POSITIVE ELECTRODE ACTIVE MATERIAL FOR LITHIUM ION SECONDARY BATTERIES

The positive electrode active material includes a compound represented by the following composition formula: [Li][LiMnM]O (wherein x satisfies 0.1 ≤ x ≤ 0.5, and M is represented by NiCoMnin which α, β and γ satisfy 0 < α ≤ 0.5, 0 ≤ β ≤ 0.33 and 0 < γ ≤ 0.5, respectively), wherein a half width of the peak of a (001) crystal plane of the compound measured by X-ray diffraction is in a range from 0.14 to 0.33 inclusive, and an average primary particle diameter of the compound is in a range from 0.03 µm to 0.4 µm inclusive.