In situ Raman spectroscopy of insertion electrodes for lithium-ion batteries and supercapacitors: First cycle effects

In situ Raman spectroscopy was used to demonstrate ion intercalation into microcrystalline graphite (KS44) during cyclic voltammetry experiments from the ionic liquid 1-ethyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)-imide (EMI-TFSI). This was seen by a split of the G-band (1578 cm−1) into the E2g2(i) band at 1578 cm−1 and E2g2(b) band at 1600 cm−1, which occurred below +1.0 V for EMI+ and above +4.65 V vs. Li/Li+ for TFSI−. Moreover, ion intercalation was seen to cause irreversible structural changes to the graphitic lattice. The Raman spectrum of activated carbon (Picactif) exhibits broad G- and D-bands around 1587 and 1315 cm−1, respectively. Changes were observed during potential cycling in 1 mol dm−3 tetraethylammonium-tetrafluoroborate (TEABF4) in acetonitrile that concerned only changes in Raman intensity and shifts in wavenumber of both D- and G-bands. It is hypothesised that the D-band could be composed of two contributions reflecting the D-band of crystalline domains and of cross-linkers. After ion insertion, the contribution from stacked sheets maybe lost, resulting in a wavenumber shift of the band.