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Nonadiabatic Effects in Raman Spectra of AlCl4− -graphite Based Batteries

Raman spectroscopy is one of the most valuable experimental techniques for quality assessment and structural characterization of sample materials. As such, it has been applied to understand the mechanism of the staging of anions and cations into graphite-based electrodes in a variety of energy storage devices such as Al batteries, dual-ion cells, and Li-ion batteries. However, the correlation between the Raman peaks and intercalation stages is still unclear in most of these systems. This is due to the fact that the modeling of electron-phonon coupling in highly doped graphite systems is beyond the standard Born-Oppenheimer approximation. Here, we simulate the Raman peaks for AlCl−4-intercalated graphite in Al batteries by using a nonadiabatic coupling theory. Specifically, we successfully correlate the Raman peaks of the G phonon in AlCl−4-doped graphite with experiment for intercalation stages 1, 2, and 4, while stage 3 appears to be absent. Stages 1 and 2 have not been observed in experimental XRD patterns. We therefore believe that the AlCl−4-graphite intercalation compound has a core-shell structure with a maximum stage of 4 or 3 in the core and 2 or 1 in the shell. In addition, the observed intense narrow Raman bands for the Al-ion battery cathode are due to the high level of graphite doping and are explained in terms of low electron-phonon decay rates.

electron-phonon coupling, graphite, batteries, dynamical effects, DFT

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