Positive electrode active material for rechargeable lithium battery and rechargeable lithium battery including same

A positive electrode active material for a rechargeable lithium battery, comprising,

• a particle comprising a core and a surface layer formed on the core,
• the core comprising a first core crystalline structure,
• the surface layer comprising a first surface crystalline structure and a second surface crystalline structure different from the first surface crystalline structure and the first core crystalline structure,
• the first surface crystalline structure being present at a higher concentration than the second crystalline structure in the surface layer,
• wherein a volume ratio of the first surface crystalline structure and the second surface crystalline structure is 9:1 to 7:3 in the surface layer,
• wherein the surface layer is the outermost layer of the particle, and
• wherein the first core crystalline structure is a layered structure, and the first surface crystalline structure is a layered structure which is a main phase, and
• the second surface crystalline structure is a spinel structure, and
• wherein
• the surface layer comprises a compound represented by Chemical Formula 1,
• LiaCo1-bXbO2 [Chemical Formula 1]
• wherein, in Chemical Formula 1,
• 0.90≤a≤1.8, 0≤b≤0.5,
• and X is selected from Al, Ni, Co, Cr, Fe, Mg, Sr, V, rare-earth elements, or a combination thereof.