NOVELTY - A non-aqueous electrolyte secondary battery comprises a positive electrode containing positive electrode active material (1), a negative electrode containing negative electrode active material, a separator positioned between positive electrode and negative electrode, and a non-aqueous electrolyte. The positive electrode active material contains aluminum atom-containing secondary particles (2). The content rate of aluminum atom in the surface side of secondary particles is more than the content rate of aluminum atom in the center portion side of secondary particles.    USE - Non-aqueous electrolyte secondary battery is used for plug-in hybrid electric vehicle (claimed). Can also be used as power supply for portable apparatus such as mobile telephone, notebook personal computer, hybrid electric vehicle, domestic electric power storage apparatus and video camcorder.    ADVANTAGE - The non-aqueous electrolyte secondary battery has excellent cycle characteristics and storage characteristics. The deterioration of positive electrode active material is suppressed while preserving at high temperature.    DETAILED DESCRIPTION - A non-aqueous electrolyte secondary battery comprises a positive electrode containing positive electrode active material, a negative electrode containing negative electrode active material, a separator positioned between positive electrode and negative electrode, and a non-aqueous electrolyte. The positive electrode active material contains aluminum atom-containing secondary particles in which several primary particles (3) having average particle diameter of 0.8 mu m or less are aggregated. The content rate of aluminum atom in the surface side of secondary particles is more than the content rate of aluminum atom in the center portion side of secondary particles. An INDEPENDENT CLAIM is included for preparation of positive electrode active material, which involves dispersing hydroxide containing transition metal element into a mixture containing water, aqueous solution of aluminum salt and aqueous alkali-solution, obtaining active material precursor by treating surface of hydroxide containing-transition metal element supported by aluminum atom, mixing active material precursor and lithium atom-containing compound, heat-processing to obtain particles containing aluminum atom, washing the particles containing aluminum atom using water, and drying.    DESCRIPTION OF DRAWING(S) - The drawing shows the longitudinal cross-sectional view of positive electrode active material contained in non-aqueous electrolyte secondary battery.    Positive electrode active material (1)    Secondary particles (2)    Primary particles (3)