JP2005158383A - Redox cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a redox cell having a structure whereby a diaphragm is not easily damaged even when a thin diaphragm is used, and causing no lowering of current efficiency while having low cell resistance. <P>SOLUTION: This redox cell has the diaphragm 1 permeable by a hydrogen ion, and an intermediate film 2 disposed on the surface of the diaphragm while being permeable by the hydrogen ion. A PTFE porous film, a polyolefine-based porous film, a polyolefine-based non-woven fabric, a vinyl chloride woven fabric, or a composite film obtained by compounding them is preferably used for the intermediate film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a redox battery having a diaphragm that separates a positive electrode solution and a negative electrode solution (hereinafter, the positive electrode solution and the negative electrode solution may be collectively referred to as an electrolytic solution).

  A redox battery such as a redox flow battery consists of a cell in which electrodes (positive and negative electrodes) are arranged on both sides of a diaphragm. A positive electrode solution is circulated in a positive electrode chamber in which a positive electrode is arranged, and at the same time a negative electrode. Is a battery in which a negative electrode solution is circulated in a negative electrode chamber in which is generated and electricity is generated by a battery reaction between electrolyte solutions. A redox battery has a main portion formed by stacking a plurality of the cells.

  In the redox battery, the diaphragm that separates the positive electrode solution and the negative electrode solution is usually made of an ion exchange membrane, and can transmit hydrogen ions. Then, when hydrogen ions permeate through the diaphragm, a battery reaction occurs between the electrolytes on both sides of the diaphragm, and electricity is generated.

  Conventionally, a diaphragm having a thickness of about 100 to 150 μm has been usually used. However, when the diaphragm is thick, hydrogen ion permeation becomes difficult and the internal resistance (cell resistance) of the battery increases. Therefore, it is preferable that the diaphragm is thinner in order to reduce the cell resistance. Moreover, the diaphragm is expensive, and a thin diaphragm is desired from this aspect. Therefore, the progress of film forming technology enables the production of thin diaphragms and the thinning of the diaphragms has been promoted. In recent years, the use of diaphragms having a thickness of 50 μm or less, and in particular about 5 μm is also considered. became.

  On the other hand, when the diaphragm is thinned, its mechanical strength is reduced, causing problems such as damage to the diaphragm. In a redox battery, since electrolyte flows through both sides of the diaphragm and pressure and vibration are applied to the diaphragm, damage due to thinning is likely to occur. For example, the following problems occur.

Normally, the diaphragm is sandwiched between frames that form battery cells, but the diaphragm may touch the edge of the frame, and cracks may occur due to pressure or vibration.
The electrode sandwiching the diaphragm from both sides is usually made of a porous material such as graphite felt. In addition, a porous insulating material such as a glass fiber nonwoven fabric may be disposed between the electrode and the diaphragm in order to improve the cross-sectional area of the liquid passage without increasing the amount of expensive graphite felt used (patent) Reference 1). Accordingly, these surfaces have rough and needle-like protrusions, and the protrusions easily pierce the diaphragm. When the diaphragm is thin, a hole connecting between both surfaces is likely to be generated by the piercing of the protrusion, and the diaphragm is easily damaged.

When the diaphragm is damaged, the positive electrode solution and the negative electrode solution are mixed, and as a result, the current efficiency, and consequently the battery efficiency, that is, the ratio of the amount of electric power that can be discharged to the amount of charged electric power is reduced.
Therefore, it has been desired to develop a method that does not cause damage to the diaphragm while making the diaphragm thinner.
JP-A-2-148658

  An object of the present invention is to provide a redox battery having a structure in which even when a thin diaphragm is used, the diaphragm is not easily damaged, and as a result, the cell efficiency is low but the current efficiency is not lowered. And

The inventors have found that the above object can be achieved by covering the surface of the diaphragm with an intermediate film, and have reached the present invention.
Furthermore, the inventors have found that a more excellent effect can be obtained by making the intermediate film, shape, and the like specific, and have completed a preferred embodiment of the present invention.

A first aspect of the present invention is a redox battery characterized by having a diaphragm that is permeable to hydrogen ions and an intermediate film that is permeable to hydrogen ions and disposed on the surface of the diaphragm.
As described above, the positive electrode solution and the negative electrode solution are in contact with each other on both surfaces of the diaphragm, and hydrogen ions can pass through the diaphragm. A membrane that does not allow hydrogen ions to permeate cannot cause a battery reaction, and therefore cannot be used as a diaphragm of the present invention. In addition, it is preferable to use a diaphragm having high hydrogen ion permeability because cell resistance does not increase.

The redox battery of the present invention is characterized in that an intermediate film is disposed on the surface of the diaphragm.
The intermediate film may be disposed only on one surface of the diaphragm, but it is preferable because the effect of preventing the diaphragm from being damaged is more marked by being disposed on both surfaces. .
The interlayer is preferably disposed in contact with the surface of the diaphragm.

The intermediate film that is not permeable to hydrogen ions hinders the movement of hydrogen ions between the positive electrode solution and the negative electrode solution, that is, the battery reaction, and therefore, an intermediate film that is permeable to hydrogen ions is used.
As in the case of the diaphragm, an intermediate film having a high hydrogen ion permeability is preferable because it does not increase cell resistance.

  Further, as this intermediate film, one that easily permeates the electrolytic solution itself containing hydrogen ions is preferable because it does not increase cell resistance. Examples of such an intermediate film include a porous film. A second aspect of the present invention corresponds to this preferred embodiment, and is the redox battery described above, wherein the intermediate film is porous.

  As a material for the porous intermediate film, either a conductive material or an insulating material can be used. Usually, a porous insulating material is preferably used, and examples of the porous insulating material include a PTFE porous film, a polyolefin-based porous film, a polyolefin-based nonwoven fabric, a vinyl chloride woven fabric, or a composite film thereof.

  The aspect of Claim 3 of this invention corresponds to this preferable aspect. That is, in the redox battery, the intermediate film is a PTFE porous film, a polyolefin-based porous film, a polyolefin-based nonwoven fabric, a vinyl chloride woven fabric, or a composite film thereof.

  Among the exemplified porous insulating materials, a PTFE porous film, a polyolefin-based porous film, a polyolefin-based nonwoven fabric, or a composite film thereof is particularly preferable.

When the film thickness of the intermediate film is small, the mechanical strength is also weakened, and the intermediate film tends to be damaged due to piercing of an electrode material or the like. On the other hand, when the film thickness is thick, the electrolytic solution containing hydrogen ions is difficult to permeate, and the cell resistance tends to increase.
As described above, the interlayer film is preferably porous, but if the porosity is low, the electrolyte solution tends to be difficult to permeate. On the other hand, if the porosity is large, the interlayer film is easily damaged. Tend.

  Therefore, the porosity and film thickness of the intermediate film are preferably within a specific range. The inventors have examined the porosity and film thickness of the PTFE porous film, the polyolefin-based porous film, the polyolefin-based nonwoven fabric, the vinyl chloride woven fabric, or the intermediate film made of these composite films. The inventors have found that a preferable result can be obtained when a predetermined relationship is satisfied.

The aspect of Claim 4 of this invention is a preferable aspect completed based on this knowledge, Comprising: The intermediate film which consists of a PTFE porous membrane, a polyolefin-type porous membrane, a polyolefin-type nonwoven fabric, a vinyl chloride woven fabric, or these composite films is provided. In the above redox battery, when the porosity of the intermediate film is V (%) and the film thickness is T (μm), (0.35T + 10) <V <(0.35T + 65) and 10 <T It is a redox battery characterized by satisfying the relationship.
The porosity is a value obtained by the following formula 1 based on the measured values of the length and width, weight, and film thickness of the sample and the specific gravity of the resin after cutting the intermediate film into about 15 cm square. .

An intermediate film satisfying the relationship (0.35T + 25) <V <(0.35T + 50) in terms of porosity and film thickness is more preferable.
Furthermore, the film thickness is more preferably in the range of 20 to 150 μm. The aspect of Claim 5 of this invention corresponds to this preferable aspect, It is the said redox battery, Comprising: The film thickness of the said intermediate film exists in the range of 20-150 micrometers, It is a redox battery characterized by the above-mentioned.

Usually, the electrolytic solution is an aqueous solution. A hydrophilic intermediate film is preferable because it easily permeates the electrolytic solution, which is an aqueous solution, and as a result, an increase in cell resistance can be suppressed.
The aspect of Claim 6 of this invention corresponds to this preferable aspect, It is the said redox battery, Comprising: The said intermediate film consists of a material provided with hydrophilic property, It is a redox battery characterized by the above-mentioned. The method for imparting hydrophilicity to the interlayer film is not particularly limited.

  The film thickness of the diaphragm used in the redox battery of the present invention is not particularly limited, and the appropriate film thickness range varies depending on the material. However, in the case of a normal material, a film having a film thickness exceeding 50 μm does not cause much damage to the diaphragm even without an intermediate film. Therefore, the range in which the film thickness exceeds 50 μm is not a range in which the effects of the present invention are remarkably exhibited.

In the case of a normal material, if the film thickness is less than 1 μm, damage or the like is likely to occur even if an intermediate film is used. Therefore, when a normal material is used, the effect of the present invention is remarkably exhibited when the film thickness is in the range of 1 to 50 μm.
The aspect of Claim 7 of this invention corresponds to this preferable aspect, It is said redox battery, Comprising: The film thickness of the said diaphragm is 1-50 micrometers, It is a redox battery characterized by the above-mentioned. The thickness of the diaphragm is more preferably in the range of 5 to 30 μm.

  The redox battery of the present invention has a structure in which even when a thin diaphragm is used, the diaphragm is not easily damaged. As a result, by using the redox battery of the present invention using a thin diaphragm, a low cell resistance can be achieved, and the problem of a decrease in current efficiency does not occur.

FIG. 1 is a schematic cross-sectional view showing a cross section of an example of a cell of the redox battery of the present invention.
In the figure, reference numeral 1 denotes a diaphragm made of an ion exchange membrane, and a porous intermediate membrane 2 is disposed on both surfaces thereof. The diaphragm 1 and the intermediate film 2 sandwiching the diaphragm 1 are further sandwiched by a pair of frames 3 made of a material such as vinyl chloride. The frame 3 has a bipolar plate 4 at the center thereof, and a recess, that is, a positive electrode chamber 5 and a negative electrode chamber 6 are formed by the frame 3 and the bipolar plate 4, and a positive electrode 7 and a negative electrode 8 made of graphite felt are formed therein. Is arranged.
Other negative electrodes and positive electrodes are in contact with the opposite side of the bipolar plate 4 with which the positive electrode 7 and the negative electrode 8 are in contact, respectively, but these are not shown.

  The frame 3 has a cathode solution inlet 9, a cathode solution outlet 10, a cathode solution inlet 11, and a cathode solution outlet 12. The cathode solution flows into the cathode chamber 5 through the inlet 9, It passes through the electrode 7 and is discharged from the discharge port 10, and the negative electrode liquid flows into the negative electrode chamber 6 from the inflow port 11, passes through the negative electrode 8 and is discharged from the discharge port 12.

Since the intermediate film 2 is porous, it passes through the positive electrode solution and the negative electrode solution. A battery reaction is performed between the positive electrode solution and the negative electrode solution through the diaphragm 1 that transmits hydrogen ions, and electricity is generated.
Since the positive electrode 7 and the negative electrode 8 are made of graphite felt, they have needle-like protrusions on their surfaces. However, since the surface of the diaphragm 1 is covered with the intermediate film 2, it is not damaged by the needle-like protrusions. Accordingly, it is possible to prevent a decrease in current efficiency.

A small battery (frame: 80 mm × 60 mm, electrode: 30 mm × 30 mm, electrolyte: vanadium sulfate solution) having the structure of FIG. 2 was assembled. The frame 13 is made of vinyl chloride, and the positive electrode 14 and the negative electrode 15 are made of graphite felt. As the diaphragm 16, an anion exchange membrane having a thickness of 30 μm was used.
The positive electrode chamber 17 and the negative electrode chamber 18 were respectively circulated with a positive electrode solution and a negative electrode solution, and the intermediate film 19 having the material, film thickness, and porosity shown in Table 1 was used, and a charge / discharge test was performed under the following conditions. Went.

Charging / discharging method: Constant current operation Current density: 70 mA / cm ²
Charging end voltage: 1.55V
Discharge end voltage: 1.00V
Temperature: 25 ° C

From the obtained charge / discharge curve, the current efficiency and the cell resistance were determined, and the interlayer film was evaluated. The results are shown in Table 1. For comparison, the charge / discharge test was performed under the same conditions even when the intermediate film 19 was not used. The results are also shown in Table 1.
In Table 1, the current efficiency and the cell resistance were determined as ◯ for 99% or more, Δ for 98% or more and less than 99%, and × for 98% or less.
Moreover, less than 1.05Omucm ² for cell resistance ○, the 1.05Omucm ² or more 1.25Omucm than ² △, and as × 1.25Omucm ² or more.

  As is clear from the results in Table 1, when the intermediate film 19 is used, the current efficiency is not lowered, but when the intermediate film 19 is not used, the current efficiency is remarkably lowered. This is probably because the protrusions on the surface of the positive electrode 14 and / or the negative electrode 15 pierced the diaphragm 16 or the diaphragm was cracked. When the diaphragm with a decrease in current efficiency was observed with an SEM, it was seen that the electrode was stuck.

  Although the embodiments and examples of the present invention have been described above, the scope of the present invention is not limited to these embodiments and examples.

It is a schematic sectional drawing showing an example of the cell of the redox battery of this invention. It is a schematic sectional drawing showing the minicell used in the Example.

Explanation of symbols

1.16. Diaphragm 2.19. Intermediate film 3.13. Frame 4. Bipolar plate 5.17. Positive electrode chamber 6.18. Negative electrode chamber 7.14. Positive electrode 8.15. Negative electrode 9.11. Inlet 10.12. Vent

Claims (7)

  A redox battery comprising: a diaphragm capable of transmitting hydrogen ions; and an intermediate film capable of transmitting hydrogen ions and disposed on a surface of the diaphragm.   The redox battery according to claim 1, wherein the intermediate film is porous.   The redox battery according to claim 1 or 2, wherein the intermediate film is a PTFE porous film, a polyolefin-based porous film, a polyolefin-based nonwoven fabric, a vinyl chloride woven fabric, or a composite film thereof.   The relationship of (0.35T + 10) <V <(0.35T + 65) and 10 <T is satisfied, where the porosity of the intermediate film is V (%) and the film thickness is T (μm). Item 4. The redox battery according to Item 3.   The redox battery according to claim 4, wherein the thickness of the intermediate film is in the range of 20 to 150 μm.   The redox battery according to any one of claims 1 to 5, wherein the intermediate film is made of a material imparted with hydrophilicity. The redox battery according to claim 1, wherein a thickness of the diaphragm is 1 to 50 μm.

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