JP2001085027A - Carbon electrode material assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon electrode material assembly capable of suppressing electroconductivity drop through a long time service by improving both the characteristics of carbonaceous fibers and the physical properties of non-woven fablic, reducing the cell resistance of a redox flow battery, and enhancing the energy efficiency. SOLUTION: The carbon electrode material assembly used in a redox flow battery using aqueous solution electrolytic solution consists of a non-woven fablic of carbonaceous fibers, wherein the fiber has a pseudo-graphite crystal structure in which the half-value, half width of the peak at 1360 cm-1 determined by the laser Raman spectrography ranges 30-60 cm-1 while the half-value half width of the peak at 1580 cm-1 ranges 30-45 cm-1 and also the ratio R of the peak intensity between the two (=Ia/Ig) ranges 0.7-1.0. Therein the amount of surface acid functional radicals determined through XPS surface analysis is 0.2-1.2% of the total number of surface carbon atoms, and the non-woven fablic has a compression ratio of 10-25% and a modulus of compression elasticity of 80% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redox flow battery using an aqueous electrolytic solution, and more particularly to a carbon electrode material assembly made of a nonwoven fabric of carbonaceous fibers, and is particularly useful for a vanadium redox flow battery. is there.

[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.

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 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 collector 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), and specifically, the amount of decrease in battery energy efficiency (η _E ) 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 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 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 is used as an electrode material for an electrolytic cell of a redox flow battery. It has been proposed to use.

[0012]

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, so that the specific resistance of the carbonaceous fiber is high, resulting in a high cell resistance and high energy efficiency. The problem was that I couldn't get it. Also, when used as an electrode in an electrolytic cell for a long time, the carbon structure changes, the specific resistance of the carbonaceous fiber gradually increases, and as a result, the cell resistance increases and the change (decrease rate) in energy efficiency increases. did.

On the other hand, the contact resistance between the surface of the carbonaceous material and the current collector plate varies depending on the physical properties of the nonwoven fabric (aggregate) made of the carbonaceous material. It was not easy to reduce the resistance sufficiently. In addition, since the physical properties of the nonwoven fabric change depending on the manufacturing method and physical properties of the carbonaceous material, the manufacturing method of the nonwoven fabric, and the like, it is necessary to optimize the manufacturing method of the nonwoven fabric according to the physical properties of the carbonaceous material.

In view of the foregoing, an object of the present invention is to improve both the properties of carbonaceous fibers and the physical properties of a nonwoven fabric, thereby suppressing a decrease in conductivity due to long-term use, and providing a cell for a redox flow battery. An object of the present invention is to provide a carbon electrode material aggregate that can reduce resistance and maintain high energy efficiency.

[0015]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and found that the three-dimensional bonding by laser Raman spectroscopy was carried out while suppressing the surface acidic functional group content of the carbon electrode material lower than before. And a two-dimensional bond (graphite phase), the intensity ratio of peaks and the half-width at half maximum of each peak are controlled to a specific range to form a nonwoven fabric of carbonaceous fibers,
By setting the compression ratio and compression elastic modulus in a specific range,
The inventors have found that the above object can be achieved, 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 in a carbon electrode material assembly made of a nonwoven fabric of carbonaceous fibers,
The carbonaceous fiber has a half width at half maximum of a peak at 1360 cm ^-1 determined by laser Raman spectroscopy of 30 to 60 cm ^-1.
And the half width at half maximum of the peak at 1580 cm ^-1 is 30 to 45 c.
At m ⁻¹ , 1360 cm ⁻¹ peak intensity Ia and 1580 c
The ratio R (= Ia / Ig) with respect to the peak intensity Ig at m ⁻¹ is 0.1.
It has a pseudo-graphite crystal structure of 7 to 1.0, the amount of surface acidic functional groups determined by XPS surface analysis is 0.2 to 1.2% of the total number of carbon atoms on the surface, and the nonwoven fabric is JIS
The compression ratio according to L1096 (1990) is 10 to 25
%, And the compression modulus is 80% or more.

According to the carbonaceous fiber of the present invention, as shown in the results of the examples, the conductivity of the carbon electrode material itself is increased and the decrease in conductivity due to long-term use is suppressed, thereby improving the energy efficiency of the battery. Can be kept high. The details of the reason why the above-mentioned parameter value obtained by laser Raman spectroscopy changes the temporal stability of the conductivity of the carbon electrode material are not clear, but the above parameter value shows the degree of graphitization and the crystal surface has ) Are reflected, and it is presumed that when these are appropriate, the decrease in conductivity can be suppressed. When the surface acidic functional group content satisfies the above requirements, the wettability with the aqueous electrolyte solution can be appropriately given while the contact resistance on the electrode material surface is kept low. Further, by setting the compression ratio and the compression elastic modulus of the nonwoven fabric in the above ranges, the contact property with the current collector plate can be improved, and the contact resistance can be reduced. As a result, the cell resistance of the redox flow battery can be reduced and the energy efficiency can be increased.

Further, the carbon electrode material assembly of the present invention is preferably used for a vanadium redox flow battery. In a vanadium-based redox flow battery, the wettability with the above-mentioned electrolyte is relatively good, so that the above-described effects are more remarkable. Further, in the battery, since the contact resistance of the electrode material surface between the fibers constituting the electrode material or the current collector plate tends to be particularly problematic, the carbon electrode material aggregate of the present invention having the above-described effects is particularly useful. Become.

[0019]

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 creating a web composed of several layers, and then applying the web to a needle punching machine. Thereby, it is suitably manufactured.

[0020] The basis weight of the non-woven fabric is sandwiched 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
A cloth is preferably used from the viewpoint of liquid permeability. Groove in that case
Width and groove depth should be at least 0.3mm, especially 0.5mm or less
Above is desirable. The thickness of the carbonaceous fiber nonwoven fabric is
At least greater than the thickness of the state, preferably filling
It is about 1.5 times the thickness of the state. However, the thickness
If it is too thick, it will break through the membrane with compressive stress.
Shrinkage stress of 1kgf / cm^Two It is preferable to design
No.

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.

The carbonaceous fiber non-woven fabric is assembled by being pressed into a battery, and a high-viscosity electrolytic solution flows through the thin gap. cm or more. Also, in order to improve the contact resistance with the current collector, the density of the diaphragm and the packed 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 0.1 kgf / cm ² or more. Is preferable.

Further, the carbonaceous fiber of the present invention is
1360 cm determined by Mann spectroscopy^-1Half peak of
Half width is 30-60cm^-1In, 1580cm^-1Of the peak
Half width at half maximum is 30-45cm^-1And 1360cm^-1The pea
Strength Ia and 1580cm^-1Ratio R to the peak intensity Ig
(= Ia / Ig) is 0.7 to 1.0, preferably
Is 1360cm^-1The half width at half maximum of the peak is 30 to 50c.
m^-1In, 1580cm ^-1The half-width at half maximum of 33 to 4
3cm^-1And R (= Ia / Ig) is 0.7 to 0.8.
You.

Each of the above parameter values is a respective upper limit value.
If greater, the specific resistance is 10 ^-2Exceeds Ω · cm,
Electrode material conductive resistance component in battery internal resistance (cell resistance)
Can no longer be ignored, resulting in increased cell resistance
(Voltage efficiency decreases), and energy efficiency decreases. Ma
In addition, the specific resistance tends to deteriorate due to long-term use.

On the other hand, when the above parameter values are smaller than the respective lower limit values, the specific resistance increases over a long period of use, and as a result, the cell resistance increases and the energy efficiency decreases. This is thought to be because the carbonaceous fiber as described above has a strain in the crystal structure or has a structure close to graphite, and is likely to be decomposed by, for example, sulfuric acid used in the electrolyte solution of a vanadium-based redox flow battery. Can be

The surface acidic functional group content of the carbonaceous fiber of the present invention needs to be at least 0.2% of the total number of surface carbon atoms, and preferably at least 0.3%. If it is less than 0.2%, the wettability of the electrolytic solution is poor, and the cell resistance is significantly increased. This is presumably because the carbon atom itself is hydrophobic, so that when the acidic functional group of the hydrophilic group is small, water is easily repelled. The surface acidic functional group content must be 1.2% or less, preferably 0.8% or less, of the total number of surface carbon atoms. When it is larger than 1.2%, the conductivity of the surface is inhibited by the functional group, and the contact resistance with the current collector plate or the contact resistance between the fibers becomes poor,
The cell resistance increases significantly.

The above-mentioned amount of surface acidic functional groups means the amount of hydroxyl groups or carboxyl groups which can be replaced with silver ions by silver nitrate treatment among oxygen-containing functional groups, and the amount of surface silver ions detected by XPS surface analysis. Of the surface carbon atoms.

The carbonaceous fiber having an excellent internal structure and wettability as described above can be obtained from polyacrylonitrile, isotropic pitch, mesophase pitch, cellulose, etc. which have been subjected to initial air oxidation at 200 to 300 ° C. under tension, or phenol. , Polyparaphenylene benzobisoxazole (PB
O) or the like as a raw material, a metal salt which becomes trivalent or more ion such as Al, Si, Bi or the like is converted to a metal ion equivalent to 10 to 10
0 ppm after uniform impregnation, 1000 ~ under inert atmosphere
It is obtained by calcining (carbonizing) at 2200 ° C. and dry-oxidizing the obtained carbon material having a pseudo-graphite crystal structure.

[0029] The metal salt impregnation is effective for Al, Si,
It is considered that by adding a trace amount of a metal salt that becomes trivalent or more ion such as Bi, the ion cross-links between crystallites of carbon, thereby making it difficult to cause structural defects and the like. By this small amount of impregnation, without much influence of the firing conditions,
The above parameters by laser Raman spectroscopy can be suitably controlled. Of course, it is also possible to control the above parameters by the firing conditions.

In the dry oxidation treatment, the above-mentioned carbon material is obtained in a gas atmosphere having an oxygen concentration of 1 to 25% in a weight yield of 90 to 9%.
It is carried out so as to be in the range of 9%, preferably 93 to 99%. The processing temperature is preferably from 500 to 900C, more preferably from 650 to 750C. 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. The amount of the surface acidic functional group depends on the degree of graphitization, but can be controlled by adjusting the oxygen concentration or the like in the dry oxidation treatment.

The carbonaceous fiber nonwoven fabric of the present invention has a compression ratio of 10 to 25% and a compression elastic modulus of 80% or more, but preferably has a compression ratio of 10 to 20% and a compression elasticity of 8%.
2% or more. When the compression ratio is less than 10%, entanglement between fibers cannot be obtained, and the form as a carbonaceous fiber nonwoven fabric cannot be maintained. On the other hand, when the compression ratio exceeds 25% or the compression elasticity is less than 80%, the contact resistance with the current collector when the battery is pressed into the battery and assembled is increased, and as a result, the cell resistance is increased. Increase (voltage efficiency decreases) and energy efficiency decreases.

The compression characteristics of such a carbonaceous fiber nonwoven fabric are premised on having the above-mentioned carbon crystal structure and surface acidic functional groups, but can be obtained by controlling the conditions of the needle punch in the preceding stage. That is, the density of the needle punch is set to 150 to 100% so as to maintain the nonwoven fabric form that is flexible and does not cause the fibers to fall off, and that the contact property (contact surface and contact force) with the current collector plate when pressed is improved. 300
Needles / cm ² , preferably 200 to 300 needles / cm ² , and the needle of the needle punch is made of an infusible fiber or an oxidized fiber which is easily entangled alternately, for example, SB # 36 or SB #
40 (Foster Needle).

In order to control the compression ratio and the compression elastic modulus of the nonwoven fabric within the above ranges, it is preferable to perform the dry oxidation treatment in a short time, specifically, within 10 minutes.

Next, laser Raman spectroscopy, XPS surface analysis, compression ratio and compression elastic modulus of the nonwoven fabric, contact resistance with the current collector and its change with time, current efficiency, voltage efficiency (cell resistance, etc.) used in the present invention. R), each measurement method of energy efficiency and change over time of the charge / discharge cycle will be described.

(1) Laser Raman Spectroscopy Using a micro Raman spectrometer (Jobin Yvonne-Atago Bussan Co., Ltd.), an Ar ion laser of 488 nm was used.
Scan from 1800 to 1000 cm ^{-1 with a} line, 1360
Analyzing the peak Ig peak Ia and 1580 ± 20 cm ^-1 of ± 20 cm ^-1. For each peak intensity, after performing the baseline correction, the measured waveform is approximated by the Lorentz function and determined by the highest point, and the half width at half maximum of the peak is determined by the half value of the peak width at half the intensity of the peak intensity. Ask.

(2) XPS Surface Analysis A device used for measurement of X-ray photoelectron spectroscopy, which is abbreviated as ESCA or XPS, is Shimadzu ESCA750, and ESCAPAC760 is used for analysis.

Each sample was immersed in an acetone solution of silver nitrate,
The proton of the acidic functional group is completely replaced with silver, washed with acetone and water, punched out to a diameter of 6 mm, attached to a heated sample stand with a conductive paste, and subjected to analysis. Before the measurement, the sample is heated to 120 ° C. and vacuum degassed for 3 hours or more. MgKα radiation (1253.6 eV) is used as the radiation source, and the degree of vacuum in the apparatus is set to 10 ⁻⁷ torr.

The measurement was carried out on the Cls and Ag3d peaks, and each peak was taken as ESCAPAC760 (JH Sco
(based on the field correction method) to determine the respective peak areas. The ratio of the obtained area multiplied by the relative intensity of 1.00 for Cls and 10.68 for Ag3d is the atomic number ratio, and the amount of surface acidic functional groups to the total number of surface carbon atoms is (the number of surface silver atoms) / Number of surface carbon atoms) is calculated as a percentage (%).

(3) Compressibility and Compressive Modulus of Nonwoven Fabric According to “6.18 Compressibility and Compressive Modulus” described in JIS L1096 (1990), five test pieces of about 5 × about 5 cm were sampled. One test piece was measured for thickness (mm) under an initial load of 0.49 kPa, and then the load was increased to 24.5 kPa.
And leave it for 1 minute under a jar to measure the thickness (mm). Next, remove the load and leave it for 1 minute, then again under initial load thickness (mm)
Is measured, and the compressibility and the compressive elastic modulus are obtained from the respective thicknesses, and are represented by an average value of five times (up to an integer).

(4) Contact resistance with current collector plate Two current collector plates were used, and the width was 10 cm and the length was 1 cm.
The resistance when pressed to a thickness of 2 mm across the carbonaceous fiber nonwoven fabric sample is simply measured with a digital multimeter,
Find the resistance per unit area. A resin-bonded graphite plate (thickness: 3 mm) having a specific resistance of 0.05 Ω · cm is used as the current collector, and the resistance when the current collectors are pressed against each other as is is negligible with respect to the contact resistance with the nonwoven fabric. .

(5) Electrode Performance A small cell having an electrode area of 10 cm ² of 10 cm in the vertical direction (liquid flow direction) and 1 cm in the width direction is prepared, 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
A 3 mol / l sulfuric acid solution of 1 vanadium sulfate is used.
The amount of electrolyte was set to a large excess with respect to the cells and piping. The liquid flow rate is 6.2 ml per minute, and the measurement is 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
・ Calculate cm ² ).

[0045]

(Equation 3) Here, I is a current value of 0.4 A in constant current charging and discharging.

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

[0047]

(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.

[0049]

(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 △ η 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 provided between a pair of current collectors disposed facing each other with a gap therebetween, and an electrode material is provided on at least one of the current collectors and the diaphragm, and the electrode material is 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 electrolytic solution include iron-chromium-based, titanium-manganese-based, manganese-chromium-based, chromium-chromium-based, iron-titanium-based, and the like, in addition to the vanadium-based electrolyte described above. Vanadium-based electrolytes are preferred. In particular, the carbon electrode material aggregate of the present invention has a viscosity of 25 ° C.
It is useful to use in a redox flow battery using a vanadium-based electrolyte solution of 0.005 Pa · s or more or a vanadium-based electrolyte solution containing 1.5 mol / l or more of vanadium ions.

[0053]

EXAMPLES Examples and the like that specifically show the structure 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 # 36 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) was made into a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The non-woven fabric is immersed in a 0.01 wt% aluminum hydroxide aqueous solution, dehydrated (impregnated with 0.006 wt% in terms of aluminum ions), and heated to 1300 ° C. in nitrogen gas at a rate of 10 ° C./min. The temperature is maintained for 1 hour, carbonized and cooled, followed by 5 hours at 680 ° C in air.
Minutes, to obtain a carbonaceous fiber nonwoven fabric.

(Example 2) Polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and felt needle SB # 36 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) was made into a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The nonwoven fabric is immersed in a 0.01% by weight aqueous solution of bismuth hydroxide and dehydrated (0.1% in terms of bismuth ion).
008 wt%), heated to 2000 ° C. in nitrogen gas at a rate of 10 ° C./min, kept at this temperature for 1 hour, carbonized and cooled, and subsequently treated in air at 750 ° C. for 10 minutes. Thus, a carbonaceous fiber nonwoven fabric was obtained.

Example 3 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then a felt needle SB # 36 was used using short fibers (about 80 mm in length) of the oxidized fibers. (Foster Needl
e) was made into a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The nonwoven fabric is immersed in a 0.01 wt% aluminum hydroxide aqueous solution, dehydrated (impregnated with 0.06 wt% in terms of aluminum ions), and heated to 1600 ° C in nitrogen gas at a rate of 10 ° C / min. The mixture was kept at the temperature for 1 hour, carbonized, cooled, and subsequently treated in air at 700 ° C. for 8 minutes to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 1) 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 # 36 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) was made into a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The nonwoven fabric was 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 subsequently treated at 680 ° C. in air for 5 minutes to obtain carbon. A fibrous nonwoven fabric was obtained.

(Comparative Example 2) Polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and felt needle SB # 36 was used using short fibers (about 80 mm in length) of the oxidized fiber. (Foster Needl
e) was made into a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The nonwoven fabric was heated to 2000 ° C. at a rate of 10 ° C./min in nitrogen gas, held at this temperature for 1 hour, carbonized and cooled, and then treated in air at 750 ° C. for 10 minutes to obtain carbon. A fibrous nonwoven fabric was obtained.

(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 # 36 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 150 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.2 mm. The non-woven fabric is immersed in a 0.01 wt% aluminum hydroxide aqueous solution, dehydrated (impregnated with 0.006 wt% in terms of aluminum ions), and heated to 1300 ° C. in nitrogen gas at a rate of 10 ° C./min. The temperature is maintained for 1 hour, carbonized and cooled, followed by 5 hours at 680 ° C in air.
Minutes, to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 4) Polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and felt needle SB # 36 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 400 / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 4.5 mm. The non-woven fabric is immersed in a 0.01 wt% aluminum hydroxide aqueous solution, dehydrated (impregnated with 0.006 wt% in terms of aluminum ions), and heated to 1300 ° C. in nitrogen gas at a rate of 10 ° C./min. The temperature is maintained for 1 hour, carbonized and cooled, followed by 5 hours at 680 ° C in air.
Minutes, to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 5 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and felt needle SB # 36 was used using short fibers (about 80 mm in length) of the oxidized fibers. (Foster Needl
e) to give a felt at a punching density of 250 pieces / cm ² to prepare a nonwoven fabric having a basis weight of 600 g / m ² and a thickness of 5.0 mm. The non-woven fabric is immersed in a 0.01 wt% aluminum hydroxide aqueous solution, dehydrated (impregnated with 0.006 wt% in terms of aluminum ions), and heated to 1300 ° C. in nitrogen gas at a rate of 10 ° C./min. The temperature is maintained for 1 hour, carbonized and cooled, and then in air at 680 ° C for 1 hour.
The treatment was performed for 5 minutes to obtain a carbonaceous fiber nonwoven fabric.

Laser Raman spectroscopy, XPS surface analysis, compressibility and compressive modulus of the nonwoven fabric, and contact resistance with the current collector of the carbonaceous fiber nonwoven fabrics obtained in Examples and Comparative Examples were
The results are shown in Table 1 together with the manufacturing conditions.

All of the above-mentioned processed products were transferred to a spacer having a thickness of 2.0 m.
electrode performance (the second cycle of charge / discharge cycle and 100
Table 1 shows the results of the measurement at the (cycle)).

[0064]

[Table 1] As is clear from the results in Table 1, the carbonaceous fiber nonwoven fabrics of Examples 1 to 3 had low contact resistance with the current collector, high voltage efficiency, and excellent energy efficiency. In addition, it is possible to suppress an increase in contact resistance, that is, a decrease in conductivity due to the consumption of carbon due to long-term repetition of charge / discharge cycles. In addition, the decrease in conductivity during long-term use, that is,
An increase in cell resistance can be suppressed, and there is almost no change over time in energy efficiency during a long-term charge / discharge cycle.

On the other hand, in Comparative Examples 1 and 2 in which the properties of the carbonaceous fiber were not suitable, both the voltage efficiency and the energy efficiency were insufficient, and in Comparative Examples 3 to 5 in which the physical properties of the nonwoven fabric were not appropriate, The contact resistance with the plate was increased, and both the voltage efficiency and the energy efficiency were further deteriorated. In addition, contact resistance increases due to long-term repetition of charge / discharge cycles,
There is a change over time in energy efficiency.

[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 collection 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

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H018 AA08 AS07 CC06 DD06 EE05 HH02 HH03 HH05 HH09 5H026 AA10 CC01 CX03 EE05 HH02 HH03 HH05 HH09 RR01

Claims (2)

[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 carbonaceous fibers have a peak at 1360 cm ⁻¹ determined by laser Raman spectroscopy. Half width at half maximum is 30 to 60 cm ^-1
And the half width at half maximum of the peak at 1580 cm ^-1 is 30 to 45 c.
At m ⁻¹ , 1360 cm ⁻¹ peak intensity Ia and 1580 c
The ratio R (= Ia / Ig) with respect to the peak intensity Ig at m ⁻¹ is 0.1.
It has a pseudo-graphite crystal structure of 7 to 1.0, the surface acidic functional group content determined by XPS surface analysis is 0.2 to 1.2% of the total surface carbon atoms, and the nonwoven fabric is JIS A carbon electrode material assembly having a compression ratio according to L1096 (1990) of 10 to 25% and a compression elastic modulus of 80% or more. 2. The carbon electrode material assembly according to claim 1, which is used for a vanadium redox flow battery.