Positive active material, positive electrode including the same, and lithium secondary battery including the positive electrode

A positive active material for a lithium secondary battery, the positive active material comprising:

• a lithium cobalt oxide containing a metal element,
• wherein the lithium cobalt oxide containing a metal element is represented by Formula 1:
• Lia(Co1.0-x-yMgxMny)O2 Formula 1
• wherein, in Formula 1,
• 0.8≦a≦1.2, 0.0025≦x≦0.005, and 0.0025≦y≦0.0075,
• wherein the lithium cobalt oxide containing a metal element has a ratio of a peak intensity of an O3 phase to a peak intensity of an H1-3 phase, IO3/IH1-3, that is greater than 1 in an X-ray diffraction (XRD) analysis spectrum using Cu-Kα radiation, and
• wherein an average particle diameter D50 of the lithium cobalt oxide containing a metal element is in a range of about 8 μm to about 20 μm, and
• the metal element is placed in a site of the cobalt in a crystal lattice of the lithium cobalt oxide.