JPH06310127A - Manufacture of electrode - Google Patents

Abstract

PURPOSE:To reduce a deterioration of an electrode using a disulfide compound by the charge and discharge cycle. CONSTITUTION:After a disulfide compound and a conductive material are mixed, it is mixed with a solution polyvinyl pyridine is solved, and then, the solvent is removed to manufacture an electrode. Furthermore, the electrode obtained in such a way, and a solution a polymer electrolyte is solved are mixed, and the solvent is removed so as to form an electrode which can be used in a large current condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing electrodes used in electrochemical devices such as batteries, electric double layer capacitors and electrochromic display devices. More specifically, an organic sulfur compound in which a sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including a proton) bond, and the sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation. (Hereinafter referred to as a disulfide compound) and a method of manufacturing an electrode mainly composed of a conductive substance.

[0002]

2. Description of the Related Art Disulfide compounds are known as organic materials which can be expected to have high energy density, for example, US Pat.
Disulfides have been proposed in 833,048. The disulfide compound is most simply designated as R-S-S-R. Here, R is an aliphatic or aromatic organic group,
S is sulfur. S-S bond is cleaved (depolymerization) by electrolytic reduction, cations in the electrolyte bath (M ⁺⁾ and R-S ^{chromatography,}
This produces a salt represented by M ⁺ . This salt returns to the original R-S-S-R by electrolytic oxidation (polymerization). A metal-sulfur secondary battery in which a metal M for supplying and capturing a cation (M ⁺ ) and a disulfide compound are combined is proposed in the above-mentioned US patent. This battery is expected to have an energy density of 150 wh / kg or more, which is comparable to or higher than that of an ordinary secondary battery.

Since the disulfide compound itself has a poor electron conductivity, when it is used for an electrode of a battery or the like, the inventors of US Pat. No. 4,833,048, Journal, Electrochemical, Society Vol. 137, Vol. 11
91 (1990), 138, 1896 (1
As reported in 991), a disulfide monomer or a prepolymerized disulfide compound polymer is impregnated into carbon felt or is used by mixing with a conductive material such as carbon black.

[0004]

However, when a battery is constructed using a liquid or an electrolyte containing a liquid as an electrolyte by impregnating or simply mixing a conductive material with the disulfide compound, the disulfide compound is introduced into the electrode. Is insufficiently retained. Therefore, there is a problem that the disulfide compound flows out from the electrode during repeated polymerization and depolymerization of the disulfide compound as the battery is charged and discharged, and the battery capacity deteriorates. Further, when a polymer solid electrolyte such as polyethylene oxide in which a lithium salt is dissolved is used, the conductive material and the disulfide compound are not uniformly dispersed, and when polymerization and depolymerization are repeated, the nonuniformity is further increased and the conductive material There is a problem that a mass of a disulfide compound that cannot be charged / discharged because it is not electrically connected to is generated in the electrode, and the battery capacity deteriorates. The present invention solves such a problem, and provides a method for producing an electrode containing a disulfide compound as a main component, which causes little capacity deterioration during charge and discharge.

[0005]

According to the method for producing an electrode of the present invention, a step of adding and mixing a first solution in which polyvinyl pyridine is dissolved in a mixture of a disulfide compound and a conductive substance, and removing a solvent from the mixture. At least the process is included. Further, in addition to the above steps, a step of adding and mixing a second solution in which a polymer electrolyte is dissolved to a mixture containing the disulfide compound, the conductive substance and polyvinyl pyridine, a step of molding the mixture, and a solvent removed from the molded article. Including the step of

[0006]

In the present invention, the disulfide compound and the conductive substance are mixed in advance, then uniformly mixed and dispersed with the first solution containing polyvinyl pyridine, and then the first solution.
Since the solvent contained in the solution is removed, it is possible to obtain an electrode in which the disulfide compound and the conductive substance are uniformly mixed and tightly adhered to each other due to the adhesive action and the surface-active action of polyvinylpyridine. When such an electrode is charged / discharged, the electrical connection between the conductive substance and the disulfide compound is kept good, and the deterioration of the capacity is reduced.

Further, the ionic conductivity of the electrode can be further improved by mixing the obtained electrode with a solution in which a polymer electrolyte is dissolved and then molding the mixture and then removing the solvent. Therefore, the electrode can be used with a larger current. The disulfide compound used in the present invention includes dithioglycol (ethanedithiol), 2,5-dimercapto-1,3,4-thiadiazole, thiocyanuric acid (s-triazine-2,4,4).
6-trithiol), thiourea and the like. Further, these disulfide compounds are chemically polymerized by using an oxidizing agent such as iodine, potassium ferricyanide, or hydrogen peroxide,
Alternatively, a polymer of a disulfide compound polymerized by the electrolytic oxidation method can be used.

As the conductive material, carbon materials such as acetylene black, artificial graphite and natural graphite, polyaniline,
Conductive polymer materials such as polypyrrole and polythiophene are used. As the conductive substance, a composite of the above conductive substances with each other, or the above conductive substance and a polyolefin such as polypropylene or polybutene, a fluororesin such as polytetrafluoroethylene, or a synthetic rubber or the like is synthesized. A composite material with a resin material can also be used. In particular, a flexible conductive polymer material, especially polyaniline having a fibril structure or a porous structure and capable of effectively dispersing and holding a disulfide compound is preferable. The amount of the conductive material mixed is preferably 0.1 to 20% of the total weight of the electrode. When it is 0.1% or less,
Sufficient electrical conductivity cannot be obtained. If it is 20% or more, it becomes difficult to form the electrode.

Polyvinyl pyridine includes poly-2-vinyl pyridine in which a vinyl chain is bonded to the 2-position of pyridine,
It is possible to use poly-4-vinylpyridine in which a vinyl chain is bonded to the 4-position of pyridine, and further an N-alkyl-2-vinylpyridinium salt or a N-alkyl-4-vinylpyridinium salt in which the N atom of pyridine is quaternized with an alkyl group. . The alkyl group is not limited in carbon number, and may be a methyl group, an ethyl group, a butyl group, a cetyl group, a linear alkyl group or a branched alkyl group.
The molecular weight is preferably 1000 or higher.
The content of polyvinyl pyridine is 0.1 to 0.1% of the total weight of the electrode.
20% is preferable. If it is 0.5% or less, sufficient adhesiveness cannot be obtained. On the other hand, if it is 20% or more, the electrode becomes too soft and it becomes difficult to handle it after molding.

Solvents for the first solution in which polypinylpyridine is dissolved include alcohols such as ethyl alcohol and butyl alcohol, ethers such as dimethoxyethane, diglyme, ethyl monoglyme and dimethoxyethane,
Nitromethane, acetonitrile or mixtures of these are used. LiBF as the polymer solid electrolyte
Polyalkylene oxide such as polyethylene oxide, polypropylene oxide, a copolymer of polyethylene oxide and polypropylene oxide, in which a lithium salt such as ₄ , LiPF ₆ , LiCF ₃ SO ₃ , or LiClO ₄ is dissolved is used. In addition, propylene carbonate,
A gel electrolyte made of polyalkylene oxide or polyacrylonitrile containing an organic electrolytic solution prepared by dissolving the lithium salt in a solvent of ethylene carbonate, sulfolane, dimethoxyethane, or a mixture thereof is used.

As the solvent of the second solution containing the polymer electrolyte, the same solvent as the solvent of the first solution is used.
The content of the polymer electrolyte is preferably 60% or less of the total weight of the electrode. When it is 60% or more, the electron conductivity of the electrode becomes small, and the redox reaction of the disulfide compound accompanied by the transfer of electrons becomes difficult to occur.

[0012]

EXAMPLES Examples of the present invention will be described below. [Example 1] 1-gr powder of 2,5-dimercapto-1,3,4-thiadiazole (hereinafter referred to as DMcT) powder and HB
Polyaniline powder doped with F ₄ (electrical resistance = 1.6
s / cm, 25 ° C., average particle size = 6 μm) and 1.5 gr were mixed in a mortar. 0.1 gr of poly-2-vinylpyridine having a molecular weight of 50,000 was dissolved in 10 ml of ethyl monoglyme and dehydrated with a zeolite adsorbent to obtain a polyvinylpyridine solution. After mixing the polyvinyl pyridine solution with the mixture of DMcT powder and polyaniline powder, diglyme was removed from the mixture under reduced pressure at 80 ° C to obtain DMc.
An electrode A containing T powder, polyaniline powder and polyvinyl pyridine was obtained.

[Comparative Example 1] An electrode B was prepared in the same manner as in Example 1 except that an ethyl monoglyme solution containing no poly-2-vinylpyridine was used in place of the ethyl monoglyme solution containing poly-2-vinylpyridine.

[Example 2] 5 gr of transparent liquid dithioglycol (referred to as DTG) was dissolved in acetone-water (1: 1) in which an equivalent amount of lithium hydroxide necessary for neutralizing the dibasic acid DTG was dissolved. (Volume ratio) 100 ml of a mixed solvent was added to neutralize and dissolve. Next, the same ethanol-water mixed solvent 10
An oxidant solution was prepared by dissolving an equivalent amount of iodine necessary to oxidize DTG and the same molar number of lithium iodide as iodine in 0 ml. The oxidizer solution was added dropwise over 2 hours while stirring the DTG solution prepared above with a homogenizer at a rotation speed of 1000 rpm to polymerize the DTG monomer.

The resulting DTG polymer white powder 1.0
Undoped polyaniline powder containing no gr and acid (electrical resistance = ^10-8 s / cm, 25 ° C., average particle size = 4μ
m) 1.25 gr were mixed in a mortar. This mixed powder was mixed and dispersed in a solution in which 0.15 gr of poly-4-vinyl-N-butylpyridinium bromide having a molecular weight of 35,000 was dissolved in 10 ml of nitromethane, and then 80 ° C.
Then, the nitromethane was removed under reduced pressure to prepare an electrode C containing the DTG polymer, the undoped polyaniline and polyvinyl pyridine.

[Comparative Example 2] Example 2 except that nitromethane containing no poly-4-vinyl-N-butylpyridinium bromide was used instead of the nitromethane solution containing poly-4-vinyl-N-butylpyridinium bromide.
An electrode D was prepared in the same manner as in. [Example 3] 3.0 g of polyacrylonitrile was added to LiB
A gel electrolyte was prepared by gelling with 20.7 g of a propylene carbonate / ethylene carbonate (1: 1 volume ratio) solution containing 1 M of F ₄ dissolved therein. The gel electrolyte obtained is
After heating to 0 ° C to make it fluid, acetonitrile 30
It was diluted with g to obtain a gel electrolyte solution. 1 part by weight of the electrode obtained in Example 1 and 1.5 parts by weight of a gel electrolyte solution were mixed in a mortar, and the obtained ink was printed on a carbon film having a thickness of 50 μm made of fluororesin and carbon black. Acetonitrile was removed by drying under reduced pressure at 60 ° C. to obtain an electrode E having a thickness of 170 μm.

[Comparative Example 3] A thickness of 17 was obtained in the same manner as in Example 3 except that the electrode B was replaced by the electrode B obtained in Comparative Example 1.
An electrode F of 0 micron was obtained. Next, each of the above electrodes was applied to a battery to evaluate the battery performance. The electrodes A, C and E obtained in Examples 1, 2 and 3 and the electrode powders B, D and F obtained in Comparative Examples 1, 2, and 3 were used as positive electrode active material materials, and a metal having a thickness of 0.3 mm was used. Using a lithium negative electrode, a gel electrolyte obtained by gelling 3.0 g of polyacrylonitrile with 20.7 g of a propylene carbonate / ethylene carbonate (1: 1 volume ratio) solution prepared by dissolving 1 M of LiBF ₄ in a thickness of 0.
A 6 mm separator layer was used to construct a battery with a diameter of 13 mm. A battery using the electrodes A, B, C, and D as the positive electrode has a constant current of 0.07 mA, and a battery using the electrodes E and F as the positive electrode has a constant current value of 0.27 mA.
A charge / discharge test was performed within the range of 4.05 to 2.50 V, and the battery characteristics of each electrode were evaluated. 1, 5,
It was evaluated by the discharge capacity after 10, 20, and 30 cycles. The powder electrodes A, B, C and D each have a thickness of 0.
A positive electrode was obtained by pressure molding into a disk shape having a diameter of 16 to 0.18 mm and a diameter of 13 mm. Further, the electrodes E and F have a diameter of 13
A punched disc having a size of mm was used. The weight of all electrodes was 20 mg. The test results are shown in Tables 1 and 2.

[0018]

[Table 1]

As is clear from the results of Table 1, the electrode powders A and C of Examples 1 and 2 produced by the method according to the present invention.
In the battery using No. 3, the capacity of 84% and 80% of the capacity at the first cycle was retained even after 30 cycles of charging / discharging, while the electrode powders B and D of Comparative Examples 1 and 2 manufactured by the conventional method were used. The battery used only holds a discharge capacity of 50% and 48%.

[0020]

[Table 2]

As is clear from the results shown in Table 2, in the battery using the electrode E of Example 3 manufactured by the method according to the present invention, the capacity of the first cycle was 81% even after 30 cycles of charge / discharge.
%, The battery using the electrode F of Comparative Example 3 manufactured by the conventional method only holds a discharge capacity of 45%.

[0022]

According to the production method of the present invention, the disulfide compound is mixed with the conductive substance, and then polyvinyl pyridine having adhesiveness and surface activity is added and mixed, so that the disulfide compound is more uniformly and strongly adhered. Therefore, the electrode in which the disulfide compound and the conductive substance are uniformly mixed and dispersed can be obtained. Then, when a battery using such an electrode is charged and discharged, the electrical and ionic connection between the conductive substance and the disulfide compound is maintained well, and the deterioration of the battery capacity is reduced.

Claims (3)

[Claims] 1. A sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond,
Polyvinylpyridine is dissolved in a step of mixing an organic sulfur compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation and a conductive material, and in a mixture of the organic sulfur compound and the conductive material. And a step of removing the solvent contained in the first solution, and a step of adding and mixing the above-mentioned first solution. 2. A step of mixing a second solution in which a polymer electrolyte is dissolved, with a mixture containing the organic sulfur compound, a conductive substance and polyvinyl pyridine, a step of molding the mixture, and a step of forming a second product from the molded article. The method for producing an electrode according to claim 1, further comprising a step of removing a solvent contained in the solution. 3. The method for producing an electrode according to claim 1, wherein the conductive substance is a conductive polymer.