NOVELTY - A lithium secondary battery (1) has a casing in which an anode (2), a cathode (4), a separator (6) interposed between the anode and the cathode, and an electrolyte (26) are provided. The electrolyte comprises a non-aqueous organic solvent, a lithium salt and vinyl sulfone. The anode comprises a silicon thin film or silicon-graphite composite material as an anode active material, and the cathode comprises a lithium intercalation compound as a cathode active material.    USE - Lithium secondary battery is used as power source of portable electronic devices such as mobile phone, notebook computer and digital camera.    ADVANTAGE - Lithium secondary battery has improved durability and charging-discharging cycle characteristics by preventing the swelling phenomenon.    DETAILED DESCRIPTION - A lithium secondary battery has a casing in which an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte are provided. The electrolyte comprises a non-aqueous organic solvent, a lithium salt and vinyl sulfone. The anode comprises a silicon thin film or silicon-graphite composite material as an anode active material, and the cathode comprises a lithium intercalation compound as a cathode active material. The content of vinyl sulfone additive is 0.5-3 wt.% based on the total weight of the electrolyte. The lithium salt is chosen from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroantimonate, lithium perchlorate, lithium trimethanesulfonate, lithium bistrifluoromethylsulfonyl imide, lithium aluminum chloride (LiAlCl4), lithium aluminate (LiAlO4), lithium chloride, lithium iodide and lithium compounds (Li(CF3SO2)2N, LiN(CxF2x+1SO2)(CyF2y+1SO2)), where x and y are natural numbers. The non-aqueous organic solvent is chosen from carbonate, ester and ketone. The carbonate is chosen from ethylene carbonate, vinylene carbonate, polypropylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and/or dipropyl carbonate. The ester is chosen from butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, n-methyl acetate, n-ethyl acetate and/or n-propyl acetate. The lithium intercalation compound is chosen from lithium cobalt dioxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxides (LiMnO2, LiMn2O4), lithium ferrite (LiFeO2), vanadium pentoxide, titanium silicide (TiS2), molybdenum silicide (MoSi2) and lithium-nickel-cobalt compound (LiNi(1-x-y)CoxMyO2), where M is aluminum, strontium, magnesium or lanthanum, x,y are more than 0 to less than 1 and x+y is more than 0 to less than 1.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of prismatic type lithium secondary battery.    Lithium secondary battery (1)    Anode (2)    Cathode (4)    Separator (6)    Electrolyte (26)