JPH0992321A - Redox cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a redox flow cell which can be reduced in resistance of battery cell, enhanced in power efficiency, minimized in pump power for permeating electrolyte, and also enhanced in energy efficiency by using liquid permeable porous electrodes of two layers or more. SOLUTION: The drawing shows the unit cell structure of a redox cell. Liquid permeable porous electrode formed of carbon fiber layers 3 and carbon compact layers 2 are arranged on both sides of a diaphragm 4, respectively, and these members are pressed in sandwich state by a current collector A1 and a current collector B1'. One of chambers partitioned by the diaphragm 4 is set to a positive electrode chamber, the other to a negative electrode chamber, and the thickness of the chambers is ensured by a proper spacer 5. A positive electrode electrolyte formed of V<4+> /V<5+> is passed to the positive electrode chamber through a passage Lp, and a negative electrode electrolyte formed of V<3+> /V<2+> is passed to the negative electrode chamber through a passage Ln. In charging, electrons are released in the positive electrode chamber to oxidize V<4+> to V<5+> . The released electrons are supplied to the negative electrode side through an external circuit. In the negative electrode chamber, V<3+> is reduced to V<2+> by the supplied electrons.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redox flow type secondary battery (sometimes abbreviated as "redox battery"), and in particular, an improvement of a liquid-permeable porous electrode used in the battery. It is about.

[0002]

BACKGROUND OF THE INVENTION At present, the concentration of carbon dioxide in the atmosphere is remarkably increased due to the large use of fossil fuels, and global warming has become a serious problem. For this reason, solar cells, which are clean energy sources, are being actively developed. However, since solar cells cannot generate power at night or in rainy weather, the development of high-performance secondary batteries to be combined with solar cells is awaited. ing. On the other hand, even in the conventional power generation equipment, there is a large difference in power demand between night and day and the power generation capacity must be provided in accordance with the peak demand, so the load factor of the power generation equipment is decreasing. Therefore, it is necessary to store nighttime electric power with a large power storage battery and utilize it during the daytime to smooth the operating load and increase the load factor of the power generation equipment for efficient operation. The development of the electric power storage battery is awaited. Furthermore, the development of a secondary battery having a high output density suitable for a mobile power source such as an electric vehicle has been awaited. A redox battery is promising as a new type of secondary battery suitable for the above-mentioned applications because it can be charged according to the output voltage of the solar cell by tapping, and has features such as a relatively simple structure and easy enlargement.

[0003]

2. Description of the Related Art A redox flow type secondary battery is a battery in which a battery active material is in a liquid state, and a battery active material of a positive electrode and a negative electrode is passed through a liquid-permeable electrolytic cell, and charge and discharge are performed using an oxidation-reduction reaction. The redox flow type secondary battery has the following advantages as compared with the conventional secondary battery. (1) In order to increase the storage capacity, it is sufficient to increase the capacity of the storage container and increase the amount of the active material, and the electrolytic cell itself can be used as long as the output is not increased. (2) Since the positive and negative electrode active materials can be completely separated and stored in a container, unlike a battery in which the active material is in contact with the electrodes,
The possibility of self-discharge is low. (3) In the liquid-permeable carbon porous electrode used in the present battery, the charge / discharge reaction of the active material ions (electrode reaction) is simply carried out by exchanging electrons on the electrode surface, and in the zinc-bromine battery, The reaction of the battery is simple because it does not deposit on the electrode like zinc ions.

However, iron-chromium batteries, which have been conventionally developed for redox flow type secondary batteries, have a low energy density and are disadvantageous in that iron and chromium are mixed through an ion exchange membrane. It has not been realized.
Therefore, all vanadium redox flow batteries (J. Elec
trochem.Soc., 1331057 (1986), Japanese Examined Patent Publication No. 62-186473), which has a higher electromotive force, a larger capacity density, and an electrolytic solution than an iron-chromium battery. Since it is a one-element system, even if the positive electrode liquid and the negative electrode liquid are mixed with each other through the diaphragm, they can be easily regenerated by charging, the battery capacity does not decrease, and the electrolytic solution can be completely closed. Etc. have advantages.

However, even in this all-vanadium redox flow type battery, the cell resistivity is reduced, high power efficiency is maintained even at a relatively high current density, and the pump power for allowing the electrolyte to permeate is reduced to save energy. Although it is necessary to increase efficiency, the conventional all-vanadium redox flow battery is not sufficient. When the cell thickness of the positive electrode chamber and the negative electrode chamber is reduced to reduce the internal resistance of the battery cell, the pump power for allowing the electrolytic solution to permeate increases and the energy efficiency decreases. On the contrary, when the cell power of the positive electrode chamber and the negative electrode chamber is increased to reduce the pump power for permeating the electrolytic solution, the resistance of the battery cell increases and the power efficiency decreases. For example, the conventional method is to press the liquid-permeable porous electrode excessively to reduce the internal resistance of the cell and reduce the cell thickness, and to fill the carbon fiber of the reactive liquid-permeable porous electrode with high density. However, a method of increasing the total number of activation points of the redox reaction per unit volume, a method of increasing the acid concentration of the electrolytic solution and increasing the electrical conductivity of the electrolytic solution have been tried.
On the other hand, in order to reduce the shunt current loss, a method of increasing the length of the slit of the electrolytic solution introducing port and decreasing the cross-sectional area was used.

However, the method of excessively pressing the liquid-permeable porous electrode to reduce the thickness of the cell, the method of filling the cell with high density to increase the number of active sites per unit volume, and the method of increasing the acid concentration of the electrolytic solution And the method of decreasing the cross-sectional area by increasing the length of the slit of the electrolytic solution inlet is to increase the pump power loss, and even if the efficiency of charging and discharging is improved by the above method, The overall energy efficiency was reduced. Also,
In JP-A-2-148659, a liquid-flowing groove is formed in the current collecting carbon plate along the flow direction of the electrolytic solution, and in JP-A-2-148658, liquid flowability is provided between the porous electrode material and the diaphragm. Highly porous porous material is placed to reduce pump power loss. However, the cell resistance at this time was as high as about 1.8 Ωcm ² , it could not be used at high current density, the power efficiency was low, and the overall energy efficiency was low. Therefore, there has been a demand for the development of a redox flow type battery which can reduce the resistance of the battery cell, has high power efficiency, low pump power for permeating the electrolytic solution, and high energy efficiency.

[0007]

In view of such a situation, the present inventors have found that the redox of which the resistance of the battery cell can be reduced, the power efficiency is high, the pump power for permeating the electrolytic solution is small, and the energy efficiency is large. As a result of intensive studies on the development of a flow type battery, the present invention has been achieved.

[0008]

That is, according to the present invention, a positive electrode liquid and a negative electrode liquid are passed through a positive electrode chamber and a negative electrode chamber separated by a diaphragm and provided with a liquid-permeable porous electrode. In a liquid-circulation type redox battery that performs an oxidation-reduction reaction and is charged and discharged, the liquid-permeable porous electrode is composed of at least two layers of the following A layer and B layer, and the B layer is arranged on the diaphragm side. A redox battery is provided. Layer A: Interplanar spacing (d) of (002) plane by X-ray wide-angle diffraction method
₀₀₂ ) is 3.75 Å or less and the bulk density is 0.01 to 0.
80 g / cc sheet-like carbon molded body layer B layer: Interplanar spacing (d) of (002) plane by X-ray wide angle diffraction method
₀₀₂ ) is 3.37Å or more, the fiber diameter is 35 μm or less, and the surface area is 0.5 m ² / g or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the redox battery of the present invention, the liquid-permeable porous electrodes in the positive electrode chamber and the negative electrode chamber are the above-mentioned A.
And at least two layers, layer B and layer B. The sheet-like carbon molded body layer corresponding to the A layer was formed by the X-ray wide angle diffraction method (0
02) surface spacing (d ₀₀₂ ) is 3.75Å or less, preferably 3.70Å or less, more preferably 3.68Å or less, still more preferably 3.35 to 3.65Å, particularly preferably 3.36. ~ 3.63Å, most preferably 3.37 ~
It is 3.62Å. When the surface spacing (d ₀₀₂ ) of the (002) plane exceeds 3.75Å, the conductivity is low and the resistance of the battery cell cannot be reduced. The A layer has a crystallite size (Lc) in the C-axis direction by the X-ray wide angle diffraction method of preferably 8 Å or more, more preferably 10 Å or more, still more preferably 11 Å or more, and even more preferably 12 ~ 8
00Å, particularly preferably 13 to 500Å, most preferably 14 to 200Å. If the crystallite size (Lc) in the C-axis direction is too small, the conductivity is low and the resistance of the battery cell is high, which is not preferable.

Further, the layer A is 0.01 to 0.80 g / c.
It is necessary to have a bulk density of c. The bulk density is preferably 0.01 to 0.60 g / cc, more preferably 0.9.
02-0.50 g / cc, more preferably 0.03-0.5.
40 g, particularly preferably 0.04 to 0.35 g / cc, most preferably 0.045 to 0.32 g / cc. When the bulk density exceeds 0.60 g / cc, the pump power for permeating the electrolytic solution becomes large. When the bulk density is less than 0.01 g / cc, the contact area between the electrode and the current collector becomes small, so that the cell resistance becomes large and the mechanical strength becomes small.

The layer A preferably has continuous pores having an average pore diameter of 3 μm or more, more preferably 10 to 300.
0 μm, more preferably 20 to 2000 μm, particularly preferably 30 to 1000 μm, and even more preferably 5
It has open pores of 0-700 μm, most preferably 70-500 μm. If the average pore size is less than 3 μm, the pump power for allowing the electrolytic solution to permeate becomes large. The average pore size can be preferably expressed as a number average pore size.
For example, it can be obtained as a value obtained by dividing the fixed length by the number of pores existing in the fixed length in the micrograph.

The layer A preferably has an atomic ratio of hydrogen / carbon of 0.12 or less, more preferably 0.10 or less, particularly preferably 0 to 0.08, and most preferably 0.
It is 0.06. When the atomic ratio of hydrogen / carbon exceeds 0.12, the conductivity of the electrode decreases and the resistance of the battery cell increases, which is not preferable.

The layer A preferably has a true density of 1.20 g / c.
c or more, more preferably 1.30 g / cc or more, further preferably 1.40 to 2.20 g / cc, particularly preferably 1.
50-2.15 g / cc, most preferably 1.55-2.1
It is 0 g / cc. If the true density is excessively low, the electrical conductivity of the electrode deteriorates, making it difficult to charge and discharge at a high current density. When the true density is excessively high, the reactivity on the electrode surface becomes low.

[0014] A layer, the surface area (BET method) is preferably from 0.1 m ² / g or more, more preferably 0.5~2000m ² /
g, more preferably 1.0 to 1000 m ² / g, particularly preferably 1.5 to 500 m ² / g, and most preferably 2.0.
It is 100 m ² / g. If the surface area is excessively small, the electrode reaction rate becomes slow and it becomes difficult to charge and discharge at a high current density. If the surface area is too large, the mechanical strength of the electrode will be low.

The layer A preferably has a thickness of 0.5 to 20 m.
m, more preferably 1.0 to 10 mm, still more preferably 1.2 to 5 mm, particularly preferably 1.4 to 3 mm, and most preferably 1.5 to 2.5 mm. If the thickness is excessively small, it is difficult to reduce the pump power for permeating the electrolytic solution, it is difficult to reduce the cell resistivity, and the mechanical strength of the electrode is reduced. If the thickness is too large,
The rate of electrode reaction becomes slow and the cell resistivity becomes high.

Since the layer A has the above-mentioned characteristics, it has excellent electrical conductivity, the pump power for permeating the electrolytic solution is reduced, and it has the function of reducing the cell resistivity.

The layer A is made of phenol resin, urethane resin,
It is obtained by molding a porous or foamed sheet from cellulose, acrylic resin, pitch or the like, and heat-treating the obtained molded body at a temperature of 500 to 3000 ° C. in an inert gas. In the heat treatment, first, the molded body is 500 to 120.
After heating to a temperature of 0 ° C., preferably 600 to 1100 ° C. for carbonization, 1200 to 3000 ° C., especially 2000 to
It is preferable to perform graphitization by treating at a temperature of 3000 ° C.

The liquid-permeable porous electrode of the present invention is constituted,
The carbon fiber layer corresponding to the layer B has a (002) plane spacing (d ₀₀₂ ) of 3.37 Å or more measured by the X-ray wide angle diffraction method. The spacing (d ₀₀₂ ) of (002) planes is preferably 3.40 Å or more, more preferably 3.43 Å or more, further preferably 3.45 Å or more, and particularly preferably 3.48 to
3.75Å, most preferably 3.50 to 3.70Å. The surface spacing (d ₀₀₂ ) of the (002) surface of layer B is 3.37Å
When it is less than the above range, the electrode reactivity of the layer becomes small.

The B layer has a crystallite size (Lc) in the C-axis direction.
However, it is preferably 180 Å or less, more preferably 150 Å
The following is more preferable, 100 Å or less, particularly preferably 8 to 70 Å, particularly preferably 8 to 50 Å, most preferably 9 to 35 Å. Crystallite size in the C-axis direction
When (Lc) exceeds 180Å, the electrode reactivity of the layer becomes small.

The layer B is made of carbon fiber having a fiber diameter of 35 μm or less. The fiber diameter is preferably 30 μm or less, more preferably 1 to 25 μm, further preferably 2 to 20 μm.
μm, particularly preferably 3 to 15 μm, most preferably 5
１２12 μm. If the fiber diameter is too small, the mechanical strength will be poor, and if it is too large, the flexibility of the fiber will be lost.

Surface area of B layer (BET method) is 0.5 m ² / g
Or more, preferably 1 m ² / g or more, more preferably 3 to 2
000 m ² / g, more preferably 5-1000 m ² / g,
Particularly preferably 7 to 500 m ² / g, most preferably 10
~ 100 m ² / g. If the surface area is excessively small, the electrode reaction rate becomes slow and it becomes difficult to charge and discharge at a high current density. If the surface area is too large, the mechanical strength of the electrode will be low.

The bulk density of the layer B is preferably 0.05 to 0.5.
50 g / cc, more preferably 0.08 to 0.45 g / c
c, more preferably 0.10 to 0.40 g / cc, particularly preferably 0.12 to 0.35 g / cc, and most preferably 0.15 to 0.32 g / cc.

The B layer preferably has a true density of 2.10 g /
cc or less, more preferably 2.05 g / cc or less, further preferably 1.00 to 2.00 g / cc, particularly preferably 1.10 to 1.95 g / cc, and most preferably 1.15 to
It is 1.90 g / cc. When the true density is excessively high, the reactivity on the electrode surface becomes low. If the true density is excessively low, the electrical conductivity of the electrode deteriorates, making it difficult to charge and discharge at a high current density.

Further, the B layer preferably has an atomic ratio (O / C) of oxygen atoms to carbon atoms on its surface of 0.02 or more. Atomic ratio of oxygen atoms and carbon atoms on the carbon fiber surface (O
/ C) is more preferably 0.04 or more, particularly preferably 0.05 to 0.30, and most preferably 0.06 to 0.20. The O / C ratio is determined by X-ray photoelectron spectroscopy (ESC
Refers to those measured according to A).

The B layer preferably has an atomic ratio of hydrogen / carbon of 0.06 or more, more preferably 0.08 or more, still more preferably 0.10 or more, and particularly preferably 0.11 to 10.
It is 0.50, most preferably 0.12 to 0.30. If the atomic ratio of hydrogen / carbon is too small, the reactivity of the electrode becomes small, which is not preferable.

The B layer can have various shapes,
It is preferably in the form of a felt shape, a woven knitting shape, a melias knitting shape or the like. The thickness of layer B is preferably 0.3.
-10 mm, more preferably 0.5-8 mm, even more preferably 0.7-5 mm, particularly preferably 0.8-3 mm.
Below, it is most preferably 1.0 to 2.5 mm or less. B
If the layer thickness is too small, the electrode reaction rate will be insufficient and it will be difficult to reduce the cell resistivity. If the thickness is too large, the pump power for permeating the electrolyte cannot be reduced. Since the B layer has the characteristics as described above, it has high electrode reactivity.

The carbon fiber layer corresponding to the layer B is obtained by heat-treating fibers made of phenol resin, cellulose, acrylic resin, pitch, etc. in an inert gas at a temperature of 500 to 2000 ° C. The heating temperature is preferably 600 to 1500 ° C, more preferably 700 ° C to 13 ° C.
00 ° C, particularly preferably 700 ° C to 1200 ° C, most preferably 800 ° C to 1100 ° C or lower. It is also possible to perform activation treatment by heating in an atmosphere containing oxygen, in carbon dioxide gas or in steam.

In the liquid-permeable porous electrode of the present invention, the electrode reaction can be carried out particularly efficiently by disposing the layer A on the side of the current collector and the layer B on the side of the diaphragm. The total thickness of the liquid-permeable porous electrode is 0.5 to 5.0 mm, preferably 1.
5 to 3.5 mm, in which case the thickness ratio of the A layer to the B layer is preferably 0.2 to 10: 1, more preferably 0.3.
˜6: 1, more preferably 0.4 to 5: 1, particularly preferably 0.5 to 4: 1 and most preferably 0.8 to 3: 1.

The liquid-permeable porous electrode of the present invention comprises an A layer and a B layer.
Although it is composed of at least two layers, not only an electrode composed of only the two layers, but also another layer of the two layers as required, for example, a sheet-like carbon molding having a bulk density of 0.60 to 1.0 g / cc. The body layer may be further laminated on the current collector side to be used as three or more layers.

The diaphragm used in the redox battery of the present invention is
It is preferable to use an ion exchange membrane made of an organic polymer, and either a cation exchange membrane or an anion exchange membrane can be used. Further, an ion exchange membrane in which the surface of the cation exchange membrane is thinly coated with an anion exchange membrane, and an ion exchange membrane in which the surface of the anion exchange membrane is thinly coated with the cation exchange membrane can be used.

As the cation exchange membrane, a cation exchange membrane obtained by sulfonation of a styrene-divinylbenzene copolymer, tetrafluoroethylene and perfluoro.
A cation exchange membrane with a sulfonic acid group introduced based on a sulfonyl / ethoxy vinyl ether copolymer, a cation exchange membrane composed of a copolymer of tetrafluoroethylene and perfluorovinyl ether having a carboxyl group as a side chain, and an aromatic polysulfone copolymer. A cation exchange membrane or the like in which a sulfonic acid group is introduced based on a polymer can be used. As the anion exchange membrane, a styrene-divinylbenzene copolymer-based chloromethyl group-introduced and aminated anion exchange membrane, a vinylpyridine-divinylbenzene copolymer quaternary pyridinized anion exchange membrane, an aromatic It is possible to use an anion exchange membrane in which a chloromethyl group is introduced based on a polysulfone copolymer and aminated.

The ion exchange capacity of the ion exchange membrane used in the battery of the present invention is preferably 1.0 to 3.0 meq / g,
More preferably, it is 2.0 to 2.5 meq / g. The thickness of the ion exchange membrane is preferably 30 to 250 μm, more preferably 55 to 180 μm.

The electrolyte used in the battery of the present invention is, for example,
The iron-chromium system uses a solution of each chloride of iron and chromium, and the all-vanadium battery uses a sulfuric acid solution of vanadium. The vanadium concentration in the electrolytic solution of the vanadium-based battery is preferably 0.5 to 6.0 mol / liter, more preferably 1.5 to 3.5 mol / liter. The concentration of sulfate in the electrolytic solution of the vanadium-based battery is preferably 0.5 to 9.0 mol / liter, more preferably 1.5 to 7.0 mol / liter.

As an example of the redox electrode of the present invention, an all-vanadium redox flow type battery will be described below. As shown in FIG. 1, the single cell structure of the battery cell is such that liquid-permeable porous electrodes composed of and are arranged on both sides of a diaphragm, and these members are pressed in a sandwich state by two current collectors A and B. Then, one of the chambers partitioned by the diaphragm serves as a positive electrode chamber and the other as a negative electrode chamber, and the thickness of the chamber is secured by an appropriate spacer. In each of these chambers, that is, in the positive electrode chamber, a positive electrode electrolyte composed of V ⁴⁺ / V ^{5+ is charged} , and in the negative electrode chamber, V ³⁺ / V
^A redox battery is formed by flowing a negative electrode electrolyte composed of ²⁺ . For redox flow batteries,
During charging, electrons are emitted from the positive electrode chamber, and V ⁴⁺ is oxidized to V ⁵⁺ . The emitted electrons are supplied to the negative electrode chamber through the external circuit. In the negative electrode chamber, V ³⁺
Is reduced to V ²⁺ . Along with this oxidation-reduction reaction, hydrogen ions H ⁺ become excessive in the positive electrode chamber. On the other hand, hydrogen ions H ⁺ are insufficient in the negative electrode chamber. The diaphragm selectively transfers excess hydrogen ions H ⁺ in the positive electrode chamber to the negative electrode chamber to maintain electrical neutrality. At the time of discharge, the opposite reaction proceeds. In the above-mentioned battery reaction, energy-efficiency is given by Equation-1.

[0035]

[Equation 1]

The charging / discharging power amount in this equation depends on the internal resistance of the battery cell, the ion selectivity of the diaphragm, the shunt current loss, and the like. The reduction of internal resistance improves voltage efficiency. Improved ion selectivity and reduced shunt current loss improve current efficiency. Also, the pump power is
It is the amount of electric power for circulating an optimal amount of electrolytic solution in the battery cell, and the amount of electric power is particularly the thickness of the positive electrode chamber and the negative electrode chamber (cell thickness) of the battery, the liquid-permeable porous electrode structure, and The influence of the slit length and cross-sectional area of the electrolyte inlet is large.

[0037]

The present invention will be specifically described below based on examples and comparative examples. [Measuring Device and Measuring Conditions] a) Charge / Discharge Experiment The redox flow battery cell structure used in Examples and Comparative Examples is a single cell type battery shown in FIG.
m ² , a polysulfone-based anion exchange membrane was used as the diaphragm, and an electrolytic solution having a total vanadium concentration of 2 M / l and a total sulfate group concentration of 4 M / l was used as the electrolytic solution. b) Pressure loss measurement The pressure loss of the liquid-permeable porous electrode was determined by the difference in pressure between the inlet and outlet of the electrolyte solution on the negative electrode side of the battery cell used in the experiment.

Example 1 Using a redox battery cell as shown in FIG. 1, the thickness of the positive electrode chamber and the negative electrode chamber was set to 3 mm, and the following sheet-like carbon molded body layer (A layer) and carbon fiber layer (B layer) were formed. The liquid-permeable porous electrode was placed with the layer B on the diaphragm side. Sheet-shaped carbon molded body layer : Preparation: A sheet-shaped molded body obtained by impregnating foamed polyurethane with a phenol resin is placed in an electric heating furnace in a nitrogen stream 1
The temperature is raised to 1000 ° C at a rate of 5 ° C / minute, and at this temperature 1
Hold for time and carbonize. This carbonaceous material is set in another electric heating furnace and heated in a nitrogen stream at a rate of 25 ° C./min.
The temperature was raised to 0 ° C. and the temperature was maintained for 1 hour to obtain a sheet-shaped carbon molded body layer. Characteristics: Interplanar spacing (d ₀₀₂ ) of (002) plane by X-ray wide angle diffraction method 3.58Å Crystallite size in the C-axis direction (Lc) 22Å Bulk density 0.20 g / cc True density 1.40 g / cc Average Pore size (continuous pores) 200 μm Surface area 3.4 m ² / g Hydrogen / carbon atomic ratio 0.03 Thickness 1.7 mm Carbon fiber layer preparation: A felt made of cellulose fibers was heated in an electric heating furnace in a nitrogen stream at 15 ° C./min. The temperature was raised to 1100 ° C. and the temperature was maintained for 1 hour to obtain a carbon fiber layer. Characteristics: Interplanar spacing of (002) plane by X-ray wide angle diffraction method (d ₀₀₂ ) 3.50Å Average fiber diameter 12 μm BET surface area by nitrogen 29.5 m ² / g Oxygen / carbon atom ratio 0.102 Hydrogen / carbon atom ratio 0 .108 Bulk density 0.098 g / cc Thickness 1.3 mm

Comparative Example 1 A charge / discharge experiment was conducted in the same manner as in Example 1 except that an electrode having a thickness of 3.0 mm and a bulk density of 0.114 g / cc, which was composed only of the layer B in Example 1, was used. Carried out. The results are shown in Table-1
Shown in

Comparative Example 2 As a sheet-shaped molded body layer, a sheet-shaped molded body obtained by impregnating foamed polyurethane with a phenol resin was heated to 800 ° C. at a rate of 15 ° C./min in a nitrogen stream in an electric heating furnace. It was kept at this temperature for 1 hour and carbonized to obtain a sheet-like carbon molded body layer. Characteristics: Interplanar spacing (d ₀₀₂ ) of (002) plane by X-ray wide angle diffraction method 3.80Å C-axis crystallite size (Lc) 8Å Bulk density 0.18 g / cc True density 1.17 g / cc Average Pore size (continuous pores) 170 μm Surface area 3.5 m ² / g Hydrogen / carbon atomic ratio 0.31 Thickness 1.7 mm A charge / discharge experiment was conducted in the same manner as in Example 1 except that the above-mentioned sheet-shaped carbon compact layer was used. Carried out. The results are shown in Table 1.

Comparative Example 3 Example 1 except that the following was used as the carbon fiber layer.
A charge / discharge experiment was carried out in the same manner as. The results are shown in Table 1. Preparation of carbon fiber layer : A felt made of pitch fibers was heated in an electric heating furnace to 1000 ° C. at a rate of 15 ° C./min in a nitrogen stream and held at this temperature for 1 hour to obtain a carbon fiber layer. This carbonaceous material was set in another electric heating furnace, heated to 2800 ° C. at a rate of 30 ° C./min in a nitrogen stream, and kept at this temperature for 1 hour to obtain a sheet-like carbon molded body layer. Characteristics: Interplanar spacing (d ₀₀₂ ) of (002) plane by X-ray wide-angle diffraction method 3.36 Å Average fiber diameter 10 μm BET surface area by nitrogen 0.1 m ² / g Oxygen / carbon atomic ratio 0 Hydrogen / carbon atomic ratio 0 Thickness 1.3 mm A charge / discharge experiment was carried out in the same manner as in Example 1 except that the above carbon compact layer was used. The results are shown in Table 1.

Example 2 A sheet-like molded product composed of short carbon fibers and a phenol resin binder was placed in an electric heating furnace in a nitrogen stream for 15 minutes.
The temperature was raised to 1000 ° C. at a rate of ° C./min, and this temperature was maintained for 1 hour for carbonization. This carbonaceous material is set in another electric heating furnace and 2300 at a rate of 30 ° C / min in a nitrogen stream.
The temperature was raised to 0 ° C. and the temperature was maintained for 1 hour to obtain a sheet-like carbon molded body layer. Characteristics: Interplanar spacing (d ₀₀₂ ) of (002) plane by X-ray wide angle diffraction method 3.50Å C-axis crystallite size (Lc) 28Å Bulk density 0.25g / cc Average pore diameter (continuous pore) 120μm Surface area 2.8 m ² / g hydrogen / carbon atomic ratio 0.04 thickness 1.7 mm A charge / discharge experiment was carried out in the same manner as in Example 1 except that the above-mentioned sheet-shaped carbon compact layer was used. The results are shown in Table 1.

Example 3 A sheet-like molded body composed of graphite particles and a phenol resin binder was heated to 1000 ° C. at a rate of 15 ° C./min in a nitrogen stream in an electric heating furnace, and kept at this temperature for 1 hour to obtain carbon. Turned into This carbonaceous substance was set in another electric heating furnace, heated to 2350 ° C. at a rate of 30 ° C./min in a nitrogen stream, and kept at this temperature for 1 hour to obtain a sheet-shaped carbon molded body layer. Characteristics: Interplanar spacing (d ₀₀₂ ) of (002) plane by X-ray wide-angle diffraction method 3.36Å C-axis crystallite size (Lc) 800Å Bulk density 0.30 g / cc Average pore diameter (continuous pore) 80 μm Surface area 1.7 m ² / g hydrogen / carbon atomic ratio 0.01 thickness 1.7 mm A charge / discharge experiment was carried out in the same manner as in Example 1 except that the above-mentioned sheet-shaped carbon compact layer was used. The results are shown in Table 1.

[0044]

[Table 1]

[0045]

The redox flow type battery of the present invention has a small cell resistance, high power efficiency, and is capable of circulating the amount of electrolyte required for charging and discharging the battery with low pump power.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a single cell constituting a redox battery of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Tayama 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Kashima Kita Kyodo Co., Ltd. V battery development room (72) Masahiro Sasaki Ami-cho, Inashiki-gun, Ibaraki Chuo 8-3-1 Kashima Kita Kyodo Co., Ltd. V Battery Development Room (72) Inventor Yoshiteru Kageyama 8-3-1 Chuo Ami-cho, Ibaraki Prefecture Kashima Kita Kyodo Co., Ltd. V Battery Development Room (72) Inventor Masato Nakajima 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Kashima Kita Kyodo Power Co., Ltd. V battery development room

Claims (7)

[Claims] 1. A liquid circulation type in which a positive electrode liquid and a negative electrode liquid are passed through a positive electrode chamber and a negative electrode chamber, which are separated by a diaphragm and in which a liquid-permeable porous electrode is disposed, to carry out an oxidation-reduction reaction and charge / discharge. 2. The redox battery according to item 1, wherein the liquid-permeable porous electrode is composed of at least two layers of the following A layer and B layer, and the B layer is arranged on the diaphragm side. Layer A: Interplanar spacing (d) of (002) plane by X-ray wide-angle diffraction method
₀₀₂ ) is 3.75 Å or less and the bulk density is 0.01 to 0.
80 g / cc sheet-like carbon molded body layer B layer: Interplanar spacing (d) of (002) plane by X-ray wide angle diffraction method
₀₀₂ ) is 3.37Å or more, the fiber diameter is 35 μm or less, and the surface area is 0.5 m ² / g or more. 2. The redox battery according to claim 1, wherein the carbon molded body layer has a pore distribution having an average pore diameter of 3 μm or more. 3. The redox battery according to claim 1, wherein the carbon compact layer has a hydrogen / carbon atomic ratio of 0.12 or less. 4. The carbon fiber layer has a hydrogen content of 0.08 or more /
The redox battery of claim 1 having a carbon atom ratio. 5. The carbon fiber layer has a surface area of 0.
The redox battery according to claim 1, having an oxygen / carbon atomic ratio of 02 or more. 6. The redox battery according to claim 1, wherein the carbon fiber layer has a bulk density of 0.50 or less. 7. The all-vanadium redox battery according to claim 1, wherein the positive electrode liquid is a pentavalent / tetravalent vanadium solution and the negative electrode liquid is a divalent / trivalent vanadium solution.