TECHNOLOGY FOCUS - ELECTRONICS - Preferred Electrode: The anode comprises composite metal oxide of lithium and transition metal element(s). The cathode comprises active substance(s) chosen from carbon materials, lithium, lithium-containing alloys and compounds which alloy with lithium, preferably lithium. The charging and/or discharging of the battery is carried out with current of 1.0 CmA or more as maximum current value for charge and/or discharge, where CmA is the smaller capacity from the anode capacity and cathode capacity as calculated from the weight of the electrode active substance used in the battery.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The supporting electrolyte salt contains inorganic lithium salt (less than 0.1 mol/l or 0.1-2 mol/l). The solvent composition further contains aprotic solvent other than cyclic carbonic acid ester, in an amount of less than 80 vol.%, preferably 10-80 vol.%. The aprotic solvent is linear carbonic acid ester of formula: RxOCOORy.Rx,Ry = straight-chain or branched 1-4C alkyl group.The halogenation ratio of the fluorine-containing solvent is 0.50-0.85. SPECIFIC COMPOUNDS - The fluorine-containing solvent is chosen from C6F13-O-CH3, C6F13-O-C2H5, CH3-O-C6F12-O-CH3, CH3-O-C3F6-O-C3F6-O-CH3, CF3CFHCF2-O-CH2CH(CH3)-O-CF2CFHCF3, H(CF2)8CH2-O-CH3, H(CF2)8CH2-O-CH3, CF3CFHCF2OCH2CH2COCF2(CFHCF3)CH2-O-CF2CFHCF3, C(CH2-O-CF2CFHCF3)4, CH3C(CH2-O-CF2CFHCF3)3 and/or C4F9-O-CH2CH2-O-C4F9. The cyclic carbonic acid ester solvent is chosen from ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and/or vinyl ethylene carbonate (all claimed).    EXAMPLE - An electrolyte solution comprising ethylene carbonate (in vol.%) (50), fluorine-containing solvent (50) of formula CF3CFHCF2OCH2CH2CH2OCF2CFHCF3, and lithium bis(penta fluoroethane sulfonyl) imide (1) was prepared. The electrolyte solution had excellent stability and produced lithium secondary battery with initial cycle efficiency of 87.9% and average cycle efficiency of 95.2%.