JPH01214105A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To improve the saleability of a unit cell, to prevent electrolyte from leaking, moisture from invasion from the outside even if an electric double layer capacitor is used under a high temperature condition for a long period of time and to reduce the deterioration of its capacity by forming a layer made of thermoplastic polyimide resin at least at one of the parts in contact with the metal cap of the capacitor and the insulating packing of a metal case. CONSTITUTION:Polar electrodes 1, 2 are disposed through a porous separator 6 in the unit capacitor 13 of an electric double layer capacitor. Thermoplastic polyimide resin layers 11, 12 made of thermoplastic polyimide resin are formed at least at one of parts in contact with the metal case 4 of the capacitor 13 and the insulating packing 7 of a metal cap 3. Then, the saleability of the capacitor 13 is improved, it prevents inner electrolyte from leaking and moisture from invasion from the outside, and reduces the deterioration of its capacity under a high temperature condition for a long period use.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric double layer capacitor, and particularly to an electric double layer capacitor with improved sealing properties.

(Prior art) Electric double layer capacitors are based on the principle of accumulating electric charge in the electric double layer formed at the interface between a polarizable electrode with a large surface area made of activated carbon or the like and an electrolyte. It is attracting attention because it has a much larger capacitance than a capacitor.

FIG. 2 shows the general structure of a coin-shaped unit cell of a conventional electric double layer capacitor.

In FIG. 2, a polarizable electrode 1 mainly composed of activated carbon powder or activated carbon fiber is fixed to a metal cap 3 by a conductive adhesive layer 5, and a conductive adhesive layer 5'
A polarizable electrode 2, which is fixed to a metal case 4 by means of a porous separator 6, is placed opposite to a polarizable electrode 1' with a porous separator 6 in between. After the polarizable electrode 1.2 and the porous separator 6 are sufficiently impregnated with an electrolytic solution in which a solute such as tetraalkylphosphonium tetrafluoroborate is dissolved in a solvent such as propylene carbonate or γ-butyrolactone, the polypropylene The peripheral ends of the metal cap 3 and the metal case 4 are caulked and sealed via the insulating packing 7 to obtain the unit cell 8. In order to improve the sealing performance of such a unit cell 8, there is one in which a sealant is applied to the outer peripheral brim of the metal cap 3 and the inner side of the metal case 4 to form sealants N9 and 10. As such sealants, blown asphalt is the most common, but other materials such as silicone resins, polybutadiene, polyisobutylene, epoxy resins, and polyolefin resins are also used singly or in combination.

(Problems to be Solved by the Invention) However, in conventional coin-shaped unit cells using such a sealant, when used for a long period of time, the sealant gradually dissolves into the electrolyte or Due to swelling, the sealing properties of the cell are impaired, and phenomena such as leakage of electrolyte to the outside of the cell or the generation of decomposed gas due to the intrusion of moisture from the outside into the cell are observed, and the internal resistance of the capacitor decreases. There is a problem in that this leads to an increase in capacity and a deterioration in capacity, and this deterioration in performance is particularly noticeable in high-temperature regions.

(Means for Solving the Problems) As a result of various studies in order to solve these problems, the present inventor has found that by using a sealant made of thermoplastic polyimide resin, electrolysis occurs even when used for a long period of time under high temperature conditions. We have discovered an electric double layer capacitor that prevents liquid leakage and moisture intrusion from the outside, and has minimal performance deterioration in internal resistance, capacity, etc.

Thus, the present invention provides an electric double layer capacitor that houses a pair of polarizable electrodes impregnated with a non-aqueous electrolyte and is caulked and sealed with an insulating packing interposed between a metal cap and a metal case. The present invention provides an electric double layer capacitor characterized in that a layer made of thermoplastic polyimide resin is formed on at least one of the metal cap and the portion of the metal case that comes into contact with the insulating packing.

In the present invention, the thermoplastic polyimide resin used as the sealant is shown in the structural formula (2), and has a low glass transition temperature, excellent thermoplasticity, and exhibits excellent adhesive strength to metals. It has the advantage of not being attacked by solvents.

To form a layer made of this thermoplastic polyimide resin on a predetermined portion of the metal cap and metal case, the structural formula I
A polyamic acid solution shown in 1 is applied to the predetermined portion, air-dried, and then heated to 180° C. or higher. As a result, a dehydration reaction of polyamic acid occurs to generate polyimide, and at the same time, a uniform thermoplastic polyimide resin layer is formed that is firmly adhered to predetermined portions of the metal cap and metal case.

The solvent for polyamic acid is not particularly limited, but dimethylacetamide, diglyme, etc. are preferably used. The concentration of polyamic acid is preferably in the range of 5 to 30% by weight in terms of forming a uniform film and workability, and the thickness of the thermoplastic polyimide resin layer is in the range of 10 to 100 μm in order to obtain stable sealing performance. is preferred.

The material of the polarizable electrode used in the present invention is not particularly limited, but it is preferable to use activated carbon powder or activated carbon fiber that is electrochemically inert to the electrolyte and has a large specific surface area.

In particular, activated carbon powder contains polytetrafluoroethylene (PT).
The electrode is made by adding a binder such as FE), roll-forming it into a sheet, and subjecting it to stretching treatment as necessary.
It is preferably used 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 electric double layer capacitors, such as a separator made of polypropylene fiber nonwoven fabric or glass fiber mixed paper nonwoven fabric, can be used.

The electrolytic solution used in the present invention is not particularly limited, as thermoplastic polyimide resin has excellent solvent resistance. (electrolyte) dissolved in a polar organic solvent is used as appropriate.Solvents for the electrolyte include propylene carbonate, butylene carbonate, T-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane, etc. is preferably used.

Examples of solutes in the electrolytic solution include alkali metal salts such as perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, perfluoroalkylsulfonic acid, tetraalkylammonium salts, and tetraalkylphosphonium salts. of solute in the above solvent at a concentration of 0.1 to 3.01 aol/
f Preferably, an electrolytic solution dissolved at a concentration of 0.5 to 1.5 mol/42 is preferably used.

The conductive adhesive used in the present invention is preferably a high-purity graphite-based adhesive containing almost no binder, but graphite- or carbon black-based conductive adhesives containing a resin binder such as phenol or an inorganic binder such as water glass are preferable. Agents can also be used.

(Examples and Comparative Examples) Examples and comparative examples of the present invention will be specifically described below based on the drawings.

Embodiment FIG. 1 is a diagram showing an embodiment of a coin type electric double layer capacitor according to the present invention. The same members as those in the prior art will be described with the same reference numerals as in FIG. 2.

First, on the inside of the metal case 4 made of 5US304, -I
Polyamic acid represented by formula I (LARC-T manufactured by Mitsui Toatsu Co., Ltd.)
A thermoplastic polyimide resin layer 11 was formed by injecting 20μ2 of an N,N'-dimethylacetamide solution containing 5% by weight of PI precursor, spin casting, air drying, and heating at 200°C for 3 hours. . Then 5U
The outer periphery of the metal cap 3 made of S447J7 was immersed in the polyamic acid solution while rotating to adhere polyamic acid, and then air-dried and heat-dried at 200° C. for 3 hours to remove the outer periphery of the metal cap 3. A thermoplastic polyimide resin layer 12 was formed on the brim.

Next, a mixture consisting of 80% by weight of activated carbon powder, 10% by weight of carbon black, and 10% by weight of polytetrafluoroethylene was wet-kneaded to form a sheet-like material, dried, and punched into a disk shape to form a polarizable electrode. 1 and 2 (diameter 1
2 m, thickness 0.65 m).

This polarizable electrode 1.2 is attached to graphite-based conductive adhesive N5.5.
' and adhered to the metal cap 3 and metal case 4, respectively, and vacuum-dried at 200°C. Next, a metal cap 3 is placed so that the polarizable electrodes 1.2 face each other with a porous separator 6 made of a polypropylene fiber nonwoven fabric interposed therebetween.
and the metal case 4, and after injecting the electrolytic solution and sufficiently impregnating the polarizable electrode 1.2 and the porous separator 6, the metal cap 3 and the metal case 4 are filled with an insulating packing 7 made of polypropylene. The peripheral end portion was caulked and sealed to obtain a unit cell 13. The electrolyte is tetraethylphosphonium tetrafluoroboret) ((cz H3
)4 PBF4 ) to propylene carbonate at 0.6
A solution dissolved at a concentration of mol/A was used.

The unit cell 13 (diameter 12
mm, thickness 0.65 mm), a sealing property test and a voltage application test were conducted. For the sealing test, unit cell 1
00 units were prepared, left in a vacuum atmosphere at 85°C for 100 hours, and the weight loss (mg) of the unit cells was measured. The voltage application test was conducted by applying a voltage of 28 V to the unit cell at 85° C. for 1000 hours, and measuring the increase in internal resistance of the capacitor, rate of change in capacity (%), and weight loss (mg).

Comparative Example A unit cell 8 was prepared and tested in the same manner as in the previous example except that a 10% by weight toluene solution of blown asphalt was used as the sealant.

The results of the sealing property test and voltage application test for Examples and Comparative Examples are shown in Tables 1 and 2, respectively.

As is clear from Table 1, the unit cell according to the present invention has extremely low weight loss due to volatilization of the electrolyte solvent under vacuum and high temperature, and is significantly superior in sealing performance, compared to the conventional unit cell. In addition, as shown in Table 2, even in voltage application tests under high temperatures, the weight loss is small and the sealing properties are excellent, so the decrease in capacity and increase in internal resistance are significantly improved compared to conventional products. has been done.

In the above embodiments, the thermoplastic polyimide resin layers 11 and 12 as a sealant were formed on both the metal cap 3 and the metal case 4, but the thermoplastic polyimide resin layer Even if it is formed on either one of the cases 4, the same effect can be obtained.

(This page, hereafter in the margin) Table 1 Table 2 (Effects of the invention) As explained above, according to the present invention, the sealing performance of the unit cell is significantly improved, even when used for a long period of time under high temperature conditions. Since there is no electrolyte leakage or moisture intrusion from the outside, it is possible to obtain an electric double layer capacitor with excellent long-term reliability and less performance deterioration such as increased internal resistance or capacity deterioration.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing an embodiment of an electric double layer capacitor according to the present invention, and FIG. 2 is a partial sectional view showing a conventional electric double layer capacitor. 1.2...Polarizable electrode, 3...Metal cap, 4...Metal case, 5.5'...Conductive adhesive layer, 6. ... Porous separator, 7 ... Insulating packing, 11.12 ... Thermoplastic polyimide resin layer, 1
3...Unit cell.

Claims (1)

[Claims] In an electric double layer capacitor that houses a pair of polarizable electrodes impregnated with a non-aqueous electrolyte and is caulked and sealed with an insulating packing interposed between a metal cap and a metal case, the metal cap and the metal An electric double layer capacitor characterized in that a layer made of thermoplastic polyimide resin is formed on at least one of the parts of the case that come into contact with the insulating packing.