U.S. patent application number 09/805921 was filed with the patent office on 2002-04-25 for supercapacitor using electrode of new material and method of manufacturing the same.
Invention is credited to An, Kay-hyeok, Lee, Young-hee, Yoo, Jae-eun.
Application Number | 20020048143 09/805921 |
Document ID | / |
Family ID | 19663804 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020048143 |
Kind Code |
A1 |
Lee, Young-hee ; et
al. |
April 25, 2002 |
Supercapacitor using electrode of new material and method of
manufacturing the same
Abstract
A supercapacitor using an electrode formed of a new material is
provided. The supercapacitor includes two electrodes facing each
other, the electrodes being composed of carbon nanotubes, an
electrolyte provided between the two electrodes, and a separator
for separating the electrolyte between the two electrodes.
Inventors: |
Lee, Young-hee;
(Chonju-city, KR) ; An, Kay-hyeok; (Chonju-city,
KR) ; Yoo, Jae-eun; (Seoul, KR) |
Correspondence
Address: |
Charles F. Wieland lll
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
19663804 |
Appl. No.: |
09/805921 |
Filed: |
March 15, 2001 |
Current U.S.
Class: |
361/502 ;
29/25.03 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01G 11/28 20130101; H01G 11/36 20130101; Y10S 977/948 20130101;
Y02E 60/13 20130101; H01G 9/155 20130101; Y02T 10/70 20130101; H01G
11/86 20130101 |
Class at
Publication: |
361/502 ;
29/25.03 |
International
Class: |
H01G 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2000 |
KR |
2000-19232 |
Claims
What is claimed is:
1. A supercapacitor comprising: two electrodes facing each other,
the electrodes being composed of carbon nanotubes; an electrolyte
provided between the two electrodes; and a separator for separating
the electrolyte between the two electrodes.
2. The supercapacitor of claim 1, wherein the carbon nanotubes are
single-wall carbon nanotubes.
3. The supercapacitor of claim 1, wherein the carbon nanotubes are
multi-wall carbon nanotubes.
4. The supercapacitor of claim 1, wherein each of the electrodes is
formed in a pallet pattern by molding the carbon nanotubes mixed
with a bonding agent.
5. The supercapacitor of claim 1, wherein each of the electrodes is
formed of carbon nanotubes which are vertically grown on respective
collectors.
6. The supercapacitor of claim 1, wherein the carbon nanotubes are
activated by a solution containing potassium hydroxide.
7. The supercapacitor of claim 1, wherein the carbon nanotubes are
electrolessly plated with nickel.
8. The supercapacitor of claim 1, wherein Raney nickel is applied
to the carbon nanotubes.
9. A method of manufacturing a supercapacitor, the method
comprising the steps of: preparing two electrodes which are
composed of carbon nanotubes; and providing a separator and an
electrolyte between the two electrodes.
10. The method of claim 9, wherein the carbon nanotubes are
single-wall carbon nanotubes.
11. The method of claim 9, wherein the carbon nanotubes are
multi-wall carbon nanotubes.
12. The method of claim 9, wherein the step of preparing each of
the electrodes comprises the steps of: molding the carbon nanotubes
mixed with a bonding agent into a pallet pattern; and attaching the
pallet pattern of the carbon nanotubes to a collector.
13. The method of claim 9, wherein the step of preparing each of
the electrodes comprises vertically growing the carbon nanotubes on
a collector.
14. The method of claim 13, wherein the carbon nanotubes are
vertically grown using a thermal chemical deposition method or a
microwave plasma chemical deposition method.
15. The method of claim 9, further comprising the step of
activating the carbon nanotubes using a solution containing
potassium hydroxide.
16. The method of claim 15, wherein the activation step comprises
the steps of: dipping the carbon nanotubes in the solution
containing potassium hydroxide; drying the carbon nanotubes; and
thermally treating the dried carbon nanotubes.
17. The method of claim 16, wherein in the thermal treatment step,
the carbon nanotubes are thermally treated at a temperature of
about 750-800.degree. C. in an inert gas atmosphere.
18. The method of claim 9, further comprising the step of
electrolessly plating the carbon nanotubes with nickel.
19. The method of claim 9, further comprising the steps of
uniformly applying Raney nickel on the carbon nanotubes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a capacitor device, and
more particularly, to a supercapacitor formed of new material
having the characteristics of high capacitance and high power.
[0003] 2. Description of the Related Art
[0004] Batteries are usually used as energy storage devices for
systems such as portable electronic equipment and electric
automobiles requiring an independent power supply unit or systems
which adjust instantaneously occurring overload or supply energy.
However, approaches of using capacitors instead of batteries have
been attempted to improve the input and output characteristics of
stored electric energy in terms of electric power, that is, in
terms of input and output of energy.
[0005] Capacitors have better input and output characteristics of
stored electric energy than batteries and are semipermanent such
that they may be reused a considerably greater number of times,
i.e., more than one hundred thousand times, than the average number
of times, i.e., 500 times, which batteries are usually used.
Representative conventional capacitors, i.e., condensers, have
capacitance on the order of only .mu.F or pF, so they are
restrictively limited. Due to new materials developed since the
early 1990s, supercapacitors such as electrochemical capacitors
having capacitance of more than several tens of F and holding the
merits of existing capacitors have been developed. Supercapacitors
cover electrochemical capacitors, electric double layer capacitors
and ultracapacitors.
[0006] Such a supercapacitor uses an electrode of activated carbon
or activated carbon fiber having a specific surface of about
1000-2000 m.sup.2/g to increase energy storage volume, that is,
capacitance. It is known that a capacitor using an electrode of
activated carbon or activated carbon fiber has capacitance per
surface area of about 10-15 .mu.F/cm.sup.2.
[0007] Supercapacitors have an energy density of about 1-10 Wh/kg,
which is one tenth of secondary cells' energy density of about
20-100 Wh/kg. Here, the energy density indicates the energy storage
volume per weight. However, supercapacitors have a power density of
1000-2000 W/kg, which is ten times higher than secondary cells'
power density of 50-200 W/kg. Here, the power density indicates the
volume of accumulated electric energy which can be supplied per
unit time. Therefore, supercapacitors are expected to function as
electric energy storage devices or load controllers in place of
secondary cells. To meet this expectation, it is required to
increase the capacitance of supercapacitors to the level of
secondary cells.
[0008] Although activated carbon or activated carbon fiber has a
relatively large specific surface as described above, its pores
have a diameter of 20 .ANG. or less so that ions cannot easily
enter the pores. Accordingly, supercapacitors using an electrode
formed of activated carbon or activated carbon fiber have a
limitation in increasing capacitance.
SUMMARY OF THE INVENTION
[0009] To solve the above problems, it is an object of the present
invention to provide a supercapacitor using an electrode of a new
material, the supercapacitor having higher capacitance.
[0010] Accordingly, to achieve the above object, there is provided
a supercapacitor including two electrodes facing each other, the
electrodes being composed of carbon nanotubes, an electrolyte
provided between the two electrodes, and a separator for separating
the electrolyte between the two electrodes.
[0011] For each of the electrodes, the carbon nanotubes mixed with
a bonding agent are molded into a pallet pattern. Here, the carbon
nanotubes may be single-wall or multi-wall carbon nanotubes.
Alternatively, each of the electrodes is formed of carbon nanotubes
which are vertically grown on respective collectors.
[0012] Meanwhile, the carbon nanotubes may be activated by a
solution containing potassium hydroxide. Alternatively, the carbon
nanotubes may be electrolessly plated with nickel, or Raney nickel
may be applied to the carbon nanotubes.
[0013] According to the present invention, a high performance
supercapacitor having high capacitance and low internal resistance
can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above object and advantages of the present invention
will become more apparent by describing in detail a preferred
embodiment thereof with reference to the attached drawing:
[0015] FIG. 1 is a schematic diagram for explaining a
supercapacitor using an electrode of a new material according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Hereinafter, an embodiment of the present invention will be
described in detail with reference to the attached drawing. The
present invention is not restricted to the following embodiment,
and many variations are possible within the sprit and scope of the
present invention. The embodiment of the present invention is
provided in order to more completely explain the present invention
to anyone skilled in the art. In the drawing, the shapes of members
are exaggerated for clarity.
[0017] In an embodiment of the present invention, an electrode
formed of carbon nanotubes is used as an electrode of a
supercapacitor. Although the specific surface of a carbon nanotube
is about one tenth through one twentieth of that of activated
carbon or activated carbon fiber, the carbon nanotube can offer
very high capacitance per unit specific surface and low internal
resistance for a supercapacitor so that a high performance
supercapacitor can be manufactured using carbon nanotubes.
[0018] FIG. 1 is a schematic diagram for illustrating a
supercapacitor according to the embodiment of the present
invention. Referring to FIG. 1, the supercapacitor includes
electrodes 100 composed of carbon nanotubes, a separator 200 and an
electrolyte 300.
[0019] An electrolyte used in typical supercapacitors can be used
as the electrolyte 300. A separating material used in typical
supercapacitors can be used as the separator 200. The separator 200
is used to separate the electrolyte 300 between the electrodes 100
but allow the exchange of charge between the electrodes 100.
[0020] Each of the electrodes 100 is composed of carbon nanotubes.
A collector 400 of a conductive material can be additionally
provided to the rear of each electrode 100. The carbon nanotube
electrodes 100 can be formed by molding carbon nanotubes mixed with
a bonding agent into a pallet pattern. In other words, carbon
nanotubes are solidified using a bonding agent and molded into a
pallet pattern to be used as each of the electrodes 100. In this
case, single-wall carbon nanotubes can be used. Here, a polymer
resin such as a polyvinylalcohol resin, a polytetrafluoroethylene
resin, a phenolic resin or a carboxylmethyl cellulose resin is used
as the bonding agent.
[0021] The carbon nanotube electrodes 100 formed in a pallet
pattern are attached to the respective collectors 400, thereby
constituting a supercapacitor. The collectors 400 may be formed of
a variety of conductive materials, but they are preferably formed
of a metal.
[0022] Once current and voltage are applied to the electrodes 100
of such a supercapacitor, ions within the electrolyte 300 are
separated into anions (-) and cations (+), which move to the
respective oppositely charged electrodes 100. Accordingly, the
potentials of the two electrodes 100 change from .PSI..sub.0 into
.PSI..sub.0+.PSI..sub.1 and .PSI..sub.0-.PSI..sub.1, respectively,
and electric energy is stored.
[0023] Such a supercapacitor as described above has high specific
capacitance due to the structural characteristics of carbon
nanotubes constituting the electrodes 100. For example, when a 7.5
N potassium hydroxide (KOH) aqueous solution was used as the
electrolyte 300, it was surveyed that a supercapacitor according to
the embodiment of the present invention had specific capacitance of
about 130 F/g. Alternatively, when an organic electrolyte obtained
by dissolving 1 mol of tetraethylamonium tetrafluoroborate in
acetonitrile was used as the electrolyte 300, a supercapacitor
according to the embodiment of the present invention had specific
capacitance of about 100 F/g. Here, a current was 10 mA/cm.sup.2,
and an operating voltage was 0.9 V when a 7.5 N KOH aqueous
solution was used as the electrolyte and 2.3 V when an organic
electrolyte obtained by dissolving 1 mol of tetraethylamonium
tetrafluoroborate in acetonitrile was used as the electrolyte
300.
[0024] Instead of forming the carbon nanotube electrodes 100 by
molding single-wall carbon nanotubes mixed with a bonding agent
into a pallet pattern, as described above, carbon nanotubes can be
directly grown on the collectors to form the carbon nanotube
electrodes 100. For example, carbon nanotubes can be directly and
vertically grown on a metal substrate (not shown) using a thermal
chemical deposition method or a microwave plasma chemical
deposition method. The vertically grown carbon nanotubes can be
used as an electrode 100. Here, the metal substrate can
spontaneously be used as a collector 400. A method of directly
synthesizing and growing carbon nanotubes on a metal substrate to
be used as a collector 400 can remove the step of molding carbon
nanotubes into a pallet pattern to make the carbon nanotubes have a
certain shape. In addition, since carbon nanotubes are directly
grown on a metal substrate, the contact resistance between a
collector 400 and a corresponding carbon nanotube electrode 100 can
be substantially reduced. Here, a carbon nanotube can be grown to
be a single-wall carbon nanotube or a multi-wall carbon
nanotube.
[0025] A supercapacitor using the electrodes 100 of vertically
grown carbon nanotubes as described above had specific capacitance
of about 100 F/g when a 7.5 N KOH water solution was used as the
electrolyte 300. Alternatively, when an organic electrolyte
obtained by dissolving 1 mol of tetraethylamonium tetrafluoroborate
in acetonitrile was used as the electrolyte 300, the supercapacitor
had specific capacitance of about 70 F/g. Here, a current was 10
mA/cm.sup.2, and an operating voltage was 0.9 V when a 7.5 N KOH
aqueous solution was used as the electrolyte and 2.3 V when an
organic electrolyte obtained by dissolving 1 mol of
tetraethylamonium tetrafluoroborate in acetonitrile was used as the
electrolyte 300.
[0026] When carbon nanotubes are shaped or grown and used for the
electrodes 100, the specific surface of the carbon nanotubes can be
increased by performing a variety of treatments thereon, so that
the capacitance of a supercapacitor can be increased. Preferably,
such treatments are directly performed on the carbon nanotubes
before shaping them into a pallet pattern. When carbon nanotubes
for each of the electrode 100 are directly grown on the
corresponding collector 300, such treatments are preferably
performed on the carbon nanotubes after having grown on the
collector 300.
[0027] For example, by activating the carbon nanotube electrodes
100 with a KOH solution, the capacitance can be increased.
Specifically, carbon nanotubes can be directly dipped in 1-5 mols
of a KOH solution to activate the carbon nanotubes. Here, the
carbon nanotubes may be dipped for about 24 hours. Thereafter, the
carbon nanotubes may be dried for about 30 minutes at a temperature
of about 750.degree. C., or dried by performing heat treatment for
about 60 minutes at a temperature of about 800.degree. C. Through
the above steps, carbon nanotubes can be substantially
activated.
[0028] It was surveyed that such activated carbon nanotubes had
considerably increased specific surfaces, and a supercapacitor
employing the carbon nanotube electrodes 100 had considerably
increased capacitance. For example, when carbon nanotubes were
activated by dipping them in 1 mol of a KOH solution, the specific
surface of a carbon nanotube was increased to about 250 m.sup.2/g,
compared to 140 m.sup.2/g before the activation. Here, the
capacitance of a supercapacitor using an electrode which is formed
by molding such activated carbon nanotubes into a pallet pattern
was about 200 F/g when a 7.5 N KOH solution was used as the
electrolyte 300. Alternatively, when an organic electrolyte
obtained by dissolving 1 mol of tetraethylamonium tetrafluoroborate
in acetonitrile was used as the electrolyte 300, the capacitance of
the supercapacitor was about 160 F/g.
[0029] Besides, when carbon nanotubes were activated by dipping
them in 5 mols of a KOH solution, the specific surface of a carbon
nanotube was increased to about 500 m.sup.2/g. The capacitance of a
supercapacitor using an electrode formed of the activated carbon
nanotubes was about 400 F/g when a 7.5 N KOH solution was used as
the electrolyte 300. Alternatively, when an organic electrolyte
obtained by dissolving 1 mol of tetraethylamonium tetrafluoroborate
in acetonitrile was used as the electrolyte 300, the capacitance of
the supercapacitor was about 300 F/g.
[0030] The above results prove that the capacitance of a
supercapacitor using the electrodes 100 formed of carbon nanotubes
which are activated by a KOH solution is greatly increased.
[0031] Moreover, when the surfaces of carbon nanotubes are plated
with a metal such as nickel (Ni), the internal resistance of a
supercapacitor can be greatly reduced. For example, carbon
nanotubes may be dipped in a solution of 0.1 mol of SnCl.sub.2 and
0.1 mol of HCl for about 30 minutes and in a solution of 0.0014
mols of PdCl.sub.2 and 0.25 mols of HCl for about 30 minutes.
Thereafter, the carbon nanotubes may be dipped in a solution in
which 0.25 mols of NiCl.sub.2.6H.sub.2O, 0.09 mols of
NiSO.sub.4.6H.sub.2O, 0.054 mols of
Na.sub.2HC.sub.6H.sub.5O.sub.7.6H.sub- .2O, 0.084 mols of
NaH.sub.2PO.sub.2.2H.sub.2O, 1.87 mols of NH.sub.4Cl, 0.0075 mols
of Pb(NO.sub.3).sub.2 and 8.75 mols of NH.sub.4OH are dissolved, so
that the carbon nanotubes can be electrolessly plated with Ni. When
the electrodes 100 are formed of such Ni-plated carbon nanotubes,
the internal resistance of the electrodes 100 is considerably
reduced to 0.3 .OMEGA..multidot.cm compared to internal resistance
of 3.5 .OMEGA..multidot.cm appearing in a case where the carbon
nanotubes are not electrolessly plated with Ni.
[0032] The reduction of internal resistance can also be achieved by
applying Raney Ni to carbon nanotubes. For example, Raney Ni is
mixed with carbon nanotubes, and then the mixture is stirred in an
acetone solution so that the Raney Ni is uniformly applied on the
carbon nanotubes. In this case, the internal resistance of the
electrodes 100 is reduced to 0.9 .OMEGA..multidot.cm. By reducing
the internal resistance of the electrodes 100 as described above,
the efficiency of a supercapacitor can be increased.
[0033] A supercapacitor according to the embodiment of the present
invention as described above can have greatly increased capacitance
and lower internal resistance. These effects produce advantages
such as fast charging, high charging/discharging efficiency of at
least 95%, a large number of possible reuses (at least one hundred
thousand) and a large power density which a secondary cell does not
have. These effects also suggest that a supercapacitor according to
the present invention can be used as an energy storage device such
as a secondary cell or a fuel cell which are used as a main device
of, for example, an electric automobile or as an energy storage
device having a load control function. In particular, it is
inferred that a supercapacitor according to the present invention
can be used in substitute for a secondary cell in a hybrid electric
automobile having a small internal-combustion engine.
[0034] A supercapacitor according to the present invention can have
capacitance of, for example, at least 0.9 F/m.sup.2 and 400 F/g,
which is much higher than the capacitance of an existing
supercapacitor, i.e., capacitance of 10-15 .mu.F/m.sup.2 and
100-250 F/g. Moreover, a supercapacitor according to the present
invention can have internal resistance of, for example, about 0.3
.OMEGA..multidot.cm, which is much lower than the internal
resistance of an existing supercapacitor, i.e., internal resistance
of about 3.2-20 .OMEGA..multidot.cm. Therefore, according to the
present invention, a supercapacitor having the characteristics of
high energy density and high power can be manufactured and used as
an energy storage device in place of an existing secondary
cell.
* * * * *