| CPC H01M 4/505 (2013.01) [C01G 53/42 (2013.01); C01G 53/44 (2013.01); H01M 4/525 (2013.01); H01M 10/0525 (2013.01); C01P 2002/50 (2013.01); C01P 2002/74 (2013.01); C01P 2002/76 (2013.01); C01P 2004/03 (2013.01); C01P 2004/50 (2013.01); C01P 2004/61 (2013.01); C01P 2004/62 (2013.01); C01P 2006/12 (2013.01); C01P 2006/40 (2013.01); H01M 2004/021 (2013.01); H01M 2004/028 (2013.01)] | 4 Claims |

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1. A positive electrode active material for a lithium ion secondary battery, the positive electrode active material comprising a lithium-nickel composite oxide having a hexagonal layered structure and configured by single primary particles or by single primary particles and secondary particles with a plurality of aggregated primary particles,
wherein a number proportion of the single primary particles to all of the single primary and secondary particles is 30% or more,
elements constituting the lithium-nickel composite oxide include lithium (Li), nickel (Ni), and optionally at least one element M (M) selected from the group consisting of Co, Mn, Al, V, Mg, Mo, Ca, Cr, Zr, Ti, Nb, Na, K, W, Fe, Zn, B, Si, P, and Ta,
a mole number ratio of the elements is represented as Li: Ni: M=a: b: c (provided that, 0.95≤a≤1.10, 0.30≤b≤1.00, 0.00≤c≤0.70, and b+c=1), a ratio of a (003) diffraction peak intensity I(003) to a (104) diffraction peak intensity I(104) (I(003)/I(104)) is 2.0 or more, the (003) diffraction peak intensity and the (104) diffraction peak intensity determined from X-ray diffraction measured using a flat plate sample holder of a Bragg Brentano optical system using a Cu-kα ray as an X-ray source,
a degree of circularity is 0.93 or more and 1.00 or less, the degree of circularity determined with a flow image analysis method using a wet flow particle size/shape analyzer, and
the positive electrode active material has a specific surface area of 1.0 m2/g or more and 5.0 m2/g or less, and the specific surface area is determined with a nitrogen adsorption method.
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