KR101690101B1 - Microporous membranes and methods for producing and using such membranes - Google Patents

Abstract

The present invention relates to a multilayer microporous polymer membrane suitable for use as a battery separator film. The present invention also relates to a method for producing such a film, a battery containing such a film as a battery separator film, a method for producing such a battery, and a method for using such a battery.

Description

TECHNICAL FIELD [0001] The present invention relates to a microporous membrane, a method of manufacturing such membrane,

The present invention relates to a multilayer microporous polymer membrane suitable for use as a battery separator film. The present invention also relates to a method for producing such a film, a battery containing such a film as a battery separator film, a method for producing such a battery, and a method for using such a battery.

The microporous membrane can be used as a battery separator in, for example, a lithium primary battery and a secondary battery, a lithium polymer battery, a nickel hydride battery, a nickel cadmium battery, a nickel zinc battery, and a silver silver secondary battery. When the microporous polyolefin membrane is used in a battery separator, particularly a lithium ion battery separator, the properties of the membrane have a significant influence on the characteristics, productivity and performance of the battery. Therefore, it is preferable that the microporous membrane has resistance to thermal shrinkage particularly at a high temperature. Resistance to thermal shrinkage (i.e., heat shrinkage) can improve the battery's resistance to internal shorts.

This internal short circuit is particularly related to the loss of dimensional stability near the edge of the battery separator film. If the width of the film is reduced at a temperature higher than the shutdown temperature of the film, the anode and the cathode may be in contact with each other. This is especially the case for prismatic and cylindrical cells, where even small changes in film width can lead to anode-cathode contact at or near the edge of the cell.

Conventionally, the heat shrinkage performance has been determined to be about 105 占 폚, but the shutdown temperature of the microporous membrane is typically in the range of 130 占 폚 to 140 占 폚. Therefore, the heat shrinkage performance at 130 占 폚 may be a better indicator for classifying the film superior to the performance under shutdown conditions. However, it has been found that the heat shrinkage performance at 130 ° C is generally unpredictable only from the heat shrinkage performance of the film at 105 ° C. That is, the separator exhibiting good heat shrinkage performance at 105 ° C will not necessarily have sufficient performance at 130 ° C. Therefore, there is still a demand for a battery separator film having improved resistance to heat shrinkage at 130 占 폚.

In an aspect, an embodiment of the present invention is a multilayer microporous membrane comprising polypropylene having an Mw in excess of 1.0 x 10 < ^{6 &} gt ;, wherein the heat shrinkage is less than or equal to 9.5% / 100 cm 3/20 탆 or less. (A) from 1 wt% to 20 wt% of polyethylene, based on the weight of the first layer, of polyethylene having an Mw of greater than 1.0 x 10 ⁶ , and from 80 wt% to 99 wt% of 1.0 x 10 ⁶ a first layer containing more than a polyethylene having a Mw each and a third layer, (b) 5 polypropylene and 0% by weight to 10 parts by weight with Mw in excess of 1.0 × 10 ⁶ wt% to 40 wt% polyethylene having a% of the Mw in excess of 1.0 × 10 ^6, and 60 wt% to 95 polyethylene with weight% of the 1.0 × 10 ⁶ Mw of less than the first layer containing (% by weight based on the weight of the second layer) And a second layer positioned between the third layer; Wherein the membrane has a total polypropylene content of 0 wt% to 10 wt%, a normalized air permeability of 300 sec / 100 cm 3/20 탆 or less, and a TD heat shrink at 130 캜 of 5% or less.

(A) the first layer comprises a first polyolefin and at least a first diluent, and the second layer comprises a second polyolefin and at least a second diluent < RTI ID = 0.0 > Wherein the second polyolefin comprises polypropylene in an amount ranging from 1% to 40% by weight relative to the weight of the second polyolefin, wherein the polypropylene has a Mw of greater than 1.0 x 10 < ⁶ & DELTA Hm to at least one of MD or TD; (b) removing at least a portion of the first diluent and the second diluent from the drawn extrudate to form a TD (C) stretching the film in TD to a second width greater than the first width by a second magnification in the range of about 1.1 to about 1.8 from the first width, and subsequently d) To a third width in the range of about 1.1 to about 1.6 times the first width to the first width.

In another embodiment, the present invention is a cell comprising a multilayer microporous membrane comprising an anode, a cathode, an electrolyte, and polypropylene having a Mw of greater than 1.0 x 10 < ⁶ > and a DELTA Hm of greater than 112 J / g, % Or less and a normalized air permeability of 400 sec / 100 cm 3 or less, and the multilayered microporous membrane separates at least the anode from the cathode. Such a battery system can be used in many applications such as electric power supply to an electric car or a hybrid electric vehicle.

1 is a cross-sectional perspective view showing an example of a cylindrical lithium ion secondary battery including an electrode assembly of the present invention.
2 is a cross-sectional view showing the battery of Fig.
Fig. 3 is an enlarged cross-sectional view showing a portion A of Fig. 2;

The present invention relates to the discovery of microporous membranes having improved heat shrinkage properties, i.e., better dimensional stability at higher temperatures. The improvement in the heat shrinkage characteristics can be achieved not only at a relatively low temperature (for example, 110 DEG C or less, which is within the operating temperature range of a conventional lithium ion battery), but also at a relatively high temperature For example, in the vicinity of the shutdown temperature of a conventional battery separator film for a lithium ion battery).

Structure and composition of multilayer microporous membrane

In one embodiment, the microporous membrane comprises a first layer and a second layer. The first layer comprises a first layer material and the second layer comprises a second layer material which is independently selected. The first layer material and the second layer material may be, for example, independently selected polyolefins. For example, the film has a flat uppermost layer when viewed in an axial direction substantially perpendicular to the plane axis along the length and width of the film, and a flat bottom layer that is parallel or nearly parallel to the uppermost layer. In another embodiment, the multilayer microporous membrane comprises a membrane having at least three layers, for example a first layer and a third layer, and a second layer positioned between the first layer and the third layer. The third layer may comprise a third layer material that is independently selected, but this is not essential. When the multilayer microporous membrane has three or more layers, at least one layer comprises a first microporous layer material, and at least one layer comprises a second microporous layer material. In one embodiment, the first and third layers are made from (and generally comprise) a mixture of substantially the same polymer or polymer (e.g., both are made from a first layer material) .

In one embodiment, the multilayer microporous membrane comprises a first layer and a third layer (also referred to as a "surface" layer or a "skin" layer) constituting the outer layer of the membrane, and a second layer between the first and third layers (Or "core" layer). In a related embodiment, the multilayer microporous membrane may comprise additional layers, i. E. Two skin layers and layers other than the core layer. For example, the membrane may contain an additional core layer between the first and third layers. The membrane can be a coated membrane, i.e. having one or more additional layers on the first and third layers or one or more additional layers as the first and third layers. Generally, the second layer of film has a thickness of 5% to 15% of the total thickness of the film; The first and third layers of the film have the same thickness, and the thicknesses of the first and third layers are respectively in the range of 42.5% to 47.5% of the total thickness of the film.

Optionally, the core layer is in planar contact with one or more skin layers that are laminated facing each other in a layered arrangement such as A / B / A. If the membrane contains a polyolefin, the membrane may be referred to as a "polyolefin membrane ". The film may contain only polyolefin, but this is not essential, and it is within the scope of the present invention that the polyolefin film contains a material that is not a polyolefin and a polyolefin. The preferred polyolefins can be prepared by various preferred processes, for example, chromium catalysts, polymerization in the presence of a Ziegler-Natta catalyst, or polymerization with one or more single site polymerization catalysts.

Hereinafter, the first layer material and the second layer material will be described in more detail.

In one embodiment, the first layer comprises polyethylene. The term polyethylene used in the present invention refers to a polyolefin homopolymer or copolymer containing repeating units derived from ethylene. These include, but are not limited to, polyethylene homopolymers and copolymers in which at least 85% (by number) of repeating units are derived from ethylene. The polyethylene may be a mixture of individual polyethylenes, such as a mixture of two or more polyethylenes, or a reactor blend. In one embodiment, the polyethylene comprises a second polyethylene having an Mw in excess of the first polyethylene and 1.0 × 10 ⁶ 1.0 × 10 ⁶ or less with a weight average molecular weight ( "Mw") of the. The third layer material comprises a first polyethylene having a Mw of less than 1.0 x 10 < ⁶ > and a second polyethylene having a Mw of greater than 1.0 x 10 < ^{6 &} gt ;. The second layer material comprises polypropylene. The term polypropylene used in the present invention refers to a polyolefin homopolymer or copolymer containing repeating units derived from propylene. Such polypropylene includes, but is not limited to, copolymers in which at least 85% (by number) of polypropylene homopolymers and / or repeating units are derived from propylene. The polypropylene may be a mixture or a reactor blend of individual polypropylenes such as a mixture of two or more polypropylenes. For example, in one embodiment the second layer material is a polypropylene having a Mw in excess of the first polyethylene, 1.0 × 10 ⁶ having 1.0 × 10 ⁶ Mw of less than, and optionally excess of 1.0 × 10 ⁶ Lt; RTI ID = 0.0 > Mw. ≪ / RTI > Optionally, the first polyethylene of the second layer material and the third layer material is the same as the first polyethylene of the first layer material. Optionally, the second polyethylene of the second layer material and the third layer material is the same as the second polyethylene of the first layer material. In one embodiment, neither the first layer material nor the third layer material contains polypropylene in an amount greater than 0.5% by weight. In a related embodiment, the first layer material and / or the third layer material consists essentially of a combination of polyethylene, for example substantially the same polyethylene or polyethylene.

In one embodiment, the first layer of material comprises about 80 wt% to about 99 wt%, for example, 92.5 wt% to about 97.5 wt% of the first polyethylene, and about 1 wt% to about 20 wt% 1 wt.% To about 5 wt.% Second polyethylene (wt.% Based on the weight of the first layer material). In one embodiment, the polyethylene of the third layer material is selected from substantially the same polyethylene in a concentration range substantially the same as the first layer material.

In one embodiment, the second layer material comprises a first polyethylene, a polypropylene, for example up to 40% by weight polypropylene, and optionally a second polyethylene. In one embodiment, the microporous membrane comprises from 1.5 to 5% by weight of polypropylene, from 75 to 98% by weight of the first polyethylene, and from greater than 0 to 5% by weight of the second polyethylene (wt% Standard).

The microporous membrane may contain a thermostable polymer such as a copolymer, an inorganic species (such as a species containing silicon and / or aluminum atoms), and / or a polymer as described in PCT Publications WO 2007/132942 and WO 2008/016174, It is not necessary. In one embodiment, the membrane is substantially free of such material. Substantially free in this context means that the amount of such material in the microporous membrane is less than 1% by weight based on the total weight of the polymer used to make the microporous membrane.

The final microporous membrane generally comprises the polymer used to make the extrudate. In addition, small amounts of diluent or other species introduced during processing may also generally be present in an amount of less than 1% by weight based on the weight of the microporous membrane. In some cases, the molecular weight of the polymer decreases slightly during processing, but this is acceptable. In one embodiment, the Mw of the polymer in the membrane is reduced by, for example, about 10% or less, or about 1% or less, or about 0.1% or less of the Mw of the polymer used to make the membrane.

Hereinafter, the polypropylene, the first polyethylene and the second polyethylene, and the diluent used for producing the extrudate and the microporous membrane will be described in more detail.

Materials used to make microporous membranes

In one embodiment, the first layer material and the third layer material are prepared from a first diluent and a first polyethylene and a second polyethylene; The second layer material is prepared from a second diluent, a first polyethylene, a polypropylene, and optionally a second polyethylene. Alternatively, polymers such as those described in PCT Publication Nos. WO 2007/132942 and WO2008 / 016174, both of which are incorporated herein by reference in their entirety, and the like, such as inorganic species (species containing silicon and / or aluminum atoms, etc.) The first layer material, the second layer material and / or the third layer material can be prepared by using the heat resistant polymer of the present invention. In one embodiment, these optional species are not used.

A. First polyethylene

The first polyethylene has a Mw in the range of about 1.0 x 10 ⁶ or less, such as about 1.0 x 10 ⁵ to about 9 x 10 ⁵ , such as about 4 x 10 ⁵ to about 8 x 10 ⁵ . Optionally, the first polyethylene has a molecular weight distribution ("MWD") ranging from about 1 to about 100, such as from about 3 to about 20. For example, the first polyethylene may be at least one of high density polyethylene ("HPDE"), medium density polyethylene, branched low density polyethylene, or linear low density polyethylene.

In one embodiment, the first polyethylene has a terminal unsaturation amount of at least 0.2 per 10,000 carbon atoms, for example, at least 5 per 10,000 carbon atoms or at least 10 per 10,000 carbon atoms. The amount of terminal unsaturated groups can be measured, for example, according to the procedure described in PCT Publication No. WO97 / 23554.

In one embodiment, the first polyethylene is a homopolymer of (i) an ethylene homopolymer or (ii) a comonomer of ethylene and up to 10 mol% of -olefins such as propylene, butene-1, hexene- At least one of the copolymers. Such polymers or copolymers can be prepared by any convenient polymerization process including Ziegler-Natta catalyst process, chromium catalyst process, or single site catalytic process. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, .

B. Second Polyethylene

The second polyethylene has a Mw of greater than 1.0 x 10 ⁶ , such as in the range of 1.0 x 10 ⁶ to about 5 x 10 ⁶ , such as from about 1.2 x 10 ⁶ to about 3 x 10 ⁶ , for example, about 2 x 10 ⁶ . The second polyethylene has an MWD of from about 2 to about 100, for example from about 3 to about 10. [ For example, the second polyethylene may be ultra high molecular weight polyethylene ("UHMWPE"). In one embodiment, the first polyethylene is at least one of (i) an ethylene homopolymer or (ii) a copolymer of a comonomer such as ethylene and up to 10 mol% of -olefins. Optionally, the comonomer is one or more of propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, . Such polymers or copolymers can be prepared by any convenient polymerization process including Ziegler-Natta catalyst process, chromium catalyst process, or single site catalytic process.

C. Polypropylene

Alternatively, the polypropylene may comprise propylene and up to 10.0 mol% comonomer (such as one or more alpha-olefins), such as ethylene, butene-1, pentene-1, hexene- -1, vinyl acetate, methyl methacrylate, and styrene; Diolefins such as butadiene, 1,5-hexadiene, 1,7-octadiene, and 1,9-decadiene; And copolymers of other comonomers.

In one embodiment, the polypropylene comprises a first polypropylene that itself comprises at least one polypropylene homopolymer or copolymer (random or block). The first polypropylene has a Mw of at least 5 x 10 ⁵ , such as from about 5.0 x 10 ⁵ to about 2.0 x 10 ⁶ , such as from about 1.1 x 10 ⁶ to about 1.5 x 10 ⁶ . Optionally, the polypropylene has an MWD of less than or equal to 100, such as from about 1 to about 50, or from 2.0 to 6.0; And a heat of fusion of not less than 100.0 J / g, such as 110.0 J / g to 120.0 J / g, for example, about 113.0 J / g to 119.0 J / g or 114.0 J / DELTA Hm "). ? Hm is disclosed in PCT Patent Publication No. As described in WO2007 / 132942, using differential scanning calorimetry according to JIS K7122.

Optionally, the polypropylene has the following characteristics: (i) the polypropylene is isotactic; (ii) an elongational viscosity of at least about 50,000 Pa sec at a temperature of 230 DEG C and a strain rate of 25 seconds ^-1 ; (iii) a melting peak of at least about 160 DEG C (second melting); And / or (iv) at least about 15 Trouton ratios when measured at a temperature of about 230 DEG C and a strain rate of 25 s < ^-1 >.

Mw and MWD of polyethylene and polypropylene are measured using high temperature size exclusion chromatography with differential refractive index detector (DRI), or "SEC" (GPC PL 220, Polymer Laboratories). The measurement is carried out according to the procedure disclosed in "Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)". Three PLgel Mixed-B columns (Polymer Laboratories) are used to measure Mw and MWD. With respect to polyethylene, the nominal flow rate is 0.5 cm 3 / min, the nominal injection volume is 300 μl, and the transfer line, column and DRI detector are contained in an oven maintained at 145 ° C. For polypropylene, the nominal flow rate is 1.0 cm 3 / min, the nominal injection volume is 300 μl, and the transfer line, column, and DRI detector are contained in an oven maintained at 160 ° C.

The GPC solvent used is 1,2,4-trichlorobenzene (TCB) in a filtered Aldrich reagent grade containing about 1000 ppm butylated hydroxytoluene (BHT). Deaerate the on-line degasser before introducing the TCB to the SEC. Use the same solvent as SEC eluent. The polymer solution is prepared by placing the dry polymer in a glass container, adding the desired amount of TCB solvent, and then heating the mixture for about 2 hours with continuous stirring at 160 캜. The concentration of the polymer solution is 0.25 to 0.75 mg / ml. The sample solution is filtered off with a 2 μm filter using Model SP260 Sample Prep Station (Polymer Laboratories) prior to injection into GPC.

Mp ("Mp" is defined as picross in Mw) is calibrated using the polystyrene standards of each of 17 types ranging from about 580 to about 10,000,000. Polystyrene standards are available from Polymer Laboratories (Amherst, MA). For each PS standard, the storage capacity at the peak in the DRI signal is recorded, and the calibration curve (log Mp vs. storage capacity) is created by substituting this data set into the second-order polynomial. Wave Metrics, Inc. Analyze the sample using the product IGOR Pro.

Method for producing microporous membrane

In one embodiment, the multilayer microporous membrane of the present invention is a two-layer membrane. In another embodiment, the multilayer microporous membrane has at least three layers. The present invention is not limited to this, but it is possible to use a second layer comprising a first layer and a third layer mainly comprising a first layer material, and a second layer material positioned between the first layer and the third layer, A description will now be given of a method for producing a microporous membrane with respect to a three-layer film.

One method of producing the multilayer microporous membrane of the present invention includes, for example, layering by extrusion or coextrusion of an extrudate or membrane, for example, a single layer extrudate or a single layer microporous membrane. For example, one or more layers comprising a first layer of material may comprise one or more layers comprising a second layer of material, e.g., one or both of layers (or layers) comprising a second layer of material Coextruded together with the layer comprising the first layer material located on the side of the first layer.

The manufacturing process of the film is carried out in a first plane direction (for example, the machine direction or "MD" of the extrusion) and a second plane direction orthogonal (for example, Lt; RTI ID = 0.0 > extrudate. ≪ / RTI > The extrudate may comprise at least a first layer, a second layer, and a third layer, wherein the second layer is positioned between the first and third layers. The first and third layers of the extrudate comprise a first layer of material and at least a first diluent and a second layer of extrudate comprises a second layer of material and at least a second diluent. The first and third layers may be outer layers of extrudates, also referred to as skin layers. Those skilled in the art will appreciate that the third layer of extrudate may be formed from another layer material, such as a third layer material, and may have a different thickness than the first layer. The process may also include stretching the cooled extrudate to MD and / or TD and removing at least a portion of the first and second diluents from the drawn extrudate to form a first dry length in the first plane direction and a second dry length in the second plane direction Lt; RTI ID = 0.0 > 1 < / RTI > dry width. This process is then associated with stretching the dried film according to TD, and optionally MD, to form the final film. Hereinafter, an embodiment for manufacturing a three-layer film will be described in more detail.

The mixture of the first layer material and the first diluent

The first layer material is prepared by mixing the first polyethylene and optionally the second polyethylene, for example by dry blending or melt blending. Mixed polymers may be mixed with one or more diluents to form a mixture of polymer and diluent. The polymer may be in the form of a polymer resin. The diluent may be, for example, a solvent for the polymer of the first layer material. When the diluent is such a solvent, the diluent may be referred to as a film-forming solvent, and the mixture of the polymer and the diluent may be referred to as a polymer solution, for example, a polyolefin solution. The mixture of the first layer material and the diluent may optionally contain additives such as one or more antioxidants. In one embodiment, the amount of such additive does not exceed 1% by weight based on the weight of the mixture of polymer and diluent.

Optionally, the first diluent is a solvent that is liquid at room temperature. While not intending to be bound by any theory or model, the use of a liquid solvent to form the first polyolefin solution makes it possible to draw the extrudate (generally a gel sheet) at a relatively high draw ratio I think.

As the diluent of the present invention, any species which can be combined with the resin at the extrusion temperature to form a single phase may be used. Examples of the diluent include aliphatic or cyclic hydrocarbons such as nonane, decane, decalin and paraffin oil; And phthalic acid esters such as dibutyl phthalate and dioctyl phthalate. A paraffin oil having a kinematic viscosity at 40 DEG C of 20 to 200 cSt can be used. The selection of the first diluent, mixing conditions, extrusion conditions and the like can be carried out, for example, in PCT Patent Publication No. 10/1994, which is incorporated herein by reference in its entirety. May be the same as those disclosed in WO2008 / 016174.

The amount of the first diluent in the mixture of the diluent and the first layer material in the first polyolefin solution is not critical. In one embodiment, the amount of the first diluent ranges from 20 wt% to 99 wt%, preferably 60 wt% to 80 wt%, based on the weight of the mixture of the first diluent and the first layer material. It is considered that the higher the concentration of the diluent contributes to the improvement of the heat shrinkability of the predetermined film described in the present invention.

The mixing of the second layer material and the second diluent

The second layer material and the second diluent may be mixed by the same method as used to mix the first layer material and the first diluent. For example, the polymer comprising the second layer material may be mixed by melt blending the first polyethylene, the polypropylene, and optionally the second polyethylene. The second diluent may be selected from the same diluent as the first diluent. In addition, the second diluent can be selected independently (and generally independently) from the first diluent, and the diluent can be the same as the first diluent, and the same as the first diluent used in the first polyolefin solution It can be used as a relative concentration.

In one embodiment, the method of producing the second polyolefin solution differs from the method of preparing the first polyolefin solution in that the mixing temperature is preferably in the range of the melting point (Tm 2) of polypropylene to Tm 2 + 90 ° C.

Extrusion

In one embodiment, the mixture of the first layer material and the first whitening agent is guided from the first extruder to the first die and the third die, and the mixture of the second layer material and the second diluent is introduced from the second extruder into the second Is guided to the die. Layered extrudate (that is, an object significantly larger in the planar direction than the thickness direction) is extruded (for example, co-extruded) from the first die, the second die, and the third die to form a multilayer first diluent A multilayer extrudate having a skin layer of a mixture of one-layer materials and a core layer of a mixture of a second layer material and a second diluent can be produced.

The choice of die or plurality of die and extrusion conditions is described, for example, in PCT Publication No. < RTI ID = 0.0 > May be the same as those disclosed in WO2008 / 016174.

Cooling of multilayer extrudates

The multilayer extrudate can be exposed to temperatures in the range of 15 ° C to 25 ° C to form a cooled extrudate. The cooling rate is not particularly important. For example, the extrudate may be cooled at a cooling rate of at least about 30 ° C / min until the temperature of the extrudate (the cooled temperature) is approximately equal to the gelation temperature of the extrudate (or less). The conditions of the cooling treatment are described, for example, in PCT Publication Nos. May be the same as those disclosed in WO2008 / 01617. In one embodiment, the cooled extrudate has a thickness in the range of 10 mm or less, such as 0.1 mm to 10 mm, or 0.5 mm to 5 mm. Generally, the second layer of cold extrudate has a thickness of 5% to 15% of the total thickness of the cooled extrudate; The first and third layers of the cooled extrudate have substantially the same thickness, and the thicknesses of the first and third layers are in the range of 42.5% to 47.5% of the total thickness of the cooled extrudate, respectively.

Stretching of cold extrudate

The cooled extrudate is then stretched in at least one direction (e.g., in at least one plane direction, such as MD or TD) (referred to as "wet" stretching) to produce a drawn extrudate. Optionally, the extrudate is simultaneously stretched in the transverse and machine directions at a magnification in the range of 4 to 6. A preferred stretching method is disclosed in, for example, PCT Publication Nos. WO2008 / 016174. Although not required, the MD and TD magnifications may be the same. In one embodiment, the draw magnification is equivalent to 5 in MD and TD. In some embodiments, the elongation is performed at a strain rate of less than or equal to about 850% per minute, less than or equal to 800% per minute, less than or equal to 775% per minute, or less than or equal to 700% per minute. Deformation rates ranging from 600% / min to about 800% / min, or from 700% / min to 800% / min are useful. Although the biaxially stretched film will be stretched both in MD and TD dimensions, the term "strain rate" as used in the present invention means that at least one of the planar dimensions of the film (e.g. MD, TD, It represents speed. For example, a film stretched at a magnification of 5 times in MD and TD over the course of a biaxial stretching process has a strain rate of 500% / min in both MD and TD, and at a strain rate of 500% It can be described that it has been stretched.

Although not required, the stretching may be performed while exposing the extrudate to a temperature in the range of about Tcd to Tm. Tcd and Tm are defined as the melting point of the crystalline dispersion temperature and of the polyethylene having the lowest melting point (i.e., the first polyethylene and the second polyethylene) among the polyethylenes used to prepare the extrudate. The crystal dispersion temperature is determined by measuring the temperature characteristic of dynamic viscoelasticity according to ASTM D 4065. In embodiments wherein the Tcd is in the range of about 90 to 100 占 폚, the stretching temperature is about 90 to 125 占 폚; Preferably about 100 to 125 캜, more preferably 105 to 125 캜, and still more preferably 119 to 125 캜. It is believed that a higher draw temperature may provide a film with less shrinkage under operating conditions.

In one embodiment, the drawn extrudate is optionally heat treated prior to diluent removal. In the heat treatment, the drawn extrudate is exposed to a temperature (warm) above the temperature at which the extrudate is exposed during stretching. In one embodiment, the drawn extrudate is exposed to a temperature in the range of 120 ° C to 125 ° C for a time in the range of 1 second to 100 seconds while the drawn extrudate is fixed, for example, using a tenter clip The wet length and the wet width are kept constant. In another embodiment, the drawn extrudate is exposed to a temperature that is not higher than the temperature at which the extrudate is exposed during stretching, preferably at a lower (colder) temperature. In one embodiment, the drawn extrudate is exposed to a temperature in the range of 90 占 폚 to 120 占 폚 for a time in the range of 1 second to 100 seconds and particularly in the range of about 90 占 폚 to 100 占 폚 for a stretching temperature of 119 to 120 占 폚 For example, the tenter clips are used to fix the drawn extrudate along its periphery so that the wet length and the wet width are kept constant. The plane dimensions (MD length and TD width) of the drawn extrudate can be kept constant while the drawn extrudate is exposed to higher temperatures. Since the extrudate contains a polymer and a diluent, its length and width are referred to as the "wet" length and the "wet" width. That is, there is no magnification or reduction (i.e., dimensional change) of the drawn extrudate to MD or TD during the heat treatment.

In other processes such as dry stretching and heat treatment where this process and samples (e.g. extrudates, dry extrudates, membranes, etc.) are exposed to high temperatures, such exposure can be accomplished by heating the air, And the like. The temperature of the heated air is generally controlled at a set point equivalent to the desired temperature, and is then conveyed to the sample through the plenum, for example. Other methods of exposing a sample to a high temperature, including a conventional method such as a method of exposing a sample to a heating surface and infrared heating in an oven, may be used together with or instead of heated air.

It is expected that not to be bound to any particular theory, but it is believed that relatively high stretching temperatures allow relaxation of polymer chain entanglement, thereby reducing heat shrinkage at higher temperatures. It is considered that the selective heat treatment contributes to improvement of the heat shrinkage performance at a higher temperature.

Removal of the first and second diluents

In one embodiment, at least a portion of the first diluent and the second diluent (e.g., a film forming solvent) is removed (or replaced) from the drawn extrudate to form a dried film. Substituted (or "cleaned") solvents may be used to remove (clean or replace) the first diluent and the second diluent. The treatment conditions for removing the first diluent and the second diluent are, for example, those disclosed in PCT Publication Nos. May be the same as those disclosed in WO2008 / 016174. The term "dry film" refers to an extrudate from which at least a portion of the diluent has been removed. It is not necessary to remove all of the diluent from the drawn extrudate, but removing the diluent may increase the porosity of the final membrane, so it may be desirable to remove all of the diluent.

In one embodiment, at least a portion of any remaining volatilized species, such as a cleaning solvent, may be removed from the dried film at any point after removal of the diluent. Any method capable of removing the cleaning solvent including conventional methods such as heat drying and air blow drying (air movement) can be used. The treatment conditions for removing the volatile species such as the washing solvent are, for example, those disclosed in PCT Publication Nos. WO2008 / 016174 and WO2007 / 132942.

Stretching the dried film

The dried film is stretched by at least TD (referred to as "dry stretching"). The dry stretched dried film is referred to as an "oriented" film. The dry film before dry stretching has an initial size (first drying length) to the MD and an initial size (first drying width) to TD. The term "first dry width" used in the present invention indicates the size in the transverse direction of the dry film before the start of the dry orientation. The term "first dry length" refers to the size of the dried film in the machine direction before initiation of the dry orientation. For example, a tenter stretching device of the kind described in WO2008 / 016174 can be used.

The dried film can be TD stretched to a second drying width which is larger than the first drying width by a magnification ("TD drying stretching magnification") in the range of about 1.1 to about 1.8 from the first drying width. Alternatively, if dry stretching is used, the dried film can be MD stretched to a second dry length that is longer than the first dry length from the first dry length to any magnification ("MD dry stretch magnification"). The stretch (diluent-containing extrudate is already stretched and hence may be referred to as re-stretch) may be sequential or simultaneous with MD and TD. The TD drying shrinkage generally does not exceed the magnitude of the MD drying shrinkage, as the effect of the TD shrinkage on the cell properties is generally greater than the MD heat shrinkage. When TD dry stretching is used, dry stretching may be simultaneous or sequential to MD and TD. When the dry stretching is sequential, MD stretching is generally performed first, and then TD stretching is performed.

Dry stretching is generally carried out while the dry film is exposed to a temperature of Tm or less, for example, a temperature in the range of about Tcd-30 ° C to Tm. In embodiments wherein the membrane is a multilayer membrane having a first layer and a third layer comprising polyethylene and a second layer comprising polypropylene positioned between the first layer and the third layer, At a temperature of about 135 占 폚, for example from about 80 占 폚 to about 132 占 폚, especially 125 占 폚 to 132 占 폚 or 128 占 폚 to 131 占 폚.

In one embodiment, the MD dry draw ratio is in the range of about 1.1 to about 1.5, such as 1.2 to 1.4; The TD dry stretching magnification is in the range of about 1.1 to about 1.3, for example, 1.15 to 1.25. First, the MD stretching is performed, and then the TD stretching is performed.

The elongation is preferably 3% / sec or more in the stretching direction (MD or TD), and this elongation can be independently selected for MD and TD stretching. The elongation is preferably 5% / second or more, more preferably 10% / second or more, for example, 5% / second to 25% / second. Although not particularly important, it is preferable that the upper limit of the elongation is 50% / sec in order to prevent the film from rupturing.

Controlled membrane width reduction

Following the dry stretching, the dry film is subjected to a controlled width reduction from a second dry width to a third width, wherein the third dry width is from about 1.1 to about 1.6 times the first dry width, 1.3 to 1.5 times. Width reduction is generally done while exposing the membrane to a temperature above Tcd-30 ° C but below Tm. For example, during width reduction, the film may be exposed to temperatures in the range of from about 70 ° C to about 135 ° C, for example from about 127 ° C to about 132 ° C, such as from about 128 ° C to about 131 ° C. In one embodiment, the reduction in film width is done while exposing the film to a temperature below Tm. In certain embodiments, the third dry width is in the range of 1.0 to about 1.6 times, or 1.2 to 1.5 times the first dry width.

It is believed that exposing the film to a temperature above the exposed temperature during TD stretching during controlled width reduction further improves the heat shrinkability of the final film.

Selective heat treatment

Alternatively, the thin film may be thermally treated (heat-treated) at least once after the removal of the diluent, for example after the dry stretching, after the reduction of the controlled width. It is considered that the heat treatment stabilizes the crystal to form a uniform thin layer in the film. In one embodiment, the heat treatment is performed by exposing the film to a temperature ranging from Tcd to Tm, such as from about 100 DEG C to about 135 DEG C, such as from about 127 DEG C to about 132 DEG C, or from about 129 DEG C to about 131 DEG C I do. In general, the heat treatment is performed for a time sufficient to form a uniform thin layer in the film, for example, a time ranging from 1 to 100 seconds. In one embodiment, the heat treatment is performed under conventional heat treatment "heat setting" conditions. The term "heat setting" refers to a heat treatment that is performed, for example, while keeping the length and width of the film substantially constant by securing the periphery of the film with a tenter clip during the heat treatment.

Alternatively, the annealing process can be performed after the heat treatment process. The annealing is a heat treatment that does not apply a load to the film, and may be performed using, for example, a heating chamber provided with a belt conveyor or an air-type heating chamber. The annealing can be continuously performed in a state in which the tenter is loosened after the heat treatment. During annealing, the film may be exposed to temperatures in the range of Tm or less, such as in the range of about 60 [deg.] C to about Tm-5 [deg.] C. It is believed that annealing provides a microporous membrane with improved permeability and strength.

Selective heating roller treatment, thermal solvent treatment, crosslinking treatment, hydrophilic treatment, and coating treatment can be carried out, for example, in PCT Publication Nos. Can be carried out as required as described in WO2008 / 016174.

Alternatively, the annealing treatment may be performed before the heat treatment, during the heat treatment, or after the heat treatment. The annealing is a heat treatment that does not apply a load to the film, and can be performed using, for example, a heating chamber having a belt conveyor or an air-type heating chamber. The annealing can be performed continuously, for example, with the tenter loosened after the heat treatment. The temperature at which the film is exposed during annealing ("annealing temperature") may range, for example, from about 126.9 ° C to 128.9 ° C. It is believed that annealing provides a microporous membrane with improved thermal shrinkage and strength.

A heating roller treatment, a heat solvent treatment, a crosslinking treatment, a hydrophilic treatment, and a coating treatment may be selectively performed, for example, in PCT Publication Nos. Can be carried out as required as described in WO2008 / 016174.

Properties of multilayer microporous membrane

In one embodiment, the membrane is a multilayer microporous membrane. The thickness of the film is generally in the range of 3 탆 or more. For example, the membrane may have a thickness in the range of about 5 占 퐉 to about 200 占 퐉, for example, in the range of about 10 占 퐉 to about 50 占 퐉. The thickness of the film can be measured by a contact type thickness measuring device over a width of 10 cm at intervals of 1 cm in the longitudinal direction, for example, and then the film thickness can be obtained by averaging. A thickness measuring device such as Litematic manufactured by Mitsutoyo Corporation is preferable. This method is also preferable for measuring a change in thickness after thermal compression as described later. Further, a noncontact thickness measurement method, for example, an optical thickness measurement method is also preferable.

Optionally, the membrane has at least one of the following properties.

A. Porosity

In one embodiment, the membrane has a porosity in the range of 25% or more, such as about 25% to about 80%, or 30% to 60%. The porosity of the membrane is measured by comparing the weights of equivalent non-porous membranes (equivalent in terms of having the same length, width, and thickness) of the same composition as the actual weight of the conventional membrane. The porosity is then measured using the following formula% = 100 x (w2-w1) / w2, where w1 is the actual weight of the microporous membrane and w2 is the equivalent weight with the same size and thickness It is the weight of sclera.

B. Normalization specularity

In one embodiment, the normalized permeability (Gurley value) of the membrane is 400 sec / 100 cm 3/20 탆 or less. The normalized permeability is measured according to JIS P8117 and the result is normalized with respect to the permeability value of an equivalent membrane having a thickness of 20 mu m using the formula A = 20 mu m x (X) / T < ₁ & ₁ , and A is a normalized permeability of an equivalent membrane having a thickness of 20 mu m. Since the permeability value is normalized to the value of an equivalent film having a thickness of 20 mu m, the permeability value is expressed in units of "sec / 100 cm3 / 20 mu m ". In one embodiment, the normalized air permeability is in the range of 20.0 sec / 100 cm 3/20 탆 to about 400 sec / 100 cm 3/20 탆, or 150 sec / 100 cm 3/20 탆 to 250 sec / 100 cm 3/20 탆.

C. Normalized puncture strength

In one embodiment, the membrane has a normalized puncture strength in the range of 130 mN / [mu] m or more, e.g., 130 mN / [mu] m to 250 mN / [mu] m. The puncture strength is defined as the maximum load measured when a microporous membrane having a thickness T ₁ is stuck at a speed of 2 mm / sec with a needle having a spherical surface (radius of curvature R: 0.5 mm) having a diameter of 1 mm at its distal end. The puncture strength is normalized to a value in a film having a thickness of 1 탆 using the formula S ₂ = 1 탆 x (S ₁ ) / T ₁ where S ₁ is a measured value of puncture strength, and S ₂ Is the normalized puncture strength, and T ₁ is the average thickness of the membrane.

D. Tensile Strength

In one embodiment, the membrane has a MD tensile strength in the range of 55,000 to 90,000 kPa, and / or TD tensile strength in the range of, for example, 75,000 kPa to 110,000 kPa. Tensile strength is measured in MD and TD according to ASTM D-882A.

E. Tensile elongation of more than 100%

Tensile elongation is measured according to ASTM D-882A. In one embodiment, the MD and TD tensile elongations of the membrane are each in the range of 150% or more, for example, 150% to 350%. In another embodiment, the MD tensile elongation of the membrane is in the range of, for example, 150% to 250%, and the TD tensile elongation is in the range of, for example, 150% to 250%.

F. Shutdown Temperature

In one embodiment, the film has a shutdown temperature in the range of about 140 占 폚 or less, for example, about 132 占 폚 to about 138 占 폚. The shutdown temperature of the microporous membrane is described in PCT Publication Nos. Is measured by the method disclosed in WO2007 / 052663. According to this method, the microporous membrane is exposed to an increasing temperature (5 DEG C / min), and the permeability of the membrane is measured during this time. The shutdown temperature of the microporous membrane is defined as the temperature when the permeability (Gurley value) of the microporous membrane is 100,000 sec / 100 cm3. The permeability of the microporous membrane was measured according to JIS P8117 using an air permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.).

G. Rupture temperature

In one embodiment, the rupture temperature of the membrane is 170 占 폚 or higher, for example, 171 占 폚 to 200 占 폚, or 172 占 190 占 폚. The rupture temperature is measured as follows. A 5 cm x 5 cm microporous membrane was sandwiched with a block having a circular opening of 12 mm in diameter, and a tungsten carbide ball having a diameter of 10 mm was placed on the microporous membrane in the circular opening. The film is then exposed to a temperature rising at a rate of 5 DEG C per minute. The rupture temperature of the film is defined as the temperature at which the rupture of the film initially occurs. The meltdown temperature of the film is defined as the temperature at which the ball completely penetrates the sample, i.e., the temperature at which the sample is destroyed.

In one embodiment, the rupture temperature is in the range of 180 ° C to 190 ° C. Since the membrane preferably has a high rupture temperature, it is preferably used as a battery separator in a high-power, high-capacity lithium ion battery such as a battery used for powering an electric vehicle or a hybrid electric vehicle.

H. Meltdown temperature

The meltdown temperature is measured according to the following procedure: A rectangular sample of 3 mm x 50 mm is cut out from the liquid permeable microstratum so that the long axis of the sample is in straight line with TD and the short axis is in line with MD. The sample is set on a thermomechanical analyzer (TMA / SS6000, manufactured by Seiko Instruments, Inc.) at a chuck distance of 10 mm, that is, a distance of 10 mm from the upper chuck to the lower chuck. The lower chuck is fixed and a load of 19.6 mN is applied to the sample from the upper chuck. Chuck and sample are sealed in a heatable tube. Start at 30 ° C, raise the tube's internal temperature at a rate of 5 ° C / min, measure the change in sample length under a load of 19.6 mN at 0.5 second intervals, and record with a rise in temperature. The temperature is raised to 200 ° C. The meltdown temperature of the sample is defined as the temperature at which the sample is broken, and is generally a temperature in the range of more than 145 ° C to about 200 ° C. In one embodiment, the melt down temperature is in the range of 180 占 폚 or higher, for example, 180 占 폚 to 200 占 폚, for example, 185 占 폚 to 195 占 폚.

I. Heat shrinkage at 105 占 폚 in at least one plane direction of not more than about 1%

In one embodiment, the film has thermal shrinkage at 105 占 폚 in at least one planar direction in the range of 1% or less, for example, 0.5% or less, for example, 0.1% to 0.25%. The shrinkage of the membrane at 105 DEG C in MD and TD is measured as follows: (i) the size of the test piece of the microporous membrane at ambient temperature is measured for both MD and TD, (ii) the test piece of the microporous membrane is measured Equilibrated without load for 8 hours at a temperature of 105 DEG C, and then (iii) the size of the membrane was measured for both MD and TD. The thermal (or "thermal") shrinkage to MD and TD can be obtained by dividing the result of measurement (i) by the result of measurement (ii) and representing the obtained quotient as a percentage.

J. Heat shrinkage at 130 ° C

In one embodiment, the membrane has a TD shrinkage of less than or equal to 8%, e.g., 1% to 7.5%, measured at 130 占 폚. A relatively low heat shrinkage value of, for example, 8% or less may be particularly important since 130 ° C is close to the upper end of this range (shutdown), but typically within the operating temperature range of a lithium ion secondary battery during charging and discharging.

The measured value is slightly different from the measured value of the heat shrinkage at 105 DEG C, and this means that the edge of the film parallel to the TD of the film is generally fixed in the cell, and particularly in the vicinity of the center of the edge of the film parallel to the MD, ) Is limited to a certain degree of freedom. Accordingly, a sample of a microporous film having a square of 50 mm according to TD and 50 mm according to MD was fixed to a frame parallel to the TD (for example, by tape or the like), and a clear aperture of 35 mm in MD and 50 mm in TD To the frame. The frame with the sample attached is then heated for 30 minutes at a temperature of 130 DEG C (e.g. in an oven, etc.) in a thermal equilibrium state and then cooled. The TD shrinkage causes the edges of the film, which is generally parallel to the MD, to bend inward (toward the center of the opening of the frame) slightly. The heat shrinkage to TD (expressed as a percentage) is equal to the TD length of the sample before heating divided by the shortest TD (within the frame) of the heated sample and multiplied by 100%.

K. Maximum heat shrinkage in the molten state

The maximum shrinkage in the melt state in the plane direction of the film is measured according to the following procedure:

Record the length of the sample measured in the temperature range of 135 ° C to 145 ° C using the TMA procedure described for the measurement of the melt-down temperature. As the membrane shrinks and the membrane shrinks, the distance between the chucks decreases. The maximum shrinkage in the molten state is obtained by subtracting the minimum length (which is equal to L2), which is generally measured in the range from about 135 ° C to about 145 ° C, at the sample length between chucks measured at 23 ° C I.e., [L1-L2] / L1 100%. When the TD maximum shrinkage is measured, since the microporous membrane of the 3 mm x 50 mm rectangular sample to be used is produced by this process, the long axis of the sample becomes straight line with the transverse direction of the microporous membrane, And cut out from the microporous membrane as much as possible. When the MD maximum shrinkage is measured, since the microporous membrane of 3 mm x 50 mm, which is used, is produced by this process, the long axis of the sample becomes straight line with the machine direction of the microporous membrane, And cut out from the microporous membrane as much as possible.

In one embodiment, the maximum MD heat shrinkage of the film in the molten state is 25% or less, or 20% or less, such as 1% to 25% or 2% to 20%. In one embodiment, the maximum TD heat shrinkage of the film in the molten state is less than or equal to 11%, or less than or equal to 6%, such as from 1% to 10% or 2% to 5.5%.

battery

The microporous membrane of the present invention is useful as, for example, a battery separator in a lithium ion primary cell, a secondary cell, and the like. Such cells are described in PCT Publication WO2008 / 016174, which is incorporated herein by reference in its entirety.

Fig. 1 shows an example of a cylindrical lithium ion secondary battery including two battery separators. The microporous membrane of the present invention is preferable for use as a battery separator of this type of battery. This battery has a wound electrode assembly 1 including a first separator 10, a second separator 11, a cathode sheet 13, and an anode sheet 12. The thickness of the separator is not constant and is greatly enlarged for the purpose of illustration. The rolled electrode assembly 1 can be wound, for example, such that the second separator 11 is disposed on the outer side of the cathode sheet 13 and the first separator 10 is disposed on the inner side of the cathode sheet. In this embodiment, as shown in Fig. 2, the second separator 11 is disposed on the inner surface side of the wound electrode assembly 1. In Fig.

In this embodiment, as shown in Fig. 3, the anode active material layer 12b is formed on both sides of the current collector 12a, and the cathode active material layer 13b is formed on both sides of the current collector 13a. 2, the anode lead 20 is attached to the distal end portion of the anode sheet 12, and the cathode lead 21 is attached to the distal end portion of the cathode sheet 13. As shown in Fig. The anode lead 20 is connected to the battery lid 27 and the cathode lead 21 is connected to the battery case 23.

The present invention is not limited to this, and the separator of the present invention may include a plurality of anode (one or more) 12 ) And a cathode (three) 13 in the form of a laminated plate.

The anode sheet 12, the cathode sheet 13 and the first and second separators 10 and 11 are impregnated with the electrolytic solution to provide ion transport through the separators 10 and 11 . The impregnation treatment can be performed, for example, by immersing the electrode assembly 1 at room temperature in an electrolytic solution. In the cylindrical lithium ion secondary battery, the wound electrode assembly 1 (see FIG. 1) is inserted into the battery case 23 having the insulating plate 22 on the bottom, the electrolyte solution is injected into the battery case 23, The assembly 1 can be manufactured by covering the battery 1 with the insulating plate 22 and caulking the battery lids 24, 25, 26 and 27 to the battery case 23 through the gasket 28. The battery lid functions as an anode terminal.

As shown in Fig. 3 (the battery lid of Fig. 1, that is, the anode terminal is oriented to the right), the advantage of using a separator having a tendency of shrinkage in the transverse direction to be small Respectively. One role of the separator is to prevent contact between the anode active material layer and the cathode active material layer. When the significant amount of TD heat shrinkage occurs, the thin edges of the separator 10 and the separator 11 are peeled off from the battery lid (peeled toward the left side in FIG. 3) and the anode active material layer and the cathode active material layer are brought into contact with each other, It happens. Since the separator is generally thinner than 200 mu m, the anode active material layer and the cathode active material layer may be very close to each other. Therefore, by slightly reducing the TD shrinkage amount of the separator at the elevated battery temperature, the resistance of the battery to an internal short circuit can be remarkably improved. Therefore, the heat shrinkage performance of the separator at a temperature close to the shutdown is important.

A battery is useful as a source or sink for power from one or more electrical components or electronic components, such as passive components such as resistors, capacitors, and inductors, including, for example, a transformer; A transmission device such as an electric motor and a generator; And electronic devices such as diodes, transistors, and integrated circuits. These components can be connected to the battery by series and / or parallel electrical circuits to form a battery system. The circuit can be directly or indirectly connected to the battery. For example, electricity flowing from a cell may be electrochemically and / or (e. G., Driven by a secondary battery or fuel cell) before it is depleted or accumulated in one or more of these components (For example, by an electric motor). The battery system can be used, for example, as a power source for driving an electric vehicle or a hybrid electric vehicle. In one embodiment, the battery is electrically connected to an electric motor and / or a generator for powering the electric vehicle or the hybrid electric vehicle.

The present invention will be described in more detail with reference to the following examples without intending to limit the scope of the invention.

Example

Example 1

(1) Preparation of the first polyolefin solution

(a) 68.6 wt.% of a first polyethylene resin having a Mw of 5.62 x 10 ⁵ and an MWD of 4.05, (b) 1.4 wt.% of a second polyethylene resin having a Mw of 1.95 x 10 ⁶ and an MWD of 5.09, 30 wt% of a polypropylene resin having a Mw of 1.1 x 10 ⁶ , a heat of fusion of 114 J / g, and an MWD of 5 was dry mixed to prepare a first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

30 wt% of the obtained first polyolefin composition was charged into a first steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) And supplied to a screw extruder to prepare a first polyolefin solution. The weight% is based on the weight of the first polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(2) Preparation of the second polyolefin solution

In the same manner as (a) 82% by weight of a first polyethylene resin having a MWD of Mw and 4.05 of 5.62 × 10 ^5, and (b) a second polyethylene resin having a MWD of 1.95 Mw and 5.09 in × 10 ⁶ 18 wt. By weight of the second polyolefin composition is dry-mixed, and the% is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

25 wt% of the obtained second polyolefin composition was charged into a second steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 75 wt% of liquid paraffin (50 cSt at 40 캜) Screw extruder to prepare a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(3) Preparation of membranes

The first polyolefin solution and the second polyolefin solution were respectively fed from a twin-screw extruder to a three-layer extruded T die and extruded therefrom to obtain a layer thickness ratio of the second polyolefin solution layer / the first polyolefin solution layer / the second polyolefin solution layer to 45.3 /9.4/45.3. ≪ / RTI > A layered extrudate (also referred to as a laminate) is prepared. The extrudate is cooled while passing through a chilled roller controlled at 20 캜 to produce an extrudate in the form of a three-layer gel sheet. The gel sheet was heated at a temperature of 119.5 DEG C for 150 seconds and then exposed to a temperature of 119.5 DEG C ("biaxial stretching temperature") while being stretched at an average strain rate of 750% (Simultaneous) biaxial stretching at a stretching ratio. The stretched gel sheet is heat-treated at 120.0 占 폚 for 18 seconds. The stretched three-layered gel sheet was fixed to an aluminum frame of 20 cm x 20 cm, immersed in a methylene chloride bath controlled at 25 캜 for 3 minutes to remove liquid paraffin, and dried at room temperature to prepare a dried film.

The dry film before dry stretching has an initial drying length (MD) and an initial drying width (TD). The dried film was dried and stretched in TD at a magnification of 1.6 times while being exposed to a temperature of 129.5 DEG C to obtain a second drying width. The length (MD) of the membrane is maintained approximately equal to the original dry length during TD dry stretching. Following the TD dry stretching, the film was subjected to a controlled width reduction (TD) at a final magnification of 1.4 times the second drying width, while being exposed to a temperature of 129.5 DEG C ("width reduction temperature"), It is based on the width of the first film. The length MD of the film is maintained approximately equal to the second drying length during width reduction. The membrane is kept fixed to the batch stretcher, and then the membrane is heat treated for 10 minutes while being exposed to a temperature of 129.5 DEG C ("heat treatment temperature") to produce a final multilayer microporous membrane. Then, the dried film is dried and stretched.

Example 2

(1) Preparation of the first polyolefin solution

(a) 68.6 wt.% of a first polyethylene resin having a Mw of 5.62 x 10 ⁵ and an MWD of 4.05, (b) 1.4 wt.% of a second polyethylene resin having a Mw of 1.95 x 10 ⁶ and an MWD of 5.09, 30 wt% of a polypropylene resin having a Mw of 1.1 x 10 ⁶ , a heat of fusion of 114 J / g, and an MWD of 5 was dry mixed to prepare a first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

30 wt% of the obtained first polyolefin composition was charged into a first steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) And supplied to a screw extruder to prepare a first polyolefin solution. The weight% is based on the weight of the first polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(2) Preparation of the second polyolefin solution

In the same manner as (a) 98% by weight of a first polyethylene resin having a MWD of Mw and 4.05 of 5.62 × 10 ^5, and (b) a second polyethylene resin, 2 parts by weight having a MWD of 1.95 Mw and 5.09 in × 10 ⁶ By weight of the second polyolefin composition is dry-mixed, and the% is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

30 wt% of the obtained second polyolefin composition was charged into a second steel mixing type twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) Screw extruder to prepare a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(3) Preparation of membranes

The first polyolefin solution and the second polyolefin solution were respectively fed from a twin-screw extruder to a three-layer extrusion T die and extruded therefrom to obtain a layer thickness ratio of the second polyolefin solution layer / the first polyolefin solution layer / the second polyolefin solution layer to 45.5 /9.0/45.5. ≪ / RTI > The extrudate is cooled while passing through a chilled roller controlled at 20 캜 to produce an extrudate in the form of a three-layer gel sheet. The gel sheet was heated at a temperature of 119.3 DEG C for 150 seconds and then exposed to a temperature of 119.3 DEG C ("biaxial stretching temperature") and stretched at an average strain rate of 710% (Simultaneous) biaxial stretching at a stretching ratio. The stretched gel sheet is heat-treated at 90.0 占 폚 for 18 seconds. The stretched three-layered gel sheet was fixed to an aluminum frame of 20 cm x 20 cm, immersed in a methylene chloride bath controlled at 25 캜 for 3 minutes to remove liquid paraffin, and dried at room temperature to prepare a dried film.

The dry film before dry stretching has an initial drying length (MD) and an initial drying width (TD). The dried film is dried and stretched in TD at a magnification of 1.5 times while being exposed to a temperature of 129.0 占 폚 to obtain a second drying width. The length (MD) of the membrane is maintained approximately equal to the original dry length during TD dry stretching. Following the TD dry stretching, the film was subjected to a controlled width reduction (TD) at a final magnification of 1.3 times the second drying width while exposing to a temperature of 129.0 占 폚 ("width reduction temperature"), It is based on the width of the first film. The length MD of the film is maintained approximately equal to the second drying length during width reduction. The membrane remains in a fixed state on the batch stretcher, and then the membrane is subjected to heat treatment for 10 minutes while being exposed to a temperature of 129.0 DEG C ("heat treatment temperature") to produce a final multilayer microporous membrane. Then, the dried film is dried and stretched.

Comparative Example 1

(1) Preparation of the first polyolefin solution

(a) 68.6 wt.% of a first polyethylene resin having a Mw of 5.62 x 10 ⁵ and an MWD of 4.05, (b) 1.4 wt.% of a second polyethylene resin having a Mw of 1.95 x 10 ⁶ and an MWD of 5.09, 30 wt% of a polypropylene resin having a Mw of 1.1 x 10 ⁶ , a heat of fusion of 114 J / g, and an MWD of 5 was dry mixed to prepare a first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

30 wt% of the obtained first polyolefin composition was charged into a first steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) And supplied to a screw extruder to prepare a first polyolefin solution. The weight% is based on the weight of the first polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(2) Preparation of the second polyolefin solution

In the same manner as (a) 82% by weight of a first polyethylene resin having a MWD of Mw and 4.05 of 5.62 × 10 ^5, and (b) a second polyethylene resin having a MWD of 1.95 Mw and 5.09 in × 10 ⁶ 18 wt. By weight of the second polyolefin composition is dry-mixed, and the% is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

25 wt% of the obtained second polyolefin composition was charged into a second steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 75 wt% of liquid paraffin (50 cSt at 40 캜) Screw extruder to prepare a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(3) Preparation of membranes

The first polyolefin solution and the second polyolefin solution were respectively fed from a twin-screw extruder to a three-layer extruded T die and extruded therefrom to obtain a layer thickness ratio of the second polyolefin solution layer / the first polyolefin solution layer / the second polyolefin solution layer to 45.8 /8.4/45.8. ≪ / RTI > The extrudate is cooled while passing through a chilled roller controlled at 20 캜 to produce an extrudate in the form of a three-layer gel sheet. The gel sheet was heated at a temperature of 117.0 占 폚 for 120 seconds and then exposed to a temperature of 117.0 占 폚 ("biaxial stretching temperature") while heating with a tenter stretcher at an average strain rate of 940% (Simultaneous) biaxial stretching at a stretching ratio. The stretched gel sheet is heat-treated at 95.0 占 폚 for 15 seconds. The stretched three-layered gel sheet was fixed to an aluminum frame of 20 cm x 20 cm, immersed in a methylene chloride bath controlled at 25 캜 for 3 minutes to remove liquid paraffin, and dried at room temperature to prepare a dried film.

The dry film before dry stretching has an initial drying length (MD) and an initial drying width (TD). The dried film was dried and stretched in TD at a magnification of 1.6 times while being exposed to a temperature of 128.7 占 폚 to obtain a second drying width. The length (MD) of the membrane is maintained approximately equal to the original dry length during TD dry stretching. Following TD dry stretching, the film was subjected to a controlled width reduction (TD) at a final magnification of 1.4 times the second dry width while exposing to a temperature of 128.7 占 폚 ("width reduction temperature"), It is based on the width of the first film. The length MD of the film is maintained approximately equal to the second drying length during width reduction. The membrane is kept fixed to the batch stretcher, and then the membrane is subjected to heat treatment for 10 minutes while being exposed to a temperature of 128.7 DEG C ("heat treatment temperature") to produce a final multilayer microporous membrane. Then, the dried film is dried and stretched.

Comparative Example 2

(1) Preparation of the first polyolefin solution

(a) 68.6 wt.% of a first polyethylene resin having a Mw of 5.62 x 10 ⁵ and an MWD of 4.05, (b) 1.4 wt.% of a second polyethylene resin having a Mw of 1.95 x 10 ⁶ and an MWD of 5.09, 30 wt% of a polypropylene resin having a Mw of 1.1 x 10 ⁶ , a heat of fusion of 114 J / g, and an MWD of 5 was dry mixed to prepare a first polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

30 wt% of the obtained first polyolefin composition was charged into a first steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) And supplied to a screw extruder to prepare a first polyolefin solution. The weight% is based on the weight of the first polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(2) Preparation of the second polyolefin solution

In the same manner as (a) 82% by weight of a first polyethylene resin having a MWD of Mw and 4.05 of 5.62 × 10 ^5, and (b) a second polyethylene resin having a MWD of 1.95 Mw and 5.09 in × 10 ⁶ 18 wt. By weight of the second polyolefin composition is dry-mixed, and the% is based on the weight of the second polyolefin composition. The first polyethylene resin in the composition has a Tm of 135 占 폚 and a Tcd of 100 占 폚.

25 wt% of the obtained second polyolefin composition was charged into a second steel mixing twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 70 wt% of liquid paraffin (50 cSt at 40 캜) Screw extruder to prepare a second polyolefin solution. The weight percent is based on the weight of the second polyolefin solution. The melt blending is performed at 210 캜 and 200 rpm.

(3) Preparation of membranes

The first polyolefin solution and the second polyolefin solution were respectively fed from a twin-screw extruder to a three-layer extruded T die and extruded therefrom to obtain a layer thickness ratio of the second polyolefin solution layer / the first polyolefin solution layer / the second polyolefin solution layer to 45.3 /9.4/45.3. ≪ / RTI > A layered extrudate (also referred to as a laminate) is prepared. The extrudate is cooled while passing through a chilled roller controlled at 20 캜 to produce an extrudate in the form of a three-layer gel sheet. The gel sheet was heated at a temperature of 115.5 DEG C for 129 seconds and then exposed to a temperature of 115.5 DEG C ("biaxial stretching temperature") while being stretched at an average strain rate of 880% (Simultaneous) biaxial stretching at a stretching ratio. The stretched gel sheet is heat-treated at 95.0 占 폚 for 16 seconds. The stretched three-layered gel sheet was fixed to an aluminum frame of 20 cm x 20 cm, immersed in a methylene chloride bath controlled at 25 캜 for 3 minutes to remove liquid paraffin, and dried at room temperature to prepare a dried film.

The dry film before dry stretching has an initial drying length (MD) and an initial drying width (TD). The dried film is dried and stretched in TD at a magnification of 1.6 times while exposed to a temperature of 127.3 캜 to obtain a second drying width. The length (MD) of the membrane is maintained approximately equal to the original dry length during TD dry stretching. Following the TD dry stretching, the film was subjected to a controlled width reduction (TD) at a final magnification of 1.3 times the second drying width, while being exposed to a temperature of 127.3 占 폚 ("width reduction temperature"), It is based on the width of the first film. The length MD of the film is maintained approximately equal to the second drying length during width reduction. The membrane remains in a fixed state on the batch stretcher, and then the membrane is heat treated for 10 minutes at a temperature of 127.3 DEG C ("heat treatment temperature") to produce the final multilayer microporous membrane. Then, the dried film is dried and stretched.

Comparative Example 3

(1) Preparation of the first polyolefin solution

(a) 82% of a first polyethylene having a Mw of 5.6 x 10 ⁵ and a Mw / Mn of 4.05, (b) 18% of a second polyethylene having an Mw of 1.9 x 10 ⁶ and an Mw / The polyolefin composition is prepared by dry blending. The polyethylene resin in the composition has a melting point of 135 캜 and a crystal dispersion temperature of 100 캜.

Twenty-five parts by weight of the first polyolefin composition thus obtained were charged into a steel-mixed twin-screw extruder having an inner diameter of 58 mm and an L / D of 42, and 65 parts by mass of liquid paraffin (50 cSt at 40 캜) were supplied to a twin screw extruder through a side feeder And a polyolefin solution is prepared. The melt blending is performed at 210 캜 and 200 rpm to prepare the first polyolefin solution.

(2) Preparation of the second polyolefin solution

A second polyolefin solution is prepared in the same manner as described above except for the following. (A) a first polyethylene having a Mw of 5.6 x 10 < ^-5 > of 63.7% and a Mw / Mn of 4.05, (b) a Mw of 1.9x10 < ⁶ > of 1.3% and a Mw / Mn And (c) a second polyolefin composition comprising a polypropylene resin having a Mw of 1.6 x 10 < ⁶ >, Mw / Mn of 5.2, and DELTA Hm of 114.0 J / g of 35% by dry blending Prepare. The polyethylene resin in the composition has a melting point of 135 캜 and a crystal dispersion temperature of 100 캜. 30 parts by weight of the obtained second polyolefin composition was charged into a strong mixed-type twin-screw extruder having an inner diameter of 58 mm and an L / D ratio of 42, and 70 parts by mass of liquid paraffin (50 cSt at 40 캜) were supplied to a twin screw extruder through a side feeder do. The melt-blending is performed at 210 캜 and 200 rpm to prepare a second polyolefin solution.

(3) Preparation of membranes

The first polyolefin solution and the second polyolefin solution were each supplied to a three-layer extruded T die from a twin-screw extruder and extruded therefrom to obtain a layer thickness ratio of the first polyolefin solution layer / the second polyolefin solution layer / the first polyolefin solution layer to 46.45 /7.1/46.45 < / RTI > (also referred to as a laminate). The extrudate was cooled while passing through a cooling roller controlled at 20 캜 to form a three-layered gel sheet, which was simultaneously biaxially stretched at 119.3 캜 at a magnification of 5 times in both the machine (length) and the transverse direction by a tenter stretcher . The stretched three-layered gel sheet was fixed on an aluminum frame of 20 cm x 20 cm and immersed in a methylene chloride bath controlled at 25 캜 for 3 minutes to remove liquid paraffin and dried in a stream of room temperature. The dried film was re-stretched at a magnification of 1.5 times in the transverse direction (TD) with a batch stretcher while being exposed to a temperature of 127.3 DEG C, relaxed at a TD magnification of 1.3 times at the same temperature (the tenter clips were readjusted to a narrower width) Is based on the width (TD) of the film before dry stretching before re-stretching. The re-stretched film remains fixed to the batch stretching machine, but it is heat-treated at 127.3 占 폚 for 10 minutes to produce a three-layer microporous film.

Table 1 shows the composition and treatment conditions of the multilayer microporous membrane of Examples and Comparative Examples. The properties of the multilayer microporous membranes of Examples and Comparative Examples are shown in Table 2.

From Table 2, it can be seen that the microporous membranes of Examples 1 and 2 exhibit important properties with excellent balance of heat shrinkage at 130 캜 of not more than 9.5%, particularly TD shrinkage at 130 캜 of not more than 9.5% . Compared with the films of Comparative Example 1 and Comparative Example 2, Example 1 and Example 2 of the present invention maintain a good 105 占 폚 heat shrinkage while realizing improved heat shrinkage at 130 占 폚 and a molten state. On the other hand, Comparative Example 3 exhibited little shrinkage in the molten state and good shrinkage at 105 캜, but the performance at 130 캜 was relatively poor. Example 1 and Example 2 provide a film that realizes shrinkage performance in a range of conditions that can not be achieved in the comparative example while maintaining other properties such as permeability and perforation.

The multilayer microporous membrane of the present invention having excellent balance characteristics and the use of such a multilayer microporous membrane as a battery separator provide a battery having excellent safety, heat resistance, holding characteristics, and productivity.

All patents, test procedures, and other documents cited herein, including priority documents, are incorporated by reference in their entirety to the extent such disclosure is not inconsistent with the present invention, .

It is to be understood that while the exemplary embodiments disclosed in this specification are described for specific purposes, various modifications will be apparent to those skilled in the art and may be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, the scope of the claims appended hereto is not intended to be limited to the embodiments and descriptions shown herein, but the claims are intended to cover all the features that are regarded as equivalents thereof by those skilled in the art to which this disclosure belongs And is intended to be construed as including all of the inventive novel features provided herein.

When the lower limit of the numerical value and the upper limit of the numerical value are listed in this specification, a range from all lower limits to all upper limits is assumed.

Claims (24)

A multilayer microporous membrane comprising polypropylene having a Mw greater than 1.0 x 10 < ^{6 &}
Wherein the multilayer microporous membrane has heat shrinkage at 130 占 폚 of not more than 9.5% in at least one planar direction for 30 minutes and a normalized permeability of not more than 400 sec / 100 cm3 / 20 占 퐉. The method according to claim 1,
And the TD shrinkage of the membrane at 130 占 폚 for 30 minutes is 5% or less. The method according to claim 1,
Wherein the TD shrinkage of the film at 105 DEG C for 8 hours is 0.5% or less. The method according to claim 1,
And the TD shrinkage of the film at 105 DEG C for 8 hours is 0.25% or less. delete 5. The method according to any one of claims 1 to 4,
A first layer, a third layer, and a second layer positioned between the first layer and the third layer,
(a) the first layer comprises polyethylene having a Mw of greater than 1.0 x 10 < ^{6 &} gt ;, based on the weight of the first layer, of from 1 wt% to 20 wt%
(b) said third layer comprises polyethylene having a Mw of greater than 1.0 x 10 < ^{6 &} gt ;, based on the weight of the third layer, of from 1 wt% to 20 wt%
(c) the second layer comprises 40% or less by weight of polypropylene based on the weight of the second layer. The method according to claim 6,
The first layer further comprises polyethylene having an Mw of less than 1.0 x 10 < ⁶ > in an amount ranging from 80% to 99% by weight relative to the weight of the first layer;
The third layer further comprises polyethylene having an Mw of less than or equal to 1.0 x 10 < ⁶ > in an amount ranging from 80% to 99% by weight relative to the weight of the third layer;
Wherein the second layer further comprises polyethylene. ≪ RTI ID = 0.0 > 8. < / RTI > The method according to claim 6,
The second layer is 5 wt% to 40 wt% of polypropylene and 0% by weight to 10% by weight of polyethylene having a Mw in excess of 1.0 × 10 ^6, and 60% by weight to 95% by weight of 1.0 × 10 ⁶ or less By weight of Mw (weight% is based on the weight of the second layer). The method according to claim 6,
(a) the second layer is in plane contact with the first layer and the third layer,
(b) the total thickness of the membrane ranges from 3 microns to 200 microns,
(c) the first layer and the third layer comprise the same amount of the same polyethylene,
(d) the second layer has a thickness of 5% to 15% of the total thickness of the film,
(e) the first layer and the third layer have the same thickness, and the thicknesses of the first layer and the third layer are in the range of 42.5% to 47.5% of the total thickness of the film, respectively Sclera. 5. The method according to any one of claims 1 to 4,
(2) 25% or more porosity; (3) normalized piercing strength of 2,600 mN / 20 m or more; (4) MD tensile strength of 55,000 kPa or more; (5) (7) TD tensile elongation of 150% or more; (8) rupture temperature of 170 DEG C or more; and (9) at least one of shutdown temperatures of 140 DEG C or less Layer porous membrane. 5. The method according to any one of claims 1 to 4,
And? Hm of the polypropylene is in the range of 110 J / g to 120 J / g. (a) of a 80% by weight, based on the weight of the first layer 1% by weight to 20% by weight of 1.0 × 10 ^6, polyethylene, and the first layer having a Mw in excess of, based on the weight of and 99% by weight of 1.0 × 10 ⁶ A first layer and a third layer, respectively, each comprising polyethylene having a Mw of less than; And
(b) 5% to 40 polypropylene and 0 polyethylene, and 60% by weight having a Mw in excess of 1.0 × 10 ⁶ at% or more by weight to 10% by weight having a Mw in excess of 1.0 × 10 ⁶ wt% ~ And a second layer positioned between the first layer and the third layer comprising polyethylene having a Mw of less than or equal to 1.0 x 10 < ⁶ > (weight percent being based on the weight of the second layer) :
A total polypropylene content of greater than 0 wt.% To 10 wt.%, A normalized permeability of 300 sec / 100 cm 3/20 μm or less and a TD heat shrinkage at 130 ° C. of 30% or less of 5% or less. (a) stretching a multi-layer lamellar extrudate comprising at least a first layer and a second layer in at least one plane direction, the first layer comprising a first polyolefin and at least a first diluent, Layer comprises a second polyolefin and at least a second diluent, said second polyolefin comprising polypropylene in an amount ranging from 1% to 40% by weight relative to the weight of said second polyolefin, said polypropylene having a density of 1.0 x 10 < A process having Mw of more than ⁶ and? Hm of 110 J / g or more;
(b) removing at least a portion of the first diluent and the second diluent from the drawn extrudate to form a dry film having a first length according to the MD and a first width according to TD;
(c) TD stretching the dried film to a second width larger than the first width at a second magnification in the range of 1.1 to 1.8 from the first width; next
(d) reducing the second width to a third width that is a magnification selected from the range of 1.1 to 1.6 times the first width from the first width and narrower than the second width. Wherein the method comprises the steps of: delete 14. The method of claim 13,
(i) the first polyolefin comprises a first polyethylene in an amount ranging from 80 wt% to 99 wt% and a second polyethylene in an amount ranging from 1 wt% to 20 wt% based on the weight of the first polyolefin Wherein the first polyethylene has a Mw of less than or equal to 1.0 x 10 < ⁶ >, the second polyethylene has a Mw of greater than 1.0 x 10 < ⁶ &
(ii) the second polyolefin is 5% by weight to 40 containing an amount of polypropylene of weight percent, (i) in an amount of 60 wt% to 90 wt% of 1.0 × 10 ⁶ Claim 1 having a Mw of less than (Ii) a second polyethylene (weight% being based on the weight of the second polyolefin) having an Mw in excess of 1.0 x 10 < ⁶ > in an amount ranging from 0 wt% to 10 wt%
(iii) said first diluent is present in the first layer of extrudate in an amount ranging from 60% to 80% by weight relative to the weight of said mixture of said first polyolefin and said first diluent, and
(iv) said second diluent is present in the second layer of extrudate in an amount ranging from 60% to 80% by weight relative to the weight of said mixture of said second polyolefin and said second diluent. Gt; 14. The method of claim 13,
Wherein the extrudate further comprises a third layer comprising a third polyolefin, wherein the third polyolefin comprises a first polyethylene in an amount ranging from 80 wt% to 99 wt% and a first polyethylene in an amount ranging from 1 wt% to 20 wt% 2 polyethylene (weight% of a third weight relative to the polyolefin) characterized in that comprises, the Mw of the first polyethylene has a 1.0 × 10 ⁶ Mw of less than, and the second polyethylene has an excess of 1.0 × 10 ⁶ By weight based on the total weight of the microporous film. 17. The method of claim 16,
(i) said extrudate is a three-layer extrudate;
(ii) the second layer is located between the first layer and the third layer and is in planar contact with the first layer and the third layer;
(iii) the types and contents of the first polyolefin and the third polyolefin are the same;
(iv) said second layer has a thickness of 5% to 15% of the total thickness of the extrudate; Also
(v) the first layer and the third layer have the same thickness, and the thicknesses of the first layer and the third layer are in the range of 42.5% to 47.5% of the total thickness of the extrudate, respectively ≪ / RTI > 17. The method of claim 16,
Wherein the first diluent and the second diluent are one or more independently selected from nonane, decane, decalin, and liquid paraffin. 14. The method of claim 13,
Wherein the stretching of the step (a) is performed by simultaneously increasing the MD dimension and the TD dimension of the extrudate. A cell comprising a multilayer microporous membrane comprising an anode, a cathode, an electrolyte, and a polypropylene having an Mw in excess of 1.0 x 10 < ^{6 &}
The multilayer microporous membrane has a heat shrinkage at 130 캜 for 30 minutes in at least one plane direction of 9.5% or less and a normalized air permeability of 400 sec / 100 cm 3 or less, and at least separates the anode from the cathode Lt; / RTI > 21. The method of claim 20,
Wherein the electrolyte contains lithium ions and is a secondary battery. Further comprising a resistive component and / or a reactive component connected to one or more of the cells of claim 20 or 21 electromagnetically and electrochemically and / or electromechanically to form a battery system, Or more of the power source of the battery. 23. The method of claim 22,
Wherein the at least one component comprises means for driving an electric vehicle or a hybrid electric vehicle. delete

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