WO2006043505A1 - Fuel cell stack and separator joining method - Google Patents

Abstract

In order to bring separators into close contact with each other without gaps to reduce contact resistance and increase conductivity even when separators are warped, a plurality of single cells, in each of which an anode separator (PS) and a cathode separator (NS) that consist of metal plates formed by press-forming flow paths in irregular shapes are respectively disposed on the opposite sides of a polyelectrolyte film, are laminated in an active area, and the anode separator (PS) and the cathode separator (NS) are integrated together by metal joining by fusing a low-melting-point alloy sheet (31) disposed at the top of a recessed streak (16) formed in the active area and a low-melting-point alloy wire (30) fitted and disposed in a seal groove (27).

Description

 Method of joining fuel cell stack and separator

 Technical field

 The present invention relates to a fuel cell stack and a method for joining a separator.

 Background art

 In a fuel cell in which hydrogen and oxygen are supplied to both surfaces of a polymer electrolyte membrane to generate an electromotive force, a metal thin plate is pressed to form a gas in order to further increase the electromotive force per unit volume. Thin metal separators that form flow paths have been developed.

 [0003] If a concave and convex gas flow path is formed in the central part of the metal plate by pressing while pressing, the entire separator is affected by the difference in local elongation (residual stress) between the front and back of the separator. Warping occurs.

 [0004] Warping of the separator causes an increase in contact resistance due to poor contact with the polymer electrolyte membrane, resulting in a decrease in power generation performance. In addition, the gas sealing performance near each separator hold is reduced.

 [0005] In addition, in a fuel cell stack using a metal separator, in the case of a separator based on stainless steel in which the contact resistance between the separators is particularly large among the in-cell resistance, a non-conductive coating (for improving corrosion resistance) It is a negative factor in terms of conductivity. Furthermore, variations in the groove height of the separator and poor flatness are factors that deteriorate contact resistance.

 [0006] Therefore, after press forming a gas flow path having a concavo-convex shape in a metal plate, minute rhombus indentations are formed on the flat portions of the concavo-convex portions, or indentations on the upper and lower surfaces of the mold, respectively. A technique has been disclosed in which formation protrusions are formed and indentation is formed at the same time as the gas flow path is formed to prevent warping (see Patent Document 1).

[0007] Of the separators disposed on both sides of the joined body (solid polymer electrolyte membrane), one separator has a plate spring interposed between two metal plates so that the single cell is thermally expanded. When the leaf spring is elastically deformed when it is tensioned or contracted, the single cell is Thus, a technique for maintaining the pressure holding force with respect to the laminated body is disclosed (see Patent Document 2).

 [0008] In addition, an outer edge cutting margin for cutting the outer edges of the negative electrode mask, the center plate, and the positive electrode mask into a predetermined shape is left, and the negative gas gas through hole and the positive electrode gas through hole are processed without being processed. A technique is disclosed that facilitates the assembly process and the welding process by joining the two separators so as to leave a hold cutting allowance and welding the outer peripheral part and then cutting the outer peripheral part (Patent Document 3). reference).

 Patent Document 1: Japanese Patent Laid-Open No. 2000-138065 (Page 5 force is also on page 8, FIGS. 2 and 3) Patent Document 2: Japanese Patent Laid-Open No. 2002-367665 (Pages 2 and 3, page 5) (Fig. And Fig. 6) Patent Document 3: Japanese Patent Application Laid-Open No. 2004-127699 (Pages 5-7, Figs. 1-3) Disclosure of the Invention

 [0009] In the technique described in Patent Document 1, since it is necessary to form a minute indentation in the mold, the indentation part wears over time, and the cost of the mold cannot be avoided. In addition, the technique described in Patent Document 2 still has problems of cost increase and weight increase due to an increase in the number of parts. In addition, in the technique described in Patent Document 3, sealing of the outer periphery of the separator is not improved in terms of contact resistance between force separators.

 [0010] The present invention provides a fuel cell stack and a separator joining method capable of reducing contact resistance by bringing the separators into close contact with each other without any gap even when the separator is warped, and improving conductivity. The task is to do.

 [0011] In order to achieve the above object, a fuel cell stack according to one aspect of the present invention includes a separator that also has a metal plate force obtained by press-forming a channel that also has an uneven shape force in an active region on both surfaces of a polymer electrolyte membrane. Convex portions formed by laminating a plurality of single cells each disposed, and having a positive electrode separator disposed on the positive electrode side of the polymer electrolyte membrane and a negative electrode separator disposed on the negative electrode side at least in the active region. They are joined together by metal bonding.

[0012] In order to achieve the above object, a separator joining method according to another aspect of the present invention is a method in which a metal plate is press-molded, and a flow path having a concavo-convex shape force in an active region and at least a seal in an outer peripheral edge portion. A separator is formed by forming a groove, and a low-melting point alloy is disposed on the top of the concavo-convex convex portion that constitutes the flow path formed in one separator, and in the seal groove. A heat treatment in which a low melting point alloy wire is fitted and disposed, the convex portions are overlapped, the other separator is overlapped with one separator, and the separator is heated to melt the low melting point alloy and the low melting point alloy wire. I do.

 [0013] The above and further objects, features, and advantages of the present invention will become apparent by reading the best mode for carrying out the invention made with reference to the accompanying drawings.

 Brief Description of Drawings

 FIG. 1 is a perspective view showing an overall configuration of a fuel cell stack.

 FIG. 2 is an enlarged cross-sectional view of a main part showing a part of a laminated structure of a fuel cell stack.

 FIG. 3 is a plan view of the separator.

 FIG. 4 is a cross-sectional view of the separator shown in FIG. 3 taken along line AA.

 [Fig. 5] Fig. 5 is an enlarged cross-sectional view of a main part showing a state in which a low melting point alloy wire is arranged in the seal groove and a low melting point alloy sheet is arranged on the top of the groove, and the positive electrode separator and the negative electrode separator are overlapped It is.

 FIG. 6 is an enlarged plan view of a main part of a separator in which a low melting point alloy wire is disposed in a seal groove and a low melting point alloy sheet is disposed on the top of a concave portion.

 FIG. 7 is an enlarged cross-sectional view of a main part showing an example in which a depression is formed at the top of a concave stripe and a low melting point alloy sheet is arranged in the depression.

 FIG. 8 is an enlarged cross-sectional view of a main part showing an example in which a paste-like low-melting-point alloy material is applied to the top of a concave strip.

 [FIG. 9] FIG. 9 is an enlarged cross-sectional view of a main part showing an example in which a paste-like low-melting-point alloy material is applied to the top of a concave stripe portion by screen printing.

 [FIG. 10] FIG. 10 is an enlarged cross-sectional view of a main part showing an example in which the tops of the concave strips are joined to each other and the separators are joined together.

 [Fig. 11] Fig. 11 (A) is an enlarged cross-sectional view of the main part of a separator in which only the joining portion corresponding to the top of the convex portion that is a concave portion is metal-bonded, and Fig. 11 (B) is a configuration example of seam welding. FIG.

FIG. 12 is an enlarged cross-sectional view of a main part of the separator showing a state where the separator shown in FIG. FIG. 13 is an enlarged cross-sectional view of a main part of the separator showing a state in which convex portions are metal-bonded by pressurization with a roller.

 BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

[0016] First, the overall configuration of the fuel cell stack will be briefly described.

[0017] FIG. 1 is a perspective view showing the overall configuration of the fuel cell stack, FIG. 2 is an enlarged cross-sectional view of a main part showing a part of the laminated structure of the fuel cell stack, FIG. 3 is a plan view of the separator, and FIG. FIG. 3 is a cross-sectional view taken along line AA of the separator shown in FIG.

[0018] As shown in Fig. 1, the fuel cell stack 1 is a laminated body 3 in which a predetermined number of single cells 2 as unit cells that generate an electromotive force by the reaction of fuel gas and oxidant gas are laminated. The current collector plate 4, the insulating plate 5 and the end plate 6 are arranged at both ends of the laminated body 3, the tie rod 7 is passed through the through-hole penetrating the inside of the laminated body 3, and a nut is screwed to the end of the tie rod 7. It is composed by combining them.

[0019] In this fuel cell stack 1, fuel gas H, oxidant gas O and cooling water LLC are respectively applied to the separators of each single cell 2 (PS, NS in Fig. 2, 15 in Fig. 3-4). Fuel gas inlet 8, fuel gas outlet 9, oxidant gas inlet 10, 0, oxidant gas outlet 11, cooling water inlet 12, and cooling water outlet 13 for flowing through the formed flow channel It is formed on one end plate 6.

[0020] The fuel gas is introduced from the fuel gas inlet 8 and flows through the fuel gas supply channel groove formed in the separator, and is discharged from the fuel gas outlet 9. The oxidant gas is introduced from the oxidant gas inlet 10, flows through the oxidant gas supply channel groove formed in the separator, and is discharged from the oxidant gas outlet 11. The cooling water is introduced from the cooling water introduction port 12, flows through the cooling water supply channel groove formed in the separator, and is discharged from the cooling water discharge port 13.

[0021] As shown in Fig. 2-4, the single-senore 2 includes a membrane electrode assembly (MEA) 14 and separators 15 disposed on both sides of the membrane electrode assembly 14, respectively. Is done. The separator 15 disposed on the positive electrode side of the membrane electrode assembly 14 is referred to as a positive electrode separator PS, and the separator 15 disposed on the negative electrode side is referred to as a negative electrode separator NS. [0022] The membrane electrode assembly 14 includes, for example, a solid polymer electrolyte membrane that is a polymer electrolyte membrane that allows hydrogen ions to pass through, a positive electrode that includes a positive electrode catalyst and a gas diffusion layer, and a negative electrode that includes a negative electrode catalyst and a gas diffusion layer. (Both are not shown). The strong membrane electrode assembly 14 has a laminated structure in which a solid polymer electrolyte membrane is sandwiched from both sides by a positive electrode and a negative electrode.

 The separator 15 is formed by forming a thin metal plate into a predetermined shape using a mold. As shown in FIG. 3 and FIG. 4, the powerful separator 15 is formed alternately with concave strips 16 and convex strips 17 in the active region that contributes to power generation (the central region in contact with the membrane electrode assembly 14). Forming a concavo-convex shape (a kind of corrugated shape).

 The recess 16 disposed in contact with the positive electrode side of the membrane electrode assembly 14 forms a fuel gas flow path 18 through which the fuel gas (hydrogen H) flows through the membrane electrode assembly 14. On the other hand, the concave strip 16 disposed in contact with the negative electrode side of the membrane electrode assembly 14 forms an oxidant gas flow path 19 through which an oxidant gas (oxygen O) flows between the concave electrode portion 16 and the membrane electrode assembly 14. . The space surrounded by the ridges 17 and 17 where the separators 15 and 15 are joined together forms a coolant channel 20 through which cooling water (LLC) flows.

 [0025] The separator 15 includes the fuel gas inlet 8, the fuel gas outlet 9, the oxidant gas inlet 10, the oxidant gas outlet 11, the cooling water inlet 12, and the cooling water outlet 13. Each of the communicating Mahonored 21, 22, 23, 24, 25, 26 forces is formed. For example, a separator 21 for introducing a fuel gas, a holder 22 for introducing cooling water, and a holder 23 for introducing an oxidant are sequentially formed from the upper right side to the lower side of the separator 15 shown in FIG. Also, in order from the upper left front of the separator 15 to the lower side, an oxidant discharge hold 24, a coolant discharge hold 25, and a fuel gas discharge hold 26 are provided. Further, the separator 15 is formed with a stacking hole 40 through which the tie rod 7 passes.

[0026] In addition, the separator 15 surrounds the concave strip 16 and the convex strip 17 constituting the flow path, and also includes a fuel gas introduction mold 21, an oxidant introduction mold 23, an oxidizer. Seal grooves 27 are formed so as to surround the discharge hold 24 and the fuel gas discharge hold 26, respectively. The seal groove 27 is formed as a groove having a semicircular cross section, and is formed as a so-called single stroke. [0027] The unit cell 2 composed of the membrane electrode assembly 14 and the separator 15 configured as described above is laminated so that the force on both sides of the membrane electrode assembly 14 is sandwiched between the positive electrode separator PS and the negative electrode separator NS, The membrane electrode assembly 14 is formed by joining and integrating the upper and lower separators 15 and 15 via a seal member 28 provided in the vicinity of the outer peripheral edge of the membrane electrode assembly 14.

 [0028] As shown in Fig. 2, the fuel cell stack 1 is formed by stacking a plurality of unit cells 2 having the above-described configuration, and a current collector plate 4, an insulating plate 5 and end plates are formed at both ends of the stack. It is configured by placing plate 6 and fastening with tie rod 7. In the fuel cell stack 1 of the present embodiment, the positive electrode separator PS and the negative electrode separator NS are metal-bonded at least between the convex portions formed in the active region (in the present embodiment, the concave strip portions 16, 16). What you do is more integrated. Further, in the present embodiment, the seal grooves 27 and 27 formed in the positive electrode separator PS and the negative electrode separator NS are metal-bonded by a low melting point metal 29 and integrated.

 [0029] In order to perform metal bonding of the positive electrode separator PS and the negative electrode separator NS, first, as shown in FIG. 5 and FIG. 6, in the seal groove 27 formed in one of the positive electrode separator PS and the negative electrode separator NS. A low melting point alloy wire 30 having a round bar shape that fits in the seal groove 27 is disposed. Further, the low melting point alloy sheet 31 is disposed on the top of the concave strip 16 (convex portion) of either the positive electrode separator PS or the negative electrode separator NS. For the low melting point alloy wire 30, for example, a solder wire can be used, and for the low melting point alloy sheet 31, for example, a solder sheet can be used.

 [0030] As shown in FIG. 6, the low-melting-point alloy wire 30 needs to be sealed with a fluid such as cooling water, and is therefore disposed in all the sealing grooves 27. In the straight groove, a low melting point alloy wire 30 having a straight shape is arranged, and in the bending groove, a low melting point alloy wire 30 having a curved shape corresponding to the shape is arranged. The low-melting-point alloy sheet 31 is formed as a long and narrow sheet having a low-melting-point alloy force, and is disposed on the tops of all the concave strips 16. When placing the low melting point alloy sheet 31, as shown in FIG. 7, a recess 32 is formed at the top of the recess 16, and the low melting point alloy sheet 31 is placed in the recess 32. In this way, since the low melting point alloy sheet 31 is guided in the recess 32, it is possible to prevent the low melting point alloy sheet 31 from being displaced with respect to the top, and to facilitate the subsequent steps.

[0031] Note that in the active region, it is only necessary to secure a path for electricity by metal bonding. A thin sheet-shaped low melting point alloy sheet 31 is used in consideration of strike reduction and weight reduction.

Further, instead of the low melting point alloy sheet 31, a paste-like low melting point alloy material 33 may be applied to the convex portion of the concave strip 16 by a dispenser 34 as shown in FIG. Alternatively, as shown in FIG. 9, a low-melting point alloy material 33 may be applied to the top of the recess 16 by a squeegee 36 using a screen plate 35.

[0033] Then, on the positive electrode separator PS on which the low-melting-point alloy wire 30 and the low-melting-point alloy sheet 31 are arranged, the negative electrode is formed so that the convex portions overlap each other and the low-melting-point alloy wire 30 fits snugly. Set separator NS and overlap. Thereby, the upper and lower seal grooves 27 are filled with the low-melting point alloy wire 30 without a gap, and the low-melting point alloy sheet 31 is disposed between the convex portions of the concave strips 16.

[0034] After these positive electrode separator PS and negative electrode separator NS are stacked, ion nitriding treatment (conductivity imparting surface treatment) is a heat treatment for heating the separator and imparting conductivity to the separator.

)I do. In the case of a metal separator based on stainless steel, a nonconductive film is formed on the surface to satisfy corrosion resistance. However, since it is a negative factor in terms of conductivity, the nonconductive film is removed by ion nitriding. It is necessary to impart conductivity. The heat treatment for imparting electrical conductivity is performed with a mixed gas of N2 and H2 (normal mixing ratio is about 1: 1) in an atmosphere during nitriding, and with heat of about 600 ° C or less. In addition, it is preferable that the nitriding treatment is further evacuated by nitriding under the condition of 02, and ammonia gas should be further mixed.

 [0035] The melting point of the low-melting-point alloy wire 30 and the low-melting-point alloy sheet 31 needs to be lower than the heat treatment temperature of 600 ° C or less, and when an alloy such as Sn, Bi, In, Ag is used, These alloys have a melting point of about 200 ° C and are easily melted by heat during heat treatment. When using stainless steel as the metal separator, it is desirable to use solder containing a small amount of flux that acts as a soldering aid and removes the oxide film.

[0036] When the positive electrode separator PS and the negative electrode separator NS are subjected to nitriding treatment under the above conditions, the non-conductive film attached to the separator surface is removed, and the low melting point alloy wire 30 and the low melting point alloy sheet 31 are removed. Melt. As a result, conductivity is imparted to the positive electrode separator PS and the negative electrode separator NS, and the seal groove 27 is filled with the low melting point metal 29. In addition, the convex portions 16 and 16 of the active region are metal-bonded to each other. Thereby, in the single cell 2, the contact resistance between the separators is reduced, and the power generation performance is improved.

 [0037] According to the present embodiment, the positive electrode separator PS and the negative electrode separator NS are integrated with at least the protrusions formed in the active region by metal bonding. Metal bonding can be performed, and the contact resistance between the separators can be greatly reduced. Therefore, according to the present embodiment, the electromotive force per unit cell 2 can be increased, and the output of the entire fuel cell can be greatly improved.

 [0038] According to the present embodiment, since the seal grooves 27 formed at least on the outer peripheral edge of the positive electrode separator PS and the negative electrode separator NS are metal-bonded to each other, they are in close contact with each other without gaps and are reliably sealed. It becomes possible.

 [0039] According to the present embodiment, since the protrusions or the seal grooves 27 are integrated together by metal bonding using a low melting point alloy, the contact resistance in the active region can be greatly reduced, and the active region The sealing effect is also improved. In addition, the fuel cell stack 1 can be manufactured at a low cost because of the metal joining using the low melting point alloy.

 [0040] According to the present embodiment, the low melting point alloy wire 30 fitted into the seal groove 27 and the groove are heated by the nitriding treatment for removing the non-conductive film and imparting conductivity. Since the low melting point alloy sheet 31 disposed on the top of the portion 16 is melted, the heat treatment step can be made one step. Therefore, it is possible to prevent additional heat treatment for melting the low melting point alloy wire 30 and the low melting point alloy sheet 31 from being added.

 [0041] According to the present embodiment, since a low melting point alloy made of a solder sheet is used, it is possible to reduce material costs and weight.

 [0042] According to the present embodiment, since the paste-like low-melting-point alloy is applied to the top of the convex portion, it is possible to automate the application work and greatly improve the application work efficiency.

[0043] In the above-described embodiment, the positive electrode separator PS and the negative electrode separator NS are disposed by placing the low melting point alloy sheet 31 on the tops of the concave strips 16 or applying a low melting point alloy material to perform heat treatment. Separator PS and negative electrode separator NS were joined together by metal bonding, but as shown in Fig. 10, the metal was melted by irradiating laser between the convex portions of these concave strips 16 and 16. These may be joined together by metal joining. In this way, if the convex portions are metal-bonded by laser welding, the base materials are melted and bonded, so that a uniform electrical contact state can be ensured.

 [0044] Instead of laser welding, the convex portions of the concave strips 16 and 16 may be spot-welded and integrated between them by metal bonding.

 [0045] As shown in (A), the positive electrode separator PS and the negative electrode separator NS are both flat plates, and only the bonding portion S corresponding to the top of the convex portion to be the concave strip portion 16 is metal-bonded. Examples of the technique for metal joining the joining portion S include laser welding, spot welding, and seam welding.

 In seam welding, for example, as shown in FIG. 11 (B), disc-shaped rotating electrodes 41 and 41 are arranged on both sides of the stacked positive electrode separator PS and negative electrode separator NS, and these rotating electrodes are arranged. While rotating 41 and 41, the positive electrode separator PS and the negative electrode separator NS are fed at a predetermined speed, and the rotary electrode 41 and 41 are energized intermittently, thereby joining the joint portion S. If such seam welding is used, the joining portion S can be joined continuously, so that productivity can be greatly improved.

 [0047] Next, the joined body of the positive electrode separator PS and the negative electrode separator NS, which are metal-bonded only at necessary positions, is placed in the cavity of the hydraulic mold composed of the upper die 37 and the lower die 38 shown in FIG. To do. After the upper mold 37 and the lower mold 38 are clamped, a liquid is introduced into the cavity with a predetermined pressure. Then, the positive electrode separator PS and the negative electrode separator NS are opened away from each other except for the joint portion S by the liquid introduced into the cavity. When the upper die 37 and the lower die 38 are opened after a lapse of a predetermined time from the introduction of the liquid, a separator assembly having the shape shown in FIG. 10 is obtained.

 [0048] In this way, if the necessary portions are metal-bonded in advance and the pressure is formed by hydraulic molding, the press carriage is compared with the case where the uneven flow path is formed by press carriage in the active region. The warping problem that sometimes occurs can be avoided.

[0049] As shown in FIG. 13, the convex portions of the concave strips 16 and 16 of the positive electrode separator PS and the negative electrode separator NS are pressurized and energized while rotating a pair of rolls 39 and 39 that also have steel strength. These are joined together by metal bonding. [0050] The shape of the separator 15 used in the above description of the embodiment is merely an example, and is not limited to the present embodiment.

 [0051] According to the above-described embodiment, a plurality of single cells in which separators, which are also metal plate plates formed by pressing a flow path having an uneven shape in the active region, are arranged on both surfaces of the polymer electrolyte membrane, respectively. In the fuel cell stack in which the positive electrode separator and the negative electrode separator arranged on the negative electrode side of the polymer electrolyte membrane are laminated, at least the protrusions formed in the active region are integrated by metal bonding. I am letting.

 [0052] Therefore, the positive electrode separator disposed on the positive electrode side of the polymer electrolyte membrane and the negative electrode separator disposed on the negative electrode side are integrated with at least the protrusions formed in the active region by metal bonding. As a result, the protrusions are metal-bonded without any gaps, and the contact resistance between the separators can be greatly reduced. Therefore, according to the present invention, the electromotive force per unit cell can be increased, and the output of the entire fuel cell can be greatly improved.

 [0053] This application claims priority based on Japanese Patent Application No. 2004-303175 filed with the Japan Patent Office on October 18, 2004, which is hereby incorporated by reference.

 [0054] While specific embodiments and modification examples to which the present invention has been applied have been described above, various modifications can be made to the present embodiment without being limited to the above-described embodiments. Industrial applicability

[0055] According to the present invention, there are provided a method of joining a fuel cell stack and a separator, in which contact resistance is reduced and high conductivity is obtained.

Claims

The scope of the claims  [1] The polymer electrolyte membrane is formed by laminating a plurality of single cells each having a metal plate force separator formed by pressing a flow path having a concavo-convex shape force in the active region, and arranged on both sides of the polymer electrolyte membrane. A fuel cell stack in which a positive electrode separator disposed on the positive electrode side and a negative electrode separator disposed on the negative electrode side are integrated by metal bonding at least the protrusions formed in the active region.  [2] The fuel cell stack according to [1], wherein the seal grooves formed at least on the outer peripheral edge of the positive electrode separator and the negative electrode separator are metal-bonded. [3] The fuel cell stack according to claim 1, wherein the convex portions or the seal grooves are integrated by metal bonding using a low melting point alloy. [4] The fuel cell stack according to [1], wherein the convex portions are integrally formed by metal bonding by pressing with a roller.  5. The fuel cell stack according to claim 1, wherein the convex portions are integrally formed by laser welding. 6. The fuel cell stack according to claim 1, wherein the convex portions are integrally formed by spot welding. [7] A metal plate is press-molded to form a separator by forming a flow path that also has an uneven shape force in the active region and a seal groove at least on the outer peripheral edge, and the flow path formed in one separator A low-melting point alloy is disposed on the top of the concavo-convex convex portion, and a low-melting point alloy wire is fitted and disposed in the seal groove, and the convex portion is overlapped with the other separator with respect to one separator. A separator joining method in which a heat treatment is performed to heat the separators and melt the low melting point alloy and the low melting point alloy wire by superposing them. 8. The separator joining method according to claim 7, wherein the heat treatment is a nitriding treatment that removes the non-conductive film on the separator surface to ensure conductivity. [9] The separator joining method according to [7], wherein a low melting point alloy made of a solder sheet is disposed on the top of the convex portion.  [10] The separator joining method according to [7], wherein a paste-like low melting point alloy is applied to the top of the convex portion.