JPH04272659A - Reversible electrode - Google Patents

Abstract

PURPOSE:To enable electrolysis at large current by composing a reversible electrode mainly of a conductive macromolecule obtained by polymerization of a compound into which groups expressed by specific formulas are introduced. CONSTITUTION:A reversible electrode is composed mainly of an ion-electron mixed conductor macromolecule obtained by polymerization of a compound into which groups expressed by the formulas I, II are introduced. Thus the conductive macromolecule acts as an electrode touching body which reduces activation energy of a reaction during electron transfer process, while having the action of increasing an effective reaction area of the electrode for an electrolyte; i.e., the potential difference between oxidation reaction and reduction reaction, which is more than IV when disulfide compound unit is used is reduced below 0.1V by the interaction of the disulfide group expressed by the formula II and the ion-electron mixed conductive macromolecule. Therefore, electrode reactions are accelerated and the effect of an increase in the substantial contact area of the electrode with the electrolyte is combined with that of the acceleration so as to enable electrolysis (charge and discharge) with large current at 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 mainly composed of a conductive polymer used in electrochemical devices such as batteries, electrochromic display devices, sensors, and memories.

0002

[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 creation of lightweight, high-energy-density batteries, large-area electrochromic devices, and microelectrodes. The practical application of conductive polymer electrodes is being actively studied, as it is expected that electrochemical devices such as biochemical sensors will be realized using them. However, polyacetylene has a problem in that it is highly reactive with moisture and oxygen in the air and is chemically unstable, making it impractical as an electrode for use in electrochemical devices. To overcome this problem, other π-electron conjugated conductive polymers were investigated, and relatively stable polymers such as polyaniline, polypyrrole, polyacene, and polythiophene were discovered, and lithium secondary batteries using these as positive electrodes were developed. It is being developed.

[0003] These polymer electrodes take in not only cations but also anions in the electrolyte during the electrode reaction, so the electrolyte not only acts as an ion transfer medium but also participates in the battery reaction. Therefore, it is necessary to maintain an amount of electrolyte within the battery that corresponds to the battery capacity. Then, the energy density of the battery decreases by the amount of retained electrolyte.
The problem is that the energy density is about 0 to 50 Wh/kg, which is about half that of ordinary secondary batteries such as nickel-cadmium storage batteries and lead-acid batteries.

On the other hand, disulfide compounds are disclosed in US Pat. No. 4,833,048 as organic materials that are expected to have high energy density. This compound is most simply represented as R-S-S-R (R is an aliphatic or aromatic organic group and S is sulfur). The S-S bond is cleaved by electrolytic reduction and forms a salt represented by R-S-M+ with the cation (M+) in the electrolytic bath, and this salt is
It has the property of returning to the original R-S-S-R by electrolytic oxidation. In addition, cations (M+) are supplied,
A metal-sulfur secondary battery that combines a trapping metal M and a disulfide compound is proposed in the above-mentioned US patent, and has an energy density of 150Wh/Kg or more, which is comparable to or higher than ordinary secondary batteries. You can expect high energy density.

[0005] Introducing an electrocatalyst into a disulfide compound electrode is described in the above-mentioned US Pat. No. 4,833,048.
No. or J. Electrochem Soc. ，
Vol. 136, p. 2570-2575 (1989
), but only organometallic compounds are disclosed as electrode catalysts. Not only is this effect not specifically demonstrated, but there is also no indication that the ion-electronic mixed conductor polymer acts as an electrocatalyst in the electrolysis of disulfide compounds.

[0006]

[Problems to be Solved by the Invention] However, such conventional disulfide compounds are
The inventors of No. 048 J. Electrochem. S
oc, Vol. 136, No. 9, p. 2570
~2575 (1989), for example, in the electrolysis of [(C2H5)2NCSS-]2, the oxidation and reduction potentials are separated by more than 1 volt, and according to electrode reaction theory, the electric potential in such materials is In chemical reactions, the electron transfer process is extremely small. Therefore, it is difficult to extract a practically large current, for example, 1 mA/cm2 or more, near room temperature, and the problem is that use is limited to high temperatures of 100-200°C.

The present invention solves these problems, and when a disulfide compound is used as a battery electrode, it does not impair the characteristic of high energy density, can be charged and discharged with a large current at room temperature, and is reversible. The purpose of this research is to provide an excellent electrode.

[0008]

[Means for Solving the Problems] In order to solve this problem, the present invention provides mixed ionic and electronic conductivity obtained by polymerizing compounds into which groups represented by general formulas (3) and (4) are introduced. The reversible electrode is mainly made of polymer.

[0009]

[Chemical formula 3]

0010

[C4]

[0011]

[Function] By configuring a reversible electrode mainly using an ion-electronic mixed conductor polymer obtained by polymerizing a compound into which a group represented by the general formula (Chemical formula 3) has been introduced, the conductive polymer can react in the electron transfer process. It acts as an electrocatalyst to reduce the activation energy of the electrolyte, and at the same time has the effect of increasing the effective reaction area for the electrolyte. In other words, the potential difference between the oxidation reaction and the reduction reaction, which was 1 volt or more with the disulfide compound alone, can be reduced to 0.0 by the interaction between the disulfide group represented by the general formula (Chemical formula 4) and the ionic/electronic mixed conductor polymer. By reducing the voltage to 1 volt or less, this accelerates the electrode reaction, and at the same time, the effective contact area with the electrolyte is greatly increased, making it possible to conduct electrolysis (charging and discharging) at large currents at room temperature. It becomes possible.

0012

[Example] The group introduced into the conductive polymer of the present invention has the general formula [
A group represented by R(S)y]n can be used. R
is an aliphatic group, an aromatic group, S is sulfur, y is an integer of 1 or more,
n is an integer of 2 or more. For example, C2N2S(SH)
2,5-dimercapto-1,3,4-thiadiazole represented by 2, S-triazine-2,4,6-trithiol represented by C3H3N3S3, etc. are used.
Examples of compounds that can constitute the conductive polymer of the present invention include thiophene, pyrrole, aniline, furan, and benzene, and these conductive polymers doped with anions such as iodine are effective. used for. In addition, polymerization conditions that allow a porous fibril structure to be formed are effectively used.

[0013] In addition to the alkali metal ions and alkaline earth metal ions disclosed in the above-mentioned US patents, protons can also be used as metal ions when the disulfide compound is reduced to form a salt. When using lithium ions as alkali metal ions, metallic lithium or a lithium alloy such as lithium-aluminum is used as an electrode for supplying and capturing lithium ions.
If an electrolyte that conducts lithium ions is used, the voltage will be 3~
A 4 volt battery can be constructed. Similarly, if protons are used as the metal ions mentioned above, a metal hydride such as LaNi5 is used as the electrode for supplying and capturing protons, and an electrolyte that conducts protons is used, a battery with a voltage of 1 to 2 volts can be constructed. can.

[0014] Specific examples will be explained in detail below. 84 g (1 mol) of thiophene and 100 ml of carbon tetrachloride were mixed and cooled to 0°C. Add this to 500g
(3.1 mol) of bromine dissolved in 300 ml of carbon tetrachloride was gradually added. After mixing everything, carbon tetrachloride was distilled off, and 15 g of sodium hydroxide was added.
Heat on a steam bath for an hour. After separating from the alkali layer and drying, a mixture of mono-, di- and tri-substituted thiophene bromides was obtained by distillation. This mixture was dissolved in xylene and fractionated using a silica gel column to obtain 30 g of 2,2,3-tribromothiophene.

32 g (0.1 m
ol) of 2,3,5-tribromothiophene and 6.5 g
(0.2 mol) of metallic zinc and 6 g (0.2 mol) of acetic acid were reacted to obtain 3-bromothiophene.

To 0.5 mol of 3-bromothiophene thus obtained, 0.5 mol of tetraethylene glycol was added.
were reacted and debromic acid was performed to obtain an ether compound of tetraethylene glycol and thiophene (hereinafter referred to as thiophene derivative 1). In this way, a group represented by the general formula (Chemical formula 3) was introduced.

Bromination was carried out once more to obtain a 4-bromo substituted thiophene derivative. 0.05 mol of the 4-bromothiophene derivative thus obtained was reacted with 4 g of thiourea in acetonitrile to obtain 0.01 mol of 4-mercaptothiophene derivative. This 4-mercaptothiophene derivative was reacted with 0.01 mol of 2,5-dimercapto-1,3,4-thiadiazole in chlorine, and tetraethylene glycol of thiophene was introduced with a disulfide group represented by the general formula (Chemical formula 4). An ether derivative (hereinafter referred to as thiophene derivative 2) was obtained.

The thus obtained thiophene derivative (1 mol/l) was used as a monomer and subjected to constant potential electrolysis at 1.2 to 1.5 V with respect to a saturated calomel reference electrode in propylene carbonate with lithium perchlorate as a supporting electrolyte. In this way, a thiophene derivative polymer film having a fibril structure with a thickness of about 20 μm was formed on the graphite electrode. The electrode was placed at a potential of 50 mV between -0.7 and +0.2 V relative to the Ag/AgCl reference electrode in dimethylformamide containing 1 mol/l of LiClO4 at room temperature.
When electrolysis was carried out by increasing and decreasing the amount linearly at a rate of /sec, the current-voltage characteristics shown by curve A in FIG. 1 were obtained. In addition, as a comparative example, 0.05 mol/l of 2,5-dimercapto 1, 3, 4-acyasol, LiClO4
When electrolyzed at a constant potential of +0.8 V with respect to the Ag/AgCl reference electrode in dimethylformamide containing 0.5 mol/l of thiophene derivative polymer, electrolysis was carried out in the same manner using a graphite electrode without a thiophene derivative polymer. The current-voltage characteristics shown were obtained. Furthermore, similar electrolysis was performed using a graphite electrode having only a thiophene derivative polymer film, and curve C in Figure 1 was used.
The current-voltage characteristics shown are obtained. Curve A gives a current-voltage characteristic in which the current-voltage curve C of a graphite electrode having only a thiophene derivative polymerized film overlaps with the current peak corresponding to the redox of 2,5-dimercapte-1,3,4-thiadiasol. ing. Among the current peaks corresponding to the redox of 2,5-dimercaphyte-1,3,4-thiasiasol, the current peak position particularly corresponding to the reduction reaction moves from -0.6 V to around -0.2 V,
Due to the presence of a thiophene derivative polymer, which is an ionic and electronic mixed conductor polymer, 2,5-dimercaphte-1,3,4-
It can be seen that the redox of thiasyl is promoted. On the other hand, in curve B obtained with a graphite electrode that does not contain a polymer, 2,5-shimerkaft-1,3,
Although a current peak corresponding to the redox of 4-thiacyasol is obtained, the potential difference between the oxidation peak and the reduction peak is close to 0.6 V, and the redox reaction is semi-reversible and the reaction rate is slow, making it difficult to use this electrode in a battery. When used as the positive electrode of a battery, the voltage difference between charging and discharging increases to 0.6 V or more, and when this battery is charged and discharged with a large current, the charging and discharging efficiency decreases.

[0019] In this example, the case where thiophene is used has been described, but the present invention is not limited thereto, and similar effects can be obtained by using other conductive polymers. Furthermore, the same effect can be obtained by crushing the polymer membrane of the present invention and mixing it with a current collector.

[0020]

Effects of the Invention As is clear from the explanation of the above embodiments, according to the present invention, an electrode mainly composed of a conductive compound obtained by polymerizing a compound into which a disulfide compound is introduced is different from the conventional disulfide compound. Electrolysis with large currents, which was difficult with electrodes made only of compounds, becomes possible. By using this electrode as a positive electrode and metallic lithium as a negative electrode, a high energy density secondary battery capable of charging and discharging at a large current can be constructed.

[0021] In addition to batteries, the present invention can provide biochemical sensors such as electrochromic elements with fast color development and fading speed and glucose sensors with fast response speed by using the electrode as a counter electrode. write·
It is also possible to construct an electrochemical analog memory with a fast readout speed.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the current-voltage characteristics of a composite electrode according to an example of the present invention and an electrode according to a comparative example.

Claims (1)

[Claims] 1. A reversible electrode mainly composed of a conductive polymer obtained by polymerizing a compound into which groups represented by formulas (1) and (2) are introduced. [Chemical formula 1] [Chemical formula 2]