Positive electrode active material containing lithium composite oxide and battery including the same

A positive electrode active material comprising:

• a lithium composite oxide containing fluorine and oxygen,
• wherein the lithium composite oxide satisfies 1<Zs/Za<8, where Zs represents a first ratio of a molar quantity of the fluorine to a total molar quantity of the fluorine and the oxygen in X-ray photoelectron spectroscopy of the lithium composite oxide, and Za represents a second ratio of a molar quantity of the fluorine to a total molar quantity of the fluorine and the oxygen in an average composition of the lithium composite oxide,
• an X-ray diffraction pattern of the lithium composite oxide includes a first maximum peak within a first range of 18° to 20° at a diffraction angle 2θ and a second maximum peak within a second range of 43° to 46° at the diffraction angle 2θ, and
• a ratio I(18°-20°)/I(43°-46°) of a first integrated intensity I(18°-20°) of the first maximum peak to a second integrated intensity I(43°-46°) of the second maximum peak satisfies 0.05≤I(18°-20°)/I(43°-46°)≤0.90.