Positive active material for rechargeable lithium battery, method of preparing the same and rechargeable lithium battery including the same

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

• a first compound represented by Chemical Formula 1, and
• a second compound having a smaller particle diameter than the first compound and represented by Chemical Formula 2,
• wherein the first compound and the second compound each have a Ni content of about 50 at % to about 60 at % based on the total amount of metal elements excluding Li, and
• a rechargeable lithium battery comprising the first compound and the second compound satisfies Relation 1, as determined from a differential capacity (dQ/dV)-voltage charge/discharge plot:
• LiaNixCoyM1zO2 [Chemical Formula 1]
• LiaNixCoyM2zO2 [Chemical Formula 2]
• wherein, in Chemical Formula 1 and Chemical Formula 2, 0.9≤a≤1.05, 0.5≤x≤0.6, 0.05≤y≤0.35, 0.05≤z≤0.35, x+y+z=1, and M1 and M2 are each independently at least one metal element selected from Mn, Al, Cr, Fe, V, Mg, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce,
• Vs<V1≤3.6 [Relation 1]
• wherein, in Relation 1, V1 is a voltage value at a point where a tangent line to a value corresponding to 50% of the first peak value of the differential capacity (dQ/dV)-voltage charge/discharge plot intersects the line dQ/dV=0, and Vs is a charge start voltage.