JP6151947B2 - Carbon fiber felt, method for producing the same, anode current collector, and sodium-sulfur storage battery - Google Patents

Description

  The present invention relates to a carbon fiber felt having a high conductivity and a fluid permeability such as an active material in a molten state and a good permeability, a manufacturing method thereof, an anode current collector made of the felt, and sodium having the anode current collector It relates to a sulfur storage battery.

  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.

  A sodium-sulfur storage battery, which is one of storage batteries, is expected to be a large storage battery with high energy density, low unit price per capacity, low performance degradation due to repeated charge and discharge, and long life.

  FIG. 15 is a conceptual diagram showing the operating principle of a sodium-sulfur storage battery.

  In FIG. 15, reference numeral 52 denotes a sodium-sulfur storage battery, which includes an outer container (anode tube) 54 and an inner container (cathode tube) 56 formed of two bottomed coaxial cylinders. A solid electrolyte such as β-alumina is used as a material of the cathode tube 56, and a molten metal sodium 58 as a negative electrode active material is accommodated inside the cathode. The sodium 58 is deionized and ionized at the time of charging / discharging and passes through the solid electrolyte constituting the cathode tube 56. The anode current collector 60 is wound between the anode tube 54 and the cathode tube 56 so that the inner peripheral surface of the anode current collector 60 containing molten sulfur of the positive electrode active material is in contact with the outer peripheral surface of the cathode tube 56. It is in contact with the peripheral surface.

  At the time of discharge, sodium 58 as the negative electrode active material emits electrons to the external circuit to become sodium ions, passes through the cathode tube 56 and moves to the positive electrode side, and is supplied from the external circuit and sulfur as the positive electrode active material. Electric power is supplied by producing sodium polysulfide that reacts with electrons.

  On the other hand, during charging, by applying a voltage from the external circuit to the storage battery, sodium polysulfide emits electrons to the external circuit to generate sulfur and sodium ions, and the sodium that has passed through the cathode tube 56 and moved to the negative electrode side Electric energy is converted into chemical energy by reacting ions with electrons supplied from an external circuit and neutralizing them electrically.

  As the anode current collector 60, a carbon material is preferably used because it is conductive and is a chemically stable material. Among these carbon materials, since it is preferable that the surface area is large because the electrode reaction needs to proceed efficiently, a carbon fiber felt that is an aggregate of thin fibers is more preferably used.

  As a carbon fiber felt used as an anode current collector, for example, in Patent Document 1, glass fiber as an insulator is punched so that sodium polysulfide can react uniformly in molten sulfur impregnated inside the anode current collector. In which a carbon fiber felt is driven. By punching the insulator, it is possible to avoid an electron transfer reaction only in the vicinity of the contact surface between the cathode tube and the anode current collector during charging. That is, during charging, sulfur, which is an insulator, concentrates on the portion, and the charge recovery is deteriorated due to the internal resistance of the battery increasing with the progress of the charging reaction (sodium polysulfide remains). Nevertheless, the charging reaction does not proceed and the charging is not completed). However, since the carbon fiber felt is brittle, there is a concern that the fiber is damaged during needle punching of the glass fiber, the fluff falls off, and the strength decreases.

  In Patent Document 2, since the carbon fiber felt obtained by needle punching of Patent Document 1 has high rigidity, it is cut and set in the outer peripheral surface of a thin cylindrical solid electrolyte tube using a mold. It is described that a process of bending in an arc shape and impregnating with sulfur is necessary.

  However, since the carbon fiber felt obtained as in Patent Documents 1 and 2 needs to be cut and used, several joints occur, and molten sulfur, sodium polysulfide, and sodium ions are contained in the anode current collector. Problems such as non-uniform flow, fragility after molding, and breakage during molding or setting to the outer periphery of the solid electrolyte tube.

Japanese Patent No. 3416607 Japanese Patent No. 3363124

  The present invention solves the above-mentioned problems of the prior art, has excellent electrical conductivity, high permeability in the thickness direction of fluid such as molten sulfur, is easy to bend and has good contact with the cathode tube, and has excellent handling. It is an object of the present invention to provide a carbon fiber felt having properties, a method for producing the same, an anode current collector made of the felt, and a sodium-sulfur storage battery having the anode current collector.

  The inventors of the present invention have been diligently studying the above problems, and forming a cut on one surface of the carbon fiber precursor felt to control the thermal contraction rate of the front and back of the felt and to control the tension in the carbonization process. It was found that a groove was formed in the carbon fiber felt by carbonization.

  The resulting carbon fiber felt has excellent permeability and permeability in the thickness direction of fluid, such as molten sulfur, and excellent conductivity in the thickness direction, good contact with the cathode tube, excellent handling properties, and groove portion. The surface area that contributes to the reaction in the above and the surface area that contributes to the reaction of the felt itself are found to be excellent in reactivity, and the present invention has been completed.

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

  [1] A carbon fiber felt having a thickness of 11 to 55 mm, having a concavo-convex shape composed of a plurality of flange portions protruding outward in a band shape on at least one surface and a groove portion formed between the plurality of flange portions.

  [2] The carbon fiber felt according to [1], wherein the groove portion is formed in a linear shape, a lattice shape, a diamond shape, or a wave shape on the felt surface.

  [3] In [1] or [2], the groove width is 0.5 to 10 mm, the groove depth is 10 to 90% with respect to the thickness of the carbon fiber felt, and the groove pitch is 0.5 to 100 mm. The described carbon fiber felt.

[4] Any one of [1] to [3] having a basis weight of 500 to 5000 g / m ² , a bulk density of 0.05 to 0.30 g / cm ³ , and an electric resistance value in the thickness direction of 1000 mΩ / cm ² or less. The carbon fiber felt described in 1.

  [5] The carbon fiber felt according to any one of [1] to [4], wherein the bending resistance measured for a test piece whose groove width direction is the felt longitudinal direction is 4000 N · cm or less.

  [6] An anode current collector comprising the carbon fiber felt according to any one of [1] to [5].

  [7] A sodium-sulfur storage battery comprising the anode current collector according to [6], an anode tube, and a cathode tube inserted into the anode tube so that the axis of the anode tube coincides with the anode tube, A sodium-sulfur storage battery in which the surface having the irregular shape is wound in contact with the outer peripheral surface of the cathode tube, and the outer peripheral surface of the anode current collector is in contact with the inner peripheral surface of the anode tube.

  [8] A method for producing a carbon fiber felt in which a carbon fiber precursor felt having a thickness of 12 to 100 mm is carbonized under an inert atmosphere, wherein the precursor felt cut on one or both sides is orthogonal to the cutting direction. A method for producing a carbon fiber felt, characterized in that carbonization is performed while applying tension in a direction.

  [9] A method for producing a carbon fiber felt in which a carbon fiber precursor felt having a thickness of 12 to 100 mm is carbonized under an inert atmosphere, the precursor felt having a structure having different heat shrinkage rates on the front and back surfaces, A method for producing a carbon fiber felt, characterized in that the felt obtained by cutting the felt on the high shrinkage side is carbonized.

  In the carbon fiber felt of the present invention, a flow path of fluid such as molten sulfur is formed in the thickness direction of the felt by the groove portion formed on the surface. Further, the carbon fiber felt of the present invention is a felt part in which the bulk density of the felt part over the entire thickness of the felt along the thickness direction of the felt in the heel part [bulk density (ridge part)] is deeper than the groove depth in the groove part. Is higher than the bulk density [bulk density (groove part)], so that the groove part formed on the surface of the carbon fiber felt is not easily crushed, does not hinder the flow of the molten material, and promotes the movement of sodium ions. The charge / discharge efficiency of the battery can be increased. Therefore, the carbon fiber felt of the present invention can be suitably used as a material for the anode current collector.

  According to the method for producing a carbon fiber felt of the present invention, since carbonization is performed in an inert atmosphere while controlling the thermal contraction rate on the front and back sides and controlling the tension in the carbonization process, The bulk density of the heel portion can be increased, and the grooves formed on the surface of the carbon fiber felt are not easily crushed. Therefore, it is possible to obtain a carbon fiber felt that can be suitably used as a material for the anode current collector and a sodium-sulfur storage battery having the anode current collector.

FIG. 2 is a conceptual diagram showing an example of the carbon fiber felt of the present invention and an example in which the shape of the groove portion on the felt surface is a straight line, and FIG. Yes, (B) is a plan view. It is a schematic plan view which shows an example which is an example of the carbon fiber felt of this invention, and the shape of the groove part in a felt surface is linear. It is a schematic plan view which shows the example which is another example of the carbon fiber felt of this invention, and the shape of the groove part in a felt surface is a grid | lattice form. It is a schematic plan view which shows the example which is another example of the carbon fiber felt of this invention, and the shape of the groove part in a felt surface is a diamond shape. It is a schematic plan view which shows another example of the carbon fiber felt of this invention, and shows the example where the shape of the groove part in a felt surface is a wave shape. It is a conceptual diagram which shows the cross-sectional shape of a groove part in an example of the carbon fiber felt of this invention, Comprising: It is sectional drawing along the surface orthogonal to the longitudinal direction of a groove part. It is a conceptual diagram which shows the cross-sectional shape of a groove part in the other example of the carbon fiber felt of this invention, Comprising: It is sectional drawing along the surface orthogonal to the longitudinal direction of a groove part. It is a conceptual diagram which shows the cross-sectional shape of a groove part in the further another example of the carbon fiber felt of this invention, Comprising: It is sectional drawing along the surface orthogonal to the longitudinal direction of a groove part. It is a conceptual diagram which shows an example when the carbon fiber felt of this invention is attached between a cathode tube and an anode tube as a cylindrical anode current collection material in a sodium-sulfur storage battery, Comprising: It is orthogonal to the longitudinal direction of a groove part. It is sectional drawing along the surface to do. FIG. 5 is a conceptual diagram showing another example when the carbon fiber felt of the present invention is attached between a cathode tube and an anode tube as a cylindrical anode current collector in a sodium-sulfur storage battery, and is a longitudinal direction of a groove portion. It is sectional drawing along the surface orthogonal to. FIG. 6 is a conceptual diagram showing still another example when the carbon fiber felt of the present invention is attached between a cathode tube and an anode tube as a cylindrical anode current collector in a sodium-sulfur storage battery, wherein It is sectional drawing along the surface orthogonal to a direction. It is a conceptual diagram which shows an example of the carbon fiber precursor felt which cut into the felt used as a raw material for the manufacturing method of the carbon fiber felt of this invention, Comprising: Section along a surface orthogonal to the surface of a carbon fiber precursor felt FIG. It is a conceptual diagram which shows the other example of the carbon fiber precursor felt which used the raw material for the manufacturing method of the carbon fiber felt of this invention, and cut the felt, Comprising: It is along the surface orthogonal to the surface of a carbon fiber precursor felt FIG. It is a conceptual diagram which shows the preparation methods of the sample for a bulk density measurement of a collar part and a groove part, Comprising: It is sectional drawing along the surface orthogonal to the longitudinal direction of a groove part. It is a conceptual diagram which shows the structure of a sodium-sulfur storage battery.

  An example of the carbon fiber felt of the present invention is shown in FIG. In FIG. 1, reference numeral 2 denotes a carbon fiber felt, and a plurality of (5 in this figure) flange portions 4 spaced apart from each other by a predetermined interval are formed on one side of the felt 2 so as to protrude outward from the one side of the felt 2. Has been. The cross section perpendicular to the length direction of the band of the flange portion 4 is formed in a rectangular shape. A groove portion 6 is formed toward the inside of the felt 2 between the flange portions 4 adjacent to each other.

  The bulk density of the felt portion over the entire thickness of the felt along the thickness direction of the felt in the heel portion 4 [bulk density (畝 portion)] is the bulk density of the felt constituting the bottom wall 8 of the groove portion 6, that is, the groove portion 6. The bulk density [bulk density (groove part)] of the felt part deeper than the groove depth at is higher than the bulk density. In the present invention, the bulk density (the ridge portion) is preferably 1.05 to 2 times the bulk density (the groove portion).

  By configuring the bulk density (the ridge portion) higher than the bulk density (the groove portion), the ridge portion 4 is not easily crushed by pressure when incorporated between the cathode tube and the anode tube as an anode current collector. 6 can be secured stably.

  Therefore, the anode current collector using the carbon fiber felt of the present invention does not hinder the flow of the molten active material, promotes the movement of sodium ions, and can increase the charge / discharge efficiency of the sodium-sulfur battery. The difference in bulk density can be controlled by adjusting the difference in specific gravity of the precursor fiber or flame resistant fiber to be used and the type and amount of the substance to be mixed (mixed cotton substance).

  In the carbon fiber felt of the present invention, the carbon fiber felt having the flange portion 4 and the groove portion 6 only on one side of the felt 2 is more preferable than the carbon fiber felt having these on both sides of the felt 2. This is because a wide contact area with the inner peripheral surface of the anode tube can be secured, the conductive resistance can be reduced, and the charge / discharge efficiency can be increased.

Bulk density (ridge portion), 0.1 g / cm ³ or more preferably, 0.1 to 0.3 g / cm ³ is more preferable. In the case of less than 0.1 g / cm ³ , the heel portion tends to be crushed and the groove portion tends to be closed due to the pressure when the felt is incorporated as the anode current collector between the cathode tube and the anode tube.

The bulk density (groove portion) is preferably 0.05 g / cm ³ or more, and more preferably 0.05 to 0.25 g / cm ³ . When it is less than 0.05 g / cm ³ , the electric resistance value in the thickness direction is high, and the internal resistance of the battery tends to be high.

  The bulk density can be controlled by the number of punching at the time of producing the carbon fiber precursor felt, the specific gravity of the precursor fiber as the raw fiber, particularly the flame resistant fiber, and the kind and amount of the substance (mixed cotton substance) mixed with the raw fiber.

  In the present invention, the shape of the groove portion on the felt surface is preferably linear, grid, diamond, or wave as shown in FIGS.

  The example of the cross-sectional shape of the groove part in this invention is shown to FIGS. FIG. 6 shows a groove portion having a V-shaped cross section that becomes narrower toward the inside of the felt 2. FIG. 7 shows a groove portion having a rectangular cross section. FIG. 8 shows a groove portion having an inverted trapezoidal cross section. 2-8, 4 is a ridge part and 6 is a groove part.

  The example which attached the carbon fiber felt of this invention to the sodium-sulfur storage battery is shown to FIGS. The carbon fiber felt is inserted between the cathode tube and the anode tube as a cylindrical anode current collector. FIG. 9 is a conceptual diagram illustrating an example when a carbon fiber felt having a groove portion with an inverted trapezoidal cross-sectional shape in FIG. 8 is attached, and is a plan sectional view along a plane orthogonal to the longitudinal direction of the groove portion. is there. FIG. 10 is a conceptual diagram illustrating an example when a carbon fiber felt having a groove portion having a V-shaped cross section in FIG. 6 is attached, and is a plan sectional view along a plane orthogonal to the longitudinal direction of the groove portion. FIG. 11 is a conceptual diagram showing an example when a carbon fiber felt having a groove portion having a rectangular cross section in FIG. 7 is attached, and is a plan sectional view along a plane perpendicular to the longitudinal direction of the groove portion.

  9 to 11, reference numeral 12 denotes a sodium-sulfur battery, in which an inner container (cathode tube) 14 is inserted into an outer container (anode tube) 16 with the central axis aligned. Between the cathode tube and the anode tube, the carbon fiber felt as the anode current collector 18 containing sulfur as the anode active material has its inner peripheral surface (the upper surface of the carbon fiber felt 2 in FIGS. 2 to 9) as the outer peripheral surface of the cathode tube 14. It is wound in contact with. The outer peripheral surface of the felt 18 (the lower surface of the carbon fiber felt 2 in FIGS. 2 to 9) is in contact with the inner peripheral surface of the anode tube 16.

  As the cathode tube 14, a solid electrolyte ceramic tube is used, and sodium 20 as a cathode active material is stored inside the cathode tube 14. Sodium 20 is ionized during charging and discharging, and passes through a cathode tube that is a solid electrolyte.

  At the time of charging the battery, the sodium 20 inside the cathode tube 14 is divided into sodium ions and electrons, enters the carbon fiber felt as the anode current collector 18 of the cathode tube-anode tube member, and the anode impregnated in the anode current collector 18 It reacts with molten sulfur as an active material to produce sodium polysulfide.

  The grooves 6 in FIGS. 2 to 8 function as flow paths 22 through which molten sulfur, sodium polysulfide, and sodium ions move in FIGS. Moreover, since the collar part 4 itself in FIGS. 2-8 is also comprised from the carbon fiber, in FIGS. 9-11, it functions as the anode current collection material 18, and does not reduce the effective area which can react.

  In the carbon fiber felt of the present invention, the bending resistance measured for the test piece having the groove width direction as the longitudinal direction of the test piece is 4000 N · cm or less, preferably 3000 N · cm or less, more preferably 500 to 2500 N · cm. .

  When the bending resistance exceeds 4000 N · cm, the flexibility is not sufficient, and when a felt is incorporated as an anode current collector between the cathode tube and the anode tube, a gap is generated between the felt and the cathode tube or anode tube. And since the contact property between these deteriorates, the shaping | molding process which raises the softness | flexibility of a felt is needed. Therefore, the process at the time of felt integration is not preferable.

  The groove width on the surface of the felt 2 is preferably 0.5 to 10 mm, and more preferably 0.7 to 5 mm.

  When the groove width is less than 0.5 mm, the flexibility is not sufficient, and when the felt is incorporated as an anode current collector between the cathode tube and the anode tube, the gap is generated, and the felt and the cathode tube or anode tube Contactability deteriorates.

  When the groove width exceeds 10 mm, it becomes difficult to manufacture depending on the method of forming the groove portion using a notch (slit) described later.

  The depth (t) of the groove portion shown in FIGS. 6 to 8 is preferably 30 to 90%, more preferably 40 to 80% based on the felt thickness (T).

  When the depth (t) of the groove portion based on the felt thickness (T) is less than 30%, the permeability of molten sulfur in the thickness direction is not sufficient, and the charge / discharge efficiency is lowered. Furthermore, the flexibility is not sufficient, and when a felt is incorporated as an anode current collector between the cathode tube and the anode tube, a gap is generated, and the contact between the felt and the cathode tube or anode tube is deteriorated.

  If the depth (t) of the groove portion based on the felt thickness (T) exceeds 90%, the strength is reduced, and there is a possibility of breaking due to the tension during carbonization or the tension during lamination. It is not preferable. The depth (t) of the groove portion can be controlled by the depth of the slit described later.

  The groove pitch (distance between the centers of the parallel groove portions) is preferably 0.5 to 50 mm, and more preferably 0.8 to 50 mm.

  When the groove pitch is less than 0.5 mm, the interval is narrow and slitting cannot be performed.

  When the groove pitch exceeds 50 mm, the permeability of the molten sulfur in the thickness direction is not sufficient, and the charge / discharge efficiency decreases. Furthermore, the flexibility is not sufficient, and when a felt is incorporated as an anode current collector between the cylindrical cathode tube and the anode tube, a gap is generated, and the contact of the felt with the cathode tube or anode tube is deteriorated. The groove pitch can be controlled by the interval of the slit blades.

  The cross-sectional shape of the groove portion can be controlled by the shape of the slit blade and the process tension.

  The carbon fiber felt has a thickness (T) of 11 to 55 mm, preferably 15 to 25 mm.

  When the thickness (T) of the carbon fiber felt is less than 11 mm, the groove portion becomes shallow and the surface area contributing to the reaction in the groove portion is reduced, and consequently the surface area contributing to the reaction of the carbon fiber felt itself is also reduced. It is not preferable.

  If the thickness (T) of the carbon fiber felt exceeds 55 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 (weight per unit) of the mixed cotton material and the number of punching during the production of the felt.

Ridge portion, the basis weight of the carbon fiber felt 2 having a groove portion is preferably 500 to 5000 g / m ^2, 1000 to 3000 g / m ² is more preferable.

When the basis weight is less than 500 g / m ² , the surface area contributing to the reaction becomes small, which is not preferable.

If the basis weight exceeds 5000 g / m ² , the system becomes too large and the degree of design freedom is lowered, which is not preferable. The basis weight can be controlled by the amount of raw material (weight per unit) charged and the number of laminated webs.

The electrical resistance value in the thickness direction is preferably 1000 mΩ / cm ² or less, and more preferably 500 mΩ / cm ² .

When the electric resistance value in the thickness direction exceeds 1000 mΩ / cm ² , when felt is used as the anode current collector, the electric 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 punching number and the carbonization temperature.

As for the bulk density of this carbon fiber felt which has a ridge part and a groove part, 0.05-0.30 g / cm < ³ > is preferable. When the bulk density is less than 0.05 g / cm ³ , the contact points between the fibers are not sufficient, and the electric resistance value becomes high. When the bulk density exceeds 0.30 g / cm ³ , the punching number is too large. In this case, the fiber damage is severely reduced and the strength is lowered.

  The bulk density can be controlled by the number of punching at the time of producing the carbon fiber precursor felt, the specific gravity of the precursor fiber as the raw fiber, particularly the flame resistant fiber, and the kind and amount of the substance (mixed cotton substance) mixed with the raw fiber.

Sectional area of the width direction of the groove portion is preferably 1.5~500mm ^2, 5~100mm ² is more preferable.

When the cross-sectional area in the width direction of the groove portion is less than 1.5 mm ² , the permeability of the molten sulfur in the thickness direction is not sufficient, and the charge / discharge efficiency decreases.

When the cross-sectional area in the width direction of the groove portion exceeds 500 mm ² , it is difficult to produce by this manufacturing method. If it is in the range of the said cross-sectional area, the shape of a groove part will not be specified in particular. The cross-sectional area can be controlled by the groove width, groove depth, tension, felt front / back heat shrinkage difference, and type of blended material.

  The ratio of the groove cross-sectional area to the felt cross-sectional area is 1 to 75%, preferably 1.5 to 60%, and more preferably 5 to 50%.

  When the ratio of the groove cross-sectional area to the felt cross-sectional area is less than 1%, the permeability of the molten sulfur in the thickness direction is not sufficient, and the charge / discharge efficiency decreases.

  When the ratio of the groove cross-sectional area to the felt cross-sectional area exceeds 75%, problems such as an increase in the electric resistance value and inability to secure a necessary strength occur.

[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.

(Production method A)
In this method, first, a carbon fiber precursor felt in which notches for forming grooves are formed on one side or both sides of the carbon fiber precursor felt is prepared. The carbon fiber precursor felt has a thickness of 12 to 100 mm, preferably 15 to 70 mm, and more preferably 15 to 50 mm. Next, carbonization is performed in an inert atmosphere while applying tension in a direction in which the cut width increases. Thereby, the carbon fiber felt of the present invention is obtained.

  Examples of the raw material for producing the carbon fiber felt include polyacrylonitrile (PAN) flame resistant fibers, or conventionally known carbon fiber precursor fibers such as pitch fibers, rayon fibers, and cellulose. Among various production raw materials, PAN-based flame resistant fibers are preferable from the viewpoints of fiber flexibility and processability. The PAN-based flame resistant fiber is a fiber obtained by oxidizing a PAN-based raw fiber at 200 to 400 ° C. in the air.

  First, the carbon fiber precursor fiber or the flame resistant fiber is felted by a known method. As a felting method, there is a method in which a card is opened and multilayered, and the multilayered web is felted using a needle punch. However, the felting method is not limited to this method as long as the felt is used.

  Also, in order to make a difference in heat shrinkage between the front and back of the felt, webs made of different types and amounts of raw fibers are laminated in layers to make a felt, or different types and amounts of raw fibers are mixed to create a web. May be made and felted.

  Next, the felt produced as described above is cut (slit) using a slit blade or the like.

  FIG. 12 shows a felt used for producing the carbon fiber felt of the present invention. This felt is formed uniformly. A cut 34 is formed in the felt 32.

  The felt 32 composed of the plain layer 38 in which the notches 34 are not formed and the slit layer 36 in which the notches 34 are formed is carbonized under an inert atmosphere while applying tensions S and R in the direction in which the notch width increases. Is done. In this case, the direction is perpendicular to the cutting direction.

  The tension is preferably 100 N / m or less, more preferably 2 to 100 N / m, and particularly preferably 3 to 50 N / m. In the case of 2 N / m or more, a target groove width is easily obtained. When it exceeds 100 N / m, deformation (undel or crease) occurs due to tension, and the obtained carbon fiber felt of the present invention cannot be used as an electrode.

(Production method B)
FIG. 13 is an explanatory view showing another method for producing the carbon fiber felt of the present invention.

  In this method, first, a low shrinkage layer 42 that is thermally shrunk when carbonized is prepared. Next, a high shrinkage layer 44 having a higher thermal shrinkage rate when carbonized than the low shrinkage layer 42 is laminated and integrated with the low shrinkage layer 42. Integration is by punching.

  Then, the notch 34 is formed. The portion where the cut is formed becomes the slit layer 36, and the portion where the cut is not formed becomes the plane layer 38. When the felt in which the cut is formed is carbonized without applying a tension or under a predetermined tension, the cut of the cut 34 is made based on the difference in shrinkage rate between the low shrinkage layer 42 and the high shrinkage layer 44 at the time of carbonization. The width widens and the groove part is formed naturally.

  In this case, the tension for forming the groove portion in the carbon fiber precursor felt composed of the high shrinkage layer and the low shrinkage layer is preferably 100 N / m or less, more preferably 0.05 to 100 N / m, and more preferably 1 to 50 N. / M is particularly preferred. When it exceeds 100 N / m, undulation is generated by stretching during firing, resulting in poor appearance.

  In the carbon fiber precursor felt, the thermal shrinkage difference between the low shrinkage layer and the high shrinkage layer is preferably 2% or more, more preferably 5 to 50% at 400 ° C. When the heat shrinkage difference is less than 2%, groove formation is insufficient when carbonized under no tension.

  As a method for producing the high shrinkage layer, a method using a flame resistant fiber having a low specific gravity as the flame resistant fiber of the main material, a method of blending a flame resistant fiber having a lower specific gravity into the flame resistant fiber of the main material, or polyvinyl alcohol (PVA), A high shrinkage layer can be formed by a method of blending high shrinkage fibers (blend material) such as organic fibers such as polyester (PET), polypropylene (PP), acrylic, and cellulose, and natural fibers into a flame resistant fiber as a main raw material. it can.

  Among these, organic fibers and natural fibers are preferably used because the fibers are soft and easy to be entangled, and polyvinyl alcohol (PVA) is particularly preferable because it has little residue during carbonization. The specific gravity of the flame resistant fiber can be controlled by the treatment temperature and treatment time during production. The amount of shrinkage can be controlled by the amount of low specific gravity flame resistant fiber and the content of high shrinkage fiber.

  The low shrinkage layer can be formed mainly by a method using flame resistant fibers having a specific gravity exceeding 1.38. Any method may be used as long as the difference in heat shrinkage rate can be 2% or more.

  Moreover, you may combine the manufacturing method (manufacturing method A and B) of the two carbon fiber felts of this invention.

  The form of the groove formed on the felt surface includes a straight line shape, a lattice shape, a diamond shape, and a wave shape, and these shapes can be controlled by the shape of the slit blade.

The density of the flame resistant fiber 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 , the 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 fragile, and often falls during confounding treatment such as felt processing, so that the workability tends to be lowered.

  When the raw fiber is a carbon fiber precursor fiber, the fineness of the raw fiber is preferably 0.1 to 5.0 dtex, more preferably 0.5 to 3.5 dtex, and 1.0 to 3. 3 dtex is particularly preferred. When the fineness of the carbon fiber precursor is less than 0.1 dtex, the spreadability is poor and uniform mixing is difficult. When the fineness of the carbon fiber precursor 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.

  Among the raw material fibers, in particular, in the case of a PAN-based flame resistant fiber, the fineness is preferably 0.5 to 3.5 dtex, and more preferably 1.0 to 3.3 dtex.

  The carbon fiber precursor used in the carbon fiber precursor felt of the present invention has a fiber length of 30 to 75 mm, a fineness of 0.5 to 3.5 dtex, a crimp number of 4 to 20 pieces / 2.54 cm, and a crimp rate of 4 to 20 % Processed into a preferable percentage.

The entanglement process such as felting is preferably a needle punch method. When the number of entanglement processes is less than 50 times / cm ² , the number of entanglement processes is small and the strength is low. Moreover, the electrical resistance value in the thickness direction increases. When the number of entanglement treatments exceeds 2500 times / cm ² , damage to the fiber due to the entanglement treatment is large, and a large amount of falling fluff may occur, which is not preferable.

  The produced carbon fiber precursor felt has a thickness of 12 to 100 mm, preferably 15 to 70 mm, and more preferably 15 to 50 mm.

  After producing the carbon fiber precursor felt as described above, the carbon fiber felt having a groove portion is obtained by subjecting the carbon fiber precursor felt to carbonization under no tension or a predetermined tension.

  The carbonization treatment is performed in both production methods A and B by firing the carbon fiber precursor felt under an inert atmosphere at a maximum temperature of 1300 to 2300 ° C. for 0.5 to 10 minutes. Preferably, the first carbonization treatment and the second carbonization treatment are performed in two stages. In that case, a 1st carbonization process bakes the carbon fiber precursor felt after a confounding process at 300-1000 degreeC by inert atmosphere. 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 10 minutes. As for the maximum temperature at the time of this 2nd carbonization process, it is more preferable that it is the range of 1400 degreeC-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. 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 content of the carbon fiber felt is preferably 93% by mass or more, and more preferably 95% by mass or more. When the carbon content is less than 93% by mass, the electric resistance is high, and when incorporated in a battery, a large amount of resistance heat is generated during charge and discharge, resulting in a loss of power, and thus the battery efficiency tends to decrease.

  It is preferable that the single fiber diameter of the carbon fiber used for carbon fiber felt is 5-20 micrometers, and 6-15 micrometers is more preferable. When the single fiber diameter of the carbon fiber is less than 5 μm, the single fiber diameter is too thin, the processability such as the carding process is poor, and the strength of the fiber is low, so that the carbon fiber may be easily dropped from the carbon fiber felt. There is. When the single fiber diameter of the carbon fiber exceeds 20 μm, the contact point between the fibers decreases, the electrical resistance value increases, and the charge / discharge efficiency tends to decrease. Furthermore, since the carbonized fiber is rigid and brittle, a large amount of fine carbon fiber powder may be easily generated.

  The carbon fiber felt of the present invention thus obtained is, for example, a current collector that requires conductivity and liquid permeability, an electrode, a gas diffusion layer for a fuel cell, a composite, a sliding material, etc. It can also be applied as a reinforcing fiber. Among them, it can be preferably used as an anode current collector for sodium-sulfur storage batteries and other structural materials that require electrical conductivity, liquid permeability, water permeability, and the like.

  Further, when used as an anode current collector of a sodium-sulfur battery, glass fibers can be further punched on the groove forming surface.

  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.

[Groove depth (t)]
On the groove forming surface, the deepest portion of the formed groove was defined as the depth.

[Groove width]
The width of the groove on the felt surface was taken as the width.

[Groove pitch]
About the adjacent groove | channel adjacent in parallel, the distance between groove | channel center parts was measured along the groove width direction, and this was made into groove pitch.

[Groove cross section]
Cut a felt sample to a length of 10 cm with a cross section orthogonal to the longitudinal direction of the groove, and approximate the groove cross section of n = 5 to a triangle, trapezoid, or rectangle according to the cross sectional shape, and each groove with n = 5 The cross-sectional area of was calculated. The average value of the cross-sectional areas was determined and this was used as the groove cross-sectional area.

[Groove cross-sectional area ratio]
A felt sample was cut out to a length of 10 cm with a cut surface orthogonal to the longitudinal direction of the groove, and an n = 5 groove cross section was approximated to a triangle, trapezoid, or rectangle according to the cross sectional shape, and each calculated with n = 5 The total sum of the cross-sectional areas of the grooves was determined, and the total sum was divided by the area [10 cm length × thickness (T)] of the cut surface perpendicular to the longitudinal direction of the grooves.

[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.

[Heat shrinkage]
Heat-shrinkage ratio (400 ° C) is the average value of the length-width and dimensional-change amount divided by the original length when heat-resistant fiber felt of 20cm length x 20cm width is cut out and heat-treated at 400 ° C for 30 minutes in a nitrogen atmosphere. It was.

[Felt thickness (T)]
The thickness was measured using a thickness gauge (6.9 kPa). Five-point thickness was measured along the width direction of the heel part. The average value of the measured thickness was defined as felt thickness (T).

[The bulk density]
FIG. 14 is a conceptual diagram showing an example of a method for producing a sample for measuring the bulk density of the flange portion and the groove portion, and is a cross-sectional view along a plane perpendicular to the longitudinal direction of the groove portion. In FIG. 14, description will be made along the example of FIG. For the rectangular cross section of the example of FIG. 7, the inverted trapezoid of the cross section of the example of FIG. 8, and other groove-shaped carbon fiber felts, the same method for preparing a sample for measuring bulk density as in the example of FIG. 14 can be used.

  In FIG. 14, reference numeral 2 denotes a carbon fiber felt, which is an uneven surface comprising a plurality of flange portions 4 protruding outward in a band shape on the upper surface and a groove portion 6 having a V-shaped cross section formed between the plurality of flange portions 4. Has a shape.

  The cut-out location is cut out at the upper end surface of the flange portion 4 along the boundary line B between the flange portion 4 and the groove portion 6 so as to be orthogonal to the upper end surface, and these cut pieces 4p and 6p are cut into the flange portion and the groove portion. The bulk density measurement sample was used.

  From the thickness and basis weight measured using the sample, the bulk density (the ridge portion) and the bulk density (the groove portion) were calculated, respectively. The calculated values of n = 20 were averaged to obtain the average bulk density.

[Electrical resistance value in the thickness direction]
A 50 mm square sample was cut out, and the sample was sandwiched between two 50 mm square (10 mm thick) gold-plated electrodes so that they were in full contact with each other, and a 10 kPa load was applied in the thickness direction of the sample. The resistance value was measured and divided by the electrode area to obtain the electric resistance value per unit area.

[Bending softness]
The test piece was cut out from the felt with a size of 2 cm × about 15 cm so that the groove width direction was the longitudinal direction of the test piece, and five test pieces were obtained. The test length was set to 10 cm and the deflection was measured. Deflection was taken as the average of the values measured on both sides. The measurement is based on JIS-L-1096 Bending Softness Method B (Slide Method), and the following bending strength (N · cm) = WL ⁴ / 8σ.
W: Gravity per unit area of the specimen (N / cm ² )
L: Length of test piece; 10 cm
σ: Deflection of specimen (cm)
It calculated | required from the numerical formula.

[Example 1]
As a high shrinkage layer, 20% by mass of polyvinyl alcohol (PVA) staple is mixed with PAN-based flame resistant fiber (OPF) staple (fiber length 51 mm, crimp rate 10%, number of crimps 4 / cm) as a carbon fiber precursor, A PVA blended cotton PAN flame resistant fiber web having a basis weight of 200 g / m ² was produced. Eight of these were laminated | stacked and the web laminated body for slit layers was obtained.

As the low shrinkage layer, a PAN-based flame resistant fiber web having a basis weight of 200 g / m ² was prepared. Seven of these were laminated to obtain a web laminated body for a plain layer.

A web laminate for the slit layer and a web laminate for the plane layer were laminated, and needle punching was performed at 1000 times / cm ² to produce a carbon fiber precursor felt having a difference in shrinkage between the front and back sides.

  A slit treatment with a pitch of 5 mm and a depth of 15 mm was performed on the highly shrinkable layer side of the carbon fiber precursor felt. Thereafter, pre-carbonization treatment was performed for 10 minutes at 700 ° C. while applying a tension of 10 N / m in a direction orthogonal to the slit cutting surface, and then carbonization was performed at 1800 ° C. for 3 minutes. A carbon fiber felt having a groove formed on the surface was obtained.

[Examples 2 to 4]
A carbon fiber felt was produced in the same manner as in Example 1 except that PVA was changed to the mixed cotton material shown in Table 1.

[Example 5]
The same as in Example 1 except that a carbon fiber precursor felt that does not have a shrinkage difference between the front and back sides is prepared without using a mixed cotton substance, and the tension during firing is 20 N / m. Carbon fiber felt was produced by the method.

[Example 6]
A carbon fiber felt was produced in the same manner as in Example 1 except that the tension during firing was 0 N / m.

[Example 7]
In the high shrinkage layer, the same as Example 1 except that 6 PVA blended cotton PAN flame resistant fiber webs having a basis weight of 400 g / m ² were laminated and ² PAN flame resistant fiber webs having a basis weight of 350 g / m ² were laminated. A carbon fiber felt was prepared by the method described above.

[Example 8]
A carbon fiber felt was produced in the same manner as in Example 1 except that only the low specific gravity flame resistant fiber having large shrinkage was used in the high shrinkage layer.

[Comparative Example 1]
A carbon fiber felt is produced in the same manner as in Example 1 except that a carbon fiber precursor felt for carbonization treatment that does not have a difference in shrinkage between the front and back sides and that is not subjected to slit treatment is used. Was made.

[Comparative Example 2]
As a raw material carbon fiber precursor felt for grooving treatment, a carbon fiber precursor simple felt having no front and back shrinkage differences was used, and the groove width was 1 mm, the groove depth was 15 mm, and the groove pitch was 6.5 mm. The raw carbon fiber precursor felt was subjected to heat press at 200 ° C. and 4.9 MPa (50 kgf / cm ² ) with a press plate to obtain a grooved carbon fiber precursor felt. Otherwise, a carbon fiber felt was produced in the same manner as in Example 1.

[Comparative Example 3]
As a carbon fiber precursor felt for carbonization treatment, a carbon fiber precursor simple felt that does not have a difference in shrinkage between the front and back sides was used, and carbon was applied in the same manner as in Example 1 except that no tension was applied during carbonization. A fiber felt was prepared.

  As shown in Tables 1 and 2, since Examples 1 to 8 have low resistance to bending as well as electrical resistance value, when an anode current collector for sodium-sulfur storage battery (NAS battery) is used, The material uniformly flowed into the carbon fiber felt of the anode current collector, and a carbon fiber felt showing good results was obtained.

  In Comparative Example 1, since the bending resistance was high and it was used as an anode current collector for NAS battery, voids were generated when it was set in a cylindrical tube, and good charge / discharge efficiency could not be obtained.

  In Comparative Example 2, as a result of forming the groove portion by pressing, the bulk density (the ridge portion) is lower than the bulk density (the groove portion), the ridge portion is crushed when assembled in the cell, and the molten active material becomes the anode. As a result, the current did not flow uniformly to the carbon fiber felt of the current collector, resulting in a decrease in charge / discharge efficiency.

  In Comparative Example 3, a sufficient groove portion was not formed, resulting in poor fluid permeability.

[Example 9]
A carbon fiber felt was produced in the same manner as in Example 1 except that the mixing ratio of PVA in the high shrinkage layer was 5%.

[Example 10]
A carbon fiber felt was produced in the same manner as in Example 1 except that the tension during carbonization was 2 N / m.

[Example 11]
A carbon fiber felt was produced in the same manner as in Example 1 except that the mixing ratio of PVA in the high shrinkage layer was 50%.

[Example 12]
A carbon fiber felt was produced in the same manner as in Example 1 except that the tension during carbonization was 50 N / m.

[Examples 13 to 16]
Carbon fiber felts were produced in the same manner as in Example 1 except that the slit depths and pitches in Tables 3 and 4 were used.

  As shown in Tables 3 and 4, in Examples 9 to 16, both the electrical resistance value and the bending resistance were low, and the active material melted by the flow path uniformly flowed to the carbon fiber felt of the anode current collector, and good results were obtained. The carbon fiber felt which shows was obtained.

[Examples 17 to 18]
A carbon fiber felt was produced in the same manner as in Example 1 except that the slit shape and pitch in Table 4 were used.

[Example 19]
A carbon fiber felt was produced in the same manner as in Example 1 except that the slit shape and pitch in Table 5 were used.

[Example 20]
In high shrinkage layer, the PVA cotton mixing PAN-based flame-resistant fiber web 10 sheets having a basis weight of 400 g / m ^2, except that by laminating 8 sheets of PAN-based flame-resistant fiber web having a basis weight of 400 g / m ² in a similar manner as in Example 1 Carbon fiber felt was produced.

  As shown in Tables 4 and 5, in Examples 17 to 20, both carbon flow loss and cell resistance were low, and carbon fiber felts showing good results were obtained.

[Comparative Example 4]
A carbon fiber was produced in the same manner as in Example 1 except that a PAN-based flame resistant fiber web having a basis weight of 200 g / m ² was laminated on ^two PVA mixed cotton PAN-based flame resistant fiber webs having a basis weight of 200 g / m ^2. A felt was prepared. As a result, the thickness was small, and the molten active material did not flow uniformly to the carbon fiber felt of the anode current collector, and the effect of improving the charge / discharge efficiency was not observed.

[Comparative Example 5]
A carbon fiber felt was produced in the same manner as in Example 1 except that in the high shrinkage layer, the mixing ratio of PVA was 2% and the tension during carbonization was 2 N / m. As a result, a sufficient groove width could not be formed, and the molten active material did not flow uniformly to the carbon fiber felt of the anode current collector, resulting in a decrease in charge / discharge efficiency.

[Comparative Example 6]
A carbon fiber felt was produced in the same manner as in Example 1 except that the specific gravity of the flame resistant fiber of the high shrinkage layer was 1.33 and the tension during carbonization was 110 N / m. The groove width was large, the contact resistance was low, and the electrical resistance value was high. Moreover, deformation after carbonization was large, and electrode evaluation as a NAS battery was impossible.

[Comparative Example 7]
A carbon fiber felt was produced in the same manner as in Example 1 except that the slit depth was 20.5 mm (93% with respect to the thickness). As a result, it broke during carbonization and could not be evaluated.

[Comparative Example 8]
A carbon fiber felt was produced in the same manner as in Example 1 except that the depth of the slit was 5.5 mm (25% with respect to the thickness). As a result, the groove portion could not be sufficiently secured, the molten active material did not flow uniformly to the carbon fiber felt of the anode current collector, and the effect of improving the charge / discharge efficiency was not observed.

[Comparative Example 9]
A carbon fiber felt was produced in the same manner as in Example 1 except that the pitch interval was increased. As a result, the groove cross-section (groove cross-sectional area ratio) with respect to the felt cross-section was small, the molten active material did not flow uniformly into the carbon fiber felt of the anode current collector, and the effect of improving charge / discharge efficiency was not observed.

[Comparative Example 10]
A carbon fiber was produced in the same manner as in Example 1 except that a PAN-based flame resistant fiber web having a basis weight of 200 g / m ² was laminated on ^two PVA mixed cotton PAN-based flame resistant fiber webs having a basis weight of 200 g / m ^2. A felt was prepared. As a result, the thickness was small, and the molten active material did not flow uniformly to the carbon fiber felt of the anode current collector, and the effect of improving the charge / discharge efficiency was not observed.

[Comparative Example 11]
A carbon fiber felt was produced in the same manner as in Example 1 except that the carbonization temperature was 1200 ° C. As a result, the electric resistance was high and the target cell resistance could not be obtained.

2 Carbon fiber felt 4 ridge portion 4p cutout piece for measuring bulk density of heel portion 6 groove portion 6p cutout piece for measuring bulk density of groove portion 8 bottom wall of groove portion B between ridge portion and groove portion on upper end surface of ridge portion Boundary line t Carbon fiber felt thickness T Groove depth 12, 52 Sodium-sulfur battery 14, 54 Anode tube 16, 56 Cathode tube 18, 58 Molten metal sodium 20, 60 Anode current collector 22 Molten sulfur, sodium polysulfide , Flow path of anode current collector through which sodium ions move 32 carbon fiber precursor felt 34 notch 36 part where no notch is formed in the felt (plain layer)
38 The part that forms the cut in the felt (slit layer)
S, R Arrows indicating the direction of tension 42 Low shrinkage layer 44 High shrinkage layer

Claims (9)

A plurality of ridges portion projecting on at least one side of the outer, an uneven shape composed of a groove portion formed between the plurality of ridges portions, thickness a carbon fiber felt 11～55Mm, ridge portion The carbon fiber felt is characterized in that the bulk density of the felt is higher than the bulk density of the felt part deeper than the groove depth in the groove part.   The carbon fiber felt according to claim 1, wherein the grooves are formed in a linear shape, a lattice shape, a diamond shape, or a wave shape on the felt surface.   The carbon fiber felt according to claim 1 or 2, wherein the groove width is 0.5 to 10 mm, the groove depth is 10 to 90% of the thickness of the carbon fiber felt, and the groove pitch is 0.5 to 100 mm. . Basis weight of 500 to 5000 g / ^{m 2,} a bulk density of 0.05~0.30g / cm ^3, the carbon fiber according to any one of claims 1 to 3 the electric resistance value in the thickness direction is 1000M / cm ² or less felt.   The carbon fiber felt according to any one of claims 1 to 4, wherein the bending resistance measured for a test piece having the groove width direction as a felt longitudinal direction is 4000 N · cm or less.   An anode current collector comprising the carbon fiber felt according to any one of claims 1 to 5.   A sodium-sulfur storage battery comprising: the anode current collector according to claim 6; an anode tube; and a cathode tube inserted into the anode tube with an axis aligned with the anode tube, wherein the anode current collector has an uneven shape. A sodium-sulfur storage battery which is wound by bringing the surface having a contact with the outer peripheral surface of the cathode tube and the outer peripheral surface of the anode current collector in contact with the inner peripheral surface of the anode tube. It is a manufacturing method of the carbon fiber felt of Claim 1 which carbonizes a carbon fiber precursor felt of thickness 12-100mm in inert atmosphere, Comprising: The cutting direction is made into the precursor felt which made the cut | incision in the single side | surface or both surfaces A carbon fiber felt manufacturing method, wherein carbonization is performed while applying tension in a direction orthogonal to the direction. The method for producing a carbon fiber felt according to claim 1, wherein a carbon fiber precursor felt having a thickness of 12 to 100 mm is carbonized under an inert atmosphere, wherein the precursor felt has a structure having different heat shrinkage rates on the front and back surfaces. A carbon fiber felt manufacturing method comprising: carbonizing a felt which has been cut into the felt on the high shrinkage side.

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