JP2006114259A - Separator for alkaline storage battery, and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for an alkaline storage battery which can improve adhesiveness of the separator base material (non-woven fabric etc.) and a gelatinous electrolyte and can improve self-discharge characteristics for a long period, and the alkaline storage battery which is improved in adhesiveness of the separator base material and the gelatinous electrolyte and improved in self-discharge characteristics for a long period. <P>SOLUTION: The separator for the alkaline storage battery is provided with a separator base material which has a three-dimensional network structure made of fiber and includes an air gap in which a plurality of holes are connected three-dimensionally, and a water absorptive polymer which is arranged at the air gap portion of the separator base material, and when contacted with the alkali electrolytic liquid, absorbs this alkali electrolytic liquid and becomes a gelatinous electrolyte. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an alkaline storage battery separator having a water-absorbing polymer, and an alkaline storage battery using the separator.

  Alkaline storage batteries are attracting attention as power sources for portable devices and portable devices, and as power sources for electric vehicles and hybrid vehicles. Various types of such alkaline storage batteries have been proposed. Of these, nickel-metal hydride including a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy is included. Secondary batteries are rapidly spreading as secondary batteries with high energy density and excellent reliability.

  By the way, in a nickel metal hydride secondary battery, when charging and discharging are repeated at a high temperature, the hydrogen storage alloy tends to react with the alkaline electrolyte and corrode. When the components of the hydrogen storage alloy become metal ions and are eluted in the alkaline electrolyte due to corrosion, the metal ions are deposited on the separator and the positive electrode, and the conductive precipitates cause continuous conduction between the positive electrode and the negative electrode. A path might be formed. For this reason, in particular, when charge and discharge are repeated at a high temperature, there is a problem that the self-discharge characteristics are deteriorated (deteriorated).

On the other hand, in recent years, alkaline storage batteries having good self-discharge characteristics have been proposed (see, for example, Patent Document 1 and Patent Document 2).
JP 2002-33093 A JP 2003-115323 A

In patent document 1, the separator layer is made into the gel form by making a separator layer contain a water absorbing polymer. This suppresses the progress of the corrosion of the hydrogen storage alloy, enhances the liquid retention of the separator layer, and improves the self-discharge characteristics and cycle life characteristics.
Further, in Patent Document 2, attention is paid to the monomer constituting the water-absorbing polymer, and 100 parts by weight of the monomer (A) having one carboxyl group and one polymerizable double bond by saponification, and a polymerizable double bond. By using a water-absorbing polymer obtained by saponifying a copolymer of 0.01 to 10 parts by weight of the monomer (B) having two or more, an alkaline storage battery with less self-discharge and excellent capacity recovery after storage is realized. Yes.

  By the way, in recent years, regarding alkaline storage batteries such as nickel hydride secondary batteries (especially when used for power sources of electric vehicles and hybrid vehicles), there is an increasing demand for longer battery life. Then, about the battery of patent document 1 and patent document 2, after performing the charge / discharge cycle test of 1000 cycles, when the self-discharge characteristic was evaluated, the favorable self-discharge characteristic was not able to be obtained. That is, in the batteries of Patent Document 1 and Patent Document 2, good self-discharge characteristics could not be maintained after repeated charging and discharging over a long period of time.

  According to the present inventors, in the batteries of Patent Document 1 and Patent Document 2, it is presumed that a large amount of ammonia was generated in the battery due to repeated charging and discharging over a long period of time. Therefore, in the batteries of Patent Document 1 and Patent Document 2, it is considered that the self-discharge characteristics are deteriorated due to the influence of ammonia.

  The present invention has been made in view of the current situation, and is a separator for an alkaline storage battery capable of improving the self-discharge characteristics of a battery over a long period of time, and has a good self-discharge characteristic over a long period of time. An object is to provide an alkaline storage battery.

  The solution includes a separator base material including a three-dimensional network structure composed of fibers, and a plurality of pores connected in three dimensions. The separator base material absorbs an alkaline electrolyte. Then, the separator base material is provided with a water-absorbing polymer to be a gel electrolyte, the separator base material is sulfonated, and the water-absorbing polymer is a separator for an alkaline storage battery having a sulfo group.

  The separator for alkaline storage batteries of this invention is equipped with the separator base material and the water absorbing polymer arrange | positioned in the space | gap part. Of these, the water-absorbing polymer becomes a gel electrolyte when absorbing the alkaline electrolyte. Therefore, in the alkaline storage battery using the separator of the present invention, the fiber surface of the separator base material can be covered with the gel electrolyte. For this reason, the liquid retention property of the separator is improved, and a conductive path connecting the positive and negative electrodes along the surface of the separator substrate fiber is less likely to be formed. Discharge can be reduced).

  Furthermore, in the separator for alkaline storage batteries of the present invention, the separator substrate is sulfonated. That is, the fiber constituting the separator substrate contains a sulfo group. Therefore, since the ammonia in the battery can be captured by the sulfo group, self-discharge due to the influence of ammonia can be suppressed.

  By the way, when performing a sulfonation process to a separator base material, it is difficult to sulfonate appropriately over the whole separator base material. Specifically, when the sulfonation treatment with sulfuric anhydride or fuming sulfuric acid is performed, the fibers on the outside (surface side) of the separator base material are easily sulfonated because they are easily contacted with sulfuric anhydride or fuming sulfuric acid. However, it is difficult to appropriately sulfonate the fibers on the inner side (back side) of the separator base material because sulfuric anhydride or fuming sulfuric acid does not easily reach that portion. In addition, since the separator base material has the density of the fibers, it is difficult to appropriately sulfonate the inner (back side) fibers even in the portion where the fibers are concentrated. On the other hand, when the sulfonation treatment is performed on the separator base material, the separator base material is severely damaged and the strength is remarkably reduced, so that the life characteristics are greatly deteriorated. For these reasons, it is difficult to adequately sulfonate the separator substrate as a whole.

  Therefore, the sulfonated separator base material alone cannot adequately capture the ammonia in the battery, and if it is repeatedly charged and discharged over a long period of time, self-discharge due to the influence of ammonia is sufficient. Can not be suppressed.

On the other hand, in the separator for alkaline storage batteries of the present invention, the water-absorbing polymer disposed in the gap portion of the separator substrate is also provided with a sulfo group. Therefore, in the battery using the separator of the present invention, the fiber surface of the separator substrate can be covered with a gel electrolyte containing a sulfo group. As a result, even in a portion of the separator substrate that is not sulfonated (or less sulfonated), a certain amount of sulfo groups can be present by the gel electrolyte. Thus, ammonia can be suitably captured by arranging sulfo groups throughout the separator substrate. Therefore, even when charging and discharging are repeatedly performed over a long period of time, ammonia in the battery can be appropriately captured, and self-discharge due to the influence of ammonia can be sufficiently suppressed.
As described above, the alkaline storage battery separator of the present invention can improve the self-discharge characteristics of the battery over a long period of time.

Furthermore, in the above separator for an alkaline storage battery, the degree of sulfonation of the separator base material is 1 × 10 ^{−3 to} 6 × 10 ⁻³ , and the amount of S element contained in the water-absorbing polymer is It is preferable that the separator for an alkaline storage battery be 0.1 to 2.0 (%) with respect to the amount of S element contained in the fiber constituting the separator substrate.

In the alkaline storage battery separator of the present invention, the separator substrate has a sulfonation degree of 1 × 10 ^{−3 to} 6 × 10 ⁻³ . By setting the degree of sulfonation to 1 × 10 ⁻³ , it is possible to appropriately capture ammonia in the battery in the separator base material. Further, by limiting the degree of sulfonation to 6 × 10 ⁻³ or less, it is possible to refrain from extreme sulfonation treatment and to suppress a decrease in strength of the separator substrate. Therefore, it is possible to ensure the strength with which the separator substrate can be used over a long period of time, and to prevent problems such as a short circuit between the positive and negative electrodes.

  In addition, in the alkaline storage battery separator of the present invention, the amount of S contained in the water-absorbing polymer is 0.1% or more with respect to the amount of S contained in the fibers constituting the separator substrate. That is, the amount of the sulfo group contained in the water-absorbing polymer is set to 0.1% or more with respect to the amount of the sulfo group contained in the fiber constituting the separator substrate in the above ratio. Therefore, in the battery using the separator of the present invention, the amount of the sulfo group contained in the gel electrolyte is set to 0.1% or more with respect to the amount of the sulfo group contained in the fiber constituting the separator substrate in the above ratio. be able to. By covering the surface of the fiber of the separator substrate with a gel electrolyte containing a sulfo group at such a ratio, a predetermined amount or more of sulfo groups can be arranged over the entire separator substrate, preferably, Ammonia can be captured. Therefore, even when charging and discharging are repeatedly performed over a long period of time, ammonia in the battery can be appropriately captured, and self-discharge due to the influence of ammonia can be sufficiently suppressed.

  However, since there is a limit to the amount of S (sulfo group amount) that can be contained in the water-absorbing polymer per unit amount, in order to increase the amount of S contained in the water-absorbing polymer, the amount of the water-absorbing polymer Must be increased. However, when the amount of the water-absorbing polymer is excessively increased, the amount of the gel electrolyte is excessively increased in the battery, resulting in a problem that the internal pressure and the electric resistance are excessively increased.

  On the other hand, in the alkaline storage battery separator of the present invention, the amount of S contained in the water-absorbing polymer is 2.0% or less with respect to the amount of S contained in the fiber constituting the separator substrate. That is, by limiting the amount of the sulfo group contained in the water-absorbing polymer to 2.0% or less with respect to the amount of the sulfo group contained in the fiber constituting the separator substrate in the above proportion, Limit the amount of polymer. Thus, since the amount of the gel electrolyte can be limited by using the separator with the limited amount of the water-absorbing polymer, the separator can be sufficiently ventilated to improve the internal pressure characteristics of the battery (internal pressure Increase). Moreover, the raise of the electrical resistance by a gel-like electrolyte can also be suppressed.

The degree of sulfonation is a value obtained by (number of S atoms contained in the fiber) / (number of C atoms contained in the fiber) and is an index representing the degree of sulfonation of the separator substrate. . The degree of sulfonation can be calculated as follows based on the weight of the S element and the weight of the C element, for example. The weight of the S element contained in the fiber of the separator substrate can be obtained by using, for example, a combustion method. Specifically, the concentration of (SO ₄ ) ²⁻ contained in the combustion gas obtained by burning the separator substrate can be measured, and the weight of the S element can be calculated from the concentration. Further, the intensity ratio between the peak of the S element and the peak of the C element can be measured using a known fluorescent X-ray measurement apparatus, and the weight of the S element can be calculated based on the intensity ratio. However, the weight of the S element can be obtained with higher accuracy by using the combustion method.

Moreover, the weight of C element contained in the fiber of a separator base material can be calculated as follows. For example, when the separator substrate is a nonwoven fabric or a woven fabric, the repeating structure of methylene groups (—CH ₂ —) occupies most of the molecules of the resin (eg, polypropylene, polyethylene, etc.) constituting the fiber. Therefore, it is considered that the fiber of the separator base material is composed of methylene groups (—CH ₂ —), and the ratio of the C element in the separator base material to the weight of the separator base material (atomic weight of C / molecular weight of methylene group = 12/14) can be multiplied to calculate the weight of the C element contained in the fiber of the separator substrate.
The degree of sulfonation can be calculated based on the weight of the S element and the weight of the C element calculated as described above.

  Further, the ratio of the amount of S element contained in the water-absorbing polymer to the amount of S element contained in the fiber constituting the separator substrate can be calculated as follows. The weight of the S element contained in the water-absorbing polymer can be calculated based on, for example, components constituting the water-absorbing polymer and the weight of the entire water-absorbing polymer. Specifically, the molar fraction of the S element in the water-absorbing polymer is calculated based on the molecular weight of the component constituting the water-absorbing polymer and the content of the component. Then, the weight of the S element contained in the water absorbent polymer can be calculated by multiplying the molar fraction by the weight of the water absorbent polymer.

Moreover, the weight of the S element contained in the fiber constituting the separator substrate can be obtained by using a combustion method or the like as described above. When the degree of sulfonation of the separator base material is known, for example, as described above, the separator base material is regarded as being composed of methylene groups (—CH ₂ —), and the separator base material The weight of the C element contained in the fibers of the S element can be calculated, and the weight of the S element can be calculated based on the weight of the C element and the degree of sulfonation. Thereby, the ratio of the amount (weight) of the S element contained in the water-absorbing polymer to the amount (weight) of the S element contained in the fiber constituting the separator substrate can be calculated. In addition, although the example which compared the ratio of the weight of S was shown here, you may make it compare the number of atoms and the number of moles of S.

Furthermore, in any of the above alkaline storage battery separators, the separator base material may be an alkaline storage battery separator having a basis weight of 40 to 70 (g / m ² ) and a thickness of 120 to 200 (μm). .

In the separator for alkaline storage batteries of the present invention, the basis weight of the separator substrate is 40 to 70 (g / m ² ) and the thickness is 120 to 200 (μm). By using a separator base material having a basis weight of 40 (g / m ² ) or more and a thickness of 120 (μm) or more, self-discharge characteristics can be further improved (self-discharge can be reduced). . This is because the basis weight is 40 (g / m ² ) or more and the thickness is 120 (μm) or more, so that the path between the positive electrode and the negative electrode along the fiber of the separator substrate (hereinafter referred to as inter-electrode path). This is considered to be because it is difficult to form a conductive path connecting the two electrodes.

Further, by setting the basis weight to 70 (g / m ² ) or less and the thickness to 200 (μm) or less, it is possible to improve the internal pressure characteristics of the battery (suppress the increase in internal pressure). By restricting the basis weight to 70 (g / m ² ) or less, it is possible to secure a large void portion of the separator base material and improve the air permeability of the separator, and the thickness is 200 (μm). By limiting to the following, it is considered that the occupied volume of the separator substrate in the battery can be suppressed.

  Furthermore, in any of the above alkaline storage battery separators, the water-absorbing polymer may be an alkaline storage battery separator formed by crosslinking with at least one of divinylbenzene and divinylnaphthalene.

  Divinylbenzene and divinylnaphthalene are monomers that act as crosslinking agents and are extremely stable in alkaline solutions. Therefore, the water-absorbing polymer can be stably present for a long period of time in the alkaline electrolyte (gel electrolyte) by crosslinking with at least one of divinylbenzene and divinylnaphthalene. That is, the gel electrolyte can be stably present over a long period of time on the fiber surface of the separator substrate. Thereby, the self-discharge characteristic of the battery can be further improved.

  Furthermore, in any of the above alkaline storage battery separators, the separator base material is preferably an alkaline storage battery separator having at least two types of fibers having different degrees of sulfonation.

  In the separator for alkaline storage batteries of the present invention, the separator substrate has at least two types of fibers having different degrees of sulfonation. That is, the separator base material is composed of two or more kinds of fibers having different hydrophilicity. For this reason, in the alkaline storage battery using the separator of the present invention, the gel electrolyte and the alkaline electrolyte can be unevenly distributed in the gap portion of the separator substrate. Specifically, by allowing a gel electrolyte and an alkaline electrolyte to be concentrated and held in a fiber having a high degree of sulfonation, an air passage can be formed around the fiber having a low degree of sulfonation. Therefore, both liquid retention and air permeability can be improved.

  Furthermore, in any of the above-described alkaline storage battery separators, the separator base material may be an alkaline storage battery separator including a split composite fiber.

In the separator for alkaline storage batteries of the present invention, the separator base material includes split-type composite fibers. By including the split-type conjugate fiber, the interelectrode path can be increased, and the formation of the conductive path connecting the electrodes can be suppressed. Therefore, the self-discharge characteristic of the battery can be further improved.
The split type composite fiber refers to an ultrafine fiber obtained by performing composite spinning of two or more different components to form a cloth and then splitting.

  Furthermore, in any of the above-described alkaline storage battery separators, the separator base material may be an alkaline storage battery separator made of a nonwoven fabric in which a plurality of papermaking web layers are laminated.

  In the separator for alkaline storage batteries of the present invention, the separator substrate is made of a nonwoven fabric in which a plurality of papermaking web layers are laminated. When a nonwoven fabric obtained by laminating a plurality of papermaking web layers is used as the separator substrate, self-discharge characteristics are improved as compared with the case of using a single-layer nonwoven fabric. This is because a non-woven fabric obtained by laminating a plurality of papermaking web layers increases the number of discontinuous surfaces between the papermaking web layers, so that a conductive path is formed to connect the positive and negative electrodes along the fibers of the separator substrate. This is thought to be difficult.

  The papermaking web layer refers to an aggregate of fibers made from a slurry with a net and is in the form of a single sheet. Further, the nonwoven fabric forming the separator substrate may be either a wet nonwoven fabric or a dry nonwoven fabric.

  Furthermore, in the above separator for an alkaline storage battery, each of the plurality of papermaking web layers includes a split type composite fiber composed of at least two kinds of components selected from polypropylene, polyethylene, polystyrene, polymethylpentene, and polybutylene. A separator for an alkaline storage battery is preferable.

  In the alkaline storage battery separator of the present invention, the plurality of papermaking web layers forming the separator base material include a split type composite fiber composed of at least two kinds of components selected from polypropylene, polyethylene, polystyrene, polymethylpentene, and polybutylene. Yes. Since the split-type composite fiber made of these fibers has a high melting point, even when heat is applied in the process of forming the nonwoven fabric, the crystal form of the split-type composite fiber is not easily broken, and the formation can be kept good. Therefore, by including such a split composite fiber, the interelectrode path can be made sufficiently large, and the formation of a conductive path that connects the electrodes can be suppressed.

  Another solution is an alkaline storage battery comprising a positive electrode, a negative electrode, and any one of the above separators for an alkaline storage battery, wherein the water-absorbing polymer absorbs the alkaline electrolyte and becomes a gel electrolyte. .

  The alkaline storage battery of the present invention has any of the separators for alkaline storage batteries described above, wherein the water-absorbing polymer absorbs the alkaline electrolyte and becomes a gel electrolyte. Therefore, in the alkaline storage battery of the present invention, the fiber surface of the separator substrate can be covered with the gel electrolyte. For this reason, while the liquid retention property of a separator becomes favorable and since it becomes difficult to form a conductive path between a positive electrode and a negative electrode, a self-discharge characteristic can be made favorable (self-discharge can be reduced).

  Furthermore, in the alkaline storage battery of the present invention, the separator substrate is sulfonated. That is, the fiber constituting the separator substrate contains a sulfo group. Therefore, since the ammonia in the battery can be captured by the sulfo group, self-discharge due to the influence of ammonia can be suppressed.

  Furthermore, in the alkaline storage battery of the present invention, since the water-absorbing polymer has a sulfo group, the fiber surface of the separator substrate can be covered with a gel electrolyte containing a sulfo group. As a result, even in a portion of the separator substrate that is not sulfonated (or less sulfonated), a certain amount of sulfo groups can be present by the gel electrolyte. Thus, ammonia can be suitably captured by arranging sulfo groups throughout the separator substrate. Therefore, even when charging and discharging are repeatedly performed over a long period of time, ammonia in the battery can be appropriately captured, and self-discharge due to the influence of ammonia can be sufficiently suppressed.

As described above, the alkaline storage battery of the present invention can improve the self-discharge characteristics (reduce self-discharge) over a long period of time.
In addition, as an alkaline storage battery of this invention, a nickel-cadmium storage battery, a nickel-hydrogen storage battery, a nickel-zinc storage battery etc. are mentioned, for example.

  Another solution includes a separator substrate including a positive electrode, a negative electrode, and a three-dimensional network structure composed of fibers, and a void portion in which a plurality of holes are three-dimensionally connected, and a position within the void portion of the separator substrate. And a gel electrolyte formed by absorbing an alkaline electrolyte in the water-absorbing polymer, the separator base material is sulfonated, and the water-absorbing polymer has a sulfo group. It is.

  The alkaline storage battery of the present invention has a gel electrolyte that is located in the gap portion of the separator substrate and has a water-absorbing polymer that absorbs an alkaline electrolyte. For this reason, while the liquid retention property of a separator becomes favorable and since it becomes difficult to form a conductive path between a positive electrode and a negative electrode, a self-discharge characteristic can be made favorable (self-discharge can be reduced).

  Furthermore, in the alkaline storage battery of the present invention, the separator substrate is sulfonated. That is, the fiber constituting the separator substrate contains a sulfo group. Therefore, since the ammonia in the battery can be captured by the sulfo group, self-discharge due to the influence of ammonia can be suppressed.

Furthermore, in the alkaline storage battery of the present invention, since the water-absorbing polymer has a sulfo group, the fiber surface of the separator substrate can be covered with a gel electrolyte containing a sulfo group. As a result, even in a portion of the separator substrate that is not sulfonated (or less sulfonated), a certain amount of sulfo groups can be present by the gel electrolyte. Thus, ammonia can be suitably captured by arranging sulfo groups throughout the separator substrate. Therefore, even when charging and discharging are repeatedly performed over a long period of time, ammonia in the battery can be appropriately captured, and self-discharge due to the influence of ammonia can be sufficiently suppressed.
As described above, the alkaline storage battery of the present invention can improve the self-discharge characteristics (reduce self-discharge) over a long period of time.

  Furthermore, the alkaline storage battery according to any one of the above, wherein the alkaline storage battery includes an excess alkaline electrolyte that maintains a liquid state without being absorbed by the water-absorbing polymer.

  The alkaline storage battery of the present invention includes an excess alkaline electrolyte that maintains a liquid state without being absorbed by the water-absorbing polymer. Therefore, in the alkaline storage battery of the present invention, the gel electrolyte is in a saturated state in which the water-absorbing polymer absorbs the alkaline electrolyte as much as possible. With this saturated gel electrolyte, the surface of the fiber of the separator substrate is covered. Can be covered. As a result, the effect of improving the liquid retention of the separator by the gel electrolyte and the effect of suppressing the conductive path connecting the positive and negative electrodes can be obtained to the maximum, so that the self-discharge characteristic is further improved (self Discharge can be reduced).

  In addition, even when the alkaline electrolyte contained in the gel electrolyte decreases with repeated charge and discharge, the water-absorbing polymer absorbs excess alkaline electrolyte present in the battery (in the voids of the separator substrate). Thus, the gel electrolyte can be returned to a saturated state. Therefore, in the alkaline storage battery of the present invention, the gel electrolyte can be maintained in a saturated state for a long period of time, so that the self-discharge characteristics can be improved for a long period of time.

  Next, an embodiment of the present invention will be described.

(Step 1: Production of separator substrate)
First, polypropylene fibers are dispersed in water to prepare a slurry. A paper web layer is then created from the slurry using a wet paper machine. Next, the papermaking web layer was subjected to dehydration treatment, heat treatment, and the like to produce a single-layer wet nonwoven fabric. Thereafter, the wet nonwoven fabric was sulfonated with sulfuric anhydride to obtain a separator substrate. In addition, the fiber density of the fiber which comprises a separator base material is 0.91 g / cm < ³ >. Further, the basis weight of the separator substrate is 60 (g / m ² ) and the thickness is 200 (μm). The degree of sulfonation of the separator base material is 3.0 × 10 ⁻³ .

(Step 2: Production of gel dispersion)
Sodium styrenesulfonate, methyl acrylate, and divinylbenzene were mixed at a molar ratio of 50: 50: 3, and the copolymerization reaction was promoted by adding pure water and stirring the mixture. Thus, a gel dispersion having a gel solid content of 6% by weight, in which the water-absorbing polymer was gelled, was obtained. In addition, since it contains and copolymerizes divinylbenzene as mentioned above, a water absorbing polymer can be bridge | crosslinked with divinylbenzene.

(Step 3: Production of separator)
The separator substrate produced in step 1 is immersed in the gel dispersion obtained in step 2 for a predetermined time. Thereafter, the separator base material is taken out from the gel dispersion and dried to dispose the water-absorbing polymer in the voids of the separator base material. By repeating such an operation, a separator in which a predetermined amount of the water-absorbing polymer was disposed in the gap portion of the separator substrate was manufactured. In Example 1, the content of the water-absorbing polymer (dry state) is 8.33 g / m ² .

Here, for the separator of Example 1, the amount of S element contained in the water-absorbing polymer is compared with the amount of S element contained in the fiber constituting the separator substrate.
First, the weight of S contained in the fiber constituting the separator substrate was calculated as follows. Separator substrate in the first embodiment, since the polypropylene fibers, the fibers of the separator substrate is a methylene group (-CH ₂ -) if regarded as being constituted by the separator base material 1 m ² per methylene group (- The number of moles of CH ₂ −) is (weight of separator) / (molecular weight of methylene group) = 60/14 = 4.29 (mol / m ² ). Therefore, the number of moles of the C element per 1 m ^{2 of} the separator base material is equal to this and is 4.29 (mol / m ² ). Therefore, the amount of S element per 1 m ^{2 of} separator base material is (number of moles of C element per 1 m ^{2 of} separator base material) × (degree of sulfonation) × (atomic weight of S) = 4.29 × 3.0 × 10 ⁻³ × 32 = 0.41 (g / m ² ).

Subsequently, the weight of S element contained in the water-absorbing polymer was calculated as follows. First, the mole fraction of S element in the water-absorbing polymer is calculated. Specifically, the water-absorbing polymer of Example 1 is composed of styrene sulfonic acid (molecular weight 207), methyl acrylate (molecular weight 86), and divinylbenzene (molecular weight 131) in a ratio of 50: 50: 3. Can be considered. At this time, the molar fraction of the S element in the water-absorbing polymer can be calculated as (32/207) × 50 / (207 × 50 + 86 × 50 + 131 × 3) = 5.14 × 10 ⁻⁴ . Therefore, the weight of the S element contained in the water-absorbing polymer per 1 m ^{2 of} the separator base material is (content of water-absorbing polymer per 1 m ^{2 of the} separator base material) × (mol fraction of S element) = 8.33 × 5.14 × 10 ⁻⁴ = 4.28 × 10 ⁻³ (g / m ² ).

Therefore, in the separator of Example 1, the amount of S element contained in the water-absorbing polymer is (4.28 × 10 ⁻³ /0.41) with respect to the amount of S element contained in the fibers constituting the separator substrate. ) × 100 = 1.04 (%).

(Step 4: Fabrication of positive electrode)
An active material paste containing nickel hydroxide particles was filled in foamed nickel, dried, and then press-molded to produce a nickel positive electrode plate. Subsequently, this nickel positive electrode plate was cut into a predetermined size to obtain a positive electrode.
(Step 5: Production of negative electrode)
A paste containing a hydrogen storage alloy was applied to a conductive electrode support, dried, and then pressure-molded to produce a hydrogen storage alloy negative electrode plate. Next, the hydrogen storage alloy negative electrode plate was cut into a predetermined size to obtain a negative electrode.

(Step 6: Assembling the alkaline storage battery)
The positive electrode, the negative electrode, and the separator manufactured as described above were alternately laminated so that the separator was interposed between the positive electrode and the negative electrode, thereby preparing an electrode group. Next, this electrode group was inserted into the case, and an alkaline electrolyte (a potassium hydroxide aqueous solution having a specific gravity of 1.27) was injected. At this time, the water-absorbing polymer contained in the separator absorbs the alkaline electrolyte and becomes a gel electrolyte. Then, the case was sealed with the sealing board provided with a safety valve, and the alkaline storage battery (nickel metal hydride storage battery) was obtained. In the first embodiment, the battery capacity is set to 6.5 Ah.

  Further, in the alkaline storage battery of Example 1, an excess alkaline electrolyte exceeding the amount that the gel electrolyte is saturated (exceeding the amount of alkaline electrolyte that can be absorbed by the water-absorbing polymer) is injected. Therefore, there is an excess alkaline electrolyte in the battery (inside the case) that remains liquid without being absorbed by the water-absorbing polymer.

(Comparative Example 1)
In Comparative Example 1, unlike Example 1, in Step 1, a separator base material was produced without applying a hydrophilic treatment to the nonwoven fabric. About others, it carried out similarly to Example 1, and produced the alkaline storage battery whose battery capacity was 6.5 Ah.

(Comparative Example 2)
In Comparative Example 2, unlike Example 1, a separator containing no water-absorbing polymer was produced. That is, the separator base material (sulphonated) prepared in Step 1 was used as a separator as it was without performing Steps 2 and 3. About others, it carried out similarly to Example 1, and produced the alkaline storage battery whose battery capacity was 6.5 Ah.

(Self-discharge characteristic evaluation test)
Next, self-discharge characteristic evaluation tests were performed on the alkaline storage batteries of Example 1 and Comparative Examples 1 and 2, respectively. First, 1000 cycles of charge / discharge cycle tests were performed for each battery. In addition, charging / discharging which is charged for 30 minutes at 2C (13A) and discharged until the battery voltage becomes 1V at 2C (13A) is defined as one cycle. Thereafter, each alkaline storage battery was charged to SOC (State Of Charge) 60% at a current of 0.6 C (3.9 A) and left in an atmosphere at 45 ° C. for 1 week. Here, 1C = 6.5A, SOC 100% = 6.5Ah.

  Next, after discharging at 0.3 C (1.95 A) until the battery voltage reached 1.0 V, the remaining SOC (%) of each battery was measured. For each battery, the maximum internal pressure (MPa) when charged at 2 A for 4 hours was measured (hereinafter, this value is simply referred to as internal pressure). Further, the electrical resistance at 50% SOC was measured for each battery in an atmosphere at 25 ° C. The results are shown in Table 1. In addition, about electrical resistance, it represents with the index | exponent when the electrical resistance of the comparative example 2 is set to 100. In Example 1, in order to investigate whether or not good self-discharge characteristics can be obtained over a long period of time, it should be noted that a very large number of cycles of 1000 cycles are performed.

  When the self-discharge characteristics of each battery were compared, the battery of Example 1 showed a high residual SOC of 34% after the test, and excellent self-discharge characteristics could be obtained over a long period of time. On the other hand, in the batteries of Comparative Examples 1 and 2, the remaining SOC after the test was as low as 17% and 14%, and the self-discharge characteristics were not preferable. Further, when comparing the internal pressure of each battery, Comparative Example 2 was extremely low at 0.18 (MPa), and the internal pressure characteristics were excellent. In the batteries of Example 1 and Comparative Example 1, the values were 0.61 and 0.55 (MPa), respectively, which were higher than those of Comparative Example 2, but the internal pressure characteristics were good. In addition, when comparing the electric resistance of each battery, the electric resistance of the batteries of Example 1 and Comparative Example 1 was larger than that of Comparative Example 2, but the rate of increase was 3.7% and 6.1%. And it was relatively small. In the batteries of Example 1 and Comparative Example 1, it is considered that the internal pressure and the electrical resistance were larger than those of Comparative Example 2 because the gel electrolyte was included in the gap portion of the separator substrate.

  Here, the difference in self-discharge characteristics between the battery of Example 1 and the batteries of Comparative Examples 1 and 2 will be examined. First, considering Example 1 and Comparative Example 1, it can be said that the difference in self-discharge characteristics is due to the difference in whether or not the separator substrate is subjected to sulfonation treatment. That is, both batteries have a gel electrolyte containing a sulfo group. However, in the battery of Comparative Example 2, the separator base material is not sulfonated, so that the ammonia in the battery is sufficiently captured. It is considered that the positive electrode active material was reduced under the influence of ammonia, and self-discharge was promoted. On the other hand, in the battery of Example 1, since the separator base material is sulfonated, the ammonia in the battery is appropriately controlled by the sulfo group of the separator base material in addition to the gel electrolyte containing the sulfo group. It is thought that self-discharge due to the influence of ammonia could be suppressed.

  Moreover, when Example 1 and Comparative Example 2 are examined, it can be said that the difference in the self-discharge characteristics is due to the difference in whether or not the gel electrolyte containing the sulfo group is present. That is, in both batteries, the separator substrate is sulfonated, but the battery of Comparative Example 2 does not have a gel electrolyte containing a sulfo group, and therefore sufficiently captures ammonia in the battery. It is considered that the positive electrode active material was reduced under the influence of ammonia, and self-discharge was promoted.

  On the other hand, since the battery of Example 1 has a gel electrolyte containing a sulfo group, the surface of the fiber of the separator substrate can be covered with a gel electrolyte containing a sulfo group. Thereby, it is considered that the sulfo group could be present to some extent by the gel electrolyte even in the part of the separator substrate that is not sulfonated (or less sulfonated). As described above, the sulfo group of the separator base material and the sulfo group contained in the gel electrolyte can arrange the sulfo group throughout the separator base material, so that the ammonia in the battery can be preferably captured. It is thought that it was made. Therefore, it is considered that self-discharge due to the influence of ammonia could be suppressed.

  From the above results, it can be said that the self-discharge characteristics can be improved over a long period of time by using a separator base material (separator) subjected to sulfonation treatment and disposing a gel electrolyte containing a sulfo group.

  In Example 2, seven types of alkaline storage batteries (samples) were used by using seven types of separators having different ratios of the amount of S element contained in the water-absorbing polymer to the amount of S element contained in the fiber constituting the separator substrate. 1 to 7).

Specifically, in Step 1, in the same manner as in Example 1, sulfonation treatment was performed on the wet nonwoven fabric to prepare a separator base material having a sulfonation degree of 3.0 × 10 ⁻³ . Next, in Step 2, a gel dispersion was prepared in the same manner as in Example 1. Next, in Step 3, seven types of separators having different water-absorbing polymer contents were produced by varying the immersion time in the gel dispersion for the separator substrate produced in Step 1.

  Thereby, although the sulfonation degree of the separator base material was the same, seven types of separators having different amounts of S element contained in the water-absorbing polymer were obtained. That is, seven types of separators having different ratios of the amount of S element contained in the water-absorbing polymer to the amount of S element contained in the fiber constituting the separator substrate (hereinafter, also simply referred to as S amount of the water-absorbing polymer). Obtained. Specifically, as shown in Table 2, the S amount of the water-absorbing polymer was 0.07, 0.10, 0.53, 1.04, 1.58, 2.00, 2.32 (%). Seven different types of separators were produced. Thereafter, in the same manner as in Example 1, seven types of nickel metal hydride storage batteries (samples 1 to 7) were produced. In all of Samples 1 to 7, the battery capacity is set to 6.5 Ah.

(Self-discharge characteristic evaluation test)
Next, the samples 1 to 7 manufactured as described above were subjected to self-discharge characteristic evaluation tests in the same manner as in Example 1. The results are shown in Table 2.
When comparing the self-discharge characteristics of each sample, in samples 2 to 7, the residual SOC after the test was as high as 34 to 36%, and excellent self-discharge characteristics could be obtained over a long period of time. On the other hand, in sample 1, the residual SOC after the test showed a relatively good value of 21%, but the self-discharge characteristics were inferior to those of the other samples.

  Here, the relationship between the S amount (%) of the water-absorbing polymer and the residual SOC (%) after the test based on the results of Table 2 is shown in FIG. As indicated by a black circle in FIG. 1, the value of the residual SOC (%) after the test is not so large when the S amount of the water-absorbing polymer is less than 0.1%, but the S amount of the water-absorbing polymer is It can be seen that when the content is 0.1% or more, the self-discharge characteristics are improved. Specifically, it can be seen that if the S amount of the water-absorbing polymer is 0.1% or more, almost the same good self-discharge characteristics can be obtained regardless of the S amount of the water-absorbing polymer. This is considered due to the following reasons.

Each sample uses a separator base material subjected to sulfonation treatment (specifically, a separator base material having a sulfonation degree of 3.0 × 10 ⁻³ ). Ammonia can be captured. However, as can be seen from the results of Example 1 and Comparative Example 2, the ammonia in the battery cannot be properly captured over a long period of time only by the separator substrate subjected to the sulfonation treatment. Therefore, in order to appropriately capture the ammonia in the battery over a long period of time, it is necessary to use a separator base material that has undergone a sulfonation treatment and to dispose a gel electrolyte having a sulfo group.

However, in Sample 1, although a gel electrolyte having a sulfo group was disposed, the S amount of the water-absorbing polymer was as low as 0.07%, so that the gel electrolyte could not contain a sufficient sulfo group. It is considered that ammonia in the battery could not be properly captured over a long period of time.
On the other hand, in Samples 2 to 7, by setting the amount of S in the water-absorbing polymer to 0.1% or more, the gel electrolyte can contain sufficient sulfo groups, and is suitable throughout the separator substrate. It is considered that a sulfo group could be arranged in Therefore, it is considered that the ammonia in the battery could be appropriately captured over a long period of time.
From the above results, by using a separator base material having a sulfonation degree of 3.0 × 10 ⁻³ and an S content of the water-absorbing polymer of 0.1% or more, excellent self-discharge over a long period of time. It can be said that characteristics can be obtained.

On the other hand, comparing the internal pressure of each sample, it can be seen from Table 2 that the internal pressure (MPa) of the battery increases in the order of samples 1-7. That is, it can be seen that the internal pressure of the battery increases as the S amount (%) of the water-absorbing polymer increases.
Here, the relationship between the S amount (%) of the water-absorbing polymer and the internal pressure (MPa) of the battery based on the results of Table 2 is shown in FIG. As indicated by Δ in FIG. 2, when the S amount of the water absorbent polymer is in the range of 0.1 to 2.0 (%), the internal pressure of the battery increases as the S amount (%) of the water absorbent polymer increases. It gradually rises, and it can be seen that the internal pressure greatly increases when it exceeds 2.0%. This is probably because the water-absorbing polymer increases as the amount of S in the water-absorbing polymer increases, so that the gel electrolyte occupying the voids of the separator substrate increases. From this result, it is possible to limit the amount of gel electrolyte by limiting the amount of S in the water-absorbing polymer to 2.0% or less, thus ensuring sufficient separator ventilation and good internal pressure characteristics of the battery. It can be said that (increase in internal pressure) can be suppressed.

  Next, the electrical resistance of each sample is compared. In Table 2, the electrical resistance is displayed as an index with the battery of Comparative Example 2 in which no water-absorbing polymer is arranged as a reference (reference value 100). From Table 2, it can be seen that the electrical resistance of the battery increases in the order of samples 1-7. That is, it can be seen that the electrical resistance increases as the S amount (%) of the water-absorbing polymer increases.

  Here, the relationship between the S amount (%) of the water-absorbing polymer and the electric resistance (index) of the battery based on the results of Table 2 is shown in FIG. As indicated by the ♦ marks in FIG. 3, when the S amount of the water-absorbing polymer is 2.0% or less, the electrical resistance gradually increases as the S amount (%) of the water-absorbing polymer increases. It can be seen that the electrical resistance sharply rises above 0.0%. This is probably because the water-absorbing polymer increases as the amount of S in the water-absorbing polymer increases, so that the gel electrolyte occupying the voids of the separator substrate increases. From this result, it can be said that by limiting the amount of S in the water-absorbing polymer to 2.0% or less, the amount of the gel electrolyte can be limited and the electric resistance of the battery can be made relatively small.

From the above results, it can be said that it is preferable to use a separator base material having a degree of sulfonation of 3.0 × 10 ⁻³ and to set the S content of the water-absorbing polymer to 0.1 to 2.0 (%). Thereby, it can be said that excellent self-discharge characteristics can be obtained over a long period of time, the internal pressure characteristics can be improved, and the electrical resistance can be made relatively small.

In Example 3, two types of separators having different separator base structures were manufactured, and then two types of alkaline storage batteries (referred to as samples 8 and 9) were manufactured using each separator.
Specifically, in Step 1, a single-layer wet nonwoven fabric composed of one papermaking web layer and a two-layer wet nonwoven fabric obtained by laminating two identical papermaking web layers were prepared. However, in both nonwoven fabrics, the basis weight is 60 (g / m ² ), the thickness is 200 (μm), and the fiber density is 0.91 (g / cm ³ ). Next, these wet nonwoven fabrics were subjected to sulfonation treatment in the same manner as in Example 1 to produce two types of separator base materials. Note that the degree of sulfonation of the separator base material is 3.0 × 10 ⁻³ .

Thereafter, two types of separators containing a water-absorbing polymer were produced in the same manner as in Steps 2 and 3 of Example 1. In both separators, 5.05 g / m ² of the water-absorbing polymer (in a dry state) is disposed in the gap of the separator substrate. Accordingly, the amount of S in the water-absorbing polymer is 0.63%. Thereafter, in the same manner as in Steps 4 to 6 of Example 1, two types of nickel metal hydride storage batteries (samples 8 and 9) were produced. Samples 8 and 9 both have a battery capacity of 6.5 Ah.

(Self-discharge characteristic evaluation test)
Next, the samples 8 and 9 manufactured as described above were subjected to a self-discharge characteristic evaluation test in the same manner as in Example 1. However, in Example 3, after performing a charge / discharge cycle test of 1000 cycles, another charge / discharge test of 1000 cycles was performed, and the remaining SOC (%) after 1000 cycles and the remaining SOC (%) after 2000 cycles ). The results are shown in Table 3.

  Comparing the self-discharge characteristics of both samples, as shown in Table 3, the remaining SOC after 1000 cycles showed high values of 35% and 34%, respectively. Further, regarding the remaining SOC after 2000 cycles, all of them showed a value of 24% or more, despite the fact that 2000 cycles of charge / discharge cycle tests were conducted. From this result, it can be said that both Samples 8 and 9 were able to obtain excellent self-discharge characteristics over a long period of time.

For the separator, the degree of sulfonation is 3.0 × 10 ⁻³ , and the amount of S in the water-absorbing polymer is 0.1 to 2.0 (%) (specifically 0.63%). In addition to this, it is considered that this is because a water-absorbing polymer crosslinked with divinylbenzene was used. The water-absorbing polymer crosslinked with divinylbenzene is stably present for a long period in the alkaline electrolyte (gel electrolyte). Therefore, it is considered that the gel electrolyte could be stably present over a long period of time on the fiber surface of the separator substrate.

Moreover, an excess alkaline electrolyte exceeding the amount that the gel electrolyte is saturated (exceeding the amount of alkaline electrolyte that can be absorbed by the water-absorbing polymer) is injected. That is, an excess alkaline electrolyte that maintains a liquid state without being absorbed by the water-absorbing polymer is present in the battery. As a result, even if the alkaline electrolyte contained in the gel electrolyte decreases with repeated charge and discharge, the water-absorbing polymer absorbs the excess alkaline electrolyte present in the battery (in the voids of the separator substrate). Thus, the gel electrolyte can be returned to a saturated state.
Therefore, since the surface of the fiber of the separator base material can be stably covered with the gel electrolyte saturated for a long period of time, it is considered that excellent self-discharge characteristics can be obtained for a long period of time.

  However, when comparing the remaining SOC after 1000 cycles and 2000 cycles, in Sample 8, the SOC value after 2000 cycles is 11% lower (from 35% to 24%) than the SOC value after 1000 cycles. In contrast, Sample 9 showed a high value (both 34%) without decreasing. From this result, it can be said that Sample 9 was able to obtain superior self-discharge characteristics over a long period of time as compared with Sample 8.

This is probably because Sample 8 used a single-layer nonwoven fabric as the separator substrate, whereas Sample 9 used a nonwoven fabric in which a plurality of papermaking web layers were laminated. That is, in sample 9, by using a nonwoven fabric in which a plurality of papermaking web layers are laminated, discontinuous surfaces increase between the papermaking web layers, and positive and negative electrodes are formed along the fibers of the separator substrate as compared with sample 8. This is thought to be because the formation of conductive paths that connect them could be suppressed.
When the internal pressure was examined, it was 0.53 (MPa) for sample 8 and 0.60 (MPa) for sample 9, and both samples exhibited relatively good internal pressure characteristics. Regarding the electrical resistance, the index values were 101 and 101.7, both of which were low resistance.
From the above results, it can be said that it is preferable to use a nonwoven fabric in which a plurality of papermaking web layers are laminated as a separator base material, rather than a single layer nonwoven fabric.

In the above, the present invention has been described with reference to the first to third embodiments. However, the present invention is not limited to the above-described embodiments and the like, and it can be applied as appropriate without departing from the gist thereof. Not too long.
For example, in Example 1 and the like, the sulfonation treatment with sulfuric anhydride was performed as the sulfonation treatment on the separator substrate, but the same effect could be obtained even when the sulfonation treatment with fuming sulfuric acid was performed.

Moreover, embodiments in Examples 1 to 3, although the degree of sulfonation of the separator substrate and 3.0 × 10 ^-3, a separator substrate sulfonation degree is in the range of 1 × 10 ^-3 ~6 × 10 ^-3 It was confirmed that the self-discharge characteristics were improved over a long period of time by using. Therefore, considering the results of Example 2, the degree of sulfonation of the separator base material is set to 1 × 10 ^{−3 to} 6 × 10 ⁻³ , and the amount of S element contained in the water-absorbing polymer is determined as follows. It can be said that the self-discharge characteristics can be improved over a long period of time by setting the content to 0.1 to 2.0 (%) with respect to the amount of S element contained in the fiber constituting the substrate. Furthermore, it can be said that the internal pressure characteristics can be improved and the electrical resistance can be kept relatively small. In addition, when the sulfonation degree was made larger than 6 × 10 ⁻³ , the separator base material was severely damaged due to the extreme sulfonation treatment on the separator base material, and the strength was significantly reduced. For this reason, the life characteristics and self-discharge characteristics of the battery were greatly reduced.

In Examples 1 to 3, the basis weight of the separator substrate was 60 g / m ² and the thickness was 200 μm. However, the separator base had a basis weight of 40 to 70 (g / m ² ) and a thickness of 120 to 200 (μm). It was confirmed that the self-discharge characteristic and the internal pressure characteristic can be improved over a long period of time by using the material. Since the basis weight is 40 g / m ² or more and the thickness is 120 μm or more, the path between the positive electrode and the negative electrode along the fiber of the separator base can be lengthened, so the positive and negative electrodes are connected. It is considered that the conductive path is hardly formed and the self-discharge characteristics are improved. On the other hand, by restricting the basis weight to 70 g / m ² or less, it is possible to secure a large gap portion of the separator base material and improve the air permeability of the separator, and to limit the thickness to 200 (μm) or less. As a result, the occupied volume of the separator base material in the battery could be suppressed, and it is considered that the internal pressure characteristics could be improved.

  Moreover, in Examples 1-3, although the separator base material was comprised with the nonwoven fabric which consists of one type of fiber (specifically polypropylene), the nonwoven fabric which consists of two or more types of fibers (for example, polypropylene and polyethylene) It may be used to produce a separator substrate. If a nonwoven fabric composed of two or more types of fibers is used and subjected to a sulfonation treatment, a separator substrate composed of two or more types of fibers having different degrees of sulfonation can be obtained. By using a separator substrate composed of two or more types of fibers having different degrees of sulfonation, the self-discharge characteristics and the internal pressure characteristics can be further improved. Specifically, when a separator base material was produced using a nonwoven fabric made of polypropylene and polyethylene and used for an alkaline storage battery, excellent self-discharge characteristics and internal pressure characteristics could be obtained.

  This is because the gel electrolyte and the alkaline electrolyte can be unevenly distributed in the void portion of the separator substrate by constituting the separator substrate with two or more types of fibers having different degrees of sulfonation, that is, hydrophilicity. it is conceivable that. Specifically, by allowing a gel electrolyte and an alkaline electrolyte to be concentrated and held in a fiber having a high degree of sulfonation, an air passage can be formed around the fiber having a low degree of sulfonation. Therefore, since both the liquid retention and air permeability of the separator can be improved, it is considered that excellent self-discharge characteristics and internal pressure characteristics can be obtained.

  Furthermore, it is preferable that the separator base material contains a split type composite fiber composed of two or more kinds of components. By including the split-type conjugate fiber, the interelectrode path can be increased, and the formation of the conductive path connecting the electrodes can be suppressed. Therefore, the self-discharge characteristic of the battery can be further improved. Specifically, a separator substrate was prepared using a nonwoven fabric (consisting of two paper-making web layers) containing 30% by weight of a split-type composite fiber composed of polypropylene and polyethylene, and this was used for an alkaline storage battery. However, excellent self-discharge characteristics and internal pressure characteristics could be obtained.

By the way, as the separator base material, a nonwoven fabric in which a plurality of papermaking web layers are laminated is used, and in the above-described battery containing split composite fibers, in particular, split composite fibers made of polypropylene and polyethylene are used. Therefore, it is considered that excellent self-discharge characteristics could be obtained. Since the split type composite fiber made of polypropylene and polyethylene has a high melting point, even when heat is applied in the process of making the nonwoven fabric, the crystal form of the split type composite fiber is not easily broken, and the formation can be kept good. . Therefore, it is considered that the inclusion of split-type composite fibers made of polypropylene and polyethylene can sufficiently increase the interelectrode path and suppress the formation of the conductive path connecting the electrodes.
In addition, as a fiber which forms a split type composite fiber, polystyrene, polymethylpentene, and polybutylene can be suitably used in addition to polypropylene and polyethylene.

  Moreover, in Examples 1-3, it laminated | stacked so that a separator might interpose between a positive electrode and a negative electrode using the sheet-like separator (separator base material). However, the present invention is not limited to such a form. For example, the separator may be formed in a bag shape, the positive electrode may be disposed therein, and the negative electrode and the negative electrode may be alternately stacked.

  Moreover, in Example 3, the separator base material was created using the nonwoven fabric which laminated | stacked the same papermaking web layer. However, the papermaking web layers to be laminated are not necessarily the same, and different papermaking web layers (for example, having a different basis weight) may be laminated. Rather, laminating different papermaking web layers is preferable because the characteristics of the alkaline storage battery can be improved.

  Specifically, in an alkaline storage battery (nickel metal hydride battery), a larger amount of conductive precipitates are deposited from the negative electrode side than the positive electrode side. Therefore, the papermaking web layer (first papermaking web layer is disposed on the positive electrode side). ), The basis weight of the papermaking web layer (referred to as the second papermaking web layer) disposed on the negative electrode side is increased, whereby the formation of the conductive path can be efficiently suppressed. Thus, selectively increasing the basis weight of the papermaking web layer (second papermaking web layer) with respect to the separator base material is the basis weight of all papermaking web layers (first papermaking web layer and second papermaking web layer). As compared with the case of increasing the value, the increase in the basis weight of the entire separator can be suppressed. For this reason, the fall of the air permeability of a separator can be suppressed and by extension, the internal pressure rise of an alkaline storage battery can be suppressed.

Moreover, in Example 3, the separator base material was created using the nonwoven fabric which laminated | stacked two papermaking web layers. However, when laminating a papermaking web layer, the nonwoven fabric to be laminated is not limited to two layers, and any layer may be used as long as it is a plurality of layers. Rather, it is preferable to increase the number of papermaking web layers to be laminated, because a conductive path connecting the positive and negative electrodes is less likely to be formed, and the self-discharge characteristics of the alkaline storage battery can be improved.
Moreover, in Example 1 etc., although the wet nonwoven fabric was used as a separator base material, you may use a dry nonwoven fabric.

  Moreover, in Examples 1-3, the nickel metal hydride storage battery which used the hydrogen storage alloy for the negative electrode was produced. However, this invention can acquire the same effect also about any alkaline storage batteries, such as a nickel zinc storage battery and a nickel cadmium storage battery.

It is a graph which shows the relationship between S amount (%) of a water absorbing polymer, and residual SOC (%) after a test about the alkaline storage battery (samples 1-7) concerning Example 2. FIG. It is a graph which shows the relationship between S amount (%) of a water absorbing polymer, and internal pressure (MPa) about the alkaline storage battery (samples 1-7) concerning Example 2. FIG. It is a graph which shows the relationship between S amount (%) of a water absorbing polymer, and an electrical resistance (index | exponent) about the alkaline storage battery (samples 1-7) concerning Example 2. FIG.

Claims (11)

A separator base material comprising a three-dimensional network structure made of fibers and including a void portion in which a plurality of holes are three-dimensionally connected;
A water-absorbing polymer that is disposed in the gap of the separator substrate and becomes a gel electrolyte when absorbing an alkaline electrolyte,
The separator substrate is sulfonated,
The water absorbing polymer is a separator for an alkaline storage battery having a sulfo group. The alkaline storage battery separator according to claim 1,
The sulfonation degree of the separator substrate is 1 × 10 ^{−3 to} 6 × 10 ⁻³ ,
The alkaline storage battery separator in which the amount of S element contained in the water-absorbing polymer is 0.1 to 2.0 (%) with respect to the amount of S element contained in the fibers constituting the separator substrate. The separator for an alkaline storage battery according to claim 1 or 2,
The separator substrate is
An alkaline storage battery separator having a basis weight of 40 to 70 (g / m ² ) and a thickness of 120 to 200 (μm). It is a separator for alkaline storage batteries according to any one of claims 1 to 3,
The water-absorbing polymer is a separator for an alkaline storage battery formed by crosslinking with at least one of divinylbenzene and divinylnaphthalene. It is a separator for alkaline storage batteries as described in any one of Claims 1-4,
The separator substrate is an alkaline storage battery separator having at least two types of fibers having different degrees of sulfonation. The separator for an alkaline storage battery according to any one of claims 1 to 5,
The separator base material is an alkaline storage battery separator including a split composite fiber. It is a separator for alkaline storage batteries as described in any one of Claims 1-6,
The separator substrate is an alkaline storage battery separator made of a nonwoven fabric in which a plurality of papermaking web layers are laminated. The separator for an alkaline storage battery according to claim 7,
Each of the plurality of papermaking web layers is a separator for an alkaline storage battery including a split type composite fiber composed of at least two kinds of components selected from polypropylene, polyethylene, polystyrene, polymethylpentene, and polybutylene. A positive electrode;
A negative electrode,
An alkaline storage battery comprising: a separator for an alkaline storage battery according to any one of claims 1 to 8, wherein the water-absorbing polymer absorbs an alkaline electrolyte and becomes a gel electrolyte. A positive electrode;
A negative electrode,
A separator base material comprising a three-dimensional network structure made of fibers and including a void portion in which a plurality of holes are three-dimensionally connected;
A gel electrolyte that is located in the gap of the separator substrate and has a water-absorbing polymer that absorbs an alkaline electrolyte; and
The separator substrate is sulfonated,
The water-absorbing polymer is an alkaline storage battery having a sulfo group. The alkaline storage battery according to claim 9 or 10,
An alkaline storage battery comprising an excess alkaline electrolyte that maintains a liquid state without being absorbed by the water-absorbing polymer in the alkaline storage battery.

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