JPH0729559A - Separator for alkaline battery - Google Patents

Abstract

PURPOSE:To improve a charging characteristic and a service life characteristic by using a separator formed by adding polyvinyl alcohol and a surface active agent to a polyorefine porous body treated by fuming sulfuric acid or concentrated sulfuric acid. CONSTITUTION:A polyorefine porous body is treated by fuming sulfuric acid or concentrated sulfuric acid, and an electrolytephilic property is improved. Polyvinyl alcohol and a surface active agent are added to this porous body, and a separator is formed. Thereby, gas permeability and an electrolyte holding property become excellent, and the utilization factor of an active material is improved, and the separator excellent in a charging characteristic and a service life characteristic can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in separators used in alkaline batteries such as nickel-cadmium batteries and nickel-hydrogen batteries.

[0002]

2. Description of the Related Art Conventionally, as a separator for an alkaline battery such as a nickel-cadmium battery or a nickel-hydrogen battery, it has a low electric resistance and is excellent in alkali resistance and oxidation resistance.
Further, it is required that the electrolyte has a good impregnation property, and gas permeation is required in the sealed battery. Therefore, as a material satisfying these conditions, a polyamide fiber cloth, a non-woven cloth, or a combination thereof with cellophane, a polyvinyl alcohol film or the like has been adopted. However, since there are problems in terms of alkali resistance and oxidation resistance, polyolefin fiber cloth and non-woven cloth have been partially used. However, polyolefin fiber cloths and non-woven fabrics are inadequate in terms of impregnation with the electrolytic solution, and the surfactant contained in the manufacturing method is inferior in electrolytic solution resistance and oxidation resistance, resulting in long-term affinity. Liquidity cannot be maintained. Therefore, the hydrophilicity of the electrolyte has been improved by treating the polyolefin porous body with fuming sulfuric acid or concentrated sulfuric acid.

[0003]

However, there is a demand for higher energy density, longer life and quick charging for batteries. In this case, the amount of electrolytic solution is important, and it is better that the amount of electrolytic solution is large in terms of capacity and life. However, from the viewpoint of gas absorption of the negative electrode during charging, the separator needs to pass gas, and the electrolytic solution is impregnated into the separator and used, so that the liquid amount is limited. One factor that governs the life of a sealed battery is the lack of electrolyte in the separator. That is, there is no problem at the beginning of the charge / discharge cycle, but the electrode expands due to repeated charge / discharge,
Alternatively, by repeating expansion and contraction, the electrolytic solution is absorbed into the electrode and almost disappears in the separator, so that the internal resistance increases and a voltage drop occurs during discharge. From this point of view, the treatment with the sulfuric acid group as described above is not sufficient.

Therefore, the present invention has a gas permeability and an excellent electrolyte retaining ability, which improves the utilization rate of the active material.
An object of the present invention is to provide a separator that provides an alkaline battery having excellent charging characteristics and life characteristics.

[0005]

Means for Solving the Problems The separator of the present invention is
It is obtained by adding polyvinyl alcohol and a surfactant to a polyolefin porous body treated with fuming sulfuric acid or concentrated sulfuric acid. Here, as the polyolefin porous body,
A porous material made of polyethylene or polypropylene is generally used, and polypropylene nonwoven fabric is preferable in consideration of heat resistance and price. The polyvinyl alcohol may be a complete saponified product in which all of the acetic acid groups of the vinyl group are converted into hydroxyl groups, but a partially saponified product in which some acetic acid groups remain is preferable.

[0006]

When the polyolefin porous material is treated with fuming sulfuric acid or concentrated sulfuric acid, the electrophilicity is improved. This is probably due to the formation of sulfone groups in the polyolefin. In the present invention, polyvinyl alcohol and a surfactant are added to this porous body. Since the non-woven fabric made of polyethylene or polypropylene uses the surfactant in the manufacturing process as described above, these non-woven fabrics on the market contain the surfactant. However, when the polyolefin is treated with fuming sulfuric acid or concentrated sulfuric acid, it is washed with water and the surfactant is removed. When the treatment with fuming sulfuric acid or concentrated sulfuric acid is extremely performed, the strength is greatly reduced when the separator is thin or the fiber diameter is small. Therefore, these treatments cannot provide sufficient lyophilic property, which requires the balance of the amount of electrolytic solution. However, the combination of both treatments of the present invention makes this possible.

That is, if the electrolyte is less lyophilic when injected, it is suitable for gas absorption because it has good gas permeability, but since the electrolyte is scarce in the separator, the essential discharge characteristics and life are shortened. It doesn't matter. By supplementing the lyophilicity with polyvinyl alcohol and a surfactant, the separator becomes easier to wet with the electrolytic solution than in the case of extreme sulfuric acid treatment, and there is no problem of uniform penetration of the electrolytic solution into the electrodes. , Performance and gas absorption are improved. In addition,
As polyvinyl alcohol, a partially saponified product in which some acetic acid groups are left is less crystalline than a completely saponified product, and therefore has a higher affinity for an electrolytic solution.

[0008]

EXAMPLES Examples of the present invention will be described below. [Example 1] Commercially available thickness of 0.15 mm, porosity of about 60%
The polypropylene non-woven fabric of is immersed in concentrated sulfuric acid containing 5% fuming sulfuric acid at room temperature for 7 minutes. Then, the sulfuric acid is removed with a centrifuge, washed with water and dried. This treatment changes the non-woven fabric from white to light brown. This was impregnated with an aqueous solution containing 1% by weight of commercially available polyvinyl alcohol and 0.5% of a commercially available alkyl ether sulfonate-based neutral surfactant,
A separator is obtained by heating and drying at ℃.

A sealed nickel-hydrogen storage battery in which a known foaming nickel electrode filled with a mixture of nickel hydroxide powder, cobalt powder and nickel powder, a paste type negative electrode using an MmNi-based hydrogen storage alloy electrode and the above separator are combined. Make up. Specific gravity of the electrolyte is 1.30
A solution obtained by dissolving 30 g / l of lithium hydroxide in the caustic potash aqueous solution is used. The battery is a SubC type. This battery is designated as A. Next, for comparison, a battery using a separator obtained by the same production method as above except that it is immersed in fuming sulfuric acid, omitting the addition of polyvinyl alcohol and a surfactant, is designated as B.

First, the initial discharge voltage and capacity were compared.
Use 10 cells each for 5 hours constant current and 1 capacity
When the battery was charged to 50% and discharged to 0.9V with a constant current of 1.0A, the average voltage was 1.22 to 1.23V and there was no difference. The discharge capacity of the battery A is 2.75 to 2.80.
Ah, and the battery B was 2.62 to 2.69 Ah. Next, 10 cells of both batteries were used to examine the life.
When charging and discharging were repeated by charging 115% of the capacity with a constant current of 2 hours and discharging to 0.9V with a constant current of 1.0 A, Battery A averaged 95% of the initial capacity in 600 cycles.
However, the average of battery B was 82%.

Finally, the rapid charging characteristics were compared using 10 cells each of both batteries. 160% of the capacity was charged at a constant current of 0.7C at 0 ° C. When the pressure inside the battery at the time of 160% charging was measured, it was found that the battery A was 2.1 to
It was 2.5 kg / cm ² , whereas the battery B had 4.
It was 1 to 4.8 kg / cm ² . Furthermore, when charged at 160% of the capacity at a constant current of 1.2C at 0 ° C,
The pressure inside the battery at 160% charge was 6.
It was 3 to 7.0 kg / cm ² , while Battery B was 7.6 to 8.1 kg / cm ² . As described above, the battery A was excellent in gas absorption.

[Example 2] A commercially available polypropylene nonwoven fabric having a thickness of 0.15 mm and a porosity of about 60% is immersed in a commercially available 95% sulfuric acid at 105 ° C for 1 hour. Then, the sulfuric acid is removed with a centrifuge, washed with water and dried. This treatment changes the non-woven fabric from white to black. To this, a commercially available 95% saponification product,
That is, an aqueous solution containing 1% by weight of partially saponified polyvinyl alcohol having 5% acetic acid group and 1% of a commercially available alkyl ether sulfonate-based neutral surfactant is impregnated and dried by heating at 100 ° C. to obtain a separator.

As in Example 1, a sealed nickel-cadmium storage battery is constructed by using the known foam nickel electrode, paste cadmium electrode and the above separator. The electrolytic solution used is 25% in a caustic potash solution with a specific gravity of 1.30.
What melt | dissolved g / l lithium hydroxide is used. The battery is a SubC type. This battery is designated as C. For comparison, a battery using a separator obtained by the same production method as above except that it is immersed in fuming sulfuric acid, omitting the addition of polyvinyl alcohol and a surfactant, is designated as D.

First, the initial discharge voltage and capacity were compared.
Use 10 cells each for 5 hours constant current and 1 capacity
When the battery was charged to 30% and discharged to 0.9 V at a constant current of 1.0 A, the average voltage was 1.23 to 1.24 V and there was no difference. The discharge capacity of the battery C is 2.25 to 2.30.
Ah, the battery D is 2.12. Was about 2.18 Ah. The tendency of the life characteristics was the same as in Example 1.

Finally, 10 cells were used for each battery, and the rapid charging characteristics were compared. At 0 ° C, 160% of the capacity was charged with a constant current of 0.1C. The pressure inside the battery at 160% charge is 2.8 to 3.5 kg / c for battery C.
m ² was found, while battery D had 4.1 to 4.8 kg
Was / cm ² . Thus, Battery C was excellent in terms of gas absorption. In any of the examples, when the treatment with fuming sulfuric acid or concentrated sulfuric acid was performed more drastically than in the examples, not only the process became complicated, but also the strength of the nonwoven fabric decreased.

[0016]

Industrial Applicability As described above, according to the present invention, there can be obtained a separator which improves the utilization rate of the active material and provides an alkaline battery excellent in charging characteristics and life.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoichiro Tsuji 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Naoko Maekawa 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. An alkaline battery separator comprising a polyolefin porous body treated with fuming sulfuric acid or concentrated sulfuric acid and containing a surfactant and polyvinyl alcohol. 2. The alkaline battery separator according to claim 1, wherein the polyvinyl alcohol is a partially saponified product.