In the Li-oxygen battery, the reactivity of superoxide radicals with the electrolyte system during discharge is known to be one of the key parameters to determine the nature of discharge product. Here, we report that lithium bis(oxalato)borate, a common electrolyte salt, is readily decomposed by superoxide radicals. The solid discharge product from cells using this electrolyte salt was identified as lithium oxalate through ex-situ X-ray diffraction and infrared spectroscopic observations. The nucleophilic substitution reaction at the boron centre by superoxide radicals, followed by a series of reduction and gas evolution reactions, are proposed to account for the overall process which also has implications for other salts. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.003112esl] All rights reserved.