TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Property: The thickness variation rate of the battery after leaving at 90 degrees C for 4 hours after charging with current of 4.2 V, is 10% or less.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compounds: The negative ion of the lithium salt is the fluorine ion, chlorine ion, bromine ion, nitrate ion, dicyanamide ion, tetrafluoroborate ion, perchlorate ion, hexafluorophosphate ion, phosphorus-containing ions ((CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-), sulfur-containing ions (CF3SO3-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CH3SO3-), trifluoroacetate ion, acetate ion, thiocyanate ion, and/or CF3CF2(CF3)2CO- ion.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The molar ratio of lithium salt and amide compound is 1-8:1. The content of nitrile compound is 5-200 parts weight with respect to 100 parts weight of eutectic mixture. The electrolyte has a viscosity of 100 cP or less, preferably 5-20 cP, and an ion conductance of 5-10 mS/cm. Preferred Compounds: The amide compound is methyl carbamate, ethyl carbamate, methyl N-methylcarbamate, ethyl N-methylcarbamate, ethyl N-ethylcarbamate, N-ethylmethylcarbamate, ethyl N,N-dimethylcarbamate, methyl N,N-dimethylcarbamate, N,N-dimethylphenylcarbamate, N-butylmethylcarbamate, N-phenylmethylcarbamate, N-ethyl-N-phenylethylcarbamate, N-methoxyethyl methylcarbamate, N-methoxyethyl-N-methyl methylcarbamate, N-methoxymethyl-N-methyl methylcarbamate, N,N-dimethyl methoxyethylcarbamate, N-methyl-N-methoxyethyl methoxyethylcarbamate, N-methyl-N-methoxyethyl methoxymethylcarbamate, N-methoxymethyl-N-methyl ethylcarbamate, N-methoxymethyl-N-ethyl methylcarbamate, N-methoxymethyl-N-methyl trifluoroethylcarbamate, N-methylurea, N,N'-dimethylurea, N-(2-methoxyethyl)-N-methyl piperidine-1-carboxamide, S-phenyl-N-2-methoxyethyl-N-methylcarbamothioate, oxazolidone, and/or N-methyloxazolidone. The nitrile compound is of formula: NC-R3.R3=1-10C alkyl optionally substituted by halo(s), alkylamino, alkenyl, aryl, alkoxyalkyl or alkoxy.Preferably, the nitrile compound is acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, methoxyacetonitrile, methoxypropionitrile, and/or ethoxypropionitrile. The electrolyte further contains carbonate compound chosen from linear carbonate and cyclic carbonate. The carbonate compound is polypropylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, butylene carbonate, methylpropyl carbonate, ethylpropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methylpyrrolidone, ethyl methyl carbonate, and/or gamma -butyrolactone.    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The electrolyte is a polymer electrolyte, which is the polymerization reaction product of a precursor solution containing a monomer. The monomer is a vinyl monomer chosen from acrylonitrile, methyl methacrylate, methyl acrylate, methylstyrene, vinyl ester group monomer, polyvinyl chloride, vinylidene chloride, acrylamide, tetrafluoroethylene, vinyl acetate, vinyl chloride, methyl vinyl ketone, ethylene, styrene, and para cyanostyrene. The weight ratio of monomer in the precursor solution is 0.5-0.95:0.05-0.5. The polymer electrolyte is a gel-like electrolyte obtained by in-situ polymerization. The polymer electrolyte is immersed in polymer chosen from polymethylmethacrylate, polyvinylidene difluoride, polyvinylchloride, polyethylene oxide, and polyhydroxyethyl methacrylate.