Spectroscopic Analysis of Surface Layers in Close Contact with Edge Plane Graphite Negative-Electrodes

Abstract

Surface films formed on edge plane pyrolytic graphite negative-electrodes were scraped off by repeated scanning of the surface in contact-mode atomic force microscopy (AFM) until no further changes were observed in AFM images. A very thin surface layer in close contact with the edge plane remained even after repeated scans by AFM. The surface layer could function effectively as a solid electrolyte interphase (SEI) upon the subsequent intercalation and de-intercalation reactions of Li+, in particular when film-forming additives, such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC), were used in electrolyte solutions. The remaining surface layer was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to characterize the SEI.