CELL STACK OF A FUEL CELL

Abstract

A cell stack of a fuel cell includes single cells stacked in a thickness direction. Each single cell includes a membrane electrode gas diffusion layer assembly and plate-shaped separators sandwiching the membrane electrode gas diffusion layer assembly from opposite sides in the thickness direction. Adjacent separators of the separators of the single cells stacked in the thickness direction are welded to each other at the tips (ends) of the projections. One of the tips of the projections of the adjacent separators has a convex portion, and the other of the tips has a concave portion. The tips of the projections of the adjacent separators are in contact with each other such that the convex portion is interlocked with the concave portion.

Description

BACKGROUND1. Field of InterestThe present disclosure relates to a cell stack of a fuel cell.2. Description of the Prior ArtAs disclosed in Japanese Patent Application Laid-Open No. 2019-129124, a cell stack of a fuel cell is formed by stacking individual cells (individual cells) in a thickness direction. Each unit cell includes a membrane electrode gas diffusion layer assembly and a plurality of plate-shaped separators that sandwich the membrane electrode gas diffusion layer assembly from opposite sides in the thickness direction (sandwiching). Each separator has recesses and protrusions formed by bending the separator such that the recesses and the protrusions are positioned alternately. The recesses are recessed toward the membrane electrode gas diffusion layer assembly. The protrusions protrude from the membrane electrode gas diffusion layer assembly. Adjacent separators of the separators of the single cells stacked in the thickness direction are welded to each other at the tips (ends) of the protrusions.In each unit cell, a fuel gas such as hydrogen flows between one of the separators and the anode-side surface of the membrane electrode gas diffusion layer assembly. Further, an oxidizing gas such as air flows between the other separator and the cathode-side surface of the membrane electrode gas diffusion layer assembly. As a result, current (energy) is generated on the basis of the reaction between the fuel gas and the oxidizing gas at the membrane electrode gas diffusion layer assembly. In order to limit (one) increase (rise) in the temperature of the fuel cell stack caused (by) such power generation, a coolant such as cooling water flows through the space between the separators of adjacent unit cells of the unit cells. The coolant cools the cell stack.During the manufacturing process, fine irregularities are formed on / on the surfaces of the separators in each unit cell. These fine irregularities also occur at the tips (ends) of the protrusions of adjacent separators of the separators that are / are welded together. The surface roughness at the tips of the protrusions due to these fine irregularities leads to a reduction in the degree (extent) of surface contact between the tips of the protrusions of the adjacent separators before welding. The reduced degree of area contact between the tips of the protrusions increases the electrical resistance, in particular the contact resistance, in the individual cells.SUMMARYThis summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.According to a general aspect, a cell stack of a fuel cell includes a plurality of unit cells (single cells) stacked in a thickness direction. Each unit cell includes a membrane electrode gas diffusion layer assembly and a plurality of plate-shaped separators that sandwich the membrane electrode gas diffusion layer assembly from opposite sides in the thickness direction (sandwiching). Each separator has recesses and protrusions formed by bending the separator such that the recesses and the protrusions are positioned alternately. The recesses are recessed toward the membrane electrode gas diffusion layer assembly. The protrusions protrude from the membrane electrode gas diffusion layer assembly. Adjacent separators of the separators of the single cells stacked in the thickness direction are welded to each other at tips (ends) of the protrusions. One of the tips of the protrusions of the adjacent separators has a convex portion curved to bulge (bulge outward), and the other tip has a concave portion curved to bulge (bulge inward). The tips of the protrusions of the adjacent separators are / are in contact with each other such that the convex portion engages with the concave portion.Other features and aspects will be apparent from the following detailed description, drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is an exploded perspective view of a single cell (single cell). FIG. 2 is a front view showing a state in which a separator accommodated in the single cell is viewed from the direction of an arrow A in FIG. 1. FIG. 3 is an enlarged sectional view of portions corresponding to membrane electrode gas diffusion layer assemblies of adjacent separators as viewed in the direction of arrows III-III in FIG. 2. FIG. 4 is a sectional view showing a concave portion and a convex portion of the separators shown in FIG. 3 according to another example. FIG. 5 is a sectional view showing concave portions and convex portions of the separators shown in FIG. 3 according to another example.In the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and representation of elements in the drawings may be exaggerated for clarity, illustration, and simplification.DETAILED DESCRIPTIONThis description provides a thorough understanding of the described methods, apparatus, and / or systems. Modifications and equivalents of the described methods, apparatus, and / or systems will be apparent to one of ordinary skill in the art. Sequences of operations (operations) are exemplary and may be changed as will be apparent to one skilled in the art, except for operations necessarily proceeding in a particular order. Descriptions of functions and constructions that are well known to those skilled in the art may be omitted.Example embodiments may take various forms and are not limited to the examples described. However, the examples described are accurate and complete, and will fully convey the full scope of the disclosure to one skilled in the art.In this specification, the term "at least A or B" is intended to mean "only A, only B, or both A and B.".A cell stack of a fuel cell according to an embodiment will be described below with reference to FIGS. 1 to 3.FIG. 1 shows a single cell (single cell) 11 used for forming a cell stack of a fuel cell. The single cell 11 includes a resin sheet 12, a membrane electrode gas diffusion layer assembly 13, and separators 14. The resin plate 12 is formed to have a square frame shape. The outer periphery of the membrane electrode gas diffusion layer assembly 13 is bonded to the resin plate 12. The resin sheet 12 and the membrane electrode gas diffusion layer assembly 13 are / are sandwiched by the separators 14 from the opposite sides in the thickness direction. The separators 14 are made of metal such as stainless steel, titanium, or aluminum, and are formed in the shape of a square plate.The cell stack of the fuel cell is / is formed by stacking the unit cells 11 in the plate thickness direction. The resin sheets 12 and the separators 14 of the cells 11 each have holes 16. three of the holes 16 are disposed at one end of the unit cell 11 toward the long side, and the other three are disposed at the other end of the unit cell 11 toward the long side. One of the holes 16 at one end toward the long side of the unit cell 11 is paired with one of the holes 16 at the other end. Each pair of holes 16 is used to allow a fluid (for example, fuel gas such as hydrogen, oxidizing gas such as air, or coolant) to flow therethrough. A sealing member 17 is disposed between each separator 14 and the resin plate 12. The seal members 17 are disposed on / on the surfaces of the resin plate 12 on the opposite sides in the thickness direction.The seal member 17 disposed on the front side of the resin plate 12 surrounds pairs of the holes 16, each pair being positioned along one of the two diagonal lines of the resin plate 12 and the corresponding separator 14. The sealing member 17 further surrounds the anode-side surface of the membrane electrode gas diffusion layer assembly 13, and thereby fuel gas can flow along the anode-side surface of the membrane electrode gas diffusion layer assembly 13 via the pair of holes 16. Further, the seal member 17 disposed on the rear side of the resin plate 12 surrounds a pair of the holes 16 positioned along the other of the two diagonal lines of the resin plate 12 and the corresponding separator 14. The sealing member 17 further surrounds the cathode side surface of the membrane electrode gas diffusion layer assembly 13, and thereby oxidizing gas can flow along the cathode side surface of the membrane electrode gas diffusion layer assembly 13 via the pair of holes 16.In the cell stack of the single cells 11, the fuel gas flows along the anode side surface of the membrane electrode gas diffusion layer assembly 13 and the oxidizing gas flows along the cathode side surface of the membrane electrode gas diffusion layer assembly 13, When the fuel gas and the oxidizing gas flow along the anode side surface and the cathode side surface of the membrane electrode gas diffusion layer assembly 13, current (energy) is generated based on the reaction between the fuel gas and the oxidizing gas in the membrane electrode gas diffusion layer assembly 13.welding adjacent separators 14 (1)FIG. 2 shows one of the separators 14 of the unit cell 11 disposed on the anode side of the membrane electrode gas diffusion layer assembly 13 as viewed in the direction of an arrow A in FIG. 1, and this separator 14 is / is adjacent to a cathode-side separator 14 of another unit cell 11 that is in contact with the above-described unit cell 11. Adjacent separators of the separators 14 are / are welded to each other as indicated by the two-dot chain line.Specifically, the adjacent separators 14 are welded to each other at two groups of the holes 16 that are arranged diagonally opposite to each other in the separators 14, specifically around the entire circumference of each hole 16. In addition, the entire outer edges of the separators 14 are welded together. This allows a flow of the coolant through the space between the adjacent separators 14 via the holes 16 disposed in / at the center of the separators 14 toward the short side.Since the coolant flows between the separators 14 of the adjacent unit cells 11, the cell stack is cooled as the temperature of the cell stack increases during power generation.welding adjacent separators 14 (2)FIG. 3 is an enlarged sectional view of a portion corresponding to the membrane electrode gas diffusion layer assemblies 13 of the adjacent separators of the separators 14 shown in FIG. 1 as viewed in the direction of arrows III-III in FIG. 2 As shown in FIG. 3, each separator 14 has recesses 18 and protrusions 19 that are / are formed by bending the separator 14 such that the recesses 18 and the protrusions 19 are positioned alternately. The recesses 18 of each separator 14 are recessed toward the membrane electrode gas diffusion layer assembly 13 that is disposed (headed) between the separators 14. The protrusions 19 of each separator 14 protrude from the membrane electrode gas diffusion layer assembly 13 disposed (headed) between the separators 14. As shown in FIG. 2, the recesses 18 and the protrusions 19 extend in the long side direction of the separator 14.Adjacent separators of the separators 14 are welded together at the tips (ends) of the protrusions 19 by laser welding or the like. One of the tips of the protrusions 19 of the adjacent separators 14 has a convex portion 20 curved to bulge (bulge outward), and the other tip has a concave portion 21 curved to bulge (bulge inward). The tips of the protrusions 19 of the adjacent separators 14 are / are in contact with each other such that each convex portion 20 engages with the corresponding concave portion 21.Specifically, the convex portions 20 and the concave portions 21 are formed at the tips of the protrusions 19 of the adjacent separators 14 as follows. Each of the protrusions 19 has convex portions 20 and a concave portion 21 at the (the) tip (end). One of the tips of the protrusions 19 that are in contact with each other has the concave portion 21 at a center in the width direction of the protrusion 19 and the convex portions 20 on the opposite sides in the width direction of the concave portion 21. The other of the tips of the protrusions 19 that are in contact with each other has the concave portion 21 at a center in the width direction of the protrusion 19 and the convex portions 20 on the opposite sides in the width direction of the concave portion 21.The adjacent separators 14 are configured such that, by shifting (offsetting) their relative positions in the width direction of the protrusions 19, one of the convex portions 20 at one of the tips of the protrusions 19 that are in contact with each other engages with the concave portion 21 at the other of the tips of the protrusions 19 that are in contact with each other. At the same time, one of the convex portions 20 on the other of the tips of the projections 19 which are in contact with each other engages with the concave portion 21 on the one of the tips of the projections 19 which are in contact with each other. As a result, the tips of the protrusions 19 on the adjacent separators 14 are in contact with each other, one of the convex portions 20 on one of the tips of the protrusions 19 which are in contact with each other engages with the concave portion 21 on the other of the tips of the protrusions 19 which are in contact with each other, and one of the convex portions 20 of the other of the tips of the protrusions 19 which are in contact with each other engages with the concave portion 21 of the one of the tips of the protrusions 19 which are in contact with each other.An operation and advantages of the cell stack of the fuel cell according to the present embodiment will be described below.(1) The tips (ends) of the protrusions 19 of the adjacent separators of the separators 14 are / are in contact with each other such that each convex portion 20 engages with the corresponding concave portion 21. This increases (increases) the contact area between the tips of the protrusions 19 of the adjacent separators 14, and therefore, as described above, even if the degree of surface contact between the tips of the protrusions 19 is decreased due to the surface roughness or other factors at the tips of the protrusions 19, the increased contact area between the tips of the protrusions 19 helps prevent a significant increase in the electric resistance, particularly the contact resistance, in the single cell 11.(2) The convex portions 20 and the concave portions 21 are formed at the tips of the separators of the separators 14 adjacent to the protrusions 19. The tips of the protrusions 19 on the adjacent separators 14 are in contact with each other, with the convex portion 20 on one of the tips engaging the concave portion 21 on the other of the tips and the convex portion 20 on the other of the tips engaging the concave portion 21 on the one of the tips. This immediately increases the contact area between the tips of the protrusions 19.(3) One of the tips of the protrusions 19 that are in contact with each other has the concave portion 21 at a center in the width direction of the protrusion 19 and the convex portions 20 on the opposite sides in the width direction of the concave portion 21. The other of the tips of the protrusions 19 that are in contact with each other has the concave portion 21 at a center in the width direction of the protrusion 19 and the convex portions 20 on the opposite sides in the width direction of the concave portion 21. The relative positions of the adjacent separators of the separators 14 are offset (shifted) in the width direction of the protrusions 19 in the following manner. Specifically, the relative positions are offset such that one of the convex portions 20 at one of the tips of the protrusions 19 that are in contact with each other engages with the concave portion 21 at the other of the tips of the protrusions 19 that are in contact with each other, and that one of the convex portions 20 of the other of the tips of the protrusions 19 that are in contact with each other engages with the concave portion 21 of the one of the tips of the protrusions 19 that are in contact with each other. In this case, even if the shapes of the tips of the protrusions 19 that are in contact with each other are the same, the contact area between the tips of the protrusions 19 is increased / increased by offsetting (shifting) the relative positions of the adjacent separators 14 as described above.The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications may be combined as long as the combined modifications remain technically compatible with each other.As shown in FIG. 4, a convex portion 20 may be formed at one of the tips (ends) of the protrusions 19 of adjacent separators 14, and a concave portion 21 may be formed at the other tip. In this case, the tips of the protrusions 19 of the adjacent separators of the separators 14 are / are in contact with each other such that the convex portion 20 at the one tip engages with the concave portion 21 at the other tip.Convex portions 20 and concave portions 21 may be formed as shown in FIG. 5. That is, the convex portion 20 is formed at the center in the width direction of the protrusion 19 at one of the tips (ends) of the protrusions 19 of the adjacent separators 14, and the concave portions 21 are formed at the opposite sides in the width direction of the convex portion 20. Further, a concave portion 21 is formed at the center in the width direction of the protrusion 19 at the other tip, and convex portions 20 are formed at the opposite sides in the width direction of the concave portion 21. In this case, the tips of the protrusions 19 on the adjacent separators 14 are / are in contact with each other, the convex portion 20 on the one of the tips engages with the concave portion 21 on the other of the tips, and the convex portions 20 of the other of the tips engage with the concave portions 21 of the one of the tips.In the foregoing examples, various changes may be made in form and detail without departing from the spirit and scope of the claims and their equivalents. The examples are for the purpose of description only and not for the purpose of limitation. Descriptions of features in each example are considered applicable to similar features or aspects in further / other examples. Suitable results may be achieved when operations are performed in a different order and / or when components in a described system, architecture, device, or circuit are combined differently and / or replaced or supplemented by other components or their equivalents. The scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2019-129124

[0002]

Claims

A cell stack of a fuel cell, the cell stack comprising a plurality of unit cells (11) stacked in a thickness direction, each unit cell (11) comprising: a membrane electrode gas diffusion layer assembly (13); and a plurality of plate-shaped separators (14) that arrange the membrane electrode gas diffusion layer assembly (13) from opposite sides in the thickness direction, each separator (14) comprising recesses (18) and protrusions (19) formed by bending the separator (14) such that the recesses (18) and the protrusions (19) are positioned alternately, the recesses (18) are recessed toward the membrane electrode gas diffusion layer assembly (13), the protrusions (19) protrude away from the membrane electrode gas diffusion layer assembly (13), adjacent separators of the separators (14) of the unit cells (11) stacked in the thickness direction are welded to each other at tips of the protrusions (19), one of the tips of the protrusions (19) of the adjacent separators (14) has a convex portion (20) curved to bulge and the other tip has a concave portion (21) curved to bulge, and the tips of the protrusions (19) of the adjacent separators (14) are in contact with each other such that the convex portion (20) engages with the concave portion (21).The cell stack of the fuel cell according to claim 1, wherein the tips of the protrusions (19) of the adjacent separators (14) each have the convex portion (20) and the concave portion (21), and the tips of the protrusions (19) of the adjacent separators (14) are in contact with each other such that the convex portion (20) at one of the tips engages with the concave portion (21) of the other of the tips, and the convex portion (20) at the other of the tips engages with the concave portion (21) of the one of the tips.The cell stack of the fuel cell according to claim 2, wherein one of the tips of the protrusions (19) that are in contact with each other has the concave portion (21) at a center in a width direction of the protrusion (19) and the convex portions (20) on opposite sides in the width direction of the concave portion (21), the other of the tips of the protrusions (19) that are in contact with each other has the concave portion (21) at a center in a width direction of the protrusion (19) and the convex portions (20) on opposite sides in the width direction of the concave portion (21), and relative positions of the adjacent separators (14) in the width direction of the protrusions (19) are offset such that one of the convex portions (20) on one of the tips of the protrusions (19) that are in contact with each other has the concave portion (21) of the other of the tips of the protrusions (19), which are in contact with each other, and one of the convex portions (20) on the other of the tips of the protrusions (19) which are in contact with each other is engaged with the concave portion (21) of the one of the tips of the protrusions (19) which are in contact with each other.The cell stack of the fuel cell according to claim 1, wherein the tips of the protrusions (19) of one of the adjacent separators (14) each have the convex portion (20), the convex portion (20) is a convex portion (20), the tips of the protrusions (19) of the other of the adjacent separators (14) each have the concave portion (21), the concave portion (21) is a concave portion (21), and the tips of the protrusions (19) of the adjacent separators (14) are in contact with each other such that the convex portion (20) at the one of the tips engages with the concave portion (21) at the other of the tips.The cell stack of the fuel cell according to claim 1, wherein the tips of the protrusions (19) of the adjacent separators (14) each have the convex portion (20) and the concave portion (21), and one of the tips of the protrusions (19) that are in contact with each other has the convex portion (20) at a center in a width direction of the protrusion (19) and the concave portions (21) on opposite sides in the width direction of the convex portion (20), the other of the tips of the protrusions (19) that are in contact with each other has the concave portion (21) at a center in a width direction of the protrusion (19) and the convex portions (20) on opposite sides in the width direction of the concave portion (21), and the tips of the protrusions (19) of the adjacent separators (14) are in contact with each other in such a manner, the convex portion (20) at the one of the tips engages the concave portion (21) of the other of the tips, and the convex portions (20) at the other of the tips engages the concave portions (21) of the one of the tips.

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