NOVELTY - A non-aqueous electrolyte secondary battery comprises a positive electrode including an active material containing a mixture of a first lithium-containing nickel-manganese oxide and a second lithium-containing nickel-manganese-cobalt oxide; or a mixture of the first lithium-containing transition metal oxide and a lithium-cobalt oxide; a negative electrode comprising a negative electrode active material; and a non-aqueous electrolyte having lithium ion conductivity.    USE - For hybrid automobiles.    ADVANTAGE - The non-aqueous electrolyte secondary battery is capable of achieving uniform high power characteristics over a wide range of charge depth and is suitable for secondary batteries for use in hybrid automobiles, etc. The addition of lithium-containing nickel-manganese-cobalt oxide to a lithium-containing nickel-manganese oxide makes it possible to improve power characteristics of the battery dramatically and to obtain uniform power characteristics over a wide range of charge depth, by using a positive electrode active material in which the first lithium-containing transition metal oxide is mixed with the second lithium-containing transition metal oxide or with lithium cobalt oxide. When the non-aqueous electrolyte secondary battery is used as a secondary battery for a hybrid automobile, a control algorithm in the hybrid automobile can be simplified and consequently the costs for the system can be reduced. The addition of the second lithium-containing transition metal oxide to the first lithium-containing transition metal oxide improves the resistance and input power characteristics; improves the electrochemical activity of the lithium-containing nickel-manganese oxide; and reduces the dependence of the power characteristics on the depth of charge and discharge.    DETAILED DESCRIPTION - A non-aqueous electrolyte secondary battery comprises a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and a non-aqueous electrolyte having lithium ion conductivity. The positive electrode active material comprises a mixture of a first lithium-containing nickel-manganese oxide having a crystal structure belonging to the space group R3m, and a second lithium-containing nickel-manganese-cobalt oxide having a crystal structure belonging to the space group R3m; or a mixture of the first lithium-containing transition metal oxide and a lithium-cobalt oxide. The first lithium-containing nickel-manganese oxide is represented by the formula LiaNixMnyO2 The second lithium-containing nickel-manganese-cobalt oxide is represented by the formula LibNipMnqCorO2    a, b = 1-1.5,    x+y, p+q+r = 0.5 - 1,    x, y, p, q and r = less than 1 and greater than 0.