Highly conductive graphene foams and process for producing same

1. A solid graphene foam composed of multiple pores and pore walls, wherein said pore walls contain a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.001% to 5% by weight of non-carbon elements wherein said non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof, and said solid graphene foam has a density from 0.01 g/cm 3 to 1.7 g/cm 3 , a specific surface area from 50 m 2 /g to 3,000 m 2 /g, a thermal conductivity of at least 200 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 2,000 S/cm per unit of specific gravity.

2. The solid graphene foam of claim 1 , wherein said pore walls contain stacked graphene planes having an inter-plane spacing d 002 from 0.3354 nm to 0.36 nm as measured by X-ray diffraction.

3. The solid graphene foam of claim 1 , wherein said pore walls contain a pristine graphene and said solid graphene foam has a density from 0.5 g/cm 3 to 1.7 g/cm 3 or an average pore size from 2 nm to 50 nm.

4. The solid graphene foam of claim 1 , wherein said pore walls contain a non-pristine graphene material selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein said solid graphene foam contains a content of non-carbon elements in the range of 0.01% to 2.0% by weight.

5. The solid graphene foam of claim 1 , wherein said pore walls contain graphene fluoride and said solid graphene foam contains a fluorine content from 0.01% to 2.0% by weight.

6. The solid graphene foam of claim 1 , wherein said pore walls contain graphene oxide and said solid graphene foam contains an oxygen content from 0.01% to 2.0% by weight.

7. The solid graphene foam of claim 1 , wherein said solid graphene foam has a specific surface area from 200 m 2 /g to 2,000 m 2 /g or a density from 0.1 g/cm 3 to 1.5 g/cm 3 .

8. The solid graphene foam of claim 1 , wherein said non-carbon elements include an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron.

9. The solid graphene foam of claim 1 , which is in a continuous-length roll sheet form having a thickness no greater than 200 μm and a length of at least 2 meters and is produced by a roll-to-roll process.

10. The solid graphene foam of claim 1 , wherein said graphene foam has an oxygen content or non-carbon content less than 1% by weight, and said pore walls have an inter-graphene spacing less than 0.35 nm, a thermal conductivity of at least 250 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 2,500 S/cm per unit of specific gravity.

11. The solid graphene foam of claim 1 , wherein said graphene foam has an oxygen content or non-carbon content less than 0.01% by weight and said pore walls contain stacked graphene planes having an inter-graphene spacing less than 0.34 nm, a thermal conductivity of at least 300 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 3,000 S/cm per unit of specific gravity.

12. The solid graphene foam of claim 1 , wherein said graphene foam has an oxygen content or non-carbon content no greater than 0.01% by weight and said pore walls contain stacked graphene planes having an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.7, a thermal conductivity of at least 350 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 3,500 S/cm per unit of specific gravity.

13. A solid graphene foam composed of multiple pores and pore walls, wherein said pore walls are comprised of stacked graphene planes having an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.4, and are selected from the group comprising a pristine graphene material having essentially zero % of non-carbon elements, a non-pristine graphene material having 0.001% to 5% by weight of non-carbon elements, and combinations thereof, wherein said non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and said solid graphene foam has a density from 0.01 g/cm 3 to 1.7 g/cm 3 , a specific surface area from 50 m 2 /g to 3,000 m 2 /g, a thermal conductivity of at least 400 W/mK per unit of specific gravity, and an electrical conductivity no less than 4,000 S/cm per unit of specific gravity.

14. The solid graphene foam of claim 1 , wherein the pore walls contain stacked graphene planes having an inter-graphene spacing less than 0.337 nm and a mosaic spread value less than 1.0.

15. The solid graphene foam of claim 1 , wherein the solid graphene foam exhibits a degree of graphitization no less than 80% and/or a mosaic spread value less than 0.4.

16. The solid graphene foam of claim 1 , wherein the solid graphene foam exhibits a degree of graphitization no less than 90% and/or a mosaic spread value no greater than 0.4.

17. The solid graphene foam of claim 1 , wherein said pore walls contain a 3D network of interconnected graphene planes.

18. The solid graphene foam of claim 1 , wherein said solid graphene foam contains mesoscaled pores having a pore size from 2 nm to 50 nm.

19. A process for producing the solid graphene foam of claim 1 , said process comprising:

(a) preparing a graphene dispersion having multiple sheets of a starting graphene material dispersed in a liquid medium, wherein said starting graphene material is selected from a pristine graphene or a non-pristine graphene material, having a content of non-carbon elements greater than 2% by weight, selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof and wherein said dispersion contains an optional blowing agent having a blowing agent-to-graphene material weight ratio from 0/1.0 to 1.0/1.0;

(b) dispensing and depositing said graphene dispersion onto a surface of a supporting substrate to form a wet layer of graphene material, wherein said dispensing and depositing procedure includes subjecting said graphene dispersion to an orientation-inducing stress;

(c) partially or completely removing said liquid medium from the wet layer of graphene material to form a dried layer of graphene material; and

(d) heat treating the dried layer of graphene material at a first heat treatment temperature from 80° C. to 3,200° C. at a desired heating rate sufficient to induce volatile gas molecules from said non-carbon elements or to activate said blowing agent for producing said sheet of solid graphene foam.

20. The process of claim 19 , further including a step of heat-treating the solid graphene foam at a second heat treatment temperature higher than said first heat treatment temperature for a length of time sufficient for obtaining a graphene foam wherein said pore walls contain stacked graphene planes having an inter-plane spacing d 002 from 0.3354 nm to 0.36 nm and a content of non-carbon elements less than 2% by weight.

21. The process of claim 19 , wherein said graphene material contains pristine graphene and said dispersion contains a blowing agent having a blowing agent-to-pristine graphene weight ratio from 0.01/1.0 to 1.0/1.0.

22. The process of claim 19 , wherein said blowing agent is a physical blowing agent, a chemical blowing agent, a mixture thereof, a dissolution-and-leaching agent, or a mechanically introduced blowing agent.

23. The process of claim 19 , wherein said graphene material is selected from the group of non-pristine graphene materials consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein the first heat treatment temperature is less than 2,500° C. and said solid graphene foam contains a content of non-carbon elements from 0.01% to 2.0% by weight.

24. The process of claim 20 , wherein said graphene material is selected from the group of non-pristine graphene materials consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and combinations thereof, and wherein both the first and second heat treatment temperatures are less than 2,500° C. and said solid graphene foam contains a content of non-carbon elements in the range of 0.01% to 2.0% by weight.

25. The process of claim 19 , wherein said graphene material in said solid graphene foam contains structural defects induced during said step (d) of heat treating.

26. The process of claim 19 , wherein said liquid medium consists of water and/or an alcohol.

27. The process of claim 19 , which is a roll-to-roll process wherein said steps (b) and (c) include feeding said supporting substrate from a feeder roller to a deposition zone, continuously or intermittently depositing said graphene dispersion onto a surface of said supporting substrate to form said wet layer of graphene material thereon, drying said wet layer of graphene material to form the dried layer of graphene material, and collecting said dried layer of graphene material deposited on said supporting substrate on a collector roller.

28. The process of claim 19 , wherein said first heat treatment temperature is from 100° C. to 1,500° C.

29. The process of claim 20 , wherein said second heat treatment temperature includes at least a temperature selected from (A) 300-1,500° C., (B) 1,500-2,100° C., and/or (C) 2,100-3,200° C.

30. The process of claim 20 , wherein said second heat treatment temperature includes a temperature in the range of 300-1,500° C. for at least 1 hour and then a temperature in the range of 1,500-3,200° C. for at least 1 hour.

31. The process of claim 19 , wherein said non-carbon elements include an element selected from oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, or boron.

32. The process of claim 19 , wherein said step (d) of heat treating the dried layer of graphene material at a first heat treatment temperature is conducted under a compressive stress.

33. The process of claim 20 , further comprising a compression step to reduce a thickness, a pore size, or a porosity level of said solid graphene foam.

34. The process of claim 19 , wherein said graphene dispersion contains a graphene oxide dispersion prepared by immersing a graphitic material in a powder or fibrous form in an oxidizing liquid in a reaction vessel at a reaction temperature for a length of time sufficient to obtain said graphene dispersion wherein said graphitic material is selected from natural graphite, artificial graphite, mesophase carbon, mesophase pitch, mesocarbon micro-bead, soft carbon, hard carbon, coke, carbon fiber, carbon nanofiber, carbon nanotube, or a combination thereof and wherein said graphene oxide has an oxygen content no less than 5% by weight.

35. The process of claim 20 , wherein said first and/or second heat treatment temperature contains a temperature in the range of 300° C.-1,500° C. and the graphene foam has an oxygen content or non-carbon content less than 1%, and pore walls having an inter-graphene spacing less than 0.35 nm, a thermal conductivity of at least 250 W/mK per unit of specific gravity to 500 W/mK per unit of specific gravity, and/or an electrical conductivity from 2,500 S/cm per unit of specific gravity.

36. The process of claim 20 , wherein said first and/or second heat treatment temperature contains a temperature in the range of 1,500° C.-2,100° C. and the graphene foam has an oxygen content or non-carbon content less than 0.01%, pore walls having an inter-graphene spacing less than 0.34 nm, a thermal conductivity of at least 300 W/mK per unit of specific gravity to 500 W/mK per unit of specific gravity, and/or an electrical conductivity from 3,000 S/cm per unit of specific gravity.

37. The process of claim 20 , wherein said first and/or second heat treatment temperature contains a temperature greater than 2,100° C. and the graphene foam has an oxygen content or non-carbon content no greater than 0.001%, pore walls having an inter-graphene spacing less than 0.336 nm, a mosaic spread value no greater than 0.7, a thermal conductivity of at least 350 W/mK per unit of specific gravity to 500 W/mK per unit of specific gravity, and/or an electrical conductivity greater than 3,500 S/cm per unit of specific gravity.

38. A process for producing a solid graphene foam composed of multiple pores and pore walls, said process comprising:

(a) preparing a graphene dispersion having multiple sheets of a starting graphene material dispersed in a liquid medium, further comprising an optional blowing agent having a blowing agent-to-graphene material weight ratio from 0/1.0 to 1.0/1.0;

(b) dispensing and depositing said graphene dispersion onto a surface of a supporting substrate to form a wet layer of graphene material, wherein said dispensing and depositing procedure includes subjecting said graphene dispersion to an orientation-inducing stress;

(c) partially or completely removing said liquid medium from the wet layer of graphene material to form a dried layer of graphene material; and

(d) heat treating the dried layer of graphene material at a first heat treatment temperature from 80° C. to 3,200° C. at a desired heating rate sufficient to induce volatile gas molecules from said non-carbon elements or to activate said blowing agent for producing said sheet of solid graphene foam;

(e) and optionally heat treating the dried layer of graphene material at a second heat treatment temperature from 80° C. to 3,200° C.;

wherein said first and/or second heat treatment temperature contains a temperature no less than 2,500° C. and wherein said pore walls contain a pristine graphene material having essentially zero percent of non-carbon elements, or a non-pristine graphene material having 0.001% to 5% by weight of non-carbon elements wherein said non-pristine graphene is selected from graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, or a combination thereof, wherein said pore walls contain stacked graphene planes having an inter-graphene spacing less than 0.336 nm, and a mosaic spread value no greater than 0.4, and the solid graphene foam has a density from 0.01 g/cm 3 to 1.7 g/cm 3 , a specific surface area from 50 m 2 /g to 3,000 m 2 /g, a thermal conductivity greater than 400 W/mK per unit of specific gravity, and/or an electrical conductivity greater than 4,000 S/cm per unit of specific gravity.

39. A roll-to-roll process for producing a continuous-length sheet of the solid graphene foam of claim 1 , said process comprising:

(a) preparing a graphene dispersion having a graphene material dispersed in a liquid medium, wherein said dispersion contains a blowing agent;

(b) continuously or intermittently dispensing and depositing said graphene dispersion onto a surface of a supporting substrate to form a wet layer of graphene material, wherein said supporting substrate is a continuous thin film supplied from a feeder roller and collected on a collector roller;

(c) partially or completely removing said liquid medium from the wet layer of graphene material to form a dried layer of graphene; and heat treating the dried layer of graphene material at a first heat treatment temperature from 100° C. to 3,000° C. at a desired heating rate sufficient to activate said blowing agent for producing said solid graphene foam.