JP2015190066A - Carbon fiber felt, manufacturing method thereof, and liquid circulation type electrolytic cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide carbon fiber felt having superior conductivity to a thickness direction, high permeability of fluid such as electrolyte liquid to the thickness direction and superior handleability for a liquid circulation type electrolytic cell.SOLUTION: Carbon fiber felt 16 and 20, in which a fiber degree of orientation of thickness direction Z is 5-40%, and difference of a fiber degree of orientation of a direction X having the highest fiber degree of orientation and a fiber degree of orientation of a direction Y at right angles to the direction X having the highest fiber degree of orientation is 3-50%, are arranged to a liquid circulation type electrolytic cell 12.

Description

  The present invention relates to a carbon fiber felt having high conductivity and good fluid permeability and permeability, such as an electrolyte solution, a method for producing the same, and a liquid flow electrolytic cell having the carbon fiber felt.

  In recent years, the demand for clean electric energy has increased rapidly, and the introduction of new energy such as solar power generation and wind power generation has been actively promoted. However, since these power generation methods are influenced by the weather, the power generation frequency and output are not stabilized, and there is a problem that control is difficult. As countermeasures, it has been studied to achieve output leveling, surplus power storage, and load leveling by outputting via a storage battery.

  Apart from these power generation methods, liquid flow type electrolytic cells are used in various batteries such as primary batteries, secondary batteries (storage batteries), fuel cells, and electrolysis industries such as electroplating, salt electrolysis and electrosynthesis of organic compounds. Increasing number of cases.

  A redox flow storage battery, which is one of the storage batteries using a liquid flow electrolytic cell, uses relatively safe ions, operates at room temperature, does not require a heat source, can be operated with high efficiency, and has a cycle life of 1 It is expected to be a large storage battery because it has excellent features such as long life and more than 10,000 times, and can be easily enlarged.

FIG. 3 is a conceptual diagram showing the operating principle of the redox flow battery.
The main part of the redox flow battery 32 is a cell part (hereinafter referred to as a liquid flow type electrolytic cell) 34 that performs a charge / discharge reaction and acts as a liquid flow type electrolytic cell, and an electrolyte tank unit that stores electric power. 36, 38. The liquid flow type electrolytic cell 34 includes a positive electrode 50 and a negative electrode 52 that function as a liquid flow type electrode, a diaphragm 44 that separates them, and current collector plates 40 and 42 provided on both sides of the liquid flow type electrolytic cell 34. It is configured.

  Two types of electrolytes (the flow directions of the electrolytes by the liquid feed pumps 46 and 48 are indicated by arrows P and Q) are supplied to the liquid circulation type electrolytic cell 34. During charging, a solute oxidation reaction is performed at the positive electrode 50, and a solute reduction reaction is performed at the negative electrode 52. During discharge, a solute reduction reaction is performed at the positive electrode 50, and a solute oxidation reaction is performed at the negative electrode 52. Charging / discharging is performed by repeating these oxidation-reduction reactions.

  As the positive electrode 50 and the negative electrode 52, a carbon material is preferably used because it is conductive and chemically stable. Among these carbon materials, a carbon fiber felt that is an aggregate of thin fibers is more preferably used because it has a high electrolyte permeability and a large surface area because it is necessary to efficiently advance the electrode reaction. . Felts used as electrodes are required to have good liquid permeability and permeability in order to circulate the electrolyte solution with a small flow resistance. As a solution to this problem, it has been proposed to form grooves for circulating an electrolytic solution on the surface of the carbon fiber felt by hot pressing or cutting (for example, Patent Document 1).

  In patent document 1, after forming a groove | channel on the single side | surface of a carbon fiber precursor felt by hot press or cutting, the carbon fiber felt by which the groove | channel was formed in the single side | surface is obtained by carbonizing a felt. However, in the carbon fiber felt obtained in this way, the fiber of the part subjected to hot pressing or cutting is damaged, so that the strength of the carbon fiber felt is reduced, and a hot pressing process is added. This increases the cost of the electrode.

Japanese Patent No. 3560181

  The present invention relates to a carbon fiber felt having good permeability and permeability of a fluid such as an electrolyte solution, high conductivity in the thickness direction, and excellent handleability, a method for producing the felt, and a liquid flow type electrolytic cell having the felt The purpose is to provide.

  While the present inventors are diligently studying the above problems, the fiber arrangement degree in the thickness direction of the carbon fiber felt is within a predetermined range, and the fiber arrangement degree is the highest in the fiber orientation in the surface direction of the felt. A carbon fiber felt in which the difference between the fiber arrangement degree in the direction and the fiber arrangement degree in the direction perpendicular to the direction in which the fiber arrangement degree is high is within a predetermined range is used when the felt is used in a liquid flow electrolytic cell. It has been found that it is excellent in permeability and penetrability of fluid such as an electrolyte solution in the liquid direction, and further excellent in conductivity and handleability in the thickness direction.

  The present inventors have found that this carbon fiber felt can be obtained by carbonizing a carbon fiber precursor felt produced under predetermined conditions, and have completed the present invention.

  The present invention for achieving the above object is as follows.

  [1] The fiber arrangement degree in the thickness direction is 5 to 40%, and in the fiber orientation in the plane direction, the fiber arrangement degree in the direction with the highest fiber arrangement degree and the fibers in the direction orthogonal to the direction in which the fiber arrangement degree is high A carbon fiber felt having a difference between the degree of alignment and 3 to 50%.

[2] Two or more carbon fiber precursor fiber webs are laminated at a lamination angle of 0 to 60 ° or 120 to 180 ° to obtain a carbon fiber precursor fiber web laminate, and the carbon fiber precursor web laminate is obtained. A method for producing a carbon fiber felt, wherein a carbon fiber precursor felt is obtained by punching in a range of 300 to 3000 punches / cm ² , and the carbon fiber precursor felt is carbonized under an inert atmosphere.

  [3] A liquid flow electrolytic cell having the carbon fiber felt according to [1].

  [4] In the carbon fiber felt arranged in the liquid flow type electrolytic cell, the difference between the fiber arrangement degree in the liquid passing direction and the fiber arrangement degree in the direction orthogonal to the liquid passing direction is 2.5% or more [3 ] The liquid circulation type electrolyzer described in the above.

  Since the carbon fiber felt of the present invention has a low electrical resistance value in the thickness direction and does not inhibit the passage of fluid such as an electrolyte solution, it can be suitably used as a carbon fiber felt disposed in a liquid flow type electrolytic cell.

  According to the method for producing a carbon fiber felt of the present invention, the fiber orientation in the thickness direction and the fiber orientation in the surface direction of the obtained carbon fiber felt can be appropriately controlled. It is possible to obtain a carbon fiber felt that is excellent in permeability and permeability of a fluid such as an electrolyte solution in a liquid direction and can be suitably used as a material to be disposed in a liquid flow type electrolytic cell.

It is a conceptual perspective view which shows the carbon fiber felt of this invention. It is a conceptual perspective view which shows the liquid flow type electrolytic cell of the redox flow type battery using the carbon fiber felt of this invention. It is a conceptual diagram which shows the operating principle of a redox flow type battery.

  FIG. 1 is a conceptual perspective view showing an example of the carbon fiber felt of the present invention.

  Hereinafter, the carbon fiber felt of the present invention will be described by taking as an example the case of using the carbon fiber felt of the present invention for an electrode of a redox flow battery.

  In FIG. 1, 2 is a carbon fiber felt, and a direction indicating the thickness (T) of the felt 2 is Z. Various shapes such as a rectangle and a circle can be applied to the surfaces C and C 'facing each other in the thickness direction Z, but a rectangle as shown in the example of FIG. 1 is preferable for use as an electrode. Hereinafter, the present invention will be described along the rectangular shapes of both surfaces C and C '. Of the rectangular surface directions, the direction in which the fiber arrangement degree is high is X, and the orthogonal direction is Y.

  The carbon fiber felt of the present invention has a fiber alignment degree in the thickness direction of 5 to 40%, preferably 7 to 35%, more preferably 10 to 30%. When the fiber arrangement degree in the thickness direction of the carbon fiber felt is 5 to 40%, the carbon fiber felt has a low electrical resistance value in the thickness direction and excellent electrolyte permeability.

  When the fiber arrangement degree in the thickness direction is less than 5%, the compressive stress is low, the conductive resistance is high, and the battery output performance is lowered. When the fiber arrangement degree in the thickness direction exceeds 40%, the liquid passing pressure loss is increased, and the energy consumption of the pump is increased. In order to reduce the conductive resistance in the thickness direction, it is necessary to increase the number of punching. If the number of punching is excessively large, the fiber is damaged and the strength of the felt is lowered. Furthermore, it is not preferable because a problem such as generation of damaged fluff is generated.

  The fiber arrangement degree in the thickness direction can be controlled by the card system at the time of producing the carbon fiber precursor felt, the number of punching, the shape of the needle, the punching depth, and the tension in the longitudinal direction at the time of carbonization.

  Furthermore, the carbon fiber felt of the present invention has a difference in the fiber orientation in the plane direction between the fiber orientation degree in the direction with the highest fiber orientation degree and the carbon fiber orientation degree in the direction perpendicular to the direction in which the fiber orientation degree is high. Is 3 to 50%, preferably 5 to 30%. When the difference in the degree of fiber alignment is 3 to 50%, the carbon fiber felt has a low flow pressure loss and greatly improves the flowability of the electrolyte. In the present invention, the fiber arrangement direction X is measured by rotating a sample 360 ° on the ZX plane (A, A ′) and the ZY plane (B, B ′) in X-ray diffraction. It is determined by obtaining the orientation peak.

  The fiber arrangement degree in the surface direction can be controlled by a card method, traversing speed in the layer process, pitch or lattice speed adjustment, and the like. For example, when adjusting the fiber arrangement degree in the plane direction in the layer process, the angle at the time of lamination is preferably 0 to 60 ° or 120 to 180 °, more preferably 10 to 50 ° or 130 to 170 °. It is possible to form a web with an adjusted degree of fiber alignment.

  The liquid passing pressure loss is preferably 20 kPa (150 mmHg) or less, more preferably 16 kPa (120 mmHg) or less per liquid flow type electrolytic cell. When the flow pressure loss exceeds 20 kPa, the pump capacity for circulating the electrolyte increases, and the power loss increases due to the power used for the pump.

  The carbon fiber felt of the present invention preferably has a fiber arrangement degree in the appropriate thickness direction and a large fiber arrangement degree in the liquid passing direction. This is because heat loss due to conductive resistance in the thickness direction of the felt and energy loss of driving the pump can be reduced, and power generation efficiency can be increased.

  The thickness of the carbon fiber felt is preferably 1 to 10 mm, and more preferably 1.5 to 7 mm. If it is less than 1 mm, the pressure loss is high and the energy loss for driving the pump becomes large, which is not preferable. If it exceeds 10 mm, the system becomes too large, and the degree of freedom in design decreases, which is not preferable. The thickness can be controlled by the amount of precursor fiber charged (weight per unit area), the fiber thickness, and the number of punching when producing the carbon fiber precursor felt.

Basis weight is preferably from ^{100~1000g / m 2, 200~800g / m} 2 is more preferable. When it is less than 100 g / m ^{2, the} surface area contributing to the reaction is reduced, and the power storage efficiency is lowered, which is not preferable. If it exceeds 1000 g / m ² , the system becomes too large, and the degree of freedom in design decreases, which is not preferable. The basis weight can be controlled by the amount of precursor fibers charged and the number of laminated webs.

Electric resistance value in the thickness direction is preferably 540mΩ / cm ² or less, more preferably 500mΩ / cm ² or less, 400mΩ / cm ² is particularly preferred. If it exceeds 540 mΩ / cm ² , when used as an electrode, the conductive resistance is high and the charge / discharge loss increases, which is not preferable. The electric resistance value in the thickness direction can be controlled by the fiber arrangement degree in the thickness direction and the carbonization temperature.

  The compressive stress is preferably 0.3 to 1.5 MPa, more preferably 0.5 to 1.2 MPa. When the pressure is less than 0.3 MPa, when the electrodes 50 and 52 (see FIG. 3) are incorporated in the liquid flow type electrolytic cell 34, the contact between the diaphragm 44 and the current collectors 40 and 42 is not sufficient, and the thickness direction This is not preferable because the electric resistance value is increased and the cell resistance of the electrolytic cell 34 is increased. When the pressure exceeds 1.5 MPa, the stress applied to the diaphragm 44 increases, and the diaphragm 44 may be damaged. The compressive stress can be adjusted by adding in advance to the precursor fiber a fiber orientation degree in the thickness direction, the thickness of the precursor fiber to be used, and a resin that is carbonized after the fiber is fired.

[Method for producing carbon fiber felt]
The method for producing the carbon fiber felt of the present invention is not particularly limited and may be produced by any method, but the following method is preferred.

  A carbon fiber precursor felt made of carbon fiber precursor fibers is prepared. It is then carbonized under an inert atmosphere. Thereby, the carbon fiber felt of the present invention is obtained.

  Production raw material of carbon fiber felt, that is, carbon fiber precursor fiber, any of known raw material fibers such as polyacrylonitrile (PAN) fiber, pitch fiber, rayon fiber, cellulose, or various raw material fibers in the air And flame-resistant fibers obtained by oxidation treatment with.

  Here, the PAN fiber means, for example, a spinning solution containing a homopolymer or a copolymer obtained by polymerizing a monomer containing 95% by mass or more of acrylonitrile, in a wet or dry wet spinning method, spinning, washing, drying, stretching, etc. It is a raw material fiber obtained by performing this process. As the monomer to be copolymerized, methyl acrylate, itaconic acid, methyl methacrylate, acrylic acid and the like are preferable.

  Among these carbon fiber precursor fibers, PAN-based flame resistant fibers obtained by oxidizing the PAN-based fibers of the raw material fibers at 200 to 400 ° C. in air are preferable from the viewpoint of fiber flexibility and processability.

  First, the carbon fiber precursor fiber is felted by a known method. The felting method is a method of obtaining a web by opening with a card, laminating two or more layers of this web in a layer process to obtain a web laminated body, and punching the web laminated body with a needle punch to make a felt. preferable.

  When making a web with a card and making a web laminate in the layer process, by controlling the web lamination angle in the layer process within the above range, in the fiber orientation in the plane direction of the final product carbon fiber felt, A carbon fiber felt in which the difference between the fiber arrangement degree in the direction having the highest fiber arrangement degree and the fiber arrangement degree in the direction orthogonal to the direction in which the fiber arrangement degree is high can be 3 to 50%. The fiber orientation in the surface direction can be controlled not only by adjusting the stacking angle in the layer process, but also by adjusting the opening in the card method, adjusting the traverse speed in the layer process, and adjusting the pitch and lattice speed. .

When the carbon fiber precursor fiber is a PAN-based flame resistant fiber, the density is not particularly limited, but is preferably 1.33-1.45 g / cm ³ . When the density of the flame resistant fiber is less than 1.33 g / cm ³ , shrinkage during carbonization is large and the process tends to become unstable. When the density of the flame resistant fiber exceeds 1.45 g / cm ³ , the fiber is brittle and often falls during the entanglement treatment such as punching, and the workability tends to be lowered.

  The fineness of the carbon fiber precursor fiber of the raw fiber is preferably 0.1 to 5.0 dtex, more preferably 0.5 to 3.5 dtex, and particularly preferably 1.0 to 3.3 dtex. When the fineness of the carbon fiber precursor fiber is less than 0.1 dtex, the spreadability is poor and uniform mixing is difficult. When the fineness of the carbon fiber precursor fiber exceeds 5.0 dtex, a high strength felt cannot be obtained. Moreover, the contact between fibers decreases and the electrical resistance value after carbonization becomes high.

  As the carbon fiber precursor staple used for the carbon fiber precursor felt of the present invention, the fiber length of the carbon fiber precursor staple is 30 to 75 mm, the fineness is 0.5 to 3.5 dtex, and the number of crimps is 4 to 20/2. What processed 54 cm and the crimp rate of 4-20% is preferable.

The entanglement process in felting or the like is performed in a range of 300 to 3000 times / cm ² by the needle punching method (number of entanglement processes). When the number of punching is less than 300 times / cm ² , the number of punching is small, so that the strength of the felt is lowered. Furthermore, since the fiber arrangement degree in the thickness direction cannot reach a predetermined amount, the compressive stress is lowered and the electric resistance value in the thickness direction is increased. When the number of punching exceeds 3000 times / cm ² , the fiber is greatly damaged by the entanglement treatment, and there is a possibility that a large amount of falling fluff may occur, which is not preferable. The punching direction in the needle punching method may be from one side or both sides of the punching surface.

  After producing a carbon fiber precursor felt as described above, a carbon fiber felt is obtained by carbonizing this.

  The carbonization treatment is performed by baking the carbon fiber precursor felt for 0.5 to 120 minutes under an inert atmosphere at a maximum temperature of 1300 to 2300 ° C. Preferably, firing is performed in two stages, a first carbonization treatment and a second carbonization treatment. In this case, in the first carbonization treatment, the carbon fiber precursor felt after the entanglement treatment is heated to 300 to 1000 ° C. in an inert atmosphere and fired for 0.5 to 120 minutes to treat the decomposition gas. The second carbonization treatment is preferably performed by firing the carbon fiber precursor felt subjected to the first carbonization treatment at a maximum temperature of 1300 to 2300 ° C. in an inert atmosphere for 0.5 to 120 minutes. As for the maximum temperature at the time of this 2nd carbonization process, it is more preferable that it is the range of 1500-2300 degreeC.

  When the maximum temperature at the time of carbonization is less than 1300 ° C., the carbon content of the obtained carbon fiber felt is not 93% by mass or more. Such carbon fiber felt is not preferred because it has low electrical conductivity and cannot provide good fuel cell performance. In addition, when the maximum temperature at the time of carbonization processing is less than 1500 degreeC, the carbon content rate of the carbon fiber felt obtained does not become 95 mass% or more. When the maximum temperature during the carbonization treatment exceeds 2300 ° C., the carbon fiber felt becomes stiff, the strength is lowered, and furthermore, problems such as the generation of fine carbon powder occur.

  The carbon fiber felt produced as described above may be used as it is incorporated in a liquid flow type electrolytic cell. However, when an aqueous solution is used as the electrolytic solution of the liquid flow type electrolytic cell, the wettability is improved. It is preferable to use an oxidized carbon fiber felt. The oxidation treatment includes a liquid phase oxidation method and a gas phase oxidation method, and is not particularly limited.

  Liquid phase oxidation methods include high-temperature oxidation with hydrogen peroxide and sodium hypochlorite, and electrolytic oxidation with electrolytes (sulfuric acid, caustic soda, ammonium sulfate, sodium chloride, etc.) in the electrolyte layer using the electrolyte. Is used.

  In the gas phase oxidation method, air oxidation (300 to 800 ° C.), ozone oxidation (25 to 400 ° C.), oxidation with water vapor or carbon dioxide (500 to 950 ° C.), or the like is used.

  For example, in the gas phase oxidation method, when performing the air oxidation treatment, it is preferable to perform the oxidation treatment for 0.5 to 180 minutes. When the time is less than 0.5 minutes, problems such as insufficient oxidation treatment and large processing spots occur. If it exceeds 180 minutes, an excessive oxidation treatment causes a problem such as an increase in contact resistance and an increase in cell resistance, and brittleness due to oxidative degradation.

  The carbon fiber felt thus obtained can be used in various liquid flow type electrolytic cells that require, for example, conductivity and liquid permeability, such as electrodes for redox flow type storage batteries, sodium-sulfur storage batteries. The present invention can also be applied as a gas diffusion layer for an electrode and a fuel cell, and also as a reinforcing fiber such as a composite or a sliding material. Especially, it can use preferably as an electrode of a redox flow type storage battery and an electrode of a sodium-sulfur storage battery.

  FIG. 2 is a conceptual perspective view showing an example of a liquid flow type electrolytic cell of a redox flow type storage battery incorporating the carbon fiber felt of the present invention as an electrode. In FIG. 2, 16 and 20 are electrodes made of carbon fiber felt. In the liquid-flowing electrolytic cell 12 of this example, between the current collector plate 14 and the diaphragm 18, and between the current collector plate 22 and the diaphragm 18, respectively. Is arranged. As indicated by an arrow on the electrode 16, the X direction in which the fiber arrangement degree of the carbon fiber felt is high is arranged in the same direction as the liquid passing direction U. Since the direction X of the high fiber arrangement degree of the carbon fiber felt is oriented in this direction U, the liquid passing pressure loss in the direction X is low. Therefore, the circulating electrolyte can be circulated with low energy, and the energy consumption of the pump operation necessary for the electrolyte circulation can be reduced.

  That is, when the carbon fiber felt of the present invention is used as the electrodes 16 and 20 that require liquid permeability such as the above-mentioned redox flow battery electrode, the electrolyte flow direction U and the fiber orientation degree in the plane direction. In the liquid flow electrolytic cell 12 between the current collector plate 14 and the diaphragm 18 and between the current collector plate 22 and the diaphragm 18 so that the high direction X of Pressure loss can be reduced.

  More specifically, in the liquid flow type electrolytic cell 12 in which the carbon fiber felt of the present invention is incorporated as the electrodes 16, 20, the fiber arrangement degree in the liquid passing direction and the fiber arrangement degree in the direction orthogonal to the liquid passing direction. And the carbon fiber felts 16 and 20 so that the difference is preferably 2.5% or more, more preferably 3 to 50%, and particularly preferably 5 to 30%. They are disposed between the current collector plate 14 and the diaphragm 18 and between the current collector plate 22 and the diaphragm 18. If it is less than 2.5%, the liquid passing pressure loss tends to increase, and the energy consumption loss of the pump tends to increase.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, evaluation of operation conditions and measurement of each physical property were based on the following methods.

[Fiber alignment]
A 360 ° sample is rotated on the ZX plane (A) and the ZY plane (B) for the X-ray diffraction peak angle (2θ = 26.0 ° vicinity). A crystallite orientation peak is obtained from the change in X-ray diffraction behavior obtained at this time. Utilizing the fact that the crystallites are highly oriented in the fiber axis direction, this orientation peak area was measured and determined by the following formula.
Calculate the peak area ratio in the X and Z directions from “a”
(Peak area in X direction) / (peak area in Z direction) ... a
Calculate the peak area ratio in the Y and Z directions from “b”
(Peak area in Y direction) / (Peak area in Z direction) ... b
Fiber alignment in the thickness direction (Z) (%)
= (Orientation peak area in the Z direction) / (X + Y + Z) orientation peak area = 1 / [(X orientation peak area / Z orientation peak area) + (Y orientation peak area) / (Z direction) Orientation peak area) +1]
= 1 / (a + b + 1)
Fiber arrangement degree in liquid flow direction (X) (%)
= A × Fiber alignment in the thickness direction (Z) (%)
Fiber orientation in the direction perpendicular to the liquid flow direction (Y) (%)
= B x fiber arrangement degree in thickness direction (Z) (%)
Here, the thickness direction of the carbon fiber felt was Z, the liquid flow direction (the direction with the highest fiber arrangement degree in the fiber arrangement degree in the plane direction) was X, and the direction orthogonal to the liquid flow direction was Y.

[Body weight]
Three 20 cm square (0.2 m square) felts were cut out as samples, and the weight after drying this at 105 ° C. for 1 hour was divided by the sample area (0.2 m × 0.2 m = 0.04 m ² ). The average value of three items was taken as the basis weight.

[Felt thickness]
An average thickness of samples measured at five points in the width direction using a thickness gauge (6.9 kPa) was defined as felt thickness (T).

[Electrical resistance value in the thickness direction]
A 50mm square sample is cut out and sandwiched between two 50mm square (thickness 10mm) gold-plated electrodes so that they are in contact with each other and compressed to a thickness of (1/2) T with respect to the felt thickness (T). The electrical resistance value in the thickness direction was measured and divided by the electrode area to obtain the electrical resistance value per unit area.

[Liquid pressure loss]
It is formed of spacers having a liquid flow direction of 30 cm, a width direction (flow channel width) of 50 cm, and a thickness of 0.22 to 0.32 cm (a spacer having a thickness that is 60% of the thickness of the carbon fiber felt is prepared). A cell stack was prepared. The produced carbon fiber felt was cut into a liquid passing direction (the direction with the highest fiber arrangement degree in the fiber arrangement degree in the surface direction) 20 cm and placed in the spacer in the width direction 50 cm. 50 liters / hour of ion-exchanged water was circulated through the cell stack, and the liquid pressure loss at the inlet / outlet of the cell stack was measured. It measured similarly by the system which does not install carbon fiber felt as a blank, and made the difference of a measured value and a blank measured value the liquid pressure loss of carbon fiber felt.

[Compressive stress]
A carbon fiber felt cut to 2 cm × 2 cm was pressed in the thickness direction and compressed. The compression load when compressed by 50% with respect to the thickness before compression was defined as compression stress.

[Example 1]
A PAN flame resistant fiber staple having a basis weight of 150 g / m ² using a PAN flame resistant fiber staple (fiber length 51 mm, crimp rate 10%, number of crimps 4 / cm) as a carbon fiber precursor and a lamination angle of 30 ° in the layer process. A fiber web was prepared. Four of these were laminated to obtain a web laminate.
Needle punching was performed on the web laminate at 400 times / cm ² to produce a carbon fiber precursor felt.
The carbon fiber precursor felt was pre-carbonized at 700 ° C. for 10 minutes and then carbonized at 1800 ° C. for 45 minutes to obtain a carbon fiber felt. The carbon fiber felt was oxidized at 700 ° C. for 30 minutes in an air atmosphere to obtain a final product carbon fiber felt. This carbon fiber felt was evaluated for fiber alignment, electrical resistance, liquid pressure loss, compressive stress, carbon content, and fluff.

[Examples 2 to 5]
A carbon fiber felt for an electrode was produced in the same manner as in Example 1 except that the punching number was changed to the punching number shown in Table 1.

[Examples 6 to 9]
A carbon fiber felt for an electrode was produced in the same manner as in Example 3 except that the layer stacking angle was changed to the angle shown in Table 2.

[Example 10]
A carbon fiber felt was produced in the same manner as in Example 3 except that the carbonization temperature was changed to the temperature shown in Table 2.

[Comparative Example 1]
A carbon fiber felt for an electrode was produced in the same manner as in Example 3 except that the punching number was 250 times / cm ² .

[Comparative Example 2]
A carbon fiber felt for an electrode was produced in the same manner as in Example 3 except that the punching number was 250 times / cm ² .

[Comparative Example 3]
A carbon fiber felt for an electrode was produced in the same manner as in Example 3 except that the layer lamination angle was 90 °.

  As shown in Tables 1 and 2, in Examples 1 to 10, carbon fiber felts having low electrical resistance values and low fluid pressure loss, and having good results with few fluffs at the time of cell production were obtained. .

  Since the comparative example 1 had few punching numbers, the fiber arrangement degree of the thickness direction fell. As a result, the obtained carbon fiber felt had a low compressive stress and a high electrical resistance value.

  Since the comparative example 2 had too many punching numbers, a lot of fallen fluff occurred. As a result, the obtained carbon fiber felt could not be used as an electrode of a redox flow battery.

  In Comparative Example 3, the layer stacking angle was outside the scope of the present invention. Therefore, the difference in the degree of fiber arrangement of the obtained carbon fiber felt is reduced, and the liquid passing pressure loss is increased.

Reference example 1
In Example 3, the carbon fiber felt was placed in the liquid flow type electrolytic cell of the redox flow type battery so that the direction showing the high fiber arrangement degree in the surface direction of the obtained carbon fiber felt was the same direction as the liquid passing direction. It is set. As a result of evaluating the storage performance, high storage performance was obtained as shown in Tables 1 and 3. As shown in Tables 1 and 3, the difference between the fiber arrangement degree in the liquid passing direction and the fiber arrangement degree in the direction orthogonal to the liquid passing direction was 6%. This Example 3 is referred to as Reference Example 1 for comparison with Reference Example 2 below.

Reference example 2
The carbon fiber felt is placed in a liquid flow electrolytic cell of a redox flow type battery so that the direction of high fiber arrangement in the surface direction of the carbon fiber felt obtained in Example 3 is a direction orthogonal to the liquid passing direction. I set it. About this, as a result of evaluating power storage performance, as shown in Table 3, the power storage performance of Reference Example 2 was inferior to that of Reference Example 1. As shown in Table 3, the difference between the fiber arrangement degree in the liquid passing direction and the fiber arrangement degree in the direction orthogonal to the liquid passing direction was −6%.

2 Carbon fiber felt A, A 'Both surfaces in a direction perpendicular to the direction in which the fiber arrangement degree of the carbon fiber felt is high B, B' Both surfaces in the direction in which the fiber arrangement degree of the carbon fiber felt is high C, C 'of the carbon fiber felt Both surfaces in the thickness direction T Thickness of the carbon fiber felt X Arrow indicating the direction in which the fiber arrangement degree of the carbon fiber felt is high Y Arrow indicating the direction orthogonal to the direction in which the fiber arrangement degree of the carbon fiber felt is high Z Thickness direction of the carbon fiber felt Indicating arrows 12, 34 Liquid flow type electrolytic cell (cell part)
14, 22, 40, 42 Current collecting plate 16, 20, 50, 52 Electrode 18, 44 Diaphragm P, Q Arrow indicating the flow direction of electrolyte 32 Redox flow type storage battery 36, 38 Electrolyte tank 46, 48 pump

Claims (4)

  The fiber arrangement degree in the thickness direction is 5 to 40%, and in the fiber orientation in the plane direction, the fiber arrangement degree in the direction with the highest fiber arrangement degree, and the fiber arrangement degree in the direction orthogonal to the direction in which the fiber arrangement degree is high The carbon fiber felt whose difference is 3 to 50%. Two or more carbon fiber precursor fiber webs are laminated at a lamination angle of 0 to 60 ° or 120 to 180 ° to obtain a carbon fiber precursor fiber web laminate, and the number of punches of the carbon fiber precursor web laminate is 300. A method for producing a carbon fiber felt, comprising punching in a range of ˜3000 times / cm ² to obtain a carbon fiber precursor felt, and carbonizing the carbon fiber precursor felt in an inert atmosphere.   A liquid flow type electrolytic cell comprising the carbon fiber felt according to claim 1.   The carbon fiber felt disposed in the liquid flow type electrolytic cell has a difference between the fiber arrangement degree in the liquid passing direction and the fiber arrangement degree in the direction orthogonal to the liquid passing direction of 2.5% or more. Liquid flow type electrolytic cell.

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