JPH05135767A - Reversible electrode - Google Patents

Abstract

PURPOSE:To improve the oxidation/reduction reaction speed of an organic compound used for an electrochemical element such as a battery, an electro- chromic display element, a sensor, and a memory. CONSTITUTION:A compound introduced with a disulfide compound into a conducting polymer is used as an electrode. When the disulfide compound is used as the electrode of a battery, a secondary battery having a large energy density of 150wh/kg or above can be constituted. The oxidation/reduction reaction of the disulfide compound is slow, a large current is difficult to be extracted by the disulfide compound alone, when it is combined with the conducting polymer, the oxidation/reduction reaction of the disulfide compound is accelerated by the electrode catalyst action of the conducting polymer, the practical contact area with an electrolyte is also remarkably increased, thus an electrolysis (charge/discharge) with a large current can be performed at the room temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible electrode made of an organic compound used in electrochemical devices such as batteries, electrochromic display devices, sensors and memories.

[0002]

2. Description of the Prior Art Since the discovery of conductive polyacetylene by Shirakawa et al. In 1971, the use of conductive polymers as electrode materials has led to the production of lightweight, high energy density batteries, large-area electrochromic devices, and microelectrodes. Conducting polymer electrodes are being actively studied because they can be expected to realize electrochemical devices such as biochemical sensors. However, polyacetylene has a problem in that it is chemically unstable with respect to moisture and oxygen in the air and is not practical as an electrode used in an electrochemical device. In order to overcome this problem, other π-electron conjugated conductive polymers have been investigated, and relatively stable polymers such as polyaniline, polypyrrole, polyacene, and polythiophene have been found, and lithium secondary batteries using these as the positive electrode. Is being developed.

Since these polymer electrodes take in not only cations but also anions in the electrolyte during the electrode reaction, the electrolyte not only acts as a transfer medium for the ions but also participates in the battery reaction, and therefore, an amount commensurate with the battery capacity. It is necessary to supply this electrolyte into the battery. Then, the energy density of the battery is about 20 to 50 Wh / kg, which is a problem that it is smaller than that of a normal secondary battery such as a nickel-cadmium storage battery or a lead storage battery by about one half.

On the other hand, as an organic material which can be expected to have a high energy density, a disulfide compound has been proposed in European Patent 415856, which has a general formula XSRS-.
A compound represented by (SRS) nSRS-X ′ can be used. However, n: 0 or an integer of 1 or more, X, X ': metal M
A metal containing hydrogen, a terminal organic group, S: sulfur, R: a sulfur atom of dithiol, which contains a carbon atom that bonds one or more S 2
Represents a functional cyclic organic group. The S—S bond is cleaved by electrolytic reduction to form a salt represented by R—S− · M + with the cation (M +) in the electrolytic bath, and this salt is again converted to the original R by electrolytic oxidation. It has the property of returning to -S-S-R. In addition, a metal-sulfur secondary battery in which a metal M that supplies and captures a cation (M +) and a disulfide compound is combined is proposed in the above-mentioned European patent, and is 1000 Wh / Kg or more, which is comparable to or more than a normal primary battery. The above energy density can be expected.

[0005]

[Problems to be Solved by the Invention] However, the proposed disulfide compound is disclosed in European Patent No. 41.
As reported in the examples of 5856, for example
When the battery assembled using [(C ₂ H ₅ ) ₂ NCSS-] 2 was charged and discharged, the discharge current was as small as 13 μA / cm ² and the charging current was 6.5 μA / cm ² . According to the teaching of electrode reaction theory, the electrochemical reaction in such a material has an extremely slow electron transfer process, and therefore a large current suitable for practical use near room temperature,
For example, it is difficult to extract a current of 1 mA / cm ² or more, and there is a problem that it is limited to use at a high temperature of 100 to 200 ° C.

[0006]

According to the present invention, a sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including a proton) bond, and electrolytic oxidation causes the sulfur-metal ion bond to become The present invention relates to a reversible electrode containing a conductive polymer having a sulfur-sulfur bond regenerated group introduced therein as a main component. According to the present invention, it is possible to extract a large current that is practically suitable near room temperature, for example, a current of 1 mA / cm ² or more. The group introduced into the conductive polymer is in the electrolytic oxidation state, XSRS- (SRS) nSRS-
A polymer of at least one sulfur organic compound characterized by a chain of the form X ', where n: 0 or an integer greater than or equal to 1, X, X': metal M or hydrogen, a terminal organic group, S: sulfur, R: a cyclic organic group containing a carbon atom having at least one sulfur atom S of dithiol bonded thereto, wherein the carbon atom has a short chain in which the SS bond is destroyed and the SR-SM group terminates at both ends. When it is in the electrolytic reduction state, it chemically bonds with at least one nitrogen atom, delocalizes the negative charge by a conjugate bond of the type SC = N <-> S = CN-, and It is a carbon atom that enables reversible electrochemical reduction). The conductive polymer contains a nitrogen atom,
The nitrogen atom is composed of a monomer conjugated with a carbon atom.

[0007]

The present invention provides an electrode which does not impair the feature of having a high energy density when a disulfide compound is used as an electrode of a battery, is capable of charging and discharging a large current even at room temperature and is excellent in reversibility. ..

[0008]

The compounds of the present invention are described in European Patent No.
No. 415856 describes the general formula XSRS- (SRS) n
A compound represented by -SRS-X 'can be used. However, n: 0 or an integer of 1 or more, X, X ': metal M, hydrogen or terminal organic group, S: sulfur, R: sulfur atom of dithiol
Represents a bifunctional cyclic organic group containing a carbon atom that binds at least one S. For example, 2,5-dimercapto-1,3,4-thiadiazole represented by C ₂ N ₂ S (SH) 2 and S-triazine-2,4 represented by C ₃ H ₃ N ₃ S ₃ .
6-trithiol or the like is used, and these compounds are further introduced into a compound capable of producing a conductive polymer. Journa
l of the American Chemical Society, Vol97, NO11, p
3235-3238, (1975) described that the oxidation reaction of a disulfide compound is promoted by adding flavin, which is a nitrogen-containing conjugated organic compound, and the sulfur atom of the disulfide compound is a nitrogen atom of the nitrogen-containing conjugated organic compound. It is said that the reaction is promoted by binding to. However, in the above-mentioned document, only the reaction rate is discussed, and the oxidation promotion phenomenon of the nitrogen-containing conjugated organic compound with respect to the disulfide compound is not measured or interpreted from the electrochemical approach. Furthermore, it is completely stated that a disulfide compound and a nitrogen-containing conjugated organic compound that promotes its redox reaction can be used to produce an electrode having excellent reversibility capable of charging and discharging a large current even at room temperature in an organic solvent. Absent. The inventors have found that by using a disulfide compound and a nitrogen-containing conjugated organic compound that promotes its redox reaction, it is possible to create an electrode having excellent reversibility capable of charging and discharging a large current in an organic solvent even at room temperature. .. It was found that a conductive polymer such as polyaniline is the most suitable as a nitrogen-containing conjugated organic compound that also has a conductive action. As a representative example of the conductive polymer of the present invention, a polymer of a nitrogen-containing conjugated organic monomer such as aniline, o-diaminobenzene, or o-diaminonaphthalene, or a derivative thereof is used. Some conductive polymers such as polyphenylene diamine develop conductivity only in the presence of acid. In this case, the electrode catalyst action can be promoted by containing an acid such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, or paratoluenesulfonic acid in the electrode.

A conductive polymer that causes a highly reversible redox reaction at 0 to ± 1.0 volt with respect to a g / AgCl electrode is effectively used. Further, those having a porous fibril structure and capable of retaining the disulfide compound in the pores are preferable. As the metal ion when the disulfide compound is reduced to form a salt, an alkali metal ion, an alkaline earth metal ion, a divalent transition metal or a proton can be used as described in the above-mentioned European Patent. When lithium ions are used as the alkali metal ions, a lithium alloy such as metallic lithium or lithium-aluminum is used as an electrode for supplying and capturing the lithium ions, and a battery having a voltage of 3 to 4 volts is used when an electrolyte that conducts the lithium ions is used. Can be configured. Similarly, protons are used as the above-mentioned metal ions, and LaNi ₅ , MmNi _3.55 Mn are used as electrodes for supplying and trapping protons.
_When a metal hydride such as _0.4 Al _0.3 Co _0.75 (Mm: misch metal) is used and an electrolyte that conducts protons is used, the voltage is 1
It is also possible to construct a 2-volt battery.

Specific Example 9.7 g (0.1 mol) of 1,2 dichloroethane and o-in a benzene solvent
By reacting 11 g (0.1 mol) of aminophenol, 4.7 g (0.03 mol) of aniline derivative A having ethylene chloride on the 2-position side chain of aniline was obtained. The aniline derivative A thus obtained was dissolved in 1 mol / cm3 and 5 mol / cm3 of a sulfuric acid aqueous solution of pH = 1.0 and subjected to constant potential electrolysis with a saturated calomel reference electrode at 1.2 to 1.5 volt to obtain a thickness of about A polyaniline derivative film having a 20 μm fibril structure was formed on a graphite electrode. The graphite electrode having the polyaniline derivative film thus obtained was vacuum-dried at 80 ° C. for one day, and then 1 g (0.01 mol) of aniline derivative A thin film was added to thiourea.
0.8 g (0.01 mol) was reacted to introduce a mercapto group, and further, 5-dimercapto-1,3,4-thiadiazole (0.01 mol) was reacted to obtain a polyaniline electrode having a disulfide introduced as shown in the figure. .. This electrode was used at room temperature in dimethylformamide in which 1M LiClO4 was dissolved to -0.7 ~ + against Ag / AgCl reference electrode.
When the potential was linearly increased and decreased at a rate of 50 mV / sec between 0.2 volt and electrolysis was performed, the current-voltage characteristics shown by the curve (a) in FIG. 1 were obtained. In addition, as a comparative example, a graphite electrode was used and 0.05 mol / cm3 of 2,5-dimercapto 1,3,4-thiadiazole, LiClO 3 was used.
Ag / Ag in dimethylformamide dissolved in 0.5mol / cm3
When a constant potential electrolysis was performed at +0.8 volt with respect to the Cl reference electrode and an electrode having no polyaniline was electrolyzed in the same manner, the current-voltage characteristic shown by the curve (b) in FIG. 1 was obtained. Further, the same electrolysis was performed on the graphite electrode having only the aniline thin film to obtain the current-voltage characteristic shown by the curve (c) in FIG. The curve (a) shows the current-voltage characteristic in which the current-voltage curve (c) of the graphite electrode having only polyaniline and the current peak corresponding to the oxidation-reduction of 2,5-dimercaptop-1,3,4-thiadiazole overlap. I'm giving. Among the current peaks corresponding to the redox of 2,5-dimercapto-1,3,4-thiadiazole, the position of the current peak particularly corresponding to the reduction reaction moves from -0.6 volt to around -0.2 volt, and in the presence of polyaniline, 2 It can be seen that the redox of 1,5-dimercapto-1,3,4-thiadiazole is promoted. On the other hand, in the curve (b) obtained with the graphite electrode having no polyaniline thin film, a current peak corresponding to the redox of 2,5-dimercaptop-1,3,4-thiadiazole is obtained, but it is not the oxidation peak. The potential difference from the reduction peak was close to 0.6 volt, the oxidation-reduction was quasi-reversible and the reaction rate was slow.When this electrode was used for the positive electrode of the battery, the voltage difference between charging and discharging was increased to 0.6 volt or more, and A battery with a large decrease in efficiency is obtained by charging and discharging with electric current.

In this embodiment, as the conductive polymer,
The case of using aniline has been described, but the same effect can be obtained with other conductive polymers. In addition, the general formula XSRS- (SR
Although the case where thiadiazole is used as R in the compound represented by -S) nSRS-X 'has been described, the same effect can be obtained even when R is uracil, triazine or pyraridine.

[0012]

INDUSTRIAL APPLICABILITY As described above, the present invention enables electrolysis at a large current, which has been difficult with conventional disulfide compounds alone. Then, by using this electrode for the positive electrode and metallic lithium for the negative electrode, a high energy density secondary battery in which large-current charging / discharging can be expected can be constructed. Furthermore, the present invention can obtain a biochemical sensor such as an electrochromic device having a fast coloring / fading rate and a glucose sensor having a fast response speed in addition to the battery.
Further, an electrochemical analog memory having a high writing / reading speed can be constructed.

[Brief description of drawings]

FIG. 1 is a current-voltage characteristic diagram of a composite electrode of an example of the present invention and an electrode of a comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Takeyama Inventor Kenichi Takeyama 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-metal ion (including a proton) bond, and electrolytic oxidation regenerates the sulfur-metal ion bond into the sulfur-sulfur bond. A reversible electrode containing a conductive polymer into which a functional group is introduced as a main component. 2. A polymer of at least one sulfur organic compound characterized by a chain of the form XSRS- (SRS) nSRS-X 'in which the groups introduced into the conductive polymer are in the electrooxidation state, provided that n: 0. Or an integer of 1 or more, X, X ': metal M,
Hydrogen or a terminal organic group, S: sulfur, R: a cyclic organic group containing a carbon atom having at least one sulfur atom S of dithiol bonded thereto, wherein the carbon atom is -SR- When the SM group produces a short chain terminating at both ends, it chemically bonds to at least one nitrogen atom when it is in an electroreduction state, and it has a negative charge due to a conjugate bond of the type SC = N <-> S = CN-. Is a carbon atom that enables the reversible electrochemical reduction of the sulfur S atom) to produce a reversible electrode according to claim 1. 3. The reversible compound of claim 1, wherein the R group is a heterocyclic group and each sulfur atom attached to the heterocyclic group forms a conjugated bond with at least one nitrogen atom of the heterocyclic group. Sex electrode. 4. When it is partially or wholly electrolytically oxidized, it takes the form of a short chain terminated by SRSM groups at both ends.
The reversible electrode according to claim 1, wherein a group (as defined in 1) is introduced. 5. The reversible electrode according to claim 1, wherein the conductive polymer promotes a redox reaction with respect to the disulfite compound. 6. The reversible electrode according to claim 5, wherein the conductive polymer contains a nitrogen atom, and the nitrogen atom is composed of a monomer conjugated with a carbon atom.