JP2003045456A - Solid high polymer fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid high polymer fuel cell stack having a stable output voltage for a long time, suitable for a power supply for an automobile, a distributed power supply for home use, and the like. SOLUTION: In this solid high polymer fuel cell stack having a layer-built cell formed by laminating plural unit cells each of which comprises a cathode electrode and an anode electrode provided on both faces of a solid high polymer electrolyte membrane and separators disposed on the respective electrodes, an end plate, and a current collecting plate for taking out the cell output, the current collecting plate comprises a conductive substrate, and the whole surface or a part of the surface of the conductive substrate is coated with a composition containing one or more kinds of conductive particles selected from a carbon particle, a metal particle, a metal carbide particle, and a composite particle of carbon and metal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer electrolyte fuel cell stack.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell can obtain a large current and a high output, has a long life, little deterioration due to start and stop, a low operating temperature (about 70 to 80 ° C.), and a precise differential pressure. Since the control has advantages such as being unnecessary, it is expected to have a wide range of applications such as a power source for electric vehicles and a distributed power source for business or home use.

A single cell of a polymer electrolyte fuel cell is a porous film having a thickness of several 10 μm in which a catalyst of Pt or Pt alloy is dispersed on both sides of a polymer film having a proton conductivity in an electrolyte and having a thickness of several 10 μm. And a gas flow path for supplying hydrogen to one electrode (anode electrode) and air (oxygen) to the other electrode (cathode electrode). A battery stack in which a plurality of such single cells are stacked according to the required output is used in an actual system.

As described above, in order to extract a large current,
It is considered that the contact resistance between the current collector plate for taking out the output of the battery stack and the separator of the battery stack has an effect, and it is important to suppress the increase of the contact resistance for long-term use as a power source. .

As a technique for reducing the internal resistance of a battery, it has been proposed to provide carbon fiber paper between a separator and an electrode (Japanese Patent Laid-Open No. 10-162838).

[0006]

A feature of the polymer electrolyte fuel cell is that a large current can be taken out and a high output can be easily obtained. However, in order to extract a large current, an output cable having a large cross-sectional area is required, and it is difficult to directly connect this cable to graphite to obtain an output from the viewpoint of strength of graphite. Therefore, a structure is provided in which a metal current collector plate is provided and the battery stack output is extracted from this.

In order to obtain a high output, it is important to suppress not only the internal resistance of the battery stack but also the increase of the contact resistance between the current collecting plate for taking out the output of the battery stack and the separator of the battery stack. Is.

Regarding the reduction of the internal resistance of a battery stack, a method of providing carbon fiber paper between a separator and an electrode has been described in Japanese Patent Application Laid-Open No. 10-162838. However, no consideration is given to a long-term increase in the contact resistance between the separator for collecting the output of the battery stack and the separator.

The collector plate for taking out the output of the battery stack is
Metals are often used in terms of strength. In this case, it is conceivable that the surface resistance of the current collector plate increases due to corrosion of the current collector plate surface, and the contact resistance with the separator also increases. Will cause a decrease in output.

In order to put it into practical use as a power source for automobiles or a distributed power source for households that requires a long life, a current collector plate that does not cause a reduction in output is essential. Also, when connecting a cable to the output terminal of the current collector for extracting a large current,
Although it is possible to connect with bolts, etc., it is also possible to weld the cable directly to the current collector plate by using metal, and there is an advantage that there is no fear of loosening etc. compared to the case of using bolts. To be

In view of the above, an object of the present invention is to provide a solid polymer type fuel cell stack suitable for a power source for automobiles, a dispersed power source for home use and the like.

[0012]

The gist of the present invention for achieving the above object is as follows.

A laminated battery, an end plate and a battery output for taking out a battery output, in which a plurality of single cells composed of a cathode electrode and an anode electrode provided on both sides of a solid polymer electrolyte membrane and separators arranged on each of the electrodes are laminated. In a polymer electrolyte fuel cell stack having a current collector plate, the current collector plate is made of a conductive substrate, and the entire surface or part of the surface of the conductive substrate is carbon particles, metal particles, metal carbide particles, carbon. A polymer electrolyte fuel cell stack is characterized in that it is coated with a composition containing one or more conductive particles of a composite particle of a metal and a metal.

As a result, the output reduction of the polymer electrolyte fuel cell stack can be suppressed.

Further, a resin composition containing one or more kinds of conductive particles selected from carbon particles, metal particles, metal carbide particles, and carbon-metal composite particles is used to cover a part or the whole surface of the conductive substrate. In the polymer electrolyte fuel cell stack to be coated. This makes it possible to reduce the decrease in the output of the battery.

As the current collector, copper, stainless steel,
Metals such as nickel and aluminum can be used as the conductive substrate of the current collector. The base is a strip-shaped plate,
It may have any shape such as a disc, hexagon, perforated plate, etc., and can be adapted to the shape of the battery stack. By providing the external terminal connection part on a part of the current collector plate,
It is possible to connect to external electric devices and secondary batteries.

Further, in the present invention, a composite of metal and resin, such as one in which a metal plate is embedded in a resin or one in which a metal plate and a resin plate are adhered, can be used as the conductive substrate.

The composition coating a part or the whole of the surface of the conductive substrate contains one or more conductive particles of carbon particles, metal particles, metal carbide particles, and carbon-metal composite particles. Further, it is more preferable that these particles do not deteriorate due to a chemical reaction with moisture or oxygen in the atmosphere, or an electrochemical oxidation reaction or reduction reaction due to the generated voltage of the fuel cell. That is, as the conductive particles used in the present invention, a material having resistance to a corrosion reaction due to moisture, oxygen, etc., or an electrochemical reaction due to the voltage of the battery stack is suitable.

The conductive particles are prepared by suspending the particles in water or an organic solvent as a paint, and are directly applied to the surface of the conductive substrate by a coating method, a dipping method or the like, and the surface of the substrate is coated. It can be performed.

It is also possible to apply the liquid containing the conductive particles to the surface of the conductive substrate and then sinter the conductive particles by heat treatment to more firmly adhere the conductive particles to the conductive substrate. Is. The conductive particles may be a mixture of two or more different materials.

As another method, it is possible to coat a part or the whole surface of the conductive substrate with the resin composition containing the conductive particles. In this case, a resin composition containing conductive particles is suspended in an organic solvent such as ethanol, alcohol such as propanol, 1-methyl-2-pyrrolidone, hexane, etc., applied to the surface of the conductive substrate and heated. By volatilizing the solvent by the treatment, the resin composition containing the conductive particles can be fixed on the surface of the conductive substrate.

Examples of the above resin include polyvinylidene fluoride, ethylene / propylene rubber, 4-fluoroethylene,
Examples thereof include epoxy resins, but the resins are not limited to these as long as they have a function of fixing the conductive particles to the surface of the conductive substrate.

The compounding ratio of the above resin needs to be in a range such that the electric resistance of the composition of the conductive particles and the resin does not become a large ratio with respect to the internal resistance of the battery. This is because when the resistance of the coating layer of the current collector formed by the composition is large, voltage resistance and output loss due to ohmic resistance occur during power generation of the fuel cell. It is desirable that the voltage drop that occurs in the coating layer be several percent or less of the output voltage of the battery stack. As a result, the output loss of the battery does not pose a practical problem.

As an example of the conductive substrate of the present invention, the surface of a metal plate made of copper, stainless steel, nickel, aluminum or the like is coated with a resin composition containing conductive particles such as carbon particles. In particular, since the carbon particles are chemically stable, it is possible to obtain a current collector excellent in durability against corrosion by moisture and oxygen in the atmosphere or electrochemical oxidation.

In this way, the resistance increase of the metal surface due to corrosion or the like is suppressed, and the contact resistance between the current collector and the separator does not increase for a long period of time, so that a stable output of the fuel cell stack can be obtained.

As the carbon particles, graphite powder and amorphous carbon powder can be used. Examples of the graphite powder include artificial graphite and natural graphite, and examples of the amorphous carbon include acetylene black and Ketjen black.

From the viewpoint of corrosion resistance and surface resistance, the thickness of the coating layer is preferably 50 to 200 μm. The sheet resistance of the coating layer varies depending on the thickness of the coating layer, the type of conductive particles used, the composition ratio of the particles and the resin, and the like, but is 1 to 50 m.
It is about Ωcm ² .

For example, in the case of a stack in which 10 single cells are stacked, the output voltage of the stack depends on the current density during operation. For example, when hydrogen is used as the anode gas and air is used as the cathode gas, the current density is about 7.5 V at a current density of 0.3 A / cm ² , and about 7.2 V at 0.5 A / cm ² .

On the other hand, the voltage drop due to the coating layer is 0.3 A /
The current density is 0.3 to 15 mV, and the current density is 0.5 A / cm ^2.
It is 0.5 to 25 mV in cm ² . Therefore, the voltage drop due to the coating layer is 0.3 with respect to the output voltage of the battery stack.
0.004 to 0.2 during operation at a current density of A / cm ^2.
%, At 0.5 A / cm ² , it is 0.007 to 0.35%.

Assuming a system for practical use, the number of stacked layers is several tens of cells or more, and the rate of voltage drop due to the coating layer is even smaller.
It is about 1 to 0.2%, and the influence of the coating layer does not pose a practical problem. The coating layer is the entire surface of the current collector, or
Part of the surface of the current collector plate that contacts the separator, by coating with a resin composition containing the conductive particles of the present invention,
Corrosion resistance of the current collector is also improved.

The contact resistance between the collector of a simple metal and the graphite separator depends on the processing accuracy of the surface of each material because the material itself is hard. Therefore, in order to reduce the contact resistance, it is necessary to improve the processing accuracy of the surface, which causes an increase in cost.

On the other hand, by providing a coating layer that is more flexible than metal or graphite on the metal surface, the contact state of the current collector plate with graphite is also improved, and the effect of reducing contact resistance is obtained without increasing the processing accuracy. be able to.

Similarly, as conductive particles having corrosion resistance, metal powder such as stainless steel, nickel and titanium, metal carbide such as tungsten carbide and titanium carbide, and metal particles such as copper, nickel and titanium are dispersed in carbon particles. By fixing the composite particles to the conductive substrate, the contact resistance between the current collector plate and the separator can be reduced, and a current collector excellent in durability over a long period can be manufactured. The metal dispersed in the carbon particles is not limited to the above metals as long as it has electronic conductivity.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described based on Examples.

Example 1 FIG. 1 is an exploded perspective view showing the structure of the solid polymer electrolyte fuel cell stack of this example.

The stack comprises a metal collector (1-) for output extraction provided with a coating layer (1-1) made of a carbon material and a resin.
2), graphite separator (1-3), gas diffusion layer (1-
4), integrated electrode (1-5), gas diffusion layer (1-4),
The graphite separators (1-3) are laminated in this order, and the end plates (1-
6) is used to fix both ends.

In this example, a stack was constructed by inserting a cooling separator (1-7) every two cells. A cooling water passage (1-8) and a gas passage (1-9) are provided in the end plate, the current collector, the graphite separator, and the integrated electrode, respectively.
The battery stack has 20 cells and the electrode area is 1
It is 00 cm ² . The output was 450 W at 30 A and 700 W at 50 A.

In the present embodiment, the coating layer is provided including the gas passage portion, etc., but depending on the battery structure, the effect may be the same even if the portion corresponding to the electrode portion is covered.

Example 2 An artificial graphite powder was used as the conductive particles, polyvinylidene fluoride was used as the resin, and 1-methyl-2-pyrrolidone was used as the solvent for the resin to prepare a coating material for coating.

80% by weight of graphite, polyvinylidene fluoride 2
Graphite was added to an N-methylpyrrolidone solution of polyvinylidene fluoride so as to be 0% by weight, and mixed for 5 hours using a ball mill. The composition ratio of the paint is graphite:
Polyvinylidene fluoride: N-methylpyrrolidone = 80:
It was 20: 220.

The conductive substrate used in this embodiment is a plate made of copper and aluminum. The prepared coating material was applied to the surface of a current collector plate made of copper and aluminum using a coater. After coating, it was dried in an oven at 80 ° C. for 1 hour, and then kept at 120 ° C. for 3 hours to form a coating layer. The coating layer thickness was 100 μm.

Four solid polymer fuel cell stacks having the structure shown in FIG. 1 were prepared by using a copper-made and aluminum-made current collecting plate provided with a coating layer and a copper-made and aluminum current collecting plate having no coating layer. did. The number of single cell stacks was 20 in each stack.

The prepared battery stack was operated at a temperature of 70 ° C. and a current density of 0.3 A / cm ² . Note that hydrogen gas was used as the anode gas and air was used as the cathode gas, and the gas utilization rates were 70% on the anode side and 40% on the cathode side. FIG. 2 shows changes with time in the stack output voltage during operation. Performance of polymer electrolyte fuel cell stack using current collector with artificial graphite coating layer at current density of 0.3 mA / cm ² .

A battery stack using a collector plate provided with a coating layer is made of copper (2-1: ◯) and aluminum (2-2:
All of the marks (Δ) showed a stable stack output voltage.

On the other hand, in the battery stack using the current collector plate not provided with the coating layer, both the copper stack (2-3: ● mark) and the aluminum stack (2-4: black Δ mark) showed a decrease in voltage. It was It was also confirmed that the initial stack output voltage had almost no effect on the output voltage due to the coating layer.

[Example 3] In this example, four solid polymer fuel cell stacks were produced in the same manner as in Example 2, using natural graphite as the graphite. Battery operating condition is current density 0.5
A / cm ² and other operating conditions are the same as in Example 1. FIG. 3 shows changes with time in the stack output voltage during operation.

The battery stack using the current collector plate provided with the coating layer (1-1) has a stable stack output for both copper (3-1: ○) and aluminum (3-2: Δ). The voltage is shown. The battery stack using the current collector plate not provided with the coating layer is made of copper (3-3: mark) as in Example 1.
In any case made of aluminum (3-4: black △ mark),
A drop in voltage was observed.

Example 4 In this example, 85% by weight of natural graphite powder and acetylene black 15 were used as conductive particles.
A weight percent mixed powder was used. The mixed powder was added to the N-methylpyrrolidone solution of polyvinylidene fluoride so that the mixed powder was 75% by weight and the polyvinylidene fluoride was 25% by weight, and the mixture was mixed using a ball mill as in Example 1. The composition ratio of the paint is a weight ratio: mixed powder: polyvinylidene fluoride:
N-methylpyrrolidone = 75: 25: 230.
The obtained coating material was applied to the surface of a current collector plate made of copper and aluminum using a coater. After coating, it was dried under the same conditions as in Example 1 to form a coating layer.

A solid polymer type fuel cell stack was produced using these two kinds of current collector plates. In this embodiment, the number of stacked layers is four.
It was set to 0 cell. The operation was carried out under the same conditions as in Example 1 with a current density of 0.3 A / cm ² . FIG. 4 shows changes with time in the stack output voltage during operation.

A battery stack using a collector plate provided with a coating layer is made of copper (4-1: ○) and aluminum (4-2:
All of the symbols (Δ) show a stable stack output voltage, and no voltage drop is observed.

Example 5 In this example, a coating material for coating was prepared by using acetylene black and Ketjen black as the conductive particles. 65% by weight of both acetylene black and Ketjen black and 35% by weight of polyvinylidene fluoride so that N of polyvinylidene fluoride
Each carbon material was added to the methylpyrrolidone solution and mixed using a ball mill in the same manner as in Example 1. The composition ratio of the acetylene black paint is acetylene black: polyvinylidene fluoride: N-methylpyrrolidone = 65: 35: 250 by weight, and that of the Ketjenblack paint is Ketjenblack: polyvinylidene fluoride: N-methylpyrrolidone. = 65: 35: 260.

The obtained coating material was applied to the surface of the copper current collector using a coater. After coating, it was dried under the same conditions as in Example 1 to form a coating layer.

A polymer electrolyte fuel cell stack was produced using two kinds of current collector plates provided with an acetylene black coating layer and a Ketjen black coating layer. In this embodiment, the number of layers is 40 cells. Current density is 0.5A
/ Cm ² , other conditions were the same as in Example 1. FIG. 5 shows changes with time in the stack output voltage during operation.

Battery stack using a current collector plate provided with an acetylene black coating layer (5-1: ○), battery stack using a current collector plate provided with a Ketjen black coating layer (5)
-2: △) Both show stable changes in output voltage over time,
No voltage drop is observed.

Example 6 In this example, as the conductive particles, tungsten carbide having an average particle size of 1 μm (chemical formula:
WC) and the particles and acetylene black
A paint was prepared by dissolving 12% by weight of polyvinylidene fluoride in methyl-2-pyrrolidone in a liquid. The composition ratio of the paint was WC: acetylene black: polyvinylidene fluoride = 20: 10: 70 by volume. The obtained coating material was applied to the surface of a stainless steel (SUS306) current collector using a coater. After coating, it was dried under the same conditions as in Example 2 to form a coating layer. A solid polymer fuel cell stack was produced using this current collector plate (6-1: ◯). The number of layers was 40 cells.

Next, as the conductive particles, the average particle size is 10
Copper was dispersed in μm natural graphite to prepare composite particles of carbon and copper. This is natural graphite with ethanol and water 1: 1
After suspending the natural graphite powder in the mixed solution of 8 (volume ratio), the weight of divalent copper ion is 5% by weight with respect to the weight of graphite.
Copper nitrate was added to the suspension so that the amount of the resulting mixture was reduced, and a reducing agent such as sodium tetrahydroborate, formaldehyde, and hydrazine was added dropwise to deposit fine copper particles on the surface of the natural graphite particles. After washing this powder with water, it was vacuum dried and used as conductive particles (Cu-C).

The Cu-C composite particles were mixed with 1-methyl-2
A coating was prepared by dissolving 12% by weight polyvinylidene fluoride in pyrrolidone in a liquid. The composition ratio of the paint was Cu-C: polyvinylidene fluoride = 90: 10 by weight.

The obtained paint was applied to stainless steel (SUS30
6) The surface of the current collector plate was coated with a coater. After coating, it was dried under the same conditions as in Example 2 to form a coating layer. A solid polymer fuel cell stack was produced using this current collector plate (6-2: Δ mark). The number of layers was 40 cells.

An operation test was carried out on these battery stacks under the same conditions as in Example 1 at a current density of 0.5 A / cm ² . FIG. 6 shows changes with time in the stack output voltage during operation. A battery stack using a current collector plate provided with a coating layer,
It showed a stable output voltage and no voltage drop was observed.

[0060]

By using the current collector of the present invention, it is possible to suppress an increase in contact resistance between the conductive substrate and the separator due to a corrosion reaction or an electrochemical reaction on the surface of the conductive substrate, and the output voltage is stable for a long period of time. The polymer electrolyte fuel cell stack is obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a configuration of a solid polymer electrolyte fuel cell stack according to an embodiment of the present invention.

FIG. 2 During operation in Example 2 (current density: 0.3 mA)
3 is a graph showing the change over time in the stack output voltage of / cm ² ).

FIG. 3 During operation in Example 3 (current density 0.5 A /
3 is a graph showing changes with time in the stack output voltage of cm ² ).

[Fig. 4] Fig. 4 is a diagram illustrating the operation in Example 4 (current density of 0.3 A /
3 is a graph showing changes with time in the stack output voltage of cm ² ).

FIG. 5: During operation in Example 5 (current density 0.5 A /
3 is a graph showing changes with time in the stack output voltage of cm ² ).

FIG. 6 During operation in Example 6 (current density 0.5 A /
3 is a graph showing changes with time in the stack output voltage of cm ² ).

[Explanation of symbols]

1-1 ... coating layer, 1-2 ... metal current collector for output extraction, 1
-3 ... Graphite separator, 1-4 ... Gas diffusion layer, 1-5 ...
Integrated electrode, 1-6 ... End plate, 1-7 ... Cooling separator, 1-8 ... Cooling water passage, 1-9 ... Gas passage, 2-1 ...
Stack performance using copper current collector with artificial graphite coating layer (0.3
A / cm ² ), 2-2 ... Stacking performance using an aluminum current collector with an artificial graphite coating layer (0.3 A / cm ² ), 2-3
… Stack performance using copper current collector (0.3 A / cm ² ), 2
-4 ... Stack performance using an aluminum collector (0.3
A / cm ^2), 3-1 ... natural graphite coating layer with copper current collector using stack performance ^{(0.5A / cm 2), 3-2} ... natural graphite coating layer with an aluminum current collector using stack performance (0 .
5A / cm ^2), 3-3 ... copper current collector using stack performance ^{(0.5A / cm 2), 3-4} ... aluminum current collector using stack performance (0.5A / cm ^2), 4-1 ... Stack performance using natural current collector made of copper with natural graphite / acetylene black coating layer, 4-2 Stack performance using natural current collector made of aluminum material with natural graphite / acetylene black coating layer, 5-1 ... Copper current collector with acetylene black coating layer Body use stack performance,
5-2 ... Stack performance using a collector made of copper with Ketjenblack coating layer.

Continued front page    (72) Inventor Jinichi Imahashi             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Norio Yamada             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Kazumi Shigeru             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Katsunori Nishimura             7-1-1, Omika-cho, Hitachi-shi, Ibaraki Prefecture             Inside the Hitachi Research Laboratory, Hitachi Ltd. F term (reference) 5H026 AA06 CX04 EE02 EE18

Claims (2)

[Claims] 1. A laminated battery comprising a cathode and an anode provided on both sides of a solid polymer electrolyte membrane, and a plurality of unit cells each composed of a separator arranged at each of the electrodes, an end plate and a battery output. In a polymer electrolyte fuel cell stack having a current collector plate for taking out, the current collector plate is made of a conductive base, and the entire surface or part of the surface of the conductive base is carbon particles, metal particles, or metal carbide. A polymer electrolyte fuel cell stack, characterized in that it is coated with a composition containing at least one kind of electrically conductive particles of particles and composite particles of carbon and metal. 2. The polymer electrolyte fuel cell stack according to claim 1, wherein the composition contains conductive particles and a resin, and the conductive substrate is partially or entirely coated with the composition.