Monitoring electrode/electrolyte interfaces of Li-ion batteries under working conditions: A surface-enhanced Raman spectroscopic study on LiCoO2 composite cathodes

Lithium-ion batteries are commonly used for electrical energy storage in portable devices and are promising systems for large-scale energy storage. However, their application is still limited due to electrode degradation and stability issues. To enhance the fundamental understanding of electrode degradation we report on the Raman spectroscopic characterization of LiCoO2 cathode materials of working Li-ion batteries. To facilitate the spectroscopic analysis of the SEI (solid electrolyte interface) we apply surface-enhanced Raman spectroscopy by using Au nanoparticles coated with a thin SiO2 layer (Au@SiO2). We observe a surface-enhanced Raman signal of Li2CO3 at 1090 cm-1 during electrochemical cycling as an intermediate. Its formation/decomposition highlights the role of Li2CO3 as a component of the SEI on LiCoO2 composite cathodes. Our results demonstrate the potential of Raman spectroscopy to monitor electrode/electrolyte interfaces of lithium-ion batteries under working conditions thus allowing relations between electrochemical performance and structural changes to be established.