Positive electrode active materials for lithium secondary battery, method for preparing the same and lithium secondary battery comprising the same

A lithium secondary battery, comprising:

• an electrode assembly having a positive electrode plate, a negative electrode plate, and a separator interposed between the positive and negative electrode plates;
• and
• a case for housing the electrode assembly,
• wherein the positive electrode plate comprises positive electrode collector coated with a lithiated metal oxide represented by the formula:
• LiMO2, wherein,
• M is a nickel-cobalt based metallic composite having a first crystalline phase that is stable at a high temperature, and a second crystalline phase that is stable at a low temperature, and
• an X-ray diffraction peak intensity ratio, of the first crystalline phase to the second crystalline phase, is at least 46%.

A method of preparing a positive electrode active material for a lithium secondary battery, the method comprising:

• mixing a lithiated metal oxide represented by the formulas Ni(1-x-y)CoxAlyO2, or Ni(1-x-y)CoxMnyO2, (0.1<x<0.15 and 0.03<y<0.1) with lithium hydrates (LiOH.H2O);
• and
• calcinating the mixture to form the positive active material,
• wherein the positive active material has an X-ray diffraction peak intensity ratio, of a first crystalline phase to a second crystalline phase (I(104)/I(003)), in the range of from 46% to 51%.