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 sulfite (ES) was investigated by temperature programmed desorption or decomposition–gas chromatography/mass spectrometry (TPD–GC/MS), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and chemical analysis in order to analyze the detailed structure of the SEI. It was proved that 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 lithium occurs, the organic SEI was formed later. On the other hand, at a low current density, the SEI composed of only an organic component was immediately formed from the starting potential (1.5 V versus Li/Li+). As a result, it has become clear that the SEI created by the additive at the initial stage of the potential suppressed the reductive decomposition of PC and plays an important role in the effective SEI formation for intercalation.