JP2001135296A - Separator for battery and nickel-hydrogen battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for battery that reveals superior self- discharging property. SOLUTION: This separator is produced through processing a synthesized resin surface with oxides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a battery separator,
In particular, the present invention relates to a separator suitable for a storage battery and a sealed nickel-metal hydride storage battery using the same.

[0002]

2. Description of the Related Art Hydrogen storage alloys are used as negative electrode materials for secondary batteries because they can store and release hydrogen by an electrochemical reaction. Conventionally, considering the life characteristics and oxygen gas ionization ability,
An alloy of MmNi ₅ (Mm is a mixture of rare earth elements) having a Cu ₅ type crystal structure is used, and many proposals have been made on such a hydrogen storage alloy.

[0003] By selecting an alloy having a large hydrogen storage capacity as a negative electrode material, a negative electrode having a large discharge electric capacity is possible, and an alkaline storage battery having a large energy density can be expected by combining it with a nickel oxide positive electrode. Also,
Considering the market for alkaline storage batteries, a completely sealed type is preferable to an open type. Against this background, high-capacity sealed nickel-hydrogen storage batteries using hydrogen storage electrodes have attracted attention. In this battery system, the corrosion resistance of the hydrogen storage alloy, the decrease in discharge capacity due to repeated charging and discharging,
Problems such as an increase in the internal pressure of the battery due to a decrease in the ability to absorb oxygen generated from the positive electrode at the time of overcharging hinder practical use. As means for solving these problems, various choices of materials for the hydrogen storage alloy have been proposed, and those satisfying the initial characteristics have been obtained.

However, in order to complete a practical battery, it is necessary to solve problems such as cycle life and self-discharge.
In particular, it has been found that the self-discharge of the sealed nickel-hydrogen storage battery becomes larger than that of the sealed nickel-cadmium storage battery when left at a high temperature. This is because the hydrogen storage alloy negative electrode has a greater reducing power than the cadmium negative electrode, and hastens the reduction rate of impurities in the electrolyte, resulting in a reduction in capacity. As a means for solving this problem, it is conceivable to select a material having a low hydrogen dissociation pressure. But,
It is known that the use of a material having an extremely low hydrogen dissociation pressure causes a decrease in the discharge capacity of the hydrogen storage electrode and a decrease in the operating voltage.

On the other hand, nonwoven fabrics made of polyamide resin and nonwoven fabrics made of polyolefin resin are used as separators for alkaline storage batteries. Polyamide resin nonwoven fabrics are superior to polyolefin-based resin nonwoven fabrics in affinity for electrolyte solution and liquid retention, but are inferior in storage characteristics, durability and the like. In addition, the sealed nickel-metal hydride storage battery using a separator made of a polyamide resin has a problem that storage characteristics, especially self-discharge amount, are large. As a cause thereof, it is possible to decompose at a high temperature to generate a nitrogen compound. I have. Therefore, the separator of the sealed nickel-metal hydride storage battery is changing from a polyamide nonwoven fabric to a polyolefin nonwoven fabric. However, the polyolefin itself has no lyophilic property, and the liquid retaining property of the electrolytic solution is insufficient. Therefore, a hydrophilic surface treatment method has been adopted. Examples include surfactant treatment, corona discharge treatment, plasma discharge treatment, acrylic acid grafting, fuming sulfuric acid treatment, and fluorine gas treatment.

In order to improve the self-discharge characteristics, it is not enough to simply change from polyamide to polyolefin, and it is said that it is necessary to add a specific surface treatment to the separator. As such a surface treatment, fuming sulfuric acid treatment (J. Electrochem. Soc., Vol. 143, No. 6, 1996: P1904-190)
7, USP5100723, USP5213722, USP4837119), acrylic acid grafting (J. Electrochem. Soc., Vol. 145, No. 3, 19)
98; P844-847). Thus, it has been suggested that the separator prepared by the acrylic acid grafting method partially elutes the grafted product in an alkaline electrolyte.
There is a concern that the storage characteristics, particularly the cycle characteristics, may be degraded. In addition, the separator made by the fuming sulfuric acid method involves denaturing the resin, which may cause a decrease in the strength of the separator, and also requires a great deal of control over the production process, such as concentration control of sulfuric anhydride, which is a toxic substance, and collection of mist. Therefore, development of a new separator that solves such a problem is expected.

[0007]

The self-discharge characteristic of an alkaline storage battery, particularly a nickel-hydrogen alkaline storage battery, is very important for both consumer use and electric vehicles. In a low temperature region, for example, -20 to 10 ° C, the problem is not so large, but in a temperature range of 20 ° C or higher, it is a serious problem. The present invention has been made in view of such circumstances, and has as its object to provide a battery separator used for a storage battery having good self-discharge characteristics, and a sealed nickel-metal hydride storage battery using such a separator.

[0008]

The present inventors have conducted intensive studies to obtain an alkaline storage battery having good self-discharge characteristics, particularly a nickel-hydrogen storage battery. As a result, a separator having a synthetic resin surface treated with peroxide is used. As a result, the inventors have found that the above-mentioned object is achieved, and have completed the present invention. That is, the gist of the present invention resides in a battery separator made of a synthetic resin whose surface has been treated with peroxide and a sealed nickel-metal hydride storage battery using the same.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The battery separator of the present invention is obtained by treating the synthetic resin surface with a peroxide. As the synthetic resin, a polyolefin resin is preferably used, and a resin mainly composed of polyethylene or polypropylene is particularly preferable. Such resin is not particularly limited in its shape,
For example, it can be used as a sheet, a film, a woven fabric, a nonwoven fabric, a microporous film, or a laminated sheet obtained by laminating these in multiple layers.

[0010] Specifically, sheets and films of polypropylene, polyethylene, their copolymers or polymer blends, or polypropylene, polyethylene, ethylene-vinyl alcohol copolymer, ethylene-
Fiber consisting of a single component such as a vinyl acetate copolymer, polyethylene mainly composed of polypropylene, polyethylene-
Vinyl alcohol copolymer, polyethylene-vinyl acetate copolymer or the like, or a mixture of polypropylene and polyethylene alone or composite fiber, for example, a composite fiber material having a core component of polypropylene and a sheath component of polyethylene, Woven fabrics, nonwoven fabrics, and the like made of a mixture of these fibers and the like are included. Alternatively, a microporous film such as a microporous film of ultra-high molecular weight polypropylene may be used.
Among these, a nonwoven fabric, a woven fabric, a porous membrane and the like are preferred, and a nonwoven fabric is particularly preferred. The manufacturing method and the standard of the nonwoven fabric are not particularly limited, and the manufacturing method and the standard used for the battery separator are applied.
m ² or less, and the thickness is 0.01 to 5 mm, preferably 0.1 to 1 mm. Various known techniques can be used for producing these materials.

It is preferable that such a synthetic resin is provided with an ion exchange ability having a trapping property in advance in order to make it hydrophilic. Specifically, a hydroxyl group, a carbonyl group, a carboxyl group, a sulfone group, and the like are provided to the synthetic resin. As a method of applying, a method of treating the synthetic resin surface by a corona discharge method, a plasma discharge method, a flame method, a fuming sulfuric acid method, an electron beam irradiation method, an ultraviolet irradiation method, a fluorine gas-containing mixed gas method, a fluorine gas treatment method, or the like. Is mentioned. These are described in JACS, 100: 6, 1948, Mar. (1978),
No. 48, No. 5-46056, No. 4-1774, JP-A-5-6760, No. 7
The method can be carried out according to the methods described in JP-A-134979, JP-A-7-142047, JP-A-7-134980 and the like. In the case of a nonwoven fabric, for example, in the case of a nonwoven fabric, either a surface treatment of the raw fiber or a surface treatment of the nonwoven fabric itself is possible. However, the surface treatment of the nonwoven fabric itself is preferable in terms of simplicity of the treatment process.
The amount of these groups introduced is not particularly limited,
If the amount is too small, there is no effect. If the amount is too large, there is a fear that physical properties such as strength and air permeability may be adversely affected. Usually, the replacement capacity is 0.
It is preferably from 01 meq / g to 1.0 meq / g. In addition, as a method for imparting ion exchange ability with trapping properties, a fibril having a hydroxyl group, a carbonyl group, a carboxyl group, a sulfone group, or the like may be blended.

It is considered that the self-discharge due to impurities derived from the positive electrode or the negative electrode is also suppressed by providing the separator with a trapping ion exchange ability. In other words, one of the causes of self-discharge is the shuttle mechanism based on nitrogen compounds, rare earth metal ions, or transition metal ions eluted from the battery members. To improve self-discharge, trap these harmful ions. It is necessary to have a sufficient amount of carboxyl groups,
Alternatively, it is considered important to provide a sulfone group.

In the present invention, the above synthetic resin is surface-treated with a peroxide. The peroxide is not particularly limited as long as it has an -O-O- bond in the molecule, and it can be used alone or in combination of two or more. In the present invention, hydrogen peroxide is particularly preferred. The surface treatment with peroxide is performed by bringing the synthetic resin into contact with peroxide. The contact can be carried out in a gas phase, but it is preferable to use a liquid phase treatment, especially an aqueous solution of hydrogen peroxide. For example, the contact is carried out by sufficiently immersing the synthetic resin in a solution containing hydrogen peroxide. At this time, a peroxide (for example, a hydrogen peroxide-containing solution)
If a surface treatment is performed using an acid in addition to the above, a more favorable effect can be obtained. As the acid used in combination, sulfuric acid, hydrochloric acid, nitric acid,
Glacial acetic acid and other various organic acids can be used, but sulfuric acid is particularly preferred. When an acid is used in combination, it is preferable to use the peroxide in a composition volume ratio of 0.001 to 5 per 1 acid, more preferably 0.01 to 1 peroxide per 1 acid.
Used in proportions. When used in combination with an acid, such an acid and the above-mentioned peroxide can be used as a mixture or separately. As immersion conditions,
There is no particular limitation as long as the synthetic resin is sufficiently immersed in the hydrogen peroxide-containing solution, but preferably at 30 to 100 ° C, more preferably at 50 to 80 ° C, preferably for 30 seconds to 2 hours, more preferably for 1 minute. Soak for ~ 30 minutes.

The synthetic resin thus treated is sufficiently washed with water or neutralized with an alkali, dried at 50 to 100 ° C., processed into a required shape, and used as a battery separator. The battery separator thus obtained can be preferably used as a storage battery separator, and more preferably as an alkaline storage battery separator. Specific examples include separators for sealed alkaline storage batteries such as nickel-hydrogen storage batteries and nickel-cadmium storage batteries.

The present invention also uses such a separator,
Related to storage batteries. The storage battery is specifically nickel-
A sealed alkaline storage battery such as a hydrogen storage battery and a nickel-cadmium storage battery can be given, and a sealed nickel-hydrogen storage battery is particularly preferable. The sealed nickel-hydrogen storage battery of the present invention has a CaCu ₅ type crystal structure, a negative electrode using a hydrogen storage alloy powder containing at least Mn, and a nickel oxide positive electrode, with the above-described separator interposed therebetween. Preferably, it is configured. The positive electrode is nickel monoxide,
It is manufactured by a known manufacturing method such as a sintering method and a paste method using a nickel oxide such as nickel dioxide or a nickel hydroxide such as nickel hydroxide as an active material.
The negative electrode is produced by using a hydrogen storage alloy powder containing Mn as an active material by a known method such as a paste method or a pressure bonding method. As the hydrogen storage alloy used for the negative electrode active material, a general formula MmNi (xyz) Mn (y) M
(Z) (where x = 4.7 to 5.3, y = 0.2 to
0.8, z = 0.2 to 1.2, Mm is a mixture of rare earth elements, and M is Al and / or Co).

As the electrolyte, an aqueous solution of an alkali such as potassium hydroxide, sodium hydroxide or lithium hydroxide is used. Usually, it is an aqueous solution of potassium hydroxide. Further, the separator of the present invention has an air permeability of 5 to 60 cc / s
It is preferably ec / cm ² and the thickness is 50 to 300 μm. The sealed nickel-metal hydride storage battery of the present invention can be manufactured according to a known technique, for example, a method described in JP-A-64-57568.

[0017]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. Example 1 To a beaker in an ice-cooled bath, 1 volume of a commercially available 30% aqueous hydrogen peroxide solution was added to 3 volumes of a commercially available concentrated sulfuric acid, and after confirming that the mixture was sufficiently homogenized, the mixture was placed in an oil bath at 75 ° C. To prepare a treatment solution. 7 mm length, 0.9 denier fiber (Chisso ESC fiber) 60 wt%, 0.7 denier polypropylene fiber (Daiwabo PZ) 25.5 wt%, and vinylon A non-woven fabric made of 14.5% by weight of fiber (manufactured by Unitika), having a thickness of 150 μm, a basis weight of 55 g / m ² , and an air permeability of 35 cc / sec / cm ² is made lyophilic using fluorine gas, and then the above-mentioned treatment liquid For 30 minutes and dried to produce a separator.

Example 2 In order to measure a discharge capacity ratio before and after standing at 45 ° C. for 1 week (hereinafter referred to as “capacity retention rate”), which is an index of self-discharge,
A single disk storage battery was created according to the following specifications. (Negative electrode) Mish metal having a CaCu ₅ type crystal structure manufactured by Shin-Etsu Chemical. (Positive electrode) On foamed nickel (1.3 mm thick, density 500 g / m ² ) manufactured by Nippon Heavy Chemical Industry Co., Ltd., nickel hydroxide: 100 parts manufactured by Tanaka Chemical Laboratory, suboxide (CoO / Co) manufactured by Starck V Tech: 10 parts, Polykin TF manufactured by Daikin Industries, Ltd.
ED-2: Prepared by applying and drying a liquid using a thickener or the like to 5 parts. (Electrolyte) An aqueous solution containing 30% by weight of potassium hydroxide and 5% by weight of lithium hydroxide was used as an alkaline electrolyte, and the amount of the solution was adjusted to 150% with respect to the weight of the separator. (Separator) The nonwoven fabric of Example 1 was used as a separator. (Assembly of Battery) A disk-type battery was prepared using the positive and negative electrodes, the electrolyte and the separator. (Charge and discharge conditions) In a thermostat at 20 ° C., the degree of overcharge was 30%,
The charge rest was 60 minutes, the voltage was cut at 0.8 V, and the charge / discharge rate was 0.2 C. The capacity retention rate as a battery characteristic was measured using the prepared battery. The capacity retention ratio indicates the percentage of the remaining capacity after being maintained at 45 ° C. for one week with respect to the discharge capacity after 10 charge / discharge cycles. The results are shown in Table 1.
1 is shown.

Comparative Example 1 A member was prepared in the same manner as in Example 2 except that a surface treatment of immersing in a concentrated sulfuric acid-hydrogen peroxide solution was not performed, a battery was assembled, and a capacity retention ratio was measured. . The results are shown in Table 1. Example 3 A battery was assembled in the same manner as in Example 2 except that the nonwoven fabric used in Example 1 was immersed in a 30% aqueous hydrogen peroxide solution at room temperature for 1 hour and a surface-treated separator was used.
The capacity retention was measured. The results are shown in Table 1.

Example 4 A non-woven fabric used in Example 1 was immersed in a processing solution having the same formulation as in Example 1 at room temperature for 1 hour, and a surface-treated separator was used. The battery was assembled, and the capacity retention was measured. The results are shown in Table 1. Example 5 The nonwoven fabric used in Example 1 was treated with 30
75% in a processing solution consisting of 1 volume of a 1% aqueous hydrogen peroxide solution.
A battery was assembled in the same manner as in Example 2 except that a separator which had been subjected to surface treatment by immersion at 1 ° C. for 1 hour was used, and the capacity retention was measured. The results are shown in Table 1.

[0021]

[Table 1]

[0022]

The separator of the present invention is effective in improving the self-discharge characteristics of a storage battery, particularly a nickel-metal hydride storage battery, and has a high industrial value in that the performance of the storage battery can be improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Watanabe 1st Bancho-cho, Sakaide City, Kagawa Prefecture Mitsubishi Chemical Corporation Sakaide Office (72) Inventor Kazuo Niwa 1st Bancho-cho, Sakaide City, Kagawa Prefecture Mitsubishi Chemical Corporation F-term in the Sakaide Office (reference) 5H021 BB09 EE02 EE04 HH02 HH03 5H028 AA05 EE01 HH01 HH05

Claims (10)

[Claims] 1. A battery separator made of a synthetic resin whose surface is treated with a peroxide. 2. The battery separator according to claim 1, comprising a synthetic resin whose surface is treated with an acid and a peroxide. 3. The battery separator according to claim 1, wherein the peroxide is hydrogen peroxide. 4. The battery separator according to claim 1, wherein the synthetic resin contains a polyolefin-based resin as a main component. 5. The battery separator according to claim 1, wherein the synthetic resin has an ion exchange ability having a trapping property. 6. The battery separator according to claim 1, wherein the battery is a storage battery. 7. The battery separator according to claim 6, wherein the battery is an alkaline storage battery. 8. A negative electrode using a hydrogen storage alloy powder having a CaCu ₅ type crystal structure and containing at least Mn via a battery separator according to any one of claims 1 to 5, and a nickel oxide positive electrode And a sealed nickel-metal hydride storage battery. 9. The air permeability of the separator is 5 to 60 cc / sec / c.
m ^{2, and} the sealed nickel-hydrogen storage battery according to claim 8, wherein the thickness of 50 to 300 [mu] m. 10. A CaCu ₅ -type hydrogen storage alloy containing Mn has a general formula of MmNi (xyz) Mn (y) M
(Z) (where x = 4.7 to 5.3, y = 0.2 to
0.8, z = 0.2 to 1.2, Mm represents a mixture of rare earth elements, and M represents Al and / or Co. 10. The sealed nickel-metal hydride storage battery according to claim 8, wherein the sealed nickel-metal hydride storage battery has a structure represented by the following formula: