JPH0275151A - Battery separator, its manufacturing method, and lithium battery using the battery separator - Google Patents

Abstract

PURPOSE:To form a lithium battery with special separators by stretching polypropylene in a specified medium, at a certain stretch strain velocity, and under specified temp. conditions, thereby forming voids in this material, and by using it to separators. CONSTITUTION:Stretched polypropylene is accomplished by the following two methods in the form of a film having a group of unstretched planes approx. oriented perpendicular to the stretching direction, a group of fibrils in continuity in the stretching direction between these unstretched planes, and a number of fine pore groups assuming approx. uniform shape expanding approx. two- dimensionally in the voids between the fibrils, wherein the share of voids shall exceed 45%. According to No.1 manufacturing method as mentioned, stretching is performed at a temp. approx. 50 deg. higher than the seathing point of the medium under -70 deg.C in the medium of nitrogen, etc., and according to No. 2 method, at a high temp. between 110-155 deg.C with the stretching strain speed below 10%/min. This porous polypropylene excels in maintaining the electrolytic liquid and electrolytes and allows cutting into different shapes to be used conveniently for forming of a battery.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a battery separator using an improved porous polypropylene film, a method for manufacturing the separator, and a lithium battery using the separator.

[Prior Art] As battery separators, synthetic resin nonwoven fabrics, glass #i fiber nonwoven fabrics, and the like are generally used.

BACKGROUND ART In recent years, electronic devices have rapidly become portable, smaller, lighter, thinner, and cart-like, and the batteries used as their power sources are also required to have higher energy density and be thinner. To this end, improvements have been made to separators in battery elements. That is,
In order to meet the demands for improving battery performance and making batteries thinner by increasing the amount of active material and reducing internal resistance, methods of using porous films as battery separators have been reported. for example,
JP-A-62-222562, JP-A-63-126
No. 159 and the like discloses a method in which a microporous polypropylene film is used as a separator and impregnated with a liquid electrolyte or a semi-solid electrolyte.

[Problems to be Solved by the Invention] However, the microporous polypropylene films used in these examples have a porosity of about 45% at most. These conventional methods for producing porous polypropylene films are disclosed, for example, in Japanese Patent Publication No. 46-40119.
Publication No. 50-2176, Special Publication No. 55-3
It is disclosed in Publication No. 2531 and the like. In most of the porous thermoplastic resin films and their manufacturing methods disclosed in the above-mentioned publications, a molded polypropylene film is first heat-treated, and then the film is heated at around room temperature or at a temperature higher than the secondary transition temperature of the thermoplastic resin used. The basic method is to stretch at a temperature of - to generate pores to form a porous body, and then to stretch again at a higher temperature and heat-set the formed pores again. be. However, the porous polypropylene film obtained by the above method cannot sufficiently retain electrolyte due to its low porosity.
In addition, since the area where ion conduction is possible is small, the internal resistance is high, and batteries using this as a separator have a problem of low performance.

In addition, when trying to increase the above-mentioned porosity using the conventional manufacturing method of porous polypropylene film, the pores formed become uneven, and when used for battery separators, fine powder in the electrode active material passes through the separator. There was a risk that it would come into contact with the counter electrode and impair battery performance.

Therefore, an object of the present invention is to provide a battery separator that exhibits excellent properties using an improved porous polypropylene film that has a uniform pore size distribution even when the porosity is increased, and a lithium battery using the same. There is a particular thing.

[Means for Solving the Problems] That is, according to the present invention, there is provided a battery separator comprising a porous polypropylene film having a large number of micropores obtained by stretching polypropylene, the porous polypropylene film comprising: A group of unstretched plate-like planes that run at approximately predetermined intervals perpendicular to the stretching direction of the film and are formed approximately parallel to a cross section perpendicular to the stretching direction of the film, and It is formed by a group of relatively thin fibrils that are stretched and oriented to run approximately parallel to the stretching direction and at approximately predetermined intervals and that are connected between the plate-like planes, and the gaps between the thin fibrils that are connected between the plate-like planes expand approximately two-dimensionally. A large number of micropores having a substantially uniform shape are formed, most of the micropores are through holes and have a substantially uniform diameter, and the porosity of the film is 45% or more. A battery separator having the above characteristics and a lithium battery using the battery separator are provided.

The method for manufacturing the battery separator includes stretching polypropylene in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane, and ethane, and at a stretching temperature of -70°C. ℃ or lower, and a low temperature range from the freezing point of the medium to a temperature 50℃ higher than the temperature of the medium (first method);
Alternatively, there is provided a method (second method) in which the polypropylene stretching step is carried out at a high temperature range of 110° C. to 155° C. at a drawing strain rate of less than io%/min without performing it at room temperature in advance.

Note that an example of the structure of the lithium battery of the present invention is as follows. Note that the constituent materials are not limited to these examples.

As the electrolyte diaphragm, the above porous polypropylene film impregnated with a liquid electrolyte or a gel electrolyte is used.

The liquid electrolyte used is one in which a lithium ion salt is dissolved in a non-aqueous solvent.

Examples of non-aqueous solvents include propylene carbonate, γ-
Examples include butyrolactone, dimethoxyethane, dioxolane, tetrahydrofuran, dimethyl sulfoxide, ethylene carbonate, acetonitrile, sulfolane, low molecular weight liquid polyethylene oxide, and terminal alkyl etherified products thereof. These may be used in combination.

In the present invention, examples of lithium ion salts include L
iC104, LiB (C, H5) 4.1 words CF35O:
There are l, 1.1PF6, etc. These may be used in combination.

The gel electrolyte is obtained by mixing the above-mentioned liquid electrolyte with a polymer material and forming a gel. Examples of polymeric materials include:
Examples include polyethylene oxide, polymethacrylate, polymers of acryloyl-modified polyethylene oxide, polyvinylidene fluoride, polyvinyl methyl ether, polyacrylonitrile, and copolymers thereof.

Examples of the negative electrode active material in the present invention include lithium and lithium alloys, such as alloys of lithium and aluminum, mercury, zinc, and the like.

In addition, as the positive electrode active material, for example, manganese dioxide,
Examples include molybdenum trioxide, vanadium pentoxide, titanium, or niobium sulfide, chromium oxide, copper oxide,
These active materials are further mixed with graphite as a conductive agent and, if necessary, a binder such as polytetrafluoroethylene, and then press-molded and used as a positive electrode plate.

The separator of the present invention is made of polypropylene film and has excellent chemical resistance, so it can be widely applied to, for example, alkaline dry batteries and lithium batteries. Also,
It is cut into various shapes depending on the shape of the battery used. An electrolytic solution, gel electrolyte, solid polymer electrolyte, etc. is impregnated or combined and sandwiched between the positive and negative electrodes of a battery to prevent short circuits between the two electrodes and to provide ionic conduction functions.

The porous polypropylene film of the present invention has a higher porosity, more uniform shape and pore diameter, and has more through holes than conventional films, so it has excellent functions as a separator.

When the porosity of the film is less than 45%, ion permeability decreases and internal resistance increases. In addition, when attempting to increase the porosity, conventional manufacturing methods result in nonuniform pore diameters, whereas the porous polypropylene film of the present invention maintains uniformity in pore diameters and functions as an excellent separator. show.

The method for producing a porous polypropylene film in the present invention will be explained below.

Since the production method of the present invention is completely different from the conventional method in terms of the conditions for making it porous, there are no particular restrictions on the polypropylene used, and propylene homopolymers and polypropylene with other polymers or oligomers are used. Block copolymers, random copolymers of propylene and other monomers or oligomers (in the present invention, when described as polypropylene without any particular limitation, the expression polypropylene is a general term for these copolymers) ) can be used. What can be used as monomers or oligomers for delivery is not limited as long as copolymerization is possible, and examples include ethylene or oligomers derived from ethylene.

In addition, polypropylene containing additives (materials) such as plasticizers, colorants, flame retardants, and fillers can also be used.

First, the polypropylene resin as described above is molded according to a known film manufacturing method to obtain an unstretched polypropylene film. Examples of film manufacturing methods that can be used include a blown film molding method, a T-die film molding method, and the like. Molding conditions in such a molding method can be appropriately selected from known techniques.

For example, the film forming temperature can be within a range above the temperature at which the polypropylene used can be discharged and below the thermal decomposition temperature of the polypropylene. Normally 170-300℃1 Preferably 190℃
~270°C.

Moreover, there is no particular limitation on the elastic recovery rate (or draft ratio) of the unstretched polypropylene film obtained by molding. However, when using an unstretched polypropylene film with an elastic recovery rate (or draft ratio) of zero (%) or extremely low, that is, an unstretched polypropylene film with extremely low crystal orientation, the stretching process of the present invention cannot be applied. However, it may be difficult to provide the resulting porous film with satisfactory properties. Therefore, it is preferable to set the forming conditions for the unstretched film in consideration of the characteristics such as the porosity and the average diameter of the fine pores of the porous polypropylene film to be obtained.

As mentioned above, there is no particular limit to the elastic recovery rate of an unstretched polypropylene film, but for the reasons stated in section 2, the elasticity of an unstretched polypropylene film at 50% elongation at 25° C. and 65% relative humidity is expressed by the following formula. Recovery rate is 20%
It is preferably 30 to 95, and considering the productivity when using normal molding equipment.
Particularly preferred is a range of %.

Elastic recovery rate (%) = [length at elongation - length after elongation] ÷
[Length when stretched - Length of original film] It is desirable that the ratio between the take-up speed and the discharge speed from the die (take-up speed/discharge speed) is in the range of lO to 6000.

The unstretched polypropylene film may be heat treated before being subjected to the stretching process. By performing this heat treatment before stretching, the crystallinity of the unstretched polypropylene film can be improved, so that the properties of the porous polypropylene film obtained by stretching are further improved.

The above heat treatment is carried out by heating the unstretched polypropylene film in air heated to, for example, 100 to 155°C for 3 seconds or more.

The stretching step of the present invention is carried out by one of the following methods.

(2) The stretching process is carried out in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, and at a temperature below -70°C, from the freezing point of the medium. The stretching process is carried out at a low temperature of 50°C higher than the boiling point of the medium, or
The stretching is carried out at a high temperature range of 155°C to 155°C and at a stretching strain rate of less than 10%/min.

First, method (■) will be explained.

In this cryogenic stretching step (2), the above-mentioned media can be used alone or in combination.

Examples of preferable stretching temperatures when using the above medium are -209°C to -146°C when nitrogen is used, and -218°C to -132°C when oxygen is used.
range, -1899C to - when using argon
In the range of 140℃, -20 when using carbon monoxide
In the range of 5℃ to -141℃, when using methane, -
The range is from 182°C to -111°C, and when ethane is used, it is from -183°C to -70°C. Stretching temperature: -70
When the temperature is higher than 0.degree. C., for example, when an unstretched film with a low elastic recovery rate is used, the effective rate of formation of pores by stretching becomes low.

In addition, in the method (2), the term 50°C higher than the boiling point or less does not mean a temperature range that is exactly 50°C higher than the boiling point or lower, but a temperature that is approximately 50°C higher than the boiling point or lower. .

Under such extremely low temperatures, the medium is in a liquid, liquid/gas, or gaseous state, and this stretching step can be carried out regardless of whether the medium is in any of the above states.

It is presumed that the above-mentioned stretching occurs because a crazing effect appears when the medium is stretched at extremely low temperatures. In ordinary media other than those mentioned above, polypropylene films become glassy at extremely low temperatures and are cut without elongation and no crazing action occurs.

The cryogenic stretching temperature is -706C or lower, and can be carried out in the range from the freezing point of the medium used to 50℃ higher than the boiling point, but in general, stretching is carried out at a temperature near the boiling point of the low-temperature liquid. It is advantageous to carry out the process at a certain temperature in terms of manufacturing control and making the properties of the resulting porous polypropylene film constant.

The stretching ratio in the above-mentioned cryogenic stretching step is generally a value in the range of 1 to 200% relative to the unstretched polypropylene film. However, the preferred stretching ratio is 10 to 150%.
is a value in the range of . At stretching ratios within these ranges, the number of pores tends to increase as the stretching ratio increases, and by taking advantage of this tendency, the average pore diameter and porosity of the resulting porous polypropylene film can be adjusted to suit the purpose. It is also possible to do so.

The cryogenic stretching process described above can be repeated two or more times until the desired average pore diameter and porosity are obtained.

Unlike the conventional stretching process near room temperature, making polypropylene film porous by using the stretching process under cooling at extremely low temperatures in the specific medium mentioned above is different from the conventional stretching process at around room temperature. The elastic recovery rate of
It works effectively even on polypropylene films of less than 30%, and can produce excellent porous polypropylene films with uniform pores and high porosity.

It is preferable that the polypropylene film made porous through the stretching process at an extremely low temperature in the specified medium described in 2 above is then subjected to a heat setting treatment. The main purpose of this heat setting treatment is to heat set the fine pores that have been formed. This heat setting treatment is performed to make the polypropylene film porous while maintaining its stretched state at extremely low temperatures, usually at 110 to 165 degrees Celsius, preferably at 130 to 15 degrees Celsius.
This is carried out by heating for 3 seconds or more in air heated to 5°C.

In addition, if the heating temperature is significantly higher than the upper limit of the listed temperature, the formed micropores may close, and
If the temperature is significantly lower than the lower limit or the heating time is shorter than 3 seconds, heat fixation tends to be insufficient, the formed through holes may close later, and heat shrinkage may occur due to temperature changes during use. It becomes easier to do. The cryogenic stretching and heat setting treatments described above can be repeated until a desired average pore diameter and porosity are obtained. That is, the temperature of the film can be returned to room temperature and subjected to a process including repeated cryogenic stretching (and heat setting treatment). By repeating cryogenic stretching, the number of through holes formed can be increased, and the average through hole diameter can be increased.

The porous polypropylene film prepared as described above has a large average pore diameter and a high porosity and exhibits good properties. This further improves its characteristics.

The hot stretching process of the polypropylene film, which has been rendered porous through at least one stretching process at a cryogenic temperature, is carried out as follows. This hot stretching process is carried out mainly for the purpose of expanding the diameter of the fine holes formed at extremely low temperatures. This hot stretching step is carried out by stretching the porous polypropylene film in air heated to 80 to 160°C, preferably 110 to 155°C. If the heating temperature is higher than the upper limit of the above temperature, the formed micropores may close, and if the temperature is lower than the lower limit, the pore diameter may not be expanded sufficiently by stretching. There is.

The stretching ratio in this hot stretching step is usually 10 to 700%, preferably 50 to 550% of the film length (initial length) before the cryogenic stretching step.

If the stretching ratio is lower than 10%, the expansion of the pores may be insufficient, and if it is higher than 700%, the film may be cut.

Note that this hot stretching step is performed alternately with the above-mentioned cryogenic stretching step, or after completing at least one cryogenic stretching step.

Next, the stretching method (2) in the present invention will be explained.

The stretching step in this case is carried out at a temperature range of 110 to 155°C, preferably 110 to 145°C, at a stretching strain rate of less than 10%/min.

If stretching is carried out at a temperature below 110°C, only a film with a small pore diameter can be obtained, or the film may be cut at a small stretching ratio, resulting in a film with a small porosity.

Furthermore, if stretching is carried out at a temperature exceeding 155°C, the thickness or width of the film may become thinner, the polypropylene may melt or partially melt, and pores may not be formed or only small pores may be obtained. happen.

On the other hand, if the stretching strain rate is 10%/min or more, only small pores or no pores may be obtained.

When the stretching strain rate is less than 10%/min, the average pore diameter and porosity of the through holes increase in accordance with the stretching ratio.

The stretching ratio can be changed depending on the average pore diameter of the pores depending on the intended use of the porous polypropylene film. The stretching ratio is 100 to 700%, preferably 15% to the initial length of the unstretched polypropylene film.
It is 0-600%. If the stretching ratio is higher than 700%,
The film may be cut.

It is preferable that the polypropylene film made porous through the stretching process described above is then subjected to heat treatment. The main purpose of this heat treatment is heat fixation to maintain the formed fine pores. This heat treatment
The polypropylene film made porous while maintaining the stretched state is heated to 110 to 155°C, preferably 130 to 15°C.
This is carried out by heating in air heated to 5° C. for 3 seconds. If the heating temperature is higher than 155°C, the formed micropores may close, and if the temperature is lower than 110°C or the heating time is shorter than 3 seconds, heat fixation tends to be insufficient. The through holes close later, and thermal shrinkage is more likely to occur due to temperature changes during use.

When observed with a scanning electron microscope, the porous polypropylene film formed by methods (1) and (2) above shows that the porous polypropylene film runs at approximately predetermined intervals perpendicular to the stretching direction of the film, and that A group of unstretched plate-like planes formed substantially parallel to each other, and a stretch-oriented relatively thin fibril space that runs approximately parallel to the stretching direction of the film and at approximately predetermined intervals between the plate-like planes, and is connected between the plate-like planes. The gaps between the thin fibrils connected between the plate-like planes form a large number of micropores with a substantially uniform shape that spread out almost two-dimensionally, and most of the micropores form through holes. In addition, it has a substantially uniform pore diameter, and it is extremely preferable to use a film having such characteristics as a battery separator in terms of battery performance.

[Example 1] Next, an example of the present invention and a comparative example will be shown and explained, but the present invention is not limited to these examples.

In addition, the water permeability shown in the following examples and comparative examples is A
According to the method specified in STM-F317, the obtained porous film is treated to make it hydrophilic by immersing it in alcohol and a surfactant, and this hydrophilized porous film is attached to a specified holder. Then, pressure was applied to one side of the film in the thickness direction of the film, and the amount of water that permeated from the pressurized side of the film to the other side per unit time was measured.

(Example 1) An unstretched polypropylene film was molded using an inflation molding machine equipped with an inflation molding die having a diameter of 50 mm and a slit gap of 0.7 mm. In the molding operation, polypropylene was heated at a resin discharge temperature of 210°C.
The film was discharged while blowing air into the valve so that the blow ratio was 0.7, and room temperature air was blown onto the outer wall surface of the discharged film at a position of 1-5 cm from the die to cool it. The desired unstretched polypropylene film was obtained by taking off at a take-off speed of 36 m/min using nip rolls at a position of 1.8 m.

The polypropylene used and molding conditions are as follows.

Polypropylene UBE-PP-YIOIJ (manufactured by Ube Industries) MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 #Lm . Moreover, the elastic recovery rate of this film from 50% elongation was 80%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was 87%.
improved.

This unstretched film was stretched by 10% of its initial length in liquid nitrogen (-196°C), and while maintaining this stretched state, it was heat-set in a heated air tank at 145°C for 10 minutes. After heat setting, the stretched length is stretched to 180% in liquid nitrogen, and while maintaining this stretched state, heat set is performed for 10 minutes in a heated air tank at 145°C to form a porous polypropylene film. was manufactured.

The resulting porous polypropylene film was tested using ASTM
The average pore diameter measured by a half-dry method (hereinafter the same) using ethanol in accordance with the method specified in F316-80 was 0.13 pm. In addition, mercury intrusion method [measurement was performed using PORO3IMET series manufactured by CARI, 0ERBA (Italy)]
The test was carried out using RO5ERIES) 1500. ) The porosity measured was 54.60%. In addition, the water permeability was 23.18 m2·min·atmospheric pressure.

When the surface and cross-section of this porous polypropylene film were observed using a scanning electron microscope, it was found that the polypropylene film ran approximately perpendicularly to the stretching direction of the film at approximately predetermined intervals and was formed approximately parallel to the cross-section perpendicular to the stretching direction of the film. formed by a group of unstretched plate-like planes, and a group of relatively thin fibrils stretched and oriented, running substantially parallel to the stretching direction of the film and at approximately predetermined intervals between the plate-like planes, and connected between the plate-like planes, The gaps between the thin fibrils connected between the plate-like planes formed a large number of micropores exhibiting a substantially uniform shape that expanded substantially two-dimensionally, and the pore diameters were also substantially uniform throughout. Furthermore, when the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

Table 1 shows the results of measuring electrical conductivity using this film.

(Comparative Example 1) An unstretched polypropylene film was molded using the same apparatus as in Example 1. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-YIOIJ (manufactured by Ube Industries Co., Ltd.) MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 JLm. Moreover, the elastic recovery rate of this film from 50% elongation was 80%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was 87%.
improved.

This film was stretched in liquid nitrogen (at 25°C).
) A porous polypropylene film was produced by carrying out the stretching and heat setting in the same manner as in Example 1, except that the stretching was replaced by stretching.

The average pore diameter of the resulting porous polypropylene film measured by the half-try method was 0.077 zm, and the porosity measured by the mercury intrusion method was 41.50%. In addition, the water permeability was 6.66 g/m2·min·atmospheric pressure.

Although the unstretched polypropylene used was the same as that used in Example 1, the average pore diameter, porosity, and water permeability of the obtained porous film were the same as those obtained in Example 1. The value was lower than that of quality polypropylene film. Furthermore, when the surface and cross section of the obtained porous polypropylene film were observed using a scanning electron microscope, it was found that holes were formed on the film surface. There were fewer pores compared to the film obtained in Example 1. Table 1 shows the results of measuring conductivity using this.

(Example 2) An unstretched polypropylene film was molded using the same apparatus as in Example 1. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-J130G (manufactured by Ube Industries, Ltd.) MFI = 30 g/10 min Resin discharge temperature 170°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 ILm.

In addition, the elastic recovery rate of this film from 50% elongation is 3
It was 0%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was 72%.
improved.

This film was stretched in liquid nitrogen and heat-set in the same manner as in Example 1.

This film was stretched in a heated air tank at 145°C to 330% of the length stretched in liquid nitrogen, and while maintaining this stretched state, it was heat-set in a heated air tank at 145°C for 10 minutes. A porous polypropylene film was produced.

The average pore diameter of the resulting porous polypropylene film measured by the half-try method was O,'yo.

m, the porosity measured with a mercury porosimeter is 65°30%
Met. In addition, the water permeability was 59.001/m2·min·atmosphere.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope, it was found that pores were formed almost uniformly on the film surface, and the pore diameters were also almost uniform throughout. Furthermore, when the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface. Table 1 shows the results of measuring electrical conductivity using this film.

(Example 3) Polypropylene (product name: UBE-PP-F 109
K, manufactured by Ube Industries, Ltd., MFI = 9 g/10 minutes) was applied to an inflation molding machine equipped with an inflation molding die with a diameter of 50 n++a and a slit gap of 0.7 I1 m to form an unstretched polypropylene film. In the molding operation, polypropylene was heated at a resin discharge temperature of 200°C.
The film was discharged while blowing air into the valve so that the blow ratio was 0.7, and room temperature air was blown onto the outer wall surface of the discharged film at a position of 5c above the die to cool it, and the blow ratio was 1.81 above the die. The desired unstretched polypropylene film was formed by taking off the film at a taking-off speed of 35 m/min using nip rolls.

The thickness of the obtained unstretched film was 20 gm.

In addition, the elastic recovery rate of this film from 50% elongation is 3
It was 8%.

This unstretched film was heated at a temperature of 145°C and at a strain rate of 8.3.
Stretched 3X/min to 300χ with respect to the initial length, and while maintaining this stretched state, stretched for 10 minutes in a heated air tank at 145°C.
A porous polypropylene film was produced by heat setting for a minute.

The average pore diameter of this film measured by the same method as in Example 1 was 0.4 g, m, and the porosity was 67%. Table 1 shows the results of measuring the electrical conductivity using this film.

Table 1 Measurement of conductivity Porosity (χ) Conductivity (S/am) Example 1
54.6 5. ], Ox 1O-3Iノ265J
5. ]]6x]0-3ノ367.05.21x1.0-' Comparative example 1 4], 5 2.48X 10-3
A porous polypropylene film was impregnated with a liquid electrolyte (equal volume mixed solution of propylene carbonate and dimethoxyethane in which 1 molar concentration of lithium perchlorate was dissolved), and the conductivity was measured using a conductivity meter.

(Example 4) A metal lithium disk with a diameter of 16 cm and a thickness of 0.75 cm was used as a negative electrode, 68 mg of manganese dioxide and 8.511 g of acetylene black were used as a positive electrode, and Teflon powder (Luflon L-5 manufactured by Daikin Co., Ltd.) was used as a binder.8. 5] 1 g, pressure molded at a pressure of 7.5 tons/am2,
Heat treated at 00℃, diameter 13m+m, thickness 1.3mm
A positive electrode plate was prepared.

The porous polypropylene film produced in Example 1 was used.

This film was impregnated with an electrolyte containing 1 molar lithium perchlorate dissolved in an equal volume mixed solvent of propylene carbonate and dimethoxyethane, and sandwiched between the positive electrode and negative electrode to create a battery.

As a battery performance test, a constant resistance discharge test of 2.8 Ω was conducted, and a battery capacity of 16 mAh was obtained by cutting off 2.0 volts.

(Comparative Example 2) Using the film produced in Comparative Example 1, a lithium battery was produced in the same manner as in Example 4. As a result of conducting a battery performance test in the same manner as in Example 4, the discharge capacity was 52
There was a h.

(Example 5) Using the film produced in Example 2, a lithium battery was produced in the same manner as in Example 4. As a result of conducting a battery performance test in the same manner as in Example 4, the discharge capacity was 16
There was a h.

(Example 6) Using the film produced in Example 3, a lithium battery was produced in the same manner as in Example 4. As a result of conducting the battery performance test in the same manner as in Example 4, the discharge capacity was 17 m.
It was Ah.

[Effects of the Invention] As explained above, the battery separator of the present invention has a special form in which most of the through holes are formed, the pores are approximately uniform in diameter, and the porosity is 45% or more. By using a porous polypropylene film having micropores, it is possible to provide a film with excellent properties such as ionic conductivity. Therefore, a lithium battery using this battery separator can have excellent battery performance.

Claims (4)

[Claims] (1) A battery separator made of a porous polypropylene film having a large number of micropores obtained by stretching polypropylene, the porous polypropylene film running at approximately predetermined intervals at right angles to the stretching direction of the film. and a group of unstretched plate-like planes formed substantially parallel to a cross section perpendicular to the stretching direction of the film; A large number of fine pores are formed by a group of stretched and oriented relatively thin fibrils that connect between the planes, and the gaps between the thin fibrils that connect between the plate-like planes expand approximately two-dimensionally and exhibit a substantially uniform shape. A separator for a battery, wherein most of the micropores form through holes and have a substantially uniform diameter, and the film has a porosity of 45% or more. (2) In the method for manufacturing a battery separator made of a porous polypropylene film having a large number of micropores obtained by stretching polypropylene, the polypropylene stretching step is performed using nitrogen, oxygen, argon, carbon monoxide, methane, and ethane. The stretching is carried out in a medium selected from the group consisting of: -70°C or lower, and at a low temperature ranging from the freezing point of the medium to a temperature 50°C higher than the boiling point of the medium. A method for producing a battery separator made of a porous polypropylene film. (3) In a method for producing a battery separator made of a porous polypropylene film having a large number of micropores obtained by stretching polypropylene, the stretching step of polypropylene is not performed at room temperature in advance, but at temperatures between 110°C and 155°C.
1. A method for producing a battery separator made of a porous polypropylene film, characterized in that the method is carried out in a high temperature range of °C at a stretching strain rate of less than 10%/min. (4) A lithium battery characterized by using the battery separator according to claim 1.