Precursor of transition metal oxide, preparation method thereof, lithium composite transition metal oxide, and positive electrode and secondary battery including the same

1. A precursor of a transition metal oxide, the precursor comprising a core unit and a shell unit,

wherein the core unit comprises a compound represented by chemical formula 1 below, and

the shell unit comprises a compound represented by chemical formula 2 below,

Ni a Mn b Co 1−(a+b+c) M c [OH (1−x)2−y ]A (y/n)   [Chemical formula 1]

wherein M is at least one selected from a group consisting of W, B, Al, Zr, Ti, Mg, Cr and Si, 0.55≤a≤0.9, 0.05≤b≤0.5, 0≤c≤0.1, a+b+c≤1, 0<x<0.5, 0≤y≤0.05, n is an oxidation number of A, and A is at least one selected from a group consisting of PO 4 , CO 3 , BO 3 , and F,

Ni a′ Mn b′ Co 1−(a′+b′+c′) M′ c′ [OH (1−x′)2−y′ ]A′ (y′/n)   [Chemical formula 2]

wherein M′ is at least one selected from a group consisting of W, B, Al, Zr, Ti, Mg, Cr and Si, 0.2≤a′≤0.55, 0.05≤b′≤0.5,0≤c′≤0.1, a′+b′+c′≤0.95, 0<x′<0.5, 0≤y′≤0.05, n is an oxidation number of A′, and A′ is at least one selected from a group consisting of PO 4 , CO 3 , BO 3 , and F.

2. The precursor of claim 1 , wherein at least one of the A and A′ comprises PO 4 and F.

3. The precursor of claim 1 , wherein a weight ratio of the core unit and the shell unit is 1:0.2to 1:2.

4. The precursor of claim 1 , wherein a tap density of the precursor of the transition metal oxide is 1.0 g/cc to 2.5 g/cc.

5. A preparation method for a precursor of a transition metal oxide, the precursor comprising a core unit and a shell unit, the method comprising:

mixing a first transition metal salt and an alkaline compound to form a core unit represented by chemical formula 1 below;

mixing a second transition metal salt and the alkaline compound with the core unit to form a shell unit represented by chemical formula 2 below on a surface of the core unit;

filtering and washing the precursor comprising the core unit and the shell unit; and

then drying the same,

Ni a Mn b Co 1−(a+b+c) M c [OH (1−x)2−y ]A (y/n)   [Chemical formula 1]

wherein M is at least one selected from a group consisting of W, B, Al, Zr, Ti, Mg, Cr and Si, 0.55≤a≤0.9, 0.05≤b≤0.5, 0≤c≤0.1, a+b+c≤1, 0<x<0.5, 0≤y≤0.05, n is an oxidation number of A, and A is at least one selected from a group consisting of PO 4 , CO 3 , BO 3 , and F,

Ni a′ Mn b′ Co 1−(a′+b′+c′) M′ c′ [OH (1−x′)2−y′ ]A′ (y′/n)   [Chemical formula 2]

wherein M′ is at least one selected from a group consisting of W, B, Al, Zr, Ti, Mg, Cr and Si, 0.2≤a′≤0.55, 0.05≤b′≤0.5, 0≤c′≤0.1, a′+b′+c′≤0.95, 0<x′<0.5, 0≤y′≤0.05, n is an oxidation number of A′, and A′ is at least one selected from a group consisting of PO 4 , CO 3 , BO 3 , and F.

6. The method of claim 5 , wherein at least one of the first transition metal salt and the second transition metal salt is sulphate or nitrate.

7. A lithium composite transition metal oxide prepared by plasticizing the precursor of claim 1 and a lithium compound.

8. The lithium composite transition metal oxide of claim 7 , wherein the lithium compound is at least one of lithium hydroxide, lithium carbonate and lithium oxide.

9. The lithium composite transition metal oxide of claim 7 , wherein the lithium compound is 0.95 to 1.2 mol to 1 mol of the precursor of the transition metal oxide.

10. The lithium composite transition metal oxide of claim 7 , wherein the plasticizing is performed at a temperature of 600° C. to 1000° C.

11. A positive electrode comprising the lithium composite transition metal oxide of claim 7 .

12. A secondary battery comprising the positive electrode of claim 11 .