JP3089707B2 - 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 a solid electrode composition, and more particularly 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 light-weight, 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. 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 ions in the battery but also participates in the battery reaction. It is necessary to supply an appropriate amount of electrolyte into the battery. In addition, there is a problem that the energy density of the battery is reduced accordingly. The energy density is about 20 to 50 wh / kg, which is about one half that of a normal secondary battery such as a nickel cadmium storage battery or a lead storage battery. On the other hand, US Pat. No. 4,833,048 discloses an organic material which can be expected to have a high energy density.
The disulfide compound is proposed in the publication. This compound is most simply represented as R-S-S-R (R is an aliphatic or aromatic organic group, and S is sulfur). S-S bond is cleaved by electrolytic reduction, de R-S and cations in the electrolyte bath (M ^{+) -} to produce the salt represented by · M ^+. This salt returns to the original RSSR by electrolytic oxidation. Cation (M
A metal-sulfur secondary battery combining a metal M and a disulfide-based compound for supplying and supplementing ⁺ ) is 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.

[0003]

However, the proposed disulfide compounds are disclosed in US Pat.
No. 3,048, J. Electrochem. Soc, Vol. 136,
No.9, p, as reported in 2570 to 2575 (1989), for example, in _{[(C 2 H 5) 2} NCSS-] 2 of the electrolysis, the electrodes are separated potential of oxidation and reduction is more 1volt reaction According to the theory, the electron transfer process is extremely slow. Therefore, it is difficult to extract a large current suitable for practical use, for example, a current of 1 mA / cm ² or more near 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. Further, since the disulfide compound has poor electron conductivity, it must be used in combination with a conductive agent. Usually, a conductive material such as graphite powder and a polymer solid electrolyte are mixed and used as a composition. However, a favorable electron-ion network was not necessarily formed in the composition, and the composition had a disadvantage of increasing polarization.
The present invention solves such a problem, and does not impair the feature of the high energy density of the disulfide compound, and provides a solid electrode composition excellent in reversibility capable of performing electrolysis (charge / discharge) with a large current even at room temperature. The purpose is to provide.

[0004]

SUMMARY OF THE INVENTION In order to solve this problem, a solid electrode composition of the present invention comprises an activated carbon carrying a disulfide compound, an electrode catalyst and polyaniline acting as a conductive material, and propylene carbonate having a lithium salt dissolved therein. An organic solvent composed of at least one of ethylene carbonate and ethylene carbonate is combined with a solid electrolyte gelled using a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate.

[0005]

According to this structure, in the solid electrode composition of the present invention, the activated carbon supporting polyaniline acts as an electrode reaction catalyst for a disulfide compound, and particularly promotes the reduction reaction. Polyaniline is mainly supported in the pores of activated carbon. The disulfide compound is also solidified while being held in the pores of the activated carbon having conductivity. A solid electrolyte in which a solution of at least one of propylene carbonate and ethylene carbonate in which a lithium salt is dissolved using a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate is gelled enters the pores of activated carbon, and disulfide In addition to providing an electrode reaction interface that is advantageous for the oxidation-reduction reaction of the system-based compound, it also acts as a binder for the activated carbon and the disulfide-based compound, and provides the solid electrode composition with good mechanical strength and workability.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrode composition according to one embodiment of the present invention will be described below with reference to the drawings.

As the disulfide compound of this embodiment, a disulfide compound represented by the general formula (R (S) _y ) _n described in US Pat. No. 4,833,048 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, C 2 N 2 S (SH} ) represented by ₂ 2,5-dimercapto-1,3,4-thiadiazole, C ₃ H ₃ N ₃ s- triazine represented by S _3-2,4,6 -Trithiol and the like are used.

The polyaniline of this embodiment can be obtained by any of electrolytic polymerization and chemical polymerization. Those having an electric conductivity of 10 ^-1 S / cm are preferably used. Loading on activated carbon can be obtained by impregnating the activated carbon with a solution obtained by dissolving polyaniline solubilized by undoping or introduction of an anion into a good solvent, and then dissipating the solvent by vacuum heating or the like. . The activated carbon has an average particle size of 5 μm, a specific surface area of 1000 m ² / g,
A powdery material having a pore volume of about 0.5 ml / g or a fibrous material is preferably used.

A copolymer of acrylonitrile and methyl acrylate or methyl methacrylate can be obtained by polymerizing an acrylonitrile monomer with methyl acrylate or methyl methacrylate by a usual 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 this embodiment is manufactured as follows. First, a lithium salt is dissolved in a solvent comprising at least one of propylene carbonate and ethylene carbonate by heating to obtain a lithium salt solution. Next, a powder of a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate was added to this solution.
Heat at 50 ° C to 180 ° C to dissolve the powder and obtain a uniform transparent solution. The solution is diluted 2-3 times by weight with acrylonitrile. A powder obtained by mixing a disulfide-based compound powder and activated carbon carrying polyaniline in a mortar is mixed with a diluted solution, and the obtained slurry is cast on a glass plate. After drying at room temperature, 1 Torr at 60 ° C
The solid electrolyte composition is obtained by vacuum drying under reduced pressure of r. If necessary, LiI, Li _{3
N-LiI-B 2 O 3} , LiI · H 2 O, Li-β-Al 2
A lithium ion conductive powder such as O ₃ may be added.

An activated carbon powder supporting polyaniline was obtained as follows. 1M (M = mol / dm ³ ) aniline and 5
M-Na ₂ SO ₄ in a sulfuric acid aqueous solution at pH = 1.0 and 1.2-1.5 volts relative to a saturated calomel reference electrode.
The polyaniline powder doped with sulfuric acid was obtained by performing constant potential electrolysis with lt. The conductivity of the sulfuric acid-doped polyaniline obtained as described above was measured by pressure molding into pellets having a density of 1.6 g / cm ³ and found to be about 2 S / cm at room temperature. This polyaniline powder was dispersed in a 1 M NaOH aqueous solution, left for about 1 hour, and then filtered and dried to obtain a undoped soluble polyaniline powder. 0.25 g of the soluble polyaniline powder was added to about 150 of 1-N-methylpyrrolidone.
g) to give a blue polyaniline solution. 150 in advance
5 g of activated carbon powder (BP-25, manufactured by Kuraray Chemical Co., Ltd.) vacuum-dried at 17 ° C. for 17 hours was impregnated with 30 g of a polyaniline solution, followed by vacuum drying at 120 ° C. for 5 hours to obtain a polyaniline-supported activated carbon powder.

Next, 3.58 g of lithium trifluorosulfonate, 10.47 g of propylene carbonate and 7.86 g of ethylene carbonate were mixed and heated to 120 ° C. to obtain a homogeneous solution. In this solution, a copolymer of polyacrylonitrile having a molecular weight of 60,000 and methyl acrylate (AN
(/ MA = 10/1, molar ratio) 3 g of powder was mixed and heated to 150 ° C. in a sealed 100 ml Erlenmeyer flask to completely dissolve the copolymer powder to obtain a viscous transparent liquid.
30 g of acetonitrile was added to this liquid to obtain a diluted solution.

2.0 g of 2,5-dimercapto-1,3,4-thiadiazole (DMTD) powder and an average particle size of 3.
An electrode slurry was obtained by mixing 5 g of activated carbon powder carrying 5 μm of polyaniline and 0.5 g of activated carbon powder in a mortar with 10 g of a dilute solution.

The electrode slurry was cast on a glass Petri dish having a diameter of 90 mm, dried for 1 hour in a dry argon gas stream at 40 ° C., and further vacuum-dried at 80 ° C. for 5 hours to obtain a flexible film having a thickness of about 280 μm. Certain sheet-shaped solid electrode composition A
I got

Comparative Example 1 A solid electrode composition B having a thickness of about 300 μm was obtained in the same manner as in Example except that an artificial graphite powder having an average particle size of 2 μm was used instead of the activated carbon powder supporting polyaniline. .

Comparative Example 2 A solid electrode composition C having a thickness of about 300 μm was prepared in the same manner as in the Example except that polyacrylonitrile having a molecular weight of 55,000 was used instead of the acrylonitrile and methyl acrylate copolymer. Obtained.

(Evaluation of Electrode Characteristics) The solid electrode compositions obtained in Examples and Comparative Examples 1 and 2 were punched into a disk having a diameter of 22 mm. In FIG. 1, a positive electrode 1 in which a solid electrode composition was punched into a disk shape was arranged so as to be in contact with the bottom surface of a case 2 made of stainless steel having an inner diameter of 22 mm to form a positive electrode module. On the other hand, 0.3mm in thickness and 17mm in diameter
The opening of the case 2 in contact with the negative electrode 3 of the metallic lithium disk was sealed with a sealing ring 4 made of polypropylene. To form a negative electrode module. The opening of the positive electrode module was closed with the negative electrode module so that the solid electrolyte 6 was in contact with the positive electrode 1, and the upper line of the case 2 was caulked to assemble a battery for evaluating electrode characteristics.

Batteries using the solid electrolyte compositions A, B and C according to the Examples, Comparative Examples 1 and 2 for the positive electrode 1 are referred to as batteries A, B and C, respectively.

Regarding the battery assembled in this manner,
Cyclic voltammograms were measured between 1.5 and 4.0V. The voltage sweep speed was 10 mV / sec.
The circuit voltage and the internal resistance after assembly of each battery were charged at a constant voltage of 4.0 V for 17 hours, and then discharged at a constant current of 500 μA, and the polarization value at a battery voltage of 2.8 V (Table 1).
Are shown together.

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 2.8 V, the polarization value is temporarily stopped and the circuit is opened. After that, the battery is allowed to stand until the battery voltage becomes constant. Obtained as the difference from the voltage. All evaluations are 20
C. was performed.

[0022]

[Table 1]

As shown in Table 1, the battery A of the embodiment
In this case, the polarization value is extremely smaller than those of the batteries B and C of the comparative example.

As is apparent from FIG. 2, in the battery A of the embodiment, the current peak corresponding to the reduction of the disulfide compound DMTD, that is, the charging of the battery is 2.0 to 2.0.
Obtained between 3.2V. Even in the case of using the same polyaniline-supported activated carbon powder, in the battery C 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.
In the battery B of Comparative Example 1, the DMT around 2.0 to 3.2 V was used.
The reduction current corresponding to the current peak of oxidation of D, that is, the discharge current of the battery, is not observed in the voltage range studied.

From the above, the reduction reaction (discharge reaction) of DMTD is catalyzed by polyaniline and activated carbon powder, and is further reduced to room temperature in the presence of a solid electrolyte containing a copolymer of polyacrylonitrile and methyl acrylate. However, it can proceed in a high voltage range of 2.0 to 3.2 V.

[0026]

As apparent from the above description of the examples, according to the solid electrode composition of the present invention, in the electrode in which the activated carbon supporting polyaniline and the disulfide compound are combined, only the conventional disulfide compound is used. This makes it possible to perform electrolysis with a large current, which was difficult. 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 in which high-current charging and discharging can be expected can be formed.

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

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a structure of a battery used for evaluating characteristics of a solid electrode composition according to one embodiment of the present invention.

FIG. 2 is a diagram showing a cyclic voltammogram of each battery using the electrode composition of one example of the present invention, Comparative Example 1 or Comparative Example 2 as a positive electrode, and using lithium metal as a negative electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Case 3 Negative electrode 4 Sealing ring 5 Sealing plate 6 Solid electrolyte

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Teruju Kamihara 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-3-93169 (JP, A) U.S. Pat. No. 4,833,048 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/60 H01B 1/06 H01M 4/02-4/04 H01M 10/40

Claims (1)

(57) [Claims] 1. 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, and polyaniline. A solid electrode composition comprising activated carbon carrying the above, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, a lithium salt, and at least one of propylene carbonate and ethylene carbonate.