JPH0732008B2 - Method for manufacturing battery separator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION At present, various types of primary batteries, secondary batteries, and fuel cells are used for portable devices, mobile devices, stationary devices, backup devices, and independent power sources. When a battery is divided into its constituent elements, most of the battery is composed of a positive electrode, a negative electrode, an electrolyte, a separator, a container, and the like.

It goes without saying that the electrodes play a major role in improving the battery characteristics, and improving the positive and negative electrodes is a task that can be continued forever, but the role of the separator is also overlooked. I can't come here. Paper separators for manganese dry batteries and similar paper separators for lead batteries for automobiles have been particularly studied for improving battery characteristics.

The most important role of the separator in the battery is to separate the positive electrode and the negative electrode to prevent an electronic short circuit. Therefore, the electrolytic solution resistance is important in the primary battery, and the secondary battery is also required to withstand oxidation during charging. The fuel cell is almost the same as the case of the primary cell. However, in this case, a gas such as oxygen or hydrogen becomes an active material, so that it is important to prevent the gas from being mixed.

Another important property of the separator is electrolyte retention. When the battery is divided into a system that uses abundant electrolyte solution and a system that retains the electrolyte solution in a separator like a sealed type, it is natural that such electrolyte retention property is particularly important in the latter system. . With a focus on such electrolyte retention, particularly in sealed primary and secondary batteries, natural fiber-based non-woven fabrics or woven fabrics are used. When an alkaline electrolyte is used, a nonwoven fabric or woven fabric made of polyamide is most often used in consideration of alkali resistance. However, such a material having excellent electrolyte retention generally has a problem with respect to alkali resistance and acid resistance. For example, polyamide has tentative alkali resistance but has a high temperature. It is known that the strength is lowered over a very long period of time and causes a short circuit. Natural fiber, of course,
That is, this tendency is more remarkable in the cellulosic system.

On the other hand, non-woven fabrics and woven fabrics made of olefin resins, particularly polyethylene and polypropylene, are excellent in electrolytic solution resistance and oxidation resistance. Therefore, it can be said that it is preferable as a separator material for extending the battery life. However, these polyethylene and polypropylene separators have extremely poor affinity for the electrolytic solution,
Also, its retention is poor. At present, in order to mitigate such a point, a non-woven fabric or a woven fabric of an olefin resin is impregnated with a surfactant so as to improve the affinity and retention of the electrolyte. However, since there is no surfactant that has an affinity for the electrolytic solution, is not affected by the electrolytic solution in the battery for a long time, and has sufficient oxidation resistance, treatment of such a surfactant is not possible. However, even if the initial battery characteristics were good, the characteristics were deteriorated due to a decrease in the retention of the electrolytic solution in the separator over a long period of time.

The simplest method for increasing the affinity of such an olefin resin separator and improving the affinity with the electrolytic solution itself is sulfonation treatment with fuming sulfuric acid or chlorosulfuric acid. For example, it has been found that fuming sulfuric acid is particularly effective in improving the affinity of the olefin-based separator with an electrolytic solution, and thus the above-mentioned drawbacks can be largely eliminated. That is, for example, when a polypropylene non-woven fabric is immersed in 10% fuming sulfuric acid at room temperature,
Polypropylene changes from white to brown. After leaving it for about 40 minutes and then dipping it in sulfuric acid and an alkaline solution alternately through washing with water, the degree of brown becomes slightly thin in alkali, thick in acid, and wet to water jumps. Improved, and with infrared absorption spectrum analysis,
It was found that the hydrophilicity of polypropylene was clearly improved, such as the confirmation of sulfone groups.

Thus, the dipping in fuming sulfuric acid is extremely effective in improving the lyophilicity and electrolyte retention of the olefin-based separator, but when a large amount of such treatment is performed, the concentration of fuming sulfuric acid is increased. The adjustment is rather complicated, and if it is not adjusted sufficiently, the processing state will vary. That is,
Upon such immersion in fuming sulfuric acid, fuming sulfuric acid is used in the treatment of the olefin-based separator and dissipates in the air. This dissipation cannot be ignored because the treatment tank is not completely sealed. In addition, since the amount (concentration) of fuming sulfuric acid has a great influence on the progress of the treatment, in order to produce a uniform sulfonated olefin-based separator in a large amount, it is necessary to make a rough adjustment of the fuming sulfuric acid concentration. Further, fuming sulfuric acid is environmentally unfavorable and expensive.

The present inventors have found that even by simply using concentrated sulfuric acid instead of such fuming sulfuric acid, by increasing the treatment temperature, the affinity and retention of the olefin-based separator to the electrolytic solution can be significantly improved. ,Proposed. That is, by using commercially available concentrated sulfuric acid as it is, it is easier to adjust the concentration than in the case of fuming sulfuric acid, and there are few environmental problems.

However, in order to process on an industrial scale, the temperature should be 10
It is necessary to keep the temperature between 0 and 120 ℃. If the temperature is less than 100 ° C, the processing speed becomes extremely slow, and if it exceeds 120 ° C, it turns into a deep black color simultaneously with sulfonation, so that carbonization occurs and the strength also decreases. Therefore, although the treatment is easier to adjust than fuming sulfuric acid, the problem remains that it is difficult to obtain an industrially uniform sulfonated separator unless the temperature and time are strictly controlled.

Therefore, in the present invention, commercially available concentrated sulfuric acid (concentration of about 98%) is not used as it is, but concentrated sulfuric acid diluted with a small amount of water to a concentration of about 90 to 97% is used. Even with such a slight dilution, the effect on blackening is somewhat alleviated, so it is not necessary to strictly control temperature and time, and a uniform separator can be obtained under industrially easy conditions. Of. The preferred conditions are 90% concentration for about 1 hour and 93% for 45
About 95 minutes, 35 minutes at 95%, 25 minutes at 97% is one guide.

With these treatments, the presence of sulfone groups can be confirmed by infrared absorption spectrum analysis, and the degree of blackening is relatively small. It should be noted that if the separator after immersion is directly washed with water, the separator will be deformed due to the dilution heat of water and concentrated sulfuric acid. It is important not to occur.

Hereinafter, the present invention will be described with reference to examples.

FIG. 1 shows a process of treating a separator according to the present invention. 1
Is a long strip-shaped separator material made of a non-woven fabric or a woven fabric of olefin resin fibers, and is wound around a roll 2. 3 is an acid-resistant container containing concentrated sulfuric acid 4 having a concentration of 90 to 97%. The temperature of concentrated sulfuric acid is controlled by a heating device (not shown).
The temperature is kept at 115 ± 2 ° C. 5 is a stirrer. Reference numerals 6 and 6 are guide rolls for immersing the separator material 1 in the concentrated sulfuric acid 4. Numerals 7 and 7 are rolls for driving the material 1 and also have a role of squeezing the concentrated sulfuric acid contained in the material 1 from the material 1.

Reference numeral 8 is a container containing dilute sulfuric acid 9, and the separator material 1 treated with concentrated sulfuric acid is dipped in the dilute sulfuric acid 9 by the guide rolls 10, 10. 11 and 11 are drive rolls, which also serve to squeeze the dilute sulfuric acid contained in the separator material.
12 is a stirrer.

The separator material 1 has a thickness of 0.2 mm and a porosity of about 60%.
The commercially available polypropylene non-woven fabric of was used. This non-woven fabric was conveyed at such a speed as to be immersed in the concentrated sulfuric acid for the time described above depending on the concentration of the concentrated sulfuric acid. Next, place the container 8 containing dilute sulfuric acid in 3
Prepare individually, put a solution of 98% concentrated sulfuric acid and water at a mixing ratio of 7: 3,5: 5,3: 7 by volume, and soak them in order, then wash and dry. did.

The separator obtained as described above is designated as A, impregnated with a 0.3 wt% aqueous solution of a surfactant and dried, and designated as B. As a comparative example, a polypropylene nonwoven fabric treated with 95% concentrated sulfuric acid is designated as C, and a non-woven fabric impregnated with a 0.3% by weight aqueous solution of a surfactant and dried is designated as D.

First, in order to compare the lyophilicity of these separators,
A 4 cm strip was soaked in a 30 wt% aqueous solution of caustic potash, and the average liquid suction height after 30 seconds was examined. As a result, C sucks up almost 0, D is about 8 mm, A is 14
mm, B was 18 mm. It can be seen that the separator of the present invention has a good affinity for the electrolytic solution.

Next, using each separator, a sealed AA nickel-cadmium alkaline storage battery was constructed. 5 of this battery
The discharge capacity at the time rate was set to 2 Ah. First, in Figure 2, 0.4A
The results of 2 A discharge (25 ° C) after charging for 7 hours are shown. C, which is inferior in lyophilicity, has slightly poor performance. Also, with 2A discharge at 0 ℃,
As shown in FIG. 3, C and D also deteriorate, and it can be seen that the lower the temperature, the worse the lyophilic property is.

Next, charging / discharging was repeated under the condition that each battery was charged at 0.4 A for 7 hours and discharged at 2 A. Figure 4 shows this cycle 600
It is the result of 2A discharge at 25 ° C after repeated, and the performance of the separator of the present invention is drastically lowered not only in C but also in D, and the performance of the separator of the present invention is clearly deteriorated. is there.

In addition, when assembling each battery, the injection speed of the electrolyte was examined, and when C6.c. of a caustic potash solution with a specific gravity of 1.25 containing 20 g / l of lithium hydroxide was added, C hardly entered as it was. It was injected under reduced pressure for about 50 seconds for D, about 42 seconds for A, and about 30 seconds for B. From this,
Also in the separator of the present invention, it is effective to include a small amount of a surfactant in order to stop the liquid injection.

In the examples, polypropylene was used as the olefin resin and an alkaline battery was used as the battery, but of course, polyethylene has the same effect, and the same can be applied to a battery using an acidic electrolyte.

Also, in the process up to washing with water after the concentrated sulfuric acid treatment, in the example,
We used dilute sulfuric acid, whose concentration is easy to adjust and other substances do not enter, but other salt solutions have the effect of reducing the heat of dilution during washing.

As described above, according to the present invention, it is possible to improve the lyophilicity by the electrolytic solution and the retention thereof while keeping the long-life property of the separator made of the woven or non-woven fabric of the olefin resin.

[Brief description of drawings]

FIG. 1 is a diagram showing a treatment process of a separator in an example of the present invention, and FIGS. 2 to 4 are comparisons of discharge characteristics of nickel-cadmium batteries using various separators.

Claims (1)

[Claims] 1. A step of immersing a woven or non-woven fabric made of an olefin resin in a concentrated sulfuric acid bath having a concentration of 90 to 97% at a temperature of 100 to 120 ° C., and then a step of immersing it in concentrated sulfuric acid having a concentration lower than the above concentration. A method for manufacturing a battery separator, which has a subsequent step of washing with water.