System and method for bonding bipolar plates made of composite material in an electrochemical device

Abstract

A joining system (S) for a first bipolar plate (1A) and a second bipolar plate (1B), each bipolar plate comprising a central electrically conductive portion (2A, 2B) and a peripheral electrically conductive portion (3A, 3B), the joining system (S) comprising a first assembly device (4) configured to be in contact with the first bipolar plate and a second assembly device (5) configured to be in contact with the second bipolar plate, the first assembly device (4) comprising a heating element having a peripheral shape and configured to provide heating in a peripheral heating zone on the peripheral portion (3A) of the first bipolar plate (1A). Abstract figure: Figure 14

Description

Title of the invention: System and method for securing bipolar plates made of composite material of an electrochemical device Technical field

[0001] The present invention relates to the field of electrochemical devices and in particular aims at a system and a method for securing bipolar plates made of composite material of an electrochemical device.

[0002] An electrochemical device is any device for carrying out an electrochemical reaction, such as a fuel cell or a proton exchange membrane electrolyser, for generating electrical energy or hydrogen respectively from an oxidation-reduction reaction. The term "electrochemical device" also refers to an oxidation-reduction flow battery for generating electrical energy from potential energy stored in the battery.

[0003] In a known manner, an electrochemical device comprises a stack of a plurality of cells extending along a stack axis and two end plates, placed at the ends of the stack. The end plates are connected by compression members which make it possible to compress the cells and ensure the sealing of the electrochemical device.

[0004] With reference to [Fig. 1], each cell 110 comprises a membrane-electrode assembly 120 and two bipolar plates 130, also called separator plates, which sandwich the membrane-electrode assembly 120 and allow the distribution of fluids in the cell 110. To form the electrochemical reaction in the electrochemical device, each cell 110 is, in a known manner, supplied with an oxidizing fluid and a reducing fluid, for example di-hydrogen and dioxygen, which react when brought into contact in an oxidation-reduction reaction. Each cell 110 is also supplied with heat transfer fluid, used for the thermal regulation of the electrochemical device.

[0005] In practice, two adjacent bipolar plates 130A, 130B of two adjacent cells 110 are secured together so as to form a bipolar module M defining several internal channels 140 which allow the passage of the heat transfer fluid between the cells 110.

[0006] The present invention relates to bipolar plates formed from composite material and not to bipolar plates formed from graphite which are heavy and have a large footprint in the electrochemical device.

[0007] In a known manner, a bipolar plate made of composite material comprises electrically conductive particles, usually carbon particles, dispersed in a polymer resin.

[0008] With reference to Figures 2 and 3, such a bipolar plate 130 comprises in a known manner a plurality of openings 131, which allow the entry and exit of the oxidizing and reducing fluids, and two inlet and outlet openings 132 for the heat transfer fluid. Each bipolar plate 130 further comprises a central portion 133, in contact with the membrane-electrode assembly 120 and on which the oxidation-reduction reaction takes place, thanks to the conductive particles. The central portion 133 comprises concave portions 135 and convex portions 136 (shown in [Fig. 3]) allowing the circulation of fluids between the different inlet / outlet openings 131, 132. In a known manner, the concave portions 135 of bipolar plates 130 are secured together so that the convex portions 136 form the internal channels 140 of a bipolar module M.Each bipolar plate 130 also comprises a peripheral portion 134 (shown in [Fig.2]) allowing the two bipolar plates 130 to be joined together to form the bipolar module M.

[0009] In a known manner, the connection of two composite bipolar plates is achieved by the addition of an elastomer seal applied to the peripheral zone of the bipolar plates, which is long and complex to implement. Production rates are then low.

[0010] A method of assembling composite panels by resistive welding is also known. Such welding is carried out using a welding tool which gradually melts the material as it moves along the edges of the panels to form a weld bead. However, such a method is not applicable to a composite bipolar plate as described above, in particular due to its composition. Indeed, a bipolar plate comprising conductive particles dispersed in a polymer resin cannot be melted without the conductive particles being carried along by the molten resin, which can affect its conductivity. In addition, such a welding method is time-consuming to implement because it requires the regular movement of a welding tool around the entire perimeter of the composite panel.

[0011] In the prior art, a bipolar plate is known made of composite material comprising conductive particles dispersed in a resin. To ensure significant conductivity, it is necessary to integrate a large number of conductive particles. When forming such a bipolar plate, the resin in the viscous state is mixed with a very large number of conductive particles, which makes the mixture thick and does not allow the formation of thin bipolar plates. Also, a bipolar plate formed of conductive particles has a thickness im load-bearing, generally between 3 and 5 mm, which increases the size and mass of the electrochemical device. This is a disadvantage for an electrochemical device intended to be integrated, for example, into an aircraft or any other vehicle.

[0012] Also, a bipolar plate is known made of composite material comprising reinforcing fibers (for example carbon fibers) impregnated with thermoplastic or thermosetting polymer resin forming a matrix. Such a bipolar plate has the advantage of being thinner, with a thickness of less than one millimeter, which makes it possible to limit its size and mass.

[0013] In order to secure two bipolar plates made of such a material, it is necessary to add an excess thickness of polymer resin to the peripheral portion of each bipolar plate so as to allow, for example, welding by melting and mixing the polymer resins of the two bipolar plates while retaining the conductivity properties of each bipolar plate on the active central portion. However, the addition of polymer resin to the peripheral portion makes the manufacturing process of each bipolar plate more complex since it requires the definition of two distinct surface conditions. Also, the manufacturing of a bipolar plate comprising reinforcing fibers impregnated with thermoplastic polymer resin for the purpose of welding them is long and complex to implement.

[0014] It is also known to assemble two bipolar plates by gluing. However, the glue can create a surface electrical resistance at the gluing area. In addition, certain fluorinated thermoplastic polymers, which are very chemically stable and particularly suitable for electrochemical devices (such as Polyvinylidene fluoride or Teflon® for example), are chemically incompatible with most glues, which cannot create an optimal bond with the thermoplastic polymer. It may then be necessary to use plasma activation of the materials, and / or to develop a particular glue in order to be able to assemble the bipolar plates by gluing. Such an implementation is complex and requires a long and expensive process, which is not desirable.

[0015] The invention thus aims to eliminate at least some of these drawbacks by proposing a system and a method for joining two bipolar plates which is simple and without adding material, allowing the rapid joining of two bipolar plates without impacting their mechanical properties and their permeability to fluids. PRESENTATION OF THE INVENTION

[0016] The invention relates to a system for securing a first bipolar plate and a second bipolar plate so as to form a bipolar module of an electrochemical device, the electrochemical device being configured to implement implements an electrochemical reaction, each bipolar plate being made of a composite material comprising conductive reinforcing fibers impregnated in a polymer resin, each bipolar plate comprising: • a central, electrically conductive portion, intended to carry out exchanges in the electrochemical device, and • a peripheral portion, electrically conductive, extending outside the central portion.

[0017] The joining system includes: • a first assembly device configured to be in contact with the first bipolar plate, and • a second assembly device configured to be in contact with the second bipolar plate.

[0018] The first assembly device comprises a heating member having a peripheral shape and configured to carry out heating according to a peripheral heating zone on the peripheral portion of the first bipolar plate so as to melt the matrix to secure the first bipolar plate with the second bipolar plate and form a peripheral welding bead extending externally to the central portion and being strictly included in the peripheral portion of the first bipolar plate.

[0019] The joining system according to the invention advantageously makes it possible to join two bipolar plates made of composite material and allows local heating only in the peripheral portion of each bipolar plate, allowing partial remelting of polymer resin of each peripheral portion of each bipolar plate, without damaging the central portion of each. The exchanges in the electrochemical device are thus not impacted.

[0020] A peripheral heating zone allows the entire periphery of the bipolar plates to be welded instantly without requiring the movement of a tool, which represents a significant time saving. Thanks to the system according to the invention, the joining of two bipolar plates is faster and more reliable.

[0021] Such a joining system also makes it possible to avoid adding additional material during the formation of the bipolar module, which represents a significant time saving and limits the number of steps required to form the bipolar module.

[0022] The joining system according to the invention advantageously makes it possible to join two bipolar plates without requiring two distinct surface conditions on the peripheral portion and on the central portion. Thanks to the invention, each bipolar plate has a single surface condition, which simplifies the upstream process of manufacturing the bipolar plates and allows a significant saving of time.

[0023] Preferably, each bipolar plate comprises carbon fibers impregnated in a thermoplastic resin.

[0024] Thanks to the invention, even in the case of bipolar plates comprising carbon fibers impregnated in a thermoplastic resin, it is not necessary to add a residual layer of thermoplastic resin on the peripheral portion, as was the case in the prior art. The joining system makes it possible to join two bipolar plates by melting the thermoplastic resin directly present in a conductive portion without the conductivity of the central portion being affected. The thermoplastic resin contained in the bipolar plate is sufficient to allow the joining of the two bipolar plates.

[0025] Preferably, the central portion and the peripheral portion have substantially the same thickness.

[0026] Preferably, each bipolar plate has a thickness of less than 1 mm. The system according to the invention allows the joining of two bipolar plates of very thin thickness for which there is currently no reliable assembly method which allows the mechanical characteristics of such bipolar plates to be preserved.

[0027] In a preferred embodiment, the first assembly device comprises a pressure member configured to apply a first pressure force along a pressure zone at least on a portion of the peripheral portion of the first bipolar plate so as to compress the first bipolar plate and the second bipolar plate between the first assembly device and the second assembly device, the heating member being mounted on the pressure member, the heating zone being in the vicinity of the pressure zone. The securing system thus advantageously makes it possible to keep the two bipolar plates immobile over their entire periphery, while ensuring local heating. In addition, pressure over the entire periphery of the bipolar plates makes it possible to limit the risks of the plates moving during the heating operation, which could result in an irregular welding bead.

[0028] In one embodiment, the pressure member having a parallelepiped shape, the pressure zone extends both over the central portion and over a part of the peripheral portion of the first bipolar plate, and the peripheral heating zone extends over the peripheral portion of the first bipolar plate outside the pressure zone.

[0029] In an alternative embodiment, the pressure member having a peripheral shape, the pressure zone extends peripherally only over the peripheral portion of the first bipolar plate. A peripheral pressure zone makes it possible to limit damage to the central portion of each plate. bipolar.

[0030] In one embodiment, the heating zone extends over the peripheral portion of the first bipolar plate external to the peripheral pressure zone.

[0031] Alternatively, the heating zone extends over the peripheral portion of the first bipolar plate internal to the pressure zone.

[0032] Preferably, the pressure member having a peripheral shape, the pressure zone extends peripherally only over the peripheral portion of the first bipolar plate and the peripheral heating zone is strictly included in the peripheral pressure zone. Such an embodiment advantageously makes it possible to apply the pressure member to the peripheral portion of the first bipolar plate on either side of the heating member, which makes it possible to ensure that the two bipolar plates are held in place relative to each other. The pressure member encompassing the heating member makes it possible to distribute pressure on either side of the weld bead. Thus, the mechanical characteristics of the peripheral portion of each bipolar plate are preserved as close as possible to the central portion and on the outer edges of the bipolar plate.

[0033] According to a preferred embodiment, the pressure member of the first assembly device comprising an interior cavity, the heating member of the first assembly device is mounted in the interior cavity of the pressure member. Such mounting of the heating member makes it possible to ensure that the heating zone is included in the pressure zone, making it possible to ensure the positioning of the weld bead.

[0034] In a first embodiment, the heating member is fixed relative to the pressure member, allowing an assembly device that is simple to produce and use. In the case of a single-piece assembly (formed by the heating member and the pressure member), the first assembly device can be controlled simply, without requiring independent control of one or the other member. The method is also faster because it does not require the successive movement of the pressure member and the heating member.

[0035] In a second embodiment, the heating member is slidably mounted in the interior cavity of the pressure member. Such an embodiment makes it possible to apply the pressure force to the two bipolar plates before heating the peripheral portions of the two bipolar plates, making it possible to ensure the positioning of the plates with respect to the heating member.

[0036] In one embodiment, the heating member being configured to come into contact with the first bipolar plate, the heating member comprises a positioning device configured to come into abutment against the pressure member of so as to precisely define the position of the heating member. Such a positioning device advantageously makes it possible to control the position of the heating member relative to the first bipolar plate.

[0037] Preferably, the heating member comprising a welding head, the welding head has a section less than or equal to 10 mm, making it possible to melt a sufficient quantity of polymer resin, so as to ensure a sufficient welding surface to secure the two bipolar plates, while limiting the dimensions of the welding bead.

[0038] Preferably, the section of the welding head is less than or equal to 5 mm.

[0039] According to one embodiment, the polymer resin of the composite material having a melting temperature, the heating member is configured to heat to a temperature between the melting temperature of the polymer resin and the melting temperature increased by 40°C. Such a temperature advantageously makes it possible to locally melt the polymer resin of the first bipolar plate.

[0040] Preferably, the pressure member, having an operating temperature, is configured to maintain the operating temperature lower than or equal to the melting temperature of the polymer resin reduced by 20°C, so as to limit the heat transfer between the heating member and the pressure member. Thus the polymer matrix does not melt on contact with the pressure member.

[0041] Preferably, the pressure member is configured to maintain the operating temperature at ambient temperature.

[0042] In a first embodiment, the pressure member is made of a thermally non-conductive material, making it possible to limit heat transfers while avoiding the addition of an additional device.

[0043] In a second embodiment, the pressure member comprises a cooling device configured to maintain the operating temperature below a predetermined threshold. Such a cooling device makes it possible to manufacture the pressure member in any material while ensuring that the operating temperature of the pressure member is limited.

[0044] In one embodiment, the first assembly device comprises a cooling member, configured to allow the circulation of a heat transfer fluid at least around the heating member, making it possible to lower the temperature of the heating member.

[0045] Preferably, at least the heating member is configured to apply a second pressure force of between 1 and 15 MPa depending on the peripheral heating zone. Such a pressure force makes it possible to guarantee the maintenance of the two bipolar plates, without risking deforming the secured bipolar plates and without risking moving the polymer resin into an area outside the welding portion. Thus the The joining system ensures that the heating zone is positioned on the peripheral portion of each bipolar plate throughout the joining process. Such a pressure force also allows for good thermal diffusion without damaging the carbon fibers of the bipolar plates.

[0046] In one embodiment, the heating member and the pressure member are configured to apply the second pressure force according to the peripheral heating zone and pressure zone.

[0047] In a preferred embodiment of the invention, the first bipolar plate being subjected to an implementation pressure force during its manufacture, the first pressure force applied by the pressure member is less than or equal to the implementation pressure force, advantageously making it possible to limit damage to the composite assembly.

[0048] In a first embodiment, the second assembly device is in the form of a support, configured to support the first bipolar plate and the second bipolar plate. The second assembly device is configured to withstand the pressure applied by the first assembly device. Such a second assembly device allows a simple joining system to be produced and used because it does not require the coordination of two pressure members and two heating members during a joining process.

[0049] In a second embodiment, the second assembly device comprises a heating member having a peripheral shape, the heating member being configured to carry out heating according to a peripheral heating zone on the peripheral portion of the second bipolar plate so as to melt the matrix of the second bipolar plate and form a peripheral welding bead extending externally to the central portion and being strictly included in the peripheral portion of the second bipolar plate.

[0050] Two similar assembly devices mounted opposite each other make it possible to reduce heating times, which advantageously makes it possible to limit thermal diffusion in the bipolar plates and thus to limit the risks of deconsolidation of the composite material. Such a configuration also makes it possible to heat the two bipolar plates symmetrically. Thus, similar mechanical properties are maintained on the two bipolar plates.

[0051] In one embodiment, the second assembly device comprises a pressure member configured to apply a first pressure force along a pressure zone at least on a part of the peripheral portion of the second bipolar plate, so as to compress the first bipolar plate and the second bipolar plate between the first assembly device and the second assembly device, the heating member being mounted on the pressure member, the pressure zone heating being in the vicinity of the pressure zone.

[0052] Preferably, the first pressure force applied by the pressure member of the first assembly device is identical to the first pressure force applied by the pressure member of the second assembly device.

[0053] In one embodiment, the thickness of the pressure member of the first assembly device is preferably between 10 and 100 mm, making it possible to ensure that the pressure member applies a pressure force in a pressure zone sufficient to maintain the bipolar plates in compression. Thanks to such a thickness, the pressure member only applies the first pressure force to the peripheral portion of the first bipolar plate, which makes it possible to protect the central portion from any force which would be likely to damage it.

[0054] The invention also relates to a method for joining a first bipolar plate and a second bipolar plate so as to form a bipolar module of an electrochemical device, the electrochemical device being configured to implement an electrochemical reaction, the joining method being carried out by means of the joining system as described previously, the joining method comprising: • a welding step, at least by the heating member of the first assembly device, for a first predetermined heating duration, the welding step being carried out according to a peripheral heating zone on the peripheral portion of the first bipolar plate so as to form a peripheral welding bead extending externally to the central portion and being strictly included in the peripheral portion of the first bipolar plate.

[0055] The method according to the invention advantageously allows simple and rapid joining of two bipolar plates to form the bipolar module. The method makes it possible to ensure the joining of two bipolar plates while guaranteeing that the conductivity characteristics of the active central portion of each bipolar plate are preserved. Thanks to the invention, the joining of two bipolar plates made of composite material is also carried out reliably by ensuring the sealing of the channels internal to the bipolar module. In addition, the joining is carried out without adding material, which makes it possible to limit costs, to avoid the need for precise positioning of an adhesive joint, for example, and to limit the number of steps required to form the bipolar module.The joining method according to the invention also makes it possible to significantly reduce the time taken to weld two bipolar plates, which makes it possible to increase production rates. The joining method also makes it possible to join two bipolar plates, each having a unique surface condition, since it eliminates the need for . adding polymer resin to the peripheral portion while ensuring that it is not damaged by the heating condition.

[0056] Preferably, the first predetermined heating time is less than or equal to 20 seconds, making it possible to limit the heating time and therefore the risks of significant thermal diffusion in the bipolar plates, which can generate deconsolidation effects of the composite material in areas remote from the welding zone. In other words, such a first duration makes it possible to limit the risks of damage to the composite assembly of each bipolar plate. The method thus makes it possible to preserve the mechanical strength characteristics of a thin bipolar plate comprising reinforcing fibers impregnated in a polymer resin.

[0057] More preferably, the first predetermined heating time is less than 2 seconds.

[0058] In one embodiment, the method comprises, simultaneously with the welding step, a compression step, by applying, at least by a pressure member of the first assembly device, a first pressure force, the first pressure force being applied according to a pressure zone at least on a part of the peripheral portion of the first bipolar plate, so as to compress the first bipolar plate and the second bipolar plate. The application of the pressure member makes it possible to ensure that the bipolar plates remain immobile throughout the joining process.

[0059] Preferably, the first pressure force is applied both by the pressure member according to the pressure zone and by the heating member according to the heating zone.

[0060] Preferably, the method comprises, after the welding step, a step of cooling the heating member of the first assembly device, the pressure member maintaining the first pressure force according to the pressure zone.

[0061] Preferably, the pressure member of the first assembly device maintains the first pressure force according to the pressure zone for a second predetermined cooling time. Maintaining the first pressure force makes it possible to ensure the solidification of the weld bead before removing the first assembly device, thus making it possible to limit the risks, for example, of slipping and therefore of shifting of one bipolar plate relative to the other or of detachment of the two bipolar plates which would be due to an unconsolidated composite matrix.

[0062] More preferably, the pressure member and the heating member of the first assembly device maintain the first pressure force according to the pressure zone and according to the heating zone during the second predetermined duration of re- coldness.

[0063] In one embodiment, the first assembly device comprising a cooling member, configured to allow the circulation of a heat transfer fluid at least on the heating member, the cooling step corresponds to the circulation of the heat transfer fluid on the heating member of the first assembly device.

[0064] Preferably, the second predetermined cooling duration is less than or equal to 60 seconds.

[0065] In one embodiment, the compression and welding steps are carried out simultaneously by the heating member of the first assembly device on the peripheral portion of the first bipolar plate and by the heating member of the second assembly device on the peripheral portion of the second bipolar plate. Thus the duration of application of the two heating members is reduced.

[0066] Preferably, the compression step by applying a first pressure force is carried out simultaneously on the peripheral portion of the first bipolar plate by the pressure member of the first assembly device and on the peripheral portion of the second bipolar plate by the pressure member of the second assembly device.

[0067] Preferably, the distance between the peripheral heating zone and the central portion of each bipolar plate is greater than or equal to 0.5 mm. Such a distance advantageously makes it possible to limit the risk of the heating member affecting the polymer matrix of the central portion and thus altering its conductive properties.

[0068] Preferably, the distance between the peripheral heating zone and the central portion of each bipolar plate is less than 30 mm. Such a distance makes it possible to secure two bipolar plates in the peripheral portion as close as possible to the central portion, which has the advantage of increasing the sealing in the bipolar module, making it possible to limit the risks of mixing the different fluids in the electrochemical device. PRESENTATION OF FIGURES

[0069] The invention will be better understood on reading the following description, given solely by way of example, and referring to the appended drawings given by way of non-limiting examples, in which identical references are given to similar objects and in which:

[0070] [Fig.l] is a schematic representation of a stack of three cells and a bipolar module of an electrochemical device;

[0071] [Fig.2] is a schematic representation of a bipolar plate of the module bipolar of [Fig.l];

[0072] [Fig.3] is a schematic representation of a view along a section plane A: A of the bipolar plate of [Fig.2];

[0073] [Fig.4] is a schematic representation of a bipolar plate comprising a central portion and a peripheral portion;

[0074] [Fig.5] is a schematic representation of a view along a section plane B:B of the bipolar plate of [Fig.4];

[0075] [Fig.6] is a schematic representation of a top view of the bipolar plate of [Fig.4];

[0076] [Fig.7] is a schematic representation of a first embodiment of a system for securing two bipolar plates according to the invention;

[0077] [Fig.8] is a schematic representation of a bottom view of a first assembly device of the securing system of [Fig.7];

[0078] [Fig.9] is a schematic representation of a second embodiment of a system for securing two bipolar plates according to the invention;

[0079] [Fig. 10] is a schematic representation of a bottom view of a first assembly device of the securing system of [Fig. 9];

[0080] [Fig. 11] is a schematic representation of a third embodiment of a system for securing two bipolar plates according to the invention;

[0081] [Fig. 12] is a schematic representation of a bottom view of a first assembly device of the securing system of [Fig. 11];

[0082] [Fig. 13] is a schematic representation of a close-up view along a section plane C:C of the first assembly device of [Fig. 12];

[0083] [Fig. 14] is a schematic representation of a close-up view of the joining system of [Fig. 11] according to an embodiment for the assembly of two bipolar plates of [Fig. 4];

[0084] [Fig. 15] is a schematic representation of a close-up view of the joining system of [Fig. 11] according to an alternative embodiment for the assembly of two bipolar plates of [Fig.4];

[0085] The [Fig. 16],

[0086] [Fig. 17],

[0087] [Fig. 18],

[0088] [Fig. 19],

[0089] [Fig.20],

[0090] [Fig.21], and

[0091] [Fig.22] are schematic representations of the steps of a method of joining two bipolar plates according to the invention.

[0092] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where applicable. DETAILED DESCRIPTION OF THE INVENTION

[0093] The invention relates to a system for securing two bipolar plates made of composite material of an electrochemical device.

[0094] Subsequently, as described previously, the term “electrochemical device” equally designates a fuel cell, a proton exchange membrane electrolyzer, an oxidation-reduction flow battery or any other device making it possible to implement an electrochemical reaction.

[0095] As described above, an electrochemical device comprises a stack of a plurality of cells, each comprising a membrane-electrode assembly and two bipolar plates, also called separator plates, which sandwich the membrane-electrode assembly. Each cell is supplied with heat transfer fluid for thermal regulation of the electrochemical device. For this, two adjacent bipolar plates of two adjacent cells are secured together so as to form a bipolar module defining several internal channels which allow the passage of the heat transfer fluid between the cells.

[0096] The invention relates to a system for securing two bipolar plates of a bipolar module to ensure the sealing of the internal channels which allow the passage of the heat transfer fluid.

[0097] With reference to [Fig.4], each bipolar plate 1 extends longitudinally along an X axis, laterally along a Y axis and vertically along a Z axis, so as to form an orthogonal reference frame (X, Y, Z).

[0098] According to the invention, each bipolar plate 1 is made of composite material and comprises conductive reinforcing fibers impregnated in a polymer resin. In a preferred embodiment, each bipolar plate 1 comprises carbon fibers impregnated in a thermoplastic resin, forming a polymer matrix. The carbon fibers are electrically conductive so as to conduct the electrical charges necessary or produced by the oxidation-reduction reaction in the electrochemical device.

[0099] With reference to Figures 4 to 6, each bipolar plate 1 comprises a central portion 2 and a peripheral portion 3, each portion being electrically conductive. The central portion 2 is preferably rectangular.

[0100] The bipolar plate 1 has a thickness Ep of between 0.1 and 1 mm, defined along the vertical axis Z and shown in [Fig. 5] and making it possible to give the bipolar plate 1 a thin and light reinforced zone. Thus the bipolar plate 1 is light and takes up little space in the electrochemical device. The bipolar plate 1 comprising a plurality of channels to allow the passage of fluids, as described above, its thickness Ep can be constant or variable while being less than 1 mm. Preferably, the central portion 2 and the peripheral portion 3 have the same thickness, less than 1 mm.

[0101] The central portion 2 is intended to carry out exchanges in the electrochemical device and for this purpose comprises conductive reinforcing fibers exposed on the surface so as to allow high electrical conductivity.

[0102] The peripheral portion 3 extends externally to the central portion 2 so as to form the periphery of the bipolar plate 1, as shown in [Fig.4]. The peripheral portion 3 comprises reinforcing fibers impregnated in the polymer resin, in a manner similar to the central portion 2. The bipolar plate 1 thus comprises two structurally identical portions and has a single surface condition. The method of manufacturing the bipolar plates is thus rapid and inexpensive. The peripheral portion 3 comprises, in an exemplary embodiment, a rectangular inner edge and a rectangular outer edge.

[0103] In a preferred embodiment of the invention, the peripheral portion 3 extends over a width L (shown in Figures 4 and 6) preferably between 3 and 100 mm, providing a sufficient surface area to allow contact with the securing system S.

[0104] In a preferred embodiment, with reference to [Fig. 6], the peripheral portion 3 comprises a welding portion 32 corresponding to the portion which will be in contact with a heating member of the securing system S, as will be described in more detail later. Such a welding portion 32 extends over the entire peripheral portion 3 of the bipolar plate 1. In other words, the welding portion 32 has a peripheral shape. Preferably, the welding portion 32 extends over a width e of between 0.1 and 15 mm, preferably less than 5 mm.

[0105] Furthermore, the welding portion 32 is preferably positioned in the peripheral portion 3 at a distance d of between 0.5 and 30 mm, preferably still greater than 0.8 mm from the central portion 2. Such a distance d advantageously makes it possible to limit the risk of the securing system S affecting the thermoplastic matrix of the central portion 2 and thus altering its conductive properties.

[0106] As described previously, the securing system S according to the invention makes it possible to secure a first bipolar plate IA and a second bipolar plate IB, to form a bipolar module M.

[0107] With reference to [Fig.7], the securing system S according to the invention comprises a first assembly device 4 and a second assembly device 5, mounted opposite the first assembly device 4. When securing the two bipolar plates IA, IB, the first assembly device 4 is configured to be in contact with the first bipolar plate IA (in this example the upper plate) and the second assembly device 5 to be in contact with the second bipolar plate IB (in this example the lower plate).

[0108] With reference to [Fig.8], showing a sectional view of the first assembly device 4, the latter comprises a heating member 41, configured to allow the welding of the two bipolar plates IA, IB. The heating member 41 makes it possible to carry out heating according to a peripheral heating zone C on the peripheral portion 3A of the first bipolar plate IA as will be described in more detail later.

[0109] In a preferred embodiment, with reference to Figures 9 to 12, the first assembly device 4 comprises a pressure member 42, configured to keep the two bipolar plates 1A, 1B stationary. The pressure member 42 is configured to apply a first pressure force F1 according to a pressure zone P (shown in Figures 10 and 12) at least on a part of the peripheral portion 3A of the first bipolar plate 1A. In this embodiment, the heating member 41 is mounted on the pressure member 42 and the heating zone C is in the vicinity of the pressure zone P.

[0110] In one embodiment, the pressure member 42 and the heating member 41 are configured to simultaneously apply the first pressure force FL

[0111] Preferably, the first pressure force F1 is between 1 and 15 MPa, so as to avoid excessive pressure which could cause material to move out of the welding portion.

[0112] In one embodiment, shown in Figures 9 and 12, the pressure member 42 has a parallelepiped shape. The pressure zone P extends both over the central portion 2A and over a part of the peripheral portion 3A of the first bipolar plate 1A, and the peripheral heating zone C extends over the peripheral portion 3A of the first bipolar plate 1A outside the pressure zone P, as shown in [Fig. 10].

[0113] In a preferred embodiment, shown in Figures 11 and 12, the pressure member 42 has a peripheral shape. The pressure member 42 is configured to apply the first pressure force F1 according to a pressure zone P extending peripherally on the peripheral portion 3A of the first bipolar plate 1A, as shown in [Fig. 11]. More preferably, the pressure zone P is configured to extend only on the peripheral portion 3A of the first bipolar plate 1A.

[0114] In this example, the heating member 41 is preferably mounted on the pressure member 42. The heating zone C is thus in the vicinity of the pressure zone P. The heating zone C extends internally or externally to the pressure zone P. In a preferred embodiment, shown in [Fig. 12], the heating zone C is included in the pressure zone P, as will be described in more detail later.

[0115] The securing system S is described below according to this last preferred embodiment, in which the first assembly device 4 comprises a pressure member 42 and in which the peripheral heating zone C is strictly included in the peripheral pressure zone P. Subsequently, the first pressure force F1 is applied simultaneously both by the pressure member 42 and by the heating member 41. The heating zone C and the pressure zone P then form a common pressure zone.

[0116] In this example, with reference to figures 12 and 13, the pressure member 42 comprises a main body 421 of peripheral shape and an internal cavity 422 extending in this example vertically throughout the pressure member 42. This document presents the example of a pressure member 42 according to a rectangular pressure zone P (as shown in [Fig. 12]), however it goes without saying that the pressure member 42 could just as well have a different peripheral shape, so as to be able to be adapted to any shape of bipolar plate 1 (circular, ovoid, trapezoidal or even a more complex shape).

[0117] The pressure member 42 has, in this example, over the entire periphery, a thickness k (shown in [Fig. 13]) preferably between 10 and 100 mm. Such a thickness k advantageously makes it possible to ensure that the pressure member 42 applies the first pressure force F1 according to a peripheral pressure zone P having a sufficient surface area to maintain the bipolar plates IA, IB in compression, while ensuring that the first pressure force F1 is only applied to the peripheral portion 3A of the first bipolar plate IA.

[0118] The pressure member 42 is configured to be maintained at an operating temperature lower than or equal to the melting temperature of the polymer resin of the composite material of each bipolar plate 1, lowered by 20°C, so as not to melt the resin during pressure. In a first embodiment, the pressure member 42 is made of a thermally non-conductive material, so as to limit the heat transfer between the heating member 41 and the pressure member 42. By way of example, in a non-exhaustive manner, the pressure member 42 is made of a thermoplastic material such as polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyetherketone (PEK), Teflon ®, or in an organic composite material, an inorganic refractory material, or by machining MICA, graphite, ceramics.In a second embodiment, the pressure member 42 comprises a cooling device (not shown), for example a liquid or gaseous cooling circuit integrated or external to the pressure member 42, for . regulate the operating temperature of the pressure member 42 by maintaining it for example at ambient temperature. Such a cooling device also makes it possible to limit the heat transfer between the heating member 41 and the pressure member 42.

[0119] With reference to [Fig. 13], in this example, the heating member 41 is mounted in the interior cavity 422 of the pressure member 42. This makes it possible to carry out heating according to a heating zone C which is optimally compressed as will be presented later.

[0120] In an exemplary embodiment, the heating member 41 is slidably mounted in the interior cavity 422 of the pressure member 42, so as to be able to be easily moved away and brought into contact with the first bipolar plate IA during the implementation of the securing method.

[0121] Alternatively, the heating member 42 is integral with the pressure member 41, so as to move relative to the bipolar plates IA, IB, according to a common movement.

[0122] In a manner similar to the pressure member 42, as shown in [Fig. 12], the heating member 41 according to the invention has a peripheral shape and is configured to carry out heating according to a peripheral heating zone C so as to melt the polymer matrix of the peripheral portion 3A of the first bipolar plate 1A and the polymer matrix of the peripheral portion 3B of the second bipolar plate 1B to secure the first bipolar plate 1A with the second bipolar plate 1B. Alternatively, the heating member 41 can make it possible to melt only the polymer matrix of the peripheral portion 3B of the second bipolar plate 1B.

[0123] In this example, the peripheral heating zone C is strictly included in the peripheral pressure zone P so as to form on the bipolar module M a peripheral welding bead extending externally to the central portion 2A and being strictly included in the peripheral portion 3A of the first bipolar plate 1A. In other words, the pressure zone P of the pressure member 42 encompasses the heating zone C of the heating member 41 so as to locally compress the first bipolar plate 1A and the second bipolar plate 1B on either side of the heating member 41 around the heating zone C.

[0124] With reference to [Fig. 13], the heating member 41 comprises a main body 411 and a welding head 412. The welding head 412 forms the heating zone C and is configured to come into contact with the welding portion 32 of the peripheral portion 3A of the first bipolar plate IA during a welding operation, as will be described in more detail later. The heating member 41 is configured to apply the first pressure force F1 to the welding portion 32 of the portion peripheral 3A of the first bipolar plate IA, in a manner analogous to the first pressure member 41. The welding head 412 preferably has a width g of between 0.1 and 10 mm, preferably less than 5 mm. The heating member 41 is preferably centered relative to the pressure member 42 so that the heating zone C is centered in the pressure zone P as illustrated in Figures 12 and 13.

[0125] Preferably, the heating member 41 is configured to carry out heating, for example infrared, or by convection, radiation, induction, conduction or ultrasonic vibration.

[0126] Preferably, the heating member 41 is configured to be maintained at a temperature between the melting temperature of the polymer resin and the degradation temperature of said polymer resin. Such a temperature advantageously makes it possible to locally melt the polymer matrix of the first bipolar plate 1A and of the second bipolar plate 1B.

[0127] In a preferred embodiment, the heating member 41 is configured to apply to the welding portion 32 of the peripheral portion 3A of the first bipolar plate IA, a second pressure force F2, designated welding pressure force, of between 1 and 15 MPa. Such a second pressure force F2 makes it possible to keep the bipolar plates IA, IB joined during the welding phase, without the pressure force damaging them. The second pressure force F2 also makes it possible to minimize the deconsolidation effects in each bipolar plate IA, IB linked to the melting of the polymer and the release of residual stresses in the composite material of each bipolar plate IA, IB. This also makes it possible to avoid undesirable movement of the resin outside the welding zone.

[0128] In one embodiment, the heating member 41 comprises a positioning device 43 configured to come into abutment against the pressure member 42 when the heating member 41 slides in the interior cavity 422 of the pressure member 42. The positioning device 43 is for example in the form of a shoulder projecting laterally from the heating member 4L. Such a positioning device 43 advantageously makes it possible to control the position of the heating member 41 relative to the first bipolar plate 1A during the welding operation.In other words, when the heating member 41 slides in the interior cavity 422 of the pressure member 42, the positioning device 43 allows the heating member 41 to come into contact with the peripheral portion 3A of the first bipolar plate 1A and to penetrate the first bipolar plate 1A, without damaging the reinforcing fibers and the strength of the composite material.

[0129] With reference to [Fig. 14], according to a first embodiment, the second assembly device 5 is mounted opposite the first assembly device 4 and is configured to come into contact with the second bipolar plate IB, so as to allow, with the first assembly device 4, the first bipolar plate 1A and the second bipolar plate IB to be compressed simultaneously.

[0130] In this example, the second assembly device 5 is in the form of a support, configured to support the second bipolar plate IB arranged under the first bipolar plate IA in order to resist the pressure applied by the first assembly device 4. Preferably, the second assembly device 5 comprises one or more centering members, for example positioning studs 59 (shown in [Fig. 14]), making it possible to precisely position the first bipolar plate IA opposite the second bipolar plate IB and also to precisely position the assembly formed by the first bipolar plate IA and the second bipolar plate IB opposite the first assembly device 4.

[0131] In this embodiment, the heating member 41 of the first assembly device 4 is configured to melt the thickness Ep of the peripheral portion 3A of the first bipolar plate 1A and the thickness Ep of the peripheral portion 3B of the second bipolar plate 1B. The heating member 41 of the first assembly device 4 is then configured to form the bipolar module M.

[0132] The assembly devices 4, 5 of the fastening system S may be different, as shown in [Fig. 14], or similar, as shown in [Fig. 15].

[0133] In a second embodiment, shown in [Fig. 15], the second assembly device 5 is similar to the first assembly device 4. As such, the second assembly device 5 comprises a heating member 51, a pressure member 52 and a positioning member 53. The heating member 51, the pressure member 52 and the positioning member 53 of the second assembly device 5 have in this case the plurality of characteristics described previously for the heating member 41, the pressure member 42 and the positioning member 43 of the first assembly device 4. Therefore, these will not be described in more detail.

[0134] In this embodiment, the first assembly device 4 and the second assembly device 5 are mounted symmetrically with respect to the first bipolar plate 1A and the second bipolar plate 1B. In other words, the first assembly device 4 and the second assembly device 5 are configured to compress the first bipolar plate 1A and the second bipolar plate 1B on either side between the pressure member 42 of the first assembly device 4 and the pressure member 52 of the second assembly device 5, as shown in [Fig. 15].

[0135] The welding head 512 of the second assembly device 5 is then mounted opposite the welding head 412 of the first assembly device 4, so as to simultaneously melting the thickness Ep of the first bipolar plate IA by means of the welding head 412 of the first assembly device 4 and the thickness Ep of the second bipolar plate IB by means of the welding head 512 of the second assembly device 5, as shown in [Fig. 15]. Simultaneous heating of the first heating member 41 and the second heating member 51 on the two bipolar plates IA, IB advantageously makes it possible to reduce the duration of application of the heating members 41, 51 on the peripheral portion 3A, 3B of each bipolar plate IA, IB.

[0136] Preferably, the securing system S further comprises an electronic device 6 (shown in FIGS. 14 and 15), electrically connected to the first assembly device 4 and to the second assembly device 5, when the latter is similar to the first assembly device 4. Such an electronic device 6 is configured for example to control the first pressure force F1 of each pressure member 42, 52 applied to the first bipolar plate IA and the second bipolar plate IB, or even to control the duration of application of the heating member 41, 51 to the welding portion 32 of the bipolar plates IA, IB. In the case of a heating member 41, 51 slidably mounted in the interior cavity 422, 522 of each pressure member 42, 52, the electronic device 6 can also be configured to control such sliding in the interior cavity 422, 522 of each assembly device 4, 5.

[0137] In one embodiment, the electronic device 6 is further configured to control the position of each heating member 41, 51 relative to the pressure member 42, 52 on which it is mounted, so as to control the second pressure force F2 applied by the heating member 41, 51 on the peripheral portion 3A, 3B of each bipolar plate 1A, 1B, without requiring the addition of a stop 43, 53.

[0138] The securing system S according to the invention simultaneously allows maintenance over the entire periphery of the bipolar plates IA, IB and local heating allowing partial remelting of the thermoplastic matrix present in the peripheral portion 3A, 3B of each bipolar plate IA, IB, without damaging the central portion 2A, 2B of each. Such a securing system S also makes it possible to avoid adding additional material during the formation of the bipolar module M, which represents a time saving and limits the number of steps necessary for the formation of the bipolar module M.The joining system S according to the invention further allows the joining of two bipolar plates IA, IB comprising carbon fibers impregnated in a polymer resin, without requiring the formation, during the production of each bipolar plate IA, IB, of an additional residual layer of polymer resin on the periphery of each bipolar IA, IB and without carrying out any surface treatment, such as sanding or . polishing.

[0139] A method for joining two bipolar plates IA, IB will now be described, so as to form a bipolar module M, with reference to FIGS. 16 to 21. In this example, the joining system S comprises a first assembly device 4 and a second assembly device 5 which are different, mounted opposite each other, on either side of the two bipolar plates IA, IB as illustrated in [Fig. 14]. In this example, the first assembly device 4 is mounted vertically along the Z axis, i.e. so that the two bipolar plates IA, IB extend horizontally in the plane (X, Y). This document presents the example of a method in which the first assembly device 4 and the second assembly device 5 are different, however it goes without saying that the first assembly device 4 and the second assembly device 5 could be similar.In this case, the first assembly device 4 and the second assembly device 5 would both be mounted vertically along the Z axis opposite each other, so as to align the welding head 412 of the heating member 41 of the first assembly device 4 and the welding head 512 of the heating member 51 of the second assembly device 5.

[0140] The securing method is described for the example of a securing system S in which the first assembly device 4 comprises a heating member 41 and a pressure member 42 and the second assembly device 5 is in the form of a flat support. The first assembly device 4 is configured to apply a first pressure force F1 according to a peripheral pressure zone P only on the peripheral portion 3A of the first bipolar plate IA and the heating member 41 is configured to heat according to a heating zone C strictly included in the pressure zone P.

[0141] The first assembly device 4 is preferably controlled by the electronic device 6 to which it is connected.

[0142] The method comprises, with reference to [Fig. 16], a preliminary step E0 of activating the heating member 41 of the first assembly device 4 to allow it to increase in temperature. Preferably, the heating member 41 heats up to an operating temperature between the melting temperature of the polymer resin and the melting temperature increased by 40°C.

[0143] The method then comprises a first positioning step E1 (shown in [Fig. 17]) of the first bipolar plate IA and the second bipolar plate IB on the second assembly device 5 forming a support. For this, the second assembly device 5 comprises in this example a positioning pad 59, making it possible to precisely position the first bipolar plate IA and the second bipolar plate IB on the second assembly device 5. The pad positioning device 59 thus makes it possible to position the welding portion 32 of the peripheral portion 3A of the first bipolar plate IA opposite the welding head 412 of the heating member 41 of the first assembly device 4.

[0144] More precisely, as illustrated in [Fig. 17], the bipolar plates IA, IB are preferably positioned so as to place the interior cavity 422 of the pressure member 42 (and incidentally the welding head 412 of the heating member 41) at a distance h of between 0.5 and 30 mm from the central portion 2A of the first bipolar plate IA. Such positioning advantageously makes it possible to limit the risks of heating the central portion 2A of each bipolar plate IA, IB, thus making it possible to limit the risks of melting the thermoplastic matrix of each central portion 2A, 2B during the joining of the two bipolar plates IA, IB. Thus the conductive properties of each central portion 2A, 2B are not altered and the risks linked to the deconsolidation of each composite bipolar plate IA, IB are minimized.

[0145] With reference to [Fig. 18], when the heating member 41 has reached the operating temperature and the two bipolar plates IA, IB are positioned, the first assembly device 4 then descends vertically, in a step E2, until it comes into contact with the peripheral portion 3A of the first bipolar plate IA.

[0146] The method then comprises a compression step E3, shown in [Fig. 19], during which the pressure member 42 of the first assembly device 4 applies a first pressure force F1, then a second pressure force F2, according to the peripheral pressure zone P and according to the heating zone C against the bipolar plate IA so as to compress and keep the first bipolar plate IA and the second bipolar plate IB immobile against the second assembly device 5. In other words, the two bipolar plates IA, IB are compressed at least in part on their peripheral portion 3A, 3B between the pressure member 42 of the first assembly device 4 and the second assembly device 5. During the compression step E2, the heating member 41 is compressed against the bipolar plates IA, IB.

[0147] The method then comprises, simultaneously with the compression step E3, a welding step E4, shown in [Fig.20], in which the heating member 41 of the first assembly device 4 heats along the peripheral heating zone C so as to melt the polymer matrix of each bipolar plate IA, IB to secure the first bipolar plate IA with the second bipolar plate IB and form the bipolar module M.

[0148] In a preferred embodiment, the hot heating member 41 is compressed for a first predetermined welding duration less than or equal to 20 seconds, so as to melt the polymer resin to weld the bipolar plates IA, IB without deconsolidating the thermoplastic assembly of each, which could damage it.

[0149] After the first predetermined heating duration, with reference to [Fig. 21], the method comprises a cooling step E5 of the heating member 41 of the first assembly device 4. For this, in this example, a heat transfer fluid is injected around the heating member 41 so as to lower its temperature. The welding portion 32 of each bipolar plate 1A, 1B then cools for a second predetermined cooling duration during which the heating member 41 and the pressure member 42 maintain the second pressure force F2. The second predetermined duration is preferably less than or equal to 60 seconds, so as to allow the consolidation of the weld bead formed by the heating member 4L

[0150] With reference to [Fig.22], after the second predetermined cooling time, during a withdrawal step E6, the heating member 41 and the pressure member 42 are moved in reverse order in step E2, so as to no longer compress the bipolar plates 1A, 1B. After the withdrawal of the heating member 41, the circulation of the heat transfer fluid is stopped, so as to stop its cooling. The temperature of the heating member 41 then rises in anticipation of the welding of two new bipolar plates.

[0151] Such a joining method advantageously allows simple and rapid welding of two bipolar plates to form the bipolar module. The method according to the invention makes it possible to ensure the welding of two bipolar plates while guaranteeing that the conductivity characteristics of the central portion of each bipolar plate comprising reinforcing fibers impregnated in a polymer resin are preserved. Thanks to the invention, the welding of two bipolar plates as described in this document is also carried out reliably by ensuring the sealing of the channels internal to the bipolar module. In addition, the welding is carried out without adding material, which makes it possible to dispense with the precise positioning of adhesive joints, for example, and limits the number of steps necessary for forming the bipolar module. The joining method according to the invention also makes it possible to significantly reduce the duration of welding two bipolar plates.The joining method according to the invention advantageously allows the joining of two bipolar plates made of reinforcing fibers impregnated in a thermoplastic resin and having the same surface condition over the entire bipolar plate (central portion and peripheral portion). It is thus no longer necessary to form a residual layer of polymer matrix on the surface of the peripheral portion of each bipolar plate for the purpose of joining them.

Claims

Claims

1. System (S) for securing a first bipolar plate (IA) and a second bipolar plate (IB) so as to form a bipolar module (M) of an electrochemical device, the electrochemical device being configured to implement an electrochemical reaction, each bipolar plate (IA, IB) being made of a composite material comprising conductive reinforcing fibers impregnated in a polymer resin, each bipolar plate (IA, IB) comprising: • a central portion (2A, 2B), electrically conductive, intended to carry out exchanges in the electrochemical device, and • a peripheral portion (3A, 3B), electrically conductive, extending externally to the central portion (2A, 2B), • the solidarity system (S) comprising: • a first assembly device (4) configured to be in contact with the first bipolar plate (IA), and • a second assembly device (5) configured to be in contact with the second bipolar plate (IB), • the first assembly device (4) comprising a heating member (41) having a peripheral shape and configured to carry out heating according to a peripheral heating zone (C) on the peripheral portion (3 A) of the first bipolar plate (IA) so as to melt the matrix to secure the first bipolar plate (IA) with the second bipolar plate (IB) and form a peripheral welding bead extending externally to the central portion (2A) and being strictly included in the peripheral portion (3A) of the first bipolar plate (IA).

2. A fastening system (S) according to claim 1, wherein the first assembly device (4) comprises a pressure member (42) configured to apply a first pressure force (Fl) according to a pressure zone (P) at least on a part of the peripheral portion (3A) of the first bipolar plate (IA) so as to compress the first bipolar plate (IA) and the second bipolar plate (IB) between the first assembly device (4) and the second assembly device (5), the heating member (41) being mounted on the pressure member (42), the heating zone (C) being in the vicinity of the pressure zone (P).

3. A fastening system (S) according to claim 2, wherein, the pressure member (42) has a peripheral shape, the pressure zone (P) extends peripherally only over the peripheral portion (3A) of the first bipolar plate (IA), and the peripheral heating zone (C) is strictly included in the peripheral pressure zone (P).

4. A joining system (S) according to one of claims 2 and 3, wherein, the pressure member (42) of the first assembly device (4) comprising an interior cavity (422), the heating member (41) of the first assembly device (4) is mounted in the interior cavity (422) of the pressure member (42).

5. A joining system (S) according to one of claims 1 to 4, in which the heating member (41) comprises a welding head (412), the welding head (412) has a section (g) less than or equal to 5 mm.

6. Fastening system (S) according to one of claims 1 to 5, in which at least the heating member (41) is configured to apply a second pressure force (F2) of between 1 and 15 MPa depending on the peripheral heating zone (C).

7. Method for joining a first bipolar plate (IA) and a second bipolar plate (IB) so as to form a bipolar module (M) of an electrochemical device, the electrochemical device being configured to implement an electrochemical reaction, the joining method being carried out by means of the joining system (S) according to one of claims 1 to 6, the joining method comprising: • a welding step (E4), at least by the heating member (41) of the first assembly device (4), for a first predetermined heating duration, the welding step (E4) being carried out according to a peripheral heating zone (C) on the peripheral portion (3A) of the first bipolar plate (IA) so as to form a peripheral welding bead extending externally to the central portion (2A) and being strictly included in the peripheral portion (3A) of the first bipolar plate (IA).

8. Method of joining according to claim 7, comprising simultaneously with the welding step (E4), a compression step (E3), by the application at least by a pressure member (42) of the first assembly device (4), of a first pressure force (F1), the first pressure force (F1) being applied according to a pressure zone (P) at least on a part of the peripheral portion (3A) of the first bipolar plate (IA), so as to compress the first bipolar plate (IA) and the second bipolar plate (IB).

9. Method of joining according to claim 8, comprising after the welding step (E4), a step of cooling (E5) the heating member (41) of the first assembly device (4), the pressure member (42) maintaining the first pressure force (F1) according to the pressure zone (P).

10. A method of securing according to claim 9, in which the pressure member (42) of the first assembly device (4) maintains the first pressure force (Fl) according to the pressure zone (P) for a second predetermined cooling duration.

11. A method of securing according to claim 10, wherein the second predetermined cooling time is less than or equal to 60 seconds.

12. Method of securing according to one of claims 7 to 11, in which the distance between the peripheral heating zone (C) and the central portion (2A, 2B) of each bipolar plate (IA, IB) is greater than or equal to 0.5 mm.

13. A method of joining according to one of claims 7 to 12, in which the first predetermined heating duration is less than or equal to 20 seconds.

Images