JP2002343330A - Battery separator and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery separator and a battery with better self-discharge inhibitory action. SOLUTION: The battery separator is made of sheets containing a polymer material, which contains SO4 -containing functional group after being macerated for 30 minutes in potassium hydroxide aqueous solution with ion intensity of 6 mol/L at 20 deg.C, of which, atomicity ratio (Sa/St) of sulfur atomicity (Sa) after the above polymer material is macerated for 30 minutes in potassium hydroxide aqueous solution with ion intensity of 6 mol/L at 20 deg.C to total sulfur atomicity (St) existing on the surface of the above polymer material before the above polymer material is macerated for 30 minutes in potassium hydroxide aqueous solution with ion intensity of 6 mol/L at 20 deg.C is not less than 1/4. And, the battery uses the battery separator as described above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a battery separator and a battery.

[0002]

2. Description of the Related Art Conventionally, batteries (eg, alkaline batteries)
A separator is used between the positive electrode and the negative electrode in order to separate the positive electrode and the negative electrode to prevent a short circuit, and to hold the electrolytic solution so that the electromotive reaction proceeds smoothly.

As a resin constituting the separator, it is preferable to use a polyolefin resin having excellent alkali resistance and oxidation resistance. However, a polyolefin-based resin has a low affinity for an electrolytic solution and has poor retention of an electrolytic solution, so that a battery using a separator made of a polyolefin-based resin cannot smoothly generate an electromotive reaction. Therefore, in order to impart an affinity with an electrolytic solution, various surface modifications have been performed on polyolefin-based resins.

As one of the surface modification methods, a sulfonation treatment for introducing a sulfonic acid group is known. In this sulfonation treatment, by introducing a sulfonic acid group, the affinity with the electrolytic solution can be imparted, and the self-discharge suppressing action is also provided.

[0005]

Although the sulfonic acid group-introduced separator has an effect of suppressing self-discharge to some extent, the market has demanded a separator having a more excellent effect of suppressing self-discharge.

The present invention has been made in order to improve the above-mentioned points, and an object of the present invention is to provide a battery separator and a battery having a more excellent self-discharge suppressing action.

[0007]

Means for Solving the Problems The battery separator of the present invention (hereinafter sometimes referred to as "separator") is a battery separator made of a sheet containing a polymer material.
The polymer material has an ionic strength of 6 mol at a temperature of 20 ° C.
/ L immersed in an aqueous solution of potassium hydroxide for 30 minutes, and have an SO ₄ -containing functional group. The polymer material is placed in an aqueous solution of potassium hydroxide having an ionic strength of 6 mol / L at a temperature of 20 ° C. After immersion for 30 minutes, the polymer material having the number of sulfur atoms (Sa) constituting the SO ₄ -containing functional group existing on the surface of the polymer material was heated at a temperature of 20 ° C.
The ratio of the number of atoms (Sa) to the total number of sulfur atoms (St) present on the surface of the polymer material before immersion in a potassium hydroxide aqueous solution having an ionic strength of 6 mol / L at 30 ° C. for 30 minutes.
/ St) is １ ／ or more, and such a separator was found to be excellent in the self-discharge suppressing action.

Although a specific self-discharge suppressing mechanism has not been elucidated yet, this polymer material has an ionic strength of 6 mol.
/ L, when incorporated into a battery containing a potassium hydroxide electrolyte solution, a structural unit containing a SO ₄ -containing functional group represented by the following general formulas (1), (2), and (3): When a nitrogen-containing compound (e.g., ammonia) is generated, any of the general formulas (1) to (3) can capture a nitrogen-containing compound (e.g., ammonia),
As a result, it is considered that the self-discharge suppressing action is excellent.

[0009]

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[0010]

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[0011]

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Further, the polymer material is introduced at a temperature of 20 ° C.
In an aqueous potassium hydroxide solution with an on-strength of 6 mol / L, 3
Before immersion for 0 minutes, it exists on the surface of the polymer material.
Of the total number of sulfur atoms (St) to the total number of carbon atoms (Ct)
Atomic ratio (St / Ct) is 5 × 10^-3Is over
And as represented by the general formulas (1) to (3) described above.
Can participate in trapping nitrogen-containing compounds in electrolyte
It is thought that SO ₄Absolute amount of functional group contained
Therefore, it is considered that the self-discharge suppressing action is more excellent.

Since the battery of the present invention uses the battery separator as described above, self-discharge does not easily occur and the battery has an excellent capacity retention rate.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The separator of the present invention, as a polymer material, is immersed in a potassium hydroxide aqueous solution having an ionic strength of 6 mol / L at a temperature of 20 ° C. for 30 minutes (hereinafter simply referred to as “after immersion”). in there) are those having sO ₄ containing functional group, sO ₄ containing functional groups present even after such immersion nitrogen-containing compounds (e.g.,
(Ammonia) can be trapped, and it has been found to be excellent in self-discharge suppressing action.

In general, when sulfonation is performed, SO ₂ ,
It is said that a functional group such as SO ₃ or SO ₄ is generated. Among them, a sulfur-containing functional group constituting a structural unit represented by the following general formula (4) is called alkyl hydrogen sulfate, Is unstable enough to be hydrolyzed into an alcohol having the same alkyl group and sulfuric acid only by heating, so that in a strong alkaline electrolyte of about 6 mol / L,
Since it is easily hydrolyzed, the nitrogen-containing compound cannot be trapped, not only does not have a self-discharge suppressing effect, but also tends to cause a problem that the electrolytic solution is neutralized by the generation of sulfuric acid.

[0016]

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On the other hand, since the polymer material constituting the separator of the present invention is not hydrolyzed even after immersion and has an SO ₄ -containing functional group, the polymer material captures the nitrogen-containing compound. The problem of suppressing self-discharge and neutralizing the electrolyte does not occur. That is, it is considered that the SO ₄ -containing functional group, for example, the SO ₄ -containing functional group represented by the following general formula (1), (2) or (3) remains without being hydrolyzed even after immersion. It is considered that these SO ₄ -containing functional groups are not hydrolyzed because they are bonded to carbon containing a double bond, and when a nitrogen-containing compound is generated, the nitrogen-containing compound can be trapped and self-discharge can be suppressed. .

[0018]

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[0019]

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[0020]

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The above general formula (1) shows a state in which an SO ₄ R group is bonded to an ethylene main chain, and a general formula (2) shows a state in which an SO ₄ functional group is cross-linked to the same ethylene main chain. In general, the general formula (3) is a state in which an SO ₄ functional group is cross-linked to a different ethylene main chain.

The separator of the present invention is capable of suppressing the self-discharge by trapping a nitrogen-containing compound and preventing the SO ₄ -containing functional group present on the surface of the polymer material after immersion so as not to neutralize the electrolytic solution. Number of sulfur atoms (S
a) total sulfur present on the surface of the polymer material before immersion in an aqueous potassium hydroxide solution having a ionic strength of 6 mol / L at a temperature of 20 ° C. for 30 minutes (hereinafter, sometimes simply referred to as “before immersion”). The ratio of the number of atoms (Sa / St) to the number of atoms (St) is １ ／ or more. This atomic ratio (S
The higher the ratio (a / St), the more excellent the self-discharge suppressing action and the neutralization suppressing action. Therefore, the atomic ratio (Sa / St) is preferably 1/3 or more, preferably 2/5 or more. Is more preferable, and ideally it is 1.

This atomic ratio (Sa / St) can be calculated as follows. (1) After washing the polymer material in pure water for 30 minutes or more,
Air dry for 24 hours. (2) The peak area (St) of a sulfur atom (2P _3/2 ) on the surface of the polymer material is measured by an X-ray photoelectron spectrometer under the following conditions. (A) Excitation source: Mg-Kα (b) Applied voltage value: 10 KV (c) Beam current value: 10 mA (d) Emission angle of photoelectrons: 90 ° (3) Ion intensity of polymer material at 20 ° C. 6mo
After immersing in 1 / L potassium hydroxide aqueous solution for 30 minutes,
Wash in pure water for 30 minutes or more and air dry for 24 hours. (4) Using an X-ray photoelectron spectrometer, under the same conditions as above,
After measuring the peak area of the sulfur atom (2P _3/2 ) in the polymer material, the amount of sulfur atom (Sa) derived from the SO ₄ -containing functional group was determined by waveform separation by the nonlinear least squares method using a Gauss-Lorentz mixture function. Is calculated. (5) From these values, the number of sulfur atoms (S) constituting the SO ₄ -containing functional group existing on the surface of the polymer material after immersion (S
The atomic ratio (Sa / St) of a) to the total sulfur atoms (St) existing on the surface of the polymer material before immersion is calculated.

Before immersion, the total number of carbon atoms (Ct) of the total number of sulfur atoms (St) existing on the surface of the polymer material
When the atomic ratio (St / Ct) with respect to is not less than 5 × 10 ⁻³ , the absolute amount of the SO ₄ -containing functional group represented by the general formulas (1) to (3) is large. Therefore, the self-discharge suppressing action is more excellent. A more preferable atomic ratio (St / Ct) is 7 × 10 ⁻³ or more, and an even more preferable atomic ratio (St / Ct) is 1 × 10 ⁻² or more.

The atomic ratio (St / Ct) of the total number of sulfur atoms (St) to the total number of carbon atoms (Ct) present on the surface of the polymer material is determined by an X-ray photoelectron spectrometer under the following conditions. After measuring the peak area of the sulfur atom (2P _3/2 ), the peak area can be calculated by waveform separation by the nonlinear least squares method using a Gauss-Lorentz mixed function. (A) Excitation source: Mg-Kα (b) Applied voltage value: 10 KV (c) Beam current value: 10 mA (d) Escape angle of photoelectrons: 90 °

In the present invention, the “polymer material surface” refers to a range that can be measured by an X-ray photoelectron spectrometer under the following conditions. (A) Excitation source: Mg-Kα (b) Applied voltage value: 10 KV (c) Beam current value: 10 mA (d) Escape angle of photoelectrons: 90 °

Such a polymer material has an excellent resistance to alkalis and acids, so that the polyolefin resin has an SO resistance.
_It is preferable that the _4- containing functional group is bonded. Examples of the polyolefin resin include polyethylene resins (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer, etc.), polypropylene resins ( For example, polypropylene, propylene copolymer, etc.), polymethylpentene resin (for example,
Polymethylpentene, methylpentene copolymer, etc.).

The sheet constituting the separator of the present invention comprises:
It is sufficient to include the above-mentioned polymer material (hereinafter, sometimes referred to as “SO ₄ -containing polymer material”). However, the polymer material constituting the sheet surface (for example, , The polymer material constituting the film surface,
The polymer material constituting the surface of the fiber constituting the fiber sheet) is preferably composed only of the SO ₄ -containing polymer material. In addition, the polymer material constituting the surface other than the sheet surface (for example, the polymer material constituting the inside of the film, the polymer material constituting the fiber inside the fiber sheet)
May be a SO ₄ -containing polymer material or may not be a SO ₄ -containing polymer material.

The sheet constituting the separator of the present invention may be, for example, a fiber sheet such as a woven fabric, a knitted fabric, or a nonwoven fabric, a microporous film, or a composite thereof. Among these, it is preferable to include a nonwoven fabric which is excellent in retention of an electrolytic solution. In particular, wet-type nonwoven fabrics are suitable because they can have a dense structure and have excellent electrolyte solution retention properties.

The separator of the present invention can be formed, for example, by using an SO ₄ -containing polymer material to form a sheet by a conventional method, or by using a polymer material having no SO ₄ -containing functional group (for example,
After forming a sheet by a conventional method using a polyolefin-based resin, structural units that can remain as SO ₄ -containing functional groups even after immersion, as represented by the following general formulas (1) to (3): Can be introduced and manufactured. According to the former method, the sheet surface and the inside are made of the SO ₄ -containing polymer material, and according to the latter method, the sheet surface is made of the SO ₄ -containing polymer material. When the sheet surface is made of the SO ₄ -containing polymer material as in the latter, the sheet surface and the inside are more excellent in mechanical strength than when the sheet surface is made of the SO ₄ -containing polymer material. It is an aspect.

[0031]

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[0032]

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[0033]

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Hereinafter, a method for producing a separator suitable for the present invention, which is made of a non-woven fabric, and in which the surface of the fibers constituting the non-woven fabric is made of an SO ₄ -containing polymer material, will be described.
This will be specifically described.

First, a fiber made of a polymer material having no SO ₄ -containing functional group after immersion (hereinafter sometimes referred to as “SO ₄ -free fiber”) is prepared. As the SO ₄ -free fiber, it is preferable to include a polyolefin-based fiber having excellent electrolytic solution resistance. More preferably, only a polyolefin-based fiber is prepared. Examples of the polyolefin fiber include, for example, polyethylene resins (eg, ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer, etc.), polypropylene resins (eg, , Polypropylene, propylene copolymer, etc.) and fibers containing one or more types of polymethylpentene resins (eg, polymethylpentene, methylpentene copolymer, etc.).

The SO ₄ -free fiber preferably contains high-strength fiber having a tensile strength of 4.5 cN / dtex (centinewton / decitex) or more. When high-strength fibers are included, when the separator is wound to form an electrode group, the separator may be cut by the electrode burr or the electrode burr may penetrate the separator, resulting in a short circuit. It can be prevented efficiently.

The tensile strength of the high-strength fiber is 6.2 cN / d
tex or more, preferably 10.1 cN / dte
x, more preferably 10.7 cN / dte
It is more preferable that the value be x or more. The upper limit of the tensile strength of the high-strength fiber is not particularly limited.
N / dtex is appropriate. This "tensile strength"
Refers to a value measured by a method specified in JIS L 1015 (Test method for chemical fiber staples).

This high-strength fiber is also preferably composed of a polyolefin resin, and is preferably composed of a polyethylene resin, a polypropylene resin, a polymethylpentene resin or the like, similar to the above-mentioned polyolefin resin. preferable. Among these, it is more preferable to be composed of a polypropylene resin or a polyethylene resin (particularly, ultrahigh molecular weight polyethylene).

The high-strength fiber may be composed of the above-mentioned polyolefin resin alone, or may be composed of two or more resin components (at least one of which is composed of a polyolefin resin, preferably both are polyolefin resins). ) May be a mixed or composite high-strength fiber. High-strength fibers having a low-melting-point resin component on the fiber surface are suitable because they can be fused by the low-melting-point resin component constituting the fiber surface and can improve the modulus strength. Examples of the cross-sectional shape of the high-strength fiber in which two or more resin components are composited include a core-sheath type, an eccentric type, a bonding type, a sea-island type, an orange type and a multi-bimetal type. Among the composite high-strength fibers, a core-sheath type, an eccentric type or a sea-island type high-strength fiber, which can increase the number of low-melting resin components that can participate in fusion, can be suitably used. It is preferably a core-sheath type.

The fineness of the high-strength fiber is 0.5 to 3.5 d.
tex (decitex), and the fiber length of the high-strength fiber is preferably 1 to 160 mm. The high-strength fiber is 10 mass% of the total weight of the nonwoven fabric constituent fibers so that the separator is not cut by the burr of the electrode plate or the burr of the electrode plate does not penetrate the separator.
Preferably, it occupies more than 20 mass%, more preferably 20 mass% or more.

[0041] In addition to such high-strength fibers, or in place of the high-strength fiber, as SO ₄ free fibers, preferably it contains fusible fibers. By including the fused fibers, the modulus and rigidity of the separator can be improved.

In the case where the high-strength fiber is not fused, the fusion-bonded fiber is lower than the resin component having the lowest melting point constituting the high-strength fiber (preferably lower than 10 ° C., more preferably lower than 20 ° C.). It is preferable that a fusion component composed of a resin having a melting point constitutes at least a part of the fiber surface. In a case where high-strength fibers are also fused, a fusion component constituting the high-strength fibers (low-melting resin) Component) (± 1
It is preferable that a fusion component made of a resin having a melting point of about 0 ° C.) constitutes at least a part of the fiber surface.

For example, when the high-strength fiber is made of a polypropylene resin alone, a polyethylene resin (for example, ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene It is preferable to use a fusion fiber having a fusion component as a fusion component. When the high-strength fiber is made of ultra-high molecular weight polyethylene alone, a low-density polyethylene or an ethylene copolymer is used as a fusion component. Preferably, fused fibers are used. When the high-strength fiber contains a polyethylene resin as a fusion component (low-melting resin component), a polyethylene having a melting point similar to that of the polyethylene resin constituting the high-strength fiber (about ± 10 ° C.) It is preferable to use a fusion fiber containing a system resin as a fusion component.

Such a fusion fiber may be composed of a single resin component (that is, only the fusion component) or may be composed of a plurality of resin components. If worn, it may impair air permeability,
It is preferable to be composed of a plurality of resin components.

Examples of the cross-sectional shape of the fused fiber comprising a plurality of resin components include a core-sheath type, an eccentric type, a bonding type, a sea-island type, an orange type and a multiple bimetal type. Among these, core-sheath type, eccentric type or sea-island type fusion fibers which can increase the number of low melting point resin components that can participate in fusion can be preferably used, and particularly, core-sheath type fusion fibers. Fibers can be suitably used. The resin component other than the fusion component of the fusion fiber is preferably made of a resin higher than the melting point of the fusion component by 10 ° C. or more, more preferably by 20 ° C. or more so that the fiber shape can be maintained. preferable.

The "melting point" in the present invention means a temperature at which a maximum value of a melting endothermic curve obtained by using a differential calorimeter at a rate of temperature increase of 10 ° C./min from room temperature is obtained.

The fineness of the fused fiber is preferably 0.05 to 3.5 dtex so as to be excellent in the retention of the electrolytic solution, and the fiber length of the fused fiber is preferably 1 to 160 mm. .

The fused fiber preferably accounts for 10% by mass or more of the total mass of the fibers constituting the nonwoven fabric, and accounts for 20% by mass or more so that the modulus strength and rigidity of the separator can be improved. Is more preferred.

In addition to the above high-strength fibers and / or fused fibers, or in place of the high-strength fibers and fused fibers, SO
_It is preferable that the non-containing fibers include ultrafine fibers having a fiber diameter of 5 μm or less. By containing the ultrafine fibers, the holding properties of the electrolytic solution are excellent, so that the electromotive reaction can be smoothly caused. Although the lower limit of the fiber diameter is not particularly limited, about 0.01 μm is appropriate.

The term "fiber diameter" in the present invention refers to the diameter of a fiber having a circular cross-sectional shape when it is circular, and a circle having the same area as the fiber cross-sectional area when the fiber has a non-circular cross-sectional shape. Is regarded as the fiber diameter of the fiber.

The ultrafine fibers are preferably composed of one or more kinds of the same polyolefin resins as described above.
When the fiber is used in combination with the above-mentioned fused fiber or when the high-strength fiber contains a fused component (low-melting resin component), the fused component (low-melting resin component) of these fibers is fused. The ultrafine fibers are higher (preferably 5 ° C or higher, more preferably 10 ° C) higher than the melting point of these fusion components (low-melting resin components) so that the ultrafine fibers are not melted by the heat generated.
It is preferable to be composed of a resin having a (higher) melting point. For example, when the fusion component (low-melting resin component) is made of low-density polyethylene, the ultrafine fibers are preferably made of a polypropylene resin and / or high-density polyethylene.

Such an ultrafine fiber can be obtained, for example, by splitting a splittable fiber by a physical action, splitting a splittable fiber by a chemical action, or by a melt blow method. The physical action for splitting the split fibers includes, for example, a fluid flow such as a water stream, a calendar or a flat press, and the chemical action for splitting the split fibers includes, for example, removal of resin, There is swelling and the like.

The split fiber which can be split by the physical action or the chemical action is composed of two or more resin components (at least one resin component is composed of a polyolefin resin). A split fiber 1 having an orange cross-section as shown in FIG. 5 and a split fiber 1 having a multi-bimetal cross-section as shown in FIG.

The fineness of the split fiber is not particularly limited as long as it can generate ultrafine fibers having a fiber diameter as described above. The fiber length of the split fibers and the ultrafine fibers is preferably 1 to 160 mm.

The ultrafine fibers preferably occupy 20 mass% or more, more preferably 30 mass% or more of the total mass of the nonwoven fabric constituent fibers so as to have excellent electrolyte retention.

Preferred combinations of the fibers constituting the nonwoven fabric of the present invention include (1) a combination of a high-strength fiber and a fusion fiber, and (2) a combination of a high-strength fiber, a fusion fiber and an ultrafine fiber. . In the case of the former (1), the mass ratio is preferably (high-strength fiber) :( fused fiber) = 10 to 60:90 to 40, and (high-strength fiber) :( fused fiber) = 2
More preferably, the ratio is from 0 to 40:80 to 60. Also,
In the case of the latter (2), the mass ratio is (high-strength fiber):
(Fused fiber): (ultrafine fiber) = 10-60: 10-7
0: 20-70, preferably (high-strength fiber):
(Fused fiber): (ultrafine fiber) = 20-40: 20-5
The ratio is more preferably 0:30 to 60.

The SO ₄ -free fibers may include undivided split fibers, fibers having a tensile strength of less than 4.5 cN / dtex, and the like.

Next, using the above-mentioned SO ₄ -free fiber (for example, high-strength fiber, fused fiber, ultrafine fiber, split fiber, etc.), dry method (including melt blow method and spun bond method) and A fiber web is formed by a wet method.
Among these methods of forming a fiber web, it is preferable to form the fiber web by a wet method that can produce a nonwoven fabric that is dense and has excellent electrolyte solution holding properties. As the wet method, for example, there is a method in which a paper machine selected from a forward flow circular net, a reverse flow circular net, a circular net former, a long net, and a short net is used alone or appropriately combined.

Next, the nonwoven fabric is manufactured by bonding the fiber webs. Examples of the bonding method include a method of entanglement with a fluid flow such as a water flow, a method of fusing a fusion component (low-melting resin component) such as a fusion fiber or a high-strength fiber, or a method of using these in combination. and so on.

The entanglement process and the fusion process can be performed any number of times, and the order is not limited.
Performing the entanglement process after the fusion process breaks the fusion, so it is preferable to perform the fusion at the end.

When the fiber web contains split fibers that can be physically split, the fibers can be entangled and split by the action of a fluid stream such as a water stream. Of course, the splitting of the split fibers does not need to be performed by the fluid flow, and apart from the action of the fluid flow, a physical action (for example, calender or flat press) or a chemical action (for example, resin removal, resin swelling, etc.) ). Further, the fiber web may be formed by using ultrafine fibers generated by division (for example, division by a chemical action) in advance.

The conditions for ejecting the fluid flow include, for example,
A fluid flow having a pressure of 1 MPa to 30 MPa may be jetted onto the fiber web from a nozzle plate having a diameter of 0.05 to 0.3 mm and a pitch of 0.2 to 3 mm and arranged in one or more rows of nozzles. Such a fluid flow may occur more than once,
What is necessary is just to eject to one side or both sides of a fiber web.

On the other hand, the fusion of the fiber web may be carried out under no pressure, under pressure, or by applying pressure after melting the fusion component (low melting point resin component) under no pressure. Is also good.

When heating and pressurizing are performed simultaneously, the heating temperature is determined from the softening temperature of the fusion component (low melting point resin component) such as fusion fiber, etc. ) Is preferably in the range up to the melting point of
When pressure is not applied, from the softening temperature of the fusion component (low-melting resin component) such as the fusion fiber to a temperature 30 ° C. higher than the melting point of the fusion component (low-melting resin component) such as the fusion fiber. It is preferable to carry out within the range.

The pressure is preferably about 5 to 30 N / cm, regardless of whether the pressure is applied simultaneously with the heating or the pressure after the heating.

The term “softening temperature” in the present invention refers to a temperature at which a starting point of a melting endothermic curve obtained by raising the temperature from room temperature at a rate of 10 ° C./min using a differential calorimeter is used.

Next, the SO ₄ -containing functional group is introduced into the non-woven fabric. As the SO ₄ -containing functional group introduction treatment, for example, (1) a nonwoven fabric is immersed in a solution made of fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, sulfuryl chloride or the like at a temperature of 62 ° C. or higher (the upper limit is a temperature at which the nonwoven fabric is not damaged). Later, it is taken out of the solution, and the temperature is 80 ° C. or more (preferably
(2) In an atmosphere at a temperature of 62 ° C. or higher (the upper limit is a temperature at which the nonwoven fabric is not damaged) in the presence of sulfur monoxide gas and / or sulfur dioxide gas. A method in which a nonwoven fabric is arranged on the substrate to cause discharge, and then heat-treated at a temperature of 80 ° C or higher (preferably 100 ° C or higher, the upper limit being a temperature at which the nonwoven fabric is not damaged);
(3) After exposing the nonwoven fabric to sulfur trioxide gas in an atmosphere at a temperature of 62 ° C. or higher (the upper limit is a temperature at which the nonwoven fabric is not damaged),
A method of performing heat treatment at a temperature of 80 ° C. or higher (preferably 100 ° C. or higher, the upper limit being a temperature at which the nonwoven fabric is not damaged) can be used. Thus, by applying sufficient heat, a double bond can be generated at the carbon bonded to the SO ₄ -containing functional group. That is, by applying sufficient heat, it is possible to form a structural unit represented by the following general formulas (1) to (3) in which an SO ₄ -containing functional group is bonded to a double-bonded carbon. .

[0068]

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[0069]

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[0070]

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In this way, the SO ₄ -containing functional group can be introduced on the surface of the fiber constituting the nonwoven fabric.
_{When the 4-} containing functional group is introduced, a by-product is also generated. Therefore, it is preferable to wash with sulfuric acid or water in order to remove the by-product. In addition, if washing is immediately performed with water after introducing the SO ₄ -containing functional group, heat may be generated and the nonwoven fabric may be damaged. Therefore, it is preferable to sequentially wash with low-concentration sulfuric acid and finally wash with water.

The non-woven fabric thus washed can be used as a separator. Even if the non-woven fabric is washed in such a manner, the non-woven fabric is represented by the following general formula (4) in an alkaline electrolyte such as an aqueous solution of potassium hydroxide. Since the SO ₄ -containing functional group may hydrolyze to generate sulfuric acid and neutralize the electrolytic solution, after washing, the temperature is 20 ° C. or higher and the ionic strength is 6 mol / L (preferably 8 mol / L). To an alkaline solution (preferably aqueous potassium hydroxide solution)
It is preferable to remove the sulfur-containing functional groups that cannot remain after the immersion by immersion for at least one minute and washing with water. Through these steps, the total number of sulfur atoms (Sa) constituting the SO ₄ -containing functional group present on the surface of the polymer material after immersion is calculated based on the total number of sulfur atoms (Sa) existing on the surface of the polymer material before immersion ( The atomic ratio (Sa / St) to St) can be 以上 or more.

[0073]

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The total number of carbon atoms (Ct) of the total number of sulfur atoms (St) existing on the surface of the polymer material before the immersion.
The separator having an atomic ratio (St / Ct) of 5 × 10 ⁻³ or more to, for example, (1) the temperature of a solution of fuming sulfuric acid, sulfuric acid, chlorosulfuric acid or sulfuryl chloride, and (2)
(3) the ambient temperature when exposing to the sulfur trioxide gas in the presence of sulfur monoxide gas and / or sulfur dioxide gas, and
It can be manufactured by increasing the time of these treatments to 20 seconds or more.

Thereafter, it is washed with water and dried. The thickness can be adjusted by passing between the rolls as necessary.

The method of introducing the SO ₄ -containing functional group after forming the non-woven fabric has been described above. However, after introducing the SO ₄ -containing functional group into the fiber or fiber web before forming the non-woven fabric, It may be formed.

The separator of the present invention preferably has a thickness of 0.25 mm or less so that the capacity of the battery can be increased. Further, the areal density is preferably from ²⁰ to 100 g / m ² .

Since the separator of the present invention has an excellent self-discharge suppressing effect, it can be suitably used as a separator for an alkaline secondary battery, particularly for a secondary battery such as a nickel-cadmium battery or a nickel-hydrogen battery. Can be suitably used as a separator.

The battery of the present invention uses the separator as described above. Therefore, self-discharge hardly occurs, and thus the battery has an excellent capacity retention rate.

The battery of the present invention can be exactly the same as a conventional battery except that the above-described separator is used.

For example, in a cylindrical nickel-hydrogen battery, an electrode plate group in which a nickel positive electrode plate and a hydrogen storage alloy negative electrode plate are spirally wound via the above-described separator is inserted into a metal case. Having a structure. As the nickel positive electrode plate, for example, a sponge-like nickel porous body filled with an active material made of nickel hydroxide solid solution powder can be used.As the hydrogen storage alloy negative electrode plate, for example, a nickel-plated perforated steel sheet, foamed nickel, or nickel net, AB ₅ type (rare earth) alloy, AB / a
₂ B system (Ti / Zr based) alloy, or _AB 2 (Lave
An alloy filled with an (s-phase) -based alloy can be used.
As the electrolyte, for example, a two-component system of potassium hydroxide / lithium hydroxide or a three-component system of potassium hydroxide / sodium hydroxide / lithium hydroxide can be used. Further, the case is sealed by a sealing plate provided with a safety valve via an insulating gasket. Further, a positive electrode current collector and an insulating plate are provided, and if necessary, a negative electrode current collector is provided.

The battery of the present invention does not need to be cylindrical, but may be a prismatic type, a button type, or the like. In the case of a square type, the battery has a laminated structure in which a separator is arranged between a positive electrode plate and a negative electrode plate.

Examples of the separator of the present invention will be described below, but the present invention is not limited to these examples.

[0084]

EXAMPLES (Example 1) (1) Tensile strength 11 cN / dtex, fineness 1.3 dt
ex, high-strength polypropylene fiber having a fiber length of 10 mm (melting point: 166 ° C.), 20 mass%; Cored sheath-fused fiber having a fineness of 2.2 dtex and a fiber length of 5 mm and a mass of 20 mass%, and (3) a polypropylene component as shown in FIG. 3 (symbol 12 in the figure, circular fiber diameter of 3.5 μm)
One polypropylene ultrafine fiber (melting point: 160 ° C.), eight triangular polypropylene ultrafine fibers (melting point: 160 ° C.) having a fiber diameter of 4.3 μm and a high-density polyethylene component (symbol in the figure) 11. Fiber diameter of approximately triangular
2 μm high density polyethylene ultrafine fiber (melting point: 125
C), which has an orange cross-section of 2.2 dtex and a fiber length of 5 mm and a length of 5 mm.
and a slurry obtained by mixing and dispersing ass.% and ass% was formed by an inclined wire short net method to form a fiber web.

Next, the fiber web is supplied to a fusing oven set at a temperature of 133 ° C. to fuse the sheath component of the core-sheath type fused fiber and the high-density polyethylene component of the split fiber to obtain a fused fiber web. Was manufactured.

Next, the fused fiber web was placed on a 100-mesh net, and a water stream at a pressure of 10 MPa was applied to the fused fiber web from a nozzle plate having nozzles arranged in a row at a diameter of 0.18 mm and a pitch of 0.6 mm. On the other hand, the split fibers were jetted twice alternately on both sides to split the split fibers.

Next, the fused fiber web obtained by dividing the divided fibers is dried by a hot air circulating dryer set at a temperature of 120 ° C., and at the same time, only the sheath component of the core-sheath type fused fiber is fused again. A fusible nonwoven fabric having a density of 70 g / m ² was produced.

Next, the re-bonded non-woven fabric was used at a concentration of 15%.
After immersion in fuming sulfuric acid at a temperature of 62 ° C for 2 minutes,
A heat treatment was carried out at a temperature of ° C. to introduce a SO ₄ -containing functional group into the surface of the fibers constituting the re-bonded non-woven fabric, thereby obtaining an SO ₄ -containing non-woven fabric.

Next, the SO ₄ -containing nonwoven fabric was washed with 75% sulfuric acid, 50% sulfuric acid and water in that order.

Then, the washed SO ₄ -containing nonwoven fabric was immersed in a potassium hydroxide aqueous solution having a ionic strength of 6 mol / L at a temperature of 20 ° C. for 5 minutes, washed with water, and heated with a hot roll set at a temperature of 98 ° C. Min. And dried.

Next, the thickness of the separator of the present invention (area density: 70 g / m 2) was adjusted by a pressure roll (normal temperature).
² , thickness: 0.18 mm).

(Example 2) The fineness of the core component was made of polypropylene (melting point: 160 ° C) and the sheath component (fused component) was made of high density polyethylene (melting point: 125 ° C).
dtex, core-sheath type fused fiber with a fiber length of 5 mm (100%)
Was dispersed in a slurry to form a fiber web.

Next, the fiber web was brought to a temperature of 133 ° C.
By supplying to the set fusing oven
And the sheath component of the core-sheath type fused fiber is fused to obtain an areal density of 70.
g / m ^TwoWas produced.

Next, this fused nonwoven fabric was heated to a concentration of 15%
After immersion in fuming sulfuric acid at 65 ° C for 2 minutes, heat at 80 ° C
By performing the treatment, on the surface of the fiber constituting the fused nonwoven fabric,
SO ₄Introducing a functional group containing SO₄The resulting nonwoven fabric was obtained.

Next, the SO ₄ -containing nonwoven fabric was sequentially washed with sulfuric acid having a concentration of 75%, sulfuric acid having a concentration of 50%, and water.

Then, the washed SO ₄ -containing nonwoven fabric was immersed in a potassium hydroxide aqueous solution having an ionic strength of 6 mol / L at a temperature of 20 ° C. for 5 minutes, washed with water, and washed at a temperature of 98 ° C.
It was dried by contacting with a hot roll set at 0 ° C for 3 minutes.

Next, the thickness of the separator of the present invention (area density: 70 g / m 2) was adjusted by a pressure roll (normal temperature).
² , thickness: 0.18 mm).

(Comparative Example 1) A fused nonwoven fabric produced in exactly the same manner as in Example 2 was immersed in fuming sulfuric acid at a concentration of 15% and at a temperature of 58 ° C for 2 minutes to obtain the surface of the fibers constituting the fused nonwoven fabric. Then, an SO ₄ -containing functional group was introduced into the resultant to obtain an SO ₄ -containing nonwoven fabric.

Next, the SO ₄ -containing nonwoven fabric was washed, immersed in an aqueous solution of potassium hydroxide, washed with water, dried, and adjusted in thickness in the same manner as in Example 2 to obtain a separator (area density: 70 g / m 2) of the present invention. ² , thickness: 0.18 mm).

(The number of sulfur atoms (Sa) constituting the SO ₄ -containing functional group present on the surface of the polymer material after immersion,
Total number of sulfur atoms existing on the surface of the polymer material before immersion (S
Measurement of atomic ratio (Sa / St) to t)) Example 1
Using the respective separators of Comparative Examples 1 and 2 and SO, the SO present on the surface of the polymer material after immersion was obtained by the method described above.
_The total number of sulfur atoms (S) existing on the surface of the polymer material before immersion is determined based on the number of sulfur atoms (Sa) constituting the _4- containing functional group.
The ratio of the number of atoms to t) (Sa / St) was calculated. The atomic ratio (Sa / St) was calculated for both surfaces of each separator, and the average value was calculated. The results were as shown in Table 1.

[0101]

[Table 1]

(Measurement of atomic ratio (St / Ct) of total sulfur atoms (St) to total carbon atoms (Ct) existing on the surface of polymer material before immersion) Examples 1-2 and Comparative Example 1 And the ratio of the total number of sulfur atoms (St) present on the surface of the polymer material before immersion to the total number of carbon atoms (Ct) (St) by the above-described method.
t / Ct) was calculated. The results were as shown in Table 1.

(Measurement of capacity retention ratio) As a current collector of an electrode, a paste-type nickel positive electrode (33 mm, 182 mm length) using a foamed nickel base material and a paste-type hydrogen storage alloy negative electrode (mesh metal alloy, 33 mm, 247mm
Long) and created.

Next, each of the separators cut into a width of 35 mm and a length of 410 mm was sandwiched between the positive electrode and the negative electrode, and spirally wound to form an SC type electrode group. Next, after storing this electrode group in an outer can, 5 mol / L-potassium hydroxide and 1 mol / L
L-lithium hydroxide was poured into an outer can and sealed to form a cylindrical nickel-hydrogen battery.

Next, each cylindrical nickel-hydrogen battery was charged at 0.1 C to 150% of its capacity, and then charged.
The battery was discharged at 0.1 C, and the initial capacity (A) at a final voltage of 1.0 V was measured. Then, at 0.1 C, 1
After being charged 50%, the battery was left in a constant temperature room at a temperature of 65 ° C. for 5 days. Thereafter, the battery was discharged again at 0.1 C, and the capacity (B) at a final voltage of 1.0 V was measured. From these results, the capacity retention was calculated by the following equation. This result is also shown in Table 1.
As shown in FIG. (Capacity maintenance rate,%) = (B / A) × 100

From the results shown in Table 1, the atomic ratio (Sa / S
It was found that the separator of the present invention comprising a polymer material having t) of more than 1/4 was excellent in self-discharge suppressing action.

[0107]

The battery separator of the present invention has a superior self-discharge suppressing effect as compared with the conventional sulfonated separator.

The battery of the present invention is a battery excellent in capacity retention since self-discharge is unlikely to occur.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a split fiber that can be used in the present invention.

FIG. 2 is a schematic cross-sectional view of another split fiber that can be used in the present invention.

FIG. 3 is a schematic cross-sectional view of another split fiber that can be used in the present invention.

FIG. 4 is a schematic cross-sectional view of another split fiber that can be used in the present invention.

FIG. 5 is a schematic sectional view of another split fiber that can be used in the present invention.

[Explanation of symbols]

 1 split fiber 11 one component 12 other component

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C08F 16/30 C08F 16/30 C08J 7/14 CES C08J 7/14 CES C08L 23:00 C08L 23: 00 (72) Inventor Akiko Kosaka 7-floor Kitatone, Sowa-cho, Sarushima-gun, Ibaraki Pref.F-term in Nihon Vilene Co., Ltd. DA00 EA02 5H021 BB12 CC01 CC08 EE02 EE18 HH00 HH01 HH06 HH07 5H028 AA05 BB03 EE06 HH01 HH03 HH08

Claims (3)

[Claims] 1. A battery separator comprising a sheet containing a polymer material, wherein the polymer material is contained in an aqueous potassium hydroxide solution having a ionic strength of 6 mol / L at a temperature of 20 ° C.
After immersion for 0 minutes, the polymer material has an SO ₄ -containing functional group, and the polymer material is immersed in an aqueous solution of potassium hydroxide having an ionic strength of 6 mol / L at a temperature of 20 ° C. for 30 minutes. SO ₄ present on molecular material surface
Before immersing the polymer material having the number of sulfur atoms (Sa) constituting the containing functional group in a potassium hydroxide aqueous solution having an ionic strength of 6 mol / L at a temperature of 20 ° C. for 30 minutes, A battery separator, wherein the atomic ratio (Sa / St) to the total number of existing sulfur atoms (St) is 1/4 or more. 2. The total number of sulfur atoms (St) present on the surface of the polymer material before immersing the polymer material in a potassium hydroxide aqueous solution having an ionic strength of 6 mol / L at a temperature of 20 ° C. for 30 minutes. 2. The battery separator according to claim 1, wherein an atomic ratio (St / Ct) to the total number of carbon atoms (Ct) is 5 × 10 ⁻³ or more. ³ . 3. A battery using the battery separator according to claim 1 or 2.