JPH09237621A - Separator for zinc-bromine battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator having excellent permeability of liquid and water retentivity without worsening bromine resistance and a method of manufacturing this separator. SOLUTION: This separator has a network structure part 1 thermally fusing the fellow ethylene system resin particles of 500,000 or more average molecular weight through a hole 2, the separator is formed by a compound structure unit of 20 to 70% total unit porosity having an aggregate structure part 3 aggregating a plurality of silica particles through a void 4 in this hole 2. In a method of manufacturing this separator, a powdery mixture, consisting of 100 pts.wt. ethylene system resin particle of 200μm or less mean grain size 500,000 or more average molecular weight and 10 to 200 pts.wt. aggregate silica particle of 100μm or less mean grain size, is pressed powder-molded at a molding temperature less than 200 deg.C with volumetric ratio 40% or more relating to a cavity.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a zinc-bromine battery separator (hereinafter referred to as a separator) and a method for producing the same.

[0002]

2. Description of the Related Art A zinc-bromine battery is a secondary battery using bromine as an active substance and has been attracting attention for a long time because of its high energy density. Improvements have been made in recent years, and a method has been adopted in which bromine generated in the positive electrode during charging is reacted with a quaternary ammonium salt compound Q ⁺ and stored as a complex compound (Q ⁺ · Br ₃ ⁻ ). Therefore, this battery is discharged and charged by the reaction represented by the following chemical formula 1.

Embedded image At the time of charging, this complex compound has a high density and therefore precipitates, and the ones accumulated at the bottom are transported to the storage tank. The separator is usually provided to prevent a short circuit between the positive electrode and the negative electrode and to keep the electrode gap constant, but recently, during charging, fine particles of the complex compound approach the negative electrode to reduce energy consumption. A porous body is used in order to prevent a decrease in efficiency and to allow a liquid to smoothly move between both electrodes.

Currently, there are various porous materials, but since bromine having a strong oxidizing power is present in a zinc-bromine battery, it is necessary to use a bromine-resistant material for the separator. Ceramics materials are typical as bromine resistant materials, but since they have a large mass and are easily broken, inexpensive plastics materials having good moldability are desired. Examples of general-purpose bromine-resistant plastic materials include olefin resins such as fluorine resins and ethylene resins, but inexpensive ethylene resins are generally adopted. Examples of the ethylene-based resin include high-density ethylene-based resin, low-density ethylene-based resin, straight-chain ethylene-based resin, and resins of copolymers or graft polymers thereof. Among them, the high-density ethylene-based resin is Most excellent bromine resistance.
In particular, high-density ethylene-based resins with an average molecular weight of 500,000 or more are more excellent in bromine resistance than general-purpose high-density ethylene-based resins and have a melting point (Vicat softening temperature) of 135.
The fluidity is extremely low at about 0 ° C., and when in powder form, the powder is partially melted by compaction to form a network structure suitable as a separator. While the high-density ethylene-based resin has many advantages as described above, it is a lipophilic substance and lacks hydrophilicity. Therefore, the high-density ethylene-based resin can be applied as it is to a separator that requires water retention (a property of having extremely low water permeation resistance). I couldn't.

[0004]

Therefore, a matrix of the above-mentioned lipophilic high-density ethylene-based resin (hereinafter simply referred to as an ethylene-based resin) is irradiated with plasma to generate polar groups, or has a hydrophilic property. A method of imparting hydrophilicity by adding and mixing particles of a compound has been studied. However, the former is not suitable for mass production because the equipment cost increases,
In the latter case, it is necessary to add process oil such as dioctyl phthalate (DOP) or liquid paraffin in advance to plasticize the matrix, and these process oils are difficult to remove and may remain to deteriorate the bromine resistance of the separator. there were. Therefore, an object of the present invention is to provide a separator having excellent liquid permeability and water retention without requiring special equipment and without impairing bromine resistance, and a method for producing the same.

[0005]

Means for Solving the Problem The separator of the present invention is provided with a network structure portion in which ethylene resin particles having an average molecular weight of 500,000 or more are thermally fused with each other through pores, and a plurality of pores are formed in the pores. It is composed of a composite structure having an aggregate structure part in which silica particles are aggregated through voids and having a total porosity of 20 to 70%. This separator has an average particle size of 2
A powdery mixture consisting of 100 parts by weight of ethylene-based resin particles having an average molecular weight of 500,000 or more and having a particle size of 00 μm or less and 10 to 200 parts by weight of aggregated silica particles having an average particle size of 100 μm or less, with a volume ratio to the cavity of 40% or more. It can be produced by compacting at a molding temperature of less than 200 ° C. The present invention, the component is composed of only ultra-high molecular weight ethylene resin and silica that does not reduce the bromine resistance,
The structure is provided with a network structure part in which ethylene-based resin particles are heat-fused through pores, and a plurality of silica particles in the pores have an aggregate structure part aggregated through voids, the whole Since it is a composite structure with a porosity of 20 to 70%,
The separator has excellent liquid permeability and water retention without requiring special equipment.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described below with reference to the sectional explanatory view illustrated in FIG. The composite structure constituting the separator of the present invention comprises a network structure portion 1 formed by thermal fusion of ultra-high molecular weight ethylene-based resin particles having an average molecular weight of 500,000 or more via pores (network) 2. , The aggregate structure portion 3 in which the primary particles of a plurality of silica existing in the pores (mesh) 2 are aggregated via the voids 4 as passages of the electrolytic solution. 20-70%
belongs to. This aggregate structure part 3 is composed of secondary particles in which primary particles of silica are aggregated and formed in a nodule shape through voids, and particularly, nodule-shaped secondary particles are in a larger nodule shape through similar voids. It exists as an aggregate of tertiary particles that are aggregated and formed in. This mesh structure 1
When an ultra-high molecular weight ethylene resin with low fluidity is pressed into powder by holding an aggregate of silica particles (hereinafter referred to as aggregated silica particles), the ethylene resin particles are partially melted by heat. Formed. On the other hand, voids 4 between silica particles
Is determined by the bulk density of aggregated silica particles as a raw material and the degree of compaction, and is a factor that determines the porosity and pore size (size of the gap that determines the particle size of suspended solids that can be shielded) that are important as separator characteristics. Becomes Therefore, the separator of the present invention, by adjusting the mixing ratio of the ethylene-based resin particles and the agglomerated silica particles, the size of the ethylene-based resin particles and the agglomerated silica particles, the conditions of the dusting step, etc.
The porosity of the entire separator can be set to 20 to 70%, and the energy efficiency of the battery can be improved.

In the production of the separator of the present invention, if the average particle size of the ethylene resin particles exceeds 200 μm, it tends to be difficult to form a network structure having fine pores. From the viewpoint of the porosity of the separator described above, it is desirable that the average particle diameter be small. However, if it is less than 1 μm, there is a risk of powder explosion. In that case, it is necessary to perform powder compaction under an inert gas or take antistatic measures. Therefore, if the average particle size is about 10 to 50 μm, It is better to use one. Aggregated silica particles are obtained by aggregating primary particles having an average particle size of several nm to 100 nm as described above.If the average particle size exceeds 100 μm, the above properties tend to be insufficient, and like the ethylene resin, From the viewpoint of porosity, it is desirable that the average particle size is small, but from the viewpoint of handling, it is preferably 5 to 30 μm. As the type of silica, wet silica,
Examples include dry silica and the like.

The separator of the present invention has a porosity of 20 to 70%.
In order to obtain this porous body by powder compaction, it is necessary to adjust the bulk density of the powdery mixture of ethylene resin particles and agglomerated silica particles to 900 g / l or less. Preferably, this allows the powdery mixture to carry a gas such as air. The smaller the bulk density, the easier it is to select the porosity by adjusting the processing conditions. However, if it is too small, the volume of the mold will be unnecessarily large.
A range of up to 500 g / l is desirable. The bulk density of the powdery mixture is highly dependent on the bulk density of the agglomerated silica particles (the ethylene-based resin particles are limited to a few kinds, but the silica particles have a wide variety and a wide selection range). ), The bulk density of the aggregated silica particles is preferably 20 to 200 g / l. The mixing ratio of the ethylene-based resin particles and the agglomerated silica particles is such that when the agglomerated silica particles are less than 10 parts by weight with respect to 100 parts by weight of the ethylene-based resin particles, the silica particles arranged in the pores of the network structure part are When the amount of the aggregated structure part becomes smaller, and conversely the aggregated silica particles exceed 200 parts by weight, the amount of the ethylene-based resin forming the network structure part becomes insufficient, and in any case, the desired composite structure can be obtained. The ethylene-based resin particles will lose its function as a separator and cannot retain its function as a separator.
Addition amount of aggregated silica particles to 100 parts by weight is 10 to 200
It is necessary to make it a weight part, and the range of 30 to 150 weight parts is particularly desirable.

In this manufacturing method, powder compaction is a type of press molding by a male mold and a female mold which is performed under heating. In other words, this is a molding method in which a powdery mixture of ethylene-based resin particles and agglomerated silica particles is filled into the female concave portion, and then the male convex portion is inserted into the female concave portion and heated and pressed at the same time. . For example, the bulk density of the powdery mixture is C
When the volume of the finished product as a separator is V [1] when adjusted to [g / l], the powder mixture is 1000
It is a volume of / C · V [1], and the volume of the female concave portion needs to be designed larger than this. Also, when the cavity is v [1] when the male mold and the female mold are completely closed, the processing condition may be such that the volume V [1] of the finished product as a separator is V> v. Absent. In this case, the porosity as a separator is obtained at a higher level, and this is largely contributed by the molding conditions. The separator of the present invention can be freely selected depending on the shape of the cavity such as a sheet shape or a cylindrical shape, and can meet the specifications of the battery.

The molding factors in the powder compacting step are the volume ratio of the powdery mixture to the cavity, the molding temperature, the press pressure, the heating time and the pressurizing time, and particularly, the volume ratio of the powdery mixture to the cavity. Molding temperature is important. The volume ratio of the powder mixture to the cavity must be 40% or more, and if it is less than this, the porosity of the entire separator obtained will exceed 70%, and the desired characteristics will not be obtained, and the mechanical strength Will start to decline. The molding temperature is preferably at least 130 ° C or higher because the melting point of ethylene resin is about 135 ° C. Further, the ethylene resin can be molded without decomposing up to about 250 ° C, but if the heat history of the matrix is high, the particles of the ethylene resin are completely melted by heat and the formation of the above-mentioned network structure is not possible. Since it will be perfect and the porosity of the entire separator cannot be 20% or more, 200
It must be kept below ℃. The volume ratio and the molding temperature are affected by the heating time, the pressing time, the pressing pressure, the heat capacity due to the material and the mass of the mold, and so on, depending on the target quality (porosity and pore diameter), It is desirable to set appropriate conditions within the above range.

In the separator obtained by powder compaction, when the amount of silica particles adhered on the surface is large, it may be removed by washing with water or brushing with a brush, and the silica particles present inside serve as a separator. Secured enough. Further, as post-treatment, modification such as irradiation with electron beam or plasma to improve bromine resistance and impart hydrophilicity may be applied.

[0012]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited to the description of the examples. (Example 1) Molecular weight of about 2 million, average particle diameter of 30 μm, bulk density
Polyethylene particles of 400 g / l: Weper-aggregated silica particles having an average particle size of 9 μm and a bulk density of 70 g / l, consisting of Miperon XM-220 (trade name, manufactured by Mitsui Petrochemical Co., Ltd.) and primary particles having an average particle size of 16 nm. : Nipseal LP (manufactured by Nippon Silica Industry Co., Ltd., trade name) was placed in a container with the composition shown in Table 1,
When shaken at 100 times / minute for about 30 seconds, three kinds of powdery mixtures having bulk density and true specific gravity shown in Table 1 were obtained. next,
(The volume of the cavity in a completely closed 24.4 cm ^3, the female recess 100 cm ³ volume) male 5 and a set of molds consisting of a female mold 6 for 2 female 6 the recess, the above three powdery mixture was charged in the amount charged as shown in Table 2 (true specific gravity of 24.4 cm ³ × powder [g / cm ^3]), after closing the male die 5 from above, the gold The mold was sandwiched in a press having a ram diameter of 300 mm, which was adjusted to the molding temperature shown in Table 2 in advance, and preheated for 5 minutes, and then, the pressure was directly applied at a gauge pressure of 100 g / cm ³ for 5 minutes. After the pressurization, the mold was cooled and the molded product was taken out to obtain a disk-shaped molded product of Sample No. 1 to 6 having a diameter of 180 mm. These molded products were subjected to calculation of porosity (%) from mass and volume, separator performance test, bromine resistance test, and observation / evaluation with an electron microscope by the following methods, and the results are also shown in Table 2.

(Calculation of Porosity (%) from Mass and Volume) A disc-shaped test piece having a diameter of 49 mm and a thickness shown in Table 2 was cut out from the obtained molded product. (Separator Performance Test) The test piece 8 obtained in the same manner as above was incorporated into the holder 7 of the apparatus shown in FIG. 3 together with the filter paper 9. On the other hand, a silicone resin powder having an average particle size of 3 μm: KP590 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.)
10% dispersed water was poured from above the device, and the passing condition of the silicone resin powder and water was observed and evaluated according to the following criteria. A: Only water accumulated in the flask 10 (pass). B: Water and silicone resin powder were collected in the flask 10 (failed). C: Neither water nor silicone resin powder was collected in the flask 10 (failed). (Bromine resistance test) A cylindrical test piece with a diameter of 20 mm and a thickness of 50 mm is cut out from the molded product, immersed in a bromine saturated solution (bromine concentration is 1 to 2%) in a sealed container, and this is heated to 60 ° C. After leaving it in the controlled thermostat for 15 days, the test piece was taken out and washed with water, and the condition of the test piece was observed and evaluated according to the following criteria. …
◯: No deterioration, X: Deterioration (observation / evaluation with an electron microscope) A cross section was taken with a magnification of 1000 times and evaluated according to the following criteria. ◯: The structure is the same as that shown in FIG. X: Does not have the same structure as shown in FIG.

[0014]

[Table 1]

[0015]

[Table 2]

As a result of the above, samples Nos. 2, 4, and 6 are
It has a very low porosity and does not function as a separator.
Further, the sample No. 1 did not even permeate water even though it had voids. This is because the matrix is not rendered hydrophilic. On the other hand, sample No. 3 according to the present invention
In Nos. 5 and 5, the porosity was high, the silicone resin powder was a barrier, and only water permeated. When the cross section of each sample was observed with an optical microscope, the samples No. 3 and 5
However, as shown in FIG. 1, the ultra high molecular weight polyethylene particles form a network-like skeleton, and the silica particles exist in the pores of the skeleton in the state of being aggregated, and the result of the performance test of the separator Matched with. From this, it was confirmed that the molded product according to the present invention is suitable as a separator for a zinc-bromine battery.

Example 2 The same material was used under the same conditions except that the wet agglomerated silica particles were 120 parts by weight with respect to 100 parts by weight of the polyethylene particles in Example 1, and the bulk density was about 150 g / l. A powdery mixture of This powdery mixture was powder compacted at a molding temperature of 160 ° C. in the same procedure as in Example 1 using the mold and press used in Example 1 and the charged amount shown in Table 3 to obtain Sample No. 7 to 10 moldings were obtained. These molded products were subjected to the same procedure as in Example 1 to calculate the porosity (%) from the mass and volume, separator performance test, bromine resistance test, and observation / evaluation using an electron microscope. The results are also shown in Table 3. did.

[0018]

[Table 3]

Sample Nos. 7 to 9 had the structure of the separator of the present invention as in the case of FIG. 1 and had a high porosity, and the silicone resin powder was a barrier to allow only water to permeate. Therefore, it was confirmed that these are suitable as a separator for zinc-bromine batteries. Sample No. 10 had a small amount of silicone resin powder accumulated in the flask together with water, but it was judged to have no problem in practical use because it had the same separator structure as above.

[0020]

EFFECTS OF THE INVENTION According to the present invention, a separator having excellent liquid permeability and water retention without impairing bromine resistance can be obtained without requiring special equipment.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a zinc-bromine battery separator according to the present invention.

FIG. 2 is a vertical cross-sectional explanatory view of a mold for powder compacting in an example.

FIG. 3 is an explanatory longitudinal sectional view of a separator performance tester in an example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Network structure part, 2 ... Hole (mesh), 3 ... Collective structure part, 4 ... Void, 5 ... Male type, 6 ... Female type, 7 ... Holder, 8
… Test piece, 9… filter paper, 10… flask.

Claims (2)

[Claims] 1. A network structure part in which ethylene-based resin particles having an average molecular weight of 500,000 or more are thermally fused with each other through pores,
A separator for a zinc-bromine battery, comprising a composite structure having an aggregate structure part in which a plurality of silica particles are aggregated through voids in the pores and having an overall porosity of 20 to 70%. 2. An average particle diameter of 200 μm or less and an average molecular weight of 50.
100 parts by weight of 10,000 or more ethylene-based resin particles and an average particle size of 1
2. The zinc according to claim 1, wherein a powdery mixture consisting of 10 to 200 parts by weight of agglomerated silica particles of 00 μm or less is compacted at a molding temperature of less than 200 ° C. with a volume ratio to the cavity of 40% or more. -A method for producing a separator for a bromine battery.