Robust, thin-sheet membranes were prepared and tested as an O-2-permeating moisture barrier for the operation of nonaqueous Li-air batteries in ambient air. A membrane sheet was attached onto a carbon air electrode filled with a nonaqueous Li-ion electrolyte solution to supply dry oxygen from ambient air for the electrode reaction and to mitigate potential loss of the solvent from the electrode by evaporation. The membrane was prepared by depositing an O-2-selective coating layer on the exterior surface of a thin (similar to 50 mu m) porous metal substrate sheet. Silicalite zeolite and poly(tetrafluoroethylene) (PTFE) were used as inorganic and polymeric hydrophobic-type materials, respectively, for the membrane preparation in this work. A thin (similar to 5 mu m), dense-phase PTFE film supported on a porous metal sheet provided the best battery performance. This kind of membrane enabled the Li-air batteries with carbon black air electrodes to operate in ambient air [at 20% relative humidity (RH)] for 21 days. The specific capacity of 1022 mAh/g carbon and specific energy of 2792 Wh/kg carbon were obtained for the battery discharged to 2.0 V. The Li-air battery equipped with the selective membrane showed a much better performance in ambient air operation (20% RH) than the reference battery tested in a dry air box (1% RH). (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3430093] All rights reserved.