Separator for power storage device and method for manufacturing the same

Abstract

The present invention relates to a separator for an electrical storage device and a method for producing the same. The present invention provides a method for producing a separator for an electrical storage device, comprising contacting a porous body formed from a sheet-like molded body containing a silane-modified polyolefin with an alkaline solution or an acid solution, and a separator for an electrical storage device comprising a microporous membrane having a melt rupture temperature of 180°C to 220°C as measured by thermomechanical analysis (TMA).

Description

[0001] This application is a divisional application of an application filed on October 11, 2019, with application number 201980007241X and invention name “Separator for lithium-ion battery”. Technical Field

[0002] The present invention relates to a separator for a power storage device and a method for producing the same, and more particularly to a microporous membrane containing a modified polyolefin suitable for use as a separator for a lithium ion battery and a method for producing the same. Background Art

[0003] Microporous membranes are widely used as separation or selective permeation separation membranes and insulating materials for various substances. Examples of their use include microfiltration membranes, separators for fuel cells and capacitors, or substrates for functional membranes for filling functional materials into pores to exert new functions, separators for batteries, etc. Among them, polyolefin microporous membranes are suitable for use as separators for lithium-ion batteries widely used in notebook personal computers, mobile phones, digital cameras, etc. In order to ensure battery safety, separators are required to take into account both the activation of the shutdown function and the increase in the membrane rupture temperature. For example, Patent Document 1 describes the adjustment of the high-order physical properties of polyolefin resins, which are essential components of separators for lithium-ion batteries. In addition, as shown in Patent Document 2, it is known that in a specific crystallinity and gel fraction region, the performance of suppressing the heat release caused by the short circuit inside the battery by the shutdown function and on the other hand, even if a high-temperature portion is locally generated in the battery cell, the membrane will not rupture (breakdown at 170°C or above) will be achieved, thereby ensuring the safety of the battery. More specifically, regarding Patent Documents 1 and 2, it has been experimentally discovered that high-temperature membrane ruptibility can be exhibited by constructing a silane crosslinking portion (gel structure) in a polyolefin separator.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 9-216964

[0007] Patent Document 2: International Publication No. 97 / 44839

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 11-144700

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 11-172036

[0010] Patent Document 5: Japanese Patent Application Laid-Open No. 2001-176484

[0011] Patent Document 6: Japanese Patent Application Laid-Open No. 2000-319441

[0012] Patent Document 7: Japanese Patent Application Laid-Open No. 2017-203145

[0013] Patent Document 8: International Publication No. 2010 / 134585

[0014] Patent Document 9: Japanese Patent Application Laid-Open No. 2016-072150

[0015] Patent Document 10: Japanese Patent Application Laid-Open No. 2007-299612 Summary of the Invention

[0016] Problems to be solved by the invention

[0017] In recent years, the high output and high energy density of lithium-ion secondary batteries for use in mobile devices or vehicles are being developed. On the other hand, miniaturization of battery cells and stable cycle discharge and charge performance during long-term use are required. Therefore, as the separator used, a separator that is thin (for example, less than 15 μm) and has high quality (for example, with uniform physical properties and no resin agglomerates) is required. Furthermore, on the basis of the above performance, the level of battery safety is more stringent than before. As also described in Patent Documents 1 and 2, it is required to have a shutdown function and high-temperature film rupture properties, and it is expected that a resin composition and a manufacturing method for separators that can be stably produced will be developed. In this regard, as the level of the shutdown temperature, the lower the lower than 150°C, the better. In addition, as the level of the film rupture temperature, the higher the temperature, the better.

[0018] For example, the method described in patent document 3 is by using a cross-linking catalyst masterbatch during extrusion process, and the cross-linking reaction of silane-modified polyethylene is carried out in an extruder, but the generation of resin coagulants has also occurred, and the physical property uniformity of separator is reduced.For this method, the method described in patent document 4,5,6 is by arranging plasticizer extraction process, silane gel cross-linking process, or controls the gel fraction of resin film, or makes uncross-linked resin be formed by hot water and then dehydrated to deal with.In addition, patent document 7 proposes to provide a kind of heat-resistant resin microporous film, it is by regulating the gel fraction of polyolefin microporous film, storage modulus, the maximum shrinkage based on thermomechanical analysis (TMA) and the free radical amount measured by electron spin resonance method (ESR), so that low thermal shrinkage, low fluidity and resistance to melting are excellent.

[0019] Furthermore, for separators for power storage devices, from the perspectives of dimensional stability, maintaining the shutdown function, and increasing the membrane rupture temperature, a proposal has been made to dispose an inorganic porous layer comprising inorganic particles such as calcined kaolin and boehmite and a resin binder on at least one surface of a polyolefin microporous membrane (Patent Documents 8 and 9). Furthermore, for example, a separator has been proposed in which the thickness ratio of a layer A exhibiting shutdown characteristics to a layer B comprising an aramid resin and an inorganic material is adjusted within a predetermined range (Patent Document 10).

[0020] However, the method disclosed in Patent Document 4 does not allow for sufficient silane crosslinking reaction, making it difficult to achieve high-temperature film breakage resistance. The plasticizer extraction steps described in Patent Documents 3 and 4 utilize a tin(II)-based crosslinking catalyst, which allows for crosslinking reaction, but there is a risk of residual crosslinking catalyst.

[0021] The heat-resistant resin microporous membrane described in Patent Document 7 is obtained by simply coating a film made porous by a dry process with a photopolymerizable coating liquid. Furthermore, Example 5 of Patent Document 7 adds a low-molecular-weight silane coupling agent, such as γ-methacryloxypropyltrimethoxysilane, to the porous membrane. However, if a low-molecular-weight silane coupling agent were used in a wet-process porous formation method, it would be expected that the low-molecular-weight silane coupling agent would readily react with or bond to the plasticizer used for the porous formation, rather than bonding to the resin of the porous membrane.

[0022] In addition, the coating layer of patent documentation 7 is recorded because after the compound with polymerizable functional group is applied to resin porous film, it is formed by external stimulation with cross-linking reaction, therefore it is expected that the liquid immersion to a part of resin porous film will occur while coating the coating layer, after cross-linking reaction is carried out, it is expected that their mixed region will also be formed near the interface of the coating layer and the resin porous film.Thus, good TMA thermal shrinkage performance can be obtained, but the reduction of battery cycle characteristics caused by the blockage of resin porous film or the reduction of fuse (closure) performance produced by the melting phenomenon of resin porous film can be expected.And then, in the composite microporous film obtained by the method recorded in patent documentation 7, a small amount of free radical species compound is detected by ESR, due to residue, when composite microporous film is assembled into battery, free radical reaction is carried out with other components, particularly with electrolyte, it is expected that the chain reaction of decomposing electrolyte can be decomposed, and it is thought that battery performance can be significantly deteriorated.

[0023] Furthermore, batteries using separators such as those described in Patent Documents 3 to 7 exhibit poor cycle performance and, during long-term use, may induce unpredictable side reactions within the battery, potentially reducing battery safety. Furthermore, as noted above, silane crosslinking methods present challenges in achieving shutdown functionality and high-temperature membrane rupture resistance. Furthermore, the porous structure crucial for separators cannot be constructed solely using silane-grafted polyolefins, necessitating the development of resin mixture compositions.

[0024] Furthermore, the microporous membranes and separators recorded in patent documents 1, 2, and 7 lack research on inorganic porous layers comprising inorganic particles and resin binders in their surface configurations. The existing separators having an inorganic porous layer on a microporous membrane appear to have increased film breakage temperatures on the temperature-resistance curve of an electrical storage device. However, in reality, resin sometimes dissolves from the microporous membrane into the inorganic porous layer, so it is expected that the membrane as a whole of the separator will be reduced in weight and the resulting reduction in stress tolerance. Therefore, although the multilayer porous membranes recorded in patent documents 8 and 9 have a polyolefin microporous membrane and an inorganic porous layer, there is room for research in terms of both the low-temperature shutdown function and the high-temperature film breakage property of a separator for an electrical storage device or the cycle characteristics and battery nail puncture safety of an electrical storage device.

[0025] Furthermore, the separators for electricity storage devices described in Patent Documents 1, 2, and 10 still have room for improvement in terms of achieving improved performance of the electricity storage devices.

[0026] In view of the above problems, the present invention aims to provide a separator and a method for producing the separator that can achieve both shutdown function and high-temperature membrane rupture properties and improve the output, cycle characteristics and / or safety of a power storage device.

[0027] Solutions for solving problems

[0028] To address the above-mentioned issues, the present inventors conducted extensive research and discovered that the above-mentioned issues can be addressed by using a resin composition having a specific resin composition to complete the process of constructing a high-order structure of a microporous membrane, followed by a crosslinking reaction (gelation) under specific conditions. This led to the completion of the present invention. Specifically, the present invention is as follows. [1]

[0030] A method for manufacturing a separator for an electricity storage device, comprising the following steps:

[0031] (1) a sheet forming step, wherein the silane grafted modified polyolefin, polyethylene and plasticizer are extruded into a sheet by an extruder, cooled and solidified, and processed into a sheet-shaped body;

[0032] (2) a stretching step of biaxially stretching the sheet-like formed body at an area ratio of 20 to 250 times to form a stretched article;

[0033] (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body;

[0034] (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing the porous body in the width direction to obtain a heat-treated porous body;

[0035] (5) an affinity treatment step of immersing the heat-treated porous body in an organic solvent having amphiphilicity toward water and organic matter to increase the affinity of the heat-treated porous body with the liquid, thereby obtaining an affinity-treated porous body having the organic solvent impregnated therein;

[0036] (6) a cross-linking treatment step, wherein the affinity-treated porous body is contacted with a mixture containing an organic metal catalyst and water, or the affinity-treated porous body is immersed in an alkaline solution or an acid solution to carry out a silane dehydration condensation reaction to form oligosiloxane bonds, thereby obtaining a cross-linked porous body; and

[0037] (7) Water washing and drying step: the cross-linked porous body is washed with water and dried. [2]

[0039] The method for producing a separator for a power storage device according to item 1, wherein a mass ratio of the silane-grafted modified polyolefin to the polyethylene (mass of the silane-grafted modified polyolefin / mass of the polyethylene) is 0.05 / 0.95 to 0.40 / 0.60. [3]

[0041] The method for producing a separator for an electricity storage device according to item 1 or 2, wherein the separator for an electricity storage device comprises a microporous membrane having a melting and rupture temperature of 180° C. to 220° C. as measured by thermomechanical analysis (TMA). [4]

[0043] The method for producing a separator for a power storage device according to any one of items 1 to 3, wherein in the cross-linking treatment step, the affinity-treated porous body is immersed in the alkaline solution or the acid solution. [5]

[0045] According to the method for producing a separator for a power storage device according to item 4, in the cross-linking treatment step, the affinity-treated porous body is immersed in the alkaline solution. [6]

[0047] The method for producing a separator for a power storage device according to item 5, wherein the alkaline solution has a temperature of 20° C. to 100° C. and a pH of 8 to 14. [7]

[0049] According to the method for producing a separator for a power storage device according to item 4, in the cross-linking treatment step, the affinity-treated porous body is immersed in the acid solution. [8]

[0051] The method for producing a separator for a power storage device according to any one of items 1 to 7, wherein the metal of the organometallic catalyst is at least one selected from the group consisting of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, and lead. [9]

[0053] The method for producing a separator for an electrical storage device according to any one of items 1 to 8, wherein the content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, or lead in the separator for an electrical storage device is 0.10 ppm to 200 ppm in total amount on an atomic basis.

[10]

[0055] The method for producing a separator for a power storage device according to any one of items 1 to 9, wherein the silane-grafted modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst for cross-linking the silane-grafted modified polyolefin before the sheet forming step.

[11]

[0057] The method for producing a separator for a power storage device according to any one of items 1 to 10, wherein in the water washing and drying step, the cross-linked porous body is washed and dried with water at a temperature of 20 to 100° C. and a pH of 6 to 8.

[12]

[0059] A method for manufacturing an electricity storage device, comprising the following steps:

[0060] a step of laminating and / or winding a positive electrode, a separator for a storage device obtained by the method for producing a separator for a storage device according to any one of items 1 to 11, and a negative electrode to obtain a laminate or a wound body;

[0061] The step of placing the aforementioned laminate or wound body into an outer shell;

[0062] a step of injecting electrolyte into the outer shell; and

[0063] A step of connecting lead terminals to the positive electrode and the negative electrode.

[13]

[0065] The method for manufacturing an electricity storage device according to item 12, wherein the electrolyte solution contains an electrolyte containing LiPF6 or another lithium salt electrolyte containing fluorine (F).

[14]

[0067] A separator for an electricity storage device includes a microporous membrane containing silane-modified polyolefin and polyethylene, wherein the microporous membrane has a melting and rupture temperature of 180° C. to 220° C. as measured by thermomechanical analysis (TMA).

[15]

[0069] The separator for an electricity storage device according to item 14, wherein the separator contains 0.10 ppm to 200 ppm of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, or lead in a total amount in terms of atoms.

[16]

[0071] The separator for an electricity storage device according to item 14 or 15, wherein the separator contains zinc or tin in an atomically converted total amount of 0.10 ppm to 200 ppm.

[17]

[0073] The separator for an electricity storage device according to any one of items 14 to 16, comprising:

[0074] The aforementioned microporous membrane, and

[0075] An inorganic porous layer comprising inorganic particles and a resin binder is disposed on at least one surface of the microporous membrane.

[18]

[0077] Item 17. The separator for a power storage device, wherein the content of the inorganic particles in the inorganic porous layer is 5% by mass to 99% by mass.

[19]

[0079] The separator for a power storage device according to item 17 or 18, wherein the content of the silane-modified polyolefin in the microporous membrane is 0.5% by mass to 40% by mass.

[20]

[0081] The separator for an electrical storage device according to any one of items 17 to 19, wherein the inorganic particles are at least one selected from the group consisting of aluminum oxide (Al2O3), silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand and glass fiber. [twenty one]

[0083] The separator for a power storage device according to any one of items 17 to 20, wherein the resin binder has a glass transition temperature (Tg) of -50°C to 100°C. [twenty two]

[0085] A separator for a power storage device comprising a first porous layer (layer A) containing a silane-modified polyolefin and having a cross-linked structure and a second porous layer (layer B) containing inorganic particles.

[0086] The ratio (TA / TB) of the thickness (TA) of the layer A to the thickness (TB) of the layer B is 0.22 or more and 14 or less. [twenty three]

[0088] The separator for a power storage device according to item 22, wherein the film rupture temperature of the A layer measured by thermomechanical analysis (TMA) is 180° C. or higher and 220° C. or lower. [twenty four]

[0090] The separator for a power storage device according to item 22 or 23, wherein the total thickness (TA+TB) of the layer A and the layer B is 3.0 μm or more and 22 μm or less.

[25]

[0092] The separator for a power storage device according to any one of items 22 to 24, wherein the amount of the inorganic particles in the layer B is 20% by mass or more and 99.5% by mass or less based on the total amount of the layer B.

[26]

[0094] The separator for a power storage device according to any one of items 22 to 25, wherein the layer B contains a resin binder.

[27]

[0096] The separator for a power storage device according to any one of items 22 to 26, wherein the layer A further contains polyethylene as a polyolefin different from the silane-modified polyolefin.

[28]

[0098] The separator for a power storage device according to any one of items 22 to 27, wherein the amount of the silane-modified polyolefin in the layer A is 3% by mass or more based on the total amount of the layer A.

[29]

[0100] A separator for an electricity storage device having a shutdown temperature of 130° C. to 160° C. measured based on electrical resistance under a pressure of 10.0 MPa and a melting temperature of 200° C. or higher.

[30]

[0102] A method for producing a separator for an electricity storage device, which is the method for producing a separator for an electricity storage device according to any one of items 14 to 29, comprising the following steps:

[0103] (1) a sheet forming step, wherein the silane grafted modified polyolefin, polyethylene and plasticizer are extruded into a sheet by an extruder, cooled and solidified, and processed into a sheet-shaped body;

[0104] (2) a stretching step of biaxially stretching the sheet-like formed body at an area ratio of 20 to 250 times to form a stretched article;

[0105] (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body;

[0106] (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing the porous body in the width direction to obtain a heat-treated porous body;

[0107] (5) an affinity treatment step of immersing the heat-treated porous body in an organic solvent having amphiphilicity toward water and organic matter to increase the affinity of the heat-treated porous body with the liquid, thereby obtaining an affinity-treated porous body having the organic solvent impregnated therein;

[0108] (6) a cross-linking treatment step, wherein the affinity-treated porous body is contacted with a mixture containing an organic metal catalyst and water, or the affinity-treated porous body is immersed in an alkaline solution or an acid solution to carry out a silane dehydration condensation reaction to form oligosiloxane bonds, thereby obtaining a cross-linked porous body;

[0109] (7) a water washing and drying step of washing and drying the cross-linked porous body to obtain a microporous membrane comprising the silane-modified polyolefin; and

[0110] (8A) A coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the microporous membrane.

[31]

[0112] An electricity storage device comprising an electrode, the separator for an electricity storage device according to any one of items 14 to 29, and a non-aqueous electrolyte.

[0113] Effects of the Invention

[0114] According to the present invention, the shutdown function and high-temperature film rupture properties of a separator for a storage device can be taken into account, thereby improving the output, cycle characteristics and / or safety of the storage device, and / or suppressing the generation of unmelted resin agglomerates in the manufacturing process of the separator for the storage device, or ensuring high-temperature and high-pressure tolerance. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] Figure 1 This is a TMA chart of the separator obtained in Example I-1.

[0116] Figure 2 This is a graph showing heat generation during a nail penetration safety test of a battery using the separator obtained in Example I-1.

[0117] Figure 3 This is a graph showing the voltage drop during a nail penetration safety test of a battery using the separator obtained in Example I-1.

[0118] Figure 4 Silane-modified polyolefin raw material 1 obtained using polyolefin 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b).

[0119] Figure 5 Silane-modified polyolefin raw material 2 obtained using polyolefin 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b).

[0120] Figure 6 is used Figure 4 The separator made of the silane-modified polyolefin raw material 1 is in a state before cross-linking. 1 H-NMR spectrum (a) and 13 C-NMR spectrum (b). DETAILED DESCRIPTION

[0121] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0122] In this specification, "to" means that the numerical values ​​at both ends are included as the upper limit and lower limit. In addition, in this specification, the upper limit and lower limit of the numerical range can be combined arbitrarily. For example, the upper limit of a preferred numerical range can be combined with the lower limit of a more preferred numerical range, and conversely, the upper limit of a more preferred numerical range can be combined with the lower limit of the preferred numerical range.

[0123] It should be noted that, in this specification, the terms "on" and "formed on the surface of" do not limit the positional relationship of the components to "directly above." For example, the phrases "layer B formed on layer A" and "layer B formed on the surface of layer A" do not exclude the inclusion of any layer between layer A and layer B that does not belong to either layer.

[0124] The properties of only the microporous membrane described below can be measured after removing layers other than the microporous membrane (for example, an inorganic porous layer) from the separator for a power storage device.

[0125] <Separator for power storage device>

[0126] One embodiment of the present invention is a separator for a power storage device (hereinafter referred to as a "separator"). Since separators are required to have both insulation and ion permeability, they generally include insulating materials such as paper, polyolefin nonwoven fabrics, or resin microporous membranes having a porous structure. In particular, in lithium-ion batteries, polyolefin microporous membranes are preferred, as they provide a dense and uniform porous structure that is resistant to redox degradation and provides a separator.

[0127] Here, the microporous membrane refers to a membrane (thin film) formed of a porous body, and the average pore diameter thereof is preferably 10 nm to 500 nm, more preferably 30 nm to 100 nm.

[0128] When the power storage device includes a separator, the separator can be removed from the power storage device.

[0129] <First embodiment>

[0130] The separator of the first embodiment of the present invention comprises a microporous membrane having a melting and rupture temperature of 180°C to 220°C as measured by thermomechanical analysis (TMA), and the microporous membrane comprises a silane-modified polyolefin and a silane-unmodified polyethylene. From the perspective of high-temperature rupture resistance and the safety of the power storage device, the microporous membrane has a melting and rupture temperature of 180°C to 220°C, preferably 180°C to 200°C, when measured by thermomechanical analysis (TMA). Even if the power storage device is abnormally exothermic due to an unexpected runaway reaction, it is expected that the movement of ions and the discharge inside or outside the power storage device associated therewith will be stopped by the shutdown function of the separator. Then, it is expected that the power storage device as a whole will be cooled by a refrigerant to ensure safety. On the other hand, if the rupture temperature of the microporous membrane is within the above-mentioned numerical range, even if the power storage device as a whole is not fully cooled, and in the event of reaching an ultra-high temperature region, the separator can also melt and rupture, penetrate into the two electrodes, and coat the active material, thereby easily suppressing further heat release. The membrane rupture temperature of the microporous membrane can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0131] From the perspective of its manufacturing process and the perspective of ensuring safety by controlling the amorphous part of the microporous membrane, the separator of the first embodiment preferably controls the content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the range of not less than 0.10 ppm and not more than 200 ppm in terms of total atomic content, more preferably controls the content of zinc or tin in the range of not less than 0.10 ppm and not more than 200 ppm in terms of total atomic content, and further preferably controls it in the range of not less than 1 ppm and not more than 150 ppm.

[0132] The separator of the first embodiment can include: a microporous membrane; and an inorganic porous layer comprising inorganic particles and a resin binder, disposed on at least one surface of the microporous membrane, to achieve both low-temperature shutdown performance and high-temperature membrane rupture resistance, thereby improving the cycle characteristics and safety of the power storage device. The separator can be a composite of the microporous membrane as a substrate and the inorganic coating layer.

[0133] <Second embodiment>

[0134] The separator of the second embodiment of the present invention comprises a first porous layer (layer A) comprising a silane-modified polyolefin and having a cross-linked structure, and a second porous layer (layer B) comprising inorganic particles. Layers A and B are each a single layer or multiple layers. Layer B is formed only on one side of layer A or on both sides.

[0135] In LIBs, a representative example of a battery, lithium (Li) ions move back and forth between the positive and negative electrodes. Therefore, placing a separator consisting of layers A and B between the positive and negative electrodes allows for relatively high-speed movement of Li ions between the electrodes while preventing contact between them.

[0136] (Thickness ratio)

[0137] The A layer functions as a cross-linked microporous membrane, and the B layer functions as an inorganic porous layer formed on the microporous membrane.

[0138] Here, the ratio (TA / TB) of the thickness of layer A (TA) to the thickness of layer B (TB) is 0.22 or more and 14 or less. When the ratio (TA / TB) is 0.22 or more, the presence ratio of layer A in the separator can be sufficiently ensured, and the function of layer A can be exerted. On the other hand, when the ratio (TA / TB) is 14 or less, the presence ratio of layer B in the separator can be sufficiently ensured, and the function of layer B can be exerted.

[0139] By specifying the structures of layer A and layer B and setting their ratio (TA / TB) within the above range, a separator capable of improving the cycle characteristics and safety of a power storage device can be provided. Such a separator can be suitably used as a constituent material of LIBs for mobile device or vehicle applications, for example.

[0140] From the viewpoint of the above-mentioned effects, the ratio (TA / TB) is preferably 0.8 or more, more preferably 1.0 or more. On the other hand, the ratio (TA / TB) is preferably 5.5 or less, more preferably 3.2 or less.

[0141] The ratio (TA / TB) can be set to, for example, less than 2.5, less than 2.0, or less than 1.0. In this case, the thickness of layer A (TA) is less than 2.5 times the thickness of layer B (TB), or less than the thickness of layer B (TB), making it easy to reduce the thickness of layer A and even the separator.

[0142] The total thickness (TA + TB) of layer A and layer B is preferably 3.0 μm or more and 22 μm or less. If the total thickness (TA + TB) is 3.0 μm or more, the membrane strength of the separator tends to be improved. On the other hand, if the total thickness (TA + TB) is 22 μm or less, the ion permeability of the separator tends to be improved.

[0143] From the viewpoint of the above effects, the total thickness (TA+TB) is more preferably 3.5 μm or more, and further preferably 4.0 μm or more. On the other hand, the total thickness (TA+TB) is more preferably 20 μm or less, and further preferably 18 μm or less.

[0144] The total thickness (TA+TB) can be set to, for example, less than 11 μm, 10 μm or less, or 8 μm or less. Even such a thin separator can improve the cycle characteristics and safety of the power storage device within the scope of the present invention.

[0145] The ratio (TA / TB) and the total thickness (TA+TB) can be measured by the methods described in the Examples section, and can be controlled by adjusting the thickness (TA) and / or the thickness (TB). The A layer and the B layer will be described later.

[0146] (Shutdown temperature and melting temperature)

[0147] Regarding layer A, it is preferred that the shutdown temperature (sometimes called the melting temperature) measured based on resistance under a pressure of more than 0.1 MPa and less than 10.0 MPa (preferably under a pressure of 10 MPa) is 130°C to 160°C and the melting temperature (sometimes called the film rupture temperature) is more than 200°C.

[0148] If the shutdown temperature is 130°C or higher, unnecessary activation of the shutdown function during normal operation of the power storage device can be avoided, thereby ensuring sufficient output characteristics of the power storage device. On the other hand, if the shutdown temperature is 160°C or lower, the shutdown function can be appropriately activated during abnormal operation of the power storage device.

[0149] Furthermore, if the melting temperature is 200° C. or higher, abnormal reactions of the power storage device can be stopped before reaching an ultrahigh temperature region, and melt-breakage of the separator during abnormal reactions of the power storage device can be prevented.

[0150] Specifically, by ensuring that the shutdown temperature and melting temperature meet the above conditions, a separator can be provided that provides an electrical storage device with excellent heat resistance, closed-cell properties (shutdown function), and melt-break film properties (melting function), while also ensuring mechanical properties and ion permeability for the separator itself. Therefore, by providing a separator with shutdown and melting temperatures that meet the above conditions, the electrical storage device can achieve improved cycle characteristics and safety.

[0151] From the viewpoint of the above effects, the shutdown temperature is preferably higher than 130°C, more preferably 135°C or higher, and even more preferably 136°C or higher. On the other hand, the shutdown temperature is preferably 150°C or lower, more preferably 148°C or lower, and even more preferably 146°C or lower.

[0152] Likewise, from the viewpoint of the above-mentioned effects, the melting temperature is preferably 175°C or higher, more preferably 178°C or higher, and further preferably 180°C or higher. On the other hand, the melting temperature is preferably 230°C or lower, more preferably 225°C or lower, and further preferably 220°C or lower.

[0153] Even if the melting temperature cannot be accurately measured in a range exceeding 200°C, the above-mentioned condition of "melting temperature is 200°C or higher" is satisfied as long as the temperature is 200°C or higher.

[0154] The "shutdown temperature" and "melting temperature" in this specification refer to values ​​obtained by measuring resistance under the aforementioned pressure. Specifically, while applying the aforementioned pressure to a stack comprising a positive electrode, separator, and negative electrode, the temperature of the stack is increased, and the shutdown temperature and melting temperature are derived based on the resulting increase in AC resistance (AC resistance between the electrodes). In a second embodiment, the temperature at which the AC resistance first exceeds a predetermined reference value (e.g., 1000Ω) is set as the shutdown temperature, and the temperature at which the AC resistance, after further heating, drops below the aforementioned reference value (e.g., 1000Ω) is set as the melting temperature.

[0155] The stack can be pressurized using a hydraulic jack, but is not limited thereto, and known pressurizing means other than the hydraulic jack can be used. In addition, the stack can be heated using an aluminum heater, but is not limited thereto, and known heating means other than the aluminum heater can be used.

[0156] The shutdown temperature and the melting temperature can be measured by the method described in the Examples section, and can also be controlled by adjusting the composition of the A layer or the production method.

[0157] (Heat shrinkage at 150°C)

[0158] In layer A, the thermal shrinkage rate (T2) at 150°C after forming the crosslinked structure is preferably 0.02 times or more and 0.91 times or less of the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure. In other words, the ratio (T2 / T1) of the thermal shrinkage rate (T2) at 150°C after forming the crosslinked structure to the thermal shrinkage rate (T1) at 150°C before forming the crosslinked structure is preferably 0.02 or more and 0.91 or less. As the thermal shrinkage rate here, the larger value of the thermal shrinkage rate of layer A in the machine direction (MD) and the thermal shrinkage rate of layer A in the width direction (TD) is used.

[0159] Because layer A can form a cross-linked structure based on silane-modified polyolefin, it is possible to focus on the changes in its thermal shrinkage before and after cross-linking.

[0160] If the ratio (T2 / T1) is 0.02 or greater, the occurrence of short circuits can be effectively suppressed, thereby reliably preventing a temperature rise in the entire power storage device and the resulting smoke and, ultimately, fire. On the other hand, if the ratio (T2 / T1) is 0.91 or less, it can be determined that the crosslinking reaction in layer A has successfully and sufficiently progressed. In other words, if the ratio (T2 / T1) is within this range, a separator for a power storage device can be provided that improves the cycle characteristics and safety of the power storage device.

[0161] Therefore, from the viewpoint of the above-mentioned effects, the ratio (T2 / T1) is preferably 0.03 or more, more preferably 0.05 or more, and even more preferably 0.07 or more. On the other hand, the ratio (T2 / T1) is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.4 or less.

[0162] The thermal shrinkage ratio (T1) at 150° C. before forming a cross-linked structure is preferably 70% or less, more preferably 60% or less.

[0163] Furthermore, the thermal shrinkage (T2) at 150°C after forming a cross-linked structure is preferably 60% or less, more preferably 50% or less. Since the formation of a cross-linked structure tends to reduce the thermal shrinkage compared to before the formation of the cross-linked structure, the thermal shrinkage (T2) is generally smaller than the thermal shrinkage (T1).

[0164] The heat shrinkage at 150° C. can be measured by the method described in the Examples section, and can also be controlled by adjusting the structure of the A layer or the production method.

[0165] The separators of the first and second embodiments can be interchangeable or combined with each other. The separators of the first and second embodiments can include layers other than the microporous membrane and the inorganic porous layer as desired. The constituent elements of the separators of the first and second embodiments are described below.

[0166] [Microporous membrane]

[0167] The microporous membrane can be formed of polyolefin or modified polyolefin.

[0168] The microporous membrane contains silane-modified polyolefin and may contain other polyolefins as desired. Due to the silane crosslinking property of the silane-modified polyolefin, the microporous membrane can undergo a crosslinking reaction during the separator manufacturing process.

[0169] The polyolefin contained in the microporous membrane is not particularly limited, and for example, a homopolymer of ethylene or propylene or a copolymer formed by at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and norbornene can be listed. Among these, from the perspective of being able to perform heat setting (sometimes abbreviated as "HS") at a higher temperature without clogging the hole, high-density polyethylene (homopolymer) or low-density polyethylene, more preferably high-density polyethylene (homopolymer) can be used. It should be noted that the polyolefin can be used alone or in combination of two or more.

[0170] Microporous membranes are preferably manufactured using both silane-modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) as raw materials to achieve resistance to redox degradation and a dense, uniform porous structure. Ultra-high molecular weight polyethylene (UHMWPE) generally has a weight-average molecular weight of 1,000,000 or greater. More preferably, in the manufacture of microporous membranes or separators, the weight ratio of silane-modified polyolefin to UHMWPE (silane-modified polyolefin weight / UHMWPE weight) is 0.05 / 0.95 to 0.40 / 0.60.

[0171] The content of the polyolefin contained in the microporous membrane is preferably 50% by weight or more and 100% by weight or less, preferably 70% by weight or more and 100% by weight or less, preferably 80% by weight or more and 100% by weight or less. In addition, the microporous membrane preferably includes a polyolefin having a weight average molecular weight of 100,000 or more and less than 1,000,000 (relative to the polyolefin as a whole, preferably 40% by weight or more, more preferably 80% by weight or more). The weight average molecular weight of the polyolefin is more preferably 120,000 or more and less than 950,000, and further preferably 130,000 or more and less than 930,000. By using a polyolefin having a weight average molecular weight of 100,000 or more and less than 1,000,000, there is a tendency to easily maintain safety in the early stage of the relaxation of the shrinkage of the polymer in the heating test of the storage device, etc., especially in the heating safety test. By adjusting the weight-average molecular weight of the microporous membrane to less than 1,000,000, it is possible to suppress poor extrusion forming (film streaking) known as melt fracture. On the other hand, by adjusting the weight-average molecular weight of the microporous membrane to 100,000 or more, it is possible to suppress the transfer of depressions when the microporous membrane is wound on a core (winding core).

[0172] The viscosity average molecular weight of the microporous membrane when the inorganic porous layer is removed and the crosslinking treatment is not performed is preferably 100,000 to 1,200,000, more preferably 150,000 to 800,000, from the viewpoint of preventing the generation of polymer powder due to frictional shear during the roll conveyance of the separator.

[0173] The thickness of the microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, and further preferably 3.0 μm or more, 4.0 μm or more, or 4.5 μm or more. By making the thickness of the microporous membrane 1.0 μm or more, there is a tendency for the membrane strength to be further improved. In addition, the thickness of the microporous membrane is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less, 22 μm or less, or 19 μm or less. By making the thickness of the microporous membrane 500 μm or less, there is a tendency for the ion permeability to be further improved. The thickness of the microporous membrane can be measured by the method described in the Examples.

[0174] [First porous layer (layer A)]

[0175] Layer A comprises a silane-modified polyolefin and has a cross-linked structure. To ensure resistance to oxidation-reduction degradation and a dense and uniform porous structure, Layer A preferably further comprises polyethylene as a polyolefin different from the silane-modified polyolefin. It should be noted that Layer A may contain components other than the silane-modified polyolefin and polyethylene.

[0176] Examples of the polyolefin constituting the silane-modified polyolefin in layer A include homopolymers of ethylene or propylene; copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene. Among these polyolefins, ethylene homopolymers (polyethylene) are preferred, with high-density polyethylene and / or low-density polyethylene being more preferred, and high-density polyethylene being even more preferred, from the perspective of avoiding pore clogging and enabling heat setting at higher temperatures. One polyolefin may be used alone or in combination of two or more.

[0177] The layer A may contain a polymer (other polymer) that is neither silane-modified polyolefin nor polyethylene, within a range that does not excessively impair the effects of the present invention.

[0178] The weight average molecular weight of the entire A layer is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

[0179] (Thickness of layer A)

[0180] The thickness (TA) of layer A is preferably 1 μm or more, more preferably 2 μm or more, and further preferably 3 μm or more. If the thickness (TA) is 1 μm or more, there is a tendency for the membrane strength to be further improved. On the other hand, the thickness (TA) is preferably 500 μm or less, more preferably 100 μm or less, and further preferably 80 μm or less. If the thickness (TA) is 500 μm or less, there is a tendency for the ion permeability to be further improved. It should be noted that the thickness (TA) can be set to, for example, 1.00 μm or more, 2.00 μm or more, or 3.00 μm or more.

[0181] In the case where the separator is a LIB separator, the thickness (TA) is preferably less than 22 μm, more preferably less than 21 μm, and further preferably less than 20.5 μm. In the case where the separator is a LIB separator, the upper limit of the thickness (TA) can be set to less than 13 μm or less than 8.5 μm. If the thickness (TA) is less than 25 μm, there is a tendency for the permeability to be further improved. It should be noted that the thickness (TA) can be set to, for example, less than 22.00 μm, less than 21.00 μm, less than 20.00 μm, less than 13.00 μm or less than 8.50. The lower limit of the thickness (TA) can be the same as above.

[0182] The thickness (TA) can be measured by the method described in the Examples section, and can also be controlled by changing the stretching ratio of the A layer, for example.

[0183] When layer A is a single layer, the thickness of layer A is regarded as thickness (TA). When layer A is a multilayer, the total thickness of the multilayer A layer is regarded as thickness (TA).

[0184] The film rupture temperature of the A layer measured by thermomechanical analysis (TMA) is preferably 180°C or higher and 220°C or lower. Even if the storage device generates abnormal heat due to an unexpected runaway reaction, it is expected that the movement of Li ions and the accompanying discharge inside or outside the storage device will be stopped by the shutdown function of the separator. Then, it is expected that the entire storage device will be cooled by a refrigerant to ensure safety. On the other hand, by making the film rupture temperature of the A layer within the above range, even if the storage device as a whole is not sufficiently cooled, and even if it reaches an ultra-high temperature area, the separator can be melted and ruptured, infiltrating into the two electrodes to coat the active material, thereby easily suppressing further heat release.

[0185] The film rupture temperature of the layer A can be measured by the method described in the Examples section, and can also be controlled by changing the stretching temperature and / or stretching ratio of the layer A.

[0186] [Porosity of the microporous membrane or layer A]

[0187] The porosity of the microporous membrane or layer A is preferably 20% or more, more preferably 25% or more, and further preferably 28% or more, 30% or more, 32% or more, or 35% or more. If the porosity is 20% or more, there is a tendency for the ability to follow the rapid movement of Li ions to be further improved. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and further preferably 60% or less. If the porosity is 90% or less, there is a tendency for the membrane strength to be further improved and the self-discharge to be further suppressed. The porosity can be measured by the method described in the Examples column. In addition, it can be controlled by changing the stretching temperature and / or stretching ratio in the manufacturing process.

[0188] [Air permeability of microporous membrane or layer A]

[0189] The air permeability of the microporous membrane or layer A is preferably 1 second / 100 cm 3 More than 50 seconds / 100 cm 3 More than 55 seconds / 100 cm 3 More preferably, it is more than 70 seconds, more than 90 seconds or more than 110 seconds. If the air permeability is 1 second / 100cm 3 Above 400 sec / 100 cm, there is a tendency for the balance of film thickness, porosity and average pore size to be further improved. On the other hand, the air permeability is preferably 400 sec / 100 cm 3 Less than 300 seconds / 100cm, more preferably less than 300 seconds / 100cm 3, more preferably 270 seconds / 100cm 3 If the air permeability is 400 seconds / 100cm 3 The air permeability can be measured by the method described in the Examples section and can be controlled by changing the stretching temperature and / or stretching ratio during the production process.

[0190] [Puncture strength of microporous membrane or layer A]

[0191] The puncture strength of the microporous membrane or layer A is preferably 200 gf / 20 μm or more, more preferably 300 gf / 20 μm or more. If the puncture strength is 200 gf / 20 μm or more, even if the active material or the like falls off when the separator and the stack of electrodes are wound, it is easy to suppress the rupture of the membrane caused by the falling active material or the like. In addition, it is easy to reduce the possibility of short circuit due to the expansion and contraction of the electrode accompanying charge and discharge. On the other hand, the puncture strength is preferably 4000 gf / 20 μm or less, more preferably 3800 gf / 20 μm or less. If the puncture strength is 3500 gf / 20 μm or less, it is easy to reduce thermal shrinkage during heating. The puncture strength can be measured by the method described in the Example column. In addition, it can be controlled by changes in the stretching temperature and / or stretching ratio in the manufacturing process.

[0192] [Tensile strength of microporous membrane or layer A]

[0193] The tensile strength of the microporous membrane or layer A is preferably 1000 kgf / cm in both the MD (longitudinal direction of the membrane or layer A, machine direction or processing direction) and the TD (direction perpendicular to the MD, width direction of the membrane or layer A). 2 More preferably, 1050 kgf / cm 2 More than 1100 kgf / cm 2 By making the tensile strength 1000kgf / cm 2 As described above, there is a tendency that the breakage during slitting or winding of the power storage device is further suppressed, and short circuits caused by foreign matter in the power storage device are further suppressed. On the other hand, the tensile strength of the microporous membrane or the A layer is preferably 5000 kgf / cm 2 Below, more preferably 4500kgf / cm 2 Below, more preferably 4000kgf / cm 2 Below. If the tensile strength is 5000kgf / cm 2 Then, during the heating test, the microporous membrane or the A layer relaxes early and the shrinkage force decreases, resulting in a tendency for safety to improve.

[0194] [Tensile modulus of microporous membrane or layer A]

[0195] The tensile modulus of the microporous membrane or A layer is preferably less than 120N / cm in both directions of MD and TD, more preferably less than 100N / cm, and further preferably less than 90N / cm. The tensile modulus of 120N / cm or less indicates that the separator for lithium ion secondary battery is not extremely oriented. In a heating test, for example, when a blocking agent such as polyethylene melts and shrinks, stress relaxation occurs in the early polyethylene, thereby suppressing the shrinkage of the separator in the battery and easily preventing the short circuit between the electrodes (i.e., the safety of the separator during heating can be improved). This low tensile modulus is easily achieved by including polyethylene having a weight average molecular weight of less than 500,000 in the polyolefin forming the microporous membrane or A layer. On the other hand, the lower limit of the tensile modulus is preferably more than 10N / cm, more preferably more than 30N / cm, and further preferably more than 50N / cm. The tensile modulus can be appropriately adjusted by adjusting the degree of stretching in the manufacturing process or by relaxing after stretching as needed.

[0196] <Silane-modified polyolefin>

[0197] Silane-modified polyolefins have a structure in which the main chain is a polyolefin and alkoxysilyl groups are grafted onto the main chain. Silane-modified polyolefins can be obtained by grafting alkoxysilyl groups onto the main chain of a non-silane-modified polyolefin.

[0198] It is presumed that the alkoxysilyl groups undergo a hydrolysis reaction with water, converting to silanol groups and causing a cross-linking reaction to form siloxane bonds (see the following formula; the ratio of T1 structure, T2 structure, and T3 structure is arbitrary). Examples of alkoxides substituted with alkoxysilyl groups include methoxides, ethoxides, and butoxides. In the following formula, R includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl.

[0199]

[0200] The main chain and the grafts are connected by covalent bonds. Examples of the structures forming these covalent bonds include alkyl groups, ethers, glycols, and esters. Before the crosslinking reaction, the silane-modified polyolefin has a modification ratio of silanol units to the main chain ethylene units of less than 2%.

[0201] The preferred density of the silane grafted modified polyolefin is 0.90 to 0.96 g / cm 3 The melt flow rate (MFR) at 190° C. is 0.2 to 5 g / min.

[0202] The amount of the silane-modified polyolefin is preferably 0.5% by mass or more or 3% by mass or more, more preferably 4% by mass or more, and further preferably 5% by mass or more or 6% by mass or more, based on the total amount of the microporous membrane or layer A, from the perspective of achieving the effect of the present invention. From the perspective of the cyclability and safety of the power storage device, the amount of the silane-modified polyolefin is preferably 40% by mass or less, more preferably 38% by mass or less, based on the total amount of the microporous membrane. In addition, the amount of the silane-modified polyolefin can be set to 30% by mass or more or 50% by mass or more, and can further be set to 100% by mass, based on the total amount of layer A.

[0203] The cross-linked structure in the microporous membrane or layer A is preferably formed by acid, alkali, or swelling.

[0204] That is, it is preferred that the cross-linked structure in the microporous membrane or layer A is a cross-linked structure in which oligosiloxane bonds are formed by immersing the treated article comprising a silane-modified polyolefin in an alkali (alkaline solution) or an acid (acid solution) to carry out a silane dehydration condensation reaction. In this case, the cross-linked structure is a cross-linked structure obtained by actively promoting the cross-linking reaction during the manufacturing process of the microporous membrane, layer A, or separator.

[0205] (Polyethylene)

[0206] In this specification, the polyethylene that may be further contained in addition to the silane-modified polyolefin (polyethylene further contained in the microporous membrane or layer A in the form of a polyolefin different from the silane-modified polyolefin) refers to polyethylene that is a homopolymer having a weight-average molecular weight of 100,000 to 10,000,000 or a copolymer containing an alkane unit.

[0207] When the microporous membrane or layer A further contains polyethylene as a polyolefin different from the silane-modified polyolefin, the content thereof is preferably 20% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the total amount of the silane-modified polyolefin and the polyethylene. When the polyethylene content is 20% by mass or more, it tends to be easier to ensure resistance to oxidation-reduction degradation and to ensure a dense and uniform porous structure.

[0208] On the other hand, the polyethylene content is preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less. If the polyethylene content is 97% by mass or less, the content of the silane-modified polyolefin in the microporous membrane or layer A can be ensured.

[0209] (Detection method of silane-modified polyolefin contained in separator)

[0210] When the silane-modified polyolefin contained in the separator is cross-linked, it is insoluble or has insufficient solubility in organic solvents, making it difficult to directly measure the content of the silane-modified polyolefin from the separator. In this case, as a pretreatment of the sample, methyl orthoformate, which does not cause side reactions, is used to decompose the siloxane bonds into methoxysilanols, and then solution NMR measurement is performed to detect the silane-modified polyolefin contained in the separator. Pretreatment experiments can be carried out with reference to Japanese Patent Nos. 3529854 and 3529858.

[0211] Specifically, the method for detecting the silane-modified polyolefin contained in the separator can effectively utilize the silane-modified polyolefin as a raw material used in the production of the separator. 1 H or 13 C NMR identification. 1 H and 13 An example of a method for measuring C by NMR will be described.

[0212] ( 1 H NMR determination)

[0213] The sample was dissolved in o-dichlorobenzene-d4 at 140°C, and a 1H-NMR spectrum with a proton resonance frequency of 600 MHz was obtained. 1 The measurement conditions of H-NMR are as follows.

[0214] Device: AVANCE NEO 600 manufactured by Bruker

[0215] Sample tube diameter: 5mmφ

[0216] Solvent: o-dichlorobenzene-d4

[0217] Measurement temperature: 130°C

[0218] Pulse angle: 30°

[0219] Pulse waiting time: 1sec

[0220] Cumulative times: more than 1000 times

[0221] Sample concentration: 1wt / vol%

[0222] ( 13 C NMR determination)

[0223] The sample was dissolved in o-dichlorobenzene-d4 at 140°C to obtain 13 C-NMR spectrum. 13 The measurement conditions of C-NMR are as follows.

[0224] Device: AVANCE NEO 600 manufactured by Bruker

[0225] Sample tube diameter: 5mmφ

[0226] Solvent: o-dichlorobenzene-d4

[0227] Measurement temperature: 130°C

[0228] Pulse angle: 30°

[0229] Pulse waiting time: 5sec

[0230] Cumulative times: more than 10,000 times

[0231] Sample concentration: 10wt / vol%

[0232] Figure 4 and Figure 5 It uses 2 kinds of polyolefins, silane-modified polyolefin raw materials 1 and 2. 1 H and 13 C-NMR spectra, and raw materials 1 and 2 have different melt indexes (MI), C3 grafting amounts, C4 grafting amounts and / or silanol modification amounts.

[0233] Figure 4 of 1 H and 13 C-NMR measurement conditions are as follows.

[0234] ( 1 H-NMR measurement conditions)

[0235] Device: Bruker Avance NEO 600

[0236] Observation core: 1 H

[0237] Observation frequency: 600MHz

[0238] Pulse program: zg30

[0239] Pulse waiting time: 1sec

[0240] Cumulative times: 1024 times

[0241] Measurement temperature: 130°C Chemical shift standard: 7.219 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4

[0242] Sample concentration: 1wt / vol%

[0243] Sample tube: 5mmφ

[0244] ( 13 C-NMR measurement conditions)

[0245] Device: Bruker Avance NEO 600

[0246] Observation core: 13 C

[0247] Observation frequency: 150.91MHz

[0248] Pulse program: zgpg30

[0249] Pulse waiting time: 5sec

[0250] Accumulation times: 24,000 or 12,800 times Measurement temperature: 130°C Chemical shift standard: 132.39 ppm (o-DCBz) Solvent: o-dichlorobenzene-d4

[0251] Sample concentration: 10wt / vol%

[0252] Sample tube: 5mmφ

[0253] Figure 5 of 1 H and 13 C-NMR measurement conditions are as follows.

[0254] ( 1 H-NMR measurement conditions)

[0255] Device: Bruker Avance NEO 600

[0256] Observation core: 1 H

[0257] Observation frequency: 600MHz

[0258] Pulse program: zg30

[0259] Pulse waiting time: 1sec

[0260] Cumulative times: 1024 times

[0261] Measurement temperature: 130°C

[0262] Chemical shift reference: 7.219 ppm (o-DCBz)

[0263] Solvent: o-dichlorobenzene-d4

[0264] Sample concentration: 1wt / vol%

[0265] Sample tube: 5mmφ

[0266] ( 13 C-NMR measurement conditions)

[0267] Device: Bruker Avance NEO 600

[0268] Observation core: 13 C

[0269] Observation frequency: 150.91MHz

[0270] Pulse program: zgpg30

[0271] Pulse waiting time: 5sec

[0272] Cumulative times: 12800 times

[0273] Measurement temperature: 130°C

[0274] Chemical shift reference: 132.39 ppm (o-DCBz)

[0275] Solvent: o-dichlorobenzene-d4

[0276] Sample concentration: 10wt / vol%

[0277] Sample tube: 5mmφ

[0278] Figure 6 is used Figure 4 The separator made of the silane-modified polyolefin raw material 1 is in a state before cross-linking. 1 H and 13 C-NMR spectrum. Figure 6 of 1 H and 13 C-NMR measurement conditions are as follows.

[0279] ( 1 H-NMR measurement conditions)

[0280] Device: Bruker Avance NEO 600

[0281] Observation core: 1 H

[0282] Observation frequency: 600MHz

[0283] Pulse program: zg30

[0284] Pulse waiting time: 1sec

[0285] Cumulative times: 1024 times

[0286] Measurement temperature: 130°C

[0287] Chemical shift reference: 7.219 ppm (o-DCBz)

[0288] Solvent: o-dichlorobenzene-d4

[0289] Sample concentration: 1wt / vol%

[0290] Sample tube: 5mmφ

[0291] ( 13 C-NMR measurement conditions)

[0292] Device: Bruker Avance NEO 600

[0293] Observation core: 13 C

[0294] Observation frequency: 150.91MHz

[0295] Pulse program: zgpg30

[0296] Pulse waiting time: 5sec

[0297] Cumulative times: 24,000 or 12,800 times

[0298] Measurement temperature: 130°C

[0299] Chemical shift reference: 132.39 ppm (o-DCBz)

[0300] Solvent: o-dichlorobenzene-d4

[0301] Sample concentration: 10wt / vol%

[0302] Sample tube: 5mmφ

[0303] In addition, for the separator in the cross-linked state, after the pre-treatment described above, it can be Figure 6 The same NMR measurement was performed (not shown).

[0304] like Figures 4-6 As shown, through 1 H and / or 13 C NMR measurement can confirm the amount of silane units modified in the silane-modified polyolefin in the polyolefin raw material, the amount of alkyl modification of the polyolefin, etc., and can also identify the content of (-CH 2 -Si: 1 H, 0.69ppm, t; 13 C, 6.11ppm,s).

[0305] [Combination of Microporous Membrane and Inorganic Porous Layer]

[0306] The combination of a microporous membrane comprising a silane-modified polyolefin and an inorganic porous layer tends to achieve both shutdown performance at temperatures below 150°C and membrane rupture resistance at higher temperatures, while also improving the cycle characteristics and nail puncture safety of the battery. It is speculated that because the silane-modified polyolefin in the microporous membrane is silane-crosslinked, silane crosslinking sometimes increases the viscosity of the resin in the microporous membrane. Therefore, when a compressive force is applied between the multiple electrodes of the battery device including the separator at abnormally high temperatures, the crosslinked, high-viscosity resin is less likely to flow into the inorganic layer (i.e., integration is difficult), thereby ensuring sufficient gaps between the electrodes and suppressing battery short circuits.

[0307] [Inorganic porous layer]

[0308] The inorganic porous layer is a layer containing inorganic particles and a resin binder, and may further contain a dispersant for dispersing the inorganic particles in the binder resin, if desired.

[0309] The thickness of the inorganic porous layer is preferably 0.5 μm to 10 μm, 0.5 μm to 7 μm, 0.5 μm to 5 μm, or 0.5 μm to 4 μm from the perspective of ion permeability of the separator and charge / discharge capacity or cycle stability of the power storage device. The thickness of the inorganic porous layer can be determined by the method described in the Examples.

[0310] [Second porous layer (layer B)]

[0311] Layer B contains inorganic particles. Layer B may further contain a resin binder. In the case where layer B contains inorganic particles and a resin binder, layer B may be the inorganic porous layer described above. It should be noted that layer B may contain components other than the inorganic particles and the resin binder.

[0312] (Thickness of layer B)

[0313] The thickness (TB) of the B layer is preferably 0.2 μm or more, more preferably 0.5 μm or more. If the thickness (TB) is 0.5 μm or more, there is a tendency for the mechanical strength to be further improved. On the other hand, the thickness (TB) is preferably less than 22 μm, more preferably less than 20 μm, and further preferably less than 15 μm. If the thickness (TB) is 30 μm or less, the volume occupied by the separator in the power storage device is reduced, so there is a tendency to be advantageous in terms of high capacity of the power storage device. In addition, it is also preferred from the perspective of preventing the air permeability of the separator from increasing excessively. It should be noted that the thickness (TB) can be set to, for example, 0.50 μm or more, 0.80 μm or more, or 1.00 μm or more, and can also be set to less than 22.00 μm, less than 20.00 μm, or less than 15.00 μm.

[0314] The thickness (TB) can be measured by the method described in the Examples section, and can also be controlled by changing the amount of coating liquid (slurry) applied for forming the B layer.

[0315] When the B layer is a single layer, the thickness of the B layer is regarded as the above-mentioned “thickness (TB)”. When the B layer is a multi-layer layer, the total thickness of the multi-layer B layer is regarded as the above-mentioned “thickness (TB)”.

[0316] When the B layer is disposed on both one side and the other side of the A layer, the total thickness of the B layer disposed on the one side and the B layer disposed on the other side is regarded as the above-mentioned "thickness (TB)".

[0317] (Inorganic particles)

[0318] Examples of the inorganic particles include: inorganic oxides (oxide-based ceramics) such as aluminum oxide (Al2O3), silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; inorganic nitrides (nitride-based ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide (AlO(OH)), potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and quartz sand; and glass fibers. These may be used alone or in combination of two or more.

[0319] The amount of the inorganic particles is preferably 5% by mass or more, or 20% by mass or more, and more preferably 30% by mass or more, based on the total amount of the inorganic porous layer or layer B, from the perspective of ensuring heat resistance. The amount of the inorganic particles can be set to 50% by mass or more, more than 80% by mass, or 85% by mass or more, based on the total amount of the inorganic porous layer or layer B. On the other hand, the amount of the inorganic particles is preferably 99.9% by mass or less, and more preferably 99.5% by mass or less, or 99% by mass or less.

[0320] The amount of the inorganic particles can be set to, for example, 20.00 mass % or more, 30.00 mass % or more, 50.00 mass % or more, more than 80.00 mass % or 85.00 mass % or more, and can be set to 99.90 mass % or less or 99.50 mass % or less.

[0321] Examples of the shape of the inorganic particles include flakes, scales, needles, columns, spheres, polyhedrons, spindles, and blocks. A plurality of inorganic particles having these shapes may be used in combination.

[0322] The number average particle size of the inorganic particles is, for example, more than 0.01 μm, more than 0.1 μm or more than 0.3 μm, preferably more than 0.5 μm. On the other hand, the number average particle size is, for example, less than 10.0 μm, less than 9.0 μm or less than 6.0 μm, preferably less than 2.5 μm, more preferably less than 2.0 μm, and further preferably less than 1.5 μm. From the perspective of improving safety during short circuit, it is preferred that the number average particle size of the inorganic particles is adjusted to within the above range. As a method for adjusting the number average particle size of the inorganic particles, a method for crushing the inorganic particles using a suitable pulverizing device such as a ball mill, a bead mill, or a jet mill can be cited.

[0323] Regarding the particle size distribution of the inorganic particles, the minimum particle size is preferably 0.02 μm or more, more preferably 0.05 μm or more, and further preferably 0.1 μm or more. The maximum particle size is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 7 μm or less. In addition, the ratio of maximum particle size / average particle size is preferably 50 or less, more preferably 30 or less, and further preferably 20 or less. From the perspective of suppressing thermal shrinkage at high temperatures, it is preferred to adjust the particle size distribution of the inorganic particles to within the above range. In addition, there may be multiple particle size peaks between the maximum particle size and the minimum particle size. It should be noted that, as a method for adjusting the particle size distribution of the inorganic particles, for example, there can be listed: a method of crushing the inorganic filler using a ball mill, a bead mill, a jet mill, etc. and adjusting it to the desired particle size distribution, a method of mixing a plurality of fillers having multiple particle size distributions after preparing them, etc.

[0324] (resin binder)

[0325] The resin binder comprises a resin that binds the inorganic particles together. The glass transition temperature (Tg) of the resin binder is preferably -50°C to 100°C, more preferably -35°C to 95°C, from the perspective of ensuring adhesion to the inorganic particles and stability of the inorganic porous layer or layer B during the separator manufacturing process, the electricity storage device manufacturing process, or the charge and discharge process.

[0326] The glass transition temperature is determined based on the DSC curve obtained in differential scanning calorimetry (DSC). Specifically, the temperature of the intersection of the straight line obtained by extending the baseline of the low temperature side in the DSC curve to the high temperature side and the tangent line at the inflection point of the step-like change portion of the glass transition can be used as the glass transition temperature. In more detail, it can be determined according to the method described in the examples. In addition, "glass transition" refers to the heat change that occurs on the endothermic side in the DSC, accompanied by the change in state of the polymer as the test piece. This heat change is observed as a step-like change in the DSC curve. "Step-like change" means the portion of the DSC curve from the baseline of the previous low temperature side to the baseline moving to the new high temperature side. It should be noted that the combination of step-like change and peak is also included in the step-like change. Furthermore, "inflection point" means the point at which the slope of the DSC curve of the step-like change portion reaches the maximum. In addition, at the step-like change portion, when the upper side is the exothermic side, it can also be expressed as a point where the convex curve changes to a convex curve. The "peak" indicates the portion of the DSC curve from the time the curve leaves the baseline on the low temperature side to the time it returns to the baseline. The "baseline" indicates the DSC curve at the temperature region where the test piece does not undergo transformation or reaction.

[0327] Examples of the resin binder include the following 1) to 7) and these can be used alone or in combination of two or more.

[0328] 1) Polyolefins: such as polyethylene, polypropylene, ethylene propylene rubber and their modifications;

[0329] 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene copolymers and their hydrogenates, acrylonitrile-butadiene-styrene copolymers and their hydrogenates;

[0330] 3) Acrylic polymers: such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers;

[0331] 4) Polyvinyl alcohol resins: such as polyvinyl alcohol and polyvinyl acetate;

[0332] 5) Fluorine-containing resins: such as PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer;

[0333] 6) Cellulose derivatives: such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose and carboxymethyl cellulose; and

[0334] 7) Resins having a melting point and / or glass transition temperature of 180°C or higher or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide and polyester.

[0335] These types of resin binders can be obtained by using desired monomers as raw materials according to known production methods such as emulsion polymerization or solution polymerization. In the polymerization, the polymerization temperature, the pressure during polymerization, the method of adding monomers, and the additives used (polymerization initiator, molecular weight modifier, pH adjuster, etc.) are not limited.

[0336] The amount of the resin binder is, for example, 0.5% by mass or more or 1.0% by mass or more, based on the total amount of the inorganic porous layer or layer B, and is, for example, 50% by mass or less or 30% by mass or less. Furthermore, as described above, the resin binder is an optional component of layer B, and thus the amount of the resin binder contained in layer B can be set to less than 20% by mass, less than 15% by mass, or 0% by mass, based on the total amount of layer B. Reducing the amount of the resin binder contained in layer B allows for a corresponding increase in the amount of the inorganic particles contained in layer B.

[0337] (Dispersant)

[0338] Dispersant is a material that is adsorbed on the surface of inorganic particles in the slurry for forming the inorganic porous layer or the B layer, and that stabilizes the inorganic particles by electrostatic rebound, etc., and can be, for example, a polycarboxylate, a sulfonate, a polyoxyether, a surfactant, etc. In the inorganic porous layer or the B layer, in addition to the above-mentioned components, within the scope of its effect, it can usually further contain other components that are added in water-based coatings, etc. As this other component, there is no particular limitation, and for example, thickener, film-forming aid, plasticizer, cross-linking agent, antifreeze, defoamer, dye, preservative, ultraviolet absorber, light stabilizer, etc. can be listed. These other components can be used alone or in combination of two or more.

[0339] (additive)

[0340] The microporous membrane, inorganic porous layer, layer A, and / or layer B may contain known additives as needed. Examples of these additives include: organic metal catalysts (dehydration condensation catalysts); plasticizers; antioxidants such as phenolic, phosphorus, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; thickeners; film-forming aids; crosslinking agents; antifreeze agents; defoaming agents; preservatives; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; dyes; and coloring pigments.

[0341] Furthermore, layer B may contain a crosslinking agent. The crosslinking agent may contain a reactive group with the inorganic particles.

[0342] <Physical Properties of Separators>

[0343] When the separator is used in a higher capacity lithium-ion secondary battery, the overall thickness of the separator is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, further preferably 18 μm or less, and particularly preferably 16 μm or less. By making the separator film thickness 25 μm or less, there is a tendency for ion permeability to be further improved. The lower limit of the overall separator film thickness can be, for example, 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, 6.0 μm or more, or 7.5 μm or more.

[0344] The air permeability of the separator is preferably 50 seconds / 100 cm 3 ~400 seconds / 100cm 3 , more preferably 75 seconds / 100cm 3 ~275 seconds / 100cm 3 , more preferably 100 sec / 100 cm 3 ~200 seconds / 100cm 3 If the separator is 50 seconds / 100cm 3 If the air permeability is above 400 seconds / 100cm, it has appropriate mechanical strength. 3 An air permeability below 500 nm is preferred because it improves battery characteristics from the perspective of permeability.

[0345] <Electrical Storage Device>

[0346] The separator described above can be used in an electrical storage device. The electrical storage device comprises a separator of the first embodiment configured between a plurality of electrodes, and an electrolyte. The electrodes are, for example, a positive electrode, a negative electrode, etc., and the separator is preferably configured between the positive and negative electrodes. As electrical storage devices, specifically listed are: lithium batteries, 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-hydrogen batteries, nickel-cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, zinc-air batteries, etc. Among these, from the perspective of practicality, lithium batteries, lithium secondary batteries, lithium ion secondary batteries, nickel-hydrogen batteries or lithium ion capacitors are preferred, and lithium batteries or lithium ion secondary batteries are more preferred.

[0347] <Lithium-ion secondary battery>

[0348] A lithium-ion secondary battery is a storage battery that uses a lithium transition metal oxide such as lithium cobalt oxide or lithium cobalt composite oxide as the positive electrode, a carbon material such as graphite or black lead as the negative electrode, and an organic solvent containing a lithium salt such as LiPF6 as the electrolyte. The electrolyte described above regarding the method for manufacturing a separator can also be used in a lithium-ion secondary battery. During the charge and discharge of a lithium-ion secondary battery, ionized lithium moves back and forth between the electrodes. In addition, it is necessary to suppress contact between the electrodes while allowing the ionized lithium to move between the electrodes at a relatively high speed, so a separator is arranged between the electrodes.

[0349] <Method for Manufacturing Separator for Electricity Storage Device>

[0350] Another embodiment of the present invention is a method for manufacturing a separator for a power storage device. The separator manufacturing method may include, for example, a step for manufacturing a microporous membrane or layer A, and, if desired, a step for manufacturing an inorganic porous layer on the microporous membrane, or a step for manufacturing layer B on layer A. Unless otherwise specified, the materials used in the separator manufacturing method may be those described in the first or second embodiment.

[0351] <Third embodiment>

[0352] The method for producing a microporous membrane according to the third embodiment includes the following steps:

[0353] (1) Sheet forming process;

[0354] (2) stretching process;

[0355] (3) porous body forming step;

[0356] (4) Heat treatment process;

[0357] (5) Affinity treatment process;

[0358] (6) a cross-linking treatment step; and

[0359] (7) Water washing and drying process.

[0360] The above-described layer A can also be formed by performing steps (1) to (7). The method for producing a microporous membrane of the third embodiment may include a kneading step before the sheet forming step (1) and / or a winding step after the water washing and drying step (7) as desired.

[0361] The method for manufacturing the separator may further include the following steps in addition to steps (1) to (7) as desired:

[0362] (8A) A step of coating an inorganic porous layer on the silane-crosslinked microporous membrane. By coating the inorganic porous layer on the microporous membrane that has been silane-crosslinked in steps (1) to (7) in step (8A), the coating properties on the microporous membrane and the wettability of the microporous membrane tend to be improved during the separator manufacturing process.

[0363] [Mixing process]

[0364] The kneading step is a step of kneading the silane-grafted modified polyolefin with other polyolefins to obtain a kneaded product. Polyethylene and the silane-grafted modified polyolefin are preferably used in combination in the kneading step. The silane-grafted modified polyolefin, the silane-unmodified polyethylene, and other polyolefins may be those described in connection with the first embodiment. If desired, the silane-grafted modified polyolefin may be kneaded with a plasticizer in the kneading step.

[0365] In addition, the mixing process preferably uses a polyolefin composition comprising a polyolefin having a weight average molecular weight less than 1,000,000 (relative to the entire polyolefin, preferably with more than 40 mass %, more preferably with a ratio of more than 80 mass %). By using a polyolefin having a weight average molecular weight less than 1,000,000, there is a tendency to easily maintain safety in the heating test of an electrical storage device, particularly in a heating safety test, by relaxing the shrinkage of the polymer in the early stage. It should be noted that if the situation using a polyolefin having a weight average molecular weight less than 1,000,000 is compared with the situation using a polyolefin having a weight average molecular weight of more than 1,000,000, there is a tendency that the elastic modulus in the thickness direction of the obtained microporous film decreases, so the concave-convex microporous film of the easier transfer core can be obtained.

[0366] The polyolefin composition used in the kneading step may contain known additives such as a dehydration condensation catalyst, a plasticizer, metal soaps such as calcium stearate and zinc stearate, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, and a coloring pigment.

[0367] (Dehydration condensation catalyst)

[0368] Alkoxysilyl forms siloxane bond through the hydrolysis reaction based on water. However, because its reaction speed is slow, therefore in most cases using containing metal catalyst to promote condensation reaction. The metal containing metal catalyst can be at least one selected from the group consisting of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel and lead. About containing metal catalyst, it is known that these substances listed as dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate etc. are based on the reaction mechanism proposed by Weij et al. (FW van.der.Weij:Macromol.Chem., 181,2541,1980.) can overwhelmingly promote reaction speed, but in recent years, in order to avoid the health hazards to the environment and human body caused by organotin, it is known that by utilizing the Lewis function of the chelate complex of copper or titanium and combining with an organic base, the reaction of forming siloxane bond between alkoxysilyl groups can be promoted in the same way as organotin complex.

[0369] (Masterbatch resin)

[0370] It is known that dehydration condensation catalysts also function as catalysts for the siloxane bond formation reaction of alkoxysilyl-containing resins. In this specification, a material obtained by pre-adding a dehydration condensation catalyst (or an organometallic catalyst) to an alkoxysilyl-containing resin or other mixed resin in a continuous process including a resin kneading step using an extruder and mixing them is referred to as a masterbatch resin.

[0371] (Plasticizer)

[0372] The plasticizer is not particularly limited, and examples thereof include organic compounds that can form a homogeneous solution with polyolefin at a temperature below the boiling point. More specifically, examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Of these, paraffin oil and dioctyl phthalate are preferred. The plasticizer may be used alone or in combination of two or more.

[0373] The ratio of the plasticizer is preferably 20% by mass or more relative to the total mass of the polyolefin from the viewpoint of the porosity of the obtained microporous membrane, and is preferably 90% by mass or less from the viewpoint of the viscosity during melt kneading.

[0374] [Sheet forming process (extrusion process)]

[0375] The sheet forming step is a step of extruding the obtained kneaded product, or a mixture of silane-grafted modified polyolefin, polyethylene, and a plasticizer, cooling and solidifying it, and then forming it into a sheet to obtain a sheet. The sheet forming method is not particularly limited, and examples thereof include a method of solidifying the melted, kneaded, and extruded melt by compression cooling. Examples of cooling methods include: (i) direct contact with a cooling medium such as cold air or cooling water; (ii) contact with a roller or press cooled with a refrigerant, etc. Method (ii) is preferred in terms of excellent film thickness controllability.

[0376] From the perspective of resin agglomerates in the separator or the maximum internal heat release rate, in the sheet forming process, the weight ratio of silane grafted modified polyolefin to polyethylene (silane grafted modified polyolefin weight / polyethylene weight) is preferably 0.05 / 0.95 to 0.40 / 0.60, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0377] [Stretching process]

[0378] The stretching step is a step in which plasticizers and inorganic materials are extracted from the resulting sheet as needed, and the sheet is then stretched in one or more directions. Examples of sheet stretching methods include MD uniaxial stretching using a roll stretcher, TD uniaxial stretching using a tenter, sequential biaxial stretching using a roll stretcher and a tenter, or a combination of two tenters, and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. Simultaneous biaxial stretching is preferred to obtain a more uniform film.

[0379] The total face ratio is preferably more than 8 times, more preferably more than 15 times, further preferably more than 20 times or more than 30 times from the perspective of the balance of uniformity, tensile elongation and porosity of film thickness and average pore size. By making the total face ratio more than 8 times, there is a tendency to easily obtain a sheet with high strength and good thickness distribution. In addition, this face ratio can be less than 250 times from the perspective of preventing fracture etc.

[0380] [Porous Body Formation Step (Extraction Step)]

[0381] The porous body forming step is a step of extracting the plasticizer from the stretched product after the stretching step and making the stretched product porous.

[0382] There are no particular limitations on the method for extracting the plasticizer, and examples thereof include immersing the stretched article in an extraction solvent, spraying the stretched article with the extraction solvent, and the like. There are no particular limitations on the extraction solvent, and examples thereof include solvents that are poor solvents for polyolefins and good solvents for plasticizers and inorganic materials, and have a boiling point lower than the melting point of polyolefins. There are no particular limitations on such extraction solvents, and examples thereof include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropyl alcohol; ketones such as acetone and 2-butanone; and alkaline water. One extraction solvent may be used alone, or two or more may be used in combination.

[0383] [Heat treatment process]

[0384] The heat treatment step is a step in which, after the stretching step, a plasticizer is extracted from the sheet as needed, and heat treatment is performed to obtain a microporous membrane.

[0385] The method of heat treatment is not particularly limited, and examples thereof include heat setting methods such as stretching and relaxation operations using a stenter or roller stretching machine. The relaxation operation refers to a shrinking operation performed at a specified temperature and relaxation rate along the machine direction (MD) and / or width direction (TD) of the film. The relaxation rate refers to the value obtained by dividing the MD size of the film after the relaxation operation by the MD size of the film before the operation, or the value obtained by dividing the TD size of the film after the relaxation operation by the TD size of the film before the operation, or when both the MD and TD are relaxed, the value obtained by multiplying the relaxation rate of the MD by the relaxation rate of the TD.

[0386] In the present embodiment, from the viewpoint of obtaining a heat-treated porous body suitable for the affinity treatment step and the cross-linking treatment step, it is preferable to perform stretching and relaxation along the TD of the porous body.

[0387] [Affinity treatment process]

[0388] The affinity treatment step involves immersing the microporous membrane obtained in the heat treatment step in an organic solvent that is amphiphilic toward both water and organic matter to improve wettability between water and the polyolefin. In this embodiment, the amphiphilic organic solvent is disposed within the affinity-treated porous body, thereby increasing its affinity for liquids. For example, during the crosslinking treatment step, this may also increase its affinity for materials or catalysts that promote crosslinking reactions.

[0389] The organic solvent used is not particularly limited, and examples thereof include alcohols, acetone, ethylene carbonate, N-methyl-2-pyrrolidone, dimethyl sulfoxide, etc. In addition, the immersion method includes immersing the heat-treated porous body in the organic solvent, spraying the heat-treated porous body with the organic solvent, etc.

[0390] [Cross-linking treatment process]

[0391] The cross-linking treatment step is a step of reacting the alkoxysilyl groups contained in the microporous membrane obtained in the affinity treatment step to form siloxane bonds (cross-linking reaction).

[0392] In this embodiment, the affinity-treated porous body is brought into contact with a mixture containing an organometallic catalyst and water, or is immersed in an alkaline solution or an acid solution to cause a silane dehydration condensation reaction to form oligosiloxane bonds.

[0393] Conventional molded products, such as hot water pipes, use a Sn-based catalyst in the extruder during the extrusion process. However, in the manufacturing process for separators for power storage devices, if silane crosslinking is promoted within the extruder during the sheet forming process, gelation can lead to production defects and make it difficult to stretch the silane-crosslinked polyolefin in the subsequent stretching process. Therefore, in this embodiment, silane crosslinking is performed after the stretching, heat treatment, and affinity treatment steps. The silane crosslinking ensures the separator's heat resistance, shape retention, and film breakage resistance.

[0394] The metal of the organometallic catalyst may be, for example, at least one selected from the group consisting of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, and lead. Among these, tin, zinc, or palladium are preferred, and tin or zinc is more preferred. Examples of organotin complexes that can be used as catalysts include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, and stannous octoate.

[0395] The alkaline solution has a pH exceeding 7 and may contain, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, amine compounds, etc. Among these, from the perspectives of safety of the power storage device and silane crosslinking, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0396] The pH of the acid solution is less than 7, and it may contain, for example, an inorganic acid, an organic acid, etc. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0397] The cross-linking treatment step is preferably performed by immersing the affinity-treated porous body in an alkaline solution or an acidic solution from the viewpoint of suppressing a thermal runaway reaction during destruction of the power storage device and improving safety.

[0398] When the affinity-treated porous body is immersed in an alkaline solution, the temperature of the alkaline solution is preferably 20°C to 100°C, and / or the pH of the alkaline solution is preferably 8 to 14, from the perspective of further improving safety. The reagent used for pH adjustment is not particularly limited, and examples include alkali metal hydroxides and alkaline earth metal hydroxides. From the same perspective, the alkaline aqueous solution preferably does not contain amine compounds such as ethylamine, dibutylamine, hexylamine, and pyridine.

[0399] When the affinity-treated porous body is immersed in an acid solution, although not wishing to be bound by theory, it is presumed that the acid catalyzes the formation of Si—O bonds in the silane-crosslinked polyolefin rather than cleaving the Si—O bonds.

[0400] In the case of contacting the affinity-treated porous body with a mixture containing an organic metal catalyst and water, from the perspective of controlling the amorphous portion of the microporous membrane and ensuring safety, the content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the microporous membrane finally obtained is preferably adjusted to a range of 0.10 ppm or more and 200 ppm or less in terms of the total amount converted by atoms, and the content of zinc or tin in the microporous membrane is more preferably adjusted to a range of 0.10 ppm or more and 200 ppm or less in terms of the total amount converted by atoms. The content of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel or lead in the microporous membrane can be adjusted, for example, by a water washing and drying process described later. It was found that by containing metals in such a limited range, while suppressing the decomposition of the cross-linked structure of the porous membrane and ensuring safety, the battery cycle characteristics showed good performance. The present inventors have found that when an excessive amount of metal is contained in a separator for an electricity storage device, eluted ions penetrate into the positive electrode, changing the structure of the metal clusters storing Li, causing electrical defects in the entire positive electrode and deteriorating cycle performance.

[0401] [Washing and drying process]

[0402] The water washing and drying step is a step of washing and drying the microporous membrane obtained in the crosslinking treatment step. Preferred conditions for the water washing and drying step are a water temperature of 20 to 100°C and / or a pH of 6 to 8 in the washing water. For example, the microporous membrane can be dried after replacing the interior with water having a pH of 6 to 8 at a temperature of 20 to 100°C. The drying method is not particularly limited, and examples include conveying with heated rollers, blowing hot air, or heating and drying with an infrared heater.

[0403] [Inorganic porous layer coating step]

[0404] The inorganic porous layer coating step (8A) is a step of forming an inorganic porous layer comprising inorganic particles and a resin binder on at least one surface of the microporous membrane obtained above. The inorganic porous layer coating step (8A) can be performed after the silane crosslinking reaction of the silane-grafted modified polyolefin.

[0405] The above-described layer B can also be formed by performing the coating step (8A). As a method for forming the layer B, a known manufacturing method can be adopted. As a method for producing a laminate comprising the layer A and the layer B, for example, there can be cited: a method of applying a slurry containing inorganic particles to the layer A, a method of laminating and extruding the raw material of the layer B and the raw material of the layer A by co-extrusion, a method of laminating the layer A and the layer B after separately producing them, etc.

[0406] The inorganic porous layer can be formed, for example, by applying a slurry comprising inorganic particles, a resin binder, water or an aqueous solvent (e.g., a mixture of water and alcohol), and an optional dispersant to at least one surface of the microporous membrane. The inorganic particles, resin binder, and dispersant can be as described in the description of the first or second embodiment.

[0407] The solvent contained in the slurry is preferably one that can uniformly and stably disperse or dissolve the inorganic particles. Examples of such solvents include N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, dichloromethane, and hexane.

[0408] Examples of methods for preparing the slurry containing inorganic particles include mechanical stirring methods using a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roller mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a stirring blade.

[0409] Examples of the coating method for the slurry containing inorganic particles include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air knife coater method, blade coater method, rod coater method, extrusion coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0410] Methods for removing the solvent from the coating film include drying at a temperature below the melting point of the material constituting the microporous membrane, drying under reduced pressure at low temperature, etc. In addition, a portion of the solvent may remain as long as it does not significantly affect the device characteristics.

[0411] [Winding / Slitting Process]

[0412] The winding step is a step of slitting the obtained microporous membrane or the microporous membrane coated with the inorganic porous layer as needed and winding the resulting membrane around a predetermined core.

[0413] The separator obtained by the method including the various steps described above can be used in a power storage device, particularly a lithium battery or a lithium ion secondary battery.

[0414] <Method for Manufacturing Electricity Storage Device>

[0415] The method for manufacturing an electric storage device includes the following steps:

[0416] (I) a step of stacking and / or winding a positive electrode, a separator produced by the method of the third embodiment, and a negative electrode to obtain a stack or a wound body;

[0417] (II) a step of placing the laminate or wound body into an outer shell;

[0418] (III) a step of injecting an electrolyte into the outer shell; and

[0419] (IV) A step of connecting lead terminals to the positive electrode and the negative electrode.

[0420] Steps (I) to (IV) can be carried out by methods known in the art except for using a separator for a storage device manufactured by the method of the third embodiment. In addition, in steps (I) to (IV), positive electrodes, negative electrodes, electrolyte solutions, and outer shells known in the art can be used.

[0421] Based on step (I), a longitudinal separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be manufactured. Next, in step (I), the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator can be stacked in the order of positive electrode-separator-negative electrode-separator, and wound into a circular or flat spiral to obtain a wound body. In steps (II) and (III), the wound body is placed in a device can (such as a battery can) and further injected with a non-aqueous electrolyte to manufacture a power storage device. In addition, the power storage device can also be manufactured by placing the wound body made by folding the electrodes and separators into a device container (such as an aluminum film) and injecting a non-aqueous electrolyte.

[0422] At this time, the wound body may be pressed. Specifically, a separator and an electrode including a current collector and an active material layer formed on at least one surface of the current collector may be stacked and pressed.

[0423] Regarding the pressing temperature, as a temperature at which adhesion can be effectively exhibited, for example, it is preferably 20°C or higher. In addition, from the perspective of suppressing clogging or thermal shrinkage of the pores in the separator caused by hot pressing, the pressing temperature is preferably lower than the melting point of the material contained in the microporous membrane, and more preferably 120°C or lower. From the perspective of suppressing clogging of the pores in the separator, the pressing pressure is preferably 20 MPa or lower. Regarding the pressing time, when using roller pressing, it can be less than 1 second or several hours of surface pressure. From the perspective of productivity, it is preferably 2 hours or less.

[0424] The above-described manufacturing process can suppress the back pressure during the press-forming of the wound body composed of electrodes and separators, thereby suppressing the reduction in yield during the device assembly process and shortening the production process time, which is preferable.

[0425] The electrolyte used in step (III) may include fluorine (F)-containing lithium salts such as LiPF6, LiBF4, LiN(SO2CF3)2, LiSO3CF3, or electrolytes such as LiBC4O8(LiBOB), preferably an electrolyte containing LiPF6 or other F-containing electrolytes, and a non-aqueous solvent.

[0426] Example

[0427] The present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples unless it exceeds the scope of the present invention. It should be noted that the physical properties in the Examples were measured by the following methods.

[0428] <Weight Average Molecular Weight (Mw)>

[0429] Using ALC / GPC 150C (trademark) manufactured by Waters, standard polystyrene was measured under the following conditions to create a calibration curve. Chromatograms were also measured under the same conditions for each of the following polymers, and the weight average molecular weight of each polymer was calculated based on the calibration curve according to the following method.

[0430] Chromatography columns: 2 GMH6-HT (trademark) + 2 GMH6-HTL (trademark) manufactured by Tosoh Corporation

[0431] Mobile phase: o-dichlorobenzene

[0432] Detector: Differential refractometer

[0433] Flow rate: 1.0ml / min

[0434] Column temperature: 140°C

[0435] Sample concentration: 0.1wt%

[0436] (Weight average molecular weight of polyethylene)

[0437] The weight average molecular weight was calculated 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) to obtain a polyethylene-equivalent molecular weight distribution curve.

[0438] (Weight average molecular weight of resin composition)

[0439] The weight average molecular weight was calculated in the same manner as in the case of polyethylene, except that the Q factor value of the polyolefin having the largest mass fraction was used.

[0440] <Viscosity Average Molecular Weight (Mv)>

[0441] The intrinsic viscosity [η] at 135° C. in a decalin solvent was determined based on ASTM-D4020. The Mv of the polyethylene was calculated according to the following formula.

[0442] [η] = 6.77 × 10 -4 Mv 0.67

[0443] <Melt Flow Rate (MFR) (g / 10min)>

[0444] The weight of the resin extruded for 10 minutes at 190° C. and a load of 2.16 kg was determined as the MFR value using a melt flow rate meter (MELT INDEXER F-F01) manufactured by Toyo Seiki Co., Ltd.

[0445] <Determination of Glass Transition Temperature>

[0446] An appropriate amount of an aqueous dispersion containing a resin sample (solids content = 38-42 wt%, pH = 9.0) was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes to obtain a dry film. Approximately 17 mg of this dry film was placed in an aluminum container for measurement, and a DSC curve and a DSC curve were obtained under a nitrogen atmosphere using a DSC analyzer (Shimadzu Corporation, Model "DSC6220"). The measurement conditions are as follows.

[0447] The first heating program: Start from 70℃ and increase the temperature at a rate of 15℃ per minute. After reaching 110℃, maintain it for 5 minutes.

[0448] Second cooling program: Start from 110℃ and cool down at a rate of 40℃ per minute. After reaching -50℃, maintain for 5 minutes.

[0449] The third temperature increase program was to increase the temperature from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third temperature increase.

[0450] The intersection point of the baseline (a straight line obtained by extending the baseline in the DSC curve obtained to the high-temperature side) and the tangent line at the inflection point (the point where the upwardly convex curve changes to the downwardly convex curve) is taken as the glass transition temperature (Tg).

[0451] <Film thickness (μm)>

[0452] The film thickness of the microporous membrane or the separator is measured at room temperature of 23 ± 2°C and relative humidity of 60% using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, Ltd. Specifically, the film thickness at 5 points is measured at substantially equal intervals along the entire width in the TD direction, and their average value is obtained. The thickness of the inorganic porous layer can be calculated by subtracting the film thickness of the microporous membrane from the thickness of the separator composed of the microporous membrane and the inorganic porous layer.

[0453] <Thickness of layer A (TA) and thickness of layer B (TB)>

[0454] The thickness of layer A (TA) is measured at room temperature of 23 ± 2°C and relative humidity of 60% using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, Ltd. Specifically, the film thickness at 5 points is measured at substantially equal intervals along the entire width in the TD direction, and their average value is obtained. In addition, by the same method, the thickness of the laminate including layer A and layer B is obtained. Then, the thickness of layer B (TB) is obtained by subtracting the thickness of layer A (TA) from the thickness of the obtained laminate.

[0455] The thickness of the obtained laminate is regarded as the total thickness of layer A and layer B (TA + TB). In addition, by dividing the thickness (TA) by the thickness (TB), the thickness ratio (TA / TB) is obtained.

[0456] <Porosity (%)>

[0457] (i) Calculated based on the density of the mixed composition

[0458] A 10 cm × 10 cm square sample is cut from the microporous membrane, and its volume (cm 3 ) and mass (g) are obtained. Based on these and the density (g / cm 3 ), the porosity is calculated using the following formula. Note that the density of the mixed composition is the value calculated and obtained based on the respective densities and mixing ratios of the raw materials used.

[0459] Porosity (%) = (Volume - Mass / Density of mixed composition) / Volume × 100

[0460] (ii) Calculated based on the membrane density

[0461] Alternatively, the porosity of the microporous membrane is calculated from the volume, mass, and membrane density (g / cm 3 ) using the following formula.

[0462] Porosity (%) = (Volume - Mass / Film density) / Volume × 100

[0463] It should be noted that in the present invention, the film density refers to the value measured by the D) density gradient tube method described in JIS K7112 (1999).

[0464] (iii) Porosity of layer A

[0465] Cut a 10 cm × 10 cm square sample from layer A, and find its volume (cm 3 ) and mass (g). Based on these and density (g / cm 3 ), use the following formula to calculate the porosity. The density of the mixed composition is the value calculated and obtained based on the respective densities and mixing ratios of the raw materials used.

[0466] Porosity (%) = (Volume - Mass / Density of the mixed composition) / Volume × 100

[0467] <Air permeability (sec / 100 cm 3 )>

[0468] According to JIS P-8117 (2009), use a Gurley type air permeability tester, G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. to measure the air permeability of the sample or layer A.

[0469] <Puncture strength of layer A>

[0470] Use a portable compression tester KES-G5 (model) manufactured by KATO TECH Co., Ltd. to fix layer A with a sample holder having a diameter of 11.3 mm at the opening. Then, for the central part of the fixed layer A, use a needle with a tip curvature radius of 0.5 mm and perform a puncture test at a puncture speed of 2 mm / sec in an atmosphere of 25°C to measure the maximum puncture load. Convert this maximum puncture load to a value equivalent to a thickness of 20 μm, and use this value as the puncture strength (gf / 20 μm). In the case where the thermoplastic polymer is present only on one side of the substrate, the needle can be punctured from the side where the thermoplastic polymer is present.

[0471] <Quantification of resin condensates in the separator>

[0472] The resin condensates in the separator are defined as regions that are opaque and have an area of 100 μm in length × 100 μm in width or more when observing the separator obtained through the film-forming process of the following Examples and Comparative Examples using a transmission type optical microscope. In the observation based on the transmission type optical microscope, measure the number of resin condensates per 1000 m 2 of the separator area.

[0473] <TMA film breaking temperature>

[0474] Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, the environmental temperature was varied between 25 and 250 °C, and the temperature at the moment when the load was completely released was determined as the TMA film breaking temperature.

[0475] Specifically, when measuring the MD direction, a microporous film with a TD dimension of 3 mm and an MD dimension of 14 mm was taken. The two ends in the MD direction were clamped by a special probe, the distance between the clamps was set to 10 mm, an initial load of 1.0 g was applied, and the furnace carrying the test piece was heated. The temperature at which the load showed 0 g was taken as the TMA film breaking temperature.

[0476] When measuring the TD direction, a microporous film with a TD dimension of 14 mm and an MD dimension of 3 mm was taken. The two ends in the TD direction were clamped by a special probe, the distance between the clamps was set to 10 mm, an initial load of 1.0 g was applied, and the same operation as above was carried out.

[0477] <Film breaking temperature of layer A>

[0478] Using the constant length mode of TMA50 (trademark) manufactured by Shimadzu Corporation, the environmental temperature was varied between 25 and 250 °C, and the temperature at the moment when the load was completely released was determined as the TMA film breaking temperature (the film breaking temperature of layer A measured by TMA).

[0479] Specifically, TD 3 mm and MD 14 mm were taken from layer A and used as a specimen piece (a specimen piece with the MD as the long side). The two ends of the MD of the specimen piece were installed on a special probe with a clamp distance of 10 mm, and a load of 1.0 g was applied to the specimen piece. The furnace carrying the test piece was heated, and the temperature at which the load showed 0 g was taken as the film breaking temperature (°C).

[0480] It should be noted that when measuring the TD of a specimen piece with the TD as the long side, TD 14 mm and MD 3 mm were taken from layer A and used as a specimen piece. The two ends of the TD were clamped by a special probe, the distance between the clamps was set to 10 mm, an initial load of 1.0 g was applied, and the same operation as above was carried out.

[0481] <Thermal shrinkage rate at 150 °C>

[0482] TD 100 mm and MD 100 mm were taken from the laminate (laminate including layer A and layer B) before the crosslinked structure was formed and used as a specimen piece. Also, the specimen piece was left in an oven at 150 °C for 1 hour. At this time, the specimen piece was sandwiched between two pieces of paper so that hot air did not directly blow on the specimen piece. After the specimen piece was taken out of the oven and cooled, the area of the specimen piece was measured, and the thermal shrinkage rate (T1) at 150 °C before the crosslinked structure was formed was calculated according to the following formula.

[0483] Thermal shrinkage at 150°C (%) = (10,000 (mm 2 )-area of ​​the heated specimen (mm 2 ))×100 / 10,000

[0484] Furthermore, a sample piece having a TD of 100 mm and a MD of 100 mm was taken from the laminate after forming the crosslinked structure, and the same operation as above was performed to calculate the heat shrinkage (T2) at 150° C. after forming the crosslinked structure.

[0485] Then, the ratio (T2 / T1) is obtained by dividing the thermal shrinkage rate (T2) by the thermal shrinkage rate (T1). The value of this ratio (T2 / T1) corresponds to the change ratio of the thermal shrinkage rate (T2) at 150°C after the cross-linked structure is formed relative to the thermal shrinkage rate (T1) at 150°C before the cross-linked structure is formed.

[0486] <Battery destruction safety test 1>

[0487] Battery Destruction Safety Test 1 involves driving an iron nail through a battery charged to 4.5V at a speed of 20mm / sec, inducing an internal short circuit. This test measures the temporal behavior of the battery voltage drop and the resulting temperature rise in the battery, clarifying the phenomenon of an internal short circuit. Furthermore, due to insufficient separator shutdown function or membrane rupture at low temperatures during an internal short circuit, rapid heat release can occur in the battery, leading to electrolyte ignition, smoke generation, and / or explosion.

[0488] (Preparation of Batteries Used in Battery Destruction Safety Test 1)

[0489] 1a. Preparation of positive electrode

[0490] Take 92.2% by mass of lithium cobalt composite oxide LiCoO2 as the positive electrode active material, 2.3% by mass of flaky graphite and acetylene black as the conductive material, and 3.2% by mass of polyvinylidene fluoride (PVDF) as the resin binder, and disperse them in N-methylpyrrolidone (NMP) to prepare a slurry. The slurry is applied to one side of a 20 μm thick aluminum foil constituting the positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roller press. At this time, the coating amount of the positive electrode active material is adjusted to 250 g / m 2 , the active material volume density is adjusted to 3.00 g / cm 3 .

[0491] 1b. Preparation of negative electrode

[0492] 96.9% by mass of artificial graphite as the negative electrode active material, 1.4% by mass of carboxymethyl cellulose ammonium salt as the resin binder, and 1.7% by mass of styrene-butadiene copolymer latex as the resin binder were dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12μm thick copper foil constituting the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press. At this time, the amount of negative electrode active material applied was adjusted to 106 g / m 2 , the active material volume density is adjusted to 1.35 g / cm 3 .

[0493] 1c. Preparation of non-aqueous electrolyte

[0494] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0495] 1d.Battery Assembly

[0496] The separator was cut into 60 mm in the width (TD) direction and 1000 mm in the length (MD) direction, and the separator was folded repeatedly, and the positive electrode and the negative electrode (12 positive electrodes and 13 negative electrodes) were alternately stacked between the separators. It should be noted that the positive electrode used an area of ​​30 mm × 50 mm and the negative electrode used an area of ​​32 mm × 52 mm. After the repeatedly folded stack was placed in a laminated bag, the non-aqueous electrolyte obtained in the above c. was injected and sealed. After being placed at room temperature for 1 day, the battery voltage was charged to 4.2 V at a current value of 3 mA (0.5 C) in an atmosphere of 25°C. After reaching 4.2 V, the current value was reduced from 3 mA to maintain the voltage. This method was used for the initial charge after the battery was made for a total of 6 hours. Then, the battery voltage was discharged to 3.0 V at a current value of 3 mA (0.5 C).

[0497] (Maximum heat release rate)

[0498] After an iron nail was passed through the obtained battery, the battery surface temperature was measured for 300 seconds using a thermocouple based on a temperature change graph. The rate at which the temperature rise per 1 second was the largest was determined as the maximum heat release rate.

[0499] (Voltage drop time)

[0500] After an iron nail was passed through the obtained battery, the time required for the voltage to decrease from 4.5 V to 3 V was determined as the voltage drop time (time until the voltage dropped to 3 V).

[0501] <Evaluation of Cycle Characteristics and Method for Making a Battery>

[0502] Batteries for cycle characteristics evaluation were prepared in the same manner as in 1a. to 1c. of the battery preparation method used in the above item <Battery destruction safety test 1>, except that the assembly was performed according to 1d-2. below.

[0503] 1d-2. Battery assembly

[0504] The separator was cut into a circular shape with a diameter of 18 mm, and the positive and negative electrodes were cut into circular shapes with a diameter of 16 mm. The positive electrode, separator, and negative electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other. The cells were then placed in a stainless steel container with a lid. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode and the lid in contact with the aluminum foil of the positive electrode. The non-aqueous electrolyte solution obtained in 1c. of the above-mentioned "Battery Destruction Safety Test 1" was injected into the container and sealed. After standing at room temperature for one day, the cell was charged at a current of 3 mA (0.5 C) at 25°C until the cell voltage reached 4.2 V. After reaching 4.2 V, the current was gradually reduced from 3 mA to maintain the voltage. This method was used for the initial charge after battery production for a total of 6 hours. Next, the cell was discharged at a current of 3 mA (0.5 C) until the cell voltage reached 3.0 V.

[0505] The resulting battery was charged and discharged for 100 cycles in an atmosphere of 60°C. Charging was performed at a current of 6.0 mA (1.0 C) until the battery voltage reached 4.2 V. After reaching 4.2 V, the current was decreased from 6.0 mA to maintain the voltage at 4.2 V. This method of charging was continued for a total of 3 hours. Discharging was performed at a current of 6.0 mA (1.0 C) until the battery voltage reached 3.0 V.

[0506] (Cycle Characteristics Evaluation 1)

[0507] The capacity retention rate was calculated from the discharge capacity at the 100th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0508] (Cycle Characteristics Evaluation 2)

[0509] The capacity retention rate (%) was calculated based on the following formula from the discharge capacity at the 300th cycle and the discharge capacity at the 1st cycle: A high capacity retention rate was evaluated as having good cycle characteristics.

[0510] Evaluation result (%) = (100 × retention capacity after 300 cycles / discharge capacity at the first cycle)

[0511] <Fusing / Melting (F / MD) Characteristics>

[0512] (i) 0.5 MPa pressure and 2°C / min heating rate

[0513] The positive electrode, separator and negative electrode are cut into a circular shape with a diameter of 200mm and stacked, and a non-aqueous electrolyte is added to the resulting stack to penetrate the whole. The stack is clamped at the center of a circular aluminum heater with a diameter of 600mm, and the aluminum heater is pressurized to 0.5MPa from the top and bottom with a hydraulic jack to complete the preparation for the measurement. While heating the aforementioned stack with an aluminum heater at a heating rate of 2°C / min, the resistance (Ω) between the electrodes is measured. The temperature at which the separator is melted and the resistance between the electrodes rises and the resistance exceeds 1000Ω for the first time is taken as the shutdown temperature. In addition, heating is continued, and the temperature at which the resistance is reduced to below 1000Ω is taken as the melting temperature (membrane rupture temperature).

[0514] (ii) 10 MPa maximum pressure and 15°C / min heating rate

[0515] Cut the positive electrode, separator and negative electrode into a circular shape with a diameter of 200mm, add a non-aqueous electrolyte to the stacked laminate, and infiltrate it into the whole. Clamp the laminate at the center of a circular aluminum heater with a diameter of 600mm, and use a hydraulic jack to apply pressure to the aluminum heater from the top and bottom to 10MPa to complete the preparation for the measurement. While heating the laminate with an aluminum heater at a heating rate of 15°C / min, measure the resistance (Ω) between the electrodes. The temperature at which the resistance between the electrodes rises and the resistance exceeds 1000Ω for the first time is taken as the shutdown temperature (°C). In addition, continue heating and the temperature at which the resistance drops below 1000Ω is taken as the melting temperature (°C).

[0516] For both evaluations (i) and (ii), a resistance measuring wire was bonded to the back surface of the aluminum foil of the positive electrode produced in "1a. Preparation of Positive Electrode" in the above-mentioned section <Battery Destruction Safety Test 1> using a conductive silver paste. Furthermore, a resistance measuring wire was bonded to the back surface of the copper foil of the negative electrode produced in "1b. Preparation of Negative Electrode" in the above-mentioned section <Battery Destruction Safety Test 1> using a conductive silver paste. Furthermore, the electrolyte-containing solution prepared in "1c. Preparation of Non-aqueous Electrolyte Solution" in the above-mentioned section <Battery Destruction Safety Test 1> was also used in the F / MD characteristics test.

[0517] <Safety Test (Nail Penetration Test) 2>

[0518] 2a. Preparation of positive electrode

[0519] The positive electrode active material is nickel, manganese, cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (element ratio), density 4.70g / cm 3 ) 90.4 mass%, graphite powder (KS6) as a conductive additive (density 2.26 g / cm 3, number average particle size 6.5 μm) 1.6 mass% and acetylene black powder (AB) (density 1.95 g / cm 3 , number average particle size 48nm) 3.8% by mass, and PVDF (density 1.75g / cm 3 ) at a ratio of 4.2 mass % and dispersed in NMP to prepare a slurry. The slurry was applied to one side of a 20 μm thick aluminum foil constituting the positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to produce a positive electrode. At this time, the amount of positive electrode active material applied was 109 g / m 2 .

[0520] 2b. Preparation of negative electrode

[0521] Graphite powder A (density 2.23 g / cm 3 , number average particle size 12.7 μm) 87.6% by mass and graphite powder B (density 2.27 g / cm 3 , number average particle size 6.5μm) 9.7% by mass, and as a resin binder, 1.4% by mass (solid content conversion) of ammonium salt of carboxymethyl cellulose (solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass (solid content conversion) of diene rubber latex (solid content concentration 40% by mass aqueous solution) are dispersed in purified water to prepare a slurry. The slurry is applied to one side of a copper foil with a thickness of 12μm constituting the negative electrode collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roller press to produce a negative electrode. At this time, the amount of negative electrode active material applied is 52g / m 2 .

[0522] 2c. Preparation of non-aqueous electrolyte

[0523] A non-aqueous electrolyte was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0524] 2d. Battery production

[0525] Using the positive electrode, negative electrode, non-aqueous electrolyte, and separator (separator of the embodiment or separator of the comparative example) obtained in the above 2a to 2c, a laminated secondary battery with a size of 100 mm × 60 mm and a capacity of 3 Ah was prepared, which was charged by constant current constant voltage (CCCV) for 3 hours at a current value of 1 A (0.3 C) and a final battery voltage of 4.2 V.

[0526] 2e. Nail evaluation

[0527] The prepared laminated secondary battery was placed on an iron plate in a temperature-controlled explosion-proof chamber. The temperature in the chamber was set to 40°C. A 3.0mm diameter iron nail was driven through the center of the laminated secondary battery at a speed of 2mm / second, with the nail maintained. The temperature of a thermocouple installed inside the nail, designed to measure the internal temperature of the laminated secondary battery after penetration, was measured to assess the presence of ignition.

[0528] The evaluation was repeated using a laminated secondary battery newly produced by the same method, and the number of samples that did not ignite (non-ignition) was calculated as a % value according to the following formula.

[0529] Evaluation result (%) = (100 × number of samples without ignition / total number of samples)

[0530] <Extrusion stability>

[0531] During the extrusion process, the state of the extruded polyolefin composition was observed and evaluated according to the following criteria.

[0532] A (good): The variation in the extruder current value is within ±0.5 A when the average value is taken over 300 seconds.

[0533] B (bad): The current value of the extruder varies by more than ±0.5 A when averaged over 300 seconds.

[0534] <Metal Content>

[0535] The mass ratios of Sn atoms, Zn atoms, Ti atoms, Cu atoms, Fe atoms, Ni atoms, etc. contained in the sample were measured using an inductively coupled plasma (ICP) emission spectrometer.

[0536] <Experimental Group I>

[0537] [Method for producing silane-grafted polyolefin]

[0538] The raw material polyolefin used in silane-grafted polyolefin modification has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be an alpha-olefin copolymerized with propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the alpha-olefin polymer chain. Trimethoxyalkoxy-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the alpha-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, to simultaneously control the free radical concentration in the system, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit chain reactions (gelation) within the alpha-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then dried by heating at 80°C for two days to remove moisture and unreacted trimethoxyalkoxy-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxy-substituted vinylsilane in the pellets was approximately 10 to 1500 ppm.

[0539] The silane-grafted polyethylene obtained by the above-mentioned production method is represented as "silane-modified polyethylene (B)" in Tables 1 to 3.

[0540] [Film Production Example I]

[0541] (Sheet forming process)

[0542] To 79.2% by mass of polyethylene (polyethylene (A)) which is a homopolymer with a weight average molecular weight of 2,000,000, 19.8% by mass of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR of 0.4 g / min, obtained by modification reaction of a polyolefin with a viscosity average molecular weight of 20,000 with trimethoxyalkoxy-substituted vinylsilane as a raw material (the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), and 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) is injected into the extruder roller.

[0543] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 230° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[0544] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[0545] (Stretching process)

[0546] The gel sheet was then introduced into a simultaneous biaxial stretching machine for biaxial stretching to obtain a stretched product. The stretching conditions were set to 7.0 times in MD, 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[0547] (Porous Body Forming Step)

[0548] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[0549] (Heat treatment process)

[0550] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Thereafter, a relaxation operation of 0.5 times in the TD direction was performed (i.e., a HS relaxation ratio of 0.5 times).

[0551] (Affinity treatment process)

[0552] Furthermore, the heat-treated porous body was introduced into an ethanol bath (affinity treatment tank), immersed and allowed to remain there for 60 seconds to perform affinity treatment on the heat-treated porous body, thereby obtaining an affinity-treated porous body.

[0553] (Cross-linking treatment step)

[0554] Furthermore, the affinity-treated porous body was introduced into a 25% caustic soda aqueous solution (crosslinking treatment tank), immersed and allowed to remain there for 60 seconds to perform crosslinking treatment on the affinity-treated porous body, thereby obtaining a crosslinked porous body.

[0555] (Washing and drying process)

[0556] The crosslinked porous body was then introduced into water (water washing tank) and immersed therein for 60 seconds to wash the crosslinked porous body. The crosslinked porous body was then introduced into a conveyor dryer and dried at 120° C. for 60 seconds to obtain a microporous membrane.

[0557] Then, the end portion of the obtained microporous membrane was cut and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[0558] [Examples I-1 to I-11, Comparative Examples I-1 to I-4]

[0559] As shown in Tables 1 to 3, the same procedures as in Membrane Formation Example 1 were performed, except that the quantitative ratio of components A and B and the crosslinking method and conditions were changed, to obtain the microporous membranes shown in Tables 1 to 3. The obtained microporous membranes were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Tables 1 to 3.

[0560] For the separator obtained in Example I-1, a TMA map was prepared ( Figure 1 ), heat release diagram of battery nail penetration safety test ( Figure 2 ) and voltage drop diagram ( Figure 3 ).

[0561] [Table 1]

[0562]

[0563] [Table 2]

[0564]

[0565] [Table 3]

[0566]

[0567] The term "resin composition" in Tables 1 to 3 indicates the ratio relative to the total amount of the silane-graft-modified polyolefin and the polyethylene.

[0568] The term "method" in Tables 1 to 3 indicates the method of the silane crosslinking reaction, and is thus classified into methods based on alkali treatment, acid treatment, hot water treatment, or a dehydration condensation catalyst.

[0569] The term "time point of cross-linking reaction" in Tables 1 to 3 indicates at which step of the above-described (1) sheet forming step, (2) stretching step, (3) porous body forming step, (4) heat treatment step, (5) affinity treatment step, (6) cross-linking treatment step, and (7) water washing and drying step the silane cross-linking reaction is carried out.

[0570] In Example I-4, a 10% hydrochloric acid solution was used instead of a 25% caustic soda aqueous solution, and in Comparative Example I-2, a 2.5 kg / m 2 hydrochloric acid solution was used instead of immersing in a 25% caustic soda aqueous solution in the cross-linking treatment step in the film forming example. 2Furthermore, in Comparative Examples I-3 and I-4, the cross-linking reaction was carried out at the time points listed in Table 3, and the cross-linking treatment step was omitted.

[0571] In Example I-11, the water washing time was changed from 60 seconds to 10 minutes in the above-mentioned production example to adjust the amount of metal ions.

[0572] The term "reagent" in Tables 1 to 3 indicates a reagent used in the cross-linking treatment step in the film forming examples except for Comparative Examples I-3 and I-4.

[0573] The term "temperature" in Tables 1 to 3 indicates the temperature in the process described at the time point of the cross-linking reaction.

[0574] The terms "pH of the crosslinking treatment tank" and "pH of the water washing treatment tank" in Tables 1 to 3 indicate the pH in each tank. For example, "7 to 12" indicates that the pH has a wide distribution from near the tank inlet to near the tank outlet.

[0575] The “silane-modified polyethylene (B)” in Tables 1 to 3 has a density of 0.95 g / cm 3 A silane-modified polyethylene having a melt flow rate (MFR) at 190° C. of 0.4 g / min.

[0576] <Experimental Group II>

[0577] [Method for producing silane-grafted polyolefin]

[0578] The raw material polyolefin used in silane-grafted polyolefin modification has a viscosity-average molecular weight (Mv) of 100,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It can be a copolymerized alpha-olefin of propylene or butene. While the raw material polyethylene is melt-kneaded in an extruder, an organic peroxide (di-tert-butyl peroxide) is added to generate free radicals within the alpha-olefin polymer chain. Trimethoxyalkoxy-substituted vinylsilane is then injected to introduce alkoxysilyl groups into the alpha-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, to simultaneously control the free radical concentration in the system, an appropriate amount of an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit chain reactions (gelation) within the alpha-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then dried by heating at 80°C for two days to remove moisture and unreacted trimethoxyalkoxy-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxy-substituted vinylsilane in the pellets was approximately 10 to 1500 ppm.

[0579] The silane-grafted modified polyolefin obtained by the above-mentioned production method is shown as "Silane-modified polyethylene (B)" in Tables 1 to 3. It should be noted that the density of the silane-grafted modified polyolefin used this time is 0.94 g / cm 3 And the MFR is 0.65 g / min.

[0580] [Film Formation and Coating Example II]

[0581] (Formation of Microporous Membrane)

[0582] To 79.2% by weight of polyethylene (polyethylene (A)) which is a homopolymer with a weight average molecular weight of 500,000, 19.8% by weight of silane-grafted polyethylene (silane-modified polyethylene (B)) with an MFR (190°C) of 0.4 g / min, obtained by modification reaction of a polyolefin with a viscosity average molecular weight of 20,000 with trimethoxyalkoxy-substituted vinylsilane (the resin compositions of (A) and (B) are 80% and 20% respectively), and 1% by weight of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) is injected into the extruder roller.

[0583] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by weight of the extruded polyolefin composition (i.e., a polymer concentration of 30% by weight). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[0584] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[0585] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[0586] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[0587] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Then, a relaxation operation of 0.5 times in the TD direction (i.e., a HS relaxation ratio of 0.5 times) was performed to obtain a microporous membrane.

[0588] Then, the end portion of the obtained microporous membrane was cut and wound into a microporous membrane mother roll having a width of 1,100 mm and a length of 5,000 m.

[0589] (Method for producing acrylic latex)

[0590] The acrylic latex used as the resin binder can be produced as follows.

[0591] To a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer were added 70.4 parts by mass of ion-exchanged water, along with 0.5 parts by mass of "Aquaron KH1025" (registered trademark, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., a 25% aqueous solution) and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, manufactured by ADEKA Co., Ltd., a 25% aqueous solution) as emulsifiers. The temperature inside the reaction vessel was then raised to 80°C, and while maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to form an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes.

[0592] The emulsion was prepared by mixing the following for 5 minutes using a homomixer: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aquaron KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "ADEKA REASOAPSR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water.

[0593] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex having a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

[0594] (Formation of Inorganic Porous Layer)

[0595] 95 parts by weight of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by weight (based on solids) of an aqueous polycarboxylate ammonium solution (SN Dispersant 5468 manufactured by SAN NOPCO LIMITED, solids concentration 40%) as an ionic dispersant were uniformly dispersed in 100 parts by weight of water to prepare a dispersion. The resulting dispersion was crushed using a bead mill (200 cc tank volume, 0.1 mm diameter zirconium oxide beads, 80% filler) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To this dispersion with adjusted particle size distribution, 4.6 parts by weight (based on solids) of an acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, monomers: butyl acrylate, methyl methacrylate, methacrylic acid) as a resin binder were added to prepare a slurry containing the inorganic particles.

[0596] Next, the microporous membrane is continuously unwound from the above-mentioned microporous membrane mother roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coater. Then, the membrane is dried in a drier at 60°C to remove water, and wound up to obtain a separator mother roll.

[0597] During the evaluation, the separators unwound from the mother roll were cut as needed and used as separators for evaluation.

[0598] [Examples II-1 to II-2, Comparative Example II-2]

[0599] As shown in Tables 1 to 3, the same operations as in Membrane Formation and Coating Example II were performed except that the ratio of components A and B, the presence or composition of the inorganic layer, and the crosslinking method and conditions were changed to obtain microporous membranes shown in Tables 1 to 3.

[0600] It should be noted that in Example II-1, the microporous membrane was introduced into a 25% caustic soda aqueous solution (temperature 80°C, pH 8.5-14), and in Example II-2, the microporous membrane was introduced into a 10% hydrochloric acid aqueous solution (temperature 60°C, pH 1-6.5), and the membrane was immersed and allowed to remain there for 60 seconds to form an inorganic porous layer after cross-linking treatment of the microporous membrane.

[0601] [Comparative Example II-1]

[0602] To 79.2% by weight of polyethylene (polyethylene (A)) which is a homopolymer with a weight average molecular weight of 500,000, 19.8% by weight of silane-grafted polyethylene (silane-modified polyethylene (B)) having an MFR (190°C) of 0.4 g / min, obtained by modification reaction of a polyolefin with a viscosity average molecular weight of 20,000 with a trimethoxyalkoxy-substituted vinylsilane (the resin compositions of (A) and (B) are 80% and 20%, respectively), and 1% by weight of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant were added and dry-blended using a drum mixer to obtain a mixture. The obtained mixture was supplied to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) is injected into the extruder roller.

[0603] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by weight of the extruded polyolefin composition (i.e., a polymer concentration of 30% by weight). The melt-kneading conditions were a set temperature of 220° C., a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[0604] Next, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25° C. and cast, thereby obtaining a gel sheet (sheet-like molded product) having a green film thickness of 1400 μm.

[0605] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were set to 7.0 times in MD and 6.0 times in TD (i.e., 7×6 times), and a biaxial stretching temperature of 125°C.

[0606] Next, the stretched gel sheet was introduced into a methyl ethyl ketone bath, fully immersed in methyl ethyl ketone to extract and remove the liquid paraffin, and then dried to remove the methyl ethyl ketone, thereby obtaining a porous body.

[0607] Next, the porous body was introduced into a TD stenter for heat setting (HS), and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8. Thereafter, a relaxation operation of 0.5 times in the TD direction was performed (i.e., a HS relaxation ratio of 0.5 times).

[0608] In Comparative Example 1, in order to use the heat-treated porous body as a separator, the obtained porous body was cut at the end and wound into a mother roll having a width of 1,100 mm and a length of 5,000 m.

[0609] Subsequently, the heat-treated porous body obtained above is guided into an ethanol bath (affinity treatment tank), immersed and left for 60 seconds to perform affinity treatment on the heat-treated porous body, thereby obtaining an affinity-treated porous body.

[0610] Subsequently, the affinity-treated porous body is guided into a 25% aqueous sodium hydroxide solution (temperature: 80 °C, pH: 8.5 - 14), immersed and left for 60 seconds to perform crosslinking treatment on the affinity-treated porous body, thereby obtaining a crosslinked porous body.

[0611] Subsequently, the crosslinked porous body is guided into water (water washing treatment tank), immersed and left for 60 seconds to wash the crosslinked porous body. Then it is guided into a conveyor dryer and dried under the conditions of 120 °C for 60 seconds to obtain a microporous membrane.

[0612] Then, for the obtained microporous membrane, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[0613] For Comparative Example II-1, during the above evaluation, the microporous membrane unwound from the master roll is slit as needed and used as a separator for evaluation.

[0614] [Evaluation Results]

[0615] For the microporous membranes and batteries obtained in Examples II-1 to II-2 and Comparative Examples II-1 to II-2, various evaluations are carried out in accordance with the above evaluation method, and the evaluation results are also shown in Table 4.

[0616] [Table 4]

[0617]

[0618] [Experimental Group III]

[0619] [Example III-1]

[0620] [Fabrication of A Layer]

[0621] [Fabrication of Silane-Grafted Modified Polyolefin]

[0622] Using polyethylene with a viscosity-average molecular weight of 100,000 as the raw material, an organic peroxide (di-tert-butyl peroxide) is added while melt-kneading the raw polyethylene in an extruder. This generates free radicals within the α-olefin polymer chain, and then trimethoxyalkoxy-substituted vinyl silane is injected. Alkoxysilyl groups are introduced into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. Furthermore, to simultaneously control the free radical concentration in the reaction system, an antioxidant (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added in appropriate amounts to inhibit chain reactions (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin is cooled in water, pelletized, and then heat-dried at 80°C for two days to remove moisture and unreacted trimethoxyalkoxy-substituted vinyl silane. The residual concentration of unreacted trimethoxyalkoxy-substituted vinyl silane in the pellets is approximately 1500 ppm or less.

[0623] By the modification reaction using the trimethoxyalkoxy-substituted vinylsilane as described above, a silane-modified polyethylene having an MFR (190° C.) of 0.4 g / min was obtained.

[0624] (Production of Layer A)

[0625] 35% by mass of the silane-modified polyethylene obtained above was blended with 65% by mass of polyethylene having a weight-average molecular weight of 700,000 homopolymer to form a resin compound. 1% by mass of pentaerythritol-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to the compound, and dry blending was performed using a drum mixer to obtain a mixture. The obtained mixture was fed to a twin-screw extruder from a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C: 7.59×10 -5 m 2 / s) is injected into the extruder roller.

[0626] The mixture and liquid paraffin were melt-kneaded in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., a polymer concentration of 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw speed of 240 rpm, and a discharge rate of 18 kg / hour. The melt-kneaded product was then extruded through a T-die onto a chill roll whose surface temperature was controlled at 25°C and cast, thereby obtaining a gel sheet (sheet-like molded body) having a film thickness of 1400 μm.

[0627] The sheet-like molded body was then introduced into a simultaneous biaxial stretching machine for biaxial stretching to obtain a stretched product. The stretching conditions were set to MD ratio 7.0 times, TD ratio 6.0 times (i.e., 7×6 times), and biaxial stretching temperature 123°C.

[0628] Next, the stretched gel sheet is guided to a methylene chloride bath, fully impregnated in methylene chloride to extract and remove liquid paraffin, and then dried to remove methylene chloride, obtaining a porous body.

[0629] Next, in order to perform heat setting (HS), the porous body is guided to a TD tentering machine, and heat setting and relaxation operations are performed. The heat setting conditions input to the TD tentering machine are to perform HS at a heat setting temperature of 132 °C and a draw ratio of 2.1 times, and then, perform a relaxation operation to 1.9 times of TD, obtaining a microporous membrane.

[0630] Then, for the obtained microporous membrane, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[0631] At the time of the above evaluation, the microporous membrane unwound from the master roll is slit as needed and used as the evaluation A layer.

[0632] For the obtained evaluation A layer, the film thickness, air permeability, porosity, etc. are measured and shown in Table 5.

[0633] <Fabrication of B layer>[

[0634] 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (in terms of solid content) of an ammonium polycarboxylate aqueous solution (SNDispersant 5468 manufactured by SAN NOPCO LIMITED, solid content concentration 40%) as an ionic dispersant are uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion is subjected to a crushing treatment using a bead mill (tank volume 200 cc, zirconia beads with a diameter of 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D₅₀ = 1.0 μm, and a slurry containing inorganic particles is produced.

[0635] Next, the microporous membrane is continuously unwound from the above microporous membrane master roll, and the slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coater, and then dried using a dryer at 60 °C to remove water, and wound up, obtaining a master roll of the separator.

[0636] At the time of evaluation, the separator unwound from the master roll is slit as needed and used as the evaluation separator.

[0637] [Examples III-2 to III-14 and Comparative Examples III-1 to III-2]

[0638] Taking the physical property values recorded in Table 5 as the target, the weight average molecular weight of the polyethylene of the homopolymer is changed, and at least any one of the draw conditions, heat setting conditions, and relaxation operation conditions is set. In addition, the composition of the B layer is changed as shown in the record of Table 5.

[0639] In addition to these changes, a separator was produced by the same method as in Example III-1, and the above evaluation was carried out using the obtained separator. The evaluation results are shown in Table 5.

[0640] [Table 5]

[0641]

[0642] <Experimental Group IV>

[0643] [Example IV-1]

[0644] <Production of Layer A>

[0645] (Production of Silane-Grafted Modified Polyolefin)

[0646] Using polyethylene with a viscosity-average molecular weight of 100,000 as the raw material polyethylene, while melt-kneading the raw material polyethylene with an extruder, an organic peroxide (di-tert-butyl peroxide) was added. After generating free radicals in the polymer chain of the α-olefin, trimethoxyalkoxysubstituted vinylsilane was injected, and an alkoxysilyl group was introduced into the α-olefin polymer through an addition reaction to form a silane-grafted structure. In addition, in order to simultaneously adjust the concentration of free radicals in the reaction system, an antioxidant (pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) was added in an appropriate amount to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin was cooled in water, granulated, and then heated and dried at 80°C for 2 days to remove moisture or unreacted trimethoxyalkoxysubstituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkoxysubstituted vinylsilane in the granulated material is about 1500 ppm or less.

[0647] Through the modification reaction using trimethoxyalkoxysubstituted vinylsilane as described above, silane-modified polyethylene with an MFR (190°C) of 0.4 g / min was obtained.

[0648] (Production of Layer A)

[0649] 35% by mass of the above-obtained silane-modified polyethylene was blended with 65% by mass of a homopolymer polyethylene with a weight-average molecular weight of 750,000 to form a resin blend. 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant was added to this blend, and dry blending was carried out using a drum mixer to obtain a mixture. The obtained mixture was fed to a twin-screw extruder by a feeder under a nitrogen atmosphere. In addition, liquid paraffin (kinematic viscosity at 37.78°C of 7.59×10 -5 m 2 / s) injection extruder drum.

[0650] In the extruder, the mixture and liquid paraffin are melt-kneaded. The feeder and pump are adjusted so that the amount of liquid paraffin in the extruded polyolefin composition is 70% by mass (i.e., the polymer concentration is 30% by mass). The melt-kneading conditions are a set temperature of 220 °C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / hour. Then, the melt-kneaded material is extruded through a T-die onto a cooling roll with a surface temperature controlled at 25 °C and cast, thereby obtaining a gel sheet (sheet-shaped molded body) with a blank film thickness of 1280 μm.

[0651] Next, the sheet-shaped molded body is guided to a simultaneous biaxial stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions are set to an MD magnification of 7.0 times, a TD magnification of 6.5 times (i.e., 7×6.5 times), and a biaxial stretching temperature of 125 °C.

[0652] Next, the stretched gel sheet is guided to a dichloromethane bath, fully immersed in dichloromethane to extract and remove the liquid paraffin, and then dried to remove dichloromethane, obtaining a porous body.

[0653] Next, in order to perform heat setting (HS), the porous body is guided to a TD stretching machine, and HS is performed at a heat setting temperature of 131 °C and a stretching ratio of 1.9 times. Then, a relaxation operation is performed to a TD of 1.7 times, obtaining a microporous membrane.

[0654] Then, for the obtained microporous membrane, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[0655] At the above evaluation, the microporous membrane released from the master roll is slit as needed and used as the evaluation A layer.

[0656] For the obtained evaluation A layer, the film thickness, air permeability, porosity, etc. are measured and shown in Table 6.

[0657] <Fabrication of Layer B>

[0658] 95 parts by mass of aluminum hydroxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (in terms of solid content) of an aqueous ammonium polycarboxylate solution (SNDispersant 5468 manufactured by SAN NOPCO LIMITED, solid content concentration 40%) as an ionic dispersant are uniformly dispersed in 100 parts by mass of water to prepare a dispersion. The obtained dispersion is subjected to a crushing treatment using a bead mill (tank volume 200 cc, zirconia beads with a diameter of 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, and a slurry containing inorganic particles is fabricated.

[0659] Next, the microporous membrane is continuously unwound from the above-mentioned microporous membrane master roll, and a slurry containing inorganic particles is coated on one side of the microporous membrane using a gravure reverse coater. Then, it is dried with a dryer at 60 °C to remove water, and wound up to obtain the master roll of the separator.

[0660] At the time of evaluation, the separator unwound from the master roll is slit as needed and used as the separator for evaluation.

[0661] [Examples IV-2 to IV-3 and Comparative Examples IV-1 to IV-2]

[0662] Taking the physical property values described in Table 6 as the target, the weight average molecular weight of the polyethylene of the homopolymer is changed, and at least any one of the stretching conditions, heat setting conditions, and relaxation operation conditions is set. In addition, the composition of the B layer is changed as described in Table 6.

[0663] Except for these changes, separators are produced by the same method as in Example IV-1, and the above evaluation is performed using the obtained separators. The evaluation results are shown in Table 6.

[0664] [Table 6]

[0665]

[0666] <Experimental Group V>

[0667] Porous membranes are formed in the same manner as in Examples 1 to 3 and Comparative Examples 2 to 3 given in Patent Document 5 (Japanese Unexamined Patent Application Publication No. 2001-176484), and are respectively designated as porous membranes V-1 to V-5. For porous membranes V-1 to V-5, the gel fraction (%), heat resistance temperature (°C), and needle penetration strength (gf / 25 μm) are evaluated according to the method described in Patent Document 5, and further, the TMA film breakage temperature under load is measured in accordance with the above item <TMA film breakage temperature> of this specification. The results are shown in Table 7.

[0668] [Table 7]

[0669]

[0670] The following points can be clarified from Table 7.

[0671] (a) Since the heat resistance temperature described in Patent Document 5 is the measurement temperature under the condition of no load applied, it is not the TMA film breakage temperature described in the first, second, and third embodiments of the present invention.

[0672] (b) As shown in Examples 1 to 3 and Comparative Examples 2 to 3 of Patent Document 5, for porous membranes V-1 to V-5 that were crosslinked under the conditions of a temperature of 90 °C, a humidity of 95%, and 4 hours, if the TMA film breakage temperature is measured under the conditions of the above item <TMA film breakage temperature> in this specification, the TMA film breakage temperature will be less than 180 °C.

Claims

1. A separator for an electrical storage device, comprising a microporous membrane containing a silane-modified polyolefin and polyethylene, wherein the microporous membrane has a melting and rupture temperature of 180°C to 220°C as measured by thermomechanical analysis (TMA), the separator containing 0.10 ppm to 200 ppm of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, or lead in a total atomic amount, the content of the silane-modified polyolefin in the microporous membrane being 0.5% to 40% by mass, and the content of the polyethylene being 20% ​​to 97% by mass, based on the total amount of the silane-modified polyolefin and the polyethylene.

2. The separator for an electricity storage device according to claim 1, wherein The separator for a power storage device contains zinc or tin in an atomically converted total amount of 0.10 ppm to 200 ppm.

3. The separator for an electricity storage device according to claim 1, comprising: The microporous membrane, and An inorganic porous layer including inorganic particles and a resin binder is disposed on at least one surface of the microporous membrane.

4. The separator for an electricity storage device according to claim 3, wherein The content of the inorganic particles in the inorganic porous layer is 5% by mass to 99% by mass.

5. The separator for an electricity storage device according to claim 3, wherein The inorganic particles are at least one selected from the group consisting of aluminum oxide (Al2O3), silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide (AlO(OH)), talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand and glass fiber.

6. The separator for an electricity storage device according to claim 3, wherein The glass transition temperature (Tg) of the resin binder is -50°C to 100°C.

7. A method for producing a separator for an electricity storage device, the method for producing a separator for an electricity storage device according to any one of claims 1 to 6, comprising the following steps: (1) a sheet forming step, wherein the silane grafted modified polyolefin, polyethylene and plasticizer are extruded into a sheet by an extruder, cooled and solidified, and processed into a sheet-shaped body; (2) a stretching step of biaxially stretching the sheet-like formed body at an area ratio of 20 to 250 times to form a stretched product; (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body; (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing the porous body in the width direction to obtain a heat-treated porous body; (5) an affinity treatment step of immersing the heat-treated porous body in an organic solvent having amphiphilicity toward water and organic matter to increase the affinity of the heat-treated porous body with the liquid, thereby obtaining an affinity-treated porous body having the organic solvent immersed therein; (6) a cross-linking treatment step, wherein the affinity-treated porous body is contacted with a mixture containing an organic metal catalyst and water, or the affinity-treated porous body is immersed in an alkaline solution or an acid solution to carry out a silane dehydration condensation reaction to form oligosiloxane bonds, thereby obtaining a cross-linked porous body; (7) a water washing and drying step of washing and drying the cross-linked porous body to obtain a microporous membrane comprising the silane-modified polyolefin; as well as (8A) A coating step of forming an inorganic porous layer containing inorganic particles and a resin binder on at least one surface of the microporous membrane. 8 . An electricity storage device comprising an electrode, the separator for an electricity storage device according to claim 1 , and a non-aqueous electrolyte.

Images