Composite cathode active material, cathode and lithium battery including the same, and method of preparing the composite cathode active material

A composite cathode active material comprising:

• a core comprising
• a plurality of primary particles comprising a nickel-containing first lithium transition metal oxide having a layered crystal structure, and
• a grain boundary between adjacent primary particles of the plurality of primary particles;
• and
• a shell on the core, the shell comprising a second lithium transition metal oxide having a spinel crystal structure,
• wherein the grain boundary comprises a first composition having a spinel crystal structure,
• wherein a concentration of cobalt in the grain boundary is greater than a concentration of cobalt in the primary particles, and
• wherein the second lithium transition metal oxide is represented by Formula 7:
• LiaMnbCocM5′dO4 Formula 7
• wherein, in Formula 7,
• M5′ comprises vanadium, chromium, iron, zirconium, rhenium, aluminum, boron, germanium, ruthenium, tin, titanium, niobium, molybdenum, or platinum,
• 0.9≤a≤1.1, 0<b<2.0, 0<c<2.0, 0≤d<0.1, and b+c+d=2.