A lithium complex oxide includes a mixture of first particles of n1 (n1>40) aggregated primary particles and second particles of n2 (n2≤20) aggregated primary particles, the lithium complex oxide represented by Chemical Formula 1 and having FWHM (deg., 2θ) of 104 peak in XRD, defined by a hexagonal lattice having R-3m space group, in a range of Formula 1: LiaNixCoyMnzM1-x-y-zO2,  [Chemical Formula 1] where M is selected from: B, Ba, Ce, Cr, F, Mg, Al, Cr, V, Ti, Fe, Zr, Zn, Si, Y, Nb, Ga, Sn, Mo, W, P, Sr, and any combination thereof, 0.9≤a≤1.3, 0.6≤x≤1.0, 0.0≤y≤=0.4, 0.0≤z≤0.4, and 0.0≤1−x−y−z≤0.4, −0.025≤FWHM(104)−{0.04+(xfirst particle−0.6)×0.25}≤0.025,  [Formula 1] where FWHM(104) is represented by Formula 2, FWHM(104)={(FWHMChemical Formula 1 powder(104)−0.1×mass ratio of second particles)/mass ratio of first particles}−FWHMSi powder(220).  [Formula 2]