JPS62237715A - 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] [Industrial application field] The present invention relates to an electric double layer capacitor.

[Conventional technology] Conventionally, perchloric acid,
Solutes such as tetraalkylammonium salts, ammonium salts, or alkali metal salts of hexafluorophosphoric acid, boron tetrafluoride, or trifluoromethanesulfonic acid are combined with organic solvents such as carbon propylene, γ-butyrolactone, acetonitrile, dimethylformamide, acetonitrile, etc. An electrolytic solution dissolved in
Japanese Patent Publication No. 49-88254. Japanese Patent Publication No. 59-2324097
etc).

However, when using these known solvents,
The resulting capacitor does not have sufficient withstand voltage, and there remains the problem that the rated capacity of the capacitor decreases when exposed to high temperatures with voltage applied.

[Problems to be Solved by the Invention] The present invention attempts to solve the above-mentioned problems in the prior art. It is something to do.

[Means for Solving the Problems] That is, the present invention provides an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, in which the electrolyte is sulfolane or a derivative thereof. An object of the present invention is to provide an electric double layer capacitor characterized by being a solution in which a solute is dissolved in a solvent consisting of:

In the present invention, preferred examples of the sulfolane derivatives used as the electrolyte solvent include 3-methylsulfolane and 2,4-dimethylsulfolane, and each of these sulfolane or its derivatives can be used alone. However, in the present invention, in some cases,
These sulfolane or its derivatives can be mixed and used as a mixed solvent. In this case, since methane or 2,4-dimethylsulfolane has a low freezing point and good low-temperature physical properties, these mixed solvents have properties that combine the characteristics of both, that is, low-temperature properties and a large dielectric constant. I can do more.

When sulfolane and its derivatives are mixed, the amount of the derivative mixed is preferably 20 to 70% by weight, particularly 30 to 70% by weight.
The content is preferably 60% by weight in order to provide sufficient low-temperature properties and internal resistance.

Of course, other known solvents such as propylene carbonate, γ-butyrolactone, acetonitrile can be added to the sulfolane or its derivatives to improve its properties.

In the present invention, the type of solute in the electrolytic solution is not particularly limited, and various conventionally known or well-known solutes can be employed. Preferred examples include electrochemically stable solutes such as alkali metals, alkaline earth metals, ammonium or tetraalkylammonium, such as 47-fluoroborates, hexafluorophosphates, perchlorates, and 6-fluorophosphates. Arsenates, tetrachloroaluminates, or trifluoroalkyl (preferably methane) sulfonates are used. Among them, from the viewpoint of solubility in solvents, electrical conductivity, and electrochemical stability, tetraalkylammonium 4
Heptafluoroborates or hexafluorophosphates are preferred solutes.The concentration of these solutes in the electrolyte of the invention is preferably from 0.1 to 3 molar, especially from 0.5 to 1.5 molar. It is dissolved in

[Example 1] Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

In addition, in the following examples and comparative examples.

The test apparatus was assembled as follows.

activated carbon fiber on cathode side (specific surface area 2000rrl'/
g, 3.14 crn', 0.4+am thickness), polypropylene nonwoven fabric separator (4.9 crn', 0.4
thickness), anode side activated carbon fa! a (3,14cm', 2
■Thickness) are placed one on top of the other. At this time, the activated carbon fibers are placed completely opposite each other with a separator in between.

Next, a polytetrafluoroethylene ring having threads on both the inside and outside surfaces is screwed into the container to fix the positions of the activated carbon fibers and the separator.

Then, a threaded polytetrafluoroethylene rod with a platinum wire mesh current collector (200 mesh) attached to the tip was screwed into the opening of the ring, and the continuity between the platinum lead wire and the nickel container was measured using an LCR meter. Complete the set by checking with the two 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 the test apparatus assembled as described above, the characteristics of capacitors were determined by sufficiently impregnating the anode and cathode electrodes made of activated carbon with various electrolytes consisting of the solutes and solvents shown in Table 1. evaluated.

The evaluation items were the decomposition voltage of the electrolytic solution, which is an indicator of withstand voltage, and the capacity retention rate after high-temperature storage, and each was measured using the following procedure.

The decomposition voltage was determined by setting the test capacitor, applying a DC voltage, measuring the leakage current 10 minutes later, and determining the voltage at which the leakage current suddenly rose when the applied voltage was gradually increased as the decomposition voltage.

The capacity retention rate (Io) after high-temperature storage was measured as follows. First, after setting the test capacitor, 2.8
Perform constant voltage charging at v for 1 hour.

After that, constant current discharge is performed at 1 mA, and the terminal voltage at the time of discharge is 1 mA.
．． The time required to reach 0V was measured, and the initial capacity (Fo) was calculated from the measured value.

Next, while applying a voltage of 2.8V to the same test cell,
After storage for 1000 hours in a constant temperature bath at °C, the capacity after storage (CF) was measured using the same method as above, and the capacity retention rate after high temperature storage, Io = F/F.

×100 was calculated.

Table 1 shows the results of tests using different types of electrolyte. Test No. 10.11.12 shows conventional examples for comparison. In Table 0, TEA represents tetraethylammonium and TBA represents tetrabutylammonium.

Table 1 [Effects of the Invention] The capacitor of the present invention is superior to conventional capacitors in terms of withstand voltage and capacity deterioration under high temperatures, and its industrial value is extremely large.

Claims (2)

[Claims] (1) In an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, the electrolyte is a solution in which a solute is dissolved in a solvent consisting of sulfolane or a derivative thereof. An electric double layer capacitor featuring: (2) The electric double layer capacitor according to claim 1, wherein the sulfolane derivative is 3-methylsulfolane or 2,4-dimethylsulfolane.