JPH0982327A - Electrode material for sulfide-lithium secondary battery and non-aqueous battery - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a sulfide-lithium secondary battery having the above-mentioned problems of the prior art, that is, having excellent cycle life and high energy density. SOLUTION: A sulfide-lithium secondary battery in which a polymer compound having a strong basicity is contained in a composition constituting a positive electrode.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery using a sulfide compound as a positive electrode active material.

[0002]

2. Description of the Related Art Sulfide compounds such as organic disulfide compounds have sulfur-sulfur bonds cleaved by electrolytic reduction to form sulfur-lithium ionic bonds, and electrolytic oxidation cleaves the sulfur-lithium ionic bonds to produce the original compounds. It is a compound that forms a sulfur-sulfur bond, and it has been drawing attention as a high energy density when it is used as a positive electrode active material of a lithium secondary battery.

However, a lithium secondary battery using the above sulfide compound as a positive electrode active material (hereinafter referred to as "sulfide-
Lithium secondary battery)) has a very slow electron transfer due to the nature of the positive electrode active material. Therefore, in order to extract a practical electric current, it is necessary to perform heating at about 60 ° C. Therefore, the applicable range is limited. It was being done.

Further, these sulfide compounds are soluble in the electrolytic solution (non-aqueous solvent) used in lithium secondary batteries. Therefore, it is difficult to use an organic electrolyte in which a lithium salt is dissolved in these non-aqueous solvents, and it is necessary to use a solid or gel electrolyte such as a polymer electrolyte.

Further, since sulfide compounds have poor electronic conductivity, they have been used as a composition mixed with a conductive material such as graphite powder and a polymer solid electrolyte. But,
These compositions also have a drawback in that a network of electrons and ions is not formed, resulting in a large polarization.

As a means for solving these problems, a method using activated carbon carrying a sulfide compound and polyaniline which acts as an electrode catalyst and a conductive material has been reported (JP-A-4-359865). It has been reported that such a structure increases the rate of oxidation and reduction of the positive electrode active material, and enables charging and discharging with a large current at room temperature.

However, also in this method, if the ratio of the sulfide to the aniline unit (one unit of aniline in polyaniline is an aniline unit; the same applies hereinafter) is 1 or more, the charge / discharge cycle life may be significantly shortened. Reported (National Technical Report Vol.40, P464-469, August 1994)
Moon). This is because the number of sulfides that can be captured by one aniline unit is about 1 in the electrode in the discharged state. Therefore, in order to improve the cycle life, it is necessary to set the ratio of the sulfide to the aniline unit to be close to 1, and therefore it is difficult to improve the energy density per unit weight.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a problem of the above-mentioned prior art, that is, an excellent sulfide-lithium secondary battery having excellent cycle life and high energy density.

[0009]

In order to solve the above problems, the present invention provides a sulfide-lithium secondary battery comprising:
It has a constitution in which a polymer compound having a strong basicity is contained in the composition constituting the positive electrode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a polymer compound having a strong basicity means a polymer compound having a basic group such as an amino group. In the above, the polymer compound includes a polyvinyl polymer compound, a polyacetylene polymer compound and the like.

Among the above, the polyvinyl polymer compound has the advantage that it is easily available and can be polymerized easily from the raw material, and at the same time, the basic group of this polymer is three-dimensionally from the main chain. Since it is arranged, the steric hindrance is small and the space for trapping lithium thiolate is large, so that it is possible to trap a large amount of lithium thiolate (when sulfides are trapped on conventionally used polyaniline, it is Holds in two dimensions). On the other hand, in the case of the strongly basic polyvinyl used in the present invention, and since the polyacetylene-based polymer compound has conductivity, it has an advantage that an addition amount of a conductive filler or the like is unnecessary when forming an electrode.

Here, the polymer compound having a strong basicity will be described more specifically. For example, a polyvinyl polymer compound can be represented by the general formula — (CH ₂ —CHX—) _n —, where X is, for example, an amino group (NH ₂
-), aminomethyl group (NH ₂ CH-), aminoethyl group _{(NH 2 CH 2 CH 2 -} , CH 3 CH (NH 2)
-), amino -n- butyl group (NH ₂ CH ₂ CH ₂ CH
_{2 -, CH 3 CH (NH} 2) CH 2 -, CH 3 CH 2 C
H (NH ₂ )-), methylaminomethyl group (CH ₃ NH
CH ₂ —), aminophenyl group (each isomer represented by the formula NH ₂ C ₆ H ₄ —), aminomethylphenyl group (formula C
_{6 H 3 (CH 3) (} NH 2) - isomers) to be expressed by, aminobenzyl group (formula _{NH 2 C 6 H 4 CH 2} - each are expressed by the isomers), a pyridyl group (NC ₅ H ₄ - Is a basic compound such as a hydrazino group (NH ₂ NH-), or an oxopyrrolidinyl group (each isomer of NOC ₄ H _6- ), and the like, it is a high basic polymer compound. There is. In the case of polyacetylene-based polymer compound,
The compound can be represented by the general formula-(CH = CX-) _n- , but when X is a basic group similar to those exemplified in the polyvinyl polymer compound,
It is called a high basic polymer compound.

These highly basic polymer compounds are powdery,
It can be used to form an electrode in any shape such as granular or fibrous. That is, the basic polymer compound having these shapes is mixed with a sulfide compound as an active material and a conductive material to form an electrode by means of compression molding or the like.

Here, when the polymer compound having a strong basicity has thermoplasticity, it can be heat-molded into an electrode by utilizing its property. Further, a thermoplastic resin may be mixed with these electrode materials and heat-molded.
The above-mentioned electrode can exert the maximum effect in terms of energy density when applied to a lithium secondary battery having a lightweight lithium cathode, but a non-aqueous solvent secondary battery using a substance other than lithium as a cathode. It can also be applied to.

As the sulfide compound which is the active material,
Commonly used disulfide compounds, or 2
So-called polysulfide compounds having three or more continuous sulfur-sulfur bonds can be used. When a polysulfide compound is used as the active material, the energy density per unit weight can be increased, so that when combined with the present invention, an extremely high energy density per unit weight can be obtained.

As the conductive material, those which are usually used as conductivity imparting materials such as furnace black can be used. Here, what is marketed as Ketjen black has a high conductivity and is excellent in handleability. From the viewpoint of workability during mixing, it is desirable that these conductive materials be in powder form.

In the lithium secondary battery according to the present invention,
The electrolytic solution is prepared by combining an organic solvent and an electrolyte. That is, since it is not necessary to be limited to the solid electrolyte or gel electrolyte, the degree of freedom of selection is extremely high.
That is, as the above-mentioned organic solvent and electrolyte, any one can be used as long as it is one that is used in a normal non-aqueous solvent battery. That is, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1. , 3-dioxolane, diethyl ether, sulfolane, acetonitrile, propionitrile, anisole and the like can be used alone or in combination.

The electrolyte is LiPF.₆, Li
ClO_Four, LiAsF₆, LiBF _Four, LiCF_ThreeSO
_ThreeEtc. can be used. These will be the right concentrations
So, it is dissolved in the organic solvent to form an electrolyte. cathode
As an electrode normally used in lithium secondary batteries
Can be used. That is, metallic lithium, lithium
Um-aluminum alloy, or lithium and graphite or carbon
Intercalation compounds and the like. These positive electrodes, electrolysis
A battery is formed by combining the liquid and the cathode, at which time
Battery shape, such as flat type, cylindrical type or prismatic type
It can be applied regardless of the shape of the pond.

[0019]

【Example】

<< Example 1 >> [Preparation of positive electrode] 2,5-dimercapto-1,3,4-thiadiazole (manufactured by Kanto Chemical Co., Ltd., powder) 7 as a positive electrode active material
0 parts by weight, 25 parts of poly-4 vinyl pyridine (manufactured by Aldridge Co.) as a basic polyvinyl compound, and 5 parts by weight of Ketjen Black as a conductive material were mixed by a kneader and then pressure-molded by a press machine. , Then 24 at 50 ° C
Vacuum dried for 21 hours, diameter 21mm, thickness 3.5mm
The electrode of was obtained.

[Assembly of Battery] The electrode prepared above was used as a positive electrode, a lithium metal plate was used as a negative electrode, and 1 mol / l of lithium perchlorate was added to an equal volume mixture of propylene carbonate and 1,2-dimethoxyethane. To obtain an electrolytic solution.

A battery A was assembled using these materials. A cross section of this battery A is shown in FIG. In the figure, reference numeral 1 is a positive electrode, and one surface thereof is in contact with the inner surface of the positive electrode can 2. The other surface of the positive electrode faces one surface of the negative electrode 3 (thickness: 1 mm) made of metallic lithium with the separator 6 made of polypropylene nonwoven fabric interposed therebetween. The other surface of the negative electrode 3 is in contact with the negative electrode can 5. It should be noted that the positive electrode 1 is not in contact with the negative electrode can 5 and the negative electrode 3 is not in contact with the positive electrode can 1 because the polypropylene insulating packing 4 is not in contact with the positive electrode can 2.
It is fixed to the inner wall surface, and the inside of the battery A is kept airtight with respect to the outside of the battery by the packing 4. The above-mentioned battery A was assembled in an argon box.

[Evaluation] The battery A was evaluated for charge / discharge cycles. Both charging and discharging were performed with a constant current of 20 mA, charging was performed for 10 hours, and discharging was performed until the voltage reached 2.0V. At this time, the capacity at the time of discharging after the first charging is 1
FIG. 2 shows the relationship between the number of cycles and the discharge capacity ratio when it is set to 00%. It can be seen from FIG. 2 that the discharge capacity in the first cycle is almost maintained even in the 25th charge / discharge cycle.

Example 2 and Comparative Example Battery A of Example 1 except that polyvinylpyrrolidone (powder, manufactured by Aldridge Co., Ltd.) was used as the high basic polymer compound instead of poly-4-vinylpyridine. A battery B was produced in the same manner as in (Example 2). In addition, polyaniline (manufactured by Nitto Denko,
A battery C was produced in the same manner as the battery A of Example 1 except that (powder) was used instead of poly-4-polyvinylpyridine (Comparative Example).

The battery B and the battery C were evaluated for charge / discharge cycles in the same manner as the battery A of Example 1.
The result is shown in FIG. According to FIG. 2, battery B of Example 2
In almost the same manner as the battery A, the discharge capacity after 25 cycles was almost unchanged from the initial capacity, but in the battery C of the comparative example, the capacity was remarkably reduced after about 8 cycles.

The amounts of active materials contained in the batteries A, B and C are equal, and the ratio of sulfide (active material) to basic unit is 2.5 or more. The utilization rate of these active materials, that is, the ratio of the active materials involved in the discharge in the 7th cycle (calculated from the discharge capacity) of the whole active materials contained in each of the batteries A, B and C was 1. The ratio was 5: 1.5: 1.0. This allows
It can be seen that a high energy density can be obtained with the sulfide-lithium secondary battery according to the present invention.

[0026]

In the conventional battery, a large amount of lithium thiolate migrated to the outside of the positive electrode due to diffusion migration during discharge. This lithium thiolate cannot return to the positive electrode even during charging and is oxidized outside the positive electrode to become a lumpy polymer, which is deposited at the interface between the electrolyte and the electrode. The bulk polymer hardly participates in charge and discharge and loses its function as an active material. Repeated charging / discharging increases the amount of such bulk polymer, resulting in a decrease in charging / discharging capacity.

Since the polymer compound having a strong basicity used in the present invention has a stronger basicity than the conventionally used polyaniline-based compound, the desorption of the lithium thiolate formed during discharge from the positive electrode is almost complete. Can be prevented. Since the lithium thiolate has a relatively low acidity, a large amount of lithium thiolate can be retained in the positive electrode by increasing the basicity of the positive electrode as in the present invention.

Due to the above action, the lithium secondary battery using the positive electrode according to the present invention can make the number of sulfide trapped per basic unit to be 1 or more, and therefore the energy density per unit weight can be improved. The cycle life can be extended. Further, due to the configuration unique to the present invention,
Lithium thiolate produced during discharge does not separate from the positive electrode, so the electrolyte is not limited to solid or gel electrolyte. As a result, it is possible to obtain a secondary battery that is excellent in charging and discharging with a large current.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a sulfide-lithium secondary battery of the present invention.

FIG. 2 is a diagram showing a change in discharge capacity rate when discharging is repeated in the batteries of Examples and Comparative Examples.

[Explanation of symbols]

 1 positive electrode 2 positive electrode can 3 negative electrode 4 insulating packing 5 negative electrode can 6 separator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Iizuka 1500 Onjuku, Susono, Shizuoka Prefecture Yazaki Corporation

Claims (8)

[Claims] 1. A sulfide-lithium secondary battery, wherein a polymer compound having a strong basicity is contained in the composition constituting the positive electrode. 2. The sulfide-lithium secondary battery according to claim 1, wherein the polymer compound having a strong basicity is a polyvinyl compound. 3. The sulfide-lithium secondary battery according to claim 1, wherein the polymer compound having a strong basicity is a polyacetylene compound. 4. The sulfide-lithium secondary battery according to claim 1, wherein a conductive powder is added to the composition constituting the positive electrode. 5. An electrode material for a non-aqueous battery, which contains a polymer compound having a strong basicity. 6. The electrode material for a non-aqueous battery according to claim 5, wherein the polymer compound having strong basicity is a polyvinyl compound. 7. The electrode material for a non-aqueous battery according to claim 5, wherein the polymer compound having a strong basicity is a polyacetylene compound. 8. The electrode material for a non-aqueous battery according to claim 5, wherein a conductive powder is added.