JPH02152172A - Manufacture of microporous membrane for zinc bromide battery - Google Patents

Abstract

PURPOSE:To reduce the membrane resistance of a microporous membrane to a limit value or less and to enable the use of the membrane as a separator for a zinc bromide battery by specifying a mixing ratio of polyethylene powder, silicon dioxide powder, and dioctyl phthalate. CONSTITUTION:Dioctyl phthalate is absorbed into silicon dioxide powder to form a muddy mixture, then polyethylene powder is mixed thereto. The mixture is kneaded at 120 deg.C or higher for 20 minutes or more, then it is pressed in a plate with a heat press at a temperature of 120 deg.C or higher. The plate is immersed in trichloroethane at room temperature for 2 hours or more to extract dioctyl phthalate until the weight reduction rate of it becomes 50% or more. The mixing ratio of dioctyl phthalate to 1g of silicon dioxide is at least 14g, and that of silicon dioxide to 1g of polyethylene is at least 0.15g. The membrane resistance can be reduced to 0.02OMEGA-100cm<2>/piece or less.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to a method for producing a microporous membrane for zinc bromide batteries.

B1 Summary of the Invention This invention provides a method for producing a microporous membrane for zinc bromide batteries, which reduces the weight loss rate by 50% before and after extraction of dioxtylphthalate.
In addition to the above, the zinc bromide battery separator is molded with a blending ratio of at least 14 g or more of dioxtylphthalate per 1 g of silicon dioxide, and a blending ratio of at least 0.15 g of silicon dioxide per 1 g of polyethylene. The membrane resistance can be lowered to below the limit value that can be used as a membrane.

C1 Conventional technology Figure 5 is an explanatory diagram showing the basic configuration of a zinc-bromine battery. In the figure, l is an electrolytic cell, 2 is a separator that partitions the inside of the electrolytic cell l into a cathode side and an anode side, and a separator on the cathode side. A cathode electrode 3 is provided and a cathode electrolyte 4 made of an aqueous solution of ZnBr* is stored therein, and an anode electrode 5 is provided on the anode side and a ZnBr* aqueous solution is provided.
An anolyte electrolyte 6 made of an aqueous solution of B rt B rt is stored therein. 7.8 are storage tanks for storing the catholyte 4 and anolyte 6, respectively; 9 is the cathode side of the electrolytic cell 1 and the storage tank 7;
IO is a circulation path provided between the anode side of the electrolytic cell l and the storage tank 8, and IO is a circulation path provided between the storage tank 8 and the anode side of the electrolytic cell 1. Pumps 13 and 14 provided in IO are cathode terminals and anode terminals connected to cathode electrode 3 and anode electrode 5, respectively.

When the metal-bromine battery described above is charged as shown, a DC power source is connected to each terminal 13.14, and each electrolyte 4.6 is circulated by a pump If, 12.

On the cathode side, Zn+1 in the electrolyte 4 and e- injected from the terminal 13 due to the reaction of Zn"" + 2e--+Zn.
reacts, and Zn is precipitated. Also, on the anode side, 2 Br
--*Brt+ 2e-,, Br*+Br--BrsD
6 Problems to be Solved by the Invention In the zinc bromide battery described above, the separator that separates the positive electrode electrolyte and the negative electrode electrolyte is an important constituent material that prevents self-discharge of the battery and a decrease in clone efficiency. A microporous membrane whose matrix is mainly polyolefin resin is used.

The polyolefin microporous membrane for this battery system is made by mixing appropriate amounts of polyethylene powder, silicon dioxide powder, and dioxtylphthalate (hereinafter referred to as 0.P) and kneading the mixture in a pressure kneader. The mixture was made into a plate shape using a heat press, and then diluted with trichloroethane. P is extracted and formed into a microporous membrane. It has long been known that the resistance value and bromine barrier properties of the membrane formed in this way vary slightly depending on the composition ratio of the mixture. Therefore, in order to obtain reliable battery characteristics, the characteristics of the membrane must also be made uniform. To achieve this, it is necessary to determine the reference value of the membrane characteristics and determine the composition ratio that will produce a membrane that can maintain that value. Need to decide.

An object of the present invention is to provide a method for manufacturing a microporous membrane for zinc bromide batteries, which reduces the membrane resistance by limiting the blending ratio of raw materials.

21 Means for Solving the Problems This invention involves the production of a microporous membrane by kneading polyethylene powder, silicon dioxide powder, and dioxtylphthalate, forming it into a plate, and then extracting the dioxtylphthalate with trichloroethane and molding it. In the method, dioxtylphthalate is adsorbed onto silicon dioxide, formed into a slurry mixture of silicon dioxide and dioxtylphthalate, and then mixed with polyethylene powder to form a mixture of at least 12
A step of kneading at 0° C. or higher for 20 minutes or more, and a step of kneading the mixture obtained in this step at least 120° C. using a heat press machine.
The process of molding into a plate at temperatures above ℃ and the extraction of dioxtylphthalate from the plate-shaped molded product obtained in this process are carried out using trichloroethane at room temperature and immersed in the same solution for 2 hours or more. and a step of extracting and removing the dioxtylphthalate present on the surface, and the weight reduction rate before and after the extraction of the dioxtylphthalate is set to be 50% or more, and the amount of dioxtylphthalate blended with respect to 1 g of silicon dioxide is at least 14 g or more, and the silicon dioxide content m per 1 g of the polyethylene is at least 0.1
It is molded with a blending ratio of 5g or more.

19 Effect Various membrane samples were prepared as porous membranes with the above-mentioned compounding ratio, and their properties were compared and examined to produce a membrane resistance value that can be used as a separator for zinc bromide batteries. To this,
0. The weight loss rate of the sample before and after removing P must be at least 50°C, and D0. P mixture 1 is 14 per gram of silicon dioxide
It was found that the amount of silicon dioxide mixed is at least 0.15 g per polyethylene Ig.

G. Example This invention will be described in detail below.

<Example 1> Showa Denko's Shorex 9600 was added to the polyethylene powder.
8G, Nippon Aerosil AERO9IL for silicon dioxide
200, and 0. Using domestically produced chemical grade P, the amounts were respectively 300g, 53g and 800g, and kneaded at various temperatures and times. In addition, D, 0. P was mixed with silicon dioxide in advance to form a slurry so that it could be easily mixed with polyethylene powder. The mixture thus prepared was heat pressed at 130°C, formed into a 1 mm thick plate, and immersed in trichloroethane for 6 hours.
0. Extract P. D, 0. The weight of the sample was measured before and after extracting P, and the weight reduction rate was determined.

The results are shown below.

Normally, the weight reduction rate is about 70% under optimal conditions, but D, 0. The P content may appear slightly lower depending on the P extraction time and subsequent drying conditions. According to the table, when the kneading time and temperature are less than 20 minutes and lower than 120°C, the weight loss rate is low in both cases, and the conditions cannot be said to be good. Moreover, the molding condition when it was made into a plate shape was also poor. Therefore, the conditions vary depending on the properties of the resin, inorganic fine powder, and organic liquid, but in the case of the above composition ratio, it can be determined that the kneading time and temperature are preferably 20 minutes or more and 120° C. or more, respectively.

<Example 2> Using the same materials as in Example 1, polyethylene, silicon dioxide, and 0. The weight ratio of P is 300g:
43g: 650g, ■300g: 53g800g,
■300g: 63g: 950g and ■300g
Four kinds of samples of 5 g: l l 30 g were kneaded and formed into a plate shape of 1 aua thickness, and immersed in trichloroethane for various times to give D, 0. The weight loss rate before and after P extraction was determined. The results are shown in Figure 1.

In addition, the kneading temperature and time for the above sample Nos.
120°C for 20 minutes. As a result, no matter the composition ratio,
At room temperature, 0. When extracting P, as shown in Figure 1, the amount of extraction increases rapidly within about 2 hours, but beyond that, the extraction does not progress much, and it takes more than 12 hours for the weight loss rate to exceed 60%. I know it will come out.

From these results, it was found that the glue at room temperature was 0. Regarding the extraction time of P, at least 2 hours are required, and 12 to 24 hours are required for the weight reduction rate to exceed about 90% of the extraction limit of 70%, that is, about 60%. It is recognized that

Example 3 Using the same materials as in the above example, polyethylene and silicon dioxide were used. Mix and mold with P. After that, D
,0. After extracting P and measuring the membrane resistance, sample glue, 0. Figure 2 shows the relationship between the weight change rate and membrane resistance before and after P extraction and is plotted. This second
From the figure, the membrane resistance value is 0. Samples that are extracted well when a large amount of P is mixed and are highly porous are
Although it tends to be lower, the reduction rate must be at least 50% in order to achieve a membrane resistance value of 0.02Ω-100cm"7 or less, which can be used as a separator for zinc bromide batteries.
It is recognized that it must be more than that.

<Example 4> From the experiment of Example 3 above, next, 0.0% per gram of silicon dioxide was added. Figure 3 shows the relationship between the amount of P and the weight loss rate of the sample. Figure 3 Karari, 0. There is a limit to the amount of P that can be absorbed by silicon dioxide. P amount is 23-24
g is the limit. On the other hand, the weight reduction rate of the sample was 0. This value can only be measured after adding polyethylene to a mixture of P and molding it to form a porous membrane. Here, in order to achieve a reduction rate of 50% or more, 0.00% is required per 1g of silicon dioxide. P amount is at least 14g
More than that is required.

<Example 5> From the experiment of Example 3 above, the relationship between the amount of silicon dioxide relative to polyethylene Ig and the membrane resistance value of the sample was investigated in FIG. 4. From Figure 4, 1g of polyethylene
As the amount of silicon dioxide mixed in the sample changes, the film resistance value of the sample also changes. In particular, when the amount of silicon dioxide is in the range of 0.1 g to 0.2 g, a rapid change in membrane resistance is observed, and the properties of the membrane are influenced by this point.

According to this FIG. 4, in order to have a resistance of 0.02Ω-100am'/sheet or less, which can be used as a separator for zinc bromide batteries of the present invention, silicon dioxide must be replaced by polyethylene I.
At least 0.15 g or more is required per g.

As described above, according to Examples 1 to 5, the membrane resistance was 002Ω100c+
A microporous membrane of less than u'/sheet is made of polyethylene,
silicon dioxide, and 0. In order to obtain P as a raw material, (1) D, 0. The change in weight loss rate of the sample before and after P extraction must be at least 50%; Pik is 1g of silicon dioxide
(3) The amount of silicon dioxide to be blended must be at least 0.15 g or more per 1 g of polyethylene. That is, as a method for manufacturing the microporous membrane for zinc bromide batteries used in the present invention using the above raw materials to have a membrane resistance of 0.02Ω-100cm” or less of 7 sheets, polyethylene silicon dioxide/D, 0.
The blending ratio may be such that P is Iglo, t5g~/2+g~.

H. Effects of the Invention As described above, according to the present invention, polyethylene powder is used as the polyolefin resin, silicon dioxide is used as the inorganic fine powder, and organic liquid extraction solvent is used. After mixing and kneading appropriate amounts of these using P, it is formed into a plate shape, and further, it is coated with trichloroethane to give a 0. When producing a microporous membrane by extracting P, depending on the kneading conditions, molding conditions, and OP extraction conditions, 0. Depending on the weight loss rate of the sample before and after P extraction and the blending ratio of each raw material, the membrane resistance value of a microporous membrane that can be used as a separator for zinc bromide batteries can be set to 0.02Ω-100cm2/sheet or less F. .

[Brief explanation of the drawing]

Figures 1 to 4 show examples of the present invention. Figure 1 shows the relationship between immersion time and weight loss rate, Figure 2 shows the relationship between weight loss rate and membrane resistance value, and Figure 3 shows the relationship between immersion time and weight loss rate. 0.0% per gram of silicon. FIG. 4 is a characteristic diagram showing the relationship between the amount of P and the relationship between silicon dioxide placement and membrane resistance value for polyethylene Ig, and FIG. 5 is an explanatory diagram of the basic configuration of a zinc-bromine battery. Figure 1 Characteristic diagram Soaking time (hr) Figure 2 Characteristic diagram Weight loss rate (%) Figure 5 Explanatory diagram of basic structure of zinc bromine battery ○ ■ Figure 3 Characteristic diagram Figure 4 Characteristic diagram Silicon dioxide for 71 g of polyethylene Amount (g) Procedural amendment (issued by ^) March 20, 1999

Claims (1)

[Claims] (1) In the method for producing a microporous membrane in which polyethylene powder, silicon dioxide powder, and dioctyl phthalate are kneaded and formed into a plate shape, dioctyl phthalate is extracted with trichloroethane and molded. A step of absorbing into silicon dioxide to form a slurry mixture of silicon dioxide and dioxtylphthalate, mixing it with polyethylene powder, and kneading it at a temperature of at least 120°C or more for 20 minutes or more, and heating the mixture obtained in this step. The step of molding into a plate shape using a press at at least 120°C or higher, and the extraction of dioxtylphthalate from the plate-shaped molded product obtained in this step, are carried out at room temperature using trichloroethane.
and immersing it in the same solution for 2 hours or more to extract and remove diostylphthalate inside and on the surface of the plate-shaped molded product, and the weight reduction rate before and after the extraction of diostylphthalate is 50% or more. and at least 14 g of dioxtylphthalate per 1 g of silicon dioxide.
A method for producing a microporous membrane for a zinc bromide battery, which is as described above, and is molded at a blending ratio of at least 0.15 g of silicon dioxide per 1 g of the polyethylene.