JP3249494B2 - Molten carbonate fuel cell with electrolyte plate crack prevention structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten carbonate fuel cell capable of preventing cracks in an electrolyte plate near a boundary between an electrode and a wet seal portion.

[0002]

2. Description of the Related Art First, a process from the assembly of a unit cell to the formation of an electrolyte plate in a molten carbonate fuel cell will be described with reference to FIG. As shown in FIG. 6A, when assembling the battery, the fuel electrode (anode) 10 and the air electrode (cathode) are used.
A holding material sheet 14 containing a ceramic powder and an organic binder for holding an electrolyte and an electrolyte sheet 16 containing a carbonate serving as an electrolyte and an organic binder are provided between the two electrodes 10 and 12. They are arranged in layers. Holding material sheet 1 sandwiched between electrodes 10 and 12
The laminate of the electrolyte sheet 4 and the electrolyte sheet 16 has a concave portion for accommodating an electrode on the inner surface, and has a plurality of gas channels 18 in the concave portion.
The peripheral portion of the cell frame 20 is in contact with the laminated body of the holding material sheet 14 and the electrolyte sheet 16.

The assembled cell is heated to about 450 ° C. as shown in FIG.
4. The organic binder contained in the electrolyte sheet 16 is degreased. In the holding material sheet 14, the organic binder is removed by burning, leaving only ceramics, and a porous body of ceramics is formed. In the electrolyte sheet 16, the organic binder is burned off and only the carbonate serving as the electrolyte remains. After that, the temperature is further raised to about 650 ° C. to melt the carbonate, and the molten carbonate is impregnated into the holding material made of the ceramic porous body, so that the electrolyte plate 22 is formed as shown in FIG. Is done. The contact surface between the electrolyte plate 22 and the peripheral portion of the cell frame 20 sandwiching the electrolyte plate 22 is sealed by being filled with molten carbonate, and a wet seal portion 24 is formed. In this state, the fuel gas is supplied to the gas flow path 18 on the fuel electrode (anode) 10 side, and the oxidant gas is supplied to the gas flow path 18 on the air electrode (cathode) 12 side to cause a reaction, thereby starting the battery. Start.

[0004]

In the molten carbonate fuel cell as described above, due to its structure, a minute gap exists between the electrode and the cell frame, or a minute gap exists between the electrode and the wet seal portion. There are steps. For this reason, cracks (cracks) occur in the electrolyte plate near the boundary between the electrode and the wet seal due to a thermal cycle or the like caused by the start / stop of the fuel cell, and the reaction gas on the fuel electrode side and the air electrode side There is a high possibility that cross leak will occur, which may hinder stable battery operation. A portion surrounded by a chain line circle in FIG. 5 (described later) is a crack frequently occurring portion. In FIG. 6, the holding material sheet 14, the electrolyte sheet 16
Has a certain degree of plasticity, the sheet shape is deformed by softening due to temperature rise and pressing from above and below the cell frame 20, and gaps and steps are absorbed to some extent by the electrolyte plate 22. However, as shown in FIGS. 7 and 8,
When the electrolyte plate 22 protrudes into the gap 26 between the electrode 12 and the cell frame 20, the electrolyte plate 22 becomes sparse at the peripheral portion 30 of the protruding portion 28, and a step or gap between the electrode 12 and the wet seal portion 24 is removed. Cracks (cracks) 32 easily occur in the electrolyte plate 22 without being absorbed completely.

As means for preventing the occurrence of cracks in the electrolyte plate, the invention described in Japanese Patent Application Laid-Open No. 63-6753 discloses an alumina having a molten salt resistance in a gap between an electrode and a frame material of a wet seal portion. Filling materials such as cement are used, but this technology complicates the manufacturing process and increases the cost. In addition, if the amount of the filling material is not accurate, cracking is more likely to occur. There is a possibility and sufficient effect cannot be expected. In addition, Japanese Patent Application Laid-Open
According to the invention described in 2013347, in order to prevent the occurrence of cracks in the electrolyte plate near the boundary between the electrode and the wet seal portion, a position corresponding to a peripheral portion including this boundary is provided.
Although a reinforcing material such as a gold foil or a platinum foil having high corrosion resistance is interposed, the cost of the gold foil or the like is increased, and the effect of preventing cracks due to deformation of the gold foil or the like is not sufficient. As described above, the technique of filling the gap or the gap between the electrode and the wet seal portion with the filler or covering the vicinity of the boundary between the electrode and the wet seal portion with gold foil or the like has problems in terms of cost, Also, it is difficult to control the amount of filler,
Deformation of gold leaf and the like also has a problem.

The present invention has been made in view of the above points, and an object of the present invention is to devise a cell structure of a molten carbonate type fuel cell, and to incline a wet seal portion inward to provide an electrolyte. Apply force to compress the board inward,
Melting that can fill the minute steps and gaps at the boundary between the electrode and the wet seal with the deformation of the electrolyte plate itself and prevent the electrolyte plate from cracking near the boundary between the electrode and the wet seal An object of the present invention is to provide a carbonate fuel cell.

[0007]

In order to achieve the above object, a molten carbonate fuel cell having a structure for preventing cracking of an electrolyte plate according to the present invention has a concave portion for accommodating an electrode on an inner surface thereof. Two cell frames with many gas flow paths
In a molten carbonate fuel cell in which two electrodes and an electrolyte plate are sandwiched between the electrodes, and the electrolyte plate is sandwiched at the periphery of the cell frame to form a wet seal portion, An inclined part is provided on the peripheral edge of the cell frame so that the gap is larger on the electrode side and smaller on the outer surface of the cell, and the wet seal part is inclined inward, and the cell frame is pressed from above and below to the inside of the electrolyte plate. Applying compressive force, the compressive force deforms the electrolyte plate
Then , the steps and gaps between the electrodes and the cell frame are filled with the material constituting the electrolyte plate (see FIGS. 1, 2 and 5).

In the molten carbonate fuel cell according to the present invention, the interval between the cell frames provided with the inclined portions in the wet seal portion is set to 0.4 to 3 mm on the electrode side, and the interval between the electrode sides on the outer surface of the cell. It is preferably at least 0.2 mm smaller and 0.2 to 2.5 mm (see FIG. 5). Further, the interval between the cell frames provided with the inclined portion in the wet seal portion is 0.5 to 3 mm on the electrode side,
On the outer surface of the cell, at least 0.2 mm smaller than the interval on the electrode side, and 0.3 to 1 mm, preferably 0.3 to 0.6 mm
Is more preferable (see FIG. 5). When the interval between the cell frames on the outer surface of the cell is within the above range, no cross leak occurs and the voltage deterioration rate is small. If the interval between the cell frames on the outer surface of the cell is smaller than the above lower limit, a short circuit may occur. On the other hand, if it exceeds the upper limit, the battery voltage may be low. Further, the difference between the interval between the cell frames on the electrode side and the interval on the outer surface of the cell is good at 0.2 mm or more, and the range of the interval between the cell frames on the electrode side is inevitably above the lower limit. Become. On the other hand, by setting the upper limit to the above value, good results can be obtained for any of the battery voltage, cross leak, short circuit current, and voltage deterioration rate within the above range. In the molten carbonate fuel cell according to the present invention, the inclination of the inclined portion of the cell frame in the wet seal portion is in the range of 0.002 to 0.14, preferably 0.01 to 0.14.
It is preferred to be in the range of 0.135. The inclination of the inclined portion of the cell frame is obtained by dividing half of the difference between the cell frames on the electrode side and the outer surface of the cell by the length of the wet seal portion. Because of this, it becomes 1/2). Usually, since the length of the wet seal portion is considered to be 10 to 50 mm, the minimum gradient is 0.2 ÷ 2 ÷ 50 = 0.002, and the maximum gradient is (3
−0.2) ÷ 2 ÷ 10 = 0.14. A more desirable range (based on a seal portion length of 10 mm that can save the material of the wet seal portion) is 0.2 ÷ 2 ÷ 10 = 0.0
1 is the lower limit, and (3-0.3) ÷ 2 ÷ 10 = 0.1
35 is the upper limit.

If the inclination of the inclined portion of the cell frame is too small, even if the electrolyte plate is deformed and filled into the gaps or steps due to the softening and pressing by increasing the temperature during the formation of the electrolyte plate, the electrolyte plate is kept inside. 8, the deformation is not sufficient, and as shown in FIG. 8 described above, the electrolyte plate becomes sparse at the periphery of the protruding portion of the electrolyte plate, and the step and the gap between the electrode and the wet seal portion are reduced. Without absorption, cracks (cracks) occur in the electrolyte plate. On the other hand, when the inclination of the inclined portion of the cell frame is too large and the gap outside the cell is small, as shown in FIGS. 3 and 4, the upper and lower cell frames come into contact with each other to cause a short circuit (short circuit) or an upper and lower cell frame. Even if the cell frame is not in contact, there is a possibility of short-circuiting (short-circuit) via a scale or the like. If the cell frames on both sides are short-circuited, electrons may flow through the internal circuit of the battery, which may make it impossible to supply electricity to the outside.

In the molten carbonate fuel cell according to the present invention, a spacer made of an insulator can be provided at a portion where the space between the cell frames is reduced on the outer surface of the cell. By providing such a spacer, a short circuit (short circuit) can be prevented even when the gap between the cell frames on the outer surface of the cell is small.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications. . 1 and 2 show a process of forming an electrolyte plate in a molten carbonate fuel cell having a structure for preventing cracking of an electrolyte plate according to an embodiment of the present invention. As shown in FIG. 1A, at the time of assembling a unit cell, an electrolyte for holding an electrolyte is provided between two electrodes 10, 12 of a fuel electrode (anode) 10 and an air electrode (cathode) 12. Holding material sheet 1 containing ceramic powder and organic binder
4 and a plurality of electrolyte sheets 16 each containing a carbonate serving as an electrolyte and an organic binder. The electrodes 10 and 12 are porous and made of, for example, nickel, a nickel alloy, or the like. As the organic binder, for example, polyvinyl butyral (PVB) or the like is used.

A holding material sheet 1 sandwiched between electrodes 10 and 12
The laminate of the electrolyte sheet 4 and the electrolyte sheet 16 has a concave portion for accommodating an electrode on the inner surface, and has a plurality of gas channels 18 in the concave portion.
The cell frame 34 is sandwiched between the cell frames 34, and the peripheral edge of the cell frame 34 is in contact with the stacked body of the holding material sheet 14 and the electrolyte sheet 16. The cell frame 34 is made of, for example, stainless steel (SUS), nickel, a nickel alloy, or the like. In addition, the cell frame is manufactured by plate combination welding, and stainless steel (S
In some cases, a corrugated sheet made of US, nickel, nickel alloy, or the like is used. FIG. 2A is an enlarged view of a portion surrounded by a chain line ellipse in FIG. 1A. As shown in FIGS. An inclined portion 36 is provided so as to be larger on the side and smaller on the outer surface of the cell.

The assembled cell is heated to about 450 ° C. as shown in FIG.
4. The organic binder contained in the electrolyte sheet 16 is degreased. The holding material sheet 14 and the electrolyte sheet 16
It has a certain degree of plasticity, and the sheet shape is deformed by softening due to temperature rise and pressing from above and below the cell frame 34. FIG. 2B is an enlarged view of a portion surrounded by a chain line ellipse in FIG. 1B. As shown in FIG. 2B, the inclined portion 36 provided on the cell frame 34
A force for compressing the sheet inward is applied, and the gap 26 between the electrode and the cell frame is filled with a material to be an electrolyte plate by the compressive force. In the holding material sheet 14, the organic binder is burned off and only the ceramic remains, and a porous ceramic body is formed. In the electrolyte sheet 16, the organic binder is burned off and only the carbonate serving as the electrolyte remains.

Thereafter, the temperature is further raised to about 650 ° C. to melt the carbonate, and the holding material made of a porous ceramic body is impregnated with the molten carbonate, as shown in FIG.
An electrolyte plate 38 is formed. FIG. 2 (c) is an enlarged view of a portion surrounded by a chain line ellipse in FIG. 1 (c). As shown in FIG. 2 (c), the electrode is compressed by a force compressing the electrolyte plate 38 inward. The gap 26 between the cell and the cell frame is filled with the material constituting the electrolyte plate 38, so that cracking of the electrolyte plate 38 near this portion is prevented. The contact surface between the electrolyte plate 38 and the inclined portion 36 of the cell frame 34 sandwiching the electrolyte plate 38 is sealed by being filled with molten carbonate, and a wet seal portion 40 is formed. In this state, the fuel gas (H ₂ , CO _2, etc.) is supplied to the gas flow path 18 on the fuel electrode (anode) 10 side, and the air electrode (cathode)
Oxidizing gas (air, CO _2, etc.) in the gas passage 18 on the 12 side
To cause a reaction to start the battery.

As described above, by inclining the wet seal portion inward, a force for compressing the electrolyte plate inward is applied, and this compressive force causes a minute step at the boundary between the electrode and the wet seal portion. The gaps and gaps are filled with deformation of the electrolyte plate itself to prevent cracking of the electrolyte plate near the boundary between the electrode and the wet seal portion. In addition, when making this inclination, in order to reduce the gap outside the cell, if it is extremely inclined, the cell frames on both sides will short,
The flow of electrons through the internal circuit of the battery may make it impossible to supply electricity to the outside. For example, FIG.
As shown in FIG. 4, when the inclination of the inclined portion 44 of the cell frame 42 is too large and the gap outside the cell becomes small, there is a possibility that the upper and lower cell frames 42 come into contact and short-circuit (short-circuit). In addition, even when the upper and lower cell frames 42 are not in contact with each other, a short circuit may occur via a scale or the like. For this reason, it is important to optimally control the degree of this inclination.

Therefore, in the wet seal portion,
The interval between the cell frames provided with the inclined portions is 0.1 mm on the electrode side.
4 to 3 mm, 0.2 mm from the electrode side on the outer surface of the cell
Preferably, it is smaller than 0.2 mm. In addition, the interval between the cell frames provided with the inclined portion,
It is more preferably 0.5 to 3 mm on the electrode side and 0.2 mm or more smaller than the interval on the electrode side on the outer surface of the cell, and 0.3 to 1 mm, more preferably 0.3 to 0.6 mm. Further, the inclination of the inclined portion of the cell frame is set to 0.002 to 0.1.
4, preferably in the range of 0.01 to 0.135. If the slope is too small or flat, in the process of forming the electrolyte plate, by softening and pressing by heating, even if the electrolyte plate is deformed and filled into gaps and steps, the electrolyte plate is compressed inward. Since the force is small, deformation is not enough, and the electrolyte plate becomes sparse around the protruding portion of the electrolyte plate, and the electrolyte plate cannot absorb the steps and gaps between the electrode and the wet seal portion. ) Will occur.

[0017]

EXAMPLES Examples and comparative examples of the present invention will be described below. In the configuration of the unit cell of the molten carbonate fuel cell shown in FIG. 5, the intervals between A and B were variously set, and the cell performance was examined. Note that the reference numerals in FIG. 5 are the same as those in FIG. 1C, and the portion surrounded by a chain line circle in FIG. 5 is a portion where cracks occur frequently. In FIG. 5, A is determined from the thickness of the sheet constituting the electrolyte plate, and B is B = A− (D−C).
× 2. The distance between A and B is 1 mm, respectively.
1 mm (Comparative Example 1), 0.6 mm, 0.4 mm (Example 1), 1 mm, 0.1 mm (Comparative Example 2), 1 mm, 0.2
mm (Example 2), 1 mm, 0.3 mm (Example 3),
1.1 mm, 0.6 mm (Example 4), 1.5 mm, 1 mm
(Example 5) Table 1 shows the results of examining the battery performance by setting 3 mm and 2.5 mm (Example 6).

In Table 1, "battery voltage" indicates the initial performance of the battery, "cross leak amount" indicates the concentration of nitrogen leaked from the air electrode side to the fuel electrode side, and the presence or absence of cracks in the electrolyte plate is determined. it can. The “short-circuit current” can determine the presence or absence of a short-circuit (short-circuit) (the rated load current is 150 mA /
cm ² , and the performance decreases if extra current flows),
“Voltage deterioration rate” is an index of long-term stability of battery performance.
As can be seen from Table 1, when the wet seal portion was not inclined (Comparative Example 1), cross leak of gas due to crack generation of the electrolyte plate was observed. When the gap on the outer surface of the cell was small (Comparative Example 2), a short circuit occurred due to contact between the upper and lower cell frames or contact via a scale or the like. On the other hand, in Examples 1 to 6, the battery performance was generally good, there was almost no gas cross leak, and no cracks were present in the electrolyte plate.

[0019]

[Table 1]

[0020]

As described above, the present invention has the following effects. (1) The cell frame is provided with an inclined portion so that the gap between the cell frames in the wet seal portion is large on the electrode side and small on the outer surface of the cell, and the wet seal portion is inclined inward so that the electrolyte is formed. By applying a force to compress the plate inward, it is configured to fill the minute steps and gaps at the boundary between the electrode and the wet seal part with the material that constitutes the electrolyte plate, so that the fuel cell can be started and stopped. Even when the resulting heat cycle is applied, cracks (cracks) do not occur in the electrolyte plate near the boundary between the electrode and the wet seal portion, and no cross leak of the reaction gas on the fuel electrode side and the air electrode side occurs, Stable battery operation can be performed. (2) By optimally controlling the degree of inclination of the cell frame at the wet seal portion, it is possible to prevent the occurrence of cracks (cracks) in the electrolyte plate, and at the same time, it is possible that the inclination is too large and the gap on the outer surface of the cell becomes too small. No short circuit occurs. (3) When an insulating spacer is provided in a portion of the outer surface of the cell between the cell frames where the space is reduced, a short circuit (short circuit) can be more reliably prevented. (4) The battery manufacturing process is as simple as before,
Also, the cost does not increase.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional configuration diagram showing a process of forming an electrolyte plate in a molten carbonate fuel cell having a structure for preventing a crack of an electrolyte plate according to an embodiment of the present invention.

FIG. 2 is an enlarged partial cross-sectional configuration diagram illustrating a portion surrounded by a chain line ellipse in FIG. 1;

FIG. 3 is a schematic partial cross-sectional configuration diagram showing an example of a problem in a molten carbonate fuel cell in which a wet seal portion is inclined.

FIG. 4 is an enlarged partial cross-sectional configuration diagram illustrating a portion surrounded by a chain line ellipse in FIG. 3;

FIG. 5 is a schematic cross-sectional configuration diagram showing a molten carbonate fuel cell in which intervals are set in Examples and Comparative Examples of the present invention.

FIG. 6 is a schematic sectional configuration diagram showing a process of forming an electrolyte plate in a conventional molten carbonate fuel cell.

FIG. 7 is a schematic partial cross-sectional configuration diagram showing an example of a problem in a conventional molten carbonate fuel cell.

FIG. 8 is an enlarged partial cross-sectional configuration diagram illustrating a portion surrounded by a chain line ellipse in FIG. 7;

[Explanation of symbols]

 10, 12 Electrode 14 Holding material sheet 16 Electrolyte sheet 18 Gas flow path 20, 34, 42 Cell frame 22, 38 Electrolyte plate 24, 40 Wet seal part 26 Gap 28 Protruding part 30 Peripheral part of protruding part 32 Crack (crack) 36 , 44 Inclined part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-107267 (JP, A) JP-A-1-63070 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/02 H01M 8/14

Claims (5)

(57) [Claims] 1. A cell frame comprising two cell frames having an inner surface having a concave portion for accommodating an electrode and having a plurality of gas flow paths in the concave portion, wherein the two electrode plates and an electrolyte plate between the electrodes are sandwiched. In a molten carbonate fuel cell having a wet seal portion formed by sandwiching an electrolyte plate at the peripheral portion of the cell frame, the cell frame in the wet seal portion is large on the electrode side and small on the outer surface of the cell. An inclined portion is provided at the peripheral edge of the wet seal portion to incline inward, and a force is applied to press the cell frame from above and below and compress the electrolyte plate inward, thereby deforming the electrolyte plate by this compression force. A molten carbonate fuel cell having a structure for preventing cracking of an electrolyte plate, wherein a step / gap between an electrode and a cell frame is filled with a material constituting the electrolyte plate. 2. The distance between the cell frames provided with the inclined portions in the wet seal portion is 0.4 to 3 mm on the electrode side, and at least 0.2 mm from the electrode side on the outer surface of the cell.
2. The molten carbonate fuel cell according to claim 1, which is small and has a structure for preventing cracking of the electrolyte plate of 0.2 to 2.5 mm. 3. The distance between the cell frames provided with the inclined portions in the wet seal portion is 0.5 to 3 mm on the electrode side, and at least 0.2 mm from the electrode side on the outer surface of the cell.
2. The molten carbonate fuel cell according to claim 1, wherein the fuel cell is small and has a structure for preventing the electrolyte plate from cracking. 4. A molten carbonate having a structure for preventing cracking of an electrolyte plate according to claim 1, wherein the slope of the inclined portion of the cell frame in the wet seal portion is in the range of 0.002 to 0.14. Type fuel cell. 5. A molten carbonic acid having a structure for preventing cracking of an electrolyte plate according to claim 1, wherein a spacer made of an insulator is provided at a portion of the outer surface of the cell between the cell frames where the space is reduced. Salt type fuel cell.