TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The lithium salt is lithium hexafluorophosphate , lithium tetrafluoroborate, lithium fluoroantimonate(V), lithium hexafluoroarsenate, lithium perchlorate, lithium triflate, lithium salt of fluorinated alkylsulfonic acid (LiC4F9SO3), lithium aluminate, lithium tetrachloroaluminate or lithium nitride of formula (LiN(CpF(2p+1)SO2)(CqF(2q+1)SO2)) (i), lithium chloride or lithium iodide. The lithium salt is present at 0.1-2.0 M.p, q = natural numbers.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: (I) is present at 0.5-5 parts by weight. The electrolyte comprises a mixture of 2 or more (I) with different n values. (I) has an endothermic peak as determined by differential thermal analysis whose lowest point is 50-90 degrees C. The electrolyte further comprises an ethylene carbonate-based compound of formula (II) i.e. fluoroethylene carbonate. The nonaqueous organic solvent is at least one solvent comprising a carbonate, an ester, an ether or a ketone. The carbonate is at least one solvent comprising dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate or pentylene carbonate. The ester is at least one solvent comprising methyl acetate, ethyl acetate, n-propyl acetate, butyl acetate, methyl propionate, ethyl propionate, gamma -butyrolactone, decanolide, gamma -valerolactone, 8-valerolactone, mevalonolactone or caprolactone. The ether is at least one solvent comprising dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The ketone is at least one solvent comprising cyclohexanone or polymethyl vinyl ketone. The ethylene carbonate-based compound is difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate fluoroethylene carbonate, nitroethylene carbonate or cyanoethylene carbonate. The carbonate is a combination of a cyclic carbonate and a chain carbonate and the mixing ratio is 1:1-1:9 vol/vol cyclic carbonate to chain carbonate. The cyclic carbonate is solvent comprising ethylene carbonate, propylene carbonate, butylene carbonate or pentylene carbonate. The chain carbonate is solvent comprising dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or ethyl methyl carbonate. The non-aqueous organic solvent further comprises an aromatic hydrocarbon-based organic solvent of formula (III). The aromatic hydrocarbon-based organic solvent is benzene, fluorobenzene, bromobenzene, chlorobenzene, toluene, xylene or mesitylene, and the volume ratio of the carbonate solvent to the aromatic hydrocarbon-based organic solvent is 1:1-30:1.R3, R4 = H, halo, CN, NO2, vinyl or 1-5C fluoroalkyl, and where R3 and R4 are not both H;R = halo or 1-10C alkyl; andl = 0-6. EXAMPLE - Lithium cobalt oxide as a positive electrode active material, polyvinylidene fluoride as a binder and carbon as a conductive material were dispersed in a weight ratio of 92:4:4 in N-methyl-2-pyrrolidone to prepare slurry of the positive electrode active material. The slurry was coated to a thickness of 15 mu m on an aluminum foil, dried and rolled to produce a positive electrode plate. Artificial graphite as a negative electrode active material, styrene-butadiene rubber as a binder and carboxymethyl cellulose as a thickener were mixed in a ratio of 96:2:2 and dispersed in water to prepare slurry of the negative electrode active material. The slurry was coated to a thickness of 10 mu m on a copper foil, dried and rolled to produce a negative electrode plate. A 16 mu m-thick polyethylene separator was interposed between the electrodes, and the three layers were wound, pressed together and inserted into a prismatic can (46 mmx 34 mmx 50 mm). Lithium hexafluorophosphate was added to a mixed solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate (1:1:1) until the final concentration of lithium hexafluorophosphate reached 1 M, and tetraphenyl 4,4'-(propane-2,2-diyl)bis(4,1-phenylene) diphosphate was added to it to form the electrolyte.