JPS6355205B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an electric double layer capacitor using activated carbon as a polarizable electrode.It can be charged and discharged at higher power and faster than conventional capacitors of this kind, and is used in electricity, automobiles, cameras, machinery, etc. It can be used in a wide range of industrial fields such as computers. Structure of conventional example and its problems The basic structure of an electric double layer capacitor using activated carbon and polarizable electrodes is as shown in Fig. 1. A separator 3 impregnated with an electrolyte is interposed between a pair of polarizable electrodes. Conventionally, there are the following three types of configurations of this type of electric double layer capacitor, and their configurations and problems are outlined below. The first one uses an aluminum punching metal as the current collector 4, as shown in FIG. A polarizable electrode material is mold-pressed or supported by rolling rolls, a pair of current collectors and a polarizable electrode are wound around a separator 3, and an electrolytic solution is injected. In polarizable electrodes manufactured using such current collectors, the metal current collector and activated carbon electrode are basically only in physical contact, and in particular, polarizable electrodes manufactured by winding the polarizable electrode into a spiral structure are Since stress is applied to the activated carbon electrode layer on the outside of the current collector and the activated carbon electrode layer on the inside of the current collector, the contact between the current collector and the activated carbon electrode becomes even weaker, and the internal resistance of the electric double layer capacitor increases. There were disadvantages such as a gradual increase in the amount of carbon and a gradual decrease in the utilization efficiency of the activated carbon electrode layer. Second, as shown in FIG. 3, a polarizable electrode 6 is made of cloth, paper, felt, etc. whose main component is activated carbon fiber, and a metal layer such as aluminum is provided as a current collector 7 on one side of the polarizable electrode 6. It is constructed by a thermal spraying method, a vapor deposition method, etc., and a pair of polarizable electrodes can be constructed into a coin shape by an outer case 9 and a gasket 10 with a separator 8 impregnated with an electrolytic solution interposed therebetween. In addition, this type of product is wound into a vortex structure and has a second
This is an advantageous method that can be constructed into a tube-like structure as shown in the figure, and can be constructed into any shape. The disadvantage of this method is that activated carbon fibers are extremely expensive (approximately 1,000 yen/Kg), and because the fiber diameter is small, the electric resistance is large and current cannot flow through it. Therefore, charging takes a long time, and discharging can only be performed with a weak current. The third method is to activate carbonize glassy graphite and use it for polarizable electrodes. The problem with this method is that synthesis of glassy carbon is extremely difficult and takes a long time, and since glass carbon is not currently produced in the world, it is even more costly than the fiber method.
Electric double layer capacitors using this method have not been manufactured because it is difficult to process them into either coin-shaped or spiral-shaped shapes. OBJECTS OF THE INVENTION An object of the present invention is to provide an electric double layer capacitor in which a polarizable electrode made of activated carbon is low in cost and is capable of discharging a large current. Structure of the Invention The present invention is characterized in that a sheet of a phenolic resin molded body mainly composed of a powdered phenolic resin having thermal fusibility is directly carbonized and activated carbonized and used for a polarizable electrode. Description of Examples The basics of the present invention are heat-fusible, high molecular weight,
The method involves obtaining a film-like or sheet-like molded product using powdered phenolic resin, directly carbonizing and activated carbonizing this phenolic resin molding, and using it as a polarizable electrode of an electric double layer. The characteristics of this phenolic resin will be explained in detail later, but the phenol sheet obtained from heat-fusible powdered phenol has a smaller three-dimensional crosslink density than the phenol sheet synthesized from conventional liquid phenol (novolac and resol resin) resin. ,
It is flexible and allows gas generated by decomposition to easily dissipate outside the sheet during carbonization activation of the phenol sheet.
The carbonization-activated sheet has a characteristic that there are few cracks, cracks, blisters, etc., and even if carbonization activation is carried out in sheet form, a sheet with a specific surface area of 1000 to 2500 m ² /g can be obtained relatively easily. However, there are limits to the mechanical strength and current collecting ability of phenolic resin sheets alone. Therefore, the invention can be further improved as in the embodiment shown in FIG. FIG. 4 is a cross-sectional view of a phenolic resin sheet reinforced with a metal substrate. Reference numeral 11 in FIG. 4a is a chop-shaped piece of fine nickel wire, and reference numeral 13 in FIG. 4b is a nickel net knitted with nickel wire. In both figures, 12 is the heat-fusible powdered phenolic resin used in the present invention at 180°C.
This is a phenolic resin layer fused at a pressure of 200Kg/cm ² . In this way, the surface of a metal substrate made of a transition element is completely coated with phenolic resin to obtain a phenolic resin sheet reinforced by the metal substrate, and this composite sheet is carbonized at a temperature of 600 to 1100°C. . According to such examples, the metal substrate improves the reinforcement and flexibility of the film-like or sheet-like phenolic resin, and after carbonization activation,
Metals are excellent current collectors, and they not only provide an extremely strong bond between activated carbon and current collector, but also improve the flexibility and mechanical strength of activated carbon polarizable electrodes.
Furthermore, when this electrode is anodically polarized, since the surface layer of the metal base is completely covered with carbon, the anode potential can be polarized more positively than in conventionally known methods. Dissolution is also extremely reduced. When the activated carbon polarized electrode reinforced with the metal substrate obtained in this way is used as an electric double layer electrode, the internal resistance can be improved to an extremely low level compared to conventionally known electric double layer capacitors, and instant charging can be achieved in an extremely short time. This makes it possible to perform instantaneous discharge. The necessary conditions for carrying out the present invention will be explained in detail. [Phenol Resin] Generally, phenol resin means phenol formaldehyde resin, and this phenol resin is broadly classified into novolak resin and resol resin. However, the phenolic resin mainly used in the present invention is a powdered phenolic resin that has heat-fusible properties and consists of fine particles of 1 to 20 μφ. This new heat fusion property,
Powdered phenolic resin is disclosed in the published patent publication, 1982-
177011 and 58-17114, and is sold by Kanebo Co., Ltd. as Bell Pearl S. The major differences between this resin and conventional phenolic resins are as follows. (1) It has good storage stability and is reactive when molded or heated, either by itself or when mixed with other resins, and is thermally fused. (2) Since the particles are spherical fine particles with a size of 1 to 20 μφ, they have good fluidity and can uniformly and completely coat the metal substrate of the present invention. (3) Free phenol content is 50 ppm or less, it is safe and easy to handle, and it can be thermally fused at a low temperature of 100 to 200°C, making it extremely advantageous industrially. Conventional cured phenolic resin products have an excessively high three-dimensional crosslinking density, making the phenolic resin molded sheet hard and brittle, and also difficult to carbonize and activate carbonize.
Although it takes a long time of up to 7 days, the heat-fusible phenolic resin molded product of the present invention can be carbonized in 1 to 3 hours.
Activated carbonization becomes possible. This seems to be due to the fact that the three-dimensional crosslinking density is low, so that thermal decomposition products can be easily dissipated out of the molded sheet during carbonization. That is, in conventional phenol molded products, cracks and cracks occur during carbonization, causing them to fall apart, so even a thin sheet takes a long time (4 to 7 days) to carbonize. In order to carbonize and activate carbonize in a short time, the specific surface area of the cured phenolic resin must be increased, as with novolak fibers, otherwise cracks and cracks would occur. In addition, when using a metal substrate, which is an embodiment of the present invention, the adhesion between the metal substrate and the cured phenol product is important, and even after carbonization and activated carbonization, the adhesion and electrical conductivity between the metal substrate and activated carbon are maintained. requested,
In order to industrially produce these products in a short period of time, a powdered phenolic resin having this thermal fusibility is optimal. In addition, this resin can be mixed well with novolac resin, resol resin, epoxy resin, furan resin, as well as paper, pulp, asbestos, wood flour, and polyvinyl alcohol (PVA), and these resins can be used to improve the properties of phenolic resin sheets and activated carbon sheets. It is possible to improve the flexibility, porosity, and workability of the sheet of the present invention depending on the intended use by adding a mixture of these as necessary. [Type and shape of metal substrate] The role of the metal substrate used in the present invention is to strengthen the phenolic resin sheet at the resin stage and the activated carbonization stage and to provide current collection properties. Therefore, the metal substrate needs to have heat resistance of 600 to 1100°C. In addition, as a polarizable electrode, it is necessary to have corrosion resistance that can withstand an anodic polarization potential. In order to satisfy these requirements, the substrate must be made of a single metal made of a transition element such as nickel, chromium, cobalt, copper, titanium, tantalum, hafnium, zirconium, or an alloy of these metals. The shape of these metal substrates is preferably a thin wire net shape, a felt shape, a chop shape, a nonwoven fabric shape, a punched thin plate shape, a lath shape, a foam shape, or the like. Further, the diameter and film thickness of the thin wires constituting these substrates are also influenced by the capacity of the electric double layer, charge/discharge conditions, mass production scale, etc. The diameter of the thin wire is 5~
The diameter is preferably 1000 μm, particularly the shape of a chop, net, felt, or nonwoven fabric having a diameter of 20 to 200 μm is preferred, and the film thickness is preferably about 50 to 300 μm. The practical thickness of the foam is about 10 to 2000 μm, and the porosity is preferably in the range of 20 to 90%. Punched and rough types have small polarizable electrodes and are suitable for small capacity coin and sheet types. The weight ratio of the metal base to the resin is about 60 to 70% when using metal powder, and if it is not added, the resin will not be conductive. However, when carbonized or activated carbonized
The conductivity can be sufficiently improved even at about 15 to 50%. However, for the purpose of the present invention, net-like, chop-like, and foamed materials are preferable to powdered materials, and it is possible to improve current collection resistance by 1 to 3 orders of magnitude by adding the metal substrate at an addition rate of about 15 to 50%. It is possible. Next, a method for preparing the polarizable electrode of the present invention using the aforementioned metal substrate and heat-fusible phenolic resin will be described in detail. FIG. 5 is a manufacturing process diagram for implementing the present invention. First, as an example, 30μmφ of Nickel
The description will be made using a 1 mm x 1 mm chop-shaped metal substrate. The nickel fine wire chop is pretreated by degreasing, washing, and drying, and 30 parts by weight of the nickel chop is mixed with a powdered phenolic resin (Belpar S) having heat-fusible properties. When mixing, since there is a difference in specific gravity, a mixer such as an omnibus is appropriate. A mixture of fine metal wire and resin is thoroughly mixed and then hot pressed. The press conditions are
Preferred conditions are 180°C for 10 minutes and a press pressure of about 200 kg/cm ² . For the purpose of the present invention, the thickness of the molded sheet is preferably about 200 μm, so the phenol resin is cured by heat-sealing to achieve a molded film thickness of 200 μm. The phenol composite sheet obtained in this way was
Carbonization activation is carried out under an inert gas atmosphere at a temperature of ~1100°C. The conditions for carbonization activation include the temperature raising conditions for carbonization activation, the amount of activation catalyst added, etc., depending on the type, film thickness, application, and shape of the phenol composite material. As an example of carbonization activation conditions, ZnCl ₂ is used as a catalyst.
Carbonization was activated at 700°C in an argon gas atmosphere, and the specific surface area of activated carbon was 1500~
2500cm ² /g was obtained. The activated carbon sheet that has undergone carbonization activation is formed with collector electrodes or provided with lead terminals as necessary, and then cut into a desired shape and assembled to obtain an electric double layer capacitor product. If the metal substrate is in the shape of a chop or flake, the above process is sufficient, but in cases where it is difficult to fill the small pores with particulate phenol because there are few pores, such as in the shape of a wire mesh, nonwoven fabric, or matte. Since this heat-fusible, powdered phenolic resin is soluble in methanol, a methanol solution is prepared so that this resin accounts for 30 to 70 wt%, and a foamed metal sheet, metal net sheet, etc. is immersed in this solution. There is also a method of first filling porous parts which are difficult to fill with powdered phenolic resin after drying, and then using powdered phenolic resin to obtain a desired phenolic composite sheet. As described above, the method for preparing the metal-reinforced phenolic resin composite sheet is arbitrarily selected depending on the type and shape of the metal substrate. Furthermore, it is also possible to use the metal base in combination with a metal net tip, or to use a foam and a tip in combination, and the effect is great. In FIG. 5, the steps from the preparation of the metal substrate to the resin fusion bonding are shown by broken lines because this step can be omitted in the case of using only phenol resin. The advantages of the method of the present invention are as follows. (1) This resin is easy to carbonize. (2) The activated carbon and the collector electrode can be bonded extremely firmly, and the current collection resistance of the polarizable electrode can be reduced to 1/10 to 1/1000. (3) The surface of the metal base of the current collector can be completely covered with carbon, the anodic polarization potential can be made higher than before, and anodic dissolution of the current collector during charging can be avoided. (4) Metal-reinforced phenolic resins and metal-reinforced activated carbon electrodes have flexibility and mechanical strength, and such configurations have extremely great industrial value in the continuous production of these sheets. [Separator] A separator is interposed between a pair of metal-reinforced polarizable electrodes to prevent mutual electron conduction. In the present invention, a porous separator made of polypropylene, nylon, polyester, polyvinyl chloride, polyethylene, etc. It is possible to use a porous sheet or the like. [Electrolyte] In the examples of the present invention, a mixed solution of propylene carbonate and tetraethylammonium perchlorate is used, but when charging and discharging at a large current density, a solution with low electrical resistance such as KOH, NaOH, H ₂ SO ₄ , etc. Preferably, an electrolyte is used. Examples As specific examples of the present invention, 16 types of experiments conducted under the conditions shown in Table 1 will be compared with two conventional examples. First of all, Examples No. 1 to No. 3 show cases in which only a heat-sealing resin was used without using a metal substrate. No. 1 is the case where the sheet was made only from heat-sealable resin. Carbonization activation shrinkage is about 28%, so taking this into account, we prepared a heat-sealed phenol resin sheet of approximately 280 μm so that the sheet film thickness after carbonization activation would be 200 μm, and heated it with argon gas using a ZnCl ₂ catalyst. Carbonization activation was carried out at 800°C to obtain an excellent activated carbon sheet with no cracks, blisters, or deformations. No. 2 uses novolac fiber with a basis weight of 270g/m ²
The case is shown in which a heat-sealable sheet with a thickness of about 280 μm was prepared using the woven fabric of No. 1 as a base material, similar to No. 1. No.3 is PVA
A heat-adhesive sheet was obtained by adding 10% of powder particles with a diameter of approximately 30 μm. Since No. 3 can be made porous by the amount of PVA added, the time required for carbonization activation can be shortened. Nos. 1 to 3 are cases in which only heat-sealing resin is used and no metal substrate is used. Therefore, No. 1 to No.
The electric double layer capacitor prepared using the resin sheet No. 3 takes time to charge and discharge, and is used for relatively small currents. For short-term charging and discharging, the metal substrate is made of nickel, copper, or chromium in the form of a 30 μm diameter thin wire chop, nickel net, nickel foam, or the like. The phenol resin is heat-fusible and is based on powdered Bell Pearl S. In Nos. 4 to 7, fine metal wires and heat-fusible resin were mixed and heat-sealed under the conditions described above to obtain phenolic resin sheets. Nos. 8 to 16 use nickel foam and nickel net. First, as described above, the phenol resin is impregnated and adhered to the metal substrate once or twice using a methyl alcohol solution of the phenol resin. Thereafter, the remaining pores were filled with heat-sealing resin, and the phenol resin was cured by heat-sealing pressing to form a sheet with a total thickness of 200 μm. In order to examine the effects of adding resins other than the heat-fusible phenolic resin of the present invention, examples in which general furan resins, novolac resins, resol resins, nylon, etc. were added were also shown. This is due to the flexibility and workability of the resin sheet and activated carbon sheet film after carbonization activation.
The aim is to take advantage of the excellent overall characteristics with total cost performance even if the characteristics of the electric double layer capacity are reduced in terms of mass productivity, porosity, etc., and by adding resins that match the target product. Can be done. The thickness of the nickel foam was 200 μm, and when using a thin wire tip, the thickness of the activated carbon sheet after carbonization activation was adjusted to 200 μm. When preparing a polarizable electrode using a phenolic resin and a resin filler, the phenolic resin was filled and carbonized and activated carbonized by the method detailed using FIG. 5. The activated carbonization shown in Table 1 was performed using a ZnCl ₂ catalyst at 800° C. in argon. The thus prepared electrode was punched out into a circular shape with a diameter of 10 mm, and both electrodes were spot-welded in the same configuration as shown in Figure 3, and propylene carbonate and tetraethylammonium perchlorate were added as an electrolyte through a polypropylene separator. The mixed solution was injected and sealed into the metal case via a gasket.

【table】

[Table] Capacity, internal resistance, and high-temperature load life of the button-type capacitor prepared as described above were measured, and the performance was compared with a conventional example whose rating is close to that of the example. A conventional cylinder type example using powdered activated carbon had poor characteristics, so no comparison was made. Note that this type of capacitor using glass carbon has not been commercially available, so it was not possible to make a comparison. From the results in Table 1, all of the inventive examples shown in No. 1 to No. 16 have the same or better characteristics in terms of polarizable electrode capacity, especially in terms of internal resistance and high-temperature load life, compared to the conventional method. It can be seen that there is a significant effect. According to the present invention, the bond between the current collector and the resin is extremely excellent, and since the current collector is carbonized and activated carbonized, the current collector is almost completely coated with carbonaceous material. It exhibits the excellent characteristics of an electric double layer capacitor because it behaves exactly as if it were a highly conductive carbon electrode. Thus, according to the present invention, it can be easily seen that even if an organic electrolyte is used, the internal resistance of the electric double layer capacitor is one to three orders of magnitude lower than that of the conventional capacitor. Next, we prepared an electric double layer capacitor using caustic potash (KOH) to enable rapid charging and rapid discharging, and tested its characteristics. FIG. 6 is a schematic diagram of a high power electric double layer capacitor suitable for rapid charging and discharging, and FIG. 7 is a cross-sectional view taken along the line AA in FIG. 6. 6 and 7, 15 and 16 are polarizable electrodes having a film thickness of 200 μm, each having lead terminals 19 and 20, and these polarizable electrodes 15 and 16 are connected to the separator 1.
7 and then sealed in a heat sealing sheet 18 having a film thickness of 100 μm, and completely sealed with a sealing portion 21. As a polarizable electrode, use one under the conditions No. 5 in Table 1.
Cut into 40×100mm size, electrolyte is 8NKOH
was used. The apparent area of the polarizable electrode was approximately 40 cm ² . When this electric double layer capacitor was charged at 6A for about 60 seconds and discharged at a constant current of 3A, the discharge was completed in about 112 seconds. Next, perform constant current charging at 12A for 30 seconds,
When discharging at a constant current of 3A, the discharge was completed in about 115 seconds, and similarly, when discharging at 6A, the discharge was completed in about 59 seconds. In this way, KOH, NaOH, H ₂ SO ₄ are added to the electrolyte.
By using an electrolyte with excellent conductivity, the electric double layer capacitor according to the present invention can be used as a high power electric double layer capacitor that can be charged and discharged at a high current density despite being extremely small and lightweight. It becomes possible to commercialize capacitors. Effects of the Invention The electric double layer capacitor according to the present invention uses, as a polarizable electrode, a molded body mainly composed of a heat-fusible phenolic resin that has been activated to carbonize, and therefore can be charged and discharged at a large current density. It is suitable for use as a starter power supply for starting liquid fuel for automobiles and machinery, and for applications such as instantaneous large power discharge when driving the motor of fully automatic cameras and portable cameras.
It has great industrial value and is expected to be applied in all industrial fields such as automobiles, machinery, cameras, electricity, and computers.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the basic configuration of an electric double layer capacitor, Figure 2 is a perspective view of an example of a conventional double layer capacitor, and Figure 3 is another example of a coin type double layer capacitor. Partial cross-sectional front view, 4th
The figure is a cross-sectional view of a metal-reinforced phenolic resin composite material according to an embodiment of the present invention, FIG. 5 is a manufacturing process diagram for carrying out the present invention, and FIGS. 6 and 7 are each an embodiment of the present invention. FIG. 1 is a plan view of a certain sheet-type high-power electric double layer capacitor and a cross-sectional view of a portion thereof. 11... Thin metal wire tip, 13... Thin wire net, 12... Phenol resin, 15, 16...
... Polarizable electrode, 17 ... Separator, 18 ... Exterior sheet.

Claims (1)

[Scope of Claims] 1. An electric double layer capacitor characterized in that a phenolic resin molded body mainly composed of a powdered phenolic resin having thermal fusibility is carbonized and activated carbonized and used as a polarizable electrode. 2. The electric double layer capacitor according to claim 1, wherein the phenolic resin molded body is a phenolic resin molded composite material reinforced with a substrate made of a transition metal. 3. The transition metal has a melting point of 600°C or higher, and is characterized by being a simple substance of nickel, chromium, copper, cobalt, aluminum, titanium, tantalum, hafnium, or zirconium, or a transition metal-based alloy based on these metals. An electric double layer capacitor according to claim 2. 4 The substrate made of transition metal has a thin choppy shape,
Claim 2, characterized in that it is disposed in a composite material in the form of a net, felt, nonwoven fabric, punched thin plate, lath, or foam.
The electric double layer capacitor described in . 5 The phenolic resin molded body is made of one or more of general resol resin, novolac resin, polyester resin, polyacrylic resin, polyvinyl alcohol, pulp, and asbestos, in addition to powdered phenolic resin having heat-fusible properties. The electric double layer capacitor according to claim 1, characterized in that the electric double layer capacitor contains 3 to 60% of the material.