JP3267126B2 - Alkaline storage battery - 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 storage battery using an improved separator.

[0002]

2. Description of the Related Art In recent years, portable devices have become multifunctional and miniaturized, and the temperature inside the device, which is the environment in which batteries are used, often rises due to increased power consumption and high-density mounting of heating elements. . In this application, the device is often used or left in an external high-temperature environment, and the inside of the device may be further heated. Further, since the voltage required for these devices is generally several volts to several tens of volts,
In particular, in a battery system having a small electromotive force, such as a nickel-hydrogen battery or a nickel-cadmium battery, a plurality of cells are often used in combination in series. In this case, since the battery is housed in the resin case, the structure has a structure in which heat dissipation is extremely difficult.

[0003]

Under such circumstances, the nonwoven fabric made of polyamide-based synthetic resin fibers used as a separator in a conventional sealed alkaline storage battery decomposes when used for a long time in a high-temperature environment. This causes a problem that the liquid retention is reduced. In order to solve this problem, there has been proposed, as the separator described above, a separator obtained by subjecting a polyolefin nonwoven fabric having heat resistance and oxidation resistance to a surfactant treatment to impart hydrophilicity.

However, among the conventional separators described above,
Surfactant-treated products have the problem that the hydrophilicity of the separator cannot be maintained for a long time because the surfactant is diffused or decomposed by long-term use, and is an excellent alternative to polyamide-based products. The development of a separator has been a major issue. In addition, in order to increase the capacity of batteries in recent years, it has been strongly desired to develop a thinner and more dense separator than before, but if a conventional thick fiber of about 2 denier was used, the weight per unit area would be reduced. It is difficult to produce a nonwoven fabric that is excellent in preventing internal short circuit of a battery and holding an electrolytic solution due to nonuniformity and deterioration of liquid retention. The present invention has been made in view of these problems, excellent liquid retention and hydrophilicity,
Another object of the present invention is to provide an alkaline storage battery using a polyolefin separator having excellent oxidation resistance at high temperatures.

[0005]

The alkaline storage battery of the present invention uses a non-woven fabric comprising a composite fiber composed of an ethylene-vinyl alcohol copolymer and a polyolefin polymer and a polyolefin-based fiber having fine pores as a separator. It is characterized by the following.

[0006] Among the fibers constituting the separator, polyolefin fibers have a high-temperature oxidation resistance, and ethylene-vinyl alcohol copolymer fibers have a function of improving the affinity for an electrolytic solution. In addition, by using a polyolefin-based fiber having micropores, the electrolyte can be retained for a long period of time. As a result, a separator having excellent liquid retention, hydrophilicity, and oxidation resistance can be obtained. By applying the separator to an alkaline storage battery, a long-life battery can be realized even at a high temperature, and a high-energy-density battery can be designed because it can be made dense and thin.

It is desirable that the pore diameter of the polyolefin fiber having micropores of the separator be 100 ° or less. This is for the following reasons. One of the causes of a decrease in capacity of an alkaline storage battery is an increase in internal resistance due to a decrease in electrolyte in the separator. This decrease in the electrolyte is due to the compression of the separator due to the swelling of the positive electrode and the movement of the electrolyte to the positive electrode due to the increase in the pore volume accompanying the cycle of nickel hydroxide used as the main component of the positive electrode.
That is, in the latter case, when the change in the pore radius accompanying the charge / discharge cycle was measured, an increase in mesopores in the region of the pore radius of 100 ° was recognized. The development of the mesopores makes the active material porous, and the electrolyte is absorbed. Therefore, if the pore diameter of the polyolefin-based fiber is 100 ° or more, the electrolyte retained in the fine pores of the separator fiber may move to the mesopores of the positive electrode active material due to capillary action, and the liquid retention may be reduced. For this reason, it is desirable that the pore diameter be 100 ° or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, a nickel metal hydride battery will be described below. The positive electrode was prepared by mixing 10% by weight of cobalt monoxide powder with nickel hydroxide powder to which a solid solution of zinc and cobalt was added, and forming a paste with a carboxymethylcellulose thickener.
A nickel electrode was prepared by filling a predetermined amount into a 5% porous nickel fiber substrate, drying and pressing.

The negative electrode is Mm (Misch metal) NiAl
After the CoMn-based (AB ₅ -based) hydrogen storage alloy powder was made into a paste using polytetrafluoroethylene as a binder,
A perforated steel plate was applied in a predetermined amount, dried and pressed to form a hydrogen storage alloy electrode.

The separator is made of polypropylene, ethylene-vinyl alcohol copolymer split conjugate fiber and fine
ポ リ エ チ レ ン A polyethylene fiber having an innumerable number of micropores is formed into a nonwoven fabric having a basis weight of 50 to 60 g / m ² by a wet papermaking method,
After dividing into fine fibers by a high-pressure water flow method, the fibers were press-bonded with a hot calender roll and adjusted in thickness to obtain 0.12 to 0.18 mm. The degree of fiber division was 80 to 100%. The polypropylene and ethylene-vinyl alcohol copolymer splittable conjugate fiber are those in which the ethylene-vinyl alcohol copolymer is interposed between the polyolefin polymers in the cross section of the single fiber, and the single fiber is composed of two polymer layers. In order to divide the splittable conjugate fibers into individual polymer layers to make fine fibers, a method of placing the fibers under a high-pressure water flow is usually used.

The nickel electrode and the hydrogen storage alloy electrode thus produced were wound around a separator, and an electrolytic solution was injected to produce a 1100 mAh AA size cylindrical nickel-metal hydride battery. As a comparative example, a battery using a conventional surfactant-treated polyolefin nonwoven fabric as a separator was produced in the same manner as described above. Table 1 shows the physical property values of these separators.

[0012]

[Table 1]

[0013] The composite type separator of the split type fiber and the fiber having fine pores according to the present embodiment has a higher liquid retention rate than a conventional surfactant-treated polyolefin separator.
Alkali immersion treatment (80 in KOH aqueous solution with specific gravity of 1.3)
Immersion at 7 ° C. for 7 days), washed again with water, and dried again. As a result, there is no decrease in wettability (reduction in liquid retention or electrical resistance) unlike conventional separators, and excellent hydrophilicity can be maintained. Understand.

For the batteries of this embodiment and the comparative example, 0.3
CmA × 5 hours, discharge 1.0 CmA (final voltage 0.8
V) was tested repeatedly. FIG. 1 shows the relationship between the number of cycles and the capacity. FIG. 1 shows that the cycle life characteristics of the battery of this example are good. In contrast, the battery of the comparative example
It can be seen that the capacity decrease is faster than that of the battery of this example.

After disassembling the battery after 500 cycles, and examining the distribution of the electrolyte, the amount of the electrolyte in the conventional surfactant-treated polyolefin-based separator was reduced as shown in FIG. The amount of the electrolyte in the separator used in the example kept the initial amount of the electrolyte.

[0016]

As described above, according to the present invention, a splittable conjugate fiber composed of an ethylene vinyl alcohol copolymer and a polyolefin polymer and a polyolefin fiber having an infinite number of fine pores having a pore diameter of 100 mm or less are used. By using a nonwoven fabric as a separator and applying it to nickel metal hydride batteries and nickel cadmium batteries, a long-life battery is realized even at high temperatures, and a dense thin separator with excellent hydrophilicity and liquid retention properties. Therefore, a battery having a higher energy density can be provided, and therefore, its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of cycles and the battery capacity.

FIG. 2 is a diagram showing a distribution of an amount of an electrolytic solution.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-238463 (JP, A) JP-A-7-130347 (JP, A) JP-A 8-111215 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 2/16

Claims (1)

(57) [Claims] 1. A composite fiber comprising an ethylene vinyl alcohol copolymer and a polyolefin polymer, and an average pore size.
An alkaline storage battery characterized in that a nonwoven fabric made of a polyolefin-based fiber having micropores having a diameter of 100 ° or less is used as a separator.