JPH0213455B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a small, thin, and large-capacity electric double layer capacitor. Structure of a conventional example and its problems FIG. 1 shows an example of the structure of a conventional wet electric double layer capacitor. Activated carbon fiber cloth is used as the polarizable electrode body 1, and a metal layer such as aluminum, titanium, nickel, stainless steel, or a conductive resin layer is formed on the polarizable electrode body 1 as the current collector 2 to constitute the polarizable electrode. The polarizable electrodes are made to face each other with a separator 3 interposed therebetween, an electrolytic solution is injected into the polarized electrodes, and then a case 4, a sealing plate 5, and a gasket 6 are used to form a sealed casing. Here, the activated carbon fibers used in the polarizable electrode body 1 are obtained by carbonizing and activating phenolic (cured novolac fibers), rayon, acrylic, and pitch fiber cloths. Considering the electrical resistance, strength, activation yield, etc. of activated carbon fibers, among the above-mentioned fibers, phenolic fibers are most suitable for polarizable electrode bodies. The metal conductive layer is formed by plasma spraying, arc spraying or gas spraying. Further, a conductive layer made of conductive resin or the like can be easily formed by a screen printing method, a press method, or a dip method. The polarizable electrode having the above shape can be punched out to a desired diameter, and the coin-shaped, flat, small, large-capacity capacitor shown in FIG. 1 can be realized. Further, such a polarizable electrode body does not require the use of a binder, and can reduce internal resistance. In particular, when the conductive layer is formed by a thermal spraying method, the adhesion strength between the thermal sprayed metal layer and the activated carbon fiber layer is good, the contact resistance is small, and good capacitor characteristics can be obtained. However, today there have been remarkable improvements in the characteristics of electronic devices, especially semiconductor memories, and their charging and discharging characteristics (rapid charging) are now possible with smaller capacity capacitors than before.
There is a strong demand for something with excellent quality. Also,
As devices become lighter, thinner, and smaller, double-layer capacitors are also required to be smaller and thinner. As long as conventional activated carbon fiber cloth is used, it is extremely difficult to reduce the thickness of the capacitor to 1 mm or less after sealing the casing. Further, as shown in FIG. 2, although the activated carbon fiber cloth 7 does not use a binding medium, the space portion 8 is very large and the volumetric efficiency cannot be improved. Furthermore, in the manufacturing process, fibers fly off during the process of cutting out the polarizable electrode body, causing dust pollution. Furthermore, as is well known, the charge accumulated in a double layer is proportional to its area. However, as activated carbon fibers are activated, their specific surface area and pore volume increase, but on the other hand, their fiber strength decreases significantly, making them unusable for practical use. Furthermore, electrolytes include aqueous ones and non-aqueous ones. In particular, when a non-aqueous electrolyte is used, a capacitor with high withstand voltage (2V or more) can be obtained, but it is known that trace amounts of water in the constituent materials and electrolyte can have a significant impact on reliability. OBJECTS OF THE INVENTION It is an object of the present invention to improve the charging and discharging characteristics of conventional electric double layer capacitors, to make them thinner, smaller, and have higher energy density, and to improve reliability. Structure of the Invention To achieve this object, the present invention provides a polarizable electrode body made by a papermaking method using a water-repellent binding medium, with a thickness of 600 μm or less and a density of 0.1.
A conductive layer is formed on at least one side of this polarizable electrode body using paper-like activated carbon fibers having a weight of at least g/cm ³ to form a polarizable electrode. It is constructed by injecting liquid, and improves charge and discharge characteristics while maintaining strength, as well as energy density per unit volume and reliability. Description of Examples Example 1 A coin-shaped capacitor shown in FIG. 3 was created using the constituent materials and steps shown below. The polarizable electrode body is made by carbonizing tow-shaped phenolic novolak resin fibers (φ15 μm) using a catalyst and steam, and measuring the specific surface area using the BET method.
2200m ² /g, pore volume 1.2cc/g, pore diameter 20
Obtain activated carbon fibers with a content of 50% or more in ~40A, wet-pulverize them using a mixer, and finely (1-3 mm length)
The resulting product is made into paper using the binding medium shown in Table 1, and a paper-like activated carbon fiber polarizable electrode body having the basis weight and density listed in the table is formed using a calendar roller or a press. An aluminum conductive layer of 30 to 100 μm is formed on at least one side of this polarizable electrode body by plasma spraying. The polarizable electrode having the conductive layer as described above is arranged and spot welded so that the conductive layer is in contact with the case 4 and the sealing plate 5.
After injection of 1 molar (C ₂ H ₅ ) ₄ NBF ₄ -propylene carbonate solution, via gasket 6,
The positive and negative electrodes are insulated and sealed in a sealed casing. The polarizable electrode in this example has a disk shape with a diameter of 14 mm. Table 1 shows various characteristics of capacitors using polarizable electrodes manufactured under each condition. From Table 1, it can be seen that more reliable capacitors can be obtained by using water-repellent polyethylene, polypropylene, acrylic, nylon, Kyubra, or polyester resins than by using pulp as the binding medium. This is thought to be because when a non-aqueous electrolyte is used, trace amounts of water in the constituent materials of the capacitor have a large effect on long-term reliability. Needless to say, the smaller the amount of binding medium and the larger the amount of activated carbon fiber, the higher the energy density. It can be seen that the thinner the electrode, the lower the impedance. The reliable capacity change rate (%) shown in Table 1 is the rate of change when comparing the capacitance after 1000 hours with the initial value when 2.0V is constantly applied to the capacitor in a 70℃ atmosphere. shows. In the case of this example, it can be seen that the capacity reduction rate is 10% or less, which is highly reliable.

[Table] Example 2 A coin-shaped capacitor similar to that shown in Fig. 1 was fabricated using a polarizable electrode having the same composition as No. 7 of Example 1 and a polarizable electrode having the thickness shown in Table 2. The thicker the polarizable electrode, the worse the current collection of the charges accumulated in the polarizable electrode, and those with a thickness of about 600 μm or less had a small initial IR drop and exhibited good capacitor characteristics.

[Table] Example 3 In order to increase the strength of a polarizable electrode body, a polarizable electrode body was prepared by mixing pulp (highly decomposed) into a binding medium of polyester and acrylic resin. Nos. 3 to 11 in Table 1 contain 5 to 5 binders.
Replacing 30 wt% with pulp slightly reduces reliability compared to no replacement, but significantly increases the strength of the electrode, which is advantageous for making capacitors. Example 4 Using a polarizable electrode having the composition and density of No. 7 of Example 1, a capacitor shown in FIGS. 3 and 4 was created. FIG. 4 shows a cross section of FIG. 3 taken along line a-a'. 9 is a polarizable electrode body with a thickness of 260 μm,
10 is an aluminum conductive layer with a thickness of 30 μm, 11
is an aluminum current collector plate with a thickness of 50 μm, and 12 is the thickness
A 50 μm polypropylene separator, 13 a heat-sealable 80 μm thick film sheet made of polyethylene terephthalate coated with an ionomer adhesive, and 14 a lead. A 1 molar (C ₂ H ₅ ) ₄ NClO ₄ -propylene carbonate solution was used as the electrolyte. The capacitor of this example is very thin, has good current collecting ability, and has strong electrode strength.
Even if the size is 100 x 200 mm ² , it can be assembled with sufficient workability. Table 3 shows various characteristics of the capacitor of this example.

[Table] Example 5 A polarizable electrode having the composition No. 7 of Example 1
A 100μm aluminum layer was thermally sprayed, and a 30μm thick etched aluminum foil was used as a current collector.
A cylindrical capacitor shown in FIG. 5 was manufactured. With this structure, the electrode area of the capacitor,
In other words, since the current collecting area can be increased, a large current can be discharged. However, in the case of this embodiment as well, when the thickness of the polarizable electrode reaches 1000 μm, the current collecting ability decreases and the workability deteriorates. If possible, it is preferable to use a polarizable electrode body of 600 μm or less. In FIG. 5, 15 is a case, 16 is a sealing packing, and 17 is a gasket. A 1 mol KPF ₆ propylene carbonate solution was used as the electrolyte. The thickness of the polarizable electrode body in this example is 300μ
The size is 30× ^200mm2 . Table 4 shows various characteristics of the capacitor. From Table 4, it can be seen that the capacitor of this example is small and large in capacity, and has excellent reliability.

[Table] Effects of the invention As described above, according to the present invention, the charge/discharge characteristics,
A thin, compact, large-capacity electric double layer capacitor with excellent reliability and easy working process can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the configuration of an electric double layer capacitor, FIG. 2 is a schematic diagram of activated carbon fibers, FIG. 3 is a plan view of an embodiment of the electric double layer capacitor of the present invention, and FIG. FIG. 3 is a sectional view taken along the line aa' in FIG. 3, and FIG. 5 is a front view showing another embodiment of the present invention in half section. 1, 9... Polarizable electrode body, 2... Current collector, 3...
... Separator, 10 ... Conductive layer, 11 ... Current collector, 12 ... Polypropylene separator.

Claims (1)

[Claims] 1. Paper-like activated carbon fibers having a thickness of 600 μm or less and a density of 0.1 g/cm ³ or more made by a papermaking method using a water-repellent binding medium are used as the polarizable electrode body, An electric double layer capacitor is constructed by forming a conductive layer on at least one side of this polarizable electrode body to form a polarizable electrode, making the polarizable electrodes face each other with a separator in between, and injecting an electrolyte into the polarizable electrode. 2. The electric double layer according to claim 1, characterized in that the binding medium is made of any one or a possible combination of polyethylene, polypropylene, acrylic, Qubra, nylon, and polyester resins. Capacita. 3. The electric double layer capacitor according to claim 2, wherein the binding medium contains pulp. 4. The electric double layer capacitor according to claim 1, wherein the binding medium accounts for 50% or less by weight of the polarizable electrode body. 5 A patent characterized in that the activated carbon fibers constituting the polarizable electrode body are obtained by carbonizing and activating phenolic resin fibers, and have a specific surface area of 1500 m ² /g by BET method and a pore volume of 0.5 cc/g or more. An electric double layer capacitor according to claim 1. 6. The electric double layer capacitor according to claim 1, characterized in that an organic electrolyte is used as the electrolyte.