TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The sulfone-based compound is of formulae (1) - (3).R1 and R2 = primary alkyl, secondary alkyl, tertiary alkyl, alkenyl, or aryl, preferably 1-4C alkyl, 2-4C alkenyl or 6-14C aryl;p = 0-3;R3 = halo or a 1-10C alkyl;q = 1-6.It includes methyl sulfone, vinyl sulfone, phenyl sulfone, benzyl sulfone, tetramethylene sulfone, butadiene sulfone, or their mixtures.The electrolyte comprises an organic peroxide including isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, m-toluoyl peroxide, t-butylperoxy-2-ethyl hexanoate, t-butyl peroxy bibarate, t-butylperoxyneodecanoate, diisopropyl peroxy dicarbonate, diethyl peroxy dicarbonate, bis-(4-t-butylcyclohexyl)peroxy dicarbonate, dimethoxy isopropyl peroxy dicarbonate, dicyclohexylperoxy dicarbonate, 3,3,5-trimethylhexanoyl peroxide, or dialkyl peroxide.It comprises 2,2'-azobisisobutyronitrile.The lithium salt includes lithium phosphorus hexafluoride, lithium boron tetrafluoride, lithium antimony hexafluoride, lithium arsenic hexafluoride, lithium chlorate, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, lithium aluminide, lithium aluminum chloride, LiN(CxF2x+1SO2)(CyF2y+1SO2), lithium chloride or lithium iodide.x and y = natural numbers.The non-aqueous organic solvent includes carbonates, esters, ethers, or ketones. The carbonate includes dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC).The electrolyte comprises a mixed solvent of a cyclic carbonate and a chain carbonate, or a mixed solvent of a carbonate solvent and an aromatic hydrocarbon solvent of formula (6).The aromatic hydrocarbon solvent includes benzene, chlorobenzene, nitrobenzene, fluorobenzene, toluene, trifluorotoluene, or xylene.The electrolyte comprises a mixed solvent of an ethylene carbonate and a carbonate having a lower boiling point.Preferred Composition: The sulfone-based compound is present in 0.001-10 wt.% based on the total amount of electrolyte. The organic peroxide or azo-based compound is present in 0.001-10 wt.% based on the total amount of electrolyte.The carbonate solvent and the aromatic hydrocarbon solvent are mixed in a volume ratio of 1:1 to 30:1.The (meth)acrylic ester and the group having no radical reactivity are present in a mole ratio of 1:0.01 to 1:100.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The electrolyte includes a poly(ester)(meth)acrylate or its polymer derived from a p(polyester)polyol with at least three -OH groups. The (polyester)polyol includes trialkylols, glycerols, or erythritols.The (meth)acrylic ester includes -OC(=O)(CH2)nOC(=O)CH=CH2 or -OC(=O)(CH2)nOC(=O)C(CH3)=CH2.The group having no radical reactivity includes 1-20C aliphatic hydrocarbons, 5-20C aromatic hydrocarbons, 1-20C ethers, or 1-20C esters. It includes -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 composition for a polymer electrolyte further comprises a base catalyst.n = 1-20.Preferred Method: The method further comprises heat-treating or UV-irradiating the solid polymer electrolyte to polymerize the poly(ester)(meth)acrylate or the polymer of a poly(ester)(meth)acrylate.Heat treating is performed at 40-110 degreesC.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The positive electrode includes a lithium-nickel-based or a lithium-nickel-manganese-based oxide.The negative electrode includes a carbonaceous material having a d002 interplanar distance of 3.35-3.38 and having an Lc (crystallite size) measured by X-ray diffraction of more than 20 nm. EXAMPLE - Ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/DEC were mixed in a volume ratio of 30/60/10 to prepare an organic mixed solvent. 1.15 M lithium phosphorus hexafluoride were added to the solvent, and an electrolyte additive including 0.75 wt.% vinyl sulfone and 0.0033 wt.% dilauroyl peroxide, based on the total weight of the electrolyte, were further added to the solution to prepare a composition to form an electrolyte. LiNi0.7Co0.1Mn0.2O2 as a positive active material, Super P (acetylene black) as a conductive agent, and polyvinylidenefluoride (PVdF) as a binder were mixed in a weight ratio of 96:2:2 in N-methyl-2-pyrrolidone to prepare a positive slurry. The slurry was coated on an aluminum foil, dried, and compressed to provide a positive electrode having an active mass density of 3.5 g/cm3. Graphite as a negative active material and PVdF as a binder were mixed in a weight ratio of 95:5 to prepare a negative slurry. The slurry was coated on a copper foil, dried, and compressed to provide a negative electrode. 2.5 g of the electrolyte were injected into a pouch containing the electrode assembly (8), and the portion for injecting electrolyte was fused, thus completing the fabrication of the 700 mAh pouch-type battery cell.