Positive electrode active material for secondary cell and nonaqueous electrolyte secondary cell using the same, and method for analysis of positive electrode active material for secondary cell

A non-aqueous electrolyte secondary cell, comprising:

• a positive electrode containing a positive electrode active material consisting essentially of a powdery metal oxide,
• a negative electrode disposing with the positive electrode through a separator,
• a cell casing for accommodating the positive electrode, the separator and the negative electrode, and
• a non-aqueous electrolyte filling in the cell casing,
• wherein, when the positive electrode active material is classified through the use of a difference in particle diameter and density of component particles of the powdery metal oxide to obtain coarse powder having a classification ratio in a range of 0.1 to 5%, a ratio (B/A) of the content B of an impurity metal element in the coarse powder obtained by the classification to the content A of an impurity metal element in the powdery metal oxide before the classification is 1.5 or below.

A method for analysis of a positive electrode active material comprising a powdery metal oxide to be used for a non-aqueous electrolyte secondary cell, comprising:

• obtaining coarse powder having a classification ratio in a range of 0.1 to 5% by classifying the powdery metal oxide through the use of a difference in particle diameter and density of its component particles;
• measuring the content A of an impurity metal element in the powdery metal oxide before the classification and the content B of an impurity metal element in the coarse powder obtained by the classification;
• and
• evaluating the amount of the particulate metal impurity contained in the powdery metal oxide before the classification based on a ratio (B/A) of the content B of the impurity metal element to the content A of the impurity metal element.