U.S. patent application number 16/752122 was filed with the patent office on 2020-08-20 for methods and apparatuses for polymer fibrillization under electric field.
The applicant listed for this patent is Maxwell Technologies, Inc.. Invention is credited to Jian Hong, Xiaomei Xi.
Application Number | 20200266419 16/752122 |
Document ID | 20200266419 / US20200266419 |
Family ID | 1000004810564 |
Filed Date | 2020-08-20 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200266419 |
Kind Code |
A1 |
Hong; Jian ; et al. |
August 20, 2020 |
METHODS AND APPARATUSES FOR POLYMER FIBRILLIZATION UNDER ELECTRIC
FIELD
Abstract
A method of fibrillizing a fibrillizable binder component of an
electrode film can include providing a negatively charged
fibrillizable binder component, and applying an electric field upon
the negatively charged binder component to fibrillize the
negatively charged fibrillizable binder component. A system for
fibrillizing a binder component of an electrode film can include a
mixing container made of a material having an affinity to donate
electron(s) to the binder component, and an actuator configured to
apply a force upon the mixing container so as to contact the mixing
container with the binder component and to move the mixing
container and the binder component relative to each other within a
speed and range of motion sufficient to create an electrostatic
force on the binder component and fibrillize the binder
component.
Inventors: |
Hong; Jian; (San Diego,
CA) ; Xi; Xiaomei; (Carlsbad, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Maxwell Technologies, Inc. |
San Diego |
CA |
US |
|
|
Family ID: |
1000004810564 |
Appl. No.: |
16/752122 |
Filed: |
January 24, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14642471 |
Mar 9, 2015 |
10547045 |
|
|
16752122 |
|
|
|
|
61950699 |
Mar 10, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/96 20130101; H01M
4/88 20130101; H01G 11/38 20130101; H01M 4/04 20130101; H01M 4/8668
20130101; H01M 4/139 20130101; H01M 4/622 20130101; H01M 4/045
20130101; H01M 4/0435 20130101; H01M 4/8896 20130101; H01M 4/623
20130101; H01M 4/133 20130101; H01M 4/587 20130101; H01M 10/0525
20130101; H01G 11/86 20130101; H01G 11/30 20130101; Y02E 60/13
20130101; H01M 4/1393 20130101 |
International
Class: |
H01M 4/04 20060101
H01M004/04; H01G 11/30 20060101 H01G011/30; H01G 11/38 20060101
H01G011/38; H01M 4/62 20060101 H01M004/62; H01M 4/139 20060101
H01M004/139; H01M 4/88 20060101 H01M004/88; H01M 4/86 20060101
H01M004/86; H01G 11/86 20060101 H01G011/86 |
Claims
1. A method of fibrillizing a binder component of an electrode
film, comprising: providing a negatively charged fibrillizable
binder component; and fibrillizing the negatively charged
fibrillizable binder component by applying an electric field upon
the negatively charged fibrillizable binder component.
2. The method of claim 1, wherein applying the electric field
comprises applying an electrostatic field.
3. The method of claim 2, wherein providing the negatively charged
fibrillizable binder component comprises contacting a fibrillizable
binder component with an electron donor.
4. The method of claim 3, wherein contacting the fibrillizable
binder component with the electron donor comprises applying an
acoustic force upon the fibrillizable binder component.
5. The method of claim 3, wherein the electron donor comprises a
mixing container of a fibrillization apparatus, wherein the mixing
container is made of a material having an affinity to donate
electrons to the fibrillizable binder component.
6. The method of claim 5, wherein contacting the fibrillizable
binder component with the electron donor comprises applying at
least one of a linear force and a rotational force upon the mixing
container to displace the mixing container relative to the
fibrillizable binder component.
7. The method of claim 2, wherein providing the negatively charged
fibrillizable binder component comprises contacting the
fibrillizable binder component with a mixing medium.
8. The method of claim 2, further comprising drying the
fibrillizable binder component prior to applying the electric field
upon the negatively charged fibrillizable binder component.
9. The method of claim 8, wherein drying the fibrillizable binder
component comprises heating the fibrillizable binder component in a
vacuum oven.
10. The method of claim 2, wherein the fibrillizable binder
component comprises polytetrafluoroethylene.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 14/642,471 filed Mar. 9, 2015 and titled "METHODS AND
APPARATUSES FOR POLYMER FIBRILLATION UNDER ELECTRIC FIELD", which
claims priority benefit to U.S. provisional Application No.
61/950,699, filed Mar. 10, 2014, each of which is hereby
incorporated by reference in its entirety for all purposes.
BACKGROUND
Field
[0002] The present invention relates to energy storage devices,
particularly to methods and apparatuses for fabricating dry
particle films for use in energy storage devices.
Description of the Related Art
[0003] There are many different types of energy storage devices
used to power electronic devices, including for example capacitors,
such as for example, ultracapacitors or lithium-ion capacitors,
batteries, such as lithium-ion batteries, and fuel cells. An energy
storage device can include one or more films, such as an electrode
film forming an electrode of the energy storage device. The
electrode film may comprise one or more active materials. The film
can include a fibrillized binder component, the fibrillized binder
component providing a plurality of fibrils which can support one or
more other components of the film (e.g., providing mechanical
structure for the film).
[0004] Fibrillization of binder components for electrode films can
be typically performed using a mechanical fibrillization process.
Components of the electrode film, including the binder component of
the electrode film, can be combined and blended in an apparatus,
such as, a blender, and/or a jet mill in which a strong shear force
can be applied upon the binder component to manipulate the binder
component so as to form fibrils. Fibrillization of the binder
component can facilitate formation of a matrix, lattice and/or web
of fibrils in which one or more other components of an electrode
film, such as an active electrode material, can be supported.
Fibrils of a binder component can provide desired mechanical
strength for an electrode film. For example, the fibrils can
provide films having desired resistance to a tensile, shear,
compressive, and/or twisting stress, facilitating fabrication of
energy storage devices having dry particle electrode films.
SUMMARY
[0005] One embodiment includes a method of fibrillizing a binder
component of an electrode film. This embodiment can include
providing a negatively charged fibrillizable binder component, and
fibrillizing the negatively charged fibrillizable binder component
by applying an electric field upon the negatively charged
fibrillizable binder component.
[0006] In some embodiments, applying the electric field can include
applying an electrostatic field.
[0007] In some embodiments, providing the negatively charged
fibrillizable binder component can include contacting a
fibrillizable binder component with an electron donor.
[0008] In some embodiments, contacting the fibrillizable binder
component with the electron donor can include applying an acoustic
force upon the fibrillizable binder component. The electron donor
may include a mixing container of a fibrillization apparatus, where
the mixing container is made of a material having an affinity to
donate electrons to the fibrillizable binder component. In some
embodiments, contacting the fibrillizable binder component with the
electron donor can include applying at least one of a linear force
and a rotational force upon the mixing container to displace the
mixing container relative to the fibrillizable binder
component.
[0009] In some embodiments, providing the negatively charged
fibrillizable binder component can include contacting the
fibrillizable binder component with a mixing medium.
[0010] In some embodiments, the method can further include drying
the fibrillizable binder component prior to applying the electric
field upon the negatively charged fibrillizable binder component.
Drying the fibrillizable binder component can include heating the
fibrillizable binder component in a vacuum oven.
[0011] In some embodiments, the fibrillizable binder component can
include polytetrafluoroethylene.
[0012] Another embodiment includes a system for fibrillizing a
binder component of an electrode film. This embodiment can include
a mixing container including a material having an affinity to
donate one or more electrons to the binder component, and an
actuator configured to apply a force upon the mixing container to
contact the mixing container with the binder component and to move
the mixing container and the binder component relative to each
other within a speed and range of motion sufficient to create an
electrostatic force on the binder component and fibrillize the
binder component.
[0013] In some embodiments, the system can further include the
binder component and a mixing medium with a material having an
affinity to transfer negative charge from the mixing container to
the binder component. The mixing medium may include a same material
as the binder component. In some embodiments, the mixing medium and
the binder component both comprise polytetrafluoroethylene.
[0014] In some embodiments, the actuator is further configured to
apply a force upon the mixing container to contact the mixing
medium with at least one of the mixing container and the binder
component.
[0015] In some embodiments, the actuator is configured to apply an
acoustic force to the binder component. In some embodiments, the
actuator is configured to apply at least one of a linear force and
a rotational force upon the mixing container.
[0016] In some embodiments, the mixing container can be made of an
aluminum material. In some embodiments, the mixing medium may
include a same material as the mixing container, such as the
aluminum material.
[0017] In some embodiments, the system can further include a mixer
for combining the binder component with one or more other
components of the electrode film. The system may include a low
shear mixer for combining the binder component with one or more
other components of the electrode film mixture. In some
embodiments, the system can further include an oven for drying the
binder component and the one or more other components of the
electrode film.
[0018] Another embodiment includes a system which can have an
electric-field generator, a container, and a fibrillizable binder
component. The electric-field generator may be configured to apply
an electric field to the fibrillizable binder component and
fibrillize the fibrillizable binder component with the electric
field when the fibrillizable binder component is contained within
the container.
[0019] For purposes of summarizing the invention and the advantages
achieved over the prior art, certain objects and advantages are
described herein. Of course, it is to be understood that not
necessarily all such objects or advantages need to be achieved in
accordance with any particular embodiment. Thus, for example, those
skilled in the art will recognize that the invention may be
embodied or carried out in a manner that can achieve or optimize
one advantage or a group of advantages without necessarily
achieving other objects or advantages.
[0020] All of these embodiments are intended to be within the scope
of the invention herein disclosed. These and other embodiments will
become readily apparent to those skilled in the art from the
following detailed description having reference to the attached
figures, the invention not being limited to any particular
disclosed embodiment(s).
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other features, aspects, and advantages of the
present disclosure are described with reference to the drawings of
certain embodiments, which are intended to illustrate certain
embodiments and not to limit the invention.
[0022] FIG. 1 shows a cross-sectional view an example of an energy
storage device including an electrode film on a surface of a
current collector.
[0023] FIG. 2 shows a schematic view of an example of an apparatus
for fibrillizing a binder component of an electrode film under an
electric field.
[0024] FIG. 3 shows a perspective view of another example of an
apparatus for fibrillizing a binder component of an electrode film
under an electric field.
[0025] FIG. 4 shows an example of a process for fibrillizing a
binder component of an electrode film.
[0026] FIG. 5 shows an example of a process for fabricating an
electrode film including a fibrillized binder component.
[0027] FIG. 6A shows a scanning electron microscope (SEM) image, at
5 k.times. magnification, of an electrode film.
[0028] FIG. 6B shows a scanning electron microscope (SEM) image, at
1 k.times. magnification, of the electrode film shown in FIG.
6A.
[0029] FIG. 7A shows a scanning electron microscope (SEM) image, at
5 k.times. magnification, of an electrode film.
[0030] FIG. 7B shows a scanning electron microscope (SEM) image, at
1 k.times. magnification, of the electrode film shown in FIG.
7A
[0031] FIG. 8A shows a scanning electron microscope (SEM) image, at
5 k.times. magnification, of an electrode film.
[0032] FIG. 8B shows a scanning electron microscope (SEM) image, at
1 k.times. magnification, of the electrode film shown in FIG.
8A.
[0033] FIG. 9A shows a scanning electron microscope (SEM) image, at
5 k.times. magnification, of an electrode film.
[0034] FIG. 9B shows a scanning electron microscope (SEM) image, at
1 k.times. magnification, of the electrode film shown in FIG.
9A.
DETAILED DESCRIPTION
[0035] Although certain embodiments and examples are described
below, those of skill in the art will appreciate that the invention
extends beyond the specifically disclosed embodiments and/or uses
and obvious modifications and equivalents thereof. Thus, it is
intended that the scope of the invention herein disclosed should
not be limited by any particular embodiments described below.
[0036] As described herein, mechanical processes of binder
fibrillization can include application of high shear forces upon
the binder. However, mechanical fibrillization processes in which
high shear forces are applied can result in damage of an active
material component of the electrode film mixture. For example, one
or more surface properties of an active material component, such as
a carbon component of the electrode film mixture, may be
undesirably changed by the strong shear force, diminishing a
chemical and/or electrical property of the active material
component. Mixing of electrode film components in a blender under
high shear stress may also contribute to local heating of the
electrode film components in the blender. Such heating can further
contribute to diminished chemical and/or electrical properties of
one or more active material components of the electrode film,
and/or can provide inefficient and/or non-uniform fibrillization of
the binder component.
[0037] One embodiment includes a method of fabricating an electrode
film that includes fibrillization of a binder component using an
electric field. A negatively charged fibrillizable binder component
can be subjected to an electric field, such that the negatively
charged binder component is manipulated by the electric field to
achieve fibrillization of the binder component. In some
embodiments, a negative charge can be placed upon a binder
component to provide the negatively charged binder component. For
example, the binder component can be made from a material having an
affinity to receive one or more electrons (i.e., an electron
acceptor) from a material having an affinity to donate one or more
electrons to the binder component (i.e., an electron donor).
Suitable binder components may be made of a material having a high
dielectric constant, such as polyethylene (PE) and/or
polytetrafluoroethylene (PTFE). Suitable material for an electron
donor can include, for example, aluminum. In some embodiments, the
binder component can contact the electron donor to transfer
negative charge from the electron donor to the binder
component.
[0038] In some embodiments, the electric field can be an
electrostatic field. In some embodiments, an apparatus for
fibrillizing a binder component of an electrode film can be
configured to generate an electrostatic field. In some embodiments,
the fibrillization apparatus can be configured to place one or more
negative charges on the binder component such that the binder
component can be manipulated by the electrostatic field and the
binder component can be fibrillized. In some embodiments, the
fibrillization apparatus can include a mixing container for
providing a negative charge to the binder component. In some
embodiments, the fibrillization apparatus can include a mixing
medium to facilitate charge transfer between the mixing container
and the binder component. In some embodiments, the mixing medium
can provide a negative charge to the binder component. Contact
between the mixing medium, the mixing container, and/or the
electrode film binder component can facilitate transfer of
electrons from the mixing container and/or the mixing medium to the
electrode binder component, and/or generation of the electrostatic
field. Movement of the mixing container, mixing medium and/or the
electrode film binder component relative to one another can
facilitate transfer of electrons and the generation of the
electrostatic field. Such contact and/or movement can be
facilitated by applying force to the mixing container, the mixing
medium, and/or the electrode film binder component, including the
electrode film mixture comprising the electrode film binder
component. For example, the apparatus for fibrillizing a binder
component can be configured to generate an electrostatic field and
to expose a binder component comprising polytetrafluoroethylene
(PTFE) to the electrostatic field such that fibrillization of the
PTFE binder component can be achieved.
[0039] In some embodiments, a fibrillization process using an
electric field can facilitate a process in which reduced shear
stress is applied upon one or more components of an electrode film.
Shear forces applied upon components of an electrode film may be
significantly diminished in an electrostatic field fibrillization
process. In some embodiments, an electrostatic field fibrillization
process can facilitate a process in which negligible shear stress
is applied to components of an electrode film. In some embodiments,
reducing shear stress can facilitate reduced damage to one or more
components of the electrode film, for example relative to a
conventional shear-based fibrillization process. For example,
electrochemical characteristics of an active material component
within the electrode mixture, such as activated carbon, can be
maintained when using an electrostatic field fibrillization
process, relative to those characteristics prior to fibrillization
of the binder component within the mixture. In some embodiments, an
electrostatic fibrillization process may facilitate effective
fibrillization while maintaining physical and/or electrochemical
integrity of active material components of the electrode film.
[0040] In some embodiments, energy storage devices, including
ultracapacitors, batteries, and/or lithium based energy storage
devices, such as for example, lithium ion capacitors, and/or
lithium ion batteries, can have electrode films made of a
fibrillizable binder component that is fibrillized using an
electrostatic fibrillization process. In some embodiments,
maintaining one or more electrochemical characteristics of an
active material component within the electrode mixture may be
particularly advantageous for energy storage devices having
electrical performances which are more sensitive to the integrity
of active material components. In some embodiments, maintaining one
or more electrochemical characteristics of an active material
component within the electrode mixture may be particularly
advantageous for batteries, including lithium ion batteries.
[0041] In some embodiments, fibrillization of binder components
using an electric field can be advantageously integrated into one
or more dry processes for fabricating electrode films. As used
herein, dry processes can refer to one or more processes of
electrode fabrication performed in the absence or substantially in
the absence of solvents, including processes in which only or
substantially only dry particles are used. In some embodiments,
fibrillization of binder components using electric field can be
integrated into a dry process for fabricating an electrode film to
provide a free standing dry particles film.
[0042] In some embodiments, using an electric field, such as an
electrostatic field, to fibrillize a binder component of an
electrode film can advantageously facilitate a more efficient
fibrillization process. For example, an electrostatic
fibrillization process can provide an increased number of fibrils
from a quantity of binder material, an increased uniformity in the
fibrils formed, and/or improved mechanical strength of fibrils
formed, relative to a conventional shear-based fibrillization
process.
[0043] In some embodiments, fibrillization using an electric field,
such as electrostatic fibrillization, can facilitate up to about a
5% reduction by weight of binder material used, including about a
2% reduction by weight of binder material used, relative to a
conventional shear-based fibrillization process. Reduced binder
content and/or improved electrochemical integrity of an active
material component may facilitate improved electrical performance
of the electrode film (e.g., improving device equivalent series
resistance, ESR, performance) relative to an electrode film formed
through a conventional shear-based fibrillization process. In some
embodiments, an ultracapacitor comprising electrode films
fabricated using an electric field, such as electrostatic
fibrillization, can demonstrate up to about 25% reduction in ESR as
compared to an ultracapacitor comprising electrode films fabricated
using a conventional shear-based fibrillization process. In some
embodiments, an energy storage device including one or more
electrode films made of a binder component fibrillized using an
electric field, such as an electrostatic fibrillization process can
have at least about a 10% to about 20% improvement in power and/or
energy performance relative to an energy storage device prepared
under similar conditions using a conventional shear-based
fibrillization process.
[0044] FIG. 1 shows an example of an energy storage device 100. The
energy storage device 100 can include an ultracapacitor, and/or a
battery. The energy storage device 100 can include a first
electrode 102, a second electrode 104, and a separator 106
positioned between the first electrode 102 and second electrode
104. The separator can be configured to electrically insulate two
electrodes adjacent to opposing sides of the separator, such as the
first electrode 102 and the second electrode 104, while permitting
ionic communication between the two adjacent electrodes. The
separator 106 can be made of a variety of porous electrically
insulating materials. In some embodiments, the separator 106 can be
made of a polymeric material. For example, the separator 106 can be
made of a cellulosic material (e.g., paper), and/or a polypropylene
material.
[0045] In some embodiments, the first electrode 102 and/or the
second electrode 104 can include a first current collector 108, and
a second current collector 110, respectively, for facilitating
electrical coupling between the corresponding electrode and an
external circuit. The first current collector 108 and/or the second
current collector 110 can be made of any combination of a number of
suitable electrically conductive materials. The first current
collector 108 and/or the second current collector 110 can have
various shapes and/or sizes suitable to facilitate transfer of
electrical charges between the corresponding electrode and an
external terminal, such as for example, a terminal of an external
electrical circuit. For example, a current collector can include a
metallic material, such as an aluminum, nickel, copper, and/or
silver material. For example, the first current collector 108
and/or the second current collector 110 can include an aluminum
foil having a rectangular or substantially rectangular shape.
[0046] Referring to FIG. 1, the first electrode 102 and the second
electrode 104 can include electrode films 112, 114, and 116, 118 on
a first surface and a second opposing surface of the electrode
current collectors 108, 110, respectively. The electrode films 112,
114, 116 and/or 118 can have a variety of suitable shapes, sizes,
and/or thicknesses. For example, an electrode film can have a
thickness of about 100 microns to about 250 microns.
[0047] In some embodiments, one or more of the electrode films 112,
114, 116 and 118 can be made from an electrode film mixture
comprising a plurality of dry particles. In some embodiments, one
or more of the electrode films 112, 114, 116 and 118 can be made
from an electrode film mixture comprising one or more carbon-based
electroactive components (i.e., "active carbon"), including for
example a porous carbon material, such as activated carbon (e.g.,
commercially available from Kuraray Chemical Co., LTD., of Osaka,
Japan). In some embodiments, an electrode film mixture can include
graphite, soft carbon, and/or hard carbon. In some embodiments, an
electrode film mixture can include one or more additives, including
for example one or more additives for improving electrical
conductivity of the electrode film (i.e., "conductive carbon"). For
example, an electrode film mixture can include a conductive carbon
component, such as conductive carbon black (e.g., Super P (ID
commercially available from Timcal Graphite & Carbon, of Bodio,
Switzerland).
[0048] The electrode film mixture can include one or more additives
for enhancing the structural integrity of the electrode film, such
as a binder component. In some embodiments, the binder components
can include one or more of a variety of polymers having an
increased dielectric constant. In some embodiments, polyethylene
(PE) can be suitable, including ultra-high-molecular-weight
polyethylene (UHMWPE). In some embodiments, polytetrafluoroethylene
(PTFE) is suitable. Polymers able to receive one or more electrons
from an electron donor may be a suitable binder. The binder
components can be fibrillizable binder. For example, one or more
electrode films 112, 114, 116, 118 may include a fibrillized binder
component made of a fibrillizable binder component which was
fibrillized using an electric field, such as an electrostatic
fibrillization process. As used herein, a fibrillized binder
component can be structurally distinguished from a fibrillizable
binder component by a person having ordinary skill in the art using
available scientific apparatus and methods, such as through
observation of the size and/or number of fibrils.
[0049] Composition of the electrode films 112, 114, 116, and/or 118
may be selected to enable a desired electrode capacitance and/or
resistance performance. In some embodiments, one or more of the
electrode films 112, 114, 116, and 118 can be made of about 50% to
about 99% by weight (e.g., including about 85% to about 90% by
weight) of activated carbon, up to about 20% by weight (e.g.,
including about 0.5% to about 15% by weight, including about 5% to
about 10% by weight) of binder material, and up to about 25% (e.g.,
including about 1% to about 10%) by weight of electrical
conductivity promoting material.
[0050] In one embodiment, an electrode film mixture can include
about 70 grams to about 100 grams (e.g., about 90 grams) of
activated carbon, up to about 5 grams of a conductive carbon
additive component (e.g., about 2 grams of a conductive carbon
black material). The electrode film mixture can include
polytetrafluoroethylene (PTFE) as binder component. For example,
the electrode film mixture can include about 5 weight % to about 10
weight % of the binder component.
[0051] In some embodiments, one or more of the electrodes 102, 104
may be fabricated using a dry electrode processing method. In dry
processing, for example, an electrode film mixture comprising
components of the electrode film (e.g., electroactive material,
electrical conductivity promoting material and/or binder material)
may be blended to form a mixture. In some embodiments, the blended
mixture is compressed to form a film-like structure, such as the
electrode films 112, 114, 116 and 118. In some embodiments, the
electrode films 112, 114, 116, 118, can be calendared onto the
corresponding current collector surface.
[0052] Forming one or more of the electrode films 112, 114, 116,
and 118, can also typically include fibrillization of the binder
component. For example, fibrillization of the binder component can
form fibrils, for example, a web of fibrils, which can provide a
matrix-like structure for supporting one or more other components
of the electrode film, such as activated carbon and/or conductive
carbon black.
[0053] In some embodiments, an electric field can be used to
facilitate fibrillization of an electrode film binder component. As
described herein, a suitable binder component can include one or
more polymers having an affinity to receive one or more electrons
from an electron donor. For example, a suitable polymer for the
binder component can have an increased dielectric constant, or a
polymer able to readily accept one or more electrons from an
electron donor. The electric field can be used to apply a force
upon the binder component carrying one or more negative charges
(e.g., a binder component which has received one or more electrons
from an electron donor), so as to facilitate fibrillization of the
binder component.
[0054] As described further herein, the electrical, chemical,
and/or mechanical properties of the active carbon and/or conductive
carbon may be undesirably altered when subjected to a conventional
high shear process, such as jet milling or blending, relative to
the properties of these materials when subjected to the electric
field processes described herein. For example, when the active
carbon and/or conductive carbon are mixed with a fibrillizable
binder, and subjected to a high shear fibrillization process to
fibrillize the binder, the active carbon and/or conductive carbon
may be undesirable altered, resulting in reduced performance of the
electrode film formed from these components. Such reduction in
performance is reduced or eliminated when the same electrode
components are combined, but the binder is fibrillized instead
through an electric field, such as through an electrostatic
fibrillization process. Additionally, the fibrillizable binder may
be more efficiently fibrillized in an electric field, relative to a
conventional high-shear process, resulting in a more efficient
electrode with reduced binder usage.
[0055] FIG. 2 is a schematic view of an example of an apparatus,
such as an electric-field generator 150 configured to apply an
electric field, such as an electrostatic field or other electric
field, to a plurality of charged particles, such as fibrillizable
binder particles 158. The apparatus 150 may include a first charged
portion 152 and a second oppositely charged portion 154. For
example, the first charged portion 152 may have a positive charge
and the second charged portion 154 may have a negative charge. As
indicated by the arrow 156, an electric field extending from the
positively charged portion 152 to the negatively charged portion
154 can be provided, such as between the two charged portions, 152,
154. The electric field provided by the positively charged portion
152 and the negatively charged portion 154 may exert an electric
force, such as an electrostatic force, upon charged particles 158
exposed to the electric field. The chemical, electrical, and/or
mechanical properties of the charged particles 158 may change when
exposed to the electric field. For example, the charged particles
158 may be fibrillized by the force exerted upon the particles 158
by the electric field provided between the first charged portion
152 and the second oppositely charged portion 154.
[0056] In some embodiments, the charged binder particles 158 may
have a negative charge. As described herein, the binder particles
158 may acquire a negative charge by accepting one or more
electrons from an electron donor. For example, the electric field
generated by the charged portions 152, 154 of apparatus 150 can
exert a force upon the negatively charged binder particles to
fibrillize the binder particles. In some embodiments, as will be
described in further details herein, a mixing container may
comprise the first charged portion 152, and a mixing medium may
comprise the second charged portion 154. For example, the mixing
container may donate one or more electrons to the mixing medium,
the mixing container thereby acquiring a positive charge, and the
mixing medium acquiring a negative charge. An electric field, such
as an electrostatic field, may be generated by the positively
charged mixing container and the negatively charged mixing medium.
Without being limited by any particular theory or mode of
operation, force exerted upon one or more negatively charged binder
particles by the generated electric field may change the properties
thereof, for example, and thereby fibrillize, the binder particles.
In some embodiments, negatively charged binder particles within the
mixing container may contribute to the electric field that exerts
force upon charged binder particles to fibrillize the binder
particles.
[0057] FIG. 3 shows an example of a fibrillization apparatus 200
for fibrillizing an electrode film binder component. The
fibrillization apparatus 200 may include a mixing container 202
with an inner volume configured to receive an electrode film
mixture 206, including a binder component. In some embodiments, the
apparatus 200 can include a mixing medium 204, to facilitate mixing
of the electrode film mixture 206, and fibrillization of the binder
component within mixture 206. For example, the mixing medium 204
and the electrode film mixture 206 may be mixed while received in
the inner volume to achieve fibrillization of the binder component
within the mixture 206.
[0058] The inner volume of the mixing container 202 can have
various suitable shapes and/or sizes suitable to contain the mixing
medium 204 and/or the electrode film mixture 206. In some
embodiments, the inner volume of the mixing container 202 can have
a cylindrical or substantially cylindrical shape. In some
embodiments, the inner volume of the mixing container 202 can have
a spherical or substantially spherical shape. In some embodiments,
the inner volume of the mixing container 202 may comprise a shape
configured to facilitate increased surface area contact for
contacting one or more components within the mixing container 202,
and/or facilitate contact between these components and the
container 202 itself. For example, the inner volume of the mixing
container 202 may comprise a shape configured to provide desired
surface area for contact between the mixing medium 204 and/or the
electrode film mixture 206 and the mixing container 202, and/or
between the mixing medium 204 and the electrode film mixture
206.
[0059] The size of the inner volume of the mixing container 202 can
be selected based on various factors, including for example, a
quantity of an electrode film mixture for processing in the mixing
container 202, a material of the mixing medium 204, and/or a
composition of the electrode film binder component. In some
embodiments, a size of the inner volume of the mixing container 202
may be selected to provide sufficient space within which the
electrode film mixture 206 and/or mixing medium 204 can move
relative to the mixing container 202 and/or one another, when an
amount of the electrode film mixture 206 and/or mixing medium 204
are contained within container 202 for processing. For example, the
inner volume of the mixing container 202 may include an amount of
unoccupied dead space, when containing and mixing the electrode
film mixture 206, and fibrillizing the binder component. For
example, the mixing container 202 can have an inner volume of
sufficient size, relative to the volume of the electrode film
mixture 206 and mixing medium 204, to facilitate sufficient
movement of the electrode film mixture 206 and/or mixing medium 204
to provide desired contact between the mixing container 202 and the
mixing medium 204, between the electrode film mixture 206 and the
mixing medium 204, and/or between the electrode film mixture 206
and the mixing container 202. Providing an inner volume within
container 202 with sufficient dead space, relative to the
components contained within container 202, such as the electrode
film mixture 206 and mixing medium 204, during processing, can
facilitate fibrillization of the electrode film binder component.
In some embodiments, the mixing container 202 has a volume
sufficient to facilitate generation of electrostatic field, so as
to provide fibrillization of the electrode film binder component.
In some embodiments, the inner volume of the mixing container 202
may have about 5% to about 45% dead space, including about 5% to
about 35% dead space, with the remainder of the inner volume
containing the electrode film mixture 206, or the mixing medium 204
and the electrode film mixture 206. In some embodiments, the inner
volume of the mixing container 202 may have about 5% to about 20%
dead space, including about 5% to about 10% dead space, with the
remainder of the inner volume containing the electrode film mixture
206, or the mixing medium 204 and the electrode film mixture
206.
[0060] A mixing container 202 comprising too large of a dead space
may reduce efficiency in generating the electrostatic field within
the container 202, reducing or preventing fibrillization of the
binder component of the electrode film mixture 206. A mixing
container 202 having too small of a dead space may reduce or
prevent desired movement of the mixing medium 204 and/or electrode
film mixture 206 within the container 202, reducing or preventing
fibrillization of the binder component of the electrode film
mixture 206.
[0061] The mixing container 202 can be made of a material having an
increased affinity to donate electrons, including natural and/or
synthetic materials. For example, the mixing container 202 may
comprise a material with an affinity to donate electrons to the
mixing medium 204 and/or a binder component of the electrode film
mixtures 206. In some embodiments, the mixing container 202 can be
made of a material comprising a metal. In some embodiments, the
mixing container 202 can be made of aluminum, lead, and/or alloys
thereof. In some embodiments, the mixing container 202 can be made
of a material comprising leather, fur, glass, polyamides (e.g.,
nylon), silk, cellulose (e.g., paper), and/or combinations thereof.
In some embodiments, at least a portion of the mixing container 202
can be coated with one or more materials having an affinity to
donate electrons. For example, one or more surfaces of the mixing
container 202 can be coated with aluminum. In some embodiments, all
or substantially all of the surfaces of a mixing container 202
configured to be in contact with the mixing medium 204 and/or the
electrode film mixture 206, such as all or substantially all
interior surfaces of the mixing container 202, are coated with
aluminum. In some embodiments, one or more surfaces of the mixing
container 202 can be coated with lead, including one or more
surfaces configured to be in contact with the mixing medium 204
and/or the electrode film mixture 206.
[0062] Material for the mixing medium 204 can be selected based on
various factors, including for example, a material of the electrode
film binder component, and/or a material of the mixing container
202. In some embodiments, the mixing medium 204 can be made of a
material having a desired tendency to accept one or more electrons
from the mixing container 202. For example, the mixing medium 204
can be an electron acceptor with respect to the mixing container
202, which can be the electron donor. In some embodiments, the
mixing medium 204 can have a sufficient affinity to donate one or
more electrons to the electrode film binder component. In this way,
the mixing medium 204 can be the electron donor with respect to the
electrode film binder component. In some embodiments, the mixing
medium 204 can be made of material having a sufficient tendency to
accept one or more electrons from the mixing container 202, while
having a sufficient tendency to donate one or more electrons to the
electrode film binder component. For example, the mixing medium 204
can be configured to transfer one or more electrons from the mixing
container 202 to the electrode film binder component. In some
embodiments, the mixing medium 204 may be made of material having
the same or similar, or lower affinity, for donating a negative
charge as the mixing container 202 such that the mixing container
202 can transfer negative charge to the mixing medium 204 with
contact between the mixing container 202 and the mixing medium 204.
In some embodiments, the mixing medium 204 may comprise a material
having the same or similar, or lower affinity for accepting a
negative charge as the binder component such that charge transfer
from the mixing medium 204 to the binder component may readily
occur with contact between the two.
[0063] In some embodiments, the mixing medium 204 can be made of a
natural and/or synthetic material, including for example, wood,
amber, rubber, silicon, and/or combinations thereof. In some
embodiments, the mixing medium 204 can be made of a metallic
material, including aluminum, nickel, copper, brass, silver, gold,
platinum, and/or combinations thereof. In some embodiments, the
mixing medium 204 can be made of a polymeric material, such as
polyester, polyurethane (PU), polyethylene (PE), polypropylene
(PP), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE,
e.g., Teflon.RTM.) and/or combinations thereof. In some
embodiments, the mixing medium 204 can be selected based on an ease
in maintaining desired chemical and/or physical integrity of the
mixing medium 204. For example, the mixing medium 204 can be
selected based on an ease of cleaning and/or restoring one or more
properties of the mixing medium after its use. In some embodiments,
the mixing medium 204 can be made of aluminum to provide transfer
of a negative charge from the mixing container 202 to the binder
component of the electrode film mixture 206. For example, the
mixing medium 204 may comprise a plurality of units made of
aluminum.
[0064] The binder component comprises a fibrillizable binder, or
may consist essentially of, or consist of a fibrillizable binder.
For example, in some embodiments, the binder component comprises
polytetrafluoroethylene (PTFE). In some embodiments, the mixing
medium 204 comprises a material having a desired tendency to donate
electrons to polytetrafluoroethylene. In some embodiments, the
mixing medium 204 may comprise a material having a similar or same
tendency to accept a negative charge as polytetrafluoroethylene.
For example, the mixing medium 204 may comprise
polytetrafluoroethylene. In some embodiments, the mixing medium 204
may comprise a material having a lower tendency to accept negative
charge as polytetrafluoroethylene. In some embodiments, the binder
component comprises polyethylene (PE), including
ultra-high-molecular-weight polyethylene (UHMWPE). In some
embodiments, the mixing medium 204 comprises a material having a
tendency to donate electrons to polyethylene and/or
ultra-high-molecular-weight polyethylene. For example, the mixing
medium 204 may comprise a material having about the same or lower
tendency to accept a negative charge as polyethylene.
[0065] The mixing medium 204 can include a plurality of units
having various suitable sizes and/or shapes suitable to facilitate
the electrostatic fibrillization described herein. In some
embodiments, one or more units of the mixing medium 204 may
comprise a shape configured to provide a desired surface area for
contacting the mixing container 202 and/or the electrode film
mixture 206. In some embodiments, each unit of the mixing medium
204 can have a spherical or substantially spherical shape. For
example, the mixing medium 204 can comprise a plurality of metallic
units and/or polymeric units. In some embodiments, the mixing
medium 204 can include a plurality of polytetrafluoroethylene
(e.g., Teflon.RTM.) units having a spherical or substantially
spherical shape. The units within the mixing medium can comprise
various other three-dimensional shapes, such as rods, pins, cubes,
pyramids, etc., and are not limited to spherical shapes.
[0066] A size of one or more units of the mixing medium 204 can be
selected based on a number of factors. For example, the size of a
unit of the mixing medium 204 can be selected based on a balance of
providing increased surface area for contact with the mixing
container 202 and/or the electrode film binder component, and/or
for carrying negative charge received from the mixing container
202, while providing units of sufficient size to facilitate
fibrillization of the binder component. For example, the units of
the mixing medium can be sized with sufficient mass to facilitate
mixing of the electrode film mixture. In some embodiments, the
mixing medium 204 can comprise a plurality of spherical or
substantially spherical units having a diameter of about 1
millimeter (mm) to about 40 mm, including about 5 mm to about 15
mm. For example, each spherical or substantially spherical unit can
have a diameter of about 12 mm. It will be understood that these
dimensions can be similarly applied to non-spherical embodiments.
For example, the mixing medium 204 can include units with
non-spherical three-dimensional shapes that have one or more
dimensions (e.g., length, width, height, diameter) corresponding
with the aforementioned diameters. For example, a cylindrical rod
with similar diameters can be employed.
[0067] The amount of mixing medium 204 to include in the
fibrillization apparatus 200, relative to other components, can be
selected based upon various factors. For example, the amount of
mixing medium 204 used can be based upon the composition of the
mixing medium 204 itself. The amount of mixing medium 204 used can
be based upon an amount and/or a type of the electrode film mixture
processed by the fibrillization apparatus 200. For example, the
amount of mixing medium 204 can be selected to facilitate increased
contact between the electrode film binder component, the mixing
medium, and/or between the mixing container 202. The amount of
mixing medium 204 can be selected to facilitate transfer of charge
to the binder component, and/or generation of an electrostatic
field. The amount of mixing medium 204 can be selected based upon
one or more of the above factors, while also reducing the amount of
mixing medium 204 used. A reduced amount of mixing medium 204 can
increase the amount of electrode film mixture 206 that can be
processed within the mixing container 202. In some embodiments, the
mixing medium 204 can be about 2 times to about 10 times the weight
of the electrode film mixture 206, including about 3 times to about
8 times the weight of the electrode film mixture 206. For example,
the mixing medium 204 may be about 8 times the weight of the
electrode film mixture 206. In one embodiment, the mixing medium
204 can have a weight of about 8 times that of the electrode film
mixture 206 processed, including an electrode film mixture
comprising a polytetrafluoroethylene binder component. Such ratios
based upon weight between the mixing medium and the electrode film
mixture can provide improved surface contact and electron donation
between the components, while increasing the amount of electrode
film mixture that is being processed.
[0068] As described above, contact between the mixing medium, the
mixing container, and/or the electrode film binder component can
facilitate transfer of electrons from the mixing container and/or
the mixing medium to the electrode binder component. Such contact
between these components can facilitate generation of the
electrostatic field for manipulating the negatively charged
fibrillizable electrode film binder component. This electron
transfer and electrostatic field generation can be provided by
moving the mixing container, mixing medium and/or the electrode
film binder component relative to one another, such as by applying
a force upon the mixing container, mixing medium and/or the
electrode film binder component.
[0069] The mixing container 202 can be moved in a variety of
manners. For example, the mixing container can be moved manually or
automatically. The fibrillization apparatus 200 can include one or
more devices, such as an actuator 201, shown schematically in FIG.
3, for applying a linear, and/or rotational force upon the mixing
container 202. Such force(s) can translate to movement of container
202 in one or more directions. The actuator 201 can include one or
more motors, linear actuators, slides, bearings, or any of a number
of suitable devices capable of providing relative motion between
container 202 and another supporting component, such as a base 203.
In some embodiments, the mixing container 202 can be moved in a
lateral direction (e.g., horizontally, as shown by the horizontal
arrow 208, or into a horizontal plane of the view shown in FIG. 3).
The mixing container 202 can be moved in a vertical direction
(e.g., vertically, as shown by vertical arrow 210 in FIG. 3). The
mixing container 202 can be moved in an angled direction (e.g., in
a direction at an angle theta (0) greater than zero, and other than
at a right angle relative to a horizontal plane, such as ground,
for example as shown by angled arrow 212 in FIG. 3). In some
embodiments, the mixing container 202 can be rotated in a clockwise
direction (arrows 214), or in a counter-clockwise direction (arrows
216). The container can be configured to move in any of a number of
different lengths (arcs) and patterns, and can be moved through
vibration, oscillation, sonication, or through other methods, in
one or more of any of the aforementioned directions. In some
embodiments, a magnitude of the force to the mixing container
and/or a rate of repetition of the applied force can be selected to
facilitate efficient fibrillization of the electrode film binder
component of the electrode film mixture 206. For example, the
magnitude of the force applied and/or the rate of repetition of the
applied force can be selected based on a weight and/or a material
of the mixing container, mixing medium, electrode film mixture,
and/or electrode film binder component. Examples of suitable
actuators 201 can include a paint shaker, an acoustic mixer, and/or
the like. In some embodiments, the actuator 201 can include a
resonant acoustic mixer.
[0070] In some embodiments, force can be applied to the mixing
medium and/or electrode film mixture to displace and move two or
more of the mixing medium, electrode film mixture (including its
binder component) and mixing container relative to each other. For
example, an actuator can use sonication to agitate the mixing
medium and/or the electrode film mixture. A frequency of the
sonication process can be selected based on a number of parameters,
including for example, a weight and/or a material of the mixing
container, mixing medium, electrode film mixture, and/or electrode
film binder component.
[0071] In some embodiments, the fibrillization apparatus 200 can
include one or more components configured to prevent or
substantially prevent electrical discharge by the mixing container
202, for example electrical discharge to an electrical ground. In
some embodiments, the mixing container 202 can include an outer
cover which is electrically insulating or substantially
electrically insulating. For example, the outer cover can enclose
or substantially enclose the mixing container 202 so as to prevent
discharge of electrical charge to ground by the mixing container
202. In some embodiments, the mixing container 202 can be
positioned on an apparatus, such as a stand made of an electrically
insulating or substantially electrically insulating material to
prevent or substantially prevent electrical discharge by the mixing
container 202. The mixing container cover and/or the apparatus upon
which the mixing container is positioned may be made of an
electrically insulating material, and/or can be coated with an
electrically insulating material.
[0072] FIG. 4 shows an example of a process 300 for fibrillizing an
electrode film binder component using an electrostatic field, such
as an electrode film suitable for use in an ultracapacitor and/or a
battery. In block 302, a mixing medium, such as mixing medium 204
as described with reference to FIG. 3, can be combined with
components of the electrode film in a mixing container, such as
mixing container 202 as described with reference to FIG. 3. The
components of the electrode film can include a fibrillizable
binder, which, when mixed with other electrode film components,
such as activated and/or conductive carbon, form an electrode film
mixture. In block 304, a force can be applied to the mixing
container, the mixing medium, and/or the electrode film components.
This force facilitates movement of the mixing container, mixing
medium, and/or the electrode film binder component relative to one
another, and/or facilitates contact between the electrode film
binder component, mixing medium and/or the mixing container. Such
movement and/or contact can result in fibrillization of the binder
component. For example, a force can be applied to the mixing
container, such as by shaking the mixing container along one or
more directions (e.g., horizontal, vertical, and/or at an angle
other than horizontal or vertical), and/or by rotating the mixing
container. For example, a force can be applied to the mixing
components and/or mixing medium (e.g., an acoustic force).
[0073] FIG. 5 shows an example of a process 400 for fabricating an
electrode film of an energy storage device. In block 402,
components for an electrode film can be combined. For example,
components of the electrode film including the electrode film
binder component, and other components, such as an activated carbon
component, and/or a conductive carbon black component, can be
combined. These components can be mixed, either during or after
they are being combined, to form a homogenous or substantially
homogenous electrode film mixture. In some embodiments, components
of the electrode film mixture may be subjected to a
universalization process. For example, the universalization process
may uniformly or substantially uniformly mix the components of the
electrode film mixture, such as creating a homogeneous or
substantially homogeneous mixture. Mixing and/or universalization
of the components of the electrode film can be performed in a
variety of suitable lower-shear mixing apparatuses, including for
example a roll mixer and/or an acoustic mixer. In some embodiments,
a lower-shear mixer may comprise a resonant acoustic mixer.
[0074] The mixing process can be performed for a period of time to
achieve desired level of mixing of the electrode film components.
In some embodiments, an electrode film mixture can be mixed in a
roll mixer for about 12 hours to about 20 hours to achieve a
desired level of mixing. In block 404, the electrode film mixture
can undergo a drying process. Drying of the electrode film mixture
can be performed in an oven, such as a vacuum oven. The drying
process can aid removal of moisture from one or more components of
the electrode film to facilitate a more efficient fibrillization
process. For example, removal of residual moisture from the
electrode film mixture can facilitate transfer of negative charge
from the mixing container and/or the mixing medium to the electrode
film binder component, and/or the generation of an electrostatic
field for manipulating negatively charged electrode film binder
components. A temperature and/or duration of the drying process can
be selected, for example, based on a quantity of the mixture being
dried, and/or a degree of dryness desired (e.g., the amount of
moisture removal desired). In some embodiments, the drying process
can be performed at a temperature of about 70.degree. C. to about
100.degree. C., including about 80.degree. C. to about 90.degree.
C. The drying process can be performed for a period of about 5
minutes to about 20 hours, including for example from about 5 hours
to about 15 hours. For example, the drying process can be performed
at a temperature of about 85.degree. C. for about 12 hours. In some
embodiments, components of the electrode film may not undergo a
drying process.
[0075] In block 406, the electrode film mixture (e.g., mixture
including components that underwent a drying process) can be
combined in a mixing container of a fibrillization apparatus (e.g.,
fibrillization apparatus 200 of FIG. 3) with a mixing medium. In
block 408, a force can be applied to the mixing container, the
mixing medium, and/or the electrode film mixture such that the
mixing container, mixing medium, and/or the electrode film mixture
can move relative to one another, and/or to facilitate contact
between the electrode film binder component, mixing medium and/or
the mixing container. The force applied in block 408 can be
selected to facilitate increased contact between the mixing
container, the mixing medium, and/or the electrode film mixture,
including the binder component. Without being limited by theory or
any particular mode of operation, increased contact between the
mixing container, the mixing medium, and/or the electrode film
binder component, may facilitate increased transfer of electrons
from the mixing container and/or mixing medium to the binder
component, and/or improve generation of a desired electrostatic
field for facilitating fibrillization of the binder component. For
example, increased contact between the mixing container, the mixing
medium, and/or the electrode film binder component, may facilitate
generation of a more uniform electrostatic field, facilitating
improved efficiency and/or uniformity in the binder fibrillization
process. In some embodiments, the mixing container can be shaken by
applying a linear or substantially linear force to move the mixing
container back and forth along one or more direction (e.g., a
horizontal, vertical, and/or angled direction), and/or along an
arced path around an axis (e.g., a horizontal, vertical, and/or
angled axis). In some embodiments, a rotational force can be
applied to the mixing container. In some embodiments, a force can
be applied to the mixing medium and/or the electrode film mixture,
including for example an acoustic force (e.g., a sonication
process).
[0076] In block 410, the electrode film mixture can be calendared
to form an electrode film (e.g., one or more of electrode films
112, 114, 116, 118 of FIG. 1). For example, the film mixture can be
calendared to form a free-standing film. In some embodiments, the
electrode film can be formed over one or more surfaces of an energy
storage device current collector (e.g., one or more of current
collectors 108, 110 of FIG. 1). In some embodiments, the electrode
film can be calendared directly onto a surface of a current
collector. In some embodiments, an adhesive material can be used to
facilitate adhesion of the electrode film to the surface of the
current collector.
[0077] Electrical performance of a first ultracapacitor, for
example in a coin cell configuration, fabricated using electrode
films which underwent shear-based fibrillization was compared to
the electrical performance of a second ultracapacitor comprising
electrode films fabricated using an electric field fibrillization
process. The electrodes of the two ultracapacitors included a
binder component comprising polytetrafluoroethylene, activated
carbon, and an electrically conductive carbon black component.
Fabrication of the two ultracapacitors included calendaring the
fibrillized electrode film mixtures onto respective current
collectors. The electrodes of the two ultracapacitors were
fabricated using dry particles electrode film mixtures. The two
electrodes of the two ultracapacitors were fabricated using
mixtures comprising a fibrillizable binder component at about 8
weight % to about 10 weight %, a carbon black component at about
0.5 weight % to about 2 weight %, and an activated carbon component
at about 88 weight % to about 92 weight %.
[0078] The coin cell ultracapacitor comprising electrodes which
underwent shear-based fibrillization demonstrated an equivalent
series resistance (ESR) of about 1.22 Ohms (.OMEGA.) and a
capacitance of about 0.606 Farads (F). The coin cell ultracapacitor
comprising electrodes which underwent electrostatic field
fibrillization demonstrated an ESR of about 0.91.OMEGA. and a
capacitance of about 0.588 F. As shown by the comparison, the coin
cell ultracapacitor comprising the electrodes fabricated using
electrostatic field fibrillization demonstrated an ESR about 25%
lower than that of the ultracapacitor comprising electrodes
fabricated using shear-based fibrillization, while maintaining
comparable capacitance performance as that of the ultracapacitor
comprising electrodes fabricated using shear-based
fibrillization.
[0079] FIGS. 6A-9B show scanning electron microscope (SEM) images
of cross-section views of various electrode films made from various
respective dry particles electrode film mixtures.
[0080] FIGS. 6A and 6B show two scanning electron microscope (SEM)
images of cross-section views of an electrode film 500. FIG. 6A
shows a cross-section view of the electrode film 500 at 5 k.times.
magnification and FIG. 6B shows a cross-section view of the
electrode film 500 at 1 k.times. magnification. The electrode film
500 shown in FIGS. 6A and 6B was fabricated without or
substantially without a process in which the electrode film mixture
underwent repeated contact with a mixing medium and/or a mixing
container of a fibrillization apparatus (e.g., the fibrillization
apparatus 200 as described with reference to FIG. 3). The electrode
film 500 was formed using an electrode film mixture having
components which were combined in a mixing apparatus (e.g., mixed
in a roll mixer, for a period of at least about 12 hours) such that
the components of the electrode film 500 were uniformly or
substantially uniformly mixed, and where the electrode film mixture
was dried in a vacuum oven (e.g., at about 85.degree. C., for a
period of about 12 hours) to facilitate removal of any residual
moisture. The electrode film 500 included an activated carbon
component, a conductive carbon black component and a binder
component comprising polytetrafluoroethylene (PTFE). The dried
electrode film mixture was subsequently calendared to form the
electrode film 500, without or substantially without a process in
which the electrode film mixture was shaken and/or otherwise
agitated within a fibrillization apparatus to provide repeated
contact between the electrode film binder component and the
fibrillization apparatus. FIGS. 6A and 6B show that minimal, and/or
no or substantially no fibrils were formed in the electrode film.
At higher magnification, FIG. 6A shows a clearer view of PTFE
particles 502 dispersed amongst the activated carbon component 504
of the electrode film 500. As can be seen in FIG. 6A, the electrode
film 500 included no or substantially no PTFE fibrils.
[0081] FIGS. 7A and 7B show two scanning electron microscope (SEM)
images of cross-section views of an electrode film 600. FIG. 7A
shows a cross-section view of the electrode film 600 at 5 k.times.
magnification and FIG. 7B shows a cross-section view of the
electrode film 600 at 1 k.times. magnification. Components of the
electrode film 600 were combined in a mixing apparatus (e.g., a
roll mixer, for a duration of at least about 12 hours). The
electrode film 600 included the same or substantially the same
composition as the electrode film 500 (e.g., including an activated
carbon component, a conductive carbon black component and a binder
component comprising polytetrafluoroethylene (PTFE)). The electrode
film mixture was dried in a vacuum oven (e.g., at about 85.degree.
C., for a period of about 12 hours) to facilitate removal of any
residual moisture. The dried electrode film mixture of electrode
film 600 was combined in a mixing container of a fibrillization
apparatus (e.g., fibrillization apparatus 200 of FIG. 3) with a
mixing medium comprising PTFE beads (e.g., PTFE beads having a
diameter of about 13 millimeters), where the mixing container is
made of a material comprising polystyrene. The electrode film
mixture and the mixing medium were shaken in a mixing container of
the fibrillization apparatus for a period of about 15 minutes, and
the shaken mixture was then calendared to form the electrode film
600. For example, the mixing container can be moved vertically
(e.g., up-and-down), horizontally (e.g., left-and-right) and/or
rotationally to facilitate fibrillization. FIGS. 7A and 7B show
that electrode film 600 includes minimal, and/or no or
substantially no fibrils. For example, FIG. 7A shows PTFE particles
602 dispersed amongst activated carbon component 604. Without being
limited by any particular theory or any particular mode of
operation, a mixing container made of a polystyrene material may
have insufficient affinity to donate negative charge. For example,
the polystyrene mixing container may have insufficient affinity to
donate negative charge to the mixing medium and/or binder component
comprising PTFE, thereby preventing or substantially preventing
generation of an electrostatic field in which binder components
carrying negative charges may be manipulated to form fibrils.
[0082] FIGS. 8A and 8B show two scanning electron microscope (SEM)
images of cross-section views of an electrode film 700. FIG. 8A
shows a cross-section view of the electrode film 700 at 5 k.times.
magnification and FIG. 8B shows a cross-section view of the
electrode 700 film at 1 k.times. magnification. Electrode film 700
had the same or substantially the same composition as electrode
films 500, 600 of FIGS. 6A/6B and 7A/7B, respectively. For example,
electrode film 700 included an activated carbon component, a
conductive carbon black component and a binder component comprising
polytetrafluoroethylene (PTFE). The electrode film 700 was
fabricated using a process similar to that used to fabricate
electrode film 600, except that a mixing container made of an
aluminum material was used in the fibrillization apparatus.
Components of the electrode film 700 were combined in a roll mixer,
for a duration of at least about 12 hours, and subsequently dried
in a vacuum oven at about 85.degree. C., for a period of about 12
hours to facilitate removal of any residual moisture. The dried
electrode film mixture of electrode film 700 was combined in a
mixing container of a fibrillization apparatus similar to
fibrillization apparatus 200 of FIG. 3 with a mixing medium. The
mixing medium was made of substantially spherical PTFE units having
a diameter of about 13 millimeters. The mixing container was made
of a material comprising aluminum. The electrode film mixture and
the mixing medium were shaken in the mixing container of the
fibrillization apparatus for a period of about 15 minutes. The
shaken mixture was then calendared to form the electrode film 700.
Referring to FIGS. 8A and 8B, PTFE fibrils 702 can be clearly seen
on surfaces of the activated carbon component of the electrode film
700, demonstrating effective fibrillization of the binder
component. Without being limited by any particular theory or any
particular mode of operation, a mixing container made of an
aluminum material can have sufficient affinity to donate electrons
to the mixing medium comprising PTFE beads and/or the PTFE binder
component, facilitating placement of negative charges on the PTFE
binder component and/or generation of an electrostatic field, such
that the negatively charged PTFE binder component can be
manipulated by the electrostatic field, facilitating fibrillization
of the PTFE binder component.
[0083] FIGS. 9A and 9B show two scanning electron microscope (SEM)
images of cross-section views of an electrode film 800. FIG. 9A
shows a cross-section view of the electrode film 800 at 5 k.times.
magnification and FIG. 9B shows a cross-section view of the
electrode film 800 at 1 k.times. magnification. The electrode film
800 had a composition similar to that of electrode films 500, 600,
and 700 described herein with reference to one or more of FIGS.
6A-8B. Components of the electrode film 800 were mixed, and the
binder component was fibrillized using a high shear mechanical
fibrillization process (by blending the electrode film mixture in a
jet mill). The electrode film mixture comprising the mechanically
fibrillized binder component was then calendared to form the
electrode film 800. FIGS. 9A and 9B show PTFE fibrils 802 on
surfaces of the activated carbon component 804 of the electrode
film 800. Based on comparison of FIGS. 8A, 8B with FIGS. 9A, 9B, it
can be seen that fibrillization of a binder component using an
electrostatic field can provide results at least as comparable to
that achieved by a high sheer mechanical fibrillization process,
while achieving improved electrode performance, as described
further above.
[0084] Although this invention has been disclosed in the context of
certain embodiments and examples, it will be understood by those
skilled in the art that the invention extends beyond the
specifically disclosed embodiments to other alternative embodiments
and/or uses of the invention and obvious modifications and
equivalents thereof. In addition, while several variations of the
embodiments of the invention have been shown and described in
detail, other modifications, which are within the scope of this
invention, will be readily apparent to those of skill in the art
based upon this disclosure. It is also contemplated that various
combinations or sub-combinations of the specific features and
aspects of the embodiments may be made and still fall within the
scope of the invention. It should be understood that various
features and aspects of the disclosed embodiments can be combined
with, or substituted for, one another in order to form varying
modes of the embodiments of the disclosed invention. Thus, it is
intended that the scope of the invention herein disclosed should
not be limited by the particular embodiments described above.
[0085] The headings provided herein, if any, are for convenience
only and do not necessarily affect the scope or meaning of the
devices and methods disclosed herein.
* * * * *