In-operando Raman study of lithium plating on graphite electrodes of lithium ion batteries

In-operando Raman spectroscopy with high spatial resolution (1 µm2) was employed to study the lithium deposition reaction on graphite electrodes. The 1850 cm−1 acetylide band, which is always found on lithium metal spectra, appeared right after reaching the full lithiation of graphite, when the G and D bands of graphite vanished. The band was observed during potestiostatic overcharge at high and low current rates and in a post-mortem analysis. The results suggest that during the constant voltage step, lithium is deposited and concurrently chemically intercalated into graphite. The second mechanism becomes the dominant after 30 min, when the current decreases. The evolution of the G and D bands of graphite and the lithium concentration in the electrolyte was also studied. The results suggest that EC is slowly consumed after the onset of lithium plating. This work demonstrates the possibility of studying locally the lithium plating onset and chemical intercalation on the graphite electrodes in real time.