TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: The positive electrode in a fully charged state has a potential of less than 4.5 V versus metallic lithium. The positive electrode further comprises a positive electrode active material, where the positive electrode active material contains lithium cobalt oxide containing aluminum or magnesium in solid solution; and zirconium is firmly adhered to the surface of the lithium cobalt oxide.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The electrolyte contains LiBF4. The concentration of the LiBF4 is 0.05-0.6 mol/l.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The amount of the chain carboxylic ester is greater than or equal to 40 volume% with respect to the total amount of the solvent. The amount of the 4-fluoroethylene carbonate is 10-50 (preferably 20-40) volume% with respect to the total amount of the solvent. The amount of the chain carboxylic ester in the secondary battery is less than or equal to 90 volume% with respect to the total amount of the solvent. The solvent contains vinylene carbonate or vinyl ethylene carbonate. SPECIFIC COMPOUNDS - 8 Compounds are specified as the chain carboxylic esters e.g. methyl acetate of formula (I'), ethyl acetate, methyl propionate, n-propyl acetate and i-propyl acetate.    EXAMPLE - A positive electrode was prepared as follows: lithium cobalt oxide as a positive electrode active material, carbon as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder agent were mixed together at a mass ratio of 95:2.5:2.5 and the mixture was kneaded in a N-methyl-2-pyrrolidone (NMP) solution, to thus prepare a positive electrode slurry. The resultant positive electrode slurry was applied onto both sides of an aluminum foil current collector in an amount of 520 g/10 cm2, and then dried. The resultant material was pressure-rolled so that the positive electrode filling density became 3.7 g/cc. Thus, a positive electrode was prepared. A negative electrode was prepared as follows: graphite as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder agent, and carboxymethylcellulose (CMC) as a thickening agent were prepared so that the weight ratio became 97.5:1.5:1, and the mixture was kneaded in an aqueous solution, to prepare a negative electrode slurry. The resultant negative electrode slurry was applied onto both sides of a copper foil current collector in an amount of 220 g/10 cm2, and then dried. The resultant material was pressure-rolled so that the negative electrode filling density became 1.7 g/cc. Thus, a negative electrode was prepared. 4-Fluoroethylene carbonate (FEC) and methyl acetate (CH3COOCH3) were mixed at a volume ratio of 20:80, and LiPF6 as an electrolyte (lithium salt) was dissolved into the solvent at a concentration of 1 mole/l. Thus, a non-aqueous electrolyte solution was prepared. The positive electrode and the negative electrode thus prepared were coiled around with polyethylene separator interposed between them to prepare a wound electrode assembly. In a glove box under an argon atmosphere, the resultant wound electrode assembly was enclosed into a battery can together with the electrolyte solution. Thus, a cylindrical 18650 size non-aqueous electrolyte secondary battery (test) was fabricated. A control non-aqueous electrolyte secondary battery was fabricated in the same manner as test except that the solvent used was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, and that vinylene carbonate (VC) was added as an addition agent in an amount of 2 mass% with respect to the total mass of the solvent and the electrolyte. The test/control battery was evaluated for discharge capacity at current rate of 2 It. The result for test/control battery was: discharge capacity at current rate of 2 It = 99/95. The result showed that test battery showed improved discharge capacity as compared to control battery.