Two-dimensional hetero-spectral Raman/XAS correlation analysis of Li[Ni0.45Co0.18Mn0.25Al0.12]O2 cathode in the overcharged state

We investigated an electrochemical reaction on the cathode surface of an overcharged Li[Ni0.45Co0.18Mn0.25Al0.12]O2/Li system at the molecular level by using Raman, X-ray absorption spectroscopy (XAS), and 2D hetero-spectral correlation analyses. Changes in the Raman spectra during the overcharging process showed that variations in the local atomic environment occurred with increasing extraction of Li+ ions. XAS spectra obtained during the overcharging process showed that oxidized transition metals coexisted with inoxidizable transition metals. Additionally, synchronous 2D hetero-spectral Raman/XAS correlation spectra clearly elucidated the correlation between the Raman and XAS bands, confirming their band assignments.