JP2003213563A - Hydrophilic carbon fiber sheetlike material, carbon fiber electrode material and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon fiber electrode material capable of maintaining high battery performances without lowering a gas diffusion ability of the electrode even by long-term continuous use, a hydrophilic carbon fiber sheetlike material suitably used for the electrode material and a method for producing the same sheetlike material. <P>SOLUTION: This carbon fiber electrode material has a layer composed of a water-repellent resin and electroconductive fine particles on one surface of the hydrophilic carbon fiber sheetlike material. The contact angle of the surface having the water repellency with water is ≥108° and the back surface and cross section preferably have water absorbency. The hydrophilic carbon fiber sheetlike material has 0.2-15 g/g water absorbing capacity when the cross section is dipped in water for 5 min. The carbon fiber sheetlike material is obtained by hydrophilizing the carbon fiber sheetlike material according to liquid-phase oxidation or vapor-phase oxidation. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon fiber sheet material, and more specifically, to a hydrophilic carbon fiber sheet material and a carbon fiber electrode which are preferably used as an electrode material of a polymer electrolyte fuel cell. The present invention relates to a material and a manufacturing method thereof.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell is a very clean power generation system in which only water is discharged, and has recently been receiving much attention. Fuel cells obtain electromotive force by an electrochemical reaction between a fuel gas containing hydrogen and an oxidizing gas containing oxygen. In order for such a reaction to proceed continuously, gas diffusivity, conductivity, heat resistance , An electrode with excellent chemical resistance is required. Since carbon materials are excellent in their characteristics, they are optimal as electrodes for fuel cells.

However, in the electrochemical reaction of the fuel cell, water is generated at the electrode, but the water has a problem that the gas diffusing ability of the electrode is lowered and the electrochemical reaction is difficult to occur.

In order to solve the problem, for example, Japanese Patent Application Laid-Open No. 11-310460 proposes a water-repellent carbon fiber material having a contact angle with water of 108 degrees or more. But,
The polymer electrolyte membrane in a fuel cell has the property of exhibiting high ionic conductivity only when it is sufficiently hydrated.Since the polymer electrolyte membrane is in contact with the electrode, an electrode made of a water repellent carbon fiber material is sufficient. However, there is a problem that various moisture does not move to the polymer electrolyte membrane. Also, humidified gas is supplied to the electrodes and the polymer electrolyte membrane during operation,
Not supplied when not in use. Therefore, if water evaporates when not in use, it not only takes time to restart,
There is a problem that the polymer electrolyte membrane is deteriorated and the life of the fuel cell itself is shortened.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its purpose is to prevent the gas diffusing ability of the electrode from being deteriorated even after continuous use for a long time.
It is intended to provide a carbon fiber electrode material capable of maintaining high battery performance, a hydrophilic carbon sheet material suitably used for the electrode material, and a method for producing the same.

[0006]

The hydrophilic carbon fiber sheet material of the present invention is characterized by having a water absorption of 0.2 to 15 g / g when its cross section is immersed in water for 5 minutes. Further, it is preferable that the carbon fiber has a non-woven fabric structure, or that the Na content is 30 ppm or less, the K content is 30 ppm or less, and the Ca content is 150 ppm or less.

The method for producing a hydrophilic carbon fiber sheet material of the present invention is characterized in that the carbon fiber sheet material is hydrophilized by liquid phase oxidation or gas phase oxidation. Furthermore, the conditions for vapor phase oxidation are 3 to 3 in water vapor at 700 to 1000 ° C.
Treatment for 45 minutes is preferable.

Still another carbon fiber electrode material of the present invention is characterized by having a layer comprising a water-repellent resin and conductive fine particles on one surface of the hydrophilic carbon fiber sheet material of the present invention. Further, the adhesion amount of the water-repellent resin and the conductive fine particles to the total weight of the carbon fibers is 0.01 to 30% by weight, and the contact angle of water on the water-repellent surface is 108 degrees or more. Is preferred.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrophilic carbon fiber sheet material of the present invention has a water absorption of 0.2 when its cross section is immersed in water for 5 minutes.
It should be ~ 15 g / g. Furthermore, 4-1
It is more preferably 0 g / g. Water absorption is 0.2g
If it is less than / g, water is not sufficiently supplied to the polymer electrolyte membrane when it is used as an electrode material, and conversely the water absorption is 15 g /
If it exceeds g, the generated water becomes excessive and gas diffusion is hindered.

Further, in the hydrophilic carbon fiber sheet material of the present invention, it is preferable that the carbon fiber is a non-woven fabric structure. When the carbon fiber has a non-woven fabric structure, the surface smoothness is high, and for example, when a pressure of several MPa is applied in a state where the carbon fiber is bonded to the polymer electrolyte membrane in the fuel cell, the polymer electrolyte membrane has a small unevenness and Hard to damage. In many carbon fiber nonwoven fabrics, the carbon fiber axial direction is oriented in the thickness direction, and the electric resistance value in the thickness direction tends to be low.

The hydrophilic carbon fiber sheet of the present invention has a Na content of 30 ppm or less and a K content of 30 pp.
It is preferable that m or less and the Ca content be 150 ppm or less. Furthermore, Na content is 10 ppm or less, K
It is preferable that the content is 10 ppm or less and the Ca content is 50 ppm or less. When the content of these metals is in the above range, in the electrode material using the hydrophilic carbon fiber sheet-like material of the present invention, migration of metal from the electrode to the polymer electrolyte membrane is small, and deterioration of the polymer electrolyte membrane is unlikely to occur. The durability of the fuel cell can be further increased.

The hydrophilic carbon fiber sheet material of the present invention is composed of carbon fibers. The carbon fiber used here is polyacrylonitrile (P
AN) series, pitch series, phenol resin series, aramid series,
There are cellulose-based materials and the like, and the materials are not particularly limited. However, in order to obtain a sheet-like material having high strength, PAN-based carbon fibers having high strength and elongation are preferable.

The unit weight of the carbon fiber sheet material of the present invention is 30.
It is preferably ˜220 g / m ² . When the basis weight of the carbon fiber sheet material is less than 30 g / m ² , the strength of the sheet material tends to decrease, and when it is used as an electrode, the gas diffusion rate tends to be too fast and the battery performance tends to decrease. When the basis weight of the sheet material exceeds 220 g / m ² , the electric resistance value in the thickness direction tends to increase.

The bulk density of the sheet material is 0.08 to 0.5.
It is preferably 0 g / cm ³ . Bulk density is 0.0
When it is less than 8 g / cm ³ , when it is used as an electrode, the internal resistance of the sheet-like material increases, so that the electric resistance value tends to increase. When the bulk density exceeds 0.50 g / cm ³ , gas diffusibility tends to decrease.

The sheet material has a thickness of 0.15 to 1.0 m.
It is preferably m. The thickness of the sheet is 0.15
If it is less than mm, the strength of the sheet-like material may decrease,
It tends to be easily cut during processing, and tends to cause elongation. When the thickness of the sheet-like material exceeds 1.0 mm, electric resistance in the thickness direction increases when it is used as an electrode, it is difficult to make the battery compact, and it is difficult to control the dimensions. is there.

The strength of the sheet material is preferably 2 N / cm or more, more preferably 5 N / cm or more. Generally, the upper limit is about 30 N / cm for a nonwoven fabric and about 100 N / cm for a woven fabric. Strength is 2N / c
If it is less than m, the sheet may be broken when tension is applied to the sheet in the continuous processing step.

The carbon fiber used in the present invention preferably has an X-ray crystallite size of 1.3 to 3.5 nm. When the X-ray crystallite size is less than 1.3 nm, the electrical conductivity is low, and the battery performance when used as an electrode tends to deteriorate. When the X-ray crystallite size exceeds 3.5 nm,
The fibers tend to be brittle.

The hydrophilic carbon fiber sheet material of the present invention preferably has a specific resistance value (conductivity) of 10 Ωcm or less, more preferably 0.01 to 6 Ωcm. When the sheet-shaped material is used as an electrode material, if the specific resistance value of the hydrophilic carbon fiber sheet-shaped material is high, the electrical conductivity is lowered, and the battery performance tends to be lowered. Furthermore, heat is generated and the carbon fibers tend to become brittle.

Such a hydrophilic carbon fiber sheet material is
It can be obtained by another method for producing a hydrophilic carbon fiber sheet material of the present invention, that is, by hydrophilizing a carbon fiber sheet material by liquid phase oxidation or gas phase oxidation.
This method is a production method in which a carbon fiber sheet material is oxidized to increase hydrophilic functional groups on the surface of the carbon fiber. In the hydrophilic sheet material according to the production method of the present invention, since no hydrophilic treatment agent or the like is used, impurities are not generated during use, and the performance is not significantly deteriorated during continuous use.

The liquid phase oxidation method as the hydrophilic treatment method includes high temperature oxidation treatment with hydrogen peroxide solution or sodium hypochlorite (50 to 80 ° C.) and electrolytes (sulfuric acid, caustic soda, ammonium sulfate, salt, etc.). ).

As the gas phase oxidation method for the hydrophilic treatment, air oxidation (300 to 600 ° C.) and ozone oxidation (25 to 400) are used.
℃) and oxidation by steam and carbon dioxide (500-120
0 ° C.) method or the like is used.

Of these hydrophilic methods, the electrolytic oxidation treatment using an electrolyte, which is less dangerous in the liquid phase oxidation method, is preferable. In the gas-phase oxidation method, it is preferable to carry out an oxidation treatment with water vapor or carbon dioxide in which a metal or the like is less mixed.

Among the vapor phase oxidation methods, in particular, the carbon fiber sheet-like material is steamed at 700 to 1000 ° C. for 3 to 45 minutes.
It is most preferable that the treatment is carried out for a minute, more preferably for 5 to 30 minutes. If the hydrophilization time is less than 3 minutes, sufficient hydrophilicity cannot be obtained. If the hydrophilization time exceeds 45 minutes, oxidative deterioration occurs due to overtreatment, and black powder tends to be generated.

The carbon fiber sheet material before the hydrophilic treatment used in the present invention can be obtained, for example, as follows.

The precursor fiber, which is a raw material for the carbon fiber sheet material, includes polyacrylonitrile (PAN) type, pitch type, phenol resin type, aramid type, cellulose type and the like and is not particularly limited, but in the present invention. ,
As mentioned above, it is most preferable to use the PAN-based precursor fiber.

PAN as a particularly preferred precursor fiber
As the system fiber, 90 acrylonitrile monomer units are used.
It is most preferable that the content of the comonomers is from about 98% by mass to about 2% to 10% by mass, and examples of the comonomer include vinyl monomers such as methyl acrylate, acrylamide, and itaconic acid.

The fineness of the precursor fiber is 0.6 to 2.4.
dtex is preferable, and 0.7 to 2.4 dtex is particularly preferable. When the fineness is less than 0.6 dtex, heat storage cutting is likely to occur during the oxidation treatment, and when the fineness exceeds 2.4 dtex, the oxidation treatment requires a long time and the strength of the oxidized fiber is lowered.

The obtained precursor fiber is oxidized in air to be an oxidized fiber. The oxidized fiber is further processed into a spun yarn woven fabric or a non-woven fabric, and finally carbonized to obtain a carbon fiber sheet.

The carbon fiber sheet-like material used in the present invention is treated with an organic acid in the course of, for example, a step of stretching precursor fibers or a step after the carbon fiber sheet-like material is formed in the middle of the process. ) It is preferable to reduce the content. As the organic acid used for the organic acid treatment, any one can be used, but it is most preferable to use hydrochloric acid, which is inexpensive and easy to remove salts. It is difficult to remove salts with sulfuric acid, and other organic acids such as oxalic acid are expensive, the precursor fibers are colored during use, and it is difficult to remove salts.

The acid concentration in the organic acid treatment is pH = 0.1.
The range of -2.0 is preferable, and the range of 0.2-1.0 is more preferable. The treatment temperature is preferably in the range of 25 to 90 ° C. If the acid is too strong or the processing temperature is too high,
The nitrile group in the precursor fiber is hydrolyzed, so that the amount of comonomer increases and the yield tends to decrease. On the contrary, if the pH exceeds 2, and if the treatment temperature is lower than 25 ° C,
There is a tendency that the metal content cannot be sufficiently removed. When hydrochloric acid is used, it is preferable to perform washing at 80 ° C. at 1.0% by mass of hydrochloric acid.

For the oxidation treatment of the precursor fiber, for example, after the oxidation treatment at an initial oxidation temperature of 215 to 245 ° C. in air, the temperature is further raised to 250 to 280 ° C. to perform the oxidation treatment. When the initial oxidation temperature exceeds 245 ° C., fusion between the fibers and the fiber surface occurs, which causes defects on the fiber surface and tends to reduce the fiber strength. When the initial oxidation temperature is lower than 215 ° C, it takes a long time for the oxidized fiber to reach a predetermined specific gravity, and the productivity tends to be lowered.

The fineness of the oxidized fiber after oxidation is 0.8 to
3.2 dtex is preferable, and more preferably 1.0 to
It is 2.5 tex. Oxidation fiber fineness is 0.8 dtex
When it is less than 1, the yarn strength of the single fiber is low, yarn breakage is likely to occur during woven or non-woven fabric processing and carbonization, and there is a tendency that the processability decreases due to fiber convergence (dispersion decrease). . When the fineness of the oxidized fiber exceeds 3.2 dtex, the oxidation time becomes long and the productivity tends to decrease, and the fiber strength decreases during carbonization in the subsequent step,
The amount of carbon fiber fine powder generated tends to increase. The fineness of the oxidized fiber can be adjusted by the fineness of the precursor fiber as a raw material for production, the relaxation condition at the time of oxidation, and the like.

At this time, the preferable strength (standard state) of the oxidized fiber is 1.5 g / dtex or more, and the elongation (standard state) is 12% or more. The strength of the oxidized fiber is 1.5g
If it is less than / dtex, or if the elongation is less than 12%, the workability into a structural material tends to decrease.

The preferred knot strength of the oxidized fiber is 0.6 g.
/ Dtex or more and the nodule elongation is 4% or more.
When the knot strength of the oxidized fiber is less than 0.6 g / dtex,
Alternatively, if the knot elongation is less than 4%, spinning processability and carbon fiber structural material strength tend to decrease.

The specific gravity of the oxidized fiber is preferably 1.30 to 1.42. When the specific gravity of the oxidized fiber is less than 1.30, carbon fiber fine powder is likely to be produced, and the strength of the obtained carbon fiber spun yarn woven fabric / nonwoven fabric tends to be lowered. When the specific gravity of the oxidized fiber exceeds 1.42, the single fiber strength and the elongation of the oxidized fiber decrease, and the processability when producing the oxidized fiber spun yarn fabric and the oxidized fiber nonwoven fabric tends to decrease. is there.

The above-mentioned oxidized fiber is cut to a fixed length or bias-cut with a tow reactor to make a short fiber, and an oxidized fiber sheet-like material is produced using this fiber. The average cut length of the single fiber is preferably 25 to 65 mm, and when it is out of this range, yarn breakage occurs during processing into an oxidized fiber structure material, which is not preferable.

The crimp ratio of the oxidized fiber staple is 8 to 1
It is preferably 6%. When the crimping rate is less than 8%, the fibers are less entangled with each other and the yarn tends to be broken during processing into the structural material. When the crimp rate of the oxidized fiber structural material is higher than 16%, the strength of the single fiber constituting the oxidized fiber structural material is lowered, and the yarn breakage tends to occur during the processing of the structural material.

An oxidized fiber sheet is prepared using the oxidized fiber thus obtained. As the sheet-like material, an oxidized fiber spun yarn can be prepared by spinning a spun yarn to give an oxidized fiber spun yarn woven fabric, but a nonwoven fabric is most preferable. When an electrode is formed from a woven fabric, a pressure of several MPa is applied in a state where the polymer electrolyte membrane and the electrode are joined in the fuel cell, so that the unevenness of the woven fabric surface may damage the polymer electrolyte membrane. Also,
When the woven fabric is cut, the spun yarn is frayed from the end of the woven fabric, and it tends to be difficult to maintain the shape. Further, the loosened spun yarn may enter between the respective members at the time of joining the fuel cell.

When the electrode is made of a non-woven fabric, the polymer electrolyte membrane and the electrode are bonded together in the fuel cell, and the number of M
Even when a pressure of Pa is applied, the fibers are uniformly dispersed, so that the polymer electrolyte is less damaged. Further, since the manufacturing process is simple and the complicated process is not performed, the damage of the fiber itself is reduced, the amount of carbon fiber fine powder generated is extremely reduced, and the cost can be reduced.

The oxidized fiber non-woven fabric is formed by, for example, processing cotton of oxidized fiber, which is cut to a fixed length, into a card, and further has a basis weight of 10 to 50 g.
It can be prepared by forming webs of / m ² and superposing them, and then continuously punching with a water stream by the water jet method.

Next, the oxidized fiber sheet material obtained as described above is carbonized to obtain a carbon fiber sheet material.

The carbon fiber sheet-like material is, for example, 1300 to 1300 continuously obtained by oxidizing the above-mentioned oxidized fiber sheet-like material in an inert atmosphere.
It can be obtained by carrying out carbonization at 2000 ° C. for 1 to 10 minutes. As the inert gas, nitrogen, helium, argon or the like is used. When the carbonization temperature is lower than 1300 ° C., the electric resistance value tends to be high, and Na and K tend to remain without sublimation. When the carbonization temperature exceeds 2000 ° C., the electric resistance value decreases and Na and K can also be reduced, but the Ca content tends to increase slightly and the fiber tends to become brittle, which reduces the strength of the carbon fiber structural material. Alternatively, the amount of carbon fine powder generated tends to increase.

At this stage, as described above, metal (Na,
In order to reduce the (K, Ca) content, it is also preferable to treat the carbon fiber sheet material with an organic acid such as hydrochloric acid.

The obtained carbon fiber sheet-like material is treated with an organic acid or untreated to be hydrophilized to be the hydrophilic carbon fiber sheet-like material of the present invention. By using this hydrophilic carbon fiber sheet material of the present invention, a high performance carbon fiber electrode material can be easily obtained.

Another carbon fiber electrode material of the present invention is
The hydrophilic carbon fiber sheet material of the present invention is a sheet material having a layer comprising a water-repellent resin and conductive fine particles on one surface.

As the water-repellent resin, for example, tetrafluoroethylene / hexafluoropropylene copolymer (FE
P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), and other fluorine-based resins are preferable from the viewpoint of water repellency and oxidation resistance required for fuel cells, and among them PTFE Is more preferable because it has the effect of reducing the electric resistance value.

As the conductive fine particles, for example, carbon black, powdered activated carbon, and milled fiber of activated carbon fiber are used. The particle size is preferably 0.1 to 10 μm or less. By attaching the conductive fine particles, the surface smoothness of the carbon fiber sheet material whose surface smoothness is lowered by the hydrophilic treatment is improved, and the electric resistance value (specific resistance) can be reduced.

The amount of adhesion is preferably 0.01 to 30% by mass with respect to the weight of the sheet material. 0.0
If it is less than 1% by mass, sufficient water repellency tends not to be obtained. When it exceeds 30% by mass, the gas diffusion electrode layer becomes too thick, and it tends to be difficult to reduce the size of the stack.

The ratio of the water-repellent resin and the conductive fine particles is a mass ratio, and the ratio of water-repellent resin: conductive fine particles is 0.05: 0.95.
To 0.95: 0.05 is preferable. If the ratio of the water-repellent resin is low, sufficient water repellency tends to be unobtainable, and if the ratio of the conductive fine particles is low, sufficient planar smoothness cannot be obtained and the contact resistance tends to increase. The one surface provided is a sheet-like material having water repellency.

The contact angle of the water-repellent surface with water is 108.
It must be at least a degree. Further, it is preferably 120 degrees or more. Due to such water repellency, it is possible to prevent a decrease in the gas diffusing ability of the electrode due to water generated in the electrode of the fuel cell.

Further, since the carbon fiber electrode material of the present invention uses the hydrophilic carbon fiber sheet, it has water absorption on the back surface and the cross section. The water absorption when the cross section is immersed in water for 5 minutes is preferably 0.2 to 15 g / g, and more preferably 4 to 10 g / g. Since the back surface and the inside have water absorbing properties in this way, water generated on the surface of the electrolyte membrane of the fuel cell can be quickly drained from the water repellent phase.

Such a carbon fiber electrode of the present invention is obtained by using the hydrophilic carbon fiber sheet material of the present invention described above and applying a treatment for adhering a water-repellent resin and conductive fine particles on one surface thereof. be able to. Water repellent treatment / conductive fine particle treatment mixes conductive fine particles with water repellent resin,
Coat only one side of the carbon fiber sheet and attach it to
The treatment is carried out in air at 00 to 400 ° C., more preferably in an inert gas.

[0053]

[Function] The polymer electrolyte membrane of the polymer electrolyte fuel cell is
It exhibits high ionic conductivity only when it is fully hydrated. Since the carbon fiber electrode material of the present invention has water absorbency, even if the supply of humidified gas to the electrode of the fuel cell is small, water is supplied from the electrode material of the present invention to the polymer electrolyte and dried. Can be prevented. Therefore, deterioration of the polymer electrolyte can be prevented and the life of the fuel cell itself can be extended. Furthermore, the operation start time at the time of restarting from the unused state where the supply of the humidifying gas is stopped becomes possible in a short time.

Further, when used, a so-called flatting phenomenon occurs in which reaction water is generated in a portion of the electrode surface which is in contact with the polymer electrolyte membrane and the diffusion of gas by the water is hindered. However, the carbon fiber electrode material of the present invention Since the surface in contact with the polymer electrolyte membrane has water repellency, the flatting phenomenon can be prevented.

[0055]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, each physical property was measured by the following methods.

(1) Battery characteristics A carbon fiber electrode material was cut into 50 mm square, and after supporting a catalyst as an electrode material on the anode side and the anode side, a polymer electrolyte membrane (Nafion membrane 117 manufactured by DuPont) was constructed as follows. By thermocompression bonding, combined with a separator, temperature 80
The cell voltage was measured at a current density of 1.6 A / cm ² under the condition of ° C. The surface having water repellency is the side in contact with the third-layer polymer electrolyte membrane. First layer: grooved separator Second layer: carbon fiber electrode material (anode side) (catalyst Pt-Ru: 0.3 mg / cm ² ) Third layer: polymer electrolyte membrane Fourth layer: carbon fiber electrode material (cathode side) ) (Catalyst Pt: 0.3 mg / cm ² ) Fifth layer: grooved separator Hydrogen: 1000 ml / min, oxygen: 1000 ml / min

(2) Specific resistance value (conductivity) 0.01MP was applied to the carbon wire of the sample with two 50 mm square (10 mm thick) gold-plated electrodes on both sides of the sheet.
The electric resistance value (R) between both electrodes was measured with the pressure of a, and calculated from the thickness (T) and the contact area (S) by the following formula.

[0058]

[Equation 1]

(3) The water-repellent sample is dried at 120 ° C. for 1 hour and then left to cool to room temperature in a desiccator. A drop of water (10μ
m) Drop. Then, using a microscope, the droplet was enlarged to the monitor TV, and the droplet height h, and
The distance a between the orthogonal point between the apex of the droplet and the horizontal plane and the intersection of the droplet and the plane is measured, and the contact angle θ is determined by the following equation.

[0060]

[Equation 2]

(4) The metal analysis sample is ashed at 750 ° C. and treated with aqua regia. The amount of metal (Ca, Na, K) was measured by flame atomic absorption.

(5) Water Absorption (Evaluation Method for Hydrophilicity) 12 samples (20 mm × 50 mm) subjected to hydrophilic treatment were used.
After drying at 0 ° C. for 1 hour, the sample is allowed to cool in a desiccator, cooled to room temperature, and then weighed (sample weight). Next, the sample is hung so that the cross section in the longitudinal direction is downward, and 5 mm from the cross section is left for 5 minutes while being immersed in water. The weight after removing from water was measured, and the water absorption (amount of attached water / weight of sample) was evaluated from the obtained amount of attached water and sample weight. The unit was g / g.

(6) Strength, elongation, knot strength, knot elongation It was measured according to JIS L1015.

(7) The weighted sheet material was calculated as the mass per unit area after drying at 120 ° C. for 1 hour.

(8) Thickness A circular pressure plate having a diameter of 30 mm was used to measure the thickness at 2.8 kPa (load of 200 g).

(9) It was measured by the specific gravity liquid replacement method (JIS R7601, replacement liquid: ethyl alcohol).

(10) Tensile strength A sheet-like material having a width of 50 mm and a length of 120 mm or more is fixed to a jig having a chuck distance of 100 mm, and a speed of 3 is set.
The breaking strength when pulled at 0 mm / min was converted to a 10 mm width.

(11) Crystallite size measuring method The crystallite size (Lc) is the wide angle X-ray measurement result (2θ = 2).
It was determined from the peak around 6 °) using the Scherrer's formula shown below.

[0069]

[Equation 3]

Here, k is a device constant (0.9 in the present invention), λ is an X-ray wavelength (0.154 nm), and β is 2θ.
Half-width of peak around = 26 °, θ is peak position (°)
Is. Measurement condition setting Tube voltage: 40 kV Setting tube current: 30 mA Measuring range: 10 ° to 40 ° Sampling interval: 0.02 ° Scanning speed: 4 ° / min Integration frequency: 1 time Sample form: Peak after baseline correction Strength is 5
A plurality of samples are stacked so that the rate becomes 000 cps or more.

[Examples 1 to 4] PAN type precursor (AN: acrylonitrile 96%, MA: methacrylic acid 4)
%, Fineness 1.7 dtex) acid (HCl 1%, 80
(° C) to prepare a precursor fiber. The metal content of this product is Na: 5 ppm, K: 5 ppm, Ca:
It was 5 ppm and the ash content was 0.02%.

This precursor is put at 235 ° C. for 1 hour + 25
Oxidation treatment in air at 5 ° C for 1.5 hours, and fineness 2.
3dtex, elongation (standard condition) 27%, knot strength 1.4
Oxidized fiber having g / dtex, knot elongation of 10% and specific gravity of 1.39 was obtained.

Further, after the oxidized fiber was washed with warm water (pure water, 80 ° C., vibro washer), crimping was performed to obtain a crimp number of 4.4 / cm and a crimp rate of 12%.
Oxidized fiber of was obtained and cut into 51 mm. Three 50 g / m ² webs of this oxidized fiber are stacked and processed into a non-woven fabric by the water jet method (water used: pure water), and an oxidized fibrous non-woven fabric (Basis weight 150 g / m ² , thickness 0.8 mm,
An X-ray crystal size of 3.0 nm) was prepared.

The obtained non-woven fabric was treated at 1900 ° C. in nitrogen gas for 1 minute to give a carbon fiber non-woven fabric (with a fabric weight of 9
0 g / m ² , thickness 0.8 mm) was obtained. By subjecting this carbon fiber nonwoven fabric to an organic acid treatment (HCl 1%, 80 ° C., water used: pure water), a carbon fiber nonwoven fabric with a small amount of metal components could be obtained. This non-woven fabric is steamed at 900 ℃ for 5,1
Hydrophilization treatment was performed for 0, 30, and 45 minutes to obtain a hydrophilic carbon fiber sheet.

Only one side of the carbon fiber non-woven fabric (hydrophilic carbon fiber sheet-like material) after the hydrophilic treatment is treated with PTFE.
A mixture of carbon black and carbon black (average particle size 0.5 μm) in a mass ratio of 0.5: 0.5 was added to the total weight of the carbon fibers in 5
Coated so as to be mass%, adhered, 300 ℃, 3
It was treated for 0 minutes. The contact angle of the surface of the obtained electrode material on the water repellent treatment side was 140 °. Further, the back surface and the cross section had water absorbency, and the contact angle could not be measured.
Thereafter, the water-repellent treated surface was coated with Pt catalyst to evaluate the battery characteristics (1 hour after operation and 200 hours after operation). The physical properties of these are shown in Table 1.

[0076]

[Table 1]

Comparative Example 1 The same treatments and evaluations as in Examples 1 to 4 were carried out except that the hydrophilic treatment of the carbon fiber nonwoven fabrics in Examples 1 to 4 was omitted. The contact angle of the surface of the obtained electrode material on the water repellent treatment side was 140 °, but it was recognized that the battery performance after 200 hours tended to deteriorate. The physical properties of this product are shown in Table 2.

[Comparative Example 2] The same treatments and evaluations as in Examples 1 to 4 were carried out except that the carbon fiber nonwoven fabrics of Examples 1 to 4 were hydrophilized under conditions of 900 ° C. steam for 60 minutes. went. The contact angle of the surface of the obtained electrode material on the water repellent treatment side was 140 °, but it was recognized that the battery performance after 200 hours tended to deteriorate. The physical properties of this product are also shown in Table 2.

[Example 5] Example 2 (hydrophilicizing treatment at 900 ° C for 10 minutes in steam) except that the precursor of Examples 1 to 4 and the carbon fiber were not treated twice with organic acid. The same treatment and evaluation were performed.

Precursor (AN: acrylonitrile 96
%, MA: methacrylic acid 4%, fineness 1.7 dtex), the metal component content is Na: 50 ppm, K: 50 pp
m, Ca: 200 ppm, ash content: 0.02%.
The contact angle of the surface of the obtained electrode material on the water repellent side is 1
It was 40 °. In addition, the back surface and cross section have water absorption,
It was not possible to measure the contact angle. The physical properties of this product are also shown in Table 2.

[Example 6] A carbon fiber non-woven fabric was used in Example 1.
Instead of hydrophilizing in steam at 900 ° C as in ~ 4, in ammonium sulfate for 20 minutes, current density 12C
The same treatments and evaluations as in Examples 1 to 4 were performed except that the hydrophilicity was imparted by electrolytically oxidizing the particles at a rate of / g. The contact angle of the surface of the obtained electrode material on the water repellent treatment side was 140 °. Further, the back surface and the cross section had water absorbency, and the contact angle could not be measured. The physical properties of this product are also shown in Table 2.

[0082]

[Table 2]

[0083]

According to the present invention, a carbon fiber electrode material capable of maintaining high battery performance without deteriorating the gas diffusivity of the electrode even after continuous use for a long time, and a hydrophilic carbon sheet material suitably used for the electrode material An object and a manufacturing method thereof are provided.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 4/96 D06M 101: 40 // H01M 8/10 7/00 A D06M 101: 40 11/00 B ( 72) Inventor Kenji Shimazaki 234, Uechikari, Nagaizumi-cho, Sunto-gun, Shizuoka F-term (reference) in Toho Tenax Co., Ltd. DD06 EE02 EE05 EE19 HH03 HH05 HH08 5H026 AA06 BB00 BB10 CX03 EE02 EE05 EE19 HH03 HH05

Claims (8)

[Claims] 1. A hydrophilic carbon fiber sheet material having a water absorption of 0.2 to 15 g / g when its cross section is immersed in water for 5 minutes. 2. The carbon fiber is a non-woven fabric structure.
The hydrophilic carbon fiber sheet material described. 3. The hydrophilic carbon fiber sheet material according to claim 1, which has a Na content of 30 ppm or less, a K content of 30 ppm or less, and a Ca content of 150 ppm or less. 4. A method for producing a hydrophilic carbon fiber sheet material, which comprises hydrophilizing a carbon fiber sheet material by liquid phase oxidation or gas phase oxidation. 5. The gas phase oxidation condition is 700 to 1000.
The method for producing a hydrophilic carbon fiber sheet according to claim 4, wherein the treatment is carried out in water vapor at 0 ° C for 3 to 45 minutes. 6. A carbon fiber comprising a hydrophilic carbon fiber sheet-like material according to any one of claims 1 to 3 having a layer comprising a water-repellent resin and conductive fine particles on one surface thereof. Electrode material. 7. The carbon fiber electrode material according to claim 6, wherein the adhesion amount of the water-repellent resin and the conductive fine particles is 0.01 to 30% by weight based on the total weight of the carbon fibers. 8. The contact angle between the water-repellent resin and the surface of the surface containing the conductive fine particles with water is 108 degrees or more.
Or the carbon fiber electrode material described in 7.