KR102478772B1 - Bipolar plate for fuel cell, method of the same - Google Patents

Abstract

A separator for a fuel cell including a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin, and having a concentration gradient of the conductive filler in a thickness direction of the unit structural layer is provided, and a manufacturing method thereof.

Description

Bipolar plate for fuel cell and manufacturing method {BIPOLAR PLATE FOR FUEL CELL, METHOD OF THE SAME}

It relates to a separator for a fuel cell and a manufacturing method.

A fuel cell is a power generation system that produces electricity by an electrochemical reaction between hydrogen and oxygen, and may be composed of a stack, which is a main component for directly generating electricity, and other devices that assist the operation of the stack.

The fuel cell stack includes a unit cell as the smallest unit that generates electrical energy, and the unit cell is a membrane electrode assembly (MEA) and a fuel provided on both sides of the membrane electrode assembly. It may include battery separator plates.

The membrane electrode assembly includes a polymer electrolyte membrane that selectively passes only hydrogen ions, and an anode electrode and a cathode electrode may be bonded to both sides of the polymer electrolyte membrane.

The fuel cell separator serves to collect the current generated from the unit cell, serves to separate to maintain insulation, and discharges water generated while supplying gas (hydrogen, oxygen) to the gas diffusion layer (GDL). can fulfill its role.

Such a fuel cell separator should be stable in an oxidation/reduction atmosphere of an anode electrode and a cathode electrode, sufficiently prevent gas mixing, and have sufficient electrical conductivity.

Conventional commercialized graphite separators have corrosion resistance and good electrical conductivity, but are vulnerable to mechanical shock or vibration and must maintain a certain thickness or more, which reduces the efficiency of the fuel cell stack and has a problem of high cost, and in addition, pores There is a problem of gas permeability.

In order to solve this problem, polymer composite separators containing polymer resins and conductive fibers have recently been used, but in order to satisfy the required electrical conductivity and thermal conductivity, a large amount of conductive fillers are separately added in addition to the conductive fibers. Should be.

In one embodiment of the present invention, a separator for a fuel cell realizing excellent electrical conductivity, excellent mechanical properties, excellent productivity and excellent processability is provided.

In another embodiment of the present invention, a method of manufacturing the separator for a fuel cell is provided.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned problem, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

In one embodiment of the present invention, there is provided a separator for a fuel cell including a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin, and having a concentration gradient of the conductive filler in the thickness direction of the unit structural layer. .

Accordingly, the fuel cell bipolar plate has low contact resistance and high electrical conductivity on the upper and lower surfaces, and realizes excellent electrical properties, and at the same time, it does not contain a large amount of the conductive filler to form an appropriate level of flexural strength, thereby exhibiting excellent mechanical properties. There are benefits that can be implemented.

In the thickness direction of the unit structural layer, a concentration gradient may be formed such that the concentration of the conductive filler decreases from both surfaces toward the center of the thickness.

The unit structural layer includes both surfaces perpendicular to its thickness direction, and a first thickness region corresponding to about 5% to about 35% of the total thickness length of the unit structural layer in a direction from each surface toward the center of the thickness. and a second thickness region, wherein the total weight of the conductive fillers respectively present in the first thickness region and the second thickness region is, for example, the total weight of the conductive fillers included in the unit structural layer 110. of about 50% to about 100%, specifically about 70% to about 90%.

Accordingly, the bipolar plate for a fuel cell can simultaneously implement better electrical properties and superior mechanical properties.

The content of the conductive filler in the entire unit structural layer may be about 5 wt % to about 15 wt %. By including the content within the above range, the electrical properties of the bipolar plate for a fuel cell may be improved, and the flexural strength may be formed at an appropriate level to realize excellent mechanical properties without breaking.

The fuel cell separator may have a contact resistance of, for example, about 5 mΩ cm ² to about 50 mΩ cm ² , specifically about 5 mΩ cm ² to about 20 mΩ cm ² , and electrical conductivity, for example, , It may be about 50 S / cm to about 300 S / cm, specifically about 100 S / cm to about 200 S / cm.

Bone strength of the separator for a fuel cell may be about 20 MPa to about 50 MPa. Excellent mechanical properties can be implemented by having a flexural strength within the above range. Specifically, when the fuel cell is less than about 20 MPa, it is difficult to withstand the injection pressure of the fuel gas during operation of the fuel cell and may be damaged, and can be easily damaged by vibrations generated during vehicle operation. may be damaged.

The bipolar plate for a fuel cell may realize excellent electrical conductivity, excellent mechanical properties, excellent productivity, and excellent processability.

1 is a schematic perspective view of a separator for a fuel cell according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a separator for a fuel cell according to an embodiment of the present invention.
3 is a schematic process flow diagram of a method of manufacturing a separator for a fuel cell according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. This invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

In order to clearly describe the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification.

In the drawings, the thickness is shown enlarged to clearly express the various layers and regions. And in the drawings, for convenience of explanation, the thicknesses of some layers and regions are exaggerated.

Hereinafter, the formation of an arbitrary configuration on the upper (or lower) or upper (or lower) substrate of the substrate means that the arbitrary configuration is formed in contact with the upper (or lower) surface of the substrate, and the substrate and any structure formed on (or under) the substrate is not limited to not including other structures.

In one embodiment of the present invention, there is provided a separator for a fuel cell including a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin, and having a concentration gradient of the conductive filler in the thickness direction of the unit structural layer. .

1 is a schematic perspective view of a separator plate 100 for a fuel cell according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of the separator plate 100 for a fuel cell according to an embodiment of the present invention.

In general, for a separator used in a fuel cell, a film is formed of a thermoplastic resin composition containing a conductive filler, the film is laminated on at least one surface of a carbon fiber fabric, and then the film is thermally compressed to manufacture a separator for a fuel cell, Alternatively, it is prepared by immersing a carbon fiber fabric in a thermoplastic resin containing a conductive filler and then drying it.

However, as described above, when the conductive filler is substantially uniformly dispersed, there is a problem in that electrical characteristics are not sufficient due to relatively high contact resistance and low electrical conductivity on the upper and lower surfaces of the separator. In addition, when a large amount of the conductive filler is added to solve this problem, the bending strength of the bipolar plate may be lowered, resulting in inferior mechanical properties.

Accordingly, in one embodiment of the present invention, the fuel cell separator 100 includes a unit structure layer 110 including carbon fiber fabric, a conductive filler 130, and an impregnated resin 140, and the unit structure A concentration gradient of the conductive filler 130 may be formed in the thickness direction of the layer 110, and accordingly, the fuel cell bipolar plate 100 has excellent electrical properties with low contact resistance and high electrical conductivity on the upper and lower surfaces. At the same time, there is an advantage in that excellent mechanical properties can be implemented by forming a flexural strength at an appropriate level by not including a large amount of the conductive filler 130.

In addition, since metal materials such as metal thin films are not included, weight reduction can be realized while implementing corrosion resistance at an excellent level. In addition, since it is formed by the process of lamination and thermal compression, it is possible to implement excellent productivity and excellent processability by reducing time and cost by not spraying and curing fibers in the fabric or going through a separate carbonization process.

In one embodiment, in the thickness direction of the unit structural layer 110, a concentration gradient may be formed such that the concentration of the conductive filler 130 decreases from both surfaces toward the center of the thickness.

In FIG. 1 , for convenience of understanding, in the thickness direction of the unit structure layer 110, the brightness of each region where the conductive filler 130 exists is darker from both surfaces toward the center of the thickness compared to the brightness of the thickness center region. It is only shown, but here, the brightness is not changed according to its concentration so that the concentration gradient of the conductive filler 130 is expressed. The concentration gradient of the conductive filler 130 can be understood with reference to FIG. 2 , and as shown in FIG. 2 , the concentration of the conductive filler 130 extends from both surfaces of the unit structure layer 110 to the thickness center. However, here, the size or position of the carbon fiber fabric and the conductive filler 130 are briefly or exaggeratedly shown for convenience of description.

In this way, by forming a high concentration of the conductive filler 130 on both surfaces of the unit structural layer 110, that is, the upper and lower surfaces, it is possible to increase electrical conductivity while reducing contact resistance. In addition, at the same time, at the center of the thickness, the concentration of the conductive filler 130 having a hard property is low to form the bending strength of the bipolar plate 100 for a fuel cell at an appropriate level, and accordingly, it is possible to form a long-term without breaking. Excellent mechanical properties can be realized.

Specifically, since the carbon fiber fabric 120 has excellent electrical conductivity, the electrical properties of the fuel cell bipolar plate 100 are excellent even though the concentration of the conductive filler 130 is low at the center of the thickness. Also, since the mechanical properties of the carbon fiber fabric 120 are excellent, the mechanical properties of the fuel cell bipolar plate 100 may also be improved.

The unit structural layer 110 includes a first thickness region corresponding to about 5% to about 35% of the total thickness length in a direction from one surface toward the thickness center, including both surfaces perpendicular to its thickness direction; and a second thickness region corresponding to about 5% to about 35% of the total thickness in a direction from the other surface toward the center of the thickness.

In this way, the unit structural layer 110 includes both surfaces perpendicular to its thickness direction, and from about 5% to about 5% of the total thickness of the unit structural layer 110 in a direction from each surface toward the center of the thickness. It includes a first thickness region and a second thickness region corresponding to 35%, and the sum of the conductive fillers 130 respectively present in the first thickness region and the second thickness region is, for example, the unit structural layer. It may be about 50% to about 100% of the total weight of the conductive filler 130 included in (110), specifically about 70% to about 90%.

At this time, the content of the conductive filler 130 present in the first thickness region; and the content of the conductive filler 130 present in the second thickness region; may be the same or different.

Based on the total weight of the conductive filler 130, a high content within the above range, that is, about 50% or more is present in the first and second thickness regions, and as shown in FIG. 2, the separator 100 for a fuel cell Both surface portions of have a higher content of the conductive filler 130 than the central portion, and thus, the separator 100 for a fuel cell can simultaneously implement better electrical properties and superior mechanical properties.

That is, for example, when the total thickness of the unit structural layer 110 is about 300 μm, the first thickness region and the second thickness region corresponding to about 15 μm to about 105 μm in a direction from each surface toward the thickness center. The sum of the contents of each of the conductive fillers 130 present in the thickness region may be about 50% to about 100% of the total weight of the conductive fillers 130 .

The carbon fiber fabric 120 is formed by weaving with the carbon fiber, and the carbon fiber is PAN-based, pitch-based, and rayon-based carbon fiber; carbon nanofibers; activated carbon fibers; And it may include at least one selected from the group consisting of combinations thereof.

The impregnation resin 140 may be a thermoplastic resin, and the thermoplastic resin may be, for example, polyethylene, polypropylene, polyurethane, polyethyleneterephthalate, or polybutyleneterephthalate. (polybutyleneterephthalate), polyurea, polyvinylchloride, polyvinylacetate, ethylenevinylacetate, melamine, phenol, polyphenylene sulfide, Selected from the group consisting of polyamide, polyimide, polybenzimidazole, polyetheretherketone, acryl, liquid crystal polymer, and combinations thereof It may include at least one, but is not limited thereto.

In addition, the conductive filler 130 is carbon black, acetylene black, carbon nanotube (CNT), graphite, graphene, graphite nanofiber (GNF), fullerene, and combinations thereof It may include at least one selected from the group consisting of, but is not limited thereto.

In one embodiment, the weight ratio of the impregnated resin 140 to the carbon fibers in the entire unit structural layer 110 may be about 1:3 to about 1:8.4. By including it at a weight ratio within the above range, it is possible to sufficiently prevent mixing of reactant gases during operation of the fuel cell by implementing a low level of gas permeability while implementing a high level of electrical properties without including a metal material.

In addition, the weight ratio of the impregnating resin 140 to the conductive filler 130 in the entire unit structural layer 110 may be about 1:0.25 to about 1:1.5. By including the weight ratio within the above range, excellent mechanical properties can be realized by sufficiently improving the electrical properties of the fuel cell bipolar plate 100 while forming the flexural strength at an appropriate level, and by implementing the gas permeability at a low level, the fuel cell Mixing of reaction gases can be sufficiently prevented during driving.

The content of the impregnating resin 140 in the entire unit structure layer 110 may be about 10 wt % to about 25 wt %. By including the amount within the above range, the empty space of the carbon fiber fabric 120 is sufficiently filled to prevent mixing of the reactant gas, and the electrical properties of the bipolar plate 100 for a fuel cell may not be deteriorated.

The content of the carbon fiber in the entire unit structural layer 110 may be about 60 wt% to about 84 wt%. By including the content within the above range, the electrical properties, gas permeability and contact resistance of the fuel cell bipolar plate 100 can all be implemented at excellent levels. Specifically, when the content of the carbon fiber is less than about 60% by weight, electrical conductivity and mechanical properties are lowered, and when it exceeds about 84%, the pores are not sufficiently filled by the impregnation resin 140, so the gas permeability is inferior while the surface It is difficult to form flat, and there is a problem in that contact resistance increases.

The content of the conductive filler 130 in the entire unit structural layer 110 may be about 5 wt % to about 15 wt %. By including the content within the above range, the electrical properties of the bipolar plate 100 for a fuel cell may be improved, and the flexural strength may be formed at an appropriate level to realize excellent mechanical properties without breaking.

The unit structure layer 110 may further include a conductive polymer, and thus, electrical properties of the fuel cell separator 100 may be improved.

On the other hand, when a metal thin film or the like is included between the carbon fiber fabrics 120, adhesion between them is low, and cracks, gaps, and the like easily occur during use, and durability may be deteriorated.

The conductive polymer is polyaniline-based polymer, polythiophene-based polymer, polypyrrole-based polymer, polyprene-based polymer, polyacetylene-based, polyphenylene-based, polyphenylene-vinylene-based, polyacene-based, polythiophene-based, and combinations thereof. It may include at least one selected from the group consisting of, but is not limited thereto.

When the conductive polymer is included, the content of the conductive polymer in the entire unit structural layer 110 may be about 0.01 wt % to about 1 wt %. By including the content within the above range, it is possible to realize sufficiently excellent electrical properties at the interface between the respective unit structural layers 110 without unnecessarily increasing the cost.

The thickness ratio of the fabric and the unit structural layer 110 may be about 1:0.9 to about 1:1.4. By having the thickness ratio within the above range, the thickness difference between the fabric and the unit structural layer 110 can be formed at a smaller level or their thicknesses can be formed to be substantially the same, and thus the fuel cell separator 100 ), excellent electrical properties can be realized on the upper and lower surfaces. As described in the manufacturing method described below, the unit structural layer 110 may be formed by thermal compression, and accordingly, when the content of the impregnation resin 140 is relatively small, the thickness of the fabric may be reduced, , When the content of the impregnation resin 140 is greater, the thickness of the fabric may be increased.

For example, the fabric may have a thickness of about 200 μm to about 400 μm measured according to the conditions of KS K 0506, and the thickness of the unit structural layer 110 may be about 180 μm to about 560 μm. In this case, when the fuel cell bipolar plate 100 includes the unit structural layer 110 as one, the thickness of the fuel cell bipolar plate 100 may be the same as that of the unit structural layer 110 .

By having a thickness within the above range, when using the fuel cell separator 100 including the same, separation performance for maintaining insulation may be sufficiently implemented without excessively increasing the specifications of the fuel cell or unit cell.

In one embodiment, the fuel cell bipolar plate 100 may have a contact resistance of, for example, about 5mΩ·cm ² to about 50mΩ·cm ² , specifically about 5mΩ·cm ² to about 20mΩ·cm ² . And, the electrical conductivity may be, for example, about 50S / cm to about 300S / cm, specifically about 100S / cm to about 200S / cm. By realizing a low level of contact resistance within the above range and a high level of electrical conductivity within the above range, excellent electrical properties can be implemented, and energy efficiency can be effectively improved.

At the same time, the bone strength of the fuel cell bipolar plate 100 may be about 20 MPa to about 50 MPa. Excellent mechanical properties can be implemented by having a flexural strength within the above range. Specifically, when the fuel cell is less than about 20 MPa, it is difficult to withstand the injection pressure of the fuel gas during operation of the fuel cell and may be damaged, and can be easily damaged by vibrations generated during vehicle operation. may be damaged.

3 schematically shows a process flow diagram of a method of manufacturing the bipolar plate for a fuel cell according to another embodiment of the present invention.

The manufacturing method includes forming a laminate including a laminated structure of a conductive filler-containing coating layer/a carbon fiber fabric layer having a resin layer formed on at least one surface/a conductive filler-containing coating layer (S1); and forming a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin by thermally compressing the laminate (S2).

According to the manufacturing method, in one embodiment, the above-described bipolar plate for a fuel cell may be manufactured, and the carbon fiber fabric, the conductive filler, and the impregnated resin are as described above in one embodiment.

The unit structural layer may be manufactured such that a concentration gradient of the conductive filler is formed in a thickness direction.

Accordingly, the fuel cell bipolar plate has low contact resistance and high electrical conductivity on the upper and lower surfaces, and at the same time, it does not contain a large amount of the conductive filler to form an appropriate level of flexural strength, thereby exhibiting excellent mechanical properties. There are benefits that can be implemented.

In addition, since metal materials such as metal thin films are not included, weight reduction can be realized while implementing corrosion resistance at an excellent level. In addition, since it is formed by the process of lamination and thermal compression, it is possible to implement excellent productivity and excellent processability by reducing time and cost by not spraying and curing fibers in the fabric or going through a separate carbonization process.

In the above manufacturing method, a laminate comprising a laminated structure of a conductive filler-containing coating layer/a carbon fiber fabric layer having a resin layer formed on at least one surface/a conductive filler-containing coating layer may be formed, and the resin layer is the carbon fiber fabric layer of the carbon fiber fabric layer. It can be formed on one side or both sides. That is, the conductive filler-containing coating layer, the resin layer, the carbon fiber fabric layer, and the conductive filler-containing coating layer are sequentially laminated, or the conductive filler-containing coating layer, the resin layer, the carbon fiber fabric layer, the resin layer, and the conductive filler-containing coating layer are sequentially stacked. A laminate comprising a laminated laminated structure may be formed.

In the manufacturing method, preparing the carbon fiber fabric layer to have a thickness of about 200 μm to about 400 μm measured according to the conditions of KS K 0506 by weaving carbon fiber; may further include, for example , The average diameter of the carbon fiber may be about 1 μm to about 10 μm.

In this way, by adjusting the average diameter of the carbon fiber and the thickness of the fabric, etc., the content of the carbon fiber in the entire unit structural layer can be appropriately adjusted, and accordingly, the electrical properties and gas permeability of the separator for the fuel cell. and contact resistance can all be implemented at an excellent level.

In the manufacturing method, the upper and lower surfaces of the fabric are coated with a first composition containing about 0.01% to about 1% by weight of a conductive polymer, about 1% to about 10% by weight of a binder resin, and an aqueous solvent to contain a conductive polymer. The carbon fiber fabric layer may be prepared as a fabric having a coating layer formed thereon.

The conductive polymer is as described above in one embodiment, and the aqueous solvent may include isopropyl alcohol, n-pentanol, 4-methyl-2-pentanol, and the like, but is not limited thereto.

Accordingly, electrical properties of the bipolar plate for a fuel cell may be improved.

The binder resin may include, for example, polystyrene sulfonic acid, polyvinyl alcohol, polyester, polyurethane, acrylic resin, etc., but is not limited thereto.

In addition, the resin layer may be formed by laminating a thermoplastic resin film having a thickness of about 40 μm to about 80 μm on one side or both sides of the carbon fiber fabric layer. The thermoplastic resin film may be formed of a thermoplastic resin, and the thermoplastic resin is as described above in one embodiment.

In this way, the content of the impregnating resin in the entire unit structural layer can be appropriately adjusted by adjusting the thickness of the resin layer, thereby sufficiently filling the empty space of the carbon fiber fabric to prevent mixing of the reactive gas while preventing the fuel. Electrical properties of the battery separator may not be reduced.

In addition, in the above manufacturing method, for example, the conductive filler-containing coating layer is prepared by coating a second composition including about 5% to about 30% by weight of a conductive filler and about 70% to about 95% by weight of a solvent. It may further include;

In this way, by adjusting the content of the conductive filler included in the second composition and the thickness of the conductive filler-containing coating layer, etc., the content of the conductive filler in the entire unit structural layer can be appropriately adjusted, and accordingly, the separation for the fuel cell While improving the electrical properties of the plate, it is possible to realize excellent mechanical properties without breaking by forming the flexural strength at an appropriate level.

For example, when the conductive filler-containing coating layer is laminated on the top or bottom of the surface of the carbon fiber fabric layer on which the resin layer is formed, the second composition is coated on one surface of the resin layer to form the conductive filler-containing coating layer. can be layered.

On the other hand, in the case of laminating the conductive filler-containing coating layer on the surface of the carbon fiber fabric layer on which the resin layer is not formed, the second composition is coated on one surface of the release film to prepare the conductive filler-containing coating layer, and then the conductive filler-containing coating layer is prepared. The conductive filler-containing coating layer may be laminated on one surface of the carbon fiber fabric layer so as to be in contact with it. The release film may be appropriately removed at a necessary time in the manufacturing process.

The release film may use a type known in the art, and for example, a group consisting of a Teflon film, a nylon film, a PVC film, a silicone film, and combinations thereof It may be formed of a material containing at least one selected from.

The solvent may be, for example, an organic solvent, toluene, isopropyl alcohol (IPA), xylene, diethylene glycol monobutyl ether, diethyl ketone, methyl butyl ketone, dipropyl ketone, cyclohexanone, n-pentane It may include at least one selected from the group consisting of ol, 4-methyl-2-pentanol, cyclohexanol, and combinations thereof, but is not limited thereto.

In the step of preparing the conductive filler-containing coating layer, for example, after coating the second composition, it is dried at about 50° C. to about 100° C. for about 5 minutes to about 20 minutes to volatilize the solvent while containing the conductive filler. A coating layer may be formed, but the temperature and time conditions may be appropriately changed according to the purpose and use of the invention.

In addition, as a coating method, for example, the coating method includes a dipping method, a forward roll coater method, a reverse roll coater method, a gravure coater method, a knife coater method, a braid coater method, a rod coater method, an air doctor coater method, and a cutane coater method, a pounding coat method, etc. may be used, but is not limited thereto.

The thickness of the conductive filler-containing coating layer may be, for example, about 10 μm to about 80 μm, but is not limited thereto.

In the manufacturing method, a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin may be formed by thermally compressing the laminate. The conductive filler and the impregnating resin may be permeated or penetrated into the carbon fiber fabric by the heat compression.

The thermal compression may be performed at a pressure of about 50 kg/cm 2 to about 300 kg/cm 2 at a temperature of about 180° C. to about 250° C. by a hot press. By performing thermal compression under conditions within the above range, the resin layer is melted while the impregnating resin flowing therefrom and the conductive filler-containing coating layer melted so that the conductive filler flowing therefrom permeates or penetrates into the carbon fiber fabric to be sufficiently impregnated. can do.

At this time, the conductive filler permeates and impregnates from both surfaces of the carbon fiber fabric in the direction of the center of the thickness, and since the degree of permeation or penetration of the conductive filler decreases in the direction of the center of the thickness, the unit structure layer is formed in the thickness direction. , A concentration gradient may be formed such that the concentration of the conductive filler decreases from both surfaces toward the center of the thickness.

In this way, by forming a high concentration of the conductive filler on both surfaces of the unit structural layer, that is, the upper and lower surfaces, it is possible to increase electrical conductivity while reducing contact resistance. In addition, at the same time, at the center of the thickness, the concentration of the conductive filler having a hard property may be low to form the flexural strength of the fuel cell bipolar plate at an appropriate level, thereby implementing excellent mechanical properties for a long time without breaking. there is.

Specifically, since the carbon fiber fabric has excellent electrical conductivity, despite forming a low concentration of the conductive filler in the central portion of the thickness, the electrical properties of the separator for a fuel cell can be implemented at an excellent level, and also, the Since the mechanical properties of the carbon fiber fabric are excellent, the mechanical properties of the separator for a fuel cell may also be improved.

The unit structural layer includes a first thickness region corresponding to about 5% to about 35% of the total thickness length in a direction from one surface toward the thickness center, including both surfaces perpendicular to its thickness direction; and a second thickness region corresponding to about 5% to about 35% of the total thickness in a direction from the other surface toward the center of the thickness.

The unit structural layer includes both surfaces perpendicular to its thickness direction, and a first thickness region corresponding to about 5% to about 35% of the total thickness length of the unit structural layer in a direction from each surface toward the center of the thickness. and a second thickness region, wherein the total amount of the conductive fillers respectively present in the first thickness region and the second thickness region is, for example, about 50 of the total weight of the conductive fillers included in the unit structural layer. % to about 100%, specifically about 70% to about 90%.

At this time, the content of the conductive filler present in the first thickness region; and the content of the conductive filler present in the second thickness region may be the same or different.

Based on the total weight of the conductive filler, a high content within the above range, that is, about 50% or more is present in the first and second thickness regions, so that both surface portions of the fuel cell bipolar plate have more of the conductive filler than the central portion. The content is higher, and thus the bipolar plate for a fuel cell can realize excellent electrical properties and excellent mechanical properties at the same time.

Since a high level of content within the above range based on the total weight of the conductive filler is present within the thickness range, both surface portions of the separator for fuel cell have a higher content of the conductive filler than the central portion of the separator for fuel cell. The plate can realize excellent electrical properties and excellent mechanical properties at the same time.

For example, when the total thickness of the unit structural layer is about 300 μm, the first thickness region and the second thickness region corresponding to about 15 μm to about 105 μm in a direction from each surface toward the center of the thickness The total weight of each conductive filler may be about 50% to about 100% of the total weight of the conductive filler.

The unit structural layer can be formed such that the thickness ratio of the fabric and the unit structural layer is from about 1:0.9 to about 1:1.4 by appropriately adjusting the thickness of each of the above-described layers and process conditions of thermal compression, etc. Accordingly, since the thickness difference between the fabric and the unit structural layer can be formed to a smaller level or the thicknesses thereof can be formed to be substantially the same, excellent electrical properties can be implemented on the upper and lower surfaces of the separator for a fuel cell.

As described above, the fabric may have a thickness of about 200 μm to about 400 μm measured according to the conditions of KS K 0506, and the thickness of the unit structure layer may be, for example, about 180 μm to about 560 μm However, it is not limited thereto.

As described above in one embodiment, the thickness of the unit structural layer may be thinner or thicker than the thickness of the fabric according to the content of the impregnating resin.

In the manufacturing method, the unit structural layer may be formed such that the weight ratio of the impregnating resin to the carbon fiber in the entire unit structural layer is about 1:3 to about 1:8.4.

By forming the fuel cell to have a weight ratio within the above range, it is possible to sufficiently prevent mixing of reactant gases during operation of the fuel cell by realizing a low level of gas permeability while implementing a high level of electrical properties without including a metal material.

In addition, the unit structural layer may be formed such that the weight ratio of the impregnating resin to the conductive filler in the entire unit structural layer is about 1:0.25 to about 1:1.5.

By forming the separator to have a weight ratio within the above range, it is possible to realize excellent mechanical properties by sufficiently improving the electrical properties of the bipolar plate for a fuel cell while forming the flexural strength to an appropriate level, and also realize a low gas permeability to drive the fuel cell. Mixing of reaction gases can be sufficiently prevented.

In addition, in the manufacturing method, the unit structural layer may be formed such that the content of the impregnating resin in the entire unit structural layer is about 10% to about 25% by weight. By forming the content to be included within the above range, it is possible to sufficiently fill the empty space of the carbon fiber fabric to prevent mixing of the reactant gas while not deteriorating the electrical properties of the fuel cell bipolar plate.

The unit structural layer may be formed such that the content of the carbon fiber in the entire unit structural layer is about 60% to about 84% by weight. By forming such that the content is within the above range, the electrical properties, gas permeability, and contact resistance of the separator for a fuel cell may all be implemented at excellent levels. Specifically, when the content of the carbon fiber is less than about 60% by weight, electrical conductivity and mechanical properties are lowered, and when it exceeds about 84%, the pores are not sufficiently filled by the impregnation resin, so the gas permeability is inferior and the surface is flat It is difficult to form, and there is a problem in that contact resistance increases.

The unit structural layer may be formed such that the content of the conductive filler in the entire unit structural layer is about 5% by weight to about 15% by weight. By forming the content within the above range, the electrical properties of the bipolar plate for a fuel cell may be improved and the flexural strength may be formed at an appropriate level to realize excellent mechanical properties without breaking.

As described above, in the case of preparing the carbon fiber fabric layer as a fabric having conductive polymer-containing coating layers formed on the upper and lower surfaces, the content of the conductive polymer in the entire unit structure layer is about 0.01% to about 1% by weight. The unit structural layer may be formed. By including the amount within the above range, it is possible to realize sufficiently excellent electrical properties at the interface between the respective unit structural layers without unnecessarily increasing the cost.

The fuel cell bipolar plate manufactured according to the manufacturing method may have a contact resistance of, for example, about 5 mΩ cm ² to about 50 mΩ cm ² , specifically about 5 mΩ cm ² to about 20 mΩ cm ² , Electrical conductivity may be, for example, about 50 S/cm to about 30 S/cm, specifically about 100 S/cm to about 200 S/cm. By realizing a low level of contact resistance within the above range and a high level of electrical conductivity within the above range, excellent electrical properties can be implemented, and energy efficiency can be effectively improved.

At the same time, the bending strength of the bipolar plate for a fuel cell may be about 20 MPa to about 50 MPa. Excellent mechanical properties can be implemented by having a flexural strength within the above range. Specifically, when the fuel cell is less than about 20 MPa, it is difficult to withstand the injection pressure of the fuel gas during operation of the fuel cell and may be damaged, and can be easily damaged by vibrations generated during vehicle operation. may be damaged.

Hereinafter, specific embodiments of the present invention are presented. However, the embodiments described below are only intended to specifically illustrate or explain the present invention, and the present invention should not be limited thereto.

Example

Example One

A fiber layer having a thickness of 300 μm was prepared using carbon fibers having an average diameter of 5 μm, and one resin layer was prepared using a polypropylene resin film having a thickness of 60 μm. A composition containing 20% by weight of a conductive filler and 80% by weight of a solvent was coated on one surface of the resin layer by a knife coater method, and dried at 70 ° C. for 15 minutes to form a coating layer containing the conductive filler having a thickness of 20 μm, The composition was coated on one side of a Teflon film by a knife coater method and dried at 70° C. for 15 minutes to form a coating layer containing the conductive filler having a thickness of 20 μm.

Subsequently, a laminate having a laminate structure of conductive filler-containing coating layer/resin layer/fiber layer/conductive filler-containing coating layer/Teflon film is formed, and a temperature of 200° C. and 142.76 kg/cm 2 are applied to the upper and lower surfaces of the laminate, that is, both surfaces. A unit structural layer was formed by performing thermal compression under a pressure condition of , and a bipolar plate for a fuel cell was prepared by removing the Teflon film, and the total thickness of the bipolar plate for a fuel cell was 300 μm.

Specifically, the weight ratio of the impregnated resin to the carbon fiber in the entire unit structural layer was 1:6.0, and the weight ratio of the impregnated resin to the conductive filler in the entire unit structural layer was 1:0.5, and the unit structural layer The content of the impregnated resin in the total was 14% by weight.

Example 2 (the content of the impregnated resin is higher than that of Example 1)

A fiber layer having a thickness of 300 μm was prepared using carbon fibers having an average diameter of 5 μm, and two resin layers were prepared using a polypropylene resin film having a thickness of 30 μm. A first composition containing 20% by weight of a conductive filler and 80% by weight of a solvent was coated on one surface of each of the resin layers using a knife coater method, and dried at 70° C. for 15 minutes to obtain a thickness of 20 μm of the conductive filler. A containing coating layer was formed.

Subsequently, a laminate having a laminated structure of conductive filler-containing coating layer/resin layer/fiber layer/resin layer/conductive filler-containing coating layer is formed, and a temperature of 200° C. and 142.76 kg/cm 2 are applied to the upper and lower surfaces of the laminate, that is, both surfaces. A separator for a fuel cell was manufactured by forming a unit structural layer by performing thermal compression under a pressure condition of 310 μm.

Specifically, the weight ratio of the impregnated resin to the carbon fiber in the entire unit structural layer was 1:3.3, and the weight ratio of the impregnated resin to the conductive filler in the entire unit structural layer was 1:0.6, and the unit structural layer The content of the impregnating resin in the total was 25% by weight.

Comparative Example 1 (In the case of mixing with a resin composition without forming a separate conductive filler-containing coating layer)

A fiber layer having a thickness of 300 μm was prepared from carbon fibers having an average diameter of 5 μm, and two conductive films having a thickness of 80 μm formed of a resin composition containing 13% by weight of polypropylene resin and 6% by weight of conductive filler were prepared. .

Subsequently, a laminate having a laminated structure of conductive film/fiber layer/conductive film is formed, and thermal compression is performed on the upper and lower surfaces of the laminate, that is, both surfaces, under conditions of a temperature of 200° C. and a pressure of 142.76 kg/cm 2 , thereby forming a unit. A separator for a fuel cell was prepared by forming a structural layer, and the total thickness of the separator for a fuel cell was 300 μm.

Specifically, the weight ratio of the impregnated resin to the carbon fiber in the entire unit structural layer was 1:2.2, and the weight ratio of the impregnated resin to the conductive filler in the entire unit structural layer was 1:0.1, and the entire unit structural layer The content of the impregnating resin was 15% by weight.

Comparative Example 2 (When the content of the conductive filler is reduced compared to Comparative Example 1)

A separator for a fuel cell was prepared under the same conditions and method as in Comparative Example 1, except that two conductive films having a thickness of 80 μm formed of a resin composition containing 16% by weight of a polypropylene resin and 3% by weight of a conductive filler were prepared. And, the total thickness of the separator for the fuel cell was 300 μm.

Specifically, the weight ratio of the impregnated resin to the carbon fiber in the entire unit structural layer was 1:2.2, and the weight ratio of the impregnated resin to the conductive filler in the entire unit structural layer was 1:0.05, and the unit structural layer The content of the impregnated resin in the total was 16% by weight.

evaluation

The physical properties of the separators for fuel cells according to Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated and listed in Table 1 below.

Experimental example

Experimental example 1: conductivity filler density gradient

Measurement method: Two fuel cell separators according to Examples 1 and 2 and Comparative Examples 1 and 2 were prepared as specimens having a size of 1 cm x 1 cm, respectively, and 600 ° C. for 1 hour according to ASTM D5630 conditions. , measured by performing an ash test under a nitrogen atmosphere.

Accordingly, for each of the two specimens for Examples 1 and 2 and Comparative Examples 1 and 2, the content of the conductive filler contained in the entire specimen was measured in one of the specimens remaining after the impregnation resin was all burned, and the other One is to sample a first thickness region and a second thickness region corresponding to a thickness range of 100 μm in a direction toward the thickness center from each surface, and the content of the conductive filler included in the first thickness region and the second thickness region. were measured respectively.

Then, the total content of conductive fillers measured as described above; and the total sum of the contents of the conductive fillers respectively included in the first thickness region and the second thickness region; the concentration gradient was calculated by converting into a percentage.

Experimental example 2: flexural strength

Measurement method: It was measured using a flexural strength tester (Instron, 5569A) according to ASTM D 790.

Experimental Example 3: electrical conductivity and contact resistance

Measurement method: It was measured using a 4-probe method by Mitsubishi (Misubishi chemical, Loresta-GP, Japan) equipment.

Specifically, the modified Davies method was used to obtain optimized constants for unit cell fastening, and when pressure was applied to the copper plate accordingly, a fuel cell separator and carbon paper (SGL, 10BA GDL (Gas Diffusion Layer) in the form of measuring the contact resistance In addition, a current supply device (KIKUSUI Co.) was used to supply current to the metal separator, and an amplitude of 0.5A and 25cm2 5A was applied as a DC current having an electrode area, and the voltage was measured using a multimeter (Fluke, 8808A).

In addition, in the contact resistance measuring device, the measurement was performed by providing a pressure of 100 N/cm ² using a compression holding tester (Instron Co., 5569A).

Concentration gradient (%) Flexural strength (MPa) electrical conductivity
(S/cm) contact resistance
(mΩ cm ² ) Example 1 85 44 150 9.3 Example 2 70 50 130 15.4 Comparative Example 1 35 40 90 50.8 Comparative Example 2 30 55 80 67.9

As shown in Table 1, in the fuel cell separator according to Examples 1 and 2, the sum of the contents of the conductive filler present in the first and second thickness regions is the total amount of the conductive filler included in the fuel cell separator. Since it accounts for more than 50% of the weight, contact resistance was low and high electrical conductivity was measured on both surfaces of the fuel cell bipolar plate, and at the same time, it was clearly confirmed that the mechanical properties were excellent as both the flexural strengths were 44 MPa or more.

On the other hand, since the bipolar plates for fuel cells according to Comparative Examples 1 and 2 had high contact resistance and low electrical conductivity measured on both surfaces thereof, it was clearly expected that the energy efficiency would be inferior, and in the case of Comparative Example 1, the flexural strength was also relatively low.

100: separator plate for fuel cell
110: unit structural layer
120: fabric
130: conductive filler
140: impregnation resin

Claims (21)

A unit structural layer comprising a carbon fiber fabric, a conductive filler and an impregnated resin,
In the thickness direction of the unit structural layer, a concentration gradient is formed so that the concentration of the conductive filler decreases from both surfaces toward the center of the thickness,
The conductive filler is at least one selected from the group consisting of carbon black, acetylene black, carbon nanotube (CNT), graphite, graphene, graphite nanofiber (GNF), fullerene, and combinations thereof containing
Separator for fuel cell.
delete According to claim 1,
The unit structural layer includes both surfaces perpendicular to its thickness direction, and a first thickness region corresponding to 5% to 35% of the total thickness length of the unit structural layer in a direction from each surface toward the thickness center, and a second thickness region 2 thickness region,
The total amount of the conductive fillers respectively present in the first thickness region and the second thickness region is 50% to 100% of the total weight of the conductive fillers included in the unit structural layer.
Separator for fuel cell.
According to claim 1,
The contact resistance is 5 mΩ·cm ² to 50 mΩ·cm ² ,
electrical conductivity of 50 S/cm to 300 S/cm
Separator for fuel cell.
According to claim 1,
Flexural strength of 20 MPa to 50 MPa
Separator for fuel cell.
According to claim 1,
The weight ratio of the impregnating resin to the carbon fiber in the entire unit structural layer is 1:3 to 1:8.4
Separator for fuel cell.
According to claim 1,
The weight ratio of the impregnating resin to the conductive filler in the entire unit structural layer is 1:0.25 to 1:1.5
Separator for fuel cell.
According to claim 1,
The content of the impregnating resin in the entire unit structural layer is 10% to 25% by weight
Separator for fuel cell.
According to claim 1,
The unit structural layer further includes a conductive polymer,
The conductive polymer is polyaniline-based polymer, polythiophene-based polymer, polypyrrole-based polymer, polyprene-based polymer, polyacetylene-based, polyphenylene-based, polyphenylene-vinylene-based, polyacene-based, polythiophene-based, and combinations thereof. Including at least one selected from the group consisting of
Separator for fuel cell.
According to claim 1,
The thickness ratio of the fabric and the unit structural layer is 1:0.9 to 1:1.4
Separator for fuel cell.
According to claim 1,
The unit structural layer has a thickness of 180 μm to 560 μm.
Separator for fuel cell.
delete According to claim 1,
The impregnation resin is a thermoplastic resin
Separator for fuel cell.
delete delete Forming a laminate comprising a laminated structure of a conductive filler-containing coating layer / a carbon fiber fabric layer having a resin layer formed on at least one surface / a conductive filler-containing coating layer; and
Forming a unit structural layer including a carbon fiber fabric, a conductive filler, and an impregnated resin by thermally compressing the laminate,
The unit structural layer is manufactured such that a concentration gradient is formed such that the concentration of the conductive filler decreases from both surfaces toward the center of the thickness in the thickness direction.
Method for manufacturing a separator for a fuel cell.
delete delete According to claim 16,
The unit structural layer includes both surfaces perpendicular to its thickness direction, and a first thickness region corresponding to 5% to 35% of the total thickness length of the unit structural layer in a direction from each surface toward the thickness center, and a second thickness region 2 thickness region,
The total amount of the conductive fillers present in the first thickness region and the second thickness region is 50% to 100% of the total weight of the conductive fillers included in the unit structural layer.
Method for manufacturing a separator for a fuel cell.
According to claim 16,
The thermal compression is performed at a pressure of 50 kg / cm 2 to 300 kg / cm 2 at a temperature of 180 ° C to 250 ° C by a hot press.
Method for manufacturing a separator for a fuel cell.
According to claim 16,
Preparing the carbon fiber fabric layer to have a thickness of 200 μm to 400 μm by weaving carbon fibers; further comprising
Method for manufacturing a separator for a fuel cell.

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