JPH01222427A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To reduce the increase in inner resistance as well as the deterioration ratio of capacitance for assuring the long term reliability by a method wherein specific corrosion resistant material is used for a metallic case and a metallic cover body. CONSTITUTION:A metallic case 4 and a metallic cover body 3 are made of an alloy mainly composed of iron containing not exceeding 21-23weight% of Cr, 16-18weight% of Ni, 4-5weight% of Mo, 15-0.45weight% of N, 0.040weight% of C, 1.00weight% of Si, 2.00weight% of Mn, 0.045weight% of P, 0.30weight% of S. Besides, preferable four elements i.e. 21.5-22.8weight% of Cr, 16.5-17.5weight% of Ni, 3.5-4.8weight% of Mo, 0.3-0.47weight% of N positively related to the corrosion resistance are especially important. Furthermore, as for the other elements, not exceeding 0.02weight% of C, 0.35weight% of Si, 1.2weight% of Mn, 0.043weight% of P, 0.028weight% of S are preferable. Through these procedures, the increase in inner resistance as well as the deterioration ratio of capacitance can be reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electric double layer capacitor.

[Prior Art] Various reports have been made regarding current collectors that extract electricity from polarizable electrodes in electric double layer capacitors and case materials that house the constituent elements of electric double layer capacitors. (Unexamined Japanese Patent Publication No. 50-44461, 5G-44484
(No. 58-208118) [Problems to be Solved by the Invention] However, even when these materials are used, when high voltage charging is performed, corrosion occurs due to 7-node melting,
There was a drawback that the rated value of the capacitor's withstand voltage had to be set low.

Conventionally, in the case of disk-shaped (coin-shaped/button-shaped) capacitors as shown in Fig. 1, the above materials are relatively expensive, so they are used only for the metal storage case material used on the Φ side during charging. Cheap materials with low corrosion resistance have been used for the sides. For this reason, capacitors are inevitably polarized, and when mounted reversely on a single circuit board, there are problems with corrosion of the metal storage case, decomposition of the electrolyte, and accompanying leakage of the electrolyte. Furthermore, in order to avoid this, a polarity test is required in the mounting process, which poses the problem of making the process extremely complicated.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a pair of polarizable electrodes impregnated with an electrolytic solution, arranged with a separator impregnated with an electrolytic solution interposed therebetween. One polarizable electrode is housed in electrical contact with the metal case, the other polarizable electrode is housed in electrical contact with the metal lid, and the metal case and metal lid are integrally caulked via a gasket. In the electric double layer capacitor having a structure, the metal case and the metal lid contain 21 to 23% by weight of Cr and Xi.
18-18% by weight, No 4-5% by weight, N 0.
15 to 0.45% by weight, G 0.040% by weight or less,
An electric double layer capacitor characterized by being made of an iron-based alloy containing 1.00% by weight or less of Si, 2.00% by weight or less of Mn, 0.045% by weight or less of P, and 0.030% by weight or less of S. is to provide.

In the present invention, it is important to use an iron-based alloy having the above-mentioned composition for the metal case and metal lid. More preferably, these four elements are 21.5-22.8% by weight of Cr, 18.5-17.5% by weight of former, 3.5-4.8% by weight of No, and 0.3-0.47% by weight of N. It is particularly important because it actively participates in corrosion resistance. Regarding other elements, C0.02% by weight or less, St 0.3
5% by weight or less, Mn 1.2% by weight or less, P 0.04
It is preferably 3% by weight or less, and S 0.028% by weight or less.

The polarizable electrode used in the present invention is not particularly limited, and various conventionally known or publicly known electrodes can be used.8 For example, activated carbon powder, carbon black, activated carbon fibers, etc. with a large specific surface area can be preferably used. be.

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, and those normally used for electric double layer capacitors, that is, those in which an electrochemically stable solute (electrolyte) is dissolved in a polar organic solvent, can be used as appropriate. be done. As the solvent for the electrolytic solution, propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane, etc. are 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. An electrolytic solution containing a solute dissolved in the above-mentioned solvent at a concentration of 0.1 to 3.0 M/Q, preferably 0.5 to 1.5 M/Q is preferably used.

Furthermore, the method of collecting current from the polarizable electrode used in the present invention is not particularly limited, and conventionally well-known methods can be used.8 For example, a metal mesh is welded to a metal case and an electrode is placed on it. Preferred methods include pressure bonding, forming a metal current collecting layer on the electrode by plasma spraying, plating, etc., and bonding with a conductive adhesive. In particular, a method using a conductive adhesive containing carbon is preferred.

The conductive adhesive used in the present invention is preferably a high-purity, high-lead adhesive that does not contain a binder.
A graphite or carbon black-based conductive adhesive containing a resin binder such as phenol or an inorganic binder such as water glass may also be used.

[Example] Next, the present invention will be specifically described using Examples and Comparative Examples.

A coin-shaped electric double layer capacitor unit cell (diameter: 20 cm, thickness: 2.0+u+) as shown in FIG. 1, which is common to the Examples and Comparative Examples of the present invention, was prepared in the following manner. First, activated carbon powder (specific surface area 2,
000m2/g) 10i% of polytetrafluoroethylene was added and formed into a sheet by wet kneading. The thus obtained sheet was punched out into a disk shape to form a polarizable electrode 1 (diameter 15 mm, thickness 0.7 mm), and a polarizable electrode 1 and a polarizable electrode 2 having the same composition and shape as the polarizable electrode 1 were formed. A graphite-based conductive adhesive layer is placed in an outer container consisting of a stainless steel metal case 3 made of various compositions and a stainless steel metal case 4 made of various compositions through a separator 6 made of polypropylene fiber nonwoven fabric. 5 and 5', respectively, and are housed. The unit cell contains tetraethylphosphonium tetrafluoroborate at a concentration of 0.5 mol/Q as an electrolyte (
After injecting a propylene carbonate solution of (C2Hs)4PBFa) to sufficiently impregnate the polarizable electrode 1.2 and separator 6 with this electrolyte, the ends of the metal cases 3 and 4 are I caulked it and sealed it.

Using this electric double layer capacitor unit cell, we measured the initial capacitance (F,) and internal resistance of each cell when a voltage of 2.8V was applied, and then applied a voltage of 2.8V to this cell. 1000 at 70℃ while applying voltage
Also measure the capacity (F) and internal resistance after storage for a time,
The capacity deterioration rate (F, -F)/F,) was calculated from these measured values and shown in Table 1. The internal resistance was measured by the AC two-terminal method (frequency I KHz).

[Effects of the Invention] As shown in Table 1, since the present invention uses highly corrosion-resistant materials, it has excellent long-term reliability with little increase in internal resistance and low capacity deterioration rate. Furthermore, since it can be used without polarity, conventional problems such as reverse mounting on a single circuit board are eliminated. Therefore, a large ripple effect can be expected in terms of implementation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of an electric double layer capacitor showing one embodiment of the present invention. 1.2...Polarizable electrode 3...Metal lid body 4...Metal case 5.5'...
conductive adhesive layer

Claims (3)

[Claims] 1. A pair of polarizable electrodes impregnated with an electrolyte are arranged through a separator impregnated with an electrolyte, one polarizable electrode is housed in electrical contact with a metal case, and the other polarizable electrode is housed in a metal lid. In an electric double layer capacitor that is housed in electrical contact with the human body, and has a structure in which the metal case and the metal lid are integrally caulked via a gasket, the metal case and the metal lid are made of 21 to 23% by weight of Cr and 16 to 16% Ni. 18% by weight,
Mo4-5% by weight, N0.15-0.45% by weight, C0
．． 040% by weight or less, Si1.00% by weight or less, Mn2
．． 00% by weight or less, P0.045% by weight or less, S0.0
An electric double layer capacitor characterized by being made of an alloy mainly containing iron containing 30% by weight or less. 2. 2. The electric double layer capacitor according to claim 1, wherein the polarizable electrode is made of carbon powder or activated carbon fiber. 3. The electric double layer capacitor according to claim 1, wherein the carbon powder is activated carbon and/or carbon black.