U.S. patent application number 14/336787 was filed with the patent office on 2015-01-15 for process of making a carbon fiber nonwoven fabric.
This patent application is currently assigned to NATIONAL UNIVERSITY CORPORATION SHINSHU UNIVERSITY. The applicant listed for this patent is Takahiro KITANO, Fujio OKINO. Invention is credited to Takahiro KITANO, Fujio OKINO.
Application Number | 20150017863 14/336787 |
Document ID | / |
Family ID | 44306571 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017863 |
Kind Code |
A1 |
KITANO; Takahiro ; et
al. |
January 15, 2015 |
PROCESS OF MAKING A CARBON FIBER NONWOVEN FABRIC
Abstract
The present invention has an object of providing the carbon
fiber (or the nonwoven fabric configured of the aforementioned
carbon fiber) of which the surface area, the graphitization degree,
and the fiber diameter are large, high, and small, respectively,
and yet of which dispersion is small. The method of producing the
carbon fiber nonwoven fabric includes a dispersion liquid preparing
step of preparing a dispersion liquid containing resin and pitch,
an electrospinning step of producing the nonwoven fabric that is
comprised of carbon fiber precursors with electrospinning from the
aforementioned dispersion liquid, and a modifying step of modifying
the carbon fiber precursors of the nonwoven fabric obtained in the
aforementioned electrospinning step into the carbon fiber.
Inventors: |
KITANO; Takahiro; (Nomi-shi,
JP) ; OKINO; Fujio; (Ueda-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KITANO; Takahiro
OKINO; Fujio |
Nomi-shi
Ueda-shi |
|
JP
JP |
|
|
Assignee: |
NATIONAL UNIVERSITY CORPORATION
SHINSHU UNIVERSITY
Matumoto-shi
JP
TEC ONE CO., LTD.
Nomi-shi
JP
|
Family ID: |
44306571 |
Appl. No.: |
14/336787 |
Filed: |
July 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13503167 |
Apr 20, 2012 |
8808609 |
|
|
PCT/JP10/66156 |
Sep 17, 2010 |
|
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14336787 |
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Current U.S.
Class: |
442/336 ;
428/367 |
Current CPC
Class: |
Y10T 442/60 20150401;
Y02E 60/10 20130101; D04H 1/728 20130101; Y10T 442/681 20150401;
H01G 11/44 20130101; H01M 4/587 20130101; D01F 9/20 20130101; D04H
3/002 20130101; D04H 13/00 20130101; B01D 39/2065 20130101; H01G
11/34 20130101; Y02E 60/13 20130101; Y10T 428/2918 20150115; Y10T
442/61 20150401; D01F 9/145 20130101; D01D 5/0038 20130101; H01G
11/40 20130101; H01M 4/133 20130101; H01M 4/583 20130101; H01M 4/80
20130101; H01G 11/26 20130101; D01D 5/20 20130101; H01M 4/806
20130101; D10B 2101/12 20130101; D04H 1/4242 20130101 |
Class at
Publication: |
442/336 ;
428/367 |
International
Class: |
D01F 9/145 20060101
D01F009/145; H01G 11/40 20060101 H01G011/40; B01D 39/20 20060101
B01D039/20; H01G 11/26 20060101 H01G011/26; D04H 13/00 20060101
D04H013/00; H01M 4/583 20060101 H01M004/583 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 21, 2010 |
JP |
2010-011457 |
Claims
1-19. (canceled)
20. A carbon fiber: wherein said carbon fiber includes a large
diameter portion and a small diameter portion; wherein a diameter
of said large diameter portion is 20 nm to 2 .mu.m; wherein a
diameter of said small diameter portion is 10 nm to 1 .mu.m; and
wherein (the diameter in said large diameter portion)>(the
diameter in said small diameter portion).
21. The carbon fiber as claimed in claim 20, wherein (a maximum
value of the diameter in said large diameter portion)/(a minimum
value of the diameter in said small diameter portion) is 1.1 to
100.
22. The carbon fiber as claimed in claim 20, wherein a length of
said small diameter portion is longer than a minimum value of the
diameter in said large diameter portion.
23. The carbon fiber as claimed claim 20, wherein the length of
said small diameter portion is shorter than the maximum value of
the diameter in said large diameter portion.
24. The carbon fiber as claimed in claim 20, wherein the length of
said small diameter portion is 10 nm to 10 .mu.m.
25. The carbon fiber as claimed in claim 20, wherein the length of
said large diameter portion is 50 nm to 10 .mu.m.
26. The carbon fiber as claimed in claim 20, wherein said carbon
fiber includes said large diameter portions in plural number, and
yet said small diameter portions in plural number; and wherein a
length of said carbon fiber is 0.1 to 1000 .mu.m.
27. The carbon fiber as claimed in claim 20, wherein a specific
surface area of said carbon fiber is 1 to 100 m.sup.2/g.
28. The carbon fiber as claimed in claim 20, wherein a peak
originating in a graphite structure (002) exists within a range of
25.degree. to 30.degree. (2.theta.) in an X-ray diffraction
measurement of said carbon fiber, and a half width of said peak is
0.1.degree. to 2.degree. (2.theta.).
29. The carbon fiber as claimed in claim 20, wherein ID/IG of said
carbon fiber is 0.2 to 2 (ID is a peak intensity existing within
1300 cm.sup.-1 to 1400 cm.sup.-1 in Raman scattering spectra of
said carbon fiber. IG is a peak intensity existing within 1580
cm.sup.-1 to 1620 cm.sup.-1 in Raman scattering spectra of said
carbon fiber.).
30. The carbon fiber as claimed in claim 20, wherein L/(S).sup.1/2
of said carbon fiber (S is an area of said carbon fiber in an image
obtained by observing said carbon fiber with a scanning electron
microscope. L is an outer length of said carbon fiber in the image
obtained by observing said carbon fiber with the scanning electron
microscope.) is 3.7 to 300.
31-48. (canceled)
49. A carbon fiber nonwoven fabric comprising 50 to 100% by mass of
the carbon fiber of claim 20.
Description
TECHNICAL FIELD
[0001] The present invention relates to carbon fiber.
BACKGROUND ART
[0002] An attention is paid to the carbon fiber in a field of
batteries (for example, a lithium-ion battery and an electric
double-layer capacitor) and fuel cells. In particular, an attention
is paid to the carbon fiber nonwoven fabric as an electrode
material of the aforementioned batteries. The aforementioned
nonwoven fabric is configured of the carbon fiber of which a fiber
diameter is 10 .mu.m or so.
[0003] Recently, the nonwoven fabric configured of the carbon fiber
of which the fiber diameter is 10 .mu.m or less (for example, 1
.mu.m 0 or so) has been required from a viewpoint of an augment in
a surface area.
[0004] The carbon nanotube produced with a vapor growth method or
an arc electric discharge method is known as the carbon fiber
having a fine fiber diameter. A fiber length of the carbon
nanotube, however, is short. For example, it is 10 .mu.m or less.
In addition, the carbon nanotube is expensive. Thus, an application
of the carbon nanotube to the electrode material causes a
problem.
[0005] From such a background, the carbon fiber produced with a
melt blow method or an electrospinning method has been
proposed.
[0006] For example, the method of spinning thermoplastic containing
a carbon source (for example, pitch etc.) with the melt blow
method, and thereafter, thermally decomposing, carbonizing and
graphitizing the aforementioned thermoplastic has been proposed
(Patent literature 1 and Non-patent literature 1). In accordance
with this method, the carbon fiber having a fine fiber diameter is
obtained. However, it is difficult to control the fiber diameter
with the melt blow method. The carbon fiber obtained with the melt
blow method is large in deviation of the fiber diameters
[0007] The method (the electrospinning method) of electrospinning a
solution having the carbon source (for example, a polymer such as
polyacrylonitrile) dissolved therein, and thereafter, carbonizing
and graphitizing it has been proposed (Patent literatures 2 to 5
and Non-patent literature 2). The carbon fiber obtained with this
method is small in deviation of the fiber diameters. However, in
the method described in the above-mentioned Patent Literatures 2 to
5, the carbon source has to be dissolved in a solvent. By the way,
hard pitch and mesophase pitch are high in a graphitization degree.
Thus, the hard pitch and the mesophase pitch are preferably
employed as the carbon source. However, the hard pitch and the
mesophase pitch are not dissolved in the solvent. Thus, the hard
pitch and the mesophase pitch are not employed as the carbon source
in the above-mentioned Patent Literatures. In the Patent literature
5, carbonization and the graphitization are performed with
microwave heating after the electrospinning. Herein, carbon black
is essential. The carbon black can be employed as the carbon
source. However, the carbon black, similarly to polyacrylonitrile,
is low in the graphitization degree. For this reason, only the
carbon fiber of which the graphitization degree is low can be
obtained.
[0008] The technology of performing the electrospinning with the
pitch kept in a molten state and thereafter, carbonizing and
graphitizing it has been proposed (Patent literature 6).
[0009] The carbon fiber obtained with this method is small in
deviation of the fiber diameters. And yet, the graphitization
degree is high. However, only the carbon source of which the
graphitization degree is high is employed in this technology,
differently from the above-mentioned technologies. For this reason,
shrinkage is small at the time of the carbonization and the
graphitization. Thus, it is difficult to obtain the carbon fiber of
which the fiber diameter is 1 .mu.m or less. In addition, only soft
pitch of which a melting point is 300.degree. C. or lower is
employed in the technology of the Patent literature 6. That is, the
high pitch and the mesophase pitch of which the melting point is
300.degree. C. or higher cannot be used. In principle, only the
carbon fiber of which the surface is flat can be obtained in this
method. That is, the carbon fiber having the characteristics of the
present invention cannot be obtained.
CITATION LIST
Non-Patent Literature
[0010] NPL 1: H. Ono, A. Oya/Carbon 44 (2006) 682-686 [0011] NP12:
Chan Kim, KapSeung Yang, Masahito Kojima, Kazuto Yoshida, YongJung
Kim, Yoong AhmKim and Morinobu Endo/Adv. Funct. Mater 16 (2006)
2393-2397 [0012] NPL 3: Shirai Sousi/Carbon 240 (2009) 250-252
Patent Literature
[0012] [0013] PTL 1: JP-P2009-079346A [0014] PTL 2:
JP-P2009-505931A [0015] PTL 3: JP-P2008-270807A [0016] PTL 4:
JP-P2007-207654A [0017] PTL 5: JP-P2006-054636A1 [0018] PTL 6:
JP-P2009-203565A
SUMMARY OF INVENTION
Technical Problem
[0019] A task that the present invention is to solve, that is, an
object of the present invention is to provide the carbon fiber (or
the nonwoven fabric configured of the aforementioned carbon fiber)
of which a surface area, a graphitization degree, a fiber diameter
are large, high, and small, respectively, and yet of which
deviation is small.
Solution to Problem
[0020] The aforementioned problems are solved by a method of
producing carbon fiber nonwoven fabric, which is characterized in
including a dispersion liquid preparing step of preparing a
dispersion liquid containing resin and pitch, an electrospinning
step of producing the nonwoven fabric comprised of carbon fiber
precursors with electrospinning from the aforementioned dispersion
liquid, and a modifying step of modifying the carbon fiber
precursors of the nonwoven fabric obtained in the aforementioned
electrospinning step into the carbon fiber.
[0021] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned modifying
step includes a step of heating the nonwoven fabric obtained in the
aforementioned electrospinning step to 50 to 4000.degree. C.
[0022] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned modifying
step includes a resin removing step of removing resin being
included in the nonwoven fabric obtained in the aforementioned
electrospinning step.
[0023] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned resin
removing step is a heating step of heating the nonwoven fabric
obtained in the aforementioned electrospinning step under an
oxidizing gas atmosphere.
[0024] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned modifying
step includes a carbonizing step of performing a carbonizing
process for the nonwoven fabric subjected to the aforementioned
resin removing step.
[0025] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned modifying
step includes a graphitizing step of performing a graphitizing
process for the nonwoven fabric subjected to the aforementioned
carbonizing step.
[0026] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned
graphitizing step is a heating step of heating the aforementioned
nonwoven fabric under an inert atmosphere.
[0027] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned heating
is heat generation due to electric current to the aforementioned
nonwoven fabric.
[0028] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned resin is
water-soluble resin.
[0029] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned resin is
pyrolytic resin.
[0030] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned resin is
polyvinyl alcohol.
[0031] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that the aforementioned pitch is
mesophase pitch.
[0032] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that of the aforementioned pitch
has a particle diameter of 1 nm to 10 .mu.m.
[0033] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that aforementioned pitch has a
particle diameter of 100 nm to 1 .mu.m.
[0034] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that an amount of the
aforementioned pitch is 20 to 200 parts by mass per 100 parts by
mass of the aforementioned resin.
[0035] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber nonwoven
fabric, which is characterized in that an amount of the
aforementioned pitch is 70 to 150 parts by mass per 100 parts by
mass of the aforementioned resin.
[0036] The aforementioned problems are solved by a method of
producing carbon fiber, which is characterized in including a
fabric unraveling step of obtaining the carbon fiber by unraveling
the carbon fiber nonwoven fabric obtained by the aforementioned
method of producing the carbon fiber nonwoven fabric.
[0037] Preferably, the aforementioned problems are solved by the
aforementioned method of producing the carbon fiber, which is
characterized in that the aforementioned fabric unraveling step is
a step of pulverizing the aforementioned nonwoven fabric.
[0038] The aforementioned problems are solved by the carbon fiber
obtained by the aforementioned method of producing the carbon
fiber.
[0039] The aforementioned problems are solved by the carbon fiber,
which is characterized in that the aforementioned carbon fiber
includes a large diameter portion and a small diameter portion, a
diameter of the aforementioned large diameter portion is 20 nm to 2
.mu.m, a diameter of the aforementioned small diameter portion is
10 nm to 1 .mu.m, and (the diameter in the aforementioned large
diameter portion)>(the diameter in the aforementioned small
diameter portion).
[0040] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that (a
maximum value of the diameter in the aforementioned large diameter
portion)/(a minimum value of the diameter in the aforementioned
small diameter portion) is 1.1 to 100.
[0041] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that a
length of the aforementioned small diameter portion is longer than
a minimum value of the diameter in the aforementioned large
diameter portion.
[0042] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that the
length of the aforementioned small diameter portion is shorter than
the maximum value of the diameter in the aforementioned large
diameter portion.
[0043] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that the
length of the aforementioned small diameter portion is 10 nm to 10
.mu.m.
[0044] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that the
length of the aforementioned large diameter portion is 50 nm to 10
.mu.m.
[0045] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that the
aforementioned carbon fiber includes the aforementioned large
diameter portions in plural number and yet the aforementioned small
diameter portions in plural number, and a length of the
aforementioned carbon fiber is 0.1 to 1000 .mu.m.
[0046] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that a
specific surface area of the aforementioned carbon fiber is 1
m.sup.2/g to 100 m.sup.2/g.
[0047] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that a peak
originating in a graphite structure (002) exists within a range of
25.degree. to 30.degree. (2.theta.) in an X-ray diffraction
measurement of the aforementioned carbon fiber, and a half width of
the aforementioned peak is 0.1.degree. to 2.degree. (2.theta.).
[0048] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that ID/IG
(ID is a peak intensity existing within 1300 cm.sup.-1 to 1400
cm.sup.-1 in Raman scattering spectra of the aforementioned carbon
fiber. IG is a peak intensity existing within 1580 cm.sup.-1 to
1620 cm.sup.-1 in Raman scattering spectra of the aforementioned
carbon fiber.) of the aforementioned carbon fiber is 0.2 to 2.
[0049] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is characterized in that
L/(S).sup.1/2 (S is an area of the aforementioned carbon fiber in
an image obtained by observing the aforementioned carbon fiber with
a scanning electron microscope. L is an outer length of the
aforementioned carbon fiber in the image obtained by observing the
aforementioned carbon fiber with the scanning electron microscope.)
of the aforementioned carbon fiber is 3.7 to 300.
[0050] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber, which is obtained with the
aforementioned method of producing the carbon fiber.
[0051] The aforementioned problems are solved by carbon fiber
nonwoven fabric, which is characterized in that a containing ratio
of the aforementioned carbon fiber is 50 to 100% by mass.
[0052] The aforementioned problems are solved by carbon fiber
nonwoven fabric, which is obtained with the aforementioned method
of producing the carbon fiber nonwoven fabric.
[0053] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber nonwoven fabric, which is characterized
in that a thickness of the aforementioned nonwoven fabric is 0.1
.mu.m to 10 mm.
[0054] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber nonwoven fabric, which is characterized
in that a weight of the aforementioned nonwoven fabric is 0.1 to
10000 g/m.sup.2.
[0055] Preferably, the aforementioned problems are solved by the
aforementioned carbon fiber nonwoven fabric, which is characterized
in that a specific surface area of the aforementioned nonwoven
fabric is 1 to 50 m.sup.2/g.
[0056] The aforementioned problems are solved by a member to be
employed for electric devices, which is characterized in being
configured by employing the aforementioned carbon fiber or the
aforementioned carbon fiber nonwoven fabric.
[0057] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being a battery part.
[0058] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being an electrode of a battery.
[0059] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being an electrode of a lithium-ion secondary
battery.
[0060] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being a negative electrode of a lithium-ion
secondary battery, and containing an anode active material that is
comprised of the aforementioned carbon fiber and/or the
aforementioned carbon fiber nonwoven fabric.
[0061] Preferably, the aforementioned problems are solved by the
aforementioned member being employed for electric devices, which is
characterized in being an electrode of a lithium-ion secondary
battery and including a conductive auxiliary that is comprised of
the aforementioned carbon fiber and/or the aforementioned carbon
fiber nonwoven fabric.
[0062] Preferably, the aforementioned problems are solved by the
aforementioned member being employed for electric devices, which is
characterized in that the aforementioned member is a negative
electrode of a lithium-ion secondary battery employing an
alloy-based anode active material, and the aforementioned
alloy-based anode active material is laminated on the
aforementioned carbon fiber and/or the aforementioned carbon fiber
nonwoven fabric.
[0063] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which
are characterized in being an electrode of a capacitor.
[0064] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being an electrode of a lithium-ion capacitor.
[0065] Preferably, the aforementioned problems are solved by the
aforementioned member to be employed for electric devices, which is
characterized in being a porous carbon electrode material for fuel
cells.
[0066] The aforementioned problems are solved by an electric
devise, which is characterized in including the member to be
employed for an electric element.
[0067] The aforementioned problems are solved by a filter, which is
configured by employing the aforementioned carbon fiber or the
aforementioned carbon fiber nonwoven fabric.
Advantageous Effect of Invention
[0068] The carbon fiber of which the surface area and the
graphitization degree and the fiber diameter are large, high and
small, respectively, and yet of which deviation is few can be
obtained.
[0069] The carbon fiber nonwoven fabric having the aforementioned
features can be obtained in a simplified manner. The surface area
of the above nonwoven fabric is large.
[0070] The carbon fiber and the nonwoven fabric having the
aforementioned features are suitable, for example, for the
electrode materials. In particular, a speed at which the
electrolyte solution is poured is high because the surface area is
large, and thus, a takt time can be shortened.
[0071] The carbon fiber having the aforementioned features is large
in an aspect ratio and high in conductivity. Thus, employing the
conductive auxiliary leads to a reduction in an internal resistance
of the battery.
[0072] The carbon fiber and the nonwoven fabric having the
aforementioned features can be employed, for example, for the
filters.
BRIEF DESCRIPTION OF DRAWINGS
[0073] FIG. 1 is a schematic view of the electrospinning
apparatus.
[0074] FIG. 2 is a schematic view of the electrospinning
apparatus.
[0075] FIG. 3 is a schematic view of the negative electrode of the
lithium-ion battery.
[0076] FIG. 4 is a schematic view of the negative electrode of the
lithium-ion capacitor.
[0077] FIG. 5 is an SEM photograph.
[0078] FIG. 6 is an XRD chart.
[0079] FIG. 7 is Raman scattering spectra.
[0080] FIG. 8 is an image obtained by processing the image employed
for measuring L/(S).sup.1/2.
[0081] FIG. 9 is an SEM photograph.
[0082] FIG. 10 is an image obtained by processing the image
employed for measuring L/(S).sup.1/2.
[0083] FIG. 11 is an SEM photograph.
[0084] FIG. 12 is an SEM photograph.
[0085] FIG. 13 is an image obtained by processing the image
employed for measuring L/(S).sup.1/2.
[0086] FIG. 14 is an SEM photograph.
[0087] FIG. 15 is an SEM photograph.
[0088] FIG. 16 is an SEM photograph.
[0089] FIG. 17 is a charge/discharge characteristic chart.
[0090] FIG. 18 is a charge/discharge characteristic chart.
[0091] FIG. 19 is an SEM photograph.
[0092] FIG. 20 is an SEM photograph.
[0093] FIG. 21 is a charge/discharge characteristic chart.
[0094] FIG. 22 is a charge/discharge characteristic chart.
[0095] FIG. 23 is a cross-sectional view of an anode electrode.
[0096] FIG. 24 is an SEM photograph.
[0097] FIG. 25 is an energy density/output density characteristic
chart.
DESCRIPTION OF EMBODIMENTS
[0098] A first invention is a method of producing the carbon fiber
nonwoven fabric. The aforementioned producing method includes a
dispersion liquid preparation step. This dispersion liquid
preparation step is a step of preparing a dispersion liquid
containing resin and pitch (carbon particles). The aforementioned
producing method includes an electrospinning step. This
electrospinning step is a step of electrospinning the
aforementioned dispersion liquid. This electrospinning step allows
the nonwoven fabric that is comprised of carbon fiber precursors to
be produced. The aforementioned producing method includes a
modifying step. This modifying step is a step of modifying the
carbon fiber precursors of the nonwoven fabric obtained in the
aforementioned electrospinning step into the carbon fiber.
[0099] The aforementioned modifying step includes a heating step.
In this heating step, the aforementioned nonwoven fabric (the
nonwoven fabric made of the carbon fiber precursors) is heated, for
example, to 50 to 4000.degree. C.
[0100] The aforementioned modifying step preferably includes a
resin removing step. This resin removing step is a step of removing
resin being included in the nonwoven fabric obtained in the
aforementioned electrospinning step. The aforementioned resin
removing step is, for example, a heating step. This heating step is
a step of heating the nonwoven fabric (the nonwoven fabric obtained
in the aforementioned electrospinning step), for example, under an
oxidizing gas atmosphere. The aforementioned modifying step
preferably includes a carbonizing step. This carbonizing step is a
step of performing a carbonizing process for the nonwoven fabric
(in particular, the nonwoven fabric subjected to the aforementioned
resin removing step). The aforementioned modifying step preferably
includes a graphitizing step. This graphitizing step is a step of
performing a graphitizing process for the nonwoven fabric (in
particular, the nonwoven fabric subjected to the aforementioned
carbonizing step). The aforementioned graphitizing step is, for
example, a heating step. This heating step is a step of heating the
nonwoven fabric (in particular, the nonwoven fabric subjected to
the aforementioned carbonizing step), for example, under an inert
atmosphere. The aforementioned heating step is, for example, a heat
generating step due to electric current to the nonwoven fabric (in
particular, the nonwoven fabric subjected to the aforementioned
carbonizing step).
[0101] The aforementioned resin is preferably is water-soluble
resin. The aforementioned resin is preferably pyrolytic resin. In
particular, the aforementioned resin is preferably water-soluble
and yet pyrolytic resin. The most preferable resin is polyvinyl
alcohol. The aforementioned carbon particles are pitch. The
aforementioned pitch is preferably hard pitch or mesophase pitch.
The most preferable pitch is the mesophase pitch. (An amount of the
aforementioned pitch)/(an amount of the aforementioned resin) is
preferably 0.2 to 2 (more preferably, 0.7 to 1.5) (mass ratio).
[0102] A second invention is a method of producing the carbon
fiber. This method of producing the carbon fiber includes a fabric
unraveling step. This fabric unraveling step is a step of
unraveling the aforementioned nonwoven fabric (the carbon fiber
nonwoven fabric obtained in the aforementioned first invention (the
aforementioned method of producing the carbon fiber nonwoven
fabric)). The aforementioned fabric unraveling step is, for
example, a step of pulverizing the nonwoven fabric. The carbon
fiber is obtained by the aforementioned fabric unraveling step.
[0103] A third invention is the carbon fiber. This carbon fiber
includes a large diameter portion and a small diameter portion. The
aforementioned large diameter portion is a portion having a large
diameter. The aforementioned small diameter portion is a portion
having a small diameter. The aforementioned carbon fiber preferably
includes the aforementioned large diameter portions in plural
number. The aforementioned carbon fiber preferably includes the
aforementioned small diameter portions in plural number. A diameter
of the aforementioned large diameter portion is preferably 20 nm to
5 .mu.m (yet preferably, 20 nm to 2 .mu.m (more preferably, 50 nm
to 1 .mu.m)). A diameter of the aforementioned small diameter
portion is preferably 10 nm to 3 .mu.m (yet preferably, 10 nm to 1
.mu.m (more preferably, 20 to 500 nm)). Needless to say, a
condition A [(the diameter (an averaged value of the diameters) in
the aforementioned large diameter portion)>(the diameter (an
averaged value of the diameters) in the aforementioned small
diameter portion)] is satisfied. Preferably, a condition B [(a
maximum value of the diameter in the aforementioned large diameter
portion)/(a minimum value of the diameter in the aforementioned
small diameter portion)=1.1 to 100] is satisfied. Yet preferably, a
condition C [(a maximum value of the diameter in the aforementioned
large diameter portion)/(a minimum value of the diameter in the
aforementioned small diameter portion)=2 to 50] is satisfied. A
length of the aforementioned small diameter portion is, for
example, longer than a minimum value of the diameter in the
aforementioned large diameter portion. The length of the
aforementioned small diameter portion is, for example, shorter than
a maximum value of the diameter in the aforementioned large
diameter portion. The length of the aforementioned small diameter
portion is preferably 10 nm to 10 .mu.m (more preferably, 50 nm to
1 .mu.m). The length of the aforementioned large diameter portion
is preferably 50 nm to 10 .mu.m (more preferably, 500 nm to 3
.mu.m). The length (full length) of the aforementioned carbon fiber
is preferably 0.1 to 1000 .mu.m (more preferably, 10 to 500 .mu.m,
and 0.5 to 10 .mu.m in a case where the crushed carbon fiber is
employed). A specific surface area of the aforementioned carbon
fiber is preferably 1 to 100 m.sup.2/g (more preferably, 2 to 50
m.sup.2/g). A peak originating in a graphite structure (002) exists
preferably within a range of 25.degree. to 30.degree. (2.theta.) in
an X-ray diffraction measurement of the aforementioned carbon
fiber. A half width of the aforementioned peak is 0.1.degree. to
2.degree.. The aforementioned carbon fiber preferably satisfies a
condition D [ID/IG=0.1 to 2]. The aforementioned ID is a peak
intensity existing within a range of 1300 cm.sup.-1 to 1400
cm.sup.-1 in Raman scattering spectra of the aforementioned carbon
fiber. The aforementioned IG is a peak intensity existing within a
range of 1580 cm.sup.-1 to 1620 cm.sup.-1 in Raman scattering
spectra of the aforementioned carbon fiber. An Ar.sup.+ laser is
preferable as an excitation source to be employed at the time of
the measurement. The aforementioned carbon fiber preferably
satisfies a condition E [L/(S).sup.1/2=2 to 300, preferably, 5 to
300]. The aforementioned S is an area of the aforementioned carbon
fiber in an image obtained by observing the aforementioned carbon
fiber with a scanning electron microscope. The aforementioned L is
an outer length of the aforementioned carbon fiber in the image
obtained by observing the aforementioned carbon fiber with the
scanning electron microscope. The carbon fiber of this feature is
obtained with the aforementioned method of producing the carbon
fiber (the preferable method of producing the carbon fiber).
[0104] A fourth invention is the carbon fiber nonwoven fabric. With
regard to the above nonwoven fabric, a containing ratio of the
aforementioned carbon fiber is preferably 50 to 100% by mass (more
preferably, 80% or more by mass). The aforementioned nonwoven
fabric is the nonwoven fabric obtained by the aforementioned first
invention (the aforementioned method of producing the nonwoven
fabric of the carbon fiber). A thickness of the aforementioned
nonwoven fabric is preferably 0.1 .mu.m to 10 mm (more preferably,
10 to 500 .mu.m). A weight of the aforementioned nonwoven fabric is
preferably 1 to 10000 g/m.sup.2 (more preferably, 10 to 1000
g/m.sup.2). A specific surface area of the aforementioned nonwoven
fabric is preferably, 1 to 50 m.sup.2/g (more preferably, 2 to 30
m.sup.2/g).
[0105] A fifth invention is the electrode of the battery. This
electrode is configured of the aforementioned carbon fiber (or the
aforementioned carbon fiber nonwoven fabric). The aforementioned
battery is, for example, a lithium-ion secondary battery. The
aforementioned battery is, for example, a capacitor (an electric
double-layer capacitor). The aforementioned capacitor is, for
example, a lithium-ion capacitor.
[0106] A sixth invention is the battery. This battery is provided
with the aforementioned electrodes.
[0107] A seventh invention is the filter. This filter is configured
of the aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber).
[0108] Hereinafter, the present invention will be explained more
detailedly.
[0109] [The Dispersion Liquid Preparing Step (Step I)]
[0110] The aforementioned dispersion liquid contains the resin and
the carbon particles.
[0111] The aforementioned resin is preferably resin that is
dissolved in a solvent (a solvent that is volatilized at the time
of the electrospinning). Specifically, the aforementioned resin is
vinyl resin (for example, polyvinyl alcohol (PVA), polyvinylbutyral
(PVB), and the like). Or the aforementioned resin is polyethylene
oxide (PEO). Or the aforementioned resin is acrylic resin (for
example, polyacrylic acid (PAA), polymethyl methacrylate (PMMA),
polyacrylonitrile (PAN), and the like). Or, the aforementioned
resin is fluorine resin (for example, polyvinylidene difluoride
(PVDF), and the like). Or, the aforementioned resin is polymer from
natural products (for example, cellulose resin and its derivatives
(poly-lactic acid, chitosan, carboxymethylcellulose (CMC),
hydroxyethylcellulose (HEC), and the like). Or, the aforementioned
resin is engineering plastic resin such as polyethersulfone (PES).
Or, the aforementioned resin is polyurethane rasin (PU). Or, the
aforementioned resin is polyamide resin (nylon). Or, the
aforementioned resin is aromatic polyamide resin (aramid resin).
Or, the aforementioned resin is polyester resin. Or, the
aforementioned resin is polystyrene resin. Or, the aforementioned
resin is polycarbonate resin. Or, the aforementioned resin is a
mixture or a copolymer of the aforementioned resin.
[0112] The aforementioned resin is preferably water-soluble resin
from a viewpoint of a countermeasure for VOC (volatile organic
compounds). The aforementioned resin is, for example, polyvinyl
alcohol (PVA), polyvinylbutyral (PVB), polyethylene oxide (PEO),
polyacrylic acid (PAA), or cellulose derivatives.
[0113] The preferable fiber is fiber of which fusion and bonding do
not occur in the aforementioned resin removing step (the thermal
treating step: the heating step). Preferably, the aforementioned
resin is pyrolytic resin from this viewpoint. The pyrolytic resin
is resin that is thermally decomposed before thermal deformation
(fusion and bonding) when the resin is heated. The pyrolytic resin
is, for example, polyvinyl alcohol, cellulose derivatives,
polyacrylic acid (PAA) or wholly aromatic polyamide resin (aramid
resin).
[0114] The aforementioned resin is preferably polyvinyl alcohol,
cellulose derivatives or polyacrylic acid (PAA). The particularly
preferable resin is polyvinyl alcohol.
[0115] The aforementioned solvent is preferably a solvent that is
volatilized at the time of the electrospinning. The aforementioned
solvent is, for example, water. Or the aforementioned solvent is
acid (acetic acid, formic acid, and the like). Or the
aforementioned solvent is alcohol (for example, methanol, ethanol,
propanol, butanol, isobutyl alcohol, amyl alcohol, isoamyl alcohol
and cyclohexanol). Or the aforementioned solvent is ester (for
example, ethyl acetate and butyl acetate). Or the aforementioned
solvent is ether (for example, diethyl ether, dibutyl ether and
tetrahydrofuran). Or the aforementioned solvent is ketone (acetone,
methyl ethyl ketone, methyl isobutyl ketone, and the like). Or the
aforementioned solvent is an aprotic polar solvent (for example,
N,N'-dimethyl formamide, dimethyl sulfoxide, acetonitrile and
dimethyl acetamide). Or the aforementioned solvent is halogenated
hydrocarbon (for example, chloroform, tetrachloromethane and
hexafluoroisopropyl alcohol). Or the aforementioned solvent is a
mixture of the aforementioned compounds.
[0116] The preferable solvent is water, alcohol or a mixture
thereof from a viewpoint of a countermeasure for VOC (volatile
organic compounds). The particularly preferable solvent is
water.
[0117] For example, carbon black, fullerene and carbon nanotubes
are known as the carbon particles. The carbon particles that are
employed in this step 1 are pitch. The preferable pitch is the hard
pitch or the mesophase pitch. The particularly preferable pitch is
the mesophase pitch. In the present invention, the carbon particles
other than the pitch are used together with the pitch. The pitch is
substantially comprised of only carbon. The pitch is not dissolved
in the aforementioned solvent. A fixed carbon content of the
aforementioned mesophase pitch is preferably 50 to 100% (more
preferably, 70 to 95% and yet more preferably, 80 to 90%). A
melting point of the aforementioned mesophase pitch is preferably
250 to 400.degree. C. (more preferably, 280 to 350.degree. C. and
yet more preferably, 300 to 330.degree. C.). A particle diameter of
the aforementioned carbon particles (a particle diameter of the
carbon particles in the dispersion liquid) is preferably 10 to 1000
nm (more preferably, 50 nm or more, yet more preferably, 100 nm or
more, more preferably, 500 nm or less, and yet more preferably, 300
nm or less).
[0118] The aforementioned pitch dispersion liquid includes carbon
nanotubes responding to a necessity from a viewpoint of the
strength and conductivity. The carbon nanotube is, for example, a
single-walled carbon nanotube (SWNT). Or the carbon nanotube is,
for example, a multi-walled carbon nanotube (MWNT). Or the carbon
nanotube is a mixture thereof. The multi-walled carbon nanotube
(MWNT) is employed from a viewpoint of practical use. As a method
of incorporating the carbon nanotubes, the method is employed of
adding carbon nanotube powders (or carbon nanotube dispersion
liquid) to the pitch dispersion liquid. The aforementioned carbon
nanotube dispersion liquid and the aforementioned pitch dispersion
liquid are preferably mixed. An amount of the aforementioned carbon
nanotubes is preferably 0.01 to 10 parts by mass (more preferably,
0.1 to 1 part by mass) per 100 parts by mass of the aforementioned
pitch.
[0119] The aforementioned pitch (carbon particles) dispersion
liquid includes a graphitization promoter responding to a
necessity. The graphitization promoter is a catalyst having an
effect of promoting the graphitization degree. The aforementioned
graphitization promoter is, for example, borons (for example,
boron, boric ester, boron carbide, and the like), or silicons (for
example, silicon, silicic ester, silicon carbide, and the like).
The preferable graphitization promoter is boron carbide or silicon
carbide. An amount of the aforementioned graphitization promoter is
preferably 1 to 10000 ppm by mass for the carbon particles (more
preferable, 10 to 1000 ppm by mass). The aforementioned
graphitization promoter and the aforementioned pitch dispersion
liquid are mixed when the aforementioned graphitization promoter is
liquid. At first, the dispersion liquid of the graphitization
promoter is prepared when the aforementioned graphitization
promoter is powders. And, the above dispersion liquid and the
aforementioned pitch dispersion liquid are mixed.
[0120] The aforementioned pitch dispersion liquid includes a
dispersant responding to a necessity. The aforementioned dispersant
is, for example, a surfactant or a polymer. An amount of the
aforementioned dispersant is preferably 1 to 200 parts by mass
(more preferably, 10 to 100 parts by mass) per 100 parts by mass of
the pitch.
[0121] A ratio of the aforementioned resin and the aforementioned
pitch is preferably the following ratio. When the aforementioned
resin is too much, the remaining carbon content after the
carbonization becomes few. Contrarily, when the aforementioned
resin is too few, the electrospinning becomes difficult. Thus, an
amount of the aforementioned pitch is preferably 20 to 200 parts by
mass (more preferably, 30 to 150 parts by mass) per 100 parts by
mass of the aforementioned resin. When the carbon fiber having the
aforementioned large diameter portion and the aforementioned small
diameter portion should be acquired, an amount of the
aforementioned pitch is preferably 50 to 200 parts by mass (more
preferably, 70 to 150 parts by mass) per 100 parts by mass of the
aforementioned resin.
[0122] When a density of solid (components other than the solvent)
in the aforementioned dispersion liquid is too high, the spinning
is difficult. Contrarily, also when the aforementioned density is
too law, the spinning is difficult. Thus, a density of the
aforementioned solid is preferably 0.1 to 50% by mass (more
preferably, 1 to 30% by mass and yet more preferably, 5 to 20% by
mass).
[0123] When a viscosity of the aforementioned dispersion liquid is
too high, drawability is lacking at the time of the spinning.
Contrarily, when the aforementioned viscosity is too law, the
spinning is difficult. Thus, the viscosity of the aforementioned
dispersion liquid (the viscosity at the time of the spinning: the
viscosity measuring instrument is a coaxial double-cylindrical
viscometer) is preferably 10 to 10000 mPaS (more preferably, 50 to
5000 mPaS and yet more preferably, 500 to 5000 mPaS).
[0124] The preparation of the aforementioned dispersion liquid
includes a mixing step and a refining step. The aforementioned
mixing step is a step of mixing the aforementioned resin and the
aforementioned pitch. The aforementioned refining step is a step of
refining the aforementioned pitch. The aforementioned refining step
is, for example, a step of affixing shear strength to the
aforementioned pitch. This allows the pitch to be refined. It
doesn't matter which step, out of the mixing step and the refining
step, is firstly performed. They may be simultaneously
performed.
[0125] In the aforementioned mixing step, there are three cases,
namely, the case in which each of the aforementioned resin and the
aforementioned pitch is powders, the case in which one is powders,
and the other is a solution (dispersion liquid), and the case in
which each of the aforementioned resin and the aforementioned pitch
is a solution (dispersion liquid). The preferable case is that each
of the aforementioned resin and the aforementioned pitch is a
solution (dispersion liquid) from a viewpoint of operability.
[0126] In the aforementioned refining step, for example, a
medialess beads mill is employed. Or a beads mill is employed. Or
an ultrasound irradiation machine is employed. When foreign
materials should be prevented from mixedly entering, the medialess
beads mill is preferably employed. When a particle diameter of the
carbon particles should be controlled, the beads mill is preferably
employed. When the refining step should be performed in a simple
operation, the ultrasound irradiation machine is preferably
employed. In the present invention, the beads mill is preferably
employed because a control of the particle diameter of the pitch
(carbon particles) is important.
[0127] In the aforementioned dispersion liquid, when the particle
diameter of the aforementioned pitch is too large, the fiber
diameter becomes too large. When the particle diameter of the
aforementioned pitch is too small, the dispersion condition becomes
unstable. Thus, the aforementioned particle diameter is preferably
1 nm to 10 .mu.m (more preferably, 10 nm to 1 .mu.m).
[0128] [The Electrospinning Step (Step of Producing the Nonwoven
Fabric that is Comprised of the Carbon Fiber Precursors) (Step
II)]
[0129] The electrospinning apparatus is employed in this step.
[0130] For example, the electrospinning apparatus of FIG. 1 is
employed. In FIG. 1, 1 is a pump-type spinning dope supplying
apparatus. 2 is a nozzle-type exit. 3 is a voltage applying
apparatus. 4 is a collector. The collector 4 is earthed. The
aforementioned dispersion liquid (spinning dope) is forced to
scatter toward the collector 4 from the exit 2. The solvent is
volatilized at the time of this scattering. The spinning dope
coming from the exit 2 is subjected to a drawing operation due to
an electromagnetic field (the electromagnetic field applied by the
voltage applying apparatus 3 (the electromagnetic field between the
exit 2 and the collector 4)). The spinning dope arrives at the
collector 4 while its solvent is volatilized. At a time point that
the spinning dope arrives at the collector 4, it becomes fibrous
(it is in a fiber-shape in which the solvent has been removed). The
above fibrous substances, which are accumulated (deposited), become
the nonwoven fabric.
[0131] The spinning dope supplying apparatus is not limited to the
apparatus of FIG. 1. The spinning dope supplying apparatus 1 is,
for example, a syringe pump, a tube pump or a dispenser. The
spinning dope supplying apparatus could be a pan-type spinning dope
supplying apparatus (see FIG. 2, 5: a pan-type spinning dope
supplying apparatus and 6: a drum-type exit). An inner diameter of
the exit is 0.1 to 5 mm (preferably, 0.5 to 2 mm) when the exit has
a nozzle shape. The exit is made of metal or non-metal. A waistline
of the exit is flat-shaped or wire-shaped in the case of the drum
type. The exit is made of metal in the case of the drum type.
[0132] The aforementioned voltage applying apparatus 3 is, for
example, a DC high-voltage generator. Or the aforementioned voltage
applying apparatus 3 is a Van de Graaff generator. The preferable
applying voltage is 5 to 50 kV or so when the nozzle-type exit is
employed. The preferable applying voltage is 10 to 200 kV or so
when the drum-type exit is employed.
[0133] The aforementioned electromagnetic field strength is, for
example, 0.1 to 5 kV/cm. When the electromagnetic field strength
exceeds 5 kV/cm, breakdown of air easily occurs. When the
electromagnetic field strength is small, namely, less than 0.1
kV/cm, the drawablility of the spinning dope is insufficient. For
this, fiberization is difficult.
[0134] The aforementioned collector 4 is a confrontation-electrode
type collector. However, the aforementioned collector is not a
confrontation-electrode type collector in some cases. That is, when
the collector is arranged between the exit and the confrontation
electrode, the above collector is not a confrontation-electrode
type collector. When the collector 4 is a confrontation-electrode
type collector, the collector 4 is preferably configured of
conductive materials (for example, metal) of which a volume
resistivity is 10 E9 .OMEGA.m or lower. The collector is configured
of, for example, the nonwoven fabric. Or the collector is
configured of fabric, knitted fabric, nets, flat plates, belts or
the like. The collector is configured of liquid such as water and
organic solvents in some cases. A configuration thereof assumes a
piece by piece system in some cases, and assumes a roll-to-roll
continuous system in some cases. The continuous operation type
collector 4 is preferably employed from a viewpoint of production
efficiency.
[0135] When a distance between the exit 2 and the collector 4 is
too short, the solvent is not volatilized. When the aforementioned
distance is too long, the voltage necessary is raised. The
preferable distance is 5 cm to 1 m. The more preferable distance is
10 to 70 cm.
[0136] The nonwoven fabric obtained in this step is configured of
the carbon fiber precursors. The carbon fiber precursors are a
mixture of resin not subjected to the thermal treatment and the
carbon particles (pitch). The aforementioned nonwoven fabric has a
suitable thickness from a viewpoint of operability. A thickness of
the nonwoven fabric after the carbonization (graphitization) is
preferably 0.1 .mu.m to 10 mm (more preferably, 1 .mu.m or more,
yet more preferably, 10 .mu.m or more, more preferably, 1 mm or
less and yet more preferably, 500 m or less). A weight of the
nonwoven fabric after the carbonization is preferably 1 to 1000
g/m.sup.2 (more preferably, 10 to 500 g/m.sup.2).
[0137] With the carbon fiber having irregularity (the carbon fiber
having the large diameter portion (the portion in which the
diameter of the carbon fiber is large) and the small diameter
portion (the portion in which the diameter of the carbon fiber is
small)), the features of the present invention are largely
exhibited. When the surface of the carbon fiber is irregularly
shaped, a surface area of the above carbon fiber is large. As a
result, the features of the present invention are largely
exhibited. The aforementioned fiber is preferably a fiber having
the following size. The diameter of the aforementioned small
diameter portion after the carbonization (graphitization) was
preferably 10 nm to 1 .mu.m (more preferably, 20 nm or more and
more preferably, 500 nm or less). The diameter of the
aforementioned large diameter portion after the carbonization
(graphitization) was preferably 20 nm to 2 .mu.m (more preferably,
50 nm or more, yet more preferably, 100 nm or more, more
preferably, 1.5 .mu.m or less and yet more preferably, 1 .mu.m or
less). Needless to say, the condition [(the diameter (an averaged
value of the diameters) in the aforementioned large diameter
portion)>(the diameter (an averaged value of the diameters) in
the aforementioned small diameter portion)] is satisfied. It was
when [(a maximum value of the diameter in the aforementioned large
diameter portion)/(a minimum value of the diameter in the
aforementioned small diameter portion)]=1.1 to 100 (more
preferably, 2 or more, more preferably, 50 or less, and yet more
preferably, 20 or less) that an effect for which the present
invention aimed was largely exhibited. When the aforementioned
large diameter portion became too large, the aforementioned fiber
was easily cut off. When the aforementioned large diameter portion
became too small, the effect for which the present invention aimed
was small. The length of the aforementioned small diameter portion
after the carbonization (graphitization) was preferably 10 nm to 10
.mu.m (more preferably, 50 nm to 1 .mu.m). The effect for which the
present invention aimed was small also when the length of the
aforementioned small diameter portion was too short and too long.
The length of the aforementioned large diameter portion after the
carbonization (graphitization) was preferably 50 nm to 10 .mu.m
(more preferably, 500 nm to 3 .mu.m). The effect for which the
present invention aimed was small also when the length of the
aforementioned large diameter portion was too short and too long.
The length of the aforementioned carbon fiber (a full length of one
fiber) after the carbonization (graphitization) was preferably 0.1
to 1000 .mu.m (more preferably, 10 to 500 .mu.m, and 0.5 to 10
.mu.m in the case that the carbon fiber was pulverized and
employed). The effect for which the present invention aimed was
small when the length of the aforementioned fiber was too
short.
[0138] The specific surface area (BET specific surface area) of the
aforementioned carbon fiber after the carbonization
(graphitization) was preferably 1 to 100 m.sup.2/g (more
preferably, 2 to 50 m.sup.2/g).
[0139] The peak originating in a graphite structure (002) of the
aforementioned carbon fiber after the carbonization
(graphitization) preferably exists within a range of 25.degree. to
30.degree. (2.theta.) in an X-ray diffraction measurement thereof.
A half width of the aforementioned peak is 0.1.degree. to 2.degree.
(more preferably, 0.1.degree. to 1.degree.). Crystallinity of the
graphite is inferior when the aforementioned half width is too
large. When the above carbon fiber was employed as the battery,
performance thereof was inferior.
[0140] The aforementioned carbon fiber after the carbonization
(graphitization) preferably satisfy the condition D [ID/IG=0.1 to
2]. More preferably, the aforementioned ratio is 0.1 to 1. The
crystallinity of the graphite is inferior when the aforementioned
ratio is too large. When the above carbon fiber was employed as the
battery, performance thereof was inferior.
[0141] The aforementioned carbon fiber preferably satisfy the
condition E [L/(S).sup.1/2=5 to 300]. More preferably, the
aforementioned ratio was 50 to 200. The number of the fiber that
enters a measurement range when the SEM observation is made is
preferably 50 or more. That is, when the number of the fiber was 50
or more, a measurement error was small. A name of a program under
which this operational processing was performed is "imageJ" (US
National Institute of Mental Health/National Institute of
Neurological Disorders and Stroke, Research Support Branch HP
http://rsb.info.nih.gov/ij/index.html)
[0142] The carbon fiber constituting the nonwoven fabric of the
present invention is preferably the carbon fiber having the
aforementioned features. However, the carbon fiber having no
aforementioned features may be incorporated. For example, the
features of the present invention were not impaired so long as (an
amount of the carbon fiber having the features of the present
invention)/(an amount of the carbon fiber having the features of
the present invention+an amount of the carbon fiber having no
features of the present invention).gtoreq.0.5 was satisfied.
Preferably, the aforementioned ratio is 0.6 or more. More
preferably, the aforementioned ratio is 0.7 or more. Yet more
preferably, the aforementioned ratio is 0.8 or more. Most
preferably, the aforementioned ratio is 0.9 or more.
[0143] Plural sheets of the aforementioned nonwoven fabric made of
the carbon fiber precursors may be laminated. The laminated
nonwoven fabric may be compressed with the roll. That is, the
compression allows the membrane thickness and the density to be
appropriately regulated.
[0144] The nonwoven fabric that is comprised of the carbon fiber
precursors is peeled off from the collector and treated. Or the
aforementioned nonwoven fabric is treated in a state of sticking to
the collector.
[0145] [The Modifying Step (Step III)]
[0146] [The Thermal Treatment of the Aforementioned Nonwoven Fabric
Made of the Carbon Fiber Precursors (Step III-1)]
[0147] The carbon fiber nonwoven fabric is obtained from the
aforementioned nonwoven fabric made of the carbon fiber precursors.
This is obtained by modifying the aforementioned carbon fiber
precursors into the carbon fiber. The modifying process is, for
example, a thermal treatment. In particular, the modifying process
is a thermal treatment under the oxidative gas atmosphere. This
thermal treatment allows the resin constituting the aforementioned
carbon fiber precursors to be removed. That is, the carbon sources
other than the carbon particles are removed. Yet, curing of the
aforementioned carbon particles is performed.
[0148] This step is preferably performed after the aforementioned
electrospinning step (the aforementioned step II).
[0149] The oxidative gas in this step is a compound containing
oxygen atoms or an electron acceptor compound. The aforementioned
oxidative gas is, for example, air, oxygen, halogen gas, nitrogen
dioxide, ozone, water vapor, or carbon dioxide. From among them,
the preferable oxidative gas is air from a viewpoint of cost
performance and quick curing at a low temperature. Or the
preferable oxidative gas is gas containing halogen gas. The
aforementioned halogen gas is, for example, fluorine, iodine and
bromine. From among them, the preferable halogen gas is iodine. Or
the preferable halogen gas is mixture gas of the aforementioned
components.
[0150] A temperature of the aforementioned thermal treatment is
preferably 100 to 400.degree. C. (more preferably, 150 to
350.degree. C.). A time of the aforementioned thermal treatment is
preferably 3 minutes to 24 hours (more preferably, 5 minutes to 2
hours).
[0151] The cured nonwoven fabric made of the carbon fiber
precursors is obtained in this step. A softening temperature of
this cured carbon fiber precursors is preferably 400.degree. C. or
higher (more preferably, 500.degree. C. or higher).
[0152] The aforementioned resin is subjected to a crystallization
process prior to this step when the aforementioned resin is
crystalline resin. That is, the aforementioned resin is preferably
kept for approximately one minute to one hour at a temperature
equal to or more than a glass transition temperature, and yet equal
to or less than a melting point. The glass transition temperature
of polyvinyl alcohol is approximately 50 to 90.degree. C., and the
melting point thereof is 150 to 250.degree. C.
[0153] This step is performed in a piece by piece system. Or this
step is performed in a roll-to-roll continuous system. Or the
aforementioned resin is thermally treated in a state of the roll.
The preferable step is a roll-to-roll continuous thermal treatment
process from a viewpoint of production efficiency.
[0154] [The Carbonizing Process (Step III-2)]
[0155] The carbonizing process is preferably performed in order to
obtain the carbon fiber nonwoven fabric. This carbonizing process
is a thermal treatment. This carbonizing process is preferably a
thermal treatment under an inert gas atmosphere. The aforementioned
cured carbon fiber precursors become the carbon fiber through this
step. This step is preferably performed after the aforementioned
step III-1.
[0156] The inert gas in this step is gas that does not chemically
react to the cured carbon fiber precursors during the carbonizing
process. The inert gas is, for example, nitrogen, argon and
krypton. From among them, the preferable inert gas is nitrogen gas
from a viewpoint of the cost.
[0157] A processing temperature of this step is preferably 500 to
2000.degree. C. (more preferably, 600 to 1500.degree. C.). The
carbonization hardly progresses at a temperature less than
500.degree. C. The graphitization occurs at a temperature exceeding
2000.degree. C. However, when a graphitizing process to be later
described is performed, a rise in the temperature exceeding
2000.degree. C. is acceptable. A processing time of this step is
preferably 5 minute to 24 hours (more preferably, 30 minute to 2
hours).
[0158] [The Graphitizing Process (Step III-3)]
[0159] The graphitizing process is preferably performed. The
graphitizing process is preferably performed under an inert gas
atmosphere. This step is an important step when the nonwoven fabric
is employed for negative electrodes of the lithium-ion batteries
and the like. This step is preferably performed after the
aforementioned step III-2.
[0160] The inert gas in this step is gas that does not chemically
react to the carbon fiber precursors during the graphitizing
process. The inert gas is, for example, argon and krypton. Nitrogen
gas is not preferable because it is ionized.
[0161] A processing temperature of this step is preferably 2000 to
3500.degree. C. (more preferably, 2300 to 3200.degree. C.). A
processing time is preferably one hour or less (more preferably,
0.1 to 10 minutes).
[0162] This step is performed by keeping the carbon fiber
precursors at the aforementioned temperature. In particular, the
above step is performed by the electric current to the carbon fiber
nonwoven fabric. That is, the aforementioned temperature is kept
owing to Joule heat being generated due to the electric current.
Also microwave heating enables the graphitization. The preferable
graphitizing process is electric-current heating from a viewpoint
of production cost. In particular, the continuous process using the
roll-to-roll system is preferably performed.
[0163] [The Fiberizing Process (Step IV)]
[0164] This step is a step of obtaining the carbon fiber from the
nonwoven fabric obtained in the aforementioned step. This step is a
step of pulverizing the nonwoven fabric obtained, for example, by
the aforementioned step II, the aforementioned step III-1, the
aforementioned step III-2, or the aforementioned step III-3.
Preferably, this step is a step of pulverizing the nonwoven fabric
obtained by the aforementioned step III-2 and the aforementioned
step III-3. Pulverizing the nonwoven fabric allows the fiber to be
obtained.
[0165] For example, a cutter mill, a hammer mill, a pin mill, a
ball mill, or a jet mill is employed for pulverizing the nonwoven
fabric. Any method of the wet method and the dry method can be
adopted. However, the dry method is preferably employed when the
fiber is employed for a field such as nonaqueous electrolyte
secondary batteries.
[0166] [The Electrodes]
[0167] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is employed for the members of the
electric elements (the electronic elements are also included in the
electric elements). For example, the aforementioned carbon fiber
nonwoven fabric (or the aforementioned carbon fiber) is employed
for the members of the batteries, the capacitors, the fuel cells
and the like.
[0168] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is applied for the electrodes of the
batteries. The batteries are, for example, a lead battery, a
nickel-cadmium battery, a nickel-hydrogen battery, a lithium-ion
battery, a sodium-sulfur battery and a redox flow battery. From
among them, the carbon fiber nonwoven fabric (or the aforementioned
carbon fiber) is applied for the electrodes of the lithium-ion
battery. The aforementioned electrode is preferably a negative
electrode. The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is preferably applied to an anode
active material. The aforementioned carbon fiber nonwoven fabric
(or the aforementioned carbon fiber) is preferably applied to a
conductant agent.
[0169] The lithium-ion battery is comprised of members such as
positive electrodes, negative electrodes, separators, and an
electrolyte solution. The positive electrode and the negative
electrode are configured as follows. That is, the positive
electrode and the negative electrode are configured by laminating a
mixture including the active substance, the conductant agent, a
binder and the like on a current collector (for example, aluminum
foil and copper foil).
[0170] As the anode active material, the carbon materials such as
non-graphitizable carbon, easily-graphitizable carbon, graphite,
pyrolytic carbons, cokes, glass-like carbons, an organic polymer
compound fired product, carbon fiber, or activated carbon can be
listed. The materials containing at least one member selected from
a group of a single body, an alloy and a compound of metal elements
capable of forming an alloy with lithium as well as a single body,
an alloy and a compound of semimetal elements capable of forming an
alloy with lithium are employed (hereinafter, these are referred to
as alloy-based anode active materials).
[0171] As the aforementioned metal element or semimetal element,
tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc
(Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg),
boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag),
zirconium (Zr), yttrium (Y) or hafnium (Hf) can be listed.
[0172] As an example of specific compounds, there exists LiAl,
AlSb, CuMgSb, SiB.sub.4, SiB.sub.6, Mg.sub.2Si, Mg.sub.2Sn,
Ni.sub.2Si, TiSi.sub.2, MoSi.sub.2, CoSi.sub.2, NiSi.sub.2,
CaSi.sub.2, CrSi.sub.2, Cu.sub.5Si, FeSi.sub.2, MnSi.sub.2,
NbSi.sub.2, TaSi.sub.2, VSi.sub.2, WSi.sub.2, ZnSi.sub.2, SiC,
Si.sub.3N.sub.4, Si.sub.2N.sub.2O, SiOv (0<v.ltoreq.2), SnOw
(0<w.ltoreq.2), SnSiO.sub.3, LiSiO, LiSnO or the like.
[0173] Lithium-titanium composite oxide (spinel-type composite
oxide, ramstellite-type composite oxide, and the like) is also
preferable.
[0174] The positive electrode active substance is acceptable so
long as it is a substance capable of absorbing and releasing
lithium ion. As a preferable example, for example, composite metal
oxide containing lithium and olivine-type lithium phosphate can be
listed.
[0175] The composite metal oxide containing lithium is metal oxide
including lithium and transition metal. Or the composite metal
oxide containing lithium is metal oxide in which one part of the
transition metal in the metal oxide was replaced with different
elements. The metal oxide containing at least one member or more
selected from a group of cobalt, nickel, manganese and iron as the
transition metal element is more preferable.
[0176] As an specific example of the composite metal oxide
containing lithium, for example, Li.sub.kCoO.sub.2,
Li.sub.kNiO.sub.2, Li.sub.kMnO.sub.2,
Li.sub.kCo.sub.mNi.sub.1-mO.sub.2,
Li.sub.kCo.sub.mM.sub.1-mO.sub.n, Li.sub.kMn.sub.2O.sub.4 and
Li.sub.kMn.sub.2-mMnO.sub.4 (M is at least one element selected
from a group of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb,
Sb and B. k=0 to 1.2, m=0 to 0.9, and n=2.0 to 2.3) can be
listed.
[0177] The compound (lithium-iron phosphorus oxide) with an
olivine-type crystalline structure represented by a general formula
Li.sub.xFe.sub.1-yM.sub.yPO.sub.4(M is at least one element
selected from a group of Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti,
Mg, Ca and Sr. 0.9<x<1.2 and 0.ltoreq.y<0.3) can be
listed. As such lithium-iron phosphorus oxide, for example,
LiFePO.sub.4 is preferred.
[0178] The compounds represented by a general formula
X--S--R--S--(S--R--S).sub.n--S--R--S--X' described in European
Patent No. 415856 are employed as lithium thiolate.
[0179] The separator is configured of porous membranes made of
synthetic resin (for example, polyurethane,
polytetrafluoroethylene, polypropylene and polyethylene), or porous
membranes made of ceramics. The separator having two kinds of the
porous membranes or more laminated therein may be used.
[0180] The electrolyte solution contains the non-aqueous solvents
and the electrolyte salts. The non-aqueous solvents are, for
example, cyclic carbonate (propylene carbonate, ethylene carbonate
and the like), chain esters (diethyl carbonate, dimethyl carbonate,
ethylmethyl carbonate and the like), ethers (.gamma.-butyrolactone,
sulfolane, 2-methyltetrahydrofuran, dimethoxyethane and the like).
They could be single and a mixture of plural kinds. Carbonate is
preferable from a viewpoint of oxidative stability.
[0181] The electrolyte salts are, for example, LiBF.sub.4,
LiClO.sub.4, LiPF.sub.6, LiSbF.sub.6, LiAsF.sub.6, LiAlCl.sub.4,
LiCF.sub.3SO.sub.3, LiCF.sub.3CO.sub.2, LiSCN, lower aliphatic
lithium carboxylate, LiBCl, LiB.sub.10Cl.sub.10, lithium halides
(LiCl, LiBr, LiI and the like), haloborates
(bis(1,2-benzenediolate(2-)-O,O') lithium borate,
bis(2,3-naphthalenediolate(2-)-O,O') lithium borate,
bis(2,2'-biphenyldiolate(2-)-O,O') lithium borate,
bis(5-fluoro-2-olate-1-benzenesulfonic acid-O,O') lithium borate
and the like), and imide salts (LiN(CF.sub.3SO.sub.2).sub.2,
LiN(CF.sub.3SO.sub.2)(C.sub.4F.sub.9SO.sub.2), and the like).
Lithium salts such as LiPF.sub.6 and LiBF.sub.4 are preferable.
LiPF.sub.6 is particularly preferable.
[0182] The gel-like electrolyte in which the electrolyte solution
has been kept in the polymer compound may be employed as the
electrolyte solution. The aforementioned polymer compounds are, for
example, polyacrylonitrile, poly(vinylidene fluoride), a copolymer
of poly(vinylidene fluoride) and polyhexafluoropropylene,
polytetrafluoroethylene, polyhexafluoropropylene, polyethylene
oxide, polypropylene oxide, polyphosphazene, polysiloxane,
poly(vinyl acetate), poly(vinyl alcohol), poly(methyl
methacrylate), polyacrylate, polymethacrylate, styrene-butadiene
rubber, nitrile-butadiene rubber, polystyrene and polycarbonate.
The polymer compounds having structures of polyacrylonitrile,
poly(vinylidene fluoride), polyhexafluoropropylene and polyethylene
oxide are preferable from a viewpoint of electrochemical
stability.
[0183] The conductant agents are, for example, graphite (natural
graphite, artificial graphite and the like), carbon black
(acetylene black, ketjen black, channel black, furnace black, lamp
black, thermal black and the like), conductive fiber (carbon fiber
and metal fiber), metal (Al etc.) powder, conductive whiskers (zinc
oxide, potassium titanate and the like), conductive metal oxide
(titanium oxide and the like), organic conductive materials
(phenylene derivatives and the like) and fluorinated carbon.
[0184] The binders are, for example, poly(vinylidene fluoride,
polytetrafluoroethylene, polyethylene, polypropylene, aramid resin,
polyamide, polyimide, poly(amide-imide), polyacrylonitrile,
polyacrylate, methyl polyacrylate, ethyl polyacrylate, hexyl
polyacrylate, polymethacrylate, methyl polymethacrylate, ethyl
polymethacrylate, hexyl polymethacrylate, poly(vinyl acetate),
polyvinylpyrrolidone, polyether, polyether sulphone,
hexafluoropolypropylene, styrene-butadiene rubber, modified acrylic
rubber and carboxymethyl cellulose.
[0185] The negative electrode of the lithium-ion battery, as a
rule, is produced by laminating the anode active material (for
example, the graphite material) 7 on a current collecting electrode
plate (for example, copper foil) 8 (see FIG. 3). The material of
the present invention can be employed for both of the anode active
material and the current collecting electrode. The material of the
present invention can be employed only for the anode active
material. When the material in accordance with the present
invention is employed for the active substance, the nonwoven fabric
can be employed as it stands. Or, the material in accordance with
the present invention can be also employed by crushing into powder.
When the material in accordance with the present invention is
crushed into powder and is employed, the material in accordance
with the present invention can be configured only of the
aforementioned carbon fiber. Additionally, the material in
accordance with the present invention may be employed together with
the conventional active substances. In such a case, an amount of
the aforementioned carbon fiber is preferably 0.1 to 50% by mass
per an amount of all anode active materials. The case that an
amount of the carbon fiber is 1 to 30% by mass is more preferable.
The case that an amount of the carbon fiber is 1 to 10% by mass is
particularly preferable.
[0186] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is also employed as the conductive
auxiliary. The materials having no conductivity such as lithium
cobalt oxide are employed for the positive electrodes of the
lithium-ion batteries. When the aforementioned carbon fiber
nonwoven fabric (or the aforementioned carbon fiber) is employed,
the internal resistance is reduced. When the alloy-based negative
electrode materials having low conductivity are employed in
lithium-ion batteries, the aforementioned carbon fiber nonwoven
fabric (or the aforementioned carbon fiber) can be utilized as the
conductive auxiliary of the negative electrodes. An amount of the
conductive auxiliaries is 0.1 to 20% by mass (more preferably, 0.5
to 10% by mass and particularly preferably, 0.5 to 3% by mass) per
an amount of all active substances that are employed for the
electrodes.
[0187] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is employed as a mother material of
the alloy-based anode active material in the lithium-ion battery.
When an alloy of silicon or tin and the carbon material is employed
as the anode active material, a charge/discharge capacity is large.
As it is, in this case, the problem that a change in the volume of
the active substance due to the charge/discharge is large surfaces.
By the way, in this case, there exist pores in the aforementioned
carbon fiber nonwoven fabric (or the aforementioned carbon fiber).
Thus, when the aforementioned alloy (the anode active material) is
laminated on the aforementioned carbon fiber nonwoven fabric (or
the aforementioned carbon fiber), that is, when the aforementioned
carbon fiber nonwoven fabric (or the aforementioned carbon fiber)
is employed as the mother material of the anode active material, a
change in the volume of the active substance at the time of the
charge/discharge is alleviated. This allows the lithium-ion battery
having a high cyclic property to be obtained. With regard to the
aforementioned carbon fiber nonwoven fabric (or the aforementioned
carbon fiber) and the alloy-based anode active material, the
following ratio thereof is preferable. An amount of the alloy-based
anode active material is 0.01 to 1000% by mass per the
aforementioned carbon fiber nonwoven fabric (or the aforementioned
carbon fiber). In addition, it is 0.1 to 100% by mass.
Particularly, it is 0.1 to 30% by mass.
[0188] A method of immersing the aforementioned carbon fiber
nonwoven fabric (or the aforementioned carbon fiber) into a
solution containing the anode active material is employed in order
to affix the alloy-based anode active material to the
aforementioned carbon fiber nonwoven fabric (or the aforementioned
carbon fiber). Or, a method of coating the aforementioned carbon
fiber nonwoven fabric (or the aforementioned carbon fiber) with the
solution containing the anode active material is employed. Or, a
physical depositing method or a chemical depositing method may be
employed. For example, a vacuum evaporation method, a sputtering
method, an ion plating method, or a laser ablation method may be
employed. A CVD (Chemical Vapor Deposition) method may be employed.
A hot CVD method and a plasma CVD method may be employed. A
wet-type plating method may be employed instead of the
above-mentioned dry-type plating method. For example, an
electroplating method or an electroless plating method may be
employed. In addition to them, a sintering method may be employed.
For example, an atmospheric sintering method, a reactive sintering
method or a hot press sintering method may be employed.
[0189] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is applied for the electrode of the
capacitor. The aforementioned capacitor is an electric double-layer
capacitor. The aforementioned capacitor is a lithium-ion capacitor.
The aforementioned electrode is preferably a negative electrode.
The negative electrode of the lithium-ion capacitor, as a rule, is
produced by laminating the anode active material (for example, a
graphite material) 9 on a current collecting electrode plate (for
example, copper foil) 10 (see FIG. 4). The material in accordance
with the present invention is employed for both of the anode active
material and the current collecting electrode. The material in
accordance with the present invention is employed only for the
anode active material. When the material in accordance with the
present invention is employed only for the active substance, the
nonwoven fabric can be employed as it stands. Or, the material in
accordance with the present invention may be employed by crushing
into powder.
[0190] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is applied for the material of the
porous carbon electrode of the fuel cell. The aforementioned fuel
cell is a solid polymer type fuel cell. The aforementioned
electrode is preferably an anode. The anode of the solid polymer
type fuel cell, as a rule, is produced by laminating a catalyst
layer 12 that is comprised of platinum-supported carbon and polymer
electrolyte on a porous carbon electrode material 11 (FIG. 23)
[0191] [Filter]
[0192] The aforementioned carbon fiber nonwoven fabric (or the
aforementioned carbon fiber) is employed for collecting or
classifying the particles. That is, the aforementioned carbon fiber
nonwoven fabric (or the aforementioned carbon fiber) is employed as
a filter.
[0193] Hereinafter, the examples are listed for explaining the
present invention. However, the present invention is not limited to
the following examples.
EXAMPLES
Example 1
[0194] Polyvinyl alcohol of 100 g (product name: POVAL 117:
produced by KURARAY CO. LTD.), mesophase pitch of 120 g (product
name: AR: produced by MITSUBISHIGAS CHEMICAL COMPANY. INC.) and
water of 800 g were mixed with the beads mill. This allowed the
mesophase pitch dispersion liquid having polyvinyl alcohol
dissolved therein to be prepared. The particle diameter of the
carbon particles within this dispersion liquid was 200 nm
(measuring apparatus: LA-950: manufactured by HORIBA, Ltd.). The
viscosity of the dispersion liquid was 4500 mPaS (measuring
apparatus: BH type Viscometer: manufactured by TOKIMEC INC.).
[0195] The electrospinning apparatus (see FIG. 1, nozzle diameter;
1.0 mm, collector (current collecting electrode); aluminum foil,
distance between the nozzle and the collector; 10 cm, voltage: 10
kV) was employed. That is, the electrospinning was performed by
employing the above-mentioned dispersion liquid. The nonwoven
fabric made of the carbon fiber precursors was produced on the
collector.
[0196] The above-mentioned nonwoven fabric was laminated. This
laminated nonwoven fabric was heated for 10 minutes at a
temperature of 150.degree. C. in the air. Thereafter, it was heated
for one hour at a temperature of 300.degree. C.
[0197] Thereafter, the laminated nonwoven fabric was heated at a
temperature of up to 900.degree. C. under an argon gas
atmosphere.
[0198] Next, the laminated nonwoven fabric was heated at a
temperature of up to 2800.degree. C. in a graphitizing furnace.
[0199] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0200] The SEM photograph of the graphitized carbon fiber nonwoven
fabric obtained in this example (SEM apparatus: name of apparatus:
VE-8800 manufactured by KEYENCE CORPORATION) is shown in FIG. 5.
According to the above SEM photograph, the fiber constituting the
nonwoven fabric was fiber having irregularities. That is, the
aforementioned fiber included a large diameter portion (the
diameter: approximately 500 to 1000 nm) and a small diameter
portion (the diameter: approximately 100 to 200 nm). The length of
the aforementioned large diameter portion was approximately 500 to
1000 nm. The length of the aforementioned small diameter portion
(the distance between the aforementioned large diameter portion and
the aforementioned large diameter portion) was approximately 500 to
1000 nm.
[0201] The thickness of the aforementioned nonwoven fabric was 125
.mu.m and the weight thereof was 210 g/m.sup.2. The BET surface
area (measurement apparatus: manufactured by Shimadzu Corporation)
was 10.8 m.sup.2/g.
[0202] The XRD measurement result of the graphitized carbon fiber
nonwoven fabric obtained in this example (XRD apparatus:
manufactured by Rigaku Corporation) is shown in FIG. 6. The half
width in this maximum peak was 0.95.degree..
[0203] The Raman measurement result of the graphitized carbon fiber
nonwoven fabric obtained in this example (Raman measurement
apparatus: manufactured by Shimadzu Corporation) is shown in FIG.
7. According to this, ID/IG was 0.87.
[0204] The S/L measurement was performed by employing the
above-mentioned SEM photograph. That is, imageJ (US National
Institute of Mental Health/National Institute of Neurological
Disorders and Stroke, Research Support Branch HP
http://rsb.info.nih.gov/ij/index.html) was employed. The carbon
fiber portion and the portion other than the carbon fiber were
separated, and the area and the length of the circumference of the
carbon fiber portion were measured. The image subjected to the
processing is shown in FIG. 8. As a result, L/(S).sup.1/2=140 was
yielded. As a result of measuring the similar image, (the maximum
value in the large diameter portion)/(the minimum value in the
small diameter portion)=10 was yielded.
Example 2
[0205] The processing similar to that of the example 1 was
performed except that an amount of the mesophase pitch was 100 g. A
result thereof is shown in Table 1. The SEM photograph of the
graphitized carbon fiber nonwoven fabric of this example (SEM
apparatus: VE-8800 manufactured by KEYENCE CORPORATION) is shown in
FIG. 9. Further, the image employed for an image analysis of the
SEM photograph is shown in FIG. 10.
Example 3
[0206] Polyethylene oxide of 100 g (product name: Polyethylene
Glycol 2,000,000: produced by Wako Pure Chemistry Industries,
Ltd.), mesophase pitch of 200 g (product name: AR) and water of 700
g were mixed with the beads mill. This allowed the mesophase pitch
dispersion liquid having polyethylene oxide dissolved therein to be
prepared. The particle diameter of the carbon particles within this
dispersion liquid was 150 nm (measuring apparatus: LA-950). The
viscosity of the dispersion liquid was 100 mPaS (measuring
apparatus: BH type Viscometer).
[0207] The electrospinning was performed similarly to that of the
example 1 by employing this dispersion liquid. That is, the
nonwoven fabric made of the carbon fiber precursors was produced on
the collector.
[0208] The above-mentioned nonwoven fabric was laminated. This
laminated nonwoven fabric was heated for one hour at a temperature
of 100.degree. C. in the air. Thereafter, it was heated for one
hour at a temperature of 200.degree. C.
[0209] Thereafter, the laminated nonwoven fabric was heated at a
temperature of up to 900.degree. C. under the argon gas
atmosphere.
[0210] Next, the laminated nonwoven fabric was heated at a
temperature of up to 2400.degree. C. in the graphitizing
furnace.
[0211] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0212] Properties of the nonwoven fabric of this example are shown
in Table 1.
Example 4
[0213] Polyacrylic acid of 20 g (product name: AQUALIC AS58:
produced by NIPPON SHOKUBAI CO., LTD), mesophase pitch of 30 g
(product name: AR) and water of 950 g were mixed with the beads
mill. This allowed the mesophase pitch dispersion liquid having
polyacrylic acid dissolved therein to be prepared. The particle
diameter of the carbon particles within this dispersion liquid was
400 nm (measuring apparatus: LA-950). The viscosity of the
dispersion liquid was 120 mPaS (measuring apparatus: BH type
Viscometer).
[0214] The electrospinning was performed similarly to that of the
example 1 by employing this dispersion liquid. That is, the
nonwoven fabric made of the carbon fiber precursors was produced on
the collector.
[0215] The above-mentioned nonwoven fabric was laminated. This
laminated nonwoven fabric was heated for one hour at a temperature
of 150.degree. C. in the air. Thereafter, it was heated for one
hour at a temperature of 300.degree. C.
[0216] Thereafter, the laminated nonwoven fabric was heated at a
temperature of up to 900.degree. C. under the argon gas
atmosphere.
[0217] Next, the laminated nonwoven fabric was heated at a
temperature of up to 2800.degree. C. in the graphitizing
furnace.
[0218] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0219] Properties of the nonwoven fabric of this example are shown
in Table 1.
Example 5
[0220] Polyvinylbutyral of 100 g (product name: Mowital: produced
by KURARAY CO. LTD.), mesophase pitch of 100 g (product name: AR)
and isopropyl alcohol of 800 g were mixed with the beads mill. This
allowed the mesophase pitch dispersion liquid having
polyvinylbutyral dissolved therein to be prepared. The particle
diameter of the carbon particles within this dispersion liquid was
350 nm (measuring apparatus: LA-950). The viscosity of the
dispersion liquid was 320 mPaS (measuring apparatus: BH type
Viscometer).
[0221] The electrospinning was performed similarly to that of the
example 1 by employing this dispersion liquid. That is, the
nonwoven fabric made of the carbon fiber precursors was produced on
the collector.
[0222] The obtained nonwoven fabric was heated for two hours at a
temperature of 150.degree. C. in the air. Thereafter, it was heated
for one hour at a temperature of 300.degree. C.
[0223] Thereafter, the nonwoven fabric was heated at a temperature
of up to 900.degree. C. under the argon gas atmosphere.
[0224] Next, the nonwoven fabric was heated at a temperature of up
to 2800.degree. C. in the graphitizing furnace.
[0225] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0226] Properties of the nonwoven fabric of this example are shown
in Table 1.
Example 6
[0227] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 190 g. A
result thereof is shown in Table 1.
Example 7
[0228] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 150 g. A
result thereof is shown in Table 1.
Example 8
[0229] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 70 g. A
result thereof is shown in Table 1.
Example 9
[0230] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 50 g. A
result thereof is shown in Table 1.
Example 10
[0231] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 30 g. A
result thereof is shown in Table 2.
Example 11
[0232] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 220 g.
The result thereof is shown in Table 2.
Example 12
[0233] The processing was performed similarly to that of the
example 1 except that an amount of the mesophase pitch was 10 g.
The result thereof is shown in Table 2.
Example 13
[0234] The processing was performed similarly to that of the
example 1 except that an amount of polyvinyl alcohol is 60 g, an
amount of the mesophase pitch was 70 g, and water is 870 g. The
result thereof is shown in Table 2.
[0235] The SEM photograph of the graphitized carbon fiber nonwoven
fabric of this example (SEM apparatus: VE-8800 manufactured by
KEYENCE CORPORATION) is shown in FIG. 11.
Example 14
[0236] Carboxymethylcellulose amine salt of 50 g (product name:
Ammonium CMC DN-400H: produced by DAICEL CHEMICAL INDUSTRIES,
LTD.), mesophase pitch of 50 g (product name: AR) and water of 900
g were mixed with the beads mill. This allowed the mesophase pitch
dispersion liquid having carboxymethylcellulose amine salt
dissolved therein to be prepared. The particle diameter of the
carbon particles within this dispersion liquid was 230 nm
(measuring apparatus: LA-950). The viscosity of the dispersion
liquid was 8300 mPaS (measuring apparatus: BH type Viscometer).
[0237] The electro spinning was performed similarly to that of the
example 1 by employing this dispersion liquid. That is, the
nonwoven fabric made of the carbon fiber precursors was produced on
the collector.
[0238] The obtained nonwoven fabric was heated for one hour at a
temperature of 300.degree. C. in the air.
[0239] Thereafter, the nonwoven fabric was heated at a temperature
of up to 900.degree. C. under the argon gas atmosphere.
[0240] Next, the nonwoven fabric was heated at a temperature of up
to 2800.degree. C. in the graphitizing furnace.
[0241] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0242] Properties of the nonwoven fabric of this example are shown
in Table 2.
Example 15
[0243] Polyvinyl alcohol of 100 g (product name: POVAL 117),
mesophase pitch of 20 g (product name: AR) and water of 800 g were
mixed with the beads mill. This allowed the mesophase pitch
dispersion liquid having polyvinyl alcohol dissolved therein to be
prepared. The particle diameter of the carbon particles within this
dispersion liquid (measuring apparatus: LA-950) was 200 nm. The
viscosity of the dispersion liquid was 4300 mPaS (measuring
apparatus: BH type Viscometer).
[0244] The electrospinning was performed similarly to that of the
example 1 by employing this dispersion liquid. That is, the
nonwoven fabric made of the carbon fiber precursors was produced on
the collector.
[0245] The above-mentioned nonwoven fabric was laminated. This
laminated nonwoven fabric was heated for ten minutes at a
temperature of 150.degree. C. in the air. Thereafter, it was heated
for one hour at a temperature of 300.degree. C.
[0246] Thereafter, the laminated nonwoven fabric was heated at a
temperature of up to 900.degree. C. under the argon gas
atmosphere.
[0247] Next, the laminated nonwoven fabric was heated at a
temperature of up to 2400.degree. C. in the graphitizing
furnace.
[0248] In a manner mentioned above, the graphitized carbon fiber
nonwoven fabric in accordance with the present invention was
obtained.
[0249] Properties of the nonwoven fabric of this example are shown
in Table 2.
Comparative example 1
[0250] The production of the nonwoven fabric was tried with melt
flow method by employing the dispersion liquid of the example 1.
However, the nonwoven fabric was not obtained.
Comparative example 2
[0251] The processing was performed similarly to that of the
example 1 except that, instead of the dispersion liquid of the
example 1 (the mesophace pitch dispersion liquid having polyvinyl
alcohol dissolved therein), a polyvinyl alcohol aqueous solution
(polyvinyl alcohol (product name: POVAL 117)) of 100 g, and water
900 g were employed, and that the carbon black and the pitch were
not included.
[0252] The diameter of the fiber of the nonwoven fabric obtained in
this comparative example 2 was uniform (50 nm). That is, there was
no fiber including both of the large diameter portion and the small
diameter portion on a piece by piece basis.
Example 16
[0253] The carbon fiber nonwoven fabric obtained in the example 1
was pulverized by employing a mortar. The pulverizing allowed the
carbon fiber to be obtained.
[0254] An investigation similar to that of the example 1 was
carried out for the above carbon fiber. A result thereof is shown
in Table 2. The SEM photograph of the graphitized carbon fiber
nonwoven fabric of this example (SEM apparatus: VE-8800
manufactured by KEYENCE CORPORATION) is shown in FIG. 12. Further,
the image subjected to the processing employed for an image
analysis of the SEM photograph is shown in FIG. 13.
Example 17
[0255] The processing was performed similarly to that of the
example 16 except that the carbon fiber nonwoven fabric obtained in
the example 13 was employed.
[0256] An investigation similar to that of the example 1 was
carried out for the above carbon fiber. A result thereof is shown
in Table 2. The SEM photograph of the graphitized carbon fiber
nonwoven fabric of this example (SEM apparatus: VE-8800
manufactured by KEYENCE CORPORATION) is shown in FIG. 14.
Comparative example 3
[0257] This is an example described in Non-Patent literature 1.
Thermoplastic resin (poly(4-methyl pentene-1): TPX: Grade RT-18
produced by Mitsui Chemicals, Inc.) of 70 g, mesophase pitch of 30
g (product name: AR) were mixed with the ball mill (P-7:
manufactured by Fritsch GmbH.). This mixture was kneaded by a
kneader (apparatus name: Laboratory Mixing Extruder Model CS-194AV:
manufactured by ATLAS ELECTRIC DEVICES, COMPANY) at a temperature
of 240.degree. C. The spinning was performed with the melt blow
method by employing the above kneaded product. The kneading
conditions are as follows. The nozzle is a single-hole nozzle with
a diameter of 0.5 mm (manufactured by NIPPON NOZZLE CO., LTD). The
spinning temperature is 380.degree. C. The resin pressure is 0.4
MPa. The blow pressure is 3.5 MPa. The obtained fiber was thermally
treated for 24 hours at a temperature of 160.degree. C. under the
oxygen atmosphere. Thereafter, the obtained fiber was thermally
treated for one hour at a temperature of 900.degree. C. and
thermally treated for thirty minutes at a temperature of
3000.degree. C. under the nitrogen atmosphere.
[0258] The SEM photograph of the fiber obtained in such a manner is
shown in FIG. 15. The fiber diameter was 100 nm to 5 .mu.m. The
dispersion of the fiber diameters between each fiber and the other
was recognized to be large. However, the fiber diameter was uniform
on a piece by piece basis. That is, there was no fiber including
both of the large diameter portion and the small diameter
portion.
Comparative example 4
[0259] This an example described in Non-Patent literature 2.
Polyacrylonitrile (molecular weight 86220: produced by Aldrich
Corporation) of 5 g was dissolved in DMF of 45 ml. And, the
electrospinning (voltage: 25 kV, the collecting plate: aluminum
foil and nozzle: 0.5 mm) was performed. The obtained nonwoven
fabric was thermally treated for one hour at a temperature of
280.degree. C. in the air. Thereafter, it was thermally treated at
a temperature of 2800.degree. C. in the argon.
[0260] The SEM photograph of the obtained fiber is shown in FIG.
16. The fiber diameter was uniform (100 nm). That is, there was no
fiber including both of the large diameter portion and the small
diameter portion on a piece by piece basis.
Example 18
[0261] The electrodes were produced. The anode active material of
the above electrodes is the fiber of the example 15. Lithium was
employed for the counter electrodes, and a charge/discharge
measurement was made. This result is shown in FIG. 17. A
charge/discharge capacity was 200 mAh/g.
[0262] Thus, the carbon fiber of the example 13 is preferred as the
negative electrode material for the lithium-ion secondary
battery.
Example 19
[0263] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the example 1.
Lithium was employed for the counter electrodes, and a
charge/discharge measurement was made. This result is shown in FIG.
18.
[0264] Thus, the nonwoven fabric of the example 1 is preferred as
the negative electrode material for the lithium-ion secondary
battery.
Example 20
[0265] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the example 6.
Lithium was employed for the counter electrodes, and a
charge/discharge measurement was made. As a result, a
charge/discharge capacity was 210 mAh/g.
[0266] Thus, the nonwoven fabric of the example 6 is preferred as
the negative electrode material for the lithium-ion secondary
battery.
Example 21
[0267] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the example 10.
Lithium was employed for the counter electrodes, and a
charge/discharge measurement was made. As a result, the
charge/discharge capacity was 150 mAh/g.
[0268] Thus, the c nonwoven fabric of the example 10 is preferred
as the negative electrode material for the lithium-ion secondary
battery.
Example 22
[0269] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the example 11.
Lithium was employed for the counter electrodes, and the
charge/discharge measurement was made. As a result, the
charge/discharge capacity was 220 mAh/g.
[0270] Thus, the nonwoven fabric of the example 11 can be employed
for the negative electrode materials for the lithium-ion secondary
battery. However, the nonwoven fabric of the example 11 is
difficult to handle as compared with that of the example 1.
Example 23
[0271] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the example 12.
[0272] Lithium was employed for the counter electrodes, and the
charge/discharge measurement was made. As a result, the
charge/discharge capacity was 100 mAh/g.
[0273] Thus, the nonwoven fabric of the example 12 can be employed
for the negative electrode materials for the lithium-ion secondary
battery. However, the charge/discharge capacity declined as
compared with that of the example 1.
Comparative example 5
[0274] The electrodes were produced. The anode active material of
the above electrodes is the nonwoven fabric of the comparative
example 2. Lithium was employed for the counter electrodes, and the
charge/discharge measurement was made. As a result, the
charge/discharge capacity was 0 mAh/g, and the above electrodes did
not function as the negative electrode material at all.
Comparative example 6
[0275] Lithium cobalt oxide (produced by Hohsen Corp.) of 96 g,
polyvinylidene difluoride (produced by Sigma-Aldrich Corporation)
of 2 g and acetylene black (produced by DENKI KAGAKU KOGYO
KABUSHIKI KAISYA) of 2 g were mixed. Addition of
N-methylpyrrolidone hereto yielded the paste-like mixture. The
copper foil was coated with the above paste-like mixture by a
bar-coater so that a membrane thickness after the drying was 20
.mu.m. Thereafter, the drying was performed, and the positive
electrodes for the lithium-ion secondary batteries were produced.
The SEM photograph is shown in FIG. 19.
[0276] The surface electric resistance of the above positive
electrodes was measured with a four-point probe method
(manufactured by Mitsubishi Chemical Analytech Co., Ltd.). A result
thereof was 0.4.OMEGA./.quadrature..
Example 24
[0277] The processing was performed similarly to that of the
comparative example 6 except that the carbon fiber of 2 g obtained
in the example 17 was employed instead of acetylene black. And, the
positive electrodes for the lithium-ion secondary batteries were
produced. The SEM photograph is shown in FIG. 20.
[0278] The surface electrical resistance of the above positive
electrodes was measured with the four-point probe method
(manufactured by Mitsubishi chemical Analytech Co., Ltd.). A result
thereof was 0.2.OMEGA./.quadrature..
Comparative example 7
[0279] The Si membrane (the membrane thickness: 500 nm) was mounted
on the copper foil with the vapor deposition (vapor deposition
apparatus: UEP-4000 manufactured by ULVAC, Inc.). And the negative
electrodes were produced. Lithium was employed for the counter
electrodes.
[0280] The charge/discharge measurement was made. A result thereof
was shown in FIG. 21. The charge/discharge capacity of the first
cycle was 580 mAh/g. The capacity declined during repetition of the
charge/discharge cycle.
Example 25
[0281] The processing was performed similarly to that of the
comparative example 7 except that the carbon fiber nonwoven fabric
obtained in the example 13 was employed instead of the copper foil.
An amount of Si was 17% by mass per the carbon fiber nonwoven
fabric. Lithium was employed for the counter electrodes.
[0282] The charge/discharge measurement was made. A result thereof
was shown in FIG. 22. The charge/discharge capacity was 667 mAh/g.
The capacity did not decline even though the charge/discharge cycle
was repeated. It can be grasped that the cyclic property was
enhanced as compared with the comparative example 7 employing the
copper foil for the mother material.
Example 26
[0283] The nonwoven fabric of the example 8 was coated with a mixed
paste of platinum-supported carbon and polymer electrolyte
(produced by Chemix Inc.). After the coating, the above nonwoven
fabric was dried for ten minutes at a temperature of 100.degree. C.
And, the anode electrode for the solid polymer type fuel cell was
produced. The cross-sectional schematic view of the above anode
electrode is shown in FIG. 23, and the SEM photograph of the
obtained sample is shown in FIG. 24.
[0284] The obtained anode electrode, and the cathode electrode, the
solid polymer electrolyte membrane and the carbon separator each of
which was produced by Chemix Inc. were employed, and the solid
polymer type fuel cells were produced.
[0285] As a result of introducing hydrogen from the anode and
measuring an open-circuit voltage, the open-circuit voltage was
0.98 V.
Example 27
[0286] Lithium was inserted into the nonwoven fabric of the example
8 by a half of the maximum capacity with a method similar to that
of the example 17, and the negative electrodes were produced. The
positive electrodes were produced by use of the active carbon. The
electrolyte solution was prepared by employing ethylene carbonate
containing lithium hexafluorophosphate and diethyl carbonate.
[0287] After the charge up to 4 v was carried out, the discharge
was carried out up to 3 v at a constant output. A correlation
between an energy density and an output density was measured. A
result thereof is shown in FIG. 25.
[0288] It can be grasped that the capacity is large in a high-rate
area as compared with that of the comparative example 7.
Comparative example 8
[0289] This an example described in Non-Patent literature 3. A
measurement similar to that of the example 27 was made except that
the graphite particles having a diameter of 10 .mu.m were employed
for the negative electrode. A result thereof is shown in FIG.
25.
Example 28
[0290] A mixed solution of a dispersion liquid of the carbon
particles having a diameter of 400 nm, and a dispersion liquid of
silicon oxide having a diameter of 10 nm was prepared. The above
mixed solution was filtered with the nonwoven fabric (filter) of
the example 13. As a result, only silicon oxide having a diameter
of 10 nm was filtered (passed).
[0291] [Properties]
TABLE-US-00001 TABLE 1 EX. 1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7
EX. 8 EX. 9 Resin PVA PVA PEO PAA PVB PVA PVA PVA PVA Carbon/resin
(wt/wt) 120/100 100/100 200/100 30/20 100/100 190/100 150/100
70/100 50/100 Small diameter portion 100 50 100 20 200 50 600 300
30 minimum value (nm) Large diameter portion 500 300 1000 30 250
1500 1000 500 100 minimum value (nm) Large diameter portion 1000
1000 1500 50 300 2000 1500 700 200 maximum value (nm) Small
diameter portion 1000 100 600 100 200 20 300 2000 3000 length (nm)
Large diameter portion 1000 2000 1000 100 500 6000 3000 500 300
length (nm) Nonwoven fabric 125 130 1010 0.5 10 200 185 210 165
thickness (.mu.m) Nonwoven fabric weight 210 200 820 0.9 13 195 165
155 172 (g/m.sup.2) BET surface area 10.8 5.8 15.6 5.4 8.6 5.6 4.9
16 24 (m.sup.2/g) XRD (half width) 0.95 0.50 0.20 0.30 1.6 0.30
0.45 1.50 1.65 Raman scattering 0.67 0.28 0.75 1.53 1.32 0.23 0.35
0.53 0.85 (ID/IG) SEM observation 140 84 75 230 65 43 86 164 153
(L/(S).sup.1/2) SEM observation (*) 10 20 15 2.5 1.5 40 1.6 2.3
6.7
TABLE-US-00002 TABLE 2 EX. 10 EX. 11 EX. 12 EX. 13 EX. 14 EX. 15
EX. 16 EX. 17 Resin PVA PVA PVA PVA CMC PVA PVA PVA Carbon/resin
(wt/wt) 30/100 220/100 10/100 60/70 50/50 20/100 120/100 60/70
Small diameter portion 10 50 30 100 500 20 100 100 minimum value
(nm) Large diameter portion 30 1500 35 150 1000 30 500 150 minimum
value (nm) Large diameter portion 100 2500 40 500 1500 100 1000 500
maximum value (nm) Small diameter portion 8000 50 50 100 100 3000
1000 100 length (nm) Large diameter portion 100 2500 50 200 1000
300 1000 200 length (nm) Nonwoven fabric 150 100 50 30 10 300 -- --
thickness (.mu.m) Nonwoven fabric weight 130 68 34 10 15 280 -- --
(g/m.sup.2) BET surface area 35 5.4 45 10.4 8.9 26 15.6 15.2
(m.sup.2/g) XRD (half width) 1.50 0.37 1.57 0.70 1.72 1.85 0.95
0.70 Raman scattering 0.75 0.31 1.02 0.25 1.64 1.05 0.87 0.25
(ID/IG) SEM observation 264 5 180 97 75 120 110 86 (L/(S).sup.1/2)
SEM observation (*) 10 50 1.3 5.0 3.0 5.0 10 5.0
[0292] *SEM observation (*): (maximum value in large diameter
portion)/(minimum value in small diameter portion)
[0293] This application is based upon and claims the benefit of
priority from Japanese patent application No. 2010-11457, filed on
Jan. 21, 2010, the disclosure of which is incorporated herein in
its entirety by reference.
REFERENCE SIGNS LIST
[0294] 1 and 5 spinning dope supplying apparatus [0295] 2 and 6
exits [0296] 3 voltage applying apparatus [0297] 4 collector [0298]
7 and 9 anode active materials [0299] 8 and 10 current collecting
electrode plates [0300] 11 porous carbon electrode material [0301]
12 catalyst layer
* * * * *
References