JPH06123050A - Carbon fiber felt and its production - Google Patents

Abstract

PURPOSE:To industrially efficiently and inexpensively obtain a carbon fiber felt for electric cell electrodes, having low electric resistance and excellent bulkiness. CONSTITUTION:This carbon fiber felt for electrodes and electrically conductive materials consists of 20-80wt.% sparingly graphitized carbon fiber and 80-20wt.% readily graphitized carbon fiber and has excellent performances of <=2OMEGAcm specific resistance and >=10cm<3>/g bulkiness. The carbon fiber felt is produced by forming a mixture consisting of a precursor for sparingly graphitized carbon fiber obtained by oxidizing and heating a polyacrylonitrile fiber and a readily graphitized carbon fiber produced from coal petroleum pitch or tar and forming into a felt and successively carbonizing the felt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon fiber felt for a battery conductive material and a method for producing the same, and more specifically, a precursor for non-graphitizable carbon fiber and an easily graphitizable carbon fiber are mixed to form a mat and a felt. The present invention relates to a carbon fiber felt characterized by being carbonized or graphitized in an inert atmosphere and a method for producing the same.

[0002]

2. Description of the Related Art Recently, attempts have been made to improve the charging efficiency of secondary batteries by using a conductive material made of felt such as carbon fiber or graphite fiber as an electrode conductive material for secondary batteries such as sodium / sulfur batteries. There is. As a method for producing such a sheet-like material made of carbon fibers, as described in JP-A-54-101985, a method for producing a nonwoven fabric substrate for a carbon fiber reinforced composite material is known. . This method makes a sheet material such as a non-woven sheet from a carbonizable fiber material that has been pretreated so as to change its chemical composition to facilitate subsequent carbonization, and then the sheet is placed in an oxygen-free atmosphere. , Temperature 100
This is a method of carbonizing at 0 ° C or higher. However, with such a method, it was difficult to produce a material having sufficient conductivity as an electrode conductive material and sufficient bulkiness for impregnating with sulfur.

On the other hand, as a method for producing a felt-like or cloth-like carbon electrode, a method described in JP-A-63-148560 is known. In this method, the organic fibers formed in the shape of electrodes are surface-oxidized at 350 to 900 ° C. in an inert gas containing 0.05 to 10 vol% oxygen, and then the temperature is 800 to in an inert gas containing 3 vol% or more chlorine or fluorine. It is a method of carbonizing at 1500 ° C. However, in this method, since the organic fiber formed in the electrode shape is directly heated to 500 to 800 ° C., a rapid exothermic reaction is likely to occur, it is difficult to maintain the electrode shape, and only the one having low performance can be obtained.

[0004]

An object of the present invention is to improve a carbon fiber felt for a battery electrode, which has a low electric resistance and an excellent bulkiness at the same time, in order to obtain the carbon fiber felt industrially efficiently and at low cost. It is to provide a manufacturing method.

[0005]

Means for Solving the Problems The first gist of the present invention consists of a mixture of 20 to 80 wt% of non-graphitizable carbon fiber and 80 to 20 wt% of easily graphitizable carbon fiber, and has a specific resistance of 2Ω.
cm or less and a bulkiness of 10 cm ³ / g or more, which is a carbon fiber felt for an electrode conductive material having excellent performance.
The gist of is that a mixture of a precursor for non-graphitizable carbon fiber obtained by oxidizing and heating polyacrylonitrile fiber and a graphitizable carbon fiber produced from coal or petroleum pitch or tar is felted, and then this is Non-graphitizable carbon fiber characterized by being carbonized 20 to 80 wt
% And 80 to 20 wt% of graphitizable carbon fiber, and a method for producing a carbon fiber felt for an electrode conductive material having excellent properties of a specific resistance of 2 Ωcm or less and a bulkiness of 10 cm ³ / g or more.

Carbon fibers such as polyacrylonitrile fibers, vinylidene chloride fibers, cellulose fibers, and phenol fibers are generally called non-graphitizable fibers, and it is difficult to increase the density in the carbonization treatment. Since the carbon fiber made of the non-graphitizable fiber has high strength, it is easy to form a felt having a relatively good workability and being bulky, but it is difficult to form a felt having excellent electric conductivity characteristics. On the other hand, carbon fibers from petroleum coke, coal pitch, etc. are said to be easily graphitized carbon fibers because they can be easily densified. These easily graphitized carbon fibers are hard to form a rigid and bulky felt, but they are easy to form a felt having excellent electric conductivity.

The felt of the present invention comprises a non-graphitizable carbon fiber 2
It is composed of a mixture of 0 to 80 wt% and graphitizable carbon fiber 80 to 20 wt%. When the content of the graphitizable carbon fiber in the mixture is less than 20 wt%, the felt exhibits excellent bulkiness, but does not exhibit satisfactory performance in terms of electrical conductivity. On the other hand, when the content of the graphitizable carbon fiber in the mixture exceeds 80 wt%, the felt shows excellent electric conductivity, but does not exhibit satisfactory performance in terms of bulkiness. Further, the felt of the present invention has a bulkiness of 10c.
It is preferably m ³ / g or more. When the bulkiness of the carbon fiber felt is 10 cm ³ / g or less, the impregnated amount of sulfur becomes small and the charging efficiency becomes low, which is not preferable.

Further, the felt of the present invention preferably has a specific resistance of 2 Ωcm or less. If it is larger than 2 Ωcm, the discharge efficiency becomes low, which is not preferable.

The greatest feature of the felt manufacturing method of the present invention is that a precursor of polyacrylonitrile-based carbon fiber used as a non-graphitizable fiber is an oxidized fiber (flame resistant fiber) obtained by oxidation and heat treatment in air. There is a point to use. Mixing of the polyacrylonitrile fiber itself and the pitch-based carbon fiber cannot be easily achieved. Furthermore, even if polyacrylonitrile-based fiber in an unoxidized state is mixed with pitch-based carbon fiber, and oxidation and carbonization are performed after mat and felt processing, exothermic reaction runaway occurs during the treatment. Shape retention is difficult. It is also possible to perform matting and felting after mixing the polyacrylonitrile-based carbon fiber itself and the pitch-based carbon fiber, but in this case cutting of the fiber occurs, not only the short fiber so-called fly becomes a problem in flying work, but also There are drawbacks such as not having a large basis weight.

In the production method of the present invention, the precursor of the non-graphitizable carbon fiber is obtained by subjecting polyacrylonitrile fiber to oxidation treatment at 200 to 300 ° C. in an oxidizing atmosphere and having a density of 1.30 to 1.45 g / cm ^3. It is preferable that the oxidized fiber is.

The polyacrylonitrile fiber used in the present invention is generally oxidized in an oxidizing atmosphere containing oxygen, sulfur, hydrochloric acid, etc., generally in air at 200 to 300 ° C. If the thermal oxidation temperature is 200 ° C. or lower, the oxidation reaction requires a long time, which is not practical, and if it is 300 ° C. or higher, an exothermic reaction may occur suddenly, which may lead to uncontrollable combustion, which is not preferable.

The flame resistant fiber used in the present invention preferably has a density of 1.30 to 1.45 g / cm ³ . If the density is less than 1.30 g / cm ³ , it will be difficult to carbonize in the subsequent carbonization step, and if it exceeds 1.45 g / cm ³ , it will cause troubles in the crimping step and the web step, which is not preferable.

In the production method of the present invention, the precursor of the non-graphitizable carbon fiber and the easily graphitizable carbon fiber are mixed to produce a mat, felt or the like, which is then carbonized and graphitized in an inert atmosphere. Preferably. When producing mats and felts, the polyacrylonitrile flame resistant fiber and the graphitizable carbon fiber are mixed at a predetermined ratio and felted by a known method, or the polyacrylonitrile flame resistant fiber and the graphitizable carbon fiber. Separate webs of carbon fibers may be created and alternately laminated and then needle punched into a felt.

Thickness of felt (mm), basis weight (g /
m ² ) can be appropriately designed, but the thickness is 10 to 30 m
m, and the basis weight is preferably 1000 to 2000 g / m ² . The number of needle punchings driven is 1 to 1000 / cm ²
Is preferred. When the number of implants increases, the resistivity in the thickness direction initially decreases, but tends to saturate at some point. The felt obtained by mixing is finally heated to 1800 to 2800 ° C., preferably 2000 to 2500 ° C. for 1 minute or more, more preferably in an inert gas atmosphere, for example, an atmosphere of nitrogen gas, argon gas, etc., by a usual method. Can be converted to carbon fiber felt by heating and heat treatment for 3 minutes or more and 10 minutes or less.

Regarding the method of carbonizing the polyacrylonitrile-based flame resistant fiber felt mixed with the graphitizable carbon fiber in the invention, carbonization of the felt made of polyacrylonitrile-based flame resistant fiber containing no graphitizable carbon fiber, graphite In order to obtain a carbon fiber felt which can be carbonized and graphitized by a batch treatment or a continuous treatment by a method similar to the carbonization method and has excellent industrial performance in a short time, see, for example, JP-A-2-139464. It is possible to carbonize and graphitize by the method described in the publication. That is, 300 to 900 ° C. is heated at a temperature rising rate of 500 ° C./min or less, preferably 200 ° C./min or less. Temperature rising rate is 5
If it exceeds 00 ° C./min, decomposition products will be generated rapidly, and the performance of the resulting carbon fiber felt will deteriorate. Further, the felt is 1000 ° C./in an inert atmosphere up to 900-2800 ° C.
1800 or less, preferably 1800 or less
Carry out carbonization and graphitization at ˜2800 ° C. for 1 minute or longer, preferably 3 minutes or longer. By performing the heat treatment in the 300 to 900 ° C. region in the first stage, it becomes possible to perform the heat treatment process in the second stage in a short time, which is a factor of cost reduction and the electric resistivity of the obtained carbon fiber felt is low, A felt which is bulky and has good compression recovery can be manufactured.

[0016]

The present invention will be specifically described with reference to the following examples. "Compression recovery" was measured as follows. A load is applied to the initial thickness (t ₀ ) of the felt to compress it by 50%. Then, the load is released and the thickness (t ₁ ) is measured. The ratio of the thickness after recovery to the initial thickness (t ₀ / t ₁ ) × 100 was defined as the compression recovery property. "Electrical resistivity" was measured as follows. The electrical resistance is measured while sandwiching the felt between copper plates having a diameter of 30 mmφ and compressing the felt. The electrical resistance decreases as the thickness decreases, but becomes constant at a certain thickness. The resistance value at this time is calculated using the following formula. Specific resistance (Ωcm) = measured resistance value (Ω) × measured sample area (cm ² ) / measured sample thickness (cm) The felt bulk density is the weight per unit volume (g / cm ³ ).
Indicated by. The "bulkness" is represented by the reciprocal of the bulk density, that is, the volume per unit weight (cm ³ / g).

(Example 1) Polyacrylonitrile fiber composed of 98 wt% of acrylonitrile and 2 wt% of other components as a raw material was heat-treated at a temperature of 240 to 280 ° C in an air atmosphere to obtain a flame resistant fiber having a density of 1.40 g / cm ³ . The fiber was crimped by a known method to obtain a stable fiber having a cut length of 60 mm. A web is made by a known method by mixing a predetermined amount of pitch-based general-purpose carbon fiber Dona Carbo S (Donac Co.) stable fiber produced from coal tar pitch as a raw material. 15,000 by stacking 4 webs
Time / m ² needle punching, thickness 18 mm, basis weight 1
A felt of 600 g / m ² was prepared. The felt thus obtained was heated to 600 ° C. at a rate of 20 ° C./min in a nitrogen gas atmosphere, then heated to 2000 ° C. at a rate of 20 ° C./min, and held at that temperature for 10 minutes. Then, the temperature was lowered and it was taken out after confirming that the temperature became 50 ° C. or lower. The production conditions and performance of the obtained carbon fiber felt are shown in Table 1.

[Table 1] FIG. 1 shows the relationship between the amount of easily graphitizable carbon fibers in the obtained carbon fiber felt and the bulkiness. Further, FIG. 2 shows the relationship between the mixing amount of the graphitizable carbon fiber and the specific resistance in the thickness direction. From both figures, it is clear that each performance is improved in the mixing range of the present invention as compared with the performance expected from the performance when each is independent.

[0018]

[Brief description of drawings]

[Figure 1]

FIG. 1 is a relationship between the amount of easily graphitizable carbon fibers mixed in the obtained carbon fiber felt and the bulkiness.

FIG. 2 is a relationship between the mixing amount of graphitizable carbon fibers and the specific resistance in the thickness direction.

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[Procedure amendment]

[Submission date] October 8, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a relationship between the amount of easily graphitizable carbon fibers mixed in the obtained carbon fiber felt and the bulkiness.

FIG. 2 is a relationship between the mixing amount of graphitizable carbon fibers and the specific resistance in the thickness direction.

Claims (4)

[Claims] 1. A mixture of 20 to 80 wt% of non-graphitizable carbon fiber and 80 to 20 wt% of easily graphitizable carbon fiber,
A carbon fiber felt for an electrode conductive material having excellent properties such as a specific resistance of 2 Ωcm or less and a bulkiness of 10 cm ³ / g or more. 2. A mixture of a precursor for non-graphitizable carbon fiber obtained by oxidizing and heating polyacrylonitrile fiber and an easily graphitizable carbon fiber produced from coal, petroleum pitch or tar, and then felted the mixture. Non-graphitizable carbon fiber characterized by being carbonized 20-80w
A method for producing a carbon fiber felt for an electrode conductive material, which comprises t% and easily graphitized carbon fiber 80 to 20 wt% and has excellent properties such as a specific resistance of 2 Ωcm or less and a bulkiness of 10 cm ³ / g or more. 3. A precursor for non-graphitizable carbon fiber, wherein a polyacrylonitrile fiber is heated at a temperature of 200 in an oxidizing atmosphere.
Density 1.30 to 1.45, oxidized at ~ 300 ° C
The method for producing a carbon fiber felt according to claim 2, wherein the carbon fiber felt is g / cm ³ oxidized fiber (flame resistant fiber). 4. A non-graphitizable carbon fiber precursor and an easily graphitizable carbon fiber are mixed to produce a mat, felt, etc., and then carbonized and graphitized in an inert atmosphere. Resistivity 2Ω consisting of non-graphitizable carbon fiber 20-80wt% and graphitizable carbon fiber 80-20wt%
cm or less and bulkiness of 10 cm ³ / g or more, a method for producing a carbon fiber felt for an electrode conductive material having excellent performance.