TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The cathode active material is a multi-component cathode active material containing at least two transition metal elements. The multi-component cathode active material has an agglomerate secondary particle structure in which primary particles are agglomerated to form secondary particles. The content of the multi-component transition metal oxide is more than 20 wt.%, based on the total weight of the cathode active material. The multi-component transition metal oxide is a lithium nickel-manganese-cobalt oxide.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The additive is added in an amount of 0.01-10 wt.% based on the total weight of the electrolyte. The additive is added in an amount of 0.05-5 wt.%, based on the total weight of the cathode mix. The additive is a modified copolymer having perfluorinated sulfonamide substituent(s) bound to either or both ends of a block copolymerization structure of polyethylene oxide (PEO) and polypropylene oxide (PPO). The PEO-PPO block copolymer is composed of a PEO block and a PPO block, and upon construction of both ends of the block copolymer, a perfluorinated sulfonamide substituent is bound to the end of the PEO block. The copolymer is of formula CF3-(CF2)3-S(=O)(=O)-N(CH3)(CH2-(O-CH2-CH2)n-(-O-CH(CH3)-CH2-)m-). The content of PEO in the PEO-PPO block copolymer is 30-80 wt.% based on the total weight of the copolymer.n = 40-1000 or Am;m = 40-200; andA = 1-5. EXAMPLE - A mixture of lithium cobaltate and lithiated nickel manganese-cobalt oxide having an average particle diameter of 10 mu m was used as a cathode active material. Artificial graphite (95.3 wt.%) having an average particle diameter of 10 mu m was used as an anode active material. An ethylene carbonate/ethylmethyl carbonate-based organic solution containing 1M hexafluoro lithium phosphate was used as an electrolyte. Celgard (RTM: Porous separator) having a thickness of 20 mu m was disposed between the cathode and the anode respectively, and the electrolyte was injected into the resulting electrode assembly to produce lithium secondary battery.