NOVELTY - A positive electrode active material contains a lithium complex oxide having a spinel structure. The ratio of maximum diffraction peak intensity (I(111)) belonging to (111) plane of lithium complex oxide, and maximum diffraction peak intensity (I(311)) belonging to (311) plane of lithium complex oxide observed in powder X-ray diffractometry using copper-K( alpha ) as ray source, is 2.1-2.7 (excluding 2.7).    USE - Positive electrode active material is used for nonaqueous electrolyte battery (claimed) for portable electronic device and motor vehicle.    ADVANTAGE - The positive electrode active material provides nonaqueous electrolyte battery having high energy density, and excellent charging/discharging cyclic characteristics.    DETAILED DESCRIPTION - A positive electrode active material contains a lithium complex oxide (LixNiyMn2-y-zMzO4-b, where x is 0.9-1.15, y is 0.51-0.65 (excluding 0.65), z is 0-0.1 (excluding 0.1), b is 0-0.3 (excluding 0.3), and M is element chosen from cobalt, magnesium, aluminum, silicon, titanium, zinc, zirconium, titanium, calcium and tin) having a spinel structure. The ratio of maximum diffraction peak intensity (I(111)) belonging to (111) plane of lithium complex oxide, and maximum diffraction peak intensity (I(311)) belonging to (311) plane of lithium complex oxide observed in powder X-ray diffractometry using copper-K( alpha ) as ray source, is 2.1-2.7 (excluding 2.7). INDEPENDENT CLAIMS are included for the following:    (1) nonaqueous electrolyte battery (1), which contains positive electrode containing positive electrode active material, negative electrode, and nonaqueous electrolyte; and    (2) manufacture of the positive electrode active material.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of flat-type nonaqueous electrolyte battery.    Nonaqueous electrolyte battery (1)    Negative electrode tab (18)    Positive electrode terminal (19)    Negative electrode terminal (20)    Negative electrode gasket (21)