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

Abstract 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, Li 2 CO 3 and Li 2 C 2 are identified as SEI components. The existence of Li 2 C 2 is further proven with mass spectrometry by analyzing the gases which are formed by hydrolysis. Raman mapping reveals that Li 2 CO 3 is homogeneously distributed over the copper substrate, on which lithium was deposited. At contrast, Li 2 C 2 is mainly located on the plated lithium. An in situ Raman spectroscopy method for SEI investigation was developed and shows that Li 2 C 2 is not formed at a potential >0 V vs. Li/Li + .