Positive electrode active material and method for producing same, and non-aqueous electrolyte secondary battery using same

A positive electrode active material comprising a layered lithium-composite oxide containing Li, Ni and Mn, and optionally containing Co, wherein

• the positive electrode active material is represented by the compositional formula (II):
• Li1+β(NiaCobMnc)1−βO2 (II)
• in the compositional formula (II), a range of B is 0.11≤β≤0.18, a range of a is 0.20 ≤a≤0.40, a range of b is 0≤b≤0.08, and a, b and c are fixed as a +b+c=1;
• a relative height intensity ratio of (IIa) to (IIb), (IIa)/(IIb), is 0.015-0.035, in which
• (IIa) is a height intensity of a maximum diffraction peak at 2θ=20.8±1° and
• (IIb) is a height intensity of a maximum diffraction peak at 2θ=18.6±1°,
• in a powder X-ray diffraction pattern obtained by using Cu-Kα ray;
• a crystallite size calculated by using Scherrer's equation from (104) diffracted X-ray is 25-40 nm, in the powder X-ray diffraction pattern obtained by using Cu-Ka ray;
• and
• a BET specific surface area obtained by using a BET method is 3.5-8.5 m2/g.