Multilayer composite strip for the manufacture of bipolar plates for fuel cells

Abstract

The present invention relates to a composite strip suitable for acting as a flow field plate or bipolar plate in a fuel cell, the composite strip comprising, stacked directly one on top of the other: A conductive layer A; a composite layer D that can result from or is the result of the infiltration of a polymer M into a porous layer C comprising a conductive filler and a reinforcing assembly that comprises reinforcing fibres bonded to one another; and, optionally, a conductive layer A'. The present invention also relates to a precursor strip of the composite strip and to a method for preparing the composite strip from the precursor strip.

Description

[0001] MULTILAYER COMPOSITE BLADE FOR PLATE MANUFACTURING

[0002] BIPOLAR CELLS FOR FUEL BATTERIES

[0003] Scope of the invention

[0004] The invention relates to the field of fuel cells. More specifically, it relates to a blade

[0005] 5. A multilayer composite that can serve as a flow field plate or a bipolar plate for a fuel cell. The invention also relates to a precursor multilayer blade from which the multilayer composite blade can be easily obtained.

[0006] Prior art

[0007] 10. A fuel cell is an electrochemical generator that produces an electrical voltage through the oxidation of a fuel (for example, dihydrogen) at one electrode, coupled with the reduction of an oxidant (for example, oxygen from the air) at the other electrode. The operation of a fuel cell requires a continuous supply of fuel and oxidant to the electrodes. In contrast, in a standard fuel cell, the compounds consumed to produce electrical energy are initially present in the cell.

[0008] 15 Fuel cells are generally composed of an assembly of a large number of electrochemical cells.

[0009] Such a cell includes a flow field plate receiving the fuel (anodic plate), for example hydrogen, an electrode-membrane assembly (EMA), and a flow field plate receiving the oxidant (cathodic plate), for example oxygen.

[0010] 20 The chemical reaction produces heat, a coolant circuit can be provided between the cells.

[0011] The AME comprises a proton exchange polymer membrane, which is usually made of Nafion, and two electrodes.

[0012] The flow field plates have flow channels on their face facing FAME,

[0013] 25 allowing the local distribution of fuel and oxidant at FAME and allowing the removal of reaction products occurring at FAME. The flow field plates must also allow the passage of current by electronic conduction. They must also be leak-proof to fuel, oxidant, and reaction products occurring at FAME. They must also be corrosion-resistant. When a single plate has channels on both of its surfaces and

[0014] 30 serves as a flow field plate in two different cells (which saves space), this plate is called a bipolar plate.

[0015] The performance of fuel cells depends on the design of these plates.

[0016] Currently, bipolar plates are most often made from graphite plates which must

[0017] 35. These plates need to be machined to etch the gas flow channels. Machining a fragile material like graphite makes manufacturing the plates very expensive. Furthermore, these plates are quite heavy and thick (typically between 1 and 5 mm), which is a drawback when trying to assemble a large number of cells together. In addition, their conductivity and sealing are still unsatisfactory without costly treatments. Thinner, easier-to-manufacture metal plates could overcome the disadvantages of bipolar graphite plates. However, their corrosion resistance under fuel cell operating conditions is still inadequate.

[0018] The objective of the present invention is to provide bipolar plates:

[0019] Stainless steel

[0020] Lightweight

[0021] Thin

[0022] Having very good electrical conductivity

[0023] Impermeable to gases and liquids such as oxygen, hydrogen, or water

[0024] High-temperature operational

[0025] Rigid and formable

[0026] Easy to produce industrially

[0027] Furthermore, the invention also aims at bipolar plates that can be used immediately by operators, i.e. without requiring the addition of any extra element such as an anti-corrosion treatment or a waterproof varnish layer.

[0028] Description of the invention

[0029] To this end, the invention relates to a composite multilayer blade that can serve as a flow field plate or a bipolar plate. The invention also relates to a precursor multilayer blade and a method for preparing the composite multilayer blade of the invention from the precursor multilayer blade of the invention. The invention further relates to a bipolar plate formed from the composite multilayer blade according to the invention.

[0030] Hereafter the term "composite blade" refers to the composite multilayer blade according to the invention and "precursor blade" refers to the precursor multilayer blade according to the invention.

[0031] The invention therefore relates to the following items:

[0032] 1. Item 1: Precursor blade comprising directly stacked one on top of the other in this order:

[0033] A conductive layer A,

[0034] A polymer layer B, and

[0035] A porous layer C comprising a conductive filler and a reinforcement assembly comprising interconnected reinforcing fibers.

[0036] 2. Item 2: precursor blade according to item 1 comprising directly stacked one on top of the other in this order: the conductive layer A, the polymer layer B, the porous layer C, and

[0037] A polymer layer B'. 3. Item 3: precursor blade according to item 2 comprising directly stacked one on top of the other in this order:

[0038] The conductive layer A, the polymer layer B, the porous layer C, the polymer layer B', and a conductive layer A'.

[0039] 4. Item 4: precursor blade according to item 2 comprising directly stacked one on top of the other in this order: conductive layer A, polymer layer B, porous layer C, polymer layer B', a porous layer C' comprising a conductive filler and a reinforcement assembly comprising reinforcing fibers bonded together, a polymer layer B', and a conductive layer A'.

[0040] 5. Item 5: precursor blade according to any one of items 1 to 4 in which at least one of the conductive layers A and, if applicable, A' is a flexible graphite layer.

[0041] 6. Item 6: precursor blade according to item 5 in which the flexible graphite layer(s) have a thickness between 20 pm and 100 pm, preferably between 25 and 50 pm.

[0042] 7. Item 7: precursor blade according to item 5 or 6 in which the flexible graphite is a natural flexible graphite.

[0043] 8. Item 8: precursor blade according to any one of items 5 to 7 comprising the two conductive layers A and A', in which the conductive layers A and A' are layers of flexible graphite.

[0044] 9. Item 9: precursor blade according to any one of items 5 to 7 comprising the two conductive layers A and A' in which one of the two conductive layers is a flexible graphite layer and the other is a metallic grid, preferably a one-piece metallic grid.

[0045] 10. Item 10: precursor blade according to any one of items 1 to 7 not including metal.

[0046] 11. Item 11: precursor blade according to any one of items 1 to 10 in which the polymer of layer B and, if applicable, of layers B' and B” is a thermoplastic polymer.

[0047] 12. Item 12: precursor slide according to item 11 in which the polymer of layer B and, if applicable, of layers B' and B” is selected from the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK), polyaryletherketones (PAEK), polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF),

[0048] Polyethylene (PE),

[0049] Polyester (PEs),

[0050] Polyphthalamide (PPA)

[0051] Polyamide (PA),

[0052] Polypropylene (PP),

[0053] Polyethersulfone (PESU),

[0054] Polyimide (PI),

[0055] Polyetherimide (PEI), polymethyl methacrylate (PMMA), polyamide-imide (PAI), fluorinated ethylene propylene copolymer (FEP),

[0056] Perfluoroalkoxy (PF A),

[0057] Polytetrafluoroethylene (PTFE), and

[0058] Polysulfone (PSU);

[0059] Preferably, among the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK), polyvinylidene fluoride (PVDF), polyphthalamide (PPA), polyimide (PI), polyetherimide (PEI), ethylene propylene fluoride copolymer (FEP), and

[0060] Perfluoroalkoxy (PF A);

[0061] More preferably, among the following polymers: ethylene polynaphthalate (PEN), polyphenylsulfone (PPSU), and polyetherketoneketone (PEKK).

[0062] 13. Item 13: precursor slide according to any one of items 1 to 12 in which the mass of the polymeric layer B and, if applicable, of the polymeric layers B' and B” represents at least 30%, preferably 40 to 80%, more preferably 45 to 75%, even more preferably 50 to 70% of the total mass of the porous layer C, and if applicable, of the porous layer C' and of the polymeric layer B and, if applicable, of the polymeric layers B' and B”.

[0063] 14. Item 14: precursor blade according to any one of items 1 to 13 in which the reinforcement assembly of layer C and, if applicable, of layer C' comprises at least 90% by mass of reinforcing fibers, relative to the total mass of the reinforcement assembly.

[0064] 15. Item 15: precursor blade according to any one of items 1 to 14 in which the reinforcing fibers of layer C and, if applicable, of layer C' are carbon fibers.

[0065] 16. Item 16: precursor sheet according to any one of items 1 to 15 in which the reinforcement assembly of layer C and, if applicable, of layer C' is a nonwoven of reinforcing fibers. 17. Item 17: precursor sheet according to any one of items 1 to 16 in which, in layer C and, if applicable, in layer C', the bonding of the reinforcing fibers is ensured by a polymeric binder, for example said polymeric binder representing 2 to 6% by mass relative to the total mass of the reinforcement assembly.

[0066] 18. Item 18: precursor blade according to any one of items 1 to 16 in which, in layer C and, if applicable, in layer C', the bonding of the reinforcing fibers is ensured by a carbon-based conductive material binder.

[0067] 19. Item 19: precursor plate according to any one of items 1 to 18 in which the mass of the conductive charge of the porous layer C and, if applicable, of the porous layer C' represents between 15 and 70%, preferably between 20 and 60%, more preferably between 25 and 55% of the total mass of all the porous layers C and, if applicable, C' and the polymeric layers B and, if applicable, B' and B'.

[0068] 20. Item 20: precursor plate according to any one of items 1 to 19 in which the conductive charge of layer C and, if applicable, of layer C' comprises a graphite powder.

[0069] 21. Item 21: precursor blade according to item 20 in which the graphite powder has a d50 between 20 and 60 pin, preferably between 30 and 50 in, measured by laser granulometry.

[0070] 22. Item 22: precursor plate according to any one of items 1 to 21 in which the conductive charge of layer C and, if applicable, of layer C' comprises carbon black.

[0071] 23. Item 23: precursor blade according to any one of items 1 to 19 in which the conductive charge of layer C and, if applicable, of layer C', is included in the reinforcement assembly.

[0072] 24. Item 24: precursor blade according to any one of items 1 to 23 in which the mass ratio of the mass of all polymer layers B and, if applicable, B' and B” to the mass of all porous layers C and, if applicable, C' is between 0.5 and 4, preferably between 1 and 2.

[0073] 25. Item 25: Composite blade comprising layers stacked directly on top of each other:

[0074] A conductive layer A, and

[0075] A composite layer D which may result or resulting from the infiltration of a polymer M into a porous layer C comprising a conductive filler and a reinforcement assembly comprising interconnected reinforcing fibers.

[0076] 26. Item 26: Composite blade according to item 25, comprising layers stacked directly one on top of the other:

[0077] The conductive layer A,

[0078] The composite layer D, and

[0079] A conductive layer A'.

[0080] 27. Item 27: Composite blade according to item 25 or 26 in which the composite layer D may result or results from the infiltration of the polymer M into the porous layer C and into a porous layer C' comprising a conductive filler and a reinforcement assembly comprising reinforcing fibers bonded together.

[0081] 28. Item 28: Composite blade according to any one of items 25 to 27 in which layer D has an area greater than the area of ​​at least one of the conductive layers A and, if applicable, A', for example, layer A and layer A'. 29. Item 29: Composite blade according to any one of items 25 to 28 comprising a principal face 1 including flow channels, and in which, preferably, the conductive layer A is located on the principal face 1.

[0082] 30. Item 30: Composite blade according to item 29 comprising a main face 2 comprising flow channels.

[0083] 31. Item 31: Composite blade according to item 30 in which the flow channels on the same face define hollows separated by partitions, the hollows formed by the flow channels on face 1 forming the partitions separating the flow channels on face 2.

[0084] 32. Item 32: Composite blade according to any one of items 25 to 31 having a total thickness between 40 and 500 µm, preferably between 75 and 300 µm, more preferably between 75 and 200 µm, if layer D comprises a single porous layer C or having a thickness between 60 and 800 µm, preferably between 125 and 500 µm, more preferably between 125 and 400 µm, if layer D comprises two porous layers C and C'.

[0085] 33. Item 33: Composite blade according to any one of items 25 to 32 having a specific surface strength in thickness of less than 15 mQ / cm² 2 .

[0086] 34. Item 34: Composite blade according to any one of items 25 to 33 having a density less than 1.7 g / L.

[0087] 35. Item 35: Composite blade according to any one of items 25 to 34 having a hydrogen permeation coefficient less than 1.3 x 10 14 mol / (msPa) measured according to ASTM D1434.

[0088] 36. Item 36: Composite blade according to any one of items 25 to 35 in which layer D has a thickness of between 20 and 300 pm, preferably between 50 and 200 pm, more preferably between 50 and 150 pm, if layer D comprises a single porous layer C or having a thickness of between 40 and 600 pm, preferably between 100 and 400 pm, more preferably between 100 and 300 pm, if layer D comprises two porous layers C and C'.

[0089] 37. Item 37: Composite blade according to any one of items 25 to 36 in which the composite layer D has a thickness greater than the thickness of the conductive layer A and, if applicable, greater than the thickness of the conductive layer A', for example greater than the sum of the thickness of the conductive layer A and the thickness of the conductive layer A'.

[0090] 38. Item 38: Composite blade according to any one of items 25 to 37 in which at least one of the conductive layers A and, if applicable, A' is a flexible graphite layer.

[0091] 39. Item 39: Composite blade according to item 38 in which the flexible graphite layer(s) have a thickness between 20 µm and 100 µm, preferably between 25 and 50 µm.

[0092] 40. Item 40: Composite blade according to item 38 or 39 in which the flexible graphite is a natural flexible graphite.

[0093] 4L Item 41: Composite blade according to any one of items 38 to 40 comprising the two conductive layers A and A', in which the conductive layers A and A' are layers of flexible graphite.

[0094] 42. Item 42: Composite blade according to any one of items 38 to 40 comprising two conductive layers A and A', wherein one of the two conductive layers is a flexible graphite layer and the other is a metal grid, preferably a one-piece metal grid. 43. Item 43: Composite blade according to any one of items 25 to 41 not comprising metal.

[0095] 44. Item 44: Composite blade according to any one of items 25 to 43 in which polymer M is a thermoplastic polymer.

[0096] 45. Item 45: Composite blade according to item 44 in which polymer M is selected from the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK),

[0097] Polyaryletherketones (PAEK),

[0098] Polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF),

[0099] Polyethylene (PE),

[0100] Polyester (PEs),

[0101] Polyphthalamide (PPA)

[0102] Polyamide (PA),

[0103] Polypropylene (PP),

[0104] Polyethersulfone (PESU),

[0105] Polyimide (PI),

[0106] Polyetherimide (PEI), polymethyl methacrylate (PMMA), polyamide-imide (PAI), fluorinated ethylene propylene copolymer (FEP),

[0107] Perfluoroalkoxy (PF A),

[0108] Polytetrafluoroethylene (PTFE), and

[0109] Polysulfone (PSU);

[0110] Preferably, among the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK), polyvinylidene fluoride (PVDF),

[0111] Polyphthalamide (PPA)

[0112] Polyimide (PI),

[0113] Polyetherimide (PEI), fluorinated ethylene propylene copolymer (FEP), and

[0114] Perfluoroalkoxy (PF A);

[0115] More preferably, among the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), and polyetherketoneketone (PEKK). 46. Item 46: Composite sheet according to any one of items 25 to 45 in which the mass of polymer M represents at least 30%, preferably 40 to 80%, more preferably 45 to 75%, more preferably 50 to 70% of the total mass of layer D.

[0116] 47. Item 47: Composite blade according to any one of items 25 to 46 in which the reinforcement assembly of layer C and, if applicable, of layer C' comprises at least 90% by mass of reinforcing fibers, relative to the total mass of the reinforcement assembly.

[0117] 48. Item 48: Composite blade according to any one of items 25 to 47 in which the reinforcing fibers of layer C and, if applicable, of layer C' are carbon fibers.

[0118] 49. Item 49: Composite blade according to any one of items 25 to 48 in which the reinforcement assembly of layer C and, if applicable, of layer C' is a non-woven reinforcement fiber.

[0119] 50. Item 50: Composite blade according to any one of items 25 to 49 in which in layer C and, if applicable, in layer C', the bonding of the reinforcing fibers is ensured by a polymeric binder, for example said polymeric binder represents 2 to 6% by mass relative to the total mass of the reinforcement assembly.

[0120] 51. Item 51: Composite blade according to any one of items 25 to 49 in which, in layer C and, if applicable, in layer C', the bonding of the reinforcing fibers is ensured by a carbon-based conductive material binder.

[0121] 52. Item 52: Composite blade according to any one of items 25 to 51 in which the mass of the conductive filler of the composite layer D represents between 15 and 70%, preferably between 20 and 60%, more preferably between 25 and 55% of the total mass of the composite layer D.

[0122] 53. Item 53: Composite blade according to any one of items 25 to 52 in which the conductive filler of layer C and, if applicable, of layer C' comprises a graphite powder.

[0123] 54. Item 54: Composite blade according to item 53 in which the graphite powder has a d50 between 20 and 60 in, preferably between 30 and 50 pin, measured by laser granulometry.

[0124] 55. Item 55: Composite blade according to any one of items 25 to 54 in which the conductive filler of layer C and, if applicable, of layer C' comprises carbon black.

[0125] 56. Item 56: Composite blade according to any one of items 25 to 52 in which the conductive charge of layer C and, if applicable, of layer C', is included in the reinforcement assembly.

[0126] 57. Item 57: Bipolar blade comprising two composite blades a and b according to any one of items 30 to 56 in which: a principal face la of blade a is welded to a principal face 1 b of blade b, the flow channels of face la face the flow channels of face 2, and the top of the partitions of the flow channels of face la is in contact with the top of the partitions of the flow channels of face 1b.

[0127] 58. Item 58: A process for manufacturing a composite blade according to any one of items 25 to 56 comprising the following steps: a. Supplying a precursor blade according to any one of items 1 to 24, b. Pressing the precursor blade so as to cause layer B and, if applicable, layers B' and B”, to penetrate layer C and, if applicable, layer C', so as to obtain a pressed blade, c. Optionally finishing the pressed blade so as to obtain the composite blade, and d. Retrieving the composite blade.

[0128] 59. Item 59: A process according to item 58 in which step a comprises stacking in the desired final order of layers A, B, C and, if applicable, A', B', B', and C' to obtain the precursor plate, preferably the stacking is carried out continuously.

[0129] 60. Item 60: A process according to item 58 or 59 in which layer C and, if applicable, layer C', are obtained by supplying a reinforcement assembly and powdering the conductive charge onto the reinforcement assembly so as to obtain layer C and, if applicable, layer C'.

[0130] 61. Item 61: A process according to any one of items 58 to 60 in which the pressing step b is carried out continuously, for example by calendering.

[0131] 62. Item 62: A process according to any one of items 58 to 61 in which pressing step b is carried out by hot calendering or compression molding.

[0132] 63. Item 63: A process according to any one of items 58 to 62 in which, in step c, flow channels are molded on a principal face 1 of the blade.

[0133] 64. Item 64: A process according to item 63 in which, in step c, flow channels are molded on a principal face 2 of the blade.

[0134] 65. Item 65: Process according to item 63 or 64 in which the molding of the channels of step c is done at the same time as the pressing of step b.

[0135] 66. Item 66: A process according to any one of items 58 to 65 in which the temperature at step b is between 200°C and 400°C.

[0136] 67. Item 67: A process according to any one of items 58 to 66 in which the pressure at step b is between 10 and 200 bar, preferably between 50 and 200 bar, more preferably between 100 and 200 bar.

[0137] It has been observed that the materials used in the precursor blade according to the invention and their arrangement make it possible to obtain a composite blade according to the invention which may have the following characteristics:

[0138] Stainless

[0139] Lightweight, for example having a density of less than 1.7 g / L

[0140] Thin

[0141] Having very good electrical conductivity, for example the composite blade according to the invention has an ASR (specific surface resistance) in the thickness of less than 15 mΩ.cm 2

[0142] Impermeable to gases and liquids such as oxygen, hydrogen, or water, for example, a hydrogen permeation coefficient of less than 1.3 x 10 can be achieved. 14 mol / (msPa) measured according to ASTM D1434.

[0143] Operates up to temperatures of 200°C

[0144] Rigid and formable

[0145] Easy to produce industrially

[0146] The invention ultimately makes it possible to obtain composite flow field plates and bipolar plates which reduce the weight and size of a fuel cell, which can be produced on a large scale using a simple and economical technique, and which have a long lifespan due to their temperature resistance and corrosion resistance characteristics.

[0147] Brief description of the figures

[0148] The manner in which the invention can be implemented and the resulting advantages will be more clearly shown in the following implementation examples, given by way of illustration and not limitation, in support of the attached Figures.

[0149] [Fig. 1 A] represents a five-layer precursor plate: conductive layer A, polymer layer B, porous layer C, polymer layer B', and conductive layer A'.

[0150] [Fig. IB] represents a four-layer precursor blade: conductive layer A, polymer layer B, porous layer C, and polymer layer B'.

[0151] [Fig. IC] represents a seven-layer precursor plate: conductive layer A, polymer layer B, porous layer C, polymer layer B', porous layer C', polymer layer B”, and conductive layer A'.

[0152] [Fig. 1D] represents a three-layer precursor blade: polymer layer B, porous layer C, and polymer layer B'.

[0153] [Fig. 2 A] represents a three-layer composite blade: conductive layer A, composite layer D, and conductive layer A'.

[0154] [Fig. 2B] represents a two-layer composite blade: conductive layer A and composite layer D.

[0155] [Fig. 2C] represents a single-layer composite blade: composite layer D.

[0156] [Fig. 3] represents the molding of a three-layer composite blade, conductive layer A, composite layer D and conductive layer A', with flow channels on the two main faces.

[0157] [Fig. 4] represents the molding of a two-layer composite blade, conductive layer A and composite layer D, with flow channels on the two main faces.

[0158] [Fig. 5] represents the molding of a two-layer composite blade, conductive layer A and composite layer D, with flow channels only on the main face where the conductive layer A is located.

[0159] [Fig. 6] represents the molding of a single-layer composite blade (composite layer D) without flow channels. [Fig. 7] represents the molding of a three-layer composite blade (conductive layer A, composite layer D, and conductive layer A') with flow channels on both faces, in which the hollows formed by the flow channels on one face form the partitions separating the flow channels on the other face.

[0160] [Fig. 8] represent the molding of a two-layer composite blade, conductive layer A and composite layer D, with flow channels on both faces, in which the hollows formed by the flow channels on one face form the partitions separating the flow channels on the other face.

[0161] [Fig. 9] represent the molding of a composite blade with a single composite layer D, with flow channels on both faces, in which the hollows formed by the flow channels on one face form the partitions separating the flow channels on the other face.

[0162] [Fig. 10] represents a composite layer D, consisting of a polymer M and a porous layer C comprising a set of reinforcement and conductive fillers.

[0163] [Fig. 11] represents the porous layer C, comprising a reinforcement set and conductive fillers. [Fig. 12] represents composite blades, viewed from above and from the side, in which the composite layer D has an area greater than the area of ​​the conductive layer(s).

[0164] [Fig. 13] represents a view of a principal face of a composite blade comprising a conductive layer A and a composite layer D of greater area than the conductive layer A, said face comprising flow channels, flow openings and sealing joints.

[0165] [Fig. 14] represents a cross-sectional view of a bipolar plate comprising two composite blades in which the flow channels on one face of one of the blades face the flow channels on one face of the other blade, thus creating three flow fields.

[0166] Detailed description of the invention

[0167] Blade configuration

[0168] In the blades according to the invention, the conductive layers are positioned so that they can be used as outer layers. This results in a composite blade with optimal conductivity and sealing. Depending on the final configuration in which the composite blades are used, a conductive layer may be desired on only one face of the blade or on both faces.

[0169] In the precursor blade according to the invention, a polymeric layer is intercalated between a porous layer and a conductive layer. In this way, strong adhesion is ensured between the conductive layer and the composite layer in the composite blade.

[0170] The precursor blade configuration, in which the porous layer is sandwiched between two polymer layers (polymer layer B - porous layer C - polymer layer B' or polymer layer B - porous layer C - polymer layer B' - porous layer C' - polymer layer B), facilitates polymer penetration into the porous layer during composite blade fabrication, as the polymer only needs to penetrate a fraction of the porous layer's thickness. It is essential that the polymer in the polymer layers penetrates the porous layer correctly because the resulting composite layer must be able to establish electrical contact with the layer(s) on which or between which it is placed. In other words, after compression, no insulating polymer film should remain on the surface of the composite layer.

[0171] In the precursor blade according to the invention, the mass ratio of the mass of all the polymer layers in contact with a porous layer to the mass of all the porous layers can be between 0.5 and 4, and preferably between 1 and 2.

[0172] The composite layer D may have a thickness of between 20 and 300 pm, preferably between 50 and 200 pm, more preferably between 50 and 150 pm, if the layer D comprises a single porous layer C or having a thickness of between 40 and 600 pm, preferably between 100 and 400 pm, more preferably between 100 and 300 pm, if the layer D comprises two porous layers C and C'.

[0173] Preferably, in the composite blade, the composite layer has a thickness greater than the thickness of the conductive layer A and, if applicable, greater than the thickness of the conductive layer A', for example, greater than the sum of the thicknesses of the conductive layer A and the conductive layer A'. It has been observed that these preferred ratios and dimensions reliably achieve optimal conductivity, sealing, mechanical and thermal resistance, and adhesion between the conductive and composite layers in the composite blades.

[0174] The composite blade according to the invention preferably has a total thickness of between 40 and 500 µm, more preferably between 75 and 300 µm, even more preferably between 75 and 200 µm if layer D comprises a single porous layer C or a thickness of between 60 and 800 µm, more preferably between 125 and 500 µm, even more preferably between 125 and 400 µm, if layer D comprises two porous layers C and C'.

[0175] In the composite blade according to the invention, the area of ​​the composite layer can be greater than the area of ​​the conductive layer(s). Thus, the portions of the composite layer not covered by the conductive layer can be easily welded together, for example, by melting the polymer contained in the composite layer. Two composite blades can therefore be joined securely while maintaining good conductivity. Furthermore, if the composite blade includes flow channels on both sides, a bipolar blade according to item 57 can be created simply and economically, featuring three flow fields: one flow field between the two blades and two flow fields on either side of the blade joint.The flow field between the two blades can, for example, be used for the circulation of a coolant, while the two other flow fields, on either side of the assembly, will be used to circulate the reactants and products of the reactions occurring at the level of the membrane-electrode assembly of the cells.

[0176] The configuration of the composite blade in which the flow channels on one face define hollows separated by partitions, the hollows formed by the flow channels on one face forming the partitions separating the flow channels on the other face makes it possible to obtain flow channels deeper than the thickness of the composite blade.

[0177] The composite blade according to the invention preferably has an ASR (specific surface resistance) in the thickness of less than 15 mQ.cm 2 .

[0178] The ASR in thickness is measured on a flat sample as follows:

[0179] Place the sample to be tested between two copper discs with a diameter of 40 mm (the sample has an area greater than the copper discs);

[0180] Apply a pressure of 1 MPa between the copper plates;

[0181] Measure the resistance between the two copper plates using an ohmmeter;

[0182] Calculate the ASR from the measured resistance and the area of ​​the copper plates.

[0183] Figures 1 A, B, C, D represent precursor strips in which the layer stacking includes a porous layer (1), sandwiched between two polymeric layers (3). Thus, the polymer of the polymeric layers (3) can penetrate the thickness of the porous layer (1) and allow adhesion between the conductive layer (2) and the porous layer.

[0184] Fig. 2A shows a three-layer composite blade after molding (5) consisting of a composite layer (reinforcement-filler-polymer) (4) sandwiched between a first (upper) conductive layer (2) and a second (lower) conductive layer (2). The composite layer (4) is formed from a porous layer (1) and a polymeric layer (3) by penetrating the polymeric layer (3) into the thickness of the porous layer (1). This penetration ensures a strong bond (13) between the porous layer (1) and the conductive layer (2). This penetration of the polymer into the porous layer creates a new, unified, and coherent structure called the composite layer (4).

[0185] Fig. 2B represents a two-layer composite blade after molding (5) consisting of a composite layer (4) and a conductive layer (2).

[0186] Fig. 2C represents a single-layer composite blade after molding (5) consisting of a composite layer

[0187] (4) only.

[0188] These composite blades can be used as a flow field plate or as a bipolar plate interposed between two cells in a fuel cell. In this case, at least one outer layer, preferably a conductive layer (2), has an outer surface in which flow channels (8)09) are molded as in Figures 3C, 4C, 5C, 7C, 8C, 9C.

[0189] Fig. 3 shows a molded three-layer composite blade consisting of a composite layer (4) sandwiched between two conductive layers (2). Flow channels (8) are created on the lower and upper surfaces during compression molding (9), which forms these channels (8) by pressing the material into the mold cavity (6) (7) under pressure. The geometry of the channels corresponds to the geometry of the compression mold cavity (6) and (7).

[0190] Fig. 4 shows a two-layer molded composite blade consisting of a composite layer (4) and a conductive layer (2). Flow channels (8) are created on the lower and upper surfaces during compression molding (9), which forms these channels (8) by pressing the material into the mold cavity (6) (7) under pressure. The geometry of the channels corresponds to the geometry of the compression mold cavity (6) and (7). A variant not shown, composite blade [Fig. 4] C, consists only of the composite layer (4).

[0191] Fig. 5 shows a two-layer, channel-free base composite blade (15) molded with a composite layer (4) and a conductive layer (2). Flow channels (8) are created on a surface during compression molding (9), which forms these channels by material creep within the cavity (6) of the mold under pressure. The channel-free surface is formed by the cavity (14) of the mold (9) under pressure. The geometry of the channels (8) corresponds to the geometry of the compression mold cavity (6).

[0192] In an alternative not shown in Figure 5C, the channels (8) are created on the surface side of the composite layer (4). In another alternative not shown, the composite blade in Figure 5C consists solely of the composite layer (4). In yet another alternative not shown, the composite blade in Figure 5C is formed from a three-layer blade.

[0193] Fig. 6 shows a composite blade (5) without channels, composed solely of the composite layer (4). A variant not shown, the composite blade in Figure 6C, is formed from a two-layer blade. Another variant, also not shown, is the composite blade in Figure 6C, formed from a three-layer blade.

[0194] Fig. 7 shows a molded three-layer composite blade consisting of a composite layer (4) sandwiched between two conductive layers (2). The blade has flow channels (19) on both faces, with the recesses formed by the flow channels on one face acting as partitions separating the flow channels on the other face. During compression molding (9), the conductive (2) and composite (4) layers form on the mold cavity to create the channels (19). The geometry of the channels corresponds to the geometry of the compression mold cavities (17) and (18). Fig. 8 shows a molded two-layer composite blade consisting of a composite layer (4) and a conductive layer (2). The blade has flow channels (19) on both faces, with the recesses formed by the flow channels on one face acting as partitions separating the flow channels on the other face.During compression molding (9), the conductive (2) and composite (4) layers form on the mold cavity to create the channels (19). The geometry of the channels corresponds to the geometry of the cavities (17) and (18) of the compression mold.

[0195] Fig. 9 shows a single-layer molded composite blade consisting solely of the composite layer (4). The blade has flow channels (19) on both faces, with the hollows formed by the flow channels on one face acting as partitions separating the flow channels on the other face. During compression molding (9), layers (1) and (3) are formed in the mold cavity to create the channels (19). The geometry of the channels corresponds to the geometry of the cavities (17) and (18) of the compression mold.

[0196] Flow channels are preferably created by calendering or compression molding, during or after the fabrication of the composite blade. Calendering or compression molding to produce flow channels (8)(19) on the external surface is carried out during and / or after the penetration of the polymer layer into the thickness of the porous layer.

[0197] Figure 12 represents composite blades, seen from above (12A) and from the side (12B and 12C) in which the composite layer D has an area greater than the area of ​​the conductive layer(s) a top view of a composite blade having a conductive layer affixed to a composite layer of greater dimension.

[0198] Figure 13 shows a top view of a composite blade after molding, representing a conductive layer bonded to a higher-area composite layer. The composite blade also includes flow channels, flow openings (24) and sealing joints (23).

[0199] Figure 14 represents a cross-sectional view of a bipolar plate comprising two composite blades in which the flow channels on one face of one of the blades face the flow channels on one face of the other blade, thus creating three flow fields.

[0200] Conductive layer

[0201] In the present invention, the conductive layer may be an electrically conductive film or foil, for example a flexible graphite layer, carbon paper, carbon veil, carbon or graphite fabric, conductive polymer film, metal foil or metal grid.

[0202] Preferably, in the present invention, at least one of the conductive layers is a flexible graphite layer.

[0203] For the purposes of this invention, flexible graphite comprises two types of graphite: synthetic flexible graphite and natural flexible graphite. These materials are commonly used for their thermal conductivity properties, particularly in electronic devices. Examples of flexible graphite layers that can be used include HALA graphite sheets, SGL Sigratherm® graphite sheets, and Panasonic PGS graphite sheets.

[0204] Natural flexible graphite is obtained by calendering exfoliated natural graphite particles, while synthetic flexible graphite is obtained by pyrolysis of a carbon precursor. It has been observed that the use of conductive layers of flexible graphite, particularly when used as outer layers in the flow field plate or bipolar plate obtained from the composite blade, is advantageous. This is because it ensures good sealing and conductivity for the composite blade using a thin, corrosion-resistant layer that can be formed by compression techniques such as compression molding or calendering. Preferably, the flexible graphite is natural flexible graphite. It has been observed that natural flexible graphite is easier to form than synthetic flexible graphite.

[0205] Preferably, the flexible graphite layer(s) have a thickness between 20 µm and 100 µm, more preferably between 25 and 50 µm. Surprisingly, it was observed that these small thicknesses were sufficient to achieve the desired sealing and conductivity for the composite blade, and that it was possible to form flow channels within the blade without tearing it. Thus, for a composite blade of a given thickness, the thickness of the composite layer can be increased, and acceptable mechanical properties can be obtained even for composite blades with a small overall thickness.

[0206] According to one embodiment, all conductive layers are flexible graphite layers.

[0207] In another embodiment, the blade comprises two conductive layers (A and A'), one conductive layer is a flexible graphite layer and the other is a metallic grid, preferably a one-piece metallic grid. Examples of such one-piece metallic grids include Microgrid® products (Dexmet). The metal can be chosen from, for example, aluminum, copper, stainless steel, titanium, or nickel. The thickness of the metallic grid can range from 50 to 150 µm, for example, 100 µm. Although introducing a metallic element that must be protected from corrosion, this configuration can be desirable, particularly for the increased conductivity provided by the metal.On the other hand, depending on the configuration in which the composite blade is used, the face containing the metal grid is not necessarily exposed to highly oxidizing conditions (particularly because the flexible graphite layer makes the composite blade exceptionally watertight). Using a metal grid rather than a solid metal sheet allows the metal sheet to be embedded by pressing it into the composite layer; thus, despite the relatively significant thickness of the grid, the overall thickness of the composite blade can remain limited. Furthermore, the areas not covered by the metal in the grid's interstices allow for easy welding of one composite blade to another.Compared to a grid made up of intertwined metal wires, a one-piece metal grid (which can, for example, be seen as a metal sheet with holes in it) has the advantage of not presenting the risks of conduction defects that contact between metal wires causes.

[0208] The different conductive layers can have the same or different thicknesses.

[0209] Polymer layer

[0210] In this disclosure, a "polymer" is defined as a thermoplastic or thermosetting polymer, whether or not it is already cured.

[0211] Preferably, the polymer (12) of the polymeric layer (3) intended to form the blade (5) and (4) is a thermoplastic. Preferably, the thermoplastic polymer is selected from the following polymers: polyethylene naphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK), polyaryletherketones (PAEK), polyetheretherketone (PEEK), polyvinylidene fluoride (PVDF), polyethylene (PE), polyester (PEs), polyphthalamide (PPA), polyamide (PA), polypropylene (PP), polyethersulfone (PESU), polyimide (PI), polyetherimide (PEI), polymethyl methacrylate (PMMA), polyamide-imide (PAI), ethylene propylene fluorinated copolymer (FEP), perfluoroalkoxy (PF A), polytetrafluoroethylene (P'IFE), and polysulfone (PSU);more preferably among the following polymers: ethylene polynaphthalate (PEN), polyphenylsulfone (PPSU), polyphenylene sulfide (PPS), polyetherketoneketone (PEKK), polyvinylidene fluoride (PVDF), polyphthalamide (PPA), polyimide (PI), polyetherimide (PEI), ethylene propylene fluoride copolymer (FEP), and perfluoroalkoxy (PF A); all preferably among the following polymers: ethylene polynaphthalate (PEN), polyphenylsulfone (PPSU) and polyetherketoneketone (PEKK).

[0212] A thermoplastic simplifies the process compared to a thermoset. The polymer must be sufficiently hard or viscous to form a layer within the precursor blade stack, but not so hard as to prevent the polymer from penetrating the porous layer. For a thermoplastic polymer, this is easily achieved by heating and compressing the material when penetration is desired, then allowing it to return to room temperature. With a thermoset, its degree of hardening must be carefully controlled throughout the process, and it may be necessary to cool the polymer below room temperature initially to ensure sufficient viscosity for it to remain as a polymeric layer within the precursor blade. Recycling the blade is also easier with a thermoplastic.

[0213] The polymer used may include a mixture of thermoplastics and / or thermosets to adjust the viscosity of the mixture and to improve the adhesion properties of the polymer.

[0214] Suitable thermosetting resins may be selected from epoxies, unsaturated polyesters, vinyl esters, phenolic resins, polyimides, bismaleimides, phenol-formaldehyde resins, urea-formaldehyde resins, 1,3,5-triazine-2,4,6-triamines, benzoxazines, cyanate esters, and mixtures thereof. Such a resin may also include one or more curing agents, well known to those skilled in the art for use with the selected thermosetting polymers.

[0215] Preferably in the composite blade, the mass of polymer M represents at least 30% more preferably from 40 to 80%, even more preferably from 45 to 75%, most preferably from 50 to 70% of the total mass of the composite layer.

[0216] Preferably in the precursor layer, the mass of the polymeric layers represents at least 30%, more preferably 40 to 80%, even more preferably 45 to 75%, most preferably 50 to 70% of the total mass of the porous layers and the polymeric layers.

[0217] Preferably, in the precursor strip, each polymer layer has a thickness of less than 0.1 mm, more preferably from 0.01 mm to 0.1 mm, even more preferably from 0.015 to 0.035 mm, for example 0.025 mm. The different polymer layers of the precursor strip may have the same or different thicknesses.

[0218] The manufacturing of the composite blade by compression molding or continuous calendering involves the penetration of the polymer into the porous layer(s), followed by a consolidation step of the part, either by cooling (in the case of a thermoplastic) or by a polymerization / crosslinking step (in the case of a thermoset). According to a particular embodiment, which is also suitable for all the implementation variants described in relation to the invention, the penetration and consolidation steps are carried out in a closed mold. Porous layer

[0219] By "porous layer" we mean a permeable layer allowing a liquid such as a resin or molten plastic to pass through.

[0220] The precursor blade according to the invention comprises a porous layer including a conductive filler and a reinforcement assembly including reinforcing fibers bonded together.

[0221] In such a porous layer, it's important to understand that the conductive filler can be added to the reinforcement assembly or be part of it. For example, if the reinforcing fibers of the reinforcement assembly are conductive, they constitute a conductive filler. Therefore, it's not always necessary to add a conductive filler to the reinforcement assembly.

[0222] Because the fibers that make it up are bonded together, the reinforcement assembly has mechanical strength on its own.

[0223] The use of a reinforcement assembly with its own inherent mechanical strength simplifies the manufacturing of the composite blade. It can be formed in a single compression step of the precursor blade, and the handling and preparation of the precursor blade are simplified.

[0224] The composite blade according to the invention is distinguishable from a composite blade obtained, for example, by mixing fibers with a liquid polymer resin and then solidifying it. Indeed, in the reinforcement assembly, the fibers necessarily touch and maintain significant porosity between them due to the overall mechanical strength, whereas for fibers dispersed in a resin, they can be packed too tightly, or conversely, some fibers may not be in contact with others. The use of a porous layer incorporating a reinforcement assembly provides better mechanical properties and improved conductivity to the composite layer (in the reinforcement assembly, the contacts between fibers provide mechanical strength and can provide conductivity if the fibers are conductive; in all cases, the porosity allows for efficient distribution of the conductive charge).

[0225] The porous layers can be found on the surface or inside the stack that makes up the precursor blade.

[0226] Reinforcing assemblies can be woven or nonwoven. Preferably, the reinforcing assembly is a nonwoven of reinforcing fibers. Nonwovens can be obtained by various processes known to those skilled in the art, either wet or dry. They may contain binders, polymeric or non-polymeric.

[0227] The reinforcing fibers (10) of the porous layer (1) can be carbon, glass, aramid, or ceramic fibers, with carbon fibers being preferred because they are conductive. A carbon fiber nonwoven fabric is preferred for the entire reinforcement assembly. Such nonwoven fabrics include, for example, Optiveil 20352E, 20301H, 20352F, or Freudenberg's E15 nonwoven fabric.

[0228] Preferably, the reinforcement assembly of layer C and, if applicable, of layer C' comprises at least 90% by mass of reinforcing fibers, relative to the total mass of the reinforcement assembly.

[0229] Preferably, the reinforcement assembly present in the porous layer(s) has a surface mass between 5g / m² 2 and 100g / m 2 , more preferably between 10 and 50 g / m 2 .

[0230] Preferably, in the precursor blade, each porous layer has a pressure-free thickness of between 10 and 200 µm, preferably between 50 and 100 in. The different porous layers and the different reinforcement assemblies of the precursor blade may have different or identical thicknesses.

[0231] According to one embodiment, in layer C and, if applicable, in layer C', the bonding of the reinforcing fibers is ensured by a polymeric binder; for example, said polymeric binder represents less than 6%, for example, 2 to 6% by mass relative to the total mass of the reinforcement assembly. In the composite sheet, this polymeric portion does not include the amount of polymer that has penetrated the porous layer.

[0232] This polymeric part can be a thermoplastic polymer, a thermosetting polymer, or a mixture of such polymers.

[0233] In one embodiment, in layer C and, if applicable, in layer C', the reinforcing fibers are carbon fibers, and the bonding of the reinforcing fibers is ensured by a carbon-based conductive binder. In this case, the conductivity is particularly good, and it is not necessary to add any conductive filler to the reinforcement assembly (the conductive filler of layer C and, if applicable, of layer C', is then included in the reinforcement assembly).

[0234] The conductive filler of the porous layer can be chosen from: carbon fibers, graphite powder, metallic fibers, carbon blacks, metallic particles, and combinations thereof.

[0235] Preferably, the mass of the conductive filler of the porous layer represents between 15 and 70%, preferably between 20 and 60%, more preferably between 25 and 55% of the total mass of the composite layer (in the composite blade) or of the total mass of all the porous layers and polymeric layers (in the precursor blade).

[0236] If a conductive filler is added to the reinforcement assembly, the conductive filler preferably comprises graphite powder. In this case, the graphite powder preferably has a d50 between 20 and 60 µm, more preferably between 30 and 50 µm, measured by laser particle size analysis. With these dimensions, it has been observed that the graphite powder fits well within the reinforcement assembly and provides advantageous conductivity for the composite blade. By definition, for a powder with a given d50, 50% by mass of the powder particles has a diameter measured by laser particle size analysis that is smaller than said d50 value. Examples of suitable graphite powders include Imerys Timrex KS75 and SFG5-75 powders or SGL Sigratherm® powders.

[0237] Carbon black (such as Cabot's Vulcan® XCMax or Ensaco 250G carbon black) can be added to the graphite powder to further improve conductivity and achieve an ASR (area specific resistance) in the thickness of less than 10 mQ / cm². 2 .

[0238] Manufacturing process for a composite blade

[0239] According to another aspect, the invention relates to a method for manufacturing a composite blade comprising the following steps: a. Supplying a precursor blade according to the invention, b. Pressing the precursor blade so as to cause layer B and, if applicable, layers B' and B'”, to penetrate layer C and, if applicable, layer C', so as to obtain a pressed blade, c. Optionally, finishing the pressed blade so as to obtain the composite blade, and d. Retrieving the composite blade. Step a may include stacking layers A, B, C and, if applicable, A', B', B'”, and C' in the desired final order.

[0240] The deposition processes that can be used to form the precursor blade stack, whether directly in a mold or prior to the introduction of the precursor blade into a mold, are well known to those skilled in the art. For example, the precursor blade can be produced by continuous assembly, for instance, from rolls of the different layers of the precursor blade.

[0241] In this case, it is advantageous to also perform the pressing step of the precursor blade continuously, for example by calendering. This allows the assembly of the precursor blade and its pressing to obtain the pressed blade to be carried out on the same continuous production line.

[0242] Calendering can be carried out using a double belt press.

[0243] In particular, if conductive fillers are added to the reinforcement assembly of the porous layer, they can be added by powdering the conductive filler onto the reinforcement assembly.

[0244] Step b of pressing can be done by hot calendering or by compression molding.

[0245] In step c, flow channels can be molded on one main face of the blade or on both main faces of the blade.

[0246] The molding of the channels in step c can be carried out at the same time as the pressing in step b. For example, it is sufficient for this that the calendering rollers or the mold used for pressing have the desired shape.

[0247] The channels can also be molded separately. This allows different channel architectures to be molded from the same batch of pressed blade production.

[0248] The temperature at step b is preferably between 200°C and 400°C.

[0249] The pressure at step b is preferably between 10 and 200 bar, preferably between 50 and 200 bar, more preferably between 100 and 200 bar.

[0250] With such parameters, a satisfactory flow of the polymer in the porous material is obtained.

[0251] Applying such parameters during channel molding also results in satisfactory shaping. In particular, this allows channel molding to be performed simultaneously with step b.

[0252] According to another embodiment, no finishing step is necessary. It should be noted that the pressed blade already includes a composite blade as defined in the present invention.

[0253] The present invention is suitable for manufacturing a wide variety of composite parts in the fields of aeronautics, automotive, space, defense, industry, and energy. Examples of such parts are given below: fuel cell flow plates, bipolar plates, battery plates, current collectors, electrodes, conductive membranes, redox cells, storage batteries, etc.

Claims

DEMANDS 1. Precursor blade comprising directly stacked one on top of the other in this order: A conductive layer A, A polymer layer B, and A porous layer C comprising a conductive filler and a reinforcement assembly comprising interconnected reinforcing fibers, and Optionally, a polymer layer B'.

2. Precursor blade according to claim 1 in which the conductive layer A is a layer of flexible graphite, preferably of natural flexible graphite.

3. Precursor blade according to claim 2 comprising the polymer layer B', the polymer layer B' being further directly stacked on: a conductive layer A', or on a stack comprising, directly stacked one on top of the other in this order: o a porous layer C' comprising a conductive filler and a reinforcement assembly comprising reinforcing fibers bonded together, o a polymer layer B”, and o a conductive layer A'; in which one conductive layer A' is a flexible graphite layer and the other is a metal grid, preferably a one-piece metal grid.

4. Precursor blade according to claim 2 or 3 in which the flexible graphite layer has a thickness of between 20 µm and 100 in. preferably between 25 and 50 µm.

5. Precursor blade according to any one of claims 1 to 4 wherein the polymer of layer B and, if applicable, of layers B' and B” is a thermoplastic polymer.

6. Precursor blade according to any one of claims 1 to 5 wherein the conductive filler comprises graphite powder and carbon black.

7. Composite blade comprising directly stacked one on top of the other in this order: A conductive layer A, A composite layer D that may result from, or result from, the infiltration of a polymer M into a porous layer C comprising a conductive filler and a reinforcement assembly comprising interbonded reinforcing fibers, and Optionally, a conductive layer A'.

8. Composite blade according to claim 7 in which layer D has a thickness between 20 and 300 µm, preferably between 50 and 200 µm, more preferably between 50 and 150 µm.

9. Composite blade according to claim 7 or 8 in which at least one of the conductive layers A and A' is a layer of flexible graphite, preferably of natural flexible graphite.

10. Composite blade according to claim 9 comprising two conductive layers A and A' in which one of the conductive layers is a flexible graphite layer and the other is a metal grid, preferably a one-piece metal grid.

11. Composite blade according to claim 9 or 10 in which the flexible graphite layer(s) have a thickness of between 20 pm and 100 pm, preferably between 25 and 50 pm.

12. Composite blade according to any one of claims 7 to 11 wherein the polymer M is a thermoplastic polymer.

13. Composite blade according to any one of claims 7 to 12, wherein the conductive filler comprises graphite powder and carbon black.

14. Bipolar blade comprising two composite blades a and b according to any one of claims 7 to 13, said composite blades each comprising flow channels on their two main faces in which: a main face la of blade a is welded to a main face 1 b of blade b, the flow channels of face la face the flow channels of face 2, and - the top of the partitions of the flow channels of face la is in contact with the top of the partitions of the flow channels of face 1b.

15. A method for manufacturing a composite blade according to any one of claims 7 to 14 comprising the following steps: a. Supplying a precursor blade according to any one of claims 1 to 6, b. Pressing the precursor blade so as to cause layer B and, if applicable, layers B' and B'', to penetrate layer C and, if applicable, layer C', so as to obtain a pressed blade, c. Optionally finishing the pressed blade so as to obtain the composite blade, and d. Recovering the composite blade.

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