Active material, method of preparing the active material electrode including the active material, and secondary battery including the electrode

1. An electrode active material comprising a vanadium oxide initially represented by Formula 1,

VO x   Formula 1

wherein vanadium in the vanadium oxide has a mixed oxidation state of a plurality of oxidation numbers,

wherein the plurality of oxidation numbers comprise an oxidation number of +3,

wherein, in Formula 1, 1.5<x<2.5, and

wherein the vanadium having an oxidation number of +3 is contained in an amount in a range of about 10 atomic percent to about 30 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5.

2. The electrode active material of claim 1 , wherein the vanadium comprises a mixed oxidation state of 3 oxidation numbers.

3. The electrode active material of claim 1 , wherein the plurality of oxidation numbers comprises an oxidation number of +4 and an oxidation number of +5.

4. The electrode active material of claim 3 , wherein the vanadium having an oxidation number of +4 is contained in an amount in a range of about 40 atomic percent to about 60 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5, and the vanadium having an oxidation number of +5 has an amount in a range of about 25 atomic percent to about 50 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5.

5. The electrode active material of claim 1 , wherein the vanadium oxide comprises a nanostructure.

6. The electrode active material of claim 5 , wherein the vanadium oxide nanostructure is a vanadium oxide nanosheet, a vanadium oxide nanotube, or a combination thereof.

7. The active material of claim 6 , wherein the vanadium oxide nanosheet is comprises a layer or a plurality of stacked layers.

8. The electrode active material of claim 6 , wherein the vanadium oxide comprises a vanadium oxide nanosheet which comprises about 1 to about 10 layers and has an interlayer distance in a range of about 2.5 nanometers to about 3.5 nanometers.

9. The electrode active material of claim 6 , wherein the vanadium oxide comprises a vanadium oxide nanosheet which has a shape of a circle, an ellipse, a triangle, a quadrangle, a pentagon, a hexagon, or combination thereof.

10. The electrode active material of claim 6 , wherein the vanadium oxide comprises a vanadium oxide nanotube which is a multiwall nanotube.

11. The electrode active material of claim 6 , wherein, the vanadium oxide comprises a vanadium oxide nanotube which has a length in a range of about 1 micrometer to about 2 micrometers, an inner diameter in a range of about 15 nanometers to about 50 nanometers, and an outer diameter in a range of about 50 nanometers to about 100 nanometers.

12. The electrode active material of claim 1 , wherein in Formula 1, wherein x satisfies the condition of 1.9≦x<2.2.

13. The electrode active material of claim 1 , wherein in Formula 1, x is in a range of about 1.995 to about 2.13.

14. The electrode active material of claim 1 , wherein, when analyzed by X-ray diffraction analysis, a (001) peak and a (002) peak occur at a Bragg angle of 10° two-theta or less, an intensity ratio of the (002) peak to the (001) peak is 0.6 or less, and a full width at half maximum of the (001) peak is 0.5 or less.

15. An electrode comprising the electrode active material of claim 1 .

16. A secondary battery comprising the electrode of claim 15 .

17. The secondary battery of claim 16 , wherein in the electrode active material of the electrode of the secondary battery comprising the vanadium oxide represented by Formula 1, the vanadium having an oxidation number of +3 is contained in an amount in a range of about 10 atomic percent to about 25 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5, and

wherein the content of the vanadium having an oxidation number of +3, +4, and +5 is determined after charging and discharging the secondary battery.

18. The secondary battery of claim 16 , wherein in the electrode active material of the electrode of the secondary battery comprising the vanadium oxide represented by Formula 1, the vanadium having an oxidation number of +4 is contained in an amount in a range of about 40 atomic percent to about 60 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5,

wherein the vanadium having an oxidation number of +5 is contained in an amount in a range of about 30 atomic percent to about 50 atomic percent, based on the total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5, and

wherein the content of the vanadium having an oxidation number of +3, +4, and +5 is determined after charging and discharging the secondary battery.

19. A magnesium secondary battery comprising the electrode of claim 15 .

20. A sodium secondary battery comprising the electrode of claim 15 .

21. A lithium secondary battery comprising the electrode of claim 15 .

22. A method of preparing an electrode active material comprising a vanadium oxide represented by Formula 1,

VO x ,  Formula 1

wherein the vanadium in the vanadium oxide has a mixed oxidation state of a plurality of oxidation numbers, wherein the oxidation numbers comprise an oxidation number of +3, wherein, in Formula 1, 1.5<x<2.5, and wherein the vanadium having an oxidation number of +3 is contained in an amount in a range of about 10 atomic percent to about 30 atomic percent, based on a total amount of vanadium having a mixed oxidation state of oxidation numbers of +3, +4, and +5 the method comprising:

contacting a reducing agent, a solvent, and a starting material comprising vanadium oxide to obtain a mixture; and

applying an electromagnetic wave to the mixture to reduce the starting material, to prepare the vanadium oxide represented by Formula 1.

23. The method of claim 22 , wherein the reducing agent comprises an amine.

24. The method of claim 23 , wherein the reducing agent comprises octadecylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, heptadecylamine, hexadecylamine, or combination thereof.

25. The method of claim 22 , wherein the electromagnetic wave is a microwave.

26. The method of claim 25 , wherein the microwave is applied to the mixture with an output in a range of about 200 watts to about 1,500 watts and a frequency in a range of about 1 gigahertz to about 2.45 gigahertz.

27. The method of claim 22 , wherein the reducing of the starting material is performed by a microwave-hydrothermal reaction.

28. The method of claim 22 , wherein an amount of the reducing agent is in a range of about 0.1 mole to about 1 mole, based on 1 mole of the vanadium oxide.

29. The method of claim 22 , wherein the starting material containing vanadium is divanadium pentoxide, vanadium oxydiacetate, or combination thereof.