JP2007194170A - Flat plate type solid oxide fuel cell and method for producing the same - Google Patents

Abstract

Cell warpage is suppressed.
An electrolyte 2 is laminated on an electrode support 1 that becomes an air electrode or a fuel electrode, the electrode support 1 and the electrolyte 2 are integrally sintered, and a counter electrode 3 is formed on the sintered electrolyte 2. Form the cell. In the entire sintering process, the shrinkage rate of the electrolyte material is always equal to or higher than the shrinkage rate of the electrode support. Further, assuming that the thickness of the electrode support 1 is Da and the thickness of the electrolyte 2 is De, the ratio De / Da of the thickness of the electrode support 1 and the electrolyte 2 is 0.001 to 0.015.
[Selection] Figure 1

Description

  The present invention relates to an electrode-supported flat solid oxide fuel cell, and more particularly to a flat solid oxide fuel cell that improves cell reliability and output characteristics.

  Solid oxide fuel cells have higher electrical conversion efficiency and power density than other fuel cells, and are therefore actively being developed as distributed power sources. In solid oxide fuel cells, since solid oxide ceramics are used as an electrolyte, the operating temperature is higher than other fuel cells in order to ensure sufficiently high ion conductivity. As a general constituent material, stabilized zirconia is used as an electrolyte, a rare earth-doped lanthanum-based composite oxide is used as an air electrode, and nickel-zirconia cermet is used as a fuel electrode. All constituent parts of the battery are ceramic materials, and have a laminated structure of different materials. The cell structure can be roughly divided into a cylindrical type and a flat plate type. From the viewpoint of cell performance, a flat plate cell in which a thin film electrolyte is formed using an air electrode or a fuel electrode as a support is widely applied (for example, non-patent literature). 1).

"Fuel cell power generation technology development: Elemental research on expanding R & D applicability of solid oxide fuel cells (study on thermal shock-resistant flat plate cell stack)", 2003-2004 NEDO commissioned work results report, Tokyo Gas Co., Ltd., p. 44, 2005

  In general, since the electromotive force of a single cell of a fuel cell is as small as about 1 V, in order to obtain a practically sufficient output, a stack in which a plurality of cells are connected is formed to generate power. In a flat type fuel cell stack, plate-like cells and current collecting members are sequentially stacked and pressed to connect the cells, but flatness of the cells is required for a good electrical connection. In addition, since compressive stress is applied to the cell during stack formation and power generation, if the flatness is insufficient, the stress may concentrate on a part of the cell, causing damage and reducing reliability. There is.

  In general, an electrode-supported flat-plate solid oxide fuel cell uses an air electrode or a fuel electrode as an electrode support, laminates this electrode support and an electrolyte, and integrally sinters them, and then forms a counter electrode on the electrolyte surface. To make. However, in the integrated sintering process of ceramics of different materials, stress is generated at the interface due to the following two factors, and this stress may cause cracking and warping in the cell. One of the causes of stress is the difference in shrinkage behavior between materials during sintering, and the other is the difference in coefficient of thermal expansion between materials in the temperature lowering process after sintering. Each dimensional change is about 10 to 25% due to the difference in shrinkage behavior between materials during sintering, whereas it is due to the difference in thermal expansion coefficient between materials in the temperature lowering process after sintering. It is about 1-2%. Therefore, it is considered that the difference in shrinkage behavior between materials during sintering has a great influence on cell warpage and cracking.

  In order to suppress such cracks and warpage, in principle, it is considered effective to match the sintering behavior of each material powder, that is, to match the shrinkage rate of each material powder in the entire process during sintering. However, since the electrolyte constituting the cell is required to be dense, and one electrode substrate is required to be porous for good gas diffusion, it is difficult to completely match the shrinkage rates of the material powders. In general, powders with high sinterability (ie, high shrinkage) are used for the production of dense sintered bodies, and powders with low sinterability (low shrinkage) are used to form porous sintered bodies. Because it is used. In addition, even if the shrinkage rates after the completion of sintering coincide with each other, if there is a deviation in the shrinkage behavior in the sintering process, the sintered body may be cracked or warped.

  Cell cracking and warping are also affected by the ratio of the thickness of the electrode support to the electrolyte. In general, electrolyte materials and electrode materials use materials with higher sinterability (larger shrinkage), but in order to suppress stress during sintering, the thickness of the electrolyte has a higher shrinkage rate. It is effective to sufficiently increase the thickness of the electrode support. However, as described in Non-Patent Document 1, it is not possible to sufficiently suppress cell warping simply by changing the thickness, and warpage in the mm order occurs in the range of the actual thickness of the cell. Such cell warpage has a particularly significant effect in the production of a large-sized cell having a practical size, and therefore needs to be improved.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a flat-plate solid oxide fuel cell capable of suppressing cell warpage and a method for manufacturing the same.

The flat plate solid oxide fuel cell of the present invention and the method for producing the same, in the process of sintering by laminating an electrolyte on an electrode support serving as an air electrode or a fuel electrode and integrally sintering the electrolyte, It is characterized in that the shrinkage rate is always greater than or equal to the contraction rate of the electrode support.
The difference in shrinkage between the electrode support and the electrolyte during firing is preferably 3% to 8%.
Further, in the flat solid oxide fuel cell and the manufacturing method thereof according to the present invention, when the thickness of the electrode support is Da and the thickness of the electrolyte is De, the ratio De / Da between the electrode support and the electrolyte is 0. 0.001 to 0.015.

  According to the present invention, the following effects can be obtained. Conventionally, in electrode-supported flat solid oxide fuel cells, it is necessary to suppress cell warpage, but due to the difference in shrinkage characteristics between the electrode support and the electrolyte during cell sintering, the cell warps and warps. For the suppression, it has been necessary to strictly adjust the sintering characteristics of the material powder. In addition, it is known that it is effective to increase the thickness of the electrode support relative to the electrolyte in order to suppress the warp. However, with this alone, there is a limit to the suppression of the warp within the practical cell thickness range. there were. In the present invention, the sintering characteristics of the electrode support and the electrolyte are adjusted, and the shrinkage rate of the electrolyte is always equal to or greater than the shrinkage rate of the electrode support in the entire sintering process, thereby suppressing the warpage of the cell. Damage can be avoided. As a result, the conventional flat type solid oxide fuel cell has a warpage of mm order, but the warpage of the cell can be suppressed to 1/10 or less, and the current collection state of the cell is improved. The output characteristics can be greatly improved. Further, since the flatness of the cells is improved, the damage of the cells at the time of stacking is suppressed, so that the reliability of the cell stack is improved.

  Moreover, in this invention, the curvature of a cell can be further suppressed by limiting the ratio of the thickness of an electrode support body and electrolyte.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of a cell of a flat plate type solid oxide fuel cell according to a first embodiment of the present invention.
A flat solid oxide fuel cell includes an electrode support 1, an electrolyte 2 formed on the electrode support 1, and a counter electrode 3 of the electrode support 1 formed on the electrolyte 2. The When the electrode support 1 is an air electrode, the counter electrode 3 is a fuel electrode, and when the electrode support 1 is a fuel electrode, the counter electrode 3 is an air electrode. In order to configure a fuel cell stack using cells as shown in FIG. 1, cells and current collecting members (separators) may be alternately stacked.

In this embodiment, in order to see the effect of the sintering characteristics of the electrode support material and the electrolyte material on the sintered body in the production of the electrode support type cell as shown in FIG. The support 1 and the electrolyte 2 were integrally sintered to prepare a half cell composed of the electrode support 1 and the electrolyte 2. As the constituent material of the half cell, as the material of the electrolyte 2, stabilized zirconia (ZrO ₂ —Y ₂ O ₃ , hereinafter referred to as YSZ) having an average particle diameter of 0.1 to 0.5 μm and a specific surface area of 7 to 17 m ² / g. La (Sr), which is a complex oxide having a perovskite structure with an average particle size of 1.7 to 1.9 μm and a specific surface area of 5 to 7 m ² / g as a material for the air electrode (electrode support 1). ) MnO ₃ (hereinafter abbreviated as LSM) was used.

  The half cell was produced by the following procedure. First, a sheet of the electrolyte 2 having a thickness of 20 to 50 μm is produced by the doctor blade method, and a plurality of sheets of the air electrode (electrode support 1) having a thickness of 300 to 600 μm are produced by the doctor blade method. After the air electrode sheet is dried, a plurality of air electrode sheets are stacked until the thickness of the air electrode reaches about 1 mm, and a single sheet of the electrolyte 2 is stacked on the air electrode and hot-pressed. The laminated body after hot pressing was appropriately cut out and sintered to prepare a half cell.

  In the present embodiment, three types of half cells having different sinterability of the electrolyte 2 (that is, characteristics of shrinkage rate in the sintering process) were produced. The shrinkage rate is obtained by ΔL / L where L is the original dimension and ΔL is the amount of shrinkage due to sintering. Hereinafter, three types of electrolytes 2 having different sinterability will be referred to as YSZ1, YSZ2, and YSZ3. In order to produce three types of electrolytes YSZ1 to YSZ3 having different sinterability, heat treatment of the raw material YSZ powder may be performed, and the temperature of the heat treatment at this time may be changed. The temperature of heat processing shall be high in order of YSZ3, YSZ2, YSZ1.

  The sintering behavior of the air electrode (electrode support 1) and the electrolytes YSZ1 to YSZ3 is shown in FIG. The horizontal axis in FIG. 2 is the temperature during sintering, and the vertical axis is the coefficient of thermal expansion. In FIG. 2, the shrinkage rate increases as the coefficient of thermal expansion goes to the negative side. According to FIG. 2, the electrolytes YSZ1 to YSZ3 generally have a large shrinkage rate, and rapidly shrink at a temperature higher than 1000 to 1200 ° C., and the air electrode sinters slowly from 1100 ° C. The inclination is small.

  While YSZ1 starts shrinking from the lowest temperature among the electrolyte materials, YSZ2 and YSZ3 shrink from higher temperatures, and it seems that the sintering behavior approaches the LSM of the air electrode material. Further, the electrolyte YSZ1 always shows a larger shrinkage rate than the air electrode, the electrolyte YSZ2 has a slightly smaller shrinkage rate than the air electrode in the vicinity of 1100 to 1200 ° C., and the electrolyte YSZ3 has a shrinkage rate near 1100 to 1300 ° C. than the air electrode. However, the shrinkage rate is significantly reduced. That is, the electrolytes YSZ2 and YSZ3 generally have a larger shrinkage rate than the air electrode, but a reversal phenomenon occurs in which the shrinkage rate is smaller than the air electrode in some temperature ranges.

  The shrinkage start temperature of the electrolytes YSZ1 to YSZ3 when the three types of half cells are sintered, the difference in shrinkage between the electrolytes YSZ1 to YSZ3 and the air electrode (electrolytic shrinkage-air electrode shrinkage), and the half cell after sintering Table 1 shows the state.

  The shrinkage difference is a value at 1300 ° C. In the half cell using the electrolytes YSZ2 and YSZ3 where the shrinkage rate difference with the air electrode is small and the shrinkage rate is smaller than the air electrode in a part of the temperature range, damage was confirmed, but at each temperature, In the half cell using the electrolyte YSZ1 having a large shrinkage rate, no damage was observed.

  The reason why the state of the half cell after sintering is divided is considered to be related to the ratio of the thickness of the air electrode and the electrolytes YSZ1 to YSZ3. In the integrated sintering of ceramics laminated with different materials, it is considered that stress is generated at the interface between different materials due to the material having a large shrinkage rate. Further, when the material having the larger shrinkage rate is thin, it is considered that the stress between the materials can be kept small even if there is a certain amount of shrinkage rate difference with the other material. However, it is considered that a larger stress is generated at the interface when the material having a larger thickness has a larger shrinkage rate. In the laminate of the air electrode and the electrolyte, the thickness of the air electrode is larger than that of the electrolyte.Therefore, when the shrinkage rate of the air electrode is larger than that of the electrolyte, the stress is larger than when the shrinkage rate of the electrolyte is larger than that of the air electrode. Is considered to occur. As described above, the electrolytes YSZ2 and YSZ3 have a temperature range in which the contraction rate of the air electrode is larger. Therefore, in the half cell using the electrolytes YSZ2 and YSZ3, between the air electrode and the electrolytes YSZ2 and YSZ3. It is considered that a large stress was generated at the interface, and the half cell was damaged by this stress.

  From the above, it can be seen that in the integral sintering of the electrode support type cell, it is desirable that the electrolyte material with a small thickness always has a larger shrinkage rate than the electrode support material in the entire process during the sintering. Although it is ideal that the shrinkage rate of the electrolyte material and the electrode support material match during the entire process during sintering, such a perfect match is actually difficult. It is sufficient that the shrinkage rate is larger than that of the support material.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the present embodiment, the material of the electrolyte 2 is scandia-stabilized zirconia (Zr (Sc, Al ₂ O ₃ ) O _{2 having} an average particle diameter of 0.4 to 0.7 μm and a specific surface area of 10 to 12 m ² / g, Hereinafter, SASZ was used, and a mixture of SASZ and nickel oxide was used as the material for the fuel electrode (electrode support 1).

  The half cell was produced by the following procedure. First, an SASZ electrolyte slurry is formed on the fuel electrode green body by screen printing. Then, the fuel electrode and the electrolyte were integrally sintered to produce a half cell. In the present embodiment, two kinds of half cells were produced using two kinds of NiO powders having different sinterability as nickel oxide of the fuel electrode. Hereinafter, two types of NiO powders having different sinterability are referred to as NiO1 and NiO2. Table 2 shows the average particle diameters, specific surface areas of nickel oxides NiO1 and NiO2, and the difference in shrinkage between the fuel electrode and the electrolyte (electrolytic shrinkage-fuel electrode shrinkage).

  The shrinkage difference is a value at 1300 ° C. In the case of the fuel electrode using either nickel oxide NiO1 or NiO2, the shrinkage rate is higher in the electrolyte than in the fuel electrode from the temperature at which shrinkage starts, and in the fuel electrode using nickel oxide NiO1, the shrinkage rate is higher. Close to the electrolyte shrinkage. Here, as shown in FIG. 1, the thickness of the fuel electrode (electrode support 1) is Da, and the thickness of the electrolyte 2 is De. By changing the thickness of the fuel electrode, the ratio De / Da of the fuel electrode and the electrolyte is adjusted to 0.012 to 0.024, and the warpage of the half cell at this time is measured around 1300 ° C. (1300 to 1350 ° C.). did. The measurement result of the half cell warpage is shown in FIG.

  In FIG. 3, the horizontal axis represents the ratio De / Da of the thickness of the fuel electrode (electrode support 1) and the electrolyte 2, and the vertical axis represents the half cell warp. Warp was measured as shown in FIG. The measurement was performed with a half cell having an outer diameter of 60 mm. In FIG. 3, NiO1 means a half cell using SASZ and nickel oxide NiO1 as the fuel electrode, and NiO2 means a half cell using SASZ and nickel oxide NiO2 as the fuel electrode.

  In either fuel electrode, the warpage of the half cell tended to decrease as the ratio De / Da decreased, but the fuel electrode (NiO 2) having a smaller shrinkage rate tended to have a smaller warpage. This coincides with the fact that in the first embodiment, no damage occurred in the half cell using the electrolyte YSZ1 that always shows a larger contraction rate than the air electrode. That is, in the electrolyte and the fuel electrode, the electrolyte has a larger shrinkage rate, and the sintering is completed in a short time. On the other hand, since the fuel electrode is sintered even after the electrolyte contraction is completed, stress is generated at the interface between the electrolyte and the fuel electrode.

It is considered that the warping of the sintered body increases because the stress applied to the sintered body increases as the shrinkage ratio of the thick material increases. That is, a fuel electrode (NiO2) having a small shrinkage rate is more preferable than a fuel electrode (NiO1) having a large shrinkage rate from the viewpoint of suppressing cell warpage (a shrinkage rate difference of 3% to 8% with respect to the electrolyte). On the other hand, even if the contraction rate of the fuel electrode decreases and the difference in contraction rate between the electrolyte and the fuel electrode becomes too large, cell damage or electrolyte leakage may occur. So far, the inventor has found that when the difference in shrinkage between the electrolyte and the fuel electrode exceeds 8%, the densification of the electrolyte is hindered due to the low shrinkage of the fuel electrode during the integral sintering of the fuel electrode and the electrolyte. It has been confirmed that the rate of leakage increases. From the above results, when the electrolyte is sufficiently thin, rather, the fuel electrode side is within the allowable range (the difference in shrinkage from the electrolyte is 3 to 8%). From this point of view, it is considered desirable.
Although the case where the electrode support 1 is a fuel electrode has been described in the present embodiment, the present invention can be similarly applied to the case where the electrode support 1 is an air electrode.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. By further reducing the thickness ratio of the electrode support 1 and the electrolyte 2 in the second embodiment, cell warpage can be suppressed. In the present embodiment, the cell was manufactured as follows. The above-mentioned NiO2 was used for the nickel oxide of the fuel electrode (electrode support 1). An electrolyte slurry of SASZ was formed on a NiO-SASZ fuel electrode green body having a thickness of 1 to 2 mm to a thickness of about 10 to 20 μm by a screen printing method, and this was sintered to prepare a half cell. The sintered fuel electrode (electrode support 1) has a thickness of 1 to 2 mm, and the electrolyte 2 has a thickness of 5 to 15 μm.

  FIG. 3 shows the result of measuring the warpage of the half cell thus produced. NiO 2 ′ in FIG. 3 indicates the warpage of the half cell produced in the present embodiment. Similar to the second embodiment, the outer diameter of the half cell is 60 mm. According to this measurement result, it is understood that the warpage of the half cell can be suppressed to 100 μm or less by setting the ratio De / Da of the thickness of the fuel electrode (electrode support 1) and the electrolyte 2 to 0.01 or less.

  A larger-diameter cell can also be produced in the same manner. FIG. 5 shows the measurement results of the warpage of a half cell having an outer diameter of 100 mm using SASZ and nickel oxide NiO 2 as the fuel electrode. As can be seen from FIG. 5, even in a half cell having an outer diameter of 100 mm, the warp of the half cell can be suppressed to around 100 μm by making the ratio De / Da of the thickness of the fuel electrode and the electrolyte 2 smaller than 0.01.

  From the results of FIG. 3, it can be seen that when the ratio De / Da of the thickness of the fuel electrode (electrode support 1) and the electrolyte 2 approaches 0, the value of cell warpage also approaches 0. However, the ratio De / Da cannot actually be set to zero. In order to reduce the ratio De / Da, it is necessary to make the electrolyte thickness De as small as possible and the fuel electrode thickness Da as large as possible. De and Da each have a limit of values that can actually be taken from the viewpoint of the strength of the electrolyte, the gas diffusivity in the electrode, and the volume output density of the cell. As a practical lower limit, the ratio De / Da is It is considered to be about 0.001.

[Fourth Embodiment]
An air electrode (counter electrode 3) made of LaNi (Fe) O ₃ was formed on the electrolyte 2 of the half cell produced in the second and third embodiments to produce a cell as shown in FIG. In order to see the influence of the cell warpage on the power generation output, cells having different warp sizes were produced by changing the ratio De / Da of the thickness of the fuel electrode and the electrolyte 2, and the power generation characteristics of the cell were measured. The measurement was performed in a cell having an outer diameter of 60 mm, and a heat-resistant alloy holder was used. The cell was installed in this holder, and the cell and the holder were sealed with glass to prevent mixing of fuel gas and oxidant gas. A heat-resistant conductive paste was applied to the air electrode surface, an upper holder was installed, and a weight was applied from above to fix the holder. The holder set in this way was installed in an electric furnace, and air and pure hydrogen were supplied to the cell at 800 ° C. to generate electricity.

  The results of measuring the power generation characteristics of the cell are shown in FIG. In FIG. 6, the horizontal axis represents cell warpage, and the vertical axis represents power. According to FIG. 6, the power generation output tends to increase as the warpage of the cell decreases. Assuming that the practical output of a single cell is 10 W, it was confirmed that an output with a target value of 10 W or more can be obtained in a cell in which the warpage of the cell is suppressed to 150 μm or less. From FIG. 3, it can be seen that the ratio De / Da of the thickness of the fuel electrode to the electrolyte 2 should be smaller than 0.015 in order to make the cell warpage 150 μm or less.

  In a conventional electrode-supported flat plate cell, the warpage of the cell exists on the order of several hundred μm to mm. As a result, when the cells are stacked to generate power, current collection in the electrode surface direction cannot be sufficiently performed, The output was insufficient. By adjusting the sintering shrinkage characteristics of the constituent material of the cell of the present invention and the thickness of the constituent material, the cell warpage is suppressed to 150 μm or less, so that the contact between the cell and the holder during stacking is improved, and the current collecting resistance Therefore, the power generation output can be improved.

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

It is sectional drawing which shows the structure of the cell of the flat type solid oxide fuel cell which concerns on the 1st Embodiment of this invention. It is a figure which shows the sintering behavior of the air electrode and electrolyte in the 1st Embodiment of this invention. It is a figure which shows the relationship between the ratio of the thickness of an electrolyte and a fuel electrode, and the curvature of a half cell with an outer diameter of 60 mm. It is sectional drawing which shows the measuring method of the curvature of a half cell. It is a figure which shows the relationship between the ratio of the thickness of an electrolyte and a fuel electrode, and the curvature of a half cell with an outer diameter of 100 mm. It is a figure which shows the relationship between the curvature of a cell, and an electric power generation output.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrode support body, 2 ... Electrolyte, 3 ... Counter electrode.

Claims (6)

In a flat plate type solid oxide fuel cell having a cell in which an electrolyte is laminated and sintered integrally on an electrode support serving as an air electrode or a fuel electrode,
A flat plate solid oxide fuel cell characterized in that the shrinkage rate of the electrolyte during the sintering process is always equal to or higher than the shrinkage rate of the electrode support. The flat plate type solid oxide fuel cell according to claim 1,
A flat solid oxide fuel cell, wherein a difference in shrinkage between the electrode support and the electrolyte during firing is 3% to 8%. The flat plate type solid oxide fuel cell according to claim 1,
A flat plate type characterized in that a ratio De / Da between the electrode support and the electrolyte is 0.001 to 0.015, where Da is the thickness of the electrode support and De is the thickness of the electrolyte. Solid oxide fuel cell. A step of laminating an electrolyte on an electrode support serving as an air electrode or a fuel electrode, a sintering step of integrally sintering the electrode support and the electrolyte, and forming a counter electrode on the sintered electrolyte. In a method for producing a flat plate solid oxide fuel cell having a step of producing a cell,
A method for producing a flat plate solid oxide fuel cell, wherein the shrinkage rate of the electrolyte in the sintering process is always equal to or higher than the shrinkage rate of the electrode support. In the manufacturing method of the flat type solid oxide fuel cell according to claim 4,
A method for producing a flat plate solid oxide fuel cell, wherein the difference in shrinkage between the electrode support and the electrolyte during firing is 3% to 8%. In the manufacturing method of the flat type solid oxide fuel cell according to claim 4,
A flat plate type characterized in that a ratio De / Da between the electrode support and the electrolyte is 0.001 to 0.015, where Da is the thickness of the electrode support and De is the thickness of the electrolyte. A method for producing a solid oxide fuel cell.

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