Electrolyte sheet for electrochemical cell, and electrochemical cell

Abstract

An electrolyte sheet (11) is provided with a first main surface (S1), a second main surface (S2), and a first warped part (21) that is warped such that the first main surface (S1) is convex and the second main surface (S2) is concave. In a plan view of the first main surface (S1), the highest point (MX1) of the first warped part (21) is positioned on the contour of the first main surface (S1).

Description

Electrolyte sheets and electrochemical cells for electrochemical cells

[0001] This invention relates to an electrolyte sheet for an electrochemical cell and an electrochemical cell.

[0002] Conventionally, fuel cell cells comprising a hydrogen electrode, an oxygen electrode, and an electrolyte sheet disposed between the hydrogen electrode and the oxygen electrode are known (see, for example, Patent Document 1).

[0003] The electrolyte sheet is manufactured by firing a green sheet containing ceramic material.

[0004] Japanese Patent Publication No. 2011-228290

[0005] When inspecting electrolyte sheets after firing (dimension measurement, foreign object inspection, warping measurement, etc.), the main surface is easily damaged. In particular, if the area of ​​the main surface where the electrodes are placed is damaged, the expected cell performance may not be achieved.

[0006] These problems are common not only to fuel cell cells but to all electrochemical cells equipped with electrolyte sheets.

[0007] The object of the present invention is to provide an electrolyte sheet for an electrochemical cell and an electrochemical cell that can suppress damage to the main surface.

[0008] An electrolyte sheet for an electrochemical cell according to the first aspect of the present invention comprises a first main surface, a second main surface, and a first curved portion which is curved such that the first main surface is convex and the second main surface is concave. In a plan view of the first main surface, the highest point of the first curved portion is located on the contour of the first main surface.

[0009] The electrolyte sheet for an electrochemical cell according to the second aspect of the present invention relates to the first aspect, wherein the first main surface is rectangular, and the highest point of the first curvature is located on the first long side constituting the first main surface.

[0010] The electrolyte sheet for an electrochemical cell according to the third aspect of the present invention relates to the second aspect, wherein the highest point of the first curved portion is located in the center when the first long side is divided into three equal parts.

[0011] An electrolyte sheet for an electrochemical cell according to a fourth aspect of the present invention further comprises a second curved portion relating to the first aspect, wherein the first main surface is convex and the second main surface is concave. In a plan view of the first main surface, the highest point of the second curved portion is located on the contour of the first main surface.

[0012] The electrolyte sheet for an electrochemical cell according to the fifth aspect of the present invention relates to the fourth aspect, wherein the first main surface is rectangular, and the highest point of the first curvature is located on the first long side constituting the first main surface.

[0013] The electrolyte sheet for an electrochemical cell according to the sixth aspect of the present invention relates to the fifth aspect, wherein the highest point of the second curved portion is located on the second long side opposite to the first long side.

[0014] The electrolyte sheet for an electrochemical cell according to the seventh aspect of the present invention relates to the fifth aspect, wherein the highest point of the second curvature is located on the first long side.

[0015] The electrolyte sheet for an electrochemical cell according to the eighth aspect of the present invention relates to any of the first to seventh aspects described above, and has an average thickness of 45 μm or less.

[0016] An electrochemical cell according to the ninth aspect of the present invention comprises a cell body and a frame-shaped separator. The cell body has an electrolyte sheet for an electrochemical cell according to any of the first to eighth aspects, a first electrode disposed on the first main surface, and a second electrode disposed on the second main surface. The separator is bonded to the electrolyte sheet for the electrochemical cell.

[0017] According to the present invention, it is possible to provide an electrolyte sheet for an electrochemical cell and an electrochemical cell that can suppress damage to the main surface.

[0018] Figure 1 is a plan view of an electrochemical cell according to an embodiment. Figure 2 is a cross-sectional view taken along line A-A in Figure 1. Figure 3 is a schematic diagram showing the height distribution of the first main surface in a plan view of the electrolyte sheet according to an embodiment. Figure 4 is a schematic diagram showing the cross-section taken along line B-B in Figure 3. Figure 5 is a schematic diagram showing the cross-section taken along line C-C in Figure 3. Figure 6 is a schematic diagram showing the height distribution of the first main surface in a plan view of the electrolyte sheet according to Modification 1.

[0019] (Electrochemical Cell 1) The electrochemical cell according to the present invention is a general term for an element in which a pair of electrodes are arranged so that an electromotive force is generated from an overall redox reaction in order to convert electrical energy into chemical energy, and an element for converting chemical energy into electrical energy. The electrochemical cell includes a solid oxide electrolysis cell (SOEC) or a solid oxide fuel cell using ions or protons as carriers.

[0020] Fig. 1 is a plan view showing the configuration of the electrochemical cell 1 according to the embodiment. Fig. 2 is a cross-sectional view taken along the line A - A of Fig. 1. In Fig. 2, a cross-section of the electrochemical cell 1 passing through the geometric center CP of the first main surface S1 of the electrolyte sheet 11 to be described later and perpendicular to the first main surface S1 is shown.

[0021] In the present embodiment, the electrochemical cell 1 is formed in a rectangular plate shape extending in the X-axis direction and the Y-axis direction. The X-axis direction is the short side direction of the electrochemical cell 1, and the Y-axis direction is the long side direction of the electrochemical cell 1. However, the planar shape of the electrochemical cell 1 is not particularly limited, and it may be a polygon other than a rectangle, an ellipse, a circle, or the like.

[0022] As shown in Figs. 1 and 2, the electrochemical cell 1 includes a cell main body portion 10 and a separator 20.

[0023] [Cell Main Body Portion 10] The cell main body portion 10 has an electrolyte sheet for an electrochemical cell (hereinafter abbreviated as "electrolyte sheet") 11, an oxygen electrode 12, and a hydrogen electrode 13.

[0024] The electrolyte sheet 11 is formed in a dense thin plate shape. The electrolyte sheet 11 has a first main surface S1, a second main surface S2, and a side surface S3. As shown in Fig. 2, each of the first main surface S1 and the second main surface S2 extends in the X-axis direction and the Y-axis direction. The first main surface S1 is provided on the opposite side of the second main surface S2. The side surface S3 is continuous with the first main surface S1 and the second main surface S2. The side surface S3 is formed in an annular shape.

[0025] The electrolyte sheet 11 can be composed of at least one or more ceramic materials selected from zirconia-based oxides, LaGaO3-based oxides, and ceria-based oxides.

[0026] Examples of zirconia-based oxides include zirconia in which one or more oxides selected from oxides of alkaline earth metals such as MgO, CaO, SrO, and BaO, oxides of rare earth elements such as Sc2O3, Y2O3, La2O3, CeO2, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, and Yb2O3, Bi2O3, and In2O3 are dissolved.

[0027] Examples of LaGaO3-based oxides include complex oxides having a perovskite crystal structure in which part of La or Ga is substituted with Sr, Y, Mg, etc. Specifically, examples of LaGaO3-based oxides include La

[0028] , Sr 0.1 Ga 0.8 Mg 0.2 O3 such as La 1-x Sr x Ga 1-y Mg y O3, La 1-x Sr x Ga 1-y Mg y Co2O3, La 1-x Sr x Ga 1-y Fe y O3, La 1-x Sr x Ga 1-y Ni y O3, etc.

[0028] Examples of ceria-based oxides include ceria doped with one or more oxides selected from CaO, SrO, BaO, Ti2O3, Y2O3, La2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Er2O3, Tm2O3, Yb2O3, PbO, WO3, MoO3, V^2O^5, Ta2O5, and Nb2O5.

[0029] The average thickness of the electrolyte sheet 11 is preferably 45 μm or less. This reduces the area resistance of the electrochemical cell 1. The average thickness of the electrolyte sheet 11 is the arithmetic mean of the thickness of the electrolyte sheet 11 measured at five randomly selected locations. The thickness of the electrolyte sheet 11 shall be measured using a micrometer.

[0030] The porosity of the electrolyte sheet 11 is not particularly limited, but can be, for example, 0.1% or more and 3% or less.

[0031] The oxygen electrode 12 is an example of the "first electrode" according to the present invention. The oxygen electrode 12 is placed on the first main surface S1 of the electrolyte sheet 11.

[0032] The oxygen electrode 12 is a porous material having ionic conductivity and electrical conductivity. For example, the oxygen electrode 12 is (La,Sr)(Co,Fe)O ３ , (La,Sr)FeO ３ , La(Ni,Fe)O ３ , (La,Sr)CoO ３ , and (Sm, Sr)CoO ３ It can be composed of one or more oxides selected from the above. The oxygen electrode 12 may also contain an ion-conducting material (such as GDC).

[0033] The porosity of the oxygen electrode 12 is not particularly limited, but can be, for example, 20% to 60%. The thickness of the oxygen electrode 12 is not particularly limited, but can be, for example, 1 μm to 50 μm.

[0034] A reaction-preventing layer may be interposed between the electrolyte sheet 11 and the oxygen electrode 12 to suppress the formation of a layer with high electrical resistance due to the reaction of the constituent elements of the electrolyte sheet 11 with the constituent elements of the oxygen electrode 12. The reaction-preventing layer can be made of an ion-conducting material (such as GDC or SDC).

[0035] The hydrogen electrode 13 is an example of the "second electrode" according to the present invention. The hydrogen electrode 13 is placed on the second main surface S2 of the electrolyte sheet 11.

[0036] The hydrogen electrode 13 is a porous material having gas diffusivity and conductivity. The hydrogen electrode 13 includes a conductive material and an ion-conducting material. As the conductive material, metallic materials such as Ni (nickel) and Fe (iron), or conductive ceramic materials can be used. As the ion-conducting material, YSZ, CSZ, ScSZ, GDC, SDC, (La,Sr)(Cr,Mn)O ３ , (La,Sr)TiO ３ , Sr ２ (Fe, Mo) ２ O ６ , (La, Sr)VO ３ , (La,Sr)FeO ３ One or more types selected from LDC, LSGM, etc. can be used.

[0037] The porosity of the hydrogen electrode 13 is not particularly limited, but can be, for example, 10% to 40%. The thickness of the hydrogen electrode 13 is not particularly limited, but can be, for example, 1 μm to 50 μm.

[0038] [Separator 20] The separator 20 is a frame-shaped component also called an interconnector. The separator 20 is made of a dense metal or ceramic material.

[0039] The separator 20 is formed in a ring shape. The separator 20 is positioned along the outer edge of the cell body 10. The separator 20 is joined to the outer edge of the electrolyte sheet 11. This separates the oxygen electrode side space T1 from the hydrogen electrode side space T2.

[0040] In this embodiment, the separator 20 is bonded to the second main surface S2 of the electrolyte sheet 11, but it may also be bonded to the first main surface S1 of the electrolyte sheet 11.

[0041] For bonding the separator 20, for example, crystallized glass can be used. As for the crystallized glass, for example, SiO ２ -B ２ O ３ system, SiO ２ -CaO system, MgO-B ２ O ３ System, or SiO ２-MgO-based crystallized glass can be used. Crystallized glass is defined as glass in which the ratio of the volume occupied by the crystalline phase to the total volume (degree of crystallinity) is 60% or more, and the ratio of the volume occupied by the amorphous phase and impurities to the total volume is less than 40%.

[0042] (Warping of the electrolyte sheet 11) Figure 3 is a schematic diagram showing the height distribution of the first main surface S1 in a plan view of the electrolyte sheet 11. Figure 4 is a schematic diagram showing the B-B cross section of Figure 3. Figure 5 is a schematic diagram showing the C-C cross section of Figure 3. In Figures 3 to 5, only the electrolyte sheet 11 as a whole is shown. In Figures 4 and 5, the warping height of the electrolyte sheet 11 is greatly exaggerated.

[0043] As shown in Figures 3 to 5, the electrolyte sheet 11 comprises a first main surface S1, a second main surface S2, a first curved portion 21, and a second curved portion 22.

[0044] In this embodiment, the first main surface S1 is substantially rectangular. Specifically, the first main surface S1 is composed of a first long side L1, a second long side L2, a first short side L3, and a second short side L4. Both ends of the first long side L1 are connected to one end of the first short side L3 and the second short side L4, respectively. The second long side L2 is provided on the opposite side of the first long side L1. Both ends of the second long side L2 are connected to the other end of the first short side L3 and the second short side L4, respectively.

[0045] The first curved portion 21 is a part of the electrolyte sheet 11 that has been curved such that the first main surface S1 is convex and the second main surface S2 is concave. In other words, the first curved portion 21 is formed when a part of the electrolyte sheet 11, which has a generally constant thickness, curves upward toward the first main surface S1.

[0046] As shown in Figure 3, in a plan view of the first main surface S1, the highest point MX1 of the first curved portion 21 is located on the contour of the first main surface S1. Specifically, the highest point MX1 of the first curved portion 21 is located on the first long side L1 that constitutes the first main surface S1. Therefore, when inspecting the electrolyte sheet 11 (dimensional measurement, foreign matter inspection, warp measurement, etc.), when the electrolyte sheet 11 is placed on a predetermined surface with the first main surface S1 facing downwards, the electrolyte sheet 11 can be supported by the first curved portion 21. Consequently, contact between the electrode placement region 12a on the first main surface S1, where the oxygen electrode 12 is placed, and the predetermined surface can be suppressed. Thus, damage to the first main surface S1 of the electrolyte sheet 11 can be suppressed, and the expected cell performance can be avoided. In this way, by deliberately providing the first curved portion 21 in a part that has little impact on cell performance, the part that has a large impact on cell performance can be protected. Furthermore, when the electrolyte sheet 11 is incorporated into the electrochemical cell 1, the separator 20 is more susceptible to thermal expansion than the cell body 10. The difference in thermal expansion between the two can be absorbed at the first warped portion 21. Therefore, it is possible to suppress the occurrence of cracks in the electrolyte sheet 11 due to the thermal expansion of the separator 20.

[0047] The first curved portion 21 can be identified by measuring the height data of the first main surface S1 across its entire surface using a 3D one-shot measuring instrument (VR-5000) manufactured by Keyence Corporation. Specifically, using the software attached to the measuring instrument, a reference plane, which is a plane, is set from each height data using the least squares method. At this time, each height data is corrected so that the reference plane is horizontal and the height of the reference plane is 0. As a result, a height distribution diagram of the first main surface S1 in a plan view, as shown in Figure 3, is obtained. In this height distribution diagram, the portion that includes the highest point MX1 located on the first long side L1 and is higher than the reference plane is the first curved portion 21. The total height H1 of the first curved portion 21 is the distance between the reference plane and the highest point MX1 in the height direction perpendicular to the reference plane. The contour of the first curved portion 21 is defined by outer edges 21a and 21b. Outer edge 21a is a line that indicates 20% of the total height H1 from the reference plane in the height direction. The outer edge 21b is the line between the two ends of the outer edge 21a of the first long side L1. In Figure 3, contour lines (dotted lines) are drawn at predetermined height intervals to make the shape of the first curved portion 21 easier to understand.

[0048] The total height H1 of the first curved portion 21 is not particularly limited, but the ratio of the total height H1 of the first curved portion 21 to the length of the first short side L3 can be 0.001 or more and 0.01 or less. Preferably, the ratio of the total height H1 of the first curved portion 21 to the length of the first short side L3 is 0.002 or more and 0.005 or less. This suppresses damage to the first main surface S1 of the electrolyte sheet 11 while also suppressing damage to the first curved portion 21 due to the first curved portion 21 being too high.

[0049] As shown in Figure 3, it is preferable that the highest point MX1 of the first curved portion 21 is located at the central part L1c when the first long side L1 is divided into three equal parts. This makes it possible to further suppress damage to the first main surface S1 of the electrolyte sheet 11 compared to when the highest point MX1 of the first curved portion 21 is located at a position other than the central part L1c of the first long side L1.

[0050] As shown in Figure 3, it is preferable that the first curved portion 21 does not include the geometric center CP of the first main surface S1. That is, it is preferable that the geometric center CP of the first main surface S1 is located outside the region enclosed by the outer edge 21a and the outer edge 21b. This makes it possible to reduce the amount of curvature of the electrolyte sheet 11 as a whole.

[0051] The second curved portion 22 is a part of the electrolyte sheet 11 that has been curved such that the first main surface S1 is convex and the second main surface S2 is concave. In other words, the second curved portion 22 is formed when a part of the electrolyte sheet 11, which has a substantially constant thickness overall, curves upward toward the first main surface S1.

[0052] Here, in a plan view of the first main surface S1, the highest point MX2 of the second curved portion 22 is located on the contour of the first main surface S1. Specifically, the highest point MX2 of the second curved portion 22 is located on the second long side L2 that constitutes the first main surface S1. Therefore, when inspecting the electrolyte sheet 11 (dimensional measurement, foreign matter inspection, warping measurement, etc.), both sides of the electrolyte sheet 11 can be supported by the first curved portion 21 and the second curved portion 22. Thus, damage to the first main surface S1 of the electrolyte sheet 11 can be further suppressed. Furthermore, when the electrolyte sheet 11 is incorporated into the electrochemical cell 1, the difference in thermal expansion between the separator 20 and the cell body 10 can be absorbed not only by the first curved portion 21 but also by the second curved portion 22, thus further suppressing the occurrence of cracks in the electrolyte sheet 11.

[0053] The second curved portion 22 includes the highest point MX2 located on the second long side L2 in the height distribution diagram described above, and is a portion that is higher than the reference plane. The total height H2 of the second curved portion 22 is the distance between the reference plane and the highest point MX2 in the height direction. The contour of the second curved portion 22 is defined by outer edges 22a and 22b. Outer edge 22a is a line that indicates 20% of the total height H2 from the reference plane in the height direction. Outer edge 22b is a line on the second long side L2 that is sandwiched between both ends of outer edge 22a.

[0054] The total height H2 of the second curved portion 22 is not particularly limited, but the ratio of the total height H2 of the second curved portion 22 to the length of the first short side L3 can be 0.001 or more and 0.01 or less. Preferably, the ratio of the total height H2 of the second curved portion 22 to the length of the first short side L3 is 0.002 or more and 0.005 or less. This prevents damage to the second curved portion 22 due to it being too high, while suppressing damage to the first main surface S1 of the electrolyte sheet 11.

[0055] As shown in Figure 3, it is preferable that the highest point MX2 of the second curved portion 22 is located at the central part L2c when the second long side L2 is divided into three equal parts. This makes it possible to further suppress damage to the first main surface S1 of the electrolyte sheet 11 compared to when the highest point MX2 of the second curved portion 22 is located at a location other than the central part L2c of the second long side L2.

[0056] As shown in Figure 3, it is preferable that the second curved portion 22 does not include the geometric center CP of the first main surface S1. That is, it is preferable that the geometric center CP of the first main surface S1 is located outside the region enclosed by the outer edge 22a and the outer edge 22b. This makes it possible to reduce the amount of curvature of the electrolyte sheet 11 as a whole.

[0057] In this embodiment, in a plan view of the first main surface S1, the first curved portion 21 and the second curved portion 22 are formed in a substantially semicircular or substantially semielliptical shape. Specifically, the first curved portion 21 is formed in a sector shape with a central angle of approximately 180 degrees centered at the highest point MX1, and the second curved portion 22 is formed in a sector shape with a central angle of approximately 180 degrees centered at the highest point MX2. However, the planar shape and size of the first curved portion 21 and the second curved portion 22 are not particularly limited and can be changed as appropriate.

[0058] (Method for manufacturing the electrolyte sheet 11) The method for manufacturing the electrolyte sheet 11 comprises a green sheet formation step and a firing step.

[0059] [Green Sheet Formation Process] In the green sheet formation process, a green sheet is formed by molding a slurry.

[0060] The slurry is prepared by mixing ceramic particles, a solvent, and a binder.

[0061] The average particle size of the ceramic particles used as raw material can be between 0.1 μm and 1.0 μm. This average particle size is calculated from the particle size distribution of the ceramic particle dispersion using a laser diffraction particle size distribution analyzer, specifically the 50% volume diameter (D ５０ )

[0062] Suitable solvents include alcohols such as methanol, ethanol, 2-propanol, 1-butanol, and 1-hexanol; ketones such as acetone and 2-butanone; aliphatic hydrocarbons such as pentane, hexane, and heptane; aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; and acetic acid esters such as methyl acetate, ethyl acetate, and butyl acetate. One solvent may be used alone, or two or more solvents may be mixed and used.

[0063] Suitable binders include ethylene copolymers, styrene copolymers, acrylate copolymers, methacrylate copolymers, vinyl acetate copolymers, maleic acid copolymers, vinyl butyral resins, vinyl acetal resins, vinyl formal resins, vinyl alcohol resins, and cellulose resins. One type of binder may be used alone, or two or more binders may be mixed and used.

[0064] The slurry may further contain dispersants, plasticizers, defoamers, etc.

[0065] A green sheet is formed by coating a slurry onto a substrate (e.g., a PET film). Methods such as the doctor blade method or the calender roll method can be used for slurry coating.

[0066] Then, by pressing the green sheet against a curved mold placed on a flat surface, a first curved portion 21 and a second curved portion 22 are formed on the green sheet. The curved mold has convex or concave portions in the region including the central portions L1c and L2c of its long sides, which are equal to or less than the target values ​​of the total heights H1 and H2. The pressing may be performed with the green sheet adhered to the base material.

[0067] The thickness of the green sheet is determined from the target thickness of the electrolyte sheet 11 and the firing shrinkage rate. The planar size of the green sheet is also determined from the target planar size of the electrolyte sheet 11 and the firing shrinkage rate.

[0068] [Firing Process] In the firing process, the electrolyte sheet 11 is formed by firing the green sheets in a single layer without stacking them.

[0069] Specifically, a single layer of green sheet is placed on a ceramic setter and fired in an atmospheric environment at a predetermined firing temperature and firing time. In this way, in this embodiment, one electrolyte sheet 11 is formed from one green sheet.

[0070] The firing temperature can be between 1100°C and 1400°C. The firing time can be between 1 hour and 10 hours.

[0071] (Modifications of Embodiments) Although embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention.

[0072] (Modification 1) In the above embodiment, the electrolyte sheet 11 has a second curved portion 22 on the opposite side of the first curved portion 21, but is not limited to this. For example, as shown in Figure 6, the second curved portion 22 may be located on the same side as the first curved portion 21. In this case, the highest point MX2 of the second curved portion 22 is located on the first long side L1 that constitutes the first main surface S1, similar to the highest point MX1 of the first curved portion 21. The configuration of the second curved portion 22 is as described in the first embodiment. However, the highest point MX2 of the second curved portion 22 does not have to be located in the central part L2c when the second long side L2 is divided into three equal parts.

[0073] (Modification 2) In the above embodiment, the oxygen electrode 12 is arranged on the first main surface S1 of the electrolyte sheet 11 and the hydrogen electrode 13 is arranged on the second main surface S2 of the electrolyte sheet 11, but the embodiment is not limited to this. The hydrogen electrode 13 may be arranged on the first main surface S1 of the electrolyte sheet 11 and the oxygen electrode 12 may be arranged on the second main surface S2 of the electrolyte sheet 11. In this case, the hydrogen electrode 13 becomes the "first electrode" according to the present invention, and the oxygen electrode 12 becomes the "second electrode" according to the present invention.

[0074] 1 Electrochemical cell 10 Cell body 11 Electrolyte sheet for electrochemical cell 21 First curved section MX1 Highest point of the first curved section 22 Second curved section MX2 Highest point of the second curved section S1 First main surface S2 Second main surface S3 Side L1 First long side L2 Second long side L3 First short side L4 Second short side 12 Oxygen electrode 13 Hydrogen electrode 20 Separator

Claims

1. An electrolyte sheet for an electrochemical cell comprising: a first main surface; a second main surface; and a first curved portion in which the first main surface is convex and the second main surface is concave, wherein, in a plan view of the first main surface, the highest point of the first curved portion is located on the contour of the first main surface.

2. The electrolyte sheet for an electrochemical cell according to claim 1, wherein the first main surface is rectangular, and the highest point of the first curvature is located on the first long side constituting the first main surface.

3. The highest point of the first curved portion is located in the central part when the first long side is divided into three equal parts, wherein the electrolyte sheet for an electrochemical cell according to claim 2.

4. The electrolyte sheet for an electrochemical cell according to claim 1, further comprising a second curved portion such that the first main surface is convex and the second main surface is concave, wherein in a plan view of the first main surface, the highest point of the second curved portion is located on the contour of the first main surface.

5. The electrolyte sheet for an electrochemical cell according to claim 4, wherein the first main surface is rectangular, and the highest point of the first curvature is located on the first long side constituting the first main surface.

6. The electrolyte sheet for an electrochemical cell according to claim 5, wherein the highest point of the second curved portion is located on the second long side opposite to the first long side.

7. The highest point of the second curved portion is located on the first long side, the electrolyte sheet for an electrochemical cell according to claim 5.

8. The electrolyte sheet for an electrochemical cell according to claim 1, wherein the average thickness is 45 μm or less.

9. An electrochemical cell comprising: an electrolyte sheet for an electrochemical cell according to claim 1; a cell body having a first electrode disposed on the first main surface and a second electrode disposed on the second main surface; and a frame-shaped separator joined to the electrolyte sheet for an electrochemical cell.

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