De‐intercalation process from Stage‐1 to Stage‐2 graphite intercalation compounds revisited

Abstract

AbstractThe identification and contribution of the different phonons present in the G‐line Raman response in Stage‐1 and Stage‐2 graphite intercalation compounds (GIC) is crucial for a correct stage determination. Different factors like laser induced de‐intercalation play an important role in the precise stage assignment of these phases, and their intrinsic Raman response. In this contribution, an in situ micro‐Raman analysis was conducted under high‐vacuum conditions. Local heating of the samples was induced by using a high laser power (8.5 mW) in order to study the de‐intercalation process from Stage‐1 to Stage‐2 GICs. A detailed Raman line‐shape analysis was performed from the recorded spectra to determine the changes from the G‐line response of KC8, CaC6, and LiC6. We confirmed the assignment of the broad E2g Fano mode at ∼1510 cm−1 to the intrinsic Stage‐1 Raman response in GICs. Additionally, the most evident change from Stage‐1 to Stage‐2 was observed in an asymmetric Fano mode in the range of 1565–1610 cm−1. This mode is linked to the first‐order stretching Raman mode of Graphite, which tends to increase in frequency and decrease in width as function of de‐intercalation. Finally, the response of the Stage‐2 phase after de‐intercalation was confirmed to be a useful benchmark for the identification of the intercalation stage in highly doped GICs.