The gas evolution related to the film formation on cathode materials for lithium-ion batteries was studied using differential electrochemical mass spectrometry and subtractively normalized interfacial Fourier transform infrared spectroscopy. With both methods the oxidative formation of CO2 was observed in standard battery electrolytes. We show the strong influence of the type of the electrolyte and especially of the additive, vinylene carbonate (VC), as well as the effect of the temperature on the CO2 gas formation rate. The VC additive significantly reduces the gas formation rate in the commonly used voltage window between 3.0 and 4.3 V. Long cycling experiments show that test cells containing VC have a higher cycling stability compared to cells cycled without this additive. Cycling at elevated temperatures (60 degrees C) results in a high, enduring CO2 gas evolution, already starting at a lower cell voltage of about 3.5 V. (c) 2007 The Electrochemical Society.