POSITIVE ELECTRODE ACTIVE MATERIAL AND BATTERY INCLUDING SAME

A positive electrode active material according to the present disclosure includes a lithium composite oxide that contains first particles having a crystal structure belonging to space group R-3m and second particles having a crystal structure belonging to space group C2/m. The crystal structure of the second particles has a larger amount of cation mixing than the crystal structure of the first particles. The second particles have a smaller particle size than the first particles. Mathematical Formula 0.05≤integrated intensity ratio I/I≤0.99 is satisfied. The integrated intensity ratio I/Iis a ratio of the integrated intensity Ito the integrated intensity I. The integrated intensity Iis the integrated intensity of a maximum peak present in the range of angle of diffraction 2θ greater than or equal to A° and less than or equal to B° in the X-ray diffraction pattern of the lithium composite oxide.