JPH1031992A - Lead storage battery separator and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead-acid battery separator in which deterioration of the separator can be suppressed to prevent the early internal short-circuit at a high temperature by locally providing a part improved in oxidation resistance and electric insulating property. SOLUTION: A separator having a fine pore formed by kneading, for example, polyethylene, an inorganic powder and mineral oil into a sheet, and then extracting a prescribed quantity of mineral oil is used. The separator has a base 1b 0.25mm in thickness, and a plurality of ribs 1a vertically continued with a height of 0.75mm on the surface, and it is worked into a bag by folding in two and thermally fusing both side surfaces. The mineral oil is impregnated in 12% in this state, but the slash line part of the drawing or both surface parts 10mm of the separator 1 are further dipped in mineral oil to increase the content. A positive electrode plate 2 is housed in the inner part, and a negative electrode plate is combined thereto to form an automotive lead-acid storage battery. A battery excellent in life characteristic, compared with a one uniformly containing the mineral oil can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a separator used for a lead storage battery.

[0002]

2. Description of the Related Art In general, a lead-acid battery is constructed by alternately stacking a plurality of positive plates and negative plates alternately with a separator interposed therebetween, and welding plates having the same polarity to each other at ears. . This electrode plate group is inserted into a battery case, and is immersed and used in dilute sulfuric acid as an electrolytic solution. The separator is
It has a porous structure in order to isolate the two electrode plates so that the positive electrode plate and the negative electrode plate do not come into direct contact, and to facilitate ion conduction between the two electrode plates. Therefore, although it has a structure with a large specific surface area and a low strength, it is required to have acid resistance that is stable in dilute sulfuric acid and oxidation resistance that can withstand contact with a positive electrode plate having strong oxidizing power. As a separator for lead-acid batteries, recently, mineral oil was added to raw materials such as polyethylene and inorganic powder, kneaded and processed into a sheet, and then a predetermined amount of mineral oil was extracted.
Those in which microporosity is formed in the extracted portion of mineral oil are becoming widespread. As the inorganic powder to be dispersed in the polyethylene, magnesium oxide, calcium oxide, titanium oxide or the like is used. This type of separator, unlike a conventional papermaking separator, is generally used without wrapping an electrode plate in a bag shape and without using a glass mat.

[0003]

In recent years, the operating temperature of lead-acid batteries for automobiles has been rapidly increasing, and it is not uncommon that the batteries are sometimes used at a temperature exceeding 70 ° C. Under such conditions, the components of the lead-acid battery deteriorate rapidly, but the separator is no exception. When the separator is used at a high temperature, deterioration of the separator proceeds and a hole is formed, which may cause an early short circuit inside the battery. A detailed examination of the state of deterioration of the separator when overcharged at a high temperature reveals that the degree of deterioration of the electrode plate peripheral portion, that is, the portion facing the side or bottom of the electrode plate, is opposite to the center portion of the electrode plate. Larger than part. One of the causes is that the portion of the bag-shaped separator facing the peripheral edge of the electrode plate comes into contact with the electrode plate with a stronger force than the portion facing the central portion of the same electrode plate. Alternatively, it is conceivable that a chemical stress is applied, thereby promoting the oxidative deterioration of the separator.

An object of the present invention is to provide a separator for a lead-acid battery which can suppress such deterioration of the separator and prevent an early internal short circuit at a high temperature.

[0005]

As a method for suppressing local deterioration of the side and bottom of the separator, it is effective to locally improve the durability of these parts of the separator. As one of the means, there is a method of locally improving the oxidation resistance and the electrical insulation of this portion where the separator is most likely to deteriorate. As a specific method, for example, polyethylene, inorganic powder, mineral oil and the like as a raw material, kneading them into a sheet, and then extracting a predetermined amount of mineral oil, the mineral oil content is reduced. It can be embodied by changing it locally.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The separator for a lead storage battery according to the present invention is provided with a portion having locally improved oxidation resistance and electrical insulation. In addition, after inorganic powder coated with mineral oil is uniformly dispersed in polyethylene and formed into a sheet, a predetermined amount of mineral oil is extracted and the separator is made porous. Is higher than the mineral oil content in the central part. Further, it is preferable that the mineral oil content at the side end is larger than the mineral oil content at the center.
It is also preferable that the mineral oil content at the bottom is greater than the mineral oil content at the center.

The method for producing a separator for a lead storage battery of the present invention comprises the steps of kneading polyethylene, inorganic powder and mineral oil and then forming the mixture into a sheet, and uniformly disposing a predetermined amount of mineral oil in the obtained sheet. It includes a step of extracting, and a step of attaching mineral oil to the peripheral portion of the sheet, and making the mineral oil content of this portion greater than the mineral oil content of the central portion. Another method for producing a separator for a lead-acid battery of the present invention comprises the steps of kneading polyethylene, inorganic powder and mineral oil, forming the mixture into a sheet, and uniformly extracting a predetermined amount of mineral oil in the sheet. And a step of further extracting the mineral oil in the central part of the sheet.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. A positive electrode plate and a negative electrode plate were produced by a conventional method using a grid produced by expanding a rolled sheet made of a lead-calcium-tin alloy. Polyethylene, a powder of calcium oxide and magnesium oxide having a particle diameter of 1 μm or less and mineral oil are kneaded and processed into a film, and then a predetermined amount of mineral oil in the film is extracted to form a microporous so-called polyethylene separator. Was used. In the following examination, as shown in FIG. 1, a base part 1b having a thickness of 0.25 mm and a surface having a plurality of ribs 1a having a height of 0.75 mm and being continuous in the vertical direction is considered as two. A separator that was bent into two pieces and heat-welded on both sides to form a bag was used. The separator 1 is usually impregnated with 12% of mineral oil, and the positive electrode plate is accommodated therein for use. The content of the mineral oil in the separator was locally increased as described below, and lead storage batteries were produced.

Example 1 A portion shown by hatching in FIG. 1, that is, both sides of the separator 1 was immersed in mineral oil with a width of about 10 mm to increase the mineral oil content in this portion. The positive electrode plate 2 was accommodated inside the separator 1, and this was combined with the negative electrode plate to produce a 55D23 type lead-acid battery for automobiles.

<< Embodiment 2 >> Similarly, the portion shown by hatching in FIG. 2, that is, the bottom of the similar separator 1 is about 10 mm.
Immersed in mineral oil with a width of to increase the mineral oil content of this part. The positive electrode plate 2 was housed inside the separator 1, and this was combined with the negative electrode plate to produce a lead storage battery similar to that of Example 1.

Example 3 Similarly, the portion indicated by hatching in FIG. 3, ie, the side and bottom of the same separator, was immersed in mineral oil with a width of about 10 mm to increase the mineral oil content in this portion. . The positive electrode plate 2 was housed inside the separator 1, and this was combined with the negative electrode plate to produce a lead storage battery similar to that of Example 1. At this time, the mineral oil content of the portion where the mineral oil was increased was about 30% in any of Examples 1 to 3.

<< Comparative Example >> As a comparative example, the same separator as that used in the battery of the above-mentioned embodiment was left untreated, that is, a separator containing 12% of mineral oil uniformly was used. A storage battery was manufactured. Further, the same separator as a whole was immersed in mineral oil, and a lead-acid battery was produced in the same manner using a separator uniformly containing 30% of mineral oil. These are referred to as batteries of Comparative Examples 1 and 2, respectively.

A separator cut to a width of 70 mm and a length of 70 mm is sandwiched between lead sheet electrodes in dilute sulfuric acid at a specific gravity of 1.300 and 50 ° C., and a load of 5 kg is applied between the two electrodes while applying a load of 5 kg in the thickness direction. A current of 0.5 A was passed, and the time until a short circuit was measured. As a result, the separator containing 12% of mineral oil was short-circuited in 700 hours, and the separator containing 30% of mineral oil was short-circuited in 1800 hours. The electrical resistance of the separator used in the lead-acid battery of Comparative Example 1 containing 12% of mineral oil uniformly was 0.0007 Ω · dm ² / sheet.
The electrical resistance of the separator used in the lead storage battery of Comparative Example 2 containing 0% was 0.009 Ω · dm ² / sheet.

The following life tests were performed on these batteries. For each battery, in a high temperature environment of 75 ° C., a constant voltage charge of 10 minutes at a voltage of 14.8 V with a maximum current of 25 A and a constant current charge of 4 minutes at a current of 25 A were defined as one cycle, and this was repeated. A so-called 75 ° C. SAE life test was performed to discharge the battery at a current value of 356 A every 480 cycles to confirm the battery performance. The result is shown in FIG. The batteries 1, 2 and 3 of the examples all have a longer life than the batteries of the comparative examples 1 and 2.

Disassembling the batteries which have completed these life tests,
When the cause of the life was examined, it was mainly due to an internal short circuit due to deterioration of the bottom and side portions of the separator. The batteries of Examples 1, 2 and 3 in which mineral oil was added to the side or bottom of the separator to locally improve the oxidation resistance and electrical insulation of this portion were compared with the battery of Comparative Example 1. It can be considered that the deterioration of this part is small or the time until the deterioration is reduced to an internal short circuit can be lengthened, thereby improving the battery life. The battery of Comparative Example 2 in which the entire surface of the separator was impregnated with a relatively large amount of mineral oil had extremely low battery performance from the beginning and had a very short life.

In the above embodiment, a method of controlling the amount of mineral oil impregnated in the separator has been described as a means for locally improving the oxidation resistance and electrical insulation of the separator. Similar effects can be expected by other methods, such as reducing the porosity by partially melting. Further, in the above embodiment, as a method of controlling the amount of the mineral oil, the mineral oil was once extracted, and then the peripheral portion was impregnated with the mineral oil again to increase the mineral oil content in this portion. After a large amount of impregnation in advance, the mineral oil in the center of the separator may be extracted using a solvent such as trichloroethylene, for example, to relatively reduce the mineral oil content in this portion.

[0017]

According to the present invention, it is possible to provide a highly reliable separator capable of preventing a local short circuit during use. Therefore, by using this,
A lead storage battery having excellent life characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a front view showing a separator according to one embodiment of the present invention and a positive electrode plate housed therein.

FIG. 2 is a front view showing a separator of another embodiment and a positive electrode plate housed therein.

FIG. 3 is a front view showing a separator of another embodiment and a positive electrode plate accommodated therein.

FIG. 4 is a front view of a separator of Comparative Example 1.

FIG. 5 is a view showing the life characteristics of a lead storage battery using the separator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 1a Rib 1b Base part 2 Separator

Claims (6)

[Claims] 1. A separator for a lead-acid battery provided with a portion having locally improved oxidation resistance and electrical insulation. 2. A separator which is obtained by uniformly dispersing an inorganic powder coated with a mineral oil in polyethylene, forming the sheet into a sheet shape, and extracting a predetermined amount of the mineral oil to make the separator porous. A separator for a lead-acid battery in which the mineral oil content of the part in contact with the part is greater than the mineral oil content of the other parts. 3. The separator for a lead-acid battery according to claim 2, wherein the mineral oil content at the side end portions is larger than the mineral oil content at the central portion. 4. The lead storage battery separator according to claim 2, wherein the mineral oil content at the bottom is greater than the mineral oil content at the center. 5. A step of kneading polyethylene, inorganic powder, and mineral oil and then forming a sheet, a step of uniformly extracting a predetermined amount of mineral oil in the obtained sheet, and a peripheral portion of the sheet. A method for producing a separator for a lead-acid battery, comprising the steps of: adhering mineral oil to a surface of a fuel cell; and increasing the mineral oil content of this portion to be greater than the mineral oil content of the central portion. 6. A step of kneading polyethylene, inorganic powder and mineral oil and then forming the mixture into a sheet, a step of uniformly extracting a predetermined amount of mineral oil in the sheet, and a step of extracting mineral oil in a central portion of the sheet. A method for producing a separator for a lead-acid battery, the method further comprising the step of extracting water.