JPS5942448B2 - electric double layer capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric double layer capacitor having characteristics of low voltage and large capacitance.

As shown in Fig. 1, an electric double layer capacitor consists of a carbon electrode body 1 made of graphite, carbon black, activated carbon, etc., and a current collector 2.
It is composed of an electrode disposed above and a separator impregnated with an electrolyte interposed between the electrodes, and the large capacitance is due to the electric double layer existing at the interface between the carbon electrode body 1 and the electrolyte. It is highly dependent on the capacitance of carbon and the large surface area of carbon electrode material.

Therefore, activated carbon is usually used as the material with a large surface area.

This activated carbon has a surface area of 500 to 1500 m per duram, and in terms of the purity of the material, activated carbon made from vegetable and steam-activated materials such as sawdust or coconut shell is most desirable.

The present inventors used activated carbon as the main material, easily attached it to a current collector, and conducted various tests to obtain the desired characteristics. We developed fluororubber-based Polyflon dispersion as a material that makes these effective, and acetylene black as a conductivity improver, and created a mixture of activated carbon, acetylene black, and Polyflon dispersion in an appropriate blending ratio. We have developed it for use as an electrode body.

FIG. 2 shows trends in the characteristics of capacitance, internal resistance, and moldability with respect to the blending ratio of Polyflon dispersion and acetylene black.

As can be seen from FIG. 2, although increasing the amount of Polyflon dispersion can improve moldability, it also causes an increase in internal resistance and a slight decrease in capacitance.

Therefore, as an improvement to this, the present inventors proceeded with the development of a binder material as a method of maintaining moldability and reducing internal resistance.

Table 1 shows the various glues and rubbery binder materials examined and the evaluation of each characteristic with respect to conventional products.

From the results shown in Table 1 above, PVP (polyvinylpyrrolidone) was found to exhibit superior time resistance compared to conventional products.

In some cases, leakage currents have been found to be improved.

Next, in order to confirm the reliability of the product according to the present invention, a high temperature accelerated life test was conducted.

An example at this time will be described below.

The product rating used was a voltage of 1.6v and a capacitance of 10.
The F1 case has a cylindrical shape with a diameter of 12.5 mm and a diameter of 35 mrn.

The conventional electrode material is as described above, and the material of the present invention is a conventional mixture of activated carbon, acetylene black, and polyflon dispersion mixed with an appropriate amount of PVP.

Furthermore, this PVP currently has a molecular weight of 12
Four types of 000 to 700,000 are on the market, and when added to the mixture depending on the type, the desired effect of the present invention can be obtained, but the viscosity differs, making it easy to manufacture. All you have to do is to appropriately select the type and blending ratio.

An electrode is made using such an electrode material and a current collector, and a separator impregnated with an electrolyte is interposed between them to form an electric double layer capacitor element, which is housed in a case.
Commercialized.

Then, while measuring the initial value, a rated voltage was applied, and an accelerated life test was conducted at 70° C. for 1000 hours.

Table 2 shows its characteristic values. In addition, FIGS. 3a to 3c show the capacitance versus elapsed time in the accelerated life test described above.
It shows changes in internal resistance and leakage current.

As described above, products to which PVP of the present invention is added show significant improvements in internal resistance and leakage current characteristics compared to conventional products, and furthermore, in accelerated life tests, there is a significant improvement in changes in capacitance. This has led to improvements in the initial characteristics and reliability of electric double layer capacitors.
Its contribution is large, and its effects are like dogs.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the basic structure of an electric double layer capacitor, Figure 2 is a diagram showing trends in various properties with respect to the blending ratio of polyflon dispersion and acetylene black as electrode materials for electric double layer capacitors, Figure 3 Diagram a ”'
-c is a characteristic diagram of capacitance, internal resistance, and leakage current for explaining the effects of the electric double layer capacitor according to the present invention. 1... Carbon electrode body, 2... Current collector, 3
・・・・・・Separate Lake.

Claims (1)

[Claims] 1. An electric double layer capacitor having an element in which a separator impregnated with an electrolyte is interposed between carbon electrode bodies made of graphite, carbon black, activated carbon, etc., characterized in that polyvinylpyrrolidone is added as a binder to the carbon electrode. electric double layer capacitor.