Electrochemical reaction cell stack, and channel forming member for electrochemical reaction cell stack

Abstract

To ensure the stress relaxation properties of a flow passage forming member, and suppress gas leakage from the flow passage forming member compared to a configuration in which the layered particles are uniformly oriented along the second direction.SOLUTION: An electrochemical reaction cell stack includes a plurality of single cells, and a communication passage is formed that communicates with a gas chamber that faces one of an air electrode and a fuel electrode. The electrochemical reaction cell stack includes a first member, a second member arranged to face the first member, a gas flow passage arranged between the first member and the second member, and including the gas chamber and the communication passage, and a flow passage forming member separating the gas passage from a space other than the gas passage. The flow passage forming member has a layered structure made of a plurality of layered particles. There is a first layered particle located at an end of the flow passage forming member, the first angle of the first layered particle is different from a second angle of a centrally located second layered particle.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The technology disclosed in this specification relates to a flow path forming member for an electrochemical reaction cell stack.

Background Art

[0002] As one type of fuel cell that generates electricity by utilizing an electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") including an electrolyte layer containing a solid oxide is known. SOFCs are generally used in the form of a fuel cell stack in which a plurality of structural units (electrochemical reaction units) are arranged side by side in a predetermined direction. Each electrochemical reaction unit includes a single cell including an electrolyte layer containing a solid oxide, an air electrode and a fuel electrode facing each other with the electrolyte layer interposed therebetween, an air flow path facing the air electrode, and an air electrode frame and a fuel electrode frame respectively surrounding the periphery of the fuel flow path facing the fuel electrode. The air electrode frame is formed of, for example, mica (see Patent Document 1). Mica has a layered structure composed of a plurality of layered particles laminated in the above-mentioned predetermined direction. Therefore, the stress generated in the fuel cell stack can be relaxed by the air electrode frame.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The air electrode frame is preferably positioned to separate the air electrode from the space other than the air electrode (e.g., the external space) to suppress gas leakage from the air passage facing the air electrode. However, conventional mica used in air electrode frames has a layered structure in which multiple layered particles are arranged parallel to each other along a plane direction perpendicular to the predetermined direction. As a result, there is a risk that gas in the air passage may leak into the external space through the gaps between the layered particles. If gas leakage occurs from the air passage, problems such as a decrease in the power generation efficiency of the fuel cell may occur.

[0005] Such problems are also common to electrolytic cell stacks, which comprise multiple electrolytic cell units, the constituent units of solid oxide type electrolytic cells (hereinafter referred to as "SOECs") that produce hydrogen using the electrolysis reaction of water. Furthermore, such problems are common not only to SOFCs and SOECs, but also to other types of electrochemical reaction cell stacks. Moreover, such problems are common not only to air electrode frames, but also to other channel forming members. A channel forming member is a member that is placed between two members constituting an electrochemical reaction cell stack and separates a predetermined gas channel formed in the electrochemical reaction cell stack from the surrounding space, and is a member having a layered structure consisting of multiple layered particles. [Means for solving the problem]

[0006] (1) The electrochemical reaction cell stack disclosed herein comprises a plurality of single cells, each containing an electrolyte layer and an air electrode and a fuel electrode facing each other with the electrolyte layer in between. The electrochemical reaction cell stack has a communication passage that communicates with a gas chamber facing one of the air electrode and the fuel electrode. The electrochemical reaction cell stack has a first member, a second member disposed opposite to the first member, and a channel forming member disposed between the first member and the second member, separating a gas flow path including the gas chamber and the communication passage from a space other than the gas flow path. The channel forming member has a layered structure consisting of a plurality of layered particles stacked in a first direction in which the first member and the second member face each other. In the flow channel forming member, in at least one specific cross section along the first direction, there exists a first layered particle located at the end of the flow channel forming member in a second direction perpendicular to the first direction, wherein the first angle with respect to the second direction is different from the second angle made with respect to the second direction by a second layered particle located in the center of the flow channel forming member in the second direction.

[0007] In this electrochemical reaction cell stack, the presence of the second layered particles ensures stress relaxation in the channel-forming member. Furthermore, the presence of the first layered particles suppresses gas leakage from the gas chamber into the external space by passing between the granular elements constituting the channel-forming member. Therefore, this electrochemical reaction cell stack can suppress gas leakage from the channel-forming member while ensuring stress relaxation in the channel-forming member, compared to a configuration where the layered particles are uniformly aligned in the second direction.

[0008] (2) In the electrochemical reaction cell stack described above, the absolute value of the difference between the first angle and the second angle may be 1.4 degrees or more. With this electrochemical reaction cell stack, for example, gas leakage from the flow path forming member can be effectively suppressed compared to a configuration in which the absolute value of the difference between the first angle and the second angle is less than 1.4 degrees.

[0009] (3) In the electrochemical reaction cell stack described above, the absolute value of the first angle may be less than 90 degrees. With this electrochemical reaction cell stack, for example, compared to a configuration in which the absolute value of the first angle is 90 degrees, it is possible to suppress the decrease in stress relaxation of the flow channel forming member caused by the presence of the first layered particles.

[0010] (4) In the electrochemical reaction cell stack described above, the width of the channel forming member in the second direction may be three times or more the width in the first direction in the specific cross-section. With this electrochemical reaction cell stack, for example, compared to a configuration in which the width of the channel forming member in the second direction is less than three times the width in the first direction, the longer path within the channel forming member between the gas chamber and the external space allows for effective suppression of gas leakage from the channel forming member while ensuring stress relaxation of the channel forming member.

[0011] (5) The channel forming member disclosed herein is a channel forming member for an electrochemical reaction cell stack, having a layered structure consisting of a plurality of layered particles stacked in a first direction, wherein in at least one specific cross section of the channel forming member along the first direction, there exists a first layered particle located at the end of the channel forming member in a second direction perpendicular to the first direction, wherein the first angle with respect to the second direction is different from the second angle made with respect to the second direction by a second layered particle located in the center of the channel forming member in the second direction. With this channel forming member, while ensuring the stress relaxation properties of the channel forming member, gas leakage from the channel forming member can be suppressed compared to a configuration in which the layered particles are uniformly aligned along the second direction. [Brief explanation of the drawing]

[0012] [Figure 1] Perspective view showing the external configuration of the fuel cell stack of the embodiment. [Figure 2] A cross-sectional view showing the fuel cell stack of the embodiment, cut along the line II-II in Figure 1. [Figure 3] A cross-sectional view showing the fuel cell stack of the embodiment, cut along the line III-III in Figure 1. [Figure 4] Cross-sectional view showing the fuel cell stack of the embodiment cut along line IV-IV in FIG. 1 [Figure 5] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment cut at the same position as line II-II in FIG. 1 [Figure 6] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the embodiment cut at the same position as line III-III in FIG. 1 [Figure 7] Schematic diagram showing an enlarged view of the first portion X1 of the air electrode frame 130 in FIG. 5 [Figure 8] Schematic diagram showing the layered structure in the divided region E1 of the air electrode frame 130 in FIG. 7 [Figure 9] Schematic diagram showing the manufacturing method of each portion X1 - X4 of the air electrode frame 130 [Figure 10] Explanatory diagram showing the gas flow of the air electrode frame 130 of the embodiment and the air electrode frame 130X of the comparative example

Mode for Carrying Out the Invention

[0013] Specific examples of the technology disclosed by this specification will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0014] <Embodiment> The embodiment will be described with reference to FIGS. 1 to 10. The fuel cell stack 10 (an example of an electrochemical reaction cell stack) of the present embodiment is used for a solid oxide type fuel cell including an electrolyte layer 112 containing a solid oxide.

[0015] (Overall Configuration of Fuel Cell Stack 10) As shown in FIGS. 1 to 4, the fuel cell stack 10 includes a power generation block 100, a terminal separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the terminal separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have substantially the same-sized rectangular outer shapes and are arranged to overlap in this order in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0016] As shown in FIGS. 1 and 4, the fuel cell stack 10 has bolt holes BH penetrating from the first end plate 210 to the second end plate 270 near each of the four corners. Bolts B are inserted into each bolt hole BH. Nuts N are screwed onto both ends of each bolt B. These bolts B and nuts N integrally fasten the members from the first end plate 210 to the second end plate 270. As shown in FIGS. 2 to 4, the first plate 232 is supported by the terminal separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0017] As shown in FIGS. 2 to 4, the power generation block 100 is composed of a plurality (seven in this embodiment) of electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction units 100U") arranged side by side in a predetermined arrangement direction (the vertical direction in FIG. 2).

[0018] (Overall configuration of the electrochemical reaction unit 100U) As shown in Figures 5 and 6, the electrochemical reaction unit 100U comprises a single cell 110, a single cell separator 120 (an example of a first component), an air electrode frame 130, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190, and two IC separators 180 (an example of a second component). One IC separator 180, the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are each supported by the two IC separators 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnectors 190.

[0019] As shown in Figures 5 and 6, the IC separator 180 and interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Figure 2, one of the multiple reaction units 100U located at one end (the lower end in Figure 2) does not have an IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 is superimposed on the fuel electrode frame 140.

[0020] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, and a fuel electrode 116. As shown in Figures 5 and 6, the air electrode 114, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the air electrode 114. The single cell 110 of this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116.

[0021] The electrolyte layer 112 is a rectangular, flat member having one side on which the air electrode 114 is located (the upper side in Figures 5 and 6) and another side parallel to the air electrode 116 (the lower side in Figures 5 and 6). The electrolyte layer 112 is a layer containing a solid oxide (for example, YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (for example, LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements (e.g., Sr) diffused from the air electrode 114 with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0022] (Single-cell separator 120) As shown in Figures 5 and 6, the single-cell separator 120 is a rectangular frame-shaped member having a roughly rectangular through-hole 121 near the center, and is made of, for example, metal. The thickness of the single-cell separator 120 is relatively thin, for example, 0.05 mm or more and 0.2 mm or less. The periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is located: the upper surface in Figures 5 and 6) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing).

[0023] (Air pole frame 130) As shown in Figures 5 and 6, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through-hole 131 near the center, and is formed of, for example, mica. The thickness of the air electrode frame 130 is preferably 0.5 mm or more and 5 mm or less.

[0024] (Fuel pole frame 140) As shown in Figure 6, the fuel electrode frame 140 is a rectangular frame-shaped member having a roughly rectangular through-hole 141 near the center, and is made of, for example, metal.

[0025] (IC separator 180) As shown in Figures 5 and 6, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center, and is made of, for example, metal.

[0026] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 5 and 6, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are conductive and made of metal (for example, ferritic stainless steel). The coating layer 193 is conductive and is arranged to cover the surface of the air electrode current collectors 192 and the surface of the flat plate portion 191 on which the air electrode current collectors 192 are arranged. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0027] The fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 5 and 6, the fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 connecting the electrode-facing portion 145 and the interconnector-facing portion 146, and is U-shaped overall. The electrode-facing portion 145 is in contact with the fuel electrode 116, and the interconnector-facing portion 146 is in contact with the flat plate portion 191 of the interconnector 190.

[0028] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 5 and 6, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent reaction units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent reaction units 100U.

[0029] However, as described above, the reaction unit 100U located at one end (the lower end of Figure 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this reaction unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0030] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the reaction unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained well.

[0031] (Air chamber 313 and fuel chamber 323) As shown in Figures 5 and 6, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 (an example of a gas chamber) through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0032] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0033] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single-cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent reaction units 100U.

[0034] (First end plate 210) The first end plate 210 is a component formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. As shown in Figures 1 to 4, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that protrude from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is formed around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner projection 214 is formed around the entire circumference of the inner peripheral portion of the planar portion 211.

[0035] (Insulation part 220) The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of, for example, an insulating material. As shown in Figure 2, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230.

[0036] (End separator 230) As shown in Figures 2 to 4, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near the center, and is made of, for example, metal.

[0037] (Plate 1, No. 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 to 4, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0038] The first plate 232 is connected to an interconnector 190 provided on a reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via a connecting member with the same structure as the fuel electrode current collector 144. In this way, the reaction unit 100U and the first plate 232 are electrically connected.

[0039] (Terminal 1 Plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0040] (Terminal 2 Plate 250) The second terminal plate 250 is a rectangular plate-shaped member, formed from a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. As described above, the second terminal plate 250 is connected to a fuel electrode 116 provided on a reaction unit 100U located at one end (the lower end in Figure 2) of the plurality of reaction units 100U via a fuel electrode current collector 144, thereby electrically connecting this reaction unit 100U and the second terminal plate 250. One end of the second terminal plate 250 (the right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0041] (Plate 2, page 260) The second plate 260 is a rectangular, flat member, formed of, for example, an insulating material. The peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0042] (Second end plate 270) The second end plate 270 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. The second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 projecting from the planar portion 271 in the opposite direction to the second terminal plate 250 (downward in Figure 2). The planar portion 271 has holes that constitute the bolt holes BH described above. The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is formed around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is formed around the entire circumference of the inner peripheral portion of the planar portion 271.

[0043] (Manifolds 311, 312, 321, 322) As shown in Figures 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are, respectively, an oxidizer gas supply manifold 311 (an example of a connecting passage), an oxidizer gas discharge manifold 312 (an example of a connecting passage), a fuel gas supply manifold 321, and a fuel gas discharge manifold 322.

[0044] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chamber 313 of each reaction unit 100U. The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chamber 313 of each reaction unit 100U, to the outside of the fuel cell stack 10. For example, air is used as the oxidizer gas OG. The oxidizer gas supply manifold 311 and the oxidizer gas discharge manifold 312 are located on opposite sides of the air chamber 313.

[0045] As shown in Figure 3, the fuel gas supply manifold 321 is a gas passage that supplies fuel gas FG, introduced from outside the fuel cell stack 10, to the fuel chamber 323 of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas passage that discharges fuel off-gas FOG, discharged from the fuel chamber 323 of each reaction unit 100U, to the outside of the fuel cell stack 10. For example, hydrogen-rich gas obtained by reforming city gas is used as the fuel gas FG. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are located on opposite sides of the fuel chamber 323.

[0046] As shown in Figure 5, the air electrode frame 130 has an oxidant gas supply communication channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communication channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312.

[0047] Furthermore, as shown in Figure 6, each fuel electrode frame 140 has a fuel gas supply communication passage 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication passage 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

[0048] (Gas passage member 280) Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 2 and 3. The main body portion 281 is cylindrical with open ends. The flange portion 282 is provided so as to protrude outward from one end of the main body portion 281 (the lower end in Figure 2). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284. One end of the main body portion 281 provided on the four gas passage members 280 (the upper end in Figures 2 and 3) is joined to the second end plate 270, for example by welding, and the internal space of the main body portion 281 communicates with the manifolds 311, 312, 321, and 322, respectively. Gas piping for gas supply or discharge is connected to each main body portion 281.

[0049] (Operation of fuel cell stack 10) As shown in Figures 2 and 5, the oxidizer gas OG is supplied to the oxidizer gas supply manifold 311 via the gas passage member 280 and then supplied to the air chamber 313 via the oxidizer gas supply communication channel 132. The oxidizer gas OG flows through the inside of the air chamber 313 from the oxidizer gas supply communication channel 132 toward the oxidizer gas discharge communication channel 133.

[0050] Furthermore, as shown in Figures 3 and 6, the fuel gas FG is supplied from the gas piping to the fuel gas supply manifold 321 via the gas passage member 280, and then supplied to the fuel chamber 323 via the fuel gas supply communication channel 142 through the holes that make up the fuel gas supply manifold 321 in each fuel electrode frame 140.

[0051] When oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures conductivity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end of Figure 2), and the first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end of Figure 2). As a result, the electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0052] As shown in Figures 2 and 5, the oxidizer off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidizer gas discharge manifold 312 via the oxidizer gas discharge communication channel 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in Figures 3 and 6, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 via the fuel gas discharge communication channel 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0053] (Detailed configuration of the air pole frame 130) As described above, the air electrode frame 130 (an example of a flow path forming member) is positioned between the single-cell separator 120 and the IC separator 180. Hereinafter, the space including the air chamber 313, the oxidizer gas supply manifold 311, and the oxidizer gas discharge manifold 312 will be referred to as the "oxidizer gas flow path." The air electrode frame 130 separates the oxidizer gas flow path from the fuel chamber 323 (an example of a space other than the gas flow path) and the external space of the fuel cell stack 10 (an example of a space other than the gas flow path).

[0054] Specifically, as shown in Figure 5, a first portion X1 of the air electrode frame 130, between the through-hole constituting the oxidant gas supply manifold 311 and the outer circumferential surface of the air electrode frame 130, separates the oxidant gas flow path from the external space of the fuel cell stack 10. A second portion X2 of the air electrode frame 130, between the through-hole constituting the oxidant gas discharge manifold 312 and the outer circumferential surface of the air electrode frame 130, separates the oxidant gas flow path from the external space of the fuel cell stack 10. Furthermore, as shown in Figure 6, a third portion X3 of the air electrode frame 130, between the through-hole constituting the fuel gas supply manifold 321 and the through-hole 131, separates the oxidant gas flow path from the fuel gas supply manifold 321 (fuel chamber 323). Of the air electrode frame 130, the fourth portion X4 between the through-hole and the through-hole 131 that constitute the fuel gas exhaust manifold 322 separates the oxidizer gas flow path from the fuel gas exhaust manifold 322 (fuel chamber 323).

[0055] The air electrode frame 130 (each portion X1 to X4) has a layered structure consisting of multiple layered particles 400 stacked in the predetermined arrangement direction (up and down direction in Figure 2, an example of the first direction) in which the single-cell separator 120 and the IC separator 180 face each other. Specifically, the air electrode frame 130 is formed of mica as described above.

[0056] Here, in the air electrode frame 130, in at least one specific cross section (e.g., XZ cross section) along the alignment direction, there are first layered particles 400R, 400L and second layered particles 400C. The first layered particle 400R is a layered particle 400 located at the right end of each part X1 to X4 of the air electrode frame 130 in a planar direction perpendicular to the alignment direction (an example of the second direction, left-right direction in Figure 2). The first layered particle 400L is a layered particle 400 located at the left end of each part X1 to X4 of the air electrode frame 130 in the planar direction. The second layered particle 400C is a layered particle 400 located in the central part of each part X1 to X4 (the part through which the center line C passes) in the planar direction.

[0057] For the first layered particles 400R and 400L, the relative angle with respect to a predetermined reference vector V along the plane direction is defined as the first angle θ1, and for the second layered particle 400C, the relative angle with respect to the reference vector V is defined as the second angle θ2. There is a difference between the first angle θ1 of the first layered particle 400R and the second angle θ2 of the second layered particle 400C. Also, there is a difference between the first angle θ1 of the first layered particle 400L and the second angle θ2 of the second layered particle 400C.

[0058] The following will be a detailed explanation using the first part X1 of the air electrode frame 130 as an example. As shown in Figure 7, the first part X1 of the air electrode frame 130 is divided into 10 regions at equal intervals in the arrangement direction (Z-axis direction). Each divided region is called a divided region E (E1 to E10). In at least one divided region E, there should be a difference between the first angle θ1 of at least one of the first layered particles 400R, 400L and the second angle θ2 of the second layered particle 400C. In each part X1 to X4 of the air electrode frame 130, the number of regions (number of divided regions E) where there is an angle difference between the first angle θ1 and the second angle θ2 is preferably 30% or more of the total region (10 divided regions E), and more preferably 50% or more.

[0059] Figure 8 shows the reference vector V and the measurement regions TR, TL, and TC. The reference vector V is parallel to the plane direction (X-axis direction) and points in the negative X-axis direction. The first angle θ1 and the second angle θ2 are both positive angles when the layered particle 400 is tilted upward (towards the positive Z-axis direction) with respect to the reference vector V, and negative angles when the layered particle 400 is tilted downward (towards the negative Z-axis direction) with respect to the reference vector V. The measurement regions TR, TL, and TC are regions for specifying the first angle θ1 and the second angle θ2. The measurement regions TR, TL, and TC are all the same size, have a predetermined width W (e.g., 300 μm) in the plane direction, and have the same height H as the divided region E.

[0060] As shown in Figure 8, in order to determine the first angle θ1 of the first layered particle 400R, the right-hand side of the measurement area TR located on the right side coincides with the right end of the air electrode frame 130. Multiple first layered particles 400R exist in this measurement area TR. For each first layered particle 400R, the relative angle with respect to the reference vector V, with the right end as the starting point, is determined as the respective first angle θ1. Note that the first angle θ1 of the first layered particle 400R shown in Figure 8 is a positive angle. The average value of the first angle θ1 of all first layered particles 400R present in the measurement area TR is taken as the first angle θ1 of the first layered particle 400R in the divided area E1.

[0061] To determine the first angle θ1 of the first layered particle 400L, the left-hand side of the measurement area TL located on the left side coincides with the left end of the air electrode frame 130. Multiple first layered particles 400L exist in this measurement area TL. For each first layered particle 400L, the relative angle with respect to the reference vector V, with the right end as the starting point, is determined as its respective first angle θ1. Note that the first angle θ1 of the first layered particle 400L shown in Figure 8 is a negative angle. The average value of the first angle θ1 of all first layered particles 400L present in the measurement area TL is taken as the first angle θ1 of the first layered particle 400L in the divided area E1.

[0062] To determine the second angle θ2 of the second layered particle 400C, the measurement area TC includes the central part (center line C) of the first part X1. Multiple second layered particles 400C exist within this measurement area TC. For each second layered particle 400C, the relative angle with respect to the reference vector V, with the right end as the starting point, is determined as its respective second angle θ2. Note that the second angle θ2 of the second layered particle 400C shown in Figure 8 is a positive angle. The average value of the second angle θ2 of all second layered particles 400C present in the measurement area TC is taken as the second angle θ2 of the second layered particle 400C in the divided area E1.

[0063] Next, it is preferable that the absolute value of the difference between the first angle θ1 of the first layered particle 400R and the second angle θ2 of the second layered particle 400C is 1.4 degrees or more. Furthermore, it is preferable that the absolute value of the difference between the first angle θ1 of the first layered particle 400L and the second angle θ2 of the second layered particle 400C is 1.4 degrees or more.

[0064] The absolute value of the first angle θ1 of the first layered particle 400R is preferably less than 90 degrees. Furthermore, the absolute value of the first angle θ1 of the first layered particle 400L is also preferably less than 90 degrees.

[0065] In a specific cross-section, it is preferable that the planar width D of each portion X1 to X4 of the air electrode frame 130 is at least three times the vertical height H (see Figure 7).

[0066] (Manufacturing method for air pole frame 130) As described above, in each portion X1 to X4 of the air electrode frame 130, within the same divided region E, the second layered particle 400C located in the center is substantially parallel to the plane direction, while the first layered particles 400R and 400C located at the edges are both inclined with respect to the plane direction. An example of a manufacturing method for each portion X1 to X4 having such a layered structure is as follows.

[0067] As shown in Figure 9, parts X1 to X4 of the air electrode frame 130 can be created by press working the mica material 130A using a mold 500. The mica material 130A has a layered structure in which almost all of the layered particles are aligned in the planar direction (the X-axis direction in Figure 9). The mold 500 includes a first mold 510 and a second mold 520. The first mold 510 has a base portion 512 and a peripheral wall portion 514. The peripheral wall portion 514 is a cylindrical portion that surrounds the mica material 130A. The base portion 512 is a flat plate-like portion that seals one end of the peripheral wall portion 514 (the positive Z-axis direction side in Figure 9). A groove 513 is formed on the peripheral edge of the surface of the base portion 512 that faces inward towards the peripheral wall portion 514. The groove 513 has a tapered surface 515 that is inclined so that its depth increases towards the peripheral wall portion 514. The second mold 520 is a flat plate-shaped member that can enter the peripheral wall portion 514 of the first mold 510.

[0068] For example, mica material 130A is placed on the second mold 520, and the mica material 130A is pressed between the first mold 510 and the second mold 520. This forms mica material 130B. Mica material 130B has a shape in which the end of mica material 130A has a projection 132B that is inclined along the shape of the groove 513 of the base portion 512. Next, mica material 130C is formed by cutting off a part of the tip of the projection 132B of mica material 130B. This mica material 130C has a layered structure of parts X1 to X4 of the air electrode frame 130.

[0069] (Effects and Benefits) As described above, the fuel cell stack 10 of this embodiment comprises a plurality of electrochemical reaction units 100U. Each electrochemical reaction unit 100U comprises a single cell 110 in which an air electrode 114, an electrolyte layer 112, and a fuel electrode 116 are stacked in this order, an air electrode frame 130 that partitions the air chamber 313 facing the air electrode 114 from the external space, a single cell separator 120 adjacent to the air electrode frame 130, and an IC separator 180 also adjacent to the air electrode frame 130. In each electrochemical reaction unit 100U, in at least one specific cross section (e.g., XZ cross section) along the arrangement direction of the air electrode frame 130, there are first layered particles 400R, 400L and second layered particles 400C. The first angle θ1 of the first layered particles 400R, 400L located at the ends of each section X1 to X4 in the air electrode frame 130 is different from the second angle θ2 of the second layered particle 400C located in the central part of each section X1 to X4. In short, in a specific cross-section of each section X1 to X4, there are first layered particles 400R, 400L located at the ends and inclined with respect to the second layered particle 400C located in the central part.

[0070] According to the above configuration, the presence of the second layered particle 400C in the air electrode frame 130 ensures the stress relaxation properties of the air electrode frame 130. Furthermore, the presence of the first layered particles 400R and 400L suppresses the leakage of gas G (oxidizer gas OG, oxidizer off-gas OOG) in the air chamber 313 from passing between the layered particles 400 constituting the flow path forming member and leaking into the external space or fuel chamber 323. Therefore, according to this embodiment, while ensuring the stress relaxation properties of the air electrode frame 130, gas leakage from the air electrode frame 130 can be suppressed compared to a configuration in which the layered particles are uniformly aligned in the planar direction.

[0071] Specifically, in the comparative example air electrode frame 130X shown in the lower part of Figure 10, not only the second layered particle 400C located in the center, but also the first layered particles 400RX and 400LX located at the ends extend along the plane direction. As a result, the air electrode frame 130X has a relatively large number of paths that extend linearly along the plane direction, making it easy for gas G to leak from the oxidizer gas flow path into other spaces. In contrast, in the air electrode frame 130 of this embodiment shown in the upper part of Figure 10, the second layered particle 400C located in the center extends along the plane direction, while the first layered particles 400RX and 400LX located at the ends are inclined with respect to the plane direction. As a result, the air electrode frame 130 has a relatively large number of paths whose ends are partially inclined with respect to the plane direction, making it less likely for gas G to leak from the oxidizer gas flow path into other spaces.

[0072] In this embodiment, it is preferable that the absolute value of the difference between the first angle θ1 of the first layered particle 400R and the second angle θ2 of the second layered particle 400C is 1.4 degrees or more. With this configuration, for example, gas leakage from the air electrode frame 130 can be effectively suppressed compared to a configuration in which the absolute value of the difference between the first angle θ1 and the second angle θ2 is less than 1.4 degrees.

[0073] In this embodiment, it is preferable that the absolute value of the first angle θ1 of the first layered particles 400R, 400L is less than 90 degrees. With this configuration, for example, compared to a configuration in which the absolute value of the first angle θ1 is 90 degrees, the decrease in the stress relaxation properties of the air electrode frame 130 caused by the presence of the first layered particles 400R, 400L can be suppressed. In this embodiment, the air electrode frame 130 is formed of an insulating material (mica). Therefore, according to this embodiment, compared to a configuration in which the first angle θ1 is 90 degrees, the creepage distance between the single-cell separator 120 and the IC separator 180 passing over the surface of the layered particles 400 is increased, thus improving insulation.

[0074] In this embodiment, it is preferable that the planar width D of each portion X1 to X4 of the air electrode frame 130 in a specific cross-section is three times or more the vertical width (height) H. According to this embodiment, compared to a configuration in which, for example, the planar width D of each portion X1 to X4 of the air electrode frame 130 is less than three times the vertical width H, the longer path within the air electrode frame 130 between the air chamber 313 and the space other than the air chamber 313 (fuel chamber 323 and external space) allows for effective suppression of gas leakage from the air electrode frame 130 while ensuring stress relaxation of the air electrode frame 130.

[0075] (Performance evaluation of this embodiment) Next, the performance evaluation of this embodiment will be described. Nine air electrode frame 130 samples were prepared, and the performance of the fuel cell stack 10 using each sample was evaluated. Table 1 below shows the results of the performance evaluation.

[0076] [Table 1]

[0077] As shown in Table 1, each sample (Samples S1 to S9) has basically the same configuration as the air electrode frame 130 described above and was manufactured by the manufacturing method described above. However, at least one of the following elements differs between the air electrode frames 130 of the nine samples (Samples S1 to S9). • The first angle θ1 of the first layered particles 400R, 400L located at the ends • The second angle θ2 of the second layered particle 400C located in the central part • The angle difference between the first angle θ1 and the second angle θ2 • The ratio of width D to height H of the part of the air pole frame 130 that separates space. The method for obtaining these values ​​is as follows: A cross-section of the air electrode frame 130 of each sample is photographed, for example, using a scanning electron microscope (SEM). By performing image analysis on the resulting SEM images, the above values ​​for each sample can be obtained.

[0078] (1) Regarding initial power generation performance For each fuel cell stack 10 using the sample, oxidizer gas OG was supplied to the air electrode 114 at approximately 700°C, fuel gas FG was supplied to the fuel electrode 116, and the current density was 0.55 A / cm². 2 The output voltage of a single 110 cell was measured at that time, and this measured value was defined as the initial voltage (output voltage before rated power generation operation).

[0079] Regarding the initial power generation performance of the fuel cell stack 10, for each sample, those with an initial voltage equal to or greater than a predetermined first judgment threshold were evaluated as "Good (△)", and those with an initial voltage below the first judgment threshold were evaluated as "Poor (×)". Samples with an initial voltage equal to or greater than a second judgment threshold, which is higher than the first judgment threshold, were evaluated as "Best (〇)".

[0080] (2) Reliability (stress relaxation characteristics) Regarding the reliability of the fuel cell stack 10, for each sample, those in which the voltage drop rate after 50 thermal cycles was below a predetermined first level were evaluated as "Best (〇)", and those in which the voltage drop rate after 50 thermal cycles exceeded the first level were evaluated as "Good (△)".

[0081] The thermal cycle test was conducted using the following procedure. First, to investigate the initial power generation performance, oxidizer gas OG was supplied to the air electrode 114 and fuel gas FG was supplied to the fuel electrode 116 at approximately 700°C, and the current density was 0.55 A / cm². 2 The output voltage of single cell 110 was measured at that time. This measured value was defined as the initial voltage (output voltage before the thermal cycle test). Next, oxidizer gas OG was supplied to the air electrode 114, fuel gas FG was supplied to the fuel electrode 116, and the current density was 0 A / cm². 2 In this state, the temperature was lowered to approximately 70°C. One cycle consisted of raising the temperature from room temperature to approximately 700°C, followed by lowering the temperature from 700°C to 70°C, and this was repeated for a total of 50 cycles. After the completion of 50 cycles, the temperature was raised again to approximately 700°C, oxidizer gas OG was supplied to the air electrode 114, and fuel gas FG was supplied to the fuel electrode 116, with a current density of 0.55 A / cm².2 The output voltage of a single 110V cell was measured. This measured value was defined as the output voltage after thermal cycling. The voltage drop rate after 50 thermal cycles was calculated using the formula: (initial voltage - output voltage after thermal cycling) ÷ initial voltage.

[0082] As shown in Table 1, sample S1, with an angle difference of 0.0 degrees, was rated as "Poor (×)" for initial power generation performance. On the other hand, samples S2 to S9, with an angle difference of 1.0 degrees or more, were rated as "Good (△)" or "Best (〇)" for initial power generation performance. This means that the difference between the first angle θ1 of the first layered particles 400R and 400L located at the ends of the air electrode frame 130 and the second angle θ2 of the second layered particle 400C located in the center suppresses gas leakage from the air electrode frame 130 and suppresses the decrease in initial voltage. Furthermore, although samples S2 to S6 shared the same ratio of width D to height H, sample S2 was rated as "Good (△)" for initial power generation performance, while samples S3 to S6 were rated as "Best (〇)" for initial power generation performance. This means that if the angle difference is 5.0 degrees or more, gas leakage from the air electrode frame 130 is effectively suppressed, and the initial voltage drop is further suppressed.

[0083] In sample S6, where the first angle θ1 is 90 degrees, the reliability was rated as "Good (△)", while in samples S1-S5 and S7-S9 (especially sample S5), where the first angle θ1 is less than 90 degrees, the reliability was rated as "Best (〇)". This means that the stress relaxation properties of the air electrode frame 130 are ensured when the first angle θ1 is less than 90 degrees.

[0084] In samples S3 to S9, although the angle difference was 1.5 degrees or more, sample S7 was evaluated as "Good (△)" for initial power generation performance, while samples S3 to S6, S8, and S9 were evaluated as "Best (〇)" for initial power generation performance. This means that if the ratio of width D to height H is 3 or more, gas leakage from the air electrode frame 130 can be effectively suppressed.

[0085] <Other Embodiments> In the above embodiment, mica was used as an example material for the channel forming member (air electrode frame 130), but any material having a layered structure consisting of multiple layered particles, such as vermiculite, may be used instead of mica. Furthermore, the material of the channel forming member may not be an insulating material.

[0086] In the above embodiment, an air electrode frame 130 was exemplified as a flow path forming member, but for example, a fuel electrode frame 140 that separates the fuel chamber 323 from the rest of the space may also be used. In short, the flow path forming member can be any member that is placed between two members and separates the gas chamber (air chamber 313 or fuel chamber 323) from the rest of the space. Furthermore, in an electrochemical reaction cell stack equipped with a metal-supported single cell, for example, the member placed between the current collector electrically connected to the single cell and the metal support is the flow path forming member. Furthermore, in an electrochemical reaction cell stack equipped with an electrolyte-supported single cell, for example, the member placed between the electrolyte of the single cell and the current collector is the flow path forming member.

[0087] In the above embodiment, the configuration may be such that only one of the first angle θ1 of the first layered particle 400R and the first angle θ1 of the first layered particle 400L differs from the second angle θ2 of the second layered particle 400C. In the above embodiment, the configuration may be such that the absolute value of the difference between the first angle θ1 of the first layered particles 400R, 400L and the second angle θ2 of the second layered particle 400C is less than 1.4 degrees. In the above embodiment, the first angle θ1 of the first layered particles 400R, 400L may be 90 degrees. In the above embodiment, the width D in the planar direction of each part X1 to X4 of the air electrode frame 130 may be less than three times the width H in the vertical direction.

[0088] In the above embodiment, the electrochemical reaction cell stack was a cell stack used in a solid oxide fuel cell (SOFC). However, the above configuration is also applicable to cell stacks used in other types of fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolytic cell stacks that include electrolytic cell units, which are constituent units of solid oxide electrolytic cells (SOECs), as single cells. [Explanation of Symbols]

[0089] 10: Fuel cell stack 100: Power generation block 100U: Reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 121: Through hole 124: Joint 130,130X: Air electrode frame 130A~130C: Mica material 132: Oxidizer gas supply communication channel 132B: Protrusion 133: Oxidizer gas discharge communication channel 140: Fuel electrode frame 142: Fuel gas supply communication channel 143: Fuel gas discharge communication channel 144: Fuel electrode current collector 145: Electrode opposing part 146: Interconnector opposing part 147: Connecting part 149: Spacer 180: Separator for IC 190: Interconnector 191: Flat plate part 192: Air electrode current collector 193: Coating layer 196: Conductive bonding material 210: First end plate 220: Insulation part 230: End separator 232: First plate 240: First terminal plate 250: Second terminal plate 260: Second plate 270: Second end plate 280: Gas passage member 281: Main body part 282: Flange part 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber 400: Layered particles 400C: Second layered particles 400R, 400L: First layered particles 400RX, 400LX: First layered particles 500: Mold 510: First mold 512: Base section 513: Groove 514: Peripheral wall section 515: Tapered surface 520: Second type B: Bolt N: Nut

Claims

1. The device comprises a plurality of single cells, each including an electrolyte layer and an air electrode and a fuel electrode facing each other with the electrolyte layer in between. In an electrochemical reaction cell stack in which a communication passage is formed that communicates with a gas chamber facing one of the air electrode and the fuel electrode, The first member and A second member is positioned opposite the first member, The first member and the second member are positioned and have a flow path forming member that separates the gas flow path, which includes the gas chamber and the communication passage, from the space other than the gas flow path, The channel forming member has a layered structure consisting of a plurality of layered particles stacked in a first direction in which the first member and the second member face each other. An electrochemical reaction cell stack characterized in that, in at least one specific cross section of the channel forming member along the first direction, there exists a first layered particle located at the end of the channel forming member in a second direction perpendicular to the first direction, wherein the first angle with respect to the second direction is different from the second angle made by a second layered particle located in the center of the channel forming member in the second direction, and the absolute value of the difference between the first angle and the second angle is 1.4 degrees or more.

2. In the electrochemical reaction cell stack according to claim 1, An electrochemical reaction cell stack characterized in that the absolute value of the first angle is less than 90 degrees.

3. In the electrochemical reaction cell stack according to claim 1, An electrochemical reaction cell stack characterized in that, in the specified cross-section, the width of the flow channel forming member in the second direction is three times or more the width in the first direction.

4. A channel forming member for an electrochemical reaction cell stack, It has a layered structure consisting of multiple layered particles stacked in a first direction, A channel forming member for an electrochemical reaction cell stack, characterized in that, in at least one specific cross section along the first direction, there exists a first layered particle located at the end of the channel forming member in a second direction perpendicular to the first direction, wherein the first angle with respect to the second direction is different from the second angle made by a second layered particle located in the center of the channel forming member in the second direction, and the absolute value of the difference between the first angle and the second angle is 1.4 degrees or more.

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