JPS61102024A - 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 the Invention 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. A polarizable electrode is constructed by using activated carbon fiber cloth as the polarizable electrode body 1, and forming a metal layer such as aluminum, titanium, nickel, or a conductive resin layer as a current collector 2 on the polarizable electrode body 1. After the polarizable electrodes are opposed to each other with a separator 3 in between and an electrolytic solution is injected, a case 4, a sealing plate 5, and a gasket 6 are used to seal the polarized electrodes. Here, the activated carbon fibers used in the polarizable electrode body 1 are obtained by carbonizing and activating phenol-based (cured novolac fibers), rayon-based, acrylic-based, and pitch-based fiber cloths. Considering the electrical resistance 2 strength, activation yield, etc. of activated carbon fibers, phenolic fibers are most suitable for polarizable electrode bodies among the above-mentioned fibers.

The metal conductive layer is formed by plasma spraying, arc spraying or gas spraying. Further, a conductive layer such as a conductive resin can be easily formed by a screen printing method, a press method, or a dipping method. The polarizable electrode having the above-mentioned shape can be punched out to a desired diameter, and the small coin-shaped flat plate 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 has been a significant improvement in the characteristics of electronic devices, particularly semiconductor memories, and there is a strong demand for capacitors with smaller capacitance than conventional ones and excellent charge/discharge characteristics (rapid charging). Furthermore, as devices become lighter, thinner, shorter, and smaller, double-layer canisters are also required to be smaller and thinner. It is extremely difficult to reduce the thickness of a conventional key capacitor using an activated carbon fiber layer to less than 1 mm after sealing the casing.

Further, as shown in FIG. 2, although the activated carbon fiber cloth does not use a binding medium, the space 8 is very large and the volumetric efficiency cannot be improved. Furthermore, in the manufacturing process, fibers fly off during the cutting process of the polarizable electrode body, causing dust pollution. It is well known that the charge accumulated in a double layer is proportional to its formation 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 a high withstand voltage (2V or more) can be obtained, but it is known that trace amounts of water in the constituent materials and the electrolyte have a large effect on reliability.

OBJECTS OF THE INVENTION The present invention aims 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 with:
Paper-like activated carbon fibers with a thickness of 600 μm or less and a density of 0.1 y/l, td or more, made by a papermaking method using a water-repellent binding medium, are used on at least one side of the polarizable electrode body. forming a conductive layer to serve as a polarizable electrode;
These polarizable electrodes are made to face each other with a separator in between, and an electrolyte is injected into the electrodes to improve the charging/discharging characteristics while maintaining the strength. It is an improved version of

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-like phenolic novolac resin fibers (φ15 μm) using a catalyst and steam, and the specific surface area is 22ooWf/S as measured by the BICT method.
', pore volume is 1.2cc/? Activated carbon fibers with a pore diameter of 20 to 40% or more were obtained, and this was wet-pulverized in a mixer to a fine powder (1 to 3 pores) using the binding medium shown in Table 1. Paper is made, and a paper-like activated carbon fiber polarizable electrode body having a 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 was arranged so that the conductive layer was in contact with the case 4 and the sealing plate 5, and was welded with nubot.
After injecting the C2H5)4NBF6-propylene carbonate solution, the positive and negative electrodes are insulated and sealed in a sealed casing via a gasket 6.

The polarizable electrode in this example has a disk shape with a diameter of 14 mm. Table 1 shows the characteristics of capacitors using polarizable electrodes prepared under each condition.

According to this Table 1, even if pulp is used as the binding medium, water-repellent polyethylene, polypropylene, acrylic,
It can be seen that more reliable capacitors can be obtained using nylon, cupro, and polyester resins.

This is thought to be because when a non-aqueous electrolyte is used, trace amounts of moisture 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. In addition, the reliability capacitance change rate % shown in Table 1 means that the capacitor is constantly maintained at 2% in a TO'C atmosphere.
．． The rate of change when comparing the capacity after 1000 hours with the initial value when OV is applied is shown. It can be seen that in the case of this example, the rate of decrease in capacity is 10% or less, which is highly reliable.

(Hereinafter referred to as gold and white) (Example 2) A coin-shaped capacitor similar to that shown in Fig. 1 was constructed using a polarizable electrode having the same composition as in Example 1 and the thickness shown in Table 2. The thicker the fabricated electrode, the worse the collection of charges accumulated in the polarizable electrode.
However, the initial IR drop was small and showed good capacitor characteristics.

Table 2 (Example 3) In order to increase the strength of the polarizable electrode body, pulp (
Polyester, Acrylic IJ
7 and mixed into a resin binding medium to produce a polarizable electrode body. Replacing 5-30 wt% of the binder with pulp in //1L3-11 of Table 1 results in a slight decrease in reliability compared to no replacement, but the strength of the electrode increases significantly and is suitable for making capacitors. be advantageous to

(Example 4) Using the polarizable electrode having the composition and density of &7 in Example 1, capacitors shown in FIGS. 3 and 4 were created. FIG. 4 shows a cross section of FIG. 3 taken along a-a'. 9 is a polarizable electrode body with a thickness of 260 μm.

10I1. Aluminum conductive layer with a thickness of 30 μm, 11
12 is an aluminum current collector plate with a thickness of 60 μm, and 12 is a thickness of 50 μm.
13 is an 80 μm thick heat-fusible film sheet made of polyethylene terephthalate coated with an ionomer adhesive, and 14 is a lead. The electrolyte contains 1 mol of (C2H5)4NGtO
A 4-propylene carbonate solution was used. The capacitor of this example is as follows.

It is extremely thin, has good current collecting ability, and has strong electrode strength.
Even if the size is 100x200-, it can be assembled with sufficient workability. Table 3 shows various characteristics of the capacitor of this example.

Table 3 (Example 5) A polarizable electrode having the composition of Example 1, 100 μm
An aluminum layer of 30 μm is formed by thermal spraying.
A cylindrical capacitor shown in FIG. 6 was fabricated using an etched foil having a thickness of m as a body.

With such a structure, it is possible to increase the current collection area behind the electrode surface of the capacitor.

Capable of large current discharge. However, in the case of this embodiment as well, when the thickness of the polarizable electrode reaches 100 μmK, 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. 1 mol of KPF in the electrolyte
6. A propylene carbonate solution was used.

The polarizable electrode body in this example has a thickness of 300 μm and a size of 30×200−. Table 4 shows various characteristics of the capacitor.

From Table 4, it can be seen that the capacitor of this example is small in size and has a large capacity, and has excellent reliability.

Effect of the invention As described above, according to the present invention, the charging and discharging characteristics.

A thin, compact, large-capacity electric double layer capacitor with excellent reliability and simple work process can be obtained.

[Brief explanation of the drawing]

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 example of the electric double layer capacitor of the present invention, and FIG. FIG. 3 is a sectional view taken along line a-a' in FIG. 3, and FIG. 6 is a front view showing another embodiment of the present invention in half section. 1.9... Polarizable electrode body, 2... Current collector, 3... Separator, 1o... Conductive layer, 11... - Current collector plate, 12...Polypropylene separator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 111b' Figure 4

Claims (6)

[Claims] (1) Using paper-like activated carbon fibers with 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 for 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 electricity according to claim 1, characterized in that the binding medium is made of any one of polyethylene, polypropylene, acrylic, cupro, nylon, and polyester resin or a possible combination thereof. double layer capacitor. (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) The activated carbon fibers constituting the polarizable electrode body obtained by carbonizing phenolic resin fibers have a specific surface area of 1500 m^2/g and a pore volume of 0.5 cc/g or more using the BET method. An electric double layer capacitor according to claim 1, characterized in that: (6) The electric double layer capacitor according to claim 1, wherein an organic electrolyte is used as the electrolyte.