Flexible supercapacitors and devices containing the same

1. A flexible supercapacitor comprising:

a. a multilevel porous graphite foam, wherein the multilevel porous graphite foam comprises a porous graphite core and a first porous graphite shell, wherein the porosity of the core and first shell are different; and

b. at least one pseudocapacitive material.

2. The flexible supercapacitor according to claim 1 , wherein the first porous graphite shell has a porosity that is less than 10% the porosity of the graphite core.

3. The flexible supercapacitor of according to claim 1 , wherein the porous graphite core has a porosity from 100-200 μm.

4. The flexible supercapacitor according to claim 1 , wherein the first porous graphite shell has a porosity from 0.5-10 μm.

5. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material comprises one or more transition metal oxides or transition metal hydroxides.

6. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material comprises one or more manganese oxides, manganese hydroxides, ruthenium oxides, ruthenium hydroxides, iridium oxides, iridium hydroxides, iron oxides, iron hydroxides, cobalt oxides, cobalt hydroxides, nickel oxides, nickel hydroxides, rhodium oxides, rhodium hydroxides, platinum oxides, platinum hydroxides, palladium oxides, or palladium hydroxides.

7. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material comprises one or more spinel metal oxides of the formula AB 2 O 4 , wherein A and B are the same or different transition metal.

8. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material comprises Mn 3 O 4 , Fe 3 O 4 , Co 3 O 4 , MnFe 2 O 4 , NiCo 2 O 4 , or MnCo 2 O 4 .

9. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material is coated on the surface of the multilevel porous graphite foam.

10. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material is present with a loading density from 0.1-0.50 mg/cm 2 .

11. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material is coated on the surface of the multilevel porous graphite foam in the form of nanoparticles.

12. The flexible supercapacitor according to claim 11 , wherein the pseudocapacitive nanoparticles have an average particle size from 1-100 nm.

13. The flexible supercapacitor according to claim 1 , wherein the pseudocapacitive material is coated on the surface on the multilevel porous graphite foam in the form of a sheet having a thickness from 1-100 nm.

14. The flexible supercapacitor according to claim 1 , wherein the multilevel porous graphite foam has a BET surface area of at least 7.5 m 2 /g.

15. The flexible supercapacitor according to claim 1 prepared by a processing comprising:

a) plating a first metal layer on a metal foam, wherein the metal in the first layer and metal in the foam are different;

b) annealing the plated foam to give a porous substrate having a smooth surface covering porous microstructures;

c) partially etching the porous substrate to give a multilevel porous substrate;

d) depositing a carbonaceous layer on the multilevel porous substrate;

e) completely etching the multilevel porous substrate to give a multilevel graphite foam; and

f) depositing a pseudocapacitive material upon the multilevel graphite foam.

16. A stretchable strain sensor comprising the flexible supercapacitor of claim 1 , and a graphite network embedded in an elastomer.

17. The sensor according to claim 16 , wherein the graphite network is at least 10 carbon sheets thick.

18. A full cell comprising:

a: a first supercapacitor according to claim 1 ;

b: an electrolyte;

c: a separator; and

d: a second supercapacitor according to claim 1 .

19. The full cell according to claim 18 , further comprising an elastomeric polymer.