Note: Descriptions are shown in the official language in which they were submitted.
213'324
72057-32
Polarizable Electrode for Electric Double-layer Capacitor, Process for Pro-
duction Thereof, and. Electric Double-layer Capacitor Using Said Polarizable
Electrode
Background of the Invention
( 1 ) Field of the Invention
The present invention relates to a polarizable electrode for elec-
tric double-layer capacitor, a process for producing the polarizable elec-
trode, and an electric double-layer capacitor using the polarizable elec-
trode.
(2) Description of Prior Art
Electric double-layer capacitors are in use in the form of a small
but large capacitance capacitor as a backup electric source for memory of
microcomputer, etc. Electric double-layer capacitors commercialized cur-
rently, however, have a high internal resistance and allows for charging
and discharging of only up to about several milliamperes. Hence, it is de-
sired to develop an electric double-layer capacitor capable of being
charged with or discharging a large electric current of several amperes t o
several hundreds of amperes momentarily.
2o With respect to the polarizable electrode for use in electric dou-
1
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72057-32
ble-layer capacitor, capable of being charged with or discharging a large
electric current, there have hitherto been made various proposals. There
were proposed, for c;xample, a paste-like polarizable electrode obtained by
mixing an active carbon powder and an electrolyte [Japanese Patent Publ i-
cation Kokai (Laid-Open) No. 102914/1989] and a polarizable electrode
using an active carbon fiber [Japanese Patent Publication Kokai
Laid-Open) No. 141ti29/1991]. These polarizable electrodes using an ac-
tive carbon powder or an active carbon fiber, however, have a high i n t a r-
nal resistance owing to the weak contact between active carbon particles,
l0 or cause reduction in capacity owing to the falling off of powder or detach-
ment of fiber.
Hence, there was proposed a polarizable electrode obtained b y
pyrolyzing a mixture of an active carbon powder and a phenol in an inert
atmosphere [Japane;~e Patent Publication Kokai (Laid-Open) No. 2 8 8 3 61 /
1992]. In this polarizable electrode, however, an electrolyte is unable to
infiltrate sufficiently into the electrode when the electrode is thick and, as
a result, the capacit~~r assembled with the electrode has an increased in-
ternal resistance. 'there was also proposed an activated porous carbon
material obtained by pyrolyzing a phenol foam having cells perpendicular
2o to the electrode surFace and then activating the resulting material [Japa-
2
2i3'~324
72057-32
nese Patent publication Kokai (Laid-Open) No. 177713/1992]. In this
polarizable electrode obtained by activating a carbon foam of block form,
there are no increa~;e in internal resistance and the falling-off of powder;
however, the activation remains only at the surface and it is impossible to
make a large electrostatic capacity per unit volume or unit weight.
Further, a very small amount of an alkali metal or alkaline earth
metal contained in I:he foam as a foaming agent, when the electrode is a s -
sembled into a capacitor, shortens the cycle life of the capacitor.
l0 Object and Summary of the Invention
An object of the present invention is to provide a polarizable
electrode for electric double-layer capacitor, which is free from the
above-mentioned drawbacks of the prior art and which has a low internal
resistance and can he charged with or discharge a large electric current of
several amperes to several hundreds of amperes momentarily; a process
for producing such a polarizable electrode; and an electric double-layer
capacitor using such a polarizable electrode.
In the course of a study to achieve the above object, the present
inventors thought of an idea that a polarizable electrode having discontin-
2o uous portions (e.g. ohroughholes) on the surface and/or inside can easily
3
21.3'~32~ X2057-32
be impregnated wil.h an electrolyte and enables easy migration of an ion
in the electrode anal, as a result, such an electrode has a low internal r a -
sistance even thoul;h it has a large thickness and need not contain any
foaming agent (e.g. alkali metal or alkaline earth metal), whereby an elec-
tric double-layer capacitor having a long cycle life may be provided. The
present inventors nnade a further study based on the idea and completed
the present invention.
The present invention provides:
a polarizalble electrode for electric double-layer capacitor, which
1 o comprises a solid active carbon obtained by pyrolyzing a mixture mainly
containing an active: carbon and a thermosetting resin and which has, on
the surface and/or inside, discontinuous portions free from the solid ac-
tive carbon,
a process for producing the above polarizable electrode for elec-
tric double-layer capacitor, which comprises heat-treating, as necessary, a
mixture mainly containing an active carbon, a thermosetting resin and a
fiber capable of vaporizing upon heating, to vaporize the fiber and then
pyrolyzing the resulting material, and
an electric double-layer capacitor comprising at least a pair of the
above polarizable electrodes and an electrolyte impregnated between the
4
213'7~~4
72052-32
polarizable electrodes.
Detailed Description of the Invention
The present invention is hereinafter described in detail.
The active carbon used in the present invention is not particular-
ly restricted with respect to the type and includes those obtained by car-
bonizing a natural fiber (e.g. sawdust or coconut husk), an aromatic poly-
cyclic compound present in coal, petroleum or the like, or a synthetic resin
of phenolic resin type, acrylic resin type, aromatic polyamide type, cellu-
lose type or the like; and then activating the resulting material by an ordi-
nary method. The form of the active carbon may be any of powder,
granules, fiber, etc. The specific surface area of the active carbon has no
particular restriction, either but is preferably 500 m2/g or more.
The thermosetting resin used in the present invention is not p a r-
ticularly restricted with respect to its composition and includes known
resins such as polycarbodiimide resin, phenolic resin, furan resin, epoxy
resin and the like.
The fiber capable of vaporizing upon heating, used in the present
invention is not particularly restricted and can be any synthetic or natural
fiber capable of vaporizing at the heat-treating temperature or pyrolyzing
5
2i3'~324
temperature adopted in the process (described later) for producing a
polarizable electrode for electric double-layer capacitor according to the
present invention. 'Che fiber can be exemplified by a polyvinyl alcohol, a
polyethylene, a polystyrene, a polypropylene, a polyester, a polyethylene
glycol and a cellulose (these are hereinafter abbreviated to "fiber compo-
nent").
In producing the polarizable electrode of the present invention
for electric double-layer capacitor, there is first prepared an active carbon
mixture by mixing an active carbon, a thermosetting resin and a fiber
component all mentioned above. In this mixing step, there can be used a
known method ordinarily used in the mixing of such components, for ex-
ample, a stirring rod, a kneader, a ball mill, a mixer, a static mixer and a
ribbon mixer.
The proportions of the active carbon and the fiber component
can be determined depending upon, for example, the intended properties
of the polarizable electrode to be produced. For example, the proportion of
the active carbon is 100 parts by weight and the proportion of the fiber
component is 0.01-100 parts by weight, preferably 0.05-80 parts by
weight. When the proportion of the fiber component is less than the
2o range, it may happen that the discontinuous portions of electrode free
6
2~ 373 2 4
from any solid active carbon are blocked owing to the shrinkage
of electrode during the pyrolyzing step described later and, as
a result, the electrode is not well impregnated with an electro-
lyte and has a high internal resistance. Conversely when the
proportion of the fiber component is more than the range, it may
happen that the electrode has a low strength and is unable to
withstand the actual use.
The proportions of the active carbon and the thermo-
setting resin can also be determined depending upon, for example,
the intended properties of the polarizable electrode to be
produced. For example, the proportion of the active carbon is
100 parts by weight and the proportion of the thermosetting resin
is 0.5-100 parts by weight, preferably 1-50 parts by weight.
Depending upon the case, there may be used, in addition
to the above components, an electrically conductive agent such as
expanded graphite, graphite, carbon black, ketjen black, carbon
whiskers, metal powder and the like. The amount of the
electrically conductive agent, where used, may vary depending on
a variety of factors but preferably is up to 1,000 parts by
weight per 100 parts by weight of the active carbon.
The above-prepared active carbon mixture is then molded,
as necessary, into a desired shape. This molding step can be
conducted by a conventionally known method such as pressure
molding, hydrostatic molding, extrusion molding, injection
molding, belt pressing, roll pressing
7
72057-32
213~32~,
or the like. Incidentally, this molding step can be omitted depending upon
the shape of the active carbon mixture.
The molded active carbon mixture is heat-treated to vaporize the
fiber component present therein. The atmosphere used in this step may
be a conventionally known gas, for example, at least one gas selected from
non-oxidizing gases ~;uch as vacuum, argon, hydrogen and the like, or from
oxidizing gases such as air, carbon dioxide, oxygen, propane gas and t h a
like. The heat-treatment temperature used in this step can be determined
depending upon, for example, the thermal decomposabilities of the f i b a r
l0 component, active carbon and thermosetting resin present in the active
carbon mixture, but is, for example, 100-600°C, preferably 150-
550°C.
The heat-treatment step may be omitted because it is conducted
to vaporize the fib~:r component beforehand to shorten the time of the
pyrolyzing step described later.
The material obtained by the heat-treatment step is then
pyrolyzed. This pyrolyzing step can be conducted by any conventionally
known method in, f~~r example, a non-oxidizing atmosphere such as vacu-
um, argon, hydrogen or the like. The pyrolyzing temperature has no up-
per limit but the pyrolyzing is conducted for example, at 600-3,000°C,
preferably at 700-1,500°C. Pyrolyzing at temperatures higher than
8
213"7324
72057-32
3,000°C invites severe oxidation and wastage of kiln and is not
realistic.
Pyrolyzing at temperatures lower than 600°C gives an electrode of high
internal resistance and of small capacity.
The material obtained by the pyrolyzing step is cut into a desired
shape to obtain a p~olarizable electrode for electric double-layer capacitor.
The cutting can be made by any conventionally known method such as
cutting by cutter, cutting by ultrasonic wave, or the like.
The cutting may be conducted not after the pyrolyzing step b a t
after or before the heat-treatment step, or may be omitted depending up-
l0 on the shape of the active carbon mixture.
The thus-obtained polarizable electrode for electric double-layer
capacitor according to the present invention comprises a solid active car-
bon obtained by pprolyzing a mixture mainly containing an active carbon
and a thermosetting resin and has, on the surface and/or inside, discontin-
uous portions free from the solid active carbon. Herein, the discontinuous
portions refer to holes, gaps, dents, grooves, etc. and are formed by the
vaporization of the fiber component, or by the deformation or compression
of the holes, etc. formed as above, occurring as a result of the shrinkage of
the active carbon mixture during its heat-treatment or pyrolyzing.
In the present invention, there is used a fiber component as the
9
213'324 72057-32
component capable ~of vaporizing upon heating, and the fiber component
has a high aspect ratio and tends to align in one direction owing to the
pressure applied during molding. Therefore, when the active carbon mix-
ture is heat-treated to vaporize the fiber component and the resulting
material is pyrolyzed in an inert gas, the resulting polarizable electrode
has discontinuous portions (e.g. throughholes) having a shape correspond-
ing to the shape of the fiber component.
Depending upon the direction of the cutting conducted after h a a t
treatment or pyrolyzing, the polarizable electrode can have holes each
having a direction parallel or nearly parallel, or perpendicular or nearly
perpendicular to the; electrode surface and thereby can easily be impreg-
nated with an electrolyte.
When the discontinuous portions are holes, the small holes hav-
ing diameters of 1 nm to 5 mm are 95% or more of the total holes present
in the polarizable ellectrode for electric double-layer capacitor according to
the present invention. The porosity (the proportion of volume of total
holes) in the present polarizable electrode for electric double-layer capaci-
for is 20-80%.
By using at least a pair of the thus-obtained polarizable electrode s
for electric double-layer capacitor as a positive electrode and a negative
213"324 72057-32
electrode, and appropriate electrolyte impregnated between these
electrodes, an electric double-layer capacitor having a low
internal resistance according to the present invention can be
produced. Preferably, these electrodes are firmly bonded to an
appropriate collector electrode.
As the electrolyte, for example, an organic electrolyte
obtained by dissolving an electrolyte such as LiAsF6, LiBF4,
LiPF6, LiC104, a tetraalkylammonium salt or a tetrafluoroborate
salt in an organic solvent such as ethylene carbonate, propylene
carbonate, butylene carbonate, dimethyl carbonate, y-butyro-
lactone,acetonitrile, 1,2-dimethoxyethane, sulfolane, nitro-
methane or a mixture thereof, and an aqueous electrolyte obtained
by dissolving an electrolyte such as KOH, NaOH, H2S04, HCl, HN03,
ZnCl, ZnBr2 in water, can be used.
The present invention is hereinafter described
specifically by way of Examples.
Example 1
There were mixed a polycarbodiimide resin powder
(average particle diameter = 10 um), an active carbon powder
(average particle diameter = 10 um, specific surface area =
1,800 m2/g) and PV.A (polyvinyl
11
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72057-32
alcohol) short fibers (fiber diameter = 20 pm, fiber length = 3 mm). The
mixing ratio of the l:hree components is shown in Table 1. In Table 1, each
number is by parts by weight (this applies also to Tables 3, 5, 8, 12 and
15).
Table 1
No. Active carbon Thermosetting resinPVA short fiber
1-1 10 0 0.5 0.01
1-2 100 0.5 100
1 - 3 10 0 10 0 0.01
1-4 100 100 ( 100
Each of the; above mixtures was stirred in a ball mill for 24 hours.
The resulting materi~.al was placed in a square mold of 50 mm x 50 m m
(internal dimension) and subjected to pressure molding at a pressure of 3 0
l0 kg/cm2 at 100°C for 30 minutes. The molded article was heat-treated
a p
to 400°C in the air to vaporize the fiber and then pyrolyzed up to
900°C in
a nitrogen gas atmosphere. The pyrolyzed product was cut so that the
throughholes were perpendicular to the product (electrode) surface, to
prepare sheet electrodes (polarizable electrodes) each of 3 mm in thick-
ness. Each electrode was measured for porosity and proportion of small
holes of 1 nm to 5 mm in diameter in total holes, by a mercury
12
213'324 72057-32
porosimetry. A collector electrode (a vitreous carbon produced by
Nisshinbo Industries, Inc. was used as the collector) was bonded to the
polarizable electrode: by the use of a conductive adhesive. Ztao of the same
such
laminate were used as a positive electrode and a negative electrode and
were vacuum-imprel;nated with a propylene carbonate solution containing
1 mole/liter of tetralbutylammonium perchlorate, whereby electric double-
layer capacitors were produced. A constant current of 1 kHz and 10 mA
was passed through each capacitor and the voltage between the electrodes
was measured to dfaermine the equivalent series resistance of the capaci-
tor. The porosity, the proportion of small holes of 1 nm to 5 mm in diame-
ter in total holes and the equivalent series resistance are shown in Table 2.
Table 2
No. Equivalent seriesPorosity Proportion of small holes (1
resistance (~) (%) nm to
5 mm in dia.) in total holes
(%)
1-1 4.00 40 95
1-2 1.00 80 98
1-3 2.00 20 95
1-4 0.-'i0 70 96
Example 2
There were mixed a phenolic resin powder (average particle di-
ameter = 10 pm), an active carbon powder (average particle diameter = 10
13
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72057-32
p.m, specific surface area = 1,800 m2/g) and PVA short fibers (fiber diam-
eter = 20 pm, fiber length = 3 mm). The mixing ratios of the three compo-
nents
are shown in Table ~s.
Table 3
No. Active carbonThermosetting resinPVA short fiber
2-1 10~D 0.5 0.01
2-2 1 0 0.5 10 0
2-3 100 100 0.01
2-4 100 100 100
Each of the above mixtures was stirred, molded and heat-treated
in the same manner as in Example 1. The pyrolyzed product was cut so
that the throughhole;s were parallel to the product (electrode) surface, to
l0 prepare sheet electrodes (polarizable electrodes) each of 3 mm in thick-
ness. Each electrode was measured for porosity and proportion of small
holes of 1 nm to 5 mm in diameter in total holes, by a mercury
porosimetry. A collector electrode (a vitreous carbon produced by
Nisshinbo Industries, Inc. was used as the collector) was bonded to the
polarizable electrode; by the use of a conductive adhesive. using two of the
same
such laminate as a positive electrode and a negative electrode, electric
14
.. 213"324
72057-32
double-layer capacitors were produced, and the equivalent series resis-
tance of the capacitor was determined in the same manner as in Example
1. The porosity, the proportion of small holes of 1 nm to 5 mm in diame-
ter in total holes and the equivalent series resistance are shown in Table 4.
Table 4
No. Equivalent seriesPorosity Proportion of small holes (1
resistance (S2) (%) nm to
5 mm in dia.) in total holes
(%)
2-1 4.~!0 4 3 96
2-2 1.06 80 99
2-3 2.112 20 95
2-4 0.-'i3 72 96
Example 3
There were mixed a polycarbodiimide resin powder (average
particle diameter = 10 pm), an active carbon powder (average particle di-
l0 ameter = 10 pm, specific surface area = 1,800 m2/g), PVA short fibers
(fiber diameter = 2(I p m, fiber length = 3 mm) and an expanded graphite
powder (average particle diameter = 10 p m). The mixing ratios ~ the four
components are shown in Table 5.
213'7324
72057-32
Table 5
No. Active carbon PolycarbodiimideExpanded PVA short
resin graphite fiber
3 - 1 I 1 01) 0.5 I 0.01 I 0.01
3-2 101) 0.5 0.01 100
3-3 100 0.5 1000 0.01
3-4 I 100 0.5 1000 100
3-S 100 100 0.01 0.01
3 -6 100 100 0.01 100
3-7 I 100 100 I 1000 0.01
3-8 100 I 100 I 1000 I 100
Each of the above mixtures was stirred) molded and heat-treated
in the same manner as in Example 1. The pyrolyzed product was cut so
that the throughholes were perpendicular to the product (electrode) sur-
face, to prepare sheet electrodes (polarizable electrodes) each of 3 mm in
thickness. Each electrode was measured for porosity and proportion of
small holes of 1 nm to S mm in diameter in total holes, by a mercury
porosimetry. A collector electrode (a vitreous carbon produced by
l0 Nisshinbo Industries, Inc. was used as the collector) was bonded to the
polarizable electrode by the use of a conductive adhesive. Using t~ao of the
same
such laminate as a positive electrode and a negative electrode, electric
double-layer capacitors were produced, and the equivalent series resis-
16
.. 213,~32~
lance of the capacitor was determined in the same manner as in Example
1. The porosity, the proportion of small holes of 1 nm to 5 mm in diame-
ter in total holes andl the equivalent series resistance are shown in Table 6.
Table 6
No. Equivalent seriesPorosityProportion of small holes (1
resistance; (ms2 (%) nm to
) 5 mm in dia.) in total holes
(%)
3 -1 300() 4 1 9 5
3 - 2 750 7 9 9 8
3-3 I 100 22 95
3-4 2.'> 75 96
3 - 5 270!) 3 1 9 5
3 - 6 96!) 8 0 9 9
3-7 31) 20 I 95
3-8 '7 70 96
Example 4
Using each of the polarizable electrodes prepared in Example 1, a
positive electrode and a negative electrode were prepared. They were
vacuum-impregnated with an aqueous solution containing 30% by weight
l0 of sulfuric acid, whf;reby electric double-layer capacitors were produced.
Each capacitor was determined for equivalent series resistance in the s ame
manner as in Example 1. The results are shown in Table 7. Each capacitor
was charged with and discharged a current of 200 A and then was ob-
17
72057-32
served. The observation results are shown in Table 18.
Table 7
No. Equivalent series resistance (rnS2
)
4-1 65
4-2 1 5
!
~
4-3 31
4-4 8
Example 5
There were mixed a phenolic resin powder (average particle di-
ameter = 10 p m), an active carbon powder (average particle diameter = 10
pm, specific surface area - 1,800 m2/g) and PVA (polyvinyl alcohol)
short fibers(fiber diameter = 20 pm, fiber length = 3 mm). The mixing ra-
tins of the three components are shown in Table 8.
Table 8
No. Active carbon Polycarbodiimide resinPVA short fiber
5-1 100 0.5 0.01
5-2 100 0.5 100
5-3 100 100 0.01
5-4 100 100 100
Each of the above mixtures was stirred, molded and heat-treated
in the same manner as in Example 1. The pyrolyzed product was cut so
18
2~.3'~4
72057-32
that the throughhole;s were perpendicular to the product (electrode) sur-
face, to prepare sheet electrodes (polarizable electrodes) each of 3 mm in
thickness. Each electrode was measured for porosity and proportion of
small holes of 1 nm to 5 mm in diameter in total holes, by a mercury
porosimetry. A collector electrode (a vitreous carbon produced by
Nisshinbo Industries,, Inc. was used as the collector) was bonded to the
polarizable electrode by the use of a conductive adhesive in the same
manner as in Example 1. using two of the same such laminate as a positive
electrode and a negative electrode, electric double-layer capacitors were
1 o produced and the equivalent series resistance of each capacitor was deter-
mined in the same manner as in Example 1. The porosity, the proportion
of small holes of 1 nm to 5 mm in diameter in total holes and the equiva-
lent series resistance are shown in Table 9.
Table 9
No. Equivalent seriesPorosity Proportion of small holes (1
resistance (S2) (%) nm to
5 mm in dia.) in total holes
(%)
5-1 6.(10 40 95
5-2 1.x;0 80 9 8
' 5-3 2. i'0 20 95
5-4 0.T0 7 0 9 6
Example 6
19
~'~ 373 2 4
using the sheet electrode produced in Example 1 and corresponding to
the electric double-layer capacitor No. 1-2, there was produced electric
double-layer capacitor in the same manner as Example 1. The capacitor
was measured for equivalent series resistances after 1, 100, 500 and
1,000 cycles in the same manner as in Example 1. The results are shown
in Table 10.
Table 10
Cycles (times)
1 100 500 1000
Equivalent series 1.00 1.01 1.01 1.02
resistance (S2)
Example 7
l0 using the sheet electrode produced in Example 1 and corresponding to
the electric double-l~iyer capacitor No. 1-2, there were produced three
electric double-layer capacitors in the same manner as in Example 1. Each
capacitor was measured for equivalent series resistance in the same man-
ner as in Example 1. The results are shown in Table 11.
72057-32
:r'
21.3'~3~4
Table 11
Electrode
thickness
(mm)
1 3 5
Equivalent series resistance 0. 8 1.0 ~ 1. 2
(S2 ) I ~
Comparative Example 1
There were; mixed a polycarbodiimide resin powder (average
particle diameter = l0 pm) and an active carbon powder (average particle
diameter = 10 pm, specific surface area = 1,800 m2/g). The mixing ratios
of the two components are shown in Table 12.
Table 12
No. Active carbon Polycarbodiimide resin
--
Comp. Ex. 1-1 10 0 0.5
Comp. Ex. 1-2 10 0 10 0
1o Each of the above mixtures was stirred) molded and heat-treated
in the same manner as in Example 1. From each pyrolyzing product was
prepared a sheet electrode (polarizable electrode) of 3 mm in thickness.
Each polarizable electrode was measured for porosity and proportion of
small holes of 1 nm~ to 5 mm in diameter in total holes, by the mercury
porosimetry. A collector electrode (a vitreous carbon produced by
Nisshinbo Industrie~~, Inc. was used as the collector) was bonded to the
21
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72057-32
polarizable electrode by the use of a conductive adhesive in the same
manner as Example 1. Using two of the same such laminate as a positive elec-
trode and a negative; electrode, electric double-layer capacitors were pro-
duced) and each capacitor was determined for equivalent series resistance
in the same manner as in Example 1. The porosity, the proportion of small
holes of 1 nm to 5 mm in diameter in total holes and the equivalent series
resistance are shown in Table 13.
Table 13
No. Equivalent seriesPorosity Proportion of small holes (1
nm to
resistance (SZ) (%) 5 mm in dia.) in total holes
(%)
Comp. 7 0 8 5 9 9
Ex. 1-1
Comp. 3 ',~ 1 0 1 2
Ex. 1-2
Comparative Example 2
Using the sheet electrode produced in Example 1 and corresponding to
the electric double-layer capacitor No. 1-1, there were produced three
electric double-layer capacitors in the same manner as in Example 1. Each
capacitor was measured for equivalent series resistance in the same man-
I S ner as in Example 1. The results are shown in Table 14.
22
21~3'~324
72057-32
Table 14
Electrode
thickness
(mm)
1 3 5
Equivalent series r~aistance 5 0 7 0 2 8 0
(s2 )
Comparative Example 3
There were mixed a phenolic resin powder (average particle di-
ameter = 10 pm) and an active carbon powder (average particle diameter
- 10 pm, specific surface area = 1,800 m 2/g). The mixing ratios of the
above two components are. shown in Table 15.
Table 1 S
No. Active carbon Phenolic resin
Comp. Ex. 3-1 10 0 0.5
Comp. Ex. 3-2 10 0 1 0 0 ',
1o Each of the above mixtures was stirred, molded and heat-treated
in the same manner as in Example 1. From each pyrolyzed product was
prepared a sheet ellectrode (polarizable electrode) of 3 mm in thickness.
Each polarizable electrode was measured for porosity and proportion of
small holes of 1 nm to 5 mm in diameter in total holes, by the mercury
porosimetry. A collector electrode (a vitreous carbon produced by
Nisshinbo Industries, Inc. was used as the collector) was bonded to the
23
213"7324 72057-32
polarizable electrode by the use of a conductive adhesive. Using two of the
same
such laminate as a positive electrode and a negative electrode, electric
double-layer capacit~~rs were produced in the same manner as in Example
1. A constant current of 1 kHz and 10 mA was passed through each capac-
itor and the voltage between the electrodes was measured to determine
the equivalent series resistance of the capacitor. The porosity, the propor-
tion of small holes of 1 nm to 5 mm in diameter in total holes and the
equivalent series resistance are shown in Table 16.
Table 16
No. Equivalent seriesPorosity Proportion of small holes (1
nm to
resistance (S2) (%) 5 mm in dia.) in total holes
(%)
Comp. 10 0 8 4 9 9
Ex. 3-1
Comp. 4 '1 9 1 1
Ex. 3-2
to
Comparative Example 4
Using each of the polarizable electrodes prepared in Comparative
Example 3, a positive electrode and a negative electrode were prepared.
They were vacuum-impregnated with an aqueous solution containing 30%
by weight of sulfuric acid, whereby electric double-layer capacitors were
produced. Each capacitor was determined for equivalent series resistance
24
213'324 72057-32
in the same manner as in Example 1. The results are shown in Table 17.
Each capacitor was charged with and discharged a current of 200 A and
then was observed. The observation results are shown in Table 18.
Table 17
No. Equivalent series resistance (mSZ)
Comp. Ex. 4-1 3 0
Comp. Ex. 4-2 1 2
Table 18
No. Appearance of electrodes
4 - 1 Normal
4 - 2 Normal
4 - 3 Normal
j 4 - 4 Normal
Comp. Ex. 4-1 Electrodes collapsed into pieces.
- -
Comp. Ex. 4-2 Electrodes collapsed into pieces.
Comparative Example 5
A phenolic foam having a bulk density of 0.1 g/cm3 and a foam
l0 direction perpendicular to the surface of the electrode to be prepared
therefrom, was pyrolyzed at 900°C in a nitrogen gas atmosphere. The
pyrolyzed product was kept for 3 hours in a mixture of nitrogen gas and
carbon dioxide gas for activation. The activation product was measured
213"324 72057-32
for porosity and proportion of small holes of 1 nm to 5 mm in diameter in
total holes, by the mercury porosimetry, which were 15% and 93%, respec-
tively. The activation product was cut into a size of 10 mm (diameter) x 3
mm (thickness) and bonded to vitreous carbon (a product of Nisshinbo
Industries) Inc.) by the use of a conductive adhesive. The resulting lami-
nate was vacuum-impregnated with a propylene carbonate solution con-
taming 1 mole/liter of tetrabutylammonium perchlorate, whereby an elec-
tric double-layer capacitor was produced. The capacitor was determined
for equivalent series resistances after 1, 100, 500 and 1,000 cycles in the
l0 same manner as in Example 1. The results are shown in Table 19.
Table 19
Cycles
(times)
1 100 500 1000
Equivalent series 2 1 5 0 15 3 2 21
resistance (S2
)
Comparative Example 6
To each of the two polarizable electrodes prepared in Compara-
tive Example 1, a hole of a size of 8 mm in diameter was made with a drill
to prepare two polarizable electrodes. Each electrode was measured for
porosity and proportion of small holes of 1 nm to 5 mm in diameter in to-
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tal holes, by the mercury porosimetry. Each electrode was bonded to a
collector electrode (; vitreous carbon produced by Nisshinbo Industries,
Inc. was used as the collector) by the use of a conductive adhesive, in t h a
same manner as in Example 1. Using two of the sate such laminate as a posi-
tive electrode and a. negative electrode, two electric double-layer capaci-
tors were produced in the same manner as in Example 1. The capacitors
were measured for electrostatic capacity. The capacitors were determined
for equivalent series resistance in the same manner as in Example 1. The
porosity, the proportion of small holes of 1 nm to 5 mm in diameter in to-
1 o tal holes, and the equivalent series resistance are shown in Table 20.
Table 20
No. Equivalent seriesPorosity Proportion of small holes (1
nm to
resistance (S2) (%) 5 mm in dia.) in total holes
(%)
Comp. 2 (10 8 5 9 0
Ex. 6-1
Comp. 5 0 0 8 7 10
Ex. 6-2
As is clear from the above, the electric double-layer capacitor of
the present invention has a sufficiently low internal resistance and yet a
long cycle life.
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