Cathode active material and lithium secondary battery containing the same

A cathode active material for a lithium secondary battery, comprising a mixture of a lithium/manganese spinel oxide represented by Formula I and a lithium/nickel/cobalt/manganese composite oxide represented by Formula II, wherein the cathode active material exhibits the life characteristics that the capacity at 300 cycles is more than 80% relative to the initial capacity, in the provision that the below conditions (i) and (ii) are satisfied,

• (i) the lithium/manganese spinel oxide of Formula I has an average particle diameter of 15-30 μm, or the lithium/manganese spinel oxide of Formula I and the lithium/nickel/cobalt/manganese composite oxide of Formula II have an average particle diameter of 15-30 μm, respectively;
• and
• (ii) the mixing ratio of the lithium/manganese spinel oxide:lithium/nickel/cobalt/manganese composite oxide is in the range of 10:90 to 70:30 (w/w),
• Li1+xMn2O4 (I)
• Li1+yNibMncCo1−(b+c)O2 (II)
• wherein,
• 0≦x≦0.2;
• 0≦y≦0.1;
• 0.2≦b≦0.7;
• 0.2≦c≦0.7;
• and
• b+c<1;
• wherein each oxide is an aggregate of large numbers of oxide units, and
• wherein an oxide unit of the lithium/manganese spinel oxide of Formula I has a particle diameter of 0.2 to 12 μm and surface area of 0.1 to 1.0 m2/g.