A positive-electrode active material contains a lithium composite oxide containing manganese. The crystal structure of the lithium composite oxide belongs to a space group Fd-3m. The integrated intensity ratio I(111)/I(400) of a first peak I(111) on the (111) plane to a second peak I(400) on the (400) plane in an XRD pattern of the lithium composite oxide satisfies 0.05≤I(111)/I(400)≤0.90.