Compression device for fuel cell stack

Abstract

A fuel cell stack includes a compression plate assembly including a second end plate having a first flat surface and an opposing second flat surface, where the first flat surface is adjacent to the fuel cell stack and the second flat surface is adjacent to a compression housing, where the first flat surface is adjacent to the fuel cell stack and the second flat surface is adjacent to the compression housing. The compression housing includes: a spring recess and a plurality of separate grooves on an inner axial surface of the spring recess; a spring assembly in the spring recess; a load plate in the spring recess and in contact with the spring assembly; and an elastic holding device in the spring recess and in contact with the load disc; wherein the resilient retention device engages with one of the plurality of separate grooves and the load disc, and the load disc and the spring assembly are physically separated from the inner axial surface of the spring recess.

Description

Technical Field

[0001] The present invention relates to a fuel cell stack, and more particularly, to a compression device for a fuel cell stack. Background Art

[0002] A fuel cell is a device in which a fuel and an oxidant fluid undergo an electrochemical reaction to generate electricity. One type of fuel cell that is being developed for various commercial applications is a solid polymer electrolyte fuel cell, which employs a membrane electrode assembly (MEA) that includes a solid polymer electrolyte made of a suitable ionomer material (e.g., ) disposed between two electrodes. Each electrode includes a suitable catalyst located near the solid polymer electrolyte. For example, the catalyst can be a noble metal, a non-noble metal, or an alloy or intermetallic compound thereof, which can optionally be supported on a suitable catalyst carrier (such as carbon, graphite, or a metal oxide). The catalyst can be disposed in a catalyst layer. The catalyst layer typically contains a binder and / or an ionomer, which can be the same as or different from the binder and / or ionomer used for the solid polymer electrolyte. A fluid diffusion layer (a porous, conductive sheet) is typically adjacent to the electrode and is used for mechanical support, current collection, and / or reactant distribution. In the case of gaseous reactants, such a fluid diffusion layer is referred to as a gas diffusion layer. If the catalyst layer is incorporated onto the gas diffusion layer, the unit is referred to as a gas diffusion electrode.

[0003] For commercial applications, multiple fuel cells are typically stacked in series to provide a greater output voltage. In a solid polymer electrolyte fuel cell, separators are typically used near the gas diffusion electrodes to separate one cell in the stack from another. The separators are typically bipolar, having an anode flow field channel on one side for supplying fuel to the MEA and a cathode flow field channel on the other side for supplying oxidant to the MEA. A coolant flow field channel is formed between the anode flow field channel side and the cathode flow field channel side. In this case, two flow field plates are typically adhered together, each flow field plate having an anode flow field channel or a cathode flow field channel on one side and a coolant flow field channel on the other side, and they are adhered together such that the coolant flow field channel sides face each other. Fluid distribution features, including inlet ports and outlet ports, fluid distribution plenum chambers, and many fluid channels, are typically formed in the surface of the separator adjacent to the electrode to distribute the reactant fluid to the MEA and remove reaction by-products from the MEA. The separator also provides a conductive and thermally conductive path for the MEA, as well as mechanical support and dimensional stability. Exemplary materials for the separator include metals, carbon, and expanded graphite.

[0004] A typical fuel cell stack also includes supply manifolds for directing fuel and oxidant to the anode flow field channels and the cathode flow field channels, respectively. The fuel cell stack typically also includes a supply manifold for directing coolant fluid to internal channels of the separators within the fuel cell stack to absorb heat generated by the exothermic reactions in the fuel cells. The fuel cell stack typically also includes an exhaust manifold for removing unreacted fuel and oxidant gases, and an exhaust manifold for discharging the coolant flow from the fuel cell stack.

[0005] Fuel cell stacks are typically compressed to ensure sufficient electrical contact. Conventional methods of compressing fuel cell stacks typically utilize springs, hydraulic or pneumatic pistons, pressure pads, or other elastic compression devices that cooperate with generally substantially rigid end plates and tie rods to force the two end plates toward each other to compress the fuel cell stack. However, the tie rods typically significantly increase the weight of the stack and are difficult to accommodate without increasing the stack volume. In addition, the associated fasteners increase the number of different components required to assemble the fuel cell stack.

[0006] Due to material creep and thermal expansion / contraction of various fuel cell components and changes in fluid pressure during operation, the thickness of the fuel cell stack changes over time, making the fuel cell stack compression more complicated. In a fuel cell stack compression assembly design described in U.S. Patent No. 6,057,053, the compression assembly includes a compression mechanism and a restraining mechanism. Even when the thickness of the fuel cell assembly changes, the compression mechanism pushes the first end plate toward the second end plate, thereby applying an internal compression force to the fuel cell assembly. The restraining mechanism prevents the first end plate from moving away from the second end plate by preventing the deflection of the compression mechanism, for example, when the internal fluid pressure increases, the deflection of the compression mechanism may occur. In one embodiment, the compression mechanism includes a plurality of stacked coil springs, and the restraining mechanism includes a rigid load ring that circumscribes the stacked coil springs. The coil spring is inserted between one of the end plates and a load disk held in place by a stack holding device (e.g., a bolt connecting rod or a retaining band). The load ring has a threaded inner circumferential surface that cooperates with the threaded outer circumferential surface of the load disk. Rotation of the load ring moves the load ring toward an adjacent end plate. The rotation of the load ring can be performed manually, for example, in a regularly scheduled maintenance check or automatically, using a device for continuously applying a rotational force to the load ring to prevent any gap from forming between the load ring and the load plate. When the first end plate moves toward the second end plate, the limiting mechanism is adjusted in conjunction with the movement of the first end plate to maintain contact between the load ring and the first end plate. However, during operation, vibrations of the stack may cause undesirable rotation of the threaded load ring, thereby loosening the disc spring and reducing the stack compression pressure. In addition, the threads on the load ring and the load disc are prone to wear and corrosion, making it difficult to disassemble the compression assembly when necessary, for example, to replace a faulty fuel cell and / or plate. In addition, the holes for the connecting rods through the fuel cell stack may require additional sealing elements, which further complicates the design of the fuel cell stack.

[0007] Although many designs for stack compression assemblies have been proposed, there remains a need for further improvements in the design of stack compression assemblies for fuel cell stacks. Summary of the invention

[0008] In one embodiment, a fuel cell stack includes a first end plate, a compression plate assembly, a plurality of fuel cells interposed between the first end plate and the compression plate assembly, and a restraint mechanism for substantially preventing movement of the first end plate from the compression plate assembly, wherein the compression plate assembly includes: a second end plate having a first flat surface and an opposite second flat surface, wherein the first flat surface is adjacent to the fuel cell stack; a compression housing adjacent to the opposite second flat surface of the second end plate, wherein the compression housing includes: a spring recess including a plurality of discrete grooves on an inner axial surface of the spring recess; a spring assembly within the spring recess and in contact with the second flat surface of the second end plate; a load disk within the spring recess and in contact with the spring assembly; and an elastic retaining device within the spring recess and in contact with the load disk; wherein the elastic retaining device engages one of the plurality of discrete grooves and the load disk; and the load disk and the spring assembly are physically separated from the inner axial surface of the spring recess.

[0009] In a further embodiment, the elastic retaining device includes a first elastic retaining ring that engages one of the plurality of grooves and an outer peripheral region of the load disk.

[0010] In another embodiment, the elastic retaining device further includes a second elastic retaining ring that engages an adjacent one of the plurality of grooves, wherein the first elastic retaining ring and the second elastic retaining ring are separated by a spacer, and whereby at least some of the compression force is transmitted from the first retaining ring to the second retaining ring through the spacer.

[0011] In a further embodiment, the fuel cell stack further includes a plurality of flat sides detachably attached to the first end plate and the compression housing.

[0012] In another embodiment, a method of assembling a fuel cell stack is provided. The method includes the steps of: disposing a spring assembly into a spring recess; disposing a load disk on top of the spring assembly within the spring recess such that the load disk is in contact with the spring assembly; axially compressing the load disk relative to the spring recess such that an axial compression force is applied to the spring assembly; radially compressing an elastic retaining device and disposing the compressed elastic retaining device on top of the load disk; and releasing the compressed elastic retaining device such that the elastic retaining device engages one of the plurality of discrete grooves and the load disk.

[0013] These and other aspects of the invention will be apparent from the drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Shows an exploded view of an exemplary fuel cell stack according to one embodiment.

[0015] Figure 2 Shows an exploded cross-sectional view of a compression assembly according to one embodiment.

[0016] Figure 3 Shows a cross-sectional view of the compression assembly in an assembled state.

[0017] Figure 4 Shows an exemplary retaining ring according to the present specification.

[0018] Figure 5 Shows a cross-sectional view of the situation where the retaining ring is tilted in the spring recess.

[0019] Figure 6 Shows a cross-sectional view of another embodiment in which a second elastic retaining ring and a spacer are used in the compression assembly. Detailed Description

[0020] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments of the present invention. However, those skilled in the art will understand that the present invention may be practiced without these details. In other instances, well-known structures related to fuel cells, fuel cell stacks, and fuel cell systems have not been shown or described in detail so as not to unnecessarily obscure the description of the embodiments of the present invention.

[0021] Unless the context otherwise requires, the word "comprise" and its variations (such as "comprises" and "comprising") shall be construed in an open, inclusive sense throughout the specification and the following claims, i.e., "including but not limited to".

[0022] Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing throughout the specification do not necessarily all refer to the same embodiment. Moreover, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner.

[0023] Figure 1A exploded view of an exemplary fuel cell stack according to an embodiment of the present invention is shown. The fuel cell stack 2 includes a first end plate 4, a compression assembly 6, and a plurality of fuel cells 7 compressed between the first end plate 4 and the compression assembly 6. The first end plate includes manifolds 8a, 8b, 10a, 10b, 12a, 12b for each of a fuel inlet, an oxidant inlet, a coolant inlet, and a coolant outlet, such that fuel, oxidant, and coolant can be introduced into and withdrawn from the fuel cell stack 2. The fuel cell stack 2 further includes a restraining mechanism in the form of an enclosure having sides 14, 16, 18, 20 that engage the first end plate 4 and the compression assembly 6. In an assembled configuration, the enclosure substantially prevents movement of the first end plate 4 from the compression assembly 6, such that the fuel cell stack 2 can maintain a fixed length. Those skilled in the art will appreciate that a fixed fuel cell stack length is desirable for integration in a fuel cell system.

[0024] Figure 2 An exploded cross-sectional view of the compression assembly 6 according to an embodiment is shown. The compression assembly 6 includes a second end plate 22 and a compression housing 24. The second end plate 22 has a first flat surface 26 adjacent to the fuel cells 7 and an opposite second flat surface 28 adjacent to the compression housing 24. The compression housing 24 includes: four spring recesses 30, each recess including a spring assembly 32 in contact with the second flat surface 28; a load plate 34 in contact with the spring assembly 32; and a retaining ring 36 in contact with the load plate 34. The spring recesses 30 have a series of spaced grooves 38 that define an inner axial surface of the spring recesses 30. The load plate 34 further includes an axial collar 40 that serves to keep the spring assemblies 32 substantially aligned. In the case of stacked disc springs, the axial collar 40 extends through the discs to keep them substantially aligned during assembly and also prevents misalignment of the disc springs and contact with the spaced grooves and inner axial surface of the spring recesses over time. The collar 40 need not contact the spring assemblies 32, but may contact at least a portion of the spring assemblies if the spring assemblies 32 are misaligned. Those skilled in the art will be able to determine the size of the collar 40 based on the disc spring size and associated tolerances. Those skilled in the art will recognize that, for purposes of understanding, Figure 2 To show the spring assemblies, load plates, and retaining rings in various assembled and unassembled states within each spring recess.

[0025] Figure 3A cross-sectional view of a simplified compression assembly 6 in an assembled state is shown. The outer peripheral region of the retaining ring 36 engages a separate groove 38, while the inner peripheral region of the retaining ring 36 engages the outer peripheral region of the load disk 34. In this way, the retaining ring 36 provides a compressive force to the load disk 34 and the spring assembly 32 (only one spring disk is shown for simplicity). Although the limiting mechanism substantially prevents the first end plate from moving from the compression assembly and maintains a fixed fuel cell stack length, the spring assembly 32 can be compressed and expanded as needed, so that even when the fuel cell thickness decreases or expands due to, for example, changes in operating pressure, thermal expansion, and / or fuel cell material creep, a continuous axial compressive force is provided to the fuel cell 7 (not shown). As a result, the axial compressive pressure applied to the fuel cell is not negatively affected during operation and over time.

[0026] The retaining ring 36 is preferably elastic such that it can elastically deform in the radial direction during the assembly of the compression assembly, but remains rigid in the axial direction of the compression assembly such that it can apply a compressive force on the load disk 34. Additionally, each groove 38 on the axial surface of the spring recess 30 is preferably separate, e.g., each groove is not connected to any other groove. This is contrary to threads, as threads are continuous and connected in a helical or spiral configuration. As described above, one disadvantage of using a threaded design is that if there is corrosion and / or wear in the threads, it is difficult to disassemble the compression assembly.

[0027] To assemble the compression assembly, the spring assembly 32 is placed in the spring recess 30, and then the load disk 34 is placed on top of the spring assembly 32. Preferably, the spring assembly 32 and the load disk 34 are smaller than the spring recess 30 (e.g., in the case of a circular spring recess, the diameter of the spring assembly 32 and the load disk 34 is smaller than the diameter of the spring recess 30), making it easier to place the spring assembly 32 and the load disk 34 into the spring recess 30. Then, an axial compression force is applied to the load disk 34 to achieve the desired compression load. Once the desired compression load is achieved, the retaining ring 36 is elastically compressed in the radial direction to fit into the spring recess 30, placed on top of the load disk 34, and then released, such that the outer peripheral region of the retaining ring 36 engages with one of the discrete grooves 38 to hold the retaining ring 36 in place, thereby applying an axial compression force to the load disk 34, which in turn compresses the spring assembly 32 and the fuel cell 7. Preferably, there are a plurality of discrete grooves 38, such that the compression load applied to the fuel cell 7 can be easily adjusted by engaging the elastic retaining ring 36 with different discrete grooves to achieve the desired range of compression loads on the fuel cell 7. For example, if the compression load of the fuel cell stack decreases over time, the retaining ring 36 can also be easily removed and adjusted to engage with a different discrete groove, or if there are issues related to corrosion and / or wear of the retaining ring, even the retaining ring 36 can be replaced. In some embodiments, a load cell can be used in the compression assembly during assembly to ensure that the desired compression load is applied and / or to monitor the compression load of the fuel cell stack over time. Those skilled in the art will understand that the more and thinner the discrete grooves (and thus, the thinner the elastic retaining ring that engages with the discrete grooves), the greater the compression load resolution when adjusting the compression load on the fuel cell stack.

[0028] In another embodiment, the spring recess 30 can include a load groove 48 on its axial surface, which extends parallel to the axial direction with respect to the spring recess 30 (i.e., in a direction substantially perpendicular to the discrete grooves 38) to allow the elastic retaining ring to be more easily placed into one of the discrete grooves. In this example of assembling the compression plate assembly, a device having a plurality of mechanical fingers holds the elastic retaining ring and the load disk, while also compressing the elastic retaining ring in the radial direction in one step. The load groove allows the mechanical fingers to slide into the spring recess and load the elastic retaining ring and the load disk onto the spring recess and on top of the spring assembly. Once the desired compression load is reached, the mechanical fingers release the elastic retaining ring, and then slide out of the spring recess through the load groove. The release of the mechanical fingers allows the elastic retaining ring to engage with one of the discrete grooves, thereby holding the load disk in the desired position in the spring recess and maintaining the desired compression load on the fuel cell.

[0029] The load disk 34 and the retaining ring 36 are preferably two separate components. Since the load disk is connected to the collar at its inner circumference and also contacts the retaining ring at its outer peripheral region, the load disk must have a relatively large flat surface and be thick enough to apply and distribute sufficient compressive force on the disc spring. However, it is difficult to design a load disk with a relatively large planar surface area to have sufficient elasticity such that it can deform to fit into the spring recess and then release into one of the separate grooves in the spring recess. As a result, a separate elastic retaining ring is employed to engage with one of the separate grooves and the outer peripheral region of the load disk. This also allows the spring assembly and the load disk to be substantially physically separated from the inner axial surface of the spring recess, so that during assembly, the spring assembly and the load disk can be more easily loaded into the spring recess. This also prevents the spring assembly and the load disk from contacting the grooves on the inner axial surface of the spring recess, thereby preventing wear of the inner axial surface of the spring recess. Additionally, this also relieves the mutual constraints between the thickness requirements of the components. For example, using two separate components allows a thinner elastic retaining ring to improve the resolution of the preferred compressive load and allows a thicker load disk to apply and distribute sufficient compressive force on the disc spring. Those skilled in the art will understand that the cross-sectional thickness of the load disk should be greater than the cross-sectional thickness of the retaining ring (and the cross-sectional thickness of the separate grooves) such that if the load disk contacts the inner axial surface of the spring recess due to movement and / or misalignment, the load disk does not engage with the separate grooves.

[0030] The retaining ring 36 can be made elastic in any manner known in the art. Preferably, the retaining ring 36 is capable of deforming in the radial direction but is substantially rigid in the axial direction. Figure 4 An exemplary retaining ring with a gap 50 for allowing radial deformation is shown. Any suitable material can be selected for the retaining ring, such as a metal (such as high-strength spring steel). Such retaining rings are typically off-the-shelf components, making these rings cost-effective.

[0031] During the assembly of the fuel cell stack, those skilled in the art will understand that the spring will be compressed in discrete steps equal to one groove pitch (i.e., the distance between each separate groove). If a higher compression pressure is required, the load ring should engage with the groove located at a lower position (i.e., closer to the second end plate) in the spring recess. Conversely, if a lower compression pressure is required, the load ring should engage with the groove located at a higher position (i.e., farther from the second end plate) in the spring recess. Those skilled in the art will understand that when determining the compression pressure applied to the fuel cell by the compression assembly, a thinner retaining ring and a smaller distance between each groove will result in a higher resolution. A higher resolution is desirable such that the compression pressure applied to the fuel cell can be adjusted more finely.

[0032] Based on the required compression pressure and the dimensions of the resilient retaining ring 36, the inventors have found that, as Figure 5 shown, after assembly, the resilient retaining ring 36 can be inclined at an angle (or frustoconical) in the spring recess, thereby increasing the risk of releasing itself from the separated groove and the compression assembly. However, simply making the cross-section of the resilient retaining ring 36 thicker to increase its stiffness to reduce the inclination will reduce the compression pressure resolution, as described above, which is undesirable. As can also be clearly seen from Figure 5 , the load disk 34 and the spring assembly 32 do not contact the inner axial surface of the spring recess.

[0033] Figure 6 Another embodiment is shown in which a second resilient retaining ring 42 and a spacer 44 are used in the spring recess. The second resilient retaining ring 40 engages in the next separated groove adjacent to (i.e., above) the separated groove in which the first resilient retaining ring 36 engages. The spacer 44 is disposed between the first resilient retaining ring 36 and the second resilient retaining ring 42 and contacts the first resilient retaining ring 36 and the second resilient retaining ring 42 such that at least part of the axial compression force from the compressed spring can be transferred from the first resilient retaining ring 36 to the second resilient retaining ring 40. Those skilled in the art will understand that the spacer 42 does not engage any of the separated grooves.

[0034] Without being bound by theory, the inventors have surprisingly found that the additional second resilient retaining ring 40 and spacer 42 not only reduce the inclination of the first resilient retaining ring 36, but also the axial compression load that the resilient retaining ring can withstand is almost doubled without the problem of inclination, thus significantly improving its safety. In addition, this additional retaining ring and spacer design is low-cost because both the retaining ring and the spacer are off-the-shelf components.

[0035] Those skilled in the art will be able to easily determine suitable materials for the resilient retaining ring and the spacer. For example, the resilient retaining ring and the spacer can be a metal (such as aluminum). The materials used for each of the resilient retaining ring and the spacer can be the same or different. The spacer can also be of any suitable shape and size as long as it can transfer the load from the first resilient retaining ring to the second resilient retaining ring and does not interfere with the function of the compression assembly. In some embodiments, the outer diameter of the spacer should be less than the diameter of the spring recess such that the spacer is physically separated from the separated groove, the cross-sectional thickness of the spacer should be approximately the distance between adjacent separated grooves, and the inner diameter of the spacer is greater than the inner diameter of the resilient retaining ring when the resilient retaining ring is compressed in the radial direction during assembly because this will allow the use of mechanical fingers as described above to install both the resilient retaining ring and the spacer simultaneously.

[0036] During assembly Figure 1In a method of a fuel cell stack 2, fuel cells 7 are stacked on top of a first current collector 44 and a first end plate 4. A second current collector 46 is placed on top of the fuel cells 7, and then a compression plate 22 and a compression housing 24 are placed on top of the second current collector 46. Flat sides 14, 16, 18, 20 are attached to the first end plate 4 and the compression housing 24 by fasteners (not shown) which can be removed and reattached, for example, when it is desired to replace fuel cells and / or flow field plates in the fuel cell stack. Spring assemblies 32 are placed in each spring recess 30, load disks 34 are placed on top of each spring assembly 32, and then the spring assemblies are compressed to a desired fuel cell stack compression pressure. Elastic retaining rings 36 are radially compressed and placed in the spring recesses 30 on top of the load disks 34 at a desired position in the spring recesses to apply a desired compression force on the load disks 34 and the spring assemblies 32 and then released such that their outer peripheral edges engage one of the separated grooves 38. In this way, the fuel cell stack maintains a fixed length while the second end plate 22 remains movable as the spring assemblies 32 are compressed and released due to, for example, fuel cell operation and / or creep of fuel cell components. If additional retaining rings and spacers are used, the load disks, elastic retaining rings, and spacers can be loaded into the spring recesses simultaneously in one step as described above.

[0037] Although the restraining mechanism has been shown in the form of a housing having sides, those skilled in the art will understand that the restraining mechanism can also be designed in other forms, for example, having compression bands and / or linkages.

[0038] Although the compression plate assembly has been described in the context of a fuel cell having a polymer electrolyte, it is contemplated that the compression assembly can also be applicable to other types of fuel cells, such as phosphoric acid and solid oxide, and their applications, such as flow batteries and electrolyzers.

[0039] All of the above-mentioned U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned and / or listed in the application data sheet are hereby incorporated by reference in their entirety.

[0040] Although specific elements, embodiments, and applications of the invention have been shown and described, it will be understood that the invention is not limited thereto since those skilled in the art can make modifications, particularly in accordance with the above teachings, without departing from the spirit and scope of the disclosure.

Claims

1. A fuel cell stack, comprising a first end plate, a compression plate assembly, a plurality of fuel cells interposed between the first end plate and the compression plate assembly, and a limiting mechanism for substantially preventing movement of the first end plate from the compression plate assembly, wherein, The compression plate assembly includes: A second end plate having a first flat surface and an opposite second flat surface, wherein the first flat surface is adjacent to the fuel cell stack; A compression housing adjacent to the opposite second flat surface of the second end plate, wherein the compression housing includes: A spring recess including a plurality of discrete grooves on an inner axial surface of the spring recess; A spring assembly within the spring recess and in contact with the second flat surface of the second end plate; A load disk within the spring recess and in contact with the spring assembly; and An elastic retaining device within the spring recess and in contact with the load disk; Wherein, The elastic retaining device engages one of the plurality of discrete grooves and the load disk; and The load disk and the spring assembly are physically separated from the inner axial surface of the spring recess.

2. The fuel cell stack according to claim 1, wherein The spring assembly includes a plurality of disc springs.

3. The fuel cell stack according to claim 1, wherein, The cross-sectional thickness of the load disk is greater than the cross-sectional thickness of the elastic retaining ring.

4. The fuel cell stack according to claim 1, wherein, The elastic retaining device further includes a first elastic retaining ring that engages one of the plurality of discrete grooves and an outer peripheral region of the load disk.

5. The fuel cell stack according to claim 4, wherein The elastic retaining device further includes a second elastic retaining ring that engages an adjacent one of the plurality of discrete grooves, wherein the first elastic retaining ring and the second elastic retaining ring are separated by a spacer, and thereby at least some of the compression force is transmitted from the first retaining ring to the second retaining ring through the spacer.

6. The fuel cell stack according to claim 4, wherein, The first elastic retaining ring includes a notch.

7. The fuel cell stack according to claim 4, wherein: The outer diameter of the spacer is less than the diameter of the spring recess, and When the elastic retaining ring is compressed in the radial direction during assembly, the inner diameter of the spacer is greater than the outer diameter of the elastic retaining ring.

8. The fuel cell stack according to claim 1, wherein, The load disk further includes an axial collar extending through the spring assembly.

9. The fuel cell stack according to claim 8, wherein, The housing further includes a collar recess on a bottom flat surface of the housing for receiving the axial collar.

10. The fuel cell stack according to claim 1, wherein, The restraint mechanism includes at least one compression band that defines the first end plate, the compression plate assembly, and the plurality of fuel cells interposed between the first end plate and the compression plate assembly.

11. The fuel cell stack according to claim 1, wherein, The spring recess includes a plurality of load grooves that extend in a direction parallel to the axial direction of the spring recess.

12. A method of assembling the fuel cell stack according to claim 1, the method comprising: Setting a spring assembly into a spring recess; Setting a load disk on top of the spring assembly into the spring recess such that the load disk is in contact with the spring assembly; Compressing the load disk in an axial direction relative to the spring recess such that an axial compression force is applied to the spring assembly; Compressing the elastic retaining device in a radial direction and setting the compressed elastic retaining device on top of the load disk; and And Releasing the compressed elastic retaining device such that the elastic retaining device engages one of the plurality of discrete grooves and the load disk.

13. The method according to claim 12, wherein, The elastic retaining device includes a first elastic retaining ring which, upon release of the compressed first elastic retaining ring, engages with one of the plurality of discrete grooves and an outer peripheral region of the load disk.

14. The method according to claim 13, wherein, The elastic retaining device further includes a second elastic retaining ring and a spacer, wherein the first elastic retaining ring and the second elastic retaining ring are separated by the spacer, and the method further comprises the steps of: Stacking the first elastic retaining ring and the second elastic retaining ring such that the first elastic retaining ring and the second elastic retaining ring are separated by the spacer; Compressing the stacked first elastic retaining ring and second elastic retaining ring in a radial direction with the spacer therebetween; Disposing the compressed first elastic retaining ring and second elastic retaining ring on top of the load disk with the spacer therebetween; and Releasing the compressed first elastic retaining ring and second elastic retaining ring such that the second elastic retaining ring engages with an adjacent one of the plurality of discrete grooves, whereby at least some of the load compression force is transferred from the first retaining ring to the second retaining ring through the spacer upon release of the compressed first elastic retaining ring and second elastic retaining ring.

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