Electrochemical system with pressure equalization plate

Abstract

Electrochemical system (1) with: - a stack (12) comprising at least a plurality of electrochemical cells and separator plates (24); - at least one end plate assembly (3, 4), - at least one pressure equalization plate (10) arranged between the stack (12) and the end plate assembly (3, 4), wherein a side of the end plate assembly (3, 4) facing the stack (12) has at least one first recess (30) and a first solid region of the pressure equalization plate (10) is opposite this first recess (30).

Description

[0001] The invention relates to an electrochemical system, in particular a fuel cell system or an electrolyzer system.

[0002] Existing electrochemical systems typically comprise a stack of a plurality of different components that are stacked one above the other along a stacking axis. The stack can alternatively also be referred to as a stack. Within the stack, a specific component sequence can occur multiple times. For example, a defined component sequence can be repeatedly present in succession within the stack. The electrochemical system disclosed here can also comprise such a stack. An example of an electrochemical system with a stacked configuration can be found in DE 20 2018 105 617 U1 and therein in particular in the Fig. 1.

[0003] The stack is typically sandwiched between so-called end-plate assemblies. These can form the outermost layers of an electrochemical system and, for example, contain connections for power and / or for the supply and / or removal of fluids. The end-plate assemblies are supported on the stack and can, in particular, be in direct contact with it. High contact forces typically occur in this case, as the electrochemical system is typically mechanically clamped. In particular, the end-plate assemblies can be pressed against the stack to a predetermined compression or clamp the stack between them.

[0004] Bracing generally serves to press the components of the stack together in a defined manner. This may be necessary, in particular, to prestress and / or deform sealing elements, such as sealing beads, or other elements within the stack that require prestressing.

[0005] It has been shown that existing solutions do not always reliably achieve the functionality of prestressed elements. This can impair the functionality and, in particular, the operating efficiency of the electrochemical system, for example, due to insufficient sealing effects.

[0006] The task therefore arises to provide an electrochemical system with increased operational reliability.

[0007] This object is achieved by the subject matter of independent claim 1. Advantageous embodiments emerge from the dependent claims, from this description and from the figures.

[0008] Accordingly, an electrochemical system is proposed with: - a stack comprising at least a plurality of electrochemical cells and separator plates; - at least one end plate assembly, - at least one pressure equalization plate arranged between the stack and the end plate assembly, wherein a side of the end plate assembly facing the stack has at least one first recess and a first solid region of the pressure equalization plate is opposite this first recess.

[0009] According to the invention, it was recognized that the functionality of elements of the stack that are to be prestressed can be impaired, in particular, if the stack is not clamped in the desired manner. This can result, for example, from contact forces and, in particular, compressive forces to be introduced into the stack not being defined and / or not being able to be generated uniformly across locations. Instead, unintentional local deviations in these forces can occur, so that the stack is, for example, locally less tightly compressed. In these local areas, for example, sealing effects may no longer be reliably achieved.

[0010] Furthermore, it was recognized according to the invention that such pressure irregularities can result from the stack and at least one of the end plate assemblies being supported unevenly against each other. For example, if a planar support and / or planar contact between these elements is locally interrupted, the described local deviations in the compressive or bracing forces can occur in this interrupted area.

[0011] To at least partially compensate for these identified causes, the present invention proposes the provision of a pressure equalization plate, which, for example, at least partially conceals and / or bridges a first recess in the end plate assembly from the perspective of the stack. The pressure equalization plate can thus enable uniform, flat contact and / or flat support between the stack and the end plate assembly, despite the described recesses in the end plate assembly.

[0012] The components of the stack can be stacked along a stacking axis. They can extend orthogonally to this stacking axis. A height of the stack can be measured along the stacking axis. The end plate assembly and / or the pressure equalization plate can also extend orthogonally to the stacking axis.

[0013] The electrochemical system may also include a further end plate assembly positioned near a side of the stack opposite the side positioned near the aforementioned end plate assembly. In other words, the electrochemical system may have two end plate assemblies, and these may be located on remote sides or ends of the stack. A pressure equalization plate of the type disclosed herein may also be provided between this further end plate assembly and the stack.

[0014] The stack may include all components of the electrochemical system arranged between two end plate assemblies, with the exception of at least one pressure equalization plate.

[0015] The separator plates can be connected in pairs to form bipolar plates. Additionally or alternatively, single-layer separator plates can be provided; for example, in an electrolyzer these can directly assume the function of a bipolar plate, i.e. without an additional second layer. Separator plates at a bottom and / or top position in the stack can form so-called unipolar plates. The unipolar plates can, for example, differ from the other bipolar plates in their fluid guidance. They can in turn be installed in single or double layers to form the unipolar plates. Furthermore, it is possible to provide dummy or temperature control cells at or adjacent to one end of the stack. These cells are electrochemically inactive but allow fluid to flow in the direction of the stack. These dummy or temperature control cells can, but do not have to, serve at least to temperature control the stack or the components adjacent to them.

[0016] An electrochemical cell may comprise an MEA (membrane electrode assembly) and at least one gas diffusion layer, in particular a gas diffusion layer on each side of the MEA.

[0017] The end plate assembly can, for example, comprise or accommodate channels for the supply and / or removal of reactants, reaction products and / or coolants. Additionally or alternatively, a current collector, a discharge section connected thereto and / or other components, such as fastening elements or mechanical interfaces for connecting to an external support structure, can be comprised by the end plate assembly or at least partially accommodated therein. Additionally or alternatively, straps, screws, bolts or other bracing means used to brace the stack can bear against or be fastened to the end plate assembly. The end plate assembly can be spaced at least partially from the stack and, more precisely, from an outermost component of the stack viewed along the stack axis by the pressure equalization plate. The end plate assembly can be supported on the stack via the pressure equalization plate.

[0018] The pressure equalization plate can optionally have recesses, in particular in the form of perforations. Solid areas of the pressure equalization plate can be free of perforations and, for example, have a continuous plate material. The pressure equalization plate can, for example, comprise a metallic material, in particular sheet metal. Alternatively, according to the following embodiments, it can be made of an electrically insulating material or additionally coated with such a material. The pressure equalization plate can be opposite the first recess of the end plate assembly in such a way that it at least partially covers, spans, or bridges it, in particular from the perspective of the stack. The opposite position can be present, in particular, along the stack axis. In particular, the stack axis or an axis parallel thereto can intersect both the recess and the pressure equalization plate.

[0019] The pressure equalization plate can be at least partially adjacent to the stack, in particular to an outermost separator plate of the stack, which can form at least part of a unipolar plate. The pressure equalization plate can be at least partially adjacent to the side of the end plate assembly facing the stack.

[0020] The pressure-equalizing effect of the pressure equalizing plate results from its arrangement opposite the first recess. This allows the contact conditions with the stack, and in particular with its outermost separator plate, to be locally equalized. Otherwise, the contact conditions in the area of ​​the first recess would deviate significantly locally. More specifically, in this area, the structural support of the stack by the end plate assembly would be interrupted, which would result in a locally significantly reduced compressive force introduction into the stack. The pressure equalizing plate at least partially compensates for such locally varying compressive force introduction.

[0021] According to one embodiment, the pressure equalization plate completely covers the first recess. This allows the pressure equalization effect to be particularly comprehensive.

[0022] According to one embodiment, the pressure equalization plate rests against the end plate assembly and / or the stack, in particular against an outermost separator plate thereof. If the pressure equalization plate rests against both the end plate assembly and the stack, as provided according to embodiments, further intermediate components can be avoided and a compact system design can be achieved. In particular, the pressure equalization plate may not rest against any components other than the end plate assembly and the stack.

[0023] According to a further embodiment, the at least one first recess—and / or all recesses of any plurality of recesses together—occupies a portion of less than 50%, preferably less than 30%, and in particular less than 20% of an area of ​​the side of the end plate assembly facing the stack. This emphasizes that the recess can be locally limited.

[0024] According to a further embodiment, the first solid region of the pressure equalization plate is opposite a region of the stack comprising at least one of the following sections: - at least one section of at least one sealing element, for example a sealing bead of at least one separator plate or for a separator plate for sealing a region of the separator plate; - at least one section of at least one support element of at least one separator plate and / or another support structure for at least partially supporting the separator plate and / or for relieving the load on a sealing element of this separator plate, in particular in the event of a crash or impact.

[0025] In this case, the opposing arrangement can particularly comprise an at least indirect succession, viewed along a stacking direction. In particular, the opposing arrangement can comprise the corresponding regions or sections being arranged one above the other and / or overlapping one another, viewed in the stacking direction. In particular, the aforementioned regions can be opposite one another in such a way that they are each intersected by a stacking axis or by an axis parallel thereto.

[0026] The support elements, which may in particular be support beads or other support structures, can serve as deformation limiters, in particular during expected normal loads during operation and / or even during bracing of the stack. Consequently, they can provide their deformation-limiting effect not only in the event of a crash, although this may be provided according to other embodiments. They can at least partially limit deformations of a separator plate under pressure, in particular by providing support and / or contact surfaces to adjacent components. This allows a separator plate to be locally stiffened.

[0027] An additional or alternative section, which can be opposite the solid region of the pressure equalization plate, can be a section of a barrier element that can specifically reduce or prevent at least one media flow along a separator plate, at least in some areas. The barrier element can, in particular, specifically influence the flow of a reaction medium. For example, the flow of a reaction medium past an active region of the separator plate can be specifically reduced or prevented by the barrier elements. Such barrier elements can be formed integrally with the separator plate and, in particular, molded therein, for example by an embossing process. An example of barrier elements, as can also be provided in the solution disclosed here, can be found in EP 3 631 884 A1.

[0028] The barrier elements can be supported on adjacent components, and in particular on an adjacent separator plate. However, they can also remain at a distance from adjacent components, and in particular from an adjacent separator plate, for example by reducing their height.

[0029] By extending the pressure equalization plate opposite any of the above-mentioned areas, sections and elements, locally evenly distributed pressure forces can be introduced into them.

[0030] According to a further embodiment, the pressure equalization plate has a thickness of at least 0.075 mm and / or up to 2 mm. It has been shown that this allows the desired pressure equalization to be reliably achieved without excessively increasing the resulting overall height of the electrochemical system.

[0031] According to a further embodiment, the thickness of the pressure equalization plate, which can be measured, for example, along the stacking direction and / or along a stacking height, is constant. Alternatively, it can be constant at least within 90% of a solid surface portion of the pressure equalization plate. This can simplify the manufacture of the pressure equalization plate and / or reduce its contribution to the overall height of the electrochemical system.

[0032] According to a further embodiment, the pressure equalization plate is de-energized during operation of the electrochemical system. This allows, for example, lower requirements for the pressure equalization plate and / or its installation in the electrochemical system due to its de-energized nature; for example, no special corrosion prevention measures are necessary.

[0033] According to a further embodiment, the pressure equalization plate comprises a plastic material and / or a metallic material. Alternatively or additionally, the pressure equalization plate can be electrically insulated, in particular by an electrically insulating coating. In other words, the pressure equalization plate can generally be electrically insulated. In this case, too, the pressure equalization plate is therefore de-energized during operation of the electrochemical system.

[0034] Due to its electrically insulating properties, the pressure equalization plate can increase the operational reliability of the electrochemical system. For example, it is known that current-carrying components are installed on or at least near end plate assemblies and thus also near the pressure equalization plate. This could be a current collector, for example. By designing the pressure equalization plate in an electrically insulating manner, the risk of short circuits can be reduced and operational reliability can be increased. In particular, this allows the pressure equalization plate to be closer to current-carrying components and / or even to come into contact with them. This can be used to provide the pressure equalization effect of the pressure equalization plate appropriately close to current-carrying components.

[0035] According to a further embodiment, the pressure equalization plate extends in a frame-like manner around a central recess. The central recess can be the largest recess and / or the only recess within the pressure equalization plate. It can occupy at least 20%, at least 40%, or even at least 50% of the base area of ​​the pressure equalization plate, whereby this total area can be defined in particular as the sum of the surface areas of the recess and the solid areas of the pressure equalization plate. For example, the base area can be spanned by the outer edges or outer edges of the pressure equalization plate. The central recess can specifically provide free space to provide installation space for certain components, such as a current collector, within the pressure equalization plate.Alternatively, several pressure equalization plates can be arranged leaving a central recess, which together form sections of a frame shape, for example.

[0036] According to a further embodiment, the central recess is located opposite at least a portion of a region of the stack in which the electrochemically active regions of the cells are stacked one above the other. These electrochemically active regions can, for example, be regions in which an MEA and / or gas diffusion layer mentioned here is / are located opposite a so-called flow field of a separator plate. Figuratively speaking, the central recess can frame at least a portion of the electrochemically active regions, for example, when viewed in a plan view and / or along the stack axis.

[0037] According to a further embodiment, the at least one first recess of the end plate assembly is formed as: - a countersunk hole, or other recess, for receiving a screw head or a section of another fastener; or - a receiving area for a discharge section.

[0038] Such counterbores and fastening elements may be provided on the side of the end plate assembly facing the stack in order to fasten further elements which are to be arranged on a side of the end plate assembly facing away from the stack.

[0039] The receiving area for the discharge section, which is for example groove-shaped, can define a recess which is larger than any countersunk holes and into which, in particular, a flat discharge section can be inserted. The discharge section can be configured to discharge current from a current collector, for example to components arranged outside the stack. The discharge section can extend parallel to the components of the stack and / or the pressure equalization plate and / or the end plate assembly and / or orthogonal to the stack axis. It can be electrically conductively connected to a current collector, in particular a flat current collector, and in particular can be formed integrally with the latter. It can span a significantly smaller area than the current collector, e.g. less than 50% or less than 10% compared to the area of ​​the current collector.In each case, a surface of the discharge section and the current collector oriented orthogonally to the stack axis can be considered.

[0040] According to a further embodiment, the pressure equalization plate has at least one recess, which is in particular different from an optionally provided central recess. This recess can be opposite a recess in at least one component of the stack, i.e. in particular a recess in at least one separator plate. Alternatively, the recess can be provided equally in an electrochemical cell and in particular in all electrochemical cells. The recess can in particular serve to pass fluid through the stack. For example, the recess can be a so-called through-opening, as is common in separator plates in the prior art. The recess in the pressure equalization plate can be deliberately opposite such a recess and in particular through-opening in order not to hinder fluid exchange with the end plate assembly.This fluid exchange can instead take place through the recess of the pressure equalization plate.

[0041] Alternatively or additionally, the recess of the pressure equalization plate can be opposite a second recess in the end plate assembly, in particular, wherein the second recess is designed as a channel opening for fluid supply into the stack and / or fluid discharge from the stack. The channel opening can be provided for the fluid exchange described above with the through-openings of the stack and, in particular, can be aligned with them. In this case, too, the pressure equalization plate can be intentionally opened locally so as not to impede this fluid exchange.

[0042] In summary, the pressure equalization plate can optionally have recesses, particularly in the form of perforations, in areas where it is located opposite areas of the stack and / or the end plate assembly that do not have increased requirements with regard to a defined pressure force introduction. Instead, a recess in the pressure equalization plate opposite such areas and as described in the above examples can improve the functionality of the electrochemical system and / or be necessary to ensure this functionality.

[0043] Embodiments of the invention are explained below with reference to the accompanying schematic figures. The same reference numerals may be used throughout the figures for identical or comparable features. Fig. 1 is a perspective view of an electrochemical system according to one embodiment. Fig. 2 is a partial sectional view of an electrochemical system according to an example of the prior art. Fig. 3 is one to Fig. 2 analogous partial sectional view, but of the electrochemical system according to the invention Fig. 1. Fig. Figure 4 shows views of an end plate assembly and an outermost separator plate in the stack of the electrochemical system of the Fig. 1 and Fig. 3. Fig. 5 is a view analogous to Fig. 4, but with an additional pressure equalization plate shown. Fig. 6 is a view analogous to Fig. 4, but with an additionally shown pressure equalization plate according to a further embodiment. Fig. 7 is one to Fig. 3 analogous view concerning a further embodiment. Fig. 8 is one to Fig. 7 analogous view concerning yet another embodiment.

[0044] Fig. 1 shows an electrochemical system 1 according to the invention with a stack 12 comprising a plurality of identical bipolar plates 2, which are stacked along a z-axis 7 and—optionally together with unipolar plates and / or dummy or temperature-control cells—clamped between two end plate assemblies 3, 4. The bipolar plates 2 each comprise two interconnected individual plates, also referred to as separator plates in this document. The z-axis 7 defines a stacking direction. A stacking axis (not shown separately) runs parallel to the z-axis 7 and, for example, through a geometric center of the stack 12.

[0045] In the present example, system 1 is a fuel cell stack. Each two adjacent bipolar plates 2 of stack 12 enclose an electrochemical cell between them, which serves, for example, to convert chemical energy into electrical energy. Unipolar plates and / or dummy or temperature-controlled cells can also be included in stack 12. The electrochemical cells usually each have a membrane electrode assembly (MEA) and gas diffusion layers (GDL). In alternative embodiments, system 1 can be designed, for example, as an electrolyzer, compressor, or redox flow battery. Bipolar plates can also be used in these electrochemical systems 1. The structure of these bipolar plates can essentially correspond to the structure of the bipolar plates 2 explained in more detail here, even if the media guided on or through the bipolar plates can differ.It can also be just a single-layer bipolar plate.

[0046] The z-axis 7, together with an x-axis 8 and a y-axis 9, spans a right-handed Cartesian coordinate system. The end plate assembly 4 has a plate-shaped component and / or a plate-shaped region 14 and a plurality of media connections 5. Media, in particular fluids, can be supplied to the system 1 via these, and media can be removed from the system 1 via these. These media that can be supplied to the system 1 and removed from the system 1 can include, for example, fuels such as molecular hydrogen or methanol, reaction gases such as air or oxygen, reaction products such as steam, or coolants such as water and / or glycol.

[0047] In Fig. 1 also marks the positions of pressure equalization plates 10. These are each arranged between the stack 12 and a side of one of the end plate assemblies 3, 4 facing this stack 12.

[0048] The Fig. 2 and Fig. 3 are schematic sectional views, wherein a sectional plane is, for example, perpendicular to an XY plane according to Fig. 1. This shows Fig. 2 an example of the state of the art without pressure equalization plates 10. Fig. 3 shows a sectional view through the embodiment according to the invention of Fig. 1 with a pressure equalization plate 10. The Fig. 2 and Fig. 3 each show a part of an end plate assembly 3, 4 and of two outermost separator plates 24 of the stack 12 that are adjacent to and / or adjacent thereto. Dash-dotted lines indicate that an area lying between the dash-dotted lines is schematically shortened and / or shown only symbolically and can, for example, be significantly wider horizontally.

[0049] In Fig. 2 shows a region of an end plate assembly 3, 4 which has a recess 18 for receiving a conventional plate-shaped current collector 20. The current collector 20 faces the stack 12, of which only an outermost two-layer unipolar plate 22 is shown. This comprises two separator plates 24 which are firmly connected to one another and in particular welded. In a manner known per se, the separator plates 24 are sheet metal plates into which various structural elements are formed and in particular embossed. The separator plates 24 extend essentially parallel to one another. The bipolar plates 2 of the stack 12 (not shown) can be designed essentially similarly to the unipolar plates 22 shown, but differ from them by a fluid guide along both outer sides of the separator plate 24, including all the additional structural features required for this purpose.

[0050] At least one GDL 26 is arranged between the current collector 18 and the unipolar plate 22. The at least one GDL can be installed alone or together with a membrane, which is preferably designed without electrodes and a catalyst layer. The number of GDLs depends in particular on the available installation space or the space to be filled.

[0051] Aside from the recess 18 for the current collector 20, the side of the end plate assembly 3, 4 facing the stack 12 is flat. It contacts the unipolar plate 22 in the area of ​​sealing beads 28, which protrude relative to a contact plane of the separator plates 24. When the stack 12 is clamped, targeted compressive forces are to be exerted on these sealing beads 28 in order to achieve a defined deformation and the associated defined sealing effect. It should be noted that the other bipolar plates 2 of the stack 12 (not shown) have sealing beads 28 at similar positions, to which compressive forces from adjacent plates in the stack 12 are transferred.

[0052] In the example from Fig. 2, the introduction of compressive force into the stack 12 is essentially problem-free due to the continuously flat shape of the compressive force-transmitting side of the end plate assembly 3, 4.

[0053] Fig. 3, however, assumes the case where the compressive force-transmitting side of the end plate assembly 3, 4 is uneven. In particular, first recesses 30 are provided there for at least partially accommodating fastening elements 32. In the case shown, the recesses 30 are each countersunk holes for accommodating a screw head.

[0054] In the area of ​​these recesses 30, an opposite section of the unipolar plate 22 as well as of all bipolar plates 2 (not shown) experiences a locally interrupted structural support by the end plate assembly 3, 4. This makes it difficult to introduce compressive forces in a defined manner when the stack 12 is clamped. Fig. 3, for example, shows that at least edge regions of two sealing beads 28, which are positioned near an electrochemically active region 29 of the stack 12, lie opposite the recesses 30 or, figuratively speaking, overlap with them. Also shown is a support element 28', which can be formed, for example, in an outer region of the unipolar plate 22 and, analogously, in an outer region of the further bipolar plates 2 (not shown). In particular, such a support element 28' can respectively encircle the corresponding plates. This support element 28' lies to an even greater extent than the sealing bead 28 of the left recess 30 in Fig. 3 opposite.

[0055] The embodiment according to Fig. 3 provides for a pressure equalization plate 10 to be arranged between the pressure-transmitting side of the end plate assembly 3, 4 and the stack 12 or its outermost unipolar plate 22 in such a way that the recesses 30 are at least partially and, in the example shown, completely covered. Thus, a flat contact surface for the stack 12 is also provided in the area of ​​the recesses 30, which enables a local equalization of the pressure force transmission. For example, all sealing beads 28 and support elements 28' can be arranged essentially analogously to the example from Fig. 2 are subjected to compressive forces evenly or across the entire surface and thus tensioned in a defined manner.

[0056] In the sectional view of the Fig. 3 also shows that the pressure equalization plate 10 has a central recess 34, which is surrounded on both sides by two solid sections of the pressure equalization plate 10. These solid sections are each marked with the reference numeral 10. The central recess 34 is opposite the current collector 20 such that the current collector can be contacted through the central recess 34. Optionally, the current collector 20 extends partially through the central recess 34, as shown.

[0057] Within the scope of this disclosure, the term "solid" section does not exclude the possibility that such a section may be at least locally perforated and, for example, perforated. However, such hypothetical perforations are preferably significantly smaller than the central recess 34. For example, they each have, on average, a maximum of 10% of the surface area of ​​the central recess 34. Alternatively or additionally, a surface portion of non-perforated regions of the solid section preferably significantly outweighs a cumulative surface portion of the hypothetical perforations, e.g., by more than double or more than four times.

[0058] Fig. 4 shows in its upper part a view of the pressure force transmitting side of the end plate assembly 3, 4 from Fig. 3. In its lower part shows Fig. 4 a view of the outer side of the unipolar plate 22 opposite the end plate assembly 3, 4 from Fig. 3. Referring first to the end plate assembly 3, 4, the recess 18 for the current collector 20 is again shown. The recess 18 is completely surrounded by a flat area of ​​the end plate assembly 3, 4. Also shown are schematic positions of recesses 30 in the form of countersunk holes, as can be seen from Fig. 3. The number, size and position of these recesses 30 are merely exemplary. Furthermore, the end plate assembly 3, 4 comprises through-openings 36, which are fluidically connected to the media connections 5 of Fig. 1 and / or are encompassed by them. These through-openings 36, which each form or comprise channel openings within the meaning of this disclosure, are shown in the schematic view of Fig. 3 not included.

[0059] The unipolar plate 22, which is generally similar to prior art examples, also includes a plurality of through holes 36. These are formed in the stacked configuration from Fig. 1 and Fig. 3 are arranged opposite one of the through-openings 36 of the end plate assembly 3, 4. Also shown is a flow field 38 of the unipolar plate 22, which is located in an electrochemically active region of the stack 12 and through which a reaction medium is guided between two of the through-openings 36, which are positioned on different sides of the flow field 38. Also shown is the circumferential outer sealing bead 28 made of Fig. 3, whereas in the schematic view of Fig. 4 the further support elements 28' from Fig. 3, which are arranged near the outer edge, are not shown.

[0060] The schematic view of Fig. 4 shows that in the stacked configuration at least the uppermost and lowermost recess 30 of the end plate assembly 3, 4 is opposite the circumferential sealing bead 28 or at least positioned very close thereto, see also Fig. 3. Further recesses 30 or additional recesses 30 not shown can, however, Fig. 4 support elements 28' not shown. Without the pressure equalization plate 10 disclosed here, each of the recesses 30 could cause a locally uneven pressure force introduction into the stack 12 and thus reduce the homogeneity of a local pressure distribution.

[0061] Fig. 5 corresponds to the representation from Fig. 4 with the difference that in this case the pressure equalization plate 10 is shown in a state adjacent to the end plate assembly 3, 4. Solid areas of the pressure equalization plate 10 are shown hatched. These enclose the frame-like Fig. 3 already explained central recess 34. Furthermore, the pressure equalization plate 10 has several recesses 37, which in the view of Fig. 3 are not included. These are each located opposite one of the through-holes 36 in the end plate assembly 3, 4 and consequently also opposite one of the through-holes 36 in the unipolar plate 22. Consequently, the pressure equalization plate 10 does not impede the fluid transfer between these through-holes 36.

[0062] Also shown are the positions of the recesses 30 in the form of countersunk holes. These are completely covered by the pressure equalization plate 10 and are analogous to a real top view. Fig. 5 not visible, in Fig. 5 is indicated by dashed lines.

[0063] As an optional feature, the current collector 20 has a web-like and / or elongated discharge section 21, which can, for example, run in a groove of the end plate assembly 3, 4. The pressure equalization plate 10 has, as a further optional feature, a covering section 23 opposite this discharge section 21. The discharge section 21 can be accommodated in a further recess 30 of the end plate assembly 3, 4. If this recess is designed with sufficient play, a guide for the discharge section 21 can additionally be provided on the rear side of the pressure equalization plate 10.

[0064] The pressure equalization plate 10 is made of or coated with an electrically insulating material so that it can touch the current collector 20 and in particular its discharge section 21 without risk of short circuit.

[0065] Fig. 6 shows a further embodiment in a Fig. 5 analogous view. In this case, the pressure equalization plate 10 is divided into two individual plates, or two pressure equalization plates 10 are provided. Each of the pressure equalization plates 10 covers at least one, and in the example shown, several, of the recesses 30. Together, the pressure equalization plates 10 cover all of these recesses 30. The dashed representations of the recesses 30 again correspond to an indication of their positions, although the recesses 30 are actually covered by the pressure equalization plates 10. Furthermore, the pressure equalization plates 10 again comprise recesses 37 to expose the through openings 36 of the end plate assembly 3, 4.

[0066] The Fig. 7 and Fig. 8 show further embodiments in Fig. 3 analogous views. The representations each correspond to a left half of the representation from Fig. 3 or are designed analogously.

[0067] Fig. Figure 7 again shows sealing beads 28 and a support element 28' of the unipolar plate 22, which are at least partially or completely opposite a recess 30 in the end plate assembly 3, 4. However, this recess 30 is concealed by a solid area of ​​a pressure equalization plate 10, which is only partially shown, so that the previously described advantages are again achieved. This pressure equalization plate 10 is made of a plastic material and can therefore be designed with a greater wall thickness than an analogous metallic plate with an insulating layer.

[0068] In the example from Fig.8, the pressure equalization plate 10 is made of a comparatively thin-walled sheet material, but is provided with an electrically insulating coating. Furthermore, an absorber element 40 is shown, which in principle can also be provided in all other exemplary embodiments, in particular also together with a support element 28'. The absorber element 40 forms a support structure or a support element, which in the case shown is arranged within the unipolar plate 22 or between the mutually facing inner sides of the separator plates 24. In a manner known per se, the absorber element 40 can prevent the separator plates 24 from coming too close together in the region of the corresponding sealing bead 28, since it supports the separator plates 24 against one another. At the same time, it can absorb impact energy in the event of excessive compression. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 20 2018 105 617 U1

[0002] EP 3 631 884 A1

[0027]

Claims

[1] Electrochemical system (1) with: - a stack (12) comprising at least a plurality of electrochemical cells and separator plates (24); - at least one end plate assembly (3, 4), - at least one pressure equalization plate (10) arranged between the stack (12) and the end plate assembly (3, 4), wherein a side of the end plate assembly (3, 4) facing the stack (12) has at least one first recess (30) and a first solid region of the pressure equalization plate (10) is opposite this first recess (30). [2] Electrochemical system (1) according to claim 1, wherein the pressure equalization plate (10) completely covers the first recess (30). [3] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) bears against the end plate assembly (3, 4) and / or the stack (12). [4] Electrochemical system (1) according to one of the preceding claims, wherein the at least one first recess (30) occupies a proportion of less than 50%, preferably less than 30%, in particular less than 20% of an area of the side of the end plate assembly (3, 4) facing the stack (12). [5] Electrochemical system (1) according to one of the preceding claims, wherein the first solid region of the pressure equalization plate (10) is opposite a region of the stack (12) comprising at least one of the following sections: - at least one section of at least one sealing element, in particular a sealing bead (28), of at least one separator plate (24) for sealing a region of the separator plate (24); - at least one section of at least one support element (28') of at least one separator plate (24) and / or another support structure (40) for at least partially supporting the separator plate (24) and / or relieving a sealing element (28) of this separator plate (24), in particular in the event of a crash or impact. [6] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) has a thickness of at least 0.075 mm and / or up to 2 mm. [7] Electrochemical system (1) according to one of the preceding claims, wherein the thickness of the pressure equalization plate (10) is constant or at least constant within 90% of a solid surface portion of the pressure equalization plate (10). [8] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) is de-energized during operation of the electrochemical system (1). [9] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) comprises a plastic material and / or a metallic material; and / or wherein the pressure equalization plate (10) is electrically insulated, in particular by an electrically insulating coating. [10] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) extends in a frame-like manner around a central pairing (34). [11] Electrochemical system (1) according to one of claims 1 to 9, wherein a plurality of pressure equalization plates are arranged leaving a central recess (34) free. [12] Electrochemical system (1) according to claim 10 or 11, wherein the central recess (34) is opposite at least part of a region of the stack (12) in which the electrochemically active regions (29) of the cells are stacked one above the other. [13] Electrochemical system (1) according to claim 12 with reference back to claim 10, wherein the central recess (34) has an area with a size of at least 50% of a base area of the frame-shaped pressure equalization plate (10). [14] Electrochemical system (1) according to one of the preceding claims, wherein the at least one first recess (30) of the end plate assembly (3, 4) is formed as: - a countersunk hole for receiving a screw head or a portion of another fastening element (32); - or a receiving area for a discharge section (21). [15] Electrochemical system (1) according to one of the preceding claims, wherein the pressure equalization plate (10) has at least one recess (37), wherein the recess (37) is opposite a recess (36) in at least one component of the stack (12) and / or a second recess (36) of the end plate assembly (3, 4), in particular wherein the second recess (36) is designed as a channel opening for fluid supply into the stack (12) and / or for fluid removal from the stack (12).

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