Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
1999-02-12
2001-07-17
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S517000, C361S504000, C361S527000, C361S525000
Reexamination Certificate
active
06262879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrochemical device for use with various electronic devices. Particularly, the present invention relates to an electrochemical device in which compositions for use in an electrolytic solution and a seal are improved.
2. Description of the Related Art
Known electrochemical devices which require an electrolytic solution in order to drive such devices include an aluminum electrolytic capacitor, an electric double layer capacitor, a lithium battery, a lithium ion battery and an electrochromic device.
Referring to
FIG. 2
, a conventional aluminum electrolytic capacitor
60
will now be described as an exemplary electrochemical device. The aluminum electro-lytic capacitor
60
includes: a capacitor element
51
as a main body; an electrolytic solution (not shown) which is impregnated in the capacitor element
51
; a tubular metallic case
56
made of aluminum which has a bottom surface and accommodates the capacitor element
51
; a seal
57
for sealing an opening of the case
56
; and a cover
58
for covering the case
56
.
The capacitor element
51
is formed by rolling up an anode foil
52
, a cathode foil
53
and a separator
54
disposed between these foils. A pair of lead wires
55
a and
55
b
are coupled to the anode foil
52
and the cathode foil
53
, respectively. The lead wires
55
a
and
55
b
each include a rod-like terminal section and a solderable lead section for external connection. The terminal section includes a flat surface which is in contact with the anode foil
52
or the cathode foil
53
.
An electrolytic solution used in such an aluminum electrolytic capacitor includes one which is obtained by dissolving an electrolyte such as an organic acid, an inorganic acid and salts thereof in a solvent such as &ggr;-butyrolactone or N,N-dimethylformamide. For example, those using a quaternary ammonium salt of a maleic acid or a citraconic acid (Japanese Patent Publication for Opposition No. 3-6646) and those using a quaternary ammonium salt of an aromatic carboxylic acid (Japanese Patent Publication for Opposition No. 3-8092) are known in the art.
As the seal material, an ethylene propylene copolymer and a butyl rubber, which are vulcanized with sulfur, are used. Known seal materials with improved heat stability include a butyl rubber which is vulcanized with a peroxide (Japanese Laid-open Publication No. 62-276819).
As another exemplary electrochemical device, a conventional electric double layer capacitor will now be described. The electric double layer capacitor has a structure which is similar to that of the aluminum electrolytic capacitor illustrated in FIG.
2
. An electrolytic solution used in such an electric double layer capacitor includes one which is obtained by dissolving an electrolyte such as an inorganic acid salt in an organic solvent such as propylene carbonate. For example, as an inorganic acid salt, a quaternary ammonium salt of perchloric acid or tetrafluoroboric acid are known in the art.
However, in such a conventional electrochemical device including the above aluminum electrolytic capacitor and the electric double layer capacitor, when a voltage, particularly a reverse voltage, is applied to the electrochemical device, an excessive amount of hydroxide ions may be generated by the electrolysis of the electrolytic solution. When such an electrochemical device is used for a long time under high temperature conditions, particularly, high temperature and high humidity conditions, the electrolytic solution often leaks through the seal. This leakage is due to an increase in the internal pressure of the electrochemical device and deterioration of the seal by the alkalinity of hydroxide ions.
In order to address such leakage problems, a seal made of a butyl rubber obtained by vulcanization with a peroxide, vulcanization with a resin, or the like, has been proposed. Such a seal is generally more resistant to the deterioration by alkalis. The leakage of the electrolytic solution due to the excessive hydroxide ions is particularly suppressed when such a seal is used in combination with an electrolytic solution containing, as an electrolyte, a quaternary salt of a compound having an alkyl-substituted amidine group (see WO 95/15572).
However, such a combination is still insufficient for eliminating leakage during long-term use of an electrochemical device under high temperature conditions, particularly, high temperature and high humidity conditions. Thus, it is desired to obtain seals having more reliable sealing properties.
SUMMARY OF THE INVENTION
According to one aspect of this invention, an electrochemical device includes: a main body formed by rolling up an anode foil, a cathode foil and a separator disposed therebetween, each of the anode foil and the cathode foil having a lead wire connected thereto, wherein the main body is impregnated with an electrolytic solution; a tubular case having a bottom surface for accommodating the main body; and a seal for sealing an opening of the tubular case, which includes a through hole for the lead wire to pass therethrough. The electrolytic solution contains about 5 to about 100 parts by weight of a quaternary salt of a compound having an alkyl-substituted amidine group as an electrolyte with respect to 100 parts by weight of an organic solvent containing at least one of &ggr;-butyrolactone and propylene carbonate. The seal is an elastic body containing a butyl rubber polymer which is a copolymer of isobutylene, isoprene and divinylbenzene, and a peroxide as a vulcanizing agent. At least a portion of the seal has a hardness of about 65 International Rubber Hardness Degrees.
In accordance with the present invention, the electrolytic solution contains an organic solvent containing &ggr;-butyrolactone and/or propylene carbonate and a quaternary salt of a compound having an alkyl-substituted amidine group as an electrolyte. This compound is quaternarized (i.e., converted into a quaternary salt) by introducing an alkyl substituent on the amidine group, which has a basic skeleton represented by N—C═N. In such an electrolytic solution, even when hydroxide ions are generated by an electrolytic reaction, such hydroxide ions are quickly consumed in a reaction involving the N—C═N skeleton of the alkyl-substituted amidine group. Such consumption of the hydroxide ions may be expressed by the following general scheme:
Thus, when a quaternary salt of a compound having an alkyl-substituted amidine group is used as an electrolyte, instead of a quaternary ammonium salt, it is possible to suppress the increase in the internal pressure and the deterioration of the seal by alkalis. As a result, it is possible to improve the sealing property of the electrochemical device.
Moreover, in accordance with the present invention, a butyl rubber vulcanized with a peroxide is used as the seal material. Such a butyl rubber is superior in heat stability and alkali resistance. As compared with seals formed by a butyl rubber vulcanized with sulfur, the sealing force (i.e., rubber elasticity) of the seal of the present invention is less likely to deteriorate even when the electrochemical device is used for an extended period of time under high temperature conditions, particularly, high temperature and high humidity conditions. Thus, a long-term stable sealing property can be obtained. As a result, it is possible to suppress the leakage of an electrolytic solution through the seal due to the increase in the internal pressure and the deterioration of the seal by alkalis.
Furthermore, in accordance with the present invention, at least a portion of the seal has a hardness of about 65 IRHD (“International Rubber Hardness Degrees”, hereinafter referred to simply as “IRHD”) or greater. Therefore, it is possible to maintain a strong sealing force which sufficiently compresses the lead wires passing through the holes provided in the seal. Thus, an even more stable sealing property can be obtained, in addition to the decreased deterioration of the seali
Matsuura Hiroyuki
Nitta Yukihiro
Shiono Katsuji
Tsubaki Yuichiro
Ha Nguyen T
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
Reichard Dean A.
LandOfFree
Electrochemical device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrochemical device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrochemical device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2444423