Positive-electrode active material for non-aqueous secondary battery and method for producing the same

The present invention provides a positive-electrode active material for non-aqueous secondary battery comprising a sodium transition metal composite oxide represented by Formula: Na x Fe 1-y M y O 2 , wherein 0.4 ¤ x ¤ 0.7, 0.25 ¤ y < 1.0, and M is at least one element selected from the group consisting of manganese, cobalt and nickel, the sodium transition metal composite oxide having a crystal structure substantially composed of P6 3 /mmc alone.