Cathode, metal-air battery including the cathode, and method of preparing the cathode

1. A metal-air battery comprising:

a cathode comprising a porous carbon structure comprising an intertwined network of a plurality of carbon nanostructures,

wherein the porous carbon structure comprises

small-diameter pores having an average diameter of about 25 nanometers to about 200 nanometers, and

large-diameter pores having an average diameter of greater than 200 nanometers to about 1.6 micrometers;

an anode; and

an electrolyte layer disposed between the cathode and the anode,

wherein the carbon nanostructures comprise at least one selected from a one-dimensional carbon nanostructure and a two-dimensional carbon nanostructure.

2. The metal-air battery of claim 1 , wherein the one-dimensional carbon nanostructure comprises at least one selected from a carbon nanotube, a carbon nanowire, a carbon nanofiber, a carbon nanobelt, and a carbon nanorod.

3. The metal-air battery of claim 1 , wherein the two-dimensional carbon nanostructure comprises at least one selected from graphene oxide, reduced graphene oxide, a graphene nanoplate, and a carbon nanosheet.

4. The metal-air battery of claim 1 , wherein the porous carbon structure has a porosity of about 40% to about 70%.

5. The metal-air battery of claim 1 , wherein the porous carbon structure has a disordered porous structure.

6. The metal-air battery of claim 1 , wherein the porous carbon structure comprises a three-dimensional channel defined by a plurality of interconnected pores.

7. The metal-air battery of claim 1 , wherein the porous carbon structure is a free-standing composite film.

8. The metal-air battery of claim 1 , wherein the porous carbon structure has a tensile modulus of about 0.001 gigapascals to about 1 gigapascal.

9. The metal-air battery of claim 1 , wherein the large-diameter pores and the small-diameter pores each independently have at least one shape selected from a sphere, an oval, a polyhedron, and a rod.

10. The metal-air battery of claim 1 , wherein the plurality of the carbon nanostructures are in the form of an aggregation.

11. The metal-air battery of claim 1 , wherein the cathode further comprises a metal catalyst supported on the porous carbon structure.

12. The metal-air battery of claim 11 , wherein the metal catalyst comprises at least one selected from Pt, Pd, Au, Ag, Ru, Os, Rh, Mn, V, Fe, Ir, Co, Cu, and Ni.

13. A method of preparing a cathode, the method comprising:

contacting a large-diameter pore-forming particle, a small-diameter pore-forming particle, a carbon nanostructure, and a solvent to form a mixture;

filtering the mixture to obtain a filtrate; and

removing the large-diameter pore-forming particle and the small-diameter pore-forming particle from the filtrate to prepare the cathode, the cathode comprising a porous carbon structure comprising an intertwined network of a plurality of carbon nanostructures,

wherein the porous carbon structure comprises

small-diameter pores having an average diameter of about 25 nanometers to about 200 nanometers, and

large-diameter pores having an average diameter of greater than 200 nanometers to about 1.6 micrometers,

wherein the carbon nanostructures comprise at least one selected from a one-dimensional carbon nanostructure and a two-dimensional carbon nanostructure.

14. The method of claim 13 , wherein the large-diameter pore-forming particle and the small-diameter pore-forming particle each independently comprise at least one selected from a polymer of a radically polymerizable monomer, a polymer of a multifunctional crosslinking monomer, a microemulsion of polymer bead; a metal oxide comprising at least one selected from SiO 2 , TiO 2 , ZrO 2 , and Al 2 O 3 ; and a metal particle comprising at least one selected from copper, nickel, and zinc.

15. The method of claim 13 , wherein the solvent is at least one selected from water, alcohol, and aqueous ammonia.

16. The method of claim 13 , wherein the removing of the large-diameter pore-forming particle and the small-diameter pore-forming particle comprises a chemical method.

17. The method of claim 13 , wherein the mixture further comprises a metal catalyst.