Sumitomo Chemical Company, Limited

Satoshi Takamatsu

Megumi Uchida

Yukimitsu Wakasugi

To provide a cathode active material for a lithium ion secondary battery, which has high packing properties and high volume capacity density, and a method for its production. A cathode active material for a lithium ion secondary battery is used, which comprises a mixture B of a collection of many large particles having different particle sizes and a collection of many small particles having different particle sizes, wherein the function F(x) of a particle size x of a particle contained in the mixture B and its frequency F has a relation of the formula 1, the function E(x) of a particle size x of a particle contained in a mixture B' after the mixture B is pressed and its frequency E has a relation of the formula 2, the rate of change of the median size &#x3bc;&#x2032;relative to &#x3bc;is at most 10%, and the rate of change of the median size &#x3bc;&#x2032;relative to &#x3bc;is at least 20%, 

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Chigasaki, Japan

Satoshi Takamatsu