A positive electrode active material, a secondary battery, a battery module, a battery pack, and an electric device. The positive electrode active material is used as a positive electrode active material for a secondary battery, and comprises a carbon material compounded iron-based polyanionic compound and an aluminum-containing oxide, and the iron-based polyanionic compound has the following general formula: Na.sub.4Fe.sub.3xM.sub.xAl.sub.y(PO.sub.4).sub.2P.sub.2O.sub.7/C, wherein M comprises a transition metal element, 0x0.5, and y is greater than 0 and less than 0.2. The positive electrode active material has relatively low residual alkali amount, and the battery has excellent cycle performance and rate capability.