Note: Descriptions are shown in the official language in which they were submitted.
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SEALING STRUCTURE OF FUEL CELL AND MANUFACTURING METHOD
OF SAME
BACKGROUND OF THE INVENTION
l. Field of Invention
[0001] The invention relates to a stack structure of a fuel cell, and a
manufacturing method of same.
2. Description of Related Art
[0002] A solid polymer electrolyte membrane fuel cell includes a plurality
of Membrane-Electrode Assemblies (i.e., MEAs) and a plurality of separators.
Each
of the MEAs includes an electrolyte membrane formed of an ion-exchange
membrane, an electrode (i.e., an anode, a fuel electrode) formed of a catalyst
layer
which is provided on one surface of the electrolyte membrane, and an electrode
(i.e., a
cathode, an air electrode) formed of a catalyst layer which is provided on the
other
surface of the electrolyte membrane. A diffusion layer is provided between the
MEA
and the separator on each of the anode side and the cathode side. A fuel gas
passage
for supplying fuel gas (i.e., hydrogen) to the anode, and an oxidizing gas
passage for
supplying oxidizing gas (i.e., oxygen, normally, air) to the cathode are
formed in the
separator. A coolant passage for supplying coolant (i.e., cooling water,
normally) is
further formed in the separator. A cell is formed by sandwiching the MEA
between
the separators. A module includes at least one cell. A cell stacked body is
formed by
stacking a plurality of modules. Terminals, insulators, and end plates are
provided at
both ends of the cell stacked body in a direction in which cells are stacked
(hereinafter, referred to as a "cell stacked direction"). The cell stacked
body is
fastened in the cell stacked direction. A fastening member (e.g., a tension
plate),
which is provided outside the cell stacked body and extends in the cell
stacked
direction, is fixed using screw bolts/nuts. A stack is thus assembled. On the
anode
side of each cell, a reaction occurs in which hydrogen is decomposed into a
hydrogen
ion (i.e., a proton) and an electron. The hydrogen ion moves through the
electrolyte
membrane to the cathode side. On the cathode side of each cell, the following
reaction occurs in which water is produced from oxygen, a hydrogen ion and an
electron (the electron produced at the anode of the adjacent MEA reaches the
cathode
side through the separator, or the electron produced at the anode of the cell,
which is
on one end of the stack in the cell stacked direction, reaches the cathode of
the cell,
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which is on the other end of the stack, through an external circuit). Anode
side: H2 -->
2H' + 2e" Cathode side: 2H' + 2e + (1/2) 02 -4 H20. An adhesive agent is
provided
between the separators which are adjacent to each other with the electrolyte
membrane therebetween, and between the separator and the electrolyte membrane,
so
as to bond the separators, and the separator and the electrolyte membrane, and
so as to
seal gaps therebetween. A cell is thus formed. A plurality of the cells is
positioned
and stacked so as to form a stack. Japanese Patent Laid-Open Publication No.
2000-
48849 discloses a method for positioning and stacking the cells. In the
method, a
notched portion is provided at an edge of each separator, and the cells are
stacked
while making the notched portion contact a guide post which is a reference
portion of
an assembly jig so as not to cause displacement between the cells.
[0003] However, there exist the following problems regarding the
conventional method for assembling the cell stacked body. First, the adhesive
agent
comes out of the gap between the separators to the notched portion when
forming a
cell, and the adhesive agent, which has come out, adheres to the reference
portion of
the assembly jig when forming a cell or a stack, which may reduce the
positioning
accuracy. Secondly, the separator is deformed due to a pressing load when the
separator is pressed to the reference portion of the assembly jig, and the
anode side
separator and the cathode side separator, which are adjacent to each other
with the
electrolyte membrane therebetween, come into contact with each other, which
may
cause a short-circuit.
SUMMARY OF THE INVENTION
[0004] It is an object of the invention to provide a stack structure of a fuel
cell in which positioning accuracy in stacking cells can be prevented from
being
reduced. The reduction of the positioning accuracy is due to adhesion of a
spreading
adhesive agent to a reference portion of an assembly jig. It is another object
of the
invention to provide a stack structure of a fuel cell in which a short-circuit
can be
prevented from occurring. Tne occurrence of the short-circuit is due to
deformation
of the separator caused by making the separator contact the reference portion
of the
assembly jig.
[0005] In order to achieve the above-mentioned objects, a stack structure
of a fuel cell according to an aspect of the invention includes a plurality of
separators
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of the fuel cell, and a protruding portion which has a tip portion that
contacts a
reference portion of an assembly jig during assembly of the fuel cell.
[0006] The stack structure of a fuel cell includes a plurality of cells each
of which is formed of the separators and an MEA. The protruding portion
protrudes
in a direction perpendicular to the cell stacked direction. The stack
structure further
includes sealants, each of which is formed of an adhesive agent, and is
provided
between the separator and the separator, or between the separator and the MEA
when
stacking the cells. The protruding portion has a predetermined height such
that the
sealant does not come out from the tip portion.
[0007] In the stack structure of a fuel cell, the protruding portion is
provided, and the tip portion thereof contacts the reference portion of the
assembly
jig. Accordingly, the adhesive agent does not come out from the tip portion of
the
protruding portion. Also, it is possible to prevent the positioning accuracy
in stacking
the cells from being reduced. The reduction of the positioning accuracy is due
to
adhesion of the spreading adhesive agent to the reference portion of the
assembly jig.
[0008] A stack structure of a fuel cell according to a further aspect of the
invention includes a plurality of cells each of which is formed of separators
and an
MEA, and a protruding portion which is formed on an end portion of each of the
separators so as to protrude in the direction perpendicular to the cell
stacked direction,
and which is formed so as not to overlap with the protruding portion of the
adjacent
separator in a cell stacked direction. Thus, the protruding portions of the
separators
adjacent to each other (e.g., the separator on an anode side and the separator
on a
cathode side, when the separators adjacent to each other are the separator on
the
anode side and the separator on the cathode side) are displaced from each
other in the
cell stacked direction. Accordingly, even if the protruding portions= are
deformed, the
protruding portions do not contact with each other, which can prevent a short-
circuit
from occurring. The occurrence of the short-circuit is due to deformation of
the
separators caused by making the separators contact the reference portion of
the
assembly jig.
[0009] A manufacturing method of a stack structure of a fuel cell
according to a further aspect of the invention includes the steps of preparing
a
plurality of separators each of which has a protruding portion on an end
portion
thereof; preparing an assembly jig used during assembly of the fuel cell; and
stacking
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the plurality of separators while making a tip portion of the protruding
portion of each
of the separators contact a reference portion of an assembly jig.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a plan view showing a cathode side separator in a stack
structure of a fuel cell according to the invention;
[0011] FIG. 2 is a plan view showing an anode side separator in the stack
structure of a fuel cell according to the invention;
[0012] FIG. 3 is a plan view when the cathode side separator and the
anode side separator overlap with each other in the stack structure of a fuel
cell
according to the invention;
[0013] FIG. 4 is a sectional view showing an example of a protruding
portion formed on the separator in the stack structure of a fuel cell
according to the
invention, and a reference portion of an assembly jig;
[0014] FIG. 5 is a sectional view showing another example of a protruding
portion formed on a separator in the stack structure of a fuel cell according
to the
invention, and a reference portion of an assembly jig;
[0015] FIG. 6 is a side view showing the stack structure of a fuel cell
shown in FIG. 4;
[0016] FIG. 7 is a plan view when a protruding portion is formed inside a
manifold in the stack structure of a fuel cell according to the invention;
[0017] FIG. 8 is a plan view when the separators adjacent to each other are
stacked in the stack structure of a fuel cell according to the invention;
[0018] FIG. 9 is a sectional view taken along line in FIG. 8;
[0019] FIG. 10 is an enlarged plan view of a manifold portion and a
vicinity thereof in FIG. 8;
[0020] FIG. 11 is a side view showing a cell stacked body; and
[0021] FIG. 12 is a sectional view showing part of the stack shown in FIG.
11.
DETAILED DESCRIPTION OF the PREFERRED EMBODIMENTS
[0022] Hereafter, a stack structure of a fuel cell according to the invention
will be described with reference to FIGS. 1 to 12. The fuel cell according to
the
invention is a solid polymer electrolyte membrane fuel cell 100. The fuel cell
100 is
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mounted, for example, on a fuel-cell vehicle. However, the fuel cell 100 may
be
employed in products other than an automobile.
[0023] As shown in FIGS. 11, 12, the solid polymer electrolyte membrane
fuel cell 100 includes a plurality of Membrane-Electrode Assemblies (i.e.,
MEAs) and
5 a plurality of separators 18. Each of the MEAs includes an electrolyte
membrane 11
formed of an ion-exchange membrane, an electrode (i.e., an anode, a fuel
electrode)
14 having a catalyst layer 12 which is provided on one surface of the
electrolyte
membrane 11, and an electrode (i.e., cathode, an air electrode) 17 having a
catalyst
layer 15 which is provided on the other surface of the electrolyte membrane
11. A
diffusion layers 13 is provided between the catalyst layer 12 and the
separator 18 on
the anode side, and a diffusion layer 16 is provided between the catalyst
layer 15 and
the separator 18 on the cathode side.
[0024] A fuel gas passage 27 for supplying fuel gas (i.e., hydrogen) to the
anode 14, and an oxidizing gas passage 28 for supplying oxidizing gas (i.e.,
oxygen,
normally, air) to the cathode 17 are formed in the separator 18. A coolant
passage 26
for supplying coolant (i.e., cooling water, normally) is also formed in the
separator 18.
Each of the passages 26, 27, 28 may be a serpentine passage which extends from
an
inlet to an outlet while winding at at least one portion, or may be a straight
passage
which extends straight from the inlet to the outlet.
[0025] A coolant manifold 29, a fuel gas manifold 30, and an oxidizing
gas manifold 31 are formed in the separator 18. The coolant manifold 29
communicates with the coolant passage 26, the fuel gas manifold 30
communicates
with the fuel gas passage 27, and the oxidizing gas manifold communicates with
the
oxidizing gas passage 28. The manifolds 29, 30, 31 are formed in opposite end
portions of the rectangular separator 18. The passages 26, 27, 28 are formed
in a
center area which is an area of the separator other than an area in which the
manifolds
are formed. The area in which the gas passages 27, 28 are formed and the
electrolyte
membrane 11 exists is the area in which electric power is generated.
[0026] The separator 18 is formed by using one of carbon, metal, metal
and resin (a metal separator and a resin frame), and resin to which
conductivity is
imparted, or is formed by using these materials in combination. The separator
shown
in the drawing is a carbon separator (i.e., a molded component made of carbon
and a
resin binder).
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[0027] As shown in FIG. 11, a stack 23 is assembled in the following
method. A cell 19 is formed by sandwiching the MEA between the separators 18.
A
module includes at least one cell (FIG. 12 shows an example in which two cells
form
one module). A cell stacked body is formed by stacking a plurality of modules.
Terminals 20, insulators 21, and end plates 22 are provided at both ends of
the cell
stacked body in a cell stacked direction. The cell stacked body is fastened in
the cell
stacked direction. A fastening member (e.g., a tension plate 24), which is
provided
outside the cell stacked body and extends in the cell stacked direction, is
fixed using
screw bolts/nuts 25.
[0028] As shown in FIG.12, in order to separate the passages 26, 27, 28
and the manifolds 29, 30, 31 (shown in FIGS. 1, 2, 3) from each other and from
the
outside (i.e., the atmosphere), an adhesive agent 32 (shown in FIG. 6) is
provided
between components (i.e., components including at least the separator 18 and
the
electrolyte membrane 11) of the fuel cell 100 in the vicinity of the passages
26, 27, 28
and in the vicinity of the manifolds 29, 30 31. The adhesive agent 32 bonds
the
components of the cell or the module while sealing a gap between the
components.
The adhesive agent 32 serves as a sealant as well. The two components between
which the adhesive agent 32 is provided are the separator 18 and the separator
18, or
the separator 18 and the electrolyte membrane 11.
[0029] As shown in FIGS. 1 to 3, a plurality of protruding portions 33
each of which has a tip portion is formed on the end portions of the
separators 18 of
the fuel cell 100. The protruding portion 33 protrudes from the end portion in
the
direction perpendicular to the cell stacked direction. The tip portion
contacts the
reference portion of the assembly jig during assembly of the fuel cell. The
end
portion of the separator 18 may be the end portion facing the outside (i.e.,
the
atmosphere) of the separator 18 as shown in FIGS. 1 to 3 (when a reference
portion
34 is positioned outside the separator), or may be the end portion facing one
of the
manifolds 29, 30, 31 as shown in FIG. 7 (when the reference portion 34 is
positioned
inside the manifold). When the adhesive agent 32 is applied to the separator
18, the
adhesive agent 32 is not applied to the surface of the protruding portion 33.
The
assembly jig may be the assembly jig for positioning the components when the
components are assembled to a cell or a module, or may be the assembly jig for
positioning the cells or the modules when stacking the cells or the modules so
as to
assemble a stack.
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[0030] The protruding portion 33 has a height enough to prevent the
adhesive agent 32 between the separators 18 from coming out from the tip
portion of
the protruding portion 33, when the adhesive agent 32 is pressed by the
separators and
spreads. The height of the protruding portion 33 with respect to the end
portion
having no protruding portion is approximately 0.5 mm. The height needs to be
at
least 0.2 mm, preferably, 0.3 mm or more. As shown in FIG. 4, when the
reference
portion 34 of the assembly jig contacting the protruding portion 33 has a
convex
curved surface, for example, when a cross section of the reference portion is
substantially circular in the direction perpendicular to the cell stacked
direction, it is
preferable that the protruding portion 33 have a flat tip portion. As shown in
FIG. 5,
when the reference portion 34 of the assembly jig has a flat surface in
parallel with the
end portion of the separator, it is preferable that the protruding portion 33
contacting
the reference portion 34 have a convex curved surface.
[0031] As shown in FIGS. 1 to 3, when the protruding portions 33 are
formed on the end portions of the separators 18 so as to protrude from the end
portions in the direction perpendicular to the cell stacked direction. The
protruding
portions 33 of the anode side separator 18 and the protruding portions 33 of
the
cathode side separator 18 are displaced from each other in a direction
perpendicular to
the cell stacked direction. Therefore, the protruding portions 33 of the anode
side
separator 18 and the protruding portions 33 of the cathode side separator 18
do not
overlap with each other in the cell stacked direction. FIG. 1 shows the
positions of
the protruding portions 33a formed on the cathode side separator 18. FIG. 2
shows
the positions of the protruding portions 33b formed on the anode side
separator 18.
FIG. 3 shows a relationship between the positions of the protruding portions
33b of
the anode side separator 18 and the positions of the protruding portions 33a
of the
cathode side separator 18, when the cell is formed by sandwiching the MEA
between
the anode side separator 18 and the cathode side separator 18 such that the
gas
passage of each of the separators 18 is on the MEA side. As can be understood
from
FIG. 3, the protruding portions 33a and the protruding portions 33b are
displaced
from each other in the direction perpendicular to the cell stacked direction
(i.e., the
separator stacked direction). Therefore, the protruding portions 33a and the
protruding portions 33b do not overlap with each other in the cell stacked
direction.
[0032] The separator 18 has a rectangular shape (including a substantially
rectangular shape) in a plan view, and the protruding portions 33 are formed
in the
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vicinity of the corner portions of the rectangular separator 18. The
protruding portion
33 may be formed on a portion of the separator 18 corresponding to a
longitudinal
side of one of the manifolds 29, 30 , 31, so as to protrude in the direction
perpendicular to the direction in which the longitudinal side extends. In such
a case, a
beam 37 is provided between the longitudinal side of the manifold (a first
longitudinal
side 35) and a second longitudinal side 36 which faces the first longitudinal
side and
extends in parallel with the first longitudinal side. By providing the beam
37, the
rigidity of a narrow separator portion 38 between the first longitudinal side
and the
end portion of the separator is enhanced in the direction perpendicular to the
cell
stacked direction.
[0033] FIGS. 8 and 9 show another embodiment of the invention. In the
structure shown in FIGS. 8 and 9, the separators 18 adjacent to each other
have
different circumferences. Accordingly, one of the separators 18 adjacent to
each other
is slightly smaller than the other separator 18. The separators 18 adjacent to
each
other may be the two separators 18 which are adjacent to each other with the
electrolyte membrane therebetween 11, or may be the anode side separator and
the
cathode side separator which are adjacent to each other. In an example shown
in FIG.
8, the circumference is the circumference of an outer edge portion of the
separator.
[0034] Seen from the cell stacked direction, compared with the outer edge
portion of the separator 18 having a shorter circumference, the outer edge
portion of
the separator 18 having a longer circumference protrudes further in an outward
direction and in a direction perpendicular to the outer edge portion of the
separator
having a shorter circumference in the direction perpendicular to the cell
stacked
direction. The amount of protrusion is shown by a reference symbol d in FIG.
8. The
entire outer edge portion of the separator 18A having a longer circumference
protrudes with respect to the entire outer edge portion of the separator 18B
having a
shorter circumference. Accordingly, as shown in FIG. 9, an adhesive agent
holding
portion 41 is formed outside an end surface 39 of the end edge portion of the
separator
18B having a shorter circumference. The adhesive agent holding portion 41 is
formed
by the end surface 39 (a surface extending in the cell stacked direction) of
the outer
edge portion of the separator 18B having a shorter circumference, and a
separator
surface 40 (a surface perpendicular to the cell stacked direction) of the
outer edge of
the separator 18A having a longer circumference.
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[0035] The position of the tip portion of the protruding portion 33 formed
on the separator 18A having a shorter circumference in the direction
perpendicular to
the cell stacked direction, and the position of the tip portion of the
protruding portion
33 formed on the separator 18B having a longer circumference in the cell
stacked
direction are the same. Also, the position of the tip portions is outside the
outer edge
portion of the separator 18 having a longer circumference. Accordingly, a
height D2
of the protruding portion 33 formed on a separator 18B having a shorter
circumference is larger than a height D, of the protruding portion 33 formed
on the
separator 18A having a longer circumference. The relationship between D2 and
D, is
expressed by an equation D2 = d + D,.
[0036] FIG. 8 shows a case in which the circumference is the
circumference of the outer edge portion of the separator. However, as shown in
FIG.
10, the circumference may be a circumference of one of the manifolds (i.e.,
the
coolant manifold 29, the fuel gas manifold 30, and the oxidizing gas manifold
31). In
this case, compared with a separator edge 44 having a longer manifold
circumference,
a separator edge 43 having a shorter manifold circumference protrudes more in
an
inward direction of the manifold. An adhesive agent holding portion 41 is
formed by
a separator surface of the edge 43 and end surface of the edge 44. FIG. 9 is
applied to
an example shown in FIG. 10. However, the adhesive agent holding portion 41 is
formed on the periphery of the manifold.
[0037] In the example shown in FIGS. 8 and 10, as shown in FIG. 9, a
convex curved surface 42 or a chamfer may be formed on the end surface (the
surface
extending in the cell stacked direction) of the outer edge portion of the
separator 18.
When the curved surface 42 or the chamfer is formed, an area of a cross
section of the
adhesive agent holding portion 41 is larger than when the curved surface or
the
chamfer is not formed.
[0038] Hereafter, effect of the invention will be described. When
assembling a cell, a module, or a stack, the separator 18 contacts the
reference portion
34 of the assembly jig at the protruding portion 33. The adhesive agent does
not
come out from the tip portion of the protruding portion. Therefore, unlike the
conventional case, the problem does not occur in which the adhesive agent,
which has
come out from the end portion of the separator, adheres to the reference
portion of the
assembly jig and thus the positioning accuracy in stacking the cells is
reduced.
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[0039] The protruding portions 33b of the anode side separator 18 and the
protruding portions 33a of the cathode side separator 18, the separators being
adjacent
to each other with the MEA therebetween, are displaced from each other in the
direction perpendicular to the cell stacked direction. Accordingly, even when
the
5 protruding portions 33 are deformed in the cell stacked direction by
receiving a
reaction force when the protruding portions 33 are pressed to the reference
portion 34,
the protruding portions 33a do not contact the protruding portions 33b.
Therefore, it
is possible to prevent a short-circuit from occurring. The occurrence of the
short-
circuit is due to the deformation of the separators 18 caused by making the
separators
10 18 contact the reference portion 34 of the assembly jig.
[0040] Also, since the beam 37 is provided on one of the manifolds 26, 27,
28, which is positioned in the vicinity of the protruding portion 33, the
separator
portion 38 between the manifold and the end portion on which the protruding
portion
is formed can be reinforced, and the separator portion 38 can be prevented
from being
deformed by receiving a reaction force when the protruding portion 33 is
pressed to
the reference portion 34. As a result, positioning can be performed with high
accuracy. Also, even when the protruding portion 33 is strongly pressed to the
reference portion 34, the separator portion 38 between the manifold and the
end
portion on which the protruding portion 33 is formed is not damaged.
Accordingly,
reliability for the rigidity of the separator is enhanced.
[0041] As shown in FIGS. 8, 9, 10, when the sizes of the separators 18
adjacent to each other are made different by making the circumferences of the
separators 18 adjacent to each other different, the adhesive agent holding
portion 41 is
formed outside the end surface 39 of the smaller sized separator 18B (in the
case in
which the protruding portion is formed in the manifold, the adhesive agent
holding
portion is formed inside the end surface of the end edge 44) by the end
surface 39 of
the smaller sized separator 18B (the surface extending in the cell stacked
direction, in
the case where the protruding portion is formed in the manifold, the end
surface of the
end edge 44) and the separator surface 40 of the larger sized separator 18A
(the
surface perpendicular to the cell stacked direction, in the case where the
protruding
portion is formed in the manifold, the separator surface of the end edge 43).
Accordingly, even when the adhesive agent 18 between the separators comes out
by
being pressed by the separators 18, the adhesive agent only comes out to the
adhesive
agent holding portion 41, and does not come out from the large sized separator
18A
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which is outside the adhesive agent holding portion 41 (in the case in which
the
protruding portion is formed in the manifold, inside the end surface of the
end edge
43). Therefore, the adhesive agent 32 does not come out to the tip portion of
the
protruding portion 33. Accordingly, the conventional problem is prevented from
occurring in which the adhesive agent comes out from the end portion of the
separator, and the positioning accuracy of the cell stacking is reduced due to
the
adhesion of the adhesive agent, which has come out from the end portion of the
separator, to the reference portion of the assembly jig.
[0042] When the curved surface 42 or the chamfer is formed on the end
surface of the outer edge portion of the separator 18 or the end surface of
the
manifold, as shown in FIG. 9, the area of the cross section of the adhesive
agent
holding portion is large. Accordingly, the ability of the adhesive agent
holding
portion 41 to absorb the adhesive agent, which has come out from the gap
between the
separators, is enhanced, which further prevents the positioning accuracy of
the cell
staking from being reduced.
