JP2010021155A - Solid oxide fuel battery stack and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce contact resistance between an air electrode of a cell and a metal separator. <P>SOLUTION: In a solid oxide fuel battery stack for connecting a plurality of single cells 4 of a flat-plate type solid oxide fuel battery wherein an electrolyte 2 made of oxide is sandwiched by the air electrode 1 and a fuel electrode 3 via the separator 5, the air electrode 1 and the separator 5 are joined by applying a conductive paste wherein a glass frit is added to conductive ceramic powder on a joining surface of the air electrode 1 against the separator 5. The glass frit having SiO<SB>2</SB>as a principal component has an added amount of 0.5-1.5% at a weight ratio against the principal component of the conductive paste, a softening point of the glass frit is lower than operation temperature of the solid oxide fuel battery, and crystallization temperature is higher than the operation temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technology for connecting a single cell air electrode and a separator in a solid oxide fuel cell stack in which a plurality of solid oxide fuel cell single cells are connected via a separator, and in particular, a metal as a separator material. The present invention relates to a solid oxide fuel cell stack to be used and a manufacturing method thereof.

  In a solid oxide fuel cell in which a fuel electrode and an air electrode are arranged via a ceramic electrolyte, and power is generated by supplying a fuel such as hydrogen and an oxidant such as air, the power generation is practically sufficient. In order to obtain electric power, it is necessary to electrically connect a plurality of unit components (single cells) of the solid oxide fuel cell. Separate the fuel gas and oxidant gas of adjacent single cells, supply the fuel gas to the fuel electrode of the single cell, and electrically connect the individual cells while supplying the oxidant gas to the air electrode In order to do so, a separator with high electron conductivity is used.

  In the conventional solid oxide fuel cell, since the operating temperature is as high as 1000 ° C., a separator made of ceramics such as lanthanum chromite has been used. However, in recent years, as solid oxide fuel cell single cells capable of operating even at temperatures of about 800 ° C. have been developed, separators mainly composed of heat-resistant alloys have become available. This separator made of a heat-resistant alloy is advantageous in that it is less expensive than a ceramic separator, has good workability, and has high electron conductivity.

  When the separator and the single cell are electrically connected, the effective contact area is reduced due to the warpage of the single cell and the unevenness of the electrode, and the power generation loss caused by the contact resistance between the single cell and the separator is large. There was a problem. Therefore, after applying a paste mixed with an organic solvent such as ethanol and toluene to the air electrode, the air electrode and the separator are joined, and the air electrode and the separator are heat-treated at 1400 ° C. to 1500 ° C. for 1 to 10 hours. Has proposed a method for reliably connecting the air electrode and the separator at low cost (see, for example, Patent Document 1 and Non-Patent Document 1).

Japanese Patent Laid-Open No. 6-223846

Keqin Huang, Peggy Y. Hou, John B. Goodenough, “Characterization of iron-based alloy interconnects for reduced temperature solid oxide fuel cells”, Solid State Ionics 129, p.237-250, 2000

However, in the methods disclosed in Patent Document 1 and Non-Patent Document 1, when a metal separator is used, the metal separator is oxidized by heat treatment at a high temperature, so that the effect of reducing the contact resistance between the air electrode and the separator is insufficient. There was a problem that there was.
The object of the present invention is to solve the above-mentioned problems of the prior art and to reduce the contact resistance between the air electrode of the cell and the separator when connecting a plurality of solid oxide fuel cell single cells via the separator. It is in.

The present invention relates to a solid oxide fuel cell stack in which a plurality of flat plate type solid oxide fuel cell single cells formed by sandwiching an oxide electrolyte between an air electrode and a fuel electrode are connected via a metal separator. And a conductive paste in which a glass frit is added to a conductive ceramic powder between the air electrode of the single cell and the metal separator, the glass frit having SiO ₂ as a main component, and the conductive It has an addition amount of 0.5% to 1.5% by weight with respect to the main component of the paste, the softening point is lower than the operating temperature of the solid oxide fuel cell, and the crystallization temperature is the above-mentioned operation It is characterized by being higher than the temperature.

The present invention also relates to a solid oxide fuel in which a plurality of flat plate type solid oxide fuel cell single cells formed by sandwiching an oxide electrolyte between an air electrode and a fuel electrode are connected via a metal separator. In the method for manufacturing a battery stack, a conductive paste in which glass frit is added to conductive ceramic powder is applied to a joint surface of the air electrode of the single cell with the metal separator, and then the air electrode and the metal separator are applied. The glass frit is composed mainly of SiO _{2 and} has an additive amount of 0.5% to 1.5% by weight with respect to the main component of the conductive paste. The softening point is lower than the operating temperature of the solid oxide fuel cell, and the crystallization temperature is higher than the operating temperature.

  According to the present invention, a conductive paste in which glass frit is added to conductive ceramic powder is applied to the joint surface of a single cell air electrode with a metal separator, so that heat treatment at a high temperature as in the prior art is required. In addition, the contact resistance between the air electrode and the metal separator can be reduced, and a low contact resistance can be realized stably for a long time. Further, in the present invention, the adhesive strength between the air electrode and the metal separator can be increased by making the softening point of the glass frit lower than the operating temperature of the solid oxide fuel cell. The reason is that the glass frit softens at the operating temperature, thereby strengthening the bond between the main components of the conductive paste or between the main components of the conductive paste and the air electrode. In the present invention, the crystallization temperature of the glass frit is set higher than the operating temperature, whereby the adhesive strength can be improved without hindering the diffusion of gas to the air electrode. This is because the crystallization temperature of the glass frit is higher than the operating temperature, so that the glass frit is not softened to a liquid state. Furthermore, in the present invention, the glass frit is added at a ratio of 0.5% to 1.5% by weight with respect to the main component of the conductive paste, thereby improving the contact resistance between the air electrode and the metal separator. Can be reduced.

It is sectional drawing which shows the structure of the single cell of the solid oxide fuel cell used as embodiment of this invention. It is a figure which shows the structure of the solid oxide fuel cell stack which laminated | stacked several single cells of FIG. It is sectional drawing which shows the sample for verifying the effect of embodiment of this invention. It is sectional drawing which shows a mode that the electrically conductive paste was apply | coated between the two sample pieces of FIG. It is a figure which shows the result of having measured the resistance between the two sample pieces of FIG. It is a figure which shows the result of having measured the time change of resistance about each of the sample which apply | coated the glass frit addition conductive paste, and the sample which apply | coated the glass frit non-addition conductive paste.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the configuration of a single cell of a solid oxide fuel cell according to an embodiment of the present invention. A unit cell 4 of a solid oxide fuel cell is formed by sandwiching a solid electrolyte layer 2 made of a flat plate oxide between a flat plate air electrode 1 and a flat plate fuel electrode 3. Examples of the material of the solid electrolyte layer 2 include yttria-stabilized zirconia (YSZ), samaria-stabilized zirconia (SSZ), scandia-stabilized zirconia (ScSZ), and cobalt-added lanthanum gallate oxide (LSGMC). Examples of the material of the air electrode 1 include lanthanum nickel ferrite (LNF), lanthanum manganate (LSM), lanthanum strontium cobaltite (LSC), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF), and samarium strontium cobaltite. (SSC). Examples of the material of the fuel electrode 3 include Ni such as nickel-doped yttria-stabilized zirconia (Ni-YSZ), nickel-doped samaria-stabilized zirconia (Ni-SSZ), nickel-doped scandia-stabilized zirconia (Ni-ScSZ), and the solids. There is a mixture with the material of the electrolyte layer.

In order to produce a stack structure in which a plurality of single cells 4 are stacked, each single cell 4 is electrically connected via a separator 5 as shown in FIG. As a material of the separator 5, for example, there is a heat-resistant alloy such as a ferritic alloy containing about 16-25% of Cr.
The present embodiment provides a method for connecting the air electrode 1 and the separator 5 when manufacturing a solid oxide fuel cell stack, and this connection method will be described below.

First, an LNF powder is prepared as a conductive ceramic, glass frit is added to the LNF powder, and an organic solvent such as toluene is further added to prepare a conductive paste in advance. The glass frit to be added has a softening point lower than the operating temperature of the solid oxide fuel cell (for example, 800 ° C.) and a crystallization temperature higher than the operating temperature of the solid oxide fuel cell. Furthermore, the shape is powdery, and it is preferable that the particle size of the ceramic powder is smaller than the ceramic powder because glass frit enters between the ceramic (for example, LNF) powder to be used. Further, the component is preferably composed mainly of SiO ₂ because the operating temperature of the solid oxide fuel cell is high.
Next, in order to verify the effect of reducing the contact resistance between the air electrode and the separator according to the present embodiment, a flat sample piece 6 made of LNF corresponding to the air electrode 1 and a heat resistant alloy corresponding to the separator 5 are used. A flat sample piece 7 is prepared as a sample. Two platinum lead wires 8 are electrically connected to the sample piece 6, and similarly, two platinum lead wires 9 are electrically connected to the sample piece 7.

  Then, as shown in FIG. 4, a conductive paste 10 prepared in advance is applied between the sample piece 6 and the sample piece 7 to electrically connect the sample piece 6 and the sample piece 7. The sample of FIG. 4 produced in this way is left in air at 800 ° C. for 100 hours, and the resistance between the lead wire 8 and the lead wire 9, that is, the resistance between the sample piece 6 and the sample piece 7 ( Area Specific Resistance (hereinafter referred to as ASR) was measured. The measurement results are shown in FIG.

  As can be seen from the results of FIG. 5, it can be seen that the ASR becomes smaller when the glass frit is added to the conductive paste 10 than when the amount of the glass frit added to the conductive paste 10 is zero. The reason for this is that the softening temperature of the glass frit is lower than the operating temperature (800 ° C.) of the solid oxide fuel cell, so that the glass frit softens at the operating temperature, and the particles of LNF which are the main components of the conductive paste 10 This is because the bond between the LNF particles and the sample piece 6 becomes stronger and the adhesive strength between the sample piece 6 and the sample piece 7 becomes stronger.

  It is expected from the measurement results shown in FIG. 5 that the amount of glass frit added is increased by 10% or more by weight with respect to the main component of the conductive paste 10 than when no glass frit is added. The Therefore, the addition amount of the glass frit is preferably at most 10% by weight with respect to the main component of the conductive paste 10. Moreover, it is particularly preferable that the addition amount of the glass frit is 0.5% to 1.5% by weight with respect to the main component of the conductive paste 10. The reason is that the effect on the conductivity of the conductive paste 10 is small, and the adhesion strength between the air electrode and the separator (sample piece 7) is improved without disturbing the diffusion of gas to the air electrode (sample piece 6). Because you can.

Next, an LNF powder is prepared as a conductive ceramic, a glass frit having a softening point lower than 800 ° C. is prepared, and the amount of the glass frit added is 1% by weight with respect to the LNF powder. Glass frit was added, and an organic solvent such as toluene was further added to prepare a glass frit-added conductive paste.
For comparison with the glass frit-added conductive paste, an organic solvent such as toluene was added to the LNF powder to prepare a glass frit-free conductive paste.

  Then, in the same manner as described above, a glass frit-added conductive paste is applied between the sample piece 6 and the sample piece 7, and a glass frit-free conductive paste is applied between the sample piece 6 and the sample piece 7. Were made. The ASR after leaving these two samples in air at 800 ° C. for 10 hours and the ASR after leaving them for 100 hours were measured in the same manner as described above for each of the two samples. The measurement results are shown in FIG.

  As can be seen from FIG. 6, in the sample coated with the glass frit-free conductive paste, the ASR value is high, and the ASR value increases with time. On the other hand, in the sample coated with the glass frit-added conductive paste, not only a low ASR value is obtained, but also the ASR value is stabilized over a long time.

  From the results shown in FIG. 5 and FIG. 6, in this embodiment, if the air electrode and the separator are combined with each other after the glass frit-added conductive paste is applied to the joint surface of the air electrode and the separator, Thus, strong adhesion can be realized without requiring heat treatment at such a high temperature, and the contact resistance between the air electrode and the separator can be reduced. Further, a low contact resistance can be realized stably for a long time. Furthermore, in this embodiment, since the crystallization temperature of the glass frit is higher than the operating temperature of the solid oxide fuel cell, the adhesive strength can be improved without hindering the diffusion of gas to the air electrode.

  In addition, this invention is not limited to the above embodiment. For example, the conductive paste is mainly composed of at least one metal selected from Fe, Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au or an alloy containing the metal, and is made of glass frit. May be added in the range of the aforementioned weight ratio with respect to the main component (hereinafter referred to as conductive paste A). In particular, Ag, Pt, Au, and Pd are desirable as the metal as the main component of the conductive paste A, and among them, Ag that is inexpensive, has the highest conductivity, and is stable in a high-temperature oxidizing atmosphere is preferable.

  The conductive paste is mainly composed of conductive ceramics containing La element, M element (M is any one element of Ni, Fe, Cu, Co, and Mn) and O element. The conductive ceramic may be added in the range of the weight ratio described above, and this conductive ceramic further contains an element A (A is any one element of Sr, Ca, and Ba). It may also contain M ′ element (M ′ is one element different from M element among Ni, Fe, Cu, Co, and Mn). These conductive pastes are hereinafter referred to as conductive paste B.

In particular, LaNi _1-y Fe _y O ₃ , La _1-x Sr _x Co _1-y Fe _y O ₃ , La _1-x Sr _x CoO ₃ , La _1-x Sr _x MnO ₃ and La _1-x Sr _x CuO _3-d (where x satisfies 0 <x <1, y satisfies 0 <y <1 and d satisfies 0 <d <1) Among them, LaNi _1-y Fe _y O ₃ or La _1-x Sr _x Co _1-y Fe _y O ₃ having high conductivity is preferable as a main component.

The conductive paste is mainly composed of a mixture of the metal used in the conductive paste A and the conductive ceramic used in the conductive paste B, and the glass frit is added in the above-mentioned weight ratio range with respect to the main component. It may be what has been done. In particular, it is preferable that a main component is a mixture of Ag and LaNi _1-y Fe _y O ₃ or La _1-x Sr _x Co _1-y Fe _y O ₃ .

  In this embodiment, an organic solvent such as toluene is used as a solvent for dispersing the main component of the conductive paste and the glass frit, and a conventionally known one can be used for this solvent. There is no particular limitation.

In the present embodiment, as a method of laminating the single cells, a method of joining the air electrode and the separator after applying the glass frit-added conductive paste on the air electrode is described. However, the present invention is not limited to this. Instead, a material such as a current collector may be sandwiched between the air electrode coated with the glass frit-added conductive paste and the separator.
In this embodiment, the case of using a metal separator has been described. However, the present invention is not limited to this, and the present invention can also be applied to the case of using an oxide separator.

  The present invention can be applied to a solid oxide fuel cell stack.

  DESCRIPTION OF SYMBOLS 1 ... Air electrode, 2 ... Solid electrolyte layer, 3 ... Fuel electrode, 4 ... Single cell, 5 ... Separator.

Claims (2)

In a solid oxide fuel cell stack in which a plurality of flat solid oxide fuel cell single cells formed by sandwiching an oxide electrolyte between an air electrode and a fuel electrode are connected via a metal separator,
Between the air electrode of the single cell and the metal separator, a conductive paste in which glass frit is added to conductive ceramic powder,
The glass frit has SiO ₂ as a main component, has an addition amount of 0.5% to 1.5% by weight with respect to the main component of the conductive paste, and has a softening point of a solid oxide fuel A solid oxide fuel cell stack characterized by being lower than the operating temperature of the battery and having a crystallization temperature higher than the operating temperature. In a manufacturing method of a solid oxide fuel cell stack in which a plurality of flat plate type solid oxide fuel cell single cells formed by sandwiching an oxide electrolyte between an air electrode and a fuel electrode are connected via a metal separator ,
A conductive paste in which glass frit is added to conductive ceramic powder is applied to the bonding surface of the single cell air electrode to the metal separator, and then the air electrode and the metal separator are bonded. Is,
The glass frit has SiO ₂ as a main component, has an addition amount of 0.5% to 1.5% by weight with respect to the main component of the conductive paste, and has a softening point of a solid oxide fuel A method for producing a solid oxide fuel cell stack, characterized in that the operating temperature of the battery is lower and the crystallization temperature is higher than the operating temperature.

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