Positive electrode active material and lithium secondary battery comprising the same

A positive electrode active material, comprising:

• a positive electrode active material comprising a lithium-based composite oxide having a single crystal structure,
• wherein a cation-mixing layer is present on the surface of the lithium-based composite oxide, and
• a ratio (d1/x1) of the thickness (d1) of the cation-mixing layer to the average particle size (x1) of primary particles ranges from more than 0.0008 and less than 0.0052, wherein the lithium-based composite oxide is represented by Formula 1 below:
• LiaNi1-(b+c+d+e)CObM1cM2dM3eOf [Formula 1]
• Here, M1 is Mn or Al,
• M2 and M3 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, and
• M1 to M3 are different metals
• (0.90≤a≤1.05, 0≤b≤0.20, 0≤c≤0.20, 0≤d≤0.05, 0≤e≤0.05, and 1.0≤f≤2.0), wherein the cation-mixing layer comprises a composite oxide represented by Formula 2 below:
• LigNi1-(h+i+j+k)CohM4iM5jM6kOl [Formula 2]
• Here, M4 is Mn or Al,
• M5 and M6 are each independently selected from Al, Ba, B, Ce, Cr, Mg, Mn, Mo, Na, K, P, Sr, Ti, W, Nb, and Zr, and
• M4 to M6 are different metals
• (0.0≤g≤1.05, 0≤h≤0.20, 0≤i≤0.20, 0≤j≤0.05, 0≤k≤0.05, and 1.0≤l≤2.0), wherein the crystal structure of the composite oxide represented by Formula 2 is different from the lithium-based composite oxide.