U.S. patent application number 15/436356 was filed with the patent office on 2018-08-23 for high performance nano/micro composite fiber capable of storing electrical energy and method for fabricating thereof.
This patent application is currently assigned to AICT. The applicant listed for this patent is AICT, PURITECH CO., LTD.. Invention is credited to KangRae CHO, YunJae CHO, HyukJoon KIM, SangYoon PARK, MinKyoon SHIN, ChangSu YEO.
Application Number | 20180240609 15/436356 |
Document ID | / |
Family ID | 63167336 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180240609 |
Kind Code |
A1 |
PARK; SangYoon ; et
al. |
August 23, 2018 |
HIGH PERFORMANCE NANO/MICRO COMPOSITE FIBER CAPABLE OF STORING
ELECTRICAL ENERGY AND METHOD FOR FABRICATING THEREOF
Abstract
Provided a nano/micro composite fiber of the present invention,
capable of storing electrical energy, comprising (a) one or more
pairs of microfiber bundles consisting of graphene or
graphene/carbon nanotube as an electrode active material; (b)
nanofiber web surrounding the microfiber bundles, wherein the
nanofiber web is coated by one or more materials selected from the
group consisting of metal, carbon nanotube, activated carbon and
metal oxide nanoparticle; (c) an electrolyte layer surrounding the
nanofiber web and filling inner void of the microfibers and
nanofiber web; (d) an insulating film sheathing the electrolyte
layer.
Inventors: |
PARK; SangYoon; (Seoul,
KR) ; SHIN; MinKyoon; (Incheon, KR) ; KIM;
HyukJoon; (Suwon-si, KR) ; YEO; ChangSu;
(Seoul, KR) ; CHO; YunJae; (Seoul, KR) ;
CHO; KangRae; (Pyeongtaek-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AICT
PURITECH CO., LTD. |
Suwon-si
Pyeongtaek-si |
|
KR
KR |
|
|
Assignee: |
AICT
Suwon-si
KR
PURITECH CO., LTD.
Pyeongtaek-si
KR
|
Family ID: |
63167336 |
Appl. No.: |
15/436356 |
Filed: |
February 17, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01G 11/36 20130101;
D01D 5/0007 20130101; H01G 11/26 20130101; H01M 10/0436 20130101;
H01M 2300/0085 20130101; H01M 4/583 20130101; H01G 11/40 20130101;
H01M 4/75 20130101; B82Y 30/00 20130101; C23C 14/18 20130101; C09D
5/448 20130101; C23C 24/00 20130101; H01G 11/54 20130101; C23C
14/26 20130101; H01M 10/0422 20130101; Y02E 60/10 20130101; D01D
5/06 20130101; H01M 4/04 20130101; D01F 9/12 20130101; H01G 11/86
20130101; C09D 5/4407 20130101; C09D 7/70 20180101; B82Y 40/00
20130101; C09D 1/00 20130101; C09D 7/61 20180101 |
International
Class: |
H01G 11/40 20060101
H01G011/40; C25D 13/04 20060101 C25D013/04; H01M 4/583 20060101
H01M004/583; H01G 11/36 20060101 H01G011/36; H01G 11/86 20060101
H01G011/86; H01M 4/04 20060101 H01M004/04; H01M 10/058 20060101
H01M010/058; D01D 5/06 20060101 D01D005/06; D01D 5/00 20060101
D01D005/00; D01F 9/12 20060101 D01F009/12; H01M 10/0565 20060101
H01M010/0565; C09D 5/44 20060101 C09D005/44 |
Claims
1. A nano/micro composite fiber capable of storing electrical
energy, comprising: (a) one or more pairs of microfiber bundles
consisting of graphene or graphene/carbon nanotube as an electrode
active material; (b) nanofiber web surrounding the microfiber
bundles, wherein the nanofiber web is coated by one or more
materials selected from the group consisting of metal, carbon
nanotube, activated carbon and metal oxide nanoparticle; (c) an
electrolyte layer surrounding the nanofiber web and filling inner
voids of the microfibers and nanofiber web; (d) an insulating film
sheathing the electrolyte layer.
2. The composite fiber of claim 1, wherein the graphene is a
reduced graphene oxide.
3. The composite fiber of claim 1, wherein the graphene has an acid
group at the edge or on the surface thereof.
4. The composite fiber of claim 3, wherein the acid group is a
carboxyl group (--COOH).
5. The composite fiber of claim 1, wherein the carbon nanotube has
a sulfonic acid group (SO.sub.3.sup.-) on the surface thereof.
6. The composite fiber of claim 1, wherein the graphene or
graphene/carbon nanotube microfibers are modified by heating at a
temperature between 60.degree. C. and 100.degree. C. under a strong
acid.
7. The composite fiber of claim 6, wherein the strong acid is
selected from sulfuric acid, nitric acid, hydrochloric acid, or a
mixed acid thereof.
8. The composite fiber of claim 6, wherein the heating is performed
at a temperature between 80.degree. C. and 85.degree. C.
9. The composite fiber of claim 1, wherein the material of the
nanofiber is one or more selected from the group consisting of
polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polymethyl
methacrylate (PMMA), polymethacrylic acid (PMAA), polyacrylic acid
(PAA), polyvinyl chloride, Polylactic acid (PLA), polycaprolactone
(PCL), polyurethane (PU), polystyrene (PS), polyethylene oxide
(PEO), polyvinyl acetate (PVAC), polyacrylonitrile (PAN), nylon,
polyetherimide (PC), polyetherimide (PEI), polyester (PET),
polyester sulfone (PES) and polybenzimidazole (PBI).
10. The composite fiber of claim 1, wherein the metal of the
nanofiber web is one or more selected from the group consisting of
aluminum, copper, silver, gold, chromium, nickel, platinum,
titanium and an alloy thereof.
11. The composite fiber of claim 1, wherein the metal oxide
nanoparticle of the nanofiber web is one or more selected from the
group consisting of manganese dioxide (MnO.sub.2), rubidium dioxide
(RuO.sub.2), and gadolinium oxide (Gd.sub.2O.sub.3).
12. The composite fiber of claim 1, wherein the first and/or second
electrolyte is selected from a gel electrolyte, a solid
electrolyte, a polymer electrolyte, a liquid electrolyte.
13. A method for fabricating a nano/micro composite fiber capable
of storing electrical energy, comprising the steps of (a) wet
spinning an aqueous dispersion of graphene or graphene/carbon
nanotube to prepare a microfiber; (b) bundling the microfibers to
prepare microfiber bundle; (c) wrapping the microfiber bundle with
a nanofiber web to prepare a nano/micro composite fiber, wherein
the nanofiber web is coated with one or more materials selected
from the group consisting of metal, carbon nanotube, activated
carbon, and metal oxide nanoparticle; (d) impregnating the
nano/micro composite fiber with an electrolyte to form an
electrolyte layer; (e) twisting one or more pairs of
electrolyte-coated nano/micro composite fibers; (f) sheathing the
electrolyte-coated nano/micro composite fiber with insulating
material.
14. The method of claim 13, wherein, after the step (a), (b) or
(c), further comprising the step of heating the microfiber at a
temperature between 60.degree. C. and 100.degree. C. under a strong
acid to modify the surface of microfibers.
15. The method of claim 14, wherein the strong acid is selected
from sulfuric acid, nitric acid or hydrochloric acid.
16. The method of claim 14, wherein the heating is performed at a
temperature between 80.degree. C. and 85.degree. C.
17. The method of claim 13, wherein further comprising the step of
impregnating one or more pairs of the electrolyte-coated nano/micro
composite fibers with an electrolyte to form a second electrolyte
later.
18. The method of claim 13, at the step (c) and/or (d) further
performing electrophoreses to penetrate the electrolyte into the
voids of the nano/micro composite fiber by using electrophoresis
method.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a high performance
nano/micro composite fiber capable of storing electrical energy and
a method of fabricating thereof.
TECHNICAL BACKGROUND OF THE INVENTION
[0002] Recently electronic devices have rapidly evolved from rigid
silicon-based electronic devices to flexible electronic devices and
are now evolving from flexible electronic devices to wearable
electronic devices. As it is predicted that the skin-attachable
flexible electronic devices will be spotlighted in the future, a
variety of research studies are conducted to manufacture wearable
devices based on a flexible material as an electrical energy
storage source.
[0003] A fibrous electrical energy storage device does not need to
carry a heavy battery separately because the cloth itself is a
power supply source. It is very useful for daily, industrial, and
military purposes in that it does not interfere with human activity
and also creates high added value. A skin-attachable fiber capable
of storing electrical energy is required to be harmless to the
human body and not to be explosive. Therefore, supercapacitor-based
electrical energy storages are mainly studied for skin-attachable
electronic devices in that supercapacitors are safer and simpler
than lithium secondary batteries.
[0004] Nano carbon materials such as graphene and carbon are very
flexible and electrically conductive, and have high specific
surface area, so these are mainly studied to use as electrodes or
electrode active materials for supercapacitors, sensors, batteries,
actuators and so on. However, the conventional graphene-based
and/or carbon nanotube-based composite fibers were difficult to
satisfy all of the fibrous toughness, mechanical strength and the
electrical energy storage capability such as high electrical
density, power density. A polymer binder, which is added to
increase the bonding force of graphene and carbon nanotube for the
purpose of the improvement of the fibrous mechanical strength,
increases the equivalent series resistance, and decreases the
electrical density and the power density, so the capability of the
electrical energy storage is lowered.
SUMMARY OF THE INVENTION
[0005] In an aspect, the present invention provides a nano/micro
composite fiber capable of storing electrical energy, comprising
(a) one or more pairs of microfiber bundles consisting of graphene
or graphene/carbon nanotube as an electrode active material; (b)
nanofiber web surrounding the microfiber bundles, wherein the
nanofiber web is coated by one or more materials selected from the
group consisting of metal, carbon nanotube, activated carbon and
metal oxide nanoparticle; (c) an electrolyte layer surrounding the
nanofiber web and filling inner void of the microfibers and
nanofiber web; (d) an insulating film sheathing the electrolyte
layer.
[0006] The graphene may be a reduced graphene oxide. The graphene
may have an acid group, preferably a carboxyl group (--COOH), at
the edge or on the surface thereof.
[0007] The carbon nanotube may have a sulfonic acid group
(SO.sub.3.sup.-) on the surface thereof.
[0008] The composite fiber of claim 1, wherein the graphene or
graphene/carbon nanotube microfibers are modified by heating at a
temperature between 60.degree. C. and 100.degree. C., preferably
between 75.degree. C. and 90.degree. C., more preferably between
80.degree. C. and 85.degree. C., most preferably at 84.degree. C.
in the presence of a strong acid. The strong acid can be selected
from sulfuric acid, nitric acid, hydrochloric acid, or a mixed acid
thereof, preferably sulfuric acid. The material of the nanofiber is
polymer.
[0009] The metal of the nanofiber web can be one or more selected
from the group consisting of aluminum, copper, silver, gold,
chromium, nickel, platinum, titanium and an alloy thereof. And the
metal oxide nanoparticle of the nanofiber web can be one or more
selected from the group consisting of manganese dioxide
(MnO.sub.2), rubidium dioxide (RuO.sub.2), and gadolinium oxide
(Gd.sub.2O.sub.3).
[0010] In another aspect, the present invention provides a method
for fabricating a nano/micro composite fiber capable of storing
electrical energy, comprising the steps of (a) wet spinning an
aqueous dispersion of graphene or graphene/carbon nanotube to
prepare a microfiber; (b) bundling the microfibers to prepare
microfiber bundle; (c) wrapping the microfiber bundle with a
nanofiber web to prepare a nano/micro composite fiber, wherein the
nanofiber web is coated with one or more materials selected from
the group consisting of metal, carbon nanotube, activated carbon,
and metal oxide nanoparticle; (d) impregnating the nano/micro
composite fiber with an electrolyte to form a electrolyte layer;
(e) sheathing the electrolyte-coated nano/micro composite fiber
with insulating material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 schematically shows a cross-sectional view of a
nano/micro composite fiber capable of storing electrical energy
according to an embodiment.
[0012] FIG. 2 shows a process diagram of fabricating a nano/micro
composite fiber capable of storing electrical energy according to
an embodiment.
[0013] FIG. 3(a) shows a SEM image of the rGO paper which has been
immersed in 4M aqueous solution of sulfuric acid, and FIG. 3(b)
shows a SEM image of the rGO paper which further was heated at
80.degree. C. after immersion of FIG. 3(a).
[0014] FIG. 4 shows a cyclic voltammetry graph of rGO papers of
FIG. 3(a) and FIG. 3(b), wherein, the internal area of the black
line means the amount of electrical energy storage of rGO paper at
FIG. 3(a), and the internal area of the red line means the amount
of the electrical energy storage of rGO paper at FIG. 3(b).
[0015] FIG. 5(a) shows an average voltammetry capacitance of rGO
electrodes after 4M sulfuric acid treatment and heat treatment
between 20.degree. C. and 90.degree. C., and FIG. 5(b) shows an
average voltammetry capacitance of rGO electrodes after 4M sulfuric
acid treatment and heat treatment at 80.degree. C., 82.degree. C.
and 84.degree. C.
[0016] FIG. 6(a) shows a wet-spun rGO/CNT microfiber through a 30
.mu.m spinning nozzle and FIG. 6(b) shows a wet-spun rGO/CNT
microfiber through a 50 .mu.m spinning nozzle according to an
embodiment.
[0017] FIG. 7(a) shows an image of nanofiber web according to an
embodiment, and FIG. 7(b) shows an image of metal-deposited
nanofiber web, and FIG. 7(c) shows the conductance according to
metal thickness of nanofiber web.
[0018] FIG. 8(a) shows an optical microscope image of a
graphene/CNT composite fiber fabricated according to an embodiment,
and FIG. 8(b) shows an SEM image of cross-section view of FIG.
8(a).
[0019] FIG. 9(a) shows a Galvanostatic charging/discharging graph
of nano/micro composite fiber according to an embodiment and FIG.
9(b) shows a Ragone chart of nano/micro composite fiber according
to an embodiment.
[0020] FIG. 10 shows large scale fabrication of graphene (rGO)
microfiber according to another embodiment (Length of fiber: 80
m).
[0021] FIG. 11 shows high knittability of the rGO microfiber of
FIG. 10.
[0022] FIG. 12 shows high performance supercapacitor which applied
nano/micro composite fiber according to an embodiment.
[0023] FIG. 13 shows high mechanical strength of nano/micro
composite fiber according to another embodiment (weight: 250
g).
DETAILED DESCRIPTION OF THE INVENTION
[0024] This disclosure will be described more fully in the
following detailed description, and with reference to the
accompanying drawings, in which some but not all embodiments of the
disclosure are disclosed. This disclosure may, however, be embodied
in many different forms and is not to be construed as limited to
the exemplary embodiments set forth herein; rather, these
embodiments are provided so that this disclosure will be thorough
and complete, and will fully convey the scope of the invention to
those skilled in the art. Like reference numerals and variables
refer to like elements throughout.
[0025] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an," and "the" are intended
to include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises" and/or "comprising," or "includes," and/or "including"
when used in this specification, specify the presence of stated
features, regions, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, regions, integers, steps, operations,
elements, components and/or groups thereof.
[0026] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs.
[0027] The present invention provides a nano/micro composite fiber
capable of storing electrical energy, comprising (a) one or more
pairs of microfiber bundles consisting of graphene or
graphene/carbon nanotube as an electrode active material; (b)
nanofiber web surrounding the microfiber bundles, wherein the
nanofiber web is coated by one or more materials selected from the
group consisting of metal, carbon nanotube, activated carbon and
metal oxide nanoparticle; (c) an electrolyte layer surrounding the
nanofiber web and filling inner void of the microfibers and
nanofiber web; (d) an insulating film sheathing the electrolyte
layer.
[0028] The present invention provides a method for fabricating a
nano/micro composite fiber capable of storing electrical energy,
comprising the steps of (a) wet spinning an aqueous dispersion of
graphene or graphene/carbon nanotube to prepare a microfiber; (b)
bundling the microfibers to prepare microfiber bundle; (c) wrapping
the microfiber bundle with a nanofiber web to prepare a nano/micro
composite fiber, wherein the nanofiber web is coated with one or
more materials selected from the group consisting of metal, carbon
nanotube, activated carbon, and metal oxide nanoparticle; (d)
impregnating the nano/micro composite fiber with an electrolyte to
form an electrolyte layer; (e) twisting one or more pairs of
electrolyte-coated nano/micro composite fibers; (f) sheathing the
electrolyte-coated nano/micro composite fiber with insulating
material.
[0029] FIG. 1 schematically shows a cross-sectional view of a
composite fiber capable of storing electrical energy according to
an embodiment. FIG. 2 shows a process diagram of fabricating a
nano/micro composite fiber capable of storing electrical energy
according to an embodiment.
[0030] As shown in FIG. 1, the composite fiber of the present
invention, capable of storing electrical energy, comprises a pair
of a microfiber bundles 1, which are consisting of graphene, or the
combination of graphene and carbon nanotube (hereinafter
`graphene/carbon nanotube`). The microfibers of the bundle can be
parallel, twisted or braided structure between microfibers,
preferably twisted or braided structure. The microfiber may have
micropores (voids) on the surface thereof. This micropores may be
formed by add an acid and heating at the particular temperature
condition according to the present invention. Also micropores
(voids) may exist between microfibers. The fiber bundle of the
present invention has high electrical conductivity and specific
surface area and acts as an electrode active material and/or an
electrode of a supercapacitor.
[0031] Meanwhile, another of the main features of the present
invention is that the microfibers of the graphene or
graphene/carbon nanotube is immersed in a strong acid, preferably
dilute sulfuric acid, the heated at a temperature between 60 and
100.degree. C., more preferably between 80.degree. C. and
85.degree. C. to modify the surface of graphene. The capability of
electrical energy storage is remarkably improved by conducting the
above acid and heat treatment. As it is first disclosed in the
present invention, the inventors found that when the graphene was
heated between 80.degree. C. and 85.degree. C. for 1 hour in the 4M
sulfuric acid, the capability of electrical energy storage
increased about 44 times.
[0032] A nanofiber web 2 surrounds the microfiber bundle 1, thereby
the nanofiber 1 and the microfiber 2 are densely in contact with
each other. The material of the nanofiber web 2, which is
comprising polymer, effectively improves the mechanical properties
of the composite fiber of the present invention. The nanofiber web
may preferably have a mesh or non-woven fabric structure. In the
present invention, the surface of the nanofiber web is coated with
a functional material 3 selected from metal, carbon nanotube,
activated carbon, and metal oxide nanoparticle. Because a metal,
carbon nanotube and activated carbon have high electrical
conductivity, these rapidly and effectively transfer the electrons
charged on the microfiber, so improve the energy output density of
the composite fiber of the present invention, and the metal oxide
nanoparticle effectively improves the energy storage density of the
composite fiber of the present invention.
[0033] An electrolyte 4, which acts as dielectric material of
supercapacitor, surrounds the nanofiber web 2. Also this
electrolyte fills micropores (voids) formed on the surface of the
microfiber and between microfibers. The electrolyte is but limited
to a solid electrolyte, gel electrolyte, polymer electrolyte and
liquid electrolyte.
[0034] The filling of electrolyte 4 may be conducted by
impregnating the metal-coated nano/micro composite fiber with
electrolyte solution. Subsequently electrolyte-coated (impregnated)
nano/micro composite fiber may be dried.
[0035] A pair of electrolyte-coated nano/micro composite fiber may
be twisted each other to form the structure of capacitor. As
needed, further filling of electrolyte may be conducted after
twisting the pair of microfiber bundles, to fill voids the between
microfiber bundles.
[0036] An insulating material was coated at the pair of
electrolyte-coated nano/micro composite fibers to form insulating
film.
[0037] Graphene
[0038] In the present invention, the term "graphene" comprises a
reduced graphene oxide (hereinafter "rGO"), which is thermally or
chemically reduced. Also a graphene comprised chemically modified
graphene, chemically modified rGO. The graphene comprises a single
layer of graphene, two layers of graphene, three layers of graphene
or four layers of graphene.
[0039] The term "graphene flake" (hereinafter "GF") means a
fragment of graphene, and the average length of the GF in the
present invention is preferably between 100 and 1,000 nm. The
graphene has high specific surface area and high conductivity,
therefore, it is very suitable of an energy storage device.
[0040] A variety of techniques are well known to produce a graphene
such as Chemical vapor deposition (CVD), Epitaxial growth, Chemical
exfoliation, Non-oxidative exfoliation.
[0041] In the present invention, the method of manufacture a
graphene is but not limited to CVD, Epitaxial growth, Chemical
exfoliation, Non-oxidative exfoliation as described above. When
considering the mass productivity and costs, the Chemical
exfoliation is very useful and provides a GF with the average
length of 100 to 1,000 nm. Therefore, the graphene of the present
invention is preferably the rGO isolated from graphite by chemical
exfoliation and reduced by chemical treatment or heat treatment at
the high temperature. Also the graphene of the present invention
may be chemically modified graphene, chemically modified rGO. In
the cases of graphene/carbon nanotube of the present invention, the
graphene preferably has an acid group at the edge and/or on the
surface thereof in order to chemically bond with the carbon
nanotube. The acid group improves the mechanical properties of the
microfiber by strong hydrogen bonding with a surfactant bonded to
the carbon nanotube. The acid group is preferably carboxyl group
(--COOH), and is effectively hydrogen-bonded to the sulfonic acid
group (SO.sub.3.sup.-) of the modified carbon nanotube.
[0042] A graphene oxide (hereinafter "GO") prepared by the chemical
exfoliation mainly has epoxy group and hydroxyl group on the
graphene surface, and has various functional groups such as
carboxyl group, phenol group, lactone group, ketone group, pyrone
group and lactate group at the edge thereof. Although a GO may be
used in the present invention, a rGO is more useful than GO because
the electrical conductivity of GO is weakened by the presence of
functional groups at the edge or on the surface thereof. A variety
of chemical reduction agents such as hydrazine, hydrazine hydrate,
hydroquinone, sodium borohydride, ascorbic acid and glucose are
already known for the reduction of the GO. The electrical
conductivity of graphene is effectively improved by reduction. It
has been reported that reduction by hydrazine hydrate improves the
electrical conductivity about 26 times in comparison with GO.
Chemical reducing agents such as hydrazine, hydrazine hydrate,
sodium hydride or sodium borohydride effectively remove the epoxy
group and/or the hydroxy group on the surface of the GO, but cannot
effectively remove the carboxyl group or the carbonyl group at the
edge of the GO. Therefore, rGO can be usefully used in the present
invention because the carboxyl group or the carbonyl group of the
rGO effectively bond to the sulfonic acid group (SO.sub.3.sup.-) of
the modified carbon nanotube. When reduction is carried out at high
temperature with concentrated sulfuric acid, the hydroxy group on
the surface of graphene can be effectively removed.
[0043] A graphene or rGO is known difficult to dissolve in water,
whereas GO is known to dissolve and disperse in water since there
are acid groups, especially a carboxyl group, at the edge or
surface as described above. Ultrasonication or surfactants may be
used for effective dispersion.
[0044] Carbon Nanotube
[0045] A carbon nanotube (hereinafter `CNT`) in the present
invention comprise a single-walled carbon nanotube (SWNT), a
double-walled carbon nanotube (DWNT), a multi-walled carbon
nanotube (MWNT). Although a MWNT can be applicable in the present
invention, preferably DWNT, more preferably SWNT is more useful in
consideration of electrical conductivity and mechanical properties.
A CNT is non-polar and poorly soluble in water and polar solvents,
therefore, it is preferable to disperse the CNT in water by using
hydrophilic surfactants and ultrasonication. The surfactant can be
selected from anionic surfactants having hydrophilic sulfonic acid
groups (SO.sub.3.sup.-) such as sodium dodecylbenzenesulfonate
(SDBS), sodium dodecylsulfonate (SDS), sodium lignosulfonate (SLS),
sodium laureth sulfosuccinate (SLES), sodium lauryl ether sulfonate
(SLES), cationic surfactants such as cetyltrimethylammonium bromide
(CTAB), cetyltrimethylammonium chloride (CTAC), cetylpyridinium
chloride (CPC), sodium myreth sulfate, dodecyltrimethylammonium
bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB),
dioctadecyldimethylammonium bromide (DODAB), dimethyl
dioctadecylammonium chloride (DODMAC), nonionic surfactants such as
Tween 20, Tween 40, Tween 60, Tween 80, Triton X-100, glycerol
alkyl esters, glyceryl laurate esters, and polyoxyethylene glycol
sorbitan alkyl esters. In the present invention, it is but not
limited preferably to disperse CNT in water with anionic
surfactants having a hydrophilic sulfonic acid group
(SO.sub.3.sup.-). Also ultrasonication may be helpful to disperse
CNT in water.
[0046] Fabrication of GF/CNT Microfiber
[0047] The diameter of the GF/CNT-based microfibers according to
the present invention is less than 1 mm, preferably several to
several hundreds of micron, and can be fabricated by wet spinning
processes. Wet spinning processes are described at several papers
("Hybrid Nanomembrane for High Power and High Energy Density
Supercapacitors and Their Yarn Application", J. A. Lee et al., ACS
Nano 6, 327-334 (2012)).
[0048] The spinning solution may be prepared in the form of 5 to 30
wt % GF/CNT aqueous dispersion, and CTAB solution at concentration
of 1 mg/mL or 37% hydrochloric acid as coagulation solution can be
used but limited thereto.
[0049] The weight ratio of GF:CNT is preferably in the range of 9:1
to 1:10, more preferably 1:1.
[0050] The spinning solution may be prepared by mixing GF aqueous
dispersion and CNT aqueous dispersion. The GF having an acid group
are easy to disperse in water, but dispersion of the GF can be
improved by adding surfactant and/or ultrasonication. GF without
acid groups are low in water solubility and can be dispersed by
adding the surfactants and/or by ultrasonication as described
above. Since CNT has low water solubility, they can be dispersed by
the above-mentioned surfactant and/or ultrasonication. The CNT is
preferably modified with an anionic surfactant having a sulfonic
acid group (SO.sub.3.sup.-) such as sodium dodecylbenzenesulfonate
(SDBS) or sodium dodecylsulfonate (SDS). In the present invention,
the carboxyl group (--COOH) of the GF and the sulfonic acid group
(SO.sub.3.sup.-) of the CNT can be hydrogen bonded and self-aligned
in the direction of the fiber axis to increase the toughness of
GF/CNT microfiber.
[0051] Nanofiber Web
[0052] The nanofiber web of the present invention is in the form of
mesh structure, a nonwoven fabric having an amorphous fiber
arrangement, and many nanopores are formed between the nanofibers.
The diameter of the nanofibers is less than 1 .mu.m, preferably
several tens to several hundreds of nanometers. Since the nanofiber
web densely surrounds the microfiber bundle, the toughness and
mechanical strength of the nano/micro composite fiber of the
present invention can be effectively increased.
[0053] The nanofibers can be obtained by well-known spinning
methods such as electrospinning, centrifugal electrospinning,
flash-electrospinning electrospray, and electrospinning
spinning.
[0054] The material of the nanofiber is but limited to polyvinyl
alcohol (PVA), polyvinyl pyrrolidone (PVP), polymethyl methacrylate
(PMMA), polymethacrylic acid (PMAA), polyacrylic acid (PAA),
polyvinyl chloride, polylactic acid (PLA), polycaprolactone (PCL),
polyurethane (PU), polystyrene (PS), polyethylene oxide (PEO),
polyvinyl acetate (PVAC), polyacrylonitrile (PAN), nylon,
polyetherimide (PC), polyetherimide (PEI), polyester (PET),
polyester sulfone (PES) and polybenzimidazole (FBI).
[0055] The solvent of the polymer is but limited to
N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO),
dimethylacetamide (DMA), N-methyl-2-pyrrolidinone (NMP),
tetrahydrofuran (THF) not limited thereto, THF, ethylene carbonate
(EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl
methyl carbonate (EMC), propylene carbonate (PC), water, acetic
acid, acetone and so on.
[0056] Coating Material of Nanofiber Web
[0057] In the present invention, the term "coating" is used to mean
including "deposition". The surface of the nanofibers is coated
with a material to improve the electrical properties or electrical
energy storage. The material coated on the nanofiber web is
selected from metals, carbon nanotube, activated carbon, and metal
oxide nanoparticles.
[0058] The coating material may be selected according to the
purpose of the composite fiber of the present invention.
[0059] A metal, carbon nanotube and activated carbon coated on the
nanofiber web improve the energy output density of the composite
fiber of the present invention because these can rapidly and
effectively transfer the electrons charged on the GF/CNT
microfiber. The metal oxide nanoparticle effectively improves the
energy storage density of the composite fiber of the present
invention.
[0060] The metal coated on the nanofiber web is but limited to
aluminum, copper, silver, gold, chromium, nickel, platinum,
titanium or an alloy thereof. The metal can be deposited or coated
on the surface of nanofiber web by metal vapor deposition, metal
particle injection. The metal vapor deposition may be performed by
conventional methods such as Resistive heating evaporation,
Sputtering, Ion plating, Arc deposition, or Ion beam assisted
deposition. The thickness of the metal layer is in the range of 1
nm to 1 .mu.m, preferably in the range of 20 to 500 nm. At an
experiment of the present invention, the thickness of metal layer
is 20 nm or more, the electrical conductivity of the composite
fiber was remarkably improved.
[0061] The metal oxide nanoparticle is but limited to manganese
dioxide (MnO.sub.2), rubidium dioxide (RuO.sub.2), gadolinium oxide
(Gd.sub.2O.sub.3).
[0062] The metal-coated nanofiber web may be cut to an appropriate
width, and spirally wrapped around the microfiber bundle.
[0063] Filling of Electrolyte
[0064] Electrical energy storage occurs at the interface between
the electrolyte and the electrode material. Therefore, the
characteristics of electrolyte as well as the interface area are
very important.
[0065] GF/CNT microfibers of the present invention are very useful
as electrode materials because they have high porosity and specific
surface area. Electrolytes are classified into liquid electrolytes,
gel electrolytes, and solid electrolytes including polymer
electrolytes depending on the material phase. In the present
invention, a gel electrolyte, and a solid electrolyte (including a
polymer electrolyte), liquid electrolyte can be applied as the
electrolyte.
[0066] The gel electrolyte is but not limited to alkaline
electrolytes such as PVA-NaOH and PVA-KOH as well as acidic
electrolytes such as PVA-H.sub.2SO.sub.4, PVA-Na.sub.2SO.sub.4,
PVA-HClO.sub.4, PVA-H.sub.3PO.sub.4, PVA-CN, Pullulan-CN, PEO and
PAN. The solid electrolytes is but not limited to
RbAg.sub.4I.sub.5, zirconium oxide (ZrO.sub.2), sodium beta-alumina
and AgI. The polymer electrolyte may also be applied to the present
invention. The liquid electrolyte is but not limited to acidic
aqueous solutions such as H.sub.2SO.sub.4, HClO.sub.4 and
H.sub.3PO.sub.4, alkaline aqueous solutions such as NaOH and KOH,
organic electrolytes such as TEABF.sub.4/propylene carbonate and
TEABF.sub.4/acetonitrile.
[0067] The electrophoresis of electrolyte may be performed to
rapidly penetrate the electrolyte into the voids of the nano/micro
composite fiber.
[0068] Modification of the Surface of GF or GF/CNT Microfibers by
Heat Treatment in the Strong Acid.
[0069] According to the present invention, when the GF and the CNT
material are heated at a temperature between 60.degree. C. and
100.degree. C., preferably between 75.degree. C. and 90.degree. C.,
more preferably between 80.degree. C. and 85.degree. C., in a
strong acid, preferably dilute sulfuric acid, nitric acid,
hydrochloric acid, more preferably dilute sulfuric acid, the
capability of electrical energy storage is remarkably improved as
the specific surface area increased.
[0070] As it is first disclosed in the present invention, the
inventors found that when the graphene was heated between
80.degree. C. and 85.degree. C. for 1 hour in the 4M sulfuric acid,
the capability of electrical energy storage increased about 44
times.
[0071] FIG. 3(a) shows a SEM image of the rGO paper which has been
immersed for 30 minutes in 4M aqueous solution of sulfuric acid,
and FIG. 3(b) shows a SEM image of the rGO paper which further was
heated at 80.degree. C. for 1 hour after immersion of FIG.
3(a).
[0072] FIG. 4 shows a cyclic voltammetry graph of rGO papers of
FIG. 3(a) and FIG. 3(b), wherein, the internal area of the black
line means the amount of electrical energy storage of rGO paper at
FIG. 3(a), and the internal area of the red line means the amount
of the electrical energy storage of rGO paper at FIG. 3(b). As
shown in FIG. 4, the curve area of the surface-modified graphene
which was heated at 80.degree. C. was increased about 44 times.
[0073] FIG. 5(a) shows an average voltammetry capacitance of rGO
electrodes after 4M sulfuric acid treatment and heat treatment at
20.degree. C., 40.degree. C., 60.degree. C., 70.degree. C.,
80.degree. C. and 90.degree. C. As shown in FIG. 5(a), it was
confirmed that the volumetric capacitance significantly increased
at 70.degree. C., 80.degree. C., and 90.degree. C., and the maximum
peak shows at 80.degree. C.
[0074] As further experiments, FIG. 5(b) shows an average
voltammetry capacitance of rGO electrodes after 4M sulfuric acid
treatment and heat treatment at 80.degree. C., 82.degree. C. and
84.degree. C.
[0075] The acid and heat treatment process of GF or GF/CNT
microfibers may be preferably carried out before the step of
wrapping with the nanofiber web, but it is also useful to carry out
after the wrapping. The ionization of the copper, silver deposited
on the nanofiber web by the sulfuric acid heat treatment after the
wrapping of the nanofibers was found to be insignificant.
[0076] Insulating Film Treatment
[0077] The insulating film of the nanofiber web is to prevent
short-circuiting of the metal layer with the external environment,
leakage of electrolyte, and protection of the core from external
impact. The insulating film can be formed by coating, injecting or
spinning method and can be sheathed by insulating material well
known in the technical art of an electric wire coating.
Embodiment 1
[0078] (1) Production of Graphene/CNT Microfibers
[0079] FIG. 6(a) shows a wet-spun rGO/CNT microfiber through a 30
.mu.m spinning nozzle and FIG. 6(b) shows a wet-spun rGO/CNT
microfiber through a 50 .mu.m spinning nozzle according to an
embodiment.
[0080] An aqueous dispersion of GFs was prepared by followings; The
GFs were obtained by reducing an aqueous dispersion of GOs with
excess hydrazine at 95.degree. C. for 2 hours in accordance with
previously reported methods (Li, D., Muller, M. B., Gilje, S.,
Kaner, R. B. & Wallace, G. G. Processable aqueous dispersions
of graphene nanosheets. Nature Nanotech. 3, 101 (2008)). The GFs
aggregated in the aqueous solution and were transferred to a
funnel, and then were washed with a large amount of Milli-Q water.
The GFs were collected by centrifugation and then the GFs were
effectively dispersed in the water by ultrasonication using 1 wt %
sodium dodecyl benzene sulfonate (SDBS).
[0081] An aqueous dispersion of SWNTs was prepared by
ultrasonication with the surfactant of 1 wt % sodium dodecyl
benzene sulfonate (SDBS) for 30 minutes.
[0082] The aqueous dispersion of GFs and the aqueous dispersion of
SWNTs were mixed to prepare a spinning solution of the GF/CNT.
Then, the spinning solution was slowly and continuously spun
through respectively a 30 .mu.m and 50 .mu.m of spinning nozzle
into CTAB aqueous solution as coagulant, then, was continuously
dipped in distilled water, washed and dried at room temperature to
produce a uniform GF/CNT microfiber.
[0083] (2) Production of Metal-Deposited Nanofiber
[0084] FIG. 7(a) shows an image of nanofiber web according to an
embodiment, and FIG. 7(b) shows an image of metal-deposited
nanofiber web, and FIG. 7(c) shows the conductance according to
metal thickness of nanofiber web.
[0085] Polyvinyl alcohol (PVA), which is a water-soluble polymer,
was added to a mixed solvent of water/ethanol (10:1) in an amount
of 25 wt % and mixed to prepare a PVA spinning solution.
[0086] The PVA spinning solution was transferred to a spinning pack
and subjected to electrospinning under the conditions of an applied
voltage of 15 kV, a spinning distance of 15 cm between the spinning
nozzle and the collector, a spinning rate of 10 .mu.l/min,
30.degree. C. and a relative humidity of 60% to produce nanofiber
web (FIG. 7 (a)). The diameter of the nanofibers was in the range
of 400 to 600 nm, and the average diameter was about 500 nm.
[0087] The metal deposition of the nanofiber web was performed by
resistive heating evaporation. The prepared nanofiber web was
placed in a vacuum chamber, and a tungsten filament as an
evaporation source was attached to a water-cooled evaporation
source holder, and 5 g of silver was charged. The vacuum pump was
operated to evacuate to a vacuum of 8.times.10.sup.-5 torr, and
then argon gas was irradiated on the surface of the nanofiber web
using a plasma generator installed in the vacuum chamber. The
plasma treatment was carried out at 400 W for 1 minute, and the
flow rate of the argon gas was set to 100 sccm (Standard Cubic
Centimeter per Minute). After the cleaning of the nanofiber web was
completed, the reaction was conducted for 30 seconds at an applied
electric power of 8 kW to vaporize the silver to deposit on the
surface of the nanofiber web (FIG. 7 (b)). The thickness of the
silver layer deposited on the nanofiber web was measured to be
about 30 nm.
[0088] As a result of the further embodiment on the thickness of
the metal layer deposition, as shown in FIG. 7 (c), it was
confirmed that the conductance was rapidly increased from the metal
layer of 20 nm or more.
[0089] (3) Wrapping of Microfiber with Metal-Deposited
Nanofiber
[0090] The microfibers prepared in the above (1) were bundled into
several tens of layers and then twisted with an electric motor to
prepare microfiber bundle. The twist angle of the microfibers is
about 30 degrees.
[0091] The metal-deposited nanofiber web prepared in the above (2)
were cut to an appropriate width, and the nanofibers were spirally
wrapped around the microfiber bundle.
[0092] (4) Filling of Electrolyte and Insulating
[0093] The fibers prepared in above (3) were impregnated with a
H.sub.2SO.sub.4/PVA gel electrolyte and then subjected to
electrophoresis so that the aqueous solution of H.sub.2SO.sub.4/PVA
gel electrolyte was effectively penetrated into voids (micropores)
of microfibers and nanofiber webs.
[0094] The composite fiber thus prepared is shown in FIG. 8 (a) is
an optical microscope photograph of a composite fiber produced
according to an embodiment of the present invention, and (b) is an
electron microscope photograph.
[0095] FIG. 9(a) shows a Galvanostatic charging/discharging graph
of nano/micro composite fiber according to an embodiment. As shown
in FIG. 9(a), It was observed that charging/discharging was normal
even though a slight potential drop occurred due to internal
resistance at 2A/g.
[0096] Ragone charts were created to evaluate the energy storage
density and power density of nano/micro composite fiber according
to an embodiment. FIG. 9(b) shows a Ragone chart of nano/micro
composite fiber according to an embodiment. As shown in FIG. 9(b),
it was observed that it has a high output density of about 200
Wh/kg and an energy density of 100 W/kg.
[0097] A pair of GF/CNT composite fibers were twisted, were
furtherly impregnated with a H.sub.2SO.sub.4/PVA gel
electrolyte.
[0098] The electrolyte coated GF/CNT composite fiber was sheathed
by insulating material.
[0099] FIG. 10 shows supercapacitor which applied nano/micro
composite fiber according to an embodiment.
Embodiment 2
[0100] The GF spinning solution was slowly and continuously spun
through respectively a 30 .mu.m of spinning nozzle into CTAB
aqueous solution as coagulant, then, was continuously dipped in
distilled water, washed and dried at room temperature to produce a
uniform GF microfiber.
[0101] FIG. 10 shows large scale fabrication of graphene (rGO)
microfiber according to above embodiment (Length of fiber: 80
m).
[0102] As shown in FIG. 11, the rGO microfiber of FIG. 10 shows
high knittability.
[0103] A nanofiber web was produced by electrospinning with 25 wt %
PVA spinning solution (solvent of water:ethanol=10:1) under the
conditions of applied voltage of 15 kV, a spinning distance of 15
cm between the spinning nozzle and the collector, a spinning rate
of 10 .mu.l/min, 30.degree. C. and a relative humidity of 60%.
[0104] Silver was deposited on the nanofiber web by resistive
heating evaporation. The thickness of the silver layer deposited on
the nanofiber web was measured to be about 30 nm.
[0105] The rGO microfibers prepared in the above were bundled into
several tens of layers and then twisted with an electric motor to
prepare microfiber bundle. The twist angle of the microfibers is
about 30 degrees.
[0106] The silver-deposited nanofiber web prepared in the above (2)
were cut to an appropriate width, and the nanofibers were spirally
wrapped around the microfiber bundle.
[0107] The silver-deposited nano/micro composite fibers prepared in
the above were impregnated with a H.sub.2SO.sub.4/PVA gel
electrolyte and then subjected to electrophoresis so that the
aqueous solution of H.sub.2SO.sub.4/PVA gel electrolyte was
effectively penetrated into voids (micropores) of microfibers and
nanofiber webs.
[0108] PVC as insulating material was sheathed the
electrolyte-coated and silver-deposited nano/micro composite
fibers.
[0109] FIG. 12 shows high performance supercapacitor which applied
nano/micro composite fiber according to the embodiment.
[0110] FIG. 13 shows high mechanical strength of nano/micro
composite fiber according to the embodiment (weight: 250 g).
* * * * *