JP2940198B2 - Solid electrode composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode composition used for an electrochemical device such as a lithium secondary battery using a solid or solid lithium ion conductive electrolyte.

[0002]

2. Description of the Related Art Electrochemical devices such as lightweight, high-energy density batteries, large-area electrochromic devices, and biochemical sensors using microelectrodes can be expected.
Conductive polymer electrodes are being actively studied. Since polyacetylene is unstable and impractical as an electrode, other π-electron conjugated conductive polymers have been studied, and relatively stable polymers such as polyaniline, polypyrrole, polyacene, and polythiophene have been developed. The lithium secondary batteries used have been developed.

[0003] Since these polymer electrodes take in not only cations but also anions in the electrolyte during the electrode reaction, the electrolyte in the battery not only acts as a transfer medium for ions but also participates in the battery reaction. It is necessary to supply an amount of electrolyte corresponding to the battery capacity into the battery. In addition, there is a problem that the energy density of the battery is reduced accordingly. Energy density is 20-50Wh / kg
It is about half that of a normal secondary battery such as a nickel cadmium storage battery or a lead storage battery.

[0004] In contrast, as organic material a high energy density can be expected, disulfide compounds have been proposed in U.S. Patent No. 4,833,048. This compound is most simply represented as R-S-S-R (R is an aliphatic or aromatic organic group and S is sulfur). The SS bond is cleaved by electrolytic reduction, and the cation (M +) in the electrolytic bath is combined with RS—
A salt represented by M + is formed. This salt returns to the original RSSR by electrolytic oxidation. A metal-sulfur secondary battery combining a metal M that supplies and traps cations (M +) with a disulfide compound has been proposed in the aforementioned U.S. Patent. With an energy density of 150 Wh / Kg or more, an energy density comparable to or higher than that of a normal secondary battery can be expected.

[0005]

However, the proposed disulfide compound is disclosed in US Pat. No. 4,833,044.
No. 8, the inventor of J. Electrochem. Soc, Vol. 136, No. 9,
As reported in pages 2570-2575 (1989), for example,
In the electrolysis of [(C2H5) 2NCSS-] 2, the potential for oxidation and reduction is 1 vo
It is separated by more than lt, and the electron transfer process is extremely slow according to the teachings of electrode reaction theory. Therefore, it is difficult to extract a large current suitable for practical use, for example, a current of 1 mA / cm 2 or more at around room temperature, and there is a problem that the use is limited to a high temperature of 60 ° C. or more. Further, since the disulfide compound is dissolved in an organic solvent, it is difficult to use an organic electrolyte in which a salt is dissolved in the organic solvent, and it is necessary to use a solid or solid electrolyte such as a polymer electrolyte. Also,
Since the disulfide compound has poor electron conductivity, it must be used in combination with a conductive agent. Usually, a conductive material such as carbon and a polymer solid electrolyte are mixed and used as a composition.

However, not necessarily good electron and ion network is formed in the composition, it had the disadvantage of polarization increases. The present invention solves such a problem and provides an electrode having excellent reversibility capable of performing electrolysis (charge / discharge) with a large current even at a room temperature even at a slightly low temperature, which impairs the feature of the high energy density of the disulfide compound. is there.

[0007]

The electrode of the present invention comprises a disulfide compound, polypyrrole acting on both a conductive material and an electrode catalyst, and an organic solvent comprising propylene carbonate and / or ethylene carbonate in which a lithium salt is dissolved. It is a solid electrode composition obtained by complexing a solid electrolyte gelled using a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate.

[0008]

In the solid electrode composition of the present invention, polypyrrole acts as a catalyst for an electrode reaction of a disulfide compound, and particularly promotes a reduction reaction. Further, it acts as a conductive material and forms a good electron conduction path in the composition.
A solid electrolyte in which a propylene carbonate or / and ethylene carbonate solution in which a lithium salt is dissolved using a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is made into a gel form, disperses polypyrrole powder well, and disulfide compound Not only provides an electrode reaction interface that is advantageous for the oxidation-reduction reaction, but also acts as a binder for polypyrrole powder and disulfide compound powder, and provides the solid electrode composition with good mechanical strength and workability.

[0009] As the disulfide compound of the present invention, the general formula set forth in U.S. Patent No. 4,833,048 (R
(S) y) A disulfide compound represented by n can be used. R is an aliphatic group, an aromatic group, S is sulfur, y is 1
N is an integer of 2 or more. For example, C2N2S (S
H) 2,5-mercaphto-1,3,4-thiazole as represented by 2, C3H3N3S
Multiple thiols such as s-triazine-2,4,6-trithiol represented by 3
Compounds Oxidized and Polymerized in the Presence of Lithium Ions
Objects are used.

[0010] The polypyrrole of the present invention may be pyrrole or
Can be obtained by any of electrolytic polymerization and chemical polymerization of a pyrrole derivative . Anion is doped
You can either have, does not matter even if it is not. Those having an average particle diameter of 0.1 to 10 microns and an electric conductivity of 10-1 S / cm or more are preferably used. You may mix a conductive material as needed. As the conductive material in this case, a carbon material is preferably used. Any of natural graphite, artificial graphite, amorphous carbon, fibrous, powdery, petroleum pitch, and coal coke can be used. Particle or fiber size, diameter or fiber diameter 0.01 to 10 microns,
The fiber length is preferably from several μm to several mm.

[0011] copolymers of acrylonitrile and methyl acrylate or methyl methacrylate is obtained by polymerizing methyl acrylonitrile monomers and acrylic acid or methyl methacrylate in a conventional polymerization method. Those having a molecular weight of 30,000 to 100,000 are preferably used. The copolymerization ratio (AN / MA) of acrylonitrile (AN) and methyl acrylate or methyl methacrylate (MA) is 50: 1 to 2: 1 (molar ratio).
The degree is preferred.

[0012]

The disulfide compound of the present invention includes a compound represented by the general formula (R (S)) described in US Pat. No. 4,833,048.
y) A disulfide compound represented by n can be used. R is an aliphatic group, an aromatic group, S is sulfur, y is an integer of 1 or more, and n is an integer of 2 or more. For example, 2,5-dimercapto-1,3,4-thiadiasol represented by C2N2S (SH) 2, s-triazine-2,4,6-trithiol represented by C3H3N3S3, and the like are used.

[0013] polypyrrole of the present invention can be obtained electrolytic polymerization, by any of the methods of chemical polymerization. Those having an average particle diameter of 0.1 to 10 microns and an electric conductivity of 10-1 S / cm or more are preferably used. You may mix a conductive material as needed. As the conductive material in this case, a carbon material is preferably used. Any of natural graphite, artificial graphite, amorphous carbon, fibrous, powdery, petroleum pitch, and coal coke can be used. Particle or fiber size, diameter or fiber diameter 0.01 to 10 microns,
The fiber length is preferably from several μm to several mm.

[0014] copolymers of acrylonitrile and methyl acrylate or methyl methacrylate is obtained by polymerizing methyl acrylonitrile monomers and acrylic acid or methyl methacrylate in a conventional polymerization method. Those having a molecular weight of 30,000 to 100,000 are preferably used. The copolymerization ratio (AN / MA) of acrylonitrile (AN) and methyl acrylate or methyl methacrylate (MA) is 50: 1 to 2: 1 (molar ratio).
The degree is preferred.

As the lithium salt, lithium iodide, lithium perchlorate, lithium trifluorosulfonate, lithium borofluoride and the like are used. The solid electrolyte composition of the present invention is manufactured as follows. First, a lithium salt solution is obtained by heating and dissolving a lithium salt in a solvent composed of propylene carbonate and / or ethylene carbonate. Next, a powder of a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is added to this solution, and the mixture is heated at 150 ° C. to 180 ° C. to dissolve the powder to obtain a uniform transparent solution. The solution is diluted 2-3 times by weight with acrylonitrile. The powder obtained by mixing the disulfide compound powder and the polypyrrole powder in a mortar is mixed with a dilute solution, and the obtained slurry is cast on a glass plate. After drying at room temperature, the solid electrolyte composition is obtained by vacuum heating and drying at 60 ° C. under a reduced pressure of 1 Torr. LiI, Li3N-LiI-B2O in the slurry if necessary
3. Lithium ion conductive powders such as LiI.H2O and Li-β-Al2O3 may be added.

[0016] (Example 1) lithium trifluoromethane sulfonate 3.58 g, propylene carbonate 10.47 g, mixture of ethylene carbonate 7.86 g, to obtain a homogeneous solution was heated to 120 ° C.. To this solution was mixed 3 g of a powder of acrylonitrile and methyl acrylate (AN / MA = 10/1, molar ratio) having a molecular weight of 60,000, and heated to 150 ° C. in a sealed 100 ml Erlenmeyer flask. The polymer powder was completely dissolved to obtain a viscous transparent liquid. 30 g of acrylonitrile was added to this liquid to obtain a diluted solution. Using iodine as the oxidant
Chemical polymerization of 2,5 dimercapto-1,3,4-thiadiazole (MTD) in the presence of lithium hydroxide
Poly (2,5-dimercapto-1,3,4-
Thiadiazole ) lithium salt (DMTD) powder 2.0 g
Then, a mixed powder obtained by mixing 0.5 g of polypyrrole powder having an average particle diameter of 3 μm with a mortar was mixed with 10 g of a diluted solution to obtain an electrode slurry. The polypyrrole powder used was 0.1 M (M = mol / dm3) pyrrole and 0.3 M LiC
In acetonitrile in which l04 was dissolved, two platinum plates were used as electrodes, and the solution was stirred between these electrodes.
It was obtained by applying a constant voltage of 5 V and performing electrolysis. The conductivity of the thus obtained polypyrrole doped with perchlorate anion was measured by pressing the powder into pellets and found to be about 8 S / cm at room temperature. Although LiClO4 was used as the salt, LiBF4, Et4NClO4, Et4NBF4 (Et = C2H5) can also be used. The electrode slurry is cast on a glass Petri dish having a diameter of 90 mm, dried for 1 hour in a dry argon stream at 40 ° C., and further vacuum-dried at 60 ° C. for 5 hours to form a flexible sheet having a thickness of about 280 μm. Was obtained.

[0017] (Comparative Example 1) approximately 250 except that the average particle size in place of polypyrrole powder was used artificial graphite powder 2μm in the same manner as in Example 1 thickness
A solid electrode composition B of μm was obtained. Comparative Example 2 A solid electrode composition C having a thickness of about 150 μm was obtained in the same manner as in Example 1 except that the amount of the polypyrrole powder was changed to 1.0 g except for the DMTD powder. (Comparative Example 3) A solid electrode composition D having a thickness of about 280 µm was obtained in the same manner as in Example 1 except that polyacrylonitrile having a molecular weight of 55,000 was used instead of the acrylonitrile and methyl acrylate copolymer. .

[0018] (electrode characteristics Evaluation) Examples and punched out electrode compositions obtained in Comparative Examples 1 to 3 into a disk form having a diameter of 22 mm. The electrode disk 1 was placed in a case 2 made of stainless steel having an inner diameter of 22 mm so as to be in contact with the bottom surface of the case to form a positive electrode module. On the other hand, an opening of the case 2 in which the metal lithium disk 3 having a thickness of 0.3 mm and a diameter of 17 mm is abutted on the concave portion is heated to 150 ° C. and flows into a sealing plate 5 which is sealed with a sealing ring 4 made of polypropylene. The solid electrolyte 6 before dilution having the property was poured thereinto to constitute a negative electrode module. A battery for evaluating electrode characteristics was assembled by closing the opening of the positive electrode module with the negative electrode module so that the solid electrolyte 6 was in contact with the electrode disk 1. FIG. 1 shows a cross-sectional structure of the test battery thus obtained.

[0019] The battery was assembled in this way,
Cyclic voltammograms were measured between 1.5 and 4.0V. The voltage sweep speed was 10 mV / sec.
Battery A of Example 1 and Battery B of Comparative Examples 1, 2, and 3
The cyclic voltammograms of C and D are shown in FIG. Also, the circuit voltage and internal resistance after assembly of each battery, 4.0
The polarization values at a battery voltage of 3.5 V when charged at a constant voltage of V for 17 hours and then discharged at a constant current of 500 μA are summarized in Table 1.

The internal resistance is an AC impedance value at a circuit voltage obtained using an AC signal of 10 mV and 10 KHz. When the discharge voltage reaches 3.5 V, the polarization value
Temporary discharge was stopped to make a circuit state, and the battery was allowed to stand until the battery voltage became constant. The difference was obtained as the difference between the voltage 0.1 sec after the discharge was stopped and the voltage one hour after the discharge. Evaluation is all 2
Performed at 0 ° C.

[0021]

[Table 1] As shown in the table, the polarization value of the battery A of the example is extremely smaller than those of the batteries B and D of the comparative example. As is clear from FIG. 2, in the battery A of the example, by adding polypyrrole to the electrode composition, the current peak corresponding to the reduction of the disulfide compound, DMTD, that is, the charging of the battery, was 2.6 to 3 times. .6V. Even in the case of using polypyrrole, in the battery D of Comparative Example 3 using the polyacrylonitrile solid electrolyte, the reduction peak of DMTD was on the low voltage side, and the polarization was larger than that of the battery A of Example 1. In the battery B of Comparative Example 1 to which the polypyrrole powder was not added, a reduction current corresponding to a DMTD oxidation current peak near 3.6 V, that is, a discharge current of the battery was not observed in the examined voltage range. Further, in the battery C of Comparative Example 2 containing no DMTD, only a current corresponding to redox of polypyrrole was observed.

From the above, the reduction reaction (discharge reaction) of DMTD is catalyzed by polypyrrole, and furthermore, even at room temperature in the coexistence of a solid electrolyte containing a copolymer of polyacrylonitrile and methyl acrylate at a temperature of 2.6. ~ 3.
It can proceed in a high voltage range of 6V.

Although only the battery is shown as an example,
In addition to batteries, an electrochromic device having a high coloring / fading speed by using the solid electrode composition of the present invention as a counter electrode,
A biochemical sensor such as a glucose sensor having a fast response speed can be obtained, and an electrochemical analog memory having a fast writing / reading speed can be configured.

[0024]

As described above, in the present invention, that is, in the electrode in which the disulfide compound and the polypyrrole are combined, electrolysis at a large current, which was difficult with the conventional disulfide compound alone, can be performed. Furthermore, polarization can be reduced by using a solid electrolyte containing a copolymer of polyacrylonitrile and methyl acrylate or methyl methacrylate. By using this solid electrode composition for the positive electrode and metallic lithium for the negative electrode, a solid high energy density lithium secondary battery that can be expected to be charged and discharged with a large current can be formed.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a battery used for evaluating characteristics of an electrode composition.

FIG. 2 is a current-voltage characteristic diagram of a battery using metallic lithium as a negative electrode and an electrode composition as a positive electrode.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroshi Uemachi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-74459 (JP, A) JP-A-4-308660 (JP, A) JP-A-4-272659 (JP, A) JP-A-4-264363 (JP, A) JP-A-4-239020 (JP, A) JP-A-4-155766 (JP, A) JP-A-62-278774 (JP, A)

Claims (1)

(57) [Claims] An organic compound in which a sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-lithium ion bond, and the sulfur-lithium ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation; polypyrrole; A solid electrode composition comprising a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, a lithium salt, and propylene carbonate and / or ethylene carbonate.