Analysis of Vinylene Carbonate Derived SEI Layers on Graphite Anode

The solid electrolyte interface (SEI) formation on composite graphite and highly oriented pyrolytic graphite in a vinylene carbonate (VC)-containing electrolyte was analyzed using evolved gas analysis, Fourier transform infrared analysis, two-dimensional nuclear magnetic resonance, X-ray photoelectron spectroscopy, time of flight-secondary-ion mass spectrometry, and scanning electron microscopy. We found that the SEI layers derived from VC-containing electrolytes consist of polymer species such as poly (vinylene carbonate) (poly(VC)), an oligomer of VC, a ring-opening polymer of VC, and polyacetylene. Moreover, lithium vinylene dicarbonate, lithium divinylene dicarbonate, lithium divinylene dialkoxide, and lithium carboxylate, RCOOLi, were formed on graphite as VC reduction products. The presence of VC in the ethylene carbonate (EC)-based electrolyte caused a decrease in the reductive gases of the EC dimethyl carbonate solvent such as and CO. The VC-derived SEI layer was formed at a potential more positive than 1.0 V vs. Effective SEI formation by reduction of VC progresses before that of EC. The thermal decomposition temperature of the SEI layer derived from VC shifted to a higher temperature compared to that derived from the VC-free electrolytes. We concluded that the thermal stability of the VC-derived SEI layer has a close relation to high-temperature storage characteristics at elevated temperatures. © 2004 The Electrochemical Society. All rights reserved.