TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The lithium salt is lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium perchlorate, lithium aluminate, lithium tetrachloroaluminate, lithium chloride, and/or lithium iodide. The lithium salt is used at 0.6-2 M.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The electrolyte may contain organic peroxide (0.3-5 pbw/100 pbw poly(ester)(meth)acrylate). Preferred Components: The (polyester)polyol is trialkylol, glycerol, or erythritol. The (meth)acrylic ester is of formulae -OC(=O)(CH2)nOC(=O)CH=CH2 or -OC(=O)(CH2)nOC(=O)C(CH3)=CH2. The group having no radical reactivity is 1-20C aliphatic hydrocarbon, 5-20C aromatic hydrocarbon, 1-20C ether, or 1-20C ester. The group having no radical reactivity is of formulae -OC(=O)(CH2)3CH3, -OC(=O)Ar, -OC(=O)(CH2)nO(CH2)nCH3, -O(C=O)(CH2)nOC(=O)(CH2)nCH3, or -(C=O)CH=CH2. The (meth)acrylic ester and the group having no radical reactivity are used in a mole ratio of 1:0.01-1:100. The lithium salt may be lithium trifluoromethane sulfonate, lithium bis(trifluoromethane sulfonyl)imide, lithium nonafluorobutane sulfonate, and/or LiN(CxF2x+1SO2)(CyF2y+1SO2). The non-aqueous organic solvent is carbonate, ester, ether, and/or ketone. The carbonate is dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, or butylene carbonate. The electrolyte comprises a mixed solvent of cyclic carbonate and chain carbonate, or a mixed solvent of carbonate solvent and aromatic hydrocarbon solvent in a volume ratio of 1:1-30:1. The aromatic hydrocarbon solvent is a compound of formula (7) or benzene, fluorobenzene, toluene, trifluorotoluene, and/or xylene. The organic peroxide is isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butylperoxy-2-ethyl hexanoate, t-butyl peroxy bibarate, t-butyloxyneodecanate, diisopropyl peroxy dicarbonate, diethoxy peroxy dicarbonate, bis-(4-t-butylcyclohexyl)peroxy dicarbonate, dimethoxy isopropyl peroxy dicarbonate, dicyclohexylperoxy dicarbonate, or 3,3,5-trimethylhexanoyl peroxide.n=1-20;Ar=optionally substituted aromatic hydrocarbon;x, y=natural numbers;R4=halo or 1-10C alkyl; andq=1-6.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The poly(ester)(meth)acrylate is added at 0.1-5 wt.%. The poly(ester)(meth)acrylate is a polymer derived from (polyester)polyol with at least three hydroxyl (-OH) groups, in which a portion of hydroxyl groups is substituted with (meth)acrylic ester and the remaining portion is substituted with a group having no radical reactivity. EXAMPLE - Lithium hexafluorophosphate (1.15 M) was added to a mixed solvent comprising ethylene carbonate, ethyl methyl carbonate, propylene carbonate and fluorobenzene in a volume ratio of 30:55:5:10. Electrolyte additive comprising chloroanisole (3 wt.%) and vinyl sulfone (0.5 wt.%) was added to the solution to prepare an electrolyte. The electrolyte (2.9 g) was injected into a prismatic can containing a polyethylene porous film separator (6) between positive and negative electrodes (2, 4) to obtain a prismatic-type lithium secondary battery cell. Capacity of battery cell was measured by charging the battery at 2 C rate. The battery cell had standard capacity of 970 mAh, capacity at 2 C of 920 mAh, capacity retention rate of 85%, and effective overcharge safety.