Nickel-based lithium metal composite oxide, method of preparing the same, and lithium secondary battery including positive electrode including the same

A nickel-based lithium metal composite oxide comprising secondary particles including aggregates of primary particles,

• wherein:
• the secondary particles comprise i) large secondary particles having a particle size of at least 14 μm and including aluminum and ii) small secondary particles having a particle size of no more than 5 μm and including manganese;
• each of the large secondary particles comprises a core and a surface layer around the core, and each of the small secondary particles comprises a core and a surface layer around the core;
• a manganese content by mole percent of the large secondary particles based on total moles of metal excluding lithium of the large secondary particles is smaller than a manganese content by mole percent of the small secondary particles based on total moles of metal excluding lithium of the small secondary particles;
• and
• the surface layer of at least some of the large secondary particles comprises aluminum and from 0.01 mol % to 0.2 mol % manganese based on a total amount of transition metals of the large secondary particles,
• the manganese on the surface layer of the large secondary particles is a kind of manganese from a precursor of the small secondary particles, and
• the surface layer of at least some of the small secondary particles comprises manganese and from 0.01 mol % to 0.2 mol % aluminum based on a total amount of transition metals of the small secondary particles,
• wherein the core of each of the small secondary particles consists of a compound represented by Formula 2:
• Lia(Ni1−x−y−zCoxMnyMz)O2±α1, and Formula 2
• wherein in Formula 2, M is boron, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, iron, copper, or zirconium,
• 0.95≤a≤1.1, 0.6≤(1-x-y-z)<1, 0<x<0.4, 0<y<0.4, 0≤z<0.4, and 0≤α1≤0.1.