JP2000195490A - Separator for battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a battery excellent in air permeability and electrolyte permeability. SOLUTION: This separator for a battery uses a porous sheet of polyethylene having an ultrahigh molecular weight, and in a hole diameter distribution of the porous sheet by a mercury porosity meter method, the ratio of a hole volume (V1) from a hole diameter of 0.001 μm to a hole diameter of 10 μm to a hole volume (V2) from 0.001 μm to a hole diameter of 200 μm (V1/V2) is set in a range of 0.1-0.5. This separator for the battery can be manufactured by mixing polyethylene powder with an average diameter of 10-50 μm having ultrahigh molecular weight and polyethylene powder with an average diameter of 60-200 μm having ultrahigh molecular weight, sintering it and molding the sintered body into a sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator using a porous sheet and a method for producing the same, and more particularly, to a battery separator preferably usable for an alkaline secondary battery for an electric vehicle and a method for producing the same.

[0002]

2. Description of the Related Art Alkaline secondary batteries such as nickel-cadmium (nickel) batteries and nickel-metal hydride batteries are widely used as small batteries for electric and electronic equipment. It is also expected.

Conventionally, as a battery separator used in an alkaline secondary battery, a hydrophilic non-woven fabric such as nylon, a hydrophilic treatment (impregnation with a surfactant, a graft treatment, a sulfonation treatment, a plasma treatment, etc.) has been used. Polyolefin nonwoven fabric is used (JP-A-4-16735).
No. 5 publication). In addition, it has been proposed to use a porous sheet made of ultra-high molecular weight polyethylene (hereinafter also referred to as “UHPE”) as a battery separator (Japanese Patent Application Laid-Open No. 8-77997).

[0004] Since the UHPE porous sheet is less likely to collapse due to electrode expansion during charge and discharge of an alkaline secondary battery than the two types of nonwoven fabric battery separators, the use of the UHPE porous sheet provides the first cycle characteristics. There is an advantage that the battery characteristics to be improved are improved.

On the other hand, in nickel-cadmium batteries and nickel-metal hydride batteries, it is necessary to suppress the rise in battery internal pressure by consuming oxygen gas and hydrogen gas generated at the positive electrode and the negative electrode at the opposite electrode. For this reason, a battery separator having good gas permeability (gas permeability) is required. Further, an important property of the separator is the permeability of an electrolytic solution (such as an aqueous alkaline solution). If the permeability is poor, it takes a long time for the electrolyte to penetrate during the production of the battery, and the production efficiency is deteriorated. In addition, the amount of the electrolyte is insufficient during use, which adversely affects the battery characteristics.

[0006] Therefore, the UHPE porous sheet having the above-mentioned advantages is required to have improved air permeability and electrolyte permeability.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery separator using a UHPE porous sheet, which is excellent in gas permeability and electrolyte permeability.

[0008]

In order to achieve the above object, a battery separator of the present invention is a battery separator using a UHPE porous sheet and has a porosity of 50% by volume.
As described above, in the pore size distribution of the porous sheet by the mercury porosimeter method, the pore size is from 0.001 μm to 10 μm.
m (V1 / V), and the ratio (V1 / V) of the pore volume (V2) from 0.001 μm pore diameter to 200 μm pore diameter (V1).
2) is set in the range of 0.1 to 0.5.

That is, the air permeability tends to be proportional to the porosity and the pore size of the separator, and the permeation rate of the electrolyte tends to be inversely proportional to the pore size due to the surface tension. For this reason, the present inventors examined the pore size distribution and the like of the UHPE porous sheet in detail, and found that by setting the ratio of the porosity and the pore volume to the predetermined range, the gas permeability and the electrolyte permeation were increased. The present inventors have found that the properties are simultaneously improved, and have reached the present invention. The battery separator of the present invention is preferably used for an alkaline secondary battery for an electric vehicle because the separator for a battery is excellent in air permeability and electrolyte permeability and has the above advantages of the UHPE porous sheet. The preferred range of the pore volume ratio (V1 / V2) is 0.2
~ 0.4.

In the present invention, the pore volume (V1, V2)
Means the total of the volumes of the holes belonging to the respective hole diameter ranges.

In the present invention, UHPE refers to polyethylene having a molecular weight of 500,000 or more as determined by a viscosity method. Also,
In the present invention, the preferred molecular weight range of UHPE is
The range is from 500,000 to 16,000,000.

Next, a method of manufacturing a battery separator according to the present invention is a method of manufacturing a battery separator by sintering UHPE powder and forming the sintered body into a sheet. This is a method in which two or more UHPE powders having different diameter distribution peaks are mixed and used.

In the thus obtained UHPE porous sheet, a plurality of UHPE particles are connected, and a porous structure is formed by voids between the particles. Therefore, if two or more kinds of UHPE powders having different particle size distribution peaks are mixed and used, a UHP having a small pore size portion and a large pore size portion may be used.
An E porous sheet can be manufactured. In this sheet, good air permeability is ensured by the large hole diameter portion, and good electrolyte permeability is ensured by the small hole diameter portion. The particle size distribution peak can be measured by a usual particle size distribution measuring device, and may be measured by the mercury porosimeter method described above. Further, since the air permeability is also proportional to the porosity, if the porosity is low, the air permeability becomes poor even if the above-mentioned void volume ratio is satisfied. Therefore, the preferable porosity is 50% by volume or more.

In the method for producing a battery separator of the present invention, it is preferable to use a mixture of a UHPE powder having an average particle size of 10 to 50 μm and a UHPE powder having an average particle size of 60 to 200 μm. Thereby, a UHPE porous sheet having the above-mentioned ratio of the pore volumes can be manufactured. More preferably, a mixture of UHPE powder having an average particle size of 20 to 40 μm and UHPE powder having an average particle size of 80 to 180 μm is used.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The porous UHPE sheet used for the battery separator of the present invention can be produced, for example, as follows.

First, UHP having an average particle size of 10 to 50 μm
E powder a and UHPE powder b having an average particle size of 60 to 200 μm are mixed, and the mixture is filled in a shape retainer. The UHP
The weight mixing ratio between E powder a and UHPE powder b is usually
a: b = 1 to 9: 9-1, preferably a: b =
2-8: 6-4. Then, after sintering the UHPE powder in a steam atmosphere heated above the melting point of UHPE, the resultant is cooled to obtain a block-shaped porous body. The UHPE porous sheet is obtained by forming the porous body into a sheet having a predetermined thickness by cutting. In this UHPE porous sheet, a plurality of UHPE particles are connected to each other, a porous structure is formed by voids between the particles, and the UHPE particles have a predetermined pore volume ratio. Incidentally, the porous structure,
It can be confirmed with an electron microscope or the like. The thickness of the UHPE porous sheet is usually in the range of 30 to 300 μm.

Since the UHPE porous sheet is hydrophobic, it is preferable to perform a hydrophilic treatment. Examples of the hydrophilic treatment include impregnation with a surfactant or a water-insoluble polymer, corona treatment, plasma treatment, sulfonation, and graft polymerization of a hydrophilic monomer.

[0018]

Next, examples will be described together with comparative examples.

(Example 1) UHPE powder a (molecular weight: 45)
100,000, melting point 135 ° C, average particle size 106μm) 1kg and U
1 kg of HPE powder b (molecular weight: 2,000,000, melting point: 135 ° C., average particle size: 30 μm) was mixed with a Hensyl mixer, and the mixture was filled in a shape retainer. The shape retainer is a metal cylindrical outer mold having a large number of holes with a polytetrafluoroethylene porous film adhered to the inner peripheral surface thereof, and is disposed at the bottom of the outer mold and fixed to fix the outer mold. It consists of a type.
The shape retainer was placed in a metal heat-resistant and pressure-resistant container (provided with a steam introduction pipe and an opening / closing valve thereof), and the atmospheric pressure was set to 1.3 kPa by a vacuum pump. The time required at this time was 30 minutes. Then, after stopping the pump, the on-off valve was opened, and steam (temperature 145 ° C., pressure 0.4MP
a) was introduced, and the mixture was heated and sintered for 1 hour. afterwards,
After cooling, a columnar porous body was obtained. The obtained porous body was cut with a cutting lathe to a thickness of 200 μm and a porosity of 55 μm.
% Of a UHPE porous sheet was obtained.

The battery separator was subjected to a hydrophilic treatment by a plasma treatment. The conditions for the plasma treatment are as follows: output: 0.5 W / cm ² , treatment time: 30 seconds, and introduced gas: oxygen.

Comparative Example 1 A battery separator having a porosity of 45% was obtained in the same manner as in Example 1 except that a UHPE porous sheet was prepared using only the UHPE powder a without using the UHPE powder b. . On the other hand, plasma treatment was performed in the same manner as in Example 1.

Comparative Example 2 A battery separator having a porosity of 50% was obtained in the same manner as in Example 1 except that a UHPE porous sheet was prepared using only the UHPE powder b without using the UHPE powder a. . On the other hand, plasma treatment was performed in the same manner as in Example 1.

The characteristics of each of the battery separators of Example 1 and Comparative Examples 1 and 2 thus obtained were examined by the following methods. The results are shown in Table 1 below. Further, the measurement results of the pore size distribution are shown in the graph of FIG. 1 for Example 1, the graph of FIG. 2 for Comparative Example 1, and the graph of FIG. 3 for Comparative Example 2.

(1) Measurement of Pore Size Distribution The pore size distribution was measured by a mercury porosimeter method using an autoscan mercury intrusion type pore distribution measuring device (Autoscan-33) manufactured by Yuasa Ionics Co., Ltd. In the pore size distribution measurement data, the pore size was 0.1 μm to 10 μm.
pore volume (V1) up to 0.1 m and pore diameter 0.1 μm to pore diameter 2
The ratio (V1 / V2) to the pore volume (V2) of 00 μm was determined.

(2) Porosity (Porosity) The measured values of the area (Scm ² ), film thickness (dcm), and weight (mg) of the sample (separator for battery) and the specific gravity of the material used (rg / cm ³⁾ ) Was calculated using the following equation.

Porosity (% by volume) = (1- (m / r) /
(S × d)) × 100

(3) Air permeability Air permeability was determined by measuring the amount of oxygen permeated through the battery separator under a pressure of 12.7 mmH ₂ O by a soap film flow method. At this time, the effective area of the film was 1.23 cm ² . The unit of air permeability is (cm ³ · cm) / (cm
² · Pa · sec).

(4) Alkaline Solution Permeation Rate The alkaline solution permeation rate of the battery separator was evaluated using an apparatus having the structure shown in FIG. That is, container 2
In it, put 7.2N KOH aqueous solution 3, and on top of this,
Scale 6 was placed. Then, the upper end of the sample (battery separator) 1 was fixed to the horizontal support bar 5 with a clip, and the lower end of the sample 1 was located at a depth of 1.0 cm below the surface of the KOH aqueous solution 3. 4 is a vertical support bar. In this state, leave Sample 1 for 30 minutes.
The suction height of the KOH aqueous solution after a lapse of minutes is measured on a scale 6, and this is measured by an alkali solution permeation rate (mm / 30 minutes).
And

[0029]

Table 1 Example 1 Comparative Example 1 Comparative Example 2 Film thickness (μm) 200 203 205 Porosity (%) 55 45 50 Air permeability 1.48 × 10 ^-3 2.46 × 10 ^-3 0.58 × 10 ^-3 Pore size distribution FIG. FIG. 2 FIG. 3 V1 / V2 0.26 0.04 0.61 Alkaline solution permeation rate 15 3 12

As shown in FIG. 1, the battery separator of Example 1 has a wide range of pore size distribution. Further, as shown in Table 1, the battery separator of Example 1 had a pore volume ratio (V1 / V2) within a predetermined range of the present invention,
It had excellent air permeability and alkali solution penetration rate. On the other hand, in the battery separator of Comparative Example 1, the pore size distribution was concentrated in the range where the pore size was large as shown in FIG. Further, as shown in Table 1 above, the battery separator of Comparative Example 1 was excellent in air permeability, but slow in permeation rate of the alkaline solution. Further, in the battery separator of Comparative Example 2, as shown in FIG. 3, the pore size distribution was concentrated in a range where the pore size was small. Further, as shown in Table 1, the battery separator of Comparative Example 2 had a high alkali solution permeation rate, but poor air permeability.

[0031]

As described above, the battery separator of the present invention has the original advantages of the UHPE porous sheet, and is excellent in air permeability and electrolyte permeability. Therefore, the battery separator of the present invention can be preferably used for, for example, an alkaline secondary battery for an electric vehicle that requires high performance.

[Brief description of the drawings]

FIG. 1 is a graph showing the pore size distribution of a battery separator according to one embodiment of the present invention.

FIG. 2 is a graph showing a pore size distribution of a battery separator of a comparative example.

FIG. 3 is a graph showing a pore size distribution of a battery separator of another comparative example.

FIG. 4 is a configuration diagram showing a configuration of an apparatus for measuring an alkali solution permeation rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery separator 2 Container 3 KOH aqueous solution 4 Vertical support bar 5 Horizontal support bar 6 Scale

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichi Moriyama 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Masakatsu Urari 1-1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. Within Nitto Denko Corporation (72) Inventor Akira Otani 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Inside Nitto Denko Corporation (72) Keiji Nakamoto 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Takashi Yamamura 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Satoshi Uda 555 Sakaijuku, Kosai-shi, Shizuoka Prefecture Panasonic Eve Energy Co., Ltd. (72) Inventor Noriyasu Morishita 555 Sakaijuku, Kosai-shi, Shizuoka Prefecture Inside Panasonic Eve Energy Co., Ltd. (72) Inventor Munehisa Ikoma Kosai, Shizuoka Prefecture Sakaijuku 555 address Panasonic Eevee Energy Co., Ltd. in the F-term (reference) 4F074 AA17 CA52 CC12Y DA24 DA49 5H021 BB00 BB01 EE03 EE04 HH02 HH03 HH07 5H028 AA05 BB05 BB06 HH05

Claims (5)

[Claims] 1. A battery separator using an ultra-high molecular weight polyethylene porous sheet, which has a porosity of 50% by volume or more and a pore size distribution of 0.001 μm to 10 μm in a pore size distribution of the porous sheet by a mercury porosimeter method. Pore volume (V1) and pore diameter 0.001 μm to pore diameter 2
Ratio (V1 / V2) to pore volume (V2) up to 00 μm
Is set in the range of 0.1 to 0.5. 2. The ultrahigh molecular weight polyethylene having a molecular weight of 5
2. The battery separator according to claim 1, wherein the range is from 10,000 to 16,000,000. 3. The battery separator according to claim 1, which is used for an alkaline secondary battery for an electric vehicle. 4. sintering ultra high molecular weight polyethylene powder,
A method for producing a battery separator in which the sintered body is formed into a sheet shape, wherein the ultrahigh molecular weight polyethylene powder is a mixture of two or more ultrahigh molecular weight polyethylene powders having different particle size distribution peaks. Manufacturing method of separators for automobiles. 5. The battery separator according to claim 4, wherein an ultrahigh molecular weight polyethylene powder having an average particle diameter of 10 to 50 μm and an ultrahigh molecular weight polyethylene powder having an average particle diameter of 60 to 200 μm are mixed and used. Method.