Fuel cell stack

Abstract

This fuel cell stack comprises a cell stack, a housing surrounding the cell stack, and a plurality of guide members that are supported by the housing and extend in a prescribed direction so that a plurality of recesses provided to the outer edge part of a separator are engaged. The separator has a pair of first opposing sides that face each other and a pair of second opposing sides that face each other. The plurality of recesses include: a target corner part that is one of a pair of corner parts where the pair of first opposing sides and the pair of second opposing sides intersect; and a slit-shaped first recess part and a slit-shaped second recess part that extend toward the central part of the separator from the substantially central part of the pair of sides that does not have the target corner part at an end section thereof, among the pair of first opposing sides and the pair of second opposing sides.

Description

fuel cell stack

[0001] The present invention relates to a fuel cell stack including a stack of multiple power generating cells.

[0002] In recent years, technological developments related to fuel cells that contribute to energy efficiency have been underway to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. A known technology for fuel cell stacks used in this type of fuel cell involves providing a guide bar upright on a mounting base, engaging recesses formed on the edges of the power-generating cells with the guide bar, and stacking the power-generating cells on the mounting base to form a stack (see, for example, Patent Document 1). In the technology described in Patent Document 1, a predetermined number of power-generating cells are stacked while being positioned by the guide bar to form a stack, and then compressing the stack by applying pressure to the stack, thereby forming a fuel cell stack.

[0003] Japanese Patent Application Laid-Open No. 2022-132847

[0004] However, when pressure is applied to the stack, the power-generating cells are crushed, the edges of the power-generating cells are displaced outward, and the recesses of the power-generating cells may interfere strongly with the guide bar. If the gap between the recesses and the guide bar is increased to avoid this, the positioning accuracy of the power-generating cells will decrease accordingly.

[0005] The fuel cell stack according to one aspect of the present invention includes a cell stack formed by stacking, in a predetermined direction, a plurality of substantially rectangular power-generating cells, each having a membrane electrode assembly including an electrolyte membrane and electrodes and a separator, a housing surrounding the cell stack, and a plurality of guide members supported by the housing and extending in the predetermined direction so as to engage with a plurality of recesses provided on the outer edge of the separator. The separator has a pair of opposing first opposing sides and a pair of opposing second opposing sides, and the plurality of recesses include a target corner, which is one of a pair of corners where the pair of first opposing sides intersects with the pair of second opposing sides, and a slit-shaped first recess and a second recess extending from approximately a center of one of the pair of first opposing sides and the pair of second opposing sides that does not have the target corner at its end, toward the center of the separator.

[0006] According to the present invention, it is possible to improve the accuracy of positioning the power generating cell while avoiding strong interference between the recess and the guide member.

[0007] 1 is an exploded perspective view schematically showing the overall configuration of a fuel cell stack according to an embodiment of the present invention. A cross-sectional view showing the configuration of a main part of the cell stack of FIG. 1. A perspective view showing the schematic configuration of an integrated electrode assembly incorporated into the fuel cell stack of FIG. 1. A cross-sectional view taken along line IV-IV of FIG. 1. A rear view of a first separator incorporated into the fuel cell stack of FIG. 1. A rear view of a second separator incorporated into the fuel cell stack of FIG. 1. A diagram explaining the rotational operation of a guide member incorporated into the fuel cell stack of FIG. 1. A flowchart showing an example of an assembly procedure for a fuel cell stack according to an embodiment of the present invention. A diagram showing an example of the procedure of FIG. 7. A diagram showing an example of the procedure following FIG. 8A. A diagram showing an example of the procedure following FIG. 8B. A diagram showing an example of the procedure following FIG. 8C. An enlarged view of a main part of FIG. 4 showing the detailed configuration of a separator positioning portion incorporated into a fuel cell stack according to an embodiment of the present invention. A cross-sectional view taken along line B-B of FIG. 9A. A rear view of a separator that is a modified example of FIG. 4.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 10. A fuel cell stack according to an embodiment of the present invention is a main component of a fuel cell. The fuel cell is mounted, for example, in a vehicle and can generate power to drive the vehicle. The fuel cell can also be mounted in mobile objects other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0009] First, the overall configuration of the fuel cell stack will be described. FIG. 1 is a perspective view showing the overall configuration of a fuel cell stack 100 according to an embodiment of the present invention. Hereinafter, for convenience, three mutually orthogonal axial directions as shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described according to these definitions. These directions are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle. The front-rear direction in FIG. 1 is the stacking direction of the fuel cell stack 100, and when assembling the fuel cell stack 100, the stacking direction is aligned with the direction of gravity.

[0010] 1, the fuel cell stack 100 has a cell stack 10, end units 40 arranged at both front and rear ends of the cell stack 10, and a case 30 arranged around the cell stack 10, and has a generally rectangular parallelepiped shape as a whole. The case 30 and the end units 40 form a housing that surrounds the cell stack 10. The length of the fuel cell stack 100 in the left-right direction is longer than the length in the up-down direction.

[0011] The case 30 has four generally rectangular side walls 300 that face the top, right, bottom, and left sides of the cell stack 10. These four side walls 300 form a generally box-shaped storage space SP0 that is open on the front and back. The case 30 is made of a metal such as aluminum or iron.

[0012] The end unit 40 has multiple plates (not shown) stacked in the front-to-rear direction. More specifically, the end unit 40 has a terminal plate arranged on the inside in the front-to-rear direction, an insulating plate arranged on the outside in the front-to-rear direction of the terminal plate, and an end plate arranged on the outside in the front-to-rear direction of the insulating plate. When assembling the fuel cell stack 100, for example, the rear end unit 40 is laid on its side, and the case 30 is fastened to the rear end unit 40. Furthermore, inside the case, multiple power-generating cells 1 are stacked on the rear end unit 40 to assemble the cell stack 10, and then the front end unit 40 is mounted on the cell stack 10.

[0013] A plurality of guide members 51 (only some of which are shown) are interposed between the cell stack 10 and the side wall 300 of the case 30. The guide members 51 are rod-shaped members extending in the front-rear direction. Both front and rear ends of the guide members 51 are supported by the front and rear end units 40.

[0014] 1 shows a cutaway view of a side wall 300 of the case 30. As shown in part A of Fig. 1, the cell stack 10 is formed by stacking a plurality of power generating cells 1 (for convenience, only a single cell 1 is shown) in the storage space SP0 in the front-to-rear direction (the up-to-down direction during assembly) while being guided by a guide member 51.

[0015] The power-generating cell 1 includes an integrated electrode assembly 2 and separators 3 arranged on both the front and rear sides of the integrated electrode assembly 2 to sandwich the integrated electrode assembly 2. The separators 3 include two types of separators (first separators 31 and second separators 32) that differ from each other in the shape of a portion of their outer edge. The integrated electrode assemblies 2 and the separators 3 are arranged alternately in the front-rear direction. Hereinafter, using an arbitrary integrated electrode assembly 2 as a reference, the separator 3 arranged opposite the front surface of this integrated electrode assembly 2 will be defined as the first separator 31, and the separator 3 arranged opposite the rear surface of this integrated electrode assembly 2 will be defined as the second separator 32.

[0016] FIG. 2 is a cross-sectional view showing the main configuration of the cell stack 10. As shown in FIG. 2, the separator 3 includes a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends vertically and horizontally and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends vertically and horizontally and has a front surface 3Ra and a rear surface 3Rb. The opposing rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R are joined at their outer peripheral edges by welding or the like. This integrally bonds the front plate 3F and the rear plate 3R to form the separator 3. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0017] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, that is, between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The flow of the coolant cools the power generation surface of the power generation cell 1. Water, for example, can be used as the coolant. The surface of the separator 3 facing the integrated electrode assembly 2 (the front surface 3Fa and the rear surface 3Rb) is formed unevenly by press molding or the like to form a gas flow path between the separator 3 and the integrated electrode assembly 2.

[0018] More specifically, an anode flow path PAa through which a fuel gas containing hydrogen flows is formed between the front surface 2a of the integrated electrode assembly 2 and the rear plate 3R of the separator 3 facing this front surface 2a. A cathode flow path PAc through which an oxidizer gas containing oxygen flows is formed between the rear surface 2b of the integrated electrode assembly 2 and the front plate 3F of the separator 3 facing this rear surface 2b. The fuel gas and the oxidizer gas are sometimes referred to as reactant gases without distinction. A compressive load F is applied to the cell stack 10 in the front-to-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete.

[0019] 3 is a perspective view showing a schematic configuration of a unitized electrode assembly 2 (hereinafter referred to as UEA). The UEA 2 is sometimes called a membrane electrode structure. As shown in FIG. 3, the UEA 2 has a membrane electrode assembly (hereinafter referred to as MEA) 20 and a frame 21.

[0020] The MEA 20 includes an electrolyte membrane, an anode electrode provided on the front surface of the electrolyte membrane, and a cathode electrode provided on the rear surface of the electrolyte membrane. The electrolyte membrane is, for example, a solid polymer electrolyte membrane. The anode electrode includes an electrode catalyst layer formed on the front surface of the electrolyte membrane and serving as a reaction field for electrode reactions, and a gas diffusion layer provided on the front surface of the electrode catalyst layer and diffusing and supplying a fuel gas. The cathode electrode includes an electrode catalyst layer formed on the rear surface of the electrolyte membrane and serving as a reaction field for electrode reactions, and a gas diffusion layer provided on the rear surface of the electrode catalyst layer and diffusing and supplying an oxidant gas.

[0021] At the anode electrode, fuel gas (hydrogen) supplied via the anode flow channel PAa (FIG. 2) and gas diffusion layer is ionized by the action of a catalyst and moves through the electrolyte membrane to the cathode electrode. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode, oxidant gas (oxygen) supplied via the cathode flow channel PAc (FIG. 2) and gas diffusion layer reacts with hydrogen ions introduced from the anode electrode and electrons transferred from the anode electrode to produce water. The produced water provides an appropriate humidity to the electrolyte membrane, and excess water is discharged outside the UEA2.

[0022] The frame 21 is a thin plate having a substantially rectangular shape and is made of insulating resin, rubber, or the like. A substantially rectangular opening 21a is provided in the center of the frame 21. The MEA 20 is provided so as to cover the entire opening 21a, and the outer edge of the MEA 20 is supported by the frame 21. On the left side of the opening 21a in the frame 21, three through-holes 201 to 203 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction. On the right side of the opening 21a, three through-holes 204 to 206 are opened in a vertical line that penetrate the frame 21 in the front-to-rear direction.

[0023] FIG. 4 is a cross-sectional view (cross-sectional view taken along line IV-IV in FIG. 1) showing the configuration of a main part of the fuel cell stack 100. FIG. 4 includes a rear view of the first separator 31. The first separator 31 and the second separator 32 are configured to have the same shape except for a portion of their outer edges. Therefore, the schematic configuration of the separator 3 will be explained using FIG. 4. FIG. 4 shows a center point P, which is the middle of the separator 3 in the left-right direction and the middle of the separator 3 in the up-down direction. Hereinafter, the side facing the center point P will be referred to as the inside of the separator 3, and the side radially away from the center point P will be referred to as the outside of the separator 3.

[0024] 4, although not shown in part, an uneven anode flow path PAa (FIG. 2) is formed in the vertical and horizontal central portion of the rear surface 3Rb of the separator 3, facing the front surface 2a of the MEA 20. Although not shown in the figure, an uneven cathode flow path PAc (FIG. 2) is formed in the vertical and horizontal central portion of the front surface 3Fa of the separator 3, facing the rear surface 2b of the MEA 20.

[0025] The separator 3 has through holes 301 to 306 that penetrate the separator 3 in the front-to-rear direction at positions corresponding to the through holes 201 to 206 ( FIG. 3 ) of the frame 21. The through holes 301 to 306 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these through holes 201 to 206 and 301 to 306 that are connected to one another forms a plurality of flow paths that penetrate the cell stack 10 and extend in the front-to-rear direction.

[0026] Although not shown, a rear surface 3Rb of the separator 3 is provided with a seal portion that protrudes rearward to seal against leakage of fuel gas from the anode flow channel PAa. The seal portion connects the through holes 301 and 306 to the anode flow channel PAa, while preventing communication between the other through holes 302 to 305 and the anode flow channel PAa. Similarly, a front surface 3Fa of the separator 3 is provided with a seal portion that protrudes forward to seal against leakage of oxidant gas from the cathode flow channel PAc. The seal portion connects the through holes 303 and 304 to the cathode flow channel PAc, while preventing communication between the other through holes 301, 302, 305, and 306 and the cathode flow channel PAc.

[0027] 1, the rear end unit 40 has a plurality of through holes 401 to 406 that penetrate the end unit 40 in the front-to-rear direction at positions corresponding to the through holes 201 to 206 and 301 to 306. The front end unit 40 does not have the through holes 401 to 406. The front end unit 40 may be referred to as the dry-side end unit, and the rear end unit 40 may be referred to as the wet-side end unit.

[0028] A fuel gas tank storing high-pressure fuel gas is connected to through-hole 401 via an ejector, injector, etc., and the fuel gas is supplied to fuel cell stack 100 via through-hole 401, as shown by the solid arrow. This fuel gas is guided to anode flow path PAa via through-holes 201 and 301. After passing through anode flow path PAa, the fuel gas passes through through-holes 206 and 306 and is discharged from through-hole 406, as shown by the solid arrow.

[0029] An oxidant gas supply compressor is connected to through-hole 404, and as indicated by the dotted arrow, oxidant gas compressed by the compressor is supplied to fuel cell stack 100 via through-hole 404. This oxidant gas is guided to cathode flow path PAc via through-holes 204 and 304. After passing through cathode flow path PAc, the oxidant gas passes through through-holes 203 and 303 and is discharged from through-hole 403 as indicated by the dotted arrow.

[0030] A pump for supplying a cooling medium is connected to through-hole 405, and as shown by the dashed-dotted arrow, the cooling medium is supplied to fuel cell stack 100 through through-hole 405. This cooling medium is guided to cooling flow passage PAw between front plate 3F and rear plate 3R of separator 3 through through-holes 205 and 305. After passing through cooling flow passage PAw, the cooling medium passes through through-holes 202 and 302 and is discharged from through-hole 402 as shown by the dashed-dotted arrow.

[0031] As shown in FIG. 4 , impact receiving members 45 are disposed between the inner surface (case inner surface) 30a of the case 30 and the outer surface 10a of the cell stack 10. Specifically, if the four sides of the separator 3 are defined as an upper side 311, a right side 312, a lower side 313, and a left side 314, a pair of impact receiving members 45 is disposed in the space between the upper side 311 and the case inner surface 30a, the space between the right side 312 and the case inner surface 30a, the space between the lower side 313 and the case inner surface 30a, and the space between the left side 314 and the case inner surface 30a. The pair of impact receiving members 45 is provided near the corners of the cell stack 10. In other words, a pair of impact receiving members 45 is disposed near each of the four corners of the cell stack 10, sandwiching the four corners therebetween.

[0032] The impact receiving member 45 has a generally rectangular cross section and extends over substantially the entire length of the cell stack 10 in the front-to-rear direction. The impact receiving member 45 is an elastic, insulating material such as resin or rubber. The impact receiving member 45 is, for example, pre-bonded to the side wall 300 of the case 30 and provided integrally with the case 30. By providing the impact receiving member 45 near the corner of the cell stack 10, when an external impact acts on the case 30 in a direction perpendicular to the stacking direction of the cell stack 10, the vicinity of the corner of the cell stack 10 abuts against the impact receiving member 45 due to inertial force. This effectively prevents the power-generating cells 1 from shifting in position. Although detailed illustration is omitted, there is a predetermined gap between the cell stack 10 and the impact receiving member 45, and the impact receiving member 45 does not have a positioning function when the power-generating cells 1 are stacked.

[0033] The fuel cell stack 100 is constructed by stacking the power generating cells 1 while positioning them via positioning parts. The UEA 2 is integrated with the separators 3 in advance by welding or the like. Therefore, the UEA 2 does not require a positioning part. The configuration of the positioning part that positions the separators 3 will be described below. The UEA 2 may be stacked alternately without being integrated with the separators 3.

[0034] The positioning portions include long side recesses 501, 502 provided in the left-right center of the long sides of the separator 3, i.e., the upper side 311 and the lower side 313, short side recesses 503, 504 provided in the up-down center of the short sides of the separator 3, i.e., the right side 312 and the left side 314, and corner recesses 505, 506 provided in the lower right corner 315 where the right side 312 and the lower side 313 of the separator 3 intersect and in the upper left corner 316 where the upper side 311 and the left side 314 intersect.

[0035] Bulging portions 317 and 318, which bulge upward and downward, respectively, are provided at the center portions of the upper and lower edges 311 and 313 in the left-right direction. Long-side recesses 501 and 502 are provided in the bulging portions 317 and 318, respectively. A plurality of guide members 51 are arranged corresponding to the plurality of positioning portions. The plurality of guide members 51 have the same shape and are configured with a constant cross-sectional shape from the lower end (rear end in FIG. 1 ) to the upper end (front end in FIG. 1 ). The cross-sectional shape of the guide member 51 is a circle with a predetermined outer diameter D0. The plurality of guide members 51 may also have different shapes (e.g., circles with different outer diameters). The lower and upper ends of the plurality of guide members 51 fit into recesses or through-holes provided in the end unit 40, thereby positioning the guide members 51 at predetermined positions within the case.

[0036] 5A and 5B are rear views of the first separator 31 and the second separator 32, respectively. For convenience, in Figures 5A and 5B, the positioning portions (recesses 501 to 506) on the outer edge of the separator 3 are exaggerated along with the guide member 51, and other components of the separator 3 are not shown.

[0037] As shown in FIG. 5A , the first separator 31 has three positioning portions: a long-side recess 501 on the top side 311, a short-side recess 504 on the left side 314, and a corner recess 505 on the lower right corner 315. These recesses 501, 504, and 505 each extend inward from the outer edge of the first separator 31 while maintaining a predetermined width W1. That is, the long-side recess 501 is recessed in a slit shape (approximately U-shaped) from the center position in the left-right direction of the top side 311 downward toward the center point P. The short-side recess 504 is recessed in a slit shape (approximately U-shaped) from the center position in the up-down direction of the left side 314 toward the center point P on the right. The corner recess 505 is recessed in a slit shape (approximately U-shaped) from the lower right corner 315 toward the center point P on the upper left.

[0038] The width W1 of the recesses 501, 504, and 505 is slightly larger than the outer diameter D0 of the guide member 51, and the guide member 51 is engaged (inserted) into each of the recesses 501, 504, and 505. The long side recess 501 regulates the left-right position of the first separator 31. The short side recess 504 regulates the up-down position. The corner recess 505 limits the rotational movement of the first separator 31.

[0039] A wide recess 512 having a generally U-shape and extending toward the center point P is provided in the horizontal center of the bottom side 313 of the first separator 31. A wide recess 513 having a generally U-shape and extending toward the center point P is provided in the vertical center of the right side 312. The wide recesses 512, 513 have the same width W2 and are larger than the width W1 of the positioning recesses 501, 504, and 505. Therefore, a gap is formed between the wide recesses 512, 513 and the guide member 51 over the entire circumference of the guide member 51. A chamfered portion 515 is provided in the upper left corner 316 of the first separator 31, on the inside of the guide member 51.

[0040] As shown in FIG. 5B , the second separator 32 has three positioning portions different from those of the first separator 31: a long-side recess 502 on the bottom side 313, a short-side recess 503 on the right side 312, and a corner recess 506 on the upper left corner 316. These recesses 502, 503, and 506 each extend inward from the outer edge of the second separator 32 while maintaining a predetermined width W1. That is, the long-side recess 502 is recessed in a slit shape (approximately U-shaped) from the center position in the left-right direction of the bottom side 313 toward the center point P upward. The short-side recess 503 is recessed in a slit shape (approximately U-shaped) from the center position in the up-down direction of the right side 312 toward the center point P leftward. The corner recess 506 is recessed in a slit shape (approximately U-shaped) from the upper left corner 316 toward the center point P on the lower right.

[0041] The width W1 of the recesses 502, 503, and 506 is slightly larger than the outer diameter D0 of the guide member 51, and the guide member 51 is engaged (inserted) into each of the recesses 502, 503, and 506. The long side recess 502 regulates the left-right position of the second separator 32. The short side recess 503 regulates the up-down position. The corner recess 506 limits the rotational movement of the second separator 32.

[0042] A wide recess 511 having a generally U-shape and extending toward the center point P is provided in the vertical center of the top side 311 of the second separator 32. A wide recess 514 having a generally U-shape and extending toward the center point P is provided in the horizontal center of the left side 314. The wide recesses 511, 514 have the same width W2 and are larger than the width W1 of the positioning recesses 502, 503, and 506. Therefore, a gap is formed between the wide recesses 511, 514 and the guide member 51 over the entire circumference of the guide member 51. A chamfered portion 516 is provided in the lower right corner 315 of the second separator 32, located inside the guide member 51.

[0043] In this way, the positioning recesses 501, 504, 505 of the first separator 31 and the positioning recesses 502, 503, 506 of the second separator 32 all extend radially outward from the center point P. Therefore, when the cell stack 10 is pressurized during assembly of the fuel cell stack 100, the recesses 501, 504, 505 of the first separator 31 and the recesses 502, 503, 506 of the second separator 32 can be displaced outward while their positions are restricted by the guide members 51.

[0044] At this time, the wide recesses 512, 513 of the first separator 31 and the wide recesses 511, 514 of the second separator 32 can be displaced outward without interfering with the guide member 51 because there is a large gap between them and the guide member 51. Furthermore, because the upper left corner 316 of the first separator 31 and the lower right corner 315 of the second separator 32 are provided with chamfered portions 515, 516, these corners 316, 315 can be displaced outward without interfering with the guide member 51. As a result, when pressure is applied to the cell stack 10, the outer edges of the separators 3 are smoothly pushed outward. Therefore, the cell stack 10 can be constructed without damaging the separators 3 and with the power-generating cells 1 positioned with high precision.

[0045] In particular, the first separator 31 is positioned by a recess 505 provided in the lower right corner 315 and recesses 501 and 504 provided on the upper side 311 and left side 314 extending opposite to the lower right corner 315. The second separator 32 is positioned by a recess 506 provided in the upper left corner 316 and recesses 502 and 503 provided on the lower side 313 and right side 312 extending opposite to the upper left corner 316.

[0046] The recesses 501 and 504 are provided at positions that divide the entire length of the outer edge of the first separator 31 into approximately three equal parts, starting from the recess 505 in the lower right corner 315. The recesses 502 and 503 are provided at positions that divide the entire length of the outer edge of the second separator 32 into approximately three equal parts, starting from the recess 506 in the upper left corner 316. This allows the outer edges of the first separator 31 and the second separator 32 to be evenly positioned at three points in the circumferential direction. This prevents the positioning recesses 501 to 506 from getting caught on the guide member 51, preventing the separators 31 and 32 from being stacked at an angle.

[0047] The first separators 31 and the second separators 32 are alternately stacked with the UEAs 2 interposed therebetween, but an insulating resin frame 21 (FIG. 3) is interposed between the separators 31 and 32 except near the positioning portions. This ensures a sufficient insulation distance between the separators 31 and 32. However, because positioning is performed by the separators 31 and 32 rather than the frame 21, the frame 21 is not interposed between the separators 31 and 32 near the positioning portions, and there is a risk that a sufficient insulation distance cannot be ensured.

[0048] Taking this into consideration, in this embodiment, the positioning recesses 501, 504, and 505 of the first separator 31 and the positioning recesses 502, 503, and 506 of the second separator 32 are provided on different sides and corners. The width W2 of the wide recesses 511 and 514 of the second separator 32, which are located behind the recesses 501 and 504 of the first separator 31, is set so as not to overlap with the recesses 501 and 504 when viewed from the front-to-rear direction. Furthermore, the width W2 of the wide recesses 512 and 513 of the first separator 31, which are located in front of the recesses 502 and 503 of the second separator 32, is set so as not to overlap with the recesses 502 and 503 when viewed from the front-to-rear direction.

[0049] Furthermore, a corner 315 of the second separator 32 located behind the recess 505 of the first separator 31 is cut to form a chamfered portion 516, and a corner of the first separator 31 located in front of the recess 506 of the second separator 32 is cut to form a chamfered portion 515. As a result, the recesses 501, 504, and 505 of the first separator 31 do not overlap with the outer edge of the second separator 32 when viewed from the front-rear direction, and the recesses 502, 503, and 506 of the second separator 32 do not overlap with the outer edge of the first separator 31 when viewed from the front-rear direction. This ensures a sufficient insulation distance between the separators 31 and 32 near the positioning recesses 501 to 506.

[0050] The guide member 51 may have a two-sided width instead of a circular cross section. FIG. 6 shows an example. As shown in FIG. 6, the guide member 51 has a two-sided width of a predetermined length D1 formed on the circumferential surface of a circle with an outer diameter D0. When assembling the cell stack 10, the direction of the outer diameter D0 (outer diameter direction) of the guide member 51 is aligned with the direction of the width W1 (width direction) of the recesses 501 to 506. This reduces the gap between the guide member 51 and the positioning recesses 501 to 506, allowing the separator 3 to be positioned with precision.

[0051] To attach or detach the guide member 51 after assembling the cell stack 10, rotate the guide member 51 by 90 degrees in the direction of arrow A1. That is, the outer diameter direction of the guide member 51 is orthogonal to the width direction of the recesses 501 to 506. This increases the gap between the guide member 51 and the recesses 501 to 506, making it easier to attach or detach the guide member 51 from the cell stack 10.

[0052] A method for assembling the fuel cell stack 100 according to this embodiment will now be described. FIG. 7 is a flowchart showing an example of the procedure for assembling the fuel cell stack 100, and FIGS. 8A to 8D are diagrams illustrating this flowchart. The fuel cell stack 100 can be assembled using guide members 51, but as an alternative, it can also be assembled using a guide jig having the same shape as the guide members 51. An example of an assembly method using a guide jig will now be described. The fuel cell stack 100 is assembled with the stacking direction (the front-to-rear direction in FIG. 1) as the up-down direction (the direction of gravity). Therefore, the assembly method will now be described with the up-down direction as the stacking direction, unlike FIG. 1.

[0053] As shown in Fig. 7, when assembling the fuel cell stack 100, first, in step S1, an insulating resin guide member 51 and a metal (e.g., iron) guide jig 510 (Fig. 8A) are prepared (preparation step). The guide member 51 and the guide jig 510 have approximately the same length as the side wall 300 of the case 30, and also have a two-face width as shown in Fig. 6. A metal extension guide member 55 (Fig. 8A) having the same cross-sectional shape as the guide member 51 and the guide jig 510 is detachably attached to the upper end surfaces of the guide member 51 and the guide jig 510.

[0054] Next, in step S2, as shown in Fig. 8A, the case 30 is fixed to the end unit 40 on the wet side (rear side in Fig. 1) using bolts (case mounting step). The upper surface of the end unit 40 is provided with a recess 40a that holds the guide member 51 and the guide jig 510, corresponding to the mounting position of the guide member 51 (Fig. 4).

[0055] Next, in step S3, the lower end of a metal guide jig 510 is fitted into the recess 40a of the end unit 40 to erect the guide jig 510 (guide jig attachment step). At this time, as shown in Figure 6, the orientation of the guide jig 510 is adjusted so that the outer diameter direction (direction perpendicular to the width across flats) of the guide jig 510, which has the same cross-sectional shape as the guide member 51, coincides with the width direction of the recesses 501 to 506 of the separator 3.

[0056] Next, in step S4, a predetermined number of UEAs 2 and separators 3 are placed in the case 30 from above along the guide jig 510 and stacked sequentially (stacking process). More specifically, a predetermined number of these are stacked in the order of first separator 31, UEA 2, second separator 32, UEA 2, first separator 31, etc. In other words, the first separators 31 and second separators 32 are stacked alternately with the UEA 2 interposed therebetween.

[0057] In this case, the guide jig 510 engages with three recesses 501, 504, and 505 evenly spaced along the outer edge of the first separator 31 and three recesses 502, 503, and 506 evenly spaced along the outer edge of the second separator 32, thereby positioning the separators 31 and 32 while stacking them. This improves the positional accuracy of the separator 3, allowing the cell stack 10 to be formed with high precision. Therefore, a predetermined gap can be secured between the cell stack 10 and the impact-receiving member 45 ( FIG. 4 ). A single separator 3 (e.g., the second separator 32) and a single UEA 2 may be previously joined by welding or the like to form a set of unit cells, and a predetermined number of these unit cells may then be stacked along the guide jig 510 to form the cell stack 10.

[0058] The separators 3 are lowered and stacked while the recesses 501 to 506 slide along the circumferential surface of the guide jig 510. Therefore, if the guide jig 510 were made of a resin material, the guide jig 510 would wear down, producing resin powder and the like, which could get mixed into the power generation cells 1 and reduce power generation performance. In this regard, in the present embodiment, the guide jig 510 is made of metal, so there is no risk of resin powder and the like being produced by wear.

[0059] Next, in step S5, the end unit 40 on the dry side (the front side in FIG. 1 ) is placed on the cell stack 10 in which a predetermined number of power-generating cells 1 are stacked (end unit placing process). The dry-side end unit 40 has a plurality of through holes 40b opened in advance to correspond to the guide jig 510. In the end unit loading process, as shown in FIG. 8B , the end unit 40 is lowered along the guide jig 510 while the guide jig 510 is inserted into the through holes 40b, and is placed above the cell stack 10.

[0060] Next, a pressure is applied from above the end unit 40 using a pressure machine 517, and the dry-side end unit 40 is pushed downward until it abuts against the upper end surface of the case 30 (pressure step). As a result, a predetermined compressive load F is applied to the cell stack 10.

[0061] Next, in step S7, the dry-side end unit 40 is fastened to the upper end surface of the case 30 using bolts (pressure case mounting step), thereby holding the cell stack 10 within the case with a predetermined compressive load F applied.

[0062] Next, in step S8, the guide jig 510 is replaced with the guide member 51 (guide replacement process). In this case, as shown in Fig. 8C, the guide jig 510 is first grasped and rotated by 90 degrees, and with both end faces of the two-sided width opposed to the end faces in the width direction of the recesses 501 to 506, the guide jig 510 is pulled upward from the case 30 through the through-hole 40b of the dry-side end unit 40. At this time, as shown in Fig. 6, a gap is generated between the guide jig 510 and the recesses 501 to 506, making it easy to pull out the guide jig 510.

[0063] Next, the extended guide member 55 is removed from the guide jig 510 and replaced with the guide member 51, and then the guide member 51 is inserted into the case through the through-hole 40b of the dry-side end unit 40. The lower end of the guide member 51 is then fitted into the recess 40a on the top surface of the wet-side end unit 40. At this time, the guide member 51 is inserted with both end surfaces of the two-flat width of the guide member 51 facing the end surfaces in the width direction of the recesses 501 to 506. This makes it easy to insert the guide member 51. After the guide member 51 is inserted, the extended guide member 55 may be attached to the top end surface of the guide member 51.

[0064] When the lower end of the guide member 51 is fitted into the recess 40a, the guide member 51 is rotated 90 degrees as indicated by arrow R1, so that the outer diameter direction of the guide member 51 coincides with the width direction of the recesses 501 to 506. As a result, the circumferential surface of the guide member 51, which is made of insulating material, abuts or approaches the recesses 501 to 506, and the cell stack 10 is held in place within the case with the cell stack 10 positioned by the guide member 51.

[0065] Next, in step S9, as shown in FIG. 8D , the extension guide member 55 is pulled out of the guide member 51 through the through hole 40b (pulling step). Finally, in step S10, the through hole 40b of the dry-side end unit 40 is covered with the cover 41 via a sealant, sealing the through hole 40b (sealing step). The cover 41 is fastened to the end unit 40 using, for example, bolts. This completes the assembly of the fuel cell stack 100.

[0066] 9A is an enlarged view of the main portion of FIG. 4 showing the detailed configuration of the positioning portion of the separator 3, and FIG. 9B is a cross-sectional view taken along line B-B in FIG. 9A. As shown in FIG. 9A, a plurality of ribs 551, 552 protruding toward the UEA 2 are provided around the positioning recess (e.g., recess 501 of the first separator 31). That is, a plurality of ribs 551, 552 protruding forward from the front plate 3F and rearward from the rear plate 3R are provided. The rib 551 extends linearly along the recess 501. Meanwhile, the rib 552 is generally circular and is provided in multiple locations along the recess 501, inside the rib 551. Similar ribs 551, 552 are provided in the other recesses 502 to 506.

[0067] 9A , the wide recess 511 of the second separator 32 corresponding to the recess 501 is indicated by a dotted line. Rib portions 551 and 552 that protrude toward the UEA 2 are also provided around the wide recess 511 of the second separator 32. However, the rib portions 551 and 552 of the second separator 32 are partially cut off by the cutting process of the wide recess 511.

[0068] As shown in FIG. 9B , the rib portion 551 of the first separator 31 and the rib portion 551 of the second separator 32, and (not shown) the rib portion 552 of the first separator 31 and the rib portion 552 of the second separator 32, face each other and abut against the frame 21 of the UEA 2. By providing the ribs 551, 552 near the recesses 501-506 in this manner and sandwiching the frame 21 between the rib portions 551, 552 of the pair of separators 31, 32, the rigidity of the vicinity of the recesses 501-506 is increased. This makes it possible to suppress deformation of the vicinity of the recesses 501-506 when the recesses 501-506 slide along the guide member 51 or guide jig 510 during assembly of the fuel cell stack 100. As a result, the separators 3 can be stacked while being positioned with high precision.

[0069] In the above embodiment, the positioning recesses 501-504 and the wide recesses 511-514 are provided in the left-right or up-down middle portions of the long or short sides of the separator 3 (see FIGS. 4, 5A, and 5B). Here, the "middle portion" does not necessarily mean the center position in the strict sense; it may be offset from the center position within a predetermined range in the left-right and up-down directions. FIG. 10 is a rear view of a separator 3 that is a modification of FIG. 4, showing an example of such an arrangement. In FIG. 10, the intersection of a first center line LN1 passing through the left-right middle portion of the long side of the separator 3 and a second center line LN2 passing through the up-down middle portion of the short side is indicated as a center point P. The recesses 501-504 and the wide recesses 511-514 are offset from the center point P by a predetermined offset amount ΔL1 or ΔL2 in the left-right and up-down directions.

[0070] The deviation amounts ΔL1 and ΔL2 are the same value. Considering that the separators 3 are guided uniformly in the circumferential direction by the guide members 51 or guide jigs 510 during stacking, the deviation amount ΔL1 is preferably equal to or less than half the length L1 from the first center line LN1 to the short side, and the deviation amount ΔL2 is preferably equal to or less than half the length L2 from the second center line LN2 to the long side. In other words, the recesses 501 to 506 are preferably provided approximately in the center of the long side and the short side. The deviation amounts ΔL1 and ΔL2 may be different values.

[0071] This embodiment can achieve the following advantageous effects: (1) A fuel cell stack 100 includes a cell stack 10 configured by stacking, in the front-to-rear direction, a plurality of substantially rectangular power-generating cells 1, each having a UEA 2 including an electrolyte membrane, an anode electrode, and a cathode electrode, and separators 3; a case 30 and end units 40 that surround the cell stack 10; and a plurality of guide members 51 that extend in the front-to-rear direction and are supported by the end units 40 so as to engage with a plurality of recesses provided on the outer edges of the separators 3 ( FIGS. 1 , 2 , and 4 ). The separators 3 have a pair of opposing long sides, i.e., an upper side 311 and a lower side 313, and a pair of opposing short sides, i.e., a right side 312 and a left side 314 ( FIG. 4 ). The multiple recesses of separator 3 include slit-shaped recesses 501 to 506 that extend from one of a pair of corners 315, 316 where a pair of long sides 311, 313 and a pair of short sides 312, 314 intersect, and from approximately the center of a pair of sides of the pair of long sides 311, 313 and the pair of short sides 312, 314 that do not have the corner at their end (upper side 311 and left side 314 that do not have corner 315, and lower side 313 and right side 312 that do not have corner 316), respectively, toward center point P, which is the center of separator 3 (Figures 5A and 5B).

[0072] When the cell stack 10 is pressurized, the outer edge of the separator 3 extends radially from the center point P, but with the above configuration, the direction of the slits in the recesses 501 to 506 coincides or nearly coincides with the direction of extension of the separator 3. This prevents the recesses 501 to 506 from strongly interfering with the guide member 51 or the guide jig 510, preventing damage to the separator 3. Furthermore, since the separator 3 (e.g., the first separator 31) is positioned via the recesses 501, 504, and 505 at three locations in the circumferential direction, the separator 3 can be positioned with high precision while minimizing the number of positioning portions.

[0073] (2) The separator 3 includes a first separator 31 and a second separator 32 alternately stacked with a UEA 2 interposed therebetween ( FIG. 1 ). The recess 505 of the first separator 31 extends in a slit-like manner from the lower right corner 315, where the lower side 313 and the right side 312 intersect, toward the center point P of the separator 3 ( FIG. 5A ). The recess 506 of the second separator 32 extends in a slit-like manner from the upper left corner 316, where the upper side 311 and the left side 314 intersect, toward the center point P of the separator 3 ( FIG. 5B ). Because the recesses 505 and 506 are provided at different corners 315 and 316 of the pair of separators 31 and 32, it is easy to ensure a large insulation distance between the separators 31 and 32. Furthermore, providing the recesses 505 and 506 at the corners 315 and 316 efficiently regulates the position of the separator 3 in both the vertical and horizontal directions. Furthermore, the corners 315 and 316 can be easily made to have high rigidity, and deformation of the separator 3 can be effectively prevented.

[0074] (3) The first separator 31 has a chamfered portion 515 at the upper left corner 316 where the top side 311 and left side 314 intersect ( FIG. 5A ). The second separator 32 has a chamfered portion 516 at the lower right corner 315 where the right side 312 and bottom side 313 intersect ( FIG. 5B ). This ensures a sufficient insulation distance between the separators 31 and 32 at the corners 315 and 316.

[0075] (4) The guide members 51 each have a rod-like shape with a substantially circular cross section or a rod-like shape with two flats (FIGS. 5A, 5B, and 6). This simplifies the shape of the guide members 51, allowing the guide members 51 to be manufactured at low cost. When the separators 3 are stacked, the recesses 501 to 506 slide along the arc-shaped circumferential surface of the guide members 51, allowing for easy sliding with less catching.

[0076] The above embodiment can be modified in various ways. Some modifications will be described below. In the above embodiment, the separator 3 is positioned by the three recesses 501, 504, and 505 or 502, 503, and 506 provided at the corners 315 and 316 and the long sides 311 and 313 and the short sides 312 and 314 of the separator 3. However, the positioning recesses may be provided at two locations, a first recess and a second recess. That is, since the recesses 505 and 506 at the corners 315 and 316 can simultaneously position the separator 3 in the left-right direction and the up-down direction, the first recess may be provided at the corners 315 and 316, and the second recess may be provided at the long sides 311 and 313 or the short sides 312 and 314.

[0077] In this case, one of a pair of corners 315, 316 at which a pair of opposing long sides 311, 313 (a pair of first opposing sides) and a pair of opposing short sides 312, 314 (a pair of second opposing sides) intersect is defined as a target corner. A slit-shaped first recess extending toward the center (center point P) of the separator 3 is provided in the target corner, and a slit-shaped second recess extending from approximately the center of one of the long sides and short sides that does not have the target corner at its end toward the center of the separator 3 is provided. In other words, the second recess may be provided on one of the pair of sides facing the target corner. Specifically, it is sufficient that at least the recesses 501, 505 or the recesses 504, 505 are provided in the first separator 31, and at least the recesses 502, 506 or the recesses 503, 506 are provided in the second separator 32. Therefore, recess 504 or recess 501 as the third recess in first separator 31 may be omitted, and recess 503 or recess 502 as the third recess in second separator 32 may be omitted.

[0078] In the above embodiment, among the upper side 311 (first side), right side 312 (third side), lower side 313 (second side), and left side 314 (fourth side) of the separator 3, the recess 505 is provided in the lower right corner 315 (first corner) where the right side 312 and the lower side 313 intersect, and the recess 506 is provided in the upper left corner 316 (second corner) where the upper side 311 and the left side 314 intersect. However, recesses may be provided in the corners where the upper side 311 and the right side 312 intersect and the corners where the lower side 313 and the left side 314 intersect. Similarly, chamfered portions may be provided at corners other than the lower right corner 315 and the upper left corner 316. In the above embodiment, the cross-sectional shape of the guide member 51 is a substantially circular rod shape or a rod shape having width across flats, but the configuration of the guide member is not limited to this. In the above embodiment, the metal guide jig 510 is configured to be the same length as the resin guide member 51, but the guide jig 510 may be configured to be longer than the guide member 51, making it unnecessary to attach the extension guide member 55 to the guide jig 510.

[0079] In the above embodiment, the guide member 51 and the guide jig 510 are provided upright from the end unit 40 fastened to the lower end surface of the case 30. However, they may also be provided upright from other components surrounding the cell stack 10. For example, an insulating plate, which is also part of the end unit 40, may be disposed above an end plate, which is also part of the end unit 40, so as to be movable up and down via a rod penetrating the end plate, and the guide member and the guide jig may be provided upright from the insulating plate. In this case, the lower end surface of the case 30 is fastened to the end plate, and the insulating plate is disposed above the end plate via a rod, spaced apart from the end plate. Thereafter, the insulating plate is gradually lowered as the power-generating cells 1 are stacked, and finally, the insulating plate is mounted on the end plate. In the above embodiment, three substantially rectangular through-holes 201-206, 301-306, and 401-406 are provided at each of the left and right ends of the integrated electrode assembly (UEA), separator, and end unit. However, the number, position, arrangement, and shape of these through-holes are not limited to those described above.

[0080] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other.

[0081] REFERENCE SIGNS LIST 1 Power generating cell, 2 Integrated electrode assembly, 3 Separator, 10 Cell stack, 30 Case, 31 First separator, 32 Second separator, 40 End unit, 51 Guide member, 100 Fuel cell stack, 311 Upper edge, 312 Right edge, 313 Lower edge, 314 Left edge, 501, 502 Long side recess, 503, 504 Short side recess, 505, 506 Corner recess, 510 Guide member, 515, 516 Chamfered portion

Claims

1. A fuel cell stack comprising: a cell stack formed by stacking in a predetermined direction a plurality of substantially rectangular power generation cells, each having a membrane electrode assembly including an electrolyte membrane and electrodes, and a separator; a housing surrounding the cell stack; and a plurality of guide members supported by the housing and extending in the predetermined direction so as to engage with a plurality of recesses provided on the outer edge of the separator, wherein the separator has a pair of first opposing sides opposed to each other and a pair of second opposing sides opposed to each other, and the plurality of recesses include a target corner which is one of a pair of corners where the pair of first opposing sides intersects with the pair of second opposing sides, and a slit-shaped first recess and second recess which extend respectively from an approximate center of one of the pair of first opposing sides and the pair of second opposing sides that does not have the target corner at its end, toward the center of the separator.

2. A fuel cell stack as described in claim 1, wherein the plurality of recesses further includes a third slit-shaped recess extending from approximately the center of the other of the pair of sides that does not have the target corner portion at its end toward the center of the separator.

3. A fuel cell stack according to claim 1 or 2, wherein the pair of first opposing sides are first and second sides, and the pair of second opposing sides are third and fourth sides, the separators include first separators and second separators alternately stacked via the membrane electrode structure, the first recess of the first separator extends in a slit-like manner from a first corner where the second and third sides intersect towards the centre of the separator, and the first recess of the second separator extends in a slit-like manner from a second corner where the first and fourth sides intersect towards the centre of the separator.

4. A fuel cell stack as described in claim 3, wherein the first separator has a chamfered portion at the second corner where the first side and the fourth side intersect, and the second separator has a chamfered portion at the first corner where the second side and the third side intersect.

5. A fuel cell stack according to claim 1 or 2, wherein the plurality of guide members have a rod shape with a substantially circular cross section or a rod shape with a width across flats.

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