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 Figure 2, a conventional aluminum electrolytic
capacitor 60 will now be described as an exemplary electrochemical device. The aluminum
electrolytic 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 55a and 55b are coupled to the anode foil 52 and the cathode 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 an
alkylphenol formalin resin (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 Figure 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 an alkylphenol formalin resin,
vulcanization with a resin, or the like, has been proposed (see for example JP-A-8321441).
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 is defined by the features of claim 1. It 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
and isoprene, and an alkylphenol formalin resin as a vulcanizing agent. At least
a portion of the seal has a hardness of about 75 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 an alkylphenol formalin resin 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 75 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 sealing force owing to the use of the butyl rubber vulcanized with an alkylphenol
formalin resin. As a result, it is possible to further suppress leakage of an electrolytic
solution through the seal.
Due to the above-described effects of the present invention,
it is possible to reduce the influence of the electrolytic reaction of the electrolytic
solution in the electrochemical device, while maintaining a good sealing property
under high temperature conditions, particularly, high temperature and high humidity
conditions.
In one preferred embodiment of the invention, the quaternary
salt is selected from the group consisting of an alicyclic amidine compound, an
imidazole compound and a benzimidazole compound, which are substituted with one
or more alkyl or arylalkyl groups and quaternarized.
In such a compound, a ring-opening decomposition of the
alkyl-substituted amidine group with hydroxide ions proceeds at a relatively high
reaction rate. Therefore, when used as an electrolyte, the compound quickly consumes
the hydroxide ions generated by the electrolytic reaction in the electrolytic solution.
As a result, it is possible to further improve the sealing property of the electrochemical
device for preventing leakage of an electrolytic solution.
In one preferred embodiment of the invention, the quaternary
salt is selected from the group consisting of 8-methyl-1,8-diazabicyclo[5,4,0]undec-7-enium,
5-methyl-1,5-diazabicyclo[4,3,0]non-5-enium, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium,
1,2-dimethyl-3-ethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium,
1,3-dimethyl-2-(1'-ethylpentyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium,
1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium
and 1,3-dimethylbenzimidazolium.
When such a compound is used as an electrolyte, the conductivity
of the electrolytic solution is improved. Therefore, it is possible to provide an
electrochemical device having a low impedance, while preventing leakage of the electrolytic
solution even under high temperature conditions, particularly, high temperature
and high humidity conditions.
Thus, the invention described herein makes possible the
advantages of: (1) providing an electrochemical device with reduced influence of
an increase in the internal pressure and deterioration of a seal by alkalis due
to electrolysis of an electrolytic solution; and (2) providing an electrochemical
device with improved stability of the seal under high temperature conditions, particularly,
high temperature and high humidity conditions, whereby leakage of an electrolytic
solution is effectively prevented.
These and other advantages of the present invention will
become apparent to those skilled in the art upon reading and understanding the following
detailed description with reference to the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
- Figure 1 is a partially cutaway view illustrating an electrochemical device
according to one embodiment of the present invention; and
- Figure 2 is a partially cutaway view illustrating a conventional electrochemical
device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now
be described.
Figure 1 is a partially cutaway view illustrating an electrochemical
device 10 according to one embodiment of the present invention. The structure of
the electrochemical device 10 may be substantially the same as that of the conventional
electrochemical device (Figure 2). Referring to Figure 1, the electrochemical device
10 includes: a capacitor element 1 as a main body; an electrolytic solution (not
shown) which is impregnated in the capacitor element 1; a tubular metallic case
6 made of aluminum, which has a bottom surface and accommodates the capacitor element
1; a seal 7 for sealing an opening of the case 6; and a cover 8 for covering the
case 6.
The capacitor element 1 is formed by rolling up an anode
foil 2, a cathode foil 3 and a separator 4 disposed between these foils. A pair
of lead wires 5a and 5b are coupled to the anode foil 2 and the cathode foil 3,
respectively. The lead wires 5a and 5b 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 2 or the cathode foil 3.
An electrolytic solution used in the aluminum electrolytic
capacitor of the present invention includes an organic solvent containing &ggr;-butyrolactone
and/or propylene carbonate. Preferably, the electrolytic solution contains, as a
main solvent, &ggr;-butyrolactone and/or propylene carbonate because these solvents
are electrochemically stable.
Any other suitable organic solvent which is compatible
with &ggr;-butyrolactone and/or propylene carbonate can be mixed as a sub-solvent
in order to improve the low temperature characteristics of the electrochemical device
and to improve the discharge voltage.
A sub-solvent which can be preferably used in the present
invention includes water, polyhydric alcohols (e.g., ethylene glycol, propylene
glycol, diethylene glycol, 1,4-butanediol, glycerin, and polyoxyalkylene polyol),
lactones other than &ggr;-butyrolactone (e.g., &ggr;-valerolactone, &dgr;-valerolactone,
3-methyl-1,3-oxazolidin-2-one, and 3-ethyl-1,3-oxazolidin-2-one), amides (e.g.,
N-methylformamide, N,N-dimethylformamide, and N-methylacetamide), ethers (e.g.,
methylal, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, and 1,2-diethoxyethane),
nitryls (e.g., acetonitrile, and 3-methoxypropionitril-e), furans (e.g., 2,5-dimethoxytetrahydrofuran),
2-imidazolidinones (e.g., 1,3-dimethyl-2-imidazolidinone), or carbonate solvents
other than a propylene carbonate (e.g., ethylene carbonate).
A single sub-solvent can be used alone, or two or more
sub-solvents can be used in combination. Preferably, with respect to 100 parts by
weight of &ggr;-butyrolactone and/or propylene carbonate, about 0 to about 40
parts by weight of sub-solvent is used. An excessive amount of sub-solvent is likely
to reduce the electrochemical stability of the electrolytic solution. The reduced
stability may promote the increase in the internal pressure of the electrochemical
device when a voltage is applied, resulting in less satisfactory performance of
the device.
The electrolytic solution used in the electrochemical device
of the present invention contains a quaternary salt of a compound having an alkyl-substituted
amidine group as an electrolyte. The quaternary salt is preferably an electrochemically
stable compound which includes an organic carboxylic acid salt or an inorganic acid
salt. Preferred organic carboxylic acids include maleic acid, phthalic acid, benzoic
acid and adipic acid. Preferred inorganic acids include perchloric acid, tetrafluoroboric
acid, hexafluorophosphoric acid and fluoromethanesulfonic acid. The use of such
organic carboxylic acid salts and/or inorganic acid salts as an electrolyte is preferable
because it reduces the amount of gas generated by the hydroxide ions produced by
an applied voltage. The reduced gas generation suppresses the increase in the internal
pressure of the electrochemical device.
More preferably, the quaternary salt of a compound having
an alkyl-substituted amidine group is a salt of a cyclic compound containing the
N-C=N skeleton as part of the ring structure. Even more preferably, the quaternary
salt is a salt of an alicyclic amidine compound, an imidazole compound or a benzimidazole
compound, which are substituted with one or more alkyl or arylalkyl groups and are
quaternarized. The alicyclic compound includes aliphatic bicyclic amidine compounds
having the skeleton of bicyclononane, bicyclodecane or bicycloundecane, as well
as an imidazoline compound and a pyrimidine compound. Such a compound is preferably
substituted with one or more alkyl groups. The total number of carbon atoms in the
substituent(s) is preferably about 1 to about 20, and more preferably about 1 to
about 15. A salt of such a compound is preferred because it quickly consumes the
hydroxide ions produced in the electrolytic solution and thus prevents the electrolytic
solution from leaking.
Preferred aliphatic bicyclic amidine compounds include
8-methyl-1,8-diazabicyclo[5,4,0]undec-7-enium, and 5-methyl-1,5-diazabicyclo[4,3,0]non-5-enium.
Preferred imidazoline compounds include 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium,
1,2-dimethyl-3-ethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium,
1,3-dimethyl-2-(1'-ethylpentyl)imidazolinium, and 1,3-dimethyl-2-dodecylimidazolinium.
Preferred pyrimidine compounds include 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium.
Preferred imidazole compounds include 1,3-dimethylimidazolium, and 1-methyl-3-ethylimidazolium.
Preferred benzimidazole compounds include 1,3-dimethylbenzimidazolium.
The salt of a compound having an alkyl-substituted amidine
group is contained in the electrolytic solution in the amount of preferably about
5 to about 100 parts by weight, more preferably about 10 to about 50 parts by weight,
and even more preferably about 20 to about 40 parts by weight, with respect to 100
parts by weight of &ggr;-butyrolactone and/or propylene carbonate.
Preferably, the water content in the main body is less
than about 10% based on the weight of the impregnated electrolytic solution. When
the water content is about 10% or more, the electrolysis reaction may be promoted
to an extent where the increase in the internal pressure of the electrochemical
device adversely affects its performance.
Any one or more of various additives can be appropriately
mixed as necessary in the electrolytic solution used in the electrochemical device
of the present invention. Preferred additives include: a phosphorus compound such
as phosphoric acid and a phosphate ester; a borate compound such as boric acid,
a complex compound of a boric acid and a polysaccharide (e.g., mannitol, sorbitol),
and a complex compound of a boric acid and a polyalcohol (e.g., ethylene glycol,
glycerin); and a nitro compound such as o-nitrobenzoic acid, m-nitrobenzoic acid,
p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol and p-nitroacetophenone.
Particularly in the case of an aluminum electrolytic capacitor,
when such an additive is mixed, an aluminum oxide film formed on the surface of
the aluminum case which is in contact with the electrolytic solution can be easily
formed. As a result, it is possible to suppress the electrolytic reaction of the
electrolytic solution, thereby further retarding the deterioration of the seal.
The seal used in the electrochemical device of the present
invention is an elastic body obtained by adding an alkylphenol formalin resin as
a vulcanizing agent to a butyl rubber polymer which is a copolymer of isobutylene
and isoprene. Any copolymer of isobutylene and isoprene can be used as the butyl
rubber polymer. The copolymer may contain a small amount of other comonomers so
long as the characteristics of the copolymer as a butyl rubber polymer are not substantially
affected.
An alkylphenol formalin resin is a resin which is produced
through a condensation reaction of metacresol and/or xylenol, or the like, with
formalin. Various alkylphenol formalin resins with various properties may be produced
depending upon the type and concentration of catalyst used in the production, the
molar ratio between the formalin and the alkylphenol, and the reaction conditions.
Preferably about 1 to about 20 parts by weight, and more preferably about 3 to about
10 parts by weight, of such an alkylphenol formalin resin is added with respect
to 100 weigh parts of the butyl rubber polymer. Other components such as carbon
and inorganic filler can further be blended as necessary. When an elastic body is
obtained by vulcanizing the butyl rubber polymer with a vulcanizing agent other
than an alkylphenol formalin resin, the rubber elasticity thereof may deteriorate
significantly under high temperature and high humidity conditions. As a result,
a sufficient sealing property is unlikely to be obtained.
At least a portion of the above-described seal has a hardness
of about 75 IRHD or greater. The phrase "hardness of at least a portion of the seal"
as used herein refers to the hardness of the seal which is measured at least one
of: on a portion of the surface of the seal to be in contact with the main body
and between two holes thereof through which a pair of lead wires pass; and on an
inner surface of the hole to be in contact with the lead wire.
Preferably, substantially the entire seal has a hardness
of about 75 IRHD or greater. More preferably, no part of the seal has a hardness
of less than about 73 IRHD. The hardness of the seal can be set to any desired value
by appropriately determining the amount of the vulcanizing agent to be added, the
molding temperature, etc. The seal having a hardness of less than about 75 IRHD
is not preferably used in the present invention because such a seal may not ensure
a sufficient sealing force for compressing the lead wires, and it is likely to result
in leakage of the electrolytic solution under high temperature and high humidity
conditions.
The lead wire used in the electrochemical device of the
present invention may be one whose rod-like terminal section has been subjected
to a corrosion prevention treatment. When subjected to the corrosion prevention
treatment, it is possible to suppress generation of a current and thereby to reduce
the electrolysis. Thus, it is possible to reduce the influence of the electrolysis,
thereby improving the sealing property of the device.
While the corrosion prevention treatment is preferably
performed for both of an anode terminal section and a cathode terminal section,
it may alternatively be performed for only one of the terminal sections.
Preferred and simple methods for the corrosion prevention
treatment include anodization in an aqueous solution, application of a metal alkoxide
followed by sintering, and application of a metallized colloidal solution (e.g.,
a colloidal solution of silicon dioxide and titanium dioxide) followed by sintering.
Any suitable material may be used for components of the
main body including the anode foil, the cathode foil, the separator and the lead
wire as well as the case and the cover.
Examples of the electrochemical device of the present invention
will now be described. However, the present invention is not limited to such specific
examples. The term "part(s)" as used hereinafter refers to "part(s) by weight".
Production of electrolytic solutions A to K:
Compositions for use in electrolytic solutions A to K of
this example are listed below. Each of the electrolytic solutions A to K was produced
by mixing and dissolving the respective compounds.
-
Electrolytic solution A:
&ggr;-butyrolactone (100 parts)
mono 8-methyl-1,8-diazabicyclo[5,4,0]undec-7-enium phthalate (30 parts)
p-nitrobenzoic acid (1 part)
-
Electrolytic solution B:
&ggr;-butyrolactone (100 parts)
mono 5-methyl-1,5-diazabicyclo[4,3,0]non-5-enium phthalate (30 parts)
monobutyl phosphate (1 part)
p-nitrophenol (1 part)
-
Electrolytic solution C:
&ggr;-butyrolactone (100 parts)
mono 1,2,3-trimethylimidazolinium phthalate (30 parts)
p-nitrobenzoic acid (1 part)
p-nitrophenol (1 part)
-
Electrolytic solution D:
&ggr;-butyrolactone (100 parts)
mono 1,2,3,4-tetramethylimidazolinium phthalate (30 parts)
o-nitrobenzoic acid (1 part)
monobutyl phosphate ester (1 part)
-
Electrolytic solution E:
&ggr;-butyrolactone (90 parts)
ethylene glycol (10 parts)
mono 1,2-dimethyl-3-ethylimidazolinium maleate (30 parts)
o-nitrophenol (1 part)
-
Electrolytic solution F:
&ggr;-butyrolactone (100 parts)
mono 1,2,3-trimethylimidazolinium phthalate (30 parts)
boric acid (1 part)
mannitol (2 parts)
p-nitrobenzoic acid (0.5 part)
phosphoric acid (0.25 part)
monobutyl phosphate ester (0.25 part)
-
Electrolytic solution G:
&ggr;-butyrolactone (100 parts)
mono 1,3-dimethyl-2-heptylimidazolinium phthalate (30 parts)
boric acid (1 part)
glycerin (2 parts)
-
Electrolytic solution H:
&ggr;-butyrolactone (100 parts)
mono 1,3-dimethyl-2-(1'-ethylpentyl)imidazolinium phthalate (30 parts)
p-nitroanisole (1 part)
-
Electrolytic solution I:
&ggr;-butyrolactone (100 parts)
mono 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium phthalate (30 parts)
p-nitrobenzoic acid (1 part)
-
Electrolytic solution J:
propylene carbonate (100 parts)
tetrafluoroboric acid 1-methyl-3-ethylimidazolium (30 parts)
-
Electrolytic solution K:
&ggr;-butyrolactone (100 parts)
mono tetramethylammonium phthalate (30 parts)
p-nitrobenzoic acid (1 part)
Production of elastic bodies X to Z:
Butyl rubber elastic bodies X to Z used as the seal in
the examples were molded as described below. The hardness of each of the molded
seals was measured at two locations: (1) on a portion of the surface of the member
to be in contact with the capacitor element and between two holes thereof through
which a pair of lead wires pass; and (2) on the inner surface of the hole in contact
with the lead wire (Measurement temperature = 25±1°C).
Elastic body X (resin vulcanization; hardness of about 75 IRHD or greater):
Elastic body X was produced by a vulcanization molding
process by adding 2 parts of an alkylphenol formalin resin, as a vulcanizing agent
to 30 parts of a copolymer of isobutylene and isoprene, 20 parts of carbon and 50
parts of an inorganic filler. The hardness measurements were about 77 IRHD at the
location (1) and about 76 IRHD at the location (2).
Elastic body Y (resin vulcanization; hardness of less than about 75 IRHD):
Elastic body Y was produced by a vulcanization molding
process by adding 2 parts of an alkylphenol formalin resin as a vulcanizing agent
to 40 parts of a copolymer of isobutylene and isoprene, 20 parts of carbon and 40
parts of inorganic filler. The temperature during the vulcanization molding process
was set to be lower than that when producing the elastic body X. The hardness measurements
were about 74 IRHD at the location (1) and about 72 IRHD at the location (2).
Elastic body Z (sulfur vulcanization; hardness of about 75 IRHD or greater):
Elastic body Z was produced by a vulcanization molding
process by adding 2 parts of sulfur as a vulcanizing agent to 30 parts of a copolymer
of isobutylene and isoprene, 20 parts of carbon and 50 parts of inorganic filler.
The hardness measurements were about 78 IRHD at the location (1) and about 77 IRHD
at the location (2).
Example 1
An aluminum electrolytic capacitor was produced as an example
of the electrochemical device illustrated in Figure 1. The anode and cathode foils
2 and 3 (made of an aluminum foil) and the separator 4 (made of a Manila fiber)
between the foils 2 and 3 were rolled up. The electrolytic solution A was impregnated
in the obtained structure, thereby obtaining the capacitor element 1 as the main
body (rated voltage: about 35 V; electrostatic capacity: about 2200 µF). The
lead wires 5a and 5b were coupled to the anode foil 2 and the cathode foil 3, respectively.
A corrosion prevention treatment was performed for the lead wire 5b, before it was
connected to the cathode foil 3, by providing the lead wire 5b with an oxide film
through a chemical treatment under low voltage conditions (about 200 V) in a boric
acid solution. The capacitor element 1 and the elastic body X as the seal 7 were
placed in the metallic case 6 made of aluminum, and the opening was sealed by curling.
The resultant structure was covered by the cover 8, thereby producing the aluminum
electrolytic capacitor (electrochemical device) 10.
Example 2
Example 2 is similar to Example 1 except that electrolytic
solution B was used instead of electrolytic solution A.
Example 3
Example 3 is similar to Example 1 except that electrolytic
solution C was used instead of electrolytic solution A.
Example 4
Example 4 is similar to Example 1 except that electrolytic
solution D was used instead of electrolytic solution A.
Example 5
Example 5 is similar to Example 1 except that electrolytic
solution E was used instead of electrolytic solution A.
Example 6
Example 6 is similar to Example 1 except that electrolytic
solution F was used instead of electrolytic solution A.
Example 7
Example 7 is similar to Example 1 except that electrolytic
solution G was used instead of electrolytic solution A.
Example 8
Example 8 is similar to Example 1 except that electrolytic
solution H was used instead of electrolytic solution A.
Example 9
Example 9 is similar to Example 1 except that electrolytic
solution I was used instead of electrolytic solution A.
Example 10
An electric double layer capacitor was produced as another
example of the electrochemical device illustrated in Figure 1. The anode and cathode
foils 2 and 3 (an activated carbon applied on the surfaces thereof) and the separator
4 (made of a porous polypropylene resin) between the foils 2 and 3 were rolled up.
The electrolytic solution J was impregnated in the obtained structure, thereby obtaining
the capacitor element 1 as the main body (rated voltage: about 2.5 V; electrostatic
capacity: about 30 µF). The lead wires 5a and 5b were coupled to the anode
foil 2 and the cathode foil 3, respectively. A corrosion prevention treatment was
performed for the lead wire 5b, before being connected to the cathode foil 3, by
providing the lead wire 5b with an oxide film through a chemical treatment under
low voltage conditions (about 200 V) in a boric acid solution. The capacitor element
1 and the elastic body X as the seal 7 were placed in the metallic case 6 made of
aluminum, and the opening was sealed by curling. The resultant structure was covered
by the cover 8, thereby producing the electric double layer capacitor (electrochemical
device) 10.
Comparative Example 1
Comparative Example 1 is similar to Example 1 except that
electrolytic solution K was used instead of electrolytic solution A.
Comparative Example 2
Comparative Example 2 is similar to Example 1 except that
elastic body Y was used instead of elastic body X.
Comparative Example 3
Comparative Example 3 is similar to Example 1 except that
elastic body Z was used instead of elastic body X.
Twenty electrochemical devices were produced for each of
the examples and the comparative examples above. A leakage test was conducted for
each electrochemical device while applying a reverse voltage of about -2.0 V for
about 2000 hours under two conditions: (1) a high temperature condition at a temperature
of about 110°C; and (2) a high temperature and high humidity condition at a
temperature of about 85°C and a relative humidity of about 85%. The results
are shown in Table 1 below.
Table 1: Leakage test results* (after 2000 hours)
Number
of electrochemical devices with leakage
Electrolytic solution
Elastic body (seal)
Temperature 110°C
Temperature 85°C
Relative humidity 85%
Example 1
A
X
0
0
Example 2
B
X
0
0
Example 3
C
X
0
0
Example 4
D
X
0
0
Example 5
E
X
0
0
Example 6
F
X
0
0
Example 7
G
X
0
0
Example 8
H
X
0
0
Example 9
I
X
0
0
Example 10
J
X
0
0
Comparative Example
1
K
X
7
20
Comparative Example
2
A
Y
0
4
Comparative Example
3
A
Z
4
8
*: 20 devices were
tested for each example
As compared with the aluminum electrolytic capacitors of
Comparative Examples 1 to 3, the aluminum electrolytic capacitors of Examples 1
to 9 of the present invention were shown to be more effective in suppressing leakage
in the presence of an applied voltage; no leakage was observed after 2000 hours
even under high temperature and high humidity conditions (i.e., at a temperature
of about 85°C and a relative humidity of about 85%). Similarly, no leakage
was observed in the electric double layer capacitor of Example 10 of the present
invention.
Comparative Example 1 employed the electrolytic solution
K which is easily denatured by alkalis because it contains a quaternary ammonium
salt as an electrolyte. Also employed was the seal X having a hardness of about
75 IRHD or greater which is produced by molding a butyl rubber polymer with an alkylphenol
formalin resin added thereto as a vulcanizing agent. In Comparative Example 1, the
deterioration of the seal by alkalis was significant, whereby leakage was not well
suppressed.
Comparative Example 2 employs the electrolytic solution
A containing a quaternary salt of a compound having an alkyl-substituted amidine
group as an electrolyte, and the seal Y having a hardness of less than about 75
IRHD which is produced by molding a butyl rubber polymer with an alkylphenol formalin
resin added thereto as a vulcanizing agent. In Comparative Example 2, no leakage
was observed under the high temperature condition (i.e., temperature: 110°C),
but leakage was not completely prevented under the more severe condition (i.e.,
temperature: 85°C; relative humidity: 85%).
Comparative Example 3 employs the electrolytic solution
A containing a quaternary salt of a compound having an alkyl-substituted amidine
group as an electrolyte, and the seal Z having a hardness of about 75 IRHD or greater
which is produced by molding a butyl rubber polymer with a vulcanizing agent other
than an alkylphenol formalin resin added thereto. In Comparative Example 3, leakage
was not completely prevented.
An electrochemical device with a reliable sealing property
which is unlikely to have any leakage even under high temperature and high humidity
conditions is obtained from a combination of an electrolytic solution containing
a quaternary salt of a compound having an alkyl-substituted amidine group, and a
seal having a hardness of about 75 IRHD or greater which is produced by molding
a butyl rubber polymer with an alkylphenol formalin resin.
As described above, according to the present invention,
it is possible to obtain an electrochemical device with reduced influence of an
increase in the internal pressure and deterioration of the seal by alkalis due to
electrolysis of the electrolytic solution. Furthermore, stability of the seal of
the device under high temperature and high humidity conditions can be improved.
Thus, there is provided an electrochemical device in which leakage of the electrolytic
solution is effectively prevented.
Various other modifications will be apparent to and can
be readily made by those skilled in the art without departing from the scope of
this invention. Accordingly, it is not intended that the scope of the claims appended
hereto be limited to the description as set forth herein, but rather that the claims
be broadly construed.
