| CPC H01M 4/364 (2013.01) [H01M 4/0471 (2013.01); H01M 4/366 (2013.01); H01M 4/505 (2013.01); H01M 4/525 (2013.01); C01G 53/42 (2013.01); C01P 2004/03 (2013.01); C01P 2004/50 (2013.01); C01P 2004/54 (2013.01); C01P 2004/61 (2013.01); C01P 2006/40 (2013.01); H01M 2004/021 (2013.01); H01M 2004/028 (2013.01); H01M 10/0525 (2013.01); Y02E 60/10 (2013.01)] | 16 Claims |

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1. A positive electrode active material for a rechargeable lithium battery, comprising:
a lithium nickel-based composite oxide, wherein the positive electrode active material is in a form of a secondary particle in which a plurality of primary particles are aggregated together and at least a portion of the primary particles are radially arranged,
the secondary particle comprises an inner portion and an outer portion, the inner portion of the secondary particle is a region from a center of the secondary particle to 50±5 length % of the total distance from the center of the secondary particle to the surface of the secondary particle, and is a region in which primary particles and pores are irregularly arranged, the outer portion of the secondary particle is the remaining region surrounding the inner portion, wherein at least a portion of the primary particles are radially arranged in the outer portion, and
a number ratio of the primary particles having an aspect ratio of greater than or equal to about 4 in the outer portion of the secondary particle is greater than or equal to about 18%.
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