JPH04359866A - Reversible electrode - Google Patents

Abstract

PURPOSE:To enhance the oxidative/reductive reaction speed of a reversible electrode, which consists of electroconductive highpolymer compound and is used to electrochemical elements such as a battery, electrochromic display element, sensor, and memory. CONSTITUTION:As a material to electrode is used a compound, in which a thiol radical is introduced to each side chain of electroconductive highpolymer, and formation of a disulphide bond between side chains is utilized to electrode reactions. Use of this type of compound to an electrode of a battery permits achieving a secondary battery having as large an energy density as 150wh/kg or more. The disulphide type compound presents slow oxidative/reactive reactions, and it is difficult to take out a large current with this solely, but combining with electroconductive highpolymer accelerates the oxidative/reductive reactions of the disulpide type compound due to the electrode catalyst action of electroconductive molecles, which together with the effect of greatly increasing the contact area substantially with the electrolyte, should enable electrolysis (charging and discharging) with large current even 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 made of a conductive organic compound used in electrochemical devices such as batteries, electrochromic display devices, sensors, and memories.

0002

2. Description of the Related Art Since conductive polyacetylene electrodes were discovered by Shirakawa et al. in 1971, conductive polymer electrodes have been actively studied. When conductive polymers are used as electrode materials, it is expected that electrochemical devices such as lightweight, high-energy-density batteries, large-area electrochromic devices, and biochemical sensors using microelectrodes will be realized. However, polyacetylene is a compound that is chemically active against moisture and oxygen in the air and is unstable in the air, making it impractical as an electrode for use in electrochemical devices. In recent years, in order to overcome this problem, other π-electron conjugated conductive polymers have been investigated, and conductive polymers that are relatively stable in air, such as polyaniline, polypyrrole, polyacene, and polythiophene, have been discovered. Lithium secondary batteries using conductive polymers as positive electrodes are being developed.

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 hold an amount of electrolyte in the battery that corresponds to the discharge capacity of the battery, and the weight of the battery increases by the amount of electrolyte consumed in the reaction, reducing the energy density of the battery to about 20 to 50 Wh/kg. do. Therefore, compared to normal secondary batteries such as nickel-cadmium storage batteries and lead-acid batteries, the energy density of this battery is 2.
The problem is that the size is reduced to about one-fold.

On the other hand, US Pat. No. 4,833,0 is an organic material that can be expected to realize high energy density batteries.
No. 48 proposes disulfide compounds. This compound is most simply represented as R-S-S-R (R is an aliphatic or aromatic organic group, S is sulfur). The S-S bond of this disulfide compound is cleaved by electrolytic reduction, and R-S-M
Produces a salt represented by +. Moreover, this salt has the property of returning to the original R-S-S-R by electrolytic oxidation. In addition, a metal-sulfur secondary battery that combines metal Mn+ that supplies and captures cations (Mn+) and a disulfide compound is proposed in the above-mentioned US patent, and has a capacity of 150Wh/Kg or more, which is comparable to ordinary secondary batteries or Higher energy density is expected.

[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. Furthermore, not only is this effect not specifically demonstrated, but there is also no indication that conductive polymers act as electrocatalysts during electrolysis of disulfide compounds.

[0006] 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 evidence that conductive polymers act as electrocatalysts during electrolysis of disulfide compounds.

[0007]

[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 V, and the electrochemical reaction in such materials is Because the movement is extremely slow, a large current suitable for practical use, such as 1 mA, is required near room temperature.
It is difficult to extract a current of /cm2 or more, and the problem is that it is limited to use at high temperatures of 100 to 200°C, where electron transfer is rapid.

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

[0009]

[Means for Solving the Problem] In order to solve this problem, the present invention consists of a reversible electrode mainly composed of a conductive polymer formed by polymerizing a monomer compound having a thiol group in its side chain. be.

[0010] Furthermore, the oxidation-reduction reaction is carried out between thiol groups introduced into the side chains of the conductive polymer.

[
0011

[Operation] By introducing a side chain having a thiol group into a monomer compound that is polymerized to form a conductive polymer, a conductive polymer having disulfide bonds in the molecule can be obtained. In this conductive polymer, disulfide bonds act as an electrocatalyst that reduces the activation energy of the reaction in the electron transfer process. That is, the potential difference between the oxidation reaction and the reduction reaction, which was 1 V or more when using the disulfide compound alone, can be reduced to 0.1 V or less by the interaction between the thiol group and the conductive polymer. Therefore, the electrode reaction is promoted, the substantial contact area with the electrolyte is significantly increased, and electrolysis (charging and discharging) at a large current is possible even at room temperature.

[0012] Furthermore, by introducing a thiol group that forms a disulfide bond into the molecule, it is possible to prevent molecular species having these thiol groups, which are the main body of the electrode reaction, from leaking into the electrolyte during the redox reaction. This means that improvements in charge and discharge characteristics can be expected.

[0013]

[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. As the monomer compound forming the conductive polymer of the present invention, thiophene, pyrrole, aniline, furan, benzene, etc. are used, and conductive polymers made by polymerizing these monomers are doped with anions such as iodine. is used effectively. Further, it is desirable that the polymerization conditions are such that a porous fibril structure can be formed.

[0014] In addition to the alkali metal ions and alkaline earth metal ions mentioned in the above-mentioned US patent, 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 the electrode for supplying and capturing lithium ions, and an electrolyte that conducts lithium ions is used to create a battery with a voltage of 3 to 4 V. can be configured. In addition, protons are used as the aforementioned metal ions, and metal hydrides such as LaNi5 are used as electrodes for supplying and capturing protons.
When using an electrolyte that conducts protons, the voltage is 1 to 2 V.
It is also possible to configure a battery of

(1) Synthesis of thiophene derivative 100ml
of benzene and 2.4 g (0.1 mo
After adding 12.1 g (0.05 mol) of 3,
4-Dibromothiophene was added and the mixture was refluxed for 1 hour. Add 6.02 g (0.1 mol) of ethylene glycol to this solution.
The mixture was mixed and refluxed for 3 hours to obtain a 3,4-dihydroxybromothiophene derivative. Add 11 g (0.1 m
3-chloro-1-propanethiol (ol) was added and the mixture was refluxed for 3 hours. In this way, 9.5 g (0
．． 025 mol) was obtained.

[0016]

[Chemical formula 1]

(2) Cyclic voltammetry The thus obtained thiophene derivative 1 (1 mol/l) was used as a monomer in propylene carbonate, and lithium perchlorate was used as a supporting electrolyte against a saturated calomel reference electrode.
By constant potential electrolysis at 1.2 to 1.5V, a thickness of about 20
A thiophene derivative polymer film having a micrometer fibril structure was formed on a graphite electrode. This electrode was heated with LiC at room temperature.
A in dimethylformamide containing 1M lO4
When electrolysis was carried out by linearly increasing and decreasing the potential between -0.7 and +0.2 V with respect to the g/AgCl reference electrode at a rate of 50 mV/sec, the current-voltage characteristics shown by curve A in FIG. 1 were obtained. Further, as a comparative example, similar electrolysis was performed on a graphite electrode having only a thiophene derivative 1 polymer film, and the current-voltage characteristics shown by curve B in FIG. 1 were obtained. Curve A represents the current-voltage characteristics in which the current-voltage curve B of the graphite electrode having only the thiophene derivative 1 polymer film overlaps with the current peak corresponding to the redox of 2,5-dimercapto-1,3,4-thiadiazole. giving. 2,5-dimercapto-1,3
, 4-thiadiazole, the current peak position corresponding to the reduction reaction is particularly at -0.
6V to around -0.2V, indicating that the redox of 2,5-mercapto-1,3,4-thiadiazole is promoted by the presence of monopolymer of thiophene derivative, which is a mixed ionic and electronic conductor polymer. Recognize. On the other hand,
In curve B obtained with a graphite electrode without polymer, 2,
A current peak corresponding to the redox of 5-dimercapto-1,3,4thiadiazole is obtained, but the potential difference between the oxidation peak and the reduction peak is close to 0.6 V, and the redox is semi-reversible and the reaction rate is slow. When this electrode is used as the positive electrode of a battery, the voltage difference between charging and discharging increases to 0.6 V or more, and the efficiency of the battery decreases significantly when charging and discharging at a large current.

[0018] In this example, the case where thiophene was used was explained, but other conductive polymers also exhibit the same effects as in this example. Furthermore, it is obvious that the same effect can be obtained even if the polymer film of this example is crushed and mixed with a current collector to form an electrode.

(3) Charge/discharge cycle characteristics Thiophene derivative 1 (1 mol/l) obtained in this example was used as a monomer in propylene carbonate, lithium perchlorate was used as a supporting electrolyte, and 1.2 to 1.2 to 1.2 to a saturated calomel reference electrode was used as a supporting electrolyte.
By performing constant potential electrolysis at 1.5 V, a thiophene derivative polymer film having a fibril structure with a thickness of about 20 μm was formed on the graphite electrode. A battery was prepared using this electrode as a working electrode, a Li wire as a reference electrode, a Li foil as a counter electrode, and an electrolyte solution containing 1M LiClO4 dissolved in dimethylformamide. Using this battery, the charging potential was set to 4.0V.
After charging for 15 hours, the final voltage was 2.0V and the discharge current was 0.
A cycle characteristic test was conducted at 5 mA. In this way, a cycle life characteristic curve shown by curve A in FIG. 2 was obtained. The horizontal axis of FIG. 2 is the number of cycles, and the vertical axis is the discharge capacity when the discharge capacity of the first cycle is set as 100. In addition, as a comparative example, a composite electrode prepared by mixing polythiophene, 2,5-dimercapto-1,3,4-thiazole, which is a sulfide compound, and polyethylene oxide at a weight ratio of 3:1:1 was used as a working electrode, and a similar electrode was used. A battery was assembled and a cycle characteristic test was conducted under the same conditions. In this way,
A charge/discharge cycle characteristic curve shown by curve B in FIG. 2 was obtained. In curve B, the charge/discharge efficiency decreases after about 10 cycles, but in curve A, the charge/discharge cycle characteristics improve at 50 cycles.

[0020] 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. It is also possible to configure an electrochemical analog memory with fast writing and reading speeds.

[0021]

Effects of the Invention As is clear from the explanation of the above examples, according to the present invention, a compound in which a side chain having a thiol group is introduced into a monomer compound that forms a conductive polymer by polymerization. An electrode made mainly of the polymer produced by this method enables electrolysis at a large current, which was difficult with conventional electrodes made only of disulfide compounds. By using this electrode as a positive electrode and using metallic lithium as a negative electrode, a high energy density secondary battery capable of charging and discharging at a large current can be constructed.

[Brief explanation of the drawing]

[Figure 1] Current of the composite electrode of the present invention and the electrode of the comparative example -
Diagram showing voltage characteristics

[Fig. 2] A diagram showing the charge/discharge cycle characteristics of the composite electrode of the present invention and the electrode of a comparative example.

[Explanation of symbols]

A Characteristics of the reversible electrode according to an embodiment of the present invention B Characteristics of the conventional reversible electrode

Claims (2)

[Claims] 1. A reversible electrode mainly composed of a conductive polymer formed by polymerizing a monomer compound having a thiol group in its side chain. 2. The reversible electrode according to claim 1, wherein a redox reaction is carried out between thiol groups introduced into the side chains of the conductive polymer.