The present invention relates to a lithium-containing metal composite oxide comprising paramagnetic and diamagnetic metals, which satisfies any one of the following conditions: (a) the ratio of intensity between a main peak of 0±10 ppm (I0ppm) and a main peak of 240±140 ppm (I240ppm), (I0ppm/I240ppm), is less than 0.117·Z wherein z is the ratio of moles of the diamagnetic metal to moles of lithium; (b) the ratio of line width between the main peak of 0±10 ppm (I0ppm) and the main peak of 240±140 ppm (I240ppm), (W240ppm/W0ppm), is less than 21.45; and (c) both the conditions (a) and (b). The peaks of the lithium-containing metal composite oxide are obtained according to the 7Li—NMR measurement conditions and means disclosed herein.