JPH047548B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a battery separator made of synthetic resin fibers having carbon-carbon bonds, such as synthetic resin fibers such as polypropylene, polyester, and vinylon. (b) Prior Art Conventionally, nylon nonwoven fabrics have been widely used as separators for, for example, nickel-cadmium storage batteries. This is due to the moderate strength of the nylon non-woven fabric.
This is because it has gas permeability and hydrophilicity.
However, it is difficult to say that nylon itself has sufficient alkali resistance and oxidation resistance, and it is known that it decomposes relatively easily, especially at temperatures above 45°C. In other words, when a battery is charged at high temperatures, nylon is decomposed into carbon dioxide gas, water, ammonia, etc. due to the oxygen gas generated within the battery, but this carbon dioxide gas and ammonia have a negative effect on battery characteristics. . Moreover, as the decomposition progresses further, 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 material of the separator to a polyolefin resin, and polypropylene nonwoven fabrics have come to be used particularly in batteries that are used at high temperatures. Although polypropylene nonwoven fabric has excellent alkali resistance and oxidation resistance, and has the same strength and gas permeability as nylon nonwoven fabric,
Because the material itself has poor hydrophilicity, it lacks the ability to retain electrolyte. Therefore, batteries using polypropylene nonwoven fabric tend to be inferior to batteries using nylon nonwoven fabric in overall battery characteristics, including battery capacity and internal resistance. In order to improve the electrolyte retention ability of this polypropylene nonwoven fabric, it is blended with nylon fibers or glass fibers to form a nonwoven fabric. Apply a surfactant to the fiber surface. Improvements will be made to the nonwoven fabric structure by making the fiber system thinner. Many attempts have been made to graft-polymerize hydrophilic groups onto the fiber surface by irradiation with radiation or the like, but no method has yet been found to sufficiently improve the electrolyte retention ability. (c) Purpose of the invention The present invention improves hydrophilicity and liquid retention by surface-treating synthetic resin fibers having carbon-carbon bonds, such as polypropylene, polyester, vinylon, etc., which are the materials of the separator. The present invention aims to provide a separator for a battery that is made of aluminum. (d) Structure of the invention The battery separator of the invention is made of synthetic resin fibers having carbon-carbon bonds, such as polypropylene,
It uses fibers made by contacting and reacting synthetic resin fibers such as polyester and vinylon with a reaction gas containing fluorine. When a synthetic resin fiber having a carbon-carbon bond is brought into contact with fluorine gas, the fluorine gas attacks, for example, the H of -CH ₂ -CH ₂ - in the main chain in the surface layer of the fiber, resulting in the formation of H and F. The main reaction is that -CF ₂ - is partially generated in the main chain by substitution of
For example, -C-O-F is partially generated by absorbing oxygen adsorbed on the surface of synthetic resin fibers, or fluorine gas attacks the H of -CH ₂ - in the main chain, but it is not cleaved. If F is not present around C in the C-H bond, the carbons will react and partially form -C=C
A side reaction occurs that produces -. This main reaction or side reaction disturbs the regularity of _-CH2 - _CH2- in the main chain on the fiber surface, and as a result, the surface energy of the synthetic resin fiber changes. and,
If the reaction heat during this reaction is high, the fiber surface will be partially melted and the surface area will increase. 1st
Figures 2 and 2 are electron micrographs of polypropylene fibers before and after fluorine gas treatment (×
5000), which clearly indicates that the surface of the specimen after the fluorine gas treatment is rough.
Now, as mentioned above, the surface energy changes due to -CF ₂ - generated on the surface of synthetic resin fibers due to the main reaction due to contact with fluorine gas, but this change is caused by a decrease in surface energy. As a result, the contact angle with water becomes smaller, making it easier to get wet with water. In addition, the aforementioned side reactions or increase in surface area,
Contributes to making fibers wettable with water. As described above, the battery separator according to the present invention has better hydrophilicity and liquid retention than conventional separators. By the way, regarding the reaction between fluorine gas and synthetic resin fibers having carbon-carbon bonds, fluorine gas is an extremely reactive gas, so simply bringing the fluorine gas and synthetic resin fibers into contact will cause a reaction. The reaction proceeds easily, and as mentioned above, −
A main reaction in which CF ₂ - is produced, or a side reaction in which -C-O-F or -C=C- is partially produced. In this way, fluorine gas and carbon
Since the reaction with synthetic resin fibers having carbon bonds occurs easily, if the side reaction substance is present in the reaction field, it becomes possible to incorporate the side reaction substance into the resin surface. By taking advantage of this effect and using fibers into which hydrophilic groups are actively introduced, a battery separator with further improved hydrophilicity can be obtained. For example, it is conceivable to use a mixture of oxygen gas and sulfur dioxide gas in addition to fluorine gas as the reaction gas.
If oxygen gas exists in the reaction field, C-O on the reaction surface
Polar groups such as -F and C=O are formed, and if sulfur dioxide gas is present, sulfonate groups and the like are formed, further improving hydrophilicity. In addition, when the fibers used in the battery separator of the present invention are coated with a thin layer of a surfactant made of a hydrophilic organic substance on the surface and reacted with a reactive gas, the fibers react with a reaction gas. The organic substance and resin applied over the coating bond together, resulting in a marked improvement in hydrophilicity. (e) Examples Examples of the present invention will be shown and explained below. Example 1 Polypropylene nonwoven fabric (thickness 0.21 mm, basis weight 65 g/
After preparing the nonwoven fabric and evacuating it in an iron reaction container, a reaction gas prepared by diluting fluorine gas with nitrogen gas was introduced into the container until the pressure reached atmospheric pressure ^. Allowed time to react. Thereafter, the gas in the container was again evacuated and nitrogen gas was introduced to completely remove the reaction gas, and then the nonwoven fabric was taken out. Using the thus prepared separator of the present invention and a separator made of a polypropylene nonwoven fabric before treatment with the fluorine gas, the hydrophilicity of the separator was measured before being incorporated into a battery and after being incorporated into a battery and subjected to charge/discharge cycles. . After the charge/discharge cycle, the separator is assembled into a sealed nickel-cadmium storage battery and left at room temperature.
After charging and discharging 50 times under the cycle of charging at a current of 0.1c for 11 hours and discharging at a current of 0.8c for 1 hour, the battery was disassembled, taken out, washed, and dried and used as a sample. To evaluate hydrophilicity, these separators were cut into 20 mm wide tanzak shapes, and one end of the separator was cut with a specific gravity of 1.23.
A method was adopted in which judgment was made based on the height at which the potassium hydroxide solution was absorbed into the separator (liquid absorption height) when the separator was immersed in a potassium hydroxide solution and allowed to stand for 10 minutes. The results are shown in Table 1.

Table 1 shows that all of the separators treated with fluorine gas have increased hydrophilicity compared to the separators that were not treated with fluorine gas. Furthermore, those treated with a reaction gas having a fluorine gas concentration of 5% are inferior in hydrophilicity to those treated with a reaction gas having a fluorine gas concentration of 1%. The reason for this is that when the amount of fluorine gas increases, the reaction between the fluorine gas and the synthetic resin fibers progresses more, the surface energy of the fibers decreases, and the hydrophilicity further _improves . If the amount increases too much, a large amount of -CF ₂ - replaces -CH ₂ -.
It is thought that this establishes surface regularity and suppresses changes in surface energy, resulting in a decrease in hydrophilicity. Example 2 As in Example 1, a polypropylene nonwoven fabric washed with a potassium hydroxide solution was placed in a reaction vessel and evacuated, then a certain amount of oxygen or sulfur dioxide gas was introduced, and then fluorine gas diluted with nitrogen was brought to atmospheric pressure. was introduced and allowed to react for a certain period of time. Thereafter, the gas in the container was evacuated again and nitrogen gas was introduced to completely remove the reaction gas, and then the nonwoven fabric was taken out. The separator thus produced was subjected to the same operation as in Example 1, and its hydrophilicity was measured. The results are shown in the table.

[Table] Compared to when fluorine gas, which is the main reaction gas, is used alone, hydrophilicity increases more when fluorine gas is used in addition to oxygen gas or sulfur dioxide gas as a side reaction gas. You can see that Example 3 About 0.2% by weight of a nonionic surfactant was sprayed onto the surface of a polypropylene nonwoven fabric washed with the same potassium hydroxide solution as in Example 1, and treated in the same manner as in Examples 1 and 2. The separator thus prepared and the separator whose surface was only coated with the surfactant were subjected to the same operation as in Example 1 to measure hydrophilicity. The results are shown in Table 3.

【table】

[Table] From Table 3, by coating and forming a thin layer of surfactant on the resin surface during the contact reaction with fluorine gas, the hydrophilicity of the polypropylene nonwoven fabric is further improved, and the charging and discharging inside the battery is improved. It can be seen that it shows good hydrophilicity even after cycling. This is thought to be because the surfactant binds to the fibers and is not easily removed even during charge/discharge cycles. On the other hand, resins in which only a thin layer of surfactant is applied and formed on the resin surface show high hydrophilicity before cycling, but the surfactant is easily removed by charge/discharge cycles, and After that, almost no hydrophilicity is maintained. In the above examples, the case where polyolefin-based polypropylene nonwoven fabric was used was described, but for example, polyester, vinylon, etc.
Since it is a synthetic resin fiber with carbon bonds, the surface energy of the synthetic resin fiber is lowered by contact reaction with a reaction gas containing fluorine, and these fibers are also more easily wetted with water than before the reaction. can do. Therefore, it is also effective in improving the hydrophilicity of separators for lead batteries and primary batteries. In addition, in the examples, synthetic resin fibers configured in the form of nonwoven fabric were brought into contact reaction with a reaction gas containing fluorine gas, but this is because heat treatment is generally used when bonding fibers together in the manufacturing process of nonwoven fabrics. This is because, if a nonwoven fabric is manufactured using resin fibers that have been previously subjected to fluorine treatment, the surface layer of the fibers may melt due to this heat treatment, and the effect of the present invention will be halved. In the examples, the surface treatment of the separator was carried out by so-called batch treatment in which the synthetic resin fibers for the separator were made into a tanzak shape and brought into contact with the reaction gas. Since it is obtained by reaction, the reaction is relatively uniform no matter what form it takes, so the synthetic resin fiber for the separator is formed into a band shape and is continuously supplied to cause a contact reaction with the reaction gas. It is also possible to perform the surface treatment of the separator by continuous treatment. (F) Effects of the Invention The battery separator of the present invention is made of synthetic resin fibers having carbon-carbon bonds, such as polypropylene,
Because it uses fibers made by contacting and reacting synthetic resin fibers such as polyester and vinylon with a reactive gas containing fluorine, the morphology of the resin surface changes, improving hydrophilicity and improving the ability to retain electrolyte. rises,
When used in batteries, battery performance can be improved. In addition, if a side reaction substance is present in the reaction field during the contact reaction with the reaction gas and hydrophilic groups are introduced onto the resin surface, a separator with further improved hydrophilicity can be obtained.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph of polypropylene fibers before fluorine gas treatment, and FIG. 2 is an electron micrograph of polypropylene fibers after fluorine gas treatment.

Claims (1)

[Scope of Claims] 1. A battery separator made of synthetic resin fibers having carbon-carbon bonds whose surface energy is reduced by contact reaction with a reaction gas containing fluorine. 2. The reaction gas is a mixed gas containing fluorine as a main reaction gas and at least one of oxygen and sulfur dioxide gas as a side reaction gas, diluted with an inert gas. Battery separator. 3. The battery separator according to claim 1, wherein the synthetic resin fiber has a thin layer of a surfactant on its surface to an extent that does not inhibit reaction with fluorine gas.