Joining method

Abstract

SOLUTION: The joining method for joining two separators comprises: a step of bringing a first separator 30 and a second separator 32 into contact with each other; a step of bringing a first electrode 90a for welding into contact with a plurality of inner projected parts 46a (first inner projected parts); a step of bringing a second electrode 90b for welding into contact with a plurality of inner projected parts 66a (second inner projected parts); and a step of welding a plurality of places where current is supplied between the first electrode 90a and the second electrode 90b to bring outer projected parts 46b (first outer projected parts) and outer projected parts 66b (second outer projected parts) into contact with each other.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a method for joining two adjacent separators in a fuel cell stack. [Background technology]

[0002] A fuel cell stack is composed of a plurality of unit cells stacked together. Each unit cell includes a membrane electrode assembly (MEA) and a pair of separators (first separator, second separator) that sandwich the MEA. The MEA includes a solid polymer electrolyte membrane, an anode electrode, and a cathode electrode. The solid polymer electrolyte membrane is made of a polymer ion exchange membrane. The anode electrode is disposed on one side of the solid polymer electrolyte membrane. The cathode electrode is disposed on the other side of the solid polymer electrolyte membrane.

[0003] Each separator has a plurality of protrusions extending in the longitudinal direction of the separator formed on both sides. As a result, a flow path for flowing fuel gas (fuel gas flow path) and a bead seal for sealing the flow path are formed between the MEA and the first separator. In addition, a flow path for flowing oxidant gas (oxidant gas flow path) and a bead seal for sealing the flow path are formed between the MEA and the second separator. In addition, in two unit cells adjacent to each other, a flow path for flowing a cooling medium (cooling medium flow path) is formed between the first separator of one unit cell and the second separator of the other unit cell.

[0004] Patent Document 1 discloses a fuel cell stack in which multiple unit cells are stacked. In this fuel cell stack, a first separator of a first unit cell and a second separator of a second unit cell are joined together. Specifically, a convex portion of the first separator and a convex portion of the second separator are welded together. This forms a temperature control medium flow path (cooling medium flow path). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-311069 A Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, spot welding is used to weld the convex portion of the first separator and the convex portion of the second separator. That is, the contact portion between the convex portion of the first separator and the convex portion of the second separator is sandwiched between a pair of electrodes, and the contact portion is welded. Depending on the shapes of the convex portion of the first separator and the convex portion of the second separator, it may not be possible to position the contact portion between the pair of electrodes. As a result, welding cannot be performed properly.

[0007] The present invention aims to solve the above-mentioned problems. [Means for solving the problem]

[0008] An aspect of the present invention is a joining method for joining two adjacent separators in a fuel cell stack in which unit cells, each having a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly, are stacked, the two adjacent separators being a first separator covering a cathode electrode of a first membrane electrode assembly and a second separator covering an anode electrode of a second membrane electrode assembly, the first separator having a first inner convex portion in contact with the cathode electrode of the first membrane electrode assembly and a first outer convex portion protruding toward the second separator. the second separator has a second inner convex portion in contact with the anode electrode of the second membrane electrode assembly and a second outer convex portion protruding toward the first separator, and the method includes the steps of contacting the first separator and the second separator with each other, contacting a first electrode for welding with the multiple first inner convex portions, contacting a second electrode for welding with the multiple second inner convex portions, and passing a current between the first electrode and the second electrode to weld the multiple locations where the first outer convex portion and the second outer convex portion contact. Effect of the Invention

[0009] According to the present invention, the portions where two adjacent separators contact each other can be welded. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view of a fuel cell stack. [Diagram 2] FIG. 2 is an exploded perspective view of the fuel cell stack. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is an exploded perspective view illustrating a unit cell that constitutes the fuel cell stack. [Diagram 5] FIG. 5 is a plan view of the first separator as viewed from the MEA side. [Figure 6] FIG. 6 is a plan view of the second separator as viewed from the MEA side. [Figure 7] FIG. 7 is a plan view of the first separator as viewed from the opposing second separator side. [Figure 8] FIG. 8 is a plan view of the second separator as viewed from the opposing first separator side. [Figure 9] FIG. 9 shows the manufacturing flow of the bonded separator. [Figure 10] FIG. 10 is an explanatory diagram of a welding process in the first embodiment. [Figure 11] FIG. 11 is an explanatory diagram of a welding process in the second embodiment. [Figure 12] FIG. 12 is an explanatory diagram of a welding area in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [1 Configuration of fuel cell stack 10] 1 and 2, a fuel cell stack 10 includes a stack 14 in which a plurality of unit cells 12 are stacked in a first direction (the direction of arrow A). The fuel cell stack 10 is used, for example, as a fuel cell vehicle, a power generation facility, etc.

[0012] [1-1 Peripheral configuration of laminate 14] At a first end of the fuel cell stack 10 in the direction of arrow A1, a terminal plate 16a, an insulator 18a, and an end plate 20a are sequentially arranged outward (in the direction of arrow A1) (see FIG. 2). At a second end of the fuel cell stack 10 in the direction of arrow A2, a terminal plate 16b, an insulator 18b, and an end plate 20b are sequentially arranged outward (in the direction of arrow A2).

[0013] The terminal plates 16a and 16b are made of a conductive material. The insulators 18a and 18b are made of an insulating material. As shown in FIG. 2, a recess 22a that opens toward the laminate 14 is formed in the center of the insulator 18a. Similarly, a recess 22b that opens toward the laminate 14 is formed in the center of the insulator 18b. The terminal plate 16a is accommodated in the recess 22a. The terminal plate 16b is accommodated in the recess 22b. The laminate 14 is located between the insulators 18a and 18b.

[0014] As shown in FIG. 1, the end plates 20a, 20b are formed in a rectangular shape having long sides extending in a second direction (arrow B direction) and short sides extending in a third direction (arrow C direction). The first direction, the second direction, and the third direction are perpendicular to each other. A connecting bar 24 is disposed between each side of the end plates 20a, 20b. One end of each connecting bar 24 is fixed to the inner surface of the end plate 20a via a bolt 26. The other end of each connecting bar 24 is fixed to the inner surface of the end plate 20b via a bolt 26. As a result, a tightening load is applied to the stack 14 in the stacking direction (arrow A direction).

[0015] The insulator 18a and the end plate 20a are provided at first ends in the direction of arrow B1 with an oxidant gas inlet manifold 34a, a coolant inlet manifold 36a, and a fuel gas outlet manifold 38b. The insulator 18a and the end plate 20a are provided at second ends in the direction of arrow B2 with a fuel gas inlet manifold 38a, a coolant outlet manifold 36b, and an oxidant gas outlet manifold 34b.

[0016] [1-2 Configuration of the laminate 14 and unit cell 12] 3 and 4, each unit cell 12 constituting the laminate 14 has a membrane electrode assembly 28 (hereinafter also referred to as "MEA 28") and a pair of separators (a first separator 30 and a second separator 32). The first separator 30 and the second separator 32 sandwich the MEA 28. The first separator 30 and the second separator 32 are made of a thin metal plate such as a steel plate, a stainless steel plate, an aluminum plate, a plated steel plate, or the like. The surface of the thin metal plate may be subjected to a surface treatment for corrosion prevention.

[0017] In two adjacent unit cells 12, the first separator 30 of one unit cell 12 and the second separator 32 of the other unit cell 12 are bonded to each other. The bonded body consisting of the first separator 30 and the second separator 32 is called a bonded separator 33. In other words, the laminate 14 is also a structure in which the MEA 28 is sandwiched between two bonded separators 33.

[0018] As shown in FIG. 2, an oxidant gas inlet manifold 34a, a coolant inlet manifold 36a, and a fuel gas outlet manifold 38b are provided at a first end of the unit cell 12 in the direction of arrow B1. The oxidant gas inlet manifolds 34a of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The oxidant gas inlet manifold 34a of the stack 14 communicates with the oxidant gas inlet manifolds 34a of the insulator 18a and the end plate 20a. The coolant inlet manifolds 36a of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The coolant inlet manifold 36a of the stack 14 communicates with the coolant inlet manifold 36a of the insulator 18a and the end plate 20a. The fuel gas outlet manifolds 38b of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The fuel gas discharge passage 38b of the stack 14 communicates with the fuel gas discharge passage 38b of the insulator 18a and the end plate 20a.

[0019] As shown in FIG. 2, a fuel gas inlet manifold 38a, a coolant outlet manifold 36b, and an oxidant gas outlet manifold 34b are provided at a second end of the unit cell 12 in the direction of arrow B2. The fuel gas inlet manifolds 38a of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The fuel gas inlet manifold 38a of the stack 14 communicates with the fuel gas inlet manifold 38a of the insulator 18a and the end plate 20a. The coolant outlet manifolds 36b of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The coolant outlet manifold 36b of the stack 14 communicates with the coolant outlet manifold 36b of the insulator 18a and the end plate 20a. The oxidant gas outlet manifolds 34b of each unit cell 12 are arranged in the direction of arrow A and communicate with each other. The oxidant gas discharge passage 34b of the stack 14 communicates with the oxidant gas discharge passage 34b of the insulator 18a and the end plate 20a.

[0020] [1-2-1 Configuration of Membrane Electrode Assembly 28 (MEA 28)] 3, each MEA 28 has an electrolyte membrane 40, an anode electrode 42, and a cathode electrode 44. A resin film (not shown) is provided on the outer periphery of the electrolyte membrane 40. The anode electrode 42 and the cathode electrode 44 sandwich the electrolyte membrane 40.

[0021] The electrolyte membrane 40 is, for example, a solid polymer electrolyte membrane (cation exchange membrane). The solid polymer electrolyte membrane is, for example, a thin film of perfluorosulfonic acid containing moisture. As the electrolyte membrane 40, in addition to a fluorine-based electrolyte, an HC-based (hydrocarbon-based) electrolyte membrane can be used.

[0022] The anode electrode 42 and the cathode electrode 44 each have a gas diffusion layer (not shown) and an electrode catalyst layer (not shown). The gas diffusion layer is made of carbon paper or the like. The electrode catalyst layer is formed by uniformly applying porous carbon particles having a platinum alloy supported on the surface of the gas diffusion layer. The electrode catalyst layer is formed on both sides of the electrolyte membrane 40.

[0023] [1-2-2 Configuration of surface 30a of first separator 30] As shown in Fig. 4, the first separator 30 covers the cathode electrode 44 of the MEA 28. The first separator 30 has a front surface 30a facing the MEA 28 and a back surface 30b facing the second separator 32. A plurality of protrusions are formed on each of the front surface 30a and the back surface 30b by press molding. The protrusions on the front surface 30a that protrude toward the MEA 28 are referred to as inward protrusions 46a. The protrusions on the back surface 30b that protrude toward the second separator 32 are referred to as outward protrusions 46b.

[0024] 4 and 5, two oxidant gas feeds 48a, 48b and an oxidant gas flow field 50 are formed on the surface 30a of the first separator 30 by a plurality of inward protrusions 46a. The oxidant gas feed 48a flows the oxidant gas from the oxidant gas inlet manifold 34a to the oxidant gas flow field 50. The oxidant gas feed 48b flows the oxidant gas from the oxidant gas flow field 50 to the oxidant gas outlet manifold 34b. The oxidant gas flow field 50 is located between the oxidant gas feeds 48a and 48b and faces the cathode 44. The two oxidant gas feeds 48a, 48b and the oxidant gas flow field 50 communicate between the oxidant gas inlet manifold 34a and the oxidant gas outlet manifold 34b.

[0025] Of the multiple inward protrusions 46a, the inward protrusion 46a that forms the oxidant gas feed 48a is referred to as a feed protrusion 52a. Each feed protrusion 52a extends linearly from the oxidant gas inlet manifold 34a to a first end (the end in the direction of arrow B1) of the oxidant gas flow field 50. A feed groove 54a is located adjacent to the feed protrusion 52a.

[0026] Of the multiple inward protrusions 46a, the inward protrusion 46a that forms the oxidant gas feed 48b is referred to as a feed protrusion 52b. Each feed protrusion 52b extends linearly from the oxidant gas discharge passage 34b to a second end (the end in the direction of arrow B2) of the oxidant gas flow field 50. A feed groove 54b is located between two adjacent feed protrusions 52b.

[0027] Of the multiple inward protrusions 46a, the inward protrusions 46a that form the oxidant gas flow path 50 are referred to as flow path protrusions 56. In a plan view of the first separator 30, each flow path protrusion 56 is wavy and extends along the direction of arrow B. A flow path groove 58 is located between two adjacent flow path protrusions 56. Each flow path groove 58 is also wavy. Each flow path protrusion 56 contacts the cathode electrode 44 of the MEA 28 located in the direction of arrow A2. The multiple flow path grooves 58 become paths through which the oxidant gas flows.

[0028] Each of the communication holes (oxidant gas inlet manifold 34a, coolant inlet manifold 36a, fuel gas outlet manifold 38b, fuel gas inlet manifold 38a, coolant outlet manifold 36b, and oxidant gas outlet manifold 34b) is surrounded by an inward protrusion 46a. These inward protrusions 46a are referred to as communication hole bead seals 60. Each communication hole bead seal 60 contacts the MEA 28 located in the direction of arrow A2. As a result, the multiple communication hole bead seals 60 seal the multiple communication holes.

[0029] The communication hole bead seal 60 surrounding the oxidant gas inlet manifold 34a has a plurality of flow paths (not shown) that connect the oxidant gas inlet manifold 34a to the oxidant gas feed 48a. Similarly, the communication hole bead seal 60 surrounding the oxidant gas outlet manifold 34b has a plurality of flow paths (not shown) that connect the oxidant gas outlet manifold 34b to the oxidant gas feed 48b.

[0030] An area including the two oxidant gas feeds 48a, 48b, the oxidant gas flow field 50, the oxidant gas inlet manifold 34a, the fuel gas outlet manifold 38b, the fuel gas inlet manifold 38a, and the oxidant gas outlet manifold 34b is surrounded by an inward protrusion 46a. This inward protrusion 46a is referred to as an outer bead seal 62. The outer bead seal 62 comes into contact with the MEA 28 located in the direction of arrow A2. As a result, the outer bead seal 62 seals the area through which the oxidant gas flows between the surface 30a and the MEA 28 (the area including the two oxidant gas feeds 48a, 48b, the oxidant gas flow field 50, the oxidant gas inlet manifold 34a, and the oxidant gas outlet manifold 34b).

[0031] [1-2-3 Configuration of surface 32a of second separator 32] As shown in Fig. 4, the second separator 32 covers the anode electrode 42 of the MEA 28. The second separator 32 has a front surface 32a facing the MEA 28 and a back surface 32b facing the first separator 30. A plurality of protrusions are formed on each of the front surface 32a and the back surface 32b by press molding. The protrusions on the front surface 32a that protrude toward the MEA 28 are referred to as inward protrusions 66a. The protrusions on the back surface 32b that protrude toward the first separator 30 are referred to as outward protrusions 66b.

[0032] 4 and 6, two fuel gas feeds 68a, 68b and a fuel gas flow passage 70 are formed on the surface 32a of the second separator 32 by a plurality of inward protrusions 66a. The fuel gas feed 68a flows the fuel gas from the fuel gas inlet manifold 38a to the fuel gas flow passage 70. The fuel gas feed 68b flows the fuel gas from the fuel gas flow passage 70 to the fuel gas outlet manifold 38b. The fuel gas flow passage 70 is located between the fuel gas feeds 68a and 68b and faces the anode 42. The two fuel gas feeds 68a, 68b and the fuel gas flow passage 70 communicate between the fuel gas inlet manifold 38a and the fuel gas outlet manifold 38b.

[0033] Of the multiple inward protrusions 66a, the inward protrusion 66a that forms the fuel gas feed 68a is referred to as a feed protrusion 72a. Each feed protrusion 72a extends linearly from the fuel gas inlet passage 38a to a first end of the fuel gas flow field 70 (the end in the direction of arrow B2). Two adjacent to each other The feed protrusion 72a between The feed groove 74a is located in the groove.

[0034] Of the multiple inward protrusions 66a, the inward protrusion 66a that forms the fuel gas feed 68b is referred to as a feed protrusion 72b. Each feed protrusion 72b extends linearly from the fuel gas discharge passage 38b to a second end (the end in the direction of arrow B1) of the fuel gas flow field 70. A feed groove 74b is located between two adjacent feed protrusions 72b.

[0035] Of the multiple inward protrusions 66a, the inward protrusions 66a that form the fuel gas flow passage 70 are referred to as flow passage protrusions 76. In a plan view of the second separator 32, each flow passage protrusion 76 is wavy and extends along the direction of arrow B. A flow passage groove 78 is located between two adjacent flow passage protrusions 76. Each flow passage groove 78 is also wavy. Each flow passage protrusion 76 contacts the anode electrode 42 of the MEA 28 located in the direction of arrow A1. The multiple flow passage grooves 78 are fuel It becomes a passageway for gas to flow.

[0036] The waveforms of the flow passage convexities 76 and flow passage grooves 78 on the surface 32a of the second separator 32 and the waveforms of the flow passage convexities 56 and flow passage grooves 58 on the surface 30a of the first separator 30 differ in at least one of phase, period, and amplitude.

[0037] Each of the communication holes (fuel gas inlet manifold 38a, coolant outlet manifold 36b, oxidant gas outlet manifold 34b, oxidant gas inlet manifold 34a, coolant inlet manifold 36a, and fuel gas outlet manifold 38b) is surrounded by an inward protrusion 66a. These inward protrusions 66a are referred to as communication hole bead seals 80. Each communication hole bead seal 80 contacts the MEA 28 located in the direction of arrow A1. As a result, the multiple communication hole bead seals 80 seal the multiple communication holes.

[0038] The communication hole bead seal 80 surrounding the fuel gas inlet manifold 38a has multiple flow passages (not shown) that connect the fuel gas inlet manifold 38a to the fuel gas feed 68a. Similarly, the communication hole bead seal 80 surrounding the fuel gas outlet manifold 38b has multiple flow passages (not shown) that connect the fuel gas outlet manifold 38b to the fuel gas feed 68b.

[0039] An area including the two fuel gas feeds 68a, 68b, the fuel gas flow channel 70, the fuel gas inlet manifold 38a, the oxidant gas outlet manifold 34b, the oxidant gas inlet manifold 34a, and the fuel gas outlet manifold 38b is surrounded by an inward protrusion 66a. This inward protrusion 66a is referred to as an outer bead seal 82. The outer bead seal 82 comes into contact with the MEA 28 located in the direction of arrow A1. As a result, the outer bead seal 82 seals the area through which fuel gas flows between the surface 32a and the MEA 28 (the area including the two fuel gas feeds 68a, 68b, the fuel gas flow channel 70, the fuel gas inlet manifold 38a, and the fuel gas outlet manifold 38b).

[0040] [1-2-4 Configuration of rear surface 30b and rear surface 32b] 7, on the back surface 30b of the first separator 30, the outer convex portion 46b is located behind the grooves (feed grooves 54a, 54b, flow path groove 58, etc.) on the front surface 30a. An outer groove 84 is located next to the outer convex portion 46b. The outer groove 84 is located behind the inner convex portion 46a (feed convex portions 52a, 52b, flow path convex portion 56, etc.) on the front surface 30a.

[0041] 8, on the back surface 32b of the second separator 32, the outer convex portion 66b is located behind the grooves (feed grooves 74a, 74b, flow path groove 78, etc.) on the front surface 32a. The outer groove 86 is located next to the outer convex portion 66b. The outer groove 86 is located behind the inner convex portion 66a (feed convex portions 72a, 72b, flow path convex portion 76, etc.) on the front surface 32a.

[0042] The waveform of the outer convex portion 46b located on the back side of the flow groove 58 of the first separator 30 and the waveform of the outer convex portion 66b located on the back side of the flow groove 78 of the second separator 32 differ in at least one of phase, period, and amplitude.

[0043] 4, the back surface 30b of the first separator 30 and the back surface 32b of the second separator 32 face each other, and some of the outer protrusions 46b and some of the outer protrusions 66b are welded to each other. Furthermore, the peripheral edge of the first separator 30 and the peripheral edge of the second separator 32 are welded to each other. Furthermore, the first separator 30 and the second separator 32 located around each communication hole are welded to each other. As a result, a coolant flow field 88 is formed between the back surface 30b of the first separator 30 and the back surface 32b of the second separator 32.

[0044] A portion of the outer protrusion 46b of the first separator 30 contacts a portion of the outer protrusion 66b of the second separator 32. A portion of the outer groove 84 of the first separator 30 overlaps a portion of the outer groove 86 of the second separator 32.

[0045] The communication hole bead seal 60 surrounding the coolant inlet manifold 36a of the first separator 30 has a plurality of flow passages (not shown) that connect the coolant inlet manifold 36a to the outer groove 84. Similarly, the communication hole bead seal 80 surrounding the coolant inlet manifold 36a of the second separator 32 has a plurality of flow passages (not shown) that connect the coolant inlet manifold 36a to the outer groove 86.

[0046] The communication hole bead seal 60 surrounding the coolant outlet communication hole 36b of the first separator 30 has a plurality of flow passages (not shown) that connect the coolant outlet communication hole 36b to the outer groove 84. Similarly, the communication hole bead seal 80 surrounding the coolant outlet communication hole 36b of the second separator 32 has a plurality of flow passages (not shown) that connect the coolant outlet communication hole 36b to the outer groove 86.

[0047] [2 Operation of fuel cell stack 10] 1, an oxidant gas (e.g., oxygen-containing gas) is supplied to an oxidant gas inlet passage 34a in the end plate 20a. A fuel gas (e.g., hydrogen-containing gas) is supplied to a fuel gas inlet passage 38a in the end plate 20a. A coolant (e.g., pure water) is supplied to a coolant inlet passage 36a in the end plate 20a. In each unit cell 12, each fluid flows as follows.

[0048] As shown in FIG. 4, the oxidant gas supplied to the oxidant gas inlet passage 34a flows into the oxidant gas feed 48a. The oxidant gas that flows into the oxidant gas feed 48a is evenly distributed to the multiple flow grooves 58 of the oxidant gas flow field 50 and flows therein. In the oxidant gas flow field 50, the oxidant gas is supplied to the cathode electrode 44 of the MEA 28. Meanwhile, the fuel gas supplied to the fuel gas inlet passage 38a flows into the fuel gas feed 68a. The fuel gas that flows into the fuel gas feed 68a is evenly distributed to the multiple flow grooves 78 of the fuel gas flow field 70 and flows therein. In the fuel gas flow field 70, the fuel gas is supplied to the anode electrode 42 of the MEA 28. In the MEA 28, a chemical reaction occurs between the oxidant gas supplied to the cathode electrode 44 and the fuel gas supplied to the anode electrode 42, generating electricity. Water is generated as a result of the chemical reaction.

[0049] Next, the unreacted oxidant gas and water flow from the oxidant gas flow field 50 into the oxidant gas feed 48b. The oxidant gas that flowed into the oxidant gas feed 48b then flows out to the oxidant gas outlet passage 34b. Meanwhile, the unreacted fuel gas flows from the fuel gas flow field 70 into the fuel gas feed 68b. The fuel gas that flowed into the fuel gas feed 68b then flows out to the fuel gas outlet passage 38b.

[0050] The cooling medium supplied to the cooling medium inlet manifold 36a flows into the cooling medium flow path 88. In the cooling medium flow path 88, the cooling medium cools the MEA 28 located in the direction of arrow A. The cooling medium in the cooling medium flow path 88 flows out to the cooling medium outlet manifold 36b.

[0051] [3. Bonding method of the bonded separator 33] In the bonded separator 33, the contact portion of the first separator 30 and the second separator 32 are bonded. In the bonded separator 33, the peripheral portion of the first separator 30 and the peripheral portion of the second separator 32 are bonded.

[0052] As shown in Figs. 7 and 8, the outer convex portion 46b of the first separator 30 and the outer convex portion 66b of the second separator 32 are not symmetrical. Therefore, when the back surface 30b of the first separator 30 and the back surface 32b of the second separator 32 face each other, a part of the outer convex portion 46b and a part of the outer convex portion 66b contact each other. In addition, the contact area of ​​each contact point is small. Therefore, it is difficult to bring the electrodes for spot welding close to each contact portion. Therefore, in this embodiment, the outer convex portion 46b and the outer convex portion 66b are joined by projection welding. As shown in Figs. 9 and 10, a pair of electrodes 90 (a first electrode 90a and a second electrode 90b) for projection welding are used in projection welding.

[0053] As shown in FIG. 9, the joining of the first separator 30 and the second separator 32 is performed in the order of a contact step, a positioning step, a projection welding step, a first laser welding step, and a second laser welding step.

[0054] [3-1 First embodiment] 10, a pair of electrodes 90 for projection welding used in the first embodiment is larger than a power generation area 92a of the first separator 30 and a power generation area 92b of the second separator 32 in a plan view. The pair of electrodes 90 are connected to an electric circuit 94 that passes a current for performing welding. The electric circuit 94 has a transformer, a power source, etc., not shown.

[0055] The power generation area 92a of the first separator 30 is a portion that includes the inward protrusion 46a that contacts the cathode electrode 44. The power generation area 92a is a portion of the first separator 30 that overlaps with the cathode electrode 44. The power generation area 92b of the second separator 32 is a portion that includes the inward protrusion 66a that contacts the anode electrode 42. Power generation area 92b is a portion of the second separator 32 that overlaps with the anode electrode 42.

[0056] First, the first separator 30 and the second separator 32 are brought into contact with each other (contact step). Here, after aligning each communication hole (such as the oxidant gas supply passage 34a) of the first separator 30 with each communication hole (such as the oxidant gas supply passage 34a) of the second separator 32, the first separator 30 and the second separator 32 are overlapped with each other. In this state, the multiple outer protrusions 46b of the first separator 30 and the multiple outer protrusions 66b of the second separator 32 are in contact with each other. Note that there are also multiple outer protrusions 46b, 66b that do not contact each other.

[0057] Next, the pair of electrodes 90 are aligned (alignment step). Here, the first electrode 90a is positioned to face the surface 30a of the first separator 30. The first electrode 90a is also positioned to overlap the entire power generation area 92a of the first separator 30 in a plan view. The first electrode 90a is further moved closer to the first separator 30 and brought into contact with the multiple inward protrusions 46a. Similarly, the second electrode 90b is positioned to face the surface 32a of the second separator 32. The second electrode 90b is further moved closer to the second separator 32 and brought into contact with the multiple inward protrusions 66a.

[0058] Next, projection welding is performed (projection welding process). Here, a current is passed between the first electrode 90a and the second electrode 90b by the electric circuit 94. In this manner, a plurality of mutually contacting locations of the outer protrusion 46b located in the power generation area 92a and the outer protrusion 66b of the second separator 32 located in the power generation area 92b are simultaneously welded.

[0059] Next, a first laser welding is performed (first laser welding step). Here, the outer periphery of each communication hole (such as the oxidant gas supply passage 34a) of the first separator 30 is laser welded to the outer periphery of each communication hole (such as the oxidant gas supply passage 34a) of the second separator 32. That is, the first separator 30 and the second separator 32 located around each communication hole are laser welded.

[0060] Finally, a second laser welding is performed (second laser welding step), where the peripheral edge of the first separator 30 and the peripheral edge of the second separator 32 are laser welded together. In this manner, the first separator 30 and the second separator 32 are joined together.

[0061] According to the first embodiment, by contacting the pair of electrodes 90 with the multiple inner convex portions 46a, 66a, all of the contact portions of the outer convex portions 46b, 66b located between the pair of electrodes 90 can be welded. Thus, according to the first embodiment, since it is not necessary to contact the pair of welding electrodes 90 with the welded portions (contact portions of the outer convex portions 46b, 66b), welding is easy. Also, according to the first embodiment, since it is not necessary to weld the welded portions one by one, welding is easy. Also, according to the first embodiment, since it is not necessary to accurately contact the welding electrodes with the welded portions as in spot welding, welding is easy. Also, according to the first embodiment, since it is not necessary to accurately grasp the welded portions, welding is easy. Also, according to the first embodiment, since it is possible to weld all of the welded portions by passing a current through the pair of electrodes 90, the welding operation is simple.

[0062] [3-2 Second embodiment] As shown in FIG. 11, a pair of electrodes 90 for projection welding used in the second embodiment is smaller than a power generation area 92a of the first separator 30 and a power generation area 92b of the second separator 32 in a plan view.

[0063] The pair of electrodes 90 used in the second embodiment is smaller than the pair of electrodes 90 used in the first embodiment. A current is supplied from the pair of electrodes 90 to the outer convex portions 46b, 66b that are distant from the pair of electrodes 90 through the metal sheet portions that do not overlap with the pair of electrodes 90. However, the metal sheet becomes a resistance, and the current flowing through the outer convex portions 46b, 66b that are distant from the pair of electrodes 90 becomes small. Therefore, the outer convex portions 46b, 66b that are distant from the pair of electrodes 90 are not sufficiently joined. Therefore, in the second embodiment, it is necessary to move the pair of electrodes 90 to multiple welding positions to perform projection welding. That is, in the second embodiment, it is necessary to perform the alignment process and the projection welding process multiple times.

[0064] In the positioning step, the first electrode 90a is disposed at a position facing the surface 30a of the first separator 30. The first electrode 90a is also disposed at a position overlapping a portion of the power generation area 92a of the first separator 30 in a plan view. The first electrode 90a is then brought closer to the first separator 30 and brought into contact with the multiple inward protrusions 46a. Similarly, the second electrode 90b is disposed at a position facing the surface 32a of the second separator 32. The second electrode 90b is also disposed at a position overlapping a portion of the power generation area 92b of the second separator 32 in a plan view. The second electrode 90b is then brought closer to the second separator 32 and brought into contact with the multiple inward protrusions 66a.

[0065] In the projection welding process, a current is applied between the first electrode 90a and the second electrode 90b by the electric circuit 94. In this manner, all of the locations of the outer protrusions 46b and 66b located between the pair of electrodes 90 that come into contact with each other are welded simultaneously.

[0066] After the projection welding process is completed, the pair of electrodes 90 is moved to an area that has not yet been welded, and an alignment process and a projection welding process are performed.

[0067] In the second embodiment, it is preferable to weld the outer protrusions 46b, 66b located on the central side of each of the power generation areas 92a, 92b before welding the outer protrusions 46b, 66b located on the peripheral side of each of the power generation areas 92a, 92b.

[0068] As shown in Fig. 12, when the area to be projection welded is divided into nine areas (a to i), it is preferable to weld the central area e first. For example, it is preferable to perform welding in the following order: area e, area b, area d, area f, area h, area a, area c, area g, and area i. Note that the welding order of area b, area d, area f, and area h is not limited. Similarly, the welding order of area a, area c, area g, and area i is not limited.

[0069] This makes it possible to reduce distortion due to swells and welding of the joint separator 33. Note that, according to the second embodiment, although the number of times projection welding is performed increases, it is possible to obtain the same effects as in the first embodiment.

[0070] [4 Inventions Obtained from the Embodiments] The invention that can be understood from the above embodiment will be described below.

[0071] An aspect of the present invention is a method for joining two adjacent separators in a fuel cell stack (10) in which unit cells (12) each having a membrane electrode assembly (28) and a pair of separators (33) sandwiching the membrane electrode assembly are stacked, the two adjacent separators being a first separator (30) covering a cathode electrode (44) of a first membrane electrode assembly and a second separator (32) covering an anode electrode (42) of a second membrane electrode assembly, the first separator having a first inward protrusion (46a) in contact with the cathode electrode of the first membrane electrode assembly and a second separator (32) protruding toward the second separator. the second separator has a first outer convex portion (46b) and a second inner convex portion (66a) that contacts the anode electrode of the second membrane electrode structure and a second outer convex portion (66b) that protrudes toward the first separator, and the method includes the steps of contacting the first separator and the second separator with each other, contacting a first electrode (90a) for welding with the multiple first inner convex portions, contacting a second electrode (90b) for welding with the multiple second inner convex portions, and passing a current between the first electrode and the second electrode to weld the multiple locations where the first outer convex portion and the second outer convex portion contact.

[0072] According to the above method, welding is easy because it is not necessary to contact the first and second welding electrodes with the points to be welded (contact portions of the outer convex portion). Also, according to the above method, welding is easy because it is not necessary to weld the points to be welded one by one. Also, according to the above method, welding is easy because it is not necessary to accurately contact the welding electrodes with the points to be welded as in spot welding. Also, according to the above method, welding is easy because it is not necessary to accurately grasp the points to be welded.

[0073] In the above method, a current may be passed between the first electrode and the second electrode in a state in which, in a plan view, the first electrode and the second electrode overlap the entire surface of the power generation area (92a) of the first separator and the entire surface of the power generation area (92b) of the second separator, to weld multiple locations where the first outer convex portion and the second outer convex portion are in contact.

[0074] According to the above method, all the parts to be welded can be welded by passing a current through a pair of electrodes once, and therefore the welding work is simple.

[0075] In the above method, a current may be passed between the first electrode and the second electrode to weld multiple locations where the first outer convex portion and the second outer convex portion are in contact with each other, while the first electrode and the second electrode overlap a portion of the power generation area of ​​the first separator and a portion of the power generation area of ​​the second separator in a planar view.

[0076] In the above method, welding of the first outer convex portion and the second outer convex portion located on the central side of each of the power generation areas may be performed prior to welding of the first outer convex portion and the second outer convex portion located on the peripheral side of each of the power generation areas.

[0077] According to the above method, it is possible to reduce undulations and distortion due to welding in a joined separator made up of a first separator and a second separator.

[0078] In the above method, each of the first separator and the second separator may have a communicating hole (34a, 34b, 36a, 36b, 38a, 38b) at the same position in a planar view, and after welding the first outer convex portion of the first separator to the second outer convex portion of the second separator, an outer periphery of the communicating hole of the first separator to an outer periphery of the communicating hole of the second separator may be laser welded.

[0079] In the above method, after joining the first outer convex portion of the first separator and the second outer convex portion of the second separator, the peripheral portion of the first separator and the peripheral portion of the second separator may be laser welded together.

[0080] The present invention is not limited to the above disclosure, and various configurations can be adopted without departing from the gist of the present invention. [Explanation of symbols]

[0081] 10...Fuel cell stack 12...Unit cell 28... membrane electrode assembly 30... first separator 32…Second separator 34a...oxidizer gas inlet passage (passage) 34b...Oxidant gas outlet communication hole (communication hole) 36a…Cooling medium inlet communication hole (communication hole) 36b…Cooling medium outlet communication hole (communication hole) 38a...Fuel gas inlet passage (passage) 38b...Fuel gas outlet communication hole (communication hole) 42...anode electrode 44...cathode electrode 46a…Inner convex portion (first inner convex portion) 46b...Outer convex portion (first outer convex portion) 66a…inner protrusion (second inner protrusion) 66b... Outer convex portion (second outer convex portion) 90a...First electrode 90b...Second electrode 92a, 92b…Power generation area

Claims

1. 1. A method for joining two adjacent separators in a fuel cell stack in which unit cells each having a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly are stacked, comprising the steps of: The two adjacent separators are a first separator covering a cathode electrode of a first membrane electrode assembly and a second separator covering an anode electrode of a second membrane electrode assembly, the first separator has a first inner convex portion that is wavy in a plan view of the first separator and that contacts the cathode electrode of the first membrane electrode assembly, and a first outer convex portion that is wavy in a plan view of the first separator and that protrudes toward the second separator, the second separator has a second inner convex portion that is wavy in a plan view of the second separator and that contacts the anode electrode of the second membrane electrode assembly, and a second outer convex portion that is wavy in a plan view of the second separator and that protrudes toward the first separator, the waveform of the first outer convex portion of the first separator and the waveform of the second outer convex portion of the second separator are different in at least one of phase, period, and amplitude; bringing the first outer convex portion of the first separator and the second outer convex portion of the second separator into contact with each other at a plurality of locations; contacting a first electrode for welding with the first inner protrusions; contacting a second electrode for welding with the second inward protrusions; a step of passing a current between the first electrode and the second electrode to weld a plurality of locations where the first outer convex portion and the second outer convex portion are in contact with each other; A bonding method comprising:

2. The bonding method according to claim 1, a joining method comprising: a current being passed between the first electrode and the second electrode in a state in which, in a plan view, the first electrode and the second electrode overlap an entire surface of a power generation area of ​​the first separator and an entire surface of a power generation area of ​​the second separator, thereby welding multiple locations where the first outer convex portion and the second outer convex portion are in contact.

3. The bonding method according to claim 1, a joining method comprising: welding multiple locations where the first outer convex portion and the second outer convex portion are in contact with each other by passing a current between the first electrode and the second electrode in a state in which the first electrode and the second electrode overlap, in a plan view, with a part of a power generation area of ​​the first separator and a part of a power generation area of ​​the second separator.

4. The joining method according to claim 3, a joining method in which welding of the first outer convex portion and the second outer convex portion located on a central side of each of the power generation areas is performed prior to welding of the first outer convex portion and the second outer convex portion located on a peripheral side of each of the power generation areas.

5. The bonding method according to claim 1, each of the first separator and the second separator has a communication hole at the same position in a plan view; A joining method comprising: welding the first outer convex portion of the first separator to the second outer convex portion of the second separator; and then laser welding an outer periphery of the communicating hole of the first separator to an outer periphery of the communicating hole of the second separator.

6. The bonding method according to claim 1, a joining method including joining the first outer convex portion of the first separator to the second outer convex portion of the second separator, and then laser welding a peripheral portion of the first separator to a peripheral portion of the second separator.

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