NOVELTY - A lithium-air battery (1) comprises negative electrode (2) containing negative-electrode active material; positive electrode using oxygen as positive-electrode active material; and electrolyte (4) medium arranged between negative electrode and positive electrode, where the electrolyte medium comprises as primary solvent at least one compound having isocyanate (-N-CO-) group in the molecule.    USE - As lithium-air battery (claimed); as rechargeable lithium-air/lithium-oxygen battery used as power source for information related devices and communication devices such as personal computers, camcorders and cellular phones; and also used in automobile industry for development of electric vehicles and hybrid vehicles.    ADVANTAGE - The battery exhibits large capacity, high energy density and high power. The rechargeable lithium-air battery has separator between the air cathode and the anode for complete electrical insulation between the electrodes. The separator is able to electrically insulate the air cathode and the anode from each other and has structure that allows the electrolyte to be present between the air cathode and the anode. The solvents used in the electrolyte medium of battery provides stability against oxygen derived radicals and other bases and nucleophiles; has low viscosity, high conductivity, high oxygen solubility and diffusion coefficient, high solubility of ions, and low vapor pressure thereby avoiding too rapid evaporation in case of an open-battery system; has reasonably low melting point and is reasonably hydrophobic thereby allowing ideal product reaction; provides good wettability of the cathode and its components; provides good wettability of the separator and good wettability of other components of the battery; exhibits compatibility with lithium anode thereby reducing problems associated with lithium anode; is highly stable; and exhibits improved thermal stability.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of rechargeable metal-air battery.    Rechargeable metal-air battery (1)    Anode/negative electrode (2)    Air cathode (3)    Electrolyte (4)    Anode collector (5)    Air cathode collector (6)