TPD-GC/MS analysis of the solid electrolyte interface (SEI) on a graphite anode in the propylene carbonate/ethylene sulfite electrolyte system for lithium batteries

The solid electrolyte interface (SEI) formed on a graphite electrode in the electrolyte system consisting of propylene carbonate (PC) and ethylene sul fite (ES) was investigated by temperature programmed desorption or decompos ition-gas chromatography/mass spectrometry (TPD-GC/MS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and chemical analy sis in order to analyze the detailed structure of the SEI. It was proved th at a lithium-oxy-sulfite film (Li2SO3 and/or ROSO2Li) was generated by the reductive decomposition of ES in advance of the decomposition of PC and the structure of the SEI structure significantly depends upon current density. In case of the high current density, the inorganic SEI was first formed at high potential and, around the potential where the intercalation of lithiu m occurs, the organic SEI was formed later. On the other hand, at a low cur rent density, the SEI composed of only an organic component was immediately formed from the starting potential (1.5 V versus Li/Li+). Asa result, it h as become clear that the SEI created by the additive at the initial stage o f the potential suppressed the reductive decomposition of PC and plays an i mportant role in the effective SEI formation for intercalation. (C) 2001 El sevier Science B.V. All rights reserved.