JP2001085024A - Carbon electrode material assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon electrode material assembly capable of reducing the cell resistance of a redox flow battery by improving both the characteristics of carbonaceous fibers and the physical properties of non-woven fabric, enhancing the energy efficiency by allowing the electrolytic solution in an electrolytic bath to flow smoothly, and maintaining low the contact resistance of the carbon electrode material for a long period of time. SOLUTION: The carbon electrode material assembly used in a redox flow battery using aqueous solution electrolytic solution consists of a non-woven fabric of carbonaceous fibers, wherein the fibers simultaneously meet the requisite conditions (a) and (b) obtained through XPS surface analysis; (a) the amount of surface acid functional radicals is 0.2-2.0% of the total number of surface carbon atoms and (b) the number of surface carbon atoms in double bond with nitrogen is 0.3-3.0% of the total number of surface carbon atoms. The non-woven fabric has a bulk density of 0.05-0.17 g/cm3.

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.

As for the cell resistance (R), 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 contribute. 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. Sho 60-232669 discloses that the <002> plane spacing determined by X-ray wide-angle analysis is 3.70 ° or less on average, and the crystallite size in the c-axis direction is average. It has been proposed to use a carbonaceous material having pseudographite crystallites of 9.0 ° or more and having a total acidic functional group content of at least 0.01 meq / g as an electrode material for an electrolytic cell of a redox flow battery.

Japanese Unexamined Patent Publication No. Hei 5-234612 discloses a carbonaceous fiber made of polyacrylonitrile-based fiber having a <002> plane spacing of 3.002 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.

[0013]

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 determined by X-ray wide-angle analysis <00
2> Since the interplanar spacing was 3.50 or more and the number of bonded oxygen atoms on the surface of the carbonaceous material was required to be 10% or more of the number of carbon atoms, the number of functional groups on the surface of the carbon electrode material was too large, and It was found that the resistance was increased, and as a result, the cell resistance was increased, and high battery energy efficiency could not be obtained.

In the electrode material disclosed in JP-A-5-234612, since polyacrylonitrile fiber is used as a raw material, nitrogen atoms easily remain on the surface of the carbonaceous fiber, and the amount thereof is not properly controlled. It has been found that when used in a redox flow battery, an ammonium salt-containing group or the like is generated with the passage of time, and this causes an increase in the contact resistance.

On the other hand, the contact resistance between the surface of the carbonaceous material and the current collector plate and the pressure loss of the electrolyte flowing through the electrolytic cell vary depending on the physical properties of the nonwoven fabric (aggregate) made of the carbonaceous material. Therefore, it has not been easy to reduce the contact resistance and the liquid pressure loss sufficiently only by improving the characteristics of the carbonaceous material. 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 such circumstances, an object of the present invention is to improve both the properties of the carbonaceous fiber and the physical properties of the non-woven fabric to reduce the cell resistance of the redox flow battery and to distribute the electrolyte in the electrolytic cell. It is an object of the present invention to provide a carbon electrode material assembly that can improve energy efficiency by smoothly progressing the process and can maintain low contact resistance of the carbon electrode material for a long period of time.

[0017]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and found that the amount of surface acidic functional groups,
It has been found that the above object can be achieved by forming a nonwoven fabric with carbonaceous fibers in which the number of surface carbon atoms that are double-bonded with nitrogen is controlled within a predetermined range, and by setting the bulk density to a specific range, The present invention has been completed.

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 simultaneously satisfies the following requirements (a) and (b) determined by XPS surface analysis, and the nonwoven fabric has a bulk density of 0.05 to 0.17 g / cm ³ %. And (A) The amount of surface acidic functional groups is 0.2 to 2.0% of the total number of surface carbon atoms. (B) The number of surface carbon atoms double-bonded to nitrogen is 0.1% of the total number of surface carbon atoms.
3 to 3.0%.

By satisfying the above requirement (a), the bending strength of the carbonaceous fiber or the like constituting the carbon electrode material assembly is improved, and the compressive stress at the time of mounting the cell (in other words, the pressure contact force with the current collector plate). Can be maintained for a long period of time, and an increase in contact resistance due to the presence of an acidic functional group or the like can be prevented. In addition, by satisfying the above requirement (b), the contact resistance is increased while maintaining the compressive stress at the time of cell attachment for a long period of time by improving the bending strength of the carbonaceous fiber or the like constituting the carbon electrode material assembly. It is possible to prevent the generation of an ammonium salt-containing group or the like over time. As a result, according to the carbon electrode material assembly of the present invention, the contact resistance of the surface of the carbon electrode material can be reduced, and the contact resistance of the carbon electrode material can be kept low for a long period of time. Can be kept high over time. Further, by setting the bulk density of the nonwoven fabric in the above range, the contact property with the current collector plate is improved, the contact resistance is reduced, and the flow of the electrolytic solution in the electrolytic cell can be smoothly advanced. As a result, the cell resistance of the redox flow battery can be reduced and the energy efficiency can be increased.

In the above, the number of quaternary ammonium nitrogen atoms on the surface determined by XPS surface analysis is preferably 1.0% or less of the total number of carbon atoms on the surface. As aforementioned,
The present inventors have found that the formation of an ammonium salt-containing group or the like over time causes an increase in contact resistance. However, even for the initial carbon electrode material, the surface quaternary ammonium nitrogen That the number is 1.0% or less,
It is preferable to make the initial contact resistance suitable.

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 and the surface of the electrode material with respect to the current collector plate tends to be particularly problematic, so that the carbon electrode material of the present invention having the above-described effects is particularly useful.

[0022]

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, then needle punching, thermal bonding It is suitably manufactured by combining known methods such as a method and a stitch bonding method.

The basis weight of the nonwoven fabric is 100 to 1000 g /
m ² is preferable, and particularly preferably 200 to 600 g / m ² . In addition, a nonwoven fabric having a groove on one side is preferably used from the viewpoint of liquid permeability. In this case, the groove width and groove depth are desirably at least 0.3 mm, particularly preferably 0.5 mm or more.
The thickness of the carbonaceous fiber nonwoven fabric is at least larger than the thickness in the above-mentioned filled state, and preferably about 1.2 to 3.3 times the thickness in the filled state. Also, if the compressive stress is high, the film breaks through the film.
/ 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 non-woven fabric is assembled by being pressed into the 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.

Furthermore, the carbonaceous fiber of the present invention has a surface acidic functional group content of 0.2 to 2.0% of the total number of surface carbon atoms, and preferably has a surface acidic functional group content of 0.2 to 1. 2%,
More preferably, it is 0.3 to 1.0%. When the surface acidic functional group content is less than 0.2%, the bending strength of the short fibers and the like constituting the electrode material is low, and the fibers and the like are broken by cell attachment, and the required compressive stress cannot be maintained. Etc., the contact pressure decreases, and the contact resistance increases with time. In addition, the wettability of the carbon electrode material is reduced, and the flow path of the electrolyte is not secured, so that the liquid permeability deteriorates. On the other hand, if it is more than 2.0%, the presence of the functional group greatly affects, and the inter-fiber contact and the conductivity between the fiber and the current collector plate constituting the electrode material are undesirably hindered. In addition, the wettability of the carbon electrode material is too high, so that the retention of the electrolyte is increased and the flow becomes difficult. The above-mentioned surface acidic functional group amount refers to the amount of hydroxyl groups or carboxyl groups that can be replaced with silver ions by silver nitrate treatment among the oxygen-containing functional groups, and indicates the surface carbon ion amount of the surface carbon ions detected by XPS surface analysis. It is expressed as a ratio to the number of atoms.

In the carbonaceous fiber of the present invention, the number of surface carbon atoms double-bonded to nitrogen is 0.1% of the total number of surface carbon atoms.
3 to 3.0%, preferably 0.5 to 2.8%, more preferably 0.8 to 2.5%, of the number of surface carbon atoms double-bonded to nitrogen. When the number of surface carbon atoms that are double-bonded to nitrogen is less than 0.3%, the crystal orientation of the carbonaceous fiber increases due to the loss of nitrogen in carbon, and the conductivity of the fiber itself improves, but the fiber The bending strength of
When the cell is mounted, the fiber is broken and the required compressive stress cannot be maintained, and the pressure contact force of contact of short fibers or the like decreases, and the contact resistance increases with time. On the other hand, if it exceeds 3.0%,
The double-bonded nitrogen combines with the impurities in the system over time during energization to form a group containing ammonium salts, which inhibits the contact between the electrodes and the conductivity between the fibers and the current collector. Is not preferred. The ratio of the number of surface carbon atoms that are double-bonded to nitrogen can be determined by C1s peak separation measured by XPS surface analysis.

Further, depending on the surface treatment method of the carbonaceous fiber, quaternary nitrogen may be formed on the carbon surface. This is thought to be because nitrogen atoms in the carbon bond with the acid to form a tetraammonium salt in the presence of an acid or the like, and such a group enhances the contact between the fibers of the electrode material and the conductivity between the fibers and the current collector. Inhibit. Therefore, the presence of such quaternary nitrogen is preferably at most 1.0% or less, more preferably 0.8% or less of the total number of surface carbon atoms. The ratio of the quaternary nitrogen to the total number of carbon atoms on the surface is C1 measured by XPS surface analysis.
It is determined by the peak separation between the s peak and the N1s peak.

The carbonaceous fibers of the present invention having such surface characteristics include polyacrylonitrile which has been subjected to an initial air oxidation at a tension of 200 to 300 ° C., isotropic pitch to which nitrogen atoms are added, mesophase pitch, and nitrogen atoms such as cellulose and phenol. A carbon material having a pseudo-graphite crystal structure which is obtained by calcining (carbonizing) at 1000 to 1800 ° C. in an inert atmosphere a material obtained by adding nitrogen to a material having no carbon, or a material such as polyparaphenylenebenzobisoxazole (PBO). It is obtained by performing a dry oxidation treatment at an oxygen concentration of, and further activating in the presence of steam or an acid gas. In particular, in order to adjust the amount of nitrogen on the surface within the range of the present invention, it is necessary to set the amount of nitrogen at 1400 to 1
It is desirable to fire at 800 ° C. In addition, known air oxidation alone is not preferable because, in addition to acidic groups that can originally contribute to the wettability of the electrode, non-acidic functional groups that suppress the electrode reaction are formed in a considerable proportion. Therefore, by performing the oxidation treatment under a controlled oxygen concentration, the generation of extra non-acidic functional groups is minimized, and furthermore, by oxidizing in the presence of steam or an acidic gas, unnecessary functional groups are eliminated. Preferably, it is converted to an effective acidic group. However, care must be taken because excessive use of an acidic gas will react with nitrogen atoms on the surface to form quaternary ammonium nitrogen atoms. Examples of the acidic gas used include, but are not particularly limited to, hydrogen chloride gas, sulfurous acid gas, carbon dioxide gas, and hydrocyanic acid gas.

In the above-mentioned production method, the raw material is fired within a predetermined carbonization temperature to have a pseudo-graphite crystal structure satisfying appropriate conductivity. Forming acidic and non-acidic functional groups by surface treatment under low-concentration oxygen, and further activation by water vapor containing acid partially promotes acidification of non-acidic functional groups and moderate carbon and A double bonded nitrogen is formed. As a result, it is possible to maintain stable contact while maintaining appropriate contact of the carbonaceous fiber.
In addition, this method makes it possible to minimize quaternary ammonium nitrogen, which causes a decrease in contact properties. As a result, good fiber-to-fiber contact and good conductivity between the fiber and the current collector plate can be maintained.

The carbon fiber nonwoven fabric of the present invention has a bulk density of 0.05 to 0.17 g / cm ³ , and preferably has a bulk density of 0.055 to 0.165 g / cm ³ %. When the bulk density is less than 0.05 g / cm ³ , although the liquid pressure loss tends to decrease, the compressive stress at the time of mounting the cell decreases and the resistance of the cell increases. On the other hand, the bulk density is 0.17
If it exceeds g / cm ³ , the liquid-flow pressure loss increases, the liquid-feeding pump loss increases, and the overall efficiency of the battery decreases.

The properties relating to the bulk density of such a carbonaceous fiber nonwoven fabric are premised on the above-described carbon crystal structure and surface acidic functional groups. In order to obtain the predetermined bulk density, it is necessary to optimize the characteristics of the needle for needle punching at the time of forming the nonwoven fabric and the conditions for forming the nonwoven fabric in the needle punching method, such as the needle density, the needle depth, and the pressing gap. Initially oxidized polyacrylonitrile (fiber diameter 16 μm, fiber length 80 mm) was used as the raw cotton, and the barb interval l. 3mm triangular needle (Foste
When rHDB) No. 40 is used, the needle density is 278 needles / in 2 or more, the depth is 4 to 8 mm, and the holding gap is 4 m.
m or less.

Further, high density, which cannot be realized by the needle punching method, can be achieved by hot pressing or thermocompression bonding in the presence of a binder. Generally, means for increasing the density of needle punch needles is adopted in order to improve the bulk density in the formation of nonwoven fabric, but when performing hot pressing or thermocompression bonding using a binder, the form of the nonwoven fabric is maintained. It is preferable to perform needle punching at a needle density and then perform hot pressing or thermocompression bonding using a binder. When performing hot pressing, it is necessary to adjust the temperature and pressure according to the properties of each fiber.
0 to 240 ° C, 6 to 6 as linear pressure by calender roll
It is preferably performed at 60 kg / cm. When using a binder, acrylic, starch paste, polyvinyl alcohol-based, epoxy resin-based, vinyl acetate-based, phenolic resin-based various types can be used without particular limitation, but carbonized after carbonization. It is most preferable to use a phenolic resin binder in order to maintain the adhesiveness. Further, as a method of adding the binder to the nonwoven fabric, a method of adding the raw cotton in a weaving process after opening the fabric, a method of dissolving or dispersing in water or an organic solvent, and attaching and drying the nonwoven fabric, and dispersing the powder binder in the air to the surface of the nonwoven fabric Although there is a method of attaching, etc., these methods are not particularly limited, and it is desirable to carry out under conditions suitable for each material.

Next, methods for measuring the bulk density, XPS surface analysis, liquid pressure loss, initial contact resistance with the current collector, and contact resistance after 100 cycles of the nonwoven fabric employed in the present invention will be described.

1. Bulk density Bulk density (g / cm ³ ) = basis weight of carbon fiber nonwoven fabric (g
/ M ² ) / thickness (mm) / 1000.

2. XPS Surface Analysis The equipment used for measurement by 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 protons of the acidic functional groups were completely replaced with silver, washed with acetone and water, punched out to a diameter of 6 mm, attached to a heated sample table with a conductive paste, and analyzed. To serve. Before the measurement, the sample is heated to 120 ° C. and evacuated for 3 hours or more. A MgKα ray (1253.6 eV) was used as a radiation source, and the degree of vacuum in the apparatus was 10 ⁻⁷ t.
orr.

The measurement was performed on the peaks of C1s, N1s, and Ag3d, and each peak was identified as ESCAPAC760 (J,
H. Correction analysis is performed using the correction method based on Scofield) to determine each peak area. C to the obtained area
1.00 for 1s, 1.77 for N1s,
The ratio of Ag3d multiplied by the relative intensity of 10.68 is the atomic ratio, and the amount of surface acidic functional groups to the total number of surface carbon atoms is expressed as a percentage (%) of (surface silver atoms / surface carbon atoms). Is calculated by

Next, the C1s peak was separated so that the peak shape matched the chemical shift value of each structure, and the area of the peak of carbon (-C = N-) double-bonded to nitrogen was determined. It is determined and the area ratio to the total surface carbon is calculated in percentage (%).

Further, the N1s peak is 400.1 eV, 4
The peak is separated into 02.5 eV peaks, the peak appearing at 402.5 eV is determined as quaternary nitrogen, the peak area is determined, and the area ratio to the total surface carbon is calculated as a percentage (%).

The chemical shift value of the carbon peak in each structure is described in the literature (A. Ishitani, Carbo).
n, 19, 269 (1981)). FIG. 3 shows an example in which the measured C1s peak is separated according to its bonding structure, and FIG. 4 shows an example in which the measured N1s peak is separated according to its bonding structure.

3. Liquid-flow pressure loss A liquid-flow-type electrolytic cell having the same shape as the liquid-flow-type electrolytic cell and formed of spacers of 20 cm in the liquid-passing direction, 10 cm in the width direction (flow path width), and 1.2 mm is prepared. The prepared electrode material (carbon fibrous nonwoven fabric) is cut into 10 cm square and placed. Liquid volume 5
The liter / hour of ion-exchanged water is allowed to flow, and the pressure loss at the entrance and exit of the electrolytic cell is measured. The same measurement is performed in a system in which the electrode material is not provided as a blank, and the difference between the measured value and the blank measured value is defined as the pressure loss through the electrode material.

4. Initial Contact Resistance The sample is cut into a size of 1 cm × 10 cm, and the sample is cut with two conductive plates from the thickness direction using a 1.2 mm thick Teflon spacer until the sample reaches a predetermined spacer thickness. After compression, the resistance at both ends of the conductive plate is measured using a digital multimeter (TR6846 manufactured by Advantest).

5. Contact resistance after 100 cycles 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 was made, and charge and discharge of 100 cycles were repeated at a constant current density. After the completion, the sample used for the positive electrode is thoroughly washed with water and dried, and then the contact resistance is measured in the manner of measuring the initial contact resistance.

In the charge / discharge test, 2 mo
A 1 mol / l vanadium oxysulfate aqueous 2 mol / l sulfuric acid solution is used, and a 2 mol / l vanadium sulfate 2 mol / l sulfuric acid aqueous solution is used as a negative electrode electrolyte. The amount of the electrolytic solution is set to a large excess with respect to the cell and the piping, and the flow rate of the solution is set to 62 ml / min.

The carbon electrode material assembly of the present invention is used for a redox flow battery using an aqueous electrolyte solution. 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 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.

[0047]

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 cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 278 needles / square inch, a depth of 8 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A nonwoven fabric having a thickness of m ² and a thickness of 4.6 mm was prepared. Next, the nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled under a nitrogen stream having an oxygen concentration of 5 vol%. At 700 ° C. until the weight yield became 93%.
Further, under a nitrogen stream containing 20 vol% of steam, 500
Activated at 10 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Example 2 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a nonwoven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 470 needles / square inch, a depth of 8 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A nonwoven fabric having a thickness of m ² and a thickness of 4.3 mm was prepared. Next, the nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled under a nitrogen stream having an oxygen concentration of 5 vol%. At 700 ° C. until the weight yield became 93%.
Further, under a nitrogen stream containing 20 vol% of steam, 500
Activated at 10 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Example 3 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a nonwoven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 8 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A non-woven fabric with m ² and a thickness of 4.0 mm was prepared. Next, the nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled under a nitrogen stream having an oxygen concentration of 5 vol%. At 700 ° C. until the weight yield became 93%.
Further, under a nitrogen stream containing 20 vol% of steam, 500
Activated at 10 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Example 4 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a nonwoven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 8 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A non-woven fabric with m ² and a thickness of 4.0 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 180 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.6 mm. Each of the nonwoven fabrics is heated at a rate of 100 ° C./min.
Temperature, held at this temperature for 1 hour, cooled by carbonization, and subsequently 700 ° C. under a nitrogen stream with an oxygen concentration of 5 vol%.
To give a weight yield of 93%. 20v more
Activated at 500 ° C. for 10 minutes under a nitrogen stream containing ol% steam to obtain a carbonaceous fiber nonwoven fabric.

Example 5 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a nonwoven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 146 needles / square inch, a depth of 4 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A nonwoven fabric of m ² and 5.2 mm in thickness was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm. Each of the nonwoven fabrics is heated at a rate of 100 ° C./min.
Temperature, held at this temperature for 1 hour, cooled by carbonization, and subsequently 700 ° C. under a nitrogen stream with an oxygen concentration of 5 vol%.
To give a weight yield of 93%. 20v more
Activated at 500 ° C. for 10 minutes under a nitrogen stream containing ol% steam to obtain a carbonaceous fiber nonwoven fabric.

Example 6 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. A phenolic resin powder (trade name: Bellpearl S890, manufactured by Kanebo Co., Ltd.) was added in an amount of 0.5% by weight based on the weight of the oxidized fiber, and the mixture was mixed. / Square inch, a depth of 4 mm, and a pressing gap of 4 mm, to form a nonwoven fabric having a basis weight of 400 g / m ² and a thickness of 5.2 mm. Next, the nonwoven fabric was heated at 180 ° C. and a linear pressure of 60 kg / cm.
And calendered to a thickness of 2.4 mm.
The non-woven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled to 700 ° C. under a nitrogen stream having an oxygen concentration of 5 vol%. It was processed at 93 ° C. until the weight yield was 93%. Further, under a nitrogen stream containing 20 vol% of steam, 5
Activated at 00 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Example 7 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. A phenolic resin powder (trade name: Bellpearl S890, manufactured by Kanebo Co., Ltd.) was added in an amount of 0.5% by weight based on the weight of the oxidized fiber, and the mixture was mixed. / Square inch, a depth of 4 mm, and a pressing gap of 4 mm, to form a nonwoven fabric having a basis weight of 400 g / m ² and a thickness of 5.2 mm. Next, the nonwoven fabric was heated at 200 ° C. and a linear pressure of 60 kg / cm.
And compressed to a thickness of 2.0 mm.
The non-woven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled to 700 ° C. under a nitrogen stream having an oxygen concentration of 5 vol%. It was processed at 93 ° C. until the weight yield was 93%. Further, under a nitrogen stream containing 20 vol% of steam, 5
Activated at 00 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Example 8 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. A phenolic resin powder (trade name: Bellpearl S890, manufactured by Kanebo Co., Ltd.) was added in an amount of 0.5% by weight based on the weight of the oxidized fiber, and the mixture was mixed. / Square inch, a depth of 4 mm, and a pressing gap of 4 mm, to form a nonwoven fabric having a basis weight of 400 g / m ² and a thickness of 5.2 mm. Next, the nonwoven fabric was heated at 220 ° C. and a linear pressure of 60 kg / cm.
And compressed to a thickness of 1.5 mm.
The non-woven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled to 700 ° C. under a nitrogen stream having an oxygen concentration of 5 vol%. It was processed at 93 ° C. until the weight yield was 93%. Further, under a nitrogen stream containing 20 vol% of steam, 5
Activated at 00 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 1 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a nonwoven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 146 needles / square inch, a depth of 4 mm and a holding gap of 4 mm, and a basis weight of 400 g /
A nonwoven fabric of m ² and 5.2 mm in thickness was prepared. Next, the nonwoven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled under a nitrogen stream having an oxygen concentration of 5 vol%. At 700 ° C. until the weight yield became 93%.
Further, under a nitrogen stream containing 20 vol% of steam, 500
Activated at 10 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 2) Polyacrylonitrile fiber having an average fiber diameter of 16 µm was oxidized in air at 200 to 300 ° C, and then cut to a length of about 80 mm to prepare oxidized short fibers. A phenolic resin powder (trade name: Bellpearl S890, manufactured by Kanebo Co., Ltd.) was added in an amount of 0.5% by weight based on the weight of the oxidized fiber, and the mixture was mixed. / Square inch, a depth of 4 mm, and a pressing gap of 4 mm, to form a nonwoven fabric having a basis weight of 400 g / m ² and a thickness of 5.2 mm. Next, the nonwoven fabric was heated at 240 ° C. and a linear pressure of 60 kg / cm.
And compressed to a thickness of 1.5 mm.
The non-woven fabric was heated to 1600 ° C. at a rate of 100 ° C./min under a nitrogen stream, held at this temperature for 1 hour, cooled by carbonization, and subsequently cooled to 700 ° C. under a nitrogen stream having an oxygen concentration of 5 vol%. It was processed at 93 ° C. until the weight yield was 93%. Further, under a nitrogen stream containing 20 vol% of steam, 5
Activated at 00 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

(Comparative Example 3) Polyacrylonitrile fibers having an average fiber diameter of 16 µm were oxidized in air at 200 to 300 ° C, and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm. The non-woven fabric is heated to 1200 ° C. at a rate of 10 ° C./min in nitrogen gas, kept at this temperature for 1 hour, cooled by carbonization, and subsequently cooled to 700 ° C. in a nitrogen stream having an oxygen concentration of 7 vol%. To obtain a carbon fiber nonwoven fabric.

Comparative Example 4 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm.

Argon gas is continuously applied to the nonwoven fabric for 600 c.
The temperature was raised to 2000 ° C. at a rate of 10 ° C./min while spraying c / min / m ² , the temperature was maintained for 1 hour, and carbonization was performed for cooling, followed by a nitrogen stream with an oxygen concentration of 7 vol%. At 700 ° C. until the weight yield became 93%. Further, under a nitrogen stream containing 20 vol% of steam, 5
Activated at 00 ° C. for 10 minutes to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 5 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm. The temperature was raised to 1600 ° C. at a rate of 10 ° C./min while continuously blowing argon gas at 600 cc / min / m ² onto the nonwoven fabric.
The mixture was kept at this temperature for 1 hour, carbonized and cooled, and subsequently treated at 700 ° C. under a nitrogen stream having an oxygen concentration of 0.5 vol% until the weight yield became 93% to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 6 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm. The temperature was raised to 1600 ° C. at a rate of 10 ° C./min while continuously blowing argon gas at 600 cc / min / m ² onto the nonwoven fabric.
It was kept at this temperature for 1 hour, cooled by carbonization, and subsequently treated in a nitrogen gas atmosphere with an oxygen concentration of 0.5 vol% at 700 ° C. until the weight yield became 93%. Further 5vol
% Of hydrogen chloride gas and 20% by volume of water vapor at 200 ° C. for 5 minutes to obtain a carbonaceous fiber nonwoven fabric.

Comparative Example 7 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm.

An argon gas was continuously applied to the nonwoven fabric for 600 c.
The temperature was raised to 1600 ° C. at a rate of 100 ° C./min while spraying c / min / m ² , kept at this temperature for 1 hour, cooled by carbonization, and subsequently nitrogen with an oxygen concentration of 0.5 vol% The treatment was performed at 700 ° C. under a gas atmosphere until the weight yield was 93%. Further, activation was performed at 500 ° C. for 60 minutes under a nitrogen stream containing 20 vol% water vapor to obtain a carbonaceous fiber nonwoven fabric.

Reference Example 1 Polyacrylonitrile fibers having an average fiber diameter of 16 μm were oxidized in air at 200 to 300 ° C., and then cut to a length of about 80 mm to prepare oxidized short fibers. This was made into a non-woven fabric under the conditions of a Foster No. 40 HDB needle, a needle density of 748 needles / square inch, a depth of 4 mm, and a holding gap of 4 mm.
A nonwoven fabric having a thickness of m ² and a thickness of 4.2 mm was prepared. Next, the nonwoven fabric was passed through a calender roll at 240 ° C. and a linear pressure of 60 kg / cm, and was compressed to a thickness of 3.1 mm.

The argon gas is continuously applied to the nonwoven fabric for 600 c.
The temperature was raised to 1600 ° C. at a rate of 10 ° C./min while spraying c / min / m ² , the temperature was maintained for 1 hour, carbonized and cooled, and then nitrogen with an oxygen concentration of 0.5 vol% The treatment was performed at 700 ° C. under a gas atmosphere until the weight yield became 98%. In addition, 5vol% hydrogen chloride gas and 20v
Activated at 200 ° C. for 5 minutes under a nitrogen stream containing ol% steam to obtain a carbonaceous fiber nonwoven fabric.

The bulk density, XPS surface analysis, liquid pressure loss, initial contact resistance with the current collector plate, and contact resistance after 100 cycles of the carbonaceous fiber nonwoven fabric obtained in the above Examples and Comparative Examples were determined together with the production conditions. It is shown in Table 1.

[0068]

[Table 1] As is evident from the results in Table 1, the carbonaceous fiber nonwoven fabrics of Examples 1 to 8 can reduce the liquid pressure loss and the contact resistance with the current collector plate, reduce the cell resistance, and increase the voltage efficiency. And the energy efficiency of the battery can be increased. Further, it is possible to reduce a decrease in the contact property of the electrode material due to a change over time in the charge / discharge cycle, which can contribute to long-term stabilization of voltage efficiency. This is particularly effective for vanadium-based redox flow batteries.

On the other hand, in Comparative Example 1 in which the bulk density of the nonwoven fabric was smaller than the range of the present invention, although the liquid pressure loss was good, the contact resistance with the current collector plate was large, while the bulk density of the nonwoven fabric of the present invention was low. In Comparative Example 2, which is larger than the range, the contact resistance with the current collector plate is good, but the liquid passing pressure loss is large, which is not preferable in terms of voltage efficiency and energy efficiency. In Comparative Examples 3 to 7, in which the properties of the carbonaceous fiber are not appropriate, the contact resistance with the current collector plate is large, which is not preferable in terms of voltage efficiency and 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.

FIG. 3 is an example of a separation diagram of a C1s peak measured by XPS surface analysis according to a bonding structure.

FIG. 4 is an example of a separation diagram of the N1s peak measured by XPS surface analysis according to a bonding structure.

[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

Claims (3)

[Claims] 1. A carbon electrode material aggregate used for a redox flow battery using an aqueous electrolytic solution and made of a nonwoven fabric of carbonaceous fibers, wherein the carbonaceous fibers are determined by the following (a) and (b) obtained by XPS surface analysis. ), And the nonwoven fabric has a bulk density of 0.05 to 0.17 g / cm ^3.
A carbon electrode material assembly, characterized in that: (A) The amount of surface acidic functional groups is 0.2 to less than the total number of surface carbon atoms.
2.0%. (B) The number of surface carbon atoms that are double-bonded to nitrogen is 0.3 to 3.0% of the total number of surface carbon atoms. 2. The carbon electrode material assembly according to claim 1, wherein the number of surface quaternary ammonium nitrogen atoms of the carbonaceous fiber determined by XPS surface analysis is 1.0% or less of the total number of surface carbon atoms. 3. The carbon electrode material assembly according to claim 1, which is used for a vanadium redox flow battery.