The band forming around 224 cm -1 is an overtone of the I3 -band . At larger Raman shifts, changes in the carbon-related G-and D-band intensity (band width and position) can be observed (Fig. , Supplementary Fig. ). With increasing cell voltage, the widths of the G-and D-modes increase, while they are slightly redand blue-shifted, respectively and the ID-to-IG ratio is lowered. This can be explained by a superposition of charge transfer and an increase of defects , which is qualitatively consistent with ex situ results reported earlier .