JPS6110228A - Electric double layer capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a large-capacity wet electric double layer capacitor in which polarizable electrodes are made of activated carbon fiber pulp.

Conventional configuration and its problems FIG. 1 shows an example of the configuration of a conventional capacitor of this type.

Activated carbon fiber cloth is used as the polarizable electrode 1, and a current collecting layer made of a metal layer such as aluminum, titanium, nickel, etc. or a conductive resin layer is formed as a current collector 2 on one side of the cloth. After the electrolytic solution is injected, a case 4, a sealing plate 6, and a gasket 6 are used to seal the casing. The activated carbon fiber used for the polarizable electrode is phenolic (cured novolac fiber).

It can be obtained by directly carbonizing and activating rayon-based, acrylic-based, or pitch-based fiber cloth, or by further activating it after carbonization.

Considering the electrical resistance, strength, activation yield, etc. of the obtained activated carbon fibers, phenolic fibers are the best among the above-mentioned fibers. Metal current collectors can be made by plasma spraying, arc spraying, or gas spraying, and conductive electrodes made of conductive materials such as conductive resin can be made by screen printing or spraying.

It can be easily formed by any of the dipping methods.

A polarizable electrode having such a shape can be punched into a circular shape with a desired diameter, and the coin-shaped flat plate small-sized large-capacity capacitor shown in FIG. 1 can be realized.

- Since this type of polarizable electrode does not use a binder, it not only can reduce the internal resistance, but also the activated carbon surface is not covered with a binder, so the loss of effective area for double layer formation is small, and it can be made smaller and have a 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-capacity capacitors using activated carbon fiber cloth. especially,
High capacity per unit volume.

Benefits include cost reduction, rapid charging and discharging, flexibility in electrode shape design, and improved manufacturing work environment.

However, although the conventional activated carbon fiber cloth has various excellent advantages, it takes four steps to obtain the desired cloth from the spinning state.
A lead time of ~6 months is required, and in order to quickly respond to user requests, this long lead time poses a manufacturing problem.In addition, it is necessary to keep inventory of fabrics with different product numbers and weaving methods with different weights and quantities. It's difficult. In addition, there is a problem in that when a special weaving force with a large basis weight is used, the weaving cost becomes several times that of the raw material.

In addition, in the process of carbonizing and activated carbonizing the raw material converging threads and woven fabrics, the weight becomes % to %, and the area also becomes large. Therefore, the porosity inside the activated carbon cloth is as high as 60 to 70 inches.

In addition, in terms of electrical resistance, as shown in FIG. The conductivity in the bb' direction is considered to be good, but the conductivity in the bb' force 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, although activated carbon fiber cloth obtained from phenolic novolac resin fibers can be activated with a trench to have a specific surface area of 2500 ff//i, 2 soorr? /
When it exceeds I/, the porosity of the activated carbon fibers increases, the mechanical strength of the activated carbon cloth decreases, and it becomes impossible to use a mass production machine or obtain dimensional accuracy. Therefore, in order to improve the characteristics of the capacitor, the carbonization activation degree of the activated carbon fiber cloth was set to 23oorr.
? /g or more is difficult.

OBJECTS OF THE INVENTION The present invention provides an electric double layer capacitor that can increase the capacitor capacity per unit volume and can significantly improve other characteristics such as high-speed charging and discharging characteristics, high-humidity storage characteristics, mass productivity, and low cost. With the goal.

Structure of the Invention In order to achieve the above object, the present invention uses activated carbon fiber pulp having a high specific surface area and, if necessary, a fibrous substance to cover the surface of a current collector with high density activated carbon fiber pulp. This structure forms a high-performance polarizable electrode body.

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 a quadripolar electrode body used in the present invention.

As raw material 10 for preparing activated carbon fiber pulp,
Phenol-based, acrylic-based, rayon-based.

Pitch-based synthetic fibers are preferred. From these raw materials 5
Long filaments 11 of ~40 μm fibers are converged into roving or tow-like fibers 12, and the converged fibers are carbonized and activated carbonized, but in the case of phenolic fibers, carbonization and activated carbonization 13 are carried out simultaneously. Let's do it. after that,
The activated carbon pulp is obtained by cutting 14 in water to a desired fiber length suitable for polarizable electrodes of 0.1 to 3oIIIl.

In this process, it is also possible to create activated carbon cloth from synthetic fiber yarn through twisting, to obtain cloth-like activated carbon cloth, and to pulp it, or from synthetic fiber cloth to felt-like, non-woven cloth, activated carbon cloth, and pulp. However, it is preferable to perform inertization.

According to the invention, the polarizable electrode body is in the form of a roll.

When obtaining sheet-shaped, stationary box-shaped electrode bodies, etc., it is possible to manufacture polarizable electrode bodies using only activated carbon fiber pulp, but other fibrous substances (pulp materials) 16 can be used as auxiliary materials. When used, it adds flexibility and shock absorption function to the electrode body, making it easier to manufacture polarizable electrode bodies, and it is stable for a long period of time. A fibrous substance may be added as necessary, since the strength is improved.

Next, the activated carbon fiber pulp and fibrous material are thoroughly mixed in water.
6L, then do Clarification 17. In this process, activated carbon fiber pulp and fibrous substances swell in water, convergent fibers loosen, fibrillation progresses, microfibrillation progresses, and activated carbon fiber pulp and fibrous substances mutually diffuse and interact. This is an important process because the entanglement and bonding force of the pulp progresses, and the pulp becomes more uniform. 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 clarifying process is coated 20 on a desired collector electrode 19 (foil-like, embossed-like, net-like, punched-like, lath-like). In the coating process to obtain this polarizable electrode body, the polarizable pulp material is coated with the 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 made of the collector electrode and activated carbon fiber pulp thus obtained has an activated carbon fiber density that is 2 to 4 times higher than that of a conventional activated carbon cross-like structure, and a bonding strength between the fibers. In terms of capacity, it has 2 to 4 times the performance of activated carbon cloth and 5 to 10 times that of powdered activated carbon, and it is effectively intertwined with the collector electrode to have appropriate strength and the resistance of the polarizable electrode is small. This makes it possible to develop low-resistance, high-capacity capacitors, which are excellent and capable of instantaneous charging and discharging.

2) Activated carbon fiber pulp The activated carbon electrode for electric double layer used in the present invention has a fiber pulp of 500 to 3
It has a high specific surface area of 000 m7y and a pore size of 18 to 60
The pore volume is preferably 0.2 to 1. scc/y
is preferred. A particularly preferable range is a specific surface area of 2000-3
000mVy, pore diameter 20-40, pore volume 0.5~
1. ts cc/y. Activated carbon fibers having such excellent properties are suitably carbonized and activated carbonized from synthetic fibers. The synthetic fibers are preferably phenol-based, acrylic-based, rayon-based, or pitch-based, and phenolic fibers with excellent carbon density are particularly suitable for the present invention.

In order to obtain the above activated carbon conditions, the fiber diameter is preferably 5 to 40 μm, particularly 10 to 2 μm.
0 μm is optimal. The fiber length of the shattered activated carbon fiber pulp is preferably 0.1 to 30 era, particularly 0.5 to 30 era.
The range of 6IO+ was optimal for activated carbon electrodes.

In addition, in producing activated carbon fibers, it is preferable from the viewpoint of quality and mass production that long filaments of 5 to 40 μm are converged into a roving or tow shape as a convergent thread, and then carbonized and activated. This is because if it is made into a twisted thread or a string, the activator will not diffuse uniformly in the center 1 of the convergent thread during carbonization and activation.

The reason why the above conditions are required as fiber conditions is that when the fiber diameter is 4oμm or more, the specific surface area is 260o~30μm.
00m7 could not be obtained, and the pore volume was 1.
sy/cc cannot be obtained.

On the other hand, if the fiber is less than 10 μm, it will be thin, the fiber efficiency will be poor, the fiber will break easily during the activated carbonization process, and the workability will be poor, and if it is configured as a polarizable electrode, it will cause problems such as leakage current and high-temperature capacity change rate. This is not a good choice because it shows characteristic deterioration. 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 crush the fibers in water using water as a medium. guillotine cutter,
Hollender, Likoaina, Giordan refiners, etc. are suitable for the purpose of this invention.

Although it is basically possible to use powdered activated carbon as a substitute for activated carbon fiber pulp in the present invention, it is inferior to activated carbon fiber pulp electrodes in terms of capacity per unit volume, low temperature characteristics, leakage current, capacity change rate characteristics, etc. So I don't like it.

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 the 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 punched into a coin shape from the sheet-like electrode body, the close contact between the collector electrode and the activated carbon fiber electrode is difficult. It is necessary to improve the properties and connectivity. Furthermore, when the polarizable electrode body is used as a pack-up for an automobile starter, it is necessary to improve the seismic resistance and impact resistance.

For such applications, a fibrous material is used for the purpose of improving the electrode strength by having the electrode itself perform a shock absorbing function.

If ordinary PVA or epoxy resin is used as an alternative to the fibrous material, the bonding strength will be improved, but the
Since most of the specific surface area of the activated carbon becomes unusable by blocking the pores of the activated carbon fiber, the activated carbon fiber pulp is reinforced with a fibrous material that does not block the pores of the activated carbon.

FIG. 4 shows this state in photographs, where the black fibrous material represents activated carbon fiber pulp, and the white fibrous material is a reinforcing fibrous material.

The fibrous material used in the present invention is natural fiber.

Unacetylated PVA fiber, acrylonitrile pulp,
Rayon pulp for paper making, PTF] i: Pulp.

PTFE dispersion and the like are preferred.

4) Other additives In the clarification process, aluminum hydroxide and polyethylene oxide are used as surfactants to promote mutual dispersion and entanglement of fibers, and fillers to improve mutual adsorption of fibers. , polyvinyl pyrrolidone, etc. are effective. Further, asbestos, inorganic fine fibers including glass fibers, etc. can also be added as necessary.

In order to improve this, it is also possible to electrolessly plate the surface of metal fibers, synthetic fibers, or carbon fibers with a conductive material, and add a desired amount of the conductive material to the pulp as needed.

6) 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 efficiently serve the purpose of current collection.

The material of the current collector includes valve metals such as Al, Ti, and Ta and their alloys, and Fe-0r, base alloys such as SUS 430. SUS444.
Showamanoku (corrosion-resistant stainless steel manufactured by Showa Denko) etc. are preferred.

The shape of the current collector is foil-like or net-like as described above.

A lath shape, a punched shape and an embossed shape are preferred. 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 perform a surface enlarging treatment such as etching or blasting on the surface of the current collector.

Although the thickness of the current collector varies depending on the shape of the capacitor and the current flowing, 20 to 500 μm is sufficient for mA order or less, and about 0.5 to 6 μm is preferable for A order.

6) Coating structure of current collector and activated carbon fiber pulp Examples of the structure of a polarizable electrode in which a current collector is coated with activated carbon fiber pulp are shown in FIGS. 6 and 7.

FIG. 6 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 26 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 a current collector 240 are coated with a pulp-like composite 26.

FIG. 7 shows a structure in which a pulp-like composite material 25 is coated on both sides of a porous 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 has become a thing.

6) Electrolyte As the electrolytic solution used in the polarizable electrode body from activated carbon fiber pulp, H2BO3, KOH, NaOH, etc. can be used in an aqueous solution system. In addition, non-aqueous electrolyte and L-1j
: An electrolytic solution containing 1 mO1/l of tetraethylammonium perchlorate and 1 mol/l of γ-butyllactone in a PC (proprene carbonate) solvent may be used, or as a substitute for (C2H6)4NClQ4, (C2H5
)4NPF6. (C2H6)4NBF4 etc. can be arbitrarily selected depending on the intended ring.

It is necessary to select a fibrous material (pulp) that is compatible with the electrolyte used. For example, KOH+H2 as an electrolyte
When SO4 or the like is used, natural pulp or PUA pulp cannot be used, so it is important to select an organic pulp material such as PTFE.

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, dispersion made of 0.1μ of PTFE is preferred as the fibrous material, regardless of the electrolyte. This type of dispersion is thoroughly mixed with the activated carbon fiber pulp, and during the clarifying process, particles consisting of 0.1μ develop into fibers and are well entangled with the activated carbon fiber pulp.
It is possible to form a coating layer with excellent mechanical strength as a polarizable electrode body with low internal resistance.

Example 1 The present invention will be described with reference to specific examples. FIG. 8 is a sectional view of a wet electric double layer capacitor which is an embodiment of the present invention. In the electrolytic cell 27, polarizable electrode bodies 28 and 29 made of activated carbon fiber pulp are connected to an electrolytic solution 31 through a separator 30 made of a polypropylene canvas.
is immersed in. The polarizable electrode body is basically non-polar, but 28 is an anode and 29 is a cathode.

The polarizable electrode body was cut into 2×3 crn pieces, and a polarizable covering layer 32 made of activated carbon fiber pulp was cut into 2×3 crn pieces as shown in FIG.
As 2 CnI, the polarizable electrode layer was peeled off by 332×1 cd of the collector electrode part to obtain an anode and a cathode. The electrolyte is propylene carbonate, tetraethylammonperchlorate,
A solution consisting of γ-butyrolactone was used.

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/, i), and the impedance (Ω/c
(converted to rn), etc., various conditions and their results are displayed. For comparison, A17. is used as a conventional example. A
18 shows an example of a polarizable electrode using activated carbon cloth and powdered activated carbon.

A1 to Ya6 use phenolic activated carbon fibers, and the specific surface area of the activated carbon fibers is 500 to 3000rr? /jiα activity is changed, 8% by weight of PTFE fiber is added as a fibrous substance, and a polarizable coating layer of 30% is formed on one side of a 60μm aluminum etched foil with the electrode configuration shown in Figure 6.
The thickness was adjusted to 0 μm.

From Table 1 below in the margin, 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 conversely increases.

When using phenol fiber, the specific surface area is 3000ff
? /g was the limit. Mechanical strength is also 300°, r
? /9 or more is not practical. On the other hand, 500rr? /
,! If it is less than i', it will be disadvantageous in terms of cost, so the preferred range of activated carbon fiber is 500 to 3oooon//g,
Is the optimal value 2000-3ooorr? /g was the most excellent in terms of cost and characteristic 9 workability.

Flats 7 to 9 are pitch-based and acrylic-based, respectively.

It uses activated carbon fiber pulp made from rayon-based fibers. The degree of activation of each activated carbon fiber was determined using the optimum value (capacity characteristics and mechanical strength) of each fiber. The pitch-based and acrylic-based materials have a small capacity compared to their specific surface area because the bulk specific gravity of the activated carbon fibers is small. In addition, rayon-based materials have a relatively large capacity, but have low fiber strength, and although not shown in Table 1, they are inferior in terms of capacity change over time and leakage current. Overall, the phenolic type was the best as an activated carbon fiber electrode.

A10-A13 investigated changes in the amount of fibrous material added in a polarizable electrode body made of activated carbon fiber pulp, and it depends on the type of fibrous material, but in the case of PTFE fiber, it is O ~ 30. Weight ratio varies from 2 to 26% by weight
was 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, the capacity decreases and the electrical resistance due to cracking gradually increases, which is not preferable. Therefore, the amount of the fibrous material added is preferably in the range of 2 to 25% by weight.

In Nos. 14 to A16, acrylonitrile, rayon pulp, and natural pulp were each added in an amount of 8% by weight as fibrous materials to form polarizable electrodes, and various characteristics of capacitors were investigated. Although it is impossible to use rayon-based or natural pulp-based electrolytes for KOH-based or H2BO3-based electrolytes, they fully perform their functions with organic electrolytes, and are excellent binders for activated carbon fiber pulp. In addition, it was found that the electrical properties of this material were almost the same as those of the PTFE-based material.

Compared to the characteristics of A17.418 of the conventional method, A1-A16 of the present invention was found to exhibit relatively equivalent to about 6 times the characteristics, and the method of the present invention also has improved electrical characteristics. It can be easily seen that it is advantageous in terms of manufacturing work environment and cost.

Example 2 As a polarizable electrode, the conditions of A6 in Table 1 (phenol-based, surface area 3000 m/17.PTFE7y ivar ax
A coin-shaped capacitor having the structure shown in FIG. 1 was constructed using an aluminum etched foil having a thickness of 60 μm and a bipolarized electrode coating layer having a thickness of 300 μm. The polarizable electrodes were punched out to a size of 14 .phi. under the conditions shown in Table 1 A6, and the etched Al collector electrodes were 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, a 100 μm thick Al plasma spray was formed on one side of an activated carbon cloth with a basis weight of 1F509/lri and a specific surface area of 5004Iρ, which was punched out into a polarizable electrode structure of 14mmφ, and a coin-shaped capacitor was assembled in the same manner as above. When various characteristics were investigated, results as shown in Table 2 were obtained.

Table 2 As shown in Table 2, the method of the present invention is similar to the conventional method 3 even in coin type.
It was confirmed that the properties were up to 4 times higher, and all other properties were also found to be superior to the conventional method.

Based on these data, we compared the capacity per unit volume (cubic inch in -16.4cII) of products using conventional commercially available powdered activated carbon and products using conventionally commercially available activated carbon fiber cloth, and the results are shown in Table 3. It became like this.

Table 3 (Capacitor Capacity F/1n3) From Table 3, it was found that the method using the activated carbon fiber pulp of the present invention exhibited extremely excellent characteristics.

Effects of the Invention As described above, according to the present invention, it is possible to use activated carbon fibers with a higher specific surface area in pulp form than in conventional polarizable electrodes, which improves the filling properties of the electrode body and provides high strength. Therefore, compared to the case of using activated carbon cross electrodes, it is possible to obtain an electric double layer capacitor that is easier to process in several stages and has a small size and a large capacity.

[Brief explanation of drawings]

Figure 1 is a cross-sectional front view showing a coin-type electric double layer capacitor, Figure 2 is a cross-sectional view of an activated carbon cross-polarizable electrode body, and Figure 3 is a cross-sectional view of a coin-type electric double layer capacitor.
The figure is a manufacturing process diagram of a polarizable electrode body using activated carbon fiber pulp in one embodiment of the present invention, Figure 4 is a photograph of a polarizable electrode body made of activated carbon fiber pulp, and Figures 5 to 7 are according to the present invention. FIG. 8 is a sectional view showing the structure of the polarizable electrode in an embodiment of the present invention. FIG. 8 is a sectional view of an electric double layer capacitor in an embodiment of the present invention. 24 - foil collector electrode, 26... activated carbon fiber pulp electrode, 26... porous collector electrode, 28.29... polarizable electrode body made of activated carbon fiber pulp, 30... separator, 31 ... Electrolyte solution, 32 ... Polarizable coating layer,
33. Collector electrode part. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 4

Claims (6)

[Claims] (1) An electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode body and an electrolyte, wherein the polarizable electrode body has a coating layer mainly composed of activated carbon fiber pulp on the surface of a current collector. An electric double layer capacitor comprising: (2) The electric double layer capacitor according to claim 1, wherein the coating layer is made of activated carbon fiber pulp and fibrous material (pulp). (3) The current collector is made of metal, alloy, or plating, and is in the form of a sheet, a net, a lath, a punching, or an embossed perforated sheet. Electric double layer capacitor. (4) The electric double layer capacitor according to claim 1, wherein the activated carbon fiber pulp is composed of activated carbon fibers having a fiber diameter of 5 to 40 μm and a fiber length of 0.1 to 30 mm. (5) The electric double layer capacitor according to claim 1, wherein phenolic activated carbon fiber is used as the activated carbon fiber pulp. (6) The electric double layer capacitor according to claim 4, wherein the activated carbon fiber has a fiber diameter of 10 to 20 μm and a fiber length of 0.5 to 6 mm.