We use differential electrochemical mass spectrometry (DEMS) to characterize the Li-O-2 battery in an electrolyte containing tetraethylene glycol dimethyl ether (TEGDME) and lithium triflate (LiOTf) and examine the effect of several cathode catalysts. Au nanoparticles increase the amount of O-2 evolved during charge and improve the cycleability of the cell. In contrast, Pt, Pd, and Cu(II) oxide catalysts are detrimental to battery performance because they catalyze solvent or carbon cathode decomposition as evidenced by CO2 evolution. Regardless of the catalyst employed, the amount of O-2 measured upon charge is significantly less than that expected for complete Li2O2 formation and decomposition, in agreement with the rapidly fading capacity observed during battery cycling. These findings suggest that TEGDME is not a suitable solvent for a reversible Li-O-2 battery. (C) 2013 The Electrochemical Society. [DOT: 10.1149/2.033304jes] All rights reserved.