Positive electrode active material and lithium ion secondary cell using same

Abstract

The positive electrode active material disclosed herein includes a base portion including a lithium transition metal complex oxide having a layered crystal structure, and a coating portion including an electroconductive oxide having a layered crystal structure. A smaller angle θ formed by a stacking plane direction of the lithium transition metal complex oxide and a stacking plane direction of the electroconductive oxide satisfies the following conditions: an average angle θave. obtained by arithmetically averaging the angle θ satisfies 0°≦θave.≦60°; and a ratio of points in which the angle θ is greater than 60° is 39% or less.

1 . A positive electrode active material for a lithium ion secondary cell, comprising:
 a base portion including a lithium transition metal complex oxide having a layered crystal structure; and   a coating portion formed on a surface of the base portion, and including an electroconductive oxide having a layered crystal structure, wherein   when electron microscope observations of the positive electrode active material are performed 10 or more times such that the base portion and the coating portion are present in the same field of view, and electron beam diffraction images of the lithium transition metal complex oxide and of the electroconductive oxide are acquired in each observed point, where a stacking plane direction of the layered crystal structure in the lithium transition metal complex oxide is represented by a first virtual line and a stacking plane direction of the layered crystal structure in the electroconductive oxide is represented by a second virtual line,   a smaller angle θ formed by the first virtual line and the second virtual line satisfies the following conditions:   an average angle θave. obtained by arithmetically averaging the angle θ satisfies 0°≦θave.≦60°; and   a ratio of points in which the angle θ is greater than 60° is 39% or less.   
     
     
         2 . The positive electrode active material according to  claim 1 , wherein the average angle θave. satisfies 0°≦θave.≦23°. 
     
     
         3 . The positive electrode active material according to  claim 1 , wherein the ratio of points in which the angle θ is greater than 60° is 10% or less. 
     
     
         4 . A lithium ion secondary cell comprising the positive electrode active material according to  claim 1 .