U.S. patent application number 11/051344 was filed with the patent office on 2005-08-18 for copolymer compound and electrochemical cell therewith.
Invention is credited to Mitani, Masaya, Nishiyama, Toshihiko, Nobuta, Tomoki, Takahashi, Naoki, Yoshinari, Tetsuya.
Application Number | 20050178659 11/051344 |
Document ID | / |
Family ID | 34836314 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050178659 |
Kind Code |
A1 |
Takahashi, Naoki ; et
al. |
August 18, 2005 |
Copolymer compound and electrochemical cell therewith
Abstract
The present invention relates to a copolymer compound prepared
by copolymerizing two or more monomers selected from indole and
indole derivatives. The copolymer compound can be used as an
electrode active material to provide an electrochemical cell with
an increased capacity and improved cycle properties.
Inventors: |
Takahashi, Naoki; (Miyagi,
JP) ; Nishiyama, Toshihiko; (Miyagi, JP) ;
Nobuta, Tomoki; (Miyagi, JP) ; Mitani, Masaya;
(Miyagi, JP) ; Yoshinari, Tetsuya; (Miyagi,
JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34836314 |
Appl. No.: |
11/051344 |
Filed: |
February 4, 2005 |
Current U.S.
Class: |
204/291 |
Current CPC
Class: |
C08G 73/0672 20130101;
H01M 4/60 20130101; Y02E 60/10 20130101; H01M 4/608 20130101; H01M
4/137 20130101; C08G 61/124 20130101; C08J 5/2256 20130101; C08J
2361/20 20130101 |
Class at
Publication: |
204/291 |
International
Class: |
C25B 011/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2004 |
JP |
2004-038444 |
Claims
1. A copolymer compound comprising copolymerized units of two or
more monomers selected from indole and indole derivatives
represented by formula (1): 6wherein Rs each independently
represent hydrogen atom, nitro group, carboxyl group, carboxylate
group, cyano group, acetyl group, aldehyde group, or halogen
atom.
2. The copolymer compound as claimed in claim 1, wherein the units
comprise a unit represented by formula (1A) and a unit represented
by formula (1B) or (1C): 7wherein Rs each independently represent
hydrogen atom, nitro group, carboxyl group, carboxylate group,
cyano group, acetyl group, aldehyde group, or halogen atom.
3. The copolymer compound as claimed in claim 1, having a structure
of formula (2): 8wherein Rs each independently represent hydrogen
atom, nitro group, carboxyl group, carboxylate group, cyano group,
acetyl group, aldehyde group or halogen atom; and n represents a
natural number.
4. The copolymer compound as claimed in claim 3, wherein the
monomer comprises an indole derivative having a substituent other
than hydrogen at least at 3-position.
5. The copolymer compound as claimed in claim 1, having a structure
of formula (3): 9wherein Rs each independently represent hydrogen
atom, nitro group, carboxyl group, carboxylate group, cyano group,
acetyl group, aldehyde group, or halogen atom; and n represents a
natural number.
6. The copolymer compound as claimed in claim 5, wherein the
monomer comprises an indole derivative having a substituent other
than hydrogen at least at 2-position.
7. The copolymer compound as claimed in claim 1, which is a
proton-conducting compound capable of initiating an electrochemical
redox reaction in a solution containing a proton source.
8. An electrochemical cell comprising at least one selected from
the copolymer compounds as claimed in claim 1 as an electrode
active material.
9. An electrochemical cell comprising at least copolymer compounds
as claimed in claim 1 as an electrode active material accounting
for 10 to 100-% by weight of the total amount of electrode active
materials in a relevant electrode.
10. An electrochemical cell comprising at least the copolymer
compounds as claimed in claim 1 as an electrode active material in
a cathode.
11. An electrochemical cell comprising, as an electrode active
material in a cathode, at least the copolymer compounds as claimed
in claim 1 accounting for 10 to 100-% by weight of the total amount
of electrode active materials in the cathode.
12. The electrochemical cell as claimed in claim 8 comprising an
electrolyte containing a proton source, wherein protons act as a
charge carrier in a redox reaction in association with
charge/discharge.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a conductive compound used as an
electrode active material in an electrochemical cell represented by
a secondary battery or an electric double-layer capacitor, as well
as an electrochemical cell with the conductive compound.
Particularly, it relates to a polymer compound whereby an
appearance capacity can be improved without deterioration in cycle
properties, as well as an electrochemical cell therewith.
[0003] 2. Description of the Related Art
[0004] There have been suggested and practically used
electrochemical cells such as secondary batteries and electric
double-layer capacitors in which a proton-conducting compound is
used as an electrode active material. FIG. 4 shows a schematic
cross-sectional view of an example of a primitive cell 1
constituting an electrochemical cell according to the prior
art.
[0005] As shown in FIG. 4, a conventional electrochemical cell has
a configuration where a cathode 2 comprising a proton-conducting
compound as an electrode active material and an anode 3 comprising
a proton-conducting compound as an electrode active material are
formed on a cathodic collector 4 and an anodic collector 5,
respectively and these electrodes are laminated via a separator 6
and which is filled with an aqueous or non-aqueous solution
containing a proton source and is sealed by a gasket 7. Operation
of the electrochemical cell involves only protons as a charge
carrier.
[0006] A cathode 2 and an anode 3 are formed using an electrode
material comprising a doped or undoped proton-conducting compound
powder, a conductive auxiliary and when necessary a binder. An
electrode may be formed by an appropriate method such as pressure
forming of an electrode material and depositing an electrode
material slurry on a conductive substrate. The cathode 2 and the
anode 3 thus formed can be mutually faced via a separator 6 to give
a primitive cell 1.
[0007] Examples of a proton-conducting compound used as an
electrode active material include .pi.-conjugated polymers such as
polyaniline, polythiophene, polypyrrole, polyacetylene,
poly-p-phenylene, polyphenylene-vinylene, polyperinaphthalene,
polyfuran, polyflurane, polythienylene, polypyridinediyl,
polyisothianaphthene, polyquinoxaline, polypyridine,
polypyrimidine, polyindole, polyaminoanthraquinone, polyimidazole
and their derivatives; indole .pi.-conjugated compounds such as an
indole trimer; quinones such as benzoquinone, naphthoquinone and
anthraquinone; quinone polymers such as polyanthraquinone,
polynaphthoquinone and polybenzoquinone where a quinone oxygen can
be converted into a hydroxyl group by conjugation; and a copolymer
from two or more monomer units constituting the above polymers.
These compounds may be doped to form a redox pair for exhibiting
conductivity. These compounds are appropriately selected as a
cathode and an anode active materials, taking a redox potential
difference into account.
[0008] Known electrolytic solutions include an aqueous electrolytic
solution consisting of an aqueous acid solution and a non-aqueous
electrolytic solution comprising an electrolyte in an organic
solvent. When using a proton-conducting compound, the former
aqueous electrolytic solution is mostly used because it can give a
high-capacity cell. The acid used may be an organic or inorganic
acid; for example, inorganic acids such as sulfuric acid, nitric
acid, hydrochloric acid, phosphoric acid, tetrafluoroboric acid,
hexafluorophosphoric acid and hexafluorosilicic acid and organic
acids such as saturated monocarboxylic acids, aliphatic carboxylic
acids, oxycarboxylic acids, p-toluenesulfonic acid,
polyvinylsulfonic acid and lauric acid.
[0009] Japanese Patent Application publication Nos. 2002-93419A,
2003-142099A and 2003-249221A have disclosed a trimerized indole or
indole derivative (indole trimer) as a compound used as the above
electrode active material. These patent references have a secondary
battery and a capacitor comprising as an electrode active material
an indole trimer having a fused cyclic structure at 2- and
3-positions of a substituted indoles.
[0010] Formula (4) shows a reaction mechanism of charge/discharge
for a substituted indole trimer in a electrolytic solution
containing a proton source. In formula (4), R represents a given
substituent; X.sup.- represents a given anion; and a moiety
encircled with a dashed line represents a redox inert site. 1
[0011] As seen from the formula, this compound has three redox
active sites, but only two of these are utilized in a redox
reaction in a practical electrochemical cell. Therefore, a capacity
obtained is only two thirds of a theoretical capacity estimated
from a monomer. Thus, a capacity density per a unit weight of the
substituted indole trimer is reduced, resulting in a reduced
appearance capacity of an electrochemical cell comprising the
trimer as an electrode active material.
[0012] Furthermore, in a substituted indole trimer, repeated doping
and dedoping in association with charge/discharge causes a crystal
structure to be altered, leading to increase in an internal
resistance of the electrode and thus deterioration in cycle
properties.
SUMMARY OF THE INVENTION
[0013] An objective of the present invention is to increase a
capacity per a unit weight of an electrode active material in an
electrochemical cell comprising a compound derived from an indole
derivative as the electrode active material, for improving cycle
properties.
[0014] In order to achieve the above objective, the present
invention is characterized in that a compound prepared by reacting
two or more of indole derivatives having different substituents or
substitution positions is used as an electrode active material.
[0015] According to an aspect of this invention, there is provided
a copolymer compound prepared by copolymerizing two or more
monomers selected from indole and indole derivatives represented by
formula (1): 2
[0016] wherein Rs independently represent hydrogen atom, nitro
group, carboxyl group, carboxylate group, cyano group, acetyl
group, aldehyde group and halogen atom.
[0017] According to another aspect of this invention, there is
provided the copolymer compound as described above, comprising a
unit represented by formula (1A) and a unit represented by formula
(1B) or (1C): 3
[0018] wherein Rs independently represent hydrogen atom, nitro
group, carboxyl group, carboxylate group, cyano group, acetyl
group, aldehyde group and halogen atom.
[0019] According to another aspect of this invention, there is
provided the copolymer compound as described above, represented by
formula (2): 4
[0020] wherein Rs independently represent hydrogen atom, nitro
group, carboxyl group, carboxylate group, cyano group, acetyl
group, aldehyde group and halogen atom; and n represents a natural
number.
[0021] According to another aspect of this invention, there is
provided the copolymer compound as described above, wherein the
monomer comprises an indole derivative having a substituent other
than hydrogen at least at 3-position.
[0022] According to another aspect of this invention, there is
provided the copolymer compound as described above, represented by
formula (3): 5
[0023] wherein Rs independently represent hydrogen atom, nitro
group, carboxyl group, carboxylate group, cyano group, acetyl
group, aldehyde group and halogen atom; and n represents a natural
number.
[0024] According to another aspect of this invention, there is
provided the copolymer compound as described above, wherein the
monomer comprises an indole derivative having a substituent other
than hydrogen at least at 2-position.
[0025] According to another aspect of this invention, there is
provided the copolymer compound as described above, which is a
proton-conducting compound initiating an electrochemical redox
reaction in a solution containing a proton source.
[0026] According to another aspect of this invention, there is
provided an electrochemical cell comprising at least one selected
from the copolymer compounds described above as an electrode active
material.
[0027] According to another aspect of this invention, there is
provided an electrochemical cell comprising at least one selected
from the copolymer compounds described above amounting to 10 to
100% by weight to the total amount of electrode active materials in
a relevant electrode.
[0028] According to another aspect of this invention, there is
provided an electrochemical cell comprising at least one selected
from the copolymer compounds described above as an electrode active
material in a cathode.
[0029] According to another aspect of this invention, there is
provided an electrochemical cell comprising, as an electrode active
material in a cathode, at least one selected from the copolymer
compounds described above amounting to 10 to 100% by weight to the
total amount of electrode active materials in the cathode.
[0030] According to another aspect of this invention, there is
provided the electrochemical cell described above comprising an
electrolyte containing a proton source, wherein protons act as a
charge carrier in a redox reaction in association with
charge/discharge.
[0031] The copolymer compound of the present invention is an
oligomer or polymer compound which has a different chemical
structure from a conventional substituted indole trimer having a
fused cyclic structure at 2- or 3-position, and a main chain
composed of a substituted indole.
[0032] A first effect of such a structure is that when used as an
electrode active material in an electrochemical cell, it allows a
redox active site to be effectively utilized. A second effect is
that a morphology of the electrode active material surface is
altered to promote doping or dedoping of ions in an electrolytic
solution, resulting in improvement in a charge/discharge
efficiency. A third effect is that an electrode active material can
be made amorphous to prevent reduction in electron conductivity due
to destruction of a crystal structure caused by doping or dedoping
in association with charge/discharge.
[0033] Thus, in an electrochemical cell in which an electrode
material comprises the above copolymer compound as an electrode
active material, a capacity per a unit weight of the electrode
active material is increased, resulting in increase in an
appearance capacity. Furthermore, increase in an internal
resistance can be prevented, resulting in improved cycle
properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIGS. 1a and 1b show SEM images of copolymer compounds in
Example and Comparative Example, respectively.
[0035] FIG. 2 is a graph showing the evaluation results for TG for
a copolymer compound.
[0036] FIG. 3 is a graph showing the measurement results of a
polymerization potential.
[0037] FIG. 4 shows a schematic cross-sectional view of an example
of a primitive cell in an electrochemical cell according to the
prior art.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0038] A copolymer compound of the present invention is suitable as
an electrode material in an electrochemical cell comprising a
proton-conducting compound as an electrode active material. As an
electrode active material, preferably as a cathode active material,
a copolymer compound prepared from two or more of compounds
selected from the indole and its derivatives represented by formula
(1) can be used to provide an electrochemical cell improved in an
appearance capacity and cycle properties.
[0039] Such a copolymer compound may be preferably a copolymer
compound having a unit represented by formula (1A) and a unit
represented by formula (1B) or (1C), including a copolymer compound
represented by formula (2) or (3). In these formulas, an alkyl
moiety in a carboxylate group may be alkyl having 1 to 8 carbon
atoms and halogen may be selected from fluorine, chlorine, bromine
and iodine.
[0040] A copolymer composition ratio of the copolymer compound,
when defined as a molar ratio of the unit of formula (1A) to the
unit of formula (1B) and/or (1C) (i.e., ((1A):(1B) and/or (1C)), is
preferably 2:1 to 1:5, more preferably 1:0.9 to 1:5, further
preferably 1:1 to 1:5 in the light of improvement in an appearance
capacity and copolymerization properties. Particularly, a 1:1
alternating copolymer is suitably used as an electrode active
material.
[0041] The copolymer compound with a weight average molecular
weight of 2,000 to 20,000, preferably 2,000 to 10,000, more
preferably 3,000 to 6,000 may be suitably used as an electrode
active material. The average molecular weight can be determined by
gel permeation chromatography (GPC) using polystyrene as a standard
sample.
[0042] Starting materials for preparing a copolymer compound of the
present invention may be appropriately selected from indole and
indole derivatives. Specific examples include indole,
mono-substituted, di-substituted and tri-substituted monomers such
as 2-nitroindole, 3-nitroindole, 4-nitroindole, 5-nitroindole,
6-nitroindole, 7-nitroindole, indole-2-carboxylic acid,
indole-3-carboxylic acid, indole-4-carboxylic acid,
indole-5-carboxylic acid, indole-6-carboxylic acid,
indole-7-carboxylic acid, methyl indole-2-carboxylate, methyl
indole-3-carboxylate, methyl indole-4-carboxylate, methyl
indole-5-carboxylate, methyl indole-6-carboxylate, methyl
indole-7-carboxylate, ethyl indole-2-carboxylate, ethyl
indole-3-carboxylate, ethyl indole-4-carboxylate, ethyl
indole-5-carboxylate, ethyl indole-6-carboxylate, ethyl
indole-7-carboxylate, 2-cyanoindole, 3-cyanoindole, 4-cyanoindole,
5-cyanoindole, 6-cyanoindole, 7-cyanoindole, 2-acetylindole,
3-acetylindole, 4-acetylindole, 5-acetylindole, 6-acetylindole,
7-acetylindole, indole-2-aldehyde, indole-3-aldehyde,
indole-4-aldehyde, indole-5-aldehyde, indole-6-aldehyde,
indole-7-aldehyde, 2-bromoindole, 3-bromoindole, 4-bromoindole,
5-bromoindole, 6-bromoindole, 7-bromoindole,
indole-2,6-dicarboxylic acid, indole-3,6-dicarboxylic acid,
indole-4,5-dicarboxylic acid, indole-4,6-dicarboxylic acid,
indole-5,6-dicarboxylic acid, methyl indole-2,6-dicarboxylate,
methyl indole-3,6-dicarboxylate, methyl indole-4,5-dicarboxylate,
methyl indole-4,6-dicarboxylate, methyl indole-5,6-dicarboxylate,
ethyl indole-2,6-dicarboxylate, ethyl indole-3,6-dicarboxylate,
ethyl indole-4,5-dicarboxylate, ethyl indole-4,6-dicarboxylate,
ethyl indole-5,6-dicarboxylate, 2,6-diacetylindole,
3,6-diacetylindole, 4,5-diacetylindole, 4,6-diacetylindole,
5,6-diacetylindole, methyl 2-acetylindole-6-carboxylate, methyl
3-acetylindole-6-carboxylate, methyl
2-acetylindole-5,6-dicarboxylate, and methyl
3-acetylindole-5,6-dicarboxy- late. Two or more appropriately
selected from these monomers may be subjected to polymerization to
give a copolymer compound.
[0043] There will be described a process for preparing a copolymer
compound of the present invention and a manufacturing process for
an electrochemical cell. First, an electrolytic polymerization
method will be described.
[0044] A copolymer compound can be prepared by dissolving an
electrolyte such as lithium tetrafluoroborate to a concentration of
about 0.3 mol/L in a solvent such as acetonitrile, adding two or
more of indoles having a given substituent as monomers to the
solution and applying a voltage under a potential sweep range of
500 to 1600 mV and a potential sweep rate of 50 mV/s using a
potentiostat. A product deposited on a working electrode is washed
with an appropriate solvent to give a powdery or film solid.
[0045] Other compounds may be used as the electrolyte without being
limited to lithium tetrafluoroborate described above. Examples
include perchloric acid, lithium perchlorate, sodium perchlorate,
tetrabutylammonium perchlorate, tetraethylammonium perchlorate,
tetraethylammonium tetrafluoroborate and tetrabutylammonium
tetrafluoroborate. A reaction period of the electrolytic
polymerization is preferably, but not limited to, 0.1 to 10 hours
in the light of preventing side reactions.
[0046] A copolymer compound may be prepared by any proper method
such as a chemical oxidative polymerization without being limited
to the electrolytic polymerization described above. The copolymer
can be prepared by dissolving two or more indoles having a given
substituent as monomers in a polymerization solvent such as
acetonitrile, adding an oxidizing agent such as ferric chloride to
the solution, and stirring the mixture. A deposited product can be
filtrated and washed with an appropriate solvent to give the
copolymer compound.
[0047] Herein, other solvents and oxidizing agents may be used as a
polymerization solvent and an oxidizing agent, without being
limited to acetonitrile and ferric chloride described above.
Examples of a polymerization solvent include aromatic hydrocarbons
such as toluene, xylenes and chlorobenzene; halogenated aliphatic
hydrocarbons such as dichloromethane and chloroform; acetates such
as methyl acetate, ethyl acetate and butyl acetate; aprotic polar
solvents such as dimethylformamide, dimethylacetamide,
N-methylpyrrolidone, tetramethylurea, hexamethylphosphoric triamide
(HMPA); ethers such as diethyl ether, tetrahydrofuran and dioxane;
aliphatic hydrocarbons such as pentane and n-hexane; aliphatic
alcohols such as methanol, ethanol, n-propanol, isopropanol,
n-butanol, s-butanol and t- butanol; acetone; acetonitrile; and
propionitrile, preferably acetone, acetonitrile, dioxane and
dimethylformamide. They may be used alone or in combination of two
or more in an appropriate mixing rate.
[0048] Examples of an oxidizing agent include ferric chloride
hexahydrate, anhydrous ferric chloride, ferric nitrate nonahydrate,
ferric nitrate, ferric sulfate n-hydrate, ferric ammonium sulfate
dodecahydrate, ferric perchlorate n-hydrate, ferric
tetrafluoroborate, cupric chloride, cupric sulfate, cupric
tetrafluoroborate, tetrafluoroborate nitrosonium, ammonium
persulfate, sodium persulfate, potassium persulfate, sodium
periodate, potassium periodate, hydrogen peroxide, ozone, potassium
hexacyanoferrate, tetraammonium cerium (IV) sulfate dihydrate,
bromine and iodine, preferably ferric chloride hexahydrate,
anhydrous ferric chloride, ferric nitrate nonahydrate, ferric
nitrate, ferric sulfate n-hydrate, ferric ammonium sulfate
dodecahydrate, ferric perchlorate n-hydrate and ferric
tetrafluoroborate. These oxidizing agents may be used alone or in
combination of two or more in an appropriate mixing rate.
[0049] In the chemical oxidative polymerization, a reaction
temperature may be within a range of 0.degree. C. to a refluxing
temperature of a solvent used, preferably 10 to 100.degree. C. A
reaction period of the chemical oxidative polymerization is
preferably, but not limited to, 0.1 to 100 hours in the light of
preventing side reactions.
[0050] In the electrolytic polymerization, a polymerization
potential is measured with a potential sweep range of 500 mV to
1600 mV and a potential sweep rate of 50 mV/s and can be used as a
measure for determining possibility of copolymerization.
Furthermore, a copolymer compound thus prepared is subjected to
scanning electron microscopy (hereinafter, referred to as "SEM")
and thermogravimetry (hereinafter, referred to as "TG") and the
results are used as means for determining formation of a copolymer
compound, which is different from compounds in the prior art.
[0051] Next, there will be described a preparation method for a
test sample and test conditions for cyclic voltammetry
(hereinafter, referred to as "CV measurement"). To a copolymer
compound formed as a conductive auxiliary is added VGCF.RTM. from
Showa Denko K.K. (hereinafter, referred to as "VGCF"), a fibrous
carbon by a vapor growth method to an amount of 30% by weight to
the copolymer compound. The mixture is mixed and applied to a
carbon fiber sheet (Toray Industries, Inc., TGP-H-030). The sheet
is dried at 120.degree. C. to prepare a measurement sample.
[0052] CV measurement is conducted using a 20 wt % sulfuric acid as
an electrolytic solution under a potential sweep range of 200 to
1200 mV and a potential sweep rate of 20 mV/s. An integrated CV
capacity in the potential sweep range of 200 to 1200 mV is
calculated and normalized per a unit weight of the copolymer
compound.
[0053] Next, there will be described a configuration of an
electrochemical cell and a manufacturing process therefor.
[0054] The present invention is characterized by a copolymer
compound used as an electrode active material, and a structure of a
primitive cell may be as in the prior art shown in FIG. 4. It will
be, therefore, described with reference to FIG. 4.
[0055] An electrochemical cell of the present invention is a
proton-conducting electrochemical cell where protons act as a
charge carrier in a redox reaction in association with
charge/discharge. More specifically, it comprises an electrolyte
containing a proton source and preferably operates such that
adsorption/desorption of protons of an electrode active material is
exclusively involved in electron transfer in a redox reaction in
association with charge/discharge.
[0056] Such an electrochemical cell may comprise respective
proton-conducting compounds as cathode and anode active materials,
and comprise an electrolytic solution containing a proton source as
an electrolyte.
[0057] A proton-conducting compound used as an electrode active
material may be, in addition to a copolymer compound of this
present invention, any of those known compounds without limitation
as long as it can initiate a redox reaction in absolution
containing a proton source.
[0058] Examples of a proton-conducting compound used as an
electrode active material include .pi.-conjugated polymers such as
polyaniline, polythiophene, polypyrrole, polyacetylene,
poly-p-phenylene, polyphenylene-vinylene, polyperinaphthalene,
polyfuran, polyflurane, polythienylene, polypyridinediyl,
polyisothianaphthene, polyquinoxaline, polypyridine,
polypyrimidine, polyindole, polyaminoanthraquinone, polyimidazole
and their derivatives; indole .pi.-conjugated compounds such as an
indole trimer compound; quinones such as benzoquinone,
naphthoquinone and anthraquinone; quinone polymers such as
polyanthraquinone, polynaphthoquinone and polybenzoquinone where a
quinone oxygen can be converted into a hydroxyl group by
conjugation; and copolymers prepared from two or more of the
monomers giving the above polymers. These compounds may be doped to
form a redox pair for exhibiting conductivity. These compounds may
be appropriately selected as a cathode and an anode active
materials, taking a redox potential difference into account.
[0059] An electrode in an electrochemical cell of the present
invention is characterized in that it comprises a proton-conducting
compound as an electrode active material, a conductive auxiliary
and when necessary a binder, and comprises a copolymer compound
prepared from two or more indole derivative monomers as an
electrode active material, preferably a cathode active
material.
[0060] A proportion of a copolymer compound of the present
invention in the total amount of active materials in the electrode
is preferably 10 to 100 wt %, more preferably 20 to 100 wt %,
further preferably 30 to 100 wt % in the light of achieving desired
effects.
[0061] A cathode 2 may comprise, for example, a copolymer compound
of the present invention as an electrode active material preferably
in an amount of 10 to 100 wt %. A conductive auxiliary such as VGCF
may be added in an amount of 1 to 50 wt %, preferably 10 to 30 wt %
to the amount of a cathode active material. A binder such as
polyvinylidene fluoride (hereinafter, referred to as "PVDF") may be
added to and mixed with a cathode active material in an amount of 1
to 20 wt %, preferably 5 to 10 wt % to the amount of the active
material. The resulting mixed powder is pressed at 0 to 300.degree.
C., preferably 100 to 250.degree. C., to give the cathode 2.
[0062] An anode 3 can be formed by pressing and firing a powdery
mixture of an electrode active material such as
polyphenylquinoxaline, a conductive auxiliary such as Ketjen
Black.TM. (Product name: Ketjen Black EC-600JD, from Ketjen Black
International) in a weight ratio of 72:28.
[0063] An electrolytic solution may be a proton-containing aqueous
or non-aqueous solution. An aqueous electrolytic solution is
preferable because it can provide a high-capacity cell. An acid
used may be an organic or inorganic acid, including inorganic acids
such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric
acid, tetrafluoroboric acid, hexafluorophosphoric acid and
hexafluorosilicic acid and organic acids such as saturated
monocarboxylic acids, aliphatic carboxylic acids, oxycarboxylic
acids, p-toluenesulfonic acid, polyvinylsulfonic acid and lauric
acid.
[0064] A content of protons in an electrolytic solution is
preferably 10.sup.-3 mol/L to 18 mol/L, more preferably 10.sup.-1
mol/L to 7 mol/L. A too low concentration may result in
insufficient performance as an electrolytic solution while a too
high concentration may give a strongly acidic solution, leading to
deterioration in material activity and dissolution of the
materials.
[0065] A separator 6 may be a polyolefin porous film or
cation-exchange film with a thickness of 10 to 50 .mu.m. A cathodic
current collector 4 or an anodic current collector 5 may be a
rubber sheet which is made conductive by dispersed conductive
carbon powder. A gasket 7 may be, for example, an butyl-rubber.
[0066] The members described above may be combined to provide a
primitive cell 1. Specifically, as shown in FIG. 1, on a cathodic
current collector 4 and an anodic current collector 5 are disposed
a cathode 2 and an anode 3, respectively, which are then laminated
via a separator 6. The cell is filled with an electrolytic solution
and sealed by a gasket 7. The cell here has a coin type of external
shape, but may have any commonly used shape such as a laminate type
and a roll type without limitation.
EXAMPLES
[0067] This invention will be more specifically with reference to
Examples.
Example 1
[0068] Methyl indole-6-carboxylate and 3-acetylindole were selected
as substituted indole monomers. In acetonitrile as a polymerization
solvent were dissolved these monomers to 20.times.10.sup.-3 mol/L
and lithium tetrafluoroborate as an electrolyte to 0.3 mol/L. The
mixture was subjected to electrolytic polymerization using a
potentiostat. Precipitation of a product on a working electrode was
observed. The product was rinsed with ethanol and dried to give a
dark green copolymer compound powder.
[0069] The copolymer compound thus obtained was analyzed. First,
its SEM photo image was taken. Here, an SEM photo image of a trimer
having a fused cyclic structure prepared by connecting 2- and
3-positions of methyl indole-6-carboxylates was taken as
Comparative Example. FIGS. 1A and 1B show SEM photo images in
Example and Comparative Example, respectively. In the SEM image of
Example, a fibrous morphology was observed and the polymerization
product had a morphology different from that of Comparative
Example.
[0070] Then, the copolymer compound prepared was evaluated by TG.
The trimer of methyl indole-6-carboxylate was also evaluated. FIG.
2 shows the TG evaluation results for the copolymer compound. The
results demonstrate that the copolymer compound of Example did not
have a clear decomposition point, indicating improvement in heat
resistance. On the other hand, the trimer of methyl
indole-6-carboxylate of Comparative Example experienced rapid
weight reduction around at 300.degree. C., indicating that it is
less heat-resistant.
[0071] Next, the copolymer compound prepared above was used as a
cathode active material to prepare an electrochemical cell. Here, a
copolymer compound, VGCF and PVDF were weighed and blended in a
weight ratio of 69/23/8. The mixture was pressed at 200.degree. C.
to form a cathode. An anode was formed by weighing and blended
polyphenylquinoxaline and Ketjen Black as an electrode active
material in a weight ratio of 72/28, pressing the mixture at
300.degree. C. and firing the product.
[0072] An electrolytic solution was a 20 wt % aqueous sulfuric acid
solution, a separator was a cation-exchange membrane with a
thickness of 15 .mu.m, a gasket was a butyl-rubber, and a current
collector was a conductive rubber sheet.
[0073] These members were used to manufacture an electrochemical
cell consisting of the primitive cells shown in FIG. 1.
Example 2
[0074] A-copolymer compound was prepared and an electrochemical
cell was formed as described in Example 1, except that methyl
indole-6-carboxylate and indole-2-aldehyde were used as substituted
indole monomers.
Example 3
[0075] A copolymer compound was prepared and an electrochemical
cell was formed as described in Example 1, except that
5-cyanoindole and indole-5-carboxylic acid were used as substituted
indole monomers and 5-cyanoindole and indole-5-carboxylic acid were
dissolved in acetonitrile to 50.times.10.sup.-3 mol/L and
25.times.10.sup.-3 mol/L, respectively, to prepare a polymerization
solution.
Example 4
[0076] A copolymer compound was prepared and an electrochemical
cell was formed as described in Example 1, except that methyl
indole-6-carboxylate, 3-acetylindole and indole-3-aldehyde as
substituted indole monomers were dissolved in acetonitrile to
40.times.10.sup.-3 mol/L, 20.times.10.sup.-3 mol/L and
20.times.10.sup.-3 mol/L, respectively, to prepare a polymerization
solution.
Example 5
[0077] Methyl indole-6-carboxylate and 3-acetylindole were selected
as substituted indole monomers. They were dissolved in acetonitrile
as a polymerization solvent and were subjected to chemical
oxidative polymerization. Using ammonium persulfate as an oxidizing
agent, the mixture was reacted by stirring at 60.degree. C. for 3
hours. The precipitate was rinsed with ethanol and dried to give a
dark green copolymer compound powder. An electrochemical cell was
formed as described in Example 1, except that the copolymer
compound was used as a cathode active material.
Example 6
[0078] A copolymer compound was prepared and an electrochemical
cell was formed as described in Example 1, except that methyl
indole-6-carboxylate and methyl 3-acetylindole-6-carboxylate were
used as substituted indole monomers.
Example 7
[0079] A copolymer compound was prepared and an electrochemical
cell was formed as described in Example 1, except that methyl
indole-5,6-dicarboxylate and methyl 3-acetylindole-6-carboxylate
were used as substituted indole monomers.
Example 8
[0080] An electrochemical cell was formed as described in Example
1, except that a cathode active material was a mixed powder of the
copolymer compound described in Example 1 and a trimer having a
fused cyclic structure prepared by connecting methyl
indole-6-carboxylates at 2- and 3-positions in a weight ratio of
50/50 and a cathode was an electrode by weighing and blending the
electrode active material, VGCF and PVDF in a weight ratio of
69/23/8 and pressed the mixture at 200.degree. C.
Example 9
[0081] An electrochemical cell was formed as described in Example
1, except that a cathode active material was a mixed powder of the
copolymer compound described in Example 1 and a trimer having a
fused cyclic structure prepared by connecting methyl
indole-6-carboxylates at 2- and 3-positions in a weight ratio of
20/80 and a cathode was an electrode by weighing and blending the
electrode active material, VGCF and PVDF in a weight ratio of
69/23/8 and pressed the mixture at 200.degree. C.
Comparative Example
[0082] A trimer having a fused cyclic structure prepared by
connecting 2- and 3-positions of 6-methylindoles (6-methylindole
trimer) was prepared and used as a cathode active material to form
an electrochemical cell. The electrochemical cell was formed as
described in Example 1, except that the 6-methylindole trimer, VGCF
and PVDF were weighed and blended in a weight ratio of 69/23/8 and
the mixture was pressed at 200.degree. C. to give a cathode.
[0083] In electrolytic polymerization in the above Examples and
Comparative Example, a polymerization potential was determined
under the conditions described above. All the copolymer compounds
in Examples and Comparative Example were subjected to CV
determination under the conditions described above. For the
electrochemical cells, an initial capacity and a capacity residual
ratio after 5,000 charge/discharge cycles were determined.
[0084] FIG. 3 shows the measurement results of a polymerization
potential. Table 1 shows initial capacities and capacity residual
ratios after 1,000 cycles. Table 2 shows initial capacities and
capacity residual ratios after 5,000 cycles for the electrochemical
cells.
1 TABLE 1 Capacity residual ratio after Capacity [C/g] 1,000 cycles
[%] Increasing Increasing rate Measured rate to Comp. Measured to
Comp. Ex. value Ex. [%] value [%] Ex. 1 297 27 94 9 2 284 21 93 8 3
260 11 92 7 4 281 20 91 6 5 295 26 97 9 6 260 11 92 7 7 248 6 91 6
8 265 13 92 11 9 251 7 91 7 Comp. 234 -- 85 -- Ex.
[0085]
2 TABLE 2 Capacity residual ratio after Initial capacity [mAh/g]
5,000 cycles [%] Increasing Increasing rate Measured rate to Comp.
Measured to Comp. Ex. value Ex. [%] value [%] Ex. 1 55 51 94 50 2
56 43 88 44 3 50 28 82 38 4 55 41 69 25 5 57 46 90 46 6 47 20 79 35
7 43 10 62 18 8 52 33 85 41 9 45 15 74 30 Comp. 39 -- 44 -- Ex.
[0086] The results in Table 1 demonstrate that the copolymer
compounds of Examples had a higher capacity per a unit weight of an
electrode active material by at least 6% and a higher capacity
residual ratio after 1,000 cycles, i. e., a cycle property, by at
least 6% than that in Comparative Example, indicating effectiveness
of the present invention. The results in Table 2 demonstrate that
the electrochemical cells in Examples have a higher capacity by at
least 10% and an improved cycle property by at least 18% than that
in Comparative Example.
[0087] As described above, an electrode comprising a copolymer
compound of the present invention as an electrode active material
can be used to provide an electrochemical cell with an increased
appearance capacity and improved cycle properties. It is because
using a copolymer compound of monomers selected from indole and
indole derivatives as electrode materials allows a redox active
site to be effectively used; an altered surface morphology results
in smooth doping and dedoping to improve a charge/discharge
efficiency; and an amorphous electrode active material with an
increased molecular weight can prevent materials from being
deteriorated due to repeated doping/dedoping in association with
charge/discharge.
* * * * *