JPH1167181A - Separator for alkaline battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a stabilized discharge capacity, while reducing the deterioration of battery during the storage time in the non-use condition by using a specified quantity of heavily beaten pulp having a specified quantity of freeness as a part or the whole of a cellulose fiber component, with respect to the total quantity of fiber. SOLUTION: Freeness to be included in the heavily beaten pulp is set at 50 ml or less so as to raise the tortuosity and improve the storing property at the time of storage. At the same time, in order to prevent the generation of internal short-circuit at the time of use and prolong the lifetime of discharge, a mean hole diameter is set at 5-20 μm. The heavy beating pulp is used for blending at 10-50 wt.% with respect to the total weight of fiber, so as to maintain the strength and electrolyte-holding property at the time of mixing with the synthetic fiber thereby showing these characteristics more effectively. Water- soaked electrolyte conductivity of the heavily beaten pulp is preferably set at 15 μS/cm or less, so as to restrict the quantity of ions dissolved in the electrolyte and further enhance the storing property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator using an alkaline electrolyte such as an alkaline manganese battery and a silver oxide battery.

[0002]

2. Description of the Related Art The functions required of a separator used in various alkaline batteries are to separate an anode active material and a cathode active material to prevent an internal short circuit due to contact, and to use an alkaline electrolyte such as potassium hydroxide or dioxide. It has sufficient durability without being deteriorated even if it comes into contact with oxidizing substances such as manganese for a long period of time. Due to the limited internal volume of the battery, it is possible to increase the battery capacity by suppressing the thickness of the separator as much as possible while maintaining the above function.

[0003] As a constituent material of a conventional separator,
In general, a mixture of synthetic fibers having chemical resistance and having a function of controlling the pore diameter of the separator and cellulose fibers having excellent liquid absorption and liquid retention properties of an electrolytic solution is used. Vinylon fibers and olefin fibers are used as synthetic fibers, and mercerized pulp, rayon fibers and cotton linter fibers are used as cellulose fibers, and sheets are formed by using a binder such as polyvinyl alcohol fiber.

In recent years, in an alkaline battery using zinc as a cathode active material, mercury-free has been generally used due to environmental problems. In this case, a needle-like crystal such as zinc oxide is used during discharge or storage during use. This needle-like crystal easily passes through the separator, causing an internal short circuit, and the battery life is remarkably deteriorated. Also, with the recent widespread use of digital devices, the use of small alkaline batteries in combination with secondary batteries is increasing. In these digital devices, unlike the conventional low-load continuous discharge, the frequency of using high-load intermittent discharge and pulse discharge increases. The crystal growth is increased, which causes a short life due to a further short circuit.

[0005] In order to prevent the passage of needle-like crystals to the counter electrode as much as possible in order to cope with a prolonged life by preventing a short circuit of the battery, measures have been taken to control the pore size of the separator to be smaller. As disclosed in Japanese Examined Patent Publication No. 5-72063 as a separator having a reduced pore diameter, an invention is disclosed in which the fiber diameter of vinylon fiber, which is a synthetic fiber, is 0.8 denier or less. Further, Japanese Patent Publication No. 7-48375 discloses that an internal short circuit can be prevented without increasing electric resistance by setting the alkali-resistant cellulose fiber to 10 to 50% by weight and setting the freeness value to 500 ml or less by beating. Is described.

On the other hand, JP-A-9-27311 discloses a means for eliminating pinholes in a separator and preventing an internal short circuit.
Discloses that organic fibers fibrillated to a fiber diameter of 1 μm or less are contained and the air permeability of Smutster is 100 mmHg or more. In addition, in order to achieve both internal short-circuit prevention in an alkaline solution and liquid absorption and liquid retention of an electrolytic solution, the present applicant uses 5% or more of a beaten aramid fiber excellent in alkali resistance to use an alkaline solution. In addition to preventing the pore diameter from increasing in the above, the liquid absorbing property of the electrolytic solution was maintained by cellulose fibers containing at least 20%.

However, in order to use a synthetic fiber having excellent chemical resistance with a small fiber diameter and to control the hole diameter to such an extent that an internal short circuit can be prevented, a vinylon fiber capable of fine denier as an existing synthetic fiber is used. It is necessary to use ultra-fine fibers of about 0.3 denier.
In this case, although it is effective to some extent to prevent internal short circuit,
Vinylon fiber is not completely alkali resistant, it is difficult to completely suppress the swelling between fibers in the electrolyte,
A phenomenon in which the pore diameter between fibers gradually widens in the electrolyte is observed.

[0008] Further, in the case of making the pores of the alkali-resistant cellulose fiber by beating, even if mercerized pulp or polynosic rayon is used, the alkali resistance is not sufficient, and the pore size tends to change with swelling in an alkaline solution. There is a risk of internal short circuit. On the other hand, a means for miniaturizing an olefin fiber excellent in alkali resistance by mechanical means to prevent an internal short circuit is considered. In this case, the hydrophilicity of the olefin fiber can be imparted by physical treatment such as plasma and contact with an acid, and chemical treatment by bonding with a resin.However, since the degree of fibrillation of the fine fiber is inferior, when used alone, A considerable amount is required, in which case the liquid retention is poor and the discharge characteristics are not sufficient for an alkaline primary battery.

On the other hand, when para-aramid fiber containing 1 μm or less of fibrillated fiber is contained, the stability of the aramid fiber in the electrolytic solution is good due to its excellent alkali resistance, but it adheres to other fibers and stabilizes the pore diameter. To impart the property, at least 5% by weight or more is required. Furthermore, in order to maintain the important liquid retention property of the alkaline primary battery, it is necessary to contain cellulose fiber at 20% or more, and the separator for the alkaline battery has a very high air permeability and is not suitable for use in a Smooster air permeability tester. It is an unmeasurable area.

The applicant of the present invention has proposed aramid fiber having a freeness of 4.
By blending the fibers beaten to 00 ml or less with 5% by weight or more of the total fibers and further blending with 20% by weight or more of the cellulose fibers, it is possible to considerably suppress the swelling in the electrolytic solution, and furthermore, the maximum pore diameter and the average 35 μm pore size
m and 20 μm or less, it was found that the battery life was good even under high load and pulse discharge. However, there is a problem in that the capacity stability during storage is reduced even if aramid fibers are used, and the discharge life after several years of storage is considerably inferior to that immediately after the battery is manufactured.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, that is, to provide a separator for an alkaline battery capable of maintaining a stable discharge capacity with little deterioration of the battery even during an unused storage period. To provide.

[0012]

The present invention adopts the following constitution in order to solve the above problems. According to a first aspect of the present invention, in a battery separator comprising a synthetic fiber component and a cellulose fiber component, heavy beating pulp having a freeness of 50 ml or less is used as a whole or a part of the cellulose fiber component in an amount of 10 to 50% by weight based on the total fiber weight. And an average pore size of the separator of 5 to 20 μm.

According to a second aspect of the present invention, the immersion liquid conductivity of the heavy beaten pulp of the first aspect is 15 μS / cm.
The present invention relates to the following alkaline battery separator.

The use of heavy beaten pulp increases the binding strength of the pulp and increases the torthio stay, which is a factor of the path length ratio in the sheet thickness direction. Thereby, even in the long-term storage state with the electrolytic solution, the increase in the pore diameter due to the decrease in the bonding force between the pulp is small, and even if the pore diameter is slightly increased, since the path length ratio is large, there is an effect that short circuit does not easily occur during discharge. . On the other hand, in the conventional mercerized pulp, although the change is relatively small with respect to the alkali solution, the bonding strength is weak due to the rigidity of the fiber, and the degree of fibrillation by beating is low, resulting in a small torthiostay. In addition, by using a beating para-aramid fiber, the effect of fibrillation can be obtained, but the fiber length is too short in heavy beating and the bonding force between the fibers is small, so the yield during papermaking is deteriorated. There's a problem. Heavy beating pulp also has an immersion liquid conductivity of 15μ
By using a material having an S / cm or less, the amount of dissolved ions in the electrolytic solution can be suppressed, and the storage stability can be further improved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the separator for an alkaline battery of the present invention will be described in detail. The heavy beating pulp used in the present invention may be any of unbleached pulp and bleached pulp produced from conventionally used wood and non-wood. Beating is typically performed using a papermaking refiner, a beater, or the like. The freeness of the heavy beating pulp used in the present invention is 50 ml or less. The freeness referred to in the present invention is a standard type freeness defined in JIS P8121. By setting the freeness range, the torch stay is increased, and the storage stability during storage is improved. At the same time, it is necessary to set the average pore diameter of the separator to 5 to 20 μm in order to prevent an internal short circuit during use and to improve the discharge life. If the average pore size is less than 5 μm, the internal resistance increases and the discharge characteristics deteriorate. 20μ
When the distance exceeds m, an internal short circuit occurs.

The amount of the heavy beating pulp of the present invention is as follows:
In order to exhibit more effectively while maintaining strength and electrolyte retention property in mixing with synthetic fibers, 1 to the total fiber weight
It is used in the range of 0 to 50% by weight. Further, in order to further enhance the preservability during storage, an immersion liquid having a conductivity of 15 μS / cm or less can be used. In this case, JIS
It is desirable to use pulp for thin paper for capacitors specified in C2302. By using the above pulp,
Elution of impurity ions during storage can be suppressed, and self-discharge due to contact with the active material can be reduced. In the present invention, heavy beaten pulp is used as all or a part of the cellulose fibers in the cellulose fibers and the synthetic fibers which are the constituent materials of the separator. Cellulose fibers other than heavy beaten pulp used in the present invention,
Those having excellent chemical resistance can be used, and examples thereof include rayon fiber and cotton linter.

As the synthetic fiber used in the present invention, vinylon fiber, nylon fiber, polyester fiber, aramid fiber, polyolefin fiber and the like can be used. As the polyolefin fiber, polyethylene fiber and polypropylene fiber are representative. Above all, by adding a pulp-like para-aramid fiber as a part of the synthetic fiber, the battery life in high-load discharge and pulse discharge is improved.

The separator of the present invention is produced from an aqueous slurry of raw fibers by a wet papermaking method, but requires an appropriate amount of a binder to maintain the strength of the sheet. As the binder, various synthetic resins such as polyvinyl alcohol resin, epoxy resin, and polyolefin resin can be used,
The form of the binder may be any of fibrous, powdery, and liquid. One example is a method of mixing a raw material slurry with a binder such as a fibrous or powdered polyvinyl alcohol to make paper. However, impregnation after forming the sheet or addition using a spray method may be used. Further, in the separator of the present invention, in order to sufficiently impart the wettability of the separator, the liquid absorbing property, after paper making, on-machine or off-machine application of a chemical such as a surfactant or corona discharge, physical treatment such as plasma treatment. Processing can be performed. Further, in order to improve the contact with the active material by adjusting the thickness of the sheet and improving the surface properties, the calendering treatment can be performed on-machine or off-machine.

[0019]

EXAMPLES Examples of the separator for an alkaline battery of the present invention will be described below. In this example, parts mean parts by weight.

Example 1 After 25 parts of unbleached softwood pulp were defibrated with a pulper and beaten with a double disc refiner (freeness: 10 ml), 20 parts of 0.7 denier rayon fiber and 40 parts of 1 denier vinylon fiber were used. As a binder, 15 parts of 1 denier fibrous polyvinyl alcohol was used as a raw material. The raw material was formed into a paper by a round paper machine to obtain a separator having a size of 36 g / m ² and a thickness of 105 μm.

Example 2 15 parts of unbleached softwood pulp were pulverized with a pulper and beaten with a double disc refiner (freeness: 7 ml), and then 30 parts of 0.7 denier rayon fiber and 35 parts of 1 denier vinylon fiber. The mixture was mixed with 5 parts of para-aramid fiber whose freeness was beaten to 50 ml, and 15 parts of 1 denier fibrous polyvinyl alcohol was used as a binder to prepare a raw material. The raw material was paper-made with a circular paper machine to obtain a separator having a thickness of 36 g / m ² and a thickness of 110 μm.

Example 3 10 parts of unbleached softwood pulp were pulverized with a pulper and beaten with a double disc refiner (freeness: 4 ml), and then 30 parts of 0.7 denier rayon fiber and 30 parts of 1 denier vinylon fiber. The mixture was mixed with 15 parts of para-aramid fiber whose freeness was beaten to 100 ml, and 15 parts of 1 denier fibrous polyvinyl alcohol was used as a binder to prepare a raw material. Basis weight 36g / m ² to paper The raw material in the cylinder paper machine, thickness 100μ
Was obtained.

<Comparative Example 1> In place of unbleached soft-leaved hardwood pulp in Example 1, mercerized hardwood pulp was used, and after pulper disintegration, beaten with a double disc refiner (freeness: 500 ml) was used. Was made in the same manner as in Example 1, and
A separator having m ² and a thickness of 120 μ was obtained.

<Comparative Example 2> 25 parts of mercerized hardwood pulp was pulverized with a pulper and beaten with a double disk refiner (freeness: 500 ml), and then 15 parts of 0.7 denier rayon fiber and 35 parts of 1 denier vinylon fiber. The mixture was mixed with 10 parts of para-aramid fiber whose freeness was beaten to 50 ml, and 15 parts of 1-denier fibrous polyvinyl alcohol was used as a binder to prepare a raw material.
The raw material was formed into a paper by a round paper machine to obtain a separator having a size of 36 g / m ² and a thickness of 105 μm.

Comparative Example 3 Twenty-five parts of mercerized hardwood pulp was pulverized with a pulper and beaten with a double disc refiner (freeness: 100 ml) to obtain 20 parts of 0.5 denier polynosic rayon fiber and 0.5 denier vinylon fiber. The mixture was mixed with 40 parts, and 15 parts of 1 denier fibrous polyvinyl alcohol was used as a binder to prepare a raw material. This raw material is made into paper by a round paper machine to make 36 g of rice tsubo /
A separator having m ² and a thickness of 100 μ was obtained.

Comparative Example 4 Ten parts of hardwood pulp in the form of mercer was pulverized with a pulper and beaten with a double disc refiner (freeness: 30 ml) to obtain 35 parts of 0.7 denier rayon fiber and 1 denier vinylon fiber 40.
And 15 parts of 1 denier fibrous polyvinyl alcohol as a binder. The raw material is paper-made by a circular paper machine to measure 36 g / m ^{2 of} rice and a thickness of 115.
A separator of μ was obtained.

The following tests were conducted for the above Examples and Comparative Examples, and the results are shown in Tables 1 and 2. Paper physical properties and pulp insulation properties (see Table 1) (1) Pore diameter The average pore diameter of the prepared separator was measured with a Coulter porometer. (2) Pulp conductivity The immersion liquid conductivity of the used pulp was measured based on a test of a capacitor thin paper according to JIS-C2302.

Electric Characteristics (See Table 2) The electric characteristics of the batteries prepared by the following method were evaluated. Electrolytic manganese dioxide (EM
D) was mixed and molded with carbon and a 40% KOH solution to prepare a cylindrical positive electrode. Next, the separator is wound in a cylindrical shape, and the bottom is sealed with an adhesive, and then inserted into the inside of the positive electrode.
The solution was kept in KOH solution. Furthermore, 40% KO is applied to the one using a zinc powder alloy as the negative electrode active material from the top inside the separator.
The solution H and a gelling zinc mixed with a gelling agent were added to prepare a battery. In addition, the following evaluation measured the thing stored at room temperature for 7 days after battery preparation, and the thing further stored at 60 degreeC high temperature for 60 days (storage at room temperature for 3 years). (3) Constant-resistance discharge characteristics The prepared batteries were continuously discharged at a low load of 10Ω and a high load of 2Ω, and the time from the initial voltage to the final voltage of 0.9V was compared. (4) Intermittent discharge short life occurrence rate 2 days / day with high load 3.9Ω
Discharge for 5 minutes every 12 hours, sharp drop in voltage (short life) in discharge curve (voltage-time) for 2 months
Was compared with the occurrence rate of each battery.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

According to the present invention, the battery is hardly deteriorated even during long-term storage, stable discharge can be maintained, and a reduction in battery life can be prevented.

Claims (2)

[Claims] In a battery separator comprising a synthetic fiber component and a cellulose fiber component, heavy beating pulp having a freeness of 50 ml or less is used as a whole or a part of the cellulose fiber component in an amount of 10 to 50% by weight based on the total fiber weight. And a separator having an average pore size of 5 to 20 μm. 2. The immersion liquid conductivity of heavy beaten pulp is 15 μS /
The separator for an alkaline battery according to claim 1, which has a diameter of not more than 1 cm.