We developed a methodology of in situ Fourier transform infrared (FTIR) measurements of gaseous products formed in an electrochemical cell upon polarization. LiNi0.8Co0.15Al0.05O2 (NCA) cathodes were explored at potentials of up to 5.5 V vs Li in the ionic liquid (IL)-based electrolyte solution, LiTFSI/N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) amide. The polarization of the NCA electrodes formed CO2 and CO due to the liberation of oxygen and the parallel dissolution of nickel ions, which oxidizes the carbon black in the composite electrode. The oxygen was mostly liberated from the NCA and also due to minor contribution from the surface groups on the carbon black additive. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3292635] All rights reserved.