JPS61203626A - 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 the Invention The present invention relates to an electric double layer capacitor used as an energy storage element.

BACKGROUND OF THE INVENTION In recent years, with the rapid growth in demand for semiconductor memories, electric double layer capacitors have been attracting attention as devices for backing up memories during instantaneous power outages.

The conventional electric double layer capacitor as described above will be explained below with reference to the drawings.

FIG. 2 schematically shows a general electric double layer capacitor. In FIG. 2, 1 is a polarizable electrode made of carbon fiber or activated carbon fiber, and 2 is a conductive electrode. 3 is a separator that maintains insulation between both polarizable electrodes and also serves to hold the electrolyte. This polarizable electrode 1 and conductive electrode 2
between the electric current ff1 consisting of propylene carbonate, r
- It is impregnated with an electrolytic solution in which a tetraethylammonium salt is dissolved in an organic solvent of butyrolactone and 1,3-dioxolane, and is wound or laminated with a separator 3 interposed therebetween.

The principle of the electric double layer capacitor configured as described above will be explained below.

In general, when looking at the interface between the electrode and the solution that make up the electrode system, it is said that layers with different properties are formed. When two different phases come into contact, positive and negative charges are distributed across the interface over a very short distance. A layer with distributed charges near this interface is called an electric double layer. An electric double layer capacitor has a structure in which a voltage is applied to this electric double layer to accumulate electric charge.

At this time, the voltage applied to the element is limited by the decomposition voltage of the electrolyte composition.

Problems to be Solved by the Invention In conventional electrolytes for electric double layer capacitors, the decomposition voltage of tetraethylammonium salt used as a solute is low, and its decomposition products are highly reactive, so it is difficult to use at high temperatures. It had the disadvantage of generating gas during use and continuous charging and discharging. In sealed devices such as electric double layer capacitors, gas generation is a major problem because it causes damage to the outer case, liquid leakage, and deterioration of electrical characteristics.

In view of the above drawbacks, the present invention provides an electric double layer capacitor that does not generate gas even when used at high temperatures or after continuous charging and discharging.

Means for Solving the Problems To achieve this objective, the electric double layer capacitor of the present invention uses tetraethylammonium tetrafluoroborate as the solute, propylene carbonate, γ-butyrolactone, 1,3-dioquinolane, etc. It is impregnated with an electrolyte dissolved in an organic solvent such as.

Effect The stability of the tetrabutylammonium salt is due to its cation, the tetrabutylammonium ion.

The difference between tetraethylammonium ion and tetrabutylammonium ion is that the nitrogen atom N at the center of the ion
in the substituents coordinating with. Considering the influence that ethyl and butyl groups have on nitrogen atoms, the electron donating property of butyl group is greater than that of ethyl group, so the electron density of the nitrogen atom at the center of the ion is correspondingly higher than that of tetrabutylammonium ion. is expected to be large. These cations tend to be reduced on the cathode side, but because the nitrogen atom of the tetrabutylammonium ion has a higher electron density than the tetraethylammonium ion1, its reduction potential becomes more base, making it electrochemically more stable. It exists as an ion. This prevents the electrolyte from electrolyzing even when voltage is applied at high temperatures, continuous charging/discharging, or electricity, and gas generation can be suppressed.

Example An embodiment of the present invention will be described below.

FIG. 1 shows the structure of an electric double layer capacitor in an embodiment of the present invention. In Figure 1, 1 to 3 are the second
This is the same part as the figure. 4 is a high chromium steel anode lid, 6 is a stainless steel cathode case, and 6 is a polypropylene sealing material for sealing and insulation.

Furthermore, the electrolyte composition is as follows.

Electrolyte! Solute...Tetrabutylammonium tetrafluoroborate salt ((n-04H9)4NBF4) Solvent...Propylene carbonate concentration...
...0.65M electrolyte■ Solute...Tetraethylammonium tetrafluoroborate salt ((C2H5)4NBF4) Solvent...Propylene carbonate concentration...
...0.65M A capacitor is made by impregnating an electric double layer capacitor constructed as shown in Fig. 1 with electrolytes I and II, respectively, and then applying a constant voltage at 70''C to the initial characteristics of each capacitor, Changes in characteristics after 1000 hours were measured.The results are shown in Table 1.

Table 1 Electrolysis of an electrolyte results in the deposition of reaction products on the electrodes.

This results in gas generation, which increases impedance and causes blistering of the device. From the results in Table 1, the change in characteristics after 100 hours is smaller for electrolytic solution I. In other words, it has become clear that properties are improved by using tetrabutylammonium salt.

As described above, according to this example, by changing the cation of the quaternary ammonium salt from tetraethylammonium ion to tetrabutylammonium ion, the electrochemical stability of the solute is increased, gas generation is suppressed, and the electric double layer capacitor characteristics and reliability can be improved.

In the examples, propylene carbonate was used as the solvent, but it goes without saying that γ-butyrolactone, 1,3-dioxolane, or a mixed solvent thereof may be used.

Effects of the Invention As described above, the present invention utilizes tetrafluoroborate of tetrabutylammonium as an electrolyte for an electric double layer capacitor to propylene carbonate, γ-butyrolactone, 1,3-
By dissolving the composition in an organic solvent such as dioxolane, it is possible to suppress gas generation during use at high temperatures and continuous charging and discharging, and improve the characteristics and reliability of electric double layer capacitors. There is something big.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electric double layer capacitor according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a general electric double layer capacitor. 1... Polarizable electrode, 2... Conductive electrode.

Claims (1)

[Claims] A conductive electrode is formed on one side of a polarizable electrode made of carbon fiber or activated carbon fiber, and a counter electrode is arranged on the other side of the polarizable electrode to form an element. An electric double layer capacitor characterized in that it is impregnated with an electrolytic solution in which borate is dissolved in an organic solvent such as propylene carbonate, γ-butyrolactone, or 1,3-dioxolane.