POSITIVE ELECTRODE ACTIVE MATERIAL AND LITHIUM SECONDARY BATTERY USING SAME

There is provided a positive electrode active material comprising a large number of crystal grains composed of lithium manganate of spinel structure, wherein the large number of crystal grains contain primary particles of 3 to 20 µm in particle diameter by 70 areal % or more relative to all the crystal grains, the primary particles contain a component having a rectangular plane, and the ratio of the total area of all the rectangular planes to the total surface area of the primary particles is 0.5 to 5%.