JP2764810B2 - Electric double layer capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric double layer capacitor.

[Prior Art] Conventionally, heat-resistant silicone, fluororesin paint, asphalt, and the like have been used as sealants for electric double layer capacitors.

[Problems to be Solved by the Invention] Among these, asphalt is preferable because it is inexpensive and has good sealing properties. When applied to the case, if the conventional method of pressing the polarizable electrode to the case and drying it is adopted, volatile components are absorbed by the activated carbon or activated carbon-based fibers constituting the polarizable electrode, and the predetermined capacity is not expressed, When subjected to a high-temperature load test, it had a disadvantage that it easily deteriorated.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned drawbacks, and an electric double layer capacitor having a structure in which a metal case and a metal lid are integrally caulked via a gasket. A coating layer of asphalt from which volatile components have been removed by heat treatment in advance on the inner wall of the metal case sealing portion is 0.2 to 4 mg / cm ^2.
The present invention provides an electric double layer condenser characterized by being provided.

That is, in the present invention, it is important to apply asphalt thinly to the inner wall of the sealing portion of the metal case within a range that does not lose the sealing property. Asphalt application amount is 0.
2-4 mg / cm ^2, preferably should be 0.5 to 2 mg / cm ^2.

If it deviates from this range, the object of the present invention cannot be achieved, which is inappropriate. In the present invention, asphalt is subjected to heat treatment to remove volatile components in advance. As such a heat treatment, it is effective to perform vacuum heating at 100 to 300 ° C.

The polarizable electrode used in the present invention is not particularly limited, and various well-known or well-known electrodes can be employed. For example, activated carbon powder having a large specific surface area,
Carbon black, activated carbon fiber and the like can be preferably used.

In particular, polytetrafluoroethylene (PT
FE) and other binders, roll-molded into sheets, and then stretched as necessary.
It is preferable because it has excellent capacity per unit volume, strength and long-term reliability.

As the separator used in the present invention, a usual separator for an electric double layer capacitor, for example, a separator made of a polypropylene fiber nonwoven fabric or a glass fiber mixed nonwoven fabric can be used.

The electrolytic solution used in the present invention is not particularly limited, and those usually used for electric double layer capacitors, that is, those obtained by dissolving an electrochemically stable solute (electrolyte) in a polar organic solvent are appropriately used. Is done. As the solvent for the electrolytic solution, propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane and the like are suitably used.

Examples of the solute of the electrolytic solution include alkali metal salts such as perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, and perfluoroalkylsulfonic acid, tetraalkylammonium salts, and tetraalkylphosphonium salts.
These solutes are added to the solvent in the range of 0.1 to 3.0 M /, preferably
An electrolyte dissolved at a concentration of 0.5 to 1.5 M / is preferably used.

The method for collecting electricity from the polarizable electrode used in the present invention is not particularly limited, and a conventionally well-known method can be used. For example, welding a metal net to a metal case and crimping the electrode on it, or plasma spraying on the electrode,
A method of forming a metal current collecting layer by plating or the like and a method of bonding with a conductive adhesive can be preferably used. In particular, a method using a conductive adhesive containing carbonaceous material is preferable.

As the conductive adhesive used in the present invention, a high-purity graphite-based material containing almost no binder is preferable, but a graphite or carbon black-based conductive material containing a resin binder such as phenol or an inorganic binder such as water glass is preferred. An adhesive or the like can also be used.

[Example] The first example is common to the example of the present invention and the comparative example.
A unit cell (diameter 20 mm, thickness 2.0 mm) of a coin-type electric double layer capacitor as shown in the figure was produced as follows. First, asphalt to be applied to the inner wall of case 5 was treated as follows. 250 ℃ of asphalt
And dried under vacuum to remove volatile components. This asphalt
10 g was dissolved in 100 ml of toluene to prepare a toluene solution of asphalt. Put this liquid in Case 5 (18.5 mm inside diameter, height
(2.4 mm) on the inner wall over a height of 2.4 mm and dried at 70 ° C. In this case, the application area was 1.39 cm ² , and the case weight was increased by 4.0 mg, which means that application was performed at 2.9 mg / cm ² . Next, the sheet electrode will be described. First, 10% by weight of polytetrafluoroethylene was added to activated carbon powder (specific surface area: about 2000 m ² / g), and a sheet was formed by wet kneading. The sheet thus obtained is punched into a disk to form a polarizable electrode 1 (diameter 15 mm, thickness 0.7 mm), and a polarizable electrode 2 having the same composition and shape as this is a separator 3 made of a nonwoven fabric. Through a metal lid 4 and a metal case 5 to which asphalt was previously applied, and bonded to each other with a graphite-based conductive adhesive 7, 7 '. The metal cover 4 and the metal case 5 integrated with the polarizable electrode were placed in a vacuum drying container, and the water in the polarizable electrode was removed at 200 ° C. Next, this vacuum drying container is carried into a dry box in which the dew point is kept constant, and a propylene carbonate solution of tetraethylphosphonium tetrafluoroborate (Et ₄ PBF ₄ ) having a concentration of 0.5 mol / is injected as an electrolyte. After the electrolytic solution was sufficiently impregnated in the polarizable electrodes 1 and 2 and the separator 3, the ends of the metal case 5 and the metal lid 4 were caulked via a polypropylene gasket 6 and sealed.

Using the unit cell of this electric double layer capacitor,
After measuring the initial capacity (F ₀ ) and the internal resistance when a voltage of 2.8 V was applied to each cell, and subsequently storing the cell at 70 ° C. for 1000 hours while applying a voltage of 2.8 V to this cell, The capacity (F) and the internal resistance were measured, and the capacity deterioration rate ((F ₀ −F) / F ₀ ) was calculated from these measured values, and the results are shown in Table 1. Measurement of internal resistance, AC two-terminal method (frequency 1kHz)
by. Further, the weight change of the unit cell after 1000 hours was also measured.

 Table 1 shows the results.

<Example 2> 0.7 mg / of asphalt heat-treated on the inner wall of the metal case
Using the case applied to cm ² , a unit cell was assembled and sealed in the same manner as in Example 1. Thereafter, the same measurement as in Example 1 was attempted.

<Example 3> Asphalt heat-treated on the inner wall of the metal case was 3.8 mg /
Using the case applied to cm ² , a unit cell was assembled and sealed in the same manner as in Example 1. Thereafter, the same measurement as in Example 1 was attempted.

<Comparative Example 1> Heat-treated asphalt was 8 mg / cm on the inner wall of the metal case.
^{Using the two} coated cases, a unit cell was assembled and sealed in the same manner as in Example 1. Thereafter, the same measurement as in Example 1 was attempted.

<Comparative Example 2> 10 g of unheated asphalt was dissolved in 100 ml of toluene, and the asphalt was applied to the inner wall of the case using this solution.
It was applied to 3.0 mg / cm ² . Using this metal case, a unit cell was assembled and sealed in the same manner as in Example 1. Thereafter, the same measurement as in Example 1 was attempted.

<Comparative Example 3> A unit cell was assembled and sealed in the same manner as in Example 1 using a metal case to which asphalt was not applied. Thereafter, the same measurement as in Example 1 was attempted.

[Brief description of the drawings]

FIG. 1 shows the structure of a unit cell according to an example of the present invention and a comparative example. 1,2: Polarizable electrode 3: Separator 4: Lid 5: Case 6: Gasket 7.7 ': Adhesive

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroshi Ariga 1-17-14 Katakura-cho, Kanagawa-ku, Yokohama-shi, Kanagawa-ken (56) References JP-A-62-200714 (JP, A) JP-A-63-190321 ( JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01G 9/10

Claims (2)

(57) [Claims] In an electric double layer capacitor having a structure in which a metal case and a metal lid are integrally caulked via a gasket, asphalt in which a volatile component has been removed by heat-treating an inner wall of a sealing portion of the metal case in advance. 0.2 coating layer
Electric double layer capacitor, characterized in that 4 mg / cm ² is provided. 2. The electric double layer capacitor according to claim 1, wherein the heat treatment condition of the asphalt is a vacuum heating at 100 to 300 ° C.