Positive electrode active material and lithium secondary battery comprising the same

A bimodal-type positive electrode active material comprising a first lithium composite oxide which is a small particle and a second lithium composite oxide which is a large particle,

• wherein the bimodal-type positive electrode active material is prepared by simultaneous calcination of a mixture of a first hydroxide precursor which is a precursor of the first lithium composite oxide, and a second hydroxide precursor which is a precursor of the second lithium composite oxide,
• wherein an Mn concentration (α) in the first lithium composite oxide and an Mn concentration (β) in the second lithium composite oxide satisfy Equation 1 below:
• |α(mol %)−β (mol %)|≤2.0, [Equation 1]
• wherein the first lithium composite oxide and the second lithium composite oxide are represented by Formula 1 below:
• LiwNi1-(x+y+z)CoxMnyM1zO2+δ, [Formula 1]
• wherein M1 is at least one selected from P, Sr, Ba, B, Ti, Zr, W, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, Gd and Cu, 0.5≤w≤1.5, 0<y≤0.046, 0≤x+y+z≤0.15, and 0≤δ≤0.02, and
• wherein the mole fraction of nickel (Ni/(Ni+Mn+Co+M1)) calculated from an average composition of the bimodal-type positive electrode active material satisfies Equation 2 below:
• Ni/(Ni+Mn+Co+M1)≥85.0, [Equation 2]
• wherein the mole fraction of nickel (Ni/(Ni+Mn+Co+M1)) calculated from the second lithium composite oxide is larger than the mole fraction of nickel (Ni/(Ni+Mn+Co+M1)) calculated from the first lithium composite oxide,
• wherein the difference (mol %) between the mole fraction of nickel (Ni/(Ni+Mn+Co+M1)) calculated from the second lithium composite oxide and the mole fraction of nickel (Ni/(Ni+Mn+Co+M1)) calculated from the first lithium composite oxide is 4.1 or more,
• wherein the mole fraction of manganese (Mn/(Ni+Mn+Co+M1)) calculated from the first lithium composite oxide is larger than the mole fraction of manganese (Mn/(Ni+Mn+Co+M1)) calculated from the second lithium composite oxide,
• wherein the first lithium composite oxide and the second lithium composite oxide have a concentration gradient in which the concentration of Ni is decreased from the center to the surface of the particle, and the concentration of Co is increased from the center to the surface of the particle, and
• wherein the first lithium composite oxide and the second lithium composite oxide have a constant Mn concentration from the center to the surface of the particle.