Device to prevent overpressure in a capacitor or ultracapacitor
The present invention relates to a device to prevent overpressure in a supercapacitor. In a supercapacitor comprising a closed chamber fitted with means for exchanging a gas with the external surroundings and in which there are positioned two electrodes with a high specific surface area, separated by a separator, the separator and the electrodes being impregnated with an electrolyte, the means for exchanging a gas comprise a metallic membrane that is permeable to hydrogen and its isotopes and impermeable to gaseous species which have an effective cross section of 0.3 nm or higher, at a temperature of between −50° C. and 100° C.
1. A supercapacitor comprising;
a closed chamber which is equipped with means for exchanging a gas with the external environment; and
in which two electrodes, each carrying a layer of activated carbon having a high specific surface area are placed while being separated by a separator, the separator and the electrodes being impregnated with an electrolyte,
wherein the means for exchanging a gas has a membrane which is permeable to hydrogen and its isotopes and impermeable to gas species which have a cross section greater than or equal to 0.3 nm, at a temperature of between −50° C. and 100° C., and
in that the membrane has a surface area S (in m 2 ) and a thickness e (in m), and in that it includes a material which is selected from the group consisting of metals and metal alloys, and the intrinsic permeability Φ of which (in mol.m −1 .s −1 Pa −1/2 ) is selective with respect to hydrogen and has a value such that 10 −15 mol.s −1 .Pa −1/2 ≦(Φ*S)/e≦10 −9 mol.s −1 .Pa −1/2 .
2. The supercapacitor as claimed in claim 1 , wherein 10 −12 mol.s −1 .Pa −1/2 ≦(Φ*S)/e≦5 10 −10 mol.s −1 .Pa −1/2 .
3. The supercapacitor as claimed in claim 1 , wherein the metals are selected from the group consisting of Pd, Nb, V, Ta, Ni and Fe and in that the metal alloys are selected from the group consisting of the alloys of a metal selected from among Pd, Nb, V and Ta and at least one other metal selected from the group consisting of Pd, Nb, V, Ta, Fe, Al, Cu, Ru, Re, Rh, Au, Pt, Ag, Cr, Co, Sn, Zr, Y, Ni, Ce, Ti, Ir and Mo.
4. The supercapacitor as claimed in claim 1 , wherein on at least one of its surfaces the membrane carries an additional layer of a hydrogen-permeable material whose limits do not extend beyond the limits of the membrane.
5. The supercapacitor as claimed in claim 4 , wherein the membrane carries two additional layers of the same hydrogen-permeable material or two additional layers of different materials.
6. The supercapacitor as claimed in claim 4 , the hydrogen-permeable material of the additional layer or layers is selected from the group consisting of polymers, ceramics, carbon and metals.
7. The supercapacitor as claimed in claim 4 , wherein the hydrogen-permeable material of the additional layer or layers is a metal or a metal alloy, in that the membrane has a surface area of from 0.0007 mm 2 to 100 mm 2 and a thickness of from 0.03 μm to 10 μm, and in that the ratio S/e varies from 0.025 mm 2 /μm to 0.1 mm 2 /μm.
8. The supercapacitor as claimed in claim 7 , wherein the hydrogen-permeable material of the additional layer or layers is palladium, in that the membrane has a surface area of from 0.0015 mm 2 to 1 mm 2 , and in that the ratio S/e varies from 0.05 mm 2 /μm to 0.1 mm 2 /μm.
9. The supercapacitor as claimed in claim 4 , wherein at least one of the elements among the membrane and the additional layer or layers is a sintered material.
10. The supercapacitor as claimed in claim 9 , wherein at least one additional layer is a sintered material having a thickness of more than 0.3 mm, and in that the membrane is a membrane made of palladium or a palladium-silver alloy having a thickness of from 0.03 μm to 10 μm and a surface area of from 0.0015 mm 2 to 10 mm 2 , and in which the ratio S/e varies from 0.05 mm 2 /μm to 1 mm 2 /μm.
11. The supercapacitor as claimed in claim 6 , wherein the hydrogen-permeable material of the additional layer or layers is a polymer or a mixture of polymers having a thickness of more than 0.05 mm, and in that the membrane is a membrane made of palladium or a palladium-silver alloy having a thickness of from 0.03 μm to 1 μm and a surface area of from 0.003 mm 2 to 1 mm 2 , and in which the ratio S/e varies from 0.09 mm 2 /μm to 1 mm 2 /μm.
12. The supercapacitor as claimed in claim 1 , wherein the membrane is a self supported membrane.
13. The supercapacitor as claimed in claim 12 , wherein the membrane has a thickness greater than or equal to 5 μm.
14. The supercapacitor as claimed in claim 12 , wherein the membrane has a surface area of between 0.15 mm 2 and 100 mm 2 and a thickness of from 5 μm to 100 μm, and in that the ratio S/e varies from 0.03 mm 2 /μm to 1 mm 2 /μm.
15. The supercapacitor as claimed in claim 13 , wherein the membrane is a palladium membrane, in that it has a surface area of between 0.25 mm 2 and 10 mm 2 , and in that the ratio S/e varies from 0.05 mm 2 /μm to 0.1 mm 2 /μm.
16. The supercapacitor as claimed in claim 15 , wherein said palladium membrane has a thickness of 25 μm and a surface area of 1.5 mm 2 , and in that the ratio S/e is 0.06 mm 2 /μm.
17. The supercapacitor as claimed in claim 12 , wherein the membrane consists of a film of a metal selected from the group consisting of Nb, V and Ta having a thickness greater than or equal to 5 μm, placed between two continuous palladium films having a thickness of less than 1 μm.
18. The supercapacitor as claimed in claim 1 , wherein the membrane is a non-self supported membrane consisting of a palladium or nickel film having a thickness of less than 5 μm.
19. The supercapacitor as claimed in claim 1 , wherein the membrane is a non-self supported membrane consisting of a film of a metal selected from among Nb, V, Ta, and Fe, having a thickness of less than 5 μm, placed between two continuous palladium films having a thickness of less than 1 μm.
20. The supercapacitor as claimed in claim 3 , wherein the alloy is selected from the group consisting of Pd 75 Ag 25 , Pd 92 Y 8 , Pd 93.5 Ce 6.5 , Pd 60 Cu 40 , V 85 Ni 15 stabilized with 0.05% yttrium or titanium, V 53 Ti 26 Ni 21 , V 50 Nb 50 , V 13 Cr 11 Al 3 Ti 73 , Nb 56 Ti 23 Ni 21 , Nb 68 Ti 17 Ni 15 and Nb 99 Zr 1 .
21. The supercapacitor as claimed in claim 1 , wherein the membrane is a metal tube which is closed at one of its ends, open at the other end and placed in the chamber so that its open end is fixed to the means for exchanging a gas.
22. The supercapacitor as claimed in claim 1 , wherein the means for exchanging a gas are in the form of an opening in the chamber.
23. The supercapacitor as claimed in claim 22 , wherein the membrane consists of a pellet of metal or a metal alloy, which is fixed around said opening by welding, brazing, diffusion brazing or crimping.