Positive electrode active material particle and manufacturing method of positive electrode active material particle

A method comprising steps of:

• analyzing each of first and second regions included in a positive electrode active material by electron energy loss spectroscopy, the first region including lithium and cobalt, the second region including magnesium, cobalt, and oxygen, and the second region being positioned outside of the first region;
• calculating a spectral intensity ratio of L3 level to L2 level of cobalt in the first region from a spectrum obtained by the analysis of the electron energy loss spectroscopy;
• determining that a number of trivalent cobalt atoms exceeds a number of cobalt atoms exhibiting other valence from the spectral intensity ratio of L3 level to L2 level of cobalt in the first region;
• calculating a spectral intensity ratio of L3 level to L2 level of cobalt in the second region from a spectrum obtained by the analysis of the electron energy loss spectroscopy;
• and
• determining that a number of divalent cobalt atoms exceeds a number of cobalt atoms exhibiting other valence from the spectral intensity ratio of L3 level to L2 level of cobalt in the second region.