Composite monolayer chemically crosslinked separator

Abstract

The purpose of this disclosure is to provide a separator for an energy storage device with enhanced safety and an energy storage device using the same. The separator for the energy storage device has a substrate comprising a polyolefin and one or more layers formed thereon. The polyolefin contained in the substrate has one or more functional groups that form a cross-linked structure within the energy storage device. In one embodiment, the layers are layers comprising inorganic particles and layers comprising a thermoplastic polymer. In another embodiment, the layers are surface layers such as a thermoplastic polymer layer, an active layer, and a heat-resistant porous layer.

Description

Technical Field

[0001] This disclosure relates to polyolefin microporous membranes, as well as separators and energy storage devices using the same. Background Technology

[0002] Polyolefin microporous membranes exhibit excellent electrical insulation and ion permeability, and are therefore used as separators in energy storage devices, such as battery separators and capacitor separators. In particular, polyolefin microporous membranes are used as separators in lithium-ion secondary batteries, which are used not only in small electronic devices such as mobile phones and laptop computers, but also in various products such as electric vehicles and electric bicycles.

[0003] In recent years, with the development of small electronic devices and electric vehicles, there has been a growing demand for energy storage devices to achieve higher output, higher energy density, and improved cycle characteristics. Along with this, the safety standards for energy storage devices have become increasingly stringent; for example, there is a need for safer energy storage devices that can withstand partial short circuits without thermal runaway.

[0004] Patent Document 1 discloses a separator for lithium-ion secondary batteries, which aims to suppress separation between the separator and the electrode and improve the heat resistance of the separator. It comprises a porous membrane, an inorganic particle layer formed on at least one surface of the porous membrane and having inorganic particles accounting for more than 80% by volume of the entire layer, and a porous resin layer formed on the surface of the inorganic particle layer and integrated with the inorganic particle layer.

[0005] Patent document 2 describes a separator that, for the purpose of improving closing characteristics and melt-down characteristics, has a porous cross-linked polyolefin material and an inorganic porous layer laminated on part or all of its surface.

[0006] Patent document 3 describes a cross-linked polyolefin separator that, with the aim of maintaining mechanical and thermal stability and reducing thickness, weight, and volume, comprises a porous polyolefin material having siloxane cross-linking bonds and a polymeric adhesive layer located on at least one side thereof.

[0007] Patent document 4 discloses a separator for an energy storage device, which aims to balance the shut-off function and high-temperature crack resistance while ensuring the safety, output and / or cycle stability of the energy storage device. The separator is characterized in that it contains a silane-modified polyolefin, and the silane crosslinking reaction of the silane-modified polyolefin begins when it comes into contact with the electrolyte.

[0008] Patent documents 5 and 6 describe a separator that combines the characteristics of electrode adhesion, heat resistance, mechanical properties, high battery output, and long battery life, with the aim of providing a separator comprising a porous substrate containing a cross-linked silane-modified polyolefin and an inorganic coating layer located on the substrate.

[0009] On the other hand, to ensure battery safety, techniques have been proposed to achieve both a shutdown function and an increased membrane rupture temperature by forming a cross-linked structure within the separator (Patent Documents 7-14). For example, Patent Documents 7-12 describe a silane cross-linked structure formed by contacting a separator containing silane-modified polyolefin with water. Patent Document 13 describes a cross-linked structure formed by ring-opening of norbornene, wherein the ring-opening is performed by irradiation with ultraviolet light, an electron beam, or the like. Patent Document 14 describes a scheme in which the insulating layer of the separator comprises a (meth)acrylic acid copolymer with a cross-linked structure, a styrene-butadiene rubber adhesive, or the like.

[0010] Regarding components for lithium-ion batteries, positive electrode, negative electrode materials, electrolyte, and separators are used. Regarding the separator, given its nature as an insulating material, it is required to be inactive against electrochemical reactions or surrounding components. On the other hand, the negative electrode material for lithium-ion batteries has, since its inception, established a technique to suppress electrolyte decomposition on the negative electrode surface by utilizing the chemical reaction during initial charging to form a solid electrolyte interface (SEI) (Non-Patent Document 3). Furthermore, examples have been reported where, even when polyolefin resin is used in the separator, oxidation reactions occur on the positive electrode surface under high voltage, leading to blackening and surface degradation of the separator.

[0011] Based on the above ideas, the materials for separators used in energy storage devices adopt chemical structures that are inactive to electrochemical reactions or other chemical reactions. Therefore, the development and practical application of microporous membranes made of polyolefins are being widely carried out.

[0012] Furthermore, it was proposed that when manufacturing separators for energy storage devices, a single microporous membrane or a laminate of multiple microporous membranes be used as a substrate, and functional layers or films such as thermoplastic resin layers, heat-resistant resin layers, and water-soluble resin layers be formed on the surface of the substrate (Patent Documents 16-19).

[0013] Furthermore, it was proposed that when manufacturing a separator for an energy storage device, a single microporous membrane or a laminate of multiple microporous membranes be used as a substrate, and an active layer such as a layer containing polyvinylidene fluoride (PVDF) resin, a layer containing PVDF resin and inorganic filler be formed on the surface of the substrate (Patent Documents 18 and 20).

[0014] Furthermore, it was proposed that when manufacturing a separator for an energy storage device, a single microporous membrane or a laminate of multiple microporous membranes be used as a substrate, and a heat-resistant resin layer such as a fully aromatic polyamide (also known as aromatic polyamide) be formed on the surface of the substrate (Patent Document 16), or a porous membrane containing aromatic polyamide and a porous membrane containing water-soluble resin such as cellulose ether are laminated on both sides of the substrate (Patent Document 19).

[0015] However, as long as polyolefins are used as the resin, there are limits to performance improvement even with improvements in the mechanical microporous structure of the separator. For example, the permeability of separators containing Li ions or solvated ion clusters is unsatisfactory due to the thermal stability of the separator above the melting point of polyolefins, or insufficient affinity or liquid retention with the electrolyte caused by the electronegativity of olefin units.

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: Japanese Patent Application Publication No. 2020-64879

[0019] Patent Document 2: Korean Patent No. 10-1943491

[0020] Patent Document 3: Korean Patent Publication No. 2019-0108438

[0021] Patent Document 4: International Publication No. 2020 / 075866

[0022] Patent Document 5: Korean Patent Publication No. 10-2018-0147041

[0023] Patent Document 6: Korean Patent Publication No. 10-2018-0147042

[0024] Patent Document 7: Japanese Patent Application Publication No. 9-216964

[0025] Patent Document 8: International Publication No. 97 / 44839

[0026] Patent Document 9: Japanese Patent Application Publication No. 11-144700

[0027] Patent Document 10: Japanese Patent Application Publication No. 11-172036

[0028] Patent Document 11: Japanese Patent Application Publication No. 2001-176484

[0029] Patent Document 12: Japanese Patent Application Publication No. 2000-319441

[0030] Patent Document 13: Japanese Patent Application Publication No. 2011-071128

[0031] Patent Document 14: Japanese Patent Application Publication No. 2014-056843

[0032] Patent Document 15: Japanese Patent Application Publication No. 10-261435

[0033] Patent Document 16: International Publication No. 2008 / 156033

[0034] Patent Document 17: Japanese Patent No. 6580234

[0035] Patent Document 18: Japanese Patent No. 6367453

[0036] Patent Document 19: International Publication No. 2012 / 018132

[0037] Patent Document 20: Korean Patent Publication No. 10-2020-0026172

[0038] Non-patent literature

[0039] Non-patent literature 1: Pekka Pyykko and Michiko Atsumi, “Molecular Single-Bond Covalent Radii for Elements 1-118”, Chem. Eur. J., 2009, 15, 186-197

[0040] Non-Patent Literature 2: Robin Walsh, “Bond dissociation energy values ​​in silicon-containing compounds and some of their implications”, Acc. Chem. Res., 1981, 14, 246-252

[0041] Non-Patent Document 3: Lithium-ion Secondary Batteries (2nd Edition) Published by Nikkan Kogyo Shimbun

[0042] Non-Patent Literature 4: Basic Polymer Chemistry, Tokyo Chemical Doujin Publishing

[0043] Non-patent literature 5: ACS Appl. Mater. Interfaces 2014, 6, 22594-22601

[0044] Non-Patent Literature 6: Energy Storage Materials 2018, 10, 246-267

[0045] Non-patent literature 7: The Chemistry of Organic Silicon Compounds Vol.2, Wiley (1998), Chap.4 Summary of the Invention

[0046] The problem the invention aims to solve

[0047] The purpose of this disclosure is to provide a separator for a more secure energy storage device and an energy storage device using the same.

[0048] For example, the separators for energy storage devices described in Patent Documents 1-6 have room for further improvement in terms of safety during partial short circuits. Therefore, in the first embodiment, the object of this disclosure is to provide a separator for energy storage devices and an energy storage device with higher safety, which reduces the possibility of thermal runaway due to partial short circuits.

[0049] Furthermore, with the increasing demand for high-output and high-energy-density lithium-ion secondary batteries for mobile devices and automotive applications in recent years, there is a growing demand for miniaturized battery cells and stable cycle-discharge performance during long-term use. Therefore, there is a need for thin-film (e.g., 15 μm or less) and high-quality separators (e.g., with uniform physical properties and free of resin aggregates). Moreover, battery safety standards have become more stringent than before; as described in Patent Documents 7 and 8, there is a demand for separators with shut-off functionality and high-temperature film-breaking properties, as well as stable manufacturing methods for them. Relatedly, a shut-off temperature below 150°C is desirable, and a higher film-breaking temperature is desired.

[0050] However, the crosslinking methods described in Patent Documents 7-14 are all performed intermittently during or immediately after the separator film is formed. Therefore, after the crosslinked structure described in Patent Documents 7-14 is formed, the separator must undergo coating and slitting (cutting). During subsequent lamination and winding processes with the electrodes, internal stress increases, potentially causing deformation of the manufactured battery. For example, if the crosslinked structure is formed by heating, the internal stress of the separator with this crosslinked structure may increase at room temperature or ambient temperature. Furthermore, if the crosslinked structure is formed by irradiating with ultraviolet light, electron beams, or other light, the irradiation becomes uneven, resulting in an uneven crosslinked structure. This can be attributed to the fact that the periphery of the crystalline portion of the resin constituting the separator is easily crosslinked by the electron beam.

[0051] It should be noted that Patent Document 15 describes a technique for improving the cycle characteristics of lithium-ion secondary batteries by adding succinimide or similar substances to the electrolyte. However, the technique described in Patent Document 15 is not intended to improve cycle characteristics by specifying the structure of the separator.

[0052] Furthermore, the formation of the resin functional layer or resin functional film located on the separator substrate as described in Patent Documents 16-19 allows for improvement in the safety of the energy storage device with the separator during nail penetration tests.

[0053] Furthermore, as shown in Non-Patent Literature 5, the high-nickelization of NMC-type cathodes has attracted attention in recent years as a strong candidate for high-capacity LIB batteries. However, as the NMC ratio changes from the previous (1:1:1) to (4:3:3), (6:2:2), (8:1:1), etc., the heat resistance of the cathode crystal structure decreases, making it prone to releasing O2 through thermal decomposition, which can lead to the ignition or explosion of organic matter in the battery. In particular, NMC (622) or NMC (811) cathodes have been observed to begin decomposition reactions at significantly lower temperatures than the previous NMC (111) or NMC (433) cathodes. In addition, due to the same tendency, crystal instability (thermal decomposition) problems also exist in cathodes such as LAC-type cathodes. Therefore, for the high-capacity development of LIB batteries, there is a potential problem of easy thermal decomposition or O2 release of the cathode.

[0054] On the other hand, Non-Patent Document 6 elucidates a series of time-varying chemical / physical changes in the battery's internal heat release caused by partial short circuits after the nail penetrates during a series of processes in a battery nail puncture test. In particular, there is a tendency for the O2 release phenomenon during positive electrode decomposition described in Non-Patent Document 5 to be strongly correlated with the switch from the battery's exothermic mode to a rapid runaway mode.

[0055] In summary, batteries with high capacity and energy density, constructed from high-nickel NMC cathodes, present a challenge compared to traditional NMC batteries: they exhibit rapid ignition and explosion within a short timeframe during nail penetration tests. Significant suppression of peripheral short circuits during nail penetration is necessary. Such batteries pose a significant safety risk in automotive applications should they be damaged in accidents or disasters. Improving nail penetration safety through simulated damage modes remains a critical challenge.

[0056] Furthermore, the conventional technique of coating a separator substrate with PVDF-based resin as described in Patent Documents 18 and 20 has issues in suppressing thermal shrinkage, and there is room for improvement in terms of thermal shrinkage at high temperatures (e.g., above 200°C) and heat box testability.

[0057] Furthermore, as shown in Non-Patent Document 5, the high-nickelization of NMC-type cathodes has attracted attention in recent years as a strong candidate for high-capacity LIB batteries. However, as the NMC ratio has changed from the previous (1:1:1) to (4:3:3), (6:2:2), (8:1:1), etc., the heat resistance of the cathode crystal structure decreases, making it prone to releasing O2 during thermal decomposition, which can lead to the ignition or explosion of organic matter in the battery. In particular, NMC (622) or NMC (811) cathodes, which are expected to have high battery capacity and high energy density, have begun to decompose from around 150°C to 160°C. For LIBs with such cathode structures, improving the heat resistance stability at 150°C to ensure safe handling in the event of an accident or fire in automotive applications has become a challenge.

[0058] Furthermore, the conventional techniques of coating the separator substrate with heat-resistant resin and / or water-soluble resin as described in Patent Documents 16 and 19 have room for improvement in rod impact damage tests at high temperatures (e.g., above 150°C) for energy storage devices equipped with separators.

[0059] Furthermore, as shown in Non-Patent Literature 5, the high-nickel content of NMC-type cathodes has attracted attention in recent years as a strong candidate for high-capacity LIB batteries. However, as the NMC ratio changes from the previous (1:1:1) to (4:3:3), (6:2:2), (8:1:1), etc., the heat resistance of the cathode crystal structure decreases (e.g., crystal decomposition and O2 release occur at approximately 250°C), making it prone to releasing O2 with thermal decomposition, which can lead to the ignition or explosion of organic matter in the battery. In particular, in the case of high-nickel NMC (622) or NMC (811) cathodes, decomposition is observed starting from around 150°C to 160°C. Currently, research institutions and companies in various countries are continuously advancing research on the stabilization of the crystal structure of high-nickel NMC. Although improvements have been observed through NMC surface treatment or adjustment of trace impurity content, the crystal decomposition and O2 release at 150°C to 160°C have not been fundamentally resolved. Furthermore, due to the same tendency, besides NMC, other cathode materials such as LAC also suffer from crystal instability (thermal decomposition). When using high-energy-density lithium-ion batteries (LIBs) employing such cathode materials in automotive applications, ensuring safety in emergency vehicle collisions becomes a challenge. That is, when external forces cause battery structural damage, the battery must not explode even under high-temperature conditions such as fires. Therefore, research is needed to improve battery safety under the most demanding conditions assuming NMC cathodes, i.e., when crystal decomposition begins at 150°C.

[0060] Therefore, in the second embodiment, the object of this disclosure is to provide a separator for a storage device that can improve at least one of the following: safety of the storage device, such as safety in a nail puncture test, thermal shrinkage and hot box testability, and high temperature bar impact failure testability; a storage device assembly kit using the separator; a storage device; and a method for manufacturing the storage device.

[0061] Solution for solving the problem

[0062] Examples of embodiments of this disclosure are described in the following items.

[0063] [1] A separator for an energy storage device, comprising at least one layer each of an A layer containing polyolefin, a B layer containing inorganic particles, and a C layer containing a thermoplastic polymer.

[0064] The polyolefin contained in layer A above has one or more functional groups.

[0065] The aforementioned functional groups include functional groups that undergo a condensation reaction with each other within the energy storage device to form a cross-linked structure based on siloxane bonds.

[0066] [2] The separator for the energy storage device according to Project 1 has the following region: when the above-mentioned A layer is subjected to TOF-SIMS measurement with a square area of ​​100 μm, one or more island structures containing alkali metals and / or alkaline earth metals are detected, and the size of the island structure is 9 μm. 2 Above and 245μm 2 The following areas.

[0067] [3] According to the separator for the energy storage device described in Project 2, there are two or more island structures containing alkali metals and / or alkaline earth metals in the separator, and the minimum and maximum distances between the weighted center positions of each island structure are both 6 μm or more and 135 μm or less.

[0068] [4] The separator for the energy storage device according to item 2 or 3, wherein the island structure contains an alkaline earth metal, wherein the alkaline earth metal is calcium.

[0069] [5] The separator for the energy storage device according to item 2 or 3, wherein the alkali metal and / or alkaline earth metal is at least one selected from the group consisting of lithium, sodium, magnesium, potassium and strontium.

[0070] [6] A separator for an energy storage device according to any one of items 1 to 4, wherein the B layer is an inorganic porous layer comprising inorganic particles and a resin binder.

[0071] [7] The separator for the energy storage device according to item 6, wherein the glass transition temperature (Tg) of the resin adhesive is -50°C to 90°C.

[0072] [8] A separator for an energy storage device according to any one of items 1 to 7, wherein, based on the total mass of the B layer, the content of inorganic particles contained in the B layer is 5% to 99% by mass.

[0073] [9] A separator for an energy storage device according to any one of items 1 to 8, wherein the inorganic particles are selected from at least one of the following: alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, diatomite, quartz sand and glass fiber.

[0074]

[10] A separator for an energy storage device according to any one of items 1 to 9, wherein the thermoplastic polymer contained in the C layer comprises (meth)acrylate or (meth)acrylic acid as a polymerization unit.

[0075]

[11] The separator for an energy storage device according to any one of items 1 to 10, wherein the area of ​​the C layer covering the B layer is 5% to 98%.

[0076]

[12] A separator for an energy storage device according to any one of items 1 to 11, wherein the thermoplastic polymer contained in the C layer comprises at least one fluorinated vinyl compound selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0077]

[13] The separator for the energy storage device according to any one of items 1 to 12, wherein, for the thermal response index of the separator for the energy storage device after being impregnated with electrolyte and heated to 150°C at 2°C / min, when the least squares approximation method is used to fit Equation (1), the range of rate is 3.5≤rate≤150.

[0078] Equation (1)

[0079]

[14] According to any one of items 1 to 13, the thermal response index of the energy storage device when the energy storage device is heated to 150°C at 2°C / min after being impregnated with electrolyte is fitted to Equation (1) using the least squares approximation method, the range of T0 is 110≤T0≤150 and the range of max is 0.1≤max≤30.

[0080]

[15] A separator for an energy storage device, characterized in that it comprises a polyolefin microporous membrane as a substrate and a surface layer formed on at least one side of the polyolefin microporous membrane.

[0081] The polyolefins contained in the aforementioned polyolefin microporous membranes have one or more functional groups, and...

[0082] After being housed in an energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with the chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0083]

[16] The separator for an energy storage device according to item 15 is characterized in that it comprises a polyolefin microporous membrane as a substrate and a thermoplastic polymer layer formed on at least one side of the polyolefin microporous membrane.

[0084] The polyolefins contained in the aforementioned polyolefin microporous membranes have one or more functional groups, and...

[0085] After being housed in an energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with the chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0086]

[17] The separator for the energy storage device according to item 16, wherein the coverage area ratio of the thermoplastic polymer layer to the substrate is 5% to 90%.

[0087]

[18] The separator for the energy storage device according to item 16 or 15, wherein the thermoplastic polymer contained in the thermoplastic polymer layer comprises polymeric units of (meth)acrylate or (meth)acrylic acid.

[0088]

[19] The separator for an energy storage device according to any one of items 16 to 18, wherein the glass transition temperature of the thermoplastic polymer contained in the thermoplastic polymer layer is -40°C to 105°C.

[0089]

[20] The separator for an energy storage device according to item 15 is characterized in that it comprises a polyolefin microporous membrane as a substrate and an active layer disposed on at least one side of the polyolefin microporous membrane.

[0090] The polyolefins contained in the aforementioned polyolefin microporous membranes have one or more functional groups, and...

[0091] After being housed in an energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with the chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0092]

[21] According to the separator for the energy storage device of item 20, the active layer contains at least one fluorinated vinyl compound selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE), and inorganic particles.

[0093]

[22] The separator for the energy storage device according to item 20 or 21, wherein the mass ratio (fluorinated vinyl compound / inorganic particle) of the above-mentioned active layer to the above-mentioned inorganic particles is 5 / 95 to 80 / 20.

[0094]

[23] A separator for an energy storage device according to any one of items 20 to 22, wherein the weight-average molecular weight of the fluorinated vinyl compound is 0.6 × 10⁻⁶. 6 ~2.5×10 6 .

[0095]

[24] The separator for the energy storage device according to item 15 is characterized in that it comprises:

[0096] Polyolefins as substrates for microporous membranes and

[0097] A heat-resistant porous layer containing a heat-resistant resin, laminated on at least one side of the above-mentioned polyolefin microporous membrane.

[0098] The polyolefins contained in the aforementioned polyolefin microporous membranes have one or more functional groups, and...

[0099] After being housed in an energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with the chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0100]

[25] The separator for the energy storage device according to item 24, wherein the heat-resistant porous layer contains 30% to 90% by mass of inorganic filler with an average particle size of 0.2 μm to 0.9 μm.

[0101]

[26] The separator for the energy storage device according to item 24 or 25, wherein the heat-resistant resin comprises at least one selected from the group consisting of fully aromatic polyamide, polyimide, polyamide-imide, polysulfone, polyketone, polyether, polyetherketone, polyetherimide and cellulose.

[0102]

[27] A separator for an energy storage device according to any one of items 24 to 26, wherein the heat-resistant resin comprises para-aromatic polyamide and / or meta-aromatic polyamide.

[0103]

[28] A separator for an energy storage device according to any one of items 16 to 27, wherein the chemical substance is any one of the electrolyte, electrolyte solution, electrode active material, additive or decomposition product contained in the polyolefin microporous membrane.

[0104]

[29] The separator for an energy storage device according to any one of items 16 to 28, wherein the crosslinking structure is an amorphous crosslinking structure formed by crosslinking the amorphous portion of the polyolefin.

[0105]

[30] The separator for the energy storage device according to item 28, wherein the amorphous portion is selectively crosslinked.

[0106]

[31] A separator for an energy storage device according to any one of items 16 to 30, wherein the polyolefin is a functionalized polyolefin or a polyolefin copolymerized from monomers having functional groups.

[0107]

[32] A separator for an energy storage device according to any one of items 16 to 31, wherein the crosslinked structure is formed by means of any one of covalent bonds, hydrogen bonds or coordination bonds.

[0108]

[33] The separator for the energy storage device according to item 32, wherein the reaction by means of the above-mentioned covalent bond is at least one selected from the group consisting of the following reactions (I) to (IV):

[0109] (I) Condensation reaction of multiple identical functional groups;

[0110] (II) Reactions between multiple heterogeneous functional groups;

[0111] (III) Chain condensation reaction between functional groups and electrolyte; and

[0112] (IV) Reaction of functional groups with additives.

[0113]

[34] The separator for the energy storage device according to item 33, wherein the reaction by means of the above-mentioned coordinate bond is the following reaction (V):

[0114] (V) A reaction in which multiple identical functional groups cross-link with metal ions via coordination bonds.

[0115]

[35] The separator for the energy storage device according to item 33, wherein the above-mentioned reactions (I) and / or (II) are catalyzed and promoted by chemical substances inside the energy storage device.

[0116]

[36] According to item 33, the separator for the energy storage device, wherein the above reaction (I) is a condensation reaction of multiple silanol groups.

[0117]

[37] According to the separator for the energy storage device described in item 33, wherein the above reaction (IV) is a nucleophilic substitution reaction, nucleophilic addition reaction or ring-opening reaction of the compound Rx constituting the separator for the energy storage device and the compound Ry constituting the additive, wherein the compound Rx has a functional group x and the compound Ry has a connecting reaction unit y1.

[0118]

[38] According to item 37, the separator for the energy storage device, wherein the above reaction (IV) is a nucleophilic substitution reaction.

[0119] The functional group x of the above compound Rx is selected from at least one of the groups consisting of -OH, -NH2, -NH-, -COOH, and -SH, and,

[0120] The linking reaction unit y1 of the above compound Ry is selected from at least two of the following groups: CH3SO2-, CF3SO2-, ArSO2-, CH3SO3-, CF3SO3-, ArSO3-, and monovalent groups represented by formulas (y1-1) to (y1-6) below.

[0121]

[0122] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0123]

[0124] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0125]

[0126] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0127]

[0128] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0129]

[0130] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0131]

[0132] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0133]

[39] A separator for an energy storage device according to item 37 or 38, wherein the above reaction (IV) is a nucleophilic substitution reaction.

[0134] The compound Ry, in addition to having the aforementioned connecting reaction unit y1, also has a chain unit y2, and...

[0135] The aforementioned chain unit y2 is selected from at least one of the groups consisting of divalent groups shown in formulas (y2-1) to (y2-6) below.

[0136]

[0137] In the formula, m is an integer from 0 to 20, and n is an integer from 1 to 20.

[0138]

[0139] In the formula, n is an integer from 1 to 20.

[0140]

[0141] In the formula, n is an integer from 1 to 20.

[0142]

[0143] In the formula, n is an integer from 1 to 20.

[0144]

[0145] In the formula, X is an alkylene or aryl group having 1 to 20 carbon atoms, and n is an integer from 1 to 20.

[0146]

[0147] {In the formula, X is an alkylene or arylene with 1 to 20 carbon atoms, and n is an integer from 1 to 20.}

[0148]

[40] The separator for the energy storage device according to item 37, wherein the above reaction (IV) is a nucleophilic addition reaction.

[0149] The functional group x of the above compound Rx is selected from at least one of the groups consisting of -OH, -NH2, -NH-, -COOH, and -SH, and,

[0150] The linking reaction unit y1 of the above compound Ry is selected from at least one group composed of the groups shown in formulas (Ay1-1) to (Ay1-6) below.

[0151]

[0152] {In the formula, R is a hydrogen atom or a monovalent organic group.}

[0153]

[0154]

[41] According to the separator for the energy storage device described in item 37, wherein the above reaction (IV) is a ring-opening reaction.

[0155] The functional group x of the above compound Rx is selected from at least one of the groups consisting of -OH, -NH2, -NH-, -COOH, and -SH, and,

[0156] The connecting reactive unit y1 of the above compound Ry consists of at least two groups as shown in the following formula (ROy1-1):

[0157]

[0158] {In the formula, each X is independently a hydrogen atom or a monovalent substituent.}

[0159]

[42] According to the separator for the energy storage device described in item 34, in the above reaction (V), the metal ion is selected from Zn. 2+ Mn 2+ Co 3+ Ni 2+ and Li + At least one of the groups.

[0160]

[43] A separator for an energy storage device according to any one of items 1 to 42, wherein the polyolefin having the above-mentioned functional groups is not a masterbatch resin containing a dehydration condensation catalyst that forms the crosslinked structure of the above-mentioned functional groups.

[0161]

[44] An energy storage device assembly kit comprising:

[0162] (A) An outer casing that houses a laminated or wound body containing electrodes and separators for an energy storage device as described in any one of items 1 to 43; and

[0163] (B) A container that contains a non-aqueous electrolyte.

[0164]

[45] An energy storage device comprising a positive electrode, a negative electrode, a separator for an energy storage device as described in any one of items 1 to 43, and a non-aqueous electrolyte.

[0165]

[46] An energy storage device comprising a positive electrode, a negative electrode, a separator for energy storage devices as described in any one of items 1 to 43, and a non-aqueous electrolyte, wherein the positive electrode is selected from at least one of the group consisting of a nickel-manganese-cobalt (NMC) lithium-containing positive electrode, an olivine-type lithium iron phosphate (LFP) positive electrode, a lithium cobalt oxide (LCO) positive electrode, a nickel-cobalt-aluminum (NCA) lithium-containing positive electrode, and a lithium manganese oxide (LMO) positive electrode.

[0166] The effects of the invention

[0167] According to this disclosure, a separator for a more secure energy storage device and an energy storage device using the separator can be provided.

[0168] In a first embodiment, according to the present disclosure, a separator for an energy storage device with higher safety, which reduces the possibility of thermal runaway due to a partial short circuit, and an energy storage device using the same, can be provided.

[0169] In a second embodiment, this disclosure may provide a separator for an energy storage device and an energy storage device using the separator, which can improve at least one of the following: safety of the energy storage device, such as safety in a nail puncture test, thermal shrinkage and hot box testability, and high temperature bar impact failure testability. Attached Figure Description

[0170] Figure 1 (A) is a schematic diagram showing the behavior of a separator for an energy storage device having a non-crosslinked polyolefin substrate layer and an inorganic particle layer when it undergoes thermal shrinkage in an open state at both ends. Figure 1 (B) is a schematic diagram showing the behavior of a separator for an energy storage device having a non-crosslinked polyolefin substrate layer and an inorganic particle layer when it undergoes thermal shrinkage while both ends are fixed.

[0171] Figure 2 This is a schematic diagram illustrating the behavior of a separator for an energy storage device, which has a non-crosslinked polyolefin substrate layer and an inorganic particle layer, when it undergoes thermal shrinkage in an open state at both ends.

[0172] Figure 3 (A) is a schematic diagram showing the behavior of a separator for an energy storage device having a cross-linked polyolefin substrate layer and an inorganic particle layer when it undergoes thermal shrinkage in an open state at both ends. Figure 3 (B) is a schematic diagram showing the behavior of a separator for an energy storage device having a cross-linked polyolefin substrate layer and an inorganic particle layer when it undergoes thermal shrinkage while both ends are fixed.

[0173] Figure 4 This is a schematic diagram illustrating the behavior of a partial short circuit in an energy storage device having a separator having a cross-linked polyolefin substrate layer, an inorganic particle layer, and a thermoplastic polymer layer.

[0174] Figure 5 This is a schematic diagram illustrating the behavior of a partial short circuit in an energy storage device having a separator having a non-crosslinked polyolefin substrate layer, an inorganic particle layer, and a thermoplastic polymer layer.

[0175] Figure 6 This is a schematic diagram illustrating the behavior of a partial short circuit in an energy storage device having a separator having a non-crosslinked polyolefin substrate layer and a thermoplastic polymer layer.

[0176] Figure 7 This is a schematic diagram illustrating the behavior of a partial short circuit in an energy storage device having a separator having a cross-linked polyolefin substrate layer and an inorganic particle layer.

[0177] Figure 8 This is a schematic diagram illustrating the behavior of a partial short circuit in an energy storage device having a separator having a non-crosslinked polyolefin substrate layer and an inorganic particle layer.

[0178] Figure 9 This is a schematic diagram of an island structure containing alkali metals and / or alkaline earth metals as determined by TOF-SIMS.

[0179] Figure 10 This is a schematic diagram illustrating a crystalline polymer having a higher-order structure consisting of a crystalline structure, amorphous portions, and intermediate layers between them.

[0180] Figure 11 This is a schematic diagram illustrating the crystal growth of polyolefin molecules.

[0181] Figure 12 This is a schematic diagram of a high-temperature bar impact failure test (impact test). Detailed Implementation

[0182] Separators for energy storage devices

[0183] Separators for energy storage devices (hereinafter also referred to as "separators") require both insulation and lithium-ion permeability, and are typically formed from insulating materials such as paper, nonwoven fabrics made of polyolefins, or microporous membranes made of resin, which have a porous structure. Especially in lithium-ion batteries, polyolefin microporous membranes, which can form a dense and uniform porous structure resistant to redox degradation, are excellent as separator substrates.

[0184] In the first embodiment, the separator for the energy storage device comprises at least one layer each of an A layer containing a polyolefin, a B layer containing inorganic particles, and a C layer containing a thermoplastic polymer. The polyolefin contained in the A layer has one or more functional groups. The functional groups include functional groups that undergo condensation reactions with each other within the energy storage device to form a cross-linked structure based on siloxane bonds.

[0185] In the second embodiment, the separator for the energy storage device includes a polyolefin microporous membrane as a substrate and a surface layer formed on at least one side thereon. The polyolefin contained in the polyolefin microporous membrane has one or more functional groups. After the separator is housed in the energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0186] In the second embodiment, the separator for the energy storage device preferably comprises a polyolefin microporous membrane as a substrate and a thermoplastic polymer layer formed on at least one side thereof. The polyolefin contained in the polyolefin microporous membrane has one or more functional groups, and after the separator is housed in the energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure.

[0187] In the second embodiment, the separator for the energy storage device preferably comprises a polyolefin microporous membrane as a substrate and an active layer disposed on at least one side thereof. The polyolefin contained in the polyolefin microporous membrane has one or more functional groups, and after the separator is housed in the energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure. By combining the chemically cross-linked separator substrate, which can form a cross-linked structure through any of the above reactions (1) to (3) after being housed in the energy storage device, with an active layer such as a PVDF-based resin layer or a layer containing PVDF-based resin and inorganic particles, the thermal shrinkage and hot box testability at high temperatures (e.g., above 200°C) can be synergistically improved based on the cross-linking and gelation of the substrate and the adhesion between the electrode material in the energy storage device and the active layer.

[0188] In the second embodiment, the separator for the energy storage device preferably comprises a polyolefin microporous membrane as a substrate and a heat-resistant porous layer containing a heat-resistant resin laminated on at least one side thereof. The polyolefin contained in the polyolefin microporous membrane has one or more functional groups, and after the separator is housed in the energy storage device, (1) the functional groups undergo a condensation reaction with each other, (2) the functional groups react with chemical substances inside the energy storage device, or (3) the functional groups react with other types of functional groups to form a cross-linked structure. To date, there has been much research on the mechanical strength of the separator film in the rod impact test, which simulates the damage to the battery structure caused by external force. It has been found that separators with high tensile strength will not break even when subjected to external force and can suppress short circuits. However, at high temperatures such as 150°C, the polyethylene (PE) microporous membrane melts and cannot suppress short circuits. On the other hand, even when heat-resistant resins such as aromatic polyamide resins are composited with microporous membranes, only the aromatic polyamide resin remains as a thin film. Therefore, the following situation exists: due to the generation of gas inside the battery caused by electrode decomposition or other chemical reactions, the thin film structure of the aromatic polyamide resin is destroyed, resulting in a short circuit between the electrodes. By combining a chemically cross-linked separator substrate that can form a cross-linked structure through any of the above reactions (1) to (3) after being housed in an energy storage device with a heat-resistant porous layer containing heat-resistant resin, the heat resistance of the porous layer stacked on the substrate can be synergistically improved in rod impact test performance at high temperatures (e.g., above 150°C) based on the cross-linking and gelation of the substrate. By setting a cross-linked structure in the crystalline melted PE microporous membrane, the fluidity is low, and the substrate cannot be compatible or mixed with the melted or softened state of the aromatic polyamide resin, thus suppressing contact between the electrodes. Such a low-fluidity resin layer at high temperatures can suppress short circuits, fires, and explosions even when accompanied by O2 generation from the decomposition of the positive electrode. Furthermore, heat-resistant resins such as aromatic polyamide resins contain a large number of polar functional groups, exhibiting high affinity for electrolytes. Experiments have demonstrated that by coating a heat-resistant resin onto a cross-linked substrate within the energy storage device, electrolyte can be uniformly supplied from the heat-resistant resin layer to the substrate after assembly and electrolyte filling, and the substrate can form a uniform cross-linked structure.

[0189] From the viewpoint of ensuring insulation, the overall thickness (total thickness) of the separator for the energy storage device is preferably 2 μm or more, more preferably 4 μm or more. From the viewpoint of improving ion permeability and the energy density of the energy storage device, the total thickness of the separator for the energy storage device is preferably 40 μm or less, more preferably 20 μm or less.

[0190] I. Separator for the energy storage device in the first embodiment

[0191] <Polyolefin substrate layer>

[0192] In this application specification, the A layer containing polyolefin will also be referred to simply as the "polyolefin substrate layer". The polyolefin substrate layer is preferably a single-layer structure. A single structure refers to a layer composed of a single material. As long as it is composed of a single material, it can also include a coarse structural layer with large pore size and a dense structural layer with small pore size.

[0193] The polyolefin substrate layer is typically a microporous membrane containing polyolefin as a main component, preferably a polyolefin microporous membrane. "Containing...as a main component" means that, based on total mass, it contains 50% or more of the target component. The polyolefin contained in the polyolefin substrate layer, based on the total mass of the resin components constituting the microporous membrane, can be, for example, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 99% or more, or 100% by mass.

[0194] The polyolefin is not particularly limited, but it is preferred to be a polyolefin containing an olefin having 3 to 10 carbon atoms as the monomer unit. Examples of such polyolefins include homopolymers of ethylene or propylene, and copolymers formed from at least two olefin monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene, with polyethylene, polypropylene, and combinations thereof being preferred.

[0195] Among polyethylene types, low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHMWPE) can be listed. From the viewpoint of not clogging micropores and being able to undergo heat setting at higher temperatures (sometimes simply referred to as "HS"), high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE) are preferred. Typically, low-density polyethylene (LDPE) has a density of less than 0.925 g / cm³. 3 Medium-density polyethylene (MDPE) refers to polyethylene with a density of 0.925 g / cm³. 3 Above and below 0.942 g / cm³ 3 High-density polyethylene (HDPE) refers to polyethylene with a density of 0.942 g / cm³. 3 Above and below 0.970 g / cm³ 3 Ultra-high molecular weight polyethylene (UHMWPE) refers to polyethylene with a density of 0.970 g / cm³. 3 The above refers to polyethylene with a weight-average molecular weight (Mw) of 1,000,000 or more. The density of polyethylene can be determined according to the "D) density gradient tube method" described in JIS K7112 (1999).

[0196] Examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Examples of copolymers of ethylene and propylene include ethylene-propylene atactic copolymers and ethylene-propylene rubber.

[0197] The polyolefin contained in the polyolefin substrate layer comprises: a polyolefin having one or more functional groups, wherein the functional groups are functional groups that form a cross-linked structure based on siloxane bonds by condensation reaction between the functional groups within the energy storage device (hereinafter also referred to as "cross-linked functional groups" in this application specification).

[0198] The crosslinking functional group is preferably grafted onto the main chain of the polyolefin. As a crosslinking functional group, it is a crosslinking silyl group, such as trialkoxysilyl (-Si(OR)3) and / or dialkoxysilyl (-Si(OR)2), where R is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, or a combination thereof, preferably methyl, ethyl, n-propyl, or a combination thereof. As a crosslinking silyl group, methoxysilyl and ethoxysilyl are more preferred, and trimethoxysilyl (-Si(OMe)3) is even more preferred. The alkoxysilyl group is converted to a silanol group via a water-induced hydrolysis reaction, initiating a condensation reaction that can form a siloxane bond within the battery. An example of a crosslinking reaction where R is methyl is shown in the following formula. The ratio of changing from a T0 structure to a T1, T2, or T3 structure is arbitrary.

[0199]

[0200] In silane-modified polyolefins (hereinafter also referred to as "resin a"), the main chain and grafts are connected by covalent bonds. There are no particular limitations on the structures that form covalent bonds; examples include alkyl groups, ethers, glycols, esters, etc.

[0201] From the viewpoint of the lifetime of the equilibrium state of uniformly configured Si-containing molecular structures and Li ion coordination intermediates, in the stage before the crosslinking reaction of resin a, it is preferable that resin a contains 0.03 to 1.0 mol% of silanol units, that is, the silanol unit modification rate is 0.03 to 1.0 mol%. The silanol unit modification rate is more preferably 0.05 to 0.35 mol%, further preferably 0.07 to 0.32 mol%, particularly preferably 0.08 to 0.30 mol%, and most preferably 0.12 to 0.28 mol%. The inventors of this application, considering that the silane-modified units are mainly present in the amorphous portion of the separator, more preferably only in the amorphous portion, the distance between the silane-modified units, and the thermal vibrational motion at -10°C to 80°C, have discovered the following tendency: if the above-mentioned silanol unit modification amount is achieved, resin a has a molecular structure that facilitates the construction of a crosslinking reaction. The aforementioned T0, T1, T2, and T3 structures can all form coordination intermediates with Li ions. However, it is believed that Li ions, when coordinated between Si atoms in the amorphous part, will randomly undergo coordination detachment and recoordination. Therefore, by adjusting the amount of silanol unit modification in resin a to the above range, a more significant effect was obtained.

[0202] From the viewpoint of the lifetime of a uniformly configured Si-containing molecular structure and the equilibrium state of Li ion coordination intermediates, resin a is preferably modified with 0.01 to 2.0 mol% of propylene (C3) units, 0.01 to 2.0 mol% of butene (C4) units, or a total of 0.01 to 2.0 mol% of C3 and C4 units. The carbon number here takes into account both the R group and the linking group in the above formula.

[0203] From the same point of view, the C3 unit modification rate of resin a is more preferably 0.01 to 1.2 mol%, more preferably 0.01 to 0.75 mol%, particularly preferably 0.02 to 0.60 mol%, and most preferably 0.05 to 0.30 mol%.

[0204] From the viewpoint of the lifetime of the equilibrium state of uniformly configured Si molecular structures and Li ion coordination intermediates, in the stage before the crosslinking reaction of resin a, the C4 unit modification rate of resin a is more preferably 0.01 to 1.0 mol%, more preferably 0.30 to 0.70 mol%, particularly preferably 0.48 to 0.65 mol%. On the other hand, in the heat setting (HS) process during the film preparation of the separator, the C4 unit modification rate of resin a is preferably 0.43 mol% or less, more preferably 0.40 mol% or less, and even more preferably 0.1 mol% or less.

[0205] From the viewpoint of the lifetime of the equilibrium state of uniformly configured Si molecular structure and Li ion coordination intermediate, the total modification rate of C3 and C4 units of resin a is more preferably 1.5 mol% or less, further preferably 1.0 mol% or less, particularly preferably 0.6 mol% or less, and most preferably 0.3 mol% or less.

[0206] From the viewpoint of the cycle characteristics and safety of the energy storage device, the number-average molecular weight (Mn) of resin a is preferably 10,000 to 20,000, more preferably 16,000 or less, and even more preferably 15,000 or less. Similarly, from the same viewpoint, the weight-average molecular weight (Mw) of resin a is preferably 45,000 to 200,000, more preferably 140,000 or less, even more preferably 129,000 or less, particularly preferably 100,000 or less, and most preferably 72,000 or less. Also from the same viewpoint, the Mw / Mn ratio of resin a is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 4.1 to 8.0.

[0207] There is no limitation on resin a, whose viscosity-average molecular weight (Mv) can be, for example, 20,000 to 150,000, and whose density can be, for example, 0.90 to 0.97 g / cm³. 3 Its melt mass flow rate (MFR) at 190°C can be, for example, 0.1 to 15 g / min.

[0208] The polyethylene constituting silane-grafted modified polyethylene can be composed of a single type of ethylene or two or more types of ethylene. Alternatively, two or more types of silane-grafted modified polyethylene composed of different types of ethylene can be used in combination.

[0209] Crosslinking reactions can occur spontaneously within the environment of the energy storage device, or they can be induced by external stimuli. Examples of external stimuli include heat and light, such as ultraviolet light. For the crosslinking reaction, it is preferable to promote the reaction under acidic conditions, alkaline conditions, and, moreover, under conditions with a base of low nucleophilicity, through catalysis. The siloxane bonds formed through condensation exhibit high thermodynamic stability. The bond energy of CC is 86 kcal·mol-1. -1 The bond energy of C-Si is 74 kcal·mol⁻¹. -1 The bond energy of Si-O is 128 kcal·mol⁻¹. -1 This demonstrates the thermodynamic stability of siloxane bonds (Non-Patent Literature 1, 2). Therefore, for example, by introducing a certain concentration of hydrogen fluoride (HF) and H2SO4 into the reaction system, the crosslinking reaction of silane-modified polyolefins in the polymer structure of the separator can be carried out in high yield, and a highly heat-resistant structure can be constructed in the separator.

[0210] Furthermore, Si-containing compounds are highly reactive with F anions, so the crosslinking points formed by siloxane bonds may decompose due to the high concentration of F anions. The bond energy of Si-F is as high as 160 kcal / cl·mol. -1 The Si-F bond possesses high thermodynamic stability, therefore it is believed that the F anion will be continuously consumed in the equilibrium reaction until its concentration in the system falls below a certain level (Non-Patent Literature 1, 2). The decomposition reaction at the crosslinking points caused by the F anion is presumably a breaking reaction of the C-Si or Si-OSi bonds of the siloxane bond. According to previous reports, in experiments estimating the bond breaking energy of Si-X using the compound Me3Si-X, the bond breaking energy D of Si-X was 394±8 kJ / mol when X = Me, 513±11 kJ / mol when X = OMe, and 638±5 kJ / mol when X = F (Non-Patent Literature 7). Furthermore, considering the stability of the products after the breaking of the C-Si or Si-OSi bonds of the siloxane bond under acidic conditions, it is presumed that the Si-OSi bond is easily broken into Si-F and HO-Si. Therefore, it is believed that when the concentration of the F anion in the reaction system is above a certain level, the siloxane bonds at the crosslinking points are decomposed, which may reduce the heat resistance of the separator.

[0211] This disclosure reveals that the HF concentration is balanced between PF5 and HF through the Young-Teller effect, which promotes the crosslinking reaction to siloxane bonds and controls the crosslinking reaction within the battery in separators with high heat resistance. Furthermore, the balanced presence of PF5 and HF allows for long-term and sustained induction of siloxane bond crosslinking, significantly increasing the probability of the crosslinking reaction. The amorphous structure of polyethylene is highly entangled; even with only partial crosslinking, its entropic elasticity increases significantly. Therefore, the molecular mobility of the amorphous portion decreases, making it difficult for all silanol units to form siloxane bonds. This disclosure investigates addition under various conditions, fundamentally solving this problem.

[0212] Together with the B layer containing inorganic particles and the C layer containing thermoplastic polymer, described later, by including the polyolefin substrate layer in a polyolefin having the crosslinking functional groups explained above, it is possible to provide a separator for an energy storage device that offers higher safety and reduces the likelihood of thermal runaway due to localized short circuits. The rationale is not limited to theoretical or illustrative methods; it will be explained below with reference to the accompanying drawings.

[0213] Figure 1(A) is a schematic diagram showing the behavior of a separator (10) for an energy storage device having an uncrosslinked polyolefin substrate layer (1a) and an inorganic particle layer (2) when thermal shrinkage occurs in the open state at both ends. When both ends are open, the substrate layer shrinks due to the stress (4) caused by thermal shrinkage, which pushes up the inorganic particle layer, resulting in buckling failure (5) of the inorganic particle layer. In addition, the substrate layer is subjected to tensile failure (6) due to the tension of the protruding inorganic particle layer. Figure 2 This diagram illustrates the behavior in stages. When the separator for an energy storage device, which has a non-crosslinked polyolefin substrate layer (1a) and an inorganic particle layer (2), undergoes thermal shrinkage with both ends open, the substrate layer experiences both vector-concentrated and sparse portions of stress (4) caused by thermal shrinkage, resulting in corrugated deformation of the separator. At this point, buckling failure (cracking) occurs at the apex of the corrugated inorganic particle layer (5), and the substrate layer is stretched by the inorganic particle layer (6). As the deformation progresses further, multiple cracks bulge, and the substrate layer undergoes tensile failure (6), creating voids. Returning to... Figure 1 , Figure 1 (B) is a schematic diagram showing the behavior of a separator (10) for an energy storage device having a non-crosslinked polyolefin substrate layer (1a) and an inorganic particle layer (2) when it undergoes thermal shrinkage while both ends are fixed. The fixed-end state simulates the state in which the separator for the energy storage device is housed within the energy storage device. With both ends fixed, the polyolefin substrate layer breaks between the fixing clamps (20) due to the stress (4) caused by thermal shrinkage, and the gap gradually increases as thermal shrinkage progresses. Accompanying this, the inorganic particle layer deforms and falls into the gap of the polyolefin substrate layer.

[0214] Figure 3 (A) is a schematic diagram showing the behavior of a separator (10) for an energy storage device having a cross-linked polyolefin substrate layer (1b) and an inorganic particle layer (2) when thermal shrinkage occurs with both ends open. In the case of the cross-linked polyolefin substrate layer, when both ends are open, it... Figure 1 (A) and Figure 2 Similarly, under the stress (4) caused by thermal shrinkage, buckling failure (5) occurs in the inorganic particle layer and tensile failure (6) occurs in the substrate layer. However, as Figure 3 As shown in (B), when both ends are fixed, the cross-linked polyolefin substrate layer (1b) tends to be stretched between the fixing clamps (20) without breaking. Based on the difference in thermal shrinkage behavior between the non-cross-linked polyolefin substrate layer and the cross-linked polyolefin substrate layer when both ends are fixed, high safety of the separator for the energy storage device is achieved by combining it with the inorganic particle layer and thermoplastic polymer layer described later.

[0215] In more detail, Figure 4This is a schematic diagram illustrating the behavior of a partial short circuit (7) occurring in an energy storage device (100) having a separator (10) comprising a cross-linked polyolefin substrate layer (1b), an inorganic particulate layer (2), and a thermoplastic polymer layer (3). In the case of lithium-ion secondary batteries, partial short circuits are sometimes caused by lithium dendrites growing from the negative electrode active material layer through repeated charge-discharge cycles at low temperatures. Figure 4 As shown, in the energy storage device, a partial short circuit (7) is easily generated when pressure (8) is applied after a low-temperature charge-discharge cycle. Once a partial short circuit occurs, the short-circuited portion releases heat, causing the surrounding cross-linked polyolefin substrate layer to thermally shrink. However, as Figure 3 As explained, the cross-linked polyolefin substrate layer is not prone to breakage. In addition, the inorganic particle layer is fixed to the positive electrode by the thermoplastic polymer layer, so the inorganic particle layer is not easily deformed. Therefore, the stress (4) caused by thermal shrinkage is concentrated at the interface between the polyolefin substrate layer and the inorganic particle layer, and the local short circuit is cut off, which results in the prevention of thermal runaway.

[0216] Figure 5 To demonstrate, besides using a non-crosslinked polyolefin substrate layer (1a), and... Figure 4 Similarly, a schematic diagram illustrating the behavior of the energy storage device (100) when subjected to low-temperature charge-discharge cycles and pressure, resulting in a partial short circuit (7). The polyolefin substrate layer is non-crosslinked, therefore, as Figure 1 and 2 As explained, the non-crosslinked polyolefin substrate layer fractures, forming voids around the local short circuit. Therefore, the stress (4) caused by thermal shrinkage is not concentrated at the interface between the polyolefin substrate layer and the inorganic particle layer, making it difficult to break the local short circuit.

[0217] Figure 6 To demonstrate that, apart from lacking an inorganic particle layer, it is similar to Figure 5 Similarly, a schematic diagram illustrating the behavior of the energy storage device (100) when subjected to low-temperature charge-discharge cycles and pressure, resulting in a partial short circuit (7). Figure 5 Similarly, the non-crosslinked polyolefin substrate layer fractures, forming voids around the local short circuit. Furthermore, as the non-crosslinked polyolefin substrate layer deforms, the thermoplastic polymer layer (3) is pulled by its surroundings, making the voids larger. Therefore, the stress (4) caused by thermal shrinkage is not concentrated, making it difficult to break the local short circuit.

[0218] Figure 7 To demonstrate that, apart from lacking a thermoplastic polymer layer, it is similar to... Figure 4 Similarly, a schematic diagram illustrating the behavior of the energy storage device (100) when subjected to low-temperature charge-discharge cycles and pressure, resulting in a partial short circuit (7). Due to the lack of a thermoplastic polymer layer, the inorganic particle layer is easily deformed, and... Figure 4In contrast, some of the stress caused by thermal shrinkage is absorbed by the deformation of the inorganic particle layer. Therefore, the stress caused by thermal shrinkage is difficult to concentrate at the interface between the polyolefin substrate layer and the inorganic particle layer, making it difficult to break the local short circuit.

[0219] Figure 8 To demonstrate, besides using a non-crosslinked polyolefin substrate layer (1a), and... Figure 7 Similarly, a schematic diagram illustrates the behavior of the energy storage device (100) when subjected to low-temperature charge-discharge cycles and pressure, resulting in a partial short circuit (7). Because it lacks a thermoplastic polymer layer, the inorganic particle layer is easily deformed. Part of the stress (4) caused by thermal shrinkage is absorbed by the deformation of the inorganic particle layer, while the non-crosslinked polyolefin substrate layer fractures, forming voids around the partial short circuit. Therefore, the stress (4) caused by thermal shrinkage is not concentrated at the interface between the polyolefin substrate layer and the inorganic particle layer, making it difficult to break the partial short circuit.

[0220] The polyolefin substrate layer preferably comprises both a silane-modified polyolefin and a polyolefin other than the silane-modified polyolefin (hereinafter also referred to as "silane-unmodified polyolefin") to obtain a dense, uniform porous structure resistant to oxidation-reduction degradation. The silane-unmodified polyolefin combined with the silane-modified polyolefin (hereinafter referred to as "resin a") is preferably a polyolefin with a viscosity-average molecular weight (Mv) of 2,000,000 or more (hereinafter referred to as "resin b"), a polyolefin with an Mv of less than 2,000,000 (hereinafter referred to as "resin c"), or a combination thereof. By combining two silane-unmodified polyolefins with specific molecular weight ranges in resin a, it is easier to interrupt local short circuits based on stress concentration, resulting in a more secure energy storage device. As resin b, polyethylene with a viscosity-average molecular weight (Mv) of 2,000,000 or more is more preferred, and as resin c, polyethylene with an Mv of less than 2,000,000 is more preferred.

[0221] From the viewpoint of the cycle characteristics and safety of the energy storage device, the number-average molecular weight (Mn) of resin b is preferably 200,000 to 1,400,000, more preferably 210,000 to 1,200,000, and even more preferably 250,000 to 1,000,000. Similarly, from the same viewpoint, the weight-average molecular weight (Mw) of resin b is preferably 1,760,000 to 8,800,000, more preferably 1,900,000 to 7,100,000, and even more preferably 2,000,000 to 6,200,000. Also from the same viewpoint, the Mw / Mn ratio of resin b is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 6.0 to 8.8. From the same point of view, the Mv of resin b is preferably 2,000,000 to 10,000,000, more preferably 2,100,000 to 8,500,000, further preferably 3,000,000 to 7,800,000, and even more preferably 3,300,000 to 6,500,000.

[0222] From the viewpoint of the cycle characteristics and safety of the energy storage device, the number-average molecular weight (Mn) of resin c is preferably 20,000 to 250,000, more preferably 30,000 to 200,000, further preferably 32,000 to 150,000, and even more preferably 40,000 to 110,000. Similarly, from the same viewpoint, the weight-average molecular weight (Mw) of resin c is preferably 230,000 to 2,000,000, more preferably 280,000 to 1,600,000, further preferably 320,000 to 1,200,000, and even more preferably 400,000 to 1,000,000. Also from the same viewpoint, the Mw / Mn ratio of resin c is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 6.0 to 8.8. From the same point of view, the Mv of resin c is preferably 250,000 to 2,500,000, more preferably 300,000 to 1,600,000, even more preferably 320,000 to 1,100,000, and even more preferably 450,000 to 800,000.

[0223] Regarding the content of resin a in the polyolefin substrate layer, from the viewpoint of the safety of the energy storage device, based on the total mass of the solid components of the polyolefin raw material, it is preferably 3% to 70% by mass, more preferably 5% to 60% by mass, and even more preferably 10% to 50% by mass. Regarding the total content of unmodified silane polyolefin in the polyolefin substrate layer, from the viewpoint of high ion permeability and high safety, based on the total mass of the solid components of the polyolefin raw material, it is preferably 40% to 95% by mass, more preferably 50% to 90% by mass, and even more preferably 60% to 80% by mass.

[0224] From the same point of view, based on the total mass of the solid components of the polyolefin raw material, the content of resin b in the polyolefin raw material is preferably 3% to 70% by mass, more preferably 5% to 60% by mass, and even more preferably 5% to 40% by mass.

[0225] From the same point of view, based on the total mass of the solid components of the polyolefin raw material, the content of resin c in the polyolefin raw material is preferably 1% to 90% by mass, more preferably 5% to 60% by mass, and even more preferably 5% to 50% by mass.

[0226] From the same point of view, the mass ratio of resin a to resin b in the polyolefin raw material (mass of resin a / mass of resin b) is preferably 0.07 to 12.00, more preferably 0.10 to 11.00, and even more preferably 0.50 to 10.00.

[0227] From the same point of view, the mass ratio of resin a to resin c in the polyolefin raw material (mass of resin a / mass of resin c) is preferably 0.07 to 12.00, more preferably 0.10 to 11.00, and even more preferably 0.20 to 10.00.

[0228] From the same point of view, the mass ratio of resin b to resin c in the polyolefin raw material (mass of resin b / mass of resin c) is preferably 0.06 to 7.00, more preferably 0.10 to 7.00, and even more preferably 0.12 to 6.90.

[0229] The thickness of the polyolefin substrate layer is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. By making the film thickness of the polyolefin substrate layer 1.0 μm or more, there is a tendency to further improve the film strength. The thickness of the polyolefin substrate layer is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. By making the film thickness of the polyolefin substrate layer 100 μm or less, there is a tendency to further improve ion permeability.

[0230] The heat shrinkage rate of the polyolefin substrate layer at 150°C is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. By making the heat shrinkage rate at 150°C 10% or more, the stress applied during heat shrinkage is increased, thus making it easier to cut off local short circuits and more effectively preventing thermal runaway.

[0231] <Inorganic Particle Layer>

[0232] The separator for the energy storage device also includes a B layer containing inorganic particles (hereinafter also referred to as the "inorganic particle layer" in this application specification).

[0233] The inorganic particles are preferably selected from at least one of the following groups: alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum hydroxide, talc, kaolinite, dickite, perlite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, diatomaceous earth, quartz sand, and glass fiber. Examples of alumina include α-alumina, β-alumina, γ-alumina, and alumina hydrates such as boehmite. From the perspective of high stability relative to the electrolyte used in lithium-ion batteries, α-alumina or boehmite is preferred.

[0234] The inorganic particle content in the inorganic particle layer is preferably 5% to 99% by mass, more preferably 10% to 99% by mass, further preferably 50% to 98% by mass, and even more preferably 90% to 97% by mass, based on the total mass of the inorganic particle layer. When the inorganic particle content is 5% by mass or more, the elastic modulus of the separator can be improved, resulting in a separator with higher heat resistance. When the inorganic particle content is 99% by mass or less, powder shedding from the separator can be prevented.

[0235] The inorganic particle layer is preferably an inorganic porous layer that includes a resin binder in addition to the inorganic particles. As the resin binder, styrene-butadiene resin, acrylate resin, methyl acrylate resin, polyvinylidene fluoride, and other fluoropolymers can be used. Regarding the content of the resin binder in the inorganic particle layer, based on the total mass of the inorganic particle layer, it is preferably 1% to 50% by mass, more preferably 3% to 10% by mass. When the resin binder content is 1% by mass or more, it can prevent powder from falling off the separator. When the content of inorganic particles is 50% by mass or less, it can improve the elastic modulus of the separator, resulting in a separator with higher heat resistance.

[0236] The glass transition temperature (Tg) of the resin adhesive is preferably -50°C to 90°C, more preferably -30°C to -10°C. When the glass transition temperature (Tg) of the resin adhesive is above -50°C, it exhibits excellent adhesion; when it is below 90°C, it tends to have excellent ion permeability.

[0237] The thickness of the inorganic particle layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. By making the thickness of the inorganic particle layer 0.5 μm or more, a separator with higher heat resistance can be obtained. The thickness of the inorganic particle layer is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 6 μm or less. By making the thickness of the inorganic particle layer 20 μm or less, there is a tendency to further improve ion permeability.

[0238] The elastic modulus of the inorganic particle layer is preferably 0.05 GPa or higher, more preferably 0.1 GPa or higher. When the elastic modulus of the inorganic particle layer is 0.05 GPa or higher, stress concentration easily occurs at the interface between the inorganic particle layer and the polyolefin substrate layer when a local short circuit is formed, which can more effectively prevent thermal runaway. The elastic modulus of the inorganic particle layer is preferably 10 GPa or lower, more preferably 5 GPa or lower, and even more preferably 2 GPa or lower. When the elastic modulus of the inorganic particle layer is 10 GPa or lower, the processability of the separator is improved.

[0239] <Thermoplastic polymer layer>

[0240] The separator for the energy storage device also includes a C layer comprising a thermoplastic polymer (hereinafter also referred to as the "thermoplastic polymer layer" in this specification). The thermoplastic polymer layer is preferably laminated on the surface of the inorganic particulate layer that is not in contact with the polyolefin substrate layer.

[0241] Examples of thermoplastic polymers include: polyolefin resins such as polyethylene, polypropylene, and α-polyolefins; fluorinated polymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers thereof; diene polymers or copolymers thereof containing conjugated dienes such as butadiene and isoprene as monomer units, or their hydrogenates; acrylic polymers containing (meth)acrylates or (meth)acrylic acid as monomer units and without polyalkylene glycol units, acrylic polymers containing (meth)acrylates or (meth)acrylic acid as monomer units and with one or two polyalkylene glycol units, or copolymers thereof, or their hydrogenates; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; polyalkylene glycols such as polyethylene glycol and polypropylene glycol that do not have polymerizable functional groups; resins such as polyphenylene ether, polyphenylene sulfide, and polyester; copolymers of olefinic unsaturated monomers having a repeating number of 3 or more alkylene glycol units as copolymer units; and combinations thereof. From the viewpoint of improving the safety of energy storage devices, the thermoplastic polymer is preferably an acrylic polymer, and more preferably a polymer that contains (meth)acrylate or (meth)acrylic acid as polymer units.

[0242] From the viewpoint of improving the safety of the energy storage device, it is also preferred that the thermoplastic polymer includes at least one fluorinated vinyl compound selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0243] The glass transition temperature (Tg) of thermoplastic polymers is preferably between -50°C and 150°C. When the glass transition temperature (Tg) of thermoplastic polymers is above -50°C, they exhibit excellent adhesion; when it is below 150°C, they tend to have excellent ion permeability.

[0244] The area ratio of the thermoplastic polymer layer covering the surface of the inorganic particle layer is preferably 5% or more, more preferably 20% or more, and even more preferably 50% or more. When the area ratio of the thermoplastic polymer layer is 5% or more, the adhesion to the electrode can be improved. The area ratio of the thermoplastic polymer layer covering the surface of the inorganic particle layer is preferably 98% or less. This helps to suppress closed pores in the polyolefin substrate layer and maintain high air permeability.

[0245] The peel strength (180° peel strength) when the thermoplastic polymer layer is peeled from the inorganic particle layer at a 180° angle is preferably 0.01 N / m or more, more preferably 0.5 N / m or more. When the 180° peel strength of the thermoplastic polymer layer is 0.01 N / m or more, the adhesion is excellent, thus suppressing the deformation of the inorganic particle layer and obtaining a separator for an energy storage device with excellent safety. From a processability point of view, the 180° peel strength of the thermoplastic polymer layer is preferably 30 N / m or less, more preferably 10 N / m or less.

[0246] The thickness of the thermoplastic polymer layer is preferably 0.1 μm or more, and more preferably 0.5 μm or more. When the thickness of the thermoplastic polymer layer is 0.1 μm or more, the adhesive strength is excellent, thus suppressing the deformation of the inorganic particle layer and obtaining a separator for energy storage devices with excellent safety. From the viewpoint of improving ion permeability, the thickness of the thermoplastic polymer layer is preferably 3 μm or less, and more preferably 1 μm or less.

[0247] <Island Structure>

[0248] Layer A is preferably characterized by the detection of at least one island structure containing an alkali metal and / or alkaline earth metal during TOF-SIMS measurements with a surface area of ​​100 μm. The island structure is preferably 9 μm in size. 2 ~245μm 2 More preferably 10μm 2 ~230μm 2 Further preferred is 11μm 2 ~214μm 2 The separator for the energy storage device is further preferably found to contain two or more calcium-containing island structures when measured by TOF-SIMS with a square area of ​​100 μm. In this case, the distance between the centroids of the island structures is preferably 6 μm to 135 μm, more preferably 8 μm to 130 μm, and even more preferably 10 μm to 125 μm. Figure 9 This is a schematic diagram illustrating island structures containing alkali metals and / or alkaline earth metals in TOF-SIMS measurements. It can be seen as follows... Figure 10 As illustrated, the island structure (9) and the distance (d) between island structures are measured with a square area of ​​100 μm. As a method to control the size of the island structure and the distance between its centroids, adjustments can be made by adjusting the extruder speed, the molecular weight of the polyolefin resin raw material, etc.

[0249] In the manufacture of energy storage devices using an electrolyte containing LiFSO3, deviations caused by moisture introduced into various components result in an uneven distribution of alkali metals and / or alkaline earth metals in island structures aggregated within the polyolefin substrate layer. This allows HF to be captured in the form of salts of the alkali metals and / or alkaline earth metals. The alkali metals and / or alkaline earth metals are gradually consumed from the surface of the island structures, thus maintaining the capture effect over a long period. This, in turn, can suppress battery degradation over a long period, making it preferable. In siloxane crosslinked separators, if excess HF exists after crosslinking, it may catalyze the reverse reaction of the crosslinking reaction, i.e., the bond-opening reaction. Therefore, it is hypothesized that by persistently capturing HF with unevenly distributed alkali metals and / or alkaline earth metals, the bond-opening reaction can be suppressed, and the long-term stability of the crosslinked structure of the siloxane crosslinked separator can be improved.

[0250] Examples of alkali metals include lithium, sodium, and potassium; examples of alkaline earth metals include magnesium, calcium, and strontium. The island structure preferably includes an alkaline earth metal, with calcium being the most preferred. By distributing calcium unevenly within the polyolefin substrate layer in an island structure, calcium consumes HF in the system as CaF2, thus enabling more efficient control of the HF concentration. Since calcium is gradually consumed from the surface of the island structure, it is not completely depleted in a short period, suggesting a long-term retention effect. This allows for long-term suppression of battery degradation, making it a preferred option. In siloxane-crosslinked separators, if excess HF exists after crosslinking, it may catalyze the reverse reaction of the crosslinking reaction, namely the bond-opening reaction. Therefore, it is speculated that by persistently capturing HF with unevenly distributed calcium, the bond-opening reaction can be suppressed, improving the long-term stability of the crosslinked structure of the siloxane-crosslinked separator. It is also assumed that when the electrolyte contains LiPF6, excess F anions may be generated due to variations in moisture content, etc. Experiments have shown that by setting up calcium-containing island structures within the polyolefin substrate layer to capture F anions, the stability of siloxane bonds can also be ensured, and the cross-linking structure of the separator can be maintained for a long time.

[0251] Characteristics of separators for energy storage devices

[0252] The porosity of the separator in the energy storage device is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more. By making the porosity of the separator 20% or more, there is a tendency to further improve the tracking ability for rapid ion movement. On the other hand, the porosity of the separator is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less. By making the porosity of the separator 80% or less, there is a tendency to further improve the film strength and further suppress self-discharge.

[0253] The air permeability of the separator in the energy storage device relative to 100cm 3The membrane volume permeability is preferably 50 seconds or more, more preferably 60 seconds or more, and even more preferably 70 seconds or more. By making the permeability of the separator 50 seconds or more, there is a tendency to further improve the balance between membrane thickness, porosity, and average pore size. The permeability of the separator relative to 100 cm 3 The membrane volume is preferably 400 seconds or less, more preferably 300 seconds or less, even more preferably 250 seconds or less, and even more preferably 200 seconds or less. By making the air permeability of the separator 400 seconds or less, there is a tendency to further improve ion permeability.

[0254] The membrane thickness of the separator in the energy storage device is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more. By making the membrane thickness of the separator 1.0 μm or more, there is a tendency to further improve the membrane strength. The membrane thickness of the separator is preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. By making the membrane thickness of the separator 100 μm or less, there is a tendency to further improve ion permeability.

[0255] The thermal shrinkage rate at 150°C for the separator and the thermal shrinkage rate at 150°C in the electrolyte of the energy storage device are preferably 50% or less, more preferably 30% or less, and even more preferably 10% or less. By making the thermal shrinkage rate at 150°C for the separator and the thermal shrinkage rate at 150°C in the electrolyte 50% or less, the battery safety in the event of a partial short circuit can be further improved. The thermal shrinkage rate at 150°C for the separator and the thermal shrinkage rate at 150°C in the electrolyte of the energy storage device are preferably 0.1% or more, more preferably 0.2% or more, and even more preferably 0.3% or less. By making the thermal shrinkage rate at 150°C for the separator and the thermal shrinkage rate at 150°C in the electrolyte 0.1% or more, there is a tendency to further improve the balance between porosity and puncture strength.

[0256] When a battery experiences abnormal heat release due to internal short circuits or other reasons, the separator, already at a high temperature, may deform. This phenomenon is referred to as "thermal response" in this application, and the rate of change in the separator's area caused by the thermal response is called the "thermal response index." It has been reported that heat-induced deformation of crystalline polymers is caused by the non-orientation of amorphous portions and the lamellar structure formation of crystalline portions. It can be considered that the thermal response index of the separator is related to the number of molecular chains in the polymer resin constituting the polyolefin substrate layer that exceed the activation energy required to cause the aforementioned changes in the crystalline and amorphous portions. However, the molecular motion of polymers depends on the bending of the main chain (intramolecular interactions) and intermolecular interactions. Especially in the case of solid polymers, the latter plays a crucial role. If the polymer temperature gradually increases, intermolecular interactions weaken, while microscopic and macroscopic Brownian motions become more active, causing changes in the crystalline and amorphous portions. Therefore, it can be considered that the activation energy for causing the transformation of polymer chains in the crystalline portion to a lamellar structure and the non-orientation of polymer chains in the amorphous portion depends on intermolecular interactions. Furthermore, intermolecular interactions depend on the molecular weight of the polymer. The molecular weight distribution of polymers varies depending on their manufacturing process and is usually approximated by distribution functions such as the Zimm distribution and the Wesslau distribution (log-normal distribution). Therefore, it can be assumed that the distribution of the activation energy of each molecular chain in the polymer also follows these distribution functions. If the thermal response index of the separator is regarded as the cumulative number of molecular chains exceeding the above activation energy, it can be expected that the thermal response can be approximated by the cumulative distribution function, such as the sigmoid function. In fact, the inventors fit the relationship between the thermal response index of the separator for the energy storage device and the temperature at a rate of 2°C / min to the following equation (1):

[0257] Equation (1)

[0258] When it is known that there exist max, T0, and rate that make the coefficient of determination R2 ≥ 0.95. In the formula, max is equivalent to the convergence value of the thermal response index, and T0 is equivalent to the inflection point of the thermal response index. In addition, rate in the formula is a parameter related to the gradient of the thermal response index, that is, the degree of deformation. Regarding the amount of deformation caused by heating in the polyolefin microporous membrane, when the thermal response index of the energy storage device separator after being impregnated with the internal porosity electrolyte is heated to 150°C at 2°C / min and the temperature is fitted to the formula (1) using the least squares method with a coefficient of determination R2 ≥ 0.95, the value of rate is preferably 3.5 or more, more preferably 4.0 or more, and even more preferably 4.5 or more. The larger the above rate is, the slower the thermal response proceeds, which can prevent the surrounding electrodes from being drawn into the thermal response of the separator. From the viewpoint of preventing battery damage caused by thermal response, the above rate value is preferably 3.5 or more. The above rate value is preferably 150 or less, more preferably 100 or less, and even more preferably 50 μm or less. The smaller the rate mentioned above, the faster the thermal response occurs, and the greater the stress applied to the lithium dendrite when a partial short circuit occurs. From the viewpoint of improving battery safety during a partial short circuit, the value of the rate mentioned above is preferably 150 or less.

[0259] In formula (1) above, the value of T0 is preferably 110≤T0≤150, more preferably 115≤T0≤140, and even more preferably 120≤T0≤135. The value of T0 is related to the temperature at which the thermal response occurs. When T0 is within the above range, it is possible to prevent the separator from undergoing a thermal response within the normal operating temperature range of the battery, and to reliably break the lithium dendrite in the event of a partial short circuit, thereby stopping the partial short circuit. In formula (1) above, the range of max is preferably 0.1≤max≤30, more preferably 0.2≤max≤20, and even more preferably 0.5≤max≤10. The value of max is related to the convergence value of the thermal response index. When max is within the above range, it is possible to prevent the occurrence of an internal short circuit caused by the thermal response of the separator in the event of a partial short circuit.

[0260] As a method for controlling the values ​​of rate, T0, and max in the above formula (1), in view of the above, methods for adjusting the molecular weight distribution of polyolefin materials and methods for controlling the mechanical strength of inorganic coating layers that have the effect of suppressing heat deformation are considered. For example, it is preferable to use a total of three types of polyolefins as polyolefin raw materials: polyolefin with Mv = 2 million to 9 million (raw material b), polyolefin with Mv = 500,000 to 2 million (raw material c), and silane-modified polyolefin raw materials with Mv = 20,000 to 150,000 (raw material a). It is further preferable to adjust the content ratio according to each molecular weight. It is further preferable to adjust the common logarithm of the ratio of puncture strength to unit area weight of inorganic coating layer calculated by the unit area weight of polyolefin substrate layer calculated by the following formula (2), so that the values ​​of rate, T0, and max are easily within the above range. It should be noted that, in the above-mentioned raw material composition, the preferred proportion of raw material a in the total mass of the polyolefin substrate layer is 3% to 70% by mass, and the ratio of raw material b to raw material c (mass of resin b / mass of resin c) is 0.06 to 7.00. The commonly used logarithm is preferably 0.1 to 3.

[0261] Equation (2)

[0262] II. Separator for the energy storage device in the second embodiment

[0263] <Polyolefin substrate layer>

[0264] It is believed that the functional groups contained in the polyolefin constituting the separator substrate do not enter the crystalline part of the polyolefin, but crosslink in the amorphous part. Therefore, after the separator of the second embodiment is housed in the energy storage device, it forms a crosslinked structure by utilizing the surrounding environment or the chemical substances inside the energy storage device. This can suppress the increase of internal stress or the deformation of the manufactured energy storage device, and can improve at least one of the following: safety during nail puncture test, thermal shrinkage and hot box testability, and high temperature bar impact failure testability.

[0265] (1) Condensation reactions between functional groups of polyolefins can be, for example, reactions of two or more functional groups A contained in polyolefins via covalent bonds. (3) Reactions of functional groups of polyolefins with other types of functional groups can be, for example, reactions of functional group A and functional group B contained in polyolefins via covalent bonds.

[0266] Furthermore, in the reaction of the functional groups of the polyolefin with the chemical substances inside the energy storage device (2), for example, functional group A contained in the polyolefin can form covalent or coordinate bonds with any of the electrolyte, electrolyte solution, electrode active material, additives or their decomposition products contained in the energy storage device, or with any of the electrolyte, electrolyte solution, electrode active material, additives or their decomposition products contained in the polyolefin microporous membrane used as the substrate. There is no restriction on the timing of including any of the electrolyte, electrolyte solution, electrode active material, additives or their decomposition products in the polyolefin microporous membrane; it can be before, during or after the separator is placed in the energy storage device. In addition, according to reaction (2), a cross-linked structure is formed not only inside the separator, but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), which can improve the strength between the multiple components of the energy storage device.

[0267] The crosslinking structure formed by any of reactions (1) to (3) is preferably an amorphous crosslinking structure formed by crosslinking the amorphous portion of the polyolefin. It is believed that the functional groups contained in the polyolefin constituting the separator substrate do not enter the crystalline portion of the polyolefin, but crosslink in the amorphous portion. Therefore, compared with existing crosslinked separators where the crystalline portion and its surrounding area are easily crosslinked, it is possible to suppress the increase of internal stress or the deformation of the manufactured energy storage device while taking into account both the shut-off function and the high-temperature rupture resistance of the membrane. This ensures at least one of the following: safety of the energy storage device during nail puncture test, thermal shrinkage and hot box test performance, and high-temperature rod impact test performance. From the same point of view, the amorphous portion of the polyolefin is more preferably selectively crosslinked, and even more preferably significantly crosslinked compared to the crystalline portion. The degree of gelation of the microporous membrane made of polyolefin having an amorphous crosslinking structure such as a silane crosslinking structure is preferably 30% or more, and more preferably 70% or more.

[0268] The crosslinking reaction mechanism and crosslinking structure mentioned above are not yet clear, but the inventors have made the following considerations.

[0269] (1) Crystal structure in microporous membranes made of high-density polyethylene

[0270] Polyolefin resins, such as high-density polyethylene, etc. Figure 10 As shown, these are generally crystalline polymers with a higher-order structure consisting of crystalline lamellar (crystalline) portions, amorphous portions, and intermediate layers between them. In the crystalline portions and the intermediate layers between the crystalline and amorphous portions, the polymer chains have low mobility and are difficult to cut; however, relaxation phenomena can be observed in solid viscoelasticity measurements in the 0–120°C region. On the other hand, the polymer chains in the amorphous portions have very high mobility, and this has been observed in solid viscoelasticity measurements in the -150–-100°C region. This is closely related to free radical relaxation, free radical transfer reactions, cross-linking reactions, etc., which will be discussed later.

[0271] Furthermore, the polyolefin molecules that make up the crystal are not singular, such as... Figure 11 As an example, multiple polymer chains form small lamellae, which then aggregate to form crystals. This phenomenon is difficult to observe directly. In recent years, simulations have been used to advance research and clarify this phenomenon. It should be noted that, here, "crystal" refers to the smallest crystalline unit measured through X-ray structural analysis, a unit whose size can be calculated as a microcrystal. Thus, although it refers to the crystalline part (the interior of the lamellae), it is predicted that there exists a portion within the crystal that is unconstrained and has slightly higher mobility.

[0272] (2) Crosslinking reaction mechanism based on electron beam

[0273] Next, the reaction mechanism of electron beam crosslinking (hereinafter referred to as EB crosslinking) of polymers is as follows: (i) irradiation by an electron beam ranging from tens to hundreds of kGy, (ii) electron beam penetration into the reactant (polymer) and generation of secondary electrons, (iii) hydrogen abstraction reaction and free radical generation in the polymer chain based on secondary electrons, (iv) abstraction of adjacent hydrogen and movement of active sites based on free radicals, and (v) crosslinking reaction or polyene formation based on recombination between free radicals. Regarding the free radicals generated in the crystalline region, due to poor mobility, they persist for a long time, and impurities cannot enter the crystal, resulting in a low probability of reaction and extinction. This type of free radical is called a stable radical, which persists for several months. Its lifetime was determined by ESR measurement. As a result, the crosslinking reaction within the crystal is considered poor. However, the free radicals generated in the slightly unconstrained molecular chains inside the crystal or in the surrounding crystalline-amorphous intermediate layer have a slightly longer lifetime. These types of free radicals are called persistent radicals, and they are thought to undergo cross-linking reactions between molecular chains with a high probability in a dynamic environment. On the other hand, due to their extremely high mobility, the free radicals generated in amorphous regions have short lifespans, and it is believed that not only cross-linking reactions between molecular chains, but also polyene reactions within a single molecular chain occur with a high probability.

[0274] As mentioned above, it can be inferred that, in the microscopic field of crystal, the cross-linking reaction based on EB cross-linking exists locally inside or around the crystal.

[0275] (3) Cross-linking reaction mechanism based on chemical reaction

[0276] Preferably, the functional groups in the polyolefin resin react with the chemical substances contained in the energy storage device or the polyolefin microporous membrane, or the chemical substances contained in the energy storage device or the polyolefin microporous membrane are used as a catalyst.

[0277] As previously mentioned, polyolefin resins contain both crystalline and amorphous portions. However, due to steric hindrance, the aforementioned functional groups are locally present in the amorphous portions and not within the crystalline portions. This is well known; units such as methyl groups, which are slightly present in polyethylene chains, can sometimes enter the crystals, but grafts larger than ethyl groups do not (Non-Patent Document 2). Therefore, crosslinking points, based on reactions different from electron beam crosslinking, are only locally present in the amorphous portions.

[0278] (4) The relationship between the differences in cross-linking structures and their effects

[0279] In cross-linking reactions based on internal chemical reactions within a battery, the reaction products exhibit different morphologies. In research up to the present disclosure, the following experiments were conducted to elucidate the cross-linking structure and clarify the changes in the physical properties of the microporous membrane accompanying the structural changes.

[0280] First, the mechanical properties of the membranes based on tensile fracture tests were investigated. Furthermore, changes in crystal structure were analyzed using in-situ X-ray structural analysis with radiation during the tensile fracture tests. The results showed that, compared to membranes without EB crosslinking or those without chemical crosslinking (before), the EB crosslinked membrane exhibited suppressed crystallinity as strain increased. This is due to selective crosslinking within or around the crystallinity. Consequently, Young's modulus and tensile strength significantly increased, demonstrating high mechanical strength. On the other hand, no difference in crystallinity was observed in the chemically crosslinked membrane before and after the crosslinking reaction, suggesting selective crosslinking of the amorphous regions. Furthermore, there was no change in mechanical strength before and after the crosslinking reaction.

[0281] Next, the behavior of both during crystal melting was studied through melting / melt fracture characteristic tests. The results showed that the melting temperature of the EB-crosslinked film increased significantly, with the melt fracture temperature exceeding 200°C. On the other hand, it was confirmed that the melting temperature of the chemically crosslinked film did not change before and after crosslinking treatment, but the melt fracture temperature increased to over 200°C. Therefore, it is believed that in the melting characteristics generated by crystal melting, the EB-crosslinked film, due to crosslinking around the crystal portion, exhibits an increase in melting temperature and a decrease in melting rate. Conversely, the chemically crosslinked film, lacking a crosslinked structure in the crystal portion, does not cause changes in melting characteristics. Furthermore, in the high-temperature region around 200°C, since both films possess a crosslinked structure after crystal melting, the resin as a whole can be stabilized in a gel state, resulting in good melt fracture characteristics.

[0282] The above understanding is summarized in the table below.

[0283] [Table 1]

[0284] project Electron beam crosslinking Chemical reaction crosslinking Crosslinking sites Crystalline interior, crystalline-amorphous intermediate layer Amorphous part Thin film strength Increase No change Fuse function Deterioration or loss of function No change resistance to melt cracking Increase stepwise according to dosage Reliably improve

[0285] The constituent elements of the separator in the second embodiment will be described below.

[0286] The polyolefin microporous membrane described above as a substrate can be a single-layer membrane composed of a single polyolefin-containing microporous layer, a multilayer membrane composed of multiple polyolefin-containing microporous layers, or a multilayer membrane consisting of a polyolefin resin layer and a layer containing other resins as the main components.

[0287] In the case of a bilayer membrane formed by two polyolefin-containing microporous layers, the polyolefin compositions of the two layers can be different. Furthermore, in the case of a multilayer membrane formed by three or more polyolefin-containing microporous layers, the polyolefin compositions of the outermost and innermost layers can be different; for example, it can be a three-layer membrane.

[0288] The multilayer membrane used as a substrate preferably has a stacked structure of two or more layers, wherein the stacked structure has at least one A layer and one B layer containing polyolefin, and more preferably has a stacked structure of three or more layers, wherein one B layer is provided on each side (both sides) of the A layer. The stacked structure is not limited to a two-layer structure of "A layer-B layer" or a three-layer structure of "B layer-A layer-B layer" as long as each of the aforementioned A layer and B layer has one layer. For example, the polyolefin microporous membrane may have one or more layers formed on any one or two B layers, or between the A layer and the B layer.

[0289] Layers A and B contain polyolefins, preferably composed of polyolefins. The polyolefins in layers A and B can be in the form of microporous polyolefins, such as fabrics (woven fabrics) made of polyolefin fibers, nonwoven fabrics made of polyolefin fibers, etc.

[0290] <Polyolefins>

[0291] The polyolefin is not particularly limited, and 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. From the viewpoint of not clogging pores and being able to undergo heat setting at higher temperatures (sometimes simply referred to as "HS"), high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene (UHMWPE) is preferred, with high-density polyethylene or UHMWPE being more preferred. It is generally known that the weight-average molecular weight of UHMWPE is 1,000,000 or more. It should be noted that a single polyolefin may be used, or two or more may be used in combination.

[0292] Furthermore, the polyolefin microporous membrane preferably contains a polyolefin with a weight-average molecular weight (Mw) of less than 2,000,000. More preferably, it contains at least 40% by mass, and even more preferably at least 80% by mass, of the polyolefin as a whole. By using a polyolefin with a Mw of less than 2,000,000, there is a tendency to relax the early shrinkage of the polymer during heating tests of energy storage devices, and especially to maintain safety during heating safety tests. It should be noted that, compared to using a polyolefin with a Mw of 1,000,000 or more, the elastic modulus in the thickness direction of the resulting microporous membrane tends to be smaller when using a polyolefin with a Mw of less than 2,000,000, thus resulting in a microporous membrane with an uneven texture that is easier to transfer to the core. The weight-average molecular weight of the polyolefin microporous membrane constituting the separator is preferably 100,000 or more and 2,000,000 or less, more preferably 150,000 or more and 1,500,000 or less.

[0293] <Polyolefins having one or more functional groups>

[0294] From the perspective of cross-linking structure formation, resistance to redox degradation, and dense and uniform porous structure, polyolefins preferred for preparing microporous membranes are polyolefins having one or more functional groups, including functional group-modified polyolefins or polyolefins copolymerized from monomers having functional groups. It should be noted that, in this specification, functional group-modified polyolefins refer to substances formed by attaching functional groups after the manufacture of polyolefins. The functional groups are attached to the polyolefin backbone or can be introduced into the comonomer, preferably participating in the selective cross-linking of the amorphous portion of the polyolefin. For example, they can be at least one group selected from the group consisting of carboxyl, hydroxyl, carbonyl, polymerizable unsaturated hydrocarbon, isocyanate, epoxy, silanol, hydrazide, carbodiimide, oxazoline, acetoacetyl, aziridinyl, ester, active ester, carbonate, azide, chain or cyclic hydrocarbon containing heteroatoms, amino, mercapto, metal chelate, and halogen-containing groups.

[0295] From the viewpoints of strength, ion permeability, resistance to redox degradation, and dense and uniform porous structure, the separator preferably comprises both a polyolefin having one or more functional groups and UHMWPE. When using a combination of a polyolefin having one or more functional groups and UHMWPE, the preferred mass ratio of the polyolefin having one or more functional groups to UHMWPE in the separator (mass of the polyolefin having one or more functional groups / mass of ultra-high molecular weight polyethylene) is 0.05 / 0.95 to 0.80 / 0.20.

[0296] <Cross-linked structure>

[0297] The cross-linked structure of the polyolefin contained in the polyolefin microporous membrane contributes to at least one of the following: safety in nail penetration tests, thermal shrinkage and hot box testing, and high-temperature rod impact failure tests of the energy storage device. It is preferably formed in the amorphous portion of the polyolefin. The cross-linked structure can be formed, for example, by a reaction utilizing any of the following bonds: covalent bonds, hydrogen bonds, or coordinate bonds. The reaction utilizing covalent bonds is at least one selected from the group consisting of reactions (I) to (IV) below:

[0298] (I) Condensation reaction of multiple identical functional groups

[0299] (II) Reactions between multiple heterogeneous functional groups

[0300] (III) Chain condensation reaction of functional groups and electrolyte

[0301] (IV) Chain condensation reaction of functional groups with additives.

[0302] Furthermore, the reaction utilizing coordinate bonds is preferably the following reaction (V):

[0303] (V) A reaction in which multiple identical functional groups cross-link with dissolved metal ions via coordination bonds.

[0304] Reaction (I)

[0305] The first functional group of the separator is denoted as A. The following is a schematic diagram of the principle of reaction (I) and a specific example.

[0306] Schematic diagram of the principle of reaction (I)

[0307]

[0308] Example of functional group A:

[0309] Silyl alcohols, etc.

[0310] Specific examples of reaction (I)

[0311]

[0312] {In the formula, R is an alkyl or heteroalkyl group having 1 to 20 carbon atoms, optionally with substituents.}

[0313] When the functional group A used for reaction (I) is a silanol group, the polyolefin is preferably modified with silane grafting. The silane-grafted modified polyolefin has a polyolefin main chain with an alkoxysilyl group as a graft on the main chain. It should be noted that the alkoxide salts that replace the alkoxysilyl group can be, for example, methanol salts, ethanol salts, butoxide salts, etc. For example, in the above formula, R can be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc. Furthermore, the main chain and the graft are connected by covalent bonds, and structures such as alkyl, ether, glycol, or ester can be used. Considering the manufacturing process of the separator, in the stage before the crosslinking treatment process, the silicon to carbon ratio (Si / C) of the silane-grafted modified polyolefin is preferably 0.2 to 1.8%, more preferably 0.5 to 1.7%.

[0314] The preferred density of the silane-grafted modified polyolefin is 0.90–0.96 g / cm³. 3 Furthermore, the melt mass flow rate (MFR) at 190°C is 0.2–5 g / min. From the perspective of suppressing resin aggregate formation during the manufacturing process of the separator and maintaining silane crosslinking until contact with the electrolyte, silane-grafted modified polyolefins are preferably not masterbatch resins containing dehydration condensation catalysts. Dehydration condensation catalysts are known to also function as catalysts for the siloxane bond formation reaction of alkoxysilyl-containing resins. In this specification, the substance prepared by pre-adding a dehydration condensation catalyst (e.g., an organometallic catalyst) to an alkoxysilyl-containing resin or other compounded resin and mixing it during a continuous process of resin compounding using an extruder is referred to as masterbatch resin.

[0315] Reaction (II)

[0316] The first functional group of the separator is denoted as A, and the second functional group is denoted as B. The following is a schematic diagram of the principle of reaction (II) and a specific example.

[0317] Schematic diagram of the principle of reaction (II)

[0318]

[0319] Examples of combinations of functional groups A and B:

[0320] Hydroxyl and carboxyl groups (esterification);

[0321] Carbonyl group condensed with alkyl group (aldehyde-alcohol condensation);

[0322] Halogens condense with carboxyl groups (intramolecular condensation);

[0323] Alkoxy groups react with alkyl groups (Claysen reaction);

[0324] Carbonyl group reacts with acid anhydride group (Perkin reaction);

[0325] Amino and halogen;

[0326] The isocyanate group reacts with the hydroxyl group (to form a carbamate bond); and

[0327]

[0328] (oxazoline) and hydroxyl, etc.

[0329] Specific example 1 of reaction (II):

[0330]

[0331] Specific example 2 of reaction (II):

[0332]

[0333] Reactions (I) and (II) can be catalyzed, for example, by chemical substances within the energy storage device assembled by the separator. These chemical substances can be, for example, any of the electrolyte, electrolyte solution, electrode active material, additives, or their decomposition products contained in the energy storage device.

[0334] Reaction (III)

[0335] The first functional group of the separator is denoted as A, and the electrolyte is denoted as Sol. The following is a schematic diagram of the principle of reaction (III) and a specific example.

[0336] Schematic diagram of reaction (III)

[0337]

[0338] Example of functional group A:

[0339] Hydroxyl, carboxyl, amino, carbonyl, ether, isocyanate, etc.

[0340] Examples of electrolytes:

[0341] Electrolytes: LiPF6, LiBF4, LiN(SO2CF3)2, LiSO3CF3, LiBC4O8 (LiBOB), etc.

[0342] Non-aqueous solvents: ethylene carbonate, methyl ethyl carbonate, or mixtures thereof, etc.

[0343] Specific example 1 of reaction (III):

[0344]

[0345] Specific example 2 of reaction (III):

[0346]

[0347] Reaction (IV)

[0348] The first functional group of the separator is denoted as A, the second functional group introduced as desired is denoted as B, and the additive is denoted as Add. The following is a schematic diagram of the principle of reaction (IV).

[0349]

[0350] From the perspective of the covalent bonds formed by the dashed lines in the above schematic diagram, reaction (IV) is preferably a nucleophilic substitution reaction, nucleophilic addition reaction, or ring-opening reaction between the compound Rx constituting the separator and the compound Ry constituting the additive (Add). Compound Rx can be a polyolefin contained in the separator, such as polyethylene or polypropylene, and preferably the polyolefin is modified by functional group x, for example by at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH, and -SH.

[0351] Since multiple compounds Rx are crosslinked via compound Ry as an additive, compound Ry preferably has two or more linking reaction units y1. These multiple linking reaction units y1 can be any structure or group, can be substituted or unsubstituted, can contain heteroatoms or inorganic substances, and can be the same or different from each other, as long as they can undergo nucleophilic substitution, nucleophilic addition, or ring-opening reactions with the functional group x of compound Rx. Furthermore, when compound Ry has a chain structure, the multiple linking reaction units y1 can each independently be a terminal group, introduced into the main chain, or a side chain or side group.

[0352] In the case of reaction (IV) being a nucleophilic substitution reaction, as an example only, the functional group x of compound Rx will be considered as a nucleophilic group and the linking reaction unit y1 of compound Ry will be considered as a leaving group. However, both functional group x and linking reaction unit y1 can form leaving groups based on their nucleophilicity.

[0353] From the perspective of nucleophiles, the functional group x of compound Rx is preferably an oxygen-based nucleophile, a nitrogen-based nucleophile, or a thiophanate-based nucleophile. Examples of oxygen-based nucleophiles include hydroxyl, alkoxy, ether, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophiles include ammonium, primary amino, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of thiophanate-based nucleophiles include -SH and thioether groups, with -SH being preferred.

[0354] In the case that reaction (IV) is a nucleophilic substitution reaction, from the perspective of the leaving group, the linking reaction unit y1 of compound Ry is preferably an alkyl sulfonyl group such as CH3SO2- or CH3CH2SO2-; an aryl sulfonyl group (-ArSO2-); a haloalkyl sulfonyl group such as CF3SO2- or CCl3SO2-; an alkyl sulfonate group such as CH3SO3- or CH3CH2SO3-; an aryl sulfonate group (ArSO3-); a haloalkyl sulfonate group such as CF3SO3- or CCl3SO3-; and a heterocyclic group, which can be used alone or in various combinations. Examples of heteroatoms contained in the heterocycle include nitrogen atoms, oxygen atoms, and sulfur atoms, among which nitrogen atoms are preferred from the perspective of leaving property. As the leaving group containing a nitrogen atom in the heterocycle, a monovalent group as shown in the following formulas (y1-1) to (y1-6) is preferred:

[0355]

[0356] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0357]

[0358] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0359]

[0360] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0361]

[0362] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0363]

[0364] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0365]

[0366] {In the formula, X is a hydrogen atom or a monovalent substituent.}

[0367] In formulas (y1-1) to (y1-6), X is a hydrogen atom or a monovalent substituent. Examples of monovalent substituents include alkyl groups, haloalkyl groups, alkoxy groups, and halogen atoms.

[0368] When reaction (IV) is a nucleophilic substitution reaction and compound Ry has a chain structure, compound Ry preferably has at least one of the following groups selected from the group consisting of divalent groups shown in formulas (y2-1) to (y2-6) as the chain unit y2, in addition to the reaction unit y1:

[0369]

[0370] In the formula, m is an integer from 0 to 20, and n is an integer from 1 to 20.

[0371]

[0372] In the formula, n is an integer from 1 to 20.

[0373]

[0374] In the formula, n is an integer from 1 to 20.

[0375]

[0376] In the formula, n is an integer from 1 to 20.

[0377]

[0378] In the formula, X is an alkylene or aryl group having 1 to 20 carbon atoms, and n is an integer from 1 to 20.

[0379]

[0380] In the formula, X is an alkylene or aryl group having 1 to 20 carbon atoms, and n is an integer from 1 to 20.

[0381] Furthermore, in the case where the compound Ry contains multiple chain units y2, they can be the same as or different from each other, and their arrangement can be block or random.

[0382] In formula (y2-1), m is an integer from 0 to 20, and from the perspective of cross-linking networks, it is preferably 1 to 18. In formulas (y2-1) to (y2-6), n is an integer from 1 to 20, and from the perspective of cross-linking networks, it is preferably 2 to 19 or 3 to 16. In formulas (y2-5) to (y2-6), X is an alkylene or aryl group having 1 to 20 carbon atoms, and from the perspective of the stability of the chain structure, it is preferably methylene, ethylene, n-propylene, n-butylene, n-hexylene, n-heptylene, n-octylene, n-dodecylene, o-phenylene, m-phenylene, or p-phenylene.

[0383] Regarding the case where reaction (IV) is a nucleophilic substitution reaction, the preferred combination of functional group x of compound Rx with linking reaction unit y1 and chain unit y2 of compound Ry is shown in Tables 2 to 4 below.

[0384] [Table 2]

[0385] Nucleophilic substitution reaction (preferred combination I)

[0386]

[0387] [Table 3]

[0388] Nucleophilic substitution reaction (preferred combination II)

[0389]

[0390] [Table 4]

[0391] Nucleophilic substitution reaction (preferred combination III)

[0392]

[0393] As a specific example of a nucleophilic substitution reaction, the following shows a polyolefin with functional group x being -NH2, additive (compound Ry) linking reaction unit y1 being a backbone derived from succinimide, and chain unit y2 being -(O-C2H5). n - Schematic diagram of the reaction principle at time.

[0394] Specific example 1 :

[0395]

[0396] As a specific example of a nucleophilic substitution reaction, the following diagram illustrates the reaction principle when the functional groups x of the polyolefin are -SH and -NH2, the linking reaction unit y1 of the additive (compound Ry) is a nitrogen-containing cyclic skeleton, and the chain unit y2 is an ortho-phenylene.

[0397] Specific example 2:

[0398]

[0399] In the case of a nucleophilic addition reaction (IV), the functional group x of compound Rx can undergo an addition reaction with the connecting reaction unit y1 of compound Ry. In the nucleophilic addition reaction, the functional group x of compound Rx is preferably an oxygen-based nucleophile, a nitrogen-based nucleophile, or a thio-based nucleophile. Examples of oxygen-based nucleophiles include hydroxyl, alkoxy, ether, and carboxyl groups, with -OH and -COOH being preferred. Examples of nitrogen-based nucleophiles include ammonium, primary amino, and secondary amino groups, with -NH2 and -NH- being preferred. Examples of thio-based nucleophiles include -SH and thioether groups, with -SH being preferred.

[0400] In a nucleophilic addition reaction, the linking reaction unit y1 of compound Ry is preferably selected from at least one group consisting of the groups shown in formulas (Ay1-1) to (Ay1-6) from the perspective of addition reactivity or availability of starting materials:

[0401]

[0402] {In the formula, R is a hydrogen atom or a monovalent organic group.}

[0403]

[0404]

[0405] In formula (Ay1-4), R is a hydrogen atom or a monovalent organic group, preferably a hydrogen atom or a C atom. 1～20 Alkyl, alicyclic or aromatic groups, more preferably hydrogen atoms, methyl, ethyl, cyclohexyl or phenyl.

[0406] Regarding the case where reaction (IV) is a nucleophilic addition reaction, preferred combinations of functional group x of compound Rx and linking reaction unit y1 of compound Ry are shown in Tables 5 and 6 below.

[0407] [Table 5]

[0408] Nucleophilic addition reaction (preferred combination I)

[0409]

[0410] [Table 6]

[0411] Nucleophilic addition reaction (preferred combination II)

[0412]

[0413] As a specific example of a nucleophilic addition reaction, the following diagram illustrates the reaction principle when the functional group x of the separator is -OH and the connecting reaction unit y1 of the additive (compound Ry) is -NCO.

[0414] Specific examples:

[0415]

[0416] When reaction (IV) is a ring-opening reaction, the functional group x of compound Rx and the linking reaction unit y1 of compound Ry can undergo a ring-opening reaction. From the perspective of the availability of raw materials, it is preferable that the ring structure on the linking reaction unit y1 side is open. From the same perspective, the linking reaction unit y1 is more preferably an epoxy group, and compound Ry is more preferably having at least two epoxy groups, and even more preferably a diepoxide compound.

[0417] When reaction (IV) is a ring-opening reaction, the functional group x of compound Rx is preferably at least one selected from the group consisting of -OH, -NH2, -NH-, -COOH and -SH, and / or the linking reaction unit y1 of compound Ry is preferably at least two groups as shown in the following formula (ROy1-1):

[0418]

[0419] {In the formula, each X is independently a hydrogen atom or a monovalent substituent.}

[0420] In formula (ROy1-1), each of the multiple X's is independently a hydrogen atom or a monovalent substituent, preferably a hydrogen atom or a C'. 1～20 Alkyl, alicyclic, or aromatic groups, more preferably hydrogen atoms, methyl, ethyl, cyclohexyl, or phenyl. Regarding the epoxy ring-opening reaction, preferred combinations of functional group x of compound Rx and the linking reactive unit y1 of compound Ry are shown in Table 7 below.

[0421] [Table 7]

[0422] Epoxy ring-opening reaction (preferred combination)

[0423]

[0424] Reaction (V)

[0425] The first functional group of the separator is denoted as A, and the metal ion is denoted as M. n+ The following is a schematic diagram of the reaction (V) and an example of functional group A.

[0426] Schematic diagram of the principle of reaction (V)

[0427]

[0428] Example of functional group A: -CHO, -COOH, acid anhydride group, -COO-, etc.

[0429] In the above schematic diagram, metal ion M n+ Preferably, it is a metal ion dissolved from the energy storage device (hereinafter also referred to as dissolved metal ions), for example, it can be selected from Zn. 2+ Mn 2+ Co 3+ Ni 2+ and Li + At least one of the groups must be present. The following example illustrates functional group A as -COO. - Coordinate key at time.

[0430]

[0431] The following shows a case where functional group A is -COOH and the dissolved metal ion is Zn. 2+ The specific schematic diagram of the reaction (V) at that time.

[0432]

[0433] In the above schematic diagram, hydrofluoric acid (HF) may be derived, for example, from any of the electrolyte, electrolyte solution, electrode active material, additives, or their decomposition products or hygroscopic substances contained in the energy storage device, depending on the charge and discharge cycle of the energy storage device.

[0434] <Other contents>

[0435] Microporous membranes made of polyolefins can, as desired, contain notable additives such as dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, coloring pigments, inorganic fillers, and inorganic particles in addition to the polyolefin.

[0436] Properties of Microporous Membranes

[0437] The following properties of microporous membranes are for flat or monolayer membranes. When the microporous membrane is in the form of a laminated membrane, the following properties can be measured after removing the layers other than the polyolefin microporous membrane from the laminated membrane.

[0438] The porosity of the polyolefin microporous membrane is preferably 20% or more, more preferably 30% or more, and even more preferably 32% or more or 35% or more. By making the porosity of the microporous membrane 20% or more, there is a tendency to further improve the tracking ability for the rapid movement of lithium ions. On the other hand, the porosity of the microporous membrane is preferably 90% or less, more preferably 80% or less, and even more preferably 50% or less. By making the porosity of the microporous membrane 90% or less, there is a tendency to further improve the membrane strength and further suppress self-discharge. The porosity of the microporous membrane can be measured by the method described in the examples.

[0439] Regarding the air permeability of microporous membranes made of polyolefins, per 100cm³ 3 The membrane volume is preferably 1 second or more, more preferably 50 seconds or more, further preferably 55 seconds or more, and even more preferably 70 seconds or more, 90 seconds or more, or 110 seconds or more. By making the air permeability of the microporous membrane 1 second or more, there is a tendency to further improve the balance between membrane thickness, porosity, and average pore size. Furthermore, the air permeability of the microporous membrane is preferably 400 seconds or less, more preferably 300 seconds or less, and even more preferably 270 seconds or less. By making the air permeability of the microporous membrane 400 seconds or less, there is a tendency to further improve ion permeability. The air permeability of the microporous membrane can be measured according to the method described in the examples.

[0440] The tensile strength of polyolefin microporous membranes is preferably 1000 kgf / cm² in both the MD and TD directions (directions orthogonal to MD and membrane width direction). 2 The above, more preferably 1050 kgf / cm 2 The above is further optimized to 1100 kgf / cm². 2 The above. By achieving a tensile strength of 1000 kgf / cm. 2 Therefore, breakage during slitting or winding of the energy storage device is further suppressed, and short circuits caused by foreign objects within the energy storage device are further suppressed. On the other hand, the tensile strength of the microporous membrane is preferably 5000 kgf / cm². 2 The following is more preferably 4500 kgf / cm² 2 The following is a further preferred value: 4000 kgf / cm² 2 The following is an example of achieving a tensile strength of 5000 kgf / cm for the microporous membrane. 2 Therefore, there is a tendency for microporous membranes to relax and contract less during heating tests, resulting in improved safety.

[0441] The tensile modulus of the polyolefin microporous membrane is preferably 120 N / cm or less in both the MD and TD directions, more preferably 100 N / cm or less, and even more preferably 90 N / cm or less. A tensile modulus of 120 N / cm or less indicates that the separator used in lithium-ion secondary batteries is not extremely oriented. During heating tests, when a blocking agent such as polyethylene melts and shrinks, stress relaxation occurs in the polyethylene in the early stages, thereby suppressing the shrinkage of the separator within the battery and easily preventing short circuits between electrodes. In other words, the safety of the separator during heating can be further improved. Such a low tensile modulus microporous membrane is easily achieved by including polyethylene with a weight-average molecular weight of 500,000 or less in the polyolefin forming the microporous membrane. On the other hand, there is no particular limitation on the lower limit of the tensile modulus of the microporous membrane, but it is preferably 10 N / cm or more, more preferably 30 N / cm or more, and even more preferably 50 N / cm or more. The ratio of the tensile modulus (MD) to the tensile modulus (TD) in the polyolefin microporous membrane (MD / TD) is preferably 0.2 to 3.0, more preferably 0.5 to 2.0, and even more preferably 0.8 to 1.2. When the ratio of the MD to the TD tensile modulus of the polyolefin microporous membrane is within such a range, the shrinkage forces in the MD and TD directions become uniform when the blocking agent, such as polyethylene, melts and shrinks. As a result, when the separator in the battery undergoes thermal shrinkage, the shear stress applied to the electrode adjacent to the separator also becomes uniform in the MD and TD directions, tending to prevent damage to the laminate of the electrode and the separator. That is, the safety of the separator during heating can be further improved. The tensile modulus of the microporous membrane can be appropriately adjusted by adjusting the degree of stretching or by relaxing it after stretching as needed.

[0442] The thickness of the polyolefin microporous membrane is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more. By making the membrane thickness of the microporous membrane 1.0 μm or more, there is a tendency to further improve the membrane strength. Furthermore, the membrane thickness of the microporous membrane is preferably 500 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less, 22 μm or less, or 19 μm or less. By making the membrane thickness of the microporous membrane 500 μm or less, there is a tendency to further improve ion permeability. The membrane thickness of the microporous membrane can be measured by the method described in the examples.

[0443] In the case of separators used in high-capacity lithium-ion secondary batteries in recent years, the thickness of the polyolefin microporous membrane 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. In this case, by making the thickness of the microporous membrane 25 μm or less, there is a tendency to further improve permeability. In this case, the lower limit value of the thickness of the microporous membrane can be 1.0 μm or more, 3.0 μm or more, 4.0 μm or more, or 5.5 μm or more.

[0444] <Surface layer>

[0445] A surface layer is formed on at least one side of a polyolefin microporous membrane, which serves as a substrate. The surface layer may be disposed on one or both sides of the substrate, and is preferably disposed such that at least a portion of the substrate is exposed. As a surface layer, it is preferably selected from at least one layer comprising a thermoplastic polymer layer, an active layer, and a heat-resistant porous layer.

[0446] (Including thermoplastic polymer layer)

[0447] A thermoplastic polymer layer is formed on at least one side of a polyolefin microporous membrane, which serves as a substrate. The thermoplastic polymer layer may be disposed on one or both sides of the substrate, and is preferably disposed such that at least a portion of the substrate is exposed.

[0448] The area ratio (coverage ratio) of the thermoplastic polymer layer in the substrate surface relative to the total area of ​​the surface where the thermoplastic polymer layer can be disposed is preferably 5% to 90%. From the viewpoint of further suppressing the blockage of substrate pores caused by the thermoplastic polymer and further improving the permeability of the separator, it is preferable to set this coverage ratio to 90% or less. On the other hand, from the viewpoint of further improving adhesion to the electrode, it is preferable to set the coverage ratio to 5% or more. From this viewpoint, the upper limit of the coverage ratio is more preferably 80% or less, 75% or less, or 70%, and the lower limit of the area ratio is more preferably 10% or more or 15% or more. This coverage ratio is determined by observing the surface of the separator where the thermoplastic polymer layer is formed using SEM. Furthermore, when the thermoplastic polymer layer is a layer mixed with inorganic particles, the area where the thermoplastic polymer exists is calculated by setting the total area of ​​the thermoplastic polymer and the inorganic particles to 100%.

[0449] When the thermoplastic polymer layer is disposed only on a portion of the surface of the separator substrate, the configuration pattern of the thermoplastic polymer layer can include, for example, dots, stripes, grids, bands, tortoise shell patterns, irregular patterns, and combinations thereof. The thickness of the thermoplastic polymer layer disposed on the substrate is preferably 0.01 μm to 5 μm on each side of the substrate, more preferably 0.1 μm to 3 μm, and even more preferably 0.1 to 1 μm.

[0450] The thermoplastic polymer layer contains a thermoplastic polymer. The thermoplastic polymer layer may contain, relatively speaking, at least 60% by mass, more preferably at least 90% by mass, further preferably at least 95% by mass, and particularly preferably at least 98% by mass of a thermoplastic polymer. The thermoplastic polymer layer may contain other components in addition to the thermoplastic polymer.

[0451] Examples of thermoplastic polymers include the following:

[0452] Polyolefin resins such as polyethylene, polypropylene, and α-polyolefin;

[0453] Fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers containing these;

[0454] Diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, or copolymers containing these, or their hydrides;

[0455] Acrylic polymers containing (meth)acrylate, (meth)acrylic acid, etc. as monomer units and without polyalkylene glycol units; acrylic polymers containing (meth)acrylate, (meth)acrylic acid, etc. as monomer units and with one or two polyalkylene glycol units; copolymers containing these; or hydrogenated forms thereof.

[0456] Rubber products such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate;

[0457] Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose;

[0458] Polyalkylene glycols such as polyethylene glycol and polypropylene glycol do not have polymerizable functional groups;

[0459] Resins such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester;

[0460] A copolymer of olefinic unsaturated monomers having alkylene glycol units repeating in a number of 3 or more as copolymer units; and

[0461] Their combination.

[0462] Among these, from the viewpoint of improving the safety of energy storage devices with separators in puncture tests, thermoplastic polymers preferably contain polymer units of (meth)acrylate or (meth)acrylic acid.

[0463] Experiments show that in nail penetration tests, minimizing the short-circuit area around the device penetrated by the nail can suppress heat release. On the other hand, the temperature of the part closest to the nail is extremely high, and the polyethylene microporous membrane is in a molten state. The experiment observed that the molten resin expands concentrically from the nail with a force that minimizes its specific surface area, and shrinks towards the unmelted portion. It can be considered that the pores formed at this point constitute the short-circuit area, determining the rate of internal heat release and ultimately whether the battery will ignite or explode.

[0464] On the other hand, during the manufacture of energy storage devices such as batteries, bending (R) portions are sometimes unavoidable in the winding assembly, resulting in uneven spacing between the positive and negative electrodes across the entire area. It can be inferred that while chemically cross-linked substrates without thermoplastic polymer coatings improve heat resistance, the relatively thinner portions within the uneven electrode spacing shrink more during nail penetration tests, creating a larger short-circuit area. Furthermore, the electrodes expand and contract during energy storage device cycling, causing overall displacement in uncoated thermoplastic polymer separators, sometimes further contributing to uneven spacing between the positive and negative electrodes. It can be inferred that portions closer to these electrodes shrink more during nail penetration tests, resulting in an even larger short-circuit area.

[0465] In contrast, in chemically cross-linked substrate films coated with thermoplastic polymers such as acrylic resins, the thermoplastic polymer layer exhibits adhesion to the separators and electrodes, maintaining a more uniform gap across the entire area between the positive and negative electrodes. Furthermore, it can adapt to the expansion and contraction deformation of the electrodes during battery cycling, ensuring a uniform gap even after long-term use. Based on this uniform gap, the thermoplastic polymer layer with adjusted coating area can swell with the electrolyte, supplying (exudating) electrolyte from the thermoplastic polymer layer to the chemically cross-linked substrate. Therefore, the chemically cross-linked substrate can undergo a cross-linking reaction relatively evenly across the total area within the battery, resulting in excellent nail penetration test results.

[0466] From the viewpoint of improving the safety of energy storage devices with separators in puncture tests, the glass transition temperature (Tg) of the thermoplastic polymer is preferably in the range of -40°C to 105°C, and more preferably in the range of -38°C to 100°C.

[0467] From the viewpoints of wettability of the polyolefin multilayer microporous membrane, adhesion between the polyolefin multilayer microporous membrane and the thermoplastic polymer layer, and adhesion to the electrode, it is preferable to blend a polymer with a glass transition temperature of less than 20°C into the thermoplastic polymer layer. From the viewpoints of adhesion resistance and ion permeability, it is also preferable to blend a polymer with a glass transition temperature of 20°C or higher.

[0468] There is no limitation on the thermoplastic polymer as long as it has at least two glass transition temperatures. It can be achieved by blending two or more thermoplastic polymers or by using a thermoplastic polymer with a core-shell structure.

[0469] Core-shell structure refers to a polymer with a dual structure, consisting of polymers in the core and polymers in the outer shell, which are composed of different polymers.

[0470] Especially in polymer blends and core-shell structures, by combining polymers with high glass transition temperatures and polymers with low glass transition temperatures, the overall glass transition temperature of the thermoplastic polymer can be controlled. Furthermore, a variety of functions can be imparted to the thermoplastic polymer as a whole.

[0471] From the viewpoint of inhibiting adhesion and reducing ion permeability of the separator, thermoplastic copolymers are preferably in particulate form when the glass transition temperature is, for example, above 20°C, above 25°C, or above 30°C.

[0472] By incorporating particulate thermoplastic copolymers into the thermoplastic polymer layer, it is possible to ensure the porosity of the thermoplastic polymer layer disposed on the substrate and the anti-adhesion properties of the separators.

[0473] The average particle size of the particulate thermoplastic copolymer is preferably 10 nm to 2,000 nm, more preferably 50 nm to 1,500 nm, further preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, especially preferably 150 nm to 800 nm, and most preferably 200 nm to 750 nm. Setting the average particle size to 10 nm or more means ensuring that the size of the particulate thermoplastic polymer is such that it will not enter the pores of the substrate when the particulate thermoplastic polymer is coated on a substrate that at least includes a porous membrane. Therefore, this is preferred from the viewpoint of improving the adhesion between the electrode and the separator and the cycle characteristics of the energy storage device. Furthermore, from the viewpoint of coating the substrate with an amount of particulate thermoplastic polymer sufficient to take into account both the adhesion between the electrode and the separator and the cycle characteristics of the energy storage device, it is preferable to set the average particle size to 2,000 nm or less.

[0474] The particulate thermoplastic polymers described above can be manufactured using the corresponding monomers or comonomers via known polymerization methods. Suitable polymerization methods include, for example, solution polymerization, emulsion polymerization, and bulk polymerization.

[0475] Thermoplastic polymer layers can be easily formed by coating; therefore, thermoplastic polymer emulsions obtained by emulsion polymerization to form particulate thermoplastic polymers and thus for use in the form of aqueous latex are preferred.

[0476] The thermoplastic polymer layer may contain only the thermoplastic polymer, or it may contain optional components in addition to the thermoplastic polymer. Examples of optional components include, for instance, additives known above as relating to polyolefin microporous membranes.

[0477] (Active layer)

[0478] An active layer is disposed on at least one side of a polyolefin microporous membrane, which serves as a substrate. By disposing the active layer on the chemically crosslinked substrate, i.e., the polyolefin microporous membrane, as described above, it tends to exhibit superior heat shrinkage and / or hot box testing performance compared to conventional resin coatings on substrates without such chemical crosslinking. Furthermore, the separator obtained by bonding the active layer to the substrate through a process of coating the active layer onto the substrate tends to provide an energy storage device with low ion permeability and high output characteristics. Moreover, the separator also exhibits smooth closing characteristics even when the temperature rises rapidly during abnormal heat dissipation, tending to easily achieve high safety. From this viewpoint, the active layer can be disposed on one or both sides of the substrate, and it is preferable to dispose of it with at least a portion of the substrate exposed.

[0479] From the viewpoint of heat shrinkage and / or hot box testability, the active layer preferably contains a fluorinated vinyl compound, more preferably a fluorinated vinyl compound and inorganic particles.

[0480] As a fluorinated vinyl compound, compounds known as fluorinated resins or adhesives may be used.

[0481] The weight-average molecular weight (Mw) of fluorinated vinyl compounds is preferably 0.6 × 10⁻⁶. 6 ~2.5×10 6 The molecular weight (Mw) of fluorinated vinyl compounds tends to be within this range, exhibiting good heat shrinkage and heat box testing properties, and is therefore preferred. From the same viewpoint, the molecular weight of the fluorinated vinyl compounds is preferably in the range of 270 kDa to 600 kDa, and it is also preferable to use a combination of fluorinated vinyl compounds with molecular weights of 270 kDa to 310 kDa and 570 kDa to 600 kDa.

[0482] From the viewpoint of heat shrinkage and hot box testing, the melting point of the fluorinated vinyl compound is preferably in the range of 130°C to 171°C. From the same viewpoint, at least one of the following can be used: a fluorinated vinyl compound with a melting point of 130°C to 136°C, a fluorinated vinyl compound with a melting point of 167°C to 171°C, and a fluorinated vinyl compound with a melting point of 150°C ± 1°C.

[0483] Among compounds known as fluorinated resins or binders, at least one is preferably selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (polymer PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene (polymer PVDF-CTFE), PVDF homopolymer, mixtures of PVDF and tetrafluoroethylene-ethylene copolymer (ETFE), or terpolymers of vinylidene fluoride-tetrafluoroethylene-ethylene; more preferably, at least one is selected from the group consisting of polymer PVDF-HFP and polymer PVDF-CTFE. By copolymerizing HFP or CTFE with vinylidene fluoride, the crystallinity of the fluorinated resin can be controlled within a suitable range, thus suppressing the flow of the active layer during the bonding process with the electrode. Furthermore, since the adhesive strength is improved during the bonding process with the electrode, no interfacial shift occurs when used as a separator for secondary batteries, thereby improving heat shrinkage and / or hot box testability. It should be noted that fluorinated resins are generally obtained by emulsion polymerization or suspension polymerization.

[0484] Specific examples of PVDF include: Arkema's Kynar Flex (registered trademark) series, such as LBG and LBG8200; and SOLVAY's Solef (registered trademark) series, such as Grade 1015 and 6020.

[0485] Specific examples of high-polymer PVDF-HFP include SOLVAY's Solef (registered trademark) series, such as grades 21216 and 21510 (both soluble in acetone). Specific examples of high-polymer PVDF-CTFE include SOLVAY's Solef (registered trademark) series, such as grade 31508 (soluble in acetone).

[0486] The proportion of PVDF-HFP and PVDF-CTFE constituent units in the aforementioned fluorinated resins preferably derived from HFP or CTFE is between 2.0% and 20.0% by mass. When the HFP or CTFE content is 2.0% by mass or more, the fluorinated resin is suppressed from excessive crystallization, and when the HFP or CTFE content is 20.0% by mass or less, the fluorinated resin exhibits moderate crystallization. From the same viewpoint, the proportion of HFP or CTFE constituent units in PVDF-HFP and PVDF-CTFE is more preferably 2.25% by mass or more, further preferably 2.5% by mass or more, even more preferably 18% by mass or less, and even more preferably 15% by mass or less.

[0487] Importantly, in the hotbox test, after the separator made of polyolefins such as polyethylene undergoes crystal melting at 150°C, an insulating layer is placed between the positive and negative electrodes. During the manufacture of batteries and other energy storage devices, bending (R) portions are sometimes unavoidable in the winding assembly, resulting in uneven spacing between the positive and negative electrodes across the entire area. It can be inferred that while chemically cross-linked substrates without fluoropolymer coatings such as PVDF improve heat resistance, short-circuit suppression is insufficient in the relatively thinner sections within the uneven gaps between the positive and negative electrodes. Furthermore, the electrodes expand and contract during energy storage device cycling, causing overall misalignment in separators without fluoropolymer coatings such as PVDF, sometimes leading to uneven spacing between the positive and negative electrodes. Consequently, short circuits are more likely to occur in areas closer to the electrodes. Moreover, during partial thermal decomposition of the positive electrode, such as the NMC positive electrode, compressive strain is presumably generated in its vicinity due to localized expansion caused by O2 release. In other words, the higher the nickel content in an NMC cathode, the more difficult it is to ensure isolation between the positive and negative electrodes when using cathodes where O2 generation is visible in lower temperature regions. Due to the same tendency, cathodes composed of materials such as LAC also suffer from crystal instability (thermal decomposition). Under the most demanding conditions for NMC cathodes, assuming crystal decomposition begins at 150°C, this problem can be solved, thereby improving thermal shrinkage and hot-box testing performance.

[0488] On the other hand, in chemically cross-linked substrate films coated with fluorinated resins such as PVDF, the fluorinated resin layer exhibits adhesion to the separator and electrodes, maintaining a more uniform gap across the entire area between the positive and negative electrodes. Furthermore, when the separator containing the active layer is immersed in the electrolyte, it can follow the deformation caused by the expansion and contraction of the electrodes during battery or other energy storage device cycling, or by the thermal decomposition of the positive electrode to generate O2, ensuring a uniform gap even after long-term use. In addition to ensuring such a uniform gap, the adjusted PVDF resin can also swell with the electrolyte, uniformly supplying (exuding) the electrolyte to the chemically cross-linked substrate, thereby enabling the chemically cross-linked substrate to undergo a uniform cross-linking reaction within the battery. Therefore, to ensure good heat resistance across the entire area of ​​the separator and obtain good hot box test results, the aforementioned fluorinated resin is preferred.

[0489] When the active layer comprises a polymer having one or more polar groups selected from the group consisting of hydroxyl (-OH), carboxyl (-COOH), maleic anhydride (-COOOC-), sulfonic acid (-SO3H), and pyrrolidone (-NCO-), it can improve the cycling characteristics of the separator at low temperatures (e.g., below 90°C, below 50°C, below 25°C, below 10°C, below 5°C, below 0°C, etc.), and is therefore more preferable. Examples of such polymers include at least one polymer selected from cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose. It is presumed that the improved cycling characteristics of the separator at low temperatures due to the inclusion of a polymer having the aforementioned polar groups in the active layer are due to the high relative permittivity of these polymers, which also reduces the resistance of the separator at low temperatures. The relative permittivity of the polymer having polar groups can be from 1 to 100 (measurement frequency = 1 kHz), and is particularly preferably 10 or higher.

[0490] The active layer may also contain resins other than those mentioned above (other resins). As other resins, for example, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, ethylene vinyl acetate copolymer, polyimide, polyethylene oxide, etc. may be used individually or in combination of two or more of these, and are not limited thereto.

[0491] There are no particular limitations on the inorganic particles used in the active layer, but inorganic particles with a melting point of over 200°C, high electrical insulation, and electrochemical stability within the operating range of lithium-ion secondary batteries are preferred.

[0492] As inorganic particles, there are no particular limitations, but examples include: oxide ceramics such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, dickite, pearl clay, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and quartz sand; and glass fiber, etc. These can be used individually or in combination.

[0493] Among these, from the perspective of improving electrochemical stability and the heat resistance of the separator, alumina compounds such as alumina and alumina hydroxide, as well as aluminum silicate compounds such as kaolinite, dickite, perlite, halloysite, and pyrophyllite that do not have ion exchange capacity are preferred.

[0494] It should be noted that alumina exists in various crystalline forms, including α-alumina, β-alumina, γ-alumina, and θ-alumina, all of which can be used appropriately. Among these, α-alumina is preferred due to its thermal and chemical stability.

[0495] Alumina hydroxide (AlO(OH)) is particularly preferred as the alumina compound. From the viewpoint of preventing internal short circuits caused by the formation of lithium dendrites, boehmite is more preferred as the alumina hydroxide. By using boehmite-based particles as the inorganic particles constituting the active layer, high permeability can be maintained, a very lightweight porous layer can be achieved, and even with a thinner porous layer, thermal shrinkage of the porous membrane at high temperatures is suppressed, exhibiting excellent heat resistance. Synthetic boehmite that reduces ionic impurities that adversely affect the characteristics of the electrochemical device is further preferred.

[0496] Kaolin, a silicate compound that does not have ion-exchange capacity, is preferred due to its low cost and easy availability. Kaolin is known to include wet kaolin and calcined kaolin, which is produced through calcination. Calcined kaolin is particularly preferred. During calcination, kaolin releases water of crystallization and removes impurities, making it particularly preferred from the viewpoint of electrochemical stability.

[0497] The average particle size (D) of inorganic particles 50 The thickness of the inorganic particles is preferably 0.2 μm or more and 2.0 μm or less, more preferably greater than 0.2 μm and less than 2.0 μm. From the viewpoint of suppressing thermal shrinkage at high temperatures (e.g., 200°C or higher) even with a small active layer thickness (e.g., 5 μm or less), it is preferable to use inorganic particles with a D... 50 Adjust to the above range. Methods for adjusting the particle size and distribution of inorganic particles include, for example, using suitable pulverizing devices such as ball mills, bead mills, or jet mills to pulverize the inorganic particles and reduce their size.

[0498] Examples of inorganic particle shapes include plate-like, scaly, needle-like, columnar, spherical, polyhedral, and blocky shapes. Multiple combinations of these shapes can also be used.

[0499] The mass ratio of the fluorinated vinyl compound to the inorganic particles in the active layer (fluorinated vinyl compound / inorganic particles) is preferably 5 / 95 to 80 / 20, more preferably 7 / 93 to 65 / 35, even more preferably 9 / 91 to 50 / 50, and even more preferably 10 / 90 to 40 / 60. When the mass ratio of the fluorinated vinyl compound to the inorganic particles is within such a range, it tends to not only have good heat shrinkage and / or hot box test performance, but also good battery winding performance, and is therefore preferred. For example, when using PVDF-HFP or the like as the fluorinated vinyl compound, due to the frictional material effect unique to this resin, the resin dissolves on the film surface, tending to improve battery winding performance.

[0500] From the viewpoint of improving heat shrinkage and / or heat box testability, the thickness of the active layer is preferably 5 μm or less, more preferably 2 μm or less. From the viewpoint of improving heat resistance and insulation, the thickness of the active layer is preferably 0.5 μm or more.

[0501] The preferred layer density of the active layer is 0.5 g / cm³. 3 ~3.0g / cm 3 More preferably 0.7 g / cm³ 3 ~2.0g / cm 3 When the layer density of the active layer is 0.5 g / cm³ 3 At the above levels, there is a tendency for the thermal shrinkage rate to improve at high temperatures, reaching 3.0 g / cm³. 3 The following conditions tend to improve breathability.

[0502] The active layer may contain optional components other than fluorinated vinyl compounds and inorganic particles. Examples of optional components include, for instance, well-known additives (excluding inorganic particles) described above concerning polyolefin microporous membranes. Furthermore, the type, quality, and grade of the fluorinated vinyl compounds, inorganic particles, and optional components used can be adjusted according to the properties imparted to the active layer and the specified thickness of the active layer.

[0503] (Heat-resistant porous layer)

[0504] The heat-resistant porous layer contains a heat-resistant resin and has many micropores inside. In the heat-resistant porous layer, these micropores can be interconnected, allowing gas or liquid to pass from one side to the other.

[0505] A heat-resistant porous layer can be laminated onto at least one side of a polyolefin microporous membrane, which serves as a substrate. By configuring a heat-resistant porous layer on a polyolefin microporous membrane, which serves as a chemically crosslinked substrate as described above, there is a tendency for superior high-temperature bar impact test performance compared to conventional heat-resistant resin coatings on substrates without such chemical crosslinking. Furthermore, the separator obtained by bonding the heat-resistant porous layer to the substrate through a process of laminating the heat-resistant porous layer onto the substrate tends to provide an energy storage device with low ion permeability and high output characteristics. Moreover, in cases of rapid temperature rise during abnormal heat dissipation, the separator exhibits smooth closing characteristics, and there is a tendency to easily obtain high safety. From this viewpoint, the heat-resistant porous layer can be configured on one or both sides of the substrate, and it is preferable to configure it with at least a portion of the substrate exposed.

[0506] From the perspective of improving the impact failure test performance of high-temperature bars, the heat-resistant porous layer preferably contains heat-resistant resin and inorganic filler.

[0507] As heat-resistant resins, resins with a melting point exceeding 150°C, resins with a melting point exceeding 250°C, or, for resins that have essentially no melting point, a thermal decomposition temperature exceeding 250°C are preferred. Examples of such heat-resistant resins include fully aromatic polyamides, polyimides, polyamide-imides, polysulfones, polyketides, polyethers, polyetherketones, polyetherimides, and cellulose. Among these, fully aromatic polyamides are preferred from the viewpoint of durability, and para-aromatic polyamides and / or meta-aromatic polyamides are more preferred. Furthermore, meta-aromatic polyamides are preferred from the viewpoint of porous layer formation and redox resistance.

[0508] The preferred molecular weight distribution of the heat-resistant resin is Mw / Mn of 5 ≤ Mw / Mn ≤ 100 and / or weight-average molecular weight Mw of 8.0 × 10⁻⁶. 3 Above and 1.0×10 6The following describes how, when using a heat-resistant resin with the aforementioned molecular weight characteristics, a better heat-resistant porous layer can be formed on a polyolefin microporous membrane using a wet coating method. This is because the heat-resistant resin with such a wide molecular weight distribution contains more low molecular weight components, thus improving the processability of the coating solution containing the resin. Therefore, it is easier to form a heat-resistant porous layer with fewer defects and uniform film thickness. Furthermore, coating can be performed well even without applying strong coating pressure, thus suppressing the clogging of pores on the surface of the polyolefin microporous membrane and preventing a decrease in air permeability at the interface between the heat-resistant porous layer and the polyolefin microporous membrane. In addition, when the coating solution is applied to the polyolefin microporous membrane and then immersed in the coagulating liquid, the resin in the coating membrane moves easily, thus forming pores well. Furthermore, the low molecular weight components contained in the resin have good compatibility with the inorganic filler, and the shedding of inorganic fillers that contribute to pore formation can be prevented. As a result, a heat-resistant porous layer with uniform micropores can be easily formed. Therefore, a separator with excellent ion permeability and good contact with the electrode can be obtained.

[0509] Furthermore, the heat-resistant resin preferably contains 1% to 15% by weight, more preferably 3% to 10% by weight, of a low molecular weight polymer with a molecular weight of 8,000 or less. In this case, a good heat-resistant porous layer can be formed in the same manner as described above.

[0510] Furthermore, when using aromatic polyamides as heat-resistant resins, the preferred concentration ratio of terminal groups in the aromatic polyamide is [COOX{where X represents hydrogen, alkali metal, or alkaline earth metal}] / [NH2]≥1. For example, terminal carboxyl groups such as COONa have the effect of removing undesirable coatings formed on the negative electrode side of the battery. Therefore, when using aromatic polyamides with more terminal carboxyl groups than terminal amine groups, there is a tendency to obtain non-aqueous electrolyte secondary batteries with long-term stable discharge capacity. For example, sometimes batteries with good discharge capacity can be obtained even after repeated 100 or 1000 charge-discharge cycles.

[0511] There are no particular limitations on the inorganic filler used in the heat-resistant porous layer, but inorganic fillers with a melting point above 200°C, high electrical insulation, and electrochemical stability within the operating range of lithium-ion secondary batteries are preferred.

[0512] Examples of inorganic filler shapes include granular, plate-like, scaly, needle-like, columnar, spherical, polyhedral, and block-like shapes. Various combinations of inorganic fillers with the above shapes can be used.

[0513] The average particle size (D) of inorganic fillers 50The thickness of the inorganic filler is preferably 0.2 μm or more and 0.9 μm or less, more preferably more than 0.2 μm or less and 0.9 μm or less. From the viewpoint of suppressing thermal shrinkage at high temperatures (e.g., 150°C or more, 200°C or more) or improving the resistance to rod impact failure at high temperatures, even when the thickness of the heat-resistant porous layer is small (e.g., 5 μm or less or 4 μm or less), it is preferable to use D... 50 Adjust to the above range. Methods for adjusting the particle size and distribution of inorganic fillers include, for example, using suitable pulverizing devices such as ball mills, bead mills, or jet mills to pulverize the inorganic fillers and reduce their particle size.

[0514] The heat-resistant porous layer preferably contains, in addition to the heat-resistant resin, 25% to 95% by mass of inorganic filler, based on the mass of the heat-resistant porous layer. 25% or more of inorganic filler is preferred for dimensional stability and heat resistance at high temperatures, while 95% or less of inorganic filler is preferred for strength, processability, or moldability.

[0515] Furthermore, from the viewpoint of improving the testability of rod impact failure at high temperatures, the heat-resistant porous layer preferably contains 30% to 90% by mass of inorganic filler with an average particle size in the range of 0.2 μm to 0.9 μm, based on the mass of the heat-resistant porous layer, and more preferably contains 32% to 85% by mass.

[0516] As inorganic fillers, there are no particular limitations, and examples include oxide ceramics such as alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics containing silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, dickite, perlite, halloysite, pyrophyllite, montmorillonite, sericite, mica, magnesia chlorite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and quartz sand; and glass fiber, etc. These can be used individually or in combination.

[0517] Among these, from the perspective of improving electrochemical stability and the heat resistance of the separator, alumina compounds such as alumina and alumina hydroxide, as well as aluminum silicate compounds such as kaolinite, dickite, perlite, halloysite, and pyrophyllite that do not have ion exchange capacity are preferred.

[0518] It should be noted that alumina exists in various crystalline forms, including α-alumina, β-alumina, γ-alumina, and θ-alumina, all of which can be used appropriately. Among these, α-alumina is preferred due to its thermal and chemical stability.

[0519] As an alumina compound, aluminum hydroxide (AlO(OH)) is particularly preferred. From the viewpoint of preventing internal short circuits caused by the formation of lithium dendrites, boehmite is more preferred as the aluminum hydroxide. By using boehmite-based particles as the inorganic filler constituting the heat-resistant porous layer, it exhibits the following advantages: it maintains high permeability, achieves a very lightweight porous layer, and suppresses thermal shrinkage of the microporous membrane at high temperatures even in thinner porous layers, thus demonstrating excellent heat resistance. Synthetic boehmite that reduces ionic impurities that adversely affect the characteristics of electrochemical devices is further preferred.

[0520] Kaolin, a silicate compound that does not have ion-exchange capacity, is preferred due to its low cost and easy availability. Kaolin is known to include wet kaolin and calcined kaolin, which is produced through calcination. Calcined kaolin is particularly preferred. During calcination, kaolin releases water of crystallization and removes impurities, making it particularly preferred from the viewpoint of electrochemical stability.

[0521] The porosity of the heat-resistant porous layer is preferably in the range of 60% or more and 90% or less. From the viewpoint of heat resistance, a porosity of 90% or less is preferred. Furthermore, from the viewpoint of battery cycle characteristics, storage characteristics, and discharge performance, a porosity of 60% or more is preferred. From the same viewpoint, the coating amount (weight per unit area) of the heat-resistant porous layer is preferably 2 g / m². 2 ~10g / m 2 .

[0522] From the viewpoint of high-temperature rod impact failure testing, the thickness of the heat-resistant resin layer on each side of the polyolefin microporous membrane used as the substrate is preferably 8 μm or less, more preferably 4 μm or less or 3.5 μm or less. From the viewpoint of improving heat resistance and insulation, the thickness of the heat-resistant resin layer can be 0.5 μm or more.

[0523] The heat-resistant resin layer may contain optional components other than the heat-resistant resin and inorganic particles. Examples of optional components include, for instance, well-known additives (excluding inorganic particles) described above concerning polyolefin microporous membranes, and resins other than the heat-resistant resin.

[0524] Manufacturing method of separators for energy storage devices

[0525] Regarding the method for manufacturing the separator for the energy storage device disclosed herein, it can be manufactured by manufacturing a substrate layer containing a polyolefin, and then forming or configuring a desired layer on the substrate layer. In the first embodiment, the desired layer is a layer containing inorganic particles (layer B) and a layer containing a thermoplastic polymer (layer C), and in the second embodiment, it is a surface layer (i.e., containing at least one of a thermoplastic polymer layer, an active layer, and a heat-resistant porous layer).

[0526] I. Method for manufacturing the separator for the energy storage device in the first embodiment

[0527] <Method for manufacturing polyolefin substrate layer>

[0528] The manufacturing method of the polyolefin substrate layer may include, for example, the following steps:

[0529] (1) Sheet forming process;

[0530] (2) Stretching process;

[0531] (3) Porous body formation process; and

[0532] (4) Heat treatment process.

[0533] The manufacturing method of the polyolefin substrate layer may include a mixing process before the sheet forming process (1) and / or a winding and slitting process after the heat treatment process (3).

[0534] The mixing process is a process of mixing the raw material resin of the polyolefin substrate layer with a plasticizer and / or inorganic filler as desired to obtain a compound. The polyolefin resin described above can be used as the raw material resin for the polyolefin substrate layer. Mixing can be performed using a mixing machine. From the viewpoint of suppressing the formation of resin aggregates during subsequent manufacturing processes, it is preferable not to add masterbatch resin containing a dehydration condensation catalyst to the compound. As a plasticizer, an organic compound capable of forming a homogeneous solution with the polyolefin at a temperature below its boiling point can be used. More specifically, examples include decahydronaphthalene, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. One plasticizer can be used alone, or two or more can be used in combination. Regarding the ratio of plasticizer to the total mass of the polyolefin resin used, from the viewpoint of the porosity of the obtained microporous membrane, it is preferably 20% by mass or more, and from the viewpoint of the viscosity during melt mixing, it is preferably 90% by mass or less.

[0535] The sheet forming process is as follows: the obtained compound or polyolefin resin raw material is extruded with any plasticizer and / or inorganic filler, cooled and solidified, and then formed into a sheet to obtain a sheet. There are no particular limitations on the sheet forming method; for example, methods that solidify the molten compound and extruded material by compression cooling are possible. As for cooling methods, methods such as direct contact with cooling media such as cold air or cooling water, or contact with rollers and / or an extruder cooled by a refrigerant are possible. From the viewpoint of excellent film thickness control, contact with rollers and / or an extruder cooled by a refrigerant is preferred.

[0536] From the viewpoint of suppressing the formation of resin aggregates in the polyolefin substrate layer, the mass ratio of silane-modified polyolefin to unmodified silane polyolefin in the sheet forming process (mass of silane-modified polyolefin / mass of unmodified silane polyolefin) is preferably 0.05 / 0.95 to 0.4 / 0.6, more preferably 0.06 / 0.94 to 0.38 / 0.62. The unmodified silane polyolefin is preferably ultra-high molecular weight polyethylene (UHMWPE).

[0537] The stretching process is a process of obtaining a stretched article by stretching a sheet along at least one axial direction. Plasticizers and / or inorganic fillers may be extracted from the sheet before stretching, if necessary. Examples of sheet stretching methods include MD uniaxial stretching based on a roll stretcher, TD uniaxial stretching based on a spreader, successive biaxial stretching based on a combination of a roll stretcher and a spreader or a spreader and a spreader, and simultaneous biaxial stretching based on a simultaneous biaxial spreader or blow molding. From the viewpoint of obtaining a more uniform film, simultaneous biaxial stretching is preferred. From the viewpoint of film thickness uniformity, and the balance between elongation and porosity and average pore size, the aspect 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. By using an aspect ratio of 8 times or more, it is easier to obtain a stretched article with high strength and good thickness distribution. From the viewpoint of preventing breakage, the aspect ratio can be 250 times or less.

[0538] The porous body forming process is a process of extracting plasticizers and / or inorganic fillers from the stretched material after the stretching process, and porousifying the stretched material to obtain a microporous membrane. Examples of methods for extracting plasticizers include: immersing the stretched material in an extraction solvent, and spraying the stretched material with an extraction solvent. There are no particular limitations on the extraction solvent; however, solvents that are poor solvents for polyolefins but good solvents for plasticizers and / or inorganic fillers, and whose boiling point is lower than the melting point of polyolefins, are preferred. Examples of such extraction solvents include: hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as dichloromethane, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol and isopropanol; ketones such as acetone and 2-butanone; and alkaline solutions. One extraction solvent may be used alone, or two or more may be used in combination.

[0539] The heat treatment process is a process of heat-treating the microporous membrane after the stretching process. If necessary, plasticizers can be further extracted from the microporous membrane before heat treatment. There are no particular limitations on the heat treatment method; examples include heat setting methods such as stretching and relaxation operations using a spreader and / or a roll stretcher. The relaxation operation refers to a reduction operation performed along the mechanical direction (MD) and / or width direction (TD) of the membrane at a specified temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation; or by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation; or, in the case of relaxation of both MD and TD, it is the value obtained by multiplying the relaxation rate of MD by the relaxation rate of TD.

[0540] The winding / slitting process is the process of slitting the obtained microporous membrane as needed and winding it onto a specified core for subsequent processing.

[0541] From the viewpoint of maintaining crosslinking until the polyolefin substrate layer comes into contact with the electrolyte, the manufacturing process of the polyolefin substrate layer preferably does not include a crosslinking treatment process. That is, it is preferable to perform the crosslinking treatment process within the energy storage device after assembling the separator having the polyolefin substrate layer into the energy storage device. The crosslinking treatment process is generally a process in which the object to be treated, containing silane-modified polyolefin, is contacted with a mixture of an organometallic catalyst and water, or immersed in an alkaline or acidic solution to perform a silane dehydration condensation reaction, thereby forming oligomeric siloxane bonds. Examples of organometallic catalysts include, for example, dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctanoate. An alkaline solution refers to an alkaline solution with a pH greater than 7 that contains, for example, alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, and amine compounds. An acidic solution refers to an acidic solution with a pH less than 7 that contains inorganic acids and / or organic acids.

[0542] <Methods of Island Structure Formation>

[0543] In the manufacturing process of polyolefin substrate layers, during the sheet forming process, when raw materials are fed into an extruder, island structures of alkali metals and / or alkaline earth metals are formed in the separators by mixing a certain concentration of alkali metal and / or alkaline earth metal compounds into the raw materials. However, when using raw materials with significantly different molecular weights, it is difficult to uniformly disperse the alkali metal and / or alkaline earth metal compounds in the resin raw materials due to the difference in melt viscosity between the raw materials. In addition, in melt mixing containing silane-modified polyolefins, dispersion is even more difficult due to the presence of units with heterofunctional groups. In the case of such complex mixed resins, shear stirring with an extruder at high speed can improve the dispersion uniformity of alkali metal and / or alkaline earth metal compounds, but due to the close and dense dispersion of the island structures, there is a problem that the F anions in the electrolyte are consumed to a necessary degree. Furthermore, shear stirring with a high-speed extruder causes the molecular weight of the polyolefin to deteriorate, thus significantly impairing the mechanical strength and openness of the separators.

[0544] To control the construction of the island structure without compromising mechanical strength and porosity, it is preferable to use three types of polyolefins: polyolefins with Mv = 2 million to 9 million (raw material b) and Mv = 500,000 to 2 million (raw material c) as raw materials, and silane-modified polyolefins with Mv = 20,000 to 150,000 (raw material a) as raw materials. It is further preferable to adjust the content ratio according to each molecular weight. This allows for the controllability of constructing island structures containing alkali metal and / or alkaline earth metal compounds with specified sizes and dispersions.

[0545] It should be noted that, in the above raw material composition, the preferred proportion of raw material a in the whole is 3% to 70% by mass, and the ratio of raw material b to raw material c (mass of resin b / mass of resin c) is 0.06% to 7.00% by mass.

[0546] Surface treatment of polyolefin substrate layer

[0547] The microporous membrane obtained by the methods comprising the various processes described above can be used as a polyolefin substrate layer for a separator in an energy storage device. Pre-treating the surface of the polyolefin substrate layer facilitates subsequent coating with a coating liquid and improves the adhesion between the substrate layer and the coating layer, which is therefore preferred. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0548] <Methods for forming inorganic particle layers>

[0549] The inorganic particulate layer can be formed by coating a polyolefin substrate layer with a coating solution containing inorganic particles and any resin binder in a solvent, and then removing the solvent. As a solvent, undesirable solvents such as water or a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol) are preferred.

[0550] The coating method can be any method that achieves the desired coating pattern, coating thickness, and coating area. Examples include mold coating, curtain coating, dip coating, blade coating, rod coating, and gravure coating.

[0551] Regarding methods for removing solvent from the coated film after coating, any method that will not adversely affect the polyolefin substrate layer and the inorganic particle layer is acceptable. Examples include methods such as heating and drying at a temperature below the melting point of the substrate while it is fixed, and methods such as drying under reduced pressure at low temperature.

[0552] <Method for forming thermoplastic polymer layers>

[0553] The thermoplastic polymer layer can be formed by coating an inorganic particulate layer with a coating solution containing a thermoplastic polymer in a solvent. In the case of manufacturing a separator for an energy storage device that does not have an inorganic particulate layer, the coating solution of the thermoplastic polymer layer can be directly coated onto the polyolefin substrate layer. Regarding the coating solution, the thermoplastic polymer can be synthesized by emulsion polymerization, and the resulting emulsion can be used directly as the coating solution. The coating solution preferably contains undesirable solvents such as water or a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol).

[0554] The coating method can be any method that achieves the desired coating pattern, coating thickness, and coating area. Examples include mold coating, curtain coating, dip coating, blade coating, rod coating, and gravure coating.

[0555] Regarding methods for removing solvent from the coated film after coating, any method that will not adversely affect the polyolefin substrate layer, inorganic particle layer, and thermoplastic polymer layer is acceptable. Examples include methods such as heating and drying at a temperature below the melting point of the substrate while it is fixed, and methods such as drying under reduced pressure at low temperature.

[0556] II. Method for manufacturing the separator for the energy storage device in the second embodiment

[0557] <Method for manufacturing microporous membranes using polyolefins as substrate>

[0558] As a method for manufacturing the separator in the second embodiment, the following description focuses on the case where the polyolefin microporous membrane used as the substrate is a single-layer membrane (flat membrane), but this is not intended to exclude methods other than flat membranes. The method for manufacturing the microporous membrane includes the following steps:

[0559] (1) Sheet forming process;

[0560] (2) Stretching process;

[0561] (3) Porous body formation process; and

[0562] (4) Heat treatment process.

[0563] The method for manufacturing microporous membranes may preferably exclude the crosslinking structure formation process or the contact process with the crosslinking promoting catalyst, from the viewpoint of maintaining the crosslinking of the microporous membrane until it is housed in the energy storage device, depending on the desired resin modification process or mixing process before the sheet forming process (1) and / or the winding / slitting process after the heat treatment process (3).

[0564] The cross-linking structure formation process includes: (1) a secondary step of causing the multiple functional groups contained in the microporous membrane to undergo a condensation reaction with each other; (2) a secondary step of causing the functional groups contained in the microporous membrane to react with chemical substances inside the energy storage device; or (3) a secondary step of causing the functional groups contained in the microporous membrane to react with other functional groups. The cross-linking promoting catalyst is any catalyst capable of promoting cross-linking reactions, such as (I) the condensation reaction of multiple identical functional groups, (II) the reaction between multiple dissimilar functional groups, (III) the chain condensation reaction of functional groups with electrolyte, and (IV) the chain condensation reaction of functional groups with additives, as described above.

[0565] In the mixing process, a mixing machine can be used to mix, for example, polyolefins, other resins as desired, and plasticizers or inorganic materials. From the viewpoint of suppressing the formation of resin aggregates during manufacturing and maintaining the crosslinking of the microporous membrane until it is housed in an energy storage device, it is preferable not to add masterbatch resin containing crosslinking promoting catalysts to the mixture.

[0566] The polyolefin supplied for the compounding or sheet forming process is not limited to olefin homopolymers, but can also be a polyolefin copolymerized from monomers having functional groups, or a functional group-modified polyolefin. Its functional groups are functional groups capable of participating in the formation of cross-linked structures, for example, functional groups A and / or B in reactions (I) to (V) described above. By preparing polyolefin raw materials containing monomer units having functional groups A and / or B in advance, the resin modification process can be omitted.

[0567] On the other hand, when the polyolefin raw material lacks functional groups capable of participating in the formation of a cross-linked structure, or when the gelation rate of such functional groups does not meet the specified ratio, the polyolefin raw material can be supplied to a resin modification process to introduce functional groups into the resin backbone, or to increase the gelation rate of the functional groups, thereby obtaining functional group-modified polyolefins. The resin modification process can be carried out by known methods. For example, to introduce functional groups A and / or B into the polyolefin backbone, the polyolefin raw material can be brought into contact with the reaction reagents through liquid spraying, gas spraying, dry mixing, impregnation, coating, etc.

[0568] As a plasticizer, there are no particular limitations, and examples include organic compounds that can form a homogeneous solution with polyolefins at temperatures below their boiling points. More specifically, examples include decahydronaphthalene, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decanol, nonanol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. A single plasticizer can be used, or two or more can be used in combination. The proportion of the plasticizer is not particularly limited, but from the viewpoint of the porosity of the resulting microporous membrane, the polyolefin and the silane-grafted modified polyolefin are preferably 20% by mass or more relative to their total mass, and from the viewpoint of the viscosity during melt mixing, preferably 90% by mass or less.

[0569] The sheet forming process is as follows: the obtained compound or mixture of polyolefin and plasticizer is extruded, cooled and solidified, and then shaped into a sheet to obtain a sheet. There are no particular limitations on the sheet forming method; examples include methods that solidify the molten compound and extruded material through compression cooling. As for cooling methods, methods such as direct contact with cooling media such as cold air or cooling water, or contact with rollers or an extruder cooled by a refrigerant, are possible. From the viewpoint of excellent film thickness control, contact with rollers or an extruder cooled by a refrigerant is preferred.

[0570] When using polyolefins copolymerized from monomers having functional groups or functionalized modified polyolefins with other polyolefins in combination, from the viewpoint of resin aggregates in the separator or the maximum internal exothermic rate, the mass ratio (polyolefins copolymerized from monomers having functional groups or functionalized modified polyolefins / other polyolefins) in the sheet forming process is preferably 0.05 to 0.4 / 0.6 to 0.95, more preferably 0.06 to 0.38 / 0.62 to 0.94.

[0571] From the viewpoint of improving safety by having low-temperature shut-off below 150°C and high-temperature rupture-resistant film at 180–220°C and suppressing thermal runaway in the event of damage to the storage device, in the sheet forming process, the polyolefin or functional group-modified polyolefin copolymerized from monomers with functional groups is preferably a masterbatch resin that does not contain a catalyst that promotes the crosslinking reaction of its functional groups before the sheet forming process.

[0572] The stretching process involves extracting plasticizers or inorganic materials from the obtained sheet as needed, and then stretching the sheet in one or more directions. Examples of sheet stretching methods include MD unidirectional stretching based on a roll stretcher, TD unidirectional stretching based on a spreader, successive bidirectional stretching based on a combination of a roll stretcher and a spreader or a spreader and a spreader, and simultaneous bidirectional stretching based on a simultaneous bidirectional spreader or blow molding. From the viewpoint of obtaining a more uniform film, simultaneous bidirectional stretching is preferred. From the viewpoint of film thickness uniformity, and the balance between elongation, porosity, and average pore size, the overall aspect 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. By making the overall aspect ratio 8 times or more, it is easier to obtain stretched materials with high strength and good thickness distribution. Furthermore, from the viewpoint of preventing breakage, this aspect ratio can be 250 times or less.

[0573] The porous body formation process involves extracting the plasticizer from the stretched material after the stretching process and making the stretched material porous. The extraction method for the plasticizer is not particularly limited, and examples include: immersing the stretched material in an extraction solvent, spraying the stretched material with the extraction solvent, etc. The extraction solvent is not particularly limited; for example, a solvent that is a poor solvent for polyolefins but a good solvent for the plasticizer or inorganic materials, and whose boiling point is lower than the melting point of the polyolefin, is preferred. Examples of such extraction solvents are not particularly limited, and examples include: hydrocarbons such as n-hexane or cyclohexane; halogenated hydrocarbons such as dichloromethane or 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol or isopropanol; ketones such as acetone or 2-butanone; and alkaline solutions. One extraction solvent can be used alone, or two or more can be used in combination.

[0574] The heat treatment process is a step following the stretching process where, if necessary, plasticizers are extracted from the sheet and further heat-treated to obtain a microporous membrane. There are no particular limitations on the heat treatment method; examples include heat setting methods such as stretching and relaxation operations using a spreader or roller stretching machine. The relaxation operation refers to a reduction operation performed along the mechanical direction (MD) and / or width direction (TD) of the membrane at a specified temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation; or by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation; or, in the case of relaxation of both MD and TD, it is the value obtained by multiplying the relaxation rate of MD by the relaxation rate of TD.

[0575] <Winding / Slitting Process / Post-processing Process>

[0576] The winding process involves cutting the obtained microporous membrane into sections as needed and winding them onto a specified core.

[0577] If the obtained polyolefin microporous membrane is pre-treated with a surface treatment, it is easier to coat with a coating solution afterward, and the adhesion between the polyolefin and the surface layer is improved, which is therefore preferred. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0578] Multilayering of Substrates

[0579] As an example of a method for manufacturing a polyolefin multilayer microporous membrane, the following describes the manufacturing of a multilayer membrane having a first microporous layer, a second microporous layer, and a third microporous layer in sequence. As a method for stacking these porous layers, a three-layer one-time stacking method can be cited as an example: After melting and mixing a polyolefin resin composition that constitutes the first and second microporous layers with a plasticizer using a twin-screw extruder to form an olefin solution, each polyolefin solution is supplied from each twin-screw extruder to a three-layer T-die. The layer thickness ratio of each layer (first polyolefin solution layer / second polyolefin solution layer / first polyolefin solution layer) formed from each solution is adjusted to a desired range, and the membrane is cooled while being pulled at a specified winding speed, thereby forming a gel-like three-layer sheet.

[0580] The above method uses a 3-layer T-mold to simultaneously stack 3 layers, or each layer can be formed separately and then made into 3 layers.

[0581] <Methods for forming surface layer>

[0582] The surface layer can be formed, for example, by coating a coating liquid containing the material of the surface layer onto a polyolefin microporous membrane as a substrate, and then drying it. Alternatively, the polyolefin microporous membrane as a substrate and the surface layer membrane can be fabricated separately and then laminated together.

[0583] (Method for forming a thermoplastic polymer layer)

[0584] Thermoplastic polymers can be applied to a substrate, for example, by coating a substrate with a coating solution containing the thermoplastic polymer. Thermoplastic polymers can be synthesized by emulsion polymerization, and the resulting emulsion can be used directly as a coating solution. The coating solution preferably contains undesirable solvents such as water or a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol).

[0585] Regarding the method of coating a coating liquid containing a thermoplastic polymer onto a polyolefin microporous membrane substrate, there are no particular limitations as long as the method can achieve the desired coating pattern, coating thickness, and coating area. For example, the coating method described above can be used to coat a coating liquid containing inorganic particles. From the viewpoint of the high degree of freedom in the coating shape of the thermoplastic polymer and the ease of adjusting the preferred coverage area ratio described above, gravure coating or spray coating is preferred.

[0586] Regarding methods for removing solvent from the coated film after coating, there are no particular limitations as long as the method does not adversely affect the substrate and the thermoplastic polymer layer. Examples include: drying at a temperature below the melting point while the substrate is fixed; drying under reduced pressure at low temperature; and immersing the thermoplastic polymer in a solvent unsuitable for it, causing the thermoplastic polymer to solidify into granules while simultaneously extracting the solvent.

[0587] (Methods for forming the active layer)

[0588] As a method for configuring or forming an active layer on a substrate, one example is coating at least one side of the substrate with a coating liquid comprising a fluorinated vinyl compound and inorganic particles. In this case, the coating liquid may contain solvents, dispersants, etc., to improve dispersion stability and coatability. The coating liquid may contain organic solvents such as cyanoethyl polyvinyl alcohol and acetone, or it may contain water, a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol), etc.

[0589] There are no particular limitations on the method of applying the coating liquid to the substrate, as long as the required layer thickness and coating area can be achieved. For example, particulate raw materials containing resin binders and polymer substrate raw materials can be laminated and extruded by co-extrusion, or the substrate and active layer can be made into films separately and then laminated together.

[0590] Regarding methods for removing solvent from the coated film after coating, there are no particular limitations as long as the method does not adversely affect the polyolefin resin, fluorinated vinyl compound, or inorganic particles. Examples include: drying the coated film at a temperature below the melting point of the polyolefin resin or fluorinated vinyl compound while the substrate is fixed; and drying under reduced pressure at low temperature.

[0591] (Method for forming a heat-resistant resin layer on a substrate)

[0592] One method for forming a heat-resistant resin layer on a substrate is to apply a coating liquid comprising a heat-resistant resin and an inorganic filler to at least one side of the substrate. In this case, the coating liquid may contain solvents, dispersants, etc., to improve dispersion stability and coatability. The coating liquid may contain organic solvents such as NMP, IPA, cyanoethyl polyvinyl alcohol, acetone, etc., or may contain water, a mixture of water and a water-soluble organic medium (e.g., methanol or ethanol), etc.

[0593] There are no particular limitations on the method of applying the coating liquid to the substrate, as long as the required layer thickness and coating area can be achieved. For example, particulate raw materials containing resin binders and polymer substrate raw materials can be laminated and extruded by co-extrusion, or the substrate and heat-resistant resin layer can be made into films separately and then laminated together.

[0594] Regarding methods for removing solvent from the coated film after coating, there are no particular limitations as long as the method does not adversely affect the polyolefin resin, heat-resistant resin, or inorganic filler. Examples include: drying the coated film at a temperature below the melting point of the polyolefin resin or heat-resistant resin while the substrate is fixed; and drying under reduced pressure at low temperature.

[0595] The separator obtained by the method including the various processes described above can be used in energy storage devices, especially lithium batteries or lithium-ion secondary batteries.

[0596] Energy Storage Devices

[0597] The energy storage device disclosed herein includes a positive electrode, a negative electrode, a separator for the energy storage device of this disclosure, a non-aqueous electrolyte, and an additive as desired. The energy storage device includes at least one energy storage element, which is configured with a positive electrode, a negative electrode, and a separator for the energy storage device located between them. Typically, multiple positive electrodes and multiple negative electrodes are alternately stacked across the separator for the energy storage device of this disclosure to form multiple energy storage elements. The energy storage elements are typically housed within a casing in a state of being immersed in a non-aqueous electrolyte.

[0598] When the energy storage device of this disclosure is housed in the device casing by a separator, the functionalized polyethylene or functionalized graft copolymer polyethylene reacts with the chemicals contained in the electrolyte or additives to form a cross-linked structure, thus creating a cross-linked structure in the manufactured energy storage device. The functionalized polyethylene or functionalized graft copolymer polyethylene is not limited and can be derived from polyolefin raw materials of microporous membranes or from polyolefins modified during the manufacturing process of microporous membranes.

[0599] Specific examples of the energy storage devices disclosed herein include: lithium batteries, lithium secondary batteries, lithium-ion secondary batteries, sodium secondary batteries, sodium-ion secondary batteries, magnesium secondary batteries, magnesium-ion secondary batteries, calcium secondary batteries, calcium-ion secondary batteries, aluminum secondary batteries, aluminum-ion secondary batteries, nickel-metal hydride batteries, nickel-cadmium batteries, double-layer capacitors, lithium-ion capacitors, redox flow batteries, lithium-sulfur batteries, lithium-air batteries, and zinc-air batteries. Among these, from a practical standpoint, lithium batteries, lithium secondary batteries, lithium-ion secondary batteries, nickel-metal hydride batteries, or lithium-ion capacitors are preferred, with lithium batteries or lithium-ion secondary batteries being more preferred.

[0600] A lithium-ion secondary battery (LIB) is a rechargeable battery that uses a lithium-containing positive electrode, a negative electrode, and an electrolyte containing an organic solvent containing lithium salts such as LiPF6. Known LIB positive electrodes can be used as the positive electrode. During charging / discharging of a lithium-ion secondary battery, ionized lithium reciprocates between the electrodes. Furthermore, it is necessary to suppress contact between the electrodes while enabling the ionized lithium to move between them at a relatively high speed; therefore, a separator is placed between the electrodes.

[0601] The following examples of lithium-ion secondary batteries are provided for illustration, but the energy storage devices disclosed herein are not limited to these.

[0602] <positive electrode>

[0603] The positive electrode typically has a positive current collector and a layer of positive active material disposed on one or both sides thereon. The positive active material layer contains positive active material, and may also contain conductive additives and / or binders if necessary.

[0604] The positive current collector can be made of metal foils such as aluminum foil, nickel foil, or stainless steel foil. The surface of the positive current collector can be carbon-coated and can be processed into a mesh shape.

[0605] The positive electrode active material preferably contains a material capable of absorbing and releasing lithium ions. More specifically, examples of positive electrode active materials include those containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co. Positive electrodes that readily undergo thermal decomposition or release O2 can also be used, such as those preferably selected from at least one of the group consisting of nickel-manganese-cobalt (NMC) lithium-containing cathodes, olivine-type lithium iron phosphate (LFP) cathodes, lithium cobalt oxide (LCO) cathodes, nickel-cobalt-aluminum (NCA) lithium-containing cathodes, and lithium manganese oxide (LMO) cathodes. From the perspective of reversibly and stably absorbing and releasing lithium ions and achieving high energy density, nickel-manganese-cobalt (NMC) lithium composite oxides are preferred. In the case of NMC lithium composite oxides, the molar ratio of nickel (Ni) to the total amount of nickel, manganese, and cobalt is preferably 4–9, 5–9, 6–9, 5–8, or 6–8.

[0606] As a positive electrode active material, olivine-type lithium iron phosphate (LFP) cathodes can be used. Olivine-type lithium iron phosphate is often used at higher temperatures such as 60°C due to its olivine structure and excellent thermal stability. However, conventional separators without cross-linking structures undergo creep deformation (deformation of the microporous structure) at 60°C, thus posing a challenge in cycle performance. The cross-linked separator of this disclosure can suppress creep deformation, and therefore, by combining it with an olivine-type lithium iron phosphate (LFP) cathode, it can be used in the temperature range where the previous cycle performance issues exist. Lithium cobalt oxide (LCO) cathodes can also be used as positive electrode active materials. Lithium cobalt oxide (LCO) cathodes can increase the battery's operating voltage due to their high oxidation potential. However, lithium cobalt oxide has high hardness and is prone to foreign matter incorporation during the molding process due to metal wear. During battery assembly, the incorporation of metal foreign matter can cause internal short circuits. The separator with the cross-linked structure of this disclosure has excellent melting / melt-breakage characteristics, thus enabling the electrochemical reaction to be safely stopped even in the event of an internal short circuit. By combining a lithium cobalt oxide (LCO) cathode with the separator disclosed herein, both the battery's operating voltage and safety during internal short circuits can be considered. As the cathode active material, a nickel-cobalt-aluminum (NCA) lithium-containing cathode can also be used. While using a nickel-cobalt-aluminum (NCA) lithium-containing cathode allows for the production of batteries with excellent charge / discharge capacity at low cost, there is a tendency for trace amounts of moisture in the battery to react with Li ions dissolved from the cathode to form lithium compounds. These lithium compounds readily react with the electrolyte to generate gas. Gas generation may cause battery swelling. Furthermore, the consumption of lithium ions dissolved from the cathode may lead to a decrease in charge / discharge capacity. In the case of the separator with a cross-linked structure having an alkali metal / alkaline earth metal island structure, the alkali metal / alkaline earth metal in this island structure reacts with HF, allowing control of the HF concentration. One of the reactions occurring within the battery is the reaction of moisture with electrolyte salts such as LiPF6 to generate HF. By controlling the HF concentration within the battery, the reaction between moisture and electrolyte salts can be promoted, effectively consuming moisture. By combining a nickel-cobalt-aluminum (NCA) lithium-containing cathode with the separator disclosed herein, the decrease in charge-discharge capacity can be suppressed. Lithium manganese oxide (LMO) cathodes can also be used as the cathode active material. Lithium manganese oxide has a spinel structure (cubic crystal), thus exhibiting a robust crystal structure, thermal stability, and excellent safety, and is therefore sometimes used at higher temperatures such as 60°C. However, conventional separators without a cross-linked structure undergo creep deformation (thermal shrinkage) at 60°C, posing a challenge in cycle performance. The cross-linked separator of this disclosure suppresses creep deformation, and therefore, by combining it with a lithium manganese oxide (LMO) cathode, it can be used in temperature ranges where previous cycle performance issues existed.

[0607] From the perspectives of low cost, long lifespan, and excellent safety, olivine-type lithium iron phosphate (LFP) cathodes can be used as positive electrode active materials. From the perspectives of high operating voltage and excellent cycle life, lithium cobalt oxide (LCO) cathodes can also be used. From the perspectives of a good balance of layered structure, capacity density, cost, and thermal stability, nickel-cobalt-aluminum (NCA) lithium-containing cathodes can also be used. From the perspectives of spinel structure (cubic crystal), robust crystal structure, thermal stability, and excellent safety, lithium manganese oxide (LMO) cathodes can also be used.

[0608] Examples of conductive additives used as the positive electrode active material layer include carbon black such as graphite, acetylene black, and Ketjen black, as well as carbon fibers. The content of the conductive additive is preferably 10 parts by mass or less relative to 100 parts by mass of the positive electrode active material, and more preferably 1 to 5 parts by mass.

[0609] Examples of binders used as the positive electrode active material layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The binder content is preferably 6 parts by mass or less per 100 parts by mass of the positive electrode active material, more preferably 0.5 to 4 parts by mass.

[0610] <negative electrode>

[0611] The negative electrode typically has a negative current collector and a layer of negative active material disposed on one or both sides thereof. The negative active material layer contains negative active material, and may also contain conductive additives and / or binders if necessary.

[0612] The negative electrode current collector is made of metal foil such as copper foil, nickel foil, or stainless steel foil. Furthermore, the surface of the negative electrode current collector can be carbon-coated and can be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5–40 μm, more preferably 6–35 μm, and even more preferably 7–30 μm.

[0613] The negative electrode active material preferably contains a component capable of operating at below 0.4V (vs. Li / Li). +Materials that absorb lithium ions at a potential of . More specifically, as negative electrode active materials, examples include carbon materials such as amorphous carbon (hard carbon), graphite (artificial graphite, natural graphite), pyrolytic carbon, coke, glassy carbon, calcined organic polymers, mesophase carbon microspheres, carbon fibers, activated carbon, carbon colloids, and carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, Si materials, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymers. A negative electrode active material can be used alone or in combination of two or more. Examples of Si materials mentioned above include silicon, Si alloys, and Si oxides.

[0614] Examples of conductive additives used as the negative electrode active material layer include carbon black such as graphite, acetylene black, and Ketjen black, as well as carbon fiber. The content of the conductive additive is preferably 20 parts by mass or less relative to 100 parts by mass of the negative electrode active material, and more preferably 0.1 to 10 parts by mass.

[0615] Examples of binders used as the negative electrode active material layer include carboxymethyl cellulose, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, and fluororubber. Additionally, diene rubbers, such as styrene-butadiene rubber, can also be used. Regarding the binder content, it is preferably set to 10 parts by mass or less relative to 100 parts by mass of the negative electrode active material, more preferably 0.5 to 6 parts by mass.

[0616] <Separator for energy storage devices>

[0617] The separator for energy storage devices disclosed herein can be used as a separator for energy storage devices.

[0618] Electrolyte

[0619] The electrolyte in a battery may contain water, and the water contained in the battery system after manufacturing may be water contained in the electrolyte or water introduced by components such as electrodes or separators. The electrolyte may contain non-aqueous solvents. Examples of non-aqueous solvents include alcohols such as methanol and ethanol, and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents.

[0620] Examples of aprotic solvents include: cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds containing sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the above aprotic solvents are replaced by halogen atoms.

[0621] Examples of cyclic carbonates include: ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentene carbonate, trans-2,3-pentene carbonate, cis-2,3-pentene carbonate, vinylene carbonate, 4,5-dimethylethyleneene carbonate, and vinyl ethyleneene carbonate.

[0622] Examples of fluoroethylene carbonates include: 4-fluoro-1,3-dioxolane-2-one, 4,4-difluoro-1,3-dioxolane-2-one, cis-4,5-difluoro-1,3-dioxolane-2-one, trans-4,5-difluoro-1,3-dioxolane-2-one, 4,4,5-trifluoro-1,3-dioxolane-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolane-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolane-2-one.

[0623] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0624] Examples of organic compounds containing sulfur atoms include: ethylene sulfite, propylene sulfite, butyl sulfite, pentene sulfite, sulfolane sulfonate, sulfolane cyclobutane, 3-cyclobutene sulfonate, 3-methyl sulfolane sulfonate, 1,3-propane sulpholactone, 1,4-butane sulpholactone, 1-propene 1,3-sulpholactone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0625] Examples of chain carbonates include: methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, etc.

[0626] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

[0627] Examples of mononitriles include acetonitrile, propionitrile, butyronitrile, valerate, benzonitrile, and acrylonitrile.

[0628] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile.

[0629] Examples of dinitrile include: malononitrile, succinate, methylsuccinate, glutaronitrile, dimethylglutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanhexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanoctane, 2,7-dicyanoctane, 1,9-dicyanonane, 2,8-dicyanonane, 1,10-dicyandecane, 1,6-dicyandecane, and 2,4-dimethylglutaronitrile, ethylene glycol bis(propionitrile) ether, etc.

[0630] Examples of cyclic nitriles include benzonitrile.

[0631] Examples of short-chain fatty acid esters include: methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl neovalerate, methyl angelic acid ester, methyl hexanoate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl neovalerate, ethyl angelic acid ester, ethyl hexanoate, propyl acetate, propyl propionate, propyl isobutyrate, propyl isovalerate, propyl valerate, propyl neovalerate, propyl angelic acid ester, propyl hexanoate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate. Isopropyl valerate, isopropyl neovalerate, hydrogenated angelic acid isopropyl ester, isopropyl hexanoate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl neovalerate, hydrogenated angelic acid ester, butyl hexanoate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl neovalerate, hydrogenated angelic acid isobutyl ester, isobutyl hexanoate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl neovalerate, hydrogenated angelic acid ester, and tert-butyl hexanoate, etc.

[0632] Examples of chain ethers include: dimethoxyethane, diethyl ether, 1,3-dioxolane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. Examples of fluorinated ethers include those with the general formula Rf. aa -OR bb (where Rf) aa It is an alkyl group containing a fluorine atom, and R bb Compounds, etc., that may contain an organic group containing a fluorine atom. Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0633] Compounds in which some or all of the H atoms of the aforementioned aprotic solvent are replaced by halogen atoms include compounds in which the halogen atom is fluorine.

[0634] Examples of fluorinated chain carbonates include, for instance, methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. These fluorinated chain carbonates can be represented by the following general formula:

[0635] R cc -OC(O)OR dd

[0636] In the formula, R cc and R dd The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2 and CH2Rf are selected. ee (where Rf) ee It consists of at least one group from the group consisting of an alkyl group having 1 to 3 carbon atoms, formed by replacing a hydrogen atom with at least one fluorine atom, and R cc and / or R dd It contains at least one fluorine atom.

[0637] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters can be represented by the following general formula:

[0638] R ff -C(O)OR gg

[0639] In the formula, R ff The free radicals are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, and CF2Rf. hh CFHRf hh and CH2Rf ii At least one of the groups, R gg The free radicals CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf are selected. ii At least one of the groups, Rf hh Rf is an alkyl group having 1 to 3 carbon atoms, in which at least one hydrogen atom is optionally replaced by a fluorine atom. ii It is an alkyl group with 1 to 3 carbon atoms formed by replacing a hydrogen atom with at least one fluorine atom, and R ff and / or R gg Contains at least one fluorine atom, in R ff In the case of CF2H, R gg Not CH3}.

[0640] In this application specification, a non-aqueous electrolyte refers to an electrolyte containing an electrolyte in a non-aqueous solvent, and having a water content of 1% or less based on the total mass. The non-aqueous electrolyte is preferably as water-free as possible, but may contain trace amounts of water. Such water content relative to the total amount of the non-aqueous electrolyte is preferably 300 ppm or less by mass, more preferably 200 ppm or less by mass.

[0641] Examples of non-aqueous solvents include alcohols such as methanol and ethanol, as well as aprotic solvents, with aprotic solvents being preferred. Examples of aprotic solvents include acetonitrile, mononitriles other than acetonitrile, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, chain carbonates, cyclic carbonates, fluorocarbonates, fluoroethylene carbonate, short-chain fatty acid esters, lactones, ketones, organic compounds containing sulfur atoms, chain ethers, cyclic ethers, fluorinated ethers, and compounds in which some or all of the H atoms are replaced by halogen atoms.

[0642] Lithium salts are preferred as electrolytes, and fluorinated lithium salts that generate HF are further preferred from the viewpoint of promoting silane crosslinking reactions. Examples of fluorinated lithium salts include lithium hexafluorophosphate (LiPF6), lithium fluorosulfonate (LiFSO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), lithium fluoroborate (LiBF4), and lithium bis(oxalatoborate) (LiBC4O8). Although not limited by theory, for example, when the electrolyte contains LiPF6, LiPF6 reacts with trace amounts of moisture contained in the energy storage device (moisture contained in components such as electrodes, separators, and electrolyte) to generate hydrogen fluoride (HF) or fluorinated organic compounds derived from HF. It can be considered that these HF or fluorinated organic compounds derived from HF dissolve in the electrolyte, swell and diffuse into the amorphous portions of the polyolefin having crosslinkable silanes, thereby catalyzing the silane crosslinking reaction.

[0643] In non-aqueous electrolytes, in addition to the substances mentioned above, acid sources such as inorganic acids or organic acids and alkali sources may also be included as catalytic agents for the silane crosslinking reaction. Examples of alkali sources include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, and amine compounds. Among these, from the viewpoint of the safety of the energy storage device and the crosslinking properties of silanes, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0644] <Outer shell>

[0645] The outer casing can use known casings, such as battery cans or laminated film casings. As a battery can, a metal can made of materials such as steel, stainless steel, aluminum, or a cladding material can be used. Regarding the laminated film casing, two pieces can be overlapped with the hot-melt resin side facing inwards, or bent with the hot-melt resin side facing inwards, and the ends can be sealed by heat sealing. When using a laminated film casing, a positive lead (or a positive terminal and a lead tab connected to the positive terminal) can be connected to the positive current collector, and a negative lead (or a negative terminal and a lead tab connected to the negative terminal) can be connected to the negative current collector. In this case, the laminated film casing can be sealed with the ends of the positive and negative leads (or the lead tabs connected to the positive and negative terminals respectively) extending to the outside of the casing. More specifically, as a laminated film casing, a laminated film consisting of, for example, a three-layer structure of hot-melt resin / metal film / resin can be used. Aluminum foil is preferred as the metal film, and polyolefin resin is preferred as the resin material on both sides.

[0646] <additive>

[0647] When additives are included, they can be at least one selected from the group consisting of, for example, dehydration condensation catalysts, metal soaps such as calcium stearate or zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, antifogging agents, and coloring pigments.

[0648] Energy Storage Device Assembly Kit

[0649] The energy storage device assembly kit disclosed herein comprises: (A) a housing that houses a laminated or wound body containing electrodes and a separator for the energy storage device of this disclosure; and (B) a container that houses a non-aqueous electrolyte. The laminated or wound body includes at least one energy storage element, said energy storage element having a positive electrode, a negative electrode, and a separator for the energy storage device located between them. Typically, multiple positive electrodes and multiple negative electrodes are alternately laminated with separators for the energy storage device of this disclosure in order to form multiple energy storage elements. For details of each component, please refer to the "Energy Storage Device" section above.

[0650] The non-aqueous electrolyte is removed from a container and injected into the outer casing, thereby enabling the assembly of the separator for the energy storage device. There are no restrictions on the form of the container holding the non-aqueous electrolyte, as long as it can preserve the electrolyte until the separator for the energy storage device is assembled. After assembling the separator for the energy storage device, the container holding the non-aqueous electrolyte can be discarded or reused in the manufacture of other components.

[0651] When assembling a battery storage device, the separator in element (A) is brought into contact with the non-aqueous electrolyte in element (B), the electrolyte is brought into contact with the laminate or winding body within the housing, and / or the assembled battery storage device is continuously charged and discharged, thereby forming a cross-linked structure within the separator, thus forming a battery storage device that balances safety and output.

[0652] While not wishing to impose theoretical constraints, it can be assumed that when the electrolyte or electrolyte solution comes into contact with the electrodes and / or during the charging and discharging of the energy storage device, substances that catalyze the cross-linking reaction, or substances with functional groups that form part of the cross-linking structure, are present in the electrolyte solution, on the inner surface of the outer casing, or on the electrode surface. These substances dissolve in the electrolyte solution and uniformly swell and diffuse into the amorphous portions of the polyolefin, thereby uniformly promoting the cross-linking reaction of the laminated or wound body containing spacers. The substances catalyzing the cross-linking reaction can be in the form of an acid solution or a membrane. In the case of an electrolyte containing lithium hexafluorophosphate (LiPF6), these can be hydrogen fluoride (HF) or fluorinated organic compounds derived from hydrogen fluoride (HF). Substances with functional groups that form part of the cross-linking structure can be, for example, compounds having functional groups A and / or B as described above, the electrolyte itself, various additives, etc.

[0653] From the perspective of promoting the cross-linking reaction of the separator, the electrolyte contained in the non-aqueous electrolyte of element (2) can be a fluorine (F) lithium salt such as LiPF6 that produces HF, an electrolyte with non-shared electron pairs such as LiN(SO2CF3)2 and LiSO3CF3, or LiBF4, LiBC4O8 (LiBOB).

[0654] From the viewpoint of promoting the cross-linking reaction of the separator, the energy storage device assembly kit may include other containers as accessories (or elements (C)) for storing catalysts used to promote the cross-linking reaction, such as mixtures containing organometallic catalysts and water, acid solutions, alkaline solutions, etc.

[0655] Manufacturing Method of Energy Storage Device

[0656] In a first embodiment, the method for manufacturing the energy storage device disclosed herein may include, for example, the following steps:

[0657] (i) A preparation process, which prepares a housing and a non-aqueous electrolyte for housing the stacked or wound body of the electrode and the separator of the energy storage device of the present disclosure.

[0658] (ii) Liquid injection process: injecting non-aqueous electrolyte into the outer casing;

[0659] (iii) Terminal connection process, wherein the lead terminals are connected to electrodes inside the housing or exposed electrodes inside the housing as desired; and

[0660] (iv) Charge and discharge process, performing at least one charge and discharge cycle as desired.

[0661] Steps (i) to (iv) can be performed according to methods known in the art, except for using the separator for the energy storage device disclosed herein. In steps (i) to (iv), electrodes and non-aqueous electrolytes described in the "energy storage device" section can be used, as well as positive electrodes, negative electrodes, electrolytes, housings, and charging / discharging devices known in the art.

[0662] Preferably, step (ii) involves contacting the separator with the non-aqueous electrolyte and initiating the silane crosslinking reaction of the silane-modified polyolefin. From the viewpoint of reliably carrying out the silane crosslinking reaction of the separator, steps (iii) and (iv) are preferred. Although not theoretically constrained, it is believed that the silane crosslinking reaction can proceed more efficiently by generating a catalytic substance in the electrolyte or on the electrode surface through charge-discharge cycles.

[0663] In the second embodiment, the method for manufacturing the energy storage device uses a separator containing a polyolefin having one or more functional groups, and may include the following steps: (1) causing the functional groups to undergo a condensation reaction with each other, (2) causing the functional groups to react with chemical substances inside the energy storage device, or (3) causing the functional groups of the polyolefin to react with other types of functional groups, thereby forming a crosslinking process. The crosslinking process can be carried out in the same way as the reaction that forms the crosslinking structure of the separator described above. Furthermore, since the crosslinking process can be carried out using compounds inside the energy storage device and the environment around the device, excessive conditions such as electron beams and high temperatures above 100°C are not required, and mild conditions such as temperatures of 5°C to 90°C and / or ambient atmosphere conditions can be used.

[0664] By performing a crosslinking process during the manufacturing of the energy storage device, the step of forming a crosslinking structure during or immediately after the film-forming process of the separator can be omitted. This allows for the relaxation or elimination of stress and strain after the energy storage device is manufactured, and / or the separator can be given a crosslinking structure even without the use of high energy such as light irradiation or heating. This reduces uneven crosslinking, the generation of unmelted resin aggregates, and environmental burden.

[0665] In the crosslinking process, by (2) reacting the functional groups with the chemical substances inside the energy storage device, or by (3) reacting the functional groups of the polyolefin with other types of functional groups, a crosslinking structure is formed not only inside the separator, but also between the separator and the electrode or between the separator and the solid electrolyte interface (SEI), which can improve the strength between multiple components of the energy storage device.

[0666] In the method for manufacturing the energy storage device disclosed herein, the energy storage device assembly kit described above can be used. In this case, the method for manufacturing the energy storage device disclosed herein includes the following steps;

[0667] (i) The process of preparing the energy storage device assembly kit described above;

[0668] (ii) The process of combining elements (A) and (B) of the energy storage device assembly kit, (1) causing the functional groups of the polyolefin contained in the separator to undergo a condensation reaction with each other, (2) causing the functional groups to react with the chemical substances inside the energy storage device, or (3) causing the functional groups to react with other types of functional groups.

[0669] (iii) The process of connecting the lead terminals to the electrodes of element (A) as desired; and

[0670] (iv) A process of performing at least one charge-discharge cycle as desired.

[0671] Processes (i) to (iv) can be performed by methods known in the art, except for the use of separators for energy storage devices. In addition, positive electrodes, negative electrodes, electrolytes, housings and charging / discharging devices known in the art can be used in processes (i) to (iv).

[0672] From the viewpoint of reliably carrying out the crosslinking reaction of the separator, it is preferable to carry out steps (iii) and (iv) during or after step (ii). It can be considered that the crosslinking reaction is achieved by generating substances that catalyze the crosslinking reaction or substances with functional groups that become part of the crosslinking structure in the electrolyte, on the inner surface of the casing, or on the electrode surface through charge-discharge cycles.

[0673] The separator of this disclosed energy storage device forms a cross-linked structure when housed in the energy storage device, thus being suitable for conventional energy storage device manufacturing processes. Furthermore, the cross-linking reaction occurs after the device is manufactured, which can improve the safety of the energy storage device. Examples of safety improvements include: reducing the possibility of thermal runaway due to partial short circuits, improving safety in nail penetration tests, improving thermal shrinkage and hot box testing performance, and improving high-temperature rod impact damage testing performance.

[0674] Energy storage devices manufactured as described above, especially LIBs, can improve safety due to the partitions provided in this embodiment. Examples of improved safety include: reducing the likelihood of thermal runaway due to partial short circuits; improving safety in nail penetration tests; and improving thermal shrinkage and hot-box testability, as well as improving high-temperature rod impact failure testability.

[0675] Example

[0676] Measurement and Evaluation Methods

[0677] Regarding the evaluation methods for the separators described below, in TOF-SIMS analysis and image processing, detection of silane-modified polyolefins contained in the separators, weight-average molecular weight, viscosity-average molecular weight, melt flow rate, unit area weight of the polyolefin substrate layer, film thickness of the polyolefin substrate layer, puncture strength, puncture strength converted from unit area weight, and porosity determination, the coating film (inorganic particle layer and thermoplastic polymer layer) is removed from each separator. The separators are then immersed in a non-aqueous electrolyte for one week, cleaned with dichloromethane, and then evaluated. Regarding the 150°C heat shrinkage rate, 150°C heat shrinkage rate in the electrolyte, thermal response index, film thickness, permeability, powder shedding, melting temperature, and short-circuit temperature, each separator is immersed in a non-aqueous electrolyte for one week, cleaned with dichloromethane, and then evaluated. Regarding electrode retention rate, battery cycle test capacity retention rate, and battery crush test, single-layer laminated non-aqueous secondary batteries are fabricated using each separator and evaluated.

[0678] <Detection Method for Silane-Modified Polyolefins in Separators>

[0679] When the silane-modified polyolefin contained in the separator is cross-linked, it is insoluble or has insufficient solubility in organic solvents, making it sometimes difficult to directly determine the content of silane-modified polyolefin from the separator. In such cases, as a sample pretreatment, methyl orthoformate, which does not cause side reactions, is used to decompose the siloxane bonds into methoxysilane alcohols, followed by solution NMR analysis. This allows for the detection of silane-modified polyolefin contained in the separator or its GPC determination. The pretreatment experiment can be performed with reference to Japanese Patent Nos. 3529854 and 3529858. Specifically, the method for detecting silane-modified polyolefin contained in the separator can effectively utilize the silane-modified polyolefin used as a raw material for manufacturing the separator. 1 H or 13 Identification by C-NMR. The following is... 1 H and 13 An example of a C-NMR measurement technique will be explained.

[0680] ( 1 (H-NMR measurement)

[0681] The sample was dissolved in o-dichlorobenzene-d4 at 140℃ to obtain a proton resonance frequency of 600MHz. 1 H-NMR spectrum. 1 The determination conditions for H-NMR are as follows.

[0682] Device: AVANCE NEO 600 manufactured by Bruker

[0683] Sample tube diameter:

[0684] Solvent: o-dichlorobenzene-d4

[0685] Measurement temperature: 130℃

[0686] Pulse angle: 30°

[0687] Pulse wait time: 1 second

[0688] Total number of times: 1000 or more

[0689] Sample concentration: 1 wt / vol%

[0690] ( 13 (NMR determination of C)

[0691] The sample was dissolved in o-dichlorobenzene-d4 at 140 °C to obtain 13 C-NMR spectra. 13 The C-NMR measurement conditions are as follows.

[0692] Device: AVANCE NEO 600 manufactured by Bruker

[0693] Sample tube diameter:

[0694] Solvent: o-dichlorobenzene-d4

[0695] Measurement temperature: 130℃

[0696] Pulse angle: 30°

[0697] Pulse wait time: 5 seconds

[0698] Total number of times: 10,000 or more

[0699] Sample concentration: 10 wt / vol%

[0700] pass 1 H and / or 13 C-NMR analysis can confirm the amount of silane unit modification and alkyl modification in silane-modified polyolefins in polyolefin raw materials. Furthermore, in the separator, the presence of (-CH2-Si) in silane-modified polyolefins can be identified. 1 H, 0.69ppm, t; 13 C, 6.11 ppm, s).

[0701] <Weight-average molecular weight (Mw)>

[0702] Using a Waters ALC / GPC 150C (trademark) chromatogram, standard polystyrene was measured under the following conditions to create a calibration curve. Additionally, for the following polymers, chromatograms were measured under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the following method.

[0703] Chromatographic columns: 2 Tosoh GMH6-HT (trademark) columns + 2 GMH6-HTL (trademark) columns

[0704] Mobile phase: o-dichlorobenzene

[0705] Detector: Differential refractometer

[0706] Flow rate: 1.0 ml / min

[0707] Column temperature: 140℃

[0708] Sample concentration: 0.1 wt%

[0709] (Weight-average molecular weight (Mw) of polyethylene)

[0710] The molecular weight distribution curve of polyethylene is obtained 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), and the weight-average molecular weight is calculated.

[0711] (Weight-average molecular weight (Mw) of the resin composition)

[0712] The Q factor value of the polyolefin with the largest mass fraction is used, and the weight-average molecular weight is calculated in the same manner as for polyethylene.

[0713] <Viscosity-average molecular weight (Mv)>

[0714] Based on ASTM-D4020, determine the intrinsic viscosity [η] of polyethylene at 135°C in decahydronaphthalene solvent. Calculate the Mv of polyethylene using the following formula.

[0715] [η] = 6.77 × 10 -4 Mv 0.67

[0716] <Mel mass flow rate (MFR) (g / 10min)>

[0717] The MFR value is determined by the weight of resin extruded for 10 minutes at 190°C and under a load of 2.16 kg using a melt flow rate tester (MELT INDEXER F-F01) manufactured by Toyo Seiki Co., Ltd.

[0718] <TOF-SIMS Analysis and Image Processing>

[0719] For the separators used in energy storage devices, TOF-SIMS analysis was performed. A nano-TOF (TRIFTV) manufactured by ULVAC-PHI, INCORPORATED, was used as the TOF-SIMS mass spectrometer. The analytical conditions were set as follows to detect calcium ions (equivalent to positive ions at m / z = 40).

[0720] [Image Measurement Conditions]

[0721] Primary ion: Bismuth (Bi1) + )

[0722] Accelerating voltage: 30kV

[0723] Ion current: approximately 0.5 nA (DC).

[0724] There is bundling.

[0725] Analysis area: 100μm × 100μm

[0726] Analysis time: 90 minutes

[0727] Detected ions: Positive ions (m / z = 40)

[0728] Neutralization: Electron gun + Ar monomer ions

[0729] Vacuum level: Approximately 5.0 × 10⁻⁶ -5 Pa

[0730] [Depth-direction measurement conditions]

[0731] Analysis conditions

[0732] Primary ion: Bismuth (Bi1) + )

[0733] Accelerating voltage: 30kV

[0734] Ion current: Approximately 1.2 nA (DC).

[0735] There is a cluster

[0736] Analysis area: 100μm × 100μm

[0737] Analysis time: 5 frames / loop

[0738] Detected ions: Positive ions (m / z = 40)

[0739] Neutralization: Electron gun + Ar monomer ions

[0740] Vacuum level: Approximately 5.0 × 10⁻⁶ -5 Pa

[0741] Sputtering conditions

[0742] Sputtered ions: GCIB(Ar 2500 + )

[0743] Accelerating voltage: 20kV

[0744] Ion current: approximately 5 nA

[0745] Sputtering area: 400μm × 400μm

[0746] Splash time: 30 seconds / cycle

[0747] Neutralization: Electron gun + Ar monomer ions

[0748] The image data of the TOF-SIMS spectrum obtained above is processed according to the following steps.

[0749] (1) Create a filter that matches the beam shape (diameter 2μm, pixel resolution 0.39μm). The filter value is calculated using the fspecial function in the Image Processing Toolbox of MATLAB, a numerical computing software manufactured by Mathworks.

[0750] fspecial("gaussian", [13 13], 1.69865)

[0751] (2) Apply the created filter to 2D data.

[0752] (3) Calculate the mean and standard deviation of the 2D data after applying the filter.

[0753] (4) Binarize the values ​​by using the mean + standard deviation × 3 as the threshold. In the case of a normal distribution, 99.74% of the values ​​will fall within the range of mean + standard deviation × 3, thus aiming to extract the special parts of the values.

[0754] (5) Perform a 7-pixel dilation / contraction to connect the nearby extraction areas.

[0755] (6) Remove areas with small size (less than 50 pixels).

[0756] (7) Calculate the parameters for the remaining regions.

[0757] Extract area (pixels) and centroid position (x0, y0).

[0758] Maximum value in the region, average value of the region, weighted center position (x) m y m )

[0759] (8) Calculate the distance between the center positions of each weight.

[0760] The calculation was performed using the WeightedCentroid option of the regionprops function in the Image Processing Toolbox of MATLAB, a numerical computation software manufactured by Mathworks.

[0761] regionprops(cc,I,'WeightedCentroid')

[0762] Here, cc is a variable representing the extracted region, and I is a variable storing the 2D data after the filter is applied.

[0763] The above processing was used to determine the island structure of calcium ions, and the number, size, and weighted distance between the central positions were calculated.

[0764] <Heat shrinkage rate at 150℃ (%)>

[0765] A sample piece measuring TD100mm × MD100mm was taken from the separator of the energy storage device and placed in an oven at 150℃ for 1 hour. During this time, the sample piece was sandwiched between two sheets of paper to avoid direct hot air blowing on it. After removing the sample piece from the oven and cooling it, the area of ​​the sample piece was measured, and the heat shrinkage rate at 150℃ was calculated using the following formula.

[0766] Heat shrinkage rate at 150℃ (%) = {(10,000 (mm)} 2 - Area of ​​the heated sample piece (mm²) 2 )) / 10,000(mm 2 )}×100

[0767] <Preparation of non-aqueous electrolytes>

[0768] A non-aqueous electrolyte was prepared by adding 0.3 mol / L lithium hexafluorophosphate (LiPF6), 1 mol / L lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), and 20 ppm lithium fluorosulfonate (LiFSO3) as electrolytes to a mixed solution of 5 vol% acetonitrile, 62.5 vol% methyl ethyl carbonate, 30 vol% ethylene carbonate, and 2.5 vol% vinylene carbonate.

[0769] <Electrolyte thermal shrinkage rate at 150℃ (%)>

[0770] A sample piece (TD100mm × MD100mm) was taken from the energy storage device using a separator and placed in an aluminum bag. The non-aqueous electrolyte was then injected until the sample piece was completely submerged, and the sample was left to stand for one week. Next, it was placed in an oven at 150°C for one hour. The sample piece was then removed from the oven, cooled, and its area was measured. The thermal shrinkage rate at 150°C in the electrolyte was calculated using the following formula.

[0771] Electrolyte thermal shrinkage rate at 150℃ (%) = {(10,000 (mm)} 2 - Area of ​​the heated sample piece (mm²) 2 )) / 10,000(mm 2 )}×100

[0772] <Film thickness (μm)>

[0773] Regarding the film thickness of the separator for the energy storage device, the film thickness was measured using a miniature thickness gauge manufactured by Toyo Seiki (trademark), at room temperature of 23±2°C and relative humidity of 60%. Specifically, the film thickness was measured at approximately equal intervals along the entire TD direction, and their average value was obtained. The film thickness of the polyolefin substrate layer (“film thickness of the substrate layer” in the table) was measured after removing the coating films (inorganic particle layer and thermoplastic polymer layer) from the separator for the energy storage device. The film thickness of the inorganic particle layer was calculated by further subtracting the film thickness of the polyolefin substrate layer from the film thickness of the inorganic coating layer after removing the thermoplastic polymer layer from the separator for the energy storage device and measuring the film thickness (film thickness of the polyolefin substrate layer and inorganic coating layer). The film thickness of the thermoplastic polymer layer was calculated by subtracting the film thickness of the polyolefin substrate layer and inorganic coating layer from the film thickness of the separator for the energy storage device.

[0774] Breathability (sec / 100cm) 3 )>

[0775] Based on JIS P-8117 (2009), the permeability of separators for energy storage devices was measured per 100 cm using a Glaley G-B2 (trademark) air permeability meter manufactured by Toyo Seiki Co., Ltd. 3 Air permeability of volume.

[0776] <Porosity (%)>

[0777] A 10cm × 10cm square sample was cut from the separator of the energy storage device after the coating was removed. Calculate the volume of the sample (cm³). 3 ) and mass (g), derived from these and density (g / cm³) 3 The porosity is calculated using the following formula. It should be noted that the density of the mixture is a value calculated from the individual densities of the raw materials used and their mixing ratio.

[0778] Porosity (%) = (Volume - Mass / Density of the mixture) / Volume × 100

[0779] <Conversion of puncture strength (gf) and weight per unit area to puncture strength (gf / (g / m²))> 2 ))>

[0780] Using a Kato-tech handheld compression tester, the "KES-G5" (trademark), a sample holder with the coating removed was used to fix a battery storage device separator. The separator was then subjected to a puncture test at the center of the fixed separator under conditions of a needle tip radius of curvature of 0.5 mm, a puncture speed of 2 mm / s, a temperature of 23°C, and a humidity of 40%. This yielded the initial puncture strength (gf), representing the maximum puncture load. The puncture strength (gf) was also calculated as the weight per unit area (gf / (g / m²)). 2 (The weight per unit area in the table is converted to puncture intensity).

[0781] <weight per unit area (g / m²) 2 )>

[0782] A 10cm x 10cm square sample was cut from the separator of the energy storage device after the thermoplastic polymer layer was removed. The weights of the polyolefin substrate layer and the inorganic coating layer were determined using an AEL-200 electronic balance manufactured by Shimadzu Corporation. The obtained weights were magnified 100 times and calculated per 1m 2 The unit area weight (g / m²) of the polyolefin substrate layer and the inorganic coating layer 2 Then, 10cm × 10cm square samples were cut from the energy storage device after the coating layers (inorganic coating layer and thermoplastic polymer layer) were removed using a separator, and the mass was measured using an AEL-200 electronic balance manufactured by Shimadzu Corporation. The obtained mass was magnified 100 times and calculated per 1m 2 The unit area weight (g / m²) of the polyolefin substrate layer 2 (Weight per unit area of ​​the substrate layer in the table). From per 1m 2 The unit area weight (g / m²) of the polyolefin substrate layer and the inorganic coating layer 2 Subtract 1m 2 The unit area weight (g / m²) of the polyolefin substrate layer 2 ), thus calculating every 1m 2 The unit area weight of the inorganic coating (the load of the inorganic coating relative to the polyolefin substrate layer, g / m²) 2 ).

[0783] <Powder shedding (%)>

[0784] Cut a 10cm × 10cm square sample from the separator of the energy storage device and weigh it (g). After fixing one side to thick paper, place a 5cm diameter, 900g weight wrapped in cotton cloth on the inorganic particle layer side and rub them at 50rpm for 10 minutes. Then accurately measure the mass (g) again and determine the powder shedding property using the following formula.

[0785] Dusting property (mass%) = {(mass before friction (g) - mass after friction (g)) / mass before friction} × 100

[0786] <Battery cycle test capacity retention rate (%) in the first embodiment>

[0787] (1) Production of the positive electrode

[0788] The positive electrode active material is a nickel, manganese, and cobalt composite oxide (LiNiMnCoO2)(NMC) (Ni:Mn:Co = 6:2:2 (elemental ratio), density 3.50 g / cm³. 3 90.4% by mass of graphite powder (density 2.26 g / cm³) used as a conductive auxiliary material 3 1.6% by mass of number-average particle size (6.5 μm) and acetylene black powder (density 1.95 g / cm³). 3 The number-average particle size was 48 nm, 3.8% by mass, and PVDF (density 1.75 g / cm³) was used as a resin binder. 3 4.2% by mass were mixed and dispersed in NMP to prepare a slurry. This slurry was then coated onto one side of a 20 μm thick aluminum foil, which would become the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the foil was compressed using a roller press to form the positive electrode. At this point, the coating amount of the positive electrode active material was 109 g / m². 2 .

[0789] (2) Fabrication of the negative electrode

[0790] Graphite powder A (density 2.23 g / cm³) is used as the negative electrode active material. 3 Number-average particle size 12.7 μm) 87.6% by mass, graphite powder B (density 2.27 g / cm³) 3A slurry was prepared by dispersing 9.7% by mass of a mixture of carboxymethyl cellulose (6.5 μm) as a number-average particle size, 1.4% by mass of ammonium salt of carboxymethyl cellulose (as a resin binder, calculated as solids) (1.83% by mass aqueous solution), and 1.7% by mass of diene rubber latex (40% by mass aqueous solution) in purified water. This slurry was then coated onto 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, the foil was compressed using a roller press to form the negative electrode. At this point, the coating amount of the negative electrode active material was 52 g / m². 2 .

[0791] (3) Preparation of non-aqueous electrolytes

[0792] A non-aqueous electrolyte was prepared by adding 0.3 mol / L lithium hexafluorophosphate (LiPF6), 1 mol / L lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), and 20 ppm lithium fluorosulfonate (LiFSO3) as electrolytes to a mixed solution of 5 vol% acetonitrile, 62.5 vol% methyl ethyl carbonate, 30 vol% ethylene carbonate, and 2.5 vol% vinylene carbonate.

[0793] (4) Fabrication of a single-layer laminated non-aqueous secondary battery

[0794] The positive and negative electrodes prepared as described above are overlapped with their coating surfaces facing each other, separated by a separator (the separator in the embodiment or the separator in the comparative example), to form a stacked electrode body. This stacked electrode body is housed in a 100mm × 60mm aluminum laminate shell and vacuum-dried at 80°C for 5 hours to remove moisture. After injecting a non-aqueous electrolyte into the shell, the shell is sealed, thereby fabricating a single-layer laminated (pouch-type) non-aqueous secondary battery. The design capacity of this single-layer laminated non-aqueous secondary battery is 3Ah, and the rated voltage is 4.2V.

[0795] (5) Determination of capacity retention rate in cyclic testing

[0796] For the single-layer laminated non-aqueous secondary battery obtained above, the initial charge treatment and cycle characteristics evaluation were performed according to the following steps. Charge and discharge were conducted using a charge / discharge apparatus ACD-M01A (trade name) manufactured by Asuka Electronics Co., Ltd. and a programmed temperature control bath IN804 (trade name) manufactured by Yamato Scientific Co., Ltd. 1C refers to the current value at which a fully charged battery is discharged at a constant current, with the discharge expected to end in 1 hour. Specifically, in the following steps, 1C specifically refers to the current value at which a fully charged battery is discharged from a 4.2V state to 3.0V at a constant current, with the discharge expected to end in 1 hour.

[0797] • First charge processing

[0798] With the ambient temperature of the battery set to 25°C, it was charged at a constant current of 0.075A (equivalent to 0.025C) until it reached 3.1V, then charged at a constant voltage of 3.1V for 1.5 hours. After a 3-hour rest period, the battery was charged at a constant current of 0.15A (equivalent to 0.05C) until it reached 4.2V, then charged at a constant voltage of 4.2V for 1.5 hours. Finally, the battery was discharged to 3.0V with a constant current of 0.45A (equivalent to 0.15C).

[0799] Cyclic testing of single-layer laminated non-aqueous secondary batteries

[0800] For batteries that have undergone their first charge-discharge treatment, a cycle test is performed. It should be noted that the cycle test begins after the ambient temperature of the battery is set to 25°C for 3 hours. First, the battery is charged at a constant current of 3A (equivalent to 1C) until it reaches 4.2V, then charged at a constant voltage of 4.2V for a total of 3 hours. Then, the battery is discharged to 3.0V at a constant current of 3A. One charge and one discharge cycle constitutes one cycle, and 100 charge-discharge cycles are performed. The discharge capacity of the 100th cycle, with the discharge capacity of the first cycle set to 100%, is calculated as the capacity retention rate (%) after 100 cycles.

[0801] <Fusion temperature and short-circuit temperature (°C) in the first embodiment>

[0802] The positive electrode, the energy storage device separator, and the negative electrode were cut into 200mm diameter circles and overlapped to obtain a laminate. A non-aqueous electrolyte was added to the laminate and allowed to permeate throughout. The laminate was clamped in the center using a 600mm diameter circular aluminum heater, and a hydraulic jack was used to pressurize the heater from above and below at 0.5MPa. While heating the laminate with the aluminum heater at a heating rate of 2°C / min, the resistance (Ω) between the electrodes was measured. The temperature at which the resistance of the separator first exceeded 1000Ω was taken as the melting temperature. Furthermore, heating was continued until the resistance dropped below 1000Ω, which was taken as the short-circuit temperature.

[0803] <Battery crush test>

[0804] The laminated battery, after undergoing low-temperature cycling test, was set up with a 1mm height difference between itself and the test stage, holding both ends of the battery. A crushing test was performed by crushing the battery with a 15.8mm diameter SUS round rod at a crushing speed of 0.2mm / s and a force of 1.95ton until the voltage dropped from 4.1V to 4.0V. The time taken for the voltage to reach 4.0V was measured. This test was conducted on 100 batteries, and the number of batteries whose voltage reached 4.0V from 4.1V for more than 5 seconds was compared.

[0805] <Electrode Residual Rate (%)>

[0806] The fabricated single-layer laminated non-aqueous secondary battery was disassembled, the separator was separated from the electrode, the negative electrode was photographed with a digital camera, and the percentage of negative electrode composite material remaining on the copper foil was calculated.

[0807] Thermal Response Index

[0808] A sample sheet, TD100mm×MD100mm, obtained from the separator of the energy storage device, was placed in an oven at 150°C for a specified time. During this time, to avoid direct hot air blowing onto the sample sheet, it was sandwiched between multiple sheets of paper. Furthermore, to determine the temperature reached by the separator, a heating label "10R-104" manufactured by Iippi Giken was also sandwiched between the multiple sheets of paper. The heating rate of the separator could be adjusted by changing the number of sheets of paper. The number of sheets of paper was adjusted to achieve a heating rate of 2°C / minute for the separator. The sample sheet was removed from the oven, cooled, and its area was measured. The thermal response index at the indicated temperature of the heating label was calculated using the following formula.

[0809] Thermal response index (%) = {(10,000 (mm)} 2 - Area of ​​the heated sample piece (mm²) 2 )) / 10,000(mm 2 )}×100

[0810] For the specified time, the experiment was repeated by changing it by 5 seconds each time, from 5 seconds to 3 minutes, and the thermal response index at each temperature was calculated.

[0811] Quantification of resin aggregates in separators

[0812] The resin aggregate in the separator is defined as an area with a length of 100 μm × width of 100 μm or more that is opaque, when observed using a transmission optical microscope after the film-forming process of the examples and comparative examples described later. In the observation based on the transmission optical microscope, the area per 1000 μm was measured. 2 The number of resin aggregates per square meter of the separator area.

[0813] <Cyclic test, nail puncture test, hot box test, and high-temperature bar impact failure test in the second embodiment>

[0814] (The fabrication of the batteries used in the safety tests)

[0815] a. Production of the positive electrode

[0816] The lithium-nickel-manganese-cobalt composite oxide (LiNi) will be used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 A slurry was prepared by dispersing 92.2% by mass O2, 2.3% by mass each of flake graphite and acetylene black as conductive materials, and 3.2% by mass polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP). The slurry was coated onto one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the foil was compressed into shape using a roller press. At this point, the coating weight of the active material for the positive electrode was adjusted to 250 g / m². 2 The bulk density of the active substance was adjusted to 3.00 g / cm³. 3 .

[0817] b. Negative electrode fabrication

[0818] A slurry was prepared by dispersing 96.9% by mass of artificial graphite (as the negative electrode active material), 1.4% by mass of ammonium salt of carboxymethyl cellulose (as a binder), and 1.7% by mass of styrene-butadiene copolymer latex in purified water. The slurry was then coated onto one side of a 12 μm thick copper foil constituting the negative electrode current collector using a die coater. After drying at 120°C for 3 minutes, the foil was compressed into shape using a roller press. At this point, the coating amount of the active material for the negative electrode was adjusted to 106 g / m². 2 The bulk density of the active substance was adjusted to 1.35 g / cm³. 3 .

[0819] c. Preparation of non-aqueous electrolytes

[0820] The product is prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate and methyl ethyl carbonate in a ratio of 1:2 (volume ratio) at a concentration of 1.0 mol / L.

[0821] d. Battery assembly

[0822] The separator was cut into circles with a diameter of 18 mm, and the positive and negative electrodes were cut into circles with a diameter of 16 mm. The positive electrode, separator, and negative electrode were stacked sequentially with their active material faces facing each other, and placed in a covered stainless steel container. The container and lid were insulated from each other; 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 step c. above was poured into the container and sealed. After being left at room temperature for one day, the battery was charged at 3 mA (0.5C) to a voltage of 4.2V at 25°C. Once reached, the current was gradually reduced from 3 mA while maintaining the voltage at 4.2V. This first charge was performed for 6 hours after battery fabrication. Then, the battery was discharged at 3 mA (0.5C) to a voltage of 3.0V.

[0823] (Cyclic performance evaluation)

[0824] The resulting battery underwent 1000 charge-discharge cycles at 60°C. Charging was performed at a current of 6.0 mA (1.0C) until the battery voltage reached 4.2V. After reaching this voltage, the current was gradually reduced from 6.0 mA while maintaining 4.2V, and this charging process was repeated for a total of 3 hours. Discharging was performed at a current of 6.0 mA (1.0C) until the battery voltage reached 3.0V. Capacity retention was calculated using the discharge capacity from the 1000th cycle and the discharge capacity from the 1st cycle. A high capacity retention indicates good cycle performance.

[0825] (Prick test)

[0826] After the aforementioned 1000 cycles, an iron nail was driven into the battery, which had been charged to 4.2V, at a speed of 20mm / s until it penetrated through, thus inducing an internal short circuit. In this test, the phenomena of an internal short circuit were elucidated by measuring the time-varying behavior of the battery voltage drop and the rise in battery surface temperature caused by the internal short circuit. Furthermore, during an internal short circuit, sometimes insufficient sealing of the separator or membrane rupture at low temperatures can trigger a rapid exothermic reaction in the battery. This can sometimes lead to electrolyte ignition, battery smoke, and / or explosion.

[0827] The pass / fail status of batteries that have undergone the nail puncture test as described above is determined. For the same separator, the nail puncture test is performed on 100 batteries, and the number of batteries that do not catch fire, smoke, or explode is calculated as the pass rate (%).

[0828] (Hot Box Test)

[0829] The batteries obtained through the above "d. Battery Assembly" were stored in a high-temperature chamber set at 150°C for 1 hour each, and the state of the batteries was observed during and after storage.

[0830] If the polyolefin separator has undergone heat shrinkage due to high-temperature storage, an internal short circuit may occur at the two terminals of the battery, namely the positive and negative terminals, sometimes resulting in fire or explosion. Batteries in which fire or explosion is observed are considered defective. Batteries in which no fire or explosion is observed are considered acceptable.

[0831] For the same separator, perform the hot box test on 100 batteries and calculate the pass rate (%).

[0832] (High-temperature rod impact failure test)

[0833] Figure 12 This is a schematic diagram of a high-temperature bar impact failure test (impact test).

[0834] In impact testing, on a specimen mounted on a test bench, the specimen and a round bar are subjected to impact. The round bar was placed roughly orthogonally, and an 18.2 kg weight was dropped from a height of 61 cm onto the round bar. The effect of the impact on the sample was then observed.

[0835] The following is for reference Figure 12 The steps of the impact tests in the examples and comparative examples are described.

[0836] For the cylindrical batteries selected for evaluation and assembled as described in “d. Battery Assembly” above, constant current constant voltage (CCCV) charging was performed for 3 hours at a current of 3000mA (1.0C) and a termination battery voltage of 4.2V.

[0837] Then, at 150°C, a cylindrical battery is placed horizontally on a flat surface, and a 15.8mm diameter stainless steel rod is positioned so as to cut across the center of the battery. The rod is positioned with its long axis parallel to the MD of the separator. An 18.2kg weight is dropped from a height of 61cm above the rod positioned at the center of the battery, applying an impact perpendicular to the longitudinal axis of the battery. After the impact, the condition of the battery is observed, and the surface temperature of the battery is measured as needed. Batteries that are observed to ignite or explode are deemed unqualified, while batteries that are not observed to ignite or explode are deemed qualified.

[0838] For the same separator, 100 batteries were subjected to the high-temperature rod impact failure test, and the pass rate (%) was calculated.

[0839] <Fuse / Melting Debris (F / MD) Characteristics in the Second Embodiment>

[0840] The positive electrode, separator, and negative electrode were cut into 200mm diameter circles and overlapped. An electrolyte containing electrolyte was added to the resulting laminate, allowing it to permeate the entire structure. The laminate was clamped in the center using a 600mm diameter circular aluminum heater, and the heater was pressurized to 0.5 MPa from top to bottom using a hydraulic jack to prepare for the measurement. The laminate was heated with the aluminum heater at a heating rate of 2°C / min while the resistance (Ω) between the electrodes was measured. The temperature at which the separator melted and the resistance between the electrodes increased, first exceeding 1000Ω, was taken as the melting temperature (shutdown temperature). Furthermore, heating was continued until the resistance decreased to below 1000Ω, which was taken as the melting and rupture temperature (film breaking temperature). It should be noted that on the back of the aluminum foil of the positive electrode produced through item "a. Production of the positive electrode" in the above-mentioned "Cyclic Test in the Second Embodiment", a resistance measuring wire was attached with conductive silver paste. Furthermore, on the back of the copper foil of the negative electrode prepared through item "b. Preparation of the negative electrode" in the "Cyclic Test in the Second Embodiment" described above, a resistance measuring wire is attached with conductive silver paste. Further, the electrolyte containing electrolyte prepared through item "c. Preparation of the non-aqueous electrolyte" in the "Cyclic Test in the Second Embodiment" described above is also used for the F / MD characteristic test.

[0841] I. Examples and Comparative Examples in the First Embodiment

[0842] Manufacturing of separators for energy storage devices

[0843] <Manufacturing of Silane-Grafted Modified Polyolefins>

[0844] Polyethylene with a viscosity-average molecular weight (Mv) of 120,000 was used as the raw material for silane-modified polyethylene (resin a). While the raw polyethylene was melt-blended using an extruder, an organic peroxide (di-tert-butyl peroxide) was added to generate free radicals within the α-olefin polymer chain. Then, trimethoxyalkylene oxide was injected into the melt blend to replace vinylsilane, initiating an addition reaction. Alkoxysilanes were introduced into the α-olefin polymer through the addition reaction, forming a silane graft structure. Simultaneously, to adjust the free radical concentration in the system, an appropriate amount of antioxidant (pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) was added to inhibit the chain-like chain reaction (gelation) within the α-olefin. The resulting silane-modified polyethylene melt resin was cooled in water and processed into granules. The granules were heated and dried at 80°C for 2 days to remove moisture and unreacted trimethoxyalkylene oxide-substituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkylene oxide-substituted vinylsilane in the feed particles is below 3000 ppm.

[0845] <Fabrication of the Substrate Layer (Layer A)>

[0846] As the resin material for layer A, 30% by mass of the silane-modified polyethylene (resin a) obtained above, 30% by mass of ultra-high molecular weight polyethylene (resin b) as a homopolymer with a viscosity-average molecular weight of 4,500,000, and 40% by mass of ultra-high molecular weight polyethylene (resin c) as a homopolymer with a viscosity-average molecular weight of 700,000 were used. Then, 1000 ppm by mass of pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant and 3000 ppm by mass of calcium stearate relative to the total mass of the resin material were added, and the mixture was dry-mixed using a drum mixer to obtain the raw material mixture for layer A.

[0847] The resulting raw material mixture (layer A) was fed into different twin-screw extruders under a nitrogen atmosphere via a feeder. The liquid paraffin (kinematic viscosity at 37.78℃ was 7.59 × 10⁻⁶) was then used. -5 m 2 The liquid paraffin ( / s) is injected into each extruder drum via a plunger pump. The raw material mixture and liquid paraffin are melt-blended within the extruder, with the feeder and pump adjusted to ensure that the liquid paraffin constitutes 70% by mass based on the total mass of the extruded melt blend. The melt-blending conditions are set at a temperature of 230°C, a screw speed of 240 rpm, and a discharge rate of 18 kg / h. The melt blend is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast, resulting in a gel sheet (sheet-shaped molded body) with a preform thickness of 1370 μm.

[0848] The gel sheet was guided to a biaxial stretching machine for biaxial stretching to obtain a stretched product. The stretching conditions were set as follows: MD ratio 7.0, TD ratio 6.4 (i.e., 7 × 6.3), and biaxial stretching temperature 122°C. The stretched gel sheet was then guided to a dichloromethane bath for thorough impregnation to remove liquid paraffin. The dichloromethane was then dried to obtain a porous sheet. The porous sheet was then guided to a TD stretching machine for heat setting (HS) at a temperature of 133°C and a stretching ratio of 1.9, followed by relaxation to a TD ratio of 1.75 to obtain a microporous membrane substrate. The ends of the microporous membrane substrate were trimmed, and the substrate was wound into a master roll 1,100 mm wide and 5,000 m long. The resulting microporous membrane substrate had a thickness of 10 μm.

[0849] <Formation of the Inorganic Particle Layer (B Layer)>

[0850] Acrylic latex used as a resin binder for inorganic particulate layers was manufactured using the following method. 70.4 parts by weight of ion-exchanged water, 0.5 parts by weight of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and 0.5 parts by weight of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers were added to a reaction vessel equipped with a mixer, reflux condenser, dropping tank, and thermometer. Next, the temperature inside the reaction vessel was raised to 80°C, and while maintaining this temperature, 7.5 parts by weight of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over a period of 150 minutes. It should be noted that the above emulsion was prepared by mixing a mixture of 70 parts by mass of butyl acrylate, 29 parts by mass of methyl methacrylate, 1 part by mass of methacrylic acid, 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) as emulsifiers, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate, and 52 parts by mass of deionized water using a high-speed mixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous solution of ammonium hydroxide, and a small amount of water was added to obtain an acrylic latex with a solid content of 40%. The number average particle size of the obtained acrylic latex was 145 nm, and the glass transition temperature was -23°C.

[0851] A dispersion was prepared by uniformly dispersing 95 parts by mass of alumina hydroxide (boehmite, average particle size 1.4 μm) as inorganic particles and 0.4 parts by mass (solid content conversion) of an aqueous solution of ammonium polycarboxylate (manufactured by SNDOS, SNDOS 5468, solid content concentration 40%) as an ionic dispersant in 100 parts by mass of water. The resulting dispersion was then pulverized using a bead mill (200 cc tank volume, 0.1 mm diameter zirconia microspheres, 80% filling rate) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm, thereby preparing a slurry containing inorganic particles. 2.0 parts by mass (solid content conversion) of the aforementioned acrylic latex as a resin binder, prepared above, were added to the particle size-adjusted dispersion to obtain a slurry containing inorganic particles. The substrate was continuously unwound from a microporous membrane substrate master roll, and the slurry containing inorganic particles was coated on both sides of the substrate using a gravure reverse coating machine. The coated substrate was dried in a dryer at 60°C to remove water, resulting in a substrate with inorganic particle layers on both sides. This substrate was then wound up to obtain a master roll of the substrate with inorganic particle layers. The inorganic particle layers contained 95% aluminum hydroxide by mass, and the film thickness of the inorganic particle layers was 5 μm on both sides (approximately 2.5 μm on one side).

[0852] <Formation of the thermoplastic polymer layer (C layer)>

[0853] The coating solution for acrylic resins is prepared as follows: 70.4 parts by weight of ion-exchanged water, 0.5 parts by weight of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and 0.5 parts by weight of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Co., Ltd.) are added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer. The internal temperature of the reaction vessel is raised to 80°C, and while maintaining this temperature, 7.5 parts by weight of ammonium persulfate (2% aqueous solution) are added. Five minutes after adding the ammonium persulfate aqueous solution, add 15.9 parts by weight of methyl methacrylate, 74.5 parts by weight of n-butyl acrylate, 2 parts by weight of 2-ethylhexyl acrylate, 0.1 parts by weight of methacrylic acid, 0.1 parts by weight of acrylic acid, 2 parts by weight of 2-hydroxyethyl methacrylate, 5 parts by weight of acrylamide, 0.4 parts by weight of glycidyl methacrylate, 0.4 parts by weight of trimethylolpropane triacrylate (A-TMPT, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.), 3 parts by weight of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and "ADEKAREASOAP". An emulsion was prepared by mixing 3 parts by weight of SR1025 (registered trademark, manufactured by ADEKA Co., Ltd., 25% aqueous solution), 0.05 parts by weight of sodium p-styrene sulfonate, 7.5 parts by weight of ammonium persulfate (2% aqueous solution), 0.3 parts by weight of γ-methacryloyloxypropyltrimethoxysilane, and 52 parts by weight of deionized water in a high-speed mixer for 5 minutes. The resulting emulsion was then added dropwise from a dropping tank to a reaction vessel over 150 minutes. After the emulsion addition was complete, the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 9.0 with ammonium hydroxide aqueous solution (25% aqueous solution) to obtain a 40% acrylic resin (acrylic copolymer latex). This was diluted with deionized water to a solid content of 5% by weight to prepare a coating solution.

[0854] The coating solution for polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared as follows: A PVDF-HFP copolymer emulsion (KYNAR FLEX2501-20, Tg: -40℃) manufactured by ARKEMA was diluted with deionized water to a weight of 5% by weight based on solids content, thereby preparing the coating solution.

[0855] The acrylic resin or PVDF-HFP coating liquid prepared above is applied to both sides of a master roll of substrate with an inorganic particle layer using a gravure coating machine to form a thermoplastic polymer layer with the thickness and coverage area ratios shown in Tables 8 to 14. The layer is then cut as needed to obtain a separator for an energy storage device.

[0856] Examples 1-68

[0857] As shown in Tables 8-14, the stacking method, materials, and film thickness of layers A through C were changed, and the separator for the energy storage device was manufactured using the method described above. The evaluation results are shown in Tables 8-14.

[0858] In Example 66, instead of the positive electrode produced in "a. Production of the positive electrode" above, a positive electrode containing a LiCoO2 layer as the positive electrode material (LCO positive electrode) was used. In Example 67, when forming the inorganic particle layer in the "Formation of the Inorganic Particle Layer (B Layer)" above, instead of acrylic latex as the resin binder, "EPOCROS K-2010E" (registered trademark, Nippon Shokubai Co., Ltd., glass transition temperature -50°C) was used. In Example 68, when forming the inorganic particle layer in the "Formation of the Inorganic Particle Layer (B Layer)" above, instead of acrylic latex as the resin binder, "JE-1056" (registered trademark, Seikatsu PMC Co., Ltd., glass transition temperature 82°C) was used.

[0859] Comparative Examples 1-6

[0860] As shown in Table 15, the separators for energy storage devices are manufactured by changing the stacking method, materials, and film thickness of layers A through C. The evaluation results are shown in Table 15.

[0861] It should be noted that in Comparative Example 4, before assembling the battery using the obtained polyolefin microporous membrane, electron beam crosslinking was performed by irradiating it with a 120 kGy electron beam using an EYE Compact EB (trademark) irradiation device manufactured by Iwasaki Electric Co., Ltd. The obtained electron beam crosslinked microporous membrane and battery were evaluated according to the evaluation methods described above.

[0862] In addition, in Comparative Examples 5 and 6, when preparing polyolefin microporous membranes, a catalyst for forming tin-based siloxane bonds was added to the extruded material during the extrusion process, and crosslinking was carried out after the separator was formed and during the liquid paraffin extraction process, respectively.

[0863] [Table 8]

[0864]

[0865] [Table 9]

[0866]

[0867] [Table 10]

[0868]

[0869] [Table 11]

[0870]

[0871] [Table 12]

[0872]

[0873] [Table 13]

[0874]

[0875] [Table 14]

[0876]

[0877] [Table 15]

[0878] Table 15.

[0879]

[0880] II. Examples and Comparative Examples in the Second Embodiment

[0881] Preparation of Silane-Grafted Modified Polyolefins

[0882] The raw material polyolefin used in silane graft-modified polyolefins can have a viscosity-average molecular weight (Mv) of 100,000 or more and 1,000,000 or less, a weight-average molecular weight (Mw) of 30,000 or more and 920,000 or less, and a number-average molecular weight of 10,000 or more and 150,000 or less. It can be a propylene or butene copolymer α-olefin. While the raw material polyethylene is melt-blended using an extruder, an organic peroxide (di-tert-butyl peroxide) is added. After free radicals are generated in the α-olefin polymer chain, trimethoxyalkylene oxide is injected to replace vinylsilane. Alkoxysilane is introduced into the α-olefin polymer through an addition reaction to form a silane graft structure. In addition, to adjust the free radical concentration in the system, an appropriate amount of antioxidant (pentaerythritol tetratetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) is added to inhibit the chain-like chain reaction (gelation) in the α-olefin. The obtained silane-grafted polyolefin molten resin was cooled in water, granulated, and then dried at 80°C for 2 days to remove moisture or unreacted trimethoxyalkylene oxide-substituted vinylsilane. It should be noted that the residual concentration of unreacted trimethoxyalkylene oxide-substituted vinylsilane in the granules is approximately 1000–1500 ppm.

[0883] In Tables 16-23, the silane-grafted modified polyolefins obtained by the above preparation method are referred to as "silane-modified polyethylene".

[0884] Preparation methods of modified PE and copolymers with various functional groups other than silane-modified PE

[0885] Modified PE and copolymers with various functional groups, excluding silane-modified PE, are manufactured according to the following methods.

[0886] For any given raw material, the molecular weight (MI) is adjusted to be within the range of 0.5 to 10. Hydroxyl-modified PE is manufactured by saponifying and neutralizing EVA copolymers. Amine-modified, oxazoline-modified, and other modified resins are subjected to hydrogen peroxide conditions, where a tungsten-based catalyst is applied to the terminal vinyl groups of PE polymerized using a chromium catalyst, converting the vinyl groups into epoxy groups. Then, using a known functional group conversion organic reaction, the target reaction site is converted into the desired functional group, yielding various modified PEs. For example, in the case of amine-modified PE, while melt-blending the epoxy-modified PE at 200°C in an extruder, a primary or secondary amine is injected in liquid form to carry out the reaction. Then, unreacted amines are removed through a pressure reducing valve, and the resulting amine-modified resin is extruded into filaments and cut into granules.

[0887] In Tables 16-23, the modified PE obtained by the above preparation method is referred to as one of "modified PE or copolymer (B)".

[0888] Example 2.1

[0889] Fabrication of polyolefin microporous membranes as substrates

[0890] To 79.2% by mass of a homopolymer polyethylene (UHMWPE(A)) with a weight average molecular weight of 720,000, 19.8% by mass of a silane-grafted polyethylene (PE(B)) with an MFR of 0.44 g / min (based on the above, the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), obtained by modifying a polyolefin with a viscosity average molecular weight of 120,000 by replacing vinylsilane with trimethoxyalkylene oxide), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, were dry-mixed using a drum mixer to obtain a mixture. The resulting mixture was fed to a twin-screw extruder under a nitrogen atmosphere via a feeder. Additionally, liquid paraffin (kinematic viscosity at 37.78°C 7.59 × 10⁻⁶) was pumped via a plunger pump. -5 m 2 / s) is injected into the extruder drum.

[0891] The mixture and liquid paraffin were melt-blended in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., the polymer concentration was 30% by mass). The melt-blending conditions were set at a temperature of 220°C, a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[0892] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with a blank film thickness of 1200 μm.

[0893] Next, the sheet-shaped molded body is guided to a biaxial stretching machine for biaxial stretching to obtain the stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 7.0 (i.e., 7.0 × 7.0), and biaxial stretching temperature 125℃.

[0894] Next, the stretched gel sheet is guided into a dichloromethane bath and fully impregnated in dichloromethane to extract and remove liquid paraffin. Then, it is dried to remove the dichloromethane and obtain a porous body.

[0895] Next, the porous body is guided to the TD stretcher for heat setting (HS) at a heat setting temperature of 123°C and a stretch ratio of 2.0. Then, a relaxation operation is performed until the stretch ratio in the TD direction is 1.8.

[0896] <Configuration containing thermoplastic polymer layer>

[0897] A coating solution was prepared by uniformly dispersing 7.5 parts by mass of a covering resin with the types and glass transition temperatures shown in Table 16 in 92.5 parts by mass of water. The solution was then coated onto one side of a polyolefin microporous membrane using a gravure coating machine to form a thermoplastic polymer layer with the film thickness and coverage area ratio shown in Table 16, thus obtaining a composite separator.

[0898] Then, for the composite separator, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[0899] During the above evaluation, the composite separators released from the master roll are cut as needed and used as evaluation separators.

[0900] For the evaluation of the separator and battery, various evaluations were conducted according to the above evaluation methods, and the evaluation results are shown in Table 16.

[0901] Examples 2.2-2.26 and Comparative Examples 2.1-2.5

[0902] As shown in Tables 16-23, the conditions for the microporous membrane used as the substrate, the composite construction conditions, the presence or absence of crosslinking during the fabrication of the microporous membrane, and the presence or absence of crosslinking after battery assembly were changed. Otherwise, the same operations as in Example 2.1 were performed to obtain the separators and batteries shown in Tables 16-23. The obtained separators and batteries were evaluated using the evaluation methods described above, and the evaluation results are also shown in Tables 16-23.

[0903] In Example 2.17, instead of the positive electrode fabricated in "a. Fabrication of the positive electrode" above, a positive electrode containing a Li(Al,Co)O2 layer as the positive electrode material (LAC positive electrode) is used.

[0904] In Example 2.18, the non-aqueous electrolyte with the same composition as the one prepared in "c. Preparation of non-aqueous electrolyte" above was used, and the LiPF6 concentration was adjusted to 5.0 mol / L.

[0905] It should be noted that in Comparative Examples 2.1 and 2.2, electron beam crosslinking was performed by irradiation with a specified dose before assembling the battery using the obtained polyolefin microporous membrane. Various evaluations were performed on the obtained electron beam crosslinked microporous membrane and battery according to the evaluation methods described above.

[0906] In addition, in Comparative Examples 2.4 and 2.5, in the fabrication of microporous membranes from polyolefins, a catalyst for forming tin-based siloxane bonds was added to the extruded material during the extrusion process, and crosslinking was performed after the separator was formed and during the liquid paraffin extraction process, respectively.

[0907] [Table 16]

[0908] Table 16.

[0909]

[0910] [Table 17]

[0911] Table 17.

[0912]

[0913] [Table 18]

[0914] Table 18.

[0915]

[0916] [Table 19]

[0917] Table 19.

[0918]

[0919] [Table 20]

[0920] Table 20.

[0921]

[0922] [Table 21]

[0923] Table 21.

[0924]

[0925] [Table 22]

[0926] Table 22.

[0927]

[0928] [Table 23]

[0929] Table 23.

[0930]

[0931] Example 3.1

[0932] Fabrication of polyolefin microporous membranes as substrates

[0933] To 79.2% by mass of a homopolymer polyethylene (UHMWPE(A)) with a weight average molecular weight of 730,000, 19.8% by mass of a silane-grafted polyethylene (PE(B)) with an MFR of 0.40 g / min (based on the above, the resin compositions of (A) and (B) are 0.8 and 0.2, respectively), obtained by modifying a polyolefin with a viscosity average molecular weight of 121,000 by replacing vinylsilane with trimethoxyalkylene oxide), and 1% by mass of pentaerythritol-tetra-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an antioxidant, were dry-mixed using a drum mixer to obtain a mixture. The resulting mixture was fed into a twin-screw extruder under a nitrogen atmosphere. Additionally, liquid paraffin (kinematic viscosity at 37.78°C 7.59 × 10⁻⁶) was pumped via a plunger pump. - 5m² / s) is injected into the extruder drum.

[0934] The mixture and liquid paraffin were melt-blended in an extruder. The feeder and pump were adjusted so that the liquid paraffin accounted for 70% by mass of the extruded polyolefin composition (i.e., the polymer concentration was 30% by mass). The melt-blending conditions were set at a temperature of 220°C, a screw speed of 240 rpm, and a discharge rate of 18 kg / h.

[0935] Next, the molten compound is extruded through a T-die onto a cooling roller with a surface temperature controlled at 25°C and then cast to obtain a gel sheet (sheet-shaped molded body) with a blank film thickness of 1250 μm.

[0936] Next, the sheet-shaped molded body is guided to a biaxial stretching machine for biaxial stretching to obtain the stretched material. The stretching conditions are set as follows: MD ratio 7.0, TD ratio 7.0 (i.e., 7×7), and biaxial stretching temperature 127°C.

[0937] Next, the stretched gel sheet is guided into a dichloromethane bath and fully impregnated in dichloromethane to extract and remove liquid paraffin. Then, it is dried to remove dichloromethane and obtain a porous body.

[0938] Next, the porous body is guided to the TD stretcher for heat setting (HS) at a heat setting temperature of 125°C and a stretch ratio of 2.0. Then, a relaxation operation is performed up to 1.9 times in the TD direction.

[0939] <Configuration of the active layer>

[0940] Alumina (Al2O3) particles as inorganic filler and the types of covering resin (fluorinated resins) shown in Table 24 are prepared. The two are mixed in the ratio of fluorinated resin mass to inorganic filler mass shown in Table 24. The mixture is further mixed with cyanoethyl polyvinyl alcohol and acetone in the mass ratio of mixture / cyanoethyl polyvinyl alcohol / acetone = 19.8 / 0.2 / 80 and uniformly dispersed to prepare a coating liquid. The coating liquid is applied to one side of a polyolefin microporous membrane using a gravure coating machine to form an active layer with the thickness shown in Table 24, thus obtaining a composite separator.

[0941] Then, for the composite separator, the ends are cut off and wound into a master roll with a width of 1,100 mm and a length of 5,000 m.

[0942] During the above evaluation, the composite separators released from the master roll are cut as needed and used as evaluation separators.

[0943] For the evaluation of the separator and battery, various evaluations were conducted according to the evaluation methods described above, and the evaluation results are shown in Table 24.

[0944] Examples 3.2–3.27 and Comparative Examples 3.1–3.5

[0945] As shown in Tables 24-31, the conditions for the microporous membrane as the substrate, the composite construction conditions, the presence or absence of crosslinking during the fabrication of the microporous membrane, the battery assembly conditions, and the presence or absence of crosslinking afte...

Claims

1. A separator for assembling an energy storage device, comprising at least one layer each of an A layer containing a polyolefin, a B layer containing inorganic particles, and a C layer containing a thermoplastic polymer. Layer A is a microporous membrane comprising silane-modified polyolefin and polyolefins other than silane-modified polyolefin. The polyolefin contained in layer A has one or more functional groups. The functional groups include those that, when the separator comes into contact with a non-aqueous electrolyte containing water and / or hydrogen fluoride during the manufacturing process of the energy storage device, undergo a condensation reaction to form a cross-linked structure based on siloxane bonds. The manufacturing process of layer A does not include a crosslinking process. The silane-modified polyolefin is not a masterbatch resin containing a dehydration condensation catalyst that crosslinks the silane-modified polyolefin. The viscosity-average molecular weight (Mv) of the silane-modified polyolefin is 500,000 to 2,000,000, and the proportion of the silane-modified polyolefin in the total mass of layer A is 3% to 70% by mass. Polyolefins other than silane-modified polyolefins include polyolefins with a viscosity-average molecular weight (Mv) of 2 million to 9 million and polyolefins with a viscosity-average molecular weight (Mv) of 500,000 or more but less than 2 million. The ratio of the polyolefins with a viscosity-average molecular weight (Mv) of 2 million to 9 million to the polyolefins with a viscosity-average molecular weight (Mv) of 500,000 or more but less than 2 million is 0.06 to 7.00 by mass.

2. The separator for assembling an energy storage device according to claim 1, comprising a region in which one or more island structures containing alkali metals and / or alkaline earth metals are detected when a 100 μm square area TOF-SIMS measurement is performed on the A layer, and the size of the island structure is 9 μm. 2 Above and 245μm 2 The following areas.

3. The separator for assembling an energy storage device according to claim 2, wherein the island structure has a size of 10 μm. 2 Above and 230μm 2 The following areas.

4. The separator for assembling an energy storage device according to claim 2, wherein the island structure has a size of 11 μm. 2 Above and 214μm 2 The following areas.

5. The separator for assembling an energy storage device according to claim 2, wherein, There are two or more island structures containing alkali metals and / or alkaline earth metals in the separator, and the minimum and maximum distances between the weighted center positions of each island structure are both greater than 6 μm and less than 135 μm.

6. The separator for assembling an energy storage device according to claim 5, wherein, The minimum and maximum distances between the weighted center positions of each of the island structures are both greater than 8 μm and less than 130 μm.

7. The separator for assembling an energy storage device according to claim 5, wherein, The minimum and maximum distances between the weighted center positions of each island structure are both greater than 10 μm and less than 125 μm.

8. The separator for assembling an energy storage device according to any one of claims 2 to 7, wherein, The island structure contains an alkaline earth metal, wherein the alkaline earth metal is calcium.

9. The separator for assembling an energy storage device according to any one of claims 2 to 7, wherein, The alkali metal and / or alkaline earth metal is at least one selected from the group consisting of lithium, sodium, magnesium, potassium and strontium.

10. The separator for assembling an energy storage device according to any one of claims 1 to 8, wherein, Layer B is an inorganic porous layer containing inorganic particles and resin binder.

11. The separator for assembling an energy storage device according to claim 10, wherein, The glass transition temperature (Tg) of the resin adhesive is -50℃ to 90℃.

12. The separator for assembling an energy storage device according to any one of claims 1 to 11, wherein, Based on the total mass of layer B, the content of inorganic particles contained in layer B is 5% to 99% by mass.

13. The separator for assembling an energy storage device according to claim 12, wherein, Based on the total mass of layer B, the content of inorganic particles contained in layer B is 90% to 97% by mass.

14. The separator for assembling an energy storage device according to any one of claims 1 to 13, wherein, The inorganic particles are selected from at least one of the following groups: alumina, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, cerium oxide, yttrium oxide, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, AlO(OH), talc, kaolinite, dickite, perlite, halloysite, pyrophyllite, montmorillonite, mica, magnesia chlorite, bentonite, asbestos, zeolite, diatomite, quartz sand, and glass fiber.

15. The separator for assembling an energy storage device according to claim 14, wherein, The mica includes sericite.

16. The separator for assembling an energy storage device according to any one of claims 1 to 15, wherein, The thermoplastic polymer contained in the C layer comprises (meth)acrylate or (meth)acrylic acid as a polymerization unit.

17. The separator for assembling an energy storage device according to any one of claims 1 to 16, wherein, The area of ​​layer C covering layer B is 5% to 98%.

18. The separator for assembling an energy storage device according to any one of claims 1 to 16, wherein, The area of ​​layer C covering layer B is 20% to 98%.

19. The separator for assembling an energy storage device according to any one of claims 1 to 18, wherein, The thermoplastic polymer contained in the C layer comprises at least one fluorinated vinyl compound selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

20. The separator for assembling an energy storage device according to any one of claims 1 to 19, wherein, For the thermal response index of the separator used to assemble the energy storage device after being impregnated with electrolyte and heated to 150°C at 2°C / min, when fitted to Equation (1) using the least squares approximation method, the range of rate is 3.5 ≤ rate ≤ 150. Equation (1) 21. The separator for assembling an energy storage device according to claim 20, wherein, The range of rate is 4.5 ≤ rate ≤ 50.

22. The separator for assembling an energy storage device according to any one of claims 1 to 21, wherein, For the thermal response index of the separator used to assemble the energy storage device after being impregnated with electrolyte and heated to 150°C at 2°C / min, when the least squares approximation method is used to fit Equation (1), the range of T0 is 110≤T0≤150 and the range of max is 0.1≤max≤30.

23. The separator for assembling an energy storage device according to claim 22, wherein, The range of T0 is 120≤T0≤135, and the range of max is 0.5≤max≤10.

24. The separator for assembling an energy storage device according to claim 22, wherein, The heat shrinkage rate of the separator used for assembling the energy storage device at 150°C and the heat shrinkage rate of the electrolyte at 150°C are both 0.1% and less than 50%.

25. An energy storage device assembly kit, comprising: (A) A housing containing a laminated or wound body of electrodes and separators for assembling an energy storage device as described in any one of claims 1 to 24; and (B) A container that contains a non-aqueous electrolyte.

26. An energy storage device comprising a positive electrode, a negative electrode, a separator for assembling the energy storage device according to any one of claims 1 to 24, and a non-aqueous electrolyte.

27. An energy storage device comprising a positive electrode, a negative electrode, a separator for assembling the energy storage device according to any one of claims 1 to 24, and a non-aqueous electrolyte, wherein the positive electrode is selected from at least one of the group consisting of a nickel-manganese-cobalt (NMC) lithium-containing positive electrode, an olivine-type lithium iron phosphate (LFP) positive electrode, a lithium cobalt oxide (LCO) positive electrode, a nickel-cobalt-aluminum (NCA) lithium-containing positive electrode, and a lithium manganese oxide (LMO) positive electrode.

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