WO2019049755A1

WO2019049755A1 - Carbon electrode material for redox flow battery, and method for manufacturing carbon electrode material

Info

Publication number: WO2019049755A1
Application number: PCT/JP2018/032012
Authority: WO
Inventors: 俊克円城寺; 貴弘松村; 良平岩原; 小林　真申; 真佐子龍田
Original assignee: 東洋紡株式会社
Priority date: 2017-09-07
Filing date: 2018-08-29
Publication date: 2019-03-14
Also published as: JP7088197B2; JPWO2019049755A1

Abstract

Provided is a carbon electrode material for a carbon-electrode-material redox flow battery with which it is possible to reduce cell resistance during initial charge/discharge and which has exceptional battery energy efficiency. This electrode material comprises carbonaceous fibers (A) and a carbonaceous material (B) binding the carbonaceous fibers (A), and satisfies the following requirements. (1) Lc(B) is less than 10 nm, where Lc(B) is the c-axis-direction crystallite size obtained by X-ray diffraction in the carbonaceous material (B). (2) Lc(B)/Lc(A) is equal to or greater than 1.0, where Lc(A) is the c-axis-direction crystallite size obtained by X-ray diffraction in the carbonaceous fiber (A). (3) The number of bound oxygen atoms on the carbon electrode material surface is at least 1% of the total number of carbon atoms on the carbon electrode material surface.

Description

Carbon electrode material for redox flow battery and method for producing the same

The present invention relates to a carbon electrode material used in a redox flow battery and a method of manufacturing the same, and more particularly to a carbon electrode material excellent in energy efficiency of the whole redox flow battery and a method of manufacturing the same.

A redox flow battery is a battery utilizing oxidation-reduction in an aqueous solution of redox ions, and is a mild reaction in the liquid phase alone, so it is a very safe large-capacity storage battery.

The main configuration of the redox flow battery is, as shown in FIG. 1, composed of external tanks 6, 7 for storing electrolytes (positive electrode electrolyte, negative electrode electrolyte), and an electrolytic cell EC. In the electrolytic cell EC, the ion exchange membrane 3 is disposed between the opposing

current collectors

1, 1. In the redox flow battery, electrochemical energy conversion is performed on the electrode 5 incorporated in the electrolytic cell EC, that is, while the electrolytic solution containing the active material is sent from the external tanks 6 and 7 to the electrolytic cell EC by the pumps 8 and 9, Charging and discharging are performed. As a material of the electrode 5, a carbon material having chemical resistance, conductivity, and liquid permeability is used.

As an electrolytic solution used for a redox flow battery, typically, an aqueous solution containing a metal ion whose valence changes by oxidation / reduction is used. The electrolytic solution has been highly densified from the type using a hydrochloric acid aqueous solution of iron for the positive electrode and the hydrochloric acid aqueous solution for chromium as the type using a sulfuric acid aqueous solution of vanadium having a high electromotive force for both electrodes.

In the case of a redox flow battery using vanadium oxysulfate as the positive electrode electrolyte and sulfuric acid acidic aqueous solution of vanadium sulfate as the negative electrode electrolyte, at the time of discharge, the electrolyte containing V ²⁺ is supplied to the liquid passage on the negative electrode side An electrolytic solution containing V 5 ⁺ (in fact, an ion containing oxygen) is supplied to the side passage. In the negative electrode side passage, V ²⁺ emits electrons and is oxidized to V ³ ⁺ in the three-dimensional electrode. The emitted electrons reduce ^V5 ^{+ to} ^V4 ⁺ (in fact, an ion containing oxygen) in the three-dimensional electrode on the positive side through an external circuit. The redox reaction of the negative electrode electrolyte SO ₄ ^2-becomes insufficient with the, for SO ₄ ^2-becomes excessive in the positive electrode electrolyte solution, the negative electrode side SO ₄ ^2-is from the positive electrode side through the ion-exchange membrane The charge balance is maintained. Alternatively, charge balance can also be maintained by moving H ⁺ from the negative electrode side to the positive electrode side through the ion exchange membrane. During charge, the reverse reaction to the discharge proceeds.

In particular, the electrode material for a redox flow battery is required to have the following performance.

1) Do not cause side reactions other than the target reaction (high reaction selectivity), specifically, high current efficiency (η _I ).
2) High electrode reaction activity, specifically, low cell resistance (R). That is, the voltage efficiency (η _V ) is high.
3) High battery energy efficiency (η _E ) related to the above 1) and 2).
η _E = η _I × η _V
4) The deterioration due to repeated use is small (high life), specifically, the decrease in battery energy efficiency (η _E ) is small.

For example, Patent Document 1 discloses, as an electrode material of an Fe—Cr battery capable of enhancing the total energy efficiency of the battery, a carbonaceous material having a specific pseudo-graphite microcrystalline structure with high crystallinity. Specifically, it has pseudo-graphite crystallites having an average <002> interplanar spacing of 3.70 Å or less as determined by wide-angle X-ray analysis and crystallite sizes in the c-axis direction of at least 9.0 Å on average. And a carbonaceous material having a total acidic functional group content of at least 0.01 meq / g.

Patent Document 2 is a carbonaceous fiber made of polyacrylonitrile fiber as a raw material, as an electrode for an electric field layer of an iron-chromium redox flow battery etc. which enhances the energy efficiency of the battery and improves the charge-discharge cycle life. Carbon consisting of carbon having a pseudo-graphite crystal structure with a <002> interplanar spacing of 3.50 to 3.60 Å determined from wide-angle line analysis, and the number of oxygen atoms bonded to the carbon surface is 10 to 25% of the number of carbon atoms An electrode material is disclosed.

Patent Document 3 has a <002> surface spacing determined from X-ray wide-angle analysis as a carbon electrode material for a vanadium-based redox flow battery which is excellent in energy efficiency in the entire battery system and in which the change in performance with long use is small. XPS surface analysis with a pseudographitic crystal structure with a crystallite size in the c-axis direction of 15-33 Å in the c-axis direction and a crystallite size in the a-axis direction of 30-75 Å An electrode is disclosed in which the surface acidic functional group content determined from the total number of surface carbon atoms is 0.2 to 1.0% and the number of surface-bound nitrogen atoms is 3% or less of the total number of surface carbon atoms.

Further, in Patent Document 4, as a carbon electrode material that enhances the overall efficiency of the vanadium-based redox flow battery and lowers the cell resistance at the time of initial charge, the crystal structure is obtained from the X-ray wide-angle analysis on the carbonaceous fiber. 002> A carbon composite material to which carbon fine particles having an interplanar spacing of 3.43 to 3.70 Å and an average primary particle diameter of 30 nm to 5 μm are attached, and the crystal structure of the carbon composite material is determined by X-ray wide-angle analysis An electrode material having a determined <002> plane spacing of 3.43 to 3.60 Å, a crystallite size in the c-axis direction of 15 to 35 Å, and a crystallite size in the a-axis direction of 30 to 75 Å It is disclosed. In the above carbon composite material, it is preferable that the carbonaceous fiber and the carbon fine particles are adhered in proximity or by an adhesive such as a phenol resin, and carbon which is an electrochemical reaction field by using an adhesive. It is stated that only the portion originally in contact as the carbonaceous fiber can be fixed without excessively reducing the quality fiber surface. In the column of Example, after immersing the nonwoven fabric in a solution in which 5% by weight of carbon fine particles (phenol resin) (Example 1) or 5% by weight of phenol resin (Examples 2 to 4) is mixed, A carbonaceous fibrous nonwoven fabric obtained by dry oxidation treatment is disclosed.

The development of electrolytes used in redox flow batteries is also underway, and as electrolytes which have a higher electromotive force than the above-mentioned vanadium-based electrolytes and can be stably and inexpensively supplied, for example, Patent Document 5 As in the above, those using manganese for the positive electrode and chromium, vanadium and titanium for the negative electrode (for example, Mn-Ti based electrolyte) have been proposed.

Japanese Patent Application Laid-Open No. 60-232669 Unexamined-Japanese-Patent No. 5-234612 gazette JP 2000-357520 A JP 2017-33758 A JP 2012-204135 A

In order to promote the spread of redox flow batteries such as vanadium-based redox flow batteries, further reduction in resistance and inexpensive electrode materials are required.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a carbon electrode material for a redox flow battery capable of improving battery energy efficiency by reducing cell resistance at the time of initial charge and discharge.

The composition of the carbon electrode material for a redox flow battery according to the present invention, which has solved the above-mentioned problems, is as follows. In the present specification, the following carbon electrode materials 1 to 4 are referred to as a first carbon electrode material, carbon electrodes material 11 to 14 below are referred to as a second carbon electrode material, and carbon electrodes material 21 to 24 below are referred to as a third carbon It may be called an electrode material.

(I) First carbon electrode material Carbonaceous fiber (A) and carbonaceous material (B) binding the carbonaceous fiber (A), and
A carbon electrode material for a redox flow battery characterized by satisfying the following requirements.
(1) Lc (B) is less than 10 nm, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (B)
(2) Lc (B) / Lc (A) is 1.0 or more, where Lc (A) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A).
(3) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material. The carbon electrode material according to the above 1, wherein the mass content of the carbonaceous material (B) relative to the total amount of the carbonaceous fiber (A) and the carbonaceous material (B) is 14.5% or more.
3. The carbon electrode material according to the above 1 or 2, wherein the Lc (A) is 1 to 10 nm.
4. The carbon electrode material according to any one of the above 1 to 3, wherein the water flow rate at the time of dropping a water drop is 0.5 mm / sec or more.
5. A redox flow battery comprising the carbon electrode material according to any one of the above 1 to 4.
6. A vanadium-based redox flow battery using the carbon electrode material according to any one of the above 1 to 4.
7. It is a method of manufacturing the carbon electrode material in any one of said 1-4, Comprising:
Attaching the carbonaceous material (B) before carbonization to the carbonaceous fiber (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.

(II) Second carbon electrode material 11. A carbon electrode material for a redox flow battery, comprising a carbonaceous fiber (A), graphite particles (B), and a carbonaceous material (C) binding them, and satisfying the following requirements.
(1) Lc (B) is less than 35 nm, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the graphite particles (B)
(2) Lc (C) is less than 10 nm, where Lc (C) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (C)
(3) Lc (C) / Lc (A) is 1.0 or more, where Lc (A) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A).
(4) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material The mass content of the carbonaceous material (C) relative to the total amount of the carbonaceous fiber (A), the graphite particles (B), and the carbonaceous material (C) is 14.5% or more, and 12. The carbon electrode material according to 11 above, wherein the mass ratio of the carbonaceous material (C) to B) is 0.2 to 3.0.
13. The carbon electrode material according to the above 11 or 12, wherein a BET specific surface area determined from a nitrogen adsorption amount is more than 8 m ² / g.
14. The carbon electrode material according to any one of the above 11 to 13, which has a water flow rate of 0.5 mm / sec or more when a water droplet is dropped.
15. A redox flow battery comprising the carbon electrode material according to any one of the above 11 to 14.
16. A vanadium-based redox flow battery using the carbon electrode material according to any one of 11 to 14 above.
17. A method for producing the carbon electrode material according to any one of 11 to 14 above,
Attaching the graphite particles (B) and the carbonaceous material (C) before carbonization to the carbonaceous fibers (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.

(III) Third carbon electrode material 21. It consists of a carbonaceous fiber (A), carbon particles (B) other than graphite particles, and a carbonaceous material (C) binding these,
A carbon electrode material for a redox flow battery characterized by satisfying the following requirements.
(1) The particle size of carbon particles (B) other than graphite particles is 1 μm or less,
(2) Lc (B) is 10 nm or less, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in carbon particles (B) other than graphite particles.
(3) Lc (A) and Lc (C) in the carbonaceous fiber (A) and the carbonaceous material (C), where Lc (A) and Lc (C) are the sizes of crystallites in the c-axis direction, respectively. C) / Lc (A) is 1.0 to 5,
(4) The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B) other than the graphite particles, and the carbonaceous material (C) is 14.5% or more
(5) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material. 22. The carbon electrode material according to the above 21, wherein the mass ratio of the carbonaceous material (C) to the carbon particles (B) is 0.2 to 10.
23. The carbon electrode material according to the above 21 or 22, wherein a BET specific surface area determined from a nitrogen adsorption amount is 0.5 m ² / g or more.
24. The carbon electrode material according to any one of the above 21 to 23, wherein the water flow rate when dripping a water drop is 0.5 mm / sec or more.
25. A redox flow battery comprising the carbon electrode material according to any one of 21 to 24 above.
26. A method for producing the carbon electrode material according to any one of 21 to 24 above,
Attaching a carbon particle (B) other than the graphite particle and a carbonaceous material (C) before carbonization to the carbonaceous fiber (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.

According to the first to third carbon electrode materials of the present invention, it is possible to obtain a carbon electrode material for a redox flow battery excellent in battery energy efficiency by reducing cell resistance at the time of initial charge and discharge.
The first and second carbon electrode materials according to the present invention are particularly useful as electrode materials for vanadium-based redox flow batteries.
Further, the third carbon electrode material according to the present invention is not only for the above-mentioned vanadium-based electrolyte solution, Mn / Ti-based electrolyte solution, but also for redox flow batteries using other metal-based electrolyte solutions and nonmetal-based electrolyte solutions. It is useful as an electrode material.
Furthermore, the first to third carbon electrode materials according to the present invention are suitably used in flow type and non-flow type redox flow batteries, or in redox flow batteries combined with lithium, capacitors and fuel cell systems.

FIG. 1 is a schematic view of a redox flow battery. FIG. 2 is an exploded perspective view of a liquid flow type electrolytic cell having a three-dimensional electrode suitably used in the present invention.

First, referring to FIG. 2, the present invention will be described in detail for each component.

FIG. 2 is an exploded perspective view of a liquid flow type electrolytic cell suitably used in the present invention. In the electrolytic cell of FIG. 2, the ion exchange membrane 3 is disposed between two opposing

current collectors

1 and 1, and the spacers 2 on both sides of the ion exchange membrane 3 are along the inner surface of the current collector 1. Passages 4a and 4b for the electrolytic solution are formed. The electrode material 5 is disposed on at least one of the liquid flow paths 4a and 4b. The current collector plate 1 is provided with a liquid inlet 10 and a liquid outlet 11 for the electrolytic solution. Assuming that the electrode is composed of the electrode material 5 and the current collector plate 1 as shown in FIG. 2 and the electrolytic solution passes through the inside of the electrode material 5 (three-dimensionalization of the electrode structure), transport of electrons by the current collector plate 1 The charge and discharge efficiency can be improved by using the entire surface of the pores of the electrode material 5 as the electrochemical reaction site while securing the As a result, the charge and discharge efficiency of the electrolytic cell is improved.

Hereinafter, the first to third carbon electrode materials (5 in FIG. 2) according to the present invention will be described in detail. In this specification, a carbon electrode material may be abbreviated as an "electrode material."

[I. First carbon electrode material according to the present invention]
[I-1. Configuration of first carbon electrode material]
The present inventors first reviewed the requirements for carbon particles in providing a carbon electrode material with reduced cell resistance at the time of initial charge and discharge. Generally, as particles showing reaction activity in redox flow batteries, carbon blacks such as acetylene black (acetylene black), oil black (furnace black, oil black), gas black (gas black), etc. Those having high reactivity, specific surface area, and low crystallinity are often used. However, they generally have to use a large amount of binder in order to bind to the carbon fiber, and sufficient reaction activity could not be obtained.

In addition to the above, carbon particles such as carbon nanotubes (CNTs, carbon nanotubes), carbon nanofibers, carbon aerogels, mesoporous carbon, graphene, graphene oxide, N-doped CNTs, boron-doped CNTs and fullerenes are also reactively active in redox flow batteries Indicates However, although they are excellent in reaction activity, they are expensive and scarce, so they are not suitable as materials for inexpensive electrode materials.

On the other hand, graphite particles are mentioned as cheap and easily available carbon particles. Graphite particles are very useful because they have good binding properties with carbonaceous materials and can support graphite particles even with small amounts of carbonaceous materials. However, since the graphite particles have low oxidation resistance, there is a problem that the durability of the electrode is reduced.

Therefore, the present inventors are binding carbonaceous materials that bind the carbonaceous fiber (A) and the carbonaceous fiber (A) as the carbonaceous material (B) without using carbon particles, It decided to adopt the low crystalline carbonaceous material which satisfies the following requirements (1) and (2).
(1) When the size of the crystallite in the c-axis direction determined by X-ray diffraction is Lc (B), Lc (B) is less than 10 nm (2) c-axis determined by X-ray diffraction in carbonaceous fibers Lc (B) / Lc (A) is 1.0 or more where the size of the crystallite in the direction is Lc (A). Here, “the carbonaceous fiber (A) and the carbonaceous fiber (A) are bound to each other (In other words, the carbonaceous material used for the first electrode material acts as a binder for carbonaceous fibers) means that the carbonaceous materials are strongly bound by the carbonaceous material, and When viewed as a whole, it means that the carbonaceous fiber surface is coated with the carbonaceous material.
However, it is preferable that the carbonaceous material after binding is not in the form of a film. Here, "does not become a coated state" means that the carbonaceous material (B) does not form a webbed state like a total foot (boxok) or a foot between fibers of the carbonaceous fiber (A). When a film state is formed, the liquid permeability of the electrolytic solution is deteriorated, and the resistance of the battery is increased.

In order to obtain such a bonding state, it is preferable to increase the content ratio of the carbonaceous material to the total amount of the carbonaceous fiber and the carbonaceous material, and in the first electrode material, for example, 14.5% or more. It is preferable to do. In this respect, the carbonaceous material in the first electrode material is different from the carbonaceous material described in Patent Document 4 described above. In Patent Document 4, based on the idea that it is only necessary to fix (adhere) only the portion where the carbonaceous fiber and the carbon fine particle originally contacted, the carbonaceous material to be used exhibits a function as a partial adhesive. There is only recognition that it is good. Therefore, in the example of Patent Document 4, the content of the carbonaceous material is at most 14.4%.

If such a binding and low crystalline carbonaceous material is used, it becomes easy to introduce an oxygen functional group, and high electrolytic solution affinity is imparted to the carbonaceous material. Moreover, since the carbonaceous material strongly bonds between the carbonaceous fibers, etc., it has been found that an efficient conductive path can be formed, and the increase in resistance can be suppressed.

Furthermore, the carbon electrode material of the first electrode material satisfies the following requirement (3).
(3) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material Thereby, oxygen atoms can be introduced to the edge surface of carbon and defect structure. As a result, on the surface of the electrode material, the introduced oxygen atom is generated as a reactive group such as a carbonyl group, a quinone group, a lactone group, or a free radical oxide, and these reactive groups greatly contribute to the electrode reaction. And the rise in resistance is further suppressed.

Since the electrode material of the first electrode material is configured as described above, the reaction activity is enhanced, and a low resistance and inexpensive electrode can be obtained.

As described above, the first electrode material 5 is composed of the carbonaceous fiber (A) and the binding carbonaceous material for binding the carbonaceous fiber (A), and the requirements of the above (1) to (3) Satisfy.

[Carbonaceous fiber (A)]
The carbonaceous fiber used in the first electrode material is a fiber obtained by subjecting an organic fiber precursor to a carbonization treatment (details will be described later), and 90% or more by mass ratio is made of carbon Mean fibers (JIS L 0204-2). Precursors of organic fibers as raw materials of carbonaceous fibers include acrylic fibers such as polyacrylonitrile; phenol fibers; PBO fibers such as polyparaphenylene benzobisoxazole (PBO); aromatic polyamide fibers; isotropic pitch fibers; Pitch fibers such as anisotropic pitch fibers and mesophase pitch; cellulose fibers; etc. can be used. Among them, from the viewpoint of being excellent in strength and elastic modulus, acrylic fiber, phenol fiber, cellulose fiber, isotropic pitch fiber and anisotropic pitch fiber are preferable as the organic fiber precursor, and acrylic fiber is more preferable. The acrylic fiber is not particularly limited as long as it contains acrylonitrile as a main component, but the content of acrylonitrile in the raw material monomer forming the acrylic fiber is preferably 95% by mass or more, and 98% by mass or more It is more preferable that

The mass average molecular weight of the organic fiber is not particularly limited, but is preferably 10000 or more and 100000 or less, more preferably 15000 or more and 80000 or less, and still more preferably 20000 or more and 50000 or less. The mass average molecular weight can be measured by gel permeation chromatography (GPC), solution viscosity, or the like.

The average fiber diameter of the carbonaceous fiber is preferably 0.5 to 40 μm. If the average fiber diameter is smaller than 0.5 μm, the liquid permeability will deteriorate. On the other hand, when the average fiber diameter is larger than 40 μm, the reaction surface area of the fiber portion is reduced and the cell resistance is increased. In consideration of the balance between the liquid permeability and the reaction surface area, it is more preferably 3 to 20 μm.

In the first electrode material, it is preferable to use the above-mentioned carbonaceous fiber structure as a base material, whereby the strength is improved and the handling and the processability are facilitated. As the above-mentioned structure, specifically, a spun yarn, a filament collected yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric or carbon described in JP-A-63-200467 etc., which is a sheet-like material comprising carbonaceous fibers The paper etc. which consist of fibers can be mentioned. Among these, non-woven fabric made of carbonaceous fiber, knitted fabric, woven fabric, special woven fabric, and paper made of carbon fiber are more preferable from the viewpoints of handling, processability, manufacturability and the like.

When non-woven fabric, knitted fabric, woven fabric or the like is used here, the average fiber length is preferably 30 to 100 mm. When a paper made of carbon fiber is used, the average fiber length is preferably 5 to 30 mm. By setting it in said range, a uniform fiber structure is obtained.

As mentioned above, although the above-mentioned carbonaceous fiber is obtained by subjecting a precursor of an organic fiber to a carbonization treatment by heating, the above-mentioned "heat carbonization treatment" includes at least a flameproofing step and a carbonization (baking) step. Is preferred. However, among these, the carbonization step does not necessarily need to be performed after the flameproofing step as described above, and after the graphite particles and the carbonaceous material are attached to the flameproofed fiber as described in the examples described later. A carbonization process may be performed, and in this case, the carbonization process after the oxidization process can be omitted.

Among the above, the above-mentioned flameproofing step means a step of heating the precursor of the organic fiber preferably at a temperature of 180 ° C to 350 ° C in an air atmosphere to obtain a flameproofed organic fiber. The heat treatment temperature is more preferably 190 ° C. or more, and still more preferably 200 ° C. or more. Moreover, it is preferable that it is 330 degrees C or less, and it is more preferable that it is 300 degrees C or less. By heating in the above temperature range, the content of nitrogen and hydrogen in the organic fiber can be reduced while maintaining the form of the carbonaceous fiber without the organic fiber being thermally decomposed, and the carbonization rate can be improved. Since the organic fibers may be thermally shrunk and the molecular orientation may collapse during the flameproofing step, and the conductivity of the carbonaceous fibers may be reduced, it is preferable to flameproof the organic fibers under tension or stretching. It is more preferable to flameproof treatment under tension.

In the carbonization step, the flame-resistant organic fiber obtained as described above is preferably heated at a temperature of 1000 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere) to obtain a carbonaceous fiber It means a process. The heating temperature is more preferably 1100 ° C. or more, further preferably 1200 ° C. or more. Moreover, More preferably, it is 1900 degrees C or less. By performing the carbonization step in the above temperature range, carbonization of the organic fiber proceeds and a carbonaceous fiber having a pseudo-graphite crystal structure can be obtained.

Since the organic fibers have different crystallinity, the heating temperature in the carbonization step can be selected according to the type of organic fibers used as the raw material. For example, when using an acrylic resin (preferably polyacrylonitrile) as the organic fiber, the heating temperature is preferably 800 ° C. or more and 2000 ° C. or less, and more preferably 1000 ° C. or more and 1800 ° C. or less.

It is preferable to carry out the above-mentioned flameproofing step and carbonizing step continuously, and the temperature raising rate when raising the temperature from the flameproofing temperature to the carbonizing temperature is preferably 20 ° C./min or less, more preferably Is less than 15 ° C./min. By setting the heating rate within the above range, it is possible to maintain the shape of the organic fiber and obtain a carbonaceous fiber excellent in mechanical properties. The lower limit of the temperature rising rate is preferably 5 ° C./min or more in consideration of mechanical properties and the like.

As described in detail in the section of carbonaceous material (B) to be described later, the first electrode material is, in the carbonaceous fiber (A) and the carbonaceous material (B), as defined in the above (2). Lc (B) / Lc (A) satisfies 1.0 or more when Lc (A) and Lc (B) are the sizes of crystallites in the c-axis direction determined by X-ray diffraction, respectively. Therefore, Lc (A) in the carbonaceous fiber (A) is not particularly limited as long as the above (2) is satisfied in the first electrode material, but it is preferably 1 to 10 nm. As a result, appropriate electron conductivity is exhibited, oxidation resistance to a sulfuric acid solvent or the like is exhibited, and functions such as easy provision of an oxygen functional group are effectively exhibited. Lc (A) is more preferably 1 to 6 nm. The measurement methods of Lc (A) and Lc (B) will be described in detail in the section of Examples described later.

[Carbonaceous material (B)]
In the first electrode material, the carbonaceous material is added as a binding agent (binder) for strongly binding the carbonaceous fiber which can not be originally bound. In the first electrode material, when the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (B) is Lc (B) as defined in (1) above, B) is less than 10 nm, and the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A) is Lc (B) as defined in the above (2) When Lc (B) / Lc (A) needs to satisfy 1.0 or more.
By using such a low crystalline binding carbonaceous material, it becomes easy to introduce an oxygen functional group, and high electrolytic solution affinity is imparted to the carbonaceous material. In addition, since the carbonaceous material strongly bonds between the carbonaceous fibers, it has been found that an efficient conductive path can be formed and the resistance lowering action can be effectively exhibited.

From the viewpoint of lowering the resistance, Lc (B) is preferably 8 nm or less, and more preferably 5 nm or less. The lower limit of Lc (B) is not particularly limited from the above viewpoint, but is preferably about 1 nm or more in consideration of the oxidation resistance and the like necessary for a vanadium-based redox flow battery.

In addition, when the ratio of Lc (B) / Lc (A) is less than 1.0, the above effect is not effectively exhibited. 1.5 or more are preferable and 3.0 or more of said ratio are more preferable. On the other hand, if the above ratio exceeds 10, it becomes difficult to impart an oxygen functional group to the carbonaceous material portion, so 10 or less is preferable. The above ratio is more preferably 5 or less, still more preferably 4 or less.

In the first electrode material, the range of Lc (B) is not particularly limited as long as the ratio of Lc (B) / Lc (A) satisfies the above range, but from the viewpoint of further lowering resistance, Lc (B) 10 nm or less is preferable and 7.5 nm or less is more preferable. The lower limit of Lc (B) is not particularly limited from the above viewpoint, but in consideration of electron conductivity and the like, approximately 3 nm or more is preferable.

The carbonaceous material (B) used for the first electrode material is contained by 14.5% or more by mass ratio to the total amount of the carbonaceous fiber (A) and the carbonaceous material (B) described above Preferably, it is 20% or more. Thus, by increasing the content of the carbonaceous material, the carbonaceous fiber can be sufficiently bonded, and the binding action by the addition of the carbonaceous material is effectively exhibited. The upper limit thereof is preferably approximately 60% or less in consideration of loss of hydraulic pressure and the like. More preferably, it is 50% or less. In addition, content of the carbonaceous fiber (A) used for calculation of said content is content of the said structure, when using structures, such as a nonwoven fabric, as a base material.

The type of carbonaceous material (B) used for the first electrode material may be any type as long as it can bind the carbonaceous fiber (A). Specifically, at the time of carbonization at the time of producing the first electrode material It is not particularly limited as long as it exhibits binding properties. Such examples include pitches such as coal tar pitch and coal pitch; phenol resin, benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde Resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins, polyacrylonitrile, etc .; furfuryl alcohol; rubbers such as acrylonitrile-butadiene rubber and the like. A commercial item may be used for these.

Among these, pitches such as coal tar pitch and coal-based pitch which are easily crystalline are preferable because the target carbonaceous material (B) can be obtained at a low firing temperature. In addition, a phenolic resin is also preferably used because the degree of increase and decrease in crystallinity is small depending on the calcination temperature and the crystallinity can be easily controlled. In addition, polyacrylonitrile resin is also preferably used because the target carbonaceous material (B) can be obtained by raising the firing temperature. Particularly preferred are pitches.
According to a preferred embodiment of the first electrode material, since no phenol resin is used, there is an advantage that no harmful effect (formaldehyde generation and formaldehyde odor at room temperature) occurs with the phenol resin and no odor is generated at normal temperature. On the other hand, in the patent document 4 mentioned above, since phenol resin is used as an adhesive agent, in addition to the above-mentioned bad effect, facilities for controlling formaldehyde concentration in a work place below management concentration are needed separately, etc. , There is a disadvantage in terms of work.

Here, pitches which are preferably used will be described in detail. In the coal tar pitch and the coal pitch described above, the content of the mesophase phase (liquid crystal phase) can be controlled by the temperature and time of the infusibilization treatment. If the content of the mesophase is low, a relatively low temperature melts or a liquid state at room temperature is obtained. On the other hand, if the content of the mesophase phase is high, it melts at high temperature and a carbonization yield is high. When pitches are applied to the carbonaceous material (B), it is preferable that the content of the mesophase be low (that is, the carbonization yield be low), for example, 10% or less is preferable. 200 degrees C or less is preferable, and, as for melting | fusing point of pitches, 100 degrees C or less is more preferable. Thereby, the above-mentioned effect is exhibited effectively.

[I-2. Characteristics of first carbon electrode material]
In the first electrode material, the number of bonded oxygen atoms on the surface of the carbon electrode material satisfies 1.0% or more of the total number of carbon atoms on the surface of the carbon electrode material. Hereinafter, the ratio of the number of bonded oxygen atoms to the total number of carbon atoms may be abbreviated as O / C. O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) or X-ray fluorescence analysis.

By using an electrode material having an O / C ratio of 1.0% or more, the electrode reaction rate can be significantly increased, so that low resistance can be obtained. Furthermore, the hydrophilicity is also enhanced by the control of O / C, and the water flow rate (preferably 0.5 mm / sec or more) of the electrode material described later can be secured. On the other hand, when an electrode material having a low oxygen concentration with an O / C of less than 1.0% is used, the electrode reaction rate at the time of discharge decreases, and the electrode reaction activity can not be enhanced. As a result, the resistance increases. Although the details of the reason why the electrode reaction activity (in other words, voltage efficiency) can be enhanced by the use of the electrode material in which many oxygen atoms are bonded to the surface of the electrode material in this way, the oxygen atoms present on the surface are carbonaceous It is considered that the material (B) effectively acts on the affinity between the electrolyte and the electrolyte, transfer of electrons, desorption of complex ions from the carbonaceous material, complex exchange reaction, and the like.

The first electrode material is excellent in hydrophilicity. The hydrophilicity can be confirmed by the water flow rate when dripping a water droplet after dry oxidation treatment of the electrode material. The water flow rate of the first electrode material is preferably 0.5 mm / sec or more. Thus, it can be determined that the catalyst has sufficient affinity to the electrolyte. The water flow rate of the electrode material is preferably as high as possible, more preferably 1 mm / sec or more, still more preferably 5 mm / sec or more, and still more preferably 10 mm / sec or more.

When using the thickness of the spacer 2 sandwiched between the current collector plate 1 and the ion exchange membrane 3 (hereinafter referred to as “spacer thickness”) at 0.3 to 3 mm, the weight per unit area of the first electrode material is 50 to 500 g / m ² is preferable, and 100 to 400 g / m ² is more preferable. By controlling the fabric weight within the above range, damage to the ion exchange membrane 3 can be prevented while securing liquid permeability. In particular, from the viewpoint of lowering resistance in recent years, the thickness of the ion exchange membrane 3 tends to be thin, and a treatment and a method for reducing damage to the ion exchange membrane 3 are extremely important. From the above point of view, it is more preferable to use, as the first electrode material, non-woven fabric or paper whose flat surface has been subjected to flat processing as the base material. As the flattening method, any known method can be applied, for example, a method of applying and drying a slurry on one side of a carbonaceous fiber; and a method of impregnating and drying on a smooth film such as PET.

The thickness of the first electrode material is preferably at least greater than the spacer thickness. For example, when using a carbon fiber having a low density, such as a non-woven fabric, and supporting a graphite particle or binding carbon material used for the first electrode material, a spacer thickness of 1.5 to 6.0 times is preferable. However, if the thickness is too thick, the compressive stress of the sheet-like material may break through the ion exchange membrane 3, so that the compressive stress of the first electrode material is 9.8 N / cm ² or less. preferable. In order to adjust compressive stress and the like in accordance with the weight and thickness of the first electrode material, it is also possible to use the first electrode material in a laminated manner such as two or three layers. Alternatively, a combination with another form of electrode material is also possible.

[I-3. Method of manufacturing first carbon electrode material]
Next, a method of manufacturing the first electrode material will be described. The first electrode material can be manufactured through a carbonization step, a graphitization step, and an oxidation treatment step after attaching a precursor (before carbonization) of a carbonaceous material to a carbonaceous fiber (base material) . In each step, known methods can be optionally applied.

Each step will be described below.

(Attachment of carbonaceous material precursor to carbonaceous fiber)
First, a carbonaceous material precursor is attached to the carbonaceous fiber. A publicly known method can be adopted arbitrarily as the above-mentioned process. For example, the above-mentioned carbonaceous material precursor may be heated and melted, and the carbonaceous fiber may be immersed in the obtained melt and then cooled to room temperature. Alternatively, the above-mentioned carbonaceous material precursor is dispersed in a solvent such as water or alcohol, or partially dissolved or partially dispersed in a solvent such as toluene, and the carbonaceous fiber is immersed in this dispersion and then heated and dried. Methods can be used. Here, excess liquid (pickup amount) of the molten liquid, dispersion liquid and solution in which the carbonaceous fiber is immersed is squeezed out of the product after attachment by passing it through a nip roller provided with a predetermined clearance, or Can be removed by a method such as scraping the surface of the product after attachment with a doctor blade or the like.

Thereafter, it is dried at, for example, 80 to 150 ° C. in an air atmosphere.

(Carbonization process)
The carbonization step is carried out to calcine the product after attachment obtained in the above step. Thereby, the carbonaceous fibers become bound. In the carbonization step, it is preferable to sufficiently remove the decomposition gas at the time of carbonization, and for example, it is preferable to heat at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere). The heating temperature is more preferably 1000 ° C. or higher, still more preferably 1200 ° C. or higher, still more preferably 1300 ° C. or higher, and further preferably 1500 ° C. or lower, even more preferably 1400 ° C. or lower.

As described above, the treatment corresponding to the carbonization step may be performed after the stabilization of the fibers, but the carbonization treatment performed after the stabilization of the fibers may be omitted. That is, the method of producing the first electrode material is roughly classified into the following method 1 and method 2.
Method 1: Flame resistance of fiber → carbonization of fiber → adhesion of carbon material → carbonization → graphitization → oxidation → Method 2: flame resistance of fiber → adhesion of carbonaceous material → carbonization → graphitization → oxidation According to method 1, although the processing cost increases because the carbonization is performed twice, the sheet used as the electrode material is hardly affected by the difference in volume contraction ratio, so the obtained sheet is hardly deformed (warpage generation) It has the advantage of On the other hand, according to the method 2, although the processing cost can be reduced because the carbonization step may be performed once, the sheet obtained is easily deformed due to the difference in volume contraction ratio at the time of carbonization of each material. Which one of the

above methods

1 and 2 is adopted may be appropriately determined in consideration of these.

(Graphitization process)
The graphitization step is a step performed to sufficiently enhance the crystallinity of the carbonaceous material, to improve the electron conductivity, and to improve the oxidation resistance to a sulfuric acid solution or the like in the electrolytic solution. After the carbonization step, heating is preferably performed at a temperature of 1300 ° C. or higher under an inert atmosphere (preferably under a nitrogen atmosphere) and higher than the heating temperature of the carbonization step, and 1500 C. or more is more preferable. In addition, the upper limit thereof is preferably 2000 ° C. or less in consideration of providing the carbonaceous material with high electrolytic solution affinity.
On the other hand, Patent Document 4 mentioned above is different from the second electrode material manufacturing method in that the graphitization process is not performed.

(Oxidation treatment process)
After the above graphitization step, by performing an oxidation treatment step, an oxygen functional group such as a hydroxyl group, a carbonyl group, a quinone group, a lactone group, or a free radical oxide is introduced onto the surface of the electrode material. Become. As a result, the above-mentioned O / C ratio O1% can be achieved. Since these oxygen functional groups greatly contribute to the electrode reaction, sufficiently low resistance can be obtained. Water flow rate can also be increased.

For the oxidation treatment step, various treatment steps such as wet chemical oxidation, electrolytic oxidation and dry oxidation can be applied, but a dry oxidation treatment step is preferable from the viewpoint of processability and production cost. The dry oxidation treatment step means a step of heating (oxidation treatment) in an air atmosphere, for example, at 500 ° C. or more and 900 ° C. or less. The heating temperature is more preferably 600 ° C. or more, and still more preferably 650 ° C. or more, in order to effectively exert the effect of the introduction of the oxygen functional group. Moreover, 800 degrees C or less is more preferable, and 750 degrees C or less is further more preferable.

Furthermore, in the dry oxidation treatment step, it is preferable to adjust the mass yield of the electrode material before and after the oxidation treatment to 90% or more and 96% or less from the viewpoint of maintaining the mechanical strength of the electrode material. This can be adjusted, for example, by a method such as adjusting the processing time and temperature of dry air oxidation appropriately.

[II. Second carbon electrode material according to the present invention]
[II-1. Configuration of Second Carbon Electrode Material]
The present inventors first reviewed the requirements for carbon particles in providing a carbon electrode material with reduced cell resistance at the time of initial charge and discharge. Generally, as particles showing reaction activity in redox flow batteries, carbon blacks such as acetylene black (acetylene black), oil black (furnace black, oil black), gas black (gas black), etc. Those having high reactivity, specific surface area, and low crystallinity are often used. However, they generally have to use a large amount of binder in order to bind to the carbon fiber, and sufficient reaction activity could not be obtained.

Therefore, the present inventors decided to use inexpensive and easily available graphite particles (B) as carbon particles. Graphite particles are very useful because they have good binding properties with carbonaceous materials and can support graphite particles even with small amounts of carbonaceous materials.

Specifically, it was decided to adopt highly crystalline graphite particles that satisfy the following requirement (1).
(1) When the size of the crystallite in the c-axis direction determined by X-ray diffraction is Lc (B), Lc (B) is less than 35 nm If graphite particles satisfying the above requirements are used, carbon as a reaction field The edge surface can be exposed abundantly, and resistance can be reduced.

Furthermore, as a carbonaceous material (C), it is a binding carbonaceous material that bonds both carbonaceous fibers (A) and graphite particles (B), satisfying the following requirements (2) and (3) It is decided to adopt a low-binding carbonaceous material.
(2) When the size of the crystallite in the c-axis direction determined by X-ray diffraction is Lc (C), Lc (C) is less than 10 nm (3) determined by X-ray diffraction in the carbonaceous fiber (A) When the size of the crystallite in the c-axis direction is Lc (A), Lc (C) / Lc (A) is 1.0 or more. Here, both of the carbonaceous fiber (A) and the graphite particle (B) (In other words, the carbonaceous material used for the second electrode material acts as a binder for the carbonaceous fiber and the graphite particles) means that the carbonaceous material and the graphite particles The surface of the graphite particles is exposed while the surface of the carbon material (between the carbonaceous fibers and the graphite particles) is strongly bound and the carbonaceous fibers are covered with the carbonaceous material when viewed as the entire electrode material. It is meant to be configured.
However, it is preferable that the carbonaceous material after binding is not in the form of a film. Here, "does not become a coated state" means that the carbonaceous material (C) does not form a webbed state like a total foot (boxok) or a foot between fibers of the carbonaceous fiber (A). When a film state is formed, the liquid permeability of the electrolytic solution is deteriorated, and the reaction surface area of the graphite particles can not be effectively used.

In order to obtain such a bonding state, it is preferable to increase the content ratio of the carbonaceous material to the total amount of the carbonaceous fiber, the graphite particles and the carbonaceous material, and in the second electrode material, for example, 20% or more I assume. In this respect, the carbonaceous material in the second electrode material is different from the carbonaceous material described in Patent Document 4 described above. In Patent Document 4, based on the idea that it is only necessary to fix (adhere) only the portion where the carbonaceous fiber and the carbon fine particle originally contacted, the carbonaceous material to be used exhibits a function as a partial adhesive. It is because there is only recognition that it is good. Therefore, in the example of Patent Document 4, the content of the carbonaceous material is at most 14.4%.

If such a binding and low crystalline carbonaceous material is used, it becomes easy to introduce an oxygen functional group, and high electrolytic solution affinity is imparted to the carbonaceous material that binds the graphite particles. In addition, since the carbonaceous material strongly bonds between the carbonaceous fibers through the graphite particles, an efficient conductive path can be formed, and the above-described resistance lowering effect by the addition of the graphite particles can be more effectively exhibited. There was found.

Furthermore, the second carbon electrode material satisfies the following requirement (4).
(4) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material Thereby, oxygen atoms can be introduced to the edge surface of carbon and defect structure. As a result, on the surface of the electrode material, the introduced oxygen atom is generated as a reactive group such as a carbonyl group, a quinone group, a lactone group, or a free radical oxide, and these reactive groups greatly contribute to the electrode reaction. And a sufficiently low resistance can be obtained.

Since the second electrode material is configured as described above, the reaction activity is enhanced, and a low resistance and inexpensive electrode can be obtained.

As described above, the second electrode material 5 is an electrode material using the carbonaceous fiber (A) as a base material and supporting the graphite particles (B) with the low crystalline carbonaceous material (C), and Satisfy the requirements of (4) to (4). The details of each requirement are as follows.

[Carbonaceous fiber (A)]
The carbonaceous fiber used for the second electrode material is a fiber obtained by subjecting an organic fiber precursor to a carbonization treatment (details will be described later), and 90% or more by mass ratio is composed of carbon Means fiber (JIS L 0204-2). Precursors of organic fibers as raw materials of carbonaceous fibers include acrylic fibers such as polyacrylonitrile; phenol fibers; PBO fibers such as polyparaphenylene benzobisoxazole (PBO); aromatic polyamide fibers; isotropic pitch fibers; Pitch fibers such as anisotropic pitch fibers and mesophase pitch; cellulose fibers; etc. can be used. Among them, from the viewpoint of being excellent in strength and elastic modulus, acrylic fiber, phenol fiber, cellulose fiber, isotropic pitch fiber and anisotropic pitch fiber are preferable as the organic fiber precursor, and acrylic fiber is more preferable. The acrylic fiber is not particularly limited as long as it contains acrylonitrile as a main component, but the content of acrylonitrile in the raw material monomer forming the acrylic fiber is preferably 95% by mass or more, and 98% by mass or more It is more preferable that

The average fiber diameter of the carbonaceous fiber is preferably 0.5 to 40 μm. If the average fiber diameter is smaller than 0.5 μm, the liquid permeability will deteriorate. On the other hand, when the average fiber diameter is larger than 40 μm, the reaction surface area of the fiber portion is reduced, and the cell resistance is increased. In consideration of the balance between the liquid permeability and the reaction surface area, it is more preferably 3 to 20 μm.

In the second electrode material, it is preferable to use the above-mentioned carbonaceous fiber structure as a base material, whereby the strength is improved and the handling and the processability are facilitated. As the above-mentioned structure, specifically, a spun yarn, a filament collected yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric or carbon described in JP-A-63-200467 etc., which is a sheet-like material comprising carbonaceous fibers The paper etc. which consist of fibers can be mentioned. Among these, non-woven fabric made of carbonaceous fiber, knitted fabric, woven fabric, special woven fabric, and paper made of carbon fiber are more preferable from the viewpoints of handling, processability, manufacturability and the like.

When the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A) is Lc (A), Lc (A) is preferably 1 to 6 nm. As a result, appropriate electron conductivity is exhibited, oxidation resistance to a sulfuric acid solvent or the like is exhibited, and functions such as easy provision of an oxygen functional group are effectively exhibited. The measurement method of Lc (A) will be described in detail in the section of Examples described later.

[Graphite particles (B)]
Graphite particles in the second electrode material are useful for abundantly exposing the carbon edge surface which is the reaction site to realize low resistance. According to the study results of the present inventors, when the size of the crystallite in the c-axis direction determined by X-ray diffraction is Lc (B), the value of Lc (B) is that of the carbon edge surface of the graphite particle. It was found that the low resistance can be realized because the carbon edge surface can be sufficiently exposed and the reactivity is improved when Lc (B) is less than 35 nm, which correlates with the degree of exposure. 33 nm or less is preferable and 30 nm or less of Lc (B) is more preferable. The lower limit of the above value is not particularly limited from the above point of view, but in consideration of securing of conductivity and oxidation resistance, it is preferably about 15 nm or more. The measurement method of Lc (B) will be described in detail in the section of Examples described later.

Graphite particles are generally classified into natural graphite and artificial graphite. Examples of natural graphite include scale-like graphite, scale-like graphite, earth-like graphite, spherical graphite, exfoliated graphite and the like, and examples of artificial graphite include exfoliated graphite, graphite oxide and the like. In the second electrode material, either natural graphite or artificial graphite can be used. Among them, graphite oxide, scale-like graphite, scale-like graphite, earth-like graphite, exfoliated graphite and exfoliated graphite are used as reaction sites. It is preferable from having a carbon edge surface of Among them, scale-like graphite, exfoliated graphite and expanded graphite are more preferable because not only the exposure of the carbon edge surface is very large, low resistance can be obtained, but also low cost and abundant resources are available. These flaky graphite, exfoliated graphite and exfoliated graphite may be added singly or in combination of two or more. Here, scale-like graphite means flake-like appearance. Scale-like graphite is different from scale-like graphite (which is massive in shape and may be called massive graphite).

The graphite particles (B) used for the second electrode material is 14.5% by mass ratio to the total amount of the above-mentioned carbonaceous fiber (A), graphite particles (B) and carbonaceous material (C) described later It is preferable that the content is more than 20%, more preferably 20% or more, and still more preferably 25% or more. As a result, the graphite particles become bound with the carbonaceous material, and the characteristics of the graphite particles (B) can be sufficiently exhibited. However, when the amount of the graphite particles (B) is excessive, the binding property to the carbonaceous material becomes insufficient, and the number of graphite particles involved in the reaction decreases. In addition, since the hydraulic pressure loss also increases, the desired low resistance can not be obtained. Therefore, the upper limit thereof is preferably approximately 60% or less, more preferably 50% or less. In addition, content of the carbonaceous fiber (A) used for calculation of said content is content of the said structure, when using structures, such as a nonwoven fabric, as a base material.

In the second electrode material, the mass ratio of the carbonaceous material (C) described later to the graphite particles (B) is preferably 0.2 or more and 3.0 or less, and is 0.3 or more and 2.5 or less. It is more preferable that If the above ratio is less than 0.2, the detachment of the graphite particles is increased, the graphite particles are not sufficiently bonded to the carbonaceous material, and the graphite particles involved in the reaction are reduced. On the other hand, when the above ratio exceeds 3.0, the carbon edge surface of the graphite particles as the reaction site is covered with the carbonaceous material, and the desired low resistance can not be obtained.

The particle diameter of the graphite particles (B) used for the second electrode material is not particularly limited, but in consideration of the specific surface area of the graphite and the like, it is preferably in the range of approximately 0.1 to 15 μm. Here, the “particle size” means an average particle size (D50) at a median 50% diameter in a particle size distribution obtained by a dynamic light scattering method or the like. The graphite particles may be commercially available products, in which case the particle sizes described in the catalog can be adopted.

Graphite particles used in the second electrode member (B), BET specific surface area determined from nitrogen adsorption amount is 20 m ² / g greater are preferred, more preferably at least 21m ² / g, more preferably more than 30 m ² / g . When the BET specific surface area is 20 m ² / g or less, the exposure of the edge surface of the graphite particles (B) is reduced and the contact area with the electrolytic solution is also reduced, so that the desired low resistance can not be obtained. The upper limit is not particularly limited from the above viewpoint, but in consideration of oxidation resistance, binding property with a binder, etc., it is preferably about 300 m ² / g or less. Here, the "BET specific surface area determined from the nitrogen adsorption amount" refers to a specific surface area calculated from the amount of gas molecules adsorbed by adsorbing gas molecules to solid particles.

[Carbonaceous material (C)]
The carbonaceous material used for the second electrode material is added as a binding agent (binder) for strongly binding the carbon fiber which can not be bound originally and the graphite particles. In the second electrode material, Lc (C) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (C) as defined in (2) above. C) satisfies less than 10 nm and, as defined in (3) above, the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A) is Lc (A) and When it does, Lc (C) / Lc (A) needs to satisfy 1.0 or more.
By using such a low crystalline binding carbonaceous material, it becomes easy to introduce an oxygen functional group, and high electrolytic solution affinity is imparted to the carbonaceous material binding the graphite particles. As a result, desired resistance reduction can be obtained. In addition, since the carbonaceous material strongly bonds between the carbonaceous fibers through the graphite particles, an efficient conductive path can be formed, and the above-described resistance lowering effect by the addition of the graphite particles can be more effectively exhibited. There was found.

From the viewpoint of reducing the resistance, Lc (C) is preferably 8 nm or less, and more preferably 5 nm or less. When Lc (C) is less than 2 nm, the conductivity of the carbonaceous material (C) can not be sufficiently exhibited, and it becomes difficult to obtain a desired resistance reduction. Therefore, 2 nm or more of Lc (C) is preferable, and 3 nm The above is more preferable.

As described above, the ratio of Lc (C) / Lc (A) is 1.0 or more. That is, in the second electrode material, since Lc (C) is larger than Lc (A), the conductivity of the carbonaceous material (C) is high, and the electrode material becomes lower resistance. The ratio is preferably 2 or more, more preferably 3 or more. However, the upper limit is preferably 5 or less, in consideration of the balance between the above-mentioned securing of conductivity and the affinity to the electrolyte.

The carbonaceous material (C) used for the second electrode material is 14.5% or more by mass ratio to the total amount of the above-mentioned carbonaceous fiber (A), graphite particles (B) and carbonaceous material (C) It is preferable to be contained, 20% or more is more preferable, and 30% or more is further preferable. Thus, by increasing the content of the carbonaceous material, both the carbonaceous fiber and the graphite particles can be sufficiently bonded, and the binding action by the addition of the carbonaceous material is effectively exhibited. The upper limit thereof is preferably approximately 60% or less in consideration of loss of hydraulic pressure and the like. More preferably, it is 50% or less.

The type of carbonaceous material (C) used for the second electrode material may be any type as long as it can bind the carbonaceous fibers (A) and the graphite particles (B). Specifically, the second electrode It is not particularly limited as long as it exhibits binding property at the time of carbonization at the time of material preparation. Such examples include pitches such as coal tar pitch and coal pitch; phenol resin, benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde Resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins, polyacrylonitrile, etc .; furfuryl alcohol; rubbers such as acrylonitrile-butadiene rubber and the like. A commercial item may be used for these.

Among these, pitches such as coal tar pitch and coal-based pitch which are easily crystalline are preferable because the target carbonaceous material (C) can be obtained at a low firing temperature. In addition, a phenolic resin is also preferably used because the degree of increase and decrease in crystallinity is small depending on the calcination temperature and the crystallinity can be easily controlled. In addition, polyacrylonitrile resin is also preferably used because the target carbonaceous material (C) can be obtained at a low firing temperature. Particularly preferred are pitches.
According to a preferred embodiment of the second electrode material, since no phenol resin is used, there is an advantage that no harmful effect (formaldehyde generation and formaldehyde odor at room temperature) occurs with the phenol resin and no odor is generated at normal temperature. On the other hand, in the patent document 4 mentioned above, since phenol resin is used as an adhesive agent, in addition to the above-mentioned bad effect, facilities for controlling formaldehyde concentration in a work place below management concentration are needed separately, etc. , There is a disadvantage in terms of work.

Here, pitches which are particularly preferably used will be described in detail. In the coal tar pitch and the coal pitch described above, the content of the mesophase phase (liquid crystal phase) can be controlled by the temperature and time of the infusibilization treatment. If the content of the mesophase is small, a relatively low temperature melts or a liquid state at room temperature is obtained. On the other hand, if the content of the mesophase phase is high, it melts at high temperature and a carbonization yield is high. When pitches are applied to the carbonaceous material (C), the content of the mesophase phase is preferably high (ie, the carbonization ratio is high), for example, 30% or more is preferable, and 50% or more is more preferable. Thereby, the fluidity at the time of melting can be suppressed, and the carbonaceous fibers can be bonded via the graphite particles without excessively covering the surface of the graphite particles. The upper limit thereof is preferably, for example, 90% or less in consideration of expression of binding property and the like.

From the same viewpoint as above, the melting point of the pitch is preferably 100 ° C. or more, and more preferably 200 ° C. or more. Thus, the above-mentioned effects can be obtained, and in addition, the odor at the time of attachment processing can be suppressed, which is preferable also from the viewpoint of processability. The upper limit thereof is preferably, for example, 350 ° C. or less in consideration of expression of binding property and the like.

[II-2. Characteristics of second carbon electrode material]
In the second electrode material, the number of bonded oxygen atoms on the surface of the carbon electrode material satisfies 1% or more of the total number of carbon atoms on the surface of the carbon electrode material. Hereinafter, the ratio of the number of bonded oxygen atoms to the total number of carbon atoms may be abbreviated as O / C. O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) or X-ray fluorescence analysis.

By using an electrode material having an O / C ratio of 1% or more, the electrode reaction rate can be significantly increased, so that low resistance can be obtained. Furthermore, the hydrophilicity is also enhanced by the control of O / C, and the water flow rate (preferably 0.5 mm / sec or more) of the electrode material described later can be secured. On the other hand, when an electrode material having a low oxygen concentration with an O / C of less than 1% is used, the electrode reaction rate at the time of discharge decreases, and the electrode reaction activity can not be enhanced. As a result, the resistance increases. Although the details of the reason why the electrode reaction activity (in other words, voltage efficiency) can be enhanced by the use of the electrode material in which many oxygen atoms are bonded to the surface of the electrode material in this way, the oxygen atoms present on the surface are carbonaceous It is considered that the material (C) works effectively on the affinity between the electrolyte and the electrolyte, transfer of electrons, desorption of complex ions from the carbonaceous material, complex exchange reaction, and the like.

The second electrode material is excellent in hydrophilicity. The hydrophilicity can be confirmed by the water flow rate when dripping a water droplet after dry oxidation treatment of the electrode material. The water flow rate of the second electrode material is preferably 0.5 mm / sec or more. Thus, it can be determined that the catalyst has sufficient affinity to the electrolyte. The water flow rate of the electrode material is preferably as high as possible, more preferably 1 mm / sec or more, still more preferably 5 mm / sec or more, and still more preferably 10 mm / sec or more.

When using the thickness of the spacer 2 sandwiched between the current collector plate 1 and the ion exchange membrane 3 (hereinafter referred to as “spacer thickness”) at 0.3 to 3 mm, the weight per unit area of the second electrode material is 50 to 500 g / m ² is preferable, and 100 to 400 g / m ² is more preferable. By controlling the fabric weight within the above range, damage to the ion exchange membrane 3 can be prevented while securing liquid permeability. In particular, from the viewpoint of lowering resistance in recent years, the thickness of the ion exchange membrane 3 tends to be thin, and a treatment and a method for reducing damage to the ion exchange membrane 3 are extremely important. From the above viewpoint, it is more preferable to use, as the second electrode material, non-woven fabric or paper whose flat surface is subjected to flat processing as the base material. As the flattening method, any known method can be applied, for example, a method of applying and drying a slurry on one side of a carbonaceous fiber; and a method of impregnating and drying on a smooth film such as PET.

The thickness of the second electrode material is preferably at least greater than the spacer thickness. For example, when using a carbon fiber having a low density, such as a non-woven fabric, and supporting a graphite particle or binding carbon material used for the second electrode material, a spacer thickness of 1.5- 6.0 times is preferable. However, if the thickness is too large, the compressive stress of the sheet-like material may break through the ion exchange membrane 3, so that the compressive stress of the second electrode material is 9.8 N / cm ² or less. preferable. In order to adjust the compressive stress and the like in accordance with the coating weight and thickness of the second electrode material, it is also possible to use the second electrode material in a laminated manner such as two layers or three layers. Alternatively, a combination with another form of electrode material is also possible.

The second electrode material, BET specific surface area determined from nitrogen adsorption amount is preferably 8m ² / g greater, 10 m ² / g or more is more preferable. When the BET specific surface area is 8 m ² / g or less, the desired low resistance can not be obtained due to the decrease in the exposure of the edge surface of the graphite particles (B) and the decrease in the contact area with the electrolyte. The upper limit of the BET specific surface area is not particularly limited from the above viewpoint, but in consideration of oxidation resistance and the like, it is preferably about 150 m ² / g or less.

[II-3. Second method for producing carbon electrode material]
Next, a method of manufacturing the second electrode material will be described. The second electrode material is produced by attaching a graphite particle and a precursor of a carbonaceous material (before carbonization) to a carbonaceous fiber (base material), and then passing through a carbonization step, a graphitization step, and an oxidation treatment step can do. In each step, known methods can be optionally applied.

Each step will be described below.

(Attachment of Graphite Particles and Carbonaceous Material Precursor to Carbonaceous Fiber)
First, a carbonaceous particle is impregnated with a graphite particle and a precursor of a carbonaceous material. In order to attach the precursor of the graphite particle and the carbonaceous material to the carbonaceous fiber, any known method can be adopted. For example, the above-mentioned carbonaceous material precursor may be heated and melted, graphite particles may be dispersed in the obtained melt, the carbonaceous fiber may be immersed in the melt dispersion, and then cooled to room temperature. Alternatively, as shown in the examples described later, the above-mentioned carbonaceous material precursor and graphite particles are added to a solvent such as water or alcohol to which a binder (temporary adhesive) which disappears at the time of carbonization such as polyvinyl alcohol is added. After dispersing and immersing the carbonaceous fiber in the dispersion, a method of heating and drying can be used. Here, excess liquid among the above-mentioned melt dispersion liquid and dispersion liquid in which the carbonaceous fiber is immersed is squeezed out excess dispersion liquid when immersed in the dispersion liquid by passing it through a nip roller provided with a predetermined clearance, Alternatively, the surface of the excess dispersion when immersed in the dispersion with a doctor blade or the like can be removed by a method such as scraping.

Thereafter, it is dried at, for example, 80 to 150 ° C. in an air atmosphere.

(Carbonization process)
The carbonization step is carried out to calcine the product after attachment obtained in the above step. As a result, the carbonaceous fibers are bound via the graphite particles. In the carbonization step, it is preferable to sufficiently remove the decomposition gas at the time of carbonization, and for example, it is preferable to heat at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere). The heating temperature is more preferably 1000 ° C. or higher, still more preferably 1200 ° C. or higher, still more preferably 1300 ° C. or higher, and further preferably 1500 ° C. or lower, even more preferably 1400 ° C. or lower.

As described above, the treatment corresponding to the carbonization step may be performed after the stabilization of the fibers, but the carbonization treatment performed after the stabilization of the fibers may be omitted. That is, the method of producing the second electrode material is roughly classified into the following method 1 and method 2.
Method 1: Flame resistance of fiber → carbonization of fiber → adhesion of graphite particles and carbonaceous material → carbonization → graphitization → oxidation → Method 2: flame resistance of fiber → adhesion of graphite particles and carbonaceous material → carbonization → Graphitization → oxidation According to the above method 1, although the processing cost increases because carbonization is performed twice, the sheet used as an electrode material is hardly affected by the difference in volume contraction ratio, so the obtained sheet is deformed There is an advantage that it is difficult to (warp). On the other hand, according to the method 2, although the processing cost can be reduced because the carbonization step may be performed once, the sheet obtained is easily deformed due to the difference in volume contraction ratio at the time of carbonization of each material. Which one of the

above methods

1 and 2 is adopted may be appropriately determined in consideration of these.

(Graphitization process)
The graphitization step is a step performed to sufficiently enhance the crystallinity of the carbonaceous material, to improve the electron conductivity, and to improve the oxidation resistance to a sulfuric acid solution or the like in the electrolytic solution. After the carbonization step, heating is preferably performed at a temperature of 1300 ° C. or higher in an inert atmosphere (preferably under a nitrogen atmosphere) and higher than the heating temperature in the carbonization step, 1500 ° C. or higher Is more preferred. In addition, the upper limit thereof is preferably 2000 ° C. or less in consideration of providing the carbonaceous material with high electrolytic solution affinity.
On the other hand, Patent Document 4 mentioned above is different from the second electrode material manufacturing method in that the graphitization process is not performed.

[III. Third carbon electrode material according to the present invention]
[III-1. Configuration of Third Carbon Electrode Material]
The present inventors conducted studies using carbon particles other than graphite particles in providing a carbon electrode material with reduced cell resistance at the time of initial charge and discharge. As a result, it was found that when carbon particles having a small particle size and low crystallinity are used, the reaction surface area is increased, the oxygen functional group is easily provided, the reaction activity is increased, and low resistance is obtained. .

Specifically, in the third carbon electrode material, carbon particles satisfying the following requirements (1) and (2) were adopted as carbon particles other than graphite particles.
(1) The particle size of carbon particles (B) other than graphite particles is 1 μm or less (2) The size of the crystallite in the c-axis direction determined by X-ray diffraction in carbon particles (B) other than graphite particles In the case of B), Lc (B) is 10 nm or less When the carbon particles having a small particle diameter as described in (1) above are used, the reaction surface area becomes large, and the resistance can be reduced. Further, as in the case of the above (2), since the low crystalline carbon particle is easily introduced with an oxygen functional group, the reaction activity is improved, so that the resistance can be further reduced.

Furthermore, in the third carbon electrode material, it is a binding carbonaceous material that binds both the carbonaceous fiber (A) and carbon particles (B) other than graphite particles as the carbonaceous material (C), It decided to use highly crystalline carbonaceous material with respect to carbonaceous fiber (A) which satisfies the requirement of (3) within the range of following (4).
(3) Lc (A) and Lc (C) in the carbonaceous fiber (A) and the carbonaceous material (C), where Lc (A) and Lc (C) are the sizes of crystallites in the c-axis direction, respectively. C) / Lc (A) is 1.0 to 5
(4) The mass content of the carbonaceous material (C) relative to the total amount of the carbonaceous fiber (A), the carbon particles (B) other than the graphite particles, and the carbonaceous material (C) is 14.5% or more “Bonded both carbon fiber (A) and carbon particles (B) other than graphite particles” (in other words, the carbonaceous material used for the third carbon electrode material is other than carbonaceous fibers and graphite particles With the carbon material, the surface and inside of carbon particles other than carbon fibers and graphite particles (including carbon particles among carbon fibers, and carbon particles other than graphite particles) are strongly affected by the carbonaceous material. It means that it is bound and it is constituted so that the surface of carbon particles other than a graphite particle may be exposed, covering a carbonaceous fiber with the said carbonaceous material, when it sees as the whole electrode material.
However, it is preferable that the carbonaceous material after binding is not in the form of a film. Here, "does not become a coated state" means that the carbonaceous material (C) does not form a webbed state like a total foot (boxok) or a foot between fibers of the carbonaceous fiber (A). When the film state is formed, the liquid permeability of the electrolytic solution is deteriorated, and the reaction surface area of the carbon particles can not be effectively used.

Here, the difference from Patent Document 4 described above will be described. Since the carbonaceous material strongly bonds between carbonaceous fibers through carbon particles other than graphite particles, it forms an efficient conductive path between the carbon particles and the carbonaceous fiber. It is necessary for the formation of the conductive path to increase the content ratio of the carbonaceous material to the total amount of the carbon fiber and the carbonaceous material other than the carbonaceous fiber and the graphite particles, and therefore the above content in the third carbon electrode material Is 14.5% or more. On the other hand, in the example of the patent document 4 mentioned above, the content rate of a carbonaceous material is 14.4% at most, and there are less than a 3rd carbon electrode material, and both differ in this point. In the first place, in Patent Document 4, based on the idea that it is only necessary to fix (adhere) only the portion where the carbonaceous fiber and the carbon fine particle originally contacted, the carbonaceous material to be used exhibits a function as a partial adhesive. It is because there is only recognition that it should be done. Furthermore, Patent Document 4 does not specifically specify the crystallinity of the carbonaceous material to be bound, but in order to form an excellent conductive path, crystallinity with respect to carbonaceous fibers like the third electrode material is disclosed. The use of a high carbonaceous material increases the electron conductivity, which enables more efficient electron transfer.

Furthermore, the third carbon electrode material satisfies the following requirement (5).
(5) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material Thereby, oxygen atoms can be introduced to the edge surface of carbon and defect structure. As a result, on the surface of the electrode material, the introduced oxygen atom is generated as a reactive group such as a carbonyl group, a quinone group, a lactone group, or a free radical oxide, and these reactive groups greatly contribute to the electrode reaction. And a sufficiently low resistance can be obtained.

Since the third electrode material is configured as described above, the reaction activity is enhanced, and a low resistance and inexpensive electrode can be obtained.

As described above, the third electrode member 5 uses the carbonaceous fiber (A) as a base material, and supports carbon particles (B) other than graphite particles with a highly crystalline carbonaceous material with respect to the carbonaceous fiber (A). Electrode material, and satisfies the above requirements (1) to (5). The details of each requirement are as follows.

[Carbonaceous fiber (A)]
The carbonaceous fiber used for the third electrode material is a fiber obtained by subjecting an organic fiber precursor to a carbonization treatment (details will be described later), and 90% or more by mass ratio is composed of carbon Means fiber (JIS L 0204-2). Precursors of organic fibers as raw materials of carbonaceous fibers include acrylic fibers such as polyacrylonitrile; phenol fibers; PBO fibers such as polyparaphenylene benzobisoxazole (PBO); aromatic polyamide fibers; isotropic pitch fibers; Pitch fibers such as anisotropic pitch fibers and mesophase pitch; cellulose fibers; etc. can be used. Among them, from the viewpoint of being excellent in strength and elastic modulus, acrylic fiber, phenol fiber, cellulose fiber, isotropic pitch fiber and anisotropic pitch fiber are preferable as the organic fiber precursor, and acrylic fiber is more preferable. The acrylic fiber is not particularly limited as long as it contains acrylonitrile as a main component, but the content of acrylonitrile in the raw material monomer forming the acrylic fiber is preferably 95% by mass or more, and 98% by mass or more It is more preferable that

In the third electrode material, it is preferable to use the structure of the above-mentioned carbonaceous fiber as a base material, whereby the strength is improved and the handling and the processability become easy. As the above-mentioned structure, specifically, a spun yarn, a filament collected yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric or carbon described in JP-A-63-200467 etc., which is a sheet-like material comprising carbonaceous fibers The paper etc. which consist of fibers can be mentioned. Among these, non-woven fabric made of carbonaceous fiber, knitted fabric, woven fabric, special woven fabric, and paper made of carbon fiber are more preferable from the viewpoints of handling, processability, manufacturability and the like.

The third electrode material is a carbonaceous material (A) and a carbonaceous material (C) as described in (3) above, which will be described in detail in the section of carbonaceous material (C) described later. Lc (C) / Lc (A) satisfies 1.0 to 5 when Lc (A) and Lc (C) are the sizes of crystallites in the c-axis direction determined by X-ray diffraction, respectively. . Therefore, Lc (A) in the carbonaceous fiber (A) is not particularly limited as long as the third electrode material satisfies the above (3), but Lc (A) is preferably 1 to 6 nm. As a result, functions such as appropriate electron conductivity, oxidation resistance to a sulfuric acid solvent, and easy provision of an oxygen functional group are effectively exhibited. The measurement methods of Lc (A) and Lc (C) will be described in detail in the section of Examples described later.

[Carbon particles other than graphite particles (B)]
In the third electrode material, “carbon particles other than graphite particles” is useful for increasing the reaction surface area to realize low resistance. As the third electrode material, materials satisfying the above (1) and (2) were used to reduce resistance.

First, the particle diameter of the "carbon particles other than graphite particles" used for the third electrode material is 1 μm or less, preferably 0.5 μm or less as defined in the above (1). When the particle size exceeds 1 μm, the reaction surface area decreases and the resistance increases. Here, the “particle size” means an average particle size (D50) at a median 50% diameter in a particle size distribution obtained by a dynamic light scattering method or the like. Commercially available carbon particles other than graphite particles may be used, and in that case, the particle sizes described in the catalog can be adopted. The preferred lower limit is 0.005 μm or more.

20 m ² / g or more is preferable, and 30 m ² / g or more is more preferable, and the BET specific surface area calculated from the nitrogen adsorption amount of “carbon particles other than graphite particles” used for the third electrode material is 40 m ² / g or more Is more preferred. When the BET specific surface area is less than 20 m ² / g, the edge exposure of the carbon particles is reduced and the contact area with the electrolytic solution is also reduced, so that the desired low resistance can not be obtained. Incidentally, when the upper limit is not particularly limited from the viewpoint, the surface area is large bulky viscosity tends to increase the dispersion liquid with particles, considering that the workability of the sheet to such deteriorates generally, 2000 m ² / g It is preferable that it is the following. Here, the "BET specific surface area determined from the amount of adsorbed nitrogen" means a specific surface area calculated from the amount of gas molecules adsorbed by causing nitrogen molecules to be adsorbed to solid particles.

Furthermore, Lc (B) in "carbon particles other than graphite particles" used for the third electrode material is 10 nm or less as defined in the above (2). When highly crystalline carbon particles with Lc (B) exceeding 10 nm are used, it is difficult to introduce an oxygen functional group, so the affinity of the carbon particles in the vicinity of the aqueous electrolyte decreases, reaction activity decreases, and resistance increases Do. Preferably it is 6 nm or less. The lower limit is not particularly limited from the above viewpoint, but in consideration of the oxidation resistance to the electrolytic solution, the thickness is preferably about 0.5 nm or more. The measurement methods of Lc (B) and La (B) will be described in detail in the section of Examples described later.

Examples of "carbon particles other than graphite particles" used for the third electrode material include acetylene black (acetylene soot), oil black (furness black, oil soot), ketjen black, gas black (gas soot) And carbon blacks having high reactivity, specific surface area, and low crystallinity. In addition to the above, carbon nanotubes (CNTs, carbon nanotubes), carbon nanofibers, carbon aerogels, mesoporous carbon, graphene, graphene oxide, N-doped CNT, boron-doped CNT, fullerene and the like can be mentioned. Carbon blacks are preferably used from the viewpoint of raw material cost and the like.

The content of “carbon particles other than graphite particles” used for the third electrode material is the total of the above-mentioned carbonaceous fibers (A), carbon particles other than graphite particles (B), and a carbonaceous material (C) described later The mass ratio to the amount is preferably 5% or more, and more preferably 10% or more. As a result, carbon particles other than graphite particles are bound by the carbonaceous material, and the resistance is reduced. However, if the amount of carbon particles (B) other than the graphite particles is excessive, the binding ability of the carbonaceous material is insufficient and the particles fall off, and the liquid permeability is deteriorated due to the improvement of the packing density, The desired low resistance can not be obtained. Therefore, the upper limit is preferably about 90% or less. In addition, content of the carbonaceous fiber (A) used for calculation of said content is content of the said structure, when using structures, such as a nonwoven fabric, as a base material.

In the third electrode material, the mass ratio of the carbonaceous material (C) described later to carbon particles (B) other than graphite particles is preferably 0.2 or more and 10 or less, and 0.3 or more and 7 or less. It is more preferable that When the above ratio is less than 0.2, the carbon particles other than the graphite particles are often detached, and the carbon particles are not sufficiently bonded to the carbonaceous material. On the other hand, when the above ratio exceeds 10, the carbon edge surface of the carbon particle which is the reaction site is coated, and the desired low resistance can not be obtained.

[Carbonaceous material (C)]
In the third electrode material, the carbonaceous material is originally added as a binder (binder) for strongly binding the non-binding carbonaceous fiber and the carbon particles other than the graphite particles. . In the third electrode material, the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A) and the carbonaceous material (C) as defined in (3) above is Lc (each In the case of A) and Lc (C), Lc (C) / Lc (A) needs to satisfy 1.0 to 5.
Thus, the use of the highly crystalline binding carbonaceous material with respect to the carbonaceous fiber (A) lowers the electron conduction resistance between the carbon particles (B) and the carbonaceous fiber (A), The electron conduction paths of the carbon particles (B) and the carbonaceous fibers (A) become smooth. In addition, since the carbonaceous material strongly bonds between carbonaceous fibers through carbon particles other than graphite particles, an efficient conductive path can be formed, and the resistance lowering action by the addition of carbon particles other than the above-described graphite particles. Was found to be more effective.

When the ratio of Lc (C) / Lc (A) is less than 1.0, the above effect is not effectively exhibited. 1.5 or more are preferable and 3.0 or more of said ratio are more preferable. On the other hand, when the above ratio exceeds 5, it becomes difficult to impart an oxygen functional group to the carbonaceous material portion. The ratio is preferably 4.5 or less, more preferably 4.0 or less.

In the third electrode material, the range of Lc (C) is not particularly limited as long as the ratio of Lc (C) / Lc (A) satisfies the above range, but from the viewpoint of further lowering resistance, Lc (C) 10 nm or less is preferable and 7.5 nm or less is more preferable. The lower limit of Lc (C) is not particularly limited from the above viewpoint, but in consideration of electron conductivity and the like, approximately 3 nm or more is preferable.

The content of the carbonaceous material (C) used for the third electrode material is the mass ratio to the total amount of the carbon fibers (B) other than the above-mentioned carbonaceous fibers (A) and graphite particles, and the carbonaceous material (C) 14.5% or more, preferably 15% or more, and more preferably 17% or more. Thus, by increasing the content of the carbonaceous material, both the carbonaceous fiber and the carbon particles other than the graphite particles can be sufficiently bonded, and the binding effect by the addition of the carbonaceous material is effectively exhibited. The upper limit thereof is preferably about 90% or less in consideration of the liquid permeability of the electrolytic solution and the like.

The type of carbonaceous material (C) used for the third electrode material may be any type as long as it can bind carbon particles other than the carbonaceous fibers (A) and the graphite particles (B). It is not particularly limited as long as it exhibits binding properties at the time of carbonization at the time of preparation of the third electrode material. Such examples include pitches such as coal tar pitch and coal pitch; phenol resin, benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde Resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins, polyacrylonitrile, etc .; furfuryl alcohol; rubbers such as acrylonitrile-butadiene rubber and the like. A commercial item may be used for these.

Among these, pitches such as coal tar pitch and coal-based pitch which are easily crystalline are preferable because the target carbonaceous material (C) can be obtained at a low firing temperature. In addition, a phenolic resin is also preferably used because the degree of increase and decrease in crystallinity is small depending on the calcination temperature and the crystallinity can be easily controlled. In addition, polyacrylonitrile resin is also preferably used because the target carbonaceous material (C) can be obtained by raising the firing temperature. Particularly preferred are pitches.
According to a preferred embodiment of the third electrode material, since no phenol resin is used, there is an advantage that no harmful effect (formaldehyde generation and formaldehyde odor at room temperature) occurs with the phenol resin and no odor is generated at normal temperature. On the other hand, in the patent document 4 mentioned above, since phenol resin is used as an adhesive agent, in addition to the above-mentioned bad effect, facilities for controlling formaldehyde concentration in a work place below management concentration are needed separately, etc. , There is a disadvantage in terms of work.

Here, pitches which are particularly preferably used will be described in detail. In the coal tar pitch and the coal pitch described above, the content of the mesophase phase (liquid crystal phase) can be controlled by the temperature and time of the infusibilization treatment. If the content of the mesophase is small, a relatively low temperature melts or a liquid state at room temperature is obtained. On the other hand, if the content of the mesophase phase is high, it melts at high temperature and a carbonization yield is high. When pitches are applied to the carbonaceous material (C), the content of the mesophase phase is preferably high (ie, the carbonization ratio is high), for example, 30% or more is preferable, and 50% or more is more preferable. Thereby, the fluidity | liquidity at the time of a fusion | melting can be suppressed, and between the carbon fibers can bind | bond together via the said carbon particle, without coat | covering the surface of carbon particles other than a graphite particle excessively. The upper limit thereof is preferably, for example, 90% or less in consideration of expression of binding property and the like.

[III-2. Characteristics of Third Carbon Electrode Material]
In the third electrode material, the number of bonded oxygen atoms on the surface of the carbon electrode material satisfies 1% or more of the total number of carbon atoms on the surface of the carbon electrode material. Hereinafter, the ratio of the number of bonded oxygen atoms to the total number of carbon atoms may be abbreviated as O / C. O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) or X-ray fluorescence analysis.

The third electrode material is excellent in hydrophilicity. The hydrophilicity can be confirmed by the water flow rate when dripping a water droplet after dry oxidation treatment of the electrode material. The water flow rate of the third electrode material is preferably 0.5 mm / sec or more. Thus, it can be determined that the catalyst has sufficient affinity to the electrolyte. The water flow rate of the electrode material is preferably as high as possible, more preferably 1 mm / sec or more, still more preferably 5 mm / sec or more, and still more preferably 10 mm / sec or more.

When using the thickness of the spacer 2 sandwiched between the current collector plate 1 and the ion exchange membrane 3 (hereinafter referred to as “spacer thickness”) at 0.3 to 3 mm, the basis weight of the third electrode material is 50 to 500 g / m ² is preferable, and 100 to 400 g / m ² is more preferable. By controlling the fabric weight within the above range, damage to the ion exchange membrane 3 can be prevented while securing liquid permeability. In particular, from the viewpoint of lowering resistance in recent years, the thickness of the ion exchange membrane 3 tends to be thin, and a treatment and a method for reducing damage to the ion exchange membrane 3 are extremely important. From the above viewpoint, it is more preferable to use, as the third electrode material, non-woven fabric or paper whose flat surface is subjected to flat processing as the base material. As the flattening method, any known method can be applied, for example, a method of applying and drying a slurry on one side of a carbonaceous fiber; and a method of impregnating and drying on a smooth film such as PET.

The thickness of the third electrode material is preferably at least greater than the spacer thickness. For example, when using a carbon fiber having a low density such as non-woven fabric and supporting carbon particles other than the graphite particles used for the third electrode material and a binding carbonaceous material, the spacer thickness 1.5 to 6.0 times is preferable. However, if the thickness is too large, the compressive stress of the sheet-like material may break through the ion exchange membrane 3, so that the compressive stress of the third electrode material is 9.8 N / cm ² or less. preferable. In order to adjust the compressive stress and the like in accordance with the coating weight and thickness of the third electrode material, it is also possible to use the third electrode material laminated in two or three layers. Alternatively, a combination with another form of electrode material is also possible.

0.5 m < ² > / g or more is preferable and, as for the BET specific surface area calculated | required from the nitrogen adsorption amount of a 3rd electrode material, 1 m < ² > / g or more is more preferable. When the BET specific surface area is less than 0.5 m ² / g, the desired low resistance can not be obtained due to the decrease in the exposure of the edge surface of the carbon particles (B) other than the graphite particles and the contact area with the electrolyte. . The upper limit of the BET specific surface area is not particularly limited from the above point of view, but in consideration of formation of conductive paths between particles, adhesion of carbon particles other than graphite particles to fibers, etc., it is about 1500 m ² / g or less Is preferred.

The third electrode material is useful as an electrode material of a redox flow battery, and the type of electrolyte is not particularly limited. Therefore, not only metal-based electrolytes such as vanadium-based electrolytes and Mn / Ti-based electrolytes, but also other metal-based electrolytes and nonmetal-based electrolytes can be used. As a metal type electrolyte solution, active materials, such as Ti, V, Cr, Mn, Fe, Cr, Cu, Zn, Ce, etc. are mentioned, for example. As a nonmetallic electrolyte, for example, organic molecules such as poly acid, quinone and flavin other than Cl ₂ , Br ₂ , I ₂ , H ₂ , and O ₂ ; organics such as TEMPO (tetramethyl piperidinyloxy radical) Active materials such as molecular radicals may be mentioned.

[III-3. Third Method of Manufacturing Carbon Electrode Material]
Next, a method of manufacturing the third electrode material will be described. The third electrode material is formed by attaching carbon particles other than graphite particles to a carbonaceous fiber (base material) and a precursor of a carbonaceous material (before carbonization), followed by carbonization step, graphitization step, oxidation treatment It can be manufactured through the process. In each step, known methods can be optionally applied.

Each step will be described below.

(Step of attaching carbon particles other than graphite particles and carbonaceous material precursor to carbonaceous fiber)
First, carbon particles other than graphite particles and a precursor of a carbonaceous material are attached to the carbonaceous fiber. In order to attach carbon particles other than graphite particles and a precursor of a carbonaceous material to a carbonaceous fiber, any known method can be adopted. For example, the above carbonaceous material precursor is heated and melted, carbon particles other than graphite particles are dispersed in the obtained melt, and the carbonaceous fiber is immersed in the melt dispersion, and then cooled to room temperature. Can be mentioned. Alternatively, as shown in the examples described later, water or alcohol added with a binder (temporary adhesive) which loses carbon particles other than the above-mentioned carbonaceous material precursor and graphite particles at the time of carbonization like polyvinyl alcohol etc. And the like, and after the carbonaceous fiber is immersed in the dispersion, a method of heating and drying may be used. Here, excess liquid among the above-mentioned melt dispersion liquid and dispersion liquid in which the carbonaceous fiber is immersed is squeezed out excess dispersion liquid when immersed in the dispersion liquid by passing it through a nip roller provided with a predetermined clearance, Alternatively, the surface of the excess dispersion when immersed in the dispersion with a doctor blade or the like can be removed by a method such as scraping.

Thereafter, it is dried at, for example, 80 to 150 ° C. in an air atmosphere.

(Carbonization process)
The carbonization step is carried out to calcine the product after attachment obtained in the above step. As a result, the carbonaceous fibers are bound via the carbon particles other than the graphite particles. In the carbonization step, it is preferable to sufficiently remove the decomposition gas at the time of carbonization, and for example, it is preferable to heat at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere). The heating temperature is more preferably 1000 ° C. or higher, still more preferably 1200 ° C. or higher, still more preferably 1300 ° C. or higher, and further preferably 1500 ° C. or lower, even more preferably 1400 ° C. or lower.

As described above, the treatment corresponding to the carbonization step may be performed after the stabilization of the fibers, but the carbonization treatment performed after the stabilization of the fibers may be omitted. That is, the method of producing the third electrode material is roughly classified into the following method 1 and method 2.
Method 1: Flame-stabilization of fiber → carbonization of fiber → adhesion of carbon particles and carbonaceous materials other than graphite particles → carbonization → graphitization → oxidation · Method 2: flame-stabilization of fiber → carbon particles other than graphite particles and Adhesion of carbon material → carbonization → graphitization → oxidation According to the above method 1, although the processing cost increases because carbonization is performed twice, the sheet used as an electrode material is affected by the difference in volume contraction ratio. Because of the difficulty, there is an advantage that the obtained sheet is unlikely to be deformed (warpage occurrence). On the other hand, according to the method 2, although the processing cost can be reduced because the carbonization step may be performed once, the sheet obtained is easily deformed due to the difference in volume contraction ratio at the time of carbonization of each material. Which one of the

above methods

1 and 2 is adopted may be appropriately determined in consideration of these.

The present application is based on Japanese Patent Application No. 2017-172133 filed on Sep. 7, 2017, Japanese Patent Application No. 2017-172134 filed on the same day, Japanese Patent Application No. 2017- Claim the benefit of priority under No.172135. Japanese Patent Application No. 2017-172133 filed on September 7, 2017, Japanese Patent Application No. 2017-172134 filed on the same day, Japanese Patent Application No. 2017-172135 filed on the same day The entire contents of the specification are incorporated herein by reference.

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. The present invention is not limited to the following examples. In the following,% means "% by mass" unless otherwise specified.

The following items were measured in this example. The details of the measurement method are as follows.

(1) Measurement of crystallite size (Lc) in c-axis direction by X-ray diffraction (1-1) First electrode material Lc (A) and carbonaceous matter of carbonaceous fiber in first electrode material The Lc (B) of the material was measured as follows.
The same heat treatment as in Example 1 was sequentially performed on each of the carbonaceous fiber and the carbonaceous material (in simple substance) used in this example, and the measurement was performed using the final-treated sample. Basically, carbon crystallinity is considered to be dominated by the thermal energy given to the sample, and the highest temperature thermal history given to the sample is considered to determine the crystallinity of Lc, but it depends on the degree of subsequent oxidation treatment It is conceivable that the graphene laminate structure formed during the graphitization process may be disturbed to cause a decrease in crystallinity due to the generation of a defect structure or the like. Therefore, the final processed sample was used.

Each single body sample collected as described above was ground with an agate mortar until the particle size became about 10 μm. About 5% by mass of high purity silicon powder for X-ray standard is mixed with the sample after grinding as internal standard substance, packed in sample cell, and wide-angle X-ray is measured by diffractometer method using CuKα ray as a radiation source did.

The carbonaceous fibers (A) and the carbonaceous material (B) used for the first electrode material were subjected to peak separation from the chart obtained by the above-mentioned wide-angle X-ray measurement to calculate their Lc values. Specifically, the peak at which the peak is observed in the range of 25.3 ° to 25.7 °, which is twice the diffraction angle θ (2θ), is regarded as the carbonaceous material (B). After determining the peak shape as a sine wave from each peak top, determine the peak shape as a sine wave from the foot portion observed around 24.0 ° to 25.0 °, and use this as the carbonaceous fiber (A ). Each Lc was computed by the following method from two peaks isolate | separated by the above method.

For the correction of the curve, the following simplified method was used without correction for so-called Lorentz factor, polarization factor, absorption factor, atomic scattering factor, and the like. That is, the substantial intensity from the baseline of the peak corresponding to the <002> diffraction was replotted to obtain the <002> correction intensity curve. The size of the crystallite in the c-axis direction according to the following equation from the length (half-width β) of the line segment where the line parallel to the angle axis drawn to 1/2 height of this peak height intersects with the correction intensity curve I asked for Lc.

Lc = (k · λ) / (β · cos θ)
Here, the structure coefficient k = 0.9, the wavelength λ = 1.5418 Å, β represents the half width of the <002> diffraction peak, and θ represents the <002> diffraction angle.

(1-2) Second electrode material: Measurement of Lc (A) of carbonaceous fiber, Lc (B) of graphite particles and Lc (C) of carbonaceous material in the second electrode material as follows did.
The same heat treatment as in Example 2 was sequentially performed on each of the carbonaceous fiber, the graphite particles, and the carbonaceous material (in simple substance) used in the present example, and the measurement was performed using the final-treated sample. Basically, carbon crystallinity is considered to be dominated by the thermal energy given to the sample, and the highest temperature thermal history given to the sample is considered to determine the crystallinity of Lc, but it depends on the degree of subsequent oxidation treatment It is conceivable that the graphene laminate structure formed during the graphitization process may be disturbed to cause a decrease in crystallinity due to the generation of a defect structure or the like. Therefore, the final processed sample was used.

The carbonaceous fiber (A) and the graphite particles (B) used for the second electrode material, and the carbonaceous material (C) binding them are subjected to peak separation from the chart obtained by the above wide angle X-ray measurement Thus, each Lc value was calculated. Specifically, the peak at which the peak is observed in the range of 26.4 ° to 26.6 °, which is twice the diffraction angle θ (2θ), is a graphitic particle (B), the range of 25.3 ° to 25.7 ° The peak where the peak is seen at was designated as the carbonaceous material (C). After determining the peak shape as a sine wave from each peak top, determine the peak shape as a sine wave from the foot portion observed around 24.0 ° to 25.0 °, and use this as the carbonaceous fiber (A ).
Each Lc was computed by the following method from three peaks isolate | separated by the above method.

(1-3) Third electrode material Lc (A) of carbonaceous fiber in the third electrode material, Lc (B) and La (B) of carbon particles other than graphite particles, Lc (C) of carbonaceous material ) Was measured as follows.
The same heat treatment as in Example 3 was sequentially performed on each of the carbonaceous fiber, the carbon particles other than the graphite particles, and the carbonaceous material (in simple substance) used in this example, and the measurement was performed using the final-treated sample. Basically, carbon crystallinity is considered to be dominated by the thermal energy given to the sample, and the highest temperature thermal history given to the sample is considered to determine the crystallinity of Lc, but it depends on the degree of subsequent oxidation treatment It is conceivable that the graphene laminate structure formed during the graphitization process may be disturbed to cause a decrease in crystallinity due to the generation of a defect structure or the like. Therefore, the final processed sample was used.

The carbonaceous fibers (A) and the carbon particles (B) other than the graphite particles used for the third electrode material, and the carbonaceous material (C) for binding them from the chart obtained by the above wide angle X-ray measurement Each Lc value was calculated by performing peak separation. Specifically, a peak whose peak is observed in the range of 26.4 ° to 26.6 °, which is twice the diffraction angle θ (2θ), is a carbon particle (B) other than a graphite particle, 25.3 ° to 25.25. The peak at which the apex is seen in the range of 7 ° was taken as the carbonaceous material (C). After determining the peak shape as a sine wave from each peak top, determine the peak shape as a sine wave from the foot portion observed around 24.0 ° to 25.0 °, and use this as the carbonaceous fiber (A ). Each Lc was computed by the following method from three peaks isolate | separated by the above method.

(2) Measurement of O / C by XPS Surface Analysis For measurement of X-ray photoelectron spectroscopy abbreviated as ESCA or XPS, an apparatus of ULVAC-PHI 5801MC was used.
First, the sample was fixed on a sample holder with a Mo plate, fully evacuated in the preliminary evacuation chamber, and then introduced into the chamber of the measurement chamber. A monochromated AlKα ray was used as a radiation source, the output was 14 kV, 12 mA, and the degree of vacuum in the apparatus was 10 ⁻⁸ torr.
A total element scan was performed to determine the composition of the surface elements, and a narrow scan was performed for the detected element and the expected element to evaluate the abundance ratio.
The ratio of the number of surface-bound oxygen atoms to the total number of surface carbon atoms was calculated as a percentage (%) to calculate O / C.

(3) Charge / Discharge Test Each electrode material obtained by the method to be described later was cut out to an electrode area of 16 cm ² of 10 cm in the vertical direction (flowing direction) and 1.6 cm in the width direction, and the cell of FIG. 1 was assembled. The ion exchange membrane used was Nafion 212 membrane.
Here, the first electrode material is one for each of the felt base materials (No. 1 to 2 and 5 to 9) described later, and each of the first electrode materials for the spunlace (No. 4) and the paper base material (No. 3). Two sheets were placed on the positive and negative electrodes, and the filling factor of the electrode material in the cell was 0.1 to 0.2 g / cc for the felt base, 0.3 to 0. 0 for the carbon paper base and the spunlace base. The spacer thickness was adjusted to 4 g / cc. The reason for changing the packing ratio in the cell for each substrate used in this way is that carbon paper and spunlace are thin and easy to be highly packed, so contact with the current collector plate with the same packing ratio as felt Is insufficient, and the contact resistance between the electrode material and the current collector plate is increased. As a specific spacer thickness, 2.5 mm for the felt base materials (Nos. 1 to 2 and 5 to 9) described later, 1.0 mm for the spunlace base material (No. 4), paper base material (No. 3) Then it was 0.5 mm.

The second electrode material is one each for felt base materials (Nos. 1 to 3 and 6 to 10) described later, and 2 for each of the spun lace (No. 5) and paper base material (No. 4). The sheet is placed on the positive and negative electrodes, and the filling factor of the electrode material in the cell is 0.1 to 0.2 g / cc for the felt substrate, 0.3 to 0.4 g for the carbon paper substrate and the spunlace substrate The spacer thickness was adjusted to be / cc. The reason for changing the packing ratio in the cell for each substrate used in this way is that carbon paper and spunlace are thin and easy to be highly packed, so contact with the current collector plate with the same packing ratio as felt Is insufficient, and the contact resistance between the electrode material and the current collector plate is increased. As a specific spacer thickness, 2.5 mm for the felt base materials (No. 1 to 3, 6 to 10) described later, 1.0 mm for the spunlace base material (No. 5), paper base material (No. 4) Then it was 0.5 mm.

For the third electrode material, one sheet is placed on each of the positive and negative electrodes, and the filling factor of the electrode material in the cell is 0.1 to 0.2 g / cc for the felt substrate, and the carbon paper substrate and spunlace The spacer thickness was adjusted to be 0.3 to 0.4 g / cc for the substrate. The reason for changing the packing ratio in the cell for each substrate used in this way is that carbon paper and spunlace are thin and easy to be highly packed, so contact with the current collector plate with the same packing ratio as felt Is insufficient, and the contact resistance between the electrode material and the current collector plate is increased.

Then, from the voltage curve after 10 cycles at a voltage range of 1.70 to 1.00 V at 100 mA / cm ² , the total cell resistance was calculated by the following equation. A 2.5 moL / L sulfuric acid aqueous solution of 2.0 moL / L vanadium oxysulfate was used as the positive electrode electrolyte, and a 2.5 moL / L sulfuric acid aqueous solution of 2.0 moL / L vanadium sulfate was used as the negative electrode electrolyte. . The amount of electrolyte was in excess to the cell and piping. The liquid flow rate was 10 mL / min and the measurement was performed at 30 ° C. The charge voltage V _C50 and the discharge voltage V _D50 corresponding to the amount of electricity when the charge ratio is 50% are respectively obtained from the voltage curves, and the current density is I (mA / cm ² ). I asked for cm ² ).

here,
V _C50 is the charge voltage with respect to the amount of electricity when the charge rate is 50% determined from the electrode curve,
V _D50 is the discharge voltage with respect to the amount of electricity when the charge rate is 50% determined from the electrode curve,
I = current density (mA / cm ² )

(4) Water flow test At a point 5 cm high from the electrode, drop 1 ion exchange water from a 3 mmφ pipette onto the electrode and measure the time until dripped water penetrates, The water flow rate was calculated by
Water flow rate (mm / sec)
= Thickness of electrode material (mm) / time until water droplet penetrates (sec)

[About the first electrode material]
Example 1
In this example, as the carbonaceous material (B), pitches of MCP250 manufactured by JFE Chemical Co., Ltd. or phenol resin (solid content 40%) manufactured by DIC Corporation TD-4304 is used to prepare an electrode material as follows. And various items were measured.

(No. 1)
<Fabrication of non-woven fabric A made of carbonaceous fiber>
A polyacrylonitrile fiber with an average fiber diameter of 16 μm is made flame-resistant by heating at 300 ° C. in an air atmosphere, and short fibers (length 80 mm) of the flame-proof fiber are used to felt needle SB # 40 (Foster Needle), punching density Felt was applied at 250 yarns / cm ² to prepare a nonwoven fabric A (felt made of flameproof polyacrylonitrile fiber) having a basis weight of 300 g / m ² and a thickness of 4.3 mm.

Attachment of Carbonaceous Material (Binder)
Ion-exchanged water: 83.0%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L 120 2.0%, JFE Chemical's MCP 250 pitch as a carbonaceous material: 14.0%, The mixture was stirred for 1 hour with a mechanical stirrer to give a dispersion.

After immersing the non-woven fabric A in the prepared dispersion, the excess dispersion is passed through a nip roller so that the non-woven fabric A before immersion is 1.9 to 2.1 times the weight of the non-woven fabric after immersion. Was removed and drying was carried out at 150.degree. C. for 20 minutes.

<Carbonization of non-woven fabric>
Next, the temperature of the non-woven fabric A after the above treatment is raised to 1000 ° C. ± 50 ° C. at a temperature rise rate of 5 ° C./min in nitrogen gas, and held at this temperature for 1 hour for carbonization (baking) After cooling, the temperature was raised to 1500 ° C. ± 50 ° C. at a temperature rising rate of 5 ° C./min in nitrogen gas, and graphitization was performed with cooling at this temperature for 1 hour for cooling. Next, oxidation treatment was performed at 700 ° C. for 10 minutes in an air atmosphere. An electrode material (a basis weight of 191 g / m ² , a thickness of 3.4 mm) was obtained.

(No. 2)
No. In 1, the excess dispersion is removed by passing through a nip roller so that the nonwoven fabric weight after immersion is 1.6 to 1.8 times the nonwoven fabric A before immersion, thereby changing the amount of carbonaceous material attached. The above-mentioned No. 1 except that No. 1 is processed. An electrode material of 2 (weight per unit area: 174 g / m ² , thickness: 3.2 mm) was obtained.

(No. 3)
No. In No. 1, carbon paper (CFP-030-PE, manufactured by Nippon Polymer Industries Co., Ltd., weight per unit area of 30 g / m ² ) made of polyacrylonitrile fiber (average fiber diameter 10 μm) instead of felt made of flameproofed polyacrylonitrile fiber as carbonaceous fiber. , Thickness 0.51 mm), the above-mentioned No. No. 1 except that drying, carbonization (calcination), graphitization, and oxidation were performed in the same manner as No. 1. In the same manner as No. 1, No. An electrode material of 3 (thickness 0.57 mm, basis weight 64 g / m ² ) was produced.

(No. 4)
No. 1. In place of felt made of flameproofed polyacrylonitrile fiber as the carbonaceous fiber in 1, the spunlace (100 to 120 g / m ^{2 in} basis weight, 0.9 mm thickness) made of polyacrylonitrile fiber (average fiber diameter 10 μm) was replaced with nitrogen gas The temperature is raised to 1000 ° C ± 50 ° C at a heating rate of 5 ° C / min in carbonized carbonized spunlace (weight per unit area of 50 to 60 g / m ² , thickness 0) by holding for 1 hour after heating. No. 5 except that 0.5 to 0.7 mm) was used. In the same manner as No. 1, No. An electrode material of 4 (thickness 0.65 mm, basis weight 105 g / m ² ) was produced.

(No. 5)
No. In 1, the excess dispersion is removed by passing through a nip roller so that the nonwoven fabric weight after immersion is 1.3 to 1.5 times the nonwoven fabric A before immersion, and the amount of carbonaceous material attached is changed The above-mentioned No. 1 except that No. 1 is processed. An electrode material of 5 (weight per unit area 159 g / m ² , thickness 3.2 mm) was obtained.

(No. 6)
The above No. No. 1 without attaching the carbonaceous material (binder) to the nonwoven fabric A described in No. 1. <Carboning of non-woven fabric> in the same manner as No. 1. An electrode material of 6 (weight per unit area 143 g / m ² , thickness 3.4 mm) was obtained.

(No. 7)
No. In 1), ion-exchanged water: 64.0%, polyvinyl alcohol: 1.0%, phenolic resin (solid content 40%): 35.0% of DIC Corporation TD-4304 as a carbonaceous material, using a mechanical stirrer The above-mentioned No. 1 was used except that the dispersion obtained by stirring for 1 hour was used. No. 1 is processed. An electrode material of 7 (weight per unit area: 188 g / m ² , thickness: 3.4 mm) was obtained.

(No. 8)
The above No. No. 1 in <carbonization of non-woven fabric> except that oxidation treatment at 700 ° C. in an air atmosphere was not performed. In the same manner as No. 1, No. Eight electrode materials (weight per unit area: 189 g / m ² , thickness: 3.3 mm) were obtained.

(No. 9)
The above No. No. 1 in <Carbonization of non-woven fabric> except that the temperature of graphitization was changed to 2000 ° C. ± 50 ° C. In the same manner as No. 1, No. 9 electrode materials (area weight 191 g / m ² , thickness 3.4 mm) were obtained.

Thus obtained No. Various items of the electrode materials 1 to 9 were measured, and the results are shown in Table 1.

No. The electrode materials 1 to 4 satisfied the requirements of the first electrode material, and low resistance could be realized.
On the other hand, no. 5 is an example in which the content of the carbonaceous material is small, and it is considered that the resistance is increased since the efficient conductive path can not be formed because the bonding between the carbonaceous fibers is insufficient.

No. 6 is an example which does not use a carbonaceous material but consists only of carbonaceous fiber, and No. 6 is an example. The resistance increased as compared to the examples of the present invention of 1 to 4.

No. 7 is an example in which the ratio of Lc (B) / Lc (A) is small, and the resistance increased. It is considered that this is because the carbon crystallinity of the carbonaceous material is lower than that of the example of the present invention, so the electron conduction resistance between the carbonaceous fibers is high, and an efficient conductive path can not be formed.

No. 8 is an example with a low O / C, resistance increased, and it did not flow. This is considered to be due to the fact that the affinity to the electrolytic solution is lowered and the reaction activity is lowered as compared with the inventive example because the amount of the oxygen functional group is small.

No. 9 is an example in which the graphitization temperature is increased to 2000 ° C. to increase Lc (B) to 12.0 nm. Since Lc (B) is excessively high, it is considered that the affinity to the electrolyte decreases and the resistance increases.

[About the second electrode material]
Example 2
In the present example, using scaly graphite particles A to D shown in Table 2, an electrode material was produced as follows, and various items were measured. Among these, A, B and D are commercial products, and the particle sizes described in Table 1 are the values described in the catalog. C is obtained by bead-milling flake-like graphite particles having a particle diameter of 5 μm for 6 hours with a Labstar Mini machine manufactured by Ashizawa Finetech, and the particle diameter was measured by a laser diffraction method. D is an example in which Lc is large.

(No. 1)
No. In 1, using polyacrylonitrile fiber as the carbonaceous fiber, A of Table 1 (example satisfying the requirements of the second electrode material) as the graphite particles, and pitches of MCP 250 manufactured by JFE Chemical Corporation as the carbonaceous material, The electrode material was manufactured.

First, a polyacrylonitrile fiber (average fiber diameter 10 μm) is heated at 300 ° C. in an air atmosphere to make it flame resistant, and a short fiber (length 80 mm) of the flameproof fiber is used to make a felt needle SB # 40 (Foster Needle) After forming a felt (thickness 4.3 mm, basis weight 150 g / m ² ) made of felt with a punching density of 250 / cm ² to obtain a flameproof polyacrylonitrile fiber, it is subsequently fired for 1 hour at 1000 ° C. in a nitrogen atmosphere ( Carbonized). The temperature raising rate when raising the temperature from the temperature for stabilization to the temperature for carbonization was 10 ° C./min or less.

Next, in ion exchange water, 1.8% of Kao's Leodol TW-L 120 (non-ionic surfactant), 1.8% of polyvinyl alcohol (temporary adhesive), MCP 250 (carbonaceous material, manufactured by JFE Chemical Co., Ltd.) The material (A) was added to 14%, and A of Table 1 was added to 9.8% as a graphite powder, and stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

After immersing the felt fired at 1000 ° C. described above in the dispersion thus obtained, it was passed through a nip roller to remove excess dispersion. Next, it was dried at 150 ° C. for 20 minutes in an air atmosphere, carbonized (baked) at 1000 ° C. for 1 hour in a nitrogen atmosphere, and then graphitized at 1500 ° C. for 1 hour. After graphitization, oxidation treatment was performed at 700 ° C. for 10 minutes in an air atmosphere to obtain an electrode material (No. 1) having a thickness of 3.8 mm and a basis weight of 278.0 g / m ² .

(No. 2)
No. In 1, the use of B in Table 1 (example satisfying the requirements of the second electrode material) as a graphite powder; inclusion of graphite particles and carbonaceous material with respect to the total amount of carbonaceous fibers, graphite particles, and carbonaceous materials The above-mentioned No. 1 except that the rate was changed as shown in Table 2. In the same manner as No. 1, No. An electrode material of 2 (thickness 3.9 mm, basis weight 301.0 g / m ² ) was produced.

(No. 3)
No. In 1, the C of Table 1 (example satisfying the requirements of the second electrode material) is used as the graphite powder; inclusion of the graphite particles and the carbonaceous material relative to the total amount of the carbonaceous fiber, the graphite particles, and the carbonaceous material The above-mentioned No. 1 except that the rate was changed as shown in Table 2. In the same manner as No. 1, No. An electrode material of 3 (thickness 4.0 mm, basis weight 294.0 g / m ² ) was produced.

(No. 4)
No. In No. 1, carbon paper (CFP-030-PE manufactured by Nippon Polymer Industries Co., Ltd., weight per unit area of 30 g / m ² ) made of polyacrylonitrile fiber (average fiber diameter 10 μm) instead of felt made of flameproofed polyacrylonitrile fiber as carbonaceous fiber. , Thickness 0.51 mm), the above-mentioned No. Drying, carbonization (baking), graphitization and oxidation treatment as in 1; content of graphite particles and carbonaceous material to total amount of carbonaceous fiber, graphite particles, carbonaceous material as shown in Table 2 No. except that it was changed to In the same manner as No. 1, No. An electrode material of 4 (thickness 0.57 mm, basis weight 137.0 g / m ² ) was produced.

(No. 5)
No. In No. 1, in place of a felt made of flameproofed polyacrylonitrile fiber as the carbonaceous fiber, a spunlace (100 to 120 g / m ² basis weight, 0.9 mm thickness) made of polyacrylonitrile fiber (average fiber diameter 10 μm) The temperature is raised to 1000 ° C. ± 50 ° C. at a temperature rising rate of 5 ° C./min, and the carbonized spunlace (carbon weight 50 to 60 g / m ² , thickness 0. No. 5 except that a dispersion liquid was obtained by adding graphite powder (A in Table 1) to be 4.9% using 5 to 0.7 mm). In the same manner as No. 1, No. An electrode material of 5 (thickness 0.65 mm, basis weight 189.0 g / m ² ) was produced.

(No. 6)
No. In 1, the use of D (example not satisfying the requirements of the second electrode material) of Table 1 as a graphite powder; inclusion of graphite particles and carbonaceous material with respect to the total amount of carbonaceous fibers, graphite particles and carbonaceous material The above-mentioned No. 1 except that the rate was changed as shown in Table 2. In the same manner as No. 1, No. An electrode material (comparative example) of 6 (thickness 3.7 mm, basis weight 278.0 g / m ² ) was produced.

(No. 7)
No. In No. 7, no. No. 1 except that a felt made of flame-resistant polyacrylonitrile fiber (thickness 4.3 mm, fabric weight 300 g / m ² ) was used as the carbonaceous fiber without using graphite particles and carbonaceous material. Process as in No. 1 An electrode material (comparative example) of 7 (thickness 4.3 mm, basis weight 150.0 g / m ² ) was produced.

(No. 8)
No. No. 1 except that carbonization (calcination) was performed at 1000 ° C. for 1 hour in a nitrogen atmosphere, graphitized at 2000 ° C. for 1 hour, and oxidation treatment in an air atmosphere at 700 ° C. for 20 minutes. Similarly to No. 1, No. An electrode material (comparative example) of 8 (thickness 3.8 mm, basis weight 278.0 g / m ² ) was produced.

(No. 9)
No. No. 1 except that 3 mass% of MCP 250 (carbonaceous material) manufactured by JFE Chemical Corporation and A of Table 1 as 2.1 mass% were added as graphite powder. In the same manner as No. 1, No. An electrode material (comparative example) of 9 (thickness 0.56 mm, basis weight 194.0 g / m ² ) was produced.

(No. 10)
No. No. 8 except that oxidation treatment at 700 ° C. was not performed in an air atmosphere. As in No. 8, No. An electrode material (comparative example) of 10 (thickness 3.8 mm, basis weight 290.0 g / m ² ) was produced.

(No. 11)
No. 10, 10% by mass of a phenolic resin water dispersion (TD4304 manufactured by DIC Corporation) is added as a carbonaceous material instead of MCP250 manufactured by JFE Chemical Co., to obtain a dispersion; carbonaceous fiber, graphite particles, No. 1 was changed except that the content of graphite particles and carbonaceous material with respect to the total amount of carbonaceous material was changed as shown in Table 2. In the same manner as No. 1, No. An electrode material (comparative example) of 11 (thickness 3.8 mm, basis weight 288.0 g / m ² ) was produced.

In Table 3, the above-mentioned No. The measurement results of various items in 1 to 11 are shown.

No. The electrode materials 1 to 5 satisfied the requirements of the second electrode material, and all obtained low resistance electrode materials.

On the other hand, no. 6 is an example using Graphite D in which Lc does not satisfy the requirement of the second electrode material, and the resistance is increased because the reactivity of the graphite particles is poor.

No. No. 7 is an example which does not use a graphite particle nor a carbonaceous material but consists only of a carbonaceous fiber, and resistance increased.

No. 8 is an example in which the graphitization temperature is increased to 2000 ° C. to increase Lc (C) to 12.0 nm. Since Lc (C) was excessively high, affinity with the electrolyte decreased and resistance increased. It is considered that the utilization rate of graphite deteriorated.

No. Although No. 9 used the graphite particle and carbonaceous material which satisfy | fill the requirements of the 2nd electrode material, since there were few content of these, resistance increased compared with the example of this invention. It is considered that the content of graphite is small and the effective surface area is insufficient.

No. 10 is an example in which the ratio of O / C is low because the oxidation treatment after graphitization is not performed. Since the amount of functional groups on the carbon surface was insufficient, the affinity to the electrolyte decreased and the resistance increased. It is considered that the utilization rate of graphite deteriorated.

No. 11 used the graphite particle which satisfies the requirements of the 2nd electrode material, but Lc (C) is not large enough and the ratio of Lc (C) / Lc (A) is as small as 1.0 or less is there. Therefore, the resistance increased as compared to the example of the present invention. Although the affinity of the electrolytic solution is high, it is considered that the conductivity of the carbonaceous material (C) is insufficient.

[About the third electrode material]
Example 3
In this example, carbon blacks of A to E shown in Table 4 as carbon particles (B) other than graphite, graphite particles of F, and a shown in Table 5 as carbonaceous material (C) (MCP250 manufactured by JFE Chemical Corporation) Using pitches, b (phenol resin of TD-4304 made by DIC, solid content 40%) or c (coal tar made by Alfa Aesar), prepare an electrode material made of a carbonaceous sheet as follows Various items were measured. All of A to F are commercially available products, and the average particle diameter described in Table 1 is a value described in the catalog.

(No. 1)
Ion-exchanged water: 19.2%, polyvinyl alcohol: 1.0%, A as shown in Table 1 as carbon particles other than graphite particles (solid content 16.5%, carbon content other than graphite particles about 8.5% , Example of satisfying the requirements of the third electrode material): 65.8%, a: 14.0% (remaining carbonization weight yield 80%) of Table 5 as a carbonaceous material, stirred with a mechanical stirrer for 1 hour , As a dispersion.

Next, a polyacrylonitrile fiber with an average fiber diameter of 16 μm is heated at 300 ° C. in an air atmosphere to make it flame resistant, and the short fibers (length 80 mm) of the flameproof fiber are used to felt needles SB # 40 (Foster Needle) A felt was formed at a punching density of 250 / cm ² to prepare a nonwoven fabric A having a basis weight of 300 g / m ² and a thickness of 4.3 mm.

After immersing the non-woven fabric A described above in the prepared dispersion, it is passed through a nip roller so that the weight of the non-woven fabric A after immersion is 2.1 to 2.3 times the weight of the non-woven fabric A before immersion. The excess dispersion was removed and drying was performed at 150.degree. C. for 20 minutes under an air atmosphere. Next, the temperature is raised to 1000 ° C. ± 50 ° C. at a temperature rising rate of 5 ° C./min in nitrogen gas, carbonization (calcination) is performed by holding at this temperature for 1 hour, and then cooled and further in nitrogen gas The temperature was raised to 1500 ° C. ± 50 ° C. at a temperature rising rate of 5 ° C./min, held at this temperature for 1 hour, graphitized and cooled. Next, oxidation treatment was performed at 700 ° C. for 10 minutes in an air atmosphere. An electrode material (weight per unit area 206 g / m ² , thickness 3.3 mm) of 1 was obtained.

(No. 2)
Ion-exchanged water: 50.9%, polyvinyl alcohol (temporary adhesive material): 1.0%, carbon particles other than graphite particles: A in Table 1: 34.1%, carbonaceous materials: a in Table 2: a. The mixture was stirred at 0% with a mechanical stirrer for 1 hour to give a dispersion.

In the prepared dispersion, no. After the non-woven fabric A in 1 is dipped, the excess dispersion is removed by passing it through a nip roller so that the weight of the non-woven fabric A after immersion is 2.3 to 2.5 times the weight of the non-woven fabric A before immersion. The above-mentioned No. 1 except that the amount of attachment of the carbonaceous material is changed. No. 1 is processed. An electrode material of 2 (weight per unit area 208 g / m ² , thickness 3.2 mm) was obtained.

(No. 3)
Ion-exchanged water: 68.1%, polyvinyl alcohol: 1.0%, carbon particles other than graphite particles: A: 16.9% in Table 1; carbonaceous materials, a: 14.0% in Table 5: mechanical The mixture was stirred for 1 hour with a stirrer to give a dispersion.

In the prepared dispersion, no. After the non-woven fabric A in 1 is dipped, the excess dispersion is removed by passing it through a nip roller so that the weight of the non-woven fabric A after immersion is 2.5 to 2.7 times the weight of the non-woven fabric A before immersion. The above-mentioned No. 1 except that the amount of attachment of the carbonaceous material is changed. No. 1 is processed. An electrode material of 3 (area weight 213 g / m ² , thickness 3.3 mm) was obtained.

(No. 4)
No. In the dispersion prepared in 2, no. Before immersion, carbon paper (CFP- 030-PE manufactured by Nippon Polymer Sangyo Co., Ltd., CFP-030-PE, basis weight 30 g / m ² , thickness 0.51 mm) consisting of polyacrylonitrile fiber (average fiber diameter 10 μm) instead of non-woven fabric A in 1 The above No. except that the amount of carbon material attached was changed by passing it through a nip roller so that the weight of carbon paper after immersion was 14 to 15 times that of carbon paper and removing excess dispersion liquid. . No. 1 is processed. An electrode material of 4 (weight per unit area 119 g / m ² , thickness 0.45 mm) was obtained.

(No. 5)
No. In the dispersion prepared in 2, no. Spunlace (weight per unit area 100 to 120 g / m ² , thickness 0.9 mm) consisting of polyacrylonitrile fiber (average fiber diameter 10 μm) instead of non-woven fabric A in No. 1 is 1000 in nitrogen gas at a heating rate of 5 ° C./min. After immersing carbonized spunlace (50 to 60 g / m ^{2 in} basis weight, 0.5 to 0.7 mm in thickness) which has been carbonized by raising the temperature to ± 50 ° C. and holding for 1 hour after raising the temperature, Other than passing through a nip roller so that the weight after immersion is 4.4 to 4.6 times that of carbonized super carbonized carbon before immersion, excess dispersion is removed to change the amount of carbonaceous material attached Is the above-mentioned No. No. 1 is processed. An electrode material of 5 (area weight 119 g / m ² , thickness 0.62 mm) was obtained.

(No. 6)
Ion-exchanged water: 36.3%, polyvinyl alcohol: 1.0%, B in Table 1 as carbon particles other than graphite particles (solid content 11.5%, carbon content other than graphite particles is about 3.5%, , Example satisfying the requirements of the third electrode material): 48.7%, a: 14.0% of Table 5 a as a carbonaceous material was stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

In the prepared dispersion, no. After the non-woven fabric A in 1 is dipped, the excess dispersion is removed by passing it through a nip roller so that the weight of the non-woven fabric A after immersion is 2.5 to 2.7 times the weight of the non-woven fabric A before immersion. The above-mentioned No. 1 except that the amount of attachment of the carbonaceous material is changed. No. 1 is processed. The electrode material of 6 (weight per unit area 209 g / m ² , thickness 3.3 mm) was obtained.

(No. 7)
Ion-exchanged water: 77.4%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L 120 2.0%, carbon particles other than graphite particles Table 4 C (third electrode material requirements Of Example 1): 5.6%, a: 14.0% of Table 5 as a carbonaceous material, and stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

No. 5 except that the dispersion prepared above was used. No. 1 is processed. An electrode material of 7 (weight per unit area: 217 g / m ² , thickness: 3.5 mm) was obtained.

(No. 8)
Ion-exchanged water: 77.4%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L 120 2.0%, as carbon particles other than graphite particles D of Table 4 (Requirement of Third Electrode Material Of Example 1): 5.6%, a: 14.0% of Table 5 as a carbonaceous material, and stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

No. 5 except that the dispersion prepared above was used. No. 1 is processed. Eight electrode materials (area weight 211 g / m ² , thickness 3.3 mm) were obtained.

(No. 9)
Ion-exchanged water: 77.4%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L 120 2.0%, as carbon particles other than graphite particles E of Table 4 (Requirement of Third Electrode Material Of Example 1): 5.6%, a: 14.0% of Table 5 as a carbonaceous material, and stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

No. 5 except that the dispersion prepared above was used. No. 1 is processed. 9 electrode materials (weight per unit area 210 g / m ² , thickness 3.3 mm) were obtained.

(No. 10)
No. 10 is an example which does not use carbon particle | grains other than a graphite particle, nor carbonaceous material, but consists only of carbonaceous fiber. Specifically, the above-mentioned nonwoven fabric A is directly treated with No. No. 1 heat treatment was carried out. Ten electrode materials (weight per unit area 143 g / m ² , thickness 3.4 mm) were obtained.

(No. 11)
No. 11 is an example which does not use carbon particles other than a graphite particle, but consists only of carbonaceous fiber and carbonaceous material.
First, ion-exchanged water: 83.0%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L120 2.0%, a: 14.0% of Table 2 as a carbonaceous material, using a mechanical stirrer Stir for 1 hour to make a dispersion.

No. 5 except that the dispersion prepared above was used. No. 1 is processed. Eleven electrode materials (area weight: 191 g / m ² , thickness: 3.4 mm) were obtained.

(No. 12)
Ion exchange water: 77.4%, polyvinyl alcohol: 1.0%, Kao Corporation Leodol TW-L 120 2.0%, Graphite particles F in Table 4 (example not satisfying the requirements): 5.6% As a carbonaceous material, a: 14.0% of Table 5 was stirred by a mechanical stirrer for 1 hour to obtain a dispersion.

No. 5 except that the dispersion prepared above was used. No. 1 is processed. Twelve electrode materials (area weight 209 g / m ² , thickness 3.4 mm) were obtained.

(No. 13)
Ion-exchanged water: 8.9%, polyvinyl alcohol: 1.0%, A as shown in Table 1 as carbon particles other than graphite particles (solid content 16.5%, carbon content other than graphite particles about 8.5% , Example of satisfying the requirements of the third electrode material): 34.1%, b (solid content 40%) of Table 2 as carbonaceous material: 56.0%, stirred with a mechanical stirrer for 1 hour, a dispersion And

In the prepared dispersion, no. No. 1 after immersing the nonwoven fabric A in No. 1. No. 2 is processed. Thirteen electrode materials (weight per unit area 208 g / m ² , thickness 3.4 mm) were obtained.

(No. 14)
No. In the dispersion prepared in 2, no. No. 1 after immersing the nonwoven fabric A in No. 1. Carbonization and graphitization were carried out in the same manner as in No. 2, but no subsequent oxidation treatment in an air atmosphere was carried out. Fourteen electrode materials (area weight 211 g / m ² , thickness 3.2 mm) were obtained.

(No. 15)
No. In the dispersion prepared in 2, no. After the non-woven fabric A in 1 was immersed, the excess dispersion was removed by passing it through a nip roller so that the non-woven fabric A before immersion was 1.5 to 1.7 times as heavy as the non-woven fabric after immersion. No. No. 1 is processed. Fifteen electrode materials (weight per unit area 175 g / m ² , thickness 3.3 mm) were obtained.

(No. 16)
Ion-exchanged water: 10.0%, polyvinyl alcohol: 1.0%, A as shown in Table 4 as carbon particles other than graphite particles (solid content 16.5%, carbon content other than graphite particles about 8.5% Example satisfying the requirements of the third electrode material): 98.0%, a: 1.0% of a in Table 5 as a carbonaceous material was stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

In the prepared dispersion, no. After the non-woven fabric A in 1 was immersed, the excess dispersion was removed by passing it through a nip roller so that the non-woven fabric A before immersion was 3.0 to 3.2 times as heavy as the non-woven fabric after immersion. No. No. 1 is processed. Sixteen electrode materials (weight per unit area 205 g / m ² , thickness 3.3 mm) were obtained.

(No. 17)
Ion-exchanged water: 71.8%, polyvinyl alcohol: 1.0%, A in Table 4 as carbon particles other than graphite particles (solid content: 16.5% carbon content other than graphite particles: about 8.5%, Example satisfying the requirements of the third electrode material: 13.2%, and a: 14.0% of a as shown in Table 5 as a carbonaceous material were stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

In the prepared dispersion, no. After the non-woven fabric A in 1 was immersed, the excess dispersion was removed by passing it through a nip roller so that the non-woven fabric A before immersion was 2.3 to 2.5 times as heavy as the non-woven fabric after immersion. No. No. 1 is processed. Seventeen electrode materials (weight per unit area: 211 g / m ² , thickness: 3.3 mm) were obtained.

(No. 18)
As carbon particles other than graphite particles, C in Table 4 (example satisfying the requirement of the third electrode material): 4.8%, and as carbonaceous material, c in Table 5 (residual carbonization weight yield 10%): 95. 2% was stirred with a mechanical stirrer for 1 hour to obtain a dispersion.

In the prepared dispersion, no. After immersing the non-woven fabric A in 1), the excess dispersion is removed by passing through a nip roller so that the non-woven fabric A before immersion is 1.9 to 2.1 times as heavy as the non-woven fabric before immersion, and graphitized No. 1 except that the temperature of the above was changed to 2000.degree. No. 1 is processed. Eighteen electrode materials (weight per unit area: 195 g / m ² , thickness: 3.2 mm) were obtained.

In Table 6, the above-mentioned No. The measurement results of various items in 1 to 18 are shown.

No. Nos. 1 to 9 are electrode materials satisfying the requirements of the third electrode material. A low resistance electrode material was obtained as compared to the comparative examples of 10 to 18. No. In Examples 1 to 9 of the present invention, A to E in Table 4 having small particle diameters are used as carbon particles other than graphite, and the reaction surface area is large, and it is considered that the electrode activity is improved by the exposure of the carbon edge surface.

On the other hand, no. No. 10 is an example which does not use carbon particles other than graphite particles and carbonaceous materials, and is composed only of carbonaceous fibers, and the reaction surface area is insufficient and resistance is remarkably increased. No. Since No. 11 contained no carbon particles other than the graphite particles, the reaction surface area was insufficient and the resistance increased remarkably.

No. Since No. 12 used F of Table 1 with a large particle diameter and large Lc (B) as carbon particles other than a graphite particle, resistance increased. In addition to the fact that the reaction surface area becomes smaller compared to the example of the present invention when carbon particles having a large particle size are used, and because it is difficult to impart an oxygen functional group when carbon particles having high carbon crystallinity are used, carbon particles near the aqueous electrolyte It is considered that the affinity decreased and the reaction activity did not improve.

No. 13 is an example in which the ratio of Lc (C) / Lc (A) is small, and the resistance increased. This is thought to be because the carbon crystallinity of the carbonaceous material is lower than in the example of the present invention, the electron conduction resistance between the carbon particles and the carbonaceous fiber is high, and the reaction activity of the carbon particles can not be used efficiently. Be

No. No. 14 is an example with a small O / C ratio, resistance increased and it did not flow. This is considered to be due to the fact that the affinity to the electrolytic solution is reduced and the reaction activity is reduced as compared with the inventive example because the amount of the oxygen functional group is small.

No. No. 15 is an example with little content of carbon particles other than graphite, and resistance increased. It is considered that when the content of the carbon particles is small, the reaction surface area decreases, and the electron conduction path becomes insufficient as the content decreases.

No. 16 is an example in which the content of carbon particles other than graphite is small and the ratio of the carbonaceous material to the carbon particles is small, and the resistance increased. This is presumably because the ratio of carbon particles other than graphite is significantly higher than that of the carbonaceous material, so that the binding property is insufficient, and the resistance is increased due to the particles falling off from the carbonaceous fiber.
No. No. 17 is an example in which the ratio of the carbonaceous material to carbon particles other than graphite is high, and the resistance also increases. This is because, since the ratio of the carbonaceous material is significantly larger than that of carbon particles other than graphite, the above-mentioned carbonaceous material covers the reactive site on the surface of the carbon particles, and the reaction surface area is not effectively used and the resistance increases. It is guessed.
No. No. 18 has a ratio of Lc (C) / Lc (A) of 7.2, which is an example in which the carbon crystallinity of the carbonaceous material is remarkably higher than that of the carbonaceous fiber, and the resistance is also increased. When a very high crystalline carbonaceous material is coated with carbon particles other than graphite, the reaction surface area of the carbon particles is not effectively used, and oxygen functional groups are generally less likely to be introduced into highly crystalline sites. It is inferred that the affinity to the electrolyte decreased and the resistance increased.

According to the first and second carbon electrode materials, the cell resistance at the time of initial charge and discharge can be reduced, and a carbon electrode material excellent in battery energy efficiency can be provided. For example, a redox flow battery using a vanadium-based electrolyte It is useful as an electrode material.
Further, according to the third carbon electrode material, the cell resistance at the time of initial charge and discharge can be reduced, and a carbon electrode material excellent in battery energy efficiency can be provided. For example, vanadium-based electrolyte, Mn / Ti-based electrolyte Is useful as an electrode material of a redox flow battery using the
The first to third carbon electrode materials are suitably used for flow type and non-flow type redox flow batteries, lithium, capacitors, redox flow batteries combined with a fuel cell system, and the like.

Reference Signs List 1 collector plate 2 spacer 3 ion exchange membrane 4a, 4b flow passage 5 electrode material 6 positive electrode electrolyte tank 7 negative electrode electrolyte tank 8, 9 pump 10 liquid inlet 11

liquid outlet

12, 13 external flow channel

Claims

Carbonaceous fiber (A) and carbonaceous material (B) binding the carbonaceous fiber (A), and
A carbon electrode material for a redox flow battery characterized by satisfying the following requirements.
(1) Lc (B) is less than 10 nm, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (B)
(2) Lc (B) / Lc (A) is 1.0 or more, where Lc (A) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A).
(3) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material
The carbon electrode material according to claim 1, wherein the mass content of the carbonaceous material (B) is 14.5% or more based on the total amount of the carbonaceous fiber (A) and the carbonaceous material (B).
The carbon electrode material according to claim 1 or 2, wherein Lc (A) is 1 to 10 nm.
A method of manufacturing a carbon electrode material according to any one of claims 1 to 3,
Attaching the carbonaceous material (B) before carbonization to the carbonaceous fiber (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.
Carbonaceous fibers (A), graphite particles (B), and carbonaceous materials (C) binding these,
A carbon electrode material for a redox flow battery characterized by satisfying the following requirements.
(1) Lc (B) is less than 35 nm, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the graphite particles (B)
(2) Lc (C) is less than 10 nm, where Lc (C) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous material (C)
(3) Lc (C) / Lc (A) is 1.0 or more, where Lc (A) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in the carbonaceous fiber (A).
(4) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material
The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the graphite particles (B), and the carbonaceous material (C) is 14.5% or more, and The carbon electrode material according to claim 5, wherein the mass ratio of the carbonaceous material (C) to the graphite particles (B) is 0.2 to 3.0.
The carbon electrode material according to claim 5 or 6, wherein a BET specific surface area determined from a nitrogen adsorption amount is more than 8 m 2 / g.
A method of producing a carbon electrode material according to any one of claims 5 to 7, wherein
Attaching the graphite particles (B) and the carbonaceous material (C) before carbonization to the carbonaceous fibers (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.
It consists of a carbonaceous fiber (A), carbon particles (B) other than graphite particles, and a carbonaceous material (C) binding these,
A carbon electrode material for a redox flow battery characterized by satisfying the following requirements.
(1) The particle size of carbon particles (B) other than graphite particles is 1 μm or less,
(2) Lc (B) is 10 nm or less, where Lc (B) is the size of the crystallite in the c-axis direction determined by X-ray diffraction in carbon particles (B) other than graphite particles.
(3) Lc (A) and Lc (C) in the carbonaceous fiber (A) and the carbonaceous material (C), where Lc (A) and Lc (C) are the sizes of crystallites in the c-axis direction, respectively. C) / Lc (A) is 1.0 to 5,
(4) The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B) other than the graphite particles, and the carbonaceous material (C) is 14.5% or more
(5) The number of bonded oxygen atoms on the surface of the carbon electrode material is 1% or more of the total number of carbon atoms on the surface of the carbon electrode material
The carbon electrode material according to claim 9, wherein a mass ratio of the carbonaceous material (C) to the carbon particles (B) is 0.2 to 10.
11. The carbon electrode material according to claim 9, wherein a BET specific surface area determined from a nitrogen adsorption amount is 0.5 m 2 / g or more.
A method of manufacturing a carbon electrode material according to any one of claims 9 to 11, wherein
Attaching a carbon particle (B) other than the graphite particle and a carbonaceous material (C) before carbonization to the carbonaceous fiber (A);
A carbonization step of heating the product after attachment at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere;
A graphitization step of heating in an inert atmosphere at a temperature of 1300 ° C. or higher and higher than the heating temperature of the carbonization step;
A method of producing a carbon electrode material, comprising: an oxidation treatment step; in this order.
The carbon electrode material according to any one of claims 1 to 3, 5 to 7, and 9 to 11, wherein a water flow rate when dripping a water drop is 0.5 mm / sec or more.
A redox flow battery comprising the carbon electrode material according to any one of claims 1 to 3, 5 to 7, 9 to 11, 13.
A vanadium-based redox flow battery using the carbon electrode material according to any one of claims 1 to 3, 5 to 7, and 13.