U.S. patent application number 14/906915 was filed with the patent office on 2016-06-16 for knitted electrochemical capacitors and heated fabrics.
The applicant listed for this patent is DREXEL UNIVERSITY. Invention is credited to Genevieve DION, Yury GOGOTSI, Kristy JOST.
Application Number | 20160165970 14/906915 |
Document ID | / |
Family ID | 52393985 |
Filed Date | 2016-06-16 |
United States Patent
Application |
20160165970 |
Kind Code |
A1 |
JOST; Kristy ; et
al. |
June 16, 2016 |
KNITTED ELECTROCHEMICAL CAPACITORS AND HEATED FABRICS
Abstract
A garment includes a supercapacitor and/or heated fabrics
including a first conductive yarn knitted to as to form a current
collector and a second conductive yarn knitted to as to form an
electrode that is in electrical contact with the current collector.
The conductive yarns are knitted into a predetermined
supercapacitor design having respective electrodes that are not in
electrical contact with each other. An electrolyte saturates at
least the electrode material either before or after knitting, and
an ionically permeable electronic separator allows the electrodes
to be in close proximity to each other without being in electrical
contact with each other. A heating element may also be formed by
knitting at least one of the first and second conductive yarns into
a linear resistor or by knitting an insulated conductive yarn into
a sheet of fabric. Such a heating element is connected to the
supercapacitor via a switch.
Inventors: |
JOST; Kristy; (Philadelphia,
PA) ; GOGOTSI; Yury; (Warminster, PA) ; DION;
Genevieve; (Philadelphia, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DREXEL UNIVERSITY |
Philadelphia |
PA |
US |
|
|
Family ID: |
52393985 |
Appl. No.: |
14/906915 |
Filed: |
July 25, 2014 |
PCT Filed: |
July 25, 2014 |
PCT NO: |
PCT/US14/48197 |
371 Date: |
January 22, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61858358 |
Jul 25, 2013 |
|
|
|
Current U.S.
Class: |
219/211 |
Current CPC
Class: |
H01G 11/24 20130101;
Y02E 60/13 20130101; H01G 11/28 20130101; A41D 31/00 20130101; A41D
13/0051 20130101; H01G 11/70 20130101 |
International
Class: |
A41D 13/005 20060101
A41D013/005; A41D 31/00 20060101 A41D031/00 |
Claims
1. A garment comprising a first conductive yarn knitted to as to
form a current collector, a second conductive yarn knitted so as to
form an electrode that is in electrical contact with the current
collector, said first and second conductive yarns being knitted
into a predetermined supercapacitor design having respective
electrodes that are not in electrical contact with each other, an
electrolyte that saturates at least said electrode material, and an
ionically permeable electronic separator that allows the electrodes
to be in close proximity to each other without being in electrical
contact with each other.
2. The garment of claim 1, wherein the first and second conductive
yarns in electrical contact with each other in an intertwining knit
structure.
3. The garment of claim 1, wherein the first and second conductive
yarns are plated to each other to remain in electrical contact with
each other.
4. The garment of claim 1, wherein the first and second conductive
yarns are plied to each other to remain in electrical contact with
each other.
5. The garment of claim 1, wherein the first conductive yarn is
integrated into material of the second conductive yarn whereby one
yarn comprises both the electrode and current collector components
and the first and second conductive yarns remain in electrical
contact with each other.
6. The garment of claim 1, wherein said first and second conductive
yarns are individual yarns that remain in electrical contact with
each other in said predetermined supercapacitor design.
7. The garment of claim 1, wherein said first and second conductive
yarns are integrated into a same strand of yarn, either as a
core-shell yarn or by twisting the first and second conductive
yarns together, and are knitted into said predetermined
supercapacitor design.
8. The garment of claim 1, wherein said first and second conductive
yarns are coated in said electrolyte prior to being knitted into
said predetermined supercapacitor design and said electrolyte acts
as the separator between the electrodes.
9. The garment of claim 1, wherein said first and second conductive
yarns are coated in said electrolyte after being knitted into said
predetermined supercapacitor design.
10. The garment of claim 9, wherein said separator comprises a
nonconductive yarn knitted between the electrodes to separate the
electrodes to prevent electrical contact.
11. The garment of claim 1, wherein said electrolyte comprises an
ion conducting polymer based electrolyte.
12. The garment of claim 11, wherein said electrolyte comprises a
PVA based electrolyte mixed with phosphoric acid so as to form a
gel that is coated onto the first and second conducting yarns.
13. The garment of claim 1, wherein at least one of said first and
said second conductive yarns comprises knitted stainless steel
and/or activated carbon embedded yarn.
14. The garment of claim 1, wherein said first and second
conductive yarns are formed into a double layer fabric having an
anode and cathode on opposite sides of the double layer fabric,
said double layers being electrically separated by layers of tucked
yarn.
15. The garment of claim 1, wherein said first and second
conductive yarns are formed into a double layer fabric having a
square anode and a square cathode on opposite sides of the double
layer fabric, said double layers being knitted together and
connected by a spacer yarn that also electrically insulates the
anode and cathode from each other.
16. The garment of claim 1, further comprising a heating element
formed by at least one of said first and second conductive yarns
knitted into a linear resistor, wherein said heating element is
connected to said supercapacitor via a switch.
17. The garment of claim 1, further comprising a heating element
formed by an insulated conductive yarn knitted into a sheet of
fabric, wherein said heating element is connected to said
supercapacitor via a switch.
18. The garment of claim 17, wherein said insulated conductive yarn
is knitted into an intarsa geometry having a high resistance.
19. The garment of claim 1, wherein the separator comprises spacing
in a knit structure formed by the first and second conductive
yarns.
20. The garment of claim 1, wherein said predetermined
supercapacitor design inter-digitates said first and second
conductive yarns.
21. The garment of claim 20, wherein the inter-digitated first and
second conductive yarns are asymmetric.
22. The garment of claim 1, wherein said predetermined
supercapacitor design comprises stripes of the first and second
conductive yarns separated by said separator.
23. The garment of claim 22, wherein at least one of said stripes
comprises insulated yarn.
24. A method of creating a garment including a supercapacitor
and/or heated fabrics, comprising the steps of forming a current
collector from a first conductive yarn, forming an electrode from a
second conductive yarn that is in electrical contact with the
current collector, knitting the first and second conductive yarns
into a predetermined supercapacitor design having respective
electrodes that are not in electrical contact with each other,
saturating at least the electrode material with an electrolyte
either before or after knitting the supercapacitor, and providing
an ionically permeable electronic separator that allows the
electrodes to be in close proximity to each other without being in
electrical contact with each other.
25. The method of claim 24 further including the steps of forming a
heating element by knitting at least one of the first and second
conductive yarns into a linear resistor or by knitting an insulated
conductive yarn into a sheet of fabric and connecting the resulting
heating element to the supercapacitor via a switch.
26. The method of claim 24, wherein the knitting step is performed
by an automatic knitting machine.
27. The method of claim 24, further comprising the steps of
calculating resistance of the first and/or second conductive yarn
as a function of length of yarn in each knitted row and knitting a
supercapacitor design with predetermined resistance and/or
capacitance characteristics.
28. The method of claim 24, wherein the knitting steps comprises
knitting the predetermined supercapacitor design and an antenna
design into a same piece of fabric.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims benefit of Provisional Application
No. 61/858,358, filed Jul. 25, 2013. The contents of that
application are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The invention relates to smart knitted fabrics and the use
of such fabrics to create capacitors and heating elements in
fabrics.
BACKGROUND
[0003] Numerous researchers have attempted to develop conductive
threads and so-called "smart fabrics." Devices including garments
made from smart fabrics are expected to make an enormous
contribution to health care by increasing patient safety and
comfort and replacing bulky medical instrumentation to measure
patient data. These types of devices are also expected to be use in
a wide variety of sensing, communication, and tactile interaction
applications. In conventional smart fabrics, sensors are being
widely studied and used as an essential component, especially in
the fields of medical and athletic applications. Such wearable
sensors provide a means to monitor the wearer's health through
physiological measurements in a natural setting or can be used to
detect or alert care providers to potential hazards around the
wearer. However, to date, such garments have generally incorporated
sewn-in sensors and generally have not been adaptable enough in
design to create the variety of shapes and sizes needed for most
useful applications.
[0004] The field of wearable electronics has shown great potential
with applications in healthcare, the military and everyday
consumption as wearable heart rate monitors, heating/cooling
garments, and other wearable devices that can relay real time
information on a patient's or soldier's vitals wirelessly. However,
many of these electronic devices require a power source, and
textile energy storage remains an underdeveloped cornerstone to the
field as conventional batteries and capacitors are still used in
devices like the Nike Fit, Adidas MiCoach, Cute-circuit Galaxy
Dress, T-shirtOS, "Hi-call" Bluetooth enabled phone glove, Google
Glass, Apple Smart Watch, and UnderArmor heart rate monitors.
Though research has reported efforts to store energy in textiles
(see, for example, the state of the art report provided in Jost et
al., "Textile Energy Storage in Perspective," Journal of Materials
Chemistry A, The Royal Society of Chemistry, Feb. 20, 2014),
devices suitable for large-scale manufacturing have not yet been
reported. It is desired to develop an energy storage device that is
formed from textile materials suitable for large-scale
manufacturing.
[0005] Heated clothing has also found many applications for people
who live and work in cold climates. Some examples include Columbia
Sportswear Company's heated jackets and Gerbing's heated gloves.
These garments/accessories are often comprised of multiple layers
of thick fabrics, and batteries to power the heating elements are
sandwiched between these layers. It is also desired to develop
energy storage devices and heating elements for use in such heated
clothing.
[0006] The present invention addresses these and other needs in the
art.
SUMMARY
[0007] The invention addresses the above-mentioned needs in the art
by providing techniques for the fabrication of a knitted
supercapacitor as a possible power source and for the fabrication
of heating elements for wearable electronic devices.
[0008] In example embodiments, a knitted garment is provided
including a supercapacitor and/or heated fabrics. The garment
includes a first conductive yarn knitted to form a current
collector and a second conductive yarn knitted to form an electrode
that is in electrical contact with the current collector. The
conductive yarns are knitted into a predetermined supercapacitor
design having respective electrodes that are not in electrical
contact with each other. An electrolyte saturates at least the
electrode material either before or after knitting, and an
ionically permeable electronic separator is provided that allows
the electrodes to be in close proximity to each other without being
in electrical contact with each other. A heating element may also
be formed by knitting at least one of the first and second
conductive yarns into a linear resistor or by knitting an insulated
conductive yarn into a sheet of fabric. Such a heating element is
connected to the supercapacitor via a switch.
[0009] Other example embodiments include methods for creating such
garments from conductive fibers. For example, a sample method
includes the steps of creating a garment including a supercapacitor
and/or heated fabrics by forming a current collector from a first
conductive yarn, forming an electrode from a second conductive yarn
that is in electrical contact with the current collector, knitting
the first and second conductive yarns into a predetermined
supercapacitor design having respective electrodes that are not in
electrical contact with each other, saturating at least the
electrode material with an electrolyte either before or after
knitting the supercapacitor, and providing an ionically permeable
electronic separator that allows the electrodes to be in close
proximity to each other without being in electrical contact with
each other. The method may further include the step of forming a
heating element by knitting at least one of the first and second
conductive yarns into a linear resistor or by knitting an insulated
conductive yarn into a sheet of fabric. The resulting heating
element is connected to the supercapacitor via a switch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The foregoing and other beneficial features and advantages
of the invention will become apparent from the following detailed
description in connection with the attached figures, of which:
[0011] FIG. 1 illustrates typical electrochemical techniques and
results for supercapacitors.
[0012] FIG. 2 three different knitted supercapacitor designs in
accordance with example embodiments.
[0013] FIG. 3 illustrates a design for a fabric having an
inter-digitated supercapacitor with a heated patch, its rendered
program, and a sample of the real fabric knitted in wool.
[0014] FIG. 4 illustrates a real knitted stainless steel striped
supercapacitor sample.
[0015] FIG. 5 illustrates a Shima Seiki knit program for knitting
the devices illustrated in FIG. 3.
[0016] FIG. 6 illustrates both a sample of the fabric made of inert
materials (top), and a short program representing the most
fundamental short section of the fabric (bottom).
[0017] FIG. 7 shows a plain weft knitted wool fabric with stainless
steel stripes, each stripe knitted with 1, 2, or 3 courses
(rows).
[0018] FIG. 8 illustrates stripe electrochemical capacitor (EC)
geometry, knitted stripe EC in stainless steel yarn, insulated
stripe EC geometry, insulated stripe EC knitted in stainless steel
yarn, and stripe EC knitted with steel and activated carbon
embedded yarn, as well as inter-digitated EC examples.
[0019] FIG. 9 illustrates an insulated inter-digitated EC of an
exemplary embodiment.
[0020] FIG. 10 illustrates a spacer EC front a showing cathode, a
spacer EC back with anode, a cross-sectional illustration of spacer
yarn acting as an electrical insulator between the two electrodes,
a front of spacer EC knitted with 5 carriers, a back of spacer EC
knitted with 5 carriers, a front of spacer EC made with 7 carriers,
and a back of spacer EC made with 7 carriers.
[0021] FIG. 11 illustrates a knitted antenna for harvesting WiFi
energy knitted in the same piece of fabric as an inter-digitated EC
which stores the collected energy.
[0022] FIG. 12 embodies two proposed circuits for the resistive
models of the stripe EC (FIG. 12a) and an inter-digitated EC (FIG.
12b).
[0023] FIG. 13 illustrates cyclic voltammetry for symmetric
stainless steel knitted supercapacitors, including a 2 finger
inter-digitated EC (.about.2 mF), a 3 finger inter-digitated EC
(.about.5 mF), and a stripe EC (.about.5 mF) as seen in FIG. 7.
[0024] FIG. 14 illustrates two possible geometries for an insulated
and non-insulated yarn that maximize the resistance per area for
use as a heated fabric.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0025] The present invention may be understood more readily by
reference to the following detailed description taken in connection
with the accompanying figures and examples, which form a part of
this disclosure. It is to be understood that this invention is not
limited to the specific products, methods, conditions or parameters
described and/or shown herein, and that the terminology used herein
is for the purpose of describing particular embodiments by way of
example only and is not intended to be limiting of any claimed
invention. Similarly, any description as to a possible mechanism or
mode of action or reason for improvement is meant to be
illustrative only, and the invention herein is not to be
constrained by the correctness or incorrectness of any such
suggested mechanism or mode of action or reason for improvement.
Throughout this text, it is recognized that the descriptions refer
both to methods and software for implementing such methods.
[0026] A detailed description of illustrative embodiments of the
present invention will now be described with reference to FIGS.
1-14. Although this description provides a detailed example of
possible implementations of the present invention, it should be
noted that these details are intended to be exemplary and in no way
delimit the scope of the invention.
[0027] The invention incorporates knit designs for embedding
supercapacitor components into 2D and 3D intarsia knitted fabrics
and for knitting heated fabrics as single or double layer textiles
with other electrical components (e.g., wiring or energy storage)
embedded within the same sheet of fabric during manufacturing.
Embodiments of knitted electrochemical capacitors (ECs) and heated
fabrics powered by same will be described below.
Knitted Electrochemical Capacitor (EC)
[0028] In a sample embodiment, the invention incorporates designs
for embedding all supercapacitor components into intarsia knitted
fabrics (i.e., insertion of other segments of yarn into the fabric
to form patterns like polka dots or stripes). A supercapacitor,
also known as a double layer capacitor, stores electrical energy in
a double layer charge between a high surface area carbon electrode
and its respectively charged counter ions in an electrolyte
solution. Typically, the more surface area available in the
electrode material, means more ions can adsorb to the surface,
resulting in more energy being stored. The fabrication processes
and designs described herein allow the integration of multiple
supercapacitors in series or parallel to increase the voltage or
current that is specific to an application. Different geometries
have been fabricated as examples of the different kinds of 2D and
3D fabrics capable of storing energy and engineered to satisfy
different size, material, resistance and energy density
specifications. Importantly, these geometries, though intended for
supercapacitors, may also be used for fabric batteries, where the
geometries would remain the same, but the materials could be
changed, (e.g., lithium ion battery would require a graphite yarn,
Lithium cobalt oxide embedded yarn, and a PVA-LiPF6 gel
electrolyte). Similarly, solar cells, triboelectric generators,
diodes, and other electronic devices have the same two electrode
geometry. The disclosed method for integration into textiles allows
for many kinds of new electronics to be fabricated quickly and
easily.
Experimental/Fabrication Description
[0029] FIG. 1 illustrates typical electrochemical techniques and
results for supercapacitors. Figure la provides an example of a
cyclic voltammogram, of which the area under the curve is
equivalent to the charge stored (C=Q/V). Figure lb provides an
example of galvanostatic cycling curve, where the capacitance is
equivalent to the constant current divided by the slope of the
discharge curve, where the inset shows the IR drop (R=dV/i). FIG.
1c provides an example of a PEIS curve for a supercapacitor having
a slanted slope at the beginning of the curve, indicative of ionic
diffusion before becoming primarily capacitive. The right side hump
shows a resistor in series with an RC circuit, the slanted part of
the curve indicates ionic diffusion, and the upright vertical curve
is representative of a perfect capacitor.
[0030] ECs, also called double layer capacitors, store charge by
adsorbing electrolyte ions to oppositely charged electrode
surfaces. Each supercapacitor has an anode and a cathode, charged
negatively and positively, respectively. The more surface area that
is available means that there are more sites for ion adsorption,
and more charge can be stored. Therefore, the energy stored is
proportional to the available surface area in the electrode
materials. The material requirements for the devices to operate
will be described in the materials section below.
How to Quantify the Energy Stored:
[0031] Helmholtz described capacitance for a parallel plate
capacitor with a dielectric between two metal plates as being
proportional to the dielectric constant of the separating material
(.epsilon.), multiplied by the surface area of the plates (A)
divided by the distance (d) between them (Eq. 1):
C = A d . Eq . 1 ##EQU00001##
When compared to supercapacitors, the area of the plates can be
increased by using a high surface area material allowing for more
sites for ions to adsorb. The distance (d) between the plates is
now on the order of a few angstroms, being the distance between the
ion and the surface of the electrode material. Thus, if one knows
how much active material comprises the electrodes, and the active
ionic species, its charge, and solvated radius, then the
theoretical capacitance can be determined However, other factors
such as diffusion of ions into the electrode material and their
mobility in solvent can greatly affect the capacitance. Thus, Eq. 1
can give one a general understanding of what capacitance one can
expect to see from a given material, but determining capacitance
experimentally (FIG. 1) is much more common, and leads to greater
insights into the material system.
[0032] Typically, bulk carbon films for supercapacitors have
different capacitances per gram of the active material. Activated
carbons have capacitances of 100 F/g, CNTs are usually lower around
50 F/g, carbon anions are usually 20-30 F/g, and graphene can be
anywhere from 20 F/g up to 240 F/g depending on how it is
processed. Graphene's theoretical gravimetric capacitance has been
reported to be 520 F/g; however, this has never been achieved.
Usually metals and ceramics have gravimetric capacitances on the
order of <1 F/g to 5 F/g, which are much lower, but are used
more commonly for circuit components that require rapid charge and
discharge. The gravimetric capacitance is typically reported for
the active mass of one electrode. The electrode capacitance for
symmetric double layer capacitors is always twice that of the
device capacitance, given that the electrodes are treated as two
capacitors in series, which gives one the relationship expressed in
Eq. 2. If one assumes the electrodes are of equal capacitance, then
one can also derive the expression in Eq. 3, where C.sub.e is the
electrode capacitance and C.sub.a is the device capacitance.
1 C e + 1 C e = 1 C d Eq . 2 C d = C e 2 Eq . 3 ##EQU00002##
[0033] Typical materials used in commercially available
supercapacitors include activated carbons (1200 m.sup.2/g to 2000
m.sup.2/g), carbon anions (.about.500 m.sup.2/g), carbon nanotubes
(200-800 m.sup.2/g), and graphene, which spans the spectrum up to a
theoretical specific surface area of 2630 m.sup.2/g. Many yarns,
including carbon fiber yarns, have 50-200 m.sup.2/g of specific
surface area depending on the fineness of the fibers, meaning by
comparison they will store less energy, but are adaptable for
textile applications. If, for example, a yarn comprised one of
these high surface area carbon materials, one could potentially
store as much energy as a conventional supercapacitor per device
weight, volume and area. Therefore, it will be appreciated that
knitted ECs can be made of yarns comprised entirely or partly of
these high surface area conductive materials.
Electrochemical Capacitor Components and Material Requirements:
[0034] In an example embodiment, the electrode material (E) comes
in the form of a yarn and consists of any high surface area,
relatively conductive material. As reported in Jost, et al.,
"Knitted and screen printed carbon-fiber supercapacitors for
applications in wearable electronics," Energ Environ Sci, Vol. 6,
DOI:10.1039/C1033EE40515J, DOI:10.1039/C3EE40515J (2013), it is
possible to use commercially available carbon fiber yarn to act as
an electrode material or current collector in a supercapacitor. For
example, activated carbon (YP17, Kuraray Japan, 1500 M.sup.2/g,
made from coconut shells) embedded in a 2-ply yarn may be used. It
is also possible to use an electrode material that is conductive
enough to act as both the current collector and electrode material,
the only concern being that more graphitized carbon has a lower
specific surface area, ultimately resulting in materials with lower
capacitances. Only inert conductive materials can be used in these
devices, i.e., materials that will not undergo redox or other
electrochemical reactions when assembled into a capacitor to store
energy. If redox does occur, the electrode material will be
degraded over time, and the capacitor will not have a long life.
Redox materials are ideal for batteries, for which these geometries
can also be used.
[0035] Suitable commercially available conductive yarn materials
include but are not limited to: [0036] Carbon fiber yarn, Pharr
Yarns, USA [0037] Stainless steel yarn, Beakart,Inc., Germany
[0038] Graphite yarn, SGL Group [0039] Carbon nanotube yarn,
Nanocomp [0040] Copper coated yarn [0041] Activated carbon, Kuraray
Japan
[0042] In an example embodiment, the current collector (CC) is a
highly conductive yarn that is in good electrical contact with the
electrode yarn, either by 1) knitting the CC alongside the
electrode (E) in an intertwining knit structure; 2) feeding both
yarns into the knitting machine together to be knitted as if they
were a single yarn, also known as plating; 3) plying the CC and E
together using the same techniques traditionally used to ply
strings and yarns; or 4) integrating the CC into the E material,
meaning one yarn holds both the electrode and collector components.
Typically, the same material is used in each CC to avoid producing
a galvanic current, which may result in completely dissolving one
CC into the electrolyte solution due to oxidation. Different CC
materials may be suitable for battery applications. The same
commercially available conductive yarn materials as noted above
also may be used.
[0043] FIG. 2 depicts three different knitted supercapacitor
designs. Changes in the design accommodate the types of smart yarns
used for the E, CC and electrolyte materials. At (1), if the E and
CC are to be knitted as individual yarns, then at (2) each
component can be knitted while maintaining electrical contact
between each other. At (3), two types of yarns are illustrated that
integrate the E and CC in the same strand of yarn, either as a
core-shell fiber/yarn, or by twisting individual yarns together.
These yarns alone make up 1/2 of the supercapacitor. At (4), a
design is depicted that accommodates the CC and E integrated in the
same yarn. At (5), the combined E and CC yarns are shown that are
coated in electrolyte prior to knitting. At (6), no spacing between
the inter-digitated fingers is needed as the solid electrolyte acts
as both the electrolyte and the separator.
[0044] FIG. 2 further illustrates what kind of spacing would be
required for knitting ECs with different forms of yarn. FIG. 2 at
(1) shows two separate electrode and current collecting yarns,
which would have to be knitted individually and into an arrangement
as seen at (2) in FIG. 2. FIG. 2 shows at (3) a combined current
collector and electrode yarn, either twisted together or in a
coaxial arrangement that could be knitted in the arrangement shown
at (4) in FIG. 2. Lastly (4) in FIG. 2. Lastly, if the combined
E-CC yarn is also pre-coated in an electrolyte (as shown at (5) in
FIG. 2), no spacing between electrodes is required (see (6) in FIG.
2), as the electrolytes electrically insulate the electrodes from
each other while facilitating ionic conduction.
[0045] In example embodiments, the electrode material is saturated
with an electrolyte. As has been reported in the literature, PVA
based electrolytes have shown excellent performance when used in
supercapacitors. PPO, PEO and Nafion have also been demonstrated as
good ion conducting polymers and have been demonstrated in use in
batteries and fuel cells. The PVA and phosphoric acids are sold
separately but are easily mixed to form a gel that is coated onto
the supercapacitive textiles. The electrolyte can either be coated
onto the yarns before knitting as in FIG. 2((5)-(6)) or coated to
the fabric surface after knitting. The advantage of coating before
knitting is that the electrolyte is enabled to act as a protective
coating from needles that may cause flaking of the activated carbon
off of the cotton. Also, coating before knitting does not require
the inter-digitated fingers to be separated as seen in FIGS. 2 at
(2) and (4).
[0046] In a sample embodiment, a recipe for a standard PVA gel
electrolyte includes: [0047] 1.4 g Polyvinylalcohol (PVA), high
molecular weight, Alfa Aesar [0048] 1-2 ml Phosphoric acid
(H.sub.3PO.sub.4) 70% concentrated, Alfa Aesar [0049] 5.16 g
Silicotungstic acid, Alfa Aesar [0050] 20 ml Deionized water, Alfa
Aesar
[0051] Lastly, the anode and cathode cannot be in electrical
contact with each other; therefore, an ionically permeable
electronic separator is used to allow the electrodes to be in close
proximity for slim packaging. In a sample embodiment, the spacing
in the knit structure saturated in electrolyte acts as the
separator (see FIG. 2(4)). If the yarns are coated in electrolyte
prior to knitting, then they are capable of being knitted without
any spacing in the knit structure. It will be appreciated that the
coating must be at least 50 .mu.m thick in order to also act as the
separator.
[0052] For the inter-digitated design depicted in FIG. 2, a plain
jersey may have two horizontal rows between each finger, and four
vertical rows between the ends in order to avoid contact with one
another. If the yarns are coated in electrolyte prior to knitting,
then they are capable of being knitted without any spacing in the
knit structure. A simple heating at 90.degree. C. for about 20
minutes will form an ionic bond between the coated yarns that are
in contact within the knit structure without forming an electrical
contact between the anodic and cathodic yarns. The coating is at
least 50 p.m thick in order to also act as the separator. A
thickness of 100 .mu.m has been used to ensure there are no
uncoated stray fibers that could cause a short.
Knitting the EC Components:
[0053] These EC components and conditions are assembled into
knitted ECs using the Shima Seiki Apex-3 Design software to design
the intarsia structure and then to subsequently render a program
for the machine to knit. The device depicted in FIG. 3 was knitted
on the First 4-cam Shima Seiki Machine, which has a limit of 28
carriers per program. This means, with the exception of the
beginning and ending waste material (2 carriers), one can create a
design that has no more than 26 different yarns. The designs in
FIGS. 3 and 6 use at least 10 carriers, and carrier designations
are depicted in FIGS. 3, 5, and 6, which are explained in the
embodiments section below.
[0054] Using the intarsia design and simulation software, one can
"paint" the desired knit geometry. Every pixel is equivalent to a
single stitch/loop. Intarsia knitting is akin to mosaic where
different patterns can be introduced as various colors, in the
present case one may use the intarsia technique to bring various
conductive materials together. One has the ability to change the
yarn color and/or the fabric structure, i.e. a loop arrangement.
The fabric depicted in FIG. 3 is a single jersey knit embedded with
different yarns, making up the intarsia pattern. In essence, the
color change controls the type of yarn(s) in the fabric, and the
structure controls how the needle moves that yarn to create a plain
jersey, ribbed knit, purl knit, etc. The simulation software
enables one to change the knit structure or the pattern
independently, both depicted in a separate data window.
[0055] In accordance with exemplary embodiments, the simulation
software used for programming custom knit structures allows the
user to create new fabric programs in two different ways. The first
is `manual` where the user must be skilled in the art of knit
programming on Shima Seiki machines. The second is automatic and
allows the user to visually design a flat fabric using color as a
representation for knit structures or different yarns; these
designs can be automatically processed by the software for machine
knitting.
[0056] However, the simulation software has limitations. For
example, it is sometimes necessary to manually program all custom
structures to be sure that conductive components are either in good
electrical contact with each other or are electrically insulated.
Automatically generating a program may also use more yarn carriers
(different yarns), which may inhibit the ability to knit other
electric components in the same fabric because each machine has a
limitation on the total number of yarns it can incorporate into a
fabric. The automatic software also cannot develop 3D spacer
fabrics, and currently must be programmed manually for developing
3D spacer fabrics.
[0057] Those skilled in the art will appreciate that it is possible
to estimate the length of yarn used in a knitted EC based on the
number of stiches it is comprised of, as well as at what stitch
value it was knitted.
[0058] FIG. 7 shows a plain weft knitted wool fabric with stainless
steel stripes, each stripe knitted with 1, 2, or 3 courses (rows).
The puma wool yarn was measured to have 25 cm of yarn in each
knitted row, while the steel yarn was measured to have 21.6 cm per
row. As illustrated, the wool fabric is knitted at a stitch value
of 45 with a stripe of steel knitted in the middle. Because the
steel yarns presented here have no stretch or ease, they must be
knitted tighter to produce a flat laying fabric that does not
buckle, and were knitted on a stitch value of 37. By unraveling the
fabric partly that it was determined that the full length of yarn
in one row of wool yarn (45 stitches) was 25 cm long while the
steel in the same fabric was only 21.6 cm long. However, if one
were to take the ratio of the stitch value (where a higher stitch
value means a loop of a longer length), it is found that 21.6/25
cm=0.86, and 37/45 stitch=0.82 are closely the same. Therefore, the
total length of yarn can be estimated if the stitch value of the
yarn knitted and the number of loops are known. For example, in
Equation 5, it is shown that the loop length per stitch
(L.sub.stich)=baseline length (L.sub.0).times.(new stitch value
(S.sub.x)/baseline stitch value (S.sub.0)):
L stitch = L 0 ( S x S 0 ) . Eq . 4 ##EQU00003## [0059] Stitch
value of 45=loop length of 0.62 cm.times.40=24.8 cm [0060] Stitch
value of 37=24.8 cm (37/45)=20.33 [0061] Stitch value of
20=20/45=0.44.times.0.62 cm=0.275 cm per loop If a knitted EC is
composed of many rows of varying lengths, the total length can
still be determined by counting the total number of stitches in
accordance with Equation 5.
[0062] Knowing the total length of yarn in the knit structure
allows one to engineer a knit with a desired capacitance and
resistance. It has previously been demonstrated that knitting
multiple rows of conductive material together is similar to wiring
resistors in parallel with each other, yielding very similar
results. Therefore, the inventors can tune the resistance in the
knit structure, not only by adjusting the length, but by knitting
multiple rows together.
[0063] The resistance of a single row can be determined by
multiplying the measured resistance per unit length (cm) by the
total length of yarn in that row, as shown in Equation 6 below. As
known by those skilled in the art, when resistors are wired in
parallel, they are equivalent to the expression in Equation 7.
Therefore, if the resistance of each row is the same (because it is
made of the same material) it can be estimated that two knitted
rows will have 1/2 the resistance of R.sub.1 (Equation 8), and
three rows will have 1/3 the resistance (Equation 9), etc. From
here, it will be appreciated that a full resistive network may be
produced for a knitted EC .
R 1 ( resistance of a single row ) = R cm L Eq . 5 1 R 1 + 1 R 1 =
1 R 2 Eq . 6 R 2 ( resistance of two rows ) = R 1 2 Eq . 7 R 3 = R
1 3 Eq . 8 ##EQU00004##
[0064] Once the design is finalized, it can be sent to the knit
programming software as a predetermined design that is converted
into machine language to be knitted by the appropriate knitting
machine. The machine is then prepared, respective
conductive/electrode yarns and regular yarns are threaded in the
designated feeders, and the fabric is knitted.
Embodiments
[0065] FIG. 3 depicts a design for an inter-digitated
supercapacitor with a heated patch in the form of a resistor
(described with respect to FIG. 14 below), its rendered program,
and a sample of the real fabric knitted in wool. This fabric has a
total electrode yarn length of 51 inches, or 129.5 cm. If this
fabric were made with stainless steel yarn as the electrode
material, weighing approximately 1 mg/cm and having 2 F/g, it would
result in an electrode having 0.258 F, resulting in a device of
0.129 F. Assuming the full device is approximately 8.89.times.6.35
cm in area, meaning per area, the device stores 2 mF/cm.sup.2,
which is comparable to conventional ceramic or metal plate
capacitors.
[0066] FIG. 3 depicts the simulation (top) and real image (bottom)
of a fabric design to integrate energy storage and a heated patch.
Yarns 1 represent electrode materials, while yarn 2 represents
current collector/leads to connect supercapacitor to other devices.
Area 3 represents an area that an electrolyte would coat after
knitting; however, as noted above, the electrolyte could also be
coated into the yarns before knitting. Yarn 4 is a non-conductive
yarn (e.g., cotton, wool, polyester, and nylon) knitted between the
electrode yarns 1 to separate the yarns and prevent electrical
contact. Yarn 5 is a heated patch, and yarn 6 comprises conductive
leads to connect the heated patch to the supercapacitor. The
spacing between the yarn 2 and yarn 5 allows for the addition of a
small sewable switch and LED (not shown). The fabric of FIG. 3 is
rendered using the Shima Seiki SDS-ONE design system.
[0067] FIG. 4 illustrates a real knitted stainless steel striped
supercapacitor sample (10 .mu.m fibers, approximately lk yarn,
Beakart, Germany) that is 4 cm long (16 cm yarn length) resulting
in a device capacitance of approximately 1 mF determined using
cyclic voltammetry and galvanostatic cycling when scanned at 2 mV/s
and 0.2 mA in an 0.8 V window. This results in a capacitance per
yarn length of 0.062 mF/cm. This test was conducted on a Biologic
VMP3 Potentiostat/galvanostat, commonly used for supercapacitor
testing, using a PVA-H.sub.3PO.sub.4 electrolyte commonly used for
supercapacitors. The device used 2 rows of inactive yarns as the
separating material.
[0068] If, however, this device had an electrode material that used
a high surface area carbon (as previously described), within the
same area, one can increase the capacitance significantly given
that one knows the mass loading of the carbon, its relative
gravimetric capacitance, and now its length of 129.5 cm.
[0069] For this prolific example, one can use an activated carbon,
with a mass loading per length of 0.25 mg/cm (carbon fabrics are
usually lighter than metal fabrics because of its lower density).
If the activated carbon has an average of 100 F/g, and one has a
total of 129.5 cm at 0.25 mg/cm, one can expect to see a device
capacitance of:
129.5 cm*0.00025 g/cm*100 F/g=3.23 F per electrode, or 1.61 F per
device.
This is more than 200 times higher capacitance than the stainless
steel example.
[0070] The afore-mentioned article to Jost et al. as well as the
article to Jost, et al. entitled "Carbon Coated Textiles for
Flexible Energy Storage," Energy and Environmental Science, Vol. 4,
pp. 5060-5067 (2011) demonstrate how activated carbon materials can
be adapted for cotton and carbon fiber textiles, while having
comparable performance and capacitance as a conventional film
supercapacitor tested under the same conditions.
[0071] FIGS. 3 and 5 depict potential knit supercapacitor
prototypes ready for manufacture based on the kind of yarn
acquired. Each inter-digitated electrode design is depicted with
its specified yarn. These designs are intended to aid a maker in
recreating a knitted supercapacitor regardless of the type of
conductive or capacitive yarn available to them. FIG. 5a
illustrates a Shima Seiki knit program for FIG. 3(2); FIG. 5b
illustrates a knit program for FIG. 3(4); and FIG. 5c illustrates a
knit program for FIG. 3(6). The programs in FIG. 5 can be easily
modified to change the dimensions of the design in FIG. 3 by
someone skilled in using the Shima Seiki Apex-3 computerized
knitting software.
[0072] FIG. 6 illustrates a side view, partly deconstructed, of a
fabric made with inert materials. The illustrated fabric is a
double layer "spacer" fabric for a textile supercapacitor, having
the anode 10 and cathode 20 on opposite sides of the fabric,
electrically separated by layers of tucked separating filler yarn
30. FIG. 6 illustrates both a sample of the fabric made of inert
materials (top), and a short program representing the most
fundamental short section of the fabric (bottom). This double layer
fabric is more similar to the sandwiched pouch and coin cell
supercapacitors conventionally found in the market. Its design is
intended to use as little surface area as possible, resulting in a
more energy dense supercapacitor, since one can fit both the anode
and cathode in the same area. This fabric is, however, thicker than
the previously described inter-digitated textiles, but would also
be produced from the knitting machine as one piece of fabric.
[0073] FIGS. 8-10 describes functional and prolific embodiments for
knitted fabrics incorporating all elements of an EC: the electrode
material, current collector, electrolyte and separator. The
material requirements for these devices to operate are described in
the materials section above.
[0074] FIG. 8 illustrates stripe EC geometry at (1), knitted stripe
EC in stainless steel yarn at (2), insulated stripe EC geometry at
(3), insulated stripe EC knitted in stainless steel yarn at (4),
and stripe EC knitted with steel and activated carbon embedded yarn
at (5). FIG. 8 further illustrates inter-digitated EC at (6),
knitted inter-digitated EC in stainless steel yarn at (7), a
modified pattern of knitted EC with smaller fingers and wider sides
at (8), and inter-digitated EC in stainless steel with modified
finger lengths on one side demonstrating the ability to make these
asymmetric at (9). All samples in FIG. 8 were knitted on a
SWG-122SV Shima Seiki machine.
[0075] In FIG. 8, the stripe EC ((1) and (2)) is appropriate for
small devices, or to act as design components (stripes) for color
in garments without appearing to be a device itself On the other
hand, insulated stripe EC ((3) and (4)) is for the same electrical
geometry as the stripe EC but is insulated inside two layers of
fabric for added safety and no skin contact. These designs may be
ideal for electrode materials that have a potential to cause skin
irritation, but can still be incorporated into the garment safely.
Inter-digitated EC ((6)-(9)) illustrate an extension of the stripe
SC, where this geometry is really multiple stripes wired in series
with each other. This is best for situations where the device must
be contained within a single-layer sheet of fabric (2D only). Also
a common geometry is used for micro-supercapacitors.
[0076] The insulated inter-digitated EC shown in FIG. 9 has the
same geometry as the inter-digitated EC, but it is knitted between
two layers of non-conductive fabric (similar to the insulated
stripe EC). In this embodiment, the spacer yarn is capacitive
between the front and back of the fabric. Such a configuration is
best for small devices that may not be ideal for direct contact
with the skin.
[0077] FIG. 10 illustrates a spacer EC front a showing cathode at
(1), a spacer EC back with anode at (2), a cross-sectional
illustration of spacer yarn acting as an electrical insulator
between the two electrodes, but with sufficient porosity to allow
electrolyte ions to flow through at (3), a front of spacer EC
knitted with 5 carriers at (4), a back of spacer EC knitted with 5
carriers at (5), a front of spacer EC made with 7 carriers at (6),
and a back of spacer EC made with 7 carriers at (7). In each
embodiment, the spacer EC includes two layers of fabric, each with
a small square electrode, knitted together and connected by a
spacer yarn that also electrically insulates the electrodes from
each other. This geometry has approximately 3 times the energy
density per area compared to the stripe/inter-digitated geometry
because the electrodes and separating space are stacked on top of
each other. Because the electrodes are also knitted in squares, as
compared to long stripes, the resistance is also the lowest in this
geometry. However, this results in a thicker fabric.
[0078] For the inter-digitated designs of FIG. 10, the electrodes
ideally have two horizontal rows between each finger, and 2
vertical rows between the ends in order to avoid contact with one
another. A single horizontal row may result in electrode touching
and an electrically shorted device. However, increasing the space
between electrodes means ions have further to travel, resulting in
slower charging times.
[0079] FIG. 11 illustrates a knitted antenna for harvesting WiFi
energy knitted in the same piece of fabric as an inter-digitated EC
which stores the collected energy. The embodiment of FIG. 6 thus
embodies a knitted inter-digitated EC combined with a knitted WiFi
harvesting antenna as an example of the ability to knit multiple
electrical devices within the same piece of fabric.
[0080] FIG. 12a illustrates a proposed circuit diagram for a
striped EC, including the resistances of the cathode, anode, and
ionic resistance due to the electrolyte. FIG. 12b illustrates a
proposed resistive network model for the inter-digitated EC, where
each resistor is representative of a loop, to be scaled up or down,
and each array of resistors is for each electrode, a voltage
source, and a resistor associated with the ionic resistance due to
the electrolyte which is determined experimentally. FIG. 12 thus
embodies two proposed circuits for the resistive models of the
stripe EC (FIG. 12a) and an inter-digitated EC (FIG. 12b). Each
anode and cathode has an internal resistance based on the
electrical resistance of the yarns used, as well as the total
length used. Because the resistance can be estimated (as shown in
FIG. 1), predictive models can be built for a capacitor's
performance and expand upon the basic circuits shown.
[0081] FIG. 13 illustrates electrochemical results for three
different kinds of knitted EC devices, tested at 20 mV/s in a
PVA-H.sub.3PO.sub.4 electrolyte in a 0.8 V window.
PVA-H.sub.3PO.sub.4 is an electrolyte commonly used for
supercapacitors. FIG. 13 illustrates cyclic voltammetry for
symmetric stainless steel knitted supercapacitors, including a 2
finger inter-digitated EC (.about.2 mF), a 3 finger inter-digitated
EC (.about.5 mF), and a stripe EC (.about.5 mF) as seen in FIG. 7.
All devices demonstrate good electrochemical performance, and
rectangular behavior. Some peaking at 0.8 V is representative of
some electrolyte decomposition or impurities, but is not caused by
the knit structure. If, however, these devices had electrode
materials that used high surface area carbon (as previously
described) within the same area, the capacitance may be increased
significantly given that the mass loading of the carbon is known,
as is its relative gravimetric capacitance and its estimated
length.
[0082] FIG. 8 at (5) embodies an example of a stripe EC knitted
with a non-commercially available carbon embedded yarn. Previous
publications of the inventors as referenced above demonstrate that
how activated carbon materials can be adapted for cotton and carbon
fiber textiles, while having comparable performance and capacitance
as a conventional film supercapacitor tested under the same
conditions.
[0083] From the above, it is apparent that the textile EC geometry
and processing can have an effect on the performance, and that
using an optimized knit structure will allow the EC materials to
perform comparably to their conventional non-textile counterparts.
For example, it will be appreciated that a striped EC's components
and function may be incorporated into a full garment.
Heated Knit Fabrics/Garments
[0084] Heated clothing has already found many applications for
people who live and work in cold climates. Some examples include
Columbia Sportswear Company's heated jackets or Gerbing's heated
gloves. These garments/accessories are often comprised of multiple
layers of thick fabrics, while batteries to power the heating
elements are sandwiched between these layers. The techniques
described herein may also be used to form heated fabrics. In
contrast with the prior art designs, the proposed heated fabrics
can be knitted as single or double layer textiles with other
electrical components (e.g., wiring or energy storage) embedded
within the same sheet of fabric during manufacturing. Additionally,
because of the whole garment capabilities of the MACH2X Shima Seiki
Knitting Machine, it is possible to also knit seamless garments and
accessories with these components. Such garments will be described
below.
Experimental/Fabrication Description:
[0085] Heated fabrics typically operate using "resistive" or
"joule" heating, where the amount of heat in joules (Q) is
equivalent to the current (I) squared, multiplied by the resistance
(R) of the fabric.
Q=I.sup.2R Eq. 9
[0086] This means one can increase or decrease the temperature by
manipulating the input current and resistance of the material. The
temperature change will also depend on the specific heat of the
conductive medium and its total mass as shown in Eq. 10:
Q=cm.DELTA.T Eq. 10
where Q again is the heat in joules, c is the specific heat (J/g-K)
of the material, m is the mass of the material (grams) and .DELTA.T
is the change in temperature. Because one wants to determine what
the temperature change will be, this equation can be rearranged for
T, where T.sub.RT is the room temperature of approximately
23.degree. C.
T-T.sub.RT=Q/cm Eq. 11
Now one can clearly see that the temperature change will depend not
only on how much current is supplied, or the resistance of the
fabric, but a material may be chosen with a low specific heat to
further increase the temperature.
[0087] By designing the resistance and mass of the fabric, ideally
more heat will be generated from materials that have high
resistance per unit mass. When designing the knitted fabric, one
can design intarsia geometries that cover large surface areas but
have high resistance. Much like wire, the longer an individual
strand of yarn is, the greater the resistance becomes, as this
linear conductor acts like many smaller resistors in series.
However, the resistance decreases when yarns are in parallel with
each other. Therefore, large intertwining patches of conductive
yarn (non-insulated) will have a lower resistance than a single
strand. If the yarn is insulated, then regardless of the geometry,
it cannot act as yarns in parallel and will result in the highest
possible resistance. Using intarsia knitting, the resistance across
a given area can be carefully tuned by knitting the material in
series and parallel as desired.
[0088] FIG. 14 depicts two possible geometries for an insulated and
non-insulated yarn that maximize the resistance per area for a
knitted conductive fabric that may be heated. Conductive yarn
(non-insulated) at (1) is knitted into a snake chain at (2), making
the entire yarn a linear resistor. Insulated conductive yarn at (3)
is knitted at (4) as a sheet of fabric. As shown at (5), a
resistive carbon fiber patch that can be warmed by a 6V battery. A
close-up of this patch is shown at (6). If the conductive yarn at
(1) is fully exposed, to have the highest resistance (and
subsequently the most heating) it would be knitted as a long
continuous strand, not overlapping itself For insulated yarns for
heating, they can be knitted in almost any arrangement, as knitting
multiple rows together will not wire them in parallel, nor
subsequently reduce their resistance.
[0089] Once Q is determined for a desired temperature change (AT),
one can also calculate what kind of energy storage will be required
to power this patch. Typically, batteries are used to supply a
constant source of power over a long period of time. However, there
are no knittable battery materials in existence at this time.
Because of this, for the demonstration of heating these fabrics,
the inventors have integrated knitted supercapacitors into the same
sheet of fabric to be connected to the heating elements to power
same.
[0090] The energy of the device is described by Eq. 13:
Q=1/2CV.sup.2 Eq. 12
where Q (joules) is the energy stored, C is the device capacitance
(Farads), and V is the operational voltage window. The knitted
supercapacitors typically operate within a 1V window; therefore, if
Q is known, one can easily determine what size supercapacitor will
be required. The time spent heating the fabric will be proportional
to the time constant (discharge time) of the capacitor, which is
usually on the order of approximately 10 seconds. However, the
inter-digitated capacitor design is easily adapted for batteries if
the electrode materials can be developed as textiles. It will be
appreciated by those skilled in the art that such knitted
supercapacitors and heating elements may be sewn into fabrics to
provide heating as desired.
Safety Concerns:
[0091] Because these fabrics are heating, it would be ideal to use
them in combination with fire resistant or retardant yarns to
eliminate the chance of the garments catching fire. In addition,
the previously described layered heated jackets and gloves also
have layers in order to prevent the chance for electric shock. It
may also be ideal to use an insulated conductive yarn for the
heated fabric. Insulation will not only protect the wearer from any
possible electric shock or fire, but also protect the conductive
material from corrosion due to sweat or other impurities.
[0092] Similarly to the knitted supercapacitor described above, the
heated fabric is made using the same intarsia knitting technique
designed on the Shima Seiki SDS Apex-3.
[0093] Potential resistive yarns to be used for the heated fabric
include but are not limited to: [0094] X-static: silver embedded
polyester spandex yarn, Nobel Biomaterials Inc. [0095] Carbon fiber
yarn: Pharr Yarns, chopped 1 k tow fiber, 7 ,um in diameter fibers
[0096] Stainless steel yarn: Beakart, Germany. 1 k tow, 10 .mu.m
fibers. 100% stainless steel. [0097] Fire retardant yarn, Aramid
Yarn Company
[0098] Insubstantial changes from the claimed subject matter as
viewed by a person with ordinary skill in the art, now known or
later devised, are expressly contemplated as being equivalently
within the scope of the claims. For example, all of the designs
described herein can be made in almost any shape--e.g., the
inter-digitated designs can be heart shaped, circular, or compose
any design as long as the electrodes remain inter-digitated and
satisfy the functional requirements to operate as a supercapacitor.
The same is true for the non-inter-digitated geometries. Therefore,
obvious substitutions now or later known to one with ordinary skill
in the art are defined to be within the scope of the defined
elements.
* * * * *