Polyolefin microporous membrane

Abstract

A polyolefin microporous membrane is provided, which has a film thickness of 1 to 30 μm and a gas permeability of 500 sec / 100 cm 3 Hereinafter, and under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes, the post-compression porosity measured in a compression test is 30% or more.

Description

Technical Field

[0001] This invention relates to polyolefin microporous membranes. Background Technology

[0002] Polyolefin microporous membranes exhibit excellent electrical insulation and ion permeability, and therefore are used in battery separators, capacitor separators, fuel cell materials, fine filtration membranes, etc., especially as separators for lithium-ion secondary batteries.

[0003] In recent years, lithium-ion secondary batteries have also been used in small electronic devices such as mobile phones and laptop computers, as well as electric vehicles such as electric cars and small electric bicycles. For separators used in lithium-ion secondary batteries, not only are mechanical properties and ion permeability required, but also safety in various safety tests. Furthermore, considering the heat resistance or rigidity of separators for lithium-ion secondary batteries and the cycle characteristics of lithium-ion secondary batteries, the crystallinity of polyolefins contained in the separators, or the pressure test characteristics of polyolefin microporous membranes used as separators, have been studied (Patent Documents 1-4).

[0004] Patent Document 1 describes the long period of the plate-like crystal portion of a dry-stretched porous polyolefin microporous film, measured by small-angle X-ray scattering (SAXS), considering its superior lithium-ion permeability and heat resistance.

[0005] Patent Document 2 describes the long period of polymer crystals measured by the SAXS method for a stretched polypropylene film, taking into account both low thermal shrinkage and high rigidity.

[0006] Patent documents 3 and 4, considering the compressibility of separators for lithium-ion secondary batteries and the cycle characteristics of lithium-ion secondary batteries, for example, record the change rate of polyolefin microporous membrane thickness before and after a heating compression test at 80°C and 1 MPa for 60 minutes (Patent document 3), or record the change rate of air permeability and membrane thickness of polyolefin microporous membrane before and after a heating compression test at 90°C and 5.0 MPa for 5 minutes (Patent document 4).

[0007] In addition, from the perspective of achieving a balance of mechanical properties, heat resistance, compression resistance, dimensional stability, liquid absorption, safety, and battery characteristics in environments such as batteries with special electrodes, high temperature, high pressure, and large size, polyolefin microporous membranes used as separators have been studied (Patent Documents 5-9).

[0008] Patent document 5 describes the change rate of air permeability of a microporous membrane and the puncture strength converted to a thickness of 12 μm, measured before and after pressurization treatment under specific pressure and temperature conditions, from the perspective of ensuring battery safety by increasing the difference between the shut-off temperature and melting temperature of the thin film separator.

[0009] Patent document 6 describes the increase in air permeability and the puncture strength per 20 μm thickness, measured before and after pressurization treatment under specific pressure and temperature conditions, from the perspective of obtaining a balance of shut-off characteristics, melting characteristics, permeability, mechanical strength, heat shrinkage resistance and compression resistance for a polyethylene multilayer microporous membrane containing a polyethylene resin layer, a layer containing a polyethylene resin and a heat-resistant resin other than polypropylene.

[0010] Patent document 7 describes a method for controlling the distribution of average pore size in the film thickness direction, considering the balance of permeability, mechanical properties, heat shrinkage resistance, compression resistance, electrolyte absorption, shut-off properties, and melting properties in the manufacture of polyethylene multilayer microporous membranes. It also illustrates the permeability and puncture strength per 20 μm thickness before and after pressurization treatment of the obtained membrane at specific pressure and temperature.

[0011] Patent document 8 describes the average compressive elastic modulus and surface roughness of a microporous membrane containing at least one of polyethylene and polypropylene, from the viewpoint of obtaining a balance between durability, safety and film properties in the thickness direction of the separator. In the manufacture of the microporous membrane, porosification is carried out in a dry manner.

[0012] In Patent Document 9, in order to balance long-term battery cycle characteristics and safety when using both separators and negative electrode materials with intense expansion and contraction, the permeability of the microporous membrane before and after the extraction of plasticizer and the permeability of the obtained separator after sandblasting are described.

[0013] Existing technical documents

[0014] Patent documents

[0015] Patent Document 1: International Publication No. 2014 / 175252

[0016] Patent Document 2: International Publication No. 2015 / 012324

[0017] Patent Document 3: International Publication No. 2018 / 164056

[0018] Patent Document 4: International Publication No. 2015 / 194504

[0019] Patent Document 5: International Publication No. 2018 / 043331

[0020] Patent Document 6: International Publication No. 2007 / 023918

[0021] Patent Document 7: International Publication No. 2007 / 037289

[0022] Patent Document 8: Japanese Patent Application Publication No. 2017-25294

[0023] Patent Document 9: Japanese Patent No. 5295834 Summary of the Invention

[0024] The problem the invention aims to solve

[0025] Non-aqueous secondary batteries, such as lithium-ion batteries, are produced in a variety of shapes, including cylindrical, square, and pouch-shaped, depending on their application. The manufacturing methods also vary depending on the shape of the battery. For example, in the manufacturing of square batteries, there is a process of pressing and inserting a wound or laminated body of electrodes and a polyolefin microporous membrane into a rectangular outer packaging can.

[0026] However, the pressurization process used in the manufacture of batteries with conventional polyolefin microporous membranes as described in Patent Documents 1-4 may result in a decrease in the battery's cycle characteristics and output characteristics. Furthermore, the same phenomenon occurs significantly even when using high-capacity electrodes that are prone to expansion.

[0027] In recent years, with the improvement of electrode materials and the high-density modularization of multiple non-aqueous secondary batteries (single cells) (increasing the volumetric energy density of modules), there is a further requirement to ensure the ion permeability of the microporous membrane used as a separator and the output or cycle characteristics of the battery containing it, even when external pressure is applied to the battery cell and separator.

[0028] On the other hand, if one simply tries to improve the porosity in order to improve the ion permeability of the separator, the safety of non-aqueous secondary batteries containing separators, such as those subjected to nail puncture safety tests, may be compromised.

[0029] Therefore, for non-aqueous secondary batteries that use polyethylene microporous membranes as separators, there is a trade-off between battery characteristics such as output characteristics and cycle characteristics under pressure and safety in tests such as nail penetration safety.

[0030] In view of the above, the object of the present invention is to provide a polyolefin microporous membrane that can achieve high output and high cycle characteristics of a non-aqueous secondary battery, and / or can achieve a balance between battery characteristics and safety of a non-aqueous secondary battery, as well as a separator for a non-aqueous secondary battery comprising the membrane and a non-aqueous secondary battery.

[0031] Solution for solving the problem

[0032] The inventors have discovered that, for polyolefin microporous membranes, specific compression porosity; the crystallinity of polyethylene, a major component in the polyolefin microporous membrane; puncture strength converted to unit area weight; the difference between the maximum and minimum values ​​of air permeability measured at three points along the width direction (TD); and air permeability under pressure of 30°C and 3 MPa, etc., can solve the above-mentioned problems, thus completing the present invention. The following examples illustrate embodiments of the present invention.

[0033] (1) A polyolefin microporous membrane with a thickness of 1 μm to 30 μm and an air permeability of 500 sec / 100 cm. 3 The porosity after compression, as determined in a compression test at 70°C, 8 MPa, and 3 minutes, is above 30%.

[0034] (2) A polyolefin microporous membrane, which is a polyolefin microporous membrane containing polyethylene as the main component, wherein the crystallization long period of the aforementioned polyolefin microporous membrane is 37.0 nm or more as determined by small-angle X-ray scattering (SAXS).

[0035] (3) The polyolefin microporous membrane according to item 1 or 2 contains polyethylene as the main component, and the microcrystal size of the aforementioned polyethylene is less than 28.0 nm.

[0036] (4) The polyolefin microporous membrane according to any one of items 1 to 3, wherein the porosity of the aforementioned polyolefin microporous membrane is 35% or more.

[0037] (5) A polyolefin microporous membrane, wherein the puncture strength per unit area weight is 50 gf / (g / m²). 2 )above,

[0038] Along the width direction (TD), the difference between the maximum and minimum air permeability measured at three points—two points at the inner edge (10% of the full width from both ends towards the center) and one point at the center—was 15 sec / 100cm. 3 Below, and

[0039] The air permeability at 30℃ and 3MPa pressure is 140sec / 100cm. 3 the following.

[0040] (6) The polyolefin microporous membrane according to any one of items 1 to 5, wherein the porosity of the aforementioned polyolefin microporous membrane under 30°C and 3MPa pressure conditions is 40% or more.

[0041] (7) The polyolefin microporous membrane according to any one of items 1 to 6, wherein the puncture strength of the aforementioned polyolefin microporous membrane is 220 gf or more.

[0042] (8) The polyolefin microporous membrane according to any one of items 1 to 7, wherein the polyethylene component of the aforementioned polyolefin microporous membrane having a weight-average molecular weight (Mw) of 1,000,000 or more as determined by GPC is 7% or more of all dissolved components as determined by GPC.

[0043] (9) The polyolefin microporous membrane according to any one of items 1 to 8, wherein the melt flow index (MI) of the aforementioned polyolefin microporous membrane is 1.0 or less.

[0044] (10) The polyolefin microporous membrane according to any one of items 1 to 9, wherein the TD heat shrinkage rate of the aforementioned polyolefin microporous membrane at 120°C is less than 20%.

[0045] (11) The polyolefin microporous membrane according to any one of items 1 to 10, wherein the ratio of the tensile strength in the length direction (MD) to the tensile strength in the width direction (TD) of the aforementioned polyolefin microporous membrane (MD / TD tensile strength ratio) is 0.5 to 2.0.

[0046] (12) A separator comprising: a polyolefin microporous membrane as described in any one of items 1 to 11; and

[0047] An inorganic porous layer disposed on at least one side of the aforementioned polyolefin microporous membrane.

[0048] (13) A separator comprising: a polyolefin microporous membrane as described in any one of items 1 to 11; and

[0049] A thermoplastic resin layer disposed on at least one side of the aforementioned polyolefin microporous membrane.

[0050] (14) A separator comprising: a polyolefin microporous membrane as described in any one of items 1 to 11; and

[0051] At least one layer selected from the group consisting of a multifunctional layer, an inorganic porous layer, and a thermoplastic resin layer is disposed on at least one side of the aforementioned polyolefin microporous membrane.

[0052] (15) A non-aqueous secondary battery comprising a polyolefin microporous membrane as described in any one of items 1 to 11, or a separator as described in any one of items 12 to 14.

[0053] The effects of the invention

[0054] This invention utilizes the porosity and / or crystallinity of a specific polyolefin microporous membrane after compression. In the fabrication of non-aqueous secondary batteries using this membrane, the membrane's resistance decreases after the pressurization process, and / or the membrane's structural uniformity and the reaction uniformity within the non-aqueous secondary battery are improved, thus achieving high output and high cycle characteristics for the non-aqueous secondary battery. Furthermore, this invention balances battery characteristics and safety by using the puncture strength converted from the unit area weight of the specific polyolefin microporous membrane, the difference between the maximum and minimum values ​​of permeability measured at three points along the TD (Transient Density Measure), and the permeability measured under 30°C and 3MPa pressurization conditions.

[0055] Furthermore, according to the present invention, even when using electrodes that are easily expandable and contractible in a battery cell of a non-aqueous secondary battery equipped with a polyolefin microporous membrane, or when the separator is compressed during the assembly of a non-aqueous secondary battery, the high porosity / low permeability, i.e., high ion permeability of the polyolefin microporous membrane is maintained, which can suppress the increase in resistance and thus ensure battery characteristics and safety. Attached Figure Description

[0056] Figure 1 Here is an example of a power-approximate curve for the porosity and permeability after compression. Detailed Implementation

[0057] The following provides a detailed description of the methods for implementing the present invention (hereinafter referred to as "implementation methods"). It should be noted that the present invention is not limited to the following embodiments and can be implemented in various ways within its scope.

[0058] In this specification, the length direction (MD) refers to the mechanical direction of continuous forming of the microporous membrane, and the width direction (TD) refers to the direction in which the MD of the microporous membrane is transversely cut at an angle of 90°.

[0059] In this specification, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, "a component contains a specific component as a main component" means that, based on the mass of the component, the content of the specific component is 50% by mass or more. Unless otherwise specified, the physical properties or numerical values ​​described in this specification are determined or calculated using the methods illustrated in the examples.

[0060] <Polyolefin Microporous Membranes>

[0061] One aspect of the present invention is a polyolefin microporous membrane. The polyolefin microporous membrane contains polyolefin resin as its main component and exhibits excellent electrical insulation and ion permeability; therefore, it can be used, for example, as a separator in non-aqueous secondary batteries.

[0062] (Implementation Method 1)

[0063] The polyolefin microporous membrane of Embodiment 1 has the following characteristics:

[0064] The film thickness ranges from 1 μm to 30 μm;

[0065] Breathability is 500 seconds / 100cm 3 The following; and

[0066] The porosity after compression, as determined in a compression test at 70°C, 8 MPa, and 3 minutes, is over 30%.

[0067] The polyolefin microporous membrane of Embodiment 1 has a thickness in the range of 1 μm to 30 μm and a strength of 500 sec / 100 cm. 3 With air permeability and a porosity of 30% or more after compression, for example, in the manufacture of non-aqueous secondary batteries using polyolefin microporous membranes as separators, the resistance of the polyolefin microporous membrane is reduced or its increase is suppressed after the pressurization process, thereby achieving high output and high cycle characteristics of the non-aqueous secondary battery. The suppression of resistance increase achieved by the polyolefin microporous membrane of Embodiment 1 is significant when electrodes that easily expand and contract are used in the battery cells of non-aqueous secondary batteries, and is even more significant when high-capacity electrodes used in automotive batteries or silicon (Si)-containing negative electrodes are used.

[0068] The method for conducting a compression test under conditions of 70°C, 8 MPa, and 3 minutes is described in detail in the examples. The porosity after compression is considered to be related to the structure of the main component of the polyolefin microporous membrane in a non-aqueous secondary battery, which reduces resistance and / or inhibits resistance increases. From the perspective described above, the porosity after compression of the polyolefin microporous membrane of Embodiment 1 is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the porosity after compression of the polyolefin microporous membrane of Embodiment 1 can be determined based on the porosity before compression, for example, it can be 50% or less, or less than 50%.

[0069] The porosity of the polyolefin microporous membrane after compression testing according to Embodiment 1 can be adjusted to the numerical range described above, for example, by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, and the heat setting temperature, etc., during the manufacturing process of the polyolefin microporous membrane. Alternatively, the porosity of the polyolefin microporous membrane after compression can be adjusted to the numerical range described above by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, and the ratio of the preheating coefficient to the stretching coefficient, etc.

[0070] For the comparison of porosity before and after compression testing of the polyolefin microporous membrane of Embodiment 1, it is preferable to focus on the structure of the main components of the membrane that can achieve high output and high cycle characteristics by reducing resistance and / or suppressing resistance increase in non-aqueous secondary batteries. The porosity of the polyolefin microporous membrane before compression testing, or without compression testing (hereinafter simply referred to as "porosity"), is determined using the method described in the examples, and its preferred numerical range is as described below.

[0071] In addition to considering the suppression of resistance reduction and resistance increase as described above, and also from the viewpoint of miniaturization, the thickness of the polyolefin microporous membrane in Embodiment 1 is preferably 3 to 20 μm, more preferably 5 μm to 16 μm, and even more preferably 6 μm to 13 μm. The thickness of the microporous membrane can be optimized, for example, by adjusting the distance between the casting rolls and the stretching ratio in the stretching process.

[0072] The air permeability of the polyolefin microporous membrane of Embodiment 1 can be measured by the item "(before compression) air permeability version 1 (seconds / 100cm)" in the example. 3 The method described in the document is used for measurement. In addition to considering the suppression of resistance decrease and increase as explained above, and also from the viewpoint of improving the ion permeability of the microporous membrane and increasing the output of non-aqueous secondary batteries, the permeability of the polyolefin microporous membrane in Embodiment 1 is preferably 400 sec / 100 cm. 3 Below, more preferably 300 sec / 100cm 3 The following is a further preferred value: 200 sec / 100 cm 3 The following is a preferred value: 160 sec / 100 cm 3 From the viewpoint of the mechanical strength of the microporous membrane, a value of 40 sec / 100 cm is preferred. 3 The air permeability of microporous membranes can be optimized in the same way as the methods described above for controlling porosity after compression.

[0073] (Implementation Method 2)

[0074] The polyolefin microporous membrane of Embodiment 2 has the following characteristics:

[0075] Contains polyethylene as the main component; and

[0076] The crystallization period of polyolefin microporous membranes, as determined by small-angle X-ray scattering (SAXS), is greater than 37.0 nm.

[0077] The polyolefin microporous membrane of Embodiment 2, containing polyethylene as its main component and possessing a long crystallization period of 37.0 nm or more, surprisingly exhibits improved structural uniformity and compression resistance. Consequently, the reaction uniformity within the non-aqueous secondary battery is also improved. For example, even after the pressurization process in the fabrication of a non-aqueous secondary battery using the polyolefin microporous membrane as a separator, high output and high cycle characteristics of the non-aqueous secondary battery can be achieved. The improved structural uniformity and compression resistance of the polyolefin microporous membrane of Embodiment 2 are significant when using electrodes that easily expand and contract within the battery cell of a non-aqueous secondary battery, and are even more significant when using high-capacity electrodes or silicon (Si)-containing negative electrodes used in automotive batteries, etc.

[0078] The SAXS measurement of the polyolefin microporous membrane is described in detail in the examples. The crystallization period obtained by the SAXS measurement is considered to be related to the structure of polyethylene, which improves the structural uniformity, compression resistance, and reaction uniformity in non-aqueous secondary batteries. Furthermore, the crystallization period of the polyolefin microporous membrane is not theoretically limited, but is considered to be related to the porosity of the membrane after compression. From the viewpoint described above, the crystallization period of the polyolefin microporous membrane in Embodiment 2 is preferably in the range of 37.0 nm to 60.0 nm, 38.0 nm to 55.0 nm, 40.0 nm to 50.0 nm, or 42.0 nm to 50.0 nm.

[0079] The long crystallization period of the polyolefin microporous membrane in Embodiment 2 can be adjusted to the numerical range described above, for example, by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, and the heat setting temperature during the biaxial stretching process.

[0080] To ensure mechanical strength and maintain insulation, the minimum thickness of the polyolefin microporous membrane in Embodiment 2 is 1 μm or more. To improve battery safety by guaranteeing the amount of resin per unit area, a membrane thickness of 2 μm or more, more preferably 3 μm or more, is preferred. To guarantee insulation even in the event of lithium dendrite growth, a membrane thickness of 6 μm or more, more preferably 10 μm or more, is preferred. From the viewpoint of increasing the capacity of non-aqueous secondary batteries, the membrane thickness of the polyolefin microporous membrane in Embodiment 2 is preferably 16 μm or less. The membrane thickness of the microporous membrane can be adjusted by controlling the distance between the casting rollers and the stretching ratio in the stretching process.

[0081] The air permeability (before compression) of the polyolefin microporous membrane of Embodiment 2 can be measured in the same manner as in Embodiment 1, preferably 30 sec / 100 cm. 3 Above and 250 sec / 100 cm 3 Below, more preferably 40 sec / 100cm 3 Above and 200 sec / 100cm 3 Below, more preferably 50 sec / 100cm 3 Above and 180sec / 100cm 3 The following is a further preferred option: 60 sec / 100 cm 3 Above and 150 sec / 100 cm 3 The following applies. From the viewpoint of ensuring puncture strength, the (uncompressed) air permeability of the microporous membrane is preferably 40 sec / 100 cm. 3 From the perspective of output characteristics, the optimal value is 200 sec / 100 cm. 3 the following.

[0082] (Implementation Method 3)

[0083] The polyolefin microporous membrane of Embodiment 3 has the following characteristics:

[0084] The puncture strength per unit area weight is 50 gf / (g / m²). 2 )above;

[0085] Along the TD, the difference between the maximum and minimum air permeability measured at three points—two points at the inner edge (10% of the full width from both ends towards the center) and one point at the center (hereinafter referred to as the difference R)—is 15 sec / 100cm. 3 The following; and

[0086] The air permeability at 30℃ and 3MPa pressure is 140sec / 100cm. 3 the following.

[0087] The polyolefin microporous membrane of Embodiment 3 is specifically designed by measuring the difference between the maximum and minimum values ​​of air permeability at three points along the TD, specifically at two points on the inner side of the full width of 10% from both ends toward the center and one point at the center, and converting the puncture strength to the unit area weight, as well as the air permeability under 30°C and 3MPa pressure conditions, as described above. For example, for non-aqueous secondary batteries containing polyolefin microporous membranes as separators, it can not only take into account battery characteristics such as rate characteristics and cycle characteristics, and safety such as nail puncture test safety, but also improve the porosity and ion permeability of the polyolefin microporous membrane. For example, even when using electrodes that are easy to expand and contract in non-aqueous secondary batteries, or when the separator is compressed during the assembly of non-aqueous secondary batteries, the high porosity / low air permeability of the polyolefin microporous membrane can be maintained.

[0088] (Conversion of puncture strength, puncture strength, and unit area weight of polyolefin microporous membranes)

[0089] 50gf / (g / m 2 The above-mentioned puncture strength per unit area weight shows that the membrane structure has high membrane strength per unit area weight and is not easily crushed by compressive stress. For example, in nail puncture tests or pressure tests, the polyolefin microporous membrane used as a separator is not easily broken even if it has high porosity and low air permeability, which tends to improve the safety of the battery. The puncture strength per unit area weight is measured by the method described in the examples. The puncture strength (hereinafter referred to as puncture strength) is measured at three points along the TD of the membrane, at two points at a position 10% inside the full width from both ends toward the center and one point at the center. The average value of these measurements is divided by the unit area weight. The advantages achieved by controlling the puncture strength in Embodiment 3 are significant when using electrodes that are easy to expand and contract in the battery cell of a non-aqueous secondary battery, and even more significant when using high-capacity electrodes used in automotive batteries or silicon (Si)-containing negative electrodes. From this point of view, the puncture strength per unit area weight of the polyolefin microporous membrane is preferably 50 gf / (g / m²). 2 )~150gf / (g / m 2 ), more preferably 55gf / (g / m 2 )~130gf / (g / m 2 Further optimization of 70gf / (g / m 2 )~120gf / (g / m 2 ).

[0090] Considering the same viewpoints as above, the need for a certain membrane strength and low permeability, and the improvement of short-circuit withstand capability of polyolefin microporous membranes and non-aqueous secondary batteries, the preferred unit area weight of the polyolefin microporous membrane is 1.0 g / m³. 2~15g / m 2 Within the range.

[0091] From the same perspective as above, and considering the need to suppress short circuits or poor voltage withstand caused by foreign matter accidentally entering the battery or membrane damage to the separator, the puncture strength of the polyolefin microporous membrane is preferably 220 gf or more, more preferably 250 gf or more, even more preferably 280 gf or more, and particularly preferably 300 gf or more. The upper limit of the puncture strength is not particularly limited and can be determined based on the crystallinity of the membrane and the suppressed resistance; for example, it can be 700 gf or less, or 680 gf or less.

[0092] The puncture strength and the puncture strength per unit area weight of the polyolefin microporous membrane in Embodiment 3 can be adjusted to the numerical range described above by controlling the molecular weight and mixing ratio of polymer raw materials such as polyolefin, the stretching ratio during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, the heating coefficient per unit resin of the resin composition during the biaxial stretching process, and the heat setting (HS) ratio, etc., in the manufacturing process of the polyolefin microporous membrane.

[0093] (The difference R between the maximum and minimum air permeability measured at TD3 points before compression, and the air permeability distribution before compression)

[0094] The difference R between the maximum and minimum values ​​of the air permeability measured at three points along the TD of the polyolefin microporous membrane as described above is determined by the method described in the examples, showing the air permeability distribution of the polyolefin microporous membrane before the compression test. From the viewpoint of accuracy in air permeability measurement, the full width W of the polyolefin microporous membrane is preferably 50 mm or more, more preferably 100 mm or more, and even more preferably 300 mm or more. The upper limit of the full width W is not particularly limited and can be determined, for example, based on the film-forming apparatus, film-forming process, master roller size, slit roller size, coating process, etc., and can be, for example, 5000 mm or less, or 4000 mm or less.

[0095] To satisfy R≤15sec / 100cm 3 The well-maintained permeability distribution, along with the permeability under 30°C and 3MPa pressure conditions described later, demonstrates a membrane structure with small deviations in in-plane permeability. For example, in non-aqueous secondary batteries containing polyolefin microporous membranes as separators, uniform in-plane electrochemical reactions are generated, tending to optimize battery characteristics such as rate characteristics and cycle characteristics. This tendency is significant when electrodes that easily expand and contract are used in the battery cells of non-aqueous secondary batteries, and is even more pronounced when using high-capacity electrodes used in automotive batteries or silicon (Si)-containing negative electrodes. From this perspective, the difference R is preferably 0 sec / 100 cm. 3 Above and 15 seconds / 100cm3 Below, more preferably 0 sec / 100cm 3 Above and 13 seconds / 100cm 3 The following is a further preferred option: 0 sec / 100cm 3 Above and 11 seconds / 100cm 3 The following is a preferred option: 0 sec / 100cm 3 Above and 9 seconds / 100cm 3 the following.

[0096] The average value of the above three measurements is shown as the (uncompressed) air permeability, which can be expressed by the item "(uncompressed) air permeability version 2 (seconds / 100cm)" in the example. 3 The method described in the document, considering the same viewpoints as above, as well as the viewpoint of maintaining high (ion) permeability even under compressed conditions and the guarantee of puncture strength, is preferably 0 sec / 100 cm. 3 Above and 200 sec / 100cm 3 Below, more preferably 30 sec / 100cm 3 Above and 180sec / 100cm 3 The following is a further preferred option: 40 sec / 100 cm 3 Above and 150 sec / 100 cm 3 the following.

[0097] The differential R and (before compression) air permeability of the polyolefin microporous membrane of Embodiment 3 can be adjusted to the numerical range described above, for example, by controlling the molecular weight and mixing ratio of polymer raw materials such as polyolefin, the stretching ratio during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, the heating coefficient per unit resin of the resin composition during the biaxial stretching process, the HS ratio, etc., in the manufacturing process of the polyolefin microporous membrane.

[0098] (Membrane properties after compression)

[0099] In Embodiment 3, it was discovered that by subjecting the polyolefin microporous membrane to a compression test under specific conditions, the characteristics of the polyolefin microporous membrane can be achieved while maintaining the battery characteristics and safety of a non-aqueous secondary battery. The compression test is detailed in the examples; at room temperature, preferably 30°C, the compression pressurization test and the compression TMA test are performed in a combination as follows:

[0100] <Compression Test>

[0101] (i) The microporous membrane or separator is pressurized using a flat plate press, and the load is unloaded after compression in the thickness direction. The porosity change is determined by the changes in air permeability and thickness of the microporous membrane or separator before and after the test.

[0102] (ii) In addition, for the microporous membrane or separator, measurements were taken under four different pressure conditions (e.g., pressures of 2.5 MPa, 5 MPa, 7.5 MPa, and 10 MPa) using the method described later in the examples, and the relationship between the porosity and air permeability of the microporous membrane or separator after unloading was obtained from the measurement results at the four points.

[0103] <Compression TMA Test>

[0104] The microporous membrane or separator is compressed in the thickness direction using a probe under a specific load, and the in-situ membrane thickness is measured under a pressure of 3 MPa.

[0105] If the air permeability of the polyolefin microporous membrane under 30℃ and 3MPa pressure (hereinafter referred to as air permeability under pressure at 30℃ and 3MPa) is 140sec / 100cm 3 The following demonstrates the properties of the polyolefin microporous membrane that maintains high ion permeability even under pressure in the thickness direction. The air permeability at 30°C and 3 MPa under pressure is obtained as follows: In the aforementioned compression TMA test, the porosity at 3 MPa under in-situ pressure is calculated from the thickness at this exact in-situ state and the unit area weight before the TMA measurement. At this in-situ porosity, the air permeability in seconds is calculated using the relationship from the aforementioned compression test (ii), thus obtaining the air permeability at 30°C and 3 MPa under pressure. The method for measuring the air permeability at 30°C and 3 MPa under pressure is detailed in the examples.

[0106] Under pressure, the air permeability at 30℃ and 3MPa is ≤140sec / 100cm. 3 In conjunction with the permeability distribution or difference R before compression described above, for example, in non-aqueous secondary batteries containing polyolefin microporous membranes as separators, there is a tendency to optimize battery characteristics such as rate characteristics and cycle characteristics. This tendency is significant for optimizing rate characteristics when using electrodes that easily expand and contract within the battery cells of non-aqueous secondary batteries, or when the separator is compressed due to pressure from outside the battery cells. It is even more significant when using high-capacity electrodes used in automotive batteries, or silicon (Si)-containing negative electrodes. From this perspective, the permeability under pressure at 30°C and 3MPa is preferably 120 sec / 100cm. 3 Below, more preferably 100sec / 100cm 3 The following is a further preferred value: 80 sec / 100 cm 3The lower limit of air permeability under pressure at 30℃ and 3MPa is not specifically defined and can be determined based on the mechanical strength or puncture strength of the microporous membrane. For example, it could be 0 sec / 100cm. 3 Above, 20 seconds / 100cm 3 Above, or 40 seconds / 100cm 3 above.

[0107] From the same perspective as above, and considering the viewpoint of improving battery cycle characteristics by achieving high porosity under conditions of electrode expansion and contraction within the battery cell or compression of the separator, the porosity of the polyolefin microporous membrane under 30°C and 3MPa pressure (hereinafter referred to as porosity under pressure at 30°C and 3MPa) is preferably 40% or more, more preferably 40% or more and 60% or less, further preferably 43% or more and 60% or less, and particularly preferably 49% or more and 60% or less. The porosity under pressure at 30°C and 3MPa can be calculated in the above-described compression TMA test from the thickness of the in-situ membrane at exactly 3MPa and the weight per unit area before the TMA measurement. The method for measuring the porosity under pressure at 30°C and 3MPa is described in detail in the examples.

[0108] The air permeability of the polyolefin microporous membrane under pressure is 30°C and 3MPa, and the porosity under pressure is 30°C and 3MPa, respectively. This can be adjusted to the numerical range described above by controlling the molecular weight and mixing ratio of the polymer raw materials such as polyolefin, the stretching ratio during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, the heating coefficient per unit resin of the resin composition during the biaxial stretching process, the HS ratio, and the HS temperature, etc., during the manufacturing process of the polyolefin microporous membrane.

[0109] (Implementation Method 4)

[0110] Embodiment 4 provides a polyolefin microporous membrane that combines the technical features of Embodiments 1 to 3.

[0111] The polyolefin microporous membrane of embodiment 4 contains polyethylene as the main component, has a membrane thickness of 1 μm to 30 μm, and an air permeability (before compression) of 500 sec / 100 cm. 3 Below, along TD, the difference between the maximum and minimum values ​​of the (before compression) air permeability measured at a total of three points—two points at the inner side of the full width at 10% from both ends towards the center and one point at the center—is 15 sec / 100cm. 3 The following is a conversion of puncture strength per unit area weight to 50 gf / (g / m²). 2The polyolefin microporous membrane, as measured by the SAXS method, has a crystallization period of ≥37.0 nm and an air permeability of 140 sec / 100 cm under 30°C and 3 MPa pressure conditions. 3 The porosity after compression, as determined in a compression test at 70°C, 8 MPa, and 3 minutes, is above 30%.

[0112] The following describes the common components, preferred components, or other components in embodiments 1 to 4.

[0113] (Components)

[0114] Examples of polyolefin microporous membranes include, for instance, porous membranes containing polyolefin resins; porous membranes containing resins other than polyolefin resins such as polyethylene terephthalate, polycyclic olefins, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycyclic olefin, nylon, and polytetrafluoroethylene; materials woven from polyolefin fibers (fabric); and nonwoven fabrics made from polyolefin fibers. Among these, from the viewpoints of suppressing the decrease or increase of membrane resistance, compressibility of the membrane, and structural uniformity, microporous membranes containing polyolefin resins (hereinafter referred to as polyolefin resin porous membranes) are preferred, and microporous membranes containing polyethylene as the main component are more preferred.

[0115] The polyolefin resin porous membrane is described below. From the viewpoint of improving the shut-off performance when forming a polyolefin microporous membrane for non-aqueous secondary batteries, the polyolefin resin porous membrane is preferably a porous membrane formed by a polyolefin resin composition in which the polyolefin resin accounts for 50% or more and 100% or less of the resin component constituting the porous membrane. The percentage of polyolefin resin in the polyolefin resin composition is more preferably 60% or more and 100% or less, further preferably 70% or more and 100% or less, and most preferably 95% or more and 100% or less.

[0116] The polyolefin resin contained in the polyolefin resin composition is not particularly limited, and examples include homopolymers, copolymers, or multi-segment polymers obtained by using monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. Furthermore, these polyolefin resins can be used alone or in combination of two or more.

[0117] From the perspectives of suppressing the decrease or increase of membrane resistance, membrane compressibility and structural uniformity, polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene copolymer with monomers other than those thereof, and mixtures thereof are preferred as polyolefin resins.

[0118] Specific examples of polyethylene include low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene. Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Specific examples of copolymers include ethylene-propylene atactic copolymers and ethylene-propylene rubber.

[0119] From the perspective of crystallinity, high strength, and compression resistance when forming polyolefin microporous membranes for non-aqueous secondary batteries, polyolefin resin porous membranes are preferably formed using a polyethylene composition in which polyethylene accounts for 50% to 100% by mass of the resin component constituting the microporous membrane. More preferably, the percentage of polyethylene in the resin component constituting the porous membrane is 60% to 100% by mass, further preferably 70% to 100% by mass, and most preferably 90% to 100% by mass.

[0120] The polyethylene contained as the main component in the polyolefin resin porous membrane preferably has a crystallite size of MDND facet (110) of less than 28 nm. The crystallite size of the MDND facet (110) of polyethylene, as detailed in the examples, can be determined by X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS).

[0121] If the crystallite size of the MDND surface (110) of polyethylene is 28.0 nm or less, the polyolefin microporous membrane containing this polyethylene becomes rigid, and there is a tendency for the membrane's compressibility to improve. Therefore, even after the pressurization process in the manufacture of non-aqueous secondary batteries, high output and high cycle characteristics can be achieved. From this point of view, the crystallite size of the MDND surface (110) of polyethylene, which is the main component of the membrane, is more preferably 27.0 nm or less, and even more preferably 10.0 nm to 27.0 nm, or 15.0 nm to 26.0 nm, or 15.0 nm to 25.0 nm, or 15.0 nm to 22.0 nm. In particular, if the crystallite size of the MDND surface (110) of polyethylene is 22.0 nm or less, the membrane's rigidity is enhanced and its compressibility to improve.

[0122] The crystallite size of the MDND surface (110) of polyethylene, which is the main component of the polyolefin microporous membrane, can be adjusted to the range of values ​​described above, for example, by controlling the molecular weight of the polyolefin raw material, the molecular weight of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, and the stretching coefficient during the biaxial stretching process in the manufacturing process of the polyolefin microporous membrane.

[0123] Furthermore, from the viewpoint of making the membrane rigid and improving its compressibility, the polyolefin resin contained in the polyolefin resin porous membrane preferably has a melting point of 120°C or higher and 150°C or lower, more preferably 125°C or higher and 140°C or lower, and / or the first peak temperature of the DSC is preferably in the range of 136°C to 144°C.

[0124] From the viewpoints of crystallinity, high strength, compression resistance, and resistance suppression when forming polyolefin microporous membranes as separators for non-aqueous secondary batteries, the proportion of polyethylene in the polyolefin resin is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and preferably 100% by mass or less, more preferably 97% by mass or less, and further preferably 95% by mass or less. It should be noted that if the proportion of polyethylene (PE) in the polyolefin resin is 100% by mass, it is preferable from the viewpoint of strength performance. If the proportion of PE in the polyolefin resin is 50% or more, it is preferable from the viewpoint of exhibiting high responsiveness in fuse behavior.

[0125] The polyolefin resin composition may contain any additives. Examples of additives include polymers other than polyolefin resins; inorganic fillers; antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; metallic soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. From the viewpoint of improving shut-off performance, it is preferable for the total amount of these additives to be 20% by mass or less relative to 100% by mass of the polyolefin resin, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0126] When the microporous membrane is a polyolefin resin porous membrane, the viscosity-average molecular weight (Mv) of the polyolefin resin used as a raw material is preferably 30,000 or more and 6,000,000 or less, more preferably 80,000 or more and 3,000,000 or less, and even more preferably 150,000 or more and 2,000,000 or less. If the viscosity-average molecular weight is 30,000 or more, there is a tendency to form high strength through the intertwining of polymers, which is therefore preferred. On the other hand, if the viscosity-average molecular weight is 6,000,000 or less, it is preferred from the viewpoint of improving formability in the extrusion and stretching processes.

[0127] When a polyolefin resin porous membrane contains polyethylene as a main component, the molecular weight (Mv) of at least one of the polyethylene components is preferably 600,000 or more, more preferably 700,000 or more, and the upper limit of the Mv of polyethylene can be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the polyolefin resin porous membrane is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and may also be 100% by mass. From the viewpoint of reducing the fluidity of the membrane during melting and improving short-circuit resistance during nail penetration tests, the proportion of polyethylene with an Mv of 600,000 or more in the polyolefin resin constituting the polyolefin resin porous membrane is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass or more, particularly preferably 70% by mass or more, and may also be 100% by mass.

[0128] The type, molecular weight, and composition of the polyolefin resin constituting the polyolefin resin porous membrane can be adjusted, for example, by controlling the type, molecular weight, and mixing ratio of polymeric raw materials such as polyolefins during the manufacturing process of the polyolefin microporous membrane, as described above. Furthermore, multilayer polyolefin resin microporous membranes having a structure in which two or more layers of the same or different types of polyolefin resin microporous membranes are stacked are also adjusted as described above.

[0129] (Detailed description of microporous membranes)

[0130] Polyolefin microporous membranes have a dense, interconnected porous structure formed by the aggregation of many very small pores. Therefore, they have excellent ion permeability and high strength even when containing electrolyte.

[0131] From the perspective of high ion permeability and good rate characteristics, and from the perspective of improving battery capacity by reducing the volume occupied by the separator when used in high-capacity batteries, the average film thickness (before compression) of the polyolefin microporous membrane is preferably 1 μm to 14 μm, more preferably 3 μm to 13 μm, and even more preferably 5 μm to 12 μm. The average film thickness of the polyolefin microporous membrane can be adjusted to the above-mentioned range by controlling the roller distance between the casting rollers, the casting gap, the stretching ratio, the HS ratio, and the HS temperature during the biaxial stretching process.

[0132] From the perspective of manufacturing non-aqueous secondary batteries, for example, those using microporous membranes as separators, to reduce membrane resistance after the pressurization process while maintaining high battery output and high cycle performance, and to achieve a certain membrane strength and low permeability, the porosity (before compression) of the microporous membrane is preferably 20% or more, more preferably 35% or more, further preferably 38% or more, even more preferably 40% or more, and particularly preferably 45% or more. From the viewpoint of battery safety and achieving a certain membrane strength and low permeability, it is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less. The porosity of the microporous membrane can be adjusted by controlling the mixing ratio of the polyolefin resin composition and plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, the relaxation rate during heat setting, or a combination thereof.

[0133] From the perspective of achieving high ion permeability, excellent voltage resistance, and high strength, the pore size of the microporous membrane, when measured using a semi-dry method, is preferably 30 nm to 70 nm, more preferably 35 nm to 60 nm. The pore size of the microporous membrane can be adjusted, for example, by controlling the stretching temperature, stretching ratio, heat setting temperature, stretching ratio during heat setting, relaxation rate during heat setting, or a combination thereof.

[0134] From the perspective of reducing the fluidity of the membrane during melting and suppressing short circuits between electrodes due to flow of the separator under exothermic conditions during nailing tests, the melt flow index (MI) of the polyolefin microporous membrane is preferably 1.0 or less, more preferably 0.001 or more and 1.0 or less, even more preferably 0.005 or more and 0.8 or less, and particularly preferably 0.01 or more and 0.4 or less. The MI of the polyolefin microporous membrane can be adjusted to the above-mentioned value range, for example, by controlling the molecular weight and mixing ratio of the polymer raw materials such as polyolefin.

[0135] Regarding the molecular weight distribution of polyolefin microporous membranes determined by GPC, from the viewpoint of reducing membrane fluidity during melting and improving short-circuit resistance during nailing tests, it is preferable that the polyethylene component with a Mw of 1,000,000 or more comprises 7% or more of the total dissolved components, more preferably 9% or more, further preferably 12% or more, and particularly preferably 15% or more. Furthermore, from the viewpoint of suppressing excessive stress during membrane shrinkage at high temperatures, it is preferable that the polyethylene component with a Mw of 1,000,000 or more comprises 57% or less of the total dissolved components, more preferably 42% or less, further preferably 33% or less, and particularly preferably 27% or less. The molecular weight distribution of the polyolefin microporous membrane can be adjusted to the above-mentioned numerical range, for example, by controlling the type, molecular weight, and blending ratio of the polyolefin raw materials.

[0136] The puncture strength (hereinafter referred to simply as puncture strength), without conversion to the area weight of the microporous membrane, is preferably 250 gf or more and 700 gf or less. From the viewpoint of battery safety, a puncture strength of 250 gf or more is preferred; from the viewpoint of suppressing the porosity, crystallinity, and electrical resistance of the polyolefin microporous membrane after compression, a puncture strength of 700 gf or less is preferred. A puncture strength more preferably is 300 gf to 690 gf, and even more preferably 310 gf to 680 gf.

[0137] From the perspective of suppressing thermal runaway in non-aqueous secondary batteries, the preferred unit area weight of the polyolefin microporous membrane is 3.0 g / m³. 2 From the perspective of increasing battery capacity, the preferred value is 10g / m³. 2 The following is a preferred embodiment: the weight per unit area of ​​the polyolefin microporous membrane is 3.0 g / m³. 2 Above and 7.0g / m 2 The following is a further preferred embodiment of the polyolefin microporous membrane, with a surface area weight of 3.0 g / m³. 2 Above and 6.0g / m 2 The following improvements in compression resistance ensure battery safety even with lower weight per unit area.

[0138] From the perspective of safety, the preferred withstand voltage per unit area weight of the microporous membrane is 0.13 kV / (g / m²). 2 )above.

[0139] For the tensile breaking strength of polyolefin microporous membranes, considering the need to ensure the membrane strength required for winding and stacking electrodes and separators in the manufacturing process of non-aqueous secondary batteries, the upper limit for both MD and TD is preferably 5000 kgf / cm². 2 Below, more preferably 4500 kgf / cm 2 The following is a further preferred option: 4000 kgf / cm² 2 The following, or even more preferred, value is 3500 kgf / cm². 2 The following is a preferred option: 3000 kgf / cm² 2 The lower limit value is preferably 500 kgf / cm³. 2 Above, or more preferably 700 kgf / cm 2 The above, further optimized, is 1000 kgf / cm². 2 Above, 1500 kgf / cm 2 Above, 2000 kgf / cm 2 Above, or 2500 kgf / cm 2That's all. Furthermore, considering the suppression of thermal shrinkage in polyolefin microporous membranes, the upper limit of the tensile breaking strength (MD) is preferably below 5000 kgf / cm² for both MD and TD. 2 .

[0140] The closer the tensile breaking strength (MD) and tensile breaking strength (TD) of the polyolefin microporous membrane are, the more uniformly the membrane breaks during the nail penetration test of the non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nail penetration test. Furthermore, the closer the tensile breaking strength (MD) and tensile breaking strength (TD) of the polyolefin microporous membrane are, the less likely the membrane will crack in the weaker direction when foreign matter is introduced or when subjected to external impact, improving safety. Additionally, the isotropic structure improves the cycle characteristics of the battery. From this perspective, the ratio of the tensile breaking strength (MD) to the tensile breaking strength (TD) of the polyolefin microporous membrane (MD / TD tensile breaking strength ratio) is preferably 0.5 or more and 2.0 or less, more preferably 0.7 or more and 1.5 or less, more preferably 0.7 or more and 1.4 or less, even more preferably 0.7 or more and 1.3 or less, further preferably in the range of 0.75 to 1.25 or 0.8 to 1.3, and most preferably in the range of 0.8 to 1.2. The MD / TD tensile breaking strength ratio of polyolefin microporous membranes can be adjusted to the numerical range described above, for example, by controlling the stretching ratio and HS ratio during the biaxial stretching process.

[0141] If the tensile elongation at break of the polyolefin microporous membrane is controlled within an appropriate range for both MD and TD, the membrane will elongate appropriately and rupture during the nailing test of the non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nailing test. If the tensile elongation at break is too high, the nailed portion elongates excessively, resulting in stretching of the surrounding area (excluding the nailed and ruptured portions) and thinning of the membrane thickness in the surrounding area, leading to a large-area short circuit. From this perspective, the tensile elongation at break of the polyolefin microporous membrane is preferably 20% or more and 200% or less for both MD and TD, more preferably 30% or more and 150% or less, further preferably 40% or more and 120% or less, and particularly preferably 50% or more and 110% or less for both MD and TD. The tensile elongation at break of the polyolefin microporous membrane (MD) and / or TD can be adjusted to the range described above, for example, by controlling the stretching ratio and HS ratio during the biaxial stretching process.

[0142] The closer the tensile elongation at break (MD) and tensile elongation at break (TD) values ​​of the polyolefin microporous membrane are, the more appropriately the membrane elongates and breaks during the nail penetration test of the non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nail penetration test. From this perspective, the ratio of the MD to TD tensile elongation at break of the polyolefin microporous membrane (MD / TD tensile elongation at break ratio) is preferably 0.3 or more and 2.0 or less, more preferably 0.35 or more and 1.5 or less, further preferably 0.4 or more and 1.3 or less, and particularly preferably 0.5 or more and 1.2 or less. The MD / TD tensile elongation at break ratio of the polyolefin microporous membrane can be adjusted to the numerical range described above, for example, by controlling the stretching ratio and HS ratio during the biaxial stretching process.

[0143] Considering the improved safety aspect that when a nail penetrates a non-aqueous secondary battery, including the separator and electrodes, and deforms, the separator is less likely to rupture and cause a short circuit, the tensile modulus of the polyolefin microporous membrane is preferably 1000 kg / cm² in both MD and TD. 2 ~10000kg / cm 2 More preferably 2000 kg / cm 2 ~90000kg / cm 2 .

[0144] The closer the tensile moduli (MD) and tensile moduli (TD) of the polyolefin microporous membrane are, the more uniformly the membrane ruptures during the nail penetration test of the non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nail penetration test. From this perspective, the ratio of the tensile modulus (MD) to the tensile modulus (TD) of the polyolefin microporous membrane is preferably 0.3 or more and 3.0 or less, more preferably 0.35 or more and 2.0 or less, even more preferably 0.4 or more and 1.5 or less, and particularly preferably 0.5 or more and 1.3 or less. The MD / TD tensile modulus ratio of the polyolefin microporous membrane can be adjusted to the range described above, for example, by controlling the stretching ratio and HS ratio during the biaxial stretching process.

[0145] For the thermal shrinkage rate of polyolefin microporous membranes, considering the high shape stability of the membrane at relatively high temperatures and the suppression of short circuits under thermal runaway conditions in non-aqueous secondary batteries during tests such as nail penetration, the thermal shrinkage rate measured at 120°C is preferably -10% or more and 20% or less, more preferably -5% or more and 15% or less, and even more preferably 0% or more and 10% or less. For the thermal shrinkage rate of polyolefin microporous membranes, when measured at 120°C using TD, the thermal shrinkage rate is preferably -10% or more and 20% or less, more preferably -5% or more and 18% or less, even more preferably 0% or more and 15% or less, and particularly preferably 0% or more and 10% or less.

[0146] The fuse temperature of the microporous membrane is preferably 150°C or lower, more preferably 149°C or lower. A fuse temperature below 150°C means that when certain abnormal reactions occur and the internal temperature of the battery rises, the pores of the separator will close until 150°C is reached. Therefore, the lower the fuse temperature, the faster the flow of lithium ions between the electrodes is stopped at low temperatures, thus improving safety. On the other hand, from the viewpoint that battery performance will not decrease even when exposed to high temperatures exceeding 100°C, the fuse temperature (melt temperature) of the microporous membrane is preferably 130°C or higher, more preferably 135°C or higher, further preferably 138°C or higher, and particularly preferably 139°C or higher.

[0147] For the surface smoothness of polyolefin microporous membranes, considering the cycling and rate characteristics under pressure, the average surface smoothness of one side and the other side of the polyolefin microporous membrane is preferably 20000 sec / 10cm. 3 Above and 200,000 seconds / 10cm 3 Below, more preferably 30000 sec / 10cm 3 Above and 180,000 seconds / 10cm 3 The following is a further preferred value: 40000 sec / 10cm 3 Above and 160,000 seconds / 10cm 3 The following is a preferred value: 50,000 sec / 10cm 3 Above and 140,000 seconds / 10cm 3 The following surface smoothness is less than 20000 sec / 10cm. 3 In such cases, the physical distance between the polyolefin microporous membrane and the electrode material becomes uneven, leading to uneven battery reaction and potentially deteriorating cycle characteristics. Additionally, a surface smoothness exceeding 200,000 sec / 10 cm... 3 In such cases, the distance between the polyolefin microporous membrane and the electrode material decreases, resulting in smaller voids between them. This hinders the uniform penetration of the electrolyte, potentially worsening the cycle characteristics. The surface smoothness of the polyolefin microporous membrane can be adjusted to the range described above by controlling factors such as the molecular weight and mixing ratio of the polyolefin and other polymer raw materials, the distance between the casting rollers, the stretching ratio during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, the heating coefficient per unit resin of the resin composition during the biaxial stretching process, the HS ratio, and the HS temperature.

[0148] (Multilayer porous membrane)

[0149] In one aspect of the present invention, a polyolefin microporous membrane having the above-described structure is also provided, and a multilayer porous membrane having at least one layer disposed on at least one side thereof. Depending on the properties of the at least one layer, the multilayer porous membrane can impart one or more functions to the polyolefin microporous membrane, and can also be used as a separator for non-aqueous secondary batteries.

[0150] From the perspective of achieving a certain membrane strength and low permeability, the porosity (before compression) of the multilayer porous membrane is preferably in the range of 20% or more and 80% or less. The porosity of the multilayer porous membrane is determined as described in the examples.

[0151] Specifically, the multilayer porous membrane can have any one of the following layer structures:

[0152] Layer structure 1: Contains a polyolefin microporous membrane and an inorganic porous layer disposed on at least one side of the polyolefin microporous membrane;

[0153] Layer structure 2: comprising a polyolefin microporous membrane and a thermoplastic resin layer disposed on at least one side of the polyolefin microporous membrane; and

[0154] Layer structure 3: comprising a polyolefin microporous membrane and at least one layer disposed on at least one side of the polyolefin microporous membrane, selected from the group consisting of a multifunctional layer, an inorganic porous layer and a thermoplastic resin layer.

[0155] (Inorganic porous layer)

[0156] Inorganic porous layers contain inorganic particles and binder polymers. Multilayer porous membranes containing inorganic porous layers maintain ion permeability and exhibit excellent thermal shrinkage suppression capabilities, even as thin films, due to the porous structure of the inorganic porous layers.

[0157] There are no particular limitations on the inorganic particles used, but inorganic particles with high heat resistance and electrical insulation, and electrochemical stability in the application range of non-aqueous secondary batteries are preferred.

[0158] Examples of inorganic particulate materials include oxide ceramics such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium dioxide, yttrium oxide, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum hydroxide, or boehmite, potassium titanate, talc, kaolinite, dickite, perlite, hydrous kaolin, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. Among these, at least one from the group consisting of alumina, boehmite, and barium sulfate is preferred from the viewpoint of stability in non-aqueous secondary batteries. Furthermore, as boehmite, synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of electrochemical elements is preferred. Various inorganic particles can be used alone or in combination.

[0159] Examples of inorganic particle shapes include plate-like, scaly, polyhedral, needle-like, columnar, granular, spherical, spindle-shaped, and blocky shapes. Multiple combinations of these shapes can also be used. Among these, from the viewpoint of balancing permeability and heat resistance, blocky shapes are preferred.

[0160] The aspect ratio of the inorganic particles is preferably 1.0 or more and 3.0 or less, more preferably 1.1 or more and 2.5 or less. An aspect ratio of 3.0 or less is preferred from the viewpoints of suppressing the amount of water adsorption in the multilayer porous membrane, suppressing capacity degradation during repeated cycling, and suppressing deformation at temperatures exceeding the melting point of the PO microporous membrane.

[0161] The proportion of inorganic particles in the inorganic porous layer is preferably 90% by mass or more and 99% by mass or less, more preferably 91% by mass or more and 98% by mass or less, and even more preferably 92% by mass or more and 98% by mass or less. A proportion of inorganic particles of 90% by mass or more is preferred from the viewpoint of ion permeability and from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the polyolefin microporous membrane. Furthermore, a proportion of 99% by mass or less is preferred from the viewpoint of maintaining the adhesive force between the inorganic particles or the interfacial adhesive force between the inorganic particles and the polyolefin microporous membrane.

[0162] The binder polymer is a material that binds multiple inorganic particles together in an inorganic porous layer, or binds an inorganic porous layer and a polyolefin microporous membrane together. When using multilayer porous membranes as separators, binder polymers that are insoluble in the electrolyte of non-aqueous secondary batteries and electrochemically stable within the application range of non-aqueous secondary batteries are preferred.

[0163] Specific examples of adhesive polymers include the following (1) to (7).

[0164] 1) Polyolefins: such as polyethylene, polypropylene, ethylene propylene rubber, and their modifiers;

[0165] 2) Conjugated diene polymers: such as styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides;

[0166] 3) Acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;

[0167] 4) Polyvinyl alcohol-based resins: such as polyvinyl alcohol and polyvinyl acetate;

[0168] 5) Fluorinated resins: such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer;

[0169] 6) Cellulose derivatives: such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose;

[0170] 7) Resins with a melting point and / or glass transition temperature of 180°C or above, or polymers that do not have a melting point but have a decomposition temperature of 200°C or above: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester.

[0171] From the viewpoint of safety during short circuits, 3) acrylic polymers, 5) fluorinated resins, and 7) polyamides as polymers are preferred. From the viewpoint of durability, fully aromatic polyamides, of which poly(m-phenylene isophthalamide) is preferred.

[0172] From the viewpoint of the compatibility of the adhesive polymer with the electrode, the above-mentioned 2) conjugated diene polymer is preferred, and from the viewpoint of voltage resistance, the above-mentioned 3) acrylic polymer and 5) fluorinated resin are preferred.

[0173] The conjugated diene polymers mentioned above (2) are polymers containing conjugated diene compounds as monomer units.

[0174] Examples of the aforementioned conjugated diene compounds include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes. These compounds can be used alone or in combination of two or more. 1,3-butadiene is particularly preferred.

[0175] The acrylic polymers mentioned above (3) are polymers containing (meth)acrylic acid compounds as monomer units. The (meth)acrylic acid compounds mentioned above represent at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylates.

[0176] Examples of (meth)acrylic acid used in acrylic polymers (3) above include acrylic acid and methacrylic acid.

[0177] Examples of (meth)acrylates used in the acrylic polymers described in section 3) above include alkyl (meth)acrylates, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; epoxy-containing (meth)acrylates, such as glycidyl acrylate and glycidyl methacrylate, may be used alone or in combination of two or more. Among these, 2-ethylhexyl acrylate (EHA) and butyl acrylate (BA) are particularly preferred.

[0178] From the perspective of the safety of non-aqueous secondary batteries, acrylic polymers are preferably polymers containing EHA or BA as the main structural unit. The main structural unit refers to the polymer portion corresponding to the monomers that account for more than 40 mol% of the total raw materials used to form the polymer.

[0179] The conjugated diene polymers (2) and acrylic polymers (3) mentioned above can be substances obtained by copolymerizing with other monomers that can copolymerize with them. Examples of other copolymerizable monomers include, for example, unsaturated alkyl carboxylic acids, aromatic vinyl monomers, acrylonitrile monomers, unsaturated monomers containing hydroxyl alkyl groups, unsaturated carboxylic acid amide monomers, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc., which can be used alone or in combination of two or more. Among the above, unsaturated alkyl carboxylic acid monomers are particularly preferred. Examples of unsaturated alkyl carboxylic acid monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconic acid, monomethyl fumarate, monoethyl fumarate, etc., which can be used alone or in combination of two or more.

[0180] It should be noted that the conjugated diene polymer mentioned above (2) can be a substance obtained by copolymerizing the above (meth)acrylic acid compounds with other monomers.

[0181] Considering that the adhesive force between multiple inorganic particles is strong even at temperatures exceeding room temperature, and that thermal shrinkage is suppressed, the adhesive polymer is preferably in the form of a latex, and more preferably in the form of an acrylic polymer latex.

[0182] In coating solutions used to form inorganic porous layers, dispersants such as surfactants can be added to stabilize dispersion or improve coatability. Dispersants are substances that adsorb onto the surface of inorganic particles in the slurry and stabilize the inorganic particles through electrostatic repulsion, such as polycarboxylates, sulfonates, and polyoxyethers. The amount of dispersant added is preferably 0.2 parts by weight or more and 5.0 parts by weight or less, more preferably 0.3 parts by weight or more and 1.0 parts by weight or less, based on solid content.

[0183] The total thickness of the inorganic porous layer is preferably 0.1 μm to 10 μm, more preferably 0.2 μm to 7 μm, and even more preferably 0.3 μm to 4 μm. The total thickness of the inorganic porous layer represents the thickness of the inorganic porous layer when it is formed on one side of the polyolefin microporous membrane, and the sum of the thicknesses of the two inorganic porous layers when it is formed on both sides of the PO microporous membrane. A total thickness of 0.1 μm or more is preferred from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the polyolefin microporous membrane, while a total thickness of 10 μm or less is preferred from the viewpoint of improving battery capacity.

[0184] (Thermoplastic resin layer)

[0185] The thermoplastic resin layer is a layer containing thermoplastic resin as the main component, and may contain other components as needed. From the viewpoint of high adhesion, it is preferable that the thermoplastic resin layer is in direct contact with the polyolefin microporous membrane.

[0186] From the viewpoint of adhesion to the electrode, the percentage of thermoplastic resin in the thermoplastic resin layer is preferably more than 3% by mass, more preferably more than 10% by mass, even more preferably more than 20% by mass, more than 40% by mass, more than 60% by mass, or more than 80% by mass, and particularly preferably more than 90% by mass.

[0187] Examples of thermoplastic resins include, for example, the binder polymer contained in the inorganic porous layer described above. From the viewpoint of adhesion and the safety of non-aqueous secondary batteries during nail penetration tests or short circuits, 2) conjugated diene polymers, 3) acrylic polymers, 5) fluorinated resins, and 7) polyamides as polymers are preferred.

[0188] The area ratio of the thermoplastic resin layer relative to the total surface area of ​​the polyolefin microporous membrane is preferably 100% or less, 95% or less, 80% or less, 75% or less, or 70% or less. Furthermore, this area ratio is preferably 5% or more, 10% or more, or 15% or more. Setting the area ratio to 100% or less is preferable from the viewpoint of suppressing pore blockage of the polyolefin microporous membrane due to the thermoplastic resin and further improving the permeability of the separator. Setting the area ratio to 5% or more is preferable from the viewpoint of further improving adhesion to the electrode.

[0189] When a thermoplastic resin layer is disposed on part of the surface of a polyolefin microporous membrane or an inorganic porous layer, the configuration pattern of the thermoplastic resin layer can be, for example, dotted, diagonal, striped, grid, striped, tortoise shell, random, and combinations thereof.

[0190] Regarding the thickness of the thermoplastic resin layer, it is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more per single side of the polyolefin microporous membrane. It is also preferably 10 μm or less, more preferably 7 μm or less, and even more preferably 4 μm or less. Setting the thickness of the thermoplastic resin layer to 0.1 μm or more is preferable from the viewpoint of uniformly exhibiting the adhesion between the electrode and the multilayer porous membrane, which improves battery characteristics. Setting the thickness of the thermoplastic resin layer to 10 μm or less is preferable from the viewpoint of suppressing the decrease in ion permeability.

[0191] (Multifunctional layer)

[0192] A multifunctional layer is a layer that imparts many functions to a polyolefin microporous membrane or separator, such as possessing the functions of both the inorganic porous layer and the thermoplastic resin layer described above. More specifically, the multifunctional layer may contain the binder polymer or thermoplastic resin described above, and inorganic particles, and may contain additional components such as dispersants as needed. The thickness of the multifunctional layer is not limited and can be determined based on the functions imparted to the polyolefin microporous membrane and the coating conditions.

[0193] <Method for Manufacturing Polyolefin Microporous Membranes>

[0194] The method for manufacturing the polyolefin microporous membrane of the present invention is not particularly limited. As an example, a method including the following steps can be listed:

[0195] (A) A process of extruding a polyolefin composition containing a polyolefin resin and a pore-forming material to form a gel sheet;

[0196] (B) The process of biaxially stretching a gel sheet to form a stretched sheet;

[0197] (C) The process of extracting porous material from a stretched sheet to form a porous membrane; and

[0198] (D) The process of heat-setting porous membranes.

[0199] The manufacturing process and preferred embodiments of polyolefin microporous membranes are described below.

[0200] [Extrusion process (A)]

[0201] In step (A), the polyolefin composition is extruded to form a gel-like sheet. The polyolefin composition may contain a polyolefin resin, a pore-forming agent, etc. It is preferable that the resin in the polyolefin composition does not contain non-resin components such as fine particles, or high-heat-resistant resins with significantly different melting points, but only polyolefins, from the viewpoint of uniform tensile stress and good air permeability and air permeability distribution of the resulting film. The gel-like sheet can be obtained by melt-blending the polyolefin resin with a pore-forming material and forming it into a sheet.

[0202] First, the polyolefin resin and the pore-forming material are melt-blended. Examples of melt-blending methods include: feeding the polyolefin resin and other additives as needed into a resin mixing apparatus such as an extruder, kneader, LABO-PLASTOMIL, mixing roller, or Banbury mixer; simultaneously heating and melting the resin components while introducing the pore-forming material at any ratio and mixing.

[0203] The polyolefin resin contained in the polyolefin composition can be determined based on the specified resin raw material of the resulting polyolefin microporous membrane. Specifically, the polyolefin resin used in the extrusion step (A) can be the polyolefin resin described as a constituent element of the polyolefin microporous membrane in Examples 1 to 4.

[0204] The plasticizer content in the resin composition is preferably 66% to 90% by mass, more preferably 68% to 88% by mass, and even more preferably 70% to 80% by mass. By adjusting the plasticizer content to 66% by mass or more, the melt viscosity of the resin composition is reduced, melt breakage is suppressed, and there is a tendency to improve film-forming properties during extrusion. On the other hand, by adjusting the plasticizer content to 90% by mass or less, it is possible to suppress the original roll elongation during the film-forming process.

[0205] From the viewpoint that uniformly dispersing a high molecular weight resin and uniformly applying tensile stress results in a membrane with good ion permeability and air permeability distribution, the PC content in the resin composition is preferably 20% to 40% by mass, more preferably 22% to 37% by mass, and even more preferably 24% to 33% by mass. Here, PC refers to "the percentage (by mass) of polymer components in the extrusion composition".

[0206] The high molecular weight raw materials contained in the polyolefin composition are used to obtain microporous membranes with molecular weight, MI, puncture strength, puncture strength converted from unit area weight, the difference between the maximum and minimum values ​​of air permeability at TD3 point R, air permeability and porosity (before compression), and air permeability under pressure. 30℃、3MPa Porosity under pressure 30℃、3MPaConsidering that the heat shrinkage rate is adjusted to the numerical range described above, for at least one of the raw materials, it is preferable that its lower limit Mv is 700,000 or more, and the upper limit Mv can be, for example, 2,000,000 or less. From the same perspective, the proportion of high molecular weight raw materials with an Mv of 700,000 or more in the resin contained in the polyolefin composition is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and can be 100% by mass.

[0207] When the polyolefin composition contains polyethylene as a main component, from the viewpoint of adjusting the compressed porosity, crystallization long period, or crystallite size of the obtained microporous membrane to the numerical range described above, the Mv of polyethylene is preferably 600,000 or more, more preferably 700,000 or more, and the upper limit of the Mv of polyethylene can be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the polyolefin composition is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, and can be 100% by mass.

[0208] When the polyolefin composition contains polyethylene as a main component, considering that the molecular weight (Mv) of the polyethylene is adjusted to the range described above for the obtained microporous membrane, including molecular weight (M), MI, puncture strength, puncture strength converted from unit area weight, the difference between the maximum and minimum values ​​of the air permeability at TD3 point (R), air permeability and porosity (before compression), air permeability under pressure (30°C, 3MPa), porosity under pressure (30°C, 3MPa), and heat shrinkage rate, for at least one of the raw materials, it is more preferably 700,000 or more, and the upper limit of the Mv of polyethylene can be, for example, 2,000,000 or less. From the same perspective, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the polyolefin composition is preferably 30% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and can be 100% by mass.

[0209] Furthermore, from the viewpoint of the heat resistance of the obtained microporous membrane, polypropylene can be mixed into the polyolefin composition. In this case, from the viewpoint of membrane strength and compression resistance, the ratio of polypropylene in the polyolefin composition relative to the total polyolefin resin is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less. Furthermore, from the viewpoint of improving formability, the ratio of polypropylene in the polyolefin composition relative to the total polyolefin resin is preferably 3% by mass or more and 10% by mass or less, more preferably 5% by mass or more and 9% by mass or less.

[0210] Plasticizers, inorganic materials, or combinations thereof can be listed as pore-forming materials.

[0211] There are no particular limitations on the type of plasticizer used, but non-volatile solvents that can form a homogeneous solution above the melting point of polyolefins are preferred. Specific examples of non-volatile solvents include hydrocarbons such as liquid paraffin and alkane waxes; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. It should be noted that these plasticizers can be recovered and reused after extraction using processes such as distillation.

[0212] Among plasticizers, liquid paraffin tends to have the following characteristics when the polyolefin resin is polyethylene or polypropylene: it has high compatibility with them, and even when the melt compound is stretched, the interface between the resin and the plasticizer is not easily delaminated, and uniform stretching is easy to implement, so it is preferred.

[0213] As inorganic materials, there are no particular limitations, but examples include oxide ceramics such as alumina, silicon dioxide (silicon oxide), titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, hydrous kaolin, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These can be used alone or in combination of two or more. Among these, silicon dioxide is particularly preferred from the viewpoint of ease of extraction.

[0214] Regarding the ratio of the polyolefin resin composition to the inorganic material, from the viewpoint of obtaining good isolation, the inorganic material is preferably 3% by mass or more, more preferably 10% by mass or more, relative to their total mass, and from the viewpoint of ensuring high strength, it is preferably 60% by mass or less, more preferably 50% by mass or less.

[0215] Next, the melt-blended compound is formed into sheets to obtain gel-like sheets. When melt-blending is performed using an extruder, the ratio of the extrusion rate of the polyolefin composition (i.e., the extrusion rate Q: kg / h) to the screw speed N (rpm) of the extruder (Q / N, unit: kg / (h·rpm)) is preferably 0.1 or more and 7.0 or less, more preferably 0.5 or more and 6.0 or less, and even more preferably 1.0 or more and 5.0 or less. If melt-blending is performed under conditions of Q / N of 0.1 or more and less than 7.0, the liquid paraffin that has undergone phase separation from the resin is more easily dispersed, and therefore, there is a tendency for the pore structure to become denser and for high strength to be achieved.

[0216] Methods for manufacturing sheet-like molded articles include, for example, extruding a molten compound into a sheet using a T-die, and then cooling it to a temperature sufficiently lower than the crystallization temperature of the resin component for curing. Examples of heat conductors used in cooling and curing include metals, water, air, and plasticizers. Among these, metal rollers are preferred due to their high thermal conductivity. Furthermore, when the extruded gel-like sheet is brought into contact with a metal roller, the heat conduction efficiency tends to be further improved, the sheet tends to align and increase film strength, and the surface smoothness of the sheet is also improved; therefore, this method is even more preferred.

[0217] From the perspective of controlling the casting gap when the molten compound is extruded into a sheet from the T-die, and adjusting the average film thickness (before compression) of the obtained microporous film to the numerical range described above, for example, for casting rolls, the roll gap is preferably 200 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less. If the roll gap of the casting roll is 200 μm or more, the risk of film breakage can be reduced in the subsequent stretching process; if the roll gap is 3000 μm or less, the cooling rate is fast and uneven cooling is prevented. In addition, from the perspective of obtaining a thin film and improving the surface orientation and crystallinity to achieve the stretching ratio required to improve compressibility, the casting thickness is preferably 500 μm to 2200 μm, more preferably 700 μm to 2000 μm.

[0218] Alternatively, the extruded sheet or gel sheet can be calendered. Calendering can be performed, for example, using rollers. Calendering, in particular, can increase the orientation of the surface portion. The calendering ratio is preferably more than 1 and less than 3, more preferably more than 1 and less than 2. If the calendering ratio is more than 1, there is a tendency for increased surface orientation and increased film strength of the resulting porous film. If the calendering ratio is less than 3, there is a tendency for a small orientation difference between the surface portion and the central interior, resulting in a uniform porous structure in the thickness direction of the film.

[0219] [Biaxial stretching process (B)]

[0220] In step (B), the gel sheet obtained in step (A) is stretched. Step (B) is performed before step (C) of extracting the pore-forming material from the sheet. In step (B), from the viewpoint of controlling the bending stiffness of the polyolefin microporous membrane, the stretching process of the gel sheet is performed at least once in both the length and width directions (i.e., by biaxial stretching).

[0221] Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-segment stretching, and multiple stretching. Among these, simultaneous biaxial stretching is preferred from the perspectives of improving membrane strength, ensuring uniform stretching, and considering that the main structure tends to become isotropic in-plane, thus isotropically dispersing stress during the nail test and improving its safety. Simultaneous biaxial stretching refers to a stretching method that simultaneously performs MD (membrane stretching) and TD (transverse stretching), with different stretching ratios in each direction. Sequential biaxial stretching refers to a stretching method that independently performs MD and TD stretching, where other directions are either unrestricted or fixed to a constant length during MD or TD stretching.

[0222] In step (B), from the viewpoint of adjusting the porosity, crystallization period, or crystallite size of the obtained microporous membrane after compression to the numerical range described above, it is preferable to preheat the gel-like sheet in the stretching furnace just before stretching, and more preferably to increase the preheating coefficient. The preheating coefficient is a value obtained by multiplying the preheating temperature by the preheating air velocity and the preheating time, preferably in the range of 130,000 °C·m to 300,000 °C·m, more preferably in the range of 150,000 °C·m to 300,000 °C·m, and even more preferably in the range of 180,000 °C·m to 300,000 °C·m. If the preheating furnace is divided into multiple rooms with different air velocities, the overall air velocity of the preheating furnace is calculated as the sum of "air velocity of each room × furnace length of each room / furnace length of the preheating furnace".

[0223] In the MD stretching process (B), considering the viewpoint of adjusting the compressed porosity, crystallization period, or crystallite size of the obtained microporous membrane to the numerical range described above, the viewpoint of forming a highly rigid backbone by highly orienting the polyethylene as the main component, and the viewpoint that in addition to increasing the strength of the membrane through stretching orientation, compressibility can be improved by increasing crystallinity, the MD stretching ratio is preferably 5 times or more, more preferably 5 times or more and 10 times or less, further preferably 5 times or more and 9 times or less, or 6 times or more and 10 times or less, and particularly preferably 6 times or more and 8 times or less. The MD stretching ratio can be adjusted, for example, according to the MD stretching temperature, MD stretching air velocity, MD stretching time, MD stretching coefficient, etc. From the same perspective as above, and considering that even high molecular weight resins can be uniformly stressed to achieve good permeability and air permeability distribution in the resulting film, the lower limit of the MD stretching temperature is preferably 122.0°C or higher, more preferably 123.0°C or higher, even more preferably 124.0°C or higher, even more preferably 125.0°C or higher, particularly preferably 126.0°C or higher, and most preferably 127.0°C or higher, and the upper limit is preferably 145.0°C or lower, more preferably 140.0°C or lower, and for example, 131.0°C or lower. If the MD stretching temperature is between -12°C and the melting point of the main component, it is presumably preferable for stretching and forming, as it applies appropriate stress to the film. If the MD stretching temperature is between -10°C and the melting point of the main component, it is even more preferable. If the MD stretching temperature is between -8°C and the melting point of the main component, it is even more preferable.

[0224] In the TD stretching of process (B), from the viewpoint of adjusting the porosity, crystallization period, or crystallite size of the obtained microporous membrane after compression to the numerical range described above, from the viewpoint of forming a highly rigid backbone by highly orienting the polyethylene as the main component, and from the viewpoint that in addition to increasing the strength of the membrane by stretching orientation, the compressibility can be improved by increasing crystallinity, the TD stretching ratio is preferably 5 times or more, more preferably 5 times or more and 10 times or less, even more preferably 5 times or more and 9 times or 6 times or more and 10 times or less, and particularly preferably 6 times to 8 times.

[0225] Furthermore, considering that even if the polyolefin composition supplied to step (A) has a high molecular weight composition, uniform TD stretching in step (B) can be easily performed, thereby improving the cycle characteristics of the non-aqueous secondary battery with the obtained microporous membrane, and considering that even high molecular weight resins can be uniformly stressed, resulting in good permeability and air permeability distribution of the obtained membrane, the lower limit of the TD stretching temperature in step (B) is preferably 122.0°C or higher, more preferably 123.0°C or higher, even more preferably 124.0°C or higher, even more preferably 125.0°C or higher, particularly preferably 126.0°C or higher, and most preferably 127.0°C or higher, and the upper limit is preferably 145.0°C or lower, more preferably 140.0°C or lower, and for example, 131.0°C or lower.

[0226] The TD stretching ratio and TD stretching temperature in process (B) can be adjusted, for example, based on the TD stretching wind speed, TD stretching time, TD stretching coefficient, etc.

[0227] In step (B), from the viewpoint of adjusting the compressed porosity, crystallization period, or crystallite size of the obtained microporous membrane to the numerical range described above, it is preferable to adjust the ratio of the preheating coefficient to the stretching coefficient (preheating coefficient / stretching coefficient) to 5.7 or higher and 7.0 or lower, particularly preferably 5.8 or higher and 7.0 or lower. If this ratio is adjusted to 5.7 or higher, the sheet is easily elongated by applying further heat during the preheating process before stretching, and a uniform structure is easily formed, which tends to improve the cycle characteristics of the non-aqueous secondary battery with the final microporous membrane. If this ratio is adjusted to 7.0 or higher, uneven stretching occurs, and an uneven membrane structure is easily formed, which tends to reduce the cycle characteristics of the non-aqueous secondary battery with the final microporous membrane. The stretching coefficient is a value obtained by multiplying the stretching temperature by the stretching air velocity and the residence time of the film during the stretching process, preferably within the range of 20,000℃·m to 50,000℃·m, and more preferably within the range of 30,000℃·m to 50,000℃·m. When the stretching furnace is divided into multiple chambers with different air velocities, the overall air velocity of the stretching furnace is calculated as the sum of "air velocity in each chamber × furnace length in each chamber / overall furnace length of the stretching furnace". Furthermore, the residence time within the stretching furnace is calculated by dividing the overall furnace length by the average velocity of the entire stretching furnace.

[0228] In step (B), considering the adjustment of the obtained microporous membrane's puncture strength, puncture strength converted from unit area weight, the difference R between the maximum and minimum values ​​of air permeability at TD3 point, air permeability and porosity (before compression), air permeability at 30°C and 3MPa under pressure, porosity at 30°C and 3MPa under pressure, heat shrinkage rate, tensile strength at break, and the MD / TD tensile strength at break ratio to the numerical ranges described above, the biaxial stretching ratio is preferably 5×5 or more, more preferably 5×5 or more and 10×10 or less, and even more preferably 6×6 or more and 10×10 or less. From the same perspective, the biaxial stretching ratio is preferably a simultaneous biaxial stretching ratio.

[0229] In step (B), considering the following factors, the puncture strength of the obtained microporous membrane converted to puncture strength per unit area weight, the difference between the maximum and minimum values ​​R of the air permeability at TD3 point, the air permeability and porosity (before compression), the air permeability at 30°C and 3MPa under pressure, the porosity at 30°C and 3MPa under pressure, the thermal shrinkage rate, and the tensile breaking strength and MD / TD tensile breaking strength ratio are adjusted to the numerical ranges described above. Therefore, the biaxial tensile temperature is preferably 122°C or higher and 147°C or lower, more preferably 123°C or higher and 146°C or lower, even more preferably 124°C or higher and 145°C or lower, and particularly preferably 127°C or higher and 140°C or lower.

[0230] From the viewpoint of increasing the heat applied to the unit resin, making the tensile stress uniform, and improving the distribution of the permeability of the resulting film, the PC content of the gel sheet supplied in step (B) is preferably 22% to 30% or 25% to 32%.

[0231] In process (B), considering the viewpoint of adjusting the puncture strength of the obtained microporous membrane, the puncture strength converted from unit area weight, the difference R between the maximum and minimum values ​​of the air permeability at TD3 point, the air permeability and porosity (before compression), the air permeability under pressure at 30°C and 3MPa, the porosity under pressure at 30°C and 3MPa, and the heat shrinkage rate to the numerical range described above, the following mathematical formula (I) is used:

[0232] The coefficient of thermal efficiency per unit resin = (biaxial tensile temperature - 115℃) ÷ PC (I)

[0233] The value expressed is preferably 0.26℃ / % or more. From the viewpoint of increasing the heat applied to the unit resin, uniformizing tensile stress, and improving the permeability distribution of the resulting membrane, this value is more preferably 0.26℃ / % or more and 1.2℃ / % or less, further preferably 0.34℃ / % or more and 1.0℃ / % or less, even more preferably 0.37℃ / % or more and 0.98℃ / % or less, and particularly preferably 0.40℃ / % or more and 0.95℃ / % or less. However, in the case of dry methods for membrane manufacturing and porosimetry in the absence of liquid, no plasticization is performed, and therefore more heat is required to uniformize the tensile stress; thus, the value calculated using the above formula is excluded.

[0234] [Extraction Process (C)]

[0235] In step (C), a porous membrane is obtained by removing the pore-forming material from the sheet-shaped body. Examples of methods for removing the pore-forming material include immersing the sheet-shaped body in an extraction solvent to extract the material and then thoroughly drying it. The method for extracting the pore-forming material can be either batch or continuous. To suppress shrinkage of the porous membrane, it is preferable to limit the ends of the sheet-shaped body during the series of immersion and drying steps. Furthermore, the residual amount of pore-forming material in the porous membrane is preferably less than 1% of the total mass of the porous membrane.

[0236] As the extraction solvent used when extracting pore-forming materials, it is preferable to use a solvent that is a poor solvent for polyolefin resins but a good solvent for pore-forming materials, and whose boiling point is lower than the melting point of polyolefin resins. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane and 1,1,1-trichloroethane; non-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. It should be noted that these extraction solvents can be recovered and reused using operations such as distillation. Furthermore, when using inorganic materials as pore-forming materials, aqueous solutions of sodium hydroxide, potassium hydroxide, etc., can be used as extraction solvents.

[0237] [Heat setting process (D)]

[0238] In the heat setting process (D), to suppress the shrinkage of the polyolefin microporous membrane, after plasticizer extraction in process (C), the microporous membrane undergoes heat treatment for heat setting (HS) purposes. Examples of heat treatments for the porous membrane include: stretching operations performed at a specified temperature atmosphere and specified stretching ratio for the purpose of adjusting physical properties, and / or relaxation operations performed at a specified temperature atmosphere and specified relaxation rate for the purpose of reducing tensile stress. The relaxation operation is a shrinkage operation of the membrane after the stretching operation. These heat treatments can be performed using a tenter frame or a roll stretching machine. It should be noted that heat setting, including stretching and relaxation operations after plasticizer extraction, is preferably performed in the TD process.

[0239] In step (D), from the viewpoint of adjusting the compressed porosity, crystallization period, or crystallite size of the obtained microporous membrane to the numerical range described above, it is preferable to preheat the microporous membrane just before stretching. Preheating in step (D) can be controlled, for example, by preheating temperature.

[0240] The TD stretching operation in step (D) is performed at a TD stretching temperature preferably above 130°C and below 150°C, more preferably above 132°C and below 145°C, and even more preferably above 133°C and below 140°C. This reduces the TD thermal shrinkage of the resulting film at 120°C, thereby improving the safety of non-aqueous secondary batteries in nail penetration tests.

[0241] The TD stretching operation in step (D) is performed with a TD stretching ratio of at least 1.1 times, more preferably at least 1.4 times, and even more preferably at least 1.5 times. Furthermore, the TD stretching ratio in step (D) is preferably 3 times or less, more preferably 2.5 times or less. By adjusting the TD stretching ratio in step (D) to the above-mentioned range, the stretching orientation increases the strength of the membrane, and the porosity can be controlled to optimize the balance between compressibility and permeability. Furthermore, the internal stress of the membrane is relaxed, suppressing thermal shrinkage. Specifically, TD thermal shrinkage at 120°C can be reduced, thereby improving safety in nail penetration tests.

[0242] From the perspective of crystallizing polyethylene, the main component of the microporous membrane, to form a rigid backbone, and considering the obtained microporous membrane's (uncompressed) average film thickness, puncture strength, and puncture strength converted from unit area weight, the difference R between the maximum and minimum values ​​of air permeability at TD3 point, (uncompressed) air permeability and porosity, and air permeability under pressure... 30℃、3MPa Porosity under pressure 30℃ , 3MPaConsidering that the heat shrinkage rate, tensile breaking strength, and MD / TD tensile breaking strength ratio are adjusted to the numerical ranges described above, the heat setting ratio of process (D), i.e., the relaxation ratio, is preferably 1.4 times or more, more preferably 1.5 times or more, and even more preferably 1.5 times or more and 3 times or less. Therefore, the stretching orientation increases the strength of the film, and the porosity can be controlled to optimize the balance between compressibility and permeability. Furthermore, it relaxes the stress inside the film, reduces TD heat shrinkage at 120°C, and improves the safety of non-aqueous secondary batteries in nail penetration tests.

[0243] From the viewpoint that adjusting the average film thickness (before compression) of the obtained microporous membrane, as well as the air permeability (30°C, 3MPa) and porosity (30°C, 3MPa) under pressure, to the numerical range described above, reduces the TD heat shrinkage of the obtained microporous membrane at a temperature of 120°C, thereby improving the safety of non-aqueous secondary batteries in nail penetration tests, the heat setting temperature, i.e., the relaxation temperature, of process (D) is preferably 130°C or higher and 150°C or lower, more preferably 132°C or higher and 145°C or lower, further preferably 133°C or higher and 140°C or lower, and particularly preferably 135°C or higher and 140°C or lower.

[0244] By employing manufacturing methods including steps (A) to (D), polyolefin microporous membranes of embodiments 1 to 4 can be obtained. The total stretch ratio of the finally obtained polyolefin microporous membrane is preferably 60 times or more, more preferably 61 times or more and 81 times or less, in order to crystallize the polyethylene, which is the main component of the microporous membrane, and form a rigid backbone.

[0245] Throughout the processes (A) to (D), from the viewpoint of increasing the heat applied to the unit resin, making the tensile stress uniform, and improving the distribution of the permeability of the final membrane, the PC content of the resin composition, gel sheet, or porous membrane is preferably 22% to 30% or 25% to 32%.

[0246] <Method for Manufacturing Multilayer Porous Membranes>

[0247] The method for manufacturing a multilayer porous membrane according to one aspect of the present invention is not particularly limited. As an example, it may include a step of configuring at least one layer selected from the group consisting of a multifunctional layer, an inorganic porous layer, and a thermoplastic resin layer on at least one side of the polyolefin microporous membrane manufactured above.

[0248] The method of preparing the multifunctional layer, inorganic porous layer, or thermoplastic resin layer is not particularly limited. Examples include coating a coating liquid containing components of any of these layers onto one or both sides of a polyolefin microporous membrane, or forming a layer on the polyolefin microporous membrane. The thickness of the coating layer is preferably 0.1–10 μm, more preferably 0.2–7 μm, and even more preferably 0.3–4 μm. Furthermore, the number of coating layers is preferably 0–5, more preferably 0–3. By appropriately controlling the thickness of the coating layer, the battery capacity can be improved. Inorganic coating has the effect of suppressing substrate shrinkage and improving battery safety, while organic coating has the effect of improving adhesion to the electrode and improving processability. By mixing inorganic and organic polymer components, the characteristics of both can be achieved in a good balance.

[0249] There are no particular limitations on coating methods if they can achieve the desired coating pattern, coating thickness, and coating area. Examples include gravure coating, small-diameter gravure coating, reverse roller coating, transfer roller coating, kiss coating, dip coating, doctor blade coating, air knife coating, scraper coating, scale measuring coating, extrusion coating, cast coating, die coating, screen printing, spraying, and inkjet coating.

[0250] The preferred medium for the coating liquid is water, or a mixture of water and a water-soluble organic medium. The water-soluble organic medium is not particularly limited, and examples include ethanol and methanol.

[0251] If the polyolefin microporous membrane is surface-treated before coating, the coating liquid is easier to apply, and the adhesion between the polyolefin microporous membrane and the coating layer is improved, which is therefore preferred. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0252] After coating, the solvent can be removed from the coated membrane by drying at a temperature below the melting point of the polyolefin microporous membrane, vacuum drying, solvent extraction, etc.

[0253] Alternatively, a polyolefin microporous membrane and at least one layer selected from the group consisting of a multifunctional layer, an inorganic porous layer, and a thermoplastic resin layer can be woven separately, and the two can be combined by pasting, lamination, bonding, welding, etc.

[0254] <Separators for non-aqueous secondary batteries, and non-aqueous secondary batteries>

[0255] The polyolefin microporous membranes of Embodiments 1 to 4 can be used, for example, in non-aqueous secondary batteries, specifically as separators for non-aqueous secondary batteries. Examples of non-aqueous secondary batteries include lithium-ion secondary batteries. By assembling the polyolefin microporous membranes of Embodiments 1 to 4 into lithium-ion secondary batteries, not only is thermal runaway of lithium-ion secondary batteries suppressed, but even when equipped with easily shrinkable electrodes, high-capacity electrodes, or Si-containing negative electrodes, battery characteristics such as high output characteristics and high cycle characteristics, as well as safety, can be maintained.

[0256] Example

[0257] The following examples and comparative examples illustrate the embodiments in more detail, but the present invention is not limited to the following examples as long as it does not deviate from its spirit. It should be noted that the physical properties in the examples were measured using the following methods. Unless otherwise specified, all measurements were performed at room temperature of 23°C ± 2°C and humidity of 40% ± 5%.

[0258] [Viscosity-average molecular weight]

[0259] According to ASTM-D4020, determine the intrinsic viscosity [η] (dl / g) of decahydronaphthalene solvent at 135°C.

[0260] For polyethylene, the following formula is used for calculation.

[0261] [η] = 6.77 × 10 -4 Mv 0.67

[0262] For polypropylene, Mv is calculated using the following formula.

[0263] [η] = 1.10 × 10 -4 Mv 0.80

[0264] [Weight-average molecular weight and number-average molecular weight]

[0265] Calibration curves were prepared by measuring standard polystyrene using a Waters ALC / GPC 150C (trademark) under the following conditions. Additionally, chromatographic measurements were performed on each of the following polymers under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curves using the following method.

[0266] Chromatographic columns: 2 GMH6-HT (trademark) columns from TOSOH CORPORATION + 2 GMH6-HT (trademark) columns

[0267] Mobile phase: o-dichlorobenzene

[0268] Detector: Differential refractometer

[0269] Flow rate: 1.0 ml / min

[0270] Column temperature: 140℃

[0271] Sample concentration: 0.1 wt%

[0272] (Weight-average molecular weight and number-average molecular weight of polyethylene and polypropylene)

[0273] By multiplying each molecular weight component in the obtained calibration curve by 0.43 (Q factor of polyethylene / Q factor of polystyrene = 17.7 / 41.3) or 0.64 (Q factor of polypropylene / Q factor of polystyrene = 26.4 / 41.3), the molecular weight distribution curves converted from polyethylene or polypropylene are obtained, and the weight-average molecular weight and number-average molecular weight are calculated.

[0274] (Weight-average molecular weight and number-average molecular weight of the resin composition or resin microporous membrane)

[0275] Using the Q factor value of the polyolefin with the largest mass fraction, the weight-average molecular weight and number-average molecular weight are calculated in the same manner as for polyethylene.

[0276] Melt Flow Index (MI)

[0277] According to JIS K7210:1999 (Plastics—Melt mass flow rate (MFR) and melt volumetric flow rate (MVR) of thermoplastics), the melt flow index (MI) of microporous membranes was determined. A load of 21.6 kgf was applied to the membrane at 190 °C, and the amount of resin (g) flowing out from a small orifice with a diameter of 2 mm and a length of 10 mm in 10 minutes was measured. The value obtained by rounding to the nearest decimal place was taken as the MI.

[0278] [DSC Measurement (Differential Scanning Calorimetry)]

[0279] DSC was performed using a DSC60 manufactured by Shimadzu Corporation. First, PO microporous membranes were cut into 5mm diameter circles, and several were stacked to prepare 3mg samples for testing. This sample was placed in a 5mm diameter open aluminum sample dish, covered with a clamping cover, and secured to the dish using a sample sealer. Under a nitrogen atmosphere, the temperature was increased from 30°C to 200°C at a rate of 10°C / min (first heating), held at 200°C for 5 minutes, and then decreased from 200°C to 30°C at a rate of 10°C / min. Next, after holding at 30°C for 5 minutes, the temperature was again increased from 30°C to 200°C at a rate of 10°C / min (second heating). The temperature reaching the maximum value in the melting endothermic curve during the second heating was taken as the melting point of the PO microporous membrane. When multiple maxima were present, the first peak and the largest peak were detected. It should be noted that the temperature at which the maximum value of the melting endothermic curve is obtained can be used as the melting point (Tm) of the PO microporous membrane.

[0280] Density (g / cm³) 3 )]

[0281] The density of the sample was determined using the density gradient tube method (23°C) according to JIS K7112:1999.

[0282] Weight per unit area (g / m²) 2 )]

[0283] Weight per unit area is the weight per unit area (1m²) 2 The weight (g) of the polyolefin microporous membrane was measured using a 1m × 1m sample and an electronic balance (AUW120D) manufactured by Shimadzu Corporation. It should be noted that if a 1m × 1m sample cannot be obtained, the membrane should be cut into appropriate areas, and the weight measured before converting the weight to the weight per unit area (m²). 2 The weight (g) of ).

[0284] [Average membrane thickness (μm) of the microporous membrane before compression]

[0285] The thickness was measured using a micro-thickness gauge (type KBN, terminal diameter Φ5mm) from Toyo Seiki Co., Ltd., at an ambient temperature of 23±2℃. It should be noted that, during thickness measurement, a 10cm×10cm sample of the microporous membrane was taken and overlapped to form a thickness of 15μm or more. Nine measurements were taken, and the average value was obtained. This average value was divided by the number of overlapped membranes to obtain the thickness of one membrane.

[0286] [Thickness (μm) of the multilayer porous membrane and coating layer (before compression)]

[0287] The thickness of the multilayer porous membrane was measured using a micro-thickness gauge (KBM trademark) manufactured by Toyo Seiki Co., Ltd., at room temperature (23±2℃). The thickness of the coating layer was calculated from the average thickness of the microporous membrane (before compression) and the individual thicknesses of the multilayer porous membrane (before compression). Alternatively, from the viewpoint of detection using the multilayer porous membrane, the thickness of each layer can also be measured using cross-sectional SEM images.

[0288] [Porosity (%) before compression]

[0289] Samples of 3cm×3cm, 1cm×1cm, 5cm×5cm, or 10cm×10cm square were cut from a polyolefin microporous membrane. The volume (cm²) was determined from the aforementioned membrane thickness measurement results. 3 ) and mass (g), which are derived from their density (g / cm³) 3 Use the following formula to calculate.

[0290] Porosity (%) = (Volume - Mass / Density of the mixture) / Volume × 100

[0291] It should be noted that the density of the mixed composition is a value calculated using the individual densities and mixing ratios of the polyolefin resin and other components used.

[0292] Furthermore, the porosity (before compression) of the multilayer porous membrane is calculated using the following formula: Porosity of the multilayer porous membrane = (Porosity of the polyolefin resin microporous membrane serving as the substrate) × (Average thickness of the polyolefin resin microporous membrane serving as the substrate) ÷ (Overall thickness of the multilayer porous membrane) + (Porosity of the coating layer) × (Thickness of the coating layer) ÷ (Overall thickness of the multilayer porous membrane)

[0293] Here, the porosity of the coating layer is set to 50%, and the porosity of the multilayer porous membrane is calculated. If the porosity of the coating layer is not 50%, the porosity can be calculated using the same formula as for polyolefin microporous membranes, as needed. Specifically, for the coated membrane, the thickness of the coating layer is determined by direct observation using SEM or by measuring the change in film thickness before and after coating. The volume of a specific area of ​​the coated layer sample is calculated, and then the mass-average density of the coating components is calculated from the material ratios of the components in the coating layer. The porosity of the coating layer is then calculated using this mass-average density.

[0294] [Porosity after compression (%)]

[0295] A 0.8 mm thick rubber cushioning material, a 0.1 mm thick PET film, two microporous membranes, the aforementioned PET film, and the aforementioned cushioning material were sequentially stacked. The resulting laminate was left to stand, and pressure was applied to one side of the cushioning material surface of the laminate to conduct a compression test. The compression test was conducted using a press at a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes. The compression ratio after relaxation was measured as needed. The compression ratio was measured between 2 and 24 hours after relaxation. After the compression test, relaxation was performed, and the microporous membrane was removed from the laminate. The microporous membrane after the compression test was used as a sample, and the porosity (%) after compression was measured using the same method as described above for "(porosity before compression)".

[0296] (Pre-compression) air permeability version 1 (seconds / 100cm) 3 )]

[0297] The air permeability was measured using the "EGO2" air permeability measuring machine manufactured by Asahi Seiko Co., Ltd.

[0298] The air permeability is measured at three points along the width of the membrane: a distance of 5 cm from each end and a point in the center. The average value of these three points is then calculated.

[0299] (Pre-compression) air permeability version 2 (seconds / 100cm) 3 )]

[0300] The air permeability was measured using the "EGO2" air permeability measuring machine manufactured by Asahi Seiko Co., Ltd.

[0301] The air permeability is measured at three points along the width direction (TD) of the membrane: two points at the inner side of the membrane at 10% of the full width from both ends toward the center and one point at the center. The average value of these three points is then calculated.

[0302] [Compression Test]

[0303] A compression test was conducted by sequentially stacking a 0.8 mm thick rubber cushioning material, a 0.1 mm thick PET film, two microporous membranes, the aforementioned PET film, and the aforementioned cushioning material. The resulting laminate was left to stand, and pressure was applied to one side of the cushioning material surface of the laminate. The microporous membrane used was 5 × 5 cm square. Before the compression test, the average membrane thickness (9-point average), weight per unit area, and air permeability were measured (using the measurement method of version 2). Furthermore, the porosity before the compression test was calculated from the weight per unit area and the average membrane thickness.

[0304] Compression tests were conducted using a press at 30°C and compression times of 3 minutes, under pressures of 2.5 MPa, 5 MPa, 7.5 MPa, and 10 MPa. One hour after unloading, the microporous membrane was removed from the laminate, and the average membrane thickness (9-point average) and air permeability after compression were measured. The porosity after compression was calculated from the weight per unit area and the average membrane thickness.

[0305] Finally, based on the measurement points at four points under the four pressures mentioned above, the porosity and air permeability after compression were approximated using a power-law approximation. Figure 1 Such an approximate curve.

[0306] [Compressed TMA]

[0307] The measurements were performed using a Hitachi High-Technologies Corporation TMA (Thermo Mechanical Analysis): SS6100. A 0.5 mm Φ quartz probe was used to apply the load to the sample.

[0308] Sixteen 1×1 cm square microporous membranes, for which the porosity was calculated by measuring the weight per unit area and membrane thickness, were stacked in the thickness direction to form a laminate. This laminate was mounted on the sample stage as the initial load, with an additional load of 0.06 MPa. After 1 minute, a load of 6 MPa / min was applied in the thickness direction, maintaining a load of 3 MPa for 3 minutes when the load reached 3 MPa. The membrane thickness after 3 minutes was taken as the in-situ membrane thickness under 3 MPa pressure.

[0309] [In-situ porosity at room temperature under 3 MPa pressure]

[0310] In the aforementioned compression TMA test, the porosity under the exact in-situ condition with 3 MPa applied was calculated from the thickness and the unit area weight before the TMA measurement. The calculation of the thickness under the exact in-situ condition with 3 MPa applied was performed using the same formula as previously described for calculating the porosity (%) (before compression).

[0311] [In-situ air permeability under 3MPa pressure at room temperature]

[0312] The in-situ porosity value under 3MPa pressure at room temperature was input into the approximate curve of porosity and permeability after compression generated in the aforementioned pressure test, and the in-situ permeability value under 3MPa pressure at room temperature was calculated.

[0313] [The difference between the maximum and minimum air permeability at 3 points in the TD direction (2 points at the inner edge of the full width of 10% from both ends and 1 point in the center, for a total of 3 points)]

[0314] Using the Oken-type air permeability tester (30mm φ diameter of the measuring part) from Asahi Seiko Co., Ltd., with the left end of the membrane set to 0% and the right end set to 100%, the air permeability was measured at three points: the center point at the 50% position, the center side 10% away from the left end (10% position), and the center side 10% away from the right end (90% position). The difference R between the largest and smallest values ​​among the three points was obtained.

[0315] Based on the width of the sample being measured, specifically when the sample width is 150 mm or less, the air permeability distribution in the width direction is measured using a nozzle with a diameter of 13 mmφ.

[0316] [Heat shrinkage rate (%) at 120℃ for 1 hour]

[0317] As samples, the length (in mm) of the porous membrane before heating was measured by cutting 100 mm from the MD and 100 mm from the TD, 50 mm from the MD and 50 mm from the TD, or 30 mm from the MD and 30 mm from the TD. The samples were then placed in an oven at 120°C for 1 hour. During this time, the samples were sandwiched between 10 sheets of paper, ensuring that the warm air did not directly contact the samples. After removing the samples from the oven and allowing them to cool, the length after heating was measured and recorded as the length (in mm). The heat shrinkage rate was calculated using the following formula. Measurements were performed separately for MD and TD, and the larger value was taken as the heat shrinkage rate.

[0318] Heat shrinkage rate (%) = {(Length before heating - Length after heating) / Length before heating} × 100

[0319] [Conversion of Penetration Strength to Weight per Unit Area]

[0320] Using a KES-G5 handheld compression tester (trademark) manufactured by KATO TECH CO.,LTD., the microporous membrane was fixed with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central portion of the fixed microporous membrane at a needle tip radius of 0.5 mm and a puncture speed of 2 mm / sec, under ambient temperature of 23°C and humidity of 40%. The puncture strength (gf) was determined in the form of the maximum puncture load. The measured value of the puncture test was obtained by averaging the values ​​at three points along the membrane's TD: two points at the inner 10% width from both ends towards the center and one point at the center.

[0321] The puncture strength can be calculated by converting the weight per unit area to the following formula.

[0322] Puncture strength converted from unit area weight [gf / (g / m]] 2 )] = Penetration strength [gf] / Weight per unit area [g / m 2 ]

[0323] Here, for multilayer porous membranes having at least one or more layers in a polyolefin microporous membrane substrate, the puncture strength and puncture strength per unit area weight are evaluated from the perspective of evaluating the strength of the resin and the strength per unit area weight, using the puncture strength and puncture strength per unit area weight of the polyolefin microporous membrane substrate as the evaluation characteristics.

[0324] [Pore size (μm): Semi-dry]

[0325] The average pore size (nm) was determined using a Perm Porometer (Porous Materials, Inc.: CFP-1500AE) according to the semi-dry method. The impregnation solution used was a perfluoropolyester (trade name "Galwick", surface tension 15.6 dyn / cm) manufactured by Porous Materials, Inc. The applied pressure and air permeability were measured for both the drying and wetting curves. The average pore size dHD (nm) was calculated using the following formula based on the pressure PHD (Pa) at the intersection of the half-curve of the drying curve and the wetting curve, and was taken as the pore size.

[0326] dHD=2860×γ / PHD

[0327] [Fuse (Off) Temperature]

[0328] Prepare two 10μm thick Ni foils (A and B). Leave a 15mm long and 10mm wide rectangular section of Ni foil A exposed, masking it with Teflon tape. Place the separator for the test sample on Ni foil B, securing both ends of the separator with Teflon tape. Immerse Ni foil B in a 1mol / L lithium tetrafluoroborate solution (solvent: a mixture of propylene carbonate / ethylene carbonate / γ-butyrolactone in a 1 / 1 / 2 volume ratio). After the electrolyte has penetrated the separator, attach the Ni foils (A and B) together, pressing them together with two glass plates and clamps. Place the prepared Ni foil electrode in a 25°C oven, heating it to 200°C at a rate of 2°C / min. Measure the impedance change at 1V and 1kHz using a resistance measuring device “AG-4311” (manufactured by Ando Electric Co., Ltd.). The temperature at which the impedance value reaches 1000Ω during the measurement is taken as the Fuse temperature (°C).

[0329] [Percentage of withstand voltage per unit area (before compression)]

[0330] A MD10cm × TD10cm section was cut at the center point along the width direction of the polyolefin microporous membrane. The membrane was clamped with a 5mm diameter aluminum plate, and its withstand voltage was measured using a withstand voltage tester (TOS9201) manufactured by Kikusui Electronics Co., Ltd. Regarding the test conditions, a DC voltage was applied starting from an initial voltage of 0V, increasing at a rate of 100V / sec. The voltage value (kV) at which a 0.2mA current flows was taken as the withstand voltage measurement value of the microporous membrane. It should be noted that a total of 25 points (MD5 × TD5) were measured at 15mm intervals, and their average value was taken as the withstand voltage measurement value. The withstand voltage per unit area weight was calculated as the ratio of withstand voltage to unit area weight (withstand voltage / unit area weight).

[0331] [Crystal Structure Analysis]

[0332] For long crystallization periods in polyolefin microporous membranes, small-angle X-ray scattering (SAX) measurements were performed using a NANOPIX detector manufactured by Rigaku Corporation. CuKα rays were irradiated onto the sample, and the scattering was detected using a HyPix-6000 semiconductor detector. Measurements were performed at a sample-detector distance of 1312 mm, an output of 40 kV, and 30 mA. The optical system employed point focusing, with slit diameters of 1st slit: φ = 0.55 mm, 2nd slit: open, and guard slit: φ = 0.35 mm. It should be noted that the sample was mounted with its surface perpendicular to the X-ray incident direction.

[0333] Furthermore, the crystallite size of the polyethylene MDND surface (110) in the polyolefin microporous membrane was determined using a Rigaku Corporation NANOPIX wide-angle X-ray scattering method via transmission. CuKα rays were irradiated onto the sample, and the scattering was detected by an imaging plate. Measurements were performed at a sample-detector distance of 110 mm, an output of 40 kV, and 30 mA. The optical system employed point focusing, with slit diameters of 1st slit: φ = 1.2 mm and guard slit: φ = 0.35 mm. It should be noted that the sample was mounted at an angle of 11.0° to the X-ray incident direction. In this configuration, the X-ray incident direction was perpendicular to the MD surface of the sample.

[0334] (Long crystallization period [nm])

[0335] For the X-ray scattering pattern obtained from HyPix-6000, the SAXS curve I(q) was obtained by annular averaging. In the Linear-Linear plot of the obtained one-dimensional curve I(q), at 0.1 nm... -1 <q<0.6nm -1 The baseline of the straight line is plotted within the range, and fitted using the Gaussian function. The location of the maximum intensity is taken as the peak position q originating from the long period of crystallization. m The long period of crystallization is calculated using Equation 4.

[0336] d = 2π / q m Formula 4

[0337] {In the formula, d(nm): crystallization long period}

[0338] q m (mm -1 ): The position of the peak originating from the thin layer in the SAXS curve.

[0339] (Crystal size)

[0340] The obtained XRD curves within the range of 2θ = 10.0° to 2θ = 30.0° were separated into three peaks: orthorhombic (110) diffraction peak, orthorhombic (200) diffraction peak, and amorphous peak. The crystallite size was calculated from the half-width at half-maximum (WWHM) of the (110) diffraction peak using the Scherrer formula (Equation 1). The (110) and (200) diffraction peaks were approximated using the Voigt function, while the amorphous peak was approximated using the Gauss function. It should be noted that the peak position of the amorphous peak was fixed at 2θ = 19.6° and the WWHM was fixed at 6.3°, while the peak position and WWHM of the crystalline peak were not specifically fixed for peak separation. The crystallite size was calculated from the WWHM of the (110) diffraction peak obtained through peak separation using the Scherrer formula (Equation 1).

[0341] D(110)=Kλ / (βcosθ) Equation 1

[0342] In the formula, D(110): crystallite size (nm)

[0343] K: 0.9 (constant)

[0344] λ: Wavelength of X-rays (nm)

[0345] β: (β1) 2 -β2 2 ) 0.5

[0346] β1: The full width at half maximum (FWHM) of the (hkl) peak calculated from the peak separation results (in rad).

[0347] β2: Full width at half maximum (rad) of the incident beam range

[0348] θ: Angle Bragg

[0349] [Tensile breaking strength (MPa) and MD / TD tensile breaking strength ratio, and tensile breaking elongation (%) and MD / TD tensile breaking elongation ratio]

[0350] According to JIS K7127, a tensile testing machine and a universal testing machine (Autograph) AG-A model (trademark) manufactured by Shimadzu Corporation were used to test MD and TD samples (shape, width 10mm × length 100mm). The chuck spacing of the tensile testing machine was set to 50mm, and celluloid tape (manufactured by NITTO DENKO CSSYSTEM CORPORATION, trade name: N.29) was applied to one side of each end of the sample (25mm on each side). Furthermore, to prevent sample slippage during the test, a 1mm thick layer of fluororubber was applied to the inside of the chuck of the tensile testing machine.

[0351] It should be noted that the measurement was conducted under the conditions of a temperature of 23±2℃, a chuck pressure of 0.40MPa, and a tensile speed of 100mm / min.

[0352] The tensile breaking strength (MPa) is calculated by dividing the strength of the polyolefin microporous membrane at break by the cross-sectional area of ​​the sample before the test. Additionally, the elongation at break of the polyolefin microporous membrane is used as the tensile breaking elongation (%).

[0353] Calculate the tensile breaking strength for both MD and TD, and also calculate the ratio of MD tensile breaking strength to TD tensile breaking strength (MD / TD tensile breaking strength ratio). Similarly, calculate the tensile elongation at break for both MD and TD, and also calculate the ratio of MD tensile elongation at break to TD tensile elongation at break (MD / TD tensile elongation at break ratio).

[0354] [Tensile modulus (MPa) of MD and TD and MD / TD tensile modulus ratio]

[0355] For the determination of tensile modulus (MD) and tensile deformation modulus (TD), MD samples (MD 120 mm × TD 10 mm) and TD samples (MD 10 mm × TD 120 mm) were cut out. Under atmospheric conditions of 23 ± 2 °C and 40 ± 2% humidity, the tensile modulus (MD) and TD of the samples were determined using a Shimadzu Autograph AG-A universal testing machine (trademark) manufactured according to JIS K7127. The samples were mounted with a chuck spacing of 50 mm, and expanded at a tensile speed of 200 mm / min until the chuck spacing reached 60 mm, i.e., the deformation reached 20.0%. The tensile modulus (MPa) was determined from the slope of the obtained stress-deformation curve from 1.0% to 4.0% of the deformation.

[0356] Calculate the tensile modulus for MD and TD respectively, and also calculate the ratio of the tensile modulus of MD to that of TD (MD / TD tensile modulus ratio).

[0357] Smoothness (sec / 10cm) 3 >

[0358] According to ISO 8791-5:2020, the smoothness of polyolefin microporous membranes was measured using a stainless steel nozzle with an inner diameter of 0.15 mm and a length of 50 mm, manufactured by Asahi Seiko Co., Ltd., in an atmosphere of 30°C and 40% humidity. The surface smoothness of one and the other surfaces of the polyolefin microporous membrane were measured separately. The average smoothness of the two surfaces was also calculated as described above.

[0359] [Battery Test]

[0360] a. Production of the positive electrode

[0361] A slurry was prepared by dispersing lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, and graphite and acetylene black as conductive materials, into polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) as binders. The slurry was then coated onto a 15 μm thick aluminum foil, which became the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the foil was compressed and shaped using a roller press. The resulting shaped body was cut into 57.0 mm wide pieces to obtain the positive electrode.

[0362] b. Negative electrode fabrication

[0363] Artificial graphite (as the negative electrode active material), ammonium salt of carboxymethyl cellulose (as a binder), and styrene-butadiene copolymer latex were dispersed in purified water to prepare a slurry. This slurry was then coated onto copper foil (the negative electrode current collector) using a die-coating machine. After drying at 120°C for 3 minutes, the foil was compressed and shaped using a roller press. The resulting shaped body was cut into 58.5 mm wide pieces to obtain the negative electrode.

[0364] c. Preparation of non-aqueous electrolytes

[0365] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate = 1:1:2 (volume ratio) at a concentration of 1 mol / L.

[0366] d. Battery assembly

[0367] After winding the positive electrode, the porous membrane obtained in the examples or comparative examples, and the negative electrode, a wound electrode body is fabricated using conventional methods and pressurized by a pressurizer to be placed into an outer can. It should be noted that the number of windings is adjusted according to the thickness and resilience of the polyolefin microporous membrane. The outermost periphery of the resulting wound electrode body is fixed by attaching insulating tape. The negative electrode lead is soldered to the battery can, and the positive electrode lead is soldered to the safety valve. The wound electrode body is then inserted into the battery can. Then, 5g of non-aqueous electrolyte is injected into the battery can, and the cover is riveted to the battery can using gaskets, thereby obtaining a square secondary battery with a width of 42.0mm, a height of 63.0mm, and a thickness of 10.5mm. The square secondary battery was charged at 0.2C (0.2 times the rated capacity at 1 hour rate (1C)) in an atmosphere at 25°C until the battery voltage reached 4.2V. After reaching 4.2V, the voltage was maintained at 4.2V, and the current was gradually reduced. This charging process was repeated for a total of 3 hours. Then, the battery was discharged at 0.2C until the battery voltage reached 3.0V.

[0368] e. Output characteristic test (25℃)

[0369] For the same prismatic secondary battery assembled as described in d. above and selected for evaluation, it was charged at a constant current of 1C at 25°C. After reaching 4.2V, it was charged at a constant voltage of 4.2V for a total of 3 hours. For the charged battery, under isothermal conditions at 25°C, the 1C discharge capacity and 5C discharge capacity up to the discharge termination voltage of 3V were measured. The 5C capacity / 1C capacity was taken as the output characteristic value. It should be noted that the output characteristic value was evaluated according to the following criteria.

[0370] A: The output characteristic value is above 0.95.

[0371] B: Output characteristic value is above 0.90 and less than 0.95.

[0372] C: Output characteristic value is above 0.85 and less than 0.90.

[0373] D: Output characteristic value is above 0.80 and less than 0.85.

[0374] E: Output characteristic value is less than 0.80.

[0375] f. Cyclic test (25℃)

[0376] Using the same prismatic rechargeable battery assembled as described in d. above and selected for evaluation, a total of 100 charge-discharge cycles were performed under the following conditions: (i) constant current and constant voltage charging at a current of 0.5C, an upper limit voltage of 4.2V, for a total of 3 hours; (ii) a 10-minute pause; (iii) constant current discharging at a current of 0.5C, a termination voltage of 3.0V; and (iv) a 10-minute pause. All of the above charge-discharge treatments were performed separately at 25°C. Then, the capacity retention rate (%) was calculated by making the ratio of the discharge capacity of the 100th cycle to the initial battery capacity X (mAh) 100 times. It should be noted that the capacity retention rate was evaluated according to the following criteria.

[0377] A: Capacity retention rate (%) is above 90%.

[0378] B: Capacity retention rate (%) is above 88% and less than 90%.

[0379] C: Capacity retention rate (%) is above 84% and less than 88%.

[0380] D: Capacity retention rate (%) is above 80% and less than 84%.

[0381] E: Capacity retention rate (%) is less than 80%.

[0382] g. Rate characteristic test (charge and discharge at 30℃ / 3MPa pressure)

[0383] For the same prismatic secondary battery assembled as described in d. above and selected for evaluation, it was charged at a constant current of 1C under an environment of 30°C and 3MPa pressure. After reaching 4.2V, it was charged at a constant voltage of 4.2V for a total of 3 hours. For the charged battery, under a constant temperature condition of 30°C, the 1C discharge capacity and 5C discharge capacity up to the discharge termination voltage of 3V were measured, and the 5C capacity / 1C capacity was taken as the output characteristic value. It should be noted that the rate characteristics were evaluated according to the following benchmarks.

[0384] A: The output characteristic value is above 90%.

[0385] B: Output characteristic value is above 80% and below 90%.

[0386] C: Output characteristic value is above 70% and below 80%.

[0387] D: Output characteristic value exceeds 50% but is less than 70%.

[0388] E: Output characteristic value is below 50%.

[0389] h. Cyclic test (charge and discharge at 30℃ / 3MPa pressure)

[0390] Using the same prismatic rechargeable battery assembled as described in d. above and selected for evaluation, a total of 100 charge-discharge cycles were performed under the following conditions: (i) constant current and constant voltage charging at 0.5C, upper limit voltage of 4.2V, for a total of 3 hours; (ii) 10-minute pause; (iii) constant current discharging at 0.5C, termination voltage of 3.0V; and (iv) 10-minute pause. All of the above charge-discharge processes were performed separately at 30°C. The capacity retention rate (%) was then calculated by making the ratio of the discharge capacity of the 100th cycle to the initial battery capacity X (mAh) 100 times. It should be noted that the capacity retention rate was evaluated according to the following criteria.

[0391] A: Capacity retention rate (%) is above 90%.

[0392] B: Capacity retention rate (%) is above 80% and less than 90%.

[0393] C: Capacity retention rate (%) is above 70% and less than 80%.

[0394] D: Capacity retention rate (%) is greater than 50% and less than 70%.

[0395] E: Capacity retention rate (%) is below 50%.

[0396] i. Nail safety test

[0397] The battery, assembled in the same manner as described in d. above and selected for evaluation, is placed on an iron plate in an explosion-proof chamber with temperature regulation capabilities. A 3.0 mm diameter iron nail is prepared, with a thermocouple installed inside. Under an environment of 30°C / 3 MPa pressure within the explosion-proof chamber, the iron nail is driven through the center of the battery at a speed of 2 mm / sec, and this process is maintained until the nail is fully penetrated. The battery is observed from the start of the penetration until it is completely pierced, and its safety is evaluated using the following criteria.

[0398] A: Nothing happened.

[0399] B: Smoke.

[0400] C: Battery cell expansion / deformation was observed.

[0401] D: Fire breaks out.

[0402] E: Explosion.

[0403] [Example 1]

[0404] (A) As shown in Table 1, the ratio of polyethylene (PE) with an Mv of 700,000 or more was adjusted to obtain a raw material resin composition. The Mv of the raw material resin composition was 900,000. Next, the raw material resin composition, liquid paraffin, and 0.1% by mass of antioxidant were mixed to form the resin content (PC) shown in Table 1 to obtain a polyolefin composition. The polyolefin composition was then fed into a biaxial extruder to extrude the molten polyolefin composition to form a gel-like sheet, which was then cooled and cured using a casting roller.

[0405] (B) Using a simultaneous biaxial stretching machine, under the conditions shown in Table 1, a biaxial stretching process is performed on the cooled and cured sheet to obtain a stretched sheet.

[0406] (C) Then, the stretch sheet is impregnated with dichloromethane, the liquid paraffin is extracted and removed, and then dried to become porous.

[0407] (D) Subsequently, using a uniaxial stretching machine, the obtained porous material was heat-set under the conditions shown in Table 1 to obtain a polyolefin microporous membrane. The total stretching ratio of the obtained polyolefin microporous membrane was 67 times. The obtained polyolefin microporous membrane was evaluated according to the above method, and the battery with the polyolefin microporous membrane was also evaluated. The evaluation results are shown in Table 3.

[0408] [Examples 2-23 and Comparative Examples 1-7]

[0409] Using the resin raw materials and manufacturing conditions shown in Tables 1 and 2, except for the method used in Example 1, polyolefin microporous membranes were obtained and evaluated. The evaluation results are shown in Tables 3 and 4 below.

[0410] [Table 1-1]

[0411]

[0412] [Table 1-2]

[0413]

[0414] [Table 1-3]

[0415]

[0416] [Table 2]

[0417]

[0418] [Table 3-1]

[0419]

[0420] [Table 3-2]

[0421]

[0422] [Table 3-3]

[0423]

[0424] [Table 4]

[0425]

[0426] [Example 24]

[0427] <Fabrication of Polyolefin Microporous Membranes>

[0428] Prepare a polyolefin microporous membrane by following these steps.

[0429] (A) As shown in Table 5, 30 parts by mass of polyethylene with an MV of 900,000 and 70 parts by mass of polyethylene with an MV of 300,000 were dry-mixed, and then 0.3 parts by mass of tetra-(methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate)methane as an antioxidant were added to obtain a raw material composition. The obtained composition was then fed into a twin-screw extruder via a feeder. Next, the total amount of resin raw material + liquid paraffin was set to 100 parts by mass, and the liquid paraffin (kinematic viscosity 75.90 cSt at 37.78°C) as a pore-forming material was injected into the extruder via a side feeder to form 30% of the "Polymer Component Ratio (PC) in the Extrusion Component" shown in Table 5. After mixing at a mixing temperature of 160°C, the mixture was extruded through a die located at the front end of the extruder.

[0430] (B) After extrusion, the film is immediately cooled and cured using a casting roller cooled to 30°C to form a sheet with a thickness of 1.530 mm. The sheet is then stretched to 7 × 6.4 times using a biaxial stretching machine at 128°C with a deformation rate of 35% / sec for MD and 30% / sec for TD.

[0431] (C) After stretching, the liquid paraffin is extracted and removed by immersion in dichloromethane.

[0432] (D) The sheet is then dried and stretched 1.85 times in the width direction (TD) using a stretching machine. The stretched sheet is then subjected to a width direction (TD) relaxation heat treatment at 131°C to form a 1.75-fold relaxation ratio at a deformation rate of -4.2% / sec, to obtain a polyolefin microporous membrane.

[0433] (E) The obtained polyolefin microporous membrane was evaluated according to the above method, and the battery with the polyolefin microporous membrane was also evaluated. The evaluation results are shown in Table 7.

[0434] [Examples 25-45 and Comparative Examples 8-21]

[0435] Using the resin raw materials, manufacturing conditions, and coating conditions shown in Tables 5 and 6, except for the method used in Example 24, polyolefin microporous membranes and their coated membranes were obtained and evaluated. The evaluation results are shown in Tables 7 and 8.

[0436] In Examples 42-45, the obtained polyolefin microporous membranes are then subjected to the following process (F).

[0437] (F) Then, the first layer, the second layer, and the third layer are coated on the polyolefin microporous membrane in a manner that forms the coating thickness shown in Table 5.

[0438] It should be noted that in Examples 42-45, boehmite was used as the inorganic filler and acrylic latex and sodium carboxymethyl cellulose were used as the binder in the inorganic coating; acrylic latex was used in the organic coating; and alumina was used as the inorganic filler and PVdF was used as the binder in the organic-inorganic mixed coating. In the coating of the substrate, the coating liquid was applied to the surface of the substrate treated with corona discharge using a gravure coating machine, and then the coating liquid was dried to obtain the separators of Examples 42-45 with the coated layer. The evaluation results of Examples 42-45 are shown in Table 7.

[0439] In Comparative Example 16, referring to Example 1 of Japanese Patent Application Publication No. 2018-162438, a polyolefin microporous membrane was obtained under the manufacturing conditions of Comparative Example 16 shown in Table 6 and evaluated.

[0440] In Comparative Example 17, referring to Example 5 of Japanese Patent Application Publication No. 2020-164861, a polyolefin microporous membrane was obtained under the manufacturing conditions of Comparative Example 17 shown in Table 6, and was evaluated.

[0441] In Comparative Example 18, referring to Example 10 of Japanese Patent Application Publication No. 2020-164861, a polyolefin microporous membrane was obtained under the manufacturing conditions of Comparative Example 18 shown in Table 6 and evaluated.

[0442] In Comparative Example 19, referring to Example 1 of Japanese Patent Application Publication No. 2002-88188, a polyolefin microporous membrane was obtained under the manufacturing conditions of Comparative Example 19 shown in Table 6 and evaluated.

[0443] In Comparative Example 20, referring to Example 7 of International Publication No. 2008 / 093572, a polyolefin microporous membrane was obtained under the manufacturing conditions of Comparative Example 20 shown in Table 6 and evaluated.

[0444] In Comparative Example 21, referring to Example 1 of Japanese Patent Application Publication No. 2017-25294 (Patent Document 8), a polyolefin microporous membrane was obtained by dry pore formation under the manufacturing conditions of Comparative Example 21 shown in Table 6, and the results were evaluated.

[0445] [Table 5-1]

[0446]

[0447] [Table 5-2]

[0448]

[0449] [Table 5-3]

[0450]

[0451] [Table 5-4]

[0452]

[0453] [Table 5-5]

[0454]

[0455] [Table 6-1]

[0456]

[0457] [Table 6-2]

[0458]

[0459] [Table 6-3]

[0460]

[0461] [Table 7-1]

[0462]

[0463] [Table 7-2]

[0464]

[0465] [Table 7-3]

[0466]

[0467] [Table 7-4]

[0468]

[0469] [Table 7-5]

[0470]

[0471] [Table 8-1]

[0472]

[0473] [Table 8-2]

[0474]

[0475] [Table 8-3]

[0476]

Claims

1. A polyolefin microporous membrane, comprising polyethylene as the main component, The polyolefin microporous membrane has a thickness of 1 μm to 30 μm and an air permeability of 40 sec / 100 cm. 3 Above and 500 sec / 100cm 3 the following, The MDND facet (110) crystallites of the polyethylene have a crystal size of 15.0 nm to 28.0 nm, and The polyolefin microporous membrane, under compression test conditions of 70°C, 8MPa, and 3 minutes, has a porosity of 30% or more and less than 50% after compression.

2. The polyolefin microporous membrane according to claim 1, wherein, The porosity after compression is above 31% and below 50%.

3. The polyolefin microporous membrane according to claim 1 or 2, wherein, The porosity after compression is greater than 33% and less than 50%.

4. The polyolefin microporous membrane according to claim 1 or 2, wherein, The film thickness is 3μm~20μm.

5. The polyolefin microporous membrane according to claim 1 or 2, wherein, The film thickness is 6μm~13μm.

6. The polyolefin microporous membrane according to claim 1 or 2, wherein, The air permeability is 40 sec / 100 cm. 3 Above and 200 sec / 100cm 3 the following.

7. A polyolefin microporous membrane, comprising polyethylene as the main component, wherein the crystallization period of the polyolefin microporous membrane, as determined by small-angle X-ray scattering (SAXS), is 37.0 nm to 60.0 nm. The MDND (110) crystallite size of the polyethylene is 15.0 nm to 28.0 nm. The air permeability of the polyolefin microporous membrane is 40 sec / 100 cm. 3 Above and 92 seconds / 100cm 3 the following.

8. The polyolefin microporous membrane according to claim 7, wherein, The crystallization period is 42.0 nm to 50.0 nm.

9. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein the crystallite size of the MDND surface (110) of the polyethylene is 15.0 nm to 22.0 nm.

10. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The porosity of the polyolefin microporous membrane is above 35%.

11. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The porosity of the polyolefin microporous membrane is above 45% and below 60%.

12. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The porosity of the polyolefin microporous membrane at 30°C and 3MPa pressure is above 43% and below 60%.

13. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The porosity of the polyolefin microporous membrane at 30°C and 3MPa pressure is above 49% and below 60%.

14. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The puncture strength of the polyolefin microporous membrane is above 220 gf.

15. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The puncture strength of the polyolefin microporous membrane is above 250 gf and below 700 gf.

16. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The puncture strength of the polyolefin microporous membrane is above 310 gf and below 680 gf.

17. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The polyethylene component of the polyolefin microporous membrane, with a weight-average molecular weight (Mw) of 1,000,000 or more as determined by GPC, accounts for more than 7% of all dissolved components as determined by GPC.

18. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The polyethylene component of the polyolefin microporous membrane, with a weight-average molecular weight (Mw) of 1,000,000 or more as determined by GPC, comprises 9% or more and 57% or less of all dissolved components as determined by GPC.

19. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The polyethylene component of the polyolefin microporous membrane, with a weight-average molecular weight (Mw) of 1,000,000 or more as determined by GPC, is 15% to 27% of the total dissolved components as determined by GPC.

20. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The polyethylene component of the polyolefin microporous membrane, with a weight-average molecular weight (Mw) of 1,000,000 or more as determined by GPC, is 7% to 27% of the total dissolved components as determined by GPC.

21. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The melt flow index (MI) of the polyolefin microporous membrane is below 1.

0.

22. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The melt flow index (MI) of the polyolefin microporous membrane is above 0.001 and below 1.

0.

23. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The melt flow index (MI) of the polyolefin microporous membrane is above 0.01 and below 0.

4.

24. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The TD heat shrinkage rate of the polyolefin microporous membrane at 120°C is less than 20%.

25. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The TD heat shrinkage rate of the polyolefin microporous membrane at 120°C is greater than -5% and less than 18%.

26. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The TD heat shrinkage rate of the polyolefin microporous membrane at 120°C is above 0% and below 10%.

27. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The shut-off temperature of the polyolefin microporous membrane is above 130°C and below 150°C.

28. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The shut-off temperature of the polyolefin microporous membrane is above 139°C and below 149°C.

29. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The ratio of the tensile strength in the length direction (MD) to the tensile strength in the width direction (TD) of the polyolefin microporous membrane (MD / TD tensile strength ratio) is 0.5 to 2.

0.

30. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The tensile strength along the longitudinal direction (MD) of the polyolefin microporous membrane is 500 kgf / cm. 2 Above and below 5000 kgf / cm 2 .

31. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The tensile strength (TD) of the polyolefin microporous membrane is 500 kgf / cm. 2 Above and below 5000 kgf / cm 2 .

32. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The ratio of the tensile strength in the length direction (MD) to the tensile strength in the width direction (TD) of the polyolefin microporous membrane (MD / TD tensile strength ratio) is 0.8 to 1.

3.

33. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The pore size of the polyolefin microporous membrane is 30nm~70nm.

34. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The pore size of the polyolefin microporous membrane is 35nm~60nm.

35. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The average surface smoothness of one and the other sides of the polyolefin microporous membrane is 20000 sec / 10cm. 3 Above and 200,000 seconds / 10cm 3 the following.

36. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The average surface smoothness of one and the other sides of the polyolefin microporous membrane is 30000 sec / 10cm. 3 Above and 180,000 seconds / 10cm 3 the following.

37. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The average surface smoothness of one and the other sides of the polyolefin microporous membrane is 40000 sec / 10cm. 3 Above and 160,000 seconds / 10cm 3 the following.

38. The polyolefin microporous membrane according to any one of claims 1, 2, 7 and 8, wherein, The voltage withstand per unit area weight of the polyolefin microporous membrane is 0.13 kV / (g / m²). 2 )above.

39. A separator comprising: a polyolefin microporous membrane according to any one of claims 1 to 38; and An inorganic porous layer disposed on at least one side of the polyolefin microporous membrane.

40. A separator comprising: a polyolefin microporous membrane according to any one of claims 1 to 38; and A thermoplastic resin layer disposed on at least one side of the polyolefin microporous membrane.

41. A separator comprising: a polyolefin microporous membrane according to any one of claims 1 to 38; and At least one layer selected from the group consisting of a multifunctional layer, an inorganic porous layer, and a thermoplastic resin layer is disposed on at least one side of the polyolefin microporous membrane.

42. A non-aqueous secondary battery comprising a polyolefin microporous membrane according to any one of claims 1 to 38, or a separator according to any one of claims 39 to 41.

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