Method for manufacturing a sheet metal for a bipolar plate of a fuel cell, and method for manufacturing such a bipolar plate

Abstract

The invention relates to a method for manufacturing an anodic or cathodic plate for a bipolar plate used in fuel cells. This method comprises supplying a flat plate having a first face and a second face, forming a seal including at least one peripheral seal on a peripheral portion of the first face of the flat plate. It then comprises deforming the flat plate by forming and defining relief patterns on it. Figure 3

Description

Title of the invention: Method for manufacturing a sheet for a bipolar plate of a fuel cell, and method for manufacturing such a bipolar plate. SCOPE OF THE INVENTION

[0001] The present invention relates to a method for manufacturing an anodic or cathodic plate of a bipolar plate for electrochemical cells, particularly for fuel cell cells. The invention also relates to a method for manufacturing a bipolar plate equipped with at least one sealing gasket. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Electrochemical systems, for example fuel cells, are usually formed from a stack of cells, defined and separated from each other by bipolar plates.

[0003] In proton exchange membrane fuel cells (PEMFCs), as illustrated in [Fig. 1A], each cell C consists of a membrane-electrode assembly 6 (MEA) comprising a solid electrolyte membrane based on a polymer, for example, a fluorinated polymer, and a catalyst layer formed on each face of the membrane. The catalyst layers form the cell electrodes. Gas diffusion layers (GDLs), which may be textile-based such as felts, are generally arranged on either side of the membrane, respectively against the anodic face 1a and cathodic face 1b of two bipolar plates 1 defining the cell C.

[0004] An electrochemical system is formed of a stack E comprising a hundred, or even several hundred, of cells C.

[0005] As recalled in document CA2701366, the bipolar plates 1 have, in particular, the following functions: - to ensure electrical contact between the cell electrodes by connecting the cells in series; - to supply the cells with reactive fluids, hydrogen and air for example, and to remove the products of the electrochemical reaction; - to dissipate the residual heat generated during the electrochemical reaction, for example using a heat transfer fluid; - to ensure the sealing of the various channels of reactive or cooling fluids between each other and with respect to the outside.

[0006] The bipolar plates 1 must also exhibit sufficient mechanical robustness to maintain these functions in the stack E forming the electrochemical system, particularly when the fluids are under significant pressure.

[0007] A bipolar plate 1 is formed of two conductive sheets, respectively designated "cathodic sheet" and "anodic sheet" in this application, joined together. The free face of the anodic sheet defines the anodic face 1a of the bipolar plate 1 intended to be exposed to the fuel fluid (for example, hydrogen) and, similarly, the free face of the cathodic sheet defines the cathodic face 1b of the plate 1, intended to be exposed to the oxidizing fluid (for example, air).

[0008] In general, the sheets are provided with patterns composed of "recessed" reliefs tending to bring the anodic face 1a and the cathodic face 1b of the same bipolar plate 1 closer together, and "ridged" reliefs tending to move the anodic face 1a and the cathodic face 1b further apart. These relief patterns are typically formed by shaping the sheets before assembly, for example by stamping, and allow the bipolar plate to be functionalized, notably by forming ribs and channels to guide the flow of fluids in a cell C.

[0009] The search for improved electrochemical reaction efficiency leads to the formation of these patterns with a high density, for example by placing the channels close together. A relatively high density improves gas diffusion, as exchanges occur at the reaction sites, and electron collection is enhanced. It is therefore possible to choose to form bipolar plates with a channel network, the channels of the network having a pitch of 1.5 mm or less. However, the formation of such raised patterns can affect the flatness of the sheet metal, causing it to curve or warp.

[0010] To prevent reactive fluids from flowing outside a cell C of the stack E, a sealing element 5 is pressed between two adjacent bipolar plates 1. This sealing element 5 is in the form of a gasket sheet pre-cut along sealing lines of the cathode and anodic plates. These sealing lines, which typically take the form of a rib, are present in particular on a peripheral portion of these plates and form the outline of an internal region Zi of each plate.

[0011] The construction of a battery therefore requires forming a complex stack E of bipolar plates 1, sealing elements 5, membrane-electrode assemblies 6.

[0012] To simplify this assembly, US patent 6436568 proposes forming sealing gaskets on a bipolar sheet in the sheet forming equipment, after the embossed patterns have been formed. This equipment is equipped with means for injecting the gasket-forming material after the sheet has been stamped. The setup However, operating such equipment is complex. In addition to the risks of equipment contamination by residues of the material used to form the seal, it ties up the forming equipment for an extended period to perform simple injection operations, which degrades the production rate. SUBJECT OF THE INVENTION

[0013] One object of the invention is to provide a method for manufacturing an anodic or cathodic plate for a bipolar plate, this plate incorporating a sealing gasket. Since this gasket is incorporated into the plates forming a bipolar plate, the need to position pre-cut gasket sheets in the stack is eliminated, thus simplifying the stack construction. Another object of the invention is to provide a method for manufacturing a bipolar plate that utilizes an anodic plate and a cathodic plate formed using the manufacturing process for these plates. BRIEF DESCRIPTION OF THE INVENTION

[0014] With a view to achieving one of these goals, the object of the invention proposes a method for manufacturing an anodic or cathodic sheet of a bipolar plate for a fuel cell, the method comprising the following steps: - provide a flat sheet metal having a first face and a second face, the second face being opposite the first face; - form a sealing joint comprising at least a peripheral sealing joint on a peripheral portion of the first face of the flat sheet, then;

[0015] deform the flat sheet metal by forming and define relief patterns on it.

[0016] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - the manufacturing process includes cutting the sheet metal, before or after its deformation, to form a plurality of collectors; - the sealing joint includes additional sealing joints arranged on the contours of the manifolds of the plurality of manifolds; - the sealing gasket is formed by molding an elastomer material onto the first face of the flat sheet using a mold placed against the first face of the flat sheet; - the elastomer material is injected under pressure into the mold of the sealing gasket; - the sealing joint is formed by dispensing or screen printing an elastomeric material onto the first face of the flat sheet; - the elastomer material is a silicone elastomer or a fluorinated elastomer of the FKM type; - the deformation of the flat sheet by forming is obtained by pressing the second face of the flat sheet against a die using a punch, the die and the punch having reliefs configured to define the relief patterns on the sheet, the punch also being configured to limit a pressure applied on the sealing joint during the deformation; - the relief pattern defines crest reliefs and hollow reliefs, relative to an average elevation plane, on the first face of the sheet metal, the sealing joint being entirely placed on a crest relief of the first face of the sheet metal;

[0017] According to another aspect, the invention also proposes a method for manufacturing a bipolar plate for a fuel cell, the plate being formed of an anodic plate and a cathodic plate assembled together and each having patterns composed of reliefs, the method comprising the following steps: - supply an anodic plate and a cathodic plate, at least one of the anodic plate and the cathodic plate having been prepared by means of a manufacturing process as described above; - assemble the second side of the anodic plate to the second side of the cathodic plate to form the bipolar plate.

[0018] Advantageously, this process includes a step of welding the anodic plate and the cathodic plate.

[0019] Sealing gaskets may be carried respectively by the anodic plate and by the cathodic plate. Alternatively, a sealing gasket is carried by one of the anodic plates and the cathodic plate. Brief description of the drawings

[0020] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0021] [Fig.1A]

[0022] Fig. 1A represents a stack of electrochemical cells of a prior art fuel cell;

[0023] [Fig.2A]

[0024] Fig. 2A represents a front view of a cathode ray tube obtained using the process of the invention;

[0025] [Fig.2B]

[0026] Fig. 2B represents a partial section of a bipolar plate using the cathode sheet of Fig. 2A, the section being made along the AA axis of this Fig. 2A;

[0027] [Fig.3]

[0028] Fig. 3 illustrates a stamping forming step of a manufacturing process according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] In order to provide a complete explanation, a cathode ray tube 10 and a bipolar plate 1, which can be manufactured using a process that will be described in a subsequent section of this description, are shown in relation to Figures 2A and 2B respectively. It should be noted that this process makes it possible to manufacture an anodic tube 20 (visible in [Fig. 2B]), similar to the cathode ray tube 10 shown in [Fig. 2A], without the need for a separate illustration of this tube.

[0030] Such a bipolar plate 1 is compatible with an electrochemical stack consisting of identical bipolar plates. It is also compatible with a mixed stack of bipolar plates of different types.

[0031] As presented in the introduction and illustrated in [Fig. 2B], a bipolar plate 1 according to the invention is formed of a cathode plate 10 and an anodic plate 20, joined together at an assembly plane Pref. The plate may be made of steel, such as stainless steel. In such a plate 1, the free face of the anodic plate 20 defines the anodic face 1a of the bipolar plate 1 intended to be exposed to the fuel fluid (for example, hydrogen) and, similarly, the free face of the cathode plate 10 defines the cathodic face 1b of the plate 1, intended to be exposed to the oxidizing fluid (for example, air). The volume between an anodic face 1a and a cathodic face 1b of two adjacent bipolar plates 1 defines a cell of a stack.

[0032] Each sheet 10,20 of a bipolar plate includes at least one peripheral sealing gasket 5 disposed on a peripheral portion of its free face, integral with this face. This sealing gasket 5 defines an internal region Zi of these sheets 10,20. It may be made of an elastomeric material such as a silicone-based or silicone elastomer, or a fluorinated elastomer of the FKM type or an EPDM rubber (“ethylene-propylene-diene monomer”).

[0033] The sealing gasket can have a width typically between 2 mm and 10 m, and a thickness typically between 30 micrometers and 600 micrometers.

[0034] In this internal region Zi, each plate 10,20 has a so-called "active" zone Za where the electrochemical reaction is intended to occur. More precisely, the active zones Za of a cathodic face 1b and an anodic face la of two adjacent bipolar plates in a stack define the cell volume in which the electrochemical reaction takes place.

[0035] The active zone Za extends longitudinally between a first distributor DI and a second distributor D2. These two distributors D1, D2 allow the reactive fluids to be injected into a cell at the level of the two active zones Za and these fluids and / or reaction residues to be collected after they have passed through these zones. The two distributors D1, D2 also allow the heat transfer fluid to circulate in the bipolar plate 1, between the two plates 10, 20 assembled together, so that this fluid circulates at the level of the active zone Za of each plate.

[0036] An active zone Za is usually formed by a network of longitudinal ribs N, i.e., a crested relief formed on each of the plates 10, 20 of the bipolar plate. These ribs N extend from the first distributor DI to the second distributor D2 to ensure the continuity of fluid flow. Two adjacent longitudinal ribs of the network define a channel C, a concave relief, allowing the reactive fluids to be distributed over a large area of ​​the electrode. The ribs N of the active zones Za of the two plates forming a bipolar plate 1 define internal channels CI within this plate. These internal channels CI allow the heat transfer fluid to circulate at the active zones Za of the cathodic face 1b and the anodic face la of the bipolar plate 1.

[0037] The anodic plate 20 and cathodic plate 10 of a bipolar plate may have other raised, ridged, or recessed patterns. In particular, these plates may have raised ridges forming sealing lines on which the peripheral sealing gasket 5 and, where applicable, other sealing gaskets are arranged.

[0038] In the example shown in [Fig.2A], the distributors D1,D2 comprise an air collector 2 and a hydrogen collector 3 separated from each other by a heat transfer fluid collector 4. On the cathodic face of the bipolar plate shown in [Fig.2A], the air collector 2 is adapted to supply channels of the active zone Za with air, via an injection zone 8 and a homogenization zone 9. The second distributor D2 has a similar arrangement to collect the airflow having passed through the active zone.

[0039] On the anodic face of the bipolar plate 1, not shown, in the first distributor DI and in the second distributor D2 there is an injection zone and a homogenization zone associated this time with the hydrogen collector.

[0040] The heat transfer fluid collector 4 is adapted to introduce and circulate this fluid in the internal channels CI of the bipolar plate, at the level of the active areas Za of the cathodic face 1b and the anodic face la of the bipolar plate.

[0041] In the example of [Fig. 2A], additional sealing gaskets 5' are also respectively arranged on the contours of the manifolds 2, 3, 4 of each distributor, and integral with these contours. It can be foreseen that these contours are defined as raised, ridged patterns are used to facilitate their formation. The additional 5' seals are advantageously formed from the same material as the peripheral seal, although this is not mandatory.

[0042] Finally, the anodic 20 and cathodic 10 plates of a bipolar plate 1 each have lateral bands B in the internal region Zi and laterally bordering the active areas Za of each plate. The lateral bands B accommodate a peripheral contour of the membrane-electrode assembly and / or the gas diffusion layers that cover these active areas Za in the stack.

[0043] Thus, in [Fig. 2B] a membrane-electrode assembly is shown, consisting of a solid electrolyte membrane 6b based on a polymer, for example a fluorinated polymer, coated with a catalyst layer on each of its faces. Gas diffusion layers 6a are arranged to cover the active areas Za of the two faces, anodic and cathodic, which face each other in a cell. A sealing strip 6c designed to fluidly isolate two half-cells from each other is also shown in [Fig. 2B]. Reference may be made in this regard to US patent 2006 / 0078781.

[0044] We now present the manufacturing process of an anodic sheet 20 and / or cathodic sheet 10 which can be used to form the bipolar plate 1 which has just been presented.

[0045] In very general terms, this process comprises a first step of supplying a flat sheet. This flat sheet, and therefore devoid of any raised pattern, has a first face and a second face opposite the first. This sheet is made of a conductive material, typically a metal such as stainless steel, as previously mentioned. It is suitable for use in a forming process, for example stamping, in order to create the raised patterns, ribs, channels, and sealing lines described in the previous section, in order to form an anodic or cathodic sheet of a bipolar plate.

[0046] The method includes, firstly, a step for forming a sealing gasket 5.5' on the first face of the flat sheet. This gasket includes at least one peripheral sealing gasket 5 on a peripheral portion of the flat sheet. Additional sealing gaskets may also be formed on the flat plate at the locations of the manifold contours.

[0047] To form these collectors, the process may include a sheet metal cutting step. In addition to forming the collectors, this cutting step may be used to adjust the dimensions of the flat sheet metal to the desired dimensions of the cathode or anodic sheet metal, and to perform any other sheet metal cutting. This cutting step may occur at any time during the manufacturing process, before or after the sealing gasket forming step, or before or after the deformation step, which will be described in a section later, or even during this deformation stage. It can implement any suitable cutting technique, by laser, by punching.

[0048] Advantageously, the sealing gasket can be formed by molding or overmolding an elastomeric material onto the first face of the flat sheet. For this purpose, a mold is placed against the first face of the flat sheet, the mold having a surface cavity whose geometry corresponds precisely to the shape of the sealing gasket to be formed. Then, the elastomeric material can be injected under pressure into the cavity of the mold to form the sealing gasket and bond it to the flat sheet. The peripheral sealing gasket and any additional sealing gaskets can thus be formed in a single step. It is also possible, of course, to form the peripheral sealing gasket and the additional sealing gaskets (or some of them) in successive molding or overmolding steps, particularly if it is desired that these gaskets be made of different materials.

[0049] It is noted that since the sheet metal is perfectly flat and devoid of any raised pattern, it is easy to place the mold in contact over the entire surface of the sheet metal to properly close the surface recess on this sheet metal and to inject the elastomer material without risking that it escapes out of the recess during its injection.

[0050] This elastomeric material may be a silicone-based elastomer, or made of silicone or formed of a fluorinated elastomer of the FKM type (fluorocarbon rubbers conforming to the ASTM D1418 classification) or of an EPDM rubber, as already stated, or of any other polymeric material used as a sealing material.

[0051] It can be foreseen that the material injected into the mold will be heated to properly fill the cavity and give the desired shape to the joint once cooled and hardened.

[0052] As an alternative to this technique of molding the sealing gasket directly onto the flat sheet, it may be provided that the gasket, or a part thereof, is formed by dispensing, by screen printing or by any other process of molding the elastomer material directly onto this flat sheet.

[0053] According to other variations, the sealing gasket can be formed by molding on an intermediate support (which can be the mold itself) and, once cooled and hardened, transferred to the flat sheet. In this case, it is preferable to shape the sealing gasket so that it has adhesive properties that allow it to bond to the flat sheet during this transfer step. In particular, the bond between the applied gasket and the flat sheet can be reinforced by a heat or chemical treatment to promote a strong bond.

[0054] Returning to the general description of the manufacturing process of the anodic or cathodic sheet, this includes, after the step of forming the sealing joint, a step of deforming the flat sheet, by forming, to define relief patterns.

[0055] These raised patterns are those, ribs, channels, sealing lines, which make the sheet functional and constitute the anodic or cathodic sheet of a bipolar plate, as illustrated in the first part of this description.

[0056] Advantageously, this forming step is carried out so that the peripheral sealing gasket and, where applicable, the additional sealing gaskets are entirely arranged on crest reliefs of the first face of the sheet, these crest reliefs defining sealing lines of the anodic or cathodic sheet which the gaskets materialize and reinforce.

[0057] Any forming technique may be suitable, but preferably a stamping technique will be used. According to this technique, the permanent deformation of the flat sheet is obtained by pressing this sheet against a die (also called the lower die) using a punch (also called the upper die or press). The die and the punch have reliefs configured to define the raised patterns on the sheet. In particular, a first die-punch assembly configured to deform the flat sheet according to a first configuration chosen to form an anodic sheet of a bipolar plate may be provided. A second die-punch assembly configured to deform the flat sheet according to a second configuration chosen to form a cathode sheet of a bipolar plate may also be provided.

[0058] To produce a stack made up of bipolar plates of different types, it may be necessary to use as many die-punch sets as required to manufacture the anodic and cathodic plates corresponding to each type of bipolar plate.

[0059] In the forming step, and as illustrated in [Fig. 3], the second face of the flat sheet T is placed against the die M, and the punch P is pressed against the first face of the sheet T. Since this first face carries the sealing gasket J, the punch P is also configured to limit the pressure applied to the sealing gasket during deformation. To this end, the punch P has a recess intended to be occupied by the gasket J when the die M and the punch P are brought together to deform the sheet. The recess is large enough to prevent the gasket from being crushed, or at least from being excessively crushed, when the punch P is brought together with the die M and the sheet is deformed.

[0060] It is of course possible to proceed in a reverse configuration in which the first face of the sheet, bearing the seal, is placed against the die M, and the punch P is pressed against the second face of the sheet T. In this case, the housing intended to be occupied by the seal J is placed on the die M.

[0061] It is noted that the positioning of the sealing gasket on the flat sheet can be ensured with great precision, which makes it possible to configure the punch by arranging the housing of the sealing gasket.

[0062] At the end of the sequence including the formation of the sealing joint on the flat sheet and then the deformation of the sheet, we have an anodic sheet or a cathodic sheet suitable for constituting a bipolar plate.

[0063] Such a bipolar plate can be obtained by joining the second face of an anodic plate to the second face of a cathodic plate. This joining may involve welding the two plates together, for example by laser.

[0064] Of course the invention is not limited to the modes of implementation described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

[0065] For example, a step of treatment of the flat sheet can be provided, for example sandblasting of at least a portion of the first face or the application of an adhesion or cleaning agent or the application of a coating, before the step of forming the sealing joint, in order to promote the adhesion of this joint to the sheet.

[0066] A step of processing the flat sheet, for example annealing, can also be provided after the step of forming the sealing joint, for example in order to strengthen its adhesion to the sheet.

[0067] Sealing gaskets can be carried respectively by the anodic plate 20 and by the cathodic plate 10 as is the case in [Fig. 2B]. Alternatively, a sealing gasket 5 can be carried by only one of the anodic plate 20 and the cathodic plate 10 and the bipolar plate 1 is provided in this case with only a single gasket 5.

Claims

Demands

1. Method of manufacturing an anodic (20) or cathodic (10) sheet of a bipolar plate (1) for a fuel cell, the method comprising the following steps: - providing a flat sheet having a first face and a second face, the second face being opposite to the first face; - forming a sealing joint comprising at least a peripheral sealing joint (5) on a peripheral portion of the first face of the flat sheet, then; - deforming the flat sheet by forming and defining relief patterns thereon.

2. A manufacturing method according to the preceding claim comprising cutting the sheet metal, before or after its deformation, to form a plurality of collectors.

3. A manufacturing method according to the preceding claim in which the sealing gasket (5) comprises additional sealing gaskets (5') arranged on contours of the manifolds of the plurality of manifolds.

4. A manufacturing method according to any one of the preceding claims in which the sealing gasket (5) is formed by molding an elastomeric material onto the first face of the flat sheet using a mold disposed against the first face of the flat sheet.

5. A manufacturing method according to the preceding claim in which the elastomer material is injected under pressure into the mold of the sealing gasket.

6. A manufacturing method according to any one of claims 1 to 3 in which the sealing gasket is formed by dispensing or screen printing an elastomeric material onto the first face of the flat sheet.

7. A manufacturing method according to any one of claims 4 to 6 wherein the elastomeric material is a silicone elastomer, a fluorinated elastomer of the FKM type or an EPDM rubber.

8. A manufacturing method according to any one of the preceding claims, wherein the deformation of the flat sheet by forming is obtained by pressing the second face of the flat sheet against a die (M) using a punch (P), the die (M) and the punch (P) having reliefs configured to define the embossed patterns on the sheet, the punch (P) is also configured to limit pressure applied to the sealing gasket (5) during deformation.

9. A manufacturing method according to any one of the preceding claims wherein the embossed pattern defines crest reliefs and indentation reliefs, relative to an average elevation plane, on the first face of the sheet, the sealing gasket being entirely disposed on a crest relief of the first face of the sheet.

10. A method for manufacturing a bipolar plate (1) for a fuel cell, the plate being formed of an anodic plate and a cathodic plate (10) assembled together and each having patterns composed of reliefs, the method comprising the following steps: - providing an anodic plate (20) and a cathodic plate (10), at least one of the anodic plate and the cathodic plate having been prepared by means of a manufacturing method according to one of the preceding claims; - assembling the second face of the anodic plate to the second face of the cathodic plate (10) to form the bipolar plate (1).

11. Method of manufacturing a bipolar plate (1) according to the preceding claim comprising a welding step of the anodic plate and the cathodic plate (10).

12. Method of manufacturing a bipolar plate according to claim 10 or 11 in which sealing gaskets (5) are respectively carried by the anodic plate and by the cathodic plate (10).

13. Method of manufacturing a bipolar plate according to claim 10 or 11 in which a sealing gasket (5) is carried by one of the anodic plate and the cathodic plate (10).

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