Galvanic cell stack and method for its production

Abstract

Method for producing a galvanic cell stack, in particular a flow battery, fuel cell or the like, with a plurality of electrode plates (10, 29, 42, 48, 53) and membranes (30) arranged between the electrode plates, wherein the electrode plates are formed by arranging porous electrodes (15, 19, 33, 44, 50, 55) on both sides of a bipolar plate (11, 17, 31, 43, 49, 54), wherein the bipolar plate is bonded to the electrodes, characterized in that a recess (34) is formed in the bipolar plate (31) into which the electrode (33) is inserted, wherein the recess is formed with a circumferential groove (36) that surrounds the electrode, wherein the groove is filled with an adhesive material (37).

Description

The invention relates to a galvanic cell stack and a method for producing a galvanic cell stack, in particular a flow battery, fuel cell or the like, with a plurality of electrode plates and membranes arranged between the electrode plates, wherein the electrode plates are formed by arranging porous electrodes on both sides of a bipolar plate, wherein the bipolar plate is or is bonded to the electrodes. Electrode plates are regularly used to construct fuel cells or flow batteries (redox flow batteries). Fuel cells are well known from the prior art and consist of a plurality of electrode plates or electrolyte membranes with an anode and a cathode, and, for example, hydrogen as the fuel gas and oxygen as the oxidizing gas. Solid polymer fuel cells feature a polymeric ion-exchange membrane with a coating on both sides, forming an electrolyte catalyst, embedded in a porous, electrically conductive layer material that forms the anode and cathode, respectively. Electrically conductive electrode plates or separator plates cover the electrolyte membrane on both sides, forming channels through which the reactants are distributed appropriately across the respective surface of the electrolyte membrane. Furthermore, the electrode plates serve as current collectors in the anode and cathode regions. To achieve a comparatively high output voltage, electrode plates are connected in series, that is, arranged in a stack configuration. The electrode plates are then configured as a bipolar plate with channels on both sides for distributing and conducting the reactants. In principle, however, it is also possible to introduce the reactants at the respective edges of the bipolar plates within the stack. The essential point, however, is that the input and output of the reactants can each occur through a single opening in the stack. In flow batteries, a salt solution or electrolyte circulates along an electrode plate instead of a gas. Unlike a gas, the salt solution is electrically conductive, so short-circuit currents between bipolar plates via the salt solution must be avoided. Therefore, in both fuel cells and flow batteries, it is known to design electrode plates such that the bipolar plate is surrounded at its edges by an insulating frame. This prevents any electrical potential from existing on the surface of a stack. Furthermore, in flow batteries, it is possible to integrate an electrolyte supply into such an electrically insulated flow plate, thereby achieving simple fluid circulation and preventing short-circuit currents. Such electrode plates are known, for example, from WO 2017 / 211423 A1. Furthermore, DE 10 2010 023 252 A1 describes a method for manufacturing a fuel cell stack with multiple fuel cells, each consisting of a bipolar plate with a surrounding frame and a membrane electrode assembly. In a first manufacturing step, a first frame element surrounding the bipolar plate is attached to a lower region of an end face. In a second step, a membrane electrode assembly is fluid-tightly attached to a lower side of the first frame element. In a third step, a second frame element is fluid-tightly attached to the bipolar plate and to the first frame element. US patent 2018 / 0102556 A1 discloses a redox flow battery in which a bipolar plate and a porous electrode are bonded with an electrically conductive adhesive, thus forming an electrode plate. Several such electrode plates are arranged in the form of a so-called stack. JP S63 80 485 A shows another redox flow battery with multiple bipolar plates and electrodes, as well as membranes. In one manufacturing process, a filler and a resin are first introduced between the plates to be joined to seal the flow channels, and then the assembly of different plates is baked together at a high temperature. Furthermore, in flow batteries, it is known to arrange a porous, electrically conductive electrode between the bipolar plate and the electrolyte membrane, either instead of or in addition to channels. To provide the largest possible contact area for the electrolyte on the bipolar plate, the porous electrode is placed directly on the bipolar plate. The electrode can then be surrounded by the flow plate, through which the electrolyte is passed. A porous electrode allows for a particularly large reaction surface, which promotes ion exchange with the electrolyte. However, assembling such a stack to form a galvanic cell stack is quite complex, as a large number of bipolar plates with their respective flow plates, electrodes, and membranes must be arranged as precisely and closely together as possible.Ideally, the electrode should fill the space formed between the bipolar plate and the electrolyte membrane and be electrically contacted with the bipolar plate. However, due to manufacturing tolerances and variations during assembly, this cannot always be optimally guaranteed. The present invention is therefore based on the objective of proposing a method for producing a galvanic cell stack and a galvanic cell stack that enables cost-effective production with high quality. This problem is solved by a method having the features of claim 1 and a galvanic cell stack having the features of claim 8. In the inventive method for producing a galvanic cell stack, in particular a flow battery, fuel cell or the like, with a plurality of electrode plates and membranes arranged between the electrode plates, the electrode plates are formed by arranging porous electrodes on both sides of a bipolar plate, wherein the bipolar plate is bonded to the electrodes, wherein a recess is formed in the bipolar plate into which the electrode is inserted, wherein the recess is formed with a circumferential groove that surrounds the electrode, and wherein the groove is filled with an adhesive material. The inventive method makes it possible to bond the bipolar plate to the electrodes in a material-bonded manner, thus ensuring correct positioning and reliability even before a stack is assembled. The method involves arranging such an electrode on each of the two sides of the bipolar plate and bonding it to the plate. Only at the ends of a stack is the electrode plate provided with a single electrode on one side of the bipolar plate, forming an end plate of the stack. By bonding the electrode to the bipolar plate, the electrode can be positioned and fixed correctly on the bipolar plate before the stack is assembled, which significantly simplifies final assembly. Furthermore, if electrodes are fixed on both sides of the bipolar plate in this way, fewer errors can occur during stack assembly.Furthermore, the metallurgical bond between the bipolar plate and the electrode ensures a constant electrically conductive contact. This contact is then unaffected by any differences in electrode material thickness, thermal expansion, or other factors. Since the metallurgical bond improves the contact resistance between the electrode and the bipolar plate, the performance of the stack or galvanic cell stack can also be increased. This improves the power-to-cost ratio of a galvanic cell stack, resulting in overall lower operating costs. If the bipolar plate is pressed or formed by pressing in a negative mold, the recess with the circumferential groove in the bipolar plate can be easily created.The electrode can then be inserted into the recess so that it essentially fills the recess. The adhesive material can then be applied to the circumferential groove, ensuring that the groove is essentially filled. The electrode is then fixed to the bipolar plate along its circumference. Alternatively, the adhesive material can be selected and applied to the groove so that it protrudes slightly from the bipolar plate or the electrode. This allows the adhesive to form an additional seal. If the bipolar plate or electrode plate is installed in a stack with a membrane, potential electrolyte bypass currents can be prevented, and the resulting galvanic cell stack can be protected against leakage. The bipolar plate can be pressed, extruded, or formed as a film. For example, it can be pressed into a negative mold by incorporating graphite or a plastic containing a conductive filler. Alternatively, it can be formed by extruding a conductive plastic or a plastic containing conductive material into a mold. The bipolar plate can also be formed as an electrically conductive film. In this case, the bipolar plate can be particularly thin and flexible. The electrode can be connected to the bipolar plate by gluing, welding, or hot pressing. In gluing, an adhesive material is applied to the bipolar plate and / or the electrode, after which the electrode and the bipolar plate are joined and the adhesive is cured. The adhesive material can be applied, for example, by screen printing or masking the bipolar plate or the electrode to apply the desired amount of adhesive to the designated bonding points. Welding can be performed, for example, using a laser or ultrasound. A surface area of ​​the bipolar plate and / or the electrode is plasticized and then joined at the designated points. Hot pressing can be carried out, for example, using a simple press or a calender.The bipolar plate and / or the electrode can be heated to such an extent that the electrode can be bonded to the bipolar plate across its entire surface. Hot pressing using a calender is particularly advantageous when the bipolar plate and / or the electrode is formed in the form of a film. The electrode can be pressed or rolled onto the bipolar plate with a defined pressure and / or thickness. Applying a defined pressure ensures a secure connection between the bipolar plate and the electrode. Maintaining the pressure until the adhesive or the bipolar plate / electrode material has cured allows for relatively precise application of the desired electrode plate thickness. The electrode plate thickness refers to the thickness of the electrode plate. This ensures that the electrode plate or electrode, in a galvanic cell constructed with the electrode plate, rests against a membrane as desired, without damaging the membrane or creating an excessively large gap between the electrode and the membrane. The electrode can be connected to the bipolar plate, either at its edges or across its entire surface. Connecting the electrode to the bipolar plate at its edges is sufficient to correctly position the electrode on the plate, thus significantly simplifying handling during the formation of a stack or galvanic cell stack. Even with a full-surface connection, correct positioning can be achieved. This offers the additional advantage of significantly reducing any potential electrical resistance at the interface between the bipolar plate and the electrode. Consequently, the performance of a galvanic cell formed with the electrode plate can be considerably increased. To form the metallurgical bond, an electrically conductive, carbon-containing, and / or compressible adhesive material can be used. The adhesive material can contain a conductive filler, such as graphite or conductive carbon black. It is particularly advantageous in this context if the adhesive material is metal-free, as it then cannot react with an electrolyte. If the adhesive material is compressible, the pressure exerted on the electrode and the bipolar plate when the electrode plate is installed in a galvanic cell stack can be at least partially or completely compensated by the adhesive material. This ensures that the electrode rests tightly against a membrane when the electrode plate is installed, without the membrane being damaged. The surface of the bipolar plate, on which the electrode can be positioned, can be mechanically and / or chemically treated before the formation of the metallurgical bond. If the bipolar plate is made of, for example, a polymeric material with a polymer skin on its surface, this polymer skin can be removed to reduce any components of the bipolar plate material that might increase electrical resistance. This makes it possible to form an even more electrically conductive connection between the bipolar plate and the electrode. The galvanic cell stack according to the invention, in particular a flow battery, fuel cell or the like, is designed with a plurality of electrode plates and membranes arranged between the electrode plates, wherein the electrode plates are formed from a bipolar plate and porous electrodes arranged on both sides of the bipolar plate, wherein the bipolar plate is bonded to the electrodes, wherein a recess is formed in the bipolar plate into which the electrode can be inserted, wherein the recess is formed with a circumferential groove that surrounds the electrode, and wherein the groove is filled with an adhesive material. For the advantages of the galvanic cell stack according to the invention, reference is made to the description of the advantages of the method according to the invention. The bipolar plate can be made of graphite or a plastic with an electrically conductive filler material. This can be achieved by pressing a powder or granules into a negative mold and curing them. The plastic can be a thermoset or a thermoplastic. When using a thermoset, the filler material can be mixed with a resin, which is then cured in the negative mold under simultaneous heating and pressure. A film containing the conductive filler material can be easily formed from a thermoplastic, resulting in a particularly thin bipolar plate. The proportion of electrically conductive filler material in the plastic can range from 70 to 95 percent by weight. The plastic with the electrically conductive filler material can have a resistivity of less than 100 Ωm.The plastic with the electrically conductive filler material then acts as an electrical conductor. The porous electrode can be made of conductive felt, paper, or foil. The conductive felt can be graphite felt or carbon fiber felt. The paper can also contain carbon, allowing for a relatively thin electrode. The foil can be made of a conductive plastic material. To increase its surface area, the foil can be structured and / or perforated. The electrode plate can be configured with a flow plate that at least partially surrounds the bipolar plate at its edges. Channels for distributing and conveying reactants or electrolytes can then be formed in the flow plate. Preferably, the flow plate can be configured such that the bipolar plate is completely surrounded by the flow plate at its edges. The flow plate can be made of a plastic with an electrically insulating filler material. The plastic, which can be a thermoset or a thermoplastic, can have a resistivity of less than 10¹² Ωm. In this case, the plastic with the electrically insulating filler acts as an insulator. If the bipolar plate is completely surrounded by the flow plate, current cannot unintentionally flow away from a galvanic cell stack formed with the electrode plate. The bipolar plate and the flow plate can be bonded together. An electrically conductive plastic of the bipolar plate can be cured together with an electrically insulating plastic of the flow plate. This can be done, for example, in a shared mold. Crucially, the curing process results in a strong cross-linking of the molecules of the plastics in the bipolar plate and the flow plate. If the curing of the plastic with the conductive filler material and the electrically insulating filler material occurs simultaneously in the negative mold, the bond within the plastic is independent of the filler material. This significantly reduces cycle times for the production of electrode plates, as the bipolar plate already incorporates the flow plate. The bipolar plate and / or the electrode can be designed with a flux field. This flux field can be located on or within a surface of the bipolar plate and / or a surface of the electrode, with both surfaces potentially in contact or being metallurgically bonded together. The flux field facilitates the passage of a reactant or electrolyte through the electrode or bipolar plate and defines a flow direction. The flux field can be formed, for example, by parallel and / or meandering grooves in the bipolar plate and / or the electrode. Media channels can be formed in a surface of the bipolar plate and / or in a surface of the electrode to create the flux field. Through-holes connected to these media channels can be formed in the flow plate to supply the media. The media channels can be formed by shaping the plastic of the bipolar plate during manufacturing in a negative mold or by subsequent machining of the electrode plate. Similarly, the through-holes can be formed in a negative mold or by drilling a hole in the electrode plate. If the through-holes are formed in the flow plate, media supply to the bipolar plate within a galvanic cell stack is particularly simple. Further advantageous embodiments of a galvanic cell stack result from the feature descriptions of the dependent claims relating back to method claim 1. Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Figure 1 shows a first embodiment of an electrode plate in a top view; Figure 2 shows a second embodiment of an electrode plate in a top view; Figure 3 shows a third embodiment of an electrode plate in a cross-sectional view; Figure 4 shows a fourth embodiment of an electrode plate in a cross-sectional view; Figure 5 shows a fifth embodiment of an electrode plate in a cross-sectional view; Figure 6 shows a sixth embodiment of an electrode plate in a cross-sectional view. Figure 1 shows a simplified representation of an electrode plate 10. The electrode plate 10 consists of a bipolar plate 11 and a flow plate 13 surrounding the bipolar plate 11 at its edges 12. The flow plate 13 thus completely encompasses the bipolar plate 11. The bipolar plate 11 is made of a plastic with an electrically conductive filler material, and the flow plate 13 is made of a plastic with an electrically insulating filler material. An electrode 15 is arranged on a surface 14 of the bipolar plate 11. The electrode 15 is bonded to the bipolar plate 11. This results in a particularly close, electrically conductive connection between the electrode 15 and the bipolar plate 11. Figure 2 shows a top view of an electrode plate 16. The electrode plate 16 consists of a bipolar plate 17, a flow plate 18, and an electrode 19, which covers the bipolar plate 17. Media channels 21, shown only in outline, are formed in a surface 20 of the bipolar plate 17, through which, for example, an electrolyte can flow. A channel distributor 23 and a conduit 24 are formed on both sides of the bipolar plate 17 in a surface 22 of the flow plate 18. The conduit 24 is connected to a through-opening 25 for supplying media to a stack (not shown in detail) or a galvanic cell stack. Through-openings 26 are also formed in the flow plate 18, through which, for example, the electrolyte can circulate within the stack.To form a liquid- and gas-tight connection between the electrode plate 16 and other membranes and electrode plates not shown here, seals 27 and 28 are provided on the electrode plate 16. The seals 27 and 28 can, for example, be made of an elastomer. Fig. 3 shows a cross-sectional view of an electrode plate 29 with a membrane 30, corresponding to an arrangement in a galvanic cell stack (not shown here) in a simplified representation. The electrode plate 29 consists of a bipolar plate 31, a flow plate 32 surrounding the bipolar plate 31, and two electrodes 33. The stack (not shown here) is formed from a sequence of electrode plates 29 and membranes 30 in a stacked arrangement. End plates, i.e., electrode plates with only one electrode 33, are provided at each end of the stack. The electrodes 33 are each inserted into a recess 34 on either side of the bipolar plate 31 and essentially fill the entire recess 34. The electrode 33 is therefore completely surrounded at its edges 35 by the bipolar plate 31.Furthermore, a circumferential groove 36 is formed on both sides of the bipolar plate 31 at the respective recess 34, which is filled with adhesive material 37. The electrode 33 is bonded to the bipolar plate 31 by means of the adhesive material 37. The membrane 30 then lies close to a surface 39 of the electrode 33 with a surface 38. Furthermore, the electrode 33 lies close to a surface 41 of the bipolar plate 31 within the recess 34 with an opposing surface 40. The flow of an electrolyte through the electrode 33 can be ensured by channels (not shown) on the bipolar plate 31 and within the flow plate 32. Figure 4 shows an electrode plate 42 with the membrane 30, where, in contrast to the electrode plate in Figure 3, a bipolar plate 42 is bonded to an electrode 44 via an adhesive material 45. The adhesive material 45 forms an adhesive layer 46 that bonds the bipolar plate 43 to the respective electrode 44 over its entire surface on both sides. The adhesive material 45 is electrically conductive and can also be compressible. A flow plate 47 completely surrounds the bipolar plate 43 and the electrodes 44. Figure 5 shows an electrode plate 48 in which, unlike the electrode plate in Figure 4, a bipolar plate 49 is connected to electrodes 50 by welding. In particular, the electrode 50 is metallurgically bonded in the area of ​​its edges 51 by a weld seam 52 or sealing seam. The welding can be carried out using a laser or ultrasound. Fig. 6 shows an electrode plate 53 which, unlike the electrode plate in Fig. 4, has a bipolar plate 54 and electrodes 55 on both sides of the bipolar plate 54, the electrodes 55 being connected to the bipolar plate 54 by hot pressing. The electrodes 55 are in full contact with the bipolar plate 54. The hot pressing process creates a bonding layer 56 in which the material of the bipolar plate 54 is fused with the material of the electrode 55. The bipolar plates described above can be made of graphite or a plastic with an electrically conductive filler material. The plastic can be a thermoset or a thermoplastic. The conductive filler material can be graphite, conductive carbon black, or an intrinsically conductive plastic. The respective porous electrode can be made of conductive felt, paper, or a film with a similar conductive filler material.

Claims

Method for producing a galvanic cell stack, in particular a flow battery, fuel cell or the like, with a plurality of electrode plates (10, 29, 42, 48, 53) and membranes (30) arranged between the electrode plates, wherein the electrode plates are formed by arranging porous electrodes (15, 19, 33, 44, 50, 55) on each of two sides of a bipolar plate (11, 17, 31, 43, 49, 54), wherein the bipolar plate is bonded to the electrodes, characterized in that a recess (34) is formed in the bipolar plate (31) into which the electrode (33) is inserted, wherein the recess is formed with a circumferential groove (36) that surrounds the electrode, wherein the groove is filled with an adhesive material (37). Method according to claim 1, characterized in that the bipolar plate (11, 17, 31, 43, 49, 54) is pressed as a molded body, extruded or formed as a film. Method according to claim 1 or 2, characterized in that the electrode (15, 19, 33, 44, 50, 55) is connected to the bipolar plate (11, 17, 31, 43, 49, 54) by means of gluing, welding or hot pressing. Method according to one of the preceding claims, characterized in that the electrode (15, 19, 33, 44, 50, 55) is pressed or rolled onto the bipolar plate (11, 17, 31, 43, 49, 54) with a defined pressure and / or a defined height. Method according to one of the preceding claims, characterized in that the electrode (15, 19, 33, 44, 50, 55) is connected to the bipolar plate (11, 17, 31, 43, 49, 54) at least in the area of ​​its edges or over its entire surface. Method according to one of the preceding claims, characterized in that an electrically conductive, carbon-containing and / or compressible adhesive material (37, 45) is used to form the material-jointed connection. Method according to one of the preceding claims, characterized in that a surface (14, 20, 41) of the bipolar plate (11, 17, 31, 43, 49, 54) on which the electrode (15, 19, 33, 44, 50, 55) is arranged is mechanically and / or chemically treated before the formation of the material-bonded connection. A galvanic cell stack, in particular a flow battery, fuel cell or the like, with a plurality of electrode plates (10, 29, 42, 48, 53) and membranes (30) arranged between the electrode plates, wherein the electrode plates are formed from a bipolar plate (11, 17, 31, 43, 49, 54) and porous electrodes (15, 19, 33, 44, 50, 55) arranged on both sides of the bipolar plate, wherein the bipolar plate is metallurgically bonded to the electrodes, characterized in that a recess (34) is formed in the bipolar plate (31) into which the electrode (33) can be inserted, wherein the recess is formed with a circumferential groove (36) that surrounds the electrode, wherein the groove is filled with an adhesive material (37). Galvanic cell stack according to claim 8, characterized in that the bipolar plate (11, 17, 31, 43, 49, 54) is made of graphite or a plastic with an electrically conductive filler material. Galvanic cell stack according to claim 8 or 9, characterized in that the electrically conductive filler material is graphite, conductive carbon black or an intrinsically conductive plastic. Galvanic cell stack according to one of claims 8 to 10, characterized in that the electrode (15, 19, 33, 44, 50, 55) is made of conductive felt, paper or foil. Galvanic cell stack according to one of claims 8 to 11, characterized in that the electrode plate (10, 29, 42, 48, 53) is formed with a flow plate (13, 18, 32, 47) which at least partially surrounds the bipolar plate (11, 17, 31, 43, 49, 54) at its edges (12). Galvanic cell stack according to claim 12, characterized in that the flow plate (13, 18, 32, 47) is made of a plastic with an electrically insulating filler material. Galvanic cell stack according to claim 12 or 13, characterized in that the bipolar plate (11, 17, 31, 43, 49, 54) and the flow plate (13, 18, 32, 47) are metallurgically connected to each other. Galvanic cell stack according to one of claims 12 to 14, characterized in that the bipolar plate (11, 17, 31, 43, 49, 54) and / or the electrode (15, 19, 33, 44, 50, 55) is designed with a flux field. Galvanic cell stack according to claim 15, characterized in that media channels (21) in a surface (14, 20, 41) of the bipolar plate (11, 17, 31, 43, 49, 54) and / or the electrode (15, 19, 33, 44, 50, 55) form the flow field, wherein through-openings (25, 26) connected to the media channels are formed in the flow plate (13, 18, 32, 47) for media supply.

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