Composite positive active material, method of preparing the same, and positive electrode and lithium battery containing the material

Provided are a composite positive active material, a positive electrode and a lithium battery containing the composite positive active material, and a method of preparing the composite positive active material. The composite positive active material includes an over-lithiated lithium transition metal oxide having a layered structure, and a Li ion layer of Li 2 MnO 3 phase is doped with metal cation. Accordingly, a change in a discharging curve of a lithium battery including the composite positive active material is suppressed when charging and discharging proceed at high voltage, and accordingly, capacity and lifetime properties of the lithium battery improve.