Raman spectrometry measurements for the 2D mapping of the degradation products on aged graphite anodes of cylindrical Li-ion battery cells

Abstract

Here, Raman spectroscopy is shown to be a suitable method for post-mortem analysis to localize and identify degradation products on the surface of Li-ion battery electrode layers. Cylindrical battery cells are charged and discharged at 4° C for up to 250 cycles. The degradation products detected on the surface of graphite anodes are shown in 2D Raman mapping and discussed. The battery cells were cycled in an argon-filled glove box. The air-sensitive electrode layers were covered on both sides with coverslips transparent to the Raman laser to keep them without coming into contact with air during the measurements. The LiFePO4 cathode showed no detectable degradation during the aging process. The vibrations of lithium acetylide species (Li-C≡C-X) at 1850 cm−1 are used to detect lithium-containing degradation products on the surface of graphite anodes. Vibrational modes corresponding to polyacetylene at 1118 and 1497 cm−1 were observed for the first time on the aged graphite layers. The described analytical method and electrode preparation are particularly relevant for the identification and localization of degradation products on environmentally sensitive electrodes of Li-ion battery cells.