WO2018167845A1 - Planar electrochemical cell stack - Google Patents

Abstract

A planar electrochemical cell stack that is provided with: a plurality of unit electrochemical cells which are laminated, and each of which comprises a planar solid oxide electrochemical cell and a conductive separator that surrounds the electrochemical cell; a frame-like sealing part which is arranged between the separator of one unit electrochemical cell and the separator of an adjacent unit electrochemical cell so as to surround the electrochemical cell; and an insulating part which is arranged between the separator of the one unit electrochemical cell and the separator of the adjacent unit electrochemical cell such that at least a part of the insulating part is positioned outside the sealing part, while having a thinner thickness than the sealing part.

Description

Flat plate electrochemical cell stack

Embodiments of the present invention relate to a flat electrochemical cell stack.

Fuel cells that convert chemical energy to electrical energy by electrochemically reacting hydrogen and oxygen are drawing attention. Fuel cells have high energy use efficiency and are being developed as large-scale distributed power sources, household power sources, and mobile power sources.

Fuel cells are classified into solid polymer type, phosphoric acid type, molten carbonate type, solid oxide type, etc., depending on the temperature range and the type of material and fuel used. Among these, from the viewpoint of efficiency and the like, a solid oxide fuel cell (SOFC) that obtains electric energy by an electrochemical reaction using an electrolyte made of a solid oxide has attracted attention. In recent years, a high-temperature steam electrolysis method in which hydrogen is produced by a solid oxide electrolysis cell (SOEC) by utilizing the reverse reaction of SOFC has been developed.

A cell, which is the minimum constituent unit of SOFC and SOEC, is generally composed of an electrolyte and an electrode. The solid oxide electrolyte has oxygen ion conductivity. As the electrolyte of the solid oxide, for example, dense stabilized zirconia, perovskite oxide, a ceria-based solid solution molded body, or the like is used.

Regarding the electrode, taking SOFC as an example, it can be roughly divided into a fuel electrode and an air electrode. At the fuel electrode, H ₂ that is the fuel gas and oxygen ions that have moved through the electrolyte react electrochemically to generate H ₂ O and electrons (e−). At the air electrode, oxygen (in the air) takes in electrons (e−), generates oxygen ions by an electrochemical reaction, and these move to the electrolyte.

A mixed sintered body (cermet) of metal and solid oxide is generally used for the fuel electrode. For example, Ni—YSZ (yttria stabilized zirconia), Ni—ScSZ (scandia stabilized zirconia) and the like are used.

On the other hand, a perovskite oxide or an oxide obtained by substituting a part of these sites is generally used for the air electrode. For example, LaSrMn oxide, LaSrCo oxide, LaSrCoFe oxide, LaSrFe oxide, and the like can be given. Further, a mixture with a solid oxide used for the electrolyte is also used, and examples thereof include LSM-YSZ, LSM-ScSZ, LSC-SDC, and LSC-GDC.

As described above, the cell is at least a laminate of an air electrode, an electrolyte, and a fuel electrode. Different materials are used for the air electrode, the electrolyte, and the fuel electrode. The air electrode and the fuel electrode are porous, and different gases are supplied to the air electrode and the fuel electrode with a dense electrolyte as a boundary. The air electrode and the fuel electrode are electrical conductors, and the electrolyte is an ionic conductor that does not conduct electricity.

The cell shape includes a flat plate type, a cylindrical type, and a cylindrical flat plate type. For example, a flat cell has a shape in which an air electrode, an electrolyte, a fuel electrode, and the like are stacked in a flat plate shape. A collection of a plurality of these cells is generally called a stack.

For example, in the case of flat cells, the stack is a stack of multiple flat cells, supplying different gases to the air electrode and fuel electrode of each cell, and the cells can be connected electrically in series. It has a simple structure. The cells are separated from each other by a separator, and the gas for each cell is separated by the separator. Since the separator is conductive, it also plays a role of electrical conduction between cells. In addition, a gas supply / discharge flow path to each cell is generally formed in the separator.

In the stack, the cell portion separates the fuel electrode and the air electrode by a dense electrolyte, while the other portions separate the atmosphere of adjacent cells by a dense separator. Further, the atmosphere of the fuel electrode and the air electrode of the same cell is isolated by closing a gap in a portion where the cell is not installed with a dense member.

In the flat cell stack, the gas flowing in the stack is prevented from flowing out of the stack, the supply gas to the fuel electrode and the air electrode is prevented from mixing inside the stack, that is, the gas sealing property is improved. It has become a big issue. In order to improve such gas sealing performance, for example, methods using various sealing materials have been proposed.

JP-A-6-325779

Since the cell has a dense electrolyte, it is possible to prevent mixing of the atmospheric gas in each of the fuel electrode and the air electrode. However, it is necessary to take measures against gas leakage in the stack components other than the cells. For example, it is necessary to seal a gap between a cell and a stack constituent member other than the cell, or a portion that supplies gas to the cell.

Also, since the cells are stacked via conductive separators, it is necessary to insulate the separators in some form. Therefore, a structure that achieves both sealing properties and insulating properties is required.

The problem to be solved by the present invention is to provide a flat plate electrochemical cell stack with improved gas sealability.

The flat plate electrochemical cell stack according to the embodiment includes a flat solid oxide electrochemical cell and a conductive separator surrounding the electrochemical cell, and a plurality of stacked unit electrochemical cells; A frame-shaped seal portion disposed between the separator of the unit electrochemical cell and the separator of the adjacent unit electrochemical cell and surrounding the periphery of the electrochemical cell; and the separator of the unit electrochemical cell And an insulating part that is disposed between the separators of the adjacent unit electrochemical cells and that is at least partially positioned on the outer peripheral side of the seal part and is thinner than the seal part.

The figure which shows typically the cross-sectional structure of a part of stack of 1st Embodiment. The figure which shows typically the whole structure of a stack. The figure which shows typically the cross-sectional structure of a part of stack of 2nd Embodiment. The figure which shows typically the cross-sectional structure of a part of stack of 3rd Embodiment. The figure which shows typically the cross-sectional structure of a part of stack of 4th Embodiment. The figure which shows typically the cross-sectional structure of a part of stack of a comparative example.

Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating a partial cross-sectional configuration of a flat plate electrochemical cell stack (hereinafter simply referred to as a stack) 100 according to an embodiment. In FIG. 1, each component is shown in a disassembled state (with a space between the components) (the same applies to FIGS. 3 to 6 described later), but these components are stacked. It is integrally held under pressure.

In this embodiment, the flat cell 101 constituting the stack 100 is an electrode-supported flat electrochemical cell. The cell 101 has a laminated structure in which an electrolyte 103 made of a thin film is formed on a porous electrode support 102 and a counter electrode 104 is further formed on the electrolyte 103. In the case of SOFC, either the electrode support 102 or the counter electrode 104 is a fuel electrode, and the other is an air electrode.

Conductive separators 105 and 106 are provided so as to surround the periphery of the cell 101, and the cell 101 is accommodated and supported in these. Between the electrode support 102 and the separator 106, a current collector (not shown) that electrically connects them is disposed. Further, a current collector (not shown) that electrically connects them is disposed between the counter electrode 104 and the adjacent separator 106.

The material of the separators 105 and 106 is a material that is dense and has conductivity even in the temperature range of 600 to 1000 ° C. that is the operating temperature, such as metal or ceramics. Moreover, as this material, a material having a thermal expansion coefficient close to that of the cell 101 is desirable. In the present embodiment, an example in which the separator is configured by two separators 105 and 106 which are separate members will be described. However, the separators 105 and 106 may be formed as a single member.

The outer shape of the flat cell 101 is, for example, a quadrangular shape. The separator 105 is configured in a rectangular frame shape so as to surround the periphery of the cell 101. A square opening 105a is formed at the center of the separator 105, and the cell 101 is disposed in the opening 105a.

The outer shape of the separator 106 is, for example, a rectangular plate shape. Further, the separator 105 and the separator 106 are formed with through holes at corresponding positions, and a gas flow path 109 for flowing gas in the stacking direction is formed by these through holes.

The separator 105 and the separator 106 constitute a support body that accommodates and supports the cell 101 in the opening 105a. These separators 105 and 106 and cell 101 constitute one unit chemical cell 110. As shown in FIG. 2, a plurality of these unit chemical cells 110 are stacked, and end plates 120 and the like are arranged at both end portions (upper end portion and lower end portion in FIG. 2) in the stacking direction. These are fastened and fixed by fastening means such as a plurality of bolts 111 and nuts 112. In FIG. 2, a part of the portion where the unit chemical cell 110 having the same structure is arranged is omitted.

As shown in FIG. 1, a sheet-like insulating member 107 formed in a frame shape is provided between the separator 105 and the separator 106 of the adjacent unit chemical cell 110. The insulating member 107 is provided to prevent an electrical short circuit between the separator 105 and the separator 106 of the adjacent cell 101. The insulating member 107 constitutes an insulating portion.

Furthermore, a sheet-like seal member 108 formed in a frame shape is provided inside the insulating member 107 between the separator 105 and the separator 106 of the adjacent unit chemical cell 110. The seal member 108 is disposed along the peripheral edge of the cell 101. The seal member 108 is disposed between the outer peripheral edge portion of the cell 101 and the inner peripheral edge portion of the separator 105. Further, the seal member 108 is disposed so as to surround the periphery of the gas flow path 109. That is, the seal member 108 is a sheet shape, and when viewed from the upper surface or the lower surface side, the outer shape is a substantially square shape, and a shape (frame shape) having a substantially square opening smaller than the outer shape of the cell 101 at the center. ). An opening corresponding to the shape of the gas flow path 109 is provided at a portion corresponding to the gas flow path 109. The seal member 108 constitutes a seal portion.

The seal member 108 is provided to prevent gas leakage from the gap between the cell 101 and the separators 105 and 106. The seal member 108 is provided to insulate between the separator 105 and the separator 106 of the adjacent unit chemical cell 110.

The material of the insulating member 107 is not particularly limited, but a material having high electrical insulation (high electrical resistance) is desirable. Examples of this material include alumina, zirconia, silica, and a material containing at least these. The density is preferably dense, but may be porous.

The material of the seal member 108 is not particularly limited, but a material having high electrical insulation is desirable. Examples of this material include alumina, zirconia, silica, and a material containing at least these. As for the density, a dense one is desirable. The material of the seal member 108 may be the same as the material of the insulating member 107.

In the present embodiment, the thicknesses of the insulating member 107 and the seal member 108 arranged in the same plane are different from each other. That is, the thickness of the insulating member 107 is smaller than the thickness of the seal member 108.

As described above, in this embodiment, the insulating portion and the sealing portion are separated, and the thick sealing member 108 and the thin insulating member 107 are used, thereby increasing the surface pressure of the sealing portion with a simple structure. Thus, the sealing performance can be improved.

In the case of a flat type stack, a pressure is applied in the stacking direction to increase the surface pressure of the seal portion to perform sealing, but it is necessary to apply a very large pressure to increase the surface pressure over a wide area. For example, like the stack 500 of the comparative example shown in FIG. 6, the insulating function and the sealing function are provided in one member, and the insulating sealing member 508 having a large surface area is connected to the separator 105 and the separator 106 of the adjacent unit chemical cell 110. When it is disposed between the two, it is necessary to apply a very large pressure to increase the surface pressure. For this reason, a surface pressure cannot fully be raised and a sealing performance may fall.

On the other hand, in this embodiment, the insulating portion and the sealing portion are separated, and the thick sealing member 108 and the thin insulating member 107 are used, compared with the insulating sealing member 508 shown in FIG. The surface area of the seal member 108 can be reduced, and the surface pressure can be easily increased. Thereby, a sealing performance can be improved.

Note that a material that is porous at room temperature and becomes dense when exposed to high temperature in a compressed state can be used as the material of the seal member 108. Pores that are porous at room temperature have high compressibility.For example, when there is a step at the end of the cell, if the pressure is applied in the stacking direction and the surface pressure is applied to the seal part, the step can be absorbed. It becomes possible. And when exposed to high temperature in the compressed state, it becomes dense and the sealing performance is improved.

When the sealing member 108 is configured using the material as described above, the thickness of the sealing member 108 before and after being stacked and compressed is changed. That is, the thickness of the sealing member 108 after being stacked and compressed becomes thinner than that before compression. Therefore, the difference between the thickness of the seal member 108 and the thickness of the insulating member 107 is also reduced. In this case, it is sufficient that the thickness of the sealing member 108 is slightly larger than the thickness of the insulating member 107 after compression.

FIG. 3 is a diagram schematically showing a partial cross-sectional configuration of the stack 200 according to the second embodiment. In FIG. 3, parts corresponding to those in FIG.

As shown in FIG. 3, in the stack 200, a coating film 207 formed by previously coating an insulating material on one surface of the separator 106 (the lower surface in FIG. 3) is used as an insulating portion. The coating film 207 is formed in a frame shape so as to surround the periphery of the seal member 108.

The material of the coating film 207 is not particularly limited, but a material having high electrical insulation is desirable. Examples of this material include alumina, zirconia, silica, and a material containing at least these. The density is preferably dense, but may be porous. Moreover, the coating method is not particularly limited, and examples thereof include a wet method, a dry method, a physical method, and a chemical method. The shape of the coating film 207 is not particularly limited, but may be provided at least in a portion that needs to be insulated.

As described above, when the insulating portion is constituted by the coating film 207, the number of parts is reduced, the number of steps for stacking and assembling the stack 200 is reduced, and the insulating member and the seal member are overlapped during construction. Can be prevented. Furthermore, the occurrence of local electrical leakage can be suppressed.

FIG. 4 is a diagram schematically illustrating a partial cross-sectional configuration of the stack 300 according to the third embodiment. In FIG. 4, parts corresponding to those in FIG.

At the end of the stack 300 in the stacking direction, an end plate 120 or the like is installed to ensure the strength of the stack 300 and the like. In this case, it is necessary to perform insulation and gas sealing between the end plate 120 and the separator 106. For this reason, in the stack 300, the insulating member 107 and the sealing member 108 are disposed between the upper end plate 120 and the separator 106.

In the stack 300 described above, the insulating member 107 and the sealing member 108 having the same shape as those disposed between the separators 105 and 106 are provided between the end plate 120 and the separator 106. As a result, a surface pressure is applied to the same portion of the stack 300, and a surface pressure is uniformly applied to each seal member 108 in the stacking direction, so that the sealing performance can be improved.

FIG. 5 is a diagram schematically showing a partial cross-sectional configuration of the stack 400 according to the fourth embodiment. In FIG. 5, parts corresponding to those in FIG.

In the stack 400, a convex portion 401 having an area smaller than that of the seal member 108 is provided at a portion where the seal member 108 of the separator 106 contacts. The convex portion 401 is formed in a frame shape along the shape of the seal member 108. As the shape of the convex portion 401, a shape having no sharp portion is desirable so that the sealing member 108 is not broken. In the stack 400 configured as described above, the surface pressure applied to the seal member 108 is further increased, and the sealing performance is improved.

According to at least one embodiment described above, the gas sealing performance can be improved.

As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

100, 200, 300, 400, 500 ... Stack, 101 ... Cell, 102 ... Electrode support, 103 ... Electrolyte, 104 ... Counter electrode, 105 ... Separator, 105a ... Opening, 106 ... Separator, 107 ... Insulating member, 108 ... Seal 109, gas flow path, 110, unit chemical cell, 111, bolt, 112, nut, 120, end plate, 207, coating film, 401, convex portion.

Claims (7)

A plurality of stacked unit electrochemical cells including a flat solid oxide electrochemical cell and a conductive separator surrounding the electrochemical cell;
A frame-shaped seal portion disposed between the separator of the unit electrochemical cell and the separator of the adjacent unit electrochemical cell, and surrounding the periphery of the electrochemical cell;
An insulating member disposed between the separator of the unit electrochemical cell and the separator of the adjacent unit electrochemical cell, wherein at least a part is located on the outer peripheral side of the seal portion and is thinner than the seal portion. And
A flat plate electrochemical cell stack comprising: The flat plate electrochemical cell stack according to claim 1, wherein the seal portion is disposed along a peripheral portion of the electrochemical cell. The flat plate electrochemical cell stack according to claim 1 or 2, wherein a gas flow path for allowing a gas to flow is formed in the separator, and the seal portion has a shape surrounding the periphery of the gas flow path. 4. The flat plate electrochemical cell stack according to claim 1, wherein the seal part and the insulating part are made of the same material. Comprising an end plate disposed at an end portion in the stacking direction of the unit electrochemical cells stacked in a plurality;
The flat plate electrochemical cell stack according to any one of claims 1 to 4, wherein the seal portion and the insulating portion are disposed between the end plate and the separator. The flat plate electrochemical cell stack according to any one of claims 1 to 5, wherein a convex portion having a smaller area than the seal portion is formed on a surface of the separator in contact with the seal portion. The flat electrochemical cell stack according to any one of claims 1 to 6, wherein the insulating portion is made of a coating film coated on the surface of the separator.

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