JPH0666232B2 - Electric double layer capacitor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric double layer capacitor used as an element for energy storage.

2. Description of the Related Art In recent years, electric double layer capacitors have been attracting attention as an element for backing up a memory in the event of a momentary power failure, along with a rapid increase in demand for a semiconductor memory.

Hereinafter, the conventional electric double layer capacitor as described above will be described with reference to the drawings.

FIG. 3 schematically shows a general electric double layer capacitor. In FIG. 3, 1 is a pair of polarizable electrodes made of carbon fiber or activated carbon fiber, and 2 is a conductive electrode. Three
Is a separator that maintains the insulation between the pair of polarizable electrodes 1 and also serves to hold the electrolytic solution. This polarizable electrode 1
An electrolytic solution in which a tetraethylammonium salt is dissolved in an organic solvent composed of one or more selected from propylene carbonate, γ-butyrolactone and 1,3-dioxolane is impregnated between the electrodes composed of the conductive electrode 2 and the conductive electrode 2. Then, the separator 3 is interposed and wound or laminated.

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

In general, it is said that layers having different properties are formed when the interface between the electrode and the solution constituting the electrode system is viewed microscopically. When two different phases come into contact with each other, positive and negative charges are relatively distributed at an interface over a very short distance. The layer in which charges are distributed near the interface is called an electric double layer. The electric double layer capacitor has a structure in which a voltage is applied to the electric double layer to accumulate charges.

Problems to be Solved by the Invention Here, the voltage that can be applied to the electric double layer capacitor differs depending on the system of the electrolytic solution used. Generally, when an aqueous electrolyte solution is used, the voltage that can be applied to the device is limited by the decomposition voltage of water, and the value is about 2V or less. On the other hand, when the organic electrolytic solution is used, the voltage that can be applied is about 3 V, which is considerably superior to the water-soluble system. However, practically 2.5V
If it is not used at the following applied voltage, electrolysis of the electrolytic solution, in particular, the solvent is reduced to cause a polymerization reaction or gas generation, which causes problems such as liquid leakage, increase in direct current resistance and decrease in capacity.

In view of the above-mentioned drawbacks, the present invention provides an electric double layer capacitor in which the characteristics do not deteriorate even when a voltage higher than 2.5 V is applied.

Means for Solving the Problems In order to achieve the above-mentioned object, the electric double layer capacitor of the present invention has a pair of polarizable electrodes made of carbon fiber or activated carbon fiber having a conductive electrode formed on one surface thereof, and tetraethylammonium tetrachloride. It is constituted by impregnating an electrolytic solution in which tetrafluoroborate or hexafluorophosphate is dissolved in 3-methyl-1,3-oxazolidin-2-one.

Action To increase the withstand voltage of the electric double layer condensor,
It is necessary that the oxidation / reduction limit potential of the electrolytic solution is sufficiently wide. FIG. 2 shows tetraethylammonium tetrafluoride borate as the electrolyte, propylene carbonate and 3-methyl-
15 wt% of 1,3-oxazolidin-2-one was dissolved in each solvent, and its current-potential curve was measured using graphite electrolysis. Oxidation limits the potential of the second figure discharge tetrafluoride borate ions of the electrolyte _{^{(BF 4 - → BF 4 ·}} +
e ^-) is due, presumably due to decomposition of the solvent because of its ramps up on one of the reduction limit potential different potential.

Since the reduction limit potential of FIG. 2 is more negative with 3-methyl-1,3-oxazolidin-2-one than with propylene carbonate, the decomposition voltage of the electrolytic solution is 3-methyl-1,3 It can be seen that the use of oxazolidine is broader.

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples.

Example 1 As shown in FIG. 1, an aluminum layer having a thickness of 5 μm was formed on the surface of a pair of polarizable electrodes 1 made of a cloth made of phenol-based activated carbon fiber (thickness 0.5 mm, specific surface area 2000 m ² / gr). Is plasma sprayed to form the conductive electrode 2. This two-layer structure is punched out into a disc having a diameter of 2 cm to obtain an electrode body.
On this electrode body, 3-methyl-1,3 oxazolidine-2
-ON was impregnated with an electrolyte solution having a composition in which 10 wt% of tetraethylammonium hexafluorophosphate (Et ₄ NPF ₆ ) was dissolved, and then a separator 3 was interposed between them to superimpose them on each other. It is sandwiched by 4, and the gasket 5 is arranged at the open end of the case 4, and sealing is performed by caulking. Table 1 shows the results of measuring the characteristic change after 1000 hours by applying a constant voltage of 2.8 V to the electric double layer capacitor according to the present invention in a constant temperature bath of 85 ° C.

Similarly, in Table 1, for comparison, the same measurement was performed for an electric double layer capacitor in which a conventional electrolytic solution was impregnated with propylene carbonate to which hexafluorophosphate of tetraethylammonium was added and dissolved, and the results were shown. Indicates.

Example 2 The electrolytic solution part of Example 1 was changed to 3-methyl-1,3.
An electrolyte solution was prepared by dissolving 10 wt% of tetraethylborate tetrafluoride borate (Et ₄ NBF ₄ ) in -oxazolidin-2-one.

The electrolyte used for comparison was tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) 1 in propylene carbonate.
The same test and measurement as in Example 1 were carried out using an electrolyte solution prepared by dissolving 0 wt%. The results are shown in Table 1.

As can be seen from the results of Examples 1 and 2, in both cases, 1
The change in characteristics after 000 hours is much smaller in the product of the present invention than in the conventional product. In other words, the decomposition voltage of the electrolytic solution became wider, so that the electrolytic solution did not react even when 2.8 V was applied.

As described above, according to this example, the withstand voltage of the electric double capacitor can be increased by changing the solvent of the electrolytic solution from propylene carbonate to 3-methyl-1,3-oxazolidin-2-one. it can.

As described above, according to the present invention, tetraethylammonium tetrafluoroborate or hexafluorophosphate is converted into 3-methyl-1,3-oxazolidin-2-one as an electrolytic solution of an electric double layer capacitor. By using a dissolved composition, an electric double layer capacitor having a high withstand voltage can be obtained, and its practical value is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view of an electric double layer capacitor in one embodiment of the present invention, and FIG. 2 is a tetramethylammonium tetrafluoride borate containing 3-methyl-1,3-oxazolidine-2.
-On and current-potential curve diagram of electrolyte solution dissolved in propylene carbonate, Fig. 3 is a schematic diagram of a general electric double layer capacitor. 1 ... Polarizable electrode, 2 ... Conductive electrode.

Claims (1)

[Claims] 1. A pair of polarizable electrodes composed of carbon fibers or activated carbon fibers each having a conductive electrode formed on one side thereof, and tetraethylammonium tetrafluoride borate or hexafluorophosphate as 3-methyl-1. , An electric double layer capacitor constituted by impregnating an electrolytic solution dissolved in 3-oxazolidin-2-one.