JPH04255666A - Separator for battery - Google Patents

Abstract

PURPOSE:To provide a separator for a battery excellent in alkali resistance, acid resistance while being provided with the good liquid absorbing and holding properties. CONSTITUTION:A separator for a battery consists of a sheet which is mainly composed of fibers consisting of a mixed polymer of polysulfon and/or polyether sulfon 15 to 40wt.%, polyvinyl chloride 20 to 40wt.% and a metacryl acid ester group polymer 20 to 65wt.% as the main part, and to which an alkali-resistant interface activator (not containing sulfur and nitrogen) of 0.05 to 0.5wt.% is stuck.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has excellent alkali resistance,
The present invention relates to a battery separator that has oxidation resistance and good liquid absorption and liquid retention properties.

0002

BACKGROUND OF THE INVENTION Conventionally, nonwoven fabrics made of nylon fibers or polypropylene fibers, which have excellent alkali resistance, have been used for separators for batteries such as nickel-cadmium batteries that use alkali as an electrolyte.

0003

However, the nylon fiber separator has a major drawback in that it is oxidized and deteriorated by oxygen gas generated during charging. Furthermore, this nylon fiber separator produces nitrate radicals when oxidized due to the nitrogen contained in the nylon. For this reason, this nylon fiber separator has the problem of being prone to self-discharge and causing corrosion of the electrodes.

On the other hand, a separator made of polypropylene fibers has the advantage of excellent chemical resistance, but on the other hand, it has poor hydrophilicity and thus has a low electrolyte retention capacity. For this reason, polypropylene fiber separators have problems such as high electrical resistance in liquid, and poor permeability to gases generated during charging, which increases internal pressure during charging in sealed batteries and poses a risk of bursting. .

[0005] In order to improve the oxidation resistance of nylon, it has been proposed to composite nylon and polypropylene, but this is only effective to the extent that deterioration can be reduced because the proportion of fibers that undergo oxidative decomposition is reduced overall. stay in,
This is not a fundamental countermeasure.

[0006] Techniques for improving the hydrophilicity of polypropylene include a method in which a separator of polypropylene fibers is treated with oleum or chlorosulfuric acid to form a sulfonate;
Many methods have been proposed, including sulfonation by treatment in hot concentrated sulfuric acid, sulfonation by treatment in sulfur trioxide (SO3) gas, and graft polymerization of acrylic acid or methacrylic acid by electron beam irradiation. Although it has been
Industrially, stable and economical mass production has not yet been achieved.

An object of the present invention is to provide a battery separator that has excellent alkali resistance and oxidation resistance, as well as good liquid absorption and liquid retention properties.

[0008]

[Means for Solving the Problems] The present invention provides polysulfone and/or polyether sulfone in an amount of 15 to 40% by weight.
, consisting mainly of fibers made of a mixed polymer of 20 to 40% by weight of polyvinyl chloride and 20 to 65% by weight of a methacrylic acid ester polymer, and containing an alkali-resistant surfactant free of sulfur and nitrogen. .05-0.5% by weight, if necessary, further polyvinyl alcohol 0.2-9%
A battery separator consisting of a sheet with a weight percent deposited on it.

The present invention will be explained in detail below.

The fibers constituting the separator sheet of the present invention are polysulfone (hereinafter abbreviated as PSF) and/or polyethersulfone (hereinafter abbreviated as PESF), polyvinyl chloride (hereinafter abbreviated as PVC) and methacrylate ester. Polymer (hereinafter abbreviated as methacrylate polymer)
The mixed composition is 15-40% by weight of PSF and/or PESF, 20-40% by weight of PVC.
, 20 to 65% by weight of the methacrylate polymer.

If the composition is outside the above range, problems will occur in terms of fiber spinning, thermal dimensional stability, and strength and elongation properties.

[0012] Here, PSF has the molecular structure shown below.

[0013]

[Chemical formula 1]

[0014] PESF has the molecular structure shown below.

[0015]

[Case 2]

PSF and PESF, which are generally used as molding materials, are sufficient.

[0017] PVC is also not particularly limited, and PVC used in ordinary molding materials is sufficient, but with a polymerization degree of 600
It is preferable that it is above.

The methacrylate polymer of the present invention refers to a methacrylic ester homopolymer or a copolymer thereof, such as a methacrylic ester, an acrylic ester, and/or a copolymer thereof.
or a copolymer with an unsaturated carboxylic acid, or a mixture of the above polymers. For purposes of the present invention, these polymers are preferably nitrogen-free. Furthermore, since the molecular weight is used to shape fibers, it is preferable that the molecular weight is at least 50,000 or more. Further, the glass transition temperature of these polymers is preferably at least room temperature or higher.

As a means for producing the fiber constituting the sheet of the battery separator of the present invention, for example, a mixed polymer of PSF and/or PESF, PVC, and a methacrylate polymer is mixed with dimethylacetamide, dimethylformamide, or dimethylsulfonate. A method is used in which a spinning dope obtained by dissolving and dispersing in oxide or acetone is shaped into fibers by wet spinning or the like.

The battery separator of the present invention is made of a sheet made of the fibers produced as described above. Examples of methods for forming fibers into sheets include a method of forming a web using card and forming a nonwoven fabric by needle punching, and a method of wet papermaking. When forming fibers into a sheet in this manner, the fibers are preferably fixed using a binder of usually 10 to 20% by weight. The binder used in the present invention is selected taking into consideration that there are no problems with alkali resistance and oxidation resistance, and that it has electrical insulation properties. Examples of binders that meet such conditions include vinyl chloride-vinyl acetate copolymer fibers or resins, polyethylene fibers or resins, and the like.

The thickness of the sheet is determined depending on the purpose, but is generally set to 0.1 to 2 mm. The thinner the sheet, the more easily wetted by the electrolyte. However, if the separator is too thin, there will be problems in terms of strength, and there will also be the disadvantage that short circuits are likely to occur. On the other hand, if the sheet is thick and dense, it will be difficult for the air sealed inside the sheet to escape, so it will take time for the liquid to completely penetrate inside, and in some cases, the air will remain trapped. This causes the inconvenience of

The sheet liquid retention rate of the separator of the present invention is 4
It has high performance of over 00%. Here, the liquid retention rate is
This is the ratio of the retained liquid weight to the sample weight after a sample was immersed in a 30% potassium hydroxide (KOH) aqueous solution for 1 hour, taken out, and allowed to drip droplets naturally for 10 minutes. The higher the liquid retention rate, the better, and it becomes possible to increase the capacity and reduce the size of the battery.

[0023] If this liquid retention rate becomes less than 300%, there will be a problem that the electrolyte will be insufficient and smooth battery reaction will not take place, resulting in a decrease in discharge capacity.

[0024] Furthermore, the liquid absorption rate of the separator of the present invention is as follows:
It has high-speed liquid absorption with a droplet disappearance rate of 5 seconds or less. Here, the droplet disappearance rate is a sample that has been left for 24 hours at 20±2℃ and 65±2%RH, and is held horizontally floating above the floor. The time required for a droplet to disappear is expressed in seconds.

[0025] If this liquid absorption speed exceeds 10 seconds, the permeation and diffusion of the electrolyte will be poor, and air will be trapped during battery assembly or charging, and the permeation of oxygen gas generated during charging will be poor, resulting in a decrease in battery performance. This inconvenience arises.

The fiber itself used in the separator sheet of the present invention has a porous surface structure and is easy to wet.
The water retention rate of the fiber itself is as high as 45-61%.

[0027] Here, the water retention rate of the fiber is a value calculated by the following method. In other words, the weight (W1) of a fiber that has been immersed in deionized water for 24 hours and then dehydrated using a centrifugal dehydrator at 3,000 rpm x 10 minutes under a load of 10G and the dry weight (W2) of this fiber can be calculated using the following formula. This is the value calculated by.

Water retention rate = [(W1 − W2 )/W2 ]×100(%
) Therefore, the sheet according to the present invention usually has a good liquid retention rate and liquid absorption rate. However, due to the influence of the binder used when forming the fibers into a sheet, the thickness, density, etc., the liquid absorption rate and liquid retention rate of the sheet for high concentration KOH electrolyte may decrease.

In the present invention, the liquid absorption rate and liquid retention rate are improved by incorporating a predetermined amount of alkali-resistant surfactant into the sheet made of fibers of the mixed polymer.

The surfactant used in the present invention must have alkali resistance, and if the surfactant is eluted into the electrolytic solution and partially decomposed, if the surfactant contains sulfur and nitrogen, Since sulfate ions and nitrate ions are generated in the electrolyte and impede battery performance, it is necessary that the surfactant does not contain sulfur and nitrogen. )n CH2 COOM
Alkyl ether carboxylic acids, alkyl ether carboxylates, and the like represented by the formula (wherein R is an alkyl group and M is Na, K, or hydrogen) are preferably used.

The amount of the alkali-resistant surfactant attached to the sheet is preferably 0.05 to 0.5% by weight based on the entire untreated sheet.

[0032] If the amount of adhesion is less than 0.05% by weight, there will be no significant improvement effect on the liquid absorption rate, and if the amount of adhesion exceeds 0.5% by weight, the amount falling into the electrolyte will increase. This inconvenience arises.

[0033] As a method for attaching a surfactant to a sheet, a method is generally used in which the surfactant is made into an aqueous solution, the sheet is immersed in the solution, and then dried.

[0034] If the sheet thickness is thin, strength problems arise. Also, depending on the method of forming the sheet, fuzz may occur, causing inconvenience in battery production. In such cases, strength and fluff can be improved by further containing polyvinyl alcohol in the sheet of the present invention.

The amount of polyvinyl alcohol attached to the sheet varies depending on the degree of saponification and degree of polymerization of the polyvinyl alcohol, but is 0.2 to 9% by weight based on the untreated sheet.
It is desirable that

If the amount of adhesion is less than 0.2% by weight, there will be no effect of improving strength and fluff, and if the amount of adhesion exceeds 9% by weight, there will be a disadvantage that a large amount will fall into the electrolyte.

[0037] As a method for attaching polyvinyl alcohol to a sheet, polyvinyl alcohol is made into an aqueous solution,
Generally, a method is used in which the sheet is immersed in a surfactant or alone and then dried.

[0038]

[Examples] The present invention will be specifically explained below using examples.

The test methods used in the examples are as follows.

Alkali resistance: Weight loss rate (%) after the separator was boiled at normal pressure for 1 hour in a 30% KOH aqueous solution.

[0041] The samples were weighed after being allowed to stand for 24 hours at a temperature of 20±2°C and a relative humidity of 65±2%.

Oxidation resistance: The sample was immersed in an aqueous solution containing 50 g/l potassium permanganate and 35 g/l KOH, boiled for 1 hour, thoroughly washed with water to remove the alkali, and then immersed in dilute oxalic acid. Dissolves and removes brown manganese dioxide. Thereafter, the sample was thoroughly washed with water and dried, and the weight loss rate (%) of the sample was determined. Weigh the sample at a temperature of 20±2
The test was carried out after being left for 24 hours at a temperature of 65±2% relative humidity.

Liquid absorption rate and liquid retention rate: Examined by the method described above.

Electrical resistance: JIS-C-2313-1
973, Section 5, 2, 4 Electrical resistance test method. The liquid has a specific gravity of 1.25±0.02 (2
A KOH solution at 0°C was used.

Example 1 PSF, PVC and polymethyl methacrylate (PMMA)
) in a weight ratio of 30:20:50, 80% by weight of fibers with a fineness of 0.9 denier and a length of 4 mm.
Binder fiber 20 consisting of polyethylene fibrils and
Using weight%, basis weight 50g/m2, thickness 0.2mm
Wet-processed nonwoven fabric was produced.

Next, this nonwoven fabric was immersed in a 0.1% aqueous solution of sodium carboxylated polyoxyethylene lauryl ether, squeezed to a liquid content of 150% with a pressing roller, and then dried with a cylinder dryer to form a sheet. The amount of carboxylated polyoxyethylene lauryl ether sodium deposited in this sheet was 0.1% based on the sheet.
It was 5% by weight. This sheet has a liquid absorption rate of 1 second and a liquid retention rate of 518%, and since the untreated sheet has a liquid absorption rate of 120 seconds or more and a liquid absorption rate of 220%, this surfactant adhesion treatment can improve the absorption of battery separators. It was confirmed that the liquid capacity and liquid retention capacity could be improved. In addition, this separator was immersed in a 30% KOH aqueous solution for about one month and its changes were observed, but this separator did not change even after being immersed in a strong alkaline solution for a long time.
The liquid absorption rate after taking it out from the H aqueous solution and drying it was also the same as the initial liquid absorption rate, and it was confirmed that the liquid absorption rate did not decrease.

Example 2 Various types of separators were prepared on the same nonwoven fabric as in Example 1 with different concentrations of sodium carboxylated polyoxyethylene lauryl ether and different amounts of adhesion.

Regarding these separators, the liquid absorption rate,
When the liquid retention rate, electrical resistance, and weight loss after washing with 30% KOH aqueous solution were investigated, as shown in Table 1, the amount of attached carboxylated polyoxyethylene lauryl ether sodium was in the range of 0.05 to 0.5% by weight. It turned out to be good.

[0049]

[Table 1]

Example 3 The same nonwoven fabric as prepared in Example 1 was subjected to the same adhesion treatment as in Example 2 using sodium carboxylated polyoxyethylene tridecyl ether and carboxylated polyoxyethylene lauryl ether.

As a result, it was confirmed that the same effects as in Example 2 could be obtained even when these surfactants were used.

Example 4 Various separators with different adhesion amounts were prepared on the same nonwoven fabric as in Example 1 by changing the concentrations of sodium carboxylated polyoxyethylene uralyl ether and polyvinyl alcohol (PVA).

Regarding these separators, the liquid absorption rate,
When the liquid retention rate and strength were investigated, as shown in Table 2, the adhesion amounts of sodium carboxylated polyoxyethylene lauryl ether and PVA were in the range of 0.05 to 0.5% by weight and 0.2 to 9% by weight, respectively. It turned out to be good.

[0054]

[Table 2]

[0055]

[Effects of the Invention] As explained above, the battery separator of the present invention has excellent liquid absorbing properties and high liquid retention capacity, and has low electrical resistance in the liquid and increases the discharge capacity of the battery. can be improved. In addition, the gas permeability generated during charging is good, and it is possible to reliably prevent an internal pressure increase accident during charging of a sealed battery. Moreover, since the battery separator of the present invention has excellent oxidation resistance, it is possible to construct a high-performance battery with a long life and little self-discharge.

Furthermore, it is possible to improve the strength and fuzziness of the sheet as a battery separator.

Claims (2)

[Claims] Claim 1: 15 to 40% by weight of polysulfone and/or polyethersulfone, 20 to 40% by weight of polyvinyl chloride
40% by weight and methacrylic acid ester polymer 20-6
A battery separator comprising a sheet mainly composed of fibers made of a mixed polymer with 5% by weight and to which 0.05 to 0.5% by weight of an alkali-resistant surfactant free of sulfur and nitrogen is attached. 2. The battery separator according to claim 1, wherein the sheet is further coated with 0.2 to 9% by weight of polyvinyl alcohol.