Positive electrode material for secondary battery and lithium secondary battery including the same

A positive electrode material for a secondary battery, comprising:

• a first positive electrode active material and a second positive electrode active material,
• wherein each of the first positive electrode active material and the second positive electrode active material consists of a lithium composite transition metal oxide including two or more transition metals selected from the group consisting of nickel (Ni), cobalt (Co) and manganese (Mn),
• an average particle size (D50) of the first positive electrode active material is at least two times larger than that of the second positive electrode active material, and
• the first positive electrode active material has a concentration gradient in which at least one of Ni, Co or Mn contained in the lithium composite transition metal oxide has a concentration difference of 1.5 mol % or more between a center and a surface of a particle of the lithium composite transition metal oxide,
• wherein the second positive electrode active material further comprises a coating layer on at least a part of the surface of the particle,
• the coating layer comprises a lithium oxide containing at least one or more selected from the group consisting of boron (B) and manganese (Mn), and
• wherein the first positive electrode active material has the concentration gradient in which a concentration of at least one of Mn or Co is gradually increased at a rate of 0.1 to 5 mol % per 1 μm from the center to the surface of the particle of the lithium composite transition metal oxide based on a total mole number of Mn or Co, respectively, included in the positive electrode active material.