JP2002237284A - Method of manufacturing separator for alkaline storage battery, separator for alkaline storage battery manufacturing by the method, and alkaline storage battery using the separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an alkaline storage battery with an excellent hydrophilic property and a liquid retaining property in stable quality at a low cost. SOLUTION: A base material comprising a polymer which has carbon- hydrogen bond in molecular structure is treated under the irradiation of activated energy beams in reactant gas containing oxalyl chloride(COCl)2 or in the state of containing oxalyl chloride in the base material, to lead a chlorocarbonyl group into the molecular structure. The chlorocarbonyl group is changed into a carboxy group by hydrolysis, and then a sulfuric group is led in to make the separator hydrophilic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for an alkaline storage battery such as a nickel-cadmium battery and a nickel-metal hydride (metal hydride) battery, a method for manufacturing the same, and an alkaline storage battery using the same.

[0002]

2. Description of the Related Art In recent years, in the field of electronics and communications, with the rapid progress of semiconductors, electronic devices have been reduced in size and weight. With the progress of such devices, there is a demand for higher performance of batteries as driving sources.
Alkaline storage batteries such as nickel-cadmium batteries and nickel-metal hydride batteries are currently in practical use for these applications. The alkaline storage battery is configured by interposing a separator between a positive electrode and a negative electrode and using an alkaline aqueous solution as an electrolytic solution. In order to further improve the performance and reduce the price of the battery, technical developments regarding the constituent materials have been actively conducted. Above all, the importance of technology for improving the separator is increasing.

[0003] Currently, polyolefin-based nonwoven fabrics widely used as base materials for alkaline storage battery separators are inherently hydrophobic. Therefore, the substrate is subjected to a hydrophilic treatment to form a separator. Conventionally, various treatment methods such as corona discharge treatment, graft polymerization treatment, and sulfonation treatment have been proposed as hydrophilic treatment methods.

A hydrophilic treatment such as a corona discharge treatment or a graft polymerization treatment improves the initial wettability. However, OH groups or CO introduced by the corona discharge treatment or the graft polymerization treatment may be improved.
Since the OH group is easily decomposed by active oxygen generated in the battery, it is difficult to maintain hydrophilicity for a long time.

[0005] As a conventional separator for an alkaline storage battery, a nylon separator, which is a kind of polyamide nonwoven fabric, which is excellent in hydrophilicity and liquid retaining property for an electrolytic solution, has been mainly used. However, polyamide-based separators have poor alkali resistance and oxidation resistance. Therefore, when a battery is used at a high temperature, nylon fibers are easily oxidized and degraded. Therefore, there are disadvantages such as a short circuit of the battery and an increase in internal resistance, and acceleration of self-discharge of the battery due to a nitrogen compound which is a decomposition product.

Accordingly, polyolefin-based nonwoven fabrics having excellent alkali resistance and oxidation resistance have been applied as separators for alkaline storage batteries, particularly nickel-metal hydride batteries. However, polyolefin resins represented by polypropylene and polyethylene are inherently hydrophobic. Therefore, it is a major technical problem how to impart permanent hydrophilicity and liquid retention to an electrolytic solution.

One of the mainstream methods of hydrophilization is a sulfonation treatment in which the surface of polyolefin fibers is reacted with hot concentrated sulfuric acid or fuming sulfuric acid to introduce sulfonic acid groups into the molecular structure of the polyolefin resin. By reacting hot concentrated sulfuric acid or fuming sulfuric acid with polyolefin fiber,
The sulfonic acid group-introduced one has oxidation resistance in a high-temperature atmosphere, and has a function of suppressing self-discharge of the nickel-metal hydride battery because the sulfonic acid group adsorbs impurities. However, this separator has a drawback that it takes a long time to complete the injection of a predetermined amount in the electrolyte injection step because the separator has a low liquid absorption rate.

Further, since only the surface of the fiber is modified, the amount of electrolyte that can be held by the separator is not sufficient. In addition, when the pore volume of the active material of the nickel electrode increases with the progress of the charge / discharge cycle, the electrolyte held in the separator moves to the nickel electrode side, so that the electrolyte in the separator is depleted and the battery is depleted. There was a problem that the life was shortened. Under these circumstances, the development of a method for manufacturing a separator for an alkaline storage battery, which is an alternative to the conventional sulfonation treatment, is excellent in hydrophilicity and liquid retention, has a simple manufacturing process, and is easy to control the quality, has been strongly developed. Is desired.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a carbon / hydrogen compound in a molecular structure of a polyolefin nonwoven fabric or a porous film. In a technology for introducing a carboxyl group and a sulfonic acid group into a molecule of a base material composed of a polymer having a bond (CH) to make it hydrophilic, the process is excellent in hydrophilicity and liquid retention, and easy and easy in quality control. It is intended to provide a separator for an alkaline storage battery which can be manufactured by the above method.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for forming a carbon-hydrogen bond (CH) in a molecular structure.
In a separator composed of a polymer material having an oxalyl chloride (COCl) ₂ or a polymer gas containing oxalyl chloride, an active energy ray Process by irradiation of
A method for producing a separator for an alkaline storage battery, wherein a sulfonic acid group is introduced after a carboxyl group is introduced by hydrolysis with water.

In the present invention, the reaction gas is a mixed gas of oxalyl chloride as a main component and an inert gas,
The active energy rays are ultraviolet light composed of ultraviolet rays. The sulfonic acid group is introduced by reacting the base material after the introduction of the carboxyl group with sulfuric acid or sulfur trioxide. Further, the polymer material is a nonwoven fabric, a woven fabric or a polyolefin porous film of polyolefin fiber.

According to the present invention, there is provided an alkaline storage battery in which a positive electrode and a negative electrode are provided via a separator, wherein the separator is composed of a polymer material having a carbon-hydrogen bond (CH) in a molecular structure. In a reaction gas containing oxalyl chloride, or in a state in which oxalyl chloride is contained in a polymer material, the mixture is treated under irradiation with active energy rays, and hydrolyzed with water to introduce a carboxyl group. A method for producing a separator for an alkaline storage battery, characterized by introducing an acid group.

[0013] In the present invention, the hydrophilicity of the separator,
Ion exchange capacity (also referred to as ion exchange capacity) is applied as a scale for evaluating liquid retention. The higher the ion exchange capacity, the better the hydrophilicity and liquid retention. The separator in the present invention is based on a polyolefin-based nonwoven fabric, and has an ion exchange capacity of 0.02 to 0.5 milliequivalent / g in terms of potassium ion exchange amount for the reason described below. It is desirable.

The present invention provides a separator comprising a polymer material having a carbon-hydrogen bond (CH) in the molecular structure and having a carboxyl group and a sulfonic acid group introduced in the molecule. In a reaction gas containing oxalyl chloride (COCl) ₂ or in a state where oxalyl chloride is contained, a treatment is performed under irradiation with active energy rays, and a carboxyl group is introduced by hydrolysis with water.
An alkaline storage battery including a separator into which a sulfonic acid group is introduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method of preparing a separator substrate composed of a polymer material having a hydrocarbon structure in a reaction gas containing oxalyl chloride or in a state where oxalyl chloride is contained in the substrate. After being treated under irradiation with active energy rays and subjected to chlorocarbonylation, hydrolyzed with water to convert the chlorocarbonyl group to a carboxyl group or a metal salt thereof, and then immersed in sulfuric acid or mixed with sulfur trioxide. The metal salt is converted into a carboxyl group at the same time as the sulfonic acid group is brought into contact with the metal salt, thereby making the metal salt hydrophilic.

The reaction is a photochemical reaction in the gas phase, as shown in the following equation, so that the treatment can be performed while maintaining the shape of the separator substrate. In addition, a polar group can be uniformly introduced into the inside.

Oxalyl chloride [(COCl) ₂ ] is a compound that is liquid at room temperature with a boiling point of 63 ° C. and has a high vapor pressure, so that the substrate can be easily treated at room temperature. On the other hand, oxalyl chloride can be easily contained by immersing the polymer material.

As the reaction gas, a mixed gas of oxalyl chloride and an inert gas such as nitrogen, argon and helium is desirable. As the active energy rays, X-rays or electron beams can be used in addition to ultraviolet rays. However, it is most preferable to irradiate ultraviolet rays composed of ultraviolet rays because the irradiation does not damage the base material.

In the above step, the amount of the chlorocarbonyl group introduced is determined by the concentration of oxalyl chloride in the applied reaction gas, the contact time with the substrate, and the ultraviolet irradiation time (irradiation dose).
Can be easily controlled by adjusting. Moreover, according to the present invention, a hydrophilic group can be introduced in a very short time. FIG.
3 is a graph showing the relationship between the ion exchange amount of the separator according to the present invention and the ultraviolet irradiation time. As shown in the figure,
A separator having a sufficient ion exchange capacity can be obtained by irradiation for several minutes to 10 minutes.

As the polymer material, non-woven fabrics, woven fabrics, and porous films made of polyamide, polyvinyl alcohol, polyester, polypropylene, polyethylene and the like, and copolymers thereof can be used. But,
As the base material of the separator for a nickel-metal hydride battery, a material made of a polyolefin resin is suitable, and a nonwoven fabric mainly composed of polypropylene fibers is particularly preferable. The nonwoven cloth has a basis weight of 30 to 100 g / m 2 and a thickness of:
0.1-0.3mm, air permeability: 6-30cc / cm2 /
Those in the range of seconds are used.

The reaction in the above step is a hydrolysis reaction represented by the following formula, in which the chlorocarbonylated separator is immersed in water to form a carboxyl group. Further, the treatment may be carried out in an aqueous alkali solution, in which case it takes the form of an alkali salt. R-COCl + H ₂ O → R-COOH + HCl R-COCl + 2KOH → R-COOK + KCl +
H ₂ O

The reaction in the above step is a reaction represented by the following formula, in which the separator converted into the carboxyl group in the above is immersed in sulfuric acid, and a sulfonic acid group is further introduced. Further, a sulfonic acid group may be introduced into sulfur trioxide. The reaction in the sulfonation step proceeds according to the following reaction formula. RH + H ₂ SO ₄ → R-SO ₃ H + H ₂ O (RH indicates a polymer chain)

According to the present invention, a carboxyl group is introduced prior to introduction of a sulfone group. As described above, the chlorocarbonyl group, which is a precursor of the carboxyl group, is introduced by a photochemical reaction in the gas phase, so that the base material after the introduction of the carboxyl group is provided with a hydrophilic polar group up to the inside of the fiber. I have. Therefore, during the sulfonate group introduction process,
Sulfuric acid molecules and SO ₃ molecules penetrate not only into the fiber surface of the base material but also into the interior of the fiber, and the introduction of sulfonic acid groups proceeds.
When the sulfonic acid group is introduced into the fiber as described above, the liquid retention rate and the speed of liquid absorption are dramatically improved as compared with the conventional case where the sulfonic acid group is introduced only on the surface of the fiber. There is.

In order to maintain sufficient hydrophilicity as a separator for an alkaline battery, it is sufficient that the ion exchange capacity is in the range of 0.02 to 0.5 meq / g by ion exchange of potassium. If it is less than 0.02 meq / g, hydrophilicity and liquid retention are poor. On the other hand, if it exceeds 0.5 meq / g, the mechanical strength of the separator will decrease as described later, which will hinder the assembly of the battery, and may cause an increase in the basis weight of the base material and a decrease in air permeability. .

Such a separator of the present invention is excellent in hydrophilicity and liquid retention, so that it can be used in an alkaline battery, for example,
When applied to primary batteries and secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, nickel zinc batteries, air zinc batteries, and alkaline manganese batteries, stable performance can be maintained over a long period of time.
Hereinafter, embodiments of the separator of the present invention will be described, but the present invention is not limited to these embodiments.

[0026]

(Example) (Preparation of separator and evaluation of physical properties) (Example) Nonwoven fabric of polyolefin-based fiber (composite splittable fiber composed of polypropylene and polyethylene was wet-formed and entangled with water, thickness 0.10 mm, weight per unit area) An amount of 40 g / m ² ) was used as a substrate. A chlorocarbonyl group was introduced using a reactor as shown in FIG. After accommodating the base material in the glass reaction vessel shown in the figure, a mixed gas of oxalyl chloride and dry nitrogen gas was introduced into the reaction vessel at normal temperature and normal pressure, and the light transmitted through a copper sulfate aqueous solution of a high-pressure mercury lamp (300 W) ( (366 nm) for 30 minutes.

Thereafter, the substrate into which the chlorocarbonyl group was introduced was immersed in water, and the chlorocarbonyl group was changed to a carboxyl group by a hydrolysis reaction. The base material into which the carboxyl group was introduced as described above was placed in concentrated sulfuric acid at a temperature of 80 ° C for 3 hours.
It was immersed for 0 minutes to perform sulfonation. The ion exchange capacity of the separator thus prepared and the electrolytic solution (7 M /
1 KOH aqueous solution) and the liquid absorption rate were measured.

(Comparative Example) A substrate made of the same nonwoven fabric as in the example was not subjected to the above-mentioned treatment for introducing a chlorocarbonyl group, but was subjected only to sulfonation treatment under the same conditions as in the example. As in the example, the ion exchange capacity of the produced separator,
The liquid retention rate and liquid absorption speed were measured.

The physical properties of the separators according to the examples and comparative examples are shown in the following table.

[Table 1]

As shown in Table 1, the separator according to the example of the present invention is superior to the separator of the comparative example in both the liquid retention rate and the liquid absorption rate with respect to the electrolytic solution. The separator manufactured by the manufacturing method according to the present invention is excellent in liquid retention.
By applying the manufacturing method according to the present invention, even a nonwoven fabric having a small basis weight and a porous film can hold a required amount of electrolyte, and therefore, the present invention improves the capacity of a battery through thinning the separator. It is also effective for planning.

Further, in order to observe the hydrophilicity persistence of the separator according to the example, the separation was carried out at 80 ° C. in a 7 mol / l KOH aqueous solution.
Was examined for ion exchange capacity after immersion for 3 months. Almost no decrease in ion exchange capacity was observed, indicating that the hydrophilicity was maintained.

The reaction time (irradiation dose) for introducing the chlorocarbonyl group was changed in the same manner as in the above-mentioned Example, and then the carboxylation and the introduction of the sulfonic acid group were carried out under the same conditions as in the Example. Was changed. The liquid retention rate and liquid absorption speed of the produced separator were examined. In the separator thus manufactured, when the ion exchange capacity is increased, the liquid retention rate is improved and the liquid absorption is increased. When the ion exchange capacity of the separator was less than 0.02 meq / g, the absorption rate of the alkaline electrolyte was low and the retention rate was low.

On the other hand, when the ion exchange capacity is increased, the mechanical strength of the substrate decreases. If the ion exchange capacity exceeds 0.5 meq / g, the mechanical strength such as the tensile breaking strength is low and easily broken. It turned out to be. For these reasons, the ion exchange capacity of the separator according to the present invention is preferably 0.02 to 0.5 meq / g.

When a chlorocarbonyl group-introducing treatment was carried out by immersing in a liquid oxalyl chloride and using a substrate containing an oxalyl chloride solution, a separator having the same physical properties as in the above example was obtained. When the sulfonation was performed by bringing the base material after the introduction of the carboxyl group into contact with sulfur trioxide at room temperature, a separator having the same physical properties as in the above example was obtained.

(Preparation of Alkaline Storage Battery and Performance Evaluation) (Example) Next, a cylindrical sealed nickel-metal hydride battery was prepared using the above separator to evaluate the performance. For the positive electrode, a nickel electrode having a predetermined size and thickness by filling a 95% porous nickel fiber or a foamed substrate with an active material mainly containing nickel hydroxide was used. The negative electrode is formed into a paste by mixing a conductive agent and a binder with a quinary rare earth-based hydrogen storage alloy powder of MmNiCoAlMn (Mm represents a misch metal), and applying the paste to a perforated steel sheet. A hydrogen storage alloy electrode having the dimensions and thickness of was used. The positive electrode and the negative electrode are spirally wound through the separator, inserted into a battery case, injected with a 7 mol / l KOH aqueous solution as an electrolytic solution, and then sealed and sealed to produce an AAA size battery. did.

(Comparative Example) As a comparative example, a conventional nylon separator and a base material made of the same polyolefin non-woven fabric as in the above-mentioned embodiment were used, and the same separator was used as described above, using a hydrophilic treatment with an anionic surfactant. Was prepared.
The former is referred to as Comparative Example Battery A, and the latter as Comparative Example Battery B.

The battery of the present invention and the battery of the comparative example were subjected to a charge / discharge cycle test at a temperature of 45 ° C. FIG. 3 shows the results of the test.
Shown in Comparative Example Battery A and Comparative Example Battery B Using Nylon Separator and Surfactant Treated Separator
The battery of the present invention showed a small decrease in capacity with the lapse of cycles, and exhibited good characteristics, whereas the battery had an early decrease in capacity.

When the battery was disassembled and the separator was examined, the nylon separator was oxidatively decomposed and shortened. On the other hand, in the separator hydrophilized by the surfactant treatment, the hydrophilicity and the liquid retention were reduced, and the electrical resistance was significantly increased. The separator of the present invention retained the same hydrophilicity, liquid retaining property and ion exchange ability as those of the initial stage, and almost no deterioration was observed.

The superiority of the battery of the present invention was also recognized in the capacity retention characteristics (storage characteristics) of the battery when the battery in a charged state was left. The capacity of the battery after charging was left for 7 days at a temperature of 45 ° C., and the ratio (capacity retention) to the capacity before leaving was determined. The capacity retention was 55% for the comparative battery A using the nylon separator, and 81% for the battery of the present invention. It was found that the battery of the present invention had small self-discharge and excellent storage characteristics.

[0040]

As described in detail above, claim 1 of the present invention
According to (3), it is possible to precisely control the product quality and to produce an alkaline storage battery separator having excellent hydrophilicity in a simple manufacturing process. Claim 4 of the present invention
According to 5, a thin separator compatible with high energy density can be provided. Further, according to claim 6 of the present invention, an alkaline battery having excellent charge / discharge cycle performance and storage stability can be provided.

[0041]

[Brief description of the drawings]

FIG. 1 is a schematic view of a reaction apparatus for introducing a chlorocarbonyl group according to the present invention.

FIG. 2 is a graph showing the relationship between the ion exchange capacity of the separator and the reaction time in the present invention.

FIG. 3 is a graph showing charge / discharge cycle performance at a temperature of 45 ° C. of a battery of the present invention and a battery of a comparative example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Watada 2-3-1-21, Kosobe-cho, Takatsuki-shi, Osaka Inside Yuasa Corporation (72) Inventor Kazuhiro Tachibana 6-23 Hondamon, Tarumizu-ku, Kobe-shi, Hyogo Prefecture No. 5 (72) Inventor Sadao Miki 20-1 Kamikoya Yamanohashicho, Sakyo-ku, Kyoto, Kyoto F-term (reference) 5H021 BB09 BB15 CC00 CC02 EE04 EE18 HH07 5H028 AA05 BB10 EE01 EE05 EE06

Claims (6)

[Claims] 1. A method of manufacturing a separator for an alkaline storage battery comprising a polymer material having a carbon-hydrogen bond (CH) in a molecular structure and having a carboxyl group and a sulfonic acid group introduced in the molecular structure. After introducing a chlorocarbonyl group into the molecular structure, the chlorocarbonyl group is converted into a carboxyl group or a metal salt thereof by a hydrolysis reaction,
Next, a method for producing a separator for an alkaline storage battery, comprising introducing a sulfonic acid group. 2. The method according to claim 1, wherein said substrate comprising a polymer having a carbon-hydrogen bond in the molecular structure is exposed to an active energy ray in a reaction gas containing oxalyl chloride (COCl) ₂ or in a state containing oxalyl chloride. The method for producing a separator for an alkaline storage battery according to claim 1, wherein the chlorocarbonyl group is introduced into the molecular structure by performing the treatment under the irradiation of (1). 3. The method according to claim 1, wherein the sulfonic acid group is introduced by a reaction with sulfuric acid or sulfur trioxide (SO ₃ ). 4. The polymer material according to claim 1, wherein a carboxyl group and a sulfonic acid group are introduced into a polymer of a nonwoven fabric, a woven fabric or a porous polyolefin film of a polyolefin fiber. A separator for an alkaline storage battery, comprising: 5. The separator according to claim 4, wherein the separator is made of a nonwoven fabric of a polyolefin fiber and has an ion exchange capacity of 0.02 to 0.5 meq / g in potassium ion exchange. For alkaline storage batteries. 6. A separator comprising a polymer material having a carbon-hydrogen bond (CH) in the molecular structure and having a carboxyl group and a sulfonic acid group introduced in the molecule, wherein the polymer material is formed of oxalyl chloride. After treatment in a reaction gas containing (COCl) ₂ or containing oxalyl chloride under irradiation with active energy rays and hydrolysis with water to introduce a carboxyl group, then a sulfonic acid group An alkaline storage battery comprising a separator into which is introduced.