Hydrophobic ionic liquid-silica-PVdF-HFP polymer composite electrolyte is synthesized and employed in lithium air batteries for the first time. Discharge performance of lithium air battery using this composite electrolyte membrane in ambient atmosphere shows a higher capacity of 2800 mAh g(-1) of carbon in the absence Of O-2 catalyst. whereas, the cell with pure ionic liquid as electrolyte delivers much lower discharge capacity of 1500 mAh g(-1). When catalyzed by alpha-MnO2, the initial discharge capacity of the cell with composite electrolyte can be extended to 4080 mAh g(-1) of carbon. which can be calculated as 2040 mAh g(-1) associated with the total mass of the cathode. The flat discharge plateau and large discharge capacity indicate that the hydrophobic ionic liquid-silica-PVdF-HFP polymer composite electrolyte membrane can effectively protect lithium from moisture invasion. (C) 2009 Elsevier B.V. All rights reserved.