A cathode active material includes a first cathode active material particle and a second cathode active material particle. The first cathode active material particle includes a lithium metal oxide including a concentration gradient and has a secondary particle structure formed from an assembly of primary particles. The second cathode active material particle includes a lithium metal oxide having a single particle structure. The first and second cathode active material particles each includes at least two metals except from lithium, and an amount of nickel is the largest among those of the metals in each of the first and second cathode active material particles.