The performance of pouch-type Li-air batteries operated in ambient conditions is reported in this work. The batteries use a heat-sealable plastic membrane to function simultaneously as the package material, an O-2 diffusion membrane, and a moisture barrier. The large variation in the internal resistance of the batteries related to unstable contacts between electrodes and separators is stabilized by a modified separator that can bind the cell stack together. Cells using the modified separators show improved and repeatable discharge performance. We have also found that 1,2-dimethoxyethane (DME) as a co-solvent in the electrolyte plays an important role in increasing the discharge voltage of these pouch-type cells. However, an overly large amount of DME co-solvent in the electrolyte may lead to decreased capacity due to the eventual loss of DME through the diffusion membrane. Pouch-type Li-air batteries with the modified separator and the optimized electrolyte have demonstrated specific capacities of 2711 mAh g(-1) based on carbon weight and specific energies of 344 Wh kg(-1) based on the complete battery weight, including the package. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3414828] All rights reserved.