JPH01102913A - Carbon paste electrode - Google Patents

Abstract

PURPOSE:To stabilize self-discharge characteristic of an electric double layer capacitor by a method wherein this capacitor is composed of powdery activated carbon whose iron content is suppressed to less than a prescribed value and of sulfuric acid. CONSTITUTION:A carbon paste electrode for an electric double layer capacitor is composed of powdery activated carbon and sulfuric acid; iron of 0.01% or less as a contained component is contained in the powdery activated carbon. That is to say, attention is directed to a relationship between the contained component of an impurity to be contained in the activated carbon constituting the carbon paste electrode and an electrical characteristic of the electric double layer capacitor, and self-discharge characteristic is stabilized while the iron content of the activated carbon is set at 0.01% or less.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to carbon paste electrodes, and particularly relates to carbon paste electrodes. P
This invention relates to carbon paste electrodes for K double layer capacitors.

[Conventional technology]

An electric double layer capacitor using carbon paste electrodes has, for example, the following configuration. That is, a pair of carbon paste electrodes made of powdered activated carbon and an electrolyte solution filled in the recesses in the gasket formed by a ring-shaped non-conductive gasket and an ion-impermeable conductive separator that completely seals one side of the gasket. are combined via an insulating and ion-permeable porous separator, and the carbon-based electrode pair is held by a non-conductive gasket and a conductive separator, shielded from the outside world, and electrically insulated by the porous separator. It consists of a structure that is

This type of electric double layer capacitor (hereinafter referred to as basic cell)
Conventionally, carbon paste electrodes, which serve as electrodes, are made of powdered activated carbon mixed with an electrolyte, and sulfuric acid is generally used as the electrolyte.

[Problem that the invention seeks to solve]

In the electric double layer capacitor using the conventional carbon paste electrode described above, due to differences in the raw material history of the powdered activated carbon that makes up the carbon paste electrode and the manufacturing history related to carbonization, activation, cleaning, and pulverization, the electric double layer capacitor Differences may occur in the self-discharge characteristics of the batteries, which poses a problem in product yield.

Therefore, the inventor diligently investigated the cause and found that
It was found that there is a clear correlation between the iron content of powdered activated carbon and the self-discharge characteristics, and in particular, it was found that as the iron content increases, the self-discharge characteristics tend to deteriorate.

[Differences between the invention and the prior art]

In contrast to the above-mentioned conventional carbon paste electrode, the present invention focuses on the relationship between the impurity components contained in the activated carbon constituting the carbon paste electrode and the electrical characteristics of the electric double layer capacitor, and increases the iron content of the activated carbon to 0.01. % or less, the difference lies in stabilizing the self-discharge characteristics.

[Means for solving problems]

The carbon paste electrode for an electric double layer capacitor of the present invention is characterized in that it is composed of powdered activated carbon and sulfuric acid, and contains iron content of 0.01% or less.

[Example 1] Next, the present invention will be explained by giving examples.

FIG. 2 is a longitudinal sectional view of a basic cell of an electric double layer capacitor used in an example of the present invention. In the figure, 1 is a carbon paste electrode, 2 is a porous separator, 3 is a non-conductive gasket, 4 is a conductive separator, and 5 is a basic cell.

FIG. 3 is an external view of a laminate of basic cells. In the figure, 5
6 is a basic cell, and 6 is a laminate.

First, phenolic resin powder activated carbon A shown in Table 1
, and B were mixed with 30% polymerization sulfuric acid to prepare a carbon paste. Next, with the structure shown in Fig. 2, a polypropylene sheet containing a disc-shaped conductive carbon punched to a diameter of 10 nm to become the conductive separator 4, and an outer diameter of 10 m to become the non-conductive gasket 3.
A recess formed by adhering a ring-shaped insulating butyl rubber punched out with an inner diameter of φ5.5M was filled with the carbon paste to form the carbon paste electrode 1, and a pair of filled sheets were made with a thickness of 110μ, Porosity 18%, φ7
．． Table 1 *1: Based on the BET method.

*2: According to JISK1470.

*3: Based on JIS Z8801.

Then, basic cell 5 was manufactured.

Next, the basic cells 5 were stacked in the structure shown in FIG. 3 to produce a laminate 6.

After applying a DC voltage of 5 V to both the upper and lower ends of 10 each of the laminates 6 containing powdered activated carbon A and B for 24 hours, both ends were opened and left at room temperature for 24 hours, and again between the upper and lower ends. When the residual potential was measured, the respective average values were as shown in Table 2.

From Table 2, it was confirmed that the self-discharge characteristics differed depending on the iron content of the active end, and other electrical characteristics were as shown in Table 3.

From Table 3, it was confirmed that there was no difference in the special series resistance and capacitance, and that the leakage current was slightly lower with less iron content.

Table 2 Table 3 [Example 2] Next, a laminate having the same material composition, structure, and shape as in Example 1 was manufactured, except that the powdered activated carbon was as shown in Table 4. The self-discharge characteristics of 10 samples each were measured using the same method as in 1, and the average values were as shown in Table 5.

Table 4 *l...Based on the BET method.

*2...According to JISK1470 *3...
...According to JISZ8801.

Further, the other electrical characteristics of each are as shown in Table 6. From Table 6, it was confirmed that there was no difference in the special series resistance and capacitance, and that the leakage current was slightly lower when the iron content was lower.

From Table 5, Table 6, Table 2 of Example 1, and Table 5 of Example 2, the relationship between the iron content of activated carbon and the residual potential is shown in FIG.

From FIG. 1, it is clear that the iron content affects the self-discharge characteristics, and it was confirmed that the self-discharge characteristics are stable when the iron content is 0.01% or less.

〔Effect of the invention〕

As explained above, the present invention has the effect of stabilizing the self-discharge characteristics of electric double layer capacitors by using a carbon paste electrode composed of powdered activated carbon with an iron content of 0.01% or less and sulfuric acid. Its industrial value is great.

[Brief explanation of the drawing]

Figure 1 is a plot diagram showing the relationship between the iron content of activated carbon and the self-discharge of an electric double layer capacitor, showing the effect of the present invention. Figure 2 is a plot of the basic cell of an electric double layer capacitor to which the carbon paste electrode of the present invention is applied. The vertical cross-sectional view and FIG. 3 are external views of a stacked body of basic cells. l...Carbon paste electrode, 2...
Porous separator, 3... Non-conductive gasket, 4... Conductive separator, 5... Basic cell, 6... Laminate. Agent Patent Attorney Oto Hara 0 0.005 0. OTQ 0OIE
O, 0200, 025 Iron content of talkability Z Figure 1 Figure 3

Claims (1)

[Claims] In carbon paste electrodes for electric double layer capacitors that use a mixture of powdered activated carbon and electrolyte solution as both electrodes,
A carbon paste electrode for an electric double layer capacitor, wherein the electrolyte is sulfuric acid and the powdered activated carbon contains iron content of 0.01% or less.