Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
1999-07-29
2002-04-23
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S503000
Reexamination Certificate
active
06377441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric double-layer capacitor, and more particularly to a large-capacity electric double-layer capacitor having solid polarizable electrodes.
2. Description of the Related Art
As shown in
FIG. 1
of the accompanying drawings, a conventional electric double-layer capacitor comprises a cell stack
109
comprising a plurality of basic cells
106
, a pair of pressure plates
107
, and a pair of terminal electrodes
108
.
As shown in
FIG. 2
of the accompanying drawings, each of the basic cells
106
comprises a pair of polarizable electrodes
101
disposed in confronting relationship to each other with a porous, electrically non-conductive, ion-permeable separator
104
interposed therebetween, and housed within a frame-shaped gasket frame
105
. Collectors
102
are joined respectively to the upper and lower surfaces of the gasket frame
105
, closing the openings defined in the upper and lower surfaces thereof. The separator
104
and the polarizable electrodes
101
are thus sealed within the gasket frame
105
. The collectors
102
are held against those surfaces of the polarizable electrodes
101
which face away from the separator
104
. Together with the separator
104
and the polarizable electrodes
101
, an electrolytic solution
103
is sealed in the gasket frame
105
. The separator
104
is impregnated with the electrolytic solution
103
thus sealed in the gasket frame
105
.
As shown in
FIGS. 3A
,
3
B, and
3
C of the accompanying drawings, each of the polarizable electrodes
101
is in the form of a rectangular plate. The polarizable electrodes
101
are made of solid activated carbon mainly comprising a compound of a powder or fibers of activated carbon and a polyacene material.
The collectors
102
are made of rubber or plastics containing electrically conductive carbon. The collectors
102
are attached under pressure to the polarizable electrodes
101
.
As shown in
FIGS. 4A
,
4
B, and
4
C of the accompanying drawings, each of the gasket frames
105
is in the form of a hollow frame with openings defined in respective upper and lower surfaces thereof.
The dielectric strength of the electric double-layer capacitor is limited by the electrolytic voltage of the electrolytic solution
103
. Therefore, depending on the dielectric strength which is required by the electric double-layer capacitor, a certain number of basic cells
106
are connected in series with each other, providing the cell stack
109
. The terminal electrodes
108
are attached to the respective opposite ends of the cell stack
109
in the direction in which the basic cells
106
are stacked. The pressure plates
107
are attached to those surfaces of the terminal electrodes
108
which face away from the cell stack
109
. Pressure plates
107
are pressed toward each other, and remain under a constant pressure for pressing the adjacent basic cells
106
against each other and also for pressing terminal electrodes
108
against adjacent basic cells
106
for thereby reducing contact resistances across contacting surfaces of the parts of the electric double-layer capacitor.
Polarizable electrodes
101
, which have recently been employed in the art, are effective for increasing the capacity of the electric double-layer capacitor and reduce the equivalent series resistance of the electric double-layer capacitor. This increased capacity and reduced equivalent series resistance have led to new applications for the electric double-layer capacitor. Such new applications include a power supply for energizing an automobile starter motor in combination with a lead storage battery, and an auxiliary power supply combined with a solar cell.
In applications of the electric double-layer capacitor, the electric double-layer capacitor is highly likely to be installed in a high-temperature environment. Accordingly, it is necessary to keep the electric double-layer capacitor highly reliable in high-temperature usage. However, when a test is conducted in a high-temperature environment to evaluate the reliability of the conventional electric double-layer capacitor shown in
FIG. 1
, basic cells
106
are expanded because electrolytic solution
103
is expanded with heat and gases are produced from cell stack
109
by the application of a voltage. The effect which the expansion of the basic cells
106
has on each of the collectors
102
of the cell stack
109
is greater on the collectors
102
that are close to the ends of the cell stack
109
than on the collectors
102
in the central region of the cell stack
109
. Particularly, the outermost collectors
102
are subject to the greatest load from the expansion of basic cells
106
. Therefore, when the electric double-layer capacitor is placed in a high-temperature environment for a long period of time, the outermost collectors
102
tend to crack or break, allowing the electrolytic solution
103
to leak from the outermost basic cells
106
.
In applications which require an electric double-layer capacitor to produce greater electric power, e.g., if an electric double-layer capacitor is used to energize an automobile starter motor, the electric double-layer capacitor needs to have a low equivalent series resistance. In order to reduce the equivalent series resistance of the electric double-layer capacitor shown in
FIG. 1
, the polarizable electrodes
101
and the collectors
102
may be electrically connected for good conductivity. For this reason, cell stack
109
is pressed by the pressure plates
107
, each in the shape of a less deformable, highly rigid metal plate, applied to the outermost collectors
102
of cell stack
109
.
However, collectors
102
, which are made of electrically conductive rubber, are not rigid. Therefore, when cell stack
109
is pressed by pressure plates
107
, collectors
102
are subjected to strong local forces. Polarizable electrodes
101
are made of sintered activated carbon, and hence are hard and highly rigid. Gasket frames
105
are often made of a hard material such as ABS resin so that they have high dimensional accuracy. Consequently, when cell stack
109
is pressed by metallic pressure plates
107
on the opposite ends of cell stack
109
, outermost collectors
102
are liable to crack due to contact with sharp portions, such as edges, of polarizable electrodes
101
and gasket frames
105
. As a result, when electric double-layer capacitors are manufactured, defective electric double-layer capacitors are produced with greater probability, and the productivity of electric double-layer capacitors is reduced.
An electric double-layer capacitor proposed in an attempt to solve the above problems is disclosed in Japanese Patent Laid-Open Publication No. 315191/93, for example. This disclosed electric double-layer capacitor comprises a cell stack of basic cells similar to basic cells
106
shown in
FIGS. 1 and 2
, with outermost collectors thicker than inner collectors.
Japanese Patent Publication No. 32529/92 discloses an electric double-layer capacitor comprising a cell stack of basic cells having collectors each in the form of a single electrically conductive polyethylene film. The electrically conductive polyethylene film is fabricated by filling carbon black with polyethylene at successively different densities. Specifically, the polyethylene in the electrically conductive polyethylene film is provided in three layers having successively low, high, and low densities across the thickness of the electrically conductive polyethylene film. Collectors thus constructed are mechanically strong and positioned as outermost collectors of the cell stack. Inasmuch as the strong outermost collectors are resistant to crack or breakage, the electrolytic solution is prevented from leaking out of the outermost basic cells.
Japanese Publication No. 36222/92 discloses an electric double-layer capacitor comprising a cell stack of basic cells having collectors each in the form of an electrically conductive sheet with a core disposed therein. Co
Inoue Yoshiki
Ohya Masako
Reichard Dean A.
Thomas Eric W
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