JPS61248513A - Improved 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 J The present invention relates to an electric double layer capacitor.

[Prior Art] Conventionally, perchlorates and hexafluorophosphates have been used as solutes in electrolytes for electric double layer capacitors.

Borofluoride salts or trifluoromethanesulfonate salts have been proposed (JP-A No. 49-88254, No. 5).
0-44463 and 59-232409).

However, when using these known solutes,
The resulting capacitor has not yet been satisfactory in terms of withstand voltage, capacitance value, etc.

[Problems to be Solved by the Invention] The present invention attempts to solve the above-mentioned problems in the prior art, and aims to provide an electric double layer capacitor with excellent withstand voltage and capacity.

[Means for Solving the Problems] That is, one aspect of the present invention is 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 general formula RrCOQM is used as a solute of the electrolyte. (
However, an electric double layer characterized by utilizing a salt represented by R in formula 1 [represents a perfluoroalkyl group having 1 to 8 carbon atoms, and M represents a tetraalkylammonium, ammonium, or an alkali metal, respectively] It is a capacitor.

In the present invention, the general formula RrCO is used as the solute of the electrolyte.
It is important to use one or more salts represented by OM (wherein Rt and M are the same as above). By employing such a solute, a capacitor with excellent withstand voltage and capacity can be obtained. When the number of carbon atoms in the perfluoroalkyl group is 9 or more, problems such as decreased solubility occur. The preferable number of carbon atoms in Rf is 1
~4.

In the above general formula, M is tetraalkylammonium, and each alkyl group thereof has 1 to 4 carbon atoms, such as a tetramethylammonium salt and a tetraethylammonium salt.

Tetrapropylammonium salt, 9-butylammonium salt, dimethyldiethylammonium salt, and the like can be preferably employed from the viewpoint of solubility, availability, and the like.

The concentration of such a solute in the electrolytic solution is preferably 0.1 to 3M mol, particularly 0.5 to 1.5M. If the concentration is too low, loss increases due to an increase in internal resistance, while if it is too high, problems such as a decrease in stability due to solute precipitation in cold weather may occur.

In the present invention, the type of solvent is not particularly limited, and various conventionally known or well-known solvents can be employed, among which electrochemically stable non-aqueous solvents such as propylene carbonate, γ-butyrolactone, Preferred examples include acetonitrile, dimethylformamide, 2-dimethoxyethane, sulfolane, and nitromethane. Preferably, such solvents are used in a substantially anhydrous state.

Further, the type of the 5-polarizable electrode is not limited, but activated carbon or activated carbon fiber, which is electrochemically inert to the electrolytic solution and has a large specific surface area, can be preferably employed.

The electric double layer capacitor of the present invention can be manufactured by filling the electrolytic solution as described above between polarizable electrodes that have been processed and formed to match the shape of the capacitor, and then sealing the electrolytic solution in a case.

[Example] 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.

First, the active blown fibers on the cathode side were each impregnated with the electrolyte to be tested in a nickel cylindrical bottomed container with a threaded inner surface. I
(Specific surface 1112000 m'/g, 3.14c+a2.
0.4mm thick), polypropylene nonwoven fabric separator (specific surface yI2000rrr'/g3.14cm2, 2
mm thickness) are arranged 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 continuity between the platinum lead wire and the nickel container was measured using an LCRC-meter. Complete the set by approving two AC terminals. Note that the platinum lead wire is drawn out to the outside through a hole provided in the center of the precursor.

Using a test device assembled as described above, we evaluated the capacitor's characteristics by changing the type of electrolyte.

The evaluation items were electrical measurements, which are indicators of capacity and withstand voltage.

To measure the capacity, first set a separator impregnated with the specified electrolytic solution and activated carbon fibers in a container, then turn on the voltage at 1.8V.
Constant voltage charging was performed for a period of time, followed by constant current discharging at 1 mA, and the time required for the voltage between the terminals to reach Ov during discharging was measured, and the capacity was calculated from that value.

To determine the decomposition voltage, set the test capacitor in the same way as when measuring capacity, apply DC voltage, and calculate the leakage current (L) after 10 minutes.
C) was measured, and the sharp rise point of LC with respect to the applied voltage was taken as the decomposition voltage of the electrolytic solution.

Table 1 shows the results of tests conducted with different types of electrolytes. The solute concentration was IM in all cases, and numbers 11 and 12 indicate conventional examples for comparison.

In Table 1, Me, Et and Bu represent a methyl group, an ethyl group and a butyl group, respectively.

[Effects of the Invention] The capacitor of the present invention is superior to conventional capacitors in terms of capacity, and also has the advantage that the electrolyte is less likely to absorb moisture, making assembly easier.

Claims (1)

[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 solute of the electrolyte is expressed by the general formula R_fCOOM (where R_f is Carbon number 1-8
and M represents tetraalkylammonium, ammonium, or an alkali metal, respectively. 2. The electric double layer capacitor according to claim 1, wherein the solute concentration is 0.1 to 3M. 3. The electric double layer capacitor according to claim 1, wherein M is tetraalkylammonium, and each alkyl group thereof has 1 to 4 carbon atoms.