Positive electrode active material for lithium secondary battery, method for preparing the same, and lithium secondary battery including the same

A positive electrode active material for secondary batteries, the positive electrode active material comprising an overlithiated layered oxide (OLO) represented by the following Chemical Formula 1:

• rLi2MnO3·(1−r)LiaNixCoyMnzM11-(x+y+z)O2, Chemical Formula 1
• (where 0<r≤0.6, 0<a≤1, 0≤x≤1, 0≤y<1, 0≤z<1, 0<x+y+z<1, and M1 is one or more selected from Ba, Sr, P, Y, Zr, Nb, Mo, Ta, and W)
• wherein primary particles are aggregated to form secondary particles,
• wherein primary particles having a size in a range of 1 μm to 10 μm are 50 to 100% by volume of the primary particles constituting the secondary particles,
• wherein the OLO represented by Chemical Formula 1 is in a solid solution phase in which Li2MnO3 having a monoclinic structure and LiMO2 having a rhombohedral structure are mixed,
• where M is one or more selected from Ni, Co, Mn, and M1,
• wherein M1 is a dopant material, and
• wherein the positive electrode active material includes a material represented by the following Chemical Formula 2:
• LiaM1Ob, Chemical Formula 2
• (where 0<a≤7, 0<b≤15, and M1 is one or more selected from Ba, Sr, P, Y, Zr, Nb, Mo, Ta, and W), and
• where M1 is included in the OLO represented by Chemical Formula 1 in an amount in a range of from 0.01 mol % to 10 mol %.