where the transition between dilute phase I and phase 4 of lithiated graphite is known to occur, i.e., 0.174 less than or equal to E less than or equal to 0.215 V vs Li/Li+. Statistical analysis of the spectroscopic data within this region made it possible to determine independently the fraction of each of the two phases present as a function of potential without relying on coulometric information and then predict, on the basis of proposed stoichiometry for the transition, a spectrally derived voltammetric feature.