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, (CHOCO 2 Li) 2 , lithium divinylene dicarbonate, (CH=CHOCO 2 Li) 2 , lithium divinylene dialkoxide, (CH=CHOLi) 2 , 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 C 2 H 4 , CH 4 , and CO. The VC-derived SEI layer was formed at a potential more positive than 1.0 V vs. Li/Li + . 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.