Lithium secondary battery

Abstract

A lithium secondary battery comprising a positive electrode, a negative electrode and an organic electrolyte, and the electrolyte comprises a solvent mixture of at least one kind of fluorine substituted propylene carbonates used as a first solvent and at least one kind of low viscous solvents for lowering the viscosity of fluorine substituted propylene carbonates, used as a second solvent. At least one solvent selected from a group of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate and methyl butyl carbonate is preferably used as the second solvent. There can be obtained resultant electrolytes which are excellent in self-extinguishing ability, resulting in high safety and easy in handling, and also excellent in battery performance, discharge characteristics at a low temperature, charge/discharge efficiency of the negative electrode at the initial stage of charge/discharge cycles, energy density, and suppression of the deterioration of the characteristics of the positive electrode, made of one kind of lithium containing complex oxides, during recharging cycles at a deep or large charging depth. When 4-trifluoromethyl-ethylene carbonate is used, the above-mentioned characteristics can be much more improved.