The theoretical energy densities of dual-electrolytes rechargeable Li-air batteries using a nonaqueous electrolyte in the anode andan aqueous electrolyte in the cathode are estimated based on the electrochemical reaction mechanisms and the solubility of thedischarge product. It is assumed that there is no solid deposition in a cathode during discharge. A number of basic and acidicelectrolytes with high solubility of the discharge product are proposed. The theoretical energy densities of these rechargeable Li-airbatteries vary from 140 to over 1100 Wh/kg depending on the type of the electrolytes in a cathode.Afew structures of Li-air flowbattery systems for possible large scale applications are also proposed.© 2010 The Electrochemical Society. DOI: 10.1149/1.3515330 All rights reserved.Manuscript submitted August 3, 2010; revised manuscript received September 19, 2010. Published November 23, 2010.