Electrochemical cell with improved frame, manufacturing process and stacking

Abstract

The invention relates to a cell (16) for water electrolysis or for a fuel cell, wherein the cell (16) is compressed in a stack, wherein the cell (16) has a frame (4, 44, 44') in which at least one insert (6) is integrated, wherein a fastening means (8) can be or is inserted into the at least one insert (6) to fix a bipolar plate (7).

Description

[0001] The invention relates to an electrochemical cell used in electrolyzers or fuel cells, a method for manufacturing such a cell, and the stack of cells formed therefrom.

[0002] Due to climate change, there is a need to equip power plants for energy generation with various technologies that include components with multiple stacked electrochemical cells, abbreviated here as stacks. Examples of applications include fuel cells and water electrolysis.

[0003] These stacks must contain various liquids, most of which are under internal pressure, which is why they are pressure devices.

[0004] In Fig. As can be seen from the prior art, cells 15' are generally similar and have a cell frame 4' made of an insulating material and bipolar plates 7' which are compressed by forces 13. Each cell frame 4' is pushed outwards by the internal compressive forces (arrows 10). The compressive strength of these cell frames 4' is safety-relevant and not easy to achieve, especially for the larger sizes required for industrial plants.

[0005] Due to the high number of 15' cells in a 1' stack of a plant, the solutions must be reliable and manufacturable on a large scale. As the size of these 1' stacks and 15' cells needs to increase to achieve significant production capacities, the design becomes increasingly complex.

[0006] Normally, cell frames 4' must be designed to withstand the forces exerted by internal pressure. This can be achieved through complex geometries, reinforcements, and intricate material systems. However, it remains a challenge, as a service life of over 10 years must be ensured. System tolerances, which limit cell sizes, must be taken into account, and complex manufacturing solutions are required, especially for custom-shaped designs.

[0007] With larger cell counts, creep and surface deformation of the many surfaces can limit the number. This design transfers the compressive forces from the frame to the bipolar plate.

[0008] Since the cell frame 4' must act as an electrical insulator to prevent short circuits between the cells, it is made of polymer compounds, for example. The disadvantage of these compounds is their low strength compared to, say, metals. To nevertheless withstand the internal fluid pressure, the frame is mechanically supported by the bipolar plate. This is traditionally achieved through frictional engagement between the frame and the bipolar plate. By applying a large preload force to the cell frame 4', it is held in place by the frictional forces between the bipolar plate and the frame. The problem with this approach is that as the internal pressure increases, more and more preload must be applied to the cell frame to ensure frictional engagement, to such an extent that the preload forces become the dominant load over the internal pressure or thermal loads.This means that the permissible internal pressure is limited by the amount of pressure load that the cell frame 4' can bear from the necessary preload.

[0009] It is therefore the purpose of the invention to solve the aforementioned problem.

[0010] The problem is solved by a cell according to claim 1, a method according to claim 8 and a stack according to claim 9.

[0011] The subclaims list further advantages that can be combined in any way to achieve further synergistic benefits.

[0012] They show Fig. 1 a stack of state-of-the-art technology and Fig. 2, Fig. 3 each a frame for a stack according to the invention.

[0013] The description and the figure represent only exemplary embodiments of the invention.

[0014] The present invention solves this problem with a hybrid design philosophy.

[0015] During the manufacturing process of the frame for a cell, especially by means of injection molding, an insert made of a harder, especially metallic or ceramic, material is placed into the frame by forming, pressing, etc.

[0016] In particular, the insert already has a type of fastening, e.g. a thread.

[0017] This insert is secured during stack production with a fastening element, in particular a screw, which creates a frictional connection between the bipolar plate and the solid. A form fit is created between the solid and the frame.

[0018] Fig. Figure 2 schematically shows a part of a frame 4 of a cell 16 according to the invention.

[0019] Frame 4 (44, 44', Fig. 3) preferably has a bulge 5 in the outer edge area in which an insert 6 can be arranged.

[0020] As mentioned above, the insertion 6 can be used in the manufacture of frame 4 (44, 44', Fig. 3) in particular, directly formed, overmolded or pressed.

[0021] It is also possible to use frame 4 (44, 44', Fig. 3) to produce with a recess 5 and the insert 6 is subsequently inserted and fixed, in particular by gluing or fusion bonding, especially by inserting a hot insert 6 into the recess 5 and by means of a fusion contact a firm connection between insert 6 and frame 4.

[0022] The material of the frame 4 (44, 44', Fig. 3) is preferably the same as from the prior art ( Fig. 1)

[0023] The insert 6 must be at least 20%, in particular at least 30%, harder than the material of the frame 4 (44, 44', Fig. 3), i.e. it is metallic, ceramic or made of a harder plastic.

[0024] Alternatively, a plastic that can be locally hardened in the desired area can be used, so that a monolithic frame 4 (44, 44', Fig. 3) without a connecting area.

[0025] Likewise, a filling compound can be introduced into the indentation 5, which hardens and thus forms the insert 6.

[0026] The insert 6 can also have a thread 11 or similar counterpart for a fastening device 8, either pre- or subsequently, into which the fastening device 8, in particular a screw 8, can be inserted.

[0027] The connection between fastener 8 and insert 6 can be detached non-destructively, but it does not have to be.

[0028] The fastener 8 can also be made of plastic, ceramic, or metal.

[0029] The insert 6 does not need to have a thread if, for example, a porous metal or ceramic is used in which the fastening element 8 is inserted, in particular if a screw can be screwed in.

[0030] The fastening 8 can be designed to be removable or non-removable (only destructive).

[0031] The bipolar plate 7 is arranged between the insert 6 and the fastening element 8.

[0032] This hybrid adjustment transfers the internal pressure to the bipolar plate 7.

[0033] Frame 4 (44, 44', Fig. 3) then has several bulges 5 and indentations 6 along its circumference.

[0034] Fig. 3 shows in addition to Fig. 2 a modified frame 44 / 44'.

[0035] The frame 44 / 44' (4, Fig.2) is generally flat and planar.

[0036] The frame 44 is shown here in sections, so that the bulge 5 for the and the insert 6 can be seen on the underside 23 of the frame 44.

[0037] On the upper surface 22 of a frame 44' opposite the insert 6 or bulge 5, a further recess 15 is provided in which the protruding part of the fastening means 8, in particular a head of the screw 8 of another frame 44' to be stacked on it, can be arranged so that the upper surface 22 and lower surface 23 of two frames 44, 44' can lie flat on top of each other on the bipolar plate 7.

[0038] The recess 15 of a frame 44, 44' on the upper surface 22 is preferably arranged offset from the bulge 5.

[0039] The frame 44, 44' has several bulges 5 and several recesses 15.

[0040] Protrusions 5 and recesses 15 in a frame 44, 44' are arranged such that by simply rotating the frame 44 (-> 44') by 180° a recess 15 is opposite a protrusion 5.

[0041] The main differences lie in a combination of the advantages from the various solutions: • Tolerances during component manufacturing can be compensated for, as fastening, e.g., by screws to the bipolar plate, can achieve this -> simple manufacturing and mass production can be realized. • The contact pressure between the inserts and the BPP can be much higher because only parts with a high modulus of elasticity are in this load path. The cell frame is not affected by this preload. The inserts support the frame through positive locking. • Embedding effects do not limit the number of cells in a stack, since the frictional connection between the insert and the bipolar plate is only valid for one cell. • The contact pressure between the frames and the bipolar plates does not need to be as high at higher internal pressures, which significantly reduces the effort required for pull rods, etc. • No complex cell frame geometry is required for other positive locking mechanisms without tolerance compensation. • Generally simple manufacturing due to modern fastening methods such as torque-controlled screws. • Additional secondary positive locking between BPP and cell frame through the screw, if the frictional locking is overcome.

Claims

[1] Cell (16), for water electrolysis or for a fuel cell, where the cell (16) is compressed in a stack, wherein the cell (16) has a frame (4, 44, 44') wherein at least one insert (6) is in the frame (4, 44, 44'), in particular several inserts (6) are integrated, wherein a fastening means (8) can be or is inserted into at least one insert (6), to fix a bipolar plate (7). [2] Cell according to claim 1, wherein the fastening means (8) is a screw. [3] Cell according to claim 1 or 2, where at least one stake (6) is at least 20%, in particular at least 30%, is harder formed than the material of the frame (4, 44, 44'), especially made of metal or ceramic. [4] Cell according to one or more of the preceding claims 1, 2 or 3, where the frame (4, 44, 44') has at least one bulge (5), in which at least one deployment (6) is ordered. [5] Cell according to one or more of the preceding claims 1, 2, 3 or 4, wherein the bipolar plate (7) of the cell (16) is arranged between insert (6) and fastening means (8). [6] Cell according to one or more of the preceding claims 1, 2, 3, 4 or 5, the insert (6) for the fastening device (8) already has a receptacle, in particular a thread exhibits. [7] Cell according to one or more of the preceding claims 1, 2, 3, 4, 5 or 6, where a first frame (44') is on a top surface (22), which is or may be opposite a bulge (5) of a second frame (44) and has a further recess (15), in which there is an end, especially a screw head, of the fastening means (8) for the second frame (44) is or can be arranged, to enable a flush and flat staggering of two frames (44, 44'). [8] Method for producing a cell (16) according to one or more of the preceding claims 1 to 7, where the insert (6) is directly integrated into the manufacture of the frame (4, 44, 44'), especially when it is overmolded or overmolded. [9] Stack comprising several cells (16) according to one or more of the preceding claims 1 to 8.

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