Electrochemical cell, electrochemical cell stack, and manufacturing methods for same

Abstract

[Problem] To provide: an electrochemical cell that exhibits high bonding strength between metallic members while a warp of the metallic members is inhibited ; an electrochemical cell stack; and manufacturing methods for the same. [Solution] The present invention comprises: a cell body 20 that is formed by laminating an air electrode, an electrolyte layer, and a fuel electrode; a first metallic member 18 that is bonded to the cell body 20; a second metallic member 17 that is laminated at and bonded by welding to a prescribed position of the first metallic member 18 in the lamination direction of the cell body 20 with respect to the first metallic member 18; and a third metallic member 16 that is laminated at and bonded by welding to a surface of the second metallic member 17 opposite from the surface bonded to the first metallic member 18 at a prescribed second position of the second metallic member 17 in the lamination direction of the cell body 20 with respect to the second metallic member 17. The parts bonded by welding are defined as welded parts 30. At least a portion of the penetration direction of the welded parts 30 is inclined with respect to the lamination direction of the cell body 20.

Description

Electrochemical cell, electrochemical cell stack, and manufacturing method thereof

[0001] The present invention relates to an electrochemical cell, an electrochemical cell stack, and a method for manufacturing the same.

[0002] Solid oxide fuel cells (SOFCs) are a type of fuel cell that generates electricity using an electrochemical reaction between hydrogen and oxygen. A single fuel cell (hereinafter referred to as a "single cell"), which is a constituent unit of an SOFC, includes an electrolyte layer containing solid oxide, an air electrode disposed on one side of the electrolyte layer in a predetermined direction, and a fuel electrode disposed on the other side of the electrolyte layer in the predetermined direction.

[0003] A fuel electrode having a porous layer (hereinafter referred to as "active layer") containing an electronically conductive material and an ionically conductive oxide is sometimes used as the fuel electrode constituting a single cell. Specifically, a metal containing Ni (nickel) is sometimes used as the electronically conductive material, and YSZ (yttria-stabilized zirconia), an ionically conductive oxide having oxygen ion conductivity, is sometimes used as the ionically conductive oxide. The active layer mainly functions to generate electrons and water vapor by reacting oxygen ions supplied to the active layer from the electrolyte layer with hydrogen and the like contained in the fuel gas supplied to the fuel chamber facing the fuel electrode.

[0004] Furthermore, the above-mentioned SOFC can be used as a solid oxide electrolysis cell (hereinafter referred to as "SOEC") by passing current in the reverse direction, and is also known to be used as an energy storage technology in the form of converting water vapor into hydrogen using surplus electricity, which is an issue in the process of introducing renewable energy. In this case, the active layer mainly functions to react with water vapor contained in the fuel gas supplied to the fuel chamber facing the anode, to generate oxygen ions and hydrogen, which are supplied from the active layer to the electrolyte layer.

[0005] Japanese Patent Application Laid-Open No. 2021-34249

[0006] To enable such a unit cell to function, multiple components are arranged and joined around the unit cell, and the unit cell is used as an electrochemical cell or an electrochemical cell stack in which electrochemical cells are stacked. Since electrochemical cells have the function of inputting or generating hydrogen, ensuring their airtightness is important for safety, and among the multiple components, metal components such as interconnectors, separators, and connector plates are joined together using brazing material or by laser welding. Laser welding is suitable for welding metal components of electrochemical cells because it can weld precise shapes.

[0007] On the other hand, in laser welding, in order to increase the joining strength and airtightness, it is necessary to widen the weld width, which requires increasing the laser output or changing the irradiation mode. However, increasing the laser output or changing the irradiation mode increases the amount of heat, which can lead to quality defects such as a decrease in airtightness due to warping of the metal members.

[0008] The present invention has been made in consideration of the above circumstances, and aims to provide an electrochemical cell, an electrochemical cell stack, and methods for manufacturing the same, in which warping of the metal members is suppressed and the bonding strength between the metal members is strong.

[0009] (1) To achieve the above object, the electrochemical cell of the present invention employs the following measures: That is, an electrochemical cell according to an application example of the present invention includes a cell body formed by stacking an air electrode, an electrolyte layer, and an anode, a first metal member joined to the cell body, a second metal member stacked on the first metal member at a predetermined position in the stacking direction of the cell body and joined by a weld, and a third metal member stacked on the second metal member at a second predetermined position on the second metal member on a surface of the second metal member opposite the surface joined to the first metal member, the second metal member being stacked on the second metal member in the stacking direction of the cell body and joined by welding, the welded portion being a weld, and the penetration direction of at least a portion of the weld is inclined with respect to the stacking direction of the cell body.

[0010] (2) Furthermore, in the electrochemical cell of the application example of (1) above, the third metal member has a fourth metal member and a fifth metal member, and the fourth metal member and the fifth metal member are joined by the welded portion.

[0011] (3) In the electrochemical cell according to the application example of (1) or (2) above, the inclination angle of the penetration direction of the welded portion is 5° or more and 60° or less.

[0012] (4) Furthermore, in the electrochemical cell according to any one of the application examples (1) to (3) above, the penetration direction of the weld is inclined in a direction from the center of the second metal member toward the outer periphery.

[0013] (5) Furthermore, in the electrochemical cell of any of the application examples (1) to (4) above, the second metal member is approximately rectangular when viewed from the stacking direction of the cell body, and the inclination angle of the penetration direction of the weld increases and the welding depth of the weld decreases as the distance from the side of the second metal member approaches the corner.

[0014] (6) In the electrochemical cell according to any one of the application examples of (1) to (5) above, the weld width of the welded portion is 80 μm or more and 400 μm or less.

[0015] (7) In the electrochemical cell according to any one of the application examples of (1) to (6) above, the penetration depth of the welded portion is 50 μm or more and 90 μm or less.

[0016] (8) In the electrochemical cell according to any one of the application examples of (1) to (7) above, the bead width of the welded portion is 100 μm or more and 500 μm or less.

[0017] (9) In the electrochemical cell according to any one of the application examples of (1) to (8) above, the second metal member has a thickness of 0.05 mm or more and 1 mm or less.

[0018] (10) In addition, in the electrochemical cell according to any one of the application examples (1) to (9) above, the thickness of the cell body in the stacking direction of the cell body is 0.5 mm or more and 5 mm or less.

[0019] (11) Furthermore, in the electrochemical cell of any of the application examples (1) to (10) above, the cross-sectional shape of the weld on the first metal member side is tapered from the first metal member side toward the second metal member side, and the cross-sectional shape of the weld on the third metal member side is tapered from the third metal member side toward the second metal member side.

[0020] (12) In addition, in the electrochemical cell of any of the application examples of (1) to (11) above, the electrochemical cell is selected from an electrolysis cell and a reversible operation fuel cell.

[0021] (13) Furthermore, an electrochemical cell stack according to an application example of the present invention is characterized in that a plurality of electrochemical cells according to any one of (1) to (12) above are stacked and joined in the stacking direction of the cell bodies.

[0022] (14) Also, a manufacturing method of an electrochemical cell according to an application example of the present invention is a manufacturing method of an electrochemical cell, characterized in that it includes the steps of: preparing a cell body formed by stacking an air electrode, an electrolyte layer, and a fuel electrode; preparing a first metal member to be joined to the cell body, a second metal member to be joined to the first metal member, and a third metal member to be joined to the second metal member; arranging the second metal member at a predetermined position on the first metal member so that it is stacked relative to the first metal member in the stacking direction of the cell body, and welding by laser welding so that the weld penetration direction is inclined relative to the stacking direction of the cell body; and arranging the third metal member at a second predetermined position on the second metal member, on the surface of the second metal member opposite the surface to be joined to the first metal member, so that it is stacked relative to the second metal member in the stacking direction of the cell body, and welding by laser welding so that the weld penetration direction is inclined relative to the stacking direction of the cell body.

[0023] (15) In the method for manufacturing an electrochemical cell according to the application example of the present invention described above in (14), the welding step is performed using a laser processing machine equipped with an optical head moving device.

[0024] (16) In addition, in the method for manufacturing an electrochemical cell according to the application example of the present invention described above in (15), the welding step is performed using a laser processing machine equipped with a galvanometer mirror or a polygon mirror.

[0025] (17) Furthermore, a manufacturing method of an electrochemical cell stack according to an application example of the present invention is a manufacturing method of an electrochemical cell stack, characterized in that it includes the steps of preparing a plurality of electrochemical cells by the manufacturing method described in any one of (14) to (16) above, stacking the plurality of electrochemical cells in the stacking direction of the cell bodies, and joining the stacked plurality of electrochemical cells.

[0026] According to the present invention, by tilting the penetration direction of the weld between the first metal member and the second metal member or the second metal member and the third metal member relative to the stacking direction of the cell body, the welding strength between the metal members can be increased even with a laser output equivalent to that of conventional methods.

[0027] 1 is a perspective view showing an example of an electrochemical cell stack according to an embodiment; FIG. 2 is a schematic cross-sectional view showing an example of an electrochemical cell according to an embodiment; FIG. 3 is a schematic cross-sectional view showing an example of an exploded electrochemical cell according to an embodiment; (a) and (b) are a schematic cross-sectional view and a top view, respectively, showing an example of an interconnector and an IC separator according to an embodiment; (a) and (b) are a schematic cross-sectional view and a top view, respectively, showing an example of an electrochemical cell according to an embodiment; (a) is a cross-sectional view of a first metal member, a second metal member, and a welded portion of an example; (b) is a cross-sectional view showing a schematic cross-section of the cross section of FIG. 6; (c) is a schematic cross-sectional view showing a step in a method for manufacturing an electrochemical cell; (a) to (c) are schematic cross-sectional views showing a step in a method for manufacturing an electrochemical cell; and (c) are schematic cross-sectional views showing a step in a method for manufacturing an electrochemical cell stack.

[0028] [Embodiments] [Configuration of Electrochemical Cell Stack] Next, embodiments of the present invention will be described with reference to the drawings. To facilitate understanding of the description, the same reference numerals are used to refer to the same components in each drawing, and duplicated descriptions will be omitted. Note that in the configuration diagrams, the size of each component is shown conceptually and does not necessarily represent the actual dimensional ratio.

[0029] FIG. 1 is a perspective view of an electrochemical cell stack 10 according to an embodiment. The electrochemical cell stack 10 is exemplified by a solid oxide fuel cell (SOFC) or a solid oxide electrolysis cell (SOEC). The electrochemical cell stack 10 may also be reversible so that it can be used for both SOFC and SOEC applications. The electrochemical cell stack 10 or electrochemical cells 11 are preferably selected from electrolysis cells and reversible fuel cell cells.

[0030] The electrochemical cell stack 10 includes rectangular electrochemical cells 11, multiple of which are stacked in the thickness direction, and rectangular end plates (upper end plate 12a and lower end plate 12b) that sandwich the electrochemical cells 11 in the thickness direction. The electrochemical cells 11 form a fuel chamber 33, which will be described later, among the reaction units. Bolts 13 are arranged at the four corners of the periphery of the electrochemical cell stack 10, and pass through the upper end plate 12a, the multiple electrochemical cells 11, and the lower end plate 12b in the thickness direction. The upper end plate 12a, the multiple electrochemical cells 11, and the lower end plate 12b are fastened together by the bolts 13.

[0031] The four spaces that penetrate the periphery of the electrochemical cell stack 10 in the thickness direction function as a passage 14a through which gas enters the fuel chamber 33 of the electrochemical cell 11 from outside the electrochemical cell stack 10, a passage 14b through which gas exits the electrochemical cell stack 10 from the fuel chamber 33, a passage 14c through which gas enters the air chamber 35 of the electrochemical cell 11 from outside the electrochemical cell stack 10, which will be described later, and a passage 14d through which gas exits the air chamber 35 to the outside of the electrochemical cell stack 10.

[0032] The electrochemical cell stack 10 includes an upper terminal plate 52 disposed between the upper end plate 12a and the electrochemical cells 11, and a lower terminal plate 53 disposed between the end plate 12b and the electrochemical cells 11. The electrochemical cells 11 are connected in series between the upper terminal plate 52 and the lower terminal plate 53. The protruding portions of the upper terminal plate 52 and the lower terminal plate 53 function as terminals. The upper terminal plate 52 and the lower terminal plate 53 may be omitted, and the electrochemical cells 11 may be electrically connected to the upper end plate 12a and the lower end plate 12b, with the upper end plate 12a and the lower end plate 12b serving as terminals for the electrochemical cell stack 10.

[0033] [Structure of Electrochemical Cell] FIG. 2 is a schematic cross-sectional view showing an example of an electrochemical cell according to an embodiment. FIG. 3 is a schematic cross-sectional view showing an example of an exploded electrochemical cell according to an embodiment. FIG. 2 shows two electrochemical cells 11 of the electrochemical cell stack 10 cut along line II-II in FIG. 1 , which passes through the passages 14a and 14b. FIG. 3 is a cross-sectional view of the components shown in FIG. 2 separated in the thickness direction. However, FIG. 3 omits the welded portion 30 of the member welded to the anode frame 17. In FIGS. 2 and 3 , the thickness of each part is exaggerated (the same applies to FIGS. 4 , 5 , and 9 to 11 ). The electrochemical cell 11 includes, from bottom to top in the thickness direction, an interconnector 15, an IC separator 16, an anode frame 17, a cell body 20, and a cell separator 18. A cathode frame 19 is disposed between the two electrochemical cells 11. In this embodiment, the electrochemical cell 11 does not include the cathode frame 19, but the electrochemical cell 11 may have the cathode frame 19 joined to the top or bottom surface of the electrochemical cell 11. Holes (passages 14a, 14b) penetrate the interconnector 15, the anode frame 17, the cell separator 18, and the cathode frame 19.

[0034] The cell body 20 includes, from bottom to top, an anode 21, an electrolyte layer 24, and an air electrode 25. The anode 21 includes a support 22 and a functional layer 23 disposed over the entire surface 22a of the support 22. The anode 21 is a rectangular, flat, porous body having higher gas permeability, with the porosity of the support 22 being higher than the porosity of the functional layer 23. The thickness of the support 22 is, for example, in the range of 200 μm to 1000 μm.

[0035] The support 22 has a constant thickness in a plane direction perpendicular to the thickness direction, except for variations due to unevenness resulting from particles constituting the support 22 and pores contained in the support 22. This makes it possible to reduce warping and undulations caused by variations in the thickness of the support 22.

[0036] The main function of the support 22 is to support the functional layer 23. The material constituting the support 22 may be the same as the material constituting the functional layer 23, or may be a material different from the material constituting the functional layer 23. When the material constituting the support 22 is different from the material constituting the functional layer 23, the material of the support 22 is exemplified by stabilized zirconia.

[0037] In a fuel cell, the functional layer 23 has a function of reacting oxide ions supplied from the electrolyte layer 24 with a fuel gas (hydrogen, carbon monoxide, hydrocarbon, etc.) to generate electrons, and in steam electrolysis, has a function of electrolyzing steam when current is applied, converting it into hydrogen and oxide ions. The thickness of the functional layer 23 is, for example, 10 μm to 40 μm.

[0038] The functional layer 23 includes a catalyst containing Ni and zirconia with Y dissolved therein. Examples of the catalyst include Ni, Ni-based alloys, and cermets, which are composites (sintered bodies) of NiO and oxides (solid electrolytes). Ni is produced in cermets by hydrogen reduction of NiO. Examples of the oxides (solid electrolytes) contained in cermets include zirconia with Y dissolved therein. However, the functional layer 23 is not limited thereto, and may include, for example, a catalyst containing Ni and ceria with Gd dissolved therein.

[0039] The electrolyte layer 24 is a plate-like member that exhibits oxide ion conductivity under the operating conditions of the electrochemical cell 11. The functional layer 23 of the anode 21 is disposed over the entire back surface 24b of the electrolyte layer 24. The porosity of the electrolyte layer 24 is lower than the porosity of the anode 21.

[0040] The electrolyte layer 24 may be made of, for example, stabilized zirconia, ceria-based solid solution, or a solid solution of alumina and one or more selected from the group consisting of stabilized zirconia and ceria-based solid solution. The stabilizer for stabilized zirconia may be CaO, MgO, Y ２ O ３ , Sc ２ O ３ , Yb ２ O ３ Examples of elements that dissolve in ceria in a ceria-based solid solution include Gd, Sm, and Y. That is, the electrolyte layer 24 is made of a solid electrolyte. The thickness of the electrolyte layer 24 is, for example, 5 μm to 40 μm. The fuel electrode 21 and the electrolyte layer 24 as a whole form a plate-shaped sintered body 26.

[0041] The air electrode 25 is disposed at the center of the surface 24a of the electrolyte layer 24. In a fuel cell, the air electrode 25 is the site where a gaseous oxidant (oxygen) reacts with electrons to become oxide ions, and in steam electrolysis, it is the site where oxide ions release electrons to become oxygen. The air electrode 25 must be able to easily adsorb gases and have high oxygen ion conductivity, and it must also have electron conductivity.

[0042] The material of the cathode 25 is a perovskite oxide, La １－Ｘ Sr Ｘ MnO ３－δ , La １－Ｘ Sr Ｘ CoO ３－δ , La １－Ｘ Sr Ｘ Co １－Ｙ Fe Ｙ O ３－δ , Pr １－Ｘ Sr Ｘ MnO ３－δ The material of the air electrode 25 may be a composite material of one or more oxides selected from these perovskite oxides and an electrolyte capable of forming the electrolyte layer 24 .

[0043] An intermediate layer may be disposed between the electrolyte layer 24 and the air electrode 25. The intermediate layer reduces reaction between the electrolyte layer 24 and the air electrode 25 when heated during fabrication of the cell body 20 or at high temperatures during operation of the electrochemical cell 11. Examples of materials for the intermediate layer include ceria-based solid solutions. Examples of elements that dissolve in ceria in ceria-based solid solutions include Gd, Sm, La, and Y.

[0044] The interconnector 15 is a conductive member arranged on both sides of the cell body 20 in the thickness direction, and has a substantially rectangular flat plate portion and a plurality of substantially columnar current collecting portions 34 protruding from the flat plate portion toward the air electrode side. Each current collecting portion 34 of the interconnector 15 is joined to the air electrode 25 of the cell body 20 via a conductive bonding material made of, for example, a spinel-type oxide, and is electrically connected to the air electrode 25. The conductive bonding material may be formed on the entire surface of the interconnector 15 on the air electrode 25 side. The interconnector 15 electrically connects adjacent electrochemical cells 11 in the thickness direction. An example of the material of the interconnector 15 is stainless steel.

[0045] The interconnector 15 and the IC separator 16 will be described with reference to Figures 4(a) and 4(b). Figures 4(a) and 4(b) are a schematic cross-sectional view and a top view, respectively, showing an example of the interconnector 15 and the IC separator 16 according to the embodiment. Figure 4(a) is a cross-sectional view of the joined interconnector 15 and the IC separator 16. Figure 4(b) is a top view of the interconnector 15 and the IC separator 16 as viewed from the direction IV in Figure 4(a).

[0046] The IC separator 16 is a rectangular frame-shaped member with an opening 16a near the center. An opening periphery 16b surrounding the opening 16a in the IC separator 16 is joined to the upper surface of the peripheral edge 15a of the flat plate portion of the interconnector 15, for example, by laser welding. An example of the material for the IC separator 16 is stainless steel. Note that in Figure 4(b), welded portions other than welded portion 30 of the interconnector 15 and the IC separator 16 are omitted.

[0047] A pair of interconnectors 15 and IC separators 16 included in a certain electrochemical cell 11 constitutes a fuel chamber 33 of the electrochemical cell 11 between the interconnector 15 and the IC separator 16 of the certain electrochemical cell 11. The pair of interconnectors 15 and IC separators 16 included in a certain electrochemical cell 11 also isolates the fuel chamber 33 of the certain electrochemical cell 11 from the air chamber 35 of another electrochemical cell 11 adjacent to the certain electrochemical cell 11 on the lower side. In this way, the interconnectors 15 and the IC separators 16 suppress gas leakage between the electrochemical cells 11 at the peripheral portions of the electrochemical cells 11.

[0048] The electrochemical cell 11 located at the top of the electrochemical cell stack 10 has an interconnector 15 and an IC separator 16 joined to its upper side, and the IC separator 16 joined to the interconnector 15 is electrically connected to the upper terminal plate 52. The IC separator 16 joined to the lower interconnector 15 of the electrochemical cell 11 located at the bottom of the electrochemical cell stack 10 is electrically connected to the lower terminal plate 53.

[0049] In this embodiment, the interconnector 15 and the IC separator 16 are formed as separate members and joined by laser welding, but the interconnector 15 and the IC separator 16 may be joined by a method other than laser welding. Also, the interconnector 15 and the IC separator 16 may be formed as an integral part.

[0050] The fuel chamber 33 will be described with reference to Figures 5(a) and 5(b). Figures 5(a) and 5(b) are a schematic cross-sectional view and a top view, respectively, showing an example of an electrochemical cell 11 according to an embodiment. Figure 5(b) is a top view of the cell body 20 and the cell separator 18 as viewed from the V direction in Figure 5(a).

[0051] The anode frame 17 is a rectangular frame-shaped member with an opening near the center. The anode frame 17 is disposed between the interconnector 15 and the IC separator 16 and the cell separator 18. The anode frame 17 is joined to the IC separator 16 by laser welding. An example of the material for the anode frame 17 is stainless steel. The anode frame 17 surrounds the cell body 20 and a current collector 32 provided in the center of the interconnector 15. A fuel chamber 33 surrounded by the interconnector 15, the IC separator 16, the anode frame 17, the cell separator 18, and the cell body 20 is provided inside the anode frame 17.

[0052] The current collector 32 disposed in the fuel chamber 33 electrically connects the fuel electrode 21 and the interconnector 15. The material of the current collector 32 is exemplified by a porous body made of a gas-permeable metal such as Ni.

[0053] The cell separator 18 is a rectangular frame-shaped member with an opening near the center that is larger than the air electrode 25. The cell separator 18 is joined to the fuel electrode frame 17 by laser welding. An example of the material for the cell separator 18 is stainless steel. The cell separator 18 is airtightly joined to the surface 24a of the electrolyte layer 24 with brazing material 27 or the like, avoiding the air electrode 25.

[0054] Hydrogen is introduced into or generated from the fuel chamber 33. Therefore, the fuel chamber 33 must be sufficiently airtight. Therefore, in this embodiment, the electrochemical cell 11 is defined as the area constituting the fuel chamber 33, rather than the entire reaction unit. Laser welding is preferably used to weld the IC separator 16 to the anode frame 17, and the cell separator 18 to the anode frame 17. The welding locations are, for example, the peripheries of the passages 14a, 14b, 14c, and 14d and the through-holes for fastening the bolts 13, the inside of the outer periphery of the IC separator 16, and the inside of the outer periphery of the cell separator 18. Note that in FIG. 5( a), the welded portion 30 on the inside of the outer periphery of the cell separator 18 is omitted. This also applies to FIG. 2 and other figures.

[0055] The cathode frame 19 is a rectangular frame-shaped member with an opening near the center. The cathode frame 19 is disposed between the interconnector 15, the IC separator 16, and the cell separator 18. The cathode frame 19 may be bonded to the IC separator 16 with an adhesive. The cathode frame 19 may be bonded to the cell separator 18 with an adhesive. An example of the material of the cathode frame 19 is an insulator such as mica. The cathode frame 19 surrounds a current collector 34 provided in the center of the interconnector 15. The current collector 34 electrically connects the cathode 25 and the interconnector 15. In this embodiment, the current collector 34 is formed integrally with the interconnector 15, but this is not limited thereto. The current collector 34 may be a separate member from the interconnector 15.

[0056] An air chamber 35 is provided inside the cathode frame 19 and is surrounded by the interconnector 15, IC separator 16, cathode frame 19, cell separator 18, and cell body 20. The cell separator 18 separates the fuel chamber 33 and the air chamber 35 within one electrochemical cell 11, preventing the fuel gas in the fuel chamber 33 from mixing with the oxidizer gas (oxygen, air, etc.) in the air chamber 35. In this embodiment, the air chamber 35 is provided between the upper electrochemical cell 11 and the lower electrochemical cell 11.

[0057] In this embodiment, the cell separator 18, the anode frame 17, the interconnector 15, and the IC separator 16 are examples of the first metal member 61, the second metal member 62, and the third metal member 63, respectively. As described above, the cell separator 18 is joined to the cell body 20. The anode frame 17 is stacked on the cell separator 18 at a predetermined position in the stacking direction of the cell body 20 and joined by a weld 30. On the surface of the anode frame 17 opposite the surface joined to the cell separator 18, the interconnector 15 and the IC separator 16 are stacked on the anode frame 17 at a second predetermined position in the stacking direction of the cell body 20 and joined by a weld 30. In this case, as shown in FIG. 2 , the penetration direction of at least a portion of the weld 30 is inclined with respect to the stacking direction of the cell body 20. This allows the penetration depth to be kept shallow even with the same laser output as before, suppressing warping of metal components, and also allows the weld width to be widened, resulting in increased weld strength.

[0058] In the welded portion 30, at least the portion where the angle between the line connecting the center of the first metal member 61 and the welded portion and the welding direction is 90° is preferably such that the penetration direction is inclined with respect to the stacking direction of the cell body 20. The welded portion 30 may include a portion where the penetration direction is not inclined with respect to the stacking direction of the cell body 20.

[0059] In this embodiment, the interconnector 15 and the IC separator 16 are examples of the fourth metal member 64 and the fifth metal member 65, respectively. The interconnector 15 and the IC separator 16 are joined by a weld 30. As shown in FIG. 2 , the penetration direction of at least a portion of the weld 30 is inclined with respect to the stacking direction of the cell body 20.

[0060] Below, we will explain the characteristics of the welded portion 30 between the first metal member 61 and the second metal member 62, but when referring to the characteristics of the welded portion between the second metal member 62 and the third metal member 63, the first metal member can be read as the third metal member.

[0061] The inclination angle of the penetration direction of the weld 30 is preferably 5° to 60°, more preferably 10° to 60°, and even more preferably 15° to 60°. By increasing the inclination angle within the above range, the weld width can be sufficiently widened, and a good balance can be achieved between the effect of maintaining a certain degree of penetration depth of the second metal member 62 and the effect of widening the weld width. The inclination angle of the penetration direction of the weld 30 is measured on a cross section parallel to the stacking direction of the cell body 20 and perpendicular to the welding progress direction. The weld 30 may include a portion where the inclination angle of the penetration direction is not included in the above range.

[0062] FIG. 6 is a cross-sectional view of a first metal member 61, a second metal member 62, and a welded portion 30 according to an embodiment. FIG. 7 is a cross-sectional view schematically illustrating the cross-section of FIG. 6. The cross-sections of FIGS. 6 and 7 are parallel to the stacking direction of the cell body 20 and perpendicular to the welding direction. As shown in FIG. 7, the penetration direction of the welded portion 30 is defined as the direction of a straight line connecting the midpoint of the joint and the point in the penetration tip region farthest from the midpoint of the joint. The penetration angle of the welded portion 30 is defined as the angle between the line in the penetration direction and the line in the stacking direction (perpendicular line).

[0063] The penetration direction of the weld 30 is preferably inclined in a direction from the center toward the periphery of the first metal member 61. The center and periphery of the first metal member 61 refer to the center and periphery when the first metal member 61 is viewed from the stacking direction of the cell body 20. Furthermore, in a cross section perpendicular to the stacking direction of the cell body 20 and perpendicular to the welding progress direction, the cross-sectional shape of the weld 30 is preferably a shape that tapers from the first metal member 61 side toward the second metal member 62 side.

[0064] Furthermore, the first metal member 61 is generally rectangular when viewed from the stacking direction of the cell body 20. Preferably, the inclination angle of the penetration direction of the weld 30 increases as one approaches the corner of the first metal member 61, and the weld depth of the weld 30 decreases. In other words, the farther the weld 30 is from the center of the first metal member 61, the greater the inclination angle of the penetration direction of the weld 30, and the shallower the weld depth of the weld 30. In other words, in FIG. 8 , the inclination angle of the penetration direction of the weld 30 increases from cross section (1) to cross section (2) to cross section (3), and the shallower the weld depth of the weld 30. FIG. 8 is a schematic top view showing an example of the first metal member 61, the second metal member 62, and the weld 30. FIG. 8 shows a schematic top view of a case where the first metal member 61 is a cell separator 18 and the second metal member 62 is a fuel electrode frame 17. 8, the cross section is taken perpendicular to the plane of the paper and perpendicular to the welding direction. Locations where the angle between the line connecting the center of the first metal member 61 and the welding direction and the welding direction is 0° may be excluded from the comparison.

[0065] As a result, the penetration direction is oriented toward the periphery, which changes the heat transfer distribution and leads to stress relaxation. Furthermore, when laser welding is performed using a laser processing machine equipped with an optical head moving device, particularly a laser processing machine equipped with a galvanometer mirror or a polygon mirror, the number of times the first metal member 61 and the second metal member 62 need to be repositioned on the jig can be reduced, thereby reducing manufacturing costs while maintaining weld strength.

[0066] The weld width of the weld 30 is preferably 80 μm or more and 400 μm or less. The penetration depth of the weld 30 is preferably 50 μm or more and 90 μm or less. The bead width of the weld 30 is preferably 100 μm or more and 500 μm or less. By setting the weld width, penetration depth, and bead width within these ranges, warping of the metal member can be suppressed. Furthermore, the weld strength can be sufficiently increased. The weld 30 may be formed in a spiral shape relative to the welding line direction. This allows the weld width to be increased while maintaining a shallow penetration depth even when the second metal member 62 is thin. The weld width, penetration depth, and bead width of the weld 30 are measured in a cross section perpendicular to the stacking direction of the cell body 20 and perpendicular to the welding progress direction.

[0067] The thickness of the first metal member 61 is preferably 0.05 mm or more and 1 mm or less. The method of the present invention can precisely weld such thin plates, suppressing warping while maintaining sufficient weld strength. The thickness of the first metal member 61 is the thickness of the welded portion 30 in the stacking direction. The joint between the first metal member 61 and the second metal member 62 is preferably flat.

[0068] The thickness of the cell bodies 20 in the stacking direction of the cell bodies 20 is preferably 0.5 mm or more and 5 mm or less. The method of the present invention can precisely weld metal members used in an electrochemical cell or electrochemical cell stack incorporating such thin cell bodies 20, and can maintain sufficient weld strength while suppressing warping of the metal members.

[0069] In this embodiment, the cell separator 18, the fuel electrode frame 17, the interconnector 15, and the IC separator 16 are described as an example of the first metal member 61, the second metal member 62, and the third metal member, respectively. However, the first metal member 61, the second metal member 62, and the third metal member may be a combination of other metal members. The present invention can maintain sufficient welding strength while suppressing warping of the metal members when joining the metal members, and is therefore preferably applicable to locations where metal members that are prone to warping are used or where welding strength or airtightness is required. The configurations of the cell body 20, the electrochemical cell 11, and the electrochemical cell stack 10 are not limited to those described above.

[0070] [Manufacturing Method] [Manufacturing Method of Electrochemical Cell] Next, an example of a manufacturing method of the electrochemical cell 11 will be described. FIGS. 9(a) to 9(c) and 10(a) to 9(c) are schematic cross-sectional views each showing a step in the manufacturing method of the electrochemical cell 11. First, a cell body 20 is prepared, which is formed by stacking an air electrode 25, an electrolyte layer 24, and an anode 21. The cell body 20 can be prepared, for example, as follows. FIG. 9(a) is a cross-sectional view of a compact 38 of the support 22, a compact 39 of the functional layer 23, and a compact 40 of the electrolyte layer 24. The compacts 38 to 40 are obtained by adding a plasticizer, a dispersant, a binder, etc. to the raw material powder to prepare a slurry, forming a sheet using a doctor blade method, and cutting the sheet to a predetermined size. If necessary, a pore-forming material is included in the slurry.

[0071] The molded body 38 can be produced by extrusion molding, press molding, or injection molding, in addition to the doctor blade method. The molded bodies 39 and 40 can be produced by thick film printing using slurry coating, in addition to the doctor blade method.

[0072] 9(b) is a cross-sectional view of the laminate 44. In the first molding step, the molded bodies 39 and 40 are stacked in this order on the surface 38a of the molded body 38. At this time, the molded bodies 39 and 40 may be placed in this order on the surface 38a of the molded body 38, or the stack of the molded bodies 39 and 40 may be placed on the surface 38a of the molded body 38.

[0073] 9(c) is a cross-sectional view of the sintered body 26, the green body 45 of the air electrode 25, and the cell separator 18. The sintered body 26 is obtained by firing the degreased laminate 44 in the firing step.

[0074] After obtaining the sintered body 26, the green body 45 of the air electrode 25 is placed at the center of the surface 24a of the electrolyte layer 24, and the brazing material 27 is placed around the periphery of the surface 24a. The green body 45 is obtained by adding a plasticizer, dispersant, binder, etc. to the raw material powder to prepare a slurry, forming it into a sheet using the doctor blade method, and cutting the sheet to a predetermined size. In addition to the doctor blade method, the green body 45 can also be produced by thick-film printing using a slurry coating. The cell separator 18 is pressed against the brazing material 27 and heated to a predetermined temperature, thereby firing the green body 45 and brazing the cell separator 18 at the same time. This results in a cell body 20 with the cell separator 18 brazed to it.

[0075] In the above description, the sintered body 26 in which the anode 21 and the electrolyte layer 24 are integrated is produced by firing the laminate 44, but this is not necessarily limited to this. The anode 21 and the electrolyte layer 24 may be produced separately by firing, and then the cell body 20 may be produced by joining them.

[0076] Separately, an interconnector 15 and an IC separator 16 each processed into a predetermined shape are prepared. The interconnector 15 and the IC separator 16 can be produced, for example, by cutting stainless steel into the predetermined shape and shaping it by press working or the like. Next, the IC separator 16 is placed at a predetermined position on the interconnector 15 so that it is stacked on the interconnector 15 in the stacking direction of the cell bodies 20, and is welded by laser welding so that the weld penetration direction is at least partially inclined with respect to the stacking direction of the cell bodies 20. In addition, a current collector 32 is joined to the interconnector 15.

[0077] Next, the anode frame 17 is prepared. The anode frame 17 can be fabricated, for example, by cutting stainless steel into a predetermined shape and shaping it by press working or the like. Next, the anode frame 17 is placed at a predetermined position on the cell body 20 to which the cell separator 18 is brazed, so that it is stacked in the stacking direction of the cell body 20, and is laser welded so that the weld penetration direction is at least partially inclined relative to the stacking direction of the cell body 20. Furthermore, the interconnector 15 to which the IC separator 16 is welded is placed at a second predetermined position on the surface of the anode frame 17 opposite the surface to be joined with the cell separator 18, so that it is stacked in the stacking direction of the cell body 20, and is laser welded so that the weld penetration direction is at least partially inclined relative to the stacking direction of the cell body 20. Either the welding of the cell separator 18 to the anode frame 17 or the welding of the IC separator 16 to the anode frame 17 may be performed first.

[0078] The welding process is preferably performed using a laser processing machine equipped with an optical head moving device. In this case, a jig may be used to tilt the penetration direction of the weld 30 relative to the cell body 20. The optical head moving device may be an optical head moving stage that moves the optical head in the X-axis and Y-axis directions, or a robot arm that changes not only the position but also the orientation of the optical head. The laser used in the laser processing machine may be, for example, a CO2 laser oscillator, a YAG laser oscillator, a fiber laser oscillator, or a laser extracted by a semiconductor laser.

[0079] The welding step is preferably performed using a laser processing machine equipped with a galvanometer mirror or a polygon mirror, which makes it easy to tilt the penetration direction of the welded portion 30 relative to the cell body 20.

[0080] The welding step may be performed by scanning a laser spirally in the direction of the line of the weld 30. Alternatively, laser welding may be performed using an additional function such as weaving or a pulse laser.

[0081] In this manner, the electrochemical cell 11 of the present invention can be manufactured. The manufactured electrochemical cell 11 is subjected to a leak test (e.g., a leak amount of 43 Pa or less at 10 kPa) to confirm its airtightness. At this stage, a cathode frame 19 may be joined to either the top or bottom surface of the electrochemical cell 11.

[0082] [Method for Manufacturing Electrochemical Cell Stack] Next, an example of a method for manufacturing an electrochemical cell stack 10 will be described. FIG. 11 is a schematic cross-sectional view showing one step of a method for manufacturing an electrochemical cell stack 10. First, a plurality of electrochemical cells 11 are prepared. The electrochemical cells 11 to be prepared are the electrochemical cells 11 manufactured as described above. The electrochemical cells 11 prepared at this time may have different component configurations between the upper electrochemical cell 11a, the middle electrochemical cell 11b, and the lower electrochemical cell 11c, or the upper electrochemical cell 11a and the lower electrochemical cell 11c may have only a portion of the configuration of the middle electrochemical cell 11b. In FIG. 11, the upper electrochemical cell 11a has an air electrode frame 19, an interconnector 15, and an IC separator 16 on its upper surface.

[0083] Next, the cathode frame 19 is prepared. The cathode frame 19 can be produced, for example, by laser cutting. Next, the electrochemical cells 11 and the cathode frames 19 are alternately arranged and stacked in the stacking direction of the cell bodies 20. The stacked electrochemical cells 11 and the cathode frames 19 are then joined together. Joining may include fastening with fastening members such as bolts and nuts. If necessary, the upper terminal plate 52 and the lower terminal plate 53 are joined, and the upper end plate 12a and the lower end plate are fastened together with bolts. In this manner, the electrochemical cell stack 10 of the present invention can be manufactured.

[0084] The present invention is not limited to the above-described embodiments, and various modifications and equivalents are included within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for the convenience of explanation and may be changed as appropriate.

[0085] REFERENCE SIGNS LIST 10 Electrochemical cell stack 11, 11a, 11b, 11c Electrochemical cell 12a Upper end plate 12b Lower end plate 13 Bolt 14a, 14b, 14c, 14d Passage 15 Interconnector 16 IC separator 17 Anode frame 18 Cell separator 19 Cathode frame 20 Cell body 21 Anode 22 Support 22a Front surface 22b Back surface 23 Functional layer 24 Electrolyte layer 24a Front surface 24b Back surface 25 Cathode 26 Sintered body 27 Brazing material 30 Welded portion 32 Current collector 33 Fuel chamber 34 Current collecting portion 35 Air chamber 38 Support body molded body 38a Front surface 38b Back surface 39 Functional layer molded body 40 Electrolyte layer molded body 44 Laminate 45 Air electrode molded body 52 Upper terminal plate 53 Lower terminal plate 61 First metal member 62 Second metal member

Claims

1. An electrochemical cell comprising: a cell body formed by stacking an air electrode, an electrolyte layer, and a fuel electrode; a first metal member joined to the cell body; a second metal member stacked on the first metal member in the stacking direction of the cell body and joined by welding at a predetermined position of the first metal member; and a third metal member stacked on the second metal member in the stacking direction of the cell body and joined by welding at a second predetermined position of the second metal member on the opposite surface of the second metal member opposite the surface joined to the first metal member, wherein the location joined by welding is a welded portion, and the penetration direction of at least a part of the welded portion is inclined with respect to the stacking direction of the cell body.

2. The electrochemical cell according to claim 1, characterized in that the third metal member has a fourth metal member and a fifth metal member, and the fourth metal member and the fifth metal member are joined by the welded portion.

3. An electrochemical cell as described in claim 1 or 2, characterized in that the inclination angle of the penetration direction of the weld is 5° or more and 60° or less.

4. An electrochemical cell as described in claim 1 or 2, characterized in that the penetration direction of the weld is inclined in a direction from the center toward the outer periphery of the first metal member.

5. An electrochemical cell as described in claim 1 or claim 2, characterized in that the first metal member is approximately rectangular when viewed from the stacking direction of the cell body, and the inclination angle of the penetration direction of the weld increases and the weld depth of the weld becomes shallower as it approaches the corner from the side of the first metal member.

6. An electrochemical cell according to claim 1 or 2, characterized in that the weld width of the welded portion is 80 μm or more and 400 μm or less.

7. An electrochemical cell as described in claim 1 or 2, characterized in that the penetration depth of the welded portion is 50 μm or more and 90 μm or less.

8. An electrochemical cell according to claim 1 or 2, characterized in that the bead width of the welded portion is 100 μm or more and 500 μm or less.

9. An electrochemical cell as described in claim 1 or 2, characterized in that the thickness of the first metal member is 0.05 mm or more and 1 mm or less.

10. An electrochemical cell as described in claim 1 or 2, characterized in that the thickness of the cell body in the stacking direction of the cell body is 0.5 mm or more and 5 mm or less.

11. An electrochemical cell as described in claim 1 or claim 2, characterized in that the cross-sectional shape of the weld on the first metal member side tapers from the first metal member side to the second metal member side, and the cross-sectional shape of the weld on the third metal member side tapers from the third metal member side to the second metal member side.

12. The electrochemical cell according to claim 1 or 2, characterized in that the electrochemical cell is selected from the group consisting of an electrolysis cell and a reversible operation fuel cell.

13. An electrochemical cell stack comprising a plurality of electrochemical cells according to claim 1 or 2 stacked and joined in the stacking direction of the cell bodies.

14. A method for manufacturing an electrochemical cell, comprising the steps of: preparing a cell body formed by stacking an air electrode, an electrolyte layer, and a fuel electrode; preparing a first metal member to be joined to the cell body, a second metal member to be joined to the first metal member, and a third metal member to be joined to the second metal member; arranging the second metal member at a predetermined position of the first metal member so that it is stacked on the first metal member in the stacking direction of the cell body, and welding by laser welding such that the weld penetration direction is inclined with respect to the stacking direction of the cell body; and arranging the third metal member at a second predetermined position of the second metal member on the opposite surface of the second metal member opposite to the surface of the second metal member to be joined to the first metal member so that it is stacked on the second metal member in the stacking direction of the cell body, and welding by laser welding such that the weld penetration direction is inclined with respect to the stacking direction of the cell body.

15. The method for manufacturing an electrochemical cell according to claim 14, wherein the welding step is performed using a laser processing machine equipped with an optical head moving device.

16. The method for manufacturing an electrochemical cell according to claim 15, wherein the welding step is carried out using a laser processing machine equipped with a galvanometer mirror or a polygon mirror.

17. A method for manufacturing an electrochemical cell stack, comprising the steps of: preparing a plurality of electrochemical cells by a manufacturing method described in any one of claims 14 to 16; stacking the plurality of electrochemical cells in the stacking direction of the cell body; and joining the stacked plurality of electrochemical cells.

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