JP2001035505A - Fuel cell stack and method and member for joining same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joining member superior in durability with respect to heat cycling by reducing electrical contact resistance between an inter-connector and an electrode film on the fuel side in a unit cell or a current collector. SOLUTION: When a fuel cell stack is formed by connecting a unit cell 4 including a solid electrolyte film 1 and electrode films 2, 3 on the fuel side and the air side respectively laminated at both surfaces of the film 1 via inter- connectors 7, a joining member is interposed between the electrode film 2 on the fuel side in the unit cell 4 or a current collector 5 and the inner-connector 7. The joining member is made of a composite material, containing NiO and LaCrO3 added with at least one kind of element selected from among Sr, Ca, Mg, Ti, Zr, V, Mn, Fe, Co, Ni, Cu, Zn, Al, Ba, Mo and Pb, wherein the content of NiO is gradually increased from the surface of the inter-connector as it nears the electrode film on the fuel side or the current collector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell stack, a joining method and a joining material thereof, and more particularly, to a fuel cell electrode of a single cell or a fuel collector and an interconnector contacting the fuel electrode. TECHNICAL FIELD The present invention relates to a fuel cell stack capable of reducing electrical contact resistance between the fuel cell stack and a joining method and a joining material thereof.

[0002]

2. Description of the Related Art A solid electrolyte type fuel cell stack is known as Y
_An oxygen-side electrode made of (La, Sr) MnO ₃ or the like and a Ni + YSZ cermet (NiO / Y ₂ O ₃ stabilized Zr) are formed on both surfaces of a solid electrolyte membrane such as 2O ₃ stabilized ZrO ₂ (YSZ).
A single cell having a three-layer structure in which fuel-side electrodes made of O ₂ cermet) or the like are stacked is stacked in large numbers via an interconnector made of LaCrO ₃ ceramics or the like. And a current collector may be interposed between them. The fuel-side current collector and the air-side current collector are made of a material having a composition close to the fuel-side electrode and the air-side electrode of a single cell, respectively. A metal material may be used.

In such a solid oxide fuel cell stack, the electrical contact resistance between the fuel cell electrode film of a single cell or a current collector contacting the fuel electrode film and the interconnector is reduced. Conventionally, a fuel cell has been conventionally connected by interposing a thin film of Ni or the like on the contact surface between the fuel-side electrode film or the fuel-side current collector and the interconnector, and pressing it during power generation. Stacks are known.

[0004]

However, in the above prior art, since the thermal expansion difference between the thin film of Ni or the like formed on the joint surface and the interconnector is large, the thin film of Ni or the like during the heat cycle is not used. There has been a problem that the electrical contact resistance increases due to separation from the interconnector surface.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an interconnector which is a constituent member of a solid oxide fuel cell stack and a fuel cell electrode film of a single cell or a fuel cell electrode film in contact with the fuel cell electrode film. Another object of the present invention is to provide a fuel cell stack which reduces electrical contact resistance with a current collector and has excellent durability against thermal cycling, and a joining method and a joining material therefor.

[0006]

Means for Solving the Problems To solve the above problems, the invention claimed in the present application is as follows. (1) A fuel cell stack is formed by electrically connecting a large number of single cells each composed of a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both sides of the solid electrolyte membrane via an interconnector. A bonding material to be interposed between the interconnector and the fuel-side electrode film of the single cell or the current collector abutted on the fuel-side electrode film when forming the NiO, Sr, Ca, Mg, Ti, Zr, V, M
n, Fe, Co, Ni, Cu, Zn, Al, Ba, Mo
L to which at least one element of Pb and Pb is added
A joining material for a solid oxide fuel cell stack, comprising a composite material containing aCrO ₃ , wherein an existing ratio of the NiO is gradually increased from a surface of the interconnector toward a fuel-side electrode film or a current collector.

(2) The content ratio of NiO is gradually increased in the range of 30% to 100% as the distance from the interconnector surface to the fuel-side electrode film or the current collector increases. The bonding material according to the above. (3) A plurality of single cells each composed of a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both surfaces of the solid electrolyte membrane are electrically connected to each other via an interconnector to form a stack. A method of joining a solid oxide fuel cell stack, wherein the above (1) or (2) is provided between the interconnector and a fuel cell electrode film of a single cell or a current collector abutted on the fuel cell electrode film. A method for joining a solid oxide fuel cell stack, comprising sintering while bonding the joining surface by interposing the joining material described in (1).

(4) The surface of the interconnector, the fuel-side electrode film, or the current collector is coated with a slurry of the composite material according to the above (1), in which the NiO content is sequentially varied, and the surface of the interconnector is formed. The fuel cell stack according to the above (3), wherein the proportion of NiO in the bonding material is gradually increased in the range of 30% to 100% as it approaches the fuel-side electrode film or the surface of the current collector. Method.

(5) A solid electrolyte in which a plurality of single cells each composed of a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both sides of the solid electrolyte membrane are electrically connected via an interconnector. A fuel cell stack of the type, wherein the interconnector and a fuel cell electrode film of a single cell or a bonding surface of a current collector abutted on the fuel electrode film,
A solid oxide fuel cell stack comprising the bonding material according to the above (1) or (2).

[0010]

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a method for joining a flat solid electrolyte fuel cell stack according to one embodiment of the present invention. In FIG. 1, a fuel cell current collector opposing the fuel electrode film 2 and the air electrode 3 of a single cell 4 in which a fuel electrode film 2 and an air electrode film 3 are laminated on both surfaces of a solid electrolyte membrane 1 respectively. The body 5 and the air-side current collector 6 are arranged, and a bonding material 8 is formed on a surface of the interconnector 7 facing the fuel-side current collector 5. The joining material 8 is made of NiO
And Sr, Ca, Mg, Ti, Zr, V, Mn, Fe,
Co, Ni, Cu, Zn, Al, Ba, Mo and Pb
LaCrO doped with at least one kind of element
_The composite ratio of NiO is gradually increased from the surface of the interconnector 7 toward the fuel-side current collector 5. A large number of such unit cells 4 having the current collector disposed on the electrode film surface and in contact with the fuel-side current collector 5 are stacked via the interconnector 7 in which the bonding material 8 is disposed on the contact surface with the fuel-side current collector 5, For example, it is fired in air at 1350 ° C. for 3 hours while being pressed under a pressure of 100 g / cm ² to form a fuel cell stack.

According to this embodiment, the bonding material 8 is made of NiO which is a main constituent material of the fuel-side electrode film 2 or the fuel-side current collector 5.
And a composite material of LaCrO ₃ ceramics, which is a constituent material of the interconnector, and
When the existence ratio of iO gradually increases as approaching the fuel-side current collector 5, that is, the existence ratio of LaCrO ₃ -based ceramics gradually increases as approaching the interconnector 7, the fuel cell stack has Since NiO in the bonding material 8 is reduced to Ni by the hydrogen-rich gas supplied to the side electrode, the electrical contact resistance of the bonding surface is reduced by the action of Ni having high conductivity. Further, by increasing the proportion of the LaCrO ₃ -based ceramic in the portion of the joining material 8 close to the interconnector 7, the difference in thermal expansion with the interconnector 7 made of the LaCrO ₃ -based ceramic is suppressed to be small, and a strong adhesive force is obtained. , The heat cycle resistance is improved, and no distortion, peeling or the like occurs. LaCrO ₃ -based ceramics are originally conductive materials, and also have the effect of reducing electrical contact resistance.

In this embodiment, when the unit cells 4 are further stacked above the upper interconnector 7 in FIG. 1, the bonding material 8 is also provided on the surface of the upper interconnector 7.
Is arranged. In the present invention, the bonding material is NiO powder, Sr, Ca, Mg, Ti, Zr, V, Mn, Fe,
Co, Ni, Cu, Zn, Al, Ba, Mo and Pb
LaCrO ₃ to which at least one element is added
It is composed of a composite material containing a base ceramic powder. Each of the powders constituting the composite material has an average particle size of 1
It is preferably 0 μm or less, and usually about 2 to 8 μm is suitably used. In the present invention, the bonding material is applied as a slurry coating film obtained by adding a binder, a solvent, and other additives as necessary to the powder of the composite material, or as a green body obtained by molding the slurry.

As the solvent, for example, an organic solvent or a water solvent in which toluene and ethanol are mixed at a volume ratio of 3: 2 is used. When using an organic solvent as a solvent, as a binder, for example, polyvinyl butyral, turpentine oil,
Polyethylene, polyvinyl chloride, polymethyl methacrylate, nitrocellulose, etc., as plasticizers, for example, dibutyl phthalate, dimethyl phthalate, butyl benzyl phthalate, butyl stearate, methyl abietate, polyethylene glycol, tricresyl phosphate, etc. However, as the dispersing agent, for example, fatty acid, fish oil, benzenesulfonic acid and the like are used. On the other hand, when an aqueous solvent is used as the solvent, as the binder, for example, acrylic acid polymer, ethylene oxide polymer, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol,
Isocyanate, wax, etc., as a plasticizer, for example, glycerin, dibutyl phthalate, ethyl toluenesulfonate, polyalkylene glycol, triethylene glycol, tributyl phosphate, etc., and as a dispersant,
For example, phosphate glass, allyl sulfonate and the like are used.

Next, a method for preparing the bonding material of the present invention will be described. FIG. 2 is an explanatory diagram illustrating an example of a method for preparing a bonding material according to the present invention. In the figure, for example, NiO powder pulverized to an average particle diameter of 7 μm and LaCr pulverized to an average particle diameter of 5 μm
The O-based ceramic powder is sampled so that its mixing ratio is within a predetermined range, for example, 65:35, and a solvent is added thereto and weighed (1), and thoroughly mixed with, for example, a pot mill (2). After drying (3), a binder, a plasticizer and / or a dispersant, if necessary, are added to the obtained mixed powder, weighed (4), mixed, kneaded (5), and then the slurry is mixed. After adjusting the clay (6) and then removing the air bubbles contained in the slurry (7), it is molded by, for example, a doctor blade method (8), and the obtained molded body is dried (9) and cut into a predetermined size ( 10) to form a green body of the bonding material.

Examples of the method for forming the green body include, in addition to the doctor blade method, an extrusion method and a tape casting method. When the bonding material is applied not as a green body but as a coating applied directly to the interconnector, the fuel-side electrode film, or the surface of the current collector, the bonding material slurry after the step (7) in FIG. Used as material. As a method for applying the bonding material slurry, for example, a brush coating method, a screen printing method, a spray method, a dipping method, a spin coater method, or the like is suitably used.

In the present invention, the thickness of the bonding material is, for example, 10 to 1000 μm, preferably 50 to 500 μm.
m. If the thickness of the joining material is too thin, the difference in thermal expansion cannot be absorbed, while if it is too thick, the electrical contact resistance tends to increase. The proportion of NiO in the thickness direction is 30 to 30% as the fuel electrode electrode film or the current collector approaches.
It is adjusted to increase by 100%, preferably in the range of 60-100%.

As a method for sequentially changing the proportion of NiO in the joining material, for example, a plurality of slurries of a composite material having sequentially different NiO contents are prepared, and a green body having sequentially different NiO contents is formed using the prepared slurry. , The green body is N
There are a method of laminating in the order of iO content, and a method of forming a bonding material layer by successively applying a slurry of a composite material having a different NiO content on the surface of a stack constituting material such as an interconnector.

In the present invention, a bonding material is interposed on a bonding surface between the interconnector and the fuel-side electrode or the fuel-side current collector abutting on the fuel-side electrode, and then the bonding is performed when firing while pressing the bonding surface. The pressure is, for example, 10 to 1000 g /
cm ^2, more preferably 50 to 500 g / cm ² , and the firing temperature is 1000 to 1500 ° C., more preferably 1200 to 500 g / cm ² .
1450 ° C. The firing atmosphere may be any of air, H ₂ gas and N ₂ gas. In the present invention, the interconnector is arranged between the single cells when forming a solid oxide fuel cell stack,
A joining member for electrically connecting the single cells.

[0019]

Next, specific examples of the present invention will be described.

Example 1 NiO powder having an average particle size of 7 μm and an average particle size of 5
μm La _0.7 Ca _0.3 CrO ₃ powder was mixed at the ratio shown in Table 1 below, toluene was added as a solvent, and the mixture was sufficiently kneaded with a pot mill, and toluene was evaporated from the mixture to obtain five types of mixed powder. Powder. To 100 g of the obtained composite material powder, 8 g of polyvinyl butyral dissolved in 200 ml of a mixed solvent of toluene and ethanol (volume ratio of 3: 2) was added, and the mixture was sufficiently mixed and kneaded in a pot mill to form a joining material slurry A to E. did.

[0020]

[Table 1] Next, the surface of the interconnector 7 consisting of La _0.7 Ca _0.3 CrO _3, the bonding material slurry A as the coating thickness is 100μm was applied, sufficient after drying, the bonding material slurry in the same manner thereon B, and thereafter, the joining material slurry C and the joining material slurry A are successively applied in this order to form a joining material layer having a thickness of 500 μm, and NiO—ZrO ₂ is formed on the surface of the interconnector on which the joining material layer is formed. -Y ₂ O ₃
Was baked at 1350 ° C. for 3 hours in an air atmosphere while being pressed with a force of 100 g / cm ² to obtain a joined body of the fuel-side current collector and the interconnector.

The obtained joined body was exposed to a hydrogen gas at 1000 ° C. (humidified at 30 ° C.) to measure the electrical contact resistance between the interconnector and the fuel-side current collector. Was 32 (mΩ · cm ² ) and the contact resistance after 5 heat cycles was 33 (mΩ · cm ² ). In addition, after 5 heat cycles, the term “from room temperature to 1000 ° C. and further 1000 ° C. in hydrogen gas (humidified at 30 ° C.)”
This means that after the heat history from the temperature to room temperature is repeated 5 times.

[0022]

Embodiment 2 Slurry B, Slurry C,
Example 1 described above except that the four kinds of the slurry D and the slurry E were used to repeatedly apply to form a bonding material layer having a thickness of 400 μm.
And the electrical contact resistance was measured in the same manner. The contact resistance immediately after joining was 19 (mΩ · c).
m ² ), the contact resistance after 5 thermal cycles is 18 (mΩ ·
cm ² ).

[0023]

Embodiment 3 Three types of joining material slurries, Slurry B, Slurry C and Slurry E, were applied in a thickness of 300 μm.
A bonded body was obtained in the same manner as in Example 1 except that a bonding material layer of m was formed, and the electrical contact resistance was measured in the same manner. The contact resistance immediately after bonding was 17 (mΩ · cm ² ), 5
The contact resistance after 18 thermal cycles was 18 (mΩ · cm ² ).

[0024]

Example 4 A joined body was obtained in the same manner as in Example 1 except that two types of joining material slurries, Slurry C and Slurry E, were applied repeatedly to form a joining material layer having a thickness of 200 μm. The contact resistance immediately after joining was 122 (mΩ · cm ² ), and the contact resistance after five thermal cycles was 209 (mΩ · cm ² ).

[0025]

[Comparative Example 1] Only slurry B was used as a joining material slurry.
A joined body was obtained in the same manner as in Example 1 except that a joining material layer having a thickness of 100 μm and having a uniform NiO content was formed, and the electrical contact resistance was measured in the same manner.
The contact resistance immediately after joining was 325 (mΩ · cm ² ), and the contact resistance after five thermal cycles was 571 (mΩ · cm ² ).

[0026]

Comparative Example 2 Example 1 except that no bonding material was used.
In the same manner as above to obtain a joined body, and in the same manner, the electrical contact resistance
When measured, the contact resistance immediately after joining was 829 (mΩ ·
cm ^Two) Contact resistance after 10 thermal cycles is 1014
(MΩ · cm^Two)Met. Examples 1-4 and Comparative Examples
Tables 1 and 2 summarize the results.

[0027]

[Table 2] In Table 2, in Examples 1 to 4 using the bonding material in which the ratio of NiO increases as approaching from the surface of the interconnector to the surface of the fuel-side current collector, Comparative Examples 1 and 4 using the bonding material in which the ratio of NiO is constant were used. It can be seen that the electrical contact resistance is significantly reduced as compared with Comparative Example 2 in which no bonding material was interposed. In Examples 2 and 3, the adhesion between the interconnector and the fuel-side current collector was extremely good, and the electrical contact resistance was very small, and did not increase even after five thermal cycles.

The electrical contact resistance of the first embodiment is higher than that of the second or third embodiment because the NiO content of the bonding material slurry A first applied to the interconnector surface is higher than that of the second or third embodiment.
This is considered to be due to the lower electric conductivity and the lower electric conductivity. The reason why the electrical contact resistance of Example 4 is higher than that of Examples 1 to 3 is that the number of layers of the bonding material slurry is small and La _0.7 C
a The surface of the interconnector made of _0.3 CrO ₃ is La
_It is considered that the difference in thermal expansion between the interconnector and the bonding material was not sufficiently reduced because the bonding material layer having a small proportion of _0.7 Ca _0.3 CrO ₃ was directly bonded.

[0029]

According to the invention described in claim 1 of the present application,
Without increasing the electrical contact resistance of the joint surface, and having excellent durability against thermal cycling, the interconnector and the fuel cell electrode film of the single cell or the current collector abutted on the fuel electrode film A joining material interposed on the joining surface is obtained.
According to the invention as set forth in claim 2 of the present application, in addition to the effects of the above invention, a bonding material having further reduced electrical contact resistance and higher bonding strength can be obtained.

According to the third aspect of the present invention, the interconnector and the fuel cell electrode film of the single cell or the current collector in contact with the fuel cell electrode film can be formed without increasing the electric contact resistance. In addition, the bonding can be performed with durability against heat cycles. According to the invention described in claim 4 of the present application, in addition to the effects of the above invention, the interconnector and the fuel-side electrode film or the current collector can be joined with higher joining strength. According to the invention described in claim 5 of the present application, the interconnector and the fuel-side electrode film of the single cell or the current collector contacting the fuel-side electrode film have a high bonding without increasing the electric contact resistance. A fuel cell stack joined with strength is obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method of joining a fuel cell stack according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing an example of a method for preparing a bonding material.

[Description of Signs] 1 ... Solid electrolyte membrane, 2 ... Fuel side electrode film, 3 ... Air side electrode film, 4 ... Single cell, 5 ... Fuel side current collector, 6 ... Air side current collector, 7 ... Interconnector , 8 ... joining material.

Claims (5)

[Claims] 1. A fuel cell comprising: a plurality of single cells each composed of a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both sides of the solid electrolyte membrane, respectively, electrically connected via an interconnector; When forming a stack, a bonding material to be interposed between the fuel cell electrode film of the single cell or the current collector abutted on the fuel cell electrode film and the interconnector, wherein NiO, Sr, Ca, Mg, Ti, Z
r, V, Mn, Fe, Co, Ni, Cu, Zn, Al,
It is made of a composite material containing LaCrO ₃ to which at least one element of Ba, Mo and Pb is added, and the existence ratio of the NiO is gradually increased as approaching the fuel-side electrode film or the current collector from the interconnector surface. A bonding material for a solid oxide fuel cell stack, comprising: 2. The method according to claim 1, wherein the proportion of the NiO is gradually increased in the range of 30% to 100% as the distance from the interconnector surface to the fuel-side electrode film or the current collector increases. Joining material. 3. A stack comprising a plurality of single cells each comprising a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both surfaces of the solid electrolyte membrane, respectively, electrically connected via an interconnector to form a stack. 3. A method for joining a solid oxide fuel cell stack to be formed, wherein said interconnector and a fuel cell electrode film of a single cell or a current collector in contact with said fuel electrode film are disposed between said interconnector and a single cell. 3. A method for joining a solid oxide fuel cell stack, comprising sintering with the joining material described in 1) interposed therebetween while pressing the joining surface. 4. The composite material slurry according to claim 1, wherein the NiO content is sequentially changed on the surface of the interconnector, the fuel-side electrode film, or the current collector, and the fuel is applied from the surface of the interconnector. The method according to claim 3, wherein the proportion of NiO in the bonding material is gradually increased in the range of 30% to 100% as approaching the side electrode film or the surface of the current collector. 5. A solid electrolyte type in which a large number of single cells each comprising a solid electrolyte membrane and a fuel-side electrode film and an air-side electrode film laminated on both sides of the solid electrolyte membrane are electrically connected via an interconnector. A fuel cell stack,
3. The bonding material according to claim 1 or 2, wherein a bonding surface of the interconnector and a fuel cell electrode film of a single cell or a current collector in contact with the fuel electrode film is interposed. Solid electrolyte fuel cell stack.