JP2006114444A - Fuel cell stack and joining method for separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell stack capable of improving conductivity by reducing contact resistance by bringing separators into contact with each other without a gap even if the separators are bent. <P>SOLUTION: In this fuel cell stack, a plurality of fuel cell single cells wherein an anode separator 15A and a cathode separator 15B which are composed of metal plates wherein flow passages having irregular shapes are press-molded in areas contributing to power generation are arranged on both sides of a polymer electrolyte film are laminated. The anode separator 15A and the cathode separator 15B are joined and integrated by a metal joint by melting a low-melting-alloy sheet 31 arranged in an apex part of a recessed part 16 formed in the area contributing to power generation and a low-melting-alloy wire rod 30 fitted and arranged in a seal groove 27. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  For example, in a fuel cell in which hydrogen and oxygen are supplied to both surfaces of a polymer electrolyte membrane to generate electromotive force, a metal thin plate is pressed to form a gas flow path in order to further increase the electromotive force per unit volume. A so-called thin metal separator that forms a thin film has been developed.

  However, when an uneven gas flow path is formed in the central portion of the metal plate by pressing, warpage occurs in the entire separator due to a difference in local elongation (residual stress) between the front and back of the separator.

  When the separator is warped, the contact resistance is increased due to poor contact with the polymer electrolyte membrane, and the power generation performance is lowered. Moreover, the gas sealing performance near the manifold of each separator is reduced.

  Further, in a fuel cell stack using a metal separator, the contact resistance between the separators is particularly large among the resistances in the cell, and in the case of a separator made of stainless steel as a base material, a non-conductive film (impairment of conductivity) for improving corrosion resistance ) Is formed on the surface, which is a negative factor in terms of conductivity. Further, variations in the groove height of the separator and poor flatness are factors that deteriorate the contact resistance.

  Therefore, after press forming a gas flow path having a concavo-convex shape on a metal plate, minute rhombus indentations are formed on the flat portion of the concavo-convex portion, or protrusions for forming indentations are formed on the upper and lower surfaces of the mold, respectively. A technique has been disclosed that prevents the occurrence of warpage by forming an indentation at the same time as forming a gas flow path (see, for example, Patent Document 1).

  In addition, among the separators disposed on both sides of the joined body (solid polymer electrolyte membrane), a leaf spring is interposed between two metal plates in one of the separators so that the fuel cell single cell is thermally expanded or A technique has been disclosed in which the pressure holding force on the stacked body is maintained by elastically deforming the leaf spring when the plate spring contracts and elastically biases the fuel cell unit cell (see, for example, Patent Document 2). .

In addition, an outer edge cutting margin for cutting the outer edges of the cathode mask, center plate, and anode mask into a predetermined shape is left, and a manifold cutting margin is left without processing the cathode gas through hole and the anode gas through hole. Thus, a technique is disclosed in which two separators are combined and the outer peripheral portion is welded, and then the outer peripheral portion is cut to facilitate the assembly process and the welding process (see, for example, Patent Document 3).
JP 2000-138065 (pages 5 to 8, FIGS. 2 and 3) Japanese Patent Application Laid-Open No. 2002-367665 (Pages 2 and 3; FIGS. 5 and 6) Japanese Unexamined Patent Publication No. 2004-127699 (pages 5 to 7, FIGS. 1 to 3)

  However, 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. Moreover, with the technique described in Patent Document 2, there remain problems of cost increase and weight increase due to an increase in the number of parts. Moreover, in the technique described in Patent Document 3, the outer periphery of the separator is sealed, but the contact resistance between the separators is not improved.

  Accordingly, the present invention provides a fuel cell stack and a separator joining method capable of reducing the contact resistance by closely contacting the separators without any gap even when the separator is warped, and improving the conductivity. Objective.

  The present invention provides a fuel in which a plurality of fuel cell single cells each having a separator made of a metal plate formed by pressing a flow path having a concavo-convex shape in a region contributing to power generation are disposed on both sides of a polymer electrolyte membrane. It is a battery stack.

  In the present invention, the anode separator disposed on the anode side of the polymer electrolyte membrane and the cathode separator disposed on the cathode side are metal-bonded at least to the convex portions formed in the region contributing to power generation. Bonded and integrated.

  According to the present invention, the anode separator disposed on the anode side of the polymer electrolyte membrane and the cathode separator disposed on the cathode side are joined by metal-bonding at least convex portions formed in a region contributing to power generation. Since they are integrated, the protrusions are metal-bonded without a gap, so that the contact resistance between the separators can be greatly reduced. Therefore, according to the present invention, the electromotive force per unit fuel cell can be increased, and the output of the entire fuel cell can be greatly improved.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  First, the overall configuration of the fuel cell stack will be briefly described. 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. 4 is shown in FIG. It is an AA line sectional view of a separator.

  As shown in FIG. 1, the fuel cell stack 1 is a laminated body 3 in which a predetermined number of fuel cell single cells 2 as unit cells that generate an electromotive force by the reaction of fuel gas and oxidant gas are laminated. Current collector plate 4, insulating plate 5, and end plate 6 are arranged at both ends of 3, and a tie rod 7 is passed through a through-hole (not shown) penetrating through the laminated body 3. And a nut (not shown) are screwed together.

  In this fuel cell stack 1, a fuel gas introduction port 8 for allowing fuel gas, oxidant gas, and cooling water to flow through channel grooves formed in the separators (not shown) of each fuel cell single cell 2. A fuel gas discharge port 9, an oxidant gas introduction port 10, an oxidant gas discharge port 11, a cooling water introduction port 12 and a cooling water discharge port 13 are formed in one end plate 6.

  The fuel gas is introduced from the fuel gas introduction port 8, flows through a fuel gas supply channel groove formed in the separator, and is discharged from the fuel gas discharge port 9. The oxidant gas is introduced from the oxidant gas introduction port 10, flows through the oxidant gas supply channel groove formed in the separator, and is discharged from the oxidant gas discharge port 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.

  As shown in FIG. 2, the fuel cell single cell 2 includes a membrane electrode assembly (MEA) 14 and separators 15 disposed on both surfaces of the membrane electrode assembly 14. The separator 15 disposed on the anode side of the membrane electrode assembly 14 is referred to as an anode separator 15A, and the separator 15 disposed on the cathode side is referred to as a cathode separator 15B.

  The membrane electrode assembly 14 includes, for example, a solid polymer electrolyte membrane that is a polymer electrolyte membrane that passes hydrogen ions, an anode electrode that includes an anode catalyst and a gas diffusion layer, and a cathode electrode that includes a cathode catalyst and a gas diffusion layer (both are (Illustration is omitted). The membrane electrode assembly 14 has a laminated structure in which a solid polymer electrolyte membrane is sandwiched from both sides by an anode electrode and a cathode 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 separator 15 has the recess 16 and the protrusion 17 alternately formed in the active region that contributes to power generation (region of the central portion in contact with the membrane electrode assembly 14). An uneven shape (so-called corrugated shape) is formed.

  The recess 16 disposed in contact with the anode side of the membrane electrode assembly 14 forms a fuel gas flow path 18 through which fuel gas (hydrogen H) flows. On the other hand, the concave strip portion 16 disposed in contact with the cathode side of the membrane electrode assembly 14 forms an oxidant gas flow path 19 through which an oxidant gas (oxygen O) flows. . And the space part enclosed by the protruding item | line parts 17 and 17 with which separators 15 and 15 were joined forms the coolant flow path 20 which distribute | circulates cooling water (LLC).

  The separator 15 communicates with the fuel gas inlet 8, fuel gas outlet 9, oxidant gas inlet 10, oxidant gas outlet 11, cooling water inlet 12, and cooling water outlet 13. The manifolds 21, 22, 23, 24, 25, and 26 are formed. For example, a fuel gas introduction manifold 21, a cooling water introduction manifold 22, and an oxidant introduction manifold 23 are sequentially formed from the upper right side to the lower side of the separator 15 shown in FIG. Further, an oxidant discharge manifold 24, a coolant discharge manifold 25, and a fuel gas discharge manifold 26 are sequentially formed from the upper left front side to the lower side of the separator 15. Further, the separator 15 is formed with a stacking hole 40 through which the tie rod 7 passes.

  In addition, the separator 15 surrounds the concave portion 16 and the convex portion 17 constituting the flow path, and also includes a fuel gas introduction manifold 21, an oxidant introduction manifold 23, an oxidant discharge manifold 24, and a fuel gas discharge. Seal grooves 27 that surround the manifolds 26 are formed. The seal groove 27 is formed as a groove having a semicircular cross section, and is formed as a so-called one stroke.

  The fuel cell single cell 2 composed of the membrane electrode assembly 14 and the separator 15 configured as described above is laminated so that the membrane electrode assembly 14 is sandwiched between the anode separator 15A and the cathode separator 15B from both sides thereof. The upper and lower separators 15 and 15 are joined and integrated with each other through a seal member 28 provided in the vicinity of the outer peripheral edge of the electrode assembly 14.

  As shown in FIG. 2, the fuel cell stack 1 is formed by stacking a plurality of fuel cell single cells 2 having the above-described configuration, and a current collector plate 4, an insulating plate 5, and an end plate are formed at both ends of the stack. 6 is arranged and fastened with a tie rod 7. Then, in the fuel cell stack 1 of the present embodiment, the anode separator 15A and the cathode separator 15B are provided with projections formed at least in a region contributing to power generation (in the present embodiment, the concave strips 16, 16). Are joined and integrated by metal joining. Further, in the present embodiment, the seal grooves 27 and 27 formed in the anode separator 15A and the cathode separator 15B are metal-bonded by a low-melting point metal 29 to be integrated.

  In order to metal-bond the anode separator 15A and the cathode separator 15B, first, as shown in FIGS. 5 and 6, the seal groove 27 is formed in the seal groove 27 formed in one of the anode separator 15A and the cathode separator 15B. A low-melting-point alloy wire 30 having a round bar shape to be fitted to the rod 27 is disposed. Further, the low-melting point alloy sheet 31 is disposed on the top of the concave strip portion 16 (convex portion) of either the anode separator 15A or the cathode separator 15B. 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.

  As shown in FIG. 6, the low melting point alloy wire 30 is disposed in all the seal grooves 27 because it is necessary to seal a fluid such as cooling water. A straight line-shaped low melting point alloy wire 30 is disposed in the straight groove, and a curved line corresponding to the shape of the low melting point alloy wire 30 is disposed in the bent groove. The low melting point alloy sheet 31 is formed as a long and narrow sheet made of a low melting point alloy, and is disposed on the tops of all the concave portions 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 by the recess 32, it is possible to prevent the position of the low melting point alloy sheet 31 from being displaced relative to the top, and to facilitate the subsequent steps.

  In the active region, it is only necessary to secure an electrical path by metal bonding, and therefore, a low melting point alloy sheet 31 having a thin sheet shape is used in consideration of material cost 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 groove 16 by a dispenser 34 as shown in FIG. 8. 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.

  Then, the cathode separator 15B is set on the anode separator 15A on which the low-melting-point alloy wire 30 and the low-melting-point alloy sheet 31 are arranged so that the convex portions overlap each other and the low-melting-point alloy wire 30 fits tightly. And repeat. As a result, the upper and lower seal grooves 27 are filled with the low melting point alloy wire 30 without any gaps, and the low melting point alloy sheet 31 is disposed between the convex portions of the concave strips 16.

After the anode separator 15A and the cathode separator 15B are stacked, ion nitriding treatment (conducting surface treatment), which is a heat treatment for imparting conductivity to the separator by heating them, is performed. In the case of a metal separator based on stainless steel, a non-conductive film is formed on the surface in order to satisfy corrosion resistance. However, since it is a negative factor in terms of conductivity, the non-conductive film is removed by ion nitriding to conduct electricity. It is necessary to impart sex. The heat treatment for imparting conductivity is performed by using a mixed gas of N ₂ and H ₂ (normal mixing ratio is about 1: 1) as an atmosphere during nitriding and applying heat of about 600 ° C. or less. In the nitriding treatment, it is preferable to perform nitriding under a condition without O ₂ by further applying a vacuum, and ammonia gas may be further mixed.

  The melting points of the low-melting-point alloy wire 30 and the low-melting-point alloy sheet 31 must 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 are about 200 It has a melting point of ° C. and is easily melted by heat during heat treatment. When stainless steel is used as the metal separator, it is desirable to use solder containing a small amount of flux that serves as a soldering aid and removes the oxide film.

  When the anode separator 15A and the cathode separator 15B are subjected to nitriding treatment under the above conditions, the non-conductive film attached to the separator surfaces is removed, and the low melting point alloy wire 30 and the low melting point alloy sheet 31 are melted. As a result, conductivity is imparted to the anode separator 15A and the cathode separator 15B, the inside of the seal groove 27 is filled with the low melting point metal 29, and the convex portions of the concave portions 16 and 16 in the active region are made of metal. Be joined. Thereby, as for the fuel cell single cell 2, the contact resistance between separators becomes small and electric power generation performance improves.

  As described above, according to the present embodiment, the anode separator 15A and the cathode separator 15B are integrally joined by metal-bonding the convex portions formed at least in the region contributing to power generation. The convex portions can be metal-bonded without a gap, and the contact resistance between the separators can be greatly reduced. Therefore, according to the present embodiment, the electromotive force per unit fuel cell 2 can be increased, and the output of the entire fuel cell can be greatly improved.

  In addition, according to the present embodiment, since the seal grooves 27 formed at least on the outer peripheral edge portions of the anode separator 15A and the cathode separator 15B are metal-bonded, they are in close contact with each other without gaps, and are reliably sealed. Is possible.

  Further, according to the present embodiment, since the convex portions or the seal grooves 27 are joined and integrated by metal joining using a low melting point alloy, the contact resistance in the active region can be greatly reduced, and the seal of the active region can be achieved. The effect is also improved. Moreover, since it is metal joining using a low melting point alloy, the fuel cell stack 1 can be manufactured at low cost.

  In addition, according to the present embodiment, the low melting point alloy wire 30 and the groove portion 16 that are fitted and arranged in the seal groove 27 by heating at the time of nitriding treatment for removing the nonconductive film and imparting conductivity. Since the low melting point alloy sheet 31 disposed on the top of the metal melts, 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.

  Further, according to the present embodiment, since a low melting point alloy made of a solder sheet is used, it is possible to reduce material cost and weight.

  Moreover, according to this Embodiment, since a paste-like low melting-point alloy is apply | coated to the top part of a convex part, it becomes possible to automate an application | coating operation | work and can raise a big application | coating work efficiency.

  The specific embodiment to which the present invention is applied has been described above, but the present embodiment is not limited to the above-described embodiment, and various modifications can be made.

  In the above-described embodiment, the anode separator 15A and the cathode separator 15A and the cathode separator 15B are disposed by placing the low-melting-point alloy sheet 31 on top of the concave portions 16 or applying a low-melting-point alloy material and performing heat treatment. Separator 15B was joined and integrated by metal joining, but as shown in FIG. 10, laser was irradiated between the convex portions of these concave strips 16 and 16 to melt the metal, and the joints were joined by metal joining. It may be integrated. 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.

  Further, instead of laser welding, the convex portions of the concave strip portions 16 and 16 may be spot welded, and the portion between them may be metal-bonded and integrated.

  Further, as shown in FIG. 11A, both the anode separator 15A and the cathode separator 15B are flat plates, and only the joining portion S corresponding to the top of the convex portion that becomes the concave strip portion 16 is metal-joined. 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. 11B, disk-shaped rotating electrodes 41 and 41 are arranged on both sides of the overlapped anode separator 15A and cathode separator 15B, and these rotating electrodes 41 and 41 are connected to each other. While rotating and feeding the anode separator 15A and the cathode separator 15B at a predetermined speed, the joining portions S are joined by intermittently energizing the rotating electrodes 41, 41. If such seam welding is used, the joining portion S can be joined continuously, so that productivity can be greatly improved.

  Next, the joined body of the anode separator 15A and the cathode separator 15B, which are metal-bonded only at necessary portions, is disposed in the cavity of the hydraulic molding die including the upper die 37 and the lower die 38 shown in FIG. After the upper mold 37 and the lower mold 38 are clamped, a liquid is introduced into the cavity at a predetermined pressure. Then, the anode separator 15A and the cathode separator 15B are opened in a direction 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.

  In this way, if hydroforming is performed after the necessary parts are metal-bonded in advance, the problem of warpage occurring during pressing is less than that of forming an uneven channel by pressing in the active region. It can be avoided.

  Further, as shown in FIG. 13, the convex portions of the concave strip portions 16 and 16 of the anode separator 15A and the cathode separator 15B are pressurized and energized while rotating a pair of steel rolls 39 and 39, These are metal-bonded and integrated.

  Moreover, the shape of the separator 15 used in the description of the above-described embodiment is an example, and is not limited to the present embodiment.

It is a perspective view which shows the whole structure of a fuel cell stack. It is a principal part expanded sectional view which shows a part of laminated structure of a fuel cell stack. It is a top view of a separator. It is the sectional view on the AA line of the separator shown in FIG. It is a principal part expanded sectional view which shows the state which has arrange | positioned the low-melting-point alloy wire in a seal groove, and has arrange | positioned the low-melting-point alloy sheet | seat on the top part of a groove part, and overlapped the anode separator and the cathode separator. It is a principal part enlarged plan view of the separator which has arrange | positioned the low melting-point alloy wire in a seal groove, and has arrange | positioned the low melting-point alloy sheet | seat on the top part of a groove part. It is a principal part expanded sectional view which shows the example which formed the hollow in the top part of a concave part, and has arrange | positioned the low melting-point alloy sheet | seat in the hollow. It is a principal part expanded sectional view which shows an example which apply | coats a paste-form low melting-point alloy material to the top part of a concave part. It is a principal part expanded sectional view which shows an example which apply | coats a paste-form low melting-point alloy material to the top part of a concave part by screen printing. It is a principal part expanded sectional view which shows the example which carried out the metal joining of the top parts of a concave part, and joined and integrated separators. FIG. 11A is an enlarged cross-sectional view of a main part of a separator in which only a joining portion corresponding to the top of a convex portion serving as a concave portion is metal-bonded, and FIG. 11B is a diagram illustrating a configuration example of seam welding. . It is a principal part expanded sectional view of the separator which shows the state which has carried out the hydraulic forming of the separator shown in FIG. It is a principal part expanded sectional view of the separator which shows the state which metal-bonds convex parts by the pressurization by a roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack 2 ... Fuel cell single cell 14 ... Membrane electrode assembly 15 ... Separator 15A ... Anode separator 15B ... Cathode separator 16 ... Concave strip 17 ... Convex strip 27 ... Sealing groove 29 ... Low melting point metal 30 ... Low Melting point alloy wire 31 ... Low melting point alloy sheet

Claims (10)

This is a fuel cell stack in which a plurality of fuel cell single cells are formed by laminating separators made of metal plates, which are formed by pressing a flow path having an uneven shape in a region contributing to power generation, on both sides of the polymer electrolyte membrane. And
The anode separator disposed on the anode side of the polymer electrolyte membrane and the cathode separator disposed on the cathode side are joined and integrated by metal-bonding at least convex portions formed in the region contributing to power generation. A fuel cell stack characterized by that. The fuel cell stack according to claim 1, wherein
A fuel cell stack, wherein seal grooves formed at least on the outer peripheral edge of the anode separator and the cathode separator are metal-bonded. The fuel cell stack according to claim 1 or 2,
The fuel cell stack, wherein the convex portions or the seal grooves are joined and integrated by metal joining using a low melting point alloy. The fuel cell stack according to claim 1, wherein
The fuel cell stack, wherein the convex portions are metal-bonded and integrated by pressing with a roller. The fuel cell stack according to claim 1, wherein
The fuel cell stack, wherein the convex portions are joined and integrated by laser welding. The fuel cell stack according to claim 1, wherein
The fuel cell stack is characterized in that the convex portions are joined together by spot welding. A step of forming a separator by pressing a metal plate, forming a channel having a concavo-convex shape in a region contributing to power generation, and forming a seal groove at least on the outer peripheral edge; and
Placing a low melting point alloy on the top of the concavo-convex shaped convex portion constituting the flow path formed in one separator, and fitting and placing a low melting point alloy wire in the seal groove;
A step of overlapping the convex portions with each other and overlapping the other separator on one separator;
A heat treatment step for heating the separator to melt the low-melting-point alloy and the low-melting-point alloy wire. A separator joining method according to claim 7,
The separator is characterized in that the heat treatment step is a nitriding treatment that removes a non-conductive film on the separator surface to ensure conductivity. A separator joining method according to claim 7 or claim 8,
A separator joining method, wherein a low melting point alloy made of a solder sheet is disposed on the top of the convex portion. A separator joining method according to claim 7 or claim 8,
A separator bonding method, wherein a paste-like low melting point alloy is applied to the top of the convex portion.