Method for manufacturing separator for power storage device

Abstract

Provided is a method for manufacturing a separator for an electricity storage device, the method comprising a step for forming a molded body by extruding powdered polyethylene, granular polypropylene, and a plasticizer in the form of a sheet by means of an extruder, and a step for making the molded body porous by means of a wet process.

Description

[0001] This application is a divisional application of Chinese patent application filed on April 13, 2021, with application number 202180004783.9 and invention title "Method for manufacturing a separator for an energy storage device". Technical Field

[0002] This invention relates to separators for energy storage devices and their manufacturing methods. Background Technology

[0003] Microporous membranes are widely used as precision filtration membranes, separators for fuel cells, separators for capacitors, master materials for functional membranes that exhibit new functions by filling functional materials into the pores, and separators or constituent materials for energy storage devices.

[0004] Lithium-ion batteries (LIBs) are widely used in notebook computers, mobile phones, and digital cameras. Polyolefin microporous membranes are known as separators or constituent materials for LIBs. Patent Document 1 discloses a method for manufacturing a polyolefin microporous membrane with high strength, high specific surface area, and high pore volume. In Patent Document 1, a polyolefin microporous membrane is manufactured by melt-blending a polyolefin resin with a weight-average molecular weight of 500,000 or more with liquid paraffin, and then extracting the liquid paraffin from the resulting resin composition. Patent Document 2 describes a method where a polyolefin resin such as polyethylene and a resin other than polyolefin (e.g., polyamide) are pre-blended and granulated using an extruder, the granules are mixed with liquid paraffin and extruded, and then the liquid paraffin is extracted to manufacture a microporous membrane. Furthermore, Patent Documents 3-5 describe conventional methods for manufacturing LIB separators that include the manufacturing process of polyolefin microporous membranes.

[0005] In recent years, research on increasing the capacity and energy density of lithium-ion batteries (LIBs) for long-distance driving of electric vehicles has made progress. For example, as known from non-patent literature 1, increasing the nickel content in NMC metal oxides used as positive electrode materials, making graphite-based materials with a high concentration of silicon, or completely replacing silicon with silicon, can significantly improve the energy density of LIBs.

[0006] On the other hand, as known from Non-Patent Document 2, silicon (containing a high concentration) negative electrodes accumulate or release lithium ions during charging and discharging, resulting in significant volume expansion and contraction. Furthermore, Non-Patent Document 3 describes how the expansion and contraction of silicon (containing a high concentration) negative electrodes during charging and discharging can repeatedly create gaps around the silicon particles, accumulating a solid electrolyte interphase (SEI) within these gaps. Consequently, with prolonged cycling, the silicon (containing a high concentration) negative electrode irreversibly expands. This results in the separator film being repeatedly subjected to compressive forces. To release these forces, the film's pore structure is either destroyed (crushed) or irreversibly compressed, potentially reducing ion permeability. Especially for the latter (the phenomenon described in Non-Patent Document 3), lithium-ion batteries using various non-aqueous electrolytes are theoretically unable to suppress SEI formation.

[0007] It should be noted that in Non-Patent Literature 4, Wu et al. reported a representative concept of the stereoscopic configuration of polymer chains, the Kuhn chain. In Non-Patent Literature 5, as a study on improving the mechanical properties of resin films using mixed resin systems, it was reported that the mechanical properties were improved by controlling the size or distance between different types of particles dispersed in the resin structure, and by achieving a dispersion structure exceeding a specific degree of dispersion.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2002-088189

[0011] Patent Document 2: Japanese Patent Application Publication No. 2002-226639

[0012] Patent Document 3: International Publication No. 2020 / 067161

[0013] Patent Document 4: Japanese Patent Application Publication No. 2020-092068

[0014] Patent Document 5: International Publication No. 2011 / 118660

[0015] Non-patent literature

[0016] Non-patent literature 1: Chem. Rev. 2018, 118, 11433-11456

[0017] Non-patent literature 2: J. Phys. Chem. C 2014, 118, 9395-9399

[0018] Non-patent literature 3: ACS Appl. Mater. Interfaces 2019, 11, 45726-45736

[0019] Non-patent literature 4: Journal of Polymer Science: Part B: Polymer Physics, Vol. 27, 723-741 (1989)

[0020] Non-patent literature 5: POLYMER, 1985, Vol 26, November 1855 Summary of the Invention

[0021] The problem the invention aims to solve

[0022] In recent years, the manufacture of microporous membranes, as constituent materials for separators in energy storage devices, has required reducing the drawbacks (i.e., the amount of unmelted material) of mixing and extruding multiple raw materials. Unmelted material from the extrusion process can become aggregates or gels in the final microporous membrane. It is hoped that by incorporating separators in the microporous membrane with reduced drawbacks, a storage device with excellent capacity retention characteristics (cycle characteristics) during repeated charge and discharge can be achieved.

[0023] However, in the microporous membranes described in Patent Documents 1 and 2, the mixture of raw materials... Considering the drawbacks of the extrusion process and the cycling characteristics of energy storage devices with separators, there is room for improvement. Furthermore, Patent Documents 3-5 do not focus on the form of the resin raw materials in the melt-blending or extrusion processes, and do not provide detailed information on the impact of the type or structure of the polyolefin in the separators for energy storage devices on cycling characteristics.

[0024] In view of the above, the object of the present invention is to provide a raw material mixing method. A separator for an energy storage device that reduces the disadvantages of the extrusion process and provides excellent cycle characteristics.

[0025] Solution for solving the problem

[0026] In order to solve the above-mentioned problems, the inventors conducted research and discovered that by using a method for manufacturing a separator for an energy storage device having the following technical features, the above-mentioned problems can be solved, thereby completing the present invention. A portion of the embodiments of the present invention are illustrated below.

[0027] [1] A method for manufacturing a separator for an energy storage device, comprising the following steps:

[0028] (1) A sheet forming process in which polypropylene, polyethylene and plasticizer are extruded in sheet form using an extruder, cooled and solidified, and processed into sheet-shaped bodies.

[0029] (2) A stretching process in which the aforementioned sheet-shaped body is stretched at a magnification ratio of 20 times or more and 250 times or less to form a stretched article;

[0030] (3) A microporous membrane forming process in which the plasticizer is extracted from the aforementioned stretching material to form a microporous membrane;

[0031] (4) A heat treatment process in which the aforementioned microporous membrane is subjected to heat treatment, stretched in the width direction, and relaxed to obtain a heat-treated microporous membrane; and

[0032] (5) The winding process of winding up the aforementioned heat-treated microporous membrane.

[0033] The aforementioned polyethylene is in powder form, and the aforementioned polypropylene is in granular form.

[0034] [2] The method for manufacturing a separator for an energy storage device according to Project 1, wherein the aforementioned polypropylene and the aforementioned polyethylene are fed into the aforementioned extruder by any one of the following methods (a) to (c):

[0035] (a) A method of feeding the aforementioned polypropylene and the aforementioned polyethylene into the aforementioned extruder using different feeders respectively;

[0036] (b) A method of feeding the mixture of the aforementioned polypropylene and the aforementioned polyethylene into an extruder using a feeder;

[0037] (c) A method of feeding multiple resin raw materials obtained by dry mixing the aforementioned polypropylene and the aforementioned polyethylene into an extruder using different feeders.

[0038] [3] The method for manufacturing a separator for an energy storage device according to item 1 or 2, wherein the mass ratio of the aforementioned polyethylene to the aforementioned polypropylene is 99 / 1 to 60 / 40.

[0039] [4] The method for manufacturing a separator for an energy storage device according to item 3, wherein the weight-average molecular weight (Mw) of the aforementioned polyethylene is 100,000 to 9,700,000, and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) is 3 to 12.

[0040] [5] According to the method for manufacturing a separator for an energy storage device as described in Item 3, the weight-average molecular weight (Mw) of the aforementioned polypropylene is 300,000 to 2,000,000, and the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) is 3 to 12, and

[0041] The isotactic pentamematic fraction (mmmm) of the aforementioned polypropylene is 85.0 mol% to 99.7 mol%.

[0042] [6] A separator for an energy storage device, which is manufactured by any one of items 1 to 5.

[0043] [7] The separator for the energy storage device according to item 6, wherein,

[0044] The aforementioned separator for the energy storage device contains a microporous membrane.

[0045] The aforementioned microporous membrane contains polyethylene and polypropylene.

[0046] In the X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS) measurements of the aforementioned microporous membranes, the crystallite size of the aforementioned polyethylene is 15 nm to 40 nm, and the crystallite size of the aforementioned polypropylene is 10 nm to 50 nm.

[0047] [8] A separator for an energy storage device, comprising a microporous membrane,

[0048] The aforementioned microporous membrane contains polyethylene and polypropylene.

[0049] In the X-ray diffraction (XRD) measurement of the aforementioned microporous membrane, the crystallite size of the aforementioned polyethylene is 15 nm to 40 nm, and the crystallite size of the aforementioned polypropylene is 10 nm to 50 nm.

[0050] [9] According to the separator for the energy storage device described in Project 8, wherein the crystallinity of the aforementioned polyethylene is 55% to 99.9% in the XRD determination of the aforementioned microporous membrane.

[0051]

[10] A separator for an energy storage device, comprising a microporous membrane,

[0052] The aforementioned microporous membrane contains polyethylene and polypropylene.

[0053] In the wide-angle X-ray scattering (WAXS) measurement of the aforementioned microporous membrane, the crystallite size of the aforementioned polyethylene is 15 nm to 40 nm, and the crystallite size of the aforementioned polypropylene is 10 nm to 50 nm.

[0054]

[11] According to the separator for the energy storage device described in item 10, the crystallinity of the aforementioned polyethylene is 50% to 90% in the WAXS measurement of the aforementioned microporous membrane.

[0055]

[12] The separator for the energy storage device according to any one of items 8 to 11, wherein the isotactic five-unit component (mmmm) of the aforementioned polypropylene contained in the aforementioned microporous membrane is 85.0 mol% to 99.7 mol%.

[0056]

[13] A battery comprising a separator for an energy storage device as described in any one of items 6 to 12.

[0057] The effects of the invention

[0058] According to the present invention, raw material mixing can be provided. A method for manufacturing microporous membranes or separators for energy storage devices achieves a reduction in the disadvantages of the extrusion process. Furthermore, according to the present invention, an energy storage device with reduced aggregate or gel content and excellent cycle characteristics can be provided by the above-described manufacturing method for separators for energy storage devices. Detailed Implementation

[0059] The following describes embodiments of the present invention; however, the present invention is not limited to these embodiments, and various modifications can be made without departing from its spirit. In this specification, unless otherwise specified, "~" signifies that the values ​​at both ends of the range are considered as an upper and lower limit. Furthermore, in this specification, the upper and lower limits of the numerical range can be arbitrarily combined.

[0060] A first embodiment of the present invention provides a separator for an energy storage device containing a microporous membrane, and a crystal structure of a resin component specifically constituting the microporous membrane. A second embodiment of the present invention provides a method for manufacturing a separator for an energy storage device containing a microporous membrane, and a specific raw material is used in this manufacturing method. The embodiments are described below.

[0061] <Separator for energy storage devices>

[0062] One aspect of the present invention provides a separator for an energy storage device. A separator for an energy storage device (hereinafter sometimes simply referred to as a "separator") refers to a component disposed between multiple electrodes in an energy storage device and having ion permeability and, as needed, shut-off characteristics.

[0063] The separator can be in the form of a flat membrane (e.g., formed by a single microporous membrane), a laminated membrane (e.g., a laminate of multiple microporous membranes, or a laminate of a microporous membrane and other membranes), or a coated membrane (e.g., in the case where a functional substance is coated on at least one side of a microporous membrane).

[0064] The separator in the first embodiment comprises a microporous membrane containing polyethylene (PE) with a crystallite size of 15 nm to 40 nm and polypropylene (PP) with a crystallite size of 10 nm to 50 nm. The crystallite size can be measured using known methods, such as X-ray diffraction (XRD) using a reflective X-ray diffraction device such as the Ultima-IV manufactured by Rigaku Corporation, or wide-angle X-ray scattering (WAXS) using a transmission X-ray scattering device such as NANOPIX. The constituent elements of the separator will be described below.

[0065] <Microporous membrane>

[0066] Microporous membranes can be used as precision filtration membranes, separators for fuel cells, separators for capacitors, separators for energy storage devices, electrolytic membranes, or constituent materials thereof.

[0067] When using microporous membranes as separators or constituent materials for energy storage devices, particularly separators or constituent materials for LIBs, the microporous membrane can be used as the separator itself, or other layers or membranes can be provided on at least one side of the microporous membrane to serve as the separator. Microporous membranes used as separators for energy storage devices are preferably those with low electronic conductivity, high ionic conductivity, high resistance to organic solvents, and fine pore size.

[0068] From the viewpoint of shut-off characteristics when used as a separator in an energy storage device, the microporous membrane is preferably formed of polyolefin (PO) at least 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 70% to 100% by mass. From the viewpoint of heat-rupture resistance and pore size reduction, the microporous membrane is preferably composed of both polyethylene (PE) and polypropylene (PP) as PO.

[0069] The microporous membrane of the first embodiment contains PE with a crystallite size of 15 nm to 40 nm and PP with a crystallite size of 10 nm to 50 nm, which means that a microporous membrane with an appropriate distribution of PE and PP crystallization states has been formed.

[0070] Furthermore, compared to conventional separators for silicon (containing high concentration) negative electrodes as described in Non-Patent Documents 1-3, microporous membranes with appropriate crystalline distributions of PE and PP exhibit easier volume recovery in the compression direction due to electrolyte swelling. For example, they readily adapt to the expansion and contraction of negative electrodes such as silicon-containing negative electrodes (i.e., they easily recover even if the pore size of the microporous membrane decreases). Moreover, / or during the contraction of the silicon-containing negative electrode, the separator adheres tightly to the negative electrode, thus reducing the likelihood of gaps forming between them. This tends to suppress the deposition and growth of excessive solid electrolyte interphase (SEI) on the negative electrode surface, thereby improving cycle life during long-term use in energy storage devices. On the other hand, the appropriate crystalline distribution of PE and PP suggests that the mixing of resin raw materials in the microporous membrane manufacturing process... The disadvantages of the extrusion process are reduced. From this point of view, the combination of PE and PP crystallite sizes is preferably PE crystallite size of 16nm to 39nm and PP crystallite size of 11nm to 49nm, more preferably PE crystallite size of 20nm to 38nm and PP crystallite size of 11nm to 47nm.

[0071] The appropriate crystallization distribution of PE and PP in microporous membranes can be achieved, for example, through mixing of resin raw materials. The specific states of PE and PP during the extrusion process, or the control of the isotactic five-unit component fraction (mmmm) and other three-dimensional regular structures of PP, are achieved.

[0072] (Polyethylene (PE))

[0073] Polyethylene (PE) is preferably found to have a weight-average molecular weight (Mw) of 100,000 to 9,700,000, and / or a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio (Mw / Mn) of 3 to 12. PE resins with such Mw and Mw / Mn are also known as ultra-high molecular weight polyethylene (UHMWPE), and are preferred from the viewpoints of optimizing the crystallization distribution of microporous membranes containing PE and PP, the amount of aggregates and gel content, and the cycling characteristics of separators and energy storage devices using them.

[0074] From the same perspective as above, the Mw of PE is more preferably 120,000 to 9,000,000, and even more preferably 200,000 to 8,500,000. In addition, its dispersity (Mw / Mn) is more preferably 4 to 11, and even more preferably 5 to 10.

[0075] For PE alone, from the viewpoint of the swelling state formed by the electrolyte in the battery, the crystallinity measured by XRD is preferably 55% to 99.9%, more preferably 80% to 99.8%, and even more preferably 85% to 97%. For PE alone, from the same viewpoint, the crystallinity measured by WAXS is preferably 50% to 90%, more preferably 65% ​​to 80%, and even more preferably 68% to 77%. Even when measuring the same microporous membrane, the XRD and WAXS methods yield different results in terms of crystallite size and crystallinity, and there is a tendency to frequently find significant differences in crystallinity measurements. This difference is presumably due to the following reasons: XRD is a reflective measurement, and the results mainly provide information about the surface of the microporous membrane. On the other hand, WAXS is a transmissive measurement, and the results provide averaged information including the surface and internal structure of the microporous membrane. The microporous membrane described in this application is believed to have a tendency to exhibit surface crystallization due to surface cooling, heating, sheeting, stretching, and other processes during its manufacturing process.

[0076] For this type of PE crystal cluster, it is believed that the overall higher-order structure of the crystals easily swells (permeates, diffuses internally) through the thermal energy such as molecular vibrations of the electrolyte within the battery's operating temperature range (-30°C to 80°C), achieving a good volume recovery rate in the compression direction. The swelling of the PE crystal structure occurs when the force of electrolyte permeation exceeds the entropic elasticity of the higher-order structure of PE. Therefore, to address the swelling of the higher-order structure of PE, it is necessary to improve the force of electrolyte permeation or construct a higher-order PE structure that is easily swellable by the electrolyte (after swelling, the overall higher-order structure is a higher-order PE structure capable of achieving thermal stabilization). In this invention, a higher-order PE structure that easily swells while maintaining the mechanical strength of the microporous membrane within the battery's operating temperature range can be constructed. Based on this tendency, the PE crystallite size is preferably 15nm to 40nm, more preferably 16nm to 39nm, and even more preferably 20nm to 38nm. The crystallite size of individual PE can be adjusted to the above-mentioned range, for example, by controlling the PE morphology or the PE raw material input method in the manufacturing process of microporous membranes, and by specifying the ratio of PE raw material to polypropylene (PP) raw material.

[0077] The PE can be a single type or contain multiple types of UHMWPE. From the viewpoint of high strength of microporous membranes, UHMWPE is preferably poly(ethylene and / or propylene-co-α-olefin), more preferably at least one selected from the group consisting of poly(ethylene-co-propylene), poly(ethylene-co-butene), and poly(ethylene-co-propylene-co-butene). From the same viewpoint, UHMWPE preferably contains structural units derived from ethylene at a concentration of 98.5 mol% or more and 100 mol% or less, more preferably contains structural units derived from α-olefins other than ethylene at a concentration of more than 0.0 mol% and 1.5 mol% or less.

[0078] In addition, PE may contain polyethylene resins other than UHMWPE. Examples of polyethylene resins other than UHMWPE include low-density polyolefins (LDPE) such as linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), high-pressure low-density polyethylene, or mixtures thereof.

[0079] (Polypropylene (PP))

[0080] Polypropylene (PP) is preferably found to have a weight-average molecular weight (Mw) of 300,000 to 2,000,000, and a weight-average molecular weight (Mw) to number-average molecular weight (Mn) ratio (Mw / Mn) of 3 to 12. Such PP resins with Mw and Mw / Mn are preferred from the viewpoints of optimizing the crystallization distribution of microporous membranes containing PE and PP, the amount of aggregates and gel content, and the cycling characteristics of separators and energy storage devices using them.

[0081] From the same perspective as above, the Mw of PP is more preferably 305,000 to 1,900,000, and even more preferably 310,000 to 1,800,000. In addition, its dispersity (Mw / Mn) is more preferably 4 to 11, and even more preferably 4.5 to 10.

[0082] For the individual PP crystallite size, considering the good volume recovery in the compression direction achieved by the electrolyte swelling of the microporous membrane containing PE and PP within the battery, a size of 10 nm to 50 nm is preferred, more preferably 11 nm to 49 nm, and even more preferably 11 nm to 47 nm. Since PP is incompatible with PE, it will not form mixed crystals with PE, and a mixed crystal system with a micro-dispersion of PE mesh structure can be constructed. As shown in Non-Patent Document 5, by controlling the size or distance between different types of particles dispersed in the resin structure, a dispersion structure exceeding a certain degree of dispersion can significantly improve mechanical properties such as impact strength; this phenomenon is known to be achieved by controlling the size of the different types of dispersed particles at a size of hundreds of nm to several μm. In contrast, in this embodiment, it was surprisingly found that, not by the particles themselves, but by controlling the previously non-existent crystal structure of PE and PP, the mechanical properties of volume recovery in the compression direction of the separator can be improved by a significantly small order of magnitude, such as tens of nm. The individual crystallite size of PP can be adjusted to the above-mentioned range, for example, by controlling the PP morphology or the PP raw material input method in the manufacturing process of microporous membranes, and by specifying the ratio of PP raw material to polyethylene (PE) raw material.

[0083] From the viewpoint of heat resistance and melt viscosity, propylene homopolymer is preferred for PP. Examples of PP include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Among these, isotactic polypropylene is preferred. The amount of isotactic PP relative to the total mass of PP in the microporous membrane is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 98% by mass or more, and even more preferably 100% by mass (total).

[0084] From the viewpoint of optimizing the crystallization distribution of PE and PP in microporous membranes, the isotactic pentad fraction (mmmm) of the stereoregular structure (pentad sequence) of PP is preferably 85.0 mol% to 99.7 mol%, more preferably 86.0 mol% to 99.6 mol%, and even more preferably 87.0 mol% to 99.5 mol%.

[0085] From the viewpoint of optimizing the crystallization distribution of PE and PP in microporous membranes, the 5-unit sequence of PP, (mmmr) is preferably 0.5 mol% to 2.5 mol%, more preferably 0.9 mol% to 2.4 mol%.

[0086] From the same point of view as above, in the five-unit group sequence of PP, (rmmr) is preferably 0.1 mol% to 1.0 mol%, more preferably 0.1 mol% to 0.6 mol%.

[0087] From the same point of view as above, in the five-unit group sequence of PP, (mmrr) is preferably 0.3 mol% to 2.5 mol%, more preferably 0.5 mol% to 2.3 mol%.

[0088] From the same point of view as above, in the five-unit group sequence of PP, (mmrm+rrmr) is preferably 0.5 mol% to 1.5 mol%, more preferably 0.7 mol% to 1.3 mol%.

[0089] From the same point of view as above, in the pentamematic sequence of PP, (mrmr) is preferably 0.5 mol% or less, more preferably 0.4 mol% or less.

[0090] From the same point of view as above, in the five-unit group sequence of PP, (rrrr) is preferably 0.1 mol% to 1.5 mol%, more preferably 0.2 mol% to 1.2 mol%.

[0091] From the same point of view as above, in the pentamematic sequence of PP, (rrrm) is preferably 0.1 mol% to 1.5 mol%, more preferably 0.2 mol% to 1.0 mol%.

[0092] From the same point of view as above, in the pentamematic sequence of PP, (mrrm) is preferably 0.1 mol% to 1.5 mol%, more preferably 0.2 mol% to 1.0 mol%.

[0093] Structures formed by linking methyl groups of polypropylene units in the same direction are known as meso (m), and structures formed by linking them in different directions are known as exo (r). In this embodiment, by using PP configured with at least one stereochemical arrangement of mmmm to mrrm in the ratios defined as described above, an excellent phenomenon of adjusting the crystallization distribution of PE was found in the manufacture of microporous membranes.

[0094] For this phenomenon, it is important that the dissolved PE and PP are well dispersed at the molecular level under the condition of plasticizer coexistence, especially requiring control of the intertwining state of PP molecular chains. As shown in Non-Patent Literature 4, Wu et al. reported that a representative concept for the stereoscopic configuration of polymer chains is the Kuhn chain model, in which the stereoscopic configuration of polymer chains is determined by the degree of unit bending of monomers. In the Kuhn chain model, "node" represents the atoms between bonds, and in the case of PP, it represents the C atom, while "l" represents the C atom. k"" represents the bond length, and in the case of PP, it represents the distance between C atoms. It can be seen that by calculating the three-dimensional angles between chain segments using this model, a theoretical formula for calculating the distance between the two ends of a polymer chain can be derived, thus logically depicting the structure of intertwined molecular chains. In this embodiment, the ratio of mmmm stereoconfiguration in PP is experimentally specified, presumably indicating that this PP exhibits good dispersibility with PE in plasticizers.

[0095] (mass ratio of PE to PP)

[0096] For the mass ratio of polyethylene to polypropylene, the preferred PE / PP mass ratio is 99 / 1 to 60 / 40, more preferably 97 / 3 to 70 / 30, even more preferably 95 / 5 to 85 / 15, and most preferably 93 / 7 to 90 / 10. When the PE / PP mass ratio in the microporous membrane is adjusted to the above-mentioned range, it is expected that PP will be uniformly dispersed in PE. In practice, in the manufacturing process of microporous membranes, it is difficult to uniformly disperse PP in PE by simply mixing PE and PP raw materials. While not wishing to be limited by theory, in the manufacturing process of separators for energy storage devices described later, by controlling the respective forms or feeding methods of PE and PP raw materials for a specific extrusion process, there is a tendency to obtain the aforementioned suitable dispersion. Therefore, based on the above method, it is easier to more appropriately disperse PP in PE at the above-mentioned mass ratio.

[0097] (Other contents)

[0098] The microporous membrane may contain polyolefin (PO) resins other than PE and PP, such as butene homopolymers with excellent crystallinity, within a range that does not hinder the effectiveness of the present invention.

[0099] Furthermore, the microporous membrane, as a resin component other than PO, can contain, for example, polyamide resins such as nylon 6, nylon 66, nylon 11, nylon 6-10, nylon 6-12, nylon 6-66, and aromatic polyamide resins; polyimide resins; polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); fluorinated resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); copolymers of ethylene and vinyl alcohol (e.g., EVAL manufactured by Kuraray Co., Ltd., melting point: 157°C~190°C), polysulfone, polyethersulfone, polyketone, and polyetheretherketone (PEEK). These resin components can be used alone or in combination.

[0100] The microporous membrane may contain additives other than resin, to the extent that it does not impede the effectiveness of the present invention. Examples of additives include, for instance, dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments.

[0101] (Various properties of microporous membranes)

[0102] The characteristics of microporous membranes are described below.

[0103] These characteristics apply when the microporous membrane used as a separator in an energy storage device is a flat membrane. However, when the separator in an energy storage device is a laminated membrane, the measurements can be taken after removing the layers other than the microporous membrane from the laminated membrane.

[0104] The porosity of the microporous membrane is preferably 20% or more, more preferably 30% or more, and even more preferably 32% or more or 35% or more. When the porosity of the microporous membrane is 20% or more, its use as a separator or constituent material for alkali metal ion batteries tends to further improve its ability to follow the rapid movement of alkali metal ions. On the other hand, the porosity of the microporous membrane is preferably 90% or less, more preferably 80% or less, and even more preferably 50% or less. When the porosity of the microporous membrane is 90% or less, its membrane strength tends to be further improved and its self-discharge further suppressed. The porosity of the microporous membrane is measured using the method described in the examples.

[0105] The air permeability of microporous membranes per 100 cm³ 3 The permeability of the microporous membrane is preferably 1 second or more, more preferably 50 seconds or more, further preferably 55 seconds or more, and even more preferably 100 seconds or more. When the permeability of the microporous membrane is 1 second or more, there is a tendency to further improve the balance between membrane thickness, porosity, and average pore size. Furthermore, the permeability of the microporous membrane is preferably 400 seconds or less, more preferably 300 seconds or less. When the permeability of the microporous membrane is 400 seconds or less, there is a tendency to further improve ion permeability. The permeability of the microporous membrane can be adjusted by adjusting the stretching ratio, stretching temperature, etc. The above-mentioned permeability was measured by the method described in the examples.

[0106] The thickness of the microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 3.0 μm or more, or 4.0 μm or more. A membrane thickness of 1.0 μm or more tends to further improve membrane strength. Furthermore, the thickness of the microporous membrane is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, 22 μm or less, or 19 μm or less. A membrane thickness of 500 μm or less tends to further improve ion permeability. The thickness of the microporous membrane can be adjusted by adjusting the stretching ratio, stretching temperature, etc. The above-mentioned membrane thickness was measured by the method described in the examples.

[0107] Especially when using a microporous membrane as a separator or constituent material for a LIB, the membrane thickness is preferably 25 μm or less, more preferably 22 μm or less, or 20 μm or less, and even more preferably 18 μm or less. In this case, with a membrane thickness of 25 μm or less, there is a tendency for further improvement in permeability. In this case, the lower limit of the microporous membrane thickness can be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, or 5.0 μm or more.

[0108] <Manufacturing Method of Separator for Energy Storage Devices>

[0109] Other aspects of the present invention provide a method for manufacturing a separator for an energy storage device containing a microporous membrane. The method for manufacturing a separator for an energy storage device according to a second embodiment may include a method for manufacturing a microporous membrane, comprising the following steps:

[0110] (1) A sheet forming process in which granular polypropylene (PP), powdered polyethylene (PE) and plasticizer are extruded into sheets using an extruder, cooled and solidified, and processed into sheet-shaped bodies.

[0111] (2) A stretching process in which a sheet-shaped body is biaxially stretched at a magnification ratio of 20 times or more and 250 times or less to form a stretched object;

[0112] (3) Microporous membrane forming process of extracting plasticizer from stretching material to form microporous membrane;

[0113] (4) A heat treatment process in which a microporous membrane is subjected to heat treatment, stretched in the width direction (TD), and relaxed to obtain a heat-treated microporous membrane; and

[0114] (5) The winding process of taking the heat-treated microporous membrane.

[0115] The method for manufacturing a separator for an energy storage device according to the second embodiment involves forming PE raw material into powder, forming PP raw material into granules, and then mixing them. Extrusion film production can reduce the mixing of multiple raw materials. Disadvantages of the extrusion process (i.e., the amount of unmelted material). Mixing Unmelted material during the extrusion process may become aggregates, gels, etc. in the final microporous membrane and the separator containing it. Therefore, by having a separator in a microporous membrane with reduced defects, it is possible to achieve the thickness maintenance characteristics (cycle characteristics) of the separator or the capacity maintenance characteristics (cycle characteristics) of the energy storage device during repeated charging and discharging.

[0116] Furthermore, in the second embodiment, not only can the separator of the first embodiment described above be obtained, but the crystal distribution of PE and PP in the microporous membrane constituting the separator is also optimized as described above. For example, it can easily deform due to the expansion and contraction of the negative electrode, such as the silicon-containing negative electrode, thereby also contributing to the tightness between the negative electrode and the separator.

[0117] The resin raw materials and additives used in the second embodiment can be the same as those used in the first embodiment for PE, PP, PO, other resins, and additives described above. Furthermore, the separator for the energy storage device manufactured by the manufacturing method of the second embodiment is also preferably, like the separator for the energy storage device of the first embodiment, comprising a microporous membrane containing PE with a crystallite size of 15 nm to 40 nm and PP with a crystallite size of 10 nm to 50 nm, and more preferably, an isotactic five-unit component (mm) with a stereoregular structure of PP of 85.0 mol% to 99.7 mol%. The steps of the second embodiment will be described sequentially below.

[0118] [Sheet forming process (1)]

[0119] In step (1), granular PP raw material, powdered PE raw material, and plasticizer are supplied to the extruder. As described above, the PE and PP raw materials described in the first embodiment can be used in a specified mass ratio as PE and PP raw materials.

[0120] (Polyethylene (PE) raw material)

[0121] Improving raw material mixing in the manufacturing process of microporous membranes From the perspective of yield in the extrusion process and from the perspective of easily reducing the amount of unmelted material in the obtained microporous membrane, the PE raw material is preferably in powder form, with the total mass of PE used as a basis, and more preferably 2% to 100% by mass as powder.

[0122] As a preferred PE raw material, "powder" refers to powder that meets the requirements of a selected number-average particle size (Nd). 50 The particle size ranges from 80 μm to 180 μm, with a volume average particle size (Vd). 50 The particle size distribution is 120 μm to 220 μm, with a number size distribution (Nd). 80 / Nd 20The particle size distribution (Vd) is 1.1–4.2, preferably 1.2–4.1. 80 / Vd 20 The powder has a number average particle size (Nd) of 1.1 to 3.3, preferably 1.15 to 3.2, a crystallite size in the range of 15 nm to 40 nm, a crystallinity of 30% to 99%, preferably 32% to 98%, more preferably 38% to 97.5%, and contains at least one of the following conditions: [missing information - likely related to a specific particle size distribution]. 50 Volume average particle size (Vd) 50 ), number of particles size distribution (Nd) 80 / Nd 20 ), volumetric particle size distribution (Vd) 80 / Vd 20 Crystallite size, crystallinity, etc., can be determined using known methods.

[0123] For example, for the number-average particle size (Nd) 50 Volume average particle size (Vd) 50 ), number of particles size distribution (Nd) 80 / Nd 20 ) and volumetric particle size distribution (Vd 80 / Vd 20 Particle size can be determined by using Micromeritics flow imaging. The shape is determined by measurement using the Particle Insight device. Additionally, for example, crystallite size and crystallinity can be obtained by XRD measurement using the Ultima-IV X-ray diffraction apparatus manufactured by Rigaku Corporation.

[0124] (Polypropylene (PP) raw material)

[0125] Improving raw material mixing in the manufacturing process of microporous membranes From the perspective of yield in the extrusion process and from the perspective of easily reducing the amount of unmelted material in the obtained microporous membrane, the PP raw material is preferably in the form of granules, with the total mass of PP used as a basis, and more preferably 2% to 100% by mass as granules.

[0126] Granular PP can be obtained, for example, by drying polymerized PP powder, extruding it into wire form using an extruder, water-cooling it, and then cutting it into granules. In this case, the viscosity-average molecular weight (Mv) of the PP powder raw material is preferably 200,000 or more and 1,000,000 or less, more preferably 250,000 or more and 900,000 or less, and even more preferably 300,000 or more and 800,000 or less. It should be noted that the Mv of PP can be calculated by measuring the intrinsic viscosity [η] (dl / g) at 135°C in decahydronaphthalene solvent based on ASTM-D4020, according to the following formula.

[0127] [η]=1.10×10 -4 Mv 0.80

[0128] Here, "granules" preferred as a PP raw material refers to a particle size (Nd) that is greater than that of "powder" preferred as a PE raw material. 50 ) and volume average particle size (Vd) 50 The resin material is large, with a maximum side length of 10 mm or less and 1 mm or more. There are no particular limitations on the shape of the granules; for example, they can be spherical, ellipsoidal, or cylindrical. The granules are obtained by melt-extruding the raw material using an extruder, followed by water or air cooling, while simultaneously shaping them into a wire and continuously cutting them. The size or specific shape of the granules can be adjusted, for example, through wire forming or cutting methods.

[0129] (A combination of powdered PE raw materials and granular PP raw materials)

[0130] By adjusting the PP raw material to a "granular" form as described above, the swelling rate achieved by the plasticizer can be significantly delayed (i.e., it is presumed that granular PP will not actually swell). It is important that the swelling of the powdered PE raw material is not hindered inside the extruder. Furthermore, in the melting process following the swelling process, from the viewpoint of uniform melting, "granules" preferred as a PP raw material component refer to granules with a larger crystallite size than "powder," which is preferred as a PE raw material component, and having the crystallite size of PP described in the first embodiment.

[0131] In the manufacturing method of granules, the temperature of resin extrusion into filaments, the cooling temperature during cutting, or the stretching speed of the filaments compared to extrusion (melt microstretching), as well as the crystallite size, crystallinity, granule size, and shape of the granules, can be adjusted. These factors include the number-average particle size (Nd). 50 Volume average particle size (Vd) 50 Crystallite size, crystallinity, etc., can be determined using known methods. For example, these number-average particle sizes (Nd) 50 Volume average particle size (Vd) 50The crystallite size and crystallinity can be determined using the same method as in the first embodiment. Furthermore, the particle size can be obtained, for example, by measuring the length of one side using a caliper.

[0132] The mixing of granulated PP and powdered PE significantly improves the uniformity of plasticizer swelling within the extruder. This is believed to be because the swelling rate of granules is significantly slower compared to powder. Therefore, granulated PP does not excessively hinder the swelling of powdered PE, and the granules themselves are essentially non-swelling, making them suitable for subsequent melt blending. Consequently, even in the melt blending process, PP components can be easily and uniformly dispersed within the PE composition down to the molecular level.

[0133] (Plasticizer)

[0134] Plasticizers can be any known material as long as they are liquid at temperatures between 20°C and 70°C and exhibit excellent dispersibility in PE or PP. The plasticizer used in step (1) is preferably a non-volatile solvent capable of forming a homogeneous solution above the melting point of PE or PP, taking into account subsequent extraction. Specific examples of non-volatile solvents include hydrocarbons such as liquid paraffin, paraffin wax, decane, and decahydronaphthalene; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Liquid paraffin is preferred because it exhibits high compatibility with polyethylene, is less prone to interfacial delamination between the resin and plasticizer even when the molten compound is stretched, and tends to facilitate uniform stretching.

[0135] (The supply of raw materials to the extruder)

[0136] Examples of extruders include single-screw extruders, twin-screw extruders, and short-shaft extruders with screws, among which twin-screw extruders are preferred. In addition, in step (1), it is preferable to shear the raw material by a continuous mixer, and more preferably to install a continuous mixer in a twin-screw extruder.

[0137] From the viewpoint of ensuring appropriate viscosity while ensuring the entanglement of polymer chains to the extent that the molecular weight of the resin raw material is not reduced, the resin raw material and / or plasticizer are preferably supplied to the extruder at a temperature of 25°C to 80°C, more preferably 30°C to 76°C, and even more preferably 30°C to 70°C.

[0138] From the perspective of controlling the crystal structure of PE and PP and controlling the swelling of plasticizers, PE and PP raw materials are preferably fed into the extruder by any one of the following methods (a) to (c):

[0139] (a) A method of feeding PP granules and PE powder into an extruder using different feeders;

[0140] (b) A method of feeding the mixture of PP granules and PE powder into an extruder using a single feeder;

[0141] (c) A method of dry mixing PP granules and PE powder to obtain multiple resin raw materials, and feeding the multiple resin raw materials into an extruder using different feeders.

[0142] Controlling the crystal structure of PE and PP is crucial in their mixed state. Therefore, this invention effectively utilizes their thermodynamically semi-compatible nature, focusing on controlling the dispersion state of PE and PP within the limited residence time in the extruder. From this perspective, the crystal structure of PE and PP is indirectly controlled by adjusting the size (e.g., powder, granules, etc.) of the fed PE and PP. Furthermore, the swelling of plasticizers such as liquid paraffin (LP) before PE melts in the extruder is critical for the uniform dispersion of PE itself (e.g., preventing the formation of unmelted material or gel). Experiments have shown that excessive molten PP mixed with LP increases the viscosity or inhomogeneity of the plasticizer, thus hindering the uniform swelling of PE. Considering the above, it is preferable that the PE and PP raw materials are fed into the extruder using any one of the methods described in (a) to (c).

[0143] In feeding method (a), PP and PE can be fed into the extruder simultaneously, sequentially, or continuously, preferably simultaneously into a twin-screw extruder. In feeding methods (b) and (c), PP and PE are fed into the extruder simultaneously.

[0144] In input method (c), PP granules and PE powder can be dry-mixed multiple times to obtain multiple resin raw materials, or the dry mixture obtained by dry-mixing PP granules and PE powder once can be divided into multiple types to obtain multiple resin raw materials.

[0145] Of the raw material input methods (a) to (c), from the viewpoint of controlling the stability of extrusion, constructing a uniformly dispersed PE and PP dispersion state, and from the viewpoint of the retention rate of separator thickness and / or the retention rate of battery cell capacity after cycle testing, (a) and (b) are more preferred, and (b) is even more preferred.

[0146] Additionally, plasticizers can be supplied to the twin-screw extruder along with PE and / or PP raw materials. After the plasticizer is supplied to the twin-screw extruder along with the PE and / or PP raw materials, it can also be supplied additionally from the same or different feeders. Such twin-screw extruders typically have an upper feed port located upstream and a middle feed port located downstream of this feed port, in the middle of the melt mixing zone. Therefore, after the mixed slurry is supplied from the upper feed port of the twin-screw extruder, plasticizers can also be supplied additionally from the middle feed port of the twin-screw extruder. This makes it easy to adjust the proportion of liquid paraffin extruded from the twin-screw extruder in the resin composition to the desired ratio, and also makes it easy to adjust the temperature of the resin composition to the desired range. Of course, the first component or the second component can also be supplied from the middle feed port.

[0147] The mixed slurry can be prepared using a continuous mixer. From the viewpoint of maximizing the swelling of the PE raw material and plasticizer, the lower limit of the set temperature of the continuous mixer is preferably 25°C or higher, more preferably 30°C or higher. Furthermore, from the viewpoint of melting the resin raw material during mixing, the upper limit is preferably 68°C or lower, more preferably 67°C or lower, 66°C or lower, or 65°C or lower.

[0148] For the shear rate of the continuous mixer, considering the goal of ensuring uniform contact between the resin raw material and the plasticizer to obtain a dispersion, it is 100 seconds. -1 ~400,000 seconds -1 Optimal 120 seconds -1 ~398000 seconds -1 , or more preferably 1000 seconds -1 ~100,000 seconds -1 .

[0149] From the viewpoint of ensuring the dispersion of resin raw materials in the plasticizer, the residence time of the continuous mixer is 1.0 second to 60 seconds, preferably 2.0 second to 58 seconds, and more preferably 2.0 second to 56 seconds.

[0150] (Melting and mixing)

[0151] In step (1), a resin composition is manufactured by melt-blending the resin raw material and plasticizer using a twin-screw extruder. In the second embodiment, as long as the uniformity of the swelling of the resin raw material with the plasticizer is ensured, there are no limitations on the type of equipment, time, or other conditions used in the melt-blending. It should be noted that, as needed, PO resin other than PE and PP, resin raw materials other than PO, known additives, such as dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, coloring pigments, etc., can also be fed into the twin-screw extruder.

[0152] (Cooling and curing, sheet forming)

[0153] In step (1), the molten compound is formed into a sheet. Methods for manufacturing the sheet include, for example, extruding the molten compound into a sheet shape using a T-die, cooling it to a temperature sufficiently low compared to the crystallization temperature of the resin component by contacting it with a heat conductor, and then curing it. Examples of heat conductors used in cooling and curing include metal, water, air, and plasticizers. Among these, metal rollers are preferred due to their high thermal conductivity. Furthermore, when the extruded compound is brought into contact with a metal roller, clamping it with at least one pair of rollers is more preferable, as it tends to further increase thermal conductivity, increase sheet orientation and film strength, and improve the surface smoothness of the sheet. The die lip spacing when extruding the resin composition into a sheet shape using a T-die is preferably 200 μm or more and 3000 μm or less, more preferably 500 μm or more and 2500 μm or less. If the die lip spacing is 200 μm or more, die burnt material is reduced, and streaks or defects have less impact on film quality, thus reducing the risk of film breakage in subsequent stretching processes. On the other hand, if the die lip spacing is 3000 μm or less, the cooling rate is faster, uneven cooling is prevented, and the thickness stability of the sheet can be maintained. In addition, the extruded sheet can also be calendered.

[0154] [Stretching process (2)]

[0155] In step (2), the sheet-shaped body obtained in step (1) is stretched at a ratio of 20 to 250 times. If the ratio is 20 times or more, there is a tendency to impart sufficient strength to the obtained microporous membrane; on the other hand, if the ratio is 250 times or less, there is a tendency to prevent membrane breakage and obtain high productivity. Step (2) can be performed before or after the porous body forming step (3). Furthermore, step (2) can also be performed before or after the extraction of plasticizer from the sheet-shaped body.

[0156] As a stretching process, biaxial stretching is preferred over uniaxial stretching, considering the reduction of film thickness and permeability distribution in the width direction (TD). By simultaneously stretching the sheet in both directions, the sheet-shaped body is repeatedly cooled during the film-forming process. The number of heating cycles is reduced, resulting in a better distribution in the width direction. Examples of biaxial stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-segment stretching, and multiple stretching. From the viewpoint of improving penetration strength and stretching uniformity, simultaneous biaxial stretching is preferred; furthermore, from the viewpoint of ease of controlling surface orientation, sequential biaxial stretching is preferred.

[0157] In this specification, simultaneous biaxial stretching refers to a stretching method that simultaneously performs stretching in the MD (mechanical direction of continuous microporous membrane formation) and TD (direction of MD traversing the microporous membrane at a 90° angle). The stretching ratios in each direction can be different. Sequential biaxial stretching refers to a stretching method that independently performs stretching in the MD and TD directions, where, while the MD or TD is being stretched, the other direction is either in an unrestricted state or fixed to a constant length.

[0158] The stretch ratio, measured in terms of area ratio, is preferably in the range of 20 times or more and 200 times or less, more preferably in the range of 25 times or more and 170 times or less, and even more preferably in the range of 30 times or more and 150 times or less. The stretch ratio in each axial direction is preferably in the range of 2 times or more and 15 times or less in the MD and TD, more preferably in the range of 3 times or more and 12 times or less in the MD and 3 times or more and 12 times or less in the TD, and even more preferably in the range of 5 times or more and 10 times or less in the MD and 5 times or more and 10 times or less in the TD.

[0159] From the viewpoint of the meltability and film-forming properties of PE / PP raw materials, the stretching temperature is preferably 90℃~150℃, more preferably 100℃~140℃, and even more preferably 110℃~130℃.

[0160] [Microporous membrane formation process (3)]

[0161] In step (3), a plasticizer is extracted from the resin composition formed in step (1) or from the stretched material formed in step (2) to form a microporous membrane. Examples of methods for extracting the plasticizer include impregnating the stretched material in an extraction solvent to extract the plasticizer and then drying it. The extraction method can be either batch or continuous. To suppress shrinkage of the microporous membrane, it is preferable to limit the ends of the sheet-shaped body during the series of impregnation and drying steps. Furthermore, the residual amount of plasticizer in the microporous membrane is preferably less than 1% by mass relative to the total mass of the microporous membrane. It should be noted that after step (3), the plasticizer can also be recovered and reused through operations such as distillation.

[0162] As the extraction solvent, it is preferable to use a solvent that is a poor solvent for PE and PP resins, a good solvent for plasticizers, and has a boiling point lower than the melting point of PE and PP 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 through operations such as distillation.

[0163] [Heat treatment process (4)]

[0164] In step (4), for example, after heat treatment of the microporous membrane obtained in step (3) at a temperature below the melting point of the microporous membrane, the microporous membrane is stretched to produce a heat-treated microporous membrane.

[0165] For microporous membranes, from the viewpoint of suppressing shrinkage, heat treatment aimed at heat setting is implemented. Methods of heat treatment include stretching operations performed with a specified atmosphere, temperature, and stretching ratio for the purpose of adjusting physical properties, and / or relaxation operations performed with a specified atmosphere, temperature, and relaxation rate for the purpose of reducing tensile stress. Relaxation operations can be performed after the stretching operation. These heat treatments can be carried out using a tenter frame or a roll stretching machine.

[0166] From the viewpoint of improving the strength and porosity of the microporous membrane, the stretching operation preferably involves a stretch of 1.1 times or more, more preferably 1.2 times or more, in terms of the membrane's maximum density (MD) and / or maximum tangent (TD). The upper limit of the stretching ratio during heat setting is preferably 3.0 times or less, more preferably 2.5 times or less, in both the MD and TD.

[0167] Furthermore, the relaxation operation is a reduction operation on the membrane's maximum diameter (MD) and / or minimum diameter (TD). The relaxation rate refers to the value obtained by dividing the membrane size after the relaxation operation by the membrane size before the relaxation operation. It should be noted that when both MD and TD are relaxed, the relaxation rate is the product of the relaxation rate of MD and the relaxation rate of TD. The relaxation rate is preferably 0.99 or less, more preferably 0.95 or less. From the viewpoint of membrane quality, the relaxation rate is preferably 0.5 or more. The relaxation operation can be performed in both directions of MD and TD, or only in one of the MD and TD directions.

[0168] For heat treatment temperatures, including stretching or relaxation operations, from the viewpoint of the melting point (hereinafter also referred to as "Tm") of PE and PP resins, a range of 100°C to 170°C is preferred. If the stretching and relaxation temperatures are within this range, it is preferable from the viewpoint of reducing heat shrinkage and balancing porosity. The lower limit of the heat treatment temperature is more preferably 110°C or higher, more preferably 115°C or higher, and the upper limit is more preferably 160°C or lower, more preferably 150°C or lower, and even more preferably 140°C or lower.

[0169] [Winding process (5)]

[0170] In step (5), the microporous membrane that has undergone heat treatment in step (4), or the microporous membrane manufactured by the second embodiment, can be wound into a roll, for example, using a winding machine. The resulting roll can be stored until the microporous membrane is used to manufacture a separator for an energy storage device.

[0171] [Other processes]

[0172] From the viewpoint of processability and storage stability, the obtained microporous membrane or roll can be cut using a slitting machine. Additionally, the microporous membrane can be post-treated as follows: hydrophilic treatment using surfactants, cross-linking treatment using ionizing radiation, etc. The microporous membrane obtained through steps (1) to (5) can be used as a single-layer separator, or multiple microporous membranes can be stacked, or microporous membranes and other membranes can be stacked, or a functional layer can be provided on the microporous membrane, or a coating can be applied to the microporous membrane.

[0173] <Electric Storage Devices>

[0174] Other embodiments of the present invention provide an energy storage device comprising a positive electrode, a negative electrode, and a separator containing the microporous membrane described above. Specifically, examples of energy storage devices include lithium secondary batteries, lithium-ion secondary batteries, sodium secondary batteries, sodium-ion secondary batteries, magnesium secondary batteries, magnesium-ion secondary batteries, calcium secondary batteries, calcium-ion secondary batteries, aluminum secondary batteries, aluminum-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, double-layer capacitors, lithium-ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, and zinc-air batteries. From a practical point of view, lithium secondary batteries, lithium-ion secondary batteries (LIBs), nickel-metal hydride batteries, or lithium-ion capacitors are preferred, and lithium-ion secondary batteries are more preferably preferred. Furthermore, from the viewpoint of ion conductivity, charge-discharge characteristics, etc., the batteries listed above preferably contain an electrolyte.

[0175] The electrolyte in the battery may contain water, and the water contained in the system after battery fabrication may be water contained in the electrolyte or water introduced from components such as electrodes or separators. The electrolyte may contain non-aqueous solvents. Examples of non-aqueous solvents in this embodiment include alcohols such as methanol and ethanol, and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents.

[0176] Examples of aprotic solvents include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds containing sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the above aprotic solvents are replaced by halogen atoms.

[0177] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentene carbonate, trans-2,3-pentene carbonate, cis-2,3-pentene carbonate, vinylene carbonate, 4,5-dimethylethyleneene carbonate, and vinylene carbonate.

[0178] Examples of fluoroethylene carbonates include 4-fluoro-1,3-dioxacyclopentan-2-one, 4,4-difluoro-1,3-dioxacyclopentan-2-one, cis-4,5-difluoro-1,3-dioxacyclopentan-2-one, trans-4,5-difluoro-1,3-dioxacyclopentan-2-one, 4,4,5-trifluoro-1,3-dioxacyclopentan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxacyclopentan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxacyclopentan-2-one.

[0179] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0180] Examples of organic compounds containing sulfur atoms include ethylene sulfite, propylene sulfite, butyl sulfite, amyl sulfite, sulfolane, 3-cyclobutene sulfone, 3-methylcyclobutene sulfone, 1,3-propane sulpholactone, 1,4-butane sulpholactone, 1-propene 1,3-sulpholactone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0181] Examples of chain carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate.

[0182] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

[0183] Examples of mononitriles include acetonitrile, propionitrile, butyronitrile, valerate, benzonitrile, and acrylonitrile.

[0184] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile.

[0185] Examples of dinitrile include malononitrile, succinate, methylsuccinate, glutaronitrile, 2-methylglutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanhexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanonane, 2,8-dicyanonane, 1,10-dicyandecane, 1,6-dicyandecane, and 2,4-dimethylglutaronitrile, ethylene glycol bis(propionitrile) ether, etc.

[0186] Examples of cyclic nitriles include benzonitrile.

[0187] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl neovalerate, methyl angelic acid ester, methyl hexanoate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl neovalerate, ethyl angelic acid ester, ethyl hexanoate, propyl acetate, propyl propionate, propyl isobutyrate, propyl isovalerate, propyl valerate, propyl neovalerate, propyl angelic acid ester, propyl hexanoate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, and so on. Isopropyl valerate, isopropyl neovalerate, hydrogenated angelic acid isopropyl ester, isopropyl hexanoate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl neovalerate, hydrogenated angelic acid ester, butyl hexanoate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl neovalerate, hydrogenated angelic acid isobutyl ester, isobutyl hexanoate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl neovalerate, hydrogenated angelic acid ester, and tert-butyl hexanoate, etc.

[0188] Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0189] Examples of fluorinated ethers include, for example, those with the general formula Rf. aa -OR bb (where Rf) aa It is an alkyl group containing a fluorine atom, and R bb Compounds, etc., that may contain organic groups containing fluorine atoms.

[0190] Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0191] Compounds in which some or all of the H atoms of the aforementioned aprotic solvent are replaced by halogen atoms include, for example, compounds in which the halogen atom is fluorine.

[0192] Examples of fluorinated chain carbonates include, for instance, methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. These fluorinated chain carbonates can be represented by the following general formula:

[0193] R cc -OC(O)OR dd

[0194] In the formula, R cc and R dd The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2 and CH2Rf are selected. ee (where Rf) ee It consists of at least one group from the group consisting of alkyl groups having 1 to 3 carbon atoms, formed by replacing a hydrogen atom with at least one fluorine atom, and R cc and / or R dd It contains at least one fluorine atom.

[0195] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters can be represented by the following general formula:

[0196] R ff -C(O)OR gg

[0197] In the formula, R ff The free radicals are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, and CF2Rf. hh CFHRf hh and CH2Rf ii At least one of the groups, R gg The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf are selected. ii At least one of the groups, Rf hh Rf is an alkyl group with 1 to 3 carbon atoms, formed by replacing a hydrogen atom with at least one fluorine atom. ii An alkyl group having 1 to 3 carbon atoms, formed by replacing a hydrogen atom with at least one fluorine atom, and R ff and / or R gg Contains at least one fluorine atom, R ff In the case of CF2H, Rgg Not CH3}.

[0198] <LIB>

[0199] A LiB battery is a rechargeable battery that uses lithium transition metal oxides such as lithium cobalt oxide and lithium-cobalt composite oxides as the positive electrode, carbon materials such as graphite and lead oxide, or silicon-containing materials as the negative electrode, and an organic solvent containing lithium salts such as LiPF6 as the electrolyte. The charging process of a LiB battery... During discharge, ionized Li oscillates between the electrodes. Furthermore, since it is necessary to move the ionized Li at a relatively high speed between the electrodes while suppressing contact, a spacer is disposed between the electrodes. From the viewpoint of achieving a seamless seal with the negative electrode, the spacer in the first embodiment, or the spacer manufactured according to the second embodiment, preferably has a silicon-containing negative electrode as the negative electrode of the LIB.

[0200] Unless otherwise specified, the condition values, physical property values, characteristic values, etc., described above shall be measured according to the methods described in the following examples. Whether the separator contains one microporous membrane and other layers, is a coated membrane, or contains multiple microporous membranes, the characteristics of the microporous membrane shall be measured or evaluated by removing one microporous membrane from the separator or by removing the coated portion from the separator.

[0201] Example

[0202] The following examples and comparative examples illustrate the present invention in more detail. However, the present invention is not limited to the following examples as long as the spirit of the invention is not followed. The physical properties in the examples were determined by the following methods.

[0203] <Weight-average molecular weight (Mw), Number-average molecular weight (Mn)>

[0204] 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 the following polymers under the same conditions, and the weight-average molecular weight and number-average molecular weight of each polymer were calculated based on the calibration curves using the following method.

[0205] Chromatographic columns: 2 GMH6-HT (trademark) columns manufactured by TOSOH CORPORATION + 2 GMH6-HT (trademark) columns

[0206] Mobile phase: o-dichlorobenzene

[0207] Detector: Differential refractometer

[0208] Flow rate: 1.0 ml / min

[0209] Column temperature: 140℃

[0210] Sample concentration: 0.1 wt%

[0211] (Weight-average molecular weight and number-average molecular weight of polyethylene and polypropylene)

[0212] 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 can be calculated.

[0213] <Regarding the five-unit fraction of the 3D regular structure>

[0214] The isotactic pentamematic fraction (mmmm) in the polypropylene composition is used as a basis for... 13 The (mmmm) peak fraction among all absorption peaks in the methyl carbon region determined by C-NMR was calculated. Additionally, the signal assignment of the methyl region containing the isotactic pentad group was based on A. Zambellie et al. (Macromolecules 8687 (1975)). Specifically, the (mmmm) pentad group fraction of the stereoregular PP structure in the raw material and microporous membrane was determined as follows.

[0215] <Regarding the number of PP-containing three-dimensional regular structured five-unit components in raw materials and microporous membranes>

[0216] The sample was dissolved in dichlorobenzene-d4 at above 130°C to form a concentration of 10 wt%. 13 C-NMR determination. The determination conditions are as described below.

[0217] Device: Bruker Avance NEO 600

[0218] Pulse program: zgpg30

[0219] Pulse wait time: 5 seconds

[0220] Sample tube diameter: 5mmφ

[0221] Measurement temperature: 130℃

[0222] 13In the C-NMR spectrum, the mmmm quintet is assigned to 21.8 ppm, and the peaks in the methyl region from 18 ppm to 22 ppm are assigned to mmmm, mmmr, rmmr, mmrr, rmrr, rmrm, mmrm, rrrr, rrrm, and mrrm. The fraction of the mmmm quintet is calculated by dividing the integral value of the mmmm quintet by the sum of the integral values ​​of these peaks.

[0223] It should be noted that the chemical shifts for each stereostructure are...

[0224] mmmm 21.8ppm,

[0225] mmMR 21.6ppm

[0226] RMMR 21.3ppm

[0227] mmrr 21.0ppm,

[0228] mmrm+rmrr 20.8ppm

[0229] rmrm 20.6ppm,

[0230] rrrr 20.3ppm,

[0231] rrrm 20.2ppm,

[0232] mrrm 19.9ppm.

[0233] <Film thickness (μm)>

[0234] The thickness of the separator sample was measured using a micro thickness gauge (Toyo Seiki type KBM) at room temperature of 23°C and humidity of 40%. A 44gf load was applied using a terminal with a terminal diameter of 5mmφ.

[0235] <Porosity (%)>

[0236] A 10cm × 10cm square sample was cut from a microporous membrane. Calculate its volume (cm³). 3 ) and mass (g), which are derived from their density (g / cm³) 3 The porosity is calculated using the following formula.

[0237] Porosity (%) = (Volume - Mass / Density) / Volume × 100

[0238] < Breathability (seconds / 100cm) 3 >

[0239] According to JIS P-8117, the air permeability resistance of polyolefin microporous membranes was measured using a G-B2 (trademark) air permeability meter manufactured by Toyo Seiki Co., Ltd. at an atmosphere of 23°C and 40% humidity, and was taken as the air permeability.

[0240] <Crystal Structure Analysis>

[0241] The crystallite size of polyolefins (e.g., PE, PP, etc.) contained in the separator or the microporous membrane contained in the separator can be determined by either reflection X-ray diffraction or transmission wide-angle X-ray scattering.

[0242] (Transmission method for wide-angle X-ray scattering measurement)

[0243] The crystallite size of polyolefins (e.g., PE, PP, etc.) contained in the separator or the microporous membrane contained in the separator was determined using a NANOPIX transmission-type X-ray scattering apparatus manufactured by Rigaku Corporation. Cu-Kα rays were irradiated onto the sample, and the scattering was detected by a Hypix-6000 semiconductor detector. Measurements were performed at a sample-detector distance of 86 mm, an output power of 40 kV, and an A of 30 mA. The optical system employed point focusing, and measurements were performed with slit diameters of 1st slit: φ = 0.55 mm, 2nd slit: open, and Guard slit: φ = 0.35 mm.

[0244] Crystallite size (nm) and crystallinity in wide-angle X-ray scattering measurements using transmission method

[0245] In the case of wide-angle X-ray scattering measurement using transmission method, when the X-ray scattering pattern obtained by a two-dimensional detector is centered on the point where the X-rays irradiating the sample travel in a straight line, pass through the sample, and reach the two-dimensional detector, the scattering intensity at the same distance from the center corresponds to the same scattering angle. Therefore, for the measured X-ray scattering pattern, the intensity average (circular average) of each scattering angle is calculated, thereby obtaining a one-dimensional scattering intensity map for the scattering angle 2θ. The obtained one-dimensional map, from 2θ=10.0° to 2θ=29.0°, is processed into six peaks: the orthorhombic (110) plane diffraction peak of polyethylene, the orthorhombic (200) plane diffraction peak of polypropylene, the α-crystal (110) plane diffraction peak of polypropylene, the α-crystal (040) plane diffraction peak of polypropylene, the α-crystal (130) plane diffraction peak, and the amorphous peak of polyethylene. The baseline was drawn by connecting 2θ=29.0° with a straight line from 2θ=10.0°. The (110) and (200) diffraction peaks of polyethylene were approximated by the VOOIT function, and the (110), (040), and (130) diffraction peaks of polypropylene and the amorphous peak of polyethylene were approximated by the Gauss function. It should be noted that the peak position of the amorphous peak was fixed at 2θ=19.6° and the full width at half maximum (FWHM) was fixed at 6.3°, while the peak position and FWHM of the crystalline peak were not separated in a particularly fixed manner. The crystallite size was calculated from the FWHM of the (110) diffraction peaks of polyethylene and polypropylene, which were obtained through peak separation, according to the Scherrer equation (below). It should be noted that the crystallinity can be obtained as a percentage value obtained by dividing the area of ​​the crystalline peak by the sum of the separated crystalline and amorphous peaks.

[0246] D=Kλ / (βcosθ)

[0247] D: Crystalline size (nm)

[0248] K: 0.9 (constant)

[0249] λ: Wavelength of X-rays (nm)

[0250] β: (β1) 2 -β2 2 ) 0.5

[0251] β1: Full width at half maximum (FWHM) of the (hkl) peak calculated from the peak separation results (rad).

[0252] β2: Full width at half maximum (FWHM) of the incident beam (rad)

[0253] θ: Angle Bragg

[0254] (Reflection X-ray diffraction measurement)

[0255] Determination of polyolefin crystallite size (nm) and crystallinity by reflectance X-ray diffraction

[0256] XRD measurements of polyolefins (e.g., PE, PP, etc.) contained in separators were performed using the Rigaku Corporation Ultima-IV X-ray diffraction apparatus. Cu-Kα rays were incident on the sample, and the diffracted light was detected using a Rigaku Corporation D / tex Ultra detector. KRD measurements were performed under conditions of a sample-detector distance of 285 mm, an excitation voltage of 40 kV, and a current of 40 mA. A concentrated optical system was used as the optical system, and measurements were performed under slit conditions of DS = 1 / 2°, SS = release, and a longitudinal slit width of 10 mm.

[0257] Analysis in X-ray diffraction measurement by reflection method

[0258] The case of polyethylene

[0259] The obtained XRD pattern, ranging from 2θ=9.7° to 2θ=29.0°, was separated into three peaks: the orthorhombic (110) diffraction peak, the orthorhombic (200) diffraction peak, and the amorphous peak. The crystallite size was calculated from the full width at half maximum (FWHM) of the (110) diffraction peak using the Scherrer equation (below). The (110) and (200) diffraction peaks were approximated using the VOOIT 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 FWHM was fixed at 6.3°, while the peak position and FWHM of the crystalline peak were not specifically fixed for peak separation. The crystallite size was calculated from the FWHM of the (110) diffraction peak obtained through peak separation using the Scherrer equation (below). It should be noted that crystallinity can be obtained as a percentage value obtained by dividing the area of ​​the crystalline peak by the sum of the separated crystalline and amorphous peaks.

[0260] Polypropylene

[0261] The obtained XRD pattern covers a range from 2θ=6° to 2θ=31°. The diffraction peaks originating from the crystal were separated into five peaks on the (110), (040), (130), (111), and (13-1) / (041) planes of the α-crystal (monoclinic crystal), while the diffraction peaks originating from the amorphous were separated into two. The separated diffraction peaks originating from the crystal and the amorphous were approximated using the Gaussian function. It should be noted that the two amorphous peaks were fixed for peak separation as described below. Amorphous peak 1 was fixed at 2θ=14.9° and a full width at half maximum (FWHM) of 4.7°, while amorphous peak 2 was fixed at 2θ=19.18° and a FWHM of 7.0°. The crystallite size was calculated from the FWHM of the (110) plane diffraction peak obtained through peak separation, according to the Scherrer equation (below). Crystallinity can be obtained as a percentage value obtained by dividing the area of ​​the crystalline peak by the sum of the separated crystalline and amorphous peaks.

[0262] D(110)=Kλ / (βcosθ)

[0263] D(110): Crystalline size (nm)

[0264] K: 0.9 (constant)

[0265] λ: Wavelength of X-rays (nm)

[0266] β: (β1) 2 -β2 2 ) 0.5

[0267] β1: Full width at half maximum (FWHM) of the (hkl) peak calculated from the peak separation results (rad).

[0268] β2: Full width at half maximum (FWHM) of the incident beam (rad)

[0269] θ: Angle Bragg

[0270] <Amount of unmelted material in separators (pieces / 1000m) 2 >

[0271] The amount of unmelted material in the separator was quantified using a transmission optical microscope when observing the separators obtained from the film-forming process of the examples and comparative examples. The unmelted material was measured in areas with an area of ​​at least 100 μm x 100 μm that were not translucent to light. The amount of unmelted material per 1000 μm was determined by observation using a transmission optical microscope. 2 The number of resin aggregates per square meter of the separator area.

[0272] <Cyclic Test (%) Test Method 1>

[0273] The positive electrode, negative electrode, and non-aqueous electrolyte are manufactured through the following steps a to c.

[0274] a. Production of the positive electrode

[0275] The nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (elemental ratio), density 4.70 g / cm³) will be used as the positive electrode active material. 3 ) Graphite powder (KS6) (density 2.26 g / cm³) was used as a conductive additive at a ratio of 90.4% by mass. 3 The number-average particle size was 6.5 μm, and the content of acetylene black powder (AB) (density 1.95 g / cm³) was 1.6% by mass. 3 The number-average particle size (48 nm) was 3.8% by mass, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm³) was used as a binder. 3 The active materials were mixed at a ratio of 4.2% by mass and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was then coated onto one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the foil was compressed using a roller press to form the positive electrode. The coating weight of the positive electrode active material at this point was 109 g / m². 2 .

[0276] b. Negative electrode fabrication

[0277] According to the method described in Non-Patent Document 3, a graphene anode containing 40% silicon is manufactured, and a copper foil with a thickness of 12 μm is loaded with a thickness of 3.6 μm to serve as the anode current collector, thereby producing the anode.

[0278] c. Manufacturing of non-aqueous electrolytes

[0279] A non-aqueous electrolyte is prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a ratio of 1:2 (volume ratio).

[0280] d. Battery manufacturing

[0281] The thickness of the microporous membrane used as a separator was measured according to the method described in the above item <Membrane Thickness (μm)>. Using the positive electrode, negative electrode, non-aqueous electrolyte, and separator (the separator of the example or the separator of the comparative example) obtained in a to c above, a laminated secondary battery with dimensions of 100 mm × 60 mm and a capacity of 3 Ah was fabricated and subjected to constant current constant voltage (CCCV) charging for 3 hours under conditions of a current value of 1 A (0.3 C) and a terminal battery voltage of 4.2 V.

[0282] e. Cyclic testing, thickness retention (%), and capacity retention (%)

[0283] (e1) Preprocessing

[0284] The battery prepared in step d above is charged at a constant current of 1 / 3C to a voltage of 4.2V, then charged at a constant voltage of 4.2V for 8 hours, and then discharged at a current of 1 / 3C to a final voltage of 3.0V. Next, it is charged at a constant current of 1C to a voltage of 4.2V, then charged at a constant voltage of 4.2V for 3 hours, and then discharged at a current of 1C to a final voltage of 3.0V. Finally, it is charged at a constant current of 1C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V for 3 hours. It should be noted that 1C represents the current value at which the battery's reference capacity is discharged for 1 hour.

[0285] (e2) Cyclic Test

[0286] For the battery that has undergone the above pretreatment (e1), it is discharged at a discharge current of 1C to a discharge termination voltage of 3V at a temperature of 25°C, and then charged at a charging current of 1C to a charging termination voltage of 4.2V. This is considered as one cycle and is repeatedly charged and discharged. The capacity retention rate after 1000 cycles relative to the initial capacity (capacity of the first cycle) is calculated as a percentage using the following formula.

[0287] Evaluation result (%) = 100 × (Retention capacity after 1000 cycles / Initial capacity)

[0288] In addition, the separator was removed from the battery after 100 cycles, and its thickness was measured according to the method described in the above item <film thickness (μm)>. The thickness retention rate of the separator after 100 cycles was calculated as a percentage using the following formula.

[0289] Evaluation result (%) = 100 × (thickness of the separator after 100 cycles / thickness of the separator measured in d. above)

[0290] It should be noted that the thickness of any 10 parts of the removed separator was measured, and the average value was used.

[0291] <Cyclic Test (%) Test Method 2>

[0292] (Battery manufacturing)

[0293] a. Production of the positive electrode

[0294] LiNi will be used as the positive electrode active material 1 / 3 Mn 1 / 3 Co 1 / 3O2, carbon black as a conductive additive, and polyvinylidene fluoride solution as a binder are mixed in a solid content mass ratio of 91:5:4. N-methyl-2-pyrrolidone is added as a dispersion solvent at 68% by mass of the solid content, and the mixture is further mixed to prepare a slurry-like solution. This slurry-like solution is coated onto both sides of a 15μm thick aluminum foil with a portion of the foil exposed. The solvent is then dried to remove the coating, resulting in a coating weight of 175g / m² per side. 2 Furthermore, the density of the positive electrode mixture is 2.8 g / cm³. 3 The positive electrode is obtained by calendering using a roller press and then cutting it with a coating area of ​​30mm × 50mm and including the exposed aluminum foil.

[0295] b. Negative electrode fabrication

[0296] Artificial graphite / silicon particles (Elkem, Sigrain e-Si 408) as the negative electrode active material were mixed in a 1:1 mass ratio, along with styrene-butadiene rubber and carboxymethyl cellulose aqueous solution as binders. The solid components were mixed at a mass ratio of negative electrode active material:styrene-butadiene rubber:carboxymethyl cellulose = 96.4:1.9:1.7. Water was added as a dispersion solvent at 50% mass of the solid components, and the mixture was further mixed to prepare a slurry-like solution. This slurry-like solution was then coated onto both sides of a 10 μm thick copper foil, with a portion of the copper foil exposed. The solvent was then dried to remove the coating, resulting in a coating weight of 86 g / m² per side. 2 Furthermore, the density of the negative electrode mixture is 1.45 g / cm³. 3 The negative electrode is obtained by rolling using a roller press and then cutting it with a coating area of ​​32mm × 52mm and including the exposed copper foil.

[0297] c. Manufacturing of non-aqueous electrolytes

[0298] LiPF6, as a solute, was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a concentration of 1:2 (volume ratio) to produce a non-aqueous electrolyte.

[0299] d. Battery assembly

[0300] By bending a 55mm wide separator between the positive and negative electrodes with their active materials facing each other, and sandwiching them between the positive and negative electrodes, a laminate containing 15 negative electrodes on both sides and 14 positive electrodes on both sides is formed. Aluminum leads with sealant are soldered to the exposed portions of the 14 positive electrode aluminum foils, and nickel leads with sealant are soldered to the exposed portions of the 15 negative electrode copper foils. The laminate is then inserted into an aluminum laminate housing. The exposed edge of the negative electrode lead and the other two edges are laminated and sealed, totaling three sides. Next, the aforementioned non-aqueous electrolyte is injected into the casing, and the opening is sealed to fabricate a 28-paired laminated battery. After the resulting battery is left at room temperature for one day, it is initially charged for a total of 8 hours at a constant voltage of 330mA (0.3C) under a 25°C atmosphere to a battery voltage of 4.2V, and then maintained at 4.2V. The battery is then discharged to a battery voltage of 3.0V at a current of 330mA (0.3C).

[0301] (Cyclic performance evaluation)

[0302] The battery obtained in "d. Battery Assembly" above was subjected to 1000 charge-discharge cycles at 25°C. For charging, the battery was charged to a constant voltage of 4.2V at a constant current of 1A (1.0C) and then maintained at 4.2V for a total of 3 hours. For discharging, the battery was discharged to a voltage of 3.0V at a current of 1A (1.0C). The capacity retention rate was calculated from the discharge capacity of the 1000th cycle and the discharge capacity of the 1st cycle. A high capacity retention rate indicates good cycle characteristics.

[0303] Evaluation result (%) = 100 × (Retention capacity after 1000 cycles / Initial capacity)

[0304] In addition, the separator was removed from the battery after 100 cycles, and its thickness was measured according to the method described in the above item <film thickness (μm)>. The thickness retention rate of the separator after 100 cycles was calculated as a percentage using the following formula.

[0305] Evaluation result (%) = 100 × (thickness of the separator after 100 cycles / thickness of the separator measured in d. above)

[0306] It should be noted that the thickness of any 10 parts of the removed separator was measured, and the average value was used.

[0307] <Polyethylene (PE) Raw Materials>

[0308] Prepare the polyethylene (PE) shown in Table 1.

[0309] <Using polypropylene (PP) raw materials>

[0310] Prepare the polypropylene (PP) shown in Table 2 or Table 3.

[0311] [Example 1]

[0312] PE1 powder and PP1 granules were fed into a screw extruder equipped with a manifold (T-die) with a die lip spacing of 1500 μm at the mass ratios listed in Table 4, according to feeding method (a), for melt mixing. During melt mixing, liquid paraffin (with a kinematic viscosity of 7.59 × 10⁻⁶ at 37.78 °C) was added. -5 m 2 The resin composition is further compounded by feeding it into a twin-screw extruder through an injection nozzle, and then extruded. At this point, liquid paraffin extruded from the twin-screw extruder is further injected through the extrusion center section (the middle feed port of the twin-screw extruder) at a mass ratio of 70% to the resin composition and a resin composition temperature of 220°C. Next, the extruded resin composition is extruded onto cooling rollers with a surface temperature controlled at 25°C for casting, thereby obtaining a sheet-like molded body.

[0313] Next, the sheet-shaped material is fed into a biaxial tenter frame for biaxial stretching to obtain the stretched material. The stretching conditions are as described in Table 4, with a stretch ratio of 55 times. Porosity, air permeability, and thickness are adjusted by appropriately adjusting the stretching temperature and heating air volume. It should be noted that the biaxial stretching temperature is set at 126℃.

[0314] The stretched material is then impregnated with dichloromethane, and liquid paraffin is extracted from the stretched material to form a microporous membrane.

[0315] Next, the microporous membrane was heat-set using a TD tenter frame at 129°C (HS), stretched to a TD stretch ratio of 2.0, and then relaxed to a TD stretch ratio of 0.9 (i.e., after stretching 2.0 times in the TD direction, it was relaxed to 1.8 times compared to before heat setting). The heat-treated microporous membrane was then evaluated as described above. Next, using the microporous membrane as a separator, the separator evaluation and battery evaluation were performed as described above. The evaluation results are shown in Table 4.

[0316] [Examples 2-20 and Comparative Examples 1-3]

[0317] As shown in Tables 4-6, the raw material composition, raw material input method, or stretching ratio of the stretching process were changed, but the microporous membrane was fabricated and evaluated using the same method as in Example 1. The evaluation results of the obtained microporous membrane, separator, and battery are shown in Tables 4-6.

[0318] [Table 1]

[0319]

[0320] [Table 2]

[0321]

[0322] [Table 3]

[0323]

[0324] [Table 4]

[0325]

[0326] [Table 5]

[0327]

[0328] [Table 6]

[0329]

[0330] (Explanation of abbreviations in Tables 4-6)

[0331] Raw material input method (a): PE and PP are fed into the extruder by different feeders.

[0332] Raw material input method (b): The dry mixture of PE and PP is fed into the extruder by a feeder.

[0333] Raw material input method (c): Multiple resin raw materials are obtained by dry mixing of PE and PP, and the obtained multiple resin raw materials are fed into the extruder by different feeders.

Claims

1. A method for manufacturing a separator for an energy storage device, comprising the following steps: (1) A sheet forming process in which polypropylene, polyethylene and plasticizer are extruded in sheet form using an extruder, cooled and solidified, and processed into sheet-shaped bodies. (2) A stretching process in which the sheet-shaped body is stretched at a magnification ratio of 20 times or more and 250 times or less to form a stretched article; (3) A microporous membrane forming process in which the plasticizer is extracted from the stretched material to form a microporous membrane; (4) A heat treatment process in which the microporous membrane is subjected to heat treatment, stretched in the width direction, and relaxed to obtain a heat-treated microporous membrane; and (5) The winding process of winding up the heat-treated microporous membrane. The polyethylene is in powder form, and the polypropylene is in granular form. The mass ratio of the polyethylene to the polypropylene is 99 / 1 to 60 / 40. The polyethylene has a weight-average molecular weight (Mw) of 100,000 to 9,700,000, and the ratio of its weight-average molecular weight (Mw) to its number-average molecular weight (Mn), i.e., Mw / Mn, is 3 to 10. The polypropylene has a weight-average molecular weight (Mw) of 300,000 to 2,000,000, and the ratio of its weight-average molecular weight (Mw) to its number-average molecular weight (Mn), i.e., Mw / Mn, is 3 to 12. The isotactic pentamematic fraction of the polypropylene is 85.0 mol% to 99.7 mol%.

2. The method for manufacturing a separator for an energy storage device according to claim 1, wherein, The polypropylene and the polyethylene are fed into the extruder by any one of the following methods (a) to (c): (a) A method of feeding the polypropylene and the polyethylene into the extruder using different feeders respectively; (b) A method of feeding the mixture of the polypropylene and the polyethylene into an extruder using a feeder; (c) A method of feeding multiple resin raw materials obtained by dry mixing the polypropylene and the polyethylene into an extruder using different feeders.

3. The method for manufacturing a separator for an energy storage device according to claim 1, wherein, The mass ratio of the polyethylene to the polypropylene is 97 / 3 to 70 / 30.

4. The method for manufacturing a separator for an energy storage device according to claim 1, wherein, The mass ratio of the polyethylene to the polypropylene is 95 / 5 to 85 / 15.

5. The method for manufacturing a separator for an energy storage device according to claim 1, wherein, The mass ratio of polyethylene to polypropylene is 93 / 7 to 90 / 10.

6. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 5, wherein, The weight-average molecular weight (Mw) of the polyethylene is 120,000 to 9,000,000.

7. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 6, wherein, The weight-average molecular weight (Mw) of the polyethylene is 200,000 to 8,500,000.

8. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 7, wherein, The weight-average molecular weight Mw of the polyethylene is 4 to 10 relative to the number-average molecular weight Mn.

9. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 8, wherein, The weight-average molecular weight Mw of the polyethylene is 5 to 10 relative to the number-average molecular weight Mn.

10. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 5, wherein, The weight-average molecular weight (Mw) of the polypropylene is 305,000 to 1,900,000.

11. A method for manufacturing a separator for an energy storage device according to any one of claims 3 to 5 and 10, wherein, The weight-average molecular weight (Mw) of the polypropylene is 310,000 to 1,800,000.

12. The method for manufacturing a separator for an energy storage device according to any one of claims 3-5 and 10-11, wherein, The weight-average molecular weight Mw of the polypropylene is 4 to 11 relative to the number-average molecular weight Mn.

13. A method for manufacturing a separator for an energy storage device according to any one of claims 3-5 and 10-12, wherein, The weight-average molecular weight Mw of the polypropylene is 4.5 to 10 relative to the number-average molecular weight Mn.

14. A method for manufacturing a separator for an energy storage device according to any one of claims 3-5 and 10-13, wherein, The isotactic pentamematic fraction of the polypropylene is 86.0 mol% to 99.6 mol%.

15. A method for manufacturing a separator for an energy storage device according to any one of claims 3-5 and 10-14, wherein, The isotactic pentamematic fraction of the polypropylene is 87.0 mol% to 99.5 mol%.

16. A separator for an energy storage device, manufactured by the manufacturing method according to any one of claims 1 to 15.

17. The separator for an energy storage device according to claim 16, wherein, The separator of the energy storage device contains a microporous membrane. The microporous membrane contains polyethylene and polypropylene. In the X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS) measurement of the microporous membrane, the crystallite size of the polyethylene is 15 nm to 40 nm, and the crystallite size of the polypropylene is 10 nm to 50 nm.

18. The separator for an energy storage device according to claim 17, wherein, In the X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS) measurements of the microporous membrane, the crystallite size of the polyethylene is 16 nm to 39 nm, and the crystallite size of the polypropylene is 11 nm to 49 nm.

19. The separator for an energy storage device according to claim 17, wherein, In the X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS) measurements of the microporous membrane, the crystallite size of the polyethylene is 20 nm to 38 nm, and the crystallite size of the polypropylene is 11 nm to 47 nm.

20. A battery comprising a separator for an energy storage device as described in any one of claims 16 to 19.

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