TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The electrolytic salt comprises lithium salt chosen from lithium hexafluorophosphate, lithium difluorophosphate, dilithium fluorophosphate, lithium tetrafluoroborate, lithium triflate, lithium bis(trifluoromethyl sulfonyl)imide, lithium bis(perfluoroethyl sulfonyl)imide, lithium bis(fluorosulfuryl) imide, difluoro bis(oxalate-O,O')lithium phosphate and tetrafluoro(oxalate-O,O')lithium phosphate. The concentration of lithium salt with respect to nonaqueous solvent is 0.3-2.5 M. The positive electrode contains a positive electrode active material comprising a lithium composite metal oxide cotaining cobalt, manganese and/or nickel or a lithium-containing olivine-type phosphate containing iron, cobalt, nickel and/or manganese. The negative electrode contains a negative electrode active material including lithium alloy, lithium, tin, tin compound, silicon, silicon compound, lithium-titanate compound and/or carbon material which occludes and discharges lithium metal.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The content of imidyl oxy group-containing compound contained in the nonaqueous electrolyte is 0.001-10 %mass. The nonaqueous solvent comprises cyclic carbonate chosen from ethylene carbonate, propylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 4-fluoro-1,3-dioxolan-2-one and trans- or cis-4,5-difluoro-1,3-dioxolan-2-one, and chain-shaped carboxylate ester. The chain-shaped ester is asymmetrical linear carbonate chosen from methyl ethyl carbonate, methylpropyl carbonate, methyl isopropyl carbonate, methylbutyl carbonate and ethylpropyl carbonate, or symmetrical linear carbonate chosen from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate and carboxylate. The nonaqueous electrolyte further contains phosphate, isocyanate, compound having S=O group, nitrile, acid anhydride, aromatic compound and/or cyclic phosphazene compound. SPECIFIC COMPOUNDS - 9 Imidyl oxy group-containing compounds are specifically claimed e.g. bis(2,5-dioxo pyrrolidin-1-yl)oxalate of formula (IA), 2,5-dioxo pyrrolidin-1-yl-2-(diethoxy phosphoryl)propanoate, 2,5-dioxo pyrrolidin-1-yl-(2-(methanesulfonyl)oxy)propanoate, 2,5-dioxo pyrrolidin-1-yl-(2-(ethanesulfonyl)oxy)propanoate and 2,5-dioxo pyrrolidin-1-yl-(2-(4-methylphenyl sulfonyl)oxy)propanoate.