JP2001167786A - Electrode material and electrolytic bath for redox flow cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic bath that has a basic property of carbonaceous fiber used in an electrode material for a redox flow cell, and reduces contact resistance in an electrolytic bath using electrode material for reducing the contact resistance. SOLUTION: The electrolytic bath includes a membrane arranged between a pair of current collecting plates which are opposed with each other through a gap, and the electrode material is pressure-contacted and pinched by at least either of the membrane or the current collecting plates. As the electrode material, carbon aggregate is used and has a layered structure in the thickness direction, in which different point compression holding rates of more layers than two are integrated with each other. A pitch ratio (low value/high value) of the point pressure holding rate is in a range of 0.80 to 0.98. The side which has a higher point compression holding rate of the electrode material is arranged at the membrane side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode material and an electrolytic cell used for an electrolytic cell of a redox flow battery using an aqueous electrolytic solution. In particular, the electrode material and the electrolytic cell for a redox flow battery of the present invention are particularly useful as an electrode material and an electrolytic cell for a vanadium-based redox flow battery.

[0002]

2. Description of the Related Art Conventionally, electrodes have been developed with emphasis on the performance of batteries. Some electrodes do not become active materials themselves, but work as a reaction field to promote the electrochemical reaction of the active material.For this type, carbon materials are often used due to their conductivity and chemical resistance. Can be In particular, a carbon fiber aggregate having chemical resistance, conductivity, and liquid permeability is used for an electrode of a redox flow battery which is actively developed for power storage.

[0003] Redox flow batteries have a higher energy density from a type using an aqueous hydrochloric acid solution of iron for the positive electrode and an aqueous solution of chromium hydrochloric acid for the negative electrode, to a type using a high-electromotive force aqueous solution of vanadium sulfuric acid for both electrodes. Recently, developments for further increasing the concentration of the active material have been advanced, and the energy density has been further increased.

The main structure of a redox flow type battery is, as shown in FIG. 1, composed of external tanks 6 and 7 for storing an electrolytic solution and an electrolytic cell EC, and pumps 8 and 9 for supplying an electrolytic solution containing an active material to the external tank. While being sent from 6, 7 to the electrolytic cell EC, electrochemical energy conversion, that is, charge / discharge, is performed on the electrodes incorporated in the electrolytic cell EC.

In general, during charging and discharging, an electrolytic solution is circulated between an external tank and an electrolytic bath, so that the electrolytic bath has a liquid flow type structure as shown in FIG. The liquid flow type electrolytic cell is referred to as a single cell, which is used as a minimum unit and is used alone or in a multi-layered structure. Since the electrochemical reaction in the liquid flowing type electrolytic cell is a heterogeneous phase reaction occurring on the electrode surface, it generally involves a two-dimensional electrolytic reaction field. When the electrolytic reaction field is two-dimensional, there is a disadvantage that the reaction amount per unit volume of the electrolytic cell is small.

In order to increase the amount of reaction per unit area, that is, the current density, three-dimensional electrochemical reaction fields have been used. FIG. 2 is an exploded perspective view of a liquid flow type electrolytic cell having three-dimensional electrodes. In the electrolytic cell, an ion exchange membrane 3 is disposed between two opposing current collectors 1, 1, and the current collectors 1, 1 are arranged on both sides of the ion exchange membrane 3 by spacers 2.
The flow paths 4a and 4b for the electrolytic solution are formed along the inner surface of the first electrode 1. An electrode material 5 such as a carbon fiber aggregate is provided in at least one of the flow passages 4a and 4b, and thus a three-dimensional electrode is formed. In addition, in the current collector 1,
A liquid inlet 10 and a liquid outlet 11 for the electrolytic solution are provided.

[0007] In the case of a redox flow battery using a sulfuric acid aqueous solution of vanadium oxysulfate as the positive electrode electrolyte and vanadium sulfate as the negative electrode electrolyte, during discharge, the electrolyte containing V ²⁺ is ^supplied to the liquid flow path 4a on the negative electrode side. And an electrolyte containing V ⁵⁺ (actually, ions containing oxygen) is supplied to the flow path 4b on the positive electrode side. In the flow path 4a on the negative electrode side, V ²⁺ emits electrons in the three-dimensional electrode 5 and is oxidized to V ³⁺ . The emitted electrons pass through an external circuit and enter V ⁵⁺ in the three-dimensional electrode on the positive electrode side.
To V ⁴⁺ (actually an ion containing oxygen). The redox reaction SO ₄ ^2-of the negative electrode electrolytic solution is insufficient with the, for SO ₄ ^2-becomes excessive in the positive electrolyte, negative electrode SO ₄ ^2-is from the positive electrode side through the ion-exchange membrane 3 Side and the charge balance is maintained. Alternatively, the charge balance can be maintained by moving H ⁺ from the negative electrode side to the positive electrode side through the ion exchange membrane. At the time of charging, a reaction reverse to that of discharging proceeds.

As the characteristics of the electrode material for a vanadium-based redox flow battery, the following performance is particularly required.

1) No side reaction other than the intended reaction should occur (high reaction selectivity), specifically, high current efficiency (η _I ).

2) High electrode reaction activity, specifically, low cell resistance (R). That is, the voltage efficiency (η
_V ) is high.

3) High battery energy efficiency (η _E ), which is related to 1) and 2) above. η _E = η _I × η _V

4) Deterioration due to repeated use is small (long life), specifically, battery energy efficiency (η)
_E ) The amount of decrease is small.

For example, Japanese Patent Application Laid-Open No. 60-232669 discloses that the <002> plane spacing determined by X-ray wide angle analysis is 3.70 ° or less on average, and the crystallite size in the c-axis direction is average. It has been proposed to use a carbonaceous material having pseudographite crystallites of 9.0 ° or more and having a total acidic functional group content of at least 0.01 meq / g as an electrode material for an electrolytic cell.

JP-A-5-234612 discloses a carbonaceous fiber made of polyacrylonitrile-based fiber having a <002> plane spacing determined by X-ray wide-angle analysis of 3.0.
A carbonaceous material having a pseudo-graphite crystal structure of 50 to 3.60 ° and having the number of bonded oxygen atoms on the surface of the carbonaceous material of 10 to 25% of the number of carbon atoms is electrolyzed in an iron-chromium redox flow battery. It has been proposed to use it as an electrode material for a bath.

[0015]

However, JP-A-60-232669 and JP-A-5-234612 disclose that in order to exhibit effective wettability between the carbonaceous material surface and the electrolyte, Total acidic functional group content is 0.01me
q / g or more, or the number of bonded oxygen atoms on the surface of the carbonaceous material is required to be 10% or more of the number of carbon atoms, and the number of functional groups on the surface of the carbon electrode material is too large. As a result, the cell resistance was increased, and high battery energy efficiency was not obtained. To address these issues,
In order to improve the conductivity of the electrode material, it is conceivable to increase the packing density of the electrode material.However, if the packing density is increased unnecessarily, the flowability of the electrolytic solution is deteriorated, and the pressure loss due to the passage increases. The power loss of the pump that circulates the liquid increases, and as a result, the efficiency of the battery decreases.

In view of such circumstances, an object of the present invention is to use an electrode material having the basic characteristics of carbonaceous fiber used for an electrode material of a redox flow battery and capable of reducing the contact resistance in an electrolytic cell. To provide an electrolytic cell with reduced contact resistance.

[0017]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and found that a predetermined difference is provided in the point compression ratio in the thickness direction of the carbon aggregate used for the electrode material, and It has been found that the above object can be achieved by arranging the side having the higher point compressibility of the material on the diaphragm side, and the present invention has been completed.

That is, according to the present invention, a diaphragm is provided between a pair of current collectors disposed to face each other with a gap therebetween,
In an electrolytic cell having a structure in which an electrode material is pressed and held between at least one of the current collector plate and the diaphragm, two or more integrated layers having different point compression retention rates in the thickness direction are used as the electrode material. A carbon aggregate having a structure and a high / low ratio (low value / high value) of the point compression retention on the front and back surfaces is 0.80 or more and 0.98 or less, and the electrode material has a high point compression retention. A redox flow using an aqueous electrolyte solution, wherein the redox flow is disposed on the diaphragm side.

The present invention further relates to an electrode material comprising a carbon aggregate used in the electrolytic cell for a redox flow battery, wherein the carbon aggregate has an integrated layer structure of two or more layers having different point compression retention rates. And an electrode material for a redox flow battery, characterized in that the point compression retention ratio of the front and back surfaces (low value / high value) is 0.80 or more and 0.98 or less.

The point compression retention is a method of evaluating the thickness change rate under a low load using a measuring element having a spherical tip in order to evaluate the local hardness of the surface layer. The higher the point compression retention ratio, the higher the rate of change in the load thickness by the spherical probe, indicating that the surface texture is softer. The high ratio of the point compression retention ratio means that there is a great difference in the hardness of the front and back surfaces of the electrode material structure.

As described above, by forming the carbon aggregate used for the electrode material into an integrated layer structure of two or more layers having different point compression holding ratios in the thickness direction, the carbon material can be geometrically assembled when the electrode material is incorporated into the electrolytic cell. By increasing the point-to-point compression retention ratio within the above-mentioned predetermined range by increasing the point-to-point compression retention ratio, the compression retention ratio is high on the high point compression retention ratio side. Sometimes, the electrode material is compressed preferentially and the surface having a high point compression retention increases the geometric surface area of the electrode material, and the compression retention is low on the low point compression retention, so that the electrode material is electrolyzed. The strong compressive stress at the time of assembling into the tank improves the adhesiveness between the electrode material and the current collector, and reduces the contact resistance by obtaining the necessary compressive stress on the surface with low point compression retention.

As described above, by forming the carbon aggregate used for the electrode material into an integrated layer structure of two or more layers having different bulk densities in the thickness direction, the side having the higher point compression ratio has a higher priority when preparing the electrolytic cell. Since the electrode material is compressed and the geometric surface area of the single fiber of the electrode material is increased, the contact property inside the electrode material is improved. In addition, by creating an electrolytic cell with the side with the higher point compression ratio of the electrode material facing the diaphragm side, the electrode reaction that is actively performed near the diaphragm is improved by increasing the geometric surface area of the single fiber, the reaction resistance is reduced, and the cell resistance is reduced. Can be reduced.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode material of the present invention is made of carbonaceous fiber, and its composition and microstructure are not particularly limited, but those capable of increasing the electrode surface area are preferred. In particular,
Examples include spun yarn, bundled filament yarn, non-woven fabric, knitted fabric, woven fabric, and special knitted fabric (such as those described in JP-A-63-200457). Is used. The nonwoven fabric is obtained by defibrating infusible or flame-resistant short fibers prior to firing (carbonization), applying a card, creating a web composed of several layers, using a needle punch method, a thermal bonding method, and the like. And a known method such as a stitch bonding method.

The carbon aggregate used as an electrode material can be obtained by firing the thus obtained nonwoven fabric or the like by a known method and, if necessary, subjecting it to a surface treatment.

Although the basis weight of the carbon aggregate varies depending on the gap set by the spacer of the electrolytic cell, it is usually 100 to 1%.
The thickness is about 000 g / m ² , and the thickness is adjusted to be at least larger than the gap, desirably 1.2 to 3.3 times the gap in order to obtain the necessary compressive stress at the time of pressing. However, if the compressive stress of the electrode material is high, damage to the diaphragm and poor handling during the preparation of the electrolytic cell become apparent, so the compressive stress up to the set gap is desirably 0.098 MPa or less.

The carbon aggregate having such a layer structure is
Usually, the thickness is about 0.5 to 15 mm, preferably 1 to 10
mm, and the bulk density is 0.05 to 0.15 g / cm ³
Level, preferably 0.06 to 0.14 g / cm ³ , in order to achieve both liquid permeability and cell resistance.

The carbon aggregate used as the electrode material has an integrated layer structure of two or more layers having different point compression retention rates in the thickness direction. The layer structure of the electrode material is not particularly limited as long as there are two or more layers having different point compression retention rates on the front and back. For example, the layer structure may be such that the point compression retention of each layer sequentially increases (or decreases) in the thickness direction, and the high point compression retention layer / low point compression retention layer / high point compression retention layer Alternatively, a layer structure in which layers having different point compression retention rates such as a low point compression retention rate layer / a high point compression retention rate layer / a low point compression retention rate layer may be repeated. However, it is necessary that the carbon aggregate has a difference in point compression retention between the front surface and the back surface.

The high-point compression retention layer and the low-point compression retention layer can be distinguished by measuring the point compression retention on the front and back surfaces, and determining which of the layers containing the surface with the higher compression retention is the high-point compression retention layer. And the layer including the other surface is a low-point compression retention layer. Even when the electrode material has three or more layer structures, the point compression retention ratio on the front and back surfaces is measured to determine the height ratio.

Further, the carbon aggregate has a high / low point compression retention ratio (low value / high value) of 0.80 for the front and back surfaces.
The one adjusted so as to be in the range of 0.98 or more is used.

If the ratio of the high and low ratios of the point compression retention ratio becomes small and becomes less than 0.80, the portion having a low point compression retention ratio has an extremely hard structure with a superficial layer.
It is not preferable because the diaphragm is damaged when the electrolytic cell is formed, and the electrolytic solution is mixed in the electrolytic cell to cause a reduction in capacity. Because of this tendency, the height ratio is preferably set to 0.82 or more, more preferably 0.85 or more. On the other hand, when the ratio of the point compression retention ratio exceeds 0.98, there is no difference in the point compression retention ratio. The geometric surface area of the fiber does not increase, and the bondability with the electrode material deteriorates. Therefore, the contact resistance increases, the cell resistance increases, and as a result, the battery efficiency decreases. Because of this tendency, the ratio of the high and low ratios is 0.
It is preferably 97 or less, more preferably 0.95 or less.

The thickness and the point compression retention of the high point compression retention layer and the low point compression retention layer are appropriately adjusted so as to achieve the above-mentioned high / low ratio. Is about 5 to 50%, preferably about 10 to 40%, and the thickness is about 30 to 99%, preferably about 50 to 9% of the space obtained by the spacer.
0% is preferable from the viewpoint of ensuring liquid permeability and contact property. The point compression retention of the low point compression retention layer is
The thickness is about 0.1 to 50%, preferably 0.2 to 40%, and the thickness is 1 to 70% of the space obtained by the spacer.
%, And preferably 10 to 50%, from the viewpoint of ensuring liquid permeability and compressive stress required at the time of forming the electrolytic cell.

When a non-woven fabric is used as the carbon aggregate,
As a method of adjusting the point compression holding ratio, there is a method of variously setting nonwoven fabric forming conditions in the needle punching method, such as the characteristics of the needle for needle punching at the time of forming the nonwoven fabric, the needle density, the needle depth, and the pressing gap.

In order to obtain a compression holding ratio which cannot be realized by the needle punching method, it can be achieved by hot pressing or thermocompression bonding in the presence of a binder.

When hot pressing is performed, it is necessary to adjust the temperature and pressure according to the properties of each fiber.

The kind of binder is not particularly available, and examples thereof include binders of acrylic type, starch paste, polyvinyl alcohol type, epoxy resin type, vinyl acetate type and phenol resin type. It is most preferable to use a phenolic resin binder as the binder in order to maintain the adhesiveness by carbonizing even after carbonization. The method of adding the binder to the nonwoven fabric is not particularly limited, and examples thereof include a method of adding the binder in the cotton mixing step after the fibrillation of raw cotton, a method of dissolving or dispersing in water or an organic solvent, and attaching and drying the nonwoven fabric. It is desirable to carry out under suitable conditions.

As a method of forming the carbon aggregate into a layer structure of two or more layers and adjusting the ratio of the point compression retention to the above-mentioned range, for example, a nonwoven fabric having different point compression retention by the above-mentioned method is used. A method of joining by overlapping and further needlepunching, a method of joining together a nonwoven fabric and a woven fabric having a high point compression retention rate of another kind, a knitted fabric, and creating a web with a different basis weight at the time of web creation and laminating in the basis weight And a method in which the binder is applied or dispersed on one surface of the nonwoven fabric and solidified. In addition, a structure such as a Russell knitted fabric or a mulie frieze having a difference in point compression retention rate on the front and back surfaces may be used.

Next, the point compression holding ratio of the electrode material used in the present invention, the high / low ratio of the point compression holding ratio,
A method for measuring the cell resistance will be described.

1. Point compression retention ratio and its height ratio A test piece (dimension 25 mm × 10 mm) is prepared by mounting a measuring element (Spherical measuring element X-1 manufactured by Ozaki Seisakusho Co., Ltd.) on a compression thickness tester. After adjusting the zero point at zero load, the tracing stylus is fitted to the surface of the test piece, a load of 0.0392 N is applied, and the thickness at that time is read (t4). afterwards,
Compress to 0.490N and read the thickness at this time (t
50). From these data, the compression retention of the surface is obtained by the equation (1). The measured sample is turned upside down, and the probe is combined in the same manner to obtain the compression retention on the back surface.

[0039]

(Equation 1) Next, the point compression holding ratio high / low ratio is calculated by Expression 2.

(Equation 2)

2. Cell Resistance A small cell having an electrode area of 10 cm ² of 1 cm in the vertical direction (liquid flowing direction) and 10 cm in the width direction is prepared, and is mounted with the high point compression retention rate side of the electrode material facing the cell membrane side. Perform charge / discharge at a constant current density and test the electrode performance. A 2 mol / l vanadium oxysulfate aqueous solution of 3 mol / l sulfuric acid was used for the positive electrode electrolyte, and 2 mol / l aqueous solution of sulfuric acid for the negative electrode electrolyte was used.
A 3 mol / l aqueous solution of sulfuric acid of mol / l vanadium sulfate was used. The amount of the electrolytic solution was set to a large excess with respect to the cells and piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

In a one-cycle test starting from charging and ending with discharging, the current density was set to 40 m per electrode geometric area.
A / cm ² (400 mA), the quantity of electricity required for charging up to 1.7 V is Q ₁ coulomb, constant current discharging up to 1.0 V, and subsequent electricity discharging at constant voltage discharging at 1.2 V. The quantities are Q ₂ and Q ₃ coulombs, respectively, and the ratio of the quantity of electricity taken out by discharge to the theoretical quantity of electricity Q _th required to completely reduce V ³⁺ in the negative electrode solution to V ²⁺ is the charging rate. Then, the charging rate is obtained by Expression 3.

[0042]

(Equation 3) Charging voltage VC corresponding to the amount of electricity when the charging rate is 50%
50 and the discharge voltage VD50 are respectively obtained from the electric quantity-voltage curve, and the cell resistance R with respect to the electrode geometrical area is obtained from Expression 4.
(Ω · cm ² ).

[0043]

(Equation 4) Here, I is a current value of 0.4 A in constant current charging and discharging.

The electrode material of the present invention is used for a redox flow battery using an aqueous electrolyte. In the redox flow battery, for example, as described above, a diaphragm is disposed between a pair of current collectors disposed facing each other with a gap therebetween, and at least one of between the current collector and the diaphragm is provided. An electrolytic cell having a structure in which an electrode material is pressed and held is provided. The same electrolytic cell can be used as in the prior art. For example, it has the structure shown in FIGS. As the current collector and the diaphragm, the same ones as those in the related art can be used. In the electrolytic cell, an aqueous solution containing an active material is used as an aqueous electrolytic solution.

Examples of the aqueous electrolytic solution include iron-chromium-based, titanium-manganese-based, manganese-chromium-based, and iron-titanium-based systems, in addition to the above-described vanadium-based electrolyte, and the vanadium-based system is preferred. The electrode material of the present invention has a viscosity of 25 ° C.
A vanadium-based electrolyte solution of 0.05 Pa · s or more,
Alternatively, it is useful to be used in a redox flow battery using a vanadium-based electrolyte containing 1.5 mol / l or more vanadium ions.

[0046]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and effects of the present invention will be specifically shown below, and embodiments and the like will be described.

Example 1 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
A non-woven fabric having a needle of No. 40 HDB manufactured by Foster, a needle density of 43.09 needles / cm ² , and a holding gap of 5.0 mm was formed into a non-woven fabric having a basis weight of 900 g / m ² and a thickness of 6.3 mm. Add phenolic resin powder (Kanebo Co., Ltd.)
Manufactured by Bellpearl S890) 3 g / m ² was sprayed from above the nonwoven fabric, and then suctioned from below the nonwoven fabric with a suction pressure of 980.6 Pa and a suction speed of 2.0 m / sec to immobilize the binder on the surface of the nonwoven fabric. This was heated in an air through oven at 180 ° C. for 10 minutes to bond the binder. The cloth was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, carbonized and cooled, and then cooled to 700 ° C. in a nitrogen stream with an oxygen concentration of 5 vol%. The mixture was treated at 93 ° C. to a weight yield of 93% to obtain a carbonaceous fiber nonwoven fabric.

Example 2 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
A non-woven fabric having a needle of No. 40 HDB manufactured by Foster, a needle density of 43.09 needles / cm ² , and a holding gap of 5.0 mm was formed into a non-woven fabric having a basis weight of 900 g / m ² and a thickness of 6.3 mm. Add phenolic resin powder (Kanebo Co., Ltd.)
(Bellpearl S890) 10 g / m ² was sprayed from above the nonwoven fabric, and then suction was applied from below the nonwoven fabric with a suction pressure of 980.6 Pa and a suction speed of 2.0 m / sec to immobilize the binder on the surface of the nonwoven fabric. This was heated in an air through oven at 180 ° C. for 10 minutes to bond the binder. The cloth was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, carbonized and cooled, and then cooled to 700 ° C. in a nitrogen stream with an oxygen concentration of 5 vol%. The mixture was treated at 93 ° C. to a weight yield of 93% to obtain a carbonaceous fiber nonwoven fabric.

Example 3 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
Foster's HDB No. 40 needle, a needle density of 43.09 needles / cm ² , and a holding gap of 3.0 mm were formed into a nonwoven fabric to prepare an oxidized nonwoven fabric 1 having a basis weight of 300 g / m ² and a thickness of 3.4 mm. A phenolic resin powder (manufactured by Kanebo K.K .: Bellpearl S890) 10 g /
Foster Co. HDB40 number of needle mix m ^2, needle density 7
A non-woven fabric was formed into a non-woven fabric under the conditions of 2.85 yarns / cm ² and a holding gap of 3.0 mm, and an oxidized non-woven fabric 2 having a basis weight of 600 g / m ² and a thickness of 4.8 mm was prepared. The two nonwoven fabrics were combined, needle-punched, and heated in an air-through oven at 180 ° C. for 10 minutes to bond a binder to obtain a laminated flame-resistant nonwoven fabric. The laminated flame-resistant nonwoven fabric was heated to 1600 ° C. at a heating rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, carbonized, and cooled.
Subsequently, treatment was performed at 700 ° C. under a nitrogen stream having an oxygen concentration of 5 vol% until the weight yield became 93%, to obtain a carbonaceous fiber nonwoven fabric.

Example 4 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
Foster's HDB No. 40 needle, a needle density of 43.09 needles / cm ² , and a holding gap of 3.0 mm were formed into a nonwoven fabric to prepare an oxidized nonwoven fabric 1 having a basis weight of 300 g / m ² and a thickness of 3.4 mm. In addition, the same flame-resistant fiber was manufactured by Foster H
A DB40 needle, a needle density of 72.85 needles / cm ² , and a holding gap of 4.0 mm were formed into a nonwoven fabric, and the basis weight was 600 g.
/ M ² , 4.8 mm thick non-flammable nonwoven fabric 2 was prepared, and a liquid phenol resin (BRE17, manufactured by Showa Polymer Co., Ltd.) was used.
4) 0.1% by weight was impregnated. The two nonwoven fabrics were combined, needle-punched, and heated in an air-through oven at 180 ° C. for 10 minutes to bond a binder to obtain a laminated flame-resistant nonwoven fabric. The laminated flame-resistant nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen gas flow, held at this temperature for one hour, carbonized and cooled, and subsequently cooled with a nitrogen gas having an oxygen concentration of 5 vol%. 700 ° C below
To obtain a carbon fiber nonwoven fabric.

Example 5 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
Foster's HDB No. 40 needle, a needle density of 43.09 needles / cm ² , and a holding gap of 5.0 mm were formed into a nonwoven fabric to prepare an oxidized nonwoven fabric 1 having a basis weight of 600 g / m ² and a thickness of 5.4 mm. In addition, the same flame-resistant fiber was manufactured by Foster H
A DB40 needle, a nonwoven fabric with a needle density of 72.85 needles / cm2 and a holding gap of 3.0 mm, a basis weight of 300 g /
An oxidized nonwoven fabric 2 having an m ² of 3.1 mm and a thickness of 3.1 mm was prepared, and a liquid phenol resin (BRE174, manufactured by Showa Polymer Co., Ltd.) was used.
0.1% by weight was impregnated. The two nonwoven fabrics were combined, needle-punched, and heated in an air-through oven at 180 ° C. for 10 minutes to bond a binder to obtain a laminated flame-resistant nonwoven fabric. The laminated flame-resistant nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen gas flow, held at this temperature for one hour, carbonized and cooled, and subsequently cooled with a nitrogen gas having an oxygen concentration of 5 vol%. The resultant was treated at 700 ° C. under a temperature of 93% to obtain a carbonaceous fiber nonwoven fabric.

COMPARATIVE EXAMPLE 1 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized at 200 to 300 ° C. in air, and then about 80 m long.
m to prepare short fibers of flame-resistant fibers. Then
A needle of No. 40 of HDB manufactured by Foster, a needle density of 43.09 needles / cm ² , and a holding gap of 5.0 mm were formed into a nonwoven fabric to prepare a nonwoven fabric having a basis weight of 900 g / m ² and a thickness of 6.3 mm. This was heated in an air through oven at 180 ° C. for 10 minutes to bond the binder. The cloth was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, carbonized and cooled, and then cooled to 700 ° C. in a nitrogen stream with an oxygen concentration of 5 vol%. The mixture was treated at 93 ° C. to a weight yield of 93% to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 2 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then the length was about 80 m.
m to prepare short fibers of flame-resistant fibers. Then
A non-woven fabric having a basis weight of 900 g / m ² and a thickness of 6.3 mm was prepared under the conditions of a Foster No. 40 HDB needle, a needle density of 43.09 needles / cm 2 and a holding gap of 5.0 mm. Add phenolic resin powder (Bellpearl S89)
0) 40 g / m ² was sprayed from above the nonwoven fabric, and then suction was applied from below the nonwoven fabric with a suction pressure of 490.3 Pa and a suction speed of 2.0 m / sec to immobilize the binder on the surface of the nonwoven fabric. This was heated in an air through oven at 180 ° C. for 10 minutes to bond the binder. The cloth was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, carbonized and cooled, and then cooled to 700 ° C. in a nitrogen stream with an oxygen concentration of 5 vol%. The mixture was treated at 93 ° C. to a weight yield of 93% to obtain a carbonaceous fiber nonwoven fabric.

The basis weight and thickness of the carbonaceous fiber nonwoven fabrics obtained in the examples and comparative examples, the high / low ratio of the point compression retention, and the cell resistance value of the electrolytic cell in which the side having the high point compression retention were installed in the direction of the diaphragm. It is described in Table 1.

[0055]

[Table 1] As is clear from the results in Table 1, the electrode materials of Examples 1 to 5 have small cell resistance values. In addition, by forming an electrolytic cell using an electrode with the high point compression retention ratio side of the electrode material facing the diaphragm side, high voltage efficiency is exhibited, and excellent energy efficiency is obtained.

On the other hand, in Comparative Example 1 in which the ratio of the high point compression retention of the electrode material was higher than 0.98, there was no difference in the point compression retention between the front and back sides. Is reduced in reactivity. Therefore, the resistance at the time of reaction increases, and the cell resistance increases. When the point compression ratio is less than 0.80, the surface of the part having a low point compression ratio becomes extremely hard, so that the membrane is damaged when the electrolytic cell is made, and the electrolyte is mixed in, resulting in a decrease in capacity. Is not preferred.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a vanadium-based redox flow battery.

FIG. 2 is an exploded perspective view of an electrolytic cell of a vanadium-based redox flow battery having a three-dimensional electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current collecting plate 2 Spacer 3 Ion exchange membrane 4a, 4b Liquid passage 5 Electrode material 6 External liquid tank (positive electrode side) 7 External liquid tank (negative electrode side) 8, 9 Pump 10 Liquid inlet 11 Liquid outlet

Claims (2)

[Claims] 1. A diaphragm is disposed between a pair of current collectors disposed opposite each other with a gap therebetween, and an electrode material is pressed and held between at least one of the current collector and the diaphragm. In the electrolytic cell having the structure described above, the electrode material has an integrated layer structure of two or more layers having different point compression retention rates in the thickness direction, and a high / low ratio of the point compression retention rates on the front and back surfaces (low value). (High value) of 0.80 or more and 0.98 or less using an aqueous electrolyte solution characterized in that a side having a higher point compression retention rate of the electrode material is disposed on the diaphragm side. For redox flow batteries. 2. An electrode material comprising a carbon aggregate used in the electrolytic cell for a redox flow battery according to claim 1, wherein the carbon aggregate has two or more integrated layer structures having different point compression retention rates. And an electrode material for a redox flow battery, characterized in that the ratio of high and low point compression retention ratios (low value / high value) on the front and back surfaces is 0.80 or more and 0.98 or less.