JP3168686B2 - Alkaline secondary battery and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery such as a nickel-cadmium battery, a nickel-zinc battery and a nickel-hydrogen battery, and more particularly to an alkaline secondary battery having a long charge / discharge life. is there.

[0002]

2. Description of the Related Art Conventionally, aliphatic polyamides, so-called nylons, have been mainly used as materials for separators of alkaline secondary batteries. Nylon itself has hydrophilicity and heat resistance is higher than polypropylene etc., so it is relatively excellent as a separator material, but it has a problem in oxidation resistance and easily causes carbonation of the alkaline electrolyte. However, there is a problem that the battery performance is deteriorated due to this.

On the other hand, recently, materials having good oxidation resistance, such as polypropylene and polysulfone, have been proposed as materials for the separator, but each has problems. For example, in a polypropylene-based or polysulfone-based separator, the fibers themselves are hydrophobic, so they are hydrophilized by a surfactant. However, the hydrophilicity is lost over a long period of use, and the internal resistance of the secondary battery increases. There was an inconvenience.

[0004] Further, in the case of a polypropylene-based separator, when a short circuit occurs due to low heat resistance, the short-circuit is immediately expanded to a large short-circuit (the heat generated by the minute short-circuit causes the separator to melt and the short-circuit area to be increased at once). This is dangerous because the battery may generate significant heat.

Further, since polysulfone fibers are not welded to each other in a polysulfone separator, binder fibers such as acrylic resin and polyvinyl chloride are required when forming the nonwoven fabric. Sex was impaired.

As can be seen from the above, conventional batteries cannot maintain stable performance over a long period of time due to insufficient characteristics of the separator.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a so-called alkaline secondary battery using an alkaline electrolyte, wherein the separator is composed of an amorphous aromatic polyamide alone or an amorphous aromatic polyamide and another heat-resistant resin. And a material having good oxidation resistance.

[0008]

[Function] Aromatic polyamide is not only hydrophilic (alkali-philic electrolyte) like aliphatic polyamide (so-called nylon), but also has remarkably excellent heat resistance and oxidation resistance as compared with aliphatic polyamide. It has been known.

As described above, the aromatic polyamide is extremely suitable as a material of the separator, but it is difficult to firmly bond the fibers to each other because carbonization occurs during heating without passing through a molten state. That is, a nonwoven fabric having high porosity and mechanical strength could not be obtained.

In addition, since the separator does not melt, it has a disadvantage that it cannot be formed into a bag by a general ultrasonic welding method as a means for winding the separator around the electrode plate. This means that an aromatic polyamide cannot be substantially used as a material of a separator of a rectangular secondary battery in which plate electrodes are laminated to form an electrode group.

However, as a result of various studies, it has been found that a separator made of an amorphous aromatic polyamide can be melted by an ultrasonic welding method and can be processed into a bag shape.

That is, the use of the amorphous aromatic polyamide provides a separator having good heat resistance and oxidation resistance and which can be processed by the ultrasonic welding method. Specifically, a separator composed of an amorphous aromatic polyamide alone, or a combination of an amorphous aromatic polyamide and a crystalline aromatic polyamide, or a combination of an amorphous aromatic polyamide and polysulfone, Is a secondary battery using a separator composed of a combination of an amorphous aromatic polyamide and an inorganic fiber such as potassium titanate, the separator has good oxidation resistance, and the aromatic polyamide has good hydrophilicity. Based on this, it maintains stable performance for a long time. Further, based on the fact that the melting point of the amorphous aromatic polyamide is about 450 ° C., which is significantly higher than that of the aliphatic polyamide, about 230 ° C., and about 110 ° C. of the polypropylene, the heat generated by the micro short circuit is a trigger. Melting → enlargement of short-circuit area → significant heat generation of the battery.

The use of an aromatic polyamide as a material for the separator has already been proposed in Japanese Patent Application Laid-Open No. 58-147956, but the performance of the secondary battery is reduced because it is mixed with nylon having poor oxidation resistance. It is not enough to stably hold for a long time, and it is a pattern that is hardly used in practice. In addition, there is no description about the difference in properties based on the crystallinity of the aromatic polyamide, and it is considered that this was not recognized.

As can be seen from the above, according to the present invention, a battery can be manufactured with the same workability as the conventional one,
A secondary battery with a small decrease in performance over a long period can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail using preferred embodiments. The present invention can be applied to alkaline secondary batteries such as nickel-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries, and silver-cadmium batteries. The embodiment will be described using a nickel-cadmium battery which is the most general among these alkaline secondary batteries.

The positive electrode plate and the negative electrode plate used for the battery were manufactured as follows. A so-called chemical impregnation process in which a sintered nickel substrate having a porosity of about 80% is impregnated with a mixed aqueous solution mainly containing nickel nitrate and containing cobalt nitrate, dried, and then neutralized in an aqueous sodium hydroxide solution. Was repeated to produce a positive electrode plate having a theoretical capacity of 200 mAh.

On the other hand, the chemical impregnation process was repeated in the same manner as in the preparation of the positive electrode plate, except that an aqueous solution of cadmium nitrate was used as the negative electrode plate, to produce a negative electrode plate having a theoretical capacity of 400 mAh. Further, this negative electrode plate was formed in an aqueous solution of potassium hydroxide to produce so-called precharged metal cadmium.

Next, the positive electrode plate 3 manufactured as described above
Using an ultrasonic welding machine, the thickness is 0.17 mm and the basis weight is 6
After attaching a separator of 5 g / m ^{2 in} a bag shape and assembling them alternately with four negative plates, an electrode plate group was prepared.
A sealed square nickel-cadmium battery having a nominal capacity of 600 mAh and having so-called reserve cadmium hydroxide was produced using an aqueous solution of potassium hydroxide having a specific gravity of 1.30 (20 ° C.) as an electrolyte. The separators used are as shown in Table 1.

[0019]

[Table 1] The performance evaluation of the battery was performed as follows. That is,
A charge / discharge cycle in which a 120% charge was performed at a current of 1 CA (600 mA) and then discharged to 1 V at a current of 1 CA was repeated, and the transition of the discharge capacity was measured.
The results are shown in FIG.

From the figure, it can be seen that the batteries A, B, C and D of the embodiment of the present invention have a cycle life about 30% longer than the batteries E and F of the prior art, and that the transition of the discharge capacity is stable. .

Table 2 shows the results of a chemical analysis of the internal resistance at the 500th cycle of each battery and the amount of carbonate in the electrolyte. From the table, the batteries A, B, C and D of the examples of the present invention are shown.
Shows that the internal resistance is low and the amount of carbonate is almost the same as that of the battery F using propylene, which is said to have good oxidation resistance.

[0022]

[Table 2] Regarding a phenomenon from a minute short circuit at the end of life to a remarkable heat generation, a temperature rise of 30 ° C. or more occurred with a probability of about 20% in the battery F using the polypropylene separator, but was not recognized in the battery of the present invention. This can be inferred from FIG. 1 showing the transition of the discharge capacity in the charge / discharge cycle.

That is, as the separator is made of a material having a lower melting temperature, the cycle life becomes shorter, and furthermore, the degree of capacity decrease at the end of the life is sharper, and a minute short circuit tends to be completely turned into a short circuit. It is thought that it is doing. As can be seen from the above, according to the present invention, a nickel-cadmium battery having a long cycle life and a stable transition of the discharge capacity can be obtained.

The amorphous aromatic polyamide can be made into a separator having a wide range of mechanical properties by changing the mixing ratio of radial (sea-island structure) fibrils and linear fibers. .

Next, the ultrasonic welding characteristics of the separator will be described. The ultrasonic welding property of the separator is such that it can withstand practical use when the content of the amorphous aromatic polyamide is 30% by weight or more. As an example, a description will be given below using the mixed separator of the amorphous aromatic polyamide and the crystalline aromatic polyamide used in Example 2 above.

In the experiment, ^two separators having a basis weight of 65 g / m ² manufactured by changing the mixing ratio of the amorphous aromatic polyamide and the crystalline aromatic polyamide were bonded by an ultrasonic welding machine, and then bonded. The tear strength of the part was measured. The results are shown in FIG.

As can be seen from the figure, the amorphous aromatic polyamide is 30%
As described above, the tear strength of the bonded portion is greatly improved, and it can be seen that the ultrasonic welding method can be applied as a method for mounting the separator. This tendency is the same when inorganic fibers such as polysulfone or potassium titanate are used in place of the crystalline aromatic polyamide.

Therefore, the material of the separator may be an amorphous aromatic polyamide alone or a mixed system of an amorphous aromatic polyamide and another substance having excellent heat resistance and oxidation resistance. By using the separator, the battery maintains stable performance for a long time.

Although the operation of the present invention has been described above, the effect of the present invention can be similarly obtained in other alkaline secondary batteries such as a nickel-zinc battery, a nickel-hydrogen battery and a silver-cadmium battery. Further, JP-A-63-250
The same applies to an alkaline secondary battery that does not have a negative electrode active material in a so-called reserve discharge state proposed in Japanese Patent No. 068 or the like.

[0030]

As described above, according to the present invention, the charge / discharge cycle life of the alkaline secondary battery and the capacity transition in the cycle can be improved, and therefore, its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a diagram comparing a change in capacity in a charge / discharge cycle of a battery of the present invention and a conventional battery.

FIG. 2 is a diagram showing the relationship between the tear strength of the ultrasonically welded portion of the separator and the content of the amorphous aromatic polyamide.

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Claims (2)

(57) [Claims] The present invention relates to an amorphous aromatic polyamide alone or an amorphous aromatic polyamide and another heat-resistant separator.
An alkaline secondary battery comprising a material having good oxidation resistance. 2. A method for manufacturing an alkaline secondary battery, comprising using an ultrasonic welding method as a means for winding a separator containing an amorphous aromatic polyamide around a flat electrode plate.