POSITIVE ELECTRODE ACTIVE MATERIAL FOR NONAQUEOUS ELECTROLYTE SECONDARY BATTERIES, POSITIVE ELECTRO

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Provided are : a positive electrode active material which is capable of exhibiting sufficient discharge capacity and excellent capacity retention rate during high-voltage charging; a positive electrode which uses this positive electrode active material; and a secondary battery. This positive electrode active material is composed of lithium-containing composite oxide particles and a surface modification material adhered to the surfaces of the particles, and has a composition represented by formula (1). The surface modification material contains one or more elements selected from among Al, Mg and M. Lix-yNayCowAlaMgbMcO2+α (1) (In formula (1), x, y, w, a, b, c and α satisfy formulae 0.986 ≤ (x - y) < 1.050, 0 < y ≤ 0.020, 0.996 ≤ x ≤ 1.050, 0.990 ≤ w ≤ 1.015, 0.005 ≤ a ≤ 0.020, 0.001 ≤ b ≤ 0.020, 0.0005 ≤ c ≤ 0.005 and -0.1 ≤ α ≤ 0.1; the ratio of (Li + Na) to (Co + Al + Mg + M), namely (x)/(w + a + b + c) is 0.930 or more but less than 0.990; and M represents one or more elements selected from among Ca, rare earth elements, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ni, Cu, Ag, Zn, B, Ga, C, Si, Sn, N, P, S, F, Cl and H.)