Separator, battery, and nonwoven fabric

Abstract

To provide a separator having excellent low heat shrinkage and shape retention in a high temperature environment and a manufacturing method thereof, a battery with high safety and long life, and a nonwoven fabric having excellent low heat shrinkage and shape retention in the high temperature environment.SOLUTION: A separator includes a nonwoven fabric, and the nonwoven fabric includes a first fiber including a polymer having a glass transition temperature of -10°C or more and 70°C or less and a polymer having glass transition temperature of 80°C or more and 150°C or less and having a fiber diameter of 5 μm or less, and a second fiber with a fiber diameter greater than 5 μm.SELECTED DRAWING: Figure 3B

Description

[Technical Field]

[0001] This invention relates to a separator, a method for manufacturing the same, a battery, and a nonwoven fabric. [Background technology]

[0002] The applications of lithium-ion (Li) batteries are expanding beyond traditional small consumer use such as batteries for mobile phones and PCs to include applications requiring large capacity and high performance, such as batteries for power tools, automobiles and bicycles, and large-scale energy storage equipment. Ensuring safety during use is therefore crucial.

[0003] Lithium-ion batteries typically function as batteries when Li ions in the electrolyte move through pores that make up the separator. Generally, a biaxially oriented film made from polyolefin resin or the like is used as the separator.

[0004] As the output of lithium-ion batteries increases, they also have a problem: they can cause fires due to abnormal heat generation. Specifically, as lithium-ion batteries undergo repeated charging and discharging, the electrolyte, negative electrode surface, and positive electrode surface deteriorate, reducing the area that can be charged and discharged. This decline in battery characteristics increases the internal resistance of the lithium-ion battery. On the other hand, because lithium-ion batteries try to operate at the same output as when they were first released, they overwork, causing abnormal heat generation to occur, first at around 60°C to 80°C. When this abnormal heat generation reaches around 100°C to 120°C, the electrolyte begins to boil, generating gas. This increases the distance between the electrodes and raises the resistance, causing further heat generation. When the temperature exceeds 200°C, the positive electrode active material ignites. This causes the packing of the vacuum-packed lithium-ion battery to rupture, resulting in an explosion.

[0005] Porous biaxially oriented polyolefin films are insoluble in organic solvents and possess excellent mechanical properties. When used as a separator for lithium-ion batteries, they are known to have excellent shutdown characteristics, such as blocking pores and interrupting current during abnormal heat generation, thereby suppressing excessive temperature rise. However, these biaxially oriented polyolefin film separators suffer significant shrinkage due to the effects of heat during abnormal heat generation. As a result, they cannot maintain a sufficient surface area to stop electron movement in the electrolyte, leading to short circuits in lithium-ion batteries.

[0006] As a separator that is less prone to thermal shrinkage, for example, a microporous battery separator membrane has been proposed, which includes a microporous polyolefin separator membrane having a thickness of less than 14 μm, wherein the microporous separator membrane is thermally shut down at a temperature of 138°C or lower, the microporous separator membrane has a thermal shrinkage rate in the mechanical direction of 7.5% or less at 120°C for 1 hour, the microporous separator membrane has a thermal shrinkage rate in the lateral direction of 1% or less at 120°C for 1 hour, and / or the microporous separator membrane is improved or modified using ionization radiation energy (see Patent Document 1).

[0007] However, the proposed microporous polyolefin battery separator membrane has a problem in that lithium dendrites are easily formed due to the high straightness of the pores. Lithium dendrites are a phenomenon in which lithium is deposited on the electrode surface in the form of dendrites (needle-shaped crystals) when current concentrates on a part of the electrode due to a battery malfunction. If these lithium dendrites grow to the point of penetrating the separator, they can cause a short circuit in the lithium-ion battery. The problem is that such lithium dendrites are easily formed when the pores of the separator have high straightness.

[0008] Therefore, there is a strong demand for separators and their manufacturing methods that exhibit excellent low thermal shrinkage, maintain their shape in high-temperature environments, and are less prone to lithium dendrite formation, as well as for batteries that are highly safe and have a long lifespan. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2021-101423 [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention aims to solve the aforementioned problems in the conventional era and achieve the following objectives. Specifically, the present invention aims to provide a separator with excellent low thermal shrinkage properties and shape retention in high-temperature environments, a method for manufacturing the same, a battery with high safety and long lifespan, and a nonwoven fabric with excellent low thermal shrinkage properties and shape retention in high-temperature environments. [Means for solving the problem]

[0011] The means to solve the aforementioned problem are as follows: <1> A separator having a nonwoven fabric, The separator is characterized in that the nonwoven fabric contains a polymer having a glass transition temperature of -10°C to 70°C and a polymer having a glass transition temperature of 80°C to 150°C, and contains first fibers with a fiber diameter of 5 μm or less and second fibers with a fiber diameter exceeding 5 μm. <2> The first fiber has a fiber diameter of 0.1 μm or more and 5 μm or less, and the second fiber has a fiber diameter of more than 5 μm and 30 μm or less, <1> This is the separator described in [the document]. <3> The first fiber contains a polymer whose glass transition temperature is between -10°C and 70°C. The second fiber contains a polymer having a glass transition temperature of 80°C or higher and 150°C or lower. <1> from <2> It is a separator as described in one of the following. <4> The orientation direction of the first fiber and the orientation direction of the second fiber are different. <1> from <3> It is a separator as described in one of the following. <5> The polymer having a glass transition temperature of -10°C to 70°C is polypropylene, and the polymer having a glass transition temperature of 80°C to 150°C is polycarbonate. <1> from <4> It is a separator as described in one of the following. <6> The above, which has an average thickness of 0.025 mm to 5 mm. <1> from <5> It is a separator as described in one of the following. <7> When the thermal shrinkage rate at 20°C is set to 0%, the thermal shrinkage rate at 130°C or below is 3% or less. <1> from <6> It is a separator as described in one of the following. <8> The aforementioned <1> from <7> This battery is characterized by having a separator as described in any of the above. <9> A dispensing step in which a first polymer solution having a glass transition temperature of -10°C or higher and 70°C or lower is dispensed from a first nozzle hole, and at the same time a second polymer solution having a glass transition temperature of 80°C or higher and 150°C or lower is dispensed from a second nozzle hole, A stretching step in which the first polymer discharged from the first nozzle hole and the second polymer discharged from the second nozzle hole are stretched with air at a temperature of 250°C to 350°C, A collection step for collecting the stretched first polymer and the stretched second polymer, This is a method for manufacturing a separator, characterized by containing [a specific component]. <10> The first nozzle hole and the second nozzle hole are arranged in a row. The number of first nozzle holes and the number of second nozzle holes are in a ratio of 10:1 to 3:1. <9> This is a method for manufacturing the separator described in [the document]. <11> This nonwoven fabric is characterized by containing a polymer having a glass transition temperature of -10°C to 70°C and a polymer having a glass transition temperature of 80°C to 150°C, and by containing a first fiber with a fiber diameter of 5 μm or less and a second fiber with a fiber diameter exceeding 5 μm. [Effects of the Invention]

[0012] According to the present invention, the above-mentioned conventional problems can be solved and the above-mentioned object can be achieved. A separator having excellent low heat shrinkage property and shape retention property under high temperature environment, a method for manufacturing the same, a battery having high safety and long life, and a non-woven fabric having excellent low heat shrinkage property and shape retention property under high temperature environment can be provided.

Brief Description of Drawings

[0013] [Figure 1] FIG. 1 is a schematic view showing an example of a nozzle used in the method for manufacturing the separator of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an example of a melt blowing apparatus used in the method for manufacturing the separator of the present invention. [Figure 3A] FIG. 3A is a diagram showing a SEM image of [PP / PC conjugated fiber non-woven fabric 2] at a magnification of 150 times in Test Example 2-1. [Figure 3B] FIG. 3B is a diagram showing a SEM image of [PP / PC conjugated fiber non-woven fabric 2] at a magnification of 1,000 times in Test Example 2-1. [Figure 3C] FIG. 3C is a diagram showing a SEM image of [PP non-woven fabric 1] at a magnification of 150 times in Test Example 2-1. [Figure 3D] FIG. 3D is a diagram showing a SEM image of [PP non-woven fabric 1] at a magnification of 1,000 times in Test Example 2-1. [Figure 4A] FIG. 4A is a histogram of the fiber diameters of [PP / PC conjugated fiber non-woven fabric 1] in Test Example 2-1. The vertical axis represents the ratio (%), and the horizontal axis represents the fiber diameter (μm). [Figure 4B] FIG. 4B is a histogram of the fiber diameters of [PP / PC conjugated fiber non-woven fabric 2] in Test Example 2-1. The vertical axis represents the ratio (%), and the horizontal axis represents the fiber diameter (μm). [Figure 4C] FIG. 4C is a histogram of the fiber diameters of [PP / PC conjugated fiber non-woven fabric 8] in Test Example 2-1. The vertical axis represents the ratio (%), and the horizontal axis represents the fiber diameter (μm). [Figure 4D]Figure 4D is a histogram of the fiber diameter of [PP / PC blended nonwoven fabric 10] in Test Example 2-1. The vertical axis shows the percentage (%), and the horizontal axis shows the fiber diameter (μm). [Figure 4E] Figure 4E is a histogram of the fiber diameter of [PP / PC blended nonwoven fabric 11] in Test Example 2-1. The vertical axis shows the percentage (%), and the horizontal axis shows the fiber diameter (μm). [Figure 4F] Figure 4F is a histogram of the fiber diameter of [PP nonwoven fabric 1] in Test Example 2-1. The vertical axis shows the percentage (%), and the horizontal axis shows the fiber diameter (μm). [Figure 5A] Figure 5A shows a 150x magnification SEM image of [PP / PC blended nonwoven fabric 4] in Test Example 2-2. [Figure 5B] Figure 5B shows a 150x magnification SEM image of the biaxially oriented PET film in Test Example 2-2. [Figure 5C] Figure 5C shows a 1,000x magnification SEM image of [PP / PC blended nonwoven fabric 4] in Test Example 2-2. [Figure 5D] Figure 5D shows a 1,000x magnification SEM image of the biaxially oriented PET film in Test Example 2-2. [Figure 5E] Figure 5E shows a 3,000x magnification SEM image of the biaxially oriented PET film in Test Example 2-2. [Figure 5F] Figure 5F shows an SEM image of the biaxially oriented PET film in Test Example 2-2 at a magnification of 5,000x. [Figure 6] Figure 6 is a graph showing the results of the heat shrinkage rate in Test Example 3. The vertical axis represents the heat shrinkage rate (%), and the horizontal axis represents the temperature (°C). The solid line represents [PP nonwoven fabric 1], the dotted line represents [PP / PC blended nonwoven fabric 2], the dashed line represents [PP / PC blended nonwoven fabric 8], and the dashed-dotted line represents [PP / PC blended nonwoven fabric 11]. [Figure 7A] Figure 7A shows the appearance of [PP / PC blended nonwoven fabric 2] before heat treatment in Test Example 4. [Figure 7B]Figure 7B shows the appearance of [PP / PC blended nonwoven fabric 2] after 12 hours of heat treatment in Test Example 4. [Figure 7C] Figure 7C shows the appearance of [PP nonwoven fabric 1] before heat treatment in Test Example 4. [Figure 7D] Figure 7D shows the appearance of [PP nonwoven fabric 1] after 12 hours of heat treatment in Test Example 4. [Figure 8A] Figure 8A is a histogram of the pore size distribution for [PP / PC blended nonwoven fabric 2] in Test Example 5. The vertical axis shows the pore size distribution (%), and the horizontal axis shows the pore size (μm). [Figure 8B] Figure 8B is a histogram of the pore size distribution for [PP / PC blended nonwoven fabric 8] in Test Example 5. The vertical axis shows the pore size distribution (%), and the horizontal axis shows the pore size (μm). [Figure 8C] Figure 8C is a histogram of the pore size distribution of [PP / PC blended nonwoven fabric 11] in Test Example 5. The vertical axis shows the pore size distribution (%), and the horizontal axis shows the pore size (μm). [Figure 8D] Figure 8D is a histogram of the pore size distribution for [PP nonwoven fabric 1] in Test Example 5. The vertical axis shows the pore size distribution (%), and the horizontal axis shows the pore size (μm). [Figure 9A] Figure 9A shows the results of the initial charge-discharge curves in Test Example 6. The vertical axis represents voltage (V), and the horizontal axis represents capacity (mAh). The solid line represents [PP nonwoven fabric 1], the dotted line represents [PP / PC blended nonwoven fabric 2], the dashed line represents [PP / PC blended nonwoven fabric 8], and the dashed-dotted line represents [PP / PC blended nonwoven fabric 11]. [Figure 9B] Figure 9B shows the results of the capacity test in Test Example 6. The vertical axis represents voltage (V), and the horizontal axis represents capacity (mAh). The solid line represents [PP nonwoven fabric 1], the dotted line represents [PP / PC blended nonwoven fabric 2], the dashed line represents [PP / PC blended nonwoven fabric 8], and the dashed-dotted line represents [PP / PC blended nonwoven fabric 11]. [Modes for carrying out the invention]

[0014] (Separator) The separator of the present invention is a separator having a nonwoven fabric, wherein the nonwoven fabric contains a polymer having a glass transition temperature of -10°C to 70°C (hereinafter sometimes referred to as "polymer A") and a polymer having a glass transition temperature of 80°C to 150°C (hereinafter sometimes referred to as "polymer B"), and also contains a first fiber with a fiber diameter of 5 μm or less and a second fiber with a fiber diameter greater than 5 μm. The separator may further have other configurations as needed.

[0015] <Nonwoven fabric> The nonwoven fabric contains a polymer (polymer A) having a glass transition temperature of -10°C to 70°C, a polymer (polymer B) having a glass transition temperature of 80°C to 150°C, the first fiber, and the second fiber.

[0016] <<A polymer (polymer A) with a glass transition temperature between -10°C and 70°C>> If the glass transition temperature (Tg) of polymer A, which has a glass transition temperature of -10°C or higher and 70°C or lower, is below -10°C, it tends to relax at room temperature, which can reduce the dimensional stability of the nonwoven fabric. If it exceeds 70°C, efficient miniaturization by hot air during melt-blowing becomes difficult. The glass transition temperature (Tg) of polymer A can be measured by the inflection point of differential scanning calorimetry.

[0017] There are no particular restrictions on the melting point (Tm) of polymer A, and it can be appropriately selected depending on the purpose, but it is preferably 80°C to 300°C, and more preferably 160°C to 200°C. If the melting point (Tm) of polymer A is 80°C or higher, continuous fibers are easily formed, and if it is 300°C or lower, melt molding is easy. The melting point (Tm) of polymer A can be measured by the endothermic peak obtained by differential scanning calorimetry.

[0018] The polymer A is not particularly limited as long as it has a glass transition temperature of -10°C or higher and 70°C or lower, and can be appropriately selected according to the purpose. Examples include thermoplastic polymers and block copolymers.

[0019] Examples of the thermoplastic resins include polypropylene (PP) resin, polyethylene (PE) resin, polyester (PES) resin, polybutylene (PB) resin, polyamide (PA) resin, polyurethane (PU) resin, polyvinyl chloride (PVC) resin, polystyrene (PS) resin, polyvinyl acetate (PVAc) resin, acrylonitrile styrene (AS) resin, acrylic (PMMA) resin, and polyethylene terephthalate (PET) resin.

[0020] Examples of the aforementioned block copolymers include styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, and acrylonitrile-butadiene-styrene block copolymer (ABS resin).

[0021] These polymers A may be used individually or in combination of two or more. Among these, polypropylene (PP) resin is preferred for polymer A.

[0022] <<Polymers with a glass transition temperature of 80°C to 150°C (Polymer B)>> The glass transition temperature (Tg) of polymer B, whose glass transition temperature is 80°C or higher and 150°C or lower, is preferably 130°C or higher and 150°C or lower. If the glass transition temperature (Tg) of polymer B is less than 80°C, shrinkage in the high-temperature range cannot be suppressed, and the shutdown function cannot be performed when abnormal heat is generated. If it exceeds 150°C, melt molding becomes difficult. The glass transition temperature (Tg) of polymer B can be measured by the inflection point of differential scanning calorimetry.

[0023] There are no particular restrictions on the melting point (Tm) of polymer B, and it can be appropriately selected depending on the purpose, but it is preferably between 220°C and 300°C. If the melting point (Tm) of polymer B is 220°C or higher, fibers that function as a skeletal material are easily formed, and if it is 300°C or lower, melt molding is easy. The melting point (Tm) of polymer B can be measured by the endothermic peak obtained by differential scanning calorimetry.

[0024] The polymer B is not particularly limited as long as it is a polymer with a glass transition temperature of 80°C or higher and 150°C or lower, and can be appropriately selected according to the purpose. Examples include resins belonging to engineering plastics and resins belonging to super engineering plastics.

[0025] Examples of resins belonging to the engineering plastics mentioned above include polycarbonate (PC) resin, polyamide 46 (PA46) resin, polyamide (PA) resin (such as nylon), polyacetal (POM) resin, modified polyphenylene ether resin, polyethylene terephthalate (PET) resin, polybutylene terephthalate (PBT) resin, glass fiber reinforced polyethylene terephthalate resin, and cyclic polyolefin resin.

[0026] Examples of resins belonging to the aforementioned super engineering plastics include polytetrafluoroethylene (PTFE) resin, polysulfone (PSF) resin, polyethersulfone (PES) resin, amorphous polyarylate (PAR) resin, liquid crystal polymer (LCP) resin, polyetheretherketone (PEEK) resin, polyphenylene sulfide (PPS) resin, polyamide-imide (PAI) resin, and the like.

[0027] These polymers B may be used individually or in combination of two or more. Among these, polycarbonate (PC) resin is preferred for polymer B.

[0028] <<First Fiber>> The first fiber is a fiber with a diameter of 5 μm or less. By including the first fiber in the nonwoven fabric, the density of the nonwoven fabric can be increased, and microshorts can be prevented.

[0029] The fiber diameter of the first fiber is 5 μm or less, but preferably between 0.1 μm and 5 μm. If the fiber diameter of the first fiber exceeds 5 μm, it may cause microshorts. Furthermore, if the fiber diameter of the first fiber is 0.1 μm or more, it is preferable because pores are more easily formed, making it easier to act as a separator. The fiber diameter of the first fiber can be observed and measured using a scanning electron microscope (SEM).

[0030] There are no particular restrictions on the material of the first fiber, and it can be appropriately selected depending on the purpose, but it is preferable that it contains a polymer (polymer A) having a glass transition temperature of -10°C to 70°C, and more preferably polypropylene. The first fiber may also be made of polymer A.

[0031] <<The second fiber>> The second fiber has a fiber diameter exceeding 5 μm. The second fiber functions as a backing agent in the nonwoven fabric and can impart low thermal shrinkage, shape retention in high-temperature environments, and impact resistance to the separator. That is, if the separator is used in a battery and abnormal heat generation occurs in the battery, even if the first fiber melts, the second fiber will not melt and will maintain its shape as a separator, thus enabling a safer and longer-lasting battery.

[0032] The fiber diameter of the second fiber is greater than 5 μm, but preferably greater than 5 μm and less than or equal to 30 μm. If the fiber diameter of the second fiber is 5 μm or less, it becomes difficult for it to function as a skeletal material. Furthermore, if the fiber diameter of the second fiber is 30 μm or less, it is preferable in that the density of the first fiber is improved. The fiber diameter of the second fiber can be observed and measured using a scanning electron microscope (SEM).

[0033] The material of the second fiber is not particularly limited and can be appropriately selected depending on the purpose, but it is preferable that it contains a polymer (polymer B) having a glass transition temperature of 80°C to 150°C, and more preferably polycarbonate. The second fiber may also be made of polymer B.

[0034] There are no particular restrictions on the orientation direction of the first fiber and the orientation direction of the second fiber, and they can be appropriately selected according to the purpose. However, it is preferable that the orientation direction of the first fiber and the orientation direction of the second fiber are different in that they have excellent low heat shrinkage, shape retention in high-temperature environments, and impact resistance. Furthermore, it is particularly preferable that the orientation directions of the plurality of first fibers are randomly oriented, the orientation directions of the plurality of second fibers are randomly oriented, and the orientation directions of the plurality of first fibers and the orientation directions of the plurality of second fibers are randomly oriented, as this provides superior low thermal shrinkage, shape retention in high-temperature environments, and impact resistance.

[0035] There are no particular restrictions on the volume ratio (first fiber:second fiber) of the first fiber to the second fiber in the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 50:50 to 99:1 is preferred, and 70:30 to 90:10 is more preferred.

[0036] There are no particular restrictions on the average thickness of the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 0.025 mm to 5 mm is preferred, 0.02 mm to 2 mm is more preferred, and 0.02 mm to 1 mm is even more preferred. When the average thickness of the nonwoven fabric is within the preferred range, lithium dendrites can be effectively suppressed. The thickness of the nonwoven fabric can be measured in accordance with ISO 9073-2. In this specification, the average of the thickness measurements taken at 10 arbitrarily selected points on the nonwoven fabric is defined as the "average thickness".

[0037] Conventional biaxially oriented polyethylene film separators have a structure in which pores penetrate both the front and back surfaces, making them prone to lithium dendrite formation. In contrast, the nonwoven fabric has a structure in which the pores are not continuous but branch out into multiple channels. Thus, the nonwoven fabric is advantageous in that it has a lithium dendrite growth inhibiting effect because the pores do not advance in a straight line with respect to the direction of lithium dendrite growth. Furthermore, the nonwoven fabric preferably has a certain thickness in order to secure channels for inhibiting lithium dendrite formation, and is suitably used within the preferred range of average thickness.

[0038] There are no particular restrictions on the average basis weight of the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 4 g / m² is acceptable. 2 ~100g / m 2 This is preferable. When the average basis weight of the nonwoven fabric is within the preferred range, lithium dendrites can be effectively suppressed. The basis weight of the nonwoven fabric can be measured in accordance with ISO 9073-1. In this specification, the average value of the basis weight measurements at 10 arbitrarily selected points on the nonwoven fabric is defined as the "average basis weight."

[0039] There are no particular restrictions on the heat shrinkage rate of the nonwoven fabric, and it can be appropriately selected according to the purpose. However, if the heat shrinkage rate at 20°C is set to 0%, the heat shrinkage rate at 130°C or below is preferably 3% or less, and more preferably 1% or less.

[0040] The thermal shrinkage rate of the nonwoven fabric can be measured using a thermomechanical analyzer (e.g., TMA / SS6100, manufactured by Hitachi High-Tech Science Co., Ltd.). Specifically, the length of the test sample at 20°C before heat treatment is measured and defined as the initial length "L0". After raising the temperature of the test sample from 20°C to 200°C at a rate of 5°C / min, the length of the test piece is measured and defined as the length after heat treatment "L n The thermal shrinkage rate (TS) is calculated based on the following formula (1). Thermal shrinkage rate (TS) (%) = (1 - (L n / L0))×100 ··· Formula (1)

[0041] From the perspective of battery safety and extended lifespan, it is important that the battery has a shutdown mechanism against initial abnormal heat generation before it reaches high temperatures (approximately 120°C) in the event of abnormal heat generation. Therefore, in the thermal shrinkage of the separator, the minimum temperature at which thermal shrinkage occurs is more important than the maximum temperature at which thermal shrinkage occurs. The aforementioned nonwoven fabric has a thermal shrinkage rate of 3% or less below 130°C, and is advantageous in that it has a shutdown mechanism against initial abnormal heat generation (approximately 60°C to 80°C) and also has a shutdown mechanism against abnormal heat generation at high temperatures (130°C).

[0042] There are no particular restrictions on the pore size of the nonwoven fabric, and it can be appropriately selected according to the purpose, but smaller is preferable because it makes it difficult for lithium dendrites to form. Therefore, there are no particular restrictions on the maximum pore diameter of the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 20 μm to 40 μm is preferred. When the maximum pore diameter of the nonwoven fabric is within the preferred range, the conductivity can be sufficiently high when the separator is used in a battery.

[0043] There are no particular restrictions on the minimum pore size of the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 2 μm to 5 μm is preferred. When the minimum pore size of the nonwoven fabric is within this preferred range, the discharge capacity can be sufficiently high when the separator is used in a battery.

[0044] There are no particular restrictions on the average pore size of the nonwoven fabric, and it can be appropriately selected depending on the purpose, but 5 μm to 15 μm is preferred. When the average pore size of the nonwoven fabric is within the preferred range, the conductivity and discharge capacity can be sufficiently high when the separator is used in a battery.

[0045] The maximum pore diameter, minimum pore diameter, and average pore diameter of the nonwoven fabric can be measured using a thin-film / porous material evaluation device (e.g., a palm porometer, manufactured by PMI).

[0046] Conventional biaxially oriented polyethylene film separators exhibit increased discharge capacity when the pore size is large and the pore size distribution is small. Biaxially oriented films have a dense structure and are excellent in terms of reducing the pore size distribution. However, the very small pore size has the problem of degrading battery characteristics. In contrast, the separator of the present invention, which has the nonwoven fabric described above, has a large pore size and exhibits excellent battery characteristics.

[0047] There are no particular limitations on the method for manufacturing the separator, and it can be appropriately selected depending on the purpose. However, it is preferable that it be manufactured by the melt-blown (MB) method. For example, the methods described in U.S. Patent No. 3,650,866 and U.S. Patent No. 3,978,185 can be used, but it is particularly preferable that it be manufactured by the separator manufacturing method of the present invention, which will be described later.

[0048] (Method of manufacturing a separator) The method for manufacturing the separator of the present invention includes a dispensing step, a stretching step, and a collection step, and further includes other steps as necessary. The method for manufacturing the separator is preferably carried out by the melt-blown (MB) method.

[0049] <Discharge process> The discharge step involves discharging a first polymer solution having a glass transition temperature of -10°C to 70°C from a first nozzle hole, and simultaneously discharging a second polymer solution having a glass transition temperature of 80°C to 150°C from a second nozzle hole.

[0050] The polymer raw material in the first polymer solution is not particularly limited as long as it is a polymer with a glass transition temperature of -10°C or higher and 70°C or lower, and can be appropriately selected according to the purpose. For example, the same as that described in the section "<<Polymer with a glass transition temperature of -10°C or higher and 70°C or lower (Polymer A)>>" of the <<Nonwoven fabric>> of the (separator) can be used.

[0051] There are no particular limitations on the method for preparing the first polymer solution, and a suitable method can be selected depending on the purpose. For example, a method of melting by applying heat can be used.

[0052] Furthermore, it is preferable that the first polymer solution be stirred under constant temperature conditions in the first polymer solution raw material tank of the melt-blown apparatus to obtain a homogeneous solution.

[0053] The temperature is not particularly limited and can be appropriately selected depending on the melting point of the polymer raw material in the first polymer solution, but 150°C to 250°C is preferred, and 200°C to 250°C is more preferred.

[0054] There are no particular restrictions on the stirring method, and it can be appropriately selected depending on the purpose, but it is preferable to stir using a single shaft at 55 rpm to 135 rpm.

[0055] There are no particular restrictions on the discharge rate of the first polymer solution, and it can be appropriately selected depending on the purpose, but 0.03 g / min / pore to 0.2 g / min / pore is preferred. When the discharge rate of the first polymer solution is 0.03 g / min / pore or more, or 0.2 g / min / pore or less, the fiber diameter of the first fibers in the nonwoven fabric can be made 5 μm or less.

[0056] The polymer raw material in the second polymer solution is not particularly limited as long as it is a polymer with a glass transition temperature of 80°C or more and 150°C or less, and can be appropriately selected according to the purpose. For example, the same as that described in the section "<<Polymer with a glass transition temperature of 80°C or more and 150°C or less (Polymer B)>>" of the <<Nonwoven fabric>> of the (separator) can be used.

[0057] There are no particular limitations on the method for preparing the second polymer solution, and a suitable method can be selected depending on the purpose, but examples include a method of melting by applying heat.

[0058] Furthermore, it is preferable that the second polymer solution be stirred under constant temperature conditions in the second polymer solution raw material tank of the melt-blown apparatus to obtain a homogeneous solution.

[0059] The temperature is not particularly limited and can be appropriately selected depending on the melting point of the polymer raw material in the second polymer solution, but a temperature of 200°C to 300°C is preferred.

[0060] There are no particular restrictions on the stirring method, and it can be appropriately selected depending on the purpose, but it is preferable to stir using a twin-shaft system at 55 rpm to 135 rpm.

[0061] There are no particular restrictions on the discharge rate of the second polymer solution, and it can be appropriately selected depending on the purpose, but 0.1 g / min / pore to 2 g / min / pore is preferred. When the discharge rate of the second polymer solution is 0.1 g / min / pore or more, or 2 g / min / pore or less, the fiber diameter of the second fibers in the nonwoven fabric can be made to exceed 5 μm.

[0062] There are no particular restrictions on the volume ratio (first polymer solution:second polymer solution) of the amount of the first polymer solution to the amount of the second polymer solution to be dispensed, and it can be appropriately selected depending on the purpose. However, a ratio of 50:50 to 90:10 is preferred, and 70:30 to 99:1 is more preferred.

[0063] There are no particular restrictions on the diameter of the first nozzle hole, and it can be appropriately selected depending on the purpose, but 0.1 mm to 0.5 mm is preferred. If the diameter of the first nozzle hole is 0.1 mm or more, the fiber diameter of the first fiber in the nonwoven fabric can be 5 μm or less, and if it is 0.5 mm or less, the discharge resin pressure will not become too high, and the desired discharge resin pressure can be achieved.

[0064] There are no particular restrictions on the diameter of the second nozzle hole, and it can be appropriately selected depending on the purpose, but 0.5 mm to 2.0 mm is preferred. If the diameter of the second nozzle hole is 0.5 mm or more, the fiber diameter of the second fiber in the nonwoven fabric can be made to exceed 5 μm, and if it is 2.0 mm or less, the discharge resin pressure will not become too high, and the desired discharge resin pressure can be achieved.

[0065] Preferably, the first nozzle hole and the second nozzle hole are arranged in a row. In this case, there are no particular restrictions on the ratio of the number of first nozzle holes to the number of second nozzle holes, and it can be appropriately selected according to the purpose. However, it is preferable that the ratio of the number of first nozzle holes to the number of second nozzle holes is 10:1 to 3:1, and more preferably 6:1.

[0066] Furthermore, when the first nozzle hole and the second nozzle hole are arranged in a row, there are no particular restrictions on the arrangement of the first nozzle hole and the second nozzle hole, and they can be appropriately selected according to the purpose. However, it is preferable that the nozzle having the first nozzle hole and the second nozzle hole has 10 to 100 repeating units of the first nozzle hole and the second nozzle hole in the aforementioned ratio, and more preferably 30 to 50 units.

[0067] There are no particular restrictions on the pitch between the first nozzle holes, and it can be appropriately selected depending on the purpose, but 0.3 mm to 1.5 mm is preferred. When the pitch between the first nozzle holes is 0.3 mm or more or 1.5 mm or less, the diameter of the pores in the nonwoven fabric does not tend to become too small, can be adjusted appropriately, and the fibers do not tend to fuse together.

[0068] There are no particular restrictions on the pitch between the first nozzle hole and the second nozzle hole, and it can be appropriately selected depending on the purpose, but 0.5 mm to 2.5 mm is preferred. When the pitch between the second nozzle holes is 0.5 mm or more or 2.5 mm or less, the pore diameter of the nonwoven fabric does not tend to become too small and can be adjusted appropriately, and the fibers do not tend to fuse together.

[0069] An example of the nozzle described below will be explained with reference to the drawings, but the method for manufacturing the separator of the present invention is not limited to this example. Figure 1 is a schematic diagram showing an example of a nozzle used in the method for manufacturing the separator. The nozzle 100 has a structural unit in which three consecutively arranged first nozzle holes 10, one second nozzle hole 11, and three consecutively arranged first nozzle holes 10 are arranged in this order, and the nozzle holes of the structural unit (number of first nozzle holes: number of second nozzle holes: number of first nozzle holes = 3:1:3) are repeated 35 times. There are no particular restrictions on the material that constitutes the nozzle 100, and it can be appropriately selected depending on the purpose. Examples include copper, stainless steel, and aluminum.

[0070] <Stretching process> The stretching step involves stretching the first polymer discharged from the first nozzle hole and the second polymer discharged from the second nozzle hole with air at a temperature of 250°C to 350°C.

[0071] The temperature of the air is between 250°C and 350°C. If the air temperature is below 250°C, the discharge resin pressure increases, making it impossible to obtain fibers of the desired diameter. If the temperature exceeds 350°C, the gelation of the resin is accelerated, leading to degradation and poor release of the nonwoven fabric from the collector, making stable production impossible.

[0072] There are no particular restrictions on the airflow rate (AFR) and it can be appropriately selected according to the purpose, but 50m 3 / hour ~400m 3 / Time is preferable, 150m 3 / hour~250m 3 Time is preferable.

[0073] <Collection process> The collection step is a step of collecting the stretched first polymer and the stretched second polymer. The collection is preferably performed by a windable collector.

[0074] There are no particular restrictions on the winding speed of the collector, and it can be appropriately selected according to the purpose, but 1 m / min to 60 m / min is preferred, and 6 m / min to 20 m / min is more preferred. The thickness of the nonwoven fabric can be adjusted by changing the winding speed of the collector.

[0075] There are no particular restrictions on the distance between the nozzle surfaces of the first nozzle and the second nozzle and the collector, and it can be appropriately selected depending on the purpose, but 100 mm to 500 mm is preferred, and 200 mm to 400 mm is more preferred.

[0076] There are no particular restrictions on the method of collection, and it can be appropriately selected depending on the purpose, but a method of suction using air is preferred. There are no particular restrictions on the amount of air used for suction, and it can be appropriately selected depending on the purpose, but 1,000 rpm to 5,000 rpm is preferred, and 2,000 rpm to 3,500 rpm is more preferred.

[0077] <Other processes> The aforementioned other processes are not particularly limited and can be appropriately selected depending on the purpose. Examples include drying processes and thickness adjustment processes.

[0078] <<Drying process>> The drying step is a step of drying the nonwoven fabric produced in the collection step. There are no particular restrictions on the drying temperature, and it can be selected as appropriate depending on the purpose.

[0079] <<Thickness adjustment process>> The thickness adjustment step is a step of adjusting the thickness of the nonwoven fabric produced in the collection step or the nonwoven fabric dried in the drying step, and specifically, it is a step of reducing the thickness of the nonwoven fabric.

[0080] There are no particular restrictions on the method for reducing the thickness of the nonwoven fabric, and it can be appropriately selected depending on the purpose. Examples include calendering and heat pressing.

[0081] The calendering process utilizes a calendering mechanism consisting of a combination of at least two metal rolls. Specifically, the nonwoven fabric is sandwiched between the two metal rolls and the calendering process is performed under temperature conditions above the glass transition temperature (Tg) of the raw resin and under pressure conditions adjusted to suppress crushing of the constituent fibers of the nonwoven fabric.

[0082] While commonly used metal calender rolls can be employed, those made of steel or an alloy material equivalent to steel are particularly preferred. The calendar's shape and roll arrangement can also be inverted L-shape, Z-shape, upright double-roll type, etc. (Practical Plastics Terminology Dictionary, p. 151, published by Plastics Age Co., Ltd.).

[0083] There are no particular restrictions on the linear pressure of the roll, and it can be appropriately selected according to the purpose, but it is preferably 200 N / mm or less, more preferably 30 N / mm to 170 N / mm, and even more preferably 50 N / mm to 150 N / mm.

[0084] The heat press process is not particularly limited and can be carried out using known equipment.

[0085] The method for manufacturing the separator can be carried out using a known melt-blowing apparatus. An example of a melt-blowing apparatus used in the method for manufacturing the separator described above will be explained below with reference to the drawings, but the method for manufacturing the separator of the present invention is not limited to this. Figure 2 is a schematic cross-sectional view showing an example of a melt-blown apparatus used in the method for manufacturing the separator. The melt-blown apparatus 200 comprises a first polymer solution raw material tank 20, a second polymer solution raw material tank 21, a nozzle 100, and a collector 22. The first polymer solution melted in the first polymer solution raw material tank 20 passes through the first polymer solution supply path 23 and is transported to the nozzle 100. At the same time, the second polymer solution melted in the second polymer solution raw material tank 21 passes through the second polymer solution supply path 24 and is transported to the nozzle 100. The mixed fibers 25 consisting of the first polymer solution and the second polymer solution discharged simultaneously from the nozzle 100 are stretched by high-pressure air A and deposited in the collector 22 by an air suction section 26. Subsequently, in the collector 22, a conveyor 27 transports the deposited resin in the direction of the arrow at a predetermined transport speed, thereby forming a long nonwoven fabric 28.

[0086] (battery) The battery of the present invention has the separator of the present invention and, if necessary, other components. The battery is preferably a lithium-ion battery. In this specification, "lithium-ion battery" refers to a rechargeable battery that charges and discharges through the movement of lithium ions between a positive electrode and a negative electrode.

[0087] The aforementioned lithium-ion battery has the same configuration as a generally known lithium-ion battery, except that it uses the separator of the present invention as the separator. Specifically, the lithium-ion battery comprises a positive electrode, a negative electrode, an electrolyte (electrolyte solution), and an outer casing, in addition to a separator. There are no particular restrictions on the positive electrode, the negative electrode, the electrolyte, and the casing; any materials usable in a lithium-ion battery can be used.

[0088] <Positive electrode> There are no particular restrictions on the positive electrode, and it can be appropriately selected according to the purpose. For example, it can be a positive electrode containing an active material (e.g., lithium transition metal oxide), a conductive material (e.g., carbon black), a binder (e.g., polymer material), etc.

[0089] <Negative electrode> There are no particular restrictions on the negative electrode, and it can be appropriately selected according to the purpose. For example, one containing an active material (typically graphite), a conductive material, a binder, etc., can be used.

[0090] <Electrolytes> The electrolyte is not particularly limited and can be appropriately selected depending on the purpose. For example, a solution containing a lithium salt such as lithium hexafluoride phosphate (LiPF6) and a solvent can be used. Examples of the aforementioned solvents include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), or mixed solvents thereof. Furthermore, the electrolyte may contain a polymer for gelling the electrolyte.

[0091] <Exterior> There are no particular restrictions on the outer packaging, and it can be appropriately selected according to the purpose. Examples include metal cans (steel cans, aluminum cans, etc.) and aluminum laminate film packs.

[0092] There are no particular limitations on the manufacturing method of the battery, and it can be appropriately selected depending on the purpose. For example, it can be manufactured by stacking the positive electrode, the negative electrode, the separator, and the electrolyte in an appropriate shape. Furthermore, other components such as an outer casing can be used as needed.

[0093] There are no particular restrictions on the method of laminating the positive electrode and the negative electrode, and a suitable method can be selected from commonly used methods. Examples include multi-layer lamination, lamination on both sides of the current collector, and winding.

[0094] There are no particular restrictions on the shape of the battery, and it can be appropriately selected according to the purpose. Examples include coin-shaped, cylindrical, rectangular, sheet-shaped, and button-shaped batteries.

[0095] The battery of the present invention has a separator that exhibits excellent low thermal shrinkage and shape retention in high-temperature environments, and therefore is highly safe and has a long lifespan.

[0096] (Non-woven fabric) The nonwoven fabric of the present invention contains a polymer (polymer A) having a glass transition temperature of -10°C to 70°C and a polymer (polymer B) having a glass transition temperature of 80°C to 150°C, and also contains a first fiber with a fiber diameter of 5 μm or less and a second fiber with a fiber diameter greater than 5 μm, and further has other components as necessary.

[0097] The nonwoven fabric of the present invention is as described in the <Nonwoven Fabric> section of the (Separator) above, and further details are omitted.

[0098] While the aforementioned nonwoven fabric is suitable as a separator, its uses are not limited to this. Other uses include clothing (e.g., interlining for clothing, bra cup lining, shoulder pads, event jackets, etc.), protective clothing (e.g., lab coats, dust masks, etc.), furniture or interior (e.g., carpets, carpet base fabrics, etc.), filters (e.g., air filters, liquid filters, etc.), vehicles (e.g., floor mats and other automotive interior materials, various automotive filters, etc.), and industrial materials (e.g., abrasives, felt for papermaking). It can be widely used for general nonwoven fabric applications such as wire securing tape, civil engineering or construction (e.g., anti-suction materials, waterproofing materials, roofing, condensation sheets, etc.), agriculture (e.g., greenhouse sheets, shading sheets, covering sheets, etc.), household use (e.g., storage bags, furoshiki wrapping cloths, suit covers, tea bags, draining sheets, cleaning wipes, etc.), medical use (e.g., surgical gowns, drape sets, maternity pads, caps, etc.), and hygiene use (e.g., disposable diapers, sanitary napkins, gauze, wet wipes, etc.). [Examples]

[0099] The present invention will be specifically described below with reference to examples, comparative examples, and test examples, but the present invention is not limited in any way to these examples and test examples.

[0100] (Example 1: Preparation of PP / PC blended nonwoven fabric 1) A melt-type composite nonwoven fabric manufacturing apparatus (model: MB-0300, manufactured by Nippon Nozzle Co., Ltd.; see Figure 2) set to the following conditions was fitted with a mixed fiber spinning nozzle of different diameters having the following configuration (see Figure 1), and using the following resin raw materials, polypropylene (PP) resin was extruded from an extrusion hole with a diameter of 0.3 mm, and polycarbonate (PC) resin was extruded from an extrusion hole with a diameter of 0.7 mm to produce [PP / PC mixed fiber nonwoven fabric 1]. [Device] • Nozzle angle (α): 60° • Setback distance (ds): 0mm • Air gap distance (da): 0.5 mm • Distance between lips: 1mm · Lip height: 1.4 mm · Resin tank temperature for PP (melting temperature): 180 °C · Resin tank temperature for PC (melting temperature): 250 °C [Nozzle] · A repeating unit consisting of 6 discharge holes with a diameter of 0.3 mm and a width of 400 mm and 1 discharge hole with a diameter of 0.7 mm is arranged in 35 units. · Pitch of discharge holes with a diameter of 0.3 mm: 1.1 mm · Pitch between discharge holes with a diameter of 0.7 mm and discharge holes with a diameter of 0.3 mm: 2.2 mm [Resin raw material] · Polypropylene (PP) resin (Prime Polypro (registered trademark) S13B, manufactured by Prime Polymer Co., Ltd., MFR 700 g / 10 minutes, glass transition temperature: -10 °C, melting point: 170 °C) · Polycarbonate (PC) resin (Iupilon (registered trademark) HL-7001, manufactured by Mitsubishi Engineering Plastics Corporation, MFR 113 g / 10 minutes, glass transition temperature: 130 °C, flow temperature: 220 °C) Note that the PC resin was dried at 120 °C for 12 hours using a resin drying device (P-30CDBS, manufactured by Kawata Co., Ltd.) and then used. [Conditions] · Conveyor speed: 6.0 m / minute · Hot air flow rate (AFR): 200 m 3 / hour · Hot air temperature: 280 °C · Distance between die and collector (DCD): 250 mm · Air suction (AS): 3,500 rpm · PP discharge rate: 0.17 g / minute / hole · PP volume per nozzle hole: 0.18 cm 3 / mm / hole · Total PP volume: 37.5 cm 3 / minute · PP (uniaxial) gear pump (GP) 1: 12.5 rpm · PP (uniaxial) gear pump (GP) 2: 5 rpm · PC discharge rate: 1.80 g / minute / hole · PC volume per nozzle hole: 1.50 cm3 / mm / hole • PC total volume: 52.5 cm³ 3 / minute • PC (two-axis) gear pump (GP) 1:17.5rpm • PC (two-axis) gear pump (GP) 2: 2.5 rpm

[0101] (Examples 2-12: Preparation of PP / PC blended nonwoven fabrics 2-12) In Example 1, the [PP / PC blended nonwoven fabric 2] to [PP / PC blended nonwoven fabric 12] of Examples 2 to 12 were prepared in the same manner as in Example 1, except that the [conditions] were changed to the conditions shown in Tables 1-1 and 1-2 below.

[0102] (Comparative Examples 1-3: Preparation of PP nonwoven fabrics 1-3) In Example 1, the [resin raw material] was changed to polypropylene (PP) resin alone, and the [conditions] were changed to the conditions shown in Tables 1-1 and 1-2 below. In the same manner as in Example 1, [PP nonwoven fabric 1] to [PP nonwoven fabric 3] of Comparative Examples 1 to 3 were prepared.

[0103] [Table 1-1]

[0104] [Table 1-2]

[0105] (Test Example 1: Measurement of basis weight and thickness) For [PP / PC blended nonwoven fabric 1] to [PP / PC blended nonwoven fabric 12] and [PP nonwoven fabric 1] to [PP nonwoven fabric 3], the basis weight was measured in accordance with ISO 9073-1, and the thickness was measured in accordance with ISO 9073-2. The basis weight and thickness were measured at 10 arbitrarily selected points, and the average values ​​of these 10 points were calculated to determine the average basis weight and average thickness. The results are shown in Table 2 below.

[0106] [Table 2]

[0107] Table 2 shows that the average basis weight and average thickness of PP / PC blended nonwoven fabrics are higher than those of PP nonwoven fabrics.

[0108] (Test Example 2-1: Measurement of Fiber Diameter) [PP / PC blended nonwoven fabric 1], [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 10], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1] were cut to a width of 10 mm and a length of 10 mm to prepare sample pieces. In the test piece, the "length" indicates the flow direction (MD) during the manufacturing of the nonwoven fabric, and the "width" is in the direction perpendicular to the MD (CD). The same applies to the measurement or observation of the following physical properties.

[0109] The sample pieces were observed using a scanning electron microscope (SEM) (3D Real Surface View Microscope VE-9800S, manufactured by KEYENCE), and the diameter of the fibers constituting each nonwoven fabric was measured. During this observation, both the MD and CD directions of the collector-side surface of the nonwoven fabric were examined. Sixteen imaging points were randomly selected from the sample pieces, and SEM images were captured at three magnifications: 50x, 150x, and 1,000x. As examples of SEM images, Figure 3A shows the 150x magnification SEM image of [PP / PC blended nonwoven fabric 2], Figure 3B shows the 1,000x magnification SEM image of [PP / PC blended nonwoven fabric 2], Figure 3C shows the 150x magnification SEM image of [PP nonwoven fabric 1], and Figure 3D shows the 1,000x magnification SEM image of [PP nonwoven fabric 1].

[0110] For 16 SEM images at a magnification of 1,000x, 10 to 30 points were arbitrarily selected from each image, and the diameter was measured until a total of 200 points were reached. The histograms of the fiber diameters measured from the 1,000x SEM images of [PP / PC blended nonwoven fabric 1] are shown in Figure 4A, the histogram of the fiber diameters of [PP / PC blended nonwoven fabric 2] is shown in Figure 4B, the histogram of the fiber diameters of [PP / PC blended nonwoven fabric 8] is shown in Figure 4C, the histogram of the fiber diameters of [PP / PC blended nonwoven fabric 10] is shown in Figure 4D, the histogram of the fiber diameters of [PP / PC blended nonwoven fabric 11] is shown in Figure 4E, and the histogram of the fiber diameters of [PP nonwoven fabric 1] is shown in Figure 4F.

[0111] Figures 4A to 4E show that the PP / PC blended nonwoven fabric contains fibers smaller than 5 μm and fibers between 5 μm and 30 μm. On the other hand, Figure 4F shows that the nonwoven fabric made only of PP consisted almost entirely of fibers smaller than 5 μm. From this, it was inferred that the fibers larger than 5 μm in the PP / PC blended nonwoven fabric were made of PC.

[0112] (Test Example 2-2: Comparison of Biaxially Oriented PET Film, Nonwoven Fabric, and Fiber) To compare the nonwoven fabric of the example with biaxially oriented PET film, which has been conventionally used as a separator, structural observation was performed using a scanning electron microscope (SEM). [PP / PC blended nonwoven fabric 4] and biaxially oriented PET film (manufactured by Toray Industries, Inc.) were cut into pieces with a width of 10 mm and a length of 10 mm to prepare sample pieces.

[0113] The sample pieces were observed using a scanning electron microscope (SEM) (3D Real Surface View Microscope VE-9800S, manufactured by KEYENCE). For the [PP / PC blended nonwoven fabric 4], SEM images were acquired at 150x and 1,000x magnification, and for the biaxially oriented PET film, SEM images were acquired at 150x, 1,000x, 3,000x, and 5,000x magnification.

[0114] Figure 5A shows an SEM image of [PP / PC blended nonwoven fabric 4] at a magnification of 150x, Figure 5B shows an SEM image of biaxially oriented PET film at a magnification of 150x, Figure 5C shows an SEM image of [PP / PC blended nonwoven fabric 4] at a magnification of 1,000x, Figure 5D shows an SEM image of axially oriented PET film at a magnification of 1,000x, Figure 5E shows an SEM image of biaxially oriented PET film at a magnification of 3,000x, and Figure 5F shows an SEM image of biaxially oriented PET film at a magnification of 5,000x.

[0115] Figures 5B and 5D-5F show that the structure of the biaxially oriented PET film could not be observed at magnifications of 150x and 1,000x, and pores could only be observed at 3,000x magnification. In contrast, Figures 5A and 5C show that individual fibers of [PP / PC blended nonwoven fabric 4] could be identified at magnifications of 150x and 1,000x. From this, it was found that the biaxially oriented PET film has a denser structure than [PP / PC blended nonwoven fabric 4]. Furthermore, from the SEM image at 5,000x magnification (Figure 5F), holes were observed to form from the stretched tears of the biaxially oriented PET film. The stretched areas around such holes tend to shrink when heated. On the other hand, although the holes in [PP / PC blended nonwoven fabric 4] were large, there was little fusion of individual fibers, and the anisotropy was also small. Therefore, it is thought that when heated, the thin PP fibers melt in place, and at this time, the thicker PC fibers inhibit the slight force that would cause each fiber to contract in volume, resulting in an extremely small shrinkage rate, as shown in the thermal shrinkage measurement results described later.

[0116] (Test Example 3: Measurement of Heat Shrinkage) [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1] were cut into strips 3 mm wide and 10 mm long to prepare sample pieces. At 20°C, the test specimen was mounted on a thermomechanical analyzer (TMA / SS6100, manufactured by Hitachi High-Tech Science Co., Ltd.), and a load of 10 mN was applied to the specimen to ensure it was taut. At this time, the length of the test specimen was measured and defined as the initial length "L0". The test specimen was then heated from 20°C to 200°C at a rate of 5°C / min, and the length of the test specimen was measured again to determine the length after heat treatment "Ln The thermal shrinkage rate (TS) was calculated based on the following formula (1). The results are shown in Figure 6. Thermal shrinkage rate (TS) (%) = (1 - (L n / L0))×100 ··· Formula (1)

[0117] Figure 6 shows that the PP / PC blended nonwoven fabric exhibits superior thermal stability compared to the PP nonwoven fabric.

[0118] (Test Example 4: Free End Heat Treatment) [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1] were cut to a width of 100 mm and a length of 100 mm to prepare sample pieces. The aforementioned sample pieces were heat-treated at 100°C for 3 hours or 12 hours using a resin drying apparatus (P-30CDBS, manufactured by Kawata Co., Ltd.). The specimens before and after heat treatment were photographed using a digital camera from the same distance, and their appearance was observed.

[0119] Figure 7A shows the appearance of [PP / PC blended nonwoven fabric 2] before heat treatment, Figure 7B shows the appearance of [PP / PC blended nonwoven fabric 2] after 12 hours of heat treatment, Figure 7C shows the appearance of [PP nonwoven fabric 1] before heat treatment, and Figure 7D shows the appearance of [PP nonwoven fabric 1] after 12 hours of heat treatment. After 12 hours of heat treatment, [PP nonwoven fabric 1] shrank more than [PP / PC blended nonwoven fabric 2].

[0120] Furthermore, for samples heat-treated at 100°C for 3 or 12 hours, the external images were captured and binarized using image processing software (Image-J, open source). The number of pixels originating from the sample before heat treatment was defined as "A0," and the number of pixels originating from the sample after heat treatment was defined as "A0." n Based on the following formula (2), the reduction rate of the test specimen area was calculated. The results of heat treatment at 100°C for 3 hours are shown in Table 4-1 below, and the results of heat treatment at 100°C for 12 hours are shown in Table 4-2 below. Decrease rate (%)=(1-(A n / A0))×100 ··· Formula (2)

[0121] [Table 4-1]

[0122] [Table 4-2]

[0123] The aforementioned reduction rate is considered to be equivalent to the result of the thermal shrinkage rate. From Tables 4-1 and 4-2, the low thermal shrinkage and shape retention of the PP / PC blended nonwoven fabric at high temperatures were confirmed.

[0124] (Test Example 5: Measurement of pore size and pore size distribution) [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1] were cut into circles with a diameter of 20 mm to prepare sample pieces. The pore diameter and pore diameter distribution of the test specimens were measured using a thin-film / porous material evaluation device (palm porometer, manufactured by PMI). During this measurement, the collector side of the nonwoven fabric was examined in both the MD and CD directions. The results are shown in Table 5 below. Furthermore, the histograms of the pore diameter distribution for [PP / PC blended nonwoven fabric 2] are shown in Figure 8A, for [PP / PC blended nonwoven fabric 8] in Figure 8B, for [PP / PC blended nonwoven fabric 11] in Figure 8C, and for [PP nonwoven fabric 1] in Figure 8D. Table 5 below also shows the maximum pore diameter, minimum pore diameter, average pore diameter, and coefficient of variation for [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1].

[0125] [Table 5]

[0126] Table 5 and Figures 8A to 8D show that the PP / PC blended nonwoven fabric has larger pore sizes and a wider pore size distribution compared to the PP nonwoven fabric.

[0127] (Test Example 6: Measurement of Battery Characteristics) [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], and [PP nonwoven fabric 1] were cut into circles with a diameter of 18.5 mm to prepare sample pieces. These test pieces were used as separators, and batteries were prepared using the following method, and the battery characteristics were measured using the following method.

[0128] - Manufacturing a secondary battery - In a dry room where the moisture concentration was controlled to 5 ppm or less, a gasket was fitted to the bottom of the case, which is a component of the coin cell, the positive electrode was placed, and 150 mL of electrolyte was added. The separator was then stacked on top of this, and another 150 mL of electrolyte was added. Furthermore, the negative electrode, spacer, wave washer, and top of the case were stacked in this order and sealed with a crimping machine to manufacture the coin cell (lithium-ion secondary battery).

[0129] The components of the coin cell are as follows: [Components of a coin cell] • Positive electrode: 14mm diameter lithium iron phosphate positive electrode (manufactured by Sekisui Chemical Co., Ltd.) • Negative electrode: 16mm diameter graphite negative electrode (manufactured by Sekisui Chemical Co., Ltd.) • Electrolyte: A 1% by mass lithium hexafluoride phosphate (LiPF6) solution (EC:DEC:DMC = 4:3:3, volume ratio) is added and uniformly mixed. • Gasket: PP gasket (manufactured by Takumi Giken Co., Ltd.) • Spacer: SUS316L (manufactured by Takumi Giken Co., Ltd.) • Wave washer: SUS316L (manufactured by Takumi Giken Co., Ltd.) • Case: SUS316L (manufactured by Takumi Giken Co., Ltd.)

[0130] -Charge / Discharge Test- Each fabricated coin cell was charged and discharged according to condition 1 below, and its initial charge / discharge capacity (mAh) was measured. The results are shown in Figure 9A. Next, each of the fabricated coin cells was charged and discharged according to condition 2 below, and its capacity (mAh) was measured. The results are shown in Figure 9B. [Condition 1] • Charging conditions: 0.1C, cutoff voltage 3.6V • Discharge conditions: 0.2C, cutoff voltage 2.5V [Condition 2] • Charging conditions: 0.3C, cutoff voltage 3.6V • Discharge conditions: 0.3C, cutoff voltage 2.5V Note that the 1C rate (constant current) is the current value required to charge or discharge the entire capacity of a secondary battery over one hour.

[0131] From Figures 9A and 9B, it was found that when [PP / PC blended nonwoven fabric 2], [PP / PC blended nonwoven fabric 8], [PP / PC blended nonwoven fabric 11], or [PP nonwoven fabric 1] was used as a separator, charging and discharging were possible in all cases, and there was little difference in discharge performance at 0.2C and 0.3C. [Explanation of Symbols]

[0132] 100 nozzles 200 Meltblown Machine 10 First nozzle hole 11 Second nozzle hole 20. First polymer solution raw material tank 21 Second polymer solution raw material tank 22 collector 23. First polymer solution supply pathway 24. Second polymer solution supply pathway 25 Blended fiber consisting of a first polymer solution and a second polymer solution 26 Air intake section 27 Conveyor 28 Nonwoven fabric A air

Claims

1. A separator having a nonwoven fabric, The aforementioned nonwoven fabric, A polymer having a glass transition temperature of -10°C to 70°C and a polymer having a glass transition temperature of 80°C to 150°C, and a first fiber with a fiber diameter of 5 μm or less and a second fiber with a fiber diameter exceeding 5 μm, The polymer having a glass transition temperature of -10°C to 70°C is polypropylene, and the polymer having a glass transition temperature of 80°C to 150°C is polycarbonate. A separator characterized in that the first fiber contains polypropylene and the second fiber contains polycarbonate.

2. The separator according to claim 1, wherein the fiber diameter of the first fiber is 0.1 μm or more and 5 μm or less, and the fiber diameter of the second fiber is greater than 5 μm and 30 μm or less.

3. The separator according to any one of claims 1 to 2, wherein the orientation direction of the first fiber and the orientation direction of the second fiber are different.

4. The separator according to any one of claims 1 to 3, wherein the average thickness is 0.025 mm to 5 mm.

5. A battery characterized by having a separator according to any one of claims 1 to 4.

6. A polymer having a glass transition temperature of -10°C or more and 70°C or less, and a polymer having a glass transition temperature of 80°C or more and 150°C or less, and a first fiber having a fiber diameter of 5 μm or less, and a second fiber having a fiber diameter greater than 5 μm, The polymer having a glass transition temperature of -10°C to 70°C is polypropylene, and the polymer having a glass transition temperature of 80°C to 150°C is polycarbonate. A nonwoven fabric characterized in that the first fiber contains polypropylene and the second fiber contains polycarbonate.

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