Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0234—Carbonaceous material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0239—Organic resins; Organic polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0243—Composites in the form of mixtures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0247—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the form
  • H01M8/0254—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the form corrugated or undulated
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/18—Regenerative fuel cells, e.g. redox flow batteries or secondary fuel cells
  • H01M8/184—Regeneration by electrochemical means
  • H01M8/188—Regeneration by electrochemical means by recharging of redox couples containing fluids; Redox flow type batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to the field of electrochemical devices and relates in particular to a method of manufacturing bipolar plates made of composite material, intended to be mounted in an electrochemical device.
• electrochemical device means any device making it possible to carry out an electrochemical reaction, such as a fuel cell or a proton exchange membrane electrolyser, making it possible to generate electrical energy or hydrogen respectively from a redox reaction.
• electrochemical device also refers to a redox flow battery for generating electrical energy from potential energy stored in the battery.
• 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 compress the cells and ensure the tightness of the electrochemical device.
• each cell 110 comprises, in known manner, 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.
• each cell 110 is supplied with an oxidizing fluid and a reducing fluid, for example dihydrogen and dioxygen, which circulate on either side of a membrane and react using a catalyst.
• Each cell 110 is also supplied with heat transfer fluid, used for thermal regulation of the electrochemical device.
• two adjacent bipolar plates 130A, 130B of two adjacent cells 110A, 110B are secured together so as to form several internal channels 140 which allow the passage of the heat transfer fluid between the cells 110.
• a bipolar plate 130 comprises, in known manner, a plurality of openings 131, which allow the entry and exit of oxidizing and reducing fluids, and two entry and exit openings 132 of the coolant.
• Each bipolar plate 130 further comprises an active central portion 133, in contact with the membrane-electrode assembly and on which the redox reaction occurs, and a peripheral portion 134 allowing the joining of two bipolar plates 130.
• the active portion 133 comprises concave portions 135 and convex portions 136 (shown on the presenting a sectional view of the bipolar plate 130 along a plane A:A shown on the ) which allow the circulation of fluids between the different inlet/outlet openings 131, 132.
• the concave portions 135 of two bipolar plates 130 are secured together so that the convex portions 136 form the internal channels 140 (represented on the ) for the circulation of the heat transfer fluid.
• bipolar plates are known made of graphite or metal (for example stainless steel, inconel, aluminum or titanium) covered with a protective coating in order to limit the impact of corrosion due to electrochemical device.
• metal for example stainless steel, inconel, aluminum or titanium
• a protective coating in order to limit the impact of corrosion due to electrochemical device.
• Bipolar graphite plates are heavy and take up a lot of space due to their thickness generally greater than 2 mm.
• Metal bipolar plates have a large mass and have a limited lifespan, taking into account the acidic and corrosive environment of the electrochemical devices in which they are mounted, despite the protective coating used.
• Bipolar plates are therefore more and more often made of composite material.
• a bipolar plate comprising conductive elements dispersed in a resin.
• the conductive elements are carbon black, crushed carbon fibers, graphite, expanded graphite, carbon nanotube or graphene for example.
• the resin is usually a thermoplastic or thermosetting polymer.
• the resin in the viscous state is mixed with a very large number of conductive elements (generally more than 85% of conductive elements for the entire bipolar plate, to ensure significant conductivity).
• the bipolar plate is formed by injecting the resin loaded with conductive elements into a mold or molded by pressing in a thermocompression press.
• the massive addition of conductive elements significantly increases the viscosity of the thermosetting or thermoplastic resin, which makes the mixture thick.
• the manufacturing processes described above do not make it possible to manufacture thin bipolar plates and the bipolar plate often has a significant thickness, generally greater than 2 mm, which increases the bulk and mass of the electrochemical device. This is disadvantageous for an electrochemical device intended to be integrated for example in an aircraft or in any other mobility application.
• injection or thermocompression molding leaves a surface layer of resin, which may be due to the use of mold release products for example, and which increases the electrical contact resistance, which is detrimental for a device application. electrochemical conversion where this value must be minimized.
• it is then necessary to implement post-treatment of the bipolar plate by chemical or mechanical treatment, such as by abrasion for example.
• bipolar plate made of composite material comprising reinforcing fibers (for example carbon fibers) impregnated with thermoplastic or thermosetting polymer resin.
• Such a bipolar plate has the advantage of being thinner (thickness less than 1 mm), which limits its size and mass.
• thermoplastic resin forms a residual layer on the surface similar to an insulating skin, which can affect the electrical conductivity. It is then necessary to expose the reinforcing fibers on the surface of the bipolar plate. Such treatment, carried out for example by sanding or dissolution by plasma irradiation, can damage the reinforcing fibers and affect the mechanical properties of the bipolar plate, which presents a significant drawback.
• WO2016182131A1 the use of a sacrificial film making it possible to expose the reinforcing fibers on the surface of the bipolar plate, without damaging them.
• the manufacture of bipolar plates is then carried out by thermo-compression, allowing the manufacture of thin and light bipolar plates.
• the manufacturing process does not make it possible to produce a bipolar plate using carbon fiber reinforcement simply and quickly.
• reinforcing fibers involves a very high shaping pressure (generally greater than 15 MPa), to allow the fibers to be properly impregnated, to reduce the porosities and to expose the fibers on the surface to allow a good electrical conductivity.
• Significant pressure can deform the initial weave of the reinforcement and generate the formation of porous cavities which can alter the impermeability of the bipolar plates to gases.
• the invention thus aims to eliminate at least some of these drawbacks by proposing a process for manufacturing a bipolar plate that is simple, rapid and does not require the use of expensive industrial machines, allowing the formation of a thin and light bipolar plate. .
• the reinforcing film is a non-woven carbon reinforcing film comprising a plurality of reinforcing fibers, each reinforcing fiber extending along an orientation axis, the rate of oriented reinforcing fibers along the stacking axis Z is between 10% and 60%.
• a non-woven carbon reinforcement film advantageously allows the application of a shaping pressure lower than the pressure used for a woven reinforcement film, which allows the use of less expensive industrial machines, allowing a manufacturing process simpler and faster.
• a lower shaping pressure also makes it possible to limit the deformation of the initial weave of the reinforcement and the formation of porous cavities which could alter the impermeability of the bipolar plates to gases.
• Orientation of the reinforcing fibers along the stacking axis makes it possible to increase the electrical conductivity of the material along this axis, in order to ensure optimal electrical transport between the faces of the bipolar plate for use in electrochemical devices.
• a rate of reinforcing fibers oriented along the stacking axis of between 10% and 60% allows good conductivity in the bipolar plate while ensuring that the bipolar plate has significant mechanical resistance.
• Such a rate of reinforcing fibers oriented along the stacking axis Z thus makes it possible to fulfill a dual mechanical and electrical conductivity function.
• the orientation of the reinforcing fibers is carried out by stitching.
• a stitching makes it possible to mechanically orient part of the reinforcing fibers along the stacking axis Z, allowing better electrical conductivity in the bipolar plate, allowing better electrical exchanges in the cells adjacent to the bipolar plate when it is mounted in an electrochemical device.
• the orientation of the reinforcing fibers can alternatively be carried out by a different method, for example by hydro entangling.
• the rate of reinforcing fibers oriented along the stacking axis Z is between 15 and 45%, allowing optimal conductivity in the bipolar plate. Such a rate also makes it possible to maintain a sufficiently high level of non-oriented reinforcing fibers to guarantee optimal mechanical strength of the bipolar plate.
• the non-woven carbon reinforcement film comprising open porosities
• the non-woven carbon reinforcement film has an open porosity rate greater than 60% before the pressurization step.
• open porosity will be described in more detail later.
• the non-woven carbon reinforcement film has an open porosity rate of between 60% and 70%.
• the non-woven carbon reinforcing film is a carbon felt.
• a carbon felt has a high open porosity rate in the reinforcing film, preferably greater than 70%, allowing optimal flow of the thermoplastic resin in the reinforcing film and more precisely between the reinforcing fibers.
• the reinforcing fibers are thus optimally impregnated with thermoplastic resin, which makes it possible to obtain a bipolar plate with a high level of consolidation, in which few pores are present.
• open porosity we mean cavities or porosity channels open towards the outside of the reinforcing film. The open porosities are accessible from the outside and can be filled with polymer resin to provide good mechanical strength of the bipolar plate.
• a carbon felt also allows the use of a known material, traditionally used as a thermal insulator or as a media allowing the diffusion of liquid electrolyte in the case of a Redox flow battery.
• the non-woven carbon reinforcement film comprising open porosities
• the non-woven carbon reinforcement film has an open porosity rate greater than 80% before the pressurization step.
• Such an open porosity rate also allows optimal deformation of the reinforcing film allowing high compressibility and adaptation of the reinforcing film to complex shapes.
• the non-woven carbon reinforcing film has an open porosity rate greater than 90%.
• the “open porosity rate” may be referred to as “open porosity”.
• a significant open porosity in the reinforcing film combined with an optimal rate of reinforcing fibers oriented along the stacking axis Z has the advantage of obtaining optimal performance for the use of the bipolar plate in an electrochemical system.
• a significant open porosity, associated with a high rate of reinforcing fibers oriented along the stacking axis Z allows both a high conductivity of the bipolar plate allowing it to fulfill its role as a conductive element optimally and a high porosity of the reinforcement allowing good impregnation and significant deformation of the reinforcement at low pressure to correctly shape the channels of the bipolar plate, and obtain a composite with negligible hydrogen porosities in order to meet its role of fluid separator.
• said open porosities have a diameter of between 1 ⁇ m and 250 ⁇ m.
• at least 50% of the open porosities of the reinforcing film have a diameter greater than 125 ⁇ m. More preferably, at least 50% of the open porosities of the reinforcing film have a diameter greater than 150 ⁇ m.
• Such porosities can easily be filled by the polymer resin without impacting the mechanical strength of the bipolar plate.
• Such a size of the porosities also allows the assembly to be highly compressible, which advantageously allows the manufacture of thin bipolar plates.
• diameter of open porosities is meant the equivalent circle diameter, that is to say the diameter of a circle having a surface area equivalent to the surface of the porosity. Analogously, it is described here more precisely that, preferably, at least 50% of the surface of the open porosities of the reinforcing film is occupied by porosities whose equivalent circle diameter is greater than 125 ⁇ m.
• said open porosities have an equivalent circle diameter of between 1 ⁇ m and 300 ⁇ m.
• at least 50% of the surface of the open porosities of the reinforcing film is occupied by porosities whose equivalent circle diameter is greater than 30 ⁇ m. More preferably, at least 50% of the surface of the open porosities of the reinforcing film is occupied by porosities whose equivalent circle diameter is greater than 80 ⁇ m, preferably greater than 90 ⁇ m.
• the shaping temperature is between 140 and 400°C, making it possible to use a wide range of families of thermoplastic polymers.
• the shaping temperature is between 240 and 360°C, allowing the shaping of polymers of the polyphenylene sulfide PPS or polyphenylsulfone PPSU type.
• the shaping temperature is between 200 and 260°C allowing the shaping of polyvinylidene fluoride (PVDF) type or polyamide type polymers.
• PVDF polyvinylidene fluoride
• the shaping temperature is between 140 and 200°C allowing the shaping of polyolefin type polymers.
• the shaping temperature is between 350 and 400°C allowing the shaping of polyaryl ether ketone type polymers (PEEK, PEK, PEKK, etc.).
• the predetermined shaping pressure is between 6 and 12 MPa. Thanks to the non-woven carbon, such shaping pressure is sufficient to optimally impregnate the reinforcing fibers in the reinforcing film and benefit from a bipolar plate having a high level of consolidation and therefore significant impermeability of the bipolar plates with hydrogen in an electrochemical device.
• the predetermined shaping pressure is between 8 and 10 MPa. Thanks to the invention, it is not necessary to raise the shaping pressure to too high a pressure. It is therefore not necessary to use a particularly expensive industrial machine. The manufacturing process is faster and simpler to implement, while allowing high manufacturing rates. Such shaping pressure also makes it possible to limit the deformation of the reinforcing fibers in the initial reinforcing film which could generate porous cavities in the bipolar plate, thus making it possible to guarantee the effectiveness of the bipolar plate by limiting any risk of dysfunction.
• the reinforcing film has a thickness of less than 5 mm.
• the reinforcing film is sufficiently thick to manufacture a bipolar plate having significant mechanical resistance while having sufficient flexibility for the reinforcing film to adapt to complex geometries.
• the initial thickness of the reinforcing film (that is to say the thickness before compression of the stack to form the bipolar plate) is between 0.5 and 3.4 mm, to allow the formation of bipolar plates with a thickness of less than 0.5 mm after compression of the stack.
• the reinforcing film has a surface mass of less than or equal to 500 g/m2, making it possible to form a lightweight bipolar plate.
• the surface mass is between 50 and 400 g/m2. More preferably, the surface mass is between 50 and 300 g/m2, making it possible to integrate the bipolar plate formed into an electrochemical device, for example in an aircraft or another vehicle, in which the mass constraints are significant.
• the manufacturing process comprises, after the pressurization step, a step of cooling the bipolar plate formed, for a third predetermined duration.
• the cooling step is carried out at a cooling speed of between 10 and 100 °C/min.
• a cooling rate allows the development of the crystalline part of the semi-crystalline polymers to enable the manufactured bipolar plate to have good impermeability to the fluid used for energy conversion in the electrochemical device.
• Such a cooling rate thus makes it possible to obtain a crystallization rate of between 43 to 47%, corresponding to a crystallization rate close to the maximum crystallization rate that can be obtained on the thermoplastic resins used, generally of the order from 40 to 55%.
• the maximum crystallization rate that can be obtained on other types of thermoplastic resins, for example for polyaryl ether ketone is between 20 and 40%.
• the maximum crystallization rate that can be obtained on different types of thermoplastic resins, such as for polyolefins is between 55 and 80%.
• the cooling step is carried out at a cooling rate greater than 80°C/min, of way to quickly cool the bipolar plate, allowing faster production rates.
• the cooling rate is between 40 and 90°C/min.
• Such a cooling speed allows the optimal development of the crystalline part of the stack, while minimizing the cooling time of the bipolar plate to reduce manufacturing cycles and enable a rapid process allowing high manufacturing rates.
• the invention also relates to a bipolar plate, intended to be mounted in an electrochemical device, the bipolar plate being manufactured by means of the manufacturing process as described above.
• the bipolar plate comprises a non-woven carbon reinforcing film comprising a plurality of reinforcing fibers, each reinforcing fiber extending along an orientation axis, the rate of reinforcing fibers oriented along the axis of Z stacking being between 10% and 60%.
• the bipolar plate has a thickness less than or equal to 0.5 mm, which advantageously makes it possible both to limit the mass and the bulk in the electrochemical device and to increase its power density (number of kW / kg).
• the electrochemical device can thus be easily mounted in a vehicle such as an aircraft for example.
• the bipolar plate has a thickness of less than 0.4 mm.
• the bipolar plate has a specific surface electrical resistance of less than 12 m ⁇ .cm2.
• the bipolar plate has a porosity rate of less than 1%, making it possible to guarantee the bipolar plate optimal permeability.
• the invention relates to a method of manufacturing a bipolar plate made of composite material of an electrochemical device.
• electrochemical device designates equally well a fuel cell, a proton exchange membrane electrolyser, an oxidation-reduction flow battery or any other device making it possible to implement an electrochemical reaction.
• 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 and allow the distribution of fluids. in the cell.
• each cell is, in known manner, supplied with an oxidizing fluid and a reducing fluid, for example dihydrogen and dioxygen, which react when brought into contact in a reaction of redox.
• a reducing fluid for example dihydrogen and dioxygen, which react when brought into contact in a reaction of redox.
• Each cell is also supplied with heat transfer fluid, used for thermal regulation of the electrochemical device.
• the bipolar plate includes concave portions and convex portions to form circulation channels.
• the bipolar plate B (shown on the ) according to the invention is formed from at least one non-woven carbon reinforcing film 2 and at least one thermoplastic resin film 3.
• the bipolar plate B is formed from a film of non-woven carbon reinforcement 2 and a thermoplastic resin film 3.
• This document describes the example of a single non-woven carbon reinforcement film 2 and a single thermoplastic resin film 3, however it goes without saying that the number of films could be different.
• the bipolar plate B could be formed from several non-woven carbon reinforcing films 2 and/or several thermoplastic resin films 3.
• the reinforcing film non-woven carbon will be designated reinforcing film 2.
• the reinforcing film 2 preferably extends in a plane (X, Y) and has two exterior surfaces 2A and 2B that are substantially flat and parallel, a lower surface 2A and an upper surface 2B.
• the reinforcing film 2 further comprises a plurality of reinforcing fibers 21.
• the reinforcing fibers 21 are formed of carbon fibers.
• the thickness Ep2 of the reinforcing film 2 is defined along a vertical axis Z, orthogonal to the plane (X, Y).
• Each reinforcing fiber 21 comprises a first end 21a and a second end 21b. At least part of the reinforcing fibers 21 of the reinforcing film 2 extends substantially, from the first end 21a to the second end 21b, along an orientation axis F.
• the orientation axis F extends , in this example, from the lower surface 2A to the upper surface 2B.
• the first end 21a of the reinforcing fibers 21 is substantially on the surface of the lower surface 2A and the second end 21b, substantially on the surface of the upper surface 2B and each reinforcing fiber 21 extends in the thickness Ep2 of the reinforcement film 2.
• the orientation axis F is defined by forming an angle Theta ⁇ with the vertical axis Z and an angle Phi ⁇ with the axis X, in a projection plane (X, Y).
• the orientation axis F extends so that the angle Theta ⁇ is less than 45° or greater than 135° and the angle Phi ⁇ is between 45° and 135°.
• the reinforcing fibers 21 comply with the preceding conditions, it is considered that the reinforcing fibers 21 extend along the stacking axis Z.
• the orientation axis F extends so that the angle Theta ⁇ is between 0° and 45° or between 135° and 180° and the angle Phi ⁇ is between 45° and 135°.
• the reinforcing fibers 21 of the reinforcing film 2 extend along the stacking axis Z between the lower surface 2A and the upper surface 2B of the reinforcing film 2, as shown in the .
• Such an orientation of the reinforcing fibers 21 makes it possible to increase the electrical conductivity and therefore, once manufactured, in the bipolar plate B while retaining important mechanical characteristics.
• a significant conductivity in the thickness of the reinforcing film 2, that is to say along the stacking axis Z, is advantageous because it ensures good conductivity in the thickness of the bipolar plate B, as will be described in more detail later.
• the reinforcing fibers 21 are oriented along the stacking axis Z by a needling, stitching or sewing process for example. Such processes are known to those skilled in the art, and will not be described in more detail in this document.
• the orientation of the reinforcing fibers 21 can alternatively be carried out by a different process, for example by hydro-entangling.
• the orientation of the reinforcing fibers 21 in the reinforcing film 2 can be determined by analyzing images obtained by X-ray tomography. Such a method makes it possible to obtain a three-dimensional 3D image. of the reinforcing film 2 and to analyze the reinforcing fibers 21 independently of each other, in order to define their orientations in the reinforcing film 2.
• the reinforcing fibers 21 are defined by gray level thresholding in order to distinguish them from porosities. This involves filtering the 3D image in a contrast range making it possible to highlight the reinforcing fibers 21.
• “Morphological operator” type image processing is used to identify the three-dimensional structure of the reinforcing fibers. 21 in the picture.
• “skeletonization” type image processing known under the designation “morphological skeleton” or “Skeletonization” in English, is chosen. Such a method is known to those skilled in the art and will not be described in more detail in this document.
• the latter is analyzed by a micro-tomograph from the RX SolutionsTM brand, for example the EasyTom 230 model.
• the analysis is carried out with an acceleration voltage of 60 kV, a current of 80 ⁇ A, and a Tungsten target.
• the exposure time is 0.4 s, averaging over 10 s, 1120 x-ray projections.
• the acquisition of X-rays is carried out using the X-Act software (RX SolutionsTM) and the three-dimensional reconstruction using the “Avizo for Industrial Inspection” software (Thermo Fisher ScientificTM).
• each reinforcing fiber 21 of the reinforcing film 2 can then be studied.
• the reinforcing fibers 21 which have a similar orientation are represented by identical continuous or dotted lines.
• the reinforcing fibers 21 are classified according to their orientations ⁇ and ⁇ between these three cones, the reinforcing fibers 21 belonging to two cones not being classified (fibers at the border between two cones).
• the rate of reinforcing fibers 21 oriented along each axis X, Y and Z of the reinforcing film 2 can then be calculated.
• the reinforcing film 2 is a carbon felt, also known as "carbon mat".
• a carbon felt allows the use of a material with a high rate of open porosity allowing efficient exchange between the liquid electrolyte and the bipolar plate of the electrochemical device.
• open porosity is meant an open cavity, that is to say not closed by the arrangement of the carbon reinforcing fibers 21 and/or by its sizing.
• the rate of open porosity in the reinforcing film 2 is greater than 70%. More preferably, the open porosity rate is greater than 80%, which allows optimal flow of the thermoplastic resin in the reinforcing film 2, allowing good impregnation of the reinforcing fibers 21.
• the high open porosity rate of the reinforcing film 2 it is possible, after the manufacturing process, to obtain a bipolar plate B having a high level of consolidation (with a percentage of remaining porosities generally less than 1%).
• Carbon felt also has the advantage of being able to be easily deformed, allowing adaptation of the reinforcing film 2 to complex shapes.
• Carbon felt also has the advantage of requiring a lower shaping pressure (generally between 6 and 10 MPa) than the shaping pressure needed for woven reinforcement (commonly greater than 15 MPa). More preferably, the non-woven carbon reinforcing film 2 has an open porosity rate greater than 90%, allowing the manufacture of a bipolar plate B whose mechanical characteristics are optimal.
• the reinforcing film 2 has an open porosity rate greater than 60%.
• the reinforcing film 2 has an open porosity rate of between 60% and 70%.
• certain materials such as carbon papers or gas diffusion layers, presenting such a rate of open porosity, allow the manufacture of a light and resistant bipolar plate of thin thickness.
• the reinforcing film 2 has porosities having a diameter of between 1 ⁇ m and 250 ⁇ m, making it possible to effectively impregnate the reinforcing fibers 21 and to guarantee a high level of consolidation in the bipolar plate. B manufactured.
• at least 50% of the porosities have a diameter greater than 125 ⁇ m, more preferably greater than 150 ⁇ m.
• diameter of the porosities we mean the equivalent circle diameter of the porosities, i.e. the diameter of a circle having a surface area equivalent to the surface area of a porosity.
• the reinforcing film 2 has porosities having an equivalent circle diameter of between 1 ⁇ m and 300 ⁇ m.
• At least 50% of the surface of the open porosities of the reinforcing film 2 is occupied by porosities whose equivalent circle diameter is greater than 30 ⁇ m, preferably greater than 80 ⁇ m, more preferably greater than 90 ⁇ m.
• one method consists of using images obtained by X-ray tomography and analyzing them in three dimensions or two dimensions. For example, a two-dimensional cut can be made in a desired direction.
• the reinforcing fibers 21 are defined by gray level thresholding in order to distinguish them from porosities.
• the image is then filtered according to a range of contrasts making it possible to highlight the reinforcing fibers 21.
• Image processing of the "morphological operator" type (for example "morphological gradient”) is then used to identify the structure in two dimensions of the porosities in the image.
• sections of three-dimensional images from X-ray tomography are made to obtain two-dimensional images. These two-dimensional images are imported in this example, into ImageJTM software. Thresholding is then carried out on a range of gray levels between 120 and 255 (in a so-called “Dark Background” mode). A morphological gradient operator in the software (in this example “Watershed”) then makes it possible to highlight the two-dimensional structure of the porosities.
• the area of each porosity is measured and the equivalent circle diameter is calculated from the measured area.
• the porosities are then characterized and classified according to their equivalent circle diameter. For example, porosities are classified according to whether their equivalent circle diameter is less than or greater than a diameter threshold of a proportion of all porosities.
• the reinforcing film 2 is highly compressible, in order to adapt to the complex geometries of the fluid circulation channels of the bipolar plate. It is also possible to form a bipolar plate B with a thickness of less than 1 mm. Preferably, the bipolar plate B formed has a thickness of less than 0.5 mm, as will be described in more detail later.
• the reinforcing film 2 has a thickness Ep2, along the Z axis, preferably less than or equal to 5 mm.
• the thickness Ep2 is between 0.5 and 2.5 mm.
• Such a thickness Ep2 advantageously makes it possible to limit the bulk of the bipolar plate B once manufactured.
• the reinforcing film 2 has a surface mass of less than or equal to 500g/m2.
• the surface mass is between 50 and 300 g/m2, allowing the use of a reinforcing film 2 having a limited mass, which makes it possible to limit the mass of the bipolar plate B in which the reinforcing film 2 is used.
• the bipolar plate B then has a limited mass, allowing it to be integrated into an electrochemical device intended to be mounted for example in an aircraft or in any other vehicle.
• thermoplastic resin film 3 (shown on the ) comprises a polymer, designated thermoplastic resin 31, to form the thermoplastic matrix of the bipolar plate B after manufacturing.
• thermoplastic resin 31 a polymer, designated thermoplastic resin 31, to form the thermoplastic matrix of the bipolar plate B after manufacturing.
• thermoplastic resin film 3 will hereinafter be referred to as thermoplastic film 3.
• the thermoplastic film 3 has a thickness Ep3 of between 50 and 600 ⁇ m. Such a thickness allows a sufficient quantity of thermoplastic resin 31 to form the thermoplastic matrix of the bipolar plate B, while limiting the volume and mass of the bipolar plate B.
• thermoplastic resin of the thermoplastic film 3 is of the semi-crystalline type, making it possible to give the bipolar plate B significant impermeability to fluids, in particular to hydrogen.
• a semi-crystalline thermoplastic resin also provides significant mechanical and chemical resistance, in particular corrosion resistance.
• thermoplastic resin of the thermoplastic film 3 is of the amorphous type, allowing greater ductility as well as a low rate of dimensional shrinkage during the cooling step.
• thermoplastic resin can be adapted according to the chemical environment of the electrochemical device in which the bipolar plate B will be mounted.
• the thermoplastic resin is preferably of the polyphenylene sulfide type (known by the acronym “PPS”). ), Polyphenylsulfone (known by the acronym “PPSU”), Polyvinylidene fluoride (known by the acronym “PVDF”), ethylene chlorotrifluoroethylene (known by the acronym “ECTFE”) or polyolefin type, poly aryl ether ketone, or polyamide.
• the thermoplastic resin is preferably of the polyphenylene sulfide (PPS), polyphenylsulfone (PPSU) type, of the ethylene chlorotrifluoroethylene (ECTFE) type, of the poly aryl ether ketone type .
• the thermoplastic resin is preferably of the polyphenylene sulfide (PPS) and polyphenylsulfone type. (PPSU) if the electrolyte is of the basic type, and of the Polyvinylidene fluoride (PVDF) type or of the ethylene chlorotrifluoroethylene (ECTFE) type if the electrolyte is of the acid type, or of the poly aryl ether ketone type.
• PPS polyphenylene sulfide
• ECTFE ethylene chlorotrifluoroethylene
• a method of manufacturing a bipolar plate B will now be described according to one embodiment of the invention.
• the bipolar plate B is manufactured, in this example, from a stack 1 of a reinforcing film 2, a thermoplastic resin film 3 and two release films 4.
• the stack 1 extends along a stacking axis A, as will be described in more detail later.
• the use of release films 4 makes it possible to expose the reinforcing fibers 21 on the surface of the bipolar plate B formed and to make it electrically conductive.
• the reinforcing film 2, the thermoplastic film 3 and the release film 4 are in the form of a roll, allowing simple storage and handling.
• the method comprises a first step of cutting E1 of the reinforcing film 2, the thermoplastic resin film 3 and the two release films 4 (only the reinforcing film 2 is shown on the ).
• the cutting is carried out for example manually on a cutting table and makes it possible to cut the different films to the dimensions of the desired final bipolar plate B.
• the reinforcing film 2 and the thermoplastic film 3 preferably have similar dimensions. More preferably, each release film 4 has dimensions larger than the dimensions of the reinforcing film 2 and the thermoplastic film 3, so as to protrude from the stack 1 to be able to be more easily removed after the formation of the bipolar plate B.
• the cutting could also be carried out in a different way, for example with a cookie cutter or using a robotic arm.
• the method then comprises, with reference to the , a second step of superposition E2, along the stacking axis A, of the first release film 4, the reinforcing film 2, the thermoplastic film 3 and the second release film 4, in order to form the stack 1.
• a second step of superposition E2 along the stacking axis A, of the first release film 4, the reinforcing film 2, the thermoplastic film 3 and the second release film 4, in order to form the stack 1.
• Such positioning makes it possible to orient the orientation axis F of the reinforcing fibers 21 of the reinforcing film 2 along the stacking axis A, which makes it possible to orient the reinforcing fibers 21 so that their ends 21a, 21b are exposed on two opposite faces of the bipolar plate B manufactured.
• the reinforcing fibers 21 thus optimally conduct electricity in the bipolar plate B and therefore in the electrochemical device in which it will be mounted.
• the stack 1 can be formed either by the successive positioning of the first release film 4, of the reinforcing film 2, of the thermoplastic film 3 and of the second release film 4, or by the successive positioning of the first release film release 4, the thermoplastic film 3, the reinforcing film 2 and the second release film 4.
• thermoplastic resin 3 in this step, an operator could just as easily superimpose successively a first release film 4, a first thermoplastic film 3, a reinforcing film 2 , a second thermoplastic film 3 and a second release film 4.
• first release film 4 a first thermoplastic film 3
• reinforcing film 2 a reinforcing film 2
• second thermoplastic film 3 a second release film 4.
• the use of two thermoplastic films 3 positioned on either side of the reinforcing film 2 makes it possible to minimize the migration of the thermoplastic resin through the reinforcing film 2 and to facilitate its impregnation.
• the superposition of the first release film 4, the reinforcing film 2, the thermoplastic film 3 and the second release film 4 can be carried out manually or by means of a robotic arm, for example.
• stack 1 is consolidated, so as to limit the risks of one of the films shifting relative to the others for example.
• Such consolidation can be carried out for example by the application of welding points (ultrasonic or localized heating type for example) or by making seams to join all the films together. Thanks to such consolidation, it is then simpler to transport the entire stack 1, for example by means of a robotic arm comprising gripping means.
• the method then comprises a step of positioning E3 of the stack 1 in a compression system, in this example in a mold M.
• the mold M comprises, in this example, a lower member and an upper member, each comprising a interior surface having an imprint G.
• the imprint G makes it possible to form the fluid circulation channels in the bipolar plate B.
• the latter is coated with a release agent, for example a liquid which can be sprayed on the interior surface of each lower and upper member, in order to facilitate subsequent release.
• the mold M is then at an initial temperature Ti.
• the initial temperature Ti is between 20 and 210°C.
• the temperature is gradually increased from the initial temperature Ti to a predetermined shaping temperature Tm.
• the shaping temperature Tm is between 140 and 400°C.
• the shaping temperature Tm is preferably still between 305 and 340°C.
• the shaping temperature Tm is between 200 and 260°C, more preferably between 210 and 240°C.
• the shaping temperature Tm is between 240 and 360°C, more preferably between 290 and 330°C.
• the rise in temperature from the initial temperature Ti to a predetermined shaping temperature Tm is carried out during a first predetermined duration ⁇ t1 (represented on the graph of the ).
• the first duration ⁇ t1 is less than 10 min, preferably less than or equal to 3 min, so as to quickly heat the mold M to save time in production and high production rates.
• the method then comprises a step of pressurizing E4 of the stack 1 in the compression mold M.
• the pressurizing step E4 is carried out, at the shaping temperature Tm, at a predetermined shaping pressure Pm, for a second predetermined duration ⁇ t2 (represented on the graph of the ).
• the pressurization step E4 makes it possible to melt the thermoplastic resin of the thermoplastic film 3 to impregnate the reinforcing film 2 and form a bipolar plate B.
• the shaping pressure Pm is between 6 and 12 MPa. More preferably, the shaping pressure Pm is between 8 and 10 MPa, making it possible to limit the deformation of the reinforcing fibers 21 in the initial reinforcing film 2, which could generate porous cavities in the bipolar plate. B, and to apply pressure in a simple way.
• the second duration ⁇ t2 is less than 2 min, preferably less than 1 min, so as to ensure the impregnation of the reinforcing fibers 21 by the thermoplastic resin 31 and thus limit the porosity of the bipolar plate b.
• the process then comprises a cooling step E5, shown on the , of the bipolar plate B formed, for a third predetermined duration ⁇ t3 (represented on the graph of the ), so as to consolidate it.
• the temperature drops from the shaping temperature Tm to a release temperature Tr, at which the pressurization is stopped.
• the release temperature Tr is equal to the initial temperature Ti.
• the third predetermined duration ⁇ t3 is defined, in the case of semi-crystalline polymers, to obtain a cooling rate of between 10 and 100 °C/min, allowing cooling sufficiently slow to allow the crystalline part of the thermoplastic resin to settle. develop, which ensures that the manufactured bipolar plate will have low permeability to hydrogen or any other fluid used in an energy conversion system, while minimizing cooling times to reduce manufacturing cycles .
• Such a cooling rate makes it possible to obtain a crystallinity rate advantageously between 43 and 47%. More preferably, the cooling speed is between 40 and 90°C/min, which makes it possible to guarantee optimal crystallization of the thermoplastic resin during the consolidation phase. In the case of amorphous polymers, the cooling speed is preferably greater than 80°C/min, so as to quickly cool the bipolar plate B and the mold M and accelerate production rates.
• the shaping cycle (i.e. temperature rise, shaping stage and cooling stage) is shown on the , which presents a graph of the evolution of the temperature T and the pressure P as a function of time t during a complete shaping cycle, as described previously.
• the mold M is opened and the formed composite bipolar plate B is removed.
• the release films 4 are then removed, in a step E6, on either side of the bipolar plate B manufactured, so as to expose the reinforcing fibers 21 on the surface of the bipolar plate B.
• the removal of the films from demolding 4 can be carried out by hand or automatically by winding the demolding film 4 at the exit from the mold for example.
• the method then comprises, in an example of implementation, a step of cutting the bipolar plate B, for example to remove the peripheral part of the bipolar plate which has manufacturing defects.
• a step of cutting the bipolar plate B for example to remove the peripheral part of the bipolar plate which has manufacturing defects.
• Such cutting can be carried out for example by water jet cutting, by milling, or using a cookie cutter.
• centering is taken into account in order to ensure precise cutting of the bipolar plate (cutting error less than or equal to 0.1 mm).
• bipolar plate B formed by the manufacturing process described above.
• the bipolar plate B extends in a plane (X, Y).
• Such a process advantageously makes it possible to form a bipolar plate B having a thickness Ep (along the Z axis, orthogonal to the plane (X, Y)) less than 1 mm.
• the bipolar plate B formed has a thickness Ep less than 0.5 mm.
• the proportions between the quantity of reinforcing fibers 21 and thermoplastic resin 31 of the final bipolar plate B are ensured so that the electrical, thermal and mechanical properties of the bipolar plate B satisfy the requirements of the device applications electrochemical.
• the final bipolar plate B thus preferably has a volume content of reinforcing fibers 21 of between 20 and 60%, and a volume content of thermoplastic matrix 31 of between 40 and 80%.
• the volume ratio of reinforcing fibers 21 is between 30 and 50%, and that of the thermoplastic matrix 31 between 50 and 70%.
• the very thin thickness of the bipolar plate thus produced makes it possible to compensate for a lower rate of conductive elements than in the manufacturing processes of the prior art, in which the rate of conductive elements is greater than 80%, while ensuring optimal conductivity.
• the mass of the bipolar plate manufactured is also reduced, which makes it possible to limit the mass of the electrochemical device in which the bipolar plate will be mounted.
• the volume ratio of reinforcing fibers 21 present in the bipolar plate B after manufacturing can be determined after separation of the thermoplastic matrix 31. This separation can be carried out by acid dissolution of the thermoplastic matrix 31 or by calcination by example. The mass of the conductive reinforcing fibers 21 is then measured by weighing and related to the initial mass of the material. The transition to volume rate is achieved using the density of the materials.
• the method according to the invention describes a type of suitable carbon reinforcement and the associated manufacturing cycles, in order to propose a process for manufacturing a bipolar plate that is simple, rapid and does not require the use of expensive industrial machines, while allowing the formation of a thin and light bipolar plate.
• the bipolar plate has a thickness less than or equal to 0.4 mm, which advantageously makes it possible both to limit the mass and the bulk in the electrochemical device and to increase its power density (kW / kg ), without having to resort to post-treatment of the surface of the material in order to increase its electrical conductivity.
• the electrochemical device can thus be easily mounted in a vehicle such as an aircraft for example.
• the present invention makes it possible to manufacture a flexible bipolar plate B, having a specific surface electrical resistance (known by the acronym ASR meaning "Areal Specific Resistance” in English) less than 12 m ⁇ .cm2, a porosity rate less than 1%.
• ASR Automatic Specific Resistance
• Such characteristics advantageously make it possible to guarantee a permeability of less than 5x10 ⁇ -8 mol/m/s/MPa and a high hydrophobicity of the surface of the bipolar plate B, with contact angles greater than 110°.
• the porosity rate of the bipolar plate B manufactured can be measured in different ways known to those skilled in the art.
• the Archimedes thrust method or Pycnometer analysis can be used to measure the real density of the bipolar plate B and compare this real density with a theoretical density. These two methods make it possible to precisely determine the exact volume of a sample, and knowing its mass, to deduce its density.
• wave absorption methods such as X-ray tomography or the use of ultrasound also make it possible to determine the porosity rate of the final bipolar B plate.
• the reinforcing fibers 21 are separated and weighed independently of the thermoplastic matrix 31. This separation can be carried out by dissolution of the matrix or by its thermal degradation (calcination or combustion) or chemical degradation (acid dissolution). Knowing the masses and densities of the initial components of the bipolar plate B, it is possible to deduce the corresponding volumes. These volumes are compared to the exact volume of the sample and the remaining volume corresponds to the volume of the porosities.
• the volume rate of porosity is calculated according to the following formula, in which corresponds to the mass of reinforcing fiber 21 obtained for example after acid dissolution of the thermoplastic matrix 31, corresponds to the density of the reinforcing fiber 21 and to that of the thermoplastic matrix 31: .

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• 2022
  • 2022-03-31 FR FR2202914A patent/FR3134245B1/fr active Active
• 2023
  • 2023-03-30 KR KR1020247026901A patent/KR20240167787A/ko active Pending
  • 2023-03-30 JP JP2024553390A patent/JP2025512712A/ja active Pending
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