Cathode active material for sodium secondary battery, method of preparing the same, and sodium secondary battery including the same

A sodium secondary battery comprising:

• a cathode;
• an anode;
• and an electrolyte between the cathode and the anode,
• wherein the cathode includes a cathode current collector, and a cathode active material layer disposed on the cathode current collector and including a cathode active material, the cathode active material including a layered sodium transition metal oxide having an O3 structure, and the layered sodium transition metal oxide includes a compound represented by Formula 1:
• wherein, in Formula 1,
• −0.33≤x≤0.1, 0.3≤a≤0.4, 0.3≤b≤0.4, 0≤c≤0.1, d>0, e>0, d>e, a+b+c+d+e=1, and −0.1≤8≤0.1.

A method of preparing a cathode active material for a sodium secondary battery, the method comprising:

• mixing a sodium precursor, a nickel precursor, a manganese precursor, a cobalt precursor, and a titanium precursor to provide a precursor mixture;
• and
• heat-treating the precursor mixture to prepare a cathode active material,
• wherein the cathode active material includes a layered sodium transition metal oxide having an O3 structure, and the layered sodium transition metal oxide includes a compound represented by Formula 1:
• wherein, in Formula 1,
• −0.33≤x≤0.1, 0.3≤a≤0.4, 0.3≤b≤0.4, 0≤c≤0.1, d>0, e>0, d>e, a+b+c+d+e=1, and −0.138≤0.1.