Patent ID: 8394541

Claim:
A lithium secondary battery which comprises a positive electrode of a composite metal oxide comprising lithium and a metal selected from the group consisting of cobalt and nickel, a negative electrode comprising a lithium metal, a lithium alloy or a material capable occluding and releasing lithium, and a non-aqueous electrolyte solution comprising an electrolyte in a non-aqueous solvent, wherein the non-aqueous electrolyte solution contains 1 to 5 weight % of a combination of a tert-butylbenzene derivative and cyclohexylbenzene, wherein the tert-butylbenzene derivative is selected from the group consisting of tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, 1-chloro-4-tert-butylbenzene, 1-bromo-4-tert-butylbenzene, 1-iodo-4-tert-butylbenzene, 5-tert-butyl-m-xylene, 4-tert-butyltoluene, 3,5-di-tert-butyltoluene, 1,3-di-tert-butylbenzene, 1,4-di-tert-butylbenzene, and 1,3,5-tri-tert-butylbenzene.