Method for manufacturing solid electrolyte assembly and method for manufacturing electrochemical cell

Abstract

The present invention addresses the problem of manufacturing an oxide ion conductor having high oxide ion conductivity by performing firing at a lower temperature through a simpler process. A laminate provided with an intermediate layer precursor layer that contains a rare earth element and a solid electrolyte layer precursor layer that contains a first element selected from Si and Ge and a second element selected from Al and the like is fired to diffuse the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming an intermediate layer containing an oxide containing the rare earth element.

Description

Method for Producing Solid Electrolyte Joined Body and Method for Producing Electrochemical Cell

[0001] The present invention relates to a method for producing a solid electrolyte joined body and a method for producing an electrochemical cell.

[0002] In recent years, electrochemical cells such as fuel cells and electrolytic cells have attracted attention ２ as an effort to prevent global warming through CO₂ reduction. Among these, solid oxide fuel cells (SOFCs) and solid oxide electrolytic cells (SOECs), which are composed of ceramic materials, can operate at high temperatures and have high power generation efficiency and electrolysis efficiency. High oxide ion conductivity is required for solid electrolytes, which are main constituent members of SOFCs and SOECs.

[0003] As materials having oxide ion conductivity, yttria-stabilized zirconia (Zr １－ｘ Y ｘ O ２ ) having a fluorite structure, gadolinium-doped ceria (Ce １－ｘ Gd ｘ O ２ ), and lanthanum gallate (La １－ｘ Sr ｘ )(Ga １－ｘ Mg ｘ )O ３ having a perovskite structure, and the like are known. It is known that oxygen vacancies exist in these oxide ion conductors, and oxide ions conduct through the oxygen vacancies.

[0004] In contrast, as oxide ion conductors in which oxide ions move between lattices, materials having apatite-type crystals such as La １０ Si ６ O ２７ have been reported. Among oxide ion conductors having apatite-type crystals, lanthanum silicate has been reported to have high oxide ion conductivity in a medium temperature range. In particular, since lanthanum silicate has low activation energy along the c-axis direction, it has attracted attention as a solid electrolyte for electrochemical cells.

[0005] In order to obtain an apatite-type lanthanum silicate-based solid electrolyte, Patent Document 1 discloses La ２ SiO５ a first layer containing, as a main component, La ２ Si ２ O ７ a method of bringing a second layer containing, as a main component, the above into contact and firing at 1600°C has been proposed. This document describes that, in this method, element diffusion occurs between the first layer and the second layer to generate lanthanum silicate having an apatite-type crystal structure, and the c-axis of the generated lanthanum silicate crystals is oriented along a direction perpendicular to the original bonding interface.

[0006] Patent Document 2 discloses (RE ２ O ３ ) ｘ (SiO ２ ) ６ wherein RE is an element selected from the group consisting of La, Ce, Pr, Nd and Sm, x satisfies the condition of 3.5 < x < 6, as a main component, an oxide ion conductive ceramic having an apatite-type crystal structure as a main constituent layer.

[0007] Patent Document 3 describes a method for producing a film made of a composite oxide represented by A ｘ B ６ O １．５ｘ＋１２ (6≦X≦30), containing a trivalent element A, a tetravalent element B, and oxygen O. This production method comprises: after supplying a first raw material containing either one of the element A and the element B onto a substrate selected from any one of a Si(100) substrate, a cermet substrate containing Ni and ceramics, or a ceramics substrate made of a perovskite-type composite oxide, supplying an oxidant to form a first film made of an oxide of either one of the element A and the element B; then supplying a second raw material containing the remaining one of the element B and the element A, and then supplying an oxidant to form a second film made of an oxide of either one of the element B and the element A; a first step of forming the above, a second step of repeating the first step to laminate a plurality of the first films and the second films respectively to obtain a laminate; and subjecting the substrate and the laminate to a heat treatment to obtain A ｘ B ６ O １．５ｘ＋１２The manufacturing method comprises a third step of forming a composite oxide film made of polycrystalline material consisting of (6 ≤ x ≤ 30) and in which the c-axis direction of each crystal grain extends along the thickness direction. This manufacturing method is characterized by controlling the composition ratio of element A and element B in the composite oxide film by the ratio of the number of times the first raw material and the second raw material are supplied in the first step. In this manufacturing method, atomic layer deposition (ALD) is employed as the film formation method. A heat treatment of 800 to 1200°C is proposed.

[0008] Patent Document 4 proposes a method for producing ion-conducting oriented ceramics by mixing and heating an oxide raw material containing lanthanide oxide powder and at least one oxide powder of Si or Ge to form a liquid state, casting it, rapidly cooling it to obtain a glassy material, and then heat-treating this glassy material at 800 to 1400°C. The document states that this method is low-cost and simple, yet allows for the easy production of large-area ion-conducting oriented ceramics.

[0009] International Publication No. 2012 / 015061 Pamphlet, Japanese Patent Publication No. Hei 11-71169, US 2013 / 052445A1, Japanese Patent Publication No. 2011-37662

[0010] As described in the aforementioned Patent Documents 1 and 2, conventional methods for producing apatite-type lanthanum silicate oxide ion conductors require high-temperature firing to obtain high-density apatite-type lanthanum silicate. Furthermore, conventional manufacturing methods have problems in that it is difficult to obtain large crystals while suppressing crack formation in the apatite-type lanthanum silicate, and the manufacturing cost is high. In the method described in Patent Document 3, although the heat treatment temperature is low at 800 to 1200°C, the use of ALD for film formation is proposed. Since ALD is a method that utilizes vacuum deposition, the manufacturing cost of apatite-type lanthanum silicate becomes high. In the method described in Patent Document 4, since a molten glass formation process is used, ceramics having an apatite-type crystal structure can be obtained with relatively low-temperature heat treatment at 800 to 1400°C. However, in order to obtain molten glass, it is necessary to go through a high-temperature heating process of 1400 to 1700°C, and impurities are present in the apatite-type crystal. Therefore, the method described in this document has not always been able to efficiently produce apatite-type crystals.

[0011] Therefore, the object of the present invention is to provide a method for producing oxide ion conductors by a simpler process that does not require firing at temperatures higher than 1400°C or film formation using a vacuum deposition apparatus.

[0012] The present invention provides a method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, either as an element or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, either as an element or a compound containing the second element, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element.

[0013] The present invention also provides a method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, the method comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound containing at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element.

[0014] The present invention also provides a method for manufacturing a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing a rare earth element, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, either as an element or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, either as an element or a compound containing the second element, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element.

[0015] Furthermore, the present invention provides a method for manufacturing a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element.

[0016] Furthermore, the present invention provides a method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, or a compound containing the second element, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[0017] Furthermore, the present invention provides a method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound containing at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[0018] Figure 1 is a schematic diagram showing the structure of an example electrochemical cell manufactured by the method of the first invention. Figure 2 is a schematic diagram showing the structure of an example electrochemical cell manufactured by the methods of the second and third inventions. Figure 3 is a schematic diagram showing the structure of a laminate used in the method of the second invention. Figure 4 is a schematic diagram showing the structure of a laminate used in the method of the third invention. Figure 5 is a scanning electron microscope image of a longitudinal section of the solid electrolyte layer in a laminate having a fuel electrode substrate, an intermediate layer, and a solid electrolyte obtained in Example 1. Figure 6 is a scanning electron microscope image of a longitudinal section of the solid electrolyte layer in a laminate having a fuel electrode substrate, an intermediate layer, and a solid electrolyte obtained in Example 2. Figure 7 is a scanning electron microscope image of a longitudinal section of the solid electrolyte layer in a laminate having a fuel electrode substrate, an intermediate layer, and a solid electrolyte obtained in Comparative Example 1. Figure 8 is a scanning electron microscope image of a longitudinal section of an electrochemical cell having a fuel electrode substrate, a fuel electrode side intermediate layer, an intermediate layer, a solid electrolyte, an air electrode side intermediate layer, and an air electrode layer obtained in Example 5. Figure 9 shows the X-ray diffraction pattern of the solid electrolyte layer surface in the laminates obtained in Examples 1 to 4, which consist of a fuel electrode layer, an intermediate layer, and a solid electrolyte. Figure 10 shows the output characteristics results from a power generation test performed on the electrochemical cell obtained in Example 5.

[0019] [First Invention] The first invention will be described below based on its preferred embodiments. The first invention relates to a method for manufacturing a solid electrolyte assembly and a method for manufacturing an electrochemical cell equipped with the solid electrolyte assembly. The solid electrolyte assembly manufactured by the method of the first invention comprises a solid electrolyte layer and an intermediate layer. This solid electrolyte laminate is suitably used in the manufacture of an electrochemical cell comprising at least a fuel electrode layer or an air electrode layer, a solid electrolyte layer, and an intermediate layer located between the two layers. First, an example of an electrochemical cell equipped with a solid electrolyte assembly manufactured by the method of the first invention will be described with reference to Figure 1.

[0020] The electrochemical cell laminate 10 shown in Figure 1 comprises an air electrode layer 12, a layer containing a solid electrolyte (hereinafter also referred to as the "solid electrolyte layer") 11, and a fuel electrode layer 13. The solid electrolyte layer 11 is made of a material that has oxide ion conductivity above a predetermined temperature. The solid electrolyte layer 11 is located between the two electrodes, namely the air electrode layer 12 and the fuel electrode layer 13. In other words, the air electrode layer 12 and the fuel electrode layer 13 are arranged on different sides of the solid electrolyte layer 11.

[0021] An air electrode-side intermediate layer 15 is positioned between the air electrode layer 12 and the solid electrolyte layer 11. On the other hand, a fuel electrode-side intermediate layer 16 is positioned between the fuel electrode layer 13 and the solid electrolyte layer 11. In Figure 1, the air electrode layer 12 and the air electrode-side intermediate layer 15 are shown as being the same size, but their relative sizes are not limited to this. For example, the air electrode layer 12 may be smaller than the air electrode-side intermediate layer 15. The same applies to the fuel electrode layer 13 and the fuel electrode-side intermediate layer 16; they may be the same size, or for example, the fuel electrode layer 13 may be larger than the fuel electrode-side intermediate layer 16. Also, in Figure 1, the size of the air electrode-side intermediate layer 15 and the solid electrolyte layer 11 are shown as being the same size, but their relative sizes are not limited to this. For example, the air electrode-side intermediate layer 15 may be smaller than the solid electrolyte layer 11. The same applies to the fuel electrode-side intermediate layer 16.

[0022] As shown in Figure 1, the air electrode side intermediate layer 15 is in direct contact with the air electrode layer 12 and the solid electrolyte layer 11. The air electrode side intermediate layer 15 is also in direct contact with the solid electrolyte layer 11. The same applies to the fuel electrode layer 13 side, where the fuel electrode side intermediate layer 16 is in direct contact with the solid electrolyte layer 11 and the fuel electrode layer 13. In the solid electrolyte assembly manufactured by the method of the first invention, the solid electrolyte layer corresponds to the solid electrolyte layer 11 shown in Figure 1, and the intermediate layer corresponds to the air electrode side intermediate layer 15 and / or the fuel electrode side intermediate layer 16.

[0023] The air electrode side intermediate layer 15 and the fuel electrode side intermediate layer 16 (hereinafter, for convenience, both may be collectively referred to simply as "intermediate layer 17") are used to improve the oxide ion conductivity between the solid electrolyte layer 11 and the air electrode layer 12 and / or the fuel electrode layer 13 in the electrochemical cell laminate 10. In order to reduce the electrical resistance in the electrochemical cell laminate 10, it is important to increase the oxide ion conductivity of the solid electrolyte layer 11. However, even if the solid electrolyte layer 11 is constructed using a material with high oxide ion conductivity, if the oxide ion conductivity between the solid electrolyte layer 11 and the fuel electrode layer 13 and / or the air electrode layer 12 is low, there is a limit to how much the oxide ion conductivity of the electrochemical cell laminate 10 as a whole can be increased. Therefore, by providing an intermediate layer 17 made of a material that can reduce interfacial resistance between the solid electrolyte layer 11 and the fuel electrode layer 13 and / or the air electrode layer 12, the conduction of oxide ions between the solid electrolyte layer 11 and the fuel electrode layer 13 and / or the air electrode layer 12 is made smoother. The electrochemical cell laminate 10 shown in Figure 1 has intermediate layers 17 (air electrode side intermediate layer 15 and fuel electrode side intermediate layer 16) on each side of the solid electrolyte layer 11, but the electrochemical cell laminate 10 may instead have only one of the air electrode side intermediate layer 15 and the fuel electrode side intermediate layer 16.

[0024] As shown in Figure 1, a support layer 14 is arranged on the outer surface of the fuel electrode layer 13. The support layer 14 is a layer that increases the mechanical strength of the electrochemical cell laminate 10. Because the mechanical strength of the electrochemical cell laminate 10 is increased by the support layer 14, it is possible to reduce the thickness of the air electrode layer 12, fuel electrode layer 13, solid electrolyte layer 11, and intermediate layer 17 compared to when the support layer 14 is not present. The support layer 14 may be made of metal, for example. The support layer 14 can be made of, for example, a metal plate-like body or a metal porous body having a plurality of through holes extending in the thickness direction. Examples of metals that make up the support layer 14 include stainless steels such as ferritic stainless steel and austenitic stainless steel, and nickel-based alloys such as Ni-Fe alloy and Ni-Cr alloy, but are not limited to these. The function of the fuel electrode layer 13 can also be given to the support layer 14, and the intermediate layer 17, solid electrolyte layer 11, and air electrode layer 12 can be laminated on the support layer 14.

[0025] The air electrode layer 12 and the fuel electrode layer 13, which are directly in contact with the intermediate layer 17, can each be independently composed of, for example, a metallic material or an oxide having oxide ion conductivity. When the air electrode layer 12 and the fuel electrode layer 13 are composed of a metallic material, it is preferable that the metallic material contains platinum group elements because it has advantages such as high catalytic activity. Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements can be used individually or in combination of two or more. In addition, cermets containing platinum group elements can be independently used as the fuel electrode layer 13 and the air electrode layer 12.

[0026] On the other hand, if either the air electrode layer 12 or the fuel electrode layer 13 is composed of an oxide having oxide ion conductivity, the oxide may be ABO ３－δ Materials having a perovskite structure represented by the formula ABO are preferably used. In the formula, A represents an alkaline earth metal element. B represents a transition metal element, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Ta, and W. δ is a fraction resulting from the valencies and amounts of A, B, and O. ABO ３－δ Various oxides having a perovskite structure represented by are known, and such oxides are known to have various crystal systems, such as cubic, tetragonal, rhombohedral, and orthorhombic. Among these crystal systems, ABO has a cubic perovskite structure. ３－δ It is preferable to use an oxide of the same type as the air electrode layer 12 and / or the fuel electrode layer 13. By directly joining the air electrode layer 12 and / or the fuel electrode layer 13 made of such an oxide with the intermediate layer 17 made of the above-mentioned material to form the electrochemical cell laminate 10, the oxide ion conductivity of the electrochemical cell laminate 10 as a whole can be further enhanced.

[0027] The air electrode layer 12 and the fuel electrode layer 13 preferably have a predetermined thickness, as this can more effectively enhance the oxide ion conductivity of the electrochemical cell laminate 10. More specifically, the thickness of the air electrode layer 12 and the fuel electrode layer 13 bonded to the intermediate layer 17 is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1000 nm to 30000 nm. The thickness of the air electrode layer 12 and the fuel electrode layer 13 can be measured by a stylus step meter or an electron microscope.

[0028] A preferred method for manufacturing the electrochemical cell laminate 10 having the above configuration is described below. This manufacturing method is broadly divided into the following steps: Step 1: Manufacturing of a laminate comprising an intermediate layer precursor and a solid electrolyte layer precursor. Step 2: Firing of the laminate. Each step will be described below.

[0029] <Step 1> In this step, an intermediate layer precursor and a solid electrolyte layer precursor are fabricated. The intermediate layer precursor is a precursor layer for forming the air electrode side intermediate layer 15 and / or fuel electrode side intermediate layer 16 shown in Figure 1. The solid electrolyte layer precursor is a precursor layer for forming the solid electrolyte layer 11 shown in Figure 1. The intermediate layer precursor and the solid electrolyte layer precursor are directly stacked to form a laminate. Therefore, in this laminate, there is no layer between the intermediate layer precursor and the solid electrolyte layer precursor.

[0030] <Intermediate Progenitor Layer> The intermediate precursor layer is a layer containing rare earth elements. The intermediate precursor layer may, for example, be a layer containing oxides of rare earth elements. Specifically, the intermediate precursor layer may be a layer containing particles of rare earth element oxides and a solvent. Examples of rare earth elements include lanthanum, samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium.

[0031] The intermediate precursor layer preferably contains cerium oxide containing lanthanum (hereinafter also referred to as "LDC"). The LDC is made of cerium oxide (CeO2) which is the base material. ２It is an oxide containing lanthanum in a solid solution (doped) form. Lanthanum can exist in the crystal lattice of cerium oxide, either by substituting the site where cerium is located, or at the grain boundaries of cerium oxide doped with rare earth elements. When both an air electrode side intermediate layer 15 and a fuel electrode side intermediate layer 16 are formed as the intermediate layer 17, the intermediate layer precursor layer for forming the air electrode side intermediate layer 15 and the intermediate layer precursor layer for forming the fuel electrode side intermediate layer 16 may be of the same type or different types.

[0032] In LDC, lanthanum is included for the purpose of improving the oxide ion conductivity of the entire electrochemical cell laminate 10 and for the purpose of diffusing into the solid electrolyte layer precursor to form the solid electrolyte layer 11. For this purpose, it is preferable that the value of La / Ce, which is the atomic ratio of lanthanum to cerium in LDC, be 0.10 or higher. Furthermore, since excessive lanthanum content actually reduces ion conductivity, it is preferable that the value of La / Ce be 1.5 or lower. From a similar viewpoint, it is even more preferable that the value of La / Ce be 0.20 or higher and 1.2 or lower, and even more preferable that it be 0.25 or higher and 1.0 or lower. The value of La / Ce is measured by energy-dispersive X-ray spectroscopy (EDS) or electron probe microanalyzer (EPMA), etc.

[0033] LDC is, for example, lanthanum oxide (La ２ O ３ ) and cerium oxide (CeO ２ It is obtained by mixing ) and in a predetermined ratio to obtain a mixed powder, and then firing this mixed powder in an oxygen-containing atmosphere. By adjusting the mixing ratio of lanthanum oxide and cerium oxide, LDC with a desired La / Ce value can be obtained. A mixture of LDC with a high La / Ce value and a compound containing La may be used as an intermediate layer precursor.

[0034] The intermediate layer precursor can be obtained, for example, by mixing the LDC particles and solvent described above to form a slurry, applying this slurry onto a pre-formed air electrode layer 12 or fuel electrode layer 13 to form a coating film, and then removing at least a portion of the solvent from this coating film. The methods for manufacturing the air electrode layer 12 and fuel electrode layer 13 are well known in the art and therefore do not require special explanation. As for the coating method, wet coating methods such as screen printing, spin coating, and spray coating can be used. Water and organic solvents can be used as solvents. Examples of organic solvents include ethanol, isopropyl alcohol, terpineol, and toluene. The organic solvents can be used individually or in combination of two or more. Mixing can be performed using, for example, a rotation-orbit mixer, an ultrasonic homogenizer, a shaker, a thin-film swirling mixer, a dissolver, a homomixer, a kneader, a roll mill, a sand mill, an attritor, a ball mill, a vibrator mill, and a high-speed impeller mill. During mixing, additives such as dispersants, defoamers, binders, and plasticizers may be used as needed. Alternatively, a green sheet may be produced using the slurry, and this green sheet may be used as an intermediate layer precursor.

[0035] <Solid Electrolyte Layer Precursor> The solid electrolyte layer precursor is a layer containing a first element and a second element. The solid electrolyte layer precursor may be, for example, (i) a layer of a mixture containing the first element in its elemental form or compound and the second element in its elemental form or compound. Alternatively, the solid electrolyte layer precursor may be, for example, (ii) a layer containing a single compound containing the first element and the second element. By firing a solid electrolyte layer precursor having the embodiment of (i) or (ii), a dense solid electrolyte layer with high oxide ion conductivity can be obtained despite firing at low temperatures.

[0036] Regardless of whether the solid electrolyte precursor layer is in embodiment (i) or (ii), the first element is at least one selected from the group consisting of Si and Ge. From the viewpoint of high conductivity of oxide ions, the first element is preferably Si.

[0037] Regardless of whether the solid electrolyte layer precursor is in embodiment (i) or (ii), the second element is preferably at least one selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba. The inclusion of the second element in the solid electrolyte layer precursor allows for the formation of a substance with a low softening point and melting temperature containing both the first and second elements in the solid electrolyte layer precursor during the firing process, which facilitates the densification of the solid electrolyte at low temperatures. From the viewpoint of facilitating the densification of the solid electrolyte at even lower temperatures, it is more preferable that the second element is at least one selected from the group consisting of Al, Mg, Ti, V, Fe, B, Zn, P, and Ca, and from the viewpoint of high oxide ion conductivity, it is even more preferable that it is at least one selected from the group consisting of Al, Mg, and B.

[0038] Regardless of whether the solid electrolyte layer precursor is in the form of (i) or (ii), in the solid electrolyte layer precursor, it is preferable to have a molar ratio of the second element to the first element of 0.50 or less from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing. From this viewpoint, it is even more preferable that the molar ratio of the second element to the first element be 0.40 or less, and even more preferable that it be 0.30 or less. From the same viewpoint as above, it is preferable that the molar ratio of the second element to the first element be 0.010 or more, even more preferable that it be 0.050 or more, and even more preferable that it be 0.10 or more. The following describes matters specific to the form of (i) and the form of (ii), respectively.

[0039] <Aspect of (i)> When the first element is contained in the solid electrolyte layer precursor in the form of a compound, examples of such compounds include oxides, hydroxides, nitrates, sulfates, and halides. Of these compounds, oxides are preferred from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0040] In particular, the first element is Si, and Si is in its oxide state, for example, silicon dioxide (SiO₂) ２It is preferable that the solid electrolyte layer precursor is contained in the state shown above, from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0041] The same applies to the second element as to the first element. When the second element is contained in the solid electrolyte precursor layer in the form of a compound, examples of such compounds include oxides, hydroxides, nitrates, sulfates, and halides. Of these compounds, oxides are preferred from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0042] In particular, the second element is Al, and Al is in its oxide state, for example, aluminum oxide (Al ２ O ３ It is preferable that the solid electrolyte layer precursor is contained in the state shown above, from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0043] The solid electrolyte layer precursor may contain, in addition to the first and second elements described above, one or more elements selected from the group consisting of La, Y, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu (hereinafter, these elements are also referred to as the "third element") in their elemental form or a compound containing the third element. By including the solid electrolyte layer precursor in its elemental form or a compound containing the third element, a solid electrolyte layer with high conductivity for oxide ions can be obtained. From this viewpoint, it is even more preferable that the third element includes its elemental form or a compound containing La.

[0044] When the solid electrolyte layer precursor contains a first element, a second element, and a third element, the following embodiments are possible: (a) an embodiment in which the solid electrolyte layer precursor contains the first element in its elemental form or a compound containing the first element, the second element in its elemental form or a compound containing the second element, and the third element in its elemental form or a compound containing the third element. (b) an embodiment in which the solid electrolyte layer precursor contains the first element in its elemental form or a compound containing the first element, and compounds containing the second and third elements. (c) an embodiment in which the solid electrolyte layer precursor contains the second element in its elemental form or a compound containing the second element, and compounds containing the first and third elements.

[0045] In case (a), examples of compounds containing the third element include oxides, hydroxides, nitrates, sulfates, and halides. Of these compounds, oxides or hydroxides are preferred from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0046] In particular, the third element is La, and La is in the form of its oxide or hydroxide, for example, La ２ O ３ Or La(OH) ３ It is preferable that the solid electrolyte layer precursor is contained in this state.

[0047] In any of the cases from (a) to (c), when the solid electrolyte layer precursor contains a third element, it is preferable to have a molar ratio of the third element to the first element of less than 1, from the viewpoint of obtaining a highly dense solid electrolyte layer by low-temperature firing. By having a molar ratio of the third element to the first element of less than 1, a highly dense solid electrolyte layer precursor can be obtained by low-temperature firing, and furthermore, the volume expansion of the solid electrolyte layer precursor due to the diffusion of rare earth elements into the solid electrolyte layer precursor can be utilized, making it easier to obtain a highly dense solid electrolyte layer. From this viewpoint, it is even more preferable that the molar ratio of the third element to the first element be 0.8 or less, even more preferable that be 0.7 or less, and even more preferable that be 0.5 or less. Also, from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions, it is preferable that the molar ratio of the third element to the first element be 0.1 or more, even more preferable that be 0.15 or more, and even more preferable that be 0.3 or more.

[0048] The solid electrolyte layer precursor can be obtained, for example, by mixing the elemental first element or a compound containing the first element, the elemental second element or a compound containing the second element, the elemental third element or a compound containing the third element, and a solvent to form a slurry, applying this slurry onto the intermediate layer precursor to form a coating film, and then removing at least some of the solvent from this coating film. Alternatively, a green sheet may be manufactured using the slurry, and this green sheet may be used as the solid electrolyte layer precursor.

[0049] <Aspect of (ii)> In (ii), the solid electrolyte layer precursor is a layer containing a single compound containing the first element and the second element. Examples of this compound include a composite oxide containing the first element and the second element. In particular, it is preferable that the first element is Si and the second element is Al, and that the solid electrolyte layer precursor contains an oxide containing Si and Al, from the viewpoint of obtaining a solid electrolyte layer with high conductivity of oxide ions by low-temperature firing.

[0050] Similar to embodiment (i), the solid electrolyte layer precursor may also contain a third element in embodiment (ii). Details of the third element are the same as those described in embodiment (i). Preferably, the third element constitutes a single compound together with the first and second elements. For example, the solid electrolyte layer precursor preferably contains a single compound containing the first, second, and third elements. Examples of such compounds include composite oxides containing the first, second, and third elements. Alternatively, the third element may be included in the solid electrolyte layer precursor in the form of the third element alone or in the form of a compound containing the third element. In this case, the solid electrolyte layer precursor is composed of a compound containing the first and second elements, and the third element alone or in the form of a compound containing the third element.

[0051] In embodiment (ii), when the solid electrolyte layer precursor contains a first element, a second element, and a third element, the molar ratio of the third element to the first element is preferably less than 1, more preferably 0.9 or less, and even more preferably 0.8 or less. From the same viewpoint as above, the molar ratio of the third element to the first element is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more.

[0052] In embodiment (ii), the solid electrolyte layer precursor can be obtained, for example, by mixing a single compound containing the first, second, and third elements described above with a solvent to form a slurry, applying this slurry onto the intermediate layer precursor to form a coating film, and removing at least a portion of the solvent from this coating film. The mixing method and the method of applying the slurry can be the same as those used to form the intermediate layer precursor. Alternatively, a green sheet may be manufactured using the slurry, and this green sheet may be used as the solid electrolyte layer precursor.

[0053] <Step 2> In this step, the laminate obtained in Step 1 is fired to form a solid electrolyte layer from the solid electrolyte layer precursor layer. In this manufacturing method, by using the above-mentioned material as the solid electrolyte layer precursor layer, the firing of the laminate can be performed at a lower temperature range than conventional methods. As a result, the solid electrolyte layer can be formed by a simple process without firing at high temperatures exceeding 1400°C or using vacuum deposition equipment such as ALD. The firing of the laminate can be performed at 1400°C or lower, preferably 1350°C or lower, and more preferably 1320°C or lower. Furthermore, from the viewpoint of exhibiting high oxide ion conductivity in the solid electrolyte layer, the firing of the laminate is preferably performed at 900°C or higher, more preferably 950°C or higher, and even more preferably 1000°C or higher. The firing atmosphere can be an oxygen-containing atmosphere such as air, an inert atmosphere such as nitrogen and argon, or a reducing atmosphere containing hydrogen. From the viewpoint of reliably exhibiting high oxide ion conductivity in the solid electrolyte layer, it is advantageous to use an oxygen-containing atmosphere. The firing time is adjusted so that the solid electrolyte layer exhibits sufficient oxide ion conductivity. Generally, a firing time of 1 hour to 40 hours, more preferably 1 hour to 30 hours, is used to achieve satisfactory oxide ion conductivity in the solid electrolyte layer.

[0054] By firing the laminate, rare earth elements, such as lanthanum, contained in the intermediate layer precursor diffuse into the solid electrolyte layer precursor. The rare earth elements diffused into the solid electrolyte layer precursor react with the first element contained in the solid electrolyte layer precursor to produce an oxide ion conductive oxide containing at least the rare earth element and the first element. This reaction forms a solid electrolyte layer containing this oxide. It is preferable that the produced oxide ion conductive oxide has an apatite-type crystal structure, as this can enhance the conductivity of oxide ions in the solid electrolyte layer. The second element contained in the solid electrolyte layer precursor may be present in the oxide ion conductive oxide in the solid electrolyte layer after firing the laminate, and / or in a compound present in the solid electrolyte layer separately from the oxide ion conductive oxide, or all of the second element may migrate to a layer other than the solid electrolyte layer by diffusion and may not be present in the solid electrolyte layer. On the other hand, with respect to the intermediate layer precursor, although some of the rare earth elements contained in the intermediate layer precursor diffuse into the solid electrolyte layer precursor, the remaining rare earth elements remain in the intermediate layer precursor, so the intermediate layer formed from the intermediate layer precursor contains rare earth elements. In particular, it is preferable that the intermediate layer contains cerium oxide doped with rare earth elements (except cerium) because this increases the oxide ion conductivity of the entire electrochemical cell. It is especially advantageous that the intermediate layer contains cerium oxide doped with lanthanum because this further increases the oxide ion conductivity of the entire electrochemical cell.

[0055] By following the above procedure, a fired laminate is obtained. This laminate comprises an air electrode layer 12 or a fuel electrode layer 13, an intermediate layer 17 located above it, and a solid electrolyte layer 11 located above that. By providing another intermediate layer 17 on the solid electrolyte layer 11 of this laminate using the procedure described above, and then providing the fuel electrode layer 13 or air electrode layer 12 on top of that using a conventional method, the desired electrochemical cell laminate can be obtained. To form another intermediate layer 17 on the solid electrolyte layer 11, wet coating methods such as screen printing, spin coating and spray coating, PVD methods (such as sputtering and pulse laser deposition), and CVD methods can also be used.

[0056] When manufacturing an electrochemical cell laminate having a support layer 14 as shown in Figure 1, the fuel electrode layer 13 is formed on the support layer 14 by a conventional method, then the intermediate layer precursor and solid electrolyte layer precursor are formed using the method described above, and then the firing described above is performed. Even if the support layer 14 is made of metal, for example, the temperature range when firing the intermediate layer precursor and solid electrolyte layer precursor can be lower than in the conventional method, which has the advantage that the support layer 14 made of metal is less susceptible to thermal damage.

[0057] In this way, the desired electrochemical cell laminate is obtained. The obtained electrochemical cell laminate can be used, for example, as an SOFC or SOEC containing it.

[0058] [Second Invention] Next, the second invention will be described. For points that are not specifically described with respect to the second invention, the description of the first invention described above will be applied as appropriate. The second invention relates to a method for manufacturing a solid electrolyte layer and a method for manufacturing an electrochemical cell equipped with the solid electrolyte layer. An electrochemical cell manufactured by the method according to the second invention comprises at least a fuel electrode layer or an air electrode layer and a solid electrolyte layer. An example of an electrochemical cell manufactured by the method of the second invention will be described with reference to Figure 2. The electrochemical cell laminate 10A shown in Figure 2 comprises an air electrode layer 12, a solid electrolyte layer 11, and a fuel electrode layer 13. The solid electrolyte layer 11 is located between the air electrode layer 12 and the fuel electrode layer 13. In other words, the air electrode layer 12 and the fuel electrode layer 13 are arranged on different sides of the solid electrolyte layer 11, respectively. Unlike the electrochemical cell laminate 10 shown in Figure 1 described above, the electrochemical cell laminate 10A of this embodiment does not have an intermediate layer. Details of the air electrode layer 12, solid electrolyte layer 11, and fuel electrode layer 13 constituting the electrochemical cell laminate 10A are the same as in the first invention.

[0059] A preferred method for manufacturing the electrochemical cell laminate 10A having the above configuration is described below. This manufacturing method is broadly divided into the following steps: Step 1: Manufacturing of a laminate comprising a precursor layer and a solid electrolyte layer precursor layer. Step 2: Firing of the laminate. Each step will be described below.

[0060] <Step 1> In this step, as shown in Figure 3, a precursor layer 20 and a solid electrolyte layer precursor layer 21 are formed on a pre-formed air electrode layer 12 or fuel electrode layer 13 to obtain a laminate 10A'. There is no layer between the precursor layer 20 and the solid electrolyte layer precursor layer 21. The precursor layer 20 is a layer for diffusing rare earth elements into the solid electrolyte layer precursor layer 21 by firing. The solid electrolyte layer precursor layer is a layer that serves as a precursor for forming the solid electrolyte layer 11 shown in Figure 2.

[0061] The precursor layer 20 is a layer containing rare earth elements. The precursor layer 20 may be, for example, a layer containing oxides of rare earth elements. Specifically, the precursor layer 20 may be a layer containing particles of rare earth element oxides and a solvent. Examples of rare earth elements include lanthanum, samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium.

[0062] Since the details of the precursor layer 20 are the same as those of the intermediate layer precursor layer in the first invention, the explanation of the intermediate layer precursor layer will be applied as appropriate to any points that are not specifically explained regarding the precursor layer 20. Similarly, since the details of the solid electrolyte layer precursor layer 21 are the same as those of the solid electrolyte layer precursor layer in the first invention, the explanation of the solid electrolyte layer precursor layer in the first invention will be applied as appropriate to any points that are not specifically explained regarding the solid electrolyte layer precursor layer 21.

[0063] <Step 2> In this step, the laminate 10A' (see Figure 3) obtained in Step 1 is fired to form a solid electrolyte layer 11 (see Figure 2) from the solid electrolyte layer precursor layer 21. In this manufacturing method, by using the above-mentioned material as the solid electrolyte layer precursor layer, the firing of the laminate 10A' can be performed at a lower temperature range than conventional methods. As a result, the solid electrolyte layer can be formed by a simple process without firing at high temperatures exceeding 1400°C or using vacuum deposition equipment such as ALD. The firing of the laminate 10A' can be performed at 1400°C or lower, preferably 1350°C or lower, and more preferably 1300°C or lower. Furthermore, from the viewpoint of exhibiting high oxide ion conductivity in the solid electrolyte layer, the firing of the laminate 10A' is preferably performed at 900°C or higher, more preferably 950°C or higher, and even more preferably 1000°C or higher. The firing atmosphere can be an oxygen-containing atmosphere such as air, an inert atmosphere such as nitrogen and argon, or a reducing atmosphere containing hydrogen. From the viewpoint of reliably achieving high oxide ion conductivity in the solid electrolyte layer, it is advantageous to use an oxygen-containing atmosphere. The firing time is adjusted so that sufficient oxide ion conductivity is achieved in the solid electrolyte layer. Generally, by employing a firing time of preferably 1 hour to 40 hours, and more preferably 1 hour to 30 hours, satisfactory oxide ion conductivity is achieved in the solid electrolyte layer.

[0064] By firing the laminate 10A', rare earth elements, such as lanthanum, contained in the precursor layer 20 (see Figure 3) diffuse into the solid electrolyte layer precursor layer 21 (see Figure 3). The rare earth elements diffused into the solid electrolyte layer precursor layer 21 react with the first element contained in the solid electrolyte layer precursor layer 21 to produce an oxide ion conductive oxide containing at least the rare earth elements and the first element. This reaction forms the solid electrolyte layer 11 (see Figure 2) containing this oxide. On the other hand, with respect to the precursor layer 20, all the rare earth elements contained in the precursor layer 20 disappear as they diffuse into the solid electrolyte layer precursor layer 21. As a result, the solid electrolyte layer 11 is formed directly on the air electrode layer 12 or the fuel electrode layer 13. In order to diffuse all the rare earth elements contained in the precursor layer 20 into the solid electrolyte layer precursor layer 21, the firing temperature and / or firing time should be appropriately adjusted.

[0065] [Third Invention] Next, the third invention will be described. For points that are not specifically described with respect to the third invention, the descriptions of the first and second inventions described above will be applied as appropriate. The third invention relates to a method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, and a method for manufacturing an electrochemical cell comprising the solid electrolyte assembly. The electrochemical cell manufactured by the method according to the third invention has the same configuration as the electrochemical cell manufactured by the method according to the second invention described above. That is, the electrochemical cell manufactured by the method according to the third invention has the configuration shown in Figure 2. Therefore, unlike the electrochemical cell laminate 10 shown in Figure 1 described above, the electrochemical cell laminate of this embodiment does not have an intermediate layer.

[0066] A preferred method for manufacturing an electrochemical cell laminate having the above configuration is described below. This manufacturing method is broadly divided into the following steps: Step 1: A process for manufacturing a laminate comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer precursor layer. Step 2: A process for firing the laminate. Each step will be described below. <Step 1> In this step, as shown in Figure 4, a solid electrolyte layer precursor layer 21 is formed on a pre-formed air electrode layer 12 or fuel electrode layer 13 to obtain a laminate 10B'. There is no layer between the air electrode layer 12 or fuel electrode layer 13 and the solid electrolyte layer precursor layer 21. The air electrode layer 12 or fuel electrode layer 13 contains rare earth elements. Examples of rare earth elements include lanthanum, samarium, gadolinium, yttrium, erbium, ytterbium, and dysprosium, and lanthanum is particularly preferred. The rare earth elements contained in the air electrode layer 12 or fuel electrode layer 13 not only impart oxide ion conductivity to the air electrode layer 12 or fuel electrode layer 13, but are also supplied to the solid electrolyte layer precursor layer 21 by diffusion during firing. The solid electrolyte layer precursor layer is a layer that serves as a precursor for forming the solid electrolyte layer 11 shown in Figure 2.

[0067] <Step 2> In this step, the laminate 10B' (see Figure 4) obtained in Step 1 is fired to form a solid electrolyte layer 11 (see Figure 2) from the solid electrolyte layer precursor layer 21. In this manufacturing method, by using the above-mentioned material as the solid electrolyte layer precursor layer, the firing of the laminate 10B' can be performed at a lower temperature range than conventional methods. The firing of the laminate 10B' can be performed at 1400°C or lower, preferably 1350°C or lower, and more preferably 1300°C or lower. Furthermore, from the viewpoint of exhibiting high oxide ion conductivity in the solid electrolyte layer, the firing of the laminate 10B' is preferably performed at 900°C or higher, more preferably 950°C or higher, and even more preferably 1000°C or higher. The firing atmosphere can be an oxygen-containing atmosphere such as air, an inert atmosphere such as nitrogen and argon, or a reducing atmosphere containing hydrogen. From the viewpoint of reliably exhibiting high oxide ion conductivity in the solid electrolyte layer, it is advantageous to use an oxygen-containing atmosphere. The firing time is adjusted so that the solid electrolyte layer exhibits sufficient oxide ion conductivity. Generally, a firing time of 1 hour to 40 hours, more preferably 1 hour to 30 hours, is used to achieve satisfactory oxide ion conductivity in the solid electrolyte layer.

[0068] By firing the laminate 10B', rare earth elements, such as lanthanum, contained in the air electrode layer 12 or fuel electrode layer 13 (see Figure 4) diffuse into the solid electrolyte layer precursor layer 21 (see Figure 4). The rare earth elements diffused into the solid electrolyte layer precursor layer 21 react with the first element contained in the solid electrolyte layer precursor layer 21 to produce an oxide ion conductive oxide containing at least the rare earth elements and the first element. This reaction forms the solid electrolyte layer 11 (see Figure 2) containing this oxide. On the other hand, with respect to the air electrode layer 12 or fuel electrode layer 13, although some of the rare earth elements contained in these layers 12 and 13 diffuse into the solid electrolyte layer precursor layer 21, the remaining rare earth elements remain in the air electrode layer 12 or fuel electrode layer 13, so these layers 12 and 13 contain rare earth elements. In order to retain some of the rare earth elements in the air electrode layer 12 or fuel electrode layer 13, the firing temperature and / or firing time should be appropriately adjusted. In this way, a solid electrolyte assembly comprising a solid electrolyte layer 11 and an air electrode layer 12 or a fuel electrode layer 13 is obtained.

[0069] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, the above embodiments relate to the application of the present invention to the manufacture of a metal-supported electrochemical cell, but the scope of application of the present invention is not limited thereto, and the present invention may also be applied to, for example, a fuel electrode-supported electrochemical cell.

[0070] With respect to the embodiments described above, the present invention further discloses the following methods for manufacturing a solid electrolyte assembly and an electrochemical cell. [1] A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element, and forming the intermediate layer containing the oxide containing the rare earth element. [2] A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound containing at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element. [3] The manufacturing method according to [1], wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the element in its elemental form or a compound containing the element in its elemental form, the element in its elemental form or a compound containing the element in its elemental form, and the element in its elemental form or a compound containing the element in its elemental form, the third element being a rare earth element, and the molar ratio of the third element to the first element being less than 1.[4] The manufacturing method according to [1], wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the element in its elemental form or a compound containing the element in its elemental form, and a compound containing the element in its elemental form,

[0071] [6] The manufacturing method according to [2], wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the compound containing the first element, the second element, and the third element, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1. [7] The manufacturing method according to [2], wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the compound containing the first element and the second element, and the third element in its elemental form or a compound containing the third element, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1. [8] The manufacturing method according to any one of [1] to [7], wherein in the solid electrolyte layer precursor, the molar ratio of the second element to the first element is 0.010 or more and 0.50 or less. [9] The manufacturing method according to any one of [1] to [8], wherein the laminate is fired at 1400°C or less.

[10] The manufacturing method according to any one of [1] to [9], wherein the oxide contained in the solid electrolyte layer has an apatite-type crystal structure.

[0072]

[11] The manufacturing method according to any one of [1] to

[10] , wherein the intermediate layer precursor contains cerium oxide doped with the rare earth element (except cerium).

[12] The manufacturing method according to [1], wherein the solid electrolyte layer precursor contains silicon oxide and aluminum oxide.

[13] The manufacturing method according to [2], wherein the solid electrolyte layer precursor contains a compound containing Si and Al.

[14] The manufacturing method according to any one of [1] to

[13] , wherein the laminate formed on a metal support is fired.

[15] The manufacturing method according to any one of [1] to

[14] , wherein a slurry containing the first element and the second element is applied to the intermediate layer precursor to form the solid electrolyte layer precursor.

[0073]

[16] A method for manufacturing a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing a rare earth element, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, or a compound containing the second element, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming a solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[17] A method for manufacturing a solid electrolyte layer, comprising the steps of: firing a laminate comprising a precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element.

[18] A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, to diffuse the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[19] A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[20] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer, a solid electrolyte layer, and an intermediate layer located between the two layers, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba or a compound containing the second element, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element, and forming the intermediate layer containing the oxide containing the rare earth element.

[0074]

[21] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer, a solid electrolyte layer, and an intermediate layer located between the two layers, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound containing at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element.

[22] The manufacturing method according to

[20] or

[21] , wherein the slurry containing the rare earth element is applied to the fuel electrode layer or the air electrode layer to form the intermediate layer precursor layer.

[23] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing rare earth elements, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge in elemental form or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba in elemental form or a compound containing the second element, thereby forming the solid electrolyte layer containing the rare earth elements contained in the precursor layer and the solid electrolyte layer precursor layer, the method for manufacturing an electrochemical cell.

[24] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming the solid electrolyte layer containing an oxide containing the rare earth element and the first element.

[25] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, to diffuse the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[26] A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

[0075] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0076] [Example 1] (1) Preparation of fuel electrode substrate NiO powder and La ９．３３ Si ６ O ２６ Powder Ni and La ９．３３ Si ６ O ２６ The materials were weighed in a volume ratio of 5:5, and ethanol was added to form a slurry. This slurry was mixed and ground in a uniaxial ball mill for 15 hours. Zirconia balls were used as the grinding media. The ethanol was evaporated and removed from the slurry to obtain a powder, which was then collected and uniaxially molded to obtain a molded body. The obtained molded body was fired in an air atmosphere at a temperature of 1500°C for 3 hours to obtain a sintered body. The surface of the obtained sintered body was polished and used as a fuel electrode substrate.

[0077] (2) Preparation of slurry for intermediate and precursor layers 29.176 g of La ２ O ３ Powder and 30.978 g of CeO ２Ethanol was added to the powder to form a slurry. This slurry was mixed and ground in a single-screw ball mill for 15 hours. Zirconia balls were used as the grinding media. The powder obtained by volatilizing and removing the ethanol from the slurry was recovered. This powder was calcined at a temperature of 1300°C for 10 hours in an air atmosphere to obtain calcined LDC powder. Ethanol was added to the obtained calcined LDC powder to form a slurry. This slurry was ground in a single-screw ball mill for 50 hours. Zirconia balls were used as the grinding media. The calcined LDC powder obtained by volatilizing and removing the ethanol from the slurry was recovered. This calcined LDC powder was dispersed in α-terpineol containing 5% ethylcellulose to form a slurry. The amount of powder was 2.34 g, and the amount of α-terpineol containing ethylcellulose was 1.00 g. This slurry was mixed and degassed using a rotation-revolution type mixer (Thinky Co., Ltd.'s "Awatori Rentaro"). In this way, a slurry for the intermediate layer precursor was prepared.

[0078] (3) Preparation of slurry for solid electrolyte layer precursor 9.40 g of SiO ２ Powder and 1.60 g of Al ２ O ３ Ethanol was added to the powder to form a slurry. This slurry was mixed and ground for 1 hour using a planetary ball mill at a rotation speed of 250 pm. Zirconia balls were used as the grinding media. The ethanol was evaporated from the slurry and the resulting powder was recovered. This powder was dispersed in α-terpineol containing 5% ethylcellulose to form a slurry. The amount of powder was 2.00 g, and the amount of α-terpineol containing ethylcellulose was 4.40 g. This slurry was mixed and degassed using a rotation-revolution type mixer (Thinky Co., Ltd.'s "Awatori Rentaro"). In this way, a slurry for the solid electrolyte layer precursor was prepared.

[0079] (4) Preparation of the intermediate layer precursor A slurry for the intermediate layer precursor prepared in (2) was applied to one surface of the fuel electrode substrate prepared in (1) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical transmission amount of 50 μm was used for screen printing. The obtained coating film was dried at 120°C. The same procedure as above was performed once more on this coating film to create an overcoat of coating film and dry at 120°C to prepare the intermediate layer precursor.

[0080] (5) Fabrication of the solid electrolyte layer precursor and laminate The slurry for the solid electrolyte layer precursor prepared in (3) was applied to the intermediate layer precursor prepared in (4) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical transmission amount of 20 μm was used for screen printing. The obtained coating film was dried at 120°C. The solid electrolyte layer precursor was thus fabricated. This resulted in obtaining a laminate in which the intermediate layer precursor and the solid electrolyte layer precursor were laminated in this order on the fuel electrode substrate.

[0081] (6) Firing of the laminate The laminate obtained in (5) was fired in an air atmosphere at a temperature of 1300°C for 20 hours. This caused the intermediate layer to form from the intermediate layer precursor layer and the solid electrolyte layer to form from the solid electrolyte layer precursor layer. In this way, a laminate comprising a fuel electrode substrate, a fuel electrode side intermediate layer, and a solid electrolyte was obtained. Hereinafter, this laminate will also be referred to as the "evaluation laminate".

[0082] [Example 2] In Example 1 (3), immediately before mixing and degassing with a rotational / revolving mixer, La(OH) ３ The La / Si molar ratio was increased to 0.2. A laminate for evaluation was prepared in the same manner as in Example 1.

[0083] [Example 3] In Example 1 (3), 4.52 g of SiO ２ Powder, 0.771g of Al ２ O ３ Powder and 5.714 g of La(OH) ３ Ethanol was added to form a slurry. The La / Si molar ratio was set to 0.4. A laminate for evaluation was prepared in the same manner as in Example 1, except for this.

[0084] [Example 4] In Example 1 (3), immediately before mixing and degassing with a rotational / revolving mixer, La(OH) ３ The La / Si molar ratio was increased to 0.6. A laminate for evaluation was then prepared in the same manner as in Example 1.

[0085] [Example 5] (1) Preparation of fuel electrode substrate A laminate in which the first sheet and the second sheet are laminated was manufactured by the following procedure. 20.757 g of NiO powder, La ９．３３ Si ６ O ２６ A slurry was obtained by mixing 19.678 g of powder, 30.35 g of ethanol, and 7.999 g of a pore-forming agent (spherical fine particles (average particle size 30 μm) consisting of cross-linked polymethyl methacrylate). To this slurry, 4.959 g of a binder (PVB resin powder) and 6.219 g of a plasticizer (dibutyl phthalate) were further mixed. Next, the slurry was applied using an applicator to form a green sheet, thereby producing the first sheet. The thickness gap of the applicator was set to 900 μm. Separately from this operation, 9.6916 g of NiO powder and La ９．３３ Si ６ O ２６ A slurry was obtained by mixing 5.5214 g of powder and 15.747 g of ethanol. To this slurry, 1.449 g of a binder (PVB resin powder) and 1.512 g of a plasticizer (dibutyl phthalate) were further mixed. Next, a second sheet was produced by applying the slurry using an applicator to form a green sheet. The thickness gap of the applicator was set to 150 μm. The first and second sheets were laminated in this order and heat-pressed from one direction to obtain a laminate. The obtained laminate was heated at 1600°C for 3 hours in an atmospheric environment. In this way, a fuel electrode substrate was obtained.

[0086] (2) Preparation of fuel electrode layer slurry 6,000 g of LDC calcined powder and 4,000 g of NiO powder obtained in Example 1 were mixed with ethanol to make a slurry. This slurry was pulverized and mixed for 1 hour using a planetary ball mill. Zirconia balls were used as the pulverizing media. The fuel electrode calcined powder obtained by volatilizing and removing the ethanol from the slurry was recovered. This fuel electrode calcined powder was dispersed in α-terpineol containing 5% ethylcellulose to make a slurry. The amount of fuel electrode calcined powder was 7,000 g, and the amount of α-terpineol containing ethylcellulose was 3,000 g. This slurry was kneaded using a three-roll mill. In this way, a slurry for the fuel electrode layer was prepared.

[0087] (3) Preparation of slurry for intermediate and precursor layers A slurry was prepared by dispersing the LDC calcined powder obtained in Example 1 in α-terpineol containing 5% ethylcellulose. The amount of powder was 30.014 g, and the amount of α-terpineol containing ethylcellulose was 12.85 g. This slurry was kneaded using a three-roll mill. In this way, a slurry for intermediate and precursor layers was prepared.

[0088] (4) Preparation of slurry for solid electrolyte layer precursor: 4.52 g of SiO ２ Powder and 0.771 g of Al ２ O ３ Powder and 5.714 g of La(OH) ３ Ethanol was added to the powder to form a slurry. This slurry was mixed and ground for 1 hour using a planetary ball mill at a rotation speed of 250 pm. Zirconia balls were used as the grinding media. The ethanol was evaporated and removed from the slurry to recover the electrolyte powder. This electrolyte powder was dispersed in α-terpineol containing 5% ethylcellulose to form a slurry. The amount of powder was 1.000 g, and the amount of α-terpineol containing ethylcellulose was 1.6558 g. This slurry was mixed and degassed using a rotation-revolution type mixer ("Awatori Rentaro" (registered trademark) from Thinky Co., Ltd.). In this way, a slurry for the solid electrolyte layer precursor was prepared.

[0089] (5) Fabrication of the fuel electrode layer The fuel electrode layer slurry prepared in (2) was applied to the surface of the second sheet side of the fuel electrode substrate fabricated in (1) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical transmission amount of 50 μm was used for screen printing. The obtained coating film was dried at 120°C. The fuel electrode layer was fabricated in this manner.

[0090] (6) Preparation of the intermediate precursor layer The intermediate precursor layer slurry prepared in (3) was applied to the surface of the fuel electrode layer prepared in (5) to form a coating film. Screen printing was used to apply the slurry. A screen mask with a theoretical transmission amount of 50 μm was used for screen printing. The obtained coating film was dried at 120°C. The intermediate precursor layer was thus prepared.

[0091] (7) Fabrication of Solid Electrolyte Layer Precursor and Laminate A coating film was formed by applying the slurry for the solid electrolyte layer precursor prepared in (4) onto the intermediate layer precursor prepared in (6). Screen printing was used to apply the slurry. A screen mask with a theoretical transmission amount of 50 μm was used for screen printing. The obtained coating film was dried at 120°C. The solid electrolyte layer precursor was thus fabricated. This resulted in a laminate in which the fuel electrode layer, intermediate layer precursor, and solid electrolyte layer precursor were laminated on the fuel electrode substrate in this order.

[0092] (8) Firing of the laminate The laminate obtained in (7) was fired in an air atmosphere at a temperature of 1300°C for 30 hours. This formed the intermediate layer from the intermediate layer precursor layer and the solid electrolyte layer from the solid electrolyte layer precursor layer. In this way, a laminate comprising a fuel electrode substrate, a fuel electrode, a fuel electrode side intermediate layer, and a solid electrolyte was obtained.

[0093] (9) Formation of the air electrode side intermediate layer Sm ０．２ Ce ０．８ O １．９ A powder slurry was prepared. This slurry was applied to the surface of the solid electrolyte layer in the laminate obtained in (8) that was opposite to the surface facing the fuel electrode side intermediate layer to a thickness of 5 μm, and heated at 1250°C for 3 hours in an air atmosphere. The air electrode side intermediate layer was thus prepared.

[0094] (10) Formation of the air electrode La ０．６ Sr ０．４ Co ０．２ Fe ０．８ O ３－δ 3.0 g of powder was weighed. This powder was mixed with 4.5 g of α-terpineol containing 5% ethylcellulose to prepare a slurry. This slurry was coated to a thickness of 10 μm on the surface of the air electrode intermediate layer opposite to the surface facing the solid electrolyte layer, and the mixture was heated at 900°C for 1 hour in an atmospheric environment to form the air electrode. In this way, the desired electrochemical cell was obtained.

[0095] [Comparative Example 1] In Example 1 (3), Al ２ O ３ Without adding powder, SiO ２ Ethanol was added to the powder only to form a slurry. A laminate for evaluation was prepared in the same manner as in Example 1, except for this step.

[0096] [Density Evaluation] The longitudinal sections of the evaluation laminates obtained in Examples 1 and 2 and Comparative Example 1, and the electrochemical cell obtained in Example 5, were observed using a scanning electron microscope. The results are shown in Figures 5 to 8. For Example 5, the observation was performed after the electrochemical evaluation described later. As is clear from these figures, in Examples 1, 2, and 5, a dense solid electrolyte layer was formed even when fired at a lower firing temperature of 1300°C than before.

[0097] [Method for Identifying the Phase of the Solid Electrolyte Layer] The phase of the solid electrolyte layer in the evaluation laminates obtained in Examples 1 to 4 was identified. X-ray diffraction (XRD) (RINT-TTR3, manufactured by Rigaku) ​​was used for phase identification. CuKα rays were used as the radiation source, with a tube voltage of 50 kV and a tube current of 300 mA. The goniometer scanning method was the 2θ / θ method. Figure 9 shows the X-ray diffraction patterns of the solid electrolyte layer surface in the evaluation laminates obtained in each example. As is clear from the figure, the solid electrolyte layer in each example contains apatite-type lanthanum silicate as the main phase. In particular, as is clear from the comparison between Example 1 and Examples 2 to 4, by forming the solid electrolyte layer from a solid electrolyte layer precursor layer containing a predetermined amount of the third element (La), La-doped CeO in the solid electrolyte layer is formed. ２ It can be seen that the amount of phase (hereinafter also referred to as "LDC phase") decreases. Since the LDC phase is an oxide ion conductor, the oxide ion conductivity of the solid electrolyte layer does not decrease significantly even if the LDC phase is included in the solid electrolyte layer. However, because it also exhibits electronic conductivity, the LDC phase tends to degrade the properties of the solid electrolyte layer. Therefore, it is desirable to have a small amount of LDC phase in the solid electrolyte layer.

[0098] [Electrochemical Evaluation of Electrochemical Cells] The power generation characteristics of electrochemical cells were evaluated by flowing 100 ccm of hydrogen through the fuel electrode and 80 ccm of nitrogen and 20 ccm of oxygen through the air electrode as fuel gases. A potentiometer-galvanostat (SP-300, BioLogic) was used to evaluate the power generation characteristics of the electrochemical cells. Figure 10 shows the output characteristics of the electrochemical cell of Example 5 at 700°C and 600°C. As is clear from the figure, the electromotive force of the electrochemical cell of Example 5 was 90% of the theoretical electromotive force at 700°C and 94% of the theoretical electromotive force at 600°C, indicating that a dense solid electrolyte layer with little gas leakage and electron leakage was formed. The maximum power density at 700°C was 321 mWcm². ―２ The maximum power density at 600°C is 152 mWcm². ―２ This indicates that it exhibits high output characteristics.

[0099] As described in detail above, the method of the present invention makes it possible to produce a solid electrolyte assembly and an electrochemical cell having an oxide ion conductor with high oxide ion conductivity using a simpler process and firing at a lower temperature than before.

Claims

1. A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, either as an element or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, either as an element or a compound containing the second element, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element, and forming the intermediate layer containing the oxide containing the rare earth element.

2. A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and an intermediate layer, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound containing at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element.

3. The manufacturing method according to claim 1, wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the element in its elemental form or a compound containing the element in its elemental form, the element in its elemental form or a compound containing the element in its elemental form, and the element in its elemental form or a compound containing the element in its elemental form, the third element being a rare earth element, and the molar ratio of the third element to the first element being less than 1.

4. The manufacturing method according to claim 1, wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the element in its elemental form or a compound containing the first element, and a compound containing the second and third elements, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1.

5. The manufacturing method according to claim 1, wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the element in its elemental form or a compound containing the second element, and a compound containing the first and third elements, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1.

6. The manufacturing method according to claim 2, wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the compound containing the first element, the second element and the third element, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1.

7. The manufacturing method according to claim 2, wherein the solid electrolyte layer precursor further comprises a third element, the solid electrolyte layer precursor comprises the compound containing the first and second elements, and the third element in its elemental form or a compound containing the third element, the third element is a rare earth element, and the molar ratio of the third element to the first element is less than 1.

8. The manufacturing method according to claim 1 or 2, wherein the molar ratio of the second element to the first element in the solid electrolyte layer precursor is 0.010 or more and 0.50 or less.

9. The manufacturing method according to claim 1 or 2, wherein the firing of the laminate is carried out at 1400°C or lower.

10. The manufacturing method according to claim 1 or 2, wherein the oxide contained in the solid electrolyte layer has an apatite-type crystal structure.

11. The manufacturing method according to claim 1 or 2, wherein the intermediate precursor layer contains cerium oxide doped with the rare earth element (excluding cerium).

12. The manufacturing method according to claim 1, wherein the solid electrolyte layer precursor layer comprises silicon oxide and aluminum oxide.

13. The manufacturing method according to claim 2, wherein the solid electrolyte layer precursor layer contains a compound containing Si and Al.

14. The manufacturing method according to claim 1 or 2, wherein the laminate formed on a metal support is fired.

15. The manufacturing method according to claim 1 or 2, wherein a slurry containing the first element and the second element is applied onto the intermediate layer precursor to form the solid electrolyte layer precursor.

16. A method for manufacturing a solid electrolyte layer, comprising the steps of: firing a laminate comprising a precursor layer containing a rare earth element, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, either as an element or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, either as an element or a compound containing the second element, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element.

17. A method for manufacturing a solid electrolyte layer, comprising the steps of: firing a laminate comprising a precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming a solid electrolyte layer containing an oxide containing the rare earth element and the first element.

18. A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, to diffuse the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer, thereby forming the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

19. A method for manufacturing a solid electrolyte assembly comprising a solid electrolyte layer and a fuel electrode layer or an air electrode layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

20. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer, a solid electrolyte layer, and an intermediate layer located between the two layers, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, either as an element or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, either as an element or a compound containing the second element, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element, and forming the intermediate layer containing the oxide containing the rare earth element.

21. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer, a solid electrolyte layer, and an intermediate layer located between the two layers, comprising the steps of firing a laminate comprising an intermediate layer precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the intermediate layer precursor layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing an oxide containing the rare earth element and the first element, and forming the intermediate layer containing an oxide containing the rare earth element.

22. The manufacturing method according to claim 20 or 21, wherein the slurry containing the rare earth element is applied to the fuel electrode layer or the air electrode layer to form the intermediate layer precursor layer.

23. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing rare earth elements, a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, to diffuse the rare earth elements contained in the precursor layer into the solid electrolyte layer precursor layer and to destroy the precursor layer, thereby forming the solid electrolyte layer containing the rare earth elements and an oxide containing the first element.

24. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising a precursor layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the precursor layer into the solid electrolyte layer precursor layer and causing the precursor layer to disappear, thereby forming the solid electrolyte layer containing an oxide containing the rare earth element and the first element.

25. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element, and a solid electrolyte layer precursor layer containing at least one element selected from the group consisting of Si and Ge, or a compound containing the first element, and at least one element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, to diffuse the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

26. A method for manufacturing an electrochemical cell comprising a fuel electrode layer or an air electrode layer and a solid electrolyte layer, comprising the steps of firing a laminate comprising the fuel electrode layer or the air electrode layer containing a rare earth element and a solid electrolyte layer precursor layer containing a compound comprising at least one first element selected from the group consisting of Si and Ge and at least one second element selected from the group consisting of Al, Mg, In, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Zr, Ta, Nb, B, Zn, Sn, P, W, Mo, Ca, Sr, and Ba, thereby diffusing the rare earth element contained in the fuel electrode layer or the air electrode layer into the solid electrolyte layer precursor layer to form the solid electrolyte layer containing the rare earth element and an oxide containing the first element.

Images