Metal-doped cobalt precursor for preparing positive electrode active material for secondary battery

1. A lithium cobalt oxide having a layered structure for a positive electrode active material, wherein the lithium cobalt oxide is represented by the following Formula 1, and doped with, as dopants, magnesium (Mg) and M′; and

the dopants have an average oxidation number of more than +2 to +2.5 or less in the lithium cobalt oxide:

Li a (Co x Mg y M′ z )O 2   (1)

wherein a satisfies 0.95≤a≤1.05;

x, y, and z satisfy the following weight ratio conditions: a content of x is in the range of 99 wt % to 99.8 wt % and a total content of y and z is in the range of 0.2 wt % to 1 wt %, when the sum of x, y, and z is regarded as 100 wt %; and

M′ is one or more selected from the group consisting of Al, Ti, Mn, Zr, Ba, B, Ca, Ta, Mo, Nb, W, Sr, and PO 4 ,

wherein the positive electrode active material is in the form of particles, and the surface of the particle is coated with Al 2 O 3 , and

wherein the Al 2 O 3 is applied at a thickness of 0.2% to 5% of a diameter of the positive electrode active material particle.

2. The lithium cobalt oxide of claim 1 , wherein the lithium cobalt oxide maintains a crystal structure in a charging range of more than 4.5 V and 4.8 V or less.

3. The lithium cobalt oxide of claim 2 , wherein the crystal structure is O3 phase.

4. The lithium cobalt oxide of claim 2 ,

wherein the lithium cobalt oxide has a structure in which a ratio of a peak intensity of O3 phase to a peak intensity of H1-3 phase is more than 1 in the spectrum of X-ray diffraction (XRD) analysis using Cu-Kα.

5. The lithium cobalt oxide of claim 1 , wherein the lithium cobalt oxide has no plateau in voltage when discharged from 4.55 V to 3.0 V at a rate of 1.0 C.