Recompressed exfoliated graphite articles
View Patent ↗This invention provides an electrically conductive, less anisotropic, recompressed exfoliated graphite article comprising a mixture of (a) expanded or exfoliated graphite flakes; and (b) particles of non-expandable graphite or carbon, wherein the non-expandable graphite or carbon particles are in the amount of between about 3% and about 70% by weight based on the total weight of the particles and the expanded graphite flakes combined; wherein the mixture is compressed to form the article having an apparent bulk density of from about 0.1 g/cm 3 to about 2.0 g/cm 3 . The article exhibits a thickness-direction conductivity typically greater than 50 S/cm, more typically greater than 100 S/cm, and most typically greater than 200 S/cm. The article, when used in a thin foil or sheet form, can be a useful component in a sheet molding compound plate used as a fuel cell separator or flow field plate. The article may also be used as a current collector for a battery, supercapacitor, or any other electrochemical cell.
1. A recompressed exfoliated graphite article free of impregnating resin comprising a mixture of:
(a) expanded or exfoliated graphite flakes; and
(b) non-expandable particles as an isotropy promoter, wherein said non-expandable particles are selected from natural graphite, synthetical graphite, highly oriented pyrolytic graphite, graphite oxide, graphite fluoride, chemically modified graphite, spheroidal graphite, meso-porous micro-beads, or a combination thereof and are in an amount of between about 3% and about 70% by weight based on the total weight of said particles and said exfoliated graphite flakes;
wherein said mixture is compressed to form said article having an apparent bulk density of from about 0.1 g/cm 3 to about 2.0 g/cm 3 , an anisotropy ratio from 1.01 to 35.5, and a thickness-direction conductivity not less than 50 S/cm.
2. The article as defined in claim 1 wherein at least a portion of said article is in a plate, sheet, or film form having a thickness-direction electrical conductivity no less than 300 S/cm.
3. The article as defined in claim 1 , further comprising a reinforcement or filler selected from the group consisting of graphite or carbon fiber, graphite or carbon nano-fiber, nano-tube, glass fiber, ceramic fiber, polymer fiber, metal fiber, metal particle, polymer particle, organic particle, inorganic particle, or a combination thereof, wherein said reinforcement or filler is between 0.5% and 30% by weight based on the total weight of said expanded graphite, particles of non-expanded graphite or carbon, and reinforcement or filler.
4. The article as defined in claim 1 wherein said expanded graphite flakes are obtained from intercalation and exfoliation of a graphite material selected from natural graphite, synthetical graphite, highly oriented pyrolytic graphite, graphite fiber, graphitic nano-fiber, spheroidal graphite, meso-carbon micro-bead, graphite oxide, graphite fluoride, chemically modified graphite, or a combination thereof.
5. The article as defined in claim 1 , wherein said article is used as a component of a fuel cell separator or flow field plate.
6. The article as defined in claim 1 , wherein said article is used as a component of a current collector for a fuel cell, battery, supercapacitor, or electrochemical cell.
7. The article as defined in claim 1 , wherein said article is in a thin flexible sheet or film form with a thickness smaller than 2 mm.
8. The article as defined in claim 1 , wherein said article is in a thin flexible sheet or film form with a thickness smaller than 0.5 mm.
9. The article as defined in claim 1 , wherein said article is in a thin flexible sheet or film form with a thickness smaller than 0.3 mm.
10. The article as defined in claim 1 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 30.
11. The article as defined in claim 1 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 10.
12. The as defined in claim 1 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 5.
13. The article as defined in claim 1 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 2.
14. The article as defined in claim 1 wherein at least a portion of said article is in a plate, sheet, or film form having a thickness-direction and a surface plane perpendicular to said thickness direction, and wherein said article has an electrical conductivity in a direction parallel to said surface plane no less than 1,000 S/cm and a thickness-direction conductivity not less than 150 S/cm.
15. The article as defined in claim 14 wherein said article has electrical conductivity values greater than 100 S/cm in three mutually perpendicular directions.
16. The article as defined in claim 15 wherein said article has electrical conductivity values greater than 200 S/cm in three mutually perpendicular directions.
17. The article as defined in claim 16 wherein said article has electrical conductivity values greater than 300 S/cm in three mutually perpendicular directions.
18. A recompressed exfoliated graphite article free of impregnating resin comprising a mixture of:
(a) expanded or exfoliated graphite flakes; and
(b) non-expandable particles as an isotropy promoter, wherein said non-expandable particles are selected from natural graphite, synthetical graphite, highly oriented pyrolytic graphite, graphite oxide, graphite fluoride, chemically modified graphite, spheroidal graphite, meso-porous micro-beads, or a combination thereof and are in an amount of between about 3% and about 70% by weight based on the total weight of said particles and said exfoliated graphite flakes;
wherein said mixture is compressed to form said article having an apparent bulk density of from about 0.1 g/cm 3 to about 2.0 g/cm 3 , an anisotropy ratio from 1.23 to 8.16 and a thickness-direction conductivity not less than 200 S/cm.
19. The article as defined in claim 18 wherein at least a portion of said article is in a plate, sheet, or film form having a thickness-direction electrical conductivity no less than 300 S/cm.
20. The article as defined in claim 18 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 5.
21. The article as defined in claim 18 , wherein said article has a first conductivity in a first direction and a second conductivity in a direction perpendicular to said first direction, wherein said first conductivity is lower than said second conductivity and the ratio of said second conductivity to said first conductivity is no greater than 2.
22. The article as defined in claim 18 wherein at least a portion of said article is in a plate, sheet, or film form having a thickness-direction and a surface plane perpendicular to said thickness direction, and wherein said article has an electrical conductivity in a direction parallel to said surface plane no less than 1,000 S/cm and a thickness-direction conductivity greater than 200 S/cm.
23. The article as defined in claim 22 wherein said article has electrical conductivity values greater than 200 S/cm in three mutually perpendicular directions.
24. The article as defined in claim 23 wherein said article has electrical conductivity values greater than 300 S/cm in three mutually perpendicular directions.