Positive active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery comprising same

A positive active material for a non-aqueous electrolyte secondary battery includes a lithium-nickel composite oxide represented by the compositional formula Li_aNi_1-b-cCO_bMn_cO₂ (a1.09, 0.05b0.35, 0.15c0.35, and 0.25b+c0.55). By X-ray diffractometry with a CuK ray, the lithium-nickel composite oxide exhibits an intensity ratio R ((I₀₁₂+I₀₀₆)/I₁₀₁) of not greater than 0.50, wherein R is the ratio of the sum of the diffraction peak intensity I₀₁₂ on the 012 plane and the diffraction peak intensity I₀₀₆ on the 006 plane to the diffraction peak intensity I₁₀₁ on the 101 plane. The crystallinity of the positive active material of the compositional formula Li_aNi_1-b-cCo_bMn_cO₂ can be kept high and it is possible to secure good capacity density and cycle life performance.