Cathode active material for lithium secondary battery and lithium secondary battery including the same

A cathode active material for a lithium secondary battery comprising a lithium-transition metal composite oxide particle,

• wherein a lattice strain (η) calculated by applying Williamson-Hall method defined by Equation 1 to XRD peaks measured through X-ray diffraction (XRD) analysis is 0.18 or less;
• an XRD peak intensity ratio defined by Equation 2 is 8.9% or less;
• and
• the lattice strain of the lithium-transition metal composite oxide particle is a slope of a straight line, and the straight line is obtained by acquiring full widths at half maximum of all peaks appearing through the XRD analysis, and substituting the acquired full widths at half maximum in Equation 1 when plotting a horizontal axis with sine, and a vertical axis with β cos θ,
• β cos θ=η sin θ+λ/D [Equation 1]
• wherein in Equation 1, β represents full width at half maximum (FWHM) (rad) of the corresponding peak acquired through the XRD analysis, θ represents a diffraction angle (rad), η represents a lattice strain (dimensionless number), λ represents an X-ray wavelength (Å), and D represents a crystallite size (Å),
• XRD peak intensity ratio (%)=100×I(110)/{I(110)+I(003)} [Equation 2]
• wherein in Equation 2, I(110) represents a maximum height of the peak of a (110) plane of the lithium-transition metal composite oxide particle by the XRD analysis, and I(003) represents a maximum height of the peak of a (003) plane of the lithium-transition metal composite oxide particle by the XRD analysis,
• wherein the lithium-transition metal composite oxide particle has a composition represented by Chemical Formula 1 below:
• LixNi1−yMyO2+z, and [Chemical Formula 1]
• wherein in Chemical Formula 1, x is in a range of 0.9≤x≤1.2, y is in a range of 0≤y≤0.7, and z is in a range of −0.1≤z≤0.1, and
• wherein M includes Mn and Co.