JPH11162496A - Carbon felt dipole plate and its forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the contact resistance between the positive and negative electrodes of a dipole late provided with the positive and negative carbon felt electrodes in a redox flow battery. SOLUTION: Multiple sheets of carbon felt cut with the carbon felt having the direction of fibers in the plane direction into a tape shape are laminated, an insulating or conductive resin in filled 2 in the carbon felt except for both faces where the cut faces of the carbon felt of a laminated product 1 are exposed and their vicinities to form a plate as a whole, and electric resistance is reduced, or a sheet of carbon felt is folded in zigzag with a strip shape used as a unit, the insulating or conductive resin is filled in the carbon felt except for both side faces of the long sides of each strip exposed on the surface by folding and their vicinities to form a plate as a whole, and electric resistance is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon felt bipolar plate for a redox flow battery and an improved method for forming the same.

[0002]

2. Description of the Related Art A redox flow battery is used in which unit cells are stacked. Each unit cell opposes a plate called a "bipolar plate", partitions the partition with a diaphragm (ion exchange membrane), and circulates a positive and negative electrolyte in each partitioned space to obtain an electromotive force. As the "bipolar plate", an electrode plate made of carbon fiber or the like is attached to both surfaces of a conductive plate (substrate) through which a current flows but through which an electrolyte does not pass. One of the electrode plates on both sides of the substrate is used as a positive electrode of a unit cell, and the other is used as a negative electrode of an adjacent unit cell.

[0003] Hereinafter, a "bipolar plate" is a plate for partitioning each unit cell in a redox flow battery, and has an electrode plate serving as a positive electrode of the unit cell on one surface and a negative electrode on the other surface. An electrode plate is provided, and between the positive and negative electrodes,
A plate that has the role of passing current but blocking the electrolyte.

FIG. 4 shows a schematic sectional structural view of a redox flow battery in which “bipolar plates” are stacked. In the figure, 11 is a bipolar plate substrate, and 12 and 12 on both sides are electrode plates. The positive and negative electrolytes are circulated through the gaps between the electrode plates 12, 12 made of carbon fiber or the like. The electromotive force is generated when ions pass through the diaphragm 13.

[0005] Since carbon is a substance that is stable against corrosion and the like by an electrolytic solution and has conductivity, a graphite plate, glassy carbon, plastic carbon (brass) is usually used as a substrate of a “bipolar plate”. Tick mixed with carbon) or the like is used. As the electrode plates on both sides, carbon cloth, carbon felt, etc., which are stable with respect to the electrolytic solution, are used. The reason why these fibrous materials are used is to increase the contact area with the electrolytic solution while securing a passage for the electrolytic solution, thereby reducing the internal electric resistance.

[0006] The efficiency of the redox flow battery depends on the power of the electrolyte circulation pump and the loss of the inverter of the orthogonal transform.
The loss of the battery body depends on the internal resistance of the battery.

[0007]

There are two problems in improving the internal resistance of the conventional "bipolar plate". One is that since the substrate and the carbon felt are only in contact, the effect of the contact resistance is inevitable, which is a factor that lowers the efficiency of the battery body.

[0008] Carbon felt is produced by firing fibers, but usually the original fibers are low in the "plane direction" (for example, 0.1 Ωcm) because the fiber direction is in the plane direction.
It shows electrical resistance, but is high in the “thickness direction” (for example, 0.6
Ωcm) Indicates electric resistance.

The carbon felt (electrode plate) on both sides attached to the bipolar plate substrate has its surface attached to the substrate, so that it is used in the "thickness direction" having high electric resistance.

For this reason, as disclosed in Japanese Patent Application No. Hei 8-226484, "Carbon Electrode", efforts are made to reduce the anisotropy of the electrical resistance of carbon felt, and the contact resistance between the substrate and the electrode plate is made by heat-sealing. Efforts have been made to reduce it by such means, but it is still not enough.

[0011] The present invention provides a carbon felt "bipolar" in which the internal resistance is reduced by removing the contact resistance in principle by structural improvement and using the carbon felt in the "plane direction" having a low electric resistance. Board ".
This is intended to reduce the internal resistance of the redox flow battery.

[0012]

According to the "bipolar plate" of the present invention, the conventional structure in which carbon felts serving as electrode plates are attached to both surfaces of a conductive substrate is not employed, and carbon fibers cut into a tape shape are employed. A "bipolar plate" is formed by laminating a felt in the thickness direction and integrating the central portion of the laminated body with a resin except for the double-sided cross section and the vicinity thereof.

Alternatively, instead of the laminate, a carbon bipolar plate is formed by folding a carbon felt at the tape width and integrating a central portion of the folded body except for both edges of the folded portion and the vicinity thereof with a resin.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A laminated body in which a plurality of carbon felts in which the direction of fibers is in a plane direction is cut into a tape shape and laminated, and the cut surfaces are made into both surfaces of a laminate, The laminated body is preliminarily filled with an insulating or conductive resin over the entire length of the laminated body in the laminating direction excluding the vicinity, and the laminated body is integrated into a “bipolar plate”.

Alternatively, the carbon felt in which the direction of the fiber is in the plane direction is folded in a zigzag form in units of strips (ie, in units of the width of the tape cut into the tape shape), and the strip long sides appearing on the surface by the folding. An insulating or conductive resin is filled over the entire length in the laminating direction of the central portion of the folded body except for both side surfaces constituted by the edges of the folded body and the vicinity thereof, and the folded body is integrally formed as a “bipolar plate”. .

In the "bipolar plate" of the present invention, the carbon felt portion solidified with the resin corresponds to the substrate of the conventional "bipolar plate", and the fracture surface of the carbon felt exposed on both surfaces through the resin. The vicinity thereof corresponds to an electrode plate attached to the substrate.

The space between the electrode plates on both sides is made of carbon felt penetrating through the resin in the "plane direction", so that two points of contact resistance from the electrode plate to the substrate to the electrode plate can be completely removed in principle. Since the direction is the “plane direction”, a low electric resistance can be secured.

In the case of the "bipolar plate" folded in a zigzag manner, the cut surface of the carbon felt does not appear on both sides, but since the electrolytic solution penetrates the porous portion of the carbon felt, the effect of reducing the electric resistance is reduced. It does not change much compared to the case of "bipolar plate" by lamination.

[0019]

1 (a) and 1 (b) are a sectional view and a plan view showing a first embodiment of the present invention. The carbon felt laminate 1 in which the tape-like carbon felt is laminated has an insulating or conductive resin 2 filled in the inside of the carbon felt except for the side surfaces 4.4 formed by the cut surface of the carbon felt and the vicinity thereof. The carbon felt laminate is a single plate solidified and integrated at its center with resin. Reference numeral 3 denotes a frame integral with the resin itself or a substrate made of another member.

As the tape-like carbon felt, for example, one obtained by cutting one piece of carbon felt into a tape shape is used. As the resin, for example, a two-component mixed-curable resin such as an epoxy-based resin or a urethane-based resin is used. In order to make it conductive, a mixture of a conductivity-imparting agent such as carbon may be used.

In FIG. 1, the substrate of the "bipolar plate" is formed integrally by curing this resin. The exposed portions 4 and 4 of the carbon felt which penetrate the resin constitute positive and negative electrode plates, respectively. The positive and negative electrode plates are directly connected, and there is no contact resistance from the electrode plate to the substrate to the electrode plate as in the related art. The direction from one electrode 4 of the bipolar plate to the other electrode 4 through the substrate coincides with the "plane direction" of the original carbon felt, so that the resistance between the electrodes 4 and 4 is greatly reduced.

FIGS. 2 (a) and 2 (b) are a sectional view and a plan view showing another embodiment 2 of the present invention. Instead of the carbon felt cut into a tape shape, a carbon felt laminate 1 in which one piece of carbon felt is folded at a tape width is used. The purpose and effect are the same as in the first embodiment.

FIGS. 3 (a) and 3 (b) show a third embodiment of a method of filling a resin at a predetermined position of carbon felt.
(A) shows the filling method, and (b) shows the shape of the carbon felt filled with the resin.

In FIGS. 1 and 2, 4, 4 exposed as an electrode plate
Is filled with resin, but in the case of carbon felt, since the material is a fiber and porous, there is a possibility that the resin may penetrate into a position not to be filled. Therefore, in the third embodiment, the unfilled portion 7 of the carbon felt 5 is
To prevent resin penetration. The carbon felt in the non-filled portion 7 is compressed by the upper and lower molds 8, 8, and the filled portion 6 is not compressed because of the resin injection groove 9. The resin is injected into the resin injection groove 9 via the resin injection pipe 10, and is injected into the filling section 6. The unfilled portion 7 is compressed by the dies 8, 8 and the porous portion is removed, so that no resin is filled. FIG. 3B shows a carbon felt in which a strip is filled with a resin. Each of the carbon felt laminates 1 shown in FIG.
Use as

Since the flowability of a resin usually decreases at a low temperature,
If necessary, the mold is cooled by internal cooling water circulation, dry ice direct cooling, or the like, so that penetration of resin into the compression section can be effectively suppressed. As shown in FIG.
1, the cooling medium passages can be circulated as a series by connecting adjacent passages with pipes.

In filling the resin into the carbon felt, it depends on the material, injection pressure and injection temperature of the resin.
If the thickness of the carbon felt is too large, the filling of the resin becomes insufficient unless the press-fitting pressure of the resin is extremely increased. When the thickness of the carbon felt is about 2 mm, the resin can be easily filled.

[0027]

According to the present invention, the contact resistance existing between the electrode plate, the substrate and the electrode plate can be removed, and the positive and negative electrodes 4, 4 can be removed.
Since the carbon felt used in between is used in the “plane direction” having a low electric resistance, the resistance between 4 and 4 is also reduced. By reducing the internal resistance of the redox flow battery body, the battery efficiency of the redox flow battery can be increased.

[0028]

[Brief description of the drawings]

FIG. 1A is a sectional view of Example 1 of a “bipolar plate” according to the present invention, and FIG. 1B is a plan view.

FIG. 2A is a cross-sectional view of Example 2 of another “bipolar plate” according to the present invention, and FIG. 2B is a plan view.

FIG. 3 shows a third embodiment of the method for forming a “bipolar plate” according to the present invention.
(A) is a perspective view of a step of filling the resin into the carbon felt, and (b) is a perspective view of the carbon felt filled with the resin.

FIG. 4 is a sectional view showing a main part of a conventional redox flow battery in which “bipolar plates” are laminated.

[Explanation of symbols]

 1: Carbon felt laminated body 2: Substrate in which carbon fiber fiber layer is filled with resin 3: Frame of substrate 4: Carbon felt electrode plate (one side positive, other side negative) Carbon felt 6: Carbon felt portion filled with resin 7: Carbon felt portion not filled with resin 8: Resin injection mold 9: Resin injection groove 10: Resin press-fitting pipe 11: Coolant passage

Claims (5)

[Claims] 1. A laminate in which a plurality of carbon felts in which the direction of a fiber exists in a plane direction is cut into a tape shape and laminated, and the cut cross section is formed on both sides of the laminate. A carbon felt bipolar plate in which an insulating or conductive resin is filled in advance over the entire length of the laminated body in the laminating direction in the center of the laminated body to make the laminated body an integral substrate. 2. A carbon felt in which the direction of a fiber is in a plane direction is folded in a zigzag manner in a strip shape unit, and both sides of the folded body formed by edges of strip long sides appearing on the surface by the folding and in the vicinity thereof A carbon felt bipolar plate in which an insulating or conductive resin is filled over the entire length in the central laminating direction except for the above, and the folded body is used as an integrated substrate. 3. The carbon felt according to claim 1, wherein a carbon felt filled with the resin in advance is laminated or folded at a position where the resin is to be filled, and then the resin is adhered to each other with the same resin to be integrated. A method for forming a bipolar plate. 4. The method for forming a carbon felt bipolar plate according to claim 3, wherein a portion of the carbon felt not filled with the resin is compressed by a mold, and a portion of the remaining carbon felt is filled with the resin without being compressed. . 5. The method for forming a carbon felt bipolar plate according to claim 4, wherein a cooled or heated mold is used.