U.S. patent application number 12/698904 was filed with the patent office on 2010-08-05 for capacitors using preformed dielectric.
This patent application is currently assigned to Space Charge, LLC. Invention is credited to John B. Read, Daniel C. Sweeney.
Application Number | 20100195261 12/698904 |
Document ID | / |
Family ID | 42396411 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100195261 |
Kind Code |
A1 |
Sweeney; Daniel C. ; et
al. |
August 5, 2010 |
CAPACITORS USING PREFORMED DIELECTRIC
Abstract
Devices for storing energy at a high density are described. The
devices include an electrode preformed to present a high exposed
area onto which a dielectric is formed. The dielectric material has
a high dielectric constant (high relative permittivity) and a high
breakdown voltage, allowing a high voltage difference between
paired electrodes to effect a high stored energy density.
Inventors: |
Sweeney; Daniel C.;
(Burbank, CA) ; Read; John B.; (San Diego,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Space Charge, LLC
Aspen
CO
|
Family ID: |
42396411 |
Appl. No.: |
12/698904 |
Filed: |
February 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61206677 |
Feb 2, 2009 |
|
|
|
61223688 |
Jul 7, 2009 |
|
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61254903 |
Oct 26, 2009 |
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Current U.S.
Class: |
361/313 ;
361/311; 361/321.5; 427/79 |
Current CPC
Class: |
H01G 4/008 20130101;
H01G 11/22 20130101; H01G 4/01 20130101; Y10T 29/435 20150115; H01G
4/1209 20130101 |
Class at
Publication: |
361/313 ;
361/311; 361/321.5; 427/79 |
International
Class: |
H01G 4/12 20060101
H01G004/12; H01G 4/06 20060101 H01G004/06; H01G 4/08 20060101
H01G004/08; B05D 5/12 20060101 B05D005/12 |
Claims
1. A storage capacitor comprising: a first electrode having a first
surface with a first surface area; a second electrode having a
second surface with a second surface area, wherein the second
electrode is physically separated from the first electrode creating
a gap between the first electrode and the second electrode; and a
dielectric material disposed within the gap and contacting the
first surface and the second surface, wherein an effective relative
permittivity between the first electrode and the second electrode
is greater than or about 500.
2. The storage capacitor of claim 1 wherein the first surface
comprises a textured surface structure, wherein the first surface
area ranges from greater than or about 4 to greater than or about
50 times larger than a flat surface similar to the first
surface.
3. The storage capacitor of claim 2, wherein the first surface of
the first electrode comprises a metallic open-cell foam.
4. The storage capacitor of claim 3, wherein the metallic open-cell
foam comprises nickel.
5. The storage capacitor of claim 1, wherein the second surface is
a textured surface wherein the second surface area ranges from
greater than or about 4 to greater than or about 50 times larger
than a flat surface similar to the second surface.
6. The storage capacitor of claim 1, wherein the effective relative
permittivity ranges between above or about 1000 to above or about
2000.
7. The storage capacitor of claim 1, wherein the dielectric
material comprises ceramic perovskite.
8. The storage capacitor of claim 1, wherein the dielectric
material comprises tungsten bronze perovskite.
9. The storage capacitor of claim 1, wherein the dielectric
material comprises two or more dielectric layers each layer being a
different dielectric material.
10. A method of forming a storage capacitor, the method comprising:
providing a first metal electrode with a first surface; providing a
second metal electrode with a second surface, wherein the second
electrode is physically separate from the first electrode creating
a gap between the first electrode and the second electrode; and
flowing a dielectric between the first electrode and the second
electrode into the gap; and converting the flowable dielectric to a
solid dielectric having a relative permittivity greater than or
about 500.
11. The method of claim 10, wherein the relative permittivity
ranges above or about 1000 to above or about 2000.
12. The method of claim 10, wherein the operation of flowing a
dielectric comprises the sequential steps of: flowing a first
dielectric; and flowing a second dielectric, wherein a viscosity of
the first dielectric is less than the viscosity of the second
dielectric.
13. The method of claim 10, wherein the first metal electrode is
textured and the operation of flowing a dielectric between the
first and second electrodes further comprises flowing the
dielectric onto the first metal electrode wherein the contact area
between the dielectric and the first metal electrode ranges from
greater than or about 4 to greater than or about 50 times the
contact area flat surface with a similar electrode having a flat
surface.
14. The method of claim 13, wherein the first metal electrode
comprises a woven metal mesh.
15. The method of claim 13, wherein the first metal electrode
comprises a metal foam.
16. The method of claim 13, wherein the first metal electrode
comprises metal fibers.
17. The method of claim 16, wherein the metal fibers comprise
carbon fibers.
18. The method of claim 10, wherein the second metal electrode is
textured and the operation of flowing a dielectric between the
first and second electrodes further comprises flowing the
dielectric in amongst the second metal electrode wherein the
contact area between the dielectric and the second metal electrode
ranges from greater than or about 4 to greater than or about 50
times a contact area with a similar electrode having a flat
surface.
19. The method of claim 10, wherein the operation of converting the
flowable dielectric to a solid dielectric comprises curing the
dielectric.
20. The method of claim 10, wherein the operation of converting the
flowable dielectric to a solid dielectric comprises annealing the
dielectric.
21. The method of claim 10, wherein the operation of converting the
flowable dielectric to a solid dielectric comprises irradiating the
dielectric with ultraviolet light.
22. The method of claim 10, wherein the dielectric comprises solid
granules of material, which increase the relative permittivity of
the solid dielectric.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Prov. Pat. App.
No. 61/206,677 filed Feb. 2, 2009, and titled "METHOD AND APPARATUS
FOR UTILIZING A HIGH VOLTAGE CAPACITOR BANK AS A SOURCE OF
SUSTAINED LOW VOLTAGE ELECTRICAL CURRENT," U.S. Prov. Pat. App. No.
61/223,688 filed Jul. 7, 2009, and titled "HIGH-VOLTAGE CAPACITOR
SOURCE," and U.S. Prov. Pat. App. No. 61/254,903 filed Oct. 26,
2009, and titled "HIGH-VOLTAGE CAPACITOR SOURCE." The entire
contents of all these applications are incorporated herein by
reference for all purposes.
FIELD
[0002] This application relates to high-density energy storage
systems, components and manufacturing methods.
BACKGROUND
[0003] Capacitive interaction occurs in all electronic circuits.
Discrete capacitors are included in the circuits to fulfill a
variety of roles including frequency filtration, impedance matching
and the production of electrical pulses and repetitive signals.
Regardless of the complexity of the design, a capacitor can be
thought of as two closely spaced conducting plates which may have
equal and opposite charges (.+-.Q) residing on them when a voltage
(V) is applied. The scalar quantity called capacitance (C) is the
ratio of the charge to the applied voltage. When capacitance
increases, a significant charge can be stored and a device can be
used like a battery.
[0004] Though basic batteries have a high energy density, they can
only deliver a relatively small current since the current must be
generated by a chemical reaction occurring within each storage
cell. By contrast, capacitors may have a low energy density but can
discharge very quickly--a flexibility which is desirable for many
applications. Superconducting magnetic energy storage (SMES) is an
alternative, but still suffers from a low storage density combined
with impractical mass and thermal complexities.
[0005] FIGS. 1A-1C show prior art capacitor designs. FIG. 1A shows
a capacitor having electrical leads connected to conducting plates
or electrodes 110. An air-gap 115-1 is left between electrodes 110
so that when a voltage is applied, a positive charge accumulates on
the electrode with a positive bias. This results in an opposite
charge on the other electrode and an electric field pointing from
left to right in FIG. 1A. Each of the capacitors depicted in FIGS.
1A-1C is symmetric, i.e. possesses the same capacitance regardless
of which electrode receives the positive voltage.
[0006] In FIG. 1B, the same capacitor has a dielectric material
inserted in the space 115-2 between the electrodes 110. The
dielectric constant or relative permittivity of the dielectric
material allows the amount of charge (the "capacity" or capacitance
of the capacitor) stored on each electrode to increase for the same
applied voltage. A higher relative permittivity increases the
ability of the dielectric to adjust its distribution of charge in
response to the applied voltage; a negative charge accumulates near
the positive electrode and a positive charge near the negative
electrode. A smaller electric field exists between the electrodes
if the relative permittivity is higher.
[0007] The stored charge can be further increased by using an
electric double-layer capacitor (EDLC) design. EDLC's have higher
energy density than traditional capacitors and are sometimes
referred to as "supercapacitors". Energy can be defined as the
amount of charge stored per unit volume. However, the storage
density of EDLC's (depicted in FIG. 1C) can still be improved upon.
Between electrodes 110, a dielectric material 116 surrounds high
surface area electrically-conducting granules 117 distributed in
the gap 115-3. A dielectric separator 118 is positioned between two
regions of the embedded granules 117. The surfaces of granules 117
on the left of separator 118 are positively charged while the
granules 117 on the right develop negative surface charging. The
effective surface area of the capacitor is increased which allows
even more charge to be stored on electrodes 110 for a given
voltage.
[0008] Despite these advances, further increases in energy storage
density of capacitors may improve upon traditional batteries.
BRIEF SUMMARY
[0009] Devices for storing energy at a high density are described.
The devices include an electrode preformed to present a high
exposed area onto which a dielectric is formed. The dielectric
material has a high dielectric constant (high relative
permittivity) and a high breakdown voltage, allowing a high voltage
difference between paired electrodes to effect a high stored energy
density in one embodiment.
[0010] Additional embodiments and features are set forth in part in
the description that follows, and in part will become apparent to
those skilled in the art upon examination of the specification or
may be learned by the practice of the disclosed embodiments. The
features and advantages of the disclosed embodiments may be
realized and attained by means of the instrumentalities,
combinations, and methods described in the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A further understanding of the nature and advantages of the
disclosed embodiments may be realized by reference to the remaining
portions of the specification and the drawings.
[0012] FIGS. 1A-1C are schematics of prior art capacitors.
[0013] FIG. 2 is a flowchart for forming a high-voltage storage
capacitor according to disclosed embodiments.
[0014] FIG. 3 is a schematic of a high-voltage storage capacitor
according to disclosed embodiments.
[0015] FIGS. 4A-B are perspective views of a wire weave or mesh for
use as an electrode within a high-voltage storage capacitor
according to disclosed embodiments.
[0016] FIG. 5 is a perspective view of a multi-layer stacked
high-voltage storage capacitor according to disclosed
embodiments.
[0017] FIG. 6 is a perspective view of a multi-layer stacked
high-voltage storage capacitor according to disclosed
embodiments.
[0018] FIG. 7 is a flowchart for forming the multi-layer stacked
high-voltage storage capacitor of FIG. 6 according to disclosed
embodiments.
[0019] In the appended figures, similar components and/or features
may have the same reference label. Further, various components of
the same type may be distinguished by following the reference label
by a dash and a second label that distinguishes among the similar
components. If only the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
DETAILED DESCRIPTION
[0020] Devices for storing energy at a high density are described.
The devices include an electrode preformed to present a high
exposed area onto which a dielectric is formed. The dielectric
material has a high dielectric constant (high relative
permittivity) and a high breakdown voltage, allowing a high voltage
difference between paired electrodes to effect a high stored energy
density in one embodiment.
[0021] The quantity of energy stored in a capacitor is proportional
to the capacitance which, in turn, is proportional to the contact
area between the dielectric material and the electrodes as well as
the effective relative permittivity of the dielectric material
between the two electrodes. The electric double-layer capacitor
(EDLC) described above owes its relatively high energy storage
capacity to an increased effective surface area of the electrodes,
which creates increased capacitance. However, the EDLC design is
not conducive to operation at elevated voltages since the electric
fields can become high enough to result in a breakdown of the
dielectric material. In some embodiments, energy storage density
and capacity can be improved by increasing the voltage across the
electrodes. This is because the storage capacity is proportional to
the square of the voltage, making this an even more attractive
parameter to increase when possible. For example, an increase in
voltage potential across a capacitor from about 1 volt to about 100
volts increases the storage capacity of the device by a factor of
10,000. Accordingly, capacitors which allow the charging voltage to
increase may rival storage battery energy densities while still
allowing high output power to be generated.
[0022] FIG. 2 provides a flow diagram of an embodiment utilized to
construct a high energy storage capacitor with preformed
electrodes. In step 201, the electrodes are textured in order to
increase surface area with a dielectric material. In step 202, a
dielectric is deposited onto the surfaces of the electrodes in a
wetting process. In step, 203, the dielectric is solidified onto
the surfaces of the electrodes in order to create a bond between
the electrode and the dielectric, increase the permittivity of the
dielectric and ensure the highest contact area between the
electrode and dielectric. In step 204, the capacitor is formed by
layering multiple opposing electrodes on which dielectric material
is deposited. Finally, in step 205, a voltage is applied to charge
the capacitor. Various embodiments of these steps are further
discussed in the following paragraphs, with specific reference
given to the description of FIG. 3.
[0023] Referring to FIG. 3, a schematic view of a capacitor
according to disclosed embodiments is illustrated. Electrodes 310
are electrically attached to electrical leads 305. The electrodes
310, may be made from metallic textiles as well as conductive
polymers. Metallic textiles may be woven, knitted or braided to
produce a mesh-like structure with a degree of porosity to increase
surface area of an electrode. The porosity may be used to describe
the roughness of the textured textile. However, it will be
understood that rugosity may also be used to describe the
roughness. Metallic textiles may be made of a variety of metals
generally chosen for their conductivity and ease of manufacture.
Exemplary metallic textiles may comprise tin to enhance ductility
and may be an alloy to maintain conductivity (example: copper (95%)
tin (5%)). The size and density of the comprising wires may be
chosen to facilitate the insertion of liquid dielectric and the
wire density may range from about ten to thousands of wires per
centimeter or more. Wire sizes and weave density may be chosen to
provide gaps in the weave structure ranging from several microns to
several hundred microns.
[0024] Metallic textiles may be sintered and calendered to improve
conductivity and to ensure a compact, low aspect ratio structure.
Sintering and calendering also helps to reduce sharp edges and high
radius curves, properties also reduce the chance of electrical
discharge between electrodes. The choice of the structure of the
metallic textile is another variable which can be beneficially
controlled. Avoiding open circuits and ensuring each comprising
wire begins and ends at the edge of the fabric also reduces the
chances of undesirable electrical discharge across the dielectric
material from one electrode to the other electrode. Wires ends may
be connected together near the edge of the metallic textile. A
single wire may be used to form one electrode and the ends of the
single wire may be joined together. Alternatively, multiple wires
(strands) may be used to form the metallic textile and the ends of
each strand may be joined. In another embodiment, ends of separate
strands may be joined, generally near the edge of the textile.
[0025] Textured electrodes may also comprise a metallic open-cell
foam or "sponge" configurations. The open cell structure is useful
since the connectivity of the voids allows the liquid dielectric to
be injected in amongst the textured electrode more easily. Metallic
open-cell foam may be formed using a sintering process and comprise
tungsten, nickel, gold or other conducting material. Textured
electrodes may also be a three dimensional repeating cage-like
structure which similarly provides pathways for liquid dielectric
to enter the metallic matrix. In a further embodiment, the
open-foam structure may comprise of carbon aerogel. Though very low
density, carbon aerogel has a high surface area due to its
porosity. The variety of techniques described herein for texturing
electrodes are exemplary. Furthermore, surface area enhancing
techniques are not mutually exclusive. A variety of porous foams
are available from INCO Special Products of Mississauga, Ontario,
Canada. An example of an appropriate film is INCOFOAM.TM. which
possess cell sizes in the range 450-800 .mu.m.
[0026] In FIG. 2, at step 201, to further increase energy storage
capacity electrodes 310 may be textured in a variety of ways to
increase their surface area in contact with dielectric material
316. A relatively simple texturing configuration will be described
initially along with a general overview of assembly considerations.
These assembly considerations apply to all the texturing
configurations unless otherwise noted. Electrodes 310 are shown
with multiple fingers 317 protruding from the base of the
electrodes 310. Each finger 317 is electrically conducting to allow
the redistribution of charge enabling electrical energy to be
stored. Fingers 317 are shown in electrical contact with electrodes
310. Fingers 317 and electrodes 310 are in mechanical contact to
control the smallest separation between fingers 317 from opposite
electrodes 310.
[0027] Exemplary finger structures may be formed by ion-milling
structures 317 into electrodes 310 or growing the finger structures
317 onto a conducting electrode 310. FIG. 3 shows two textured
electrodes 310, however one textured electrode is also possible in
disclosed embodiments regardless of the type of texture. Microtube
fingers and other microstructures may be formed on one or both
electrodes of a variety of compositions including carbon-containing
structures. A vendor for carbon-containing structures is Energy
Science Laboratories, Inc. of San Diego, Calif. Textured electrodes
may more generally have metal fibers or conducting carbon fibers
and the fibers may have a variety of orientations and do not need
to be straight. A textured surface may have a surface area which is
larger than that of a flat surface but otherwise similar electrode
by a factor of above or about 4, above or about 10, above or about
20, above or about 50, above or about 100 or above or about 200 in
different embodiments.
[0028] The surface areas of the textures electrodes are calculated
by methods appropriate for the nature of the surface. Some surfaces
may be accessible by an atomic force microscope (AFM) when
overhanging portions or fibers do not complicate or interfere with
measurement by a physical tip. In the interest of unambiguously
defining the area ratio, the lateral spacing of the data points may
be several nanometers, the tip is applied with a moderate force to
avoid crashing and is operated in tapping mode. Imaging software is
capable of estimating the total surface area by tiling the surface
with triangles. The surface can be tiled completely and the area of
the triangles can be summed to determine the total area. In the
case of columns, fibers or nanostructures, the dimensions can be
estimated by approximating the objects on the surface as one or
more geometric shapes. For example, a metal fiber from a "carpet"
of metal fibers attached to an electrode base may be modeled as a
cylinder having a diameter of a given number of microns. The
exposed area of the carpet (i.e., the textured electrode) may be
calculated by determining the outer area of a cylinder having
average height for the metal fiber carpet. The total area supplied
by the fibers themselves may be estimated by further multiplying by
an estimate of the areal density of fibers and the base area. The
estimate of the area of the fibers is added to the areas of the
electrode base which are not covered by fibers to calculate the
total exposed area. The estimate of the exposed area of the carpet
is divided by the area of a flat (featureless) surface of the same
planar dimensions. The surface area of a flat but otherwise similar
electrode to an etched aluminum foil 2 cm by 4 cm would be 8 cm
squared (cm.sup.2), for example.
[0029] In other embodiments, microtomography may be utilized to
render a 2-D or 3-D image of the surface of the textured electrode
through x-rays. In such an embodiment, different mathematical
calculations, such as root means square deviation and others known
within the art, may be utilized to measure the surface area of the
rendered image.
[0030] Referring back to FIG. 2, at step 201, a dielectric material
may be deposited onto the electrodes. A dielectric material 316
with a high relative permittivity and high breakdown field is
utilized. The high relative permittivity may be above or about 500,
above or about 1,000, above or about 2,000, above or about 5,000,
above or about 10,000 or above or about 20,000 in various
embodiments. The breakdown voltage of assembled devices may be
above or about 1 kilovolt (kV), above or about 2 kV or above or
about 4 kV in various embodiments. Suitable ultra-high permittivity
dielectric materials 316 include dielectric suspended "Tungsten
Bronze" crystals which exhibit a breakdown field of greater than 60
kilovolts per centimeter (kV/cm). Other exemplary high permittivity
dielectric materials include ceramic perovskite.
[0031] The depositing and formation of dielectric material 316 onto
the electrodes is more complex when using textured electrodes 310.
Herein, the term dielectric material will be used to refer to the
region of dielectric between the extremum 315 of the texture where
a solid slab of dielectric material can be physically slid
in-between and/or also the region along the surface of the texture.
The energy storage capacity is increased when the dielectric is
inserted within the texturing, for example, between the fingers
317. This may involve grinding a dielectric into small enough
granules to flow within fingers 317 and then placing the granules
in amongst the fingers when assembling the device. A greater
filling fraction increases the amount of energy which can be stored
in the device.
[0032] Alternatively, a flowable dielectric may be flowed into the
region between fingers 317. A flowable dielectric may provide a
greater filling fraction provided that the wetting properties are
such that the flowable dielectric is drawn into the region between
the fingers 317 rather than repulsed. Flowable dielectric may be
actively induced to fill the gaps in the texture by applying a
positive pressure to press the liquid into the gaps. A vacuum may
also be created in the vicinity of the texture to draw the liquid
into the gaps. Depending on the chemistry of the liquid dielectric
and the chemical structure/content on the surface of fingers 317,
wetting can often be manipulated by performing a surface
pretreatment of either an acidic or basic aqueous solution. The
wetting may also be improved by providing an additive to the liquid
dielectric itself, keeping in mind that relative permittivity and
electric breakdown field should both remain high enough for the
intended application.
[0033] A flowable dielectric may include a liquid solution along
with dielectric granules in suspension. During subsequent
processing, for example during a firing step, the liquid solution
may be evaporated leaving the dielectric granules in amongst the
texture of the electrode(s). Generally speaking, flowable
dielectrics may have a flow-enabling component which allows the
material to be flowed onto the texture of electrodes 310. Another
approach involves applying molten dielectric into the texture of
electrodes 310 to fill the gaps. Voids or apertures in the
dielectric material may be avoided to increase the energy storage
capacity.
[0034] Depending on the dielectric material, penetration into all
regions may not readily occur. Accordingly, two flowable
dielectrics may be flowed within the region between the two
electrodes. A low viscosity dielectric may be flowed first to
better penetrate the texture of one or both electrodes. A higher
viscosity dielectric may then be flowed. The higher viscosity
dielectric does not need to penetrate the texture as completely as
the low viscosity dielectric, but is utilized to provide a higher
dielectric constant in the penetrated regions. The viscosity may be
adjusted by altering the viscosity of the liquid component of the
flowable dielectric and/or by increasing the concentration of the
solid dielectric granules which have high dielectric constant. A
dielectric material in this example as well as the other exemplary
materials may include two or more dielectric layers each comprising
a different dielectric material.
[0035] Suitable dielectrics for flowing between textured electrodes
310 include polymer electrolytes designed for high permittivity and
high voltage. A vendor for these types of dielectric materials is
Strategic Polymer Sciences in Pennsylvania and Sigma Technologies
in Arizona. Alternatively, polymer dielectrics loaded with ceramic
powders may be utilized. A vendor for these types of dielectric
materials is TPL, Inc. of Albuquerque, N.M.
[0036] The flowable dielectric may be formed by grinding high
relative permittivity material into granules and introducing the
granules into a liquid. Such a solution may be referred to as a
slurry and may contain crystals, binders and carrier fluids to
promote flowability. A slurry, as with a liquid dielectric, is
injected in and around the textured electrode. The liquid
dielectric and the solid granules will likely have different
relative permittivities. Typically, the liquid dielectrics display
a lower permittivity and the solid granules display a higher
permittivity. The combined or effective permittivity of the
material between and amongst textured electrodes will depend on
both permittivities and display values between the lower and higher
permittivities. A sol-gel process may also be used, in which a
fluid transition from a more fluid solution into a more viscous
solution during use. A slurry may be actively inserted in amongst
the texture of an electrode through pressurizing, applying a vacuum
to draw the slurry into the texture, relying on capillary forces or
by applying an electromagnetic field (electrophoresis). Following
penetration of the texture by the flowable dielectric, the flowable
dielectric may be solidified by any number of processes including
firing.
[0037] Solid or semi-solid dielectric material may also be placed
into the region adjacent to the textured electrode. Heating one or
both the dielectric and the electrode may allow the dielectric to
become fluid and flow into the texture. The dielectric may be
extruded and then braided, woven or knitted to facilitate the
process. The dielectric mass may then be heated or fired to produce
a cohesive mass where the dielectric lies in intimate contact with
the texture of the electrode. Firing the dielectric may promote the
bond between the electrode and the dielectric and is also helpful
in increasing the electrical permittivity of many dielectrics. The
process of firing occurs when a material is heated near to its
melting point.
[0038] During assembly, discrete spacers may be used to maintain a
separation between the electrodes during insertion and processing
of the dielectric material. High-temperature-tolerant separator
films are also available for this purpose. A cut-out in the shape
of the dielectric material may be made in the separator film and
the film may be used to provide a contiguous separation around the
perimeter of the capacitor between the electrodes.
[0039] Referring again to FIG. 2, in step 203, the flowable
dielectric material is formed into a solid structure. As
illustrated in FIG. 3, the flowable dielectric solidifies after
flowing into the region between fingers 317 in an embodiment. The
solidification may result from simply waiting for the flow-enabling
additive to evaporate from the material or the dielectric material
may be actively cured by shining light (e.g. ultraviolet light),
raising the temperature (annealing), irradiating with an e-beam
and/or similar processes known to those of skill in the art. Molten
dielectric can solidify by cooling to a temperature below the
melting temperature of the dielectric.
[0040] In FIG. 2, at step 204, a capacitor may be formed from one
or more layers of dielectric. An electrode with deposited
dielectric material may be placed adjacent to similar, opposing
electrodes. In the case of a multi-layer capacitor, processing of
the dielectric materials may be done simultaneously in some
embodiments. Upon completion of a multi-layer capacitor, they may
be combined in series or in parallel depending on the application.
In a parallel configuration every other electrode is connected
electrically.
[0041] As indicated, many designs are possible for increasing the
effective surface area the electrodes through texturing the surface
in various embodiments. A plane of parallel conducting wires can be
used for the electrode(s) and the flowable dielectric may be
introduced on either side of the multiple parallel wires as well as
between each adjacent pair of wires. In addition, other surface
patterns may be formed utilizing conducting wires.
[0042] In one embodiment, as illustrated in FIGS. 4A-4B,
perspective views of a metallic weave or mesh may be used to
produce one or both of the electrodes for a storage capacitor.
Metallic weaves and meshes are a subset of as the aforementioned
metallic textiles. As shown, the metallic weave 400 produces a
series of peaks 401 and valleys 402 which create a high surface
area on which the dielectric material may be deposited. The
structure of the metallic weave may include multi-ply weaves,
triaxial weaves, multi-axial weaves and/or any other weave known in
the art. Stock and custom knitted wire weaves or meshes can be
obtained from ACS Industries of Woonsocket, R.I. Customized
metallic meshes may have approximate pore sizes in the range from
100 .mu.m up to several millimeters in different embodiments. The
size of the weave is important because, if a weave is made too
tightly or too small, the dielectric materials may not be able to
penetrate the surface. As discussed, maximizing surface area and
contact between that area and the dielectric is desirable.
Accordingly, when utilizing a weave, the rugosity of the type of
dielectric utilized is selectively chosen based on the type of
weave.
[0043] Referring to FIG. 5, a capacitor using metallic textile
electrodes during assembly is illustrated in another embodiment.
Each post 504 serves as a portion of an electrical lead and
connects to alternating electrodes, enhancing the energy storage of
the completed device. Each electrode layer 501 may be of opposite
charge and textured to create an increased surface area. In the
embodiment illustrated in FIG. 5, a metallic textile weave is
utilized as the electrode 501, similar to that shown in FIG. 4A-4B.
The weave may include a dielectric material 502 which has be flowed
onto each electrode and solidified, prior to layering the
electrodes. The layers of combined dielectric material and
electrode may be further separated by spacers 503 and/or dielectric
slabs in order to ensure separation of charge between the opposing
electrodes and reduce leakage. The spacers may be made of similar
to the dielectric materials utilized within the electrodes.
[0044] FIG. 6 shows another method of texturing the electrode in an
embodiment. For purposes of illustration, a serpentine electrode
configuration 600 can be constructed using open-cell foam material
in such an embodiment. This embodiment involves arranging the
conducting electrode material in a serpentine pattern to increase
surface area. The material may be heated and formed into the
serpentine electrode 601 structure and then sintered or calendared
to reduce sharp edges. Dielectric material 602 in the form of slab
structures, may be inserted into the spaces created between the
crests and troughs of the serpentine structure. In addition,
spacers may be utilized between each successive layer of an
opposing electrode. The spacers may also be a dielectric of the
same material for the slabs, or other suitable high permittivity
dielectric.
[0045] In a further embodiment, to increase contact between the
serpentine electrodes 601 and the dielectric material 602, the
assembled device may be submerged in a liquid dielectric (not
shown) to fill voids 603 between dielectric material and the
serpentine electrodes. Following the insertion of dielectric
material between and into the electrodes, the dielectric may be
fired in an oxidizing environment (e.g., air) in order to increase
the permittivity. The electrode material is selected to withstand
firing in order to maintain the structure of the system. Therefore,
electrode materials with higher melting temperatures than the
dielectric is used in these embodiments. Preferably, the electrode
material resists oxidation. Noble metals, refractory metals and
specialized alloys are examples of electrode material and include
silver, platinum, tungsten, iridium, ruthenium, tantalum, monel,
inconel, and/or fecralloy. Additional non-oxidizing materials
suitable for electrodes include carbon, graphene, and conductive
resins and plastics. Regardless of the type of texturing used,
liquid dielectric with or without a permittivity-enhancing
suspension may be injected in and around the metallic weaves or
serpentine electrodes to increase the storage capacity.
[0046] FIG. 7 provides a flowchart of a two stage dielectric
deposition process for forming the capacitor of FIG. 6, in an
exemplary embodiment. The structure of the electrodes is formed in
step 701. As previously discussed, this may be through molding a
metallic textile, or purchasing a preformed metallic textile in a
weave or open-cell foam structure. For illustration in the
embodiment shown in FIG. 6, the structure is formed in step 701 as
a serpentine pattern.
[0047] In step 702, a first dielectric is deposited onto the formed
electrode structure. The first dielectric may be viscose and flowed
onto the surface of the electrode structure or simply inserted into
voids created by the geometry of the electrode structure, such as
those illustrated in FIG. 6. The first dielectric may be solidified
onto the electrode structure prior to the deposition of the second
dielectric or inserted into the voids in an solid form, such as a
dielectric slab.
[0048] Accordingly, in step 703, the solidified electrode structure
containing two deposited dielectrics, may be layered with other
opposing electrode structures to form a capacitor as illustrated in
FIG. 6. Spacers of the same material of the first dielectric may be
included between each successive layer of electrode in order to
further separate the opposing electrodes and prevent leakage during
operation. The opposing dielectric layers may be electrically
connected to leads supplying opposite charges in series or
parallel. In FIG. 6, the opposing electrodes are connected to a
leads in a parallel configuration, with every other electrode being
connected to a lead.
[0049] In step 704, a second dielectric may be added to the
electrode structure. The second dielectric may be flowed into the
voids created by the electrode structure and the solidified first
dielectric. In order to bond the second dielectric to the
structure, the entire structure may be fired. In alternative
embodiments, the second dielectric may be heated to a temperature
in order to cause fluidity and solidifying when cooled. For
example, dielectric soda glass, which has a low melting temperature
may be utilized in such an embodiment.
[0050] Having disclosed several embodiments, it will be recognized
by those of skill in the art that various modifications,
alternative constructions, and equivalents may be used without
departing from the spirit of the disclosed embodiments.
Additionally, a number of well known processes and elements have
not been described in order to avoid unnecessarily obscuring the
present invention. While the principles of the disclosure have been
described above in connection with specific apparatuses and
methods, it is to be clearly understood that this description is
made only by way of example and not as limitation on the scope of
the disclosure.
[0051] As used herein and in the appended claims, the singular
forms "a", "an", and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a process" includes a plurality of such processes and reference to
"the dielectric material" includes reference to one or more
dielectric materials and equivalents thereof known to those skilled
in the art, and so forth.
[0052] Also, the words "comprise," "comprising," "include,"
"including," and "includes" when used in this specification and in
the following claims are intended to specify the presence of stated
features, integers, components, or steps, but they do not preclude
the presence or addition of one or more other features, integers,
components, steps, acts, or groups.
* * * * *