JP2000100409A - Separator for alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve oxidation resistance, and to stably manufacture a battery by constituting a separator of a fiber sheet containing para type aromatic polyamide fiber having tensile strength not less than a specific value. SOLUTION: Fiber having the tensile strength not less than 20 g/d is used as para aromatic polyamide fiber to thereby prevent a separator from tearing by a short circuit caused by a burr on a plate and the edge of the plate. The fiber can exhibit stable performance over along period since it is also excellent in oxidation resistance. The fiber can be constituted of a resin component such as poly-p-phenylene terephthalic amide. The fiber is desirably contained by 3 mass % or more so as not to cause a short circuit by a burr on the plate, but while, since tensile strength of the separator lacks when nonwoven fabric is formed only of this, it is preferable to set 80 mass % as the upper limit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separator for an alkaline battery.

[0002]

2. Description of the Related Art Conventionally, a positive electrode and a negative electrode of an alkaline battery are separated so as to prevent a short circuit and to maintain an electrolytic solution so that an electromotive reaction can be carried out smoothly. A separator is used.

In recent years, as electronic devices have become smaller and lighter, the space occupied by alkaline batteries has also become smaller. Nevertheless, alkaline batteries are required to have at least the same performance as conventional batteries, and therefore, higher capacity alkaline batteries are required. In order to increase the capacity, it is necessary to increase the amount of the active material of the electrode, so that the volume occupied by the separator is inevitably reduced. That is, it is necessary to reduce the thickness of the separator. However, if a conventional separator is simply made thinner, when manufacturing a battery (electrode group configuration), the burr of the electrode plate penetrates through the separator to short-circuit each other, or the separator may be separated by the edge of the electrode plate. However, there is a problem that the yield may be deteriorated because the wafer may be torn.

[0004] Further, in an alkaline secondary battery mainly composed of a nickel-cadmium battery, a nonwoven fabric made of 6 nylon fibers or 66 nylon fibers has been used as a separator, but the nonwoven fabric made of these fibers is generated from a positive electrode. Since the battery is easily oxidized by oxygen, the discharge capacity of the battery is easily reduced, and the battery life is short.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a separator for an alkaline battery which can stably produce a battery and has excellent oxidation resistance. The purpose is to do.

[0006]

The separator for an alkaline battery of the present invention (hereinafter simply referred to as "separator") comprises a fiber sheet containing para-aromatic polyamide fibers having a tensile strength of 20 g / d or more. Since the para-aromatic polyamide fiber used in the present invention has an excellent tensile strength of not less than 20 g / d, the burr of the electrode plate penetrates through the separator to cause short-circuiting between the electrode plates, Since the separator is not torn by edges etc.,
A battery can be manufactured stably. Moreover, since the para-aromatic polyamide fiber having a tensile strength of 20 g / d or more has excellent oxidation resistance, a separator made of a fiber sheet containing the para-aromatic polyamide fiber has excellent oxidation resistance. .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, by using para-aromatic polyamide fibers having a tensile strength of 20 g / d or more, short-circuiting due to burr of an electrode plate and edge of an electrode plate can be achieved. It has been found that tearing of the separator can be prevented, and furthermore, since the para-aromatic polyamide fiber is also excellent in oxidation resistance, it can exhibit stable performance for a long period of time. The tensile strength of this para aromatic polyamide fiber is 2
If it is less than 0 g / d, it tends to be difficult to exert the above effects, and more preferable tensile strength is 23
g / d or more. In addition, this tensile strength is JIS L
1015 (chemical fiber staple test method).

Incidentally, para-aromatic polyamide fibers include, for example, poly-p-phenylene terephthalamide, poly-p
-Benzamide, poly-p-amide hydrazide, poly-
It can be composed of a resin component such as p-phenylene terephthalamide-3,4-diphenyl ether terephthalamide. Since the para-aromatic polyamide fiber having a tensile strength of 20 g / d or more is commercially available, it can be easily obtained.

The para-aromatic polyamide fiber is preferably contained in an amount of 3 mass% or more so that burrs of the electrode plate do not penetrate through the separator and short-circuit between the electrode plates. 5 mass%
More preferably, the content is more preferably 10 mass% or more. On the other hand, if the non-woven fabric is formed only from the para-based aromatic polyamide fiber, the tensile strength of the separator may be insufficient. Therefore, it is preferable that the non-woven fabric also contains an adhesive fiber. % Or more, the para-aromatic polyamide fiber is preferably contained at 80 mass% or less, more preferably at 75 mass% or less, and more preferably at 70 mass% or less. Most preferred.

[0010] As described above, the fibers constituting the separator of the present invention preferably include adhesive fibers in addition to the para-aromatic polyamide fibers. The adhesive fiber does not adversely affect the para-aromatic polyamide fiber depending on the bonding temperature. For example, a polyolefin resin (for example, polyethylene, polypropylene, polymethylpentene, a copolymer of these monomers, etc.), a polyamide resin ( For example, fibers having at least one resin component such as 6 nylon, 66 nylon, 12 nylon, etc.) on the fiber surface can be mixed. Among these, fibers containing a polyamide-based resin having excellent adhesion to para-aromatic polyamide fibers are preferable.

[0011] When the adhesive fiber is composed of a single component, the adhesive fiber is formed into a film when bonded, which tends to reduce the retention of the electrolyte and the oxygen permeability.
It is preferable to use an adhesive fiber composed of two or more resin components. When the adhesive fiber is composed of two or more resin components, the cross-sectional shape of the fiber can be, for example, a core-sheath type, a side-by-side type, a sea-island type, a multiple bimetal type, or an orange type. Among them, a core-sheath type or a sea-island type having a large bonding area is preferable. Such adhesive fibers can be easily produced by melt spinning, and are readily available because they are commercially available.

[0012] In order to increase the tensile strength of the separator, the adhesive fiber is preferably contained in an amount of at least 20 mass%, more preferably at least 25 mass%, and more preferably at least 30 mass%. Is most preferred. On the other hand, the content is preferably 97 mass% or less so as not to decrease the short-circuit property of the electrode plate due to the burr of the para-aromatic polyamide fiber and the tear prevention property of the separator due to the edge of the electrode plate,
More preferably, it is contained in an amount of 95 mass% or less.
Most preferably, it is contained at 0 mass% or less.

[0013] The separator of the present invention is a fiber other than the above-mentioned para-aromatic polyamide fiber and adhesive fiber (hereinafter referred to as "fiber").
"Other fibers").
As the other fibers, there are those having a resin component on the fiber surface that does not adhere at the temperature at which the adhesive fiber is adhered.For example, when the adhesive component of the adhesive fiber is made of low-density polyethylene, high-density polyethylene is used. Polyolefin resins such as polypropylene, polymethylpentene, copolymers of these monomers, and polyamide resins such as 6 nylon, 66 nylon, and 12 nylon can be used. If the adhesive component consists of 6 nylon, 66 nylon or 1
A fiber having a polyamide resin such as nylon 2 on the fiber surface can be used. The other fibers may be fibers that can be split by an external force such as a water flow.
These other fibers can be easily produced by melt spinning and are readily available because they are commercially available.

[0014] The amount of the other fibers is determined to be 77 ma from the balance between the para-aromatic polyamide fiber and the adhesive fiber.
It is preferably at most ss%, more preferably at most 70 mass%, most preferably at most 60 mass%.

[0015] The fibers constituting the separator of the present invention, that is,
Para-aromatic polyamide fibers, adhesive fibers, and other fibers should have a fineness of 0.3 to 6 denier so as to be excellent in the retention of the electrolyte and to be excellent in the dispersibility of each fiber. Preferred and more preferred fineness is 0.5 to 5 denier.

Further, when the fibers constituting the separator, that is, para-aromatic polyamide fibers, adhesive fibers, and other fibers are fibrillated, the fibers (particularly, para-aromatic polyamide fibers) are formed by fibrillation. )
The tensile strength of the separator is reduced or the fibrillation makes the structure of the separator too dense, and when oxygen is generated from the positive electrode, as in a sealed nickel-cadmium battery, oxygen is transmitted to the negative electrode side. These fibers (particularly, para-aromatic polyamide fibers) are preferably not fibrillated because they are difficult to consume.

The separator of the present invention comprises a fiber sheet containing the above-mentioned fibers. As an embodiment of this fiber sheet,
For example, it can be a nonwoven fabric, a woven fabric, a knitted fabric, or a composite thereof. Among these, it is preferable to include a nonwoven fabric in which fibers can be arranged three-dimensionally and which is more excellent in the retention of electrolyte. In addition, the separator of the present invention can be manufactured by an ordinary method. For example, a suitable nonwoven fabric can be manufactured as follows.

First, a para-aromatic polyamide fiber as described above, preferably an adhesive fiber, and optionally other fibers are prepared. The fiber length of these fibers differs depending on the method of forming a fiber web described later. When forming a fiber web by a wet method, a fiber having a length of about 1 to 25 mm is used, and the fiber is formed by a dry method such as a card method or an air lay method. When forming a web, fibers having a length of about 25 to 110 mm are used.

Next, a fiber web is formed from these fibers. Examples of a method for forming the fiber web include a wet method and a dry method (for example, a card method, an air-lay method, and the like). A separator may be manufactured from these single fiber webs, or a separator may be manufactured from two or more of the same or different types of fiber webs, but it is better to use a fiber web containing fibers having a long fiber length. The separator preferably contains a fiber web formed by a dry method, since the strength of the separator can be increased and the separator is hardly broken even by a tension at the time of manufacturing a battery (electrode plate group configuration). When uniform dispersion of fibers is also required, it is preferable to laminate a fiber web formed by a dry method and a fiber web formed by a wet method. When two or more different types of fiber webs are laminated (for example, when a fiber web formed by a dry method and a fiber web formed by a wet method) are laminated, the battery performance is substantially reduced so as not to deteriorate. It is preferable to mix the fibers sufficiently so that the fibers consist of one layer. Examples of the mixing method include a process using a fluid flow as described below.

[0020] Then, the formed fiber web is bonded to produce a nonwoven fabric. Examples of the method for bonding the fiber web include, for example, a method in which a fluid flow such as a water stream is jetted to the fiber web to bond the fiber web, and when the fiber web contains an adhesive fiber, the adhesive fiber There is a method of bonding. Note that these methods may be used in combination.
When the adhesive fibers and / or other fibers can be divided by an external force, the division can be performed simultaneously by the action of a fluid flow such as a water flow.

More specifically, the condition for jetting the former fluid stream to the fiber web and for entanglement is, for example, a nozzle diameter of 0.05 to 0.3 mm, a pitch of 0.2 to 3 mm, or From the nozzle plate with nozzles arranged in two or more rows,
What is necessary is just to eject the fluid flow of pressure 1MPa-30MPa.
Such a fluid stream is ejected at least once onto one or both sides of the fiber web. When the non-opening portion of the net or the perforated plate supporting the fiber web is thick at the time of entanglement by the fluid flow, the obtained nonwoven fabric has large holes, and a short circuit easily occurs. 0.25m thick
It is preferred to use a support of m or less.

The latter bonding treatment of the adhesive fiber may be performed under no pressure, under pressure, or may be performed after bonding under no pressure. For this purpose, it is preferable to apply pressure simultaneously or after bonding. This bonding can be performed by, for example, a heat calender, a hot air penetration type heat treatment device, a cylinder contact type heat treatment device, or the like. The heating temperature is preferably a temperature within the range from the softening temperature of the adhesive component of the adhesive fiber to the melting point when heating and pressurizing are performed simultaneously, and when pressurizing after heating, The temperature is preferably in the range from the softening temperature of the adhesive component of the adhesive fiber to a temperature 20 ° C. or more higher than the melting point. The pressurizing condition is a linear pressure of 5 to 30.
It is preferably about N / cm.

[0023] The nonwoven fabric thus produced is excellent in physical properties such as short resistance and tear strength, and also contains para-aromatic polyamide fibers. Are better. However, a hydrophilic treatment such as a surfactant treatment or a discharge treatment can be performed to further enhance the retention of the electrolytic solution.

As the surfactant treatment, for example, an anionic surfactant (for example, an alkali metal salt of a higher fatty acid, an alkyl sulfonate, or a sulfosuccinate) or a nonionic surfactant (for example, The nonwoven fabric can be immersed in a solution of oxyethylene alkyl ether or polyoxyethylene alkylphenol ether, or the solution can be applied, sprayed, or coated on the nonwoven fabric.

As the discharge treatment, for example, corona discharge treatment,
Examples include plasma treatment, glow discharge treatment, surface discharge treatment, and electron beam treatment. Among these discharge treatments, a non-woven fabric is supplied between a pair of electrodes each carrying a dielectric on the facing surface side under atmospheric pressure in the air, and the non-woven fabric is sandwiched by the dielectric, between the electrodes. Apply AC voltage,
With plasma treatment that generates discharge in the internal voids of the nonwoven fabric, not only the outer surface of the nonwoven fabric, but also the fiber surface inside the nonwoven fabric is treated, so that the electrolyte retention is excellent, and the nonwoven fabric is not damaged by spark discharge. This is preferable because it hardly occurs.

The separator of the present invention has an areal density of 30 to 100 g.
/ M ² . If the areal density is less than 30 g / m ² , the tensile strength may be insufficient, and 100 g / m ²
If the thickness exceeds 100 g, the thickness becomes too large and it is difficult to increase the capacity of the alkaline battery.
m ² .

Since the separator of the present invention is excellent in short-circuit prevention and tear strength, a battery can be stably manufactured. Further, since it is excellent in oxidation resistance and electrolyte solution retention, an alkaline battery capable of stably generating an electromotive reaction for a long period of time can be manufactured. Therefore, the separator of the present invention is, for example, primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, air batteries, nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, nickel-nickel batteries. It can be used for secondary batteries such as hydrogen batteries.

Hereinafter, embodiments of the separator of the present invention will be described, but the present invention is not limited to these embodiments.

[0029]

EXAMPLES (Examples 1 to 3, Comparative Examples 1 to 5) After mixing fibers at the mass ratios shown in Table 1, the fibers were opened by a carding machine to form a fiber web. Next, after heating each fiber web at a temperature of 250 ° C. for 10 seconds, a linear pressure of 10 N was applied.
Only the sheath component of the core-sheath type composite fiber was fused through a calender roll of / cm. Then, a nonionic surfactant was adhered to produce a separator.

[0030]

【table 1】 A: Poly-p-phenylene terephthalamide fiber having a tensile strength of 23 g / d (denier 1.5 denier, fiber length 38)
B: Poly-p-phenylene terephthalamide fiber having a tensile strength of 17 g / d (denier 1.5 denier, fiber length 38)
mm, not fibrillated) C: Poly-m-phenylene isophthalamide fiber having a tensile strength of 5.6 g / d (fineness: 2 denier, fiber length: 51 m)
m, not fibrillated) D: 6,6 nylon (core) -6 nylon (sheath, melting point: 2
Core-sheath type composite fiber (15 denier, 1.5 denier, fiber length 38 mm) E: 6,6 nylon fiber (1.5 denier, fiber length 38 mm) F: 6,6 nylon fiber (0.1 denier) 8 denier, fiber length 38mm)

(Tensile strength in the vertical direction) Each of the separators cut to a width of 50 mm was fixed to a tensile strength tester (manufactured by Orientec, Tensilon UTM-III-100) (distance between chucks: 100 mm). Tensile speed 30
The tensile strength in the vertical direction of each separator was measured at 0 mm / min. The results were as shown in Table 1. Thus, since the separator of the present invention is excellent in tensile strength, it does not break even by the tension at the time of manufacturing the battery.

(Penetration resistance index) Each separator is overlapped to have a thickness of about 2 mm in total, and the uppermost separator is subjected to a handy compression tester (KES-tech, KES-
G5) Stainless steel jig (thickness: 0.5m)
m, the cutting edge angle of the tip: 60 °) was pierced vertically at a speed of 0.01 cm / s, and the force required to cut the uppermost separator was measured. At this time, when the force required to cut the separator of Comparative Example 1 was set as a reference (100), the ratio of the force required to cut each separator was defined as the penetration resistance index (%) of each separator. Table 1 shows the results.
As shown in FIG. As described above, since the separator of the present invention is hard to penetrate, without causing a short circuit,
The battery could be manufactured with good yield.

(Thickness retention rate) The thickness of each separator was measured using a micrometer (diameter of mandrel: 6.35 mm).
The thickness (normal thickness) under a g load was measured. Next, the thickness of each separator under a load of 1100 g was measured. The thickness under a load of 1100 g was expressed as a percentage of the thickness under a load of 500 g. The results were as shown in Table 1. As described above, the separator of the present invention hardly changes in thickness even when pressure is applied, and is hardly short-circuited because it is hard to be crushed even by the pressure when forming the electrode plate group. It has been predicted that since the shape of the separator can be maintained even by the pressure of expansion and contraction (particularly, expansion during charging), a dry-out phenomenon is less likely to occur and a short circuit is less likely to occur, so that a long-life battery can be manufactured.

(Short-circuit resistance) When a battery was actually manufactured using each separator, short-circuiting was caused by a short circuit due to burrs of the electrodes, and the battery could not be manufactured. The results were as shown in Table 1. As described above, since the separator of the present invention is not easily short-circuited,
Batteries can be manufactured with good yield.

(Cycle Life Test) A paste-type nickel positive electrode (33
mm, 182 mm length) and a paste-type hydrogen storage alloy negative electrode (mesh metal alloy, 33 mm, 247 mm length). Next, each separator cut into a width of 33 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, the electrode group was housed in an outer can, and 5N-potassium hydroxide and 1N-lithium hydroxide were injected into the outer can as an electrolytic solution, and sealed to form a cylindrical nickel-hydrogen battery.

Next, each cylindrical nickel-metal hydride battery was subjected to a charge / discharge cycle consisting of 0.2 C, 150% charge, 1 C discharge and 1.0 V discharge at the end voltage, and the discharge capacity was reduced to 50% of the initial capacity. At this point, it was determined that the charge / discharge cycle life had expired, and the charge / discharge cycle life was measured. Then, the percentage of the number of cycles of each separator when the number of cycles in Comparative Example 1 was set as a reference (100) was calculated. The results were as shown in Table 1. Thus, the separator of the present invention had an excellent service life.

[0037]

As described above, the separator for an alkaline battery of the present invention comprises:
Since the burr of the electrode plate does not penetrate the separator and short-circuit between the electrode plates or the separator is not torn by the edge of the electrode plate, the battery can be stably manufactured. Further, since it has excellent oxidation resistance, it has an excellent service life.

Claims (1)

[Claims] 1. A separator for an alkaline battery, comprising a fiber sheet containing a para-aromatic polyamide fiber having a tensile strength of 20 g / d or more.