JPH04293218A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To improve pitting resistance and grain boundary corrosion resistance, and increase the workability to a specified shape, by forming a metal case and a metal lid body of alloy whose main component is iron and which contains specified kinds of metal. CONSTITUTION:A pair of polarizable electrodes 1, 2 impregnated with electrolyte are arranged via a separator 6 impregnated with electrolyte. One polarizable electrode 2 is accommodated so as to electrically contact with a metal case 4, and the other polarizable electrode 1 is accommodated so as to electrically contact with a metal lid body 3. The metal case 4 and the metal lid body 3 are constituted of an alloy whose main component is iron and which contains the following; Ni: 24-38wt.%, Cr: 17-23wt.%, Cu: 2-5wt.%, Mo: 1-4wt.%, Mn: 1-4wt.%, Si: 1wt.% or less, C: 0.07wt.% or less, P: 0.04wt.% or less, and S: 0.03wt.% or less. Thereby pitting resistance, the resistance to grain boundary corrosion and the workability to a specified shape are improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electric double layer capacitors.

0002

2. Description of the Related Art Conventionally, there have been various reports regarding current collectors for extracting electricity from polarizable electrodes in electric double layer capacitors and case materials for housing constituent elements of electric double layer capacitors. (Unexamined Japanese Patent Publication No. 50-44461,
50-44464, 58-206116, and Japanese Unexamined Patent Publication No. 1-246813)

0003

[Problem to be solved by the invention] However, even when these ferrite-based materials are used, corrosion occurs due to anode melting when high voltage charging is performed, and the withstand voltage rating of the capacitor inevitably deteriorates. There was a drawback that the value had to be set low.

[0004] Conventionally, disk-shaped (coin-shaped/button-shaped)
Since the above materials are relatively expensive in capacitors,
Cheap materials with low corrosion resistance have been used only for the metal storage case material used on the positive side during charging, and for the material used on the negative side during charging. For this reason, the capacitor is inevitably polarized, and when it is reverse mounted on a circuit board, there are problems with corrosion of the metal storage case, decomposition of the electrolyte, and the 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.

[0005]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and consists of a pair of polarizable electrodes impregnated with an electrolyte and arranged through a separator impregnated with an electrolyte. , 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 caulked together via a gasket. In an electric double layer capacitor having a structure, the metal case and metal lid are made of Ni.
24-38% by weight Cr 17-23% by weight Cu 2-5% by weight Mo 1-4% by weight Mn 1-4% by weight Si 1% by weight or less C 0.07% by weight or less P
An object of the present invention is to provide an electric double layer capacitor characterized in that it is made of an alloy mainly composed of iron containing 0.04% by weight or less S and 0.03% by weight or less.

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 Ni 28-30% by weight Cr
19-21% by weight Cu 3-
4% by weight Mo 2-3% by weight Mn 2.5-3.5% by weight Si
0.5% by weight or less C
By adopting P of 0.02% by weight or less and S of 0.03% by weight or less, pitting corrosion resistance, intergranular corrosion resistance, and workability into a predetermined shape can be improved.

[0007] The polarizable electrode used in the present invention is not particularly limited, and various conventionally known or well-known ones can be employed. For example, activated carbon powder, carbon black, activated carbon fiber, or the like having a large specific surface area can be preferably used. In particular, electrodes made by adding a binder such as polytetrafluoroethylene (PTFE) to activated carbon powder, roll-forming it into a sheet, and then subjecting it to stretching treatment as necessary, have a high capacity, strength, and strength per unit volume. It is preferably used because it has excellent 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 nonwoven fabric, can be used.

The electrolytic solution used in the present invention is not particularly limited, and may be one commonly used for electric double layer capacitors, such as one in which an electrochemically stable solute (electrolyte) is dissolved in a polar organic solvent. is used as appropriate. As the electrolyte solvent, propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane, etc. are preferably used, for example.

Examples of the electrolyte include alkali metal salts, tetraalkylammonium salts, and tetraalkylphosphonium salts such as perchloric acid, hexafluorophosphoric acid, boron tetrafluoride, and perfluoroalkylsulfonic acid. Solute in the above solvent 0.1-3.0
An electrolytic solution dissolved at a concentration of mol/liter, preferably 0.5 to 1.5 mol/liter 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. For example, methods such as welding a metal net to a metal case and crimping an electrode on it, forming a metal current collecting layer on the electrode by plasma spraying, plating, etc., or bonding with a conductive adhesive are preferably used. Although possible, a method using a conductive adhesive containing carbon is particularly preferred.

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

[0013]

[Examples] Next, the present invention will be specifically explained using Examples and Comparative Examples. A unit cell of a coin-shaped electric double layer capacitor (diameter 20 mm, thickness 2.0 m) as shown in FIG. 1 is common to the examples and comparative examples of the present invention.
m) was produced as follows.

First, activated carbon powder (specific surface area approximately 2,00
0 m2/g) was added with 10% by weight of PTFE and formed into a sheet by wet kneading. The sheet obtained in this way was punched out into a disk shape, and the polarizable electrode 1 (diameter 15 m) was punched out.
m, 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 are interposed between a separator 6 made of a polypropylene fiber nonwoven fabric and made of stainless steel metal made of various compositions. The device is housed in an outer container consisting of a case 3 and a metal case 4 made of stainless steel of various compositions, each bonded by graphite-based conductive adhesive layers 5 and 5'.

0.5 as an electrolyte in the unit cell
Tetraethylphosphonium tetrafluoroborate ((C2H5)4PBF4) at a concentration of moles/liter
After injecting a propylene carbonate solution to sufficiently impregnate the polarizable electrodes 1 and 2 and the separator 6 with this electrolyte,
The ends of the metal cases 3 and 4 were caulked and sealed via the polypropylene packing 7.

Using this unit cell of the electric double layer capacitor, the initial capacitance (F0) and internal resistance of each cell when a voltage of 2.8 V was applied were measured. Capacity (F
) and internal resistance were measured, and the capacity deterioration rate ((F0-F)/F0) was calculated from these measured values and shown in Tables 1 to 3. The internal resistance is measured using the AC two-terminal method (frequency 1k).
Hz).

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

Effects of the Invention As shown in Table 1, the present invention uses highly corrosion-resistant materials, so 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, the conventional problems associated with reverse mounting on a circuit board are eliminated. Therefore, a large ripple effect can be expected in terms of implementation.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of an electric double layer capacitor showing one embodiment of the present invention.

[Explanation of symbols]

1, 2 Polarizable electrode 3 Metal lid body 4 Metal case 5, 5' Conductive adhesive layer 6 Separator 7 Gasket

Claims (3)

[Claims] Claim 1: A pair of polarizable electrodes impregnated with an electrolytic solution are arranged through a separator impregnated with an electrolytic solution, one polarizable electrode is housed in electrical contact with a metal case, and the other polarizable electrode is housed in electrical contact with a metal case. In an electric double layer capacitor having a structure in which the polar electrode is housed in electrical contact with the metal lid, and the metal case and the metal lid are integrally caulked via a gasket, the metal case and the metal lid are made of Ni24~ 38% by weight Cr 17-23% by weight Cu 2-5% by weight Mo 1-4% by weight Mn 1-4% by weight Si 1% by weight or less C 0.07% by weight or less P
An electric double layer capacitor characterized by being made of an iron-based alloy containing 0.04% by weight or less of S 0.03% by weight or less. 2. The electric double layer capacitor according to claim 1, wherein the polarizable electrode is made of carbon powder or carbon fiber. 3. The electric double layer capacitor according to claim 2, wherein the carbon powder is activated carbon and/or carbon black.