U.S. patent application number 10/397861 was filed with the patent office on 2003-11-20 for fibrous articles and electrode systems.
Invention is credited to Huang, Yuhong, Wei, Qiang, Zheng, Haixing.
Application Number | 20030215718 10/397861 |
Document ID | / |
Family ID | 24920989 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030215718 |
Kind Code |
A1 |
Huang, Yuhong ; et
al. |
November 20, 2003 |
Fibrous articles and electrode systems
Abstract
An apparatus including a body having dimensions suitable as an
electrode component of an electrical storage device, the body
having a fibrous form comprised of a moiety of the general formula:
(M.sub.a).sub.x(Y.sub.b).sub.y, wherein M is one or more metals
(i.e., a is greater than or equal to one) selected from Groups IV
through IX of the Periodic Table of the Elements. Examples include,
but are not limited to, ruthenium, iridium, and manganese. Y
includes one or more heteroatoms (i.e., b is greater than or equal
to one) selected from oxygen, nitrogen, carbon, and boron.
Subscripts x and y represent the valence state of the cation and
anion, respectively.
Inventors: |
Huang, Yuhong; (West Hills,
CA) ; Wei, Qiang; (West Hills, CA) ; Zheng,
Haixing; (Oak Park, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
24920989 |
Appl. No.: |
10/397861 |
Filed: |
March 25, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10397861 |
Mar 25, 2003 |
|
|
|
09727018 |
Nov 28, 2000 |
|
|
|
6551533 |
|
|
|
|
Current U.S.
Class: |
429/235 ;
429/245 |
Current CPC
Class: |
C04B 2235/3289 20130101;
H01G 9/155 20130101; H01G 11/46 20130101; C04B 35/62231 20130101;
H01G 11/24 20130101; H01G 11/30 20130101; C04B 30/02 20130101; C04B
35/62259 20130101; C04B 35/6365 20130101; H01G 11/86 20130101; D01F
9/10 20130101; Y02E 60/13 20130101; C04B 30/02 20130101; C04B 14/46
20130101; C04B 14/4606 20130101; C04B 41/455 20130101; C04B 30/02
20130101; C04B 14/46 20130101; C04B 41/455 20130101; C04B 2103/0067
20130101 |
Class at
Publication: |
429/235 ;
429/245 |
International
Class: |
H01M 004/80; H01M
004/66 |
Goverment Interests
[0002] This invention was made with Government support under
contract DASG60-00-M-0148 awarded by the U.S. Army Space and
Missile Defense Command. The Government has certain rights in the
invention.
Claims
What is claimed is:
1. An apparatus comprising: a body having dimensions suitable as an
electrode component of an electrical storage device, the body
having a fibrous form comprised of a moiety of the general formula:
(M.sub.a).sub.x(Y.sub.b).sub.y, wherein M is a metal selected from
at least one of Groups IV through IX of the Periodic Table of the
Elements, wherein a is greater than or equal to one, wherein Y
includes a heteroatom selected from one of oxygen, nitrogen,
carbon, and boron, wherein x is the valence state of the cation,
and wherein y is the valence state of the cation.
2. The apparatus of claim 1, wherein M is selected from the group
consisting of molybdenum, tungsten, hafnium, zirconium, ruthium,
iridium, and manganese.
3. The apparatus of claim 1, wherein the body comprises a plurality
of fibers, each fiber comprising the moiety.
4. The apparatus of claim 3, wherein the plurality of fibers are
combined in a weave.
5. An apparatus comprising: a first electrode and a second
electrode disposed in a cell; and an electrolyte in fluid contact
with the first and second electrode, wherein each of the first
electrode and the second electrode comprises a body having a
fibrous form comprised of a moiety of the general formula:
(M.sub.a).sub.x(Y.sub.b).sub.y, wherein M is a metal selected from
at least one of Groups IV through IX of the Periodic Table of the
Elements, wherein a is greater than or equal to one, wherein Y
includes a heteroatom selected from one of oxygen, nitrogen,
carbon, and boron, wherein x is the valence state of the cation,
and wherein y is the valence state of the cation.
6. The apparatus of claim 5, wherein M is selected from the group
consisting of molybdenum, tungsten, hafnium, zirconium, ruthium,
iridium, and manganese.
7. The apparatus of claim 5, wherein the body comprises a plurality
of fibers, each fiber comprising the moiety.
8. The apparatus of claim 7, wherein the plurality of fibers are
combined in a weave.
Description
[0001] This is a divisional of U.S. patent application Ser. No.
09/727,018 filed on Nov. 28, 2000, entitled "Fibrous Electrode
Materials".
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention generally relates to the field of methods for
and products of manufacturing component parts in energy storage
devices and more particularly, to high surface area electrodes for
supercapacitor applications.
[0005] 2. Description of Related Art
[0006] In general, electrochemical capacitors are capacitive energy
storage devices based on double-layer capacitance or
pseudocapacitance. The potential, power density and cycle life of
electrochemical capacitors are generally two orders of magnitudes
higher than those of rechargeable batteries. As compared with
batteries, electrochemical capacitors can be characterized as
having low energy density, high power density and a high cycle
life. Further, in an electric circuit, an electrochemical capacitor
behaves more like a classic dielectric capacitor than a battery,
hence its name.
[0007] The requirement of high energy and power density of an
electrochemical capacitor intrigues development in miniaturization
and weight reduction. The component parts of an electrochemical
capacitor generally include at least two electrodes, electrolyte,
and a separator. The material of the electrode is typically a key
element. One approach to increase energy and power density of an
electrochemical capacitor is to increase the accessible surface
area of the electrodes. Generally, the pore size of the electrode
material must be large enough to allow electrolyte access into the
pores, yet small enough to provide a high surface area per volume
or per weight of the electrode material. Lowering the internal
resistance (e.g., resistivity of the electrode material or
interface resistance between electrode constituents) of the
electrode material is also a key point toward increasing
conductivity and power density of electrode materials. A contact
resistance between an electrode and the electrolyte and/or current
collector can also increase the resistance of the capacitor.
[0008] There are four basic types of electrode materials for
electrochemical capacitor applications. Activated carbon or foam
represents one type of electrode material, as disclosed by U.S.
Pat. No. 5,601,938. Typical capacitance obtained from an electric
double layer is in the range of about 20-40 mF/cm.sup.2.
[0009] Certain transition metal oxides such as rubidium oxide
(RuO.sub.2) and iridium oxide (IrO.sub.2) possess pseudocapacitance
thus rendering metal oxides as a candidate for a second type of
electrode material. Pseudocapacitance arises from highly reversible
reactions, such as oxidation-reduction ("redox") reactions, which
occur at or near the electrode surfaces. Capacitance of 150-200
mF/cm.sup.2 have been observed for RuO.sub.2 films. A specific
capacitance of 380 F/g has been reported using high temperature
thermal treatment and 720 F/g with low temperature thermal
treatment. Low temperature treatment generally forms amorphous
hydra-ruthenium oxide, which tends to crystallize at temperatures
above 100.degree. C. Ruthenium electrode material also tends to be
relatively expensive. In order to reduce the cost of the expensive
ruthenate electrode materials, bi-metal oxides or tri-oxides were
studied, such as lead ruthenate systems having a formula
A.sub.2[B.sub.2-xPb.sub.x]O.sub.7- -y, where A is lead (Pb) or
bismuth (Bi); B is ruthenium (Ru) or iridium (Ir); x is greater
than zero and less than or equal to one; and y is greater than zero
and less than 0.5 as disclosed by U.S. Pat. No. 5,841,627.
[0010] The third type of electrode material is metallic bodies
which are mechanically- or chemically-etched to provide a roughened
surface and a high specific surface area, as disclosed by U.S. Pat.
No. 5,062,025. High surface area metal electrodes are limited by
electrochemical stability. Metals are generally unstable in
oxidizing environments, therefore their use is generally limited to
the positive, reducing electrode or anode.
[0011] The fourth type of electrode material is metal nitride.
Metal nitrides are generally conductive and exhibit
pseudocapacitance. Molybdenum nitride, for example, as pointed out
at the Seventh International Seminar on "Double Layer Capacitors
and Similar Energy Storage Devices, Dec. 8-10, 1997, Deerfield
Beach, Fla., exhibits high energy density.
[0012] In addition to the different types of electrode materials,
it has been found that the electrical performance of devices based
on electrodes of consolidated powders is often limited by
inter-particle electrical resistance (e.g., internal resistance),
and this requires addition of conductivity-enhancing additives such
as metal fibers which are themselves generally not capacitive.
Consolidated powders typically have a lower powder density per unit
weight of capacitor. U.S. Pat. No. 4,562,511 discusses carbon fiber
electrodes. The mechanical strength of the electrode is high, and
small type capacitors in various shapes are obtainable, furthermore
capacitance per unit volume can be made relatively large and
internal resistance and leakage current can be made relatively
low.
[0013] It is desirable to provide a new type of electrode material
with improved mechanical strength, reduced internal resistance and
leakage current, and increased capacitance per unit volume. It is
also desirable that the new type of electrode material possess high
surface area and a desirable pore size.
SUMMARY
[0014] The invention relates to an apparatus suitable as an
electrode in an energy storage device, including an electrochemical
capacitor. The apparatus comprises a body having a fibrous form
comprised of a moiety of the general formula:
(M.sub.a).sub.x(Y.sub.b).sub.y,
[0015] wherein M is one or more metals (i.e., a is greater than or
equal to one) selected from Groups IV through IX of the Periodic
Table of the Elements. Examples include, but are not limited to,
ruthenium, iridium, and manganese. Y includes one or more
heteroatoms (i.e., b is greater than or equal to one) selected from
oxygen, nitrogen, carbon, and boron. Subscripts x and y represent
the valence state of the cation and anion, respectively. The
invention further relates to an apparatus such as an energy storage
device. In one embodiment, an energy storage device includes an
electrolyte between two electrodes of fibrous material. Advantages
of the device described or as formed herein in terms of electrode
properties and performance compared generally to prior art devices
include: (1) reduced internal resistance and leakage current of the
supercapacitive device, therefore improving power density; (2)
increased specific surface area of fibrous electrode material,
therefore higher energy density; (3) enhanced mechanical strength
of the electrode, therefore lowering the contact resistance.
[0016] Additional features, embodiments, and benefits will be
evident in view of the figures and detailed description presented
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The features, aspects, and advantages of the invention will
become more thoroughly apparent from the following detailed
description, appended claims, and accompanying drawings in
which:
[0018] FIG. 1 is a schematic flow of forming a body of fibrous
material according to an embodiment of the invention.
[0019] FIG. 2 is a schematic top side perspective view of a body
that is an electrode according to an embodiment of the
invention.
[0020] FIG. 3 is a schematic side view of an electrical storage
device according to an embodiment of the invention.
[0021] FIG. 4 is a schematic side view of an electrical storage
device of a bipolar ultracapacitor.
DETAILED DESCRIPTION
[0022] In one embodiment, a method is disclosed. The method
comprises synthesizing polymeric precursors via organic acid
modification and fabricating a fibrous material of the polymeric
precursors. The fibrous material is then fabricated into a body of
fibrous material. The method of making these fibrous electrode
materials include forming whiskers, fibers, clothes, and other
collections assembled in the form of fiber electrodes. The method
is suitable for forming electrodes for electrical storage devices
such as electrodes for electrochemical cells. Such electrical
storage devices generally have both a high energy and a high power
density with the use of fibrous electrode materials. Such fibrous
electrode materials (e.g., nanostructure electrode materials) in
electrical storage device applications also show reduced resistance
properties both internally (e.g., resistivity and interface
resistance between electrode constituents) and externally (e.g.,
contact resistance) are disclosed with improved mechanical
strength.
[0023] In another embodiment, an apparatus suitable as an electrode
for electrical storage device applications, including
electrochemical storage devices, is disclosed. The apparatus
includes a body having dimensions suitable as an electrode
component of an electrical storage device. The body is composed of
a moiety of the general formula:
(M.sub.a).sub.x(Y.sub.b).sub.y,
[0024] wherein M is one or more metals (i.e., a is greater than or
equal to one) selected from Groups IV through IX of the Periodic
Table of the Elements. Examples include, but are not limited to,
ruthenium, iridium, and manganese. Y includes one or more
heteroatoms (i.e., b is greater than or equal to one) selected from
oxygen, nitrogen, carbon, and boron. Subscripts x and y represent
the valence state of the cation and anion, respectively. A
plurality of such moieties are linked in a fibrous form through the
modification of a polymeric fiber to form the body. Such fibrous
forms include, but are not limited to, a collection of whiskers,
partial or continuous fiber weaves, clothes, or other collections
assembled to form the electrode.
[0025] Suitable nanostructure electrode materials include nitrides,
carbonitrides, oxycarbonitride and/or oxides and methods of
fabrication thereof for supercapacitor applications. The electrodes
disclosed have reduced internal resistance and leakage current.
Such electrodes also offer high mechanical strength which may yield
large capacitance per unit volume. One characteristic with respect
to fibrous oxides, nitrides, oxynitrides and oxycarbonitrides
electrodes according to the invention is reduced resistance.
Resistance may be divided into individual components. A contact
resistance, R.sub.1, between a current collector and electrode; a
resistance, R.sub.2, attributable to the electrode material itself
(e.g., resistivity of electrode material); an interface resistance,
R.sub.3, between the constituents (e.g., particles) of the
electrode; and a resistance, R.sub.4, attributable to the
electrolyte (e.g., the resistivity of the electrolyte material).
The fibrous electrode of the invention show at least a reduced
interface resistance, R.sub.3. The contact resistance, R.sub.1, may
also be reduced due to the higher mechanical strength of the
fibrous electrode material, therefore permitting the application of
higher pressure to compress the electrode and thereby improve the
contact between electrode and current collector.
[0026] In one embodiment, the invention relates to a method for
making and product of nanostructure porous fibrous materials with
high specific surface area by utilizing a sol-gel related
technology. In one sol-gel process, a precursor solution is
subjected to hydrolysis, condensation and polymerization to yield a
nanostructure gel. The structure of the gel can be built by
controlling the coordination through the electrophillicity of the
ligand.
[0027] In another embodiment, the invention relates to a method for
making and product of nanostructure porous fibrous materials with
high specific surface area by amine polymerization. In one process,
a precursor solution is subjected to aminolysis to form a
polymer.
[0028] FIG. 1 illustrates a representative process flow for forming
a body of fibrous material according to an embodiment of the method
of the invention. Referring to block 110, in a first embodiment,
polymeric precursors are prepared by modifying precursor solutions
with unhydrolyzed organic acid or other organic ligands. In one
example, metal alkoxides are condensed with unhydrolyzed organic
acids, esters, or other organic ligands. Suitable metal alkoxides
include those of the general formula M(OR).sub.x, where M is
selected from one or more metals (e.g., double alkoxides) from the
Groups IV through IX of the Periodic Table of the Elements, such as
rubidium (Ru), iridium (Ir), and manganese (Mn); R is an alkyl
group, having for example, one to eight carbon atoms or carbon atom
equivalents; and x is equal to the valence state of the cation.
Suitable organic acids include, but are not limited to,
2-ethylhexanoic acid (2-EHA), benzoic acid. Organic esters are also
suitable and include, but are not limited to,
o-xylene-.alpha.,.alpha.'-d- iacetate.
[0029] The contemplated alkoxides, when combined with the organic
acid, ester or other ligand and optionally water undergo hydrolysis
and condensation reactions to form a polymeric network. The organic
acid ligand, for example, can be used to hydrolyze the alkoxide and
also a chelating agent to link alkoxides together to form a
generally non-hydrolyzable chelation bonded polymeric network.
Suitable mole ratios of alkoxide to organic acid to water include
n:1:0.3 to n:(n-2):1, where n is the valence of the metal. A
general representation is: 1
[0030] Reaction (1) shows the reaction between the alkoxide and the
organic acid and, optionally, the alkoxide and water. Combining the
products of reaction (1) produces a polymeric precursor (e.g., a
monomer) in reaction (2). The polymeric precursor contains
hydrolyzable moieties for further polymerization (the terminal
"--OR"), and a non-hydrolyzable moiety represented by the
pseudo-carbonyl.
[0031] In a second embodiment, polymeric precursors are formed by
aminolysis. In one example, metal alkylamides undergo aminolysis by
reaction with an amine. Suitable metal alkamides include those of
the general formula M((N.sub.wC.sub.x)R.sub.y).sub.z, where M is
selected from metals from the Groups IV, V, and VI of the Periodic
Table of the Elements, rubidium (Ru), iridium (Ir), and manganese
(Mn); R is an alkyl group having, for example, one to eight carbon
atoms or carbon atom equivalents; w is one to four; x is zero to
three; y is the number of alkyl groups bonded to each nitrogen
and/or carbon; and z is the valence state of the cation. Suitable
amines are of the general formula R'NH.sub.2, where R' includes,
but is not limited to, an alkyl of one to eight carbon atoms or
carbon atom equivalents.
[0032] The contemplated metal alkylamides, when combined with the
amine, preferably in the absence of moisture or oxygen to
discourage hydrolysis, undergo aminolysis to form the polymeric
precursor (e.g., monomer) and a polymeric network. A general
representation is: 2
[0033] Upon forming the polymeric precursors, block 120 shows that
such polymeric precursors may be fabricated into fibrous material,
typically by extrusion or spinning. The fibrous material may be
short whiskers on the order of a few to several hundred microns to
a continuous weavable single strand fiber.
[0034] Referring to block 130 in FIG. 1, the fibrous material is
transformed into a body of fibrous material suitable for use as an
electrode for use in an electrical storage device. In one approach,
"green" fibrous materials formed of polymeric precursors through a
sol-gel process or aminolysis are dispersed in a cellulose matrix
in preparing the body of fibrous materials. The approach is
analogous to that described in U.S. Pat. Nos. 5,080,963; 5,096,663;
and 5,102,745. The green fibrous materials are dispersed in a fluid
medium along with cellulose acting as a binder and matrix for the
fibrous materials. The resulting dispersion is then cast into a
predetermined shape. One purpose of the cellulose is to permit the
fabrication of a solid preform of an otherwise structurally
unstable dispersion of fibrous material where the preform can be
shaped, stored, and otherwise handled prior to subsequent
processing. The cellulose provides a stable, although relatively
weak, physical structure which maintains the spatial relationship
of the dispersed fibrous materials. Cellulose, in its forms and
modifications, is a desirable matrix material because it may be
completely volatilized at relatively low temperatures with little
ash formation, is generally unreactive toward other components in
the preform, and is readily available. Cellulosic materials
typically used in the paper-making process are suitable. A person
of skill in the art will recognize the elements of the paper-making
process in the foregoing description.
[0035] After the dispersion of high surface area fibrous materials
and cellulose in a liquid is attained, the solids are collected, as
on a mat. Excess liquid may be removed, such as by pressing, and
the resulting solid dispersion is dried (e.g., liquid is removed)
to form a body of fibrous material, especially where it is to be
stored prior to further treatment. The drying process may be
performed in air, under elevated temperatures, or in a flowing gas.
The mass also may be compacted under pressure to a greater or
lesser extent. The dispersion may be cast into a predetermined
shape prior to, coincident with, or after drying. It may be
desirable to cast the dispersion into sheets which can then be
rolled up and stored prior to subsequent treatment. The fibrous
content of the dry preform may be as low as about 50 weight percent
and as high as about 95 weight percent, although typically it will
range from about 90 to about 95 weight percent.
[0036] In a second approach, fibrous materials formed of polymeric
precursors through a sol-gel or aminolysis process are directly
pressed, or cast into a sheet, or woven into cloths constituting
the body in the absence of a preform, or binder, or matrix. The
green sheet or cloths are then subjected to a heat treatment in
controlled atmosphere or in air.
[0037] Referring to block 140 of FIG. 1, following drying of the
body of polymeric fibrous materials, the body is subjected to a
sintering process. The sintering process converts a portion,
including the entire portion, of the polymeric fibrous material of
the body from an organic material to a substantially inorganic
material. A suitable sintering process is performed in gaseous
ambient, such as, for example, in the presence of oxygen and/or
nitrogen for 5 to 20 hours. In one embodiment, the temperature is
slowly stepped toward the final desired temperature, residing at
the final temperature for 4 to 6 hours. The sintering converts the
polymeric fiber to moieties of fiber-like units of generally
inorganic (e.g., metal-heteroatoms) of oxides, nitrides,
oxynitrides or oxycarbonitrides with desired crystallographic
phases, which can be amorphous or crystalline.
[0038] By controlling the sintering atmosphere, oxide, carbide,
oxycarbide and oxycarbonitride materials can be obtained. Oxide can
be obtained by sintering air. Carbide and oxycarbide can be formed
in N.sub.2/H.sub.2 atmosphere or in methane. Ammonia gas will
promote the formation of the oxynitride, oxycarbonitride and
nitride.
[0039] Sintering at a low temperature (e.g., 200.degree. C. to
400.degree. C.) produces a generally amorphous phase fiber while
sintering at temperatures than 400.degree. C. (e.g., 700.degree. C.
to 900.degree. C.) produces a generally crystalline phase fiber.
Crystalline phase fibers generally have a decreased surface area
and higher conductivity compared to amorphous phase fibers.
[0040] In addition to rendering the fibrous material generally
inorganic, the sintering process also renders the material porous.
In the example of an alkoxide-based polymeric precursor shown as
the product of reaction (2), the pseudo-carbonyl gives up its
oxygen atom during sintering leaving voids in the network.
Similarly, in the alkamide-based polymeric precursor shown as the
product of rection (4), the amine gives up its alkyl constituent R'
during sintering leaving voids in the network.
[0041] FIG. 2 shows a body of the inorganic fiber material. Body
150 in this example is formed in the shape of an electrode suitable
in an electrical storage device including an electrochemical device
(e.g., electrochemical capacitor). It is to be appreciated that the
size and dimensions of any such electrode will primarily depend on
the scale of the electrical storage device and the suitable
applications of an electrode as described herein should not be
limited.
[0042] Referring to FIG. 2, body 150 is comprised of a plurality of
fibers 155 wound, weaved, or otherwise collected. Fibers 155 are
compressed to reduce the internal resistance of body 150 (R.sub.2).
In one example, a collection of weaved fiber materials or a single
woven fiber material strand is assembled into a body of 0.5 inches
and 0.1 grams of electrode materials is compressed by the
application of approximately 2,000 pounds per square inch
(psi).
[0043] FIG. 3 shows an electrical storage device that is an
electrochemical device. Electrochemical device 200 includes
electrodes 150A and 150B disposed in a cell and separated by
separator 230. Electrochemical device 200 also includes electrolyte
220. One example is an electrochemical cell in which an electrical
current is produced by chemical reactions. Effecting a chemical
change by passing an electrical current or electrolysis are induced
by application of a direct current of electricity.
EXAMPLE 1
Synthesis of Spinable Polymer Precursors for Titanium Oxide or
Oxycarbonite
[0044] Polymer precursors are formed by reacting titanium alkoxide
with certain cross-linking agents. One example uses titanium
isopropoxide, and the cross-linking organics of
o-xylene-.alpha.,.alpha.'-diacetate, 2-ethylhexanoic acid (2-EHA),
benzoic acid, or other organic acids.
[0045] The carboxylic or carboxolate ligand hydrolyzes the titanium
alkoxide and acts as a chelating agent to link titanium alkoxide
molecules together. A small amount of water is added to hydrolyze
the remaining alkoxide ligands to form a polymeric titanate. Using
benzoic acid as the cross-linking organic acid the reactions and
polymer structure may be represented as follows: 3
[0046] In the above representation, a suitable mole ratio of
titanium alkoxide, benzoic acid, and water is 1:1:0.3.
[0047] Titanium isopropoxide is dissolved into isopropanol,
followed by adding diluted benzoic acid in isopropanol under the
stirring. The solution is heated to 80.degree. C. and refluxed
overnight. Water is then introduced and the solution refluxed for
another two hours. The solution is then heated to 130 to
150.degree. C. under vacuum to remove solvent and form the spinable
polymeric precursor. The viscosity can be further adjusted by
changing solvent content.
EXAMPLE 2
Fiber Made by Extrusion Process
[0048] Fibers obtained from spinning process are homogenous in
diameter. Continuous fibers become possible by an extrusion
process. Fiber formation is possible when viscosity of the solution
is between about 1 to 100 Pa-s. Solvent content and also the
extrusion temperature can adjust the viscosity of the polymeric
precursor. The diameter of the green fiber can be controlled by
orifice diameter, extrusion rate and pick-up rate.
[0049] The extruded green fiber can be cured by at least two
methods: UV-curing and thermal-curing. Fibers cured at 254 mm
UV-light with 320 .mu.m/cm.sup.2 intensity for 8 hours showed a
sufficient cross-linking reaction. The green fiber is cured also at
180 to 250.degree. C. in air for 8 to 12 hours. After curing, the
green fiber is converted from thermal plastic to thermal set.
[0050] The cured fiber can be sintered at a high temperature and
the shape maintained. By controlling the sintering temperature,
amorphous or crystalline phase fibrous structures can be
obtained.
EXAMPLE 3
High Power Density Supercapacitor by Using Ruthenium Oxide Fibers
as Electrodes
[0051] Procedure for Making Ruthenium Alkoxide and Polymer.
[0052] Dissolve strictly anhydrous ruthenium chloride in proper
amount of tolunene. Sodium metal is added to excess alcohol (e.g.,
ethanol, isopropanol) to produce sodium alkoxide. Then three
equivalent sodium alkoxide is added to ruthenium chloride under
stirring. Heat and precipitation is resulted after the addition.
The precipitate which is sodium chloride can be removed either by
filtration or centrifuge. The reaction equation is shown as below.
1 Na + ROH -- NaOR + H 2 NaOR + RuCl 3 -- Ru ( OR ) 3 + NaCL ( R =
C 2 H 5 - , C 3 H 7 - ) Na + ROH + RuCl 3 Ru ( OR ) 3 + NaCl
[0053] Ruthenium alkoxide from procedure A is modified with
acetylacetone (aca) and/or 2-ethyl hexanoic acid (2-EHA) before
hydrolysis and polycondensation. The molar ratio of aca and 2-EHA
to ruthenium is about 0.5 to 2. After modification, water is added
at a molar ratio of about 05. to 1 and the solution is heated and
refluxed for about 3 hours. After the polymer has been obtained,
most of the solvent was removed by heating in vacuo until the
viscosity reaches an empirical value of 4 cm/min. at which the
polymer flowed from top to bottom of a vial.
[0054] Fiber Drawing and Pyrolysis:
[0055] Polymeric fiber is fabricated by using both hand drawing and
spinnete extruding. The obtained fiber is cured in an oven for
strengthening to avoid a large shape change in the later high
temperature furnace and heat treated in air at 550.degree. C. for
more than three hours to burn off the organic content.
[0056] Fabrication of Ultracapacitor
[0057] A schematic of an ultracapacitor is shown in FIG. 4.
Ultracapacitor 300 is configured in a bipolar construction.
Ultracapacitor 300 includes six capacitors 310A, 310B, 310C, 310D,
310E, and 310F, each with an electrode area of 1 to about 2.85
cm.sup.2. Ruthenium oxide fibers were used as the electrode
material, and 2.5 M to about 4.5 M sulfuric acid was used as the
electrolyte. Current collector 320 in one embodiment is a 0.25 mm
thick Ti foil. Glass fiber filter disks 325A, 325B, and 325C are
used as the separators. The stack was sealed inside Teflon cylinder
330 with rubber o-rings 340 and aluminum end plates 350 and
360.
[0058] In the preceding detailed description, the invention is
described with reference to specific embodiments thereof. It will,
however, be evident that various modifications and changes may be
made thereto without departing from the broader spirit and scope of
the invention as set forth in the claims. The specification and
drawings are, accordingly, to be regarded in an illustrative rather
than a restrictive sense.
* * * * *