Supercapacitor electrode having highly oriented and closely packed expanded graphite flakes and production process

1. A process for producing a supercapacitor electrode containing electrolyte-impregnated flakes of exfoliated graphite worms or expanded graphite, said process comprising:

(a) preparing a deformable mass of said flakes of exfoliated graphite worms or expanded graphite dispersed in or impregnated by a liquid or gel electrolyte; and

(b) subjecting said deformable mass to a forced assembling and orientating procedure, forcing said deformable mass to form said electrode, wherein said flakes are spaced by thin electrolyte layers, having an electrolyte layer thickness from 0.4 nm to 10 nm, and said flakes are substantially aligned along a desired direction, and wherein said electrode has a physical density from 0.5 to 1.7 g/cm 3 and a specific surface area from 50 to 3,300 m 2 /g, when measured in a dried state of said flakes without said electrolyte.

2. The process of claim 1 , wherein said step (a) further comprises a sub-step of subjecting said flakes of exfoliated graphite worms or expanded graphite to a chemical or physical activation treatment to obtain activated graphite flakes and then dispersing said activated graphite flakes in said liquid or gel electrolyte or impregnating said activated graphite flakes with said liquid or gel electrolyte.

3. The process of claim 1 , wherein said flakes are pre-deposited with a nanoscaled coating or particles of a redox pair partner, having a coating thickness or particle diameter less than 100 nm, selected from an intrinsically conductive polymer, a transition metal oxide, and/or an organic molecule, wherein said redox pair partner and said flakes form a redox pair for pseudo-capacitance.

4. The process of claim 2 , wherein said activated graphite flakes, prior to said dispersing or impregnating, are pre-deposited with a nanoscaled coating or particles of a redox pair partner, having a coating thickness or particle diameter less than 100 nm, selected from an intrinsically conductive polymer, a transition metal oxide, and/or an organic molecule, wherein said redox pair partner and said flakes form a redox pair for pseudo-capacitance.

5. The process of claim 3 , wherein said intrinsically conducting polymer is selected from polyaniline, polypyrrole, polythiophene, polyfuran, sulfonated polyaniline, sulfonated polypyrrole, sulfonated polythiophene, sulfonated polyfuran, sulfonated polyacetylene, or a combination thereof.

6. The process of claim 4 , wherein said intrinsically conducting polymer is selected from polyaniline, polypyrrole, polythiophene, polyfuran, sulfonated polyaniline, sulfonated polypyrrole, sulfonated polythiophene, sulfonated polyfuran, sulfonated polyacetylene, or a combination thereof.

7. The process of claim 1 , wherein said liquid electrolyte contains an aqueous electrolyte, an organic electrolyte, an ionic liquid electrolyte, or a mixture of an organic and an ionic electrolyte.

8. The process of claim 1 , wherein said flakes of exfoliated graphite worms or expanded graphite contain chemically or physically activated flakes.

9. The process of claim 1 , wherein said forced assembling and orientating procedure is conducted in the presence of a current collector, which current collector is embedded in said deformable mass or bonded to said deformable mass to form said supercapacitor electrode.

10. The process of claim 1 , wherein said forced assembling and orientating procedure includes introducing said deformable mass, having an initial volume V 1 , in a mold cavity cell and driving a piston into said mold cavity cell to reduce the deformable mass volume to a smaller value V 2 , allowing excess electrolyte to flow out of said cavity cell and aligning said flakes along a desired direction.

11. The process of claim 1 , wherein said forced assembling and orientating procedure includes introducing said graphene dispersion in a mold cavity cell having an initial volume V 1 , and applying a suction pressure through a porous wall of said mold cavity to reduce the deformable mass volume to a smaller value V 2 , allowing excess electrolyte to flow out of said cavity cell through said porous wall and aligning said flakes along a desired direction.

12. The process of claim 1 , wherein said forced assembling and orientating procedure includes introducing a first layer of said deformable mass onto a surface of a supporting conveyor and driving said layer of deformable mass supported on said conveyor through at least a pair of pressing rollers to reduce a thickness of said deformable mass layer and align said flakes along a direction parallel to said conveyor surface for forming a layer of electrolyte-impregnated flakes.

13. The process of claim 12 , further including a step of introducing a second layer of said deformable mass onto a surface of said layer of electrolyte-impregnated flakes to form a two-layer structure, and driving said two-layer structure through at least a pair of pressing rollers to reduce a thickness of said second layer of deformable mass and align said flakes along a direction parallel to said conveyor surface for forming a layer of electrolyte-impregnated flakes.

14. The process of claim 1 , further including a step of compressing or roll-pressing said electrolyte-impregnated flakes to reduce a thin electrolyte layer thickness in said impregnated flakes, improve orientation of flakes, and squeeze excess electrolyte out of said impregnated flakes for forming said supercapacitor electrode.

15. The process of claim 12 , which is a roll-to-roll process wherein said forced assembling and orientating procedure includes feeding said supporting conveyor, in a continuous film form, from a feeder roller to a deposition zone, continuously or intermittently depositing said deformable mass onto a surface of said supporting conveyor film to form said layer of electrolyte-impregnated flakes thereon, and collecting said layer of electrolyte-impregnated flakes supported on conveyor film on a collector roller.

16. The process of claim 1 , further comprising a step of cutting said electrolyte-impregnated flakes into multiple sheets and stacking said multiple sheets to form a supercapacitor electrode.

17. The process of claim 1 , further comprising a step of attaching said electrolyte-impregnated flakes to a current collector, wherein said flakes are aligned parallel to a primary surface of said current collector.

18. The process of claim 1 , further comprising a step of attaching said electrolyte-impregnated flakes to a current collector, wherein said flakes are aligned perpendicular to a primary surface of said current collector.

19. A process of producing a supercapacitor electrode, comprising stacking a current collector with at least a layer of said electrolyte-impregnated flakes of claim 1 to form a multiple-layer structure and further comprising a step of compressing and consolidating said multi-layer structure to increase a physical density and decrease a thickness of said multi-layer structure to form said supercapacitor electrode.

20. The process of claim 19 , wherein at least one layer of said electrolyte-impregnated flakes is attached to one surface of said current collector and at least one layer of said electrolyte-impregnated flakes is attached to the opposing surface of said current collector prior to said step of compressing and consolidating.

21. A supercapacitor comprising an anode, a cathode, an ion-permeable separator that electronically separates said anode and said cathode, and an electrolyte in ionic contact with said anode and said cathode, wherein the anode and/or the cathode contains the electrolyte-impregnated flakes of claim 1 .

22. The supercapacitor of claim 21 , further comprising an anode current collector and/or a cathode current collector and said flakes in said electrolyte-impregnated flakes are parallel to a primary surface of said anode current collector or said cathode current collector.

23. The supercapacitor of claim 21 , further comprising an anode current collector and/or a cathode current collector and said flakes in said electrolyte-impregnated flakes are perpendicular to a primary surface of said anode current collector or said cathode current collector.