A positive electrode active material for a secondary battery, the positive electrode active material being a secondary particle that includes a primary particle having a rectangular parallelepiped shape, the rectangular parallelepiped having at least one portion of vertices and edges formed in a round shape that is convex outward, wherein:
- 1% to 40% of a total surface area of the secondary particle has open porosity;
- and
- the primary particle includes a lithium composite metal oxide of Formula 1 below:
- LiaNi1-x-yCoxM1yM3zM2wO2 [Formula 1]
- (In Formula 1, M1 is at least one selected from the group consisting of Al and Mn, M2 is any one or two or more elements selected from the group consisting of Zr, Ti, Mg, Ta, and Nb, M3 is any one or two or more elements selected from the group consisting of W, and Mo, and 1.0≤a≤1.5, 0<x≤0.5, 0<y≤0.5, 0.002≤z≤0.03, 0≤w≤0.02, 0<x+y≤0.7).