| 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 2002/74 (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); H01M 2004/021 (2013.01); H01M 2004/028 (2013.01)] | 9 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 particles including at least either single primary particles or secondary particles with a plurality of aggregated primary particles, 
            wherein metal 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 metal 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), and 
                the particles included in the positive electrode active material have a cross section having an area proportion of a crystal face having a maximum area to the cross section of 80% or more when one crystal face is defined as a region having a crystal misorientation of 15° or less with respect to an orientation of the cross section measured by Electron Backscatter Diffraction method. 
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