To provide a lithium-nickel complex oxide which has a low reactivity with an electrolyte liquid and a low internal electric resistance when used for a cell.

The oxide has a composition expressed by the general formula: LixNi1-p-q-rCopAlqArO2-y (wherein, 0.8≤x≤1.3, 0<p≤0.2, 0<q≤0.1, 0<r≤0.1 and -0.3<y<0.1; and A is at least one element selected from among the group consisting of Ti, In, Cr, Fe, Sn, Cu, Zn, Mn, Mg, Ga, Ni, Co, Zr, Bi, Ge, Nb, Ta, Be, Ca, Sr, Ba and Sc.), and is a spherical or ellipsoidal secondary particle into which a primary particle of 1 to 3 μm is aggregated or sintered and which has an average particle size of 5 to 20 μm.