| CPC H01M 4/525 (2013.01) [H01M 4/0471 (2013.01); H01M 4/1391 (2013.01); H01M 4/366 (2013.01); H01M 4/485 (2013.01); H01M 4/505 (2013.01); H01M 10/052 (2013.01); C01P 2002/32 (2013.01); C01P 2002/72 (2013.01); C01P 2004/04 (2013.01); H01M 2004/028 (2013.01); H01M 10/0525 (2013.01)] | 23 Claims |

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1. 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 manganese and cobalt in the grain boundary is greater than a concentration of manganese and cobalt in the primary particles respectively, 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.
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