JP2001126698A - Separator for alkaline storage battery and method of fabricating it, and alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an alkaline storage battery that has both durability and permeability. SOLUTION: The separator 5 comprises a first non-woven fabric layer 5a made of polyolefin ultra-fine fiber with an average diameter of 0.5-9 μm to have permeability, and a second woven fabric layer 5b made of polyolefin fiber with an average diameter of at least 10 μm to have permeability. It is arranged in the alkaline storage battery with the positive electrode 6 positioned in the first layer 5a and the negative electrode 7 in the second layer 5b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a battery, and more particularly to a separator for an alkaline storage battery.

[0002]

2. Description of the Related Art With the reduction in size and weight of electronic devices such as mobile phones, it has been required to increase the energy density of alkaline storage batteries, which are portable power sources, while reducing the size and weight. ing. In order to meet such demands, various improvements and reforms of battery components have been studied, such as increasing the capacity of the active materials of the positive electrode and the negative electrode and reducing the thickness of the battery case material. Here, the separator, which is one element of the battery component, is a battery component that is not directly related to the battery capacity unlike the active material and the like, but is a member that affects the miniaturization of the battery by the volume occupancy in the battery. For this reason, the reduction in thickness is pending.

[0003] By the way, a separator used for an alkaline storage battery is usually a fabric formed using polyolefin fibers having excellent heat resistance and oxidation resistance.
It is manufactured by a dry method or a wet method. Here, the dry method is a method of producing a nonwoven fabric from a polyolefin-based fiber by a method such as a needle punch method, but the nonwoven fabric obtained by the method is often inhomogeneous with a high density and a low density. In order to achieve the property, it is necessary to set at least the thickness to about 120 μm, and it is difficult to reduce the thickness of the separator. In addition, the average fiber diameter of the polyolefin fibers used here is as large as ten and several μm, and therefore, the retention of the electrolyte decreases with the thinning, and it is difficult to hold a necessary amount of the electrolyte for the battery. become.

[0004] On the other hand, the wet method is a method of producing a nonwoven fabric by making a polyolefin fiber, and can use a polyolefin fiber having a smaller fiber diameter than the dry method. It is possible to obtain a dense and uniform thin film non-woven fabric having excellent electrolyte retention. However, when the nonwoven fabric obtained by this method holds the electrolytic solution, the nonwoven fabric is held uniformly throughout, so that the air permeability is reduced. For this reason, when such a nonwoven fabric is used as a separator for an alkaline storage battery, particularly for a sealed high-energy density alkaline storage battery, it is difficult to smoothly transmit oxygen gas generated in the positive electrode during overcharge to the negative electrode side. , Which hinders the oxygen gas absorption reaction on the negative electrode side, which may increase the internal pressure of the battery and shorten the battery life. In particular, a phenomenon in which the electrolyte is taken into the positive electrode by repeated charge / discharge cycles and the electrolyte in the separator becomes insufficient, and the internal resistance of the battery increases, leading to a life earlier than the expected life (separator dryout phenomenon) If the excess electrolyte is used to prevent the shortage of the electrolyte on the positive electrode side, the air permeability on the negative electrode side is further reduced, and the internal pressure of the battery increases. easy.

[0005] Nonwoven fabrics manufactured by the wet method are:
Insufficient strength, especially when subjected to sulfonation treatment to suppress self-discharge and increase capacity retention, the strength tends to further decrease, there is a high possibility of damage in the alkaline storage battery manufacturing process In addition, there is a possibility that the deterioration may proceed early to cause a short circuit in the battery.

An object of the present invention is to realize a separator for an alkaline storage battery, which has both an electrolyte retaining property and a gas permeability. Another object of the present invention is to realize an alkaline storage battery that is unlikely to cause a separator dryout phenomenon and that does not easily cause an increase in internal pressure even during overcharge.

[0007]

According to the present invention, there is provided a separator for an alkaline storage battery, comprising: a first layer comprising a breathable nonwoven fabric formed by using polyolefin-based ultrafine fibers having an average fiber diameter of 0.5 to 9 μm; A second layer made of a breathable fabric formed using polyolefin fibers having an average fiber diameter of at least 10 μm and laminated on the first layer.

Here, the air permeability of the first layer is, for example, at least 4 cc / cm ² / sec, and the air permeability of the second layer is set, for example, higher than the air permeability of the first layer. I have. The separator has an ion exchange capacity of, for example, 0.03 to 0.5 meq / g as an exchange amount of potassium ions. In this case, the separator of the present invention has, for example, a sulfonic acid group, and exhibits the above-described ion exchange ability by the sulfonic acid group.

[0009] Such a separator of the present invention is usually
The thickness is set to 90 to 190 μm, and the ratio of the thickness of the first layer to the second layer (first layer / second layer) is 0.1 to 0.1.
6 is set.

[0010] The method for producing a separator for an alkaline storage battery according to the present invention is characterized in that an air-permeable cloth formed using polyolefin fibers having an average fiber diameter of at least 10 µm is coated with an average fiber diameter of 0.5 to 9 µm. The method includes a step of directly disposing the polyolefin-based ultrafine fibers, a step of sulfonating the cloth on which the polyolefin-based ultrafine fibers are disposed, and a step of thermally bonding the polyolefin-based ultrafine fibers to the cloth.

[0011] The alkaline storage battery of the present invention comprises a first layer made of a breathable non-woven fabric formed of polyolefin microfine fibers having an average fiber diameter of 0.5 to 9 µm and a polyolefin-based non-woven fabric having an average fiber diameter of at least 10 µm. A separator comprising a second layer laminated to the first layer, the separator comprising a second layer laminated to the first layer; a positive electrode disposed on the first layer side of the separator;
And a negative electrode disposed on the layer side.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The separator for an alkaline storage battery according to the present invention has a two-layer structure including a first layer and a second layer. The first layer is made of a breathable nonwoven fabric formed using ultrafine fibers. The ultrafine fibers used here are those obtained by spinning a polyolefin-based resin,
That is, it is a polyolefin-based ultrafine fiber having an average fiber diameter of 0.5 to 9 μm, preferably 2 to 7 μm.
belongs to. When the average fiber diameter is less than 0.5 μm, the air permeability of the first layer is reduced, and it becomes difficult to smoothly transmit oxygen gas generated when the alkaline storage battery is overcharged. Conversely, if it exceeds 9 μm, the retention of the electrolyte by the separator is reduced.

The first layer made of a nonwoven fabric using such polyolefin-based ultrafine fibers has an air permeability of at least 4c.
It is preferably set to c / cm ² / sec. When the air permeability is less than 4 cc / cm ² / sec, it may be difficult to smoothly transmit oxygen gas generated during overcharging of the alkaline storage battery. When the separator of the present invention is used in an alkaline storage battery, The internal pressure of the battery may easily increase. The upper limit of the air permeability of the first layer is not particularly limited, but is usually preferably set to 30 cc / cm ² / sec or less from the viewpoint of maintaining good retention of the electrolyte. , 25 cc / cm ² / sec or less.

The thickness of the first layer is usually 20 to 60.
It is preferably set to μm, and more preferably set to 25 to 50 μm. This thickness is 20 μm
If it is less than 3, the electrolyte retention of the separator of the present invention may be reduced. Conversely, if it exceeds 60 μm,
Although the electrolyte retention of the separator of the present invention is further improved, the thickness of the entire separator is increased, which may be an obstacle to downsizing the alkaline storage battery.

The non-woven fabric constituting the first layer can be produced, for example, by a melt blow method. Specifically, the molten polyolefin-based resin extruded from the spinning hole (nozzle) is spun into ultrafine fibers by a high-temperature, high-speed airflow blown from around the spinning hole, and is spun onto a collecting conveyor net or a rotating drum. To form a fibrous web.

On the other hand, the second layer is made of a breathable cloth. This fabric is formed using polyolefin fibers obtained by spinning a polyolefin resin, and is in various forms such as a nonwoven fabric, a woven fabric or a knitted fabric. Here, the polyolefin fiber used has an average fiber diameter of at least 10 μm. When the average fiber diameter is less than 10 μm, the mechanical strength of the separator decreases. As a result, the handleability of the separator at the time of assembling the alkaline storage battery and the like is reduced,
In addition, the separator is likely to be damaged during the repetition of the charge / discharge cycle to cause a short circuit, and the possibility of shortening the life of the alkaline storage battery is increased.

The upper limit of the average fiber diameter of the polyolefin fibers constituting the above-mentioned cloth is not particularly limited, but is usually set to 50 μm or less from the viewpoint of obtaining a cloth with good fiber dispersion. Is preferably set to 40 μm or less.

The second layer made of the above-described cloth has a higher air permeability than the first layer. When the air permeability of the second layer is smaller than that of the first layer, the permeability of oxygen gas generated at the time of overcharging of the alkaline storage battery may decrease, and the internal pressure of the alkaline storage battery may easily increase. By the way, the second
Usually, the air permeability of the layer is preferably set to 35 to 150 cc / cm ² / sec, and 40 to 100 cc / cm 2
More preferably, it is set to ² / sec. 1 air permeability
If it exceeds 50 cc / cm ² / sec, it may be difficult to impart required mechanical strength to the separator. In the present invention, the air permeability of the first and second layers is determined by a gas permeability test using a Frazier tester described in JIS-1096.

The thickness of the second layer is usually 50 to 15
It is preferably set to 0 μm,
More preferably, it is set to m. This thickness is 50
If it is less than μm, the mechanical strength of the separator of the present invention may be insufficient. Conversely, if it exceeds 150 μm,
Although the mechanical strength of the separator of the present invention increases, the thickness of the entire separator increases, which may be an obstacle in reducing the size of the alkaline storage battery.

The polyolefin-based ultrafine fiber and the polyolefin-based resin constituting the polyolefin-based fiber used for the first layer and the second layer, respectively, are not particularly limited, and are usually polyethylene resin or polypropylene resin. And various known compounds, or mixtures thereof. Incidentally, the polyolefin-based ultrafine fiber and the polyolefin-based fiber made of such a polyolefin-based resin can realize a separator having higher strength and short-circuit resistance when an ultrahigh molecular weight polyethylene fiber is blended.

The separator of the present invention has the first
Although it has a two-layer structure in which a layer and a second layer are laminated, the total thickness is usually preferably set to 90 to 190 μm, and more preferably set to 95 to 180 μm. If the thickness is less than 90 μm, the strength of the separator may be insufficient. Conversely, 190
If it exceeds μm, the volume occupancy of the separator in the alkaline storage battery will increase, and it may be difficult to reduce the size of the alkaline storage battery.

Further, the separator of the present invention is set to the above-mentioned thickness, and the ratio of the thickness of the first layer to the second layer (first layer / second layer) is 0.1 to 0.6. It is preferably set, and more preferably set to 0.2 to 0.5. If this ratio exceeds 0.6, the strength of the separator may decrease, and the permeability of oxygen gas generated when the alkaline storage battery is overcharged may decrease. vice versa,
If it is less than 0.1, the retention of the electrolyte by the separator may be reduced.

The separator of the present invention has the first
It has a two-layer structure in which a layer and a second layer are laminated, and preferably has an ion exchange ability.
The ion exchange capacity here is a cation exchange capacity, for example, due to an acidic group such as a sulfonic acid group, a carboxyl group, and an acidic hydroxyl group. Here, the separator of the present invention is:
Those having a sulfonic acid group and exhibiting ion exchange ability by the sulfonic acid group are particularly preferable. In this case, the separator of the present invention can effectively suppress self-discharge of an alkaline storage battery, particularly a nickel-metal hydride battery, and can increase the capacity retention of the battery.

The ion exchange capacity of the separator of the present invention is preferably from 0.03 to 0.5 meq / g as the exchange amount of potassium ions. If the exchange amount is less than 0.03 meq / g, the hydrophilicity and the electrolyte retention of the separator may be reduced, and it may be difficult to increase the energy density of the alkaline storage battery. Further, it becomes difficult to effectively suppress self-discharge of the alkaline storage battery, and as a result, it may be difficult to enhance the capacity retention of the alkaline storage battery. On the other hand, if it exceeds 0.5 meq / g, the strength of these fibers is reduced when the above-mentioned fibers constituting the first layer and the second layer are given such ion exchange capacity. As a result, the mechanical strength of the separator decreases.

The ion exchange capacity in the present invention is measured by the following method. When the terminal of the ion exchange group is a proton, the separator is immersed in a 1/10 mol / dm ³ aqueous solution of KOH (potassium hydroxide), and the amount of KOH consumed by the neutralization reaction at that time is titrated with a normal hydrochloric acid solution. And calculate based on the result.
On the other hand, when a salt is bonded to the terminal of the ion exchange group,
After preliminarily immersing the separator in a 1 mol / dm ³ aqueous hydrogen chloride solution to replace the ends of the ion exchange groups with protons,
The same measurement method as in the case where the terminal of the ion exchange group is a proton is used.

In the separator of the present invention, the electrolytic solution is mainly held by the first layer, and the required mechanical strength and the required air permeability are secured mainly by the second layer. As a result, in the alkaline storage battery using this separator, the electrolyte is mainly held on the first layer side, and the distribution of the electrolyte is dense on the first layer side and sparse on the second layer side. become. For this reason, the second layer
Since the gas permeability can be secured without being hindered by the electrolytic solution, oxygen gas generated at the time of overcharging of the alkaline storage battery can be smoothly transmitted. In addition, this separator is provided with the required mechanical strength by the second layer,
Even when it is set in the same thin film shape as the conventional thin type manufactured by the wet method, it has good handleability at the time of assembling the alkaline storage battery, and it is hard to break even during repeated charge and discharge cycles, and short-circuiting occurs. Hard to invite.

Next, a method for manufacturing the alkaline storage battery separator of the present invention will be described. Here, two methods will be described by taking as an example a case where a separator having an ion exchange ability by a sulfonic acid group is manufactured.

Method 1 In this method, a nonwoven fabric comprising the above-mentioned polyolefin-based ultrafine fibers constituting the first layer and a cloth comprising the above-mentioned polyolefin-based fibers constituting the second layer are separately prepared.
Then, the nonwoven fabric for the first layer and the fabric for the second layer are laminated, and both are integrated. As a method for integrating the two, a method of bonding the two with an adhesive, a method of heat-sealing the two, and a method of embossing or pinsonic processing the laminated nonwoven fabric and cloth Etc. can be adopted.

Next, the laminate of the first layer and the second layer formed as described above is subjected to a sulfonation treatment to give a sulfonic acid group. Thereby, an intended separator is obtained. In this step, the laminate is treated with a sulfonating agent such as fuming sulfuric acid, sulfur dioxide, and concentrated sulfuric acid. As a treatment method, a method of immersing the laminate in fuming sulfuric acid or concentrated sulfuric acid, a method of arranging the laminate in a sulfur dioxide gas stream, or the like can be employed. In the present invention,
In order to maintain the strength of the first layer and the second layer, it is preferable that the laminate be immersed in concentrated sulfuric acid set at a temperature of 100 ° C. or lower and subjected to a sulfonation treatment.

Method 2 In this method, first, a fabric for the second layer is prepared, and the first layer is directly formed thereon. Here, the polyolefin-based ultrafine fibers are sprayed directly onto the fabric for the second layer while being produced by the melt blow method, and the fiber web composed of the ultrafine fibers is directly disposed on the fabric. That is, the nonwoven fabric for the first layer is formed on the cloth for the second layer by directly spraying the polyolefin-based ultrafine fibers.

Next, the cloth on which the nonwoven fabric of the polyolefin-based ultrafine fibers is directly formed, that is, the laminate of the first layer and the second layer is subjected to a sulfonation treatment. Thereby, an intended separator is obtained.
The sulfonation treatment here can be performed in the same manner as in the above-mentioned method 1, but in order to maintain the strength of the first layer and the second layer, the concentration is set to a temperature of 100 ° C. or less. It is preferable to use a method of immersing the laminate in sulfuric acid.

In such a manufacturing method, the laminate is
Usually, hot pressing is performed to thermally bond the first layer and the second layer. The heat press treatment may be performed before the sulfonation treatment on the laminate, or may be performed after the sulfonation treatment. However, in order to efficiently and uniformly sulfonate the first layer and the second layer and uniformly impart a sulfonic acid group to the entire separator, it is preferable to perform a hot press treatment after the sulfonation treatment.

In the above-described production method, the case where a separator having a sulfonic acid group as an ion exchange group is described. However, when a separator having a carboxyl group or an acidic hydroxyl group as an ion exchange group is produced, for example, a graft polymerization method is used. It is preferable to introduce these ion exchange groups in advance into the polyolefin resin for forming the fibers for the first layer and the second layer by such a technique.

The separator of the present invention can be used as a separator for an alkaline storage battery such as a nickel cadmium storage battery or a nickel hydride storage battery. An example of a nickel-metal hydride battery using the separator of the present invention will be described with reference to FIG. In the figure, a nickel-metal hydride storage battery 1 mainly includes a cylindrical liquid-tight battery case 2 having a safety valve (not shown), an electrode group 3 arranged in the battery case 2, and an electrolytic solution 4 injected into the battery case 2. In preparation.

As shown in FIG. 2, the electrode group 3 is composed of a sheet-like member on which a positive electrode 6 and a negative electrode 7 are arranged with a separator 5 interposed therebetween. Are located in Here, the separator 5 is the one of the present invention composed of a laminate of the above-described first layer 5a and second layer 5b. The positive electrode 6 is a nickel electrode in which a nickel foam substrate is filled with an active material mainly composed of nickel hydroxide,
It is arranged on the first layer 5 a side of the separator 5. on the other hand,
The negative electrode 7 is a hydrogen electrode obtained by applying a hydrogen storage alloy together with a binder to a perforated steel sheet, and is disposed on the second layer 5 b side of the separator 5.

The electrolytic solution 4 is, for example, an aqueous solution of potassium hydroxide.
And is impregnated in the separator 5.
Since the nickel-metal hydride battery 1 uses the thin-film separator of the present invention as the separator 5, the volume occupancy of the separator 5 in the battery case 2 can be reduced, and as a result, it is suitable for a mobile phone or the like. It can be effectively used as a small portable power supply.

In this nickel-metal hydride storage battery 1, the electrolyte 4 impregnated in the separator 5 is mainly retained on the first layer 5a side, which has good liquid retention, and relatively on the second layer 5b side. Will be kept low. That is, the distribution of the electrolytic solution 4 in the separator 5 is set densely on the first layer 5a, that is, on the side of the positive electrode 6 that mainly requires the electrolytic solution, and on the side of the second layer 5b, that is, on the side of the negative electrode 7 that requires air permeability. It will be set sparsely. For this reason, in the nickel-metal hydride storage battery 1, even when an excessive electrolytic solution 4 is injected into the battery case 2 in order to prevent a separator dry-out phenomenon, air permeability on the side of the negative electrode 7 in the separator 5 is ensured. Therefore, oxygen gas generated on the positive electrode 6 side during overcharge can be smoothly transmitted to the negative electrode 7 side and absorbed. Therefore, this nickel hydrogen storage battery 1
In the case of overcharging, the internal pressure due to oxygen gas hardly increases even at the time of overcharging, and it is hard to cause the operation of the safety valve and the shortening of the battery life due to leakage of liquid.

Further, in the nickel-metal hydride storage battery 1, since the separator 5 is provided with the hydrophilic property showing the ion exchange ability as described above, self-discharge is difficult and the capacity retention is good.

[0039]

Example 1 (Production of separator for alkaline storage battery)
Production) A polypropylene resin having a melt index of 130 g / 10 min is extruded at a temperature of 295 ° C. at a rate of a single hole discharge of 0.5 g / min, and is extruded at 0.8 kg / cm ² with an air flow set at 300 ° C. It is made of polypropylene resin ultrafine fiber having an average fiber diameter of 3 to 4 μm by melt blow method of drawing and thinning, and has a basis weight of 20 g / m ² and a thickness of 40 μm.
(A first-layer nonwoven fabric) was produced. The air permeability of the first layer nonwoven fabric was 10 cc / m ² / sec when measured using a Frazier-type air permeability tester.

In addition, polypropylene resin filaments having an average fiber diameter of 18 μm were formed into a nonwoven fabric (a second-layer nonwoven fabric) having a basis weight of 22 g / m ² and a thickness of 95 μm. This second-layer nonwoven fabric had high air permeability and air resistance was substantially negligible.

Next, the first-layer nonwoven fabric and the second-layer nonwoven fabric were laminated, and both were integrated by pin sonic processing to obtain a laminate. The pressure of the laminate was adjusted by a calender roll to obtain a thin separator base fabric having a thickness of 95 μm and a basis weight of 42 g / m ² . 80 ° C.
In 98% concentrated sulfuric acid for 1 hour for sulfonation. Thereafter, the base fabric for the thin separator was removed from the concentrated sulfuric acid to remove the attached concentrated sulfuric acid, and further washed with an aqueous potassium hydroxide solution and then washed with water. Thus, a thin separator in which a sulfonic acid group as an ion exchange group was introduced into the first layer nonwoven fabric and the second layer nonwoven fabric was obtained. The ion exchange capacity of the obtained thin separator was 0.06 meq / g as potassium ion exchange capacity.

Comparative Example 1 (of the separator for an alkaline storage battery)
Production) The thin separator base fabric obtained in the production process of Example 1 was treated with polyoxyethylene alkylphenol ether, which is a nonionic surfactant, to impart hydrophilicity. Thus, a thin separator was obtained.

Comparative Example 2 (of an alkaline storage battery separator)
Production) Using a polypropylene resin fiber having an average fiber diameter of 15 μm, a thin separator base fabric made of a nonwoven fabric having a thickness of 95 μm and a basis weight of 42 g / m ² was obtained by a needle punch method. This thin separator base fabric is subjected to a sulfonation treatment and a washing treatment in the same manner as in Example 1,
A thin separator was obtained.

Example 2 (Production of Nickel Metal Hydride Battery) A nickel foam substrate having a porosity of 95% was filled with an active material mainly composed of nickel hydroxide to produce a flexible positive electrode plate. In addition, MmNiAlCoMn 5
A rare earth AB ₅ type hydrogen storage alloy having a primary composition was applied together with a binder to produce a flexible negative electrode plate.

The first separator of the thin separator obtained in Example 1
A positive electrode plate was laminated on the layered nonwoven fabric side, and a negative electrode plate was laminated on the second layered nonwoven fabric side, and the laminate was spirally wound to produce an electrode group. At this time, there was no breakage of the thin separator, and no short circuit between the positive electrode plate and the negative electrode plate occurred. Next, this electrode group was inserted into a cylindrical battery case having a safety valve, and an alkaline electrolytic solution comprising a potassium hydroxide aqueous solution was injected into the battery case. Then, the battery case was closed and hermetically sealed. Thus, an AA-size nickel-metal hydride storage battery (A) having an energy density of 1,500 mAh was manufactured.

Comparative Example 3 (Production of Nickel-Hydrogen Storage Battery) Using the thin separator obtained in Comparative Example 1, a nickel-hydrogen storage battery (B) similar to that of Example 2 was produced.

Comparative Example 4 (Production of Nickel-Hydrogen Storage Battery) Using the thin separator obtained in Comparative Example 2, a nickel-metal hydride storage battery (C) similar to that of Example 2 was produced. At this time, cracks occurred in the thin separator when the laminate composed of the positive electrode plate, the thin separator, and the negative electrode plate was involved, and a short circuit was observed.

Comparative Example 5 (Manufacture of Nickel-Metal Hydride Battery) Except that a negative electrode plate was laminated on the first layer nonwoven fabric side and a positive electrode plate was laminated on the second layer nonwoven fabric side of the thin separator obtained in Example 1 respectively. The same nickel-metal hydride storage battery (D) as in Example 2 was manufactured.

The nickel-metal hydride batteries (A) to (D) obtained in Evaluation Example 2 and Comparative Examples 3 to 5 were subjected to an overcharge test by the following method. For the nickel-metal hydride batteries (A) to (C), a self-discharge test and a cycle durability test were further performed by the following methods.

Overcharge Test Each nickel-metal hydride battery was charged and discharged several cycles to activate it, and then continuously charged at 20 ° C. with a current value of 0.1 CmA for 48 hours. In the battery (A) of Example 2, no abnormality was found due to an increase in the internal pressure of the battery, such as the operation of the safety valve or leakage. On the other hand, the batteries (B) to (D) of the comparative examples are:
The safety valve was activated and leakage was observed.

The batteries (B) and (C) attained the above-mentioned results because the electrolyte was not easily retained by the thin separator, and a free electrolyte was present on the electrode surface. It is considered that the oxygen gas generated on the side was prevented from permeating to the negative electrode side, and the absorption reaction by the negative electrode did not proceed smoothly. In addition, the result of the battery (D) is that the electrolyte is densely distributed on the negative electrode side of the separator, so that the permeation of oxygen gas is similarly prevented, and the absorption reaction of oxygen gas by the negative electrode is inhibited. It seems to be.

Incidentally, for the thin separator according to Example 1 used in the battery (A) and the thin separator according to Comparative Example 2 used in the battery (C), the retention rate of the electrolyte during pressurization (1 kgf / cm ² ) were 170% and 90%, respectively, and it was found that the thin separator according to Example 1 had excellent electrolytic solution holding power.

Self-discharge test Each nickel-metal hydride storage battery was fully charged to a capacity of 150% of the capacity at a current value of 0.1 CmA in an environment of an ambient temperature of 20 ° C., and then the battery voltage was reduced to 1 V at a current value of 0.2 CmA. Discharge was performed until the battery capacity reached, and the initial battery capacity was determined. Next, each battery was fully charged again under the same conditions and left in a 45 ° C. constant temperature bath. The leaving period is 2 days of 7 days and 35 days.
Set to type.

After leaving, the battery was discharged under the same conditions as above, and the battery capacity was determined. Then, the ratio of the battery capacity after being left to the initial battery capacity was determined, and this was defined as the capacity retention rate. The results are shown in FIG. From FIG. 3, it can be seen that the battery (A) exhibits an excellent capacity retention ratio as compared with the batteries (B) and (C) and is less likely to self-discharge.

Cycle Endurance Test Each nickel-metal hydride battery was charged to 120% of its capacity at a current value of 0.3 CmA at an ambient temperature of 20 ° C., and the battery voltage was raised to 1 V at a current value of 0.5 CmA. It was discharged until it became. Each battery was repeatedly charged and discharged with this charge-discharge operation as one cycle, and the discharge capacity and change in internal resistance for each cycle were measured. FIG. 4 shows the results.

As shown in FIG. 4, the battery (A) shows stable cycling characteristics for a long period of time, but the battery (B) has an internal resistance that increases early and its capacity decreases, and the battery (C) has a battery (B) It can be seen that although the cycle characteristics are relatively stable as compared with the case of, the internal resistance starts to increase gradually and the capacity decreases. The reason why the internal resistance increased early in the battery (B) is presumably because the surfactant applied to the separator was released or decomposed at an early stage, whereby the hydrophilicity of the separator itself was decreased at an early stage. On the other hand, the reason why the internal resistance gradually increased in the battery (C) is considered to be that the positive electrode gradually swelled as the charge / discharge cycle was repeated, thereby causing a separator dryout phenomenon.

Incidentally, when the battery (A) was disassembled, although swelling of the positive electrode was observed, the battery (A),
It is recognized that the electrolyte is held on the layer nonwoven fabric side,
It was confirmed that it suppressed the separator dryout phenomenon.

[0058]

The separator for an alkaline storage battery according to the present invention is obtained by laminating the first layer and the second layer as described above, so that the separator can be made thin while maintaining both the retention of the electrolyte and the air permeability. be able to.

Further, in the alkaline storage battery of the present invention, the positive electrode is disposed on the first layer side of the separator of the present invention, and the negative electrode is disposed on the second layer side. Even when charging, the internal pressure is unlikely to rise.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a nickel-metal hydride storage battery according to an embodiment of the present invention.

FIG. 2 is a partial sectional view of an electrode group used in the nickel-metal hydride storage battery.

FIG. 3 is a diagram showing a result of a self-discharge test of a battery performed in an example.

FIG. 4 is a view showing the results of a cycle endurance test of a battery performed in an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nickel-metal hydride storage battery 5 Separator 5a 1st layer 5b 2nd layer 6 Positive electrode 7 Negative electrode

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) D04H 3/00 D04H 3/00 D 3/14 3/14 Z H01M 10/28 H01M 10/28 A (72 ) Inventor Masahiko Oshitani 2-3-1, Kosobe-cho, Takatsuki-shi, Osaka Inside Yuasa Corporation (72) Inventor Toshio Tanaka 2-1-1 Katata, Otsu-shi, Shiga Prefecture Toyobo Co., Ltd. (72) ) Inventor Naohiko Takimoto 2-1-1 Katata, Otsu-shi, Shiga F-Term in Toyobo Co., Ltd. Research Laboratory (reference) CA05 CA19 CB08 CC12 DA00 5H021 BB09 BB11 CC01 CC02 CC04 EE04 HH00 HH02 HH03 HH07 5H028 AA05 HH00 HH05

Claims (7)

[Claims] 1. A first layer made of a nonwoven fabric having air permeability formed using polyolefin-based ultrafine fibers having an average fiber diameter of 0.5 to 9 μm, and an average fiber diameter laminated on the first layer is At least 10
and a second layer made of a breathable fabric formed using a polyolefin-based fiber having a thickness of μm. 2. The air permeability of the first layer is at least 4 cc /
cm ² / sec, and the air permeability of the second layer is
The alkaline storage battery separator according to claim 1, wherein the separator is set to have a larger air permeability than the layer. 3. The method according to claim 3, wherein the exchange amount of potassium ion is 0.03 to
3. The alkaline storage battery separator according to claim 1, wherein the separator has an ion exchange capacity of 0.5 meq / g. 4. The alkaline storage battery separator according to claim 3, wherein the separator has a sulfonic acid group, and exhibits the ion exchange ability by the sulfonic acid group. 5. The method according to claim 1, wherein the thickness is set to 90 to 190 μm, and the ratio of the thickness of the first layer to the thickness of the second layer (first layer /
The alkaline storage battery separator according to claim 1, wherein the second layer is set to 0.1 to 0.6. 6. A step of directly arranging ultrafine polyolefin fibers having an average fiber diameter of 0.5 to 9 μm on a breathable cloth formed using polyolefin fibers having an average fiber diameter of at least 10 μm. A method for producing a separator for an alkaline storage battery, comprising: a step of sulfonating the cloth on which the polyolefin-based ultrafine fibers are arranged; and a step of thermally bonding the polyolefin-based ultrafine fibers to the cloth. 7. A first layer made of a nonwoven fabric having air permeability formed by using ultrafine polyolefin fibers having an average fiber diameter of 0.5 to 9 μm, and an average fiber diameter of at least 10 μm.
A separator comprising a second layer laminated on the first layer, the separator comprising a second layer laminated on the first layer, and a positive electrode disposed on the first layer side of the separator. An alkaline storage battery comprising: a negative electrode disposed on the second layer side of the separator.