JP3237261B2 - Reversible composite electrode and lithium secondary battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible composite electrode made of an organic compound used for electrochemical devices such as a battery, an electrochromic display device, a sensor and a memory, and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art U.S. Pat. No. 4,833,048 proposes a disulfide compound as a cathode material for a high energy-density lithium secondary battery using lithium metal or a lithium alloy as a negative electrode. 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 is combined with the cation (M ⁺ ) in the electrolytic bath by RS ^- M ^+.
To produce the salt represented by This salt returns to the original RSSR by electrolytic oxidation. A metal-sulfur secondary battery combining a metal M for supplying and trapping cations (M +) and 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.

[0003] The inventors of the present invention have a high energy density of a disulfide compound and have a large current electrolysis (charge / discharge) even at room temperature.
A reversible composite electrode in which a disulfide compound and a π-electron conjugated conductive polymer are combined has been proposed as an electrode with excellent reversibility that can be used.

A π-electron conjugated conductive polymer complexed with a disulfide compound acts as an electrode catalyst during the electrolytic oxidation and reduction of the disulfide compound, and the oxidation reaction and reduction reaction of the disulfide compound alone having a voltage of 1 volt or more. The potential difference between the electrodes is reduced to 0.1 volt or less to promote the electrode reaction and enable electrolysis (charge / discharge) with a large current even at room temperature. In electrolytic oxidation, first, a π-electron conjugated conductive polymer (hereinafter referred to as PAI) is oxidized,
The oxidized form of AI oxidizes the disulfide compound (hereinafter referred to as SS) to return to the original reduced form, and SS forms polymer.
An oxidized form is formed. In the electrolytic reduction, the PAI is first reduced, and the reduced form of the PAI reduces the polymerized oxidized form of SS and returns to the oxidized form, and a reduced form (monomer) of SS is generated.

[0005]

However, if such an oxidation-reduction process of SS is repeated, the oxidized and polymerized SS aggregates to form an insulating mass, and the polymerized oxidized product is removed. 100% of original monomer even if reduced
I couldn't go back, and there was a problem that gradually became inactive. When such a composite electrode is used as the positive electrode of the battery, there is a problem that the discharge capacity gradually decreases when the battery is repeatedly charged and discharged.

According to the present invention, it has been found that the easiness and difficulty of the generation of the insulating lump vary greatly depending on the type of SS used, and as a result, the above-mentioned problem has been solved.

[0007]

According to the present invention, 4,5-diamino-2,6-dimercapto, a specific SS compound in which oxidized and polymerized SS hardly aggregates to form an insulating mass. Pyrimidine (hereinafter, referred to as DDPy) is used in combination with a π-electron shared electron conductive polymer.

[0008]

[Function] 4,5-Diamino-2,6-dimercaptopyrimidine (DDPy) has two amino groups in one molecule, and due to the action of these amino groups, it can be transferred to the electrolyte even when polymerized. Satisfactorily is maintained, and the formation of insulating lumps is suppressed.

[0009]

EXAMPLE As a π-electron shared conductive polymer complexed with DDPy, 0 to ±± with respect to an Ag / AgCl electrode such as polyaniline, polypyrrol, polythiophene, and polyacene.
A conductive polymer that causes a highly reversible oxidation-reduction reaction at 1.0 volt is effectively used. In particular, DDPy having two amino groups has a very good affinity for polyaniline having a quinone diimine structure and a phenylenediamine structure, and in addition to the good solubility of DDPy in the electrolyte,
When complexed with polyaniline, the formation of insulating lumps is further alleviated due to the good affinity.

As the metal ions when the polymerized DDPy is reduced to form a salt, protons can be used in addition to alkali metal ions and alkaline earth metal ions. When a proton is used, a metal hydride such as LaNi ₅ is used as an electrode for supplying and capturing the proton, and an electrolyte that conducts the proton is used, a battery having a voltage of 1 to 2 volts can be formed. When lithium ion is used as the alkali metal ion, a lithium battery such as lithium metal or lithium-aluminum is used as an electrode for supplying and capturing lithium ion, and a battery having a voltage of 3 to 4 volts is obtained by using an electrolyte that conducts lithium ion. Can be configured. In this case, particularly as an electrolyte, a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, a lithium salt, propylene carbonate,
By using a solid electrolyte composition containing at least one solvent selected from ethylene carbonate, diethylene carbonate, dimethoxyethane, and sulfolane, the formation of an insulating mass can be further reduced. A solid electrode composition is obtained by dispersing and mixing a composite electrode composed of DDPy and polyaniline in a solid electrolyte composition. In such a solid electrode composition, DDPy or DDPy polymer is used.
Is partially or entirely dissolved in the solid electrolyte composition, and the dissolved monomer or polymer is well fixed on or in the solid polyaniline by the interaction with the polyaniline, so that DDPy or DDPy
The present inventors believe that the polymer is in a very uniformly dispersed state, and that the formation of insulating lumps is effectively suppressed.

The compounding of DDPy and the π-electron conjugated conductive polymer can be carried out by a known method such as mixing, impregnation, eutectoid, and recoating. For example, a composite electrode can be obtained by forming a fibril layer of a conductive polymer on a stainless steel substrate by electrolytic polymerization, impregnating the fibril layer with a solution in which a salt of DDPy is dissolved, and removing the solvent. it can. The DDPy particles are dispersed in a solvent in which a π-electron conjugated polymer is dissolved, and then the solvent is removed.
The composite may be formed by forming a layer of a π-electron conjugated polymer on the surface of the Py particles. Compounding can also be performed by mixing the π-electron conjugated polymer powder obtained by chemical polymerization or electrolytic polymerization with DDPy powder.

Example 1 Lithium borofluoride (LiB)
F ₄ ) 2.33 g, propylene carbonate 10.47
g of ethylene carbonate and 7.86 g of ethylene carbonate.
Heated to ℃ to obtain a homogeneous solution. To this solution was added a polyacrylonitrile / methyl acrylate having a molecular weight of 50,000 (20: 1).
(Mole ratio) 3 g of the copolymer 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 an electrolyte solution.

1.5 g of DDPy powder (manufactured by Aldrich)
And borofluoric acid (HBF)_Four) Acid persulfate in acid
H obtained by chemically polymerizing aniline using monium
BF _FourMortar with 1.0 g of polyaniline powder doped with
Mix the mixed powder obtained by mixing with 10 g of electrolyte solution
Thus, an electrode slurry was obtained. Electrode slurry with a diameter of 90m
m, and dried in a 60 ° C dry argon atmosphere.
Dry for 1 hour in a stream and vacuum dry at 60 ° C for 1 hour
As a result, a flexible sheet-like solid having a thickness of about 160 μm is formed.
A shaped electrode composition A was obtained. Separately, the electrolyte solution
Only 10 g is cast on a 90 mm glass dish, and
And dried at 60 ° C. to form a gel electrolyte membrane A having a thickness of 380 μm.
Obtained.

A solid electrode composition A, a gel electrolyte membrane A, and a 80 μm-thick lithium metal foil were punched into a 13 mm diameter to produce a battery having the configuration shown in FIG. 1 in a Teflon cylinder having an inner diameter of 13 mm. In FIG. 1, 1 is a metal lithium anode,
2 is a gel electrolyte membrane and 3 is a solid electrode composition A acting as a positive electrode.

Comparative Example 1 As a disulfide compound, D
Commercially available special grade reagent 2,5-dimercapto- in place of DPy
A solid electrode composition B having a thickness of 170 μm was prepared in the same manner as in Example 1, except that 1,3,4-thiadiazol (hereinafter referred to as DMcT) was used. Further, in the same manner as in Example 1, a battery B having a diameter of 13 mm comprising a gel electrolyte A and a lithium metal negative electrode was formed using the solid electrode composition B as a positive electrode.

These batteries A and B are referred to as 4.05-5.0.
A charge / discharge test was performed at 20 ° C. at a constant current of 0.27 mA within a range of 1.5 V. FIG. 2 shows the relationship between the value of the discharge capacity in each cycle and the number of charge / discharge cycles when the discharge capacity in the first cycle is 100%.

As is clear from FIG. 2, the battery A using DDPy as the disulfide compound according to the present invention has a capacity of 3
Even after 0 cycles, a capacity of 90% or more in the first cycle can be obtained. On the other hand, the battery B of the comparative example using DMcT as the disulfide compound gives only about 60% of the capacity in the first cycle after 30 cycles.

Example 2 In a polyethylene triol solution obtained by dissolving 1 part by weight of polyethylene triol having a molecular weight of 3000 in 20 parts by weight of methyl ethyl ketone, the molar ratio (EO / Li) of ethylene oxide to lithium was 8 /
1 is obtained by dissolving lithium perchlorate so as to obtain 1 part by weight of artificial graphite powder having an average particle size of 0.3 μm, and neutralizing DDPy with lithium hydroxide and then oxidizing and polymerizing with iodine. 4 parts by weight of the powder were dispersed. To this dispersion, an equimolar amount of tolylene diisocyanate was added and mixed with polyethylene triol, reacted at 80 ° C. for 2 hours, cast on a 90 mm-diameter dish, and dried at 80 ° C. in vacuo.
By holding for 4 hours, a solid electrode composition C having a thickness of 160 μm was obtained. Further, an equimolar amount of tolylene diisocyanate was added to a polyethylene triol solution in which lithium perchlorate was dissolved, and the mixture was reacted at 80 ° C. for 2 hours.
And a polymer electrolyte having a thickness of about 300 .mu.m was obtained by holding at 80.degree. C. in vacuum for 24 hours. A battery C was prepared in which the electrode composition thus obtained was used as a positive electrode, the polymer electrolyte was used as an electrolyte membrane, and lithium metal having a structure similar to that shown in FIG. 1 was used as a negative electrode.

Comparative Example 2 A solid electrode composition D having a thickness of 170 μm was prepared in the same manner as in Example 2 except that DMcT was used instead of DDPy. Battery D was configured in the same manner as in Example 2. These batteries C and D were 4.05 to 1.5
A charge / discharge test was performed at 100 ° C. at a constant current of 0.27 mA within the range of V. FIG. 3 shows the relationship between the value of the discharge capacity in each cycle and the number of charge / discharge cycles when the discharge capacity in the first cycle is 100%.

As is apparent from FIG. 3, the battery C using the polymer of DDPy as the disulfide compound according to the present invention has a 90% charge in the first cycle even after 30 cycles.
The above capacity can be obtained. On the other hand, a battery D of a comparative example using a polymer of DMcT as a disulfide compound
Then, after 30 cycles, about 65% of the first cycle
Only give the capacity.

[0021]

According to the present invention, a composite electrode using 4,5-diamino-2,6-dimercaptopyrimidine (DDPy) as a disulfide compound and a π-electron conjugated conductive polymer is reversible. In particular, when used for a positive electrode of a lithium secondary battery, extremely excellent charge / discharge cycle characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a lithium secondary battery using a composite electrode as a positive electrode;

FIG. 2 is a diagram showing a relationship between a relative value of a discharge capacity and the number of charge / discharge cycles.

FIG. 3 is a diagram showing a relationship between a relative value of a discharge capacity and the number of charge / discharge cycles.

Continuation of front page (56) References JP-A-4-359865 (JP, A) JP-A-4-264363 (JP, A) JP-A-5-135768 (JP, A) JP-A-5-135769 (JP) JP-A-5-74459 (JP, A) JP-A-50-53381 (JP, A) JP-A-56-103870 (JP, A) JP-A-63-225475 (JP, A) 2-158059 (JP, A) JP-A-5-135767 (JP, A) US Pat. Electrochem. SoC. , Vol. 136, no. 9 (Sep. 1989) p. 2570−2575 (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02 H01M 4/60 H01M 10/40

Claims (5)

(57) [Claims] 1. A reversible composite electrode comprising 4,5-diamino-2,6-dimercaptopyrimidine and a π-electron conjugated conductive polymer. 2. The method according to claim 1, wherein the 4,5-diamino-
In 2,6-dimercaptopyrimidine, a sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-metal ion (including proton) bond, and the sulfur-metal ion bond is replaced with the original sulfur-sulfur bond by electrolytic oxidation. A reversible composite electrode that is a regenerated organic compound. 3. The method according to claim 1, wherein 4,5-diamino-
2,6-dimercaptopyrimidine is 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. Some reversible composite electrodes. 4. A composition comprising: 4,5-diamino-2,6-dimercaptopyrimidine; polyaniline, which is a π-electron conjugated conductive polymer; and an electrolyte, wherein the electrolyte is propylene carbonate, ethylene carbonate. At least one solvent selected from the group consisting of -carbonate, diethylene carbonate, dimethoxyethane, and sulfolane; and a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate;
A reversible composite electrode comprising a lithium salt. 5. A positive electrode layer, an electrolyte layer, and a negative electrode layer made of metallic lithium or a lithium alloy, wherein said positive electrode layer comprises 4,5-diamino-2,6-dimercaptopyrimidine, acrylonitrile and acrylic acid. A copolymer of methyl or methyl methacrylate, a lithium salt, and a solvent, wherein the electrolyte layer includes a copolymer of acrylonitrile and methyl acrylate or methyl methacrylate, a lithium salt, and a solvent. A lithium secondary battery, wherein the solvent is at least one solvent selected from propylene carbonate, ethylene carbonate, diethylene carbonate, dimethoxyethane, and sulfolane.