JPS6290916A - Electrode for 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 Industrial Application] The present invention relates to an electrode for an electric double layer capacitor.

[Prior Art] It is known to use a fabric made of activated carbon fiber as the electrode of a double m-layer capacitor. (Unexamined Japanese Patent Publication No. 5
Publication No. 5-99714, Japanese Patent Application Publication No. 59-48018,
No. 87617, No. 105312 and H'138327
It is also known to use dry activated carbon fiber or activated carbon powder. (Unexamined Japanese Patent Publication No. 1113
Go-35509, 43809, 43810
(Refer to the publication) Electric double layer capacitors are often used in a form built into a board for memory backup etc. Therefore, a capacitor with a volume as small as possible for the desired capacity is required, but conventional products do not have this point. There was a problem that the results were not completely satisfactory.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems and provide an electrode for an electric double layer capacitor having a large capacity per unit volume (F/cm'). It is.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and provides an electrode for an electric double layer capacitor mainly made of a carbonaceous material heat-treated in an oxidizing liquid. It provides:

In the present invention, the carbonaceous material is not particularly limited, but particularly good results can be obtained when using a carbonaceous material with a large specific surface area, especially activated carbon, carbon black, or activated carbon fiber, and the specific surface area is 2000+a2/ It is desirable to use a carbonaceous material with a gr (measured by the BET method, the same applies hereinafter) or higher. When using a carbonaceous material with an extremely large specific surface area,
'1 There is a risk that the mechanical strength of the two poles will decrease and the durability of the capacitor will decrease accordingly, so the specific surface area should be 3500.
m2/gr (It is desirable to use the following.

A carbonaceous material is heat-treated in a liquid. As the liquid, solutions of nitric acid, nitric acid solutions, dichromates such as potassium dichromate sulfate, permanganates such as potassium permanganate, and nitrates such as sodium nitrate can be suitably used. The concentration is preferably about 0.1 to 1 mole (M), and in the case of a salt solution, it is preferably acidic with sulfuric acid. Although the heating temperature is appropriately determined depending on the liquid used, it is appropriate to heat the liquid at 50° C. or higher, preferably with the lamp turned on.

The heating time is determined in relation to the heating temperature, the type of liquid used, the type of carbonaceous material, and the specific surface area, but is usually 1"1.
It is about Ohr.

As for the above-mentioned treatment, the carbonaceous material is washed with water and dried if necessary.
If the material is in the form of fibers, it can be used as an electrode as is, but if it is in the form of powder, it is appropriate to form it into a paste or use a molding machine to form a sheet. When molding into a sheet, if necessary, a binder is added to the carbon powder, kneaded, and molded using a roll r&mold machine or the like. Particularly when tetrafluoroethylene is used as the binder, an electrode with #9 durability and excellent mechanical strength can be produced. The amount of binder used is 5 to 30% by weight of the carbonaceous material.
The appropriate thickness of the sheet material is approximately 500 to 700 microns.

The electrolytic solution used in combination with the electrode of the present invention is not particularly limited, and various conventionally known or well-known electrolytes can be employed.

Such electrolytes include propylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1,
A tetraalkylammonium salt of perchloric acid, hexafluorosonic acid, perfluoroalkylsulfonic acid, or tetrafluoroboric acid (alkyl group has 1 to 4 carbon atoms) in a solvent such as 2-dimethoxyethane, sulfolane or nitromethane.
Alternatively, a solution in which about 0.5 to 1.5 M of a solute such as an alkali metal salt (the alkali metal is lithium or sodium, etc.) is exemplified.

A capacitor using the electrode of the present invention can be manufactured by processing the electrode as described above to match the shape of the capacitor, filling the space between the electrodes with the electrolytic solution as described above, and sealing this in a case.

[Action J Carbon-based materials such as activated carbon are generally non-polar and cannot be used with polar solvents,
Alternatively, it has a somewhat poor affinity with the electric double layer, which is disadvantageous from the viewpoint of the electric double layer formation mechanism. Therefore, when wet activation treatment is performed using an oxidizing agent as in the present invention, the surface area increases and polar carbon is added to the surface, improving affinity with polar solvents and ions, and as a result, electric double layer formation is facilitated. This is considered to be the case.

Example 1 Ichisaka activated carbon powder (specific surface area: 2000 m2/gr) was ground in a mortar and classified using a 500 mesh sieve. The powder under the sieve was boiled in 30% HNO3 solution for 1 hour,
Furthermore, it is washed with ion-exchanged water and dried.

PTFE powder is mixed with the wet activated powder obtained by the above operation at a ratio of 10% by weight, an appropriate amount of ethanol is added, and the mixture is ground and mixed in a mortar. Further, the thus prepared paste was molded into a sheet with a thickness of 0.7 mm using a roll molding machine, and using this sheet, the capacitance per unit volume of the electrode (F/ca+j) was determined by the following method.

First, the test cathode side sheet electrode (
3.14cm2, 0.7m layer thickness), polypropylene nonwoven fabric separator (4.9cm2, 0.4m layer thickness), sheet electrode on the anode side to be tested (3.14c+s2.0.7+s
m thickness) are arranged one on top of the other. At this time, the sheet electrodes are arranged so as to completely face each other with the separator in between.

Next, a polytetrafluoroethylene ring having threads on both the inside and outside of the container is screwed into the container to fix the positions of the sheet electrode and separator.

Then, a threaded polytetrafluoroethylene rod with a platinum wire mesh aggregate (200 mesh) attached to the tip was screwed into the opening of the ring, and continuity between the platinum lead wire and the nickel container was established using an LCR meter AC Complete the set by checking with the terminal method. Note that the platinum lead wire is drawn out to the outside through a hole provided in the center of the body.

Using an electrolytic solution, specifically, 1M tetraethylammonium verchlorate-propylene carbonate, a separator impregnated with this electrolytic solution and a sheet electrode were set in a container, and then constant voltage charging was performed at 1.8 V for 1 hour. Then 1m
A constant current discharge was performed, and the time required for the voltage between the terminals to reach Ov during discharge was measured, and the capacity was calculated from that value.

Example 2 Example 1 (7) 98% 82SO4 instead of HNO3 solution
Example 1
A similar experiment was conducted.

Example 3 An experiment similar to Example 1 was conducted using commercially available carbon black (specific surface area: 1500 m2/gr) instead of the activated carbon used in Example 1.

Example 4 An experiment similar to Example 1 was conducted using the carbon black of Example 3 instead of the activated carbon of Example 2.

Example 5 An experiment similar to Example 1 was conducted by immersing the activated carbon of Example 1 in a 1M potassium dichromate-30X H2SO4 solution and boiling it at 100°C for 1 hr.

[Comparative Example] An experiment similar to Example 1 was conducted using the activated carbon powder of Example 1 which was not subjected to the treatment of the present invention.

The results of the above experiment are shown in Table 1 below, and the electrode made of the carbonaceous material treated according to the present invention (electrode of the present invention)
It was observed that the capacity of the electrode was improved by about 40% compared to the capacity of the electrode using untreated carbonaceous material.

Table 1 Capacity (F/cm3) Example 1 52.6 //2 55.6 //3 50.6 tt4 52.2 /15 50.8 Comparative example! 36.8 //2 34.5

Claims (7)

[Claims] (1) Electrodes for electric double layer capacitors that are mainly made of carbonaceous material that has been heat-treated in an oxidizing liquid. (2) The electrode for an electric double layer capacitor according to claim 1, wherein the oxidizing liquid is nitric acid or a nitric acid solution. (3) The electrode for an electric double layer capacitor according to claim 1, wherein the oxidizing liquid is sulfuric acid. (4) The electrode for an electric double layer capacitor according to claim 1, wherein the oxidizing liquid is a solution of dichromate, permanganate or nitrate. (5) The electrode for an electric double layer capacitor according to claim 4, wherein the solution is an acidic sulfuric acid solution. (6) The electrode for an electric double layer capacitor according to any one of claims 1, 2, 3, 4, and 5, wherein the carbonaceous material is activated carbon fiber, activated carbon, or carbon black. (7) Carbonaceous materials have a specific surface area of 2000 to 3500 m^
Claims 1, 2, 3, 4, 5, which are 2/gr.
An electrode for an electric double layer capacitor according to any one of Item 6.