| abstract |
A composite oxide represented by the general formula (I): LiyNi1-xCox1Mx2O2, wherein M represents at least one member selected from the group consisting of Al, Fe, Mn, and B; 0.9 ≤ y ≤ 1.3; 0 < x ≤ 0.5; 0 < x1 < 0.5; x1 + x2 = x; when M represents at least one member selected from among Al, Fe, and Mn, then 0 < x2 ≤ 0.3; when M represents B, then 0 < x2 < 0.1; when M represents B and at least one member selected from among Al, Fe, and Mn, then 0 < x2 < 0.3; provided that the proportion of B is in the range of from 0 to 0.1. This composite oxide can provide a cathode active material for rechargeable batteries which possesses excellent discharge-charge cycle properties, can maintain a high battery capacity comparable to the conventional LiNiO2 even after an increased number of cycles, and has an improved cycle property (stability) at high temperatures. |