Inorganic coated cross-linked separator

Abstract

To provide a separator for a power storage device, which can enhance a performance of a power storage device (e.g. the cycle characteristic and the safety to be evaluated in a device breakdown or heating test).SOLUTION: A separator for a power storage device comprises a polyolefin resin-made microporous film, and an inorganic porous layer disposed on at least one surface of the polyolefin resin-made microporous film. The inorganic porous layer has at least one kind selected from a group consisting of (i) a covalent bond between inorganic particles, (ii) a covalent bond among the resin binder, and (iii) a covalent bond between an inorganic particle and a resin binder. The polyolefin resin-made microporous film contains silane graft-modified polyolefin. When the separator for a power storage device is put in contact with an electrolyte solution, a silane crosslink reaction of the silane graft-modified polyolefin is caused to start.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator for an electricity storage device, and more particularly to a separator for an electricity storage device including an inorganic coating layer (inorganic porous layer) that forms a crosslinked structure. [Background technology]

[0002] Microporous membranes are widely used as separation or permselective separation membranes for various substances, separators, etc., and examples of their applications include microfiltration membranes, separators for fuel cells and capacitors, base materials for functional membranes in which functional materials are filled into the pores to exhibit new functions, separators for electricity storage devices, etc. In particular, microporous membranes made of polyolefin resins are preferably used as separators or constituent materials for lithium ion secondary batteries (LIBs) that are widely installed in notebook personal computers, mobile phones, digital cameras, etc.

[0003] Here, separators have been proposed that have a crosslinked coating layer (for example, an inorganic porous layer containing inorganic particles and a resin binder) on the surface of a microporous membrane for the purpose of improving heat resistance, etc. (see Patent Documents 1 to 5). Also, to ensure the safety of batteries, it has been proposed to form a crosslinked structure within the microporous membrane by ring-opening of norbornene through irradiation with ultraviolet light, electron beams, or the like (see Patent Document 6). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6187464 [Patent Document 2] International Publication No. 2013 / 080938 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-211006 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-287888 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-179321 [Patent Document 6] Japanese Patent Application Laid-Open No. 2011-071128 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, LIBs have become increasingly dense and have higher energy densities. This has led to expectations for further improvements in LIB cycling characteristics and safety (e.g., safety evaluated by battery breakdown tests). Further improvements are also expected for LIB separators. However, the separators described in Patent Documents 1 to 5 still have room for improvement in terms of improving the above-mentioned LIB performance. Furthermore, when a crosslinked structure is formed in a microporous membrane by light irradiation, as described in Patent Document 6, the light irradiation can become non-uniform, resulting in a non-homogeneous crosslinked structure. This is thought to be because the periphery of the crystalline portion of the resin constituting the microporous membrane is easily crosslinked by light. When a microporous membrane with a non-homogeneous crosslinked structure is used as a LIB separator, the LIB may deform upon heating. This problem is not limited to LIB separators; it also exists in separators for power storage devices, such as LIBs.

[0006] In view of the above problems, an object of the present invention is to provide a separator for an electricity storage device that can further improve the performance of the electricity storage device (for example, cycle characteristics and safety evaluated by device destruction or heating tests). Another object of the present invention is to provide a secondary battery, an electricity storage device, etc. that include such a separator for an electricity storage device. [Means for solving the problem]

[0007] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by incorporating into an electricity storage device separator a polyolefin resin microporous membrane containing a silane-grafted polyolefin and a crosslinked inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, and / or by disposing an inorganic porous layer on the polyolefin resin microporous membrane and controlling the peeling rate of the inorganic porous layer from the polyolefin resin microporous membrane in a solvent immersion test within a predetermined range, and have completed the present invention. (1) A separator for an electricity storage device comprising: a polyolefin resin microporous membrane; and an inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, the inorganic porous layer has at least one selected from the group consisting of (i) covalent bonds between inorganic particles, (ii) covalent bonds between resin binders, and (iii) covalent bonds between inorganic particles and resin binders; The polyolefin resin microporous membrane contains a silane-grafted polyolefin, and when the separator for an electricity storage device comes into contact with an electrolyte, a silane crosslinking reaction of the silane-grafted polyolefin is initiated. (2) 2. The separator for an electricity storage device according to item 1, wherein the electrolytic solution is non-aqueous and contains a fluorine (F)-containing lithium salt. (3) 3. The separator for an electricity storage device according to item 1 or 2, wherein the polyolefin resin microporous film contains a polyolefin other than the silane-grafted polyolefin. (4) 4. The separator for an electricity storage device according to any one of items 1 to 3, wherein the inorganic porous layer includes a crosslinked structure. (5) A separator for an electricity storage device comprising: a polyolefin resin microporous membrane; and an inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, A separator for an electricity storage device, wherein in a solvent immersion test, the area of ​​the inorganic porous layer that peels off from the polyolefin resin microporous membrane is 0 to 35% of the area of ​​the inorganic porous layer before the test. (6) 6. The separator for an electricity storage device according to item 5, wherein the inorganic porous layer has at least one selected from the group consisting of (i) covalent bonds between inorganic particles, (ii) covalent bonds between resin binders, and (iii) covalent bonds between inorganic particles and resin binders. (7) 7. The separator for an electricity storage device according to item 6, wherein the inorganic porous layer includes a crosslinked structure formed by at least one selected from the group consisting of the covalent bonds (i) to (iii). (8) 8. The separator for an electricity storage device according to any one of items 5 to 7, wherein the polyolefin resin microporous film contains a silane-grafted modified polyolefin. (9) Item 9. The separator for a power storage device according to item 8, wherein a silane crosslinking reaction of the silane-grafted modified polyolefin is initiated when the separator for a power storage device comes into contact with an electrolyte solution. (10) 10. The separator for an electricity storage device according to item 9, wherein the electrolytic solution is non-aqueous and contains a fluorine (F)-containing lithium salt. (11) 11. The separator for an electricity storage device according to any one of items 8 to 10, wherein the polyolefin resin microporous film contains a polyolefin other than the silane-grafted polyolefin. (12) 12. The separator for an electricity storage device according to any one of items 5 to 11, wherein the surface roughness of the polyolefin resin microporous membrane in the region facing the inorganic porous layer is 0.2 to 3.0 μm. (13) 8. The separator for an electricity storage device according to item 4 or 7, wherein the crosslinked structure in the inorganic porous layer is formed by at least one reaction selected from the group consisting of a nucleophilic substitution reaction, a nucleophilic addition reaction, an electrophilic addition reaction, and a silane coupling reaction. (14) 14. The separator for an electricity storage device according to any one of items 1 to 4, 6, 7, and 13, wherein the resin binder is in the form of an emulsion, a suspension, or a colloid. (15) 15. The separator for a power storage device according to any one of items 1 to 4, 6, 7, 13, and 14, wherein the resin binder has a nucleophilic substitution or nucleophilic addition reactive functional group. (16) 16. The separator for a power storage device according to any one of items 1 to 4, 6, 7, and 13 to 15, wherein the nucleophilic substitution or nucleophilic addition reactive functional group of the resin binder is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and an amino group. (17) 17. The separator for an electricity storage device according to any one of items 1 to 16, wherein the inorganic porous layer contains inorganic particles, and the inorganic particles have polar functional groups on their surfaces. (18) 18. The separator for a power storage device according to any one of items 1 to 17, wherein the inorganic porous layer contains inorganic particles, and the inorganic particles have silicon-containing functional groups on their surfaces. (19) Item 19. The separator for an electricity storage device according to item 18, wherein the silicon-containing functional group is at least one selected from the group consisting of an alkoxysilyl group, a halogen-substituted silyl group, and a silazane group. (20) Item 20. The separator for an electricity storage device according to any one of items 1 to 19, wherein the inorganic porous layer contains a crosslinking agent. (twenty one) 21. The separator for an electricity storage device according to item 20, wherein the crosslinking agent has a nucleophilic substitution reactive functional group and / or an electrophilic addition reactive functional group. (twenty two) Item 22. The separator for an electricity storage device according to item 20 or 21, wherein the crosslinking agent has a nucleophilic substitution reactive functional group and an electrophilic addition reactive functional group. (twenty three) Item 23. The separator for an electricity storage device according to Item 21 or 22, wherein the nucleophilic substitution reactive functional group of the crosslinking agent is an oxazoline group and / or an epoxy group. (twenty four) 23. The separator for an electricity storage device according to item 21 or 22, wherein the electrophilic addition reactive functional group of the crosslinking agent is at least one selected from the group consisting of an isocyanate group, a thioisocyanate group, a carbodiimide group, an allene group, an oxime group, and a carbonyl group. (twenty five) 25. The separator for an electricity storage device according to any one of items 20 to 24, wherein the inorganic porous layer contains inorganic particles and a resin binder, polar functional groups are present on surfaces of the inorganic particles, the crosslinking agent is present between the polar functional groups and the resin binder, and a crosslinked structure is formed by a covalent bond between the polar functional groups, the crosslinking agent, and the resin binder. (26) 26. The separator for an electricity storage device according to any one of items 20 to 25, wherein the crosslinking agent is in the form of an emulsion, a suspension, or a colloid. (27) 27. An electricity storage device comprising an electrode, an electrolyte solution, and the electricity storage device separator according to any one of items 1 to 26. (28) 27. A secondary battery comprising an electrode, an electrolytic solution, and the separator for an electricity storage device according to any one of items 1 to 26. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a separator for an electricity storage device that can further improve the performance of the electricity storage device (for example, cycle characteristics and safety evaluated by device destruction or heating tests). Furthermore, according to the present invention, it is possible to provide a secondary battery and an electricity storage device that include such a separator. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 10 is a diagram showing an example of a histogram used to derive the percentage (%) of peeled area according to one embodiment of the present invention. [Figure 2] FIG. 10 shows another example of a histogram used to derive the percentage of peeled area according to one embodiment of the present invention. [Figure 3] FIG. 10 is a diagram illustrating an example of a monochrome image according to one embodiment of the present invention. [Figure 4] FIG. 1 illustrates an example of a binarized image according to one aspect of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (referred to as "the present embodiment") will be described, but the present invention is not limited to only this embodiment. The present invention can be modified in various ways without departing from the gist of the present invention. In this specification, unless otherwise specified, the symbol "to" means that the numerical values ​​at both ends thereof are included as upper and lower limits. Furthermore, in this specification, the upper and lower limits of a numerical range can be combined arbitrarily. Furthermore, the term "separator for an electricity storage device" may be abbreviated to "separator" hereinafter.

[0011] <Separators for electricity storage devices> The separator for an electricity storage device can be used in an electricity storage device, and can be disposed, for example, between the positive and negative electrodes of the electricity storage device.

[0012] <Embodiment 1> The separator for an electricity storage device according to embodiment 1 comprises a polyolefin resin microporous membrane containing a silane-grafted polyolefin and an inorganic porous layer disposed on at least one surface thereof, and may further comprise layers other than the polyolefin resin microporous membrane and the inorganic porous layer, as desired. Inorganic porous layers may be disposed on both surfaces of the polyolefin resin microporous membrane, or an inorganic porous layer may be disposed on one surface of the polyolefin resin microporous membrane and a layer other than the polyolefin resin microporous membrane and the inorganic porous layer may be disposed on the other surface of the polyolefin resin microporous membrane.

[0013] The inorganic porous layer of the separator according to embodiment 1 has at least one covalent bond selected from the group consisting of (i) covalent bonds between inorganic particles, (ii) covalent bonds between resin binders, and (iii) covalent bonds between inorganic particles and resin binders. When the separator according to embodiment 1 comes into contact with an electrolytic solution, a silane crosslinking reaction of the silane-grafted modified polyolefin contained in the microporous polyolefin resin membrane is initiated.

[0014] The inorganic porous layer according to embodiment 1 is disposed on at least one surface of the polyolefin resin microporous membrane. Thus, both an embodiment in which the inorganic porous layer is disposed on only one surface of the polyolefin resin microporous membrane and an embodiment in which the inorganic porous layer is disposed on both surfaces of the polyolefin resin microporous membrane are included in the scope of embodiment 1. When inorganic porous layers are disposed on both surfaces of the polyolefin resin microporous membrane, the inorganic porous layers may have the same configuration, or inorganic porous layers with different configurations may be disposed.

[0015] The inorganic porous layer according to the first embodiment may contain inorganic particles and / or a resin binder.

[0016] The inorganic porous layer according to the first embodiment can form a crosslinked structure or include a crosslinked structure by any of the covalent bonds (i) to (iii). The above description does not necessarily mean that a crosslinked structure is formed between inorganic particles. For example, if a crosslinked structure is formed between inorganic particles and a resin binder, a crosslinked structure does not necessarily need to be formed between inorganic particles. Similarly, the above description does not necessarily mean that a crosslinked structure is formed between resin binders. For example, if a crosslinked structure is formed between inorganic particles and a resin binder, a crosslinked structure does not necessarily need to be formed between resin binders. That is, it is sufficient that at least one of the above crosslinked structures is formed in the inorganic porous layer, but from the viewpoint of easily achieving the effects of the present invention, it is preferable that crosslinked structures are formed in all of the covalent bonds (i) to (iii). In the first embodiment, the covalent bonds between inorganic particles, the covalent bonds between resin binders, and the covalent bonds between inorganic particles and resin binders include those formed via a crosslinking agent, if necessary.

[0017] The polyolefin resin microporous membrane according to embodiment 1 contains a silane-grafted polyolefin as the polyolefin resin, and may optionally contain polyolefins other than the silane-grafted polyolefin, additional components, etc. Contacting the separator according to embodiment 1 with an electrolyte allows crosslinking of the silane-grafted polyolefin, thereby controlling the timing of the silane crosslinking reaction. This allows, for example, the crosslinking reaction to be avoided during the separator manufacturing process, but rather during the energy storage device manufacturing process or by placing the separator within the energy storage device. This avoids separator production defects and achieves energy storage device safety (e.g., safety evaluated by device destruction or heating tests), improved cycle characteristics, and higher power output. From the perspective of the silane crosslinking reaction, the electrolyte in contact with the silane-grafted polyolefin is preferably nonaqueous and / or preferably contains a fluorine (F)-containing lithium salt.

[0018] <Embodiment 2> The power storage device separator according to embodiment 2 comprises a polyolefin resin microporous membrane and an inorganic porous layer disposed on at least one surface thereof, and may further comprise layers other than the polyolefin resin microporous membrane and inorganic porous layer, as desired. Inorganic porous layers may be disposed on both surfaces of the polyolefin resin microporous membrane, or an inorganic porous layer may be disposed on one surface of the polyolefin resin microporous membrane and a layer other than the polyolefin resin microporous membrane and inorganic porous layer may be disposed on the other surface of the polyolefin resin microporous membrane.

[0019] In a solvent immersion test of the separator according to embodiment 2, the area of ​​the inorganic porous layer peeled from the polyolefin microporous membrane is 0 to 35% of the area of ​​the inorganic porous layer before the test. By keeping this area 35% or less, it is possible to prevent the inorganic porous layer peeled from the polyolefin microporous membrane in the electrolyte from adversely affecting the charge / discharge reaction or reliability of the electricity storage device, and as a result, it is possible to provide a separator that can further improve the performance of the electricity storage device (e.g., cycle characteristics and safety evaluated by destructive testing or heating testing of devices such as batteries). This area is measured according to the method described in the examples.

[0020] The significance of the solvent immersion test described in the examples is as follows. Typically, the electrolyte used in batteries is a mixed liquid of a cyclic alkane carbonate, such as propylene carbonate, and a linear alkane carbonate, such as ethyl methyl carbonate. Furthermore, each battery manufacturer adjusts the functional groups or composition of these components depending on the battery design. This changes the solubility parameter (SP) of the electrolyte, making it difficult to uniformly evaluate the penetration of the electrolyte into the inorganic porous layer, the swelling of the inorganic porous layer, and peeling due to structural breakdown of the inorganic porous layer. Therefore, to appropriately evaluate the above-mentioned area, a solvent immersion test can be performed as described in the Examples. For example, acetone has a lower molecular weight than various electrolytes and contains aprotic polar functional groups. Therefore, it has been experimentally demonstrated that using a relatively low-molecular-weight solvent (e.g., acetone) in the solvent immersion test allows the solvent to penetrate the inorganic porous layer, easily swelling the inorganic porous layer, and causing peeling due to structural breakdown of the inorganic porous layer. Therefore, if a good evaluation result is obtained in the solvent immersion test described in the examples, it can be determined that the material is stable in various other electrolyte solutions.

[0021] One factor for controlling the area of ​​the inorganic porous layer that peels off from the polyolefin microporous membrane is the control of the crosslinked structure in the inorganic porous layer. Specifically, this area can be controlled by controlling the parameters related to the inorganic porous layer listed in Tables 3 to 6 in the examples.

[0022] If a crosslinked structure is not formed in the inorganic porous layer, the resin binder in the inorganic porous layer will swell in the electrolyte, increasing the likelihood that the swollen resin binder will fall off from the inorganic porous layer into the electrolyte. On the other hand, if an excessive crosslinked structure is formed in the inorganic porous layer, the flexibility of the inorganic porous layer will be reduced, increasing the likelihood that the resin binder will fall off from the inorganic porous layer into the electrolyte. In other words, by appropriately forming a crosslinked structure in the inorganic porous layer, swelling of the resin binder due to the electrolyte can be suppressed and appropriate flexibility of the inorganic porous layer can be ensured. This is expected to prevent the resin binder from falling off into the electrolyte and ultimately control the area of ​​the inorganic porous layer peeling off from the polyolefin microporous membrane to 0 to 35%. From the perspective of shape stability of the separator during long-term use in an electricity storage device such as a battery, the area of ​​the inorganic porous layer peeling off from the polyolefin resin microporous membrane is preferably 0 to 30%, more preferably 0 to 15%, and even more preferably 0 to 8%.

[0023] The inorganic porous layer according to embodiment 2 is disposed on at least one surface of the polyolefin microporous membrane. Thus, both an embodiment in which the inorganic porous layer is disposed on only one surface of the polyolefin microporous membrane and an embodiment in which the inorganic porous layer is disposed on both surfaces of the polyolefin microporous membrane are included in the scope of embodiment 2. When inorganic porous layers are disposed on both surfaces of the polyolefin microporous membrane, the inorganic porous layers may have the same configuration, or may have different configurations.

[0024] The inorganic porous layer according to the second embodiment preferably contains inorganic particles and / or a resin binder from the viewpoints of the performance of the electricity storage device and control of the crosslinked structure in the inorganic porous layer.

[0025] From the viewpoint of the performance of the electricity storage device and the control of the crosslinked structure in the inorganic porous layer, it is preferable that the inorganic porous layer of embodiment 2 has at least one selected from the group consisting of (i) covalent bonds between inorganic particles, (ii) covalent bonds between resin binders, and (iii) covalent bonds between inorganic particles and resin binders, and it is more preferable that a crosslinked structure is formed by any of the covalent bonds (i) to (iii) or that the inorganic porous layer contains a crosslinked structure. The above description does not necessarily mean that a crosslinked structure is formed between inorganic particles. For example, if a crosslinked structure is formed between inorganic particles and a resin binder, a crosslinked structure does not necessarily need to be formed between inorganic particles. Similarly, the above description does not necessarily mean that a crosslinked structure is formed between resin binders. For example, if a crosslinked structure is formed between inorganic particles and a resin binder, a crosslinked structure does not necessarily need to be formed between resin binders. That is, it is sufficient that at least one of the above crosslinked structures is formed in the inorganic porous layer. However, from the viewpoint of easily achieving the effects of the present invention, it is more preferable that crosslinked structures are formed in all of the covalent bonds (i) to (iii). In the second embodiment, the covalent bonds between inorganic particles, the covalent bonds between resin binders, and the covalent bonds between inorganic particles and resin binders include those formed via a crosslinking agent, if necessary.

[0026] From the viewpoint of further improving the performance of the electricity storage device, the polyolefin resin microporous membrane according to embodiment 2 preferably contains a silane-grafted polyolefin as the polyolefin resin, and more preferably contains a polyolefin other than the silane-grafted polyolefin in addition to the silane-grafted polyolefin. If desired, the polyolefin resin microporous membrane may contain additional components other than the polyolefin resin.

[0027] When the separator according to embodiment 2 comes into contact with an electrolyte, a silane crosslinking reaction of the silane-grafted polyolefin contained in the polyolefin resin microporous membrane is preferably initiated. Contacting the separator according to embodiment 2 with an electrolyte allows crosslinking of the silane-grafted polyolefin, thereby controlling the timing of the silane crosslinking reaction. This allows the crosslinking reaction to be performed, for example, during the manufacturing process of the separator, or within the electrical storage device, rather than during the separator manufacturing process. This avoids separator production defects and achieves electrical storage device safety (e.g., safety evaluated by device destruction or heating tests), improved cycle characteristics, and higher power output. From the perspective of the silane crosslinking reaction, the electrolyte that comes into contact with the silane-grafted polyolefin is more preferably nonaqueous and / or contains a fluorine (F)-containing lithium salt.

[0028] In embodiment 2, by controlling the surface roughness of the region of the polyolefin microporous membrane facing the inorganic porous layer within a predetermined range, it is easier to prevent the resin binder from peeling off from the inorganic porous layer. In embodiment 2, a crosslinked structure is suitably formed in the inorganic porous layer, thereby ensuring the desired binding strength between the inorganic porous layer and the polyolefin microporous membrane, which makes the inorganic porous layer more susceptible to the effects of controlling the surface roughness of the polyolefin microporous membrane. Furthermore, controlling the surface roughness of the polyolefin microporous membrane makes it easier to further suppress swelling of the resin binder by the electrolyte solution, and as a result, it is expected that the area of ​​the inorganic porous layer that peels off from the polyolefin microporous membrane can be controlled to 0 to 35%. Conversely, if no crosslinked structure is formed in the inorganic porous layer or if an excessive crosslinked structure is formed in the inorganic porous layer, the inorganic porous layer is hardly affected by controlling the surface roughness of the polyolefin microporous membrane, and therefore, no idea of ​​controlling the surface roughness of the polyolefin microporous membrane can be obtained.

[0029] Therefore, the surface roughness of the region of the polyolefin microporous film facing the inorganic porous layer is preferably 0.2 to 3.0 μm, from the viewpoint of making it easier to exhibit the effects of the present invention. Specifically, the surface roughness is preferably 0.20 μm or more, more preferably 0.21 μm or more, and even more preferably 0.220 μm or more. On the other hand, the surface roughness is preferably 3.00 μm or less, more preferably 2.80 μm or less, and even more preferably 0.80 μm or less. The surface roughness is measured according to the method described in the Examples and can be controlled by changing various components of the polyolefin microporous membrane or various production conditions.

[0030] Components common to the first and second embodiments and components preferred for both embodiments will be described below.

[0031] <Polyolefin resin microporous membrane> The polyolefin resin microporous membrane (hereinafter sometimes referred to as "polyolefin microporous membrane") may itself be one that has been conventionally used as a separator. The polyolefin microporous membrane is not limited to a single layer, but may include multiple layers. Therefore, for example, a laminate in which multiple polyolefin microporous membranes containing different polyolefin resins are laminated is also included in the polyolefin microporous membrane of embodiment 1 or 2.

[0032] The content of polyolefin resin in the polyolefin resin microporous membrane is preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may be 100% by mass, based on the total mass of the polyolefin resin microporous membrane.

[0033] (Polyolefin resin) The polyolefin resin is not particularly limited, but examples thereof include homopolymers of ethylene or propylene, and 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, high-density polyethylene (homopolymer) or low-density polyethylene is preferred, with high-density polyethylene (homopolymer) being more preferred, from the viewpoint of being able to perform heat setting (sometimes abbreviated as "HS") at higher temperatures without pore clogging. The polyolefin resin may contain a polyolefin resin other than polyethylene in addition to or instead of polyethylene. Examples of polyolefin resins other than polyethylene include polypropylene and polybutene. The polyolefins may be used alone or in combination of two or more.

[0034] From the viewpoints of resistance to oxidation-reduction degradation and a dense, uniform porous structure, the polyolefin resin microporous membrane preferably contains both a silane-grafted polyolefin and an ultra-high molecular weight polyethylene (UHMWPE). It is generally known that the weight-average molecular weight of ultra-high molecular weight polyethylene (UHMWPE) is 1,000,000 or more. More preferably, the mass ratio of the silane-grafted polyolefin to the ultra-high molecular weight polyethylene in the separator (mass of the silane-grafted polyolefin / mass of the ultra-high molecular weight polyethylene) is 0.05 / 0.95 to 0.40 / 0.60.

[0035] Furthermore, the polyolefin resin microporous membrane preferably contains a polyolefin having a weight-average molecular weight of less than 1,200,000. Using a polyolefin having a weight-average molecular weight of less than 1,200,000 tends to facilitate early relaxation of polymer shrinkage during heating tests of electrical storage devices, and tends to facilitate maintaining safety, particularly in heating safety tests. From the same perspective, the weight-average molecular weight of the polyolefin is more preferably less than 1,000,000, even more preferably 100,000 to 1,000,000, and particularly preferably 150,000 to 800,000. When a polyolefin having a weight-average molecular weight of less than 1,000,000 is used, the resulting microporous membrane tends to have a smaller modulus of elasticity in the thickness direction than when a polyolefin having a weight-average molecular weight of 1,000,000 or more is used, resulting in a microporous membrane to which the irregularities of the core are transferred more easily. The polyolefin having a weight average molecular weight within this range can be contained in a proportion of preferably 40% by mass or more, more preferably 80% by mass or more, based on the total mass of the polyolefin resins contained in the polyolefin microporous membrane.

[0036] (Silane-grafted modified polyolefin) The silane-graft-modified polyolefin has a structure in which a polyolefin main chain is grafted with an alkoxysilyl group. The alkoxide substituted for the alkoxysilyl group is not particularly limited, but examples thereof include methoxide, ethoxide, and butoxide. The main chain and the graft are connected by a covalent bond, and examples thereof include an alkyl, ether, glycol, or ester structure. Considering the manufacturing process of the separator according to the first or second embodiment, the silane-graft-modified polyolefin has a modified amount of silanol-containing units of 10 mol % or less, preferably 5 mol % or less, and more preferably 2 mol % or less, relative to the total ethylene units in the main chain, prior to the crosslinking treatment step described below.

[0037] The preferred silane-grafted polyolefin has a density of 0.90 to 0.96 g / cm 3and the melt flow rate (MFR) at 190°C is 0.2 to 5 g / min.

[0038] Silane-graft-modified polyolefins can be obtained, for example, by grafting alkoxysilyl onto the main chain of a silane-graft-unmodified polyolefin from the polyolefin resins described above. In this specification, a microporous membrane made of a polyolefin resin that does not contain a silane-graft-modified polyolefin has a change in solid content (hereinafter referred to as "gelation degree") of 10% or less before and after heating in a decalin solution at 160°C. When measuring the gelation degree, the solid content refers to only the resin and does not include other materials such as inorganic substances.

[0039] A polyolefin resin microporous membrane free of silane-grafted polyolefin can be produced using, for example, any one selected from the group consisting of polyethylene (PE) (X, viscosity-average molecular weight 100,000 to 400,000), first ultra-high molecular weight PE (Y, viscosity-average molecular weight 400,000 to 800,000), and second ultra-high molecular weight PE (Z, viscosity-average molecular weight 800,000 to 9,000,000), or two or three selected from the group consisting of X, Y, and Z, mixed in any ratio. Polyolefins composed solely of a hydrocarbon skeleton, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and olefin-based thermoplastic elastomers, may also be added to the mixed composition. On the other hand, the gelation degree of a microporous polyolefin resin membrane having a crosslinked structure such as a silane crosslinked structure is preferably 30% or more, more preferably 70% or more.

[0040] (Physical properties of polyolefin resin microporous membrane) The weight average molecular weight of the entire polyolefin resin microporous membrane is preferably 100,000 or more and 1,200,000 or less, and more preferably 150,000 or more and 800,000 or less.

[0041] The porosity of the polyolefin resin microporous membrane is preferably 20% or more, more preferably 30% or more, and even more preferably 32% or more or 35% or more. A porosity of 20% or more tends to further improve the ability to follow the rapid movement of lithium ions. On the other hand, the porosity is preferably 90% or less, more preferably 80% or less, and even more preferably 50% or less. A porosity of 90% or less tends to further improve membrane strength and further suppress self-discharge. The porosity can be measured by the method described in the examples and can be controlled by changing the stretching ratio of the polyolefin resin microporous membrane, for example.

[0042] The air permeability of the polyolefin resin microporous membrane is preferably 1 sec / 100 cm 3 More than 50sec / 100cm, preferably 3 More preferably, 55 sec / 100 cm 3 More preferably, 70 sec / 100 cm 3 Above, 90sec / 100cm 3 or more than 110sec / 100cm 3 The air permeability is 1 sec / 100 cm 3 By setting the thickness to 400 sec / 100 cm or more, the balance between the membrane thickness, porosity, and average pore size tends to be further improved. 3 Less than 300sec / 100cm, preferably less than 300sec / 100cm 3 , and more preferably 270 sec / 100 cm 3 This air permeability is 400sec / 100cm or less. 3 The air permeability can be measured by the method described in the examples and can be controlled by changing the stretching temperature and / or stretch ratio of the polyolefin resin microporous membrane.

[0043] The membrane thickness of the polyolefin resin microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more. A membrane thickness of 1.0 μm or more tends to further improve membrane strength. On the other hand, the membrane thickness is preferably 500 μm or less, more preferably 100 μm or less, even more preferably 80 μm or less, 22 μm or less, or 19 μm or less. A membrane thickness of 500 μm or less tends to further improve ion permeability. This membrane thickness can be measured by the method described in the Examples and can be controlled by changing the stretch ratio of the polyolefin resin microporous membrane, for example.

[0044] When a polyolefin resin microporous membrane is used as a constituent material of a LIB separator, the membrane thickness is preferably 25 μm or less, more preferably 22 μm or less or 20 μm or less, even more preferably 18 μm or less, and particularly preferably 16 μm or less. A membrane thickness of 25 μm or less tends to further improve permeability. In this case, the lower limit of the membrane thickness may be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more.

[0045] <Inorganic porous layer> The thickness of the inorganic porous layer is not particularly limited, but is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 1.0 μm or more. On the other hand, the thickness is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. A thickness of 0.01 μm or more is preferable from the viewpoint of improving mechanical strength. On the other hand, a thickness of 15 μm or less is preferable because it reduces the volume occupied by the separator in the electricity storage device, which tends to be advantageous from the viewpoint of increasing the capacity of the electricity storage device. Furthermore, a thickness of 15 μm or less of the inorganic porous layer is also preferable from the viewpoint of preventing an excessive increase in the air permeability of the separator. This thickness is measured according to the method described in the Examples and can be controlled by, for example, changing the amount of slurry for forming the inorganic porous layer (slurry for inorganic porous layer) applied to the polyolefin resin microporous membrane.

[0046] The air permeability of the inorganic porous layer may be a value that does not excessively increase the air permeability of the separator. The air permeability of the inorganic porous layer corresponds to the increase in the air permeability of the separator due to the formation of the inorganic porous layer on the polyolefin resin microporous membrane. This increase is preferably 200 sec / 100 cm. 3 Less than 150sec / 100cm, preferably less than 150sec / 100cm 3 Less than 130 sec / 100 cm, more preferably 3 This rise is 200 sec / 100 cm. 3 The following is preferable from the viewpoint of allowing ions to permeate suitably in a nonaqueous electrolyte (hereinafter also simply referred to as "electrolyte") during charging and discharging of the electricity storage device. This increase is measured in accordance with the method described in the Examples, and can be controlled by changing various configurations of the inorganic porous layer or various manufacturing conditions, etc.

[0047] <Crosslinked structure> In the inorganic porous layer, the crosslinked structure is preferably formed by at least one reaction selected from the group consisting of a nucleophilic substitution reaction, a nucleophilic addition reaction, an electrophilic addition reaction, and a silane coupling reaction. The presence of such a crosslinked structure in the inorganic porous layer facilitates the achievement of the effects of the present invention. From a similar perspective, when the inorganic porous layer contains a crosslinking agent, it is preferable that the inorganic porous layer has polar functional groups on the surfaces of the inorganic particles, a crosslinking agent between the polar functional groups and the resin binder, and a crosslinked structure is formed by a covalent bond between the polar functional groups, the crosslinking agent, and the resin binder. This type of crosslinked structure may be formed (i) during or immediately after the film-forming process, or (ii) after installation in an electricity storage device by utilizing the surrounding environment or chemicals within the electricity storage device. Depending on the degree of progress of the crosslinking reaction (i) during or immediately after the film-forming process of the inorganic porous layer, the environment within the electricity storage device in which the inorganic porous layer is housed, the configuration of the microporous membrane on which the inorganic porous layer is laminated, and the timing of crosslinking if the microporous membrane has crosslinking properties, the crosslinking reaction in the inorganic porous layer may further progress after the separator including the inorganic porous layer is housed in the electricity storage device. Therefore, it is preferable that the inorganic porous layer be configured to allow the crosslinking reactions (i) and / or (ii) to proceed.

[0048] Although a layer (another layer) that does not fall into either category may be interposed between the inorganic porous layer and the polyolefin resin microporous membrane, it is preferable that such a layer is not interposed. That is, it is preferable that the inorganic porous layer is disposed directly on the polyolefin resin microporous membrane. This makes it easier to control the configuration or properties of the inorganic porous layer by the configuration of the polyolefin resin microporous membrane (for example, the surface roughness of the region of the polyolefin resin microporous membrane facing the inorganic porous layer).

[0049] Examples of the crosslinked structure (crosslinking reaction) by a covalent bond include the following reaction (I) or (II): (I) Reactions between multiple heterogeneous functional groups (II) Chain condensation reaction of functional groups with crosslinkers It is preferable that the compound is at least one selected from the group consisting of:

[0050] The combination of functional groups or reactants that form a crosslinked structure by a covalent bond based on reaction (I) is not particularly limited, but examples thereof include: hydroxyl and carboxyl groups (esterification); Carbonyl and alkyl groups (aldol condensation); Halogens and carboxyl groups (intramolecular condensation); Alkoxy and alkyl groups (Claisen condensation) Carbonyl groups and acid anhydrides (Perkin reaction); Amino groups and halogens; isocyanate groups and hydroxy groups (forming urethane bonds); and oxazoline group and hydroxy group; etc. are preferred.

[0051] The combination of functional groups that forms a crosslinked structure through a covalent bond based on reaction (II) is not particularly limited, but is preferably, for example, a reaction (including a ring-opening reaction) between inorganic particles and / or a resin binder and a crosslinking agent. When inorganic particles and / or a resin binder are crosslinked via a crosslinking agent, the crosslinking agent preferably has two or more functional groups. The multiple functional groups may be of any structure or group, may be substituted or unsubstituted, may contain heteroatoms or inorganic substances, and may be the same or different, as long as they are capable of undergoing a crosslinking reaction with the inorganic particles and / or the resin binder.

[0052] (Inorganic particles) The inorganic particles according to this embodiment form a crosslinked structure through covalent bonds with other inorganic particles and / or with a resin binder. Materials that can be used as such inorganic particles are not particularly limited, but include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone or in combination of two or more.

[0053] The mass ratio of the inorganic particles in the inorganic porous layer (100 × mass of inorganic particles / mass of inorganic porous layer) is preferably 30 mass% or more, more preferably 50 mass% or more, from the viewpoint of ensuring heat resistance, while the mass ratio is preferably 99.5 mass% or less, more preferably 99.0 mass% or less, and even more preferably 98 mass% or less, from the viewpoint of ensuring room for incorporating a binder into the inorganic porous layer.

[0054] Examples of the shape of the inorganic particles include plate-like, scale-like, needle-like, columnar, spherical, polyhedral, and block-like shapes. A combination of inorganic particles having these shapes may be used.

[0055] The number average particle size of the inorganic particles is, for example, 0.01 μm or more, 0.1 μm or more, or 0.3 μm or more. The number average particle size is 10.0 μm or less, 9.0 μm or less, or 6.0 μm or less. Examples of methods for adjusting the particle size include grinding the inorganic particles using an appropriate grinding device such as a ball mill, a bead mill, or a jet mill to reduce the particle size.

[0056] Here, it is preferable that the inorganic particles have polar functional groups on their surfaces. That is, it is preferable that the inorganic particles have polar functional groups on their surfaces. This can enhance reactivity with other compounds (such as resin binders, other inorganic particles, and crosslinking agents that are optionally included). Therefore, a suitable crosslinked structure can be easily formed by covalent bonds between the inorganic particles and the resin binder, or, if multiple inorganic particles are used, by covalent bonds between multiple inorganic particles. From the same perspective, it is preferable that the polar functional group is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and an amino group.

[0057] It is also preferable that the inorganic particles have silicon-containing functional groups on their surfaces. In other words, it is also preferable that the inorganic particles have silicon-containing functional groups on their surfaces. This can enhance reactivity with other compounds (such as resin binders, other inorganic particles, and optionally included crosslinking agents). Therefore, a suitable crosslinked structure can be easily formed by the covalent bond between the inorganic particles and the resin binder, or, in the case of multiple inorganic particles, by the covalent bond between multiple inorganic particles. From the same perspective, it is preferable that the silicon-containing functional group is at least one selected from the group consisting of an alkoxysilyl group, a halogen-substituted silyl group, and a silazane group.

[0058] (resin binder) The resin binder forms a crosslinked structure through covalent bonds with other resin binders and / or with inorganic particles. Materials that can be used as such resin binders are not particularly limited, but for example, resins that are insoluble in the electrolyte of an electricity storage device, such as a LIB, and are electrochemically stable within the range of use of the electricity storage device can be used alone or in combination of two or more.

[0059] Specific examples of materials that can be used as resin binders include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; rubbers such as styrene-butadiene copolymer and its hydrogenated product, acrylonitrile-butadiene copolymer and its hydrogenated product, acrylonitrile-butadiene-styrene copolymer and its hydrogenated product, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins with a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. These may be used alone or in combination of two or more.

[0060] Specific examples of the resin binder include the following 1) to 7). 1) Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; 3) Acrylic polymers: for example, methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers; 4) Polyvinyl alcohol-based resins: for example, polyvinyl alcohol and polyvinyl acetate; 5) Fluorine-containing resins: for example, PVdF, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; 6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) Resins with a melting point and / or glass transition temperature of 180°C or higher, or polymers that have 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.

[0061] This type of resin binder can be obtained by using a desired monomer as a raw material through a known manufacturing method such as emulsion polymerization or solution polymerization, etc. In the polymerization, the polymerization temperature, the pressure during polymerization, the method of adding the monomer, and the additives used (polymerization initiator, molecular weight adjuster, pH adjuster, etc.) are not particularly limited.

[0062] The resin binder and / or the crosslinking agent described below are preferably in the form of an emulsion, suspension, or colloid. Among these, emulsions are preferably formed of a core made of predetermined particles and a shell containing a predetermined polymer compound surrounding the core, from the viewpoints of film-forming properties and the strength of the resulting inorganic porous layer. The particles forming the core may be organic polymer compounds or inorganic fine particles, but organic polymer compounds are more preferred from the viewpoint of imparting greater flexibility to the inorganic porous layer finally obtained. A suspension refers to, for example, a dispersion of solid particles in a solvent to the extent that they are visible under a microscope, and a colloid refers to a dispersion of macromolecules that are visible to the naked eye.

[0063] The resin binder preferably has a functional group (nucleophilic substitution reactive functional group) that undergoes a nucleophilic substitution reaction or a functional group (nucleophilic addition reactive functional group) that undergoes a nucleophilic addition reaction with the polar functional group and / or silicon-containing functional group present on the surface of the inorganic particles. This enhances reactivity with other compounds (e.g., inorganic particles, resin binder, and optionally, a crosslinking agent). Therefore, a favorable crosslinked structure is easily formed by the covalent bond between the inorganic particles and the resin binder, or, in the case of multiple resin binders, by the covalent bond between multiple resin binders. From the same perspective, the nucleophilic substitution reactive functional group or nucleophilic addition reactive functional group of the resin binder is preferably at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and an amino group.

[0064] The mass ratio of the resin binder in the inorganic porous layer (100 × mass of resin binder / mass of inorganic porous layer) is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, from the viewpoint of ensuring heat resistance. On the other hand, this mass ratio is preferably 50 mass% or less, more preferably 20 mass% or less, from the viewpoint of ensuring room for incorporating inorganic particles into the inorganic porous layer.

[0065] (Crosslinking agent) The inorganic porous layer preferably contains a crosslinking agent in addition to the inorganic particles and the resin binder. This makes it easier to form a suitable crosslinked structure in the inorganic porous layer. The mass ratio of the crosslinking agent in the inorganic porous layer (100 × mass of crosslinking agent / mass of inorganic porous layer) is appropriately selected, for example, from the range of 0.01% to 5% by mass. The mass ratio of the crosslinking agent in the inorganic porous layer is more preferably 0.1% to 5% by mass, and even more preferably 0.1% to 3% by mass.

[0066] The crosslinking agent preferably contains a functional group reactive with the inorganic particles and / or the resin binder. For example, the crosslinking agent preferably has a functional group (nucleophilic substitution reactive functional group) that undergoes a nucleophilic substitution reaction and / or a functional group (electrophilic addition reactive functional group) that undergoes an electrophilic addition reaction with the inorganic particles and / or the resin binder. In particular, the crosslinking agent preferably has a nucleophilic substitution reactive functional group and an electrophilic addition reactive functional group. This further facilitates the formation of a suitable crosslinked structure in the inorganic porous layer. Among these, the nucleophilic substitution reactive functional group of the crosslinking agent is preferably an oxazoline group and / or an epoxy group. Furthermore, among these, the electrophilic addition reactive functional group of the crosslinking agent is preferably at least one selected from the group consisting of an isocyanate group, a thioisocyanate group, a carbodiimide group, an allene group, an oxime group, and a carbonyl group. Examples of crosslinking agents that can be used include the Epocross series (K-2010E, K-2020E, K-2030, WS-300, WS-500, WS-700) manufactured by Nippon Shokubai Co., Ltd. as an oxazoline-based crosslinking agent, the Carbodilite series (V-02, V-02-L2, SV-02, V-04, V-10, SW-12G, E-02, E-03A) manufactured by Nisshinbo Chemical Co., Ltd. as a carbodiimide-based crosslinking agent, and the Duranate series (WB40-100, WB40-80D, WT20-100, WT30-100) manufactured by Asahi Kasei Corporation as an isocyanate-based crosslinking agent. , WL70-100, WR80-70P, WE50-100), epoxy crosslinking agents such as the Denacol series (EX-61B, EX-313, FCA-678, etc.) manufactured by Nagase ChemteX Corporation, alkoxysilanes such as triethoxysilane (X-12-1273ES), dimethyldimethoxysilane, methyltrimethoxysilane, and tetraethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd., and crosslinking agents for alkoxysilane compounds containing various functional groups such as KBM Silaz (3-aminopropyltrimethoxysilane KBM-903, etc.), and the KBE series manufactured by Shin-Etsu Chemical Co., Ltd.

[0067] The crosslinking agent may also be used as a silane coupling agent, which is an organic silicon compound having a hydrolyzable functional group that can bond with inorganic particles containing silica or the like after hydrolysis.

[0068] <Other additives> The polyolefin resin microporous membrane and / or the inorganic porous layer may contain any additives, including, but not limited to, phenolic, phosphorus, and sulfur-based antioxidants, metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and color pigments.

[0069] <Separator manufacturing method> (Method for producing a microporous polyolefin resin membrane) The method for producing a polyolefin resin microporous membrane can adopt known production methods, and for example, can adopt either wet porosity method or dry porosity method.Examples of wet porosity method include the method of melt-kneading a polyolefin resin composition with a plasticizer, forming it into a sheet, and then optionally stretching it, and then extracting the plasticizer to make it porous; the method of melt-kneading a polyolefin resin composition that mainly comprises a polyolefin resin, extruding it at a high draw ratio, and then heat-treating and stretching it to peel the polyolefin crystal interface to make it porous; the method of melt-kneading a polyolefin resin composition with an inorganic filler, forming it into a sheet, and then stretching it to peel the interface between the polyolefin and the inorganic filler to make it porous; and the method of dissolving a polyolefin resin composition, immersing it in a poor solvent for polyolefin, solidifying the polyolefin, and simultaneously removing the solvent to make it porous.

[0070] As an example of a method for producing a polyolefin microporous membrane, a method of melt-kneading a polyolefin resin composition and a plasticizer, forming the composition into a sheet, and then extracting the plasticizer will be described below. First, the polyolefin resin composition and the plasticizer are melt-kneaded. Examples of melt-kneading methods include adding a polyolefin resin and, if necessary, other additives to a resin kneading device such as an extruder, kneader, Labo Plastomill, kneading roll, or Banbury mixer, and then introducing and kneading the plasticizer at a desired ratio while heating and melting the resin components. In this case, it is preferable to pre-knead the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before adding them to the resin kneading device. More preferably, only a portion of the plasticizer is added during pre-kneading, and the remaining plasticizer is kneaded while being side-fed into the resin kneading device.

[0071] As the plasticizer, a nonvolatile solvent capable of forming a homogeneous solution at or above the melting point of the polyolefin can be used. Specific examples of such nonvolatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

[0072] The ratio of the polyolefin resin composition to the plasticizer may be within a range that allows them to be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of the polyolefin resin composition and the plasticizer is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. By setting the mass fraction of the plasticizer within this range, it is preferable to achieve both melt tension during melt molding and the ability to form a uniform and fine pore structure.

[0073] Next, the molten kneaded product obtained by heating, melting, and kneading as described above is molded into a sheet. Examples of methods for producing a sheet-shaped molded product include extruding the molten kneaded product into a sheet through a T-die or the like, contacting it with a thermal conductor, and solidifying it by cooling to a temperature sufficiently lower than the crystallization temperature of the resin component. Thermal conductors used for cooling and solidifying include metal, water, air, and plasticizer itself, but metal rolls are preferred due to their high thermal conductivity. In this case, sandwiching the molten kneaded product between the metal rolls when contacting them further increases the thermal conductivity efficiency, orients the sheet, increasing film strength and improving the surface smoothness of the sheet, making it more preferable. When extruding into a sheet through a T-die, the die lip spacing is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less.

[0074] The sheet-like molded article thus obtained is then preferably stretched. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching treatment. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous membrane. When the sheet-like molded article is stretched biaxially at a high ratio, the molecules are oriented in the plane direction, and the finally obtained polyolefin microporous membrane becomes less likely to tear and has high pin puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improved pin puncture strength, stretching uniformity, and shutdown properties.

[0075] The areal stretching ratio is preferably in the range of 20 to 100 times, more preferably in the range of 25 to 50 times. The stretching ratios in each axial direction are preferably in the range of 4 to 10 times in MD and 4 to 10 times in TD, more preferably in the range of 5 to 8 times in MD and 5 to 8 times in TD. A stretching ratio within this range is preferred in that it can impart more sufficient strength, prevent film rupture during the stretching step, and achieve high productivity. Here, MD means the machine direction when, for example, a polyolefin microporous membrane is continuously molded, and TD means the direction crossing MD at an angle of 90°.

[0076] The sheet-like molded article obtained as described above may be further rolled. Rolling can be carried out, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion of the sheet-like molded article. The rolling areal ratio is preferably more than 1 and not more than 3, and more preferably more than 1 and not more than 2. A rolling ratio within this range is preferred in that it increases the membrane strength of the polyolefin microporous membrane finally obtained and allows for the formation of a more uniform pore structure in the membrane thickness direction.

[0077] The plasticizer is then removed from the sheet-like molding to obtain a polyolefin microporous membrane. Examples of methods for removing the plasticizer include immersing the sheet-like molding in an extraction solvent to extract the plasticizer, followed by thorough drying. The plasticizer extraction method may be either a batch method or a continuous method. To prevent shrinkage of the polyolefin microporous membrane, it is preferable to restrain the edges of the sheet-like molding during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the polyolefin microporous membrane be less than 1% by mass.

[0078] It is preferable to use an extraction solvent that is a poor solvent for polyolefin resins and a good solvent for plasticizers, and has a boiling point lower than the melting point of polyolefin resins. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation.

[0079] To suppress shrinkage of the polyolefin microporous membrane, a heat treatment such as heat setting or heat relaxation may be performed after the stretching step or after the formation of the polyolefin microporous membrane. The polyolefin microporous membrane may also be subjected to post-treatment such as hydrophilization treatment with a surfactant or the like, crosslinking treatment with ionizing radiation or the like.

[0080] (Method for producing a microporous membrane made of polyolefin resin containing silane-grafted polyolefin) As a method for producing a microporous membrane made of a polyolefin resin containing a silane-grafted polyolefin, the case of a microporous membrane (flat membrane) will be described below, but it is not intended to exclude forms other than flat membranes. The method for producing a microporous membrane containing a silane-grafted polyolefin includes the following steps: (1) Sheet forming process; (2) Stretching process; (3) porous body forming step; and (4) Heat treatment process; The method for producing a microporous membrane containing a silane-grafted modified polyolefin may, if desired, include a kneading step before the sheet-forming step (1) and / or a winding and slitting step after the heat-treatment step (3). However, from the viewpoint of maintaining silane crosslinkability until contact with the electrolyte, it is preferable not to include a silane crosslinking treatment step. The silane crosslinking treatment step is generally a step in which a workpiece containing a silane-grafted modified polyolefin is brought into contact with a mixture of an organometallic catalyst and water, or is immersed in a basic solution or an acid solution, and a silane dehydration condensation reaction is carried out to form oligosiloxane bonds.

[0081] The metal of the organometallic catalyst may be, for example, at least one selected from the group consisting of scandium, titanium, vanadium, copper, zinc, aluminum, zirconium, palladium, gallium, tin, and lead. Examples of organometallic catalysts include dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctoate. These catalysts are known to dramatically accelerate the reaction rate using the reaction mechanism proposed by Weij et al. (FW van. der. Weij: Macromol. Chem., 181, 2541, 1980). In recent years, in order to avoid the environmental and human health hazards posed by organotins, it has been discovered that the Lewis function of copper or titanium chelate complexes can be combined with an organic base to accelerate the reaction of forming siloxane bonds between alkoxysilyl groups, similar to organotin complexes.

[0082] The base solution has a pH greater than 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 viewpoints of safety and silane crosslinkability of the electricity storage device, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0083] The acid solution has a pH of less than 7 and may contain, for example, an inorganic acid, an organic acid, etc. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0084] In the kneading step, the silane-grafted polyolefin, and optionally a plasticizer or inorganic material and other polyolefins can be kneaded using a kneader. From the viewpoints of suppressing the generation of resin aggregates in the production process and maintaining silane crosslinkability until contact with the electrolytic solution, it is preferable not to add a masterbatch resin containing a dehydration condensation catalyst to the kneaded mixture.

[0085] The plasticizer is not particularly limited, but examples thereof include organic compounds that can form a homogeneous solution with polyolefin at temperatures below the boiling point. More specific examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. One plasticizer may be used alone, or two or more may be used in combination. The proportion of the plasticizer is not particularly limited, but the proportion of polyolefin and silane-grafted polyolefin is preferably 20% by mass or more, based on the total mass of the microporous membrane, as needed, from the viewpoint of the porosity of the resulting microporous membrane, and preferably 90% by mass or less from the viewpoint of the viscosity during melt-kneading.

[0086] The sheet forming step is a step of extruding the obtained kneaded product or a mixture of silane-grafted modified polyolefin, ultra-high molecular weight polyolefin, and plasticizer, cooling and solidifying it, and molding it into a sheet. The sheet forming method is not particularly limited, but an example is a method in which the melt extruded after melt kneading is solidified by compression cooling. Examples of cooling methods include a method in which the melt is directly contacted with a cooling medium such as cold air or cooling water, or a method in which the melt is contacted with a roll or press cooled with a refrigerant, and among these, the method in which the melt is contacted with a roll or press cooled with a refrigerant is preferred because of its excellent film thickness controllability.

[0087] From the viewpoint of resin aggregates or the maximum internal heat generation rate in the microporous membrane, the mass ratio of the silane-grafted polyolefin to the ultra-high molecular weight polyethylene (mass of silane-grafted polyolefin / mass of ultra-high molecular weight polyethylene) in the sheet forming step is preferably 0.05 / 0.95 to 0.4 / 0.6, and more preferably 0.06 / 0.94 to 0.38 / 0.62.

[0088] From the viewpoint of improving safety by suppressing thermal runaway during breakdown of the power storage device while providing the separator with low-temperature shutdown capability at 150°C or below and membrane rupture resistance at high temperatures of 180°C or above, it is preferable that the silane-grafted polyolefin used in the sheet-forming step is not a masterbatch resin that contains a dehydration condensation catalyst that crosslinks the silane-grafted polyolefin before the sheet-forming step. Resistance to membrane rupture can be ensured preferably at temperatures of 190°C or above, 200°C or above, 210°C or above, 220°C or above, 230°C or above, 240°C or above, or 250°C or above. The upper limit of the separator membrane rupture temperature is not limited, and it is understood in this technical field that membrane rupture can occur even at temperatures above 250°C.

[0089] The stretching step involves extracting plasticizers or inorganic materials from the resulting sheet as needed, and then stretching the sheet in one or more directions. Examples of sheet stretching methods include MD uniaxial stretching using a roll stretching machine, TD uniaxial stretching using a tenter, sequential biaxial stretching using a roll stretching machine and a tenter, or a combination of a tenter and a tenter, and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. Simultaneous biaxial stretching is preferred from the viewpoint of obtaining a more uniform membrane. The total areal stretching ratio is preferably 8 times or more, more preferably 15 times or more, and even more preferably 20 times or more or 30 times or more, from the viewpoints of uniformity of membrane thickness and the balance between tensile elongation, porosity, and average pore size. A total areal stretching ratio of 8 times or more tends to facilitate the production of a membrane with high strength and good thickness distribution. Furthermore, from the viewpoint of preventing breakage, this areal stretching ratio may be 250 times or less.

[0090] The porous body forming step is a step of extracting a plasticizer from the stretched material after the stretching step to make the stretched material porous. The method for extracting the plasticizer is not particularly limited, but examples include a method of immersing the stretched material in an extraction solvent and a method of showering the stretched material with the extraction solvent. The extraction solvent is not particularly limited, but for example, it is preferable that it is a poor solvent for polyolefins and a good solvent for plasticizers or inorganic materials, and has a boiling point lower than the melting point of polyolefins. Examples of such extraction solvents are not particularly limited, but examples include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropanol; ketones such as acetone and 2-butanone; and alkaline water. The extraction solvents may be used alone or in combination.

[0091] The heat treatment step is a step in which, after the stretching step, plasticizer is extracted from the sheet as needed, followed by further heat treatment to obtain a microporous membrane. The heat treatment method is not particularly limited, but examples include a heat setting method in which stretching and relaxation are performed using a tenter or roll stretching machine. The relaxation operation refers to a shrinking operation performed in the machine direction (MD) and / or transverse direction (TD) of the membrane at a predetermined temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation, or the value obtained by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation, or, when both MD and TD are relaxed, the value obtained by multiplying the MD relaxation rate by the TD relaxation rate. Furthermore, in the winding step, the obtained microporous membrane can be slit as needed and wound around a predetermined core.

[0092] (Method of manufacturing inorganic porous layer) The method for producing the inorganic porous layer is not particularly limited, and known production methods can be used. For example, a method of applying a coating liquid containing inorganic particles and a resin binder (slurry for inorganic porous layer) to a polyolefin resin microporous membrane, regardless of whether the polyolefin resin microporous membrane contains a silane-grafted polyolefin resin. If desired, the slurry for inorganic porous layer may contain a crosslinking agent. A raw material containing inorganic particles and a resin binder and a raw material for a polyolefin resin microporous membrane containing a polyolefin resin may be laminated and extruded by a coextrusion method, or the polyolefin resin microporous membrane and the inorganic porous layer (membrane) may be produced separately and then bonded together.

[0093] The solvent for the coating liquid is preferably one that can uniformly and stably disperse or dissolve the inorganic particles and resin binder, and examples thereof include N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0094] The coating solution may contain the above-mentioned crosslinking agent and various additives such as dispersants such as surfactants, thickeners, wetting agents, antifoaming agents, and pH adjusters including acids and alkalis.

[0095] Examples of methods for dispersing or dissolving the inorganic particles and the resin binder in the medium of the coating liquid include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade or the like.

[0096] Examples of methods for applying the coating liquid to a polyolefin resin microporous membrane 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 doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0097] The method for removing the solvent from the coated film after coating is not particularly limited as long as it does not adversely affect the polyolefin resin microporous film. Examples include a method of drying the polyolefin resin microporous film while fixing it at a temperature below the melting point of the material that constitutes the polyolefin resin microporous film, a method of drying under reduced pressure at a low temperature, and a method of immersing the film in a poor solvent for the resin binder to solidify the resin binder and simultaneously extract the solvent. In addition, some of the solvent may remain as long as it does not significantly affect the device characteristics.

[0098] <Electricity storage device> The separators according to the first and second embodiments can be used in an electricity storage device. The electricity storage device includes a positive electrode, a negative electrode, the separator according to the first or second embodiment disposed between the positive and negative electrodes, and an electrolyte. Specific examples of electricity storage devices include lithium batteries, lithium secondary batteries, lithium ion secondary batteries (LIBs), sodium secondary batteries, sodium ion secondary batteries, magnesium secondary batteries, magnesium ion secondary batteries, calcium secondary batteries, calcium ion secondary batteries, aluminum secondary batteries, aluminum ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, electric double layer capacitors, lithium ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, and zinc-air batteries. Among these, from the viewpoint of practicality, lithium batteries, lithium secondary batteries, LIBs, nickel-metal hydride batteries, and lithium ion capacitors are preferred, and lithium batteries and LIBs are more preferred.

[0099] The electrolyte in the battery may contain water, and the water contained in the system after the battery is fabricated may be water contained in the electrolyte or water carried over from components such as electrodes or separators. The electrolyte may contain a non-aqueous solvent. Examples of the solvent contained in the non-aqueous solvent of this embodiment include alcohols such as methanol and ethanol; aprotic solvents, etc. Among these, aprotic solvents are preferred as the non-aqueous solvent.

[0100] Examples of aprotic solvents include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles, alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the above aprotic solvents have been substituted with halogen atoms.

[0101] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate.

[0102] Examples of fluoroethylene carbonate include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one.

[0103] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0104] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0105] Examples of the chain carbonate include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate.

[0106] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

[0107] Examples of mononitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile.

[0108] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile.

[0109] Examples of dinitriles include malononitrile, succinonitrile, methylsuccinonitrile, glutaronitrile, 2-methylglutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, 2,4-dimethylglutaronitrile, and ethylene glycol bis(propionitrile) ether.

[0110] Examples of cyclic nitriles include benzonitrile.

[0111] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, and isopropyl pivalate. , isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate.

[0112] Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme. Examples of fluorinated ethers include those represented by the general formula Rf aa -OR bb (In the formula, Rf aa is an alkyl group containing a fluorine atom, and R bb is an organic group which may contain a fluorine atom). Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0113] Examples of the compounds in which some or all of the H atoms of the above aprotic solvents have been substituted with halogen atoms include compounds in which the halogen atoms are fluorine atoms.

[0114] Examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonates are represented by the following general formula: R cc -OC(O)OR dd {where, R cc and R dd is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and the formula CH2Rf ee (In the formula, Rf ee is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom), and R cc and / or R dd contains at least one fluorine atom. It can be expressed as:

[0115] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R ff -C(O)OR gg {where, R ff is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, CF2Rf hh , CFHRf hh, and CH2Rf ii and R is at least one selected from the group consisting of gg are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ii and Rf hh is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom, and Rf ii is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ff and / or R gg contains at least one fluorine atom, and R ff If is CF2H, R gg can be expressed as {is not CH3}.

[0116] LIBs, a typical example of an energy storage device, are storage batteries that use lithium transition metal oxides such as lithium cobalt oxide and lithium cobalt composite oxide as the positive electrode, carbon materials such as graphite as the negative electrode, and a non-aqueous organic solvent containing a fluorine-containing lithium salt such as LiPF6 as the electrolyte. When LIBs are charged and discharged, ionized Li (lithium) travels back and forth between the electrodes. Furthermore, because the ionized Li needs to move between the electrodes relatively quickly while suppressing contact between the electrodes, a separator is placed between the electrodes.

[0117] <Method of manufacturing an electricity storage device> The method for producing an electricity storage device using a separator is not particularly limited, but the following method can be exemplified. First, a vertically elongated separator having 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) is produced. Next, positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are laminated in this order and wound into a circular or flat spiral to obtain a wound body. The wound body is placed in a device can (e.g., a battery can) and an electrolyte solution is further injected to produce the device. Alternatively, the device may be produced by folding the electrodes and separator to form a wound body, placing it in a device container (e.g., an aluminum film), and injecting the electrolyte solution.

[0118] At this time, the wound body can be pressed. Specifically, a method can be exemplified in which the separator, the current collector, and the electrode having the active material layer formed on at least one surface of the current collector are stacked together and pressed.

[0119] The pressing temperature is preferably, for example, 20°C or higher, which is a temperature at which adhesiveness can be effectively exhibited. Furthermore, in order to prevent clogging of pores in the separator or thermal shrinkage due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the polyolefin resin microporous membrane, and more preferably 120°C or lower. The pressing pressure is preferably 20 MPa or lower, from the viewpoint of preventing clogging of pores in the separator. The pressing time may be 1 second or less when using a roll press, or may be several hours of surface pressing, but is preferably 2 hours or less from the viewpoint of productivity. Using the separator for an electricity storage device of embodiment 1 or 2 through the above-described manufacturing process can prevent press-back when a wound body consisting of electrodes and a separator is press-molded. Therefore, this is preferable because it can prevent a decrease in yield in the device assembly process and shorten the production process time.

[0120] The electricity storage device, particularly the LIB, manufactured as described above includes the separator according to embodiment 1 or 2, and therefore its performance (e.g., cycle characteristics and safety evaluated by device destruction or heating tests) can be further improved.

[0121] From the viewpoint of ensuring that the silane crosslinking reaction of the polyolefin resin microporous membrane containing the silane-grafted polyolefin is carried out in the produced electricity storage device, it is preferable to carry out the steps of connecting lead terminals to at least one pair of electrodes of the electricity storage device and connecting it to a power source, and performing at least one charge / discharge cycle. The charge / discharge cycle generates a substance that has a catalytic effect on the silane crosslinking reaction in the electrolyte or on the surface of the electrodes, thereby achieving the silane crosslinking reaction.

[0122] Without wishing to be bound by theory, it is believed that the methoxysilane graft moieties are converted to silanols by the presence of trace amounts of moisture in the energy storage device (e.g., moisture contained in components such as electrodes, separators, and electrolytes), undergo crosslinking, and convert to siloxane bonds. Furthermore, when the electrolyte or electrolyte comes into contact with the electrodes, a substance that catalyzes the silane crosslinking reaction is generated in the electrolyte or on the electrode surface. This substance dissolves in the electrolyte and uniformly swells and diffuses into the amorphous portion of the polyolefin where the silane-modified graft moieties are present, thereby uniformly promoting the crosslinking reaction of the separator-containing laminate or wound body. The substance that catalyzes the silane crosslinking reaction may be in the form of an acid solution or film. When the electrolyte contains lithium hexafluorophosphate (LiPF), it may be hydrogen fluoride (HF) generated by the reaction of LiPF with moisture, or a fluorine-containing organic substance derived from hydrogen fluoride (HF).

[0123] When the separator for an electricity storage device according to embodiment 1 or 2 is incorporated into an electricity storage device, the silane-grafted polyolefin in the polyolefin resin microporous membrane is crosslinked, and / or a crosslinked structure is formed by covalent bonds between multiple components in the inorganic porous layer. This is thought to improve the cycle characteristics and / or safety of the electricity storage device while being compatible with conventional manufacturing processes for electricity storage devices. [Example]

[0124] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples and comparative examples. Physical properties in the examples were measured by the following methods.

[0125] (Method for detecting silane-modified polyolefin contained in separators) When the silane-modified polyolefin contained in the separator is crosslinked, it is insoluble or has insufficient solubility in organic solvents, making it difficult to measure the content of the silane-modified polyolefin directly from the separator. In such cases, sample pretreatment can be performed using methyl orthoformate, which does not cause side reactions, to decompose the siloxane bonds into methoxysilanols, followed by solution NMR measurement to detect the silane-modified polyolefin contained in the separator or perform GPC measurement. Pretreatment experiments can be performed with reference to Japanese Patent Nos. 3529854 and 3529858.

[0126] Specifically, the silane-modified polyolefin used as a raw material for separator production 1 H or 13 The NMR identification of C can be used to detect silane-modified polyolefins contained in separators. 1 H and 13 An example of a C NMR measurement technique is described below.

[0127] ( 1 H NMR measurement) The sample was dissolved in o-dichlorobenzene-d4 at 140°C, and the proton resonance frequency was 600 MHz. 1 Obtain a H-NMR spectrum. 1 The H-NMR measurement conditions are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 1 sec Accumulation count: 1000 times or more Sample concentration: 1 wt / vol%

[0128] ( 13 C NMR measurement) The sample was dissolved in o-dichlorobenzene-d4 at 140°C. 13 Obtain a C-NMR spectrum. 13 The measurement conditions for C-NMR are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 5 seconds Accumulation count: 10,000 times or more Sample concentration: 10 wt / vol%

[0129] 1 H and / or 13 By measuring C NMR, it is possible to confirm the amount of silane unit modification in the silane-modified polyolefin and the amount of alkyl group modification in the polyolefin in the raw polyolefin material, and in the separator, it is possible to identify the content of silane-modified polyolefin (-CH2-Si: 1 H, 0.69 ppm, t; 13 C, 6.11 ppm, s) is possible.

[0130] (1) Weight average molecular weight A calibration curve was created by measuring standard polystyrene under the following conditions using a Waters ALC / GPC 150C (trademark). Chromatograms of the following polymers were also measured under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the following method. Column: Tosoh GMH6-HT (trademark) x 2 + GMH6-HTL (trademark) x 2 Mobile phase: o-dichlorobenzene Detector: Differential refractometer Flow rate: 1.0ml / min Column temperature: 140℃ Sample concentration: 0.1 wt% (weight average molecular weight of polyethylene) Each molecular weight component in the obtained calibration curve was multiplied by 0.43 (Q factor of polyethylene / Q factor of polystyrene=17.7 / 41.3) to obtain a molecular weight distribution curve converted into polyethylene, and the weight average molecular weight was calculated. (Weight average molecular weight of resin composition) The weight average molecular weight was calculated using the Q factor value of the polyolefin with the largest mass fraction, in the same manner as for polyethylene.

[0131] (2) Viscosity average molecular weight (Mv) The intrinsic viscosity [η] in decalin solvent at 135°C was determined based on ASTM-D4020. The Mv of polyethylene was calculated using the following formula: [η]=6.77×10 -4 Mv 0.67

[0132] (3) Melt mass-flow rate (MFR) (g / 10 min) Using a melt mass flow rate measuring instrument (Melt Indexer F-F01) manufactured by Toyo Seiki Seisaku-sha, the weight of the resin extruded for 10 minutes under conditions of 190°C and a load of 2.16 kg was determined as the MFR value.

[0133] (4) Thickness of the microporous membrane and inorganic porous layer (μm) The thickness of the microporous membrane was measured using a micro thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, at room temperature of 23±2°C and a relative humidity of 60%. Specifically, the thickness was measured at five points at approximately equal intervals across the entire width in the TD direction, and the average value was obtained. The thickness of the separator was also measured in the same manner, and the thickness of the microporous membrane was subtracted from the thickness of the separator, and the resulting value was taken as the thickness of the inorganic porous layer.

[0134] (5) Porosity of the microporous membrane (%) A 10cm x 10cm square sample was cut from the microporous membrane and its volume (cm 3 ) and mass (g), and then calculate the density (g / cm 3 ), the porosity was calculated using the following formula. The density of the mixed composition was calculated from the density of each of the raw materials used and the mixing ratio. For example, in the case of a polyolefin microporous membrane made of polyethylene, the density of the mixed composition is 0.95 (g / cm 3 ) can be calculated assuming that Porosity (%) = (volume - mass / density of mixed composition) / volume × 100

[0135] (6) Air permeability and air permeability increase (sec / 100cm) of the microporous membrane 3 ) The air permeability of the microporous membrane was measured using a Gurley air permeability meter, G-B2 (trademark), manufactured by Toyo Seiki Co., Ltd., in accordance with JIS P-8117 (2009). The air permeability of the separator was also measured in the same manner, and the air permeability of the separator was subtracted from the air permeability of the microporous membrane, and the resulting value was defined as the increase in air permeability.

[0136] (7) Surface roughness of the microporous membrane (μm) In accordance with JIS B0671-2002, the surface roughness (μm) of the microporous membrane was calculated using a Keyence VK-X200 under the following conditions: measurement mode: surface profile; measurement pitch: 0.2 μm; surface roughness calculation area: 216 μm × 287 μm (observation magnification: 50x).

[0137] (8) Battery Destruction Safety Test 1 (Battery Destruction Test 1) The safety test involves driving an iron nail into a battery charged to 4.5V at a speed of 20mm / sec, penetrating it to cause an internal short circuit. This test can clarify the phenomenon that occurs during an internal short circuit by measuring the time-dependent behavior of the battery's voltage drop and the behavior of the battery's surface temperature rise due to an internal short circuit. In addition, in the event of an internal short circuit, insufficient shutdown function of the separator or rupture at low temperatures may cause the battery to suddenly heat up, which may result in the electrolyte igniting, causing the battery to smoke and / or explode.

[0138] (Preparation of batteries for use in safety tests) a. Preparation of the positive electrode A slurry was prepared by dispersing 92.2% by mass of lithium-cobalt composite oxide LiCoO2 as the positive electrode active material, 2.3% by mass each of flake graphite and acetylene black as conductive materials, and 3.2% by mass of PVdF as a resin binder in NMP. This slurry was applied to one side of a 20 μm thick aluminum foil that served as a positive electrode current collector using a die coater, dried at 130 °C for 3 minutes, and then compression molded using a roll press. At this time, the amount of applied positive electrode active material was 250 g / m 2 , the bulk density of the active material is 3.00 g / cm 3 It was adjusted to be.

[0139] b. Preparation of negative electrode A slurry was prepared by dispersing 96.9% by mass of artificial graphite as the negative electrode active material, and 1.4% by mass of ammonium salt of carboxymethyl cellulose and 1.7% by mass of styrene-butadiene copolymer latex as the resin binder in purified water. This slurry was applied to one side of a 12 μm-thick copper foil that served as the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press. The amount of active material applied to the negative electrode was 106 g / m. 2 , the active material bulk density is 1.35 g / cm 3 It was adjusted to be.

[0140] c. Preparation of non-aqueous electrolyte The solution 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.

[0141] d. Battery assembly The separator was cut into strips measuring 60 mm in the transverse (TD) direction and 1000 mm in the longitudinal (MD) direction, folded zigzag, and stacked alternately between the separators (12 positive electrodes, 13 negative electrodes). The positive electrodes measured 30 mm x 50 mm, and the negative electrodes measured 32 mm x 52 mm. The zigzag stack was placed in a laminated bag, and the nonaqueous electrolyte prepared in step c above was poured into the bag and sealed. After leaving the battery at room temperature for one day, the battery was charged at 3 mA (0.5 C) in a 25°C atmosphere up to a battery voltage of 4.2 V. After reaching 4.2 V, the current was reduced from 3 mA to maintain the battery voltage at 4.2 V. This method performed the initial charge after battery fabrication for a total of 6 hours. The battery was then discharged at 3 mA (0.5 C) down to a battery voltage of 3.0 V.

[0142] (Maximum heat generation rate) An iron nail was driven into the resulting battery at a speed of 20 mm / sec until it penetrated the battery. The battery surface temperature was then measured over 300 seconds using a thermocouple. From the temperature change graph, the rate at which the temperature change per second was greatest was determined to be the maximum heat generation rate.

[0143] (Voltage drop time) An iron nail was driven into the resulting battery at a speed of 20 mm / sec until it penetrated the battery, and the time required for the voltage to drop from 4.5 V to 3 V was determined as the voltage drop time (3 V drop time).

[0144] (9) Evaluation of cycle characteristics 1 (battery cycle stability 1) and the method for manufacturing the battery A battery for evaluating cycle characteristics was fabricated according to the same methods as a. to c. of the battery fabrication method used in the above item "(8) Battery Destruction Test 1", except that assembly was performed according to the following d. The resulting battery was charged and discharged 100 times in a 60°C atmosphere. The battery was charged at a current of 6.0 mA (1.0 C) up to a battery voltage of 4.2 V, and then the current was reduced from 6.0 mA to maintain 4.2 V. This method of charging for a total of 3 hours was used. The battery was discharged at a current of 6.0 mA (1.0 C) down to a battery voltage of 3.0 V. 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 in the battery cycle stability was evaluated as having good cycle characteristics. d. Battery assembly The separator was cut into 18 mm diameter circles, and the positive and negative electrodes were cut into 16 mm diameter circles. 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, and then placed in a lidded stainless steel container. 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 nonaqueous electrolyte obtained in section (8) Battery Destruction Test 1 above was poured into the container and sealed. After leaving the battery at room temperature for one day, the battery was charged at a current of 3 mA (0.5 C) in a 25°C atmosphere up to a battery voltage of 4.2 V. After reaching this voltage, the current was reduced from 3 mA to maintain the battery voltage at 4.2 V. This was the first charge after battery fabrication, for a total of 6 hours. The battery was then discharged at a current of 3 mA (0.5 C) down to a battery voltage of 3.0 V.

[0145] (10) Shutdown & Membrane Rupture Temperature Measurement 1 (Fuse / Meltdown (F / MD) Characteristics 1) The positive electrode, separator, and negative electrode were cut into a 200 mm diameter circle and stacked together to form a laminate. The electrolyte was then added and allowed to soak throughout. The laminate was then placed in the center of a 600 mm diameter circular aluminum heater, which was then pressurized from above and below to 0.5 MPa using a hydraulic jack. The resistance (Ω) between the electrodes was measured while the laminate was heated with the aluminum heater at a temperature increase rate of 2°C / min. The fuse temperature (shutdown temperature) was determined as the temperature at which the resistance between the electrodes, including the separator fuse, rose and exceeded 1000 Ω for the first time. The meltdown temperature (rupture temperature) was determined as the temperature at which the resistance dropped below 1000 Ω after further heating. For the measurements, a resistance measurement wire was attached to the back of the aluminum foil of the positive electrode prepared as described in "(8) Battery Destruction Test" under "a. Preparation of the Positive Electrode" using conductive silver paste. In addition, in the measurement, a negative electrode prepared in the above-mentioned "(8) Battery Destruction Test" item "b. Preparation of Negative Electrode" was used, with a resistance measurement wire attached to the back of the copper foil with conductive silver paste. Furthermore, in the measurement, the electrolyte prepared in the above-mentioned "(8) Battery Destruction Test" item "c. Preparation of Non-Aqueous Electrolyte" was also used for the F / MD characteristic test.

[0146] (11) Solvent immersion test The microporous membrane on which the inorganic porous layer was formed was cut into a 5.0 x 5.0 cm square, which was then immersed in acetone at 25°C in a glass sample can, and the entire glass sample can was vibrated at a frequency of 40 Hz for 10 minutes using an ultrasonic cleaner. Thereafter, the microporous membrane with the inorganic porous layer formed thereon was removed from the acetone and air-dried. Then, using an Epson scanner, the side with the inorganic porous layer formed thereon was scanned as a monochrome image with 8-bit gradation and 600 dpi resolution (see Figure 3). The captured images were subjected to image processing according to the following methods (I) to (IV), and the percentage of the peeled area (peeled area (%)) was calculated.

[0147] (I) The captured image was designated as evaluation image P, and the lengths of one side of evaluation image P were designated as X and Y. X and Y can be equivalent to the lengths of one side of the cut-out microporous membrane. Therefore, here, X = 5 cm and Y = 5 cm.

[0148] (II) In the evaluation image P, the direction along the X side is the X axis and the direction along the Y side is the Y axis, and the gray value of the pixel at the coordinate position (x, y) constituting the evaluation image P is defined as P(x, y). Then, a histogram was created for all Xp × Yp gray values ​​P(x, y) contained in the evaluation image P. An example of a histogram obtained by evaluation of Example 15 is shown in Figure 1. In Figure 1, the vertical axis (logarithmic) represents frequency values, and the horizontal axis represents gray values. From Figure 1, peaks representing bright areas (peaks on the side with smaller gray values) and peaks representing dark areas (peaks on the side with larger gray values) were confirmed. The gray value corresponding to the apex of the peak representing the bright area was determined as the gray value Pb in the bright area, and the gray value corresponding to the apex of the peak representing the dark area was determined as the gray value Pd in ​​the dark area. In Figure 1, the frequency value giving the gray value Pb in the bright area and the frequency value giving the gray value Pd in ​​the dark area are each represented by an "x" mark.

[0149] If the number of pixels corresponding to either the bright or dark areas is relatively small, the peak of the area with the smaller number of pixels may not be clearly visible. Even in this case, it is possible to determine the grayscale values ​​Pb in the bright areas and Pd in ​​the dark areas according to the shape of the histogram obtained, as follows:

[0150] (II-1) Another example of a histogram is shown in Figure 2. The vertical and horizontal axes are the same as in the example in Figure 1. When the number of pixels corresponding to the dark areas is relatively small, as shown in Figure 2, peaks indicating bright areas can be identified, but peaks indicating dark areas may not be clearly identified. In this case, the frequency value on the histogram remains approximately constant in the range where the gray value is greater than the peak corresponding to brightness, but the frequency value begins to suddenly drop as the gray value increases (the portion corresponding to the right shoulder of the histogram) can be determined as the gray value Pd in ​​the dark areas. In Figure 2, the frequency value that gives the gray value Pb in the bright areas and the frequency value that gives the gray value Pd in ​​the dark areas are each represented by an "x" mark.

[0151] (II-2) When the number of pixels corresponding to the bright areas is relatively small, although a peak indicating the dark areas can be confirmed, the peak indicating the bright areas may not be clearly confirmed (although this is not shown in the figure). In this case, the gradation value of the part (the left shoulder of the histogram) where the frequency value remains approximately constant in the range of gradation values ​​smaller than the peak corresponding to the dark areas but where the frequency value begins to suddenly drop as the gradation value becomes smaller can be determined as the gradation value Pb in the bright areas.

[0152] (III) Using the gradation value Pb in the bright area and the gradation value Pd in ​​the dark area determined as described above, their average value was calculated using the following formula, and the obtained value was determined as the threshold value Ps. In Figures 1 and 2, the frequency value that gives the threshold value Ps is represented by an "x" mark. Threshold Ps = (gray value in bright areas Pb + gray value in dark areas Pd) / 2

[0153] (IV) An array BW(x,y) was prepared as a binarized image of the same size as the evaluation image P. For pixels P(x,y) in the evaluation image P that had a gray value greater than the threshold Ps, 1 was assigned to the BW(x,y) corresponding to that pixel P(x,y), and the pixel was treated as a bright area. For pixels P(x,y) that had a gray value equal to or less than the threshold Ps, 0 was assigned to the BW(x,y) corresponding to that pixel P(x,y), and the pixel was treated as a dark area. In this way, a binarized image BW was obtained in which the bright and dark areas of the evaluation image P were distinguished (see Figure 4).

[0154] (V) The number of BW(x,y) values ​​in the binarized image BW that have a value of 1 was determined as the number of bright pixels Br. Similarly, the number of BW(x,y) values ​​in the binarized image BW that have a value of 0 was determined as the number of dark pixels Dk. The equation Br + Dk = Xp × Yp holds between Br, Dk, Xp, and Yp.

[0155] (VI) The percentage of bright areas (Brp) was calculated using the formula Brp = Br / (Xp × Yp), and the percentage of dark areas (Dkp) was calculated using the formula Dkp = Dk / (Xp × Yp). The percentage of bright areas (Brp) was determined as the percentage (%) of the area of ​​peeled areas, and the percentage of dark areas (Dkp) was determined as the percentage (%) of the area of ​​normal areas.

[0156] [Production example of silane-grafted polyolefin] The raw polyethylene was polyethylene with a viscosity-average molecular weight of 20,000. While melt-kneading the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) was added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane was added, and an addition reaction was carried out to introduce alkoxysilyl groups into the α-olefin polymer, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) was added to adjust the radical concentration in the reaction system and suppress chain reaction (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water, pelletized, and then heated and dried at 80°C for 2 days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1500 ppm or less. The modification reaction using trimethoxyalkoxide-substituted vinylsilane as described above yielded a silane-grafted polyethylene with an MFR (190° C.) of 0.24 g / min (shown as "Silane-modified polyethylene (B)" in Tables 1, 2, 5, or 6).

[0157] [Example 1] (Production of silane-crosslinkable polyolefin microporous membrane) 79.2% by mass of homopolymer polyethylene with a weight-average molecular weight of 700,000 (referred to as "polyethylene (A)" in Tables 1, 2, 5, and 6) was combined with 19.8% by mass of the silane-modified polyethylene (B) obtained above to form a resin blend with resin compositions of polyethylene (A) and (B) of 0.8 and 0.2, respectively. 1% by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to the blend, and the mixture was dry-blended using a tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder under a nitrogen atmosphere using a feeder. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1100 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product under the following conditions: MD magnification 7.0 times, TD magnification 6.2 times, and biaxial stretching temperature 120°C. Next, the stretched gel sheet was introduced into a dichloromethane tank and thoroughly immersed in dichloromethane to extract and remove the liquid paraffin, and then the dichloromethane was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 133°C and a stretch ratio of 2.1 times, followed by a relaxation operation to a stretch ratio of 2.0 times in the TD direction. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a microporous membrane for evaluation. The thickness, air permeability, porosity, surface roughness, etc. of the obtained microporous membrane for evaluation were measured and the results are shown in Table 1.

[0158] (Production of inorganic porous layer) (Acrylic latex manufacturing method) The acrylic latex used as the resin binder is produced by the following method. A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation). 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 obtain 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. The above emulsion was prepared by mixing a mixture of: 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 "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and 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 with 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.

[0159] (Formation of inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.6 parts by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by weight (solids equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids concentration) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion was milled using a bead mill (cell volume 200 cc, zirconia beads 0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To the dispersion with the adjusted particle size distribution, 2.0 parts by weight (solids equivalent) of acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Thereafter, 3.0 parts by mass (solid content equivalent) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. was added as a crosslinking agent to prepare an inorganic particle-containing slurry. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0160] [Examples 2-14, Comparative Examples 1-18] Separators with various physical properties were produced using the same method as in Example 1, except that the presence or absence of silane-modified polyethylene (B), various raw material compositions, HS ratios, stretching temperatures, etc. were adjusted as shown in Tables 1 and 2. The crosslinking agent used in Examples 2, 3, 11-14 and Comparative Examples 1-3 was Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. The crosslinking agent used in Example 4 was Carbodilite V-02 manufactured by Nisshinbo Chemical Inc. The crosslinking agent used in Example 5 was Duranate WB40-100 manufactured by Asahi Kasei Corporation, and the crosslinking agent used in Example 6 was Denacol EX-61B manufactured by Nagase ChemteX Corporation, which is an epoxy-based crosslinking agent. In Examples 7, 9, and 10, tetraethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd. was used; in Example 8, 3-aminopropyltrimethoxysilane KBM-903 manufactured by Shin-Etsu Chemical Co., Ltd. was used; in Comparative Examples 9 and 14, Hardener 12A manufactured by Asahi Kasei Corporation was used; in Comparative Examples 10, 12, 15, and 17, ethylenediaminetetraacetic acid (EDTA) manufactured by Sigam-Aldrich was used; and in Comparative Examples 11, 13, 16, and 18, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) manufactured by Sigam-Aldrich was used.

[0161] The separators obtained in the above examples and comparative examples were used to carry out the various measurements and tests described above. The test results are shown in Tables 1 and 2.

[0162] [Table 1-1]

[0163] [Table 1-2]

[0164] [Table 1-3]

[0165] [Table 2-1]

[0166] [Table 2-2]

[0167] [Table 2-3]

[0168] [Table 2-4]

[0169] [Table 2-5]

[0170] [Example 15] (Production of microporous polyolefin membranes) A mixture of polymers was obtained by dry blending again using a tumbler blender. The resulting mixture of polymers was then purged with nitrogen and fed to a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also used. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The feeder and pump were adjusted so that the ratio of liquid paraffin to the total mixture extruded after melt-kneading was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 230°C, a screw rotation speed of 240 rpm, and a discharge rate of 18 kg / h.

[0171] The melt-kneaded mixture was then extruded through a T-die and cast onto a cooling roll whose surface temperature was controlled at 25°C, yielding a gel sheet with a raw film thickness of 1,400 μm. The membrane was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched. The stretching conditions were an MD magnification of 7.0x, a TD magnification of 6.0x (i.e., 7x6x), and a biaxial stretching temperature of 125°C. The membrane was then introduced into a methyl ethyl ketone bath and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin. The methyl ethyl ketone was then dried and removed. The membrane was then introduced into a TD tenter for heat setting (sometimes abbreviated as "HS"), where it was subjected to HS at a heat setting temperature of 125°C and a stretching ratio of 1.8x, followed by relaxation to 1.2x. The resulting microporous membrane was then trimmed and wound into a mother roll with a width of 1,100 mm and a length of 5,000 m, yielding a microporous membrane. The film thickness, air permeability, porosity, and surface roughness of the obtained film were measured and are shown in Table 3.

[0172] (Production of inorganic porous layer) (Acrylic latex manufacturing method) The acrylic latex used as the resin binder is produced by the following method. A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation). 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 obtain 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. The above emulsion was prepared by mixing a mixture of: 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 "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and 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 with 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.

[0173] (Formation of inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.6% by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.40% by weight (solids content equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids content) as an ionic dispersant in 100% by weight of water. The resulting dispersion was milled using a bead mill (cell volume 200 cc, zirconia beads 0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To the dispersion with the adjusted particle size distribution, 2.0% by weight (solids content equivalent) of acrylic latex (40% solids content, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Thereafter, 3.0% by mass (solid content equivalent) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. was added as a crosslinking agent to prepare a slurry containing inorganic particles. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0174] [Examples 16-27, Comparative Examples 19-29] Separators with various physical properties were produced by adjusting the HS ratio and stretching temperature in the same manner as in Example 15. The crosslinking agent used in Examples 16, 24-27 and Comparative Examples 19-21 was Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. The crosslinking agent used in Example 17 was Carbodilite V-02 manufactured by Nisshinbo Chemical Inc. The crosslinking agent used in Example 18 was Duranate WB40-100 manufactured by Asahi Kasei Corporation, and the crosslinking agent used in Example 19 was Denacol EX-61B manufactured by Nagase ChemteX Corporation as an epoxy crosslinking agent. Examples 20, 22, and 23 used alkoxy oligomer (KR-500) manufactured by Shin-Etsu Chemical Co., Ltd.; Example 21 used 3-aminopropyltrimethoxysilane KBM-903 manufactured by Shin-Etsu Chemical Co., Ltd.; Comparative Example 25 used Hardener 12A manufactured by Asahi Kasei Corporation; Comparative Examples 26 and 28 used ethylenediaminetetraacetic acid (EDTA) manufactured by Sigam-Aldrich; and Comparative Examples 27 and 29 used 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) manufactured by Sigam-Aldrich.

[0175] The various tests described above were carried out using the separators obtained in the above examples and comparative examples. The test results are shown in Tables 3 and 4. In the tables, the unit "mass %" is written as "wt%".

[0176] [Table 3-1]

[0177] [Table 3-2]

[0178] [Table 4-1]

[0179] [Table 4-2]

[0180] [Example 28] (Production of silane-crosslinkable polyolefin microporous membrane) 79.2% by mass of homopolymer polyethylene (A) with a weight-average molecular weight of 800,000 was combined with 19.8% by mass of the silane-modified polyethylene (B) obtained above to form a resin blend in which the resin compositions of polyethylene (A) and (B) were 0.8 and 0.2, respectively. 1% by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant to the blend, and the mixture was dry-blended using a tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 70% by mass (i.e., the polymer concentration was 30% by mass). The melt-kneading conditions were a set temperature of 220°C, a screw rotation speed of 300 rpm, and a discharge rate of 18 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1150 µm. The sheet was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product under the following conditions: MD magnification 7.0 times, TD magnification 6.7 times, and biaxial stretching temperature 119°C. Next, the stretched gel sheet was introduced into a dichloromethane tank and thoroughly immersed in dichloromethane to extract and remove the liquid paraffin, and then the dichloromethane was dried and removed to obtain a porous body. Next, the porous body was introduced into a TD tenter for heat setting (HS), where HS was performed at a heat setting temperature of 132°C and a stretch ratio of 2.1 times, followed by a relaxation operation to a stretch ratio of 1.7 times in the TD direction. Thereafter, the ends of the obtained microporous membrane were cut off and taken up into a mother roll having a width of 1,100 mm and a length of 5,000 m. In the above evaluation, the microporous membrane unwound from the mother roll was slit as needed and used as a microporous membrane for evaluation. The obtained microporous membrane for evaluation was measured for thickness, surface roughness, air permeability, porosity, etc., and the results are shown in Table 5.

[0181] (Production of inorganic porous layer) (Acrylic latex manufacturing method) The acrylic latex used as the resin binder is produced by the following method. A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as an emulsifier, and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation). 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 obtain 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. The above emulsion was prepared by mixing a mixture of: 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 "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and 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 with a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -20°C.

[0182] (Formation of inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.60 parts by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.40 parts by weight (solids equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids concentration) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion was milled using a bead mill (cell volume 200 cc, zirconia beads 0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 0.8 μm. To the dispersion with the adjusted particle size distribution, 2 parts by weight (solids equivalent) of acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -20°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Thereafter, 3 parts by mass (solid content equivalent) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. was added as a crosslinking agent to prepare a slurry containing inorganic particles. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0183] [Examples 29-41, Comparative Examples 30-44] Separators with various physical properties were produced using the same method as in Example 28, except that the presence or absence of silane-modified polyethylene (B), the various raw material compositions, HS ratios, stretching temperatures, etc. were adjusted as shown in Table 5 or Table 6. The crosslinking agent used in Examples 29, 30, and 38-41 was Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. The crosslinking agent used in Example 31 was Carbodilite V-02 manufactured by Nisshinbo Chemical Inc. The crosslinking agent used in Example 32 was Duranate WB40-100 manufactured by Asahi Kasei Corporation, and the crosslinking agent used in Example 33 was Denacol EX-61B manufactured by Nagase ChemteX Corporation as an epoxy crosslinking agent. In Examples 34, 36, and 37, tetraethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd. was used; in Example 35, 3-aminopropyltrimethoxysilane KBM-903 manufactured by Shin-Etsu Chemical Co., Ltd. was used; in Comparative Examples 35 and 40, Hardener 12A manufactured by Asahi Kasei Corporation was used; in Comparative Examples 36, 38, 41, and 43, ethylenediaminetetraacetic acid (EDTA) manufactured by Sigam-Aldrich Co., Ltd. was used; and in Comparative Examples 37, 39, 42, and 44, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) manufactured by Sigam-Aldrich Co., Ltd. was used.

[0184] The separators obtained in the above Examples and Comparative Examples were used to carry out the various measurements and tests described above, particularly solvent immersion tests, F / MD measurements, measurements of air permeability increase after coating, battery cycle tests, and battery destruction tests. The test results are shown in Tables 5 to 6. In Examples 28-41 and Comparative Examples 30-44, the positive electrode active material was LiNi, which has poorer thermal stability than LiCoO2, as shown below. 3 / 5 Mn 1 / 5 Co 1 / 5 Because the temperature was changed to O2 and the speed at which the iron nails were driven into the battery was changed from 20 mm / sec to 30 mm / sec, the evaluation system became stricter than the above-mentioned "Battery Cycle Stability 1" and "Battery Destruction Test 1," and therefore in Tables 5 and 6, they are displayed as "Battery Cycle Stability 2" and "Battery Destruction Test 2."

[0185] (12) Battery cycle stability 2 (cycle test 2), battery destruction test 2 (nail penetration test 2) a. Preparation of the positive electrode LiNi as the positive electrode active material 3 / 5 Mn 1 / 5 Co1 / 5 O2, carbon black as a conductive additive, and polyvinylidene fluoride solution as a binder were mixed in a solids mass ratio of 91:5:4, and N-methyl-2-pyrrolidone was added as a dispersion solvent to a solids content of 68 mass%. The mixture was further mixed to prepare a slurry solution. This slurry solution was applied to one side of a 15 μm thick aluminum foil so that part of the aluminum foil was exposed, and the solvent was then dried and removed to obtain a coating amount of 175 g / m. 2 Furthermore, the density of the positive electrode mixture was 2.8 g / cm 3 The coated area was then cut to a size of 30 mm x 50 mm, including the exposed aluminum foil area, to obtain a positive electrode.

[0186] b. Preparation of negative electrode Artificial graphite as the negative electrode active material, styrene butadiene rubber as the binder, and a carboxymethyl cellulose aqueous solution were mixed in a solids mass ratio of 96.4:1.9:1.7, and water was added as a dispersion solvent to a solids content of 50 mass%. The mixture was further mixed to prepare a slurry solution. This slurry solution was applied to one side of a 10 μm thick copper foil so that part of the copper foil was exposed, and the solvent was then dried and removed to obtain a coating amount of 86 g / m. 2 Furthermore, the density of the negative electrode mixture was 1.45 g / cm 3 The coated area was then cut to a size of 32 mm x 52 mm, including the exposed copper foil area, to obtain a negative electrode.

[0187] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution 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, and further adding vinylene carbonate to the solution to a concentration of 1.0 wt %.

[0188] d. Battery assembly A 60 mm x 40 mm square was cut out from the separator to prepare a sample. A 55 mm-wide long separator was folded zigzag to form a stack consisting of 15 double-sided negative electrodes and 14 double-sided positive electrodes, with the active material surfaces of the positive and negative electrodes facing each other and interposed between the positive and negative electrodes. The inorganic porous layer of the sample was positioned facing the positive electrode. Aluminum lead strips with sealant were welded to the exposed portions of 14 aluminum foil positive electrodes, and nickel lead strips with sealant were welded to the exposed portions of 15 copper foil negative electrodes. The stack was then inserted into an aluminum laminate exterior, and three sides (the exposed sides of the positive and negative electrode lead strips and the other two sides) were laminated and sealed. The nonaqueous electrolyte was then poured into the exterior, and the opening was sealed to form a 28-sided laminated battery. The resulting battery was left at room temperature for one day, then charged at a constant current of 330 mA (0.3 C) in an atmosphere of 25°C up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V. This method was used for the first charge after battery fabrication for a total of 8 hours. The battery was then discharged at a current of 330 mA (0.3 C) down to a battery voltage of 3.0 V.

[0189] Evaluation of battery cycle stability2 The battery obtained in "d. Battery assembly" above was charged and discharged 1000 times in a 25°C atmosphere. The battery was charged at a constant current of 1 A (1.0 C) up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V for a total of 3 hours. The battery was discharged at a current of 1 A (1.0 C) down to a battery voltage of 3.0 V. The capacity retention rate was calculated from the discharge capacity at the 1000th cycle and the discharge capacity at the first cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0190] Battery Destruction Safety Test 2 (Battery Destruction Test 2) The safety test involves driving an iron nail into a battery charged to 4.5V at a speed of 30mm / sec, penetrating it to cause an internal short circuit. This test can clarify the phenomenon that occurs during an internal short circuit by measuring the time-dependent behavior of the battery's voltage drop and the behavior of the battery's surface temperature rise due to an internal short circuit. In addition, in the event of an internal short circuit, insufficient shutdown function of the separator or rupture at low temperatures may cause the battery to suddenly heat up, which may result in the electrolyte igniting, causing the battery to smoke and / or explode.

[0191] (13) Shutdown & Membrane Rupture Temperature Measurement 2 (Fuse / Meltdown (F / MD) Characteristics 2) In Examples 28-41 and Comparative Examples 30-44, the F / MD characteristics were measured as follows. The positive electrode, separator, and negative electrode were cut into a circular shape with a diameter of 200 mm and stacked together to form a laminate. The resulting laminate was then filled with electrolyte and allowed to soak through. The laminate was then sandwiched in the center of a circular aluminum heater with a diameter of 600 mm. A hydraulic jack was used to pressurize the heater from above and below to 0.5 MPa, completing the preparation for measurement. The resistance (Ω) between the electrodes was measured while heating the laminate with the aluminum heater at a temperature increase rate of 2°C / min. The fuse temperature (shutdown temperature) was determined as the temperature at which the resistance between the electrodes, including the separator fuse, rose and exceeded 1000 Ω for the first time. Further heating was continued, and the temperature at which the resistance dropped below 1000 Ω was determined as the meltdown temperature (film rupture temperature). For the measurements, a resistance measurement wire was attached to the back of the aluminum foil of the positive electrode prepared in section (12) "a. Preparation of the Positive Electrode" using conductive silver paste. In addition, in the measurement, a negative electrode prepared in the above item (12) "b. Preparation of negative electrode" was used, with a resistance measurement wire attached to the back of the copper foil with conductive silver paste. Furthermore, in the measurement, the electrolyte prepared in the above item (12) "c. Preparation of non-aqueous electrolyte" was also used for the F / MD characteristic test.

[0192] [Table 5-1]

[0193] Table 5-2

[0194] Table 5-3

[0195] Table 6-1

[0196] Table 6-2

[0197] Table 6-3

[0198] Table 6-4

Claims

1. A separator for an electricity storage device comprising: a polyolefin resin microporous membrane; and an inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, the inorganic porous layer contains inorganic particles, a resin binder, and a crosslinking agent in a mass ratio of 0.1 mass % to 5 mass %; the inorganic porous layer has at least one selected from the group consisting of (i) covalent bonds between the inorganic particles, (ii) covalent bonds between the resin binders, and (iii) covalent bonds between the inorganic particles and the resin binder; the inorganic porous layer has a thickness of 0.05 μm or more and 5 μm or less; the crosslinking agent is any one of an oxazoline-based crosslinking agent, a carbodiimide-based crosslinking agent, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an alkoxysilane, and a polyfunctional group-containing alkoxysilane compound, or any combination thereof; The polyolefin resin microporous membrane has a thickness of 4.0 μm or more and 20 μm or less, the porosity of the polyolefin resin microporous membrane is 30% or more and 80% or less; The polyolefin resin microporous membrane contains a silane-grafted polyolefin, and when the separator for an electricity storage device comes into contact with an electrolyte, a silane crosslinking reaction of the silane-grafted polyolefin is initiated.

2. 2. The separator for an electricity storage device according to claim 1, wherein the electrolytic solution is non-aqueous and contains a fluorine (F)-containing lithium salt.

3. The separator for an electricity storage device according to claim 1 or 2, wherein the polyolefin resin microporous film contains a polyolefin other than the silane-grafted polyolefin.

4. The separator for an electricity storage device according to any one of claims 1 to 3, wherein the inorganic porous layer includes a crosslinked structure.

5. 5. The electricity storage device separator according to claim 4, wherein the crosslinked structure in the inorganic porous layer is formed by at least one reaction selected from the group consisting of a nucleophilic substitution reaction, a nucleophilic addition reaction, an electrophilic addition reaction, and a silane coupling reaction.

6. 6. The separator for an electricity storage device according to claim 1, wherein the resin binder has a nucleophilic substitution or nucleophilic addition reactive functional group.

7. The separator for an electricity storage device according to any one of claims 1 to 6, wherein the nucleophilic substitution or nucleophilic addition reactive functional group of the resin binder is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and an amino group.

8. A separator for an electricity storage device described in any one of claims 1 to 7, wherein the inorganic particles have polar functional groups on their surfaces.

9. A separator for an electricity storage device according to claim 1, wherein the inorganic particles have silicon-containing functional groups on their surfaces.

10. The separator for an electrical storage device according to claim 9, wherein the silicon-containing functional group is at least one selected from the group consisting of an alkoxysilyl group, a halogen-substituted silyl group, and a silazane group.

11. The separator for an electricity storage device according to any one of claims 1 to 10, wherein the crosslinking agent has a nucleophilic substitution reactive functional group and / or an electrophilic addition reactive functional group.

12. The separator for an electricity storage device according to any one of claims 1 to 11, wherein the crosslinking agent has a nucleophilic substitution reactive functional group and an electrophilic addition reactive functional group.

13. The separator for an electricity storage device according to claim 11 or 12, wherein the nucleophilic substitution reactive functional group of the crosslinking agent is an oxazoline group and / or an epoxy group.

14. 13. The separator for an electricity storage device according to claim 11 or 12, wherein the electrophilic addition reactive functional group of the crosslinking agent is at least one selected from the group consisting of an isocyanate group, a thioisocyanate group, a carbodiimide group, an allene group, an oxime group, and a carbonyl group.

15. A separator for an electricity storage device described in any one of claims 1 to 14, wherein polar functional groups are present on the surface of the inorganic particles, the cross-linking agent is present between the polar functional groups and the resin binder, and a cross-linked structure is formed by covalent bonds between the polar functional groups, the cross-linking agent, and the resin binder.

16. An electricity storage device comprising an electrode, an electrolyte solution, and the electricity storage device separator according to any one of claims 1 to 15.

17. A secondary battery comprising an electrode, an electrolytic solution, and the separator for an electricity storage device according to any one of claims 1 to 15.

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