Separator for electrochemical system, method for producing such separator and corresponding electrochemical system comprising such separator

Abstract

The invention relates to a separator for an electrochemical system, comprising a first individual plate and a second individual plate connected to the first individual plate by means of a welded joint, each individual plate comprising at least one through-opening for the passage of a fluid, a flow field, a distribution or collection region fluidly connecting the through-opening to the flow field, the distribution or collection area is arranged between the flow field and the distribution or collection area, the welding joint is arranged in the flow field and / or in the transition area, the welding joint extends longitudinally from a first end located in the first end area to a second end located in the second end area, and the welding joint is arranged between the distribution or collection area and the flow field. The weld joint forms an end pocket between the first end and the second end, and the end pocket is spaced apart from the first end and from the second end.

Description

Technical Field

[0001] The present invention relates to a separator for an electrochemical system, a method for producing such a separator and an electrochemical system comprising such a separator. Background Art

[0002] Known electrochemical systems, such as fuel cell cell systems or electrochemical compressor systems, redox flow batteries and electrolyzers, usually include a plurality of separators arranged in a stack so that in each case two adjacent separators enclose an electrochemical cell. A separator usually includes two separate plates, which are connected to each other along their rear sides facing away from the electrochemical cell. The separator can be used, for example, to electrically contact the electrodes of individual electrochemical cells (e.g. fuel cell cells) and / or to electrically connect adjacent cells (cells connected in series). In the case of fuel cell cells, bipolar plates are usually used as separators.

[0003] The individual plates of the separator may include such a channel structure, which is used to supply one or more media to the battery cells and / or to transport the media away from the battery cells. The medium can be, for example, a fuel (for example, hydrogen or methanol), a reaction gas (for example, air or oxygen) or a coolant as a feed medium, and a reaction product and a heated coolant as a discharged medium. In addition, the separator can also be used to transfer waste heat generated in the electrochemical battery cells, such as waste heat generated during the conversion of electrical energy or chemical energy in the fuel cell cells, and can be configured to seal various media channels or cooling channels from each other and / or from the outside. In the case of fuel cell cells, the reaction medium is the fuel and the reaction gas, and the reaction medium is usually conducted on the mutually opposite surfaces of the individual plates, while the coolant is conducted between the individual plates. The electrochemical battery cells and in particular the electrochemical battery cells of the fuel cell cells can, for example, each include a membrane electrode assembly (or MEA) with a corresponding polymer electrolyte membrane (PEM) and electrodes. The MEA can also include one or more gas diffusion layers (GDL), which are usually oriented toward the separator and in particular toward the bipolar plates of the fuel cell cell system, and are, for example, in the form of carbon felt.

[0004] The structure and function of a separate plate generally require that the channels of the separate plates of the same partition run parallel to each other in some areas and / or intersect each other in at least some areas. The rear side of the channel base can be made to contact and connect in the areas running parallel to each other and / or in the intersecting areas. The connection of two separate plates ensures that the space between the separate plates and the space between the separate plates and the adjacent components on the opposite side maintain their volume during operation and will not be deformed or significantly deformed due to operating pressure and / or other forces. Therefore, narrow channel widths and / or intersecting channels place high demands on the positioning accuracy of the separate plates relative to each other and the positioning of the tools for forming the connection relative to the separate plates. Conventional methods for connecting separate plates to each other are, for example, welding and, in particular, laser welding, brazing or adhesive bonding. If the required positioning accuracy is not observed when connecting separate plates, deviations can cause the connection to be too weak or at least partially completely without a connection. In particular, the pressure of the coolant conducted between the separate plates may then cause the connection to tear, which is, for example, opened between the plates, or, for example, the welding plug is torn from one or two separate plates, so that a hole is generated in at least one plate. If the joint (joint) is designed as a welded joint (joint), the rapid cooling of the weld pool will usually form a so-called end pit at the end of the weld seam. In particular, in the area of ​​the end pit, star-shaped cracks may occur, which may lead to immediate leakage or reduced durability. Additionally or alternatively, deviation may cause excessive energy to enter a point of a separate plate and burn it through, thereby also producing holes. The separate plate may therefore be damaged along the connection position to the extent that it cannot be used. This may cause the electrochemical battery cells enclosed between adjacent separators to be flooded by such a cooling fluid, which is conducted between the separate plates and passes through the cracks in the separate plates. If both separate plates include holes, uncontrolled reactions between the reaction media may also occur. Both of these situations may lead to failure of the entire stack. The methods used to combine separate plates in the region so far may therefore lead to high waste levels in production or short system service life in operation. Summary of the invention

[0005] The invention is therefore based on the object of providing a separator for an electrochemical system which is as stable as possible and can be produced with the lowest possible rejection rate.

[0006] This object is achieved by means of a separator for an electrochemical system, a method for producing such a separator and an electrochemical system according to the independent claims. Special configurations are described in the dependent claims and in the following description.

[0007] Correspondingly, a separator for an electrochemical system is proposed. The separator for an electrochemical system comprises a first separate plate and a second separate plate connected to the first separate plate by means of a welded joint.

[0008] Each individual plate comprises at least one through-opening for the passage of a fluid, a flow field and a transition region which is arranged between the flow field and the through-opening and fluidically connects the through-opening to the flow field.

[0009] Weld joints are located in flow fields and / or transition areas.

[0010] Furthermore, both individual plates can have a distribution or collecting region which fluidically connects the through-opening with the flow field and is therefore arranged between the through-opening and the flow field.

[0011] The weld joint extends longitudinally from a first end located in the first end region to a second end located in the second end region. The weld joint forms an end recess between the first end and the second end. The end recess is spaced apart from the first end of the weld joint and from the second end of the weld joint.

[0012] In pressure pulsation tests, in which a medium is forced under high and alternating pressure between the individual layers of the separator in order to test the durability of the separator, it has been shown that the welded joints can crack or even tear open completely in their end regions, in other words, at the start and / or at the end of the welded joint, where the welding tool starts or closes. This tearing open is sometimes also referred to as debonding of the welded joint and generally has a negative impact on the service life of the separator. The end region is therefore generally the weak point of the welded joint.

[0013] The ends of a weld joint may be subject to greater stresses than the areas between the ends of the weld joint, in particular in the case of pulsating pressure stresses caused by the coolant conducted between the individual plates. An advantage of the proposed weld joint design is that the areas of the end pits, where the weld joint usually has a weaker bond, are located at a distance from the particularly stressed ends of the weld joint. In this way, cracks and the resulting leaks can be reduced or even prevented.

[0014] In one embodiment, the weld joint may be designed such that no end recess is formed in the first end region and / or in the second end region.

[0015] The first end region of the weld joint can be defined as an area extending from the first end of the weld joint in the direction of the second end of the weld joint. The first end region can extend from the first end of the weld joint to be closely adjacent to the end pit. The second end region of the weld joint can be defined as an area extending from the second end of the weld joint in the direction of the first end of the weld joint. The second end region can extend from the second end of the weld joint to be closely adjacent to the end pit. Alternatively, the end region can be defined by the area of ​​the weld joint where the welding tool or welding laser beam is applied. Therefore, the end region can be referred to as the approach region of the welding tool or welding laser beam. With the welding tool approaching, for example, two separate plates may not be completely welded together locally in the end region compared to the rest of the weld joint.

[0016] The weld joint may include a first weld seam and a second weld seam that at least partially overlap. The end recess may be arranged in the overlap region. The overlap region may be defined as a region in which the first weld seam at least partially overlaps the second weld seam. For example, the length of the first end region and / or the second end region may correspond to at most twenty times the length of the end recess in the overlap region, preferably at most fifteen times the length of the end recess in the overlap region, and particularly preferably at most twelve times the length of the end recess in the overlap region. For example, the length of the first end region and / or the second end region may correspond to at least 100% of the length of the end recess in the overlap region, preferably at least 150% of the length of the end recess in the overlap region, and particularly preferably at least 200% of the length of the end recess in the overlap region. The length of the first end region and / or the second end region may substantially correspond to the length of the end recess in the overlap region. The length may be measured on the side of the component where the laser beam enters the component during the production of the weld joint.

[0017] In one embodiment, the end dimple may be located in the center 85% position, particularly the center 70% position, between the first end and the second end of the weld joint. The advantage of arranging the end dimple in the center region between the first end and the second end of the weld joint is that the end dimple is spaced apart from the particularly stressed end of the weld joint.

[0018] In one embodiment, the weld joint may have a scaly weld solidification line in a first direction in the first end region, in particular in the region from the first end of the weld joint to the end pit. The weld joint may have a scaly weld solidification line in a second direction opposite to the first direction in the second end region, in particular in the region from the second end of the weld joint to the end pit.

[0019] In one embodiment, the first weld seam may extend from the first end of the weld joint toward the second end of the weld joint, surrounding the end recess and beyond the end recess. The second weld seam may extend from the second end of the weld joint in the direction of the first end of the weld joint, surrounding the end recess, to an end of the end recess facing the first end of the weld joint.

[0020] It should be noted that in the present disclosure, the end recess may be defined such that a welding mirror is surrounded by the end recess.

[0021] The weld joint may be formed by welding a first weld seam in a first direction such that an end recess of the first weld seam is formed at the end of the first weld seam. Then, a second weld seam may be welded in a second direction opposite to the first direction. The second weld seam may at least partially overlap the first weld seam. During production of the weld joint, the end recess of the first weld seam may be traversed by the second weld seam such that the end recess of the second weld seam at least partially overlaps the end recess of the first weld seam, or is preferably located directly beside the end recess of the traversed first weld seam along the weld joint, or is located at a distance close to the end recess of the traversed first weld seam along the weld joint.

[0022] The end recess of the second weld seam may form the end recess of the above-mentioned weld joint.

[0023] In one embodiment, the weld joint can be designed such that the first weld seam at least partially overlaps the second weld seam in the overlap region. The center lines of the first weld seam and the second weld seam can be directly above each other or at a distance from each other. For example, the distance between the center line of the first weld seam and the center line of the second weld seam can be at most 25%, preferably at most 20%, particularly preferably at most 15% of the width of the first weld seam and / or the second weld seam. The width of the weld seam refers to the actual width of the weld seam, not the width spanned by the curved section of the weld seam.

[0024] In one embodiment, the distance between the end recess and the first end and / or the second end of the weld joint can be at least 20%, preferably at least 50%, and / or a maximum of 1000%, preferably a maximum of 800% of the width of the first weld seam and / or the second weld seam.

[0025] The length of the end recess may correspond to at least 25%, preferably at least 40%, and / or at most 600%, in particular at most 400%, in particular at most 250% of the width of the first and / or second weld seam.

[0026] The first weld seam may at least partially, in particular in the first end region, have a scaly weld solidification line in a first direction, and the second weld seam may at least partially, in particular in the second end region, have a scaly weld solidification line in a second direction, wherein the second direction is opposite to the first direction. In particular, the first weld seam exhibits a scaly weld solidification line in the first direction only in the region not overlapped by the second weld seam.

[0027] The length of the overlapping area may correspond to at least 400%, preferably at least 500%, in particular at least 600% of the length of the end recess. The length of the overlapping area may correspond to at least 10% of the length of the welded joint, or to at least 20% of the length of the welded joint, or to at least 30% of the length of the welded joint. The length of the overlapping area may correspond to a maximum of 80%, or a maximum of 60%, or a maximum of 50%, or a maximum of 40%, or a maximum of 35% of the length of the welded joint.

[0028] In one embodiment, the weld joint may include at least one straight section or have a straight path. For example, the entire weld joint may run in a straight line. Alternatively, a first section of the weld joint may run along a first straight line, and a second section of the weld joint may run along a second straight line. The first weld seam may run completely or partially along the first straight line. The second weld seam may run completely or partially along the second straight line. The first straight line may be substantially parallel to the second straight line, preferably exactly parallel to the second straight line. The first straight line and the second straight line may be biased to the side.

[0029] The weld joint may have a first curved portion, wherein the first curved portion extends and is curved such that a virtual straight line extending vertically through the first end region intersects the weld joint at least twice. Alternatively or additionally, the weld joint may have a second curved section, wherein the second curved section extends and is curved such that a second virtual straight line extending vertically through the second end region intersects the weld joint at least twice. Thus, the welding geometry may be designed such that a further section of the weld joint, typically a curved section, runs close to the associated end region, which may stabilize or reinforce the end region of the weld joint.

[0030] The welded joint may be a laser welded joint. Laser welded joints can be produced in a particularly precise manner. However, this document is not limited to laser welded joints.

[0031] The weld joints can be designed as continuous weld joints, i.e. without interruptions. The partition, in particular the flow field and / or transition region of the partition, can have a large number of such weld joints. Preferably, the partition has corresponding weld joints at least in the flow field and / or transition region; corresponding weld joints can also be provided in the distribution and / or collection region, but these weld joints can differ from the above-mentioned weld joints in their detailed design. It is also possible not to provide any weld joints in the distribution or collection region.

[0032] In some embodiments, at least one of the end regions and, for example, the associated curved segments merge continuously into each other. For example, it can be provided that the first end region adjoins the first curved segment or is a part of the first curved segment, and / or the second end region adjoins the second curved segment or is a part of the second curved segment.

[0033] The shape of the welded joint can be designed so that it can be formed by at most one application of the welding tool and / or the welding laser beam. After the application, the end pit of the previously applied weld seam can be traversed by the applied weld seam. This has the advantage that the welded joint has only one end pit. Alternatively, the shape of the welded joint can be designed so that it can be formed by repeated applications of the welding tool and / or the welding laser beam.

[0034] In one embodiment, the first individual plate in the flow field has a structure for guiding the reaction medium along the front side of the first individual plate on the front side facing away from the second individual plate. The second individual plate may have a structure for guiding the reaction medium along the rear side of the second individual plate on the rear side facing away from the first individual plate.

[0035] These structures for guiding reaction medium can be provided by a plurality of webs and the passage extending between the webs and defined by the webs, for example. The first independent plate can also have distribution and collection area on the outside of the dividing plate respectively. Distribution or collection area can respectively include such structure, and these structures are arranged to distribute the medium introduced into the distribution area from a through opening via flow field or collect or gather the medium flowing from the active area to the second through opening. Transition area can be arranged between distribution or collection area and flow field, and passage and web can continue through this transition area, or they can be interrupted in the transition area. The structure for guiding reaction medium can be designed as medium conduction convex pressure structure.

[0036] In one embodiment, a plurality of weld joints can be arranged at the bottom of the channel. The bottom of the channel can be defined as the lowest point of the channel. In this area, there is usually a contact surface with another separate plate (on the back). The weld seam can not only run along this base, but can also extend through the entire thickness of the material, such as in a first separate plate on the beam entry side. In another separate plate, such as in a second separate plate, the weld seam can penetrate deeper than just penetrating the surface.

[0037] In one embodiment, the channel may be widened in the area of ​​the weld joint. In one embodiment, only the channel of an individual plate may be widened in the area of ​​the weld joint. Alternatively, the channel of the first individual plate and the second individual plate may each be widened in the area of ​​the weld joint. In some embodiments, the first individual plate may have channels of different widths and / or depths than the second individual plate. In particular, the cathode plate may have wider and / or deeper gas channels than the anode plate. In particular, in this case, the channel of the individual plates may be widened in the area of ​​the weld joint, which area has a smaller width. Additionally or alternatively, during welding, the channel of the individual plates may be widened in the area where the welding beam enters the weld joint.

[0038] The webs and the channels can be straight in the flow field and run parallel to each other, in particular parallel to the main flow direction. Additionally or alternatively, the webs and the channels in the flow field can be partially or completely wavy, in particular have essentially the same wavy shape, in particular run close to each other with the same phase, and / or periodically repeatingly trapezoidal, in particular run close to each other with essentially the same trapezoidal shape.

[0039] The flow field can be characterized, for example, by the fact that all the webs and channels it comprises are straight and run parallel to each other and to the main flow direction. Alternatively, the webs and channels can also be wavy and run close to each other in the same phase and along the main flow direction, in particular with the same wave shape. Furthermore, the flow field can be characterized by the fact that the webs and channels in the flow field have a constant flow cross section and / or a substantially constant height. In the transition region, the webs and channels can have a reduced cross section and / or height compared to the flow field.

[0040] In one embodiment, at least one weld joint is arranged in a plurality of channels in the flow field. Typically, a weld joint can be arranged in each channel of the flow field. However, it has been shown that it is advantageous if there is a certain distance between the two nearest weld joints at least in a section that is orthogonal or transverse to the main extension direction of the channel, thus at an angle greater than 0° and less than 90°. For example, there may be at most four channels, preferably at most three channels, in particular at most two channels, between the two nearest weld joints. This means that five, in particular four, and in particular two webs are located between the closest weld joints.

[0041] Additionally or alternatively, a plurality of spaced apart weld joints may be arranged along the channel. Advantageously, the length of the weld joints and / or the distance between the weld joints closest to each other within a channel is between 0.2 mm and 3 mm, in particular between 0.5 mm and 1.5 mm, at least in the region within a channel. It has been shown that, in terms of the total peripheral resistance associated with the weld joints, the ratio of distance to length is preferably less than 3, preferably less than 2.5.

[0042] Along their extension, the welded joints may have a substantially constant distance from the webs delimiting the channel. Deviations roughly corresponding to the width of the welded joint may still be considered as substantially constant distances. In this context, the distance between the welded joint and the centerline of the respective immediately adjacent web in an orthogonal projection onto a plane parallel to the diaphragm plane may be considered in particular.

[0043] In particular, the welded joints can be arranged substantially following the main flow direction and transversely to the main flow direction, each welded joint being substantially in the center of the channel. In order to provide sufficient space for the welded joints, the channel can be widened in the corresponding section. For this purpose, the flanks connecting the channel bottom with the web top can be steeper than in other sections of the channel without welded joints.

[0044] The shape of the weld joints may follow the shape of the channels in which they are arranged.

[0045] The present invention also relates to a method for producing a separator of the above type. The method comprises the following steps:

[0046] I. Provide a first separate plate and a second separate plate, each separate plate 2a, 2b comprising at least one through opening 11a-11c for fluid passage, a flow field 17 and a transition region, which is arranged between the flow field 17 and the through openings 11a-11c and fluidically connects the through openings 11a-11c and the flow field 17 to each other.

[0047] II. Two separate plates are connected in the contact area of ​​the separate plates by means of a welding joint, the welding joint being designed so that the welding joint extends longitudinally from a first end located in the first end area to a second end located in the second end area, and the welding joint forms an end recess between the first end and the second end, and the end recess is spaced apart from the first end and the second end.

[0048] The produced separator then comprises a first individual plate and a second individual plate connected to the first individual plate, wherein the two individual plates are in contact with each other in the contact region.

[0049] In step II, the first weld seam may be welded in a first direction. The second weld seam may be welded in a second direction opposite to the first direction, and the second weld seam overlaps the first weld seam in an overlap region.

[0050] The end recess of the first weld seam can be at least partially, preferably completely traversed by the second weld seam. In this way, a continuous weld joint with only one end recess can be generated, which is spaced apart from the first end of the weld joint and from the second end of the weld joint.

[0051] In another aspect, an electrochemical system is provided, the electrochemical system comprising a plurality of stacked separators or bipolar plates of the above-described type.

[0052] In an electrochemical system, a membrane electrode assembly (MEA) may be arranged between stacked adjacent separators, the membrane electrode assembly comprising a membrane and an edge portion at least partially surrounding the membrane. The edge portion may be particularly useful for strengthening the MEA. The flow field of the separator may be located within the edge portion.

[0053] The membrane may have a diaphragm as well as a catalyst layer and electrodes. In addition, a gas diffusion layer (GDL) may be arranged on one or both surfaces of the MEA. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Exemplary embodiments of separators and electrochemical systems are shown in the accompanying drawings and will be explained in more detail according to the following description. In the drawings:

[0055] Figure 1 schematically illustrates a perspective view of an electrochemical system including a plurality of separators or bipolar plates arranged in a stack;

[0056] Figure 2 Schematically shows the Figure 1 A perspective view of two bipolar plates of a system, wherein a membrane electrode assembly (MEA) is arranged between the bipolar plates;

[0057] Figure 3 Schematically shows the Figure 1The system's approach to the cross-section of the system's plate stacking;

[0058] Figure 4 Shown according to Figures 1 to 3 A schematic cross-section of a top view of an exemplary separator of , wherein a series of weld joints are arranged in an end region of the flow field adjacent to the transition region;

[0059] Figure 5 Shown according to Figure 4 A schematic cross-section of a top view of a separator, wherein welded joints are also arranged in two outer channels of the flow field;

[0060] Figure 6 Shown according to Figure 5 A schematic cross-section of a top view of a separator, wherein the weld joint is also arranged in the central channel of the flow field;

[0061] Figure 7 Shown as Figure 6 A schematic cross-section of a top view of a separator is shown, wherein a row of welded joints is arranged in the transition region and additional welded joints are arranged in the distribution region;

[0062] Figure 8A-8D Various configurations of welded joints are shown;

[0063] Figure 8C 'Scheme showing the Figure 8C The indicated passage Figure 8C Height profile of the end pit section BB;

[0064] Fig. 9 The diagram shows the beam entering side. Fig. 8A A cross-section of a top view of a bulkhead showing a welded joint;

[0065] Fig.10 The diagram shows a view from the rear side. Fig. 8A A cross-section of a top view of a bulkhead showing a welded joint;

[0066] Fig.11 A cross section showing a top view of the separator in the region of two welded joints;

[0067] Fig.12 Shown is a crossover in an area without end pits Figure 4 A schematic cross section of a welded joint of a bulkhead;

[0068] Fig.13 The diagram shows the region where the end recess is located. Figure 4 A schematic cross section of a welded joint of a bulkhead;

[0069] Figures 14A-14Bschematically showing a cross-section of a top view of the flow field of individual plates having different channel shapes;

[0070] Fig. 14C shows a welded joint Fig.14A and 14B A partition assembled from separate panels;

[0071] Fig.15 is based on Figures 1 to 3 A schematic top view of an example separator having a non-continuous straight weld joint;

[0072] Fig.16 a top view schematically showing a cross section of an exemplary separator having a large number of weld joints; and

[0073] Fig.17 A method for producing an exemplary separator is schematically shown.

[0074] Here and below, features that appear repeatedly in different figures are in each case denoted by the same or similar reference numerals. For the sake of clarity, reference is sometimes made to a complete set of figures (e.g., FIG. 8 instead of FIG. Figures 8A-8C 'one). DETAILED DESCRIPTION

[0075] Figure 1 An electrochemical system 1 is shown, which comprises a plurality of structurally identical metal separators or bipolar plates 2, which are arranged in a stack 6 and stacked in the z-direction 7. The bipolar plates 2 of the stack 6 are sandwiched between two end plates 3, 4. The z-direction 7 is also referred to as the stacking direction. In the present example, the system 1 is a stack of fuel cell cells. In each case two adjacent bipolar plates 2 of the stack enclose an electrochemical cell cell between them, which is used, for example, to convert chemical energy into electrical energy. In order to form an electrochemical cell cell of the system 1, a corresponding membrane electrode assembly (MEA) is arranged between adjacent bipolar plates 2 of the stack (see, for example Figure 2 ). MEAs typically each include at least one membrane, such as an electrolyte membrane. A gas diffusion layer (GDL) may also be arranged on one or both surfaces of the MEA. Figure 1 and Figure 2 Not shown.

[0076] In alternative embodiments, the system 1 may likewise be in the form of an electrolyzer, an electrochemical compressor or a redox flow battery. In these electrochemical systems, separators may likewise be used. Although the medium conducted on or through the separators in the case of an electrolyzer, in an electrochemical compressor or in a redox flow battery may in each case be different from the medium used for a fuel cell monomer system, the structure of these separators may correspond to the structure of the separator 2 described in detail herein.

[0077] The z-axis 7 together with the x-axis 8 and the y-axis 9 define a right-handed Cartesian coordinate system. The partitions 2 each define a plate plane, each of the plate planes of the individual plates being oriented parallel to the xy plane and thus perpendicular to the stacking direction 7 or z-axis 7. The end plate 4 comprises a plurality of media ports 5 via which media can be fed to the system 1 and via which media can be discharged from the system 1. These media that can be fed to the system 1 and discharged 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 water vapor or depleted fuel, or coolants such as water and / or ethylene glycol.

[0078] Figure 2 Shown in stereogram form Figure 1 Two adjacent separators 2 of an electrochemical system of the type of system 1, and a membrane electrode assembly (MEA) 10 known in the prior art arranged between the two adjacent separators 2, Figure 2 The MEA 10 is largely hidden by the separator 2 facing the viewer. The separator 2 is formed by two separate plates 2a and 2b, which are joined together in a material connection (see for example Figure 3 ), where only the first individual panel 2a facing the observer and hiding the second individual panel 2b is in Figure 2 The individual plates 2a, 2b can each be made of a metal sheet, for example a stainless steel sheet. The individual plates 2a and 2b can be welded to each other by, for example, laser welding the connection.

[0079] The individual plates 2a and 2b comprise through-openings which are aligned with one another and form through-openings 11a-11c in the partition 2. When a plurality of partitions of the type of partition 2 are stacked, the through-openings 11a-11c form lines extending through the stack 6 in the stacking direction 7 (see Figure 1). Typically, each of the lines formed by the through-openings 11a-11c is fluidically connected to one of the ports or media ports 5 in the end plate 4 of the system 1. By means of the lines formed by the through-openings 11a, for example, a coolant can be introduced into the stack or discharged from the stack. Conversely, the lines formed by the through-openings 11b, 11c can be configured to supply fuel and reaction gases to the electrochemical cells of the fuel cell cell stack 6 of the system 1 and to discharge reaction products from the cell stack. The through-openings 11a-11c for medium conduction are substantially parallel to the plate plane.

[0080] In order to seal the through-openings 11a-11c with respect to the interior of the stack 6 and with respect to the environment, the first individual plates 2a each comprise a sealing arrangement in the form of a sealing bead 12a-12c, which is each arranged around the through-opening 11a-11c and each completely surrounds the through-opening 11a-11c. Figure 2 The rear side of the optical disc 100 comprises corresponding sealing beads (not shown) for sealing the through-openings 11a - 11c. Alternatively, an elastomeric seal may be used.

[0081] In the electrochemically active region 18, the first individual plates 2a are arranged on their facing sides. Figure 2 On the outside of the observer there is a flow field 17 with structures for guiding the reaction medium along the outside of the individual plates 2a. Figure 2 In the embodiment, these structures are provided by a plurality of webs and channels running between and defined by these webs. Figure 2 On the outer side of the observer, the first individual plates 2a each also have a distribution and collection area 20. The distribution or collection area 20 in each case comprises structures which are designed to distribute the medium introduced into the distribution area 20 from the first of the two through-openings 11b over the entire active area 18 or to collect or combine the medium flowing from the active area 18 toward the second through-opening 11b. The fluid guiding structures 29 of both the distribution or collection areas 20 are also located in Figure 2 The distribution area 20 is provided by webs and channels running between the webs and bounded by the webs. In the following, for simplicity, only the distribution area 20 will be discussed; a corresponding description also applies to the collection area 20.

[0082] The sealing ridges 12a-12c have passages 13a-13c, wherein the passage 13a is formed on both the lower side of the upper individual plate 2a and the upper side of the lower individual plate 2b, while the passage 13b is formed in the upper individual plate 2a, and the passage 13c is formed in the lower individual plate 2b. For example, the passage 13a is designed as a local protrusion of the ridge, allowing the coolant to pass between the through-opening 12a and the distribution area 20, allowing the coolant to enter the distribution area between the partitions, or to be drawn out from the collection area 20. In addition, the passages 13b enable hydrogen to pass between the through-opening 12b and the distribution area on the top side of the upper individual plate 2a, and these passages 13b are characterized by perforations facing the distribution area and running obliquely relative to the plate plane. Thus, for example, hydrogen flows through the passage 13b from the through-opening 12b to the distribution area on the top side of the upper individual plate 2a, or flows from the collection area in the opposite direction. The passage 13c enables, for example, air to pass between the through-opening 12c and the distribution area, so that the air passes into the distribution area on the underside of the lower individual plate 2b or is conducted out of the collection area. The relevant perforations are not visible here.

[0083] The first individual plates 2a each also include a further sealing arrangement in the form of a peripheral lip 12d which runs around the flow field 17 of the active area 18, the distribution and collecting area 20 and the through-openings 11b, 11c and seals them with respect to the through-opening 11a, i.e. with respect to the coolant circuit, and with respect to the environment of the system 1. The second individual plates 2 each include a corresponding peripheral lip. The structure of the active area 18, the distribution structure of the distribution area and the collecting area 20 and the sealing lip 12a-12d are each formed in one piece with the individual plates 2a and are each formed into the individual plates 2a in an embossing process or a deep drawing process or by means of hydraulic forming. The same applies to the corresponding structure of the second individual plates 2b.

[0084] The two through-openings 11b or the lines formed by the through-openings 11b through the plate stack of the system 1 each face the first individual plate 2a via a passage 13b in the sealing collar 12b, via a distribution structure of the distribution or collecting area 20, and via the Figure 2 Similarly, the two through-openings 11c or the pipelines formed by the through-openings 11c through the plate stack of the system 1 each lead away via a corresponding flange passage, via a corresponding distribution and collection structure and via a second separate plate 2b. Figure 2The through-openings 11a or the lines formed by the through-openings 11a through the plate stack of the system 1 are fluidically connected to each other via cavities 19 enclosed by the individual plates 2a and 2b. The cavities 19 are used in each case to conduct a coolant through the separator 2 and in particular to cool the electrochemically active regions 18 of the separator 2.

[0085] Figure 3 Schematically shows the Figure 1 The section plane is oriented in the z-direction and is therefore perpendicular to the plate plane of the partition wall 2. Figure 3 In the example, the section plane runs along the curved section, i.e. along Figure 2 The cutting line CC in the figure proceeds.

[0086] The stacked, structurally identical separators 2 each comprise the above-mentioned first metal individual plate 2a and the above-mentioned second metal individual plate 2b. Structures for guiding the medium along the outer surface of the separator 2 are evident, these structures here in particular in each case being in the form of webs and channels defined by the webs. In particular, channels are shown on the surfaces of the individual plates 2a and 2b adjacent to each other, which surfaces are oriented away from each other, as well as cooling channels in the cavity 19 between the individual plates 2a and 2b adjacent to each other. Between the cooling channels in the distribution or collection area 20 and in the active area 18, the two individual plates 2a, 2b rest on each other in the contact area 24 and are connected to each other there, in this case by means of a laser welded seam 50.

[0087] A corresponding membrane electrode assembly (MEA) 10, such as is known from the prior art, is arranged between adjacent separators 2 of the stack. The MEA 10 generally comprises a membrane, such as an electrolyte membrane, and an edge portion 15 connected to the membrane 14. For example, the edge portion 15 can be attached to the membrane 14, such as by an adhesive connection or by lamination. The lower transition region 21 of the separator 2 is placed opposite the overlapping region of the edge portion 15 and the membrane 14.

[0088] The membrane of the MEA 10 extends in each case at least over the active area 18 of the adjacent separator plates 2 and enables the transfer of protons over or through the membrane 14. However, the membrane does not reach into the distribution or collection area 20. The edge sections 15 of the MEA 10 serve in each case to position, secure and seal the membrane between the adjacent separator plates 2.

[0089] The edge portion 15 in each case covers the distribution or collection area 20 of the adjacent partition 2. The edge portion 15 can also extend outwards beyond the peripheral flange 12d and abut or protrude beyond the outer edge area of ​​the individual plates 2a and 2b (see Figure 2 ).

[0090] Furthermore, a gas diffusion layer 16 can be additionally arranged in the active region 18. The gas diffusion layer 16 can guide the flow to the membrane over the largest possible area of ​​the surface of the membrane and can thus improve the proton transfer through the membrane. The gas diffusion layer 16 can in each case be arranged, for example, on both sides of the membrane in the active region 18 between adjacent separators 2. The gas diffusion layer 16 can be formed, for example, by a fiber mat or include a fiber mat.

[0091] Also refer to Figure 4 , which shows Figures 1 to 3 Schematic cross section of a top view of an exemplary separator 2 in FIG. Figure 4 The partition plate 2 in FIG. 1 has a series of welded joints 50', which are arranged in the end region of the flow field 17. The end region 17 of the flow field is adjacent to a transition region 17'. The transition region 17' is located between the collection or distribution region 20 and the flow field 17. For the sake of clarity, only some of the multiple welded joints 50' shown are provided with reference numerals as examples.

[0092] Pressure pulsation tests carried out by the applicant have shown that welded joints may form weak points in the diaphragm 2, particularly at their start and end. When high fluid pressures are applied, welded joints sometimes crack at their start and end.

[0093] The present invention is therefore intended to further increase the durability of the partition plate 2. In particular, the use of the welded joint 50' is intended to achieve a higher service life, at least in the case of excessive operating pressures and / or pulsations in the operating pressure of the medium, in particular the coolant. Fig. 8A As can be seen, according to the present invention, the weld joint 50' extends longitudinally from a first end 51 located in the first end region to a second end 61 located in the second end region. The weld joint 50 forms an end recess 63 between the first end 51 and the second end 61. The end recess 63 is spaced apart from the first end 51 of the weld joint 50' and from the second end 61 of the weld joint 50'.

[0094] The weld joint 50 ′ has a first weld seam 50 , a second weld seam 60 and an end recess 63 .

[0095] The first weld seam 50 is welded in a first direction starting from the first end 51 towards the second end 61 .

[0096] The second weld seam 60 is welded in a second direction starting from the second end 61 in the direction of the first end 51. The length of the first weld seam 50 measured from the first end 51 in the direction of the second end extends beyond the end recess 63 but does not reach as far as the second end 61. The second weld seam 60 starts at the second end and extends around the end recess 63 to an end of the end recess 63 closer to the first end 51. The end recess 63 of the weld joint 50' is an end recess formed by pausing at the end of the second weld seam 60 during welding of the second weld seam 60. The end recess of the first weld seam 50 is crossed by the second weld seam 60, so that Figure 4 or Fig. 8A Not visible in Figures 4 to 7 In the example shown, the first weld seam 50 and the second weld seam 60 run along a straight line. In other examples, the first weld seam 50 and / or the second weld seam 60 can include a curved portion.

[0097] In addition to the weld joint 50', the partition 2 may also have further weld seams connecting the first individual plate 2a to the second individual plate 2b. In contrast to the weld joint 50', the further weld seams may comprise only one weld seam. The end recesses of these weld seams may be present, for example, in the end region of the weld seam.

[0098] In particular, the weld joint 50 ′ can be arranged in the region of the respective individual plate spanned by the gas diffusion layer 16 , ie in the flow field 17 or in the transition region 21 .

[0099] Figure 5 A cross-section of a top view of an alternative separator is schematically shown. Figure 5 The partition 2 corresponds to Figure 4 A partition 2 is provided in which additional weld joints 50' are arranged in two outer channels of the flow field. The outer channels of the partition 2 are in this case two lateral outer channels of the flow field, which are at a minimum distance from the corresponding lateral outer edge of the partition 2. In this example, the outermost channels run parallel to the outer edge of the partition 2. In other examples, the outer channels can have different shapes. A plurality of weld joints 50' are arranged along these channels in the main flow direction and are spaced apart from each other. Instead of some or all of these weld joints 50', weld seams can be arranged along and in the outer channels, which are formed by only one weld seam.

[0100] Figure 6 Shown as Figure 5 Schematic cross section of a top view of a separator 2 is shown, wherein an additional weld joint 50' is arranged in a channel located in the center of the flow field 17. The channels of the flow field 17 shown run parallel to each other and parallel to the outer edge of the separator 2, i.e. in the x-direction in this example. Figure 5 In the embodiment, a plurality of weld joints 50' are arranged in the x-direction along at least some of the centrally located channels in the flow field 17. Preferably, the plurality of weld joints 50' are arranged at a distance from each other along a straight line parallel to the y-axis, wherein each weld joint 50' extends substantially in the x-direction. In the example shown, the weld joint 50' in the first channel is arranged to be offset from the weld joint 50' in the next channel in which the weld joint 50' is arranged. In other examples, the weld joint 50' in the first channel may be at the same level as the weld joint 50' in the next channel in which the weld joint 50' is arranged. For example, the latter Figure 7 shown.

[0101] Figure 7 Schematically shows the Figure 6 The cross section of the top view of the partition shown, wherein a row of welded joints 50 'is also arranged in the transition area 17 ', which is placed in the flow direction between the distribution or collection area 20 and the flow field 17. In addition, the central channel of the flow field 17 is arranged Figure 7 The welded joints 50' are arranged in rows at substantially the same height (rather than Figure 6 In other embodiments, the first region of the flow field may have a Figure 7 The plurality of parallel rows of welded joints 50' are shown, and the second region may have a Figure 6 Staggered welded seams shown.

[0102] exist Figure 7 In the embodiment of the invention, the welded joints 50' are also arranged in the distribution area and / or the collecting area 20. In particular, the welded joints 50' are arranged in the distribution or collecting area 20 at the ends of the channels of the distribution or collecting area 20 facing the passage opening 11b. The welded joints 50' of the distribution or collecting area preferably extend in the main flow direction. The welded joints 50' can have the same length or different lengths.

[0103] Figures 8A to 8D Various embodiments of weld joints 50 ′ are shown, which may be used, for example, in the diaphragm 2 shown in the previous figures. Fig. 8A The weld joint 50' comprises a first weld seam 50 which is welded in a first direction represented by the direction of arrow I and welded along a first imaginary straight line starting from a first end 51 of the weld joint 50'. The first weld seam 50 terminates in a first end recess 53 which is only Fig. 8A The length of the first welded joint 50 is indicated by the length of the directional arrow I. Fig. 8AThe weld joint 50' includes a second weld seam 60 that is welded in a second direction represented by the direction of arrow II, starting from a second end 61 of the weld joint 50' and welded along the same first imaginary straight line. The second weld seam 60 overlaps the first weld seam 50 and is welded so that it extends beyond the first end recess 53. The second weld seam ends in the second end recess 63. Fig. 8A , the end recess 63 is arranged substantially centrally between the first end 51 and the second end 63 and is illustrated by means of substantially two ovals. The length of the second weld seam 60 is indicated by the length of the directional arrow II. The width of the first weld seam 50 substantially corresponds to the width of the second weld seam 60 and the width of the weld joint 50'.

[0104] Figure 8B The weld joint 50' comprises a first weld seam 50 which is welded in a first direction represented by the direction of arrow I and welded along a first imaginary straight line starting from a first end 51 of the weld joint 50'. The first weld seam 50 terminates in a first end recess 53 which is only Figure 8B The length of the first welded joint 50 is indicated by the length of the directional arrow I. Figure 8B The weld joint 50' includes a second weld seam 60, which is welded in a second direction represented by the direction of arrow II, and welded along a second imaginary straight line starting from the second end 61 of the weld joint 50'. The first imaginary straight line and the second imaginary straight line correspond to the center lines of the first weld seam 50 and the second weld seam 60. The first imaginary straight line and the second imaginary straight line are parallel to each other, but have a certain distance from each other. The second weld seam 60 overlaps with the first weld seam 50 and is welded so that it extends beyond the first end recess 53. The second weld seam terminates in the second end recess 63. Figure 8B 60 . The end recess 63 is also arranged substantially centrally between the first end 51 and the second end 61. The length of the second weld seam 60 is indicated by the length of the directional arrow II. The width of the first weld seam 50 substantially corresponds to the width of the second weld seam 60. The width of the weld joint 50 'can vary. In the overlap region where the first weld seam 50 and the second weld seam 60 overlap, the weld joint has a maximum width.

[0105] Figure 8C Welded joint 50' with Fig. 8A The weld joint of is substantially corresponding, wherein the end recess 63 completely coincides with the end recess 53 and is arranged closer to the first end 51 than to the second end 61. In this example, the end recess 63 is about one end recess length away from the first end 51.

[0106] Figure 8C 'Scheme showing the Figure 8C The cross section BB shown is through the weld joint 50' and Figure 8C Graph K shows the height profile of the weld seam in a cross section of its length in the region of the end recess 63. The double arrow indicates the length of the end recess 63. In the region outside the end recess 63, the surface of the weld seam is noisy, while the surface in the end recess 63 is smoother.

[0107] Fig. 9 A section from a top view of an individual plate of a partition 2 according to one of the preceding figures is shown, viewed from the beam entry side, ie on plate 2b, with an end recess 63. A welded joint 50' is shown corresponding to Fig. 8A The first weld seam 50 has a first scaly weld solidification line in a region not overlapping with the second weld seam 60, while the second weld seam 60 has a second scaly weld solidification line extending in a direction opposite to the first scaly weld solidification line.

[0108] Fig.10 A cross-section of a top view of an individual plate of the partition 2 according to one of the preceding figures is shown, viewed from the light beam exit side, ie, viewing the rear side of the plate 2a. The welded joint 50' is shown corresponding to Fig. 8A Welded joints in.

[0109] Fig.11 A schematic cross-section of a top view of a separator 2 is shown, wherein the channel 26 is designed as a wider channel section 26a and has a steeper channel wall in the region in which the weld joint 50' is provided, or the web 27 is designed with a steeper web wall 27a. This results in an enlargement of the contact surface of the two individual plates 2a, 2b, so that even in the case of a slight deviation of the laser beam, it is possible to ensure that the weld joint 50' is achieved in the region in which the two individual plates 2a, 2b are superimposed on each other without a gap. The end recesses 63 are also not terminal here.

[0110] Fig.12 and 13 Each shows a schematic section through a partition 2 in the region of an exemplary weld joint 50'. The cut is substantially perpendicular to the direction of the weld joint 50'. Fig.12 shows a region in which the weld joint 50 ′ extends through the entire material thickness of the second plate 2 b , but only through approximately one third of the material thickness of the first plate 2 a , Fig.13 The weld seam 50' in FIG. 2 is shown in an area that completely passes through the material thickness of the second plate 2b and the first plate 2a. The weld seam 50' thus extends from the outer side 22 of the first plate 2a to the outer side 23 of the second plate 2b. Fig.12As shown, the weld joint can also be visible only on one of the two outer sides 22, 23 - the beam entry side - and not extend all the way to the respective other outer side 23, 22. Fig.12 and 13 As indicated, the thickness of the first individual plate 2a and / or the second individual plate 2b may be at least 50 μm, in particular at least 70 μm. The thickness of the plate may also be at most 200 μm, in particular at most 150 μm, in particular at most 100 μm. In view of these relatively small thicknesses, as Fig.13 As shown, the weld joint 50 ′ may be in the form of a through-weld.

[0111] Figures 14A-14B Each schematically shows a cross-section of a top view of a flow field 17 of an individual plate having different channel shapes; for example, Fig.14A A top view of a section of the flow field of a single plate 2a is shown, and Fig. 14B A cross section of the flow field 17 of the respective individual plate 2b is shown in a top view. A plurality of wavy webs having a wavy shape in plan view, for example a sine wave or a sawtooth shape, define channels for medium guidance between the wavy webs. Fig. 14C The view that results when two separate plates 2a, 2b are overlapped in the region of their flow field 17 is shown. This results in a large number of transfer points for fluid, in particular coolant, between the two separate plates 2a, 2b. Welded joints 50' as described above can also be formed in flow fields shaped in this way; for the sake of clarity, only some of them are marked with reference numerals.

[0112] Fig.15 is a schematic top view of another embodiment of a weld joint 50' according to the present invention, having a first weld seam 50 and a second weld seam 60, which overlaps the first weld seam in some sections. Unlike the previous example, the first and second ends of the weld joints 51, 62 are not located in the straight section of the weld joint 50', but in the curved end region. Similarly, the end recesses 63 of the weld joint and the second weld seam are positioned away from the first end region 52 and the second end region 62 of the weld joint 50'. Therefore, neither the first end and the second end 51, 62 of the weld joint form the outermost end of the weld joint 50', which makes the weld joint 50' more resistant to pulsating fluids, but requires more space. Therefore, Fig.11 The channel extension 26a shown in FIG. Fig.15 The combination of the embodiments of the weld joint 50 ′ shown in FIG. 5 is advantageous.

[0113] Fig.16A top view of a cross section of the active area of ​​another exemplary separator is schematically shown. The weld joint 50' is shown here with a length LS, for example 0.6 mm, which is substantially equal to the distance DS between one end of the weld joint 50' and the start of the nearest weld joint 50' in the same channel 95 in the section shown. There is one channel 90 without a weld joint and two webs 27, one channel 90 and two webs 27 are arranged between two weld joints 50' that are closest to each other in a direction transverse to the main extension direction of the channels 90, 95, and therefore at an angle greater than 0° but less than 90°. If the weld joints 50' that are located closest to each other on a line orthogonal to the main extension direction of the channels 90, 95 are considered, then in the section considered, three channels and four webs 27 are arranged between these weld joints 50', two of which are channels 90 without weld joints, and one of the channels 95 includes a weld joint.

[0114] Fig.17 Finally, a method for producing a partition 2 is schematically shown. In a first step S1, a first separate plate 2a and a second separate plate 2b are provided. Each of them comprises at least one through opening for the passage of a fluid, a flow field and a transition region arranged between the flow field and the through opening. The transition region fluidically connects the through opening and the flow field to each other. In a further second step S2, the two separate plates 2a, 2b are placed on top of each other to form a contact zone. In a first joining step V1, the two separate plates 2a, 2b are joined to each other in the contact zone of each separate plate by means of a first welding seam 50, the first welding seam 50 extending perpendicular to the plane of the accompanying drawing. In a second joining step V2, the two separate plates 2a, 2b are joined to each other in the contact zone of the separate plates by means of a second welding seam 60, the second welding seam 60 extending perpendicular to the plane of the accompanying drawing. The two weld seams 50, 60 overlap each other in sections and together form a weld joint 50' which extends longitudinally from a first end in the first end region of the weld joint 50' to a second end in the second end region of the weld joint 50'. The weld joint forms an end recess between the first end and the second end and the end recess is spaced apart from the first end and the second end.

[0115] List of reference numerals:

[0116] 1 Electrochemical system

[0117] 2 Separator or bipolar plate

[0118] 2a Separate board

[0119] 2b Separate board

[0120] 3 End plate

[0121] 4 End plate

[0122] 5 Media ports

[0123] 6 Stack

[0124] 7 z direction

[0125] 8 x direction

[0126] 9 y direction

[0127] 10. Membrane Electrode Assembly

[0128] 11a-11c through opening

[0129] 12a-12d Sealing flange

[0130] Pathway 13a-13c

[0131] 14 Membrane

[0132] 15 Edge part.

[0133] 16 Gas Diffusion Layer

[0134] 17 Flow Field

[0135] 17' Transition Zone

[0136] 18 Electrochemically active area

[0137] 19 Cavity

[0138] 20 Distribution or collection area

[0139] 22 The outer side of the first separate plate 2a

[0140] 23 The outer side of the second separate plate 2b

[0141] 25 Contact area

[0142] 26 channels

[0143] 26a Widening channel

[0144] 27 belly plate

[0145] 27a Steeper web wall 29 Fluid guiding structure in the distribution area or collection area 30 External channel of flow field

[0146] 40 Central channel of the flow field

[0147] 50' Welded Joint

[0148] 50 First weld seam

[0149] 51 First end of welded joint

[0150] 52 first end region

[0151] 53 End pit of first weld seam

[0152] 60 Second welding seam

[0153] 61 Second end of welded joint

[0154] 62 Second end region

[0155] 63 Second weld seam and end pit of weld joint

[0156] 90 Channel without welded joint

[0157] 95 Channel with welded joint

[0158] K-curve chart

Claims

1. A separator (2) for an electrochemical system (1), comprising a first separate plate (2a) and a second separate plate (2b), the second separate plate being connected to the first separate plate (2a) by means of a welded joint (50'), Each individual plate (2a, 2b) comprises at least one through-opening (11a-11c) for the passage of a fluid, a flow field (17), a distribution or collection area (20) fluidically connecting the through-opening (11a-11c) to the flow field (17), and a transition area arranged between the flow field (17) and the distribution or collection area (20), in, The weld joint is arranged in the flow field (17) and / or in the transition region, The weld joint (50') extends longitudinally from a first end (51) located in a first end region (52) to a second end (61) located in a second end region (62), wherein the weld joint (50') forms an end recess (63) between the first end (51) and the second end (61), and the end recess (63) is spaced apart from the first end (51) and the second end (61).

2. A separator (2) according to any one of the preceding claims, characterized in that The end recess is located in a central 85% position, in particular a central 70% position, between the first end (51) and the second end (61) of the weld joint (50').

3. A separator (2) according to any one of the preceding claims, characterized in that The weld joint (50') includes a first weld seam (50), which extends from the first end of the weld joint (50') toward the second end of the weld joint (50'), surrounds the end recess (63) and extends beyond the end recess (63), and the weld joint (50') includes a second weld seam (60), which extends from the second end of the weld joint (50') toward the first end of the weld joint (50'), surrounds the end recess (63), and reaches the end of the end recess facing the first end (51) of the weld joint (50').

4. A separator (2) according to any one of the preceding claims, characterized in that The distance between the end recess and the first end and / or the second end of the weld joint (50') is at least 20%, preferably at least 50%, and / or at most 1000%, preferably at most 800% of the width of the first weld seam and / or the second weld seam.

5. A separator (2) according to any one of the preceding claims, characterized in that The end recess has a length corresponding to at least 25%, preferably at least 40%, and / or at most 600%, in particular at most 400%, preferably at most 250% of the width of the first weld seam and / or the second weld seam.

6. A separator (2) according to any one of the two preceding claims, characterised in that The first weld seam (50) has a scaly weld solidification line in a first direction at least in some sections, in particular in the first end region (52), and the second weld seam (60) has a scaly weld solidification line in a second direction at least in some sections, in particular in the second end region (62), wherein the second direction is opposite to the first direction.

7. A separator (2) according to any one of the preceding claims, characterised in that The overlapping region has length, - said length corresponds to at least 400%, preferably at least 500%, in particular at least 600% of the length of said end recess, and / or - corresponds to at most 80% or at most 60% or at most 50% or at most 40% or at most 35% of the length of the weld joint, and / or - corresponds to at least 10% of the length of the welded joint or at least 20% of the length of the welded joint or at least 30% of the length of the welded joint.

8. A separator (2) according to any one of the preceding claims, characterised in that The weld joint (50') has a shape designed so that it can be formed by at most one application of a welding tool and / or a welding laser beam.

9. A separator (2) according to any one of the preceding claims, characterised in that The first separate plate (2a) has a structure in the flow field (17) on the front side facing away from the second separate plate (2b) for guiding the reaction medium along the front side of the separate plate (2a), and wherein the second separate plate (2b) has a structure on the rear side facing away from the first separate plate (2a) for guiding the reaction medium along the rear side of the separate plate (2b), and wherein the structure for guiding the reaction medium is in some cases formed by a plurality of webs and channels extending between the webs and defined by the webs.

10. A separator (2) according to the preceding claim, characterised in that A plurality of weld joints (50') are arranged at the bottom of the channel.

11. The separator (2) according to claim 9, characterized in that The channel of at least one individual plate is widened in the region of the weld joint.

12. The separator (2) according to claim 9, characterized in that The webs and channels in the flow field are rectilinear and run parallel to one another, in particular parallel to the main flow direction.

13. The separator (2) according to claim 9, characterized in that The webs and channels in the flow field are wavy and run close to each other in particular in substantially the same wavy shape and / or are periodically repeated trapezoidal and run close to each other in particular in substantially the same trapezoidal shape.

14. The separator (2) according to claim 9, characterized in that In each case, at least one weld joint (50') is arranged in a plurality of channels in the flow field (17), wherein, at least in some sections orthogonal to or transverse to the main extension direction of the channel, at most four channels, in particular at most three channels, in particular two channels, are arranged between two weld joints (50') that are closest to each other.

15. The separator (2) according to claim 9, characterized in that A plurality of spaced-apart weld joints (50') are arranged along the channel, wherein, at least in an area within a channel, the length of the weld joints (50') and / or the distance between the weld joints (50') closest to each other within a channel is between 0.2 mm and 3 mm, in particular between 0.5 mm and 1.5 mm.

16. A method for producing a separator (2) according to any one of the preceding claims, comprising the following steps: I. providing a first separate plate and a second separate plate, each separate plate (2a, 2b) comprising at least one through opening (11a-11c) for the passage of a fluid, a flow field (17), and a transition region, the transition region being arranged between the flow field (17) and the through opening (11a-11c) and fluidically connecting the through opening (11a-11c) and the flow field (17) to each other, and II. The two separate plates (2a, 2b) are connected in the contact area of ​​the separate plates by means of a welding joint (50'), the welding joint being designed so that the welding joint (50') extends longitudinally from a first end (51) located in a first end area (52) to a second end (61) located in a second end area (62), and the welding joint forms an end recess (63) between the first end (51) and the second end (61), and the end recess is spaced apart from the first end and the second end.

17. An electrochemical system (1) comprising a plurality of stacked separators (2) according to any one of claims 1 to 15.

18. The electrochemical system (1) according to the preceding claim, characterized in that A membrane electrode assembly is arranged between each pair of adjacent separators (2) of the stack, the membrane electrode assembly comprising a membrane and an edge portion at least partially surrounding the membrane.

19. The electrochemical system (1) according to the preceding claim, characterized in that The flow field is located within the edge portion and, in particular, is surrounded by the edge portion and / or framed by the edge portion at least in sections.

20. The electrochemical system (1) according to the preceding claim, characterized in that The membrane of the membrane electrode assembly extends in each case at least over the flow field (17) of an adjacent separator, wherein a gas diffusion layer (16) is preferably arranged between each pair of adjacent separators (2) of the stack and preferably extends over the transition region of the separators and the flow field (17).

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