Method For Producing Sodium Composite Transition Metal Oxide, Positive Electrode Active Material For Sodium Secondary Battery, Positive Electrode And Sodium Secondary Battery Comprising The Same

A positive electrode active material for a sodium secondary battery includes a sodium composite transition metal oxide represented by Formula 1 and having a P3 crystal structure, and a positive electrode and a sodium secondary battery which include the positive electrode active material. Na[LiM]O [Formula 1] wherein M is at least one transition metal, 0.64≤x≤0.7, and 0.01≤a≤0.1.