An additive in the trimethyl phosphate (TMP)-based non-flammable electrolyte was investigated in order to improve the poor reductive stability for the graphite anode. We found that the charge-discharge characteristic of the TMP-based non-flammable electrolyte was improved by adding ethylene ethyl phosphate (EEP) which had function of non-flammability. The solid electrolyte interface (SEI) layers formed on the graphite anode were analyzed with X-ray photoelectron spectroscopy (XPS) and Fourier transformation type infrared spectroscopy (FT-IR). Moreover, evolved gases in the battery were analyzed with gas chromatography/mass spectrometry (GUMS) to understand the electro-chemical reaction in SEI formation. We concluded that the SEI layers including phosphorus created by the EEP additive suppressed the reductive decomposition of TMP. (C) 2003 Published by Elsevier Science B.V.