The in situ electrochemical impedance spectroscopy (in situ EIS) in which the impedance spectra are measured simultaneously with the charge (intercalation)-discharge (deintercalation) sequence of lithium-ion rechargeable batteries has been developed. This method was applied to the investigation of the graphite electrode of lithium-ion rechargeable batteries. The resistance R-sei for lithium-ion permeation in the solid electrolyte interphase (SEI) film were determined, and the formation mechanisms of SEI was discussed. Moreover, the role of vinylene carbonate (VC) as an additive to LiPF6-ethylene carbonate/ethyl methyl carbonate electrolyte solution was investigated. It was clarified that R-sei decreases by the addition of VC, indicating the formation of a high quality SEI film. (C) 2004 Elsevier B.V. All rights reserved.