KR20170020764A - Polyolefin microporous membrane, separator for cell, and cell - Google Patents

Abstract

The present invention provides a polyolefin microporous film which can prevent the deterioration of the air permeability of the separator by high-pressure pressing in the production process of a battery and is excellent in compressibility. Further, by using the polyolefin microporous membrane of the present invention, a battery having excellent cycle characteristics can be provided. The rate of change in the durability after heat compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes was 50% or less, and the rate of change in the film thickness after heating and compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes was not more than the film thickness of the polyolefin microporous film 100% < / RTI > by weight of the polyolefin microporous membrane.

Description

POLYOLEFIN MICROPOROUS MEMBRANE, SEPARATOR FOR CELL, AND CELL [0002]

The present invention relates to a polyolefin microporous membrane, a battery separator and a battery.

The polyolefin microporous membrane is widely used as a separator, a filter, and the like. For example, the separator may be a lithium ion secondary battery, a nickel-hydrogen battery, a nickel-cadmium battery, a battery separator used for a polymer battery, a separator for an electric double layer capacitor, a reverse osmosis filtration membrane, an ultrafiltration membrane, It is used for breathing and waterproof medical treatment (clothing) and medical (medical treatment) materials. In particular, it is preferably used as a separator for a lithium ion secondary battery.

BACKGROUND ART [0002] Lithium ion secondary batteries are widely used not only in small electronic devices such as notebook computers and mobile phones, but also in power tools such as power tools and hybrid electric vehicles.

In the lithium ion secondary battery, the separator has a function of preventing the short circuit between the positive electrode and the negative electrode while maintaining the permeability of the ions. However, due to the influence of the expansion / contraction of the electrode due to the charging / discharging of the battery, the separator is repeatedly subjected to load / release of force with respect to the thickness direction to cause a change in deformation or permeability, It is pointed out. Therefore, in order to maintain the cycle characteristics of the battery, it is required to suppress the deformation of the separator and the change of the permeability due to compression to a small extent.

Therefore, in recent years, development of a separator paying attention to compressibility has been progressing.

Patent Document 1 describes a microporous film containing polyethylene as a main component in which the content of ultrahigh molecular weight polyethylene having a mass average molecular weight of 1 x 10 ⁶ or more is 5% by mass or less based on 100% by mass of all the polyethylene. The microporous film of Patent Document 1 has a porosity of 25 to 80% and a film thickness change rate after heat compression at 90 degrees for 5 minutes under a pressure of 2.2 MPa is 20% or less, assuming that the film thickness before compression is 100% Fig reached dumping resistance after heat compression under the condition (Gurley value) is described not more than ^{700 sec / 100 cm 3/20} ㎛.

Patent Document 2 discloses that a polyolefin having a viscosity average molecular weight (Mv) of less than 300,000, a polyolefin having an Mv of 500,000 or more and electrochemically inert particles larger than the film thickness as essential components and having a height A A < A / B x 100 < 25 is established between the thickness (mu m) and the film thickness B (mu m) of the polyolefin microporous film. Since the particles protruding from both sides are selectively compressed, the compression load on other portions having pore structures is reduced. The porosity is 39 to 43%, the samples are cut to 50 mm x 50 mm, It is described that the durability against dipping in a press machine at 55 캜 for 5 seconds to be 80% of the initial total thickness including projected particles is 190 to 430 sec.

Patent Document 3 proposes a microporous film having heat resistance and flexibility by extruding an α-olefin and a propylene-based elastomer with a polyolefin resin to form a sheet, stretching, washing and drying. The microporous membrane preferably has a porosity of 35 to 75% and a film thickness change rate after heat compression at 90 캜 for 5 minutes under a pressure of 2.2 MPa by a press machine is preferably 20% or less, It is described that the arrival dumping resistance (gully value) after heating and compression under the above conditions is 600 sec / 100 ml / 20 m or less.

Patent Document 1: JP-A-2008-81513 Patent Document 2: JP-A-2007-262203 Patent Document 3: JP-A-2013-57045

Although the compression resistance is improved by the technique disclosed in Patent Documents 1 to 3 to suppress deterioration of the cycle characteristics of the battery, it is still not sufficient.

As a cause of deterioration of cycle characteristics, precipitation of lithium at the time of initial charging of the lithium ion secondary battery can be exemplified. When lithium precipitates, the cycle characteristics deteriorate due to a decrease in the lithium ion concentration in the electrolyte or the like. It has been found that, in order to suppress the precipitation of lithium at the time of initial charging, the permeability of the separator and the adhesion of the separator and the electrode are important. If the durability of the separator is high, the flow of ions is inhibited. If the adhesion is insufficient, a gap is formed between the separator and the electrode due to the expansion of the electrolyte or the electrode, thereby accelerating the precipitation of lithium. Therefore, in order to suppress the deterioration of the cycle characteristics, it is necessary to suppress the increase of the specular resistance of the separator and to improve the adhesion of the separator and the electrode.

The present inventors have made intensive investigations on the durability of the separator and the adhesion between the separator and the electrode. As a result, in the course of manufacturing the battery, the battery element is manufactured, Process. However, it has been found that the air permeability of the separator and the adhesion between the separator and the electrode are impaired by hot pressing at a high pressure, leading to deterioration of cycle characteristics. That is, it has been found that the deterioration of the cycle characteristics can be suppressed by the separator capable of maintaining the durability and the adhesiveness with the electrode by the pressure in the hot press, and reached the present invention. The techniques of Patent Documents 1 to 3 assume a pressure of about 2.2 MPa accompanied by charging and discharging of the battery, and the pressure (about 3 to 5 MPa) in the hot press is not considered.

The present invention provides a polyolefin microporous membrane which can prevent the deterioration of air permeability of the separator due to high-pressure pressing in a battery manufacturing process and is excellent in compressibility. Further, by using the polyolefin microporous membrane of the present invention, a battery having excellent cycle characteristics can be provided.

In order to solve the above problems, a separator for a battery of the present invention has the following constitution.

In other words,

It was confirmed that the rate of change in the durability of the polyolefin microporous membrane after heat compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes was 50% or less and the rate of change in film thickness after heating and compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes, Is a polyolefin microporous film having a thickness of 10% or less, assuming that the thickness of the microporous film is 100%.

The polyolefin microporous membrane of the present invention preferably has a content of ultrahigh molecular weight polyethylene having a weight average molecular weight (Mw) of 1 x 10 ⁶ or more in an amount of 10 to 40% by mass based on 100% by mass of the entire polyethylene.

The polyolefin microporous membrane of the present invention preferably has a thickness of 16 탆 or less.

The polyolefin microporous membrane of the present invention preferably has a porosity of 25 to 40%.

The polyolefin microporous membrane of the present invention preferably has an average pore diameter of 0.05 m or less and a bubble point (BP) pore diameter of 0.06 m or less as determined by a Perm-Porometer.

The polyolefin microporous membrane of the present invention is preferably a battery separator.

In order to solve the above problems, the battery of the present invention has the following configuration.

In other words,

And a battery separator composed of the polyolefin microporous membrane.

According to the present invention, the present invention provides a polyolefin microporous film excellent in compressibility, which can prevent the deterioration of the specular resistance of the separator due to the high-pressure press working in the battery manufacturing process. Further, by using the polyolefin microporous membrane of the present invention, a battery having excellent cycle characteristics can be provided.

Hereinafter, the polyolefin microporous membrane of the present invention will be described in detail.

[1] Polyolefin resin

The polyolefin resin constituting the polyolefin microporous membrane of the present invention comprises a polyethylene resin as a main component. The content of the polyethylene resin is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass, based on 100% by mass of the total mass of the polyolefin resin. Therefore, the polyolefin microporous membrane of the present invention is preferably composed of a polyethylene resin as the polymer component, and does not contain polypropylene in this case.

Examples of the polyolefin include a two-stage polymer or copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methylpentene-1, 1-hexene or the like, and blends thereof.

(Hereinafter referred to as &quot; polyethylene (A) &quot;) having a weight average molecular weight (Mw) of less than 1 x 10 ⁶ and an ultrahigh molecular weight polyethylene having an Mw of 1 x 10 ⁶ or more (B) &quot;) is more preferable.

As the polyethylene (A), any of high density polyethylene (HDPE), medium density polyethylene (MDPE) and low density polyethylene (LDPE) may be used and two or more Mw or different density may be used. Particularly, it is preferable to use high-density polyethylene as the polyethylene (A). The Mw of the polyethylene (A) is preferably 1 x 10 ⁴ or more and less than 5 x 10 ⁵ , more preferably 5 x 10 ⁴ or more and less than 4 x 10 ⁵ .

The polyethylene (B) is an ultrahigh molecular weight polyethylene (UHMWPE) having an Mw of 1 x 10 ⁶ or more, and a Mw of 1 x 10 ⁶ to 3 x 10 ⁶ . When the Mw of the polyethylene (B) is 3 x 10 ⁶ or less, melt extrusion can be facilitated.

The content of the polyethylene (B) in the polyethylene resin is preferably 10% by mass or more and 40% by mass or less, more preferably 15% by mass or more and 30% by mass or less, based on 100% by mass of the total mass of the polyethylene resin. When the content of the polyethylene (B) is within the above preferable range, the average pore diameter of the film as a whole can be reduced under the same production conditions, and pores are not easily damaged by compression. When the content of the polyethylene (B) is within the above preferable range, the heat shrinkage can be suppressed to a low level.

The Mw of the polyolefin resin is preferably 1 × 10 ⁶ or less, more preferably 1 × 10 ⁵ to 1 × 10 ⁶ , and still more preferably 2 × 10 ⁵ to 1 × 10 ⁶ . By setting the Mw of the polyolefin resin within the above-described preferable range, extrusion in the twin-screw extruder is easy and breakage can be prevented at the time of stretching.

The ratio (Mw / Mn (molecular weight distribution)) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of polyethylene (A), polyethylene (B) and polyolefin resin is not limited, but is preferably 5 to 300, More preferably from 5 to 100, and still more preferably from 5 to 25. When the Mw / Mn is in the above-mentioned preferable range, melt extrusion is easy, and the strength of the resulting polyolefin microporous film can be increased.

In order to improve the characteristics as a battery separator application, the polyolefin resin may include a polyolefin which imparts a shutdown function. As the polyolefin which imparts the shutdown function, for example, LDPE or polyethylene wax may be added. The LDPE is preferably at least one selected from the group consisting of branched LDPE, linear LDPE (LLDPE) and ethylene /? - olefin copolymer produced by a single site catalyst. However, the addition amount thereof is preferably 20% by mass or less based on 100% by mass of the total mass of the polyolefin resin. By reducing the addition amount within the above-described preferable range, the strength reduction can be prevented.

If necessary, various additives such as an antioxidant and a fine silicic acid (pore-forming agent) may be added within a range that does not impair the effect of the present invention.

[2] Process for producing a microporous polyolefin membrane

The method for producing the polyolefin microporous membrane of the present invention comprises the steps of (1) adding a solvent for film formation to the polyolefin resin and then melt-kneading to prepare a polyolefin resin solution, (2) extruding the polyolefin resin solution from the die lips, (3) a step of stretching the gel-like shaped material in at least one axial direction (first stretching step), (4) a step of removing the solvent for film formation, (5) a step of drying the obtained film, 6) a step of re-stretching the dried film at least in the uniaxial direction (second stretching step), (7) a heat treatment step, and (8) a winding step. If necessary, the step (4) may include any one of a heat fixing treatment step, a heat roll treatment step and a thermal solvent treatment step before the step of removing the solvent for film formation. After the steps (1) to (7), the step may include a drying step, a heat treatment step, a crosslinking treatment step by ionizing radiation, a hydrophilic treatment step, a surface coating treatment step and the like.

As the method of producing the polyolefin microporous membrane of the present invention, it is important that the method is a wet method through the step of "preparing a polyolefin resin solution" and "a step of forming a gel-like molded article". The production method not subjected to the &quot; process for preparing a polyolefin resin solution &quot; is called a dry process.

(1) Preparation process of polyolefin resin solution

After a suitable solvent for film formation is added to the polyolefin resin, the resultant is melt-kneaded to prepare a polyolefin resin solution. The melt-kneading method is well known in the art, and a detailed description thereof is omitted. As a melt-kneading method, for example, a method using a twin-screw extruder described in Japanese Patent Publication No. 2132327 and Japanese Patent Publication No. 3347835 can be used. However, the polyolefin resin concentration of the polyolefin resin solution is preferably 25 to 50 mass%, more preferably 25 to 45 mass%, based on 100 mass% of the total mass of the polyolefin resin and the film forming solvent. By keeping the ratio of the polyolefin resin within the above-described preferable range, the productivity can be prevented from lowering and the moldability of the gel-like molded article can be prevented from lowering.

(2) Process for forming a gel-like shaped article

The polyolefin resin solution is extruded into a die equipped with an extruder and cooled to form a gel-like molded product. The rate of cooling the polyolefin resin solution extruded from the die to 50 캜 or lower is preferably 180 캜 / min or higher, more preferably 200 캜 / min or higher, even more preferably 210 캜 / min or higher. By setting the cooling rate within the preferable range, crystal nuclei are increased to increase the number of fine crystals. As a result, the gel-like molded product is easy to orient crystals at the time of stretching to improve the fibril strength, and the resulting microporous membrane is not easily damaged by improving the strength against compression in the film thickness direction. The extrusion method and the method for forming the gel-like shaped article are well known in the art and thus the description thereof is omitted. For example, the methods disclosed in Japanese Patent Publication No. 2132327 and Japanese Patent Publication No. 3347835 can be used.

(3) First drawing step

The gel-like molded product is stretched at least in the uniaxial direction. Cleavage occurs between the polyethylene crystalline lamellar layers by the first stretching, so that the polyethylene phase is refined and a large number of fibrils are formed. The resulting fibrils form a three-dimensional network structure (a three-dimensionally irregularly connected network structure). Since the gel-like molded product contains a solvent for forming a film, it can be stretched uniformly. The first stretching can be performed at a predetermined magnification after heating the gel-like shaped article by a conventional tentering method, a roll method, an inflation method, a rolling method, or a combination of these methods. The first stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred. In the case of biaxial stretching, either biaxial stretching or continuous stretching may be performed.

Although the stretching magnification depends on the thickness of the gel-like shaped article, it is preferably 2 times or more, and more preferably 3 to 50 times, in the uniaxial stretching. In biaxial stretching, at least three times or more is preferable in any direction.

The temperature of the first stretching is preferably within a range of from a crystalline dispersion temperature of the polyolefin resin to a crystalline dispersion temperature + 30 ° C, more preferably within a range of crystal dispersion temperature + 10 ° C to crystal dispersion temperature + 25 ° C, It is particularly preferable to set the temperature within the range of the crystal dispersion temperature + 15 deg. C to the crystal dispersion temperature + 20 deg. When the stretching temperature is within the above-mentioned preferable range, deterioration of the orientation of the molecular chains after stretching is prevented, and the resin is sufficiently softened to prevent the film from being stretched, and high-magnification stretching is possible. Here, the crystal dispersion temperature refers to a value obtained by measuring the temperature characteristic of dynamic viscoelasticity based on ASTM D4065. When the polyolefin resin is polyethylene, the crystal dispersion temperature is generally 90 to 100 ° C. Therefore, the stretching temperature is usually 90 to 130 占 폚, more preferably 100 to 125 占 폚, and even more preferably 105 to 120 占 폚.

Multi-step stretching in which the temperature is different at the time of the first stretching may be performed. In this case, it is preferable to conduct stretching at two different temperatures at a higher temperature than the temperature of the former stage. As a result, a high-order microporous film having a large pore diameter and high permeability is obtained without accompanied by a decrease in strength or a decrease in physical properties in the width direction. Although not particularly limited, the difference in drawing temperature between the front end and the rear end is preferably 5 ° C or more. When the temperature of the film is increased from the front end to the rear end, it is possible to raise the temperature while continuing the stretching (a), (b) to stop the stretching while raising the temperature and to start the stretching at the rear end after reaching the predetermined temperature, a) is preferred. In either case, it is desirable to rapidly heat the sample at the time of heating. Specifically, the heating is preferably performed at a heating rate of 0.1 ° C / second or more, and more preferably, the heating is performed at a heating rate of 1 to 5 ° C / second. Needless to say, the stretching temperature and the total stretching ratio at the front end and the rear end are within the above ranges.

Depending on the desired physical properties, the polyolefin microporous film can be stretched with a temperature distribution in the film thickness direction, thereby obtaining a polyolefin microporous film having further excellent mechanical strength. As such a method, for example, a method disclosed in Japanese Patent Publication No. 3347854 can be used.

(4) Process for removing solvent for film formation

A cleaning solvent is used to remove (clean) the solvent for film formation. Since the polyolefin phase is phase-separated with the solvent for film formation, a porous film can be obtained by removing the solvent for film formation. The method of removing the cleaning solvent and the solvent for forming a film using the cleaning solvent is well known in the art, and therefore the description thereof is omitted. For example, the method disclosed in Japanese Patent Publication No. 2132327 or Japanese Patent Laid-Open Publication No. 2002-256099 can be used.

(5) Drying process of membrane

The polyolefin microporous membrane obtained by removing the solvent for film formation is dried by the heat drying method, the air drying method, or the like.

(6) Second drawing step

The film after drying is again stretched in at least one uniaxial direction. The second stretching can be performed by a tenter method or the like as in the first stretching while heating the film. The second stretching may be uniaxially stretched or biaxially stretched.

The temperature of the second stretching is preferably within the range of not less than the crystalline dispersion temperature of the polyolefin resin constituting the microporous membrane to not more than the crystal dispersion temperature of not more than 40 캜 and not more than the crystal dispersion temperature of not less than 10 캜 and not more than 40 캜 And more preferably within the range. By setting the second stretching temperature within the above-mentioned preferable range, it is possible to prevent the deterioration of the air permeability and the occurrence of the physical property deviation in the sheet width direction when stretched in the transverse direction (width direction: TD direction). By setting the temperature of the second stretching within the above-mentioned preferable range, it is possible to suppress the occurrence of a deviation in the widthwise direction of the stretched sheet, particularly the damping resistance. By setting the temperature of the second stretching within the above preferable range, the polyolefin resin can be sufficiently softened, and the film can be prevented from being stretched and stretched uniformly. When the polyolefin resin comprises only polyethylene, the stretching temperature is usually within the range of 90 to 140 占 폚, preferably within the range of 100 to 140 占 폚.

The magnification of the second stretching in the uniaxial direction is preferably 1.0 to 1.8 times. For example, in the case of uniaxial stretching, the length is set to 1.0 to 1.8 times in the longitudinal direction (machine direction: MD direction) or TD direction. In the case of biaxial stretching, the MD direction and the TD direction are set to 1.0 to 1.8 times, respectively. In the case of biaxial stretching, the stretching magnifications in the MD and TD directions may be different from each other in the direction of 1.0 to 1.8, but they are preferably the same. By setting the magnification within the above-described preferable range, it is possible to prevent the permeability, the electrolyte-absorbing property, and the compression resistance from being lowered. Further, by setting the magnification within the above-mentioned preferable range, it is possible to prevent the fibrils from becoming excessively thin and the deterioration of the heat shrinkability. The magnification of the second stretching is more preferably 1.2 to 1.6 times.

The speed of the second elongation is preferably 3% / second or more in the elongation axis direction. For example, in the case of uniaxial stretching, it is set to 3% / second or more in the MD direction or TD direction. In the case of biaxial stretching, it is set to 3% / second or more in MD direction and TD direction respectively. The elongation speed (% / sec) in the elongation axis direction indicates the ratio of the elongation per one second with the length in the elongation axis direction before re-stretching in the region where the film (sheet) is re-stretched as 100%. By setting the stretching speed within the above-mentioned preferable range, it is possible to prevent the permeability from lowering and prevent the variation of the physical properties in the sheet width direction from becoming large when stretched in the TD direction. By setting the stretching speed within the above-described preferable range, it is possible to prevent the deviation of the specular resistance particularly in the width direction of the stretched sheet. The speed of the second stretching is preferably 5% / second or more, and more preferably 10% / second or more. In the case of biaxial stretching, the stretching speeds in the MD and TD directions may be different from each other in the MD direction and the TD direction as long as the elongation speed is 3% / sec or more, but they are preferably the same. The upper limit of the second stretching speed is not particularly limited, but is preferably 50% / second or less from the viewpoint of preventing breakage.

(7) Heat treatment process

The film after the second stretching is heat-treated. As the heat treatment method, heat fixing treatment and / or thermal relaxation treatment can be used. Particularly, the crystal of the film is stabilized by heat fixing treatment. By carrying out the heat fixing treatment, a microporous film having a large pore diameter and high strength can be produced, in which the network structure of the fibril formed by the second stretching is maintained. The heat setting treatment is carried out within a temperature range of not lower than the crystal dispersion temperature of the polyolefin resin constituting the microporous film to a temperature not higher than the melting point. The heat fixing process is performed by a tenter method, a roll method, or a rolling method. The thermal relaxation treatment may be performed by a tenter system, a roll system or a compression system, or a belt conveyor or a floating roll. The thermal relaxation treatment is preferably carried out in a range of not more than 20% of the relaxation rate in at least one direction, and more preferably in the range of not more than 10% of the relaxation rate.

The heat setting treatment temperature and the heat relaxation temperature are preferably within the range of the temperature of the second drawing of 占 쏙옙 5 占 폚, thereby stabilizing the physical properties. This temperature is more preferably within the range of the temperature of the second stretching ± 3 ° C. As the thermal relaxation treatment method, for example, the method disclosed in Japanese Laid-Open Patent Publication No. 2002-256099 can be used.

(8) Coiling process

The polyolefin microporous membrane after the film formation is wound around a cylindrical core and heat-treated in a film roll state. The heat treatment temperature is preferably 50 to 70 占 폚. In the present invention, the core for winding the film is cylindrical, and its material is not particularly limited, and may include paper, plastic, and the like. The winding method is a method in which a polyolefin microporous membrane is wound around a core by applying tension by a winding motor. The winding tension at the time of winding the polyolefin microporous film on the core is preferably 5 to 15 N, more preferably 7 to 15 N. If it is wound with a winding tension of 15 N or more, it is likely to be deformed by stretching in a roll state after winding, and heat shrinkage after winding becomes large. At a winding tension of 1 N or less, irregular winding or winding shape is defective, which causes a defective wrinkle. Further, when the film roll is heat-treated at 60 占 폚, the three-dimensional structure is not easily deformed due to shrinkage, and the obtained polyolefin microporous film has less shrinkage at the time of hot pressing, and the rate of change of durability after heat compression becomes small.

It is preferable to adopt an in-line method in which the first stretching, the solvent removal for film forming, the drying treatment, the second stretching, and the heat treatment are continuously performed on a series of lines. However, an off-line method may be employed in which the film after the drying treatment is once wound into a film roll as necessary, and the second stretching and heat treatment are performed while rewinding the film.

(9) Other processes

The method may include any one of a heat fixation treatment process, a heat roll treatment process, and a thermal solvent treatment process before removing (cleaning) the film forming solvent from the gel-like molded product subjected to the first stretching. The method may further include a step of heat-fixing the film after the cleaning or the second stretching step.

(i) thermal fixation treatment

The stretched gel-like shaped article before and / or after the cleaning, and the method of heat-fixing the film in the second stretching step may be the same as described above.

(ii) heat roll treatment process

(Heat roll treatment) in which the heat roll is brought into contact with at least one surface of the drawn gel-like shaped product before cleaning. As the heat roll treatment, for example, the method described in Japanese Patent Application Laid-Open No. 2007-106992 can be used. When the method described in Japanese Patent Application Laid-Open No. 2007-106992 is used, a drawn gel-like molded product is brought into contact with a heating roll whose temperature is adjusted to a crystal dispersion temperature of the polyolefin resin + 10 ° C or higher to less than the melting point of the polyolefin resin. The contact time between the heated roll and the drawn gel-like molded product is preferably 0.5 seconds to 1 minute. As the thermal roll treatment, the heating oil may be held in contact with the roll surface. As the heating roll, any of a roll having a function of sucking a smooth roll or a drawn gel-like shaped material to the roll side, or a concavo-convex roll having a concavo-convex surface on the contact surface (outer circumferential surface) with the drawn gel-like shaped material may be used.

(iii) thermal solvent treatment process

A process of contacting the drawn gel-like molded product before cleaning with a heat solvent may be performed. As the thermal solvent treatment method, for example, the method disclosed in WO2000 / 20493 can be used.

[3] Properties of polyolefin microporous membrane

The polyolefin microporous membrane according to the preferred embodiment of the present invention has the following properties.

(1) Film thickness (占 퐉)

The film thickness of the polyolefin microporous film is preferably from 3 to 16 탆, more preferably from 5 to 12 탆, still more preferably from 6 to 10 탆, since the battery has recently been in high-density and high capacity.

(2) Average pore diameter (average flow pore diameter) and bubble point (BP) Pore diameter (nm)

The polyolefin microporous membrane preferably has an average pore diameter of 0.05 mu m or less as determined by a permeometer. The bubble point (BP) pore diameter is preferably 0.06 mu m or less. When the pore diameter of the whole membrane is made small, the pores are not easily damaged, and the change of the film thickness and the specimen resistance is small.

(3) Speculative resistance (sec / 100 cm ³ )

The speculative resistance (gull value) is preferably 300 sec / 100 cm ³ or less. When it is 300 sec / 100 cm ³ or less, it has good permeability when used in a battery.

(4) Porosity (%)

The porosity is preferably 25 to 80%. When the porosity is 25% or more, good durability is obtained. When the porosity is 80% or less, the strength when the microporous membrane is used as a battery separator is sufficient, and short-circuiting can be suppressed. When the porosity is 25 to 40%, pores of the separator are not easily damaged at the time of compression, which is preferable.

(5) Stubbing Strength (mN)

The puncture strength is greater than 1,300 mN. If the penetration strength is less than 1,300 mN, there is a risk of short-circuiting between the electrodes when the microporous membrane is inserted into the battery as a battery separator.

(6) Tensile breaking strength (MPa)

The tensile fracture strength is preferably 80 MPa or more in both the MD and TD directions. There is no worry about the breakage. The tensile fracture strength in the MD direction is preferably 110 MPa or more, and more preferably 140 MPa. The tensile fracture strength in the TD direction is preferably 120 MPa or more, and more preferably 170 MPa. If the tensile breaking strength is within the above-mentioned preferable range, even if hot pressed at a high pressure in the manufacturing process of the battery, it is difficult to break and the pores are not easily damaged.

(7) Tensile elongation at break (%)

The tensile elongation at break is 60% or more in both the MD and TD directions. There is no worry about the breakage.

(8) Heat shrinkage (%) after exposure (exposure) at a temperature of 105 ° C for 8 hours

The heat shrinkage rate after 8 hours of exposure at a temperature of 105 占 폚 is 15% or less in both the MD and TD directions. If the heat shrinkage ratio exceeds 15%, when the microporous membrane is used as a separator for a lithium battery, there is a high possibility that the end of the separator shrinks during heat generation and short-circuiting occurs between the electrodes. The heat shrinkage ratio is preferably 8% or less in both the MD direction and the TD direction. The heat shrinkage percentage is more preferably 4% or less in both the MD and TD directions.

(9) Film thickness change rate after heat compression (%)

The film thickness change rate after heating and compression at 5.0 占 폚 under a pressure of 5.0 MPa for 5 minutes is preferably 10% or less, more preferably 5% or less, still more preferably 3% or less, Or less. When the film thickness change ratio is 10% or less, precipitation of lithium is prevented when a microporous film is used as a battery separator, and a battery having good cycle characteristics can be obtained.

(10) Rate of change in durability after heat compression (%)

The change rate of the durability (the rate of change of the gravel value (sec / 100 cm &lt; 3 &gt;) before and after heat compression) after heating and compression at 5.0 DEG C under a pressure of 5.0 MPa for 5 minutes is preferably 50% or less, more preferably 40% , And even more preferably 35% or less. When the rate of change in durability is 50% or less, the cycle characteristic of the target battery can be obtained even when the battery is used as a battery separator, even if the battery is subjected to a hot press process at a high pressure during production.

The rate of change in film thickness after heat compression and the rate of change (%) in durability after heat compression are susceptible to the orientation of the crystal, the pore structure of the film, the heat shrinkage rate and the like. Therefore, the composition can be controlled by the composition of the polyolefin resin, the cooling rate after extruding the polyolefin resin solution from the die lips, the heat treatment of the wound body, and the like.

[4] Properties of cell using polyolefin microporous membrane

An electrochemical cell comprising an electrolyte and a separator using a polyolefin microporous membrane according to a preferred embodiment of the present invention disposed between the anode and the cathode has the following properties.

(1) Impedance change rate (%)

The rate of change in impedance of the cell measured by a measuring method described later is preferably 7% or less. If the impedance change rate is within the above preferable range, deterioration of the cycle characteristics of the battery can be suppressed.

(2) Cell Thickness Change Rate (%)

It is preferable that the rate of change in thickness of the cell measured by a measuring method described later is 15% or less. If the rate of change in the thickness of the cell is 15% or less, the separator and the electrode are sufficiently in close contact with each other by thermal press, so that lithium does not readily precipitate at the time of initial charging.

[5] batteries

The separator comprising the polyolefin microporous membrane of the present invention is not particularly limited in the type of the battery using the separator, but is particularly preferable for use in a lithium secondary battery. For the lithium secondary battery using the separator made of the microporous film of the present invention, well-known electrodes and electrolytes can be used. The structure of the lithium secondary battery using the separator made of the microporous membrane of the present invention may also be known.

Example

The present invention is described in more detail by the following examples, but the present invention is not limited to these examples.

The physical properties of the polyolefin microporous membrane were measured by the following methods.

(1) average pore diameter (average flow pore diameter) and bubble point (BP) pore diameter (nm)

The average pore diameter (average flow pore diameter) and the bubble point (BP) pore diameter (nm) of the polyolefin microporous membrane were measured as follows.

(Dry-up) and wet-up (wet-up) were measured in this order using a commercially available PMK Corporation (trade name, CFP-1500A). The pressure was applied to the polyolefin microporous membrane sufficiently wetted with Galwick (Galwick (trade name)) for which surface tension was previously known, and the pore diameter converted from the pressure at which the air began to penetrate was defined as the maximum pore diameter. With regard to the average flow diameter, the pore diameter was calculated from the pressure at the point where the curve showing the slope of 1/2 of the pressure and the flow curve and the pressure at the point where the curve of the pore-up measurement crossed in the dry- The following equation was used for the conversion of pressure and pore diameter.

(dynes / cm) is the surface tension of the liquid, P (Pa) is the pressure, and C is the pressure constant (2860). )

(2) Speculative resistance (sec / 100 cm ³ )

The specular resistance (Gurley value) was measured according to JIS P8117 for the microporous membrane having an average film thickness T _AV .

(3) Porosity (%)

Porosity of the microporous porosity (%) from the free pores of the same size film weight w ₂ w ₁ and made of a porous film mass microporous membrane of the same polyethylene composition as = (w ₁ -w ₂₎ / w calculated by the ₂ × 100 did.

(4) Sting intensity (mN)

The maximum load was measured when the microporous polyolefin membrane was pierced with a needle having a diameter of 1 mm (0.5 mmR) at a speed of 2 mm / sec.

(5) Tensile breaking strength (kPa)

The tensile breaking strength was measured by ASTM D882 using a 10 mm wide strip test specimen.

(6) Tensile elongation at break (%)

The tensile elongation at break was determined by taking three points of the strip-like test piece having a width of 10 mm from the central portion in the width direction of the polyolefin microporous membrane and measuring the value by ASTM D882 and calculating an average value.

(7) Heat shrinkage (%) after exposure at a temperature of 105 ° C for 8 hours

The heat shrinkage ratios were obtained by measuring the shrinkage ratios in the MD and TD directions when the microporous membrane was exposed at 105 ° C for 8 hours, three times each, and calculating the average value.

(8) Film thickness change rate after heat compression (%)

The film thickness was measured by a contact thickness meter (manufactured by Mitutoyo Corporation).

The polyolefin microporous membrane was sandwiched between a pair of press plates having a high smooth surface, and this was heat-pressed under a pressure of 5.0 MPa at 90 占 폚 for 5 minutes by a press machine. A value obtained by dividing the film thickness b (占 퐉) after compression by the film thickness a (占 퐉) before compression (a (占 퐉)) and dividing it by a (占 퐉) (%). The film thickness was determined by taking three points from the central portion in the width direction of the polyolefin microporous membrane and calculating the average value.

(9) Rate of change in durability after heat compression (sec / 100 cm ³ )

(Sec / 100 cm ³ ) after heating and compressing the polyolefin microporous membrane under the same conditions as in the above (8) and heating and compressing the durability (α (sec / 100 cm ³ ) (? -?) /? 100), which is obtained by dividing a value obtained by subtracting (? (Sec / 100 cm ³ ) The durability of the polyolefin microporous membrane was measured by taking three points in the widthwise central portion of the polyolefin microporous membrane and calculating the average value.

The physical properties of the cell using the polyolefin microporous membrane were measured by the following methods.

(1) Impedance change rate of cell (%)

The cells were sandwiched between a pair of press plates having a high smooth surface and were then heat-pressed at 90 占 폚 for 5 minutes under a pressure of 3.0 MPa and 5.0 MPa, respectively. Thereafter, an impedance measuring device (Solartron product, SI1250 , SI1287). The value obtained by dividing the impedance value (B) at a high pressure (5.0 MPa) by the normal press pressure (3.0 MPa) and divided by (A) is taken as the impedance change rate (%).

Impedance change rate (%) = {(A) - (B)} / (A) 100

(2) Cell Thickness Change Rate (%)

The cells were sandwiched between a pair of press plates having a high smooth surface, and they were heated and pressed at 90 占 폚 for 5 minutes under a pressure of 3.0 MPa and 5.0 MPa, respectively, and then filled in the following conditions. Respectively. The thickness of the cell was measured with a contact thickness meter (manufactured by Mitutoyo Co., Ltd.) at the center of the cell. The value obtained by dividing the cell thickness (a) before compression by the cell thickness (b) after compression and divided by (a) is taken as the cell thickness variation rate (%).

Cell thickness change rate (%) = {(a) - (b)} / (a) 100

Example 1

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) 18 % by weight and a Mw of 3.0 × 10 ⁵ of HDPE (Mw / Mn: 6) polyethylene comprising 82% by weight (melting point: 135 ℃, crystal dispersion temperature: Methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane as an antioxidant was added in an amount of 0.2 mass per 100 parts by mass of polyethylene at 100 ° C., Mw / Followed by secondary dry blending to prepare a polyethylene composition. 30 parts by mass of the obtained polyethylene composition was fed into a twin-screw extruder, and 70 parts by mass of liquid paraffin [50 cSt (40 占 폚)] was fed from a side feeder of the twin-screw extruder and melted and kneaded at 210 占 폚 and 300 rpm To prepare a polyolefin solution. This polyolefin solution was extruded from a T-die provided in a twin-screw extruder, and drawn at a cooling rate of 210 DEG C / min with a cooling roll adjusted to 30 DEG C to form a gel-like molded product. The obtained gel-like molded product was simultaneously biaxially stretched at a temperature of 115 ° C in a longitudinal direction and in a width direction by 5 times (surface magnification: 25 times) by a tenter stretching apparatus (first stretching), and then stretched by a tenter stretching device in both longitudinal and transverse directions Fixed so as not to change in dimension, and heat-fixed at a temperature of 110 캜. Subsequently, the stretched gel-like molded product was immersed in a methylene chloride bath to remove liquid paraffin, and the microporous membrane thus obtained was air-dried. Subsequently, the resulting microporous membrane was re-stretched at 130 占 폚 in the width direction at 1.36 times in the tenter stretching apparatus (second stretching), then relaxed in the width direction at a relaxation rate of 3% And a heat fixation treatment at a temperature of 130 캜 so that there is no dimensional change in both directions in the width direction. Then, the polyolefin microporous membrane was cooled to room temperature, and wound up with a winding roll of 7 N by a winding roll to produce a polyolefin microporous membrane having a thickness of 7.1 탆.

In order to confirm the effect of the separator in the battery, the aforementioned physical properties were measured by using an electrochemical cell including an anode, a cathode, a separator and an electrolyte as follows. The cathode was made of LiCoO ₂ having a density of 3.55 g / cm ³ on an aluminum substrate having a mass per unit area of 13.4 mg / cm ² and a thickness of 15 탆 A 40 mm x 40 mm sheet was used. The anode used a 45 mm x 45 mm sheet containing natural graphite with a density of 1.65 g / cm ³ on a copper film substrate with a unit area weight of 5.5 mg / cm ² and a thickness of 10 탆. The anode and cathode were dried in a vacuum oven at 120 DEG C and then the cell was assembled. The separator is a polyolefin microporous film produced in this example having a length of 50 mm and a width of 60 mm. After the separator was dried in a vacuum oven at 50 캜, the cell was assembled and LiPF ₆ was dissolved in a mixture of ethylene carbonate and methyl ethyl carbonate (ethylene carbonate / methyl ethyl carbonate = 4/6, V / V (volume ratio) An electrolyte was prepared to form a 1 M solution. A cell was fabricated by stacking an anode, a separator and a cathode between aluminum laminates, impregnating the separator with an electrolyte, and then vacuum sealing.

Example 2

The procedure of Example 1 was repeated except that the temperature of the first stretching was set to 117.0 占 폚, the magnification of the second stretching was set to 1.41, the relaxation rate in the relaxation after the second stretching was set to 7%, and the coiling tension was set to 9 N. , A polyolefin microporous membrane having a thickness of 9.4 탆 was prepared. A cell was also fabricated in the same manner as in Example 1 using the polyolefin microporous membrane.

Example 3

A polyolefin having a thickness of 5.3 占 퐉 was produced in the same manner as in Example 1 except that the temperature of the first stretching was 112.0 占 폚, the magnification of the second stretching was 1.34 times, and the relaxation rate in the relaxation after the second stretching was set to 2% A microporous membrane was produced. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Example 4

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) is 3.0 × 10 30 mass% and Mw ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 70% by weight (melting point: 135 ℃, crystal dispersion temperature: 100 占 폚, Mw / Mn: 10.0), the cooling rate in the cooling roll was set to 200 占 폚 / min, the temperature of the first stretching was set to 118.5 占 폚, the magnification of the second stretching was set to 1.40 times, A microporous polyolefin membrane having a thickness of 11.7 탆 was prepared in the same manner as in Example 1 except that the relaxation rate in the relaxation after 2 stretching was set to 14% and the coiling tension was set to 9 N. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Example 5

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) 40 % by weight and a Mw of 3.0 × 10 ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 60% by weight (melting point: 135 ℃, crystal dispersion temperature: 25 parts by mass of the obtained polyethylene composition was supplied to a twin-screw extruder under the conditions of a temperature of 110 deg. C, a second stretching magnification of 1.60 times and a stretching temperature of 127 deg. C And the relaxation rate in the relaxation after the second stretching was set to 9%, a polyolefin microporous membrane having a thickness of 3.0 탆 was prepared. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Example 6

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) 40 % by weight and a Mw of 3.0 × 10 ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 60% by weight (melting point: 135 ℃, crystal dispersion temperature: 25 parts by mass of the obtained polyethylene composition was supplied to a twin-screw extruder using a twin-screw extruder at 100 占 폚 and Mw / Mn of 10.0, and the first stretching magnification was set to 7 times (surface magnification: 49 times) A polyolefin microporous membrane having a thickness of 3.0 占 퐉 was produced in the same manner as in Example 1 except that the magnification was set to 1.60 times, the stretching temperature was set to 127 占 폚, and the relaxation rate in the relaxation after the second stretching was set to 6%. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Example 7

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) is 3.0 × 10 30 mass% and Mw ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 70% by weight (melting point: 135 ℃, crystal dispersion temperature: 28.5 parts by mass of the obtained polyethylene composition was supplied to a twin-screw extruder at a temperature of 110 deg. C, a second stretching magnification of 1.60 times and a stretching temperature of 127 deg. C, 2 A polyolefin microporous membrane having a thickness of 3.0 탆 was prepared in the same manner as in Example 1 except that the relaxation rate in the relaxation after stretching was set to 9%.

Example 8

A polyolefin microporous film having a thickness of 3.0 탆 was produced in the same manner as in Example 1 except that the first drawing temperature was 110 캜, the second drawing magnification was 1.60, and the relaxation rate in the relaxation after the second drawing was set to 9% did. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Comparative Example 1

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) 2 mass% and an Mw of 3.0 × 10 ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 98% by weight (melting point: 135 ℃, crystal dispersion temperature: 100 占 폚, Mw / Mn: 10.0), a polyolefin solution was prepared from 40 parts by mass of the obtained polyethylene composition and 60 parts by mass of liquid paraffin. The polyolefin solution was extruded, and the temperature of the first stretching was set to 119.5 DEG C, the magnification of the second stretching was set to 1.4 times, and after the second stretching, the film was wound with a force of 9 N without relaxation, In the same manner, a polyolefin microporous membrane having a thickness of 9.0 mu m was produced. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Comparative Example 2

A polyolefin microporous membrane having a thickness of 7.0 mu m was produced in the same manner as in Example 1 except that the cooling rate was set at 160 DEG C / min and the coiling was carried out at a force of 16 N. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Comparative Example 3

An Mw of 2.0 × 10 ⁶ of UHMWPE (Mw / Mn: 8) 40 % by weight and a Mw of 3.0 × 10 ⁵ of HDPE (Mw / Mn: 6) polyethylene consisting of 60% by weight (melting point: 135 ℃, crystal dispersion temperature: 100 占 폚, Mw / Mn: 10.0), a polyolefin solution was prepared from 23 parts by mass of the obtained polyethylene composition and 77 parts by mass of liquid paraffin. The polyolefin solution was extruded, and the temperature for the first stretching was 117.0 占 폚, the temperature for the second stretching was stretched at 128 占 폚 to 1.6 times, then relaxed by 12% in the width direction, Was prepared in the same manner as in Example 1 to prepare a polyolefin microporous membrane having a thickness of 11.8 占 퐉. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

Comparative Example 4

A polyolefin solution was prepared from 25 parts by mass of the polyethylene composition and 75 parts by mass of liquid paraffin. The polyolefin solution was extruded and cooled at a cooling rate of 160 占 폚 / min .; the temperature for the first stretching was 118.0 占 폚; A polyolefin microporous membrane having a thickness of 12.0 占 퐉 was produced in the same manner as in Example 1 except that stretching was carried out at 126 占 폚 to 1.4 times and no relaxation was carried out after the second stretching. A cell was fabricated in the same manner as in Example 1 using this polyolefin microporous membrane.

The manufacturing conditions of Examples 1 to 8 and Comparative Examples 1 to 4, and the physical properties of the resulting polyolefin microporous membrane and the cell using the polyolefin microporous membrane are shown in Tables 1 to 4.

Yes No, Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 PO resin composition UHMWPE Molecular Weight 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ content
(wt%) 18 18 18 30 40 40 HDPE Molecular Weight 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ content
(wt%) 82 82 82 70 60 60 Manufacturing conditions The resin concentration (wt%) of the melt- 30 30 30 30 25 25 Cooling
speed ℃ / min 210.0 210.0 210.0 200.0 210.0 210 1st
Stretching Temperature (℃) 115.0 117.0 112.0 118.5 110.0 115.0 Face magnification 25.0 25.0 25.0 25.0 25.0 49.0 Second
Stretching Temperature (℃) 130 130 130 130 127 127 Magnification (TD) 1.36 1.41 1.34 1.40 1.60 1.60 Second
Relaxation after stretching Temperature (℃) 130 130 130 130 130 130 Relaxation rate / magnification (TD) 3% / 1.32 7% / 1.32 2% / 1.32 14% / 1.2 9% / 1.46 6% / 1.5 Coiling
tension (N) 7 9 7 9 7 7

Yes No, Example 7 Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 PO resin composition UHMWPE Molecular Weight 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ 2.0 × 10 ⁶ content
(wt%) 30 18 2 18 40 18 HDPE Molecular Weight 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ 3.0 × 10 ⁵ content
(wt%) 70 82 98 82 60 82 Manufacturing conditions The resin concentration (wt%) of the melt- 28.5 30 40 30 23 25 Cooling
speed ℃ / min 210.0 210.0 210 160.0 210 160 1st
Stretching Temperature (℃) 110.0 110.0 119.5 115.0 117.0 118.0 Face magnification 25.0 25.0 25.0 25.0 25.0 25.0 Second
Stretching Temperature (℃) 127 130 130 130 128 126 Magnification (TD) 1.60 1.60 1.40 1.36 1.60 1.40 Second
Relaxation after stretching Temperature (℃) 130 130 - 130 128 - Relaxation rate / magnification (TD) 9% / 1.45 9% / 1.45 - 3% / 1.32 12% / 1.4 - Coiling
tension (N) 7 7 9 16 16 7

Yes No, Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Properties of microporous membrane Film thickness (占 퐉) 7.1 9.4 5.3 11.7 3.0 3.0 Air permeability (sec / 100 cm ³ ) 187 201 137 228 45 45 Porosity (%) 31 31 32 31 40 40 Sting Strength (mN) 2393 2846 2160 2771 1568 1960 Tensile breaking strength (MPa) MD 160 140 181 117 196 216 TD 193 170 216 121 245 255 Tensile elongation at break (%) MD 143 194 152 172 95 80 TD 121 152 124 171 70 64 Heat Shrinkage (%) MD 3.3 2.8 3.6 2.2 9.2 11.0 TD 2.2 0.5 1.6 0.7 2.6 4.0 Pore diameter distribution A: average flow diameter (nm) 38 43 37 40 30 35 B: Bubble Point
Pore Diameter (nm) 53 59 51 58 47 51 A-B 15.0 15.9 14.0 18.0 17.0 16.0 Compressibility
[Film thickness] (占 퐉) Film thickness
[Before the test] 7.1 8.8 4.9 11.8 3.2 3.0 Film thickness
[After the test] 6.9 8.6 4.8 11.6 3.0 2.7 Film thickness
Rate of change (%) 2.2 2.3 2.0 1.7 6.3 10.0 Compressibility
[Specularity]
(sec / 100 cm ³ ) speculation
Resistance
[Before the test] 212 218 133 266 45 45 speculation
Resistance
[After the test] 286 279 176 347 60 65 Percentage change of dumping resistance (%) 35 28 32 31 33 44 Properties of Cell Specularity Press
Pressure 3 MPa 259 256 155 306 53 56 Press
Pressure 5 MPa 286 279 176 347 60 65 Impedance change rate (%) 4.7 4.0 6.0 5.9 5.8 6.9 Thickness change ratio (%) Press
Pressure 3.0 MPa 12 13 12 13 12 12 Press
Pressure 5.0 MPa 9 10 9 10 9 9

Yes No, Example 7 Example 8 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Properties of microporous membrane Film thickness (占 퐉) 3.0 3.0 9.0 7.0 11.8 12.0 Air permeability (sec / 100 cm ³ ) 50 55 129 165 127 150 Porosity (%) 40 40 39 30 43 45 Sting Strength (mN) 1470 1372 2603 2156 3350 2058 Tensile breaking strength (MPa) MD 181 172 115 132 133 118 TD 230 211 164 157 162 157 Tensile elongation at break (%) MD 112 125 218 145 183 155 TD 87 95 127 120 153 124 Heat Shrinkage (%) MD 7.0 5.0 2.7 4.0 4.2 3.7 TD 1.5 1.0 2.4 3.0 0.7 4.5 Pore diameter distribution A: average flow diameter (nm) 33 35 42 45 40 45 B: Bubble Point
Pore Diameter (nm) 49 51 69 72 70 73 A-B 16.0 16.0 26.4 27.0 30.0 27.1 Compressibility
[Film thickness] (占 퐉) Film thickness
[Before the test] 3.0 3.0 8.2 7.0 11.0 12.0 Film thickness
[After the test] 2.8 2.8 6.7 6.4 9.7 9.9 Film thickness
Rate of change (%) 6.7 6.7 17.9 8.6 11.9 17.2 Compressibility
[Specularity]
(sec / 100 cm ³ ) speculation
Resistance
[Before the test] 50 55 129 165 122 150 speculation
Resistance
[After the test] 64 69 220 300 212 289 Percentage change of dumping resistance (%) 28 25 71 82 74 93 Properties of Cell Specularity Press
Pressure 3 MPa 58 63 160 215 157 190 Press
Pressure 5 MPa 64 69 220 300 212 289 Impedance change rate (%) 4.7 4.3 13.6 14.2 13.0 17.1 Thickness change ratio (%) Press
pressure
3.0 MPa 11 11 13 12 13 13 Press
pressure
5.0 MPa 8 8 10 10 10 10

Claims (8)

The rate of change in the durability after heat compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes was 50% or less, and the rate of change in the film thickness after heating and compression at a temperature of 90 占 폚 and a pressure of 5.0 MPa for 5 minutes was not more than the film thickness of the polyolefin microporous film 100% &lt; / RTI &gt; by weight of the polyolefin microporous membrane. The method according to claim 1,
A polyolefin microporous membrane having a tensile strength in the MD direction of 110 MPa or more and a tensile strength in the TD direction of 120 MPa. 3. The method according to claim 1 or 2,
Wherein the content of ultrahigh molecular weight polyethylene having a weight average molecular weight (Mw) of 1 x 10 &lt; ⁶ &gt; or more is 10 to 40% by mass based on 100% by mass of the total polyethylene. 4. The method according to any one of claims 1 to 3,
A polyolefin microporous membrane having a film thickness of 16 탆 or less. 5. The method according to any one of claims 1 to 4,
A microporous polyolefin membrane having a porosity of 25-40%. 6. The method according to any one of claims 1 to 5,
A microporous polyolefin membrane having an average pore diameter of 0.05 탆 or less and a bubble point (BP) pore diameter of 0.06 탆 or less as determined by a permeometer. A separator for a battery comprising the polyolefin microporous membrane according to any one of claims 1 to 6. A battery using the battery separator of claim 7.