ELECTRODE ACTIVE MATERIAL AND BATTERY

Disclosed is an electrode active material having an O3-type structure, wherein the electrode active material has high capacity and high coulombic efficiency. The electrode active material of the present disclosure comprises a Na-containing transition metal oxide. The Na-containing transition metal oxide has an O3-type structure. The Na-containing transition metal oxide comprises, as constituent elements, Na, Ni, Mn, and O. An X-ray diffraction pattern of the Na-containing transition metal oxide satisfies 0.476 < I003/I104 < 0.554 (where I003 is the diffraction peak intensity of the (003) plane in the X-ray diffraction pattern, and I104 is the diffraction peak intensity of the (104) plane in the X-ray diffraction pattern).