Lithium Insertion into Graphitic Carbon Observed via Operando Kerr-Gated Raman Spectroscopy Enables High State of Charge Diagnostics

Monitoring the precise lithium inventory of the graphitic carbon electrode within the Li-ion battery, in order to assess cell aging, has remained challenging. Herein, operando electrochemical Kerr-gated Raman spectroscopy measurements on microcrystalline graphite during complete lithium insertion and extraction are reported and compared to conventional continuous-wave Raman microscopy. Suppression of the fluorescence emission signals via use of the Kerr gate enabled the measurement of the Raman graphitic bands of highly lithiated graphite where 0.5 ≤ x ≤ 1 for Li _x C₆. The broad graphitic band initially centered at ca. 1590 cm^-1 for Li_0.5C₆ linearly shifted to ca. 1564 cm^-1 with further lithiation to LiC₆, thus offering a sensitive diagnostic tool to interrogate high states of charge of graphitic carbon-based negative electrodes.