JP2002319387A - Separator for alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a battery excellent in an internal pressure restraining effect. SOLUTION: An unevenness is provided at least on one face, the face is opposed to a negative electrode to absorb efficiently, in the negative electrode, oxygen gas generated in a positive electrode when overecharged, and the internal pressure restraining effect is remarkably exhibited thereby inside the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed alkaline battery such as a nickel-hydrogen storage battery and a nickel-cadmium storage battery, and more particularly to an improvement in a battery separator.

[0002]

2. Description of the Related Art Generally, in a sealed alkaline storage battery,
A method is adopted in which oxygen gas generated at the positive electrode during overcharging is absorbed by the negative electrode to prevent the internal pressure of the battery from rising.
However, when the generation rate of oxygen gas becomes higher than the absorption rate, the internal pressure of the battery gradually increases. Since an increase in the internal pressure of the battery causes destruction of the battery and a shortened life, various studies have been made to improve the oxygen absorption rate of the negative electrode. In particular, with respect to the separator, studies are being made to smoothly transmit the generated oxygen gas from the positive electrode to the negative electrode.

On the other hand, as the capacity and output of a battery have been increased, it has been desired to reduce the thickness of the separator so that the volume occupied in the battery is reduced as much as possible.
In this case, simply reducing the basis weight increases the probability of short-circuiting when forming the electrode group. Therefore, methods for increasing the fiber density are being studied. However, when the fiber density is increased in this way, the space volume in the separator is reduced, and the liquid retention and gas permeability are reduced, so that there is a problem that the internal pressure of the battery greatly increases.

In order to solve such a problem, for example, JP-A-10-106525 discloses a high-density layer on the side facing the positive electrode plate and a low-density layer having a lower fiber density than the high-density layer on the side facing the negative electrode plate. There has been proposed a separator having a two-layer structure in which a density layer is provided. But,
In this method, the thickness is increased by the low density layer,
There is a disadvantage that it is not suitable for increasing the capacity of a battery.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a separator exhibiting an excellent internal pressure suppressing effect and an alkaline storage battery provided with the separator. It is an object of the present invention.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an alkaline battery separator having at least one surface having irregularities.

The present invention also relates to the separator for an alkaline battery according to claim 1, wherein the size of the recess is not less than 5% and not more than 50% with respect to the apparent thickness of the separator.

The present invention also relates to the separator for an alkaline battery according to claim 1 or 2, wherein the area of the projections with respect to the total area of the separator is in the range of 5% to 50%.

Further, the present invention relates to an alkaline battery using the separator according to any one of claims 1 to 3, wherein the surface having irregularities faces at least the negative electrode.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the battery separator of the present invention, the form is preferably a non-woven fabric or a film-type porous body, but other porous bodies, for example, a fiber aggregate such as a woven fabric or a knitted fabric, Alternatively, a foam-type porous body or the like can be used.

When a non-woven fabric is used as the battery separator of the present invention, any known method can be used for its production, such as a spun bond method, a melt blow method, a flash spinning method, an air lay method, or the like. Various dry methods such as a card method and a wet papermaking method are exemplified.

Any film-type porous material can be effectively used as long as it is prepared by a known method. For example, a porous material obtained by a stretching method, a solvent extraction method, a perforation method, or the like can be used. can give.

As the resin constituting the battery separator of the present invention, any organic resin material can be used. However, in the case of nickel-metal hydride storage batteries, polyolefin resin is used in view of resistance to electrolyte and oxidation resistance. It is preferable to use Here, the polyolefin resin is a resin composed of a polyolefin alone or a resin composed of a copolymer of an olefin and another monomer. Examples of the polyolefin include polyethylene, polypropylene, polymethylpentene, and polybutene. , Polyethylene-propylene, polyethylene-butene-propylene, and the like, and other monomers copolymerizable with the olefin include styrene, vinyl butyrate, and vinyl acetate.

The above-mentioned resin may be used alone, or a core-sheath type conjugate fiber, an eccentric body-sheath type conjugate fiber, a parallel type conjugate fiber,
Two or more kinds of resins may be mixed, such as sea-island composite fibers and splittable composite fibers, and are not particularly limited. For nickel cadmium storage batteries, polyamide resins can be effectively used in addition to the above resins.

In the case where a hydrophobic resin such as a polyolefin resin is used in the alkaline battery separator of the present invention, it is preferable to perform a hydrophilic treatment. Examples of the method of the hydrophilic treatment include a graft treatment, a sulfonation treatment, a surfactant attachment treatment, a corona treatment, a plasma treatment, a fluorine gas treatment, and a resin coating treatment. Of these, sulfonation or grafting is particularly preferred from the viewpoint of hydrophilic durability.

As the sulfonation treatment, treatment with hot sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, sulfur trioxide or the like can be used. As the grafting method, any known method such as a method of applying energy such as a UV irradiation treatment, a plasma treatment, a corona treatment and the like using a catalyst at the same time as bringing a vinyl monomer into contact with a resin may be used. It is possible.

The method for providing the separator with irregularities in the present invention is not particularly limited, and any known method for forming irregularities can be used. For example, pressing with an embossing roll or gear roll, pressing with a mold or metal mesh, resin net, etc., transferring the unevenness, cutting with a sharp blade, etc., squeezing or rubbing, having unevenness Examples of the method include a method of forming a nonwoven fabric on a net, a method of bonding a resin spot or string-like resin to the surface, and a method of partially melting and compressing or removing the resin.

The above-mentioned concavo-convex processing may be performed before or after the hydrophilization treatment step, and the concavo-convex processing may be performed simultaneously with the hydrophilization treatment.

The cross-sectional shape of the concavities and convexities formed by the above concavo-convex processing may be any of a U-shape, a V-shape, or a square shape as shown in FIG. Also, bird's-eye view from the top
The shape of the recessed portion may be a continuous shape such as a groove or a ridge, or a discontinuous shape in which each recessed portion independently exists, and these may be used alone or in combination. In the case of continuous concave portions, there are those arranged in one direction as shown in FIG. 2 and those which intersect at a lattice or randomly. In the case of a discontinuous concave portion, its shape may be a polygon such as a circle, a star, a triangle, a square, or a cross as shown in FIG. 3, an irregular shape, or a combination thereof. It is not something to be done.

Due to the irregularities provided by the above method, a minute space can be formed between the negative electrode and the separator when the battery is wound. Oxygen gas generated at the positive electrode passes through the separator, is temporarily held in this space, and is then consumed on the negative electrode surface, thereby suppressing an increase in battery internal pressure. Therefore, in the present invention, the unevenness needs to be such that a sufficient minute space can be formed between the separator and the electrode surface in the battery.

In the present invention, the depth of the concave portion is preferably in the range of 5% to 50% with respect to the apparent thickness of the separator, and more preferably 10% to 50%.
% Or less. If the depth of the recess is less than 5%, no sufficient space is formed between the electrode surface and the separator, and the effect of the unevenness cannot be obtained. In addition, the depth of the concave portion is 5
When it is larger than 0%, an extremely thin portion is formed, so that the strength of the portion is reduced, and the battery is easily broken or short-circuited at the time of winding. Further, if the thickness of the concave portion is increased to avoid this, the thickness of the entire separator increases.

The area of the recess with respect to the entire area of the separator is preferably in the range of 5% to 50%, more preferably 10% to 35%.
If this range, oxygen gas generated at the time of overcharge can be effectively dispersed on the interface between the electrode and the separator,
Oxygen gas absorption at the negative electrode proceeds efficiently. At the same time, it also prevents oxygen gas from remaining on the separator to reduce the effective area in charge and discharge, and discharge characteristics,
In particular, it is possible to improve the discharge characteristics at a high rate. However, when the area is outside the above range, if the area of the concave portion is less than 5%, the effect of providing the unevenness cannot be obtained. I do.

When a battery is formed using the separator according to the present invention, it is necessary to arrange the battery so that the surface having irregularities faces at least the negative electrode. By arranging the irregularities on the negative electrode side, a space is formed between the negative electrode surface and the separator, and oxygen gas generated from the positive electrode can be efficiently moved to the negative electrode side, thereby suppressing an increase in internal pressure. .

The basis weight of the separator used in the present invention is 3
It is desirably in the range of 0 to 100 g / m ² , and more preferably 35 to 70 g / m ² . The apparent thickness of the separator may be in the range of 50 to 250 μm, and preferably 70 to 200 μm. By providing irregularities having an apparent thickness in this range, the effect of suppressing the internal pressure inside the battery can be exhibited more than before.

Hereinafter, methods for measuring the physical properties of various separators according to the present invention will be described.

-Weight, apparent thickness, depth of recess (1) A test piece (width 5 cm, length 10 c)
m) was collected and dried at 60 ° C. ± 2 ° C. for 10 hours.
The basis weight was [g / m ² ]. The test piece n was determined by averaging 20 points. (2) The thickness at the center of the test piece was measured to have a diameter of 31.
5mm digital thickness gauge (Peacock digital thickness gauge,
The load was measured using 8.8 g / cm ² ). (3) The cross-sectional shape of the separator is magnified 300 times with an optical microscope, and the thickness of the concave portion is measured. The difference between the recess thickness and the apparent thickness was defined as the recess depth.

Air permeability According to the air permeability measurement method of JIS L1096-1990,
It was measured by a Frazier type testing machine.

Battery Evaluation Battery evaluation was performed by producing an SC type sealed battery. First, a paste-type nickel hydroxide positive electrode, a paste-type hydrogen storage alloy negative electrode, and a separator are spirally wound, inserted into an outer can, and then injected with a potassium hydroxide aqueous solution to which lithium hydroxide is added as an electrolyte. To obtain a sealed battery (capacity 2500 mAh). As the initial activation treatment of the battery, after maintaining at 45 ° C. for 6 hours, the operation of charging at 0.2 C for 6 hours and discharging at 0.2 C (discharge end voltage 1.0 V) in an air atmosphere at 20 ° C. is repeated 10 times. Was.
The ratio of the 10th discharge capacity to the theoretical capacity was defined as the discharge capacity ratio of this battery. The above-mentioned 0.2C discharge is to discharge a densely charged battery in 5 hours, and at this time, the current value of the discharge is set to an appropriate value.

High-rate discharge test As a high-rate discharge test, a battery that had been subjected to the above-mentioned initial activation was charged at 0.2 C for 6 hours, and then discharged at 4 C to 0.8 V. The ratio to volume was calculated.

Measurement of internal pressure of battery The battery which had been subjected to the initial activation described above was charged at 0.5 C for 3 hours at an ambient temperature of 20 ° C. (with a charging depth of 150
%) The internal pressure of the battery was measured.

Cycle Test For the battery that has been subjected to initial activation, a cycle test is performed in which one cycle consists of charging at 0.5 C for 2.4 hours (120%) and discharging at 0.5 C at a final voltage of 1.0 V. did. At this time, it was determined that the life was reached when the discharge capacity reached 80% of the initial value.

Hereinafter, a specific description will be given using embodiments of the present invention.

Example 1 A commercially available nonwoven fabric made of polypropylene (Nippon Kodoshi SLF5
0120: Gear roll having an average fiber diameter of 12 μm and a basis weight of 50 g / m ² ) having a projection area ratio of 20% (roll temperature 150 ° C.)
And a flat roll made of stainless steel at 140 ° C., and pressurized at a linear pressure of 3 MPa to form a groove-shaped concave portion only on one surface. This was immersed in concentrated sulfuric acid at 97% and 130 ° C. for 5 minutes, washed with pure water, and dried at 60 ° C. to obtain a separator. Table 1 shows the various physical properties of the separator and the evaluation results of the battery used with the surface of the separator having the concave portion facing the negative electrode.

Example 2 In Example 1, instead of the gear roll, an embossing roll heated to 150 ° C. and having a projection area ratio of 10% was used to perform a pressure treatment, and a dot-shaped recess was formed only on one surface. . This was treated at 97 ° C. for 5 minutes using 97% concentrated sulfuric acid. Further, after washing with pure water, drying was performed at 60 ° C. to obtain a separator. Table 1 shows various physical properties of the separator and evaluation results of the battery using the separator.

Example 3 A separator was prepared in the same manner as in Example 2 except that the pressure treatment was performed with an embossing roll (temperature: 150 ° C.) having a convex area ratio of 40%. Table 1 shows various physical properties of the separator and evaluation results of the battery using the separator.

Example 4 The same nonwoven fabric as in Example 1 was overlaid on a glass fiber net (Kurenet G3300 manufactured by Kurashiki Spinning Co., Ltd.) and calender rolls (both upper and lower silicone rubber flat rolls, linear pressure 3) were used.
(MPa) to transfer and mold lattice-like irregularities.
The area ratio of the recess at this time was 25%. 97% of this,
After immersion treatment in concentrated sulfuric acid at 130 ° C. for 5 minutes, washing with pure water, and drying at 60 ° C., a separator was obtained. Table 1 shows the various physical properties of the separator, the discharge capacity of the battery used with the concave surface of the separator facing the negative electrode, and the evaluation results.
Shown in

Comparative Example 1 A separator was prepared in the same manner as in Example 1 except that the linear pressure of the roll was changed to 0.5 MPa. Table 1 shows various physical properties of the separator and evaluation results of a battery using the separator.

Comparative Example 2 A separator was prepared in the same manner as in Example 1 except that the temperature of the roll was changed to 165 ° C. Table 1 shows various physical properties of the separator. When this separator was used for a battery, all of the separators were broken or short-circuited at the time of winding, and the battery could not be obtained.

Comparative Example 3 In Example 1, the pressure treatment with the calendar roll was
The same process was performed except that the process was repeated twice to obtain a separator. The pressing was performed so that the concave portions did not overlap. Table 1 shows various physical properties of the separator and evaluation results of a battery using the separator.

Comparative Example 4 The same nonwoven fabric as in Example 1 was pressed with an embossing roll heated to 140 ° C. and having a convex area ratio of 3%.
A point-like concave portion was formed only on one surface. This was treated at 130 ° C. for 5 minutes using 97% concentrated sulfuric acid. After washing with pure water, drying was performed at 60 ° C. to obtain a separator.
Table 1 shows various physical properties of the separator and evaluation results of the battery using the separator.

Comparative Example 5 With respect to the separator of Example 1, a battery was prepared with the surface having no irregularities facing the negative electrode. Table 1 shows the evaluation results of this battery.
Shown in

Comparative Example 6 The commercially available nonwoven fabric made of polypropylene in Example 1 was not subjected to unevenness processing, but was subjected only to the same hydrophilic treatment as in Example 1 to obtain a separator. Table 1 shows various physical properties of the separator and evaluation results of a battery using the separator.

[0043]

[Table 1]

In the separators of Examples 1 to 4, the internal pressure of the battery was suppressed, whereas in the separators of Comparative Examples 1, 4 and 6, the effect of suppressing the internal pressure was not observed. In Comparative Example 1, since the depth of the concave portion was insufficient, and in Comparative Example 4, the area of the concave portion was too small, and in each case, a sufficient space was formed between the separator and the negative electrode surface. Because there was no. Similarly, in Comparative Example 6, the internal pressure was significantly increased because no unevenness processing was performed.

In Comparative Example 2, all the batteries were short-circuited or broken when the batteries were wound. This is because the depth of the concave portion was too large, so that a thin portion was formed.
On the other hand, in the separators of Examples 1 to 4, the battery can be wound without causing breakage or short circuit.

Further, in the battery of Comparative Example 3, although the increase in the internal pressure was suppressed, the discharge capacity at high rate discharge was low. This is because the area of the concave portion was too large, and the contact area with the electrode was reduced, resulting in an increase in internal resistance. Furthermore, the batteries of Comparative Examples 3 and 6 also have a low discharge capacity at high rate discharge. These are due to the fact that the area of the concave portion is too small, so that oxygen gas remains on the separator, the contact portion effective for discharge decreases, and the internal resistance increases. In contrast, all of the batteries of Examples 1 to 4 have a high discharge capacity.

Further, in the battery of Comparative Example 5, the internal pressure rise could not be suppressed. This is because no space is formed between the surface having the unevenness and the negative electrode surface because the surface having the unevenness does not face the negative electrode.

Embodiment 1 in which the rise in internal pressure is suppressed.
All of the batteries No. to No. 4 show good cycle durability, and it is shown that suppressing the increase in the internal pressure leads to prolonging the life of the battery.

As described above, the battery separator and the alkaline battery according to the present invention have been specifically described with reference to the examples. However, the present invention is not limited to the above-described examples, and the invention is not limited thereto. It is also possible to carry out the present invention with appropriate modifications within a compatible range, and all of them are included in the technical scope of the present invention.

[0050]

As described above, in the battery separator of the present invention, a minute space can be formed between the separator and the surface of the negative electrode, and oxygen gas generated at the positive electrode and passing through the separator accumulates in this space. Therefore, the oxygen gas absorption reaction on the negative electrode surface proceeds smoothly, and it is possible to effectively suppress an increase in battery internal pressure during overcharge. Therefore, an alkaline battery using this separator has excellent safety and high durability, and can further improve discharge characteristics.

[Brief description of the drawings]

FIG. 1 is an example of a sectional view of unevenness.

FIG. 2 shows an example of a concave portion viewed from above a separator (continuous).

FIG. 3 shows an example of a concave shape as viewed from above a separator.

FIG. 4 is an example (discontinuous) in which a concave portion viewed from above a separator has a round shape.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Yamashita 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. General Research Laboratory F-term (reference) 5H021 CC11 EE02 HH01 HH03 HH04 HH10 5H028 AA05 CC07 CC10 EE06 HH01 HH05

Claims (4)

[Claims] 1. An alkaline battery separator having irregularities on at least one surface. 2. The separator for an alkaline battery according to claim 1, wherein the depth of the recess is not less than 5% and not more than 50% with respect to the apparent thickness of the separator. 3. The area of the recess is 5 with respect to the total area of the separator.
The separator for an alkaline battery according to claim 1, wherein the separator is in a range of not less than 50% and not more than 50%. 4. An alkaline battery comprising the alkaline battery separator according to claim 1, wherein a surface having irregularities faces at least a negative electrode.