JPH1021920A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery whose charging and discharging capacities are scarcely decreased even after repeated charging and discharging by using a material consisting of a polymer compound and alkali siloxyaluminate for a conductive material. SOLUTION: In a secondary battery containing a sulfide type compound as a positive electrode active material, a material consisting of polymer compound such a alkyl methacrylate type polymer and alkali siloxyaluminate is used as a conductive material. As the alkali siloxyaluminate, lithium siloxyaluminate may be used. As the alkyl methacrylate type polymer, methyl methacrylate-2-(trimethylamino)ethyl methacrylate halide copolymer may be used. The mixing ratio of the alkali siloxyaluminate to the alkyl methacrylate type polymer is preferably set to be 0.05-20 by weight. Metal lithium, lithium- aluminum compound, etc., which are generally used for a lithium secondary battery, may be used as an anode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a secondary battery using a sulfide compound as a positive electrode active material.

[0002]

2. Description of the Related Art Lithium secondary batteries generally have a voltage between electrodes of 3 V or more, and are lightweight and high in capacity, and are therefore used in various applications. Many of such lithium-based secondary batteries use cobalt lithium oxide as an active material, but recently, disulfide-based compounds have been attracting attention as an active material because higher capacity is possible. . However, disulfide compounds are
It is soluble in a non-aqueous solvent used as a solution component of an electrolytic solution in a lithium secondary battery, and therefore needs to be insolubilized in order to be used as an electrode active material. As a means of insolubilization, a method has been used in which a disulfide compound is wrapped in a polymer solid electrolyte to form an electrode material.However, even in such an electrode material, when charge and discharge are repeated, the active material is eluted into the electrolytic solution. And resulted in a significant capacity loss.

A technique for solving such a problem is proposed in Japanese Patent Application Laid-Open No. Hei 4-369865 or disclosed in National Technical Report Vol. 40, N
o. As a technique reported by U.S. Pat. No. 4,1994 (hereinafter referred to as "Document A"), there is a method of mixing activated carbon carrying polyaniline, a positive electrode active material (a disulfide-based compound), and a solid polymer electrolyte.

In this method, a high molecular weight copolymer containing methacrylic acid as a main component is mixed with an organic solvent in a gel-like substance (gel body).
Before the gelation occurs, the lithium salt is dissolved in the system, and then the gelled one is processed into a sheet and used as a separator, and the positive electrode is similarly gelled. Before the formation, a disulfide compound, carbon powder, and polyaniline (by chemical polymerization), which are active materials, are dissolved and dispersed, and then gelled.

[0005] In the lithium secondary battery according to this technique, the above-mentioned problem of the capacity reduction was alleviated, but the solution was not completely solved, and the capacity reduction due to repeated charging and discharging was inevitable. The reason for this is that, as described in Document A above, the doping reaction of the disulfide compound into polyaniline is related to the doping reaction of the electrolyte anion into polyaniline and the competitive reaction. It is considered that a disulfide compound is generated which is not doped to the metal oxide and is not involved in the subsequent charge / discharge capacity, and is gradually accumulated.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an excellent secondary battery which solves the above-mentioned drawbacks of the prior art and in which the decrease in charge / discharge capacity due to repetition of charge / discharge is extremely small.

[0007]

The secondary battery of the present invention has a structure using a conductive material comprising a polymer compound and an alkali siloxyaluminate. With such a configuration, only a sulfide compound causes a doping reaction to polyaniline, and a secondary battery with a very small decrease in capacity even after repeated charging and discharging can be configured.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The alkali in the above-mentioned alkali siloxyaluminate indicates an alkali metal. Such materials include, for example, lithium siloxy aluminate and sodium siloxy aluminate. Here, the alkali siloxy aluminate has a structure as shown in Chemical formula 1. In the chemical formula 1, M represents an alkali metal atom. Incidentally, when the alkali metal is, for example, lithium, as an electrolyte of a lithium ion battery,
For example, when it is sodium, it can be used as an electrolyte of a sodium ion battery.

It is preferable that the terminal group of the above-mentioned alkali siloxyaluminate is protected with an aromatic hydrocarbon such as a phenyl group or an alkyl group because it is chemically stable. Where ethyl,
Synthesized as propyl, butyl or phenyl group
It is easy to obtain. In addition, when the said terminal group is a methyl group, there exists some difficulty in the preservability and stability of a raw material.

[0010]

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Such an alkali siloxy aluminate can be obtained, for example, by reacting a dialkylsilane diol with lithium aluminum hydride. It is also possible to appropriately select different functional groups instead of the alkyl groups. When the alkali siloxyaluminate is used together with a polymer compound, the degree of freedom of its movement is reduced, and as a result, the cation transport number of this system is improved.
Here, the polymer compound is desirably a crosslinkable polymer compound. That is, the mobility of alkali siloxyaluminate is greatly reduced by the three-dimensional network structure of the crosslinkable polymer, so that the cation transport number is significantly improved. Particularly, when the molecular weight of the alkali siloxyaluminate is large (for example, when it is larger than about 1000), a good effect can be obtained.

Here, it is preferable that the alkali siloxyaluminate and the above-mentioned polymer compound are chemically bonded because the movement of anions is extremely reduced. Such a chemical bond between the alkali siloxyaluminate and the polymer compound may be an ordinary covalent bond. However, by using an organic polymer compound having a quaternized amino group, nitrogen of the amino group and aluminum of the alkali siloxyaluminate can be ion-bonded. Examples of a method for quaternizing an amino group include a method of reacting an alkyl halide with a tertiary amino group. here,
Since the alkyl group of the alkyl halide affects the gel-forming ability described below, it is necessary to study in advance to obtain a good gel. Here, in the alkyl halide,
Methyl iodide has sufficient reactivity and is liquid at room temperature, so it is easy to handle. Further, the quaternization of the tertiary amino group with an alkyl halide such as methyl iodide does not need to be performed for all the tertiary amino groups, and even if there is a tertiary amino group remaining without being quaternized. Good. Here, when the number of quaternary amino groups is increased, the number of sites that can be bonded to alkali siloxyaluminate increases, and the number of cross-linking sites increases. Therefore, the flexibility of the electrode material can be adjusted by adjusting the number of quaternary amino groups.

Examples of such organic polymer compounds having a quaternized amino group include a methyl methacrylate / 2- (trimethylamino) ethyl iodide copolymer (methyl methacrylate unit (hereinafter also referred to as “MMA”). ) And 2- (trimethylamino) ethyl iodide methacrylate unit (hereinafter also referred to as "TMAEMA")
A copolymer comprising: Hereinafter, it may be referred to as “MMA-TMAEMA”). Further, instead of methyl methacrylate, a copolymer having a vinyl monomer such as ethyl methacrylate, butyl methacrylate, methyl acrylate, and styrene can be used. Further, the copolymer of the above vinyl monomer and vinylpyridine can be quaternized and used, which is easy.

MMA-TMAEMA can be obtained by copolymerizing methyl methacrylate and 2- (dimethylamino) ethyl methacrylate in the presence of a catalyst, and then reacting with methyl iodide. The organic polymer compound obtained by chemically bonding alkali siloxyaluminate to MMA-TMAEMA by the above-mentioned ionic bond (the concept of this is shown as Chemical Formula 2) is an excellent electrode material satisfying all of the transport number, conductivity and flexibility. Can be formed.

[0015]

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It is desirable that the amount of the alkali siloxyaluminate to be mixed with the polymer compound having a quaternary amino group is 0.05 to 20.
When the amount of the alkali siloxyaluminate is 0.05
If it is less than 20, the conductivity is low, while if it exceeds 20, the flexibility tends to decrease.

Further, a polymer comprising a vinyl monomer unit having no quaternary amino group and a vinyl monomer unit having a quaternary amino group, such as a methyl methacrylate / 2- (trimethylamino) ethyl iodide copolymer. In the compound, the molar ratio of a vinyl monomer unit having no quaternary amino group such as a methyl methacrylate unit to a vinyl monomer unit having a quaternary amino group such as a 2- (trimethylamino) ethyl iodide methacrylate unit (hereinafter referred to as “copolymerization”) Ratio) is preferably 5 or more and 50 or less. When the molar ratio is less than 5, the crosslinking of the polymer compound having a quaternary amino group by the alkali siloxyaluminate becomes too much and becomes hard. On the other hand, when the molar ratio is more than 50, the crosslinking decreases and the solvent is used. No gel body is formed.

The above gel body can be used as an electrolyte. Further, it can be used also as a separator and an electrolyte for preventing a short circuit between electrodes. Such a separator / electrolyte is an excellent one with little polarization. The gel body may be mixed with a conductive material such as carbon black, a stabilizer or the like or a reinforcing material as necessary to improve various performances and various characteristics.

In the present invention, the term "sulfide compound" means not only a disulfide organic compound, but also a trisulfide organic compound having a trisulfide bond such as sulfur-sulfur-sulfur, or a compound having a sulfur-sulfur bond continuous thereto. including. It is generally said that up to six such continuous sulfur bonds are possible. Also,
In the present invention, the sulfide-based secondary battery refers to electrolytic oxidation
1 shows a secondary battery having, as an active material, a sulfide-based compound having a sulfur-sulfur bond, which is combined and restarted by electrolytic reduction.

As the solvent used in the present invention, an organic solvent generally used for a non-aqueous secondary battery can be used.
For example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxymethane, γ-butyrolactone, tetrahydrofuran,
It is a single solvent or a mixed solvent of two or more of 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, dimethyl ether, sulfolane, acetonitrile, propionitrile, anisole and the like. However, depending on the combination of the gel-forming substance and the above-mentioned solvent, there is a possibility that a gel body is not formed or a trouble such as instability is caused. Therefore, it is necessary to examine in advance whether or not these troubles occur.

As the negative electrode, an electrode usually used for a lithium secondary battery can be used. That is, examples thereof include metallic lithium, a lithium-aluminum alloy, and an interlayer compound of lithium and graphite or carbon.
A secondary battery is formed by combining the positive electrode, the electrolytic solution, and the negative electrode. The secondary battery can be applied regardless of the secondary battery shape at that time, that is, a secondary battery shape such as a flat type, a cylindrical type, or a square type.

[0022]

Embodiments of the present invention will be described below. In the following, all operations in which nitrogen, oxygen, water, and the like were liable to have an adverse effect were performed in an argon atmosphere. [Preparation of Secondary Battery Using MMA-TMAEMA Bridged Polymer: Example 1] [Synthesis of Lithium Siloxyaluminate: See Chemical Formula 3] A lithium siloxyaluminate having a phenyl substituent was selected as an alkali siloxyaluminate. Were synthesized as shown in Table 1.

That is, diphenylsilanediol 40 mm dried in a 200 ml flask under a nitrogen atmosphere.
ol and 75 ml of tetrahydrofuran were dissolved therein.
This was cooled to -80 ° C and stirred, and 1 mol / l- lithium lithium hydride was adjusted to 20 mmol.
Was slowly added dropwise lithium aluminum hydride-tetrahydrofuran solution, gradually returned to room temperature, it reacted by stirring an additional 2 hours, and then dried under reduced pressure to obtain a lithium siloxy aluminate ⁽¹ H-NMR (dimethyl formamide deuterium substituted compounds _{(DMF-d 6) / TMS} )
δ (ppm): 6.90 (m. 10H, Arom)
Here, δ is a value when tetramethylsilane is used as the internal standard. Hereinafter the same). FIG. 1 shows the infrared absorption spectrum of this product. When the molecular weight was separately measured by GPC chromatography, it was found that the molecular weight was 580.
It was found that the compound had a two-edge molecular weight distribution having peaks near 0 and 2300, respectively.

[0024]

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[Methyl methacrylate / methacrylic acid 2-
Synthesis of (dimethylamino) ethyl copolymer: see Chemical formula 4]
According to the following procedure, a methyl methacrylate-methacrylic acid 2- (trimethylamino) ethyl iodide copolymer (MMA-TMAEMA) was selected and synthesized.

First, methyl methacrylate 2 from which a polymerization inhibitor was removed by vacuum distillation was placed in a 100 ml flask.
00 mmol, similarly, 2- (dimethylamino) ethyl methacrylate 10 mmol from which the polymerization inhibitor was removed, α,
α'-azobisisobutyronitrile (hereinafter “AIBN”)
10 mmol) and tetrahydrofuran 50
ml was added. Then, the reaction was carried out by heating to 60 ° C. The reaction solution was dropped into 200 ml of methanol, and then the lower layer polymer was taken out by decantation. After washing several times with methanol, a milky white methyl methacrylate / 2- (dimethylamino) ethyl methacrylate copolymer was obtained. The molar ratio of methyl methacrylate unit to 2- (dimethylamino) ethyl methacrylate unit was 18.7: 1 as a result of NMR analysis. Analysis by GPC showed that the product had an average molecular weight of 25 × 10 ⁴ .

[Synthesis of MMA-TMAEMA: see Chemical Formula 4] 10 g of the above methyl methacrylate-2- (dimethylamino) ethyl methacrylate copolymer was placed in a 200 ml flask and dissolved in 100 ml of acetone. To this was slowly added methyl iodide (15 mmol), and the mixture was stirred at room temperature for 2 hours to react (the solution turned yellow). This one
The synthesized product was precipitated by dropping into 00 ml of hexane, and the lower layer material was taken out by decantation. The synthesized product was further washed twice with 50 ml of hexane and then dried under reduced pressure to obtain yellow solid MMA-TMAEMA.

[0028]

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[Preparation of cross-linked polymer] The above-mentioned lithium siloxyaluminate was prepared using MMA-TM as described below.
The crosslinked polymer was obtained by chemical bonding to AEMA. First, 3 g of lithium siloxyaluminate was placed in a 100 ml flask, and dissolved by adding 50 ml of dimethylformamide.

On the other hand, 2.5 g of MMA-TMAEMA
In a 00 ml flask, 15 ml of dimethylformamide was added and dissolved, and this solution was slowly added dropwise to the lithium siloxyaluminate-dimethylformamide solution prepared above, and reacted at room temperature for 2 hours. This reaction solution is
By dropping into 00 ml of acetone, the crosslinked polymer α was precipitated. This was washed twice with 50 ml of acetone and dried under reduced pressure.

[Synthesis of Active Material] As the active material, 2,5-
Dimercapto-1,3,4-thiadiazole polymer was selected and synthesized as shown below. A solution prepared by dissolving 0.2 mmol of 2,5-dimercapto-1,3,4-thiadiazole in 50 ml of acetone is placed in a 200 ml flask, and 0.45 mmol of iodine is added to 100 ml of acetone.
1 was slowly added dropwise, and a brown precipitate was obtained. The precipitate was taken out, washed with acetone until it became pale yellow, and dried under reduced pressure to give 2,5-dimercapto-
A 1,3,4-thiadiazole polymer was obtained. (Preparation of Positive Electrode) The above-mentioned crosslinked polymer α0.5g, gamma-butyrolactone 5g, carbon black 0.1g, 2,5-dimercapto-1,3,4-
1.5 g of thiadiazole polymer and 0.9 g of polyaniline (Nitto Denko's Anilead) were mixed and dispersed uniformly, and the mixture was uniformly applied to one surface of a copper sheet (thickness: 20 μm) as a current collector, Subsequently, the sheet was dried under reduced pressure at 80 ° C. to obtain a sheet having a thickness of 1500 μm,
m and used as a positive electrode hereinafter. (Preparation of separator) The above-mentioned crosslinked polymer α1.5g and γ-butyrolactone 3.5g, which were pulverized into fine powder, were uniformly mixed, developed on a glass petri dish, and then heated to 50 ° C to be uniform. Thus, a sheet-like polymer gel film (thickness: 800 μm) was obtained. This is 16
mm, and was used as a separator hereinafter. (Preparation of Sealed Secondary Battery) The positive electrode, the separator, and a metal lithium foil having a thickness of 200 μm punched out to a diameter of 15 mm were stacked, placed in a stainless steel case having an inner diameter of 16 mm, and a sealed secondary battery A was prepared. Example 1).

[Preparation of Secondary Battery Using Methyl Methacrylate / 4-vinylpyridine Copolymer Crosslinking Polymer: Example 2] In Example 2, methyl methacrylate / 4-vinylpyridine methyl iodide copolymer was converted to lithium. A secondary battery using a material in which siloxyaluminate was immobilized (the concept is shown in Chemical Formula 5) was produced.

[0033]

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[Synthesis of methyl methacrylate / 4-vinylpyridine copolymer] In a 100 ml flask, 200 mmol of methyl methacrylate (the polymerization inhibitor was removed in advance by distillation under reduced pressure), 10 mmol of 4-vinylpyridine
1, α, α'-azobisisobutylnitrile 1 mmol
And 50 ml of tetrahydrofuran, and then reacted by heating to 60 ° C. This reaction solution was dropped into 200 ml of methanol to precipitate a reaction product. This was washed twice with 100 ml of methanol and then dried under reduced pressure to obtain a milky white methyl methacrylate-4-vinylpyridine copolymer.

[Quaternization of Copolymer] 10 g of the above methyl methacrylate / 4-vinylpyridine copolymer was added to 200 ml.
It was dissolved in 100 ml of acetone in a flask, and 15 mmol of methyl iodide was slowly added dropwise thereto, and reacted at room temperature for 2 hours. Thereafter, the reaction solution was dropped into 100 ml of hexane to precipitate a quaternized copolymer. This was washed twice with 50 ml of hexane and dried under reduced pressure to obtain a quaternized copolymer (quaternized organic polymer compound) as a yellow solid.

[Immobilization of Lithium Siloxyaluminate and Preparation of Battery B] The same lithium siloxyaluminate used in Battery A was immobilized on the quaternary organic polymer compound. That is, the above methyl methacrylate-4-
3 g of a quaternary organic polymer compound of vinyl pyridine copolymer with methyl iodide was placed in a 200 ml flask, and dissolved by adding 15 ml of dimethylformamide. In this solution,
Separately, a solution in which 2.5 g of lithium siloxyaluminate was dissolved in 15 ml of dimethylformamide was slowly dropped in a 200 ml flask, and reacted at room temperature for 2 hours.

The reaction solution was added dropwise to 100 ml of acetone to cause precipitation, and the precipitate was washed twice with 50 ml of acetone to obtain a crosslinked polymer β. Hereinafter, Battery B was produced in the same manner as Battery A, except that the bridging polymer β was used instead of the bridging polymer α.

[Preparation of Secondary Battery According to Prior Art] Polyacrylonitrile-methyl acrylate copolymer in the form of fine powder (MONOMER-POLYMER & DAJACL)
ABORATORIES, INC. Made. Catalog No.
8966) 1.5 g and 1 mol / l-lithium perchlorate (LiClO ₄ ) -gamma-butyrolactone solution 3.0 g
Was mixed and made uniform, then spread on a glass Petri dish, and heated to 120 ° C. to obtain a uniform polymer gel sheet (800 μm in thickness). This sheet is 16mm in diameter
And used as a separator.

On the other hand, the positive electrode was manufactured as follows. That is, the same finely powdered polyacrylonitrile-methacrylate copolymer as used in Example 1 (0.4 g, 0.1 g) was used.
mol / l-lithium perchlorate (LiClO ₄ ) -gamma-butyrolactone solution 10 ml, carbon black 0.1.
1 g, 1.5 g of the same 2,5-dimercapto-1,3,4-thiadiazole polymer used in Example 1 and 0.9 g of polyaniline were uniformly mixed. This was applied to a copper sheet in the same manner as the positive electrode of the secondary battery A, and dried under reduced pressure at 80 ° C. to obtain a 1500 μm thick sheet, which was punched out to a diameter of 14 mm and used as a positive electrode hereinafter.

The above-mentioned positive electrode, separator and metallic lithium foil having a thickness of 200 μm punched out to a diameter of 15 mm were overlaid and placed in a stainless steel case having an inner diameter of 16 mm, thereby producing a sealed secondary battery C (Comparative Example).

[Evaluation of Characteristics of Secondary Battery] A change in discharge capacity with respect to the capacity at the first discharge when charging and discharging were repeated was examined. At this time, charging is performed until the secondary battery voltage reaches 4.5 V under a current regulation of 1.5 mA, and discharging is performed at 1.5 mA.
Under the condition that the battery was discharged until the discharge end voltage reached 2.0 V. The results are shown in FIG. As is clear from FIG. 1, the secondary battery C of Comparative Example 2 was significantly deteriorated as the charge and discharge were repeated, but the cycle batteries of the secondary batteries A and B according to the present invention showed extremely little cycle deterioration.

That is, in the secondary battery C of the comparative example, the doping of 2,5-dimercapto-1,3,4-thiadiazole of the cathode material into polyaniline and the lithium salt of the electrolyte were repeated during repeated charging and discharging. It is considered that the doping of polyaniline with perchlorate ion (ClO ₄ ⁻ ), which is an anion, is a competitive reaction. For this reason, the remaining 2,5-dimercapto-1,
It is considered that 3,4-thiadiazole is generated and is not involved in the next charge / discharge, and the discharge capacity is reduced each time charge / discharge is repeated.

On the other hand, in the secondary battery A according to the present invention, since the anion is bound to the polymer compound, and the anion is bound and collected by the gel-forming polymer compound, no migration occurs. Therefore, it is considered that since the doping of the anion of the electrolyte hardly occurs, the result that the decrease in the discharge capacity was extremely small even when the cycle was repeated was obtained.

[0044]

According to the present invention, it is possible to obtain a sulfide-based secondary battery in which the discharge capacity is not significantly reduced when charge and discharge are repeated.

[Brief description of the drawings]

FIG. 1 is a view showing an infrared absorption spectrum of lithium siloxyaluminate obtained in an example.

FIG. 2 is a diagram showing the influence on the discharge capacity of a battery A and a battery B of an example according to the present invention and a battery C of a comparative example when charging and discharging are repeated.

Claims (6)

[Claims] 1. A secondary battery using a conductive material comprising a polymer compound and an alkali siloxyaluminate. 2. The secondary battery according to claim 1, wherein the polymer compound is an alkyl methacrylate polymer. 3. The method according to claim 1, wherein the alkyl methacrylate-based polymer is selected from the group consisting of methyl methacrylate / methacrylic acid 2- (trimethylamino) ethyl halide copolymer and methyl methacrylate / 4-vinylpyridine ethyl halide copolymer / Alternatively, the secondary battery is a mixture thereof. 4. The composition according to claim 2, wherein the amount of the alkali siloxyaluminate to the alkyl methacrylate-based polymer is 0.05 to 20 by weight.
Or the secondary battery according to claim 3. 5. The alkyl methacrylate-based polymer is a copolymer comprising methyl methacrylate and a quaternized nitrogen-containing comonomer, wherein a quaternary methyl methacrylate unit present in the copolymer is present. The secondary battery according to any one of claims 2 to 4, wherein a molar ratio to a comonomer unit having a converted nitrogen is 5 or more and 50 or less. 6. The secondary battery according to claim 2, wherein the alkali siloxy aluminate is lithium siloxy aluminate.