U.S. patent application number 13/237218 was filed with the patent office on 2012-03-22 for manufacturing method of aluminum structure and aluminum structure.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. Invention is credited to Tomoyuki Awazu, Akihisa HOSOE, Shinji Inazawa, Masatoshi Majima, Koji Nitta, Kazuki Okuno, Shoichiro Sakai.
Application Number | 20120067731 13/237218 |
Document ID | / |
Family ID | 44834070 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120067731 |
Kind Code |
A1 |
HOSOE; Akihisa ; et
al. |
March 22, 2012 |
MANUFACTURING METHOD OF ALUMINUM STRUCTURE AND ALUMINUM
STRUCTURE
Abstract
There is provided a manufacturing method of an aluminum
structure, including a conductive treatment process of forming an
electrically conductive layer made of aluminum on a surface of a
resin molded body and a plating process of plating the resin molded
body subjected to the conductive treatment process with aluminum in
a molten salt bath. Even with a porous resin molded body having a
three-dimensional network structure, the method allows the surface
of the porous resin molded body to be plated with aluminum, thus
forming a high-purity aluminum structure having a uniform thick
film. Porous aluminum having a large area is also provided.
Inventors: |
HOSOE; Akihisa; (Osaka,
JP) ; Inazawa; Shinji; (Osaka, JP) ; Majima;
Masatoshi; (Osaka, JP) ; Nitta; Koji; (Osaka,
JP) ; Sakai; Shoichiro; (Osaka, JP) ; Awazu;
Tomoyuki; (Itami-shi, JP) ; Okuno; Kazuki;
(Itami-shi, JP) |
Assignee: |
Sumitomo Electric Industries,
Ltd.
Osaka-shi
JP
|
Family ID: |
44834070 |
Appl. No.: |
13/237218 |
Filed: |
September 20, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2011/058782 |
Apr 7, 2011 |
|
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13237218 |
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Current U.S.
Class: |
205/50 ; 205/112;
205/165; 205/166 |
Current CPC
Class: |
H01G 9/155 20130101;
H01G 11/44 20130101; H01M 10/399 20130101; C22C 1/08 20130101; H01M
10/052 20130101; H01G 11/86 20130101; H01M 4/131 20130101; Y02E
60/10 20130101; H01G 11/26 20130101; H01G 11/70 20130101; H01G
11/74 20130101; H01M 4/661 20130101; H01M 4/80 20130101; Y02E 60/13
20130101; C25D 5/56 20130101; H01G 11/04 20130101; H01G 9/045
20130101; H01G 11/02 20130101 |
Class at
Publication: |
205/50 ; 205/165;
205/166; 205/112 |
International
Class: |
C25D 5/56 20060101
C25D005/56; C25D 7/00 20060101 C25D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2010 |
JP |
2010-098335 |
Claims
1. A manufacturing method of an aluminum structure, comprising: a
conductive treatment process of forming an electrically conductive
layer made of aluminum on a surface of a resin molded body; and a
plating process of plating the resin molded body subjected to the
conductive treatment process with aluminum in a molten salt
bath.
2. The manufacturing method of an aluminum structure according to
claim 1, further comprising an anode electrolysis process of
performing electrolysis treatment using the electrically conductive
layer as an anode between the conductive treatment process and the
plating process.
3. The manufacturing method of an aluminum structure according to
claim 1, wherein the resin molded body subjected to the conductive
treatment process is transported between the conductive treatment
process and the plating process without being exposed to an
oxidizing atmosphere.
4. The manufacturing method of an aluminum structure according to
claim 1, wherein the conductive treatment process is a process of
depositing aluminum on the surface of the resin molded body by a
gas phase method.
5. The manufacturing method of an aluminum structure according to
claim 1, wherein the conductive treatment process is a process of
dipping the resin molded body in a coating material containing
aluminum to deposit aluminum on the surface of the resin molded
body.
6. The manufacturing method of an aluminum structure according to
claim 1, wherein the resin molded body is a porous resin article
having a three-dimensional network structure.
7. The manufacturing method of an aluminum structure according to
claim 1, wherein the resin molded body is made of urethane or
melamine.
8. The manufacturing method of an aluminum structure according to
claim 1, further comprising a process of removing the resin molded
body after the plating process.
9. An aluminum structure manufactured by the method according to
claim 1.
10. An aluminum structure, comprising an aluminum layer having a
thickness in the range of 1 to 100 .mu.m as a metal layer, wherein
the metal layer has an aluminum purity of 99.0% or more and a
carbon content of 1.0% or less and contains inevitable impurities
as the balance.
11. The aluminum structure according to claim 10, further
comprising a resin molded body, on which the metal layer is
disposed.
12. The aluminum structure according to claim 10, wherein the
aluminum layer has a tubular skeleton structure and forms a porous
body having generally contiguous pores.
13. The aluminum structure according to claim 12, wherein the
skeleton structure has almost triangular sections, and the aluminum
layer has a larger thickness at the vertexes of each of the
triangular sections than at the middle of each side of the
triangular sections.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of International
Application No. PCT/JP2011/058782, which claims the benefit of
priority from Japanese Patent Application No. 2010-098335, filed on
Apr. 22, 2010each of which is hereby incorporated by reference in
their entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method for forming an
aluminum structure on a resin surface by aluminum plating and, more
particularly, to an aluminum structure that can be suitably used as
a porous metal body in applications, such as various filters and
battery electrodes, and a manufacturing method of the aluminum
structure.
BACKGROUND ART
[0003] Porous metal bodies having a three-dimensional network
structure have been used in a wide range of applications, such as
various filters, catalyst supports, and battery electrodes. For
example, Celmet (manufactured by Sumitomo Electric Industries,
Ltd., registered trademark) made of nickel has been used as an
electrode material for batteries, such as nickel-hydrogen batteries
and nickel-cadmium batteries. Celmet is a porous metal body having
continuous pores and characteristically has a higher porosity (90%
or more) than other porous bodies, such as metal non-woven fabrics.
Celmet can be manufactured by forming a nickel layer on a surface
of the skeleton of a porous resin having continuous pores, such as
urethane foam, decomposing the resin expansion molded body by heat
treatment, and reducing the nickel. The nickel layer can be formed
by performing a conductive treatment of applying a carbon powder to
the surface of the skeleton of the resin expansion molded body and
then depositing nickel by electrodeposition.
[0004] Aluminum has excellent characteristics, such as conductive
property, corrosion resistance property, and lightweight. For use
in batteries, for example, aluminum foil to which an active
material, such as lithium cobalt oxide, is applied has been used as
a positive electrode of lithium-ion batteries. In order to increase
the capacity of a positive electrode, an aluminum body can be
processed into a porous body having a large surface area, and the
inside of the aluminum body can be filled with an active material.
This allows the active material to be utilized even in an electrode
having a large thickness and improves the active material
availability ratio per unit area.
[0005] As a manufacturing method of porous aluminum, Patent
Literature 1 describes a method for subjecting a plastic substrate
having an inner continuous space and a three-dimensional network to
an aluminum vapor deposition process by an arc ion plating method
to form a metallic aluminum layer having a thickness in the range
of 2 to 20 .mu.m. Patent Literature 2 describes a method for
forming a porous metal body, including forming a film made of a
metal (such as copper) on the skeleton of a resin expansion molded
body having a three-dimensional network structure, the metal having
an ability to form an eutectic alloy at a temperature of the
melting point of aluminum or less, applying an aluminum paste to
the film, and performing heat treatment in a non-oxidizing
atmosphere at a temperature of 550.degree. C. or more and
750.degree. C. or less to evaporate the organic constituent (resin
foam) and sinter the aluminum powder.
[0006] Since aluminum has high chemical affinity to oxygen and a
lower electric potential than hydrogen, the electrodeposition in a
plating bath containing an aqueous solution is difficult to perform
in aluminum plating. Aluminum electrodeposition has been studied in
a plating bath containing a non-aqueous solution, in particular a
plating bath containing an organic solvent. For example, as a
technique for plating a metal surface with aluminum, Patent
Literature 3 discloses an aluminum electrodeposition method
characterized in that a low melting composition, which is a blend
melt of an onium halide and an aluminum halogenide, is used in a
plating bath, and aluminum is deposited on a cathode while the
water content of the plating bath is maintained 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] In accordance with the method described in Patent Literature
1, porous aluminum having a thickness in the range of 2 to 20 .mu.m
can be manufactured. However, it is difficult to produce a large
area by the gas phase method and, depending on the thickness or
porosity of a substrate; it is difficult to form a layer having a
uniform interior. There are additional problems of a low rate of
formation of the aluminum layer and high manufacturing costs
because of expensive installation. Furthermore, the formation of a
thick film may cause cracking in the film or falling of aluminum.
In accordance with the method described in Patent Literature 2,
unfortunately, a layer that forms an eutectic alloy with aluminum
is formed instead of a high-purity aluminum layer. Although an
aluminum electrodeposition method is known, plating of only a metal
surface is possible, and there is no known method for
electrodeposition on a resin surface, in particular
electrodeposition on the surface of a porous resin molded body
having a three-dimensional network structure. This is probably
influenced by the dissolution of a porous resin in a plating bath
and other problems.
[0011] Accordingly, it is an object of the present invention to
provide a method for forming a high-purity aluminum structure,
including performing aluminum plating on the surface of a resin
molded body, in particular even a porous resin molded body having a
three-dimensional network structure, to form a uniform thick film,
and a manufacturing method of porous aluminum having a large
area.
Solution to Problem
[0012] In order to solve the problems described above, the present
inventors have arrived at a method for aluminum electrodeposition
of a surface of a resin molded body made of polyurethane, melamine,
or the like. The present invention provides a manufacturing method
of an aluminum structure, including a conductive treatment process
of forming an electrically conductive layer made of aluminum on a
surface of a resin molded body and a plating process of plating the
resin molded body subjected to the conductive treatment process
with aluminum in a molten salt bath (the first invention of the
present application). As described above, although aluminum plating
has been performed on metal surfaces, electrodeposition of resin
molded body surfaces has not been considered. The present invention
is characterized in that making a resin molded body surface be
electrically conductive (conductive treatment) was found to make it
possible to perform aluminum plating in a molten salt bath.
Furthermore, conductive treatment performed by forming an
electrically conductive layer made of aluminum can produce an
aluminum structure substantially free of metals other than
aluminum.
[0013] Since aluminum can easily react with oxygen, a thin oxide
film tends to be formed on a surface of an electrically conductive
layer made of aluminum. The oxide film reduces plating adhesion and
therefore results in poor plating. Thus, it is preferable to
provide an anode electrolysis process of performing electrolysis
treatment using the electrically conductive layer as an anode
between the conductive treatment process and the plating process
(the second invention of the present application). The anode
electrolysis treatment can melt and remove an oxide film formed on
the surface of the electrically conductive layer in the conductive
treatment process, allowing satisfactory aluminum plating in a
molten salt.
[0014] Preferably, the resin molded body subjected to the
conductive treatment process is transported between the conductive
treatment process and the plating process without being exposed to
an oxidizing atmosphere (the third invention of the present
application). This allows satisfactory aluminum plating in a molten
salt without oxidation of the electrically conductive layer.
[0015] The conductive treatment process may be a process of
depositing aluminum on the surface of the resin molded body by a
gas phase method (the fourth invention of the present application).
The conductive treatment process may also be a process of dipping
the resin molded body in a coating material containing aluminum to
deposit aluminum on the resin molded body (the fifth invention of
the present application). Both of these methods allow the
manufacture of a structure substantially composed of aluminum as a
metal without the contamination of metals other than aluminum.
[0016] Such a process allows the formation of a uniform thick
aluminum layer on a surface of a complicated skeleton structure, in
particular a porous resin article having a three-dimensional
network structure (the sixth invention of the present application).
The resin molded body is preferably made of urethane or melamine,
with which a porous resin article having a high porosity can be
manufactured (the seventh invention of the present
application).
[0017] An aluminum structure that includes a resin molded body
having a metal layer on a surface thereof is manufactured through
these processes (the eleventh invention of the present
application). Depending on the application, such as a filter or a
catalyst support, the aluminum structure may be directly used as a
resin-metal composite. In order to use a metal structure without
resin owing to constraints resulting from the usage environment,
the resin may be removed (the eighth invention of the present
application).
[0018] An aluminum structure manufactured by one of the methods
described above includes an aluminum layer having a thickness in
the range of 1 to 100 .mu.m as a metal layer, wherein the whole
metal layer without the resin has an aluminum purity of 99.0% or
more and a carbon content of 1.0% or less and contains inevitable
impurities as the balance (the tenth invention of the present
application). The carbon content is measured by an infrared
absorption method after combustion in a high-frequency induction
furnace in accordance with Japan Industrial Standard G1211. The
aluminum purity is measured with an inductively-coupled plasma
emission spectrometer after the aluminum structure has been
dissolved in nitromuriatic acid.
[0019] When a porous resin having a three-dimensional network
structure is used as the resin, the aluminum structure thus
manufactured includes an aluminum layer having a tubular skeleton
structure and forming a porous body having generally contiguous
pores (the twelfth invention of the present application).
[0020] An aluminum structure can also be manufactured in which the
skeleton structure has almost triangular sections, and the aluminum
layer has a larger thickness at the vertexes of each of the
triangular sections than at the middle of each side of the
triangular sections (the thirteenth invention of the present
application).
[0021] When a urethane foam or a melamine foam having a
three-dimensional network structure is used as the porous resin
molded body, the skeleton of the network structure generally has
triangular sections. The term "triangular", as used herein, has no
stringent definition and refers to a shape having approximately
three vertexes and three curved lines as the sides. Thus, the shape
of the aluminum structure formed by plating also has an almost
triangular skeleton. As an example of the conductive treatment
method, the deposition of aluminum by a gas phase method will be
described below. An electrically conductive layer having a
relatively uniform thickness can be formed by a gas phase method.
The conductivity of the electrically conductive layer is
substantially constant at all positions on each of the triangular
sections. In aluminum plating under such conditions, an electric
field is concentrated at the corners (the vertexes of a triangular
section), resulting in a greater thickness at the vertexes than at
the middle of each side of the triangular section. Thus, the shape
described above can be achieved. Such a shape can advantageously
increase the strength of the tubular skeleton structure and improve
the retention capacity of an active material in battery electrodes
and other applications.
Advantageous Effects of Invention
[0022] The present invention can provide a method for performing
aluminum plating on the surface of a resin molded body, in
particular the surface of a porous resin molded body having a
three-dimensional network structure, and forming a high-purity,
large-area aluminum structure having a substantially uniform and
large thickness. The present invention can also provide an aluminum
structure.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a flow chart of a process of manufacturing an
aluminum structure according to the present invention.
[0024] FIG. 2 shows schematic cross-sectional views of a process of
manufacturing an aluminum structure according to the present
invention.
[0025] FIG. 3 is an enlarged photograph of a surface of the
structure of a urethane foam as an example of a porous resin molded
body.
[0026] FIG. 4 is a schematic view of a cross-section of the
skeleton of porous aluminum.
[0027] FIG. 5 is an explanatory view of a continuous aluminum
plating process utilizing molten salt plating.
[0028] FIG. 6 is a schematic cross-sectional view of a structure in
which porous aluminum is applied to a molten salt battery.
[0029] FIG. 7 is a schematic cross-sectional view of a structure in
which porous aluminum is applied to an electrical double layer
capacitor.
[0030] FIG. 8 is a scanning electron microscope (SEM) photograph of
a cross-section of porous aluminum.
DESCRIPTION OF EMBODIMENTS
[0031] Embodiments of the present invention will be described below
in which a representative example is a process of manufacturing
porous aluminum. Throughout the reference figures, like numerals
designate like parts. The dimensions in the figures are not
necessarily consistent with their descriptions. The present
invention is defined by the appended claims rather than by these
embodiments. All modifications that fall within the scope of the
claims and the equivalents thereof are intended to be embraced by
the claims.
(Process of Manufacturing Aluminum Structure)
[0032] FIG. 1 is a flow chart of a process of manufacturing an
aluminum structure according to the present invention. FIG. 2 shows
schematic views of the formation of an aluminum structure using a
resin molded body as a core material in accordance with the flow
chart. The general flow of the manufacturing process will be
described below with reference to these figures. First, the
preparation of a base resin molded body 101 is performed. FIG. 2(a)
is an enlarged schematic view of a portion of a cross-section of a
resin, which is the magnification of a surface of a resin expansion
molded body having continuous pores serving as an example of a base
resin molded body. Pores are formed in the skeleton of a resin
expansion molded body 1. The conductive treatment of the surface of
the resin molded body 102 is then performed. As illustrated in FIG.
2(b), through this process, a thin electrically conductive layer 2
made of aluminum is formed on the surface of the resin molded body
1. Aluminum plating in a molten salt 103 is then performed to form
an aluminum plated layer 3 on the surface of the electrically
conductive layer of the resin molded body (FIG. 2(c)). Thus, an
aluminum structure is manufactured in which the aluminum plated
layer 3 is formed on a surface of a base resin molded body serving
as the base material. Removal of the base material formed by a base
resin molded body 104 may be further performed. The resin expansion
molded body 1 can be evaporated by decomposition to form an
aluminum structure (porous body) containing only the metal layer
(FIG. 2(d)). These processes will be described below process by
process.
(Preparation of Porous Resin Molded Body)
[0033] A porous resin molded body having a three-dimensional
network structure and continuous pores is prepared. The material of
the porous resin molded body may be any resin. The material may be
exemplified by a resin expansion molded body made of polyurethane,
melamine, polypropylene, or polyethylene. The resin expansion
molded body may be a resin molded body having any shape provided
that the resin molded body has contiguous pores (continuous pores).
For example, a nonwoven fabric containing tangled fibrous resin may
be used in place of the resin expansion molded body. Preferably,
the resin expansion molded body has a porosity in the range of 80%
to 98% and a pore size in the range of 50 to 500 .mu.m. Urethane
foams and melamine foams have a high porosity, continuous pores,
and an excellent pyrolysis property and are therefore suitable for
the resin expansion molded body. Urethane foams are preferred in
terms of the uniformity of pores and availability. Urethane foams
are preferred because of their small pore size.
[0034] Porous resin molded bodies often contain residue materials,
such as a foaming agent and an unreacted monomer in the manufacture
of the foam, and are therefore preferably subjected to washing
treatment before the subsequent processes. As an example of the
porous resin molded body, FIG. 3 illustrates a urethane foam
subjected to a washing treatment as a preliminary treatment. The
resin molded body has a three-dimensional network skeleton, which
includes generally contiguous pores. The skeleton of the urethane
foam has an almost triangular section perpendicular to the lateral
direction. The porosity is defined by the following equation:
Porosity=(1-(the weight of porous body [g]/(the volume of porous
body [cm.sup.3].times.material density))).times.100 [%]
[0035] The pore size is determined by magnifying a surface of the
resin molded body in a photomicrograph or the like, counting the
number of cells per inch (25.4 mm), and calculating the average
pore size by the following equation: average pore size=25.4 mm/the
number of cells.
(Conductive Treatment of Resin Molded Body Surface: Gas Phase
Method)
[0036] An electrically conductive layer made of aluminum is formed
on the surface of a resin expansion molded body. The electrically
conductive layer may be formed by any method, for example, a gas
phase method, such as vapor deposition, sputtering, or plasma
chemical vapor deposition (CVD), or application of an aluminum
paint. A vapor deposition method is preferred because a thin film
can be uniformly formed. Preferably, the electrically conductive
layer has a thickness in the range of 0.05 to 1 .mu.m, preferably
0.1 to 0.5 .mu.m. When the electrically conductive layer has a
thickness of less than 0.01 .mu.m, conductive treatment is
insufficient, and electrolytic plating cannot be properly performed
in the next process. A thickness of more than 1 .mu.m results in an
increase in the cost of the conductive treatment process.
(Conductive Treatment of Resin Molded Body Surface: Coating
Material)
[0037] The conductive treatment may be performed by dipping a resin
expansion molded body in a coating material containing aluminum.
The aluminum component in the coating material is deposited on the
surface of the resin expansion molded body to form an electrically
conductive layer made of aluminum, producing an electrically
conductive state that allows plating in a molten salt. The coating
material containing aluminum may be a liquid containing aluminum
fine particles having a particle diameter in the range of 10 nm to
1 .mu.m dispersed in water or an organic solvent. The resin foam
can be dipped in the coating material and heated to evaporate the
solvent to form the electrically conductive layer.
(Pretreatment for Plating: Anode Electrolysis)
[0038] Aluminum is plated by molten salt plating on the
electrically conductive layer formed by the process described above
to form an aluminum plated layer. The presence of an oxide film on
the surface of the electrically conductive layer may result in a
poor adhesive property of aluminum in the next plating process,
resulting in the deposition of island-shaped aluminum or variations
in the thickness of the aluminum plated layer. Thus, an anode
electrolysis treatment is preferably performed before the plating
process to dissolve and remove an oxide film (aluminum oxide layer)
formed on the electrically conductive layer (aluminum layer). More
specifically, while a resin molded body subjected to conductive
treatment and a counter electrode, such as an aluminum sheet, is
dipped in a molten salt, a direct current is applied between the
resin molded body subjected to conductive treatment (an
electrically conductive layer) functioning as an anode and the
counter electrode functioning as a cathode. The molten salt may be
the same as or different from the molten salt used in the next
molten salt plating process.
(Pretreatment for Plating: Non-oxidizing atmosphere)
[0039] In accordance with another method for preventing the
oxidation of an electrically conductive layer (aluminum layer),
after the electrically conductive layer has been formed, a resin
molded body having the electrically conductive layer (a resin
molded body subjected to conductive treatment) is transported to
the next plating process without being exposed to an oxidizing
atmosphere. For example, a vapor deposition apparatus and a molten
salt plating apparatus are placed in an argon atmosphere. After a
conductive treatment process utilizing vapor deposition is
performed in an argon atmosphere, the sample is transported in an
argon atmosphere to the next process, in which molten salt plating
is performed. Thus, the surface of the electrically conductive
layer formed in the conductive treatment process can be plated
without oxidation.
(Formation of Aluminum Layer: Molten Salt Plating)
[0040] The aluminum plated layer 3 is then formed on the surface of
the resin molded body by electrolytic plating in a molten salt. A
direct current is applied between a cathode of the resin molded
body having a surface subjected to conductive treatment and an
anode of a 99.99% aluminum plate in a molten salt. The aluminum
plated layer has a thickness in the range of 1 to 100 .mu.m,
preferably 5 to 20 .mu.m. In contrast to the anode electrolysis
treatment, a direct current is applied between a cathode of the
resin molded body subjected to conductive treatment and an anode of
the counter electrode in a molten salt. The molten salt may be an
organic molten salt that is an eutectic salt of an organic halide
and an aluminum halogenide or an inorganic molten salt that is an
eutectic salt of an alkaline metal halide and an aluminum
halogenide. Use of a bath of an organic molten salt that can melt
at a relatively low temperature is preferred because it allows
plating without the decomposition of the base material, a resin
molded body. The organic halide may be an imidazolium salt or a
pyridinium salt. Among others, 1-ethyl-3-methylimidazolium chloride
(EMIC) and butylpyridinium chloride (BPC) are preferred. The
imidazolium salt is preferably a salt that contains an imidazolium
cation having alkyl groups at 1,3-position. In particular, aluminum
chloride and 1-ethyl-3-methylimidazolium chloride (AlCl.sub.3-EMIC)
molten salts are most preferred because of their high stability and
resistance to decomposition.
[0041] The contamination of a molten salt by water or oxygen causes
a deterioration of the molten salt. Thus, plating is preferably
performed in an atmosphere of an inert gas, such as nitrogen or
argon, in a sealed environment. When an EMIC bath is used as the
organic molten salt bath, the temperature of the plating bath
ranges from 10.degree. C. to 60.degree. C., preferably 25.degree.
C. to 45.degree. C.
[0042] FIG. 5 is a schematic view of an apparatus for continuously
performing a metal plating treatment of a strip of resin. A strip
of resin 22 having a surface subjected to conductive treatment is
transferred from the left to the right in the figure. A first
plating bath 21a includes a cylindrical electrode 24, a positive
electrode 25 disposed on the inner wall of a container, and a
plating bath 23. The strip of resin 22 passes through the plating
bath 23 along the cylindrical electrode 24. Thus, a uniform
electric current can easily flow through the entire resin,
achieving uniform plating. A plating bath 21b for performing thick
uniform plating is composed of a plurality of baths so that plating
can be performed multiple times. The strip of resin 22 having a
thin metal bath on a surface thereof is transferred by electrode
rollers 26, which function as feed rollers and power feeding
cathodes on the outside of container, through a plating bath 28 to
perform plating. The plurality of baths include positive electrodes
27 facing both faces of the resin via the plating bath 28, allowing
more uniform plating on both faces of the resin.
[0043] An aluminum structure (porous aluminum) having a resin
molded body as the core of its skeleton is manufactured through
these processes. Depending on the application, such as a filter or
a catalyst support, the aluminum structure may be directly used as
a resin-metal composite. In order to use a metal structure without
resin because of constraints resulting from the usage environment,
the resin may be removed. The resin may be removed by decomposition
(dissolution) with an organic solvent, a molten salt, or
supercritical water, decomposition by heating, or any other method.
Decomposition by heating at high temperature is convenient but
causes the oxidation of aluminum. Unlike nickel, once oxidized,
aluminum is difficult to reduce. Thus, for use in an electrode
material for batteries, aluminum cannot be used because its
conductive property is lost by oxidation. In order to prevent the
oxidation of aluminum, therefore, a method for removing a resin by
decomposition by heating in a molten salt as described below is
preferably used.
(Removal of Resin: Decomposition by Heating in Molten Salt)
[0044] Decomposition by heating in a molten salt is performed in
the following manner. A resin expansion molded body having an
aluminum plated layer on a surface thereof is dipped in a molten
salt. The resin expansion molded body is decomposed by heating
while a negative potential is applied to the aluminum layer. The
application of the negative potential while dipping the resin
expansion molded body in the molten salt can prevent the oxidation
of aluminum. Heating under such conditions allows the decomposition
of the resin expansion molded body without the oxidation of
aluminum. The heating temperature can be appropriately determined
in accordance with the type of the resin expansion molded body. The
heating temperature must be lower than the melting point
(660.degree. C.) of aluminum so as not to melt aluminum. A
preferred temperature range is 500.degree. C. or more and
600.degree. C. or less. A negative potential to be applied is on
the minus side of the reduction potential of aluminum and on the
plus side of the reduction potential of the cation in a molten
salt.
[0045] The molten salt used in the decomposition of a resin by
heating may be an alkaline metal or alkaline earth metal halide
salt such that the aluminum electrode potential is less-noble. More
specifically, a preferred molten salt contains one or more selected
from the group consisting of lithium chloride (LiCl), potassium
chloride (KCl), sodium chloride (NaCl), and aluminum chloride
(AlCl.sub.3). Removal of the resin by such a method can result in
porous aluminum having a thin oxide layer on a surface thereof (a
low oxygen content) and a low carbon content.
[0046] FIG. 4 is a schematic view of a cross-section taken along
the line A-A' in FIG. 2(d). An aluminum layer composed of the
electrically conductive layer 2 and the aluminum plated layer 3 has
a tubular skeleton structure. A cavity 4 in the skeleton structure
has almost triangular sections. The thickness (t1) of the aluminum
layer at the vertexes of each of the triangular sections is greater
than the thickness (t2) of the aluminum layer at the middle of each
side of the triangular sections. This is probably because an
electric field is concentrated at the corners (the vertexes of a
triangular section) in the formation of the aluminum layer by
plating. Thus, in an aluminum structure manufactured by a method
according to the present invention, the skeleton structure has
almost triangular sections, 2 0 and the aluminum layer has a larger
thickness at the vertexes of each of the triangular sections than
at the middle of each of the triangular sections.
(Lithium-Ion Battery)
[0047] A battery electrode material and a battery each including
porous aluminum will be described below. When porous aluminum is
used in a positive electrode of a lithium-ion battery, the active
material may be lithium cobalt oxide (LiCoO.sub.2), lithium
manganese oxide (LiMn.sub.2O.sub.4), or lithium nickel dioxide
(LiNiO.sub.2). The active material is used in combination with a
conduction aid and a binder. In a known positive electrode material
for lithium-ion batteries, an active material is applied to the
surface of aluminum foil. In order to increase the battery capacity
per unit area, the application thickness of the active material is
increased. In order to effectively utilize the active material, the
active material must be in electrical contact with the aluminum
foil. Thus, the active material is mixed with a conduction aid.
Porous aluminum according to the present invention has a high
porosity and a large surface area per unit area. Thus, even a thin
layer of the active material on the surface of the porous aluminum
can effectively utilize the active material, increasing the battery
capacity and decreasing the amount of conduction aid to be mixed
with. Lithium-ion batteries include the positive electrode material
described above as the positive electrode, graphite as the negative
electrode, and an organic electrolyte as the electrolyte. Such
lithium-ion batteries can have an increased capacity even with a
small electrode area and accordingly have a higher energy density
than conventional lithium-ion batteries.
(Molten Salt Battery)
[0048] The porous aluminum can also be used as an electrode
material for molten salt batteries. When the porous aluminum is
used as a positive electrode material, the active material is a
metal compound, such as sodium chromite (NaCrO.sub.2) or titanium
disulfide (TiS.sub.2), into which a cation of a molten salt serving
as an electrolyte can be intercalated. The active material is used
in combination with a conduction aid and a binder. The conduction
aid may be acetylene black. The binder may be
polytetrafluoroethylene (PTFE). For the active material of sodium
chromate and the conduction aid of acetylene black, the binder is
preferably PTFE because PTFE can tightly bind sodium chromate and
acetylene black.
[0049] The porous aluminum can also be used as a negative electrode
material for molten salt batteries. When the porous aluminum is
used as a negative electrode material, the active material may be
sodium alone, an alloy of sodium and another metal, or carbon.
Sodium has a melting point of approximately 98.degree. C. and
becomes softer with an increase in temperature. Thus, it is
preferable to alloy sodium with another metal (such as Si, Sn, or
In). In particular, an alloy of sodium and Sn is preferred because
of its excellent handleability. Sodium or a sodium alloy can be
supported on the surface of the porous aluminum by electroplating,
hot dipping, or another method. Alternatively, a metal (such as Si)
to be alloyed with sodium may be deposited on the porous aluminum
by plating and converted into a sodium alloy by charging the molten
salt battery.
[0050] FIG. 6 is a schematic cross-sectional view of a molten salt
battery manufactured by using the battery electrode material
described above. 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 of porous
aluminum, a negative electrode 122, in which a negative electrode
active material is supported on the surface of the aluminum
skeleton of porous aluminum, and a separator 123 impregnated with a
molten salt electrolyte, in a case 127. A pressing member 126 is
disposed between the top surface of the case 127 and the negative
electrode. The pressing member 126 includes a presser plate 124 and
a spring 125 for pressing the presser plate. The pressing member
can uniformly press the positive electrode 121, the negative
electrode 122, and the separator 123 into contact with one another
even when the volumes of them have changed. A collector (porous
aluminum) of the positive electrode 121 and a collector (porous
aluminum) of the negative electrode 122 are connected to a positive
electrode terminal 128 and a negative electrode terminal 129,
respectively, through a lead wire 130.
[0051] The molten salt serving as an electrolyte may be an
inorganic salt or an organic salt that can melt at the operating
temperature. The cation of the molten salt may be one or more
selected from alkaline 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).
[0052] In order to decrease the melting point of the molten salt,
it is preferable to use a mixture of at least two salts. For
example, use of potassium bis(fluorosulfonyl)amide (KFSA) and
sodium bis(fluorosulfonyl)amide (NaFSA) in combination can decrease
the battery operating temperature to 90.degree. C. or less.
[0053] The molten salt is used in the form of a separator
impregnated with the molten salt. The separator prevents the
contact between the positive electrode and the negative electrode
and may be a glass nonwoven fabric or porous resin. A laminate of
the positive electrode, the negative electrode, and the separator
impregnated with the molten salt housed in a case is used as a
battery.
(Electrical Double Layer Capacitor)
[0054] The porous aluminum can also be used as an electrode
material for electrical double layer capacitors. When the porous
aluminum is used as an electrode material for an electrical double
layer capacitor, the electrode active material may be activated
carbon. The activated carbon is used in combination with a
conduction aid and a binder. The conduction aid may be graphite or
carbon nano-tube. The binder may be polytetrafluoroethylene (PTFE)
or styrene-butadiene rubber.
[0055] FIG. 7 is a schematic cross-sectional view of an electrical
double layer capacitor manufactured by using the electrode material
for an electrical double layer capacitor. A polarizable electrode
141 is disposed in an organic electrolyte 143 partitioned with a
separator 142. The polarizable electrode 141 is made of an
electrode material, which is an electrode active material supported
on the porous aluminum. The electrode material 141 is connected to
a lead wire 144. All the components are housed in a case 145. Use
of the porous aluminum as a collector can increase the surface area
of the collector. Thus, even a thin layer of activated carbon as
the active material on the surface of the porous aluminum can
result in an electrical double layer capacitor with a high power
and a high capacity.
[0056] Although the resin expansion molded body is used as the
resin molded body as described above, the present invention is not
limited to the resin expansion molded body. A resin molded body
having any shape can be used to manufacture an aluminum structure
having a desired shape.
(Example: Manufacture of Porous Aluminum: Formation of Aluminum
Layer by Vapor Deposition Method)
[0057] An example of the manufacture of porous aluminum will be
specifically described below. A urethane foam having a thickness of
1 mm, a porosity of 95%, and approximately 20 pores per centimeter
was prepared as a resin expansion molded body and was cut into a 10
mm.times.30 m square. Vapor deposition of aluminum on the surface
of the urethane foam was performed to form an electrically
conductive layer having a thickness of approximately 0.3 .mu.m.
(Anode Electrolysis)
[0058] The urethane foam having an electrically conductive layer on
the surface thereof was mounted in a jig having an electricity
supply function and was then dipped in a molten salt aluminum
plating bath (67% by mole AlCl.sub.3-33% by mole EMIC) at a
temperature of 40.degree. C. The jig holding the urethane foam was
connected to the anode of a rectifier, and an aluminum plate
(purity 99.99%) of the counter electrode was connected to the
cathode. A direct current having a current density of 1 A/dm.sup.2
was applied for one minute to perform anode electrolysis. The
calculation of the current density was based on the apparent area
of the porous aluminum.
(Molten Salt Plating)
[0059] While the urethane foam having an electrically conductive
layer on the surface thereof was dipped in the molten salt aluminum
plating bath, the anode and the cathode of the rectifier was
switched therebetween. A direct current was then applied to the
urethane foam at a current density of 3.6 A/dm.sup.2 at a
temperature of 40.degree. C. for 90 minutes to perform aluminum
plating.
(Manufacture of Porous Aluminum: Decomposition of Resin Expansion
Molded Body)
[0060] The resin foam having the aluminum plated layer was dipped
in a LiCl-KCl eutectic molten salt at a temperature of 500.degree.
C. A negative potential of -1 V was applied to the resin foam for
30 minutes. Air bubbles were generated in the molten salt,
indicating the decomposition reaction of the polyurethane. The
product was cooled to room temperature in the atmosphere and was
washed with water to remove the molten salt, thus forming porous
aluminum. The amount of aluminum deposit was 150 g/m.sup.2. FIG. 8
is a scanning electron microscope (SEM) photograph of the porous
aluminum.
[0061] The porous aluminum was dissolved in nitromuriatic acid and
was subjected to an inductively-coupled plasma emission
spectrometer. The aluminum purity was 99.1% by mass. The carbon
content was 0.8% by mass as measured by an infrared absorption
method after combustion in a high-frequency induction furnace in
accordance with Japan Industrial Standard G1211. The energy
dispersive X-ray spectroscopy (EDX) of the surface at an
accelerating voltage of 15 kV showed a negligible oxygen peak,
indicating that the oxygen content of the porous aluminum was lower
than the detection limit of EDX (3.1% by mass).
(Evaluation of Porous Aluminum in Battery)
[0062] The practical evaluation of porous aluminum used as a
battery electrode will be described below in comparison with a
conventional structure having an aluminum foil electrode.
[0063] A positive electrode active material LiCoO.sub.2 having an
average particle diameter of 7 .mu.m, a conduction aid carbon
black, and a binder resin polyvinylidene fluoride were mixed at
10:1:1 (mass ratio). A solvent N-methyl-2-pyrrolidone was added to
the mixture to prepare a paste. Porous aluminum having a
three-dimensional network structure and a porosity of approximately
95% was filled with the paste, was dried under vacuum at
150.degree. C., and was role-pressed to a thickness corresponding
to 70% of the initial thickness to form a battery electrode
material (positive electrode). The battery electrode material was
punched in a diameter of 10 mm and was fixed to a coin battery
container made of stainless steel SUS304 by spot welding. The
positive electrode filling capacity was 2.4 mAh.
[0064] For comparison purposes, the mixture paste of LiCoO.sub.2,
carbon black, and polyvinylidene fluoride was applied to aluminum
foil having a thickness of 20 .mu.m and was dried and role-pressed
in the same manner as described above to prepare a battery
electrode material (positive electrode). The battery electrode
material was punched in a diameter of 10 mm and was fixed to a coin
battery container made of stainless steel SUS304 by spot welding.
The positive electrode filling capacity was 0.24 mAh.
[0065] A polypropylene porous film having a thickness of 25 .mu.m
was used as a separator. A solution of 1 M LiPF.sub.6 in ethylene
carbonate (EC)/diethyl carbonate (DEC) (volume ratio 1:1) was
dropped at 0.1 ml/cm.sup.2 on the separator, which was then
subjected to vacuum impregnation. A lithium aluminum foil having a
thickness of 20 .mu.m and a diameter of 11 mm was fixed to the top
lid of a coin battery container as a negative electrode. The
battery electrode material (positive electrode), the separator, and
the negative electrode were laminated in this order and were
caulked with a Viton (registered trademark) o-ring placed between
the top lid and the bottom lid to manufacture a battery. In deep
discharge, the upper limit voltage was 4.2 V, and the lower limit
voltage was 3.0 V. Charging to the positive electrode filling
capacity was followed by discharging at each discharge rate. The
lithium secondary battery containing the porous aluminum as the
positive electrode material had a capacity approximately five times
the capacity of a conventional battery containing aluminum foil as
the electrode material at 0.2 C.
[0066] The above description includes the following
characteristics.
(Additional Entry 1)
[0067] A manufacturing method of an aluminum structure, including a
conductive treatment process of forming an electrically conductive
layer made of aluminum on a surface of a resin molded body and a
plating process of plating the resin molded body subjected to the
conductive treatment process with aluminum in a first molten salt
bath, wherein while the resin molded body having the aluminum
plated layer is dipped in a second molten salt and while a negative
potential is applied to the aluminum plated layer, the resin molded
body is heated to a temperature of the melting point of aluminum or
less to decompose the resin molded body.
Additional Entry 2
[0068] The manufacturing method of porous aluminum according to
Additional Entry 1, wherein the resin molded body is a resin
expansion molded body having contiguous pores.
Additional Entry 3
[0069] An electrode material in which an active material is
supported on an aluminum surface of an aluminum structure according
to the present invention.
Additional Entry 4
[0070] A battery containing the electrode material according to
Additional Entry 3 in one or both of the positive electrode and the
negative electrode.
Additional Entry 5
[0071] An electrical double layer capacitor containing the
electrode material according to Additional Entry 3 as an
electrode.
Additional Entry 6
[0072] A filtration filter including an aluminum structure
according to the present invention.
Additional Entry 7
[0073] A catalyst support in which a catalyst is supported on the
surface of an aluminum structure according to the present
invention.
Industrial Applicability
[0074] The present invention can provide a structure in which a
surface of a resin molded body is plated with aluminum and an
aluminum structure manufactured by removing the resin molded body
from the structure. Thus, the present invention can be widely
applied as porous aluminum to cases where the characteristics of
aluminum can be exploited, for example, in electric materials, such
as battery electrodes, various filters for filtration, and catalyst
supports.
Reference Signs List
[0075] 1 Resin Foam
[0076] 2 Electrically Conductive Layer
[0077] 3 Aluminum Plated Layer
[0078] 4 Cavity
[0079] 21a, 21b Plating Bath
[0080] 22 Strip of Resin
[0081] 23, 28 Plating Bath
[0082] 24 Cylindrical Electrode
[0083] 25, 27 Positive Electrode
[0084] 26 Electrode Roller
[0085] 121 Positive Electrode
[0086] 122 Negative Electrode
[0087] 123 Separator
[0088] 124 Presser Plate
[0089] 125 Spring
[0090] 126 Pressing Member
[0091] 127 Case
[0092] 128 Positive Electrode Terminal
[0093] 129 Negative Electrode Terminal
[0094] 130 Lead Wire
[0095] 141 Polarizable Electrode
[0096] 142 Separator
[0097] 143 Organic Electrolyte
[0098] 144 Lead Wire
[0099] 145 Case
* * * * *