JPH11317231A - Carbon-based electrode material for electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon-based electrode material for an electrolytic cell having an enhanced energy efficiency by suppressing a detrimental side reaction improving current efficiency and by reducing a cell resistance and hence improving voltage efficiency. SOLUTION: This carbon-based electrode material for an electrolytic cell consists of a carbon material having a pseudo-graphite crystal structure with spacing between the <002> planes obtained by X-ray wide angle analysis <=3.70 Å and a BET surface area >=5 m<2> /g. The number of bonded nitrogen atoms to the surface of the carbon material is set >=0.3% in relation to the number of carbon atoms, and the nitrogen atoms bonded to the surface are made to exist in the form of a nitrogen-containing acidic functional group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material used for an electrolytic cell of a redox flow battery or the like, and more particularly to a carbon-based electrode material having excellent energy efficiency.

[0002]

2. Description of the Related Art As a field in which an electrolytic cell is used, various batteries and an electrolytic industry such as electroplating, salt electrolysis, and electrolytic synthesis of organic compounds are representative. Electrode materials used in these electrolyzers include those that cause an electrochemical reaction as an active material, such as those commonly found in batteries such as lead-acid batteries, those that cause an electrochemical reaction of the active material,
Some act as a reaction field for promoting the electrochemical reaction of the active material and do not themselves change. The latter electrode material is mainly applied to the electrolytic industry and new type secondary batteries.

[0003] This new type of secondary battery stores excess power at night and discharges it when the demand increases in the daytime to level out fluctuations in demand in order to use energy efficiently in the future. For example, sodium-sulfur batteries, metal-halogen batteries, redox flow batteries, and the like are known. In addition, these new type secondary batteries are also being developed as backup power sources for power generation using natural energy such as sunlight, wind, and wave power, or as power sources for electric vehicles.

The structure of a new type of secondary battery, for example, in the case of a redox flow type battery, usually comprises an external tank for storing an electrolytic solution and an electrolytic cell, and an electrolytic solution containing an active material is incorporated into the electrolytic cell from the external tank. Above, electrochemical energy conversion, that is, charging and discharging is performed. In general, at the time of charging and discharging, an electrolytic solution is circulated between an external tank and an electrolytic cell, so that the electrolytic cell has a liquid sulfuric type structure as shown in FIG. The liquid sulfuric acid type electrolyzer is called a single cell, which is used as a minimum unit and is used alone or in a multi-layered structure. Since the electrochemical reaction in the liquid sulfuric acid type electrolytic cell is a heterogeneous phase reaction occurring on the electrode surface, it generally involves a two-dimensional electrolytic reaction field. When the electrolytic reaction field is two-dimensional, there is a disadvantage that the reaction amount per unit volume of the electrolytic cell is small.

[0005] Therefore, in order to increase the amount of reaction per unit area, that is, the current density, the electrochemical reaction field has been made three-dimensional.

FIG. 2 is a schematic view of a liquid sulfuric acid type electrolytic cell having three-dimensional electrodes.

In the electrolytic cell, two opposing current collector plates 1,
An ion exchange membrane is provided between the two, and an electrolyte exchange flow path 4a, 4b is formed on both sides of the ion exchange membrane 3 by spacers 2 along the inner surfaces of the current collector plates 1, 1. The flow passage 4a,
4b is provided with an electrode material 5 such as a carbon fiber assembly pair.
Are provided, and thus a three-dimensional electrode is configured.

[0008] In the case of a redox flow battery using an aqueous hydrochloric acid solution of iron chloride as a positive electrode electrolyte and chromium chloride as a negative electrode electrolyte, the discharge flow from the electrolyte containing Cr ²⁺ to the liquid flow path on the negative electrode side 4a, and Fe ³⁺ is supplied to the flow path 4b on the positive electrode side.
Is supplied. In the flow path 4a on the negative electrode side, Cr ²⁺ emits electrons in the three-dimensional electrode 5 and is oxidized to Cr ³⁺ . The emitted electrons pass through an external circuit and reduce Fe ³⁺ to Fe ²⁺ in the three-dimensional electrode on the positive electrode side.

Move from the positive electrode side to the negative ^- [0009] Cl of the negative electrode electrolytic solution in accordance with this redox reaction ^- is insufficient, Cl is positive electrode electrolyte ^- for is excessive, through the ion exchange membrane 3 Cl The charge balance is maintained. Alternatively, the charge balance can be maintained by moving H ⁺ from the negative electrode side to the positive electrode side through the ion exchange membrane. At present, there are many schemes in which a cation exchange membrane is used as an ion exchange membrane and charges are balanced by the movement of H ⁺ . At the time of charging, a reaction reverse to that of discharging proceeds.

[0010] The characteristics of the electrode material for the electrolytic cell used in these new type secondary batteries and the like are particularly required to have the following performance. No side reaction other than the desired reaction should occur (high reaction selectivity), specifically, high current efficiency (η _I ). High electrode reaction activity, specifically, low cell resistance (R). That is, the voltage efficiency (η _V ) is high. , But high battery energy efficiency (η _E ). η _E = η _I × η _V Deterioration due to repeated use is small (long life), specifically, the increase in cell resistance (R) and the decrease in current efficiency (η _I ) are small.

[0011]

However, these new models 2
There are inherent problems that need to be solved in order to put a secondary battery into practical use. That is, improvement of performance such as energy efficiency and extension of life. For example, in the redox flow type battery, the electrode material of the iron-chromium redox flow type secondary battery using an aqueous solution of iron chloride as the positive electrode active material and an aqueous solution of chromium chloride as the negative electrode active material, which is currently under development, has chemical resistance. And a conductive carbon fiber polymer is used.

The oxidation-reduction reaction of iron ions at the positive electrode using the carbon fiber aggregate in the battery is not so problematic because the reaction rate is relatively high and side reactions hardly occur. However,
In the negative electrode, since the oxidation-reduction reaction rate of chromium complex ions including a complex exchange reaction is slower than that of iron ions, the cell resistance R increases (voltage efficiency η _V decreases), and hydrogen is generated as a side reaction during charging. Therefore, there has been a problem that the current efficiency η _I decreases.

In view of such circumstances, the present inventors have made intensive studies on an electrode material for an electrolytic cell that enhances the energy efficiency of a battery, and have reached the present invention.

[0014]

According to the present invention, there is provided a carbon material having a pseudo-graphite crystal structure with a <002> plane spacing of 3.70 ° or less and a BET surface area of 5 m ₂ / g or more determined by X-ray wide-angle analysis. A carbon-based electrode material for an electrolytic cell comprising a material, wherein the number of bonded nitrogen atoms on the surface of the carbon material is 0.3% or more with respect to the number of carbon atoms, and the carbon material contains nitrogen atoms bonded to the surface. A carbon-based electrode material for an electrolytic cell, characterized by being present in the form of a nitrogen acidic functional group.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, carbon having a pseudo-graphite crystal structure is defined as having a <002> plane spacing of 3.70 ° or less and 3.354 ° (graphite structure) determined by X-ray wide-angle analysis, preferably. Is a carbon material of 3.40 to 3.70 °. By using the carbon material as the electrode material, side reactions such as generation of hydrogen at the negative electrode during charging can be suppressed, and the current efficiency η _I can be significantly increased.

On the other hand, when a carbon material having a <002> plane spacing larger than 3.70 ° is used, a side reaction such as generation of hydrogen at the negative electrode proceeds during charging, and the current efficiency η _I cannot be increased. In addition, the pseudo-graphite crystal structure is easier to perform surface oxidation treatment described later than the perfect graphite structure having high crystallinity,
And a larger BET surface area is obtained.

As the raw material of the carbon material of the present invention, any carbonizable raw material can be used. For example, pitch, phenolic, acrylic, aromatic polyamide, and cellulose raw materials from coal and petroleum can be used. And the like. Further, as a constituent structure of the carbon material, a spun yarn, a filament bundled yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special woven or knitted fabric (as disclosed in Japanese Patent Application Laid-Open No. 63-200467), or a mixed structure thereof is used. Carbonaceous woven fiber aggregates, porous carbon bodies, carbon-carbon composites, particulate carbon materials, etc., which are not particularly limited. Although the basis weight of the carbonaceous material depends on the structure, it is 50 g / m ^{2 to} 1,000 g / m ² , preferably 10 g / m ^2.
0g / m ² ~500g / m ² is desirable.

In the present invention, the nitrogen-containing acidic functional group refers to a surface hydroxyamino group (> -NH-
OH) and / or hydroxyimino groups (> = NO)
H) and the like. The number of bonded nitrogen atoms on the surface means the amount of bonded nitrogen on the surface of the carbonaceous material detected by ESCA surface analysis, and is expressed as a ratio of the number of bonded nitrogen atoms to the number of carbon atoms (%, hereinafter referred to as N / C ratio). .

The carbonaceous material having the number of bonded nitrogen atoms of 0.3% or more of the number of carbon atoms and having the nitrogen atoms bonded to the surface in the form of a nitrogen-containing acidic functional group is used as an electrode. The use rate of the surface area can be increased by using the material.

The BET surface area in the present invention is a specific surface area per weight of the carbonaceous material obtained by a method described later (BET method). This BET surface area is 5 m ² / g or more,
Preferably in the case of using the carbonaceous material of 5m ² / g~100m ² / g to the electrode material, and the number of attached nitrogen atom described above is 0.3% with respect to the number of carbon atoms, and, attached to said surface When the nitrogen atoms are present in the form of a nitrogen-containing acidic functional group, the cell resistance R decreases and the voltage efficiency η _V can be significantly increased. On the other hand, when the BET surface area is less than 5 m ² / g, the cell surface resistance R increases due to the small electrode surface area, and the voltage efficiency η
_V decreases. If the BET surface area is larger than 100 m ² / g, the surface of the carbonaceous material becomes rough, so that the contact resistance increases, the electrolyte stagnates into the pores, and side reactions such as hydrogen generation progress. It is not preferable because it becomes easier.

The carbonaceous material in which such a nitrogen-containing acidic functional group is present, the number of bonded nitrogen atoms thereof is at least 0.3% based on the number of carbon atoms, and the BET surface area is increased is the above-described pseudographite. It is obtained by dry-oxidizing a carbon material having a crystal structure. For example, 1 × 10 ^-2 torr
The weight yield under the oxygen atmosphere having the above oxygen partial pressure is in the range of 65 to 99%. The processing temperature is usually preferably 400 ° C. or higher. Low temperature (for example, 300 ° C
In the case of (1), the reactivity of the carbon material to be treated is lowered, so that the oxidation effect cannot be obtained. If the oxidation treatment is performed by a wet method, there are many problems such as generation of an intercalation compound and generation of harmful gas during the treatment, so that it should be avoided. This dry oxidation treatment may be a one-step method or a method in which two or more steps are performed at different humidity. Further, instead of heating, plasma may be generated, or processing may be performed using both plasma generation and heating. By performing the dry oxidation treatment so that the BET surface area becomes 5 m 2 / g or more, nitrogen having a stable crystal structure existing inside the carbon material appears at the end, and the nitrogen reacts with the acidic functional group. It is considered that this results in an electrochemically stable nitrogen-containing acidic functional group. In the dry oxidation treatment in the presence of nitrogen, the BET surface area is 5 m ² / g.
The nitrogen-containing acidic functional group is obtained by the dry oxidation treatment as described above.

A carbonaceous material having an increased surface-bound nitrogen amount (N / C ratio) can be obtained by carbonizing a raw material containing nitrogen, such as an acrylic or aromatic polyamide raw material. At this time, if the carbonization temperature is too high, volatilization of nitrogen proceeds, and the amount of remaining nitrogen decreases.
On the other hand, if the processing temperature is too low, the crystallinity becomes low, and the above-mentioned <002> plane spacing becomes 3.70 ° or more. It is preferable to perform a carbonization treatment. By subjecting the carbon material thus obtained to the dry oxidation treatment described above, bound nitrogen effective for electrode performance is formed near the surface.

On the other hand, in the case of a raw material which does not originally contain nitrogen or has a low nitrogen content such as coal, petroleum pitch-based, phenol-based, and cellulosic raw materials, the above-mentioned dry oxidation treatment is performed after the carbonization treatment. The obtained carbon material is immersed in, for example, a solution of a nitrogen-containing reagent such as hydroxylamine hydrochloride and heat-treated, whereby nitrogen atoms can be similarly bonded to the surface (introducing a nitrogen-containing functional group). In addition, after halogenating the surface of the carbon material, it is similarly treated with a solution such as a hydroxylamine salt, or carbonized in the presence of a nitrogen-containing substance (for example, ammonia gas) in the atmosphere, and then subjected to dry oxidation treatment. May go. In any case, there is no particular limitation on the method of forming bonded nitrogen on the carbon material surface.

In this way, the problem can be solved by forming bonded nitrogen on the surface of the carbonaceous material having the above-mentioned pseudo-graphite crystal structure and surface structure.

Next, <002> employed in the present invention.
Measurement methods of the plane spacing (d ₀₀₂ ), current efficiency η _I , cell resistance R, voltage efficiency η _V , battery energy efficiency η _E , BET surface area, and N / C ratio will be described.

<002> Spacing: d _{002 The} electrode material is pulverized in an agate mortar until the particle size becomes about 10 μm, and about 5% by weight of the sample as a high purity silicon powder for X-ray standard is used as an internal standard substance. The mixture is mixed, packed in a sample cell, and a wide-angle X-ray analysis curve is measured by a diffractometer method using CuKα radiation as a radiation source.

For the correction of the curve, the following simple method is used without correcting the so-called Lorentz factor, polarization factor, absorption factor, atomic scattering factor and the like. That is, the midpoint where the line parallel to the angle axis drawn to the height of 2/3 of the peak height corresponding to <002> diffraction crosses the corrected intensity curve is determined, and the angle of the midpoint is corrected by the internal standard. This is set to twice the diffraction angle, and C
<00 from the wavelength λ of uKα by the Bragg equation
2> Find the surface spacing. d ₀₀₂ = λ / 2 sin θ, where λ = 1.5418 ° θ = <002> diffraction angle

Electrode Characteristics An electrode area of the same shape as the liquid flow type electrolytic cell shown in FIG. 2 having an electrode area of 10 cm in the vertical direction (liquid flowing direction) and 1 cm in the width direction.
A small cell with ² is made, charge and discharge are repeated at a constant current density, and the electrode performance is tested. 4N mixed with ferrous chloride and ferric chloride at a concentration of 1 M / l each for the positive electrode electrolyte
A hydrochloric acid aqueous solution was used, and a 1 M / l chromium chloride 4N hydrochloric acid aqueous solution was used as a negative electrode electrolyte. The amount of the positive electrode electrolyte was made to be a large excess with respect to the amount of the negative electrode electrolyte so that the characteristics of the negative electrode could be examined mainly. The spacer thickness used was 1.5 m
m, the liquid flow rate was 4.8 ml per minute, and the measurement was performed at 40 ° C.

(1) Current efficiency: In a one-cycle test starting from η _I charge and ending with discharge, the current density was set to 40 mA / cm ² (4
00 mA), the quantity of electricity required for charging up to 1.2 V is Q ₁ coulomb, the quantity of electricity extracted by constant-current discharge up to 0.2 V and the subsequent quantity of constant voltage discharge at 0.8 V is Q ₂ , and Q ₃ coulombs, obtains the current efficiency eta _I by the following equation. _{η I = (Q 2 + Q} 3) / Q 1 × 100 (%) reactions other than reduction of C _r ³⁺ upon charging to the C _r ^2+, for example H
^When a side reaction (generation of hydrogen gas) such as reduction of ⁺ occurs, the amount of electricity that can be taken out decreases, and the current efficiency η _I decreases.

[0030] (2) the cell resistance: the C _r ³⁺ in R negative electrode solution on the theoretical quantity of electricity Q _th required to completely reduce the C _r ^2+, for, the quantity of electricity taken out by the discharge Is defined as the charging rate, the charging rate = (Q ₂ + Q ₃ ) / Q _th × 100 (%) The resistance R (Ωcm 2) with respect to the electrode geometric area is obtained from the slope of the current / voltage curve when the charging rate is 50%. .

(3) Voltage efficiency: η _V Using the cell resistance R obtained by the above method, the voltage efficiency η _V is obtained by a simple method of the following equation. η _V = (E−I · R / 10) / (E + I · R / 10) × 100
(%) Here, E is an open circuit voltage (V) of the cell when the charging rate is 50%, and I is a current value (A) in constant current charging and discharging. For E, 0.987 V which is an actually measured value was used, and I = 0.
The voltage efficiency η _V at 4 A, that is, at a current density of 40 mA / cm ² was evaluated. R is the cell resistance (Ωcm ² ) described above. As the cell resistance R is smaller, the oxidation-reduction reaction of the ions of the active material occurs more quickly, so that the discharge voltage at a high current density becomes higher, and the voltage efficiency η _{V of the} cell becomes higher.

(4) Energy efficiency of battery: η_E Current efficiency η described above_IAnd voltage efficiency η_VAnd the following equation
Battery energy efficiency η _EAsk for. η_E= Η_I× η_V× (1/100) (%) Current efficiency η_IAnd voltage efficiency η_VThe higher the
Lugie efficiency η_EIs high, and therefore the
Energy loss is small and it is judged to be an excellent electrode
You.

BET Surface Area About 0.1 g of the electrode material was sampled, vacuum-dried at 120 ° C. for 12 hours and weighed, and the nitrogen gas adsorption amount at the boiling point of liquid nitrogen (−195.8 ° C.) was measured at a relative pressure of 0.1%. A few points were measured while gradually increasing in the range of 0 to 0.2. E. FIG. T. The specific surface area (m ² / g) per electrode material weight was determined by plotting.

N / C Ratio The N / C ratio on the surface of the carbonaceous material is measured by X-ray photoelectron spectroscopy, which is abbreviated as ESCA or XPS. The measuring device is Shimadzu ESCA750, and the analysis is ESCA PA
C760 was used. The electrode material was cut out to a diameter of 6 mm and attached to a heated sample stage with a conductive paste.
While heating at 0 ° C., measurement was performed after degassing for 3 hours or more. The MgKα ray (1253.6 eV) was used as the radiation source, and the surface of the sample was analyzed under the condition that the degree of vacuum in the apparatus was 10 −7 torr. Here, the surface means a region having a depth from the outermost layer of the sample to several tens of mm.

The measurement is performed on the Cls and N1s peaks, and the area of each peak is determined using ESCA PAC760.

The obtained area is divided by the relative intensity of 1.00 for C1s and 1.77 for N1s based on the correction method by JHScofieid, and the surface (nitrogen / nitrogen) atom number is directly calculated from the value. The ratio was calculated in%.

(Function) The characteristics of the electrode material for an electrolytic cell of a new type secondary battery or the like mainly include the current efficiency η _I and the voltage efficiency η _V as described above.
(Cell resistance R) and battery energy efficiency η _E.

The current efficiency η _I decreases mainly because part of the charged electricity is consumed by side reactions such as generation of hydrogen during charging. Although the degree of the ordinary carbon material varies depending on the raw material system, crystallization progresses with an increase in the processing temperature, and the value of d ₀₀₂ decreases and approaches the value of graphite crystal. The state of the crystallization approaches the value of the carbon material. If the crystallization state, that is, the crystal structure of the carbon material is different, the corresponding electron energy structure is also different.
In general, when a metal element is used for an electrode, the crystal structure of carbon greatly affects the electrochemical reaction selectivity, that is, the current efficiency η _I , as can be seen that the electrochemical reaction selectivity differs for each element. It is thought that. The present invention, d ₀₀₂ is if it has the following擬黒lead crystal structure 3.70A, can significantly increase the current efficiency eta _I.
It is presumed that the reaction selectivity based on the electron energy structure of the carbon material having the above structure is in an optimum state for the system to be used. In addition, the internal structure of carbon is made uniform (averaged) with the progress of crystallization due to the heat treatment, and structural defects are reduced or eliminated. Therefore, the electrode potential when used as an electrode material is made uniform (electrode potential). distribution is presumed that also contribute to the increase of the current efficiency eta _I narrowing made). As is well known, metal impurities, particularly transition metals such as iron, chromium, and nickel, act as catalysts for accelerating side reactions. Therefore, it is important to use a carbon material with a minimum amount of these impurities.

By controlling the crystal structure of the carbon material within the above-described range of the present invention, the current efficiency η _I can be increased. Further, if carbon materials having the same crystal structure are considered to have the same electrode (reaction) activity per unit surface area, electrode activity is considered to be proportional to the surface area if the weight of the electrode material is the same. Can be

However, since carbon is inherently hydrophobic, when a highly polar electrolyte such as an aqueous electrolyte is used, the wettability of the surface of the carbon material with these electrolytes is insufficient, and the utilization of the surface area is low. Become. Therefore, the present invention provides a carbon-containing material having a nitrogen-containing acidic functional group which contributes to the wettability of the electrolytic solution on the surface of the carbon material so that the number of bonded nitrogen atoms is 0.3% or more of the carbon atom. The wettability with the liquid is improved, and the utilization rate of the surface area is significantly increased without the acidic functional group being eliminated in the initial stage (first cycle). If the carbonaceous material has an increased number of nitrogen-containing acidic functional groups, the electrode activity is considered to be proportional to the surface area of the carbonaceous material (for example, the relationship between platinum and platinum black). The carbon-based electrode material for the electrolytic cell in the present invention is a carbonaceous material having an increased surface area because of ensuring the wettability of the electrolytic solution with the nitrogen-containing acidic functional group, so that the electrode effective surface area is significantly increased, The resistance R is reduced, so that the voltage efficiency η _V can be increased significantly. In addition, as the surface area increases, the surface resistance of the carbonaceous material progresses, so that the contact resistance increases, the stagnation of the electrolytic solution accompanying the increase in the pores, etc., and the supply of active material ions to this portion occurs. The surface area is preferably not more than 100 m ² / g, since the reaction is not carried out smoothly and the overvoltage rises to easily cause side reactions such as hydrogen generation.

The above-described pseudo-graphite crystal structure and surface structure
Current effect by using carbonaceous material with
Rate η_I, Voltage efficiency η_VRise, and therefore the battery energy efficiency
Rate η _ECan be greatly increased.

At this time, the effect of the bonded nitrogen is unknown, but, for example, a hydroxyamino group (> @ NH-OH) or a hydroxyimide group (>) on the surface of the carbonaceous material.
N-OH), and it is considered that these nitrogen-containing acidic groups contribute to the wettability of the electrode material surface similarly to the above-mentioned oxygen-containing acidic groups. Furthermore, it is considered that these nitrogen-containing acidic functional groups are in a state where they are less likely to be reduced than the oxygen-containing acidic functional groups (they are less likely to be altered; the altered potential is at a lower potential). Is also stable,
It is presumed that it contributes to the wettability of the electrode material surface and suppresses an increase in cell resistance.

[0043]

The present invention will be described below with reference to examples.

Example 1 A polyacrylonitrile fiber having an average fiber diameter of 16 μm was oxidized at 250 ° C. in air.
The short fiber of the flame-resistant fiber is used to make a felt and the basis weight is 4
A fabric of 00 g / m ² was produced. The fabric was heated in an inert gas at a rate of 10 ° C./min to 1250 ° C., kept at this temperature for 1 hour, carbonized and cooled, and subsequently 650 ° C. in air at 91% weight yield. To obtain a fabric A. The basis weight of the fabric A was 203 g / m ² , the average fiber diameter was 10 μm, d ₀₀₂ was 3.55 °, BE
The T surface area was 8.62 m ² / g, and the N / C ratio was 2.8%. As a result of measuring the electrode performance using the cloth A, the current efficiency η _I = 98.6 at the second charge / discharge cycle.
%, Cell resistance R = 1.04 Ωcm ² , voltage efficiency η _V = 9
1.9% and battery energy efficiency η _E = 90.6%.

Example 2 Aromatic polyamide short fibers having an average fiber diameter of 23 μm were made into felts, and the basis weight was 283 g / m ^2.
Was produced. This fabric is heated at 10 ° C /
The temperature was raised to 1500 ° C. at a rate of 1 minute, and kept at this temperature for 1 hour to perform carbonization and cooling.
To obtain a fabric B by oxidizing until the weight yield became 90%. Fabric B has a basis weight of 210 g / m ² and an average fiber diameter of 1
8 μm, d ₀₀₂ is 3.60 °, BET surface area is 6.51
m ² / g, N / C ratio was 2.2%. The electrode performance was measured using the cloth B. As a result, at the second charge / discharge cycle, the current efficiency η _I = 98.0% and the cell resistance R =
1.30 Ωcm ² , voltage efficiency η _V = 90.0%, and battery energy efficiency η _E = 88.2%.

Example 3 A fabric having a basis weight of 260 g / m ² prepared by felting phenol novolak short fibers having an average fiber diameter of 14 μm was heated to 1800 ° C. in an inert gas at a rate of 10 ° C./min. After heating at this temperature for 1 hour, carbonization was performed and cooling was performed, followed by oxidation treatment at 700 ° C. in air until the weight yield became 93%, to obtain a fabric made of carbon fibers. The carbonaceous fiber fabric was placed in a 10 wt% aqueous solution of hydroxylamine dihydrochloride (NH ₂ OH · 2HCl),
After treating at 95 ° C. for 5 hours, it was washed with water and dried to obtain Fabric C. Fabric C has a basis weight of 195 g / m ² and an average fiber diameter of 1
0.3 μm, d ₀₀₂ was 3.65 °, BET surface area was 30.00 m ² / g, and N / C ratio was 1.7%.
As a result of measuring the electrode performance using the cloth C, the current efficiency η _I = 98.1%, the cell resistance R = 1.35 Ωcm ² , the voltage efficiency η _V = 89.6% in the second charge / discharge cycle,
The battery energy efficiency η _E was 87.9%.

(Example 4) The carbonaceous fiber cloth before the hydroxylamine dihydrochloride treatment used in Example 3 was used as the cloth G, and the electrode performance was measured using the cloth G. Current efficiency η _I = 9 at cycle
8.2%, cell resistance R = 1.38Ωcm ² , voltage efficiency η _V
= 89.4%, and the battery energy efficiency η _E was 87.8%. The basis weight of the fabric G was 193 g / m ² , the average fiber diameter was 10.3 μm, d ₀₀₂ was 3.65 °, the BET surface area was 30.00 m ² / g, and the N / C ratio was 0.3%. .

Example 5 A regenerated cellulose short fiber having an average fiber diameter of 25 μm, which was sufficiently desulfurized, bleached, washed and dried, was made into a felt, and a fabric having a basis weight of 313 g / m ² was prepared in an inert gas. The temperature was raised to 270 ° C. at a rate of 10 ° C./min (flame-resistant treatment) and then 20 ° C.
The temperature was raised to 00 ° C., kept at this temperature for 1 hour, carbonized and cooled, and then oxidized at 700 ° C. in air until the weight yield became 93% to obtain a carbonaceous fiber fabric H. . As a result of measuring the electrode performance using the cloth H, the current efficiency η _I = 97.5%, the cell resistance R = 1.35 Ωcm ² , the voltage efficiency η _V = 89.6%, and the battery in the second charge / discharge cycle. The energy efficiency η _E was 87.4%. The fabric H had a basis weight of 197 g / m ² , an average fiber diameter of 21.0 μm, d ₀₀₂ of 3.61 °, and a BET surface area of 65.00 m ^2.
/ G, N / C ratio was 0.4%.

Example 6 An isotropic pitch fiber having an average fiber diameter of 15 μm was heated in air at a rate of 1.5 ° C./min.
C., and kept at this temperature for 1.5 hours to infusibilize. Then, a short fiber of the infusibilized fiber was made into a felt, and a fabric having a basis weight of 241 g / m ² was produced in an inert gas at 10 ° C. / The temperature is raised to 1500 ° C. at a temperature rising rate of 1 minute, the temperature is maintained for 1 hour, carbonization is performed, and cooling is performed. Fabric I was obtained. As a result of measuring the electrode performance using the cloth I, the current efficiency η _I = 9 at the second charge / discharge cycle.
7.7%, cell resistance R = 1.35Ωcm ² , voltage efficiency η _V
= 89.6%, and the battery energy efficiency η _E was 87.5%. The basis weight of Fabric I was 245 g / m ² , the average fiber diameter was 13 μm, d ₀₀₂ was 3.67 °, the BET surface area was 76.50 m ² / g, and the N / C ratio was 0.4%.

(Comparative Example 1) An anisotropic pitch fiber (mesophase pitch fiber) having an average fiber diameter of 13 µm was used in air.
The temperature was raised to 350 ° C. at a temperature rising rate of 5 ° C./min, and the temperature was maintained at this temperature for 1.5 hours to infusibilize, and then the short fiber of the infusibilized fiber was felted to produce a basis weight of 255 g / m ^2. Is heated in an inert gas at a heating rate of 10 ° C./min to 1300 ° C., kept at this temperature for 1 hour, carbonized and cooled, and subsequently 650 ° C. in air at 94% weight yield. To obtain a carbonaceous fiber fabric J. As a result of measuring the electrode performance using the cloth J, the current efficiency η _I = 98.4% and the cell resistance R = 2.
10 Ωcm ² , voltage efficiency η _V = 84.3%, and battery energy efficiency η _E = 83.0%. The basis weight of the fabric J was 225 g / m ² , the average fiber diameter was 10 μm, d ₀₀₂ was 3.50 °, the BET surface area was 3.96 m ² / g, and N / C
The ratio was 0.3%.

(Comparative Example 2) The carbonized fiber cloth before the oxidation treatment used in Example 3 was used as cloth M, and the electrode performance was measured using this cloth M. As a result, the current efficiency in the second charge / discharge cycle was measured. η _I = 98.0%, cell resistance R = 10.0
Ωcm ² , η _V = 42.3%, battery energy efficiency η _E =
41.5%. The basis weight of the fabric L was 204 g /
m ² , average fiber diameter is 10.9 μm, and d ₀₀₂ is 3.65
Å, BET surface area: 0.53 m ² / g, N / C ratio: 0.3
2%.

Comparative Example 3 Phenol used in Example 3
A felt-like fabric made of novolak fiber is treated with an inert gas.
In the medium, the temperature was raised to 1300 ° C at a rate of 10 ° C / min.
Temperature for 1 hour, carbonized, cooled and carbonized fiber
Fabric Q was obtained. The electrode performance was measured using this cloth Q.
As a result, the current efficiency η at the second charge / discharge cycle_I= 6
8.0%, cell resistance R = 9.2Ωcm^Two, Voltage efficiency η_V=
45.7%, battery energy efficiency η _E= 31.1%
Was. The basis weight of the fabric Q was 224 g / m.^Two, Average fiber
The diameter is 11.8 μm, d002 is 3.74 °, BET
The surface area is 0.83m^Two/ G, N / C ratio is 0.4%.
Was.

Table 1 summarizes the results of the above examples and comparative examples. In the present embodiment, the case of felt (non-woven fabric) is described as a constituent structure of the electrode material. However, other structures such as a knitted fabric, a woven fabric, a special knitted fabric, a filament bundled yarn, and the like are similar to the present embodiment. Effect is recognized.

[0054]

[Table 1]

[0055]

By using the electrode material of the present invention, in the field of using various electrolytic cells, it is possible to suppress harmful side reactions to increase the current efficiency and to suppress the cell resistance to increase the voltage efficiency. Battery energy efficiency. Furthermore, it can bring great industrial utility.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a battery using a flow-through electrolytic cell such as a redox flow battery.

FIG. 2 is a schematic exploded perspective view of a liquid flow type electrolytic cell having a three-dimensional electrode according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current collecting plate, 2 ... Spacer, 3 ... Ion exchange membrane, 4a,
b: liquid passage, 5: electrode material, 11: liquid inlet, 12: liquid outlet

Claims (1)

[Claims] 1. A carbon system for an electrolytic cell comprising a carbon material having a pseudo-graphite crystal structure having a <002> plane spacing of 3.70 ° or less and a BET surface area of 5 m ² / g or more determined by X-ray wide-angle analysis. An electrode material, wherein the number of bonded nitrogen atoms on the surface of the carbon material is 0.3% or more of the number of carbon atoms, and the nitrogen atoms bonded to the surface are present in the form of a nitrogen-containing acidic functional group. A carbon-based electrode material for an electrolytic cell, comprising: