Positive electrode active material and lithium secondary battery comprising the same

1. A positive electrode active material, comprising:

a lithium composite oxide comprising primary particles and secondary particles formed by agglomerating the primary particles; and

at least one lithium alloy oxide represented by Formula 1 below and existing at least at a part of a) the interface between the primary particles and b) the surface of the secondary particle;

wherein the lithium alloy oxide exhibits a concentration gradient which decreases from the surface to the center of the secondary particle:

Li a M1 b O c   [Formula 1]

(wherein, M1 is at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd, 0≤a≤6, 0<b≤6, and 0<c≤10),

wherein the lithium alloy oxide comprises a first lithium alloy oxide represented by Formula 2 below; and at least one second lithium alloy oxide represented by Formula 3 below:

Li d W e O f   [Formula 2]

(wherein, 0≤d≤6, 0<e≤6, 0<f≤10)

Li g M2 h O i   [Formula 3]

(wherein, M2 is at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, Nd and Gd, 0≤g≤6, 0<h≤6, and 0<i≤10).

2. The positive electrode active material of claim 1 , wherein the first lithium alloy oxide and the second lithium alloy oxide exhibit concentration gradients which decrease from the surface to the center of the secondary particle, and the second lithium alloy oxide has a higher concentration reduction rate than the first lithium alloy oxide.

3. The positive electrode active material of claim 1 , wherein the second lithium alloy oxide comprises a lithium zirconium oxide represented by Formula 4 below, and a lithium titanium oxide represented by Formula 5 below:

Li j Zr k O l   [Equation 4]

(wherein, 0≤j≤6, 0<k≤6, 0<l≤10)

Li m Ti n O p   [Equation 5]

(wherein, 0≤m≤6, 0<n≤6, 0<p≤10).

4. The positive electrode active material of claim 3 , wherein the lithium zirconium oxide has a higher concentration reduction rate than the lithium titanium oxide.

5. The positive electrode active material of claim 1 , wherein the primary particles forming the lithium composite oxide are represented by Formula 6 below:

Li w Ni 1-(x+y+z) Co x M3 y M4 z O 2   [Formula 6]

(wherein, M3 is at least one selected from Mn and Al, M4 is at least one selected from Ti, Zr, Mg, V, B, Mo, Zn, Nb, Ba, Ta, Fe, Cr, Sn, Hf, Ce, W, Nd and Gd, 0.5≤w≤1.5, 0<x≤0.50, 0≤y≤0.20, and 0≤z≤0.20).

6. A lithium secondary battery comprising a positive electrode including the positive electrode active material according to claim 1 .