TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The lithium salt comprises the first lithium salt at a concentration of 0.8-1.2 M, and the second lithium salt at a concentration of 0.3-0.7 M. The second lithium salt is selected from LiBC2O4F2, LiN(SO2C2F5)2 and/or LiN(SO2CF3)2 (preferably LiBC2O4F2). The first lithium salt and the second lithium salt are included in a mole ratio of 1:0.2 to 1:1.2 (preferably 1:0.25 to 1:1.14). The lithium-vanadium-based oxide is of formula LixMyVzO2+d. The positive active material is selected from 24 compounds e.g. compounds of formulae LiaA1-bBbD2, LiaE1-bBbO2-cF'c, LiE2-bBbO4-cF'c, LiaNi1-b-cCobB1cD alpha , LiaNi1-b-cCObB1cO2- alpha F alpha ; , LiaNi1-b-cCObB1cO2- alpha ; F'2, LiaNi1-b-cMnbB1cD alpha ; , LiaNi1-b-cMnbB1cO2-cF'alpha ; , LiaNi1-b-cMnbB1cO2-cF'2, or Lia1Nib1Ec1Gd1O2.x=0.1-2.5;y and d=0.1-0.5;z=0.5-1.5;M=aluminum, chromium, molybdenum, titanium, tungsten or zirconium;a=0.95-1.1;b=0-0.5;c=0-0.05;alpha =0-2;a1=0.90-1.1;b1=0-0.9;c1=0-0.5;d1=0.001-0.1;A=nickel, cobalt or manganese;B1=aluminum, nickel, cobalt, manganese, chromium, iron, magnesium, strontium, vanadium or rare earth element;D=O, F, S or P;E=cobalt or manganese;F'=F, S or P;andG=aluminum, chromium, manganese, iron, magnesium, strontium, vanadium or lanthanide element.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The non-aqueous organic solvent comprises a carbonate-based solvent, ester-based solvent, ketone-based solvent, alcohol-based solvent and/or aprotic solvent. The electrolyte comprises an additive containing an ethylene carbonate-based compound (1-7 parts by weight) and an ether-based compound (0.01-5 parts by weight), with respect to the non-aqueous organic solvent (100 parts by weight). The ethylene carbonate-based compound is selected from fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate and/or cyanoethylene carbonate; and is represented by a formula (1,3)dioxolan-2-one (substituted by R1 on 4 position and by R2 on 5 position). The ether-based compound comprises dimethoxyethane, bis(2-methoxyethyl)ether, triethylene glycol dimethylether, tetraethylene glycol dimethylether, polyethylene glycol dimethylether, propylene glycol dimethylether and/or dioxolane.R1 and R2=H, halo, CN, NO2 or 1-5C fluoroalkyl.Where at least one of R1 and R2 is selected from halo, CN, NO2, and 1-5C fluoroalkyl. EXAMPLE - A rechargeable lithium battery was prepared as follows: ethylenecarbonate and diethylcarbonate were mixed in a volume ratio of 30:70, to prepare a mixed solvent. Fluoroethylenecarbonate (5 parts by weight) and triethylene glycol dimethylether (3 parts by weight) were added to the mixed solvent (100 parts by weight), to prepare a non-aqueous organic solvent. Then, a first lithium salt, LiPF6 (0.7 M) and a second lithium salt, LiBC2O4F2 (0.3 M) were added to it, to prepare an electrolyte. An Li1.1V0.9O2 negative active material, a polyvinylidene fluoride binder, and a super-P conductive material were mixed in a weight ratio of 94/3/3, in an N-methylpyrrolidone mixed solvent, to prepare a negative active material slurry (S1). The slurry (S1) was coated on a current collector made of a thin aluminum film, dried, and pressed to fabricate a negative electrode. A lithium cobalt oxide (LiCoO2) positive active material, a polyvinylidene fluoride binder, and a super-P conductive material were mixed in a weight ratio of 94/3/3, in an N-methylpyrrolidone mixed solvent, to prepare a positive active material slurry (S2). The slurry (S2) was coated on a current collector made of a thin aluminum film, dried, and pressed, to prepare a positive electrode. The positive and negative electrodes and the electrolyte were used to fabricate in a rechargeable lithium battery (test). A control rechargeable lithium battery was prepared in a similar manner as that of the test rechargeable lithium battery, except that an electrolyte was prepared by dissolving the first lithium salt, LiPF6 (0.5 M) and second lithium salt, LiBC2O4F2 (0.2 M) in the non-aqueous solvent. The test/control lithium batteries were measured for initial reversible efficiency. The test/control lithium batteries showed initial reversible efficiency of 90.64/80.22%.