Electrochemical cell and method of manufacturing the same

Abstract

To provide an electrochemical cell and manufacturing method of the same in which the electrochemical cell is constituted by thin film type electrolyte with a larger area and excellent in cell characteristic.SOLUTION: An electrochemical cell 1 comprises: a solid electrolyte film 10; a cathode 2; and an anode 3. The solid electrolyte film 10 includes one layer or two layers or more of polycrystal layers 11 in a film thickness direction Z in which the polycrystal layer is constituted by aggregating crystal grains C of apatite-type composite oxides in a film plane direction X, Y, film thickness t is 0.2 μm or more and 5.0 μm or less, film area S is 1.0 cm2 or more, and film surface roughness Rz is 20 nm or less. The cathode 2 and the anode 3 are porous electrodes arranged at two film surfaces 101, 102 facing the solid electrolyte film 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrochemical cell and a method for manufacturing the same. [Background technology]

[0002] Electrochemical cells used in fuel cells and the like have a single cell structure in which a cathode and an anode are arranged on either side of an electrolyte membrane. Known oxide ion conductors that serve as electrolyte membranes include zirconia-based oxides such as stabilized zirconia and perovskite-type oxides. Furthermore, apatite-type compounds, which have excellent oxide ion conductivity, have recently attracted attention. Apatite-type compounds have a hexagonal crystal structure, and it is expected that, for example, by imparting a predetermined orientation, they can facilitate the movement of oxide ions and enhance ion conductivity.

[0003] For example, Patent Document 1 discloses a substrate-oriented apatite-type complex oxide film composite having an oriented apatite-type complex oxide on a substrate, and a method for producing the same. The oriented apatite-type complex oxide is a lanthanum silicate-based complex oxide, and is formed on the substrate as a film having a thickness of more than 0.5 μm and not more than 5 μm and an orientation degree of 0.6 or more as measured by the Lotgering method. The substrate is a metal, alloy, ceramic, or composite material thereof, and the amorphous complex oxide formed on the substrate is heat-treated in an atmosphere of not more than a predetermined oxygen partial pressure to crystallize it into an apatite structure and impart orientation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6088715 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a composite oxide of a desired composition is prepared in advance, and then formed on a substrate by, for example, sputtering, followed by heat treatment to form a composite of an oriented apatite-type composite oxide film and a substrate. Although this method is said to be unrestricted in terms of the substrate material, there are restrictions on bonding with functional materials such as electrodes, and the desired cell structure is not necessarily obtained. For example, to form a dense body to be used as an electrolyte membrane for an electrochemical cell, it is desirable that the substrate is also dense, and therefore it is difficult to use a porous body that functions as the cathode or anode of an electrochemical cell as a substrate.

[0006] On the other hand, there are also electrochemical cells in which the electrolyte is produced as a free-standing film not supported by a substrate or the like, and then electrodes are formed on both end surfaces. Such free-standing electrolytes are made of single crystals of apatite-type composite oxides formed, for example, by the Czochralski method, and are thinned by polishing or the like. However, to avoid cracks caused by polishing, the conventional limit for thickness is about 50 μm. In addition, methods for obtaining thinner plate-like crystals include, for example, the flux method, but it is difficult to increase the crystal size.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide an electrochemical cell which is constructed using a thin-film electrolyte having a larger area and has good cell characteristics, and a method for manufacturing the same. [Means for solving the problem]

[0008] One aspect of the present invention is an electrochemical cell (1) comprising a solid electrolyte membrane (10) made of an apatite-type composite oxide, a cathode (2), and an anode (3), The solid electrolyte membrane has one or more polycrystalline layers (11) in the thickness direction (Z) in which the crystal particles (C) of the apatite-type composite oxide are aggregated in the plane direction (X, Y) of the membrane with their grain boundaries (C1) in contact with each other. The membrane has a thickness t of 0.2 μm or more and 5.0 μm or less, and a membrane area S of 1.0 cm 2 or more, and the film has a film surface roughness Rz of 20 nm or less, At least one of the polycrystalline layers is an oriented layer in which the c-axis orientation rate with respect to the film thickness direction is 0.25 or more as calculated by the Lotgering method, and the grain boundaries are aligned in the film thickness direction, and the angle between the direction of the grain boundaries of the crystal grains appearing in a layer cross section and the film thickness direction is 10° or less in the oriented layer; The cathode and the anode are in an electrochemical cell, which is a pair of porous electrodes provided on either side of the two opposing membrane surfaces (101, 102) of the solid electrolyte membrane.

[0009] Another aspect of the present invention is a method for producing the electrochemical cell described above, comprising the steps of: forming a first layer (300) on the surface of the substrate (200) that is made of a composition that can be sublimated at a heat treatment temperature for crystallizing the apatite-type composite oxide; forming an amorphous complex oxide film (100) containing the same constituent elements as the apatite-type complex oxide on the surface of the first layer; forming a second layer (400) made of an oxide containing some of the constituent elements of the apatite-type complex oxide or a precursor thereof on the surface of the amorphous complex oxide film; forming an electrode material layer (21) that will become one of the cathode and the anode on the surface of the second layer; By heating the amorphous composite oxide film at a temperature equal to or higher than the crystallization temperature, Promoting integration and crystallization of the amorphous complex oxide film and the second layer, The polycrystalline layer made of the apatite-type composite oxide and one of the cathode and the anode are formed, and the first layer is removed by sublimation. and separating the substrate and the polycrystalline layer. and The substrate and The first layer was removed The polycrystalline layer and forming an electrode material layer (31) that will become the other of the cathode and the anode on the surface and heat-treating the layer to form the other of the cathode and the anode. [Effects of the Invention]

[0010] In the electrochemical cell of the above embodiment, the solid electrolyte membrane is composed of a polycrystalline layer in which crystal grains of an apatite structure are aggregated, and it is thought that the numerous crystal grain boundaries that separate the grains improve membrane strength and contribute to maintaining the thin film shape. In addition, since the membrane surface roughness Rz is 20 nm or less and the membrane surface is flat with small irregularities, it is thought that stress concentration due to surface irregularities is alleviated and membrane strength is maintained. As a result, it is possible to maintain the membrane strength by reducing the surface roughness of 1.0 cm. 2 It is possible to form a thin membrane with an area of ​​1000 or more, and by sandwiching the two membrane surfaces to form a cathode and an anode, a highly active electrochemical cell can be created that takes advantage of the high oxide ion conductivity of the apatite-type complex oxide.

[0011] Such an electrochemical cell can be manufactured by the method described in the other embodiment above. Specifically, a first layer made of a composition that can be sublimated by heat treatment is formed on a substrate in advance, and the first layer is sublimated and removed during the heat treatment to crystallize the apatite, allowing the cell to be separated from the substrate. The formation of the second layer on the amorphous complex oxide film facilitates the diffusion of the constituent elements of the apatite during crystallization of the amorphous complex oxide film, facilitating the formation of crystalline grains that are oriented in the film thickness direction. This is thought to form numerous grain boundaries in the film plane direction and reduce the film surface irregularities. Furthermore, the formation of an electrode material layer on the second layer allows the formation of a half-cell during separation from the substrate. Furthermore, an electrode material layer can be formed on the surface from which the first layer has been removed and then heat-treated to form an electrochemical cell.

[0012] As described above, according to the above aspect, it is possible to provide an electrochemical cell that is configured using a thin-film electrolyte having a larger area and has good cell characteristics, and a method for manufacturing the same. In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is an overall perspective view schematically illustrating the configuration of an electrochemical cell according to a first embodiment. [Figure 2] 1 is an overall perspective view schematically illustrating the configuration of a solid electrolyte membrane that is a main part of an electrochemical cell in Embodiment 1. FIG. [Figure 3] FIG. 2 is a diagram schematically showing the crystal structure of an apatite-type composite oxide constituting the solid electrolyte membrane in the first embodiment. [Figure 4] 2 is an enlarged view of a portion A in FIG. 1 and an enlarged view of a portion A1 in FIG. 2, which are diagrams schematically showing the cross-sectional structure of an electrochemical cell and a solid electrolyte membrane in the first embodiment. [Figure 5] FIG. 1 is an overall perspective view schematically illustrating the configuration of a solid electrolyte membrane in a first embodiment. [Figure 6] 1 is a process diagram illustrating a method for producing a solid electrolyte membrane in the first embodiment. [Figure 7] FIG. 10 is an overall perspective view schematically showing the configuration of a solid electrolyte membrane in a second embodiment. [Figure 8] FIG. 10 is an enlarged view of part B in FIG. 1, schematically illustrating the structure of a main part of a solid electrolyte membrane in a second embodiment. [Figure 9] FIG. 10 is a diagram schematically illustrating the structure of a main part of a solid electrolyte membrane in a third embodiment. [Figure 10] FIG. 2 is a diagram showing the overall configuration of an apparatus used to evaluate the strength of a film in the examples. [Figure 11] FIG. 2 is a diagram schematically illustrating the structure of a main part of a thin film in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Embodiment 1) An embodiment of an electrochemical cell and a manufacturing method thereof will be described with reference to the drawings. As shown in Fig. 1 to Fig. 5, the electrochemical cell 1 includes a solid electrolyte membrane 10, a cathode 2, and an anode 3. The solid electrolyte membrane 10 is a solid electrolyte membrane made of an apatite-type composite oxide, and the cathode 2 and anode 3 are provided across two opposing membrane surfaces 101, 102. The cathode 2 and anode 3 are configured as a pair of porous electrodes.

[0015] The solid electrolyte membrane 10 is a polycrystalline membrane composed of crystalline particles C of an apatite-type composite oxide, and can include one or more polycrystalline layers 11 formed by an aggregation of the crystalline particles C. In the configuration example shown in FIGS. 1 and 2, the polycrystalline layer 11 has a single-layer structure. In the case of a multi-layer structure, as will be described later, a plurality of polycrystalline layers 11 are stacked in the thickness direction Z of the solid electrolyte membrane 10 (i.e., the Z-axis direction shown in FIGS. 1 and 2). The solid electrolyte membrane 10 can be configured as a thin film that can exist independently without being supported by a support such as a substrate on either side of two membrane surfaces 101, 102 opposing each other in the thickness direction Z.

[0016] The polycrystalline layer 11 constituting the solid electrolyte membrane 10 is a dense body in which a large number of crystal grains C are continuously aggregated with grain boundaries C1 in contact with each other in a membrane plane direction (for example, the X-axis direction or Y-axis direction shown in FIGS. 1 and 2) perpendicular to the membrane thickness direction Z. When the solid electrolyte membrane 10 is a single-layer membrane, two particle surfaces of the crystal grains C in the membrane thickness direction Z are located in contact with the cathode 2 and the anode 3, respectively, and adjacent particle surfaces are connected to form two membrane surfaces 101 and 102.

[0017] Each crystal particle C is a thin plate-like particle made of a complex oxide having an apatite-type crystal structure as shown in FIG. 3, and it is desirable that the c-axis of the hexagonal apatite is oriented along the film thickness direction Z (see, for example, FIG. 4). The a-axis and b-axis of the apatite are in a plane perpendicular to the c-axis. The polycrystalline layer 11 in which such crystal particles C are aggregated is desirably formed so that the grain boundaries C1 are aligned along the film thickness direction Z and are evenly arranged over the entire film plane, which is considered to have the effect of improving the film strength against stress. In addition, the apatite-type complex oxide has oxide ions (O 2- ) has a property of being easily conductive, and is therefore advantageous when used as a solid electrolyte membrane 10 that conducts ions in the membrane thickness direction Z.

[0018] The solid electrolyte membrane 10 is formed to have a thickness t in the range of 0.2 μm to 5.0 μm. As shown in FIG. 5, the thickness t is the thickness of the polycrystalline membrane, i.e., the thickness of the polycrystalline layer 11 in the case of a single-layer membrane, and can be appropriately set so as to obtain the desired membrane strength and ionic conductivity. A thickness t of 0.2 μm or more allows the membrane to be maintained as a free-standing thin film, while a thickness t of 5.0 μm or less shortens the migration distance of oxide ions, thereby increasing ionic conductivity. Preferably, the thickness t is 1.0 μm or more. The thickness t can be calculated, for example, as the average thickness based on cross-sectional observation using a transmission electron microscope (TEM).

[0019] The membrane area S of the solid electrolyte membrane 10 is 1.0 cm 2 or more, and is formed so that the film surface roughness Rz is 20 nm or less. The film surface roughness Rz (JIS B0601) is the maximum height of a roughness curve in a reference length, and can be measured using a device capable of measuring minute irregularities on the nano-order, for example, an atomic force microscope (AFM). By making the film surface roughness Rz 20 nm or less, the irregularities on the film surfaces 101 and 102 are reduced, the stress caused by the irregularities is alleviated, and the occurrence of stress concentration points is suppressed, thereby achieving a film surface roughness of 1.0 cm. 2 It is believed that it will be possible to maintain a thin film shape of 5.0 μm or less having an area of ​​5.0 μm or less. Preferably, the film surface roughness Rz is about 15 nm or less.

[0020] The upper limit of the membrane area S of the solid electrolyte membrane 10 is not particularly limited, and the membrane area S can be obtained according to the area of ​​the substrate used in the manufacturing method described later. Therefore, it can be set appropriately depending on the application, etc., but from the viewpoint of manufacturing, for example, 500 cm 2 It is desirable that the membrane area S is in the range of about 200 cm or less. 2The film area S can be calculated based on the results of measuring the planar shape with a laser microscope using laser light, for example.

[0021] The detailed structure of the electrochemical cell 1 in this embodiment will be described below. In the upper diagrams of Figures 1 and 4, the electrochemical cell 1 has a three-layer cell structure in which a pair of porous electrodes, which serve as a cathode 2 and an anode 3, are stacked in the thickness direction Z, sandwiching a solid electrolyte membrane 10 therebetween. In the lower diagrams of Figures 2 and 4, the solid electrolyte membrane 10 is a single-layer membrane made of a single polycrystalline layer 11, and the two surfaces of the polycrystalline layer 11 facing each other in the thickness direction Z serve as membrane surfaces 101 and 102. Here, the cathode 2 is disposed in contact with the membrane surface 101 (e.g., the upper surface in Figure 1), and the anode 3 is disposed in contact with the membrane surface 102 (e.g., the lower surface in Figure 1).

[0022] In the polycrystalline layer 11, at least some of the crystal grains C of the apatite structure are oriented in one direction, and preferably the layer has a c-axis orientation in which the c-axis direction of the crystal grains C and the film thickness direction Z are approximately aligned. Furthermore, it is desirable that a grain boundary C1 is formed between adjacent crystal grains C in a direction that is approximately aligned with the film thickness direction Z. Specifically, when the ratio of crystal grains C having c-axis orientation among the crystal grains C that constitute the polycrystalline layer 11 is defined as the c-axis orientation ratio, a polycrystalline layer 11 in which the c-axis orientation ratio calculated using the Lotgering method is 0.25 or more and the grain boundaries C1 are aligned in the same direction can be considered an oriented layer.

[0023] When the c-axis orientation ratio is 0.25 or more, the c-axes of more crystal grains C are aligned along the film thickness direction Z or are less deviated from the film thickness direction Z throughout the polycrystalline layer 11 (the c-axis directions of the crystal grains C are indicated by dotted arrows in FIG. 4). In this case, the C-planes of the apatite are more likely to be exposed as film surfaces 101 and 102, which is preferable from the viewpoint of improving oxide ion conductivity and film strength. More preferably, the c-axis orientation ratio is 0.6 or more as calculated by the Lotgering method. The c-axis orientation ratio can be calculated, for example, using the known Lotgering equation from the peak intensity in an X-ray diffraction pattern obtained by an X-ray diffractometer.

[0024] 4, it is desirable that crystal grains C having c-axis orientation are aggregated in the cross section of the polycrystalline layer 11, and that the direction of the grain boundary C1 appearing in the cross section of the layer substantially coincides with the film thickness direction Z. It is believed that the grain boundary C1's effect of improving film strength is enhanced when the direction of the grain boundary C1 is perpendicular (90°) to the film surfaces 101 and 102 or a direction close to this. Therefore, it is desirable that the grain boundary angle θ, which is the angle between the direction of the grain boundary C1 appearing in the cross section of the layer and the direction parallel to the film surfaces 101 and 102 (film plane direction X, Y), be 80° or more; in other words, the angle (deviation angle) between the direction of the grain boundary C1 and the film thickness direction Z be 10° or less. The grain boundary angle θ (or deviation angle) can be calculated, for example, as the average value of the measured angles of multiple grain boundaries C1 based on cross-sectional TEM observation. .

[0025] The average particle diameter (D50) of the crystal particles C observed on the film surfaces 101, 102 is preferably, for example, 5 μm or more and 500 μm or less. If the average particle diameter is less than 5 μm, the number of grain boundaries C1 formed in the polycrystalline layer 11 increases, and there is a concern that the grain boundaries C1, which are structural defects, may affect the oxide ion conductivity. Furthermore, if the average particle diameter exceeds 500 μm, the number of grain boundaries C1 decreases, and there is a risk that the effect of improving the film strength will be reduced.

[0026] As shown in Figure 5, the solid electrolyte membrane 10 is a flat membrane with a large membrane area S relative to the membrane thickness t. The uniform formation of grain boundaries C1 extending in a substantially perpendicular direction between membrane surfaces 101 and 102 is believed to contribute to maintaining the strength of the entire membrane. In addition, the area of ​​membrane surfaces 101 and 102 exposed to the atmosphere is larger than in conventional membranes, making it easier for structural defects such as oxygen vacancies to form. Furthermore, the increased c-axis orientation rate increases the proportion of C-planes in the surfaces exposed to the atmosphere, which is believed to act in a direction that makes structural defects more likely to form, resulting in stress relaxation due to structural defects and improved oxide ion conductivity.

[0027] Thus, it is believed that a larger membrane area S relative to the thickness t of the solid electrolyte membrane 10 is advantageous for improving membrane strength and exhibiting oxide ion conductivity. Alternatively, when the shape of the solid electrolyte membrane 10 shown in FIG. 5 is, for example, approximately square, a larger ratio of the length of one side, L, to the thickness t (i.e., aspect ratio: L / t) allows the membrane to function as a film electrolyte with high ion conductivity and flexural modulus. Such a film electrolyte is suitable for use in various applications, such as electrochemical cells.

[0028] For example, when the thickness t of the solid electrolyte membrane 10 is 5.0 μm, the membrane area S is 1.0 cm 2 (That is, if the side length L is 1 cm = 10,000 μm) or more, the aspect ratio will be 2,000 (L / t = 10,000 μm / 5 μm) or more. The shape of the solid electrolyte membrane 10 is not limited to a rectangular shape and can be any shape. In this case, the aspect ratio can also be expressed using the side length L of a square having the same area as the membrane area S.

[0029] As the composite oxide with an apatite structure that constitutes the solid electrolyte membrane 10, an apatite composite oxide represented by the following formula 1 can be suitably used. Formula 1:A 10-x B 6-y M y O 27-z However, in Equation 1, A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba; B is an element containing Si or Ge or both, M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W, and Mo; x, y, and z are numbers that satisfy the following conditions: -0.5≦x≦2.0, 0.0≦y≦3.0, and -6.0≦z≦4.2.

[0030] The element A in formula 1 is a lanthanoid or alkaline earth metal that can form a positively charged ion and form an apatite-type hexagonal crystal structure. For example, from the viewpoint of further increasing the oxide ion conductivity, it is preferably a combination with one or more elements selected from the group consisting of La, Ce, Nd, Ca, Sr, and Ba, and particularly preferably a combination of La or Nd, or La with one or more elements selected from the group consisting of Ce, Nd, Ca, Sr, and Ba. Furthermore, the B element in formula 1 may be an element containing Si or Ge or both.

[0031] The M element in formula 1 is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W, and Mo. For example, from the viewpoint of increasing oxide ion conductivity, it is preferable to use Al, Ti, Y, Zr, B, and the like.

[0032] In terms of increasing the degree of orientation and oxygen ion conductivity, x in formula 1 is preferably −0.5 or more and 2.0 or less. In terms of filling the B element positions in the apatite-type crystal lattice, y in formula 1 is preferably 0.0 or more and 3.0 or less. In order to maintain electrical neutrality within the apatite-type crystal lattice, z in formula 1 is preferably −6.0 or more and 4.2 or less.

[0033] As the apatite-type composite oxide represented by the above formula 1, for example, a rare earth silicate-based composite oxide can be used, in which the element A in formula 1 is a rare earth element and the element B in formula 1 is Si. Examples of rare earth silicate-based composite oxides include La 9.33 Si 6.0 O 26 , La 9.33 Si 5.3 B 0.7 O 25.65 , La 9.33 Si 5.3 Ti 0.7 O 26 , La 9.33 Si 5.3 Al 0.7 O 25.65 , La 9.33 Si 5.3 Y 0.7 O 25.65 , La 9.33 Si 5.3 Zr 0.7 O 26 , La 9.00 Ce 0.33 Si 6.0 O 26 However, the present invention is not limited to these. In the apatite-type crystal structure shown in FIG. 3, the arrows A, B, and O in the figure represent the positions occupied by the A element, B element, and O element in formula 1.

[0034] The electrochemical cell 1 is composed of a dense solid electrolyte membrane 10 that selectively conducts oxide ions, and a porous body made of a catalytically active electrode material that is provided on each of the opposing membrane surfaces 101, 102 and serves as the cathode 2 or anode 3. When the electrochemical cell 1 is operated for the purpose of fuel synthesis, for example, water vapor or carbon dioxide is introduced as a raw material gas into one of the porous bodies, and electrons are supplied using electrical energy to synthesize a fuel gas such as hydrogen, carbon monoxide, or hydrocarbon. In this case, the porous electrode on the fuel synthesis side serves as the cathode 2, and the opposite porous electrode serves as the anode 3. Oxide ions generated on the cathode 2 side migrate inside the solid electrolyte membrane 10 and are released as oxygen on the anode 3 side.

[0035] In this case, the solid electrolyte membrane 10, which serves as an oxide ion conductor, is desirably thinned so as to shorten the distance between the cathode 2 and the anode 3, from the viewpoint of reducing the conduction resistance of oxide ions. Furthermore, it is desirable that both the cathode 2 and the anode 3 be formed of a porous body, from the viewpoint of improving the diffusibility of the raw material gas or the synthesis gas. Since increasing the porosity of the porous body facilitates gas diffusion and improves the energy density of the electrochemical cell, it is desirable that the cathode 2 and the anode 3 be configured to have a porosity of preferably 20% or more, more preferably 40% or more. On the other hand, since a high porosity tends to decrease the strength, it is desirable to appropriately select a porosity in the range of 80% or less so as to obtain the desired strength.

[0036] The cathode 2 and anode 3 each preferably have a thickness of 15 μm or more, and a combined thickness of 1000 μm or less. The closer the cathode 2 and anode 3 are to the solid electrolyte membrane 10, the more likely they are to function as a reaction field. Therefore, by reducing the thickness of the porous electrodes, the source gas can be concentrated in a location close to the solid electrolyte membrane 10 that contributes most to the reaction field, thereby achieving a highly active cell. On the other hand, if the thickness of the porous electrodes is reduced, there is a concern that the source gas may be concentrated and the reaction field may become insufficient. Therefore, it is preferable that each thickness be 15 μm or more. Furthermore, a highly active cell can be achieved by setting the combined total thickness of the cathode 2 and anode 3 to 1000 μm or less. The thicknesses of the two porous electrodes do not need to be the same; it is preferable that the thickness of at least one of the porous electrodes be selected appropriately so that it is in the range of 30 μm or more and 500 μm or less.

[0037] The porous electrodes that become the cathode 2 and anode 3 are formed by agglomerating particles of the electrode material with voids between the particles. The particles of the electrode material preferably have an average particle diameter (D50) of 100 nm or more. If the particle diameter is less than 100 nm, the void distance becomes smaller than the mean free path of the gas, making it difficult to ensure gas diffusibility. Furthermore, as the particle diameter increases, gas diffusibility improves, but the opportunity for the gas to collide with and react with the electrode material decreases. Therefore, it is preferable to appropriately select a particle diameter in the range of 100 nm to 10 μm so as to obtain the desired gas diffusibility and reactivity.

[0038] The porous electrodes constituting the cathode 2 and anode 3 are preferably made of an electrode material that has catalytic activity and electronic conductivity for transmitting the electrical energy required for the electrode reaction, and that has good bonding strength with the electrolyte membrane 10 made of an apatite-type complex oxide. Examples of such electrode materials include precious metal materials such as Pt and complex oxide materials. A porous body containing such an electrode material can be bonded to the membrane surface 101, 102 of the solid electrolyte membrane 10 to form the cathode 2 or the anode 3. A suitable electrode material made of a complex oxide is a complex oxide material in which a portion of a metal oxide containing one or more elements selected from alkali metal elements, alkaline earth metals, and lanthanoid elements is substituted with one or more transition metal elements. By adjusting the type of constituent elements and the amount of substitution of the substituted elements in such a complex oxide material, a porous electrode with desired characteristics can be obtained.

[0039] Specifically, such a composite oxide material is represented by the following general formula 2. Formula 2: (M1) 1-x1 (M2) x1 O 2-y1 However, in Equation 2, M1 is one or more elements selected from alkali metal elements, alkaline earth metal elements, and lanthanoid elements, M2 is one or more elements selected from the group consisting of Sc, Y, Zr, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pa, Ag, Au, and Pt; x1 and y1 are numbers that satisfy the following conditions: 0.1≦x1≦0.6, 0.0≦y1≦1.0, respectively.

[0040] In the above formula 2, examples of alkali metal elements serving as the M1 element include Li, Na, and K, examples of alkaline earth metal elements include Mg, Ca, Sr, and Ba, and examples of lanthanoid elements include La and Ce. The composite oxide of the above formula 2 has a structure in which at least one of these alkali metal elements, alkaline earth metals, and lanthanoid elements is included as the M1 element, and the M2 element is added in the form of substituting a portion of the M1 element. Preferably, La, Ce, Sr, or the like is used as the M1 element, and Ti, Mn, Fe, Co, Rh, or the like is used as the M2 element.

[0041] In formula 2, x1 is preferably 0.1 or more and 0.6 or less, more preferably 0.2 or more and 0.4 or less, from the viewpoint of being able to improve electrode properties by being substituted at the M1 element position. In formula 2, y1 is preferably 0.0 or more and 1.0 or less, from the viewpoint of maintaining electrical neutrality. Preferably, one or both of the M1 element and the M2 element are a combination of multiple element species, which allows the above properties to be adjusted and makes it possible to obtain a more suitable electrode material. Examples of such composite oxides include Ce 0.6 Mn 0.3 Fe 0.1 O 1.8 , La 0.4 Sr 0.1 Ti 0.45 Rh 0.05 O 1.63 , La 0.33 Sr 0.33 Co 0.33 O 2.0 However, the examples are not limited to these.

[0042] 6, when manufacturing an electrochemical cell 1 having such a structure, a method can be employed in which a film including a solid electrolyte film 10 made of an apatite-type composite oxide is formed on the surface of a substrate 200 and then separated from the substrate 200. In addition, by integrally forming one of the cathode 2 and the anode 3 at this time, the electrochemical cell 1 can be manufactured efficiently. Examples of materials for the substrate 200 include metal materials such as Si and Pt, and oxide materials such as sapphire (Al2O3) and ZrO, and preferably, a substrate made of an oxide material can be used.

[0043] Specifically, as shown below: (1) a first step of forming a first layer 300 made of a composition that can be sublimated at the crystallization temperature of an apatite-type composite oxide on the surface of a substrate 200; (2) a second step of forming an amorphous complex oxide film 100 containing the same constituent elements as the apatite-type complex oxide on the surface of the first layer 300; (3) a third step of forming a second layer 400 made of an oxide containing some of the constituent elements of the apatite-type complex oxide or a precursor thereof on the surface of the amorphous complex oxide film 100; (4) a fourth step of forming an electrode material layer 21, which will become one of the cathode 2 and the anode 3, on the surface of the second layer 400; (5) A fifth step of forming a polycrystalline layer 11 made of an apatite-type complex oxide by heating the amorphous complex oxide film 100 to a temperature equal to or higher than the crystallization temperature thereof and forming one of the cathode 2 and the anode 3, and removing the first layer 300 by sublimation; (6) A sixth step of forming an electrode material layer 31, which will become the other of the cathode 2 and the anode 3, on the surface from which the first layer 300 has been removed, and then heat-treating the layer to form the other of the cathode 2 and the anode 3, allows the electrochemical cell 1 to be manufactured.

[0044] The first step is a method for separating the solid electrolyte membrane 10 during the manufacturing process, in which a composition layer (hereinafter referred to as the first layer) 300, which will be removed in the fifth step, is formed in advance on the surface that will become the main surface 200a of the substrate 200. The composition that forms the first layer 300 may be any composition with a high vapor pressure that can be removed by sublimation during the heat treatment of the amorphous complex oxide film 100, and can crystallize the amorphous complex oxide film 100 into an apatite structure and allow the oriented apatite to be peeled off from the substrate 200 after the heat treatment. Examples of compositions with a high vapor pressure include bismuth oxide, zinc oxide, boron oxide, sulfur, and phosphorus. From the viewpoints of reducing element diffusion and internal stress in apatite during the heat treatment, it is preferable to use an oxide composition.

[0045] Examples of methods for forming a composition with a high vapor pressure include atomic layer deposition, ion plating, pulsed laser deposition, plating, sputtering, and vapor deposition. Furthermore, any film-forming method can be used, such as screen printing or spin coating, of an amorphous oxide prepared by a wet method such as coprecipitation or sol-gel. From the viewpoints of film quality and productivity, it is preferable to select the sputtering method.

[0046] Sputtering can be performed using an existing sputtering device. A target composed of the composition forming the first layer 300 is placed opposite the substrate 200, and sputtering is performed to form a film composed of the desired composition on the substrate 200. An oxide substrate is suitable for the substrate 200, as it suppresses structural defects such as cracks due to differences in thermal expansion coefficients during the heat treatment in the fifth step described below. For example, a sapphire substrate having a C-plane as the main surface 200a can be used. Forming a c-axis-oriented film composed of a hexagonal material (e.g., ZnO) as the first layer 300 on the main surface 200a is desirable from the viewpoint of facilitating c-axis orientation of hexagonal apatite. Alternatively, the substrate 200 may be preheated and maintained at a predetermined temperature in the range of 300 to 800°C during sputtering.

[0047] In the second step, the amorphous complex oxide film 100 can be formed on the surface of the first layer 300 by a similar method, preferably a sputtering method. Specifically, the amorphous complex oxide film 100 can be formed on the substrate 200 by a sputtering method using a target made of a complex oxide having the same constituent elements as the apatite to be produced. The composition of the complex oxide (sintered body) used as the sputtering target can be the same as that of the amorphous complex oxide film 100 to be formed, and a composition can be used in which the amount of oxide or precursor added used in the third step is subtracted from the composition of the target apatite-type complex oxide.

[0048] Next, in the third step, a second layer 400 made of an oxide containing some of the constituent elements of the apatite-type complex oxide or a precursor thereof is formed on the surface of the amorphous complex oxide film 100 on the substrate 200. The oxide or precursor thereof contains one or more of the elements A, B, and M that constitute apatite. The film formation method can be the same as that of the above step, and preferably, sputtering can be used.

[0049] In the first to third steps, when a sputtering method is employed, a radio frequency (RF) sputtering method is preferably used. This allows the use of a high-resistance oxide target. Specifically, a replacement gas is introduced into a vacuum chamber in which a sputtering target and a substrate 200 (opposing electrode) are placed, and the pressure in the chamber is maintained at a predetermined level. In this state, a radio frequency voltage is applied between the electrodes to perform plasma processing. The degree of vacuum in the vacuum chamber is, for example, 1×10 -5 More than 1×10 -2 The pressure for the plasma treatment can be in the range of 0.5 Pa to 30 Pa. Inert gases such as Ar, He, Ne, Kr, Xe, and Rn are used as replacement gases, and reactive sputtering can also be performed using gases such as O2 and N2.

[0050] Preferably, O2 gas is introduced into the chamber during film formation to improve the film density. By introducing O2 gas, the formation of large structural defects such as voids in the film can be suppressed, resulting in the formation of a more suitable film when applied to highly active cells used in, for example, solid oxide fuel cells (SOFCs). The proportion of O2 gas in the atmosphere is preferably selected within the range of 5% to 20%. If the O2 gas content is less than 5%, the effect of suppressing the formation of voids and the like may be insufficient. If the O2 gas content is greater than 20%, the rate of formation of the amorphous complex oxide film 100 on the substrate 200 may be slowed down, potentially reducing production efficiency.

[0051] The power density during plasma treatment is, for example, 1.0 to 4.0 W / cm 2 The power is selected within the following range, and film formation can be performed efficiently while preventing abnormal deposition and sparks. Preferably, it is 1.5 W / cm 2 More than 3.0W / cm 2 The following ranges are preferred: The method for producing the sputtering target is not particularly limited, and for example, a method such as that described in Patent Document 1 in which raw materials for the composition to be the target are mixed and fired to form a sintered body can be used.

[0052] Next, in a fourth step, an electrode material layer 21 that will become, for example, the cathode 2 is formed on the surface of the second layer 400 formed on the surface layer of the amorphous complex oxide film 100 on the substrate 200 to form one of the cathode 2 and the anode 3. The electrode material layer 21 is a layer containing particles of the electrode material described above, and can be formed by printing using a printing paste, for example. The thickness of the electrode material layer 21 can be adjusted as appropriate so that a porous electrode of the desired thickness is obtained after heat treatment.

[0053] Thereafter, in a fifth step, the amorphous complex oxide film 100 on the substrate 200 and the second layer 400 formed on its surface are further heat-treated. This allows the amorphous complex oxide film 100 and the second layer 400 to be integrated and crystallized into an apatite structure and oriented, thereby forming a polycrystalline layer 11 made of an apatite-type complex oxide. Furthermore, a porous electrode that will become one of the cathode 2 and anode 3 (e.g., cathode 2) can be integrally formed on the polycrystalline layer 11. Furthermore, the formed polycrystalline layer 11 can be separated from the substrate 200 to form a composite of the solid electrolyte membrane 10 and the porous electrode having a half-cell structure.

[0054] From the viewpoint of the efficiency of crystallizing the amorphous complex oxide film 100 into an apatite structure, the heat treatment temperature is preferably 800°C or higher, more preferably 850°C to 1200°C, and more preferably 900°C to 1100°C. A complex oxide film formed by a sputtering method is obtained as an amorphous material and crystallizes by heat treatment, but a long time is required for crystallization to proceed at temperatures below 800°C. Furthermore, when the heat treatment furnace is a muffle furnace, it is not easy to set the temperature above 1200°C, and generally, heating furnaces that can be set to temperatures above 1200°C are expensive and therefore not practically advantageous.

[0055] During this heat treatment, the second layer 400 formed on the surface of the amorphous complex oxide film 100 diffuses into the amorphous complex oxide film 100, forming a large number of grain boundaries C1 extending perpendicular to the film plane, which is thought to improve the film strength and the c-axis orientation rate of the crystal grains C. Furthermore, the first layer 300 formed on the substrate 200 is removed by sublimation, and the polycrystalline layer 11 that will become the solid electrolyte film 10 can be separated from the substrate 200.

[0056] The atmosphere for the heat treatment can be an air atmosphere. The heat treatment for peeling off the amorphous complex oxide film 100 from the substrate 200 can be carried out in the same temperature range as the heat treatment for crystallizing the amorphous complex oxide film 100 into an apatite structure, but can be carried out more efficiently by flowing the above-mentioned inert gas or a reducing gas such as hydrogen. Preferably, the heat treatment is carried out in an air atmosphere for a time sufficient for crystallization into an apatite structure, and then the atmosphere is replaced with a reducing gas atmosphere for heat treatment, thereby enabling efficient production of the solid electrolyte film 10.

[0057] In the sixth step, an electrode material layer 31 that will become the other of the cathode 2 and anode 3, for example, the anode 3, is formed on the surface of the polycrystalline layer 11 that will become the solid electrolyte membrane 10, from which the first layer 300 has been removed. The electrode material layer 31 is a layer containing particles of the electrode material described above, and can be formed by printing, for example, using a printing paste. The thickness of the electrode material layer 31 can be adjusted appropriately so that a porous electrode of the desired thickness is obtained after heat treatment. Thereafter, heat treatment is performed to obtain an electrochemical cell 1 in which porous electrodes that will become the cathode 2 and anode 3 are formed on both surfaces of the solid electrolyte membrane 10. The heat treatment can be performed under the same conditions as in the fifth step.

[0058] The method for converting the oriented apatite-type complex oxide film into the solid electrolyte membrane 10 by the heat treatment in the fifth step is not limited to the method of separating the oriented apatite-type complex oxide film from the substrate 200 using a composition with a high vapor pressure, as in the first and fourth steps described above, but any method can be used. For example, a method may be used in which a highly soluble composition is used as the substrate 200, an oriented apatite-type complex oxide film is produced as in the second to fourth steps, and the substrate 200 is then removed by dissolving in water or the like, to obtain the solid electrolyte membrane 10 consisting of the polycrystalline layer 11. The highly soluble composition is not particularly limited, but it is preferable to use an oxide composition from the viewpoint of reducing diffusion and internal stress during the heat treatment of the apatite. Examples of such highly soluble oxide compositions include strontium chromate and strontium aluminate.

[0059] It is not necessarily necessary to form a composite with a half-cell structure as in steps 4 and 5. After forming the solid electrolyte membrane 10 as a free-standing thin film, porous electrodes to become the cathode 2 and anode 3 can be formed on both sides of the membrane. Alternatively, a layer to become an intermediate layer may be formed between the solid electrolyte membrane 10 and at least one of the cathode 2 and anode 3, or a layer to become a surface layer may be formed on the surface of at least one of the cathode 2 and anode 3. These films can be formed integrally when the solid electrolyte membrane 10 or the porous electrodes are formed.

[0060] For example, a dense film made of a complex oxide other than apatite may be formed at the interface between the solid electrolyte membrane 10 and the cathode 2 and anode 3. The formation of such a dense film improves the bonding strength between the cathode 2 and anode 3 and the solid electrolyte membrane 10 made of an apatite complex oxide, thereby ensuring good oxide ion conductivity. Such a dense film can be formed using, for example, Gd-doped ceria (CeO2) or Y-doped zirconia (ZrO2) to a thickness of, for example, 5 nm to 100 nm.

[0061] Alternatively, a porous metal film having electron conductivity can be formed on the surfaces of the cathode 2 and the anode 2. The porous metal film can be made of Fe, Ni, an FeNi alloy, an FeCr alloy, or the like, and by forming the porous metal film to a thickness of 100 nm to 1 μm, the strength of the film constituting the electrochemical cell 1 can be improved.

[0062] (Embodiment 2) A second embodiment of the electrochemical cell will be described with reference to the drawings. As shown in Figs. 7 and 8, the solid electrolyte membrane 10 constituting the electrochemical cell 1 can have a multi-layer structure with two or more polycrystalline layers 11. In this case, it is desirable that at least one of the polycrystalline layers 11 constituting the polycrystalline body is an oriented layer having c-axis orientation and aligned grain boundaries C1. In this embodiment, a two-layer structure having two oriented layers is used. The following description will focus on the differences from the first embodiment. Note that, among the symbols used in the second and subsequent embodiments, the same symbols as those used in the previous embodiments represent the same components, etc. as those in the previous embodiments, unless otherwise specified.

[0063] 7 and 8, the electrochemical cell 1 is configured such that polycrystalline layers 11A and 11B having the same structure are stacked in the film thickness direction Z between two opposing film surfaces 101 and 102, so that the overall film thickness t, film area S, and surface roughness Rz are within the above-mentioned ranges. The exposed surfaces of polycrystalline layer 11A and polycrystalline layer 11B form film surfaces 101 and 102, respectively, and a layer interface 12 is formed between polycrystalline layer 11A and polycrystalline layer 11B. Both polycrystalline layer 11A and polycrystalline layer 11B are c-axis oriented layers.

[0064] In this way, the solid electrolyte membrane 10 has a layer interface 12, and the crystal grains C of the two polycrystalline layers 11A and 11B are in contact with each other at the grain boundary in the film thickness direction Z, which acts in the same way as the grain boundary C1 in the film plane direction, thereby achieving the effect of further improving the film strength.

[0065] The solid electrolyte membrane 10 is not limited to a two-layer structure, but may also be configured by stacking three or more polycrystalline layers 11. In that case, a layer interface 12 is formed between each polycrystalline layer 11, resulting in a plurality of layer interfaces 12. The number of layers can be set arbitrarily within a predetermined film thickness range, and the formation of the layer interfaces 12 is thought to have little effect on the oxide ion conductivity. However, from the viewpoint of manufacturing, it is preferable to have, for example, about five layers or less.

[0066] (Embodiment 3) A third embodiment of an electrochemical cell will be described with reference to the drawings. As shown in FIG. 9, when the solid electrolyte membrane 10 constituting the electrochemical cell 1 has a multi-layer structure, it can also have a structure including two or three or more polycrystalline layers 11 having different layer thicknesses and c-axis orientation rates. The upper diagram of FIG. 9 shows a two-layer structure in which a polycrystalline layer 11C serving as an oriented layer is disposed on the surface of the polycrystalline layer 11 in the first embodiment. As shown in the lower diagram of FIG. 8, a three-layer structure can also be formed by disposing the polycrystalline layer 11C between the polycrystalline layer 11A and the polycrystalline layer 11B in the second embodiment. The following description will focus on the differences from the first and second embodiments.

[0067] In the upper diagram of FIG. 9 , the polycrystalline body that becomes solid electrolyte membrane 10 has polycrystalline layer 11C, a random grain boundary layer, laminated in the film thickness direction Z on one surface of polycrystalline layer 11, an oriented layer with c-axis orientation and aligned grain boundaries C1. The overall film thickness t, film area S, and surface roughness Rz of film surfaces 101 and 102 are configured to fall within the above-mentioned ranges. Polycrystalline layer 11C has a grain boundary angle θ shown in FIG. 4 above of less than 80° and a deviation angle of more than 10°, and the grain boundaries C1 are oriented in a random direction (random direction). In other words, it can be said to be a layer in which the grain boundaries C1 are not aligned. The c-axis orientation of the random grain boundary layer is not particularly limited, and the c-axis orientation ratio measured by the Lotgering method may be 0.25 or more or less than 0.25. From the viewpoint of oxide ion conductivity, a c-axis orientation ratio of 0.25 or more is preferable.

[0068] To suppress the effects of the random grain boundary layer on oxide ion conductivity and surface irregularities, it is desirable to form the thickness t2 of polycrystalline layer 11C, which becomes the random grain boundary layer, sufficiently thinner than the thickness t1 of polycrystalline layer 11, which becomes the oriented layer. As long as the thickness t2 is within a range in which stress concentration due to surface irregularities is not apparent, the grain boundaries are highly effective in alleviating stress, which is believed to effectively improve film strength together with layer interface 12 in the film thickness direction Z. The thickness t2 can be preferably set to approximately 1 / 50 or less, more preferably approximately 1 / 100 or less, of the thickness t1 of polycrystalline layer 11. For example, by forming polycrystalline layer 11C with a thickness t2 of 0.05 μm (50 nm) on the surface of polycrystalline layer 11 with a thickness t1 of approximately 5 μm, it is possible to improve film strength while suppressing stress concentration.

[0069] As shown in the lower diagram of FIG. 9 , when the solid electrolyte membrane 10 has a three-layer structure, the polycrystalline layer 11A and the polycrystalline layer 11B, which are oriented layers, are stacked in the film thickness direction Z, sandwiching the polycrystalline layer 11C, which is a random grain boundary layer. The overall film thickness t, the film area S, and the surface roughness Rz of the film surfaces 101 and 102 are configured to be within the above-mentioned ranges. The solid electrolyte membrane 10 can also be configured to have multiple polycrystalline layers 11C, which are random grain boundary layers. In this case, for example, the strength of the entire membrane can be improved by configuring the random grain boundary layers and the oriented layers to be alternately arranged. Such a solid electrolyte membrane 10 has excellent processability and can be applied to various uses by processing it into shapes other than flat shapes, such as curved or cylindrical shapes. [Example]

[0070] Example 1 An electrochemical cell 1 having the same configuration as that of the first embodiment was fabricated and evaluated. The electrochemical cell 1 using the solid electrolyte film 10 with an oriented apatite structure was fabricated based on the method shown in FIG. 6 above. An oriented ZnO layer, which is the first layer 300, was formed on a substrate 200 by high-frequency sputtering (first step). Then, an amorphous composite oxide film 100 with an apatite composition, an amorphous SiO layer, which is the second layer 400, and an electrode material layer 21 were formed (second to fourth steps), followed by a heat treatment (fifth step). Thereafter, an electrode material layer 31 was formed and then a heat treatment was performed (sixth step). The specific method is described below.

[0071] <Preparation of electrochemical cell 1> First, a sapphire substrate 200 and a ZnO sputtering target were placed facing each other in the chamber of a known high-frequency sputtering device, and a vacuum of 1×10 -4 The chamber was evacuated to a pressure of 1.0 Pa or less. Ar gas was introduced into the chamber and maintained at 1.0 Pa. The high-frequency power supply was then operated to apply high-frequency power. The substrate 200 was a square substrate (10 mm x 10 mm x 1.0 mm) made of hexagonal sapphire C-face. A high-frequency power of 400 W was applied for 30 minutes to form a ZnO film with its c-axis oriented perpendicular to the substrate plane. The thickness of this ZnO layer was 300 nm.

[0072] Next, the substrate 200 on which the ZnO layer was formed and a rare earth silicate-based apatite composition (La 9.33 Si 5.8 O 25.6 ) and a sputtering target consisting of 1×10 -4 After evacuating the chamber to a pressure of 1.0 Pa or less, Ar gas mixed with 10% O was introduced. With the pressure inside the chamber maintained at 1.0 Pa, a high-frequency power of 500 W (2.73 W / cm) was applied. 2 ) and the film formation time was 600 minutes, and an amorphous composite oxide film 100 having an apatite composition was formed on the ZnO layer.

[0073] Thereafter, the substrate 200 on which the amorphous complex oxide film 100 and the ZnO layer were formed and a sputtering target made of SiO2 were placed opposite each other in a chamber, and a vacuum of 1×10 -4 After evacuating the chamber to a pressure of 1.0 Pa or less, Ar gas was introduced. With the chamber interior maintained at 1.0 Pa, a high-frequency power of 500 W (2.73 W / cm) was applied. 2 ) and the film formation time was 1 minute, and an amorphous SiO2 layer was formed on the amorphous complex oxide film 100.

[0074] Pt powder was used as the electrode material for the cathode 2 and anode 3, and was mixed in a ball mill with zirconia beads having a diameter of 10 mm for 16 hours in terpineol containing 1% by mass of acrylic resin as a dispersant. The mixture was then kneaded to adjust the viscosity, yielding a printing paste. The resulting printing paste was applied by printing to the surface of an amorphous SiO2 layer formed on the substrate 200 to a predetermined film thickness, and then dried to form an electrode material layer 21. The film thickness was adjusted by the number of printing operations.

[0075] The film-substrate composite thus obtained was heat-treated at 1000°C to crystallize the amorphous composite oxide film 100 into apatite, imparting orientation, and to remove the ZnO layer by sublimation, thereby separating it from the substrate 200. The heat treatment was carried out by heating the film to 1000°C in an air atmosphere over 5 hours, maintaining the temperature for 4 hours, and then introducing a 4% H2 mixed N2 gas over 100 minutes to completely replace the air atmosphere. After maintaining this condition for 10 hours, the film was cooled to room temperature over 2 hours.

[0076] In this way, a half cell was obtained in which the solid electrolyte membrane 10 having an oriented apatite structure was made into a free-standing thin film not supported by the substrate 200, and a porous electrode membrane that would become the cathode 2 was formed on one surface of the half cell. On the surface of this half cell opposite the cathode 2, an electrode material layer 31 of the same thickness was formed using the same printing paste as used to form the electrode material layer 21. The obtained composite was then heated to 1000°C in an air atmosphere over 5 hours, held at that temperature for 4 hours, and then cooled to room temperature over 2 hours to form the electrochemical cell 1.

[0077] Here, the porous electrode that constitutes the half cell together with the solid electrolyte membrane 10 is the cathode 2, but it is of course also possible to form a half cell having a porous electrode that will become the anode 3, and then form the cathode 2.

[0078] <Evaluation of Solid Electrolyte Membrane 10> The solid electrolyte membrane 10 constituting the obtained electrochemical cell 1 was subjected to X-ray diffraction pattern analysis by X-ray diffraction and elemental analysis by ICP optical emission spectrometry. Furthermore, the membrane shape and sample cross section were observed using various microscopes. Specifically, the surface roughness was measured using an atomic force microscope (AFM), the planar shape was measured using a laser microscope, and cross-sectional structural analysis was performed using a transmission electron microscope (TEM). These results are shown in Table 1 as Example 1.

[0079] As shown in Table 1 as the membrane structure (parent phase), the obtained solid electrolyte membrane 10 was composed of La 9.33 Si 6.0 O 26 It was confirmed that the film was made of a polycrystalline body in which crystals C of the apatite structure with the composition of 1.0 cm2 were aggregated. In addition, the film thickness t was 5.0 μm and the film area S was 1.0 cm2. 2 It was confirmed that the film was a single layer consisting of a polycrystalline layer 11 (oriented layer) of oriented apatite with a film surface roughness Rz of 15 nm, a c-axis orientation rate of 0.25, and a grain boundary angle θ of 80°, and that it had no layer interface 12 in the film thickness direction Z. The equipment used for these measurements is shown below. X-ray diffraction equipment: Rigaku Corporation, SmartLab ICP emission spectrometer: Shimadzu Corporation, ICPS-7510 Laser microscope: Olympus Corporation, LEXT OLS4100 Transmission electron microscope: JEOL Ltd., GRAND-ARM300

[0080] The film thickness t in Table 1 is a calculated value based on a TEM image of a cross-sectional sample, and is the arithmetic mean value of film thicknesses measured at 40 arbitrary points within a 10-μm range along the film plane. The c-axis orientation rate is the ratio calculated by the Lotgering method from the X-ray diffraction patterns of 40 arbitrary grains observed in the cross-sectional TEM, and the grain boundary angle θ is the arithmetic mean value of the angles of 40 arbitrary grain boundaries C1 measured in the cross-sectional TEM.

[0081] [Table 1]

[0082] <Evaluation of Electrochemical Cell 1> Next, the electrolysis current value by steam electrolysis was measured for the obtained electrochemical cell 1. Using an evaluation device in which the electrochemical cell 1 was arranged so that gas flow between the cathode 2 side and the anode 3 side was blocked, a gas containing steam was introduced into the cathode 2 side at a predetermined flow rate, and a voltage was applied between the cathode 2 and the anode 3 to cause an electrolysis reaction. The evaluation conditions were as follows. The measured electrolysis current value (unit: A / cm 2 The evaluation results based on the above are shown in Table 2. Electrochemical cell temperature: 500℃ Intake gas: Water vapor concentration 10% (base gas: nitrogen) Flow rate: 50cc / min Voltage: -1.3V

[0083] The fracture strain of the obtained electrochemical cell 1 was measured using the apparatus shown in Fig. 10. In Fig. 10, a jig 501 and a top-pan balance 502 are placed on a base 500, and the electrochemical cell 1, which serves as a sample for evaluation, is supported on the tip side of an arm 503 attached to the upper end of the ceramic jig 501. The electrochemical cell 1 is disposed between a pair of arms 503a and 503b extending parallel to the base 500, and is positioned above one pan 504 of the top-pan balance 502. An arbitrary weight 506 can be placed on the other pan 505 of the top-pan balance 502.

[0084] As shown in an enlarged view of the configuration of the sample evaluation unit in FIG. 10, a protrusion 507 that abuts against the underside of the electrochemical cell 1 is provided on the lower arm 503b, allowing a load to be applied using a weight 506. An opening 503c is provided on the upper arm 503a above the protrusion 507, allowing a laser microscope 508 to measure the strain that occurs in the electrochemical cell 1 when a load is applied. The strain measurement was performed using a device similar to the laser microscope used to measure the planar shape described above. The evaluation results based on the measured fracture strain (unit: %) are listed in Table 2, along with the electrode configuration.

[0085] [Table 2]

[0086] In Table 2, the electrolysis current value (unit: A / cm 2 ) and breaking strain (unit: %) were evaluated on a three-level scale of A to C as follows. Electrolysis current value (unit: A / cm 2 ) A: 0.5 or more and less than 12 B: 0.1 or more and less than 0.5 C: Less than 0.1 Breaking strain (unit: %) A: 1.5 or more and less than 2.5 B: 0.5 or more and less than 1.5 C: Less than 0.5

[0087] As shown in Table 2, the electrochemical cell 1 of Example 1 had a cathode 2 and an anode 3 each made of a Pt porous electrode with a film thickness of 500 μm, and both the electrolysis current value and the breaking strain were rated B, indicating that good cell characteristics were obtained.

[0088] Examples 2 to 5 Electrochemical cells 1 were fabricated by the same manufacturing method as in Example 1, except that the thicknesses of the Pt porous electrodes serving as the cathode 2 and anode 3 were changed. Specifically, Example 2 was prepared by fabricating electrochemical cells 1 in the same manner except that the thickness of the cathode 2 was 30 μm and the thickness of the anode 3 was 15 μm. Furthermore, electrochemical cells 1 were fabricated as Examples 3 to 5, with the thicknesses of the cathode 2 and anode 3 changed as follows, and the results of evaluation were similarly performed. The results are shown in Tables 1 and 2, respectively. Example 3: Cathode 300 μm, Anode 195 μm Example 4: Cathode 15 μm, Anode 30 μm Example 5: Cathode 195 μm, Anode 300 μm

[0089] As shown in Table 2, the electrochemical cells 1 of Examples 2 and 4, in which the thickness of the cathode 2 and anode 3 was 15 μm to 30 μm, showed an improved breaking strain rating of A, and the electrochemical cells 1 of Examples 3 and 5, in which the thickness was 195 μm to 300 μm, showed an improved electrolysis current rating of A, and both cells showed good cell characteristics.

[0090] (Examples 6 to 8) An electrochemical cell 1 was produced by the same manufacturing method as in Example 1, except that the types of porous electrodes serving as the cathode 2 and anode 3 were changed. Specifically, the electrode materials for the cathode 2 and anode 3 were changed to the composite oxides shown below, but the rest of the configuration was the same. Example 6: Ce 0.6 Mn 0.3 Fe 0.1 O 1.8 Example 7: La 0.4 Sr 0.1 Ti 0.45 Rh 0.05 O 1.63 Example 8: La 0.33 Sr 0.33 Co 0.33 O 2.0

[0091] For the composite oxides of Examples 6 to 8, electrode material powders for forming printing pastes were prepared using the single oxides that served as the raw materials for each composite oxide. Specifically, the raw single oxides were weighed to the desired blend ratio, and mixed in a ball mill with 10 mm diameter zirconia beads in ethanol containing 1% by mass of polyvinyl alcohol as a dispersant for 16 hours. The powder was then removed from a tray and dried. The resulting powder was then heat-treated at 1100°C to obtain a composite oxide powder. Using the composite oxide powder thus obtained, electrochemical cell 1 was similarly fabricated, and the evaluation results are shown in Tables 1 and 2.

[0092] As shown in Table 2, the electrochemical cells 1 of Examples 6 to 8, in which composite oxide was used as the electrode material for the cathode 2 and anode 3, showed an improved electrolysis current value, earning an A rating, and all of them exhibited good cell characteristics.

[0093] Examples 9 to 14 Electrochemical cells 1 using solid electrolyte films 10 with different apatite compositions were fabricated by the same manufacturing method as in Example 1. Specifically, when forming an amorphous composite oxide film 100 with an apatite composition on a substrate 200 on which a ZnO layer was formed, the apatite composition used as a sputtering target was La 9.33 Si 5.3 B 0.7 O 25.65 Except for this, an electrochemical cell 1 was produced using the solid electrolyte membrane 10 in the same manner as above, and the evaluation results are shown in Tables 3 and 4 as Example 9.

[0094] Furthermore, the rare earth silicate-based apatite composition used as the sputtering target was changed as follows to give Examples 10 to 14. Electrochemical cell 1 was produced in the same manner, and the evaluation results are shown in Tables 3 and 4, respectively. Example 10: La 9.33 Si 5.3 Ti 0.7 O 26 Example 11: La 9.33 Si5.3 Al 0.7 O 25.65 Example 12: La 9.33 Si 5.3 Y 0.7 O 25.65 Example 13: La 9.33 Si 5.3 Zr 0.7 O 26 Example 14: La 9.00 Ce 0.33 Si 6.0 O 26

[0095] As shown in Table 3, it was confirmed that in Examples 9 to 14, which used an apatite-type composite oxide containing an M element (Al, Ti, Y, Zr, or B) represented by the above formula, or an apatite-type composite oxide containing two A elements (La, Ce), the solid electrolyte membrane 10 was a single layer membrane of oriented apatite having the same membrane structure as in Example 1. Furthermore, as shown in Table 4, the electrolytic current value of the electrochemical cells 1 of Examples 9 to 14 was improved to an A rating, and good cell characteristics were obtained in all cases.

[0096] [Table 3]

[0097] [Table 4]

[0098] Example 15 In the same manufacturing method as in Example 1, the film formation conditions were changed to fabricate an electrochemical cell 1 using a solid electrolyte film 10 of an apatite composition. Specifically, an apatite composition (La 9.33 Si 5.8 O 25.6) was used as a sputtering target, and the deposition time for depositing the amorphous complex oxide film 100 was changed to 24 minutes. Furthermore, the deposition time for depositing the amorphous SiO layer was changed to 2.4 seconds, but otherwise an electrochemical cell 1 using the solid electrolyte membrane 10 was produced in the same manner. This was designated Example 8, and the results of similar evaluations are shown in Tables 3 and 4.

[0099] As shown in Table 3, the obtained solid electrolyte membrane 10 had a film thickness t of 0.2 μm, which was thinner than that of Example 1, and it was confirmed that the membrane area S and c-axis orientation were equivalent to those of Example 1, making it a single layer membrane of oriented apatite. Furthermore, as shown in Table 4, the electrochemical cell 1 of Example 15 was rated B for both the electrolysis current value and fracture strain, and good cell characteristics were obtained.

[0100] Example 16 In the same manufacturing method as in Example 1, an electrochemical cell 1 was fabricated using a solid electrolyte film 10 of apatite composition, with the layer formed on the substrate 200 being changed. Specifically, when forming the first layer 300 in contact with the substrate 200, SiO2 was used as the sputtering target instead of ZnO, and otherwise the substrate 200 on which an oriented SiO2 layer was formed was fabricated in the same manner. Furthermore, when forming the amorphous complex oxide film 100, the apatite composition used as the sputtering target was changed to La 9.33 Si 5.6 O 25.2 An electrochemical cell 1 was produced using the solid electrolyte membrane 10 in the same manner, except for the above changes. This was designated as Example 16, and the results of evaluation carried out in the same manner are shown in Tables 3 and 4.

[0101] As shown in Table 3, the obtained solid electrolyte membrane 1 had a film thickness t and a film area S equivalent to those of Example 1, and was confirmed to be a single layer of oriented apatite with improved c-axis orientation, with a surface roughness Rz reduced to 8 nm, a c-axis orientation rate of 0.6, and a grain boundary angle θ of 88°. Furthermore, as shown in Table 4, both the electrolysis current value and fracture strain were improved to an A rating, and good cell characteristics were obtained.

[0102] Example 17 In the same manufacturing method as in Example 1, the film formation conditions were changed to fabricate an electrochemical cell 1 using a solid electrolyte membrane 10 having a multilayer structure and an apatite composition as shown in Example 2. Specifically, an apatite composition (La 9.33 Si 5.8 O 25.6 ) was used as a sputtering target to form the amorphous complex oxide film 100, the film formation time was changed to 300 minutes, and the film formation time when forming the amorphous SiO layer thereon was changed to 0.5 minutes. Next, a heat treatment was similarly performed, and the temperature was raised to 1000°C in an air atmosphere over 5 hours, maintained at that temperature for 4 hours, and then lowered to room temperature over 2 hours.

[0103] In this way, a layer of oriented apatite was formed on the substrate 200. Then, an amorphous composite oxide film 100 was formed on the surface of the substrate 200 for 300 minutes using the same procedure, and an amorphous SiO layer was formed on top of that for 0.5 minutes. Next, an electrode material layer 21 was formed in the same manner, and then heat-treated. The temperature was raised to 1000°C in an air atmosphere over 5 hours and held there for 4 hours. Then, as in Example 1, a 4% H2 mixed N2 gas was introduced to replace the air atmosphere, and the temperature was held for 10 hours, and then cooled to room temperature over 2 hours. An electrode material layer 31 was then formed and heat-treated, resulting in an electrochemical cell 1. This is Example 17. The results of similar evaluations are listed in Tables 3 and 4.

[0104] As shown in Table 3, the obtained solid electrolyte membrane 10 had a film thickness t and a film area S equivalent to those of Example 1, a surface roughness Rz of 20 nm, and was confirmed to be a multilayer membrane in which two oriented apatite layers were stacked with a layer interface 12 sandwiched therebetween. Furthermore, as shown in Table 4, the fracture strain was improved to an A rating, and good cell characteristics were obtained.

[0105] Example 18 In the same manufacturing method as in Example 17, the film formation conditions were changed to fabricate an electrochemical cell 1 using a solid electrolyte membrane 10 having a multilayer structure and an apatite composition as shown in Example 3. Specifically, an apatite composition (La 9.33 Si 5.8 O 25.6 ) was used as a sputtering target, the deposition time for forming the first amorphous complex oxide film 100 was changed to 594 minutes, and the deposition time for forming the amorphous SiO2 layer thereon was changed to 1 minute. In addition, when forming the second amorphous complex oxide film 100, the apatite composition serving as the sputtering target was changed to La 9.33 Si 6.0 O 26 The temperature was changed to 100°C, and film formation was performed for 6 minutes. Thereafter, the same heat treatment was performed without forming an amorphous SiO layer. An electrochemical cell 1 using the solid electrolyte membrane 10 was fabricated by the same method as above. This was designated Example 18, and the results of evaluation were similarly performed. The results are shown in Tables 3 and 4.

[0106] As shown in Table 3, the obtained solid electrolyte membrane 10 had a film thickness t and film area S equivalent to those of Example 1, a surface roughness Rz of 14 nm, and was confirmed to be a multilayer membrane in which a random grain boundary layer having a layer thickness t2 of 0.05 μm was laminated on the surface of an oriented layer (parent phase) having a layer thickness t1 of 4.95 μm. Specifically, the oriented layer had a c-axis orientation rate of 0.25 and a grain boundary angle θ of 80°, and the random grain boundary layer had a c-axis orientation rate of 0.25 and a grain boundary angle θ of 45°. Furthermore, as shown in Table 4, the electrochemical cell 1 using the obtained solid electrolyte membrane 10 had an improved fracture strain rating of A, and good cell characteristics were obtained.

[0107] Example 19 A solid electrolyte membrane 10 having a similar multilayer structure was produced by the same manufacturing method as in Example 18, but by changing the film formation conditions. Specifically, the layer formed on the substrate 200 was the same SiO2 layer as in Example 16, and when forming the first amorphous composite oxide membrane 100, the apatite composition serving as the sputtering target was changed to La 9.33 Si 5.6 O25.2 Otherwise, the first and second amorphous composite oxide films 100 were formed in the same manner, and an electrochemical cell 1 using the solid electrolyte membrane 10 was produced. This was designated Example 18, and the results of evaluation carried out in the same manner are shown in Tables 3 and 4.

[0108] As shown in Table 3, the obtained solid electrolyte membrane 10 was confirmed to be a multilayer membrane having a surface roughness Rz of 9 nm, in which a random grain boundary layer having a layer thickness t2 of 0.05 μm was laminated on the surface layer of an oriented layer (parent phase) having a layer thickness t1 of 4.95 μm, as in Example 18. Specifically, the c-axis oriented layer had a c-axis orientation rate of 0.6 and a grain boundary angle θ of 88°, and the random grain boundary layer had a c-axis orientation rate of 0.25 and a grain boundary angle θ of 45°. Furthermore, as shown in Table 4, the electrochemical cell 1 using the obtained solid electrolyte membrane 10 was improved to an A rating in both electrolysis current value and fracture strain, and good cell characteristics were obtained.

[0109] (Comparative Example 1) For comparison, an electrochemical cell 1 was fabricated using a solid electrolyte film 10 of an apatite composition by changing the film formation conditions in the same manufacturing method as in Example 1. Specifically, when forming an amorphous complex oxide film 100 on a substrate 200 on which a ZnO layer had been formed, the apatite composition serving as a sputtering target was changed to La 9.33 Si 6.0 O 26 The temperature was changed to 100°C, and film formation was carried out for 600 minutes. Thereafter, film formation and heat treatment were carried out in the same manner as above, except that the heat treatment was carried out without forming an amorphous SiO layer, to produce an electrochemical cell 1 using a solid electrolyte membrane 10. This was designated Comparative Example 1, and the results of evaluation carried out in the same manner are shown in Tables 3 and 4.

[0110] As shown in Table 3, the solid electrolyte membrane 10 obtained under the membrane forming conditions of Comparative Example 1 had a membrane thickness t of 5 μm and a membrane area S of 0.25 cm 2 and the area of ​​the substrate 200 (1.0 cm 2) was smaller than that of the solid electrolyte membranes 10 of Examples 1 to 19. The surface roughness Rz was 30 nm, which was larger than that of the solid electrolyte membranes 10 of Examples 1 to 19. The c-axis orientation rate was 0.25, and the grain boundary angle θ was 45°, confirming that the grain boundaries C1 were not aligned but oriented in random directions. As shown in Table 4, the electrolysis current value and fracture strain were both rated C.

[0111] FIG. 11 is a schematic diagram illustrating the structure of a solid electrolyte membrane 10 obtained by the method described in Comparative Example 1 as Comparative Example 1. In Comparative Example 1, unlike Examples 1 to 12, an amorphous SiO layer, which is the second additive layer 400, is not formed on the surface of the amorphous complex oxide membrane 100, making it difficult to control the orientation of the crystal grains C. This tends to result in a polycrystalline body in which the grain boundaries C1 deviate from the film thickness direction Z and the crystal grains C are clustered in random directions. In this case, the surface irregularities on the membrane surface 101 opposite the substrate 200 become large, stress concentration reduces membrane strength, and it is thought that this makes it difficult to maintain a membrane shape with a large area equivalent to that of the substrate 200.

[0112] In contrast, the solid electrolyte membrane 10 obtained in Examples 1 to 19 is a free-standing thin film having a larger area than that of Comparative Example 1, which is equivalent to the substrate 200, and has high cell characteristics. Therefore, by using such a solid electrolyte membrane 10 and forming a cathode 2 and an anode 3 on both surfaces thereof, a highly active electrochemical cell 1 can be obtained, and the cell can be used in a fuel cell or the like, thereby improving its performance.

[0113] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the spirit of the present invention. Furthermore, the electrochemical cell 1 using the solid electrolyte membrane 10 obtained as described above can be used as a single cell for a fuel cell or for any other purpose. [Explanation of symbols]

[0114] 1. Electrochemical cell 10 Solid electrolyte membrane 11, 11A, 11B, 11C polycrystalline layer 101, 102 Membrane surface 12 layer interface 2 cathodes 3 anode C crystal particles C1 grain boundary

Claims

1. An electrochemical cell (1) comprising a solid electrolyte membrane (10) made of an apatite-type composite oxide, a cathode (2), and an anode (3), The solid electrolyte membrane has one or more polycrystalline layers (11) in the thickness direction (Z) in which the crystal grains (C) of the apatite-type composite oxide are aggregated in the plane direction (X, Y) of the membrane with their grain boundaries (C1) in contact with each other. The membrane has a thickness t of 0.2 μm or more and 5.0 μm or less, and a membrane area S of 1.0 cm 2 or more, and the film has a film surface roughness Rz of 20 nm or less, At least one of the polycrystalline layers is an oriented layer in which a c-axis orientation rate with respect to the film thickness direction is 0.25 or more as calculated by the Lotgering method, and the grain boundaries are aligned in the film thickness direction, and the angle between the direction of the grain boundaries of the crystal grains appearing in a layer cross section and the film thickness direction is 10° or less in the oriented layer; The electrochemical cell, wherein the cathode and the anode are a pair of porous electrodes provided on either side of two opposing membrane surfaces (101, 102) of the solid electrolyte membrane.

2. 2. The electrochemical cell of claim 1, wherein the cathode and the anode each have a thickness of 15 μm or more and a combined thickness of 1000 μm or less.

3. An electrochemical cell as described in claim 1 or 2, wherein the aspect ratio, expressed as L / t, of the length L of one side of a square having the same area as the membrane area S to the membrane thickness t is 2000 or more.

4. 4. The electrochemical cell according to claim 1, wherein a plurality of the orientation layers are stacked in the film thickness direction.

5. At least one of the polycrystalline layers is a random grain boundary layer in which the grain boundaries are oriented in a random direction, 5. The electrochemical cell according to claim 1, wherein the orientation layer and the random grain boundary layer are laminated.

6. 6. The electrochemical cell according to claim 5, wherein a thickness t1 of the orientation layer and a thickness t2 of the grain boundary random layer satisfy the relationship t1>t2.

7. 7. The electrochemical cell according to claim 1, wherein the c-axis orientation rate of the orientation layer is 0.6 or more as calculated by the Lotgering method.

8. An electrochemical cell according to any one of claims 1 to 7, wherein the apatite-type composite oxide is represented by the following formula 1: Formula 1: A 10-x B 6-y M y O 27-z However, in the formula, A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba; B is an element containing Si or Ge or both; M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Y, Zr, Ta, Nb, B, Ge, Zn, Sn, W, and Mo; x, y, and z are numbers that satisfy the following conditions: -0.5≦x≦2.0, 0.0≦y≦3.0, and -6.0≦z≦4.2, respectively.

9. An electrochemical cell described in any one of claims 1 to 8, wherein the porous electrode is made of a complex oxide represented by the following formula 2. Formula 2: (M1) 1-x1 (M2) x1 O 2-y1 However, in formula 2, M1 is one or more elements selected from alkali metal elements, alkaline earth metals, and lanthanoid elements; M2 is one or more elements selected from the group consisting of Sc, Y, Zr, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pa, Ag, Au, and Pt; x1 and y1 are numbers that satisfy 0.1≦x1≦0.6 and 0.0≦y1≦1.0, respectively.

10. A method for producing an electrochemical cell according to any one of claims 1 to 9, comprising: forming a first layer (300) on the surface of the substrate (200) comprising a composition that can be sublimated at a heat treatment temperature for crystallizing the apatite-type composite oxide; forming an amorphous complex oxide film (100) containing the same constituent elements as the apatite-type complex oxide on the surface of the first layer; forming a second layer (400) made of an oxide containing a part of the constituent elements of the apatite-type complex oxide or a precursor thereof on the surface of the amorphous complex oxide film; forming an electrode material layer (21) that will be one of the cathode and the anode on the surface of the second layer; a step of increasing the temperature to a crystallization temperature of the amorphous complex oxide film or higher and performing a heat treatment to promote integration and crystallization of the amorphous complex oxide film and the second layer, thereby forming the polycrystalline layer made of the apatite-type complex oxide and one of the cathode and the anode, and removing the first layer by sublimation to separate the substrate from the polycrystalline layer; and forming an electrode material layer (31) to be the other of the cathode and the anode on the surface of the polycrystalline layer from which the substrate and the first layer have been removed, and then heat-treating the layer to form the other of the cathode and the anode.

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