JP2000357522A - Carbon electrode material for redox flow battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon electrode material for a redox flow battery capable of increasing conductivity of the carbon electrode material itself, suppressing drop in conductivity due to use for a long tine, and keeping energy efficiency of the battery high. SOLUTION: This carbon electrode material for a redox flow battery using an aqueous electrolyte has pseudo graphite crystal structure in which a half width at half maximum at a peak of 1360 cm-1 as determined by a laser Raman spectroscopic analysis is 30-60 cm-1, that at a peak of 1580 cm-1 is 30-45 cm-1, and the ratio (R=Ia/Ig) of the peak intensity Ia of 1360 cm-1 to the peak intensity Ig of 1580 cm-1 is 0.7-1.0, and the amount of surface acidic functional groups as determined by XPS surface analysis is 0.2-1.2% of the number of carbon atoms on the whole surface.

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 for a redox flow battery using an aqueous electrolyte solution, and is particularly useful for a vanadium 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 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. 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. 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 pseudographite 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 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. When used as an electrode in an electrolytic cell for a long time, it was found that the carbon structure deteriorated, the specific resistance of the carbonaceous fiber gradually increased, and as a result, the cell resistance increased and the change (decrease rate) in energy efficiency increased. did.

In view of the above, an object of the present invention is to increase the conductivity of the carbon electrode material itself, suppress a decrease in conductivity due to long-term use, and maintain a high energy efficiency of the battery. An object of the present invention is to provide a carbon electrode material for a redox flow battery.

[0014]

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. It has been found that the above-mentioned object can be achieved by controlling the intensity ratio of peaks derived from the two-dimensional bond (graphite phase) and the half-width at half maximum of each peak to a specific range. Reached.

That is, the carbon electrode material of the present invention is a carbon electrode material for a redox flow battery using an aqueous electrolyte solution, and is a carbon electrode material obtained by laser Raman spectroscopy.
The half-width at half maximum of the peak at m ^-1 is 30 to 60 cm ^-1 and 158
Half width at half maximum of the peak of the 0 cm ^-1 is in 30~45cm ^-1, 1
360cm ratio of the peak intensity Ig of the peak intensity Ia and 1580 cm ^-1 of ^-1 R (= Ia / Ig) is 0.7 to 1.0
And the amount of surface acidic functional groups determined by XPS surface analysis is 0.2-1.
2%.

According to the carbon electrode material 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.

The carbon electrode material 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 between the fibers constituting the electrode material and the surface of the electrode material with respect to the current collector plate tends to be particularly problematic, the carbon electrode material of the present invention having the above-mentioned effects is particularly useful.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The carbon electrode material of the present invention is made of a carbonaceous material, and its structure and microstructure are not particularly limited, but those capable of increasing the electrode surface area are preferred. Specifically, a spun yarn, a bundle of filaments, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric (as disclosed in JP-A-63-200457), or a carbonaceous material composed of a hybrid structure thereof Fiber aggregate, or porous carbon, carbon-
Examples include a carbon composite and a particulate carbon material.
Of these, sheet-like ones made of carbonaceous fiber are
It is preferable in terms of handling, processability, manufacturability and the like.

The basis weight of the sheet-like material or the like depends on the structure thereof, but the thickness of the filled state sandwiched between the diaphragm and the current collector is 2 to 3 times.
When used in mm, 100~1000g / m ^2, in the case of non-woven tissue 200 to 600 g / m ² is desirable. A nonwoven fabric or the like having a groove on one side is preferably used because of its liquid permeability. In this case, the groove width and the groove depth are at least 0.3 mm, preferably 0.5 mm or more. It is desirable that the thickness of the carbonaceous fiber sheet is at least larger than the thickness in the above-described filled state, and that the thickness of the carbonized fiber sheet in the case of a low-density nonwoven fabric is about 1.5 times the thickness in the filled state. However, if the thickness is too thick, it will break through the film with compressive stress,
Preferably, the compressive stress is designed to be 1 kgf / cm ² or less.

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 sheet is press-fitted into a battery, and a high-viscosity electrolytic solution flows through the thin gap.
m ² or more is desirable for shape retention. In order to improve the contact resistance with the current collector, the density of the membrane and the filling layer sandwiched between the current collectors in the nonwoven fabric is set to 0.05 g / c.
m ³ or more, the repulsive force with respect to the electrode surface 0.1 kgf / c
It is preferably at least m ² .

The carbon electrode material of the present invention, at the peak of the half width at half maximum is 30-60 cm ^-1 in 1360 cm ^-1 as determined by laser Raman spectroscopy, the half width at half maximum of the peak of 1580 cm ^-1 is in 30～45Cm ^-1, the ratio R (= I and the peak intensity Ig of the peak intensity Ia and 1580 cm ^-1 in 1360 cm ^-1
a / Ig) is 0.7 to 1.0, and preferably 1
The half width at half maximum of the peak at 360 cm ^-1 is 30 to 50 cm.
^-1 and the half width at half maximum of the peak at 1580 cm ^-1 is 33 to 43.
At cm ⁻¹ , R (= Ia / Ig) is 0.7 to 0.8.

The above parameter values are the respective upper limit values.
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 carbon electrode material 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 an electrolyte solution of a vanadium-based redox flow battery. Can be

The surface acidic functional group content of the carbon electrode material of the present invention must 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. Further, the amount of surface acidic functional groups needs to be 1.2% or less of the total number of surface carbon atoms,
Preferably it is 0.8% or less. If it is more than 1.2%, the conductivity of the surface is impaired by the functional group, the contact resistance with the current collector or the contact resistance between the fibers becomes poor, and the cell resistance is significantly increased.

The above-mentioned amount of surface acidic functional groups means the amount of hydroxyl groups and 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 carbon electrode material having the excellent internal structure and wettability as described above is made of 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.

It is effective to impregnate the metal salt with Al, Si,
It is considered that by adding a trace amount of a metal salt that becomes a trivalent or higher 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.

Next, measurement of laser Raman spectroscopy, XPS surface analysis, specific resistance of single fiber, current efficiency, voltage efficiency (cell resistance R), energy efficiency and change over time of charge / discharge cycle employed in the present invention. The method 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 a solution of silver nitrate in acetone,
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 performed on the Cls and Ag3d peaks, and each peak was measured using 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) Specific Resistance of Single Fiber Measured according to “6.7 Volume Resistivity” described in JIS R7601 (1986).

(4) Electrode Performance A small cell having an electrode area of 10 cm ² of 1 cm in the vertical direction (liquid flow direction) and 10 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 geometric 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).

[0038]

(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.

[0039]

(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 ).

[0040]

(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 a simple method of Expression 4.

[0042]

(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.

[0044]

(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 from its initial state △ η_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 of the present invention is used for a redox flow battery using an aqueous electrolyte. As described above, the redox flow battery has, for example, a diaphragm disposed between a pair of current collectors disposed to face each other with a gap therebetween, and at least one of the diaphragms disposed between the current collector and the diaphragm. The electrode material is provided with an electrolytic cell having a structure containing an electrolytic solution composed of an aqueous solution containing an active material.

Examples of the aqueous electrolytic solution include iron-chromium-based, manganese-chromium-based, chromium-chromium-based, iron-titanium-based and the like, in addition to the above-mentioned vanadium-based electrolyte. preferable. In particular, the carbon electrode material of the present invention has a viscosity of not less than 0.005 Pa · s at 25 ° C., or 1.5 mol / l.
It is useful for use in a redox flow battery using a vanadium-based electrolytic solution containing vanadium ions as described above.

[0048]

EXAMPLES Examples and the like that specifically show the structure and effects of the present invention will be described below.

Example 1 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C. and then felted using short fibers (about 80 mm in length) of the oxidized fibers to obtain a basis weight. 400 g / m ² , thickness 4.0
mm nonwoven fabric was prepared. 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 mixture was kept at a temperature for 1 hour, carbonized, cooled, and subsequently oxidized at 650 ° C. in air until the weight yield became 93%, to obtain a carbonaceous fiber nonwoven fabric. Table 1 shows the results of laser Raman, XPS surface analysis, and specific resistance measurement.

Example 2 Polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then felted using short fibers (about 80 mm in length) of the oxidized fiber. 400 g / m ² , thickness 4.0
mm nonwoven fabric was prepared. The nonwoven fabric is immersed in a 0.01% by weight aqueous solution of bismuth hydroxide, dehydrated (impregnated with 0.008% by weight in terms of bismuth ions), and dried in a nitrogen gas atmosphere.
The temperature was raised to 2000 ° C. at a rate of temperature rise of 2000 ° C./min, kept at this temperature for 1 hour, carbonized, cooled, and
Oxidation treatment was carried out at 93 ° C. until the weight yield became 93% to obtain a carbonaceous fiber nonwoven fabric. Laser Raman, XPS surface analysis results,
Table 1 shows the specific resistance measurement results.

Example 3 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C. and then felted using short fibers (about 80 mm in length) of the oxidized fibers to obtain a basis weight. 400 g / m ² , thickness 4.0
mm nonwoven fabric was prepared. 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 a temperature for 1 hour, carbonized, cooled, and subsequently oxidized at 650 ° C. in air until the weight yield became 93%, to obtain a carbonaceous fiber nonwoven fabric. Table 1 shows the results of laser Raman, XPS surface analysis, and specific resistance measurement.

(Comparative Example 1) Polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then made into felt using short fibers (about 80 mm in length) of the oxidized fiber. 400 g / m ² , thickness 4.0
mm nonwoven fabric was prepared. The nonwoven fabric is placed in nitrogen gas for 10 minutes.
The temperature was raised to 1300 ° C. at a rate of temperature rise of 1 ° C./min, kept at this temperature for 1 hour, carbonized and cooled, and then 650 in air.
Oxidation treatment was carried out at 93 ° C. until the weight yield became 93% to obtain a carbonaceous fiber nonwoven fabric. Laser Raman, XPS surface analysis results,
Table 1 shows the specific resistance measurement results.

(Comparative Example 2) Polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then made into felt using short fibers (about 80 mm in length) of the oxidized fiber. 400 g / m ² , thickness 4.0
mm nonwoven fabric was prepared. The nonwoven fabric is placed in nitrogen gas for 10 minutes.
The temperature was raised to 2000 ° C. at a rate of temperature rise of 2000 ° C./min, kept at this temperature for 1 hour, carbonized, cooled, and
Oxidation treatment was carried out at 93 ° C. until the weight yield became 93% to obtain a carbonaceous fiber nonwoven fabric. Laser Raman, XPS surface analysis results,
Table 1 shows the specific resistance measurement results.

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

[0055]

[Table 1]

According to the present invention, the specific resistance of the carbon electrode material is reduced, the conductivity is improved, and the specific resistance which depends on the consumption of carbon due to long-term repetition of charge / discharge cycles, that is, the conductivity is increased. Can be suppressed.
In addition, the electrode activity is extremely good because an appropriate functional group is provided. As a result, the cell resistance R, which reflects the conductivity and the electrode activity, is reduced, that is, the voltage efficiency is improved, and the energy efficiency is greatly improved. Further, it is possible to suppress a decrease in conductivity during long-term use, that is, an increase in cell resistance, and also to reduce a temporal change in energy efficiency during a long-term charge / discharge cycle.

[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

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Satoshi Takase 2-1-1 Katata, Otsu-shi, Shiga F-Term in Toyobo Co., Ltd. Research Laboratory 5H018 AA08 AS07 CC06 DD01 DD06 EE05 HH03 HH05 5H026 AA10 CX03 CX05 EE05 HH03 HH05 RR01

Claims (2)

[Claims] 1. A carbon electrode material for a redox flow battery using an aqueous electrolytic solution, wherein a half width at half maximum of a peak at 1360 cm ⁻¹ determined by laser Raman spectroscopy is 3
In 0~60cm ^-1, a peak of half width at half maximum 30～45Cm ^-1 of 1580 cm ^-1, a peak intensity of 1360 cm ^-1 I
a to the peak intensity Ig of 1580 cm ^-1 R (= Ia
/ Ig) has a pseudo-graphite crystal structure of 0.7 to 1.0, and the amount of surface acidic functional groups determined by XPS surface analysis is 0.2 to 1.2% of the total number of surface carbon atoms. A carbon electrode material characterized by the following. 2. The carbon electrode material according to claim 1, which is used for a vanadium redox flow battery.