U.S. patent application number 09/779145 was filed with the patent office on 2002-03-14 for sealed ultracapacitor.
Invention is credited to Day, James, DeJager, Katherine Dana.
Application Number | 20020031884 09/779145 |
Document ID | / |
Family ID | 22586045 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031884 |
Kind Code |
A1 |
Day, James ; et al. |
March 14, 2002 |
Sealed ultracapacitor
Abstract
A multilayer cell is provided that comprises two solid,
nonporous current collectors, two porous electrodes separating the
current collectors, a porous separator between the electrodes and
an electrolyte occupying pores in the electrodes and separator. A
thermoplastic vinyl acetate polymer or thermoplastic polyamide is
applied to the multilayer structure; and pressure or heat is
applied to seal layers of the cell by means of the thermoplastic
vinyl acetate polymer or thermoplastic polyamide to form the
ultracapacitor.
Inventors: |
Day, James; (Scotia, NY)
; DeJager, Katherine Dana; (Goes, NL) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
22586045 |
Appl. No.: |
09/779145 |
Filed: |
February 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09779145 |
Feb 8, 2001 |
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09162533 |
Sep 29, 1998 |
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6212062 |
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Current U.S.
Class: |
438/239 ;
438/381 |
Current CPC
Class: |
H01G 11/72 20130101;
H01G 11/12 20130101; H01G 9/012 20130101; H01G 11/68 20130101; H01G
11/52 20130101; H01G 11/28 20130101; Y02E 60/13 20130101; H01G
9/155 20130101 |
Class at
Publication: |
438/239 ;
438/381 |
International
Class: |
H01G 009/00; H01L
021/8242; H01L 021/20 |
Goverment Interests
[0001] This invention was made with government support under
Contract No. 38-83CH10093 awarded by DOE. The government may have
certain rights in the invention.
Claims
What is claimed is:
1. A method of making an ultracapacitor, comprising; (A) providing
at least one cell, said cell comprising, nonporous current
collectors, two porous electrodes separating said current
collectors, a porous separator between said electrodes and an
electrolyte occupying pores in said electrodes and separator; (B)
applying a thermoplastic vinyl acetate polymer or thermoplastic
polyamide to said multilayer structure; and (C) applying pressure
or heat to seal layers of said cell by means of said thermoplastic
vinyl acetate polymer or thermoplastic polyamide to form said
ultracapacitor.
2. The method of claim 1, comprising (B) applying said
thermoplastic vinyl acetate polymer or thermoplastic polyamide as a
layer between a current collector and a separator of said
multilayer structure
3. The method of claim 1, comprising (B) applying said
thermoplastic vinyl acetate polymer or thermoplastic polyamide as a
layer between a collector plate and electrode to extend on said
collector plate peripherally to said electrode and (C) applying
pressure or heat to seal said collector plate to a separator where
said thermoplastic vinyl acetate polymer or thermoplastic polyamide
extends peripherally to said electrode to form said
ultracapacitor.
4. The method of claim 3, comprising (C) applying a sealant to
outer edges of said multilayer cell and applying pressure or heat
to seal said collector plate to a separator where said
thermoplastic vinyl acetate polymer or thermoplastic polyamide
extends peripherally to said electrode to form said
ultracapacitor.
5. The method of claim 1, comprising fitting an elastomeric gasket
onto a current collector and peripherally to an electrode to secure
said electrode on said current collector and (B) applying said
thermoplastic vinyl acetate polymer or thermoplastic polyamide to
said multilayer structure at the edges of said cell.
6. The method of claim 1, wherein (B) comprises applying a
thermoplastic vinyl acetate polymer to said cell wherein said
thermoplastic vinyl acetate is an ethylene vinyl acetate copolymer
having a vinyl acetate content of between 18% and 35% by weight of
the EVA.
7. The method of claim 1, wherein (B) comprises applying a
thermoplastic vinyl acetate polymer or thermoplastic polyamide to
said cell wherein said thermoplastic vinyl acetate is an ethylene
vinyl acetate copolymer having a softening point of at least 100
C.
8. The method of claim 1, wherein said thermoplastic polyamide is
HYSOL thermoplastic polyamide.
9. A method of making a stacked ultracapacitor, comprising: (A)
providing a stack of ultracapacitors produced according to the
method of claim 1; and (B) sealing said stack of ultracapacitors to
form said stacked ultracapacitor.
10. A method of making a stacked ultracapacitor, comprising: (A)
providing a stack of ultracapacitors produced according to the
method of claim 1; and (B) applying a thermoplastic vinyl acetate
polymer or thermoplastic polyamide to said stack; and (C) applying
pressure or heat to seal said stack by means of said thermoplastic
vinyl acetate polymer or thermoplastic polyamide to form said
stacked ultracapacitor.
11. A method of making a stacked ultracapacitor, comprising: (A)
providing a stack of multilayer cells according to the cell of
claim 11; (B) applying a thermoplastic vinyl acetate polymer or
thermoplastic polyamide to said stack; and (C) applying pressure or
heat to seal said stack by means of said thermoplastic vinyl
acetate polymer or thermoplastic polyamide to form said stacked
ultracapacitor.
12. An ultracapacitor comprising at least one cell, said cell
comprising two solid, nonporous current collectors, two porous
electrodes separating said current collectors, a porous separator
between said electrodes and an electrolyte occupying pores in said
electrodes and separator, wherein at least one electrode is sealed
to one of said conductors by means of a thermoplastic vinyl acetate
polymer or thermoplastic polyamide.
13. The ultracapacitor of claim 12, wherein said at least one
electrode is sealed to one of said conductors by means of an
ethylene vinyl acetate copolymer wherein said thermoplastic vinyl
acetate is an ethylene vinyl acetate copolymer having a vinyl
acetate content of between 18% and 35% by weight of the ethylene
vinyl acetate.
14. The ultracapacitor of claim 12, wherein said at least one
electrode is sealed to one of said conductors by means of a
thermoplastic ethylene vinyl acetate copolymer having a softening
point of at least 100 C.
15. The ultracapacitor of claim 12, wherein said at least one
electrode is sealed to one of said conductors by means of a HYSOL
thermoplastic polyamide.
16. The ultracapacitor of claim 12, wherein said current collectors
comprise an aluminum substrate.
17. The ultracapacitor of claim 12, wherein said electrodes
comprise carbon.
18. The ultracapacitor of claim 12, wherein said separator is
polypropylene or cellulosic tissue material.
19. The ultracapacitor of claim 12, wherein said electrolyte
comprises a polar aprotic organic solvent and a quaternary ammonium
salt, a hexasubstituted quanidium salt or a lithium salt.
20. A stack of ultracapacitor cells, comprising at least one of the
cells of claim 12.
21. A stack of ultracapacitor cells, comprising at least one of the
cells of claim 13.
22. A stack of ultracapacitor cells, comprising at least one of the
cells of claim 14.
23. A stack of ultracapacitor cells, comprising at least one of the
cells of claim 15.
Description
BACKGROUND OF THE INVENTION
[0002] Capacitors are storage devices that store electrical energy
on an electrode surface. Electrochemical cells create an electrical
charge at electrodes by chemical reaction. The ability to store or
create electrical charge is a function of electrode surface area in
both applications. Ultracapacitors, sometimes referred to as double
layer capacitors, are a third type of storage device. An
ultracapacitor creates and stores energy by microscopic charge
separation at an electrical chemical interface between electrode
and electrolyte.
[0003] Ultracapacitors are able to store more energy per weight
than traditional capacitors and they typically deliver the energy
at a higher power rating than many rechargeable batteries.
Ultracapacitors comprise two porous electrodes that are isolated
from electrical contact by a porous separator. The separator and
the electrodes are impregnated with an electrolytic solution, which
allows ionic current to flow between the electrodes while
preventing electronic current from discharging the cell. On the
back of each electrode is a current collector. One purpose of the
current collector is to reduce ohmic loss. If the current
collectors are nonporous, they can also be used as part of the
capacitor case and seal.
[0004] When electric potential is applied to an ultracapacitor
cell, ionic current flows due to the attraction of anions to the
positive electrode and cations to the negative electrode. Upon
reaching the electrode surface, the ionic charge accumulates to
create a layer at the solid liquid interface region. This is
accomplished by absorption of the charge species themselves and by
realignment of dipoles of the solvent molecule. The absorbed charge
is held in this region by opposite charges in the solid electrode
to generate an electrode potential. This potential increases in a
generally linear fashion with the quantity of charge species or
ions stored on the electrode surfaces. During discharge, the
electrode potential or voltage that exists across the
ultracapacitor electrodes causes ionic current to flow as anions
are discharged from the surface of the positive electrode and
cations are discharged from the surface of the negative electrode
while an electronic current flows through an external circuit
between electrode current collectors.
[0005] In summary, the ultracapacitor stores energy by separation
of positive and negative charges at the interface between electrode
and electrolyte. An electrical double layer at this location
consists of sorbed ions on the electrode as well as solvated ions.
Proximity between the electrodes and solvated ions is limited by a
separation sheath to create positive and negative charges separated
by a distance which produces a true capacitance in the electrical
sense.
[0006] During use, an ultracapacitor cell is discharged by
connecting the electrical connectors to an electrical device such
as a portable radio, an electric motor, light emitting diode or
other electrical device. The ultracapacitor is not a primary cell
but can be recharged. The process of charging and discharging may
be repeated over and over. For example, after discharging an
ultracapacitor by powering an electrical device, the ultracapacitor
can be recharged by supplying potential to the connectors.
[0007] The physical processes involved in energy storage in an
ultracapacitor are distinctly different from the electrochemical
oxidation/reduction processes responsible for charge storage in
batteries. Further unlike parallel plate capacitors,
ultracapacitors store charge at an atomic level between electrode
and electrolyte. The double layer charge storage mechanism of an
ultracapacitor is highly efficient and can produce high specific
capacitance, up to several hundred Farads per cubic centimeter.
[0008] Ultracapacitors are multilayer structures that include two
solid, nonporous current collectors, two porous electrodes
separating the collectors and a porous separator between the
electrodes. A nonaqueous electrolyte solution saturates the
electrodes and separator layer. The electrolyte solution includes
an organic solvent and an electrolyte. The structure is sealed to
form the multilayer ultracapacitor. The electrolyte solution
presents a deleterious environment that adversely affects sealants
that are used to close and seal the layers of the ultracapacitor.
The dielectric constant of the ultracapacitor depends upon the
proportion of electrolyte salt to solute. The electrolyte solution
breaks down sealant and causes loss of electrolyte through
evaporation to change the proportion of electrolyte to solute. The
present invention relates to a sealant and method of sealing an
ultracapacitor that eliminates chemical interaction and mechanical
degradation to an ultracapacitor seal that is caused by degradation
of sealant by electrolyte solution. According to the present
invention, the ultracapacitor conductor layer is sealed to an
electrode by means of a vinyl acetate polymer or polyamide fusible
binder. These polymeric fusible binders withstand electrolyte
chemical attack to maintain ultracapacitor integrity, flexibility
and barrier properties.
SUMMARY OF THE INVENTION
[0009] The invention relates to a method of making an
ultracapacitor. In the method, a cell is provided that comprises
two solid, nonporous current collectors, two porous electrodes
separating the current collectors, a porous separator between the
electrodes and an electrolyte occupying pores in the electrodes and
separator. A thermoplastic vinyl acetate polymer or thermoplastic
polyamide is applied to the multilayer structure; and pressure or
heat is applied to seal layers of the cell by means of the
thermoplastic vinyl acetate polymer or thermoplastic polyamide to
form the ultracapacitor.
[0010] The invention also relates to an ultracapacitor that is
sealed by means of the thermoplastic vinyl acetate polymer or
thermoplastic polyamide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a front sectional view of an ultracapacitor;
[0012] FIG. 2 is a front sectional view of a series stack of
ultracapacitor cells;
[0013] FIG. 3 is a cross-sectional view of an exemplary apparatus
for sealing an ultracapacitor; and
[0014] FIG. 4 is an exploded schematic view of an ultracapacitor
sealed in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The method of the invention may be used to make a wide
variety of ultracapacitors such as described in U.S. Pat. Nos.
5,464,453; 5,420,747; 5,150,283; 5,136,472; and 4,803,597; as well
as PCT Application WO96/11486 (PCT/US95/12772; Apr. 18, 1996), all
of which are incorporated herein by reference. FIGS. 1 and 2
herein, are based on PCT Application WO 96/11486 and show
non-limiting examples of structures made by the method of the
present invention.
[0016] In all of the Figures of this application, like structures
are identified by the same numbers.
[0017] Referring to FIG. 1, ultracapacitor 10 includes a
nonconductive enclosing body 12, a pair of carbon electrodes 14 and
16, an electronic porous separator layer 18, an electrolyte 20, a
pair of conductive layers which are current collectors 22 and 24
and electrical leads 26 and 28, extending from the current
collectors 22 and 24. One of the pair of current collectors 22 and
24 is attached to the back of each electrode 14 and 16. In FIG. 1,
electrodes 14 and 16 can each represent a plurality of electrodes
so long as the electrodes are porous to electrolyte flow.
[0018] The current collectors 22, 24 commonly are made of aluminum
because of its conductivity and cost. In the drawings, the current
collectors 22 and 24 are thin layers of aluminum foil. However, the
electrodes can be any suitable material as described above.
[0019] The electronic separator 18 is preferably made from a highly
porous material which acts as an electronic insulator between the
carbon electrodes 14 and 16. The separator 18 assures that opposing
electrodes 14 and 16 are never in contact with one another. Contact
between electrodes can result in a short circuit and rapid
depletion of the charges stored in the electrodes. The porous
nature of the separator 18 allows movement of ions in the
electrolyte 20. A wide variety of types and arrangements of
separation layers can be employed, as those of ordinary skill in
the electrochemical arts realize. Separation layers are usually
made from nonconductive materials such as cellulosic materials;
glass fiber; polymers such as polyesters or polyolefins; and the
like. In those embodiments in which the separator layers will be in
contact with sealant material, they should have a porosity
sufficient to permit the passage of sealant and should be resistant
to the chemical components in the sealant. In a typical
ultracapacitor, the separator layers have a thickness in the range
of about 0.5 mil to about 10 mils. Preferred separators 18 are
porous polypropylene and tissue cellulosic materials.
[0020] Exemplary organic solvents for electrolyte 20 include but
are not limited to nitrites such as acetonitrile, acrylonitrile and
propionitrile; sulfoxides such as dimethyl, diethyl, ethyl methyl
and benzylmethyl sulfoxide; amides such as dimethyl formamide and
pyrrolidones such as N-methylpyrrolidone. Preferrably, the
electrolyte 20 includes a polar aprotic organic solvent such as a
cyclic ester, chain carbonate, cyclic carbonate, chain ether and/or
cyclic ether solvent and a salt. Preferred cyclic esters are esters
having 3 to 8 carbon atoms. Examples of the cyclic esters include
-butyrolactone, -butyrolactone, -valerolactone and -valerolactone.
The chain carbonates are preferred to be carbonates having 3 to 8
carbon atoms. Examples of the chain carbonates include dimethyl
carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl
carbonate, methyl propyl carbonate and ethyl propyl carbonate. The
preferred cyclic carbonates have 5 to 8 carbon atoms. Examples of
the cyclic carbonates include 1,2-butylene carbonate, 2,3-butylene
carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate and
propylene carbonate. The preferred chain ethers have 4 to 8 carbon
atoms. Examples of the chain ethers include dimethoxyethane,
diethoxyethane, methoxyethoxyethane, dibutoxyethane,
dimethoxypropane, diethoxypropane and methoxyethoxypropnane. The
preferred cyclic ethers have 3 to 8 carbon atoms. Examples of the
cyclic ethers include tetrahydofuran, 2-methyl-tetrahydrofuran,
1,3-dioxolan, 1,2-dioxolan, 2-methyldioxolan and
4-methyl-dioxolan.
[0021] Suitable electrolyte salts include quaternary ammonium salts
such as tetraethylammonium tetraflouroborate ((Et).sub.4NBF.sub.4),
hexasubstituted guanidinium salts such as disclosed in U.S. Pat.
No. 5,726,856, the disclosure of which is incorporated herein by
reference, and lithium salts such as disclosed by Ue et al.,
Mobility and Ionic Association of Lithium Salts in a Propylene
Carbonate-Ethyl Carbonate Mixed Solvent, Electrochem. Soc., vol.
142, No. 8, August 1995, the disclosure of which is incorporated
herein by reference.
[0022] In a preferred embodiment, the electrodes 14, 16 in FIG. 1,
are both carbon electrodes on aluminum current collectors. The
electrode can be fabricated by a forming process or by pressing
electrode materials in a die and slurry pasting or screen printing
carbon as a paste with a liquid phase binder/fluidizer. The liquid
phase may be water or an electrolyte solvent with or without a
thinner such as acetone. Both dry and wet electrode formations may
include a binder such as polymers, starches, Teflon.RTM. particles
or Teflon.RTM. dispersions in water.
[0023] The enclosing body 12 can be any known enclosure means
commonly used with ultracapacitors. It is an advantage to minimize
the weight of the packaging means to maximize the energy density of
the ultracapacitor. Packaged ultracapacitors are typically expected
to weigh 1.25 to 2 times more than the unpackaged ultracapacitor.
The electrical leads 26 and 28 extend from the current collectors
22 and 24 through the enclosing body 12 and are adapted for
connection with an electrical circuit (not shown).
[0024] Ultracapacitor 10 of FIG. 1 includes a bipolar double layer
cell 30 that includes two solid, nonporous current collectors 22,
24, two porous electrodes 14, 16 separating the current collectors
22, 24 and a porous separator 18 between the electrodes 14, 16 and
an electrolyte 20 occupying pores in the electrodes 14, 16 and
separator 18. Individual ultracapacitor cells can be stacked in
series to increase operating voltage. The optimum design is to have
adjacent cells separated with only a single current collector. This
collector is non-porous so that no electrolytic solution is shared
between cells. This type of design is called bipolar and is
illustrated in FIG. 2 of the drawings. In a bipolar double layer
capacitor, one side of the current collector contacts a positive
electrode and the other side contacts a negative electrode of an
adjacent cell. A series stack 40 of the high performance bipolar
double layer cells 30 (A, B, C and D) is illustrated in FIG. 2. In
FIG. 2, each pair of polarized carbon electrodes, 14, 16 is
separated with a separator 18. A current collector 32 is attached
at one surface to charged electrode 14 of a first cell. Attached to
an opposite surface of the current collector 32, is an oppositely
charged electrode 16 of a second cell. If one side of the current
collector 32 is in contact with the negative electrode for a first
capacitor cell "A," then the other side of the same current
collector 32 is in contact with a positive electrode for an
adjacent cell "B." A sufficient amount of an electrolyte 20 is
introduced such that the electrolyte 20 saturates the electrodes 14
and 16 and separator 18 within each cell. Exterior current
collectors 22 and 24 are placed at each end of the stack.
[0025] The internal current collectors 32 of the series stack of
cells are preferably nonporous layers of aluminum foil designed to
separate the electrolyte 20 between adjacent cells. The exterior
current collectors are also nonporous such that they can be used as
part of the external capacitor case seal, if necessary. The
electronic separator 18 is located between the opposing carbon
electrodes 14 and 16 within a particular capacitor cell. The
electronic separator 18 allows ionic conduction via charged ions in
the electrolyte.
[0026] The ultracapacitor cell can be constructed by placing the
layers of conductor, electrode and separator along with electrolyte
within an enclosing body. The structure can then be subjected to
pressure to seal the layers within the enclosing body.
Alternatively, the enclosing body can be subjected to pressure and
vacuum. The vacuum acts to remove gases while the ultracapacitor is
sealed. Alternatively, the ultracapacitor cell can be constructed
by providing adhesive between layers and applying pressure and or
heat throughout the adhesive to seal the cell.
[0027] FIG. 3 depicts one, non-limiting illustration of a method of
sealing an ultracapacitor or series stack of ultracapacitor cells
according to the present invention. Referring to FIG. 3, structure
50 is a frame, platform, or other construction but is often a press
as described below. An enclosable region is depicted in FIG. 3 as
recess 52, in which an ultracapacitor series stack 40 is disposed.
The embodiment illustrated in FIG. 3 permits application of vacuum
while the ultracapacitor is being sealed. Primary vacuum tube 60
communicates with recess 52. A collapsible membrane 64 can be
fastened over the ultracapacitor to maintain a vacuum while the
cell is being sealed by pressing.
[0028] FIG. 3 shows an ultracapacitor cell disposed in the recess
area of the press 50. The cell includes a separator system,
comprising an upper separator layer 42 and a lower separator layer
44. Sealant portions 46 and 48 are disposed in a peripheral area
between the bottom surface of separator 42 and the top surface of
separator 44. In FIG. 4, collector plate 22 is an aluminum foil
coated with a thin electrode 14 and collector plate 24 is coated
with electrode 16. Separator layer 18 is positioned between the
collector plate plates 22, 24. Heat sealant layer 90 is disposed
between the collector plates 22, 24 and separator layer 18 and
comprises a thermoplastic vinyl acetate polymer or thermoplastic
polyamide. A thermoplastic polymer softens when exposed to heat and
returns to its original condition when cooled to room temperature.
Ethylene vinyl acetate copolymer ("EVA") and polyamide
thermoplastic polymers are preferred thermoplastic polymers in the
present invention. Preferably, the EVA has a softening point of at
least 100 C. Preferably, the EVA has a vinyl acetate content of
between 18% and 35% by weight of the EVA, even more preferably the
EVA has a vinyl acetate content of about 28% by weight of the EVA.
Several commercially available EVA thermoplastic polymers are
suitable for the sealant layer. These include ELVAX 4260 having a
melt index of 6 and a 28% vinyl acetate content by weight of the
EVA, ELVAX 3175 having a melt index of 6 and a 28% vinyl acetate
content by weight of the EVA. Also useful is ELVAX 3182, a 3 melt
index resin with a vinyl acetate content of about 28% by weight of
the EVA. These resins are available from DuPont. Additionally,
Exxon 767.36 (2.5 melt index, 30% vinyl acetate) and Exxon 760.36
(3 melt index, 27.5% vinyl acetate) are suitable for the sealant
layer. SEARS HOT GLUE, an ethylene/vinyl acetate copolymer from
Sears is a most preferred EVA thermoplastic polymer. SEARS HOT GLUE
is characterized by a vinyl acetate content of about 28%, a
softening point of about 158 C. and a melt index of about 6.
[0029] Suitable polyamides are hot melt, elastomeric thermoplastic
adhesives. Preferably the polyamides have a softening point of at
least 100 C. The HYSOL polyamide adhesives are thermoplastic
polymers available from HYSOL Engineering & Industrial
Productions Division of Dexter Corporation. HYSOL 7802, HYSOL 7804
and HYSOL 7811 are preferred thermoplastic polyamides in the
present invention.
[0030] Again referring to FIG. 4, this invention encompasses
several embodiments for applying sealant to seal an ultracapacitor
cell or stack of cells. In a first embodiment as shown in FIG. 4,
the sealant 90 is applied onto a collector plate 22 or 24
peripherally to respective electrode 14 or 16. The sealant layer 90
extends beyond the area of electrode 14 or 16 to contact separator
18. When compression and/or heat is applied, the sealant seals all
of a collector plate, electrode and separator. The sealed cell body
including collector plates 22, 24, electrodes 14, 16 and separator
18 can then be further sealed by the application of a sealant of
the invention or another suitable sealant to hermetically seal the
cell at its outer edges either singly or as a stack of cells. In
another embodiment, a gasket of elastomeric material can be applied
peripherally as layer 90 to hold the electrodes 14, 16 in place and
the sealant of the invention can be applied to hermetically seal
the cell at its outer edges either singly or as a stack of
cells.
[0031] A compressive force is applied to promote the flow of the
sealant--especially in the case of sealant compositions with very
high softening points or glass transition temperatures, such as the
EVA based types. Compression can be applied indirectly to the
sealant through upper ultracapacitor layers by means of the
mechanical press 50 of FIG. 3. Other devices to seal an
ultracapacitor include an hydraulic press or pneumatic press or any
device for applying compressive force. The press 50 of FIG. 3
includes structural frame 70 and adjustable beam 72. The length of
beam 72 moves in a direction perpendicular to the base portion of
the structural frame as controlled by the selective action of hand
lever 74 and gears 76 and 78. Compression element 80 is detachably
attached as the base of beam 72. Bottom surface 82 can be similar
in shape to the peripheral area of the top planar surface of
ultracapacitor 40. The force applied by the press should be
sufficient to cause the sealant to become substantially fluid, to
flow and form a continuous bead or strip around the peripheral area
of the layer on which it is deposited. Thus, the particular press
force depends in large part on the nature of the sealant. In
general, the pressure will be in the range of about 1 psi to about
1,000 psi and preferably, in the range of about 10 psi to about 100
psi. A lower press force will be suitable for lower viscosity
sealants and a higher press force will be required for higher
viscosity materials.
[0032] The sealant can be heated while being compressed. Heating
enhances the flow characteristics of the sealant. Heating
temperature should be sufficient to soften the sealant. Preferably,
the temperature is high enough to melt the sealant. For a sealant
made from an EVA based material, a suitable temperature will be in
the range of about 100.degree. C. to about 300.degree. C.
[0033] Heat is applied to the sealant in the press 50 of FIG. 3 by
means of a standard electrical heating element that is encased
within element 80 and is connected to an electrical outlet by way
of cord 82. The bottom surface 84 of element 80 has a shape that
aligns with sealant-containing peripheral regions of ultracapacitor
10. Thus, when compression element 80 is lowered for compression of
the ultracapacitor through membrane 64, heat is transmitted
primarily to the sealant containing regions.
[0034] A vacuum can be applied to press together the layers of the
ultracapacitor and to evacuate ambient gasses from the internal
region of the cell structure. In FIG. 3, vacuum tube 60 is
connected to a vacuum source through vacuum valve 88 with backfill
vacuum tube 86. When vacuum is applied, the collapsible membrane 64
is positioned over recess 52. The membrane 64 maintains the vacuum
within the recess and transmits the applied compressive force to
the layers of the ultracapacitor. The membrane 64 is heat-resistant
to a temperature of about 400.degree. C. The amount of vacuum
applied ranges from about 700 mm mercury to 0.1 mm mercury. A
typical vacuum pressure is in the range of about 500 mm mercury to
about 0.1 mm mercury.
[0035] In operation, the applied vacuum pressure draws collapsible
membrane 64 tightly against the top of ultracapacitor 10,
compressing the individual layers of the ultracapacitor against
platform layer 58 while the action of compression element 80
presses against sealant-containing regions to induce sealant 46, 48
to permeate the peripheral regions of separator layers 18. The
sealant contacts substantially aligned peripheral areas 60 of the
facing surfaces of conductive layers 22 and 24. As the sealant
cures or solidifies, it forms a strong bond to join layers 22 and
24. After sealing is complete, compression element 80 is retracted
and the ultracapacitor is allowed to cool.
[0036] The following examples are illustrative of the
invention.
EXAMPLE 1
[0037] A series of studies were conducted to determine the
stability of various sealants under conditions of ultracapacitor
use. In a first set, the sealants were studied for resistance to
electrolyte solvent over time under various temperature
conditions.
[0038] Constant temperature ovens set to 37.degree. C., 57.degree.
C., 66.degree. C., and 85.degree. C. were used for elevated
temperature measurements. In each case, a sample of a cured sealant
material was allowed to soak in a closed jar filled with solvent at
room temperature and the four elevated temperatures. Periodically,
the samples were removed from the jars, dried quickly of surface
liquid by sandwiching samples between very absorbent laboratory
wipes, and weighed. The materials were then returned to the jars
and the ovens for further soaking.
[0039] A number of the candidates failed this test very quickly.
Polysulfones, polycarbonates, polyurethanes, methacrylate esters
and low-cure, low-molecular-weight epoxies dissolved within a day
or two at room temperature or slightly elevated temperature. Other
candidates, such as the polysulfides, fared only slightly better,
rapidly gaining weight in a day at room temperature and completely
dissolving at elevated temperatures. Highly crosslinked epoxies
maintained mechanical integrity but swelled over longer periods of
time. Only silicones and EVA materials were resistant to attack and
swelling. The silicones, however, allowed solvent in a gas phase to
diffuse over time. Example 2
[0040] Adhesion to aluminum was measured on a polyamide, an
ethylene vinyl acetate copolymer, several silicone sealants and a
polypropylene.
[0041] The sealants were cured on an aluminum plate with an upper
mesh substrate. The mesh was pulled away from the aluminum plate in
an Instron tensile strength instrument under controlled conditions
and peel strength (in-lb) was calculated. This test was run at room
temperature. A polyamide and an ethylene vinyl acetate copolymer
[which polyamide and which EVA?] scored the highest average peel
strength of all tested sealants.
EXAMPLE 3
[0042] Creep is the movement or flow of a solid under load. If
creep occurs in a sealant material, it starts very early at
elevated temperatures and plateaus at nearly zero or starts early
and gradually increases with time. Polyamide HYSOL 7802 (a
polyamide adhesive from HYSOL Aerospace & Industrial Products
Division of Dexter Corporation) was evaluated for creep in a creep
test jig. Results on the 7802 HYSOL polyamide showed no creep at 60
C. and 40 psi compressive load over 15 days. This result indicates
good resistance to creep for this sealant material.
EXAMPLE 4
[0043] Five strips of each of the following samples were soaked in
propylene carbonate for eighteen days at room temperature and
weight gain or loss was determined:
1 TABLE Percent Weight Initial Weight (gms.) Gain/Loss Barco Bond
3.1299 -1.1% Electronic Grad RTV 2.8782 +0.21 Devcon 5 minute Epoxy
1.81.90 +7.7 Sears Hot Glue 4.6909 0.0% Barco Bond is an epoxy
resin. RTV stands for "Room Temperature Vulcanizable" and is a
silicone adhesive. Deacon 5 is an epoxy resin corsslinked with a
hardener.
[0044] The above test data show zero transmissions through the EVA
sealant. Further, no mechanical changes were noted in the
ultracapacitors during the testing operations. Adhesion tests show
that EVA exhibits excellent adhesion to aluminum conductors even
after months of soaking in solvent polypropylene carbonate
* * * * *