JPH09283108A - Alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the structure of a spiral electrode group at the time of forming a battery so that internal short-circuiting is hard to be caused by providing a separator, which is formed of a hydrophilic porous film made of polyolefine and having the vein-like open hole structure, between a positive and a negative electrodes, which are spirally wound. SOLUTION: A negative electrode 1 made of hydrogen storage alloy and a positive electrode 2, which includes nickel hydroxide as an active material thereof, are spirally wound through a separator 3, and inserted into a case 4, which works as a negative electrode terminal. The separator 3 has tensile strength at 2kgf/5cm width or more and tensile ductility at 5-100%. Structure of a spiral electrode group of a battery is thereby stabilized, and an alkaline storage battery, in which internal short-circuit is hard to be caused, is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved alkaline storage battery, and more particularly to an improved separator thereof.

[0002]

2. Description of the Related Art In recent years, as electric devices have become lighter, thinner, shorter, and smaller, there has been an increasing demand for small high-capacity batteries as their power sources. In line with this trend, alkaline storage batteries, which are highly reliable batteries, have been developed in line with this trend, and the development and improvement of metal oxide-hydrogen storage batteries using hydrogen storage alloys with a high energy density for the negative electrode have been promoted. I have. This type of alkaline storage battery is generally constructed by interposing a separator between a negative electrode and a positive electrode and injecting a predetermined amount of an alkaline aqueous solution as an electrolytic solution. A polyamide or polyolefin nonwoven fabric is usually used as the separator. With the aim of further increasing the capacity of batteries, thinning and improvement of separators that are not originally involved in battery reactions are being studied. However, if the separator is simply thinned, the space volume of the separator is reduced and the electrolyte retaining performance is deteriorated. As a result, the internal resistance of the battery increases and the discharge performance decreases.

In order to solve this problem, it is necessary to reduce the fiber amount (weight per unit area) of the separator to secure a space volume. However, in the case of a non-woven fabric, when the amount of fibers is reduced, the surface area of the separator is reduced, and variations in thickness and weight are large, so that a space volume can be secured, but conversely, an internal short circuit defect is likely to occur during battery construction. Therefore, in place of the non-woven fabric, development and improvement of a separator made of a film-like porous film which is uniform and can be made thin are also under study.

[0004]

As these porous membranes, a polyethylene porous membrane is disclosed in JP-A-3-105851, and a polyolefin biaxially stretched polyolefin membrane is disclosed in JP-A-3-219552. However, the pores of these porous membranes are all of the through-hole type. A porous film having these through-hole type pores has a reduced mechanical strength when it is made thin. Further, there is a concern that burrs and cracks on the positive electrode and the negative electrode, which are extremely likely to occur, easily penetrate the holes to cause an internal short circuit.

[0005]

In order to solve the above-mentioned problems, the present invention provides a separator obtained by hydrophilizing a porous membrane made of polyolefin and having a vein-like open structure between positive and negative electrode plates. The separator preferably has a tensile strength of 2 kgf / 5 cm width or more and a tensile elongation of 5 to 100%.

As a result, the strength characteristics of the porous film in the battery construction can be improved, and the occurrence rate of defective internal short circuit in the battery can be reduced.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 is one in which a polyolefin-based resin having at least a leaf vein-like opening structure is subjected to a hydrophilic treatment. The polyolefin of the film material may be any one of polyethylene (PE), polypropylene (PP), a mixture thereof, or a composite porous membrane thereof. The thickness of the film is preferably 10 μm to 120 μm, the porosity is preferably 20 to 90%, and sulfonation is preferable as the hydrophilic treatment. However, as long as it has the tensile strength and elongation described in claim 2, other It may be electrical discharge machining, graft treatment, or treatment with a surfactant.

[0008]

【Example】

(Example 1) Hereinafter, the present invention will be described in detail with reference to a nickel-hydrogen storage battery using a PE porous membrane as a separator.

The tensile strength and elongation of the porous film used in this example are described in JIS L1096, 6.12.1. According to the item A, the measurement was carried out by the following procedure using Autograph AG-500A manufactured by Shimadzu.

A 50 × 200 mm test piece was measured for tensile strength (maximum load value during tension) at a chuck interval of 100 mm and a tension rate of 300 mm / min, and the elongation at break was measured. The degree was calculated.

[0011]

[Equation 1]

The material for the porous membrane having a leaf vein-like opening structure has a thickness of 35 μm, a basis weight of 10 g / m ² , and a porosity of 75.
% PE film manufactured by Mitsui Petrochemical Co., Ltd. was used. First, a surfactant treatment was performed with KAO Emulgen 709 manufactured by Kao Corporation in order to impart wettability to this PE porous film. Next, a sulfo group was introduced into the surface of this PE porous membrane to prepare a sulfonated PE porous membrane a. The porous membrane was prepared by immersing the porous membrane in 25% fuming sulfuric acid for 10 minutes at 60 ° C., removing fuming sulfuric acid, washing with KOH with an alkali, and washing excess alkali with water. For comparison, a PE film-made porous membrane b equivalent to a that was not subjected to hydrophilization and sulfonation treatment and a through-hole type PE porous membrane c that was subjected to sulfonation treatment under the same conditions were also prepared. Table 1 shows the specifications of the porous films a, b and c.

[0013]

[Table 1]

As a positive electrode to be combined with this separator, a foamed nickel substrate filled with an active material containing nickel hydroxide as a main component was used. The composition of the negative electrode is MmNi _3.55 C
The o hydrogen storage alloy of _{0. 75} Mn _0.4 Al _0.3 (Mm represents a mixture of rare earth elements), and pulverized in a wet ball mill,
An average particle size of about 30 μm was used. This alloy powder was stirred in a KOH aqueous solution at 80 ° C., and then 0.15 parts by weight of carboxymethyl cellulose, 0.3 part by weight of carbon black and 100 parts by weight of styrene-butadiene co-weight with respect to 100 parts by weight of hydrogen storage alloy powder. 0.8 parts by weight of the combined product was added, and water was added as a dispersant to prepare a paste. This paste was applied to a punching metal, dried, and then pressed to a predetermined thickness. These electrode plates were cut into a predetermined size to manufacture the sealed alkaline storage battery shown in FIG.

In FIG. 1, a negative electrode 1 made of a hydrogen storage alloy and a positive electrode 2 having nickel hydroxide as an active material are spirally wound via a separator 3 and inserted in a case 4 which also serves as a negative electrode terminal. 4 / 5A by such a method
Three kinds of size ABC batteries were prepared for each 1000 pieces.

Using the batteries A, B and C, the presence or absence of internal short circuit after the battery was constructed was evaluated. As an evaluation method,
A non-defective product having an internal resistance value of 5 MΩ or more when a voltage of 500 V is applied to the positive electrode and the negative electrode of the constituent battery before injecting the electrolytic solution,
The number of short-circuits was examined by using those below that as internal short-circuit batteries. The results are shown in (Table 2).

[0017]

[Table 2]

As is clear from the results of (Table 2), Battery A using the sulfonation-treated PE porous membrane as the separator was compared with Battery B using the untreated PE porous membrane as the separator. The number of short circuits in the battery has decreased dramatically.
This is because, as shown in (Table 1), the tensile elongation was reduced by the hydrophilization treatment, so that the short circuit due to the elongation and breakage of the separator was eliminated when the battery was constructed.

The cause of this is presumed as follows. Generally, in the case of forming a spiral electrode plate group, the separator is pulled with a certain amount of force as the group is wound, so that a certain strength and elongation are required. If the tensile strength is not sufficient, the separator will break during the construction of the battery, causing an internal short circuit. Further, if the tensile strength is sufficient but the elongation is too large, the separator is stretched, and the burrs and cracks of the positive electrode and the negative electrode easily break through the separator because the thickness and the weight per unit area are uneven, and a short circuit is likely to occur. Become.

Therefore, when an untreated porous film having a high elongation is used as the separator, the elongation is large during the constitution, and the thickness and the weight per unit area are uneven, and the burrs and cracks of the positive electrode penetrate the porous film. A short circuit occurs.

On the other hand, it is presumed that the sulfonation treatment can reduce the elongation, make it less likely to cause unevenness in thickness and basis weight, and prevent short circuits due to burrs and cracks.

In addition, the through-hole type porous membrane had a larger number of battery short circuits than the leaf vein type. This is presumed to be because, in the through-hole type porous film, burrs and cracks of the positive electrode easily penetrate the porous film. On the other hand, it is presumed that in the porous membrane having a leaf vein-like open structure, the pores did not simply penetrate through the front and back sides, and positive and negative electrode burrs and cracks did not easily penetrate through the separator, resulting in no battery short circuit.

(Example 2) A sulfonated PE porous film was prepared in the same manner as in Example 1 by using this PE porous film (thickness 40 μm).
The tensile strength can be adjusted to 1 to 1 by changing the weight per unit area, the temperature at the time of sulfonation treatment, and the immersion time in fuming sulfuric acid
A separator having a width of 30 kgf / 5 cm and a tensile elongation changed to 150% was produced, and using these separators, as shown in (Table 3), nickel similar to that of Example 1 was formed.
1000 hydrogen storage batteries were produced.

[0024]

[Table 3]

In the same manner as in Example 1, the battery was evaluated for internal short circuit after the battery was constructed. The results are shown in (Table 4).

[0026]

[Table 4]

As is clear from (Table 4), battery E,
It has been found that if the tensile strength is 2 kgf / 5 cm width or more like F and G, it is possible to prevent an internal short circuit due to breakage of the separator when the spiral electrode plate group is configured. However, when the tensile elongation was 150% even when the width was as large as 30 kgf / 5 cm like the battery G, internal short circuit defects were reduced as compared with the low strength separators such as the battery D, but some defective batteries were generated. From this, the upper limit of tensile elongation is 100%
A degree is desirable. It is presumed that this is because unevenness in thickness and weight per unit area due to elongation when the electrode plate assembly is configured can be suppressed, and thus breakthrough due to burrs and cracks on the positive electrode can be suppressed.
However, if the elongation is too low, handling and the like will be hindered when constructing the battery. As a result of various studies, in order to ensure the practical ease of constructing the electrode plate group, the tensile elongation is 5
It was desired to be at least%.

From the above results, the practical tensile strength of the porous film is preferably 2 kgf / 5 cm width, and the tensile elongation is 5 to 5.
Desirably, it is 100%.

In the above-mentioned embodiments, the nickel-hydrogen storage battery has been described as an example. However, the battery is constructed in a spiral shape and other porous alkaline storage batteries using an alkaline electrolyte can also be used by using the porous membrane of the present invention as a separator. The same effect can be obtained.

The shape of the positive electrode and the negative electrode used in the battery of the present invention may be any of a foam metal type, a sinter type and a coating type, and similar effects can be obtained.

[0031]

INDUSTRIAL APPLICABILITY As described above, the present invention is provided with a separator obtained by hydrophilizing a porous film made of a polyolefin between positive and negative electrode plates wound in a spiral shape and having a vein-like open structure. It is possible to obtain an alkaline storage battery in which the configuration of the spiral electrode plate group of the battery is stable and an internal short circuit is unlikely to occur.

[Brief description of drawings]

FIG. 1 is a cutaway sectional view of a battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nickel positive electrode plate 2 Hydrogen storage alloy negative electrode plate 3 Separator 4 Battery case

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Kaitani 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. An alkaline storage battery comprising a separator made of polyolefin between a positive electrode plate and a negative electrode plate wound in a spiral shape and having a hydrophilic treatment applied to a porous film having a leaf vein-like opening structure. 2. The tensile strength of the separator is 2 kgf.
The alkaline storage battery according to claim 1, which has a width of / 5 cm or more and a tensile elongation of 5 to 100%.