Sodium manganese composite oxide and electrode and sodium secondary battery using the same
A sodium manganese composite oxide represented by Formula 1: Na x Ma y Mn z Mb v O 2+d Formula 1 wherein, 0.2≦x≦1, 0<y≦0.2, 0<z≦1, 0≦v<1, 0<z+v≦1, −0.3≦d<1, Ma is an electrochemically inactive metal, and Mb is different from Ma and Mn, and is at least one transition metal selected from elements in Groups 4 to 12 of the periodic table of the elements.
1. A sodium manganese composite oxide represented by Formula 1:
Na x Ma y Mn z Mb v O (2+d) Formula 1
wherein, 0.2≦x≦0.8, 0<y≦0.2, 0<z≦1, 0≦v<1, 0<z+v≦1, and −0.3≦d<1,
Ma is a metal which is electrochemically inactive between 2 volts and 3.8 volts versus Na/Na + ,
Mb is different from Ma and Mn, and is at least one transition metal selected from elements of Groups 4 to 12 of the periodic table of the elements, and
the sodium manganese composite oxide has at least one of a monoclinic structure and an orthrorhombic structure.
2. The sodium manganese composite oxide of claim 1 , wherein 0.6≦x≦0.8, and 0.01≦y≦0.1.
3. The sodium manganese composite oxide of claim 1 , wherein 2/3≦x≦0.8, y=0.1, and z=0.9.
4. The sodium manganese composite oxide of claim 1 , wherein an oxidation number of Ma does not change during intercalation and deintercalation of sodium.
5. The sodium manganese composite oxide of claim 1 , wherein Ma is at least one metal selected from aluminum (Al), molybdenum (Mo), tungsten (W), zirconium (Zr), ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt).
6. The sodium manganese composite oxide of claim 1 , wherein Mb is at least one transition metal selected from elements of Groups 8 to 10 of the periodic table of the elements.
7. The sodium manganese composite oxide of claim 1 , wherein Mb is at least one transition metal selected from iron (Fe), nickel (Ni), cobalt (Co), vanadium (V), titanium (Ti), and chromium (Cr).
8. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide has a monoclinic structure.
9. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide has an orthorhombic structure.
10. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide has a monoclinic-orthorhombic composite structure.
11. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide is represented by Formula 2:
Na x Al y Mn z Mb v O (2+d) Formula 2
wherein, 0.2≦x≦0.8, 0≦y≦0.2, 0<z≦1, 0<v<1, 0<z+v≦1, −0.3≦d<1, and
Mb is different from aluminum (Al) and manganese (Mn), and is at least one transition metal selected from elements of Groups 4 to 12 of the periodic table of the elements.
12. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide comprises an Al—O bond near a surface of the sodium manganese composite oxide.
13. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide is represented by Formula 3:
Na x Al y Mn z Mc v O 2+d Formula 3
wherein, 0.2≦x≦0.8, 0<y≦0.2, 0<z≦1, 0≦v<1, 0<z+v≦1, −0.3≦d<1, and
Mc is at least one transition metal selected from iron (Fe), nickel (Ni), cobalt (Co), vanadium (V), Ti (titanium), and chromium (Cr).
14. The sodium manganese composite oxide of claim 11 , wherein 0.6≦x≦0.8, 0.01≦y≦0.1.
15. The sodium manganese composite oxide of claim 11 , wherein 2/3<x≦0.8, y=0.1, z=0.9.
16. The sodium manganese composite oxide of claim 1 , wherein the sodium manganese composite oxide has an electrical conductivity of 6×10 −6 Siemens per centimeter or greater under a load of 40 kilonewtons or greater.
17. An electrode comprising the sodium manganese composite oxide of claim 1 .
18. The electrode of claim 17 , wherein the sodium manganese composite oxide has a monoclinic-orthorhombic composite structure, and wherein the sodium manganese composite oxide having the monoclinic-orthorhombic composite structure has a greater initial discharge capacity than a sodium manganese composite oxide having an orthorhombic structure.
19. The electrode of claim 17 , wherein, in a sodium secondary battery comprising the sodium manganese composite oxide, a capacity retention rate after 100 cycles of charge and discharge between 2.0 volts and 3.8 volts versus Na metal, with a constant current of a 0.1 C rate, is 40 percent or greater.
20. A sodium secondary battery comprising:
the electrode according to claim 17 .
21. The sodium secondary battery of claim 20 , further comprising a counter electrode which is opposed to the electrode, wherein the counter electrode comprises a sodium metal, a sodium metal alloy, a sodium intercalation compound, or a carbonaceous material.
22. The sodium secondary battery of claim 21 , further comprising a separator disposed between the electrode and the counter electrode.