CATHODE ACTIVE MATERIAL FOR SECONDARY BATTERY, PREPARATION METHOD THEREFOR, AND LITHIUM SECONDARY BATTERY COMPRISING SAME

The present invention relates to a positive electrode active material for a secondary battery which includes a first positive electrode active material and a second positive electrode active material, wherein an average particle diameter (D50) of the first positive electrode active material is twice or more an average particle diameter (D50) of the second positive electrode active material, and the second positive electrode active material has a crystallite size of 200 nm to 400 nm.