In Situ Raman Microscopy of a Single Graphite Microflake Electrode in a Li +-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 LiClO ₄ 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 1 and phase 4 of lithiated graphite is known to occur, i.e., 0.174 ≤ E ≤ 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.