To elucidate the mechanism of gas generation during charge–discharge cycling of a lithium-ion cell, the generated gases and passive films on the carbon electrode are examined by means of gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy. In ethyl carbonate/dimethyl carbonate and ethyl carbonate/diethyl carbonate 1M LiPF6 electrolytes, the detected gaseous products are CO2, CO, CH4, C2H4, C2H6, etc. The FTIR spectrum of the surface of the carbon electrode shows bands which correspond to Li2CO3, ROCO2Li, (ROCO2Li)2, and RCO2Li. These results suggest that gas evolution is caused by electrode decomposition, reactive trace impurities, and electrolyte reduction. The surface of the electrode is composed of electrolyte reduction products. When 0.05M Li2CO3 is added as an electrolyte additive, the total volume of generated gases is reduced, and the discharge capacity and the conductivity of lithium-ions are increased. These results can be explained by a more compact and thin ‘solid electrolyte interface’ film on the carbon electrode formed by Li2CO3, which effectively prevents solvent co-intercalation and carbon exfoliation.