Disclosed is an electrochemical double-layer capacitor which comprises a capacitor element having a pair of polarization electrodes and a spacer interposed between the electrodes and impregnated with an electrolyte solution, and a film enclosure made of two film sheets which have been thermally bonded by heat sealing along their entire periphery. The film sheets are bonded directly or through a heat-fusible resin plate having an opening in which the capacitor element is received. When using the heat-fusible resin plate, the film sheet is made electrically conductive for allowing easy connection to electric appliances or allowing easy connection of a plurality of capacitor elements in series.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to electrochemical double-layer capacitors, and more 
particularly to an improved enclosure or casing therefor. 
2. Description of the Prior Art 
Electric or electrochemical double-layer capacitors make use of an electric 
double layer formed at an interface between each polarization electrode 
and an electrolyte, and are usually comprised of a pair of polarization 
electrodes each made of carbon which is usually applied to a conductive 
metal plate and a spacer or separator impregnated with an electrolyste 
solution, the spacer being interposed between the pair of electrodes which 
are facing each other. 
the electrochemical double-layer capacitor of the just-mentioned type has a 
much greater electrostatic capacity than ordinary electrolytic capacitors 
and is rapidly chargeable similarly to the electrolytic condensers or 
capacitors, so that it has become of major interest as a substitute for 
known secondary cells or batteries for its application to power units for 
back-up or stand-by purpose. 
In the manufacture of the electrochemical double-layer capacitor, it is the 
common practice to use as an enclosure or casing a combination of a metal 
container shaped by press work and a sealing plate therefor. However, 
since there is a recent trend of making the thickness of the 
electrochemical double-layer capacitor very small from viewpoints of its 
characteristic properties and applications, a relatively large proportion 
of production cost is occupied by the container and the cost of the 
material for the container now presents a problem of economy. 
Further, the electrochemical double-layer capacitor has an advantage that a 
great electrostatic capacity is obtained as compared with those obtained 
from other types of capacitor but has a disadvantage that the withstand 
voltage is as low as below several volts. Thus, its application is 
restricted to an extent. In other words, due to the low withstand voltage, 
it can not be applied to electric appliances using high voltage. 
On application to such electric appliances as operated under high voltage, 
it is necessary to use a plurality of electrochemical double-layer 
capacitors connected in series. However, the known electrochemical 
double-layer cpacitor is not suitable for that purpose and thus there is a 
further demand of developement of an electrochemical double-layer 
capacitor of a novel enclosure construction. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electrochemical 
double-layer capacitor which has an improved casing or enclosure made of a 
film material. 
It is another object of the present invention to provide an electrochemical 
double-layer capacitor which is simple in construction of casing and 
inexpensive. 
It is a further object of the invention to provide an electrochemical 
double-layer capacitor with an improved enclosure suitable for making the 
capacitor thin. 
It is a still further object of the invention to provide an electrochemical 
double-layer capacitor in which a plurality of capacitor elements are 
electrically connected in series or in parallel but are separated from one 
another by a simple way. 
It is another object of the invention to provide an electrochemical 
double-layer capacitor in which a plurality of capacitor elements are 
connected in series and each element has a resistor connected in parallel, 
so that the individual capacitor elements are applied with almost the same 
voltage thereby keeping the electrostatic capacities of the plurality of 
the capacitor elements nearly at the same level. 
It is another object of the invention to provide an electrochemical 
double-layer capacitor which can withstand high voltage by connecting a 
plurality of capacitor elements in series or which is imparted with a 
desired level of electrostatic capacity by connecting a plurality of the 
capacitor elements in parallel by a simple way. 
It is an additional object of the invention to provide an electrochemical 
double-layer capacitor which has wide utility in the field of the back-up 
or stand-by service for DC power sources. 
According to one aspect of the invention, there is provided an 
electrochemical double-layer capacitor which comprises a capacitor element 
including a pair of polarization electrodes and a spacer interposed 
between the pair of polarization electrodes and impregnated with an 
electrolyte solution, and a film enclosure for enclosing the capacitor 
element in a hermetically sealed condition, the film enclosure being 
formed of two film sheets each of which has at least a heat-fusible resin 
film layer for heat sealing and which have been thermally sealed along the 
entire periphery thereof after placing said capacitor element inbetween 
said two film sheets. 
The film sheet may be a single layer film such as a heat-fusible 
polyethylene film but preferably various types of composite film which 
will be described in detail hereinafter are used. 
According to another aspect of the invention, the film sheets for enclosing 
the capacitor element are made conductive and are bonded together through 
an insulating or resistor plate having an opening at the central portion 
thereof for receiving the capacitor element, by which a plurality of 
capacitor elements can be compactly arranged to lie one on top of another 
while connecting them in series or in parallel through the conductive film 
sheets.

DESCRIPTION OF EMBODIMENTS 
Referring now to FIG. 1, there is shown a basic arrangement of an 
electrochemical double-layer capacitor element 1 which includes a pair of 
polarization electrodes 2,2' supported respectively, on conductive metal 
plates 3,3' and a spacer or separator 3 intervening between the pair of 
the electrodes and impregnated with an electrolyte solution. The 
conductive metal plates 3,3' are respectively attached with lead wires 
5,5' with external terminals 6,6'. The electrode is usually made of a 
major proportion of a carbon material such as graphite, carbon black, 
active carbon or the like and a minor proportion of a binder. 
The electrochemical double-layer capacitor of the types mentioned above is 
as small in thickness of the dielectric layer as several A and the area in 
face-to-face relation between the dielectric layer and the electrode is as 
great as 700-1400 m.sup.2 /g, while in the case of an aluminium 
electrolytic capacitor or condenser using an aluminium oxide film as a 
dielectric layer, the thickness of the dielectric layer is about 14 A/V 
and the area is only several square meters/g. As a results, a great 
electrostatic capacity can be obtained by the electrochemical double-layer 
capacitor. 
The polarization electrode of the electrochemical double-layer capacitor is 
usually fabricated by the procedure shown in FIGS. 2(a)-(d), i.e. a 
rubber-like material 7 for the polarization electrode is uniformly applied 
to and kept on a conductive metal plate 8 such as of an aluminum expand 
metal by a rolling technique, and the applied plate is cut in a given 
size. Then, a lead wire or band such as of aluminium is attached to the 
metal plate 7 to obtain the electrode. 
FIG. 3 shows one embodiment of an electrochemical double-layer capacitor 
according to the present invention. The capacitor, generally indicated by 
10, includes a capacitor element 12 which has a pair of polarization 
electrodes 13, 13', each supported by a conductive metal plate 14 or 14' 
and a spacer 16 interposed between the paired electrodes 13, 13' and 
impregnated with an electrolyte solution. The capacitor element 12 is 
enclosed or accommodated in a film enclosure or casing 18. As is well 
known, the polarization electrode is ordinarily formed of graphite, carbon 
black of active carbon and a binder in minor proportion may be supported 
by a conductive metal plate as shown or may not be supported. The spacer 
16 is made of finely perforated film or non-woven fabric of polyethylene 
or polypropylene. The electrolyte may be any of known ones including, for 
example, an electrolyte comprised of 5-30 wt% of propylene carbonate, 
70-90 wt% of .gamma.-butyrolactone and 5-20 wt% of tetraethylammonium 
perchlorate. The electrolyte is usually dissolved in a non-aqueous solvent 
such as as alcohols. 
The film enclosure or casing is made of two film sheets of a heat-fusible 
synthetic resin, typical of which is polyethylene or polypropylene. The 
film sheet has generally a thickness of 100-200.mu. in order to impart 
satisfactory mechanical or other desirable properties to the enclosure. In 
order to enclose the element, it is placed between the two sheets of resin 
film and the sheets are bonded together along the entire periphery thereof 
by heat-sealing or other suitable techniques. 
As mentioned above, the films suitable for enclosing the element are those 
obtained from heat-fusible synthetic resins, for instance polyethylene 
resin. However, especially when a polyethylene film alone is used as the 
enclosure film, there may arise a problem that the thermal stress is 
produced in the neighborhood of the heat-sealed portion and thus fine 
pinholes or cracks are apt to be produced though such problem is avoidable 
when the heat-sealing procedure is conducted under severaly controlled 
conditions. The occurrence of such pinholes or cracks undesirably leads to 
the leakage of the internal electrolyte solution to outside through the 
pinholes or cracks or, even though the electrolyte solution does not 
escape from the inside in a liquid state, such occurrence may cause a 
facilitated dissipation of the electrolyte solution to outside by 
evaporating during storage or use at high temperature through the defects 
as well as through the film itself. As a consequence, the electrolyte 
solution gradually reduces and the performance of the capacitor is 
lowered. 
In order to solve the problem as may occur, enclosure films have been 
studied and it has been found that composite films obtained by lamination 
of at least two kinds of film are preferably usable as the film for the 
enclosure. Preferable composite films are those in which at least one of 
the films is excellent in heat stability and solvent resistance and does 
not suffer from pinholes or cracking when subjected to heat-sealing 
operation. 
Examples of such composite film are schematically sectionally shown in 
FIGS. 4 to 7. In FIG. 4, there is shown a composite film 20 including a 
polyethylene film 22 and a polypropylene film 24 which is excellent in 
heat stability and solvent resistance, these films being combined or 
bonded together by lamination. When applied as an enclosure, two sheets of 
the composite film are placed so that the polyethylene films of the 
respective sheets are facing each other and thus the polypropylene films 
which are excellent in heat stability and solvent resistance turn outside. 
When the two sheets are heat sealed, formation of pinholes or cracks in 
the vicinity of the heat-sealed portion along the periphery of the sheets 
are prevented due to the heat stability of the polypropylene film 
laminated. 
Aside from the polypropylene film used for lamination with polyethylene 
film, other resin films which are excellent in heat stability and solvent 
resistance and are thus free of formation of pinholes or cracks on 
application of heat include a polyethyleneterephthalate film, polyimide 
film and various metal films. 
It will be noted that the polyethyleneterephthalate film or polyimide film 
is excellent in heat stability and mechanical strength but is 
disadvantageous in relatively poor solvent resistance. Among metal films, 
an aluminium or tin film has a number of advantages that it is flexible 
and shows good workability, that aluminium or tin can be readily converted 
into from a relatively thick foil to a thin film and the film or foil 
shows little or no gas permeability as is experienced in synthetic resin 
films, thus being excellent as a barrier for inhibitting the leakage or 
evaporation of the electrolyte solution. Accordingly, the film of alumnium 
or tin which has been laminated with a resin film on the both surfaces 
thereof for electric insulation and for heat-sealing purpose is also 
preferably used in the practice of the invention. Additionally, zinc is 
likewise usable. The resin film suitable for lamination with the metal 
film may be any of resin films which are heat-sealable, inexpensive and 
easy for lamination, e.g. a polyethylene film is used. This is because 
even if the resin film is readily formed with pinholes or cracks therein 
on heat-sealing, the metal film can prevent communication of from inside 
to outside. 
Different types of composite film suitable as the enclosure film are shown 
in FIGS. 5--9 in which three or more types of film are used and laminated. 
In FIG. 5, there is shown a composite or laminated film 26 which includes a 
polyethylene film 28, an aluminium film 30, a polyethylene film 28' and a 
polypropylene film 32. In practical application, the film 26 is applied 
for enclosing the capacitor element so that the outer layer is the 
polypropylene film 32. In the event that fine pinholes or cracks are 
formed in the polyethylene films 28, 28' due to the thermal stress caused 
by heat sealing, the leakage or evaporation of the electrolyte solution 
can be inhibited by means of the polypropylene film 32 and the aluminium 
film 30. In addition, when an indication of a desired trade mark or rating 
mark has been made on one surface of the aluminium film 30 in advance, it 
is protected with the resin film and thus is free of being stained. The 
resin films are very thin and transparent and thus the enclosure shows a 
good appearance. 
FIGS. 6 and 7 show further examples of composite films, generally indicated 
by 34 and 44, respectively, consisting of four and five film layers in 
which polyethyleneterephthalate or polyimide films are used. Though 
relatively poor in solvent resistance, the polyethyleneterephthalate or 
polyimide film is more excellent in heat stability and mechanical strength 
and higher in strength of adhesion to the metal film than the polyethylene 
or polypropylene film. 
The composite film 34 is composed of a polyethylene film 36 or 
polypropylene film 38, a polyethyleneterephthalate or polyimide film 40, 
and aluminium film 42, and a polyethyleneterephthalate or polyimide film 
40' arranged in this order. Similarly, as shown in FIG. 7, the composite 
film 44 is composed of a polyethylene film 46, a polypropylene film 48, a 
polyethyleneterephthalate or polyimide film 50, an aluminium film 52 and a 
polyethyleneterephthalate or polyimide film 50' arranged in this order. 
When applied for enclosure, these composite films 34 and 44 are used so 
that the surface of the polyethylene or polypropylene film having good 
solvent resistance is in face-to-face relation with the capacitor element. 
As mentioned, the polyethylene terephthalate or polyimide film shows high 
strength of adhesion to the metal film and is excellent in heat stability 
and resistance to mechanical stress, so that the composite film using 
these films is much more excellent in heat stability and mechanical 
strength than that using a combination of the polyethylene film, 
polypropylene film and the metal film such as shown in FIG. 5. 
In the above examples, the aluminium film is used, as the metal film, 
stainless steel, zinc or tin film is likewise usable. 
As illustrated above, the composite film suitable for the purpose of the 
invention should include at least one film which is excellent in heat 
stability including, for example, a polypropylene film, a metal film such 
as of Al, Zn or Sn, a polyethyleneterephthalate or polyimide film. By 
using such heat-stable film, when the composite film sheets are thermally 
fused along the periphery thereof to hermetically seal the capacitor 
element, undesirable formation of pinholes or cracks in the film sheets 
due to the thermal stress occuring in the vicinity of the heat-sealed 
portion can be prevented. Most preferably, a composite film using a metal 
film which is laminated with at least one resin film on each surface 
thereof is used. 
When the heat sealing is conducted on the polyethylene film which is 
readily fusible by application of heat, a heating resistor of a simple 
construction such as a nichrome wire or band is used. On the other hand, 
the heat-sealing of a rather heat-resistant film such as a polypropylene 
film is suitably conducted by a method of self-heating of the film itself 
such as a high frequency heating technique as is well known in the art. In 
order to sealingly, enclose the capacitor element while reducing the air 
remaining in the enclosure to a degree as small as possible, it is 
effective to conduct the heat sealing operation in vacuo. 
When two sheets of the enclosure film are thermally sealed to accommodate 
the capacitor therein, there may arise a problem that electrical leads 60, 
60' from the respective electrodes of the capacitor element as shown in 
FIG. 8 impede the sealing of the film sheets due to differences in heat 
capacity and heat conductivity between the resin film and the electrical 
metal lead. To solve the problem, a hot melt resin such as a modified 
polyolefin resin typical of which is an ionomer resin is applied as a 
layer to the inner surfaces of the respective film sheets along the entire 
periphery thereof or partially at the portions a, a' of FIG. 8, by which 
the electrical leads 60, 60' are bonded to the film sheets through the hot 
melt resin layers so as to be embedded in the resin layers. This is 
schematically shown in FIG. 9, in which an electrical lead 60 or 60' is 
bonded to the composite film 62 through a hot melt resin layer 64 or 64'. 
When the enclosure of the capacitor 10 of FIG. 10 is partially cut away as 
66 at the heat-sealed portion as shown in FIG. 10, this serves for an 
explosion proof. 
Several types of the films as described above have been provided and 
experimentally confirmed as to whether they are suitable as an enclosure 
for the capacitor element in comparison with a prior-art capacitor. The 
results are shown in Table 1. 
It will be noted that the samples used for the experiment are as follows: 
(1) A prior-art capacitor having a casing composed of a cylindrical 
aluminium case and a rubber packing; (2) Electrochemical double-layer 
capacitor A of the invention having an enclosure made of a laminated 
composite film of a polyethylene film and a polypropylene film; (3) 
Capacitor B of the invention having an enclosure made of a laminated 
composite film of four layers of a polyethylene film, aluminium film, 
polyethylene film and polypropylene film; (4) Capacitor C of the invention 
having an enclosure made of a laminated composite film of four layers of a 
polyethyleneterephthalate film, aluminium film, polyethyleneterephthalate 
film and polyethylene film; (5) Capacitor D having an enclosure made of a 
laminated composite film of four layers of a polyethyleneterephthalate 
film, aluminium film, polyethyleneterephthalate film and polypropylene 
film; (6) Capacitor E of the invention having an enclosure made of a 
laminated composite film of four layers of a polyimide film, aluminium 
film, polyimide film and polyethylene film; and (7) Capacitor F of the 
invention having an enclosure made of a laminated composite film of four 
layers of a polyimide film, aluminium film, polyimide film and 
polypropylene film. The prior-art capacitor has a rated voltage of 1.6 V 
and a rated electrostatic capacity of 1.5 F, and a size of the casing of 8 
mm.phi..times.20 mm. As for the capacitors according to the invention, a 
rolled capacitor element is converted into a flat element in which the 
electrode material used is a conventionally employed one and the size of 
the capacitor was 3 cm in width, 4 cm in length and 1 mm in thickness. The 
thickness of all the composite films is set at 100.mu.. 
In the experiment, the rated voltage is applied to each of the sample 
capacitors at 70.degree. C. to determine its characteristic change after 
500 hours of the application. 
TABLE 1 
______________________________________ 
Variation rate of electrostatic 
capacity of capacitor applied 
with 1.6V at 70.degree. C. for 500 hours 
______________________________________ 
Prior-art -6.9% 
capacitor 
Capacitors of 
Invention 
A -25.1% 
B -8.3% 
C -7.8% 
D -7.5% 
E -7.7% 
F -7.6% 
______________________________________ 
As is clear from the results of Table 1, the electrochemical double-layer 
capacitors using the film enclosures according to the invention are not so 
much different in characteristic from the prior-art capacitor and are 
readily applicable to various electronic apparatuses which have a tendency 
of being made smaller in thickness. 
In the practice of the invention the polyethylene film alone or composite 
films for enclosing the capacitor element has, a thickness ranging from 50 
to 200.mu., preferably 70 to 100.mu., to impart sufficient mechanical 
strengths to the enclosure or casing. Where a metal film is used, its 
thickness is preferably in the range of 15-50.mu.. 
In the capacitors according to the invention, the leads are arranged as 
extending directly from the respective electrodes as usual. In order to 
show the effectiveness of the thin construction of the capacitor according 
to the invention, the lead or terminal may be arranged in different ways. 
FIG. 11 shows another embodiment of an electro-chemical double-layer 
capacitor 70 which comprises a capacitor element 72 including a pair of 
polarization electrodes 74, 75 backed with metal conductive plates 76, 77, 
respectively and a spacer 78 sandwitched between the electrodes 74, 75 and 
impregnated with an electrolyte solution as in FIG. 1 except that the 
metal conductive plates have each an outwardly bent portion 80 or 81. The 
capacitor element 72 is encased in a film enclosure 82 made of two 
composite film sheets 84. In this case, the composite film sheet 84 is 
formed of a laminate of four films 84a, 84b, 84c and 84d, for instance, a 
polypropylene film, polyethylene film, aluminium film and polyethylene 
film, respectively, and should have a metal film such as an aluminium or 
stainless steel film which has been laminated with the resin film or films 
on the both surfaces thereof. The composite film 84 has recesses 86, 87 in 
its opposite sides to expose the metal film 84c. An inner exposed surface 
89 of the metal film 84c is contacted with the bent portion 80 of the 
capacitor element 72 for allowing electrical connection between the metal 
film 84c and the capacitor element 72. An outer exposed surface 88'of the 
metal film 84c serves as an external terminal. In other words, the metal 
film itself is used as a terminal for external connection. The size and 
shape of the recesses may optionally be changed depending on the purpose 
of the capacitor in end use. 
Since the outer exposed surface 88 is in the form of a recess as shown in 
FIG. 11, a difficulty may be in some cases encountered in connection with 
an external appliance. In the case, a metal connection 90 such as of 
aluminium, stainless steel, copper or brass is fitted in the recess 86 in 
connection with the exposed surface 88 of the metal film 84c so that the 
metal connection 90 projects above the surface of the resin film 84a. This 
allows easy connection with an external electrical appliance. 
In case where the resin films 84a, 84b and 84d of the composite film 84 are 
partially removed to form the recesses 86, 86' as shown in FIG. 11, the 
enclosed capacitor element 72 is isolated from outside by means of the 
aluminium film alone at the film-removed portions. Accordingly, the 
exposed portion becomes smaller in mechanical strength than the other 
portion. If the exposed portion 88 of the metal film 84c is made with a 
cut on its surface to permit easier breakage of the metal film, it can 
perform a function in explosion proof. In addition, when the cut is made 
to indicate either a mark showing a polarity 92 as shown in FIG. 13 or a 
rating mark, the exposed portion 88 of the metal film 84c has functions as 
the external connection and the indication of a desired mark and also in 
explosion proof. 
The capacitor of the above-described type has a number of advantages that 
the position of the external connection terminal can be arbitrarily 
changed as required by removing desired portions of the resin films 
laminated on both surfaces of the aluminium film, that since no specific 
part or only a part of a simple construction is used as an external 
terminal, the capacitor becomes inexpensive, and that the capacitor hardly 
suffers corrosion during storage or use since only a part of the metal 
film is exposed. 
In general, the electrochemical double-layer capacitor has several 
advantages that its electrostatic capacity is large but has a disadvantage 
that the withstand voltage is as low as about 1.6 V. In some cases, it is 
required to connect a plurality of the capacitors in series so as to 
increase the withstand voltage to a desired degree. In some cases, it is 
also required to produce a great electrostatic capacity as will not be 
obtained by only one capacitor unit. 
The above requirements can be readily satisfied according to the invention 
by a simple way. This will be particularly illustrated with reference to 
FIGS. 14 to 17. 
FIG. 14 shows a capacitor pair 100 including two capacitor units each 
having a similar construction as illustrated with reference to FIG. 11 and 
similar parts are indicated by similar numerals. The two units are 
separated from each other at the sealed portion 102. The capacitor pair 
can be readily made by placing two capacitor elements 72a, 72b on a sheet 
of the composite film 84 at a distance, then providing another sheet of 
the composite film 84 to cover the capacitor elements 72a, 72b, and 
bonding the two sheets by the heat-sealing technique so that the capacitor 
elements are separately enclosed as shown. The capacitor elements 72a, 72b 
are electrically connected each other through the metal conductive plates 
74a, 74b and the aluminium film 84c. In FIG. 14, the capacitor elements 
72a, 72b are connected in parallel, showing the electrostatic capacity two 
times as much. 
As shown in FIG. 15, when the capacitor pair 100 is folded at the 
heat-sealed portion 102 at which the two capacitor elements 72a, 72b are 
separated and the outer sheet of the composite film is cut off as shown, 
the capacitor elements 72a, 72b are connected in series and thus the 
capacitor pair 100 shows a withstand voltage two times that of one 
capacitor unit. In FIGS. 14 and 15, 88a' and 88b indicate external 
connection terminals, respectively. 
Similarly, a plurality of the capacitor elements can be electrically 
connected in a compact way using the capacitor pairs by putting one on top 
of another while electrically connecting them in series. Alternatively, 
the capacitor pairs 100 can be successively electricallt connected through 
the metal films 84c and the metal connections 90a, 90b in a manner as 
shown in FIGS. 16 and 17. When each pair is folded at the sealed portion 
to lie one on the top of another, the plurality of capacitor elements are 
vertically piled as shown in FIG. 18, and connected in series when the 
upper sheet of the sealed portion is cut off at the folded portion of each 
pair. The thus assembled capacitor has a withstand voltage of 6 times as 
much as that of the capacitor unit. When it is desired to connect the 
plurality of capacitor elements in parallel, it is sufficient not to cut 
off the aluminium film 84c of the outer sheet of the composite film 84 at 
the sealed portion when the capacitor pair is folded. 
In the practice of the invention, the composite film for enclosing the 
capacitor element is usually in a thickness of 50-200.mu. as defined 
hereinbefore and the capacitor element has generally a thickness of about 
800.mu., and a total thickness of one capacitor unit is about 1 mm. One 
capacitor element is generally rated to have to withstand voltage of 1.6 V 
and an electrostatic capacity of 1.5 F, and is designed to have a size of 
3 cm in width and 4 cm in length. When a plurality of such capacitor 
elements are arranged to be electrically connected as shown in FIG. 18, 
there can be obtained a very thin electrochemical double-layer capacitor 
having a withstand voltage of 9.6 V, an electrostatic capacity of 0.25 F 
and a size of 3 cm in width and 4 cm in thickness. 
As will be appreciated from the above, the assembled electrochemical 
double-layer capacitor according to the invention in which a plurality of 
capacitor elements are separately enclosed and electrically connected in 
series or in parallel can be fabricated by a simple manner to have desired 
levels of withstand voltage and electrostatic capacity. In this 
embodiment, the metal film of the composite film sheet which is laminated 
with the resin film or films on each surface thereof is partially exposed 
for use as a connection terminal. 
When a plurality of the capacitor elements are connected in series as 
described, there may arise a problem that due to the scatter of 
characteristics, particularly leakage current, of the individual elements, 
the applied voltage is not satisfactorily divided into 1/n where n is the 
number of capacitors connected in series and thus the voltage applied to 
the individual capacitors disperses. 
That is, the electrochemical double-layer capacitor consists of an 
equivalent series resistance R and an electrostatic capacity C, and an 
insulating resistance R.sub.L representing the leakage current as shown in 
FIG. 19. When the electrostatic capacities C.sub.1, C.sub.2 . . . Cn of a 
plurality of the capacitors connected in series are C.sub.1 
.apprxeq.C.sub.2 . . . .apprxeq. Cn, the entire applied voltage is divided 
based on differences in the insulating resistance R.sub.L. Accordingly, in 
order to apply almost the same voltage to the individual capacitors 
connected in series, it is necessary to add an external resistor to the 
individual capacitors in parallel. 
A still further embodiment of the electrochemical double-layer capacitor 
according to the invention is shown in FIG. 20, generally indicated by 
110. The capacitor 110 includes the capacitor element 12 having the pair 
of polarization electrodes 13, 13' intervening the spacer 14 impregnated 
with an electrolyte solution, a resistor plate 112 having an opening 114 
for receiving the capacitor element 12 therein, and conductive film sheets 
116 brought in contact with the upper and lower sides of the element 12, 
the resistor plate 112 and the conductive film sheets being thermally 
fused to hermetically seal the element 12. In this case the conductive 
film sheet 116 is composed of a laminate of a conductive polymer film 117 
and a metal film 118. The sheet 116 may be composed of the conductive 
polymer film 117 alone. 
The electric circuit of the capacitor incorporated with the resistor is 
shown in FIG. 21, in which R.sub.p represents a resistance of the resistor 
plate 112 and is connected in parallel with the capacitor element. 
The resistor plate 112 having the opening 114 may be in the form of a ring, 
square or other suitable shapes. The resistor plate is made of a mixture 
of a heat-fusible polymeric material such as polyethylene, polypropylene, 
butyl rubber, ethylene-propylene rubber and silicon rubber and a carbon 
black such as acetylene black. The conductive polymer 117 used has a 
similar mixture composition as mentioned above. The conductive polymer is 
prepared to have a volume specific resistance of 10-10.sup.6 .OMEGA..cm. 
As the conductive polymer film 116a the conductive polymer mixture of a 
relatively low specific resistance of about 10 .OMEGA..cm is used and the 
conductive polymer of a high specific resistance ranging 10.sup.3 
-10.sup.6 .OMEGA..cm is used as the resistor plate 112. 
The metal film 11 of the conductive film sheet 116 serves as a gas barrier 
layer which is not satisfactorily attained only by using the conductive 
polymer film 117. Especially when the capacitor is used at high 
temperature, the metal film can prevent the deterioration of the 
electrical characteristics of the capacitor. The metal film is formed of 
aluminium, zinc, tin or the like metal. 
In this embodiment, the resistor plate is used in order to solve the 
problem encountered when a plurality of capacitor elements are connected 
in series, but when only one capacitor of the above-described type is 
used, an insulating resin plate may be used instead of the resistor plate. 
The insulating resin plate is made of a heat-fusible, insulating resin 
such as polyethylene, polypropylene, butyl rubber, ethylenepropylene 
rubber and silicon rubber. That is, in the practice of the invention, the 
two film sheets of the enclosure may be bonded directly or through a 
heat-fusible plate having an opening for receiving the capacitor element 
therein. 
In Table 2, there are shown electrical characteristics of the capacitor of 
this embodiment of the invention in comparison with those of a prior art 
electrochemical double-layer capacitor. In the table, the characteristic 
values of one capacitor are each an average of 100 capacitors and those of 
10 capacitors connected in series are each an average of 10 units as shown 
in FIG. 22. 
In FIG. 22, there is shown a circuit diagram in case where 10 
electrochemical double-layer capacitors according to the invention are 
connected in series and in which C.sub.1, C.sub.2 . . . C.sub.10 represent 
capacitor elements and r.sub.1, r.sub.2 . . . r.sub.10 represent resistor 
elements based on the individual resistor plates 112. 
TABLE 2 
__________________________________________________________________________ 
electro- 
rated 
static 
internal 
leakage 
insulating 
applied 
voltage 
capacity 
resistance 
current 
resistance 
voltage 
(V) (F) (.OMEGA.) 
(mA) (K.OMEGA.) 
(V) 
__________________________________________________________________________ 
One Prior art 
1.6 10.5 0.35 0.1-0.5 
3.2-16 
-- 
Capacitor 
capacitor 
Capacitor 
1.6 10.4 0.34 0.5-0.55 
2.9-3.2 
-- 
of 
invention 
10 capaci- 
Prior art 
16 1.05 3.5 0.3-0.4 
40-53 
0.46-3.1 
tor con- 
capacitor 
nected in 
Capacitor 
16 1.04 3.4 0.5-0.55 
29-32 
1.52-1.68 
series 
of 
Invention 
__________________________________________________________________________ 
In order to confirm the effect of the conductive film 116, capacitor A 
using no metal film and capacitor B using the metal film 116b were 
fabricated each five in number and were subjected to lifetime test under 
application of rated voltage for 1000 hours at 70.degree. C. The test 
results are shown in Table 3 below. 
TABLE 3 
______________________________________ 
Rate of variation 
of electrostatic 
Internal resistance 
Leakage current 
capacity (.OMEGA.) (mA) 
______________________________________ 
A -21% 0.35 .fwdarw. 0.80 
0.35 .fwdarw. 0.30 
B -5.8% 0.35 .fwdarw. 0.51 
0.35 .fwdarw. 0.25 
______________________________________ 
FIG. 23 shows a plurality of the capacitors 110 of FIG. 20 which are piled 
up successively for permitting their connection in series and encased in a 
metal casing 120. At the top of the piled capacitors are placed a 
conductive plate 122 from which an external terminal 124 extends and an 
insulating plate 126 which is distant from the conductive plate and on 
which is placed a conductive metal sheet 128 with a terminal 129. The 
conductive sheet 128 is in an L form and has a portion 128a extending 
along the inner wall of the casing 120 and connected to the conductive 
film of the capacitor at the bottom. The free end of the casing 120 is 
enfolded and has an insulating member 130 at the tip thereof by which the 
conductive plate 122, and the conductive plate 128 is rather forced 
against the bottom of the casing assuring an electrical contact of the 
capacitors. 
FIG. 24 shows two capacitors connected in parallel, in which the capacitor 
elements 12 are placed at a distance similarly to the case of FIG. 20 but 
they are mounted on a common conductive base of the film sheet 116. 
In the foregoing embodiments, the capacitor element 12 as in FIG. 3 is of 
the type in which a pair of electrodes are in face-to-face relation but 
are separated with a spacer. Other types of the capacitor element as shown 
in FIGS. 25 to 28 are also usable. 
FIG. 25 shows a capacitor element 130 which comprises a polarization 
electrode plate 132 with an aluminium conducting member 134 which is 
substantially completely covered with a spacer 136. The spacer 136 is 
surrounded by another electrode plate 138 with an aluminium conducting 
member 140. Aluminium leads 142, 144 are disposed on the respective 
electrodes or conducting members. 
FIGS. 26 and 27 show a similar capacitor element 150, in which two 
polarization electrode sheets or films 152, 154 are convolutely wound 
through two spacers 156, 158, in the form of a cylinder or oval. Aluminium 
leads are indicated by numerals 160, 162, respectively. 
FIG. 28 shows another type of the capacitor element comprises a plurality 
of element units 170 each having a pair of polarization electrodes 172, 
174, having aluminium conducting members 176,178, respectively. The 
electrodes 172, 174 are in face-to-face relation through a spacer 180. 
Adjacent two element units are connected through one of the conducting 
members 176,178 which is used in common. Another conducting member is in 
connection with an adjacent element unit in the opposite side. In this 
manner, a plurality of element units are successively connected to form a 
capacitor element. The element units at opposite ends are provided with 
metal leads 182, 184, respectively. 
The electrochemical double-layer capacitor according to the invention has 
wide utility in the field of electrical or electronic apparatuses. Typical 
examples of application of such capacitor are shown in FIGS. 29 to 31 in 
which the capacitor is indicated by C. 
In FIG. 29, the capacitor C is connected in parallel to a load and used as 
a back-up or stand-by power source for electronic appliances, particularly 
useful as a back-up power source for semiconductor memory elements. 
In FIG. 30, the capacitor C is connected in parallel to various types of 
small-size battery by which it serves as a compensator at the time of 
overload or at low temperature. 
In a safety device of FIG. 31 using a thermocouple for preventing the flame 
of gas fittings from dying out during use, the capacitor is usable as a 
power source for instantaneously retaining a safety valve.