Hydrogen fuel cell with multiple current collection points

Abstract

The invention relates to a hydrogen fuel cell comprising: - two end plates; - at least one cell arranged between the end plates; - two electrical-current collector plates each comprising electrical-current collection points, these collector plates being inserted respectively between one of the end plates and the at least one cell. According to the invention, the number of collection points of each of the collector plates is greater than or equal to 3, and the fuel cell comprises means for controlling the collection points, the control means being configured to allow the selective opening / closing of the collection points from which an electrical current can be collected.

Description

Description Title of the invention: Hydrogen fuel cell with multiple current collection points 1. Field of the invention

[0001] The field of the invention is that of hydrogen fuel cells. More specifically, the invention relates to the improvement of such cells, and in particular with regard to the collection of the electric current produced during the implementation of such cells.

[0002] Such batteries find applications in many fields, whenever it is necessary to produce electrical energy, particularly autonomously, for example in vehicles (cars, utility vehicles, trucks, buses, trains, boats, aircraft, etc.), generator sets, etc. 2. Prior art

[0003] The principle of the fuel cell has been known for many years. It has been implemented in the space sector, and numerous projects have also been developed by various car manufacturers.

[0004] A hydrogen fuel cell is based on the principle illustrated in [Fig.l], and produces electrical energy by a chemical reaction between dihydrogen (H2) and dioxygen (O2). This chemical reaction is described by the equations below:

[0005] [Chem 1] H2--> 2H + + 2nd

[0006] O2+ 4 H + + 2nd --> 2H2O

[0007] >

[0008] H2+ l / 2O2--> H2O ; A r H < 0

[0009] The optional term A r H < 0 only indicates that the reaction is exothermic.

[0010] This reaction occurs in what is called an active zone of an assembly of an electrolyte membrane and electrodes (MEA), i.e. a stack of membranes allowing the exchange of H ions. + , placed between an anode, receiving dihydrogen from a reservoir, and a cathode receiving dioxygen (O2) from the outside air.

[0011] As illustrated in [Fig.l], the fuel, dihydrogen (H2), is introduced (Fl) into the cell, to come into contact with the anode A. A part of the dihydrogen enters (F2) the anode A, in which the dihydrogen molecules are separated into electrons e and H ions + which pass through the electrolyte E towards the cathode C. The latter is in contact with the air brought from outside (F3) whose oxygen molecules O2(F4) combine with the H ions +and the electrons e to produce (F5) water (H2O). This water (F6) and the unused air (F7) are evacuated.

[0012] Anode A is therefore the element in which oxidation occurs: H2-^2H + + 2e, and the cathode C is the element in which the reduction occurs: O2+ 4H + + 4e — > 2H2O. The electrons e circulate (F8) between the anode A and the cathode C, producing an electric current E, which is used to drive an electric motor and / or charge a battery.

[0013] This reaction is exothermic, and the various components of the battery can heat up quickly. The entire system must therefore be cooled. The design of the mechanical parts must therefore be adapted to be supplied with coolant, or heat transfer fluid.

[0014] The structure of a fuel cell implementing this chemical reaction is illustrated in [Fig. 2]. The cell 21 consists of a stack of cells 22, placed between two end plates 231 and 232.

[0015] A current collector plate 24 is interposed between each end plate 23i and 232 and the cells 22 (only one of the two collector plates 24 is visible in [Fig.2]).

[0016] The constituent elements of a 22 cell are detailed, exploded, in [Fig. 3]. It comprises two plates, bipolar or monopolar, between which is placed an electrolyte membrane. The monopolar plates are the first and last plates of the cell stack. They generally have the same design as a bipolar plate, but the inlets are closed so that the plate does not receive one of the gases. The cell thus comprises a monopolar cathode plate not receiving dihydrogen and a monopolar anodic plate not receiving dioxygen.

[0017] The bipolar plates, stacked between the two monopolar plates, are formed by the assembly of two metal half-plates 31, 32 (one anode half-plate 31 and one cathode half-plate 32), which can be welded, brazed or glued. A space between the two metal half-plates is defined by the forming of these to define on the one hand zones 33, 34 receiving a cooling liquid and on the other hand channels allowing the circulation of gases, respectively dihydrogen and dioxygen (extracted from the air). MEA membranes 35 are interposed between the half-plates.

[0018] The collector plates 24 according to the prior art each comprise one to two current collection points 25. As a result of this reduced number of collection points 25, the quantity of current absorbed by each collection point 25 is significant. To withstand this, the collection points 25 must be sufficiently sized. Since the collector plates 24 are made of copper, this results in a significant consumption of copper to manufacture them, which represents a significant cost item. In addition, the significant sizing of the collection points induces losses which are detrimental to the efficiency of the battery.

[0019] Given this small number of collection points, the currents are not uniform in the cells. This can lead to the formation of hot spots. The temperature and humidity are then not uniform in the cells, which can affect the operation of the battery and reduce its durability.

[0020] There is therefore a need for a new approach to the production of such batteries, to improve their operation and / or their efficiency.

[0021] 3. Main characteristics of the invention

[0022] The invention addresses at least part of this need using a new type of hydrogen fuel cell, said cell comprising:

[0023] - two end plates;

[0024] - at least one cell arranged between said end plates;

[0025] - two electric current collector plates each comprising electric current collection points, these collector plates being interposed respectively between one of said end plates and said at least one cell.

[0026] According to the invention, the number of collection points of each of said collector plates is greater than or equal to 3, and said stack comprises means for controlling said collection points, said control means being configured to allow the selective opening / closing of the collection points from which an electric current is likely to be collected.

[0027] In other words, the invention consists of implementing, in a hydrogen fuel cell, collector plates each comprising at least three current collection points and control means for selectively opening / closing the collection points from which an electric current is likely to be collected.

[0028] It is thus possible to choose, according to the invention, the collection points from which the current produced by the battery is drawn, which provides numerous advantages, in particular: - this allows, depending on the position of the collection points, and depending on the choice of open and closed collection points, a homogenization of the currents in the plates of the cell(s) of the battery; - to better regulate the temperature in the battery and avoid hot spots, and to better regulate the humidity level in the battery, and therefore improve the durability of the battery; - increasing the number of collection points makes it possible to reduce the section and thus reduce the consumption of raw materials; - the control of the collection points allows for more calibrated sizing and therefore a reduction in sections, which contributes to reducing losses and increasing the efficiency of the battery.

[0029] The number of collection points of each of said collector plates may in particular be determined as a function of the size of the active surface of said at least one cell, or of each active surface, if there are several.

[0030] According to a particular embodiment, said collection points are distributed in a substantially uniform manner around the periphery of said collector plates.

[0031] In particular, the number of collection points of each of said collector plates may be equal to 4, the four collection points of each of said collector plates being arranged near the four corners of said collector plates.

[0032] Said means for controlling said collection points may in particular be configured to allow opening / closing of collection points taking into account a current phase of the life of said at least one cell.

[0033] Said means for controlling said collection points can also be configured to allow opening / closing of collection points taking into account at least one condition of use and / or operation of said battery.

[0034] In this case, the opening / closing of said collection points can be carried out according to a predefined control law, depending on the power to be delivered by said battery and / or depending on operating conditions.

[0035] Many uses are conceivable for a battery as described above, in particular for at least one of the applications belonging to the group comprising:

[0036] - motor vehicles;

[0037] - utility vehicles;

[0038] - buses or trucks;

[0039] - trains;

[0040] - boats;

[0041] - aircraft;

[0042] - generators.

[0043] The invention also relates to a method for controlling a fuel cell as described above, said method comprising a step of selectively opening / closing the collection point(s) of each of said collector plates from which an electric current is likely to be collected.

[0044] According to a particular embodiment, the selective opening / closing of the collection point(s) from which an electric current is likely to be collected takes into account a current phase of the life of said at least one cell.

[0045] According to another particular embodiment, which may or may not be combined with the previous one, the selective opening / closing of the collection point(s) from which an electric current is likely to be collected takes into account at least one condition of use and / or operation of said battery.

[0046] In this case, the choice of the collection point(s) can in particular be made according to a predefined control law depending on the power to be delivered by said battery and / or depending on operating conditions. 4. list of figures

[0047] Other characteristics and advantages of the invention will appear more clearly on reading the following description of an example of implementation, given as a simple illustrative and non-limiting example, and the appended figures among which:

[0048] [Fig-1]: [Fig.l], already described in the preamble, illustrates the general principle of a fuel cell;

[0049] [Fig.2]: [Fig.2], already described in the preamble, presents the structure of a fuel cell, comprising a stack of cells;

[0050] [Fig.3]: [Fig.3], already described in the preamble, presents the constituent elements of a cell of [Fig.2], in exploded view;

[0051] [Fig.4]: [Fig.4] shows the structure of a fuel cell comprising collector plates according to the invention;

[0052] [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9], [Fig.10]: Figures 5 to 10 illustrate different examples of collector plates according to the invention;

[0053] [Fig.11]: [Fig.11] illustrates a diagram illustrating the means for controlling the collection points of a stack according to the invention;

[0054] [Fig.l2C], [Fig.l2B], [Fig.l2C], [Fig.l2D] illustrate four examples of selection made by the control means of [Fig.11];

[0055] [Fig.13], [Fig.14]: Figures 13 and 14 illustrate different current densities generated in a cell depending on the open collection points.

[0056] 5. Description of a particular embodiment

[0057] 5.7 Main elements of a hydrogen fuel cell

[0058] With reference to [Fig. 4], a fuel cell according to the invention conventionally comprises at least one cell 22 positioned between a first 231 and a second 232 end plates. The cell may comprise a single cell 22 but preferably comprises a plurality of cells 22 stacked against each other between the two end plates 231, 232.

[0059] The battery also conventionally comprises a first and a second collector plate 24. The first collector plate 24 is located between the first end plate 231 and the cell(s) 22. The second collector plate 24 is located between the second end plate 232 and the cell(s) 22. In [Fig. 4], only the first collector plate is visible.

[0060] Each of the collector plates 24 comprises current collection points 25, the number of which, according to the principle of the invention, is greater than or equal to 3. These collector plates are described in more detail below.

[0061] The battery comprises, or is connected to, means for controlling the collection points 25, these control means being configured to allow the selective opening / closing of the collection points 25 from which an electric current is likely to be collected. These control means are described in more detail below.

[0062] 5.2 Collection plates

[0063] In relation to Figures 5 to 10, some illustrative and non-limiting examples of collector plates 24 according to the invention are presented.

[0064] As shown in Figures 5, 6 and 7, the collector plates 24 may comprise three collection points 25. In this case, two collection points 25 may be located on one side of the collector plate 24 near two opposite corners, the other collection point 25 being located on the other side of the collector plate 24, for example near one or other of the corners (see Figures 6 and 7) or else substantially in the center (see [Fig.5]).

[0065] [Fig.8] illustrates an embodiment in which the collector plates 24 comprise four collection points 25 located near the corners of the collector plate 24, two collection points 25 being placed on one side and two on the opposite side of the collector plate 24.

[0066] Preferably, the collector plates 24 comprise four collection points 25. However, they may comprise more.

[0067] [Fig.9] illustrates by way of example a collector plate 24 comprising six collection points 25, four being placed near the four corners of the collector plate 24, two others being located approximately in the center of two opposite sides of the collector plate 24.

[0068] [Fig. 10] illustrates by way of example a collector plate 24 comprising five collection points 25, three collection points 25 being distributed uniformly on one side of the collector plate 24 and the other two being distributed uniformly on the opposite side of the collector plate 24.

[0069] Within the same stack, the number and distribution of collection points on the first and second collector plates are identical. However, they could be different from one collector plate to another.

[0070] The number of collection points will preferably be even but may alternatively be odd. The collection points are ideally distributed evenly around the periphery of the collector plates.

[0071] Within a hydrogen fuel cell, each cell includes an active surface. This surface is the area in which the chemical reactions leading to the production of electric current take place. The number of collection points on each collector plate may, but is not required, be determined based on the size of the active surface.

[0072] 5.3 Means of control

[0073] As mentioned above, the stack includes, or is connected to, means of controlling the collection points.

[0074] These control means are configured to allow the selective opening / closing of the collection points 25 from which an electric current is likely to be collected. In other words, they make it possible to select the collection points 25 from which the current produced by the battery will be collected.

[0075] According to a first approach, the means for controlling the collection points are configured to allow selective opening / closing of collection points during different phases of life of the cell(s) of the battery. In this case, it is possible, when the battery is still in working order, to select the collection points which will be opened / closed during phases during which the battery is stressed differently, and / or to take into account a variation in the current concentration in the battery, depending on the evolution of the battery over time.

[0076] It is also possible to produce, with the same battery structure, batteries with different current densities depending on the applications.

[0077] According to a second approach, which can of course be combined with the first, the means for controlling the collection points are configured to allow selective opening / closing of collection points during use of the battery, depending on usage and operating conditions. In this case, it is possible to select, in real time, the collection points which will be opened / closed during phases during which the battery is required to produce more or less electric current. It is thus possible to vary the current density in its cells during use of the battery.

[0078] [Fig.11] illustrates the diagram of an example of the principle of means of controlling collection points.

[0079] The control means comprise a control unit 31 and a battery of switches 32 b 322, 323, 324, each switch being respectively connected to a collection point 33 b 332, 333, 334 of the collection plate 33 so as to control its opening or closing. The control unit 31 is programmed to ensure the selective opening / closing of each of the collection points, by delivering a suitable opening / closing signal to the switches to open / close the collection points as required.

[0080] The control program implemented by the control means (which can be stored in a memory provided for this purpose and, if necessary, modifiable, by an update) implements one or more control laws, which can in particular take into account medium and long-term aspects, i.e. the evolution of the battery over time. during its life and / or short-term, instantaneous or near-instantaneous aspects, such as a need for power, or current operating conditions.

[0081] In particular, when the opening / closing of the collection points is done in real time, the opening / closing of the collection points will be carried out according to a predefined control law depending on the power to be delivered by the battery and / or depending on operating conditions.

[0082] The control means receive a series of information 34, from sensors or reference data, for example statistics on the evolution of the battery during its life, such as: - immediate need for electrical power; - operating preset ("economy" mode or "sport" mode for example); - temperature of the battery and / or other vehicle components; - external conditions, such as humidity and outside temperature; - management of water produced by the battery; - life phase, or age, of the battery; - specific information about the battery, for example, particular wear of a region;

[0083] Figures 12A to 12D illustrate four specific examples: - [Fig.l2A]: in the context of battery wear management ("aging management" in English), the current is concentrated in a zone 41 corresponding to the upper right zone of the battery. In this case, only the collection point 332 is active, and only the corresponding switch 322. The current is thus directed towards the nearest collection point, without a portion of it crossing the battery towards the other collection points, at the risk of generating losses and / or disturbances; - [Fig.l2B]: selective use of half of the catalyst surface, zone 42 corresponding to the upper part of the collection plate 33. This approach corresponds for example to an optimized management of the water, in particular according to hygrometry conditions. In this case, only the switches 32i and 322 are closed, so that the current is collected on the collection points 331 and 332 close to the current concentration zone 42 - [Fig.l2C]: in the context of battery wear management, we note that the lower right portion becomes little or non-functional, and that the concentration of current is present essentially in zone 43. In this hypothesis, only switches 32 b 322 and 323 are closed, so that the current be collected at collection points 331, 332 and 333 close to current concentration zone 44; - [Fig.l2D]: in this configuration, the entire surface 44 of the collection plate 33 is used, which corresponds to a balanced use, for example for a new battery and / or a high need for electrical power. All the switches are then closed, and all the collection points are used.

[0084] In the case where the stack includes several active zones that can be selectively activated, the selection of collection points also takes into account the location of these active zones.

[0085] 5.4 Current density

[0086] The selective opening / closing of different collection points 25 makes it possible to vary the current density in the cell(s) 22 of the battery.

[0087] We can thus observe in [Fig.13] that the opening of two collection points 25 Oplaced on two opposite sides of the collector plates 24 and at two facing angles makes it possible to generate a current density profile 26. It is observed in [Fig.14] that the opening of two collection points 25 O placed on two opposite sides of the collector plates 24 and at two diametrically opposite angles makes it possible to generate another current density profile 26.

[0088] It is thus possible to create a multitude of current density profiles depending on the number of open collection points and their position around the collector plate 24.

[0089] 5.5 Advantages

[0090] The implementation of the invention allows in particular: - depending on the position of the collection points, and depending on the choice of open and closed collection points, a homogenization of the currents in the plates of the cell(s) of the battery; - to better regulate the temperature in the battery and avoid hot spots, and to better regulate the humidity level in the battery, and therefore improve the durability of the battery; - increasing the number of collection points makes it possible to reduce the section and thus reduce the consumption of raw materials; - the control of the collection points allows for more calibrated sizing and therefore a reduction in sections, which contributes to reducing losses and increasing the efficiency of the battery.

Claims

Claims

1. Hydrogen fuel cell comprising: - two end plates; - at least one cell for producing an electric current, arranged between said end plates; - two electric current collector plates each comprising electric current collection points, these collector plates being interposed respectively between one of said end plates and said at least one cell, characterized in that the number of collection points of each of said collector plates is greater than or equal to 3, and in that said battery comprises means for controlling said collection points, said control means being configured to allow the selective opening / closing of the collection points from which an electric current is likely to be collected.

2. A hydrogen fuel cell according to claim 1 wherein said at least one cell has an active surface, the number of collection points of each of said collector plates being determined as a function of the size of said active surface.

3. A hydrogen fuel cell according to claim 1 or 2 wherein said collection points are distributed substantially uniformly around the periphery of said collector plates.

4. A hydrogen fuel cell according to claim 1 wherein the number of collection points of each of said collector plates is 4, the four collection points of each of said collector plates being arranged near the four corners of said collector plates.

5. Hydrogen fuel cell according to any one of claims 1 to 4 wherein said means for controlling said collection points are configured to allow opening / closing of collection points taking into account a current phase of the life of said at least one cell.

6. Hydrogen fuel cell according to any one of claims 1 to 4 wherein said means for controlling said collection points are configured to allow opening / closing of collection points taking into account at least one condition of use and / or operation of said cell.

7. Hydrogen fuel cell according to claim 6 in which the openings / closings of said collection points are carried out according to a predefined control law depending on the power to be delivered by said cell and / or depending on operating conditions.

8. Use of a fuel cell according to any one of claims 1 to 7 for at least one of the applications belonging to the group comprising: - motor vehicles; - utility vehicles; - buses or trucks; - trains; - boats; - aircraft; - generators.

9. Method for controlling a fuel cell according to any one of claims 1 to 7, said method comprising a step of selectively opening / closing the collection point(s) of each of said collector plates from which an electric current is likely to be collected.

10. Method according to claim 9 in which the selective opening / closing of the collection point(s) from which an electric current is likely to be collected takes into account a current phase of the life of said at least one cell.

11. Method according to claim 9 or 10 in which the selective opening / closing of the collection point(s) from which an electric current is likely to be collected takes into account at least one condition of use and / or operation of said battery.

12. Method according to claim 11 in which the choice of the collection point(s) is carried out according to a predefined control law depending on the power to be delivered by said battery and / or depending on operating conditions.

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