JPH0456062A - Manufacture of separator for battery - Google Patents

Abstract

PURPOSE:To prevent lower of discharge characteristic of a cadmium negative electrode plate by making polyolefine group resin fiber to contact to the reaction gas including fluorine for reaction, and thereafter, performing interfacial active agent processing to form a separator. CONSTITUTION:Polyolefine group resin fiber is made to contact to the reaction gas including fluorine for reaction, and thereafter, interfacial active agent processing is performed to form a separator. At this stage, nonwoven fabric is desirable as polyolefine group resin fiber. Form of the surface of the resin is changed to improve the hydrophilic property, and a holding capacity of the electrolyte is improved, and lower of a battery capacity with lower of the discharge characteristic of a cadmium negative electrode plate at initial stage of a cycle can be prevented by performing the interfacial active agent processing after the gas processing. A battery having excellent cycle characteristic can be thereby obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing a battery separator made of polyolefin synthetic resin fibers.

(b) Prior Art Conventionally, nylon nonwoven fabrics have been widely used as separators for nickel-cadmium storage batteries, for example. This is because nylon nonwoven fabric has appropriate strength, gas permeability, and hydrophilicity. However, nylon is difficult to say that the material itself has sufficient alkali resistance and oxidation resistance, and it decomposes relatively easily at high temperatures (45°C or higher), and contains carbonate radicals and ammonia, which have a negative effect on battery performance. Furthermore, as the decomposition progresses, the insulating ability of the separator decreases, eventually causing an internal short circuit in the battery.

In order to solve this problem, attempts have been made to change the separator material to polyolefin-based resins, and polypropylene nonwoven fabrics have come to be used especially in batteries that are used at high temperatures. Ta. Although polypropylene nonwoven fabric has excellent alkali resistance and oxidation resistance, and is equivalent to nylon nonwoven fabric in terms of strength and gas permeability, the material itself has poor hydrophilicity, so its ability to retain electrolyte is poor. low. Therefore, batteries using polypropylene nonwoven fabric as a separator have the disadvantage that as the charge/discharge cycle progresses, the electrolyte in the separator depletes, and the life of the battery decreases more quickly due to so-called dryout than with nylon.

In order to improve the electrolyte retention ability of this polypropylene nonwoven fabric, attempts have been made to use thin I&fibers or fibers with irregular cross sections, but the effects are not sufficient, and the graft polymerization of hydrophilic groups due to irradiation with radiation etc. , measures to improve the hydrophilicity of separators through sulfonation treatment have also been proposed;
There was a problem that the effect could not be sustained for a long period of time.

Furthermore, JP-A-60-109171 proposes imparting hydrophilicity to a polypropylene separator by reacting it with a fluorine-containing reaction gas. According to this method, hydrophilicity can be maintained for a relatively long period of time. can be expected. However, this method is not without problems,
In a battery using a separator treated with fluorine gas, the discharge performance of the cadmium negative electrode plate decreases in the early stage of the cycle, and the battery becomes dominated by the negative electrode, resulting in a significant decrease in capacity.

(c) Problems to be Solved by the Invention The present invention solves the above-mentioned problem, that is, the discharge performance of the cadmium negative electrode plate decreases when it is incorporated into a battery using a separator treated with fluorine gas. We aim to solve this problem and provide a separator 7M that can take advantage of the effect of imparting hydrophilicity through fluorine gas treatment.

(d) Means for Solving the Problems The method for producing a battery separator of the present invention involves contacting and reacting polyolefin resin fibers with a reaction gas containing fluorine, and then treating the fibers with a surfactant to produce a separator. It is characterized by this.

At this time, it is preferable that the polyolefin resin fiber is previously formed into a nonwoven fabric.

(e) Effect The reason why the separator treated with fluorine gas inhibits the discharge performance of the cadmium negative electrode plate is considered to be as follows. Generally, when fibers are spun, a surfactant called an oil agent is used for purposes such as preventing static electricity. Even before fluorine gas treatment, polypropylene separators contain surfactants on the fiber surface unless they are washed with water or other treatment, and the surfactants are decomposed when fluorine gas treatment is applied. it is conceivable that.

Surfactants generally reduce the discharge performance of cadmium negative electrodes as they cycle, i.e., the agglomeration of metallic cadmium that cannot be discharged.
It is known that fluorine gas has the effect of suppressing the accumulation of cadmium, and it is thought that the surfactant on the surface of the fibers of the separator treated with fluorine gas has decomposed, so that the effect of suppressing the decline in discharge performance of the cadmium negative electrode plate has disappeared. .

Therefore, by treating the fiber surface of the separator with a surfactant again after the gas treatment, it is possible to suppress a decrease in the discharge performance of the cadmium negative electrode plate.

(f) Examples Hereinafter, comparisons between examples of the present invention and comparative examples will be mentioned and explained in detail.

[Example 1] A known polypropylene fiber having a fiber diameter of about 1.0 to 1.5 denier and ES, which is a polyethylene-polypropylene composite fiber of about 1°0 denier, were used as adhesive fibers.
After uniformly mixing fibers (manufactured by Chisso Corporation) at a weight ratio of 1:1, this was heat-fused to obtain a fabric weight of 80 g/m',
A nonwoven fabric with a thickness of Q and 2Qnun was produced. This nonwoven fabric was housed in an iron reaction container and evacuated, and then a reaction gas prepared by diluting fluorine gas with nitrogen gas was introduced into the container until the pressure reached atmospheric pressure, and a contact reaction was carried out for a certain period of time. Thereafter, the nonwoven fabric was taken out, and about 0.2% by weight of a nonionic surfactant was sprayed onto the surface of the nonwoven fabric to obtain a separator a of the present invention.

[Comparative Example 1] Separator b was obtained in the same manner as in Example 1 except that no surfactant treatment was performed after the gas reaction (Japanese Patent Application Laid-open No. 1983
Based on the technical idea disclosed in Publication No.-109171).

[Comparative Example 2] Separator C was an oil-tight polypropylene nonwoven fabric that had not been subjected to fluorine gas treatment or surfactant treatment. Incidentally, a surfactant used during spinning is present on the fiber surface.

Using the separators a-C produced in this way, they are wound together with a known sintered nickel positive electrode and a sintered cadmium negative electrode to create SC size sealed nickel-cadmium storage batteries A, B, and C with a nominal capacity of 1.2 A11, respectively. was created.

[experiment] A battery cycle test was conducted using batteries A to C described in .

The conditions at this time are 1.8A I:1 at 25℃ for each battery.
．． After charging for 1 hour at a current of 5c), 1.2A
At a current of (Ic), the final voltage is 1. This means that the battery is discharged to OV. Figure 1 shows the results. FIG. 1 is a diagram showing the number of cycles at this time and the capacity ratio to the initial capacity of the battery.

From this, it can be seen that the battery A of the present invention shows a smaller decrease in battery capacity as the number of cycles progresses than the comparative batteries B and C, and has extremely excellent cycle characteristics. In Comparative Battery B, the fluorine gas treatment imparted hydrophilicity to the separator and increased its electrolyte retention ability, so the battery life due to separator dryout was much longer than Comparative Battery C, which used a separator that had not been gas-treated. However, it can be seen that the discharge performance of the cadmium negative electrode plate decreases due to the decomposition of the surfactant on the fiber surface during gas treatment, and the capacity decrease is large at the early stage of the cycle. Comparative battery C shows almost no deterioration in the early stages of the cycle due to the influence of the surfactant originally present in the fibers, but due to the lack of hydrophilicity in the ladle, the lifespan decreases quickly due to dryout. It becomes.

In contrast, the battery A of the present invention has a long battery life by imparting hydrophilicity to the separator through fluorine gas treatment, and also solves the problem of decreased discharge performance of the cadmium negative electrode due to decomposition of the surfactant during gas treatment. It can be seen that since this is supplemented by the surfactant treatment after the treatment, there is almost no decrease in capacity at the initial stage of the cycle, and extremely excellent cycle characteristics are exhibited.

In this example, a nonwoven fabric made of mixed fibers of polypropylene and polyethylene was used, but it goes without saying that similar effects can be expected if polyolefin resin fibers are used.

(g) Effects of the Invention According to the method for manufacturing a battery separator of the present invention, since the fibers formed by contacting and reacting polyolefin resin fibers with a fluorine-containing reaction gas are used, the morphology of the resin surface is As a result, the hydrophilicity improves, the electrolyte retention capacity increases, and the surfactant treatment after the gas treatment reduces the battery capacity due to the decrease in the discharge performance of the cadmium negative electrode plate at the early stage of the cycle. Since it is possible to prevent this and provide a battery with excellent cycle characteristics, its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a cycle characteristic diagram of the battery. A: Invention battery, B, C: Comparative battery.

Claims (2)

[Claims] (1) A method for producing a battery separator, which comprises subjecting polyolefin resin fibers to a catalytic reaction with a fluorine-containing reactive gas and then treating the fibers with a surfactant to obtain a separator. (2) The method for manufacturing a battery separator according to claim (1), wherein the polyolefin resin fiber is formed into a nonwoven fabric in advance.