JPH01239767A - Electrode substrate and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an electrode substrate having thick size, good conductivity, and large compression repulsion by stacking fabrics or knits made of fire resistant fibers and a nonwoven fabric, punching to entangle the fibers, and carbonizing. CONSTITUTION:Fire resistant fibers which are a precursor of carbon fiber such as polyacrylonitrile fiber are heated at 150-400 deg.C, and fabrics or knits made of these fibers and nonwoven fabrics are alternately stacked to obtain specified thickness. The stack obtained is punched with a needle punch to entangle fibers, then heated in a nitrogen atmosphere, for example, at 1300-3000 deg.C to obtain carbon fibers. By this process, an electrode substrate having a specified thickness, low electric resistance in the thickness direction, and large compression repulsion is obtained. This substrate is effective as the electrode substrate of a redox-flow cell or a sodium-sulfur battery.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to secondary batteries such as redox flow batteries and sodium-sulfur batteries, and to electrolysis of organic compounds, synthesis by electrolysis, oxidation, and reduction reactions. The present invention relates to a base material suitable for forming electrodes of electrolytic towers, etc., and a method of manufacturing the same.

[Prior Art] In recent years, attempts have been made to use secondary batteries to store surplus power generated at night, etc., and release it when demand increases to respond to fluctuations in demand.

There are various types of secondary batteries used for such purposes, but among them, redox flow batteries are
The electrolytic chamber, which performs electrochemical energy changes during charging and discharging, and the tank for the redox aqueous solution, which is the electrolytic solution, are installed separately, making it easy to increase the amount of electricity stored by increasing the tank capacity. Not only is it suitable for storing large amounts of electricity, but it is also attracting a lot of attention because it has relatively little self-discharge. Also, there is a sodium-sulfur type battery that is used for a similar purpose.

This is a well-known method that uses sodium at the cathode and sulfur or polysulfide monolithium at the anode as active materials, and converts both materials into only sodium ions at a high temperature of around 300'C. anti-1 through a solid electrolyte that passes through
It is used to generate electromotive force.

Now, the base material used to cover the electrodes of such redox flow batteries and sodium-sulfur batteries must have high conductivity, corrosion resistance against electrolytes and active materials, etc. Various properties are required, such as good reactivity of the electrolyte and active material on the surface. Therefore,
Carbon fiber is often used.

For example, Special Publication No. 53-18603 Tan Publication, Special Publication No. 53-18603,
-43920, JP 57-129814, JP 57-166354, JP 60-44
Publication No. 963 (this publication describes an electrode base material made of carbon YJ woven fiber carbon that is randomly oriented two-dimensionally or three-dimensionally. However, in this conventional base material, the short fibers are There is a problem that the resistance when the electrolyte flows is large because the voids formed in the carbon fibers are small.Also, since the short carbon fibers are bonded together with carbon, they have high rigidity, so they can be compressed to an appropriate thickness. Even if an attempt is made to improve electrical contact with, for example, a current collecting electrode by utilizing the repulsive force generated when the repulsive force is applied, there is a problem that the repulsive force cannot be increased by 1q.

Also, Japanese Patent Publication No. 52-24972, Japanese Patent Publication No. 59-1
No. 19680, Japanese Patent Application Laid-open No. 60-232669,
JP-A-63-21754, JP-A-63-2175
No. 5 describes an electrode base material made of a woven or knitted fabric of carbon fibers.

Although such a base material has large voids formed by weaves and stitches, the flow glJ resistance (see above) is low, but the electrolyte, active material, etc. The problem is that it is difficult to make contact with the single fibers that form the grooves, so it is difficult to secure a large area for the reaction. The fact that the reaction area of the electrode cannot be made too large also means that it is difficult to make the size of the battery or electrolytic cell larger or to increase its capacity.

Zarani, JP 56-33826, JP 61-
No. 198576 and Japanese Unexamined Patent Publication No. 63-2261 disclose electrode base materials made of carbon fiber non-woven materials such as FEL 1 to FEL 5. However, although this base material has the advantage of having a large reaction area because the carbon single fibers are dispersed, it also has problems such as a small repulsive force because the single fibers tend to move in the planar direction when compressed, and the fact that the fibers are Since it is short, there is a problem that the conductivity is low, especially in the plane direction.

A common problem with the above-mentioned sli%+ materials is that it is difficult to obtain materials that are thick and have good shape retention.For electrodes for batteries, electrolytic cells, etc. Since thickness is required, it becomes necessary to stack several base materials to ensure the thickness, but this greatly increases the electrical resistance at the contact surface between the base materials, so the thickness The electrical resistance in this direction becomes large.

On the other hand, Japanese Patent Application Laid-Open No. 60-235371 proposes placing carbon single fibers on the solid electrolyte side of the anode chamber and graphite felt on the can body side in J5 for sodium to lium-sulfur type batteries. are doing.

This is an attempt to improve the reactivity of the active material by using two types of base materials with different shapes (1), but it still creates a large electrical resistance on the contact surface of the base materials, and it is difficult to assemble. It's also troublesome.

As described above, conventional electrode base materials have both advantages and disadvantages, and improvements are desired.

[Problems to be Solved by the Invention] The purpose of the present invention is to solve the problems of conventional electrode base materials, to make them thicker, to have very low electrical resistance in the thickness direction, and to have excellent compressive repulsion. An object of the present invention is to provide an electric current base material that is flexible enough to maintain sufficient contact with a current collector, and has excellent shape retention properties, and a method for producing the same.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a woven or knitted fabric made of carbon fibers and a nonwoven fabric j made of carbon fibers are arranged in a layered manner, and these woven or knitted fabrics and There is provided an electrode base material characterized in that a nonwoven fabric is integrated by intertwining carbon fibers forming the woven or knitted fabric with carbon fibers forming the nonwoven fabric. In addition, in the present invention, as a method for manufacturing such a base material, a woven or knitted fabric made of flame-resistant fiber, which is a precursor fiber of carbon fiber, and a non-woven fabric 5 made of the above-mentioned flame-resistant fiber are superimposed, and the The above-mentioned flame-resistant a! which constitutes the above-mentioned woven or knitted fabric by punching a polymer! After the woven or knitted fabric and the non-woven fabric are intertwined with the flame-retardant fibers constituting the non-woven fabric 15, the woven fabric or knitted fabric and the non-woven fabric are integrated, and then heat-treated in a non-oxidizing atmosphere to make the flame-retardant fibers. A method for manufacturing an electrode base material is provided, which comprises carbonizing fibers.

To explain this invention in more detail, in this invention, first, a flame-resistant fiber that is a precursor fiber of carbon fiber is prepared. This production may be performed by a well-known method for producing carbon fibers. In other words, raw material fibers (fiber bundles), such as polyacrylonitrile fibers, cellulose fibers, and pitch fibers, which can be made into carbon fibers through a flame-retardant process and a carbonization process, in an oxidizing atmosphere and without being ignited. It can be prepared by heat-treating at 150 to 400'C to make it flame resistant.The raw material fibers include:
Finally, in order to improve the impregnability of the electrolytic solution to the electrode base material (A3) and improve the contact efficiency with the electrolytic solution, it is recommended to use a material with a single thread diameter of 3 to 20 μm. is preferred.

Here, the flame-resistant fiber is not a raw material fiber that has high knot strength and is difficult to handle, but in order to avoid making it difficult to manufacture woven fabrics, knitted fabrics, and non-woven fabrics described later, the above-mentioned flame-resistant process is carried out. It is preferable to perform this so that the LOI value is about 20 to 40%.

Here, the LOI value is a score indicating the degree of flame resistance, and the formula is: LOI value = [Amount of oxygen required for the flame resistant fiber to continue burning / (Amount of oxygen necessary for the flame resistant fiber to continue burning) + amount of nitrogen)] X100 (%). Here, the LOI value is JIs
It is measured as follows according to the method specified in K7201.

That is, a test piece was made by winding a flame-resistant fiber around a wire with a diameter of about Q, 3 mm to a diameter of about 7 mm.
Place the test piece inside the combustion cylinder. Next, a mixed gas of oxygen and nitrogen is flowed into the combustion tube and ignited at the upper end of the test piece. Determine the amount of nitrogen and the amount of nitrogen at that time. Then, use the above formula to make a needle.

Now, in this invention, a woven fabric or a non-woven material 45 is prepared using the above-mentioned flame-resistant fiber (fiber bundle).

The fabric can be made 1q by weaving flame-resistant fibers by conventional methods. The weave structure may be any one of a plain weave, a twill weave, a satin weave, etc., but a plain weave is preferable in the sense that it has good weavability.

A knitted fabric can also be obtained by a conventional method, but it is preferable that the knitted structure is a warp knitted structure such as a raschel structure or a tricot structure, which has relatively low elasticity.

The nonwoven fabric is made by crimping flame-resistant fibers, preferably having a
It can be cut into strips of 200 mm, more preferably 30 to 100 mm, and printed by roller cards, flat cards, or random uniforms using high-speed airflow, which are commonly used in the production of nonwoven fabrics. If necessary, several pieces of the nonwoven fabric are stacked one on top of the other and punched using a method such as needle punching or water jet punching to entangle the flame-resistant fibers. Although this operation is preferable for improving shape retention and electrical properties, it is not essential. At this time, the higher the panning density, the better the above-mentioned characteristics will be. Less than 30 pieces/cm
It is better to set it to 2.

Now, in this invention, next, the above-mentioned woven or knitted fabric and non-woven fabric are overlapped and punched to make the woven or knitted fabric flame-resistant, and the fibers and the non-woven fabric are interlaced with the flame-resistant fibers that make up the non-woven fabric. Then, the two are integrated to obtain a so-called intermediate base material. Here, the woven or knitted fabric and the nonwoven fabric may be overlaid in any manner. For example, the nonwoven fabric 5 may be superimposed on one or both sides of a woven or knitted fabric, or conversely, the woven or knitted fabric may be superimposed on one or both sides of a nonwoven fabric. Furthermore, woven or knitted fabrics and nonwoven fabrics can be alternately layered. It may be determined depending on the purpose, required characteristics, etc. Note that punching can be performed using a well-known method such as needle punching or water jet punching. Further, the woven fabric or knitted fabric and the nonwoven fabric may be used either individually or as a set of a plurality of woven fabrics or knitted fabrics. In general, for example, by overlapping a nonwoven fabric with a low basis weight on one side of a woven or knitted fabric and a nonwoven fabric with a higher basis weight on the other side, electrode groups with different reaction areas, electrical resistances, etc. can be created in the thickness direction. It can be used as a material.

In this invention, next, the above-mentioned intermediate, 11, and J are heated to 1300 to 300
The flame-resistant fiber is carbonized by 7JO heat treatment at 00'C. In other words, carbon fiber is used. At this time, the flame-resistant fibers shrink slightly. In this way, the electrode base material of the present invention is obtained, but in order to improve its activity in battery reactions, it may be subjected to oxidation treatment such as air oxidation, nitric acid oxidation, electrolytic oxidation, plasma oxidation, etc., or may be subjected to oxidation treatment during the heat treatment. Halogenation treatment may be performed by flowing halogen gas.

The overall basis weight and overall thickness of the electrode base material affect the reaction area in battery reactions and electrolytic reactions, the flow resistance of the electrolytic solution, the amount of active material retained, and the like. The overall basis weight and overall thickness are determined by various factors, such as the combination and number of woven or knitted fabrics and nonwoven fabrics arranged in layers, the structure and basis weight of individual materials, and the thickness and length of carbon fibers. It depends on the factors.

For example, for woven and knitted fabrics, it depends on the structure, basis weight, thickness of carbon fiber bundles, whether or not they are twisted, etc. For nonwoven fabrics, it depends on the date, length of carbon fibers, and density when punching. .

Therefore, by using these factors inversely, the overall basis weight and overall thickness can be changed to make an electrode base material particularly suitable for a specific application. For example, for redox flow type secondary batteries, the overall basis weight is 300 to 1500 CI/m2,
It is preferable that the total thickness is about 3 to 251111 Tl. Further, for sodium-sulfur type secondary batteries and flow-through type electrolytic cells, it is preferable that the overall basis weight is 500 to 1500 g/m2 and the overall thickness is about 10 to 25 mm.

Similarly, the compressive repulsion force also changes depending on the factors mentioned above. This compressive repulsion force is used for any of the above applications.
Preferably, the culm degree is 0.4 to 2 Kg/c+n2.

[Embodiment] In FIG. 1, the electrode base material has a nonwoven fabric b2 made of carbon fibers arranged on one side of a woven fabric or knitted fabric 1 made of carbon fibers, and a woven fabric or knitted fabric 1 and a nonwoven fabric 2 made of carbon fibers. Alternatively, the carbon fibers constituting the knitted fabric 1 and the carbon fibers constituting the non-woven fabric 52 are intertwined by punching to be integrated. Woven or knitted fabric 1
A plurality of sheets of each of the nonwoven material 52 and the nonwoven material 52 are used. In the case shown in FIG. 2, woven or knitted fabrics are placed on both sides of the nonwoven fabric.
．． 1 is arranged, and the one shown in FIG. 3 has a structure in which woven or knitted fabrics 1 and nonwoven fabrics 2 are alternately laminated. It goes without saying that the electrode base materials of these embodiments are also integrated by intertwining, similar to that shown in FIG.

FIG. 4 is an exploded view of a cell unit of a redox flow type secondary battery using the electrode base material of the present invention for the anode and cathode.
b> and a spacer 58 having a discharge pipe 4a (4b)
(5b) is an electrode 6a using the electrode base material of the present invention.
(6b) is opposed via a cation exchange membrane 7 made of polystyrene sulfonic acid or the like. One electrode) or 6a (6b) is a positive electrode, and the other electrode 6a (6b) is
b(6a) each act as a cathode. When the cell units 9 are stacked, a separation plate 8 made of glassy carbon or the like is inserted between adjacent cell units.

FIG. 5 shows a redox flow type secondary battery constructed by laminating a large number of cell units as shown in FIG. 4. In FIG. 5, for the stacked n cell units 91 to 9n, the electrolyte supply pipes are connected to the piping system that connects the anode electrolyte tank 10 and the circulation pump 11 so that the cell units 1 to 1 are connected in parallel. 3a and the discharge pipe 4a, and similarly connect the cathode electrolyte tank 12 and the circulation pump 1.
The electrolyte supply pipe 3b and the discharge pipe 4b are connected to the piping system having 3 so that each cell unit is in parallel, and a circulation pump is connected to the electrode 6a (6b) shown in FIG. 4 of each cell unit. 11 (13) by electrolyte tank 10 (12)
Charging and discharging are performed while circulating and contacting the electrolyte. Cell units 1-91-9n are electrically connected in series. As the electrolyte, a Jnn pig iron hydrochloric acid solution or the like is used for the anode, and a chromium chloride hydrochloric acid solution or the like is used for the cathode.

FIG. 6 shows a sodium-sulfur type secondary battery using the electrode base material of the present invention as an anode, in which a tubular solid electrolyte 17 is placed inside a can 16, and the solid electrolyte 7 and the can 1
Anode 1B using a cylindrical electrode base material impregnated with sulfur or sodium polysulfide, which is an anode active material, between
On the other hand, the inside of the solid N solute 17 accommodates sodium, which is a cathode active material, and the cathode 15 in contact with it is arranged, and the solid N solute 17 is sealed with a lid 14. Anode 1B
The base material used in this is placed between the solid electrolyte 17 and the can body 16 in a compressed state, and is brought into electrical contact with the solid electrolyte IW4f17.15 and the can body 16 due to the repulsive force of the base material. However, since the base material of the present invention has a large compressive repulsion force, the electrical contact resistance between the two is reduced, the internal resistance of the battery is reduced, and the battery performance is improved.

[Example] Example 1 A fiber bundle of flame-resistant fiber, which is a precursor fiber of the carbon fiber Patreca "Ta2O" manufactured by Toshi Co., Ltd., was cut into a fiber length of about 5''1 mm and made into a nonwoven fabric using a roller card.

Furthermore, 5 layers of this nonwoven 5 are stacked and needle punched,
A thick flame-resistant fiber nonwoven A5 was obtained. Note that the punching density was 100 punches/cm2.

Next, the above-mentioned thick non-woven fabric was layered on both sides of the flame-resistant fiber fabric “Pyromex” manufactured by Toho Rayon Co., Ltd.
Needle punching was performed to intertwine the flame-resistant fibers constituting the nonwoven fabric with the flame-resistant fibers constituting the woven fabric, and the two were integrated to obtain an intermediate base material. Punching density is 20
It was set to 0 pieces/Cm2.

Next, the above intermediate base material was heat-treated at 1500'C for 30 minutes in a nitrogen atmosphere to carbonize the flame-resistant fibers and obtain a low base material 8 as a carbon fiber.

The overall thickness of this electrode base material 1,1 is approximately Qmm, the overall thickness is 640Q/m2, and the compressive repulsion force is 0.8kg/m2.
Cll12, and the electrical resistance in the thickness direction was 9 mΩ. Compressive repulsive force and electrical resistance were measured as follows.

In other words, the repulsive force was determined by measuring the electrode group (A) cut into a size of 50 mm x 50 mm using a compression testing machine AG manufactured by Shimadzu Corporation.
-500B, 1 mm/min (7) black, 71
゜The base material is compressed at head speed, and the cart is 20CI/C
The thickness of the base material at m2 is taken as the initial thickness, and the load when the thickness of the base material becomes 1/2 of the initial thickness (kMCm
2> was defined as the repulsive force.

In addition, the electrical resistance in the thickness direction is determined by applying a load of 100Q/cm2 to an electrode base material with an area of 2acm2, and applying a load of 1A in the thickness direction.
It was determined from the outside potential when a current of .

Example 2 When a cell unit as shown in Figure 4 was assembled using the electrode base material obtained in Example 1 and a charge/discharge test was performed, the current efficiency was approximately 96% and the electrical conductivity was approximately 0.253. /cm2
Met. Here, current efficiency and electrical conductivity were measured as follows.

Current efficiency: Cell unit 1~ (electrode base material area:
'lQcm2, spacer thickness: 3mm, partition plate: Clara Sea Carbon), and as an anode electrolyte,
A 4N hydrochloric acid solution containing 1 mole of iron chloride was used as the negative and electrode electrolytes, and a 4N hydrochloric acid solution containing 1 mole of n-chromium chloride was used as the negative and electrode electrolytes, and these electrolytes were applied to the electrode base material at a rate of 0.5 cm/min. Constant current charging is performed at a current density of 40 mA/cm2 while contacting at a speed, then constant current discharge is performed at a current density of 40 mA/cm2, and further constant voltage discharge is performed at 0.8 V. The amount of electricity charged at this time is 0.1 , when the amount of electricity discharged at constant current is Q2, and the amount of electricity discharged at constant voltage is 03, the value obtained by the formula: [(Q203)/Ql]X100 is the current efficiency.

Electrical conductivity: All Or of 4N hydrochloric acid solution of 1 mol/1 chromium chloride
When the amount of electricity required to reduce Cr2+ to Cr2+ is the theoretical amount of electricity, and the slope of the current-voltage curve when charging and discharging to 50% of this theoretical amount of electricity is the resistance value,
The reciprocal of the resistance value is the electrical conductivity.

Example 3 Ten cell units used in Example 2 were stacked and connected as shown in FIG. 5, and charged and discharged.

At this time, the current efficiency was about 95%, and the electrical conductivity per cell unit was about 0.233/cm2.

[Effects of the Invention] The electrode base material of the present invention comprises a woven or knitted fabric made of carbon fibers and a nonwoven fabric made of carbon fibers arranged in a layered manner. It is integrated by intertwining carbon fibers, and the carbon fibers extend in the thickness direction, reducing the electrical resistance at the contact surface when multiple base materials are stacked together. As a result, the electrical resistance in the thickness direction can be significantly reduced. Also,
In terms of reaction area, conductivity in the plane direction, flow resistance of electrolyte, etc., it is now possible to combine the advantages of woven or knitted fabrics with those of non-woven fabrics. It becomes possible to easily configure batteries, electrolyzers, and IG.

In other words, since the carbon fibers are punched, the binding force of the carbon fibers is moderate, so a large compressive repulsion force can be obtained, and good electrical contact with the current collecting electrode etc. can be obtained. In addition, by changing the combination of woven or knitted fabrics and non-woven fabrics, etc., it is possible to change the overall basis weight or overall thickness, or by changing the basis weight in the thickness direction, the reaction area or electrical resistance can be changed in that direction. Since it becomes possible to do this, the degree of freedom in setting h1 according to the purpose etc. is improved. In addition, not only can even thick objects be easily reduced to 1Q, but they also have excellent shape retention and make it easier to assemble batteries, etc.

The present invention also provides an electrode base material as described above in which a polymer of a woven or knitted fabric made of a flame-resistant fiber as a precursor fiber of carbon fiber and a non-woven fabric 5 made of the above-mentioned flame-resistant fiber is used. Manufactured by punching and intertwining the flame resistant fibers constituting the woven or knitted fabric with the flame resistant fibers constituting the nonwoven fabric to integrate the 1-reduced fabric or knitted fabric and the nonwoven fabric. Therefore, it is possible to prevent the nonwoven iron from deforming during punching, and it is possible to easily produce a thick base material with a large compressive repulsion force. In addition, since punching is performed at the stage of flame-retardant fibers, production is much easier than when carbon fibers, which have very low bending strength, are used as the so-called starting material.

[Brief explanation of the drawing]

Figures 1 to 3 are WXX front views showing different embodiments of the electrode base material of the present invention. Figure 4 is cell units 1 to 1 of a redox flow type secondary battery using the electrode base material of the present invention. FIG. 5 is a schematic block diagram of a redox flow type secondary battery using the cell unit shown in FIG. 4, and FIG. 6 is a schematic exploded perspective view of a redox flow type secondary battery using the cell unit shown in FIG. - A schematic vertical cross-sectional view of a sulfur type secondary battery. 1: Woven or knitted fabric of carbon fiber 2: Non-woven fabric of carbon fiber Ion exchange membrane 8: Separation plates 9.91 to 9n: Cell unit] O: Anode electrolyte tank 11: Circulation pump 12: Cathode electrolyte tank 13: Circulation pump 14: Benefit body 15: Cathode 16: Can body 17: Solid electrolyte 18: Anode

Claims (5)

[Claims] (1) A woven fabric or knitted fabric made of carbon fibers and a nonwoven fabric made of carbon fibers are arranged in a layered manner, and the woven fabric or knitted fabric and the nonwoven fabric constitute the carbon fibers and the nonwoven fabric that make up the woven fabric or knitted fabric. An electrode base material characterized by being integrated by intertwining with carbon fibers. (2) A cell unit for a redox flow type secondary battery having the electrode base material according to claim (1). (3) A redox flow type secondary battery comprising the cell unit according to claim (2). (4) A sodium-sulfur secondary battery comprising the electrode base material according to claim (1). (5) The flame-resistant fabric is constructed by laminating a woven or knitted fabric made of flame-resistant fibers that are precursor fibers of carbon fibers and a non-woven fabric made of the flame-resistant fibers, and punching the polymer. After the woven or knitted fabric and the nonwoven fabric are intertwined with the flame resistant fibers constituting the nonwoven fabric, the flame resistant fibers are carbonized by heat treatment in a non-oxidizing atmosphere. A method for manufacturing an electrode base material, characterized in that: