JPH04192256A - Separator for alkali storage battery and its manufacture - Google Patents

Abstract

PURPOSE:To enhance durability, and keep hydrophilic property for a long time as well as to prevent strength from being lowered by making up unwoven cloth from polyolefins containing benzine sulfonic groups as a side chain. CONSTITUTION:A separator for an alkali storage battery is provided, which is composed of unwoven cloth made of polyolefins containing benzine sulfonic groups as a side chain. As a manufacturing method of the separator, styrene sulfonic groups are graft-polymerized with polyolefins. Or after styrenes have been graft-polymerized with polyolefins, benzine nucleuses are then sulfonated. Furthermore, each main chain or each side chain of unwoven cloth fibers is crosslinke, the separator can thereby be provided, which is excellent in durability, can keep hydrophilic property for a long time, and prevents strength from being lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention uses an aqueous solution of potassium hydroxide or sodium hydroxide as an electrolytic solution, and uses nickel hydroxide, ferrous oxide, ferric oxide, etc. as a positive electrode material. used for cadmium, zinc,
This invention relates to a nonwoven fabric separator used in storage batteries that use hydrogen storage alloys, iron, etc. as the negative electrode material.

Conventional technology and its problems Nonwoven fabrics made of synthetic resin are widely used as separators for alkaline storage batteries. Conventionally, a nonwoven fabric made of polyamide resin (nylon) has been particularly often used for this separator. The reason for this is that polyamide resin has hydrophilic properties, so this separator has excellent electrolyte retention properties, and also under the conditions where it is exposed to oxygen generated from the positive electrode while immersed in alkaline electrolytic iα. However, it did have some degree of durability.

However, this polyamide resin is gradually decomposed in an alkaline battery to produce nitrogen and carbonate radicals, such as nitrate radicals. When the amount of nitrogenous radicals such as nitrate radicals increases, a disadvantage arises in that the rate of self-discharge increases due to a reaction process called a "shuttle" mechanism. Furthermore, when carbonate radicals are generated, the conductivity of the electrolyte decreases, causing an inconvenience that the internal resistance of the battery increases.

In an attempt to solve these problems with nonwoven fabric separators made of polyamide resin, attempts have been made to use nonwoven fabrics of polyolefins, which have excellent durability in alkaline batteries and do not generate nitrogen radicals, for separators.

However, polyolefins have significantly poor hydrophilicity, so
As it is, it can barely hold alkaline electrolyte.

Therefore, as one means of imparting hydrophilicity to this separator, it has been attempted to attach a surfactant to the polyolefin fiber or to dissolve the surfactant in the polyolefin fiber itself. However, in this method, the surfactant dissolves in the alkaline electrolyte and is oxidized by oxygen scum generated from the positive electrode, resulting in a lack of sustainability of the effect.

As described above, when the sustainability of hydrophilicity is lost, scum is trapped in the separator, resulting in an increase in the internal resistance of the battery and an increase in voltage drop during high rate discharge.

Another method is to impart hydrophilicity by sulfonating the polyolefin fiber itself (see, for example, JP-A-62-11!5657). Although this method maintains the hydrophilicity of the separator, it requires harsh conditions such as reacting with fuming sulfuric acid when sulfonating the polyolefin, which may destroy part of the polymer skeleton. However, the disadvantage is that the strength of the fibers is reduced.

Therefore, if the separator is wrapped in a bag without pulling the separator, or if the separator is used in the manufacture of a battery in which the separator is wound together with the electrode plate without being pulled too hard, there is a problem that the separator is likely to break. Occurred.

Therefore, the incidence of separator breakage accidents during the manufacture of alkaline storage batteries is low, and after long-term use of the battery, the internal resistance does not increase and the voltage drop during high rate discharge does not increase, and the self-discharge rate increases. There was a desire for a separator that would not increase in size, would have excellent durability in alkaline batteries, would maintain hydrophilicity for a long period of time, and would not lose strength.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a separator for alkaline storage batteries made of a nonwoven fabric of polyolefins having Hensensulfonic acid groups in the side chains. As a method for producing the separator, the present invention provides a method of craft polymerizing styrene sulfonate to polyolefin, or a method of craft polymerizing styrene to polyolefin and then sulfonating the Hensen nucleus. Furthermore, in order to further improve the effects of the present invention, a separator for an alkaline storage battery is provided in which the main chain or side chain of this nonwoven fabric fiber is crosslinked.

Function Polyolefins such as polypropylene and polyethylene have high mechanical strength and are chemically stable, but on the other hand, they have the property of being difficult to wet with alkaline electrolytes. Therefore, in the present invention, a polyolefin having a main chain made of this polyolefin and a Hensensulfonic acid group (chemical formula '-CaHa-SJ-), which is a dissociable group stable in an alkaline electrolyte, is used.
A nonwoven fabric in which fibers consisting of zero and zero chains are intertwined is used as a separator for alkaline storage batteries.

This separator has high mechanical strength due to the polyolefin that is the main chain of its fibers, and high hydrophilicity due to the Hensensulfonic acid group in the side chain. Since this sulfone group is a hydrophilic group with high chemical stability and is chemically bonded to the main chain, this separator can be used in alkaline storage batteries to prevent alkaline electrolyte attack. It maintains its hydrophilic properties even under harsh conditions where it is exposed to oxygen gas generated from the positive electrode.

In the present invention, the following two methods are used to introduce a Hensensulfonic acid group as a chain marker.

The first is to add a styrene sulfonate monomer (chemical formula: CH2"CH-CsH4-5Oito1;
N is a cation such as a sodium ion, potassium ion, or lithium ion. ) by graft polymerization to obtain [
This is a method of adding a side chain represented by the structural formula -C)I(-C6)14-5O3M)-CH2-con. This graft polymerization can be achieved by irradiating the polyolefin with radiation such as electron beams or gamma rays or ultraviolet rays to generate radicals, which are reacted with the monomer.

The second method is as follows. That is, styrene monomer (chemical formula: CH2=CH-C8I) is added to polyolefin.
s) to form [-CH(C6Hs)-C
A side chain represented by the structural formula H2-)]n is added. This graft polymerization involves irradiating polyolefin with radiation such as electron beams or gamma rays or ultraviolet rays to generate radicals.
This can be achieved by reacting with this monomer. This polymer is then reacted with fuming sulfuric acid or concentrated sulfuric acid to form a sulfonate. Since the sulfonation reaction occurs preferentially from the l\benzene nucleus of the side chain, by stopping the reaction before the polyolefin main chain is significantly sulfonated, this reaction can be achieved without causing significant deterioration of the polyolefin main chain. A sulfone group is bonded to the nucleus, and the side chain is converted into one represented by the structural formula [-CH(-CsHa-5O3M)-CH2-ln.

As described above, in the present invention, hydrophilicity is not imparted by direct sulfonation of polyolefins, but hydrophilicity is imparted by the Hensensulfonic acid group in the side chain, so that significant deterioration of the main chain does not occur. Therefore, according to the present invention, it is possible to obtain a separator for alkaline storage batteries that has sustained hydrophilicity without significantly impairing high mechanical strength.

Comparing the first method and the second method, the first method requires fewer operations to introduce a Hensensulfonic acid group into the side chain than the second method, and the sulfonation The second method is superior to the first method in that no treatment is performed, so no acid waste is generated, and the second method is superior to the first method in that it uses styrene monomer, which is cheaper than styrene sulfonate.

In addition, in the separator of the present invention, the sulfonic acid group has cation exchange properties, and when this exchange capacity is large, the separator absorbs water from the alkaline electrolyte and swells.
May lack dimensional stability. Therefore, in the present invention,
To increase the dimensional stability of the separator, the main chains or side chains of the nonwoven fibers are crosslinked. Crosslinking is, for example,
Divinylbenzene (chemical formula '
This can be achieved by adding monomers such as (CH2=CH-)2CsH4) or butadiene (chemical formula: C1(2=CH-C)l=cH2). Such crosslinking prevents the separator from swelling and provides a separator for alkaline storage batteries that has excellent dimensional stability in the battery.

Incidentally, as separators for graft polymerizing hydrophilic side chains to polyolefins, there have been some that use acrylic acid, methacrylic acid, maleic acid, etc., each having a carboxyl group. However, these hydrophilic carboxyl groups have poorer oxidation resistance than the sulfone groups used in the present invention.

Example The present invention will be explained in detail using preferred embodiments.

[Separator tamco (product of the present invention)] This separator was manufactured as follows.

First, a nonwoven fabric made of polypropylene fibers with a diameter of about 30 μIn, a thickness determined by applying a load of 20 kg/dm' to 0.20 mm, and a basis weight of 45 g/m'' was prepared. Then, this nonwoven fabric was given a dose of 5
Radicals (reactive active sites) were formed in the main chain by irradiation with an accelerated electron beam of Mr.ad. Next, this nonwoven fabric was soaked in a dimethylformamide (abbreviation: DMF) solution (i1
Kraft polymerization was carried out by immersing the sample in 0.1 M) to introduce Hensensulfonic acid groups into the side chains. Then, after washing the DMF lever nonwoven fabric that does not contain monomer,
Separator A was manufactured by washing with ether and drying.

[Separator B] (Product of the present invention) This separator was manufactured as follows.

First, a styrene monomer was used in place of the DMF solution of sodium styrene sulfonate monomer in separator A, and the method was the same as that of separator A except that
Styrene was craft-polymerized onto the main chain of butylene. Next, this nonwoven fabric was immersed in fuming sulfuric acid to perform a sulfonation treatment.

Sulfonation proceeds preferentially from the Hensen nucleus of the side chain than from the main chain polyolefin, so sulfonation proceeds from the Hensen nucleus of the side chain.
At the point when less than 5% of the hydrogen atoms in the main chain have been sulfonated, the nonwoven fabric is heated from high to low concentrations of sulfuric acid to stop the reaction. Separator B was produced by dipping, finally washing with water, and drying.

[Separator C (product of the present invention)] This separator contains, instead of the styrene sulfonic acid sodium salt monomer alone used in the manufacturing method of separator A,
DMF containing both styrene sulfonic acid sodium salt 0.1M and Schichnirhensen monomer 0.05M
Separator C was manufactured in the same manner as separator A except for using the solution. By this method, a separator A whose main chain or side chain is crosslinked with divinylhensen is obtained.

[Separator D Co (product of the present invention) This separator uses a mixture of 1 part by weight of styrene monomer and 0.5 part by weight of dihinylhensen monomer instead of the styrene monomer alone used in the manufacturing method of separator B, Separator D is otherwise the same as separator B.
was produced. By this method, a main chain or a side chain of separator B is obtained which is crosslinked by divinylhensen.

[Separator E (Conventional Product) This separator is made of a polyamide nonwoven fabric whose fiber diameter, thickness, and weight are approximately equal to those of the nonwoven fabric used for Separator A.

[Separator Toko (Conventional product) This separator is made of the same polypropylene nonwoven fabric as used for Separator A, and does not have Hensensulfonic acid groups in the side chains. & It is made by adhering a nonionic surfactant to the navy blue surface.

[Separator G (conventional product) This separator is made of the same non-woven polypropylene cloth as that used for separator A, and is made by immersing it in fuming sulfuric acid without having a sense sulfonic acid group in the side chain. , which is obtained by performing a sulfonation treatment in which hydrogen atoms in the main chain of polypropylene are replaced with sulfone groups. In addition, in order to impart hydrophilicity to the same level as separators B and 'cJD, this separator needed to be immersed in fuming sulfuric acid for about five times as long as separators B and D.

[Separator H1 (Conventional Example) This separator is made in the same manner as Separator A except that an acrylic acid monomer is used instead of the DMF solution of sodium styrene sulfonate in Separator A. This separator has a hydrophilic carboxyl group added to the side chain.

Next, using the above separator, an alkaline storage battery was manufactured in the following manner.

One known band-shaped sintered nickel hydroxide electrode and one bonded nickel hydroxide electrode were used as the positive and negative electrodes, and one of the separators described above was interposed between these electrodes. , I rolled this separator without pulling it. This is then stored in a cylindrical metal case,
Injecting an alkaline electrolyte mainly consisting of potassium hydroxide,
Attach the battery cover with safety valve and the nominal capacity is 0.7A.
We manufactured a sealed nickel-cadmium battery of hO AA size.

In these alkaline storage batteries, separators A, B, C, and D
, E, F, G and H, respectively, as a battery (
A), (B), (tsu), (1), (o), (power),
(ki) and (ri)toyofu.

In addition, when styrene sulfonate or acrylic acid is not craft-polymerized to the nonwoven fabric used for separator A, when a surfactant is not attached to the nonwoven fabric used for separator A, the nonwoven fabric used for separators B, D, and G However, if sulfonation treatment is not performed after craft polymerization of styrene, these nonwoven fabrics have remarkable water repellency, so if these nonwoven fabrics are used for the separator, the alkaline electrolyte will not penetrate into the separator, and the battery was unable to perform its functions.

In addition, polystyrene non-woven fabrics, sulfonated fabrics, or surfactant-treated fabrics have extremely low tensile strength, so if these nonwoven fabrics are used for separators, they may be difficult to assemble during battery assembly. It broke so many times that I couldn't even get the battery to work properly.

Therefore, the following experiments were conducted using eight types of batteries from (a) to (ri) above.

(Experiment 1) First, when assembling 100 batteries each of the above eight types, the number of separator cutting accidents during the electrode plate winding process was investigated.

(Experiment 2) After Experiment 1, in order to chemically form the above eight types of batteries, the batteries were charged at 25° C. for 15 hours at a current rate of 10 hours.
Charging and discharging was repeated twice by discharging at a current rate of 1 hour until the terminal voltage reached 0.8V. Then, charge and discharge at 25°C for 1.2 hours at a current rate of 1 hour, and discharge at a current rate of 1 hour until the conductive pressure at the terminal reaches 8V, repeating this process for 100 cycles. The discharge capacity of the eye was measured.

Next, after charging at 25°C for 1.2 hours at a current rate of 1 hour, and leaving it at 45°C for 30 days, the terminal voltage was 0.8V at a current rate of 1 hour at 25°C.
The discharge capacity was examined. In this experiment, the self-discharge rate per month is defined as the difference between the discharge capacity immediately before leaving at 45°C for 30 days and the discharge capacity after leaving it, divided by the discharge capacity immediately before leaving it. .

(Experiment 3) After Experiment 2, the five types of batteries mentioned above were charged at 25°C for 1.2 hours at a current rate of 1 hour, and then the terminal voltage was charged at a current rate of 5 hours (0.14 A). The battery was discharged until it reached 0.8■. Then, at 25°C and 1 hourly current
．． After charging for 2 hours, the terminal voltage decreased to 0. It was discharged until it reached 8V. And 1
The terminal voltage was measured at the time when 0.35 Ah was discharged by time rate and 20 minute rate discharge, and the difference therebetween was calculated as a voltage drop.

The results obtained in the above experiments are summarized in Table 1.

(Margin below) Table 1 The following can be seen from Table 1.

In other words, batteries (a), (b), (t), and (1) equipped with the products of the present invention have no separator breakage accident, have the lowest self-discharge rate, and have a higher voltage drop due to high-rate discharge. small.

On the other hand, as the conventional separator made of polyamide non-woven fabric progresses, the separator deteriorates and generates nitrogen roots, which increases the self-discharge rate, and carbonate roots are generated, so the voltage during high-rate discharge increases. The drop is getting bigger.

Batteries with a conventional separator made of polypropylene nonwoven fabric treated with a surfactant, and batteries with a conventional separator made of polypropylene grafted with acrylic acid, tend to degrade as the charge/discharge cycle progresses. , the hydrophilicity of the separator is impaired and carbonate radicals are generated, resulting in a large voltage drop during high rate discharge.

Batteries (K) equipped with conventional separators made by directly sulfonating polypropylene non-woven fabrics that do not graft-polymerize styrene have a high self-discharge rate after charge/discharge cycles. The voltage drop during discharge is as follows:
This is a small value similar to A), (B), (T), and (1), but the separator is likely to be cut during battery manufacturing. This occurs when polypropylene is sulfonated into its fibers.

This is due to a decrease in strength due to partial destruction of the steel.

As described above, by using the separator of the present invention in an alkaline storage battery, the separator is less likely to be cut during assembly of the electric power, and the self-discharge rate after repeated charge/discharge cycles is small. An alkaline storage battery can be obtained that has the advantage of a small voltage drop during high rate discharge.

In addition, in these examples, the case of a sealed alkaline storage battery was explained, or the present invention was explained in the case of an open type (Ghent type).
When used continuously in an alkaline storage battery, the same effects as in the case of a sealed battery can be obtained.

(Experiment 4) Next, in order to confirm the effect of crosslinking in separators A, B, C, and U'D of the present invention, the following batteries were manufactured. That is, through one of these separators, the width is 144 mm, the height is 150 mm, and the heat is 0.9 mm.
10 sintered nickel positive electrode plates with a thickness of 0.0 mm and 11 sintered cadmium negative electrode plates with a thickness of 0.80 mm and the same width and height as the positive electrode plates are stacked, and this electrode plate group is is 3
It was installed in a polypropylene battery case of 100 mL, and an open type (Ghent type) nickel cadmium storage battery was sheathed therein.

In this nickel cadmium battery, separators A, B, and C
Those using 1 and D are called batteries (ke), (k), (su) and (shi), respectively.

Add 5.8 MI ○H water to these batteries (ke) - (shi).
An alkaline electrolyte consisting of a liquid was injected, and the amount of increase in battery thickness caused by each injection was measured at the center of the battery case. The results are shown in Table 2.

(Leaving space below) Table 2 From Table 2, among the separators of the present invention, batteries (C) and (C) using crosslinked separators are compared with batteries (C) and (S) using non-crosslinked separators. Therefore, the increase in thickness is suppressed. This is the battery (ke) and U (su)
In the case of batteries (C) and (C), non-crosslinked separators A and C are immersed in an alkaline electrolyte and swell, causing the electrode plate group to expand and the plastic battery case to be significantly deformed. This is due to the fact that the main chain or side chain is cross-linked, so that swelling during separation is effectively suppressed. Thus, it can be seen that when using a battery case with relatively low strength, an alkaline storage battery with excellent dimensional stability can be obtained by using the separator of the present invention whose main chain or side chain is crosslinked. .

In addition, since batteries (A) to (I) use cylindrical metal containers with high mechanical strength, in this case, even if a non-crosslinked separator is used, the external dimensions of the battery will be significantly reduced. There will be no inconvenience caused by the change.

In addition, in the above examples, the case where polypropylene is used as the polyolefin has been explained, but instead of polypropylene, polyethylene alone, a mixture of polypropylene and polyethylene, or a copolymer of polyethylene and polypropylene can also be used. , similar effects to those of the above embodiment can be obtained.

In addition, in the above example, the case of a nickel cadmium battery was explained, but the above-mentioned problems caused by cutting of the separator during battery assembly, deterioration of the separator as the charge/discharge cycle progresses, and the persistence of hydrophilicity of the separator The phenomenon is
Not only in the case of nickel-cadmium batteries, nickel hydroxide, ferrous oxide, ferric oxide, etc. are used as the main positive electrode active material, and cadmium, hydrogen storage alloy, zinc, iron, etc. are used as the main negative electrode active material. The same thing happens in alkaline storage batteries in combinations such as those used.

Therefore, for example, when using 1st silver oxide or 2nd silver oxide for the positive electrode, or when using zinc for the negative electrode, a non-woven fabric separator is used to prevent minute short circuits due to precipitation of metallic silver or metallic zinc. Although it is necessary to use a film-like barrier separator in addition to the above, the effects of the non-woven fabric separator are the same as those of the present invention in any of these combinations of positive electrode active material and negative electrode active material. is also obtained in the same manner as in the above embodiment.

Effects of the Invention The separator of the present invention is an alkaline material that has the following effects: it is difficult to break the separator during battery manufacturing, the self-discharge rate after the charge/discharge cycle is low, and the voltage drop during high-rate discharge is low. Storage batteries can be provided. Furthermore, even when using a battery case with low mechanical strength, it is possible to provide an alkaline storage battery with excellent dimensional stability.

Claims (1)

[Scope of Claims] 1. A separator for alkaline storage batteries characterized by being made of a nonwoven fabric made of polyolefin having benzenesulfonic acid groups in the side chains. 2. The method for producing a separator for an alkaline storage battery according to claim 1, which comprises graft polymerizing styrene sulfonate to the polyolefin. 3. The method for producing a separator for an alkaline storage battery according to claim 1, characterized in that styrene is graft-polymerized to the polyolefin and then the benzene nucleus is sulfonated. 4. The separator for alkaline storage batteries according to claim 1, wherein the main chain or side chain is crosslinked.