U.S. patent application number 13/648680 was filed with the patent office on 2013-05-16 for method for producing aluminum structure and aluminum structure.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. The applicant listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Kengo GOTO, Akihisa HOSOE, Koutarou KIMURA, Junichi NISHIMURA, Kazuki OKUNO, Hajime OTA.
Application Number | 20130121873 13/648680 |
Document ID | / |
Family ID | 47259075 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121873 |
Kind Code |
A1 |
KIMURA; Koutarou ; et
al. |
May 16, 2013 |
METHOD FOR PRODUCING ALUMINUM STRUCTURE AND ALUMINUM STRUCTURE
Abstract
An object is to provide a method for producing an aluminum
structure using a porous resin body having a three-dimensional
network structure, with which an aluminum structure having a low
impurity content can be formed, and in particular, a porous
aluminum body having a large area can be obtained. A method for
producing an aluminum structure includes a conductivity-imparting
step of applying a conductive coating material containing
conductive carbon onto a surface of a resin body to impart
electrical conductivity to the resin body; a plating step of
plating a surface of the resin body, to which electrical
conductivity has been imparted, with aluminum in a molten salt to
form an aluminum layer; and a heat treatment step of conducting
heat treatment to remove the resin body, wherein the conductive
carbon is carbon black having an average particle diameter of 0.003
.mu.m or more and 0.05 .mu.m or less.
Inventors: |
KIMURA; Koutarou; (Osaka,
JP) ; HOSOE; Akihisa; (Osaka, JP) ; NISHIMURA;
Junichi; (Osaka, JP) ; OKUNO; Kazuki; (Osaka,
JP) ; OTA; Hajime; (Osaka, JP) ; GOTO;
Kengo; (Osaka, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD.; |
Osaka |
|
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
Osaka
JP
|
Family ID: |
47259075 |
Appl. No.: |
13/648680 |
Filed: |
October 10, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2012/063007 |
May 22, 2012 |
|
|
|
13648680 |
|
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Current U.S.
Class: |
420/528 ;
205/166 |
Current CPC
Class: |
C25D 1/08 20130101; C25D
3/665 20130101; C25D 3/44 20130101 |
Class at
Publication: |
420/528 ;
205/166 |
International
Class: |
C25D 3/44 20060101
C25D003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 3, 2011 |
JP |
2011-124707 |
Claims
1. A method for producing an aluminum structure comprising: a
conductivity-imparting step of applying a conductive coating
material containing conductive carbon onto a surface of a resin
body to impart electrical conductivity to the resin body; a plating
step of plating a surface of the resin body, to which electrical
conductivity has been imparted, with aluminum in a molten salt to
form an aluminum layer; and a heat treatment step of conducting
heat treatment to remove the resin body, wherein the conductive
carbon is carbon black having an average particle diameter of 0.003
.mu.m or more and 0.05 .mu.m or less.
2. The method for producing an aluminum structure according to
claim 1, wherein the heat treatment step is conducted at a
temperature of 500.degree. C. or higher and 640.degree. C. or lower
in an atmosphere containing oxygen.
3. The method for producing an aluminum structure according to
claim 1, wherein the resin body is a porous resin body having a
three-dimensional network structure.
4. The method for producing an aluminum structure according to
claim 1, wherein the resin body is composed of polyurethane.
5. An aluminum structure produced by the method according to claim
1.
6. An Aluminum structure according to claim 5, wherein a carbon
content is 2% by weight or less.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation application of
International Application No. PCT/JP2012/063007, filed May 22,
2012, which claims priority to Japanese Patent Application No.
2011-124707, filed Jun. 3, 2011. The contents of these applications
are incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present invention relates to an aluminum structure
suitable for use as a porous metal body used in various filters,
battery electrodes, etc. and a method for producing the aluminum
structure.
BACKGROUND ART
[0003] Porous metal bodies having a three-dimensional network
structure are used in various applications such as filters,
catalyst supports, and battery electrodes. For example, Celmet
(manufactured by Sumitomo Electric Industries, Ltd.: registered
trademark) composed of nickel is used as an electrode material of a
battery such as a nickel-metal hydride battery or a nickel-cadmium
battery. Celmet is a porous metal body having continuous pores, and
has a feature that the porosity thereof is higher (90% or more)
than that of other porous bodies such as metal nonwoven fabrics.
Celmet is produced by forming a nickel layer on a surface of a
skeleton of a resin foam body having continuous pores, such as
urethane foam, decomposing the resin foam body by heat treatment,
and then conducting a reduction treatment on nickel. The nickel
layer is formed by performing a conductivity-imparting treatment by
applying a carbon powder or the like onto the surface of the
skeleton of the resin foam body, and then depositing nickel by
electroplating.
[0004] Aluminum is excellent in terms of electrical conductivity
and corrosion resistance, and is a lightweight material. Regarding
the applications of aluminum to batteries, for example, an aluminum
foil whose surface is coated with an active material such as
lithium cobalt oxide is used as a positive electrode of a
lithium-ion battery. One conceivable method for improving the
capacity of a positive electrode is to process aluminum into a
porous body so as to increase the surface area and to fill the
interior of the porous aluminum body with an active material. This
is because, with this structure, the active material can be
efficiently utilized even in an electrode having a large thickness,
and the ratio of utilizing the active material per unit area can be
improved.
[0005] As for a method for producing a porous aluminum body, PTL 1
describes a method for forming a metallic aluminum layer of 2 to 20
.mu.m on a plastic base having inner continuous spaces and a
three-dimensional network shape by performing an aluminum vapor
deposition process by an arc ion plating method. PTL 2 describes a
method for obtaining a porous metal body by forming a coating film
of a metal (such as copper), which will form a eutectic alloy at a
temperature equal to or lower than the melting point of aluminum,
on a skeleton of a resin foam body having a three-dimensional
network structure, then applying an aluminum paste thereto, and
conducting heat treatment at a temperature of 550.degree. C. or
higher and 750.degree. C. or lower in a non-oxidizing atmosphere to
eliminate an organic component (resin foam) and sinter an aluminum
powder.
[0006] As for plating of aluminum, it is difficult to conduct
aluminum electroplating in an aqueous solution-based plating bath
because aluminum has high affinity to oxygen and an electric
potential lower than that of hydrogen. Therefore, for aluminum
electroplating, non-aqueous solution-based plating baths have been
studied. For example, as for a technique of aluminum plating for
the purpose of preventing oxidation of a metal surface or the like,
PTL 3 discloses a method of electroplating of aluminum in which a
low-melting-point composition prepared by mixing and melting an
onium halide and an aluminum halide is used as a plating bath and
aluminum is deposited on a cathode while maintaining the water
content in the bath at 2% by weight or less.
CITATION LIST
Patent Literature
[0007] [PTL 1] Japanese Patent No. 3413662
[0008] [PTL 2] Japanese Unexamined Patent Application Publication
No. 8-170126
[0009] [PTL 3] Japanese Patent No. 3202072
SUMMARY OF INVENTION
Technical Problem
[0010] PTL 1 describes that a porous aluminum body having a
thickness of 2 to 20 .mu.m is obtained by the method disclosed
therein. However, it is difficult to produce a porous aluminum body
having a large area because a gas phase method is employed, and it
is also difficult to form a layer that is uniform even in the
interior of the base depending on the thickness and the porosity of
the base. In addition, this method has problems in that the rate of
formation of the aluminum layer is low and the production cost
increases because the equipment is expensive. Furthermore, in the
case of the formation of a thick film, cracks may be formed in the
film and the aluminum film may be detached. According to the method
disclosed in PTL 2, a layer that forms a eutectic alloy with
aluminum is formed and thus an aluminum layer having a high purity
cannot be formed. Although aluminum electroplating methods are
known, only metal surfaces can be plated by the methods and a
method for electroplating a surface of a resin body, in particular,
a method for electroplating a surface of a porous resin body having
a three-dimensional network structure, has not been known. It is
believed that this is due to problems such as dissolution of porous
resins in plating baths.
[0011] The inventors of the present invention have conceived, as a
method with which aluminum plating can be conducted even on a
porous resin body having a three-dimensional network structure and
a porous aluminum body having a high purity can be formed by
uniformly forming a thick film, a method for producing a porous
aluminum body including imparting electrical conductivity to a
surface of a resin body having a three-dimensional network
structure and composed of polyurethane, a melamine resin, or the
like, and then plating aluminum in a molten-salt bath, and have
filed an application for a patent. Examples of the method for
imparting electrical conductivity to a surface of a resin body
include non-electrolytic plating of a conductive metal such as
nickel, deposition of a metal such as aluminum by a gas phase
method (such as sputtering or vapor deposition), and application of
a conductive coating material containing conductive particles such
as carbon particles. After the plating of aluminum, the resin body
is removed. Thus, an aluminum structure mainly composed of aluminum
is obtained.
[0012] When electrical conductivity is imparted to a resin body
using a metal other than aluminum, such as nickel, the metal other
than aluminum remains as an impurity in the resulting aluminum
structure. For use where the purity of aluminum is required, e.g.,
for use as a battery electrode, since the presence of such an
impurity prevents satisfactory characteristics from being realized,
this method for imparting electrical conductivity is not suitable.
An aluminum structure having a high purity can be produced by
imparting electrical conductivity using aluminum. However, in order
to impart electrical conductivity using aluminum, it is necessary
to employ a gas phase method such as vapor deposition or
sputtering, and thus the production cost is increased.
[0013] The application of a conductive coating material containing
conductive carbon is a relatively easy method, and production can
be performed at a low cost. In addition, a metal other than
aluminum, such as nickel, does not remain. However, in the case
where electrical conductivity is imparted by using conductive
carbon, it is difficult to completely remove the conductive carbon
in a step of removing a resin body after a plating step of
aluminum, and carbon remains as an impurity in the resulting
aluminum structure. When the amount of carbon remaining in the
aluminum structure is increased, the aluminum structure is easily
broken from a starting point due to the residual carbon, which may
cause a decrease in the strength of the aluminum structure.
Residual carbon may also cause welding defects in a step of
preparing a battery electrode.
[0014] Accordingly, an object of the present invention is to
provide a method for producing an aluminum structure using a resin
body, in particular, a porous resin body having a three-dimensional
network structure, the method being capable of preparing an
aluminum structure having a low impurity content, and being capable
of obtaining an aluminum structure having a large area and, in
particular, suitable for use as an electrode.
Solution to Problem
[0015] The present invention provides a method for producing an
aluminum structure, the method including a conductivity-imparting
step of applying a conductive coating material containing
conductive carbon onto a surface of a resin body to impart
electrical conductivity to the resin body; a plating step of
plating a surface of the resin body, to which electrical
conductivity has been imparted, with aluminum in a molten salt to
form an aluminum layer; and a heat treatment step of conducting
heat treatment to remove the resin body, wherein the conductive
carbon is carbon black having an average particle diameter of 0.003
.mu.m or more and 0.05 .mu.m or less.
[0016] Hitherto, in order to impart electrical conductivity to a
resin body in producing nickel Celmet or the like, graphite having
an average particle diameter of about 1.5 .mu.m has been used as
conductive carbon. In producing of nickel Celmet, a resin body is
removed in a high-temperature atmosphere at about 600.degree. C. to
800.degree. C. in the air, and a reduction treatment is further
conducted at 1,000.degree. C. In such a high-temperature
atmosphere, conductive carbon can be satisfactorily decomposed and
removed even when graphite having a relatively large average
particle diameter is used. However, the melting point of aluminum
is 660.degree. C., and it is necessary to remove a resin body at a
temperature equal to or lower than this temperature. Furthermore,
aluminum is easily oxidized, and once aluminum is oxidized, a
reduction treatment cannot be performed at a temperature equal to
or lower than the melting point. Thus, the heat treatment
temperature is preferably low. As a result of studies on the type
of conductive carbon that can be satisfactorily removed by such a
low-temperature treatment, it was found that carbon can be
satisfactorily removed by a treatment at a relatively low
temperature and an aluminum structure having a low residual carbon
content can be obtained by using conductive carbon black that does
not have crystallinity but is amorphous and that has an average
particle diameter of 0.003 .mu.m or more and 0.05 .mu.m or
less.
[0017] The heat treatment step is preferably conducted at a
temperature of 500.degree. C. or higher and 640.degree. C. or lower
in an atmosphere containing oxygen. When the temperature exceeds
640.degree. C., oxidation of aluminum easily proceeds. Thus, when
the resulting aluminum structure is used as an electrode material
for batteries, current collecting characteristics decrease. When
the temperature is lower than 500.degree. C., the amount of
residual conductive carbon increases. The heat treatment
temperature is more preferably 580.degree. C. or higher and
620.degree. C. or lower. When the heat treatment step is conducted
in an atmosphere containing oxygen, conductive carbon can be
removed within a short time.
[0018] In particular, a resin body having a complex skeleton
structure, such as a porous resin body having a three-dimensional
network structure, may be used. In this case, an aluminum structure
having a high porosity can be obtained and suitably used in
application to an electrode, etc. In addition, the resin body is
preferably composed of polyurethane, which can provide a porous
resin body having a high porosity and can be satisfactorily
decomposed in the heat treatment step.
[0019] An aluminum structure is produced through the above steps.
The aluminum structure has a high purity, and a carbon content of
the aluminum structure may be 2% by weight or less. The carbon
content in the aluminum structure can be measured by a
high-frequency combustion infrared absorption method using a
high-frequency induction heating furnace.
Advantageous Effects of Invention
[0020] According to the present invention, it is possible to
provide a method for forming an aluminum structure having a low
impurity content using a resin body, in particular, a porous resin
body having a three-dimensional network structure, and the aluminum
structure.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a flowchart showing steps of producing an aluminum
structure according to the present invention.
[0022] FIG. 2 includes schematic cross-sectional views illustrating
steps of producing an aluminum structure according to the present
invention.
[0023] FIG. 3 is an enlarged photograph of a surface showing the
structure of urethane foam, which is an example of a porous resin
body.
[0024] FIG. 4 is a view illustrating an example of a continuous
step of imparting electrical conductivity to a surface of a resin
body by using a conductive coating material.
[0025] FIG. 5 is a view illustrating an example of a continuous
step of aluminum plating by molten-salt plating.
[0026] FIG. 6 is a schematic cross-sectional view illustrating a
structural example in which a porous aluminum body is applied to a
molten-salt battery.
[0027] FIG. 7 is a schematic cross-sectional view illustrating a
structural example in which a porous aluminum body is applied to an
electrical double layer capacitor.
DESCRIPTION OF EMBODIMENTS
[0028] Embodiments of the present invention will now be described.
In the drawings referred to below, parts that are assigned the same
numeral are the same or corresponding parts. Note that the present
invention is not limited to the embodiments but defined by the
claims, and is intended to include all modifications within the
scope and meaning of equivalents of the claims.
Steps of Producing Aluminum Structure
[0029] FIG. 1 is a flowchart showing steps of producing an aluminum
structure according to the present invention. FIG. 2 schematically
illustrates steps of forming the aluminum structure using a resin
body as a core material in accordance with the flowchart. The
overall flow of the production steps will be described with
reference to the two figures. First, preparation 101 of a resin
body serving as a base is conducted. FIG. 2(a) is an enlarged
schematic view of an enlarged surface of a resin foam body having
continuous pores. Pores are formed by a resin foam body 1 serving
as a skeleton. Next, impartation of electrical conductivity 102 to
the surface of the resin body is conducted. In this step, a thin,
electrically conductive layer 2 is formed on the surface of the
resin body 1, as illustrated in FIG. 2(b). Subsequently, aluminum
plating 103 in a molten salt is conducted to form an aluminum
plating layer 3 on the surface of the resin body having the
electrically conductive layer thereon (FIG. 2(c)). Thus, an
aluminum-coated resin body in which the aluminum plating layer 3 is
formed on the surface of the resin body serving as the base is
prepared. Subsequently, removal 104 of the resin body is conducted.
The aluminum-coated resin body is heat-treated to decompose and
remove the resin foam body 1, thereby obtaining an aluminum
structure (porous body) constituted by only the metal layer (FIG.
2(d)). These steps will be sequentially described below.
Preparation of Porous Resin Body
[0030] A resin foam body composed of polyurethane and having a
three-dimensional network structure and continuous pores is
prepared. A resin body having any shape may be selected as long as
the resin body has pores that are continuous (continuous pores).
For example, a nonwoven fabric including entangled resin fibers may
also be used instead of the resin foam body. The resin foam body
preferably has a porosity of 80% to 98% and a pore diameter of 50
to 500 .mu.m. Urethane foam is preferably used as the resin foam
body because urethane foam has a high porosity and pore continuity,
and is good in terms of uniformity of pores.
[0031] A resin foam body often contains residues such as a foaming
agent and an unreacted monomer in the process of producing the
foam. Therefore, a washing treatment is preferably performed for
the subsequent steps. FIG. 3 shows, as an example of a resin foam
body, urethane foam that has been subjected to a washing treatment.
The resin body serving as a skeleton constitutes a network
three-dimensionally, thereby forming continuous pores as a whole.
The skeleton of polyurethane foam has a substantially triangular
shape in a cross section perpendicular to a direction in which the
skeleton extends. Herein, the porosity is defined by the following
formula.
Porosity=(1-(weight of porous material [g]/(volume of porous
material [cm.sup.3].times.density of raw
material)).times.100[%]
[0032] The pore diameter is determined by magnifying a surface of
the resin body by means of a photomicrograph or the like, counting
a cell number per inch (25.4 mm), and calculating an average value
as mean pore diameter=25.4 mm/cell number.
Impartation of Electrical Conductivity to Resin Body Surface:
Application of Conductive Coating Material
[0033] A conductive coating material is prepared in which carbon
black having an average particle diameter of 0.003 .mu.m or more
and 0.05 .mu.m or less is used as conductive carbon. The conductive
coating material is a suspension containing conductive carbon, a
binder, a dispersant, and a dispersion medium. In order to
uniformly apply conductive particles, it is necessary that the
suspension maintain a uniform suspension state. Accordingly, the
suspension is preferably maintained at 20.degree. C. to 40.degree.
C. This is because when the temperature of the suspension is lower
than 20.degree. C., a uniform suspension state is impaired, and
only the binder is concentrated on a surface of the skeleton
constituting a strip-shaped structure of the resin body and forms a
layer. In such a case, the applied layer of carbon particles is
easily separated and it is difficult to form metal plating that
tightly adheres to the layer of carbon particles. On the other
hand, when the temperature of the suspension exceeds 40.degree. C.,
the amount of evaporation of the dispersion medium is large.
Accordingly, the suspension is concentrated with the lapse of the
application process time, and the amount of carbon applied tends to
vary.
[0034] Carbon black which is amorphous carbon is used as the
conductive carbon. The average particle diameter of the conductive
carbon is 0.003 .mu.m or more and 0.05 .mu.m or less, and more
preferably 0.005 .mu.m or more and 0.02 .mu.m or less. When the
average particle diameter is excessively large, decomposability in
a heat treatment step decreases. When the average particle diameter
is excessively small, it is difficult to ensure sufficient
electrical conductivity. Note that the average particle diameter is
a value calculated from a specific surface area measured using a
specific surface area measuring device.
[0035] The porous resin body can be coated with carbon particles by
immersing a target resin body in the suspension and squeezing and
drying the resin body. FIG. 4 is a view that schematically
illustrates, as an example of a practical production process, the
structure of a treatment apparatus that imparts electrical
conductivity to a strip-shaped porous resin body serving as a
skeleton. As illustrated in the figure, this apparatus includes a
supply bobbin 12 that supplies a strip-shaped resin 11, a vessel 15
that contains a suspension 14 of a conductive coating material, a
pair of squeeze rolls 17 arranged above the vessel 15, a plurality
of hot air nozzles 16 provided so as to face each other on the
sides of the travelling strip-shaped resin 11, and a take-up bobbin
18 that takes up the strip-shaped resin 11 after a treatment.
Deflector rolls 13 for guiding the strip-shaped resin 11 are
arranged at appropriate positions. In the apparatus having the
above structure, the strip-shaped resin 11 having a
three-dimensional network structure is unwound from the supply
bobbin 12, guided by the deflector rolls 13, and immersed in the
suspension in the vessel 15. The strip-shaped resin 11 immersed in
the suspension 14 in the vessel 15 is turned upward and travels
between the squeeze rolls 17 above the liquid surface of the
suspension 14. At this time, the gap between the squeeze rolls 17
is smaller than the thickness of the strip-shaped resin 11 and the
strip-shaped resin 11 is compressed. Thus, excess suspension
impregnated in the strip-shaped resin 11 is squeezed out and
returns to the vessel 15.
[0036] Subsequently, the direction in which the strip-shaped resin
11 travels is changed again. Here, the dispersion medium etc. in
the suspension are removed by hot air blown from the hot air
nozzles 16, which are constituted by a plurality of nozzles, and
the strip-shaped resin 11 that are thoroughly dried is taken up by
the take-up bobbin 18. The temperature of the hot air blown from
the hot air nozzles 16 is preferably in the range of 40.degree. C.
to 80.degree. C. With the apparatus described above, a
conductivity-imparting treatment can be conducted automatically and
continuously and a skeleton having a network structure free of
clogging and a uniform conductive layer is formed. Thus, metal
plating, which is the subsequent step, can be smoothly
conducted.
Formation of Aluminum Layer: Molten-Salt Plating
[0037] Next, electrolytic plating is conducted in a molten salt to
form an aluminum plating layer 3 on the surface of the resin body.
A direct current is supplied between the resin body having a
surface to which electrical conductivity is imparted, the resin
body serving as a cathode, and an aluminum plate having a purity of
99.99% and serving as an anode in a molten salt. The aluminum
plating layer has a thickness of 1 to 100 .mu.m, and preferably 5
to 20 .mu.m. The molten salt may be an organic molten salt that is
a eutectic salt of an organohalide and an aluminum halide or an
inorganic molten salt that is a eutectic salt of an alkali metal
halide and an aluminum halide. An organic molten-salt bath that
melts at a relatively low temperature is preferably used because
plating can be performed without decomposition of a resin body
serving as a base. An imidazolium salt, a pyridinium salt, or the
like can be used as the organohalide. Specifically,
1-ethyl-3-methylimidazolium chloride (EMIC) and butylpyridinium
chloride (BPC) are preferred. A salt containing an imidazolium
cation having alkyl groups at the 1- and 3-positions is preferably
used as the imidazolium salt. In particular, a molten salt of
aluminum chloride and 1-ethyl-3-methylimidazolium chloride
(AlCl.sub.3-EMIC) is most preferably used because it has high
stability and is not easily decomposed.
[0038] Mixing of moisture or oxygen into the molten salt degrades
the molten salt. Therefore, plating is preferably conducted in an
inert gas atmosphere such as nitrogen or argon in a closed
environment. In the case where an EMIC bath is used as an organic
molten-salt bath, the temperature of the plating bath is 10.degree.
C. to 60.degree. C., and preferably 25.degree. C. to 45.degree.
C.
[0039] In the case where an imidazolium salt bath is used as a
molten-salt bath, an organic solvent is preferably added to the
molten-salt bath. Xylene is particularly preferably used as the
organic solvent. Addition of an organic solvent in particular,
xylene, achieves advantages specific to the formation of a porous
aluminum body. Specifically, it is possible to obtain a first
feature that the aluminum skeleton forming a porous body is not
easily broken and a second feature that uniform plating can be
performed in which a difference in plating thickness between a
surface portion and an inner portion of the porous body is small.
The first feature is due to the fact that the addition of an
organic solvent improves the shape of plating on the skeleton
surface from a granular state (which is significantly uneven and
appears to be granules in surface observation) to a flat shape,
thereby increasing the strength of the skeleton having a small
thickness and a small width. The second feature is due to the fact
that the addition of an organic solvent to a molten-salt bath
decreases the viscosity of the molten-salt bath and the plating
bath easily passes through the inner portion of the fine network
structure. More specifically, when the viscosity is high, a fresh
plating bath is easily supplied to the surface of the porous body,
but is not easily supplied to the inner portion. In contrast, by
decreasing the viscosity, the plating bath is easily supplied to
the inner portion, and thus plating that provides a uniform
thickness can be performed. The amount of organic solvent added to
the plating bath is preferably 25% to 57% by mole. When the amount
of organic solvent is 25% by mole or less, it is difficult to
achieve the effect of reducing the difference in plating thickness
between a surface layer and an inner portion. When the amount of
organic solvent is 57% by mole or more, the plating bath becomes
unstable and a plating solution and xylene are partially
separated.
[0040] Furthermore, subsequent to the step of conducting plating
using the molten-salt bath containing an organic solvent, a washing
step in which the organic solvent is used as a washing liquid is
preferably performed. It is necessary to wash a surface of a plated
resin in order to wash away a plating bath. Such washing after
plating is usually performed with water. However, it is essential
that moisture be avoided in an imidazolium salt bath. If washing is
performed with water, water is taken in a plating solution in the
form of water vapor or the like. Thus, washing with water should be
avoided in order to prevent adverse effects on plating.
Accordingly, washing with an organic solvent is effective.
Furthermore, in the case where an organic solvent is added to a
plating bath as described above, a more advantageous effect can be
obtained by conducting washing with the organic solvent added to
the plating bath. Specifically, the washed plating solution can be
relatively easily recovered and reused, and the cost can be
reduced. For example, it is supposed that a plated body formed in a
bath prepared by adding xylene to a molten salt AlCl.sub.3-EMIC is
washed with xylene. The resulting liquid after washing is a liquid
that contains xylene in an amount larger than that of the plating
bath that is originally used. A certain amount or more of the
molten salt AlCl.sub.3-EMIC is not mixed with xylene. Thus, the
liquid after washing is separated into xylene on the upper side and
the molten salt AlCl.sub.3-EMIC containing about 57% by mole of
xylene on the lower side. Therefore, the molten liquid can be
recovered by collecting the separated liquid on the lower side.
Furthermore, since the boiling point of xylene is as low as
144.degree. C., the xylene concentration in the recovered molten
salt is adjusted to the xylene concentration in the plating
solution by applying heat, and the resulting solution can be
reused. After the washing with an organic solvent, it is also
preferable to further conduct washing with water in another place
that is separated from the plating bath.
[0041] FIG. 5 is a view that schematically illustrates the
structure of an apparatus for continuously conducting a metal
plating treatment on a strip-shaped resin. This figure illustrates
a structure in which a strip-shaped resin 22 having a surface to
which electric conductivity has been imparted is transported from
the left to the right of the figure. A first plating vessel 21a
includes a cylindrical electrode 24, a positive electrode 25
provided on the inner wall of the container, and a plating bath 23.
The strip-shaped resin 22 passes through the plating bath 23 along
the cylindrical electrode 24. Thus, an electrical current can
evenly and easily flows in the entire resin body and uniform
plating can be obtained. A second plating vessel 21b is a vessel
for further forming thick and uniform plating and is configured so
that plating is repeatedly performed in a plurality of vessels.
Plating is conducted by allowing the strip-shaped resin 22 having a
thin metal layer on a surface thereof to pass through a plating
bath 28 while sequentially feeding the strip-shaped resin 22 using
electrode rollers 26 functioning as both transfer rollers and
out-of-vessel power-supply negative electrodes. Positive electrodes
27 are provided in the plurality of vessels so as to face two
surfaces of the resin with the plating bath 28 therebetween. With
this structure, the two surfaces of the resin can be coated with a
more uniform plating film.
Decomposition of Resin: Heat Treatment
[0042] Through the above steps, an aluminum-coated resin body
including a resin body as a core of the skeleton is prepared. Next,
the resin body is removed. The aluminum-coated resin body is
heat-treated at a temperature of 500.degree. C. or higher and
640.degree. C. or lower to decompose the resin body and conductive
carbon. When the heat treatment is conducted in the presence of
oxygen, a urethane decomposition reaction easily proceeds and the
conductive carbon can also be satisfactorily decomposed. Heat
treatment performed with a gas flow is preferable because
decomposition products are effectively removed.
Lithium-Ion Battery
[0043] Next, a battery electrode material and a battery that use an
aluminum structure will be described. For example, when an aluminum
structure is used in a positive electrode of a lithium-ion battery,
lithium cobalt oxide (LiCoO.sub.2), lithium manganese oxide
(LiMn.sub.2O.sub.4), lithium nickel oxide (LiNiO.sub.2), or the
like is used as an active material. The active material is used in
combination with a conductive aid and a binder. A known positive
electrode material for a lithium-ion battery is obtained by coating
a surface of an aluminum foil with an active material. The
thickness of the active material coating is increased in order to
improve the battery capacity per unit area. In order to effectively
utilize the active material, it is necessary that the aluminum foil
and the active material electrically contact with each other, and
thus the active material is mixed with a conductive aid. In
contrast, the aluminum structure of the present invention has a
high porosity and a large surface area per unit area. Accordingly,
the active material can be effectively utilized even when an active
material having a small thickness is supported on the surface of
the aluminum structure, the capacity of the battery can be
improved, and the amount of conductive aid mixed can be reduced. In
a lithium-ion battery, the positive electrode material described
above is used as the positive electrode, graphite is used as the
negative electrode, and an organic electrolyte solution is used as
an electrolyte. Such a lithium-ion battery can have an improved
capacity even when it has a small electrode area. Therefore, the
energy density of the battery can be made higher than the energy
densities of known lithium ion batteries.
Molten-Salt Battery
[0044] An aluminum structure can also be used as an electrode
material for a molten-salt battery. When a porous aluminum body is
used as a positive electrode material, a metal compound that can
intercalate a cation of a molten salt serving as an electrolyte,
for example, sodium chromate (NaCrO.sub.2) or titanium disulfide
(TiS.sub.2)), is used as the active material. The active material
is used in combination with a conductive aid and a binder.
Acetylene black and the like can be used as the conductive aid.
Polytetrafluoroethylene (PTFE) and the like can be used as the
binder. When sodium chromate is used as the active material and
acetylene black is used as the conductive aid, PTFE is preferred
because it can more firmly bond the two substances to each
other.
[0045] An aluminum structure can also be used as a negative
electrode material of a motel-salt battery. When a porous aluminum
body is used as the negative electrode material, elemental sodium,
an alloy of sodium and another metal, carbon, or the like can be
used as the active material. Since the melting point of sodium is
about 98.degree. C. and the metal softens with an increase in
temperature, sodium is preferably alloyed with another metal (such
as Si, Sn, or In). Among these, an alloy of sodium and Sn is
particularly preferable because the alloy is easy to handle. Sodium
or a sodium alloy can be supported on the surface of the porous
aluminum body by electrolytic plating, hot dipping, or the like.
Alternatively, a sodium alloy can be formed by depositing a metal
(such as Si) to be alloyed with sodium on a porous aluminum body by
plating or the like and then conducting charging in the molten-salt
battery.
[0046] FIG. 6 is a schematic cross-sectional view illustrating an
example of a molten-salt battery that uses the above-described
electrode material for a battery. The molten-salt battery includes
a positive electrode 121 in which a positive electrode active
material is supported on the surface of the aluminum skeleton
portion of an aluminum structure, a negative electrode 122 in which
a negative electrode active material is supported on the surface of
the aluminum skeleton portion of an aluminum structure, and a
separator 123 impregnated with a molten salt serving as an
electrolyte. The positive electrode 121, the negative electrode
122, and the separator 123 are housed in a case 127. A pressing
member 126 including a pressing plate 124 and a spring 125 that
presses the pressing plate is arranged between the upper surface of
the case 127 and the negative electrode. Since the pressing member
is provided, even when the positive electrode 121, the negative
electrode 122, and the separator 123 are subjected to volume
changes, all the components can be uniformly pressed and brought
into contact with each other. A collector (porous aluminum body) of
the positive electrode 121 and a collector (porous aluminum body)
of the negative electrode 122 are respectively connected to a
positive electrode terminal 128 and a negative electrode terminal
129 through lead wires 130.
[0047] Various inorganic salts or organic salts that melt at an
operating temperature can be used as the molten salt serving as an
electrolyte. At least one selected from alkali metals such as
lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium
(Cs) and alkaline earth metals such as beryllium (Be), magnesium
(Mg), calcium (Ca), strontium (Sr), and barium (Ba) can be used as
the cation of the molten salt.
[0048] In order to decrease the melting point of the molten salt,
two or more salts are preferably used as a mixture. For example,
when potassium bis(fluorosulfonyl)amide (KFSA) and sodium
bis(fluorosulfonyl)amide (NaFSA) are used in combination, the
operating temperature of the battery can be controlled to be
90.degree. C. or lower.
[0049] The molten salt is used by impregnating the separator. The
separator is provided in order to prevent the positive electrode
and the negative electrode from contacting each other. A glass
nonwoven fabric, a porous resin, and the like can be used as the
separator. The positive electrode, the negative electrode, and the
separator impregnated with the molten salt are stacked, housed in
the case, and used as a battery.
Electrical Double Layer Capacitor
[0050] An aluminum structure can also be used as an electrode
material for an electrical double layer capacitor. When an aluminum
structure is used as an electrode material for an electrical double
layer capacitor, activated carbon or the like is used as an
electrode active material. Activated carbon is used in combination
with a conductive aid and a binder. Graphite, carbon nanotubes, and
the like can be used as the conductive aid. Polytetrafluoroethylene
(PTFE), styrene-butadiene rubber, and the like can be used as the
binder.
[0051] FIG. 7 is a schematic cross-sectional view illustrating an
example of an electrical double layer capacitor that uses the
above-described electrode material for an electrical double layer
capacitor. An electrode material in which an electrode active
material is supported on an aluminum structure is arranged as
polarizable electrodes 141 in an organic electrolyte solution 143
partitioned by a separator 142. Each of the polarizable electrodes
141 is connected to a lead wire 144. All of these components are
housed in a case 145. By using a porous aluminum body as a
collector, the surface area of the collector is increased. Thus, an
electrical double layer capacitor that can realize high output and
high capacity can be produced even when activated carbon serving as
an active material is thinly applied.
[0052] A description has been made of a case where a resin foam
body is used as a resin body, but the present invention is not
limited to a resin foam body. An aluminum structure having any
shape can be obtained by using a resin body having any shape.
Formation of Electrically Conductive Layer: Example 1
[0053] A production example of an aluminum structure will be
specifically described below. A urethane foam having a thickness of
1 mm, a porosity of 95%, and the number of pores per centimeter of
about 20 was prepared as a resin foam body and cut into a 15
mm.times.15 mm square. The urethane foam was immersed in a carbon
suspension and dried to form an electrically conductive layer, the
entire surface of which had carbon particles adhering thereon. The
suspension contained, as components, 80% by weight of conductive
carbon black having an average particle diameter of 0.01 .mu.m, a
resin binder serving as a binder, a penetrant, an antifoamer, and a
dispersion medium.
Formation of Electrically Conductive Layer: Comparative Example
1
[0054] A urethane foam having a thickness of 1 mm, a porosity of
95%, and the number of pores per centimeter of about 20 was
prepared as a resin foam body and cut into a 15 mm.times.15 mm
square. The urethane foam was immersed in a carbon suspension and
dried to form an electrically conductive layer, the entire surface
of which had carbon particles adhering thereon. The suspension
contained, as components, 80% by weight of graphite having an
average particle diameter of 1.5 .mu.m, a resin binder serving as a
binder, a penetrant, an antifoamer, and a dispersion medium.
Formation of Electrically Conductive Layer: Comparative Example
2
[0055] A urethane foam having a thickness of 1 mm, a porosity of
95%, and the number of pores per centimeter of about 20 was
prepared as a resin foam body and cut into a 15 mm.times.15 mm
square. The urethane foam was immersed in a carbon suspension and
dried to form an electrically conductive layer, the entire surface
of which had carbon particles adhering thereon. The suspension
contained, as components, 80% by weight of graphite having an
average particle diameter of 1.0 .mu.m, a resin binder serving as a
binder, a penetrant, an antifoamer, and a dispersion medium.
Molten-Salt Plating
[0056] Each of the urethane foams produced in Example 1,
Comparative Example 1, and Comparative Example 2 and having an
electrically conductive layer on the surface thereof was set to a
fixture having a power-supplying function, and then immersed in a
molten salt aluminum plating bath (67 mol % AlCl.sub.3-33 mol %
EMIC) at a temperature of 40.degree. C. The fixture to which the
urethane foam was set was connected to the cathode side of a
rectifier, and an aluminum plate (purity: 99.99%) serving as a
counter electrode was connected to the anode side. Plating was
conducted for 90 minutes at a current density of 3.6 A/dm.sup.2.
Herein, the current density is a value calculated on the basis of
the apparent area of the urethane foam. As a result, an aluminum
plating layer having a weight of 150 g/m.sup.2 could be formed.
Decomposition of Resin Foam Body
[0057] The resin foam bodies each having an aluminum plating layer
thereon were heat-treated at a temperature of 600.degree. C. for 30
minutes in the air atmosphere to prepare aluminum structures of
Example 1, Comparative Example 1, and Comparative Example 2. The
residual carbon content of each of the aluminum structures was
measured by a high-frequency combustion infrared absorption method.
The residual carbon content of the aluminum structure of Example 1
was low; 1.3% by weight (2.0 g/m.sup.2). In contrast, the residual
carbon content of Comparative Example 1 was 5.5% by weight (8.2
g/m.sup.2) and the residual carbon content of Comparative Example 2
was 3.0% by weight (4.5 g/m.sup.2).
[0058] The above description encompasses other embodiments
described below.
Other Embodiment 1
[0059] An electrode material in which an active material is
supported on an aluminum surface of an aluminum structure obtained
by the present invention.
Other Embodiment 2
[0060] A battery in which the electrode material described in Other
Embodiment 1 is used in at least one of a positive electrode and a
negative electrode.
Other Embodiment 3
[0061] An electrical double layer capacitor in which the electrode
material described in Other Embodiment 1 is used as an
electrode.
Other Embodiment 4
[0062] A filtration filter including an aluminum structure obtained
by the present invention.
Other Embodiment 5
[0063] A catalyst support in which a catalyst is supported on a
surface of an aluminum structure obtained by the present
invention.
INDUSTRIAL APPLICABILITY
[0064] As described above, according to the present invention, a
porous aluminum structure can be obtained. Thus, for example, the
present invention can be widely used in various fields in which
characteristics of aluminum are utilized, for example, in electric
materials such as battery electrodes, filters for various types of
filtration, and catalyst supports.
REFERENCE SIGNS LIST
[0065] 1 resin foam body 2 electrically conductive layer 3 aluminum
plating layer 11 strip-shaped resin 12 supply bobbin 13 deflector
roll 14 suspension 15 vessel 16 hot air nozzle 17 squeeze roll 18
take-up bobbin [0066] 21a, 21b plating vessel 22 strip-shaped resin
[0067] 23, 28 plating bath 24 cylindrical electrode [0068] 25, 27
positive electrode 26 electrode roller [0069] 121 positive
electrode 122 negative electrode 123 separator 124 pressing plate
125 spring 126 pressing member 127 case 128 positive electrode
terminal 129 negative electrode terminal 130 lead wire [0070] 141
polarizable electrode 142 separator 143 organic electrolyte
solution 144 lead wire 145 case
* * * * *