JP2001196071A - Carbon electrode material assembly and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon electrode material assembly capable of improving energy efficiency by reducing cell resistance of a battery and of maintaining high-energy efficiency for a long time, and a manufacturing method thereof. SOLUTION: A carbon electrode material assembly is used in a redox flow battery using aqueous solution electrolyte and consists of a non-woven cloth of carbonaceous fibers. Fibers of the non-woven cloth are bonded each other with carbides of diameters less than or equal to 20 μm and an existence ratio of bonded portion of the fibers is 0.2-10%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon electrode material assembly made of a nonwoven fabric of carbonaceous fibers and a method for producing the same, particularly to a redox flow battery using an aqueous electrolyte solution. Useful for flow batteries.

[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 nonwoven fabric of carbon fiber 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.

As shown in FIG. 1, a redox flow type battery comprises external tanks 6 and 7 for storing an electrolytic solution and an electrolytic cell E.
C, the electrolytic solution containing the active material is sent from the external tanks 6 and 7 to the electrolytic bath EC by the pumps 8 and 9,
Electrochemical energy conversion, that is, charging and discharging, is performed on the electrode incorporated in C.

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 arranged between two opposing current collector plates 1 and 1, and the current collector plates 1 and 1 are disposed on both sides of the ion exchange membrane 3 by spacers 2.
Are formed along the inner surface of the cell. At least one of the flow passages 4a, 4b is provided with an electrode material 5 made of a nonwoven fabric of carbonaceous fiber or the like, thus forming a three-dimensional electrode. The current collecting plate 1 is provided with a liquid inlet 10 and a liquid outlet 11 for the electrolytic solution.

[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 cell resistance (R)
Is small. That is, the voltage efficiency (η _V ) is high. 3) High battery energy efficiency (η _E ) related to 1) and 2) above. η _E = η _I × η _V 4) Deterioration due to repeated use is small (long life)
Specifically, the amount of decrease in battery energy efficiency (η _E ) is small.

As for the cell resistance (R), the ratio of the contact resistance between the electrode material such as the carbonaceous fiber aggregate and the current collector and the contact resistance between the carbonaceous fibers constituting the electrode material greatly increases. The effect of these contact resistances and changes over time on battery energy efficiency and changes over time is large.

On the other hand, 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 of a redox flow battery.

Japanese Unexamined Patent Publication (Kokai) No. 5-234612 discloses a carbonaceous fiber made of polyacrylonitrile-based fiber having a <002> plane spacing of 3.0 obtained by X-ray wide-angle analysis.
A carbonaceous material having a pseudo-graphite crystal structure of 50 to 3.60 ° and having a number of bonded oxygen atoms of 10 to 25% of the number of carbon atoms on the surface of the carbonaceous material may be used as an electrode material of a redox flow battery. Proposed.

[0012]

However, in the carbon electrode material aggregates disclosed in JP-A-60-232669 and JP-A-5-234612, the single fibers that are in contact with each other are bonded with a binder or the like. The contact resistance between the single fibers is not sufficiently reduced because the fibers are not bound together and are merely in contact with each other, and it is difficult to maintain the contact state and the pressure contact state with the current collector plate for a long time. It turned out to be. For this reason, there has been a problem that the initial cell resistance becomes high and the energy efficiency becomes insufficient, and the energy efficiency is apt to be reduced during long-term use.

On the other hand, Japanese Patent Application Laid-Open No. 9-245805 discloses a technique of using a carbonized porous sheet made of carbon fibers and a resin binder as an electrode material. The gazette discloses an electrode material obtained by spraying a resin binder of a powder on a carbon fiber nonwoven fabric and then hot-pressing the carbonized nonwoven fabric.

However, all of the techniques use a resin binder to maintain the shape such as forming a groove in the nonwoven fabric, so that the amount of the resin binder attached is too large or the particle size is too large. It has been found that the electrical resistance of the binding portion between them cannot be sufficiently reduced, and that problems such as a decrease in the effective reaction field on the fiber surface are likely to occur. For this reason, the initial cell resistance was increased and energy efficiency was likely to be insufficient.

In view of the foregoing, an object of the present invention is to provide a carbon electrode material assembly capable of reducing the cell resistance of a battery to increase energy efficiency and maintaining high energy efficiency for a long period of time. , And a method of manufacturing the same.

[0016]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive research on a method for producing a carbon electrode material assembly using a resin binder, and have found that a resin binder having a smaller particle size than usual is produced. After being suitably attached to the raw material nonwoven fabric in the form of granules, by heating and pressurizing, it is possible to bind the single fibers with carbide of an appropriate size and amount,
As a result, the inventors have found that the above object can be achieved by reducing the electric resistance of the binding portion, and have completed the present invention.

That is, the carbon electrode material assembly of the present invention is used in a redox flow battery using an aqueous electrolyte solution, and is used in a carbon electrode material assembly comprising a nonwoven fabric of carbonaceous fibers.
The non-woven fabric is characterized in that the single fibers are bound by a carbide having a major axis of 20 μm or less, and the binding ratio between the single fibers is 0.2 to 10%. The distinction between carbides and other substances can be determined by elemental analysis using an X-ray microanalyzer.

According to the carbon electrode material aggregate of the present invention, since the single fibers of the nonwoven fabric are bonded by a small carbide having a major axis of 20 μm or less, the electrical resistance of the bonded portion between the single fibers is low due to the conductivity. Thus, the cell resistance of the battery can be reduced and the energy efficiency can be increased. In addition, since the binder is bonded by the carbide, the resistance value of the binding portion between the fibers is maintained for a long time, and since the compression elastic modulus of the nonwoven fabric is hardly reduced, the contact resistance with the current collector is also maintained for a long time. You. Furthermore, since the existing ratio of the binding portion between the single fibers is 0.2 to 10%, an appropriate binding force can be obtained, and the reduction of the effective reaction field due to the excessive amount of the carbide is less likely to occur. As a result, the cell resistance of the redox flow battery can be reduced to increase the energy efficiency, and the energy efficiency can be maintained for a long time.

In the above, it is preferable that the nonwoven fabric has a void of 90% or more. When having the porosity, the abundance ratio of the binding portion and the amount of carbide tend to be appropriate,
The above operation and effect can be obtained more reliably.

On the other hand, according to the production method of the present invention, the granules obtained by aggregating an organic binder having a primary average particle diameter of 20 μm or less are dispersed and attached to a raw nonwoven fabric of carbonaceous fibers, and then heated and pressed to form single fibers. And a step of carbonizing the single fiber and the organic binder after binding.

According to the production method of the present invention, since the granules obtained by aggregating the organic binder having a small particle diameter are used, the granules can be suitably dispersed and held inside the raw nonwoven fabric.
In addition, since the granules are agglomerated, they can be easily granulated at the time of heating and pressing, and the single fibers can be bound together in a small particle size state. For this reason, since the carbon electrode material aggregate after carbonization is bound by small carbides, the above-described action can reduce the cell resistance of the redox flow battery and increase energy efficiency, And energy efficiency can be maintained over a long period of time.

The method for fixing a single fiber is CC
There is carbide fusion on the entire fiber surface such as a composite, but if carbide fusion is on the entire surface, the fiber surface which is a reaction field will be significantly reduced, and as a result, the fiber will not be in contact as a nonwoven fabric as in the present invention. It is effective to immobilize only the part that has been used. When the specific resistance of the carbide is high or the compound is a metal compound, the contact resistance does not decrease or a side reaction due to a different metal occurs.

Further, the carbon electrode material assembly of the present invention is preferably used for a vanadium redox flow battery. In vanadium redox flow batteries, iron-
The reaction rate between the active material and the electrode material surface is higher than that of the chromium-based electrolyte, and the contact resistance of the electrode material tends to be relatively higher than the resistance (reaction resistance) associated with the reaction with the electrode material.
Therefore, the contact resistance between the fibers constituting the electrode material tends to be particularly problematic, and the carbon electrode material of the present invention having the above-mentioned effects is particularly useful.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon electrode material aggregate of the present invention is made of carbonaceous fiber, and a nonwoven fabric of carbonaceous fiber is used from the viewpoint of handling, workability, manufacturability and the like. The non-woven fabric is obtained by opening infusible or flame-resistant short fibers before firing (carbonization), applying them to a card, first producing a web composed of several layers, and then applying the web to a needle punching machine. Thereby, it is suitably manufactured.

The basis weight of the non-woven fabric is determined by the distance between the diaphragm and the current collector.
When the thickness of the filled state is 2-3 mm, 100
~ 1000g / m^Two Is preferred, especially 200 to 600 g
/ M ^Two Is desirable. Non-woven fabric with a groove on one side
Cloth or the like is preferably used because of liquid permeability. Groove width in that case,
The groove depth should be at least 0.3mm, especially 0.5mm or more
desirable. The thickness of the carbonaceous fiber non-woven fabric is in the above-mentioned filled state.
At least larger than the thickness of
Is about 1.5 times the thickness of However, the thickness is thick
If too much, the membrane will break through with compressive stress.
Force 9.8 N / cm^Two It is preferable to design as follows.

The average fiber diameter of the carbonaceous fibers is 5
About 20 μm is preferable, and the average length is 30 to 100 m.
m is preferable.

[0027] The carbonaceous fiber non-woven fabric is assembled by being pressed into the battery, and a high-viscosity electrolytic solution flows through the thin gap. Therefore, in order to prevent falling off and to maintain the form, the tensile strength is 0.98 N / N. cm ² or more. In order to improve the contact resistance with the current collector, the density of the diaphragm and the filling layer sandwiched between the current collectors is set to 0.05 g / cm ³ or more, and the repulsive force to the electrode surface is set to 0.98 N / cm ² or more. Is preferable.

Further, in the carbonaceous fiber of the present invention, the single fibers of the non-woven fabric are bound with carbide, and the long diameter of the carbide binding between the single fibers is 20 μm or less, and the ratio of the bound portion is 0.1%. 2 to 10%. If the long diameter of the carbide binding between the single fibers is larger than 20 μm and the proportion of the binding portion is more than 10%, the bound carbide will have a diameter of the single fiber (5 to 5%).
(Approximately 20 μm), and the carbide covers the surface of the single fiber, thereby significantly reducing the effective reaction field and increasing the cell resistance. Even when the carbide is not covered, the carbide acts as an obstacle, and the diffusion of ions to be reacted in the electrolytic solution to the surface of the single fiber is rate-limiting, and the diffusion resistance increases. In any case, the cell resistance increases. On the other hand, if the binding portion is less than 0.2%, the adhesive force between the fibers is weak, and the carbides come off when the battery is pressed into the battery and incorporated, thereby losing the effect of bonding between the fibers. In addition, the contact resistance between fibers increases even after long-term use. From this viewpoint, preferably, the major axis of the carbide that binds between the single fibers is 15 μm or less, and the proportion of the binding part is 0.5 to 5%, more preferably the major axis of the carbide that binds between the single fibers. Is 10 μm or less, and the abundance of single fibers bound by carbide is 0.5 to 3%.

Further, the carbonaceous fiber nonwoven fabric preferably has a void of 90% or more. When the porosity is less than 90%, the major axis of the carbide tends to increase, and the proportion of the binding portion tends to increase, and the effect of both tends to increase the cell resistance.

The carbonaceous fiber non-woven fabric in which the single fibers are bonded with a carbide as described above employs a manufacturing method as described later in order to fix only a portion which originally came into contact as a non-woven fabric structure. Preferably, the structure has specific voids and compression properties. Specific voids and compression characteristics can be obtained, for example, by controlling the conditions of the previous stage needle punch. That is, the density of the needle punch is set to 150 to 30.
0 / cm ² , preferably 200 to 300 / cm ²
An infusible fiber or an oxidized fiber is likely to be entangled alternately with the needle of the needle punch, and the contact between the fibers, particularly the contact between the intersecting fibers increases, for example, SB # 40 (Fo)
(ster Needle).

Further, a specific binder is attached to the non-fusible fiber or non-flammable fiber non-woven fabric, hot-pressed, baked, and dry-oxidized to thereby provide carbonaceous fibers having single fibers bound by carbide. A non-woven fabric is obtained. Preferably, the production method of the present invention, that is, when the primary average particle size is 2
After agglomeration of the organic binder of 0 μm or less is dispersed and attached to the raw nonwoven fabric of carbonaceous fibers, heating and pressing are performed to bind the single fibers together, and then the single fibers and the organic binder are carbonized. It can be obtained by a method for producing a carbon electrode material aggregate having a step of performing.

As the granules of the organic binder, those obtained by coagulating granular or spherical particles which are hard to coagulate with a nonionic organic coagulant such as polyacrylamide, polyoxyethylene, and caustic starch are preferable.
As the organic binder, any organic binder may be used as long as it is nonionic, exhibits adhesiveness when heated, and carbonizes while maintaining the binding force during firing (carbonization) at a high temperature. For example, a phenolic resin binder, a melamine resin binder A thermosetting resin-based binder or the like can be suitably used. Among them, phenolic resin binders having good adhesion and conductivity after carbonization are more preferable, and those having low hygroscopicity and hardly coagulating, for example, Bellpearl S890 (Kanebo Co., Ltd.)
Is preferred.

The agglomerated material is prepared by sieving such an organic binder so as to have a particle size of preferably 5 to 20 μm, so as to have a size such that the organic binder does not fall off from the inside of the nonwoven fabric. And then dried, and then preferably granulated to a particle size of 50 to 100 μm.

Using the granules, spraying and suction are repeated so as to be uniformly dispersed in the nonwoven fabric. The nonwoven fabric to which the agglomerated binder is attached is preferably 150 to 3
After hot pressing at 00 ° C. to such an extent that the single fibers are not broken, it is preferable to remove the flocculant and unnecessary binder by suction.
As the pressing conditions, the thickness of the nonwoven fabric is 1/10
A pressure of up to ２ is preferred. Due to such deformation of the nonwoven fabric at the time of pressurization, the granulated material becomes fine particles, and the single fibers can be bound with the organic binder having a small particle size.

The carbonaceous fiber having an internal structure and surface characteristics suitable for a redox flow battery is 200 to 30 under tension.
Using polyacrylonitrile, isotropic pitch, mesophase pitch, cellulose, etc., which have undergone initial air oxidation at 0 ° C., or phenol, polyparaphenylenebenzobisoxazole (PBO), etc., under an inert atmosphere
It is obtained by subjecting a carbon material having a pseudo-graphite crystal structure calcined (carbonized) at 000 to 1800 ° C. to a dry oxidation treatment.

In the above description, the carbonization temperature is not limited to the temperature because the crystallinity differs depending on the raw material, and it is preferable to optimize the temperature according to the raw material. The dry oxidation may be performed by a known method, but it is preferable to adjust the weight yield after oxidation to 90 to 96% in consideration of the mechanical strength of the material. However, the treatment method is not limited to this. For example, similar effects can be obtained by performing electrolytic oxidation instead of the dry oxidation treatment.

Next, the major diameter of the carbide binding between the single fibers employed in the present invention, the proportion of the binding portion of the carbide, the porosity of the nonwoven fabric, the current efficiency, the voltage efficiency (cell resistance R), Each method of measuring the energy efficiency and the change over time in the charge / discharge cycle will be described.

1. The scanning electron microscope photograph of the long diameter non-woven fabric of the carbide binding between the single fibers was taken at a magnification of 150 times,
The major axis of the carbide binding between 10 or more single fibers arbitrarily extracted from the photograph was measured and determined by arithmetic mean. It should be noted that the measurement was performed by excluding carbides that adhered to the fiber surface and could not be distinguished from fibers.

2. Existence ratio of binding part Similar to 1 above, a scanning electron micrograph of the nonwoven fabric was taken at a magnification of 150 times, and the photograph was divided into 100 parts evenly. Was measured and determined by the ratio. In addition, it measured as what does not exist the carbide which adheres to the fiber surface and cannot be distinguished from a fiber.

3. Porosity of nonwoven fabric Porosity of nonwoven fabric (%) = 100− (weight per unit area of carbonaceous fiber nonwoven fabric (g / m ² ) × thickness (mm) / 1000 / specific gravity (g)
/ Cm ³ ) × 100) Here, the thickness is a value at a load of 0.086 N / cm ² , and the specific gravity is 6.3.2 of JISR7601-1986.
It was determined by a measurement method using a liquid displacement method.

4. Electrode Characteristics A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid flowing direction) and 1 cm in the width direction is made, and charge and discharge are repeated at a constant current density to test the electrode performance. 3 m of 2 mol / l vanadium oxysulfate was used for the positive electrode electrolyte.
ol / l sulfuric acid aqueous solution, and 2 mol / l
1 vanadium sulfate aqueous solution of 3 mol / l sulfuric acid 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.

(A) Current efficiency: η _{I In a} one-cycle test starting from charging and ending with discharging, the current density was set to 40 mA / cm ² per electrode geometrical area.
(400 mA), the quantity of electricity required for charging up to 1.7 V is Q ₁ coulomb, the quantity of electricity taken out by constant current discharge up to 1.0 V, and the subsequent quantity of electricity taken out by constant voltage discharge at 1.2 V are Q ₂ , Q ₃ coulomb, and the current efficiency η _I is obtained by equation (1).

[0043]

(Equation 1) (B) Cell resistance: R The ratio of the amount of electricity taken out by discharging to the theoretical amount of electricity Q _th required to completely reduce V ³⁺ in the negative electrode solution to V ²⁺ is defined as a charging rate. The charging rate is determined in step 2.

[0044]

(Equation 2) Charging voltage V corresponding to the amount of electricity when the charging rate is 50%
_C50 and discharge voltage _VD50 were obtained from the electric quantity-voltage curve, respectively, and the cell resistance R (Ω
· Find cm ² ).

[0045]

(Equation 3) (C) Voltage efficiency: η _V Using the cell resistance R obtained by the above method, the voltage efficiency η _V is obtained by a simple method of Expression 4.

[0046]

(Equation 4) Here, E is the cell open circuit voltage when the charging rate is 50%.
432 V (actual measurement value), and I is a current value of 0.4 A in constant current charging and discharging.

(D) Energy efficiency: η_E Current efficiency η described above_I And voltage efficiency η_V And using equation 5
More energy efficiency η _E Ask for.

[0048]

(Equation 5)(E) Temporal change of charge / discharge cycle After measurement of (a), (b), (c), and (d),
40 mA / cm^Two Cell voltage at constant current density of
Charge and discharge are repeatedly performed between 1.0 and 1.7V. Regulation
(A), (b), (c), (d)
Is measured, and η _E And the change Δη from the beginning_E To
Ask.

The characteristics of an electrode for an electrolytic cell such as a redox flow battery mainly include the current efficiency η _I and the voltage efficiency η _V as described above.
(Cell resistance R) and energy efficiency η _E (η _I and η _V
) And the charge / discharge cycle stability (lifetime) of these efficiencies.

The carbon electrode material assembly of the present invention is used for a redox flow battery using an aqueous electrolyte. The redox flow battery, as described above,
For example, a diaphragm is disposed between a pair of current collectors disposed to face each other with a gap therebetween, and an electrode material is pressed and sandwiched between at least one of the current collector and the diaphragm. An electrolytic cell having a structure containing an electrolytic solution composed of an aqueous solution containing an active material is provided.

Examples of the aqueous electrolyte include iron-chromium, titanium-manganese-chromium, chromium-chromium, iron-titanium and the like, in addition to the vanadium-based electrolyte described above. Liquids are preferred. In particular, the carbon electrode material aggregate of the present invention has a viscosity of 0.005% at 25 ° C.
It is useful to use a redox flow battery using a vanadium-based electrolyte solution of 5 Pa · s or more or a vanadium-based electrolyte solution containing 1.5 mol / l or more of vanadium ions.

[0052]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and the like specifically showing the configuration and effects of the present invention will be described below.

(Example 1) A polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. A phenol resin S890 (Kanebo Co., Ltd.) sieved with a mesh dish so as to have a particle size of 5 to 20 μm is agglomerated with a 1% polyacrylamide aqueous solution on the nonwoven fabric.
Spraying and suctioning were repeated so that the binder dried at 00 ° C. and granulated to a particle size of 50 to 100 μm was uniformly dispersed and attached at 10 g / m ² . The nonwoven fabric was pressed with a flat plate press at a temperature of 220 ° C., a gap of 1 mm, a time of 1 minute, and a pressure of 588 N /
hot press under the condition of cm ² and then 10 ° C. /
The temperature is raised to 1300 ° C. at a heating rate of 1 minute, the temperature is maintained for 1 hour, carbonized, cooled, and treated in air at 700 ° C. until the weight yield becomes 95% to obtain a carbonaceous fiber nonwoven fabric. Was.

(Example 2) Polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and then a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. A phenol resin S890 (Kanebo Co., Ltd.) sieved with a mesh dish so as to have a particle size of 5 to 20 μm is agglomerated with a 1% polyacrylamide aqueous solution on the nonwoven fabric.
Spraying and suctioning were repeated so that the binder dried at 00 ° C. and granulated to a particle size of 50 to 100 μm was dispersed and attached uniformly at 3 g / m ² . The nonwoven fabric is heated at a temperature of 2
20 ° C., gap 1 mm, time 1 minute, pressure 588 N / c
hot press under the condition of m ² , and then heated to 1300 ° C. at a rate of 10 ° C./min in nitrogen gas, kept at this temperature for 1 hour, carbonized and cooled, and further cooled in air at 700 ° C. To give a weight yield of 95% 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 a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. A phenol resin S890 (Kanebo Co., Ltd.) sieved with a mesh dish so as to have a particle size of 5 to 10 μm is agglomerated with a 1% polyacrylamide aqueous solution on the nonwoven fabric.
Spraying and suctioning were repeated so that the binder dried at 00 ° C. and granulated to a particle size of 50 to 100 μm was dispersed and applied uniformly at 15 g / m ² . The nonwoven fabric was heated at a temperature of 250 ° C., a gap of 0.5 mm, a time of 1 minute and a pressure of 588 with a flat plate press.
Hot pressing under the condition of N / cm ² ,
The temperature was raised to 1300 ° C. at a temperature rising rate of 1 ° C./min, kept at this temperature for 1 hour, carbonized and cooled, and
The mixture was treated at 95 ° C. until the weight yield became 95% to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 1) A polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and then a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The nonwoven fabric is hot-pressed with a flat plate press at a temperature of 250 ° C., a gap of 0.5 mm, a time of 1 minute and a pressure of 588 N / cm ² , and then heated to 1300 ° C. in nitrogen gas at a rate of 10 ° C./min. The temperature was raised, maintained at this temperature for 1 hour, carbonized, cooled, and further treated in air at 700 ° C. until the weight yield became 95% 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 a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. A phenol resin S890 (Kanebo Co., Ltd.) sieved with a mesh dish so as to have a particle size of 5 to 20 μm is agglomerated with a 1% polyacrylamide aqueous solution on the nonwoven fabric.
Spraying and suction were repeated so that the binder dried at 00 ° C. and granulated to a particle size of 50 to 100 μm was dispersed and adhered uniformly at 60 g / m ² . The nonwoven fabric was pressed with a flat plate press at a temperature of 220 ° C., a gap of 1 mm, a time of 1 minute, and a pressure of 588 N /
hot press under the condition of cm ² and then 10 ° C. /
The temperature is raised to 1300 ° C. at a heating rate of 1 minute, kept at this temperature for 1 hour, carbonized and cooled, and further treated in air at 700 ° C. to a weight yield of 95% to obtain a carbonaceous fiber nonwoven fabric. Was.

(Comparative Example 3) A polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and then a felt needle SB # 40 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to produce a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. A phenol resin S890 (Kanebo Co., Ltd.) sieved with a mesh dish so as to have a particle size of 5 to 20 μm is agglomerated with a 1% polyacrylamide aqueous solution on the nonwoven fabric.
Spraying and suctioning were repeated so that the binder dried at 00 ° C. and granulated to a particle size of 50 to 100 μm was uniformly dispersed and attached at 1 g / m ² . The nonwoven fabric is heated at a temperature of 2
50 ° C., gap 0.5 mm, time 1 minute, pressure 588 N
/ Cm ² at 10 ° C in nitrogen gas
/ Min at a heating rate of 1 / min.
Hold for a while, cool by carbonization, and then 700 ° C in air
To give a weight yield of 95% to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 4) In Example 1, instead of using the phenol resin granules, the primary particle size was 50 to 1
00 μm phenolic resin binder (manufactured by Showa High Polymer,
A carbonaceous fiber nonwoven fabric was obtained under the conditions shown in Table 1 in the same manner as in Example 1 except that BRP-534A) was used.

The major diameter, the proportion of binders, the basis weight, the thickness, the specific gravity and the porosity of the carbonized fiber nonwoven fabric obtained in the above Examples and Comparative Examples are shown in Table 1 together with the production conditions. Shown in In addition, all of the above-mentioned processed materials are used for the spacer thickness 2.
At 0 mm, the electrode performance (2nd cycle of charge and discharge cycle and 1
As a result of the measurement at the (00th cycle), the results are as shown in Table 1.

[0061]

[Table 1] As is clear from the results in Table 1, the carbonaceous fiber nonwoven fabrics of Examples 1 to 3 had high voltage efficiency and excellent energy efficiency. In addition, an increase in contact resistance between fibers during long-term use, that is, a decrease in conductivity can be suppressed, and a change over time in energy efficiency during a long-term charge / discharge cycle can be suppressed.

On the other hand, in Comparative Examples 1 and 3 in which the single fibers were not bonded with carbides or were insufficient, the voltage efficiency was low and the change in energy efficiency over a long period was large.
In Comparative Example 2 in which the single fibers were excessively bonded with carbide, and in Comparative Example 4 in which a binder having a large primary particle size was used instead of the granulated product, the initial voltage efficiency was insufficient due to an increase in cell resistance and the like. It became.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of a vanadium-based redox flow battery.

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

[Explanation of symbols]

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

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4L047 AA03 AB02 BA13 BC14 CA19 CC14 5H018 AA08 AS01 BB01 BB03 BB05 BB06 BB08 DD06 EE05 EE17 HH01 HH04 HH05

Claims (3)

[Claims] 1. A carbon electrode material aggregate used for a redox flow battery using an aqueous electrolyte and comprising a nonwoven fabric of carbonaceous fibers, wherein the single fibers of the nonwoven fabric are bound with a carbide having a long diameter of 20 μm or less. A carbon electrode material assembly, wherein the proportion of the binding portion between the single fibers is 0.2 to 10%. 2. The carbon electrode material assembly according to claim 1, wherein the nonwoven fabric has a void of 90% or more. 3. A granulated product obtained by agglomerating an organic binder having a primary average particle size of 20 μm or less is dispersed and attached to a raw nonwoven fabric of carbonaceous fibers, and then heated and pressed to bind the single fibers together. A method for producing a carbon electrode material aggregate, comprising a step of carbonizing the single fiber and the organic binder.