JPH06150938A - Electrode material and manufacture thereof - Google Patents

Abstract

PURPOSE:To lower electric resistance, improve stack performance, and manufacture electrode material efficiently and economically by arranging carbon fiber or graphite fiber randomly in the plane of the vertical direction of a cylinder wall surface so as to set stack performance and specific resistance to a fixed value. CONSTITUTION:In cylindrical electrode material, carbon fiber or graphite fiber is randomly arranged in the plane of the vertical direction of a cylinder wall surface so as to set stack performance to 5cm<3>/g or more and the specific resistance of a cylinder wall surface to 0.33OMEGAcm or less. Mixture containing precursor for hardly-graphitizing carbon fiber or easily-graphitizing carbon fiber is made felt-like, is punched, and two sheets or more thereof are superimposed and joined mutually. Thereafter, the same is carbonized or further graphitized. The carbon fiber or the graphite fiber arranged randomly on the wall surface of the cylindrical electrode material is obtained by making polyacrylonitrile fiber or pitch fiber flame resistant (infusible), carbonized, or further graphitized. Thereby the impregnating characteristic of sulfur and battery performance can be improved as conductivity is made excellent and stack performance is also made excellent.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrode material and a method for producing the same.

[0002]

2. Description of the Related Art Recently, by using a sheet-like material such as carbon fiber or graphite fiber or a conductive material made of felt as an electrode conductive material for a secondary battery such as a sodium / sulfur battery,
Attempts have been made to improve the charging efficiency of secondary batteries.
As a method for producing a sheet-like material made of carbon fiber for an electrode material, a method for producing a non-woven fabric substrate for carbon fiber reinforced composite material is known as described in JP-A-54-101985. There is. This method makes a sheet, such as a non-woven sheet, from a pretreated carbonizable fiber material so as to change its chemical composition to facilitate subsequent carbonization, which is then free of oxygen. It is a method of carbonizing at a temperature of 1000 ° C. or higher in an atmosphere. However, with such a method, it is difficult to obtain 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, Japanese Patent Laid-Open No. 63-148560 discloses an electrode-shaped organic fiber having an oxygen content of 0.05-10.
A method is disclosed in which surface oxidation is carried out at 350 to 900 ° C. in an inert gas containing vol% and then carbonization is carried out at a temperature of 800 to 1500 ° C. in an inert gas containing 3 vol% or more of chlorine or fluorine. However, in this method, since the organic fiber formed in the electrode shape is directly heated to 350 to 900 ° C., a rapid exothermic reaction is liable to occur, it is difficult to maintain the electrode shape, and only those having low performance can be obtained.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a cylindrical electrode material having a low electric resistance and at the same time excellent bulkiness, and an improved production method for obtaining it efficiently and economically. To provide.

[0005]

The present invention is a cylindrical electrode material in which carbon fibers or graphite fibers are randomly arranged in the plane of the wall surface of the cylinder in the vertical direction, and the bulkiness is 5
The electrode material is characterized in that the specific resistance of the cylindrical wall surface is 0.3 Ωcm or less at cm ³ / g or more.

Further, the present invention is to prepare a mixture containing a precursor for non-graphitizable carbon fiber or a graphitizable carbon fiber further into a felt, punch it into a doughnut-like shape, and laminate and bond two or more thereof, and then carbonize or further The method for producing an electrode material described above is characterized by graphitization.

The present invention will be described in detail below. On the wall surface of the cylindrical electrode material of the present invention, short fibers of carbon fibers or graphitized fibers are randomly arranged in the vertical direction with respect to the wall surface. This carbon fiber or graphite fiber can be obtained by subjecting polyacrylonitrile fiber or pitch fiber to flame resistance (non-melting), carbonization or further graphitization.

Generally, the electrical resistivity of carbon fiber varies depending on the heat treatment temperature, but the resistivity in the direction parallel to the fiber axis is 10
It is on the order of ^-2 Ωcm, and the specific resistance in the fiber cross section is 1
It is on the order of 0 ^-1 Ωcm. Therefore, the arrangement of the matt and felt carbon fibers produced from the short fiber web is randomly arranged in the plane direction of the sheet in parallel with the plane, and is partially arranged in the thickness direction (perpendicular to the plane) by needle punching. The effect on the specific resistance value of the felt in the thickness direction is small, and is usually 0.4 Ωcm or more.

In the cylindrical carbon fiber electrode, a flat plate-like felt has conventionally been rounded into a cylindrical shape, but wrinkles are likely to occur in the inner layer due to its thickness. Therefore, the flat plate-like felt is currently divided into 2 to 4 pieces, and the base is Each of them has a shape and is inserted into a cylindrical metal case by being rolled up, and in each case, the specific resistance in the thickness direction is as high as 0.4 Ωcm or more. The present inventors focused on the fact that the specific resistance value of the felt in the surface direction is low, punching out a felt-like carbon fiber mat in a donut shape, and laminating and joining two or more donut-like felts in the height direction, It has been found that an excellent electrode material having a specific resistance of the cylindrical wall in the thickness direction of 0.3 Ωcm or less can be provided.

The bulkiness of the cylindrical electrode material of the present invention is preferably 5 cm ³ / g or more. When the bulkiness of the cylindrical electrode material is less than 5 cm ³ / g, the impregnated amount of sulfur is small and the charging efficiency is low, which is not preferable.

Further, although the cylindrical electrode material of the present invention has a specific resistance in the thickness direction of the cylindrical wall of 0.3 Ωcm or less,
It is preferably 2 Ωcm or less. The specific resistance value of the electrode material is preferably as small as possible, and the discharge efficiency decreases as the resistance value increases, which is not preferable.

The method for producing the electrode material of the present invention is not particularly limited, but about 100 to 30% by weight of a precursor for non-graphitizable carbon fiber obtained by heating and oxidizing polyacrylonitrile fiber, and coal or petroleum pitch or tar. It can be obtained by making a mixture composed of about 0 to 70% by weight of the easily graphitized carbon fiber produced into a felt, punching it into a donut shape and laminating and bonding it, and carbonizing or further graphitizing it.

The content of graphitizable carbon fiber in the mixture is 0.
In the case of, the felt shows excellent bulkiness, but the electric conductivity tends to decrease. When the content of the graphitizable carbon fiber precursor exceeds 70 wt%, the felt exhibits excellent electric conductivity, but the bulkiness tends to decrease.

One of the features of the production method of the present invention is that a precursor of non-graphitizable carbon fiber as a raw material of felt, that is,
The point is to use an oxidized fiber (flame resistant fiber) obtained by heat-oxidizing a polyacrylonitrile fiber or the like in air.
Mixing of the polyacrylonitrile fiber itself and the pitch carbon fiber cannot be easily achieved. The reason is that even if unoxidized polyacrylonitrile fiber is mixed with pitch carbon fiber and it is made into felt and then subjected to oxidation treatment and carbonization treatment, runaway of exothermic reaction occurs during the treatment and its shape retention. Because it is difficult. It is also conceivable to perform 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 a problem on the working environment where short fibers so-called flies fly, but also There are drawbacks such as the one having a large basis weight (weight per unit area) cannot be obtained.

In the production method of the present invention, the precursor for non-graphitizable carbon fiber is obtained by heat-oxidizing polyacrylonitrile fiber at 200 to 300 ° C. in an oxidizing atmosphere to have a density of 1.30 to 1.45 g / cm 3. It is preferably ³ oxidized fiber. The polyacrylonitrile fiber is heat-oxidized in an oxidizing atmosphere containing oxygen, sulfur, hydrochloric acid, etc., generally in air at 200 to 300 ° C. When the heating oxidation temperature is 200 ° C. or lower, the oxidation reaction takes a long time, which is not practical, and when it is 300 ° C. or higher, an exothermic reaction suddenly occurs, which may lead to uncontrollable combustion, which is not preferable.

As described above, the oxidized fiber (flame resistant fiber) used in the present invention has a density of 1.30 to 1.45 g / cm.
³ is preferable. 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 , a cause of troubles such as fiber cutting in the crimping step or the web step. Is not preferable.

In the production method of the present invention, the precursor for the non-graphitizable carbon fiber and the easily graphitizable carbon fiber are mixed to produce a felt, which is then punched into a donut shape, connected and joined, and then inert. It is preferable to carbonize or graphitize in an atmosphere. When producing mats and felts, etc., the polyacrylonitrile-based flame resistant fiber and the easily graphitizable carbon fiber are mixed in a predetermined ratio and felted by a known method, or the polyacrylonitrile-based flame resistant fiber and the easily graphitizable carbon are used. Individual webs of fibers may be made, alternately laminated and then needle punched to create a felt.

The thickness and basis weight (g / m ² ) of the electrode material can be appropriately designed, but the thickness is 10 to 50 mm and the basis weight is 100.
0 to 6000 (g / m ² ) is preferable. The number of needle punching is preferably 10 to 1000 / cm ² . When punching into a donut shape, inner diameter 30-70 mm,
The outer diameter is preferably in the range of 35 to 90 mm. The connection joint length is 50 to 200 mm. Needle punching,
Any method such as stitching or adhesion may be used, but if high strength is not required, simple lamination may be used.

The obtained cylindrical felt laminate is finally heated to a temperature of 1800 to 28 by an ordinary method in an inert gas atmosphere such as nitrogen gas or argon gas.
00 ° C., more preferably 1 at a temperature of 2000-2500 ° C.
It can be converted into a cylindrical electrode material by heat treatment for at least 3 minutes, more preferably at least 3 minutes and not more than 10 minutes.

Regarding the method of carbonizing the polyacrylonitrile-based flame resistant fiber felt mixed with the graphitizable carbon fiber in the present invention, carbonization of felt made of polyacrylonitrile-based flame resistant fiber containing no graphitizable carbon fiber, graphite It is possible to carbonize or graphitize by a batch process or a continuous process by a method similar to the carbonization method.

Further, in order to industrially obtain an electrode material having excellent performance in a short time, carbonization or graphitization can be carried out, for example, by the method described in JP-A-2-139464. That is, from 300 to 900 ° C, 500 ° C /
The heating is performed at a rate of temperature rise of not more than minutes, preferably not more than 200 ° C./minute. If the rate of temperature increase exceeds 500 ° C./min, decomposition products will be generated rapidly, and the performance of the obtained electrode material will deteriorate. Further, the felt is 10 to 900-2800 ° C in an inert atmosphere.
The treatment is performed at 00 ° C./minute or less, preferably 200 ° C./minute or less, and carbonization and graphitization treatment is performed at 1800 to 2800 ° C. for 1 minute or more, preferably 3 minutes or more. Previous stage 300-900 ℃
By performing the heat treatment in the region, the heat treatment process in the subsequent stage can be performed in a short time, which is a factor of cost reduction and the electric resistivity of the obtained electrode material is low, which is bulky and has a compression recovery property. A good electrode material can be manufactured.

[0022]

The present invention will be described in more detail with reference to the following examples. The evaluation items in Table 1 are measured as follows. Compression recovery: 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. Ratio of thickness after recovery to initial thickness (t ₁
/ T ₀ ) × 100. Specific resistance: The electric resistance is measured while sandwiching the felt between steel plates having a diameter of 30 mmφ and the felt is compressed. The electric 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) × measurement sample area (c
m ² ) / measured sample thickness (cm) Bulk density: The weight per unit volume (g / cm ² ) is shown. Bulkiness: It is shown by the reciprocal of the bulk density. That is, the volume per unit weight (cm ³ / g) was used.

Example Acrylonitrile 98% as raw material and other copolymerization component 2
% Polyacrylonitrile fiber in an air atmosphere,
Heat treated at a temperature of 240-280 ° C, density 1.40 g / c
m ³ flame resistant fibers were obtained. This fiber was crimped by a known method to obtain a staple fiber having a cut length of 60 mm.
The staple fiber of this flame resistant fiber, which is a precursor for non-graphitizable fiber, and the pitch-based general-purpose carbon fiber Donacarb S (trade name, manufactured by Donac Co.), which is an easily graphitizable carbon fiber manufactured from coal tar pitch as a raw material, are shown. The webs were made by mixing in the proportions shown in 1 and by a known method. Next, four sheets of the web were piled up and 15000 times / m ² needle punching was performed to prepare a felt having a thickness of 30 mm and a basis weight of 5000 g / m ² . The felt was punched into a donut shape having an inner diameter of 40 mm and an outer diameter of 80 mm with a cutter, and five sheets were stacked and needle punched to join and join.

The cylindrical felt laminate thus obtained was heated to 600 ° C. at a rate of 20 ° C./min in a nitrogen gas atmosphere while inserting a graphite rod of 40 mmφ into the cylinder to prevent the inner diameter of the cylinder from shrinking. It was Then, the temperature was raised to 2000 ° C. at 20 ° C./min, and the temperature was maintained for 10 minutes. Then, the temperature was lowered and it was taken out after confirming that the temperature became 50 ° C. or lower. The performance of the obtained electrode material is shown in Table 1.

[0025]

[Table 1]

From Table 1, the specific resistances in the thickness direction of the cylindrical wall surfaces of the cylindrical electrode materials of the present invention examples of Experiment Nos. 1 to 5 are all 0.
It is 2 Ωcm or less.

[0027]

EFFECT OF THE INVENTION The cylindrical electrode material of the present invention has excellent conductivity as an electrode material for a secondary battery and is also bulky, so that it has a good impregnation property with sulfur and contributes to improvement of battery performance.

Front page continued (72) Inventor Yoshihisa Otani 180 Jotomachi, Himeji City, Hyogo Prefecture Japan Felt Industry Co., Ltd.

Claims (2)

[Claims] 1. A cylindrical electrode material, wherein carbon fibers or graphite fibers are randomly arranged in a plane in a vertical direction of the cylindrical wall surface, and the bulkiness is 5 cm ³ / g or more, and the specific resistance of the cylindrical wall surface. Is 0.3 Ωcm or less. 2. A mixture containing a non-graphitizable carbon fiber precursor or an easily graphitizable carbon fiber is made into a felt, punched into a donut shape, and two or more sheets thereof are laminated and joined, and then carbonized or further graphitized. The method for producing an electrode material according to claim 1, wherein