Patent ID: 7381497

Claim:
A non-aqueous electrolyte secondary battery, comprising: a positive electrode; a negative electrode; a separator interposed between said positive electrode and said negative electrode; and a non-aqueous electrolyte, wherein said positive electrode comprises a lithium-containing composite oxide, said composite oxide is represented by the general formula: Li z Co 1-x-y Mg x M y O 2 , the element M included in said general formula is at least one selected from the group consisting of Al, Ti, Sr, Mn, Ni and Ca, the values x, y and z contained in said general formula satisfy: (i) 0>z≦1.03; (ii) 0.005≦x≦0.1; and (iii) 0.001≦y≦0.03, said composite oxide has a crystal structure attributed to a hexagonal system in an overcharged state having a potential over 4.25 V relative to metallic Li, and a maximum value of an oxygen generation peak in a chromatograph mass spectrometry measurement of said composite oxide in said overcharged state is in the range of 330 to 370° C., wherein an end-of-charge voltage normal operating state is set to 4.25 V or higher.