A positive electrode active material contains a lithium composite oxide and a covering material. The lithium composite oxide contains at least one element selected from the group consisting of fluorine, chlorine, nitrogen, and sulfur. The lithium composite oxide has a crystal structure that belongs to space group C2/m. The ratio I(003)/I(104) of a first integrated intensity I(003) of a first peak corresponding to a (003) plane to a second integrated intensity I(104) of a second peak corresponding to a (104) plane in an XRD pattern of the lithium composite oxide satisfies 0.05≤I(003)/I(104)≤0.90. The covering material has an electron conductivity of 106 S/m or less.