Positive active material for rechargeable lithium battery, preparing method thereof and rechargeable lithium battery comprising positive electrode including positive active material

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

• subjecting a first precursor to a first heat-treatment in a first oxidizing gas atmosphere to obtain a first nickel-based oxide;
• subjecting a second precursor to a second heat-treatment in a second oxidizing gas atmosphere to obtain a second nickel-based oxide having a monolith structure;
• mixing the second nickel-based oxide and a boron-containing precursor and subjecting the mixture to a third heat-treatment to obtain the second nickel-based oxide coated with a boron-containing compound;
• and
• mixing the first nickel-based oxide and the second nickel-based oxide coated with the boron-containing compound to obtain a positive active material comprising a first positive active material and a second positive active material having a monolith structure and coated with the boron-containing compound,
• wherein,
• the boron-containing compound is coated on only a surface of the second positive active material, and
• an amount of boron based on a total amount of the second positive active material is 0.3 mol % or less.