Positive Electrode Active Material, Method for Preparing the Same, Positive Electrode and Lithium Secondary Battery Comprising the Same

A positive electrode active material includes a lithium-rich manganese-based oxide represented by the following Chemical Formula 1, and has a structure in which a rock-salt-type lithium manganese oxide and a layered lithium transition metal oxide are mixed. The lithium-rich manganese-based oxide may have a prescribed internal porosity.