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

Abstract

Provided is a positive electrode active material which suppresses a reduction in capacity due to charge and discharge cycles when used in a lithium ion secondary battery. A covering layer is formed by segregation on a superficial portion of the positive electrode active material. The positive electrode active material includes a first region and a second region. The first region exists in an inner portion of the positive electrode active material. The second region exists in a superficial portion of the positive electrode active material and part of the inner portion thereof. The first region includes lithium, a transition metal, and oxygen. The second region includes magnesium, fluorine, and oxygen.

1 . A method comprising steps of:
 analyzing a positive electrode active material comprising a composite oxide including lithium and cobalt by electron energy loss spectroscopy;   calculating a spectral intensity ratio of L 3  level to L 2  level of cobalt 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 L 3  level to L 2  level of cobalt,   wherein the analysis is performed at a depth of about 1 nm from a surface of the positive electrode active material.   
     
     
         2 . The method according to  claim 1 , wherein the spectral intensity ratio of L 3  level to L 2  level of cobalt is larger than or equal to 3.8. 
     
     
         3 . 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 L 3  level to L 2  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 L 3  level to L 2  level of cobalt in the first region;   calculating a spectral intensity ratio of L 3  level to L 2  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 L 3  level to L 2  level of cobalt in the second region.   
     
     
         4 . The method according to  claim 3 ,
 wherein the spectral intensity ratio of L 3  level to L 2  level of cobalt in the first region is less than 3.8, and   wherein the spectral intensity ratio of L 3  level to L 2  level of cobalt in the second region is larger than or equal to 3.8.