JPH0315814B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a large capacity wet electric double layer capacitor in which polarizable electrodes are formed from activated carbon fiber pulp. Conventional Structure and Its Problems FIG. 1 shows an example of the structure of a conventional capacitor of this type. Activated carbon fiber cloth is used as the polarizable electrode 1, and on one side of the cloth as the current collector 2, aluminum,
A current collection layer made of a metal layer such as titanium, nickel, or a conductive resin layer was formed, and the current collecting layer was made to face each other with a separator 3 in between. After injecting an electrolytic solution, a sealed casing was formed using a case 4, a sealing plate 5, and a gasket 6. It has a configuration. The activated carbon fibers used for the polarizable electrodes are obtained by directly carbonizing and activating phenolic (cured novolac fibers), rayon, acrylic, or pitch fiber cloth, or by further activating the fibers after carbonization. Considering the electrical resistance, strength, activation yield, etc. of the activated carbon fibers thus obtained, phenolic fibers are the best among the above fibers. In addition, metal current collectors can be easily formed by plasma spraying, arc spraying, or gas spraying, and conductive electrodes made of conductive materials such as conductive resin can be easily formed by screen printing, spraying, or dip methods. can be formed into A polarizable electrode having such a shape can be punched into a circular shape with a desired diameter, and the coin-shaped small-sized large-capacity capacitor shown in FIG. 1 can be manufactured. In addition, since this type of polarizable electrode does not use a binder, it not only can reduce internal resistance, but also the active carbon surface is not covered with a binder, which reduces the loss of the effective area for forming a double layer and allows for a smaller size and larger capacity. In particular, when the current collector is formed by a thermal spraying method, the adhesive strength between the thermal sprayed metal layer and the activated carbon fiber layer is strong, the contact resistance is small, and good capacitor characteristics can be obtained. However, technological progress in the electronics industry is remarkable, and even higher performance is required for high-performance, large-volume capacitors using activated carbon fiber cloth. In particular, higher capacity per unit volume,
These include cost reduction, rapid charge/discharge performance, freedom in designing electrode shapes, and improvement in the manufacturing work environment. However, although the conventional activated carbon fiber cloth has various excellent advantages, it requires a lead time of 4 to 6 months from the spinning state to obtaining the desired cloth. Long lead times pose manufacturing problems, and it is also difficult to keep inventory of fabrics with different fabric weights and different weaving methods. In addition, if a special weaving method with a large basis weight is used, there is a problem that the weaving allowance becomes several times that of the raw yarn. In addition, the weight of the raw material convergent yarn or woven fabric becomes 1/3 to 1/4 during the carbonization or activated carbonization process, and the area becomes about 1/2. Therefore, the internal porosity of activated carbon cloth varies depending on the weaving method, but is as high as 50 to 70%. In addition, in terms of electrical resistance, as shown in FIG. Although the conductivity in the ′ direction is good,
The conductivity in the b-b' direction is considered to be very poor.
Therefore, the impedance becomes large, making the capacitor unsuitable for rapid charging. Furthermore, when constructing larger capacitors, activated carbon fiber cloth, which does not require a binder, has good volumetric efficiency. However, activated carbon fiber cloth obtained from phenolic novolac resin fiber has a small specific surface area.
Although it is possible to activate up to 2,500 m ² /g, if the porosity exceeds 2,300 m ² /g, the porosity will increase and the mechanical strength of the activated carbon cloth will decrease, making it impossible to mass-produce it or reducing its dimensions. Precision cannot be obtained. Therefore, it has been difficult to increase the carbonization activation degree of the activated carbon fiber cloth to 2300 m ² /g or more in order to improve the characteristics of the capacitor. Purpose of the Invention The present invention provides an electric double layer that improves carbon fiber density per unit volume, increases capacitor capacity, and significantly improves various properties such as high-speed charging and discharging characteristics, high-temperature storage characteristics, mass productivity, and cost reduction. The purpose of this invention is to provide a method for manufacturing capacitors. Structure of the Invention In order to achieve the above object, the present invention carbonizes and activates long filament-like synthetic fibers to obtain long filament-like activated carbon fibers, and then cuts the activated carbon fibers to produce activated carbon fiber pulp. , the activated carbon fiber pulp is used as a polarizable electrode. This method has excellent workability and makes it possible to use activated carbon fibers with a high specific surface area. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and requirements of the present invention will be described with reference to the accompanying drawings. (1) Manufacturing process First, the manufacturing process of a polarizable electrode body composed of activated carbon fiber pulp and fibrous material necessary for carrying out the present invention will be explained. FIG. 3 is a manufacturing process diagram of the polarizable electrode body used in the present invention. Raw material 10 for preparing activated carbon fiber pulp
As the material, phenol-based, acrylic-based, rayon-based, and pitch-based synthetic fibers are preferable. From these raw materials, long filaments 11 of fibers of 5 to 40 μm are converged into roving-like or tow-like fibers, and the converged fibers are carbonized and activated. In the case of phenolic fibers, carbonization and activated carbon are performed. Chemical formula 13 is performed at the same time. then in the water
The activated carbon pulp is obtained by cutting 14 the desired fiber length suitable for polarizable electrodes of 0.1 to 30 mm. In this process, the synthetic fiber yarn is turned into twisted yarn to obtain an activated carbon cloth in the form of a cloth, which is then made into pulp.
It is conceivable to convert the material into pulp through an activated carbon cloth, but the cost would be high if the material is processed into a woven cloth, so it is preferable to carry out carbonization and activated carbonization in the form of long filaments as much as possible. Furthermore, carbonization and activated carbonization in the form of long filaments yields homogeneous fibers with a higher specific surface area. According to the present invention, when obtaining a polarizable electrode body in the form of a roll, a sheet, a box-shaped electrode body for stationary use, etc., it is possible to manufacture the polarizable electrode body using only activated carbon fiber pulp, but other fibers may be used to produce the polarizable electrode body. Using pulp material as an auxiliary material adds flexibility and shock absorber function to the electrode body, making it easier to manufacture polarizable electrode bodies, ensuring long-term stability, and making it easier to wind the electrolyte. Since the mechanical strength is improved against processing stress during processing, a fibrous substance may be added as necessary. Next, the activated carbon fiber pulp and the fibrous material are thoroughly mixed 16 in water, and then cracked 17 is performed.
In this process, the activated carbon fiber pulp and fibrous material swell in water, the convergent fibers loosen, fibrillation progresses, and microfibrillation progresses, resulting in mutual diffusion of the activated carbon fiber pulp and fibrous material. This is an important process because the mutual entanglement and bonding force progresses, and the homogenization of the pulp progresses. In this step, if necessary, a dispersion aid 18 and a binding aid required in subsequent steps may be added. The polarizable pulp material that has undergone the disassembly process is coated 20 on a desired collector electrode 19 (foil-like, neck-like, punched-like, lath-like, embossed-like). In the coating process to obtain this polarizable electrode body, polarizable pulp material is coated with a current collector by methods such as crimping, rolling, pressing, brushing, etc. to form a continuous sheet or roll of polarizable material. Obtain an electrode body. This continuous polarizable electrode body is dried 21 and cut 22 into a desired shape. The polarizable electrode body 23 composed of the collector electrode and activated carbon fiber pulp obtained in this way has an activated carbon fiber density of 2 to 30% higher than that of the conventional activated carbon cross-shaped one.
It has 4 times the density and bond strength between fibers, and has a capacity 2 to 4 times that of activated carbon cloth and 5 times more than powdered activated carbon.
~10 times the performance can be obtained, and since it is effectively intertwined with the collector electrode to have appropriate bonding strength and the resistance of the polarizable electrode is small, it becomes possible to develop low-resistance, large-capacity capacitors. In addition, it becomes possible to manufacture an excellent polarizable electrode body that enables instantaneous charging and discharging. (2) Activated carbon fiber pulp The activated carbon electrode for electric double layer used in the present invention is
It has a high specific surface area of 500 to 3000 m ² /g, preferably a pore diameter of 18 to 50 Å, and a pore volume of 0.2 to
1.5cc/g is preferred. Particularly preferred ranges are a specific surface area of 2000 to 3000 m ² /g, a pore diameter of 20 to 40 Å, and a pore volume of 0.6 to 1.5 cc/g. Activated carbon fibers having such excellent properties are suitably carbonized and activated carbonized from synthetic fibers. The synthetic fibers are preferably phenolic, acrylic, rayon, or pitch-based, and phenolic fibers with excellent carbon density are particularly suitable for the present invention. In order to obtain the above-mentioned activated carbon conditions, the fiber diameter is preferably 5 to 40 μm, most preferably 10 to 20 μm. Further, the fiber length of the activated carbon fiber pulp is preferably 0.1 to 30 mm, and a range of 0.5 to 5 mm is particularly suitable for the activated carbon electrode. In addition, in producing activated carbon fiber, 5 to
40 μm long filaments are converged into a roving or tow shape as a convergent thread as described above,
Carbonization and activation are preferable from the viewpoint of quality and mass production. This is because if it is made into a twisted thread or a string, the activator will not diffuse uniformly to the center of the converging thread during carbonization and activation. The reason why the above conditions are required as fiber conditions is that when the fiber diameter is 40 μm or more, a specific surface area of 2500 to 3000 m ² /g cannot be obtained, and a pore volume of 1.3 cc / g cannot be obtained. There is no such thing. On the other hand, if the fiber is less than 10 μm, it will be thin and the fiber efficiency will be poor, and during the activated carbonization process, the fiber will break easily and workability will be poor, and if it is configured as a polarizable electrode, the characteristics will deteriorate due to leakage current, high-temperature capacity change rate, etc. This is not desirable because it indicates The fiber conditions must be determined within the above range, taking into consideration the characteristics of the polarizable electrode, mass productivity, etc. Although it is possible to cut the fibers in the air, it also scatters dust and becomes too fine, so it is preferable to cut the fibers in water using water as a medium.
To avoid turning into fine powder when cutting,
Jusa mixers, guillotine cutters, hollenders, refiners, dijordan refiners, etc. are suitable for the purpose of the present invention. The activated carbon fiber pulp used in the present invention preferably has a ratio of fiber length to fiber diameter of 2 to 3,000 times, and in particular, fibers with a fiber length of 50 to 200 times are easy to fibble in the cracking process and are most suitable as activated carbon fiber electrodes. . Although it is basically possible to use powdered activated carbon as a substitute for activated carbon fiber pulp in the present invention,
It is not preferable because it is inferior to activated carbon fiber pulp in terms of capacity per unit volume, low temperature characteristics, leakage current, capacity change rate characteristics, etc. (3) Fibrous substance (pulp) The polarizable electrode body made of activated carbon fiber pulp used in the present invention can also be configured into a flat or coin-shaped polarizable electrode body by the activated carbon fiber pulp and a current collector. However, as mentioned above, when the polarizable electrode body is processed into a sheet or roll shape and used in a wound form or when a coin shape is punched from the sheet-like electrode body, it is necessary to make close contact between the collector electrode and the activated carbon fiber electrode. It is necessary to improve the properties and connectivity. In addition, when using a polarizable electrode body as a back-up for an automobile starter, the seismic properties
Impact resistance properties need to be improved. For such applications, a fibrous material is used for the purpose of improving the electrode strength by having the electrode itself play the role of a shock absorber. When ordinary PVA or epoxy resin is used as a substitute material for the fibrous material, the bond strength is improved, but the 20-40 Å pores of the activated carbon fibers are blocked and most of the specific surface area of the activated carbon becomes unusable. Therefore, the activated carbon fiber pulp is reinforced with a fibrous material that does not block the pores of the activated carbon. Figure 4 shows this condition as a photograph.
The black fibrous material indicates activated carbon fiber pulp, and the white fibrous material is a reinforcing fibrous material. The fibrous materials used in the present invention include natural fibers, non-acetylenized PVA fibers, acryltrile pulp, rayon pulp for papermaking, and PTFE.
Pulp, PTFE dispersion, etc. are preferred. (4) Other additives In the cracking process, aluminum hydroxide and polyethylene oxide are used as surfactants to promote mutual dispersion and entanglement of fibers, and as fillers to improve mutual adsorption of fibers. , polyvinyl pyrrolidone, etc. are effective. It is also possible to add asbestos, inorganic fine fibers including glass fibers, etc., if necessary. These fiber materials are selected based on their acid resistance, alkali resistance, solvent resistance, etc., depending on the intended use. In addition, in order to improve the internal resistance of a polarizable electrode body made of activated carbon fiber pulp, a conductive material is electrolessly plated on the surface of metal fibers, synthetic fibers, or carbon fibers, and the desired amount is added to the pulp as necessary. It is also possible. (5) Current collector One of the important objectives of the present invention is to improve instantaneous charging and discharging characteristics. Therefore, polarizable electrodes made of activated carbon fiber pulp must be constructed to effectively serve the purpose of current collection. Preferable materials for the current collector include valve metals such as Al, Ti, and Ta, alloys thereof, and Fe-Cr-based alloys such as SUS430, SUS444, and Showa Denko (corrosion-resistant stainless steel). As mentioned above, the shape of the current collector is preferably foil-like, net-like, lath-like, punched-like, or embossed. Further, in order to improve the adhesion between the activated carbon fiber pulp or pulp-like reinforcing material and the current collector, it is preferable to subject the surface of the current collector to surface enlarging treatment such as etching or blasting. The thickness of the current collector varies depending on the shape of the capacitor and the current flowing, but it is 20~20 mA or less.
500μm is sufficient, and 0.5 to 5mm for A order
degree is preferred. (6) Method for forming a current collector and activated carbon fiber pulp A method for forming a polarizable electrode in which a current collector is coated with activated carbon fiber pulp is shown in FIGS. 5 to 7. Figure 5 shows a structure in which one side of a current collector 24 made of an etched aluminum sheet or an embossed aluminum sheet is coated with a pulp-like composite 25 made of activated carbon fiber pulp and a fibrous material by a rolling method or a coating method. . FIG. 6 shows a configuration in which both sides of the current collector 24 are coated with a pulp-like composite 25. FIG. 7 shows a configuration in which a pulp-like composite is coated on both sides of a perforated current collector sheet 26 in the form of punching or lath wire mesh. Here, the activated carbon fiber pulp and the fibrous material are well intertwined with each other as described above, and have appropriate flexibility and shock absorption properties, while the mutual bond between the fibers is strong like paper or nonwoven fabric. It's summery. (6) Electrolyte In an aqueous solution system, H ₂ SO ₄ ,
KOH, NaOH, etc. can be used. In addition, as a non-aqueous electrolyte, 1 molg of tetraethylammonium perchlorate and γ-butyllactone are added to a PC (propylene carbonate) solvent.
Using an electrolyte solution with 1 mol/solute,
As an alternative to (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NPF ₆ ,
(C ₂ H ₅ ) ₄ NBF ₄ , thionyl chloride, etc. can be arbitrarily selected depending on the intended use. Furthermore, it is necessary to select a fibrous material (pulp) that is compatible with the electrolyte used. For example, when using KOH or H ₂ SO ₄ as an electrolyte, natural pulp or PVA pulp cannot be used.
The selection of organic pulp material such as PTFE is important. When using a non-aqueous electrolyte, it is important to select a fibrous material that is stable to organic electrolytes and solvents. To achieve the purpose of the present invention, a dispersion of 0.1μ of PTFE is preferred as the fibrous material, regardless of the electrolyte. This type of dispersion is thoroughly mixed with activated carbon fiber pulp, and during the dissolution process, particles of 0.1μ develop into fibers.
It is possible to form a coating layer that is well entangled with activated carbon fiber pulp, has low internal resistance, and has excellent mechanical strength as a polarizable electrode body. Example 1 The present invention will be explained by giving specific examples. FIG. 8 is a sectional view of a wet electric double layer capacitor in one embodiment of the present invention. The electrolytic cell 27 has a polarizable electrode body 2 made of activated carbon fiber pulp.
8 and 29 are immersed in an electrolytic solution 31 via a separator 30 made of a polypropylene canvas. The polarizable electrode body is basically non-polar, but 28 is an anode and 29 is a cathode. The polarizable electrode body is cut into pieces of 2 x 3 cm, and a polarizable coating layer 32 made of activated carbon fiber pulp is added as shown in Fig. 8.
was set to 2×2 cm ² , and the polarizable electrode layer of the collector electrode portion 33 was peeled off by 2×1 cm ² to form an anode and a cathode. The electrolytic solution used was a solution consisting of propylene carbonate, tetraethylammonperchlorate, and γ-butyllactone. Table 1 shows the constituent conditions of activated carbon fiber pulp, fibrous materials, etc., the thickness of the polarizable electrode, the type of current collector, the capacitance of the polarizable electrode (converted to F/ ^cm2 ), and the impedance (converted to Ω/ ^cm2). ), various conditions and their results are displayed. For comparison, conventional examples No. 17 and No. 18 show examples of polarized electrodes using activated carbon cloth and powdered activated carbon. No. 1 to No. 6 use phenolic activated carbon fibers, and the non-surface area of the activated carbon fibers is changed to 500 to 3000 m ² /g, and is used as a fibrous material.
PTFE fiber was added in an amount of 8% by weight, and a polarizable coating layer of 300 μm in thickness was prepared on one side of a 60 μm aluminum etched foil with the electrode configuration shown in FIG.

[Table] From Table 1, it can be seen that the capacitance of the capacitor increases in proportion to the increase in the specific surface area, and the resistance value of the polarizable electrode increases on the contrary. When using phenolic fiber, the specific surface area is 3000
The limit was up to m ² /g. Mechanical strength is also 3000
m ² /g or more is not practical. Conversely, 500m ² /
Since it becomes disadvantageous in terms of cost if it is less than 1.5 g, the preferable range of activated carbon fiber is 500 to 3000 m ² /g, and the optimum value is 2000 to 3000 m ² /g, which is the most excellent from the viewpoint of cost, properties, and workability. No. 7 to No. 9 use activated carbon fiber pulp whose raw material fibers are pitch, acrylic, and rayon fibers, respectively. The degree of activation of each activated carbon fiber was determined using the optimum value (capacity characteristics and mechanical strength) of each fiber. The reason why the capacity of the pitch type and acrylic type is small compared to the specific surface area is because the bulk specific gravity of the activated carbon fiber is small. Furthermore, rayon-based materials have relatively high capacity but low fiber strength, and although not shown in Table 1, are inferior in capacity aging and leakage current characteristics. Overall, the phenolic type was the best as an activated carbon fiber electrode. Nos. 10 to 13 examine changes in the amount of fibrous material added in a polarizable electrode body made of activated carbon fiber pulp. Although it depends on the type of fibrous material, it is 0 in the case of PTFE fiber. ~30% by weight, with 2-25% by weight being effective. If it is less than 2%, the strength of the coating layer cannot be obtained, and if it is more than 25% by weight,
This is not preferable because the capacitance decreases and the electrical resistance gradually increases. Therefore, the amount of fibrous material added is preferably in the range of 2 to 25% by weight. No. 14 to No. 16 contain 80% each of acrylonitrile, rayon pulp, and natural pulp as fibrous materials.
% by weight was added to form a polarizable electrode, and the various characteristics of the capacitor were investigated. Although it is impossible to use rayon-based or natural pulp-based electrolytes for KOH-based or H ₂ SO ₄ -based electrolytes, they fully demonstrate their functions with organic electrolytes, and activated carbon fiber pulp has excellent properties. It was recognized that it plays the role of a binder, and it was also found to have almost the same electrical properties as PTFE pulp material. Compared to the characteristics of conventional methods No. 17 and No. 18, Nos. 1 to 16 of the present invention were found to exhibit relatively equivalent to approximately 5 times the characteristics, and the method of the present invention It can be easily seen that this method is advantageous in terms of electrical characteristics, manufacturing work environment, and cost. Example 2 As a polarizable electrode, the conditions of No. 6 in Table 1 (phenol-based, surface area 3000 m ² /g PTFE fiber 8% by weight, 60μ aluminum etching foil, polarizable electrode coating layer thickness 300μm) were used. , 1st
A coin-shaped capacitor having the configuration shown in the figure was constructed. The size of the polarizable electrode is 14 under the conditions of No. 6 in Table 1.
Using a punched piece with a diameter of mmφ, the Al-etched collector electrode was spot welded to the sealing plate or the sealing case. An electrolyte was added through a propylene separator under the electrolyte conditions shown in Table 1, and the mixture was sealed through a gasket. For comparison, the basis weight is 150g/m ² and the specific surface area is 2500.
A 100 μm Al plasma spray was formed on one side of activated carbon cloth of m ² /g, punched into a polarizable electrode structure of 14 mmφ, a coin-shaped capacitor was assembled in the same manner as above, and various characteristics were investigated.
The results shown in the table were obtained.

[Table] As shown in Table 2, the method of the present invention can be used even if the coin type is used.
It was confirmed that the properties were 3 to 4 times higher than that of the conventional method, and all other properties were also found to be superior to the conventional method. Based on these data, the unit volume (cubic inch in ³ =
A comparison of the capacities per 16.4 cm ³ ) resulted in the results shown in Table 3.

[Table] From Table 3, it can be seen that the method of producing a polarizable electrode by carbonizing and activated carbonizing the long filaments of the present invention to obtain activated carbon fiber pulp is a method for producing a polarizable electrode with high density and flexibility. It is easily recognized that this is an extremely excellent manufacturing method that can be configured. Effects of the Invention As described above, according to the manufacturing method of the present invention, it is possible to manufacture polarizable electrodes using activated carbon pulp with a high specific surface area compared to conventional methods for manufacturing polarizable electrodes. In addition to improving filling properties,
The electrode strength is improved, the process is easy, and it is possible to manufacture a capacitor with significantly improved electrical characteristics compared to activated carbon cross electrodes or powdered activated carbon electrodes.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional front view showing a coin-shaped electric double layer capacitor, Fig. 2 is a cross-sectional view of an activated carbon cross-polarizable electrode body, and Fig. 3 is a polarizable electrode using activated carbon fiber pulp in an embodiment of the present invention. 4 is a photograph of a polarizable electrode body made of activated carbon fiber pulp, FIGS. 5 to 7 are cross-sectional views showing the structure of a polarizable electrode in an example of the present invention, and FIG. 8 is a photograph of a polarizable electrode body made of activated carbon fiber pulp. FIG. 1 is a sectional view of an electric double layer capacitor in one embodiment of the present invention. 24... Foil collector electrode, 25... Activated carbon fiber pulp electrode, 26... Porous collector electrode, 28, 29...
Polarizable electrode body made of activated carbon fiber pulp, 30...
... separator, 31 ... electrolyte, 32 ... polarizable coating layer, 33 ... collector electrode part.

Claims (1)

[Claims] 1. Carbonizing and activating long filament-like synthetic fibers to obtain long filament-like activated carbon fibers, cutting the activated carbon fibers to produce activated carbon fiber pulp,
A method for producing an electric double layer capacitor characterized by using this activated carbon fiber pulp as a polarizable electrode. 2. A method for manufacturing an electric double layer capacitor according to claim 1, characterized in that a polarizable electrode is formed by coating the surface of a current collector with activated carbon fiber pulp. 3. Claim 2, characterized in that a fibrous substance (pulp) is further added to the activated carbon fiber pulp to coat the surface of the current collector to form a polarizable electrode.
A method for manufacturing an electric double layer capacitor as described in . 4. The method for producing an electric double layer capacitor according to claim 1, wherein the activated carbon fiber pulp has a fiber diameter of 5 to 40 μm and a fiber length of 0.1 to 30 mm. 5. The method for producing an electric double layer capacitor according to claim 1, wherein the activated carbon fiber pulp is formed using phenolic activated carbon fibers. 6. A patent claim characterized in that a polarizable electrode is formed using a perforated sheet-like current collector made of metal, alloy, or plating, such as sheet-like, net-like, lath-like, punched-like, or embossed form. A method for manufacturing an electric double layer capacitor according to item 1. 7. The method for producing an electric double layer capacitor according to claim 4, wherein the activated carbon fiber pulp has a fiber diameter of 10 to 20 μm and a fiber length of 0.5 to 5 mm.