Nickel-based active material for lithium secondary battery, preparing method thereof, and lithium secondary battery including positive electrode including the same

A method of preparing a nickel-based active material for a lithium secondary battery, the method comprising:

• mixing a lithium precursor and a metal hydroxide to form a mixture, and
• conducting a primary heat treatment on the mixture under an oxidizing gas atmosphere at 600° C. to 800° C.,
• wherein the nickel-based active material comprises a porous inner portion having closed pores and an outer portion,
• the porous inner portion has a density less than that of the outer portion, and
• the nickel-based active material has a net density of 4.7 g/cc or less, and
• wherein a volume of the porous inner portion is 20 to 35% based on a total volume of the nickel-based active material.