JPS6051781B2 - Battery separator and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a separator containing chlorine and a method for producing the same, and an object of the present invention is to provide a battery separator that is inexpensive and has high performance.

Chlorine-containing polymers have been widely used as separator materials for lead-acid batteries.

That is, in Europe and the United States, separators made by sintering polyvinyl chloride powder, and those made by mixing polyvinyl chloride with a solvent and starch, and then removing the solvent and starch to form microporous separators, have been used. Furthermore, woven fabrics made of vinyl chloride-acrylonitrile copolymer fibers have also been used as separators for holding positive electrode active materials. Although chlorine in the electrolyte is harmful to battery performance because it accelerates corrosion of the electrode grid, the reason why chlorine-containing polymers have been widely used is that they This is because it has excellent acid resistance and oxidation resistance and is inexpensive compared to general-purpose polymers. However, in recent years, the actual operating temperature of automobile batteries has decreased due to the reduction of engine compartment space and the installation of afterburners.
As opposed to ~50°C, the amount of chlorine decomposed free has become a problem because it has come to be exposed to high temperatures of 60~800°C.

Our experiments have revealed that the deterioration of chlorine-containing polymers at such high temperatures is accelerated by the following process. 1) Chlorine-containing polymers release constituent chlorine as HCl or Cl2 at high temperatures.

(2) Dehydrochloric acid reacts with lead dioxide as shown in the following reaction formula.

2HCl + yen. 2+H2SO4→PbSO4+C12+
2H2O A part of the chlorine gas generated here is P mountain.

These oxides are oxidized in the form of CIO-, C1O2-, and C1O3-, but these oxides have an extremely strong oxidizing effect and dissolve or disperse in the liquid and enter the fine pores of the separator. deteriorate. Its oxidizing effect is greater than that of oxygen gas generated during charging. When such chlorine gas or lower chlorine oxides are generated in the battery, the chlorine-containing compounds are oxidized by this oxidizing agent to liberate chlorine ions, which react with lead dioxide again to generate chlorine gas or chlorine ions. The compound becomes a compound that attacks the chlorine-containing polymer again, creating a vicious cycle.

The present invention is based on the discovery that if this initial release of chlorine can be prevented, the deterioration of the chlorine-containing polymer can be almost prevented.

As a method of preventing the release of chlorine, we added carbon, silica, oil, etc. as thermal stabilizers to the polymer, and when we confirmed their effects, we found that the thermal stabilizing effect of oil was particularly remarkable. Furthermore, we investigated the thermal stability effect of oil and found that the oil has an affinity with polymers, has high acid and oxidation resistance, and is made of a solution that is uniformly compatible with polymers at the molecular level. The one coated with a film was effective. That is, it has been found that it is particularly effective to dissolve the oil in a solvent and add it to the film forming solution, and that this shows better performance than impregnating the film with oil after film formation. The oils mentioned here include process oils, petroleum-based oils such as petroleum-based lubricating oils, polyglycols, phosphate esters,
These include synthetic lubricating oils such as silicate esters, silicone oils, and fluorine oils, animal oils such as fish oil and whale oil*8, and vegetable oils such as linseed oil, sesame oil, soybean oil, and olive oil. The present invention will be explained by examples. Example 1 15 parts of chlorinated vinyl chloride resin with a degree of chlorination of 68% was completely dissolved in the area marked with tetrahydrofuran, and then 25 parts of isopropyl alcohol was added to make a homogeneous solution, and the chlorine generation shown in Table 1 was added to this solution. A film forming solution was prepared by adding various preventive additives and further adding 0.5 part of a surfactant (sodium alkyl sulfonate).

Next, this solution was applied to a polyester nonwoven fabric having a thickness of 0.15 Trm to form a film in the form of a sheet, and then volatile substances were removed to form a microporous body to prepare a separator. This separator was placed between an anode plate containing a lead dioxide active material and a cathode plate containing a sponge lead active material, and sulfuric acid was added to form a battery with a capacity of 60AH.The battery was left at a constant temperature of 80°C to open the battery. The amount of decrease in voltage and specific gravity was measured. Since sulfuric acid is consumed according to equation (2), chlorine generation can be measured by the voltage and the decrease in specific gravity. 1st above
The reason that the relationship between specific gravity and voltage in the table does not necessarily match theoretically is thought to be due to the difference in concentration near the active material and offshore. The electrical resistance in the table is a value measured in sulfuric acid with a specific gravity of 1.20.

4. It is also possible to form a film into a sheet by pouring the solution onto a flat plate without using a nonwoven fabric. Example 2 A microporous body was formed by forming a film in the same manner as in Example 1 except that no additives were added, and then immersed in an isopropyl alcohol solution containing 10% process oil.

The electrical resistance of this separator was 0.14 Ω·Dm2, which was too high for a battery separator. However, even in this case, the electrical resistance can be reduced to 0.0006 to 0.00 by immersing it in a solution containing a surfactant, or by immersing it in a surfactant solution after impregnating it with oil.
It was possible to reduce the resistance to about 1ΩDm2. Example 1
Although it is effective even when the amount of process oil added is 10% or less, the longer the amount added, the more effective the sustainability of the effect of the oil is.

However, if it exceeds 50%, the electrical resistance will increase. A typical implementation of the present invention is to uniformly disperse oil together with a surfactant in a solution containing a solvent in advance as described above, thereby effectively exhibiting a coating effect without increasing electrical resistance. Methods for forming a film from a solution containing a solvent that is compatible with oil include a method in which the solvent is evaporated and dried from a solution whose main components are a polymer, a solvent, and a non-solvent;
An effective method is to immerse a solution containing a polymer and a solvent as main components in a non-solvent, remove the solvent, and then dry the solution. In such a method, it is desirable that the solvent be contained at least three times the weight of the polymer in order to expect compatibility at the molecular level. The method of forming a film by immersion in a non-solvent has the disadvantage that if the oil becomes compatible with the non-solvent, there will be some loss of oil, so it is desirable that the oil is not compatible with the non-solvent. The present invention is not limited to the above embodiments, but it is effective to add oil to a chlorine-containing polymer and uniformly coat the surface of the polymer, and it is made by sintering polyvinyl chloride powder. It is also effective to coat the powder particle surface with oil by pre- or post-treatment of the separator.

Various process oils are effective as the oil used in the present invention, and those containing paraffinic, naphthenic, and aromatic organic compounds are preferred. However, the material is not limited to the above materials as long as it has acid resistance and oxidation resistance and does not precipitate on the cathode plate in the battery electrolyte. The deposits on the cathode plate have the disadvantage of increasing the charging pressure of the battery and reducing the charging efficiency. Another feature of the invention is the use of surfactants. That is, this surfactant is particularly effective in a method of forming a film from a polymer solution containing a solvent. In this case, because the affinity between oil and resin is strong, the oil sticks to the polymer dissolved in the solvent at the molecular level, and the part of the surfactant that has a hydrophobic group sticks to the oil, and the part that has the opposite hydrophilic group sticks to the oil. In order for the film to be formed uniformly with the surface facing outward, 10
Hydrophilic separators can be made without any increase in electrical resistance despite the addition of % of oil. This is considered to be because the effects of the oil and surfactant made it easier to form a film and form micropores. In recent years, a method has been proposed in which oil is kneaded with silica as a type of plasticizer for polyolefin as a polyolefin polymer separator, and then the oil is removed to form micropores, but this is necessary for forming micropores. In this method, oil is used as a pore-forming agent, and micropores are simply formed where the oil is removed in a subsequent process, and the effect of the present invention is not achieved.

Claims (1)

[Scope of Claims] 1. A separator for a battery, characterized in that the separator is made of a chlorine-containing polymer and contains oil. 2. The battery separator according to claim 1, wherein the separator contains a surfactant. 3. A method for producing a battery separator, which comprises uniformly dissolving a chlorine-containing polymer together with oil in a solvent, forming the solution into a sheet-like film, and removing the solvent.