The theoretical energy densities of dual-electrolytes rechargeable Li-air batteries using a nonaqueous electrolyte in the anode and an aqueous electrolyte in the cathode are estimated based on the electrochemical reaction mechanisms and the solubility of the discharge product. It is assumed that there is no solid deposition in a cathode during discharge. A number of basic and acidic electrolytes with high solubility of the discharge product are proposed. The theoretical energy densities of these rechargeable Li-air batteries vary from 140 to over 1100 Wh/kg depending on the type of the electrolytes in a cathode. A few structures of Li-air flow battery systems for possible large scale applications are also proposed. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3515330] All rights reserved.