Inorganic coating layer crosslinking 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 a power storage device, and more particularly to a separator for a power storage device including an inorganic coating layer (inorganic porous layer) forming a crosslinked structure.

Background Art

[0002] Microporous membranes are widely used as separation or selective permeation separation membranes for various substances, and as isolation materials. Examples of their applications include precision filtration membranes, separators for fuel cells, capacitors, or base materials for functional membranes for filling pores with functional materials to exhibit new functions, separators for power storage devices, and the like. Among them, microporous membranes made of polyolefin resins are suitably used as separators for lithium ion secondary batteries (LIBs) or constituent materials thereof, which are widely mounted in notebook personal computers, mobile phones, digital cameras, and the like.

[0003] Here, for the purpose of improving heat resistance and the like, separators provided with a crosslinked coating layer (for example, an inorganic porous layer containing inorganic particles and a resin binder) on the surface of the microporous membrane have been proposed (see Patent Documents 1 to 5). In addition, in order to ensure the safety of the battery, it has also been proposed to form a crosslinked structure in the microporous membrane by ring-opening of norbornene by irradiation with ultraviolet rays, electron beams, or the like (see Patent Document 6).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0005] In recent years, as lithium-ion batteries (LIBs) have become more densely packed and have higher energy densities, further improvements in cycle characteristics and safety (e.g., safety as evaluated by battery destruction tests) are expected for LIBs, and 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 enhancing the above-mentioned performance of LIBs. Furthermore, when a crosslinking structure is formed in a microporous membrane by light irradiation as described in Patent Document 6, the light irradiation may become uneven, resulting in a non-uniform crosslinking structure. This is thought to be because the area around the crystalline portion of the resin constituting the microporous membrane is easily crosslinked by light. When a microporous membrane with a non-uniform crosslinking structure is used as a separator for LIBs, the LIB may deform when heated. Such problems are not limited to separators for LIBs, but also exist for separators for energy storage devices such as LIBs.

[0006] In view of the above problems, the present invention aims to provide a separator for energy storage devices that can further improve the performance of energy storage devices (for example, cycle characteristics and safety evaluated by device failure or heating tests). The present invention also aims to provide a secondary battery and an energy storage device, etc., including such a separator for energy storage devices. [Means for solving the problem]

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

[0008] The present invention provides a separator for energy storage devices that can further improve the performance of the energy storage device (e.g., cycle characteristics and safety as evaluated by device failure or heating tests). Furthermore, the present invention provides a secondary battery and an energy storage device equipped with such a separator. [Brief explanation of the drawing]

[0009] [Figure 1] A figure showing an example of a histogram used to derive the percentage of peeling area according to one aspect of the present invention. [Figure 2] A figure showing another example of a histogram used to derive the percentage of peeling area according to one aspect of the present invention. [Figure 3] A figure showing an example of a monochrome image according to one aspect of the present invention. [Figure 4] A figure showing an example of a binarized image according to one aspect of the present invention. [Modes for carrying out the invention]

[0010] The following describes embodiments of the present invention ("this embodiment"), but the present invention is not limited to this embodiment. The present invention can be modified in various ways without departing from its spirit. In this specification, unless otherwise specified, "~" means that the numerical values ​​at both ends are included as the upper and lower limits. In this specification, the upper and lower limits of the numerical range can be arbitrarily combined. In addition, the term "separator for energy storage devices" may be abbreviated as "separator" below.

[0011] <Separator for energy storage devices> A separator for energy storage devices can be used in energy storage devices, for example, by being placed between the positive and negative electrodes of the energy storage device.

[0012] <Embodiment 1> The separator for the energy storage device according to Embodiment 1 includes a microporous membrane made of polyolefin resin containing a silane graft-modified polyolefin, and an inorganic porous layer disposed on at least one surface thereof. Optionally, it may further include layers other than the polyolefin resin microporous membrane and the inorganic porous layer. The inorganic porous layer can be disposed on both sides of the polyolefin resin microporous membrane, or the inorganic porous layer can be disposed on one side of the polyolefin resin microporous membrane, and the other side of the polyolefin resin microporous membrane can be disposed of layers other than the polyolefin resin microporous membrane and the inorganic porous layer.

[0013] The inorganic porous layer of the separator according to Embodiment 1 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 when the separator according to Embodiment 1 comes into contact with an electrolyte, a silane crosslinking reaction of the silane graft-modified polyolefin contained in the microporous membrane made of polyolefin resin is initiated.

[0014] The inorganic porous layer according to Embodiment 1 is arranged on at least one surface of a microporous membrane made of polyolefin resin. Therefore, both the configuration in which the inorganic porous layer is arranged on only one surface of the microporous membrane made of polyolefin resin and the configuration in which the inorganic porous layer is arranged on both sides of the microporous membrane made of polyolefin resin are included within the scope of Embodiment 1. When the inorganic porous layer is arranged on both sides of the microporous membrane made of polyolefin resin, inorganic porous layers with the same configuration may be arranged, or inorganic porous layers with different configurations may be arranged.

[0015] The inorganic porous layer according to Embodiment 1 may include inorganic particles and / or a resin binder.

[0016] The inorganic porous layer according to Embodiment 1 may form a crosslinked structure by any of the covalent bonds (i) to (iii), or may include a crosslinked structure. The above statement does not mean that cross-linking structures will necessarily be formed between inorganic particles. For example, if cross-linking structures are formed between inorganic particles and resin binders, cross-linking structures do not need to be formed between inorganic particles. Similarly, the above statement does not mean that cross-linking structures will necessarily be formed between resin binders. For example, if cross-linking structures are formed between inorganic particles and resin binders, cross-linking structures do not need to be formed between resin binders. In other words, it is sufficient for at least one of the above-mentioned crosslinking structures to be formed in the inorganic porous layer. However, from the viewpoint of making it easier to exert the effects of the present invention, it is preferable that crosslinking structures are formed in all of the covalent bonds (i) to (iii). In Embodiment 1, the covalent bonds between inorganic particles, covalent bonds between resin binders, and covalent bonds between inorganic particles and resin binders include, if necessary, those in which a crosslinking agent is interposed.

[0017] The microporous membrane made of polyolefin resin according to Embodiment 1 includes a silane graft-modified polyolefin as the polyolefin resin, and optionally includes other polyolefins, additional components, etc. When the separator according to Embodiment 1 is brought into contact with an electrolyte, the silane graft-modified polyolefin can be crosslinked, so the timing of the silane crosslinking reaction can be controlled. This makes it possible, for example, to avoid performing the crosslinking reaction in the separator manufacturing process and instead perform the crosslinking reaction in the energy storage device manufacturing process or by placing the separator inside the energy storage device, thereby avoiding separator production defects and achieving safety of the energy storage device (e.g., safety evaluated by device failure or heating tests), improved cycle characteristics, and higher output. From the viewpoint of the silane crosslinking reaction, the electrolyte that comes into contact with the silane graft-modified polyolefin is preferably non-aqueous and / or contains a fluorine (F)-containing lithium salt.

[0018] <Embodiment 2> The separator for the energy storage device according to Embodiment 2 includes a microporous membrane made of polyolefin resin and an inorganic porous layer disposed on at least one surface thereof, and optionally further includes layers other than the polyolefin resin microporous membrane and the inorganic porous layer. The inorganic porous layer can be disposed on both sides of the polyolefin resin microporous membrane, or the inorganic porous layer can be disposed on one side of the polyolefin resin microporous membrane, and the layer other than the polyolefin resin microporous membrane and the inorganic porous layer can be disposed on the other side of the polyolefin resin microporous membrane.

[0019] In the solvent immersion test of the separator according to Embodiment 2, the area of ​​the inorganic porous layer that peels off from the polyolefin microporous membrane is 0 to 35% of the area of ​​the inorganic porous layer before the test. By keeping this area below 35%, it is possible to suppress adverse effects of the inorganic porous layer peeled off from the polyolefin microporous membrane in the electrolyte on the charge-discharge reaction or reliability of the energy storage device. As a result, it is possible to provide a separator that can further improve the performance of the energy 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: Generally, the electrolyte used in batteries is a mixed liquid of cyclic alkane carbonates such as propylene carbonate and linear alkane carbonates such as ethyl methyl carbonate. Furthermore, each battery manufacturer adjusts the functional groups or formulations of these compounds according to the battery design. Consequently, the SP value (Solubility Parameter) of the electrolyte changes, making it difficult to evaluate the penetration of the electrolyte into the inorganic porous layer, the swelling of the inorganic porous layer, and the peeling due to structural destruction of the inorganic porous layer. Therefore, in order to suitably evaluate the above area, the solvent immersion test described in the examples can be performed. For example, acetone has a lower molecular weight than various electrolytes and is a solvent with aprotic polar functional groups. For this reason, it has been experimentally found that by using a relatively low molecular weight solvent (such as acetone) in the solvent immersion test, the solvent can be penetrated into the inorganic porous layer, easily causing it to swell and peeling due to structural destruction 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 product is stable in various other electrolytes as well.

[0021] One factor that controls the area over which the inorganic porous layer peels off from the polyolefin microporous membrane is the control of the crosslinking structure in the inorganic porous layer. Specifically, this area can be controlled by controlling the items related to the inorganic porous layer, as described in Tables 3 to 6 in the examples.

[0022] If a crosslinking structure is not formed in the inorganic porous layer, the resin binder in the inorganic porous layer will swell due to the electrolyte, and the swollen resin binder is likely to detach from the inorganic porous layer into the electrolyte. On the other hand, if an excessive crosslinking structure is formed in the inorganic porous layer, the flexibility of the inorganic porous layer tends to decrease, and as a result, the likelihood of the resin binder detaching from the inorganic porous layer into the electrolyte increases. In other words, by suitably forming a crosslinking 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 detaching into the electrolyte, and consequently, to control the area in which the inorganic porous layer peels off from the polyolefin microporous membrane to 0-35%. From the viewpoint of shape stability of the separator during long-term use in energy storage devices such as batteries, the area in which the inorganic porous layer peels off from the polyolefin resin microporous membrane is preferably 0-30%, more preferably 0-15%, and even more preferably 0-8%.

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

[0024] The inorganic porous layer according to Embodiment 2 preferably includes inorganic particles and / or a resin binder, from the viewpoint of the performance of the energy storage device and the control of the crosslinking structure in the inorganic porous layer.

[0025] The inorganic porous layer according to Embodiment 2 preferably 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, from the viewpoint of the performance of the energy storage device and the control of the crosslinking structure in the inorganic porous layer, and more preferably forms a crosslinking structure by any of the covalent bonds (i) to (iii), or includes a crosslinking structure. The above statement does not mean that cross-linking structures will necessarily be formed between inorganic particles. For example, if cross-linking structures are formed between inorganic particles and resin binders, cross-linking structures do not need to be formed between inorganic particles. Similarly, the above statement does not mean that cross-linking structures will necessarily be formed between resin binders. For example, if cross-linking structures are formed between inorganic particles and resin binders, cross-linking structures do not need to be formed between resin binders. In other words, it is sufficient for at least one of the above-mentioned crosslinking structures to be formed in the inorganic porous layer. However, from the viewpoint of making it easier to exert the effects of the present invention, it is even more preferable that crosslinking structures be formed in all of the covalent bonds (i) to (iii). In Embodiment 2, the covalent bonds between inorganic particles, covalent bonds between resin binders, and covalent bonds between inorganic particles and resin binders include, if necessary, those in which a crosslinking agent is interposed.

[0026] The microporous membrane made of polyolefin resin according to Embodiment 2 preferably contains silane graft-modified polyolefin as the polyolefin resin, and more preferably contains polyolefins other than silane graft-modified polyolefin, from the viewpoint of further improving the performance of the energy storage device. If desired, the microporous membrane made of polyolefin resin may contain additional components other than polyolefin resin.

[0027] When the separator according to Embodiment 2 comes into contact with the electrolyte, it is preferable that the silane crosslinking reaction of the silane graft-modified polyolefin contained in the microporous membrane made of polyolefin resin is initiated. Since the silane graft-modified polyolefin can be crosslinked by bringing the separator according to Embodiment 2 into contact with the electrolyte, the timing of the silane crosslinking reaction can be controlled. This makes it possible, for example, to avoid performing the crosslinking reaction in the separator manufacturing process and instead perform the crosslinking reaction in the energy storage device manufacturing process or by placing it inside the energy storage device, thereby avoiding separator production defects and achieving safety of the energy storage device (e.g., safety evaluated by device failure or heating tests), improved cycle characteristics, and higher output. From the viewpoint of the silane crosslinking reaction, the electrolyte that comes into contact with the silane graft-modified polyolefin is more preferably non-aqueous and / or contains a fluorine (F)-containing lithium salt.

[0028] In Embodiment 2, controlling the surface roughness of the region of the polyolefin microporous membrane facing the inorganic porous layer within a predetermined range makes it easier to prevent the resin binder from detaching from the inorganic porous layer. In Embodiment 2, a crosslinking structure is suitably formed in the inorganic porous layer, thereby ensuring the desired adhesion between the inorganic porous layer and the polyolefin microporous membrane. This 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 the swelling of the resin binder due to the electrolyte, and as a result, it is expected that the area in which the inorganic porous layer peels off from the polyolefin microporous membrane can be controlled to 0-35%. Conversely, if cross-linking structures are not formed in the inorganic porous layer, or if cross-linking structures are excessively formed in the inorganic porous layer, the inorganic porous layer is hardly affected by the control of the surface roughness of the polyolefin microporous membrane, and therefore, the idea of ​​controlling the surface roughness of the polyolefin microporous membrane cannot be derived.

[0029] Therefore, the surface roughness of the region of the polyolefin microporous membrane facing the inorganic porous layer is preferably 0.2 to 3.0 μm, from the viewpoint of easily exhibiting 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, this 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. This surface roughness is measured according to the method described in the examples and can be controlled by changing various configurations of the polyolefin microporous film or various manufacturing conditions.

[0030] The components common to Embodiment 1 and Embodiment 2, and the components preferred for both embodiments, are described below.

[0031] <Microporous membrane made of polyolefin resin> A 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 obtained by laminating multiple polyolefin microporous membranes containing different polyolefin resins is also included in the polyolefin microporous membrane according to Embodiment 1 or 2.

[0032] The polyolefin resin content 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 even more preferably 95% by mass or more, particularly preferably 98% by mass or more, and may also 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 include homopolymers of ethylene or propylene, or 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 that pore blockage can be prevented and heat fixation (sometimes abbreviated as "HS") can be performed at higher temperatures. The polyolefin resin may include a polyolefin resin other than polyethylene in addition to or in place of polyethylene. Examples of polyolefin resins other than polyethylene include polypropylene and polybutene. The polyolefin may be used alone or in combination of two or more types.

[0034] Microporous membranes made of polyolefin resin preferably contain both silane-graft modified polyolefin and ultra-high molecular weight polyethylene (UHMWPE) from the viewpoint of resistance to oxidation-reduction degradation and a dense and uniform porous structure. Generally, the weight-average molecular weight of ultra-high molecular weight polyethylene (UHMWPE) is known to be 1,000,000 or more. More preferably, in the separator, the mass ratio of silane-graft modified polyolefin to ultra-high molecular weight polyethylene (mass of silane-graft modified polyolefin / mass of ultra-high molecular weight polyethylene) is 0.05 / 0.95 to 0.40 / 0.60.

[0035] Furthermore, the microporous membrane made of polyolefin resin preferably contains a polyolefin with a weight-average molecular weight of less than 1,200,000. By using a polyolefin with a weight-average molecular weight of less than 1,200,000, the shrinkage of the polymer is relieved earlier in heating tests of energy storage devices, and safety tends to be maintained more easily, especially in heating safety tests. From a similar viewpoint, 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 using a polyolefin with a weight-average molecular weight of less than 1,000,000, the elastic modulus in the thickness direction of the resulting microporous membrane tends to be smaller, so a microporous membrane that is relatively easy to transfer the irregularities of the core can be obtained. Polyolefins having a weight-average molecular weight within this range can be included 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 resin contained in the polyolefin microporous membrane.

[0036] (Silane-grafted modified polyolefin) Silane-grafted polyolefins have a structure in which the main chain is a polyolefin and an alkoxysilyl is grafted onto the main chain. The alkoxide substituted for the alkoxysilyl is not particularly limited, but examples include methoxide, ethoxide, and butoxide. The main chain and the graft are connected by covalent bonds, and examples include alkyl, ether, glycol, or ester structures. Considering the manufacturing process of the separator according to Embodiment 1 or 2, in the stage prior to the crosslinking treatment step described later, the silane-grafted polyolefin has a modification amount of 10 mol% or less, preferably 5 mol% or less, and more preferably 2 mol% or less, relative to the total ethylene units of the main chain.

[0037] Preferred silane-graft modified polyolefins have a density of 0.90–0.96 g / cm³. 3Furthermore, the melt flow rate (MFR) at 190°C is 0.2 to 5 g / min.

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

[0039] Microporous membranes made of polyolefin resin that do not contain silane-graft modified polyolefins can be manufactured using any one type selected from the group consisting of polyethylene (PE) (X, viscosity-average molecular weight 100,000 to 400,000), a first ultra-high molecular weight PE (Y, viscosity-average molecular weight 400,000 to 800,000), and a second ultra-high molecular weight PE (Z, viscosity-average molecular weight 800,000 to 9,000,000), or two or three types selected from the group consisting of X, Y, and Z, mixed in any proportion. Polyolefins composed solely of hydrocarbon backbone, 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 degree of gelation of a microporous membrane made of polyolefin resin having a crosslinked structure such as a silane crosslinked structure is preferably 30% or more, more preferably 70% or more.

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

[0041] The porosity of the microporous membrane made of polyolefin resin is preferably 20% or more, more preferably 30% or more, still more preferably 32% or more or 35% or more. When the porosity is 20% or more, the followability to the rapid movement of lithium ions tends to be further improved. On the other hand, this porosity is preferably 90% or less, more preferably 80% or less, still more preferably 50% or less. When the porosity is 90% or less, the membrane strength tends to be further improved and self-discharge tends to be further suppressed. This porosity can be measured by the method described in the examples and can be controlled by changing the draw ratio of the microporous membrane made of polyolefin resin, etc.

[0042] The air permeability of the microporous membrane made of polyolefin resin is preferably 1 sec / 100 cm 3 or more, more preferably 50 sec / 100 cm 3 or more, still more preferably 55 sec / 100 cm 3 or more, even more preferably 70 sec / 100 cm 3 or more, 90 sec / 100 cm 3 or more or 110 sec / 100 cm 3 or more. When the air permeability is 1 sec / 100 cm 3 or more, the balance among the membrane thickness, porosity, and average pore diameter tends to be further improved. On the other hand, the air permeability is preferably 400 sec / 100 cm 3 or less, more preferably 300 sec or less / 100 cm 3 , still more preferably 270 sec / 100 cm 3 or less. When this air permeability is 400 sec / 100 cm 3 or less, the ion permeability tends to be further improved. This air permeability can be measured by the method described in the examples and can be controlled by changing the draw temperature and / or draw ratio of the microporous membrane made of polyolefin resin, etc.

[0043] The film thickness of the microporous film made of polyolefin resin 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 film thickness of 1.0 μm or more tends to improve film strength. On the other hand, the film 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 film thickness of 500 μm or less tends to improve ion permeability. This film thickness can be measured by the method described in the examples and can be controlled by changing the stretching ratio of the microporous film made of polyolefin resin, etc.

[0044] When a microporous film made of polyolefin resin is used as a constituent material for a LIB separator, the film thickness of the polyolefin resin microporous film 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 film thickness of 25 μm or less tends to improve permeability. In this case, the lower limit of the film 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 energy storage device, which tends to be advantageous from the viewpoint of increasing the capacity of the energy storage device. Furthermore, a thickness of 15 μm or less for 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 changing the amount of slurry for forming the inorganic porous layer (slurry for inorganic porous layer) applied to the microporous membrane made of polyolefin resin.

[0046] The air permeability of the inorganic porous layer should be such that it 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 More preferably, 150 sec / 100 cm 3 More preferably, 130 sec / 100 cm 3 The following is the result. This ascent rate is 200 sec / 100 cm. 3 The following is preferable from the viewpoint of allowing ions to pass through the non-aqueous electrolyte (hereinafter also simply referred to as "electrolyte") during charging and discharging of the energy storage device. This increase can be measured according to the method described in the examples and can be controlled by changing various configurations of the inorganic porous layer or various manufacturing conditions.

[0047] <Crosslinked structure> In an inorganic porous layer, it is preferable that the crosslinking structure is formed by at least one selected from the group consisting of nucleophilic substitution reactions, nucleophilic addition reactions, electrophilic addition reactions, and silane coupling reactions. The presence of such a crosslinking structure in the inorganic porous layer facilitates the exertion of the effects of the present invention. From a similar viewpoint, if the inorganic porous layer contains a crosslinking agent, it is preferable that in the inorganic porous layer, polar functional groups are present on the surface of the inorganic particles, a crosslinking agent is present between the polar functional groups and the resin binder, and the crosslinking structure is formed by covalent bonds between the polar functional groups, the crosslinking agent and the resin binder. This type of crosslinked structure may be formed (i) during or immediately thereafter the film-forming process, or (ii) after being housed in an energy storage device using the surrounding environment or chemical substances inside the energy storage device. Depending on the progress of the crosslinking reaction (i) during or immediately thereafter the film-forming process of the inorganic porous layer, the environment inside the energy 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 such microporous membrane is crosslinkable, the crosslinking reaction in the inorganic porous layer may proceed further after the separator containing the inorganic porous layer is housed in the energy storage device. Therefore, it is preferable that the inorganic porous layer be configured to allow the above-mentioned crosslinking reactions (i) and / or (ii) to proceed.

[0048] Furthermore, a layer that does not fall under either of the two (another layer) may be interposed between the inorganic porous layer and the polyolefin resin microporous membrane, but it is preferable that no such other layer is interposed. In other words, it is preferable that the inorganic porous layer be placed directly on top of the polyolefin resin microporous membrane. This makes it easier to control the composition or properties of the inorganic porous layer by the composition 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 crosslinking structures formed by covalent bonds (crosslinking reactions) include the following reactions (I) or (II): (I) Reactions between multiple heterogeneous functional groups (II) Chain condensation reaction between functional groups and crosslinking agents Preferably, it is at least one selected from the group consisting of the following:

[0050] The combination of functional groups or reactants that form a crosslinked structure by covalent bonding based on reaction (I) is not particularly limited, but for example, Hydroxyl group and carboxyl group (esterification); Carbonyl group and alkyl group (aldol condensation); Halogen and carboxyl group (intramolecular condensation); Alkoxy group and alkyl group (Claisen condensation) Carbonyl group and acid anhydride (Parkin reaction); Amino groups and halogens; Isocyanate group and hydroxyl group (formation of urethane bond); and Oxazoline group and hydroxyl group; The like are preferable.

[0051] The combination of functional groups that form a crosslinked structure by covalent bonding based on reaction (II) is not particularly limited, but for example, the reaction (including ring-opening reaction) between inorganic particles and / or a resin binder and a crosslinking agent is preferred. When inorganic particles and / or a resin binder are crosslinked via a crosslinking agent, it is preferable that such a crosslinking agent has two or more active groups. The multiple active groups may be any structure or group, may be substituted or unsubstituted, may contain heteroatoms or inorganic substances, and may be the same or different from each other, as long as they can undergo a crosslinking reaction with the inorganic particles and / or a resin binder.

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

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

[0054] Examples of inorganic particle shapes include plate-like, flaky, needle-like, columnar, spherical, polyhedral, and lumpy (block-like) shapes. Multiple types of inorganic particles having these shapes may be used in combination.

[0055] The number-average particle size of inorganic particles is, for example, 0.01 μm or larger, 0.1 μm or larger, or 0.3 μm or larger. Furthermore, this number-average particle size is 10.0 μm or smaller, 9.0 μm or smaller, or 6.0 μm or smaller. Methods for adjusting this particle size include, for example, using appropriate grinding equipment such as a ball mill, bead mill, or jet mill to grind the inorganic particles and reduce their particle size.

[0056] Here, it is preferable that the inorganic particles have polar functional groups on their surface. That is, it is preferable that the inorganic particles have polar functional groups on their surface. This enhances the reactivity to other compounds (resin binder, other inorganic particles, and crosslinking agents, if necessary). Therefore, it becomes easier to form a suitable crosslinked structure through covalent bonding between the inorganic particles and the resin binder, and, in the case of multiple inorganic particles, through covalent bonding between multiple inorganic particles. From a similar viewpoint, it is preferable that this polar functional group is at least one selected from the group consisting of carboxyl groups, hydroxyl groups, and amino groups.

[0057] Furthermore, it is preferable that the inorganic particles have silicon-containing functional groups on their surface. That is, it is preferable that the inorganic particles have silicon-containing functional groups on their surface. This enhances the reactivity to other compounds (resin binder, other inorganic particles, and crosslinking agents, etc., as needed). Therefore, it becomes easier to form a suitable crosslinked structure through covalent bonding between the inorganic particles and the resin binder, and, in the case of multiple inorganic particles, through covalent bonding between multiple inorganic particles. From a similar viewpoint, it is preferable that the silicon-containing functional group is at least one selected from the group consisting of alkoxysilyl groups, halogen-substituted silyl groups, and silazane groups.

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

[0059] Specific examples of materials that can be used as resin binders include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; fluororubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; rubbers such as styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid ester-acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile-acrylic acid ester copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; 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 can be used individually or in combination of two or more types.

[0060] Specific examples of resin binders include the following 1) to 7). 1) Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified versions thereof; 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides; 3) Acrylic polymers: for example, methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, and acrylonitrile-acrylic acid ester 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, ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; and 7) Resins with a melting point and / or glass transition temperature of 180°C or higher, or polymers that do not have a melting point but have 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 from a desired monomer as a raw material according to known manufacturing methods such as emulsion polymerization or solution polymerization. In polymerization, the polymerization temperature, the pressure during polymerization, the method of adding monomers, and the additives used (polymerization initiators, molecular weight adjusters, pH adjusters, etc.) are not particularly limited.

[0062] The resin binder described above, and / or the crosslinking agent described later, is preferably in the form of an emulsion, suspension, or colloid. Of these, the emulsion is preferably formed of a core consisting of predetermined particles and a shell containing a predetermined polymer compound around the core, from the viewpoint of film-forming ability and the strength of the resulting inorganic porous layer. The particles forming the core may be an organic polymer compound or inorganic fine particles, but from the viewpoint of imparting flexibility to the final inorganic porous layer, an organic polymer compound is more preferred. A suspension refers to, for example, a solvent in which solid particles are dispersed to the extent that they are visible under a microscope, and a colloid refers to a solvent in which macromolecules that can be seen with the naked eye are dispersed.

[0063] The resin binder preferably has a functional group that undergoes a nucleophilic substitution reaction (nucleophilic substitution-reactive functional group) or a functional group that undergoes a nucleophilic addition reaction (nucleophilic addition-reactive functional group) with polar functional groups and / or silicon-containing functional groups present on the surface of the inorganic particles. This enhances the reactivity with other compounds (e.g., inorganic particles, resin binder, and crosslinking agent as needed). Therefore, a suitable crosslinked structure is easily formed by covalent bonding between the inorganic particles and the resin binder, and by covalent bonding between multiple resin binders if there are multiple resin binders. From a similar viewpoint, 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 carboxyl groups, hydroxyl groups, and amino groups.

[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% by mass or more, and more preferably 1.0% by mass or more, from the viewpoint of ensuring heat resistance. On the other hand, this mass ratio is preferably 50% by mass or less, and more preferably 20% by mass or less, from the viewpoint of ensuring room for inorganic particles to be contained in 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 mentioned above. 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, in the range of 0.01% to 5% by mass. More preferably, the mass ratio of the crosslinking agent in the inorganic porous layer is 0.1% to 5% by mass, and even more preferably 0.1% to 3% by mass.

[0066] The crosslinking agent preferably contains active groups that are reactive with the inorganic particles and / or the resin binder. For example, the crosslinking agent preferably has functional groups that undergo nucleophilic substitution reactions with the inorganic particles and / or the resin binder (nucleophilic substitution reactive functional groups) and / or functional groups that undergo electrophilic addition reactions (electrophilic addition reactive functional groups). In particular, the crosslinking agent preferably has nucleophilic substitution reactive functional groups and electrophilic addition reactive functional groups. This makes it easier to form 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 isocyanate group, thioisocyanate group, carbodiimide group, allene group, oxime group, and carbonyl group. Suitable crosslinking agents include, for example, the oxyzoline-based crosslinking agents: Nippon Shokubai's Epocross series (K-2010E, K-2020E, K-2030, WS-300, WS-500, WS-700); the carbodiimide-based crosslinking agents: Nisshinbo Chemical's Carbodilite series (V-02, V-02-L2, SV-02, V-04, V-10, SW-12G, E-02, E-03A); and the isocyanate-based crosslinking agents: Asahi Kasei Corporation's Duranate series (WB40-100, WB40-80D, WT20-100, WT30-100). Examples of crosslinking agents include WL70-100, WR80-70P, WE50-100), the Denacol series from Nagase ChemteX (EX-61B, EX-313, FCA-678, etc.) as epoxy crosslinking agents, triethoxysilane (X-12-1273ES), dimethyldimethoxysilane, methyltrimethoxysilane, tetraethoxysilane, etc. from Shin-Etsu Chemical Co., Ltd. as crosslinking agents for alkoxysilane compounds containing various functional groups include those from Shin-Etsu Chemical Co., Ltd. (KBM Shiraz (3-aminopropyltrimethoxysilane KBM-903, etc.), KBE series), etc.

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

[0068] <Other additives> Microporous membranes made of polyolefin resin and / or inorganic porous layers may contain any additives. These additives are not particularly limited, but examples include antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments.

[0069] <Method of manufacturing a separator> (Method for manufacturing microporous membranes made of polyolefin resin) A known manufacturing method can be used to produce a microporous membrane made of polyolefin resin, for example, either a wet porosization method or a dry porosization method may be employed. Examples of wet porosization methods include: a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, which is then optionally stretched, and the plasticizer is extracted to create porosity; a method in which a polyolefin resin composition mainly containing a polyolefin-based resin is melt-kneaded together, extruded at a high draw ratio, and then porosized by heat treatment and stretching to peel off the polyolefin crystal interface; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded together to form a sheet, which is then porosized by stretching to peel off the interface between the polyolefin and the inorganic filler; and a method in which a polyolefin resin composition is dissolved, immersed in a poor solvent for polyolefin, and the polyolefin is solidified while the solvent is removed to create porosity.

[0070] The following describes an example of a method for producing a polyolefin microporous membrane, which involves melt-kneading a polyolefin resin composition with a plasticizer to form a sheet, followed by extraction of the plasticizer. First, the polyolefin resin composition and the plasticizer are melt-kneaded. As a melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin mixing device such as an extruder, kneader, laboplast mill, kneading roll, and Banbury mixer, and the plasticizer is introduced and kneaded in an arbitrary ratio while the resin components are heated and melted. 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 putting them into the resin mixing device. More preferably, only a portion of the plasticizer is added during the pre-kneading, and the remaining plasticizer is kneaded while being fed to the side of the resin mixing device.

[0071] As a plasticizer, a non-volatile solvent capable of forming a homogeneous solution above the melting point of the polyolefin can be used. Specific examples of such non-volatile 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 should 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 the composition consisting of the polyolefin resin composition and the plasticizer is preferably 30% to 80% by mass, more preferably 40% to 70% by mass. Setting the mass fraction of the plasticizer within this range is preferable from the viewpoint of achieving both melt tension during melt molding and the formation of a uniform and fine pore structure.

[0073] Next, the molten mixture obtained by heating, melting, and kneading as described above is formed into a sheet. One method for producing a sheet-shaped molded body is to extrude the molten mixture into a sheet through a T-die or the like, and then cool and solidify it in contact with a heat conductor to a temperature sufficiently lower than the crystallization temperature of the resin components. Examples of heat conductors used for cooling and solidification include metal, water, air, and the plasticizer itself, but metal rolls are preferred because they have high heat conduction efficiency. In this case, it is even more preferable to sandwich the molten mixture between the metal rolls when contacting it, as this further increases the heat conduction efficiency, aligns the sheet, increases film strength, and improves the surface smoothness of the sheet. The die lip spacing when extruding the mixture into a sheet from the T-die is preferably 400 μm to 3000 μm, and more preferably 500 μm to 2500 μm.

[0074] It is preferable to then stretch the sheet-like molded article obtained in this manner. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching process. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous film. When the sheet-like molded article is stretched at high magnification in the biaxial direction, the molecules become oriented in the planar direction, and the resulting polyolefin microporous film becomes less prone to tearing and has high puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and multiple-pass stretching. Simultaneous biaxial stretching is preferred from the viewpoint of improving puncture strength, stretching uniformity, and shutdown properties.

[0075] The stretching ratio is preferably in the range of 20 to 100 times in terms of surface magnification, and more preferably in the range of 25 to 50 times. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times for MD and 4 to 10 times for TD, and more preferably in the range of 5 to 8 times for MD and 5 to 8 times for TD. Setting the stretching ratio within this range is preferable because it allows for more sufficient strength to be imparted, prevents film breakage during the stretching process, and enables high productivity. Note that MD refers to the machine direction when, for example, continuously molding a polyolefin microporous membrane, and TD refers to the direction that intersects the MD at a 90° angle.

[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. Rolling can particularly increase the orientation of the surface layer of the sheet-like molded article. The rolling ratio is preferably greater than 1 and 3 or less, and more preferably greater than 1 and 2 or less. A rolling ratio within this range is preferable because it increases the film strength of the final polyolefin microporous film and allows for the formation of a more uniform porous structure in the film thickness direction.

[0077] Next, the plasticizer is removed from the sheet-like molded body to obtain a polyolefin microporous membrane. Methods for removing the plasticizer include, for example, immersing the sheet-like molded body in an extraction solvent to extract the plasticizer and then thoroughly drying it. The extraction method can be either batch or continuous. To suppress shrinkage of the polyolefin microporous membrane, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. Furthermore, it is preferable that the residual amount of plasticizer 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 whose boiling point is lower than the melting point of the polyolefin resin. 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-chlorinated halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation.

[0079] To suppress shrinkage of the polyolefin microporous membrane, heat treatment such as thermal fixation or thermal relaxation may be performed after the stretching process or after the formation of the polyolefin microporous membrane. Post-treatment such as hydrophilization treatment with surfactants or crosslinking treatment with ionizing radiation may also be performed on the polyolefin microporous membrane.

[0080] (Method for producing microporous membranes made of polyolefin resin containing silane-grafted polyolefins) The following describes a method for producing a microporous membrane made of polyolefin resin containing silane-graft modified polyolefin, specifically for the case of a microporous membrane (flat membrane). This description does not exclude other forms of the membrane. The method for producing a microporous membrane containing silane-graft modified polyolefin involves the following steps: (1) Sheet forming process; (2) Stretching process; (3) Porous body formation process; and (4) Heat treatment process; The method for producing a microporous membrane containing a silane graft-modified polyolefin may optionally 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 crosslinking properties until contact with the electrolyte, it is preferable not to include a silane crosslinking treatment step. The silane crosslinking treatment step generally involves contacting the material to be treated, which contains a silane graft-modified polyolefin, with a mixture of an organometallic catalyst and water, or immersing it in a basic solution or an acidic solution to carry out a silane dehydration condensation reaction to form oligosiloxane bonds.

[0081] The metal in the organometallic catalyst may be at least one selected from the group consisting of, for example, sgandy, titanium, vanadium, copper, zinc, aluminum, zirconium, palladium, gallium, tin, and lead. Examples of organometallic catalysts include di-butyltin-di-laurate, di-butyltin-di-acetate, and di-butyltin-di-octoate, and 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). Furthermore, in recent years, in order to avoid environmental and human health damage caused by organotin compounds, it has been known that by utilizing the Lewis function of copper or titanium chelate complexes and combining them with organic bases, the reaction that forms siloxane bonds between alkoxysilyl groups can be promoted in a similar manner 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, alkali metal hydroxides or alkaline earth metal hydroxides are preferred from the viewpoint of the safety of the energy storage device and silane crosslinking properties, 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, inorganic acids or organic acids. Preferred acids are hydrochloric acid, sulfuric acid, carboxylic acids, or phosphoric acids.

[0084] In the kneading process, a kneader can be used to knead the silane graft-modified polyolefin with, optionally, a plasticizer or inorganic material and other polyolefins. From the viewpoint of suppressing the generation of resin aggregates in the manufacturing process and maintaining silane crosslinking properties until contact with the electrolyte, 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 include organic compounds that can form a homogeneous solution with polyolefin at temperatures below their boiling point. More specifically, examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil, etc. Among these, paraffin oil and dioctyl phthalate are preferred. The plasticizer may be used alone or in combination of two or more. The proportion of the plasticizer is not particularly limited, but the proportion of polyolefin to silane-graft modified polyolefin is preferably 20% by mass or more relative to the total mass of the microporous film, as needed, from the viewpoint of the porosity of the resulting microporous film, and preferably 90% by mass or less from the viewpoint of viscosity during melt kneading.

[0086] The sheet forming process involves extruding the resulting kneaded material, or a mixture of silane graft-modified polyolefin, ultra-high molecular weight polyolefin, and plasticizer, cooling and solidifying it, and then molding it into a sheet to obtain a sheet. The sheet forming method is not particularly limited, but for example, one method involves solidifying a molten material that has been melt-kneaded and extruded by compression cooling. Examples of cooling methods include directly contacting the molten material with a cooling medium such as cold air or cooling water, or contacting the molten material with a roll or press machine cooled with a refrigerant. Among these, contacting the molten material with a roll or press machine cooled with a refrigerant is preferred because it offers excellent control over film thickness.

[0087] From the viewpoint of resin aggregates in the microporous membrane or the maximum internal heat generation rate, in the sheet molding process, the mass ratio of silane graft-modified polyolefin to ultra-high molecular weight polyethylene (mass of silane graft-modified polyolefin / mass of ultra-high molecular weight polyethylene) 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 energy storage device failure while possessing low-temperature shutdown properties of 150°C or below for the separator and film rupture resistance at high temperatures of 180°C or above, it is preferable that the silane graft-modified polyolefin used in the sheet molding process is not a masterbatch resin that contains a dehydration condensation catalyst for crosslinking the silane graft-modified polyolefin from before the sheet molding process. Film rupture resistance can preferably be ensured at 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. It should be noted that the upper limit of the film rupture temperature of the separator is not limited, and in this art, it is understood that film rupture can occur even at temperatures above 250°C.

[0089] The stretching process involves extracting plasticizers or inorganic materials from the obtained sheet as needed, and further stretching the sheet in one or more axial directions. Methods for stretching the sheet include MD uniaxial stretching using a roll stretcher, TD uniaxial stretching using a tenter, sequential biaxial stretching using a combination of a roll stretcher and a tenter, or two tenters, and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferable. The total surface 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 viewpoint of uniformity of film thickness and balance between tensile elongation, porosity, and average pore diameter. A total surface ratio of 8 times or more tends to make it easier to obtain a film with high strength and a good thickness distribution. Furthermore, from the viewpoint of preventing breakage, this surface ratio may be 250 times or less.

[0090] The porous material formation step is a step in which a plasticizer is extracted from the stretched material after the stretching step to make the stretched material porous. The method of extracting the plasticizer is not particularly limited, but examples include immersing the stretched material in an extraction solvent or showering the stretched material with an extraction solvent. The extraction solvent is not particularly limited, but is preferably a poor solvent for polyolefins and a good solvent for plasticizers or inorganic materials, with a boiling point lower than the melting point of polyolefins. Examples of such extraction solvents are not particularly limited, but 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 solvent may be used alone or in combination of two or more.

[0091] The heat treatment process involves extracting plasticizer from the sheet as needed after the stretching process, and then performing further heat treatment to obtain a microporous film. The heat treatment method is not particularly limited, but examples include a heat-setting method that uses a tenter or roll stretcher to perform stretching and relaxation operations. Relaxation operation refers to a reduction operation performed in the mechanical direction (MD) and / or width direction (TD) of the film at a predetermined temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the film after the relaxation operation by the MD dimension of the film before the operation, or the value obtained by dividing the TD dimension of the film after the relaxation operation by the TD dimension of the film before the operation, or, if both MD and TD are relaxed, the value obtained by multiplying the relaxation rate of MD and the relaxation rate of TD. Furthermore, in the winding process, the obtained microporous film can be slit as needed and wound onto a predetermined core.

[0092] (Method for manufacturing an inorganic porous layer) The method for producing the inorganic porous layer is not particularly limited, and known production methods can be employed. For example, regardless of whether the polyolefin resin microporous membrane contains silane graft-modified polyolefin resin, a method of applying a coating solution (slurry for inorganic porous layer) containing inorganic particles and a resin binder to the polyolefin resin microporous membrane can be used.Optionally, the slurry for inorganic porous layer may contain a crosslinking agent.The raw material containing inorganic particles and a resin binder and the raw material for the polyolefin resin microporous membrane containing polyolefin resin may be laminated and extruded by co-extrusion, 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 solution is preferably one that can uniformly and stably disperse or dissolve the inorganic particles and the resin binder. Examples include N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0094] The above-mentioned crosslinking agent may be added to the coating solution. In addition, various additives such as dispersants including surfactants, thickeners, wetting agents, defoamers, and pH adjusters containing acids and alkalis may be added to the coating solution.

[0095] Methods for dispersing or dissolving inorganic particles and a resin binder in a coating medium include, for example, ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc.

[0096] Methods for applying a coating solution to a microporous film made of polyolefin resin include, for example, 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] There are no particular limitations on the method for removing the solvent from the coated film after coating, as long as it does not adversely affect the polyolefin resin microporous film. For example, methods include drying the polyolefin resin microporous film at a temperature below the melting point of the materials constituting the polyolefin resin microporous film while fixing the film, drying under reduced pressure at low temperatures, and immersing the resin binder in a poor solvent to solidify the resin binder while simultaneously extracting the solvent. Furthermore, some solvent may be left in place as long as it does not significantly affect the device characteristics.

[0098] <Energy storage devices> The separators according to Embodiments 1 and 2 can be used in energy storage devices. The energy storage device comprises a positive electrode, a negative electrode, a separator according to Embodiment 1 or 2 disposed between the positive and negative electrodes, and an electrolyte. Specific examples of energy 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, or lithium-ion capacitors are preferred, and lithium batteries or LIBs are more preferred.

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

[0100] Examples of aprotic solvents include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds containing sulfur atoms, linear fluorinated carbonates, cyclic ethers, mononitriles, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, linear ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the above aprotic solvents are 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 carbonates 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 containing sulfur atoms include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methylsulfolane, 1,3-propanesultone, 1,4-butanesultone, 1-propene-1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

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

[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, methyl succinonitrile, 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, and 2,4-dimethylglutaronitrile, ethylene glycol bis(propionitrile) ether, etc.

[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 hydroangelicaate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelicaate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelicaate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, and isopropyl pivalate. Examples include isopropyl hydroangelicate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelicate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyrate, isobutyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelicate, 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 hydroangelicate, and tert-butyl caproate.

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

[0113] Examples of compounds in which some or all of the H atoms in the above-mentioned aprotic solvent are substituted with halogen atoms include compounds in which the halogen atom is fluorine.

[0114] Examples of fluorinated chain carbonates include methyltrifluoroethyl 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 above fluorinated chain carbonates have the following general formula: R cc -OC(O)OR dd {where, R cc and R dd These are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and formula CH2Rf ee (In the formula, Rf ee (where is at least one selected from the group consisting of groups represented by a C1-C3 alkyl group in which at least one hydrogen atom is substituted with a fluorine atom), and R cc and / or R dd It contains at least one fluorine atom. It can be expressed as follows.

[0115] Furthermore, 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 At least one selected from the group consisting of R gg These are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ii At least one selected from the group consisting of Rf hh Rf is a C1-C3 alkyl group in which at least one fluorine atom may substitute for a hydrogen atom. ii is an alkyl group having 1 to 3 carbon atoms in which at least one fluorine atom replaces a hydrogen atom, and R ff and / or R gg It contains at least one fluorine atom, R ff If R is CF2H, gg It can be represented as {not CH3}.

[0116] A typical example of an energy storage device is a lithium-ion battery (LIB), which uses lithium transition metal oxides such as lithium cobalt oxide and lithium cobalt composite oxide as the positive electrode, a carbon material such as graphite as the negative electrode, and a non-aqueous organic solvent containing fluorine-containing lithium salts such as LiPF6 as the electrolyte. During charging and discharging of an LIB, ionized Li (lithium) moves back and forth between the electrodes. Furthermore, because it is necessary for the ionized Li to move between the electrodes at a relatively high speed while suppressing contact between the electrodes, a separator is placed between the electrodes.

[0117] <Manufacturing method for energy storage devices> The method for manufacturing an energy storage device using a separator is not particularly limited, but the following method can be exemplified. First, a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) is manufactured. Next, the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are stacked in that order and wound into a circular or flat spiral shape to obtain a wound body. The wound body is then placed in a device container (e.g., a battery container) and an electrolyte is injected to manufacture the device. Alternatively, the electrodes and separators may be folded to form a wound body, which may then be placed in a device container (e.g., an aluminum film) and an electrolyte may be injected.

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

[0119] The press temperature is preferably 20°C or higher, as this is the temperature at which adhesion can be effectively achieved. Furthermore, in order to suppress clogging of pores or thermal shrinkage in the separator due to hot pressing, the press temperature is preferably lower than the melting point of the material contained in the microporous film made of polyolefin resin, and more preferably 120°C or lower. The press pressure is preferably 20 MPa or lower from the viewpoint of suppressing clogging of pores in the separator. The press time may be 1 second or less when using a roll press, or it may be a surface press for several hours, but from the viewpoint of productivity, 2 hours or less is preferred. When the above manufacturing process is carried out using the separator for energy storage devices of Embodiment 1 or 2, press back when the wound body consisting of electrodes and separators is press-molded can be suppressed. Therefore, it is preferable that the yield reduction in the device assembly process is suppressed and the production process time is shortened.

[0120] Energy storage devices, particularly LIBs, manufactured as described above, are equipped with a separator according to Embodiment 1 or 2, and their performance (e.g., cycle characteristics and safety as evaluated by device failure or heating tests) can be further improved.

[0121] In a manufactured energy storage device, from the viewpoint of reliably carrying out the silane crosslinking reaction of a microporous membrane made of polyolefin resin containing a silane graft-modified polyolefin, it is preferable to perform the steps of connecting lead terminals to at least one pair of electrodes of the energy storage device and connecting it to a power source, and performing at least one charge-discharge cycle. Through the charge-discharge cycle, a substance that acts as a catalyst for the silane crosslinking reaction is generated in the electrolyte or on the electrode surface, thereby achieving the silane crosslinking reaction.

[0122] While we do not wish to be bound by theory, it is presumed that the methoxysilane graft portion is converted to silanol by the small amount of moisture contained in the energy storage device (moisture contained in components such as electrodes, separators, and electrolytes), undergoes a crosslinking reaction, and changes to a siloxane bond. Furthermore, when the electrolyte or electrolyte comes into contact with the electrode, a substance that catalytically affects the silane crosslinking reaction is generated in the electrolyte or on the electrode surface, dissolves into the electrolyte, and uniformly swells and diffuses into the amorphous portion of the polyolefin where the silane-modified graft portion is present, thereby uniformly promoting the crosslinking reaction of the separator-containing laminate or wound body. The substance that catalytically affects the silane crosslinking reaction may be in the form of an acid solution or a film, and if the electrolyte contains lithium hexafluorophosphate (LiPF6), it may be hydrogen fluoride (HF) generated by the reaction of LiPF6 with moisture, or a fluorine-containing organic substance derived from hydrogen fluoride (HF).

[0123] When the separator for energy storage devices according to Embodiment 1 or 2 is incorporated into an energy storage device, the silane-grafted polyolefin in the microporous film made of polyolefin resin crosslinks, and / or a crosslinked structure is formed by covalent bonding between multiple components in the inorganic porous layer. Therefore, it is conceivable that the cycle characteristics and / or safety of the energy storage device can be improved while remaining compatible with the manufacturing process of conventional energy storage devices. [Examples]

[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. The physical properties in the examples were measured by the following methods.

[0125] (Method for detecting silane-modified polyolefins contained in separators) In the case of silane-modified polyolefins contained in separators, the cross-linked state makes them insoluble or insufficiently soluble in organic solvents, making it difficult to directly measure the content of silane-modified polyolefins from the separator. In such cases, as a sample pretreatment, the siloxane bonds are decomposed to methoxysilanol using methyl orthoformate, which does not cause side reactions, and then solution NMR measurement is performed to detect the silane-modified polyolefins contained in the separator or to perform GPC measurement. The pretreatment experiment can be performed with reference to Japanese Patent Publication No. 3529854 and Japanese Patent Publication No. 3529858.

[0126] Specifically, silane-modified polyolefins as raw materials used in separator manufacturing 1 H or 13 Identifying 1C NMR can be used as a method for detecting silane-modified polyolefins contained in separators. 1 H and 13 An example of a measurement method for NMR of 13C is described below.

[0127] ( 1 (NMR measurement of H) The sample was dissolved in o-dichlorobenzene-d4 at 140°C, and the proton resonance frequency was 600 MHz. 1 Obtain the 1H-NMR spectrum. 1 The measurement conditions for H-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: 1 sec Total number of times: 1000 or more Sample concentration: 1 wt / vol%

[0128] ( 13 (NMR measurement of 1C) The sample was dissolved in o-dichlorobenzene-d4 at 140°C. 13 Obtain a 1C-NMR spectrum. 13 The measurement conditions for 1C-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 Total number of times: 10,000 or more Sample concentration: 10 wt / vol%

[0129] 1 H and / or 13 NMR measurements of 1C allow for the confirmation of the amount of silane unit modification in silane-modified polyolefins and the amount of alkyl group modification in polyolefins in polyolefin raw materials, and the identification of the silane-modified polyolefin content in separators (-CH2-Si: 1 H, 0.69 ppm, t; 13 C, 6.11 ppm, s) is possible.

[0130] (1) Weight average molecular weight Using a Waters ALC / GPC 150C™ (trademark), standard polystyrene was measured under the following conditions to create a calibration curve. Similarly, chromatograms were measured for each of the polymers listed below under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the method described below. Columns: 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) By multiplying each molecular weight component in the obtained calibration curve by 0.43 (Q factor of polyethylene / Q factor of polystyrene = 17.7 / 41.3), a molecular weight distribution curve in polyethylene terms was obtained, and the weight-average molecular weight was calculated. (Weight-average molecular weight of resin composition) The Q-factor value of the polyolefin with the largest mass fraction was used, and the weight-average molecular weight was calculated for the others in the same manner as for polyethylene.

[0131] (2) Viscosity average molecular weight (Mv) The intrinsic viscosity [η] at 135°C in decalin solvent 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) Meltmas flow rate (MFR) (g / 10min) Using a Toyo Seiki melt mass flow rate measuring instrument (Melt Indexer F-F01), the weight of the extruded resin material over 10 minutes under conditions of 190°C and a load of 2.16 kg was defined as the MFR value.

[0133] (4) Thickness (μm) of microporous membranes and inorganic porous layers The film thickness of a microporous film was measured at room temperature (23±2°C) and relative humidity (60%) using a microthickness gauge manufactured by Toyo Seiki, KBM (trademark). Specifically, the film thickness was measured at five points at approximately equal intervals across the entire width in the TD direction, and the average value was obtained. Furthermore, the film thickness of the separator was measured using a similar method. The film thickness of the microporous membrane was then subtracted from the film thickness of the separator, and the resulting value was defined as the film thickness of the inorganic porous layer.

[0134] (5) Porosity of microporous membrane (%) A 10cm x 10cm square sample is cut from the microporous membrane, and its volume (cm³) is measured. 3 Calculate the mass (g) and density (g / cm³), and then compare them with the density (g / cm³). 3 The porosity was calculated using the following formula. The density of the mixed composition was calculated from the density of each raw material used and their 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 / cm³). 3 ) can be assumed and the calculation can be performed. Porosity (%) = (Volume - Mass / Density of mixed composition) / Volume × 100

[0135] (6) Permeability of the microporous membrane and the increase in permeability (sec / 100cm) 3 ) In accordance with JIS P-8117 (2009), the air permeability of the microporous membrane was measured using a Gurley-type air permeability meter, model G-B2 (trademark), manufactured by Toyo Seiki Co., Ltd. Furthermore, the air permeability of the separator was measured using a similar method. The air permeability of the separator was then 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 microporous membrane (μm) In accordance with JIS B0671-2002, the surface roughness (μm) of a microporous film was calculated using a Keyence VK-X200 under the following conditions: measurement mode: surface shape, measurement pitch: 0.2 μm, surface roughness calculation area: 216 μm × 287 μm (observation magnification: 50x).

[0137] (8) Safety test against battery destruction 1 (Battery destruction test 1) The safety test involves driving an iron nail through a battery charged to 4.5V at a speed of 20mm / sec to induce an internal short circuit. This test clarifies the phenomena that occur 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. Furthermore, in the event of an internal short circuit, insufficient shutdown function of the separator or film rupture at low temperatures may cause rapid overheating of the battery, which may lead to the electrolyte igniting, the battery smoking, and / or exploding.

[0138] (Preparation of batteries used in safety testing) a. Fabrication 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, which would serve as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, it was compressed and molded using a roll press. At this time, the amount of active material applied to the positive electrode was 250 g / m². 2 The bulk density of the active material is 3.00 g / cm³. 3 I adjusted it so that it would work.

[0139] b. Fabrication of the 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 carboxymethylcellulose salt and 1.7% by mass of styrene-butadiene copolymer latex as a resin binder in purified water. This slurry was applied to one side of a 12 μm thick copper foil, which would serve as the negative electrode current collector, using a die coater. After drying at 120°C for 3 minutes, it was compressed and molded using a roll press. At this time, the amount of active material applied to the negative electrode was 106 g / m². 2 The bulk density of the active material is 1.35 g / cm³. 3 I adjusted it so that it would work.

[0140] c. Preparation of non-aqueous electrolyte A solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:2 to a concentration of 1.0 mol / L.

[0141] d. Battery assembly The separator was cut to 60 mm in the horizontal (TD) direction and 1000 mm in the vertical (MD) direction. The separator was folded in a zigzag pattern, and the positive and negative electrodes were alternately stacked between the separators (12 positive electrodes, 13 negative electrodes). The positive electrodes used had an area of ​​30 mm x 50 mm, and the negative electrodes had an area of ​​32 mm x 52 mm. After placing this zigzag-folded laminate into a laminate bag, the non-aqueous electrolyte obtained in c. above was injected and the bag was sealed. After leaving it at room temperature for one day, the battery was charged to a voltage of 4.2 V at a current of 3 mA (0.5 C) under a 25°C atmosphere, and after reaching 4.2 V, the current was gradually reduced from 3 mA to maintain the voltage, for a total of 6 hours for the first charge after the battery was made. Subsequently, the battery was discharged to a voltage of 3.0 V at a current of 3 mA (0.5 C).

[0142] (Maximum heat generation rate) An iron nail was driven into the obtained battery at a speed of 20 mm / sec until it penetrated. After that, the surface temperature of the battery was measured using a thermocouple over a period of 300 seconds, and the maximum heat generation rate was defined as the rate at which the temperature increase per second was greatest, based on the temperature change graph.

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

[0144] (9) Evaluation of cycle characteristics 1 (battery cycle stability 1), and method for manufacturing the battery thereof. The battery used for cycle characteristic evaluation was manufactured according to the same methods as a. to c. of the battery manufacturing method used in item (8) Battery Destruction Test 1 above, except that the assembly was carried out according to d. below. The obtained batteries were subjected to 100 charge-discharge cycles under a 60°C atmosphere. Charging was performed for a total of 3 hours, using a current of 6.0mA (1.0C) until the battery voltage reached 4.2V, then gradually reducing the current from 6.0mA to maintain the voltage at 4.2V. Discharging was performed using a current of 6.0mA (1.0C) until the battery voltage reached 3.0V. The capacity retention rate (%) was calculated from the discharge capacity at cycle 100 and cycle 1. A high capacity retention rate in battery cycle stability was considered indicative of good cycle characteristics. d. Battery assembly The separator was cut into a circle with a diameter of 18 mm, and the positive and negative electrodes into circles with a diameter of 16 mm. The positive electrode, separator, and negative electrode were stacked in that order so that the active material surfaces of the positive and negative electrodes faced each other, and placed in a stainless steel metal container with a lid. The container and lid were insulated, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode. The non-aqueous electrolyte obtained in item c. of "(8) Battery Destruction Test 1" above was poured into this container and sealed. After being left at room temperature for 1 day, the battery was charged to a voltage of 4.2V at a current of 3 mA (0.5 C) in a 25°C atmosphere, and after reaching 4.2V, the current was gradually reduced from 3 mA to maintain the voltage, for a total of 6 hours for the first charge after the battery was made. Subsequently, the battery was discharged to a voltage of 3.0V at a current of 3 mA (0.5 C).

[0145] (10) Measurement of shutdown and film rupture temperature 1 (Fuse / Meltdown (F / MD) Characteristics 1) A positive electrode, separator, and negative electrode were cut into a circular shape with a diameter of 200 mm, and the resulting laminate was created by overlapping them. Electrolyte was added to the laminate and allowed to permeate the entire structure. The laminate was placed in the center of a circular aluminum heater with a diameter of 600 mm, and the aluminum heater was pressurized to 0.5 MPa from above and below using hydraulic jacks to complete the preparation for measurement. The resistance (Ω) between the electrodes was measured while heating the laminate with the aluminum heater at a heating rate of 2°C / min. The temperature at which the resistance between the electrodes, including the fuse of the separator, first exceeded 1000 Ω was defined as the fuse temperature (shutdown temperature). Furthermore, the temperature at which the resistance dropped below 1000 Ω after continued heating was defined as the meltdown temperature (rupture temperature). For the measurement, a wire for resistance measurement was attached to the back of the aluminum foil of the positive electrode prepared according to item "a. Preparation of positive electrode" in "(8) Battery destruction test" above, using conductive silver paste. Furthermore, for the measurements, a negative electrode prepared according to item "b. Preparation of negative electrode" in "(8) Battery destruction test" above was used, with a resistance measurement wire attached to the back of the copper foil using conductive silver paste. In addition, for the measurements, the electrolyte prepared according to item "c. Preparation of non-aqueous electrolyte" in "(8) Battery destruction test" above was also used for the F / MD characteristic test.

[0146] (11) Solvent immersion test A microporous membrane with an inorganic porous layer was cut into a 5.0 × 5.0 cm square, immersed in acetone at 25°C in a glass sample container, and the entire glass sample container was vibrated at a frequency of 40 Hz for 10 minutes using an ultrasonic cleaner. Subsequently, the microporous membrane with the inorganic porous layer was removed from the acetone and air-dried. Then, using an Epson scanner, the side with the inorganic porous layer was captured as a monochrome image under conditions of 8-bit grayscale and 600 dpi resolution (see Figure 3). The captured images were processed according to the following methods (I) to (IV) to derive the percentage of the peeled area (peeled area (%)).

[0147] (I) The captured image was designated as evaluation image P, and the lengths of the sides of evaluation image P were denoted as X and Y. X and Y can be made to correspond to the lengths of the sides of the excised microporous membrane. Therefore, X = 5 cm and Y = 5 cm were used here.

[0148] (II) In the evaluation image P, the direction along the X side was defined as the X-axis and the direction along the Y side as the Y-axis. The grayscale value of the pixel at coordinate position (x,y) that constitutes the evaluation image P was defined as P(x,y). A histogram was then created for all Xp × Yp grayscale values ​​P(x,y) contained in the evaluation image P. Figure 1 shows an example of a histogram obtained from the evaluation of Example 15. In Figure 1, the vertical axis (logarithmic scale) shows frequency values, and the horizontal axis shows intensity values. From Figure 1, peaks representing bright areas (peaks with small intensity values) and peaks representing dark areas (peaks with large intensity values) were identified. The intensity value corresponding to the peak representing the bright areas was determined as the intensity value Pb in the bright areas, and the intensity value corresponding to the peak representing the dark areas was determined as the intensity value Pd in ​​the dark areas. In Figure 1, the frequency values ​​that give the intensity value Pb in the bright areas and the frequency values ​​that give the intensity value Pd in ​​the dark areas are represented by the "×" mark, respectively.

[0149] If the number of pixels corresponding to the bright areas or the number of pixels corresponding to the dark areas is relatively low, the peak corresponding to the area with fewer 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 resulting histogram, 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, a peak indicating the bright areas may be observed, but a peak indicating the dark areas may not be clearly observed. In this case, the grayscale value in the dark areas can be determined as the grayscale value Pd in ​​the dark areas. This grayscale value can be determined as the grayscale value Pd in ​​the dark areas, which was maintained at approximately a constant frequency on the histogram in the range where the grayscale value is greater than the peak corresponding to the brightness, but then began to decrease sharply as the grayscale value increased, corresponding to the upper right corner of the histogram. In Figure 2, the frequency values ​​that give the grayscale value Pb in the bright areas and the frequency values ​​that give the grayscale value Pd in ​​the dark areas are represented by "×" marks.

[0151] (II-2) When the number of pixels corresponding to the bright areas is relatively small, although not shown in the illustration, a peak indicating the dark areas may be observed, but a peak indicating the bright areas may not be clearly observed. In this case, the grayscale value in the range where the grayscale value is smaller than the peak corresponding to the dark areas, and which maintains a nearly constant frequency value on the histogram, can be determined as the grayscale value Pb in the bright areas, by taking the grayscale value in the region where the frequency value begins to decrease sharply as the grayscale value decreases (the upper left corner of the histogram).

[0152] (III) Using the grayscale values ​​Pb in the bright areas and Pd in ​​the dark areas determined as described above, the average value was calculated using the following formula, and the obtained value was determined as the threshold Ps. In Figures 1 and 2, the frequency values ​​that give the threshold Ps are represented by the "×" mark. Threshold Ps = (Gray value in bright areas Pb + Gray value in dark areas Pd) / 2

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

[0154] (V) The number of BW(x,y) pixels with a value of 1 in the binarized image BW was determined as the number of bright pixels Br. Similarly, the number of BW(x,y) pixels with a value of 0 in the binarized image BW 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 proportion of the light area, Brp, was determined using the formula Brp = Br / (Xp × Yp), and the proportion of the dark area, Dkp, was determined using the formula Dkp = Dk / (Xp × Yp). The obtained proportion of the light area, Brp, was determined as the proportion of the peeled area (%), and the obtained proportion of the dark area, Dkp, was determined as the proportion of the normal area (%).

[0156] [Example of Silane Graft Modified Polyolefin Production] Polyethylene with an average viscosity and molecular weight of 20,000 was used as the raw material. While the raw material polyethylene was melt-kneaded in an extruder, an organic peroxide (di-t-butyl peroxide) was added to generate radicals within the polymer chain of the α-olefin. Then, trimethoxyalkoxide-substituted vinylsilane was injected, and an addition reaction introduced alkoxysilyl groups into the α-olefin polymer, forming a silane graft structure. Simultaneously, 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 the chain reaction (gelation) within the α-olefin. The resulting silane graft polyolefin molten resin was cooled in water, processed into pellets, and then heated and dried at 80°C for 2 days to remove water or unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was approximately 1500 ppm or less. As described above, a modification reaction using trimethoxyalkoxide-substituted vinylsilane yielded silane-grafted polyethylene with an MFR (190°C) of 0.24 g / min (indicated as "silane-modified polyethylene (B)" in Tables 1, 2, 5, or 6).

[0157] [Example 1] (Production of silane-crosslinkable polyolefin microporous membranes) 79.2% by mass of homopolymer polyethylene (indicated as "polyethylene (A)" in Tables 1, 2, 5, or 6) with a weight-average molecular weight of 700,000 was combined with 19.8% by mass of the silane-modified polyethylene (B) obtained above to form a resin compound 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 to the compound as an antioxidant, and the mixture was obtained by dry blending using a tumbler blender. The obtained mixture was supplied to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was also used. -5 m2 The solution ( / s) was injected into the extruder cylinder using a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the amount of liquid paraffin 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. Next, the molten mixture was extruded and cast onto a cooling roll with a surface temperature controlled to 25°C via a T-die to obtain a gel sheet (sheet-shaped molded body) with a raw material thickness of 1100 μm. Next, the sheet-like molded material was guided into a simultaneous biaxial tenter stretcher and biaxial stretching was performed to obtain a stretched product. The set stretching conditions were an MD ratio of 7.0x, a TD ratio of 6.2x, and a biaxial stretching temperature of 120°C. Next, the stretched gel sheet was introduced into a dichloromethane bath and thoroughly immersed in the dichloromethane to extract and remove the liquid paraffin. After that, the dichloromethane was dried off to obtain a porous body. Next, the porous material was guided into a TD tenter for heat setting (HS), and HS was performed at a heat setting temperature of 133°C and a stretching ratio of 2.1 times. After that, relaxation operations were carried out to 2.0 times in the TD direction. Subsequently, the obtained microporous membrane was trimmed at the ends and wound into a mother roll with a width of 1,100 mm and a length of 5,000 m. During the evaluation described above, the microporous membrane unwound from the mother roll was slit as needed and used as the evaluation microporous membrane. The obtained microporous membranes for evaluation were measured for thickness, air permeability, porosity, and surface roughness, and the results are shown in Table 1.

[0158] (Manufacturing of inorganic porous layers) (Manufacturing method of acrylic latex) Acrylic latex, used as a resin binder, is manufactured using the following method. In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts by mass of deionized water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 0.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added as emulsifiers. Next, the temperature inside the reaction vessel was 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 the 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 a period of 150 minutes. The above emulsified solution was prepared by mixing the following mixtures for 5 minutes using a homomixer: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adekaria Soap 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. 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 acrylic latex with a solid 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 an inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.6 parts by mass of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (based on solid content) of an aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468, solid content concentration 40%) as an ionic dispersant in 100 parts by mass of water. The obtained dispersion was crushed using a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%) 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 mass (based on solid content) of acrylic latex (solid content concentration 40%, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Subsequently, an inorganic particle-containing slurry was prepared by adding 3.0 parts by mass (in terms of solid content) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. as a crosslinking agent. Next, the microporous membrane was continuously unwound from the microporous membrane mother roll, an inorganic particle-containing slurry was applied to one side of the microporous membrane using a gravure reverse coater, and then dried in a 60°C dryer to remove water, and wound up to obtain a separator mother roll. During evaluation, the separator unwound from the mother roll was slit as needed and used as an evaluation separator.

[0160] [Examples 2-14, Comparative Examples 1-18] Using the same method as in Example 1, separators with various physical properties were prepared, with the exception of adjusting the presence or absence of silane-modified polyethylene (B), various raw material compositions, HS ratio, and stretching temperature as shown in Table 1 or 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 in Example 4 was Carbodilite V-02 manufactured by Nisshinbo Chemical Co., Ltd., the crosslinking agent in Example 5 was Duranate WB40-100 manufactured by Asahi Kasei Corporation, and the crosslinking agent in Example 6 was Denacol EX-61B manufactured by Nagase ChemteX Corporation as an epoxy crosslinking agent. Examples 7, 9, and 10 used tetraethoxysilane manufactured by Shin-Etsu Chemical Co., Ltd., Example 8 used 3-aminopropyltrimethoxysilane KBM-903 manufactured by Shin-Etsu Chemical Co., Ltd., Comparative Examples 9 and 14 used hardener 12A manufactured by Asahi Kasei Corporation, Comparative Examples 10, 12, 15, and 17 used ethylenediaminetetraacetic acid (EDTA) manufactured by SIGAM-ALDRICH, and Comparative Examples 11, 13, 16, and 18 used 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) manufactured by SIGAM-ALDRICH.

[0161] The separators obtained in the above examples and comparative examples were used to perform 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] (Manufacturing of polyolefin microporous membranes) A polymer mixture was obtained by dry blending 99% by mass of homopolymer polyethylene (PE(A)) with a weight-average molecular weight of 700,000 and 1% by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant, and then again using a tumbler blender. The obtained polymer mixture was purged with nitrogen and then supplied to a twin-screw extruder via a feeder under a nitrogen atmosphere. The kinematic viscosity of liquid paraffin (at 37.78°C was 7.59 × 10⁻⁶) was also measured. -5 m 2 The solution ( / s) was injected into the extruder cylinder using a plunger pump. The feeder and pump were adjusted so that the proportion of liquid paraffin in 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] Next, the molten mixture was extruded and cast onto a cooling roll with a surface temperature controlled to 25°C via a T-die to obtain a gel sheet with a raw material thickness of 1400 μm. Then, it was led to a simultaneous biaxial tenter stretcher and biaxial stretched. The set stretching conditions were an MD ratio of 7.0x, a TD ratio of 6.0x (i.e., 7 × 6x), and a biaxial stretching temperature of 125°C. Next, it was led to a methyl ethyl ketone bath and thoroughly immersed in methyl ethyl ketone to extract and remove the liquid paraffin, after which the methyl ethyl ketone was dried off. Next, to perform heat setting (sometimes abbreviated as "HS"), it was led to a TD tenter and HS was performed at a heat setting temperature of 125°C and a stretching ratio of 1.8x, followed by a relaxation operation to 1.2x. After that, the obtained microporous film was cut at the ends and wound into a mother roll with a width of 1100 mm and a length of 5000 m to obtain a microporous film. The film thickness, air permeability, porosity, and surface roughness of the obtained films were measured and are shown in Table 3.

[0172] (Manufacturing of inorganic porous layers) (Manufacturing method of acrylic latex) Acrylic latex, used as a resin binder, is manufactured using the following method. In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts by mass of deionized water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 0.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added as emulsifiers. Next, the temperature inside the reaction vessel was 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 the 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 a period of 150 minutes. The above emulsified solution was prepared by mixing the following mixtures for 5 minutes using a homomixer: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adekaria Soap 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. 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 acrylic latex with a solid 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 an inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.6% by mass of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.40% by mass (based on solid content) of an aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468, solid content concentration 40%) as an ionic dispersant in 100% by mass of water. The obtained dispersion was crushed using a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%) 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 mass (based on solid content) of acrylic latex (solid content concentration 40%, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Subsequently, an inorganic particle-containing slurry was prepared by adding 3.0% by mass (based on solid content) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. as a crosslinking agent. Next, the microporous membrane was continuously unwound from the microporous membrane mother roll, an inorganic particle-containing slurry was applied to one side of the microporous membrane using a gravure reverse coater, and then dried in a 60°C dryer to remove water, and wound 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 evaluation separator.

[0174] [Examples 16 - 27, Comparative Examples 19 - 29] By adjusting the HS magnification and stretching temperature in the same manner as in Example 15, separators with various physical properties were produced. The crosslinking agents for Examples 16, 24 - 27, and Comparative Examples 19 - 21 were Epocros K - 2010E manufactured by Nippon Shokubai Co., Ltd., the crosslinking agent for Example 17 was Carbodilite V - 02 manufactured by Nisshinbo Chemical Co., Ltd., the crosslinking agent for Example 18 was Duranate WB40 - 100 manufactured by Asahi Kasei Corporation, the crosslinking agent for Example 19 was Denacol EX - 61B manufactured by Nagase ChemteX Corporation as an epoxy - based 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 Co., Ltd., and Comparative Examples 27 and 29 used 1,4,7,10 - tetraazacyclododecane - 1,4,7,10 - tetraacetic acid (DOTA) manufactured by SIGAM - ALDRICH Co., Ltd.

[0175] Using the separators obtained in the above - mentioned examples and comparative examples, the above - mentioned various tests were conducted. The test results are shown in Tables 3 - 4. In the tables, the unit "mass%" is denoted 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 membranes) 79.2% by mass of polyethylene (A), a homopolymer 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 compound 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 to this compound as an antioxidant, and a mixture was obtained by dry blending using a tumbler blender. The obtained mixture was supplied to a twin-screw extruder via a feeder under a nitrogen atmosphere. Furthermore, liquid paraffin (kinematic viscosity at 37.78°C: 7.59 × 10⁻⁶) was used. -5 m 2 The solution ( / s) was injected into the extruder cylinder using a plunger pump. The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the amount of liquid paraffin 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. Next, the molten mixture was extruded and cast onto a cooling roll with a surface temperature controlled to 25°C via a T-die to obtain a gel sheet (sheet-shaped molded body) with a raw material thickness of 1150 μm. Next, the sheet-like molded material was guided into a simultaneous biaxial tenter stretcher and biaxial stretched to obtain a stretched product. The set stretching conditions were an MD ratio of 7.0x, a TD ratio of 6.7x, and a biaxial stretching temperature of 119°C. Next, the stretched gel sheet was introduced into a dichloromethane bath and thoroughly immersed in the dichloromethane to extract and remove the liquid paraffin. After that, the dichloromethane was dried off to obtain a porous body. Next, the porous material was guided into a TD tenter for heat setting (HS), and HS was performed at a heat setting temperature of 132°C and a stretching ratio of 2.1 times. After that, relaxation operations were carried out to 1.7 times in the TD direction. Subsequently, the obtained microporous membrane was trimmed at the ends and wound into a mother roll with a width of 1,100 mm and a length of 5,000 m. During the evaluation described above, the microporous membrane unwound from the mother roll was slit as needed and used as the evaluation microporous membrane. The obtained microporous films for evaluation were measured for thickness, surface roughness, air permeability, porosity, etc., and the results are shown in Table 5.

[0181] (Manufacturing of inorganic porous layers) (Manufacturing method of acrylic latex) Acrylic latex, used as a resin binder, is manufactured using the following method. In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts by mass of deionized water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 0.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added as emulsifiers. Next, the temperature inside the reaction vessel was 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 the 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 a period of 150 minutes. The above emulsified solution was prepared by mixing the following mixtures for 5 minutes using a homomixer: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adekaria Soap 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. 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 acrylic latex with a solid 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 an inorganic porous layer) A dispersion was prepared by uniformly dispersing 94.60 parts by mass of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.40 parts by mass (based on solid content) of an aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468, solid content concentration 40%) as an ionic dispersant in 100 parts by mass of water. The obtained dispersion was crushed using a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%) 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 mass (based on solid content) of acrylic latex (solid content concentration 40%, average particle size 145 nm, glass transition temperature -20°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder. Subsequently, an inorganic particle-containing slurry was prepared by adding 3 parts by mass (in terms of solid content) of Epocross K-2010E manufactured by Nippon Shokubai Co., Ltd. as a crosslinking agent. Next, the microporous membrane was continuously unwound from the microporous membrane mother roll, an inorganic particle-containing slurry was applied to one side of the microporous membrane using a gravure reverse coater, and then dried in a 60°C dryer to remove water, and wound up to obtain a separator mother roll. During evaluation, the separator unwound from the mother roll was slit as needed and used as an evaluation separator.

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

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

[0185] (12) Battery cycle stability 2 (cycle test 2), battery failure test 2 (nail penetration test 2) a. Fabrication of the positive electrode LiNi 3 / 5 Mn 1 / 5 Co1 / 5 Oxygen, carbon black as a conductive aid, and a polyvinylidene fluoride solution as a binder were mixed at a solid content mass ratio of 91:5:4. N-methyl-2-pyrrolidone was added as a dispersion solvent so that the solid content was 68% by mass, and further mixed to prepare a slurry-like solution. This slurry-like solution was applied to one side of an aluminum foil with a thickness of 15 μm so that a part of the aluminum foil was exposed. After the solvent was dried and removed, the coating amount was 175 g / m 2 was obtained. Furthermore, the density of the positive electrode mixture part was 2.8 g / cm 3 and rolled by a roll press to achieve this. Then, it was cut so that the coated part was 30 mm × 50 mm and included the aluminum foil exposed part, and a positive electrode was obtained.

[0186] b. Preparation of negative electrode Artificial graphite as a negative electrode active material, styrene-butadiene rubber and an aqueous carboxymethyl cellulose solution as binders were mixed at a solid content mass ratio of 96.4:1.9:1.7. Water was added as a dispersion solvent so that the solid content was 50% by mass, and further mixed to prepare a slurry-like solution. This slurry-like solution was applied to one side of a copper foil with a thickness of 10 μm so that a part of the copper foil was exposed. After the solvent was dried and removed, the coating amount was 86 g / m 2 was obtained. Furthermore, the density of the negative electrode mixture part was 1.45 g / cm 3 and rolled by a roll press to achieve this. Then, it was cut so that the coated part was 32 mm × 52 mm and included the copper foil exposed part, and a negative electrode was obtained.

[0187] c. Preparation of non-aqueous electrolyte LiPF6 was dissolved 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 vinylene carbonate was further added to a content of 1.0% by weight to prepare a non-aqueous electrolyte.

[0188] d. Battery assembly A 60 mm × 40 mm square was cut from the separator as a sample. A laminate consisting of 15 double-sided negative electrodes and 14 double-sided positive electrodes was constructed by folding a long separator with a width of 55 mm in a zigzag pattern, so that the active material surfaces of the positive and negative electrodes faced each other and were interposed between the positive and negative electrodes. At this time, the inorganic porous layer of the sample was positioned to face the positive electrode. Sealant-coated aluminum lead pieces were welded to the exposed parts of the 14 positive electrode aluminum foils of this laminate, and sealant-coated nickel lead pieces were welded to the exposed parts of the 15 negative electrode copper foils. After that, the laminate was inserted into an aluminum laminate casing, and the three sides in total—the sides where the positive and negative electrode lead pieces are exposed and the other two sides—were laminate-sealed. Next, the above non-aqueous electrolyte was injected into the casing, and then the opening was sealed to create a 28-pair laminate-type battery. The resulting batteries were left at room temperature for one day. Then, under a 25°C atmosphere, they were charged with a constant current of 330mA (0.3C) until the battery voltage reached 4.2V. After reaching this point, constant voltage charging was performed to maintain the voltage at 4.2V, for a total of 8 hours. Subsequently, the batteries were discharged to a battery voltage of 3.0V with a current of 330mA (0.3C).

[0189] Battery cycle stability 2 evaluation The batteries obtained in "d. Battery Assembly" above were subjected to 1000 cycles of charging and discharging under a 25°C atmosphere. For charging, the batteries were charged for a total of 3 hours using a constant current of 1A (1.0C) until the battery voltage reached 4.2V, and then constant voltage charging was performed to maintain 4.2V. For discharging, the batteries were discharged to a battery voltage of 3.0V using a current of 1A (1.0C). The capacity retention rate was calculated from the discharge capacity at the 1000th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as indicating good cycle characteristics.

[0190] Battery destruction safety test 2 (Battery destruction test 2) The safety test involves driving an iron nail through a battery charged to 4.5V at a speed of 30mm / sec to induce an internal short circuit. This test clarifies the phenomena that occur 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. Furthermore, in the event of an internal short circuit, insufficient shutdown function of the separator or film rupture at low temperatures may cause rapid overheating of the battery, which may lead to the electrolyte igniting, the battery smoking, and / or exploding.

[0191] (13) Measurement of shutdown and film rupture temperature 2 (Fuse / Meltdown (F / MD) Characteristics 2) In Examples 28-41 and Comparative Examples 30-44, the F / MD characteristics were measured as follows. A positive electrode, separator, and negative electrode were cut into a circular shape with a diameter of 200 mm, and the resulting laminate was created by overlapping them. Electrolyte was added to the laminate and allowed to permeate the entire structure. The laminate was placed in the center of a circular aluminum heater with a diameter of 600 mm, and the aluminum heater was pressurized to 0.5 MPa from above and below using hydraulic jacks to complete the preparation for measurement. The resistance (Ω) between the electrodes was measured while heating the laminate with the aluminum heater at a heating rate of 2°C / min. The temperature at which the resistance between the electrodes, including the fuse of the separator, first exceeded 1000 Ω was defined as the fuse temperature (shutdown temperature). Furthermore, the temperature at which the resistance dropped below 1000 Ω after continued heating was defined as the meltdown temperature (rupture temperature). For the measurement, a wire for resistance measurement was attached to the back of the aluminum foil of the positive electrode prepared according to item (12) "a. Preparation of the positive electrode" above using conductive silver paste. Furthermore, for the measurements, a negative electrode prepared according to item (12) "b. Preparation of negative electrode" was used, with a resistance measurement wire attached to the back of the copper foil using conductive silver paste. In addition, for the measurements, the electrolyte prepared according to 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 energy storage device comprising a microporous membrane made of polyolefin resin and an inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, The inorganic porous layer comprises inorganic particles, a resin binder, and a crosslinking agent in a mass ratio of 0.1% to 5% by mass. The resin binder has nucleophilic substitution or nucleophilic addition reactive functional groups, A separator for energy storage devices, wherein, in a solvent immersion test, the area in which the inorganic porous layer peels off from the polyolefin resin microporous membrane is 0 to 35% of the area of ​​the inorganic porous layer before the test.

2. A separator for an energy storage device comprising a microporous membrane made of polyolefin resin and an inorganic porous layer disposed on at least one surface of the polyolefin resin microporous membrane, The rupture temperature of the aforementioned microporous membrane made of polyolefin resin is higher than 200°C. The inorganic porous layer comprises inorganic particles, a resin binder, and a crosslinking agent in a mass ratio of 0.1% to 5% by mass. The resin binder has nucleophilic substitution or nucleophilic addition reactive functional groups, A separator for energy storage devices, wherein, in a solvent immersion test, the area in which the inorganic porous layer peels off from the polyolefin resin microporous membrane is 0 to 35% of the area of ​​the inorganic porous layer before the test.

3. The separator for an energy storage device according to claim 1 or 2, wherein 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.

4. The separator for an energy storage device according to claim 3, wherein the inorganic porous layer includes a crosslinked structure formed by at least one selected from the group consisting of covalent bonds (i) to (iii).

5. The microporous membrane made of polyolefin resin comprises a silane graft-modified polyolefin, as described in any one of claims 1 to 4, for use as a separator for an energy storage device.

6. The separator for an energy storage device according to claim 5, wherein the microporous membrane made of polyolefin resin includes a polyolefin other than the silane graft-modified polyolefin.

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

8. The separator for an energy storage device according to any one of claims 3, 4, or 7, wherein the resin binder is in the form of an emulsion, suspension, or colloid.

9. The resin binder has nucleophilic substitution or nucleophilic addition reactive functional groups, as described in any one of claims 3, 4, 7, or 8, for use as a separator for energy storage devices.

10. The separator for an energy storage device according to any one of claims 3, 4, 7 to 9, 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.

11. A separator for an energy storage device according to any one of claims 1 to 10, wherein the inorganic particles have polar functional groups on their surface.

12. A separator for an energy storage device according to any one of claims 1 to 11, wherein the inorganic particles have silicon-containing functional groups on their surface.

13. The separator for an energy storage device according to claim 12, 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.

14. The crosslinking agent is a separator for an energy storage device according to any one of claims 1 to 13, wherein the crosslinking agent has a nucleophilic substitution reactive functional group and / or an electrophilic addition reactive functional group.

15. The crosslinking agent comprises a nucleophilic substitution-reactive functional group and an electrophilic addition-reactive functional group, wherein the separator for an energy storage device is according to any one of claims 1 to 14.

16. The separator for an energy storage device according to claim 14 or 15, wherein the nucleophilic substitution reactive functional group of the crosslinking agent is an oxazoline group and / or an epoxy group.

17. The separator for an energy storage device according to claim 14 or 15, wherein the electrophilic addition-reactive functional group of the crosslinking agent is at least one selected from the group consisting of isocyanate group, thioisocyanate group, carbodiimide group, allene group, oxime group, and carbonyl group.

18. A separator for an energy storage device according to any one of claims 1 to 17, wherein the inorganic particles have polar functional groups on their surface, the crosslinking agent is between the polar functional groups and the resin binder, and a crosslinked structure is formed by covalent bonding between the polar functional groups, the crosslinking agent and the resin binder.

19. The separator for an energy storage device according to any one of claims 1 to 18, wherein the crosslinking agent is in the form of an emulsion, suspension, or colloid.

20. An energy storage device comprising an electrode, an electrolyte, and a separator for an energy storage device according to any one of claims 1 to 19.

21. A secondary battery comprising an electrode, an electrolyte, and a separator for an energy storage device according to any one of claims 1 to 19.

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