U.S. patent application number 11/607409 was filed with the patent office on 2007-10-04 for porous metal oxide and method of preparing the same.
Invention is credited to Yong-nam Ham, Dong-min Im.
Application Number | 20070231250 11/607409 |
Document ID | / |
Family ID | 38559244 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070231250 |
Kind Code |
A1 |
Im; Dong-min ; et
al. |
October 4, 2007 |
Porous metal oxide and method of preparing the same
Abstract
Porous metal oxides are provided. The porous metal oxides are
prepared by heat treating a coordination polymer. A method of
preparing the porous metal oxide is also provided. According to the
method, the shape of the particles of the metal oxide can be easily
controlled, and the shape and distribution of pores of the porous
metal oxide can be adjusted.
Inventors: |
Im; Dong-min; (Yongin-si,
KR) ; Ham; Yong-nam; (Yongin-si, KR) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
38559244 |
Appl. No.: |
11/607409 |
Filed: |
December 1, 2006 |
Current U.S.
Class: |
423/592.1 ;
429/218.1; 502/300 |
Current CPC
Class: |
H01M 4/9016 20130101;
B01J 23/78 20130101; H01M 4/8885 20130101; H01M 4/485 20130101;
H01M 4/525 20130101; C01G 1/02 20130101; Y02E 60/50 20130101; C01P
2006/17 20130101; C01P 2004/03 20130101; B01J 37/08 20130101; B01J
35/002 20130101; B01J 23/755 20130101; C01B 13/322 20130101; C01P
2002/72 20130101; C01P 2004/10 20130101; C01P 2004/20 20130101;
B01J 37/14 20130101; H01M 4/9025 20130101; C01P 2006/16 20130101;
Y02E 60/10 20130101; B01J 37/086 20130101 |
Class at
Publication: |
423/592.1 ;
429/218.1; 502/300 |
International
Class: |
C01B 13/14 20060101
C01B013/14; H01M 4/48 20060101 H01M004/48; B01J 23/00 20060101
B01J023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2006 |
KR |
10-2006-0028395 |
Claims
1. A method of preparing a porous metal oxide, comprising heat
treating a coordination polymer.
2. The method of claim 1, wherein the heat treating comprises: a
first heat treatment process conducted under an inert atmosphere;
and a second heat treatment process conducted under an
oxygen-containing atmosphere.
3. The method of claim 2, wherein the first heat treatment process
is conducted at a temperature ranging from about 300.degree. C. to
about a melting point of a metal included in the coordination
polymer.
4. The method of claim 1, wherein the second heat treatment process
is conducted at a temperature ranging from about 300 to about
1500.degree. C.
5. The method of claim 1, wherein the coordination polymer
comprises a compound having a unit structure represented by Formula
1: M.sub.xL.sub.yS.sub.z Formula 1 wherein M is a metal selected
from the group consisting of transition metals, Group 13 metals,
Group 14 metals, Group 15 metals, lanthanides, actinides and
combinations thereof, L is a multi-dentate ligand capable of
forming ionic or covalent bonds with at least two metal ions, S is
a mono-dentate ligand capable of forming an ionic or covalent bond
with one metal ion, wherein d represents a number of functional
groups of L capable of binding to a metal ion, and wherein x, y and
z are integers satisfying Equation 1: yd+z.ltoreq.6x. Equation
1
6. The method of claim 5, wherein the coordination polymer forms a
network by connecting metal ions with the multi-dentate ligand.
7. The method of claim 5, wherein the multi-dentate ligand is
selected from the group consisting of trimesate-based ligands
represented by Formula 4, terephthalate-based ligands represented
by Formula 5, 4,4'-bipyridine-based ligands represented by Formula
6, 2,6-naphthalenedicarboxylate-based ligands represented by
Formula 7, pyrazine-based ligands represented by Formula 8 and
combinations thereof: ##STR00005## wherein R.sub.1 to R.sub.25 are
each independently selected from the group consisting of hydrogen
atoms, halogen atoms, hydroxy groups, substituted C.sub.1-20 alkyl
groups, unsubstituted C.sub.1-20 alkyl groups, substituted
C.sub.1-20 alkoxy groups, unsubstituted C.sub.1-20 alkoxy groups,
substituted C.sub.2-20 alkenyl groups, unsubstituted C.sub.2-20
alkenyl groups, substituted C.sub.6-30 aryl groups, unsubstituted
C.sub.6-30 aryl groups, substituted C.sub.6-30 aryloxy groups,
unsubstituted C.sub.6-30 aryloxy groups, substituted C.sub.2-30
heteroaryl groups, unsubstituted C.sub.2-30 heteroaryl groups,
substituted C.sub.2-30 heteroaryloxy groups, unsubstituted
C.sub.2-30 heteroaryloxy groups and combinations thereof.
8. The method of claim 5, wherein the metal is selected from the
group consisting of Fe, Pt, Co, Cd, Cu, Ti, V, Cr, Mn, Ni, Ag, Pd,
Ru, Mo, Zr, Nb, La, In, Sn, Pb, Bi and combinations thereof.
9. A porous metal oxide prepared according the method of claim
1.
10. A porous metal oxide prepared according to the method of claim
5.
11. A porous metal oxide comprising a plurality of pores having an
average diameter of about 10 nm or greater, wherein the porous
metal oxide has a multilateral shape.
12. The porous metal oxide of claim 11, wherein the average
diameter of the pores ranges from about 20 to about 100 nm.
13. The porous metal oxide of claim 11, wherein particles of the
porous metal oxide have a shape selected from the group consisting
of needles and plates.
14. The porous metal oxide of claim 11, wherein the porous metal
oxide is obtained by heat-treating a coordination polymer.
15. The porous metal oxide of claim 14, wherein the coordination
polymer comprises a compound having a unit structure represented by
Formula 1: M.sub.xL.sub.yS.sub.z Formula 1. wherein M is a metal
selected from the group consisting of transition metals, Group 13
metals, Group 14 metals, Group 15 metals, lanthanides, actinides
and combinations thereof, L is a multi-dentate ligand capable of
forming ionic or covalent bonds with at least two metal ions, S is
a mono-dentate ligand capable of forming an ionic or covalent bond
with one metal ion, wherein d represents a number of functional
groups of L capable of binding to a metal ion, and wherein x, y and
z are integers satisfying Equation 1: yd+z.ltoreq.6x. Equation
1
16. The porous metal oxide of claim 15, wherein the coordination
polymer forms a network by connecting metal ions with the
multi-dentate ligand.
17. The porous metal oxide of claim 15, wherein the multi-dentate
ligand is selected from the group consisting of trimesate-based
ligands represented by Formula 4, terephthalate-based ligands
represented by Formula 5, 4,4'-bipyridine-based ligands represented
by Formula 6, 2,6-naphthalenedicarboxylate-based ligands
represented by Formula 7, pyrazine-based ligands represented by
Formula 8 and combinations thereof: ##STR00006## wherein R.sub.1 to
R.sub.25 are each independently selected from the group consisting
of hydrogen atoms, halogen atoms, hydroxy groups, substituted
C.sub.1-20 alkyl groups, unsubstituted C.sub.1-20 alkyl groups,
substituted C.sub.1-20 alkoxy groups, unsubstituted C.sub.1-20
alkoxy groups, substituted C.sub.2-20 alkenyl groups, unsubstituted
C.sub.2-20 alkenyl groups, substituted C.sub.6-30 aryl groups,
unsubstituted C.sub.6-30 aryl groups, substituted C.sub.6-30
aryloxy groups, unsubstituted C.sub.6-30 aryloxy groups,
substituted C.sub.2-30 heteroaryl groups, unsubstituted C.sub.2-30
heteroaryl groups, substituted C.sub.2-30 heteroaryloxy groups,
unsubstituted C.sub.2-30 heteroaryloxy groups and combinations
thereof.
18. The porous metal oxide of claim 15, wherein the metal is metal
selected from the group consisting of Fe, Pt, Co, Cd, Cu, Ti, V,
Cr, Mn, Ni, Ag, Pd, Ru, Mo, Zr, Nb, La, In, Sn, Pb, Bi and
combinations thereof.
19. An active material for a secondary battery comprising the
porous metal oxide of claim 11.
20. An active material for a secondary battery comprising the
porous metal oxide of claim 15.
21. A catalyst comprising the porous metal oxide of claim 11.
22. A catalyst comprising the porous metal oxide of claim 15.
23. A support for a catalyst comprising the porous metal oxide of
claim 11.
24. A support for a catalyst comprising the porous metal oxide of
claim 15.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2006-0028395 filed on Mar. 29,
2006 in the Korean Intellectual Property Office, the entire content
of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a porous metal oxide and a
method of preparing the same, and more particularly, to a porous
metal oxide having a particle shape that can be easily-controlled
and pores having an adjustable shape and distribution, and a method
of preparing the same.
[0004] 2. Description of the Related Art
[0005] Porous metal oxides are used as electrode materials in the
energy field. In general, electrode materials must have good
electronic conductivity and good ionic conductivity, while ionic
conductivity is typically lower than electronic conductivity.
However, in porous electrode materials, ions can be delivered to
the inside of the particles of the porous metal oxide, thereby
reducing the distance that ions travel. Nano-materials may have
similar effects as porous electrode materials, but have high
contact resistance between the particles of the nano-materials and
it is difficult to manufacture electrodes formed of nano-materials.
Therefore, practical application of nano-materials is
difficult.
[0006] Examples of porous metal oxides used as electrode materials
include MnO.sub.2, LiCoO.sub.2, LiNiO.sub.2,
LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2 which are used as cathode
materials for lithium secondary batteries. In electrochemical
capacitors, RuO.sub.2, NiO, etc. are used as pseudocapacitance
materials. Porous metal oxides can also be used as electrode
materials for solid oxide fuel cells (nickel oxide or cobalt
oxide), molten carbonate fuel cells, borohydride fuel cells, or dye
sensitized solar cells (titanium oxide).
[0007] Such porous metal oxides are typically prepared by a
sintering method or a template method. Sintering is most frequently
used to prepare porous metal oxides. It is difficult to prepare
porous metal oxides in the form of a powder. To form the porous
metal oxide in a predetermined shape, pressure molding can be
performed.
[0008] A template method is frequently used for preparing porous
materials having mesopores with a diameter of 50 nm or less.
However, processing costs of the template method are high and mass
production is difficult.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the present invention, a method of
preparing a porous metal oxide is provided in which particles of
the porous metal oxide can be easily controlled and the shape and
distribution of pores can be adjusted.
[0010] In another embodiment of the present invention, a porous
metal oxide is prepared by the above-described method.
[0011] According to one embodiment of the present invention, a
method of preparing a porous metal oxide comprises heat treating a
coordination polymer. The heat treatment may comprise a first heat
treatment process conducted under an inert atmosphere and a second
heat treatment process conducted under an oxygen-containing
atmosphere. The temperature for the first heat treatment process
may range from about 300.degree. C. to the melting point of the
main metal included in the coordination polymer.
[0012] The coordination polymer may be a compound having a unit
structure represented by Formula 1 below:
M.sub.xL.sub.yS.sub.z Formula 1
In Formula 1, M is a metal selected from transition metals, Group
13 metals, Group 14 metals, Group 15 metals, lanthanides, actinides
and combinations thereof. L is a multi-dentate ligand that
simultaneously forms ionic or covalent bonds with at least two
metal ions. S is a mono-dentate ligand that forms an ionic or
covalent bond with one metal ion. When d is the number of L's
functional groups that can bind to metal ions, x, y and z are
integers satisfying the equation yd+z.ltoreq.6x.
[0013] According to another embodiment of the present invention, a
porous metal oxide has a multilateral shape and has pores with an
average diameter of about 10 nm or greater. In one embodiment, for
example, the average diameter of the pores ranges from about 20 to
about 100 nm.
[0014] According to one embodiment, the particles of the porous
metal oxide may be needle-shaped or plate-shaped.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The above and other features and advantages of the present
invention will become more apparent by reference to the following
detailed description when considered in conjunction with the
attached drawings in which:
[0016] FIG. 1 is a scanning electron microscope (SEM) image of the
coordination polymer prepared according to Example 1;
[0017] FIG. 2 is a SEM image of the carbon-nickel composite
prepared according to Example 1;
[0018] FIGS. 3A and 3B are SEM images of the porous nickel oxide
prepared according to Example 1;
[0019] FIG. 4 is an X-ray diffraction (XRD) graph of the porous
nickel oxide prepared according to Example 1;
[0020] FIG. 5 is a graph illustrating the nitrogen adsorption of
the porous nickel oxide prepared according to Example 1;
[0021] FIGS. 6A and 6B are SEM images of the porous nickel oxide
prepared according to Example 2;
[0022] FIGS. 7A and 7B are SEM images of the porous nickel oxide
prepared according to Example 3;
[0023] FIGS. 8A and 8B are SEM images of the porous nickel oxide
prepared according to Example 4;
[0024] FIGS. 9A and 9B are SEM images of the porous nickel oxide
prepared according to Example 5;
[0025] FIG. 10 is an XRD graph of the porous nickel oxide prepared
according to Examples 1 through 5;
[0026] FIG. 11 is a graph illustrating the nitrogen adsorption of
the porous nickel oxide prepared according to Example 4;
[0027] FIGS. 12A and 12B are SEM images of the porous
Ni.sub.0.8Co.sub.0.2O prepared according to Example 6;
[0028] FIGS. 13A and 13B are SEM images of the porous
Ni.sub.0.8Co.sub.0.2O.sub.2 prepared according to Example 7;
[0029] FIG. 14 is a graph illustrating the charge/discharge
properties of the cell prepared according to Example 8; and
[0030] FIG. 15 is a graph illustrating capacitance variation when
the cells prepared according to Example 8 and the Comparative
Example were charged and discharged 100 times.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention will now be described with reference
to the accompanying drawings, in which exemplary embodiments of the
invention are shown.
[0032] A porous metal oxide according to one embodiment of the
present invention has a multilateral shape and an average pore
diameter of about 10 nm or greater. The porous metal oxide can be
prepared by heat-treating a coordination polymer. The shape of the
oxide, and the size and shape of the pores of the porous metal
oxide can be controlled. Using the coordination polymer is a new
approach to the synthesis of composites. The coordination polymer
has a repeating unit with a one-, two-, or three-dimensional
morphology as compared to a general coordination compound which is
represented by Formula 2:
##STR00001##
[0033] Nonlimiting examples of two-dimensional coordination
polymers include compounds represented by Formula 3:
##STR00002##
In Formula 3, where M, L and S are as defined below.
[0034] In the two-dimensional coordination polymers represented by
Formula 3, four ligands (L) having multiple functional groups
("multi-dentate ligands") and two mono-dentate ligands (S)
coordinate to a metal (M) atom. The multi-dentate ligands (L) also
coordinate to other adjacent metal (M) atoms. In this embodiment,
the metal (M) atoms act as coordination sites for the ligands in
the same manner as in the general coordination compound represented
by Formula 2. However, the ligands of the two-dimensional
coordination polymer represented by Formula 3 coordinate to
multiple metal atoms at the same time. Multi-dentate ligands (in
which one ligand coordinates to two metals at the same time) form a
coordination polymer having a very regular lattice structure. Such
a structure can be extended to a three-dimensional structure
because, unlike in a planar-type coordination polymer, the
multi-dentate ligands shown in Formula 3 can further coordinate to
metal atoms or ligands located above or below them to form a
three-dimensional coordination polymer.
[0035] The coordination polymer used to form a carbon-metal
composite according to one embodiment of the present invention may
be a compound represented by Formula 1:
M.sub.xL.sub.yS.sub.z (1)
In formula 1, M is a metal selected from transition metals, Group
13 metals, Group 14 metals, Group 15 metals, lanthanides, actinides
and combinations thereof. L is a multi-dentate ligand that
simultaneously forms ionic or covalent bonds with at least two
metal ions. S is a mono-dentate ligand that forms an ionic or
covalent bond with one metal ion. When d is the number of
functional groups of L that can bind to the metal ion x, y and z
are integers satisfying the equation yd+z.ltoreq.6x.
[0036] In the coordination polymers represented by Formula 1, the
multi-dentate ligand L links metal atoms or ions to form a network
structure. Thus, the compound of Formula 1 is primarily
crystalline. Such a coordination polymer may optionally include a
mono-dentate ligand S which can bind to a metal atom or ion
irrespective of the multi-dentate ligand L.
[0037] The structure of the coordination polymer according to this
embodiment is different from that of a chelate compound. A chelate
compound is a general compound in which a multi-dentate ligand
binds to a metal ion, and has a different structure from the
coordination polymer of the present embodiment. That is, in a
chelate compound, for example, a multi-dentate ligand such as
ethylene diamine coordinates to a metal ion, but does not form a
network structure as in the coordination polymer of the present
embodiment. Rather, a single coordination compound in which the
multi-dentate ligand forms a chelate ring is obtained. In the
coordination polymer of the present embodiment, neighboring metals
are linked to each other via multi-dentate ligands to form a
network structure. In contrast, in the chelate compound,
multi-dentate ligands coordinate to only one metal ion at multiple
sites, and thus, do not form a network structure.
[0038] When a network structure is formed via multi-dentate ligands
L, core metal ions or atoms can form coordination bonds not only
with multi-dentate ligands L, but may also bind to mono-dentate
ligands S if necessary. The mono-dentate ligands S may be any
ligands used in general coordination compounds, for example,
ligands containing N, O, S, P, As, etc. having lone pair electrons.
Nonlimiting examples of suitable mono-dentate ligands include
H.sub.2O, SCN.sup.-, CN.sup.-, Cl.sup.-, Br.sup.-, NH.sub.3 and the
like. However, the mono-dentate ligands S can also have multiple
functional groups. In addition, when a chelate ring is formed, a
multi-dentate ligand L can be used. That is, although multi-dentate
ligands L such as bi-dentate ligands, tri-dentate ligands,
tetra-dentate ligands, etc. can be used, if metal atoms or ions can
form a network structure through mono-dentate ligands S,
mono-dentate ligands S can also be used.
[0039] A multi-dentate ligand L capable of linking metal ions or
atoms to form a network may be any ligand having at least two
functional groups capable of forming covalent or ionic bonds with
the core metal to form a network structure. In particular, the
multi-dentate ligand L of the present embodiment is distinguishable
from a multi-dentate ligand L coordinating to only one metal ion to
form a chelate ring (chelate ligand) as described above. This is
because it is difficult to form a coordination polymer having a
network structure with a chelate ligand.
[0040] Nonlimiting examples of suitable multi-dentate ligands L
include trimesate-based ligands represented by Formula 4,
terephthalate-based ligands represented by Formula 5,
4,4'-bipyridine-based ligands represented by Formula 6,
2,6-naphthalenedicarboxylate-based ligands represented by Formula 7
and pyrazine-based ligands represented by Formula 8:
##STR00003##
In formulae 4 to 8, R.sub.1 through R.sub.25 are each independently
selected from hydrogen atoms, halogen atoms, hydroxy groups,
substituted C.sub.1-20 alkyl groups, unsubstituted C.sub.1-20 alkyl
groups, substituted C.sub.1-20 alkoxy groups, unsubstituted
C.sub.1-20 alkoxy groups, substituted C.sub.2-20 alkenyl groups,
unsubstituted C.sub.2-20 alkenyl groups, substituted C.sub.6-30
aryl groups, unsubstituted C.sub.6-30 aryl groups, substituted
C.sub.6-30 aryloxy groups, unsubstituted C.sub.6-30 aryloxy groups,
substituted C.sub.2-30 heteroaryl groups, unsubstituted C.sub.2-30
heteroaryl groups, substituted C.sub.2-30 heteroaryloxy groups, and
unsubstituted C.sub.2-30 heteroaryloxy groups.
[0041] The multi-dentate ligands L are described in more detail in
Chistoph Janiak, Dalton Trans., 2003, p 2781-2804, and Stuart L.
James, Chem. Soc. Rev., 2003, 32, 276-288, the entire contents of
which are incorporated herein by reference.
[0042] The metal bound to the multi-dentate ligands L to form the
coordination polymer is not limited as long as it can provide
coordination sites for the multi-dentate ligands L. Nonlimiting
examples of suitable metals include transition metals, Group 13
metals, Group 14 metals, Group 15 metals, lanthanides, actinides
and combinations thereof. For example, Fe, Pt, Co, Cd, Cu, Ti, V,
Cr, Mn, Ni, Ag, Pd, Ru, Mo, Zr, Nb, La, In, Sn, Pb, Bi, etc. can be
used.
[0043] In Formula 1, x, y and z are integers satisfying the
equation yd+z.ltoreq.6x, where d denotes the number of functional
groups of the multi-dentate ligand L which can bind to the metal.
For example, when L is a tetra-dentate ligand and two mono-dentate
ligands S coordinate to the metal, the coordination polymer has a
basic structure of MLS.sub.2 and satisfies the equation 1
(y).times.4(d)+2(z)=6.times.1 (x). Since the multi-dentate ligand L
is essential to form a network, y is at least 1. Also, since the
mono-dentate ligand S is an optional element, z is at least 0. It
will be understood by those skilled in the art that x, y and z do
not represent the specific number of atoms but they indicate ratios
of metals and ligands in view of the nature of polymers. When a
core metal M is Cd and the multi-dentate ligand L is
4,4'-bipyridine, the coordination polymer of the present embodiment
is a compound represented by Formula 9 (where x is 1, and y and z
are 2):
##STR00004##
[0044] In the coordination polymer of Formula 9, 4,4'-bipyridine
coordinates to Cd, the core metal M. Specifically, a terminal
nitrogen atom of 4,4'-bipyridine binds to a Cd ion and another
terminal nitrogen atom of 4,4'-bipyridine binds to another Cd ion.
This binding pattern is repeated to form a network, thereby
obtaining a coordination polymer having a two-dimensional lattice
structure. Such a coordination polymer structure affects the final
shape, for example, periodicity, etc. of a carbon-metal composite
obtained by heat-treating the coordination polymer. Thus, when the
process of forming the coordination polymer is properly controlled,
the shape of the final product can be controlled. The crystalline
shape of the coordination polymer can be controlled by properly
modifying the reaction temperature, pH and reaction time for the
metal precursor and ligands to bind to each other. The shape may
also be controlled by modifying the type of metal, the type of
ligand and the concentrations thereof, or by properly controlling
the drying temperature and drying time to obtain the coordination
polymer in a crystalline state.
[0045] As described above, a porous metal oxide according to one
embodiment of the present invention is obtained by heat-treating a
coordination polymer. The heat treatment may include a first heat
treatment process conducted under an inert atmosphere and a second
heat treatment process conducted under an oxygen-containing
atmosphere. Alternatively, the heat treatment may be performed in a
single operation either under an inert atmosphere or under an
oxygen-containing atmosphere to prepare the porous metal oxide.
[0046] The first and second heat treatment processes are performed
as follows. First, a carbon-metal nano-composite is formed during
the first heat treatment process under an inert atmosphere. Then
carbon is removed and metal is oxidized during the second heat
treatment process under an oxygen-containing atmosphere to form the
porous metal oxide.
[0047] The first heat treatment process under an inert atmosphere
may be performed at a temperature ranging from about 300.degree. C.
to about the melting point of the corresponding metal. In one
embodiment, for example, the first heat treatment process is
performed at a temperature ranging from about 500.degree. C. to
about the melting point of the corresponding metal. The period of
time that the first heat treatment process is performed is not
particularly limited. However, in one embodiment, the first heat
treatment process is performed for a period of time ranging from
about 0.1 to about 10 hours. For example, the first heat treatment
process may be performed for a period of time ranging from about
0.5 to about. 3 hours. When the temperature of the first heat
treatment process is less than about 300.degree. C., carbonization
is not sufficient. When the temperature of the first heat treatment
process is greater than about the melting point of the
corresponding metal, the structure of the nano-composite itself is
likely to collapse due to the melting and aggregation of metal
particles. When the first heat treatment process is performed for a
period of time less than about 0.1 hours, the effect of the heat
treatment is insufficient. When the first heat treatment process is
performed for a period of time greater than about 10 hours, the
heat treatment is not economical.
[0048] When the coordination polymer is subjected to the first heat
treatment process as described above, the volatile and combustible
parts are mostly vaporized and removed. Thus, the shape of the
carbon-metal composite remains unchanged and has a reduced volume
after the first heat treatment process. Since the shape of the
coordination polymer is maintained even after the first heat
treatment process, the shape of the final product can be easily
controlled, as indicated above.
[0049] The second heat treatment process conducted under an
oxygen-containing atmosphere may be performed at a temperature
ranging from about 300 to about 1500.degree. C. In one embodiment,
for example, the second heat treatment process is performed at a
temperature ranging from about 300 to about 800.degree. C. The
period of time that the second heat treatment process is performed
is not particularly limited. However, in one embodiment, the second
heat treatment process is performed for a period of time ranging
from about 0.1 to about 24 hours. For example, the second heat
treatment process may be performed for a period of time ranging
from about 0.5 to about 5 hours. When the temperature of the second
heat treatment process is less than about 300.degree. C., oxidation
of carbon is difficult and thus it is difficult to remove carbon
from the carbon-metal composite. When the temperature of the second
heat treatment process is greater than about 1500.degree. C.,
sintering is performed at the high temperature and the shape of the
pores collapses.
[0050] The carbon-metal composite prepared using the first heat
treatment process under an inert atmosphere may have a specified
periodicity. Such periodicity is due to the repeating unit having a
one-, two-, or three-dimensional morphology, and denotes that the
repeated high regularity of the coordination polymer is maintained
after heat treatment. Such periodicity can be measured by X-ray
diffraction analysis of the carbon-metal composite obtained after
the first heat treatment process, and at least one peak is present
at d-spacings of 6 nm or greater. Such periodicity affects the
properties of the porous metal oxide prepared from the carbon-metal
composite and thus a metal oxide having uniformly arranged pores
with an average diameter of about 10 nm or greater can be achieved.
In one embodiment, pores having an average diameter ranging from
about 20 to about 100 nm can be achieved. Such a porous metal oxide
having pores with an average diameter greater than about 10 nm is
difficult to obtain using only a structure directing agent.
[0051] Since the shape of the particles of the porous metal oxide
according to this embodiment of the present invention can be easily
controlled, the final particle shape can be easily controlled by
appropriate selection of the coordination polymer or the heat
treatment conditions. In one embodiment, needle-shaped or
plate-shaped porous metal oxide particles are obtained.
[0052] In the porous metal oxide according to this embodiment of
the present invention, the coordination polymer forming the porous
metal oxide can be synthesized mostly in an aqueous state, which is
both economical and highly stable. Furthermore, simple heat
treatment processes suggest that mass production is easy, and no
template is required. Also, various shapes of the desired porous
metal oxide can be easily controlled according to the desired use
by controlling the shape of the coordination polymer. Moreover, the
porous metal oxide is prepared by heat treating the uniform
carbon-metal nano-composites in which the carbon portion and the
metal portion are periodically repeated, thereby obtaining an
appropriate diameter and distribution of pores and causing ions and
gas to flow more easily. Consequently, the porous metal oxide
provides excellent high rate performance in electrochemical devices
and can be efficiently used in catalysts, catalyst supports,
electrode materials for secondary batteries, fuel cells, or
electric double layer capacitors.
[0053] Hereinafter, the present invention will be described with
reference to the following examples. However, these examples are
provided for illustrative purposes only and do not limit the scope
of the invention.
EXAMPLE 1
[0054] 37.33 g of nickel (II) acetate tetrahydrate and 19.96 g of
trimesic acid were added to 500 ml of distilled water and stirred
at 55.degree. C. for 2 hours. Powders produced in the solution were
removed using a nylon filter, washed with distilled water several
times, and then dried in an oven at 80.degree. C. for 12 hours to
obtain a crystalline coordination polymer. FIG. 1 is a scanning
electron microscope (SEM) image of the crystalline coordination
polymer prepared according to this example.
[0055] The obtained crystalline coordination polymer was subjected
to heat treatment under an Ar atmosphere at 600.degree. C. for 1
hour to prepare a carbon-nickel composite having the same shape as
the untreated crystalline coordination polymer and a reduced
volume. FIG. 2 is a SEM image of the obtained carbon-metal
composite.
[0056] FIGS. 3A and 3B are SEM images of a porous nickel oxide
obtained by heat treating the obtained carbon-nickel composite in
air at 700.degree. C. for 1 hour. FIGS. 3A and 3B show that the
oxide powder is porous and that the particle shape of the oxide
powder is maintained. FIG. 4 is an XRD graph of the obtained porous
nickel oxide, indicating that a pure NiO material is formed. The
porous nickel oxide was analyzed using a nitrogen adsorption
method. The pore diameter distribution was analyzed using a BJH
adsorption method and is illustrated in FIG. 5. As shown in FIG. 5,
the pore diameters were mainly 20 nm or greater.
EXAMPLES 2 THROUGH 5
[0057] Synthesis of the coordination polymer and heat treatment
were performed as in Example 1, except that the heat treatment
temperature for forming the carbon-metal composite was adjusted
from 700 to 1000.degree. C. as listed in Table 1 below.
TABLE-US-00001 TABLE 1 Heat treatment temperature (.degree. C.)
First heat Second heat Sample Precursor treatment (Argon) treatment
(Air) Example 2 Nickel(II) trimesate 700 700 Example 3 Nickel(II)
trimesate 800 700 Example 4 Nickel(II) trimesate 900 700 Example 5
Nickel(II) trimesate 1000 700
FIGS. 6A and 6B are SEM images of the porous nickel oxide prepared
according to Example 2. FIGS. 7A and 7B are SEM images of the
porous nickel oxide prepared according to Example 3. FIGS. 8A and
8B are SEM images of the porous nickel oxide prepared according to
Example 4. FIGS. 9A and 9B are SEM images of the porous nickel
oxide prepared according to Example 5.
[0058] These results show that the size of the primary particles
and the diameters of the pores increase as the temperature
increases from a heat treatment temperature of greater than
800.degree. C.
[0059] FIG. 10 is an X-ray diffraction (XRD) graph of the porous
nickel oxide prepared according to Examples 1 through 5.
[0060] FIG. 11 is a graph illustrating the nitrogen adsorption of
the porous nickel oxide prepared according to Example 4, and
indicates that most pores have a diameter of 20 nm or greater.
EXAMPLE 6
[0061] 14.93 g of nickel (II) acetate tetrahydrate, 3.73 g of
cobalt (II) acetate tetrahydrate, and 9.98 g of trimesic acid were
added to 500 ml of distilled water and stirred at 55.degree. C. for
2 hours. Powders produced in the solution were removed using a
nylon filter, washed with distilled water several times, and then
dried in an oven at 80.degree. C. for 12 hours to obtain a
needle-shaped coordination polymer crystal.
[0062] The obtained crystalline coordination polymer was subjected
to a heat treatment process under an Ar atmosphere at 900.degree.
C. for 1 hour to prepare a carbon-(nickel, cobalt) composite, and
then subjected to a heat treatment process at 700.degree. C. for 1
hour to prepare a porous Ni.sub.0.8Co.sub.0.2O material. FIGS. 12A
and 12B are SEM images of the prepared porous Ni.sub.0.8Co.sub.0.2O
material.
EXAMPLE 7
[0063] 14.93 g of nickel (II) acetate tetrahydrate, 3.73 g of
cobalt (II) acetate tetrahydrate, and 9.98 g of trimesic acid were
added to 500 ml of distilled water and stirred at 55.degree. C. for
2 hours. Powders produced in the solution were removed using a
nylon filter, washed with distilled water several times, and then
dried in an oven at 80.degree. C. for 12 hours to obtain a
crystalline coordination polymer.
[0064] The obtained crystalline coordination polymer was subjected
to a heat treatment process under an Ar atmosphere at 900.degree.
C. for 1 hour to prepare a carbon-(nickel, cobalt) composite. LiOH
was mixed with the prepared carbon-(nickel, cobalt) composite such
that the atom ratio of the transition metal and lithium was 1:1 and
the mixture was subjected to a heat treatment process at
700.degree. C. for 12 hours. FIGS. 13A and 13B are SEM images of
the prepared porous LiNi.sub.0.8Co.sub.0.2O.sub.2 material. The
results show that although primary particles were grown during the
formation of LiNi.sub.0.8Co.sub.0.2O.sub.2 by reaction with Li, the
needle shape of the particles and some of the pores were
maintained.
EXAMPLE 8
Manufacture of Electrochemical Capacitor
[0065] 93 weight % of the porous nickel oxide prepared according to
Example 2, 4 weight % of a conductive carbon material, and 3 weight
% of PVDF were dispersed in N-methylpyrrolidone to prepare a
slurry. The slurry was coated on aluminum foil to a thickness of
100 um and dried.
[0066] A test cell was manufactured by forming a plurality of
electrodes from the dried product. Each electrode had a circular
shape with a diameter of 13 mm. Two of these electrodes having the
same weight were inserted into a CR2016 sized coin cell made of
stainless steel and were positioned to overlap and face each other.
A separator was placed between the electrodes. Then, 0.6M
tetraethylammonium tetrafluoro borate (TEATFB) in propylene
carbonate (PC) solution was injected into the test cell as an
electrolyte. Here, the separator was a Model 3501 polyethylene
membrane available from Celgard, Inc. (Charlotte, N.C.).
[0067] The assembled cell was repeatedly charged and discharged at
a current of 0.1 mA to a voltage ranging from 0 to 3.0 V. FIG. 14
is a graph illustrating the initial charge/discharge of the
manufactured cell, indicating the characteristics of the
capacitor.
COMPARATIVE EXAMPLE
[0068] A test cell was manufactured as in Example 8, except that
non-porous NiO powder obtained by subjecting nickel (II) acetate
tetrahydrate powder to a heat treatment process at 700.degree. C.
for 1 hour in air was used instead of the porous NiO powder
obtained in Example 2.
[0069] FIG. 15 is a graph illustrating capacitance variation of the
cells prepared in Example 8 and the Comparative Example after
charging and discharging 100 times. As shown in FIG. 15, the
initial performance and cycle life of the cell prepared according
to Example 8 (including a porous nickel oxide according to an
embodiment of the present invention) was better than that of the
Comparative Example (in which a nonporous nickel oxide was used as
an electrode).
[0070] The porous metal oxides according to the present invention
are obtained by heat-treating a coordination polymer and can be
mass-produced. The shape of the produced porous metal oxides can be
easily controlled, and the shape and distribution of the pores of
the porous metal oxides can be adjusted to be uniform. Thus, ions
or gases can easily flow. Thus, the porous metal oxides of the
present invention have excellent high-rate characteristics, and can
be used as catalysts, catalyst supports, electrode materials for
secondary batteries, fuel cells, or electric double layer
capacitors.
[0071] While certain exemplary embodiments of the present invention
have been described and illustrated, those of ordinary skill in the
art will understand that various modifications and changes to the
described embodiments can be made without departing from the spirit
and scope of the present invention as defined by the following
claims.
* * * * *