JPH06325779A - Stack for solid electrolytic fuel cell and its manufacture - Google Patents

Abstract

PURPOSE:To provide a stack for a fuel cell, which can maintain electrical connection excellent for a long time by interposing an incompressible insulating spacer and a conductive spacer composed of material in a metallic felt state between single cells. CONSTITUTION:Each single cell is disposed via an incompressible spacer 16 and a metallic felt 28, and is fastened by each assembling bolt 13. The thickness of the spacer 16 is made identical to a space between grooves 20 for installing each substrate, which are provided for a lower fixing plate for fixing each cell, and the thickness of the felt 28 is made larger than the aforesaid space. When the incompressible spacer as mentioned above is used for fastening the stack, the space between the cells is compressed only to the extent of the thickness of the spacer 16, the felt 28 is only partially compressed, so that deformation beyond plastic deformation can thereby be prevented. By this constitution, the respective cells are fixed with the space kept identical to the space between the grooves 20, dislocation of each cell is prevented, and concurrently electrical connection can thereby be secured by the felt 28.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell stack and a method for producing the same.

[0002]

2. Description of the Related Art Solid oxide fuel cells (SOFC) are
This is a fuel cell in which all the single cells including electrodes and electrolytes are made of a ceramic material, and zirconia (YSZ) whose crystal structure is stabilized by the addition of yttria is used as the electrolyte. This YSZ
Shows high oxygen ion conductivity, but the temperature dependence is similar to that of other ceramic materials, and the conductivity is low when the temperature is low, and it is necessary to use it at a sufficiently high temperature to obtain high conductivity. Therefore, the operating temperature is set to a value of 900 to 1000 ° C. in order to obtain high conductivity when the SOFC is manufactured. Since it is used at such a high temperature, the electrodes other than the electrolyte are also made of ceramics. By the way, the conductivity of the above-mentioned YSZ electrolyte is 1000 ° C.
Since the maximum value is 0.1 S / cm, it is necessary to reduce the thickness of YSZ when the cell is formed. Conventionally, SOF
In C, for example, a flat type single cell as shown in FIG. 5A has been studied. This example is YSZ
In which a thin solid electrolyte layer 1 is prepared, and two electrodes, an air electrode 3 and a fuel electrode 2, are formed on the thin solid electrolyte layer 1. Like this method, YSZ needs to have sufficient mechanical strength in order to serve as a support for electrodes, but it has a characteristic that YSZ added with yttria has a high electrical conductivity at 1000 ° C. Since the mechanical strength of YSZ containing 8 mol% of yttria is weak, it was necessary to increase the thickness of the support. As a result, there has been a problem that the iR drop in the electrolyte portion increases, and a sufficiently satisfactory cell output cannot be obtained. Therefore, a new type SOFC single cell has been proposed in which the electrode material itself also serves as a support of the cell and has one gas flow path to improve the overall gas sealability (Japanese Patent Laid-Open No. 5- No. 36417: Hollow thin plate type solid electrolyte fuel cell). This single cell has a structure as shown in FIG. That is, a hollow air electrode substrate 8 is formed by providing a through-hole 10 that serves as a gas flow path using an air electrode material, and the solid electrolyte layer 1 and the fuel electrode 2 are formed on the surface of the air electrode substrate 8. Further, the interconnector 4 is arranged on the surface opposite to the fuel electrode 2. The air electrode substrate 8 is made of a commonly used material such as LaSrMnO ₃ or LaCoO ₃ and is manufactured by, for example, an extrusion molding method. Each layer of the solid electrolyte layer 1 and the fuel electrode 2 is made of YSZ,
Both are formed by a thermal spraying method using nickel and zirconia. The interconnector 4 is also made of Ni-Al ₂ O ₃
A stable material layer is formed by thermal spraying in a reducing atmosphere such as or LaCrO ₃ . Further, since it is necessary to prevent the permeation of gas except for the portion where the solid electrolyte layer 1 and the interconnector 4 are provided, the gas impermeable layer 9 made of Al ₂ O ₃ or the like is used.
Is covered with. In addition, not only the thermal spraying method but also the CVD method
It can also be manufactured by a method, a tape casting method, a slurry coating method, or the like. By adopting the cell having the above-mentioned configuration, the solid electrolyte layer is no longer required to serve as a support for the cell, and as long as it is a dense membrane, it can be made as thin as possible, making a leap forward in improving the performance of a single cell. The power generation characteristics of the single cell can be remarkably improved. However, a single SOFC cell is not used, and single cells are connected in series and, if necessary, in parallel to form a fuel cell stack having a predetermined output.

FIG. 6 shows an example of a conventional power generation module using a single cell of the above system. Note that FIG. 6 is an example of a cell using a substrate made of an air electrode material. In the figure, 30 is a fixed plate, 31 is a groove, 32 is a separation plate, 33 is a gas discharge slit, 34 is an outer container, 35 is an oxidant gas supply port, 36 is a fuel gas supply port, 37 is a front chamber, 38 Is a combustion chamber, 39 is a gas outlet, 40 is a felt-like conductor, 41
Is a conducting wire and 42 is a sealant. In constructing the module, the air electrode substrate 8 forming the power generation part is fixed to the fixing plate 30.
Then, the separation plate 32 is penetrated, and in this state, it is stored inside the outer container 34. The fixing plate 30 is provided with a groove 31 for mounting the air electrode substrate 8.
Is fitted in the groove 31, and the fitting portion is filled with a sealing material 42 made of a non-conductive melt such as borosilicate glass in order to ensure gas tightness. On the other hand, the separation plate 32 has
A gas discharge slit 33 is provided so that unreacted fuel gas can be discharged. In power generation, this power generation module is installed under temperature conditions such as 1000 ° C. and each gas is supplied. The oxidant gas is supplied from the oxidant gas supply port 35, passes through the inside of each cell, reacts in the cell forming portion, and then the residual gas reaches the combustion chamber 38.
On the other hand, the fuel gas is supplied from the fuel gas supply port 36 provided on the side surface of the outer container 34, and power is generated here. Although the fuel gas supply port 36 is shown on the left side surface of the outer container 34 in FIG. 6, it may be provided on the front side (or back side) of the paper surface from the viewpoint of improving the contact between the gas and the fuel electrode. It is possible. The supplied fuel gas flows into the gaps between the cells and reacts therewith. However, since the porous conductor 40, which is a conductive spacer disposed between the cells, is porous, Diffusion to the electrodes is done without any problems. Then, the fuel gas which has not reacted here and which has not been consumed is guided to the combustion chamber 38, where it is mixed with the remaining oxidant gas and burned. Then, the high temperature gas after such combustion is discharged to the outside from the gas discharge port 39. By the way, the power generation characteristics of the stack of the fuel cell are greatly affected by the quality of the electrical connection state of each cell. That is, the breakdown of the output of the single cell in the stack is the electrode overvoltage, the iR loss of the electrolyte, and the iR loss due to the contact resistance. However, if the connection status is poor, the contact resistance at this portion increases and The voltage drop becomes large. In the power generation module using the hollow flat plate type cell described above, the porous conductor 40 made of Ni felt or the like is arranged between the substrates forming the single cell, but in order to improve the electrical connection between the substrates. In this case, it is necessary to dispose the Ni felt in such a state that it is sufficiently pressed against the substrates on both sides to make sufficient contact. In addition, it is necessary for each substrate to have an interval matching the groove of the fixing plate 30 and the separating plate 32. It is therefore structurally necessary to fix the substrate in the groove and dispose the Ni felt in a state of being sufficiently pressed against the substrates on both sides. It is difficult, and conversely, it is also difficult to attach the individual substrates to the grooves of the fixing plate 30 with the Ni felt sandwiched between the substrates. In addition, since this Ni felt is a porous body, it tends to be plastically deformed by compression, and there is a problem that it is gradually compressed by being used for a long time and deformed in a plastically deformed state. Then, if Ni felt is simply arranged between the cells on the substrate, the Ni may be excessively deformed in only a part. In such a state, electrical transformation between the cells in that part may occur. There is a problem that the connection state becomes poor and the power generation characteristics of the entire fuel cell stack deteriorate.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art, that is, a solid oxide fuel cell in which hollow single cells are connected in series to obtain a predetermined output voltage. It is related to the structure of the stack and its assembling method, and prevents excessive compression of the metal felt when arranging the metal porous conductor (metal felt) between each cell, and makes good electrical connection for a long time. A fuel cell stack capable of maintaining the above and a method for manufacturing the same.

[0005]

In order to achieve the above-mentioned object of the present invention, a metal porous conductor (a metal felt) is arranged between cells constituting a stack of a solid oxide fuel cell. At this time, a spacer having a predetermined interval is arranged between the cells, and a metallic felt and an incompressible member are used together to enhance the function of the spacer.
The entire fuel cell stack is fixed by uniformly tightening it from both end faces, so that even pressure is applied to each cell face, ensuring good electrical connection between the cells, and It is intended to prevent the displacement of the cell and improve the fitting state with the cell mounting holder. The present invention forms a single cell by forming a flat plate type substrate having a through hole in the inside using an electrode material and forming a layer of a solid electrolyte and another electrode on one side of the substrate, At the time of forming a fuel cell stack by forming a hole at a position that does not overlap the through-hole provided in the inside, and connecting a plurality of this single cell,
A spacer made of a metallic felt-like substance that is a porous conductor and an incompressible substance that does not participate in the battery reaction is provided in the gap between the unit cells, and the holes at the unit cell surface are provided with holes on both end surfaces of the cell group. Through bolts to tighten the whole body evenly and integrate them, place holders with grooves to fit each single cell in this assembled state on top and bottom to perform gas sealing, and store the stack of this structure in a container The stack constitutes a solid oxide fuel cell stack. In the conventional fuel cell, no fixing hole is provided in the single cell, and the connecting conductor between cells is only sandwiched in the gap between cells, ensuring sufficient electrical contact. It was difficult to do. Further, in the configuration of the conventional fuel cell, even in the assembling work when actually fixing the cells, there is a problem that the assembling work efficiency is extremely poor because the cells are attached via the stretchable nickel metal felt. The present invention solves these conventional problems.

[0006]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a perspective view showing an example of an assembly structure of a unit cell group of a stack of a solid oxide fuel cell of the present invention. 11 is a single cell formed on the air electrode hollow substrate, 12 is an end holding plate, 13 is an assembly bolt, 14
Is an inter-cell connecting portion, and more specifically, it is configured by combining the incompressible spacer 16 shown in FIGS. 3A and 3B with the metal felt 28 which is a conductive spacer shown in FIG. Further, 19 is a lower fixing plate for fixing the cell. Further, FIG. 2 shows an appearance of a single cell used in the stack shown in FIG. A single cell is provided with a cell fixing hole 15 for passing a fixing bolt. Further, FIG. 3 shows an example of the shape of the non-compressible spacer. In this example, an incompressible spacer having the shape shown in FIG. 3B was used. The inter-cell connecting portion has a structure in which a metal felt is housed in the center of the spacer. At this time, a metal felt having a thickness larger than that of the spacer was used so that the metal felt was elastically deformed even when the cell was pressed. In this example, the fixed cell group was housed in a container to form a power generation stack. Further, FIG. 3A shows an example of another shape of the non-compressible spacer. An example of the structure of the power generation stack is shown in FIG. In this embodiment, each unit cell is arranged via the incompressible spacer 16 and the metal felt 28,
In this state, it is fastened by the assembling bolt 13. Non-compressible spacer 16 and assembly bolt 1
As the material of No. 3, a material containing zirconia as a main component was used from the viewpoint of matching the coefficient of thermal expansion with the cell and heat resistance.
By thus integrating the entire cell, the cell can be easily fixed. The thickness of the incompressible spacer 16 used at this time is made equal to the distance between the substrate mounting grooves 20 provided in the lower fixing plate for fixing the cell, and the thickness of the metal felt 28 is set to be larger than the above distance. Also keep it large. By using such an incompressible spacer, even when the stack is tightened, the cell spacing is compressed only up to the thickness of the incompressible spacer 16, and the metal felt 28 is used.
Even if only partially compressed, it is possible to prevent deformation beyond plastic deformation. With this configuration,
When the cell group is tightened with the assembling bolts 13, each cell is fixed at the same interval as the board mounting groove 20 of the lower fixing plate 19, and the displacement of the cell is prevented. At the same time, the electrical connection between the cells can be ensured by the metal felt 28 which is in a state of being only partially compressed and having an extension force. The non-compressible spacer 16 is required not to interfere with the flow of gas fed between the single cells, and in the present embodiment, it has a frame shape as shown in FIG. A spacer provided with a notch (or hole) 17 for supplying and exhausting gas is used as the spacer. This spacer has holes 17 for gas supply and exhaust.
The hole 15 for fixing the cell through which the bolt is passed is provided so as not to overlap with, and when the cell is fixed to form the stack, the bolt is passed through the hole 15 for fixing the cell to tighten the entire cell group, It is possible to ensure the contact with the metal felt 28 as well as the alignment of each cell. In addition,
In this embodiment, a frame-shaped spacer is used as shown in FIG. 3 (b), but as the shape of this spacer, a flat plate having a predetermined thickness may be used in combination with a metal felt. Is. In the stack of the present invention, the cell fixing holes 15 for passing the fixing bolts through the single cells.
Is provided. A single cell is basically manufactured by forming a hollow substrate by extrusion molding or sintering a laminate of sheet molded bodies, and then forming an electrolyte on the surface by thermal spraying or EVD. It can also be produced by co-sintering the electrode sheet and the electrolyte sheet. Therefore, the hole 15 for fixing the cell through which the bolt is inserted can be easily obtained by making a hole in the pre-sintering state. The number of holes through which the assembling bolts 13 are provided in the cell of the present invention is not particularly limited as long as the metal felt 28 is uniformly pressed on the surface of each cell, but is not limited to a particular size. According to this, about 2 to 6 pieces are sufficient.

A production example of a single cell used in the stack of the solid oxide fuel cell of the present invention will be shown below by taking a single cell used as a cathode material as a hollow substrate as an example. As the air electrode material, generally used La _0.8 Sr _0.2 MnO ₃
Powder (particle size 1 to 3 μm) was used. Then, the hollow flat plate was produced by a method of heat-sealing the sheet molded body and a method of extrusion molding. First, an example of a method for heat-sealing a sheet molded body will be described below. The sheet molded body was manufactured by the doctor blade method, and after cutting such a sheet molded body into a predetermined size, it was heated and pressed to manufacture a hollow fused body. The heating and pressurizing conditions at this time need to be changed depending on the softness of the sheet, but the molding conditions were generally 70 to 80 ° C. and 30 to 70 kg / cm ² . Then, a hole for fixing the cell was provided in the peripheral portion of this fused body. The hollow flat plate fused in this way is about 400
Degreasing at ℃, and then 2 at 1250 ~ 1350 ℃
A hollow substrate for an air electrode was produced by firing for 5 hours.
The size of the hollow substrate was 100 mm × 150 mm square and the thickness was about 5 mm. Since the progress of sintering is influenced by the particle size of the raw material powder used and the amount of the binder / plasticizer added, the temperature and time were selected according to the raw material in consideration of these influences. As described above, by appropriately selecting the firing conditions according to the addition amount of the raw material powder, the binder and the like and firing, it is possible to obtain a sintered body having a porosity of about 20 to 30% even if the raw material powder is changed. it can. The conductivity of the air electrode depends to some extent on the porosity, but the conductivity of the sintered body in this example is about 100 S / 1000 at 1000 ° C.
It was cm. On the other hand, a clay-like material is required for extrusion molding. Such a material is a raw powder 100
5 parts by weight of the binder and 10 to 15 parts by weight of the solvent were added to the parts by weight. A methylcellulose-based water-soluble polymer was used as the binder. In the case of extrusion molding, the finish condition of the molded body is greatly affected by the viscosity of the raw material, for example, when the amount of water is low, the extrusion pressure becomes high and cracks occur during molding, and on the contrary, when it is too high, it is difficult to maintain the hollow structure. It becomes. Therefore, 2 to 5 parts by weight of a plasticizer was added as necessary for adjustment. When firing the extruded body, it is also necessary to degrease after drying the water content. Although the degreasing temperature varies depending on the binder used, the methylcellulose-based water-soluble polymer used here was subjected to thermal decomposition at about 400 ° C. Regarding the firing temperature, the same conditions as those of the doctor blade sheet laminate were used, and as a result, the same product as that obtained by the doctor blade method could be obtained. A thin film of the solid electrolyte and the fuel electrode was formed on the hollow substrate thus manufactured. In all of the examples, the thermal spraying method was used for film formation. The thermal spraying machine used was an atmospheric thermal spraying method, and 8 mol-stabilized YSZ (particle size: 10 to 50 μm) was used as an electrolyte material. The target electrolyte thickness was 100 μm, and the gas permeability of this membrane was 1 to 5 × 10 ⁶ [cc · cm / sec · (g / cm ² ) cm ² ]. As the fuel electrode, nickel oxide powder (particle size: 10 to 50 μm) and 8 mol-stabilized YSZ were used. The thickness of the fuel electrode was about 200 to 300 μm. The gas permeability of this fuel electrode is 10 ~ ⁴ [cc ・ cm / sec
・ (G / cm ² ) cm ² ]. In this example, the single cells formed by the above method were combined to form a power generation module having a predetermined output. FIG. 4 shows an example of assembling the power generation module. Reference numeral 19 is a lower fixing plate, 20 is a groove for mounting a substrate, 21 is an upper fixing plate, 43 is a gas discharge slit, 22 is an outer container, 23 is an oxidant gas supply port, 24 is a fuel gas supply port, and 25 is power generation. A chamber, 26 is a combustion chamber, 27 is an exhaust port, 28 is a metal felt, and 29 is a conducting wire. In constructing the module, a group of single cells 11 in which the single cells are stacked and fixed with bolts are housed inside the outer container 22 while being held by the upper fixing plate 21 and the lower fixing plate 19.
On the other hand, a groove 20 for mounting a substrate is provided in a portion where the group of unit cells 11 is fitted to the lower fixing plate 19,
The above group was combined with this groove portion, and gas sealing was performed using a sealing material 42 made of a non-conductive melt such as borosilicate glass. The operation of the SOFC of the present invention is exactly the same as that of the conventional SOFC module.
It is installed under a temperature condition such as 0 ° C. and each gas is supplied. As shown in FIG. 4, the oxidant gas is supplied from the oxidant gas supply port 23, passes through the inside of each cell, reacts in the unit cell formation portion, and then the residual gas reaches the combustion chamber 26. On the other hand, the fuel gas is supplied from the fuel gas supply port 24 provided on the side surface of the outer container 22, and power is generated on the substrate surface. The supplied fuel gas flows into the gaps between the cells and causes a reaction, but the incompressible spacers 16 arranged between the cells are provided with holes 17 for supplying and discharging the gas. Therefore, the diffusion of the fuel gas to the electrode surface through the hole 17 can be performed without any trouble. Since the electric contact of each cell is secured by the metal felt 28, the generated electric power can be taken out to the outside through the conducting wire 29 while suppressing the loss.

[0008]

As described above in detail, in the solid oxide fuel cell (SOFC) of the present invention, a hollow flat plate type electrode substrate having a through hole for allowing gas to pass is used, and a solid electrode is formed on the surface of the electrode substrate. An electrolyte layer and another electrode different from the substrate material are formed to electrically connect cells having a structure in which at least one power generation element is formed to assemble a cell group, which is fixed to each single cell during stacking. By providing holes for the bolts to pass through and using the non-compressible spacers and the metal felt between the cells to evenly tighten the whole body, it is possible to prevent misalignment of each single cell without misalignment. This is a high-performance SO that is fully integrated and has good electrical connection between cells.
FC is obtained. Although there was a power generation module having a similar structure before the present invention, this conventional method merely arranges a metal felt for conduction between cells, and the electrical connection between cells is not always good. Was not.
Therefore, the power generation characteristics of the power generation module were poor. Also, when assembling each unit cell, the cell is attached to the groove of the fixing plate while sandwiching the stretchable metal felt, but the production efficiency of the power generation module was extremely low. According to the stack assembling method of the present invention, the electrical connection between cells and the close fixing between cells can be easily performed, and the positional deviation does not occur, so that the reliability of the power generation module can be further improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an assembly structure of a unit cell group exemplified in an embodiment of the present invention.

FIG. 2 is a perspective view showing the appearance of a single cell exemplified in the embodiment of the present invention.

FIG. 3 shows two types [(a), illustrated in the examples of the present invention.
FIG. 3B is a perspective view showing the outer appearance of the incompressible spacer of FIG.

FIG. 4 is a schematic diagram showing a structure of a power generation stack exemplified in an embodiment of the present invention.

FIG. 5 is a schematic diagram showing a structure of a fuel cell single cell using a conventional flat plate type (a) and a hollow electrode substrate (b).

FIG. 6 is a schematic diagram showing a structure of a power generation module composed of a conventional fuel cell single cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte layer 2 ... Fuel electrode 3 ... Air electrode 4 ... Interconnector 5 ... Fuel gas flow path 6 ... Oxidant gas flow path 7 ... Single cell power generation part 8 ... Air electrode substrate 9 ... Gas impermeable layer 10 ... Through-hole 11 ... Single cell 12 ... End pressing plate 13 ... Assembly bolt 14 ... Cell connecting part 15 ... Cell fixing hole 16 ... Incompressible spacer 17 ... Gas supply / exhaust notch (or hole) 18 ... Space for storing metal felt 19 ... Lower fixing plate 20 ... Groove for mounting substrate 21 ... Upper fixing plate 22 ... Outer container 23 ... Oxidant gas supply port 24 ... Fuel gas supply port 25 ... Power generation chamber 26 ... Combustion chamber 27 ... Exhaust port 28 ... Metal felt 29 ... Conductive wire 30 ... Fixed plate 31 ... Groove 32 ... Separation plate 33 ... Gas discharge slit 34 ... Outer container 35 ... Oxidant gas supply port 36 ... Fuel gas supply port 37 ... Front chamber 38 ... Combustion chamber 3 ... gas discharge port 40 ... porous conductive material 41 ... wire 42 ... sealing member 43 ... gas discharge slit

Claims (3)

[Claims] 1. A cell group is formed by stacking a plurality of single cells formed by laminating a solid electrolyte layer and an electrode layer on a flat substrate made of an electrode material and having a through hole therein. In a stack of a solid oxide fuel cell, an electric insulating spacer made of an incompressible substance is provided between the single cells, and a thickness equal to or larger than the thickness of the electric insulating spacer is used. A stack of a solid oxide fuel cell, characterized in that a conductive spacer made of a metallic felt-like substance that is elastically deformable even when compressed to a small size is arranged. 2. The solid according to claim 1, wherein the entire cell group formed by stacking a plurality of single cells is uniformly tightened in a direction perpendicular to the surface of the electrode layer. Electrolyte fuel cell stack. 3. A cell group is formed by stacking a plurality of single cells formed by stacking a solid electrolyte layer and an electrode layer on a flat plate type substrate made of an electrode material and having a through hole therein. In the method for producing a stack of a solid oxide fuel cell, on the surface of a single cell formed by laminating a solid electrolyte layer and an electrode layer on a flat plate type substrate having the above through hole, the position of the above through hole does not overlap. At the position, forming a plurality of common holes penetrating the single cell, and forming a cell group by stacking a plurality of the single cells, a step of passing bolts through the common hole and uniformly tightening the entire cell group is performed. A method for manufacturing a stack of a solid oxide fuel cell, comprising: