ALIGNMENT DEVICE FOR AN ELECTRIC CELL STACK, PARTICULARLY A FUEL CELL STACK

Abstract

Disclosed is an electric cell stack comprising at least a plurality of electric plates and a plurality of insulating layers, wherein the stack of the plurality of electric plates and insulating layers are alternatingly stacked in such a way that the electric plates are separated by insulating layers, and the electric plates and/or the insulating layers are aligned to each other, wherein each electric plate has a first alignment through hole and a second alignment through hole, wherein at and/or in the alignment through holes inner alignment elements are provided for aligning the electric plates and the insulating layers, wherein each inner alignment element has a base plate and an adjusting portion protruding from the base plate, wherein the adjusting portion of one alignment element extends through at least a first electric plate, a first insulating layer, a second electric plate and a second insulating layer.

Claims

1-13. (canceled)

14. Electric cell stack comprising at least a plurality of electric plates and a plurality of insulating layers, wherein the stack of the plurality of electric plates and insulating layers are alternatingly stacked in such a way that the electric plates are separated by insulating layers, and the electric plates and/or the insulating layers are aligned to each other, wherein each electric plate has a first alignment through hole and a second alignment through hole, wherein at and/or in the alignment through holes inner alignment elements are provided for aligning the electric plates and the insulating layers, wherein each inner alignment element has a base plate and an adjusting portion protruding from the base plate, wherein the adjusting portion of one alignment element extends through at least a first electric plate, a first insulating layer, a second electric plate and a second insulating layer, so that an overall height H of the alignment element is equal to or greater than two cell pitches H2*(D.sub.EP+D.sub.IL), and wherein the adjusting portion of each alignment element has a first adjusting part and a second adjusting part, wherein a size and/or shape of the first adjusting part is adapted to the size and/or shape of the first alignment through hole and/or a size and/or shape of the second adjusting part is adao the size and/or shape of the second alignment through hole.

15. Electric cell stack according to claim 14, wherein the first alignment through hole has a first shape, preferably an elongated shape, and the second alignment through hole has a second shape, preferably circular shape, wherein the first and second shape are different.

16. Electric cell stack according to claim 14, wherein the adjusting portion of the alignment element is recessed from the base plate, so that a step is formed between the base plate and the adjusting portion.

17. Electric cell stack according to claim 14, wherein at the opposite side of the adjusting portion, the base plate of the alignment element has a recess which is dimensioned to accommodate the adjusting portion of an adjacent second alignment element, so that one alignment element is adapted to be stacked on a further alignment element.

18. Electric cell stack according to claim 14, wherein the second adjusting part is recessed from the first adjusting part, thereby forming a step between the first and the second adjusting part of the alignment element.

19. Electric cell stack according to claim 14, wherein a height h.sub.a1 of the first adjusting part of the adjusting portion is designed to correspond to at least one cell pitch, i.e. the thickness of one electric plate plus one insulating layer, or an integer multiple of cell pitches, h.sub.a1=x* (D.sub.EP+D.sub.IL), with x being an integer, and a height h.sub.a2 of the second adjusting part of the adjusting portion is designed to be equal to or greater than at least one cell pitch, or an integer multiple of cell pitches, i.e. the thickness of one electric plate and one insulating layer, h.sub.a2x*(D.sub.EP+D.sub.IL), with x being an integer.

20. Electric cell stack according to claim 19, wherein the height h.sub.a2 of the second adjusting part of the adjusting portion is designed to be greater than at least one cell pitch, or an integer multiple of cell pitches h.sub.a2>x*(D.sub.EP+D.sub.IL), with x being an integer, so that the second adjusting portion exceeds the height of one cell pitch or of an integer multiple of one cell pitch by an excess portion, and wherein at the opposite side of the adjusting portion, the base plate of the alignment element has a recess which is dimensioned to accommodate the excess portion of the second adjusting part of the adjusting portion of an adjacent second alignment element, so that one alignment element is adapted to be stacked on a further alignment element, wherein a depth of the recess is adapted to accommodate the excess portion of the second adjusting part of the adjusting portion (34), so that h.sub.a2x*(D.sub.EP+D.sub.IL)+h.sub.r.

21. Electric cell stack according to claim 14, wherein the alignment elements are arranged in such a way that for each single electric plate one of the alignment through holes is in contact with the base plate of a first alignment element, wherein the other alignment through hole of the very same electric plate is in contact with the adjusting portion of another second alignment element.

22. Electric cell stack according to claim 15, wherein the base plate of the inner alignment element is arranged at/in the first alignment through hole having the first shape.

23. Electric cell stack according to claim 14, wherein adjacent electric plates and the corresponding first and second alignment through hole are arranged in such a way that the first alignment through hole of one electric plate is aligned with the second alignment through hole of the adjacent electric plate.

24. Electric cell stack according to claim 14, wherein the electric plate has at least one protruding structure which protrudes from a basis of the electric plate in direction to the adjacent insulating layer with a height D.sub.PS, and wherein a height h.sub.b of the base plate of the alignment element is designed to be equal or less than the height D.sub.PS of the protruding structure.

25. Electric cell stack according to claim 14, wherein the alignment element is made of an electrically isolating material, preferably a plastic material; wherein preferably, the alignment element is molded, preferably injection molded.

26. Electric cell stack according to claims 14, wherein the electric cell stack is a fuel cell stack, the electric plate is a bipolar plate (BPP) consisting of an anode plate and a cathode plate which are fixed to each other, and the insulating layer is a multilayer membrane electrode assembly (MEA).

Description

The figures show:

[0037] FIG. 1: a schematic top view of a bipolar plate of fuel cell stack according to a first embodiment,

[0038] FIG. 2: a schematic top view of a membrane electrode assembly of fuel cell stack according to a first embodiment,

[0039] FIG. 3: a schematic cross section through a part of a fuel cell stack according to a first embodiment,

[0040] FIG. 4: a schematic cross section through a part of a fuel cell stack according to a second embodiment,

[0041] FIG. 5: a schematic enlarged cross section view through alignment elements as illustrated in FIG. 3, and

[0042] FIG. 6: a schematic enlarged cross section view through alignment elements as illustrated in FIG. 4.

[0043] In the following same or similar functioning elements are indicated with the same reference numerals.

[0044] In the following the principle of the invention is described for the case of a fuel cell stack. However, the principle can be likewise applied to any other kind of electric cell or electric cell stack.

[0045] FIG. 1 shows a simplified schematic top view of a bipolar plate 2 (electric plate) of a fuel cell stack 1 according to a first embodiment. Usually, each bipolar plate 2 is a combination of an anode plate and a cathode plate which are fixed to each other. Each anode and cathode plate has a front side and a back side, wherein the front or reactant side faces an adjacent membrane electrode assembly (not shown in FIG. 1) and the back or coolant sides faces each other. Further each bipolar plate 2 has a plurality of openings 4, 6, namely manifolds, for providing (openings 4) and discharging (openings 6) reactant and coolant to and from the bipolar plate 2. For distributing the reactant and coolant over the plate the bipolar plates may further have protruding structures (not shown) which form fluid flow fields 8 for the respective reactant/coolant. For sealing the flow fields to the environment, the plates are further equipped with so called bead seals 10 which protrude from a basis 12 of the plate and may also extend over the height of the flow field structures.

[0046] Furthermore, the bipolar plate 2 has a first alignment through hole 14 and a second alignment through hole 16, wherein the first alignment through hole 14 is arranged at a different location than the second alignment through hole 16. In FIG. 1, the first alignment through hole 14 is diametrically opposite arranged to the second alignment through hole 16. Thereby, the first and second alignment through holes 14, 16 are symmetric concerning a rotation of 180 around a surface normal of the bipolar plate.

[0047] As further illustrated in FIG. 1, the first alignment through hole 14 has an elongated shape, whereas the second alignment through hole 16 has a circular shape. Thus, both alignment through holes differ in shape and size. However, it would be also possible that the first and the second alignment through holes 14; 16 have both elongated shapes, wherein a longitudinal axis of the first alignment through hole 14 is may be perpendicular to the longitudinal axis of the second alignment through hole 16.

[0048] FIG. 2 illustrates a membrane electrode assembly 18, which may be used in combination with the bipolar plate of FIG. 1 in a fuel cell stack. As can be seen in FIG. 2, also the membrane electrode assembly 18 is equipped with alignment through holes 20, 22 which allows for an alignment of the membrane electrode assembly 18 with bipolar plate 2. As can be seen form a comparison of FIG. 1 and FIG. 2, the membrane electrode assembly 18 may have the same or a similar shape as the bipolar plate 2, and has an active region 24 which is in the same area as the flow field region of the bipolar plate 2. The active region 24 of the membrane electrode assembly 18, is usually the 3-layered electrode membrane assembly consisting of the membrane which is sandwiched between an anode and a cathode. The other structures, such as manifold openings 26 or alignment through holes 20, 22 are preferably provided in a subgasket material 28, which surrounds and carries the active region 24 of the 3-layer membrane electrode assembly, and electrically isolates the sandwiching bipolar plates. Additionally, the membrane electrode assembly may further comprise, on both sides gas, diffusion layers (not illustrated), which are also arranged in the active region 24 and cover the anode and cathode of the 3-layer membrane electrode assembly 18.

[0049] FIGS. 3 and 4 and their enlarged view 3a and 4a, how each a schematic cross section along a line II-II of FIG. 1 through the alignment through holes 14; 16 of two embodiments for a fuel cell stack 1 comprising a plurality of bipolar plates 2-1, 2-2, 2-3, 2-4 with interlaying membrane electrode assemblies 18-1, 18-2, 18-2, 18-4. For the sake of simplicity, in the cross-section views of FIGS. 3, as well as of FIG. 4, the bipolar plates 2 are schematically illustrated as single plates with protruding structures 10, which protrude over a basis 12 by the height D.sub.PS.

[0050] Additionally, the embodiments of the fuel cell stack 1 illustrated in FIGS. 3 and 4 show a special stacking order for the bipolar plate and membrane electrode assemblies. In that, every second bipolar plate 2-2, 2-4 . . . is rotated by 180 compared to bipolar plates 2-1, 2-3 . . . , so that the first alignment through holes 14-1, 14-3 . . . of the first bipolar plates 2-1, 2-3 . . . are aligned with the second alignment through hole 16-2, 16-4 . . . of the second bipolar plates 2-2, 2-4 . . . . The same may apply for the membrane electrode assemblies 18.

[0051] The bipolar plates 2 and the multi-layer membrane electrode assembly 18 are aligned to each other by means of several alignment elements 30. FIG. 5 and FIG. 6 show enlarged views of the alignment elements 30 according to the embodiment shown in FIG. 3 (FIG. 5), wherein in FIG. 6 an enlarged view of an alignment element 30 according the second embodiment of FIG. 4 is illustrated.

[0052] Due to the voltage potential difference between the bipolar plates 2, the alignment element 30 is made of an electrically isolating material, for example a plastic material, which is molded, preferably injection molded. In a special embodiment, which is not illustrated, the alignment element 30 may also be an integral part of the multi-layer membrane electrode assembly 18, preferably of the subgasket 28.

[0053] As can be seen in FIGS. 5 and 6, the alignment element 30 has a base plate 32 and a adjusting portion 34, wherein the adjusting portion 34 is recessed from the base plate 32 so that a step 33 is formed between the base plate 32 and the adjusting portion 34. Thus, the base plate 34 has a height h.sub.b and the adjusting portion has an overall height h.sub.a.

[0054] The adjusting portion 34 in turn comprises a first adjusting part 36 and a second adjusting part 38, wherein the second adjusting part 38 is recessed to the first adjusting part 38, thereby forming a further step 37 between the first and the second adjusting part 36, 38 of the adjusting portion 34. Thereby the first adjusting part 36 has a height h.sub.a1 and the second adjusting part 38 has a height h.sub.a2.

[0055] Opposite to the adjusting portion 34, the base plate 32 of the alignment element 30 has a recess 39. A size and depth h.sub.r of the recess 39 is chosen such that the adjusting portion 34, and particularly the adjusting part 38, of an adjacent alignment element 30 can be accommodated in the recess 39, so such that the alignment elements 30 can be stacked onto each other. This will be described in detail further below.

[0056] Referring again to FIGS. 3 and 4, a height of the base plate 32 is preferably designed to resemble a thickness D.sub.PS of the protruding structure 10, e.g. a bead seal, of the bipolar plate 2: h.sub.bD.sub.PS, preferably h.sub.bD.sub.PS. This allows for an arrangement of the inner alignment element 30 at the bipolar plate 3 without any further space requirement for the alignment element 30. Preferably, the size or the height of the base plate is designed so that even after compression of the stack the height h.sub.b of the base plate 32 is still less than the height of the protruding structure 10. Thereby it should be noted that all heights relation as described in this application may also apply after compression of the stack.

[0057] As can also be seen in FIGS. 3, 4, the overall height of the alignment element H is designed to be at least equal to or greater than two cell pitches d=D.sub.MEA+D.sub.BPP, wherein one cell pitch is defined as the distance between two unit fuel cells, wherein each unit fuel cell consists of a bipolar plate 2 and a membrane electrode assembly 18: H2*(D.sub.MEA+D.sub.BPP).

[0058] In the illustrated embodiments of FIGS. 3 and 5, and FIGS. 4 and 6, respectively, the heights h.sub.a1, h.sub.a2 of the adjusting potion 34 are differently designed. In the embodiment as illustrated in FIG. 5 and FIG. 3, the height h.sub.a1 of the first adjusting part 36 resembles one cell pitch (h.sub.a1D.sub.BPP+D.sub.MEA), whereas the height h.sub.a2 of the second adjusting part 38 is greater than one cell pitch: (h.sub.b2D.sub.BPP+D.sub.MEA). In this embodiment, it is preferred that also the membrane electrode assembly 18 is equipped with first and second alignment through holes 20, 22, which differ in size and shape.

[0059] In the other preferred embodiment, which is shown in FIG. 6 and FIG. 4, the height h.sub.a1 of the first adjusting part 36 is less than the height of the protruding structure (h.sub.a1D.sub.PS), whereas the height h.sub.a2 of the second adjusting part 38 is greater than the one cell pitch plus the heights of a membrane electrode assembly: (h.sub.a2D.sub.BPP+2*D.sub.MEA). This allows for a fuel cell stack 1, wherein only the bipolar plates 2 need to be equipped with first and second alignment through holes 14, 16. The membrane electrode assembly 18 may be provided with equal sized alignment through holes 20, 22.

[0060] As can be seen in FIGS. 3 and 4, the size of the first adjusting part 36 may resemble the size of the first alignment through hole 14 of the bipolar plate 2 and the size of the second adjusting part 38 may resemble the size of the second alignment through hole 16 of the bipolar plate 2. For the membrane electrode assembly 18, the situation is different as for example in FIG. 3, likewise the bipolar plate 2, the size of the first adjusting part 36 may resemble the size of the first alignment through hole 20 of the membrane electrode assembly 18 and the size of the second adjusting part 38 may resemble the size of the second alignment through hole 22 of the membrane electrode assembly 18. In the embodiment of FIG. 4, in contrast, the sizes of both alignment through holes 20 and 22 of the membrane electrode assembly 18 may both resemble the size of the second adjusting portion 38.

[0061] Further with reference to FIGS. 3 and 4, the alignment elements are alternatingly arranged at the bipolar plates 2. That means, at bipolar plate 2-1, a first alignment element 30-1 is arranged at the first alignment through hole 14-1 of the first bipolar plate 2-1, so that the base plate 32 contacts the first bipolar plate 2-1 and the first adjusting portion 36-1 of the first alignment element 30-1 extends through the first alignment hole 14-1. In the second alignment through hole 16-1 of the first bipolar plate 2-1 in turn, a second alignment element 30-2 is arranged in such a way that its second adjusting portion 38-2 extends through the second alignment through hole 16-1 of the first bipolar plate 2-1.

[0062] At the adjacent bipolar plate 2-2, the situation is the same, but the alignment through holes 14-2, 16-2 are vice versa, as the bipolar plate 2-2 is rotated by 180. Thus, the second adjusting portion 38-1 of the first alignment element 30-1 extends through the corresponding second alignment through hole 16-2 of the second bipolar plate 2-2, whereas at the first alignment through hole 14-2 of the second bipolar plate 2-2, the base plate 32-3 of a third alignment element 30-3 is arranged, and its first adjusting portion 36-3 extends through the first alignment through hole 14-2 of the second bipolar plate 2-2.

[0063] For the third bipolar plate 2-3 or in general for the n+1 bipolar plate in the stack, the situation is the same as for the first bipolar plate and for the fourth bipolar plate 2-4 or in general the 2n bipolar plate the situation is the same as for the second bipolar plate 2-2.

[0064] As mentioned above and illustrated in the enlarged views of FIGS. 3a and 4a, the overall height ha of the adjusting portion 34 of the alignment element 30 is adapted to be greater than two cell pitches d. In other words, the adjusting portion 34-1 of the first alignment element 30 extends through the second alignment through hole 16-2 of the second bipolar plate 2-2 and the second membrane electrode assembly 18-2 and protrudes over the second membrane electrode assembly 18-2 and into the space provided by the protruding structure 10-3 of the third bipolar plate 23. This design allows for a stacking of the alignment elements 30-1 and 30-3, as the part of the adjusting part 38 which extends into the space of the third bipolar plate can be accommodated in the recess 39-2 of the adjacent alignment element 30-2.

[0065] For that, the recess 39 of a first alignment element 30-1 and the second adjusting part 38-1 of the first alignment element 30-1, are preferably designed so that the second adjusting part 38 of the second alignment element 30-2 can be accommodated in the recess 29 of the first alignment element 30-1. Thus, a depth h.sub.r of the recess 39 is designed so that the part of the adjusting part 38 which extends into the space of the third bipolar plate is adapted to the depth h.sub.r of the recess.

[0066] For compensating for the height reductions, when the stack is compressed after stacking, the alignment through holes and the alignment elements may be designed so that during stacking only a loose fit is provided between the aligning parts 36, 38 and the corresponding alignment through holes 14, 16. When the stack is compressed, the alignment elements may be deformed for filling out the remaining space. Alternatively or additionally, the recess 39 of the base plate 22 may be made deeper than necessary for accommodating the additional height of the alignment element during the compression.

[0067] In summary by providing alignment through holes that cooperate with respective alignment elements it is possible to provide a fuel cell stack which allows for a more efficient stacking and a more reliable alignment of the stack components without the risk of loosing the alignment when the stack is removed from the alignment feature. Simultaneously, the cooperating alignment through holes and alignment elements allow balancing of manufacturing tolerance in the thickness of the plates.

REFERENCE NUMERALS

[0068] 1 Fuel cell stack

[0069] 2 Bipolar plate

[0070] 4, 6 reactant/coolant manifold

[0071] 8 Flow field part

[0072] 10 protruding element

[0073] 12 basis of the bipolar plate

[0074] 14 first alignment through hole (bipolar plate)

[0075] 16 Second alignment through hole (bipolar plate)

[0076] 18 Membrane electrode assembly

[0077] 20 First alignment through hole (membrane electrode assembly)

[0078] 22 Second alignment through hole (membrane electrode assembly)

[0079] 24 active region

[0080] 26 manifold openings

[0081] 28 subgasket

[0082] 30 Alignment element

[0083] 32 Base plate

[0084] 34 adjusting portion

[0085] 33 Step between base plate and adjusting portion

[0086] 36 first adjusting part

[0087] 38 second adjusting part

[0088] 37 step between first and second adjusting part

[0089] 39 Recess

[0090] H Overall height of the alignment element

[0091] h.sub.b Height of the base plate

[0092] h.sub.a Height of the adjusting portion

[0093] h.sub.a1 Height of the first adjusting part

[0094] h.sub.a2 Height of the second adjusting part

[0095] D.sub.MEA Thickness of the membrane electrode assembly

[0096] D.sub.BPP Thickness of the bipolar plate

[0097] D.sub.PS Thickness of the protruding portion of the bipolar plate d Cell pitch