JPH0795504B2 - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To obtain an electric double layer capacitor having a small size and a large capacity by using powdered active charcoal containing 20wt.% to less than 35wt.% of oxygen. CONSTITUTION:In an electric double layer capacitor having mixture of powdered active charcoal and electrolyte solution as polarizable electrodes, powdered charcoal containing 20wt.% to less than 35wt.% of oxygen content is used as powdered active charcoal 1 in a base element 8. That is, the oxygen in the charcoal is not contained in a carbon skeleton, but exists in a surface functional group state, and the functional group containing the oxygen contributes to an increase in an electric double layer capacity. Thus, an electric double layer capacitor having a small size and a large capacity is obtained.

Description

Description: TECHNICAL FIELD The present invention relates to an electric double layer capacitor, and particularly to an electrode material for an electric double layer capacitor.

(Prior Art) As shown in FIG. 2, a basic element 8 (hereinafter referred to as a basic element) of an electric double layer capacitor includes powdered activated carbon 1 and a current collector 2.
Is used as a unit polarizable electrode, an electrolytic solution is impregnated between a pair of polarizable electrodes, and an electronic short circuit is prevented by an electronically insulating and ion-permeable porous separator 3. 4 is an insulating gasket. The electric double layer capacitor has a structure in which one or more sheets are laminated according to the operating voltage because the maximum operating voltage of the basic element is equal to or lower than the electrolysis voltage of the electrolyte solution. By the way, electric double layer capacitors are widely used as backup capacitors for microcomputers, memories, etc., as auxiliary power sources that can supply a large current instantaneously, as compact, large-capacity capacitors. Along with the reduction in weight, it is strongly desired that the electric double layer capacitors used therein be small in size. In order to realize the miniaturization of this electric double layer capacitor, it is very important to increase the electric double layer capacity per unit volume. Since the electric double layer capacity per unit volume is expressed by the product of the specific surface area of activated carbon and the packing density, conventionally, activated carbon having a large specific surface area and a high packing density has been required.

In recent years, according to the research and investigation by the present inventors, the capacitance of an electric double layer capacitor has a correlation with the oxygen content of activated carbon,
It has been found that the activated carbon having a higher oxygen content has a larger capacitance. Conventionally, the activated carbon used for electric double layer capacitors has an oxygen content of less than 15%.
There is no case where activated carbon containing more than% oxygen is used.

(Problems to be Solved by the Invention) The above-described conventional powdered activated carbon has a drawback that the electric double layer capacity per unit volume is small because the oxygen content in the activated carbon is small.

The object of the present invention is to have a current collector and oxygen content of 20% by weight or more and 35% or more.
An object of the present invention is to provide a small-sized and large-capacity electric double layer capacitor by using powdered activated carbon whose content is less than wt% as a polarizable electrode of the electric double layer capacitor.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an electric double layer capacitor using a mixture of powdered activated carbon and an electrolyte solution as a polarizable electrode, wherein the oxygen content of the powdered activated carbon is 20% by weight. % To less than 35% by weight.

(Examples) Next, the present invention will be described with reference to Examples.

An electric double layer capacitor was manufactured by using powdered activated carbon having an oxygen content of 30% by weight or more and less than 35% by weight as the powdered activated carbon 1 in the basic element 8 of FIG. For analysis of oxygen content, sc
An oxygen analyzer was used to determine the amount of oxygen by decomposing bound oxygen into carbon monoxide by the hutze decomposition method and detecting carbon monoxide by non-dispersive infrared spectroscopy.

A powdered activated carbon having an oxygen content of 20% by weight or more and less than 30% by weight was used as 1 of the powdered activated carbon in the basic element 8 of FIG. 2 to manufacture an electric double layer capacitor. The analysis of oxygen content is
An analyzer similar to that described above was used.

A powdered activated carbon having an oxygen content of 35% by weight or more was used as 1 of the powdered activated carbon in the basic element 8 of FIG. 2 to manufacture an electric double layer capacitor. The oxygen content was analyzed using the same analyzer as above.

The electric double layer capacitor of the above-mentioned embodiment is as follows. In FIG. 2, the thickness of the current collector 2 is 200 μm.
An unvulcanized conductive butyl rubber having a diameter of 8.2 mm and a diameter of 8.2 mm was used.
The insulating gasket 4 has a film thickness of 500 μm and a diameter of 8.2.
Unvulcanized butyl rubber with 3.8 mm holes concentric with 3.8 mm was used. As the porous separator 3, a polyethylene film having a thickness of 100 μm and a diameter of 6.0 mm was used. A unit polarizable electrode was obtained by filling the concave portion formed by pressure-bonding the current collector 2 and the insulating gasket 4 with the paste in which the powdered activated carbon 1 obtained in each example and the electrolyte solution were mixed. As the electrolyte solution, a 40 wt% sulfuric acid aqueous solution was used. The pair of unit-polarizable electrodes are pressure-bonded to each other via the porous separator 3 in a direction in which the paste faces each other, and the mixture is left at a temperature of 120 ° C. for 3 hours while a pressure of 7 kg / cm ² is applied. 2 and the insulating gasket 4 and the insulating gasket 4 were bonded by vulcanization to obtain a basic element 8 of the electric double layer capacitor. An electric double layer capacitor having an operating voltage of 5V was manufactured by laminating six basic elements 8 and caulking and sealing them with a metal case 5 and an insulating case 6 as shown in FIG. .

With respect to the electric double layer capacitors manufactured in the examples, the capacitance and the equivalent series resistance, which are the capacitor characteristics, were measured.
The capacitance was measured by inserting a 1 kΩ resistor in series with the capacitor and calculating from the time constant when a constant voltage of 5 V was applied.
Also, the equivalent series resistance is 1kHz
It was determined by applying a constant current of 10 mA and measuring the voltage across the electric double layer capacitor.

Table 1 shows the oxygen content of activated carbon and the characteristics of electric double layer capacitors. For comparison with the examples, the same measurements as in the examples were performed for the five types of powdered activated carbon that have been conventionally used in electric double layer capacitors, and the results are shown in Table 1. Further, FIG. 1 shows the relationship between the oxygen content and the capacitance and the relationship between the oxygen content and the equivalent series resistance.

As is apparent from FIG. 1, the capacitance of the electric double layer capacitor composed of the basic element using the powdered activated carbon having a high oxygen content is the electric double layer composed of the basic element using the powdered activated carbon having a low oxygen content. It can be seen that the capacitance is larger than that of the capacitor, and that the oxygen content of 20% by weight or more is very effective in increasing the capacitance. However, the equivalent series resistance increases as the oxygen content of the powdered activated carbon increases, and becomes significantly higher than that of the conventional one when the oxygen content exceeds 35% by weight.

The detailed mechanism by which the powdered activated carbon having a large oxygen content obtained in the present invention contributes to the high capacity of the electric double layer capacitor is unknown. However, oxygen in these activated carbons is not incorporated in the carbon skeleton but exists in the form of surface functional groups, and the surface functional groups containing this oxygen contribute to the increase of the electric double layer capacity. It is considered to be a thing. Also,
It is considered that the increase of the electric double layer capacity due to the surface functional group is not limited to the activated carbon powder, and the similar effect can be expected in the fibrous or solid state. The reason why the equivalent series resistance increases as the oxygen content increases is considered to be that in the case of powdered activated carbon, the contact resistance between powders increases due to the increase of surface functional groups.

Therefore, it is understood that the activated carbon of the present invention is more suitable as an electrode material for an electric double layer capacitor than ever before and is effective in increasing the electric double layer capacity.

Since the capacitance per weight (F / g) increases almost linearly with the oxygen content, it is difficult to set a clear lower limit for the oxygen content. However, when the oxygen content is around 20% by weight, it is possible to clearly divide the population into different F / g. Therefore, there is no problem in setting the lower limit of the oxygen content to 20% by weight. It can be seen that although the oxygen content is 37% by weight, the capacitance is large, but the equivalent series resistance is almost twice as large as that of the conventional one, and is far from the straight line. The deviation from the straight line is considered to be due to an increase in electrochemically unstable surface functional groups that do not contribute to the electrostatic capacitance, and therefore it can be said that it is unsuitable as a capacitor electrode. Therefore, it is considered appropriate to set the upper limit of the oxygen content to 35% by weight with a margin.

(Effects of the Invention) As described above, the present invention provides a small-sized and large-capacity electric double layer capacitor by using activated carbon containing 20 wt% or more and less than 35 wt% oxygen for a polarizable electrode. You can

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the oxygen content of powdered activated carbon and the capacitance of an electric double layer capacitor, and the relationship between the oxygen content of the powdered activated carbon of the present invention and the equivalent series resistance of an electric double layer capacitor, and FIG. A sectional view of a basic element of an electric double layer capacitor using the powdered activated carbon of the present invention, and FIG. 3 is a sectional view of an electric double layer capacitor having an operating voltage of 5 V in which six basic elements of the present invention are stacked and housed in a metal case. is there. In the figure, 1 ... Powder activated carbon, 2 ... Current collector, 3 ... Porous separator, 4 ... Insulating gasket, 5 ... Metal case, 6
…… Insulation case, 7,7 ′ …… Electrode, 8 …… Basic element

Claims (1)

[Claims] 1. An electric double layer capacitor comprising a mixture of powdered activated carbon and an electrolyte solution as a polarizable electrode, wherein the powdered activated carbon has an oxygen content of 20% by weight or more and less than 35% by weight. Capacitors.