JPH02174056A - Manufacture of separator for alkaline storage battery - Google Patents

Abstract

PURPOSE:To form a high-performance separator with a simple method by impregnating a sulfuric acid solution in a woven fabric or a nonwoven fabric made of fibers coated with polyvinyl alcohol on the surface of polypropylene fibers and heat-treating it. CONSTITUTION:Fibers coated with polyvinyl alcohol on polypropylene are used as a base, a dilute sulfuric acid solution is impregnated in a woven fabric or a nonwoven fabric made of the fibers, moisture in dilute sulfuric acid is evaporated in the air or the inert gas phase, a small quantity of concentrated sulfuric acid is left and held in the high-temperature atmosphere, and sulfonic group is combined with polyvinyl alcohol. The degree of sulfonation is determined by the quantity of impregnated sulfuric acid and the heat treatment temperature. Polyvinyl alcohol is shrunk in concentrated alkali when used alone, but it is not shrunk when coated on polypropylene, and a higher hydrophilic property is obtained by the sulfonation processing. A separator with a good liquid holding property and a good hydrophilic property and stable in an alkaline electrolyte can be formed with simple processing.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for manufacturing a separator for alkaline storage batteries used in nickel-cadmium storage batteries, etc., and relates to improvement of liquid retention or heat-resistant alkalinity, which are important characteristics of the separator. be.

BACKGROUND OF THE INVENTION In general, characteristics required for battery separators are prevention of short circuits by separating positive and negative electrodes, and retention of electrolyte required for battery reactions.

As the demand for portable devices has increased in recent years, their uses have also expanded. For example, sealed nickel-cadmium storage batteries and the like need to be improved to accommodate an expanded operating temperature range or to extend their service life. Separators used in alkaline storage batteries such as nickel-cadmium storage batteries are generally mainly made of nylon or polypropylene.

Problems to be Solved by the Invention However, for example, nylon separators have the disadvantage that they are easily decomposed when used at high temperatures, reducing the isolation function of the positive and negative electrodes, and promoting self-discharge of the battery due to impurities produced by decomposition. be. Furthermore, since polypropylene separators have low hydrophilicity, their discharge performance is inferior to that of nylon. Another drawback is that the charge/discharge cycle life characteristics are poor. In order to increase the hydrophilicity of polypropylene separators and improve the above-mentioned drawbacks, a method of attaching a surfactant to the fiber surface has been used, but the surfactant decomposes after long-term use.
There was a drawback that the effect was reduced, and there was room for further improvement. Furthermore, a method has been proposed in which hydrophilic groups such as sulfone groups are bonded to the surface of polypropylene to extend its life. However, for example, sulfonation of polypropylene requires the use of fuming sulfuric acid, making industrial production difficult. Difficulties are expected.

The present invention solves the above-mentioned problems and provides a method of manufacturing a high-performance separator for alkaline storage batteries using an extremely simple method.

Means for Solving the Problems In order to solve the problems above, the present invention is based on fibers made of polypropylene coated with polyvinyl alcohol, which has excellent heat and alkaline resistance and oxidation resistance. , a sulfone group is bonded to polyvinyl alcohol.

Sulfone groups are added to polyvinyl alcohol by impregnating a woven fabric or non-woven fabric made using the above fibers with a dilute sulfuric acid solution, and evaporating the water in the dilute sulfuric acid in air or an inert gas phase. With a small amount of concentrated sulfuric acid remaining,
This is done simply by keeping it in a high temperature atmosphere. The bonding of the sulfone group to polyvinyl alcohol is determined by the amount of sulfuric acid impregnated into the woven or nonwoven fabric and the heat treatment temperature, and by controlling these, the degree of sulfonation can be arbitrarily controlled.

Function: As mentioned above, polypropylene or polyvinyl alcohol has good heat and alkaline resistance or oxidation resistance, and when polyvinyl alcohol is used alone, it shrinks in concentrated alkali, causing changes in separator shrinkage. However, when polypropylene is coated as in the present invention, the above-mentioned problems do not occur because polypropylene is stable. In addition, polyvinyl alcohol itself is a highly hydrophilic material, and higher hydrophilicity can be obtained through sulfonation treatment, which is easier to process than polypropylene. It has great industrial advantages as it can be chemically treated.

In addition, the sulfone group bonded to the polyvinyl alcohol coated on the surface of the polypropylene fiber is extremely stable, similar to the sulfone group bonded directly to polypropylene. For example, when used in a sealed nickel-cadmium storage battery, etc. Because it is less prone to deterioration due to use and long-term charge/discharge cycles, it has better initial discharge characteristics than batteries using ordinary polypropylene separators, and its effect is stable over a long period of time, making it easier to charge and discharge batteries. Cycle life characteristics are greatly improved.

Example Examples of the present invention will be shown below.

A fiber with a thickness of 0.2 μm and made of polypropylene single fibers coated with polyvinyl alcohol and having a diameter of approximately 20 μm.
A nonwoven fabric of 20 mm and a porosity of about 50% is prepared. Here, the volume ratio of polypropylene in the single fiber to polyvinyl alcohol on the surface is about 1:1.

The nonwoven fabric is impregnated with a 10% dilute sulfuric acid solution at 20°C, and the entire pores in the nonwoven fabric are impregnated with dilute sulfuric acid. It is 10%. Next, the nonwoven fabric impregnated with dilute sulfuric acid is left for about 20 minutes in air at a temperature of 80°C. The water content in the dilute sulfuric acid impregnated into the nonwoven fabric becomes 5% or less in about 5 minutes, and the dilute sulfuric acid solution becomes almost concentrated sulfuric acid, and from this point on, the sulfonation of polyvinyl alcohol proceeds rapidly. After 20 minutes, the nonwoven fabric was washed with water until there was no residual sulfuric acid content, and then dried.

The nonwoven fabric separator according to the present invention is referred to as (a). Furthermore, four types of separators shown below were prepared as comparative examples.

One of them is (b) above, which is not treated with sulfuric acid. Next, a normal nylon separator is prepared (e). Next, a normal polypropylene separator is prepared (d). Next, the above-mentioned (d) was subjected to a sulfonation process, and this is designated as (e). The sulfonation treatment of the polypropylene separator was performed by immersing the polypropylene nonwoven fabric in fuming sulfuric acid with a concentration of 20% at a temperature of 35° C. for about 10 minutes, washing with water, and drying. A sealed nickel-cadmium storage battery equivalent to 1.2 Ah was fabricated using the above five types of separators, a normal paste-type cadmium negative electrode, a sintered-type nickel electrode, and an alkaline electrolyte. The batteries are (A) a battery using the separator (a) according to the present invention, and (B) a battery using the separators of comparative examples (b), (c), (d), and (e). C), (d), and (e).

The separator was evaluated based on the discharge characteristics and charge/discharge cycle life characteristics of the battery.

The discharge characteristics are the discharge capacity when the battery was charged at 20°C at a current equivalent to 0.1 CmA for 15 hours, and then discharged at a current equivalent to 1 to 100 mA, and the discharge capacity when the battery was discharged at a current equivalent to 0.20 mA. The evaluation was made based on the ratio to the discharge capacity at that time.

In addition, the charge/discharge cycle life characteristics are 1/3 Cm at 60°C.
The battery was charged with a current equivalent to A for 4.5 hours and then completely discharged with a resistive load equivalent to 1 CmA. The battery was repeatedly charged and discharged, and the capacity drop due to the cycles was evaluated.

FIG. 1 shows the discharge characteristics of the battery in terms of the relationship between discharge current and discharge capacity ratio. In general, a normal nylon separator has good liquid retention properties and therefore has good discharge characteristics. A battery (A) using the separator (a) according to the present invention and a separator (e) subjected to polypropylene sulfonation treatment
As shown in Figure 1, the battery (E) using the nylon separator (C) shows the same characteristics as the battery (C) using the nylon separator (C), and has the same liquid retention properties as nylon. Recognize. A battery (D) using a normal polypropylene separator (d) has deteriorated discharge characteristics because the separator's liquid retention and hydrophilicity are inferior to those of other batteries. In addition, fibers made of polypropylene coated with polyvinyl alcohol and not subjected to sulfuric acid treatment as in the present invention (b
) battery (B) using polypropylene has slightly better discharge characteristics than a battery using only polypropylene due to improved hydrophilicity due to polyvinyl alcohol, but it is further treated with sulfuric acid to add sulfone groups. The discharge characteristics are inferior to those according to the present invention.

FIG. 2 similarly shows the relationship between charge and discharge cycle life characteristics. Like the discharge characteristics, the life characteristics also have a large relationship with the liquid retention hydrophilicity of the separator. Generally, by repeating charge/discharge cycles, the electrode plates expand and the electrolyte tends to migrate from the separator into the electrode plates. At this time, if the separator has low liquid retention and hydrophilicity, the electrolytic solution will migrate to the electrode plates at an early stage, degrading the charge/discharge characteristics and shortening the cycle life. The battery (A) using the separator (a) according to the present invention and the comparative batteries (E), (B), and (D) are as follows:
The tendency was similar to the initial discharge characteristics described above, and this is thought to be due to the difference in liquid-retentive hydrophilicity of the separators.

For batteries (C) using nylon with good liquid-retaining hydrophilicity, (A) and (E
), but the decomposition of nylon progresses during removal, and eventually the isolation function of the positive and negative electrodes deteriorates, causing internal short circuits.

As described above, if the separator according to the present invention is used, the initial discharge characteristics are equivalent to those of a nylon separator with good liquid-retaining hydrophilicity, and the stability of the liquid-retaining hydrophilicity and the stability of the substrate Due to the durability of polypropylene and polyvinyl alcohol due to their heat and alkaline resistance and oxidation resistance, their cycle life characteristics at high temperatures are much better than that of nylon.

As mentioned above, the degree of sulfonation of polyvinyl alcohol depends on the amount of sulfuric acid impregnated into the nonwoven fabric and the temperature of the heat treatment. Regarding the amount of sulfuric acid to be impregnated, the appropriate value was examined by changing the porosity of the nonwoven fabric and the concentration of dilute sulfuric acid. The heat treatment temperature at this time was 80° C. and the time was 20 minutes. In addition, the processing temperature ranges from room temperature to 150℃.
The appropriate value was examined by varying the value up to Further, the amount of impregnated sulfuric acid at this time was 10% in terms of concentrated sulfuric acid based on the amount of fibers in the nonwoven fabric. In addition, the separator was evaluated based on the discharge characteristics of the battery, and other characteristics were considered.

Sulfonation of polyvinyl alcohol proceeds from the time when the water in dilute sulfuric acid evaporates and reaches a concentration close to that of concentrated sulfuric acid. The concentration of sulfuric acid at that point is thought to be about 5%, and below this concentration, the sulfonation of polyvinyl alcohol is difficult to proceed even if the amount of sulfuric acid is increased, so the conditions for heat treatment are as follows: It is necessary that the sulfuric acid content in the nonwoven fabric be 95% or more. Further, the concentration of dilute sulfuric acid during impregnation is not important, but the amount of sulfuric acid remaining in the nonwoven fabric after heat treatment is important relative to the amount of fibers. If the amount is small, polyvinyl alcohol will not be sufficiently sulfonated. The lower limit value is about 1V% in terms of concentrated sulfuric acid based on the volume of the nonwoven fabric. Also,
If the amount is too large, the polyvinyl alcohol will decompose, and during subsequent washing with water, the heat of dilution from the concentrated sulfuric acid remaining in the nonwoven fabric will cause heat shrinkage of the nonwoven fabric. , which is about 20% in terms of concentrated sulfuric acid. The same can be said about the heat treatment temperature; if the temperature is low, the sulfonation of polyvinyl alcohol will not proceed sufficiently and evaporation of water will take a long time, which is disadvantageous for industrial production. Its lower limit is about 50°C. Also, regarding the upper limit,
The evaporation of water and the progress of sulfonation are also good, but at 120
Since thermal deformation of the polypropylene base material occurs at a temperature of about 120°C, a temperature of about 120°C is considered to be appropriate.

Although the present example has been described with respect to non-woven fabric, it is of course possible to treat woven fabric in the same manner, and the atmosphere for heat treatment is not limited to air.
The type of gas is not important as long as it does not adversely affect the base polypropylene or polyvinyl alcohol, as long as it is an inert gas such as nitrogen.

Effects of the Invention As described above, according to the present invention, it is possible to manufacture a separator that has good liquid retention and hydrophilicity and is stable in alkaline electrolytes through simple processing, and is suitable for use in nickel-cadmium storage batteries, etc. For example, cycle life characteristics at high temperatures can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the discharge current and the discharge capacity ratio of a sealed nickel-cadmium storage battery, and FIG. 2 is a characteristic diagram of the charge-discharge cycle life. Name of agent Patent attorney Shigetaka Awano and 1 other person Figure 1 Kut (5L (C fee-) Figure 2 5t) O1000/5t) 0 Mitsukata (t Puik JL/Kan (times) Procedural amendment 1989 July 3, 1988 Patent Application No. 332955 2. Name of the invention Method for manufacturing separators for alkaline storage batteries 3. Relationship to the amended case Patent application Office 1006 Kadoma, Kadoma City, Osaka Prefecture Name (582) ) Representative of Matsushita Electric Industrial Co., Ltd.
Akio Tanii 4 Agent Address: 6, Matsushita Electric Industrial Co., Ltd., 1006 Oaza Kadoma, Kadoma City, Osaka Prefecture, 571 Contents of the amendment (1) Changed "Amount of sulfuric acid" on page 4, line 18 of the specification to "sulfuric acid" Quantity and "K" correction. (2) "J to impregnate" on page 6, line 15 will be corrected to "impregnate." (3) "Sulfonation J" on page 7, line 12 will be corrected to "sulfonation." (4) "Removal" on page 10, line 12 will be corrected to "gradually."

Claims (3)

[Claims] (1) It is characterized by comprising the steps of impregnating a woven fabric or non-woven fabric made of polypropylene fibers coated with polyvinyl alcohol on the surface with a sulfuric acid solution, and heat-treating the woven fabric or non-woven fabric impregnated with the sulfuric acid. Method for manufacturing separators for alkaline storage batteries. (2) Claim 1, characterized in that the amount of the sulfuric acid solution impregnated into the woven fabric or non-woven fabric is 20 to 1 V%, calculated as concentrated sulfuric acid, based on the fiber volume of the woven fabric or non-woven fabric. A method for producing a separator for an alkaline storage battery as described in . (3) A patent characterized in that the heat treatment involves leaving a woven fabric or nonwoven fabric impregnated with a sulfuric acid solution in a gas phase at 50 to 120°C until the water content in the sulfuric acid solution becomes 5V% or less. A method for producing a separator for an alkaline storage battery according to claim 1 or 2.