SEI investigations on copper electrodes after lithium plating with Raman spectroscopy and mass spectrometry

The composition and formation of the SEI which is formed on lithium, which has been electrochemically deposited on a Cu substrate, is investigated by Raman spectroscopy and mass spectrometry. Semicarbonates, Li2CO3 and Li2C2 are identified as SEI components. The existence of Li2C2 is further proven with mass spectrometry by analyzing the gases which are formed by hydrolysis. Raman mapping reveals that Li2CO3 is homogeneously distributed over the copper substrate, on which lithium was deposited. At contrast, Li2C2 is mainly located on the plated lithium. An in situ Raman spectroscopy method for SEI investigation was developed and shows that Li2C2 is not formed at a potential >0 V vs. Li/Li+.

► The SEI on deposited Lithium metal was investigated by Raman and mass spectrometry.
► Li2C2 was detected as one of the main components.
► The distribution of Li2C2 and Li2CO3 on the surface was studied by Raman mapping.
► A special in situ Raman method was developed to investigate the SEI-formation.
► In situ experiments showed that Li2C2 is formed at potentials below 0 V vs. Li/Li+.