Electrochemical cell

Abstract

This invention provides an electrochemical cell with improved airtightness between two adjacent units in the stacking direction. [Solution] The electrochemical cell has a unit assembly made up of multiple stacked units 1, each unit 1 including a power generation cell 2, a cell frame 3 that holds the power generation cell 2, a separator 6 that separates the fuel electrode and the air electrode, and an anode spacer 9 sandwiched between the cell frame 3 and the separator 6, having a first central hole 9a through which gas flows. On the opposite side of the anode spacer 9, across the separator 6, is a compression seal 7 that airtightly seals the space between two adjacent units 1 in the stacking direction. The total thermal expansion of the anode spacer 9, separator 6, and compression seal 7 is greater than the thermal expansion of the energizing section 14.

Description

Technical Field

[0001] The present invention relates to an electrochemical cell.

Background Art

[0002] Patent Document 1 relates to a solid oxide fuel cell. In this fuel cell, an electrolyte / electrode assembly that constitutes the current-carrying portion of the fuel cell is disposed between a pair of separators arranged in the stacking direction of the power generation cells. Further, a seal is disposed between the pair of separators to ensure airtightness while suppressing leakage of fuel gas. This seal has a thick first seal portion made of a heat-resistant alloy or a ceramic material, and a pair of thin second seal portions made of a flexible material and disposed on both sides in the stacking direction of the first seal portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the solid oxide fuel cell of Patent Document 1, when the fuel cell is at a high temperature, the electrolyte / electrode assembly and the seal thermally expand. However, for the thin second seal portion made of a flexible material, there is a problem that the followability of displacement caused by the difference in the linear expansion coefficients between the electrolyte / electrode assembly and the seal is low.

[0005] Furthermore, in this fuel cell, since a pair of second seal portions are provided on both sides in the stacking direction of the first seal portion, there is a problem that the seal surface increases and the airtightness decreases as compared with the case where a single seal portion is provided on one side in the stacking direction of the first seal portion.

[0006] This invention was devised in view of conventional practices, and one of its objectives is to provide an electrochemical cell in which the airtightness between two adjacent units in the stacking direction is improved. [Means for solving the problem]

[0007] The present invention relates to an electrochemical cell, which has a unit assembly made up of multiple stacked units, each unit including a cell, a cell frame that holds the cell, a separator that separates the fuel electrode and the air electrode and faces the cell and cell frame, and a spacer sandwiched between the cell frame and the separator and having a communication port through which gas flows. An energizing section is arranged between two adjacent cells in the stacking direction of the units to electrically connect them. A compression seal is arranged on the opposite side of the spacer, across the separator, to hermetically seal the space between two adjacent units in the stacking direction. The total thermal expansion of the spacer, separator and compression seal is greater than the thermal expansion of the energizing section. [Effects of the Invention]

[0008] Therefore, at high temperatures in the electrochemical cell, the spacer continues to press against the compression seal via the separator without causing compression leakage, thereby improving the airtightness between two adjacent units in the stacking direction. [Brief explanation of the drawing]

[0009] [Figure 1] This is an exploded perspective view showing the cell unit of a solid oxide fuel cell according to the first embodiment. [Figure 2] This is a schematic cross-sectional view of a solid oxide fuel cell according to the first embodiment. [Figure 3] This is a schematic cross-sectional view of a solid oxide fuel cell according to the second embodiment. [Figure 4] This is a schematic cross-sectional view of the anode spacer according to the second embodiment. [Figure 5] This is a schematic cross-sectional view of a solid oxide fuel cell according to the third embodiment. [Modes for carrying out the invention]

[0010] Embodiments of the electrochemical cell of the present invention will be described below with reference to the drawings. In the following embodiments, a fuel cell, more specifically a solid oxide fuel cell, will be described as an example of an electrochemical cell. Furthermore, this fuel cell utilizes the reverse principle of water electrolysis, and the configuration of the device is common to that of a water electrolysis device that utilizes the principle of water electrolysis. Therefore, the electrochemical cell of the present invention can also be applied to a water electrolysis device.

[0011] Figure 1 is an exploded perspective view showing Unit 1 of a solid oxide fuel cell according to the first embodiment.

[0012] As shown in Figure 1, Unit 1 mainly comprises a power generation cell 2, a cell frame 3, a fuel flow path forming member 4, an air flow path forming member 5, a separator 6, a pair of compression seals 7, a compression seal member 8, a pair of anode spacers 9, and an anode spacer member 10. A solid oxide fuel cell is formed by stacking multiple of these Unit 1s in the stacking direction (up and down direction in Figure 1) to form a unit assembly. The anode spacers 9 and anode spacer member 10 correspond to the "spacers" described in the claims. The compression seals 7 and compression seal member 8 also correspond to the "compression seals" described in the claims.

[0013] For the convenience of the following explanation, we will describe austenitic stainless steel (hereinafter referred to as "ASS"), alumina scale-forming austenitic stainless steel (hereinafter referred to as "AFA"), ferritic stainless steel (hereinafter referred to as "FSS"), thermiculite, and mica, which can be used as materials for the fuel flow path forming member 4, air flow path forming member 5, separator 6, compression seal 7, compression seal member 8, anode spacer 9, and anode spacer member 10. ASS is, for example, SUS304. AFA is FSS with aluminum added, in this embodiment, 1-6% aluminum. FSS is, for example, SUS430. Thermiculite is a gasket material with excellent heat resistance and sealing properties, manufactured by Flexitalic Ltd. in the UK and formed mainly from vermiculite. Mica is a natural mineral whose main components are SiO2, Al2O3, K2, and crystal water. The coefficients of thermal expansion for ASS, AFA, FSS, and thermiculite are as follows: ASS has the highest coefficient, AFA the second highest, FSS the third highest, and vermiculite the lowest. Furthermore, the coefficient of thermal expansion for mica is lower than that of FSS but higher than that of thermiculite.

[0014] The power generation cell 2 is configured as a membrane electrode assembly in which a solid electrolyte layer is placed between a fuel electrode (anode electrode) and an air electrode (cathode electrode). In this embodiment, the fuel electrode is located on the lower side in the stacking direction of unit 1, that is, on the lower side in the vertical direction of Figure 1, while the air electrode is located on the upper and lower side in Figure 1. Fuel gas and air are supplied to the power generation cell 2, and electricity is extracted by the well-known electrochemical conversion of hydrogen in the fuel gas and oxygen in the air. In addition, the fuel electrode of the power generation cell 2 has a uniformly arranged reforming catalyst for reforming the fuel gas. Furthermore, the power generation cell 2 has a first metal support cell (not shown) having a first metal support layer provided on the side of the fuel electrode facing the separator 6, and a second metal support cell (not shown) having a second metal support layer provided on the side of the air electrode facing the separator (not shown).

[0015] The cell frame 3 is formed from a metal material in the shape of a rectangular frame. The cell frame 3 holds the power generation cell 2 by being fixed to the outer circumference of the power generation cell 2 via a sealing member 11 which is also formed in the shape of a rectangular frame. The cell frame 3 has a pair of rectangular first frame overhangs 3b that protrude outward from both ends of one of the pair of long sides 3a (the long side on the front side in Figure 1). A first hole 3c is formed in this first frame overhang 3b through which the unit 1 penetrates in the stacking direction. This first hole 3c is an elongated rectangle in the longitudinal direction of the power generation cell 2, that is, from the lower left to the upper right in Figure 1. A second rectangular overhang (not shown) is formed on the other long side 3a of the cell frame 3 (the long side on the back side in Figure 1). A second hole is formed in this second frame overhang that penetrates through the unit 1 in the stacking direction. The shapes of the second frame protrusion and the second hole correspond to the shapes of the second separator protrusion 6d and the second hole 6e, which will be described later.

[0016] The fuel channel forming member 4 is made of a conductive material made of metal, more specifically, a conductive material with a lower coefficient of thermal expansion than the anode spacer 9 and anode spacer member 10. Examples of materials for the fuel channel forming member 4 include AFA or FSS. In this embodiment, the fuel channel forming member 4 is made of FSS. The fuel channel forming member 4 is placed between the fuel electrode of the power generation cell 2 and the separator 6. Of the two surfaces of the fuel channel forming member 4, the surface facing the fuel electrode of the power generation cell 2 is formed in a wave-like shape with a continuous rectangular wave in the longitudinal direction of the power generation cell 2. As a result, a plurality of fuel channels 4a (see Figure 2) through which fuel gas (An) flows are formed between the fuel electrode of the power generation cell 2 and the separator 6. The fuel channel forming member 4 is electrically connected to the first metal support layer of the first metal support cell (not shown) of the power generation cell 2. This conductive connection is, for example, a connection using brazing. Alternatively, the conductive connection may be made using a metal paste, a conductive adhesive, or diffusion bonding instead of brazing.

[0017] The air channel forming member 5, like the fuel channel forming member 4, is made of a conductive material made of metal, more specifically, a conductive material with a lower coefficient of thermal expansion than the anode spacer 9 and anode spacer member 10. Examples of materials for the air channel forming member 5 include AFA or FSS. In this embodiment, the air channel forming member 5 is made of FSS, similar to the fuel channel forming member 4. The air channel forming member 5 is positioned between the air electrode of the power generation cell 2 and the separator of a unit (not shown) located above the stacking direction of unit 1 in Figure 1. Of the two surfaces of the air channel forming member 5, the surface facing the air electrode of the power generation cell 2 is formed in a wave-like shape with a continuous rectangular wave pattern, similar to the fuel channel forming member 4. Therefore, multiple air channels through which air (Ca) flows are formed between the air electrode of the power generation cell 2 and the separator of the unit (not shown). These multiple air channels are similar to the air channel 5a shown in Figure 2. In this embodiment, air flows from the anode spacer member 10 to the anode spacer 9 based on a so-called open cathode configuration, while fuel gas flows from the anode spacer 9 to the anode spacer member 10. The airflow channel forming member 5 is electrically connected to the second metal support layer of the second metal support cell (not shown) of the power generation cell 2.

[0018] Although Figure 1 illustrates an example in which the fuel flow path forming member 4 and the air flow path forming member 5 are each divided into an upstream and a downstream side, the fuel flow path forming member 4 and the air flow path forming member 5 may also be formed as single members.

[0019] The separator 6 is formed in a rectangular plate shape corresponding to the outer shape of the cell frame 3 by a conductive material made of metal. In the present embodiment, the separator 6 is formed by AFA. Note that the separator 6 may be formed by ASS or FSS instead of AFA. The upper surface of the separator 6 (the upper surface in FIG. 1) is conductively connected to the fuel flow path forming member 4. Thereby, the separator 6 is electrically connected to the fuel electrode of the power generation cell 2 via the fuel flow path forming member 4 and the first metal support layer of the first metal support cell (not shown). Also, the lower surface of the separator 6 is conductively connected to the air forming flow path of the unit disposed below the unit 1 (the unit 1 located on the lower side in FIG. 2).

[0020] Also, as shown in FIG. 1, at positions corresponding to the pair of first frame overhang portions 3b of the cell frame 3 in the separator 6, a pair of first separator overhang portions 6a having the same outer shape as the outer shape of the first frame overhang portions 3b are formed. In each first separator overhang portion 6a, a first hole portion 6b having the same shape as the first hole portion 3c of the cell frame 3 is formed to penetrate along the stacking direction of the unit 1. Also, at the central portion of the long side 6c of the separator 6 located on the opposite side of the first hole portion 6b, a second separator overhang portion 6d is formed. The second separator overhang portion 6d has an elongated rectangular shape that is longer and narrower than the first separator overhang portion 6a. In the second separator overhang portion 6d, a second hole portion 6e having an elongated rectangular shape that is longer and narrower than the first hole portion 3c of the cell frame 3 is formed to penetrate along the stacking direction of the unit 1.

[0021] Further, around the first hole portion 6b of the separator 6 that overlaps in the stacking direction of the unit 1 and the first hole portion 3c of the cell frame 3, an annular compression seal 7 for hermetically sealing between two adjacent units 1 in the stacking direction of the unit 1 is disposed. As shown in FIG. 1, the compression seal 7 is continuously annular along the outer shape of the first frame overhanging portion 3b and the first frame overhanging portion 3b. The compression seal 7 is formed of a material suitable for ensuring excellent sealing performance between two units 1, such as thermiculite, mica, etc. In the present embodiment, the compression seal 7 is formed of thermiculite. Further, the compression seal 7 has a through hole 7a formed in the central portion thereof.

[0022] Also, around the second hole portion 6e of the separator 6 that overlaps in the stacking direction of the unit 1 and the second hole portion of the second frame overhanging portion (not shown) of the cell frame 3, an annular compression seal member 8 for hermetically sealing between two adjacent units 1 in the stacking direction of the unit 1 is disposed. The compression seal member 8 is formed in an annular shape that is longer and thinner than the compression seal 7, but has the same material and function as the compression seal 7.

[0023] The anode spacer 9 is formed from a metallic material to form an annular shape corresponding to the shape of the compression seal 7. The anode spacer 9 is formed from a material with a higher coefficient of linear expansion than the fuel flow path forming member 4 and air flow path forming member 5 that constitute the energized section 14, which will be described later. As mentioned above, since the fuel flow path forming member 4 and air flow path forming member 5 are formed from FSS, the anode spacer 9 is formed from ASS or AFA. In this embodiment, the anode spacer 9 is formed from AFA. Also, when the fuel flow path forming member 4 and air flow path forming member 5 are formed from AFA, the anode spacer 9 is formed from ASS. The anode spacer 9 is positioned between the first frame protrusion 3b of the cell frame 3 and the first separator protrusion 6a of the separator 6. The anode spacer 9 has a first central hole 9a formed in its center. The first central hole 9a communicates with the first hole 3c of the cell frame 3, the second hole 6e of the separator 6, and the through hole 7a of the compression seal 7. In Unit 1 shown in Figure 1, the through-hole 7a, first hole 3c, first central hole 9a, and second hole 6e are arranged in that order from the top to the bottom in the stacking direction of Unit 1, and flow paths for fuel gas are formed inside these through-holes 7a and the like.

[0024] Furthermore, the anode spacer 9 has a pair of opposing long sides 9b. On the upper surface of the long side 9b located on the power generation cell 2 side, a plurality of first grooves (communication openings) 9c are formed to guide fuel gas from the first central hole 9a into the fuel flow path 4a (see Figure 2) of the fuel flow path forming member 4. The first grooves 9c are continuous from the edge of the first central hole 9a to the outer edge of the long side 9b on the power generation cell 2 side.

[0025] The anode spacer member 10 is formed in an elongated ring shape, but is made of the same material as the anode spacer 9. The anode spacer member 10 has a second central hole 10a formed in its center. On the upper surface of the long side portion 10b of the pair of long sides 10b of the anode spacer member 10 that is located on the power generation cell 2 side, a plurality of second groove portions (communication ports) 10c are formed to discharge the fuel gas in the fuel flow path 4a (see Figure 2) of the fuel flow path forming member 4 to the second central hole 10a.

[0026] Furthermore, a frame member 13 having an outer shape corresponding to the outer shapes of the cell frame 3 and the separator 6 is fixed between them. A first holding portion 13a for holding the anode spacer 9 is formed on the frame member 13 at a position corresponding to each anode spacer 9. A second holding portion 13b for holding the anode spacer member 10 is formed on the frame member 13 at a position corresponding to the anode spacer member 10.

[0027] Figure 2 is a schematic cross-sectional view of a solid oxide fuel cell according to the first embodiment. More specifically, Figure 2 schematically shows a cross-section of a part of the solid oxide fuel cell, including two power generation cells 2 aligned along line AA in Figure 1 and in the stacking direction of unit 1. Note that the power generation cell 2 located on the upper side of Figure 2 corresponds to the power generation cell 2 shown in Figure 1.

[0028] As shown in Figure 2, the air channel forming member 5 has a plurality of air channels 5a through which air flows. Cathode spacers 12 made of a metallic conductive material, such as FSS, are provided in the air channels 5a, and the lower surface of the separator 6 is electrically connected to the cathode spacers 12. As a result, the separator 6 is electrically connected to the air electrode of the power generation cell 2 (the power generation cell 2 located on the lower side of Figure 2) via the air channel forming member 5 and the second metal support layer of the second metal support cell (not shown).

[0029] Furthermore, as shown in Figure 2, two adjacent power generation cells 2 in the stacking direction of unit 1 are electrically connected via a current-carrying section 14. The current-carrying section 14 includes a separator 6 that separates the fuel electrode of the power generation cell 2 located on the upper side in the stacking direction from the air electrode of the power generation cell 2 located on the lower side in the stacking direction, a fuel flow path forming member 4 disposed on the upper surface of the separator 6, a first metal support layer of a first metal support cell (not shown) provided on the power generation cell 2 on the upper side in the stacking direction, adjacent to the fuel flow path forming member 4 in the stacking direction of unit 1, an air flow path forming member 5 disposed on the lower surface of the separator 6, and a second metal support layer of a second metal support cell (not shown) provided on the power generation cell 2 on the lower side in the stacking direction, adjacent to the air flow path forming member 5 in the stacking direction of unit 1.

[0030] Furthermore, between two cell frames 3 adjacent to each other in the stacking direction of unit 1, an anode spacer 9, a separator 6, and a compression seal 7 are arranged in order from the top in the stacking direction. The separator 6 has a first bent portion 6f formed by bending its outer circumference perpendicularly to the cell frame 3 located on the upper side in the stacking direction of unit 1, and a second bent portion 6g formed by bending perpendicularly outward from one end of the first bent portion 6f and extending parallel to the cell frame 3. The second bent portion 6g is electrically connected to the cell frame 3 located on the upper side in the stacking direction of unit 1.

[0031] In order to prevent compression leakage of the compression seal 7 at high temperatures in the solid oxide fuel cell and to maintain airtightness between two adjacent units 1, the total thermal expansion of the anode spacer 9, separator 6, and compression seal 7 is set to be greater than the thermal expansion of the energized section 14. In this embodiment, the total thermal expansion of the ASS constituting the anode spacer 9, the AFA constituting the separator 6, and the thermiculite constituting the compression seal 7 is set to be greater than the total thermal expansion of the FSS constituting the fuel flow path forming member 4 and air flow path forming member 5, the thermal expansion of the AFA constituting the separator 6, the thermal expansion of the material constituting the cathode spacer 12, for example, the FSS, and the thermal expansion of the first and second metal support cells (not shown). As shown in Figure 2, since the majority of the length of the energized section 14 along the stacking direction of the unit 1 is occupied by the fuel flow path forming member 4 and the air flow path forming member 5, the thermal expansion of the energized section 14 is highly dependent on the material of the fuel flow path forming member 4 and the air flow path forming member 5. In this way, by setting the total thermal expansion amount of the anode spacer 9, separator 6, and compression seal 7, and the thermal expansion amount of the energized section 14, the compression seal 7 is always kept compressed when the solid oxide fuel cell is at high temperatures, and airtightness between two adjacent units 1 is ensured.

[0032] Furthermore, since the anode spacer 9 presses against the compression seal 7 via the separator 6, the pressing force on the compression seal 7 can be controlled by changing the material of the anode spacer 9 to alter its coefficient of thermal expansion. In this embodiment, the anode spacer 9 is made of ASS, but if AFA, which has a lower coefficient of thermal expansion than ASS, is used as the material for the anode spacer 9, the pressing force on the compression seal 7 can be reduced, thereby decreasing the airtightness between two adjacent units 1.

[0033] As described above, in the first embodiment, the total thermal expansion of the anode spacer 9, separator 6, and compression seal 7 is set to be greater than the thermal expansion of the energized section 14. Therefore, when the solid oxide fuel cell is at a high temperature, the anode spacer 9 continues to press against the compression seal 7 via the separator 6 between two cell frames 3 adjacent to each other in the stacking direction of the unit 1, thus maintaining the compressed state of the compression seal 7. Consequently, the airtightness between two adjacent units 1 in the stacking direction can be improved.

[0034] Furthermore, in this embodiment, the separator 6, the first metal support layer of the first metal support cell, the second metal support layer of the second metal support cell, the fuel flow path forming member 4, and the air flow path forming member 5 are electrically joined. More specifically, the separator 6 is electrically connected to the fuel flow path forming member 4 and electrically connected to the air flow path forming member 5 via the cathode spacer 12. In addition, the fuel flow path forming member 4 is electrically connected to the first metal support layer of the first metal support cell, while the air flow path forming member 5 is electrically connected to the second metal support layer of the second metal support cell. Therefore, with the separator 6 fixed at the energized part 14, when the anode spacer 9 expands at high temperatures in the solid oxide fuel cell, the separator 6 deforms toward the compression seal 7 in accordance with the expansion of the anode spacer 9. Thus, the sealing performance of the compression seal 7 can be improved.

[0035] Figure 3 is a schematic cross-sectional view of the solid oxide fuel cell of the second embodiment. Figure 4 is a schematic cross-sectional view of the anode spacer 9 of the second embodiment.

[0036] In the second embodiment, the anode spacer 9 is composed of two parts, a first anode spacer 15 and a second anode spacer 16. The anode spacer 9 may be composed of three or more parts instead of just two. As shown in Figure 3, the second anode spacer 16 is positioned below the first anode spacer 15 in the stacking direction of unit 1. The second anode spacer 16 is formed of a material with a different coefficient of thermal expansion than the first anode spacer 15. More specifically, the second anode spacer 16 is formed of a material with a larger coefficient of thermal expansion than the first anode spacer 15. In this embodiment, the first anode spacer 15 is formed of AFA, while the second anode spacer 16 is formed of ASS. Furthermore, if the first anode spacer 15 is formed of FSS, the second anode spacer 16 is formed of ASS or AFA.

[0037] As shown in Figure 4, the lower surface 15a of the first anode spacer 15 has a plurality of first recesses 17 that are recessed upward from the lower surface 15a. The first recesses 17 have a trapezoidal cross-sectional shape that widens towards the lower surface 15a. The first recesses 17 have a bottom portion 17a and a pair of first inclined portions 17b that are inclined in a widening manner towards the lower surface 15a from both ends of the bottom portion 17a. The first recesses 17 are formed, for example, by press working. Alternatively, the first recesses 17 may be formed by etching instead of press working.

[0038] Similarly, as shown in Figure 4, the upper surface 16a of the second anode spacer 16 has a plurality of second recesses 18 that are recessed downward from the upper surface 16a. The second recesses 18 have a trapezoidal cross-sectional shape that widens towards the upper surface 18a. The second recesses 18 are formed, for example, by press working. Alternatively, the second recesses 18 may be formed by etching instead of press working. Between two adjacent second recesses 18 in the left-right direction in Figure 4, a convex portion 19 with a trapezoidal cross-sectional shape is formed. The cross-sectional shape of the convex portion 19 is larger than the cross-sectional shape of the first recess 17. The convex portion 19 has the upper surface 16a described above and a pair of second inclined portions 19a that are inclined in a widening manner from both ends of the upper surface 16a toward the opposite side of the first anode spacer 15. As shown in Figure 4, the portion of the convex portion 19 toward the upper surface 16a is fitted into the opening surface side of the first recess 17 of the first anode spacer 15. A first gas passage (communication port) 20 is formed between the convex portion 19 and the first recess 17 through which fuel gas flows. Similarly, a second gas passage (communication port) 21 is formed between the portion of the first anode spacer 15 other than the first recess 17 and the second recess 18 of the second anode spacer 16 through which fuel gas flows.

[0039] As described above, the second anode spacer 16 is made of a material with a higher coefficient of thermal expansion than the first anode spacer 15. Therefore, at high temperatures in the solid oxide fuel cell, the expansion of the convex portion 19 of the second anode spacer 16 becomes greater than the expansion of the first concave portion 17 of the first anode spacer 15. As a result, the expansion of the first concave portion 17 cannot keep up with the expansion of the convex portion 19 (indicated by arrow P in Figure 4), and the first inclined portion 17b of the first concave portion 17 slides upward along the second inclined portion 19a of the convex portion 19, causing the first anode spacer 15 to be lifted in the direction indicated by arrow Q in Figure 4. The reaction force when the first anode spacer 15 is lifted causes the second anode spacer 16 to press against the compression seal 7 via the separator 6.

[0040] Furthermore, since ASS is prone to oxidation scale peeling, it is preferable to select FSS as the material for the first anode spacer 15 and AFA as the material for the second anode spacer 16.

[0041] As described above, in the second embodiment, the anode spacer 9 includes a first anode spacer 15 and a second anode spacer 16 having a different coefficient of thermal expansion than the first anode spacer 15. Therefore, by appropriately selecting the materials of the first anode spacer 15 and the second anode spacer 16, the pressing force of the compression seal 7 via the separator 6 can be adjusted, and the airtightness between two adjacent units 1 in the stacking direction of the unit 1 can be precisely controlled.

[0042] Furthermore, in this embodiment, the lower surface 15a of the first anode spacer 15 has a first recess 17 having a pair of first inclined portions 17b, while the upper surface 16a of the second anode spacer 16 has a convex portion 19 having a pair of second inclined portions 19a. The convex portion 19 of the second anode spacer 16 fits into the first recess 17 of the first anode spacer 15. Therefore, if the materials of both are selected such that the coefficient of thermal expansion of the second anode spacer 16 is higher than that of the first anode spacer 15, the difference in their expansion amounts will cause the expansion amount of the first recess 17 to be unable to keep up with the expansion amount of the convex portion 19, as described above. As a result, the first inclined portion 17b of the first recess 17 slides upward along the second inclined portion 19a of the convex portion 19, lifting the first anode spacer 15. Furthermore, the reaction force when the first anode spacer 15 is lifted causes the second anode spacer 16 to press against the compression seal 7 via the separator 6, thereby improving the sealing performance of the compression seal 7.

[0043] Furthermore, in this embodiment, a first gas passage 20 through which fuel gas flows is formed between the convex portion 19 of the second anode spacer 16 and the first concave portion 17 of the first anode spacer 15. Therefore, the first gas passage 20 can be efficiently formed by utilizing the shapes of the first anode spacer 15 and the second anode spacer 16.

[0044] Figure 5 is a schematic cross-sectional view of a solid oxide fuel cell according to the third embodiment. In the third embodiment, unlike the first and second embodiments, the separator 6 has an expandable portion 22 formed adjacent to the outer end 16a of the second anode spacer 16. This expandable portion 22 is formed to be elastically deformable in the stacking direction of the unit 1. The expandable portion 22 is configured to be folded to form a concave folded portion relative to the second anode spacer 16, that is, to be folded downward in the stacking direction of the unit 1 so as to be separated from the second anode spacer 16, and then folded back upward in the stacking direction of the unit 1. The expandable portion 22 has a gradient portion 22a that extends outward from a position adjacent to the outer end 16b of the second anode spacer 16 in the stacking direction of the unit 1 while inclining downward, and a straight portion 22b that extends from one end of the gradient portion 22a upward in the stacking direction of the unit 1 so as to be perpendicular to the cell frame 3. Furthermore, the expandable portion 22 may be formed not at a position adjacent to the outer end portion 16b of the second anode spacer 16 within the separator 6, but at a position adjacent to the inner end portion 16c of the second anode spacer 16 within the separator 6.

[0045] Furthermore, the expandable portion 22 may be formed to be convex relative to the second anode spacer 16, rather than forming a concave folded portion relative to the second anode spacer 16. In this case, the expandable portion 22 is formed by folding the separator 6 from a position adjacent to the outer end 16a of the second anode spacer 16 toward the upper side in the stacking direction of the unit 1, and then folding it toward the lower side in the stacking direction of the unit 1.

[0046] Alternatively, instead of forming a concave or convex folded portion on the separator 6, the concave or convex folded portion may be formed on the cell frame 3.

[0047] As described above, in the third embodiment, the expandable portion 22 is formed to be elastically deformable in the stacking direction of the unit 1. The expandable portion 22 is formed on the separator 6 and has a folded portion that is concave with respect to the second anode spacer 16. As described above in the first embodiment, the second folded portion 6g of the separator 6 is electrically connected to the cell frame 3 located on the upper side in the stacking direction of the unit 1. Therefore, if the expandable portion 22 is not formed on the separator 6, the first anode spacer 15 and the second anode spacer 16 will be pulled toward the cell frame 3, and there is a risk that the followability of the separator 6 will deteriorate when the first anode spacer 15 and the second anode spacer 16 expand at high temperatures in the solid oxide fuel cell. Therefore, as in this embodiment, by forming an expandable / contractable portion 22 on the separator 6 that can be elastically deformed in the stacking direction of unit 1, the separator 6 bends appropriately toward the compression seal 7 side via the expandable / contractable portion 22 when the first anode spacer 15 and the second anode spacer 16 expand. As a result, the first anode spacer 15 and the second anode spacer 16 press appropriately against the compression seal 7 via the separator 6, thereby improving the sealing performance of the compression seal 7. [Explanation of Symbols]

[0048] 1 unit 2. Power generation cell 3-cell frame 4. Fuel flow path forming member 5. Air channel forming member 6... Separator 7. Compression seal 9. Anode Spacer 14. Power supply section 15. First anode spacer 16. Second anode spacer 17. First recess 17b...First slope part 19···Convex part 19a...Second slope part 22...Extendable part

Claims

1. The unit assembly comprises a plurality of stacked units, each including a cell, a cell frame that holds the cell, a separator that separates the fuel electrode and the air electrode and faces the cell and the cell frame, and a spacer sandwiched between the cell frame and the separator, having a communication port through which gas flows. Between two adjacent cells in the stacking direction of the aforementioned unit, an energizing section is arranged to electrically connect them. On the opposite side of the spacer, with the separator in between, a compression seal is positioned to airtightly seal the space between two adjacent units in the stacking direction. An electrochemical cell characterized in that the total thermal expansion of the spacer, the separator, and the compression seal is greater than the thermal expansion of the energized portion.

2. The electrochemical cell according to claim 1, characterized in that the spacer is composed of at least two parts, comprising a first spacer and a second spacer having a different coefficient of thermal expansion than the first spacer.

3. The electrochemical cell according to claim 2, characterized in that the first spacer and the second spacer are fitted together via a recess and a protrusion having an inclined portion.

4. The electrochemical cell according to claim 3, characterized in that the recess and the protrusion form the communication port through which the gas flows.

5. The electrochemical cell according to any one of claims 1 to 4, characterized in that at least one of the separator and the cell frame has an expandable portion that is elastically deformable in the stacking direction at at least one of the inner end and outer end of the spacer.

6. The electrochemical cell according to claim 5, characterized in that the expandable portion is formed in the separator and is configured as a folded portion that is concave or convex with respect to the spacer.

7. The energizing section comprises the separator, a first metal support cell having a first metal support layer provided on the side of the fuel electrode facing the separator, a second metal support cell having a second metal support layer provided on the side of the air electrode facing the separator, a fuel channel forming member that forms a fuel channel supplied to the fuel electrode, and an air channel forming member that forms an air channel supplied to the air electrode. The electrochemical cell according to claim 1, wherein the separator, the first metal support layer, the second metal support layer, the fuel flow path forming member, and the air flow path forming member are electrically bonded.

8. The electrochemical cell according to claim 7, characterized in that the fuel flow path forming member, the air flow path forming member, the separator, and the cell frame are made of alumina scale forming austenitic stainless steel containing 1 to 6% aluminum.

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