A cathode active material includes: (a) first oxide including (1) lithium
(Li), nickel (Ni) and manganese, (2) a first element MI selected from
Group 2 to Group 14 elements, and (3) oxygen; (b) a second oxide
including (1) lithium, (2) a second element MII including nickel and
cobalt, (3) manganese, (4) a third element including at least one of the
elements of Group 2 to Group 14 elements, except for nickel, cobalt and
manganese, and (5) oxygen.