JPH1027598A - Battery separator, method of manufacturing the same, and battery using the same - Google Patents

Abstract

(57) [Problem] To provide a battery separator excellent in high-temperature film shape maintenance characteristics and self-closing property. SOLUTION: The film thickness is 2 to 60 μm, which is made of a substantially fluorine-free ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 1,500,000 or more and less than 4,000,000.
And the surface element composition ratio measured using ESCA is as follows: 0.01 <F / C <0.6 and 0.01 <O / C <5 A battery separator comprising a combination with a polyolefin resin nonwoven fabric to be filled and a method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator suitably used for a lithium secondary battery or the like, a method for manufacturing the same, and a battery using the same.

[0002]

2. Description of the Related Art With the development of portable small devices, small and high-performance batteries have been demanded. Lithium batteries have a high electromotive voltage by using lithium, which is the most basic metal, and are very useful as electrode materials for high-performance batteries. However, lithium is highly reactive and improper handling may cause the battery to burst. In the past, fires and other incidents have occurred in lithium batteries, and prevention of shortage is an important issue.

[0003] The separator of a lithium battery is formed of a porous membrane, interposed between a positive electrode and a negative electrode, and allows ions to pass between the positive electrode and the negative electrode but prevents physical contact between the positive electrode and the negative electrode. . The separator is required to maintain the film shape at a high temperature and to close the pores at a high temperature. In other words, if these are insufficient, when a large current flows in a short time due to an external short circuit accident or the like, the lithium battery generates heat, and the heat makes it impossible for the separator to maintain the membrane shape, and the positive electrode and the negative electrode are physically separated. Contact may cause an internal short circuit and cause an accident such as rupture. Therefore, the separator has a property that the pores of the separator are automatically closed by heat when the internal temperature of the battery rises (self-closing property) and a property that maintains the membrane shape and separates the electrodes even at high temperatures (high-temperature membrane). (Shape maintaining property) is required.

[0004]

The separator made of a polypropylene porous membrane is excellent in shape retention at high temperatures, but when used as a lithium battery separator, the temperature at which self-occluding property is about 175 ° C. Since the ignition temperature of lithium is close to 180 ° C., there is a problem of explosion if the self-blocking does not occur reliably in the event of a short circuit or the like. Also, in the separator membrane, usually stretched to improve the strength, the stretched membrane has a low high-temperature film shape retention characteristics low 150-160 ℃ for polyethylene, shrinkage or breakage near 180 ℃ for polypropylene made However, there is a possibility that a problem may occur in the isolation of the electrodes.

In order to solve this problem, it is known that a polyolefin microporous membrane and a polyolefin nonwoven fabric are laminated or combined and used as a separator (see, for example, JP-A-7-22014 and JP-A-7-22014). And polyolefin microporous membranes or nonwoven fabrics have good chemical resistance but are hydrophilic or poor in polarity. Therefore, they are used as they are in liquids with high surface tension, especially in aqueous electrolytes and lithium batteries. However, it is difficult to allow a non-aqueous electrolyte such as propylene carbonate to pass therethrough, and the electrolyte retention ability is lacking. As a method for solving this problem and improving the ability to hold an electrolyte, there is a method of applying a surfactant (for example, Japanese Patent Application Laid-Open No. 60-255107). Outflow is a problem. In addition, once dried, the solution no longer exhibits hydrophilicity, and is not a fundamental solution.

Further, there is a method of modifying the surface by plasma treatment. However, this method is difficult to uniformly treat a large material, and is unsuitable as a simple and general-purpose treatment which requires a high equipment cost. Also, after laminating or laminating a polyolefin microporous membrane and a polyolefin nonwoven fabric,
It is known that hydrophilization is carried out using a mixed gas of fluorine and oxygen (Japanese Patent Application Laid-Open No. Hei 7-272710). However, microporous polyolefin membranes treated with fluorine suffer from deterioration in elongation and strength, Since the optimum treatment conditions for the porous membrane and the nonwoven fabric are different, if the treatment is performed under conditions that provide sufficient hydrophilicity of the nonwoven fabric in the treatment of the integrated product, the elongation of the microporous membrane is sufficient for the production of the battery. There was a drawback that strength was difficult to obtain.

[0007]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by using a special porous membrane and a special nonwoven fabric as a battery separator, the low-temperature occluding property has been improved. The inventors have invented a separator which is highly satisfactory, has a high-temperature film shape maintaining property, does not cause a short circuit, and is extremely satisfactory as a separator.

[0008] That is, the gist of the present invention is to provide a polyethylene fine particle having a thickness of 2 to 60 µm and comprising a fluorine-free ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 1,500,000 or more and less than 4,000,000. A porous membrane,
The surface element composition ratio measured using ESCA is

[0009]

(2) a battery separator comprising a combination with a polyolefin resin nonwoven fabric satisfying the relational expressions of 0.01 <F / C <0.6 and 0.01 <O / C <5; and The present invention relates to a method for manufacturing the battery, and a battery using the same.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The polyethylene microporous membrane is generally, from a resin composition containing ultrahigh molecular weight polyethylene and a plasticizer, once melt-extruded a film or sheet, and then isopropanol, ethanol, and a plasticizer contained in the film or sheet. After being dissolved and removed with an organic solvent such as hexane, it is manufactured by stretching with a stretching machine such as a roll stretching machine or a tenter transverse stretching machine for improving mechanical strength.

As the ultra-high molecular weight polyethylene, an ethylene homopolymer having a melting temperature of 110 to 140 ° C. can be suitably used because of its easy melting deformation. As the molecular weight, the viscosity average molecular weight is 1,500,000 or more,
Ultra high molecular weight polyethylene of less than 00,000 is used. If the viscosity average molecular weight is 1,500,000 or less, micropores are difficult to be formed due to insufficient entanglement of the polyethylene chains, and the separator incorporated in the battery may generate heat due to self-heating in the battery or heat from the outside. When heated, for example, when heated to 180 ° C., it becomes difficult to maintain the shape of the separator. Conversely, if the viscosity average molecular weight is 4,000,000 or more, the flowability is too low, so that when heated, the pores of the separator are not blocked, and there is a risk of short-circuit and ignition of the battery.

As the plasticizer, various known plasticizers can be used as long as they have good compatibility with ultrahigh molecular weight polyethylene and do not evaporate during melt kneading or molding, for example, those having a boiling point higher than the melting temperature of ultrahigh molecular weight polyethylene. Can be used. Specifically, for example, paraffin wax which is solid at room temperature, or higher aliphatic alcohol such as stearyl alcohol or ceryl alcohol, or n which is liquid at room temperature
-Decane, n-alkanes such as n-dodecane, liquid paraffin, kerosene and the like. The usage ratio of the ultrahigh molecular weight polyethylene and the plasticizer is usually 5 to 60% by weight, preferably 10 to 50% by weight of the ultrahigh molecular weight polyethylene, and 40 to 95% by weight, preferably 90% by weight of the plasticizer.
-50% by weight.

The resin composition may contain various known additives such as an antioxidant in an amount of about 0.01 to 5% by weight in the resin composition. Each component of the resin composition is uniformly kneaded with a known single-screw or twin-screw extruder, and is melt-extruded. A biaxial extruder is preferably used in terms of extrusion amount, extrusion stability, and kneading strength. Melt extrusion is usually performed at a temperature of 140 to 240 ° C., and is extruded into a film or sheet at a thickness of 5 to 50 μm or 50 to 300 μm. After extruding, melt deformation may be performed. The melt deformation is performed by applying a deformation stress while keeping the resin composition constituting the extruded film or sheet in a molten state.
By melting and deforming, it is possible to obtain a porous resin molded article having a small residual stress and excellent heat-resistant film rupture properties. Usually, a deformation stress is applied while maintaining the temperature of the resin composition in a range of about 130 to 240 ° C., preferably 160 to 200 ° C. At this time, the deformation can be performed not only in one direction but also in multiple directions. Specifically, for example, in the case of applying a deformation in one direction, the gap of the die is increased in the T-die or inflation molding method, preferably in the inflation molding method, and the pulling speed is increased, that is, the draft ratio is increased. , A deformation is applied in the MD (machine) direction.
When deformation is applied in multiple directions, melting and deformation can be applied in the MD and TD (width) directions by increasing the draft rate and blow ratio in the inflation molding method.

After cooling the melt-deformed film or sheet, the plasticizer contained in the film or sheet is dissolved and removed by extraction with an organic solvent such as isopropanol, ethanol, hexane, etc. to make the film or sheet porous. I do. The thickness of the porous membrane is 2-60μ
m is good, and it is more preferably in the range of 15 to 60 μm. A film thinner than 2 μm has a small absolute strength, and is likely to be broken at the time of film formation, surface treatment, or lamination, or to be broken after battery processing. On the other hand, if the film thickness exceeds 60 μm, the water permeability may decrease, or the ratio of the separator in the battery may increase, resulting in a decrease in the capacity of the battery.

Fluorine treatment of a microporous polyethylene membrane is not preferred because the strength is reduced. On the other hand, in the case of the polyolefin resin nonwoven fabric, when the F / C value in ESCA measurement is 0.01 or less, the effect of the surface treatment for lyophilicity is insufficient.
Conversely, the effect of water repellency increases. When the O / C value in the ESCA measurement is 0.01 or less, the amount of oxygen existing on the outermost surface is too small to obtain sufficient wetting with the electrolytic solution. The effect is too large and causes a reduction in strength.

The material of the nonwoven fabric used in the present invention includes polyethylene (PE), polypropylene (P
P) and polyvinyl acetate (PV)
AC), a polyolefin resin containing polyvinyl alcohol (PVA) or the like, or an ethylene-vinyl acetate copolymer (EVA) or a saponified product of EVA (EV
OH) is used at 0.1 to 90%, preferably about 0.1 to 75% of the fiber surface.

The fiber diameter of the polyolefin resin nonwoven fabric is preferably 0.1 to 5 denier, and the basis weight is preferably 5 to 100 g / m ² . Various shapes can be used as the nonwoven fabric fiber. Those using microporous fibers or those combining two or more types of fibers with different fiber diameters,
Alternatively, a nonwoven fabric having a two-layer or three-layer structure can be used. Above all, a nonwoven fabric in which the outer layer is made of a sheath-core fiber whose main component is polyethylene and the middle core is polypropylene, and the thickness of the nonwoven fabric is in the range of 10 to 100 μm, is preferably used. A film thinner than 10 μm has a small absolute strength, and is likely to be broken at the time of film formation, surface treatment, or lamination, or to be broken after battery processing. On the other hand, when the thickness exceeds 100 μm, the ratio of the separator in the battery becomes large, and the capacity of the battery may be reduced. Further, if the film thickness changes, the electric resistance and eventually the electric capacity of the battery as a whole may change. Therefore, the film thickness is preferably as constant as possible. In terms of ease of handling, etc., those coated with oils such as polyethylene oxide and polyacrylamide,
Further, a cationic or nonionic surfactant may be applied before or after the hydrophilic treatment.

The method for obtaining the battery separator of the present invention is not particularly limited. For example, it can be obtained by treating a polyolefin resin nonwoven fabric with a mixed gas containing a fluorine gas and an oxygen gas. The water content of the polyolefin resin nonwoven fabric when performing such a treatment is 5
It is preferably at most 00 ppm, more preferably 3 ppm.
It is not more than 00 ppm. If the water content is more than 500 ppm, fluorine is wasted by the reaction with water, and the treatment effect becomes insufficient because fluorine effective for the reaction is reduced, and sufficient hydrophilic performance as a separator cannot be obtained. .

As a simple and effective method for producing a separator having characteristics such as high electrolyte retention ability, the present invention employs a method of contacting with a gas containing specific amounts of fluorine (F2) and oxygen (O2). Preferably adopted. Hereinafter, such contact processing will be described. First, the partial pressure of fluorine in the processing gas is preferably 1 to 500 mmHg, more preferably 5 to 50 mmHg. When the partial pressure of fluorine is less than the lower limit, the reaction between the fluorine and the separator is insufficient, so that the effect of the surface treatment becomes insufficient or the treatment unevenness occurs, which is not preferable. In addition, if the upper limit is exceeded, excessive reaction occurs,
This is not preferable because the effect of hydrophilicity is reduced or the mechanical strength is severely impaired.

Further, oxygen needs to coexist in the processing gas, and the content in the mixed gas containing fluorine is usually 100 mmHg or more, preferably 200 mmHg to 750 mmHg.
In addition, it may be diluted with an inert gas such as nitrogen, carbon dioxide or argon. As the amount of dilution gas used,
Up to about 85 vol%, usually 1 to 70 vol%. The temperature when treating the separator with this mixed gas is usually -50 to 90 ° C,
The range is preferably from 0 to 60 ° C, more preferably from 10 to 40 ° C.

The processing time is appropriately selected from a wide range, usually from 1 second to 10 days, preferably from 1 second to 3 hours. If the time is less than 1 second, the reaction is insufficient and the effect of the present invention cannot be sufficiently obtained. The method for bringing the raw material cloth of the battery separator into contact with the mixed gas of fluorine and oxygen is not particularly limited, and examples thereof include a batch processing method and a continuous processing method. As a batch-type treatment method, there is a method in which a raw material cloth is placed in a closed reaction vessel, and the gas in the container is replaced with a gas containing fluorine and oxygen to contact the raw cloth. On the other hand, as a continuous treatment method, there is a method in which treatment is performed by passing a mixed gas atmosphere containing fluorine and oxygen through a separator. In this case, a gas containing fluorine and oxygen is put in a closed container, and an inlet and an outlet are provided so that the gas inside does not leak outside. Alternatively, the contact treatment can be carried out by using a device in which fluorine is prevented from leaking by lowering the partial pressure of fluorine or using a method such as an air curtain.

The total pressure during the contact treatment of the separator containing the fluorine-containing gas mixture with the raw material cloth in this treatment may be atmospheric pressure, negative pressure or positive pressure. In any case, it suffices that the partial pressures of fluorine and oxygen in the mixed gas containing fluorine satisfy predetermined conditions. The fluorine used in the present invention is usually obtained by electrolysis of hydrogen fluoride. Fluorine obtained by such electrolysis may be used directly for fluorine treatment, fluorine or fluorine and other gas,
For example, it may be used by being guided from a cylinder filled with a gas mixture with nitrogen or the like.

In the present invention, the amount of adhered fluorine removed by immersion in water is preferably 0.005 wt% or less. That is, the fact that the amount of adhered fluorine removed by immersion in water is 0.005 wt% or less indicates that the amount of eluted fluorine when immersed in the electrolytic solution is extremely small. Usually, 0.001 to 0.05 wt% by hydrophilizing the surface with fluorine and oxygen containing gas.
There is some degree of adhesion or adsorption of fluorine. However,
Such adhered fluorine is sucked by an operator when performing a battery assembling operation or the like, and becomes a cause of harm to health.

[0024] When the amount of attached fluorine is 0.005% by weight or less, preferably 0.002% by weight or less, such a problem is considerably solved. Examples of such a defluorination method include a method of performing a hot water washing treatment at about 0 ° C. to 100 ° C. for about 1 second to about 1 hour, preferably at a temperature of 50 ° C. to 70 ° C. for 1 to 5 minutes, a method of blowing with nitrogen, air, or the like. No. Further, in the case of washing using a solvent such as hot water or alcohol, it is necessary to subsequently dry the solvent.
1 to 30 hours at about 100 to 100 ° C., preferably 50 to 100 ° C.
Dry at 70 ° C. for about 1 minute to 10 hours.

As the method of combining the polyethylene microporous membrane and the polyolefin resin nonwoven fabric, a bag-shaped polyolefin resin nonwoven fabric for enclosing the positive electrode and a polyethylene microporous membrane for sandwiching between the bag-shaped nonwoven fabric and the negative electrode are used. Method, a polyolefin-based resin nonwoven fabric and a polyethylene microporous membrane laminated on each other are formed into a bag shape for enclosing the positive electrode, and a method using a polyethylene microporous membrane for sandwiching between the negative electrode and the nonwoven fabric. Laminating with a microporous membrane after the hydrophilization treatment, a method of interposing by winding between the positive electrode and the negative electrode, only the positive electrode,
Alternatively, wrap both electrodes in a bag-shaped microporous membrane and wrap it further in a bag-shaped nonwoven fabric, or conversely, wrap each electrode in a nonwoven fabric first, and then wrap it in a microporous membrane. And a method using a microporous membrane and a third layer other than the non-woven fabric. The former is particularly preferable.

Thus, a combination of a microporous polyethylene film having a specific molecular weight, an electrolyte solution having a surface element composition ratio measured by ESCA within a specific range, and a polyolefin resin nonwoven fabric exhibiting good wettability is obtained by combining By using, a battery separator having excellent physical properties having both high electrolyte retention ability and short-circuit prevention property is obtained, and by using such a separator, safety as a battery and charge / discharge cycle characteristics are significantly improved. .

As a battery using the above-mentioned battery separator, a nickel-cadmium battery, a nickel-hydrogen battery, a lithium secondary battery, and the like can be used, and particularly, a lithium secondary battery is preferable. For example, in the case of a lithium secondary battery, lithium metal, an alloy of lithium and aluminum, or a carbon electrode capable of absorbing and releasing lithium ions is used as a negative electrode, and a known electrode such as manganese dioxide is used as a positive electrode. Used. As the shape of the battery, for example, a microporous membrane and a nonwoven fabric are subjected to a hydrophilic treatment, then laminated, wound around between a positive electrode and a negative electrode, each electrode is wrapped in a bag-shaped microporous membrane, and further A battery sealed in a bag-shaped nonwoven fabric, or conversely, each electrode is first wrapped in a nonwoven fabric, and further wrapped in a microporous membrane and stored in a case together with an electrolytic solution can be exemplified. In the case of a lithium secondary battery, ethylene carbonate (E
C), a non-aqueous solution in which an electrolyte such as LiPF ₆ is dissolved in an aprotic polar solvent such as dimethyl carbonate (DMC) is used.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the present invention. In the following examples, each measurement was performed by the following method. (1) Absorption height of electrolyte solution A sample was cut into a strip having a width of 15 mm and a length of 250 mm, and the sample end was immersed in the electrolyte solution at room temperature, and the absorption height after 30 minutes was measured. (2) ESCA measurement The binding energy of the surface F _1S measured by ESCA was PE
RKIN ELMERPHI, ESCA-5500
Using MC, the source was set to 14 kV,
It is measured under the conditions of 50 W (using a monochromator) and an extraction angle of 65 degrees. The surface element composition ratio was calculated from the peak area of each element and the sensitivity coefficient.

(3) Method of measuring the amount of adhering fluorine About 0.2 g of a sample is immersed in 10 ml of pure water, and ultrasonic extraction is performed
After a period of time, the amount of fluorine in the extract is determined using an ion chromatograph. The ion chromatograph uses Dionex DX-100, and the column is IC
The measurement was carried out at 4.4 mM Na ₂ CO ₃ /1.2 mM NaHCO ₃ as eluent, at 25 mM H ₂ SO _{4 as} the eluent, and at a flow rate of 1.5 cc / min. (4) Pin stab strength According to Japanese Agriculture and Forestry Standard Notification No. 1019, pin stab strength is 300m
It was measured at m / min. The measured value is 25 μm for comparison.
m. (5) Air permeability According to JIS L1096-1979, the air permeability was measured by an air permeability tester manufactured by Toyo Seiki Seisaku-sho, Ltd.

Example 1 25 parts by weight of ultrahigh molecular weight polyethylene powder having a melting point of 135 ° C. and a viscosity average molecular weight of 2.5 million and stearyl alcohol 7
5 parts by weight are fed to a 50 mmφ twin screw extruder, continuously extruded from an inflation die having a die diameter of 40 mm while kneading at 200 ° C., and a take-up speed of 10 mm / min (die temperature 17
The film was taken up at 0 ° C. and a draft rate of Dr 17.6) and melt-deformed at a blow ratio (BUR) of 5.5 to obtain a sheet having a thickness of 52 μm. This sheet was immersed in isopropyl alcohol at 60 ° C. to extract stearyl alcohol, and heat-treated with a heated pinch roll having a surface temperature of 125 ° C.
An 8 μm polyethylene microporous membrane was obtained. The pin puncture strength of this microporous membrane was 180 g / 25 μm.

On the other hand, in a reactor which is resistant to fluorine and can be rolled inside by setting a roll,
PE / PP fiber nonwoven fabric roll of 50 g width x 300 m with a basis weight of 15 g / m ² and a thickness of 60 μm composed of PE / PP sheath / core structure fibers
Length), and after evacuation, a mixed gas having a partial pressure ratio of fluorine (F ₂ ) / oxygen (O ₂ ) / nitrogen (N ₂ ) = 5/660/95 mmHg was introduced to 760 mmHg. Nonwoven was treated (at atmospheric pressure by opening the exhaust _line), F ₂ while changing the winding at a line speed of 10m / min 400cc / min feed while at room temperature, after completion of changing winding, the mixed gas was evacuated, then Nitrogen gas was introduced to 760 mmHg. After that, remove the sample,
The surface adsorbed fluorine was removed by washing with hot water and drying. Washing conditions were 50 ° C. for 2 minutes in deionized water. For drying, hot air drying was performed at 80 ° C. for 2 minutes. F in surface ESCA measurement
_From the peak area ratios of _1S , O _1S and C _1S , the surface element composition ratio F /
When the values of C and O / C were measured, they were 0.12, 0.
A value of 17 was obtained. When the amount of attached fluorine was measured by ion chromatography, it was found to be 0.002 wt%.
Was obtained. Further, the electrolytic solution (EC / DMC (1 /
When the liquid absorption height of 1), LiPF ₆ (1M)) was measured, a value of 8 mm was obtained after 30 minutes. In addition, a value of air permeability of 400 cm ³ / cm ² / sec or more was obtained.

The above polyethylene microporous membrane and hydrophilized nonwoven fabric sample were treated at 100 ° C. for 60 hours in a nitrogen atmosphere.
After the heat treatment, the pin puncture strength of the microporous polyethylene film and the air permeability of the polyolefin resin nonwoven fabric were measured.
0g / 25μm, air permeability of polyolefin resin non-woven fabric is
Again, it was 400 cm ³ / cm ² / sec or more.

Comparative Example 1 The same microporous membrane as in Example 1 was placed in a reactor resistant to fluorine, evacuated, and then subjected to fluorine (F ₂ ) / oxygen (O ₂ ).
A mixed gas having a partial pressure ratio of ₂ ) / nitrogen (N ₂ ) = 0.2 / 660 / 99.8 mmHg was introduced to 760 mmHg. After standing at room temperature for 1 minute,
The mixed gas is evacuated, and then nitrogen gas is introduced to 760 m
mHg. Thereafter, the sample was taken out, and the surface adsorbed fluorine was removed by washing with hot water and drying. Washing conditions are 50 ° C. for 1 minute while irradiating ultrasonic waves in deionized water. Drying was performed by air drying at room temperature for 3 hours and then hot air drying at 50 ° C. for 7 hours. The values of the surface element composition ratios F / C and O / C at the outermost surface (analysis depth of about 50 Å) were determined from the peak area ratios of F _1S , O _1S , and C _1S in the ESCA measurement of the surface.
A value of 0.10 was obtained. When the amount of attached fluorine was measured by ion chromatography, it was found to be 0.001 wt%.
Was obtained. Further, the electrolytic solution (EC / DMC (1 /
When the liquid absorption height of 1), LiPF ₆ (1M)) was measured, a value of 10 mm was obtained after 30 minutes. The above polyethylene microporous membrane was treated at 100 ° C. in a nitrogen atmosphere at 60 ° C.
After the partial heat treatment, the pin piercing strength was measured.
A value of g / 25 μm was obtained.

Comparative Example 2 The same microporous film not treated with fluorine and a nonwoven fabric as in Example 1 were laminated, and thermocompression-bonded with a roll heated to 140 ° C. to obtain a laminated film. The laminate film is placed in a reactor resistant to fluorine, evacuated, and a mixed gas having a partial pressure ratio of fluorine (F ₂ ) / oxygen (O ₂ ) / nitrogen (N ₂ ) = 10/660/90 mmHg. To 760 mmHg. After standing at room temperature for 5 minutes, the mixed gas was evacuated, and then nitrogen gas was introduced to 760 mmHg. Thereafter, the sample was taken out, and the values of the surface element composition ratios F / C and O / C of the polyolefin resin nonwoven fabric were calculated from the peak area ratios of F _1S , O _1S , and C _1S in the ESCA measurement of the surface.
A value of 5,0.24 was obtained. On the other hand, when the values of the surface element composition ratios F / C and O / C of the polyethylene microporous membrane were calculated to be 0.42 and 0.04, respectively, the surface of the microporous membrane became partly wrinkled brown. Site was seen. When the amount of attached fluorine was measured by ion chromatography, a value of 0.01 wt% was obtained. Further, an electrolytic solution (EC / DMC (1/1), LiPF ₆ (1
When the liquid absorption height of M)) was measured, a value of 7 mm was obtained only in the nonwoven fabric portion after 30 minutes, but 1 m in the microporous membrane portion.
m.

The above polyethylene microporous membrane and hydrophilized nonwoven fabric sample were treated at 100 ° C. for 60 hours in a nitrogen atmosphere.
After the heat treatment, the pin piercing strength of the microporous polyethylene membrane, the air permeability and the liquid absorption rate of the electrolytic solution of the polyolefin resin nonwoven fabric were measured, and the pin piercing strength of the microporous membrane was 5 g / 25 μm. The air permeability was 400 cm ³ / cm ² / sec, but the absorption rate of the electrolyte was only 2 mm after 30 minutes.

[0036]

The battery separator of the present invention has a high degree of lyophilicity and anti-short-circuit property, which has never been seen in the prior art, and the battery using it has high industrial value.

Continued on the front page (72) Inventor Akira Watanabe 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Institute (72) Inventor Bunichiro Oshima 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Inside Yokohama Research Institute

Claims (9)

[Claims] An ultra-high molecular weight polyethylene having a viscosity average molecular weight of not less than 1,500,000 and less than 4,000,000 and containing substantially no fluorine and having a thickness of 2 to 60 μm.
And the surface element composition ratio measured using ESCA is as follows: 0.01 <F / C <0.6 and 0.01 <O / C <5 A battery separator comprising a combination with a polyolefin resin nonwoven fabric to be filled. 2. A combination of the polyolefin resin nonwoven fabric processed into a bag shape for enclosing the positive electrode and a polyethylene microporous membrane for sandwiching between the bag-shaped polyolefin resin nonwoven fabric enclosing the positive electrode and the negative electrode. The battery separator according to claim 1. 3. A polyolefin resin nonwoven fabric and a microporous polyethylene film laminated on each other are processed into a bag shape for enclosing the positive electrode, and a microporous polyethylene film for sandwiching between the bag and the negative electrode. The battery separator according to claim 1, comprising a combination of: 4. A polyolefin resin nonwoven fabric having a basis weight of 5
4 to 100 g / m ² , a fiber diameter of 0.1 to 5 denier, an outer layer mainly composed of polyethylene and polypropylene fibers, and a film thickness of 10 to 100 μm. The battery separator according to the item. 5. The battery separator according to claim 1, wherein the amount of attached fluorine removed when immersed in water is 0.005 wt% or less. 6. The polyolefin resin nonwoven fabric is subjected to a contact treatment with a mixed gas containing a fluorine gas and an oxygen gas, then subjected to a washing and drying treatment, and then combined with a microporous polyethylene membrane. A method for producing the battery separator according to any one of claims 1 to 5. 7. A contact treatment of a polyolefin resin nonwoven fabric with a mixed gas having a partial pressure of fluorine of 1 to 100 mmHg.
3. The method for producing a battery separator according to item 1. 8. The partial pressure of oxygen in the mixed gas is 100 to 759.
The method for producing a battery separator according to claim 6, wherein the battery separator is mmHg. 9. A battery using the battery separator according to any one of claims 1 to 5.