Electrolyte particle for use in manufacture of solid oxide electrochemical cells and manufacturing method thereof, electrolyte-forming dispersion, and electrolyte sintered body and manufacturing method thereof

Abstract

To provide an electrolyte particle for use in the manufacture of a solid oxide electrochemical cell, which is a solid electrolyte sintered body constituting a solid oxide electrochemical cell and which can be efficiently manufactured by sintering a densified sintered body having a high relative density at, for example, 1200°C or lower, and a dispersion liquid containing the electrolyte particle.SOLUTION: The present invention relates to an electrolyte particle containing at least one selected from (A) stabilized zirconia consisting of 3.0 to 10.0 mol% scandium oxide, 0 to 2.0 mol% cerium oxide, and 88.0 to 97.0 mol% zirconium oxide, (B) stabilized zirconia consisting of 0.5 to 15.0 mol% yttrium oxide and 85.0 to 99.5 mol% zirconium oxide, and (C) stabilized zirconia consisting of 0.5 to 15.0 mol% ytterbium oxide and 85.0 to 99.5 mol% zirconium oxide, and having a volume average particle diameter of 50 to 150 nm measured using a laser diffraction method.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to electrolyte particles for manufacturing a solid oxide type electrochemical cell that provides a dense electrolyte sintered body, a method for manufacturing the same, and a dispersion for forming an electrolyte.

Background Art

[0002] Conventionally, as solid oxide type electrochemical cells, solid oxide fuel cells and solid oxide electrolytic cells are known. Among these, a solid oxide fuel cell includes a solid electrolyte layer made of a sintered body containing an oxygen ion conductive solid oxide such as yttria-stabilized zirconia or scandia-stabilized zirconia, and a fuel electrode and an air electrode disposed opposite to each other on both sides of the solid electrolyte layer. It is a three-layer power generation cell that supplies a fuel gas such as hydrogen to the fuel electrode and, on the other hand, supplies an oxidizing gas such as air to the air electrode to generate direct current power based on an electrochemical reaction.

[0003] Since the solid electrolyte layer is a medium for oxygen ion movement and also functions as a partition that does not directly contact the fuel gas and air, it is required to have a gas-impermeable dense structure. For example, Patent Document 1 discloses a method for manufacturing a solid oxide fuel cell having a pair of porous electrode layers sandwiching an electrolyte layer, wherein the electrolyte layer is provided on at least one surface of a porous electrode substrate, and then heated from the electrolyte layer side. A method for manufacturing a solid oxide fuel cell is disclosed.

[0004] By the way, in recent years, a metal-supported cell type solid oxide fuel cell has been known in which a power generation cell is supported by a metal support part (metal support part) having gas permeability and electrical conductivity through a fuel electrode. As a method for manufacturing such a metal-supported cell type solid oxide fuel cell, for example, a fuel electrode forming slurry is applied and dried on the surface of a metal substrate having air permeability from one surface side to the other surface side to form a fuel electrode film, and then a solid electrolyte layer forming slurry containing a solid electrolyte containing an oxygen ion conductive solid oxide is applied and dried to form a solid electrolyte layer film. A method is known that includes a step of heat-treating (co-sintering) the obtained laminate to produce an integrated body of a breathable metal support part, a fuel electrode, and a solid electrolyte layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] For example, in the case of manufacturing a fuel cell having a dense solid electrolyte layer, such as the above-described metal-supported cell type solid oxide fuel cell, in order to perform heat treatment (co-sintering) of a laminate sequentially including a breathable metal substrate, a fuel electrode film, and a solid electrolyte layer film containing solid electrolyte particles having a conventionally known particle size of about 0.5 to 20 μm, it is necessary to set a high temperature of at least 1250 °C. At such a temperature, the breathable metal substrate may shrink depending on its constituent materials. Therefore, for example, it is preferable to obtain an electrolyte layer made of a dense sintered body while ensuring the air permeability of the metal support part at a low heat treatment temperature with an upper limit of 1200 °C.

[0007] In addition, not only in a solid oxide fuel cell but also in a solid oxide electrolysis cell for producing hydrogen by electrolysis of steam, for example, a hydrogen electrode, a solid electrolyte layer, and an oxygen electrode are sequentially provided and have a structure similar to that of a solid oxide fuel cell. Therefore, a means for densifying the solid electrolyte layer is required.

[0008] An object of the present invention is to provide electrolyte particles for manufacturing a solid oxide electrochemical cell, a method for manufacturing the same, and a dispersion of the electrolyte particles for manufacturing a solid oxide electrochemical cell, which can have a heat treatment (sintering) temperature of 1200°C or lower and can be composed of a sintered body with a high relative density and high density when manufacturing a sintered body constituting a solid electrolyte layer of the solid oxide electrochemical cell. Another object of the present invention is to provide a method for efficiently manufacturing a solid electrolyte sintered body with a high relative density and high density by heat treatment (sintering) at 1200°C or lower, for example.

Means for Solving the Problems

[0009] The present inventors have found that when using stabilized zirconia fine particles having a specific composition and size alone or in combination with particles made of a known zirconia-based electrolyte material larger than the stabilized zirconia fine particles, a dense sintered body can be obtained at a temperature lower than the heat treatment temperature (1250°C or higher) conventionally applied to obtain a dense sintered body. As a dispersion containing such stabilized zirconia fine particles, a dispersion using ethanol as a dispersion medium is used. This dispersion is dropped onto a molded body made of known zirconia-based electrolyte material particles larger than the stabilized zirconia fine particles to fill the voids formed between the zirconia-based electrolyte material particles of the molded body with specific stabilized zirconia fine particles, and then sintered to obtain a dense electrolyte sintered body. In this specification, "stabilized zirconia" means zirconia in which a rare earth element oxide is solid-solved, and includes partially stabilized zirconia.

[0010] The present invention is shown below. [1]Stabilized zirconia composed of 3.0 to 10.0 mol% of scandium oxide, 0 to 2.0 mol% of cerium oxide, and 88.0 to 97.0 mol% of zirconium oxide (B) Stabilized zirconia composed of 0.5 to 15.0 mol% of yttrium oxide and 85.0 to 99.5 mol% of zirconium oxide And (C) Stabilized zirconia composed of 0.5 to 15.0 mol% of ytterbium oxide and 85.0 to 99.5 mol% of zirconium oxide Containing at least one selected from An electrolyte particle for manufacturing a solid oxide type electrochemical cell, characterized in that the volume average particle diameter measured by using a laser diffraction method is 50 to 150 nm. [2] In the particle size distribution based on volume measured by using a laser diffraction method, D 10 , D 50 And D 90 Are the particle diameters (unit: nm) at which the cumulative frequencies are 10%, 50%, and 90% respectively. The electrolyte particles for manufacturing a solid oxide type electrochemical cell according to [1] above satisfy the following formulas (1), (2), and (3). 30 ≤ D 10 ≤ 90 (1) 70 ≤ D 50 ≤ 150 (2) 120 ≤ D 90 ≤ 250 (3) [3] A method for manufacturing the electrolyte particles for manufacturing a solid oxide type electrochemical cell according to [1] or [2] above, Dissolve a water-soluble compound containing at least one stabilizing element selected from scandium, yttrium, ytterbium, and cerium and a water-soluble compound containing zirconium in water, mix the obtained aqueous solution with a basic material to form a precipitate consisting of an electrolyte precursor, then dry the precipitate, heat-treat the obtained dried product, and then pulverize it. A method for manufacturing electrolyte particles for manufacturing a solid oxide type electrochemical cell, characterized by the above. [4] A dispersion for forming an electrolyte of a solid oxide type electrochemical cell, characterized by containing the electrolyte particles for manufacturing a solid oxide type electrochemical cell according to [1] or [2] above and ethanol. [5] A method for manufacturing an electrolyte sintered body, characterized by subjecting a molded article for sintering containing the electrolyte particles for manufacturing a solid oxide type electrochemical cell according to [1] or [2] above to sintering. [6] A method for manufacturing an electrolyte sintered body, characterized by bringing the dispersion for forming an electrolyte according to [4] above into contact with a molded article containing a solid electrolyte, producing an adherend in which the electrolyte particles for manufacturing a solid oxide type electrochemical cell contained in the dispersion for forming an electrolyte adhere to the molded article, and subjecting the adherend to sintering as a molded article for sintering. [7] An electrolyte sintered body, characterized by being obtained by the manufacturing method according to [5] or [6] above. [Effect of the Invention]

[0011] The electrolyte particles for manufacturing a solid oxide type electrochemical cell of the present invention are a solid electrolyte sintered body constituting a solid oxide type electrochemical cell, and are suitable as a manufacturing raw material for providing a sintered body constituting a dense solid electrolyte layer at a relatively low sintering temperature, for example, 1200°C or lower. The dispersion for forming an electrolyte of the solid oxide type electrochemical cell of the present invention is a solid electrolyte sintered body constituting a solid oxide type electrochemical cell, and is suitable as a manufacturing raw material for providing a sintered body constituting a dense solid electrolyte layer. The electrolyte sintered body of the present invention is suitable as a constituent material of a solid electrolyte layer constituting a solid oxide type electrochemical cell. According to the method for manufacturing an electrolyte sintered body of the present invention, when the electrolyte particles for manufacturing a solid oxide type electrochemical cell are used alone, or when these electrolyte particles for manufacturing a solid oxide type electrochemical cell are used in combination with particles made of a known zirconia-based electrolyte material that is larger than these, a dense sintered body can be manufactured at a temperature lower than the heat treatment temperature (1250°C or higher) conventionally applied to obtain a dense sintered body, for example, 1200°C or lower. [Brief Description of the Drawings]

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0013] The electrolyte particles for manufacturing a solid oxide type electrochemical cell of the present invention (hereinafter referred to as "electrolyte particles X") are (A) 3.0 to 10.0 mol% scandium oxide (Sc 2 O 3 ), 0 to 2.0 mol% cerium oxide (CeO 2 ), and 88.0 to 97.0 mol% zirconium oxide (ZrO 2 )-composed stabilized zirconia (hereinafter referred to as "component (A)"), (B) 0.5 to 15.0 mol% yttrium oxide (Y 2 O 3 ) and 85.0 to 99.5 mol% zirconium oxide-composed stabilized zirconia (hereinafter referred to as "component (B)"), and (C) 0.5 to 15.0 mol% ytterbium oxide (Yb 2 O 3 ) and 85.0 to 99.5 mol% zirconium oxide-composed stabilized zirconia (hereinafter referred to as "component (C)"), and is characterized in that the volume average particle diameter measured using the laser diffraction method is 50 to 150 nm.

[0014] The components (A), (B), and (C) according to the present invention are components that can produce a dense sintered body by combining electrolyte particles X composed of component (A), (B), or (C), or electrolyte particles X composed of component (A), (B), or (C) and particles composed of a solid electrolyte in the same series, and heat-treating (low-temperature sintering) preferably at 1200°C or lower, but 800°C or higher.

[0015] Component (A) is stabilized zirconia composed of 3.0 to 10.0 mol% of scandium oxide, 0 to 2.0 mol% of cerium oxide, and 88.0 to 97.0 mol% of zirconium oxide. When component (A) does not contain cerium oxide, it is preferably stabilized zirconia composed of 3.0 to 10.0 mol% of scandium oxide and 90.0 to 97.0 mol% of zirconium oxide. When component (A) contains cerium oxide, it is preferably stabilized zirconia composed of 8.0 to 12.0 mol% of scandium oxide, 0.5 to 1.5 mol% of cerium oxide, and 86.5 to 91.5 mol% of zirconium oxide, and more preferably stabilized zirconia composed of 9.0 to 11.0 mol% of scandium oxide, 0.5 to 1.5 mol% of cerium oxide, and 87.5 to 90.5 mol% of zirconium oxide. Here, as the solid electrolyte constituting the electrolyte particles Y1 in the case of low-temperature sintering using the electrolyte particles X composed of component (A) and the solid electrolyte particles in the same series (hereinafter referred to as "electrolyte particles Y1"), it is preferably a conventionally known solid electrolyte containing Sc, Y, Yb, Ce, etc., and examples include scandia-stabilized zirconia, yttria-stabilized zirconia, ytterbia-stabilized zirconia, etc. The electrolyte particles Y1 can be used in the "method for manufacturing an electrolyte sintered body" described later.

[0016] Component (B) is stabilized zirconia composed of 0.5 to 15.0 mol% of yttrium oxide and 85.0 to 99.5 mol% of zirconium oxide, preferably stabilized zirconia composed of 3.0 to 10.0 mol% of yttrium oxide and 90.0 to 97.0 mol% of zirconium oxide. Here, as the solid electrolyte constituting the electrolyte particles Y2 in the case of low-temperature sintering using the electrolyte particles X composed of component (B) and the solid electrolyte particles of its series (hereinafter referred to as "electrolyte particles Y2"), preferably, it is a conventionally known solid electrolyte containing Y, Yb, Ce, etc., and examples thereof include yttria-stabilized zirconia, ytterbia-stabilized zirconia, etc. The electrolyte particles Y2 can be used in the "method for manufacturing an electrolyte sintered body" described later.

[0017] Component (C) is stabilized zirconia composed of 0.5 to 15.0 mol% of ytterbium oxide and 85.0 to 99.5 mol% of zirconium oxide, preferably stabilized zirconia composed of 3.0 to 10.0 mol% of ytterbium oxide and 90.0 to 97.0 mol% of zirconium oxide. Here, as the solid electrolyte constituting the electrolyte particles Y3 in the case of low-temperature sintering using the electrolyte particles X composed of component (C) and the solid electrolyte particles of its series (hereinafter referred to as "electrolyte particles Y3"), preferably, it is a conventionally known solid electrolyte containing Y, Yb, Ce, etc., and examples thereof include yttria-stabilized zirconia, ytterbia-stabilized zirconia, etc. The electrolyte particles Y3 can be used in the "method for manufacturing an electrolyte sintered body" described later.

[0018] The volume-average particle diameter of the electrolyte particles for manufacturing a solid oxide type electrochemical cell of the present invention by the laser diffraction method is, for example, when producing a sintered body by combining electrolyte particles X composed of component (A), (B) or (C) and solid electrolyte particles (electrolyte particles Y1, Y2 or Y3) of the series thereof, particularly when the average particle diameter of the electrolyte particles Y1, Y2 or Y3 used in combination is 300 nm or more, it can be 50 to 150 nm, preferably 60 to 120 nm, more preferably 70 to 90 nm because a dense sintered body can be efficiently produced by low-temperature sintering.

[0019] The electrolyte particles for manufacturing a solid oxide type electrochemical cell of the present invention are preferably monodisperse particles. The particle size distribution of the electrolyte particles for manufacturing a solid oxide type electrochemical cell of the present invention by the laser diffraction method is not particularly limited, but in terms of volume basis, D 10 , D 50 and D 90 are defined as the particle diameters (unit: nm) at which the cumulative frequency becomes 10%, 50% and 90% respectively. Since a dense sintered body can be efficiently obtained, the preferable upper and lower limits of D 10 , D 50 and D 90 are as follows. The lower limit of D 10 is preferably 30 nm, more preferably 40 nm, still more preferably 50 nm, and the upper limit of D 10 is preferably 90 nm, more preferably 80 nm, still more preferably 70 nm. The lower limit of D 50 is preferably 70 nm, more preferably 75 nm, still more preferably 80 nm, and the upper limit of D 50 is preferably 150 nm, more preferably 110 nm, still more preferably 90 nm. The lower limit of D 90 is preferably 120 nm, more preferably 125 nm, still more preferably 130 nm, and the upper limit of D 90 is preferably 250 nm, more preferably 200 nm, still more preferably 150 nm.

[0020] The method for manufacturing electrolyte particles for manufacturing a solid oxide type electrochemical cell in the present invention (hereinafter referred to as "electrolyte particle manufacturing method" or "manufacturing method of electrolyte particle X") includes a step of dissolving a water-soluble compound containing at least one stabilizing element selected from scandium, yttrium, ytterbium, and cerium prepared according to the composition of component (A), (B), or (C) and a water-soluble compound containing zirconium in water (hereinafter referred to as "raw material dissolution step"), a step of mixing the obtained raw material aqueous solution and a basic material to form a precipitate composed of an electrolyte precursor (hereinafter referred to as "electrolyte precursor synthesis step"), a step of drying the precipitate and heat-treating the obtained dried product to obtain a target electrolyte body (hereinafter referred to as "electrolyte body production step"), and a step of pulverizing the obtained electrolyte body (hereinafter referred to as "pulverization step") are sequentially provided.

[0021] The production raw materials in the electrolyte particle manufacturing method of the present invention are a water-soluble compound containing at least one stabilizing element selected from scandium, yttrium, ytterbium, and cerium (hereinafter referred to as "raw material (R1)"), and a water-soluble compound containing zirconium (hereinafter referred to as "raw material (R2)"). In any of the raw materials, the solubility in water is not particularly limited. Further, it can be made into a hydrate if necessary.

[0022] Examples of the scandium compound for raw material (R1) include scandium oxide, scandium oxyhydroxide, scandium nitrate, scandium chloride, and the like. Examples of the yttrium compound for raw material (R1) include yttrium oxide, yttrium nitrate, yttrium chloride, and the like. Examples of the ytterbium compound for raw material (R1) include ytterbium oxide, ytterbium nitrate, ytterbium chloride, and the like. Examples of the cerium compound for raw material (R1) include cerium chloride, cerium nitrate, cerium oxide, and the like.

[0023] Examples of the zirconium compound for raw material (R2) include zirconium chloride, zirconium oxychloride, zirconium oxide, zirconium nitrate, and the like.

[0024] When producing the electrolyte particles X composed of component (A), the above-mentioned scandium compound, cerium compound and zirconium compound are used, and preferably, scandium oxide, cerium chloride heptahydrate and zirconium chloride are used. When producing the electrolyte particles X composed of component (B), the above-mentioned yttrium compound and zirconium compound are used, and preferably, yttrium oxide and zirconium chloride are used. When producing the electrolyte particles X composed of component (C), the above-mentioned ytterbium compound and zirconium compound are used, and preferably, ytterbium oxide and zirconium chloride are used.

[0025] In the raw material dissolution step, the method of dissolving the raw materials (R1) and / or (R2) in water is not particularly limited. For example, a method of dissolving a predetermined amount of all the raw materials in water, a method of using the raw materials by type and dissolving them in water, a method of dissolving them in a solution having water as the main solvent such as hydrochloric acid and then mixing them, etc. can be used. The amount of water used is not particularly limited, but from the viewpoint of the yield of the electrolyte particles X obtained by the present invention, the solid concentration of the total amount of the raw materials is preferably 1.0 to 15.0% by mass, more preferably 3.0 to 8.0% by mass. Also, when preparing the raw material aqueous solution, either normal temperature water or warm water (including hot water) may be used.

[0026] The raw material aqueous solution obtained in the raw material dissolution step can be mixed with a basic material in the electrolyte precursor synthesis step to form a precipitate composed of the electrolyte precursor. The basic material used here may be either solid or liquid as long as it dissolves in water and the pH (25°C) becomes 8 or more, and ammonia, sodium hydroxide, barium hydroxide, etc. can be used. In the present invention, it is preferable to use an aqueous solution of a base.

[0027] In the electrolyte precursor synthesis step, it is preferable to add (supply) an aqueous solution of a base to the aqueous raw material solution obtained in the raw material dissolution step. In this case, the method of adding the aqueous solution of the base may be either batch addition or divided addition. When an aqueous solution of a base is added to the aqueous raw material solution, the electrolyte precursor is instantaneously generated. Therefore, when sufficient stirring is performed, a precipitate of the electrolyte precursor composed of fine powder and containing water can be obtained.

[0028] In addition, regarding the constitution of each electrolyte precursor that will form component (A), (B), or (C), the present inventors presume as follows. When component (A) is produced using scandium oxide, cerium chloride heptahydrate, and zirconium chloride, the electrolyte precursor is preferably a scandium- and cerium-substituted zirconia hydrate gel. When component (B) is produced using yttrium oxide and zirconium chloride, the electrolyte precursor is preferably a yttrium-substituted zirconia hydrate gel. When component (C) is produced using ytterbium oxide and zirconium chloride, the electrolyte precursor is preferably an ytterbium-substituted zirconia hydrate gel.

[0029] Next, in the electrolyte body production step, the precipitate obtained in the electrolyte precursor synthesis step is dried, and the resulting dried product (electrolyte precursor) is heat-treated to obtain a fired product, that is, an electrolyte body composed of component (A), (B), or (C). The conditions for heat-treating the dried product in the electrolyte body production step are not particularly limited. The atmosphere is preferably air. Also, the temperature is usually 80°C or higher, preferably 100°C to 500°C, more preferably 150°C to 500°C. The heat treatment temperature may be constant throughout or may be increased while heating. Note that the dried product to be subjected to the heat treatment may be pulverized in advance.

[0030] Thereafter, in the pulverization step, the electrolyte particles X of the present invention can be produced by pulverizing the electrolyte obtained in the electrolyte production step. In this pulverization step, either one or both of dry pulverization and wet pulverization can be applied, but in the present invention, it is preferable to perform at least wet pulverization.

[0031] In the case of dry pulverization, a ball mill, bead mill, jet mill, cyclone mill, roller mill, rod mill, etc. can be applied.

[0032] In the case of wet pulverization, a ball mill, bead mill, high-pressure homogenizer, etc. can be applied. Among these, a bead mill is preferable. When using a bead mill, the bead diameter is preferably 50 to 100 μm. When performing wet pulverization, it is preferable to use an organic solvent in combination. This organic solvent is not particularly limited, and conventionally known alcohols, ketones, etc. can be used. In addition, it is preferable to use an organic solvent having a boiling point of 60°C or higher at normal pressure, and ethanol is particularly preferably used.

[0033] The method for producing electrolyte particles of the present invention can include other steps after the pulverization step, if necessary. For example, when wet pulverization is performed in the presence of an organic solvent in the pulverization step, thereafter, since a mixture containing electrolyte particles is obtained in the organic solvent, a desolvation step of removing the organic solvent can be provided to recover the electrolyte particles. Further, in order to size the particles, the recovered electrolyte particles may be subjected to a classification step.

[0034] The dispersion for forming an electrolyte of a solid oxide type electrochemical cell (hereinafter referred to as "dispersion for forming an electrolyte") in the present invention contains electrolyte particles for manufacturing a solid oxide type electrochemical cell (electrolyte particles X) and ethanol, and is a liquid in which the electrolyte particles X are dispersed in ethanol.

[0035] The content ratio of the electrolyte particles X in ethanol is not particularly limited. The lower limit is preferably 0.01% by mass, more preferably 0.1% by mass, and the upper limit is preferably 20% by mass, more preferably 1.0% by mass. Since the dispersion liquid for forming an electrolyte of the present invention has good dispersibility without sedimentation of the electrolyte particles X, it is easy to handle. Therefore, when producing an electrolyte sintered body by heat-treating (low-temperature sintering) a sintering molded article Z2 or Z3 according to the first method for manufacturing an electrolyte sintered body described below, or a sintering molded article according to the second method for manufacturing an electrolyte sintered body, the dispersion liquid for forming an electrolyte of the present invention can be preferably used.

[0036] In the present invention, the first method for manufacturing an electrolyte sintered body is a method of subjecting a sintering molded article containing the above-described electrolyte particles (electrolyte particles X) for manufacturing a solid oxide fuel cell to sintering to manufacture a dense electrolyte sintered body. Further, in the present invention, the second method for manufacturing an electrolyte sintered body is to bring the above-described dispersion liquid for forming an electrolyte into contact with a molded article containing a solid electrolyte (a molded article containing a solid electrolyte), and an adherend in which the electrolyte particles (electrolyte particles X) for manufacturing a solid oxide fuel cell contained in the dispersion liquid for forming an electrolyte are adhered to the molded article containing a solid electrolyte is produced, and the adherend is used as a sintering molded article and subjected to sintering to manufacture a dense electrolyte sintered body. In any of these manufacturing methods, when heat-treating the sintering molded article containing the electrolyte particles X in order to obtain a sintered body, for example, it can be sintered at a low temperature of 1200°C or lower.

[0037] The green compact for sintering according to the first method for manufacturing an electrolyte sintered body may consist only of electrolyte particles X, or may consist of electrolyte particles X and electrolyte particles Y1, Y2, or Y3 which are solid electrolyte particles of the same series. Each solid electrolyte constituting the electrolyte particles Y1, Y2, and Y3 is as described above. Also, the volume average particle diameter of the electrolyte particles Y1, Y2, and Y3 is preferably 200 to 1000 nm, more preferably 300 to 700 nm. Incidentally, the green compact for sintering may contain a sintering aid, a binder, etc., but in the present invention, it preferably consists of an aggregate of electrolyte particles that does not contain a sintering aid, a binder, etc.

[0038] As a preferable method for producing a green compact for sintering according to the first method for manufacturing an electrolyte sintered body, (1) a method of subjecting raw material particles containing electrolyte particles X and not containing electrolyte particles Y1, Y2, and Y3 to pressure molding to obtain a green compact for sintering (hereinafter referred to as "green compact for sintering Z1"), (2) a method of subjecting raw material particles containing electrolyte particles X and electrolyte particles Y1, Y2, or Y3 to pressure molding to obtain a green compact for sintering (hereinafter referred to as "green compact for sintering Z2"), (3) bringing the above-described dispersion liquid for forming an electrolyte into contact with the green compact for sintering Z2 or a sintered product thereof (however, heat-treated at a temperature lower than the sintering temperature), and then removing the medium (ethanol) of the dispersion liquid for forming an electrolyte to attach the electrolyte particles X contained in the dispersion liquid for forming an electrolyte to the green compact for sintering Z2 (preferably filling the gaps between the electrolyte particles constituting the green compact for sintering Z2) to obtain a green compact for sintering (hereinafter referred to as "green compact for sintering Z3"), (4) subjecting raw material particles containing electrolyte particles Y1, Y2, or Y3 and not containing electrolyte particles X to pressure molding, bringing the above-described dispersion liquid for forming an electrolyte into contact with the obtained pressure molded product or a sintered product thereof (however, heat-treated at a temperature lower than the sintering temperature), and then removing the medium (ethanol) of the dispersion liquid for forming an electrolyte to attach the electrolyte particles X contained in the dispersion liquid for forming an electrolyte to the pressure molded product (preferably filling the gaps between the electrolyte particles constituting the pressure molded product) to obtain a green compact for sintering (hereinafter referred to as "green compact for sintering Z4"), and the like can be mentioned.

[0039] Here, a method (4) for producing the sintering compact Z4 using the dispersion for forming an electrolyte will be described. The pressure-formed product brought into contact with the dispersion for forming an electrolyte is, for example, obtained by subjecting raw material particles containing electrolyte particles Y1 and not containing electrolyte particles X to pressure molding. Examples of the method of bringing the dispersion for forming an electrolyte into contact with this pressure-formed product include a method of spraying the dispersion for forming an electrolyte onto the pressure-formed product, and a method of immersing the pressure-formed product in the dispersion for forming an electrolyte. Thereafter, the sintering compact Z4 can be obtained by volatilizing ethanol, which is the medium of the dispersion for forming an electrolyte. Incidentally, when bringing the dispersion for forming an electrolyte into contact with the pressure-formed product, only a specific dispersion for forming an electrolyte may be brought into contact, but several kinds of dispersions for forming an electrolyte having different concentrations of electrolyte particles X can be used. For example, a method of sequentially bringing them into contact starting from the dispersion for forming an electrolyte having a lower concentration can be applied. Further, the amount of the adhered electrolyte particles X can be easily determined by calculating the mass difference between the pressure-formed product and Z4.

[0040] In the method for manufacturing the first electrolyte sintered body of the present invention, for example, the sintering compacts Z2, Z3, and Z4 obtained by using electrolyte particles X and electrolyte particles Y1 in combination have the structure (reference numeral 10) shown in FIG. 1, that is, the electrolyte particles X (reference numeral 1) are included in the gaps between the electrolyte particles Y1 (reference numeral 3). Therefore, the sintered body 20 obtained by heat-treating such a sintering compact 10 has a relatively high relative density and tends to be dense compared to the sintered body of the sintering compact Z1 obtained by subjecting only the electrolyte particles X to pressure molding. Further, for example, the sintered bodies 20 of the sintering compacts Z2, Z3, and Z4 obtained by using electrolyte particles X and electrolyte particles Y1 in combination have a tendency of having a lower shrinkage rate compared to the sintered body 22 of the pressure-formed product (sintering compact 12) obtained by subjecting raw material particles containing electrolyte particles Y1 and not containing electrolyte particles X to pressure molding, as shown in FIG. 2.

[0041] A low shrinkage rate and the ability to obtain a dense sintered body are advantageous in the production of solid oxide type electrochemical cells. When laminates of a fuel electrode forming layer, a solid electrolyte forming layer, and an air electrode forming layer are heat-treated and co-sintered, an integrated sintered body having a desired layer thickness and the like can be easily produced. In recent years, electrochemical cells having a metal support portion on the fuel electrode side have also been widely used. Therefore, the present invention is also suitable for the case of heat-treating and co-sintering a laminate of a breathable metal substrate, a fuel electrode forming layer, a solid electrolyte forming layer, and an air electrode forming layer.

[0042] The sintered molded article according to the second method for manufacturing a solid electrolyte sintered body is a molded article containing a solid electrolyte (solid electrolyte-containing molded article) to which electrolyte particles X are attached, and may be the above-described sintered molded article Z2, Z3, or Z4 composed of an aggregate of electrolyte particles. Alternatively, the electrolyte particles may be attached to a solid electrolyte molded article in which the electrolyte particles are connected to each other, or a solid electrolyte molded article that does not contain a portion derived from the particles, and then the medium (ethanol) of the electrolyte-forming dispersion is removed.

[0043] The electrolyte sintered body of the present invention obtained by the first method for manufacturing a solid electrolyte sintered body and the second method for manufacturing a solid electrolyte sintered body of the present invention is dense as described above, and the relative density, which is the ratio of the measured density to the theoretical density, can be preferably 85% or more, more preferably 90% or more, and particularly preferably 94% or more.

Examples

[0044] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” are based on mass unless otherwise specified.

[0045] 1. Production of electrolyte fine particles and their dispersion Electrolyte particles were produced using the following raw materials. (1) Zirconium chloride (manufactured by Fujifilm Wako Pure Chemical Corporation) (2) Scandium Oxide (manufactured by High Purity Chemical Research Institute) (3) Cerium Chloride Heptahydrate (manufactured by Fujifilm Wako Pure Chemical Corporation) (4) Ytterbium Oxide (manufactured by Fujifilm Wako Pure Chemical Corporation)

[0046] Example 1-1 Zirconium chloride was put into ion-exchanged water and stirred to obtain an aqueous zirconium chloride solution. Next, scandium oxide was put into this aqueous zirconium chloride solution and dissolved, and it was stirred well until it became transparent. Furthermore, cerium chloride heptahydrate was put into this aqueous solution and dissolved, and it was stirred sufficiently until it became completely transparent to obtain a raw material aqueous solution. The usage amount of each raw material was adjusted so that the molar ratio equivalent to the oxide was 89.0 mol% for zirconium oxide, 10.0 mol% for scandium oxide, and 1.0 mol% for cerium oxide. Thereafter, aqueous ammonia was added to the raw material aqueous solution, and the reaction was carried out at room temperature with stirring. In order to purify the product (electrolyte precursor) from the obtained reaction solution, filtration and washing with water were performed. Then, the recovered electrolyte precursor powder was dried at 300 °C for 24 hours in the air to obtain a dried solid. Next, the obtained dried solid was pulverized in an alumina mortar and passed through a 300 μm mesh sieve. Then, the obtained fine powder was fired at 500 °C for 1 hour in the air to obtain a fired powder composed of stabilized zirconia (hereinafter, also referred to as "electrolyte P1") consisting of 10.0 mol% of scandium oxide, 1.0 mol% of cerium oxide, and 89.0 mol% of zirconium oxide. Thereafter, this fired powder and ethanol were put into a polyethylene container at a mass ratio of 10:90, and further, zirconia balls (diameter: 5 mm) having the same volume as this mixed solution were put into this polyethylene container. Next, this polyethylene container was rotated at 150 rpm for 10 hours to obtain a mixed solution containing a pulverized product of the fired powder and ethanol. Thereafter, this mixed solution and zirconia balls (diameter: 0.1 mm) were placed in a zirconia pot. At this time, the zirconia balls were used in an amount corresponding to 6 times the mass of the mixed solution. Then, using a bead mill, it was pulverized at 4000 rpm for 1 hour. Thereafter, by removing the zirconia balls, a dispersion (hereinafter also referred to as "dispersion Q1") in which fine particles composed of electrolyte P1 (hereinafter also referred to as "P1 fine particles") were dispersed without sedimentation was obtained. The content ratio of the P1 fine particles contained in this dispersion Q1 was 13.4%. Thereafter, in order to be used for the production of an electrolyte sintered body, ethanol was added to this dispersion Q1 to obtain 20-fold diluted dispersions and 100-fold diluted dispersions having a mass concentration of 1 / 20 and 1 / 100, respectively. In either of these, there was no sedimentation of the P1 fine particles.

[0047] Furthermore, the particle size distribution of the P1 fine particles contained in the obtained dispersion Q1 was measured using a laser diffraction / scattering type particle size distribution measuring device "LA-960V2" (model name) manufactured by Horiba, Ltd. The results are shown in FIG. 3. Also, according to the software attached to the device, the 10% frequency diameter D 10 on a volume diameter basis is 62 nm, the 50% frequency diameter D 50 is 85 nm, and the 90% frequency diameter D 90 is 132 nm.

[0048] Example 1-2 Zirconium chloride was put into ion-exchanged water and stirred to obtain an aqueous zirconium chloride solution. Next, ytterbium oxide was put into this aqueous zirconium chloride solution and dissolved, and it was sufficiently stirred until it became completely transparent to obtain a raw material aqueous solution. The usage amount of each raw material was such that the molar ratio in terms of oxide was 10.0 mol% of ytterbium oxide and 90.0 mol% of zirconium oxide. Thereafter, aqueous ammonia was added to the raw material aqueous solution, and the reaction was carried out at room temperature with stirring. In order to purify the product (electrolyte precursor) from the obtained reaction solution, filtration and washing with water were performed. Then, the recovered electrolyte precursor powder was dried at 150 ° C. for 24 hours in the air to obtain a dried solid. Next, the obtained dry solid was pulverized in an alumina mortar and passed through a 300-μm mesh sieve. Then, the obtained fine powder was calcined in air at 150 °C for 12 hours to obtain a calcined powder composed of stabilized zirconia (hereinafter also referred to as "electrolyte P2") consisting of 10.0 mol% ytterbium oxide and 90.0 mol% zirconium oxide. Thereafter, the same operations as in Example 1-1 were performed to obtain a dispersion liquid (hereinafter also referred to as "dispersion liquid Q2") in which fine particles composed of electrolyte P2 (hereinafter also referred to as "P2 fine particles") were dispersed without sedimentation.

[0049] The particle size distribution of the P2 fine particles contained in the obtained dispersion liquid Q2 was measured, and the results shown in FIG. 4 were obtained. Also, according to the software attached to the apparatus, the 10% frequency diameter D based on the volume diameter 10 was 61 nm, the 50% frequency diameter D 50 was 83 nm, and the 90% frequency diameter D 90 was 131 nm.

[0050] 2. Production of electrolyte sintered body An electrolyte sintered body was produced using the electrolyte fine particles obtained above.

[0051] Example 2-1 The dispersion liquid Q1 obtained in Example 1-1 and scandia-stabilized zirconia particles "Zirconia for Fuel Cell 10Sc1CeSZ" (trade name, particle size: 0.4 to 0.6 μm) manufactured by Daiichi Rare Element Chemical Industry Co., Ltd. were mixed so that the mass ratio of P1 fine particles and scandia-stabilized zirconia particles was 20:80 to obtain a mixed liquid. Thereafter, this mixed liquid and zirconia balls (diameter: 0.1 mm) were placed in a zirconia pot. At this time, the amount of zirconia balls used was the same volume as the mixed liquid. Then, using a planetary ball mill, the mixture was mixed at 450 rpm for 1 hour, and then ethanol was distilled off and the solid component was dried to obtain mixed electrolyte particles. Next, 1.0 g of the obtained mixed electrolyte particles was subjected to uniaxial pressure molding (pressure: 90 kN) to obtain a disk-shaped molded body (diameter: 20 mm, thickness: 0.5 to 1.0 mm). Then, this disk-shaped molded body was heat-treated in the air at 1100 °C or 1200 °C for 5 hours to obtain each electrolyte sintered body. Then, the bulk density of the obtained electrolyte sintered body was measured, and the relative density was calculated from the ratio of this measured density to the density of scandia-stabilized zirconia (5.70 g / cm 3 ). The bulk density of the electrolyte sintered body obtained by sintering at 1100 °C was 4.92 g / cm 3 , and the relative density was 86.3%. Also, the bulk density of the electrolyte sintered body obtained by sintering at 1200 °C was 5.14 g / cm 3 , and the relative density was 90.2%.

[0052] Also, instead of the mixed electrolyte particles, the P1 fine particles contained in the dispersion liquid Q1 and the above-mentioned scandia-stabilized zirconia particles were each used alone to prepare a sintered body in the same manner, and the relative density with respect to the density of scandia-stabilized zirconia was calculated. The bulk density of the electrolyte sintered body obtained by sintering the molded body composed of P1 fine particles at 1100 °C was 4.87 g / cm 3 , and the relative density was 85.5%. Also, the bulk density of the electrolyte sintered body obtained by sintering at 1200 °C was 5.41 g / cm 3 , and the relative density was 94.8%. The bulk density of the electrolyte sintered body obtained by sintering the molded body composed of the above-mentioned scandia-stabilized zirconia particles at 1100 °C was 4.66 g / cm 3 , and the relative density was 81.8%. Also, the bulk density of the electrolyte sintered body obtained by sintering at 1200 °C was 5.04 g / cm 3 , and the relative density was 88.5%.

[0053] From the above results, it was found that when the sintered molded body contains P1 fine particles and is sintered, a dense electrolyte sintered body can be obtained at 1100 °C to 1200 °C.

[0054] Example 2-2 Weighed 1.5 g of the mixed electrolyte particles obtained in Example 2-1, and subjected them to uniaxial pressing (pressure: 90 kN) and cold isostatic pressing (CIP, pressure: 300 MPa) in this order to obtain a disc-shaped compact (diameter: 28 mm, thickness: about 1.0 mm). Then, this disc-shaped compact was heat-treated in air at 1100 °C for 5 hours to obtain an electrolyte sintered body. And in the same manner as in Example 2-1, the bulk density of the obtained electrolyte sintered body was measured, and the relative density was calculated from the ratio of this measured density (5.32 g / cm 3 ) to the density of scandia-stabilized zirconia (5.70 g / cm 3 ), and it was 93.3%. Next, platinum electrodes with a diameter of 6 mm were formed on both sides of the above electrolyte sintered body, and two platinum wires were connected to each platinum electrode. Then, while flowing pure hydrogen on one side of the electrolyte sintered body and air on the other side, it was fired at 750 °C for 2 hours. After that, the open circuit voltage (OCV) was measured at 743 °C, 695 °C, 642 °C, 595 °C, and 544 °C, and they were 1.013 V, 1.027 V, 1.040 V, 1.057 V, and 1.072 V, respectively.

[0055] 3. Manufacture of fuel cell A fuel electrode layer and a solid electrolyte layer were sequentially formed on a porous circular substrate (diameter: 28 mm) made of stainless steel 430 having pores inside and air permeability from one side to the other side to produce a half cell. Then, an air electrode layer was formed on the surface of the solid electrolyte layer to manufacture a metal-supported cell type solid oxide fuel cell.

[0056] Production Example 1 A fuel electrode and a solid electrolyte layer were sequentially formed on a porous circular substrate (diameter: 28 mm, thickness: 1.2 mm) made of stainless steel 430 having pores inside and air permeability from one side to the other side to produce a half cell. Then, an air electrode was formed on the surface of the solid electrolyte layer to obtain a fuel cell. For the formation of the fuel electrode, nickel oxide powder and scandia-stabilized zirconia powder were mixed at a mass ratio of 60:40. Then, a slurry for forming the fuel electrode was prepared by mixing this mixed powder with dibutyl phthalate, an acrylic binder, and a mixed solvent of toluene and 2-propanol using a ball mill, and this slurry was used. For the formation of the solid electrolyte layer, a slurry for forming the solid electrolyte layer was prepared by mixing scandia-stabilized zirconia powder (particle size: 0.4 - 0.6 μm) with ethyl cellulose and a mixed solvent containing terpineol using a ball mill, and this slurry was used. Also, for the formation of the air electrode, (Ba,Sr)(Co,Fe)O 3 powder and (Ce,Gd)O 2 powder were mixed at a mass ratio of 70:30. Then, a slurry for forming the air electrode was prepared by mixing them with ethyl cellulose and a mixed solvent containing terpineol using a ball mill, and this slurry was used.

[0057] The slurry for forming the fuel electrode was coated (doctor blade method) on the surface of a release PET film, and the coating film was dried sufficiently to obtain a green sheet for the fuel electrode. Next, this green sheet for the fuel electrode (size, diameter: 28 mm, thickness: 0.02 mm) was placed on the above-mentioned porous circular substrate and integrated by heating and pressing. Then, the slurry for forming the fuel electrode was coated (screen printing method) on the surface of the formed fuel electrode before sintering to form a fuel electrode before sintering. And a circular substrate equipped with the fuel electrode before sintering was heat-treated (debinding) at 850 °C for 0.5 hours in an argon atmosphere to obtain a laminate equipped with the fuel electrode. The size of the fuel electrode is 28 mm in diameter and 0.8 mm in thickness. Next, a slurry for forming a solid electrolyte layer was applied (screen printing method) to the surface of the fuel electrode in the above laminate to form a pre-sintered solid electrolyte layer. Then, a circular substrate sequentially including the fuel electrode and the pre-sintered solid electrolyte layer was heat-treated at 1150 °C for 1 hour in an environment where a gas containing hydrogen and no oxygen was circulated, and further vacuum sintered at 1240 °C for 3 hours to form a solid electrolyte layer (hereinafter referred to as the "first solid electrolyte layer"). The size of the first solid electrolyte layer is 23.3 mm in diameter and 13 μm in thickness. This laminate is referred to as the "first half cell". The obtained first half cell was in the shape of a circular plate with a diameter of 22 to 28 mm. Thereafter, a total of 100 μL of the 100-fold diluted dispersion (ethanol dispersion containing P1 fine particles) prepared in Example 1-1 was dropped (the amount of each drop: 100 μL) onto the entire surface of the first solid electrolyte layer in the first half cell. After the dropping was completed, it was heated to 80 °C to remove ethanol as the dispersion medium. This operation, that is, the process of dropping the 100-fold diluted dispersion and removing ethanol, was repeated a total of 5 times. Next, the same operation (repeated a total of 5 times) was performed using a 20-fold diluted dispersion instead of the 100-fold diluted dispersion. Then, a circular substrate sequentially including the fuel electrode and the first solid electrolyte layer containing pre-sintered P1 fine particles was heat-treated at 1200 °C for 3 hours in an environment where a gas containing hydrogen and no oxygen was circulated to form a solid electrolyte layer (hereinafter referred to as the "second solid electrolyte layer") obtained by densifying the first solid electrolyte layer. The thickness of the second solid electrolyte layer is 13 μm. This laminate is referred to as the "second half cell".

[0058] Thereafter, an air electrode was formed on each surface of the first solid electrolyte layer in the first half cell and the second solid electrolyte layer in the second half cell to obtain two types of fuel cells (metal-supported cell type solid oxide fuel cells).

[0059] Specifically, an air electrode forming slurry was applied (screen printing method) to the surface of each solid electrolyte layer to form a pre-sintering air electrode. A platinum current collector layer with a diameter of 6 mm was formed directly above the pre-sintering air electrode and on the surface of the porous metal substrate, and two platinum wires were connected to each from this platinum current collector layer. Then, pure hydrogen was circulated through the fuel electrode using the pores on the surface of the porous metal substrate, and air was circulated through the pre-sintering air electrode. By firing at 750°C for 1 hour, an integrated product equipped with an air electrode, that is, a metal-supported cell type solid oxide fuel cell, was obtained. Thereafter, in each fuel cell, when the open circuit voltage (OCV) was measured at 750°C, it was 0.78 V for the fuel cell obtained using the first half cell and 0.92 V for the fuel cell obtained using the second half cell. From these results, it is considered that the solid electrolyte layer of the fuel cell obtained using the second half cell is denser, and it can be seen that the dispersion liquid of the electrolyte fine particles used for its formation is suitable.

Industrial Applicability

[0060] The electrolyte particles for manufacturing a solid oxide electrochemical cell and its dispersion liquid of the present invention are suitable for manufacturing a sintered body constituting the solid electrolyte layer of a solid oxide electrochemical cell typified by a solid oxide fuel cell and a solid oxide electrolysis cell.

Explanation of Symbols

[0061] 1: Electrolyte particles for manufacturing a solid oxide electrochemical cell 3: Electrolyte particles 10: Formed product for sintering 12: Formed product for sintering 20: Electrolyte sintered body 22: Electrolyte sintered body

Claims

1. (A) Stabilized zirconia composed of 3.0 to 10.0 mol% of scandium oxide, 0 to 2.0 mol% of cerium oxide, and 88.0 to 97.0 mol% of zirconium oxide (B) Stabilized zirconia composed of 0.5 to 15.0 mol% of yttrium oxide and 85.0 to 99.5 mol% of zirconium oxide and (C) Stabilized zirconia composed of 0.5 to 15.0 mol% of ytterbium oxide and 85.0 to 99.5 mol% of zirconium oxide containing at least one selected therefrom, An electrolyte particle for manufacturing a solid oxide type electrochemical cell, characterized in that the volume average particle diameter measured by using a laser diffraction method is 50 to 150 nm.

2. In the particle size distribution based on volume standard measured using the laser diffraction method, D １０ , D ５０ and D ９０ are defined as the particle diameters (unit: nm) at which the cumulative frequencies are 10%, 50% and 90% respectively. The electrolyte particles for manufacturing a solid oxide type electrochemical cell according to claim 1 satisfy the following formulas (1), (2) and (3). 30 ≤ D １０ ≤ 90 (1) 70 ≤ D ５０ ≤ 150 (2) 120 ≤ D ９０ ≤ 250 (3)

3. A method for manufacturing the electrolyte particle for manufacturing a solid oxide type electrochemical cell according to Claim 1, dissolving a water-soluble compound containing at least one stabilizing element selected from scandium, yttrium, ytterbium and cerium and a water-soluble compound containing zirconium in water, mixing the obtained aqueous solution and a basic material to form a precipitate consisting of an electrolyte precursor, then drying the precipitate, heat-treating the obtained dried product, and then pulverizing it. A method for manufacturing an electrolyte particle for manufacturing a solid oxide type electrochemical cell, characterized by the above steps.

4. A dispersion for forming an electrolyte of a solid oxide type electrochemical cell, characterized by containing the electrolyte particle for manufacturing a solid oxide type electrochemical cell according to Claim 1 and ethanol.

5. A method for manufacturing an electrolyte sintered body, characterized by subjecting a sintered molded article containing the electrolyte particle for manufacturing a solid oxide type electrochemical cell according to Claim 1 to sintering.

6. Contacting a molded article containing a solid electrolyte with the dispersion for forming an electrolyte according to Claim 4, and producing an adherend in which the electrolyte particles for manufacturing a solid oxide type electrochemical cell contained in the dispersion for forming an electrolyte are adhered to the molded article, and subjecting the adherend to sintering as a sintered molded article. A method for manufacturing an electrolyte sintered body, characterized by the above steps.

7. An electrolyte sintered body, characterized by being obtained by the manufacturing method according to Claim 5 or 6.

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