JP6702585B2 - Flat electrochemical cell stack - Google Patents

Description

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

BACKGROUND ART Fuel cells, which convert chemical energy into electrical energy by electrochemically reacting hydrogen and oxygen, are drawing attention. Fuel cells have high energy utilization efficiency and are being developed as large-scale distributed power sources, household power sources, and mobile power sources.

Fuel cells are classified into a solid polymer type, a phosphoric acid type, a molten carbonate type, a solid oxide type, and the like, depending on the temperature range, the material used, and the type of fuel. Among these, solid oxide fuel cells (SOFC), which obtain electric energy by an electrochemical reaction using an electrolyte made of a solid oxide, are drawing attention from the viewpoint of efficiency and the like. Further, 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.

An electrochemical cell (hereinafter, simply referred to as a cell), which is the minimum constitutional unit of SOFC and SOEC, is at least a laminated body of an air electrode, an electrolyte, and a fuel electrode, and uses materials having different characteristics. 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 electric conductors, and the electrolyte is an ionic conductor that does not conduct electricity.

The shape of the cell includes a flat plate type, a cylinder type, a cylindrical flat plate type, and the like. For example, a flat plate type 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 stack of a plurality of cells is generally called a stack. For example, in the case of a flat plate type cell, the stack is a stack of multiple flat plate type cells, supplies different gas to the air electrode and the fuel electrode of each cell, and the cells can be electrically connected in series. It has a unique structure.

The cells are separated from each other by a separator, and the gas is separated for each cell by the separator. Further, since the separator is conductive, it also plays a role of electrical conduction between cells. Gas supply/exhaust channels for each cell are also generally formed in the separator.

FIG. 4 shows an example of a structure of a stack 400 using a flat plate type cell. An example of a flat plate type cell is a fuel electrode supporting type cell. The gas to be flown to the air electrode side and the fuel electrode side of the cell is not particularly limited, but FIG. 4 shows an example of flowing air to the air electrode side of the cell and hydrogen to the fuel electrode side on the assumption that power generation is performed. It was

The cell 414 is mainly composed of a porous fuel electrode 413, a porous air electrode 412, and a dense electrolyte 411. In the stack 400, the portion where the cell 414 is installed has the dense electrolyte 411, and thus the atmosphere of the fuel electrode 413 and the air electrode 412 is isolated by this electrolyte 411. On the other hand, in the portion where the cell 414 is not installed, it is necessary to separate the atmospheres of the fuel electrode 413 and the air electrode 412 with some dense member.

In the example shown in FIG. 4, a dense separator 423 separates the atmosphere between adjacent cells 414. Regarding the atmosphere of the fuel electrode 413 and the air electrode 412 of the same cell 414, a sealing plate 424 is provided on the electrolyte 411 which is a dense layer to separate the fuel electrode 13 and the air electrode 412. The sealing between the sealing plate 424 and the separator 423 is achieved by installing a compressive sealing material 421, which is deformed by applying pressure, on the sealing plate 424. A gas passage 422 for supplying gas to each cell 414 is formed in the separator 423 and the sealing plate 424. A current collector 426 is provided between the fuel electrode 413 and the separator 423. Similarly, a current collector (not shown) for electrically connecting the air electrode 412 and the adjacent separator 423 is provided between them.

In the stack 400 using the flat plate type cell 414, in particular, the gas flowing in the stack 400 flows out to the outside of the stack 400, and the supply gases to the fuel electrode 413 and the air electrode 412 are mixed inside the stack 400. To prevent this, that is, gas sealability is a major issue. The structure that separates the fuel electrode 413 and the air electrode 412 greatly influences the gas sealability, and a structure capable of achieving high sealability is required. In a conventional flat plate type stack, in order to isolate the atmosphere of the fuel electrode 413 and the air electrode 412, a sealing plate 424 and a compressive sealing material 421 are often used together as shown in FIG.

JP, 2016-126893, A

By preventing the gas flowing in the stack from flowing out to the outside of the stack or mixing the atmosphere gas of each of the fuel electrode and the air electrode inside the stack, for example, in the case of SOFC, the loss of the fuel gas necessary for power generation is reduced, The power generation performance can be improved.

As described above, in the conventional flat plate type stack, a sealing plate and a compressive sealing material are often used together to separate the atmospheres of the fuel electrode and the air electrode. However, in this structure, there are many gas leakage paths between the separator and the cell and the sealing plate, between the sealing plate and the sealing material, and between the sealing material and the separator, and it is difficult to improve the sealing performance. ..

Further, a compressive seal seals when pressure is applied, but if the sealing plate is thin, it deforms and becomes a factor that reduces the sealing property. On the other hand, if the sealing plate is thickened to increase the strength, there is a problem that the size of the stack becomes large.

The problem to be solved by the present invention is to provide a flat plate type electrochemical cell stack having a small size and high gas sealability.

The flat plate electrochemical cell stack of the embodiment is a flat plate electrochemical cell stack in which a plurality of unit units are stacked, and the unit units are flat solid oxide type cells and a peripheral portion of the cells. A conductive separator having a sealing plate disposed so as to abut, a cell housing portion that houses the cell, and a recessed portion that is provided around the cell housing portion for fitting the sealing plate, At least a sealing member having a sealing surface that seals the outer peripheral side of the recess of the separator and the sealing plate in the same plane is provided.

The figure which shows typically the one part cross-section structure of the stack of 1st Embodiment. The figure which shows typically the whole structure of a stack. The figure which shows typically the one part cross-section structure of the stack of 2nd Embodiment. The figure which shows typically the one part cross-section structure of an example of a stack.

Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a partial cross-sectional structure of a flat plate type electrochemical cell stack (hereinafter, simply referred to as a stack) 100 of an embodiment.

The stack 100 includes a flat plate type cell 104. The flat plate type cell 104 has a structure in which a porous air electrode 102, a dense electrolyte 101, and a porous fuel electrode 103 are laminated. Gas can pass through the air electrode 102 and the fuel electrode 103, but gas cannot pass through the electrolyte 101. The cell 104 has a rectangular plate shape.

The electrolyte 101 is made of a solid oxide and has oxygen ion conductivity. As the solid oxide electrolyte 101, for example, dense stabilized zirconia, a perovskite type oxide, a ceria-based solid solution compact, or the like is used.

For the fuel electrode 103, a mixed sintered body (cermet) of metal and solid oxide is generally used. For example, Ni-YSZ (yttria-stabilized zirconia), Ni-ScSZ (scandia-stabilized zirconia), etc. are used.

On the other hand, for the air electrode 102, a perovskite type oxide or an oxide in which some of these sites are substituted is generally used. Examples thereof include LaSrMn oxide, LaSrCo oxide, LaSrCoFe oxide, and LaSrFe oxide. 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.

A separator 123 made of a conductive material is arranged so as to surround the cell 104. The separator 123 is formed into a rectangular plate shape as a whole, and has a cell housing portion 123a formed of a recess in the center thereof. The cell 104 is installed in the cell housing portion 123 a of the separator 123. As the material of the separator 123, a dense and conductive material such as metal or ceramics is used. Further, as this material, a material having a thermal expansion coefficient close to that of the cell 104 is desirable.

In order to reduce the electric resistance between the cells 104 and the separator 123, a current collector made of a conductive material or the like is arranged. Between the fuel electrode 103 and the separator 123, a current collector 126 made of a conductive material having a cushioning property is installed. Note that the current collector 126 needs to allow gas to pass therethrough. Therefore, the current collector 126 is made of, for example, a metal mesh. Similarly, in FIG. 1, the air electrode 102 and the separator 123 located above the air electrode 102 are electrically connected by a current collector (not shown) or the like.

Recesses 123b are formed around the cell housing portion 123a of the separator 123 along the two opposing sides (the left side and the trunk side in FIG. 1) of the cell housing portion 123a. In the stack 100 shown in FIG. 1, the depth of the recess 123b is shallower than the depth of the cell containing portion 123a.

A sealing plate 124 is fitted in each of the recesses 123b formed along the two opposite sides of the cell containing portion 123a. The sealing plate 124 is configured in a plate shape, and an inner edge portion thereof is configured to abut the periphery of the electrolyte 101 of the cell 104. The thickness of the sealing plate 124 is the same as the depth of the recess 123b. Therefore, the surface 124s of the sealing plate 124 and the surface 123s of the separator 123 on the outer peripheral side of the sealing plate 124 are located in the same plane. That is, the surface 123s of the separator 123 and the surface 124s of the sealing plate 124 are flush with each other. The separator 123 and the sealing plate 124 are preferably joined by welding or the like. As a result, the gas sealing property can be improved.

Further, the surface 123s of the separator 123 and the surface 124s of the sealing plate 124, and the surface 101s of the electrolyte 101 of the cell 104 are located on the same plane. In other words, these are the same. The term “in the same plane” means that the state is completely the same plane, and also includes a state in which there is a certain level difference or the like due to a tolerance due to dimensional accuracy.

Then, a compressive sealing material 121 that is crushed by exerting pressure and exhibits sealing performance is provided on these surfaces. The sealing material 121 has a rectangular frame shape. The material of the sealing material 121 is not particularly limited, but a material having high electrical insulation is desirable. Examples of the material of the sealing material 121 include alumina, zirconia, silica, and materials containing at least these. As for the density, it is desirable that the density be fine.

A separator 123 that accommodates the adjacent cells 104 is stacked on the sealing material 121. Through holes are formed in the separator 123, the sealing plate 124, and the sealing material 121 to form a gas flow path 122 for supplying and discharging gas. The gas flow path 122 allows the gas to flow along the stacking direction of the stack 100 (the vertical direction in FIG. 1 ). A gap 125 is provided between the sealing plate 124 and the separator 123. The gap 125 constitutes a gas path for circulating the fuel gas between the gas flow path 122 and the fuel electrode 103.

As shown in FIG. 2, an arbitrary number of unit units having the above structure are stacked to form a stack 100. In addition, the end plates 120 and the like are arranged at both end portions (the upper end portion and the lower end portion in FIG. 2) in the stacking direction. Then, these are fastened and fixed by fastening means such as a plurality of bolts 111 and nuts 112. Note that, in FIG. 2, a part of the portion where the separators 123 and the like having the same structure are arranged is omitted.

In the stack 100, pressure is applied in the stacking direction by the bolts 111 and the nuts 112 and the like, whereby the compressive sealing material 121 is pressed and the gas sealing function is exerted. In order to prevent the deformation of the sealing plate 124 when such a pressure is applied, as shown in FIG. 1, the sealing plate support 127 is provided between the sealing plate 124 and the bottom of the cell accommodating portion 123 a of the separator 123. It is provided so as to intervene. The sealing plate support 127 may have any shape, but preferably has a shape that does not hinder the flow of gas on the fuel electrode 103 side.

As described above, when pressure is applied in the stacking direction, as shown in FIG. 1, the total thickness of the cells 104 and the thickness of the current collector 126 is equal to the depth of the cell housing portion 123a of the separator 123. It is the same.

On the other hand, for example, when assembling the stack 100, in the state before the pressure is applied in the stacking direction, the total thickness may be larger than the depth of the cell accommodating portion 123a. Then, when pressure is applied in the stacking direction, the cells 104 are pushed by the sealing material 121 and the current collector 126 is crushed, so that the thickness is reduced, and the total thickness becomes equal to the depth of the cell accommodating portion 123a. It may be configured as follows. That is, before the pressure is applied in the stacking direction, the surface 123s of the separator 123 and the surface 101s of the electrolyte 101 are not flush with each other, and when pressure is applied in the stacking direction, they are flush with each other. Good.

In the stack 100 having the above configuration, the surface 123s of the separator 123, the surface 124s of the sealing plate 124, and the surface 101s of the electrolyte 101 of the cell 104 are located in the same plane. Then, the sealing material 121 is sandwiched between these surfaces and the adjacent separator 123 for gas sealing. Therefore, the gas may leak to the outside only at two positions on both sides of the sandwiched sealing material 121.

On the other hand, for example, in the stack 400 shown in FIG. 4, three parts between the separator 423 and the sealing plate 424, between the sealing plate 424 and the sealing material 421, and between the sealing material 421 and the separator 423 are provided. There is a possibility that gas may leak outside. Therefore, in the stack 100 shown in FIG. 1, compared with the stack 400 shown in FIG. 4, the possibility of gas leakage to the outside can be reduced, and the sealing performance can be improved. Further, the stack 100 shown in FIG. 1 can be downsized because the apparent number of stacked layers is smaller than that of the stack 400 shown in FIG.

Next, a second embodiment will be described. FIG. 3 is a diagram schematically showing a partial cross-sectional structure of the stack 200 according to the second embodiment. Note that, in FIG. 3, the same parts as those in FIG.

As shown in FIG. 3, in the stack 200, the recesses 223b are formed along the two opposing sides (the left side and the trunk side in FIG. 1) of the cell housing portion 223a of the separator 223. The recesses 223b and the cell housing 223a have the same depth and are integrally formed. A sealing plate 224 having the same height as the depth of the recess 223b is provided in each recess 223b.

Therefore, the surface 223s of the separator 223 and the surface 224s of the sealing plate 224 on the outer peripheral side of the recess 223b are located in the same plane. That is, the surface 223s of the separator 223 and the surface 224s of the sealing plate 224 are flush with each other. The separator 223 and the sealing plate 224 are preferably joined by welding or the like. As a result, the gas sealing property can be improved.

Further, the surface 223s of the separator 223 and the surface 224s of the sealing plate 224, and the surface 101s of the electrolyte 101 of the cell 104 are located on the same plane. In other words, these are the same. Then, a compressive sealing material 221 is installed on these surfaces via a plate material 228, and is sealed by a flat sealing surface 221s. The plate member 228 is formed in a frame shape from a flat plate and is for protecting the mechanically fragile seal member 221.

That is, although the surface 223s, the surface 224s, and the surface 101s described above are located on the same plane, there is a case where there is a step or the like to some extent due to the tolerance due to dimensional accuracy, etc. included. In this case, when the layers are stacked and pressure is applied, the force applied to the sealing surface of the sealing material 221 becomes non-uniform, and the sealing material 221 may be damaged. In order to prevent the seal member 221 from being damaged, a flat plate member 228 is provided to equalize the force applied to the sealing surface. Since the plate member 228 may be thinner than the sealing plate or the like, it is possible to suppress an increase in the thickness of the stack 200. The plate member 228 is not always necessary and may be omitted.

In the sealing plate 224, a gas for flowing gas from the gas flow path 122 toward the fuel electrode 103 of the cell 104 is provided in addition to the through holes that form the gas flow path 122 provided along the stacking direction shown in FIG. A gas channel 229 is formed.

In the stack 200 having the above configuration, since the sealing plate 224 is thick and there is no gap between the sealing plate 224 and the separator 223, deformation when pressure in the stacking direction is applied is suppressed. Thereby, the sealing property can be improved. In addition, the stack 200 does not increase in size due to the increase in the thickness of the sealing plate 224.

Although the embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are also included in the invention described in the claims and the scope equivalent thereto.

100... Stack, 101... Electrolyte, 102... Air electrode, 103... Fuel electrode, 104... Cell, 111... Bolt, 112... Nut, 120... End plate, 121... Sealing material, 122... Gas flow path, 123... Separator, 123a... Cell accommodation part, 123b... Recessed part, 124... Sealing plate, 125... Gap, 126... Current collector, 127... Sealing plate support, 101s... Electrolyte surface, 121s... Sealing surface, 123s... Separator surface, 124s ... Surface of sealing plate, 200... Stack, 221... Sealing material, 223... Separator, 223a... Cell accommodating portion, 223b... Recessed portion, 224... Sealing plate, 228... Plate material, 229... Gas flow path, 221s... Sealing surface 223s... Separator surface, 224s... Sealing plate surface, 400... Stack, 411... Electrolyte, 412... Air electrode, 413... Fuel electrode, 414... Cell, 421... Seal material, 422... Gas channel, 423... Separator, 424... Sealing plate, 426... Current collector.

Claims (4)

A flat-type electrochemical cell stack in which a plurality of unit units are stacked,
The unit unit is
A flat solid oxide cell,
A sealing plate arranged so as to contact the peripheral portion of the cell,
A cell containing portion for containing the cell, a conductive separator having a recessed portion provided around the cell containing portion for fitting the sealing plate,
A flat plate type electrochemical cell stack comprising at least a sealing member having a sealing surface for sealing the outer peripheral side of the recess of the separator and the sealing plate in the same plane. The flat plate type electrochemical cell stack according to claim 1, wherein a gas flow path for allowing gas to flow is formed between the sealing plate and the separator. The flat plate type electrochemical cell stack according to claim 1, wherein at least a part of a contact portion between the sealing plate and the separator is joined. The flat plate type electrochemical cell stack according to any one of claims 1 to 3, further comprising a sealing plate support interposed between a bottom portion of the cell housing portion of the separator and the sealing plate.

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