Device and method for assembling a cell stack

Abstract

A device for assembling a cell stack (7), in particular fuel cell stack, comprises a handling device (2) including a gripper (6) and a positioning and pressure system (10), which is designed for compressing a partially finished cell stack (7). The positioning and pressure system (10) comprises a lifting device (11) which is provided for receiving the cell stack (7) at any manufacturing stage, and a lateral fixing device (12) which is located above the lifting device (11) and is constructed from a plurality of assemblies (13, 14), wherein said assemblies (13, 14) are provided for bearing against the cell stack (7) in the vertical and horizontal direction and are adjustable and fixable in the two directions mentioned.

Description

[0001] Device and method for assembling a cell stack

[0002] The invention relates to a method for assembling a cell stack, in particular a stack of electrochemical cells, for example a fuel cell stack. Furthermore, the invention relates to a device suitable for carrying out such an assembly method.

[0003] DE 10 2016220 173 A1 discloses an assembly device for stacking a fuel cell stack. This assembly device is used to stack a fuel cell stack consisting of alternating membrane electrode assemblies and bipolar plates vertically. The known assembly device has a substantially cuboid-shaped assembly space defined by a plurality of vertically oriented support bars. The support bars, which are designed to position the membrane electrode assemblies and bipolar plates relative to one another during stacking, are movable horizontally.

[0004] DE 10 2017 100 362 A1 discloses a system for assembling and compressing fuel cell stacks. This system comprises a fuel cell stack housing and a press with a plurality of press rods that compress the fuel cell stack, which was created by stacking the fuel cell components in the fuel cell stack housing.

[0005] A device for automatically stacking a fuel cell stack described in DE 102015 220 399 A1 comprises a pressure element that is provided for pressurizing the stacked fuel cells and is also rotatable. The automatic stacking device is also intended to offer the possibility of detecting defective parts and testing a stacked body for airtightness. Various compression systems for fuel cell stacks are described in the documents DE 10 2020 127 917 A1 and DE 10 2021 112 699 A1. In these cases, tensioning straps or strip-shaped retaining devices connected to the end plates of a cell stack are provided for compressing fuel cell stacks.

[0006] DE 10 2018 119 633 A1 proposes an encapsulation for assembling a fuel cell stack, which prestresses and seals a fuel cell arrangement in a stacking direction of the fuel cell.

[0007] A fuel cell stack assembly device described in DE 20 2020 105 427 U1 comprises a magnetic attachment part that extends perpendicular to a base of the assembly device and attracts multiple fuel cell units. The magnetic attachment part engages notches or recesses in fuel cell elements.

[0008] A device described in US 2020 / 0091542 A1 uses a robot to handle battery plates. The orientation of battery components is supposed to be detectable using a sensor.

[0009] Further devices and methods for handling components of electrochemical systems are known from documents CN 207265167 U, CN 107706438 A, and CN 113036200 A. In the latter case, binding elements are provided for holding a compressed cell stack together.

[0010] The invention is based on the object of achieving progress in the production of cell stacks, in particular fuel cell stacks, compared to the cited prior art, wherein a particularly favorable ratio between assembly effort and process reliability is sought. This object is achieved according to the invention by a device suitable for assembling a cell stack, in particular a stack of electrochemical cells, having the features of claim 1. The object is likewise achieved by a method for assembling a cell stack, in particular a fuel cell stack, according to claim 8. Configurations and advantages of the invention explained below in connection with the assembly method also apply mutatis mutandis to the assembly device, and vice versa.

[0011] The device provided for assembling a cell stack comprises a handling device including a gripper suitable for lifting flat objects, for example in the form of a vacuum gripper, or a plurality of such grippers, as well as a positioning and pressure system that interacts with the gripper(s) and is designed to compress a partially completed cell stack. The term "compression" does not necessarily mean that the vertical dimensions of the cell stack will be significantly reduced at any time. In any case, the cell stack to be assembled is aligned vertically, which is equivalent to a horizontal alignment of the flat components of the cell stack to be stacked on top of one another. The horizontal position of the cell components facilitates high-speed assembly of the stack.

[0012] The positioning and pressure system comprises a lifting device designed to accommodate the cell stack at any stage of production, as well as a lateral fixing device located above the lifting device. This device is designed to position the cell stack vertically and horizontally and is adjustable in a variety of ways in these directions and can be locked as needed. The fixing device comprises several assemblies that engage at various points on the cell stack.

[0013] For example, two such assemblies are provided, with a first assembly and a second assembly arranged mirror-symmetrically to each other next to the cell stack, i.e., flanking the cell stack on both sides. Likewise, configurations are possible in which the fixing device is constructed from three, four, or more identical or different assemblies. The at least two assemblies, which are arranged in particular in a symmetrical arrangement, can be adjusted simultaneously or independently of one another.

[0014] The cell stack, which consists of several assemblies, is held in place by applying pressure during its formation, not just after completion. This, together with the horizontal alignment of the cell components, promotes not only high-speed assembly but also high geometric precision. In particular, the compression of the cell stack during the assembly process prevents cell components from slipping within the stack.

[0015] According to a first possible group of embodiments, each of the two or more assemblies of the entire, multi-part fixing device of the assembly device comprises a plurality of horizontally displaceable fixing elements, which are provided for supporting superimposed bipolar plates contained in the cell stack both laterally and vertically. Support in the vertical direction implies the introduction of a force acting in the vertical direction into the cell stack.

[0016] For example, three or more fixing elements arranged one above the other, each intended for contacting a bipolar plate, are mounted in an individually spring-loaded manner in a common, horizontally and vertically adjustable holder. A single clamping device can be assigned to the adjustable holder, which is designed to simultaneously clamp or release all fixing elements located in the holder, as needed.

[0017] In addition to the horizontally movable fixing elements, there is an optional switchable MEA retention device, which is designed to press down a membrane electrode assembly (MEA) located at the top of the partially completed cell stack. If a bipolar plate is placed on the MEA, the MEA retention device is deactivated.

[0018] According to a second possible group of configurations, the lateral assemblies of the fixing device each have an angular gripper against which the cell stack rests both laterally and upwardly. Compared to the first possible group of configurations, this results in a significantly simplified assembly device design. This design is particularly suitable in cases where the bipolar plates are bent during assembly, as will be explained in more detail below.

[0019] In each of the two possible groups of configurations, the lifting device provided for receiving the cell stack can comprise three plates arranged parallel to one another, namely a base plate, a middle plate, and an upper plate intended for supporting the cell stack. A pressure measuring system can be provided between the base plate and the middle plate, while the upper plate is mounted vertically displaceably on the middle plate by means of springs. In particular, the two lower plates can be perforated in any desired manner, provided the intended supporting function is fulfilled.

[0020] Optionally, a distance measuring device designed to measure the distance between the upper plate and the middle plate is available. With knowledge of the properties of the springs mentioned, the distance measuring device can also be used for pressure measurement, thus providing redundancy in force measurement together with the pressure measuring system located below on the base plate.

[0021] The process for assembling a cell stack is characterized by the fact that the cell stack being constructed, which comprises bipolar plates arranged horizontally parallel to one another and membrane electrode assemblies, is subjected to pressure during its creation. This occurs when, after the addition of each additional bipolar plate, a downward pressure is exerted on the cell stack, which is still unfinished at this stage of production, in addition to the weight of the cell components. This pressure pushes the cell stack downwards as a whole, compressing the springs located beneath the cell stack that support it, a process known as overpressing. After the overpressing that occurs during the assembly of the cell stack, the vertically downward pressure is reduced so that the cell stack is raised again somewhat by the springs.Finally, in the then assumed state with at least partially expanded springs, at least the upper bipolar plate is fixed in the vertical and lateral direction while maintaining a partial amount of the downward pressure.

[0022] The springs, which are compressed during the overpressure, can be arranged, in particular as described, between height-adjustable plates and are designed, for example, as coil springs or leaf springs. Pneumatic support is also possible. In all cases, a lifting system that enables height adjustment of the plates can use force measurements, length measurements, or a combination of force measurements and geometric measurements for adjustment.

[0023] A first process variant provides that the bipolar plates as well as the membrane electrode assemblies are placed alternately on the cell stack in a completely flat state.

[0024] According to an alternative method variant, at least the bipolar plates are placed in a curved state onto the cell stack while exerting a vertically downward force. First, the central region of the bipolar plate is pressed onto the cell stack and, while maintaining pressure, the entire bipolar plate is then brought into contact with the cell stack, returning it to its original flat shape. A particular advantage of the invention lies in the fact that the cell stack is continuously compressed during its formation. This advantage applies regardless of the type of cell involved, for example, fuel cells or electrolysis cells. Tilting the stack during assembly is never necessary.Depending on the design of the positioning and pressure system, which prevents stack components from slipping during assembly, the stack components can be aligned not only to their outer geometry but also to structures further inside, such as an active field. Mounting the stack components in their final alignment is particularly advantageous in cases where subsequent movement of components for adjustment purposes would no longer be easily possible. Such a limitation of subsequent adjustability can arise, for example, due to seals, such as silicone seals, located in the cell stack.

[0025] Two exemplary embodiments of the invention are explained in more detail below with reference to a drawing. These show, partly schematically:

[0026] Fig. 1 shows a first embodiment of a device for assembling a stack of electrochemical cells,

[0027] Fig. 2 shows a schematic section of a second embodiment of a device for assembling a cell stack in a first operating state,

[0028] Fig. 3 shows the assembly device according to Fig. 2 in a second operating state.

[0029] The following explanations refer to both exemplary embodiments, unless otherwise stated. Parts that correspond to one another or have essentially the same function are identified by the same reference numerals in all figures. A production system, identified overall by the reference numeral 1, is designed as a device for assembling a cell stack 7, namely a fuel cell stack. The production system 1, i.e. assembly device, comprises a handling device 2 for lifting and positioning flat fuel cell components to be assembled. The handling device 2 includes load-bearing elements 3 and movable elements 4, wherein the movable elements 4 can be arms of a not further shown articulated-arm robot. In a manner not shown, the handling device 2 can also comprise movable elements 4 that are exclusively linearly movable.

[0030] The elements 3, 4 carry a gripper 6 of known design, for example, a vacuum gripper. Alternatively, the gripper 6 can utilize other physical principles, such as adhesion or magnetism. A position detection system 5, only indicated in Fig. 1 but also present in the embodiment according to Figs. 2 and 3, is designed in the present case to detect the positioning of an object relative to the vacuum gripper 6. In a manner not shown, stationary position detection devices can be provided in addition to the position detection system 5 shown in Fig. 1.

[0031] With the help of the handling device 2, a fuel cell stack 7 is constructed, which is also referred to as a stack for short. Flat components of the stack 7 are bipolar plates 8 and membrane electrode assemblies 9. The fuel cell stack 7, which is currently being formed, is kept under pressure during its construction. For this purpose, a positioning and pressure system, designated overall by 10, is provided. The positioning and pressure system 10 includes a lifting device 11, on which the partially completed stack 7 is located. Furthermore, the positioning and pressure system 10 has a lateral fixing device, designated overall by 12, which in the present case comprises exactly two assemblies 13, 14, i.e., a first assembly 13 and a second assembly 14, wherein the assemblies 13, 14 are mirror-symmetrical to one another.Without limiting the generality, in the present case, the first assembly 13 is referred to as the left assembly and the second assembly 14 as the right assembly of the fixing device 12. In modified embodiments, for example, there are four assemblies 13, 14, which are located on all four sides of the stack 7, which is rectangular in plan view.

[0032] The stack 7 is constructed vertically, which means that the various components 8, 9 of the stack 7 are always aligned horizontally during its construction. The height of the stack 7 is adjustable using a lifting system 15, which is part of the lifting device 11. The lifting system 15 is designed to vary the height of a base plate 16, which is located below a center plate 18. Between the aforementioned plates 16, 18 is a pressure measuring system 17, i.e., a measuring system similar to a scale. On the center plate 18, in turn, are several springs 19 designed as compression springs, which support an upper plate 21, also referred to as a support device, and which supports the stack 7 to be assembled. A distance measuring device 20 acting between the center plate 18 and the upper plate 21 can be used as an additional force measuring device—given known properties of the springs 19.

[0033] A linear guide 22 is provided to enable a defined linear displacement between the center plate 18 and the support device 21. When the support device 21 is lifted to its maximum height from the center plate 18 and thus also from the base plate 16, an end stop 35 is activated. The footprint of the support device 21 is adapted to the dimensions of the components 8, 9 of the fuel cell stack 7.

[0034] In order to hold the various components 8, 9 of the fuel cell stack 7 in their intended position during its formation and to exert a force F in the vertical direction on the stack 7, the aforementioned fixing device 12 and an MEA retainer 23 are provided. The MEA retainer 23 is intended exclusively for contacting the membrane electrode assembly 9 located at the top of the stack 7. As soon as this membrane electrode assembly 9 is covered by a bipolar plate 8, the MEA retainer 23 is deactivated. An actuating mechanism of the MEA retainer 23, i.e., a device for retaining a membrane electrode assembly 9, is designated by 24.

[0035] In the embodiment according to Fig. 1, each assembly 13, 14 of the fixing device 12 has several, in the present case three, displaceable fixing elements 25. A spring 26 acts on each of the fixing elements 25, designed as a slider, which pushes the respective fixing element 25 towards the stack 7. The entirety of the fixing elements 25 and springs 26 of each assembly 13, 14 is arranged in a receptacle 27. A guide device for horizontally displacing the receptacle 27 is designated 28. The guide device 28 can be actuated by means of an actuating device 29. To block the fixing elements 25 in the receptacle 27, a clamping device 30 is provided, which comprises a clamping plate 31. A spring 32 acts on the clamping plate 31 in a vertical, clamping direction. A pulling element 33 acts in the opposite direction and can be actuated by means of an actuating device 34.

[0036] 2 and 3 differs from the embodiment according to Fig. 1 in that the assemblies 13, 14 of the lateral fixing device 12 are designed to be considerably simpler. In the case of Figs. 2 and 3, the function of the assemblies 13, 14 is each taken over by a gripper 36, which both represents a lateral stop against the components 8, 9 of the fuel cell stack 7 and also compresses the stack 7 as a whole. The bipolar plates 8 are, as sketched in Fig. 2, initially picked up in a completely horizontal orientation by the vacuum gripper 6. The same applies to the picking up of the membrane electrode assemblies 9 by the handling device 2. In this respect, there is no difference between the method that can be carried out with the device according to Figs. 2 and 3 and the method that is carried out with the device according to Fig. 1. Instead of a single vacuum gripper 6, in the case of Fig.2 and 3 a plurality of vacuum grippers 6 are present.

[0037] Following the lifting of the bipolar plate 8, the method illustrated in Figs. 2 and 3 has a special feature compared to the method carried out with the production system 1 according to Fig. 1. As can be seen in Fig. 3, the bipolar plate 8, which has been lifted with the grippers 6, for example vacuum grippers, is bent before being placed on the stack 7, so that the edges of the bipolar plate 8 are bent upwards. In this state, the central region of the bipolar plate 8 is first placed on the stack 7. Subsequently, the bipolar plate 8 is returned to its original flat shape with increasing force F. Once this process is complete, the two grippers 36 grip the stack 7 so that it remains in its compressed form. The grippers 36 are then temporarily removed from the stack 7 to enable the next initially curved component 8, 9 to be placed on the fuel cell stack 7.

[0038] In the embodiment according to Fig. 1, as already mentioned, the bipolar plates 8 are not deformed during the construction of the stack 7. If a bipolar plate 8 is to be placed on the stack 7, the MEA retainer 23 is first opened. The correct placement position of the bipolar plate 8 is monitored with the aid of the position detection system 5. After the bipolar plate 8 has been placed, it initially remains fixed to the gripper 6. The handling device 2 then presses the bipolar plate 8 onto the stack 7 in such a way that the latter is pressed against the springs 19. Compared to the deformation of the springs 19, the stack 7 itself is deformed at most insignificantly. The overpressure in the vertical direction, expressed in mm, corresponds to the sum of the thickness of the bipolar plate 8 and a defined additional travel, which is significantly less than the thickness of the bipolar plate 8.

[0039] If the amount of additional travel is reached by the overpressure, there is no longer any compression force on the lateral fixing elements 25. The lateral, movable fixing elements 25 are, as can be seen from Fig. 1, designed such that they enable both lateral and vertical support of the bipolar plates 8. In the state in which no vertical force acts on the fixing elements 25, they are moved laterally away from the stack 7 with the aid of the guide device 28 and actuating device 29. The stack 7 is then pressed further downwards by the handling device 2 until the maximum amount of overpressure is reached. In this state, the fixing elements 25 are brought back into contact with the bipolar plates 8 with the clamping device 30 open, but offset by exactly one bipolar plate 8. The clamping device 30 can now be closed again.The setting of the lifting device 11 is adjusted during the described process, with measurement redundancy being provided by the various measuring devices 17, 20. If a membrane electrode assembly 9 is placed on the fuel cell stack 7 under construction, the described overpressure does not occur.

[0040] List of reference symbols

[0041] manufacturing facility

[0042] Handling device supporting element movable element

[0043] Position detection system

[0044] Gripper, vacuum gripper

[0045] Fuel cell stack, stack

[0046] Bipolar plate

[0047] Membrane electrode assembly, MEA

[0048] Positioning and pressure system

[0049] Lifting device lateral fixing device first assembly of the fixing device second assembly of the fixing device

[0050] Lifting system

[0051] Base plate

[0052] Pressure measuring system

[0053] center plate

[0054] Feather

[0055] Distance measuring device upper plate, receiving device

[0056] Linear guide

[0057] MEA retention

[0058] Actuating mechanism of the MEA restraint lateral, movable fixing element

[0059] Spring acting on fixing element 25

[0060] Holder for the fixing elements

[0061] Guide device for horizontal displacement of the holder 27

[0062] Actuating device for the guide device 28

[0063] clamping device

[0064] Clamping plate 32 spring, acting on the clamping plate 31

[0065] 33 Tension element, acting against the clamping force

[0066] 34 Actuating device for actuating the pulling element

[0067] 35 End stop

[0068] 36 grippers

[0069] F Force

Claims

Patent claims 1. Device for assembling a cell stack (7), comprising a handling device (2) which has a gripper (6) designed to lift flat objects, and a positioning and pressing system (10) which is designed to compress a partially finished cell stack (7) and which comprises a lifting device (11) provided for receiving the cell stack (7) which is at any stage of production, and a lateral fixing device (12) located above the lifting device (11) which is constructed from a plurality of assemblies (13, 14), wherein the said assemblies (13, 14) are provided for positioning the cell stack (7) in the vertical and horizontal directions and are adjustable and lockable in both of the said directions.

2. Device according to claim 1, characterized in that each of the said assemblies (13, 14) of the fixing device (12) comprises a plurality of fixing elements (25) which are displaceable in the horizontal direction and which are provided for supporting bipolar plates (8) arranged one above the other both in the lateral and in the vertical direction.

3. Device according to claim 2, characterized in that at least three fixing elements (25) arranged one above the other, each intended for contacting a bipolar plate (8), are arranged in an individually spring-loaded manner in a common, horizontally and vertically adjustable receptacle (27).

4. Device according to claim 3, characterized in that the receptacle (27) is assigned a single clamping device (30) which is designed to simultaneously clamp all of the fixing elements (25) located in the receptacle (27).

5. Device according to one of claims 2 to 4, characterized in that in addition to the fixing elements (25) which can be displaced in the horizontal direction, there is a switchable MEA retention (23) which is designed to press against a membrane electrode arrangement (9) located at the top in the partially completed cell stack (7).

6. Device according to claim 1, characterized in that the two lateral assemblies (13, 14) of the fixing device (12) each have an angular gripper (36) against which the cell stack (7) strikes laterally and at the same time upwards.

7. Device according to one of claims 1 to 6, characterized in that the lifting device (11) has three plates (16, 18, 21) arranged parallel to one another, namely a base plate (16), a middle plate (18) and an upper plate (21) provided for receiving the cell stack (7), wherein a pressure measuring system (17) acting between the base plate (16) and the middle plate (18) exists and the upper plate (21) is mounted on the middle plate (18) with the aid of springs (19) so as to be vertically displaceable, and wherein a distance measuring device (20) designed to measure the distance between the upper plate (21) and the middle plate (18) is provided.

8. A method for assembling a cell stack (7), wherein the cell stack (7) being constructed, comprising bipolar plates (8) arranged parallel to one another in a horizontal alignment and membrane electrode assemblies (9), is subjected to pressure during its formation by exerting a vertically downward pressure on the cell stack (7) after the placement of each additional bipolar plate (8), whereby the cell stack (7) is pressed downwards as a whole, which represents a transition to an over-compressed state in which springs (19) located below the cell stack (7) and supporting it are compressed, and wherein after the over-compression, the vertically downward pressure is reduced, so that the cell stack (7) is raised again by the springs (19), and in the then given,expanded state of the springs (19) at least the upper bipolar plate (8) is fixed in the vertical and lateral direction while maintaining a partial amount of the downward pressure., 9. Method according to claim 8, characterized in that the bipolar plates (8) and membrane electrode arrangements (9) are each placed alternately on the cell stack (7) in a completely flat state.

10. Method according to claim 8, characterized in that at least the bipolar plates (8) are placed in a curved state on the cell stack (7), wherein first the central region of the bipolar plate (8) is pressed onto the cell stack (7) and while maintaining pressure then the entire bipolar plate (8) is brought into contact with the cell stack (7) while being converted into its flat form.

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