U.S. patent application number 10/106585 was filed with the patent office on 2003-04-03 for electrochemical device and process for manufacturing same.
Invention is credited to Inoue, Koshi, Mushiake, Naofumi, Sassa, Robert L..
Application Number | 20030062259 10/106585 |
Document ID | / |
Family ID | 23197266 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030062259 |
Kind Code |
A1 |
Mushiake, Naofumi ; et
al. |
April 3, 2003 |
Electrochemical device and process for manufacturing same
Abstract
A plurality of polarizable electrodes, a laminate of a collector
layer, a polarizable electrode layer of a porous sheet, and a
carbon-based conductive material interposed therebetween, are
disposed in a row arrangement, interposing separators between the
polarizable electrodes, and an electrolyte is packed between said
polarizable electrodes and said separators; the carbon-based
conductive material penetrating into the voids in the polarizable
electrode layers. A process is provided whereby the polarizable
electrode is manufactured by applying a conductive material
solution to the collector and/or polarizable electrode sheet
surface, superposing the two, and then evaporating out the
dispersion medium of the conductive material solution.
Inventors: |
Mushiake, Naofumi;
(Okinawa-shi, JP) ; Inoue, Koshi; (Okayama-shi,
JP) ; Sassa, Robert L.; (Newark, DE) |
Correspondence
Address: |
W. L. Gore & Associates, Inc.
551 Paper Mill Road
P.O. Box 9206
Newark
DE
19714-9206
US
|
Family ID: |
23197266 |
Appl. No.: |
10/106585 |
Filed: |
April 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10106585 |
Apr 1, 2002 |
|
|
|
09309227 |
May 10, 1999 |
|
|
|
Current U.S.
Class: |
204/290.01 ;
204/284; 204/294 |
Current CPC
Class: |
H01G 11/38 20130101;
H01M 4/663 20130101; H01M 4/667 20130101; H01M 4/368 20130101; H01M
4/661 20130101; H01G 11/02 20130101; H01G 9/155 20130101; H01M 4/02
20130101; H01G 11/28 20130101; H01M 4/00 20130101; H01M 6/14
20130101; Y02E 60/13 20130101 |
Class at
Publication: |
204/290.01 ;
204/284; 204/294 |
International
Class: |
C25B 011/00 |
Claims
What is claimed is:
1. In an electrochemical device having an electrode layer having
pores and a thickness, and a collector layer, the improvement
comprising an adhesive for attaching said electrode layer to said
collector layer, said adhesive comprising electrically conductive
carbon and a binder, wherein a portion of said adhesive is disposed
within the pores of the electrode layer to a depth of about 0.15%
to 30% of the thickness of the electrode layer.
2. An electrochemical device as defined in claim 1 wherein said
portion of said adhesive disposed within the pores of the electrode
layer extends to a depth of about 0.25% to about 15% of the
thickness of the electrode layer.
3. An electrochemical device as defined in claim 1 wherein said
electrically conductive material is graphite or carbon black.
4. An electrochemical device as defined in claim 1 wherein said
electrically conductive material has an average particle size of
about 0.5 microns to about 50 microns.
5. An electrochemical device as defined in claim 1 wherein said
binder consists of at least one material selected from the group
consisting of thermoplastic resins, cellulose derivatives, and
water glass.
6. An electrochemical device as defined in claim 1 wherein said
electrically conductive carbon is present in an amount of about 20%
to about 30% and said binder is present in an amount by weight of
from about 4% to about 20%.
7. An electrochemical device as defined in claim 1 wherein said
electrically conductive carbon and said binder are present in a
relative amount by weight of about 5:1 to about 1:1, electrically
conductive carbon to binder.
8. An electrochemical device as defined in claim 6 further
comprising a dispersion medium present in an amount by weight of
about 45% to about 75%.
9. An electrochemical device as defined in claim 8 further
comprising an additive.
10. An electrochemical device as defined in claim 9 wherein said
electrically conductive adhesive is natural graphite present in an
amount by weight of about 30%, said binder is carboxymethyl
cellulose sodium salt present in an amount by weight of about 8%,
said dispersion medium is water present in an amount by weight of
about 60%, and said additive is ammonia present in an amount by
weight of about 2%, said adhesive being disposed in the pores of
the electrode layer to a depth of about 0.25% to about 15% of the
thickness of the electrode layer.
11. An electrochemical device as defined in claim 5 wherein said
binder is waterglass.
12. An electrochemical device as defined in claim 11 for use in a
lithium thionyl chloride battery.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of pending application Ser.
No. 09/309,227, filed May 10, 1999.
FIELD OF THE INVENTION
[0002] The present invention relates to an electrochemical device,
such as a capacitor, an electric double layer capacitor, a battery,
a fuel cell, or an electrolysis device, which employs electrodes
and collector layers, and to a method for manufacturing such an
electrochemical device.
BACKGROUND OF THE INVENTION
[0003] Conventional electrochemical devices come in various types.
Electric double layer capacitor examples include coin and button
types, in which the separator is interposed between the pair of
electrodes, and this, together with the electrolyte, is sealed
within a metal case, a sealing plate, and a gasket that insulates
the two from each other; coil types, in which the electrodes and
separator are coiled to produce an electric double layer capacitor
unit, which is then placed in a metal case and impregnated with the
electrolyte; and stacked types in which a plurality of rectangular
electrodes and separators interposed between the electrodes are
superposed in alternating fashion to produced an electrode
laminate, a positive electrode lead is connected to the positive
terminal and a negative electrode lead is connected to the negative
terminal to produce a electric double layer capacitor unit, which
is then placed in a metal case, impregnated with the electrolyte,
and sealed.
[0004] Energy storage devices for use in power applications must
provide both high energy density and high power density. Typically,
energy density and power density may be traded off, by adjusting
the thickness of the elctrodes. Thicker electrodes favor high
energy density while thinner electrodes favor high power density.
However, increased power density can be obtained without decreasing
the energy density if the internal resistance of the device can be
lowred by improved design. In particular, effecting a low
resistance bond between the active material and the current
collector will lower the internal resistance of the device without
providing an energy penalty.
[0005] The electrodes used in electrochemical energy storage
devices are ordinarily manufactured by (1) a process in which a
mixture of paste or ink form containing the electrode material is
applied to the collector by coating or other means, dried (solvent
removal), and then calendered or the like, or (2) a process in
which a sheet which will serve as the electrode material is first
prepared, and this is then integrated with the collector using a
calender roll or the like. The largest drawback of these methods is
the questionable ability to produce good contact between the
collector and the electrode material powder. Techniques effective
for producing an electric double layer capacitor having good
contact between the collector and the electrode material and
exhibiting low internal resistance include increasing the contact
area and creating adequate interpenetration between the collector
and the electrode material.
[0006] Specific examples of processes falling under (1) are a
method in which a paste consisting of activated carbon powder, a
fluoropolymer, and methyl alcohol is coated onto an aluminum net
which serves as the collector (Japanese Laid-Open Patent
Application 4-162510); a method in which a slurry prepared by
adding an aqueous solution of carboxymethyl cellulose to a mixed
solution containing activated carbon powder, acetylene black,
water, and methanol is applied to the roughened surface of aluminum
foil serving as the collector (Japanese Laid-Open Patent
Application 4-162510); and a method in which a mixture of polyvinyl
pyrrolidone and an aqueous dispersion of polytetrafluoroethylene is
added as a binder to activated carbon powder and acetylene black,
and this is applied to aluminum expanded metal which serves as the
collector (U.S. Pat. No. 4,327,400). Specific examples of processes
falling under (2) are a method in which an electrode material sheet
is prepared from activated carbon powder, a conductive agent, and
polytetrafluoroethylene used as binder to bind, the electrode
material sheet is superposed on a collector consisting of a metal
foil with a surface roughened by etching, an expanded metal, or
other material, and is then fed through a calender roll to produce
a thin electrode (Japanese Patent Publication 54-12620).
[0007] Since the electrode material is actually a powder aggregate,
its surface may be imagined as having extremely tiny peaks and
valleys. Accordingly, contact between the collector surface and the
electrode surface occurs in a point-contact configuration. Where
the surface of the metal foil serving as the collector has been
roughened, the increased surface area reduces the internal
resistance of the electric double layer capacitor.
[0008] However, contact area cannot be considered to reach adequate
levels, even where the collector surface has been roughened. The
bonding strength between the electrode material sheet and the
collector is not adequate to withstand the feed tension and winding
during continuous production of electrodes in roll form, and
contact tends to weaken over time.
[0009] In a collector consisting of expanded metal or the like
provided with openings, contact is improved by causing the
electrode material to penetrate into the openings provided in the
collector. However, increasing the opening size to facilitate
penetration has the effect of reducing strength and reducing the
unit cross section of the collector, thereby increasing resistance
of the collector. Thus, the effect in reducing the internal
resistance of the electric double layer capacitor is less than
anticipated.
[0010] The present invention was developed with the foregoing in
view, and is intended to provide an electric double layer capacitor
exhibiting low internal resistance, provided with polarizable
electrodes in which the collector and the electrode material are
securely integrated in such as way as to produce adequate bonding
strength and good contact.
SUMMARY OF THE INVENTION
[0011] The present invention is an electrochemical device provided
with a plurality of electrodes disposed in a row arrangement, a
collector layer laminated to a electrode layer that is fabricated
from a porous sheet consisting principally of activated carbon; a
separator being interposed between said electrodes; and an optional
electrolyte (depending on the type of electrochemical device used)
being packed between said polarizable electrodes and said
separator; characterized in that a carbon-based conductive material
is interposed while laminating said collector layer and said
electrode layer; and said carbon-based conductive material
penetrates into the voids in said electrode layer. Preferably, the
electrodes disposed in a row arrangement, excepting the two
terminal members thereof, include a carbon-based conductive
material interposed at both faces of the collector layer while
laminating the electrode layers thereto, and the carbon-based
conductive material penetrates into the voids of the electrode
layers.
[0012] Preferably, the porosity of the electrode layer is 40 to
90%, and the maximum pore size is 0.5 to 20 .mu.m. The collector
layer preferably consists of at least one type of metal selected
from the group consisting of aluminum, stainless steel, titanium,
and tantalum, and taking the form of a foil, plate, sheet, expanded
metal, punched metal, or mesh. The carbon-based conductive material
preferably consists of a conductive material and a binder. The
conductive material is preferably graphite or carbon black. The
graphite or carbon black preferably has an average particle size of
0.5 to 50 .mu.m. The binder preferably consists of at least one
selected from the group consisting of thermoplastic resins,
cellulose derivatives, and water glass.
[0013] The method for manufacturing an electrochemical device which
pertains to the present invention is characterized by comprising a
step in which a carbon-based conductive material solution prepared
by dispersing a carbon-based conductive material in a dispersion
medium is applied to the electrode material sheet and/or collector
surface; a step in which said electrode material sheet and said
collector are laminated to produced a laminate sheet in which said
carbon-based conductive material solution is interspersed; and a
step in which the dispersion medium is removed from said
carbon-based conductive material solution layer in said laminate
sheet.
DESCRIPTION OF THE DRAWINGS
[0014] The operation of the present invention should become
apparent from the following description when considered in
conjunction with the accompanying drawings, in which:
[0015] FIG. 1 is an illustration of an electrode in an embodiment
of the present invention.
[0016] FIG. 2 is a simplified illustration of an electric double
layer capacitor single unit constitution in an embodiment of the
present invention.
[0017] FIG. 3 is a simplified illustration of the constitution of
an electric double layer capacitor of the present invention
employing the unit depicted in FIG. 2.
[0018] FIG. 4 is a schematic diagram of an embodiment of a process
for making the present invention.
[0019] FIG. 5 is a schematic diagram of another embodiment of a
process for making the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The invention is described herein in connection with an
electric double layer capacitor. The invention applies equally to
all electrochemical devices, however, involving electrodes and
collector layers. These electrochemical devices include, by way of
example and not limitation, capacitors, electric double layer
capacitors, batteries, fuel cells, and electrolysis devices. The
invention specifically includes lithium thionyl chloride batteries
having electrodes, collectors and an interposed adhesive as
described herein.
[0021] First, the polarizable electrode employed in the electric
double layer capacitor which pertains to the present invention will
be described.
[0022] The electric double layer capacitor employed in the present
invention is characterized by a collector layer that is laminated
on each side to a polarizable electrode layer fabricated from a
porous sheet consisting principally of activated carbon, and a
separator being interposed between two or more of such
collector-electrode assemblies, where an adhesive carbon-based
conductive material is disposed between the polarizable electrode
layers and the collector and penetrates into the voids in the
polarizable electrode layer.
[0023] The porous sheet which constitutes the polarizable electrode
layer is produced by combining activated carbon powder with
suitable carbon black, polytetrafluoroethylene, or other powder,
adding ethanol, oil, or the like to the mixture, and then
subjecting the product to roll calendering or other process.
[0024] The porous sheet which constitutes the polarizable electrode
layer has porosity ranging from 40-90%, and preferably 60-80%.
Where the porosity is below 40%, the carbon-based conductive
material does not readily penetrate into the voids of the
polarizable electrode layer. Above 90%, the carbon-based conductive
material tends to penetrate depthwise far into the pores of the
polarizable electrode layer, with the result that the carbon-based
conductive material does not readily stay at the
collector-polarizable electrode interface, and the activated carbon
pore interiors become covered by the carbon-based conductive
material. Capacitor function is impaired as a result. The diameter
of the largest pores (maximum pore size) should be 0.5-20 .mu.m.
Where the maximum pore size is smaller than 0.5 .mu.m, the
carbon-based conductive material does not readily penetrate into
the voids of the polarizable electrode layer. Where it exceeds 20
.mu.m, the carbon-based conductive material tends to penetrate
depthwise far into the pores of the polarizable electrode layer,
with the result that the carbon-based conductive material does not
readily stay at the collector-the polarizable electrode interface,
and the activated carbon pore interiors become covered by the
carbon-based conductive material. Capacitor function is impaired as
a result.
[0025] The collector layer preferably consists of a metal such as
aluminum, stainless steel, titanium, and tantalum. The metal
preferably takes the form of a foil, plate, sheet, expanded,
punched, or mesh; a foil is especially preferred.
[0026] The carbon-based conductive material which is interposed
between the polarizable electrode layer and the collector layer has
the function of providing electrical connection between collector
surfaces on the one hand and the outside and inside surfaces of
polarizable electrode layer on the other, as well as a bonding
function. In particular, on the polarizable electrode layer side,
the carbon-based conductive material penetrates into the pores in
the polarizable electrode layer, creating an anchoring effect which
improves both bonding strength and conductivity. Accordingly,
sufficient electrical connection is provided between the
polarizable electrode layer and the collector layer, thereby
obviating the need for a process to increase the collector contact
area or to provide openings for adequate interpenetration of the
collector and the electrode material.
[0027] The carbon-based conductive material consists of graphite,
carbon black, or other conductive material combined with a binder.
Examples of binders are water glass; the sodium salt or ammonium
salt of carboxymethyl cellulose, or other cellulose derivative; and
polyvinyl alcohol, polyvinyl butyral, polyvinyl acetate,
polybis(polybutene), or other thermoplastic resin.
[0028] The graphite or carbon black conductive material preferably
has an average particle size of 0.5 to 50 .mu.m. Where the average
particle size is greater than 50 .mu.m, the carbon-based conductive
material does not readily penetrate into the voids of the
polarizable electrode layer. Where it is smaller than 0.5 .mu.m,
the carbon-based conductive material tends to penetrate depthwise
far into the pores of the polarizable electrode layer, with the
result that the carbon-based conductive material does not readily
stay at the collector-polarizable electrode interface, and the
activated carbon particles become covered by the carbon-based
conductive material. The activated carbon pore interiors are thus
inaccessible, and capacitor function is impaired as a result.
[0029] The carbon-based conductive material present in the voids of
the polarizable electrode layer should fill up 0.5%-10%, and
preferably 1%-5%, of the total void volume in the polarizable
electrode layer. Amounts below 0.5% produce a collector
layer-polarizable electrode surface contact configuration in which
the space other than the points of contact of the powder of the
polarizable electrode with the metal foil of the collector layer is
not adequately filled in, making it difficult to improve contact
area through increased surface contact. Conversely, amounts
exceeding 10%, while improving surface contact, can result in
activated carbon pore interiors becoming covered by the
carbon-based conductive material, impairing capacitor function as a
result.
[0030] The carbon-based conductive material should penetrate 0.15
to 30%, preferably 0.25 to 15% of the thickness of the polarizable
electrode layer as determined by scanning electron microscopy.
[0031] A polarizable electrode having the constitution described
above can be manufactured by a process like the following.
[0032] First, a carbon-based conductive material solution prepared
by dispersing the carbon-based conductive material in a dispersion
medium is applied to the surface of the sheet which constitutes the
polarizable electrode layer (hereinafter termed "polarizable
electrode material sheet"), to the collector surface, or to
both.
[0033] Here, water, a lower alcohol, or the like can be used as the
dispersion medium for preparing the carbon-based conductive
material solution. The conductive material concentration is
preferably 20-30 wt %. The use of a carbon-based conductive
material solution having a composition similar to those given in
Table 1 is preferred. Favorable results are obtained by selecting
an appropriate composition and using it in concentrations that may
be further diluted in amounts ranging from 1/1 to 1/30 (and hence
up to 30 times as much applied).
1 Conducing material Dispersion (avg. particle size) Binder medium
Other 1 natural graphite (3 carboxymethyl water ammonia .mu.m)
cellulose Na salt 50-75 wt % several 20-30 wt % 4-16 wt % wt % 2
natural graphite (3 methyl cellulose isopropyl .mu.m) 5-20 wt %
alcohol 25-30 wt % 45-75 wt % 3 natural graphite (3 polyvinyl
alcohol isopropyl .mu.m) 5-20 wt % alcohol 25-30 wt % 45-75 wt % 4
natural graphite (3 polyvinyl butyral isopropyl .mu.m) 5-20 wt %
alcohol 25-30 wt % 45-75 wt % 5 natural graphite (3 polyvinyl
acetal isopropyl .mu.m) 5-20 wt % alcohol 25-30 wt % 45-75 wt % 6
natural graphite (3 polybis isopropyl .mu.m) (polybutylene) alcohol
25-30 wt % 5-20 wt % 45-75 wt % 7 natural graphite (3 acrylic
resin-styrene water ammonia .mu.m) copolymer 50-75 wt % several
20-30 wt % 2-8 wt % wt % 8 natural graphite (3 water glass water
.mu.m) 5-20 wt % 45-75 wt % 25-30 wt % 9 natural graphite (60
carboxymethyl water ammonia .mu.m) cellulose Na salt 50-75 wt %
several 20-30 wt % 4-16 wt % wt % 10 acetylene black (40
carboxymethyl water ammonia .mu.m) cellulose Na salt 50-75 wt %
several 20-30 wt % 4-16 wt % wt %
[0034] The carbon-based conductive material solution can be applied
to the lamination face of either the polarizable electrode material
sheet or the collector, or applied to both. The preferred method is
to apply the solution to at least the lamination face of the
collector. The polarizable electrode material sheet is actually a
powder aggregate, and peaks and valleys are present over the entire
surface of the polarizable electrode material sheet. Thus, by
interposing the carbon-based conductive material between the
polarizable electrode layer and the collective layer, it is
possible to fill in the space other than the points of contact of
the powder of the polarizable electrode with the collector, thereby
improving contact to the point that it approximates planar contact.
However, if the carbon-based conductive material solution is
applied to an electrode surface, the carbon-based conductive
material solution penetrates into the polarizable electrode
material sheet so that a sufficient amount of carbon-based
conductive material solution does not remain on the surface of the
polarizable electrode material sheet, making it difficult to fill
in the space other than the points of contact of the powder of the
polarizable electrode with the collector. From a productivity
standpoint as well, it is preferably to apply the solution to the
collector, which has a higher degree of strength than the
polarizable electrode material sheet.
[0035] The polarizable electrode material sheet and the collector
are then superposed such that the applied carbon-based conductive
material solution lies between them, producing a laminate sheet.
Various lamination processes are possible. The materials can be
simply stacked, but it is preferable to compress them through
passage between rolls or other means in order to produce reliable
adhesion at the lamination interface.
[0036] Next, the laminate sheet so obtained is subjected to a
procedure to remove the dispersion medium from the carbon-based
conductive material solution layer. Various methods of removal are
possible; the preferred method is to remove the dispersion medium
through hot air drying. The hot air temperature should be selected
so as to approximate the boiling point of the dispersion medium.
Removing the dispersion medium through drying or other process
results in the formation of a carbon-based conductive material
consisting of the binder and the conductive material; this has the
effect of bonding the collector layer and the polarizable electrode
layer together.
[0037] The foregoing discussion described an embodiment in which a
single polarizable electrode material sheet and a single collector
are laminated. Lamination of a polarizable electrode material sheet
to each side of the collector would be performed analogously. For
example, a process in which a polarizable electrode material sheet
is laminated to one side of the collector, and another polarizable
electrode material sheet is laminated to the other side of the
collector using an analogous procedure, or a single-step lamination
process in which one polarizable electrode material sheet is
laminated each side of the collector, could be used.
[0038] Polarizable electrodes so obtained are disposed in opposing
pairs while interposing a separator between the polarizable
electrodes, producing a single unit. The electrolyte is injected,
and the assembly is sealed within a container to produce the
electric double layer capacitor which pertains to the present
invention. An electric double layer capacitor can alternatively be
produced by disposing a plurality of polarizable
electrode/separator units in an row arrangement, injecting the
electrolyte, and sealing the assembly within a container. In such
an arrangement, it is not necessary to use the polarizable
electrode which pertains to the present invention for the
polarizable electrodes located at the two ends of the row of
polarizable electrodes. That is, it is only necessary]to use the
polarizable electrode which pertains to the present invention,
wherein the polarizable electrode layers are laminated to both
sides of the collector layer while imposing a carbon-based
conductive material such that the carbon-based conductive material
penetrates into the pores of the polarizable electrode layers,
where a polarizable electrode is to be disposed next to another
polarizable electrode with a separator placed between them.
EXAMPLES
[0039] The present invention will be described in further detail
below through working examples.
Example 1
[0040] A polarizable electrode assembly was made as follows, with
reference to FIG. 4:
[0041] To a mixture consisting of 85 wt % activated carbon powder
(specific surface area 2200 m.sup.2/g; average particle size 7
microns), 7 wt % kitchen black, and 8 wt % polytetrafluoroethylene
was added ethanol as a lubricant. Subsequently, the materials were
mixed together, ram-extruded into sheet form and calendered to
produce a sheet 1 of polarizable electrode material 10 cm wide and
0.8 mm thick. The sheet had a pore volume of 66% and 18 .mu.m
maximum pore size (measured according to ASTM-E-128-61 using the
ethanol bubble point).
[0042] High-purity aluminum foil 50 microns thick and 15 cm wide
was used for the collector 2.
[0043] A layer 3 of an electrically-conductive adhesive material
solution, 30 wt % natural graphite (average particle size 3 .mu.m)
as the conductive material, 8 wt % carboxymethyl cellulose Na salt
as the binder, 60 wt % water, and 2 wt % ammonia was coated on one
surface of the collector sheet 2 by passage through coating rolls
21, 22. After applying the conductive material solution, the
aforementioned continuous polarizable electrode material sheet was
superposed onto the coated portions of the high-purity aluminum
foil collector, and the assembly was passed through compression
rolls 23,24 to produce a 3-layer laminated sheet in which a portion
of the electrically-conductive adhesive solution 3 was forced into
the pores of the surface region of the sheet 1 and form a layer on
the surface of sheet 1 to form a bond to the collector sheet 2.
This procedure of coating with conductive material solution and
applying the polarizable electrode was then repeated for the
opposite side of collector 2. In an alternative method, both sides
of collector 2 may be coated simultaneously as depicted in FIG.
5.
[0044] The laminate sheet was then fed into a continuous hot air
drier (drying temperature set to 110.degree. C.) at a speed such
that the residence time was three minutes, thereby removing the
dispersion medium form the conductive material solution. This
procedure afforded a polarizable electrode sheet having the
constitution depicted in FIG. 1. The sheet comprised polarizable
electrode sheet layers 1 adhesive-laminated to both sides of the
collector layer through the interposed carbon-based conductive
material 3. The carbon-based conductive material 3 penetrated into
the pores in the polarizable electrode sheet layers 1.
[0045] The electrically-conductive adhesive material solution was
present in an amount of 20 g/square meter and the thickness of the
electrically-conductive adhesive material was about 10 microns
(excluding the amount that penetrated into the polarizable
electrode).
[0046] The sheet was punched into 10 cm squares to produce
polarizable electrodes 4 of sheet form. As shown in FIG. 2, a pair
of polarizable electrodes 4 was disposed in opposing fashion,
interposing a separator 5. A collector terminal 9 (2 cm.times.4 cm)
and a collector lead 7 were attached to the collector layer 2 of
one of the polarizable electrodes 4, and collector terminal 9' (2
cm.times.4 cm) and a collector lead 7' were attached to the
collector layer 2 of the other polarizable electrode 4, producing a
single unit.
[0047] Next, as shown in FIG. 3, polarizable electrodes and
separators were disposed in a row to produce a total of 13 units.
This assembly was vacuum dried for three hours at 200.degree. C.
and then placed in an aluminum case 6. The positive terminal,
negative terminal, and lid 12 were attached. An electrolyte 10
consisting of a 1 molar concentration tetraethylammonium
tetrafluoroborate propylene carbonate solution was injected and the
case 6 was sealed to produce a square electric double layer
capacitor.
Example 2
[0048] A square electric double layer capacitor was produced
following the procedure of Working Example 1, with the exception
that the carbon-based conductive material solution consisted of 30
wt % acetylene black (average particle size 40 .mu.m), 8 wt %
carboxymethyl cellulose Na salt, 60 wt % water, and 2 wt %
ammonia.
Comparative Example 1
[0049] A square electric double layer capacitor was produced
following the procedure of Working Example 1, with the exception
that the carbon-based conductive material solution consisted of 30
wt % natural graphite (average particle size 60 .mu.m), 8 wt %
carboxymethyl cellulose Na salt, 60 wt % water, and 2 wt %
ammonia.
[0050] In the polarizable electrodes in this electric double layer
capacitor, the natural graphite particle size was larger than the
polarizable electrode sheet pore size (and due to the particle size
distribution, more of such large particles were present), and as a
result the material did not penetrate sufficiently into the voids
of the polarizable electrode layers.
Comparative Example 2
[0051] A square electric double layer capacitor was produced
following the procedure of Working Example 1, with the exception
that the sheet constituting the polarizable electrode layers was 10
cm wide and 0.8 mm thick, and exhibited 66% porosity and 30 .mu.m
maximum pore size.
[0052] In the polarizable electrodes in this electric double layer
capacitor, the polarizable electrode sheet pore size was too large
relative to the carbon-based conductive material particle size; the
carbon-based conductive material thus penetrated far into the
voids, with the result that only a small amount of the carbon-based
conductive material stayed at the collector-polarizable electrode
contact interface.
Comparative Example 3
[0053] A square electric double layer capacitor was produced
following the procedure of Working Example 1, with the exception
that high-purity aluminum foil having a roughened metal foil
surface was employed as the collector, and the laminate sheet was
prepared by roll-calendering conducted so as to form the
polarizable electrode layers directly on both sides thereof without
interposing a carbon-based conductive material.
Comparative Example 4
[0054] A square electric double layer capacitor was produced
following the procedure of Working Example 1, with the exception
that high-purity aluminum expanded metal (dimensions 1.0 mm SW
(short width), 2.0 mm LW (long width), St (strand width) 0.23 mm, t
(original thickness) 80 microns) was employed as the collector, and
the laminate sheet was prepared by roll-calendering conducted so as
to form the polarizable electrode layers directly on both sides
thereof without interposing a carbon-based conductive material.
[0055] The capacitance and internal resistance of the electric
double layer capacitors prepared in Working Examples 1 and 2 and
Comparative Examples 1 through 4 were measured on double layer
capacitor assemblies of the type described in connection with FIG.
3. The capacitance was determined by discharging at the current of
1 mA/square centimeter from 2.5 V to 0 V. The internal resistance
was obtained by measuring the impedance at 100 kHertz. Results are
given in Table 2.
2 TABLE 2 Polarizable electrode Max. pore Characteristics size in
Conductive Capacitance polarizable material Internal per unit of
electrode pore size resistance Capacitance volume layer (.mu.m)
(.mu.m) (m.OMEGA.) (F) Volume (F/cc) Working 18 7 16 4300 460 9.3
Ex. 1 Working 18 40 16 4300 460 9.3 Ex. 1 Compar. 18 60 19 4300 460
9.3 Ex 1 Compar. 30 7 19 4210 460 9.2 Ex 2 Compar. -- -- 19 4300
460 9.3 Ex 3 Compar. -- -- 23 4300 460 9.3 Ex 4
[0056] As may be seen from Table 2, the electric double layer
capacitor which pertains to the present invention provides an
electric double layer capacitor that exhibits low internal
resistance. In contrast, electric double layer capacitors employing
either polarizable electrodes having no interspersed carbon-based
conductive material (Comparative Examples 3 and 4) or polarizable
electrodes in which the carbon-based conductive material either
does not adequately penetrate into the voids in the polarizable
electrode layers, or does not remain in sufficient quantities at
the polarizable electrode layer-collector layer interface
(Comparative Examples 1 and 2) exhibit high internal resistance and
low capacitance.
[0057] The electric double layer capacitor which pertains to the
present invention provides both high capacitance per unit of volume
and low internal resistance. According to the method of the present
invention the polarizable electrode can be manufactured as a
continuous sheet, thereby affording excellent productivity.
Example 3
[0058] A conductive carbon tape consisting of 92% Vulcan XC72
carbon and 8% PTFE with a thickness of 19 mils and a width of 0.75
inches was prepared by ram extrusion. A nickel foil grid useful in
a lithium thionyl chloride battery with a thickness of 3 mil was
cleaned with ethanol to remove oils and any other hydrophobic
material. The grid was then coated on both sides with the adhesive
described on page 10, example 8. The coating was carried out using
a natural bristle paint brush. While wet, conductive carbon tape
was applied to both sides of the grid. The assembly was rolled flat
between 5 mil PTFE sheets using a 1 kg cylindrical weight. This
assembly was set aside to air dry for several hours. It was then
baked in air at 130 C for 10 minutes. The assembly appeared to be
well adhered. It was wound around a mandrel with a 0.55 inch
diameter and did not delaminate.
Example 4
[0059] A conductive carbon tape consisting of 92% Vulcan XC72 and
8% PTFE with a thickness of 45 mil and a width of 6 inches was
prepared by ram extrusion. A nickel foil grid useful in a lithium
thionyl chloride battery with a thickness of 3 mil was cleaned with
ethanol to remove oils and any other hydrophobic material. The grid
was coated on both sides with the adhesive described on page 10,
example 8. The coating was applied by dipping the grid into the
adhesive. While wet, the conductive carbon tape was applied to one
side of the grid. The assembly was rolled flat between 5 mil PTFE
sheets using a 1 kg cylindrical weight. The assembly was set aside
to air dry for several hours. It was then baked in air at 130 C for
10 minutes. The assembly appeared to be well adhered. A DC ohmmeter
with pointed probes measured a resistance of 0.2 ohm between the
current collector and the surface of the carbon PTFE tape. The
assembly was wound around a mandrel with a 0.55 inch diameter.
First it was wound with the tape on the inside of the wind. Next,
it was rewound with the tape on the outside of the wind. Although
it was still adhered, slight delamination was noted at the inside
edge of the assembly.
[0060] While particular embodiments of the present invention have
been illustrated and described herein, the present invention should
not be limited to such illustrations and descriptions. It should be
apparent that changes and modifications may be incorporated and
embodied as part of the present invention within the scope of the
following claims.
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