JP3411064B2 - Method for producing solid electrolyte sintered body for solid oxide fuel cell - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a solid electrolyte sintered body used for a solid oxide fuel cell. [0002] In recent years, so-called solid electrolytes have been researched and developed in various technical fields and applications. As a technical field using a solid electrolyte, for example, a solid electrolyte fuel cell (hereinafter referred to as “SOFC”) has a higher power generation efficiency than other fuel cells such as a phosphoric acid type and a molten carbonate type which have been conventionally developed. In recent years, attention has been paid particularly to the fact that a power generation system that can be efficiently used due to a high exhaust heat temperature can be constructed. The SOFCs are generally classified into a flat type shown in FIG. 5 and a cylindrical type (not shown). Also, in the flat type shown in FIG. 5, the external manifold type shown in FIG. 6A and the internal manifold type shown in FIG. 6B are representative. No. The SOF shown in FIGS. 5 and 6 (a) and (b)
The structure of C will be briefly described. The solid electrolyte plate 30 is sandwiched between a fuel electrode 20a in contact with a fuel gas and an oxygen electrode 20b in contact with air, and separators 40a, 40a outside the fuel electrode 20a and outside the oxygen electrode 20b, respectively. A single cell having a structure provided with 40b is provided in a stacked manner over many layers. [0005] In the SOFC thus configured, a fuel gas (hydrogen, carbon monoxide or the like) contacts the fuel electrode, and an oxidizing gas (air or oxygen) contacts the oxygen electrode. Then, oxygen ions (O 2) generated at the oxygen electrode
^2- ) moves through the solid electrolyte and reaches the fuel electrode, where oxygen ions react with hydrogen (H ₂ ) to emit electrons. As a result, a potential difference is generated between the oxygen electrode and the fuel electrode, and a flow of electricity is generated. [0006] In this SOFC, the electrical characteristics of the solid electrolyte used, particularly the electrical conductivity, greatly affect the performance of the battery. Conventionally, stabilized zirconia has been used as this type of solid electrolyte. This stabilized zirconia is
High temperature of zirconia (ZrO ₂ ) (around 1150 ° C)
As the crystal structure changes from monoclinic to tetragonal, the volume change occurs, and as a means to prevent this volume change, oxides such as calcium (Ca) and yttrium (Y) are dissolved to form crystals. This is to stabilize the structure. In recent years, scandia-stabilized zirconia (Sc ₂ O ₃ Stabilized Zr) in which a scandium oxide is dissolved in place of calcium or yttrium has been dissolved.
O ₂ , hereinafter referred to as “ScSZ”. ) Has attracted attention due to its characteristics such as high conductivity. Such Sc
The SZ solid electrolyte is produced by mixing the raw materials Sc ₂ O ₃ and ZrO ₂ by physical means such as a ball mill, heat-treating at a high temperature, and then pulverizing the obtained ScSZ powder to form and sinter. Was normal. [0008] However, in the case of the ScSZ solid electrolyte obtained by the above-mentioned conventional method, since the ScSZ powder obtained by physical means is used, Sc ₂ O in the powder is used. ₃ and ZrO ₂ were not sufficiently mixed and dissolved, and the composition was uneven. Therefore, it has the following problems. First, a high sintering temperature of 1700 ° C. or more and a long sintering time were required due to non-uniform composition, and the production cost was high. Further, a part of scandia compounded for stabilizing the crystal phase of zirconia sometimes remains unreacted. In such a case, scandia was insufficient in the zirconia portion, so that the crystal phase was not completely stabilized, and problems such as volume change accompanying the crystal phase transformation could not be completely eliminated. In addition, it does not become a cubic single phase which is ideal as a ScSZ solid electrolyte, but becomes a mixed crystal with a tetragonal crystal or a monoclinic crystal, thereby lowering the electrical conductivity. Further, since the unreacted scandia phase also hinders ionic conduction in the solid electrolyte, it cannot utilize the original high conductivity of ScSZ, and the conductivity of the resulting solid electrolyte sintered body is not so high. Was. Further, the obtained solid electrolyte sintered body was porous, had a low density, and had low mechanical strength. For this reason, there are the following disadvantages when considering application to SOFC. Since a volume change occurs during heating and cooling of the SOFC, distortion occurs (stress occurs) inside the battery. If the volume change is large, the electrode material may peel off due to stress. Fuel electrode and oxygen electrode are ScSZ
This is because the material is different from that of the solid electrolyte plate. The electric conductivity decreases and the power generation efficiency deteriorates. For this reason, the power generated by the SOFC cannot be obtained. In particular, when a solid electrolyte plate is coated with a fuel electrode or an oxygen electrode, that is, used in a so-called self-supporting flat plate type SOFC, the solid electrolyte is required to have mechanical strength, so that the mechanical strength is insufficient. Furthermore, in addition to these, impurities are liable to be mixed during mixing and pulverization by physical means, which is a problem in quality control. The present invention has been made in order to solve such problems, and it is an object of the present invention to mix uniformly at the atomic level, have excellent sintering properties, and retain unreacted scandia phase. Accordingly, it is an object of the present invention to provide a dense solid electrolyte sintered body which has a single crystal phase, has excellent stability, has high electrical conductivity and high mechanical strength, and hardly contains impurities. Thereby, for example, the power generation performance of the solid electrolyte of the SOFC is improved, and the volume change of the material during the heating and cooling is eliminated to achieve the permanent use. In order to achieve the above object, the present inventors have repeated experimental studies on scandia-zirconia-based solid electrolytes by various production methods, and found that the sol-gel method or coprecipitation method was used. It has been found that a dense and homogeneous solid electrolyte sintered body can be obtained by molding and firing the scandia-stabilized zirconia powder as a main material using this scandia-stabilized zirconia powder as a raw material. That is, the method for producing a solid electrolyte sintered body for a solid oxide fuel cell according to the present invention comprises the steps of:
Scange for zirconia in dia-stabilized zirconia
Zirconium so that the solid solution amount of
Nitrate or halide obtained by dissolving
Formic acid and polyethylene as sols in a mixed solution of
Glycol to form a mixed sol.
After drying to form a mixed gel, heat the mixed gel.
By dissolving Scandia in zirconia
Zirconia and scandi with an amount of 8 to 15 mol%
And a cubic single-phase
A powder of scandia-stabilized di- zirconia having a crystal structure
None, this scandia stabilized zirconia powder has the prescribed shape
The main point is to mold and bake it . According to the manufacturing method of the solid electrolyte fuel cell for a solid electrolyte sintered body, solid solution amount of scandia is 8-1
A sol is added to a mixed solution of a nitrate or a halide in which a powder of scandium and zirconium dissolved in a range of 5 mol% is mixed to form a mixed sol, and the mixed sol is dried and mixed. Since the gel is used, this mixed gel is obtained in a state where scandia and zirconia in the respective precursor states are uniformly mixed at the atomic level. The powder obtained by subjecting the mixed gel to heat treatment is such that scandia and zirconia are homogeneously mixed at the atomic level and do not contain any monoclinic crystal, tetragonal crystal, unreacted scandia, etc. Since it has a crystal structure composed of a cubic single phase, it exhibits excellent electrical characteristics. The scandia-stabilized zirconia powder is fine and excellent in sinterability, and can be fired at a temperature lower than 1700 ° C., which has been used as a firing temperature of zirconia powder, in a short time. . [0016] Here, it is added in order to obtain a mixed sol
Formic acid and polyethylene glycol used as sol
Is a mixture of zirconia and scandia
Quality can be further improved and
A mixed sol without residual zirconia can be obtained.
You. The sintered body obtained by firing this powder has a dense and homogeneous structure with a small number of voids, and thus has excellent mechanical strength and excellent electrical conductivity. Further, since there is no change in volume due to phase transformation of zirconia at high temperature, a solid electrolyte sintered body that can be used stably for a long time as a solid oxide fuel cell can be provided. [0018] EXAMPLES below examples according to an embodiment of the present invention will be described in detail. In the embodiments described below, a description will be made assuming a solid electrolyte sintered body to be used in a flat solid electrolyte fuel cell. FIG. 1 shows scandia-stabilized zirconia (Sc ₂ O ₃ Stabiliz) which is a raw material powder of a solid electrolyte sintered body for a solid oxide fuel cell according to the present invention.
ed ZrO ₂ , hereinafter referred to as “ScSZ”. 1) shows the steps for producing the powder. Figure 1 shows a higher production <br/> Engineering by a sol-gel method. Here, as an example, the manufacturing process by the sol-gel method of FIG. 1 and the ScSZ obtained by it
A powder and a solid electrolyte plate (hereinafter, referred to as “ScSZ plate”) formed in a plate shape using the ScSZ powder as a raw material will be described. According to the sol-gel method, it is prepared scandium powder 1 and the zirconium powder 2 as a raw material initially.
Then, these powders are blended at an appropriate ratio and dissolved in nitric acid and water while heating to form a mixed solution 3. As the compounding ratio of the powder, the scandia-stabilized zirconia after the heat treatment has a solid solution amount of scandia to zirconia of 8 to 1%.
Scandium powder and zirconium powder are preferably blended so as to correspond to 5 mol%. Mixed solution 3 at this time
Is a mixed solution of scandium and zirconium nitrate. Next, the addition of the sol product 4 in the mixed solution 3. Here, formic acid and polyethylene glycol (hereinafter referred to as “PEG”) are added as the sol 4. The addition amount is about twice as much as the above nitric acid in mol% for formic acid, and 200 m
About 1/1 kg is good. Thereby, a mixed sol 6 of scandia and zirconia is obtained. [0021] Then, the mixed sol 6 and the heating to dryness to mixed gel 8. The heating temperature is about 120 ° C., and the mixture is dried for one day to obtain a mixed gel 8. And this mixed gel 8
Is heated at 700 to 800 ° C. for about 12 hours,
The cSZ powder 10 can be obtained. The ScSZ powder 10 thus obtained is a cubic single phase obtained by mixing scandia and zirconia at an atomic level with good uniformity, and contains other phases such as tetragonal and unreacted scandia phase. I haven't. This will be described with reference to the results of X-ray diffraction measurement shown in FIG. FIG. 2 shows the ScSZ powder 10 obtained by the sol-gel method.
FIG. 5 is an X-ray diffraction pattern (with a scandia blending ratio of 8 mol%), in which the vertical axis represents diffraction intensity (cps) and the horizontal axis represents diffraction angle (2θ). According to FIG. 2, only a sharp peak corresponding to a cubic crystal of zirconia is detected, and it is clearly shown that the crystal is a single phase having no other phase and a good crystal without crystal distortion. . [0023] Here, the X-ray diffraction pattern of ScSZ powder produced by conventional physical mixing method (scandia content rate was 8 mol% similarly) for comparison in Fig.
In FIG. 3, in addition to the peak corresponding to the cubic crystal of zirconia (indicated by c in the figure), the peak corresponding to the tetragonal zirconia (indicated by t in the figure) is detected.
It can be seen that, unlike Z powder 10, it is composed of multiple phases and has poor crystallinity. [0024] Incidentally, the diffraction intensity of the strongest peak seen at about 30 ° diffraction angle, while about 9000cps in Figure 2 of the present embodiment, as small as in FIG. 3 about 2700cps comparative example. This is considered to be due to the fact that the conventional ScSZ powder has a small volume ratio occupied by the cubic crystals in which other phases are present, and conversely, shows the good crystallinity of the ScSZ powder 10 of the present embodiment. It can be said that there is. Next, ScS having such good crystallinity
A process of manufacturing a ScSZ plate from the Z powder 10 will be described.
First, the ScSZ powder 10 obtained in the above process is 20 to 3
Since it has a particle diameter of about 0 μm, after pulverizing and adjusting the particle diameter to about 2 to 3 μm,
Provide for firing. FIG . 4 shows the process. According to this, first, the sized SiSZ powder is added to a sheet thickness of 100 to 3 mm.
Form into a 00 μm plate (approximately 20 cm square plate). In this experimental example, a hydrostatic pressing machine (C
Pressure molding is performed using IP) with a pressing force of 1 t / cm ² . However, the present invention is not limited to this forming means, and a thin plate may be manufactured by a doctor blade method or a calender roll method generally used conventionally. Then, after a while, this formed plate is put into a range of 1500 to 170
Bake at a temperature of 0 ° C. As a result, scandia (Sc ₂
O ₃₎ is dissolved in the range of 8 to 15 mol% in zirconia (ZrO _2), and, ScSZ plate formed in a plate shape from ScSZ consisting cubic Akiratansho is obtained. [0027] In this case, since in this embodiment and fired from compositional uniformity and good crystallinity ScSZ powder was prepared by a sol-gel method may sinterability of the powder, 1700 ° C. or less of the relatively low firing temperature It is possible to obtain a ScSZ plate as a sintered body. Also, the firing time is shorter than that of the conventional one. Further, the obtained sintered body has a dense structure with few voids and has excellent mechanical strength. The thus obtained ScSZ plate conductivity of (S
/ Cm) was measured and compared with the conductivity of a solid electrolyte plate obtained from ScSZ powder by a conventional physical mixing method. Table 1 shows the results. According to Table 1, the conductivity of the ScSZ plate according to the present invention obtained by the sol-gel method is 0.38 S /
cm, the conductivity of the conventional ScSZ plate is 0.25 S / c.
The value is about 50% better than m. [ Table 1] [0030] As ScSZ plate of the present embodiment thus, a uniform mixing of scandia and zirconia in an atomic level good sinterability, no residual unreacted scandia phase, thus crystalline phase in a single phase It is a dense sintered body that is excellent in stability, has high electrical conductivity and high mechanical strength, and hardly contains impurities. And this ScSZ
When the plate is applied to a solid electrolyte plate of an SOFC, a fuel electrode and an oxygen electrode may be formed on both surfaces thereof. In forming these electrodes, ceramic powder of these electrode materials is formed into a mud-like form by, for example, a so-called slurry coating method, and applied to one surface and the opposite surface of the ScSZ-based solid electrolyte plate, and then a predetermined temperature is applied. Should be fired. In the case of a fuel electrode, for example, nickel (N
i) 40% by weight of zirconia (ZrO ₂ ) 60% by weight of a Ni-zirconia cermet material is coated on one surface of the ScSZ-based solid electrolyte plate at a thickness of about 50 μm, and fired at a temperature of 1400 to 1500 ° C. Thus, a thin-film fuel electrode is formed on one surface of the ScSZ-based solid electrolyte plate. In the case of an oxygen electrode, for example, a lanthanum strontium manganate (La (Sr) MnO ₃ ) material is coated to a thickness of about 50 μm on the surface of the solid electrolyte plate opposite to the fuel electrode, It is fired at a temperature around 1150 ° C. Thus, a thin-film oxygen electrode is formed on the opposite surface of the ScSZ-based solid electrolyte plate. It is appropriate that the mixing ratio of the material of the oxygen electrode is about 5 to 15 mol% of strontium with respect to 95 to 85 mol% of lanthanum manganate. In such a solid oxide fuel cell (SOFC), since the solid electrolyte according to the present invention is used, it is excellent in power generation performance as an SOFC, and has a small volume change of a material during heating and cooling, and can be used permanently. it can. As described above, the sol-gel method is used.
As a result , Sc having excellent crystallinity, uniformity, denseness, etc.
By obtaining SZ powder, molding and firing it, ScS having excellent conductivity required for a solid oxide fuel cell is obtained.
A Z plate can be obtained. In the above embodiment , ScSZ
Although the molar ratio between scandia and zirconia in the material has been described as being 8 mol% for scandia, it is needless to say that the ratio is not limited to this ratio. Further, both the front you施例, it is assumed that prepared from a mixed solution of nitrate prepared by dissolving scandium and zirconium nitrate, it is also possible to use a starting material other than nitrates. As the starting materials usable here, sulfates and / or halides can be considered. As described above, according to the solid electrolyte sintered body for a solid oxide fuel cell and the method for producing the same according to the present invention, a dense, homogeneous, cubic single-phase crystal is provided. Due to having the structure, it is possible to obtain a solid electrolyte sintered body for a solid electrolyte fuel cell exhibiting excellent electrical conductivity, and this solid electrolyte sintered body for a solid electrolyte fuel cell is converted into a solid electrolyte fuel cell. If used, it is possible to achieve both power generation performance and permanent use, so that the industrial benefit is extremely high.

ScS in the production method of the BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1] according to the present invention using a zone Rugeru method solid oxide fuel cell solid electrolyte sintered body
Is a diagram that shows the manufacturing process of the Z powder. FIG. 2 is a view showing X-ray diffraction data of ScSZ powder by a sol-gel method. FIG. 3 is a view showing X-ray diffraction data of ScSZ powder according to a conventional manufacturing method. FIG. 4 is a view showing a manufacturing process for manufacturing a solid electrolyte plate for a solid oxide fuel cell according to an embodiment of the present invention. FIG. 5 is a diagram showing an example of a single-cell structure of a conventionally known plate-type solid oxide fuel cell (SOFC). 6 (a) is a diagram showing a schematic configuration of an external manifold type in the flat fuel cell shown in FIG. 5, and FIG. 6 (b) is a diagram showing a schematic configuration of an internal manifold type of the flat fuel cell.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-215259 (JP, A) JP-A-5-33179 (JP, A) JP-A-60-255622 (JP, A) JP-A-3-255 199163 (JP, A) JP-A-4-317414 (JP, A) {}, {23, No. 4 (1987), p. 590-593 Metal, Vol. 52, No. 7 (1982), p. 24 to 26 JOURNAL OF MATERIAL ALS SCIENCE LETTER S, Vol. 8 (1989), p. 198-200 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 8/02 C04B 35/48 H01M 8/12

Claims (1)

(57) [Claims 1] The amount of scandia dissolved in zirconia in the scandia-stabilized zirconia after heat treatment is 8 to 1.
To a mixed solution of nitrate or halide obtained by dissolving zirconium and scandium so as to correspond to 5%
Added formic acid and polyethylene glycol as sol
To a mixed sol, then the mixed sol was mixed gel dryness by heating the gel mixture, di
8-15 mol% of scandia dissolved in luconia
And at the atomic level zirconia and scandia
A solid having a cubic single-phase crystal structure uniformly mixed and formed into a powder of scandia-stabilized zirconia; and forming the scandia-stabilized zirconia powder into a predetermined shape and firing. A method for producing a solid electrolyte sintered body for an electrolyte fuel cell.