| abstract |
Provided is a positive electrode active material for lithium ion secondary batteries which comprises lithium composite oxide particles containing Li, Ni, Mn, Zr and an additional element M in the ratio Li:Ni:Mn:Zr:M=a:b:c:d:e in terms of an amount of substance ratio (where 0.95≤a≤1.20, 0.10≤b<0.70, 0.01≤c≤0.50, 0.0003≤d≤0.02, 0.01≤e≤0.50, and the additional element M is at least one element selected from Co, W, Mo, V, Mg, Ca, Al, Ti and Ta). The full width at half maximum FWHM(003) of the (003) plane peak and the full width at half maximum FWHM(104) of the (104) plane peak as calculated from an X ray diffraction pattern of the lithium composite oxide satisfy the relationship FWHM(104)≥FWHM(003)×2.90-0.10. |